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Retinoids in the treatment of skin aging: an overview of clinical efficacy and safety
Published: Feb 2007
Aging of skin is an intricate biological process consisting of two types. While intrinsic or chronological aging is an inevitable process, photoaging involves the premature aging of skin occurring due to cumulative exposure to ultraviolet radiation. Chronological and photoaging both have clinically differentiable manifestations. Various natural and synthetic retinoids have been explored for the treatment of aging and many of them have shown histological and clinical improvement, but most of the studies have been carried out in patients presenting with photoaged skin. Amongst the retinoids, tretinoin possibly is the most potent and certainly the most widely investigated retinoid for photoaging therapy. Although retinoids show promise in the treatment of skin aging, irritant reactions such as burning, scaling or dermatitis associated with retinoid therapy limit their acceptance by patients. This problem is more prominent with tretinoin and tazarotene whereas other retinoids mainly represented by retinaldehyde and retinol are considerably less irritating. In order to minimize these side effects, various novel drug delivery systems have been developed. In particular, nanoparticles have shown a good potential in improving the stability, tolerability and efficacy of retinoids like tretinoin and retinol. However, more elaborate clinical studies are required to confirm their advantage in the delivery of topical retinoids.
Submitted by Kayla Burris
31
Pseudospectral Calculation of the Wavefunction of Helium and the Negative Hydrogen Ion
Authors:
Paul E. Grabowski, David F. Chernoff
Published: Sep 2009
We study the numerical solution of the non-relativistic Schr\"{o}dingerequation for two-electron atoms in ground and excited S-states usingpseudospectral (PS) methods of calculation. The calculation achievesconvergence rates for the energy, Cauchy error in the wavefunction, andvariance in local energy that are exponentially fast for all practicalpurposes. The method requires three separate subdomains to handle thewavefunction's cusp-like behavior near the two-particle coalescences. The useof three subdomains is essential to maintaining exponential convergence. Acomparison of several different treatments of the cusps and the semi-infinitedomain suggest that the simplest prescription is sufficient. For many purposesit proves unnecessary to handle the logarithmic behavior near thethree-particle coalescence in a special way. The PS method has many virtues: noexplicit assumptions need be made about the asymptotic behavior of thewavefunction near cusps or at large distances, the local energy is exactlyequal to the calculated global energy at all collocation points, local errorsgo down everywhere with increasing resolution, the effective basis usingChebyshev polynomials is complete and simple, and the method is easilyextensible to other bound states. This study serves as a proof-of-principle ofthe method for more general two- and possibly three-electron applications.
Retrieved from arxiv
30
Spin effects in the phasing of gravitational waves from binaries on eccentric orbits
Authors:
Antoine Klein, Philippe Jetzer
Published: May 2010
We compute here the spin-orbit and spin-spin couplings needed for an accuratecomputation of the phasing of gravitational waves emitted by comparable-massbinaries on eccentric orbits at the second post-Newtonian (PN) order. We use aquasi-Keplerian parametrization of the orbit free of divergencies in the zeroeccentricity limit. We find that spin-spin couplings induce a residualeccentricity for coalescing binaries at 2PN, of the order of$10^{-4}$-$10^{-3}$ for supermassive black hole binaries in the LISA band.Spin-orbit precession also induces a non-trivial pattern in the evolution ofthe eccentricity, which could help to reduce the errors on the determination ofthe eccentricity and spins in a gravitational wave measurement.
Retrieved from arxiv
30
Compact binary waveform recovery from the cross-correlated data of two detectors by matched filtering with spinning templates
Authors:
Veréb, L., et al
Published: May 2010
We investigate whether the recovery chances of highly spinning waveforms bymatched filtering with randomly chosen spinning waveforms generated with theLAL package are improved by a cross-correlation of the simulated output of theL1 and H1 LIGO detectors. We find that a properly defined correlated overlapimproves the mass estimates and enhances the recovery of spin angles.
