4,527 research outputs found
Non-linear response of single-molecule magnets: field-tuned quantum-to-classical crossovers
Quantum nanomagnets can show a field dependence of the relaxation time very
different from their classical counterparts, due to resonant tunneling via
excited states (near the anisotropy barrier top). The relaxation time then
shows minima at the resonant fields H_{n}=n D at which the levels at both sides
of the barrier become degenerate (D is the anisotropy constant). We showed that
in Mn12, near zero field, this yields a contribution to the nonlinear
susceptibility that makes it qualitatively different from the classical curves
[Phys. Rev. B 72, 224433 (2005)]. Here we extend the experimental study to
finite dc fields showing how the bias can trigger the system to display those
quantum nonlinear responses, near the resonant fields, while recovering an
classical-like behaviour for fields between them. The analysis of the
experiments is done with heuristic expressions derived from simple balance
equations and calculations with a Pauli-type quantum master equation.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. B, brief report
Hydra tropomyosin TROP1 is expressed in head-specific epithelial cells and is a major component of the cytoskeletal structure that anchors nematocytes
A cDNA clone encoding a 253 amino acid tropomyosin was
isolated from
Hydra in a differential screen for headspecific
genes. The Hydra tropomyosin gene, designated
trop1, is a single copy gene, lacks introns and is strongly
expressed in tentacle-specific epithelial cells. Analysis of
protein synthesis in head and gastric tissue indicated a high
rate of tropomyosin synthesis in head tissue. Immunolocalization
of tropomyosin in tentacle tissue revealed a
cushion-like tropomyosin-containing structure within
battery cells at the base of nematocytes. The structure
appears to form part of the cytoskeletal anchor for nematocytes.
Tropomyosin cushions were also observed in
epithelial cells along the body column, which contain
mounted stenotele nematocytes
Analysis of genetic variability and mapping of point mutations in influenza virus by the RNase A mismatch cleavage method
We have applied the RNase A mismatch cleavage method to analyze genetic variability in RNA viruses by using influenza virus as a model system. Uniformly labeled RNA probes synthesized from a cloned hemagglutinin gene of a given viral strain were hybridized to RNA isolated from other strains of characterized or uncharacterized genetic composition. The RNA.RNA heteroduplexes containing a variable number of base mismatches were digested with RNase A, and the resistant products were analyzed by denaturing polyacrylamide gel electrophoresis. We show that many of these single base mismatches are cleaved by RNase A, generating unique and characteristic patterns of resistant RNA fragments specific for each of the different viral strains. Comparative analysis of the cleavage patterns allows a qualitative estimation of the genetic relatedness and evolution of field strains. We also show that cleavage by RNase A at single base mismatches can readily detect and localize point mutations present in monoclonal antibody-resistant variants. This method should have wide applications in the study of RNA viruses, not only for epidemiological analysis but also in some diagnostic problems, such as characterization of phenotypic mutants.This work was supported by National Institutes of Health Grant CA33021 awarded by the Nationa l Cancer Institute to M.P. and by grants from the Comision Asesora de Investigacion Cientificay Tecnica (Grant 608/438) and Fondo de Investigaciones Sanitarias to J.O. and J.A.M.C.L.-G. was a recipient of a NATO short-term post doctoral fellow-ship while on leave from the Centro Nacional de Microbiologia, Majadahonda, Madri
Identities of Choi-Lee-Srivastava involving the Euler-Mascheroni’s constant
We give an elementary deduction of the Choi-Lee-Srivastava’s identities involving the Euler Mascheroni’s constant, thus from them is immediate the identity of Wilf
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Genome-wide analyses of cassava Pathogenesis-related (PR) gene families reveal core transcriptome responses to whitefly infestation, salicylic acid and jasmonic acid.
