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941.
Ernesto I. Badano Héctor A. Regidor Hector A. Núñez Rebeca Acosta Ernesto Gianoli 《Journal of Biogeography》2005,32(2):221-227
Aim To assess how ant species richness and structure of ant communities are influenced by island age (disturbance history) in a dynamic archipelago. Location Cabra Corral dam, Salta Province, north‐west Argentina (25°08′ S, 65°20′ W). Methods Ant species richness on remaining fragments (islands) of a flooded forest was determined, as well as island area, isolation and age. Simple linear regressions were performed to assess relationships between ant species richness and those insular variables. Furthermore, a stepwise multiple linear regression analysis was conducted in order to determine the relative influence of each insular variable on ant species richness. Islands were categorized in two age classes (old and young) and co‐occurrence analyses were applied within each class to evaluate changes in community structure because of interspecific competition. Results Simple regression analyses indicated a moderate, positive effect of island area on ant species richness. Weak, marginally non‐significant relationships were found between ant species richness and both island isolation and island age, showing the tendency for there to be a decrease in ant species richness with island isolation and that ant species richness might be higher in old islands. The multiple regression analysis indicated that island isolation and age had no significant effects on the number of ant species, island area being the only independent variable retained in the analysis. On the contrary, whereas a random pattern of species co‐occurrence was found on young islands, ant communities in old islands showed a significantly negative pattern of species co‐occurrence, suggesting that the effect of competition on community structure was stronger on older islands than on younger islands. Main conclusions Island area was the most important variable explaining ant species richness on the islands of Cabra Corral dam. However, both island isolation and island age (or disturbance history) might also contribute to shape the observed community patterns. The present study also shows that island age significantly affects the strength with which interspecific interactions structure ant communities on islands. 相似文献
942.
943.
Andres Juan Kreiner Javier Bergueiro Daniel Cartelli Matias Baldo Walter Castell Javier Gomez Asoia Javier Padulo Juan Carlos Suárez Sandín Marcelo Igarzabal Julian Erhardt Daniel Mercuri Alejandro A. Valda Daniel M. Minsky Mario E. Debray Hector R. Somacal María Eugenia Capoulat María S. Herrera Mariela F. del Grosso Leonardo Gagetti Manuel Suarez Anzorena Nicolas Canepa Nicolas Real Marcelo Gun Hernán Tacca 《Reports of Practical Oncology and Radiotherapy》2016,21(2):95-101
Aim
This work aims at giving an updated report of the worldwide status of Accelerator-Based BNCT (AB-BNCT).Background
There is a generalized perception that the availability of accelerators installed in hospitals, as neutron sources, may be crucial for the advancement of BNCT. Accordingly, in recent years a significant effort has started to develop such machines.Materials and methods
A variety of possible charged-particle induced nuclear reactions and the characteristics of the resulting neutron spectra are discussed along with the worldwide activity in suitable accelerator development.Results
Endothermic 7Li(p,n)7Be and 9Be(p,n)9B and exothermic 9Be(d,n)10B are compared. In addition to having much better thermo-mechanical properties than Li, Be as a target leads to stable products. This is a significant advantage for a hospital-based facility. 9Be(p,n)9B needs at least 4–5 MeV bombarding energy to have a sufficient yield, while 9Be(d,n)10B can be utilized at about 1.4 MeV, implying the smallest possible accelerator. This reaction operating with a thin target can produce a sufficiently soft spectrum to be viable for AB-BNCT. The machines considered are electrostatic single ended or tandem accelerators or radiofrequency quadrupoles plus drift tube Linacs.Conclusions
7Li(p,n)7Be provides one of the best solutions for the production of epithermal neutron beams for deep-seated tumors. However, a Li-based target poses significant technological challenges. Hence, Be has been considered as an alternative target, both in combination with (p,n) and (d,n) reactions. 9Be(d,n)10B at 1.4 MeV, with a thin target has been shown to be a realistic option for the treatment of deep-seated lesions. 相似文献944.
Heterojunction‐Depleted Lead‐Free Perovskite Solar Cells with Coarse‐Grained B‐γ‐CsSnI3 Thin Films
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Ning Wang Yuanyuan Zhou Ming‐Gang Ju Hector F. Garces Tao Ding Shuping Pang Xiao Cheng Zeng Nitin P. Padture Xiao Wei Sun 《Liver Transplantation》2016,6(24)
Perovskite solar cells (PSCs) have been emerging as a breakthrough photovoltaic technology, holding unprecedented promise for low‐cost, high‐efficiency renewable electricity generation. However, potential toxicity associated with the state‐of‐the‐art lead‐containing PSCs has become a major concern. The past research in the development of lead‐free PSCs has met with mixed success. Herein, the promise of coarse‐grained B‐γ‐CsSnI3 perovskite thin films as light absorber for efficient lead‐free PSCs is demonstrated. Thermally‐driven solid‐state coarsening of B‐γ‐CsSnI3 perovskite grains employed here is accompanied by an increase of tin‐vacancy concentration in their crystal structure, as supported by first‐principles calculations. The optimal device architecture for the efficient photovoltaic operation of these B‐γ‐CsSnI3 thin films is identified through exploration of several device architectures. Via modulation of the B‐γ‐CsSnI3 grain coarsening, together with the use of the optimal PSC architecture, planar heterojunction‐depleted B‐γ‐CsSnI3 PSCs with power conversion efficiency up to 3.31% are achieved without the use of any additives. The demonstrated strategies provide guidelines and prospects for developing future high‐performance lead‐free PVs. 相似文献
945.
