9,711 research outputs found
1/f spectrum and memory function analysis of solvation dynamics in a room-temperature ionic liquid
To understand the non-exponential relaxation associated with solvation
dynamics in the ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate,
we study power spectra of the fluctuating Franck-Condon energy gap of a
diatomic probe solute via molecular dynamics simulations. Results show 1/f
dependence in a wide frequency range over 2 to 3 decades, indicating
distributed relaxation times. We analyze the memory function and solvation time
in the framework of the generalized Langevin equation using a simple model
description for the power spectrum. It is found that the crossover frequency
toward the white noise plateau is directly related to the time scale for the
memory function and thus the solvation time. Specifically, the low crossover
frequency observed in the ionic liquid leads to a slowly-decaying tail in its
memory function and long solvation time. By contrast, acetonitrile
characterized by a high crossover frequency and (near) absence of 1/f behavior
in its power spectra shows fast relaxation of the memory function and
single-exponential decay of solvation dynamics in the long-time regime.Comment: 10 pages, 4 figure
Supernova 2009kf: An Ultraviolet Bright Type IIP Supernova Discovered with Pan-STARRS 1 and GALEX
We present photometric and spectroscopic observations of a luminous Type IIP Supernova (SN) 2009kf discovered by the Pan-STARRS 1 (PS1) survey and also detected by the Galaxy Evolution Explorer. The SN shows a plateau in its optical and bolometric light curves, lasting approximately 70 days in the rest frame, with an absolute magnitude of M_V = -18.4 mag. The P-Cygni profiles of hydrogen indicate expansion velocities of 9000 km s^(-1) at 61 days after discovery which is extremely high for a Type IIP SN. SN 2009kf is also remarkably bright in the near-ultraviolet (NUV) and shows a slow evolution 10-20 days after optical discovery. The NUV and optical luminosity at these epochs can be modeled with a blackbody with a hot effective temperature (T ~ 16,000 K) and a large radius (R ~ 1 × 10^(15) cm). The bright bolometric and NUV luminosity, the light curve peak and plateau duration, the high velocities, and temperatures suggest that 2009kf is a Type IIP SN powered by a larger than normal explosion energy. Recently discovered high-z SNe (0.7 < z < 2.3) have been assumed to be IIn SNe, with the bright UV luminosities due to the interaction of SN ejecta with a dense circumstellar medium. UV-bright SNe similar to SN 2009kf could also account for these high-z events, and its absolute magnitude M_(NUV) = -21.5 ± 0.5 mag suggests such SNe could be discovered out to z ~ 2.5 in the PS1 survey
The Detection of Outflows in the IR-Quiet Molecular Core NGC 6334 I(North)
We find strong evidence for outflows originating in the dense molecular core
NGC 6334 I(North): a 1000 Msol molecular core distinguished by its lack of HII
regions and mid-IR emission. New observations were obtained of the SiO 2-1 and
5-4 lines with the SEST 15-m telescope and the H2 (1-0) S(1) line with the ESO
2.2-m telescope. The line profiles of the SiO transitions show broad wings
extending from -50 to 40 km/s, and spatial maps of the line wing emission
exhibit a bipolar morphology with the peaks of the red and blue wing separated
by 30". The estimated mass loss rate of the outflow is comparable to those for
young intermediate to high-mass stars. The near-IR images show eight knots of
H2 emission. Five of the knots form a linear chain which is displaced from the
axis of the SiO outflow; these knots may trace shock excited gas along the path
of a second, highly collimated outflow. We propose that I(N) is a rare example
of a molecular core in an early stage of cluster formation.Comment: 4 pages, LaTeX, 3 ps figures, accepted by ApJ
Evidence for glutamate-mediated excitotoxic mechanisms during photoreceptor degeneration in the rd1 mouse retina
PURPOSE: Kinetic studies of photoreceptor cell death in the retinal degeneration (rd1) mouse model suggest that photoreceptor degeneration could result from cumulative damage. Since alterations in glutamate metabolism have been described in different models of retinitis pigmentosa, we investigated in the present work whether changes in glutamate turnover occur in the degenerating rd1 retina and whether glutamate-mediated excitotoxic mechanisms may contribute to rod photoreceptor death in this model. METHODS: Free amino acid levels were quantified in rd1 and wild-type retinas using an amino acid analyzer selecting times corresponding to early, intermediate, and terminal phases of rod photoreceptor degeneration. Reverse transcription-polymerase chain reaction (RT-PCR) was used to compare the mRNA expression levels of the glial L-glutamate/L-aspartate transporter GLAST, glutamine synthetase (GS), and vimentin, a marker for retinal glia, between rd1 and wild-type mouse retinas. 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an antagonist of both AMPA and kainate subtypes of ionotropic glutamate receptors, was then daily administered from postnatal day 3 (PN3) to PN21 to rd1 mice while control rd1 mice received only physiological saline solution (7 per treatment). At PN22, the respective numbers of surviving rods i
DISTANCE EDUCATION IN AGRICULTURAL ECONOMICS: AN ASSESSMENT OF STUDENT ACCEPTANCE AND PERFORMANCE.
