211 research outputs found
Fast high-efficiency integrated waveguide photodetectors using novel hybrid vertical/butt coupling geometry
We report a novel coupling geometry for integrated waveguide photodetectors−a hybrid vertical coupling/butt coupling scheme that allows the integration of fast, efficient, photodetectors with conventional double heterostructure waveguides. It can be employed to yield a planar, or pseudo-planar, surface that supports further levels of integration. The approach is demonstrated with a 25-µm-long p-i-n detector integrated with an InP/InGaAsP/InP waveguide, which displays a high (~90%) efficiency and large (~15 GHz) bandwidth. This is the fastest high-efficiency integrated waveguide photodetector reported to date
Kinematic modeling of disk galaxies III. The warped "Spindle" NGC 2685
This is the third of a series of papers in which the structure and kinematics
of disk galaxies is studied. Employing direct tilted-ring fits to the data cube
as introduced in Paper I, we perform an analysis of the "Spindle" galaxy NGC
2685, previously regarded as two-ringed polar ring galaxy.
Deep HI and optical (i'-band) observations are presented. The HI observations
strongly suggest that the gaseous structure of NGC 2685 does not consist of two
separate mutually inclined regions, but forms a coherent, extremely warped
disk, the appearance of two rings being due to projection effects. By comparing
the HI total-intensity maps with the optical image we demonstrate that at large
radii a faint stellar disk is well aligned with the outer HI disk. The shape of
the dust-lanes obscuring the NE part of the inner stellar body indicates that
also at smaller radii NGC 2685 possesses a disk containing gas, dust, and stars
in which the various constituents are aligned. At smaller radii, this disk is
kinematically decoupled from the central stellar body. Hence, in the region of
the bright, central stellar body, NGC 2685 appears to consist of two disks that
share a common centre, but have different orientation: a bright stellar
lenticular body apparently devoid of dust and gas, and a heavily warped
low-surface brightness disk containing stars, gas and dust. The
low-surface-brightness disk changes its orientation gradually and at large
radii assumes the orientation of the central stellar S0 disk. Since, according
to our analysis, the intrinsic orientation of the low-surface-brightness disk
changes through 70 degrees, the gaseous disk is coherent, and is at no radius
orientated perpendicularly with respect to the central stellar body, NGC 2685
is likely not a classical polar-ring galaxy.Comment: 26 pages, 14 figures, 6 tables, accepted for publication in Astronomy
& Astrophysics. For a high-resolution version see
http://www.astron.nl/~jozsa/publications
The star formation rate history in the FORS Deep and GOODS South Fields
We measure the star formation rate (SFR) as a function of redshift z up to z
\~4.5, based on B, I and (I+B) selected galaxy catalogues from the FORS Deep
Field (FDF) and the K-selected catalogue from the GOODS-South field. Distances
are computed from spectroscopically calibrated photometric redshifts accurate
to (Delta_z / (z_spec+1)) ~0.03 for the FDF and ~0.056 for the GOODS-South
field. The SFRs are derived from the luminosities at 1500 Angstroem. We find
that the total SFR estimates derived from B, I and I+B catalogues agree very
well (\lsim 0.1 dex) while the SFR from the K catalogue is lower by ~0.2 dex.
We show that the latter is solely due to the lower star-forming activity of
K-selected intermediate and low luminosity (L<L_*) galaxies. The SFR of bright
(L>L_*) galaxies is independent of the selection band, i.e. the same for B, I,
(I+B), and K-selected galaxy samples. At all redshifts, luminous galaxies
(L>L_*) contribute only ~1/3 to the total SFR. There is no evidence for
significant cosmic variance between the SFRs in the FDF and GOODs-South field,
~0.1 dex, consistent with theoretical expectations. The SFRs derived here are
in excellent agreement with previous measurements provided we assume the same
faint-end slope of the luminosity function as previous works (alpha ~ -1.6).
