Characterizing the influence of stress-induced microcracks on thelaboratory strength and f

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The Effects of Stress

Stress is a common problem that many people experience in theirdaily lives. It can have a wide range of effects on both the body and the mind, and can impact various aspects of a person's well-being. Understanding the effects of stress is important in order to find ways to manage and reduce it.One of the most well-known effects of stress is its impact on mental health. Chronic stress can lead to anxiety, depression, and other mood disorders. It can also impair cognitive function, making it difficult to concentrate and make decisions. Additionally, stress can contribute to the development of unhealthy coping mechanisms such as substance abuse or overeating.In addition to mental health, stress can also take a toll on the body. It can weaken the immune system, making a person more susceptible to illnesses and infections. Chronic stress has also been linked to an increased risk of cardiovascular disease, as it can raise blood pressure and contribute to the buildup of plaque in the arteries. Furthermore, stress can lead to physical symptoms such as headaches, muscle tension, and digestive issues.Stress can also affect relationships and social interactions. When a person is under a lot of stress, they may become irritable, withdrawn, or less patient with others. This can strainrelationships with family, friends, and colleagues, and may lead to feelings of isolation and loneliness.Overall, the effects of stress are far-reaching and can impact every aspect of a person's life. It is important to find healthy ways to cope with and manage stress, such as practicing relaxation techniques, exercising, seeking support from others, and making time for enjoyable activities. By addressing stress and its effects, individuals can work towards improving their overall well-being and quality of life.。

