Contribution from normal and starburst galaxies to the extragalactic gamma-ray background (EGRB)

The extragalactic diffuse emission at gamma-ray energies has interesting cosmological implications since these photons suffer little or no attenuation during their propagation from the site of origin. The emission could originate from either truly diffuse processes or from unresolved point sources such as AGNs, normal galaxies and starburst galaxies. Here, we examine the unresolved point source origin of the extragalactic gamma-ray background emission from normal galaxies and starburst galaxies. gamma-ray emission from normal galaxies is primarily coming from cosmic-ray interactions with interstellar matter and radiation (similar to 90%) along with a small contribution from discrete point sources (similar to 10%). Starburst galaxies are expected to have enhanced supernovae activity which leads to higher cosmic-ray densities, making starburst galaxies sufficiently luminous at gamma-ray energies to be detected by the current gamma-ray mission(Fermi Gamma-ray Space Telescope).

Results from PAMELA, ATIC and FERMI: Pulsars or dark matter?

It is well known that dark matter dominates the dynamics of galaxies and clusters of galaxies. Its constituents remain a mystery despite an assiduous search for them over the past three decades. Recent results from the satellite-based PAMELA experiment show an excess in the positron fraction at energies between 10 and 100 GeV in the secondary cosmic ray spectrum. Other experiments, namely ATIC, HESS and FERMI, show an excess in the total electron (e(+) + e(-)) spectrum for energies greater than 100 GeV. These excesses in the positron fraction as well as the electron spectrum can arise in local astrophysical processes like pulsars, or can be attributed to the annihilation of the dark matter particles. The latter possibility gives clues to the possible candidates for the dark matter in galaxies and other astrophysical systems. In this article, we give a report of these exciting developments.

Multiwavelength features of Fermi bubbles as signatures of a Galactic wind

Using hydrodynamical simulations, we show for the first time that an episode of star formation in the centre of the Milky Way, with a star formation rate (SFR) similar to 0.5 M-circle dot yr(-1) for similar to 30 Myr, can produce bubbles that resemble the Fermi bubbles (FBs), when viewed from the solar position. The morphology, extent and multiwavelength observations of FBs, especially X-rays, constrain various physical parameters such as SFR, age, and the circumgalactic medium (CGM) density. We show that the interaction of the CGM with the Galactic wind driven by star formation in the central region can explain the observed surface brightness and morphological features of X-rays associated with the FBs. Furthermore, assuming that cosmic ray electrons are accelerated in situ by shocks and/or turbulence, the brightness and morphology of gamma-ray emission and the microwave haze can be explained. The kinematics of the cold and warm clumps in our model also matches with recent observations of absorption lines through the bubbles.

Isotopes in cosmochemistry: recipe for a Solar System

Extreme isotopic variations among extraterrestrial materials provide great insights into the origin and evolution of the Solar System. In this tutorial review, we summarize how the measurement of isotope ratios can expand our knowledge of the processes that took place before and during the formation of our Solar System and its subsequent early evolution. The continuous improvement of mass spectrometers with high precision and increased spatial resolution, including secondary ion mass spectrometry (SIMS), thermal ionization mass spectrometry (TIMS) and multi collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS), along with the ever growing amounts of available extraterrestrial samples have significantly increased the temporal and spatial constraints on the sequence of events that took place since and before the formation of the first Solar System condensates (i.e., Ca-Al-rich inclusions). Grains sampling distinct stellar environments with a wide range of isotopic compositions were admixed to, but possibly not fully homogenized in, the Sun's parent molecular cloud or the nascent Solar System. Before, during and after accretion of the nebula, as well as the formation and subsequent evolution of planetesimals and planets, chemical and physical fractionation processes irrevocably changed the chemical and isotopic compositions of all Solar System bodies. Since the formation of the first Solar System minerals and rocks 4.568 Gyr ago, short-and long-lived radioactive decay and cosmic ray interaction also contributed to the modification of the isotopic framework of the Solar System, and permit to trace the formation and evolution of directly accessible and inferred planetary and stellar isotopic reservoirs.

