7,479 research outputs found
Two Dimensional Clustering of Gamma-Ray Bursts using durations and hardness
Gamma-Ray Bursts (GRBs) have been conventionally bifurcated into two distinct
categories: ``short'' and ``long'' with durations less than and greater than
two seconds respectively. However, there is a lot of literature (although with
conflicting results) regarding the existence of a third intermediate class. To
investigate this issue, we extend a recent study (arXiv:1612.08235) on
classification of GRBs to two dimensions by incorporating the GRB hardness in
addition to the observed durations. We carry out this unified analysis on GRB
datasets from four detectors, viz. BATSE, RHESSI, Swift (observed and intrinsic
frame), and Fermi-GBM. We consider the duration and hardness features in
log-scale for each of these datasets and determine the best-fit parameters
using Gaussian Mixture Model. This is followed by information theoretic
criterion (AIC and BIC) to determine if a three-component fit is favored
compared to a two-component one or vice-versa. For BATSE, we find that both AIC
and BIC show preference for three components with decisive significance. For
Fermi and RHESSI, both AIC and BIC show preference for two components, although
the significance is marginal from AIC, but decisive using BIC. For Swift
dataset in both the observed and rest frame, we find that three components are
favored according to AIC with decisive significance, and two are preferred with
BIC with marginal to strong significance.Comment: 13 pages, 10 figures. This is an extension of arXiv:1612.08235 to
two-dimension
Associated HI absorption in the z=3.4 radio galaxy B2 0902+343 observed with the GMRT
We have made observations of the associated HI absorption of a high redshift
radio galaxy 0902+34 at z=3.395 with the Giant Meterwave Radio Telescope in the
MHz band. We find a narrow absorption line with a flux density of
11.5 mJy at a redshift of 3.397 consistent with that observed by Uson et al.
(1991), Briggs et al. (1993) and de Bruyn (1996).A weak broad absorption
feature reported by de Bruyn (1996) has not been detected in our observations.
We also place an upper limit of 4 mJy (2 ) on emission line strength at
the position where Uson et al. (1991) claimed to have found a narrow emission
line.Comment: To appear in Journal of Astronomy and Astrophysic
Distribution of the second virial coefficients of globular proteins
George and Wilson [Acta. Cryst. D 50, 361 (1994)] looked at the distribution
of values of the second virial coefficient of globular proteins, under the
conditions at which they crystallise. They found the values to lie within a
fairly narrow range. We have defined a simple model of a generic globular
protein. We then generate a set of proteins by picking values for the
parameters of the model from a probability distribution. At fixed solubility,
this set of proteins is found to have values of the second virial coefficient
that fall within a fairly narrow range. The shape of the probability
distribution of the second virial coefficient is Gaussian because the second
virial coefficient is a sum of contributions from different patches on the
protein surface.Comment: 5 pages, including 3 figure
Magnetic properties and complex magnetic phase diagram in non centrosymmetric EuRhGe and EuIrGe single crystals
We report the magnetic properties of two Eu based compounds, single
crystalline EuIrGe and EuRhGe, inferred from magnetisation, electrical
transport, heat capacity and Eu M\"{o}ssbauer spectroscopy. These
previously known compounds crystallise in the non-centrosymmetric, tetragonal,
, BaNiSn-type structure. Single crystals of EuIrGe and EuRhGe
were grown using high temperature solution growth method using In as flux.
