We employ first-principles density-functional calculations to study structural and topological electronic transitions in two-dimensional bismuth layers. Our calculations reveal that a free-standing ...hexagonal bismuthene phase (the most stable one in the absence of strain) should become thermodinamically unstable against transformation to a putative 'pentaoctite' phase (composed entirely of pentagonal and octagonal rings), under biaxial tensile strain. Moreover, our results indicate that 2D bismuth layers in the pentaoctite phase should undergo a topological electronic phase transition under either a biaxial or uniaxial tensile strain. More specifically, at its equilibrium lattice parameters the pentaoctite lattice is a topologically trivial system with a direct band gap. Strain-induced parity inversion of valence and conduction bands is obtained, and the pentaoctite structure undergoes a transition to a topological-insulator phase at a biaxial tensile strain of 5%. In the case of uniaxial tensile strains, the topological transition happens at a tensile strain of 6% along the armchair direction of the pentaoctite lattice, and at a 5% tensile strain in the zigzag direction. Our study indicates that 2D bismuth layers may prove themselves a rich platform to realize topologically non-trivial 2D materials upon strain engineering.
Quasar microlensing Schmidt, R. W.; Wambsganss, J.
General relativity and gravitation,
09/2010, Letnik:
42, Številka:
9
Journal Article
Recenzirano
Quasar microlensing deals with the effect of compact objects along the line of sight on the apparent brightness of the background quasars. Due to the relative motion between quasar, lenses and ...observer, the microlensing magnification changes with time which results in uncorrelated brightness variations in the various images of multiple quasar systems. The amplitudes of the signal can be more than a magnitude with time scales of weeks to months to years. The effect is due to the “granular” nature of the gravitational microlenses—stars or other compact objects in the stellar mass range. Quasar microlensing allows to study the quasar accretion disk with a resolution of tens of microarcseconds, hence quasar microlensing can be used to explore an astrophysical field that is hardly accessible by any other means. Quasar microlensing can also be used to study the lensing objects in a statistical sense, their nature (compact or smoothly distributed, normal stars or dark matter) as well as transverse velocities. Quasar microlensing light curves are now being obtained from monitoring programs across the electromagnetic spectrum from the radio through the infrared and optical range to the X-ray regime. Recently, spectroscopic microlensing was successfully applied, it provides quantitative comparisons with quasar/accretion disk models. There are now more than a handful of systems with several-year long light curves and significant microlensing signal, lending to detailed analysis. This review summarizes the current state of the art of quasar microlensing and shows that at this point in time, observational monitoring programs and complementary intense simulations provide a scenario where some of the early promises of quasar microlensing can be quantitatively applied. It has been shown, e.g., that smaller sources display more violent microlensing variability, first quantitative comparison with accretion disk models has been achieved, and quasar microlensing has been used to determine the fraction of dark matter in a lensing galaxy for the first time. This is the quantitative beginning. The future of quasar microlensing is bright.
Sea ice affects primary production in polar regions in multiple ways. It can dampen water column productivity by reducing light or nutrient supply, provide a habitat for ice algae and condition the ...marginal ice zone (MIZ) for phytoplankton blooms on its seasonal retreat. The relative importance of three different carbon sources (sea ice derived, sea ice conditioned, non-sea-ice associated) for the polar food web is not well understood, partly due to the lack of methods that enable their unambiguous distinction. Here we analysed two highly branched isoprenoid (HBI) biomarkers to trace sea-ice-derived and sea-ice-conditioned carbon in Antarctic krill (Euphausia superba) and relate their concentrations to the grazers' body reserves, growth and recruitment. During our sampling in January–February 2003, the proxy for sea ice diatoms (a di-unsaturated HBI termed IPSO25,δ13C = -12.5 ± 3.3 ‰) occurred in open waters of the western Scotia Sea, where seasonal ice retreat was slow. In suspended matter from surface waters, IPSO25 was present at a few stations close to the ice edge, but in krill the marker was widespread. Even at stations that had been ice-free for several weeks, IPSO25 was found in krill stomachs, suggesting that they gathered the ice-derived algae from below the upper mixed layer. Peak abundances of the proxy for MIZ diatoms (a tri-unsaturated HBI termed HBI III,δ13C = -42.2 ± 2.4 ‰) occurred in regions of fast sea ice retreat and persistent salinity-driven stratification in the eastern Scotia Sea. Krill sampled in the area defined by the ice edge bloom likewise contained high amounts of HBI III. As indicators for the grazer's performance we used the mass–length ratio, size of digestive gland and growth rate for krill, and recruitment for the biomass-dominant calanoid copepods Calanoides acutus and Calanus propinquus. These indices consistently point to blooms in the MIZ as an important feeding ground for pelagic grazers. Even though ice-conditioned blooms are of much shorter duration than blooms downstream of the permanently sea-ice-free South Georgia, they enabled fast growth and offspring development. Our study shows two rarely considered ways that pelagic grazers may benefit from sea ice: firstly, after their release from sea ice, suspended or sinking ice algae can supplement the grazers' diet if phytoplankton concentrations are low. Secondly, conditioning effects of seasonal sea ice can promote pelagic primary production and therefore food availability in spring and summer.
