NMR and LDA evidence for spiral magnetic order in the chain cuprate LiCu2O2

We report on {6,7}Li nuclear magnetic resonance measurements of the spin-chain compound LiCu2O2 in the paramagnetic and magnetically ordered states. Below T about 24 K the NMR lineshape presents a clear signature of incommensurate (IC) static modulation of the local magnetic field consistent with an IC spiral modulation of the magnetic moments. {7}Li NMR reveals strong phason-like dynamical fluctuations extending well below 24 K. We hypothesize that a series of phase transitions at 24.2, 22.5, and 9 K reflects a "Devil's staircase" type behavior generic for IC systems. LDA based calculations of exchange integrals reveal a large in-chain frustration leading to a magnetical spiral.Comment: 4 pages, 4 figure

B-T phase diagram of CoCr2O4 in magnetic fields up to 14 T

We have measured the magnetization and specific heat of multiferroic CoCr2O4 in magnetic fields up to 14 T. The high-field magnetization measurements indicate a new phase transition at T* = 5 - 6 K. The phase between T* and the lock-in transition at 15 K is characterized by magnetic irreversibility. At higher magnetic fields, the irreversibility increases. Specific-heat measurements confirm the transition at T*, and also show irreversible behavior. We construct a field-temperature phase diagram of CoCr2O4.Comment: 4 page

Magnetic phase diagram of the frustrated S=1/2 chain magnet LiCu_2O_2

We present the results of the magnetization and dielectric constant measurements on untwinned single crystal samples of the frustrated S=1/2 chain cuprate LiCu_2O_2. Novel magnetic phase transitions were observed. A spin flop transition of the spiral spin plane was observed for the field orientations H||a,b. The second magnetic transition was observed at H~15 T for all three principal field directions. This high field magnetic phase is discussed as a collinear spin-modulated phase which is expected for an S=1/2 nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic chain system

Recovery of critically endangered Nassau grouper (Epinephelus striatus) in the Cayman Islands following targeted conservation actions.

Many large-bodied marine fishes that form spawning aggregations, such as the Nassau grouper (Epinephelus striatus), have suffered regional overfishing due to exploitation during spawning. In response, marine resource managers in many locations have established marine protected areas or seasonal closures to recover these overfished stocks. The challenge in assessing management effectiveness lies largely in the development of accurate estimates to track stock size through time. For the past 15 y, the Cayman Islands government has taken a series of management actions aimed at recovering collapsed stocks of Nassau grouper. Importantly, the government also partnered with academic and nonprofit organizations to establish a research and monitoring program (Grouper Moon) aimed at documenting the impacts of conservation action. Here, we develop an integrated population model of 2 Cayman Nassau grouper stocks based on both diver-collected mark-resight observations and video censuses. Using both data types across multiple years, we fit parameters for a state-space model for population growth. We show that over the last 15 y the Nassau grouper population on Little Cayman has more than tripled in response to conservation efforts. Census data from Cayman Brac, while more sparse, show a similar pattern. These findings demonstrate that spatial and seasonal closures aimed at rebuilding aggregation-based fisheries can foster conservation success

Computing the entropy of user navigation in the web

Navigation through the web, colloquially known as "surfing", is one of the main activities of users during web interaction. When users follow a navigation trail they often tend to get disoriented in terms of the goals of their original query and thus the discovery of typical user trails could be useful in providing navigation assistance. Herein, we give a theoretical underpinning of user navigation in terms of the entropy of an underlying Markov chain modelling the web topology. We present a novel method for online incremental computation of the entropy and a large deviation result regarding the length of a trail to realize the said entropy. We provide an error analysis for our estimation of the entropy in terms of the divergence between the empirical and actual probabilities. We then indicate applications of our algorithm in the area of web data mining. Finally, we present an extension of our technique to higher-order Markov chains by a suitable reduction of a higher-order Markov chain model to a first-order one

Нейтронографическое исследование структурного перехода кубическая–тетрагональная фаза в монокристаллах твердых растворов оксида циркония с оксидом иттрия

