3,048 research outputs found
Measurement of the electronic compressibility of bilayer graphene
We present measurements of the electronic compressibility, , of bilayer
graphene in both zero and finite magnetic fields up to 14 T, and as a function
of both the carrier density and electric field perpendicular to the graphene
sheet. The low energy hyperbolic band structure of bilayer graphene is clearly
revealed in the data, as well as a sizable asymmetry between the conduction and
valence bands. A sharp increase in near zero density is observed for
increasing electric field strength, signaling the controlled opening of a gap
between these bands. At high magnetic fields, broad Landau level (LL)
oscillations are observed, directly revealing the doubled degeneracy of the
lowest LL and allowing for a determination of the disorder broadening of the
levels.Comment: 5 pages, 3 figures; final version for publicatio
Possible mechanism for changes in glycogen metabolism in unloaded soleus muscle
Carbohydrate metabolism has been shown to be affected in a number of ways by different models of hypokinesia. In vivo glycogen levels in the soleus muscle are known to be increased by short-term denervation and harness suspension. In addition, exposure to 7 days of hypogravity also caused a dramatic increase in glycogen concentration in this muscle. The biochemical alterations caused by unloading that may bring about these increases in glycogen storage in the soleus were sought
Non-isothermal X-ray Emitting Gas in Clusters of Galaxies
We have analyzed X-ray spectra from six galaxy clusters which contain cooling
flows: A85, A478, A1795, A2142, A2147, & A2199. The X-ray spectra were taken
with the HEAO1-A2 Medium and High Energy Detectors and the Einstein Solid State
Spectrometer. For each cluster, we simultaneously fit the spectra from these
three detectors with models incorporating one or more emission components
comprised of either thermal or cooling flow models. Five of the clusters (all
but A2142) are better fit by a multi-component model (a cooling flow plus one
or two thermal components or a two thermal component model) than by isothermal
models. In four of the clusters (A85, A1795, A2147, & A2199), we find evidence
for cool gas outside of the canonical cooling flow region. These latter four
clusters can be characterized by three temperature components: a temperature
inversion in the central region, a hotter region with an emission-weighted
temperature which is higher than that of an isothermal model fit to the entire
cluster, and a cooler region with an emission-weighted temperature of ~1 keV.
The cool component outside the cooling flow region has a large minimum emission
measure which we attribute, in part, to diffuse cool gas in the outer cluster
atmosphere. If at least some of the cool exterior gas is virialized, this would
imply a radially decreasing temperature profile. Together with the density
profiles we have found, this leads to a baryon fraction in gas which increases
with radius and is larger than that for an isothermal cluster atmosphere.
Consequently, if clusters of galaxies trace the mass distribution in the
Universe, the gas mass fraction we have calculated for an isothermal gas (which
is ~15%) together with the nominal galaxy contribution (~5%) gives a baryon
fraction of ~20%. Using the upper limit to the baryon density derived from BigComment: gzipped tar file of 26 PostScript pages, including 2 figures, 7
tables. Also available at
http://www.astr.ua.edu/preprints/white/INDEX_READ_ME_1st.htm
Electronic structure and time-dependent description of rotational predissociation of LiH
Adiabatic potential energy curves of the and states of
the LiH molecule have been calculated. They correlate asymptotically to atomic
states, like 2s+1s, 2p+1s, 3s+1s, 3p+1s, 3d+1s, 4s+1s, 4p+1s and 4d+1s. Very
good agreement is found between our calculated spectroscopic parameters and
experimental ones. The dynamics of the rotational predissociation process of
the state has been studied by solving the time-dependent
Schr\"{o}dinger equation. The classical experiment of Velasco [Can. J. Phys.
