Downregulation of BDNF mRNA and protein in the rat hippocampus by corticosterone

Previously, we showed that corticosterone regulates BDNF mRNA levels in the hippocampus. In the present study, we have investigated the time course and dose-dependency of this effect at both the mRNA and the protein level. Corticosterone was administered in doses of 30 and 1000 microgram/kg b.w. subcutaneously to adrenalectomized animals. At 3, 6, 12 and 24 h after administration BDNF and trkB mRNA levels in hippocampal subfields were measured by in situ hybridization. Our results show a dose-dependent decrease in BDNF mRNA in dentate gyrus and CA1 at 3 h. After the high dose, this decrease was 70% and 40% respectively. In addition, ELISA was performed to study if this downregulation is also detectable at the protein level. Hippocampal tissue was used from adrenalectomized animals which had received 1000 microgram/kg b.w. corticosterone 4 and 6 h before decapitation. At both time points, a decrease in BDNF protein was observed; 17% at 4 h and 14% at 6 h after corticosterone, as compared to the vehicle injected controls. TrkB mRNA levels were not affected by corticosterone. However, between 6 and 24 h after treatment, increases in trkB mRNA were observed. In conclusion, we have found a transient, dose-dependent decrease in BDNF mRNA and protein in the hippocampus, which may underly changes in neuronal plasticity in the hippocampus after short-term changes in corticosterone concentrations.     

Filter‐Free Wavelength Conversion Using Mach‐Zehnder Interferometer with Integrated Multimode Interference Semiconductor Optical Amplifiers

We propose a filter‐free wavelength conversion using a Mach‐Zehnder interferometer with monolithically integrated 2×2 multimode interference semiconductor optical amplifiers (MMI‐SOAs). The device has been optimized by considering a non‐homogeneous carrier distribution due to the self‐imaging properties of the MMI‐SOA. Static measurements show an extinction ratio of up to 18 dB and an input signal rejection ratio of up to 20 dB.     

Native tissue imaging at superharmonic frequencies

The second harmonic imaging mode has been adapted to image tissue and shown considerable improvements in image quality in several applications compared to the fundamental mode. The improvements were attributed to the effects of wave distortion due to nonlinear propagation in tissue. However, imaging tissue at the second harmonic frequency only has various drawbacks. Because the energy in the second harmonic frequency band is much lower than that in the fundamental frequency band, there must be excellent sensitivity and dynamic range in the receiving system to achieve an acceptable amount of signal-to-noise ratio. To increase the sensitivity, the spectral overlap between the fundamental and the second harmonic has to be diminished, which in return deteriorates the imaging resolution. Consequently, a trade-off is mandatory between resolution and sensitivity. Using simulations and measurements, we show that, at appropriate scanning acoustic settings, higher harmonics are generated in tissue. The higher harmonics represent additional, relevant information for tissue imaging and characterization. An elegant way to take advantage of the higher harmonics and to bring all the information together is to combine and incorporate all the multiple higher harmonics into a single component that we call the superharmonic component. Using a newly developed array transducer having a wide frequency band, B-mode images of a phantom were made in the superharmonic mode transmitting at 1.2 MHz. These images have exceptionally improved clarity and yield a dramatically cleaner and sharper contrast between the different structures being imaged. In addition to increased signal-to-noise ratio, superharmonic imaging shows better contrast and axial resolution as well as acceptable penetration depth.     

Controlled Growth of Layered Silver Stéarate on 2D and 3D Surfaces

This investigation confirms that silver stearate consists of an infinite‐sheet, two‐dimensional, nonmolecular layered structure. Scanning electron microscopy, X‐ray diffraction, and infrared spectroscopy reveal the following: plate‐like morphology is identified from the SEM image, XRD peaks can be indexed to the (0k0) reflections of a layered structure, and infrared peaks show that alkyl chains are present in an all‐trans conformational state with little or no significant gauche population. Based on these structural characteristics, we demonstrate that silver stearate, a prototype of layered organic‐inorganic hybrid material, can be grown not only in a designed two‐dimensional pattern but also in three‐dimensionally ordered ways by using carboxyl‐group terminated nanoparticles as a template.     

Digital Simulation of an Adaptive System for Long-Term Ventilation of the Lungs

Digital simulation of a model reference adaptive control scheme for long-term ventilation of the lungs is presented. This adaptive scheme is capable of bringing the instantaneous alveolar pressure of the patient to its normal level within one inspiration period, following a possible change in the patient's respiratory parameters (i.e., airway resistances or lung and chest wall compliances).     

Studies on melt spinning. V. Elongational viscosity and spinnability of two-phase systems

Isothermal melt spinning experiments were carried out to investigate the elongational flow behavior and spinnability of polymer blends and a calcium carbonate-filled polypropylene. Blends chosen for study were mixtures of polystyrene (Dow Chemical, Styron 678) with high-density polyethylene (Union Carbide, DMDJ 4309), and mixtures of polystyrene (Dow Chemical, Styron 686) with high-density polyethylene (Union Carbide, DMDJ 4309). For the study, measurements were taken of the thread diameter by photographic techniques and of the thread tension by means of a Saxl tensiometer. These measurements were later used to determine the elongational viscosity of the material investigated. It was found that, in all the blends and filled systems investigated, the elongational viscosity decreases with elongation rate and that the relationship between the elongational viscosity and blending ratio is very complex. An attempt is made to offer explanations of the observed complicated relationship with the aid of microphotographs of fiber samples, which display the complexity of fiber morphology in two-phase systems. It was also found that there exists some correlation between the elongational viscosity and the maximum stretch ratio which may be considered as representing fiber spinnability.     

Novel four quadrant DC-link soft switching inverter generating sinusoidal waveforms

A novel high frequency resonant link inverter using zero-voltage switching (except for one device where zero-current switching is used) operable in four quadrants is proposed. It provides several excellent advantages over the conventional resonant link inverters, such as low VA ratings, low acoustic noise and low harmonic distortion.<>