491 research outputs found
The Influence of Chemical Short Range Order on Atomic Diffusion in Al-Ni Melts
We use inelastic neutron scattering and molecular dynamics (MD) simulation to
investigate the chemical short range order (CSRO), visible through prepeaks in
the structure factors, and its relation to self diffusion in Al-Ni melts. As a
function of composition at 1795K Ni self diffusion coefficients from experiment
and simulation exhibit a non-linear dependence with a pronounced increase on
the Al-rich side. This comes along with a change in CSRO with increasing Al
content that is related to a more dense packing of the atoms in Ni-rich Al-Ni
systems.Comment: 11 pages, 4 figure
Magnetic and structural properties of GeMn films: precipitation of intermetallic nanomagnets
We present a comprehensive study relating the nanostructure of Ge_0.95Mn_0.05
films to their magnetic properties. The formation of ferromagnetic nanometer
sized inclusions in a defect free Ge matrix fabricated by low temperature
molecular beam epitaxy is observed down to substrate temperatures T_S as low as
70 deg. Celsius. A combined transmission electron microscopy (TEM) and electron
energy-loss spectroscopy (EELS) analysis of the films identifies the inclusions
as precipitates of the ferromagnetic compound Mn_5Ge_3. The volume and amount
of these precipitates decreases with decreasing T_S. Magnetometry of the films
containing precipitates reveals distinct temperature ranges: Between the
characteristic ferromagnetic transition temperature of Mn_5Ge_3 at
approximately room temperature and a lower, T_S dependent blocking temperature
T_B the magnetic properties are dominated by superparamagnetism of the Mn_5Ge_3
precipitates. Below T_B, the magnetic signature of ferromagnetic precipitates
with blocked magnetic moments is observed. At the lowest temperatures, the
films show features characteristic for a metastable state.Comment: accepted for publication in Phys. Rev. B 74 (01.12.2006). High
resolution images ibide
Motor skill learning-induced functional plasticity in the primary somatosensory cortex: A comparison between young and older adults
While in young adults (YAs) the underlying neural mechanisms of motor learning are well-studied, studies on the involvement of the somatosensory system during motor skill learning in older adults (OAs) remain sparse. Therefore, the aim of the present study was to investigate motor learning-induced neuroplasticity in the primary somatosensory cortex (S1) in YAs and OAs. Somatosensory evoked potentials (SEPs) were used to quantify somatosensory activation prior and immediately after motor skill learning in 20 right-handed healthy YAs (age range: 19–35 years) and OAs (age range: 57–76 years). Participants underwent a single session of a 30-min co-contraction task of the abductor pollicis brevis (APB) and deltoid muscle. To assess the effect of motor learning, muscle onset asynchrony (MOA) between the onsets of the contractions of both muscles was measured using electromyography monitoring. In both groups, MOA shortened significantly during motor learning, with YAs showing bigger reductions. No changes were found in SEP amplitudes after motor learning in both groups. However, a correlation analysis revealed an association between baseline SEP amplitudes of the N20/P25 and N30 SEP component and the motor learning slope in YAs such that higher amplitudes are related to higher learning. Hence, the present findings suggest that SEP amplitudes might serve as a predictor of individual motor learning success, at least in YAs. Additionally, our results suggest that OAs are still capable of learning complex motor tasks, showing the importance of motor training in higher age to remain an active part of our society as a prevention for care dependency
New physiological activities of myosuppressin, sulfakinin and NVP-like peptide in Zophobas atratus beetle
Three neuropeptides Zopat-MS-2 (pEDVDHVFLRFa), Zopat-SK-1 (pETSDDYGHLRFa) and Zopat-NVPL-4trunc. (GRWGGFA), recently isolated from the neuroendocrine system of the Zophobas atratus beetle, were tested for their myotropic and hyperglycaemic activities in this species. These peptides exerted differentiated dose-dependent and tissue specific physiological effects. Zopat-MS-2 inhibited contractions of the isolated heart, ejaculatory duct, oviduct and hindgut of adult beetles and induced bimodal effects in the heart contractile activity of pupae in vivo. It also increased the haemolymph free sugar level in larvae of this species, apart from myotropic activity. Zopat-SK-1 showed myostimulatory action on the isolated hindgut of the adult beetles, but it decreased contractions of the heart, ejaculatory duct and oviduct. Injections of this peptide at a dose of 2 μg also caused delayed cardioinhibitory effects on the heartbeat of the pupae. Together with the ability to increase free sugar level in the haemolymph of larvae these were new physiological activities of sulfakinins in insects. Zopat-NVPL-4trunc. inhibited the muscle contractions of the two organs: hindgut and ejaculatory duct but it was inactive on the oviduct and the heart of the adult beetles. This peptide also increased free sugar level concentration in the haemolymph of Z. atratus larvae. These physiological actions are the first biological activities discovered for this group of the insect peptides. The present work showed pleiotropic activity of three neuropeptides and indicates that the visceral muscle contractions and the haemolymph sugar homeostasis in Z. atratus are regulated by complex mechanisms
Microscopic View on Short-Range Wetting at the Free Surface of the Binary Metallic Liquid Gallium-Bismuth: An X-ray Reflectivity and Square Gradient Theory Study
We present an x-ray reflectivity study of wetting at the free surface of the
binary liquid metal gallium-bismuth (Ga-Bi) in the region where the bulk phase
separates into Bi-rich and Ga-rich liquid phases. The measurements reveal the
evolution of the microscopic structure of wetting films of the Bi-rich,
low-surface-tension phase along different paths in the bulk phase diagram. A
balance between the surface potential preferring the Bi-rich phase and the
gravitational potential which favors the Ga-rich phase at the surface pins the
interface of the two demixed liquid metallic phases close to the free surface.