我们正在研究的各种英文表述

: glen_almond@W e are currently establishing methods to characterize porcine T-lymphocyte subpopulations for two different studies. One involves evaluation of the T cells in weaned pigs following vaccination with a novel adjuvant; the other focuses on the influence of stress on T-lymphocyte populations and immunity in young pigs. Lymphocyte trapping is associated with stress, and we plan to explore this perturbation of the immune system. In addition, other studies focus on understanding the physiological roles of tumor necrosis factor and prostaglandin-E prior to and after the initiation of luteolysis. We are examining the significance of vascular endothelial growth factor (VEGF) and hypoxia-induc ible factor (HIF) in porcine corpus luteum. We utilize RT-PCR and additional genomic methodologies to characterize the expression of the factors and their receptors. We anticipate that future studies will determine the respective signal transduction pathways and re-visit the influence of the cytokines and the immune system on corpus luteum function.Birkenheuer, Adam, DVM, PhDDepartment of Clinical SciencesNCSU College of V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919) 513-8288E-mail: ajbirken@My research is focused on companion animal infectious diseases. Tick-transmitted protozoan parasites are emerging infectious diseases causing substantial morbidity and mortality worldwide. Our studies address discovery and characterization of novel pathogens, development of improved diagnostic assays, enhanced understanding of the epidemiology of tick-transmitted protozoan parasites, and identification of treatment strategies resulting in significantly improved survival rates.Breitschwerdt, Ed, DVMDepartment of Clinical SciencesNCSU College of V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919) 919-513-8277E-mail: ed_breitschwerdt@My research interests are focused in the area of infectious diseases, with a particular emphasis on diagnostic, therapeutic, and immunopathologic aspects of zoonotic vector-transmitted bacterial and rickettsial diseases. The laboratory has contributed substantially to current understanding of Rickettsia rickettsii, Ehrlichia canis, and Bartonella vinsonii infection in dogs and Bartonella henselae in cats. We are currently capable of handling biosafety P3-level. It is increasingly obvious that vector borne pathogens contribute to a substantial quantity of animal and humandisease and suffering. In most instances the immunopathologic consequences of infection with one or simultaneous infection with multiple vector-transmitted infectious agents remains unknown. It is our goal to better define the clinical consequences of chronic infection with these organisms. Dean, Gregg, DVM, PhDDepartment of Molecular Biomedical SciencesNCSU College of V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919) 513-2819E-mail: gregg_dean@My research focuses on the immunopathogenesis and prevention of human and feline immunodefic iency virus infection (HIV and FIV, respectively). FIV is a valuable model of human immunodeficiency virus infection in people and represents a significant health threat to the feline population world-wide. We are investigating the role of innate immune defects induced by HIV/FIV infection. These studies focus on the function of dendritic cells, natural killer cells, and Toll-like receptors in the immunopathogenesis of opportunistic infections during chronic retroviral infection. Ongoing vaccine studies seek to employ recombinant bacteria as vaccine vectors. We are evaluating recombinant Lactobacillus spp. engineered to express FIV/HIV Gag and consensus Env genes as a means to provide effective mucosal and systemic immune responses through oral immunization.Fogle, Jonathan, DVM, PhDDepartment of Population Health and PathobiologyNCSU College of V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919) 513-6304E-mail: jonathan_fogle@Using the FIV model for HIV, we have shown that CD4+CD25+ T regulatory cells are constitutively activated and suppress CD4+CD25- T helper cell immune responses during the acute phase and chronic phase of infection. Results of our recent experiments indicate that CD4+CD25+ T regulatory cells suppress the CD8+ immune response during the acute and chronic stages of FIV infection. We are currently investigating the mechanism(s) of CD8+ cell mediated suppression and the intracellular signaling events that occur in CD8+ targets, following their interaction with activated CD4+CD25+ cell from FIV+ cats.Gilmour, Ian, BSc, PhDCardiopulmonary and Immunotoxicology BranchEnvironmental Public Health DivisionNational Health and Environmental Effects Research LaboratoryU.S. Environmental Protection AgencyResearch Triangle Park, NC 27711Phone: (919) 541-0015E-mail: Gilmour.Ian@We study the effect of air pollutant exposure on pulmonary immunity and subsequent development of allergic and infectious lung disease. Air pollutants are generated in the inhalation exposure facility at the EPA which has the capability to aerosolize simple gases and vapors, various particles including nanomaterials, as well as fossil fuel combustion emissions. The staff also operates mobile field sampling laboratories that collect size-fractionated particles from various locations across the country. The relative toxicity of various air pollutants are compared and then applied in animal models of asthma, influenza, or cardiac dysfunction. Parallel studies are conducted with in vitro systems in order to extrapolate between cell based and whole body responses for the purposes of predicting potential effects in humans. Hammerberg, Bruce, DVM, PhDDepartment of Population Health and PathobiologyNCSU College of V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919) 513-7712E-mail: bruce_hammerberg@My current research expertise is in allergic diseases and nematode biology. Regarding allergic disease research, we have developed canine x murine heterohybridomas. One of these produces canine monoclonal IgE specific for a filarial nematode antigen. Another produces canine IgG antibody specific for canine IgE. Using these tools, I have developed mouse monoclonal antibodies against heat stable epitopes of canine IgE and have the opportunity to make canine monoclonal antibodies against canine IgE epitopes that will be useful in preventing allergic disease in the dog. The unlimited supply of canine IgE of known antigen specificity has directed my research toward characterizing inherited differences in mast cell function in the dog, and at this time I am investigating the role of stem cell factor in inherited canine atopic dermatitis.My work with filarial nematodes over the last 25 years has recently turned to investigating how fatty acid binding proteins function in nematode physiology.Havell, Edward, PhDDepartment of Population Health and PathobiologyNCSU College V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919) 515-6184E-mail: ed_havell@The major objective of our research is to determine the roles that tumor necrosis factor (TNF), interferon-gamma (IFN-gamma) and host cells play in both innate and adaptive immunity toenteric bacterial pathogens. To study possible roles of cytokines and host cells in anti-bacterial resistance, specific inhibitors (e.g., anti-cytokine antibodies) that block the actions of a given cytokine or host cell are administered before or at progressive times during bacterial infection in mice. The subsequent course of infection is monitored to determine the effect of such treatment on bacterial pathogenesis. The long-range goal of our research is to acquire an understanding of how TNF, IFN-gamma, and host cells having anti-bacterial function interact in the defense of the host against bacterial pathogens. Studies are underway to develop a reproducible model of inflammatory bowel disease that will enable the study of the roles of cytokines and host cells in chronic inflammatory intestinal disease. Finally, we have generated an avirulent Listeria monocytogenes mutant that does not translocate from the intestinal lumen but induces very strong protective T cell-mediated anti-listerial immunity. We plan to evaluate this avirulent mutant as an orally administered vaccine platform to present secreted recombinant tuberculosis antigens to the intestinal immune system in order to elicit protective anti-TB T cell immunityHess, Paul, DVM, PhDDepartment of Clinical SciencesNCSU, College of V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919) 513-6183E-mail: paul_hess@My principal interests are CD8-positive T cell immunology and immunotherapy. One focus of the laboratory is examining how the interaction of the MHC class I molecule and the T cell receptor can be manipulated to induce stable tolerance in animal models of autoimmunity and allotransplantation. The second focus is the discovery of new peptide epitopes in viral diseases. Lastly, we are investigating novel clinical predictors of chemotherapy-induced toxicity in the dog. Hudson, Lola C., DVM, PhDDepartment of Molecular Biomedical SciencesNCSU College V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919) 513-6306E-mail: lola_hudson@Research in this laboratory focuses on the study of viral neuropathogenesis and blood-brain barrier (BBB) function. We are currently investigating feline immunodeficiency virus (FIV), which has divergent mechanisms of CNS entry, as a model for AIDS neuropathogenesis. We have developed an in vitro feline blood-brain barrier model system to determine the conditions under which immune cells in normal and FIV-infected animals are capable of penetrating the BBB. Additional studies focus on characteristics of attaching cells and mechanisms of attachment to the barrier such as up-regulation of specific adhesion molecules. Additionally, in vivo studies parallel in vitro studies with the aim of increasing detection of neural infection during the early stages ofdisease. We are currently focusing on various cognitive-motor behavioral tests in normal and infected cats to determine acute losses in neurologic function. Such tests can then be used to assess the efficacy of various therapeutics to delay or prevent CNS infection.Jones, Samuel L., DVM, PhDDepartment of Clinical SciencesNCSU College of V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh NC 27606Phone: (919) 513-7722E-mail: sam_jones@My research interests focus on how inflammation is triggered and regulated and how inflammation contributes to the pathophysiology of diseases such as colitis, equine colic, sepsis, and endotoxemia. A primary objective of our work is to understand the cellular and molecular details of cell migration with a focus on the key innate immune cell, the neutrophil. We are particularly interested in how the signaling molecules protein kinase A, phosphatidylinositol 3-kinase, and p38 and the actin binding proteins MARCKS, V ASP, and L-plastin regulate the actin cytoskeleton, integrin function, and signaling during migration of neutrophils and other cell types. We use human and equine primary cells, cell lines, and in vivo models including mice and zebrafish for these studies. We are also studying how inflammation is triggered and how pro-inflammatory genes, particularly genes in the prostaglandin synthesis cascade that encode cyclooxygenase-2 and prostaglandin synthase-1, are upregulated in equine leukocytes. In collaborative work, we are studying the effects of neutrophils and inflammatory mediators on intestinal mucosal repair following ischemic injury that occurs in some forms of equine colic. Koci, Matt, PhDDepartment of Poultry ScienceNCSU Scott Hall, Campus Box 7608Raleigh, NC 27695Phone: (919) 515-5388E-mail: mdkoci@The overall focus of my research is to understand how the immune system responds to viral challenges. The majority of our work focuses on the innate aspects of host resistance to viral infection, particularly addressing how the innate immune system recognizes and responds to infection and thus can have profound affects on the adaptive immune response and