960 resultados para SLOW RELAXATION
Resumo:
We present early photometric and spectroscopic observations of SN 2013ej, a bright Type IIP supernova (SN) in M74. SN 2013ej is one of the closest SNe ever discovered. The available archive images and the early discovery help to constrain the nature of its progenitor. The earliest detection of this explosion was on 2013 July 24.125 UT and our spectroscopic monitoring with the FLOYDS spectrographs began on July 27.7 UT, continuing almost daily for two weeks. Daily optical photometric monitoringwas achieved with the 1mtelescopes of the Las Cumbres Observatory Global Telescope (LCOGT) network, and was complemented by UV data from Swift and near-infrared spectra from Public ESO Spectroscopic Survey of Transient Objects and Infrared Telescope Facility. The data from our monitoring campaign show that SN 2013ej experienced a 10 d rise before entering into a well-defined plateau phase. This unusually long rise time for a Type IIP has been seen previously in SN 2006bp and SN 2009bw. A relatively rare strong absorption blueward of Hα is present since our earliest spectrum. We identify this feature as Si II, rather than high-velocity Hα as sometimes reported in the literature.
Resumo:
Relative strengths of surface interaction for individual carbon atoms in acyclic and cyclic hydrocarbons adsorbed on alumina surfaces are determined using chemically resolved 13C nuclear magnetic resonance (NMR) T1 relaxation times. The ratio of relaxation times for the adsorbed atoms T1,ads to the bulk liquid relaxation time T1,bulk provides an indication of the mobility of the atom. Hence a low T1,ads/T1,bulk ratio indicates a stronger surface interaction. The carbon atoms associated with unsaturated bonds in the molecules are seen to exhibit a larger reduction in T1 on adsorption relative to the aliphatic carbons, consistent with adsorption occurring through the carbon-carbon multiple bonds. The relaxation data are interpreted in terms of proximity of individual carbon atoms to the alumina surface and adsorption conformations are inferred. Furthermore, variations of interaction strength and molecular configuration have been explored as a function of adsorbate coverage, temperature, surface pre-treatment, and in the presence of co-adsorbates. This relaxation time analysis is appropriate for studying the behaviour of hydrocarbons adsorbed on a wide range of catalyst support and supported-metal catalyst surfaces, and offers the potential to explore such systems under realistic operating conditions when multiple chemical components are present at the surface.
Resumo:
We present a new regime to generate high-energy quasimonoenergetic proton beams in a "slow-pulse" regime, where the laser group velocity vg<c is reduced by an extended near-critical density plasma. In this regime, for properly matched laser intensity and group velocity, ions initially accelerated by the light sail (LS) mode can be further trapped and reflected by the snowplough potential generated by the laser in the near-critical density plasma. These two acceleration stages are connected by the onset of Rayleigh-Taylor-like (RT) instability. The usual ion energy spectrum broadening by RT instability is controlled and high quality proton beams can be generated. It is shown by multidimensional particle-in-cell simulation that quasimonoenergetic proton beams with energy up to hundreds of MeV can be generated at laser intensities of 1021W/cm2.
Resumo:
Recent high-resolution observations of sunspot oscillations using simultaneously operated ground- and space-based telescopes reveal the intrinsic connection between different layers of the solar atmosphere. However, it is not clear whether these oscillations are externally driven or generated in situ. We address this question by using observations of propagating slow magnetoacoustic waves along a coronal fan loop system. In addition to the generally observed decreases in oscillation amplitudes with distance, the observed wave amplitudes are also found to be modulated with time, with similar variations observed throughout the propagation path of the wave train. Employing multi-wavelength and multi-instrument data, we study the amplitude variations with time as the waves propagate through different layers of the solar atmosphere. By comparing the amplitude modulation period in different layers, we find that slow magnetoacoustic waves observed in sunspots are externally driven by photospheric p-modes, which propagate upward into the corona before becoming dissipated.
