Spin liquid phase in a spatially anisotropic frustrated antiferromagnet

We explore the effect of the third nearest-neighbors on the magnetic properties of the Heisenberg model on an anisotropic triangular lattice. We obtain the phase diagram of the model using Schwinger-boson mean-field theory. Competition between N\'eel, spiral and collinear magnetically ordered phases is found as we vary the on the ratios of the nearest, J1, next-nearest, J2, and third-nearest, J_3, neighbor exchange couplings. A spin liquid phase is stabilized between the spiral and collinear ordered states when J2/J1 < 1.8 for rather small J3/J1 < 0.1. The lowest energy two-spinon dispersions relevant to neutron scattering experiments are analyzed and compared to semiclassical magnon dispersions finding significant differences in the spiral and collinear phases between the two approaches. The results are discussed in the context of the anisotropic triangular materials: Cs2CuCl4 and Cs2CuBr4 and layered organic materials, kappa-(BEDT-TTF)2X and Y[Pd(dmit)2]2.Comment: 11 pages, 9 figure

Spin liquid phase due to competing classical orders in the semiclassical theory of the Heisenberg model with ring exchange on an anisotropic triangular lattice

Linear spin wave theory shows that ring exchange induces a quantum disordered region in the phase diagram of the title model. Spin wave spectra show that this is a direct manifestation of competing classical orders. A spin liquid is found in the `Goldilocks zone' of frustration, where the quantum fluctuations are large enough to cause strong competition between different classical orderings but not strong enough to stabilize spiral order. We note that the spin liquid phases of $\kappa$-(BEDT-TTF)${_2}X$ and $Y$[Pd(dmit)$_2$]$_2$ are found in this Goldilocks zone.Comment: 5 pages, 3 figure

The Cyclical Behavior of Industrial Labor Markets: A Comparison of the Pre-War and Post-War Eras

This paper studies the cyclical behavior of a number of industrial labor markets of the pre-war (1923-1939) and post-war (1954-1982) eras. In the spirit of Burns and Mitchell we do not test a specific structural model of the labor market but instead concentrate on describing the qualitative features of the (monthly, industry-level) data.The two principal questions we ask are: First, how is labor input (as measured by the number of workers, the hours of work, and the intensity of utilization) varied over the cycle ? Second, what is the cyclical behaviorof labor compensation (as measured by real wages, product wages, and real weekly earnings) ? We study these questions in both the frequency domain and the time domain. Many of our findings simply reinforce, or perhaps refine, existing perceptions of cyclical labor market behavior. However, we do find some interesting differences between the pre-war and the post-war periods in ther elative use of layoffs and short hours in downturns, and in the cyclical behavior of the real wage.

ATPase cycle and DNA unwinding kinetics of RecG helicase

The superfamily 2 bacterial helicase, RecG, is a monomeric enzyme with a role in DNA repair by reversing stalled replication forks. The helicase must act specifically and rapidly to prevent replication fork collapse. We have shown that RecG binds tightly and rapidly to four-strand oligonucleotide junctions, which mimic a stalled replication fork. The helicase unwinds such DNA junctions with a step-size of approximately four bases per ATP hydrolyzed. To gain an insight into this mechanism, we used fluorescent stopped-flow and quenched-flow to measure individual steps within the ATPase cycle of RecG, when bound to a DNA junction. The fluorescent ATP analogue, mantATP, was used throughout to determine the rate limiting steps, effects due to DNA and the main states in the cycle. Measurements, when possible, were also performed with unlabeled ATP to confirm the mechanism. The data show that the chemical step of hydrolysis is the rate limiting step in the cycle and that this step is greatly accelerated by bound DNA. The ADP release rate is similar to the cleavage rate, so that bound ATP and ADP would be the main states during the ATP cycle. Evidence is provided that the main structural rearrangements, which bring about DNA unwinding, are linked to these states

Productivity in Hampshire, Dorset and Southdown flocks of sheep and evaluation of factors affecting performance of lambs