Retrieved from arxiv
29
Primordial features due to a step in the inflaton potential
Authors:
Dhiraj Kumar Hazra, Moumita Aich, Rajeev Kumar Jain, L. Sriramkumar, Tarun Souradeep
Published: May 2010
Certain oscillatory features in the primordial scalar power spectrum areknown to provide a better fit to the outliers in the cosmic microwavebackground data near the multipole moments of $\ell=22$ and 40. These featuresare usually generated by introducing a step in the popular, quadratic potentialdescribing the canonical scalar field. Such a model will be ruled out, if thetensors remain undetected at a level corresponding to a tensor-to-scalar ratioof, say, $r\simeq 0.1$. In this work, in addition to the popular quadraticpotential, we investigate the effects of the step in a small field model and atachyon model. With possible applications to future datasets (such as PLANCK)in mind, we evaluate the tensor power spectrum exactly, and include itscontribution in our analysis. We compare the models with the WMAP (five as wellas seven-year), the QUaD and the ACBAR data. As expected, a step at aparticular location and of a suitable magnitude and width is found to improvethe fit to the outliers (near $\ell=22$ and 40) in all these cases. We pointout that, if the tensors prove to be small (say, $r\lesssim 0.01$), thequadratic potential and the tachyon model will cease to be viable, and moreattention will need to be paid to examples such as the small field models.
Retrieved from arxiv
29
A two-mass expanding exact space-time solution
Authors:
Jean-Philippe Uzan, George F. R. Ellis, Julien Larena
Published: May 2010
In order to understand how locally static configurations aroundgravitationally bound bodies can be embedded in an expanding universe, weinvestigate the solutions of general relativity describing a space-time whosespatial sections have the topology of a 3-sphere with two identical masses atthe poles. We show that Israel junction conditions imply that two sphericallysymmetric static regions around the masses cannot be glued together. If one isinterested in an exterior solution, this prevents the geometry around themasses to be of the Schwarzschild type and leads to the introduction of acosmological constant. The study of the extension of the Kottler space-timeshows that there exists a non-static solution consisting of two static regionssurrounding the masses that match a Kantowski-Sachs expanding region on thecosmological horizon. The comparison with a Swiss-Cheese construction is alsodiscussed.
Retrieved from arxiv
28
Dense gas in nearby galaxies: XV. Hot ammonia in NGC253, Maffei2 and IC342
Authors:
R. Mauersberger, C. Henkel, A. Weiss, A. B. Peck, Y. Hagiwara
Published: Mar 2003
The detection of NH3 inversion lines up to the (J,K)=(6,6) level is reportedtoward the central regions of the nearby galaxies NGC253, Maffei2, and IC342.The observed lines are up to 406K (for (J,K)=(6,6)) and 848K (for the (9,9)transition) above the ground state and reveal a warm (T_kin= 100 - 140 K)molecular component toward all galaxies studied. The tentatively detected(J,K)=(9,9) line is evidence for an even warmer (>400K) component toward IC342.Toward NGC253, IC342 and Maffei2 the global beam averaged NH3 abundances are1-2 10^-8, while the abundance relative to warm H2 is around 10^-7. Thetemperatures and NH3 abundances are similar to values found for the Galacticcentral region. C-shocks produced in cloud-cloud collisions can explain kinetictemperatures and chemical abundances. In the central region of M82, however,the NH3 emitting gas component is comparatively cool (~ 30K). It must be dense(to provide sufficient NH3 excitation) and well shielded from dissociatingphotons and comprises only a small fraction of the molecular gas mass in M82.An important molecular component, which is warm and tenuous and characterizedby a low ammonia abundance, can be seen mainly in CO. Photon dominated regions(PDRs) can explain both the high fraction of warm H_2 in M82 and the observedchemical abundances.
