共查询到20条相似文献,搜索用时 15 毫秒
1.
S. P. D. Bhade P. J. Reddy A. Narayanan K. K. Narayan D. A. R. Babu D. N. Sharma 《Journal of Radioanalytical and Nuclear Chemistry》2010,284(2):367-375
Simultaneous measurement of gross alpha and gross beta activities by liquid scintillation counting technique using LKB Wallac
Quantulus 1220 liquid scintillation counter (LSC) equipped with Pulse Shape Analyzer (PSA) is described. Three sets of pure
alpha and pure beta standards simulating the activity concentration values of real samples in terms of α/β activity ratios
were used to calibrate the LSC. Calibration methodology for the Quantulus 1220 with respect to the above measurements using
241Am and 90Sr/90Y standards of respective activity concentrations of ~25 dpm and ~104 dpm is described in detail. Also highlighted the need to calibrate the LSC using another set of 241Am and 90Sr/90Y standards of low and high activity concentrations respectively. The practicability and working performance of these calibration
plots was checked by the validation trials with test samples spiked with 241Am and 90Sr/90Y covering range of α/β activity ratios from 1:1 to 1:50. 相似文献
2.
A. T. Abdul Rahman A. T. Ramli 《Journal of Radioanalytical and Nuclear Chemistry》2007,273(3):653-657
A survey was carried out to determine terrestrial gammaradiation dose rates, the concentration level of 238U and 232Th and α and β activities for the surface soil in Ulu Tiram, Malaysia A 125 measurements were performed using a NaI(T1) gamma-ray
detector with crystal size of 1″ × 1″ on 15 soil samples collected from the site area about 102 km2
238U and 232Th concentrations were determined in soils by using hyper pure germanium (HPGe) gamma-ray spectrometry. The activity of α
and β from the surface soil was counted by using alpha beta counting system. The average value of 238U and 232Th concentrations in soil samples collected are 3.63±0.39 ppm within the range of 1.74±0.20 to 4.58±0.48 and 43.00±2.31 ppm
within the range of 10.68±0.76 to 82 10±4.01 ppm, respectively. The average estimate of α and β activity in soil samples collected
are 0.65±0.09 Bqg−1 and 0.68±0.08 Bqg−1, respectively. The average of terrestrial gamma-radiation dose rates measured in Ulu Tiram was found to be 200 nGy h−1, within the range of 96 to 409 nGy h−1. The population weighted outdoor annual effective dose was 1.2 mSv. 相似文献
3.
Vasil Simeonov Costel Sarbu Desire-Luc Massart Stefan Tsakovski 《Mikrochimica acta》2001,137(3-4):243-248
A data set (48×19) consisting of Danube river water analytical data collected at Galati site, Romania, during a four-year
period has been treated by principal components analysis (PCA). The PCA indicated that seven latent factors (“hardness”, “biochemical”,
“waste inlets”, “turbidity”, “acidity”, “soil extracts” and “organic wastes”) are responsible for the data structure and explain
over 80 % of the total variance of the system. Its complexity is further proved by the application of multiple linear regression
analysis on the absolute principal components scores (APCS) where the contribution of each natural or anthropogenic sources
in the factor formation is shown. The apportioning makes clear that each variable participates to a different extent to each
source and, in this way, no pure natural or pure anthropogenic influence could be determined. No specific seasonality for
the variables in consideration is found.
Received January 24, 2001. Revision July 6, 2001. 相似文献
4.
J. T. Hann 《Chromatographia》1987,24(1):510-512
Summary A quaternary mobile phase was optimized in conjunction with Fast LC techniques to separate α and β acids extracted from hops
in less than 4 minutes. The method is proposed for automated analysis of large numbers of hop samples and its usefulness is
demonstrated by comparing α-acid levels obtained by liquid chromatographic and conductometric techniques. Both assays provided
similar values for “fresh” hops but in “aged” hops liquid chromatography showed a lower level of α-acids. 相似文献
5.
