3,804 research outputs found
Complementarity of perturbations driving insulator-to-metal transition in a charge ordered manganite
Modulation of charge carrier dynamics and hence electrical conductivity of
solids by photoexcitation has been a rich field of research with numerous
applications. Similarly, electric and magnetic field assisted enhancement of
conductivity are of fundamental importance and technological use. Hole doped
manganites of the type (ABMnO, where A and B are rare and
alkaline earth metals respectively have the distinction of showing all three
effects. Here we establish the complementarity of the electric, magnetic and
photon fields in driving an insulator-metal transition in epitaxial thin films
of LaPrCaMnO whose electrical ground state
is insulating. Both pulsed and CW lasers cause a giant photon flux dependent
enhancement of conductivity. It is further observed that electric and magnetic
fields trigger the persistent enhancement of conductivity whose magnitude can
be accentuated by application of these fields in parallel.Comment: 17 pages 6 figure
Near-linear Time Algorithm for Approximate Minimum Degree Spanning Trees
Given a graph , we wish to compute a spanning tree whose maximum
vertex degree, i.e. tree degree, is as small as possible. Computing the exact
optimal solution is known to be NP-hard, since it generalizes the Hamiltonian
path problem. For the approximation version of this problem, a
time algorithm that computes a spanning tree of degree at most is
previously known [F\"urer \& Raghavachari 1994]; here denotes the
minimum tree degree of all the spanning trees. In this paper we give the first
near-linear time approximation algorithm for this problem. Specifically
speaking, we propose an time algorithm that
computes a spanning tree with tree degree for any constant .
Thus, when , we can achieve approximate solutions with
constant approximate ratio arbitrarily close to 1 in near-linear time.Comment: 17 page
suppression in Pb+Pb collisions and broadening
We have analysed the NA50 data, on the centrality dependence of
broadening of 's, in Pb+Pb collisions, at the CERN-SPS. The data were
analysed in a QCD based model, where 's are suppressed in 'nuclear'
medium. Without any free parameter, the model could explain the NA50
broadening data. The data were also analysed in a QGP based threshold model,
where suppression is 100% above a critical density. The QGP based
model could not explain the NA50 broadening data. We have also predicted
the centrality dependence of suppression and broadening at RHIC
energy. Both the models, the QGP based threshold model and the QCD based
nuclear absorption model, predict broadening very close to each other.Comment: The paper was completely revised. The conclusion is also changed. 5
pages, 4 figure
Assessment of creep and rupture behavior of 2.25Cr-1Mo steel – A strain-based approach and its limitation
Increasing demand of 2.25Cr-1Mo steel, among different grades of low alloy Cr-Mo steels, in power plants and petrochemical industries is mainly because of its high creep resistance. Application of a strain based approach for a reliable assessment of creep and rupture behavior is thus of great importance. Creep data were generated under different microstructural conditions in the laboratory and collected from literature as well. The influence of thermal ageing and pre-strain on the shape of creep curves has been studied. Analysis of data revealed that irrespective of initial microstructures, thermal ageing increases the tendency to soften but not the pre-strain. Softening due to carbide coarsening thus appears to be the dominant mechanism of creep. Based on this, a strain based approach for creep life assessment was developed. A fairly accurate prediction of creep life up to 5% creep is achieved using eight materials constants extracted from the creep curves of steel having similar initial microstructure. The limitation and reliability of the approach used to assess creep behavior of service-exposed steels have been discussed
Generalization of escape rate from a metastable state driven by external cross-correlated noise processes
We propose generalization of escape rate from a metastable state for
externally driven correlated noise processes in one dimension. In addition to
the internal non-Markovian thermal fluctuations, the external correlated noise
processes we consider are Gaussian, stationary in nature and are of
Ornstein-Uhlenbeck type. Based on a Fokker-Planck description of the effective
noise processes with finite memory we derive the generalized escape rate from a
metastable state in the moderate to large damping limit and investigate the
effect of degree of correlation on the resulting rate. Comparison of the
theoretical expression with numerical simulation gives a satisfactory agreement
and shows that by increasing the degree of external noise correlation one can
enhance the escape rate through the dressed effective noise strength.Comment: 9 pages, 1 figur
Photoassociative creation of ultracold heteronuclear 6Li40K* molecules
We investigate the formation of weakly bound, electronically excited,
heteronuclear 6Li40K* molecules by single-photon photoassociation in a
magneto-optical trap. We performed trap loss spectroscopy within a range of 325
GHz below the Li(2S_(1/2))+K(4P_(3/2)) and Li(2S_(1/2))+K(4P_(1/2)) asymptotic
states and observed more than 60 resonances, which we identify as rovibrational
levels of 7 of 8 attractive long-range molecular potentials. The long-range
dispersion coefficients and rotational constants are derived. We find large
molecule formation rates of up to ~3.5x10^7s^(-1), which are shown to be
comparable to those for homonuclear 40K_2*. Using a theoretical model we infer
decay rates to the deeply bound electronic ground-state vibrational level
X^1\Sigma^+(v'=3) of ~5x10^4s^(-1). Our results pave the way for the production
of ultracold bosonic ground-state 6Li40K molecules which exhibit a large
intrinsic permanent electric dipole moment.Comment: 6 pages, 4 figures, submitted to EP
Investigations of Ra properties to test possibilities of new optical frequency standards
The present work tests the suitability of the narrow transitions $7s \
^2S_{1/2} \to 6d ^2D_{3/2}7s ^2S_{1/2} \to 6d ^2D_{5/2}^+6d^+$ to be considered as a potential
candidate for an atomic clock. This is further corroborated by our studies of
the hyperfine interactions, dipole and quadrupole polarizabilities and
quadrupole moments of the appropriate states of this system.Comment: Latex files, 5 pages, 1 figur
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