5,331 research outputs found
Recommended from our members
Guttate leukoderma and acrokeratosis verruciformis of Hopf: a rare combination in Darier disease
A distinct Darier phenotype presenting with confetti-like hypopigmented macules was first described in 1965. Designated as "guttate leukoderma," this skin finding is a rarely-reported presentation of Darier disease. It has been theorized that the mutation in ATP2A2 causes defective E-cadherin, which in turn disrupts the adhesion of melanocytes to keratinocytes, thus leading to impaired dendrite formation, hindered melanin transfer, and ultimately to melanocyte apoptosis. Herein, we contribute a case of a 56-year old woman who presented with the rarely-described guttate leukoderma of Darier disease and acrokeratosis verruciformis of Hopf
Dual Gate Graphene FETs with fT of 50 GHz
A dual-gate graphene field-effect transistors is presented, which shows
improved RF performance by reducing the access resistance using electrostatic
doping. With a carrier mobility of 2700 cm2/Vs, a cutoff frequency of 50 GHz is
demonstrated in a 350-nm gate length device. This fT value is the highest
frequency reported to date for any graphene transistor, and it also exceeds
that of Si MOSFETs at the same gate length, illustrating the potential of
graphene for RF applications
Operation of Graphene Transistors at GHz Frequencies
Top-gated graphene transistors operating at high frequencies (GHz) have been
fabricated and their characteristics analyzed. The measured intrinsic current
gain shows an ideal 1/f frequency dependence, indicating an FET-like behavior
for graphene transistors. The cutoff frequency fT is found to be proportional
to the dc transconductance gm of the device. The peak fT increases with a
reduced gate length, and fT as high as 26 GHz is measured for a graphene
transistor with a gate length of 150 nm. The work represents a significant step
towards the realization of graphene-based electronics for high-frequency
applications
The Relationship Between Galaxies and Low Redshift Weak Lyman alpha Absorbers in the Directions of H1821+643 and PG1116+215
To study the nature of low z Lya absorbers in the spectra of QSOs, we have
obtained high signal-to-noise UV spectra of H 1821+643 (z = 0.297) and PG
1116+215 (z = 0.177) with the GHRS on the HST. The spectra have minimum S/N of
70-100 and 3 sigma limiting equivalent widths of 50-75 mA. We detect 26 Lya
lines with Wr > 50 mA toward H1821+643 and 13 toward PG1116+215, which implies
a density of 102+/-16 lines per unit redshift. The two-point correlation
function shows marginal evidence of clustering on ~500 km/s scales, but only if
the weakest lines are excluded. We have also used the WIYN Observatory to
measure galaxy redshifts in the ~1 degree fields centered on each QSO. We find
17 galaxy-absorber pairs within projected distances of 1 Mpc with velocity
separations of 350 km/s or less. Monte Carlo simulations show that if the Lya
lines are randomly distributed, the probability of observing this many close
pairs is 3.6e-5. We find that all galaxies with projected distances of 600 kpc
or less have associated Lya absorbers within 1000 km/s, and the majority of
these galaxies have absorbers within 350 km/s. We also find that the Lya
equivalent width is anticorrelated with the projected distance of the nearest
galaxy out to at least 600 kpc, but this should be interpreted cautiously
because there are potential selection biases. Statistical tests using the
entire sample also indicate that the absorbers are not randomly distributed. We
discuss the nature of the Lya absorbers in light of the new data.Comment: Accepted for publication in ApJ. 17 pages plus 11 tables and 17
figure
A Preliminary Discussion of the Kinematics of BHB and RR Lyrae Stars near the North Galactic Pole
The radial velocity dispersion of 67 RR Lyrae variable and blue horizontal
branch (BHB) stars that are more than 4 kpc above the galactic plane at the
North Galactic Pole is 110 km/sec and shows no trend with Z (the height above
the galactic plane). Nine stars with Z < 4 kpc show a smaller velocity
dispersion (40 +/-9 km/sec) as is to be expected if they mostly belong to a
population with a flatter distribution. Both RR Lyrae stars and BHB stars show
evidence of stream motion; the most significant is in fields RR2 and RR3 where
24 stars in the range 4.0 < Z < 11.0 kpc have a mean radial velocity of -59 +/-
16 km/sec. Three halo stars in field RR 2 appear to be part of a moving group
with a common radial velocity of -90 km/sec. The streaming phenomenon therefore
occurs over a range of spatial scales. The BHB and RR Lyrae stars in our sample
both have a similar range of metallicity (-1.2 < [Fe/H] < -2.2). Proper motions
of BHB stars in fields SA 57 (NGP) and the Anticenter field (RR 7) (both of
which lie close to the meridional plane of the Galaxy) show that the stars that
have Z 4 kpc have a Galactic V motion that is
< -200 km/sec and which is characteristic of the halo. Thus the stars that have
a flatter distribution are really halo stars and not members of the metal-weak
thick-disk.Comment: Accepted for publication in the March 1996 AJ. 15 pages, AASTeX V4.0
latex format (including figures), 2 eps figures, 2 separate AASTeX V4.0 latex
table
Recommended from our members
Exploratory analysis using machine learning to predict for chest wall pain in patients with stage I non-small-cell lung cancer treated with stereotactic body radiation therapy.