I. Stanimirova S. Tsakovski V. Simeonov 《Fresenius' Journal of Analytical Chemistry》1999,365(6):489-493
Multivariate statistical analysis of sediment data (information matrix 123 × 16) from the Gulf of Mexico, USA shows that
the data structure is defined by four latent factors conditionally called “inorganic natural”, “inorganic anthropogenic”,
“bioorganic” and “organic anthropogenic” explaining 39.24%, 23.17%, 10.77% and 10.67% of the total variance of the data system,
respectively. The receptor model obtained by the application of the PCR approach makes it possible to apportion the contribution
of each chemical component for the latent factor formation. A separation of the contribution of each chemical parameter is
achieved within the frames of “natural” and “anthropogenic” origin of the respective heavy metal or organic matter to the
sediment formation process. This is a new approach as compared to the traditional “one dimensional” search with a limited
number of preliminary selected tracer components. The model suggested divides natural from anthropogenic influences and allows
in this way each participant in the sediment formation process to be used as marker of either natural or anthropogenic effects.
Received: 20 March 1999 / Revised: 1 June 1999 / Accepted: 3 June 1999 相似文献
6.
Multivariate statistical analysis of sediment data (information matrix 123 × 16) from the Gulf of Mexico, USA shows that
the data structure is defined by four latent factors conditionally called “inorganic natural”, “inorganic anthropogenic”,
“bioorganic” and “organic anthropogenic” explaining 39.24%, 23.17%, 10.77% and 10.67% of the total variance of the data system,
respectively. The receptor model obtained by the application of the PCR approach makes it possible to apportion the contribution
of each chemical component for the latent factor formation. A separation of the contribution of each chemical parameter is
achieved within the frames of “natural” and “anthropogenic” origin of the respective heavy metal or organic matter to the
sediment formation process. This is a new approach as compared to the traditional “one dimensional” search with a limited
number of preliminary selected tracer components. The model suggested divides natural from anthropogenic influences and allows
in this way each participant in the sediment formation process to be used as marker of either natural or anthropogenic effects.
Received: 20 March 1999 / Revised: 1 June 1999 / Accepted: 3 June 1999 相似文献
7.
Using time-resolved CIDEP and conventional ESR as well as optical studies much can be elucidated concerning the initial photochemical
reactions of lignin model compounds such as α-guaiacoxyacetoveratrone and α-guaiacoxy-β-propioveratrone. The resulting transient
radicals are models for intermediates in the processes of photoyellowing of lignin containing mechanical pulps and papers.
Model solution experiments which produce evidence for the roles of free radicals in reductive bleaching of mechanical pulps
and in the oxidative aging of papers are also described. The more thorough understanding of these complex processes allows
the development of strategies to try to “protect” mechanical pulps and papers from light and thermally induced damage and
to “repair” any damage which invevitably occurs. 相似文献
8.
The spin-polarization mechanism in aromatic systems is analyzed with reference to the prototypical phenoxyl, cyclohexadienyl
and benzyl radicals. In particular, a decomposition into “first-order” and “second-order” contributions is proposed, which
helps to rationalize the different nature of the spin density for atoms in α or in β positions with respect to the radical
center. The different weights of the two contributions are discussed on the basis of Hartree–Fock and density functional computations.
Received: 17 September 1999 / Accepted: 3 February 2000 / Published online: 29 June 2000 相似文献
9.
T. Ishikawa M. Hosoda A. Sorimachi S. Tokonami S. Katoh S. Ogashiwa 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(3):709-713
Nowadays, artificial “radon spa sources” for home baths are commercially available. Although these sources could give a potential
radiation exposure to the users, few studies have been reported on their radiological measurements. In the present study,
five types of radon spa sources were collected and their radiological characterization was investigated. The followings were
estimated for these samples: (1) radon emanation coefficients (dry and water-saturated conditions), (2) surface γ-ray dose
rate, (3) surface count rates for α- and β-rays, (4) activity concentrations of 226Ra, 232Th and 40K, and (5) concentrations of radon and thoron generated from the sources located in an air flow system. The activity concentrations
were very high (except for one sample (named “sample B”), although radon emanation coefficient was low compared with soil.
This leads to high concentrations of radon/thoron generated from the sample. The maximum surface γ-ray dose rate was observed
for sample A (2.7 μGy h−1). If people stay very close to the sample for a long time, the exposure might be significant. 相似文献
10.
