摘要:

AbstractActivation analysis in general and mainly reactor neutron activation analysis (NAA) has been used extensively for measuring trace elements in high purity materials, particularly semiconductor materials. The advantages of NAA in determination of trace elements differ from one semiconductor material to another. For all of them the inherent properties of activation analysis especially those of non contamination with the reagents, low blanks and high sensitivity are the reasons for the choice of NAA as the main analytical procedure. These inherent properties are essential for analysis of high‐purity materials where concentrations of ppb's and sub ppb's have to be measured.NAA is specially suitable for the determination of trace elements in silicon due to the very short lived very low activity induced by neutron reaction in silicon. This enables easy instrumental (i.e. without chemical separations) determination of trace elements in silicon. In the HFR reactor at Peten, Netherlands, a special facility was constructed for irradiation of silicon samples of Philips, in which silicon wafers of up to 15 cm diameter can be irradiated with 4 × 1013n. cm−2. sec−1and the irradiation is done for 72–96 hours. using large Ge(Li) detectors (100 to 150cc) and long counting time (8–16 hours) they measured 22 elements in concentrations below ppb and 10 others between ppb and 300 ppm. Trace elements in germanium have been determined both instrumentally after very long decay time (100 days) or after short decay time removing the activities from the matrix by chemical separation. Trace elements in GaAs are determined only after chemical separtion. Several other semiconductor material such as Sc, Te, GaP and CuInS2were also determined by NAA.Some trace elements cannot be determined by neutron activation. Carbon, nitrogen and oxygen are determined by activation with protons, alphas or3He particles. Boron and hydrogen are determined by prompt emission induced by charged particle activation, which gives not only the total concentration but also the depth profile. Carbon, nitrogen, oxygen and phosphorus were also determined by prompt proton activation analysis.The environmental samples studied by activation analysis can be divided into three categories: atmospheric aerosols, water samples and solid wastes. NAA of atmospheric aerosols have been used for their posible toxicological hazards, their source identification and for studies of atmospheric transport

ISSN:0009-4536    

DOI:10.1002/jccs.199000015

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractTrace element speciation has recently become one of the most important problems in water analysis. Proper combination of preconcentration techniques with instrumental determination methods is essential to speciation analysis, because sensitivity and selectivity of direct determination methods are generally lacking. The present paper describes such preconcentration techniques as filtration, centrifugation, flotation and sorption, which have been developed in the author's laboratory for the speciation of heavy metals in river and pond waters by electron microscopy, X‐ray microanalysis and chemical analysis. The application of freeze concentration to the speciation of silica in high‐purity waters is also discus

ISSN:0009-4536    

DOI:10.1002/jccs.199000016

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractIn our laboratory, we have applied the tools of nuclear magnetic resonance (NMR) spectroscopy and moleculargenetics to investigatethe structural and dynamic properties of membrane‐associated proteins and their interactions with membrane components. There are two general classes of membrane proteins, i.e., intrinsic and peripheral ones. For the intrinsic membrane proteins, we have chosen the membranebound D‐lactate dehydrogenase (D‐LDH) ofEscherichia colias a model to study protein‐lipid interactions in membranes. D‐LDH is a respiratory enzyme of molecularweight 65, 000 containing flavin adenine dinucleotide (FAD) as a cofactor. The activity of purified D‐LDH is enhanced up to 100‐fold by lipids and detergents. The gene for D‐LDH has been sequenced, and production of the enzyme amplified up to 300‐times normal levels. We have biosynthetically incorporated 5‐fluorotryptophan (5F‐Trp) into D‐LDH and studied the five Trp residues by19F‐NMR spectroscopy. In order to gain additional information using19F‐NMR, site‐specific, oligonucleotide‐directed mutagenesis has been used to insert a sixth Trp into D‐LDH at various positions throughout the 571‐amino acid chain. These mutant D‐LDHs are being characterized biochemically and through NMR. For peripheral membrane proteins, we have chosen two periplasmic binding proteins, histidine‐binding protein J (J protein) ofSalmonella Typhimuriumand glutamine‐binding protein (GlnBP) ofE. colias models to investigate the structure‐function relationship in periplasmic binding protein‐mediated active transport systems. These two proteins both have molecular weights of approximately 25, 000. By using mutant J proteins and GlnBPs and site‐specific, oligonucleotide‐directed mutagenesis techniques, we have assigned several resonances to specific amino acid residues. We are investigating the relationship between ligand‐induced conformational changes in these two proteins and their roles in the active transport of ligand across the cell membrane. We have found that a combination of isotopic labeling, biochemistry, molecular biology, and NMR is a very useful approach to investigate various

ISSN:0009-4536    

DOI:10.1002/jccs.199000017

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe uranyl ion in 5‐sulfosalicylic acid (5‐SSA) solution has been investigated by polarography. The constitution of the chelate species was confirmed by conductometric titration, under the experimental conditions: temperature 25±0.1C. pH = 2.0‐9.0. ligand concentration 10‐200 mM. At pH<4.8, the chelate species, UO2(HA)22−, is predominant. At pH 6.0. the complex species. UO2(A)24mainly exists. The chelate species. UO2(HA)22−, and UO2(A)24, co‐exist between pH 4.8‐6.0. The diffusion coefficients and stability constants have been determined by equations derived from

