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

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

NN final-state interaction in two-nucleon knockout from 16O^{16}O

The influence of the mutual interaction between the two outgoing nucleons (NN-FSI) in electro- and photoinduced two-nucleon knockout from $^{16}O$ 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 $(e,e'pp)$ channel to a strong increase of the cross section, that is mainly due to a strong enhancement of the $\Delta$-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

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

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

A Statistical Model of Abstention under Compulsory Voting

Invalid voting and electoral absenteeism are two important sources of abstention in compulsory voting systems. Previous studies in this area have not considered the correlation between both variables and ignored the compositional nature of the data, potentially leading to unfeasible results and discarding helpful information from an inferential standpoint. In order to overcome these problems, this paper develops a statistical model that accounts for the compositional and hierarchical structure of the data and addresses robustness concerns raised by the use of small samples that are typical in the literature. The model is applied to analyze invalid voting and electoral absenteeism in Brazilian legislative elections between 1945 and 2006 via MCMC simulations. The results show considerable differences in the determinants of both forms of non-voting; while invalid voting was strongly positively related both to political protest and to the existence of important informational barriers to voting, the influence of these variables on absenteeism is less evident. Comparisons based on posterior simulations indicate that the model developed in this paper fits the dataset better than several alternative modeling approaches and leads to different substantive conclusions regarding the effect of different predictors on the both sources of abstention