Gerhard Friedrich Thorsten Rose Alexander Wawkuschewski Sabine Kafert-Kasting Britta Laube Lubomir Arseniev Klaus Rissler 《Chromatographia》2008,67(1-2):31-39
In a recently published paper development of a sensitive automated “on-line” solid-phase extraction (SPE)/RP-HPLC assay for
6β-hydroxytestosterone (6β-OHT) with corticosterone as the internal standard (IS) was reported and its potential for quantification
of various testosterone metabolites in culture media reflecting metabolic activity of cultured human and animal hepatocytes
demonstrated [1]. In this following contribution the technique has been extended to determination of another five testosterone metabolites
in cultured rat hepatocytes using an identical “on-line” SPE/RP-HPLC procedure and detection by tandem MS-MS with an atmospheric
pressure chemical ionization (APCI) source in the selected reaction monitoring (SRM) mode as that described in [1]. All six testosterone metabolites, namely 2α-OHT, 2β-OHT, 6α-OHT, 6β-OHT, 7α-OHT and 16α-OHT, could be sufficiently separated
from each other and thus an unequivocal assignment to the individual structures was achieved. Validation data are presented
specifying the limits of quantitation as well as the mean values of the coefficients of variation (CV) for the target analytes
and the accuracy obtained at five different days. Regio- and stereoselective testosterone hydroxylation by rat hepatocytes
was measured in a long-term culture system with and without exposure to rifampicin as an inducer of liver CYP 3A4 activity.
In addition, testosterone hydroxylation was analyzed in cultures of cryopreserved hepatocytes that had been stored at −196 °C.
The rat hepatocytes were cultured after thawing for up to 11 days and induction of testosterone hydroxylase activity could
be demonstrated in cultures which underwent a new cryopreservation protocol.
This paper is dedicated to Professor Hinrich Cramer on the occasion of his 75th birthday. 相似文献
11.
A. V. Prosyanik S. V. Bondarenko V. I. Markov I. I. Chervin M. D. Isobaev S. D. Kushch R. G. Kostyanovskii 《Chemistry of Heterocyclic Compounds》1980,16(2):154-158
Esters of β-alkoxyamino-α-bromopropionic acids were obtained by reaction of α,β-dibromopropionic acid esters with alkoxyamines
in the presence of triethylamine at 20°C for 1 month. When the products are refluxed in acetonitrile in the presence of triethylamine,
they are converted to aziridines. Selective amidation of the alkoxyaziridines with excess dimethylamine in absolute methanol
in the presence of sodium methoxide leads to enrichment with the cis isomer. The parameters of inversion of the nitrogen atom
in the alkoxyaziridines were determined.
Communication 20 from the series “Asymetric Unbridged Nitrogen”; see [1] for communication 19.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 212–215. February, 1980. 相似文献
12.
A. S. Merenga C. M. Papadakis F. Kremer J. Liu A. F. Yee 《Colloid and polymer science》2001,279(11):1064-1072
Broadband dielectric spectroscopy (1–106 Hz, 183–423 K) and differential scanning calorimetry are employed to analyze the inter- and intramolecular dynamics of a
series of random copolymers based on poly(ethylene terephthalate) and poly(1,4-cyclohexylene dimethylene terephthalate). In
addition to an interfacial relaxation (α*-process), three dielectric relaxation processes are observed: The α-relaxation (“dynamic
glass transition”) and two secondary relaxations (β- and β*-relaxations). The α-relaxation depends sensitively on the composition
of the copolymer and shows a rapid slowing down with increasing content of cyclohexylene dimethylene (CHDM) linkages. Besides
the β-relaxation, attributed to local motion of the ester group, an additional process (β*-relaxation) is observed on introducing
the CHDM linkages. Increasing the content of the latter reduces the strength of the β-relaxation strongly and increases its
activation energy by more than 30%. This proves that owing to interactions between the cylohexylene rings and the ester group
the β-relaxation no longer has local character only.
Received: 28 September 2000 Accepted: 29 January 2001 相似文献
13.
Stefania?Gaudino Chiara?Galas Maria?Belli Sabrina?Barbizzi Paolo?de?Zorzi Radojko?Ja?imovi? Zvonka?Jeran Alessandra?Pati Umberto?Sansone
The measurement of trace-element concentration in soil, sediment and waste, is generally a combination of a digestion procedure
for dissolution of elements and a subsequent measurement of the dissolved elements. “Partial” and “total” digestion methods
can be used in environmental monitoring activities. To compare measurement results obtained by different methods, it is crucial
to determine and to maintain control of the bias of the results obtained by these methods. In this paper, ICP-MS results obtained
after matrix digestion with modified aqua regia (HCl+HNO3+H2O2) method and two “total” digestion methods (microwave aqua regia+HF and HNO3+HF) are compared with those obtained by instrumental neutron activation analysis, a non-destructive analytical method for
the determination of the total mass concentrations of inorganic components in environmental matrices. The comparison was carried
out on eight agricultural soil samples collected in one test area and measured by k0-INAA and ICP-MS to determine As, Co, Cr, Sb and Zn mass concentration. The bias of results for As, Cd, Co, Cr, Cu, Ni, Pb,
Sb and Zn of the three digestion methods were assessed using selected measurement standards. This paper highlights that the
digestion procedure is an integral part of the measurement and can affect the measurement result in environmental analysis. 相似文献
14.
