Dynamic rotor mode in antiferromagnetic nanoparticles

We present experimental, numerical, and theoretical evidence for a new mode of antiferromagnetic dynamics in nanoparticles. Elastic neutron scattering experiments on 8 nm particles of hematite display a loss of diffraction intensity with temperature, the intensity vanishing around 150 K. However, the signal from inelastic neutron scattering remains above that temperature, indicating a magnetic system in constant motion. In addition, the precession frequency of the inelastic magnetic signal shows an increase above 100 K. Numerical Langevin simulations of spin dynamics reproduce all measured neutron data and reveal that thermally activated spin canting gives rise to a new type of coherent magnetic precession mode. This "rotor" mode can be seen as a high-temperature version of superparamagnetism and is driven by exchange interactions between the two magnetic sublattices. The frequency of the rotor mode behaves in fair agreement with a simple analytical model, based on a high temperature approximation of the generally accepted Hamiltonian of the system. The extracted model parameters, as the magnetic interaction and the axial anisotropy, are in excellent agreement with results from Mossbauer spectroscopy

Magnetoresistance of a 2-dimensional electron gas in a random magnetic field

We report magnetoresistance measurements on a two-dimensional electron gas (2DEG) made from a high mobility GaAs/AlGaAs heterostructure, where the externally applied magnetic field was expelled from regions of the semiconductor by means of superconducting lead grains randomly distributed on the surface of the sample. A theoretical explanation in excellent agreement with the experiment is given within the framework of the semiclassical Boltzmann equation.Comment: REVTEX 3.0, 11 pages, 3 Postscript figures appended. The manuscript can also be obtained from our World Wide Web server: http://roemer.fys.ku.dk/randmag.ht

Effect of reduced dietary protein on productivity and plasma, urine, and milk metabolites in organic sows during winter conditions

Oversupply of protein is a challenge in organic sow production. Currently, organic sow feed is composed in accordance with feeding standards of conventional sows, which do not take the higher daily feed allowance and nutritional contribution from roughage into consideration. The objective of the current study was to investigate the effect of reduced dietary protein in gestational compound feed for organic outdoor sows during winter conditions, using metabolites in plasma, urine, and milk as indicators of sows’ metabolic status. In total, 20 sows (Topigs Norsvin; TN70) were included in the experiment, lasting from d30 of gestation until weaning at d49 of lactation under outdoor conditions during winter. During gestation, sows were fed one of two isoenergetic diets containing 88 g SID CP pr. kg DM (Control) and 72 g SID CP pr. kg DM (Low protein), corrresponding to 16% and 31% below the current recommendation for indoor sows. In lactation, all sows were fed a standard diet containing 125 g SID CP pr. kg DM. Sow performance traits were not affected by dietary protein level during gestation. An interaction indicated that sows fed the control diet had 23% and 11% higher urinary urea concentrations at d60 and d100 of gestation, respectively, compared with the low protein diet. During lactation, the milk yield of sows fed low protein in gestation increased more than that of control sows (P < 0.05). Concurrently, the litter gain of the low protein sows was improved, and their litters were heavier at d49 compared to control sows (276 kg vs. 238 kg; P < 0.001). In conclusion, organic outdoor sows benefitted from reduced dietary protein during gestation in winter conditions, as indicated by urinary urea concentration, milk yield, and litter gain

Photoprotection in intact cells of photosynthetic bacteria: quenching of bacteriochlorophyll fluorescence by carotenoid triplets.

Upon high light excitation in photosynthetic bacteria, various triplet states of pigments can accumulate leading to harmful effects. Here, the generation and lifetime of flash-induced carotenoid triplets (3Car) have been studied by observation of the quenching of bacteriochlorophyll (BChl) fluorescence in different strains of photosynthetic bacteria including Rvx. gelatinosus (anaerobic and semianaerobic), Rsp. rubrum, Thio. roseopersicina, Rba. sphaeroides 2.4.1 and carotenoid- and cytochrome-deficient mutants Rba. sphaeroides Ga, R-26, and cycA, respectively. The following results were obtained: (1) 3Car quenching is observed during and not exclusively after the photochemical rise of the fluorescence yield of BChl indicating that the charge separation in the reaction center (RC) and the carotenoid triplet formation are not consecutive but parallel processes. (2) The photoprotective function of 3Car is not limited to the RC only and can be described by a model in which the carotenoids are distributed in the lake of the BChl pigments. (3) The observed lifetime of 3Car in intact cells is the weighted average of the lifetimes of the carotenoids with various numbers of conjugated double bonds in the bacterial strain. (4) The lifetime of 3Car measured in the light is significantly shorter (1-2 mus) than that measured in the dark (2-10 mus). The difference reveals the importance of the dynamics of 3Car before relaxation. The results will be discussed not only in terms of energy levels of the 3Car but also in terms of the kinetics of transitions among different sublevels in the excited triplet state of the carotenoid

Continuum Surface Energy from a Lattice Model

We investigate connections between the continuum and atomistic descriptions of deformable crystals, using certain interesting results from number theory. The energy of a deformed crystal is calculated in the context of a lattice model with general binary interactions in two dimensions. A new bond counting approach is used, which reduces the problem to the lattice point problem of number theory. The main contribution is an explicit formula for the surface energy density as a function of the deformation gradient and boundary normal. The result is valid for a large class of domains, including faceted (polygonal) shapes and regions with piecewise smooth boundaries.Comment: V. 1: 10 pages, no fig's. V 2: 23 pages, no figures. Misprints corrected. Section 3 added, (new results). Intro expanded, refs added.V 3: 26 pages. Abstract changed. Section 2 split into 2. Section (4) added material. V 4, 28 pages, Intro rewritten. Changes in Sec.5 (presentation only). Refs added.V 5,intro changed V.6 address reviewer's comment

Factor and Simplex Models for Repeated Measures: Application to Two Psychomotor Measures of Alcohol Sensitivity in Twins

As part of a larger study, data on arithmetic computation and motor coordination were obtained from 206 twin pairs. The twins were measured once before and three times after ingesting a standard dose of alcohol. Previous analyses ignored the time-series structure of these data. Here we illustrate the application of simplex models for the genetic analysis of covariance structures in a repeated-measures design and compare the results with factor models for the two psychomotor measures. We then present a bivariate analysis incorporating simplex processes common and specific to the two measures. Our analyses confirm the notion that there is genetic variation affecting psychomotor performance which is "switched on" in the presence of alcohol. We compare the merits of analysis of mean products versus covariance matrices and confront some practical problems that may arise in situations where the number of subjects is relatively small and where the causal structure among the latent variables places a heavy demand on the data. © 1989 Plenum Publishing Corporation

Parallel genetics of regulatory sequences using scalable genome editing in vivo

How regulatory sequences control gene expression is fundamental for explaining phenotypes in health and disease. Regulatory elements must ultimately be understood within their genomic environment and development- or tissue-specific contexts. Because this is technically challenging, few regulatory elements have been characterized in vivo. Here, we use inducible Cas9 and multiplexed guide RNAs to create hundreds of mutations in enhancers/promoters and 3' UTRs of 16 genes in C. elegans. Our software crispr-DART analyzes indel mutations in targeted DNA sequencing. We quantify the impact of mutations on expression and fitness by targeted RNA sequencing and DNA sampling. When applying our approach to the lin-41 3' UTR, generating hundreds of mutants, we find that the two adjacent binding sites for the miRNA let-7 can regulate lin-41 expression independently of each other. Finally, we map regulatory genotypes to phenotypic traits for several genes. Our approach enables parallel analysis of regulatory sequences directly in animals