The Experts below are selected from a list of 48 Experts worldwide ranked by ideXlab platform
Pavel Kroupa - One of the best experts on this subject based on the ideXlab platform.
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Mass distributions of star clusters for different star formation histories in a galaxy cluster environment
Astronomy & Astrophysics, 2015Co-Authors: Christine Schulz, Jan Pflamm-altenburg, Pavel KroupaAbstract:Clusters of galaxies usually contain rich populations of globular clusters (GCs). We investigate how different star formation histories (SFHs) shape the final mass distribution of star clusters. We assume that every star cluster population forms during a formation epoch of Length Dt at a constant star-formation rate (SFR). The mass distribution of such a population is described by the embedded cluster mass function (ECMF), which is a pure power law extending to an upper limit M_max. Since the SFR determines M_max, the ECMF implicitly depends on the SFR. Starting with different SFHs, each SFH is divided into formation epochs of Length Dt at different SFRs. The requested mass function arises from the superposition of the star clusters of all formation epochs. An improved optimal sampling technique is introduced that allows generating number and mass distributions, both of which accurately agree with the ECMF. Moreover, for each SFH the distribution function of all involved SFRs, F(SFR), is computed. For monotonically decreasing SFHs, F(SFR) always follows a power law. With F(SFR), we develope the theory of the integrated galactic embedded cluster mass function (IGECMF). It describes the distribution function of birth stellar masses of star clusters that accumulated over a formation episode much longer than Dt. The IGECMF indeed reproduces the mass distribution of star clusters created according to the superposition principle. Interestingly, all considered SFHs lead to a turn-down with increasing star cluster mass in their respective IGECMFs. In the past, a turn-down at the high-mass end has been observed for GC systems in different galaxy clusters and in the cluster initial mass function. This behavior can be explained naturally if the observed star cluster ensembles are superpositions of several individual star cluster populations that formed at different times at different SFRs.
K. G. M. Nair - One of the best experts on this subject based on the ideXlab platform.
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Ion beam mixing of Fe with alumina: RBS studies
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999Co-Authors: S.k. Sinha, D.c. Kothari, K. M. Vigen, Tapobrata Som, Vishwas N. Kulkarni, S Panchapakesan, K. G. M. NairAbstract:Abstract We have studied ion beam mixing of Fe with alumina and Al using different masses of the ions (Ne+, Ar+), different fluences (5×1015 to 2×1017 ions/cm2) and different temperatures (RT, 423 and 573 K). Fe thin films of different thicknesses ranging from 20 to 50 nm were deposited by a thermal evaporation method. The ion energy was chosen from 30 to 110 keV such that Fd is maximum at the interface. All the specimens were analysed with RBS technique. It is found that the square of the diffusion Length Dt of Fe in alumina is proportional to the ion fluence implying that mixing is due to ballistic effects (i.e., cascade mixing). Comparison of Dts shows that mixing is less in alumina than in Al. The decrease in Dt with increase in irradiation temperature for the same energy and ion fluence imply de-mixing of Fe from alumina. Annealing of the irradiated samples also show de-mixing.
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Ion beam mixing of Fe with sapphire and silica
AIP Conference Proceedings, 1999Co-Authors: S.k. Sinha, D.c. Kothari, K. M. Vigen, Tapobrata Som, Vishwas N. Kulkarni, K. G. M. NairAbstract:We have studied ion beam mixing of Fe with sapphire, silica, Al & Si using different mass of the ions (Ne+,Ar+), different doses (5×1015 to 2×1017 ions/cm2) and different temperatures (273 °K, 423 °K & 573 °K). Thin film of Fe was deposited by thermal evaporation method. Ion energy was chosen from 30 to 110 keV so that Fd is maximum at the interface. All the specimens were analyzed by RBS. It is found that the square of the diffusion Length Dt is proportional to the ion dose for both types of the substrates (Al2O3 & SiO2) implying that mixing is due to the ballistic effect (i.e. cascade mixing). Also mixing is more when irradiated by Ar+ ions than Ne+ ions. Comparison of Dt’s shows that mixing is less in ceramics than in pure-elements Al & Si. In Fe-Al2O3 samples, mixing decreases with increase in irradiation temperatures implying de-mixing in crystalline ionic bonded oxide whereas mixing increases in the covalently bonded oxide SiO2. Irradiated annealed samples of Fe/Al2O3 & Fe/SiO2 show de-mixing and mi...
Christine Schulz - One of the best experts on this subject based on the ideXlab platform.
