462 research outputs found
Formation, Manipulation, and Elasticity Measurement of a Nanometric Column of Water Molecules
Nanometer-sized columns of condensed water molecules are created by an
atomic-resolution force microscope operated in ambient conditions. Unusual
stepwise decrease of the force gradient associated with the thin water bridge
in the tip-substrate gap is observed during its stretch, exhibiting regularity
in step heights (~0.5 N/m) and plateau lengths (~1 nm). Such "quantized"
elasticity is indicative of the atomic-scale stick-slip at the tip-water
interface. A thermodynamic-instability-induced rupture of the water meniscus
(5-nm long and 2.6-nm wide) is also found. This work opens a high-resolution
study of the structure and the interface dynamics of a nanometric aqueous
column.Comment: 4 pages, 3 figure
Effects of charge doping and constrained magnetization on the electronic structure of an FeSe monolayer
The electronic structural properties in the presence of constrained
magnetization and a charged background are studied for a monolayer of FeSe in
non-magnetic, checkerboard-, and striped-antiferromagnetic (AFM) spin
configurations. First principles techniques based on the pseudopotential
density functional approach and the local spin density approximation are
utilized. Our findings show that the experimentally observed shape of the Fermi
surface is best described by the checkerboard AFM spin pattern. To explore the
underlying pairing mechanism, we study the evolution of the non-magnetic to the
AFM-ordered structures under constrained magnetization. We estimate the
strength of electronic coupling to magnetic excitations involving an increase
in local moment and, separately, a partial moment transfer from one Fe atom to
another. We also show that the charge doping in the FeSe can lead to an
increase in the density of states at the Fermi level and possibly produce
higher superconducting transition temperatures
Shiga toxin-producing Escherichia coli (STEC) O157 outbreak, The Netherlands, September - October 2005.
In September 2005, the first national food-related outbreak of Shiga toxin (Stx)-producing Escherichia coli (STEC) O157 was investigated in the Netherlands. A total of 21 laboratory-confirmed cases (including one secondary case), and another 11 probable cases (two primary and nine secondary cases) were reported in patients who became ill between 11 September and 10 October 2005. Preliminary investigation suggested consumption of a raw beef product, steak tartare (in the Netherlands also known as 'filet americain'), and contact with other symptomatic persons as possible risk factors. A subsequent case-control study supported the hypothesis that steak tartare was the source of the outbreak (matched odds ratio (OR) 272, 95% confidence interval (CI) 3 - 23211). Consumption of ready-to-eat vegetables was also associated with STEC O157 infection (matched OR 24, 95% CI 1.1 - 528), but was considered a less likely source, as only 40% of the cases were exposed. Samples of steak tartare collected from one chain of supermarkets where it is likely that most patients (67%) bought steak tartare, all tested negative for STEC O157. However, sampling was done three days after the date of symptom onset of the last reported case. Since 88% of the cases became ill within a two week period, point source contamination may explain these negative results. It is concluded that steak tartare was the most likely cause of the first national food-related outbreak of STEC O157 in the Netherlands
Electronic structure and mechanical stability of the graphitic honeycomblattice
A family of crystal structures of carbon composed of alternating sp2 and sp3 bonds is investigated. Graphitic strips are connected by sp3 bonds to form an array of hexagonal pillars exhibiting a honeycomb lattice in the perpendicular plane. The electronic structure and elastic properties of this family of structures are calculated using an ab initio pseudopotential as well as the environment-dependent tight-binding method. Their electronic structure has a similar size dependence to zigzag nanotubes; they are metallic if twice the strip width is a multiple of three hexagonal units, and otherwise semiconducting with a wider range of the band gap than for carbon nanotubes. The structural stability is studied and compared with other carbon structures.open252
Magnetic Quantum Dot: A Magnetic Transmission Barrier and Resonator
We study the ballistic edge-channel transport in quantum wires with a
magnetic quantum dot, which is formed by two different magnetic fields B^* and
B_0 inside and outside the dot, respectively. We find that the electron states
located near the dot and the scattering of edge channels by the dot strongly
depend on whether B^* is parallel or antiparallel to B_0. For parallel fields,
two-terminal conductance as a function of channel energy is quantized except
for resonances, while, for antiparallel fields, it is not quantized and all
channels can be completely reflected in some energy ranges. All these features
are attributed to the characteristic magnetic confinements caused by nonuniform
fields.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
Pseudospin rotation and valley mixing in electron scattering at graphene edges
