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151.
Narrow autoionizing resonances have been observed in Yb and Tl using direct 3-photon excitation of ground state atoms. The linewidth is 0.9 cm-1 in Yb and 0.4 cm-1 in Tl. Autoionizing levels in both atoms correspond to doubly excited electronic states. This is the first observation of such states in Tl. 相似文献
152.
BinaS. Siddiqui Munawwer Rasheed Shaheen Faizi Firdous S.Tariq Ali RajputM. Tariq SyedNaeem‐ul‐Hassan Naqvi 《Helvetica chimica acta》2003,86(10):3342-3353
During studies on the structure? pesticidal‐activity relationship of Azadirachta indica constituents, azadiradione ( 1 ) was treated with methanolic K2CO3 to obtain 7‐deacetyl derivative nimbocinol ( 2 ). Unexpectedly, 17β‐hydroxynimbocinol ( 3 ), reported earlier as a natural product, was also formed. The structure? pesticidal‐activity relationship of triterpenoids 1 – 16 against Anopheles stephensi Liston is described towards understanding the active functionalities responsible for the pesticidal activity of triterpenoids having apoeuphane(apotirucallane) and gedunin skeleta. The pesticidal activities of triterpenoids 2 – 8 are reported for the first time. 相似文献
153.
H. A. Naqvi C. Bahri D. Troltenier J. P. Draayer A. Faessler 《Zeitschrift für Physik A Hadrons and Nuclei》1995,351(3):259-270
An algebraic realization of the quantum rotor for non-zero spin values (integer as well as half-integer) is established by constructing a model Hamiltonian out of rotationally invariant functions of the generators ofSU(3). The eigenvalues of this Hamiltonian in the leading normal-SU(3) symmetry for25Mg and the so-called leading pseudo-SU(3) symmetries for159Dy and165Er are compared with the corresponding rotor results. For spinfree systems the internal symmetry group of the rotor and itsSU(3) realization are known to be D2, the Vierergruppe. This symmetry extends to integral spin values, while for half-integer spins the rotor and itsSU (3) realization are shown to display an internal quaternion group symmetry. The theory points to a microscopic (many-particle shell-model) picture of nuclear rotational motion with spin degrees of freedom taken fully into account. An algebraic realization of the many-particle Nilsson model for odd-A nuclei, with the orbit-orbit and spin-orbit terms included, is given and applied to23Na. 相似文献
154.
K. Razi Naqvi 《Chemical physics letters》1979,67(1):205-206
It is stressed that the “long-time” rate constant of a diffusion-mediated bimolecular reaction does not equal the product of the reaction probability per encounter with kD, the encounter rate constant, and that kD ≠ 4πD? where D is the sum of the diffusion coefficients of the reactants and ? the encounter diameter. Neglect of these points has vitiated the analysis used by Stevens and his associates for estimating diffusive displacement parameters. 相似文献
155.
156.
Metal carboxylate stabilisers are believed to replace labile chlorines in PVC with more stable ester linkages resulting in an increase in the stability of the polymer. In the present work, effects of combinations of stearates, palmitates and laurates respectively of zinc and calcium, in various proportions, on the thermal stability of PVC were studied. Combinations of palmitates and stearates having more than 75 mol% of calcium salt were found to increase the stability of the polymer. The combinations of the three carboxylates showed the following order of stabilising: palmitate > stearate > laurate. This effect is explained in terms of a critical chain length of the n-alkyl group of the carboxylate anion which is most effective in the stabilising process. Highly crystalline, low molecular weight polyethylenes are used as plasticisers for PVC. They were found to have a stabilising effect explained in terms of a dilution effect by the non-polar polyethylenes on the polar interactions in PVC; compatibility of polyethylenes with PVC is the limiting factor in this stabilisation. 相似文献
157.
StineNalum Naess Arnljot Elgsaeter BenteJeanette Foss Baojun Li Hans‐Richard Sliwka Vassilia Partali ThorBernt Mel K.Razi Naqvi 《Helvetica chimica acta》2006,89(1):45-53
The surface and aggregation properties of the naturally occurring carotenoid crocin ( 1 ), examined through measurements of surface tension and UV/VIS absorption, have been used to determine the following parameters: critical aggregate concentration, surface‐saturation concentration, molecular area, free energy of adsorption and micellation, adsorption‐micellar energy relationship, equilibrium constants, and aggregate size. On structural grounds and based on the determined molecular area at the interface, the digentiobiosyl ester of the conjugated, highly unsaturated carotenoid diacid crocetin C20 : 7 should be classified as a bolaamphiphile. Crocin forms true monomolecular solutions in H2O; only at rather high concentrations aggregation occurs. 相似文献
158.
