High-temperature properties of the Bi-Sr-Ca-Cu-O system: Simultaneous occurrence of melting, oxygen desorption, and a metal-insulator transition

We have investigated the temperature dependence of the electrical transport and the thermogravimetric properties, from -200°C to +1000, of the Bi-Sr-Ca-Cu-O high-temperature superconductor. We conclude that this system has a cooperative, simultaneous-melting/oxygen desorption/metal-insulator transition that occurs near 900°C. We speculate on its nature and on its relationship to phenomena found in other high-T _c superconductors.     

A novel electrochemical method for visual detection of surface inclusions in metallic substrates

An electrochemical method is presented for fast and non-destructive detection of surface inclusions in metals and alloys. Using electrode modification techniques, the sample surface is coated with a dark layer; the non-conductive inclusions remain uncoated and thus appear bright and highly visible. The new technique is demonstrated on different alloys with simulated and real inclusions.     

Further developments of a damage theory for filled polymers

This paper investigates matrix debonding from filler particles as a mechanism for weakening of a filled polymer. We analyze several simplified models of debonding. Our main concern is its effect on the overall elastic instants; for each debonding model, we calculate the change ΔW in overall strain energy density due to debonding. The resulting formulas for ΔW are all special cases of one general expression. Accordingly, we propose that this expression describes a broad class of debonding models, including some for which a detailed stress and strain analysis is not possible.     

Relationship between donor age and the replicative lifespan of human cells in culture: a reevaluation

Normal human diploid fibroblasts have a finite replicative lifespan in vitro, which has been postulated to be a cellular manifestation of aging in vivo. Several studies have shown an inverse relationship between donor age and fibroblast culture replicative lifespan; however, in all cases, the correlation was weak, and, with few exceptions, the health status of the donors was unknown. We have determined the replicative lifespans of 124 skin fibroblast cell lines established from donors of different ages as part of the Baltimore Longitudinal Study of Aging. All of the donors were medically examined and were declared "healthy," according to Baltimore Longitudinal Study of Aging protocols, at the time the biopsies were taken. Both long- and short-lived cell lines were observed in all age groups, but no significant correlation between the proliferative potential of the cell lines and donor age was found. A comparison of multiple cell lines established from the same donors at different ages also failed to reveal any significant trends between proliferative potential and donor age. The rate of [3H]thymidine incorporation and the initial rates of growth during the first few subcultivations were examined in a subset of cell lines and were found to be significantly greater in fetal lines than in postnatal lines. Cell lines established from adults did not vary significantly either in initial growth rate or in [3H]thymidine incorporation. These results clearly indicate that, if health status and biopsy conditions are controlled, the replicative lifespan of fibroblasts in culture does not correlate with donor age.     

Effects of neural refractoriness on spatio-temporal variability in spike initiations with Electrical stimulation.

In this paper, the effects of neural refractoriness on action potential (spike) initiations with electrical stimulation are investigated using computer modeling and simulation techniques. The computational model was composed of a myelinated nerve fiber with 50 nodes of Ranvier, each consisting of stochastic sodium and potassium channels, making it possible to represent the fluctuations of spike initiation. A series of two-pulse stimuli was presented by a stimulating electrode above the central (26th) node of Ranvier. The amplitude of the first (masker) pulse stimulus was set such that the masker pulse stimulus evoked spikes on each trial, while that of the second (probe) pulse stimulus was set such that the probe pulse stimulus evoked spikes on a half of trials, threshold values. Then the transmembrane potentials in response to the probe pulse stimulus were recorded at each node (i.e., 1-50 nodes) in order to determine the spike initiation node and time. From the observation of the spike initiation node and time, a spatio-temporal histogram as well as a spatial variability and a temporal variability of spike initiations was generated which allowed us to interpret fluctuations in spike initiation node and time. It was shown that the distribution of spike initiations tended to become greater spatially and longer temporally as the masker-probe intervals (MPIs) of the two-pulse stimuli shortened. It was also shown that the number of activated sodium channels as functions of space and time tended to become smaller due to inactivation of sodium channels and varied spatially and temporally as MPIs shortened. These findings may imply that the stochastic sodium channels during a relative refractory period may contribute to enhancing the fluctuations in spike initiations, and give us an insight into encoding information with electric stimuli to improve the performance of the prosthetic devices, especially cochlear implants.     