{35}, 1204 (1957)] on dissociation in the state is explained in
detail
Quantum Hall Effect and Semimetallic Behavior of Dual-Gated ABA-Stacked Trilayer Graphene
The electronic structure of multilayer graphenes depends strongly on the
number of layers as well as the stacking order. Here we explore the electronic
transport of purely ABA-stacked trilayer graphenes in a dual-gated field-effect
device configuration. We find that both the zero-magnetic-field transport and
the quantum Hall effect at high magnetic fields are distinctly different from
the monolayer and bilayer graphenes, and that they show electron-hole
asymmetries that are strongly suggestive of a semimetallic band overlap. When
the ABA trilayers are subjected to an electric field perpendicular to the
sheet, Landau level splittings due to a lifting of the valley degeneracy are
clearly observed.Comment: 5 figure
Electronic structure and rovibrational predissociation of the 2sPi state in KLi
Adiabatic potential energy curves of the 3sSigma+, 3tSigma+, 2sPi and 2tPi
states correlating for large internuclear distance with the K(4s) + Li(2p)
atomic asymptote were calculated. Very good agreement between the calculated
and the experimental curve of the 2sPi state allowed for a reliable description
of the dissociation process through a small (20 cm-1 for J = 0) potential
energy barrier. The barrier supports several rovibrational quasi-bound states
and explicit time evolution of these states via the time-dependent nuclear
Schroedinger equation, showed that the state populations decay exponentially in
time. We were able to precisely describe the time-dependent dissociation
process of several rovibrational levels and found that our calculated spectrum
match very well with the assigned experimental spectrum. Moreover, our approach
is able to predict the positions of previously unassigned lines despite their
low intensit
Responses of skeletal muscle to unloading, a review
Suspension models were used to study muscle response to reduced activity. During 6 days of tail casting, the soleus (SOL) atrophies while the extensor digitorum longus grows relatively normally. After discounting those changes in both muscles due primarily to increased secretion of adrenal hormones, the following conclusions regarding the specific responses of the SOL could be drawn: (1) Atrophy is probably due primarily to increased protein degradation; (2) Decreased synthesis of glutamine may result from reduced availability of ammonia due to diminished use of ATP; (3) Greater muscle glycogen seems to reflect an increased response to insulin of glucose uptake which leads to greater glucose metabolism; and (4) Faster catabolism of branched-chain amino acids can be attributed to enhanced flux through ketoacid dehydrogenase. Studies by others using tail casted suspended rats showed in the SOL: (1) a gradual switch from type 1 to type 2 fibers; (2) increased acid protease activity; and (3) altered muscle function and contractile duration. Using harness suspended rats, others showed in the SOL: (1) significant atrophy; (2) increased numbers of glucocorticoid receptors; and (3) no change in muscle fatigability
Response of rat hindlimb muscles to 12 hours recovery from tail-cast suspension
Previous work has shown a number of biochemical changes which accompany atrophy or reduced muscle growth in hindlimb of tail-casted, suspended rats. These results clearly show that altered muscle growth was due to changes in protein turnover. Accordingly, the rise in soleus tyrosine following unloading reflects the more negative protein balance. Other major changes we found included slower synthesis of glutamine as indicated by lower ratios of glutamine/glutamate and reduced levels of aspartate which coincide with slower aspartate and ammonia metabolism in vitro. In conjunction with the study of SL-3 rats, which were subjected to 12 h of post-flight gravity, a study of the effects of 12 h eight bearing on metabolism of 6-day unloaded hindlimb muscles was carried out
Muscle protein and glycogen responses to recovery from hypogravity and unloading by tail-cast suspension
Previous studies in this laboratory using the tail-bast hindlimb suspension model have shown that there are specific changes in protein and carbohydrate metabolism in the soleus muscle due to unloading. For example, 6 days of unloading caused a 27% decrease in mass and a 60% increase in glycogen content in the soleus muscle, while the extensor digitorum longus muscle was unaffected. Also, fresh tissue tyrosine and its in vitro release from the muscle are increased in the unloaded soleus, indicating that this condition causes a more negative protein balance. With these results in mind, studies to investigate the effect of hypogravity on protein and carbohydrate metabolism in a number of rat hindlimb muscles were carried out
An X-ray survey of variable radio bright quasars
A sample consisting primarily of radio bright quasars was observed in X-rays with the Einstein Observatory for times ranging from 1500 to 5000 seconds. Detected sources had luminosities ranging from 0.2 to 41.0 x 10 to the 45th power ergs/sec in the 0.5 to 4.5 keV band. Three of the fourteen objects which were reobserved showed flux increases greater than a factor of two on a time scale greater than six months. No variability was detected during the individual observations. The optical and X-ray luminosities are correlated, which suggests a common origin. However, the relationship (L sub x is approximately L sub op to the (.89 + or - .15)) found for historic radio variables may be significantly different than that reported for other radio bright sources. Some of the observed X-ray fluxes were substantially below the predicted self-Compton flux, assuming incoherent synchrotron emission and using VLBI results to constrain the size of the emission region, which suggests relativistic expansion in these sources. Normal CIV emission in two of the sources with an overpredicted Compton component suggests that although they, like BL Lac objects, have highly relativistic material apparently moving at small angle to the line of sight, they have a smaller fraction of the continuum component in the beam
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