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91.
Klaus van Benthem Stephan Krämer Wilfried Sigle Manfred Rühle 《Mikrochimica acta》2002,138(3-4):181-193
An understanding of the correlation between microstructures and properties of materials require the characterization of the
material on many different length scales. Often the properties depend primarily on the atomistics of defects, such as dislocations
and interfaces. The different techniques of transmission electron microscopy allow the characterization of the structure and
of the chemical composition of materials with high spatial resolution to the atomic level: high resolution transmission electron
microscopy allows the determination of the position of the columns of atoms (ions) with high accuracy. The accuracy which
can be achieved in these measurements depends not only on the instrumentation but also on the quality of the transmitted specimen
and on the scattering power of the atoms (ions) present in the analyzed column.
The chemical composition can be revealed from investigations by analytical microscopy which includes energy dispersive X-ray
spectroscopy, mainly quantitatively applied for heavy elements, and electron energy-loss spectroscopy. Furthermore, the energy-loss
near-edge structure of EELS data results in information on the local band structure of unoccupied states of the excited atoms
and, therefore, on bonding. A quantitative evaluation of convergent beam electron diffraction results in information on the
electron charge density distribution of the bulk (defect-free) material.
The different techniques are described and applied to different problems in materials science. It will be shown that nearly
atomic resolution can be achieved in high resolution electron microscopy and in analytical electron microscopy. Recent developments
in electron microscopy instrumentation will result in atomic resolution in the foreseeable future. 相似文献
92.
Ahlen S Ambrosio M Antolini R Auriemma G Baker R Baldini A Bam BB Barbarino GC Barish BC Battistoni G Bellotti R Bemporad C Bernandini P Bilokon H Bisi V Bloise C Bower C Bussino S Cafagna F Calicchio M Campana D Campana P Carboni M Cecchini S Cei F Chiarella V Cormack R Corona A Coutu S De Cataldo G Dekhissi H De Marzo C De Vincenzi M Di Credico A Diehl E Erriquez O Favuzzi C Ficenec D Forti C Fusco P Giacomelli G Giannini G Giglietto N Giubellino P Grassi M Green P Grillo A Guarino F 《Physical review letters》1994,72(5):608-612
93.
S. Diehl 《Communications in Mathematical Physics》1996,176(1):23-44
The equation
, whereH is Heaviside's step function, appears for example in continuous sedimentation of solid particles in a liquid, in two-phase flow, in traffic-flow analysis and in ion etching. The discontinuity of the flux function atx=0 causes a discontinuity of a solution, which is not uniquely determined by the initial data. The equation can be written as a triangular 2×2 non-strictly hyperbolic system. This augmentation is non-unique and a natural definition is given by means of viscous profiles. By a viscous profile we mean a stationary solution ofu
t
+(F
)
x
=u
xx
, whereF
is a smooth approximation of the discontinuous flux, i.e.,H is smoothed. In terms of the 2×2 system, the discontinuity atx=0 is either a regular Lax, an under-or overcompressive, a marginal under- or overcompressive or a degenerate shock wave. In some cases, depending onf andg, there is a unique viscous profile (e.g. undercompressive and regular Lax waves) and in some cases there are infinitely many (e.g. overcompressive waves). The main purpose of the paper is to show the equivalence between a previously introduced uniqueness condition for the discontinuity of the solution atx=0 and the viscous profile condition. 相似文献
94.
95.
Qian K Diehl JW Dechert GJ DiSanzo FP 《European journal of mass spectrometry (Chichester, England)》2004,10(2):187-196
We report the first coupling of supercritical fluid chromatography (SFC) with field ionization time-of-flight high-resolution mass spectrometry (FI-ToF HRMS), in parallel with ultraviolet (UV) detection and flame ionization detection (FID), for rapid and quantitative analysis of petroleum middle distillates. SFC separates petroleum middle distillates into saturates and 1- to 3-ring aromatics. FI generates molecular ions for hydrocarbon species eluted from the SFC. The high resolution and exact mass measurements by ToF mass spectrometry provide elemental compositions of the molecules in the petroleum product. The amounts of saturates and aromatic ring types were quantified using the parallel SFC-FID assisted by SFC-UV. With a proper carbon-number calibration, the detailed composition of the petroleum middle distillate was rapidly determined. 相似文献
96.
97.
Trifluoromethoxy-substituted anilines undergo hydrogen/lithium permutation ("metalation") with optional site selectivity depending on the N-protective group employed. N-tert-Butoxycarbonyl-2- and -4-(trifluoromethoxy)aniline react with tert-butyllithium at the nitrogen-adjacent 6- and 2-position affording, after electrophilic trapping, products 1-6. In contrast, deprotonation of the para isomer occurs at the oxygen-neighboring 3-position, giving rise to the acid 12, when the amino group is carrying two trimethylsilyl groups. sec-Butyllithium attacks 3-trifluoromethoxy-N-mono(trimethylsilyl)aniline at the 2-position, but 3-trifluoromethoxy-N,N-bis(trimethylsilyl)aniline at the 4-position to provide respectively the acids 10 and 11 after carboxylation. The synthesis of two new benzodiazepines illustrates (19 and 22) the preparative potential of the aniline functionalization mediated by organometallic reagents. 相似文献
98.
A new base-labile anchoring group, derived from 9-(hydroxymethyl)fluorene-4-carboxylic acid (HO2CFmoH or HOFmCO2H; 7), for polymer-supported peptide synthesis os described. The synthesis of 7 starting from 2,2′-biphenyldicarboxylic acid ( 1 ) proceeds in an overall yield of 53%. The group HO2CFmo exhibits properties similar to the well known Fmoc protecting group: It is stable to acidic conditions and cleavable by 15% piperidine in DMF. In combination with acid labile Nα-protecting groups (e.g. Boc, Ddz, Bpoc, Nps etc.), it renders more flexibility to the stepwise synthesis using polymer supports. The versatility of the new anchoring group in solid- and liquid-phase peptide synthesis is demonstrated for the synthesis of a model peptide. 相似文献
99.
Synthesis and Crystal Structure of Hydronium-tris-ethylenediamine-cobalt(rhodium)-μ-trichloro-nonachlorotrirhenate(III)-chloride, H3O[MEn3][Re3Cl12]Cl (M=Co, Rh) The chlorides H3O[MEn3][Re3Cl12]CI (M = Co, 1 ; Rh, 2 ) crystallize from hydrochloric acid solutions of ReCl3 and MEn3 · 3H2O as deep red hexagonal columns. They are isotypic and crystallize with the hexagonal system (P6 , Z = 1; 1: a = 1010.87(3); c = 794.30(4) pm, R = 0.023, Rw = 0.016; 2: a = 1018.58(3); c = 794.74(4) pm, R = 0.026, Rw = 0.018). The anions [Re3Cl12]3? are connected via H3O+ cation (C.N. 3). The large channels that run in the [001] direction contain, alternatively, the cations [MEn3]3+ and the lonesome Cl?-anions 相似文献
100.
The synthesis and structure of an acetal protected 10-membered cyclic enediyne-1,2-diol rac-10 is reported. The conformational constrain of the unsaturated macrocycle by the acetal protection group prevents the thermal cyclization reaction of the endiyne during synthesis and purification. 相似文献