1,721,604 research outputs found
A Novel Paradigm For Short Gamma-Ray Bursts With Extended X-Ray Emission
Full text linkThe merger of a binary of neutron stars provides natural explanations for many of the features of short gamma-ray bursts (SGRBs), such as the generation of a hot torus orbiting a rapidly rotating black hole, which can then build a magnetic jet and provide the energy reservoir to launch a relativistic outflow. However, this scenario has problems explaining the recently discovered long-term and sustained X-ray emission associated with the afterglows of a subclass of SGRBs. We propose a new model that explains how an X-ray afterglow can be sustained by the product of the merger and how the X-ray emission is produced before the corresponding emission in the gamma-band, though it is observed to follow it. Overall, our paradigm combines in a novel manner a number of well-established features of the emission in SGRBs and results from simulations. Because it involves the propagation of an ultra-relativistic outflow and its interaction with a confining medium, the paradigm also highlights a unifying phenomenology between short and long GRBs.DFG SFB/Transregio 7"NewCompStar," COST Action MP1304HICAstronom
Magnetic Fields In Relativistic Collisionless Shocks
Full text linkWe present a systematic study on magnetic fields in gamma-ray burst (GRB) external forward shocks (FSs). There are 60 (35) GRBs in our X-ray (optical) sample, mostly from Swift. We use two methods to study is an element of(B) (fraction of energy in magnetic field in the FS): (1) for the X-ray sample, we use the constraint that the observed flux at the end of the steep decline is >= X-ray FS flux; (2) for the optical sample, we use the condition that the observed flux arises from the FS (optical sample light curves decline as similar to t(-1), as expected for the FS). Making a reasonable assumption on E (jet isotropic equivalent kinetic energy), we converted these conditions into an upper limit (measurement) on is an element of(n2/(p+1))(B) for our X-ray (optical) sample, where n is the circumburst density and p is the electron index. Taking n = 1 cm(-3), the distribution of is an element of(B) measurements (upper limits) for our optical (X-ray) sample has a range of similar to 10 (8)-10 (3) (similar to 10 (6)-10 (3)) and median of similar to few x 10 (5) (similar to few x 10 (5)). To characterize how much amplification is needed, beyond shock compression of a seed magnetic field similar to 10 mu G, we expressed our results in terms of an amplification factor, AF, which is very weakly dependent on n (AF alpha n(0.21)). The range of AF measurements (upper limits) for our optical (X-ray) sample is similar to 1-1000 (similar to 10-300) with a median of similar to 50 (similar to 50). These results suggest that some amplification, in addition to shock compression, is needed to explain the afterglow observations.NSF ast-0909110ERC advanced grant (GRB)I-CORE Program of the PBCISF 1829/12Astronom
SNARE protein analog-mediated membrane fusion
No full textFusion of lipid membranes to form a single bilayer is an essential process for life and provides important biological functions including neurotransmitter release. Membrane fusion proteins facilitate approximation of interacting membranes to overcome the energy barrier. In case of synaptic transmission, proteins involved are known as soluble N-ethylmaleimide-sensitive-factor attachment receptor (SNARE) proteins. The SNAREs from synaptic vesicles interact with the SNAREs from the target membrane to form a coiled-coil bundle of four helices, thus pulling the membranes tightly together and initiating fusion. However, it remains unclear how these proteins function at molecular level. Natural systems are often too complex to obtain unambiguous results. Simple model systems mimicking natural proteins in synthetic lipid bilayers are powerful tools for obtaining insights into this essential biological process. An important advantage of such systems is their well-defined composition, which can be systematically varied in order to fully understand events at molecular level. In this review, selected model systems are presented based upon specific interactions between recognition units embedded in separate lipid bilayers mimicking native SNARE protein-mediated membrane fusion. Copyright (c) 2015 European Peptide Society and John Wiley & Sons, Ltd
Site-specific optical encryption via nanoscale integration of carbon on monolayer WS2
No full textWe would like to express our gratitude to the "Department of Science and Technology-Innovation in Science Pursuit for Inspired Research" program (DST-INSPIRE, IF-180717) and Ministry of Education (STARS/APR2019/NS/654/FS) for providing a doctoral fellowship to Deepa Thakur and financial support for the project respectively. We also thank "Advanced Materials and Research Centre" (AMRC) at IIT Mandi for providing the necessary characterization facilities. Additionally, we extend our appreciation to Prof. Kamanio Chattopadhyay and Prof. N. Ravishankar for their valuable inputs on EBID. P.K., D.J., and E.A.S acknowledge primary support for this work from the National Science Foundation (DMR-1905853) and partial support from the University of Pennsylvania Materials Research Science and Engineering Center (MRSEC) (DMR-1720530) , in addition to the usage of MRSEC supported facilities
