Interleaved-contact electroabsorption modulator usingdoping-selective electrodes with 25°C to 95°C operating range

A multiple-quantum-well (MQW) modulator with multiple stacked p-i(MQW)-n-i(MQW)-p-regions is demonstrated. Electrodes are deposited such that all the n-layers are connected to one contact and all the p-layers to the other. This allows high fields to be produced in the i-regions with relatively low voltages, since the i-regions may be made thin while retaining large optical interaction because they are stacked. A large usable wavelength range which translates into a large operating temperature range is obtained because of large Stark shifts in the MQWs at high fields. For a 0 to 6 V swing >22% reflectivity change from 25°C to 95°C, or alternatively over a wavelength range of 15 nm at 25°C, is achieved     

Inhibition of vascular endothelial growth factor prevents retinal ischemia-associated iris neovascularization in a nonhuman primate

The antiestrogenic drug tamoxifen induces liver tumors in rats by a genotoxic mechanism. The key step has been proposed to be the formation of a reactive carbocation from the metabolite alpha-hydroxytamoxifen. This compound reacts with DNA in vitro to a small extent (1 in 10(5) DNA bases), giving products identical to those found in rat liver cells treated with tamoxifen. Now we have prepared the more reactive alpha-acetoxytamoxifen, which reacts with DNA in vitro to a much greater extent (1 in 50 bases). The products of this reaction were subjected to 32P postlabeling and shown by both TLC and reverse-phase liquid chromatography to be identical to those isolated from DNA treated with alpha-hydroxytamoxifen and to those found in the liver DNA of rat hepatocytes treated with tamoxifen or of the livers of rats treated with tamoxifen. The major product was also isolated as the nucleoside and characterized by UV, mass, and proton magnetic resonance spectroscopy. It is an adduct of tamoxifen and deoxyguanosine in which the alpha position of tamoxifen is linked covalently to the exocyclic amino group of deoxyguanosine.     

Potentially reactive cyclic carbamate metabolite of the antiepileptic drug felbamate produced by human liver tissue in vitro

To gain insights into the different forms of modified amyloid beta peptides (A beta) in the Alzheimer disease (AD) and Down syndrome (DS) brain, we used two-site ELISAs with antibodies specific for isomerized (i.e. A beta with L-isoaspartate at positions 1 and 7) and pyroglutamate-modified (i.e. A beta beginning with pyroglutamate at position 3) forms of A beta to quantitate the levels of these different A beta peptides in formic acid extracts of AD and DS frontal cortex. Despite variations in the proportions of distinct forms of A beta in AD and DS frontal cortex, the major species of A beta in these samples were A betaN3(pyroGlu)-42 as well as A beta x-42 (where x is a residue at position 2 or less in A beta), whereas isomerized A beta was a minor species. Further, the levels of isomerized and pyroglutamate-modified forms of A beta terminating at amino acid 42 were higher than those ending at amino acid 40. The abundance of the distinct forms of A beta reported here in formic acid extracts of AD and DS frontal cortex suggests that these A beta species could play important roles in the deposition of A beta in AD and DS brains.     

Human corneal studies with a vitrification solution containing dimethyl sulfoxide, formamide, and 1,2-propanediol

We tested the tolerance of human corneas to a vitrification solution, modified VS41A, containing 3.1 M dimethyl sulfoxide, 3.1 M formamide, and 2.2 M 1,2-propanediol in a carrier solution consisting of the corneal storage medium CPTES with 2.5% w/v chondroitin sulfate. Seven human corneas were exposed for 10 min each to graded concentrations of the solution at 0 degree C, remaining in the full-strength solution for 10 min. The corneas had significantly more endothelial cell damage (P < 0.05) than seven mated control corneas, but it was minimal (4.3% cell loss). Attempts at vitrification and rewarming of three corneas exposed to the solution by this protocol, however, resulted in ice formation in the peripheral corneal stroma and severe endothelial damage. Presumably, equilibration with the cryoprotectant in the thicker periphery of the human cornea had not occurred. Ice did not form on the center of one cornea, and substantial numbers of central endothelial cells survived after vitrification in this case. Immersion of the human corneas for 25 min in each of the four graded solutions at 0 degree C was required for sufficient penetration of the cryoprotectant to allow total corneal vitrification and rewarming without ice formation. This prolonged exposure to modified VS41A caused unacceptable damage to the corneal endothelium, however. Successful vitrification of human corneas with this solution will require a safe method for obtaining corneal equilibration with the cryoprotectant.     

Black bear femoral porosity decreases and mechanical properties increase with age despite annual periods of disuse (hibernation)

Inactivity causes bone loss, and a remobilization period that is 2-3 times longer than the disuse period is required to recover lost bone. Black bears (Ursus americanus), however, experience annual disuse (hibernation) and active periods that are approximately equal in length, but maintain bone material properties with age. Here, the effects of annual hibernation periods on whole bone properties were investigated. This study shows that mineral, geometrical and whole bone mechanical properties increase with age in black bear femurs, whereas porosity decreases with age. These results provide further support that black bears possess a biological mechanism to avoid disuse osteoporosis.     

Long‐Range,Entangled Carbon Nanotube Networks in Polycarbonate

A method is presented for dispersing ropes or bundles of single‐walled carbon nanotubes (RCNTs) in a polycarbonate (PC) matrix. Films of PC/RCNT composites are produced, with thicknesses ranging from 10 to 60 μm, and containing small concentrations (0.06–0.25 wt.‐%) of RCNT. Our process is based on a unique method of hot casting, annealing, and drying from dichlorobenzene solution. A wet annealing prior to complete drying yields a uniform and transparent film. Despite the low RCNT loading, scanning electron microscopy (SEM) analysis of the films after fracture reveals that the RCNTs form an entangled network throughout the film, which is a key requirement for enhanced properties. An increase of up to 30 % in the Young's modulus, as compared to PC, results with this method of composite fabrication.     

Nonlinear dynamic study of a bistable MEMS: model and experiment

In the Journal of Microelectromechanical Systems (see vol. 11, pp. 574-583, Oct. 2002), we presented an actuation scheme for toggling a bistable MEMS, a buckled beam, from one stable state to the other using radiation pressure of light. The experiments revealed some anomalous behavior of the beam. While long duration laser pulses at a power level slightly above the toggle threshold reliably toggled the beam every time, short duration pulses of the same power toggled the beam only about two-thirds of the time. In addition, when excessively high power levels (far above the toggle threshold) were used, the beam would not reliably toggle regardless of the pulse duration. This paper resolves the anomaly. It presents a nonlinear dynamical analysis of the bistable beam device which explains the anomaly as follows: a slightly higher than threshold force, applied for sufficient time, toggles the beam. If the force duration is longer than the time of decay of the oscillation of the beam about the toggled state, then the beam remains in that state after the force is removed. Otherwise, the beam may return to the original state. On the other hand, if the beam is toggled by a force far above the threshold, then after removal of the force, the beam may oscillate spanning both the states until the motion decays and the beam settles down to one of the states, not necessarily the toggled state, which may appear to be an anomalous behavior. The theoretical model is validated by a series of toggling experiments.