Generation of radially polarized beams in a Nd:YAG laser with self-adaptive overcompensation of the thermal lens

Thermal effects such as lensing and birefringence negatively affect the beam quality and limit the power range of solid-state lasers. Self-adaptive overcompensation of the thermal lens is an answer to this problem. It provides a laser system with good beam quality and large stability range. Because the focal length of the thermally induced lens is different for the radial and the tangential polarization, overcompensation can be used to discriminate these two polarizations. Exploiting this method, we demonstrate the generation of radially polarized beams in a self-adaptively overcompensated high-power Nd:YAG laser with an output power of 155 W and an M2 of less than 10.     

Contrast-enhanced high-resolution magnetic resonance imaging of autologous cartilage implants of the knee joint

Over the past decade, a number of interventions for durable cartilage repair have emerged. Magnetic resonance (MR) tomography is an excellent noninvasive method for monitoring cartilage repair tissues throughout the postsurgical period. However, evaluating cartilage morphology after matrix-based autologous cartilage implantation (ACI) with MR imaging (MRI) still remains a challenge. In this study, we combined a high-resolution cartilage-sensitive fast-spin echo (FSE) sequence with intravenous application of a contrast agent for enhancing synovial fluid. Two independent musculoskeletal radiologists interpreted the pictures for the thickness, length and surface of the cartilage implants. A multivariate two-way analysis of variance with two repeated measures was performed and showed that evaluation of cartilage implant morphology was significantly improved after the application of gadodiamide on proton density FSE images. Contrast-enhanced MRI of articular cartilages is a promising technique in the postoperative follow-up of patients after ACI.     

Superconducting MgB2 films on MgO substrates

We report the preparation of homogeneous, polycrystalline MgB₂ films on single-crystalline MgO substrates by screen printing and airbrush methods. The superconducting material was obtained by the reaction of Mg vapor with boron precursor layers in special steel casings under argon/hydrogen atmosphere at 800 °C and ambient pressure. After polishing of the surface, films with a thickness of about 2 m were obtained. Electrolytic polishing improved the surface smoothness of the samples. Transition temperatures of about 33 K were measured with irreversibility fields of up to 6 T at 20 K. Transport critical current densities of 2×10⁹ Am^-2 were obtained at 4.2 K in self-field for a MgB₂ film on single-crystalline MgO. PACS 74.72.Yg; 74.76.Db; 74.60.Jg     

Receptor occupancy on an ellipsoidal cell in the presence of a point source of a chemoattractant

Diffusion of a chemoattractant from a micropipet is routinely used to examine the different aspects of a cell's chemotactic response. To quantify the effect of cell elongation on chemotactic sensitivity in the micropipet assay, the chemoattractant concentration at the cell plasma membrane was determined by solving the equation for diffusion from a point source in the presence of a prolate ellipsoid of varying eccentricity. The results show that cell elongation can significantly increase the difference in receptor occupancy between near and far cell ends and thereby enhance the sensitivity of chemotactic cells to shallow chemoattractant gradients.     

Correlation of bilayer membrane cation transport and biological activity in alkyl-substituted lariat ethers

Dialkyldiaza-18-crown-6 lariat ethers having twin n-octyl, n-decyl, n-dodecyl, n-tetradecyl, n-hexadecyl, 1-oxodecyl and 1-oxododecyl side arms were prepared and studied. Cation transport in liposomes mediated by these compounds showed discontinuous activity that correlated with toxicity to the bacteria E. coli and B. Subtilis, and the yeast S. Cerevisiae. Transport, toxicity and membrane depolarization studies all suggest that side chain length affords very different interactions in a bilayer membrane compared with bulk phases. An explanation for activity in terms of carrier transport and restricted transverse relaxation is proposed.     

Correlating the molecular electrostatic potentials of some organic peroxides with their antimalarial activities

The molecular electrostatic potentials (MEPs) of artemisinin (also known as qinghaosu), yingzhaosu A, and some synthetic analogues have been calculated and studied as a means of distinguishing between high and low antimalarial activity. To facilitate comparison, the dimensionality of the MEP was reduced by Kohonen Neural Network transforms. The reduction revealed that peroxides exhibiting high antimalarial activity are characterized by a continuous strip of negative electric potential surrounding the molecule, whereas peroxides of lesser activity show a broken strip.     

White-light Detection for Nanoparticle Sizing with the TSI Ultrafine Condensation Particle Counter

Several of the most common methods for measuring nanoparticle size distributions employ the ultrafine condensation particle counter (UCPC) for detection purposes. Among these methods, the pulse height analysis (PHA) technique, in which the optical response of the UCPC detector is related to initial particle diameter in the 3–10nm range, prevails in applications where fast sampling is required or for which concentrations of nanoparticles are frequently very low. With the PHA technique, white light is required for particle illumination in order to obtain a monotonic relationship between initial particle diameter and optical response (pulse height). However, the popular, commercially available TSI Model 3025A UCPC employs a laser for particle detection. Here, we report on a novel white-light detection system developed for the 3025A UCPC that involves minimal alteration to the instrument and preserves normal counting operation. Performance is illustrated with pulse height spectra produced by differential mobility analyzer (DMA) – generated calibration aerosols in the 3–50nm range.     

A rapid technique to determine the internal area function of finite-length ducts using maximum length sequence analysis

This paper describes a rapid technique for reconstruction of the internal area function of a duct using blockage-induced eigenvalue shifts determined from eigenfrequencies measured under two sets of duct termination boundary conditions. A single broad band maximum length sequence (MLS) measurement of short duration is utilized to obtain the transfer function of the duct, which in turn can be utilized to determine its eigenvalue shifts and subsequently its internal area function using an inverse perturbation technique. The reconstruction results display the same order of accuracy as those obtained previously using swept sine measurements of extended duration. An expression for the determination of the area function is presented utilizing resonant frequency information alone, thus rendering duct length determination unnecessary. A computational routine further simplifies the process such that the accuracy of the technique could be ascertained for a range of configurations including longer ducts and ducts that initially have nonuniform internal cross section over their length. Development of a relationship between obstacle length and wavelength of the lowest eigenfrequency required for successful reconstruction is also described. This is an important result for longer ducts where measurement of lower eigenfrequencies may present problems using standard measurement equipment.     

Frobenius-perron resonances for maps with a mixed phase space

Resonances of the time evolution (Frobenius-Perron) operator P for phase space densities have recently been shown to play a key role for the interrelations of classical, semiclassical, and quantum dynamics. Efficient methods to determine resonances are thus in demand, in particular, for Hamiltonian systems displaying a mix of chaotic and regular behavior. We present a powerful method based on truncating P to a finite matrix which not only allows us to identify resonances but also the associated phase space structures. It is demonstrated to work well for a prototypical dynamical system.     

Out-diffusion and precipitation of copper in silicon: An electrostatic model

Concentrations of mobile interstitial copper and precipitated copper in silicon were studied after a high temperature intentional contamination and quench to room temperature. It was found that below a critical contamination the copper predominantly diffuses out to the surface, while for higher initial copper concentrations it mainly precipitates in the bulk. The critical copper contamination equals the acceptor concentration plus 10(16) cm (-3). This behavior can be explained by the electrostatic interaction between the positively charged interstitial copper and the forming copper precipitates.