Low-temperature and high-pressure Raman and x-ray studies of pyrochlore Tb2Ti2O7: Phonon anomalies and possible phase transition

We have carried out temperature- and pressure-dependent Raman and x-ray measurements on single crystals of Tb2Ti2O7. We attribute the observed anomalous temperature dependence of phonons to phonon-phonon anharmonic interactions. The quasiharmonic and anharmonic contributions to the temperature-dependent changes in phonon frequencies are estimated quantitatively using mode Grüneisen parameters derived from pressure-dependent Raman experiments and bulk modulus from high-pressure x-ray measurements. Further, our Raman and x-ray data suggest a subtle structural deformation of the pyrochlore lattice at ~9 GPa. We discuss possible implications of our results on the spin-liquid behavior of Tb2Ti2O7.

Electron and x-ray diffraction studies on Al86Fe14, Al82Fe18 and Al75Fe25 quasicrystals

Electron and x-ray diffraction experiments on the metlt-spun Al100−x Fe x (x=14, 18, 25) alloys are carried out. It is observed that all the melt-spun alloys possessing the quasi-crystalline phases have icosahedral point-group symmetry.

X-ray crystallographic and NMR studies of pantothenate synthetase provide insights into the mechanism of homotropic inhibition by pantoate

The structural basis for the homotropic inhibition of pantothenate synthetase by the substrate pantoate was investigated by X-ray crystallography and high-resolution NMR spectroscopic methods. The tertiary structure of the dimeric N-terminal domain of Escherichia coli pantothenate synthetase, determined by X-ray crystallography to a resolution of 1.7 Å, showed a second molecule of pantoate bound in the ATP-binding pocket. Pantoate binding to the ATP-binding site induced large changes in structure, mainly for backbone and side chain atoms of residues in the ATP binding HXGH(34–37) motif. Sequence-specific NMR resonance assignments and solution secondary structure of the dimeric N-terminal domain, obtained using samples enriched in 2H, 13C, and 15N, indicated that the secondary structural elements were conserved in solution. Nitrogen-15 edited two-dimensional solution NMR chemical shift mapping experiments revealed that pantoate, at 10 mm, bound at these two independent sites. The solution NMR studies unambiguously demonstrated that ATP stoichiometrically displaced pantoate from the ATP-binding site. All NMR and X-ray studies were conducted at substrate concentrations used for enzymatic characterization of pantothenate synthetase from different sources [Jonczyk R & Genschel U (2006) J Biol Chem 281, 37435–37446]. As pantoate binding to its canonical site is structurally conserved, these results demonstrate that the observed homotropic effects of pantoate on pantothenate biosynthesis are caused by competitive binding of this substrate to the ATP-binding site. The results presented here have implications for the design and development of potential antibacterial and herbicidal agents.

Studies of the wetting characteristics of liquid iron on dense alumina by the X-ray sessile drop technique

In the present work, the reaction between a molten iron drop and dense alumina was studied using the X-ray sessile-drop method under different oxygen partial pressures in the gas atmosphere. The changes in contact angles between the iron drop and the alumina substrate were followed as functions of temperature and varying partial pressures of oxygen in the temperature range 1823 to 1873 K both in static and dynamic modes. The results of the contact angle measurements with pure iron in contact with dense alumina in extremely well-purified argon as well as under different oxygen partial pressures in the gas atmosphere showed good agreement with earlier measurements reported in the literature. In the dynamic mode, when argon was replaced by a CO-CO2-Ar mixture with a well-defined PO, in the gas, the contact angle showed an initial decrease followed by a period of nearly constant contact angle. At the end of this period, the length of which was a function of the P-O2 imposed, a further steep decrease in the contact angle was noticed. An intermediate layer of FeAl2O4 was detected in the scanning electron microscope (SEM) analysis of the reacted substrates. An interesting observation in the present experiments is that the iron drop moved away from the site of the reaction once the product layer covered the interface. The results are analyzed on the basis of the various forces acting on the drop.

Microstructural characterization of ultrafine-grain interstitial-free steel by X-ray diffraction line profile analysis

This paper highlights the microstructural features of commercially available interstitial free (IF) steel specimens deformed by equal channel angular pressing (ECAP) up to four passes following the route A. The microstructure of the samples was studied by different techniques of X-ray diffraction peak profile analysis as a function of strain (epsilon). It was found that the crystallite size is reduced substantially already at epsilon=2.3 and it does not change significantly during further deformation. At the same time, the dislocation density increases gradually up to epsilon=4.6. The dislocation densities estimated from X-ray diffraction study are found to correlate very well with the experimentally obtained yield strength of the samples.