Micromechanical digital-to-analog converter for out-of-plane motion

This paper describes a novel micromechanical digital-to-analog converter (MDAC) for out-of-plane motion using electrostatic parallel-plate actuators. The proposed mechanism converts an N-bit digital signal to a mechanical out-of-plane displacement that is proportional to the analog value represented by the N-bit binary word. The mechanism is analogous to that of an electrical binary-weighted-input digital-to-analog converter (DAC). It consists of a movable platform, an array of parallel-plate microactuators each operating in an ON/OFF mode and a set of connection springs that connect the actuators to the platform. The spring constants of the connection springs are weighted so that the stiffness of successive springs is related by a factor of 2. A 4-bit mechanism has been fabricated using the Poly-MUMPS process, achieving a total stroke of 675 nm (full-scale output) and step size (LSB) of 45 nm in a highly repeatable and stable manner. The linearity error (LE) of the device is within /spl plusmn/0.28 LSB, and the differential linearity error (DLE) is within /spl plusmn/0.25 LSB. This mechanism can be configured for many promising applications, particularly in optical devices and systems such as tunable external cavity diode laser, tunable VCSELs, adaptive micromirror array and tunable wavelength filter.     

RAFT polymerization of temperature- and salt-responsive block copolymers as reversible hydrogels

Reversible-addition fragmentation chain transfer (RAFT) polymerization enabled the synthesis of novel, stimuli-responsive, AB and ABA block copolymers. The B block contained oligo(ethylene glycol) methyl ether methacrylate (OEG) and was permanently hydrophilic in the conditions examined. The A block consisted of diethylene glycol methyl ether methacrylate (DEG) and [2-(methacryloyloxy)ethyl]trimethylammonium chloride (TMA). The A block displayed both salt- and temperature-response with lower critical solution temperatures (LCSTs) dependent on the molar content of TMA and the presence of salt. Higher TMA content in the AB diblock copolymers increased the critical micelle temperatures (CMT) in HPLC-grade water due to an increased hydrophilicity of the A block. Upon addition of 0.9 wt% NaCl, the CMTs of poly(OEG-b-DEG₉₅TMA₅) decreased from 50 °C to 36 °C due to screening of electrostatic repulsion between the TMA units. ABA triblock copolymers displayed excellent hydrogel properties with salt- and temperature-dependent gel points. TMA incorporation in the A block increased the gel points for all triblock copolymers, and salt-response increased with higher TMA composition in the A block. For example, poly(DEG₉₈TMA₂-b-OEG-b-DEG₉₈TMA₂) formed a hydrogel at 40 °C in HPLC-grade water and 26 °C in 0.9 wt% NaCl aqueous solution. These salt- and temperature-responsive AB diblock and ABA triblock copolymers find applications as drug delivery vehicles, adhesives, and hydrogels.     

Transient electric and magnetic fields associated with establishinga finite electrostatic dipole, revisited

The authors reexamine the analysis of M.J. Master and M.A. Uman (1983), who derived and plotted the electromagnetic field waveforms generated by a square wave of current propagating with constant speed along a finite linear path, resulting in the formation of a finite electrostatic dipole. It was concluded that such a square pulse of current had charge only at its front and rear. The authors argue that errors were made in that analysis, correct these errors, and extend the overall analysis: (1) to show that the decomposition of the electromagnetic fields into electrostatic, induction, and radiation components on the basis of distance dependence is not general; (2) to demonstrate the use of the continuity equation in finding the charge distribution along a current path when the current distribution is known; and (3) to show how a seemingly simple analytical technique, the treatment of an abrupt step of current as a linearly rising current in the limit that the risetime goes to zero, can lead to erroneous results if there is not a good physical and mathematical understanding of all the variables involved     

The effect of intravenous and oral fluconazole on the pharmacokinetics and pharmacodynamics of intravenous alfentanil

The growth-promoting activity of PDGF-BB was studied on the adult osteoclasts in the present study. The PDGF receptor beta was detected on the osteoclast membrane through immunohistochemistry (LSAB method) and immunomicroscopy. The PDGF-BB was exerted on the osteoclasts that adhered to the bone slice at concentrations of 0, 10, 20, 30, and 40 ng/ml. The volume of Howship's lacuna augmented significantly and the number of resorption pits also increased with its dose (p < 0.01). The activity of both total acid phosphatase (ACP) and tartrate-resistant acid phosphatase (TRAP) increased significantly. These results suggest that PDGF-BB promotes adult osteoclastic bone resorption directly through PDGF receptor beta and is believed to play important roles in the bone healing process and reconstruction.     

Clenbuterol and anabolic steroids: a previously unreported cause of myocardial infarction with normal coronary arteriograms

During the last 10 years, several cases of myocardial infarction associated with anabolic steroid use have been reported. Postulated mechanisms to explain this association have included changes in lipid levels, the fibrinolytic system, and platelet aggregation. Clenbuterol is a beta 2-agonist with anabolic properties that has not been seen previously with myocardial infarction. We report a case of myocardial infarction in an otherwise healthy 26-year-old body-builder who recently used clenbuterol and anabolic steroids. In this case, synergistic effects of the two agents seem likely to have played a role in the infarct. The normal coronary arteriograms before any anticoagulant or thrombolytic therapy strongly suggest coronary spasm as the mechanism of the infarct.