共查询到20条相似文献,搜索用时 15 毫秒
1.
S. Y. Zhu M. O. Scully H. Fearn L. M. Narducci 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1992,22(2):471-481
We present a nonlinear theory for lasing without inversion in three-level atomic systems by utilizing initial atomic coherence between two closely spaced lower levels. We discuss nondegenerate and degenerate cases for closed and open atomic systems. The equations of motion for the laser fields, and the steady state intensities of the fields are obtained. The realization of lasing without inversion is due to the absorption cancellation by the atomic coherence, i.e., the quantum interference. The quantum interference can bring about gain enhancement in the nondegenerate cases. 相似文献
2.
Henryk Matusiewicz 《Mikrochimica acta》1993,111(1-3):71-82
A commercial laboratory microwave acid digestion system was evaluated for the acid dissolution of ceramic powders (Al2O3, AlN, BN and Si3N4) prior to the determination of their trace element content by microwave induced plasma atomic emission spectrometry. Newly designed vessels, capable of withstanding internal pressures of over 110 bar, provide rapid and satisfactory results for sample dissolution. Sample preparation time was approximately 30 min (including the subsequent cooling time and preparation of the final solution). Results from conventional stainless-steel acid digestion vessel (Teflon bomb) dissolution are compared with the microwave bomb results of microwave plasma atomic emission spectrometry. 相似文献
3.
Krzysztof Jankowski Anna Jerzak Anna Sernicka-Poluchowicz Ludwik Synoradzki 《Analytica chimica acta》2001,440(2):67-221
A method for multielement determination of major elements in polymer additives by microwave induced plasma atomic emission spectrometry (MIP-AES) has been elaborated. Microwave digestion with nitric acid was selected for sample preparation because of its speed and versatility. Sodium nitrate was added to the digestion mixture in order to reduce phosphorus losses. The precision obtained varied between 2 and 4.5% depending on the element determined. The accuracy of the method was studied by analyzing the Spex 5-element oil standard. The method was applied to a variety of commercial and in-house prepared compositions. 相似文献
4.
《Tetrahedron letters》1986,27(2):131-134
Acylsulfonamide dianions function as efficient synthetic intermediates and are especially suitable for Doubly Unsymmetrical Çarbanion Oxidation. 相似文献
5.
Jankowski K 《Talanta》2001,54(5):855-862
The direct determination of trace sodium by microwave induced plasma atomic emission spectrometry (MIP-AES) in water-soluble organic substances utilized in pharmaceutical preparations was developed. No decomposition of the organic constituents was required. Samples were dissolved with water and introduced to the plasma after ultrasonic nebulization without desolvation. A limit of detection (3sigma) of 0.91-3.0 ng ml(-1) was obtained under experimental conditions. The quantitative MIP-AES procedure involved the standard addition method. The sodium content determined in reference material NIST SRM 1568A Rice Flour agreed with the certified value (6.6+/-0.8 mug g(-1)). Physical and chemical interferences were investigated. It was found for the microwave plasma that it is possible to introduce organic substances solutions of concentration up to 5% without sensitivity losses. This direct technique is fast and sensitive and helps to reduce contamination connected with the sample preparation procedure. 相似文献
6.
A stable, low gas-flow torch has been developed for use with a helium microwave induced plasma (MIP). A toroidal plasma with central analyte introduction is obtained by the addition of a tantalum coupling probe injector tube. This injector penetrates through 100% of the total cavity depth and aids in the efficiency of power transfer to the cavity, in plasma initiation, and in circumventing the effects of a lack of homogeneity in the microwave field on analyte distribution in the plasma. The tangential helium flow was 41/min and the microwave power was 60 W.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria 相似文献
7.