However, our deep FDF data indicate a shallower slope of alpha=-1.07, implying
a SFR lower by ~0.3 dex. We find the SFR to be roughly constant up to z ~4 and
then to decline slowly beyond, if dust extinctions are assumed to be constant
with redshift.Comment: 6 pages, 2 figures, Accepted for publication in ApJ
The Cluster Mass Function from Weak Gravitational Lensing
We present the first measurement of the mass function of galaxy clusters
based directly on cluster masses derived from observations of weak
gravitational lensing. To investigate the degree of sample incompleteness
resulting from the X-ray based selection of the target clusters, we use a
sample of 50 clusters with weak lensing mass measurements to empirically
determine the relation between lensing mass and X-ray luminosity and the
scatter about this relation. We use a complete, volume-limited sub-sample of 35
X-ray luminous clusters of galaxies at 0.15<z<0.3 to constrain the abundance of
very massive (M >~ 10^15/h M_sun) clusters. From this, we constrain
sigma_8(Omega_m/0.3)^{0.37} = 0.67^{+0.04}_{-0.05} (68% confidence limits),
agreeing well with constraints from the 3-year WMAP CMB measurements and
estimates of cluster abundances based on X-ray observations, but somewhat lower
than constraints from ``cosmic shear'' weak lensing measurements in random
fields.Comment: 10 pages, 3 figures. Accepted for publication in Ap
First Results On Shear-Selected Clusters From the Deep Lens Survey: Optical Imaging, Spectroscopy, and X-ray Followup
We present the first sample of galaxy clusters selected on the basis of their
weak gravitational lensing shear. The shear induced by a cluster is a function
of its mass profile and its redshift relative to the background galaxies being
sheared; in contrast to more traditional methods of selecting clusters, shear
selection does not depend on the cluster's star formation history, baryon
content, or dynamical state. Because mass is the property of clusters which
provides constraints on cosmological parameters, the dependence on these other
parameters could induce potentially important biases in traditionally-selected
samples. Comparison of a shear-selected sample with optically and X-ray
selected samples is therefore of great importance. Here we present the first
step toward a new shear-selected sample: the selection of cluster candidates
from the first 8.6 deg of the 20 deg Deep Lens Survey (DLS), and
tabulation of their basic properties such as redshifts and optical and X-ray
counterparts.Comment: v2 as published in ApJ, 45 pages, 18 figures. Biggest change from v1
is addition of a figure showing the 1-point distribution of pixels in the
mass maps and control "mass maps" using the non-tangential component of
shear, demonstrating that all candidate peaks are higher than any peak seen
in the control map
Klotho Lacks a Vitamin D Independent Physiological Role in Glucose Homeostasis, Bone Turnover, and Steady-State PTH Secretion In Vivo
Apart from its function as co-receptor for fibroblast growth factor-23 (FGF23), Klotho is thought to regulate insulin signaling, intracellular oxidative stress, and parathyroid hormone (PTH) secretion in an FGF23 independent fashion. Here, we crossed Klotho deficient (Kl−/−) mice with vitamin D receptor (VDR) mutant mice to examine further vitamin D independent functions of Klotho. All mice were fed a rescue diet enriched with calcium, phosphorus, and lactose to prevent hyperparathyroidism in VDR mutants, and were killed at 4 weeks of age after double fluorochrome labeling. Kl−/− mice displayed hypercalcemia, hyperphosphatemia, dwarfism, organ atrophy, azotemia, pulmonary emphysema, and osteomalacia. In addition, glucose and insulin tolerance tests revealed hypoglycemia and profoundly increased peripheral insulin sensitivity in Kl−/− mice. Compound mutants were normocalcemic and normophosphatemic, did not show premature aging or organ atrophy, and were phenocopies of VDR mutant mice in terms of body weight, bone mineral density, bone metabolism, serum calcium, serum phosphate, serum PTH, gene expression in parathyroid glands, as well as urinary calcium and phosphate excretion. Furthermore, ablation of vitamin D signaling in double mutants completely normalized glucose and insulin tolerance, indicating that Klotho has no vitamin D independent effects on insulin signaling. Histomorphometry of pancreas islets showed similar beta cell volume per body weight in all groups of animals. In conclusion, our findings cast doubt on a physiologically relevant vitamin D and Fgf23 independent function of Klotho in the regulation of glucose metabolism, bone turnover, and steady-state PTH secretion in vivo
