Raman scattering in a Heisenberg {\boldmath S=1/2S=1/2} antiferromagnet on the triangular lattice

We investigate two-magnon Raman scattering from the $S=1/2$ Heisenberg antiferromagnet on the triangular lattice, considering both the effect of renormalization of the one-magnon spectrum by 1/S corrections and final-state magnon-magnon interactions. The bare Raman intensity displays two peaks related to one-magnon van-Hove singularities. We find that 1/S self-energy corrections to the one-magnon spectrum strongly modify this intensity profile. The central Raman-peak is significantly enhanced due to plateaus in the magnon dispersion, the high frequency peak is suppressed due to magnon damping, and the overall spectral support narrows considerably. Additionally we investigate final-state interactions by solving the Bethe-Salpeter equation to $O(1/S)$. In contrast to collinear antiferromagnets, the non-collinear nature of the magnetic ground state leads to an irreducible magnon scattering which is retarded and non-separable already to lowest order. We show that final-state interactions lead to a rather broad Raman-continuum centered around approximately twice the 'roton'-energy. We also discuss the dependence on the scattering geometry.Comment: 7 pages, 5 figure

Finishing store lambs from organic hill and upland farms OF0119

1. The aim of this study was to assess the economics and constraints associated with home finishing lambs on a range of organic hill and upland farms in England and Wales, and to evaluate the potential for further finishing on registered farms in the lowlands. 2. The current state of the organic sheep sector is briefly reviewed. This identifies problems of scale, limited premia and uneveness of supply as limiting factors to more rapid development of the market and associated production systems. 3. To quanitfy the effect of organic management on financial performance, hill and upland farms were classified under four typical systems, depending on the degree of intensification. 4. Without a sizeable area of improved ground, to which fertiliser and other inputs could have been applied conventionally, flocks based on high hill or marginal hill systems were least affected by switching to organic management. Flock Gross Margin on the marginal hill declined by approximately 7%. 5. On more intensive farms, typified by Welsh hill or upland farming systems, there is greater potential to finish lambs at higher stocking rates under conventional management, and the consequences of changing to organic management are greatly increased. Assuming a 10% premium for fnished organic lambs, deviating from convetional practice to produce store lambs or finish lambs at higher production cost, reduced flock Gross Margin by approximately 12-15%. Without a premium, this deficit increased to 15-20%. 6. The Organic Aid Scheme can make good the likely income loss during the first two years after conversion, when the highest rates are payable. However, in the long-term organic flocks must compete solely on the basis os a premium paid for finished, and ideally, for store lambs. 7. Physical and financial constraints were identified as t wy systems had not developed linking potential production of store lambs in the hills/uplands with finishing on organic farms in the lowlands. These were mainly scale and infrastructure, availability of suitable feeds and the likely level of return to the lowland farmer from a store lamb finishing enterprise. Potential sources of feed for finishing organic lambs were assessed. These include permanent pasture, short-term leys, catch crops, grazed set-aside land and conserved fodder. 8. Integration with existing organic systems of all types was estimated to have the potential to finish an extra 10-15,000 lambs per annum, equivalent to the number of lambs currently receiving an organic premium. 9. Further opportunities to expand finishing capacity on lowland farms were examined. Mixed organic farms are likely to have little or no capacity to finish bought in store lambs, except where overall stocking rates are constrained by insufficient ewe/suckler cow quota, or where catch crops are added to the rotation. 10. The addition of a store lamb enterprise to lowland systems was calculated to increase farm Gross MArgin by 2-3%, depending on the type of farm (dairy, stockless arable, or mixed). This represented a marginal return on capital invested in a store lamb finishing enterprise of 9-24%. 1. The financial risks involved, the availability of suitable labour and fixed equipment, and reluctance to vary arable rotations, make store lamb finishing enterprises less attractive to the lowland farmer. 12. Beyond the capacity to increase the number of certified lambs currently offered by up to 50%, greater opportunities are only likely to develop, when there is a significant increase in land (particularly on arable farms) entering conversion

