Magnetohydrodynamic modeling of the accretion shocks in classical T Tauri stars: the role of local absorption on the X-ray emission

We investigate the properties of X-ray emission from accretion shocks in classical T Tauri stars (CTTSs), generated where the infalling material impacts the stellar surface. Both observations and models of the accretion process reveal several aspects that are still unclear: the observed X-ray luminosity in accretion shocks is below the predicted value, and the density versus temperature structure of the shocked plasma, with increasing densities at higher temperature, deduced from the observations, is at odds with that proposed in the current picture of accretion shocks. To address these open issues we investigate whether a correct treatment of the local absorption by the surrounding medium is crucial to explain the observations. To this end, we describe the impact of an accretion stream on a CTTS by considering a magnetohydrodynamic model. From the model results we synthesize the X-ray emission from the accretion shock by producing maps and spectra. We perform density and temperature diagnostics on the synthetic spectra, and we directly compare the results with the observations. Our model shows that the X-ray fluxes inferred from the emerging spectra are lower than expected because of the complex local absorption by the optically thick material of the chromosphere and of the unperturbed stream. Moreover, our model including the effects of local absorption explains in a natural way the apparently puzzling pattern of density versus temperature observed in the X-ray emission from accretion shocks.Comment: Accepted for publication in Astrophysical Journal Letters; 5 pages, 4 figure

Brown Dwarfs and the Cataclysmic Variable Period Minimum

Using improved, up-to-date stellar input physics tested against observations of low-mass stars and brown dwarfs we calculate the secular evolution of low-mass donor cataclysmic variables (CVs), including those which form with a brown dwarf donor. Our models confirm the mismatch between the calculated minimum period (Pmin ~ 70 min) and the observed short-period cut-off (~ 80 min) in the CV period histogram. We find that tidal and rotational corrections applied to the one-dimensional stellar structure equations have no significant effect on the period minimum. Theoretical period distributions synthesized from our model sequences always show an accumulation of systems at the minimum period, a feature absent from the observed distribution. We suggest that non-magnetic CVs become unobservable as they are effectively trapped in permanent quiescence before they reach Pmin, and that small-number statistics may hide the period spike for magnetic CVs.Comment: 10 pages; accepted for publication in MNRA

MMP-13 Selective Isonipecotamide Alpha-sulfone Hydroxamates

A series of N-aryl isonipecotamide α-sulfone hydroxamate derivatives has been prepared utilizing a combination of solution-phase and resin-bound library technologies to afford compounds that are potent and highly selective for MMP-13

An Extensive Census of HST Counterparts to Chandra X-ray Sources in the Globular Cluster 47 Tucanae. II. Time Series and Analysis

We report time series and variability information for the optical identifications of X-ray sources in 47 Tuc reported in Paper I. The eight CVs with secure orbital periods have fainter accretion disks, in the V band, than field CVs with similar periods. These faint disks and the faint absolute magnitudes (Mv) of the 47 Tuc CVs suggests they have low accretion rates. The median Fx/Fopt value for the 47 Tuc CVs is higher than that of all known classes of field CV, because of both the faint Mv values and the relatively high X-ray luminosities (Lx). The latter are only seen in DQ Her systems in the field, but the 47 Tuc CVs are much fainter optically than most field DQ Hers. Some combination of magnetic behavior and low accretion rates may be able to explain our observations, but the results at present are ambiguous, since no class of field CV has distributions of both Lx and Mv that are consistent with those of the 47 Tuc CVs. The radial distribution of the X-ray detected active binaries is indistinguishable from that of the much larger sample of optical variables detected in previous WFPC2 studies. The X-ray properties of these objects are consistent with those of active binaries found in field studies. One reasonable and one marginal candidate for optical identification of a quiescent LMXB was found (one is already known). Finally, we study the blue variables showing little or no evidence for X-ray emission. Their generally long periods and the absence of flickering suggests they are not CVs. At present we have no satisfactory explanation for these objects, although some may be detached WD-main sequence star binaries.Comment: Accepted for publication in Astrophysical Journal. 34 pages, 24 figures, 5 tables, abridged abstract. Some figures at reduced resolutio

D-braneworld cosmology

We discuss D-braneworld cosmology, that is, the brane is described by the Born-Infeld action. Compared with the usual Randall-Sundrum braneworld cosmology where the brane action is the Nambu-Goto one, we can see some drastic changes at the very early universe: (i)universe may experience the rapid accelerating phase (ii)the closed universe may avoid the initial singularity. We also briefly address the dynamics of the cosmology in the open string metric, which might be favorer than the induced metric from the view point of the D-brane.Comment: 6 pages, 3 figures, minor corrections, accepted for publication in Phys. Rev.

