We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.
To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure no-reply@cambridge.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Depression is an independent risk factor for cardiovascular disease (CVD), but it is unknown if successful depression treatment reduces CVD risk.
Methods
Using eIMPACT trial data, we examined the effect of modernized collaborative care for depression on indicators of CVD risk. A total of 216 primary care patients with depression and elevated CVD risk were randomized to 12 months of the eIMPACT intervention (internet cognitive-behavioral therapy [CBT], telephonic CBT, and select antidepressant medications) or usual primary care. CVD-relevant health behaviors (self-reported CVD prevention medication adherence, sedentary behavior, and sleep quality) and traditional CVD risk factors (blood pressure and lipid fractions) were assessed over 12 months. Incident CVD events were tracked over four years using a statewide health information exchange.
Results
The intervention group exhibited greater improvement in depressive symptoms (p < 0.01) and sleep quality (p < 0.01) than the usual care group, but there was no intervention effect on systolic blood pressure (p = 0.36), low-density lipoprotein cholesterol (p = 0.38), high-density lipoprotein cholesterol (p = 0.79), triglycerides (p = 0.76), CVD prevention medication adherence (p = 0.64), or sedentary behavior (p = 0.57). There was an intervention effect on diastolic blood pressure that favored the usual care group (p = 0.02). The likelihood of an incident CVD event did not differ between the intervention (13/107, 12.1%) and usual care (9/109, 8.3%) groups (p = 0.39).
Conclusions
Successful depression treatment alone is not sufficient to lower the heightened CVD risk of people with depression. Alternative approaches are needed.
OBJECTIVES/GOALS: Glioblastoma (GBM) is the most common and aggressive adult primary brain malignancy. Clinically, GBM is refractory to T cell immune checkpoint blockade (ICB), in part due to its dense immune suppressive myeloid stroma. Here we show that myeloid-targeting STING agonists can repolarize the GBM microenvironment to cure ICB-refractory GBM models. METHODS/STUDY POPULATION: Using the synthetic cyclic di-nucleotide STING agonist IACS-8803 (8803) we treated orthotopic ICB-refractory QPP8 orthotopic murine GBM tumors intratumorally. We then analyzed survival and performed high parameter flow cytometry profiling of the tumor immune microenvironment following STING agonist treatment. To assess the contribution of adaptive immunity to STING agonist therapeutic efficacy, we treated orthotopic QPP8 tumors implanted in RAG1 KO mice and monitored survival. RESULTS/ANTICIPATED RESULTS: We found that STING agonist therapy cured murine orthotopic QPP8 tumors, in contrast to ICB that showed no survival benefit. In RAG1-/- mice bearing QPP8 tumors STING agonist therapy extended survival, however, the curative effect observed in wild-type mice was lost in the absence of adaptive immunity. STING agonist-treated QPP8 tumors displayed increased counts of CD8 T cells and NK cells, and decreased CD8 T cell PD1 expression. Infiltration of STING-treated gliomas by Ly6C+ F4/80+ Mono-MDSC substantially increased; however, these cells expressed reduced CD206 and CD163, suggestive of reduced immuno-suppression. Finally, in the cervical LN of QPP8-treated mice the frequency and CD80/CD86 expression of cDC1 cells increased.​ DISCUSSION/SIGNIFICANCE: ICB has failed in GBM, and the suppressive myeloid stroma remains a major barrier to generating anti-GBM T cell responses. Our work shows that STING activation, which primarily targets innate immunity myeloid cells 'upstream' of T cells in the antitumor immunity cycle, can cure ICB-refractory GBM tumors in an adaptive immunity-dependent manner.
Newly arriving Syrian refugees can present with specific health characteristics and medical conditions when entering the United States. Given the lack of epidemiological data available for the refugee populations, our study examined the demographic features of Syrian refugees resettled in the state of Kentucky. Specifically, we examined mental and physical health clinical data in both pre-departure health screenings and domestic Refugee Health Assessments (RHA; Kentucky Office for Refugees, n.d.) performed after resettlement.
Method:
The current study adopted a cross-sectional research design. We analyzed outcome data collected from participants from 2013 and 2015. Specifically, a comparative cross-sectional analysis was performed using clinical data from Syrian refugees who underwent an RHA as part of the resettlement process between January 2015 and August 2016. Those data were compared to data derived from refugees from other countries who resettled in Kentucky between 2013 and 2015.
