5,121 research outputs found
Constitutively Active Galpha q and Galpha 13 Trigger Apoptosis through Different Pathways
We investigated the effect of expression of constitutively active Galpha mutants on cell survival. Transfection of constitutively active Galphaq and Galpha13 in two different cell lines caused condensation of genomic DNA and nuclear fragmentation. Endonuclease cleavage of genomic DNA was followed by labeling the DNA fragments and subsequent flow cytometric analysis. The observed cellular phenotype was identical to the phenotype displayed by cells undergoing apoptosis. To distinguish between the apoptosis-inducing ability of the two Galpha-subunits, the signaling pathways involved in this cellular function were investigated. Whereas Galpha q induced apoptosis via a protein kinaseC-dependent pathway, Galpha13 caused programmed cell death through a pathway involving the activation of the small G-protein Rho. Both of the pathways leading to apoptosis were blocked by overexpression of bcl-2. In contrast to other apoptosis-inducing systems, expression of constitutively active Galphaq and Galpha13 triggered apoptosis in high serum as well as in defined medium
Conductance anomaly near the Lifshitz transition in strained bilayer graphene
Strain qualitatively changes the low-energy band structure of bilayer
graphene, leading to the appearance of a pair of low-energy Dirac cones near
each corner of the Brillouin zone, and a Lifshitz transition, (a saddle point
in the dispersion relation) at an energy proportional to the strain [M.
Mucha-Kruczynski, I.L. Aleiner, and V.I. Fal'ko, Phys. Rev. B 84, 041404
(2011)]. Here, we show that in the vicinity of the Lifshitz transition the
conductance of a ballistic n-p and n-p-n junction exhibits an anomaly: a
non-monotonic temperature and chemical potential dependence, with the size
depending on the crystallographic orientation of the principal axis of the
strain tensor. This effect is characteristic for junctions between regions of
different polarity (n-p and n-p-n junctions), while there is no anomaly in
junctions between regions of the same polarity (n-n' and n-n'-n junctions).Comment: 10 pages, 4 figures;
http://link.aps.org/doi/10.1103/PhysRevB.85.16542
Evolution of postglacial vegetation in the Western Laptev Sea region (Siberian Arctic)
On the basis of a detailed study of the pollen-spore spectra and a detailed radiocarbon chronology of a sediment core obtained from the western outer Laptev Sea shelf, the long-term and high-resolution changes of vegetation in the northwestern Laptev Sea region were reconstructed for the last 12.0 cal. ka. Three major phases in the development of paleoenvironments and vegetation on the surrounding hinterland and the exposed Laptev Sea shelf were recognized. The period between 12.0 and 10.3 cal. ka BP was characterized by predominance of grass-sedge and moss tundra. Rapid expansion of herbaceous tundra with dwarf birch and alder started at about 10.3 and lasted until 8.0 cal. ka. Pollen spectra from this time interval evidence the warmest and most favorable climate conditions. After 8.0 cal. ka mosses and lichen vegetation with scare herbs typical for the modern arctic tundra dominated.
German:
Auf der Grundlage detaillierter Pollen- und Sporenspektren aus einem 14C-datierten Sedimentkern vom äußeren Schelf des westlichen Laptewmeeres wurden die langfristigen und hochaufgelösten Veränderungen der Vegetation in den letzten 12 cal. ka in der nordwestlichen Laptewmeer-Region rekonstruiert. Es wurden drei Hauptphasen der Entwicklung von Umwelt und Vegetation im umgebenden Hinterland erkannt. Die Zeit zwischen 12,0 und 10,3 cal. ka BP war charakterisiert durch Riedgras- und Moos-Tundra. Rasche Ausdehnung der Kraut-Tundra mit Zwergbirke und Erle begann etwa um 10,3 cal. ka und dauerte bis 8,0 cal. ka. Pollenspektren aus diesem Zeitintervall beschreiben die wärmsten und besten Klimabedingungen. Nach 8,0 cal. ka dominierte die für die heutige arktische Tundra typische Moos- und Flechtenvegetation mit wenigen Kräutern
Strain-induced modifications of transport in gated graphene nanoribbons
We investigate the effects of homogeneous and inhomogeneous deformations and
edge disorder on the conductance of gated graphene nanoribbons. Under
increasing homogeneous strain the conductance of such devices initially
decreases before it acquires a resonance structure, and finally becomes
completely suppressed at larger strain. Edge disorder induces mode mixing in
the contact regions, which can restore the conductance to its ballistic value.
