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The flow and fracture behavior of ceramic and other brittle materials under the influence of contact loading is important to both component fabrication and performance. The ease of machining, severity of residual surface damage and rate of wear during subsequent service are controlled to a large degree by the character and extent of the flow zone and its influence on the fracture mode. This Investigation was undertaken to provide experimental verification of the results obtained through elastic/plastic finite element modeling cf the stress distribution and deformations introduced by static contact loading. Experimentally, X-ray double-crystal diffractometry (DCD) was applied to obtain a mapping of the distortions produced beneath a Vickers indenter, and hence to evaluate the effect of material and geometric parameters on the flow and fracture mechanisms.
Twenty-two consecutive VLBI images of supernova 1993J in the galaxy M81 taken over 7 years show, in unprecedented detail, the dynamic evolution of the expanding radio shell of an exploded star. High precision astrometry using phase-referencing shows that the supernova expands isotropically, and that its geometric center has a formal proper motion of 190±110 km s−1 w.r.t. the core of M81. Systematic changes in the images most likely reflect a pattern of inhomogeneities in the medium left over from the progenitor star, or possibly instabilities in the expanding shell. As the shockfront sweeps up the medium, it is progressively decelerated, and after 7 years it has slowed to less than 1/2 its original expansion velocity. SN1993J is likely now entering the early stages of the adiabatic phase common in much older supernova remnants.
Twenty consecutive VLBI images of supernova 1993J in M81 from the time of explosion to the present show the dynamic evolution of the expanding radio shell of an exploded star. No clear sign of a pulsar nebula, expected to have a spectral luminosity 10 to 1,000 times larger than that of the Crab, has yet been seen. The upper limit on the brightness at 8.4 GHz in the center of the shell in one of the latest images is 0.15 mJy per beam of 0.4 mas2, corresponding to a spectral luminosity of that of the Crab. Any nebula that may have formed in the center is probably still obscured by the surrounding thermal matter with no substantial filamentation having yet occurred in the latter.
Effects of soil tillage systems and nitrogen (N) fertilizer management on spring wheat yield components, grain yield and N-use efficiency (NUE) were evaluated in contrasting weather of 2013 and 2014 on a clay soil at the Royal Agricultural University's Harnhill Manor Farm, Cirencester, UK. Three tillage systems – conventional plough tillage (CT), high intensity non-inversion tillage (HINiT) and low intensity non-inversion tillage (LINiT) for seedbed preparation – were compared at four rates of N fertilizer (0, 70, 140 and 210 kg N/ha). Responses to the effects of the management practices were strongly influenced by weather conditions and varied across seasons. Grain yields were similar between LINiT and CT in 2013, while CT produced higher yields in 2014. Nitrogen fertilization effects also varied across the years with no significant effects observed on grain yield in 2013, while in 2014 applications up to 140 kg N/ha increased yield. Grain protein ranged from 10·1 to 14·5% and increased with N rate in both years. Nitrogen-use efficiency ranged from 12·6 to 49·1 kg grain per kg N fertilizer and decreased as N fertilization rate increased in both years. There was no tillage effect on NUE in 2013, while in 2014 NUE under CT was similar to LINiT and higher than HINiT. The effect of tillage and N fertilization on soil moisture and soil mineral N (SMN) fluctuated across years. In 2013, LINiT showed significantly higher soil moisture than CT, while soil moisture did not differ between tillage systems in 2014. Conventional tillage had significantly higher SMN at harvest time in 2014, while no significant differences on SMN were observed between tillage systems in 2013. These results indicate that LINiT can be used to produce similar spring wheat yield to CT on this particular soil type, if a dry cropping season is expected. Crop response to N fertilization is limited when soil residual N is higher, while in conditions of lower residual SMN, a higher N supply is needed to increase yield and improve grain protein content.
Previous research supports gene–environment interactions for polymorphisms in the corticotropin hormone receptor 1 gene (CRHR1) and the serotonin transporter gene linked polymorphic region (5-HTTLPR) in predicting depression, but it has rarely considered genetic influences on stress sensitization processes, whereby early adversities (EA) increase depressive reactivity to proximal stressors later in life. The current study tested a gene–environment–environment interaction (G × E × E; specifically, gene–EA–proximal stress interaction) model of depression in a 20-year longitudinal study. Participants were assessed prospectively for EA up to age 5 and recent chronic stress and depressive symptoms at age 20 and genotyped for CRHR1 single nucleotide polymorphism rs110402 and 5-HTTLPR. EA predicted stronger associations between recent chronic stress and depression, and the effect was moderated by genes. CRHR1 A alleles and 5-HTTLPR short alleles were associated with greater stress sensitization (i.e., greater depressive reactivity to chronic stress for those also exposed to high levels of EA). The results are consistent with the notion that EA exposure results in neurobiological and cognitive–emotional consequences (e.g., altered hypothalamic–pituitary–adrenal axis functioning), leading to emotional distress in the face of recent stressors among those with certain genetic characteristics, although further research is needed to explore explanatory mechanisms.
