Semiclassical action based on dynamical mean-field theory describing electrons interacting with local lattice fluctuations

We extend a recently introduced semiclassical approach to calculating the influence of local lattice fluctuations on electronic properties of metals and metallic molecular crystals. The effective action of electrons in degenerate orbital states coupling to Jahn-Teller distortions is derived, employing dynamical mean-field theory and adiabatic expansions. We improve on previous numerical treatments of the semiclassical action and present for the simplifying Holstein model results for the finite temperature optical conductivity at electron-phonon coupling strengths from weak to strong. Significant transfer of spectral weight from high to low frequencies is obtained on isotope substitution in the Fermi-liquid to polaron crossover regime.Comment: 10 pages, 7 figure

Magnetic resonance imaging findings and the clinical characteristics of children with cerebral palsy at a public sector hospital in Gauteng Province, South Africa

The research for this study was done in partial fulfilment of the requirements for CN’s master’s degree from the University of the Witwatersrand.BACKGROUND. Cerebral palsy (CP) is a common cause of physical impairment in children. Brain magnetic resonance imaging (MRI) can define different neuropathological patterns of brain injury in CP. There are limited data available on MRI findings of children with CP in Africa. Objective. To describe the clinical characteristics, risk factors and MRI findings of children with CP attending a developmental clinic at a tertiary hospital in South Africa; and to assess possible associations between the clinical characteristics and pathogenic neuro-imaging patterns. METHODS. This was a retrospective cross-sectional study. The cohort of 112 children was identified from the clinic’s REDcap database. Clinical information was obtained from existing medical records of the patients. Findings from brain MRI reports were classified according to the MRI classification system (MRICS) for CP. The MRI reports were rated independently by two study investigators. A descriptive analysis was conducted. RESULTS. A total of 112 patient files and MRI brain reports were reviewed. Spastic CP was the most common type of CP (n=75%). The most common perinatal risk factors included prematurity (31%) and low birthweight (28%). Nineteen (17%) children acquired CP after the neonatal period. CP sub-type showed a significant association with functional motor impairment classified as per the gross motor function classification system (GMFCS), p<0.001. Predominant grey matter injury (PGMI) was the most common pathogenic MRI pattern identified (30%). The radiological findings (per MRICS) had a significant association with both the CP sub-type (p<0.005) and functional impairment according to the GMFCS (p<0.001). CONCLUSION. Standardised classification of neuro-imaging findings can assist in defining the pathogenesis and clinical manifestations of CP.http://www.sajch.org.za/index.php/SAJCHam2023Immunolog

Bradyrhizobium ingae sp. nov., isolated from effective nodules of Inga laurina grown in Cerrado soil

Root-nodule bacteria were isolated from lnga laurina (Sw.) Willd. growing in the Cerrado Amazon region, State of Roraima, Brazil. The 16S rRNA gene sequences of six strains (BR 10250(T), BR 10248, BR 10249, BR 10251, BR 10252 and BR 10253) showed low similarities with currently described species of the genus Bradyrhizobium. Phylogenetic analyses of sequences of five housekeeping genes (dnaK, gyrB, recA and rpoB) revealed Bradyrhizobium iriomotense EKO5(T) to be the closest type strain (97.4% sequence similarity or less). Chemotaxonomic data, including fatty acid profiles [with the major components C-16:0 and summed feature 8 (C-18:1 omega 6c/C-18:1 omega 7c)], the slow growth rate and carbon compound utilization patterns supported the assignment of our strains to the genus Bradyrhizobium. Results from DNA DNA hybridizations and physiological traits differentiated our strains from the closest related species of the genus Bradyrhizobium with validly published names. Sequences of symbiosis-related genes for nodulation (nodC) and nitrogen fixation (nifH) grouped together with those of B. iriomotense EKO5(T) and Bradyrhizobium sp. strains BR 6610 (used as a commercial inoculant for Inga marginata in Brazil) and TUXTLAS-10 (previously observed in Central America). Based on these data, the six strains represent a novel species, for which the name Bradyrhizobium ingae sp. nov. is proposed. The type strain is BR 10250(T) (=HAMBI 3600(T))

Growth and properties of ferromagnetic In(1-x)Mn(x)Sb alloys

We discuss a new narrow-gap ferromagnetic (FM) semiconductor alloy, In(1-x)Mn(x)Sb, and its growth by low-temperature molecular-beam epitaxy. The magnetic properties were investigated by direct magnetization measurements, electrical transport, magnetic circular dichroism, and the magneto-optical Kerr effect. These data clearly indicate that In(1-x)Mn(x)Sb possesses all the attributes of a system with carrier-mediated FM interactions, including well-defined hysteresis loops, a cusp in the temperature dependence of the resistivity, strong negative magnetoresistance, and a large anomalous Hall effect. The Curie temperatures in samples investigated thus far range up to 8.5 K, which are consistent with a mean-field-theory simulation of the carrier-induced ferromagnetism based on the 8-band effective band-orbital method.Comment: Invited talk at 11th International Conference on Narrow Gap Semiconductors, Buffalo, New York, U.S.A., June 16 - 20, 200

Burkholderia dipogonis sp. nov., isolated from root nodules of Dipogon lignosus in New Zealand and Western Australia

