Magnetization of undoped 2-leg S = 1/2 spin ladders in La4Sr10Cu24O41

Magnetization data of single crystalline La4Sr10Cu24O41 are presented. In this compound, doped spin chains and undoped spin ladders are realized. The magnetization, at low temperatures, is governed by the chain subsystem with a finite interchain coupling which leads to short range antiferromagnetic spin correlations. At higher temperatures, the response of the chains can be estimated in terms of a Curie-Weiss law. For the ladders, we apply the low-temperature approximation for a S=1/2 2-leg spin ladder by Troyer et al.Comment: 2 pages, 2 figure

Everyday pain, analgesic beliefs and analgesicbehaviours in Europe and Russia: An epidemiologicalsurvey and analysis

Беше проведено анкетно проучване в осем държави, в т.ч. Белгия, Германия, Великобритания, Италия, Полша, Русия и Испания. Оценена беше честотата на оплакване от болка при 8 506 души (52% жени), както и използването на аналгетици и нагласите спрямо тях. Предварителните анализи потвърждават високата честота на оплаквания от болка, като 70% от анкетираните посочват, че поне веднъж в месеца изпитват такава. Най-често се съобщава за главоболие и болки в гърба, a болшинството анкетирани лица - 77%, споделят, че използват аналгетични средства, когато страдат от болка. Предмет на по-нататъшните анализи бяха различията по пол, статус на заетост, държава по местоживеене и възраст. В сравнение с мъжете, жените по-често изпитват болка, употребата на аналгетици сред тях е по-голяма, както и притесненията им във връзка с тази употреба, като проявяват склонност да базират употребата върху своите познания относно лекарствените продукти. Безработните също съобщават за по-голямо използване на аналгетици и повече притеснения във връзка с това, сравнено със заетите лица. Като цяло при хората, живеещи в Русия и Полша, се отчита по-рядко болка и по-малко използване на обезболяващи средства в сравнение с останалата част на Европа. Те също така се тревожат повече във връзка с аналгетиците и по отношение на това, че използването на аналгетици от тяхна страна е слабо свързано с познания относно лекарствата. Отчитането на фактора „възраст` показва, че при по-младите епизодите на болка са по-малко, употребата на аналгетици - по-честа, a притесненията относно аналгетиците са по-слаби в сравнение с по-възрастните. Също така, по-младите са по-склонни да използват аналгетици въз основа на своите познания за продукта. Тези резултати повтарят съществуващи констатации във връзка с честотата на болката. Дават и нови сведения за различията при изпитването на болка, използването на аналгетици и нагласите към аналгетиците в Европа и Русия.

SOME RESULTS ON THE DESIGN OF EXPERIMENTS FOR COMPARING UNREPLICATED TREATMENTS

In early generation variety trials, large numbers of new varieties may be compared, and little seed is usually available for each variety. A so-called unreplicated trial has each new variety on just one plot at a site, but includes several (often around 5) replicated check or control (or standard) varieties. The total proportion of check plots is usually between 10% and 20%. The aim of the trial is to choose some (around 1/3) good performing varieties to go on for further testing, rather than precise estimation of their mean yield. Now that spatial analyses of data from field experiments are becoming more common, there is interest in an efficient layout of an experiment given a proposed spatial analysis. Some possible design criteria are discussed, and efficient layouts under spatial dependence are considered

The Mid-Infrared Instrument for the James Webb Space Telescope, VIII: The MIRI Focal Plane System

We describe the layout and unique features of the focal plane system for MIRI. We begin with the detector array and its readout integrated circuit (combining the amplifier unit cells and the multiplexer), the electronics, and the steps by which the data collection is controlled and the output signals are digitized and delivered to the JWST spacecraft electronics system. We then discuss the operation of this MIRI data system, including detector readout patterns, operation of subarrays, and data formats. Finally, we summarize the performance of the system, including remaining anomalies that need to be corrected in the data pipeline

Sr_14Cu_24O_41Sr\_{14}Cu\_{24}O\_{41} : a complete model for the chain sub-system

A second neighbor $t-J+V$ model for the chain subsystem of the $Sr\_{14}Cu\_{24}O\_{41}$ has been extracted from ab-initio calculations. This model does not use periodic approximation but describes the entire chain through the use of the four-dimensional crystallographic description. Second neighbors interactions are found to be of same order than the first neighbors ones. The computed values of the second neighbors magnetic interaction are coherent with experimental estimations of the intra-dimer magnetic interactions, even if slightly smaller. The reasons of this underestimation are detailed. The computed model allowed us to understand the origin of the chain dimerisation and predicts correctly the relative occurrence of dimers and free spins. The orbitals respectively supporting the magnetic electrons and the holes have been found to be essentially supported by the copper 3d orbitals (spins) and the surrounding oxygen $2p$ orbitals (holes), thus giving a strong footing to the existence of Zhang-Rice singlets

Temperature-dependent spin gap and singlet ground state in BaCuSi2O6

Bulk magnetic measurements and inelastic neutron scattering were used to investigate the spin-singlet ground state and magnetic gap excitations in BaCuSi2O6, a quasi-2-dimensional antiferromagnet with a bilayer structure. The results are well described by a model based on weakly interacting antiferromagnetic dimers. A strongly temperature-dependent dispersion in the gap modes was found. We suggest that the observed excitations are analogous to magneto-excitons in light rare-earth compounds, but are an intrinsic property of a simple Heisenberg Hamiltonian for the S=1/2 magnetic bilayer.Comment: 10 pages, 4 figures, REVTeX and PS for text, PS for figures direct download: http://papillon.phy.bnl.gov/preprints/bacusio.htm

Dynamical Spin Response Functions for Heisenberg Ladders

We present the results of a numerical study of the 2 by L spin 1/2 Heisenberg ladder. Ground state energies and the singlet-triplet energy gaps for L = (4-14) and equal rung and leg interaction strengths were obtained in a Lanczos calculation and checked against earlier calculations by Barnes et al. (even L up to 12). A related moments technique is then employed to evaluate the dynamical spin response for L=12 and a range of rung to leg interaction strength ratios (0 - 5). We comment on two issues, the need for reorthogonalization and the rate of convergence, that affect the numerical utility of the moments treatment of response functions.Comment: Revtex, 3 figure

Quasi-two-dimensional hole ordering and dimerized state in the CuO2-chain layers in Sr14Cu24O41

Neutron scattering experiments have been performed on Sr$_{14}$Cu$_{24}$O$_{41}$ which consists of both chains and ladders of copper ions. We observed that the magnetic excitations from the CuO$_2$ chain have two branches and that both branches are weakly dispersive along the $a$ and $c$ axes. The $\omega$-$Q$ dispersion relation as well as the intensities can be reasonably described by a random phase approximation with intradimer coupling between next-nearest-neighbor copper spins $J$=11 meV, interdimer coupling along the c axis $J_c$=0.75 meV, and interdimer coupling along the a axis $J_a$=0.75 meV. The dimer configuration indicates a quasi-two-dimensional hole ordering, resulting in an ordering of magnetic Cu$^{2+}$ with spin-1/2 and nonmagnetic Cu, which forms the Zhang-Rice singlet. We have also studied the effect of Ca substitution for Sr on the dimer and the hole ordering.Comment: 7 pages, Revtex, 10 figures, Submitted to Phys. Rev.