Camuña JF Montes M Pereiro R Sanz-Medel A Katschthaler C Gross R Knapp G 《Talanta》1997,44(4):535-544
This paper describes a comparative study of the microwave induced plasma (MIP) and the stabilized capacitive plasma (SCP) for halide determinations. The MIP is generated in a Beenakker cavity TM(010) using a tangential flow torch and the SCP consists of a 27.12 MHz discharge sustained in a liquid-cooled, fused silica tube surrounded by two annular electrodes. Both discharges are operated in helium at atmospheric pressure and detection was carried out by Atomic Emission Spectrometry (AES). The halides (I(-), Br(-), Cl(-)) are converted to volatile halogens by continuous flow generation based on chemical oxidation and on-line separation from the aqueous phase, via a gas-liquid separator, to be finally introduced into the plasma. The different factors affecting the emission intensity of the volatile halogens generated are compared for both discharges and the analytical performance characteristics are also evaluated. Detection limits of 17 ng ml(-1), 24 ng ml(-1) and 55 ng ml(-1) are obtained for the determination of Cl(-), Br(-), and I(-), respectively, in the ultraviolet-visible (UV-VIS) region using the MIP-AES and 45 ng ml(-1), 135 ng ml(-1) and 400 ng ml(-1) for Cl(-), Br(-), and I(-) with the SCP-AES. Lines in the near infrared (NIR) region were also evaluated for the SCP-AES detection; improvements in detection limits higher than 30 times were observed in the NIR region as compared with the UV-VIS with detection limits in the NIR of 1.4 ng ml(-1) for Cl(-), 3 ng ml(-1) for Br(-) and 13 ng ml(-1) for I(-). 相似文献
8.
《Spectrochimica Acta Part B: Atomic Spectroscopy》1996,51(1):117-126
Different types of microwave induced plasma (MIP) discharge operated in liquid-cooled tubes, namely a glass tube of Duran®, a quartz tube of Herasil®, and a very simple demountable discharge tube made of glass and quartz have been investigated. The last tube leads to the best analytical properties and the longest lifetime. The intensities of silicon lines and of the continuum spectral background, together with the signal-to-background ratios for B, Ca, Cd, Co and Zn in the case of the pneumatic nebulization of solutions have been measured and used as an indicator for the cooling efficiency. The MIP torch was cooled with a thermostated silicon oil. The decrease of the temperature of the cooling medium causes a measurable decrease of the spectral background intensity. Diagnostic measurements of the plasma include radial profiles of spectral line intensities and excitation temperatures with the lines of Fe I; values of 5000–6000 K are found. The influence of different plasma parameters, e.g. microwave power and helium flow rate, is investigated. The preliminary analytical characterization of a helium MIP maintained with the liquid-cooled demountable discharge tube is presented. Limits of detection for Al, B, Ca, Co, Fe, P, Sb and Zn (between 0.002 and 1.2 μg ml−1) are comparable with or better than those reported for low power helium MIPs with sample introduction in the form of a wet aerosol. 相似文献
9.
Inversion symmetry is included in the operator formulation of the centroid molecular dynamics (CMD). This work involves the development of a symmetry-adapted CMD (SA-CMD), here particularly for symmetrization and antisymmetrization projections. A symmetry-adapted quasidensity operator, as defined by Blinov and Roy [J. Chem. Phys. 115, 7822 (2001)], is employed to obtain the centroid representation of quantum mechanical operators. Numerical examples are given for a single particle confined to one-dimensional symmetric quartic and symmetric double-well potentials. Two SA-CMD simulations are performed separately for both projections, and centroid position autocorrelation functions are obtained. For each projection, the quality of the approximation as well as the accuracy are similar to those of regular CMD. It is shown that individual trajectories from two separate SA-CMD simulations can be properly combined to recover trajectories for Boltzmann statistics. Position autocorrelation functions are compared to the exact quantum mechanical ones. This explicit account of inversion symmetry provides a qualitative improvement on the conventional CMD approach and allows the recovery of some quantum coherence. 相似文献
10.
Yixiang Duan Mingyi Huo Jun Liu Qinhan Jin 《Fresenius' Journal of Analytical Chemistry》1994,349(4):277-282
A low-power surface-wave plasma device (surfatron) is employed as an atomizer for microwave induced plasma atomic absorption spectrometry (MIP-AAS) and a desolvation-condensation apparatus has been used to remove the solvent in the aerosol. An axial viewing absorption technique is adopted for the determination of calcium. The matrix effect on its determination has been investigated in detail. Some enhancing effects are observed on the calcium absorbance in the presence of organic additives. A possible mechanism for this enhancement is discussed. 相似文献
11.
12.
