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排序方式: 共有183条查询结果,搜索用时 93 毫秒
1.
S. J. Cheng W. Sheng P. Hawrylak S. Raymond S. Studenikin A. Sachrajda Z. Wasilewski A. Babinski M. Potemski G. Ortner M. Bayer 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):211
We present results of calculations and experiments on electron–hole complexes in InGaAs/GaAs self-assembled quantum dots in high magnetic field (B). Due to hidden symmetries, the chemical potential of an N-exciton system at special B fields becomes insensitive to the exciton number as well as the magnetic field. This results in plateau regions of high intensity in measured magneto-PL spectrum. Theoretical calculations using exact diagonalization techniques successfully explain the measured magneto-photoluminescence spectrum with B fields up to 28 T. 相似文献
2.
In the present article, we aim at treating the existence of fundamental solutions of linear partial differential operators with constant coefficients from the viewpoint of setting up explicit formulae yielding fundamental solutions. 相似文献
3.
Ronald Ortner 《Operations Research Letters》2007,35(5):619-626
In ergodic MDPs we consider stationary distributions of policies that coincide in all but n states, in which one of two possible actions is chosen. We give conditions and formulas for linear dependence of the stationary distributions of n+2 such policies, and show some results about combinations and mixtures of policies. 相似文献
4.
Gottfried Ortner 《Fresenius' Journal of Analytical Chemistry》1938,112(3-4):96-101
Ohne Zusammenfassung 相似文献
5.
H. M. Ortner H. H. Xu J. Dahmen K. Englert H. Opfermann W. Görtz 《Fresenius' Journal of Analytical Chemistry》1996,355(5-6):657-664
Surface characterization of new unused PTFE, PFA and PVDF labware has been carried out by light microscopy, scanning electron microscopy, profilometry and atomic force microscopy. It has been found that in spite of higher micro-roughness, PFA exhibits the lowest nano-roughness and hence seems best suited as vessel material for relatively mild pressureless chemical operations for sample preparation of ultrapure substances, as container material for storage of ultrapure liquids, and for transport of such liquids, e.g., from the producer in the chemical to the end user in the microelectronics industry. This suitability refers only to the surface quality of the investigated materials. PTFE-surfaces, due to the sintering process of production, exhibit the most unfavourable surface quality of the investigated fluorinated polymers. 相似文献
6.
P. Hoffmann V. K. Karandashev T. Sinner H. M. Ortner 《Analytical and bioanalytical chemistry》1997,357(8):1142-1148
Data are reported for a first measurement campaign for a great number of cations (the range of concentrations for main components
is given in ng/mL: Na:<70–880; Mg: 12–160; Al:<7–120; K: 200–1600; NH4
+: 2500–9000; Ca: 300–2500; Fe:<140–1200; Zn: 20–320) and anions (HCOO-: 100–1800; CH3COO-: 400–14500; C2O2-
4: <100–460; NO-
2: <20–55; NO-
3: 660–9900; SO2-
3:<100–1150; SO4
2-: 450–19700; Cl-: 170–3200) in rain and snow samples of the Chernogolovka region 80 km northeast of the centre of Moscow. These data serve
as a first assessment of the situation of the atmosphere in this region. For the determination of fluoride, formate, acetate,
nitrite, bromide, nitrate, sulfite, and sulfate by IC, a relevant development of the method was carried out. For some metallic
cations, a critical quality control was achieved by parallel measurements with ICP-MS, TXRF, and IC. Furthermore, time resolved
measurements were performed for a rain event. Filtration experiments were undertaken to differentiate between the presence
of a series of elements and species in liquid or solid state in the collected aqueous samples.
Received: 25 July 1996 / Revised: 26 September 1996 / Accepted: 13 October 1996 相似文献
7.
