825 research outputs found
New first integral for twisting type-N vacuum gravitational fields with two non-commuting Killing vectors
A new first integral for the equations corresponding to twisting type-N
vacuum gravitational fields with two non-commuting Killing vectors is
introduced. A new reduction of the problem to a complex second-order ordinary
differential equation is given. Alternatively, the mentioned first integral can
be used in order to provide a first integral of the second-order complex
equation introduced in a previous treatment of the problem.Comment: 7 pages, LaTeX, uses ioplppt.sty and iopl12.sty; to be published in
Class. Quantum Gra
Evidence that phosphorylation of the alpha-subunit of eIF2 does not essentially inhibit mRNA translation in wheat germ cell-free system.
A mechanism based on reversible phosphorylation of the α-subunit of eukaryotic initiation factor 2 (eIF2α) has been confirmed as an important regulatory pathway for inhibition of protein synthesis in mammalian and yeast cells, while plants constitute the significant exception. We studied the induction of TaeIF2α phosphorylation in germinated wheat (Triticum aestivum) embryos subjected to different adverse conditions. Data confirmed that formation of TaeIF2(αP) was not a general response, as no phosphorylation was observed under salt, oxidative or heat stress. Nevertheless, treatment by salicylic acid, UV-light, cold shock and histidinol did induce phosphorylation of TaeIF2α of wheat, as has been established previously for AteIF2α in Arabidopsis (Arabidopsis thaliana). Influence of TaeIF2α phosphorylation on translation of reporter mRNA with different 5âČ-untranslated regions (5âČUTRs) was studied in wheat germ cell-free system (WG-CFS), in which TaeIF2α was first phosphorylated either by heterologous recombinant human protein kinase, HsPKR (activated by double-stranded (ds)RNA), or by endogenous protein kinase TaGCN2 (activated by histidinol). Pre-treatment of WG-CFS with HsPKR in the presence of dsRNA or with histidinol resulted in intense phosphorylation of TaeIF2α; however, the translation levels of all tested mRNAs decreased by only 10â15% and remained relatively high. In addition, factor OceIF2 from rabbit (Oryctolagus cuniculus) bound GDP much more strongly than the homologous factor TaeIF2 from wheat germ. Furthermore, factor OceIF2B was able to stimulate guanine nucleotides exchange (GDPâGTP) on OceIF2 but had no effect on the similar exchange on TaeIF2. These results suggest that the mechanism of stress response via eIF2α phosphorylation is not identical in all eukaryotes and further research is required to find and study in detail new plant-specific mechanisms that may inhibit overall protein synthesis in plants under stress
Association between loss of Y chromosome and poor prognosis in male head and neck squamous cell carcinoma
BACKGROUND: Head and neck squamous cell carcinoma (HNSCC) is more prevalent in men than women and this disparity cannot be fully explained by known risk factors. Recent studies have shown that loss of Y chromosome (LoY) confers an increased risk of solid cancer and reduces life expectancy in men. METHODS: Using publicly available data from The Cancer Genome Atlas, we investigated the prevalence of LoY and its association with clinicopathological features in male HNSCC. RESULTS: LoY was detectable in around 25% of male HNSCC. Men with human papillomavirus-negative tumors exhibiting LoY experienced significantly worse overall survival than those with no LoY. Moreover, LoY tumors exhibited overexpression of genes involved in redox processes, including genes previously implicated in resistance to both radiotherapy and cisplatin-based chemotherapeutics. CONCLUSION: LoY may be an indicator of poor prognosis in male HNSCC that is linked to the overexpression of genes associated with resistance to standard care therapies
Thin Domain Walls in Lyra Geometry
This paper studies thin domain walls within the frame work of Lyra Geometry.
We have considered two models. First one is the thin domain wall with
negligible pressures perpendicular and transverse direction to the wall and
secondly, we take a particular type of thin domain wall where the pressure in
the perpendicular direction is negligible but transverse pressures are existed.
It is shown that the thin domain walls have no particle horizon and the
gravitational force due to them is attractive.Comment: 8 pages, typos are corrected, published Astrophysics and Space
Sciences 305, 337 (2006
Collision Chronology Along the Ä°zmirâAnkaraâErzincan Suture Zone: Insights From the Sarıcakaya Basin, Western Anatolia
An edited version of this paper was published by AGU. Copyright 2019 American Geophysical Union.Debate persists concerning the timing and geodynamics of intercontinental collision, style of syncollisional deformation, and development of topography and foldâandâthrust belts along the >1,700âkmâlong Ä°zmirâAnkaraâErzincan suture zone (Ä°AESZ) in Turkey. Resolving this debate is a necessary precursor to evaluating the integrity of convergent margin models and kinematic, topographic, and biogeographic reconstructions of the Mediterranean domain. Geodynamic models argue either for a synchronous or diachronous collision during either the Late Cretaceous and/or Eocene, followed by Eocene slab breakoff and postcollisional magmatism.