A trace amount of carbon was determined by atmospheric-pressure helium microwave induced plasma atomic emission spectrometry (He-MIP-AES) with gas-phase sample introduction technique. This method was applied for the generation of a continuous flow of carbon dioxide by the acidification of carbonate ion and hydrogen carbonate ion for the determination of carbon. The generated carbon dioxide was separated from the solution by a simple gas-liquid separator, dried with a desiccant and swept into the MIP with helium carrier gas for analysis. Of the acids and drying agents investigated, hydrochloric acid for acidification and anhydrous calcium chloride as a desiccant were found to be the most appropriate for the generation of carbon dioxide. Under the optimized experimental conditions, the best attainable detection limits at C (I) 193.09 and C (I) 247.86 nm lines were 7.89 and 8.10 microg/l with linear dynamic ranges of 100 to 10,000 and 100 to 20,000 microg/l for carbon, respectively. The presence of many diverse elements and ions was found to cause a more or less depressing interference by the proposed technique. However, no interference was observed from the following elements and ions: Ca, K, Rb, Br-, Cl-, F- and I-. Finally, the present method has been applied to the determination of carbon in several water samples. 相似文献
13.
Ilga Mutule 《Tetrahedron》2005,61(47):11168-11176
Arylmagnesium species can be efficiently generated from magnesium turnings and aryl chlorides or aryl bromides under dielectric heating conditions. Subsequent microwave assisted transmetallation using ZnCl2-TMEDA afforded the corresponding arylzinc reagents. A sequential microwave assisted arylmagnesium formation-transmetallation-Negishi coupling protocol suitable for automated multiple parallel synthesis has been developed. 相似文献
14.
A flat sheet membrane desolvator (FSMD) was used to extend the applicability of a 120 W helium microwave induced plasma (He-MIP) to elemental analysis of organic-solvent-based samples and element selective liquid chromatographic detection. With the FSMD on-line, methanol could be nebulized with a sample flow rate of 1.5 ml/min and a carrier gas flow rate of 1.2 l/min without extinguishing the plasma. Under these conditions, applying desolvator countercurrent gas flows in the range 0–8 l/min restored of the original pink color of the pure helium MIP from the bluish-green caused by methanol. Significant reductions in the emission intensities of C2 species at 436.5, 473.7, 512.9, and 563.6 nm were observed with the application of the FSMD. The intensities of chlorine analyte emission lines at 479.5, 481.0 and 481.9 nm increased with increasing countercurrent gas flow rates and reached a maximum intensity with a flow rate of 5.0 l/min. Detection limits for Cl and Pb were 2.1 and 0.1 ppm using a 1 m focal length monochromator. Other elements and solvent combinations were also examined. Element selective liquid chromatographic detection was preliminarily examined by monitoring 2,6-dichlorobenzene and 5,7-dichlorohydroxyquinoline at the 479.5 nm Cl atomic emission line. Chlorine detection limits in the 3–7 μg range (70–190 ng/s) were obtained. 相似文献
15.
《Spectrochimica Acta Part B: Atomic Spectroscopy》1995,50(9):963-969
A new element selective detector for gas chromatography is presented. The detector, based on wavelength modulation diode laser atomic absorption spectrometry in a microwave induced helium plasma, is used for measurements of chlorinated hydrocarbons by absorption of excited, metastable chlorine atoms. Indications of complete dissociation of the halocarbons in the plasma have been found. Preliminary detection limits of the order of 1 μg ml−1 or 80 pg s−1 have been found for different halocarbons. 相似文献
16.
C. Dietz 《Analytica chimica acta》2004,501(2):157-167
Microwave induced plasma atomic emission spectrometry (MIP-AES) in combination with multicapillary (MC) gas chromatography could be proven to be useful for element specific detection of volatile species. Solid phase microextraction (SPME) was used for preconcentration and sample-matrix separation. The fiber desorption unit as well as the heating control for the MC column were in-house developed and multicapillary column was operated at moderate temperatures (30-100 °C). The method was optimized for organo-selenium species (dimethylselenide (DMSe), diethylselenide (DEtSe) and dimethyldiselenide (DMDSe)), using a chemometric approach. Stationary phases for the separation column were optimized using a conventional GC and contrasted with the results obtained with the MC. Application was focussed on selenium accumulating biological matter, such as lupine, yeast, Indian mustard and garlic. These samples were grown in hydroponic solution containing inorganic selenium (Na2SeO3 and Na2SeO4). SPME sampling was carried out in fixed volume flow boxes in headspace above the living plants and in vials using treated samples. Results demonstrate inorganic selenium transformation into volatile organic species during metabolism. Separation is fast, a chromatogram can be obtained in less than 3 min and detection limits were at sub-ppb level for all investigated species. The system is independent from the use of a conventional gas chromatographic oven and can be used as a versatile alternative to highly cost intensive methods such as GC-ICP-MS. 相似文献
17.