Results:
Mental health screenings using the Refugee Health Screener (RHS-15; Hollifield et al., 2013) found that 19.5% (n = 34) of adult Syrian refugees reported signs and symptoms from posttraumatic stress, depressive symptoms, and/or anxiety, and nearly 40% (n = 69) reported personal experiences of imprisonment or violence, and/or having witnessed someone experiencing torture or violence. Intestinal parasites and lack of immunity to varicella were the most prevalent communicable diseases among Syrian refugees. Dental abnormalities and decreased visual acuity account for the first and second most prevalent non-communicable conditions. When comparing these results to all refugees arriving during the same years, significant differences arose in demographic variables, social history, communicable diseases, and non-communicable diseases.
Conclusion:
This study provides an initial health profile of Syrian refugees resettling in Kentucky, which reflects mental health as a major healthcare concern. Posttraumatic stress and related symptoms are severe mental health conditions among Syrian refugees above and beyond other severe physical problems.
A number of governmental and nongovernmental organizations have made significant efforts to encourage the development of artificial intelligence in line with a series of aspirational concepts such as transparency, interpretability, explainability, and accountability. The difficulty at present, however, is that these concepts exist at a fairly abstract level, whereas in order for them to have the tangible effects desired they need to become more concrete and specific. This article undertakes precisely this process of concretisation, mapping how the different concepts interrelate and what in particular they each require in order to move from being high-level aspirations to detailed and enforceable requirements. We argue that the key concept in this process is accountability, since unless an entity can be held accountable for compliance with the other concepts, and indeed more generally, those concepts cannot do the work required of them. There is a variety of taxonomies of accountability in the literature. However, at the core of each account appears to be a sense of “answerability”; a need to explain or to give an account. It is this ability to call an entity to account which provides the impetus for each of the other concepts and helps us to understand what they must each require.
To describe the association between successful weaning of inhaled nitric oxide and trends in dead space ratio during such weans in patients empirically initiated on nitric oxide therapy out of concern of pulmonary hypertensive crisis.
Patients:
Children in a cardiac intensive care unit initiated on inhaled nitric oxide out of clinical concern for pulmonary hypertensive crisis retrospectively over 2 years.
Measurements and Main Results:
Twenty-seven patients were included, and nitric oxide was successfully discontinued in 23/27. These patients exhibited decreases in dead space ratio (0.18 versus 0.11, p = 0.047) during nitric oxide weaning, and with no changes in dead space ratio between pre- and post-nitric oxide initiation (p = 0.88) and discontinuation (p = 0.63) phases. These successful patients had a median age of 10 months [4.0, 57.0] and had a pre-existent diagnosis of CHD in 6/23 and pulmonary hypertension in 2/23. Those who failed nitric oxide discontinuation trended with a higher dead space ratio at presentation (0.24 versus 0.10), were more likely to carry a prior diagnosis of pulmonary hypertension (50% versus 8.7%), and had longer mechanical ventilation days (5 versus 12).
Conclusions:
Patients empirically placed on nitric oxide out of concern of pulmonary hypertensive crisis and successfully weaned off showed unchanged or decreased dead space ratio throughout the initiation to discontinuation phases of nitric oxide therapy. Trends in dead space ratio may aid in determining true need for nitric oxide and facilitate effective weaning. Further studies are needed to directly compare trends between success and failure groups.
Studying phenotypic and genetic characteristics of age at onset (AAO) and polarity at onset (PAO) in bipolar disorder can provide new insights into disease pathology and facilitate the development of screening tools.
Aims
To examine the genetic architecture of AAO and PAO and their association with bipolar disorder disease characteristics.
Method
Genome-wide association studies (GWASs) and polygenic score (PGS) analyses of AAO (n = 12 977) and PAO (n = 6773) were conducted in patients with bipolar disorder from 34 cohorts and a replication sample (n = 2237). The association of onset with disease characteristics was investigated in two of these cohorts.
Results
Earlier AAO was associated with a higher probability of psychotic symptoms, suicidality, lower educational attainment, not living together and fewer episodes. Depressive onset correlated with suicidality and manic onset correlated with delusions and manic episodes. Systematic differences in AAO between cohorts and continents of origin were observed. This was also reflected in single-nucleotide variant-based heritability estimates, with higher heritabilities for stricter onset definitions. Increased PGS for autism spectrum disorder (β = −0.34 years, s.e. = 0.08), major depression (β = −0.34 years, s.e. = 0.08), schizophrenia (β = −0.39 years, s.e. = 0.08), and educational attainment (β = −0.31 years, s.e. = 0.08) were associated with an earlier AAO. The AAO GWAS identified one significant locus, but this finding did not replicate. Neither GWAS nor PGS analyses yielded significant associations with PAO.
