785 research outputs found
Absolute Dimensions and Apsidal Motion of the Young Detached System LT Canis Majoris
New high resolution spectra of the short period (P~1.76 days) young detached
binary LT CMa are reported for the first time. By combining the results from
the analysis of new radial velocity curves and published light curves, we
determine values for the masses, radii and temperatures as follows: M_1= 5.59
(0.20) M_o, R_1=3.56 (0.07) R_o and T_eff1= 17000 (500) K for the primary and
M_2=3.36 (0.14) M_o, R_2= 2.04 (0.05) R_o and T_eff2= 13140 (800) K for the
secondary. Static absorbtion features apart from those coming from the close
binary components are detected in the several spectral regions. If these
absorbtion features are from a third star, as the light curve solutions
support, its radial velocity is measured to be RV_3=70(8) km s^-1. The orbit of
the binary system is proved to be eccentric (e=0.059) and thus the apsidal
motion exists. The estimated linear advance in longitude of periastron
corresponds to an apsidal motion of U=694+/-5 yr for the system. The average
internal structure constant log k_2,obs=-2.53 of LT CMa is found smaller than
its theoretical value of log k_2,theo=-2.22 suggesting the stars would have
more central concentration in mass. The photometric distance of LT CMa
(d=535+/-45 pc) is found to be much smaller than the distance of CMa OB1
association (1150 pc) which rules out membership. A comparison with current
stellar evolution models for solar metallicity indicates that LT CMa (35 Myr)
is much older than the CMa OB1 association (3 Myr), confirming that LT CMa is
not a member of CMa OB1. The kinematical and dynamical analysis indicate LT CMa
is orbiting the Galaxy in a circular orbit and belongs to the young thin-disk
population.Comment: 19 pages, 6 figures and 6 tables, accepted for publication in
Publication of the Astronomical Society of Japa
Study of Eclipsing Binary and Multiple Systems in OB Associations: I. Ori OB1a - IM Mon
All available photometric and spectroscopic observations were collected and
used as the basis of a detailed analysis of the close binary IM Mon. The
orbital period of the binary was refined to 1.19024249(0.00000014) days. The
Roche equipotentials, fractional luminosities (in (B, V) and H_p bands) and
fractional radii for the component stars in addition to mass ratio q,
inclination i of the orbit and the effective temperature T_eff of the secondary
cooler less massive component were obtained by the analysis of light curves. IM
Mon is classified to be a detached binary system in contrast to the contact
configuration estimations in the literature. The absolute parameters of IM Mon
were derived by the simultaneous solutions of light and radial velocity curves
as M_1,2=5.50(0.24)M_o and 3.32(0.16)M_o, R1,2=3.15(0.04)R_o and 2.36(0.03)R_o,
T_eff1,2=17500(350) K and 14500(550) K implying spectral types of B4 and B6.5
ZAMS stars for the primary and secondary components respectively. The modelling
of the high resolution spectrum revealed the rotational velocities of the
component stars as V_rot1=147(15) km/s and V_rot2=90(25) km/s. The photometric
distance of 353(59) pc was found more precise and reliable than Hipparcos
distance of 341(85) pc. An evolutionary age of 11.5(1.5) Myr was obtained for
IM Mon. Kinematical and dynamical analysis support the membership of the young
thin-disk population system IM Mon to the Ori OB1a association dynamically.