X-Ray Studies On The Bilayer Structure Of Trypsin-Treated Rat-Brain Myelin

Trypsin-treated rat brain myelin was subjected to biochemical and X-ray studies. Untreated myelin gave rise to a pattern of three rings with a fundamental repeat period of 155 Angstrom consisting of two bilayers per repeat period, whereas myelin treated with trypsin showed a fundamental repeat period of 75 Angstrom with one bilayer per repeat period. The integrated raw intensity of the h=4 reflection with respect to the h=2 reflection is 0.38 for untreated myelin. The corresponding value reduced to 0.23, 0.18, 0.17 for myelin treated with 5, 10, 40 units of trypsin per mg of myelin, respectively, for 30 min at 30 degrees C. The decrease in relative raw intensity of the higher-order reflection relative to the lower-order reflection is suggestive of a disordering of the phosphate groups upon trypsin treatment or an increased mosaicity of the membrane or a combination of both these effects, However, trypsin treatment does not lead to a complete breakdown of the membrane, The integrated intensity of the h=1 reflection, though weak, is above the measurable threshold for untreated myelin, whereas the corresponding intensity is below the measurable threshold for trypsin-treated myelin, indicating a possible asymmetric to symmetric transition of the myelin bilayer structure about its centre after trypsin treatment.

X-ray Structure of Gelonin at 1.8 Å Resolution

Gelonin is a single chain ribosome inactivating protein (RIP) with potential application in the treatment of cancer and AIDS. Diffraction quality crystals grown using PEG3350, belong to the space group P2(1), with it a = 49.4 Angstrom b = 44.9 Angstrom, c = 137.4 Angstrom and beta = 98.4 degrees, and contain two molecules in the asymmetric unit. Diffraction data collected to 1.8 Angstrom resolution has a R(m) value of 7.3%. Structure of gelonin has been solved by the molecular replacement method, using ricin A chain as the search model. Crystallographic refinement using X-PLOR resulted in a model for which the r.m.s deviations from ideal bond lengths and bond angles are 0.012 Angstrom and 2.7 degrees, respectively The final R-factor is 18.4% for 39,806 reflections for which I > 1.0 sigma(I).The C-alpha atoms of the two molecules in the asymmetric unit superpose to within 0.38 Angstrom for 247 atom pairs. The overall fold of gelonin is similar to that of other RIPs such as ricin A chain and alpha-momorcharin, the r.m.s.d. for C-alpha superpositions being 1.3 and 1.4 Angstrom, respectively The-catalytic residues (Glu166, Arg169 and Tyr113) in the active site form a hydrogen bond scheme similar to that observed in other RIPs. The conformation of Tyr74 in the active site, however, is significantly different from that in alpha-momorcharin. Three well defined water molecules are located in the active site cavity and one of them, X319, superposes to within 0.2 Angstrom of a corresponding water molecule in the structure of alpha-momorcharin. Any of the three could be the substrate water molecule in the hydrolysis reaction catalysed by gelonin.Difference electron density for a N-linked sugar moiety has been observed near only one of the two potential glycosylation sites in the sequence. The amino acid at position 239 has been established as Lys by calculation of omit electron density maps.The two cysteine residues in the sequence, Cys44 and Cys50, form a disulphide bond, and are therefore not available for disulphide conjugation with antibodies. Based on the structure, the region of the molecule that is involved in intradimer interactions is suggested to be suitable for introducing a Cys residue for purposes of conjugation with an antibody to produce useful immunotoxins.

