Bücherschau

Ohne Zusammenfassung VDI     

Hyper-Rayleigh scattering with picosecond pulse trains

We propose a method for measuring hyper-Rayleigh scattering employing pulse trains produced by a Q-switched and mode-locked Nd:YAG laser. The use of the entire pulse train under the Q-switch envelope avoids the need of any device to scan the irradiance, as is usually done with nanosecond and femtosecond single-pulse lasers. To verify the feasibility of the technique, we performed measurements in different solutions of para-nitroaniline and compared the results with those obtained with nanosecond pulses. In both cases, the agreement with the hyperpolarizability values reported in the literature is about the same, but the measurements carried out with pulse trains are at least 20 times faster. Besides the advantage of acquisition speed, the use of pulse trains also allows the instantaneous inspection of slow luminescence contributions arising from multiphoton absorption.     

Direct evidence for the role of haem doming as the primary event in the cooperative transition of haemoglobin

The study of cooperative ligand binding among the four subunits of haemoglobin has played a central role in the understanding of allosteric transitions in a large number of enzymes. Haem iron out-of-plane motion has been suggested to be the trigger for the cooperative transition of haemoglobin. To function as a trigger in a dynamic sense, haem-iron doming must be the first conformational change to occur following ligand dissociation. Here we present the first direct demonstration that haem-iron doming occurs on the same time scale as the breaking of the iron-ligand bond, thus establishing haem-iron doming as the primary event which lead to the R-->T transition in haemoglobin.     

Determining the mode-field diameter of single-mode optical fiber: An interlaboratory comparison

The National Bureau of Standards, in cooperation with the Electronic Industries Association, conducted an interlaboratory measurement comparison among fiber manufacturers. Evaluated were transverse splice offset, near-field, far-field, and variable aperture far-field methods for determining mode-field diameter. Measurements were performed on five single-mode fibers at both 1300- and 1550-nm wavelengths. At 1300 nm, agreement was fairly good with the average one standard deviation being 0.15 μm for mode-field diameters in the8-11 mum range. Distinct systematic differences among various techniques were observed at 1550 nm where mode distributions are not as Gaussian.     

Basal cell adenocarcinoma of the parotid gland: a rare tumor entity. Case report and review of the literature

Basal cell adenocarcinoma is a rare entity that was first defined as a malignant salivary gland tumor in 1991. We present another case report and discuss pathology, pathogenesis, differential diagnosis, therapy and prognosis on the basis of currently available literature. Although histomorphologic features of the tumors are similar to basal cell adenomas, proof of an infiltrative and destructive growth is essential for diagnosis. Adenoid cystic carcinoma and basaloid squamous carcinoma must also be considered in any differential diagnosis. Tumor development within a pre-existing basal cell adenoma and de novo development are discussed. Most of the tumors appear to be benign clinically. Facial pain is rare and facial nerve palsy was noted in only one case. Metastases have occurred in less than 10% of patients, with only one involving the lung. Due to their biologic behavior and prognosis, basal cell adenocarcinomas should be classified as low-grade carcinomas. The therapy of choice is parotidectomy with preservation of the facial nerve. Neck dissection has to be added in cases with cervical metastases. Radiation is advisable in patients with recurrent disease. Since there is a nearly 30% local recurrence rate, intensive follow-up is necessary.     

LED source for determining optical detector time response at 1.06 microm

A gallium indium arsenide light emitting diode (LED) is investigated as a source for determining optical detector time response at 1.06 microm. To obtain either impulse or step-shaped waveforms, the diode is driven by a charged transmission line switched by a transistor operating in the avalanche mode. A pulse with a 2.5-ns full width at half-maximum and a step with a 3-4-ns transition time are produced at repetition rates to 1 kHz. The effects of wavelength change during the pulse (chirping) are discussed and evaluated.     

Highly Efficient Fluorescent Interstrand Photo‐crosslinking of DNA Duplexes Labeled with 5‐Fluoro‐4‐thio‐2′‐O‐methyluridine

The formation of a fluorescent photoadduct between 5‐fluoro‐4‐thiouridine ( ^FS U ), in the sequence context 5′‐A ^FS U A‐3′ and incorporated into a synthetic oligonucleotide either at its 3′‐ or 5′‐end, and one of the thymines of the TAT motif in a complementary target DNA strand led to photo‐crosslinking of the two strands for several oligonucleotide constructs. Enzymatic digestion, MS, UV, and fluorescence spectral analyses of the interstrand crosslinked oligonucleotides revealed the identity of the thymidine that participates in the photo‐crosslinking reaction as well as the diastereomeric structures of the crosslinks. The proposed pathways of interstrand photo‐crosslinking are supported by experiments with isotopically labeled oligonucleotide constructs and visualized by means of molecular dynamics simulations.     

Removal of zinc layers from coated steel strip by thermal and mechanical processing

In this research project, basic investigations on the low temperature reactions of the zinc coating layer with the iron substrate were performed in order to develop novel methods for zinc removal from scrap material by baking the material at a moderate temperature to produce brittle intermetallic compounds, which may be subsequently removed under mechanical load, for instance by shredder treatment. The investigations have shown that it is possible to prepare a fragile Fe/Zn-intermetallic layer on the substrate by proper baking of the material at moderate temperatures. Mechanical working removes zinc from the strip substrate. The plane of cleavage is the phase boundary between the δ- and the Γ-compound. A precise control of the heating cycle adjusted to the layer thickness is mandatory to attain an effective zinc removal. This requirement is difficult to meet in the operation of an industrial installation.