Background and purposeChest wall toxicity is observed after stereotactic body radiation therapy (SBRT) for peripherally located lung tumors. We utilize machine learning algorithms to identify toxicity predictors to develop dose-volume constraints.Materials and methodsTwenty-five patient, tumor, and dosimetric features were recorded for 197 consecutive patients with Stage I NSCLC treated with SBRT, 11 of whom (5.6%) developed CTCAEv4 grade ≥2 chest wall pain. Decision tree modeling was used to determine chest wall syndrome (CWS) thresholds for individual features. Significant features were determined using independent multivariate methods. These methods incorporate out-of-bag estimation using Random forests (RF) and bootstrapping (100 iterations) using decision trees.ResultsUnivariate analysis identified rib dose to 1 cc < 4000 cGy (P = 0.01), chest wall dose to 30 cc < 1900 cGy (P = 0.035), rib Dmax < 5100 cGy (P = 0.05) and lung dose to 1000 cc < 70 cGy (P = 0.039) to be statistically significant thresholds for avoiding CWS. Subsequent multivariate analysis confirmed the importance of rib dose to 1 cc, chest wall dose to 30 cc, and rib Dmax. Using learning-curve experiments, the dataset proved to be self-consistent and provides a realistic model for CWS analysis.ConclusionsUsing machine learning algorithms in this first of its kind study, we identify robust features and cutoffs predictive for the rare clinical event of CWS. Additional data in planned subsequent multicenter studies will help increase the accuracy of multivariate analysis
The BTC40 Survey for Quasars at 4.8 < z < 6
The BTC40 Survey for high-redshift quasars is a multicolor search using
images obtained with the Big Throughput Camera (BTC) on the CTIO 4-m telescope
in V, I, and z filters to search for quasars at redshifts of 4.8 < z < 6. The
survey covers 40 sq. deg. in B, V, & I and 36 sq. deg. in z. Limiting
magnitudes (3 sigma) reach to V = 24.6, I = 22.9 and z = 22.9. We used the
(V-I) vs. (I-z) two-color diagram to select high-redshift quasar candidates
from the objects classified as point sources in the imaging data. Follow-up
spectroscopy with the AAT and CTIO 4-m telescopes of candidates having I < 21.5
has yielded two quasars with redshifts of z = 4.6 and z = 4.8 as well as four
emission line galaxies with z = 0.6. Fainter candidates have been identified
down to I = 22 for future spectroscopy on 8-m class telescopes.Comment: 27 pages, 8 figures; Accepted for publication in the Astronomical
Journa
Photometric Properties of 47 Clusters of Galaxies: I. The Butcher-Oemler Effect
We present gri CCD photometry of 44 Abell clusters and 4 cluster candidates.
Twenty one clusters in our sample have spectroscopic redshifts. Fitting a
relation between mean g, r and i magnitudes, and redshift for this subsample,
we have calculated photometric redshifts for the remainder with an estimated
accuracy of 0.03. The resulting redshift range for the sample is 0.03<z<0.38.
Color-magnitude diagrams are presented for the complete sample and used to
study evolution of the galaxy population in the cluster environment. Our
observations show a strong Butcher-Oemler effect (Butcher & Oemler 1978, 1984),
with an increase in the fraction of blue galaxies (f_B) with redshift that
seems more consistent with the steeper relation estimated by Rakos and
Schombert (1995) than with the original one by Butcher & Oemler (1984).
However, in the redshift range between ~ 0.08 and 0.2, where most of our
clusters lie, there is a wide range of f_B values, consistent with no redshift
evolution of the cluster galaxy population. A large range of f_B values is also
seen between ~ 0.2 and 0.3, when Smail at al. (1998) x-ray clusters are added
to our sample. The discrepancies between samples underscore the need for an
unbiased sample to understand how much of the Butcher-Oemler effect is due to
evolution, and how much to selection effects. We also tested the idea proposed
by Garilli et al. (1996) that there is a population of unusually red galaxies
which could be associated either with the field or clusters, but we find that
these objects are all near the limiting magnitude of the images (20.5<r<22) and
have colors that are consistent with those expected for stars or field galaxies
at z ~ 0.7.Comment: 35 pages including 8 figures, submitted to A
Decision Support Systems in Water Resources Planning and Management: Stakeholder Participation and the Sustainable Path to Science-Based Decision Making
- …