882 resultados para Direction of time
Resumo:
We present late-time ( 590 - 994 days) mid-IR photometry of the normal but highly reddened Type IIP supernova SN 2002hh. Bright, cool, slowly fading emission is detected from the direction of the supernova. Most of this flux appears not to be driven by the supernova event but instead probably originates in a cool, obscured star formation region or molecular cloud along the line of sight. We also show, however, that the declining component of the flux is consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IR emission could also be coming from newly condensed dust and/or an ejecta/CSM impact, but their contributions are likely to be small. For the case of a CSM-IR echo, we infer a dust mass of as little as 0.036 M-. with a corresponding CSM mass of 3.6(0.01/ r(dg)) M-., where rdg is the dust-to-gas mass ratio. Such a CSM would have resulted from episodic mass loss whose rate declined significantly about 28,000 years ago. Alternatively, an IR echo from a surrounding, dense, dusty molecular cloud might also have been responsible for the fading component. Either way, this is the first time that an IR echo has been clearly identified in a Type IIP supernova. We find no evidence for or against the proposal that Type IIP supernovae produce large amounts of dust via grain condensation in the ejecta. However, within the CSM-IR echo scenario, the mass of dust derived implies that the progenitors of the most common of core-collapse supernovae may make an important contribution to the universal dust content.
Resumo:
We present a detailed analysis of time-resolved optical spectra of the ZZ Ceti white dwarf, HS 0507+0434B. Using the wavelength dependence of observed mode amplitudes, we deduce the spherical degree, l, of the modes, most of which have l = 1. The presence of a large number of combination frequencies (linear sums or differences of the real modes) enabled us not only to test theoretical predictions but also to indirectly infer spherical and azimuthal degrees of real modes that had no observed splittings. In addition to the above, we measure line-of-sight velocities from our spectra. We find only marginal evidence for periodic modulation associated with the pulsation modes: at the frequency of the strongest mode in the lightcurve, we measure an amplitude of 2.6 +/- 1.0 kms(-1), which has a probability of 2% of being due to chance; for the other modes, we find lower values. Our velocity amplitudes and upper limits are smaller by a factor of two compared to the amplitudes found in ZZ Psc. We find that this is consistent with expectations based on the position of HS 0507+0434B in the instability strip. Combining all the available information from data such as ours is a first step towards constraining atmospheric properties in a convectionally unstable environment from an observational perspective.
Resumo:
The first report of time-resolved resonance Raman (TR(3)) scattering in a supercritical fluid is presented. TR(3) spectra of the lowest triplet excited state (T-1) of anthracene in supercritical (SC) CO2 have been obtained over the pressure range 90-500 bar. These data have been complemented by conventional flash photolysis measurements of the excited state lifetime, transient absorbance difference, and fluorescence spectra over a similar pressure range. The spectroscopic data show systematic changes with increasing pressure; the Delta A spectra of the TI state recorded at two different temperatures display a red shift with increasing fluid pressure, which is in agreement with earlier work carried out over a smaller range of pressures. Similar shifts in the fluorescence are also observed. The vibrational frequencies of the T-1 state of anthracene are found to be relatively insensitive to applied pressure; indeed, the transient bands are readily identified by comparison with resonance Raman (RR) spectra of the T-1 state in cyclohexane solution. Small but well-defined shifts to lower cm(-1) with increasing pressure are observed in some of the vibrational bands of SC COE. The most marked change in the excited state Raman spectra is that the intensity of the T-1 anthracene features, relative to those of CO2, increases with applied pressure. The information which each of the above spectroscopic methods gives on the question of how pressure changes affect the structure and local environment of the excited state probe molecule in the SCF is discussed. Possible explanations for the observed increase in RR band intensities in terms of increased resonance Raman enhancement arising from the spectral shifts and/or the increased solubility of anthracene in CO2 with increasing pressure are also considered.
Resumo:
The issue of inherited disorders in pedigree dogs is not a recent phenomenon and reports of suspected genetic defects associated with breeding practices date back to Charles Darwin's time. In recent years, much information on the array of inherited defects has been assimilated and the true extent of the problem has come to light. Historically, the direction of research funding in the field of canine genetic disease has been largely influenced by the potential transferability of findings to human medicine, economic benefit and importance of dogs for working purposes. More recently, the argument for a more canine welfare-orientated approach has been made, targeting research efforts at the alleviation of the most suffering in the greatest number of animals.
Resumo:
Aims. We use high spatial and temporal resolution observations from the Swedish Solar Telescope to study the chromospheric velocities of a C-class flare originating from active region NOAA 10969.
