1,958 research outputs found
Charged Magnetic Brane Solutions in AdS_5 and the fate of the third law of thermodynamics
We construct asymptotically AdS_5 solutions to 5-dimensional Einstein-Maxwell
theory with Chern-Simons term which are dual to 4-dimensional gauge theories,
including N=4 SYM theory, in the presence of a constant background magnetic
field B and a uniform electric charge density \rho. For the solutions
corresponding to supersymmetric gauge theories, we find numerically that a
small magnetic field causes a drastic decrease in the entropy at low
temperatures. The near-horizon AdS_2 \times R^3 geometry of the purely
electrically charged brane thus appears to be unstable under the addition of a
small magnetic field. Based on this observation, we propose a formulation of
the third law of thermodynamics (or Nernst theorem) that can be applied to
black holes in the AdS/CFT context.
We also find interesting behavior for smaller, non-supersymmetric, values of
the Chern-Simons coupling k. For k=1 we exhibit exact solutions corresponding
to warped AdS_3 black holes, and show that these can be connected to
asymptotically AdS_5 spacetime. For k\leq 1 the entropy appears to go to a
finite value at extremality, but the solutions still exhibit a mild singularity
at strictly zero temperature. In addition to our numerics, we carry out a
complete perturbative analysis valid to order B^2, and find that this
corroborates our numerical results insofar as they overlap.Comment: 45 pages v2: added note about subsequent results found in
arXiv:1003.130
Olfactory and solitary chemosensory cells: two different chemosensory systems in the nasal cavity of the American alligator, Alligator mississippiensis
<p>Abstract</p> <p>Background</p> <p>The nasal cavity of all vertebrates houses multiple chemosensors, either innervated by the Ist (olfactory) or the Vth (trigeminal) cranial nerve. Various types of receptor cells are present, either segregated in different compartments (e.g. in rodents) or mingled in one epithelium (e.g. fish). In addition, solitary chemosensory cells have been reported for several species. Alligators which seek their prey both above and under water have only one nasal compartment. Information about their olfactory epithelium is limited. Since alligators seem to detect both volatile and water-soluble odour cues, I tested whether different sensory cell types are present in the olfactory epithelium.</p> <p>Results</p> <p>Electron microscopy and immunocytochemistry were used to examine the sensory epithelium of the nasal cavity of the American alligator. Almost the entire nasal cavity is lined with olfactory (sensory) epithelium. Two types of olfactory sensory neurons are present. Both types bear cilia as well as microvilli at their apical endings and express the typical markers for olfactory neurons. The density of these olfactory neurons varies along the nasal cavity. In addition, solitary chemosensory cells innervated by trigeminal nerve fibres, are intermingled with olfactory sensory neurons. Solitary chemosensory cells express components of the PLC-transduction cascade found in solitary chemosensory cells in rodents.</p> <p>Conclusion</p> <p>The nasal cavity of the American alligator contains two different chemosensory systems incorporated in the same sensory epithelium: the olfactory system proper and solitary chemosensory cells. The olfactory system contains two morphological distinct types of ciliated olfactory receptor neurons.</p
Declining uncertainty in transient climate response as CO2 forcing dominates future climate change
Carbon dioxide has exerted the largest portion of radiative forcing and surface temperature change over the industrial era, but other anthropogenic influences have also contributed. However, large uncertainties in total forcing make it difficult to derive climate sensitivity from historical observations. Anthropogenic forcing has increased between the Fourth and Fifth Assessment Reports of the Intergovernmental Panel of Climate Change (IPCC; refs,), although its relative uncertainty has decreased. Here we show, based on data from the two reports, that this evolution towards lower uncertainty can be expected to continue into the future. Because it is easier to reduce air pollution than carbon dioxide emissions and because of the long lifetime of carbon dioxide, the less uncertain carbon dioxide forcing is expected to become increasingly dominant. Using a statistical model, we estimate that the relative uncertainty in anthropogenic forcing of more than 40% quoted in the latest IPCC report for 2011 will be almost halved by 2030, even without better scientific understanding. Absolute forcing uncertainty will also decline for the first time, provided projected decreases in aerosols occur. Other factors being equal, this stronger constraint on forcing will bring a significant reduction in the uncertainty of observation-based estimates of the transient climate response, with a 50% reduction in its uncertainty range expected by 2030
