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21.
22.
S. I. Kiselev V. V. Khmelenko D. A. Geller D. M. Lee J. R. Beamish 《Journal of Low Temperature Physics》2000,119(3-4):357-366
The velocity and attenuation of ultrasound passing through porous impurity-helium solids immersed in liquid 4He have been measured in the temperature range 1.1–2.3 K. These solids were formed by injecting a mixture of impurity (e.g. D2, Ne, N2 or Kr) and helium gases into superfluid 4He. The sound signal seemed to propagate mainly in the helium contained in the pores, rather than through the solid sample itself. We found that the speed of sound at low temperatures is close to and decreases more rapidly with temperature than first sound in bulk helium, similar to behavior observed in aerogel. The attenuation of sound in helium in the compressed impurity-helium solids is bigger than in bulk helium and increases rapidly with temperature up to 1.65 K, after which a crossover to a much weaker temperature dependence was observed. 相似文献
23.
The last decade has witnessed the convergence of three giant worlds:electronics,computer science and telecommunications.The next decade should follow this convergence in most of our activities with the generalization of sensor networks.In particular with the progress in medicine,people live longer and the aging of population will push the development of wireless person- 相似文献
24.
Fathy A.E. Pendrick V.A. Geller B.D. Perlow S.M. Tormey E.S. Prabhu A. Tani S. 《Microwave Theory and Techniques》2002,50(10):2247-2252
We have developed an innovative semianalytical technique for various substrate material characterization. The developed technique is a measurement procedure and data-reduction formulation that takes into consideration the radiation loss in a resonant structure, allowing for a more effective means of dielectric- and conductor-loss determination for a microstrip ring resonator and its substrate material. We separate dielectric and conductor loss precisely, evaluate the contribution of each term in the overall loss performance, and analytically predict the error in their respective predicted value. 相似文献
25.
Antonio H. Miguel Aarantzazu Eiguren-Fernandez Constantinos Sioutas Philip M. Fine Michael Geller Paul R. Mayo 《Aerosol science and technology》2013,47(5):415-418
Particle size distribution measurements of twelve USEPA priority pollutant polycyclic aromatic hydrocarbons (PAHs)—collected in Riverside, California, down to 10 nm aerodynamic diameter (Dp)—observed on integrated nocturnal samples (7:00 p.m.-6:30 a.m.) revealed that between 46 and 100% of the mass of particles in the Aitken size range was found in the 10–18 nm size bin. Particles in this size range have high alveolar deposition efficiency. 相似文献
26.
Leonidas Ntziachristos Andrea Polidori Harish Phuleria Michael D. Geller Constantinos Sioutas 《Aerosol science and technology》2013,47(6):571-580
Particle surface area has recently been considered as a possible metric in an attempt to correlate particle characteristics with health effects. In order to provide input to such studies, two Nanoparticle Surface Area Monitors (NSAMs, TSI, Inc.) were deployed in different urban sites within Los Angeles to measure the concentration levels and the diurnal profiles of the surface area of ambient particles. The NSAM's principle of operation is based on the unipolar diffusion charging of particles. Results show that the particle surface concentration decreases from ~150 μ m2 cm?3 next to a freeway to ~ 100 μ m2 cm?3 at 100 m downwind of the freeway, and levels decline to 50–70 μ m2 cm?3 at urban background sites. Up to 51% and 30% of the total surface area corresponded to particles < 40 nm next to the freeway and at an urban background site, respectively. The NSAM signal was well correlated with a reconstructed surface concentration based on the particle number size distribution measured with collocated Scanning Mobility Particle Sizers (SMPSs, TSI, Inc.). In addition, the mean surface diameter calculated by combination of the NSAM and the total particle number concentration measured by a Condensation Particle Counter (CPC, TSI, Inc.) was in reasonable agreement with the arithmetic mean SMPS diameter, especially at the urban site. This study corroborates earlier findings on the application of diffusion chargers for ambient particle monitoring by demonstrating that they can be effectively used to monitor the particle surface concentration, or combined with a CPC to derive the mean surface diameter with high temporal resolution. 相似文献
27.
V. E. Geller 《Fibre Chemistry》2001,33(5):353-363
Theoretical and technological aspects of orientational strengthening of polyester fibres are examined. High strength of polyester fibres is attained by the combination of the high molecular weight of poly(ethylene terephthalate) with stage-wise (in several stages) drawing. Current schemes for production of high-strength polyester fibres are reported. 相似文献
28.
The author examines the impact of changing technology and the changing marketplace on the telecommunications industry. He points out that telecommunications policy must permit the industry to respond quickly to these changes. He sets forth what he believes are the principles that govern this policy area and gives some examples of their applications 相似文献
29.
Twelve brands of plastic refractories, representing the products of nine manufac- turers, were subjected to standard and modified laboratory tests for high grade refractories. The data obtained show the chemical and physical characteristics of the material now furnished to the trade and indicate the results which may be expected from a technical examination of this type of product. 相似文献
30.
Different types of awareness sessions to promote employee safety belt use were evaluated. Across eight different employee safety meetings three dichotomous variables were manipulated: the type of presentation format (lecture vs discussion), the presence or absence of safety belt pledge cards, and the presence or absence of an incentive component. All groups showed a four-fold increase in safety belt use. Five months after the interventions, belt use was still significantly higher than baseline levels. Generalization across employees was demonstrated by a significant increase in safety belt use for those who did not attend the awareness session. The awareness session with a discussion format influenced greater increases in safety belt use than did the lecture-based sessions, but pledge cards and incentives did not increase the impact of these awareness sessions. 相似文献