Evidence of clustering in an aqueous electrolyte solution: a small-angle X-ray scattering study

The work reported hen was motivated by a desire to verify the existence of structure - specifically MP-rich clusters induced by sodium bromide (NaBr) in the ternary liquid mixture 3-methylpyridine (Mf) + water(W) + NaBr. We present small-angle X-ray scattering (SAXS) measurements in this mixture. These measurements were obtained at room temperature (similar to 298 K) in the one-phase region (below the relevant lower consolute points, T(L)s) at different values of X (i.e., X = 0.02 - 0.17), where X is the weight fraction of NaBr in the mixture. Cluster-size distribution, estimated on the assumption that the clusters are spherical, shows systematic behaviour in that the peak of the distribution shifts rewards larger values of cluster radius as X increases. The largest spatial extent of the clusters (similar to 4.5 nm) is seen at X = 0.17. Data analysis assuming arbitrary shapes and sizes of clusters gives a limiting value of cluster size (- 4.5 nm) that is not very sensitive to X. It is suggested that the cluster size determined may not be the same as the usual critical-point fluctuations far removed from the critical point (T-L). The influence of the additional length scale due to clustering is discussed from the standpoint of crossover from Ising to mean-field critical behaviour, when moving away from the T-L.

Studies on abrasive jet machining through statistical design of experiments

The main objective of statistical analysis of experi- mental investigations is to make predictions on the basis of mathematical equations so as the number of experiments. Abrasive jet machining (AJM) is an unconventional and novel machining process wherein microabrasive particles are propelled at high veloc- ities on to a workpiece. The resulting erosion can be used for cutting, etching, cleaning, deburring, drilling and polishing. In the study completed by the authors, statistical design of experiments was successfully employed to predict the rate of material removal by AJM. This paper discusses the details of such an approach and the findings.

An asymmetric homodinuclear complex containing the mu-x-oxobis(mu-x-carboxylato)diruthenium(III) core: X-ray structure of [Ru20(o2ec6H4-p-OMe)3(en) (PPh3)2] (C104)" 3CHC13

Asymmetric tri-bridged diruthenium(III) complexes, [Ru2O(O(2)CR)(3)(en) (PPh(3))(2)](ClO4) (R = C6H4-p-X: X = OMe (1a), Me (1b); en=1,2-diaminoethane), were prepared and structurally characterized. Complex 1a 3CHCl(3), crystallizes in the triclinic space group P (1) over bar with a = 14.029(5), b = 14.205(5), c = 20.610(6) Angstrom, alpha= 107.26(3), beta = 101.84(3), gamma= 97.57(3)degrees, V= 3756(2) Angstrom(3) and Z = 2. The complex has an {Ru-2(mu-O)(mu-O(2)CR)(2)(2+)} core and exhibits [O4PRu(mu-O)RuPO2N2](+) coordination environments for the metal centers. The novel structural feature is the asymmetric arrangement of ligands at the terminal sites of the core which shows an Ru... Ru separation of 3.226(3) Angstrom and an Ru-O-Ru angle of 119.2(5)degrees. An intense visible band observed near 570 nm is assigned to a charge transfer transition involving the d pi-Ru(III) and p pi-mu-O Orbitals. Cyclic voltammetry of the complexes displays a reversible Ru-2(III,III) reversible arrow Ru-2(III,IV) couple near 0.8 V (versus SCE) in MeCN-0.1 M TBAP.

Experiments on a plume with off-source heating: Implications for cloud fluid dynamics

We report here on a series of laboratory experiments on plumes, undertaken with the object of simulating the effect of the heat release that occurs in clouds on condensation of water vapor. The experimental technique used for this purpose relies on ohmic heating generated in an electrically conducting plume fluid subjected to a suitable alternating voltage across specified axial stations in the plume flow [Bhat et al., 1989]. The present series of experiments achieves a value of the Richardson number that is toward the lower end of the range that characteristics cumulus clouds. It is found that the buoyancy enhancement due to heating disrupts the eddy structures in the flow and reduces the dilution owing to entrainment of ambient fluid that would otherwise have occurred in the central region of the plume. Heating also reduces the spread rate of the plume, but as it accelerates the flow as well, the overall specific mass flux in the plume does not show a very significant change at the heat input employed in the experiment. However, there is some indication that the entrainment rate (proportional to the streamwise derivative of the mass flux) is slightly higher immediately after heat injection and slightly lower farther downstream. The measurements support a previous proposal for a cloud scenario [Bhat and Narasimha, 1996] and demonstrate how fresh insights into certain aspects of the fluid dynamics of clouds may be derived from the experimental techniques employed here.