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Mass distributions of star clusters for different star formation histories in a galaxy cluster environment
Astronomy & Astrophysics, 2015Co-Authors: Christine Schulz, Jan Pflamm-altenburg, Pavel KroupaAbstract:Clusters of galaxies usually contain rich populations of globular clusters (GCs). We investigate how different star formation histories (SFHs) shape the final mass distribution of star clusters. We assume that every star cluster population forms during a formation epoch of Length Dt at a constant star-formation rate (SFR). The mass distribution of such a population is described by the embedded cluster mass function (ECMF), which is a pure power law extending to an upper limit M_max. Since the SFR determines M_max, the ECMF implicitly depends on the SFR. Starting with different SFHs, each SFH is divided into formation epochs of Length Dt at different SFRs. The requested mass function arises from the superposition of the star clusters of all formation epochs. An improved optimal sampling technique is introduced that allows generating number and mass distributions, both of which accurately agree with the ECMF. Moreover, for each SFH the distribution function of all involved SFRs, F(SFR), is computed. For monotonically decreasing SFHs, F(SFR) always follows a power law. With F(SFR), we develope the theory of the integrated galactic embedded cluster mass function (IGECMF). It describes the distribution function of birth stellar masses of star clusters that accumulated over a formation episode much longer than Dt. The IGECMF indeed reproduces the mass distribution of star clusters created according to the superposition principle. Interestingly, all considered SFHs lead to a turn-down with increasing star cluster mass in their respective IGECMFs. In the past, a turn-down at the high-mass end has been observed for GC systems in different galaxy clusters and in the cluster initial mass function. This behavior can be explained naturally if the observed star cluster ensembles are superpositions of several individual star cluster populations that formed at different times at different SFRs.
Biplab Bose - One of the best experts on this subject based on the ideXlab platform.
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recombinant receptor binding domain of diphtheria toxin increases the potency of curcumin by enhancing cellular uptake
Molecular Pharmaceutics, 2014Co-Authors: A Ashok R Kumar, Gopal Das, Biplab BoseAbstract:Diphtheria toxin (Dt) binds to a specific cell surface receptor, gets internalized, and causes cytotoxicity through its catalytic domain. The toxicity of Dt is used in several therapeutic molecules. Here, we have exploited the receptor-binding ability of Dt to increase cellular uptake of curcumin, a hydrophobic molecule with low bioavailability and cellular uptake. We have expressed only the receptor-binding domain of Dt (RDt) in Escherichia coli. Purified RDt binds to the receptor with an affinity equivalent to that of full-Length Dt. It also binds to curcumin forming a curcumin–RDt complex, and this increases the fluorescence intensity and fluorescence lifetime of curcumin. The curcumin–RDt complex binds to the receptor and associates with human glioblastoma cells (U-87 MG) expressing the receptor. The cellular uptake of curcumin is higher for the curcumin–RDt complex than curcumin alone. This increase in uptake enhances the antiproliferative effect of curcumin and induces apoptosis of these cells even ...
David M. Neville - One of the best experts on this subject based on the ideXlab platform.
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An anti-CD3 single-chain immunotoxin with a truncated diphtheria toxin avoids inhibition by pre-existing antibodies in human blood.
The Journal of biological chemistry, 1995Co-Authors: John F. Thompson, Joshua Scharff, David M. NevilleAbstract:Diphtheria toxin (Dt) is often used in the construction of immunotoxins. One potential problem using Dt-based immunotoxins is the pre-existing anti-Dt antibodies present in human blood due to vaccination. The present study examined the effect of human serum with pre-existing anti-Dt antibodies on the toxicity of UCHT1-CRM9, an immunotoxin directed against CD3 molecules on T-lymphocytes. Sera with detectable anti-Dt antibodies at 1:100 or greater dilutions inhibited the immunotoxin toxicity. Experiments with radio-labeled UCHT1-CRM9 indicate that anti-Dt antibodies partially block its binding to the cell surface as well as inhibit the translocation from the endosome to the cytosol. The inhibitory effect could be adsorbed using a full-Length Dt mutant or B-subfragment. A C-terminal truncation mutant could not adsorb the inhibitory effect, suggesting that the last 150 amino acids contain the epitope(s) recognized by the inhibitory antibodies. Therefore, an anti-CD3 single-chain immunotoxin, sFv-Dt390, was made with a truncated Dt. The IC50 of sFv-Dt390 was 4.8 x 10(-11) M, 1/16 the potency of the divalent UCHT1-CRM9. More importantly, sFv-Dt390 toxicity was only slightly affected by the anti-Dt antibodies in human sera.