The valley-antisymmetric pseudo-magnetic field induced by inhomogeneous
deformations leads to the formation of additional resonance states, which
either originate from the coupling into Fabry-Perot states that extend through
the system, or from the formation of states that are localized near the
contacts, where the pseudo-magnetic field is largest. In particular, the n=0
pseudo-Landau level manifests itself via two groups of conductance resonances
close to the charge neutrality point.Comment: 10 pages, 6 figure
The Onset of Planet Formation in Brown Dwarf Disks
The onset of planet formation in protoplanetary disks is marked by the growth
and crystallization of sub-micron-sized dust grains accompanied by dust
settling toward the disk mid-plane. Here we present infrared spectra of disks
around brown dwarfs and brown dwarf candidates. We show that all three
processes occur in such cool disks in a way similar or identical to that in
disks around low- and intermediate-mass stars. These results indicate that the
onset of planet formation extends to disks around brown dwarfs, suggesting that
planet formation is a robust process occurring in most young circumstellar
disks.Comment: Published in Science 2005, vol 310, 834; 3 pages in final format, 4
figures + 8 pages Supporting Online Material. For final typeset, see
http://www.sciencemag.org/cgi/content/abstract/310/5749/834?eto
The Herschel/PACS view of disks around low-mass stars in Chamaleon-I
Circumstellar disks are expected to be the birthplaces of planets. The
potential for forming one or more planets of various masses is essentially
driven by the initial mass of the disks. We present and analyze Herschel/PACS
observations of disk-bearing M-type stars that belong to the young ~2 Myr old
Chamaleon-I star forming region. We used the radiative transfer code RADMC to
successfully model the SED of 17 M-type stars detected at PACS wavelengths. We
first discuss the relatively low detection rates of M5 and later spectral type
stars with respect to the PACS sensitivity, and argue their disks masses, or
flaring indices, are likely to be low. For M0 to M3 stars, we find a relatively
broad range of disk masses, scale heights, and flaring indices. Via a
parametrization of dust stratification, we can reproduce the peak fluxes of the
10 m emission feature observed with Spitzer/IRS, and find that disks
around M-type stars may display signs of dust sedimentation. The Herschel/PACS
observations of low-mass stars in Cha-I provide new constraints on their disk
properties, overall suggesting that disk parameters for early M-type stars are
comparable to those for more massive stars (e.g., comparable scale height and
flaring angles). However, regions of the disks emitting at about 100 m may
still be in the optically thick regime, preventing direct determination of disk
masses. Thus the modeled disk masses should be considered as lower limits.
Still, we are able to extend the wavelength coverage of SED models and start
characterizing effects such as dust sedimentation, an effort leading the way
towards ALMA observations of these low-mass stars
Investigation of vertical cavity surface emitting laser dynamics for neuromorphic photonic systems
We report an approach based upon vertical cavity surface emitting lasers (VCSELs) to reproduce optically different behaviors exhibited by biological neurons but on a much faster timescale. The technique proposed is based on the polarization switching and nonlinear dynamics induced in a single VCSEL under polarized optical injection. The particular attributes of VCSELs and the simple experimental configuration used in this work offer prospects of fast, reconfigurable processing elements with excellent fan-out and scaling potentials for use in future computational paradigms and artificial neural networks. © 2012 American Institute of Physics
High-resolultion reconstruction of Lena River discharge during the Late Holocene inferred from microalgae assemblages
On the basis of a detailed study of the diatom and aquatic palynomorph assemblages and a detailed radiocarbon chronology of sediment cores obtained from the south-eastern inner Laptev Sea shelf adjacent to the Lena Delta the spatial and temporal variability in the Lena River discharge during the last 6 cal. ka were reconstructed. It was shown that in the area adjacent to the Lena Delta variations in surface water salinities, reconstructed using freshwater diatoms as a proxy, were mainly caused by changes in the volume of the Lena River runoff through the major riverine channels Trofimovskaya, Bykovskaya and Tumatskaya. Several paleohydrological phases are recognized:
(i) establishment of modern-like conditions within the eastern Lena River Valley occurred from 6-4.2 cal. ka;
(ii) Lena River outflow increased in north-eastward direction via the Trofimovskaya or Bykovskaya channels from 4.2-2.7 cal. ka, coeval with a reduction of runoff toward the north via the Tumatskaya Channel;
(iii) generally stable hydrological conditions northward of the Tumatskaya Channel and variations in riverine discharge north-eastward of the Trofimovskaya and Bykovskaya channels prevail since 2.7 cal. ka.
Using indicator species of dinocysts as principle marine proxy, an influence of Atlantic water to the southeast inner Laptev Sea shelf could be inferred, possibly along the Eastern Lena paleovalley, brought into this area by winddriven reversed bottom currents.