Multivariate statistical assessment of polluted soils 总被引:9,自引:0,他引:9
Vasil Simeonov Juergen Einax Stafan Tsakovski Joerg Kraft 《Central European Journal of Chemistry》2005,3(1):1-9
This study deals with the application of several multivariate statistical methods (cluster analysis, principal components
analysis, multiple regression on absolute principal components scores) for assessment of soil pollution by heavy metals. The
sampling was performed in a heavily polluted region and the chemometric analysis revealed four latent factors, which describe
84.5 % of the total variance of the system, responsible for the data structure. These factors, whose identity was proved also
by cluster analysis, were conditionally named “ore specific”, “metal industrial”, “cement industrial”, and “steel production”
factors. Further, the contribution of each identified factor to the total pollution of the soil by each metal pollutant in
consideration was determined. 相似文献
15.
We studied the size scaling behaviour in an ensemble of 8,614 non-redundant protein domains belonging to the all-α, all-β,
α / β, and α + β folding classes. We find that the most compact structural domains can be characterized by an effective exponent
ν
eff
= 0.39 ± 0.01, which is larger than the value for “collapsed-polymers,” i.e., ν = 1/3. We also show that the global ν
eff
-exponent is an average of the scaling regimes for short and long compact chains, where the values change from ν
eff
≈ 0.37 to ν
eff
≈ 0.45 at chain length of ca. 269. A transition from short-chain to long-chain scaling behaviour is found in all major folding classes, over a window
of chain lengths between 216 and 269 residues. In addition, variations in scaling exponent with respect to folding class indicates
that the smallest domains in the (all-β) and (α / β) families appear to be more compact structures than the smallest (all-α)-
and (α + β)-domains. 相似文献
16.
Matioli Graciette Zanin Gisella M. Gljimarães Manoel F. De moraes Flávio f. 《Applied biochemistry and biotechnology》1998,(1):267-275
Alkalophylic bacilli that produce cyclodextringlycosyltransferase (CGTase) were isolated from Brazilian soil, with a scheme
of two plating steps. In the first step, the bacterial isolate forms a halo in the cultivation medium that contains γ-cyclodextrin
(CD) complexing dyes. The CGTase of an isolate was purified 157-fold by biospecific affinity chromatography, with β-CD showing
a mol wt of 77,580 Daltons. It produces a γ- to β-CD ratio of 0.156 and a small amount of α-CD, using maltodextrin 10% as
substrate, at 50°C, pH 8.0 and 22 h reaction time, reaching 21.4% conversion of the substrate to cyclodextrins. In the second
screening step, the isolates chosen give larger halos with β-CD complexing dyes, and smaller halos with β-CD complexing dyes,
leading to a 30% improvement in γ-CD selectivity, although at lower total yield for cyclodextrins (11.5%). 相似文献
17.
Diastereoisomeric [(1R,5S)-5-“[(1R)-1-phenylethyl]aminocarbonyl”cyclopent-2-en-1-yl]methyl acetate and [(1S,5R)-5-“[(1R)-1-phenylethyl]aminocarbonyl”cyclopent-2-en-1-yl]methyl acetate reacted with m-chloroperoxybenzoic acid to give the corresponding stereoisomeric α- and β-epoxy derivatives, which were identified on the
basis of their spectral parameters. 相似文献
18.