ultimately the outcome of the infection. Understanding how stimulation of the innate immune system leads to different clinical outcomes is critical to understanding the genetic basis of disease resistance. Laster, Scott M., PhD- Immunology Program DirectorDepartment of MicrobiologyNCSU Gardner Hall, Campus Box 7615Raleigh, NC 27695Phone: (919) 515-7958E-mail: scott_laster@Research in my laboratory focuses on the anti-viral immune response. One aspect of this response currently under investigation is the apoptosis-inducing activity of tumor necrosis factor (TNF). TNF is a product of many cells, including macrophages and monocytes, and is released by these cells during infection. TNF is able to act in an anti-viral manner by causing the death of infected cells before virus replication is complete, thereby reducing the number of infectious virions that are produced. The apoptosis-inducing activity of TNF is selective for infected cells because these cells are unable to transcribe appropriate levels of NF-kB-dependent, anti-apoptotic gene products. The virus under investigation in my laboratory is the human adenovirus. While not a major human pathogen, the adenovirus represents an excellent model system for studies of molecular and cellular immunology. Recent studies from my laboratory suggest that adenovirus induces susceptibility to TNF by preventing the expression of a tyrosine or dual specificity phosphatase, leading us to propose that this phosphatase normally acts in an anti-apoptotic manner by inhibiting apoptotic signal transduction through the dephosphorylation of cytosolic phospholipase A2.Miller, Jennifer, PhDDepartment of MicrobiologyNCSU Gardner Hall, Campus Box 7615Raleigh, NC 27695Phone: (919) 515-7867E-mail: jen_miller@My research focuses on the interaction between the tick-borne spirochete Borrelia burgdorferi and the innate immune system. B. burgdorferi is the causative agent of Lyme disease, a multi-system disorder whose symptoms include the development of subacute arthritis within both a large joint of afflicted humans and the rear ankle joints of susceptible inbred mouse strains. This subacute arthritis is associated with the presence of B. burgdorferi within the joints. My laboratory utilizes tissue culture and mouse models to examine both the bacterial and host-derived mechanisms driving the induction of Lyme arthritis. We are currently focusing on a novel and previously unappreciated role for Type I interferon (IFN) in the development of severe Lyme arthritis. The goal of these studies is to identify additional bacterial effectors, innate immune components, and mechanistic pathways that drive both Type I IFN production and the development of Lyme arthritis.Nordone, Shila, PhDDepartment of Molecular Biomedical SciencesNCSU College V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919) 515-7410E-mail: shila_nordone@My research involves studying the mechanisms and consequences of the molecular interactions between pathogenic organisms and the innate immune system. Pathogen-mediated modulation of innate immunity can dictate the pathological consequences of infection, the duration of survival of the pathogen in the host, and ultimately, the ability of the adaptive immune response to evolve and clear infection. At the center of my research is the role of Toll-like receptor (TLR) and Triggering Receptor Expressed on Myeloid Cells-1 (TREM-1) activation in pathogen-immune system interactions. We are currently engaged in the following research areas: 1) Modulation of TLR-mediated responses by HIV-1 infection and 2) TREM-1 mediated inflammation during canine sepsis. The overall aim of both areas of research is to increase our understanding of the basic mechanisms of pathogen-innate immune cell crosstalk and to identify new therapeutic targets for treating HIV and sepsis.Olivry, Thierry, DrV et, PhDDepartment of Clinical SciencesNCSU, College of V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919) 513-6276E-mail: thierry_olivry@My principal research interests involve investigating the pathogenesis and therapy of canine atopic dermatitis and autoimmune skin diseases. Current projects on atopic dermatitis include clinical trials on the pharmacotherapy of this disease, modeling skin lesions experimentally, researching novel methods for immunotherapy as well as investigating the genetics of this trait in West Highland White Terriers. My research on autoimmune skin diseases involves the characterization of clinical signs, histopathology and immunological aspects of novel pathological entities of dogs, cats and horses. Additionally, we are investigating the autoantibody response in the blistering disease pemphigus foliaceus in dogs.Selgrade, Mary Jane, PhDImmunotoxicology BranchU.S. Environmental Protection AgencyResearch Triangle Park, NC 27711Phone: (919) 541-1821E-mail: selgrade.maryjane@My research interests center around the interactions between xenobiotic compounds (ambient and indoor air pollutants) and the immune system and consequent effects on susceptibility to infectious and allergic disease. The laboratory has developed several infectivity and allergy models in laboratory rodents. The focus is to understand the effects that exposure to environmental agents may have on both local and systemic immune responses, the underlying mechanisms associated with these effects, and the consequent impact on susceptibility to disease.Sherry, Barbara, PhDDepartment of Molecular Biomedical SciencesNCSU College V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone; (919) 515-4480E-mail: barbara_sherry@We study reovirus-induced myocarditis (cardiac inflammation and tissue damage) in mice as a model for this important human disease. Recently, we have focused on the cardiac response to viral infection, with particular emphasis on viral induction of the anti-viral cytokine interferon-beta in cardiac cells. We are interested in both the viral genes that stimulate this response, and the cardiac transcription factors and anti-viral proteins that are central to protection against disease. Our approaches, using primarily molecular techniques, include the use of transgenic mice and primary cardiac myocyte cell cultures.Sikes, Michael, PhDDepartment of MicrobiologyNCSU Gardner Hall, Campus Box 7615Raleigh, NC 27695Phone: (919) 513-0528E-mail: mike_sikes@As different cells in the body develop, they selectively use specific genes while ignoring others. In fact, development of multicellular organisms is absolutely dependent on differential gene regulation. But how genes are programmed to be activated or silenced at the right time remains a mystery. The research in our laboratory investigates the epigenetic changes that govern selective gene usage during lymphocyte development. Unlike other tissues, lymphocytes develop in discreet stages that can be easily followed using cell surface marker proteins, and for which individual cell line models exist. Specifically, we study the epigenetic programs that regulate the developmentally-timed activation and inactivation of the genes that encode the antibody and T cell receptor molecules. These genes are unique in the body in that they undergo a process of genetic recombination. We believe that transcriptional promoters positioned throughout each gene serve as nucleation points for transcription factors and histone modifiers that work together to shape local windows of accessible chromatin in response to developmental cues. Work is underway to test this hypothesis and to define the protein factors involved.Suter, Steven, VMD, MS, PhDDepartment of Clinical SciencesNCSU College of V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919) 513-0813E-mail: steven_suter@My research interests focus primarily on hematologic malignancies in companion animals, specifically canine and feline lymphoma. Elucidating the underlying molecular abnormalities associated with these diseases, as well as the development of novel therapeutics is the main thrust of my research. Although canine lymphoma is phenotypically and biologically similar to human non-Hodgkin’s diffuse large B-cell lymphoma, it is not known if these diseases share similar genetic perturbations. We aim to begin to elucidate these perturbations in dogs with lymphoma to both enhance dog lymphoma as a pertinent large animal model of human non-Hodgkin’s lymphoma and develop more targeted therapeutics for this disease.Tompkins, Mary, DVM, PhDDepartment of Population Health and PathobiologyNCSU College of V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606(919) 513-6255E-mail: mary_tompkins@The research in my laboratory is directed towards understanding the immunopathogenesis of feline retrovirus infection. In particular, we are examining mechanisms of virus-induced immunosuppression and persistence, especially alterations in cytokine regulation and cell-mediated immunity. We have been studying the immunopathogenesis of feline immunodefic iency virus (FIV), which is one of the best animal models for HIV infection. Our early studies described alterations in peripheral blood lymphocyte subset numbers, in vivo virus tropism, and disease progression. More recently we have described in detail cytokine dysregulation associated with FIV infection that leads to the inability of the infected cat to mount a successful cell mediated immune response to a secondary intracellular pathogen.Tompkins, Wayne, PhDDepartment of Population Health and PathobiologyNCSU College of V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919) 515-7394E-mail: wayne_tompkins@The focus of my research is immunopathogenesis of FIV infection in the cat: a model for human HIV infection. We are studying the cellular and molecular basis of T cell dysfunction and progression to AIDS in FIV-infected cats, utilizing RT-qcPCR and multi-color flow cytometry to define the receptor phenotype and cytokine profiles of CD4-positive and CD8-positive T cells. We are specifically exploring the role of B7 co-stimulatory molecules and the cytokines IL-10 and TGF-beta in mediating T cell anergy and apoptosis.Tonkonogy, Susan, PhDDepartment of Population Health and PathobiologyNCSU College of V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919) 513-6252E-mail: sue_tonkonogy@The overall goal of my research is to identify the molecular mechanisms that regulate the intestinal immune response. Our current approach is to determine the patterns of cytokines produced by T cells, B cells, macrophages, and dendritic cells isolated from mucosal lymphoid tissue of genetically manipulated rodents that spontaneously develop chronic intestinal inflammation when maintained in specific pathogen free housing. Germ-free rodents with identical genetic alterations do not develop inflammation, implicating the microorganisms that colonize the intestinal tract in the initiation of disease. The long-range goal of these studies is to provide a basis for designing therapeutic strategies aimed towards down-regulating the intestinal immune response that we postulate to be an underlying cause of the chronic inflammation that occurs in inflammatory bowel diseases.Ward, Marsha, PhDImmunotoxicology BranchU.S. Environmental Protection AgencyResearch Triangle Park, NC 27711Phone: (919) 541-1193E-mail: ward.marsha@My research interests involve the assessment of indoor environmental contaminants, particularly fungi for the potential to cause allergy/asthma using laboratory rodent models. The focus of our studies is hazard identification including 1) the identification and characterization of the allergenic proteins and 2) the identification of potential biomarkers that differentiate an allergic response from a non-allergic inflammatory response. Additionally, we are interested in the area of food allergies that could occur due to the introduction of genetically modified crops.Y oder, Jeffrey, PhDDepartment of Molecular Biomedical SciencesNCSU College of V eterinary Medicine, Campus Box 84014700 Hillsborough StRaleigh, NC 27606Phone: (919)-515-7406E-mail: jeff_yoder@Web site: /~jayoder/。

