6,089 research outputs found
Stability of Few-Charge Systems in Quantum Mechanics
We consider non-relativistic systems in quantum mechanics interacting through
the Coulomb potential, and discuss the existence of bound states which are
stable against spontaneous dissociation into smaller atoms or ions. We review
the studies that have been made of specific mass configurations and also the
properties of the domain of stability in the space of masses or inverse masses.
These rigorous results are supplemented by numerical investigations using
accurate variational methods. A section is devoted to systems of three
arbitrary charges and another to molecules in a world with two
space-dimensions.Comment: 101 pages, review articl
Guidelines for fabrication of hybrid microcircuits
Document is summary of approaches that may be taken in designing hybrid microcircuits similar to those for aerospace application
Identification of Young Stellar Object candidates in the DR2 x AllWISE catalogue with machine learning methods
The second Data Release (DR2) contains astrometric and photometric
data for more than 1.6 billion objects with mean magnitude 20.7,
including many Young Stellar Objects (YSOs) in different evolutionary stages.
In order to explore the YSO population of the Milky Way, we combined the
DR2 database with WISE and Planck measurements and made an all-sky
probabilistic catalogue of YSOs using machine learning techniques, such as
Support Vector Machines, Random Forests, or Neural Networks. Our input
catalogue contains 103 million objects from the DR2xAllWISE cross-match table.
We classified each object into four main classes: YSOs, extragalactic objects,
main-sequence stars and evolved stars. At a 90% probability threshold we
identified 1,129,295 YSO candidates. To demonstrate the quality and potential
of our YSO catalogue, here we present two applications of it. (1) We explore
the 3D structure of the Orion A star forming complex and show that the spatial
distribution of the YSOs classified by our procedure is in agreement with
recent results from the literature. (2) We use our catalogue to classify
published Science Alerts. As measures the sources at multiple
epochs, it can efficiently discover transient events, including sudden
brightness changes of YSOs caused by dynamic processes of their circumstellar
disk. However, in many cases the physical nature of the published alert sources
are not known. A cross-check with our new catalogue shows that about 30% more
of the published alerts can most likely be attributed to YSO activity.
The catalogue can be also useful to identify YSOs among future alerts.Comment: 19 pages, 12 figures, 3 table
Interaction-assisted propagation of Coulomb-correlated electron-hole pairs in disordered semiconductors
A two-band model of a disordered semiconductor is used to analyze dynamical
interaction induced weakening of localization in a system that is accessible to
experimental verification. The results show a dependence on the sign of the
two-particle interaction and on the optical excitation energy of the
Coulomb-correlated electron-hole pair.Comment: 4 pages and 3 ps figure
Shell model on a random gaussian basis
Pauli-projected random gaussians are used as a representation to solve the
shell model equations. The elements of the representation are chosen by a
variational procedure. This scheme is particularly suited to describe cluster
formation and cluster decay in nuclei. It overcomes the basis-size problem of
the ordinary shell model and the technical difficulties of the
cluster-configuration shell model. The model reproduces the -decay
width of Po satisfactorily.Comment: Latex, Submitted to Phys. Lett. B, 7 pages, 2 figures available upon
request, ATOMKI-1994-
Comment on ``Critical Behavior in Disordered Quantum Systems Modified by Broken Time--Reversal Symmetry''
In a recent Letter [Phys. Rev. Lett. 80, 1003 (1998)] Hussein and Pato
employed the maximum entropy principle (MEP) in order to derive interpolating
ensembles between any pair of universality classes in random matrix theory.
They apply their formalism also to the transition from random matrix to Poisson
statistics of spectra that is observed for the case of the Anderson-type
metal-insulator transition. We point out the problems with the latter
procedure.Comment: 1 page in PS, to appear in PRL Sept. 2
Unlocking the value of real options: how firm-specific learning conditions affect R&D investments under uncertainty
Research Summary Why do some firms increase R&D investments in the face of uncertainty, while others do not? Contrary to common wisdom, this study posits that uncertainty prompts firms to invest in R&D. The value to invest under uncertainty is, however, bounded by a firm's learning conditions (i.e., human capital, relatedness of innovation activities, and industry maturity). An empirical test on a crossâindustry panel of 551 business divisions of manufacturing firms reveals how organizationâenvironment interactions determine the firmâspecific value to invest in learning prior to fullâscale commercialization. The insights help to bridge real options theory and the learning literature. Managerial Summary Uncertainty about the market environment makes investment decisions in R&D and the commercialization of new products a challenge: should firms âwait and seeâ until uncertainty resolves to avoid the risk of betting on the wrong product or commit further resources regardless? Our analysis suggests that manufacturing firms often take a mixed approach (âact and seeâ). While deferring investments in the commercialization of new products, they undertake further R&D to inform decision making by insights that would otherwise be unavailable. However, we find that the benefit of such practice depends on the learning conditions of the individual firm. What is risky for firms with disadvantages in human capital and technology development is value enhancing for firms with good foundations for learning through R&D
Off-diagonal disorder in the Anderson model of localization
We examine the localization properties of the Anderson Hamiltonian with
additional off-diagonal disorder using the transfer-matrix method and
finite-size scaling. We compute the localization lengths and study the
metal-insulator transition (MIT) as a function of diagonal disorder, as well as
its energy dependence. Furthermore we investigate the different influence of
odd and even system sizes on the localization properties in quasi
one-dimensional systems. Applying the finite-size scaling approach in
conjunction with a nonlinear fitting procedure yields the critical parameters
of the MIT. In three dimensions, we find that the resulting critical exponent
of the localization length agrees with the exponent for the Anderson model with
pure diagonal disorder.Comment: 12 pages including 4 EPS figures, accepted for publication in phys.
stat. sol. (b
Second bound state of the positronium molecule and biexcitons
A new, hitherto unknown bound state of the positronium molecule, with orbital
angular momentum L=1 and negative parity is reported. This state is stable
against autodissociation even if the masses of the positive and negative
charges are not equal. The existence of a similar state in two-dimension has
also been investigated. The fact that the biexcitons have a second bound state
may help the better understanding of their binding mechanism.Comment: Latex, 8 pages, 2 Postscript figure
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