Quantum effects controlling electron beams

Quantum effects accompanying the transport of electron beams in nanodimensional structures have been studied. The possibility of controlling the electron beam in such structures by external electric field is considered. A two-dimensional control system is proposed comprising a resonator connected to a finite number of waveguides. A method of calculation of the scattering matrix and the wave function in such structures is developed. It is possible to select the control field parameters for which the beam is reliably transferred to a preset channel.     

Comparative effects of increased extracellular potassium and pacing frequency on the class III activities of methanesulfonanilide IKr blockers dofetilide, D-sotalol, E-4031, and MK-499

In order to analyze whether the referral system and nature of care exert any effect on the characteristics of patients, subjects aged 60 or above attending three medical centers on the Hong Kong Island between August and December 1990 were studied with respect to their age, sex, and psychiatric diagnosis. Psychiatric diagnoses were made in 98% of subjects at the psychogeriatric assessment service (PAC) (predominantly chronic organic brain syndrome), in 79.6% at the university psychiatric unit (mainly acute psychiatric problems, substance abuse, and deliberate self-harm), and in 20% at the general outpatient clinic (largely sleep and anxiety-related disorders). There was overrepresentation of the very old (above 80) and underutilization of counseling service at PAC. In Hong Kong, the psychogeriatric needs of the very old and of those with minor emotional disturbances associated with aging, retirement, and bereavement deserve reassessment.     

Protein kinase C delta (PKCdelta) inhibits the expression of glutamine synthetase in glial cells via the PKCdelta regulatory domain and its tyrosine phosphorylation

Protein kinase C (PKC) plays an important role in the proliferation and differentiation of glial cells. In a recent study we found that overexpression of PKCdelta reduced the expression of the astrocytic marker glutamine synthetase (GS). In this study we explored the mechanisms involved in the inhibitory effect of PKCdelta on the expression of glutamine synthetase. Using PKC chimeras we first examined the role of the catalytic and regulatory domains of PKCdelta on the expression of glutamine synthetase. We found that cells stably transfected with chimeras between the regulatory domain of PKCdelta and the catalytic domains of PKCalpha or epsilon inhibited the expression of GS, similar to the inhibition exerted by overexpression of PKCdelta itself. In contrast, no significant effects were observed in cells transfected with the reciprocal PKC chimeras between the regulatory domains of PKCalpha or epsilon and the catalytic domain of PKCdelta. PKCdelta has been shown to undergo tyrosine phosphorylation in response to various activators. Tyrosine phosphorylation of PKCdelta in response to phorbol 12-myristate 13-acetate and platelet-derived growth factor occurred only in chimeras which contained the PKCdelta regulatory domain. Cells transfected with a PKCdelta mutant (PKCdelta5), in which the five putative tyrosine phosphorylation sites were mutated to phenylalanine, showed markedly diminished tyrosine phosphorylation in response to phorbol 12-myristate 13-acetate and platelet-derived growth factor and normal levels of GS. Our results indicate that the regulatory domain of PKCdelta mediates the inhibitory effect of this isoform on the expression of GS. Phosphorylation of PKCdelta on tyrosine residues in the regulatory domain is implicated in this inhibitory effect.     

Visualization of individual single-walled carbon nanotubes by fluorescent polymer wrapping

Manipulating optical properties of single-walled nanotubes (SWNTs) is necessary for the development of nanoscale optical devices and probes for biomedical research. In life sciences it will make possible the direct observation of SWNTs inside living cells using optical microscopes. In the nanotechnology field it will enable the development of nanosensors with fluorescent reporting. However, the direct fluorescent labeling of SWNTs is obstructed by their strong light quenching qualities. Besides, chemical functionalization of SWNTs needed for the covalent attachment of fluorescent dyes could change favorable properties of nanotubes. Here we report that optical properties of SWNTs can be manipulated without their covalent modification by wrapping them with fluorescently labeled polymer poly(vinylpyrrolidone) (PVP-1300). Fluorescent PVP-1300 forms a monomolecular approximately 2.5 nm thick layer coiling around individual SWNTs and nanotube bundles. PVP casing is fluorescent although it is only several nanometers thick. This makes individual SWNTs observable by a fluorescent microscope. The spare polymer strands left over after wrapping around the relatively shorter nanotubes form junctions between SWNTs tying them together into new configurations, primarily Y- and psi-type junctions. The ability to use a single fluorescent polymer strand to fasten nanotubes together can be useful in assembly of nanotube-made devices. In PVP-covered SWNTs multiple fluorophores are attached to each single nanotube making them unique composite fluorophores attractive as parts of biological fluorescent probes and in the development of the new materials in photonics and nanotechnology.     

Estimation of the p-n junction depth in LWIR HgCdTe detectors from the spatial profile of the lateral photocurrent and transverse photovoltage induced by an infrared small spot

A new, simple nondestructive procedure for the estimation of the junction depth in planar long wavelength HgCdTe photodiodes is presented. The technique uses a combination of scanning light beam-induced current data with a transversal photovoltage measurement to extract the junction depth. The technique is applicable to both homojunction and heterojunction diodes. It is assumed that in the cross-section perpendicular to the device surface, the junction has a two-dimensional structure, and the length of the vertical junction is treated as the junction depth. The spatial profile of the lateral photocurrent produced by the spot scan marks the boundaries of the horizontal junction. Of these boundaries, only one of the vertical junctions contributes to the photocurrent. Using weakly absorbed infrared light insures the homogeneous profile of the photogenerated carriers along the vertical junction. A uniformly irradiated vertical junction produces the transverse photovoltage between its terminals. When the remote contacts are grounded, this photovoltage is dependent on the series resistance between the junction and the contacts. In the case when the circuit between the remote contacts is opened, the current is zero, and the photovoltage reaches its maximum value, equal to the junction open circuit voltage. From comparison of the two voltages, we extract the value of the series resistance. We have derived an analytical expression for the series resistance, which includes the junction depth. Comparison between the observed R_s values and those of the analytical expression, enable us to extract the junction depth value. The validity of the method is shown using a two-dimensional numerical simulation, and experimentally from ion-implanted and diffused p-n junctions.