8,221 research outputs found
Variable-Speed-of-Light Cosmology and Second Law of Thermodynamics
We examine whether the cosmologies with varying speed of light (VSL) are
compatible with the second law of thermodynamics. We find that the VSL
cosmology with varying fundamental constant is severely constrained by the
second law of thermodynamics, whereas the bimetric cosmological models are less
constrained.Comment: 15 pages, LaTeX, Revised version with minor corrections to appear in
Phys. Rev.
Stress-Induced Cocaine Seeking Requires a Beta-2 Adrenergic Receptor-Regulated Pathway from the Ventral Bed Nucleus of the Stria Terminalis That Regulates CRF Actions in the Ventral Tegmental Area
The ventral bed nucleus of the stria terminalis (vBNST) has been implicated in stress-induced cocaine use. Here we demonstrate that, in the vBNST, corticotropin releasing factor (CRF) is expressed in neurons that innervate the ventral tegmental area (VTA), a site where the CRF receptor antagonist antalarmin prevents the reinstatement of cocaine seeking by a stressor, intermittent footshock, following intravenous self-administration in rats. The vBNST receives dense noradrenergic innervation and expresses β adrenergic receptors (ARs). Footshock-induced reinstatement was prevented by bilateral intra-vBNST injection of the β-2 AR antagonist, ICI-118,551, but not the β-1 AR antagonist, betaxolol. Moreover, bilateral intra-vBNST injection of the β-2 AR agonist, clenbuterol, but not the β-1 agonist, dobutamine, reinstated cocaine seeking, suggesting that activation of vBNST β-2 AR is both necessary for stress-induced reinstatement and sufficient to induce cocaine seeking. The contribution of a β-2 AR-regulated vBNST-to-VTA pathway that releases CRF was investigated using a disconnection approach. Injection of ICI-118,551 into the vBNST in one hemisphere and antalarmin into the VTA of the contralateral hemisphere prevented footshock-induced reinstatement, whereas ipsilateral manipulations failed to attenuate stress-induced cocaine seeking, suggesting that β-2 AR regulate vBNST efferents that release CRF into the VTA, activating CRF receptors, and promoting cocaine use. Last, reinstatement by clenbuterol delivered bilaterally into the vBNST was prevented by bilateral vBNST pretreatment with antalarmin, indicating that β-2 AR-mediated actions in the vBNST also require local CRF receptor activation. Understanding the processes through which stress induces cocaine seeking should guide the development of new treatments for addiction
Linearisation Instabilities of the Massive Nonsymmetric Gravitational Theory
The massive nonsymmetric gravitational theory is shown to posses a
linearisation instability at purely GR field configurations, disallowing the
use of the linear approximation in these situations. It is also shown that
arbitrarily small antisymmetric sector Cauchy data leads to singular evolution
unless an ad hoc condition is imposed on the initial data hypersurface.Comment: 14 pages, IOP style for submission to CQG. Minor changes and
additional background material adde
The Dynamical Instability of Static, Spherically Symmetric Solutions in Nonsymmetric Gravitational Theories
We consider the dynamical stability of a class of static,
spherically-symmetric solutions of the nonsymmetric gravitational theory. We
numerically reproduce the Wyman solution and generate new solutions for the
case where the theory has a nontrivial fundamental length scale \mu^{-1}. By
considering spherically symmetric perturbations of these solutions we show that
the Wyman solutions are generically unstable.Comment: 13 pages, uses amslatex, graphicx and subfigure package
Comments on "Note on varying speed of light theories"
In a recent note Ellis criticizes varying speed of light theories on the
grounds of a number of foundational issues. His reflections provide us with an
opportunity to clarify some fundamental matters pertaining to these theories
Structure Formation Inside Triaxial Dark Matter Halos: Galactic Disks, Bulges and Bars
We investigate the formation and evolution of galactic disks immersed in
assembling live DM halos. Disk/halo components have been evolved from the
cosmological initial conditions and represent the collapse of an isolated
density perturbation. The baryons include gas (which participates in star
formation [SF]) and stars. The feedback from the stellar energy release onto
the ISM has been implemented. We find that (1) The growing triaxial halo figure
tumbling is insignificant and the angular momentum (J) is channeled into the
internal circulation; (2) Density response of the disk is out of phase with the
DM, thus diluting the inner halo flatness and washing out its prolateness; (3)
The total J is neathly conserved, even in models accounting for feedback; (4)
The specific J for the DM is nearly constant, while that for baryons is
decreasing; (5) Early stage of disk formation resembles the cat's cradle -- a
small amorphous disk fueled via radial string patterns; (6) The initially
puffed up gas component in the disk thins when the SF rate drops below ~5
Mo/yr; (7) About 40%-60% of the baryons remain outside the SF region; (8)
Rotation curves appear to be flat and account for the observed disk/halo
contributions; (9) A range of bulge-dominated to bulgeless disks was obtained;
Lower density threshold for SF leads to a smaller, thicker disk; Gravitational
softening in the gas has a substantial effect on various aspects of galaxy
evolution and mimics a number of intrinsic processes within the ISM; (10) The
models are characterized by an extensive bar-forming activity; (11) Nuclear
bars, dynamically coupled and decoupled form in response to the gas inflow
along the primary bars.Comment: 18 pages, 16 figures, accepted by the Astrophysical Journal. Minor
revisions. The high-resolution figures can be found at
http://www.pa.uky.edu/~shlosman/research/galdyn/figs07a
Detecting the harmonics of oscillations with time-variable frequencies
A method is introduced for the spectral analysis of complex noisy signals containing several frequency components. It enables components that are independent to be distinguished from the harmonics of nonsinusoidal oscillatory processes of lower frequency. The method is based on mutual information and surrogate testing combined with the wavelet transform, and it is applicable to relatively short time series containing frequencies that are time variable. Where the fundamental frequency and harmonics of a process can be identified, the characteristic shape of the corresponding oscillation can be determined, enabling adaptive filtering to remove other components and nonoscillatory noise from the signal. Thus the total bandwidth of the signal can be correctly partitioned and the power associated with each component then can be quantified more accurately. The method is first demonstrated on numerical examples. It is then used to identify the higher harmonics of oscillations in human skin blood flow, both spontaneous and associated with periodic iontophoresis of a vasodilatory agent. The method should be equally relevant to all situations where signals of comparable complexity are encountered, including applications in astrophysics, engineering, and electrical circuits, as well as in other areas of physiology and biology
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