Two late prehistoric circular enclosure settlements near Harlech, Gwynedd were excavated by the Gwynedd Archaeological Trust in 1980–81 in advance of upland pasture improvements. Both produced evidence for the change from timber to mainly stone as a building material, commonplace in upland Britain at this time. At Moel y Gerddi there was some evidence for earlier activity in the Neolithic period, but the principal occupation occurred in the mid-first millennium BC, and comprised a roughly circular timber palisade enclosing a fairly substantial timber roundhouse. As these structures deteriorated, they were consolidated and embanked with stone, but despite this the occupation did not last very long and the site was abandoned. Erw-wen a short distance away produced similar evidence but there was no Neolithic phase and the site was re-used in the Medieval period. The principal late prehistoric settlement there comprised a single large roundhouse standing within an imposing enclosure wall but whether or not this had been preceded by a timber palisade is not known. It was clear, however, that the stone roundhouse was a replacement for an earlier timber counterpart and, quite unlike Moel y Gerddi, the occupation lasted a considerable period of time, possibly two or even three centuries. Dating evidence from either site was poor, and acid soil conditions mitigated against the preservation of most finds. The sites were apparently aceramic and probably relied on pastoralism rather than arable farming. The environmental setting and background has been considered in some detail in the preceding paper with particular reference to soil pollen studies and a bog core dug near Moel y Gerddi. Typologically the sites belong to the Gwynedd stone-built hut-circle settlements and it is argued that they could mark the first appearance of these monuments in the landscape. But in any case, the use of timber as witnessed here, was far more commonplace than has previously been supposed on these sites.
This chapter addresses changes in weather and climate events relevant to extreme impacts and disasters. An extreme (weather or climate) event is generally defined as the occurrence of a value of a weather or climate variable above (or below) a threshold value near the upper (or lower) ends (‘tails’) of the range of observed values of the variable. Some climate extremes (e.g., droughts, floods) may be the result of an accumulation of weather or climate events that are, individually, not extreme themselves (though their accumulation is extreme). As well, weather or climate events, even if not extreme in a statistical sense, can still lead to extreme conditions or impacts, either by crossing a critical threshold in a social, ecological, or physical system, or by occurring simultaneously with other events. A weather system such as a tropical cyclone can have an extreme impact, depending on where and when it approaches landfall, even if the specific cyclone is not extreme relative to other tropical cyclones. Conversely, not all extremes necessarily lead to serious impacts. [3.1]
Many weather and climate extremes are the result of natural climate variability (including phenomena such as El Niño), and natural decadal or multi-decadal variations in the climate provide the backdrop for anthropogenic climate changes. Even if there were no anthropogenic changes in climate, a wide variety of natural weather and climate extremes would still occur. [3.1]
A changing climate leads to changes in the frequency, intensity, spatial extent, duration, and timing of weather and climate extremes, and can result in unprecedented extremes. Changes in extremes can also be directly related to changes in mean climate, because mean future conditions in some variables are projected to lie within the tails of present-day conditions. Nevertheless, changes in extremes of a climate or weather variable are not always related in a simple way to changes in the mean of the same variable, and in some cases can be of opposite sign to a change in the mean of the variable. Changes in phenomena such as the El Nino-Southern Oscillation or monsoons could affect the frequency and intensity of extremes in several regions simultaneously. [3.1]
The field emission properties of hydrogenated amorphous carbon containing up to 29at% nitrogen (a-C:N:H), grown in an integrated distributed electron cyclotron resonance (IDECR) reactor were studied using a sphere-plane geometry. All films were smooth in character and required a high field (20-70V/νm) activation process before emission, which created micron- sized craters in the emission region. Further analysis suggested that the emission originates from activation-created geometrically enhanced areas around the crater region. Upon low-level nitrogen incorporation (N/N+C≤0.2), the field required for activation decreased from 54V/νm to a minimum value of 20V/νm. The turn-on field required for 1νA of current also decreased, reaching a minimum of 11.3V/νm. The decrease in activation and turn-on field was related to the increase in conductivity observed with increasing nitrogen content. At higher nitrogen concentrations, the increase in activation energy and turn on field for emission may be due to changes in overall material structure, as indicated by the decreasing optical gap
We have studied the photoconductivity in pure tetrahedral amorphous carbon (ta-C) and hydrogenated tetrahedral amorphous carbon (ta-C:H). Good photoconductive properties are demonstrated for ta-C:H, showing that the hydrogenated form of ta-C is of a higher electronic quality. Transport and recombination parameters are derived. Ta-C:H are low mobility solids with a μτ product of the order of 10−12 cm2 V−1 and a recombination time τr of about 10−7 s. At low energy excitation, the photoconductivity shows a sublinear dependence on the light intensity over a wide temperature range. The relationship between the photoconductivity and the density of spin defect centers is discussed. UV light is used to excite carriers into the extended states. Competitive recombination centers may be involved at high excitation energy.