This enables us to resolve it on an Angstrom level and to apply a mean-field,
square gradient model extended by thermally activated capillary waves as
dominant thermal fluctuations. The sole free parameter of the gradient model,
i.e. the so-called influence parameter, , is determined from our
measurements. Relying on a calculation of the liquid/liquid interfacial tension
that makes it possible to distinguish between intrinsic and capillary wave
contributions to the interfacial structure we estimate that fluctuations affect
the observed short-range, complete wetting phenomena only marginally. A
critical wetting transition that should be sensitive to thermal fluctuations
seems to be absent in this binary metallic alloy.Comment: RevTex4, twocolumn, 15 pages, 10 figure
Neuroarchitecture of Peptidergic Systems in the Larval Ventral Ganglion of Drosophila melanogaster
Recent studies on Drosophila melanogaster and other insects have revealed important insights into the functions and evolution of neuropeptide signaling. In contrast, in- and output connections of insect peptidergic circuits are largely unexplored. Existing morphological descriptions typically do not determine the exact spatial location of peptidergic axonal pathways and arborizations within the neuropil, and do not identify peptidergic in- and output compartments. Such information is however fundamental to screen for possible peptidergic network connections, a prerequisite to understand how the CNS controls the activity of peptidergic neurons at the synaptic level. We provide a precise 3D morphological description of peptidergic neurons in the thoracic and abdominal neuromeres of the Drosophila larva based on fasciclin-2 (Fas2) immunopositive tracts as landmarks. Comparing the Fas2 “coordinates” of projections of sensory or other neurons with those of peptidergic neurons, it is possible to identify candidate in- and output connections of specific peptidergic systems. These connections can subsequently be more rigorously tested. By immunolabeling and GAL4-directed expression of marker proteins, we analyzed the projections and compartmentalization of neurons expressing 12 different peptide genes, encoding approximately 75% of the neuropeptides chemically identified within the Drosophila CNS. Results are assembled into standardized plates which provide a guide to identify candidate afferent or target neurons with overlapping projections. In general, we found that putative dendritic compartments of peptidergic neurons are concentrated around the median Fas2 tracts and the terminal plexus. Putative peptide release sites in the ventral nerve cord were also more laterally situated. Our results suggest that i) peptidergic neurons in the Drosophila ventral nerve cord have separated in- and output compartments in specific areas, and ii) volume transmission is a prevailing way of peptidergic communication within the CNS. The data can further be useful to identify colocalized transmitters and receptors, and develop peptidergic neurons as new landmarks
Unique Features of a Global Human Ectoparasite Identified Through Sequencing of the Bed Bug Genome
The bed bug, Cimex lectularius, has re-established itself as a ubiquitous human ectoparasite throughout much of the world during the past two decades. This global resurgence is likely linked to increased international travel and commerce in addition to widespread insecticide resistance. Analyses of the C. lectularius sequenced genome (650 Mb) and 14,220 predicted protein-coding genes provide a comprehensive representation of genes that are linked to traumatic insemination, a reduced chemosensory repertoire of genes related to obligate hematophagy, host-symbiont interactions, and several mechanisms of insecticide resistance. In addition, we document the presence of multiple putative lateral gene transfer events. Genome sequencing and annotation establish a solid foundation for future research on mechanisms of insecticide resistance, human-bed bug and symbiont-bed bug associations, and unique features of bed bug biology that contribute to the unprecedented success of C. lectularius as a human ectoparasite
Intrinsic phase separation in superconducting K0.8Fe1.6Se2 (Tc= 31.8 K) single crystals
Temperature dependent single-crystal x-ray diffraction (XRD) in transmission
mode probing the bulk of the newly discovered K0.8Fe1.6Se2 superconductor (Tc =
31.8 K) using synchrotron radiation is reported. A clear evidence of intrinsic
phase separation at 520 K between two competing phases, (i) a first majority
magnetic phase with a ThCr2Si2-type tetragonal lattice modulated by the iron
vacancy ordering and (ii) a minority non-magnetic phase having an in-plane
compressed lattice volume and a weak superstructure, is reported. The XRD peaks
due to the Fe vacancy ordering in the majority phase disappear by increasing
the temperature at 580 K, well above phase separation temperature confirming
the order-disorder phase transition. The intrinsic phase separation at 520K
between a competing first magnetic phase and a second non-magnetic phase in the
normal phase both having lattice superstructures (that imply different Fermi
surface topology reconstruction and charge density) is assigned to a
lattice-electronic instability of the K0.8Fe1.6Se2 system typical of a system
tuned at a Lifshitz critical point of an electronic topological transition that
gives a multi-gaps superconductor tuned a shape resonance.Comment: 10 pages, 4 figure
- …