Scintillation Caustics in Planetary Occultation Light Curves

We revisit the GSC5249-01240 light curve obtained during its occultation by Saturn's North polar region. In addition to refractive scintillations, the power spectrum of intensity fluctuations shows an enhancement of power between refractive and diffractive regimes. We identify this excess power as due to high amplitude spikes in the light curve and suggest that these spikes are due to caustics associated with ray crossing situations. The flux variation in individual spikes follows the expected caustic behavior, including diffraction fringes which we have observed for the first time in a planetary occultation light curve. The presence of caustics in scintillation light curves require an inner scale cut off to the power spectrum of underlying density fluctuations associated with turbulence. Another possibility is the presence of gravity waves in the atmosphere. While occultation light curves previously showed the existence of refractive scintillations, a combination of small projected stellar size and a low relative velocity during the event have allowed us to identify caustics in this occultation. This has led us to re-examine previous data sets, in which we have also found likely examples of caustics.Comment: 4 pages, 3 figures; ApJL submitte

Double Charge Exchange And Configuration Mixing

The energy dependence of forward pion double charge exchange reactions on light nuclei is studied for both the Ground State transition and the Double-Isobaric-Analog-State transitions. A common characteristic of these double reactions is a resonance-like peak around 50 MeV pion lab energy. This peak arises naturally in a two-step process in the conventional pion-nucleon system with proper handling of nuclear structure and pion distortion. A comparison among the results of different nuclear structure models demonstrates the effects of configuration mixing. The angular distribution is used to fix the single particle wave function.Comment: Added 1 figure (now 8) corrected references and various other change

Facile Protocol for Water-Tolerant “Frustrated Lewis Pair”-Catalyzed Hydrogenation

Despite rapid advances in the field of metal-free, “frustrated Lewis pair” (FLP)-catalyzed hydrogenation, the need for strictly anhydrous reaction conditions has hampered wide-scale uptake of this methodology. Herein, we report that, despite the generally perceived moisture sensitivity of FLPs, 1,4-dioxane solutions of B(C6F5)3 actually show appreciable moisture tolerance and can catalyze hydrogenation of a range of weakly basic substrates without the need for rigorously inert conditions. In particular, reactions can be performed directly in commercially available nonanhydrous solvents without subsequent drying or use of internal desiccants

Observation of a temperature dependent electrical resistance minimum above the magnetic ordering temperature in Gd2_2PdSi3_3

Results on electrical resistivity, magnetoresistance, magnetic Results on electrical resistivity, magnetoresistance, magnetic susceptibility, heat capacity and Gd Mossbauer measurements on a Gd-based intermetallic compound, Gd$_{2}$PdSi$_{3}$ are reported. A finding of interest is that the resistivity unexpectedly shows a well-defined minimum at about 45 K, well above the long range magnetic ordering temperature (21 K), a feature which gets suppressed by the application of a magnetic field. This observation in a Gd alloy presents an interesting scenario. On the basis of our results, we propose electron localization induced by s-f (or d-f) exchange interaction prior to long range magnetic order as a mechanism for the electrical resistance minimum.Comment: 4 pages, 4 figure

Color in context: psychological context moderates the influence of red on approach- and avoidance-motivated behavior.

A basic premise of the recently proffered color-in-context model is that the influence of color on psychological functioning varies as a function of the psychological context in which color is perceived. Some research has examined the appetitive and aversive implications of viewing the color red in romance- and achievement-relevant contexts, respectively, but in all existing empirical work approach and avoidance behavior has been studied in separate tasks and separate experiments. Research is needed to directly test whether red influences the same behavior differently depending entirely on psychological context. The present experiment was designed to put this premise to direct test in romance- and achievement-relevant contexts within the same experimental paradigm involving walking behavior. Our results revealed that exposure to red (but not blue) indeed has differential implications for walking behavior as a function of the context in which the color is perceived. Red increased the speed with which participants walked to an ostensible interview about dating (a romance-relevant context), but decreased the speed with which they walked to an ostensible interview about intelligence (an achievement-relevant context). These results are the first direct evidence that the influence of red on psychological functioning in humans varies by psychological context. Our findings contribute to both the literature on color psychology and the broader, emerging literature on the influence of context on basic psychological processes