Resumo:
Geological, biological, morphological, and hydrochemical data are presented for the newly discovered Moytirra vent field at 45oN. This is the only high temperature hydrothermal vent known between the Azores and Iceland, in the North Atlantic and is located on a slow to ultraslow-spreading mid-ocean ridge uniquely situated on the 300 m high fault scarp of the eastern axial wall, 3.5 km from the axial volcanic ridge crest. Furthermore, the Moytirra vent field is, unusually for tectonically controlled hydrothermal vents systems, basalt hosted and perched midway up on the median valley wall and presumably heated by an off-axis magma chamber. The Moytirra vent field consists of an alignment of four sites of venting, three actively emitting "black smoke," producing a complex of chimneys and beehive diffusers. The largest chimney is 18 m tall and vigorously venting. The vent fauna described here are the only ones documented for the North Atlantic (Azores to Reykjanes Ridge) and significantly expands our knowledge of North Atlantic biodiversity. The surfaces of the vent chimneys are occupied by aggregations of gastropods (Peltospira sp.) and populations of alvinocaridid shrimp (Mirocaris sp. with Rimicaris sp. also present). Other fauna present include bythograeid crabs (Segonzacia sp.) and zoarcid fish (Pachycara sp.), but bathymodiolin mussels and actinostolid anemones were not observed in the vent field. The discovery of the Moytirra vent field therefore expands the known latitudinal distributions of several vent-endemic genera in the north Atlantic, and reveals faunal affinities with vents south of the Azores rather than north of Iceland. © 2013. American Geophysical Union. All Rights Reserved.
Resumo:
Research findings suggest that switching between competing response sets can be resource demanding. The current study focused on concurrent health-relevant physiological effects of task switching by assessing cardiovascular response at varying levels of switch frequency. The participants performed a response-switching task at three different levels of response set switching frequency (low, medium and high) while measurements of blood pressure and heart rate were taken. One group was exposed to response-switching frequency conditions in the order low → medium → high, while the other group was exposed to the same task conditions in the reverse order (i.e. high → medium → low). The results showed that the participants in the low → medium → high switch frequency group recovered faster from initially heightened systolic blood pressure when compared with participants in the high → medium → low group. It is concluded that the results point to a physiological "carry over" effect associated with beginning a task at rapid response switching frequency levels, and suggest the importance of habituation to task demands as a means of offsetting potentially unhealthy levels of reactivity. Implications for modern work environments are discussed.
Resumo:
Ultrasound absorption spectra of four 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide were determined as a function of the alkyl chain length on the cation from 1-propyl- to 1-hexyl- from 293.15 to 323.15 K at ambient pressure. Herein, the ultrasound absorption measurements were carried out using a standard pulse technique within a frequency range from 10 to 300 MHz. Additionally the speed of sound, density and viscosity have been measured. The presence of strong dissipative processes during the ultrasound wave propagation was found experimentally, i.e. relaxation processes in the megahertz range were observed for all compounds over the whole temperature range. The relaxation spectra (both relaxation amplitude and relaxation frequency) were shown to be dependent on the alkyl side chain length of the 1-alkyl-3-methylimidazolium ring. In most cases, a single Debye model described the absorption spectra very well. However, a comparison of the determined spectra with the spectra of a few other imidazolium-based ionic liquids reported in the literature (in part recalculated in this work) shows that the complexity of the spectra increases rapidly with the elongation of the alkyl chain length on the cation. This complexity indicates that both the volume viscosity and the shear viscosity are involved in relaxation processes even in relatively low frequency ranges. As a consequence, the sound velocity dispersion is present at relatively low megahertz frequencies.