Objectives. The determination of the phase relations, crystallographic characteristics, microstructure features, and atomic crystal structure of zirconium oxide crystals that are partially and completely stabilized by yttrium oxide additives, and the identification of the crystallographic and crystal-chemical correlations with the physicochemical properties of single crystals.Methods. The neutron structure of the crystals was studied using the neutron time-of-flight and constant wavelength methods using a high-resolution Fourier diffractometer on the IBR-2 pulsed fast reactor and a four-circle neutron diffractometer “Syntex.” Single crystals were grown by directed crystallization from the melts of mixtures (1 − х)ZrO2 ∙хY2O3 , х = 0.03 and х = 0.12 with different growth rates (10 and 40 mm/h).Results. It was observed that when growing single crystals with x = 0.03–0.05, the crystal was stratified into cubic and tetragonal phases, and the ratio between the phases depended on the growth rate. At a growth rate of 40 mm/h, the content of the cubic phase was insignificant. In the crystals of partially stabilized zirconium dioxide (ZrO2) with the additions of 3 mol % Y2O3, the coherent coexistence of cubic and tetragonal phases was established, and the twin law for a tetragonal component (rotation of unit cell axis by 90° around the a (b) axis) that was observed during the phase transition from high-temperature cubic phase to tetragonal phase was determined. For the fully stabilized zirconium oxide of the cubic symmetry (with 12 mol % Y2O3), the 0.3 Å displacements of oxygen atoms from their partial structural positions in the directions [100] and [111] were determined. These displacements correlated with the directions of the ion transport.Conclusions. Previous studies have shown that the ratio between the cubic and tetragonal phases of the single crystals of the ZrO2 –Y2O3 system depends on the growth rate of the single crystals. The content of Y2O3 in the cubic and tetragonal phases of a single crystal was determined using the non-destructive neutronography method on the same volume sample of a solid solution of this system. Moreover, the displacements of oxygen atoms from the main position of the crystal were determined.Цели. Определение фазовых соотношений, кристаллографических характеристик, особенностей микроструктуры и атомно-кристаллической структуры кристаллов оксида циркония, частично и полностью стабилизированных добавками оксида иттрия, выявление кристаллографических и кристаллохимических корреляций с физико-химическими свойствами монокристаллов.Методы. Нейтроноструктурные исследования кристаллов проведены методами времени пролета нейтронов и постоянной длины волны с использованием Фурье дифрактометра высокого разрешения на импульсном быстром реакторе ИБР-2 и четырехкружного нейтронного дифрактометра «Синтекс». Монокристаллы были выращены направленной кристаллизацией из расплавов смесей (1 – х)ZrO2 ∙хY2O3 , х = 0.03 и 0.12 с разными скоростями роста (10 и 40 мм/ч).Результаты. Установлено, что при выращивании монокристаллов с х = 0.03–0.05 происходит расслоение кристалла на кубическую и тетрагональную фазы, соотношение между которыми зависит от скорости выращивания. При скорости роста 40 мм/ч содержание кубической фазы незначительно. В кристаллах частично стабилизированного диоксида циркония ZrO2 (c добавками 3 mol % Y2O3) установлено когерентное сосуществование кубической и тетрагональной фаз и определен закон двойникования для тетрагональной компоненты (вращение осей элементарной ячейки на 90° вокруг осей a (b)), возникающего при фазовом переходе из высокотемпературной кубической фазы в тетрагональную. Для полностью стабилизированного диоксида циркония кубической симметрии (с 12 mol % Y2O3) определены смещения атомов кислорода на 0.3 Å из их частных структурных позиций в направлениях [100] и [111]. Эти смещения коррелирует с направлениями ионного транспорта.Выводы. Исследования показали, что соотношение между кубической фазой и тетрагональной фазой монокристаллов системы ZrO2 –Y2O3 зависит от скорости выращивания монокристаллов. На одном и том же объемном образце твердого раствора этой системы неразрушающим методом нейтронографии определено содержание Y2O3 и в кубической, и в тетрагональной фазе монокристалла. Определены смещения атомов кислорода из основной позиции кристалла

Chaotic and pseudochaotic attractors of perturbed fractional oscillator

We consider a nonlinear oscillator with fractional derivative of the order alpha. Perturbed by a periodic force, the system exhibits chaotic motion called fractional chaotic attractor (FCA). The FCA is compared to the ``regular'' chaotic attractor. The properties of the FCA are discussed and the ``pseudochaotic'' case is demonstrated.Comment: 20 pages, 7 figure

Statistical Communication Theory

Contains reports on three research projects.National Science Foundation (Grant GP-2495)National Aeronautics and Space Administration (Grant NsG-496)National Institutes of Health (Grant MH-04737-04

In vivo validation of the origin of the esophageal electrocardiogram

Esophageal electrocardiography is a clinical and investigational technique that is useful for determining atrial conduction intervals, analyzing atrial rhythms and mapping conduction pathways. Although the left atrial origin of the esophageal electrocardiogram has long been implied, recently that origin has been questioned. In the present study, the origin of the esophageal deflection is defined by direct right and left atrial mapping studies performed with simultaneous esophageal electrograms obtained from three positions (high, mid and low). Seven patients with normal left atrial dimensions (group I) and five patients with left atrial enlargement (group II) underwent transseptal catheterization during the course of electrophysiologic study.In group I (normal left atrial dimensions), conduction time from the high right atrium to each of the three esophageal positions corresponded to conduction times to left atrial sites ranging from 1 to 3 em lateral to the left interatrial septum. The mid- and low esophageal conduction times were all significantly longer than conduction time to the left side of the septum (p < 0.05). In group II (enlarged left atrium), conduction times to each of the esophageal sites corresponded to conduction times to left atrial sites lying between the mid-left atrium and a point 1 em lateral to the left side of the septum. A significant trend toward longer conduction time to the mid-esophageal position than to the left septum was noted (p < 0.1). In both groups, conduction times measured with the esophageal catheter were significantly longer than conduction time to the right interatrial septum (p < 0.05).The esophageal electrogram corresponds to atrial deflections recorded within the left atrium distinct from the interatrial septum and right atrium. Esophageal electrocardiography is a valid technique for investigation of left atrial rhythms and interatrial conduction