11,526,686 research outputs found
Scaling of the spin stiffness in random spin-1/2 chains : Crossover from pure-metallic behaviour to random singlet-localized regime
In this paper we study the localization transition induced by the disorder in
random antiferromagnetic spin-1/2 chains. The results of numerical large scale
computations are presented for the XX model using its free fermions
representation. The scaling behavior of the spin stiffness is investigated for
various disorder strengths. The disorder dependence of the localization length
is studied and a comparison between numerical results and bosonization
arguments is presented. A non trivial connection between localization effects
and the crossover from the pure XX fixed point to the infinite randomness fixed
point is pointed out.Comment: Published version, 7 pages, 6 figure
Secure direct communication using Einstein-Podolsky-Rosen pairs and teleportation
A novel scheme for secure direct communication between Alice and Bob is
proposed, where there is no need for establishing a shared secret key. The
communication is based on Einstein-Podolsky-Rosen pairs and teleportation
between Alice and Bob. After insuring the security of the quantum channel (EPR
pairs), Bob encodes the secret message directly on a sequence of particle
states and transmits them to Alice by teleportation. In this scheme
teleportation transmits Bob's message without revealing any information to a
potential eavesdropper. Alice can read out the encoded messages directly by the
measurement on her qubits. Because there is not a transmission of the qubit
which carry the secret message between Alice and Bob, it is completely secure
for direct secret communication if perfect quantum channel is used
A description of the ratio between electric and magnetic proton form factors by using space-like, time-like data and dispersion relations
We use the available information on the ratio between the electric and
magnetic proton form factors coming from recently published space-like data and
from the few available time-like data. We apply a dispersive procedure on these
data to evaluate the behaviour of this ratio, as a complex function, for all
values of q^2.Comment: 12 pages, 7 Encapsulated Postscript figures, uses epsfig, rotating,
exscale, amsmath, cite, latexsym, graphics, color packages, added reference
NN final-state interaction in two-nucleon knockout from
The influence of the mutual interaction between the two outgoing nucleons
(NN-FSI) in electro- and photoinduced two-nucleon knockout from has
been investigated perturbatively. It turns out that the effect of NN-FSI
depends on the kinematics and on the type of reaction considered. The effect is
generally larger in pp- than in pn-knockout and in electron induced than in
photoinduced reactions.
In superparallel kinematics NN-FSI leads in the channel to a
strong increase of the cross section, that is mainly due to a strong
enhancement of the -current contribution. In pn-emission, however, this
effect is partially cancelled by a destructive interference with the seagull
current. For photoreactions NN-FSI is considerably reduced in superparallel
kinematics and can be practically negligible in specific kinematics.Comment: 16 pages, 9 figure
B decays into light scalar particles and glueball
The recent observations of f_0(980) in charmless B-decays motivate further
studies of scalar particle and glueball production in these processes.
Amplitudes for charmless 2-body B decays involving the members of the scalar
nonet are presented based on the symmetries of the dominant penguin
contribution. Different scenarios for the lightest scalar nonet are
investigated in view of the presently available data. We describe the evidence
from B-decays for f_0(1500) with a flavour octet like mixing and the hints
towards the members of the q qbar nonet of lowest mass. There is further
support for the hypothesis of a broad 0^{++} glueball acting as coherent
background especially in B -> K Kbar K. The estimated B decay rates into
gluonic mesons represent a sizable fraction of the theoretically derived decay
rate for b -> sg.Comment: 34 pages, 5 figures, 8 tables, version to appear in Eur.Phys.J.C.,
with some clarifications in the text, additional refs. and several overall
signs in Tab.2,3 adde
High-contrast dark resonance on the D2 - line of 87Rb in a vapor cell with different directions of the pump - probe waves
We propose a novel method enabling to create a high-contrast dark resonance
in the 87Rb vapor D2-line. The method is based on an optical pumping of atoms
into the working states by a two-frequency, linearly-polarized laser radiation
propagating perpendicularly to the probe field. This new scheme is compared to
the traditional scheme involving the circularly-polarized probe beam only, and
significant improvement of the dark resonance parameters is found. Qualitative
considerations are confirmed by numerical calculations.Comment: 7 pages, 4 figure
Analytic Continuation of Resolvent Kernels on noncompact Symmetric Spaces
Let X=G/K be a symmetric space of noncompact type and let L be the Laplacian
associated with a G-invariant metric on X. We show that the resolvent kernel of
L admits a holomorphic extension to a Riemann surface depending on the rank of
the symmetric space. This Riemann surface is a branched cover of the complex
plane with a certain part of the real axis removed. It has a branching point at
the bottom of the spectrum of L. It is further shown that this branching point
is quadratic if the rank of X is odd, and is logarithmic otherwise. In case G
has only one conjugacy class of Cartan subalgebras the resolvent kernel extends
to a holomorphic function on a branched cover of the complex plane with the
only branching point being the bottom of the spectrum.Comment: 16 pages, 3 figures, LaTe
From Grounded Foot to Leaping Foot: Practice and Pedagogy Forum
A sharing and demonstration of research by Central School of Speech & Drama Senior Lecturer, Debbie Green, and Academy of Live and Recorded Arts Movement Tutor/Director, Ita O’Brien, into the development of the leaping foot from the grounded foot. The focus of their exploration is on the actor’s experience of being grounded to her/his experience of lightness through elevation from an anatomical awareness of the feet and the mechanism of leaping. They discuss various disciplines of movement that foreground working the feet and encourage a mindful approach to the use of the feet in a progressive practice
Correlation between the reliability of HEMT devices and that of a combined oscillator-amplifier
We evaluate an oscillator-amplifier MMIC submitted to high-temperature operating life time tests. To relate adequately these results with individual components’ results, it is important to realise that failure mechanisms in non-linear MMICs are governed by the maximally instantaneous voltages/currents and hence that comparisons should be conducted at equal instantaneous conditions
Library project management in a collaborative web-based working environment
This paper discusses the emerging paradigm of project management performed in a web-based
working environment. It highlights how project management and its associated features are
strongly linked to fulfilling quality and value criteria for customers, and it examines how
collaborative working environments can greatly reduce the administrative burden of managing
large projects, especially and almost paradoxically, when resources are limited. Specifically, the
paper examines the application of a project management methodology (PRINCE2) together
with the use of a collaborative web-based working environment over a number of pilot projects
at Leeds University Library. It describes the pilot phase of a library management decision to
run a series of major Library projects using project management methodology, while
continuing to run other projects through the existing locally developed planning mechanisms
and describes the pitfalls of these latter alternatives, less sophisticated project management
tools, and describes the main issues that this change in practice has brought to light. It draws
preliminary conclusions about the effectiveness of this change in practice in one of the UK’s
largest academic libraries
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