9,053 research outputs found
Reply to ``Comment on `Insulating Behavior of -DNA on the Micron Scale' "
In our experiment, we found that the resistance of vacuum-dried -DNA
exceeds at 295 K. Bechhoefer and Sen have raised a number of
objections to our conclusion. We provide counter arguments to support our
original conclusion.Comment: 1 page reply to comment, 1 figur
Ferromagnetism below 10 K in Mn doped BiTe
Ferromagnetism is observed below 10 K in [Bi0.75Te0.125Mn0.125]Te. This
material has the BiTe structure, which is made from the stacking of two
Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure
analysis shows that Mn is localized in the Bi2 blocks, and is accompanied by an
equal amount of TeBi anti-site occupancy in the Bi2Te3 blocks. These TeBi
anti-site defects greatly enhance the Mn solubility. This is demonstrated by
comparison of the [Bi1-xMnx]Te and [Bi1-2xTexMnx]Te series; in the former, the
solubility is limited to x = 0.067, while the latter has xmax = 0.125. The
magnetism in [Bi1-xMnx]Te changes little with x, while that for
[Bi1-2xTexMnx]Te shows a clear variation, leading to ferromagnetism for x >
0.067. Magnetic hysteresis and the anomalous Hall Effect are observed for the
ferromagnetic samples.Comment: Accepted for publication in Phys. Rev.
Reactive Hall constant of Strongly Correlated Electrons
The zero-temperature Hall response within tight-binding models of correlated
electrons is studied. Using the linear response theory and a linearization in
the magnetic field B, a general relation for the reactive (zero frequency) Hall
constant in the fast (transport) limit is derived, involving only matrix
elements between the lowest excited states at B=0; for noninteracting fermions,
the Boltzmann expression is reproduced. For a Fermi liquid with a well defined
Fermi surface and linear gapless excitations an analogous expression is found
more generally. In the specific case of quasi-one-dimensional correlated
systems a relation of to the charge stiffness D is recovered. Similar
analysis is performed and discussed for D and the compressibility.Comment: 8 pages, submitted to Phys.Rev.
Effects of chronic exposure to low doses of trichloroethylene on steroid hormone and insulin levels in normal men.
The aim of this study was to examine the serum levels of insulin and some adrenal steroid hormones in men chronically exposed to low doses of trichloroethylene (TCE). A total of 85 workers participated in this study. Each worker had urine collected and analyzed for trichloroacetic acids (UTCA) on the same day that a blood sample was taken for analyses of serum testosterone, sex hormone-binding globulin (SHBG), androstenedione, cortisol, aldosterone, and insulin. The mean concentration of environmental TCE was 29.6 ppm and the mean UTCA was 22.4 mg/g creatinine (range 0.8-136.4). TCE exposure did not cause any significant changes to the adrenal steroid hormone productions. The results showed that UTCA was significantly correlated to serum insulin levels. Insulin and SHBG responded in tandem, with the highest levels found in workers exposed to TCE for less than 2 years; levels of both parameters were significantly lowered in those exposed for more than 2 years. A triphasic response in insulin levels to TCE, which depended on the duration of exposure, was noted. Initial exposure caused an acute rise in insulin levels. This was followed by a fall to normal levels in those exposed 2-4 years and then a slight rise in those exposed for more than 6 years. The mechanism for this pattern of response to TCE exposure is yet unknown
Optical investigation of the charge-density-wave phase transitions in
We have measured the optical reflectivity of the quasi
one-dimensional conductor from the far infrared up to the
ultraviolet between 10 and 300 using light polarized along and normal to
the chain axis. We find a depletion of the optical conductivity with decreasing
temperature for both polarizations in the mid to far-infrared region. This
leads to a redistribution of spectral weight from low to high energies due to
partial gapping of the Fermi surface below the charge-density-wave transitions
at 145 K and 59 K. We deduce the bulk magnitudes of the CDW gaps and discuss
the scattering of ungapped free charge carriers and the role of fluctuations
effects
Memory function approach to the Hall constant in strongly correlated electron systems
The anomalous properties of the Hall constant in the normal state of
high- superconductors are investigated within the single-band Hubbard
model. We argue that the Mori theory is the appropriate formalism to address
the Hall constant, since it aims directly at resistivities rather than
conductivities. More specifically, the frequency dependent Hall constant
decomposes into its infinite frequency limit and a memory function
contribution. As a first step, both terms are calculated perturbatively in
and on an infinite dimensional lattice, where is the correlation strength.
If we allow to be of the order of twice the bare band width, the memory
function contribution causes the Hall constant to change sign as a function of
doping and to decrease as a function of temperature.Comment: 35 pages, RevTex, 3 ps figures include
Collapse of the vortex-lattice inductance and shear modulus at the melting transition in untwinned
The complex resistivity of the vortex lattice in an
untwinned crystal of 93-K has been measured at frequencies
from 100 kHz to 20 MHz in a 2-Tesla field ,
using a 4-probe RF transmission technique that enables continuous measurements
versus and temperature . As is increased, the inductance increases steeply to a cusp
at the melting temperature , and then undergoes a steep collapse
consistent with vanishing of the shear modulus . We discuss in detail
the separation of the vortex-lattice inductance from the `volume' inductance,
and other skin-depth effects. To analyze the spectra, we consider a weakly
disordered lattice with a low pin density. Close fits are obtained to
over 2 decades in . Values of the pinning parameter
and shear modulus obtained show that collapses by
over 4 decades at , whereas remains finite.Comment: 11 pages, 8 figures, Phys. Rev. B, in pres
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