Der Umzug der Menschheit: Die transformative Kraft der Städte
Die Wucht der derzeitigen Urbanisierungsdynamik und ihre Auswirkungen sind so groß, dass sich weltweit Städte, Stadtgesellschaften, Regierungen und Internationale Organisationen diesem Trend stellen müssen. Ein „Weiter so wie bisher“, würde ohne gestaltende Urbanisierungspolitik zu einer nicht-nachhaltigen Welt-Städte-Gesellschaft führen. Nur wenn Städte und Stadtgesellschaften ausreichend handlungsfähig werden, können sie ihre Kraft für eine nachhaltige Entwicklung entfalten: In den Städten wird sich entscheiden, ob die Große Transformation zur Nachhaltigkeit gelingt. In diesem Buch werden die Erfolgsbedingungen dafür diskutiert
Hen 2-104: A close-up look at the Southern Crab
The kinematics, shaping, density distribution, expansion distance, and
ionized mass of the nebula Hen 2-104, and the nature of its symbiotic Mira are
investigated. A combination of multi-epoch HST images and VLT integral field
high-resolution spectroscopy is used to study the nebular dynamics both along
the line of sight and in the plane of the sky. These observations allow us to
construct a 3-D spatio-kinematical model of the nebula, which together with the
measurement of its apparent expansion in the plane of the sky over a period of
4 years, provides the expansion parallax for the nebula. The integral field
data featuring the [S{\sc ii}] 671.7,673.1 emission line
doublet provide us with a density map of the inner lobes of the nebula, which
together with the distance estimation allow us to estimate its ionized mass. We
find densities ranging from n=500 to 1000 cm in the inner lobes and
from 300 to 500cm in the outer lobes. We determine an expansion parallax
distance of 3.30.9 kpc to Hen 2-104, implying an unexpectedly large
ionized mass for the nebula of the order of one tenth of a solar mass.Comment: 11 pages, 12 figures, accepted for publication in A&
Humanity on the move: Unlocking the transformative power of cities
The momentum of urbanization and its impacts are so massive that we must face up to this trend. In view of the existing cognitive, technical, economic and institutional path dependencies, a policy of business as usual – i.e. an unstructured, quasi-automatic urbanization – would lead to a non-sustainable ‘world cities society’. Only if cities and urban societies are sufficiently empowered can they make use of the opportunities for sustainability and successfully follow the urban transformation pathways. The success or failure of the Great Transformation will be decided in the cities. The WBGU discusses the relevant conditions for the success of this transformation in this report
Impact of antimicrobial drug restrictions on doctors' behaviors
Background/aim: Broad-spectrum antibiotics have become available for use only with the approval of infectious disease specialists (IDSs) since 2003 in Turkey. This study aimed to analyze the tendencies of doctors who are not disease specialists (non-IDSs) towards the restriction of antibiotics.Materials and methods: A questionnaire form was prepared, which included a total of 22 questions about the impact of antibiotic restriction (AR) policy, the role of IDSs in the restriction, and the perception of this change in antibiotic consumption. The questionnaire was completed by each participating physician.Results: A total of 1906 specialists from 20 cities in Turkey participated in the study. Of those who participated, 1271 (67.5%) had 5 years of occupational experience in their branch expressed that they followed the antibiotic guidelines more strictly than the JSs (P < 0.05) and 755 of physicians (88%) and 720 of surgeons (84.6%) thought that the AR policy was necessary and useful (P < 0.05).Conclusion: This study indicated that the AR policy was supported by most of the specialists. Physicians supported this restriction policy more so than surgeons did
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