153 research outputs found
The quantum Casimir operators of \Uq and their eigenvalues
We show that the quantum Casimir operators of the quantum linear group
constructed in early work of Bracken, Gould and Zhang together with one extra
central element generate the entire center of \Uq. As a by product of the
proof, we obtain intriguing new formulae for eigenvalues of these quantum
Casimir operators, which are expressed in terms of the characters of a class of
finite dimensional irreducible representations of the classical general linear
algebra.Comment: 10 page
Enabling organizational change – leadership, commitment to change and the mediating role of change readiness
There has been little empirical analysis on the complex relationship between leadership, change readiness and commitment to change in the context of Asian countries. In this paper, we propose a research model to analyze the interrelationship between leadership, change readiness and commitment to change using the partial least square technique. Results of the study suggest that leadership positively and significantly affect change readiness but not commitment to change. Consequently, change readiness is found to significantly affect commitment to change. In other words, change readiness is found to mediate the relationship between transformational leadership and commitment to change. This may suggest that the influence of leadership is a sequential process affecting change readiness, and in turn, the commitment to change as opposed to the conventional belief that it affects both change readiness and commitment to change simultaneously. The implication of the study is further discussed
Optimal dual martingales, their analysis and application to new algorithms for Bermudan products
In this paper we introduce and study the concept of optimal and surely optimal dual martingales in the context of dual valuation of Bermudan options. We provide a theorem which give conditions for a martingale to be surely optimal, and a stability theorem concerning martingales which are near to be surely optimal in a sense. Guided by these theorems we develop a regression based backward construction of such a martingale in a Wiener environment. In turn this martingale may be utilized for computing upper bounds by non-nested Monte Carlo. As a by-product, the algorithm also provides approximations to continuation values of the product, which in turn determine a stopping policy. Hence, we obtain lower bounds at the same time. The proposed algorithm is pure dual in the sense that it doesn't require an (input) approximation to the Snell envelope, is quite easy to implement, and in a numerical study we show that, regarding the computed upper bounds, it is comparable with the method of Belomestny, et. al. (2009)
Crab in Amber Reveals an Early Colonization of Nonmarine Environments During the Cretaceous
Amber fossils provide snapshots of the anatomy, biology, and ecology of extinct organisms that are otherwise inaccessible. The best-known fossils in amber are terrestrial arthropods—principally insects—whereas aquatic organisms are rarely represented. Here, we present the first record of true crabs (Brachyura) in amber—from the Cretaceous of Myanmar [~100 to 99 million years (Ma)]. The new fossil preserves large compound eyes, delicate mouthparts, and even gills. This modern-looking crab is nested within crown Eubrachyura, or “higher” true crabs, which includes the majority of brachyuran species living today. The fossil appears to have been trapped in a brackish or freshwater setting near a coastal to fluvio-estuarine environment, bridging the gap between the predicted molecular divergence of nonmarine crabs (~130 Ma) and their younger fossil record (latest Cretaceous and Paleogene, ~75 to 50 Ma) while providing a reliable calibration point for molecular divergence time estimates for higher crown eubrachyurans
Terahertz parametric amplification as a reporter of exciton condensate dynamics
Condensates are a hallmark of emergence in quantum materials with
superconductors and charge density wave as prominent examples. An excitonic
insulator (EI) is an intriguing addition to this library, exhibiting
spontaneous condensation of electron-hole pairs. However, condensate
observables can be obscured through parasitic coupling to the lattice.
Time-resolved terahertz (THz) spectroscopy can disentangle such obscurants
through measurement of the quantum dynamics. We target , a
putative room-temperature EI where electron-lattice coupling dominates the
structural transition (=326 K), hindering identification of excitonic
correlations. A pronounced increase in the THz reflectivity manifests following
photoexcitation and exhibits a BEC-like temperature dependence. This occurs
well below the , suggesting a novel approach to monitor exciton
condensate dynamics. Nonetheless, dynamic condensate-phonon coupling remains as
evidenced by peaks in the enhanced reflectivity spectrum at select
infrared-active phonon frequencies. This indicates that parametric reflectivity
enhancement arises from phonon squeezing, validated using Fresnel-Floquet
theory and density functional calculations. Our results highlight that coherent
dynamics can drive parametric stimulated emission with concomitant
possibilities, including entangled THz photon generation.Comment: 51 pages, 14 figures, 1 tabl
ASASSN-18am/SN 2018gk : An overluminous Type IIb supernova from a massive progenitor
ASASSN-18am/SN 2018gk is a newly discovered member of the rare group of
luminous, hydrogen-rich supernovae (SNe) with a peak absolute magnitude of mag that is in between normal core-collapse SNe and superluminous
SNe. These SNe show no prominent spectroscopic signatures of ejecta interacting
with circumstellar material (CSM), and their powering mechanism is debated.