EuIrGe exhibits two magnetic orderings at = 12.4 K, and
= 7.3 K. On the other hand EuRhGe presents a single magnetic
transition with a = 12 K. Eu M\"{o}ssbauer spectra present
evidence for a cascade of transitions from paramagnetic to incommensurate
amplitude modulated followed by an equal moment antiferromagnetic phase at
lower temperatures in EuIrGe, the transitions having a substantial first
order character. On the other hand the Eu M\"{o}ssbauer spectra at 4.2
and 9 K in EuRhGe present evidence of a single magnetic transition. In both
compounds a superzone gap is observed for the current density
[001], which enhances with transverse magnetic field. The magnetisation
measured up to 14 T shows the occurrence of field induced transitions, which
are well documented in the magnetotransport data as well. The magnetic phase
diagram constructed from these data is complex, revealing the presence of many
phases in the phase space
A novel hybrid optimization methodology to optimize the total number and placement of wind turbines
Due to increasing penetration of wind energy in the recent times, wind farmers tend to generate increasing amount of energy out of wind farms. In order to achieve the target, many wind farms are operated with a layout design of numerous turbines placed close to each other in a limited land area leading to greater energy losses due to ‘wake effects’. Moreover, these turbines need to satisfy many other constraints such as topological constraints, minimum allowable capacity factors, inter-turbine distances, noise constraints etc. Thus, the problem of placing wind turbines in a farm to maximize the overall produced energy while satisfying all constraints is highly constrained and complex. Existing methods to solve the turbine placement problem typically assume knowledge about the total number of turbines to be placed in the farm. However, in reality, wind farm developers often have little or no information about the best number of turbines to be placed in a farm. This study proposes a novel hybrid optimization methodology to simultaneously determine the optimum total number of turbines to be placed in a wind farm along with their optimal locations. The proposed hybrid methodology is a combination of probabilistic genetic algorithms and deterministic gradient based optimization methods. Application of the proposed method on representative case studies yields higher Annual Energy Production (AEP) than the results found by using two of the existing methods
Anisotropic magnetic and superconducting properties of pure and Co-doped CaFeAs single crystals
We report anisotropic dc magnetic susceptibility , electrical
resistivity , and heat capacity measurements on the single
crystals of CaFeCoAs for = 0 and 0.06. Large sized single
crystals were grown by the high temperature solution method with Sn as the
solvent. For the pure compound with = 0, a high temperature transition at
170 K is observed which is attributed to a combined spin density wave (SDW)
ordering and a structural phase transition. On the other hand, for the Co-doped
samples for = 0.06, the SDW transition is suppressed while
superconductivity is observed at 17 K. The superconducting transition
has been confirmed from the magnetization and electrical resistivity studies.
The Fe M\"ossbauer spectrum in CaFeAs indicates that the SDW
ordering is incommensurate. In the Co-doped sample, a prominent paramagnetic
line at 4.2 K is observed indicating a weakening of the SDW state.Comment: 4 pages 5 figures. Submitted to Phys. Rev.
Tetrachloro Phthalic Anhydride Based Chloropolyesters for Inhibition of Double Base Rocket Propellants
The choice of inhibiting materials for double base and composite modified double base rocket propellants has always been a difficult problem because of the presence of nitroglycerine in these propellants and its subsequent migration from the propellant towards the inhibitor. The inhibition of double base rocket propellants with unsaturated polyesters has become popular in recent years, but they usually suffer from the drawback of high nitroglycerine absorption. This may be considerably lowered by exploiting the concept of introduction of electron acceptance sites in one of the components used for the synthesis of unsaturated polyesters. Chloropolyester-1 (CP-1) based on tetrachlorophthalic anhydride (TCPAn), propylene glycol (PG) and maleic anhydride (MAn) and chloropolyester-2 (CP-2) based on TCPAn, polyethylene glycol mol. wt. 200 (PEG-200) and MAn have been synthesised and characterised for ge ltime, exotherm peak temperature, tensile strength, % elongation, bond strength, water absorption, nitroglycerine absorption, heat resistance and flame retardance. The blends of CP-1 and CP-2 designated as CPB-2 (CP-1 : CP-2 : : 20 : 80), CPB-4 CPB-6 and CPB-8 have also been formulated and characterised for these properties. Based on the data for various characteristics, CPB-4 has been selected for inhibition and static evaluation of rocket propellants. The double base rocket propellant sustainers containing 2-NDPA have been inhibited with CPB-4 without the application of any barrier coat and statically fired at ambient, cold (-40°C) and hot (+5O°C) temperatures after conditioning. The pressure-time profiles were found to be smooth and flat in all cases, inferring that the CPB-4 inhibition system (without application of any barrier coat) is working satisfactorily
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