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741.
G. F. Torres del Castillo 《International Journal of Theoretical Physics》1986,25(8):883-890
It is shown that under certain weak conditions (the vanishing of the field strength along a family of self-dual or anti-self-dual geodesic two-surfaces), in a curved or flat space-time, the linear perturbations of a given gauge field configuration can be expressed in terms of the solutions of a single second-order linear partial differential equation for a matrix potential. The particular case of the self-dual gauge fields is treated in some detail. 相似文献
742.
This paper is concerned with the maximum likelihood estimation problem for the singly truncated normal family of distributions. Necessary and suficient conditions, in terms of the coefficient of variation, are provided in order to obtain a solution to the likelihood equations. Furthermore, the maximum likelihood estimator is obtained as a limit case when the likelihood equation has no solution. 相似文献
743.
J. R. Castillo J. M. Mir C. Martinez M. T. Gomez 《Fresenius' Journal of Analytical Chemistry》1986,325(2):171-174
Summary Optimum for the generation of arsine from As(III) and (V) in a generating system without carrier gas and with atomization in an air-acetylene flame were established. A 3% solution of NaBH4 was used as reducer. The effect of 26 different species on the determination of arsenic was studied. The method has been applied to determine arsenic in copper.A linear relationship exists between 0.5 and 3 g for As(III) and between 1 and 4 total g of As(V). The sensitivity, expressed as the slope of the calibration curve is 0.067 g–1 for As(III) and 0.054 g–1 for As(V); the characteristic masses are 1.22 g and 0.44 g, and the limits of detection 0.27 g and 0.33 g, respectively.
This work has been sponsored by the CAICYT (project 3378/83) of the Spanish Education and Science Department. 相似文献
Direkte Flammen-AAS — Erzeugung flüchtiger kovalenter HydrideStörungen durch das Verhältnis der As(III/V)-Valenzstufen und Arsenbestimmung in Kupfer
Zusammenfassung Optimale Bedingungen wurden ausgearbeitet für die Arsinerzeugung aus As(III) und As(V) in einem System ohne Trägergas mit Atomisierung in einer Luft-Acetylen-Flamme. Zur Reduktion dient eine 3%ige NaBH4-Lösung. Der Einfluß von 26 Fremdionen wurde geprüft und das Verfahren zur Arsenbestimmung in Kupfer angewendet. Eine lineare Beziehung ergab sich für 0,5–3 g As(III) und 1–4 g As(V). Die Empfindlichkeit (als Neigung der Eichkurve) beträgt 0,067 g–1 für As(III) und 0,054 g–1 für As(V). Die charakteristischen Massen sind 1,22 g bzw. 0,44 g und die Nachweisgrenzen 0,27 g bzw. 0,33 g.
This work has been sponsored by the CAICYT (project 3378/83) of the Spanish Education and Science Department. 相似文献
744.
Jesus Sanz Felix Gallarta Javier Galban Juan R. Castillo 《Fresenius' Journal of Analytical Chemistry》1988,330(6):510-515
Summary A method for antimony determination is described comprising hydride generation and transport into a flow-cell placed in a UV-visible molecular absorption spectrophotometer with diode-array detection. Nitrogen is employed as carrier gas. The measurement is performed at 198 nm. The calibration curve is linear from 3 to 440 g/ml of antimony. The method was successfully applied to the analysis of PVC.
Antimonbestimmung durch Hydridbildung. UV-vis-molekularabsorptions-spektrophotometrisches Verfahren mit Dioden-array-Detektion相似文献
745.
An SCF LCAO MO calculation on the methane–methane–methane system is presented, in order to analyze the deviation from pairwise additivity of the interaction energy. Three-body terms are shown to be remarkably similar to those of noble gas trimers both in magnitude and in their dependence on the geometrical arrangements of the three molecules. 相似文献
746.
Adler C Ahammed Z Allgower C Anderson M Averichev GS Balewski J Barannikova O Barnby LS Baudot J Bekele S Belaga VV Bellwied R Berger J Bichsel H Bland LC Blyth CO Bonner BE Bossingham R Boucham A Brandin A Caines H de la Barca Sánchez MC Cardenas A Carroll J Castillo J Castro M Cebra D Chattopadhyay S Chen ML Chen Y Chernenko SP Cherney M Chikanian A Choi B Christie W Coffin JP Conin L Cormier TM Cramer JG Crawford HJ DeMello M Deng WS Derevschikov AA Didenko L Draper JE Dunin VB Dunlop JC 《Physical review letters》2001,86(21):4778-4782
We report results on the ratio of midrapidity antiproton-to-proton yields in Au+Au collisions at sqrt[s(NN)] = 130 GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of /y/<0.5 and 0.4
相似文献
747.