Zusammenfassung:
Untersuchungen von Diatomeen- und aquatischen Palynomorphen-Vergesellschaftungen wurden an Radiokohlenstoff datierten Sedimentkernen aus der inneren südöstlichen Laptevsee nahe des Lenadeltas durchgeführt. Anhand dieser Daten wurde die zeitliche und räumliche Veränderlichkeit des Flusswasserausstromes der Lena für die letzten 6 ka (Kalenderjahre) rekonstruiert. Zeitliche Veränderungen in den Häufigkeiten von Süßwasserdiatomeen sind begründet durch Wechsel in der Menge des Lenaausflusses durch die drei großen Haupkanäle im Delta: Trofimovskaja, Bykovskja, sowie Tumatskaja. Darauf basierend konnten prinzipiell drei große paläohydrologische Phasen unterschieden werden:
(1) heutigen Verhältnissen vergleichbare Bedingungen wurden östlich des Lenadeltas zwischen 6 und 4.2 ka etabliert;
(2) Erhöhung des Flusswasseraustrags in nordöstliche Richtung über die Kanäle Trofimovskaja und/oder Bykovskaja zwischen 4.2 und 2.7 ka bei gleichzeitiger Reduzierung Richtung Norden via Tumatskaja;
(3) Ausbildung relativ stabiler Bedingungen nördlich des Deltas sowie Auftreten wechselhafter Flusswasserausträgen in östliche Richtung nach 2.7 ka.
Das Auftreten von marinen Dinocysten in den Sedimenkernen belegt den Einfluss von Wassermassen mit vermutlich atlantischem Ursprung. Es ist zu vermuten, dass diese durch windgetriebene Bodenströmungen entlang der alten versunkenen Flusstäler auf den östlichen inneren Schelf verfrachtet werden
Hindrance of ^{16}O+^{208}Pb fusion at extreme sub-barrier energies
We analyze the fusion data for O+Pb using coupled-channels
calculations. We include couplings to the low-lying surface excitations of the
projectile and target and study the effect of the (O,O)
one-neutron pickup. The hindrance of the fusion data that is observed at
energies far below the Coulomb barrier cannot be explained by a conventional
ion-ion potential and defining the fusion in terms of ingoing-wave boundary
conditions (IWBC). We show that the hindrance can be explained fairly well by
applying the M3Y double-folding potential which has been corrected with a
calibrated, repulsive term that simulates the effect of nuclear
incompressibility.
We show that the coupling to one-neutron transfer channels plays a crucial
role in improving the fit to the data. The best fit is achieved by increasing
the transfer strength by 25% relative to the strength that is required to
reproduce the one-neutron transfer data. The larger strength is not unrealistic
because the calculated inelastic plus transfer cross section is in good
agreement with the measured quasielastic cross section. We finally discuss the
problem of reproducing the fusion data at energies far above the Coulomb
barrier. Here we do not account for the data when we apply the IWBC but the
discrepancy is essentially eliminated by applying the M3Y+repulsion potential
and a weak, short-ranged imaginary potential.Comment: text and 8 fifure
Physical properties, starspot activity, orbital obliquity, and transmission spectrum of the Qatar-2 planetary system from multi-colour photometry
We present seventeen high-precision light curves of five transits of the
planet Qatar-2b, obtained from four defocussed 2m-class telescopes. Three of
the transits were observed simultaneously in the SDSS griz passbands using the
seven-beam GROND imager on the MPG/ESO 2.2-m telescope. A fourth was observed
simultaneously in Gunn grz using the CAHA 2.2-m telescope with BUSCA, and in r
using the Cassini 1.52-m telescope. Every light curve shows small anomalies due
to the passage of the planetary shadow over a cool spot on the surface of the
host star. We fit the light curves with the prism+gemc model to obtain the
photometric parameters of the system and the position, size and contrast of
each spot. We use these photometric parameters and published spectroscopic
measurements to obtain the physical properties of the system to high precision,
finding a larger radius and lower density for both star and planet than
previously thought. By tracking the change in position of one starspot between
two transit observations we measure the orbital obliquity of Qatar-2 b to be
4.3 \pm 4.5 degree, strongly indicating an alignment of the stellar spin with
the orbit of the planet. We calculate the rotation period and velocity of the
cool host star to be 11.4 \pm 0.5 d and 3.28 \pm 0.13 km/s at a colatitude of
74 degree. We assemble the planet's transmission spectrum over the 386-976 nm
wavelength range and search for variations of the measured radius of Qatar-2 b
as a function of wavelength. Our analysis highlights a possible H2/He Rayleigh
scattering in the blue.Comment: 20 pages, 14 figures, to appear in Monthly Notices of the Royal
Astronomical Societ
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