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排序方式: 共有298条查询结果,搜索用时 390 毫秒
61.
Sudhir Kumar Pandey 《Microchemical Journal》2009,91(1):40-46
In this study, the reliability of thermal desorbing technique was investigated using the gaseous standards of five reduced sulfur compounds (RSCs: hydrogen sulfide, methane thiol, dimethyl sulfide, carbon disulfide, and dimethyl disulfide). A series of calibration experiments for RSCs were performed using gas chromatography (GC) with pulsed flame photometric detector (PFPD) that is interfaced with a thermal desorber (TD) unit. These calibration data were evaluated by means of two contrasting concepts: fixed standard concentration method (FSC: variable volumetric injection of standard gases prepared at a given concentration) and fixed standard volume method (FSV: injection of multiple standards with varying concentrations at a given volume). When the results of both methods were compared, RSCs generally showed enhanced sensitivity with increasing concentration (FSC) and sample loading volume (FSV). This study highlights that TD-based calibration properties are practically undistinguishable between different sample transfer approaches (e.g., FSV and FSC). As a result, the calibration properties of RSCs derived by thermal desorption technique are greatly distinguished from those of direct injection into GC. 相似文献
62.
Rotational diffusion of two organic solutes, coumarin153 (C153) and 4-aminophthalimide (AP) has been investigated in four ionic liquids (ILs), viz. 1-ethyl-3-methylimidazolium trifluoroacetate (EMIMTFA), 1-ethyl-3-methylimidazolium ethylsulfate (EMIMESU), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMTFB) and 1-ethyl-3-methylimidazolium tetracyanoborate (EMIMTCB), as a function of temperature. Between the two probes, AP can act as hydrogen-bond-donor to the solvents having hydrogen bond acceptor ability. The results indicate that the rotational dynamics of C153 is mainly governed by the viscosity of the medium. On the other hand, the rotational motion of AP is found to be significantly hindered in the ILs depending on the nature of anions of the ILs. Rotational coupling constant values for AP in the ILs follow the order TFA?>?ESU?>?TCB?>?TFB. The slower rotational motion of AP in these ILs has been attributed to the specific hydrogen bonding interaction between AP and anions of ILs. Figure
Rotational diffusion of two organic solutes, coumarin153 (C153) and 4-aminophthalimide (AP) has been investigated in four different ionic liquids (ILs) so as to monitor the effects of anions on the rotational dynamics of the solutes exclusively. Figure showing the anisotropy decay profile of AP at 293 K in two isoviscous room temperature ionic liquids having different hydrogen bond acceptors ability 相似文献
63.
Eigenfunctions of integrable planar billiards are studied — in particular, the number of nodal domains, ν of the eigenfunctions with Dirichlet boundary conditions are considered. The billiards for which the time-independent Schrödinger equation (Helmholtz equation) is separable admit trivial expressions for the number of domains. Here, we discover that for all separable and non-separable integrable billiards, ν satisfies certain difference equations. This has been possible because the eigenfunctions can be classified in families labelled by the same value of mmodkn, given a particular k, for a set of quantum numbers, m,n. Further, we observe that the patterns in a family are similar and the algebraic representation of the geometrical nodal patterns is found. Instances of this representation are explained in detail to understand the beauty of the patterns. This paper therefore presents a mathematical connection between integrable systems and difference equations. 相似文献
64.