Agriculture is entering an age where, to survive, the Tennessee farmer must either purchase more land or improve production on the land he has. Most of the time it is more economical to improve one\u27s production per acre or per animal. One method of accomplishing greater production is through selection of superior producing animals. Selection has been done for centuries through visual observation. To justify their existence as a group, breeders of registered sheep must produce a type of sheep superior to those in the hands of the commercial producers they serve. This superiority must be expressed in demonstrated ability to increase the quantity and quality of the products the operator has for sale, or in increased efficiency of production. Purebred sheep flocks have been instrumental in establishing the type of commercial lamb which has been produced for several decades. Successful purebred breeders in the future must not only raise sheep of an acceptable breed-type or character, but they also must produce individuals of an excellent known productive ability. These seed stock producers must gear their breeding and selection programs on performance indexes which include a combination of characters such as the pounds of lamb and wool produced per ewe and the quality of the carcass produced, as well as on an acceptable breed type. Growth rate and other traits of sheep are controlled by both genetic and environmental factors. Heritability estimates for genetic effects have been established as approximately 25 per cent for weaning weight, 35 per cent for rate of gain, and 40 per cent for yearling body weight. Therefore, under desirable management conditions, relatively rapid progress could be made in selection for improved gaining ability within each flock, among various types within breeds, or in the existing breeds of sheep which are prevalent today. By utilizing selection indexes for rigid culling and replacement ewe selection over a five-year span, commercial sheep producers in Ohio have increased their 120-day lamb weights by 30 pounds. Performance tested flocks in the state of Wisconsin have shown 16 pounds increase in terms of lamb produced per ewe at four months of age. By eliminating the poor performing ewes in both commercial as well as purebred flocks, the total productivity of the Tennessee sheep industry can be increased. The improvement in lamb production can occur and at the same time, the type of sheep can be produced which will meet the approval of veteran sheep breeders. Gains through breeding are often slower of achievement and less spectacular than gains through improvements in feeding and management. However, genetic gains are permanent, and since the inherited capacities of animals to produce place a ceiling on the production per individual, genetic improvement must accompany improvements in other phases of production if continued progress is to be made. Estimating the gains which might be achieved by improving the inherited abilities of sheep to produce is not easy. Among other reasons, it is difficult to estimate the net profit resulting from a given genetic change because the benefits of almost any such change are not obtained without some increase in cost. For example, if producers were suddenly presented with ewes all of which consistently produced twins, they would not realize the advantages of this increased potential unless management improved so that these twins had a good chance of survival, nor could they carry the larger number of lambs to market without some increase in feed. Nevertheless, such a genetic change would undoubtedly lead to an increase in efficiency and in profit in almost all sheep enterprises. Likewise, increased rate of gain to weaning or wool production would not be achieved solely by using genetically superior stock. Some additional feed would be required, but raising the more productive individuals would be expected to increase net income. The problem of an objective measure for selection among potential breeding animals, where more than one trait, or character is to be considered, is always faced by breeders. It has been shown that selection is more effective when based on total score or index, combining and properly weighting the several traits under consideration, than it is for single traits or for several traits with independent culling levels. The purposes of this study were (1) to compare the performance of ewes and lambs from three different breeds of sheep and (2) to evaluate the effects of various factors including year, age of dam, type of birth and rearing, sex of lamb, month of birth, and sire on birth weight, weaning weight, average daily gain, condition grade, type score, and 120-day weight of lambs

Emergent particles and gauge fields in quantum matter

I give a pedagogical introduction to some of the many particles and gauge fields that can emerge in correlated matter. The standard model of materials is built on Landau's foundational principles: adiabatic continuity and spontaneous symmetry breaking. These ideas lead to quasiparticles that inherit their quantum numbers from fundamental particles, Nambu-Goldstone bosons, the Anderson-Higgs mechanism, and topological defects in order parameters. I then describe the modern discovery of physics beyond the standard model. Here, quantum correlations (entanglement) and topology play key roles in defining the properties of matter. This can lead to fractionalised quasiparticles that carry only a fraction of the quantum numbers that define fundamental particles. These particles can have exotic properties: for example Majorana fermions are their own antiparticles, anyons have exchange statistics that are neither bosonic nor fermionic, and magnetic monopoles do not occur in the vacuum. Gauge fields emerge naturally in the description of highly correlated matter and can lead to gauge bosons. Relationships to the standard model of particle physics are discussed.Comment: Pedagogical review submitted to Contemporary Physics; 50 pages, 20 figures. Minor corrections to previous postin

Fast, accurate enthalpy differences in spin crossover crystals from DFT+U

Spin crossover materials are bi-stable systems with potential applications as molecular scale electronic switches, actuators, thermometers, barometers, and displays. However, calculating the enthalpy difference, ΔH, between the high spin and low spin states has been plagued with difficulties. For example, many common density functional theory (DFT) methods fail to even predict the correct sign of ΔH, which determines the low temperature state. Here, we study a collection of Fe(II) and Fe(III) materials, where ΔH\ua0has been measured, which has previously been used to benchmark density functionals. The best performing hybrid functional, TPSSh, achieves a mean absolute error compared to experiment of 11 kJ mol−1\ua0for this set of materials. However, hybrid functionals scale badly in the solid state; therefore, local functionals are preferable for studying crystalline materials, where the most interesting spin crossover phenomena occur. We show that both the Liechtenstein and Dudarev DFT+U methods are a little more accurate than TPSSh. The Dudarev method yields a mean absolute error of 8 kJ mol−1\ua0for\ua0Ueff\ua0= 1.6 eV. However, the mean absolute error for both TPSSh and DFT+U is dominated by a single material, for which the two theoretical methods predict similar enthalpy differences—if this is excluded from the set, then DFT+U achieves chemical accuracy. Thus, DFT+U is an attractive option for calculating the properties of spin crossover crystals, as its accuracy is comparable to that of meta-hybrid functionals, but at a much lower computational cost

Unconventional superconductivity near a flat band in organic and organometallic materials

We study electron correlation driven superconductivity on a decorated honeycomb lattice (DHL), which has a low-energy flat band. On doping, we find singlet superconductivity with extended-s, extended-d and f-wave symmetry mediated by magnetic exchange. f-wave singlet pairing is enabled by the lattice decoration. The critical temperature is predicted to be significantly higher than on similar lattices lacking flat bands. We discuss how high-temperature superconductivity could be realized in the DHL materials such as Rb3TT. 2 H2O and Mo3S7(dmit)3.Comment: 4 pages, 4 figures + Supplemental materia