Conclusions
AAO and PAO are associated with indicators of bipolar disorder severity. Individuals with an earlier onset show an increased polygenic liability for a broad spectrum of psychiatric traits. Systematic differences in AAO across cohorts, continents and phenotype definitions introduce significant heterogeneity, affecting analyses.
Emerging from the warehouse of knowledge about terrestrial ecosystem functioning and the application of the systems ecology paradigm, exemplified by the power of simulation modeling, tremendous strides have been made linking the interactions of the land, atmosphere, and water locally to globally. Through integration of ecosystem, atmospheric, soil, and more recently social science interactions, plausible scenarios and even reasonable predictions are now possible about the outcomes of human activities. The applications of that knowledge to the effects of changing climates, human-caused nitrogen enrichment of ecosystems, and altered UV-B radiation represent challenges addressed in this chapter. The primary linkages addressed are through the C, N, S, and H2O cycles, and UV-B radiation. Carbon dioxide exchanges between land and the atmosphere, N additions and losses to and from lands and waters, early studies of SO2 in grassland ecosystem, and the effects of UV-B radiation on ecosystems have been mainstays of research described in this chapter. This research knowledge has been used in international and national climate assessments, for example the IPCC, US National Climate Assessment, and Paris Climate Accord. Likewise, the knowledge has been used to develop concepts and technologies related to sustainable agriculture, C sequestration, and food security.
Antipsychotics are widely used for treating patients with psychosis, and target threshold psychotic symptoms. Individuals at clinical high risk (CHR) for psychosis are characterized by subthreshold psychotic symptoms. It is currently unclear who might benefit from antipsychotic treatment. Our objective was to apply a risk calculator (RC) to identify people that would benefit from antipsychotics.
Methods
Drawing on 400 CHR individuals recruited between 2011 and 2016, 208 individuals who received antipsychotic treatment were included. Clinical and cognitive variables were entered into an individualized RC for psychosis; personal risk was estimated and 4 risk components (negative symptoms-RC-NS, general function-RC-GF, cognitive performance-RC-CP, and positive symptoms-RC-PS) were constructed. The sample was further stratified according to the risk level. Higher risk was defined based on the estimated risk score (20% or higher).
Results
In total, 208 CHR individuals received daily antipsychotic treatment of an olanzapine-equivalent dose of 8.7 mg with a mean administration duration of 58.4 weeks. Of these, 39 (18.8%) developed psychosis within 2 years. A new index of factors ratio (FR), which was derived from the ratio of RC-PS plus RC-GF to RC-NS plus RC-CP, was generated. In the higher-risk group, as FR increased, the conversion rate decreased. A small group (15%) of CHR individuals at higher-risk and an FR >1 benefitted from the antipsychotic treatment.
Conclusions
Through applying a personal risk assessment, the administration of antipsychotics should be limited to CHR individuals with predominantly positive symptoms and related function decline. A strict antipsychotic prescription strategy should be introduced to reduce inappropriate use.
This chapter comprises the following sections: names, taxonomy, subspecies and distribution, descriptive notes, habitat, movements and home range, activity patterns, feeding ecology, reproduction and growth, behavior, parasites and diseases, status in the wild, and status in captivity.
The objects of town and country planning … are to secure a proper balance between the competing demands for land, so that all the land of the country is used in the best interests of the people…. The people whose surroundings are being planned must be given every chance to take an active part in the planning process … and when they have had it, the provisional plan may need a good deal of alteration…. In the past, plans have been too much the plans of officials…. (Lewis Silkin MP, Minister for Town and Country Planning, in the House of Commons Debate on the Second Reading of the Town and Country Planning Bill, Hansard, 29 January 1947, quoted in Silkin, 1947)
Lewis Silkin was a minister in the postwar Labour government, which introduced the Town and Country Planning Act in 1947, and this Act figures in every history of UK planning as the landmark mid-century coming of age of a new practice of spatial governance that promised to make cities civilized. It is a useful reminder that the 1945 Labour government did contain radicals like Silkin, whose ambition was to change (not consolidate) urban planning practice, where his notions of participation went well beyond representative democracy and trade union balloting. Silkin argued from democratic first principles that urban planning in ‘the interests of the people’ exists to articulate a collective purpose, and that only becomes possible if plan making is participative and involves active citizens who can challenge priorities and change official plans.
