2,707 research outputs found
A new proof of the Vorono\"i summation formula
We present a short alternative proof of the Vorono\"i summation formula which
plays an important role in Dirichlet's divisor problem and has recently found
an application in physics as a trace formula for a Schr\"odinger operator on a
non-compact quantum graph \mathfrak{G} [S. Egger n\'e Endres and F. Steiner, J.
Phys. A: Math. Theor. 44 (2011) 185202 (44pp)]. As a byproduct we give a new
proof of a non-trivial identity for a particular Lambert series which involves
the divisor function d(n) and is identical with the trace of the Euclidean wave
group of the Laplacian on the infinite graph \mathfrak{G}.Comment: Enlarged version of the published article J. Phys. A: Math. Theor. 44
(2011) 225302 (11pp
Study of interaction of low dose power source radiation fields with selected space scientific instruments Quarterly progress report
Interaction of low dose power source radiation fields with selected space scientific instrument
Comment on "Quantum Monte Carlo Evidence for Superconductivity in the Three-Band Hubbard Model in Two Dimensions"
In a recent Letter, Kuroki and Aoki [Phys. Rev. Lett. 76, 440 (1996)]
presented quantum Monte-Carlo (QMC) results for pairing correlations in the
three-band Hubbard model, which describes the Cu-d_{x^2-y^2} and O-p_{x,y}
orbitals present in the CuO_2 planes of high-T_c materials. In this comment we
argue that (i) the used parameter set is not appropriate for the description of
high-T_c materials since it does not satisfy the minimal requirement of a
charge-transfer gap at half-filling, and (ii) the observed increase in the
d_{x^2-y^2} channel is dominantly produced by the pair-field correlations
without the vertex part. Hence, the claim of evidence of ODLRO is not
justified.Comment: 1 page latex and 2 eps-figures, uses epsfig, submitted to PR
Friedel oscillations induced by non-magnetic impurities in the two-dimensional Hubbard model
We study the interplay of correlations and disorder using an unrestricted
Slave-Boson technique in real space. Within the saddle-point approximation, we
find Friedel oscillations of the charge density in the vicinity of a
nonmagnetic impurity, in agreement with numerical simulations. The
corresponding amplitudes are suppressed by repulsive interactions, while
attractive correlations lead to a charge-density-wave enhancement. In addition,
we investigate the spatial dependence of the local magnetic moment and the
formation of a magnetic state at the impurity site.Comment: 9 pages, RevTeX, includes 8 figure
Isospin properties of electric dipole excitations in 48Ca
Two different experimental approaches were combined to study the electric
dipole strength in the doubly-magic nucleus 48Ca below the neutron threshold.
Real-photon scattering experiments using bremsstrahlung up to 9.9 MeV and
nearly mono-energetic linearly polarized photons with energies between 6.6 and
9.51 MeV provided strength distribution and parities, and an
(\alpha,\alpha'\gamma) experiment at E_{\alpha}=136 MeV gave cross sections for
an isoscalar probe. The unexpected difference observed in the dipole response
is compared to calculations using the first-order random-phase approximation
and points to an energy-dependent isospin character. A strong isoscalar state
at 7.6 MeV was identified for the first time supporting a recent theoretical
prediction.Comment: 6 pages, 5 figures, as accepted in Phys. Lett.
Complex microwave conductivity of Na-DNA powders
We report the complex microwave conductivity, , of
Na-DNA powders, which was measured from 80 K to 300 K by using a microwave
cavity perturbation technique. We found that the magnitude of near
room temperature was much larger than the contribution of the surrounding water
molecules, and that the decrease of with decreasing temperature was
sufficiently stronger than that of the conduction of counterions. These results
clearly suggest that the electrical conduction of Na-DNA is intrinsically
semiconductive.Comment: 16 pages, 7 figure
Using Synchronic and Diachronic Relations for Summarizing Multiple Documents Describing Evolving Events
In this paper we present a fresh look at the problem of summarizing evolving
events from multiple sources. After a discussion concerning the nature of
evolving events we introduce a distinction between linearly and non-linearly
evolving events. We present then a general methodology for the automatic
creation of summaries from evolving events. At its heart lie the notions of
Synchronic and Diachronic cross-document Relations (SDRs), whose aim is the
identification of similarities and differences between sources, from a
synchronical and diachronical perspective. SDRs do not connect documents or
textual elements found therein, but structures one might call messages.
Applying this methodology will yield a set of messages and relations, SDRs,
connecting them, that is a graph which we call grid. We will show how such a
grid can be considered as the starting point of a Natural Language Generation
System. The methodology is evaluated in two case-studies, one for linearly
evolving events (descriptions of football matches) and another one for
non-linearly evolving events (terrorist incidents involving hostages). In both
cases we evaluate the results produced by our computational systems.Comment: 45 pages, 6 figures. To appear in the Journal of Intelligent
Information System
Dynamics of an SO(5) symmetric ladder model
We discuss properties of an exactly SO(5) symmetric ladder model. In the
strong coupling limit we demonstrate how the SO(3)-symmetric description of
spin ladders in terms of bond Bosons can be upgraded to an SO(5)-symmetric
bond-Boson model, which provides a particularly simple example for the concept
of SO(5) symmetry. Based on this representation we show that antiferro-
magnetism on one hand and superconductivity on the other hand can be understood
as condensation of either magnetic or charged Bosons into an RVB vacuum. We
identify exact eigenstates of a finite cluster with general multiplets of the
SO(5) group, and present numerical results for the single particle spectra and
spin/charge correlation functions of the SO(5)-symmetric model and identify
`fingerprints' of SO(5) symmetry in these. In particluar we show that SO(5)
symmetry implies a `generalized rigid band behavior' of the photoemission
spectrum, i.e. spectra for the doped case are rigorously identical to spectra
for spin-polarized states at half-filling. We discuss the problem of adiabatic
continuity between the SO(5) symmetric ladder and the actual t-J ladder and
demonstrate the feasibility of a `Landau mapping' between the two models.Comment: Revtex-file, 16 pages with 15 eps-figures. Hardcopies of Figures (or
the entire manuscript) obtainable by e-mail request to
[email protected]
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