Methods. A time-distance analysis is employed to estimate directional velocity components in Hα and Ca ii K image sequences. Also, imaging spectroscopy has allowed us to determine flare-induced line-of-sight velocities. A wavelet analysis is used to analyse the periodic nature of associated flare bursts.
Results. Time-distance analysis reveals velocities as high as 64 km s-1 along the flare ribbon and 15 km s-1 perpendicular to it. The velocities are very similar in both the Hα and Ca ii K time series. Line-of-sight Hα velocities are red-shifted with values up to 17 km s-1. The high spatial and temporal resolution of the observations have allowed us to detect velocities significantly higher than those found in earlier studies. Flare bursts with a periodicity of ≈60 s are also detected. These bursts are similar to the quasi-periodic oscillations observed at hard X-ray and radio wavelength data.
Conclusions. Some of the highest velocities detected in the solar atmosphere are presented. Line-of-sight velocity maps show considerable mixing of both the magnitude and direction of velocities along the flare path. A change in direction of the velocities at the flare kernel has also been detected which may be a signature of chromospheric evaporation.
Resumo:
Invasive species pose a major threat to biodiversity but provide an opportunity to describe the processes that lead to changes in a species’ range. The bank vole (Myodes glareolus) is an invasive rodent that was introduced to Ireland in the early twentieth century. Given its continuing range expansion, the substantial empirical data on its spread thus far, and the absence of any eradication program, the bank vole in Ireland represents a unique model system for studying the mechanisms influencing the rate of range expansion in invasive small mammals. We described the invasion using a reaction–diffusion model informed by empirical data on life history traits and demographic parameters. We subsequently modelled the processes involved in its range expansion using a rule-based spatially explicit simulation. Habitat suitability interacted with density-dependent parameters to influence dispersal, most notably the density at which local populations started to donate emigrating individuals, the number of dispersing individuals and the direction of dispersal. Whilst local habitat variability influenced the rate of spread, on a larger scale the invasion resembled a simple reaction–diffusion process. Our results suggest a Type 1 range expansion where the rate of expansion is generally constant over time, but with some evidence for a lag period following introduction. We demonstrate that a two-parameter empirical model and a rule-based spatially explicit simulation are sufficient to accurately describe the invasion history of a species that exhibits a complex, density-dependent pattern of dispersal.
Resumo:
Recent research on Variable Stiffness (VS) laminates, which are constructed by steering the fiber orientation as a spatial function of location, have shown to improve laminate performance under mechanical loads. Two distinct cases of stiffness variation can be achieved either by variation of the fiber orientation in the direction of the global x-axis, or perpendicular to it. In the present paper, thermal analysis of a VS laminate is performed to study the effect of steering fibers on transient heat conduction under uniform heat flux using finite element method. The goal of the present paper is a parametric study of the effect of variable stiffness properties on transient response including time to reach steady state and temperature profile. Also, stress resultants and maximum stress location are investigated under different boundary conditions. A FEM algorithm is applied to exactly incorporate the boundary conditions for stress resultant analysis.
Resumo:
Recent research on Variable Stiffness (VS) laminates, which are constructed by steering the fiber orientation as a spatial function of location, have shown to improve laminate performance under mechanical loads. Two distinct cases of stiffness variation can be achieved either by variation of the fiber orientation in the direction of the global x-axis, or perpendicular to it. In the present paper, thermal analysis of VS laminate is performed to study the effect of steering fibers on transient heat conduction under uniform heat flux using finite element method. The goal of the present paper is a parametric study of the
effect of variable stiffness properties on transient response including time to reach steady state and temperature profile. Also, stress resultants and maximum stress location are investigated under different boundary conditions. A FEM algorithm is applied to exactly incorporate the boundary conditions.
Resumo:
We investigate the acceleration of particles by Alfven waves via the second-order Fermi process in the lobes of giant radio galaxies. Such sites are candidates for the accelerators of ultra-high-energy cosmic rays (UHECR). We focus on the nearby Fanaroff-Riley type I radio galaxy Centaurus A. This is motivated by the coincidence of its position with the arrival direction of several of the highest energy Auger events. The conditions necessary for consistency with the acceleration time-scales predicted by quasi-linear theory are reviewed. Test particle calculations are performed in fields which guarantee electric fields with no component parallel to the local magnetic field. The results of quasi-linear theory are, to an order of magnitude, found to be accurate at low turbulence levels for non-relativistic Alfven waves and at both low and high turbulence levels in the mildly relativistic case. We conclude that for pure stochastic acceleration via Alfven waves to be plausible as the generator of UHECR in Cen A, the baryon number density would need to be several orders of magnitude below currently held upper limits.