ASASSN-18am declines extremely rapidly for a Type II SN, with a
photospheric-phase decline rate of . Owing to the
weakening of HI and the appearance of HeI in its later phases, ASASSN-18am is
spectroscopically a Type IIb SN with a partially stripped envelope. However,
its photometric and spectroscopic evolution show significant differences from
typical SNe IIb. Using a radiative diffusion model, we find that the light
curve requires a high synthesised mass and ejecta with high kinetic energy erg. Introducing a magnetar central engine still requires
and erg. The high
mass is consistent with strong iron-group nebular lines in its
spectra, which are also similar to several SNe Ic-BL with high
yields. The earliest spectrum shows "flash ionisation" features, from which we
estimate a mass-loss rate of . This wind density is too low to power the luminous light
curve by ejecta-CSM interaction. We measure expansion velocities as high as km/s for , which is remarkably high compared to other SNe
II. We estimate an oxygen core mass of using the [OI]
luminosity measured from a nebular-phase spectrum, implying a progenitor with a
zero-age main sequence mass of
MTHFR C677T and MTR A2756G polymorphisms and the homocysteine lowering efficacy of different doses of folic acid in hypertensive Chinese adults
<p>Abstract</p> <p>Background</p> <p>This study aimed to investigate if the homocysteine-lowering efficacy of two commonly used physiological doses (0.4 mg/d and 0.8 mg/d) of folic acid (FA) can be modified by individual methylenetetrahydrofolate reductase (MTHFR) C677T and/or methionine synthase (MTR) A2756G polymorphisms in hypertensive Chinese adults.</p> <p>Methods</p> <p>A total of 480 subjects with mild or moderate essential hypertension were randomly assigned to three treatment groups: 1) enalapril only (10 mg, control group); 2) enalapril-FA tablet [10:0.4 mg (10 mg enalapril combined with 0.4 mg of FA), low FA group]; and 3) enalapril-FA tablet (10:0.8 mg, high FA group), once daily for 8 weeks.</p> <p>Results</p> <p>After 4 or 8 weeks of treatment, homocysteine concentrations were reduced across all genotypes and FA dosage groups, except in subjects with MTR 2756AG /GG genotype in the low FA group at week 4. However, compared to subjects with MTHFR 677CC genotype, homocysteine concentrations remained higher in subjects with CT or TT genotype in the low FA group (<it>P </it>< 0.05 for either of these genotypes) and TT genotype in the high FA group (<it>P </it>< 0.05). Furthermore, subjects with TT genotype showed a greater homocysteine-lowering response than did subjects with CC genotype in the high FA group (mean percent reduction of homocysteine at week 8: CC 10.8% vs. TT: 22.0%, <it>P </it>= 0.005), but not in the low FA group (CC 9.9% vs. TT 11.2%, <it>P </it>= 0.989).</p> <p>Conclusions</p> <p>This study demonstrated that MTHFR C677T polymorphism can not only affect homocysteine concentration at baseline and post-FA treatment, but also can modify therapeutic responses to various dosages of FA supplementation.</p
SN 2017gmr: An Energetic Type II-P Supernova with Asymmetries
We present high-cadence UV, optical, and near-infrared data on the luminous Type II-P supernova SN2017gmr from hours after discovery through the first 180 days. SN2017gmr does not show signs of narrow, high-ionization emission lines in the early optical spectra, yet the optical light-curve evolution suggests that an extra energy source from circumstellar medium (CSM) interaction must be present for at least 2 days after explosion. Modeling of the early light curve indicates a ∼500 Re progenitor radius, consistent with a rather compact red supergiant, and latetime luminosities indicate that up to 0.130±0.026 Me of 56Ni are present, if the light curve is solely powered by radioactive decay, although the 56Ni mass may be lower if CSM interaction contributes to the post-plateau luminosity. Prominent multipeaked emission lines of Hα and [O I] emerge after day 154, as a result of either an asymmetric explosion or asymmetries in the CSM. The lack of narrow lines within the first 2 days of explosion in the likely presence of CSM interaction may be an example of close, dense, asymmetric CSM that is quickly enveloped by the spherical supernova ejecta
Automated Force Volume Image Processing for Biological Samples
Atomic force microscopy (AFM) has now become a powerful technique for investigating on a molecular level, surface forces, nanomechanical properties of deformable particles, biomolecular interactions, kinetics, and dynamic processes. This paper specifically focuses on the analysis of AFM force curves collected on biological systems, in particular, bacteria. The goal is to provide fully automated tools to achieve theoretical interpretation of force curves on the basis of adequate, available physical models. In this respect, we propose two algorithms, one for the processing of approach force curves and another for the quantitative analysis of retraction force curves. In the former, electrostatic interactions prior to contact between AFM probe and bacterium are accounted for and mechanical interactions operating after contact are described in terms of Hertz-Hooke formalism. Retraction force curves are analyzed on the basis of the Freely Jointed Chain model. For both algorithms, the quantitative reconstruction of force curves is based on the robust detection of critical points (jumps, changes of slope or changes of curvature) which mark the transitions between the various relevant interactions taking place between the AFM tip and the studied sample during approach and retraction. Once the key regions of separation distance and indentation are detected, the physical parameters describing the relevant interactions operating in these regions are extracted making use of regression procedure for fitting experiments to theory. The flexibility, accuracy and strength of the algorithms are illustrated with the processing of two force-volume images, which collect a large set of approach and retraction curves measured on a single biological surface. For each force-volume image, several maps are generated, representing the spatial distribution of the searched physical parameters as estimated for each pixel of the force-volume image
FAK-ERK activation in cell/matrix adhesion induced by the loss of apolipoprotein E stimulates the malignant progression of ovarian cancer
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