We investigate the collision chronology in western Anatolia as recorded in the sedimentary archives of the 90âkmâlong Sarıcakaya Basin perched at shallow structural levels along the Ä°AESZ. Based on new zircon UâPb geochronology and depositional environment and sedimentary provenance results, we demonstrate that the Sarıcakaya Basin is an Eocene sedimentary basin with sediment sourced from both the Ä°AESZ and SöÄĂŒt Thrust fault to the south and north, respectively, and formed primarily by flexural loading from northâsouth shortening along the syncollisional SöÄĂŒt Thrust. Our results refine the timing of collision between the Anatolides and Pontide terranes in western Anatolia to MaastrichtianâMiddle Paleocene and Early Eocene crustal shortening and basin formation. Furthermore, we demonstrate contemporaneous collision, deformation, and magmatism across the Ä°AESZ, supporting synchronous collision models. We show that regional postcollisional magmatism can be explained by renewed underthrusting instead of slab breakoff. This new Ä°AESZ chronology provides additional constraints for kinematic, geodynamic, and biogeographic reconstructions of the Mediterranean domain
The wheat SnRK1α family and its contribution to Fusarium toxin tolerance.
Deoxynivalenol (DON) is a mycotoxin produced by phytopathogenic Fusarium fungi in cereal grain and plays a role as a disease virulence factor. TaFROG (Triticum aestivum Fusarium Resistance Orphan Gene) enhances wheat resistance to DON and it interacts with a sucrose non-fermenting-1 (SNF1)-related protein kinase 1 catalytic subunit α (SnRK1α). This protein kinase family is central integrator of stress and energy signaling, regulating plant metabolism and growth. Little is known regarding the role of SnRK1α in the biotic stress response, especially in wheat. In this study, 15 wheat (Triticum aestivum) SnRK1α genes (TaSnRK1αs) belonging to four homoeologous groups were identified in the wheat genome. TaSnRK1αs are expressed ubiquitously in all organs and developmental stages apart from two members predominantly detected in grain. While DON treatment had either no effect or downregulated the transcription of TaSnRK1αs, it increased both the kinase activity associated with SnRK1α and the level of active (phosphorylated) SnRK1α. Down-regulation of two TaSnRK1αs homoeolog groups using virus induced gene silencing (VIGS) increased the DON-induced damage of wheat spikelets. Thus, we demonstrate that TaSnRK1αs contribute positively to wheat tolerance of DON and conclude that this gene family may provide useful tools for the improvement of crop biotic stress resistance
The Importance of Recruitment and Retention in Heliophysics: It\u27s Not Just a Pipeline Problem
A major obstacle in cultivating a robust Heliophysics (and broader scientific) community is the lack of diversity throughout science, technology, engineering, and mathematics (STEM) fields. For many years, this has been understood as a âleaky pipelineâ analogy, in which predominately minority students initially interested in STEM gradually fall (or are pushed) out of the field on their way to a scientific research position. However, this ignores critical structural and policy issues which drive even later career Ph.D.s out of a career in Heliophysics. We identify here several systemic problems that inhibit many from participating fully in the Heliophysics community, including soft money pressure, lack of accessibility and equity, power imbalances, lack of accountability, friction in collaboration, and difficulties in forming mentorship bonds. We present several recommendations to empower research-supporting organizations to help create a culture of inclusion, openness, and innovative science
Spin Foam Models of Riemannian Quantum Gravity
Using numerical calculations, we compare three versions of the Barrett-Crane
model of 4-dimensional Riemannian quantum gravity. In the version with face and
edge amplitudes as described by De Pietri, Freidel, Krasnov, and Rovelli, we
show the partition function diverges very rapidly for many triangulated
4-manifolds. In the version with modified face and edge amplitudes due to Perez
and Rovelli, we show the partition function converges so rapidly that the sum
is dominated by spin foams where all the spins labelling faces are zero except
for small, widely separated islands of higher spin. We also describe a new
version which appears to have a convergent partition function without drastic
spin-zero dominance. Finally, after a general discussion of how to extract
physics from spin foam models, we discuss the implications of convergence or
divergence of the partition function for other aspects of a spin foam model.Comment: 23 pages LaTeX; this version to appear in Classical and Quantum
Gravit
Bianchi Type-II String Cosmological Models in Normal Gauge for Lyra's Manifold with Constant Deceleration Parameter
The present study deals with a spatially homogeneous and anisotropic
Bianchi-II cosmological models representing massive strings in normal gauge for
Lyra's manifold by applying the variation law for generalized Hubble's
parameter that yields a constant value of deceleration parameter. The variation
law for Hubble's parameter generates two types of solutions for the average
scale factor, one is of power-law type and other is of the exponential form.
Using these two forms, Einstein's modified field equations are solved
separately that correspond to expanding singular and non-singular models of the
universe respectively. The energy-momentum tensor for such string as formulated
by Letelier (1983) is used to construct massive string cosmological models for
which we assume that the expansion () in the model is proportional to
the component of the shear tensor . This
condition leads to , where A, B and C are the metric coefficients
and m is proportionality constant. Our models are in accelerating phase which
is consistent to the recent observations. It has been found that the
displacement vector behaves like cosmological term in the
normal gauge treatment and the solutions are consistent with recent
observations of SNe Ia. It has been found that massive strings dominate in the
decelerating universe whereas strings dominate in the accelerating universe.
Some physical and geometric behaviour of these models are also discussed.Comment: 24 pages, 10 figure
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