Collective Excitations of Holographic Quantum Liquids in a Magnetic Field
We use holography to study N=4 supersymmetric SU(Nc) Yang-Mills theory in the
large-Nc and large-coupling limits coupled to a number Nf << Nc of
(n+1)-dimensional massless supersymmetric hypermultiplets in the Nc
representation of SU(Nc), with n=2,3. We introduce a temperature T, a baryon
number chemical potential mu, and a baryon number magnetic field B, and work in
a regime with mu >> T,\sqrt{B}. We study the collective excitations of these
holographic quantum liquids by computing the poles in the retarded Green's
function of the baryon number charge density operator and the associated peaks
in the spectral function. We focus on the evolution of the collective
excitations as we increase the frequency relative to T, i.e. the
hydrodynamic/collisionless crossover. We find that for all B, at low
frequencies the tallest peak in the spectral function is associated with
hydrodynamic charge diffusion. At high frequencies the tallest peak is
associated with a sound mode similar to the zero sound mode in the
collisionless regime of a Landau Fermi liquid. The sound mode has a gap
proportional to B, and as a result for intermediate frequencies and for B
sufficiently large compared to T the spectral function is strongly suppressed.
We find that the hydrodynamic/collisionless crossover occurs at a frequency
that is approximately B-independent.Comment: 45 pages, 8 png and 47 pdf images in 22 figure
Phase diagram for non-axisymmetric plasma balls
Plasma balls and rings emerge as fluid holographic duals of black holes and
black rings in the hydrodynamic/gravity correspondence for the Scherk-Schwarz
AdS system. Recently, plasma balls spinning above a critical rotation were
found to be unstable against m-lobed perturbations. In the phase diagram of
stationary solutions the threshold of the instability signals a bifurcation to
a new phase of non-axisymmetric configurations. We find explicitly this family
of solutions and represent them in the phase diagram. We discuss the
implications of our results for the gravitational system. Rotating
non-axisymmetric black holes necessarily radiate gravitational waves. We thus
emphasize that it would be important, albeit possibly out of present reach, to
have a better understanding of the hydrodynamic description of gravitational
waves and of the gravitational interaction between two bodies. We also argue
that it might well be that a non-axisymmetric m-lobed instability is also
present in Myers-Perry black holes for rotations below the recently found
ultraspinning instability.Comment: 1+22 pages, 3 figures. v2: minor corrections and improvements,
matches published versio
In-medium hadronic spectral functions through the soft-wall holographic model of QCD
We study the scalar glueball and vector meson spectral functions in a hot and
dense medium by means of the soft-wall holographic model of QCD. Finite
temperature and density effects are implemented through the AdS/RN metric. We
analyse the behaviour of the hadron masses and widths in the plane,
and compare our results with the experimental ones and with other theoretical
determinations.Comment: 16 pages, 6 figures. matching the published versio
The "Ram Effect": A "Non-Classical" Mechanism for Inducing LH Surges in Sheep
During spring sheep do not normally ovulate but exposure to a ram can induce ovulation. In some ewes an LH surge is induced immediately after exposure to a ram thus raising questions about the control of this precocious LH surge. Our first aim was to determine the plasma concentrations of oestradiol (E2) E2 in anoestrous ewes before and after the "ram effect" in ewes that had a "precocious" LH surge (starting within 6 hours), a "normal" surge (between 6 and 28h) and "late» surge (not detected by 56h). In another experiment we tested if a small increase in circulating E2 could induce an LH surge in anoestrus ewes. The concentration of E2 significantly was not different at the time of ram introduction among ewes with the three types of LH surge. "Precocious" LH surges were not preceded by a large increase in E2 unlike "normal" surges and small elevations of circulating E2 alone were unable to induce LH surges. These results show that the "precocious" LH surge was not the result of E2 positive feedback. Our second aim was to test if noradrenaline (NA) is involved in the LH response to the "ram effect". Using double labelling for Fos and tyrosine hydroxylase (TH) we showed that exposure of anoestrous ewes to a ram induced a higher density of cells positive for both in the A1 nucleus and the Locus Coeruleus complex compared to unstimulated controls. Finally, the administration by retrodialysis into the preoptic area, of NA increased the proportion of ewes with an LH response to ram odor whereas treatment with the α1 antagonist Prazosin decreased the LH pulse frequency and amplitude induced by a sexually active ram. Collectively these results suggest that in anoestrous ewes NA is involved in ram-induced LH secretion as observed in other induced ovulators