This paper reports an analysis of student evaluation of and performance in three agricultural economics classes offered at distance by audio-visual connection in real time. Multiple regression analyses of student questionnaire data are used to examine the relationship between student attributes and their evaluation of and performance in the distance-offered course.Teaching/Communication/Extension/Profession,
Energy budget constraints on historical radiative forcing
Radiative forcing is a fundamental quantity for understanding anthropogenic and natural drivers of past and future climate change1, yet significant uncertainty remains in our quantification of radiative forcing and its model representation2,3,4. Here we use instrumental measurements of historical global mean surface temperature change and Earth’s total heat uptake, alongside estimates of the Earth’s radiative response, to provide a top-down energy budget constraint on historical (1861–1880 to near-present) effective radiative forcing of 2.3 W m−2 (1.7–3.0W m−2; 5–95% confidence interval). This represents a near 40% reduction in the 5–95% uncertainty range assessed by the IPCC Fifth Assessment Report2. Although precise estimates of effective radiative forcing in models do not widely exist, our results suggest that the effective radiative forcing may be too small in as many as one-third of climate models in the fifth phase of the Coupled Model Intercomparison Project. Improving model representation of radiative forcing should be a priority for modelling centres. This will reduce uncertainties in climate projections that have persisted for decades4,5
Magnetothermal Transport in Spin-Ladder Systems
We study a theoretical model for the magnetothermal conductivity of a
spin-1/2 ladder with low exchange coupling () subject to a strong
magnetic field . Our theory for the thermal transport accounts for the
contribution of spinons coupled to lattice phonon modes in the one-dimensional
lattice. We employ a mapping of the ladder Hamiltonian onto an XXZ spin-chain
in a weaker effective field B_{eff}=B-B_{0}B_{0}=(B_{c1}+B_{c2})/2B{\rm
Br_4(C_5H_{12}N)_2}$ (BPCB).Comment: 14 pages, 4 figure
A Reanalysis of the Hydrodynamic Theory of Fluid, Polar-Ordered Flocks
I reanalyze the hydrodynamic theory of fluid, polar ordered flocks. I find
new linear terms in the hydrodynamic equations which slightly modify the
anisotropy, but not the scaling, of the damping of sound modes. I also find
that the nonlinearities allowed {\it in equilibrium} do not stabilize long
ranged order in spatial dimensions ; in accord with the Mermin-Wagner
theorem. Nonequilibrium nonlinearities {\it do} stabilize long ranged order in
, as argued by earlier work. Some of these were missed by earlier work; it
is unclear whether or not they change the scaling exponents in .Comment: 6 pages, no figures. arXiv admin note: text overlap with
arXiv:0909.195
QTL Analysis and Trait Dissection in Ryegrass (\u3cem\u3eLolium\u3c/em\u3e Spp.)
Key points Molecular marker-based genetic analysis permits the dissection of complex phenotypes through resolution of the locations of pleiotropic and interacting genetic factors. Several QTLs for agronomically important characters such as flowering time, winter hardiness and forage quality have been identified in perennial ryegrass by molecular marker-based map analysis. Some QTLs were putatively orthologous to those for equivalent traits in cereals. The identification of co-location between QTLs and functionally-associated genetic markers is critical for the future implementation of marker-assisted selection programs
Object-guided Spatial Attention in Touch: Holding the Same Object with Both Hands Delays Attentional Selection
Abstract
Previous research has shown that attention to a specific location on a uniform visual object spreads throughout the entire object. Here we demonstrate that, similar to the visual system, spatial attention in touch can be object guided. We measured event-related brain potentials to tactile stimuli arising from objects held by observers' hands, when the hands were placed either near each other or far apart, holding two separate objects, or when they were far apart but holding a common object. Observers covertly oriented their attention to the left, to the right, or to both hands, following bilaterally presented tactile cues indicating likely tactile target location(s). Attentional modulations for tactile stimuli at attended compared to unattended locations were present in the time range of early somatosensory components only when the hands were far apart, but not when they were near. This was found to reflect enhanced somatosensory processing at attended locations rather than suppressed processing at unattended locations. Crucially, holding a common object with both hands delayed attentional selection, similar to when the hands were near. This shows that the proprioceptive distance effect on tactile attentional selection arises when distant event locations can be treated as separate and unconnected sources of tactile stimulation, but not when they form part of the same object. These findings suggest that, similar to visual attention, both space- and object-based attentional mechanisms can operate when we select between tactile events on our body surface.</jats:p
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