Arias-Zugasti M García-Ybarra PL Castillo JL 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(3):2930-2941
The heating of a cold fluid package introduced, at critical conditions, in a hotter environment of the same fluid at the critical pressure is analyzed. Critical anomalies of the fluid transport properties as well as an arbitrary equation of state are taken into account. In unconfined microgravity conditions and for times much longer than the characteristic acoustic time, the heat transfer becomes a convective-diffusive isobaric transient process. An asymptotic theory valid in the limit of very small ratio between the fluid densities in the hot and cold regions is developed. The divergency of the thermal conductivity kappa at the critical temperature controls the heat transfer to the cold region. In the present model it is shown that there exists a well defined border, denoted by R(t), delimiting two distinguishable regions. The outer region extends from the far field down to R(t) where the critical temperature T(c) is reached. There, the temperature gradient vanishes due to the divergency of kappa. Thus, heat does not penetrate in the inner cold region where the temperature remains equal to T(c). The heating of the initially cold fluid package takes place by the recession of the border R(t). The model predicts a temperature profile in the outer region which is quasisteady in a reference system receding with R(t). It is shown that R2(t) decreases linearly with time. The recession velocity and thus the vaporization time are obtained as a function of the geometry and of the far-field conditions. Furthermore, the restrictions imposed by the long-time isobaric hypothesis are analyzed. 相似文献
748.
Oscar Díaz Rizo Margaret Suárez Muñoz Patricia González Hernández Alina Gelen Rudnikas Katia D´Alessandro Rodríguez Clara M. Melián Rodríguez Juan R. Fagundo Castillo Nadia V. Martínez-Villegas Juan Tomás Zerquera 《Journal of Radioanalytical and Nuclear Chemistry》2018,315(1):95-101
In this work, an approach for determining both the outer dead layer thickness of the p-type coaxial HPGe detector and the inner dead layer thickness of the n-type coaxial HPGe detector was proposed by using two full energy peak area count ratios of a X-ray and a gamma ray emitted from the same radioisotope of 137Cs. Monte Carlo calculations and experimental measurements were conducted to determine these dead layer thicknesses. The results showed that the outer dead layer thickness reached 0.57 ± 0.03 mm on 06 Jan 2017 after nearly 3 years of use for the p-type detector. The inner dead layer thickness reached 1.21 ± 0.24 mm on 01 Aug 2016 after more than 3 years of operation for the n-type detector. Simulation model with the modified dead layer thicknesses was used to estimate full energy peak efficiencies and gamma spectra from seven radioactive sources. The results were in good agreement with the corresponding experimental values in the gamma energy region of interest. 相似文献
749.
Juan-Carlos Castillo Elizabeth Jiménez Jaime Portilla Braulio Insuasty Jairo Quiroga Rodolfo Moreno-Fuquen Alan R. Kennedy Rodrigo Abonia 《Tetrahedron》2018,74(9):932-947
A useful and efficient method to construct diversely substituted 1,2,3,4-tetrahydroquinolines in good to excellent yields has been developed through a catalyst-free Domino Mannich and intramolecular Friedel-Crafts alkylation reactions of N-arylamines with paraformaldehyde and electron-rich olefins via the formation of N-aryl-N-alkylmethyleneiminium ions as the key intermediates to afford the target products. Nine of the new compounds were evaluated in the US National Cancer Institute (NCI), where compound 5f (R1?=?6-MeO, R2?=?p-ClC6H4 and X?=?pyrrolidin-2-onyl) presented a remarkable activity against 57 cancer cell lines, with the most important GI50 values ranging from 1.46 to 8.28?μM from in vitro assays. Further studies performed over the active compound 5f on HCT116 colon cancer cells indicated that its effect on cell death is exerted through a cell cycle arrest (S phase) in a dose dependent manner, as well as suppression on the cell proliferation process. 相似文献
750.
Rebeca G. Castillo Justin T. Henthorn Jeremy McGale Dimitrios Maganas Serena DeBeer 《Angewandte Chemie (International ed. in English)》2020,59(31):12965-12975
In recent years, X‐ray emission spectroscopy (XES) in the Kβ (3p‐1s) and valence‐to‐core (valence‐1s) regions has been increasingly used to study metal active sites in (bio)inorganic chemistry and catalysis, providing information about the metal spin state, oxidation state and the identity of coordinated ligands. However, to date this technique has been limited almost exclusively to first‐row transition metals. In this work, we present an extension of Kβ XES (in both the 4p‐1s and valence‐to‐1s [or VtC] regions) to the second transition row by performing a detailed experimental and theoretical analysis of the molybdenum emission lines. It is demonstrated in this work that Kβ2 lines are dominated by spin state effects, while VtC XES of a 4d transition metal provides access to metal oxidation state and ligand identity. An extension of Mo Kβ XES to nitrogenase‐relevant model complexes shows that the method is sufficiently sensitive to act as a spectator probe for redox events that are localized at the Fe atoms. Mo VtC XES thus has promise for future applications to nitrogenase, as well as a range of other Mo‐containing biological cofactors. Further, the clear assignment of the origins of Mo VtC XES features opens up the possibility of applying this method to a wide range of second‐row transition metals, thus providing chemists with a site‐specific tool for the elucidation of 4d transition metal electronic structure. 相似文献