A novel method was developed for analysing geological materials for Au, Ag, Pd and Pt by continuous powder introduction microwave induced plasma atomic emission spectrometry (CPI-MIP-AES). The preconcentration of the trace metals on activated carbon (AC) was performed before conducting MIP-AES measurements in order to obtain accurate and precise analytical results. The method proposed is based on the selective sorption of precious metals that are subsequently introduced to the plasma as a dry particulate aerosol consisted of analytes collected on the sorbent. The technical design and operating conditions of the novel sample introduction system based on the fluidized-bed concept has been optimized. The microwave excitation source with integrated rectangular cavity TE101 and vertically positioned plasma torch has been used. The signal stability proved to be adequate for sequential mode of measurements due to the vertical plasma configuration as well as the MIP-AES system compatibility with the CPI technique. Calibration was done using home-made standards obtained by sorption of metals of interest from standard solutions on activated carbon. Precision is typically 1-4% relative standard deviation at the 1 μg g−1 level. Under measurement conditions the detection limits for Ag, Au, Pd and Pt were 24, 43, 57 and 550 ng per 1 g of AC, respectively. The proposed procedure was used for Au, Ag, Pd and Pt determination in the platinum ore SARM-7 as well as Au and Ag in the Chinese soil GBW-07405 certified reference materials. The standard addition technique was used and recoveries revealed that the proposed method shows good accuracy and precision. 相似文献
18.
I. López-García M. Sánchez-Merlos P. Viñas M. Hernández-Córdoba 《Spectrochimica Acta Part B: Atomic Spectroscopy》1996,51(14):1761-1768
The use of a simple continuous manifold, together with data treatment by means of Fourier transforms, permits the dynamic range of flame atomic absorption spectrometry to be extended. A peristaltic pump is used to move the analyte solution, the difference between the pumping flow rate and the nebulizer uptake rate being compensated by aspirating solvent through a T-piece. The time-variable absorbance profile which results from the action of the rollers is transformed into a frequency spectrum, the large signal caused by the periodical roller movement being used as the analytical signal. The effect of different experimental conditions on the signal is studied and the improvement in the signal/noise ratio lowers the determination limit. The dynamic range can be further extended, since the system also permits the measurement of solutions which are too concentrated to be measured by direct aspiration. Calibration is performed by means of a single standard solution. 相似文献
19.
Shashidhar Kumar Akubathini 《Tetrahedron letters》2009,50(16):1809-4175
Several unsymmetric and symmetric alkynes were prepared excellent to modest yields by generating benzyne from the reaction of 2-(trimethylsilyl)phenyl triflate with CsF in the presence of CuI and terminal alkyne under microwave heating for 30 min at 150 °C. Using conventional heating, the reactions required 24 h reaction time. 相似文献
20.
The 1(01)-0(00) (9-10 GHz) and 2(02)-1(01) (18-19 GHz) rotational transitions of HSi 79Br and HSi 81Br have been measured in a pulsed discharge jet expansion to an experimental uncertainty of approximately 1 kHz using Fourier transform microwave spectroscopy. The data have yielded an effective rotational constant, the centrifugal distortion constant Dj, the bromine nuclear quadrupole coupling constants, and the bromine nuclear spin-molecular rotation interaction parameter for both isotopomers. The derived parameters have been compared to their values calculated ab initio, and the nuclear quadrupole coupling tensor has been used to investigate the Si-Br bond, giving a sigma bond ionic character of 0.60, a pi bond character of 0.22, and a total Si-Br ionic character of 0.38. These bond characteristics have been compared to trends in other halosilylenes, silanes, and the analogous carbenes. 相似文献