1,524 research outputs found
Wave excitations of drifting two-dimensional electron gas under strong inelastic scattering
We have analyzed low-temperature behavior of two-dimensional electron gas in
polar heterostructures subjected to a high electric field. When the optical
phonon emission is the fastest relaxation process, we have found existence of
collective wave-like excitations of the electrons. These wave-like excitations
are periodic in time oscillations of the electrons in both real and momentum
spaces. The excitation spectra are of multi-branch character with considerable
spatial dispersion. There are one acoustic-type and a number of optical-type
branches of the spectra. Their small damping is caused by quasi-elastic
scattering of the electrons and formation of relevant space charge. Also there
exist waves with zero frequency and finite spatial periods - the standing
waves. The found excitations of the electron gas can be interpreted as
synchronous in time and real space manifestation of well-known
optical-phonon-transient-time-resonance. Estimates of parameters of the
excitations for two polar heterostructures, GaN/AlGaN and ZnO/MgZnO, have shown
that excitation frequencies are in THz-frequency range, while standing wave
periods are in sub-micrometer region.Comment: 26 pages and 6 figure
TURBULENCE IN MOLECULAR CLOUDS
We generate random Gaussian turbulent velocity fields with a Kolmogorov
spectrum and use these to obtain synthetic line-of-sight velocity profiles. The
profiles are found to be similar to line profiles observed in molecular clouds.
We suggest methods for analysing measured line profiles to test whether they
might arise from Gaussian Kolmogorov turbulence.Comment: accepted in ApJ, compressed postscript, figures not included.
Complete preprint available at http://ucowww.ucsc.edu/~dubinski/home.html or
by request to [email protected]
Mechanisms of Neutrophil‐Mediated Killing of Endothelial Cells
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141751/1/jlb0097.pd
Essential structural requirements for specific recognition of HIV TAR RNA by peptide mimetics of Tat protein
The pharmacological disruption of the interaction between the HIV Tat protein and its cognate transactivation response RNA (TAR) would generate novel anti-viral drugs with a low susceptibility to drug resistance, but efforts to discover ligands with sufficient potency to warrant pharmaceutical development have been unsuccessful. We have previously described a family of structurally constrained β-hairpin peptides that potently inhibits viral growth in HIV-infected cells. The nuclear magnetic resonance (NMR) structure of an inhibitory complex revealed that the peptide makes intimate contacts with the 3-nt bulge and the upper helix of the RNA hairpin, but that a single residue contacts the apical loop where recruitment of the essential cellular co-factor cyclin T1 occurs. Attempting to extend the peptide to form more interactions with the RNA loop, we examined a library of longer peptides and achieved >6-fold improvement in affinity. The structure of TAR bound to one of the extended peptides reveals that the peptide slides down the major groove of the RNA, relative to our design, in order to maintain critical interactions with TAR. These conserved contacts involve three amino acid side chains and identify critical interaction points required for potent and specific binding to TAR RNA. They constitute a template of essential interactions required for inhibition of this RN
Cell growth on microcarriers: comparison of proliferation on and recovery from various substrates
Three commercially-important types of cell were grown on four different microcarrier substrates. The cells, which included normal human diploid fibroblasts (MRC-5), primary chick embryo cells and Madin-Darby bovine kidney cells (MDBK), were compared with regard to proliferation on the substrates and with regard to recovery of viable cells from the same substrates. The substrates used included glass-coated microcarriers (Biosil), collagen microcarriers (Ventregel), DEAE-dextran microcarriers (Cytodex I) and collagen-linked DEAE-dextran microcarriers (Cytodex III). The established cell line (MDBK) grew well on all of the substrates and a high percentage of viable cells could be harvested from each substrate. The MRC-5 cells also grew well on all four substrates but high recovery rates were achieved only with cells grown on the glass-coated microcarriers or collagen microcarriers. In contrast, the primary chick embryo cells grew well only on the glass microcarriers and the recovery rate of cells harvested from this substrate was high. In some industrial operations, the re-utilization of cells after removal from the substrate is necessary. In these situations the appropriate choice of microcarriers for the cultivation of the cells may be critical.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26400/1/0000487.pd
Anomalous crossover between thermal and shot noise in macroscopic diffusive conductors
We predict the existence of an anomalous crossover between thermal and shot
noise in macroscopic diffusive conductors. We first show that, besides thermal
noise, these systems may also exhibit shot noise due to fluctuations of the
total number of carriers in the system. Then we show that at increasing