In many organisms, telomeric DNA consists of long tracts of short repeats. Shorter tracts are preferentially lengthened by telomerase, suggesting a conserved mechanism that recognizes and elongates short telomeres. Tel1p, an ATM family checkpoint kinase, plays an important role in telomere elongation, as cells lacking Tel1p have short telomeres and show reduced recruitment of telomerase components to telomeres. We show that Tel1p association increased as telomeres shortened in vivo in the presence or absence of telomerase and that Tel1p preferentially associated with the shortest telomeres. Tel1p association was independent of Tel1p kinase activity and enhanced by Mre11p. Tel1p overexpression simultaneously stimulated telomerase-mediated elongation and Tel1p association with all telomeres. Thus, Tel1p preferentially associates with the shortest telomeres and stimulates their elongation by telomerase. 相似文献
946.
Felix CF Oliveira VH Moreira OC Mignaco JA Barrabin H Scofano HM 《The international journal of biochemistry & cell biology》2007,39(3):586-596
Heparin is related to several protein receptors that control Ca2+ homeostasis. Here, we studied the effects of heparin on the plasma membrane Ca2+-ATPase from erythrocytes. Both ATP hydrolysis and Ca2+ uptake were inhibited by heparin without modification of the steady-state level of phosphoenzyme formed by ATP. Calmodulin did neither modify the inhibition nor the binding of heparin. Inhibition by heparin was counteracted by K+ but not by Li+. This effect was extended to other sulfated polysaccharides with high number of sulfate residues. Hydrolysis of p-nitrophenylphosphate was equally inhibited by heparin. No evidence for enzyme uncoupling was observed: Ca2+ uptake and ATP hydrolysis remained tightly associated at any level of heparin, and heparin did not increase the passive Ca2+ efflux of inside-out vesicles. Vanadate blocked this efflux, indicating that the main point of Ca2+ escape from these vesicles was linked to the Ca2+ pump. It is discussed that sulfated polysaccharides may physiologically increase the steady-state level of Ca2+ in the cytosol by inhibiting the Ca2+ pumps in a K+ (and tissue) regulated way. It is suggested that heparin regulates the plasma membrane Ca2+-ATPase by binding to the E2 conformer. 相似文献
947.
948.
The 13Cα chemical shifts for 16,299 residues from 213 conformations of four proteins (experimentally determined by X-ray crystallography
and Nuclear Magnetic Resonance methods) were computed by using a combination of approaches that includes, but is not limited
to, the use of density functional theory. Initially, a validation test of this methodology was carried out by a detailed examination
of the correlation between computed and observed 13Cα chemical shifts of 10,564 (of the 16,299) residues from 139 conformations of the human protein ubiquitin. The results of
this validation test on ubiquitin show agreement with conclusions derived from computation of the chemical shifts at the ab initio Hartree–Fock level. Further, application of this methodology to 5,735 residues from 74 conformations of the three remaining
proteins that differ in their number of amino acid residues, sequence and three-dimensional structure, together with a new
scoring function, namely the conformationally averaged root-mean-square-deviation, enables us to: (a) offer a criterion for an accurate assessment of the quality of NMR-derived protein conformations; (b) examine whether X-ray or NMR-solved structures are better representations of the
observed 13Cα chemical shifts in solution; (c) provide evidence indicating that the proposed methodology is more accurate than automated
predictors for validation of protein structures; (d) shed light as to whether the agreement between computed and observed
13Cα chemical shifts is influenced by the identity of an amino acid residue or its location in the sequence; and (e) provide evidence
confirming the presence of dynamics for proteins in solution, and hence showing that an ensemble of conformations is a better
representation of the structure in solution than any single conformation.
Electronic Supplementary Material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. 相似文献
949.
DeLuca HF Plum LA Clagett-Dame M 《The Journal of steroid biochemistry and molecular biology》2007,103(3-5):263-268
New analogs of 1alpha,25-dihydroxyvitamin D(3) synthesized in our research group that show selective activity in vivo are presented along with supporting biological results. Compounds that act preferentially on intestine are 2-(3'-propylidene-19-nor-(20S or 20R))-1alpha,25-dihydroxyvitamin D(3) and 2-methylene-19-21-dinor-1alpha,25-dihydroxyvitamin D(3). Compounds that act anabolically to induce bone formation are 2-methylene-19-nor-(20S)-1alpha,25-dihydroxyvitamin D(3) (2MD), the 2alpha-methyl derivative, the 26,27-dimethyl derivative, and the 26-dimethylene derivative. Compounds that act preferentially on parathyroid glands are 2-methylene-19-nor-1alpha-hydroxy-homopregnacalciferol, the 20S-bishomo derivative and the 2-methylene-19,26,27-trinor-1alpha,25-dihydroxyvitamin D(3). These latter compounds do not elevate serum calcium until doses of the order of >300 microg/kg body weight are used, while parathyroid hormone levels are suppressed at much lower doses. Some of these novel analogs may ultimately be useful as new and safer therapeutic agents. Regardless of their clinical utility, they represent valuable research tools that can be used to study the specific functions of the Vitamin D hormone in vivo. 相似文献
950.