Finally, we derived the distance, age and metallicity information of Ori OB1a
sub-group using the information of IM Mon parameters.Comment: 26 pages, 5 figures and 6 tables, accepted for publication in
Publication of the Astronomical Society of Japa
Experimental and computational study on dynamic analysis of cracked simply supported structures under moving mass
In this study, the influences of crack parameters like crack location from the left end, crack height, number of cracks and the magnitude of mass and the velocity of the transit load on the vertical displacements of the cracked simply supported beams subjected to transit mass are investigated. The transverse open cracks with numerous damage scenerios are considered for the mathematical modelling of the system. The governing equations of motion for the system have been obtained and the equations have been solved by the help of Duhamel integral technique. The theoretical formulation has been exemplified with numerical studies. By utilizing ANSYS Workbench 2020, transient structural analysis has been carried out. The mode shapes and the frequency ratios of damaged simply supported beam have also been determined. To validate the numerical and FEM models, the experiments with damaged beams have been carried out in the laboratory. It has been proven that the results of the theoretical and FEM models are well convergent with the experimental data. The results gathered from the numerical analysis, FEA as well as experimental study have been presented with comparative graphs and tables. The outcomes of the examinations have been interpreted in the conclusions part. It has been observed that subject parameters are of considerable significance on the time dependent response of the cracked beams
Buckling and d-Wave Pairing in HiTc-Superconductors
We have investigated whether the electron-phonon interaction can support a
d-wave gap-anisotropy. On the basis of models derived from LDA calculations, as
well as LDA linear-response calculations we argue that this is the case, for
materials with buckled or dimpled CuO2 planes, for the so-called buckling
modes, which involve out-of-plane movements of the plane oxygens.Comment: 5pages, Latex2e, 6 Postscript figure
Comparison of three-dimensional facial morphology between upright and supine positions employing three-dimensional scanner from live subjects
Facial soft tissue thicknesses (FSTT) measurements collected from Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) imaging techniques are most commonly taken in the supine position for forensic craniofacial reconstruction. FSTT have been shown to be different in comparison to the upright position due to gravity. The variation of facial morphology between the upright and supine position of laser-scanned images taken from 44 individuals was investigated using volumetric analysis with deviation maps. Between 82.4% and 86.7% of the facial surface area were within the error range of ±2 mm between the supine and the upright position. This indicates that most anatomical landmarks taken from the MRI and CT data can be an accurate representative of the FSTT in the upright position. Seven landmarks located around the buccal region, masseteric region and the nasolabial region of the face showed the greatest FSTT deviation between the upright and supine position, thus these landmarks may affect the accuracy of facial reconstructions when using a CT or MRI database
A dynamic rationing policy for continuous-review inventory systems
Stock rationing is an inventory policy that allows differential treatment of customer classes without using separate inventories. In this paper, we propose a dynamic rationing policy for continuous-review inventory systems, which utilizes the information on the status of the outstanding replenishment orders. For both backordering and lost sales environments, we conduct simulation studies to compare the performance of the dynamic policy with the static critical level and the common stock policies and quantify the gain obtained. We propose two new bounds on the optimum dynamic rationing policy that enables us to tell how much of the potential gain the proposed dynamic policy realizes. We discuss the conditions under which stock rationing - both dynamic and static - is beneficial and assess the value of the dynamic policy. © 2009 Elsevier B.V. All rights reserved
Quasiparticle Dispersion of the 2D Hubbard Model: From an Insulator to a Metal
On the basis of Quantum-Monte-Carlo results the evolution of the spectral
weight of the two-dimensional Hubbard model is studied from
insulating to metallic behavior. As observed in recent photoemission
experiments for cuprates, the electronic excitations display essentially
doping-independent features: a quasiparticle-like dispersive narrow band of
width of the order of the exchange interaction and a broad valence- and
conduction-band background. The continuous evolution is traced back to one and
the same many-body origin: the doping-dependent antiferromagnetic spin-spin
correlation.Comment: 11 pages, REVtex, 4 figures (in uuencoded postscript format
OH+ in astrophysical media: state-to-state formation rates, Einstein coefficients and inelastic collision rates with He
The rate constants required to model the OH observations in different
regions of the interstellar medium have been determined using state of the art
quantum methods.
First, state-to-state rate constants for the H+ O()
H + OH reaction have been obtained using
a quantum wave packet method. The calculations have been compared with
time-independent results to asses the accuracy of reaction probabilities at
collision energies of about 1 meV. The good agreement between the simulations
and the existing experimental cross sections in the 1 eV energy range
shows the quality of the results.
The calculated state-to-state rate constants have been fitted to an
analytical form. Second, the Einstein coefficients of OH have been obtained
for all astronomically significant ro-vibrational bands involving the
and/or electronic states.
For this purpose the potential energy curves and electric dipole transition
moments for seven electronic states of OH are calculated with {\it ab
initio} methods at the highest level and including spin-orbit terms, and the
rovibrational levels have been calculated including the empirical spin-rotation
and spin-spin terms. Third, the state-to-state rate constants for inelastic
collisions between He and OH have been calculated using a
time-independent close coupling method on a new potential energy surface. All
these rates have been implemented in detailed chemical and radiative transfer
models. Applications of these models to various astronomical sources show that
inelastic collisions dominate the excitation of the rotational levels of
OH. In the models considered the excitation resulting from the chemical
formation of OH increases the line fluxes by about 10 % or less depending
on the density of the gas
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