Seven strains, ICMP 19430T, ICMP 19429, ICMP 19431, WSM4637, WSM4638, WSM4639 and WSM4640, were isolated from nitrogen-fixing nodules on roots of the invasive South African legume Dipogon lignosus (subfamily Papilionoideae, tribe Phaseoleae) in New Zealand and Western Australia, and their taxonomic positions were investigated by using a polyphasic approach. All seven strains grew at 10–37 °C (optimum, 25–30 °C), at pH 4.0–9.0 (optimum, pH 6.0–7.0) and with 0–2 % (w/v) NaCl (optimum growth in the absence of NaCl). On the basis of 16S rRNA gene sequence analysis, the strains showed 99.0–99.5 % sequence similarity to the closest type strain, Burkholderia phytofirmans PsJNT, and 98.4–99.7 % sequence similarity to Burkholderia caledonica LMG 19076T. The predominant fatty acids were C18 : 1ω7c (21.0 % of the total fatty acids in strain ICMP 19430T), C16 : 0 (19.1 %), C17 : 0 cyclo (18.9 %), summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c; 10.7 %) and C19 : 0 cyclo ω8c (7.5 %). The polar lipid profile consisted of a mixture of phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol and several uncharacterized aminophospholipids and phospholipids. The major isoprenoid quinone was Q-8 and the DNA G+C content of strain ICMP 19430T was 63.2 mol%. The DNA–DNA relatedness of the novel strains with respect to the closest neighbouring members of the genus Burkholderia was 55 % or less. On the basis of 16S rRNA and recA gene sequence similarities and chemotaxonomic and phenotypic data, these strains represent a novel symbiotic species in the genus Burkholderia, for which the name Burkholderia dipogonis sp. Nov. is proposed, with the type strain ICMP 19430T (=LMG 2841T =HAMBI 3637T)

Resonant nonstationary amplification of polychromatic laser pulses and conical emission in an optically dense ensemble of neon metastable atoms

Experimental and numerical investigation of single-beam and pump-probe interaction with a resonantly absorbing dense extended medium under strong and weak field-matter coupling is presented. Significant probe beam amplification and conical emission were observed. Under relatively weak pumping and high medium density, when the condition of strong coupling between field and resonant matter is fulfilled, the probe amplification spectrum has a form of spectral doublet. Stronger pumping leads to the appearance of a single peak of the probe beam amplification at the transition frequency. The greater probe intensity results in an asymmetrical transmission spectrum with amplification at the blue wing of the absorption line and attenuation at the red one. Under high medium density, a broad band of amplification appears. Theoretical model is based on the solution of the Maxwell-Bloch equations for a two-level system. Different types of probe transmission spectra obtained are attributed to complex dynamics of a coherent medium response to broadband polychromatic radiation of a multimode dye laser.Comment: 9 pages, 13 figures, corrected, Fig.8 was changed, to be published in Phys. Rev.

Quantum walk on distinguishable non-interacting many-particles and indistinguishable two-particle

We present an investigation of many-particle quantum walks in systems of non-interacting distinguishable particles. Along with a redistribution of the many-particle density profile we show that the collective evolution of the many-particle system resembles the single-particle quantum walk evolution when the number of steps is greater than the number of particles in the system. For non-uniform initial states we show that the quantum walks can be effectively used to separate the basis states of the particle in position space and grouping like state together. We also discuss a two-particle quantum walk on a two- dimensional lattice and demonstrate an evolution leading to the localization of both particles at the center of the lattice. Finally we discuss the outcome of a quantum walk of two indistinguishable particles interacting at some point during the evolution.Comment: 8 pages, 7 figures, To appear in special issue: "quantum walks" to be published in Quantum Information Processin

External control of the direction of magnetization in ferromagnetic InMnAs/GaSb heterostructures

In this paper, we demonstrate external control over the magnetization direction in ferromagnetic (FM) In_{1-x}Mn_{x}As/GaSb heterostructures. FM ordering with T_C as high as 50 K is confirmed by SQUID magnetization, anomalous Hall effect (AHE), and magneto-optical Kerr effect (MOKE) measurements. Even though tensile strain is known to favor an easy axis normal to the layer plane, at low temperatures we observe that the magnetization direction in several samples is intermediate between the normal and in-plane axes. As the temperature increases, however, the easy axis rotates to the direction normal to the plane. We further demonstrate that the easy magnetization axis can be controlled by incident light through a bolometric effect, which induces a pronounced increase in the amplitude of the AHE. A mean-field-theory model for the carrier-mediated ferromagnetism reproduces the tendency for dramatic reorientations of the magnetization axis, but not the specific sensitivity to small temperature variations.Comment: 11 pages, 3 figures, submitted to NGS-1

Feedback-control of quantum systems using continuous state-estimation

We present a formulation of feedback in quantum systems in which the best estimates of the dynamical variables are obtained continuously from the measurement record, and fed back to control the system. We apply this method to the problem of cooling and confining a single quantum degree of freedom, and compare it to current schemes in which the measurement signal is fed back directly in the manner usually considered in existing treatments of quantum feedback. Direct feedback may be combined with feedback by estimation, and the resulting combination, performed on a linear system, is closely analogous to classical LQG control theory with residual feedback.Comment: 12 pages, multicol revtex, revised and extende

Correlated electrons in the presence of disorder

Several new aspects of the subtle interplay between electronic correlations and disorder are reviewed. First, the dynamical mean-field theory (DMFT)together with the geometrically averaged ("typical") local density of states is employed to compute the ground state phase diagram of the Anderson-Hubbard model at half-filling. This non-perturbative approach is sensitive to Anderson localization on the one-particle level and hence can detect correlated metallic, Mott insulating and Anderson insulating phases and can also describe the competition between Anderson localization and antiferromagnetism. Second, we investigate the effect of binary alloy disorder on ferromagnetism in materials with $f$-electrons described by the periodic Anderson model. A drastic enhancement of the Curie temperature $T_c$ caused by an increase of the local $f$-moments in the presence of disordered conduction electrons is discovered and explained.Comment: 17 pages, 7 figures, final version, typos corrected, references updated, submitted to Eur. Phys. J. for publication in the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator Transitions and Ordering of Microscopic Degrees of Freedom