ISSN:0009-4536    

DOI:10.1002/jccs.199000018

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe crystal structure of Rb2V3P4O17has been determined from single‐crystal X‐ray diffraction data. Rb2V3P4O17crystallizes in the orthorhombic space group Pnma (No. 62) with a = 17.502(7), b = 7.292(2), c = 11.399(6) Å3, V = 1455(1) Å3, Z=4, R=0.0295, RW= 0.0320 for 1129 unique reflections with I>2.5 σ(I). The structure contains intersecting tunnels where the Rb+cations are located. The framework can be described as consisting of V2O10units formed from one VO5square pyramid and one VO6octahedron sharing a corner, and infinite chains of corner‐shared VO6octahedra, which are linked in three dimensions by pyrophosphate groups. The structural formula is Rb2(VO)3(P2O7)2. A single‐phase product can be obtained by heating appropriate amounts of Rb4V2O7, VO2, V, and P2O5in an evacuated fused silica tube at 950°C. Powder magnetic susceptibility data confirm the presence of V4+(d1) ions without magnetic ordering

ISSN:0009-4536    

DOI:10.1002/jccs.199000019

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractFe/TiO2catalyst was prepared by incipient wetness impregnation of TiO2with aqueous solution of ferric nitrate. The reduction behavior of the catalyst was studied by temperature programmed reduction profiles, Mössbauer spectroscopy, x‐ray diffraction and x‐ray photoelectron spectroscopy. The results show that the reduction of Fe/TiO2was accompanied by a phase transition of anatase to rutile titania. α‐Fe2O3was reduced to Fe3O4in the initial reduction stage. Due to the strong support effect of TIO2, FeTiO3was gradually formed as the reduction temperature reached 450°C. Complete reduction to the metallic Fe° particles occurred at temperatures higher than 670°C. The anatase‐rutile transition was initiated by the reduced Ti3+ions and led to the formation of TiOx. At higher reduction temperature, TiOxmigrated to the surface of metallic Fe° particles forming FeTiOxin the so‐called strong metal‐support interac

ISSN:0009-4536    

DOI:10.1002/jccs.199000020

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractMicelles formed from gelatin solutions were studied by sedimentation and optical mixing spectroscopy (OMS). We sampled gelatin solutions at various centrifugal speeds. Single exponential autocorrelation functions of the gelatin solutions were measured at 27°C and at 90° scattering angle by OMS. Calculation of the diffusion coefficient D from the measured autocorrelation function of scattered light has been carried out in this studied. A calculation of the micellar radius from the Stokes‐Einstein equation was carried out. We also calculated the sedimentation coefficient and molecular weight of gelatin micelles and found that the polydisperse gelatin micelles were formed at 50mg

ISSN:0009-4536    

DOI:10.1002/jccs.199000021

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractWe have developed a video‐microscopic computer imaging system for observing meso‐scale nonequilibrium physicochemical structures. Chargcd‐coupled device (CCD) in optical detection, and computer‐enhancement of digitized image, have greatly improved the resolution, sensitivity, and dynamical range of this technique. We apply this system to the observation of various complex crystallization patterns from Suberic acid melts and Camphene condensation. These patterns are of the scale one to 100 micrometers. They are resulted from nonlinear dynamical instabilities of a growing crystal fronts. The following patterns are observed: dendrites, destabilization of flat surface, cellular solidification, tip‐splitting, and dense branches. A computer simulation based on diffusion‐limited aggregates (DLA) model is performed to show this instability. The DLA model with surface tension effect is able to result in fractal‐like, dendrite, and needle‐like

ISSN:0009-4536    

DOI:10.1002/jccs.199000022

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractRadiative lifetimes and total deactivation cross sections of K(72S) and K(52D) by collision with NO are studied. The K atomic vapor in either the 72S or the 52D state was prepared by two‐ photon absorption using a dye laser. The decay signal of the time‐resolved fluorescence from the 72S – 42P1/2or 52D – 42P3/2transition was then monitored. Based on a Stern‐Volmer analysis, the radiative lifetimes are 155 ±8 ns and 561 ± 18 ns for the K(72S) and K(52D) states, respectively. The total deactivation cross sections are 88 ±1Å2and 70 ±2Å2for the K(72S)‐NO and K(52D)‐NO collisions, respectively. In the absence of NO collisions the radiative lifetimes obtained in this work show excellent agreement with those previously reported. The quenching cross sections for NO have been measured for the first time, and have values in a reasonable range, when compared w

ISSN:0009-4536    

DOI:10.1002/jccs.199000023

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractAnalytic expressions of matrix elements of x″, exp(‐2cx) and exp(‐cx2/2) for displaced linear oscillators with unequal vibrational frequencies are eval

ISSN:0009-4536    

DOI:10.1002/jccs.199000024

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY