6,806 research outputs found
Field Dependence of the Superconducting Basal Plane Anisotropy of TmNi2B2C
The superconductor TmNi2B2C possesses a significant four-fold basal plane
anisotropy, leading to a square Vortex Lattice (VL) at intermediate fields.
However, unlike other members of the borocarbide superconductors, the
anisotropy in TmNi2B2C appears to decrease with increasing field, evident by a
reentrance of the square VL phase. We have used Small Angle Neutron Scattering
measurements of the VL to study the field dependence of the anisotropy. Our
results provide a direct, quantitative measurement of the decreasing
anisotropy. We attribute this reduction of the basal plane anisotropy to the
strong Pauli paramagnetic effects observed in TmNi2B2C and the resulting
expansion of vortex cores near Hc2.Comment: 8 pages, 6 figures, 1 tabl
An X-ray Bright Nucleus in the Low Surface Brightness Galaxy UGC 6614
We report a study of the X-ray emission from the nuclear region of the low
surface brightness (LSB) galaxy UGC 6614. Very little is known about the
central objects in LSB galaxies especially their X-ray properties and X-ray
spectra. In this study we have used XMM-Newton archival data to study the
characteristics of the X-ray spectrum and the X-ray flux variability of the AGN
in the LSB galaxy UGC 6614. The nucleus of UGC 6614 is very bright in X-ray
emission with an absorption corrected 0.2-10.0 keV luminosity of ~1.1 x 10^{42}
erg s^{-1}. The X-ray spectrum is found to be power-law type with a moderate
column density. A short time scale of intensity variation and large X-ray flux
is indicative of the presence of a black hole at the centre of this galaxy.
Using the method of excess variance, we have determined the black hole mass to
be ~0.12 x 10^{6} solar mass. The X-ray spectral properties are similar to that
of the Seyfert I type AGNs. Our study thus demonstrates that although LSB
galaxies are poor in star formation, they may harbour AGNs with X-ray
properties comparable to that seen in more luminous spiral galaxies.Comment: 5 pages, 4 figures, Accepted for publication in MNRA
Hyperspherical partial wave theory applied to electron hydrogen-atom ionization calculation for equal energy sharing kinematics
Hyperspherical partial wave theory has been applied here in a new way in the
calculation of the triple differential cross sections for the ionization of
hydrogen atoms by electron impact at low energies for various
equal-energy-sharing kinematic conditions. The agreement of the cross section
results with the recent absolute measurements of R\"oder \textit {et al} [51]
and with the latest theoretical results of the ECS and CCC calculations [29]
for different kinematic conditions at 17.6 eV is very encouraging. The other
calculated results, for relatively higher energies, are also generally
satisfactory, particularly for large geometries. In view of the
present results, together with the fact that it is capable of describing
unequal-energy-sharing kinematics [35], it may be said that the hyperspherical
partial wave theory is quite appropriate for the description of ionization
events of electron-hydrogen type systems. It is also clear that the present
approach in the implementation of the hyperspherical partial wave theory is
very appropriate.Comment: 16 pages, 9 figures, LaTeX file and EPS figures. To appear in Phys.
Rev.
Ytterbium doped nano-crystalline optical fiber for reduced photodarkening
We report suppression of photodarkening in Yb-doped nano-crystalline fibers in silica host. The photodarkening induced loss reduced by 20 times compared to Yb-doped aluminosilicate fibers. The laser efficiency of the nano-crystalline fiber was 79%
Global entanglement and quantum criticality in spin chains
Entanglement in quantum XY spin chains of arbitrary length is investigated
via a recently-developed global measure suitable for generic quantum many-body
systems. The entanglement surface is determined over the phase diagram, and
found to exhibit structure richer than expected. Near the critical line, the
entanglement is peaked (albeit analytically), consistent with the notion that
entanglement--the non-factorization of wave functions--reflects quantum
correlations. Singularity does, however, accompany the critical line, as
revealed by the divergence of the field-derivative of the entanglement along
the line. The form of this singularity is dictated by the universality class
controlling the quantum phase transition.Comment: 4 pages, 2 figure
Structural Transitions in A Crystalline Bilayer : The Case of Lennard Jones and Gaussian Core Models
We study structural transitions in a system of interacting particles arranged
as a crystalline bilayer, as a function of the density and the distance
between the layers. As is decreased a sequence of transitions involving
triangular, rhombic, square and centered rectangular lattices is observed. The
sequence of phases and the order of transitions depends on the nature of
interactions.Comment: 11 pages,6 figure
Burning a binary tree and its generalization
Graph burning is a graph process that models the spread of social contagion.
Initially, all the vertices of a graph are unburnt. At each step, an
unburnt vertex is put on fire and the fire from burnt vertices of the previous
step spreads to their adjacent unburnt vertices. This process continues till
all the vertices are burnt. The burning number of the graph is the
minimum number of steps required to burn all the vertices in the graph. The
burning number conjecture by Bonato et al. states that for a connected graph
of order , its burning number . It is
easy to observe that in order to burn a graph it is enough to burn its spanning
tree. Hence it suffices to prove that for any tree of order , its
burning number where is the spanning
tree of . It was proved in 2018 that for a tree where is the number of degree vertices in
. In this paper, we provide an algorithm to burn a tree and we improve the
existing bound using this algorithm. We prove that which is an improved bound for . We also provide
an algorithm to burn some subclasses of the binary tree and prove the burning
number conjecture for the same
Hyperspherical partial wave calculation for double photoionization of the helium atom at 20 eV excess energy
Hyperspherical partial wave approach has been applied here in the study of
double photoionization of the helium atom for equal energy sharing geometry at
20 eV excess energy. Calculations have been done both in length and velocity
gauges and are found to agree with each other, with the CCC results and with
experiments and exhibit some advantages of the corresponding three particle
wave function over other wave functions in use.Comment: 11 pages, 1 figure, submitted to J. Phys B: At. Mol. Opt. Phys; v2 -
revised considerably, rewritten using ioplatex clas
Multi-wavelength fiber laser with erbium doped zirconia fiber and semiconductor optical amplifier
Multi-wavelength hybrid fiber lasers are demonstrated in both ring and linear cavities using a fabricated Erbium-doped Zirconia fiber (EDZF) and semiconductor optical amplifier (SOA) as gain media. In both configurations, the a fiber loop mirror, which is constructed using a 3 m long polarization maintaining fiber (PMF) and a polarization insensitive 3dB coupler is used as a comb filter for the fiber laser. In the ring cavity, 10 simultaneous lines with peak power above -26 dBm is obtained at 1550 nm region. This is an improvement compared to the linear cavity configuration which has only 5 simultaneous lines observed from wavelength 1556.1 nm to 1563.0 nm with the peak power above -40 dBm. Both hybrid lasers has a constant line spacing of 1.7 nm, which is suitable for wavelength division multiplexing and sensing applications and shows a stable operation at room temperature
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