Retrieved from arxiv
29
Kaluza-Klein Theory with Torsion confined to the Extra-dimension
Authors:
Karthik H. Shankar, Kameshwar C. Wali
Published: Apr 2009
Here we consider a variant of the 5 dimensional Kaluza-Klein theory withinthe framework of Einstein-Cartan formalism that includes torsion. By imposing aset of constraints on torsion and Ricci rotation coefficients, we show that thetorsion components are completely expressed in terms of the metric. Moreover,the Ricci tensor in 5D corresponds exactly to what one would obtain fromtorsion-free general relativity on a 4D hypersurface. The contributions of thescalar and vector fields of the standard K-K theory to the Ricci tensor and theaffine connections are completely nullified by the contributions from torsion.As a consequence, geodesic motions do not distinguish the torsion free 4Dspace-time from a hypersurface of 5D space-time with torsion satisfying theconstraints. Since torsion is not an independent dynamical variable in thisformalism, the modified Einstein equations are different from those in thegeneral Einstein-Cartan theory. This leads to important cosmologicalconsequences such as the emergence of cosmic acceleration.
Retrieved from arxiv
29
The New Minimal Supersymmetric GUT : Spectra, RG analysis and Fermion Fits
Authors:
Charanjit S. Aulakh, Sumit K. Garg
Published: Jul 2008
The supersymmetric SO(10) GUT based on the ${\bf{210\oplus 10\oplus 120\oplus126\oplus {\bar {126}}}}$ Higgs system provides a minimal framework for theemergence of the R-parity exact MSSM at low energies and a viablesupersymmetric seesaw explanation for the observed neutrino masses and mixingangles. We present formulae for MSSM decomposition of the superpotentialinvariants, tree level light charged fermion effective Yukawa couplings,Weinberg neutrino mass generation operator, and the $d=5,\Delta B=\Delta L \neq0$ effective superpotential in terms of GUT parameters. We use them todetermine fits of the 18 available fermion mass-mixing data in terms of thesuperpotential parameters of the NMSGUT and SUGRY(NUHM) type soft supersymmetrybreaking parameters ($\{m_{\tilde f},m_{1/2},A_0,M^2_{H,\bar H}\} $) specifiedat the MSSM one loop unification scale $M_X^0=10^{16.33} $ GeV. Our fits arecompatible with electroweak symmetry breaking and Unification constraints andyield right-handed neutrino masses in the leptogenesis relevant range :$10^8-10^{13} $ GeV. Matching the SM data requires lowering the strange anddown quark Yukawas in the MSSM via large $\tan\beta$ driven thresholdcorrections and characteristic soft Susy breaking spectra. The Susy spectrahave light pure Bino LSP, heavy exotic Higgs(inos) and large $\mu,A_0,M_{H,\bar{H}}$ parameters $\sim 100$ TeV. Typically third generationsfermions are much \emph{heavier} than the first two generations. The smuon isoften the lightest charged sfermion thus offering a Bino-CDM co-annihilationchannel. The parameter sets obtained are used to calculate B violation rateswhich are found to be generically much faster($\sim 10^{-28}\, yr^{-1}$) thanthe current experimental limits. Improvements which may allow acceptable Bviolation rates are identified.
Retrieved from arxiv
28
Spherical Collapse in Chameleon Models
Authors:
Ph. Brax, R. Rosenfeld, D. A. Steer
Published: May 2010
We study the gravitational collapse of an overdensity of nonrelativisticmatter under the action of gravity and a chameleon scalar field. We show thatthe spherical collapse model is modified by the presence of a chameleon field.In particular, we find that even though the chameleon effects can bepotentially large at small scales, for a large enough initial size of theinhomogeneity the collapsing region possesses a thin shell that shields themodification of gravity induced by the chameleon field, recovering the standardgravity results. We analyse the behaviour of a collapsing shell in acosmological setting in the presence of a thin shell and find that, in contrastto the usual case, the critical density for collapse depends on the initialcomoving size of the inhomogeneity.
Retrieved from arxiv
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