Simulations Of Accretion Powered Supernovae In The Progenitors Of Gamma-Ray Bursts
Full text linkObservational evidence suggests a link between long-duration gamma-ray bursts (LGRBs) and Type Ic supernovae. Here, we propose a potential mechanism for Type Ic supernovae in LGRB progenitors powered solely by accretion energy. We present spherically symmetric hydrodynamic simulations of the long-term accretion of a rotating gamma-ray burst progenitor star, a "collapsar," onto the central compact object, which we take to be a black hole. The simulations were carried out with the adaptive mesh refinement code FLASH in one spatial dimension and with rotation, an explicit shear viscosity, and convection in the mixing length theory approximation. Once the accretion flow becomes rotationally supported outside of the black hole, an accretion shock forms and traverses the stellar envelope. Energy is carried from the central geometrically thick accretion disk to the stellar envelope by convection. Energy losses through neutrino emission and nuclear photodisintegration are calculated but do not seem important following the rapid early drop of the accretion rate following circularization. We find that the shock velocity, energy, and unbound mass are sensitive to convective efficiency, effective viscosity, and initial stellar angular momentum. Our simulations show that given the appropriate combinations of stellar and physical parameters, explosions with energies similar to 5 x 10(50) erg, velocities similar to 3000 km s(-1), and unbound material masses greater than or similar to 6 M-circle dot are possible in a rapidly rotating 16 M-circle dot main-sequence progenitor star. Further work is needed to constrain the values of these parameters, to identify the likely outcomes in more plausible and massive LRGB progenitors, and to explore nucleosynthetic implications.National Science Foundation AST-0708795, AST-1009928, AST-0909110DOEAstronom
Increased duplex stabilization in porphyrin-LNA zipper arrays with structure dependent exciton coupling
No full textData files containing the melting curves of modified DNA, and fitting procedures to extract thermodynamic data.
This dataset was used in:
Singleton DG, Hussain R, Siligardi G, Kumar P, Hrdlicka PJ, Berova N and Stulz E (2015) Increased duplex stabilization in porphyrin-LNA zipper arrays with structure dependent exciton coupling. Organic & Biomolecular Chemistry, DOI: 10.1039/C5OB01681A </span
Increased duplex stabilization in porphyrin-LNA zipper arrays with structure dependent exciton coupling
No full textPorphyrins were attached to LNA uridine building blocks via rigid 5-acetylene or more flexible propargyl-amide linkers and incorporated into DNA strands. The systems show a greatly increased thermodynamic stability when using as little as three porphyrins in a zipper arrangement. Thermodynamic analysis reveals clustering of the strands into more ordered duplexes with both greater negative ??S and ??H values, and less ordered duplexes with small positive ??S differences, depending on the combination of linkers used. The exciton coupling between the porphyrins is dependent on the flanking DNA sequence in the single stranded form, and on the nature of the linker between the nucleobase and the porphyrin in the double stranded form; it is, however, also strongly influenced by intermolecular interactions. This system is suitable for the formation of stable helical chromophore arrays with sequence and structure dependent exciton coupling
Effect of honey and its major royal jelly protein 1 on cytokine and MMP-9 mRNA transcripts in human keratinocytes
No full textHoney has been used since ancient times as a remedy in wound healing. However, even though the results from randomized clinical trials document that honey accelerates wound healing, no study dealing with its influence on human skin cells (epidermal keratinocytes and dermal fibroblast) has been performed. We demonstrate that keratinocytes, which are known to be involved in wound healing, are responsible for elevated production of mediators including cytokines (TNF-?, IL-1? and TGF-?) and matrix metalloproteinase-9 (MMP-9) after incubation with honey. Real-time PCR was performed for the quantification of mRNA level of selected cytokines and MMP-9. Furthermore, we show that the increased level of MMP-9 in the epidermis following incubation with honey leads to degradation of type IV collagen in the basement membrane. These data indisputably demonstrate that honey activates keratinocytes and support the findings that honey may accelerate wound healing process.<br/
Appendix_Supplementary_material - On 3D-printed ZnO-reinforced PLA matrix composite: Tensile, thermal, morphological and shape memory characteristics
No full textAppendix_Supplementary_material for On 3D-printed ZnO-reinforced PLA matrix composite: Tensile, thermal, morphological and shape memory characteristics by Mohit Singh, Rupinder Singh, Ranvijay Kumar, Pawan Kumar and Pawan Preet in Journal of Thermoplastic Composite Materials</p
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