This radical theme – planning reshaped by active citizens – runs like a motif throughout the subsequent academic literature. The Oxford Handbook of Urban Planning includes a chapter on planning and citizenship by Miraftab (2012), who writes from the point of view that citizenship is not a political status with formal rights but an active process of making and doing. So the question is not about what citizenship is as given by the state, but what citizenship can do when grounded in civil society. In a scholarly and broad-ranging book, Mazza (2017) distinguishes between spatial planning and governance; planning is the technical knowledge and professional know-how that properly supports broad political choices, better described as spatial governance.
A growing body of evidence suggests that synaptic plasticity is involved in addictive behaviour and nicotine dependence (ND). Neurotrophic factors, such as neurotrophin 3 (NT3) play a key role in modulating neuronal plasticity. Therefore, an association between nicotine, smoking and neurotrophic factors has been suggested. However, the role of NT3 in ND has not been thoroughly investigated in humans so far.
We investigated the influence of chronic (long-term smoking) and acute nicotine administration on the plasma level of NT3. We measured plasma NT3 levels at baseline and then 15 and 45 minutes after nicotine or placebo administration using an enzyme-linked-immunoabsorbent-assay (ELISA). Smokers showed higher NT3 level than non-smokers at baseline. Interestingly, 15 minutes after acute nicotine injection, plasma level of NT3 in both smokers and non-smokers decreased significantly and went back to baseline levels after 30 minutes. We found that plasma nicotine and NT3 levels were positively correlated in smokers at baseline.
There is a direct interaction of nicotine with NT3, which is different in acute and chronic exposure. Interestingly, the concentration of NT3 is correlated and up-regulated in smokers. We propose that neuroplasticity, which plays a role in addictive behaviour such as smoking or nicotine dependence (ND) might be mediated by these interactions of nicotine and NT3. We speculate that these might even play a part in the so called “self-medicating” with cigarettes that is often seen in patients with certain mental disorders.
Only 30% or fewer of individuals at clinical high risk (CHR) convert to full psychosis within 2 years. Efforts are thus underway to refine risk identification strategies to increase their predictive power. Our objective was to develop and validate the predictive accuracy and individualized risk components of a mobile app-based psychosis risk calculator (RC) in a CHR sample from the SHARP (ShangHai At Risk for Psychosis) program.
Method
In total, 400 CHR individuals were identified by the Chinese version of the Structured Interview for Prodromal Syndromes. In the first phase of 300 CHR individuals, 196 subjects (65.3%) who completed neurocognitive assessments and had at least a 2-year follow-up assessment were included in the construction of an RC for psychosis. In the second phase of the SHARP sample of 100 subjects, 93 with data integrity were included to validate the performance of the SHARP-RC.
Results
The SHARP-RC showed good discrimination of subsequent transition to psychosis with an AUC of 0.78 (p < 0.001). The individualized risk generated by the SHARP-RC provided a solid estimation of conversion in the independent validation sample, with an AUC of 0.80 (p = 0.003). A risk estimate of 20% or higher had excellent sensitivity (84%) and moderate specificity (63%) for the prediction of psychosis. The relative contribution of individual risk components can be simultaneously generated. The mobile app-based SHARP-RC was developed as a convenient tool for individualized psychosis risk appraisal.
Conclusions
The SHARP-RC provides a practical tool not only for assessing the probability that an individual at CHR will develop full psychosis, but also personal risk components that might be targeted in early intervention.