Resumo:
The suppression of drug consumption and trade is high on the Government of Vietnam’s agenda. To accomplish this goal, Vietnam employs repressive policies that often contravene international human rights law. Among the most detrimental and problematic policies are the incarceration of drug users in compulsory treatment centers, and the stigmatization and abuse of consumers by the police. That said, Vietnamese drug policy is slowly changing in the face of one of Asia’s worst ongoing HIV epidemics. While the Communist Government of the early-1990s designated illicit drugs as a “social evil” to be eradicated through punitive and often repressive means, the recent implementation of harm reduction approaches have reduced the level of needle sharing, and thus HIV transmission. This briefing will explore the current trends in drug consumption, production, and trafficking before looking at the key harms and threats associated with drugs in Vietnam. This will be followed by a summary of Vietnam’s drug policies, including the country’s approach to drug treatment, harm reduction, and illicit opium suppression—Vietnam is one of a small number of states to have suppressed illicit opium production, an intervention that centred upon coercive negotiations with limited alternative development. The briefing will conclude with some tentative recommendations for reform and thoughts on what could be expected from Vietnam during the Special Session of the United Nations General Assembly on the World Drug Problem (UNGASS 2016).
Resumo:
The pathogenesis of Duchenne muscular dystrophy (DMD), characterised by lack of the cytoskeletal protein dystrophin, is not completely understood. An early event in the degenerative process of DMD muscle could be a rise in cytosolic calcium concentration. In order to investigate whether this leads to alterations of contractile behaviour, we studied the excitability and contractile properties of cultured myotubes from control (C57BL/10) and mdx mice, an animal model for DMD. The myotubes were stimulated electrically and their motion was recorded photometrically. No significant differences were found between control and mdx myotubes with respect to the following parameters: chronaxy and rheobase (0.33 +/- 0.03 ms and 23 +/- 4 V vs. 0.39 +/- 0.07 ms and 22 +/- 2 V for C57 and mdx myotubes, respectively), tetanisation frequency (a similar distribution pattern was found between 5 and 30 Hz), fatigue during tetanus (found in 35% of both types of myotubes) and post-tetanic contracture. In contrast, contraction and relaxation times were longer (P < 0.005) in mdx (36 +/- 2 and 142 +/- 13 ms, respectively) than in control myotubes (26 +/- 1 and 85 +/- 9 ms, respectively). Together with our earlier findings, these results suggest a decreased capacity for calcium removal in mdx cells leading, in particular, to alterations of muscle relaxation.
Resumo:
PURPOSE: To present the long-term follow-up of 10 adolescents and young adults with documented cognitive and behavioral regression as children due to nonlesional focal, mainly frontal, epilepsy with continuous spike-waves during slow wave sleep (CSWS). METHODS: Past medical and electroencephalography (EEG) data were reviewed and neuropsychological tests exploring main cognitive functions were administered. KEY FINDINGS: After a mean duration of follow-up of 15.6 years (range, 8-23 years), none of the 10 patients had recovered fully, but four regained borderline to normal intelligence and were almost independent. Patients with prolonged global intellectual regression had the worst outcome, whereas those with more specific and short-lived deficits recovered best. The marked behavioral disorders resolved in all but one patient. Executive functions were neither severely nor homogenously affected. Three patients with a frontal syndrome during the active phase (AP) disclosed only mild residual executive and social cognition deficits. The main cognitive gains occurred shortly after the AP, but qualitative improvements continued to occur. Long-term outcome correlated best with duration of CSWS. SIGNIFICANCE: Our findings emphasize that cognitive recovery after cessation of CSWS depends on the severity and duration of the initial regression. None of our patients had major executive and social cognition deficits with preserved intelligence, as reported in adults with early destructive lesions of the frontal lobes. Early recognition of epilepsy with CSWS and rapid introduction of effective therapy are crucial for a best possible outcome.
