813 research outputs found
Canonical Transformation Path to Gauge Theories of Gravity
In this paper, the generic part of the gauge theory of gravity is derived,
based merely on the action principle and on the general principle of
relativity. We apply the canonical transformation framework to formulate
geometrodynamics as a gauge theory. The starting point of our paper is
constituted by the general De~Donder-Weyl Hamiltonian of a system of scalar and
vector fields, which is supposed to be form-invariant under (global) Lorentz
transformations. Following the reasoning of gauge theories, the corresponding
locally form-invariant system is worked out by means of canonical
transformations. The canonical transformation approach ensures by construction
that the form of the action functional is maintained. We thus encounter amended
Hamiltonian systems which are form-invariant under arbitrary spacetime
transformations. This amended system complies with the general principle of
relativity and describes both, the dynamics of the given physical system's
fields and their coupling to those quantities which describe the dynamics of
the spacetime geometry. In this way, it is unambiguously determined how spin-0
and spin-1 fields couple to the dynamics of spacetime.
A term that describes the dynamics of the free gauge fields must finally be
added to the amended Hamiltonian, as common to all gauge theories, to allow for
a dynamic spacetime geometry. The choice of this "dynamics Hamiltonian" is
outside of the scope of gauge theory as presented in this paper. It accounts
for the remaining indefiniteness of any gauge theory of gravity and must be
chosen "by hand" on the basis of physical reasoning. The final Hamiltonian of
the gauge theory of gravity is shown to be at least quadratic in the conjugate
momenta of the gauge fields -- this is beyond the Einstein-Hilbert theory of
General Relativity.Comment: 16 page
Adjudication of Federal Causes of Action in State Court
The first section of this article considers the power of state courts to hear federal cases. Since it is now well established that state courts have the constitutional power to adjudicate federal causes of action if Congress so desires, the significant questions concern the method by which the judiciary is to decipher congressional intent. Although the courts have no difficulty where Congress has explicitly addressed the issue of state court jurisdiction, problems do arise in situations where Congress has remained silent on the question. The first section critically examines the traditional criteria employed by the courts for determining congressional intent in the face of congressional silence and then suggests a substantial alteration in the judiciary\u27s approach to the matter.
The second section of the article considers the obligation of state courts to hear federal cases. After first evaluating constitutional questions surrounding such an obligation, this section wilI also examine difficult questions involving congressional intent-specifically, the circumstances under which Congress\u27 silence is intended to permit state courts to avoid hearing federal cases
Young Brown Dwarfs in the Core of the W3 Main Star-Forming Region
We present the results of deep and high-resolution (FWHM ~ 0".35) JHK NIR
observations with the Subaru telescope, to search for very low mass young
stellar objects (YSOs) in the W3 Main star-forming region. The NIR survey
covers an area of ~ 2.6 arcmin^2 with 10-sigma limiting magnitude exceeding 20
mag in the JHK bands. The survey is sensitive enough to provide unprecedented
details in W3 IRS 5 region and reveals a census of the stellar population down
to objects below the hydrogen-burning limit. We construct JHK color-color (CC)
and J-H/J and H-K/K color-magnitude (CM) diagrams to identify very low
luminosity YSOs and to estimate their masses. Based on these CC and CM
diagrams, we identified a rich population of embedded YSO candidates with
infrared excesses (Class I and Class II), associated with the W3 Main region. A
large number of red sources (H-K > 2) have also been detected around W3 Main.
We argue that these red stars are most probably pre-main-sequence (PMS) stars
with intrinsic color excesses. Based on the comparison between theoretical
evolutionary models of very low-mass PMS objects with the observed CM diagram,
we find there exists a substantial substellar population in the observed
region. The mass function (MF) does not show the presence of cutoff and sharp
turnover around the substellar limit, at least at the hydrogen-burning limit.
Furthermore, the MF slope indicates that the number ratio of young brown dwarfs
and hydrogen-burning stars in the W3 Main is probably higher than those in
Trapezium and IC 348. The presence of mass segregation, in the sense that
relatively massive YSOs lie near the cluster center, is seen. The estimated
dynamical evolution time indicates that the observed mass segregation in the W3
Main may be the imprint of the star formation process.Comment: 39 pages, 15 figures. Accepted for publication in the Astrophysical
Journa
Gravity on a parallelizable manifold. Exact solutions
The wave type field equation \square \vt^a=\la \vt^a, where \vt^a is a
coframe field on a space-time, was recently proposed to describe the gravity
field. This equation has a unique static, spherical-symmetric,
asymptotically-flat solution, which leads to the viable Yilmaz-Rosen metric. We
show that the wave type field equation is satisfied by the pseudo-conformal
frame if the conformal factor is determined by a scalar 3D-harmonic function.
This function can be related to the Newtonian potential of classical gravity.
So we obtain a direct relation between the non-relativistic gravity and the
relativistic model: every classical exact solution leads to a solution of the
field equation. With this result we obtain a wide class of exact, static
metrics. We show that the theory of Yilmaz relates to the pseudo-conformal
sector of our construction. We derive also a unique cosmological (time
dependent) solution of the described type.Comment: Latex, 17 page
The Initial Mass Function as given by the fragmentation
The dichotomy between a universal mass function (IMF) and a variable IMF
which depends on local physical parameters characterises observational and
theoretical stellar astronomy. In this contribution the available distributions
of probability are briefly reviewed. The physical nature of two of them, gamma
variate and lognormal, is then explained once the framework of the
fragmentation is introduced. Interpolating techniques are then applied to the
sample of the first 10 pc and to the open cluster NGC6649: in both cases
lognormal distribution produces the best fit. The three power law function has
also been investigated and visual comparison with an artificially generated
sample of 100000 stars suggests that the variations in the spectral index are
simply due to the small number of stars available in the observational sample.