Maternal supraphysiological estradiol (E2) environment during pregnancy leads to adverse perinatal outcomes. However, the influence of oocyte exposure to high E2 levels on perinatal outcomes remains unknown. Thus, a retrospective cohort study was conducted to explore the effect of high E2 level induced by controlled ovarian stimulation (COH) on further outcomes after frozen embryo transfer (FET). The study included all FET cycles (n = 10,581) between 2014 and 2017. All cycles were categorized into three groups according to the E2 level on the day of the human Chorionic Gonadotropin trigger. Odds ratios (ORs) and their confidence intervals (CIs) were calculated to evaluate the association between E2 level during COH and pregnancy outcomes and subsequent neonatal outcomes. From our findings, higher E2 level was associated with lower percentage of chemical pregnancy, clinical pregnancy, ongoing pregnancy, and live birth as well as increased frequency of early miscarriage. Preterm births were more common among singletons in women with higher E2 level during COH (aOR1 = 1.93, 95% CI: 1.22–3.06; aOR2 = 2.05, 95% CI: 1.33–3.06). Incidence of small for gestational age (SGA) was more common in both singletons (aOR1 = 2.01, 95% CI: 1.30–3.11; aOR2 = 2.51, 95% CI: 1.69–3.74) and multiples (aOR1 = 1.58, 95% CI: 1.03–2.45; aOR2 = 1.99, 95% CI: 1.05–3.84) among women with relatively higher E2 level. No association was found between high E2 level during COH and the percentage of macrosomia or large for gestational age. In summary, oocyte exposure to high E2 level during COH should be brought to our attention, since the pregnancy rate decreasing and the risk of preterm birth and SGA increasing following FET.
Resource allocation planning for emergency medical services (EMS) systems determines appropriate resources including what paramedic qualification and how rapidly to respond to patients for optimal outcomes. The British Columbia Emergency Health Services implemented a revised response plan in 2013.
Methods
A pre- and post-methodology was used to evaluate the effect of the resource allocation plan revision on 24-hour mortality. All adult cases with evaluable outcome data (obtained through linked provincial health administrative data) were analyzed. Multivariable logistic regression was used to adjust for variations in other significant associated factors. Interrupted time series analysis was used to estimate immediate changes in level or trend of outcome after the start of the revised resource allocation plan implementation, while simultaneously controlling for pre-existing trends.
Results
The derived cohort comprised 562,546 cases (April 2012–March 2015). When adjusted for age, sex, urban/metro region, season, day, hour, and dispatch determinant, the probability of dying within 24 hours of an EMS call was 7% lower in the post-resource allocation plan-revision cohort (OR = 0.936; 95% CI: 0.886–0.989; p = 0.018). A subgroup analysis of immediately life-threatening cases demonstrated similar effect (OR = 0.890; 95% CI: 0.808–0.981; p = 0.019). Using time series analysis, the descending changes in overall 24-hour mortality trend and the 24-hour mortality trend in immediately life-threatening cases, were both statistically significant (p < 0.001).
Conclusion
Comprehensive, evidence-informed reconstruction of a provincial EMS resource allocation plan is feasible. Despite change in crew level response and resource allocation, there was significant decrease in 24-hour mortality in this pan-provincial population-based cohort.
Despite its long coastline, relatively little is known about mainland China’s intertidal communities compared to Europe and the United States, although more is known from Taiwan and Hong Kong. In general, northern areas are dominated by temperate species, with tropical species in the south and subtropical areas supporting a diversity of species from both regions. Studies of intertidal systems are in their infancy, developing since the 1930s and particularly after the 1960s with a primary focus on taxonomy and distribution patterns. While species lists and distributions have been available for mainland China since the 1930s, and more recently Taiwan and Hong Kong, many of these are outdated and recent approaches reveal many cryptic species complexes. Basic information of spatial and temporal patterns is available, but is focussed on few locations, while larger-scale or temporally replicated studies are rare, with Hong Kong being an exception. As a result, we know a lot about a few small areas, and have often used this to generalise much larger areas. This bias is even more true for studies investigating intertidal processes. Clearly, this is an under-studied region and, given the unprecedented anthropogenic pressures it faces, we may already be documenting a highly degraded intertidal system.
This textbook provides students with a complete working knowledge of the properties of imperfections in crystalline solids. Readers will learn how to apply the fundamental principles of mechanics and thermodynamics to defect properties in materials science, gaining all the knowledge and tools needed to put this into practice in their own research. Beginning with an introduction to defects and a brief review of basic elasticity theory and statistical thermodynamics, the authors go on to guide the reader in a step-by-step way through point, line, and planar defects, with an emphasis on their structural, thermodynamic, and kinetic properties. Numerous end-of-chapter exercises enable students to put their knowledge into practice, and with solutions for instructors and MATLAB® programs available online, this is an essential text for advanced undergraduate and introductory graduate courses in crystal defects, as well as being ideal for self-study.