Jávorfi T Garab G Naqvi KR 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,(1):211-214
A comparison of the triplet-minus-singlet (TmS) absorption spectrum of spinach chloroplasts, recorded some thirty years ago, with the more recently published TmS spectrum of isolated Chla/b LHCII (light-harvesting complexes associated with photosystem II of higher plants) shows that the two spectra are very similar, which is to be expected, since only the carotenoid pigments contribute to each spectrum. Be that as it may, the comparison also reveals a dissimilarity: photoexcitation of the sample does, or does not, affect the absorbance in the Qy region (650-700 nm), depending on whether the sample is a suspension of chloroplasts or of isolated LHCII. The Qy-signal in the TmS spectrum of LHCII decays, it should be noted, at the same rate as the rest of the difference spectrum, and its most prominent feature is a negative peak. As the carotenoids do not absorb in the Qy region, the presence of a signal in this region calls for an explanation: van der Vos, Carbonera and Hoff, the first to find as well as fathom the phenomenon, attributed the Qy-signal to a change, in the absorption spectrum of a chlorophyll a (Chla) molecule, brought about by the presence of triplet excitation on a neighbouring carotenoid (Car). The difference in the behaviours of chloroplasts and LHCII, if reproducible, would imply that the Car triplets which give rise to the TmS spectrum of chloroplasts do not influence the absorption spectra of their Chla neighbours. With a view to reaching a firm conclusion about this vexed issue, spinach chloroplasts and thylakoids have been examined with the aid of the same kinetic spectrometer as that used for investigating LHCII; the TmS spectra of both chloroplasts and thylakoids contain prominent bleaching signals centred at 680 nm, and the triplet decay time in each case is comparable to that of the Chla/b LHCII triplets. Results pertaining to other closely related systems are recalled, and it is concluded that, so far as the overall appearance of the TmS spectrum is concerned, spinach chloroplasts are by no means abnormal. 相似文献
159.
Monte Carlo calculations were carried out to study the dependence of γ-ray yield on the bulk density and moisture content
of a sample in a thermal-neutron capture-based prompt gamma neutron activation analysis (PGNAA) setup. The results of the
study showed a strong dependence of the γ-ray yield upon the sample bulk density. An order of magnitude increase in yield
of 1.94 and 6.42 MeV prompt γ-rays from calcium in a Portland cement sample was observed for a corresponding order of magnitude
increase in the sample bulk density. On the contrary the γ-ray yield has a weak dependence on sample moisture content and
an increase of only 20% in yield of 1.94 and 6.42 MeV prompt γ-rays from calcium in the Portland cement sample was observed
for an order of magnitude increase in the moisture content of the Portland cement sample. A similar effect of moisture content
has been observed on the yield of 1.167 MeV prompt γ-rays from chlorine contaminants in Portland cement samples. For an order
of magnitude increase in the moisture content of the sample, a 7 to 12% increase in the yield of the 1.167 MeV chlorine γ-ray
was observed for the Portland cement samples containing 1 to 5 wt.% chlorine contaminants. This study has shown that effects
of sample moisture content on prompt γ-ray yield from constituents of a Portland cement sample are insignificant in a thermal-neutrons
capture-based PGNAA setup. 相似文献
160.
M. S. Abdelmonem A. A. Naqvi Hanan Al-Ghamdi Ghada Al-Misned 《Journal of Radioanalytical and Nuclear Chemistry》2007,274(1):131-137
Performance of a 241Am-Be neutron source-based and 2.8 MeV neutrons-based moisture measurement setups have been compared using Monte Carlo simulation.
In the setup fast neutrons transmitted through the sample were detected by a fast neutron detector, which was placed behind
a massive long double truncated collimator. The setup geometry was optimized to detect maximum effect of 1–7 wt.% moisture
on the neutron intensity transmitted through the sample. The yield of neutrons transmitted through concrete, coal, wood and
soil samples containing 1–7 wt.% moisture was calculated for 2.8 MeV neutrons and neutrons from an 241Am-Be source. The slopes of the fast neutron intensities transmitted through the samples vs. their moisture contents are very
sensitive to the neutron energy and the sample composition. Higher slopes have been observed for the samples with larger bulk
density. The slopes of fast neutron yield show dependence on the incident neutron energy. Larger slopes have been observed
for neutrons with samller energy. Due to the overall large slopes of the transmitted intensity data of the samples for 2.8
MeV neutrons, it is expected to achieve better sensitivity in moisture measurements for a 2.8 MeV neutrons based moisture
setup. 相似文献