419 research outputs found
Angle-Resolved Spectroscopy of Electron-Electron Scattering in a 2D System
Electron-beam propagation experiments have been used to determine the energy
and angle dependence of electron-electron (ee) scattering a two-dimensional
electron gas (2DEG) in a very direct manner by a new spectroscopy method. The
experimental results are in good agreement with recent theories and provide
direct evidence for the differences between ee-scattering in a 2DEG as compared
with 3D systems. Most conspicuous is the increased importance of small-angle
scattering in a 2D system, resulting in a reduced (but energy-dependent)
broadening of the electron beam.Comment: 4 pages, 4 figure
Effects of Electron-Electron Scattering on Electron-Beam Propagation in a Two-Dimensional Electron-Gas
We have studied experimentally and theoretically the influence of
electron-electron collisions on the propagation of electron beams in a
two-dimensional electron gas for excess injection energies ranging from zero up
to the Fermi energy. We find that the detector signal consists of
quasiballistic electrons, which either have not undergone any electron-electron
collisions or have only been scattered at small angles. Theoretically, the
small-angle scattering exhibits distinct features that can be traced back to
the reduced dimensionality of the electron system. A number of nonlinear
effects, also related to the two-dimensional character of the system, are
discussed. In the simplest situation, the heating of the electron gas by the
high-energy part of the beam leads to a weakening of the signal of
quasiballistic electrons and to the appearance of thermovoltage. This results
in a nonmonotonic dependence of the detector signal on the intensity of the
injected beam, as observed experimentally.Comment: 9 pages, 7 figure
Relaxation of high-energy quasiparticle distributions: electron-electron scattering in a two-dimensional electron gas
A theory is developed for the evolution of the non-equilibrium distribution
of quasiparticles when the scattering rate decreases due to particle
collisions. We propose a "modified one-collision approximation" which is most
effective for high-energy quasiparticle distributions. This method is used to
explain novel measurements of the non-monotonic energy dependence of the signal
of scattered electrons in a 2D system. The observed effect is related to a
crossover from the ballistic to the hydrodynamic regime of electron flow.Comment: 6 pages, 3 figure
Prediabetes conversion to Normoglycemia is superior adding a low-carbohydrate and energy deficit formula diet to lifestyle intervention - a 12-month subanalysis of the ACOORH trial
Lifestyle interventions have been shown to reverse hyperglycemia to normoglycemia. However, these effects are not long-lasting and are accompanied with high dropout rates. As formula diets have been shown to be simple in usage and effective in improving glycemic control, we hypothesised that adding a low-carbohydrate and energy deficit formula diet to a low-intensity lifestyle intervention is superior in reversing prediabetes compared with lifestyle intervention alone. In this predefined subanalysis of an international, multicenter randomised controlled trial (Almased Concept against Overweight and Obesity and Related Health Risk (ACOORH) study (ID DRKS00006811)), 141 persons with prediabetes were randomised (1:2) into either a control group with lifestyle intervention only (CON, n = 45) or a lifestyle intervention group accompanied with a formula diet (INT, n = 96). Both groups were equipped with telemonitoring devices. INT received a low-carbohydrate formula diet substituting three meals/day (~1200 kcal/day) within the first week, two meals/day during week 2–4, and one meal/day during week 5–26 (1300–1500 kcal/day). Follow-up was performed after 52 weeks and 105 participants (75%, INT: n = 74; CON: n = 31) finished the 26-week intervention phase. Follow-up data after 52 weeks were available from 93 participants (66%, INT: n = 65; CON: n = 28). Compared with CON, significantly more INT participants converted to normoglycemia after 52 weeks (50% vs. 31%; p 0.05). The risk reduction led to a number-needed-to-treat of 5.3 for INT. Lifestyle intervention with a low-carbohydrate formula diet reduces prediabetes prevalence stronger than lifestyle intervention alone and is effective for type 2 diabetes prevention
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
Platinum Assisted Vapor–Liquid–Solid Growth of Er–Si Nanowires and Their Optical Properties
We report the optical activation of erbium coated silicon nanowires (Er–SiNWs) grown with the assist of platinum (Pt) and gold (Au), respectively. The NWs were grown on Si substrates by using a chemical vapor transport process using SiCl4 and ErCl4 as precursors. Pt as well as Au worked successfully as vapor–liquid–solid (VLS) catalysts for growing SiNWs with diameters of ~100 nm and length of several micrometers, respectively. The SiNWs have core–shell structures where the Er-crystalline layer is sandwiched between silica layers. Photoluminescence spectra analyses showed the optical activity of SiNWs from both Pt and Au. A stronger Er3+ luminescence of 1,534 nm was observed from the SiNWs with Pt at room- and low-temperature (25 K) using the 488- and/or 477-nm line of an Ar laser that may be due to the uniform incorporation of more Er ions into NWs with the exclusion of the formation of catalyst-induced deep levels in the band-gap. Pt would be used as a VLS catalyst for high performance optically active Er–SiNWs
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
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
Effects of a protein-rich, low-glycaemic meal replacement on changes in dietary intake and body weight following a weight-management intervention—the ACOORH trial
Although meal replacement can lead to weight reduction, there is uncertainty whether this dietary approach implemented into a lifestyle programme can improve long-term dietary intake. In this subanalysis of the Almased Concept against Overweight and Obesity and Related Health Risk (ACOORH) study (n = 463), participants with metabolic risk factors were randomly assigned to either a meal replacement-based lifestyle intervention group (INT) or a lifestyle intervention control group (CON). This subanalysis relies only on data of participants (n = 119) who returned correctly completed dietary records at baseline, and after 12 and 52 weeks. Both groups were not matched for nutrient composition at baseline. These data were further stratified by sex and also associated with weight change. INT showed a higher increase in protein intake related to the daily energy intake after 12 weeks (+6.37% [4.69; 8.04] vs. +2.48% [0.73; 4.23], p 0.001) of intervention compared to CON. Fat and carbohydrate intake related to the daily energy intake were more strongly reduced in the INT compared to CON (both p 0.01). After sex stratification, particularly INT-women increased their total protein intake after 12 (INT: +12.7 g vs. CON: −5.1 g, p = 0.021) and 52 weeks (INT: +5.7 g vs. CON: −16.4 g, p = 0.002) compared to CON. Protein intake was negatively associated with weight change (r = −0.421; p 0.001) after 12 weeks. The results indicate that a protein-rich dietary strategy with a meal replacement can improve long-term nutritional intake, and was associated with weight loss
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