The role of right and left parietal lobes in the conceptual processing of numbers

Neuropsychological and functional imaging studies have associated the conceptual processing of numbers with bilateral parietal regions (including intraparietal sulcus). However, the processes driving these effects remain unclear because both left and right posterior parietal regions are activated by many other conceptual, perceptual, attention, and response-selection processes. To dissociate parietal activation that is number-selective from parietal activation related to other stimulus or response-selection processes, we used fMRI to compare numbers and object names during exactly the same conceptual and perceptual tasks while factoring out activations correlating with response times. We found that right parietal activation was higher for conceptual decisions on numbers relative to the same tasks on object names, even when response time effects were fully factored out. In contrast, left parietal activation for numbers was equally involved in conceptual processing of object names. We suggest that left parietal activation for numbers reflects a range of processes, including the retrieval of learnt facts that are also involved in conceptual decisions on object names. In contrast, number selectivity in right parietal cortex reflects processes that are more involved in conceptual decisions on numbers than object names. Our results generate a new set of hypotheses that have implications for the design of future behavioral and functional imaging studies of patients with left and right parietal damage

The Hubble Space Telescope high speed photometer

The Hubble Space Telescope will provide the opportunity to perform precise astronomical photometry above the disturbing effects of the atmosphere. The High Speed Photometer is designed to provide the observatory with a stable, precise photometer with wide dynamic range, broad wavelenth coverage, time resolution in the microsecond region, and polarimetric capability. Here, the scientific requirements for the instrument are examined, the unique design features of the photometer are explored, and the improvements to be expected over the performance of ground-based instruments are projected

College student's academic goals and learning strategies

Tomando en cuenta que no existe concordancia en la literatura entre los resultados de diferentes estudios respecto de la relevancia de la adopción de un tipo u otro de meta para el aprendizaje académico, en el presente artículo se estudia la relación entre los diferentes tipos de orientaciones motivacionales (metas de aprendizaje, metas de rendimiento y metas de evitación del trabajo) y el uso de estrategias cognitivas y de autorregulación. En el trabajo participan 632 estudiantes universitarios de diversas titulaciones de la universidad española. Aunque el estudio es de tipo correlacional, los análisis de los datos obtenidos, corroborando estudios anteriores, aportan información de interés para la discusión del problema que se investigó, por ejemplo que sólo los niveles más altos de metas de aprendizaje se encuentran asociados con una mayor utilización de estrategias de aprendizaje. Son discutidas implicaciones educativas de estos datos.Tomando em consideração que não existe concordância na literatura entre os resultados dos diferentes estudos a respeito da relevância da adopção de um ou de outro tipo de meta na aprendizagem académica; no presente artículo é estudada a relação entre os diferentes tipos de orientações motivacionais (metas de aprendizagem, metas de rendimento e metas de evitação do trabalho) e a utilização de estratégias cognitivas e de autoregulação. Neste trabalho participam 632 estudantes universitários de diversas licenciaturas da Universidade espanhola. Apesar de este estudo ser de tipo correlacional, a análise dos dados obtidos, corroborando estudos anteriores, aporta informação de interesse para a discussão do problema investigado; por exemplo que só os níveles mais altos de metas de aprendizagem se encontram associados con uma maior utilização de estratégias de aprendizagem. São discutidas implicações educativas destes dados.Assuming that there isn’t much agreement among the results from different studies relating to the relevance of adopting one or another kind of academic learning goal, this paper intends to study the relationship between the several types of motivational orientations (learning goals, achievement goals and avoidance goals) and the use of cognitive and self-regulatory strategies. 632 Spanish college students from various university courses participated in this research. Although this is a correlacional study data analysis, in line with previous studies, brings to light interesting information and highlights the investigated issue for example only higher levels of learning goals are positively related with the use of learning strategies. Future educational implications are also discussed