学生对我人格的重大影响英语作文

学生对我人格的重大影响英语作文In my early years of education, a teacher emerged as a pivotal figure who profoundly shaped my character. Their guidance was not just academic but also moral, instilling in me the importance of honesty and integrity.The classroom was not merely a place for learning facts but a sanctuary where values were imparted. Lessons on empathy and respect were woven into the curriculum, teaching me to see the world through a lens of compassion and understanding.One incident stands out where I faced a moral dilemma, and it was the teacher's unwavering support that helped me make the right choice. The courage to stand up for what is right was a lesson that has stayed with me ever since.The influence of this educator extended beyond the school walls, shaping my interactions with peers and family. I learned to communicate effectively, to listen with an open mind, and to approach conflicts with a spirit of resolution rather than confrontation.The impact of a good teacher is timeless. Years later, I find myself applying the principles they taught me in my professional life and personal relationships. Their lessons on perseverance and resilience have been invaluable in navigating the challenges I face.In conclusion, the role of a student's mentor is multifaceted, affecting not just their academic performance but also their growth as a person. The imprint left by a dedicated educator can be a guiding light for a lifetime, shaping the very core of one's being.。

导致研究生压力大的原因英语作文

导致研究生压力大的原因英语作文The Causes of Stress among Graduate StudentsGraduate students face various sources of stress throughout their academic journey. Understanding these causes is crucial in finding effective ways to manage and alleviate the pressures they experience. This essay will discuss several primary reasons that contribute to the high level of stress experienced by graduate students.Firstly, the heavy workload is a significant factor leading to stress among graduate students. These students are required to complete numerous assignments, research papers, and projects within limited timeframes. The constant pressure to meet deadlines and submit high-quality work can be overwhelming and taxing on their mental and physical well-being.Secondly, the competitiveness within the academic environment intensifies pressure on graduate students. They are constantly surrounded by peers who are equally driven and ambitious. The fear of falling behind or not keeping up with the academic standards can lead to self-doubt and anxiety. The constant comparison to other students' achievements further adds to their stress levels.Thirdly, financial concerns also contribute to the stress experienced by graduate students. Many of them have to juggle full-time or part-time jobs to support their education and living expenses. The need to balance work, studies, and personal life can be extremely demanding and overwhelming. The constant financialburden and the fear of not being able to meet their financial obligations can significantly impact their stress levels.Another contributing factor to graduate students' stress is the pressure to secure future job prospects. In today's competitive job market, graduate students are well aware of the importance of building a strong resume and gaining relevant work experience. The uncertainty about future career prospects and the fear of not meeting their professional goals can greatly impact their mental well-being.Lastly, the lack of work-life balance is a significant cause of stress among graduate students. The rigorous academic demands often leave little time for leisure activities, hobbies, and socializing. The constant feeling of always having to work or study can lead to burnout and negatively affect their overall well-being.In conclusion, graduate students face a multitude of factors that contribute to their high levels of stress. The heavy workload, competitiveness, financial concerns, pressure for future job prospects, and lack of work-life balance all play a significant role in their stress levels. It is important for academic institutions and individuals themselves to recognize these causes and work towards implementing effective stress management strategies to support the mental health and well-being of graduate students.。

高中生英语作文分析压力对学生的影响

高中生英语作文分析压力对学生的影响Title: The Impact of Stress on StudentsStress is an inevitable part of life, and it affects everyone, including students.However, the impact of stress on students can be particularly significant due to the demands of education and future expectations.In this essay, we will analyze the effects of stress on students and explore possible ways to mitigate its negative impacts.Firstly, stress can have detrimental effects on students' physical health.When students experience stress, their bodies release stress hormones such as cortisol, which can lead to increased heart rate, elevated blood pressure, and even stomachaches or headaches.In the long term, chronic stress can weaken the immune system, making students more susceptible to illnesses.Secondly, stress can negatively affect students' mental health.The pressure to perform well academically and socially can lead to feelings of anxiety, depression, and isolation.Students may become overwhelmed by the fear of failure or the expectation to excel in all areas of life.This can result in a decline in self-esteem and a negative impact on their overall well-being.Furthermore, stress can hinder students' academic performance.When students are preoccupied with their stressors, they may find it difficult to concentrate on their studies or completeassignments.This can lead to a decrease in productivity and a decline in academic grades.Additionally, stress can affect students' memory and cognitive function, making it harder for them to retain information and perform well on exams.To mitigate the negative impacts of stress on students, it is essential to implement effective coping strategies.One way is to encourage students to engage in regular physical exercise.Exercise has been proven to reduce stress levels and improve mental health.Additionally, students can benefit from learning mindfulness and relaxation techniques, such as meditation or deep breathing exercises, to help them manage stress more effectively.Moreover, schools and parents should create a supportive environment that emphasizes the importance of a balanced lifestyle.This includes adequate sleep, a healthy diet, and leisure time for students to pursue their interests and hobbies.It is also crucial to promote open communication and encourage students to seek help when they are feeling overwhelmed.In conclusion, stress can have profound effects on students' physical and mental health, as well as their academic performance.By implementing effective coping strategies and creating a supportive environment, we can help students manage stress more effectively and promote their overall well-being.It is essential to prioritize mental healthand ensure that students have the necessary support to thrive during their academic journey.。

应对压力的重要性及原因英语作文

应对压力的重要性及原因英语作文The Importance and Reasons for Dealing with StressIntroductionIn today's fast-paced world, stress has become a common phenomenon that affects individuals in various aspects of their lives. The ability to effectively cope with stress is crucial for maintaining mental and physical well-being. In this essay, we will discuss the importance and reasons for dealing with stress.Importance of Dealing with Stress1. Mental HealthOne of the primary reasons for dealing with stress is to protect mental health. Chronic stress can lead to anxiety, depression, and other mental health issues. By learning how to manage stress effectively, individuals can reduce the risk of developing mental health problems and improve their overall well-being.2. Physical HealthStress has a significant impact on physical health as well. It can weaken the immune system, increase the risk of heart disease, and contribute to other chronic health conditions. Byaddressing and managing stress, individuals can reduce the negative effects on their physical health.3. Relationship QualityStress can also affect relationships with others. When individuals are stressed, they may become irritable, withdrawn, or emotionally distant, which can strain relationships with family, friends, and colleagues. By learning how to cope with stress, individuals can maintain healthier and more fulfilling relationships.Reasons for Dealing with Stress1. Improved Coping SkillsLearning how to deal with stress effectively can help individuals develop better coping skills. By identifying triggers, implementing stress-reducing techniques, and seeking support when needed, individuals can build resilience and adaptability in the face of challenges.2. Enhanced ProductivityStress can impair cognitive functions, leading to decreased productivity and performance at work or school. By managing stress, individuals can improve focus, concentration, anddecision-making abilities, resulting in increased efficiency and effectiveness in their tasks.3. Better Emotional RegulationStress can trigger intense emotions such as anger, sadness, or frustration, making it difficult to regulate one's feelings. By addressing stress proactively, individuals can better control their emotions, respond to situations calmly, and maintain a more balanced emotional state.4. Increased Self-awarenessDealing with stress requires individuals to reflect on their thoughts, emotions, and behaviors. This self-awareness allows individuals to identify patterns, triggers, and coping mechanisms related to stress, leading to personal growth andself-improvement.5. Overall Well-beingUltimately, the importance of dealing with stress lies in promoting overall well-being. By prioritizing self-care, setting boundaries, and seeking help when needed, individuals can create a healthier and more balanced lifestyle that enhances their physical, mental, and emotional health.ConclusionIn conclusion, the ability to effectively deal with stress is essential for maintaining optimal health and well-being. By recognizing the importance of addressing stress and understanding the reasons for doing so, individuals can take proactive steps to manage stress, build resilience, and lead happier, more fulfilling lives.。