Resumo:
To explore the idea of education to close the ingenuity gap I use Thomas Homer-Dixon's work to define ingenuity. The notion that the supply of ingenuity to solve our technical and social problems is not keeping pace with the ingenuity required to solve those problems is called the ingenuity gap. Man-made technological developments are increasing the density, intensity, and pace of globalisation. People must reorganise decision-making organisations and problem-solving methods to pragmatically combat the growing ingenuity gap. John Dewey's work illustrates the fundamental attitudes for the thinking and judgment associated with educating for ingenuity. Howard Gardner's idea that truth, beauty, and morality ought to form the core values and tenets of the philosophy of educating for ingenuity is integral to this thesis. The act of teaching facilitates the invitation to the communication necessary to foster ingenuity. John Novak-discusses the five relationships of educational leadership that enhance an environment of ingenuity. The International Baccalaureate (IB) is an existing model of global education, one that defines some of the school experiences and academic development of core values of educating for ingenuity. Expanding upon the structure of the IB and other research within this thesis, I speculate upon what my school, where educating for ingenuity so as to close the ingenuity gap is the goal, would be like.
Resumo:
This research investigated the impact of stress management and relaxation techniques on psoriasis. It had a dual purpose to see if stress management and relaxation techniques, as an adjunct to traditional medical treatment, would improve the skin condition of psoriasis. In addition it attempted to provide psoriasis patients with a sense of control over their illness by educating them about the connection between mind and body through learning stress management and relaxation techniques. The former purpose was addressed quantitatively, while the latter was addressed qualitatively. Using an experimental design, the quantitative study tested the efficacy of stress management and relaxation techniques on 38 dermatological patients from St. John's, Newfoundland. The study which lasted ten weeks, suggested a weak relationship between psoriasis and stress. These relationships were not statistically significant. The qualitative data were gathered through unstructured interviews and descriptive/interpretative analysis was used to evaluate them. Patients in the experimental group believed in the mind body connection as it related to their illness and stress. The findings also showed that the patients believed that the stress reduction and relaxation techniques improved their quality of life, their level of psoriasis, and their ability to live with the condition. Based on the contradictory nature of the findings, further research is needed. It is posited that replication of this study would be vastly improved by increasing the sample size to increase the possibility of significant findings. As wel~ increasing the length of time for the experiment would control for the possibility of a lag effect. Finally, the study looked at linear relationships between stress and psoriasis. Further study should ascertain whether the relationship might be nonlinear
Resumo:
A ~si MAS NMR study of spin-lattice relaxation behaviour
in paramagnetic-doped crystalline silicates was undertaken,
using synthetic magnesium orthosilicate (forsterite) and
synthetic zinc orthosilicate (willemite) doped with 0.1% to
20% of Co(II), Ni(II), or CU(II), as experimental systems.
All of the samples studied exhibited a longitudinal
magnetization return to the Boltzmann distribution of nuclear
spin states which followed a stretched-exponential function of
time:
Y=exp [- (tjTn) n], O
Resumo:
Second-rank tensor interactions, such as quadrupolar interactions between the spin- 1 deuterium nuclei and the electric field gradients created by chemical bonds, are affected by rapid random molecular motions that modulate the orientation of the molecule with respect to the external magnetic field. In biological and model membrane systems, where a distribution of dynamically averaged anisotropies (quadrupolar splittings, chemical shift anisotropies, etc.) is present and where, in addition, various parts of the sample may undergo a partial magnetic alignment, the numerical analysis of the resulting Nuclear Magnetic Resonance (NMR) spectra is a mathematically ill-posed problem. However, numerical methods (de-Pakeing, Tikhonov regularization) exist that allow for a simultaneous determination of both the anisotropy and orientational distributions. An additional complication arises when relaxation is taken into account. This work presents a method of obtaining the orientation dependence of the relaxation rates that can be used for the analysis of the molecular motions on a broad range of time scales. An arbitrary set of exponential decay rates is described by a three-term truncated Legendre polynomial expansion in the orientation dependence, as appropriate for a second-rank tensor interaction, and a linear approximation to the individual decay rates is made. Thus a severe numerical instability caused by the presence of noise in the experimental data is avoided. At the same time, enough flexibility in the inversion algorithm is retained to achieve a meaningful mapping from raw experimental data to a set of intermediate, model-free