We present results from the analysis of cosmic microwave background (CMB), large-scale structure (galaxy redshift survey) and X-ray galaxy cluster (baryon fraction and X-ray luminosity function) ...data, assuming a geometrically flat cosmological model and allowing for tensor components and a non-negligible neutrino mass. From a combined analysis of all data, assuming three degenerate neutrino species, we measure a contribution of neutrinos to the energy density of the Universe, Ωνh2= 0.0059+0.0033−0.0027 (68 per cent confidence limits), with zero falling on the 99 per cent confidence limit. This corresponds to ∼4 per cent of the total mass density of the Universe and implies a species-summed neutrino mass , or mν∼ 0.2 eV per neutrino. We examine possible sources of systematic uncertainty in the results. Combining the CMB, large-scale structure and cluster baryon fraction data, we measure an amplitude of mass fluctuations on 8 h−1 Mpc scales of σ8= 0.74+0.12−0.07, which is consistent with measurements based on the X-ray luminosity function and other studies of the number density and evolution of galaxy clusters. This value is lower than that obtained when fixing a negligible neutrino mass (σ8= 0.86+0.08−0.07). The combination of CMB, large-scale structure and cluster baryon fraction data also leads to remarkably tight constraints on the Hubble constant, H0= 68.4+2.0−1.4 km s−1 Mpc−1, mean matter density, Ωm= 0.31 ± 0.02, and physical baryon density, Ωbh2= 0.024 ± 0.001, of the Universe.
We present Chandra observations of RX J1347.5−1145, the most X-ray-luminous cluster of galaxies known. We report the discovery of a region of relatively hot, bright X-ray emission, located ...approximately 20 arcsec to the south-east of the main X-ray peak at a position consistent with the region of enhanced Sunyaev–Zel'dovich effect reported recently by Komatsu et al. We suggest that this region contains shocked gas resulting from a recent subcluster merger event. Excluding the data for the south-east quadrant, the cluster appears relatively relaxed. The X-ray gas temperature rises from kT∼ 6 keV within the central 25 h50−1 kpc radius to a mean value of ∼16 keV between 0.1 and 0.5 h50−1 Mpc. The mass profile for the relaxed regions of the cluster, determined under the assumption of hydrostatic equilibrium, can be parametrized by a Navarro, Frenk and White model with a scale radius rs∼ 0.4 h50−1 Mpc and a concentration parameter c∼ 6. The best-fitting Chandra mass model is in good agreement with independent measurements from weak gravitational lensing studies. Strong lensing data for the central regions of the cluster can also be explained by the introduction of an additional mass clump centred on the second brightest galaxy. We argue that this galaxy is likely to have been the dominant galaxy of the recently merged subcluster.
Objective
Obesity has emerged as a prominent risk factor for multiple serious disease states, including a variety of cancers, and is increasingly recognized as a primary contributor to preventable ...cancer risk. However, few studies of leukemia have been conducted in animal models of obesity. This study sought to characterize the impact of obesity, diet, and sex in a murine model of acute promyelocytic leukemia (APL).
Methods
Male and female C57BL/6J.mCG+/PR mice, genetically predisposed to sporadic APL development, and C57BL/6J (wild type) mice were placed on either a high‐fat diet (HFD) or a low‐fat diet (LFD) for up to 500 days.
Results
Relative to LFD‐fed mice, HFD‐fed animals displayed increased disease penetrance and shortened disease latency as indicated by accelerated disease onset. In addition, a diet‐responsive sex difference in APL penetrance and incidence was identified, with LFD‐fed male animals displaying increased penetrance and shortened latency relative to female counterparts. In contrast, both HFD‐fed male and female mice displayed 100% disease penetrance and insignificant differences in disease latency, indicating that the sexual dimorphism was reduced through HFD feeding.
Conclusions
Obesity and obesogenic diet promote the development of APL in vivo, reducing sexual dimorphisms in disease latency and penetrance.
Accurate measurements of the physical characteristics of a large number of exoplanets are useful to strongly constrain theoretical models of planet formation and evolution, which lead to the large ...variety of exoplanets and planetary-system configurations that have been observed. We present a study of the planetary systems WASP-45 and WASP-46, both composed of a main-sequence star and a close-in hot Jupiter, based on 29 new high-quality light curves of transits events. In particular, one transit of WASP-45 b and four of WASP-46 b were simultaneously observed in four optical filters, while one transit of WASP-46 b was observed with the NTT obtaining a precision of 0.30 mmag with a cadence of roughly 3 min. We also obtained five new spectra of WASP-45 with the FEROS spectrograph. We improved by a factor of 4 the measurement of the radius of the planet WASP-45 b, and found that WASP-46 b is slightly less massive and smaller than previously reported. Both planets now have a more accurate measurement of the density (0.959 ± 0.077 ρJup instead of 0.64 ± 0.30 ρJup for WASP-45 b, and 1.103 ± 0.052 ρJup instead of 0.94 ± 0.11 ρJup for WASP-46 b). We tentatively detected radius variations with wavelength for both planets, in particular in the case of WASP-45 b we found a slightly larger absorption in the redder bands than in the bluer ones. No hints for the presence of an additional planetary companion in the two systems were found either from the photometric or radial velocity measurements.
As described in sect; 2.3, each HSsub 4 unit is controlled by a single control computer running Linux with a special kernel that is capable of real-time operations. In addition, a node-computer is ...responsible for weather sensing and synchronizing the time to the GPS time. A large suite of software is running on the control and node computers, responsible for the instrument control. We broadly classify the control software components to "low-level", meaning direct control of instruments, and "high-level", referring to more general observatory control, usually connected to the "low-level" software. The control of the telescope mount is performed through a Xenomai-based (real-time) character device driver, called the scope module. This module depends on the basic built-in printer port control modules of Linux. When the scope kernel module is loaded, a number of initial parameters are supplied, such as the choice of the hemisphere (to determine the direction of tracking), the resolution of the axes, settings for ramping up the motors to maximal slewing speed, and the level of verbosity.
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