压力的影响英语作文

压力的影响英语作文Title: The Impact of Stress: A Reflection。

In today's fast-paced world, stress has become an inevitable part of life for many individuals. The effects of stress are far-reaching, influencing not only our physical health but also our mental and emotional well-being. In this essay, we will delve into the various aspects of stress and its impact on individuals.First and foremost, let us explore the physiological effects of stress. When we experience stress, our bodies undergo a series of biochemical changes. The release of stress hormones such as cortisol and adrenaline triggers the body's "fight or flight" response, preparing us to deal with perceived threats. While this response is essentialfor survival in dangerous situations, chronic stress can take a toll on our health. Prolonged exposure to stress hormones can weaken the immune system, increase the risk of cardiovascular disease, and contribute to conditions suchas hypertension and diabetes.Moreover, the effects of stress extend beyond the physical realm to encompass our mental and emotional well-being. Chronic stress can lead to anxiety, depression, and other mood disorders. It can impair cognitive function, making it difficult to concentrate, remember information, and make decisions. In addition, stress can strain interpersonal relationships, leading to conflicts with family members, friends, and colleagues. The constant pressure to perform can also diminish one's sense of self-worth and fulfillment, exacerbating feelings of inadequacy and self-doubt.Furthermore, the impact of stress is not confined to individuals but can also permeate entire communities and societies. In the workplace, stress can contribute to absenteeism, decreased productivity, and high staff turnover rates. It can create a negative work environment characterized by tension, conflict, and low morale. Similarly, stress in educational settings can impair students' academic performance and hinder their personaldevelopment. The pressure to excel academically can lead to unhealthy competition, cheating, and academic misconduct.In conclusion, stress is a pervasive force that can exert a profound influence on individuals, communities, and societies. Its effects are multifaceted, encompassing physical, mental, and emotional dimensions. As we navigate the complexities of modern life, it is crucial to recognize the impact of stress and take proactive steps to manage it effectively. By prioritizing self-care, seeking support from others, and cultivating resilience, we can mitigate the adverse effects of stress and lead healthier, more fulfilling lives.。

对我人格的重大影响小作文英语

The Significant Impact on My PersonalityIn the tapestry of life, each thread holds a story, and among those threads, some stand out, leaving indeliblemarks on our personalities. For me, one such thread is the significant impact English has had on my life and character. From a young age, English was not just a subject in school but a window to a vast and diverse world. It was the language that introduced me to the classics of literature, the profound thoughts of philosophers, and the beauty of poetry. As I delved deeper into the language, I foundmyself drawn to its versatility and the power it held to convey complex emotions and ideas.English taught me patience and perseverance. The challenges of grammar, vocabulary, and sentence structure required constant practice and dedication. In learning to express myself more eloquently, I learned to persevere inthe face of difficulties and to appreciate the beauty of hard work.Moreover, English became a tool for self-discovery. Through writing, I found a voice that allowed me to expressmy thoughts and feelings. It was a medium that helped me understand myself better, my strengths, weaknesses, and the values I hold dear.The influence of English on my personality is also reflected in my approach to life. The lessons learned from literature about resilience, empathy, and understandinghave shaped the way I interact with others. The ability to communicate effectively in English has opened doors to new experiences and opportunities, broadening my horizons and enriching my life.English has not only been a subject of study but a constant companion in my journey of growth and self-discovery. It has molded my personality, making me moreopen-minded, tolerant, and understanding. As I continue to explore the depths of this language, I am confident that it will continue to influence and shape me, guiding me towards a more enriched and fulfilling life.**英语对我人格的重大影响**在生命的织锦中，每一根线都承载着一个故事，而在这些线中，有些线特别突出，在我们的性格上留下了不可磨灭的印记。