Resumo:
This programme of research aimed to understand the extent to which current UK medical graduates are prepared for practice. Commissioned by the General Medical Council, we conducted: (1) A Rapid Review of the literature between 2009 and 2013; (2) narrative interviews with a range of stakeholders; and (3) longitudinal audio-diaries with Foundation Year 1 doctors. The Rapid Review (RR) resulted in data from 81 manuscripts being extracted and mapped against a coding framework (including outcomes from Tomorrow's Doctors (2009) (TD09)). A narrative synthesis of the data was undertaken. Narrative interviews were conducted with 185 participants from 8 stakeholder groups: F1 trainees, newly registered trainee doctors, clinical educators, undergraduate and postgraduate deans and foundation programme directors, other healthcare professionals, employers, policy and government and patient and public representatives. Longitudinal audio-diaries were recorded by 26 F1 trainees over 4 months. The data were analysed thematically and mapped against TD09. Together these data shed light onto how preparedness for practice is conceptualised, measured, how prepared UK medical graduates are for practice, the effectiveness of transition interventions and the currently debated issue of bringing full registration forward to align with medical students’ graduation. Preparedness for practice was conceptualised as both a long- and short-term venture that included personal readiness as well as knowledge, skills and attitudes. It has mainly been researched using self-report measures of generalised incidents that have been shown to be problematic. In terms of transition interventions: assistantships were found to be valuable and efficacious for proactive students as team members, shadowing is effective when undertaken close to employment/setting of F1 post and induction is generally effective but of inconsistent quality. The August transition was highlighted in our interview and audio-diary data where F1s felt unprepared, particularly for the step-change in responsibility, workload, degree of multitasking and understanding where to go for help. Evidence of preparedness for specific tasks, skills and knowledge was contradictory: trainees are well prepared for some practical procedures but not others, reasonably well prepared for history taking and full physical examinations, but mostly unprepared for adopting an holistic understanding of the patient, involving patients in their care, safe and legal prescribing, diagnosing and managing complex clinical conditions and providing immediate care in medical emergencies. Evidence for preparedness for interactional and interpersonal aspects of practice was inconsistent with some studies in the RR suggesting graduates were prepared for team working and communicating with colleagues and patients, but other studies contradicting this. Interview and audio-diary data highlights concerns around F1s preparedness for communicating with angry or upset patients and relatives, breaking bad news, communicating with the wider team (including interprofessionally) and handover communication. There was some evidence in the RR to suggest that graduates were unprepared for dealing with error and safety incidents and lack an understanding of how the clinical environment works. Interview and audio-diary data backs this up, adding that F1s are also unprepared for understanding financial aspects of healthcare. In terms of being personally prepared, RR, interview and audio diary evidence is mixed around graduates’ preparedness for identifying their own limitations, but all data points to graduates’ difficulties in the domain of time management. In terms of personal and situational demographic factors, the RR found that gender did not typically predict perceptions of preparedness, but graduates from more recent cohorts, graduate entry students, graduates from problem based learning courses, UK educated graduates and graduates with an integrated degree reported feeling better prepared. The longitudinal audio-diaries provided insights into the preparedness journey for F1s. There seems to be a general development in the direction of trainees feeling more confident and competent as they gain more experience. However, these developments were not necessarily linear as challenging circumstances (e.g. new specialty, new colleagues, lack of staffing) sometimes made them feel unprepared for situations where they had previously indicated preparedness.
Resumo:
We have obtained H$\alpha$ high spatial and time resolution observations of the upper solar chromosphere and supplemented these with multi-wavelength observations from the Solar Dynamic Observatory (SDO) and the {\it Hinode} ExtremeUltraviolet Imaging Spectrometer (EIS). The H$\alpha$ observations were conducted on 11 February 2012 with the Hydrogen-Alpha Rapid Dynamics Camera (HARDcam) instrument at the National Solar Observatory's Dunn Solar Telescope. Our H$\alpha$ observations found large downflows of chromospheric material returning from coronal heights following a failed prominence eruption. We have detected several large condensations ("blobs") returning to the solar surface at velocities of $\approx$200 km s$^{-1}$ in both H$\alpha$ and several SDO AIA band passes. The average derived size of these "blobs" in H$\alpha$ is 500 by 3000 km$^2$ in the directions perpendicular and parallel to the direction of travel, respectively. A comparison of our "blob" widths to those found from coronal rain, indicate there are additional smaller, unresolved "blobs" in agreement with previous studies and recent numerical simulations. Our observed velocities and decelerations of the "blobs" in both H$\alpha$ and SDO bands are less than those expected for gravitational free-fall and imply additional magnetic or gas pressure impeding the flow. We derived a kinetic energy $\approx$2 orders of magnitude lower for the main eruption than a typical CME, which may explain its partial nature.