currents the crossover between the two noise behaviors is anomalous, in the
sense that the low frequency current spectral density displays a region with a
superlinear dependence on the current up to a cubic law. The anomaly is due to
the non-trivial coupling in the presence of the long range Coulomb interaction
among the three time scales relevant to the phenomenon, namely, diffusion,
transit and dielectric relaxation time.Comment: 4 pages, 2 figure
Labelling and clinical performance of human leukocytes labelled with 99m Tc-HMPAO using leukokit® with gelofusine versus leukokit® with HES as sedimentation agent
The scintigraphy with radiolabelled autologous leukocytes (WBCs) is considered the gold-standard technique for imaging infections. Leukokit (R) is a commercially available, disposable, sterile kit for labelling WBCs ex vivo. In this kit, WBCs isolation from red blood cells (RBCs) was performed using poly(O-2-hydroxyethyl)starch (HES) as the RBCs sedimentation agent. Due to its poor availability, HES has been recently replaced by Gelofusine as the RBC sedimentation agent. The aim of this study was to compare the labelling efficiency and the diagnostic accuracy of WBCs labelled with Leukokit (R) with HES vs Leukokit (R) with Gelofusine. WBCs were isolated using HES or Gelofusine for 45minutes and then purified from platelets (PLTs) and labelled with 1.1 +/- 0.3 GBq of freshly prepared Tc-99m- HMPAO. The following parameters were evaluated: the number and type of recovered WBCs, RBCs contamination, PLTs contamination, vitality of neutrophils, and chemotactic properties of neutrophils. Clinical comparison was performed between 80 patients (33 males; age 67.5 +/- 14.2) injected with Tc-99m-HMPAO-WBCs, using HES as the sedimentation agent, and 92 patients (38 males; age 68.2 +/- 12.8) injected with Tc-99m-HMPAO-WBCs using Gelofusine as the sedimentation agent. Patients were affected by prosthetic joint infections, peripheral bone osteomyelitis, or vascular graft infection. We compared radiolabelling efficiency (LE), final recovery yield (RY), and diagnostic outcome based on microbiology or 2-year follow-up. Results showed that HES provides the lowest RBCs and PLTs contamination, but Gelofusine provides the highest WBC recovery. Both agents did not influence the chemotactic properties of WBCs, and no differences were found in terms of LE and RY. Sensitivity, specificity, and accuracy were also not significantly different for WBCs labelled with both agents (diagnostic accuracy 90.9%, CI = 74.9-96.1 vs 98.3%, CI = 90.8-100, for HES and Gelofusine, respectively). In conclusion, Gelofusine can be considered a suitable alternative of HES for WBCs separation and labelling
Rapid communications Ongoing outbreak of visceral leishmaniasis in Bologna
(VL) cases has recently been reported in Bologna Province in northern Italy. Over six months from November 2012 to May 2013, 14 cases occurred, whereas the average number of cases per year was 2.6 (range: 0–8) in 2008 to 2012. VL was diagnosed in a median of 40 days (range: 15–120) from disease onset. This delay in diagnosis shows the need for heightened awareness of clinicians for autochthonous VL in Europe. From November 2012 to May 2013, public health authorities, microbiologists and clinicians in Bologna Province, northern Italy, noted an upsurge in human cases of visceral leishmaniasis. During these six months, 14 cases were notified, an over five-fold increase compared with the annual average of 2.
Room Temperature Coherent and Voltage Tunable Terahertz Emission from Nanometer-Sized Field Effect Transistors
We report on reflective electro-optic sampling measurements of TeraHertz
emission from nanometer-gate-length InGaAs-based high electron mobility
transistors. The room temperature coherent gate-voltage tunable emission is
demonstrated. We establish that the physical mechanism of the coherent
TeraHertz emission is related to the plasma waves driven by simultaneous
current and optical excitation. A significant shift of the plasma frequency and
the narrowing of the emission with increasing channel's current are observed
and explained as due to the increase of the carriers density and drift
velocity.Comment: 3 figure
Evaluation of synthetic substituted 1,2-dioxanes as novel agents against human leishmaniasis
The treatment of human leishmaniasis is currently based on few compounds that are highly toxic, expensive and have a high rate of treatment failure. A number of recent studies on new drugs focuses on natural or semi-synthetic compounds. Among them, the endoperoxide artemisinin, extracted from Artemisia annua, and some of its derivatives have shown leishmanicidal activity. In the present work, a series of structurally simple, fully synthetic 1,2-dioxanes were evaluated for in vitro antileishmanial activity against promastigotes of Leishmania donovani; the cytotoxicity for mammalian cells was also assessed. The six most promising compounds in terms of activity and selectivity were further investigated for their antileishmanial activity on the promastigote forms of L. tropica, L. major and L. infantum and against L. donovani amastigotes. The good performance in terms of potency and selectivity makes these six hits promising candidates for a preliminary lead optimization as antileishmanial agents
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