BACKGROUND:Whiteflies are a threat to cassava (Manihot esculenta), an important staple food in many tropical/subtropical regions. Understanding the molecular mechanisms regulating cassava's responses against this pest is crucial for developing control strategies. Pathogenesis-related (PR) protein families are an integral part of plant immunity. With the availability of whole genome sequences, the annotation and expression programs of the full complement of PR genes in an organism can now be achieved. An understanding of the responses of the entire complement of PR genes during biotic stress and to the defense hormones, salicylic acid (SA) and jasmonic acid (JA), is lacking. Here, we analyze the responses of cassava PR genes to whiteflies, SA, JA, and other biotic aggressors. RESULTS:The cassava genome possesses 14 of the 17 plant PR families, with a total of 447 PR genes. A cassava PR gene nomenclature is proposed. Phylogenetic relatedness of cassava PR proteins to each other and to homologs in poplar, rice and Arabidopsis identified cassava-specific PR gene family expansions. The temporal programs of PR gene expression in response to the whitefly (Aleurotrachelus socialis) in four whitefly-susceptible cassava genotypes showed that 167 of the 447 PR genes were regulated after whitefly infestation. While the timing of PR gene expression varied, over 37% of whitefly-regulated PR genes were downregulated in all four genotypes. Notably, whitefly-responsive PR genes were largely coordinately regulated by SA and JA. The analysis of cassava PR gene expression in response to five other biotic stresses revealed a strong positive correlation between whitefly and Xanthomonas axonopodis and Cassava Brown Streak Virus responses and negative correlations between whitefly and Cassava Mosaic Virus responses. Finally, certain associations between PR genes in cassava expansions and response to biotic stresses were observed among PR families. CONCLUSIONS:This study represents the first genome-wide characterization of PR genes in cassava. PR gene responses to six biotic stresses and to SA and JA are demonstrably different to other angiosperms. We propose that our approach could be applied in other species to fully understand PR gene regulation by pathogens, pests and the canonical defense hormones SA and JA
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The Local Volume HI Survey: star formation properties
We built a multi-wavelength dataset for galaxies from the Local Volume HI
Survey (LVHIS), which comprises 82 galaxies. We also select a sub-sample of ten
large galaxies for investigating properties in the galactic outskirts. The
LVHIS sample covers nearly four orders of magnitude in stellar mass and two
orders of magnitude in HI mass fraction (fHI). The radial distribution of HI
gas with respect to the stellar disc is correlated with fHI but with a large
scatter. We confirm the previously found correlations between the total HI mass
and star formation rate (SFR), and between HI surface densities and SFR surface
densities beyond R25. However, the former correlation becomes much weaker when
the average surface densities rather than total mass or rate are considered,
and the latter correlation also becomes much weaker when the effect of stellar
mass is removed or controlled. Hence the link between SFR and HI is
intrinsically weak in these regions, consistent with what was found on kpc
scales in the galactic inner regions. We find a strong correlation between the
SFR surface density and the stellar mass surface density, which is consistent
with the star formation models where the gas is in quasi-equilibrium with the
mid-plane pressure. We find no evidence for HI warps to be linked with
decreasing star forming efficiencies.Comment: 31 pages, 20 figures, 4 tables. Accepted for publication at MNRA
The role of magnetic islands in modifying long range temporal correlations of density fluctuations and local heat transport
This work explores the relation between magnetic islands, long range temporal correlations and heat transport. A low order rational surface (t = 3/2) was purposely scanned outward through an electron cyclotron resonance heated (ECRH) plasma in the TJ-II stellarator. Density turbulence and the poloidal flow velocity were characterized using a two channel Doppler reflectometer. Simultaneously, the ECRH power was modulated to characterize heat transport, using measurements from a 12 channel electron cyclotron emission diagnostic. A systematic variation of the poloidal velocity was found to be associated with the t = 3/2 rational surface. Near the rational surface, the Hurst exponent, quantifying the nature of long-range correlations, was reduced below 0.5 (indicating subdiffusion), while at radii smaller than that of the rational surface, it was found to be significantly enhanced (superdiffusion). In the latter region, heat transport was enhanced as well, thus establishing a link between density fluctuations and anomalous heat transport. The observed variation of the Hurst exponent was consistent with a magnetohydrodynamic turbulence simulation
Effect of oxygen plasma etching on graphene studied with Raman spectroscopy and electronic transport
We report a study of graphene and graphene field effect devices after
exposure to a series of short pulses of oxygen plasma. We present data from
Raman spectroscopy, back-gated field-effect and magneto-transport measurements.
The intensity ratio between Raman "D" and "G" peaks, I(D)/I(G) (commonly used
to characterize disorder in graphene) is observed to increase approximately
linearly with the number (N(e)) of plasma etching pulses initially, but then
decreases at higher Ne. We also discuss implications of our data for extracting
graphene crystalline domain sizes from I(D)/I(G). At the highest Ne measured,
the "2D" peak is found to be nearly suppressed while the "D" peak is still
prominent. Electronic transport measurements in plasma-etched graphene show an
up-shifting of the Dirac point, indicating hole doping. We also characterize
mobility, quantum Hall states, weak localization and various scattering lengths
in a moderately etched sample. Our findings are valuable for understanding the
effects of plasma etching on graphene and the physics of disordered graphene
through artificially generated defects.Comment: 10 pages, 5 figure
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