The ‘gateway’ pattern of drug initiation describes a normative sequence, beginning with alcohol and tobacco use, followed by cannabis, then other illicit drugs. Previous work has suggested that ‘violations’ of this sequence may be predictors of later problems but other determinants were not considered. We have examined the role of pre-existing mental disorders and sociodemographics in explaining the predictive effects of violations using data from the US National Comorbidity Survey Replication (NCS-R).
The NCS-R is a nationally representative face-to-face household survey of 9282 English-speaking respondents aged 18 years and older that used the World Health Organization (WHO) Composite International Diagnostic Interview (CIDI) to assess DSM-IV mental and substance disorders. Drug initiation was estimated using retrospective age-of-onset reports and ‘violations’ defined as inconsistent with the normative initiation order. Predictors of violations were examined using multivariable logistic regressions. Discrete-time survival analysis was used to see whether violations predicted progression to dependence.
Gateway violations were largely unrelated to later dependence risk, with the exception of small increases in risk of alcohol and other illicit drug dependence for those who initiated use of other illicit drugs before cannabis. Early-onset internalizing disorders were predictors of gateway violations, and both internalizing and externalizing disorders increased the risks of dependence among users of all drugs.
Drug use initiation follows a strong normative pattern, deviations from which are not strongly predictive of later problems. By contrast, adolescents who have already developed mental health problems are at risk for deviations from the normative sequence of drug initiation and for the development of dependence.
S. Guimond, Professor of Psychology Université Blaise Pascal Clermont-Ferrand France,
A. Chatard, Université de Genève Genève Switzerland,
N. R. Branscombe, Department of Psychology University of Kansas USA,
S. Brunot, Département de Psychologie Université Rennes 2 France,
A. P. Buunk, Unit of Social and Organisational Psychology University of Groningen Netherlands,
M. A. Conway, Institute of Psychological Sciences The University of Leeds England,
R. J. Crisp, School of Psychology The University of Birmingham England,
M. Dambrun, Laboratoire de Psychologie Sociale et Cognitive (CNRS) Université Blaise Pascal France,
M. Désert, Laboratoire de Psychologie Sociale et Cognitive (CNRS) Université Blaise Pascal France,
D. M. Garcia, Department of Psychology University of Kansas USA,
S. Haque, Department of Psychology International Islamic University Malaysia Malaysia,
J.-P. Leyens, Catholic University of Louvain Department of Psychology Belgium,
F. Lorenzi-Cioldi, Université de Genève, FPSE Genève Switzerland,
D. Martinot, Laboratoire de Psychologie Sociale et Cognitive (CNRS) Université Blaise Pascal France,
S. Redersdorff, Laboratoire de Psychologie Sociale et Cognitive (CNRS) Université Blaise Pascal France,
V. Yzerbyt, Catholic University of Louvain Department of Psychology Belgium
Serge Guimond, Université de Clermont-Ferrand II (Université Blaise Pascal), France
This chapter reports on the results of a cross-cultural study of the effects of social comparison on self-construal among eight nations/cultures. It follows a previous report on five of these cultures (Guimond, Branscombe, Brunot, Buunk, Chatard, Désert, Garcia, Haque, Martinot, and Yzerbyt, 2005) and is linked to the previous chapter outlining some findings of the study in terms of gender stereotyping.
Past research and the specific contributions found in this volume indicate that social comparison processes are involved in many different attitudes and social behaviors. At the most general level, social comparison is a fundamental process by which knowledge is acquired. Indeed, most social psychologists would agree that social comparison is perhaps first and foremost critical for the creation of self-knowledge. To know who we are, we compare ourselves with others, or with ourselves in the past (see Part One, this volume). Some major developments in personality and social psychology have occurred by studying the self across cultures (see Berry, Poortinga, Segall, and Dasen, 1992; Markus and Kitayama, 1991; Shweder and Bourne, 1984; Triandis, 1989; see also Lorenzi-Cioldi and Chatard, this volume). For example, in their influential paper, Markus and Kitayama (1991) reviewed evidence suggesting that the self is defined in fundamentally different ways in western as opposed to eastern cultures. The western conception of self, and for several decades the only conception as far as social and personality psychologists were concerned, is that of an individual who is separate, autonomous, and composed of a set of discrete traits, abilities, and motives.