In order to derive the sample of masses, a new formula that allows us to
express the mass as a function of the absolute magnitude and (B-V) for MAIN V,
GIANTS III and SUPERGIANTS I is derived.Comment: 6 pages 9 figure
Non-synonymous single nucleotide polymorphisms in the P2X receptor genes: Association with diseases, impact on receptor functions and potential use as diagnosis biomarkers
P2X receptors are Ca2+-permeable cationic channels in the cell membranes, where they play an important role in mediating a diversity of physiological and pathophysiological functions of extracellular ATP. Mammalian cells express seven P2X receptor genes. Single nucleotide polymorphisms (SNPs) are widespread in the P2RX genes encoding the human P2X receptors, particularly the human P2X7 receptor. This article will provide anoverview of the non-synonymous SNPs (NS-SNPs) that have been associated with or implicated in altering the susceptibility to pathologies or disease conditions, and discuss the consequences of the mutations resulting from such NS-SNPs on the receptor functions. Disease-associated NS-SNPs in the P2RXgenes have been valuable in understanding the disease etiology and the receptor function, and are promising as biomarkers to be used for the diagnosis and development of stratified therapeutics. © 2014 by the authors; licensee MDPI, Basel, Switzerland
Discovery of superthermal hydroxyl (OH) in the HH211 outflow
We present a 5-37 micron infrared spectrum obtained with the Spitzer Space
Telescope toward the southeastern lobe of the young protostellar outflow HH211.
The spectrum shows an extraordinary sequence of OH emission lines arising in
highly excited rotational levels up to an energy E/k~28200K above the ground
level. This is, to our knowledge, by far the highest rotational excitation of
OH observed outside Earth. The spectrum also contains several pure rotational
transitions of H2O (v=0), H2 (v=0) S(0) to S(7), HD (v=0) R(3) to R(6), and
atomic fine-structure lines of [Fe II], [Si II], [Ne II], [S I], and [Cl I].
The origin of the highly excited OH emission is most likely the
photodissociation of H2O by the UV radiation generated in the terminal outflow
shock of HH211.Comment: ApJ Letters, in pres
On the width of the equatorial deep jets
The equatorial deep jets (EDJ) are a striking feature of the equatorial ocean circulation. In the Atlantic Ocean, the EDJ are associated with a vertical scale of between 300 and 700 m, a time scale of roughly 4.5 years and upward energy propagation to the surface. It has been found that the meridional width of the EDJ is roughly 1.5 times larger than expected based on their vertical scale. Here we use a shallow water model for a high order baroclinic vertical normal mode to argue that mixing of momentum along isopycnals can explain the enhanced width. A lateral eddy viscosity of 300 m2 s−1 10 is found to be sufficient to account for the width implied by observations
Structure-Based Identification and Characterization of Inhibitors of the Epilepsy-Associated KNa1.1 (KCNT1) Potassium Channel
Drug-resistant epileptic encephalopathies of infancy have been associated with KCNT1 gainof-function mutations, which increase the activity of KNa1.1 sodium-activated potassium channels. Pharmacological inhibition of hyperactive KNa1.1 channels by quinidine has been proposed as a stratified treatment, but mostly this has not been successful, being linked to the low potency and lack of specificity of the drug. Here we describe the use of a previously determined cryo-electron microscopy-derived KNa1.1 structure and mutational analysis to identify how quinidine binds to the channel pore and, using computational methods, screened for compounds predicated to bind to this site. We describe six compounds that inhibited KNa1.1 channels with low- and sub-micromolar potencies, likely also through binding in the intracellular pore vestibule. In hERG inhibition and cytotoxicity assays, two compounds were ineffective. These may provide starting points for the development of new pharmacophores and could become tool compounds to study this channel further
Do Lognormal Column-Density Distributions in Molecular Clouds Imply Supersonic Turbulence?
Recent observations of column densities in molecular clouds find lognormal
distributions with power-law high-density tails. These results are often
interpreted as indications that supersonic turbulence dominates the dynamics of
the observed clouds. We calculate and present the column-density distributions
of three clouds, modeled with very different techniques, none of which is
dominated by supersonic turbulence. The first star-forming cloud is simulated
using smoothed particle hydrodynamics (SPH); in this case gravity, opposed only
by thermal-pressure forces, drives the evolution. The second cloud is
magnetically subcritical with subsonic turbulence, simulated using nonideal
MHD; in this case the evolution is due to gravitationally-driven ambipolar
diffusion. The third cloud is isothermal, self-gravitating, and has a smooth
density distribution analytically approximated with a uniform inner region and
an r^-2 profile at larger radii. We show that in all three cases the
column-density distributions are lognormal. Power-law tails develop only at
late times (or, in the case of the smooth analytic profile, for strongly
centrally concentrated configurations), when gravity dominates all opposing
forces. It therefore follows that lognormal column-density distributions are
generic features of diverse model clouds, and should not be interpreted as
being a consequence of supersonic turbulence.Comment: 6 pages, 6 figures, accepted for publication in MNRA
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