In graphene, the pseudospin and the valley flavor arise as new types of
quantum degrees of freedom due to the honeycomb lattice comprising two
sublattices (A and B) and two inequivalent Dirac points (K and K') in the
Brillouin zone, respectively. Unique electronic properties of graphene result
in striking phenomena such as Klein tunnelling, Veselago lens, and
valley-polarized currents. Here, we investigate the roles of the pseudospin and
the valley in electron scattering at graphene edges and show that they are
strongly correlated with charge density modulations of short-wavelength
oscillations and slowly-decaying beat patterns. Theoretical analyses using
nearest-neighbor tight-binding methods and first-principles density-functional
theory calculations agree well with our experimental data from the scanning
tunneling microscopy. We believe that this study will lead to useful
application of graphene to "valleytronics" and "pseudospintronics".Comment: 13 pages, 4 figures, Supplementary Information available upon reques
Direct observation of localized defect states in semiconductor nanotube junctions
Scanning tunneling microscopy of semiconductor-semiconductor carbon nanotube junctions with different band gaps was studied. Characteristic features of the wave functions at different energy levels were exhibited in the atomically resolved scanning tunneling microscopy. The experimental observations in terms of the pentagon-heptagon defects in the junction were interpreted.open888
Association of MCP-1 and CCR2 polymorphisms with the risk of late acute rejection after renal transplantation in Korean patients
Among the factors modulating transplant rejection, chemokines and their respective receptors deserve special attention. Increased expression of monocyte chemoattractant protein-1 (MCP-1) and its corresponding receptor (chemokine receptor-2, CCR2) has been implicated in renal transplant rejection. To determine the impact of the MCP-1-2518G and CCR2-64I genotypes on renal allograft function, 167 Korean patients who underwent transplantation over a 25-year period were evaluated. Genomic DNA was genotyped using polymerase chain reaction followed by restriction fragment length polymorphism analysis. Fifty-five (32.9%) patients were homozygous for the MCP-1-2518G polymorphism. Nine (5.4%) patients were homozygous for the CCR2-64I polymorphism. None of the investigated polymorphism showed a significant shift in long-term allograft survival. However, a significant increase was noted for the risk of late acute rejection in recipients who were homozygous for the MCP-1-2518G polymorphism (OR, 2.600; 95% CI, 1.125–6.012; P = 0.022). There was also an association between the MCP-1-2518G/G genotype and the number of late acute rejection episodes (P = 0.024). Although there was no difference in the incidence of rejection among recipients stratified by the CCR2-V64I genotype, recipients with the CCR2-V64I GG genotype in combination with the MCP-1-2518G/G genotype had a significantly higher risk of acute or late acute rejection among the receptor-ligand combinations (P = 0.006, P = 0.008, respectively). The MCP-1 variant may be a marker for risk of late acute rejection in Korean patients
Rotation Curve of Galaxies by the Force Induced by Mass of Moving Particles
We suggest that there is a novel force which is generated by the mass of
relatively moving particles. The new force which we named Mirinae Force is a
counterpart of the magnetic force operating between electrically charged moving
particles. Instead of using the conventional dark matter, we applied the
mirinae force to a particular model system of the spiral galaxy in which most
of the galaxy's mass is located within the central region where some portion of
the inner mass is in revolving motion at a relativistic speed. The calculation
yielded three important results that illustrate the existence of mirinae force
and validate the proposed model: First, the mirinae force in this model
explains why most of the matters in the galactic disk are in the circular
motion which is similar to cycloid. Second, the mirinae force well explains not
only the flat rotation curve but also the varied slope of the rotation curve
observed in the spiral galaxies. Third, at the flat velocity of 220 Km/s, the
inner mass of the Milky Way calculated by using the proposed model is
6.0\times10^11 M\odot, which is very close to 5.5\times10^11 M\odot (r <50 Kpc,
including Leo I) estimated by using the latest kinematic information. This
means that the mirinae force well takes the place of the dark matter of the
Milky Way
Effects of oxygen adsorption on carbon nanotube field emitters
Effects of oxygen adsorption on the field emission of carbon nanotubes are studied through first-principles calculations. Calculated emission currents are significantly enhanced when oxygen is adsorbed at the tip and the underlying physics is explained in terms of the change in the electronic structure by oxidation and the local field increase at the adsorption site. The issue of the current degradation accompanied by the oxidative etching is also addressed. The field-emission-microscopy images on the phosphor screen are simulated, displaying various patterns characteristic of each adsorption configuration.open546
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