A new multicompartmental reaction-diffusion modeling method links transient membrane attachment of E. coli MinE to E-ring formation
Many important cellular processes are regulated by reaction-diffusion (RD) of molecules that takes place both in the cytoplasm and on the membrane. To model and analyze such multicompartmental processes, we developed a lattice-based Monte Carlo method, Spatiocyte that supports RD in volume and surface compartments at single molecule resolution. Stochasticity in RD and the excluded volume effect brought by intracellular molecular crowding, both of which can significantly affect RD and thus, cellular processes, are also supported. We verified the method by comparing simulation results of diffusion, irreversible and reversible reactions with the predicted analytical and best available numerical solutions. Moreover, to directly compare the localization patterns of molecules in fluorescence microscopy images with simulation, we devised a visualization method that mimics the microphotography process by showing the trajectory of simulated molecules averaged according to the camera exposure time. In the rod-shaped bacterium _Escherichia coli_, the division site is suppressed at the cell poles by periodic pole-to-pole oscillations of the Min proteins (MinC, MinD and MinE) arising from carefully orchestrated RD in both cytoplasm and membrane compartments. Using Spatiocyte we could model and reproduce the _in vivo_ MinDE localization dynamics by accounting for the established properties of MinE. Our results suggest that the MinE ring, which is essential in preventing polar septation, is largely composed of MinE that is transiently attached to the membrane independently after recruited by MinD. Overall, Spatiocyte allows simulation and visualization of complex spatial and reaction-diffusion mediated cellular processes in volumes and surfaces. As we showed, it can potentially provide mechanistic insights otherwise difficult to obtain experimentally
Micro-manufacturing : research, technology outcomes and development issues
Besides continuing effort in developing MEMS-based manufacturing techniques, latest effort in Micro-manufacturing is also in Non-MEMS-based manufacturing. Research and technological development (RTD) in this field is encouraged by the increased demand on micro-components as well as promised development in the scaling down of the traditional macro-manufacturing processes for micro-length-scale manufacturing. This paper highlights some EU funded research activities in micro/nano-manufacturing, and gives examples of the latest development in micro-manufacturing methods/techniques, process chains, hybrid-processes, manufacturing equipment and supporting technologies/device, etc., which is followed by a summary of the achievements of the EU MASMICRO project. Finally, concluding remarks are given, which raise several issues concerning further development in micro-manufacturing
A Stochastic Model for Microtubule Motors Describes the In Vivo Cytoplasmic Transport of Human Adenovirus
Cytoplasmic transport of organelles, nucleic acids and proteins on microtubules is usually bidirectional with dynein and kinesin motors mediating the delivery of cargoes in the cytoplasm. Here we combine live cell microscopy, single virus tracking and trajectory segmentation to systematically identify the parameters of a stochastic computational model of cargo transport by molecular motors on microtubules. The model parameters are identified using an evolutionary optimization algorithm to minimize the Kullback-Leibler divergence between the in silico and the in vivo run length and velocity distributions of the viruses on microtubules. The present stochastic model suggests that bidirectional transport of human adenoviruses can be explained without explicit motor coordination. The model enables the prediction of the number of motors active on the viral cargo during microtubule-dependent motions as well as the number of motor binding sites, with the protein hexon as the binding site for the motors
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