280 research outputs found
Capillary abnormalities in workers occupationally exposed to ionizing and nonionizing radiations
Cilj studije je bio metodom kapilaroskopije upozoriti na mogući utjecaj ionizacijskog i neionizacijskog zračenja na periferni krvotok profesionalno izloženih osoba. Kapilaroskopski smo pregledali 100 osoba profesionalno izloženih ionizacijskom zračenju, 110 osoba profesionalno izloženih neionizacijskom zračenju i 80 kontrolnih, neizloženih osoba. U obje test-skupine oštećenja mikrocirkulacije su bila statistički značajno učestalija nego u kontrolnoj skupini.The aim of the study was to determine a possible effect of ionizing and nonionizing radiations on peripheral blood flow in occupationally exposed persons by means of capillaroscopic analysis. Altogether 290 subjects were examined. Of these 100 were occupationally exposed to ionizing radiation, 110 were occupationally exposed to nonionizing radiation and 80 control subjects never worked with radiation sources. Statistical analysis showed that microvascular abnormalities occurred significantly more frequently among occupationally exposed persons than in the control group
Anisotropy of superconducting MgB2 as seen in electron spin resonance and magnetization data
We have observed the conduction electron spin resonance (CESR) in fine
powders of MgB2 both in the superconducting and normal states. The Pauli
susceptibility is chi_s=2.0*10^{-5} emu/mole in the temperature range of 450 to
600 K. The spin relaxation rate has an anomalous temperature dependence. The
CESR measured below T_c at several frequencies suggests that MgB_2 is a
strongly anisotropic superconductor with the upper critical field, H_c2,
ranging between 2 and 16 T. The high-field reversible magnetization data of a
randomly oriented powder sample are well described assuming that MgB_2 is an
anisotropic superconductor with H_c2^{ab} / H_{c2}^{c} \approx 6--9.Comment: 4 pages, 4 eps figure
Role of dynamic Jahn-Teller distortions in Na2C60 and Na2CsC60 studied by NMR
Through 13C NMR spin lattice relaxation (T1) measurements in cubic Na2C60, we
detect a gap in its electronic excitations, similar to that observed in
tetragonal A4C60. This establishes that Jahn-Teller distortions (JTD) and
strong electronic correlations must be considered to understand the behaviour
of even electron systems, regardless of the structure. Furthermore, in metallic
Na2CsC60, a similar contribution to T1 is also detected for 13C and 133Cs NMR,
implying the occurence of excitations typical of JT distorted C60^{2-} (or
equivalently C60^{4-}). This supports the idea that dynamic JTD can induce
attractive electronic interactions in odd electron systems.Comment: 3 figure
Influence of Adult Knee Height, Age at First Birth, Migration, and Current Age on Adult Physical Function of Bangladeshi Mothers and Daughters in the United Kingdom and Bangladesh
Economic and Social Research Council, New Dynamics of Ageing Programme, UK
DNA nucleotide-specific modulation of \mu A transverse edge currents through a metallic graphene nanoribbon with a nanopore
We propose two-terminal devices for DNA sequencing which consist of a
metallic graphene nanoribbon with zigzag edges (ZGNR) and a nanopore in its
interior through which the DNA molecule is translocated. Using the
nonequilibrium Green functions combined with density functional theory, we
demonstrate that each of the four DNA nucleotides inserted into the nanopore,
whose edge carbon atoms are passivated by either hydrogen or nitrogen, will
lead to a unique change in the device conductance. Unlike other recent
biosensors based on transverse electronic transport through DNA nucleotides,
which utilize small (of the order of pA) tunneling current across a nanogap or
a nanopore yielding a poor signal-to-noise ratio, our device concept relies on
the fact that in ZGNRs local current density is peaked around the edges so that
drilling a nanopore away from the edges will not diminish the conductance.
Inserting a DNA nucleotide into the nanopore affects the charge density in the
surrounding area, thereby modulating edge conduction currents whose magnitude
is of the order of \mu A at bias voltage ~ 0.1 V. The proposed biosensor is not
limited to ZGNRs and it could be realized with other nanowires supporting
transverse edge currents, such as chiral GNRs or wires made of two-dimensional
topological insulators.Comment: 6 pages, 6 figures, PDFLaTe
A neutron scattering study of two-magnon states in the quantum magnet copper nitrate
We report measurements of the two-magnon states in a dimerized
antiferromagnetic chain material, copper nitrate (Cu(NO3)2*2.5D2O). Using
inelastic neutron scattering we have measured the one and two magnon excitation
spectra in a large single crystal. The data are in excellent agreement with a
perturbative expansion of the alternating Heisenberg Hamiltonian from the
strongly dimerized limit. The expansion predicts a two-magnon bound state for q
~ (2n+1)pi*d which is consistent with the neutron scattering data.Comment: 11 pages of revtex style with 6 figures include
Gaps and excitations in fullerides with partially filled bands : NMR study of Na2C60 and K4C60
We present an NMR study of Na2C60 and K4C60, two compounds that are related
by electron-hole symmetry in the C60 triply degenerate conduction band. In both
systems, it is known that NMR spin-lattice relaxation rate (1/T1) measurements
detect a gap in the electronic structure, most likely related to
singlet-triplet excitations of the Jahn-Teller distorted (JTD) C60^{2-} or
C60^{4-}. However, the extended temperature range of the measurements presented
here (10 K to 700 K) allows to reveal deviations with respect to this general
trend, both at high and low temperatures. Above room temperature, 1/T1 deviates
from the activated law that one would expect from the presence of the gap and
saturates. In the same temperature range, a lowering of symmetry is detected in
Na2C60 by the appearance of quadrupole effects on the 23Na spectra. In K4C60,
modifications of the 13C spectra lineshapes also indicate a structural
modification. We discuss this high temperature deviation in terms of a coupling
between JTD and local symmetry. At low temperatures, 1/TT tends to a
constant value for Na2C60, both for 13C and 23Na NMR. This indicates a residual
metallic character, which emphasizes the proximity of metallic and insulting
behaviors in alkali fullerides.Comment: 12 pages, 13 figure
Propagation of Magnetic Fields from Electrical Domestic Appliances
The article presents a research into propagation of magnetic fields from electrical domestic devices. A safe distance at which magnetic induction does not exceed the background level is determined for each type of devices. It is proved that there are two stages of increasing magnetic induction as the distance from the source increases. At the first stage magnetic induction rises and electromagnetic field is formed. At the second stage exponential decrease of magnetic field induction takes place. Mathematical regularities of propagation of magnetic field from electrical domestic devices are experimentally educed
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