Ten ice-sheet models are used to study sensitivity of the Greenland and Antarctic ice sheets to prescribed changes of surface mass balance, sub-ice-shelf melting and basal sliding. Results exhibit a large range in projected contributions to sea-level change. In most cases, the ice volume above flotation lost is linearly dependent on the strength of the forcing. Combinations of forcings can be closely approximated by linearly summing the contributions from single forcing experiments, suggesting that nonlinear feedbacks are modest. Our models indicate that Greenland is more sensitive than Antarctica to likely atmospheric changes in temperature and precipitation, while Antarctica is more sensitive to increased ice-shelf basal melting. An experiment approximating the Intergovernmental Panel on Climate Change’s RCP8.5 scenario produces additional first-century contributions to sea level of 22.3 and 8.1 cm from Greenland and Antarctica, respectively, with a range among models of 62 and 14 cm, respectively. By 200 years, projections increase to 53.2 and 26.7 cm, respectively, with ranges of 79 and 43 cm. Linear interpolation of the sensitivity results closely approximates these projections, revealing the relative contributions of the individual forcings on the combined volume change and suggesting that total ice-sheet response to complicated forcings over 200 years can be linearized.
These post hoc analyses evaluate the efficacy, safety, and tolerability of vortioxetine versus placebo in patients aged ≥55 years with major depressive disorder (MDD).
Methods
Study-level efficacy data from 12 short-term, fixed-dose, randomized, placebo-controlled trials of vortioxetine 5–20 mg/day were assessed using a random-effects meta-analysis. Adverse events (AEs), vital signs, ECG values, liver enzymes, and body weight were pooled from the same studies. Patients had baseline Montgomery–Åsberg Depression Rating Scale (MADRS) total scores ranging from 22–30.
Results
1508 patients (mean age=62.4 years; range, 55–88 years) were included. Mean differences from placebo in change from baseline to study end (6/8 weeks) in MADRS were –2.56 (5 mg, n=324, P=0.035), –2.87 (10 mg, n=222, P=0.007), –1.32 (15 mg, n=90, P=NS), and –4.65 (20 mg, n=165, P=0.012). Odds ratios for response versus placebo were 1.6 (5 mg, P=NS), 1.8 (10 mg, P=0.002), 1.2 (15 mg, P=NS), and 2.5 (20 mg, P<0.001), and for remission versus placebo were 1.5 (5 mg, P=NS), 1.5 (10 mg, P=NS), 1.4 (15 mg, P=NS), and 2.7 (20 mg, P=0.001). The proportion of patients with AEs for placebo and vortioxetine 5–20 mg was 61.5% and 62.3%, respectively, with no increase at increased doses. Vortioxetine demonstrated a placebo-level incidence of serious AEs (1.2%). AEs occurring in ≥5% of any treatment group were nausea, headache, diarrhea, dizziness, dry mouth, constipation, fatigue, vomiting, and anxiety. No clinically significant mean changes in vital signs, ECG values, liver enzymes, or body weight emerged during treatment.
Conclusion
Vortioxetine 5–20 mg/day is efficacious and well tolerated in MDD patients aged ≥55 years, a group that is often comorbid with other conditions and treated with other medications.
Here we give a brief review of the principles of stress, strain, and isotropic elasticity that will be needed in the study of defects. Readers familiar with this elementary material can skip on to the next chapter. The review is given here as a reference that will be used from time to time in the remainder of this book. A more thorough treatment of this subject can be found in many elasticity textbooks, such as [10, 11].
Stress
Stress is a measure of the intensity of force transmitted through a surface separating different parts of a body. The basic definition of stress is force per unit area. There are two types of stress: axial and shear, as shown in Fig. 2.1a, b, respectively. The axial stress is σ = P/A, where the force P is perpendicular to the surface area A. In other words, the force P acts along the surface normal. Hence the axial stress is also called the normal stress. The shear stress is τ = P/A, where the shear force P is parallel to the surface area A. The dimension of stress is f/l2, where f is the dimension of force and l is the dimension of length. The unit of stress is N/m2= Pa (pascal).
Stress as a second-rank tensor
To completely specify the stress state at a point, we need to consider a small cube around this point and specify the traction forces per unit area on all faces of this cube. The edges of the cube are chosen to be parallel to the axes of a given coordinate system. The positive faces of the cube are defined as the three faces whose outward normal vectors are along the positive x, y, and z axes, respectively. Because the size of the cube is vanishingly small, it suffices to specify the forces on the positive faces of the cube. The forces on the negative faces must be opposite to the forces on the corresponding positive faces.