Resumo:
This chapter considers judicial reasoning in ‘human rights’ cases. Are there techniques that courts share, or are different techniques adopted, to decide how human rights, in this broader sense, are protected? The chapter aims to adopt a comparative approach to the examination of this reasoning, through a detailed examination of similar human rights issues in a range of jurisdictions. The aim of the chapter is to examine the similarities and divergences in the reasoning developed by courts when addressing comparable human rights questions. The chapter shows that human rights reasoning involves distinctive and particular forms of legal reasoning, but that its form and content differ significantly
from jurisdiction to jurisdiction, and over time within jurisdictions. Building upon these findings, the chapter explores what these similarities and differences tell us about the nature, and the direction of travel, of human rights law which comprises notionally universal norms.
Resumo:
A strong link between drug use and homelessness has long since been documented in the international literature. However, much of the research has concentrated on the direction of the relationship between drug use and homelessness, seeking to establish drug use as a cause or consequence of homelessness, with far less attention to the intersection of drug and homeless ‘careers’. This paper examines the drug and homeless pathways of young people who are participants in a qualitative longitudinal study of homeless youth in Dublin, Ireland. The findings highlight downward drug transitions as associated with exiting homelessness and continued or escalated consumption as associated with remaining homeless. Analyses of the meanings young people attach to drug use over time reveal the importance of housing as an enabler to engaging with treatment and as assisting the process of becoming and remaining drug free. Young people who remained homeless did not accept their situations, as ‘acculturation’ accounts would suggest; rather, they aspired to changing their situations. However, they also face strong barriers to accessing housing which in turn hamper their efforts to address the matter of their drug use. The implications for how the homeless/drug use ‘nexus’ is conceptualised and understood, as well as implications for policy, are discussed.
Resumo:
Whole genome sequencing (WGS) technology holds great promise as a tool for the forensic epidemiology of bacterial pathogens. It is likely to be particularly useful for studying the transmission dynamics of an observed epidemic involving a largely unsampled 'reservoir' host, as for bovine tuberculosis (bTB) in British and Irish cattle and badgers. BTB is caused by Mycobacterium bovis, a member of the M. tuberculosis complex that also includes the aetiological agent for human TB. In this study, we identified a spatio-temporally linked group of 26 cattle and 4 badgers infected with the same Variable Number Tandem Repeat (VNTR) type of M. bovis. Single-nucleotide polymorphisms (SNPs) between sequences identified differences that were consistent with bacterial lineages being persistent on or near farms for several years, despite multiple clear whole herd tests in the interim. Comparing WGS data to mathematical models showed good correlations between genetic divergence and spatial distance, but poor correspondence to the network of cattle movements or within-herd contacts. Badger isolates showed between zero and four SNP differences from the nearest cattle isolate, providing evidence for recent transmissions between the two hosts. This is the first direct genetic evidence of M. bovis persistence on farms over multiple outbreaks with a continued, ongoing interaction with local badgers. However, despite unprecedented resolution, directionality of transmission cannot be inferred at this stage. Despite the often notoriously long timescales between time of infection and time of sampling for TB, our results suggest that WGS data alone can provide insights into TB epidemiology even where detailed contact data are not available, and that more extensive sampling and analysis will allow for quantification of the extent and direction of transmission between cattle and badgers. © 2012 Biek et al.
Resumo:
A significant portion of the UK’s transportation system relies on a network of geotechnical earthworks (cuttings and embankments) that were constructed more than 100 years ago, whose stability is affected by the change in precipitation patterns experienced over the past few decades. The vulnerability of these structures requires a reliable, cost- and time-effective monitoring of their geomechanical condition. We have assessed the potential application of P-wave refraction for tracking the seasonal variations of seismic properties within an aged clay-filled railway embankment, located in southwest England. Seismic data were acquired repeatedly along the crest of the earthwork at regular time intervals, for a total period of 16 months. P-wave first-break times were picked from all available recorded traces, to obtain a set of hodocrones referenced to the same spatial locations, for various dates along the surveyed period of time. Traveltimes extracted from each acquisition were then compared to track the pattern of their temporal variability. The relevance of such variations over time was compared with the data experimental uncertainty. The multiple set of hodocrones was subsequently inverted using a tomographic approach, to retrieve a time-lapse model of VPVP for the embankment structure. To directly compare the reconstructed VPVP sections, identical initial models and spatial regularization were used for the inversion of all available data sets. A consistent temporal trend for P-wave traveltimes, and consequently for the reconstructed VPVP models, was identified. This pattern could be related to the seasonal distribution of precipitation and soil-water content measured on site.