Vaisakh Mohan A. Nijamudheen Sudhir Kumar Das Prabhat K. Sahu Usha Pallabi Kar Dr. Abdur Rahaman Dr. Moloy Sarkar 《Chemphyschem》2012,13(17):3882-3892
A new multi‐component chemosensor system comprising a naphthalimide moiety as fluorophore is designed and developed to investigate receptor–analyte binding interactions in the presence of metal and non‐metal ions. A dimethylamino moiety is utilized as receptor for metal ions and a thiourea receptor, having acidic protons, for binding anions. The system is characterized by conventional analytical methods. The absorption and fluorescence spectra of the system consist of a broad band typical for an intramolecular charge transfer (ICT). The effects of various metal‐ion additives on the spectral behavior of the present sensor system are examined in acetonitrile. It is found that among the metal ions studied, alkali/alkaline earth‐metal ions and transition‐metal ions modulate the absorption and fluorescence spectra of the system. As an additional feature, the anion signaling behavior of the system in acetonitrile is studied. A decrease in fluorescence efficiency of the system is observed upon addition of fluoride and acetate anions. Fluorescence quenching is most effective in the case of fluoride ions. This is attributed to the enhancement of the photoinduced electron transfer from the anion receptor to the fluorophore moiety. Hydrogen‐bond interactions between the acidic NH protons of the thiourea moiety and the F? anions are primarily attributed to the fluoride‐selective signaling behavior. Interestingly, a negative cooperativity for the binding event is observed when the interactions of the system are studied in the presence of both Zn2+ and F? ions. NMR spectroscopy and theoretical calculations are also carried out to better understand the receptor–analyte binding. 相似文献
65.
JPC – Journal of Planar Chromatography – Modern TLC - 相似文献
66.
The solvent relaxation and rotational dynamics of coumarin 153 have been investigated in a new room temperature ionic liquid, 1-(2-methoxyethyl)-1-methylpyrrolidiniumtris(pentafluorethyl)trifluorophosphate [[MOEMPL][FAP]], at three different excitation wavelengths with a variation in temperature. Wavelength -dependent fluorescence decay behavior of the probe molecule in the present medium has been investigated by studying the time dependent fluorescence Stokes shift in the ps–ns time scale. The dynamic fluorescence Stokes shift measurements suggest that the time-resolvable part of the solvation dynamics is biphasic in nature and the average solvation time depends on the excitation wavelengths. Rotational coupling constants, obtained from the time- resolved anisotropy data, indicate no specific interaction between the probe molecule and the ionic liquids. The excitation wavelength dependent solvation dynamics is attributed to the heterogeneous nature of the present ionic liquid. 相似文献
67.
Experimental data on masses and lifetimes of unstable particles falls into a pattern, a brief review of some interesting consequences
is presented here. From the experience in semiclassical methods and recent advances in quantum chromodynamics, it is proposed
that an appropriate generalization of the Gutzwiller trace formula for field theories may lead to a systematic semiclassical
chromodynamics theory. The theory can be developed to get appropriate dynamics leading to an explanation of pattern discovered
in the empirical data. 相似文献
68.
Sudhir Malik S. K. Soni R. K. Shivpuri 《Zeitschrift fur Physik C Particles and Fields》1995,67(2):239-244
Experimental results on multiplicity distributions for full phase space and in different pesudorapidity windows of charged secondary particles produced in proton-nucleon collisions at 800 GeV are presented and discussed. It is found that all these multiplicity distributions are well described by negative binomial distributions. We interpret our results on the basis of clan model. The bin size dependence of multiplicity distribution of charged secondary particles in proton-nucleon interactions is analysed in terms of multifractals. The values of generalised dimensions obtained from fitted distributions show a good agreement with those obtained from the data. 相似文献
69.
Efficient solid phase synthesis of oligoribonucleotide and its phosphorothioate analogue is described that utilizes the dimethoxytrityl (DMTr) for 5′-protection and t-butyldimethylsilyl (t-BDMS) group for 2′-protection of ribonucleoside monomers and the H-phosphonate coupling procedure. The synthetic cycles have been optimised to use only 8–10 fold excess of monomer at each coupling step, leading to an average coupling yield of 97%. 相似文献
70.
INDEPENDENT EFFECTS OF PHYTOCHROME AND NITRATE ON NITRATE REDUCTASE AND NITRITE REDUCTASE ACTIVITIES IN MAIZE 总被引:1,自引:0,他引:1
Abstract— Involvement of phytochrome in the regulation of nitrate reductase (NR) and nitrite reductase (NIR) activities in excised, etiolated leaves of Zea mays (L.) variety 'Ganga-5' is demonstrated using low energy and high irradiance responses of phytochrome action. Photoreversibility by far-red light of red light stimulated increases in NR and NIR activities was lost by 2 h. Red light given to the leaves, when induction by NO- 3 , was saturated, further increased both enzyme activities. Even if red light was given 4–8 h before NO- 3 , it still increased both NR and NIR activities. 相似文献