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M Sirota

Publications and source records attributed to M Sirota.

12 recordsLinked to original sources
PubMed2006

Air-stable PbSe/PbS and PbSe/PbSexS1-x core-shell nanocrystal quantum dots and their applications.

The optical properties and functionality of air-stable PbSe/PbS core-shell and PbSe/PbSexS1-x core-alloyed shell nanocrystal quantum dots (NQDs) are presented. These NQDs showed chemical robustness over months and years and band-gap tunability in the near infrared spectral regime, with a reliance on the NQD size and composition. Furthermore, these NQDs exhibit high emission quantum efficiencies of up to 65% and an exciton emission band that is narrower than that of the corresponding PbSe NQDs. In addition, the emission bands showed a peculiar energy shift with respect to the relevant absorption band, changing from a Stokes shift to an anti-Stokes shift, with an increase of the NQD diameter. The described core-shell structures and the corresponding PbSe core NQDs were used as passive Q-switches in eye-safe lasers of Er:glass, where they act as saturable absorbers. The absorber saturation investigations revealed a relatively large ground-state cross-section of absorption (sigma gs = 10(-16) - 10(-15) cm2) and a behavior of a "fast" absorber with an effective lifetime of tau eff approximately 4.0 ps is proposed. This lifetime is associated with the formation of multiple excitons at the measured pumping power. The product of sigma gs and tau eff enables sufficient Q-switching performance and tunability in the near infrared spectral regime. The amplified spontaneous emission properties of PbSe NQDs were examined under continuous illumination by a diode laser at room temperature, suitable for standard device conditions. The results revealed a relatively large gain parameter (g = 2.63 - 6.67 cm-1). The conductivity properties of PbSe NQD self-assembled solids, annealed at 200 degrees C, showed an Ohmic behavior at the measured voltages (up to 30 V), which is governed by a variable-range-hopping charge transport mechanism.

Air↗
PubMed1999

Crystal lattice and phase transitions in Na4TiP2O9 (NTP) and Na4.5FeP2O8(O,F) (NFP) superionic conductors as a function of high pressures and temperatures.

The lattice dynamics of Na(4)TiP(2)O(9) (tetrasodium titanium diphosphorus nonaoxide, NTP) and Na(4.5)FeP(2)O(8)(O,F) (nonasodium diiron tetraphosphorus difluoride octadecaoxide, NFP) crystals, which are superionic conductors with Na(+)-ion conductivity, were studied under high pressures. Lattice constants as a function of hydrostatic pressure were measured on a four-circle diffractometer using a high-pressure cell with diamond anvils. At 1.78 +/- 0.15 GPa NTP undergoes a reversible phase transition from the modulated monoclinic (pseudo-orthorhombic) modification which is stable under atmospheric conditions. A similar phase transition in NTP is observed at 523 K. For NFP, it may be assumed that at least three phase transitions occur when the pressure increases from atmospheric to 12 GPa, at 1.39 +/- 0.08, 4.52 +/- 0.32, and 6.02 +/- 0.02 GPa, as concluded from the change in the unit-cell parameters and in the color of the crystals: the color changes from ginger (dark orange) to pink at ~1.5-2.0 GPa pressure and to violet at ~6.0 GPa.

Journal Article↗
PubMed1992

Vestibuloocular reflex of rhesus monkeys after spaceflight.

The vestibuloocular reflex (VOR) of two rhesus monkeys was recorded before and after 14 days of spaceflight. The gain (eye velocity/head velocity) of the horizontal VOR, tested 15 and 18 h after landing, was approximately equal to preflight values. The dominant time constant of the animal tested 15 h after landing was equivalent to that before flight. During nystagmus induced by off-vertical axis rotation (OVAR), the latency, rising time constant, steady-state eye velocity, and phase of modulation in eye velocity and eye position with respect to head position were similar in both monkeys before and after flight. There were changes in the amplitude of modulation of horizontal eye velocity during steady-state OVAR and in the ability to discharge stored activity rapidly by tilting during postrotatory nystagmus (tilt dumping) after flight: OVAR modulations were larger, and tilt dumping was lost in the one animal tested on the day of landing and for several days thereafter. If the gain and time constant of the horizontal VOR change in microgravity, they must revert to normal soon after landing. The changes that were observed suggest that adaptation to microgravity had caused alterations in way that the central nervous system processes otolith input.

Animals↗
PubMed1987

Fluorophotometric study of intravenous carbonic anhydrase inhibitors in rabbits.

The ability of fluorophotometry to measure the time course of changes in aqueous humor flow in rabbits was evaluated by measuring the effect of intravenous carbonic anhydrase inhibitors on aqueous humor flow determinations. The abrupt changes in aqueous humor flow which were found by fluorophotometry agreed well with the expected changes in aqueous humor flow calculated from the time course of the intraocular pressure. Therefore, it was concluded that fluorophotometry could measure the time course of changes in aqueous humor flow in rabbits. Furthermore, it was suggested that the initial abrupt changes in aqueous humor flow after the administration of a carbonic anhydrase inhibitor were induced by the base content of the drug, followed by a more gradual decrease in aqueous humor flow caused by the direct effect of the drug on aqueous humor formation.

Animals↗
PubMed1980

Health status of cable splicers with low-level exposure to lead: results of a clinical survey.

The results of a cross-sectional clinical field survey of 90 telephone cable splicers are presented. Despite the rare occurrence of clinically overt lead poisoning among cable splicers, the observed prevalence of symptoms was 29% for lead-associated central nervous system symptoms and 21% for gastrointestinal symptoms. These two groups of symptoms were directly related to zinc protoporphyrin (ZPP) levels but no relationship was found between them and blood lead concentrations. Only 5% of the workers had significantly elevated blood lead levels (greater than 40 microgram/100ml). Because of the intermittent lead exposure encountered in this trade, individuals were identified with "normal" blood lead levels associated with "elevated" zinc protoporphyrin concentrations, indicating the difference in biological significance between exposure-(blood lead) and biological-response tests (ZPP). Suggestion is made that both types of diagnostic tests be utilized in the medical surveillance of lead-exposured workers.

Adult↗
PubMed1979

Asbestos disease in maintenance workers of the chemical industry.

In several large groups of workers employed in chemical plants, chest x-ray abnormalities (small irregular opacities and/or pleural changes) of the type known to be induced by asbestos were found in a proportion of those examined. A cross-sectional study of maintenance workers in a large chemical plant was undertaken to evaluate the prevalence of asbestosis; 185 workers were examined. Radiologic evidence of parenchymal interstitial fibrosis was found in 24% of those examined; in 10% of workers, parenchymal fibrosis was the only abnormality. Pleural fibrosis and/or calcification was found in the absence of parenchymal fibrosis in 14% of cases; in another 14% of workers, both parenchymal and pleural abnormalities were detected. The prevalence was significantly higher in those employed 20 or more years. Pleural abnormalities were more prevalent than were parenchymal changes. The increased risk of lung cancer and mesothelioma remains to be studied.

Adult↗