B. Bastian T. P. Knepper P. Hoffmann H. M. Ortner 《Fresenius' Journal of Analytical Chemistry》1994,348(10):674-679
A method for the identification and quantification of aromatic sulfonic acids in industrial waste water has been developed. The preparation of the samples comprises a clean-up step and an enrichment step, utilizing i) reversed-phase extraction and ii) ion-pair solid phase extraction. The aromatic sulfonic acids are separated by ion-pair chromatography with diode-array detection. An advantage of the developed ion-pair chromatographic method is the separation of linear alkylbenzenesulfonic acids (LAS), lignosulfonic acids and aromatic sulfonic acids in one chromatographic run. Also described is an optimized clean-up procedure for collected fractions of a preparative chromatographic run to identify monosulfonic acids with GC/MS after methylation. The detection limits for aromatic sulfonic acids in industrial waste waters are at the g/l level. 相似文献
8.
Stephan Weinbruch Michael Wentzel Manfred Kluckner Peter Hoffmann Hugo M. Ortner 《Mikrochimica acta》1997,125(1-4):137-141
In this paper procedures for the characterization of individual aerosol particles by element mapping in the electron microprobe are presented. The number, size and qualitative chemical composition of particles is derived from a combination of secondary or backscattered electron images and element distribution maps. Accuracy of the size distribution and reliability of the qualitative analysis procedure were checked with silicate samples. In order to obtain a semi-quantitative estimate of the chemical composition of individual particles the count rates taken from element distribution maps are corrected for matrix and geometric effects using particle ZAF procedures.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday 相似文献
9.
Hugo M. Ortner 《Fresenius' Journal of Analytical Chemistry》1992,343(11):825-826
Conclusion Analytical Chemistry, as we have seen, is quite an established science but also a very vivid and young one. Its boundaries have always been and will be at the very frontiers of natural science: we are approaching the detection of single atoms as well as the analysis of matter at the very fringes of our universe. Analytical Chemistry is essential for the development of taylor-made high-tech materials and equally for the evolution of our knowledge about the toxicity of elements and compounds. It needs specialists with a profound insight in certain fields, for methods development or the handling of very complex instrumentation as e.g. a high resolution secondary ion mass spectrometer. But it also needs allrounders with a broad view not only of the capability of Analytical Chemistry as a whole but with an understanding for the complexity of modern social and economic structures. Frequently new ideas, new concepts and progress are forming on the seams between disciplines, on the grain boundaries of scientific fields too often kept strictly separated from each other. Analytical Chemistry is certainly a discipline which is predestinated for scientific communication collaborating with practically all fields of natural science as well as politics and economics.As a branch of natural science it is neutral in its moral value and therefore needs responsible and courageous analysts to use it for the benefit of mankind. 相似文献
10.
Three methods of determination for uranium and thorium traces and ultratraces in glass were developed: a simple and powerful ICP-MS method exhibiting limits of determination in the one ng/g-range; a complex method with end-determination by classical photometry and a limit of determination for U and Th of 20 ng/g; and a method with chelate-complex formation for U and Th and subsequent GC-detection with a 63Ni-ECD with limits of determination in the g/g-range. These methods are critically compared and tested for real type samples of special glasses.Abbreviations used AAS
Atomic absorption spectrophotometry
- ECD
Electron capture detector
- FOD
1,1,1,2,2,3,3-Heptafluoro-7,7-dimethyl-4,6-octanedion
- GC
Gas chromatography
- HFA
1,1,1,5,5,5-Hexafluoro-2,4-pentanedione
- ICP-AES, -MS
Inductively coupled plasma-atomic emission spectrometry, metry, -mass spectrometry
- LAS
Liquid absorption spectrophotometry = classical photometry
- NAA
Neutron activation analysis
- NIST
National Institute of Standardization and Technology (Gaithersburg, U.S.A.)
- TBP
Tri-(n-butyl)-phosphate
- TFA
1,1,1-Trifluoro-2,4-pentanedione
- TTFA
1-(2-Thenoyl)-3,3,3-trifluoroacetone
- XRS
X-ray (fluorescence) spectrometry 相似文献