An orifice shape-based reduced order model of patient-specific mitral valve regurgitation

Mitral valve regurgitation (MR) is one of the most prevalent valvular heart diseases. Its quantitative assessment is challenging but crucial for treatment decisions. Using computational fluid dynamics (CFD), we developed a reduced order model (ROM) describing the relationship between MR flow rates, transvalvular pressure differences, and the size and shape of the regurgitant valve orifice. Due to its low computational cost, this ROM could easily be implemented into clinical workflows to support the assessment of MR. We reconstructed mitral valves of 43 patients from 3D transesophageal echocardiographic images and estimated the 3D anatomic regurgitant orifice areas using a shrink-wrap algorithm. The orifice shapes were quantified with three dimensionless shape parameters. Steady-state CFD simulations in the reconstructed mitral valves were performed to analyse the relationship between the regurgitant orifice geometry and the regurgitant hemodynamics. Based on the results, three ROMs with increasing complexity were defined, all of which revealed very good agreement with CFD results with a mean bias below 3% for the MR flow rate. Classifying orifices into two shape groups and assigning group-specific flow coefficients in the ROM reduced the limit of agreement predicting regurgitant volumes from 9.0 ml to 5.7 ml at a mean regurgitant volume of 57 ml

Cooperative coupling of ultracold atoms and surface plasmons

Cooperative coupling between optical emitters and light fields is one of the outstanding goals in quantum technology. It is both fundamentally interesting for the extraordinary radiation properties of the participating emitters and has many potential applications in photonics. While this goal has been achieved using high-finesse optical cavities, cavity-free approaches that are broadband and easy to build have attracted much attention recently. Here we demonstrate cooperative coupling of ultracold atoms with surface plasmons propagating on a plane gold surface. While the atoms are moving towards the surface they are excited by an external laser pulse. Excited surface plasmons are detected via leakage radiation into the substrate of the gold layer. A maximum Purcell factor of $\eta_\mathrm{P}=4.9$ is reached at an optimum distance of $z=250~\mathrm{nm}$ from the surface. The coupling leads to the observation of a Fano-like resonance in the spectrum.Comment: 9 pages, 4 figure

Interferometric Astrometry with Hubble Space Telescope Fine Guidance Sensor 3:The Parallax of the Cataclysmic Variable TV Columbae

TV Columbae (TV Col) is a 13th magnitude Intermediate Polar (IP) Cataclysmic Variable (CV), with multiple periods found in the light curves. Past estimates predicted a distance of 400 parsec to greater than 500 parsec. Recently completed Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) interferometric observations allow us to determine the first trigonometric parallax to TV Col. This determination puts the distance of TV Col at 368 -15+17 parsecs. CD-32 2376, a 10th magnitude Tycho Catalog star, is a reference star in the TV Col frame. We find a distance of $127.7 -1+1 parsecs.Comment: 24 pages, 2 figure

Osteoarthritic changes in vervet monkey knees correlate with meniscus degradation and increased matrix metalloproteinase and cytokine secretion

Meniscus injury increases osteoarthritis risk but its pathobiology in osteoarthritis is unclear. We hypothesized that older adult vervet monkeys would exhibit knee osteoarthritic changes and the degenerative menisci from these animals would secrete matrix metalloproteinases (MMPs) and pro-inflammatory cytokines that contribute to the development of osteoarthritis

Fano resonances in plasmonic core-shell particles and the Purcell effect

Despite a long history, light scattering by particles with size comparable with the light wavelength still unveils surprising optical phenomena, and many of them are related to the Fano effect. Originally described in the context of atomic physics, the Fano resonance in light scattering arises from the interference between a narrow subradiant mode and a spectrally broad radiation line. Here, we present an overview of Fano resonances in coated spherical scatterers within the framework of the Lorenz-Mie theory. We briefly introduce the concept of conventional and unconventional Fano resonances in light scattering. These resonances are associated with the interference between electromagnetic modes excited in the particle with different or the same multipole moment, respectively. In addition, we investigate the modification of the spontaneous-emission rate of an optical emitter at the presence of a plasmonic nanoshell. This modification of decay rate due to electromagnetic environment is referred to as the Purcell effect. We analytically show that the Purcell factor related to a dipole emitter oriented orthogonal or tangential to the spherical surface can exhibit Fano or Lorentzian line shapes in the near field, respectively.Comment: 28 pages, 10 figures; invited book chapter to appear in "Fano Resonances in Optics and Microwaves: Physics and Application", Springer Series in Optical Sciences (2018), edited by E. O. Kamenetskii, A. Sadreev, and A. Miroshnichenk