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Full length articleCharacterizing the in ﬂuence of stress-induced microcracks on the laboratory strength and fracture development in brittle rocks using a ﬁnite-discrete element method-micro discrete fracture network FDEM-m DFN approachPooya Hamdi a ,*,Doug Stead a ,Davide Elmo ba Simon Fraser University,8888University Drive,Burnaby,British Columbia,CanadabNBK Institute of Mining Engineering,University of British Columbia,Vancouver,Canadaa r t i c l e i n f oArticle history:Received 9April 2015Received in revised form 9July 2015Accepted 22July 2015Available online 21September 2015Keywords:Finite-discrete element method (FDEM)Micro discrete fracture network (m DFN)Brittle fracturea b s t r a c tHeterogeneity is an inherent component of rock and may be present in different forms including mineral heterogeneity,geometrical heterogeneity,weak grain boundaries and micro-defects.Microcracks are usually observed in crystalline rocks in two forms:natural and stress-induced;the amount of stress-induced microcracking increases with depth and in-situ boratory results indicate that the physical properties of rocks such as strength,deformability,P-wave velocity and permeability are in ﬂuenced by increase in microcrack intensity.In this study,the ﬁnite-discrete element method (FDEM)is used to model microcrack heterogeneity by introducing into a model sample sets of microcracks using the proposed micro discrete fracture network (m DFN)approach.The characteristics of the microcracks required to create m DFN models are obtained through image analyses of thin sections of Lac du Bonnet granite adopted from published literature.A suite of two-dimensional laboratory tests including uniaxial,triaxial compression and Brazilian tests is simulated and the results are compared with laboratory data.The FDEM-m DFN models indicate that micro-heterogeneity has a profound in ﬂuence on both the me-chanical behavior and resultant fracture pattern.An increase in the microcrack intensity leads to a reduction in the strength of the sample and changes the character of the rock strength envelope.Spalling and axial splitting dominate the failure mode at low con ﬁnement while shear failure is the dominant failure mode at high con ﬁnement.Numerical results from simulated compression tests show that microcracking reduces the cohesive component of strength alone,and the frictional strength component remains unaffected.Results from simulated Brazilian tests show that the tensile strength is in ﬂuenced by the presence of microcracks,with a reduction in tensile strength as microcrack intensity increases.The importance of microcrack heterogeneity in reproducing a bi-linear or S-shape failure envelope and its effects on the mechanisms leading to spalling damage near an underground opening are also discussed.Ó2015Institute of Rock and Soil Mechanics,Chinese Academy of Sciences.Production and hosting byElsevier B.V.All rights reserved.1.IntroductionHeterogeneity is an inherent component of rock and has a major in ﬂuence on both the overall rock strength and the stress-induced fracture pattern at both the small (laboratory)and large (ﬁeld)scales.Material heterogeneity is evident at varied scales from the microscale,e.g.grain scale heterogeneity,to the large scale,i.e.faults of several hundred meters length within a rock mass.Themicroscopic behavior of rock is governed by several parameters including the variation in grain size,shape and mineral composi-tion as well as the presence of micro-defects,i.e.microcracks (Lan et al.,2010).For example,it has been reported that the compres-sive strength of a ﬁne-grained granite (with an average grain size of 1mm)can be nearly 10e 20%greater than that of medium-grained granite (4mm)(Martin and Stimpson,1994).Stress-induced damage is a well-known phenomenon for sam-ples extracted from deep boreholes,and the intensity of micro-cracking increases with depth.As more stress-induced microcracks are produced in the sample core,disking may occur (Fig.1).Martin and Stimpson (1994)concluded that stress-induced damage begins to affect the laboratory properties of Lac du Bonnet granite when the maximum in-situ stress exceeds about 10%of the uncon ﬁned compressive strength.Lim and Martin (2010)also demonstrated*Corresponding author.Tel.:þ16049167175.E-mail address:phamdi@sfu.ca (P.Hamdi).Peer review under responsibility of Institute of Rock and Soil Mechanics,Chinese Academy of Sciences.1674-7755Ó2015Institute of Rock and Soil Mechanics,Chinese Academy of Sci-ences.Production and hosting by Elsevier B.V.All rights reserved./10.1016/j.jrmge.2015.07.005Contents lists available at ScienceDirectJournal of Rock Mechanics and Geotechnical Engineeringjournal homepage:www.rockgeoJournal of Rock Mechanics and Geotechnical Engineering 7(2015)609e 625that core disking initiates when the ratio of major principal stress to the tensile strength is around boratory testing of samples taken at depths ranging from near-surface to 1000m at the Un-derground Research Laboratory (URL)experiment in Pinawa,Manitoba,Canada showed that the physical properties of rocks such as strength,deformability,P-wave velocity and permeability are all in ﬂuenced by an increase in microcrack intensity (Martin and Stimpson,1994).Although the importance of micro-structures,i.e.microcracks,on the mechanical behavior of rock samples has been long recog-nized,relatively little research has been carried out to quantify the effect of micro-structures on brittle rocks such as granite (Martin and Stimpson,1994).It has been shown that several stages of brittle fracturing process including crack closure,crack initiation,crack damage and peak strength are in ﬂuenced by the presence of microcracks (Chernis,1984;Martin and Stimpson,1994;Diederichs,2007).In this study,the effects of stress-induced microcracks on the mechanical behavior and fracture pattern of Lac du Bonnet granite are investigated numerically using a combined ﬁnite-discrete element method (FDEM)code,ELFEN (Rock ﬁeld,2012).The data from image analysis of thin sections illustrated by Lim and Martin (2010)are used to establish a micro discrete fracture network (m DFN)model which is then incorporated into the geo-mechanical model.The in ﬂuence of microcracks is investigated by simulating a series of conventional laboratory tests including uni-axial,triaxial compression and Brazilian tests incorporating varied microcrack intensity,re ﬂecting the increase in stress-induced microcracks with depth.Numerical results are compared with URL data presented in the literature (Martin and Stimpson,1994;Eberhardt,1998).Finally,the importance of microcracking on fracture mechanisms leading to spalling damage near an under-ground opening is brie ﬂy discussed.2.The in ﬂuence of microcrack heterogeneity on the brittle fracture processMicrocracks in crystalline rocks are formed when the localized stress concentrations exceed the local rock strength and can be classi ﬁed into two groups:(1)natural microcracks,which are produced by natural processes including pressure or temperature over geological time or (2)stress-induced (mechanically-induced)microcracks associated with changes in stresses and stress con-centrations during the coring process or excavation (Nur and Simmons,1970).According to Nadan and Engelder (2009),natural microcracks can be classi ﬁed into three types:(1)healed micro-cracks often associated with ﬂuid inclusion planes that formed during isobaric cooling,(2)ﬁlled microcracks containing foreign minerals,and (3)open microcracks produced during the isothermal decompression process and tectonic activities.Stress-induced microcracks due to the drilling process are common in rock cores taken from depth.Research has shown that drilling of a borehole results in stress concentrations and redistribution of initial stresses;when the magnitude of stress concentrations exceeds the stress required to initiate a microcrack,a stress-induced microcrack may nucleate (Obert and Stephenson,1965;Stacey,1982;Lim and Martin,2010).There is a general correlation between the mean in-situ stress and the microcrack intensity (Carlson and Wang,1986).Chernis (1984)examined microcrack intensity in Lac du Bonnet granite with respect to depth and concluded that the in-tensity of stress-induced microcracking in the samples extracted from 800m depth is nearly twice that of samples from a depth of 480m.Natural and stress-induced microcracks can be differentiated by their surface morphology and orientation characteristics.Natural microcracks often have rough or irregular walls containing limited in ﬁll.Stress-induced microcracks are characterized by smooth and parallel walls,lack of in ﬁll or bridging material and an orientation usually parallel to the major principal stress,re ﬂecting their extensional nature (Tapponnier and Brace,1976;Chernis,1984).With reference to the shape,microcracks can be classi ﬁed,as shown in Fig.2,into three types (Lim et al.,2012):(1)Grain boundary cracks:microcracks formed on the boundary of grains;(2)Intragranular cracks:microcracks which are enclosed within mineral grains;and (3)Transgranular cracks:microcracks that cut across several mineral grains and grain boundaries.Several experimental studies have been conducted in the past to analyze the modes of crack initiation and coalescence in laboratory samples containing one or several arti ﬁcial ﬂaws (Bobet and Einstein,1998;Wong and Einstein,2006,2007).Bobet and Einstein (1998)performed a series of laboratory uniaxial and biaxial compression tests to study the in ﬂuence of con ﬁning pres-sure on the fracture coalescence of rock samples containing two pre-existing ﬂaws.They suggested three principal modes of crack coalescence:the shear mode (S),the tensile (wing)mode (W)and the mixed shear/tensile mode (M),and concluded that formation of each crack coalescence is in ﬂuenced by the ﬂaw location,con ﬁning pressure,friction angle and heterogeneity.Several researchers have also attempted to simulate the crack coalescence in rock samples containing pre-existing ﬂaws using different numerical ing a ﬁnite element code RFPA,Tang et al.