A sub-Doppler resolution double resonance molecular beam infrared spectrometer operating at chemically relevant energies (~2 eV)

A molecular beam spectrometer capable of achieving sub-Doppler resolution at 2 eV (~18 000 cm^–1) of vibrational excitation is described and its performance demonstrated using the CH stretch chromophore of HCN. Two high finesse resonant power-buildup cavities are used to excite the molecules using a sequential double resonance technique. A v = 0-->2 transition is first saturated using a 1.5 µm color center laser, whereupon a fraction of the molecules is further excited to the v = 6 level using an amplitude modulated Ti:Al2O3 laser. The energy absorbed by the molecules is detected downstream of both excitation points by a cryogenically cooled bolometer using phase sensitive detection. A resolution of approximately 15 MHz (i.e., three parts in 10^8) is demonstrated by recording a rotational line in the v = 6 manifold of HCN. Scan speeds of up to several cm^–1/h were obtained, with signal-to-noise ratios in excess of 100. The high signal-to-noise ratio and a dynamic range of 6×10^4 means that future experiments to study statistical intramolecular vibrational energy redistribution in small molecules and unimolecular isomerizations can be attempted. We would also like to point out that, with improved metrology in laser wavelengths, this instrument can also be used to provide improved secondary frequency standards based upon the rovibrational spectra of molecules

Thermal Particle and Photon Production in Pb+Pb Collisions with Transverse Flow

Particle and photon production is analyzed in the presence of transverse flow using two approximations to describe the properties of the hadronic medium, one containing only $\pi, \rho, \omega$, and $\eta$ mesons (simplified equation of state) and the other containing hadrons and resonances from the particle data table. Both are considered with and without initial quark gluon plasma formation. In each case the initial temperature is fixed by requiring $dN_{ch}/dy \sim$ 550 in the final state. It is shown that most observables are very sensitive to the equation of state. This is particularly evident when comparing the results of the simplified equation of state in the scenarios with and without phase transition. The hadronic gas scenario leads to a substantially higher rate for the $p_T$-distribution of all particles. In the complete equation of state with several hundreds of hadronic resonances, the difference between the scenarios with and without phase transition is rather modest. Both photon and particle spectra, in a wide $p_T$ range, show very similar behavior. It is therefore concluded that from the $p_T$ spectra it will be hard to disentangle quark gluon plasma formation in the initial state. It is to be stressed however, that there are conceptual difficulties in applying a pure hadronic gas equation of state at SPS-energies. The phase transition scenario with a quark gluon plasma present in the initial state seems to be the more natural one.Comment: 9 pages RevTeX figures in postscript forma

Bremsstrahlung from an Equilibrating Quark-Gluon Plasma

The photon production rate from a chemically equilibrating quark-gluon plasma likely to be produced at RHIC (BNL) and LHC (CERN) energies is estimated taking into account bremsstrahlung. The plasma is assumed to be in local thermal equilibrium, but with a phase space distribution that deviates from the Fermi or Bose distribution by space-time dependent factors (fugacities). The photon spectrum is obtained by integrating the photon rate over the space-time history of the plasma, adopting a boost invariant cylindrically symmetric transverse expansion of the system with different nuclear profile functions. Initial conditions obtained from a self-screened parton cascade calculation and, for comparison, from the HIJING model are used. Compared to an equilibrated plasma at the same initial energy density, taken from the self-screened parton cascade, a moderate suppression of the photon yield by a factor of one to five depending on the collision energy and the photon momentum is observed. The individual contributions to the photon production, however, are completely different in the both scenarios.Comment: 14 pages, 4 figures, shortened version to be published in Phys. Rev.

Comparative study of magnetic and magnetotransport properties of Sm0.55Sr0.45MnO3 thin films grown on different substrates

Highly oriented polycrystalline SSMO thin films deposited on single crystal substrates by ultrasonic nebulized spray pyrolysis have been studied. The film on LAO is under compressive strain while LSAT and STO are under tensile strain. The presence of a metamagnetic state akin to cluster glass formed due to coexisting FM and antiferromagnetic/charge order (AFM/CO) clusters. All the films show colossal magnetoresistance but its temperature and magnetic field dependence are drastically different. In the lower temperature region the magnetic field dependent isothermal resistivity also shows signature of metamagnetic transitions. The observed results have been explained in terms of the variation of the relative fractions of the coexisting FM and AFM/CO phases as a function of the substrate induced strain and oxygen vacancy induced quenched disorder.Comment: 21 page

Magnetoelastic Torsional Vibration of Non-homogeneous Aeolotropic Cylindrical Shell of Viscoelastic Solids

This study investigates magnetoelastic torsional vibration of a non-homogeneous aeolotropic cylindrical shell of viscoelastic solids. The non-homogeneity of the shell obeyingpower law variation of elastic constants and density given by Aij= Crjf', p = por"(i, j = 1,2 ,... 6), where Cu (i, j = 1,2, ... 6) and po are constants and r is the radius vector. Frequency equation and phase velocity in several cases have been derived. Such problems of interaction of elastic  and electromagnetic fields have numerous applications in various branches of science, particularly in the detection of mechanical explosions in the interior of the earth and in the electromagnetic energy into vacuum

S-OHEM: Stratified Online Hard Example Mining for Object Detection

One of the major challenges in object detection is to propose detectors with highly accurate localization of objects. The online sampling of high-loss region proposals (hard examples) uses the multitask loss with equal weight settings across all loss types (e.g, classification and localization, rigid and non-rigid categories) and ignores the influence of different loss distributions throughout the training process, which we find essential to the training efficacy. In this paper, we present the Stratified Online Hard Example Mining (S-OHEM) algorithm for training higher efficiency and accuracy detectors. S-OHEM exploits OHEM with stratified sampling, a widely-adopted sampling technique, to choose the training examples according to this influence during hard example mining, and thus enhance the performance of object detectors. We show through systematic experiments that S-OHEM yields an average precision (AP) improvement of 0.5% on rigid categories of PASCAL VOC 2007 for both the IoU threshold of 0.6 and 0.7. For KITTI 2012, both results of the same metric are 1.6%. Regarding the mean average precision (mAP), a relative increase of 0.3% and 0.5% (1% and 0.5%) is observed for VOC07 (KITTI12) using the same set of IoU threshold. Also, S-OHEM is easy to integrate with existing region-based detectors and is capable of acting with post-recognition level regressors.Comment: 9 pages, 3 figures, accepted by CCCV 201

Cold atoms at unitarity and inverse square interaction

Consider two identical atoms in a spherical harmonic oscillator interacting with a zero-range interaction which is tuned to produce an s-wave zero-energy bound state. The quantum spectrum of the system is known to be exactly solvable. We note that the same partial wave quantum spectrum is obtained by the one-dimensional scale-invariant inverse square potential. Long known as the Calogero-Sutherland-Moser (CSM) model, it leads to Fractional Exclusion Statistics (FES) of Haldane and Wu. The statistical parameter is deduced from the analytically calculated second virial coefficient. When FES is applied to a Fermi gas at unitarity, it gives good agreement with experimental data without the use of any free parameter.Comment: 11 pages, 3 figures, To appear in J. Phys. B. Atomic, Molecular and Optical Physic