G. Wakabayashi H. Ohura T. Okai M. Matoba H. Kakiuchi N. Momoshima H. Kawamura 《Journal of Radioanalytical and Nuclear Chemistry》1999,240(3):929-930
Stability and reproducibility of gel-suspension samples were investigated in order to evaluate the characteristic feature
of the gel-suspension method for14C activity measurement. Commercially available gelling agent, N-lauroyl-L-glutamic-α,γ-dibutylamide, was used for the gelformatio
of the samples. No change of the counting rate for the gel-suspension sample was observed for more than 2 years after the
sample preparation. Four samples used for checking the reproducibility of the sample preparation method. The same values were
obtained for the counting rate of14C activity within the counting error. No change of the counting rate was observed for the “re-gelated” sample. These results
show that the gel-suspension method is appropriate for the14C activity measurement by the liquid scintillation method and is useful for a long-term preservation of the sample for repeated
measurement. 相似文献
19.
V. G. Avakyan V. B. Nazarov M. V. Alfimov A. A. Bagatur'yants 《Russian Chemical Bulletin》1999,48(10):1833-1844
The structure of β-cyclodextrin (β-CD), as well as the structure and energetics of β-CD-naphthalene, β-CD-fluorene, β-CD-phenanthrene, β-CD-cyclohexane (1:1), and β-CD-naphthalene (2:2) inclusion complexes was studied by the semiempirical MNDO/PM3 method. Calculations of a β-CD-naphthalene-cyclohexane (1:1:1) complex were also performed. The minimum heat of formation was found for the symmetric β-CD conformation withC 7 symmetry axis. The structure is stabilized by the ring of interunit H-bonds formed by the protons of the 2-OH groups and the O atoms of the 3′-OH groups of the glucose units. Preferableness of this orientation of interunit H-bonds was confirmed byab initio calculations of the molecule of α-(1–4)-glucobiose (maltose) in the MP2/6-31G(d,p)//6-31G(d,p) approximation. The formation of any inclusion compounds of β-CD with arenes is energetically favorable: the complexation energy varies in the range −9 to −12 kcal mol−1. Among complexes with naphthalene, that of composition 2:2 is the most energetically favorable, which is in agreement with experimental data. In this complex, β-CD exists as a dimer of the “head-to-head” type, in which both partners are linked by a system of H-bonds. The structure of the “head-to-head” dimer of β-CD was simulated byab initio calculations of the H-bonded dimer of α-d-glucose in the RHF/6-31G(d,p) approximation. In the dimer, both components are linked by a pair of H-bonds formed by the protons of the 3-OH groups and the O atoms of the, 2-OH groups. The dimerization energies obtained fromab initio and semiempirical MNDO/PM3 and AM1 calculations differ by about 2.5 times (8.6vs 3.2 and 3.8 kcal mol−1, respectively). 相似文献
20.
Nordling E Kallberg Y Johansson J Persson B 《Journal of computer-aided molecular design》2008,22(1):53-58
Diseases associated with protein fibril-formation, such as the prion diseases and Alzheimer’s disease, are gaining increased
attention due to their medical importance and complex origins. Using molecular dynamics (MD) simulations in an aqueous environment,
we have studied the stability of the α-helix covering positions 15–25 of the amyloid β-peptide (Aβ) involved in Alzheimer’s
disease. The effects of residue replacements, including the effects of Aβ disease related mutations, were also investigated.
The MD simulations show a very early (2 ns) loss of α-helical structure for the Flemish (Aβ(A21G)), Italian (Aβ(E22K)), and
Iowa (Aβ(D23N)) forms associated with hereditary Alzheimer’s disease. Similarly, an early (5 ns) loss of α-helical structure
was observed for the Dutch (Aβ(E22Q)) variant. MD here provides a possible explanation for the structural changes. Two variants
of Aβ, Aβ(K16A,L17A,F20A) and Aβ(V18A,F19A,F20A), that do not produce fibrils in vitro were also investigated. The Aβ(V18A,F19A,F20A)
initially loses its helical conformation but refolds into helix several times and spends most of the simulation time in helical
conformation. However, the Aβ(K16A,L17A,F20A) loses the α-helical structure after 5 ns and does not refold. For the wildtype
Aβ(1–40) and Aβ(1–42), the helical conformation is lost after 5 ns or after 40 ns, respectively, while for the “familial”
(Aβ(A42T)) variant, the MD simulations suggest that a C-terminal β-strand is stabilised, which could explain the fibrillation.
The simulations for the Arctic (Aβ(E22G)) variant indicate that the α-helix is kept for 2 ns, but reappears 2 ns later, whereafter
it disappears after 10 ns. The MD results are in several cases compatible with known experimental data, but the correlation
is not perfect, indicating that multimerisation tendency and other factors might also be important for fibril formation. 相似文献