(2001)studied the ﬁnal fracture pattern in a rock sample with three pre-existing ﬂaws and concluded that crack coalescence follows a “weakest coalescence path ”which is controlled by the geometrical location of crack with respect to each other.Yan (2008)simulatedFig.1.Relationship between stress-induced microcracking and depth.The stress e strain plots illustrate the change in behavior as microcrack intensity increases (after Martin and Stimpson,1994).P.Hamdi et al./Journal of Rock Mechanics and Geotechnical Engineering 7(2015)609e 625610the crack coalescence of a rock sample with two pre-existing fractures using several numerical approaches:continuum method using Phase2(Rocscience Inc,2010),discontinuum method UDEC (Itasca,2010)and the hybrid method ELFEN (Rock ﬁeld,2012),and compared the results from these simulations.Regardless of the origin of the microcracks,the main role of microcrack heterogeneity is to act as stress concentrating mecha-nism that can produce local stress concentrations causing local failures which may ultimately result in failure (Dyskin,1999).Another role of microcracks in the fracturing process,noted by Dyskin (1999),is to promote stress ﬂuctuations which can inducehigh local tensile stresses,and initiate local fracture even if the magnitude of external load is less than the material strength.Fig.3illustrates an example of a simulated uniaxial compression test with pre-existing cracks using the hybrid FDEM code ELFEN,clearly showing the in ﬂuence of pre-existing microcracks on the resulting stress ﬁelds.Due to microcrack heterogeneity,the tensile stress is concentered at the tips of microcracks.Wing cracks are formed as a result of tensile stress concentration when the local stresses exceed the local strength.By increasing the applied stress,additional wing cracks are formed and coalesce to create a larger crack (macrocrack)which eventually results in the ultimate failure of the sample.3.Micro discrete fracture network (m DFN)The discrete fracture network (DFN)method is being increas-ingly used to realistically consider the in ﬂuence of discontinuity geometries within in-situ rock masses encountered in rock engi-neering projects.The general approach adopted in the DFN method is to treat fractures as discrete features whose properties,e.g.lo-cations,sizes,orientations,are de ﬁned by random variables with inferred probability distributions (Xu and Dowd,2010).Dershowitz and Herda (1992)proposed a method of fracture intensity mea-sures in one (linear),two (areal)and three (volume)dimensions that allow the quanti ﬁcation of fracture frequency.The fracture intensity measures proposed by Dershowitz and Herda (1992)have been proved as a useful quanti ﬁer for characterizing fractures and signi ﬁcantly improves discrete fracture analysis and modeling for mechanical applications.Fracture intensity measures are classi ﬁed based upon the dimension of the sampling region and the dimen-sion of the feature.In this study,the (areal)fracture intensity P 21,which is the ratio of the sum of total fracture traces to the sampling area is used to quantify the microcrack intensity (Fig.4).The ﬁrst stage in the process of creating DFN models at large scale is to collect discontinuity data using conventional disconti-nuity mapping techniques such as scanlines or window mapping of outcrops or remote sensing methods such as photogrammetryorTime interval 125 mmTime interval 2Time interval 3Stress concentra ƟonWing crack(a) Stress concentra Ɵon at theƟps of cracks(b)Forma Ɵon of wing cracks (c) Coalescence of wing cracksPre-exis Ɵng cracks-5 MPa325 MPaFig.3.Uniaxial compression test of a sample with pre-existing microcracks simulated in ELFEN.(a)Stress concentration around tips of pre-existing microcracks,(b)wing cracks formation and (c)coalescence of wing cracks as the sample is further stressed.Red color denotes tensile regime.Fig.2.An example of a thin section of Lac du Bonnet granite showing the presence of microcracks.Image size is 8.3mm Â8.3mm (Lim et al.,2012).P.Hamdi et al./Journal of Rock Mechanics and Geotechnical Engineering 7(2015)609e 625611laser scanning.A new class of DFN is proposed here,referred to as m DFN,to differentiate the stochastic nature of microscale cracks from large scale discontinuities.At microscale (laboratory scale),data collected from image analysis of thin sections are used to build appropriate m DFN models.Input parameters then include micro-crack size,orientation and intensity.In this study,a DFN generator developed by Mayer et al.(2014)is used which by considering the geomechanical model mesh gen-eration requirements allows seamless integration between the DFN and geomechanical simulation.An enhancement to the general Baecher disk model algorithm (Baecher et al.,1977)is implemented in the proposed algorithm with three added constraints including (1)a minimum overlapping/separation distance to prevent the development of unnecessarily small elements which would slow down overall numerical simulation run-times,(2)intersection dis-tance to ensure that the intersection points between generated microcracks are spaced at a distance greater than the speci ﬁed overlap/separation distance,and (3)intersection angle to ensure generated microcracks intersect at angles greater than the mini-mum internal angle used in the unstructured mesh generation.These three enhancements avoid the development of unacceptable microcrack con ﬁgurations which cannot be incorporated into the numerical codes using standard meshing algorithms and free the user from the need to manually modify the generated m DFN models prior to incorporation within numerical models.More details on the modi ﬁed DFN algorithm and its application in different nu-merical codes can be found in Mayer et al.(2014)and Mayer (2015)c du Bonnet graniteConsiderable research has been done on Lac du Bonnet granite as part of AECL ’s URL experiment in Manitoba,Canada.Extensive laboratory testing has been carried out by numerous researchers (Chernis,1984;Martin and Stimpson,1994;Eberhardt,1998;Eberhardt et al.,1998;Lim et al.,2012)focusing on the effect of microcrack intensity on the physical properties of samples that were taken from different depths,ranging from the ground surface to 1000m.Chernis (1984)examined several Lac du Bonnet granite samples obtained from different depths to study the characteristics of stress-induced and natural microcracks.Martin and Stimpson (1994)found that the laboratory P-wave velocity of Lac du Bon-net granite samples decreases continuously from ground surface to 1000m depth.They attributed this continuous velocity reduction to an increase in microcrack intensity as the magnitude of in-situstress increases with depth.Recent laboratory research by Lim et al.(2012)indicated that the volume of stress-induced micro-cracks increases linearly with sampling depth.The main charac-teristics of induced microcracks in Lac du Bonnet granite including microcrack origin,orientation,length and intensity were identi ﬁed by Lim et al.(2012)by analyzing several thin sections obtained from different depths.Grain size distribution plots from image analysis showed that the average grain size was 1mm.The primary types of microcracks were classi ﬁed as:(1)grain boundary microcracks,(2)intragranular microcracks,and (3)transgranular microcracks.Overall,it was observed that the intensity of all types of micro-cracks increases with depth.Lim et al.(2012)concluded that the microcrack length was very similar for each microcrack type regardless of the magnitude of stress-induced damage in the sample.The average length was reported to be 0.2e 0.4mm for intragranular microcracks and 1e 2mm for transgranular micro-cracks.The orientation of natural and stress-induced microcracks depends on the stress history and the current state of in-situ stress.Lim et al.(2012)compiled the results of microcrack orientation from each thin section and presented the data as rosette plots,as shown in Fig. 5.They concluded that while the intragranular microcracks are fairly uniformly distributed,transgranular micro-cracks tend to be aligned perpendicular to the core axis with a very shallow dipping (sub-horizontal)orientation.Fig.5presents the distribution of length and orientation of the transgranular and intragranular microcracks in Lac du Bonnet granite obtained from the URL 420-level.These data are used to create the m DFN models for importing into the FDEM models.5.Modeling methodologyIn this study,the in ﬂuence of microcrack heterogeneity on the behavior of brittle rock is investigated using the combined FDEM code ELFEN (Rock ﬁeld,2012).This code can readily simulate the complete brittle fracture processes including crack initiation,propagation and coalescence.Due to the hybrid nature of the code,the transition from a continuum to a discontinuum state as the rock is loaded can be seamlessly modeled.The algorithm is such that if the failure criterion within the intact rock (initially represented as a ﬁnite element domain)is met,then a crack is initiated (Cai and Kaiser,2004),and the model evolves into a discrete element geometry.Applicability of the combined FDEM to brittle fracture modeling has been demonstrated both at small and large scales by many researchers.Klerck (2000)carried out a series of two-dimensional (2D)uniaxial/triaxial compression and borehole breakout tests and illustrated the suitability of the FDEM for simulating both load e displacement response and the observed evolution of discrete fracturing.The mechanical behavior of anisotropic laboratory rock samples has been recently studied with the combined FDEM by Cai and Kaiser (2004)and by Lisjak et al.