Picosecond optoelectronic characterization of diode lasers

New optoelectronic techniques for measuring semiconductor laser turn-on delay times and jitter with a picosecond temporal resolution are proposed and were employed for both conventional, homogeneous cavity and ion-bombarded picosecond diode laser characterization. Distinct differences in the characteristics of those lasers were found.     

Order parameters and molecular shapes of phosphonic acid dialkyl esters in a uniaxial hydrophobic environment. A theoretical study

The conformational behaviour of phosphonic acid dialkyl ester (PAE) molecules in a uniaxial hydrophobic environment was studied using the Monte Carlo method with the well-known Metropolis algorithm. The influence of the surrounding molecules on ordering processes of the intrinsic PAE molecules was taken into account by a molecular field. The intramolecular energy was calculated using 6–12 atom-atom and torsion potential functions. Conformations were analysed using torsion angle distributions, segment and bond order parameters. The order parameters of the C-H bonds are compared with experimental results of²H NMR. Further a general method of determining the effective shape of a molecule is presented. The shape is defined by probability distribution for finding atomic coordinates within volume elements during a Monte Carlo run. Thus the asymmetry of a molecule can be visualized. PAE molecules studied show a positive asymmetry in all cases.     

Comparison of the effects of 5- and 6-HOAt on model peptide coupling reactions relative to the cases for the 4- and 7-Isomers

Synthesis of 5- and 6-HOAt has completed the full set of the four HOAt isomers derived from HOBt by insertion of a single nitrogen atom in the benzenoid nucleus. Comparison of the reactivity of all four isomers in model peptide coupling reactions has confirmed the unique character of the 7-isomer in promoting selectivity and maintaining configuration at the reactive carboxylic acid residue.     

Analysis of the mouse proteome. (I) Brain proteins: separation by two-dimensional electrophoresis and identification by mass spectrometry and genetic variation

The total protein of the mouse brain was fractionated into three fractions, supernatant, pellet extract and rest pellet suspension, by a procedure that avoids any loss of groups or classes of proteins. The supernatant proteins were resolved to a maximum by large-gel two-dimensional electrophoresis. Two-dimensional patterns from ten individual mice of the commonly used inbred strain C57BL/6 (species: Mus musculus) were prepared. The master pattern was subjected to densitometry, computer-assisted image analysis and treatment with our spot detection program. The resulting two-dimensional pattern, a standard pattern for mouse brain supernatant proteins, was divided into 40 squares, calibrated, and specified by providing each spot with a number. The complete pattern and each of the 40 squares are shown in our homepage (http://www.charite.de/ humangenetik). The standard pattern comprises 8767 protein spots. To identify the proteins known so far in the brain fraction investigated, a first set of 200 spots was analyzed by matrix-assisted laser desorption/ionization - mass spectrometry (MALDI-MS) after in-gel digestion. By screening protein databases 115 spots were identified; by extending the analysis to selected, genetically variant protein spots, 166 spots (including some spot series) were identified in total. This number was increased to 331 by adding protein spots identified indirectly by a genetic approach. By comparing the two-dimensional patterns from C57BL/6 mice with those of another mouse species (Mus spretus), more than 1000 genetically variant spots were detected. The genetic analysis allowed us to recognize spot families, i.e., protein spots that represent the same protein but that are post-translationally modified. If some members of the family were identified, the whole family was considered as being identified. Spot families were investigated in more detail, and interpreted as the result of protein modification or degradation. Genetic analysis led to the interesting finding that the size of spot families, i.e., the extent of modification or degradation of a protein, can be genetically determined. The investigation presented is a first step towards a systematic analysis of the proteome of the mouse. Proteome analysis was shown to become more efficient, and, at the same time, linked to the genome, by combining protein analytical and genetic methods.     

Pole condition: A numerical method for Helmholtz-type scattering problems with inhomogeneous exterior domain

This paper presents a new numerical method for the solution of exterior Helmholtz scattering problems, which is applicable to inhomogeneous exterior domains and a wide class of geometries. The algorithm is based on the pole condition, which is a general radiation condition and allows a treatment of exterior Helmholtz problems without an explicit knowledge of Green's functions or a series representation. Our algorithm is based on a numerical approximation of the singularities of a Laplace transform of the exterior solution. Numerical examples illustrate the performance of the method.     

Protein model refinement using structural fragment tessellation

A method is described for the refinement of rough protein models based on finding a selection of structural fragments that match the model. Unlike most fragment-based methods, these are not necessarily contiguous in the sequence and form a tiling (tessellation) that covers most of the structure. The residue positions of the fragments are then used as a target for the model atoms to generate a revised model which is used as the basis of a subsequent pattern definition and search. The method was shown to improve the recognition of the native fold in a series of decoys largely as a result of improved secondary structure representation.     

Acute colonic diverticulitis: visualization in magnetic resonance imaging

The incidence of acute colonic diverticulitis (ACD) is increasing. To allow rational therapeutic decisions to be made, a timely diagnosis is required. The feasibility of “on-admission-MRI” to establish the diagnosis has not yet been studied. Therefore, a prospective observational study was carried out in 20 patients with an established diagnosis of ACD. The diagnostic criteria for the MRI diagnosis of ACD were the demonstration of at least one diverticulum, pericolic exudation, and edema of the colonic wall. MRI was diagnostic in all but one patient. It is concluded that MRI has considerable diagnostic potential in ACD and should be formally evaluated.     

Laser-induced dendritic structures on PET (polyethylene- terephthalate): the importance of redeposited ablation products

Single-pulse excimer-laser irradiation of poly-ethylene-terephthalate (PET) with fluences around and above the ablation threshold leads to the formation of surface dendrites. The lateral size and the number density of dendrites depend on the laser wavelength and the type and pressure of the ambient atmosphere. The results are discussed on the basis of excimer-laser-induced polymer fragmentation and the redeposition of ablation products.     

New Water‐Stable Ionic Liquids Based on Tetrakis‐(2,2,2‐trifluoroethoxy)borate

Several new ionic liquids (ILs) were prepared from Na[B(tfe)4] (tfe=OCH₂CF₃) via metathesis, including one room temperature IL (RTIL). Prior to synthesis, suitable cations were chosen via predictive quantum‐chemical calculations. Nuclear magnetic resonance monitoring over almost a month showed a total stability of the anion in the presence of water. The temperature‐dependent viscosities and melting points of all the new ILs were determined. The data indicate that [B(tfe)₄]^? ILs may be too viscous for electrochemical applications, but are interesting candidates for lubricant research.