(2014)using Y-Geo code (Mahabadi et al.,2012a).Elmo and Stead (2010)used this method along with DFN to study the failure mechanism of fractured rock pillars.The application of the combined FDEM to large scale problems such as block cave mining was illustrated by Vyazmensky et al.(2010).Here,2D uniaxial and triaxial compression tests are simulated on samples with a height of 100mm and width of 50mm.A 50mm radius circular disc is modeled for the Brazilian test.The m DFN models are incorporated into the intact rock medium to study the effect of micro-heterogeneity.Several m DFN models with increasing values of intensity (P 21)are created to simulate an increased degree of sample disturbance with depth.The material properties of Lac du Bonnet granite obtained from the published literature (Hajiabdolmajid et al.,2002),as listed in Table 1,are assumed.InFig.4.Concept of areal fracture intensity,P 21,adopted in the FDEM modeling.P.Hamdi et al./Journal of Rock Mechanics and Geotechnical Engineering 7(2015)609e 625612this study,fracture energy (G f )is estimated based upon the empirical relation presented by Zhang (2002),in which the mode I fracture toughness K IC is related to the tensile strength bys t ¼6.88K IC and fracture energy is then calculated as K 2Ic=E .Me-chanical properties assigned to the m DFN models are also presented in Table 2.Zero tensile strength and cohesion are assumed for all microcracks and a friction angle of 26 .Loading is simulated by a constant velocity of 0.5mm/s applied on the upper platen and the reaction and displacement of the platen are continuously monitored.A sensitivity analysis has been carried out to ensure that the assumed loading rate has no signif-icant effect on the simulation results.Triangular elements with an average size of 0.5mm,corresponding to the average grain size observed from image analysis,are selected for this study.This re-sults in approximately 35,000unstructured elements for the sim-ulations of uniaxial and triaxial compression tests and 55,000elements for the Brazilian test.To capture a more realistic fracture pattern,an intra-element fracturing scheme is used,allowing new fractures to cut across the existing meshed elements (Fig.6).The geometrical properties of the microcracks used to create the m DFN models are listed in Table 3.Two sets of m DFNs are assumed,one representing the intragranular and the other the transgranular microcracks.The spatial location of the microcracks is modeled assuming a homogeneous (Poisson)algorithm.Since DFN models are based on stochastic distribution,each creation of a model will result in a different realization.In this study,three realizations for each data set are generated.The intensity of microcracks is measured by the microcrack intensity P 21and the distribution of orientations identi ﬁed using the crack rosette plot (Fig.7).The conventional method to determine the microcrack intensity parameter at the laboratory sample scale is to consider the whole sample area as the sampling area.This approach is appropriate for uniaxial and triaxial compression tests in which the whole sample is loaded.In the Brazilian test,however,only a narrow region along the sample diameter is signi ﬁcantly in ﬂuenced by loading,hence the characteristics of microcracks in this area determine the overall behavior of the test.Two methods of identifying the microcrack intensity are proposed which are referred to as:(1)distributed microcrack intensity and (2)focused microcrack intensity.In determination of distributed microcrack intensity,the whole area of sample is considered while for focused microcrack intensity,only the particular sample area in ﬂuenced by loading is considered.Since the testing con ﬁguration is taken into account in the deter-mination of sampling area in the focused microcrack intensity approach,a better understanding of in ﬂuence of microcracks can be achieved.In this study,the distributed microcrack intensity parameter is considered for simulations of uniaxial and triaxial compression tests and focused microcrack intensity for Brazilian tests.The concept of focused microcrack intensity is discussed in more detail in Section 7.1.6.Modeling of uniaxial and triaxial compression testsA series of uniaxial/triaxial compression tests with varied microcrack intensities is modeled to account for an increase in stress-induced microcracks with depth.Fig.8shows the simulated models and their associated microcrack rosette plots.As mentioned above,three m DFN realizations are created for each data set.A wide range of triaxial compression tests from low (2MPa)to high (50MPa)con ﬁnement is simulated for each model toinvestigateFig.5.Distribution of length and orientation for intragranular and transgranular microcracks in Lac du Bonnet granite obtained from the URL 420-level (Lim et al.,2012).Table 1The assumed intact rock properties of Lac du Bonnet granite (Hajiabdolmajid et al.,2002).Young ’s modulus,E (GPa)Poisson ’s ratio,n Density,r (kg m À3)Cohesion,c (MPa)Friction angle,4( )Tensile strength,s t (MPa)Fracture energy,G f (N m À1)600.25240034546.515Table 2Assumed properties of pre-existing and newly generated microcracks considered in this study.Normal contact penalty,P n (GPa m À1)Tangentialcontact penalty,P t (GPa m À1)Friction angle,4f ( )Cohesion,c f (MPa)Tensile strength,s t (MPa)50526P.Hamdi et al./Journal of Rock Mechanics and Geotechnical Engineering 7(2015)609e 625613the in ﬂuence of con ﬁning pressure on the behavior of the rock sample.6.1.In ﬂuence of microcrack intensity on the uniaxial compression testThe in ﬂuence of sample size on rock strength has been widely discussed in the geotechnical literature,and it is generally accepted that there is a signi ﬁcant strength reduction with increasing sample size.Hoek and Brown (1980)suggested an empirical relationship s cd ¼s c50(50/d )0.18that relates the uniaxial compressive strength (UCS)s cd of a rock specimen with a diameter d (in mm)to the UCS s c50of a 50mm diameter sample.They concluded that the strength reduction is attributed to the greater opportunity for failure through and around grains and pre-existing microcracks.As thesample size increases,more defects can be included in the test sample contributing to a strength reduction.This relationship also suggests that when a suf ﬁciently large number of defects are included in the sample,the strength may reach a constant value.This corresponds to the representative elementary volume (REV)which by de ﬁnition is the minimum sample size at which the test results become independent of size.Complete simulated stress-strain curves for an intact rock sample and samples with microcrack intensity of P 21¼0.063mm/mm 2and 0.21mm/mm 2are presented in Fig.9.The plot shows that the modeled peak strength of the rock sample decreases with in-crease in microcrack intensity.Wawersik and Fairhurst (1970)classi ﬁed the post-peak behavior of rocks under uniaxial condi-tions into two classes:Class I and Class II.According to Fig.9,the post-peak behavior for all model simulations can be classi ﬁed as Class I,implying that fracture propagation is stable such that work must be done on the specimen for an incremental decrease in load-carrying ability.All three models exhibit a brittle post-peak behavior.Fig.10shows the fracture evolution at selected stress levels for the models presented in Fig.8,indicating stages of crack initiation,propagation and coalescence with increasing load.Due to lack of con ﬁning pressure,fractures parallel to the direction of the major principal stress (vertical in this case)are formed.More de-tails concerning the in ﬂuence of microcracks on the simulated fracture pattern is presented in Section6.4.gn i r u t c a r f t n e m e l e -r e t n I )c (n o i t c e r i d e r u l i a f l a u t c A )a ((b) Intra-element fracturing Fig.6.Crack insertion procedure in ELFEN showing (a)actual failure direction de ﬁned by a weighted-average con ﬁguration,(b)intra-element fracturing,and (c)inter-element fracturing (Rock ﬁeld,2012).Table 3Characteristics of microcracks used in this study.TypeLength (mm)Orientation ( )MeanStandard deviation Mean Standard deviation m DFN set 1(intragranular)0.50.19030m DFN set 2(transgranular)0.80.230036912(b)90Fracture orientationF e r q u e n c y %()Microcrack orientationFig.7.An example of simulated sample with microcracks.(a)2D sample with microcracks for uniaxial and triaxial compression tests.(b)Corresponding rosette plot showing the frequency of generated microcracks with respect to horizontal.Fracture orientation is in degree.P.Hamdi et al./Journal of Rock Mechanics and Geotechnical Engineering 7(2015)609e 625614。