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1.
A new technique for mixing optical waves to generate microwave-frequency signals using an injection laser diode and a fibre-optic interferometer is reported. A beat signal is produced by interfering light from the laser with light from the same laser emitted earlier at a different frequency. The interferometer consists of an evanescent-field fibre coupler joined to a length of single-mode optical fibre. The laser is tuned by pulsed or bipolar current waveforms superimposed on a DC bias current. Feedback from an external cavity stabilises the laser frequency and reduces its linewidth. Efficient mixing at difference frequencies from 250 MHz to 2 GHz is obtained, with spectral widths of less than 1% of the centre frequency. 相似文献
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Summary Methacrylic acid was photopolymerised using CdS and composite, CdS/HgS and CdS/TiO2, colloidal semiconductor particles as initiators. The previously proposed photoinitiation mechanism involving the photogenerated positive hole in the valence band of the CdS colloid was confirmed by the electron scavenging action of TiO2. The effect of pH on the course of the polymerisation was investigated and is discussed. 相似文献
3.
The regulation of programmed cell death in the developing nervous system involves target-derived survival factors, afferent synaptic activity, and hormone- and cytokine-dependent signaling. Cultured immature cerebellar granule neurons die by apoptosis within several days in vitro unless maintained in depolarizing (high) concentrations of potassium (25 mM K+). Here we report that transforming growth factors (TGF)-beta1, -beta2, and -beta3 accelerate apoptosis of these neurons when maintained in physiological (low) K+ medium (5mM K+) as assessed by measures of viability, quantitative DNA fragmentation, and nuclear morphology. TGF-beta-induced apoptosis of these neurons is not blocked by CNTF and LIF, cytokines that enhance neuronal survival when applied alone, or by IGF-I, which prevents apoptosis upon potassium withdrawal. In contrast, neurons that differentiate in high K+ medium for several days in vitro acquire resistance to TGF-beta-mediated cell death. Granule neurons maintained in either low or high K+ medium produce latent, but not bioactive, TGF-beta1 and -beta2. Because neutralizing TGF-beta antibodies fail to augment survival of low K+ neurons, the cerebellar neurons are apparently unable to activate latent TGF-beta. Thus, apoptosis of low K+ neurons is not attributable to endogenous production of TGF-beta. Taken together, our data suggest that TGF-beta may limit the expansion of postmitotic neuronal precursor populations by promoting their apoptosis but may support survival of those neurons that have maturated, differentiated, and established supportive synaptic connectivity. 相似文献
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Weller SC 《Textile rental》1992,75(6):40-42
If you supply healthcare linen, OSHA's new ruling comes with a price tag, but it may be a marketing boon as well. The costs of compliance are high--about $1.19 million annually. One of the most costly and important parts of the ruling is the required employer-paid hepatitis B vaccination of employees. But behind the costs, there's good news for the textile rental industry. The opportunity to serve small medical facilities and nursing homes as well as hospitals with reusable healthcare garments could create a revenue source estimated to be at least $177 million a year. 相似文献
6.
Weller SC 《Textile rental》1992,75(10):56, 58-56, 62
A potential $177 million-a-year market has been opened to textile rental operators, thanks to OSHA's recent ruling on bloodborne pathogens. Healthcare providers nationwide are now searching for solutions to their protective apparel needs. Such customer needs are what drive niche markets. Whether you've been serving the healthcare market for years or are just now targeting it, here are the marketing strategies you need. 相似文献
7.
Weller SC 《Textile rental》1992,76(1):44, 46
The last phase of the federal OSHA standard on occupational exposure to bloodborne pathogens became effective July 6. However, compliance deadlines may vary in the 23 states and two U.S. territories that have their own OSHA offices. The states and territories have the option of adopting the federal standard or drafting their own plans. Here's a status report on the OSHA-approved state programs for bloodborne pathogens. 相似文献
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Weller SC 《Textile rental》1991,75(3):32-33
Textile rental companies are poised on the edge of a boom in the healthcare marketplace. The detonator is outpatient care. Between 1984 and 1990, outpatient visits increased from almost 233 million to more than 310 million, or about 33 percent. The shift from traditional hospital care to outpatient or ambulatory service is creating a new market opportunity for textile rental services. Innovative medical services are cropping up in suburban malls and neighborhoods, and demand is high for high-quality linen supply or contract laundry services. 相似文献
10.
Kirk Weller Ilana Arnon Ed Dubinsky 《Canadian Journal of Science, Mathematics, & Technology Education》2013,13(2):129-159
Abstract In an earlier study of preservice elementary and middle school teachers’ beliefs about repeating decimals, Weller, Arnon, and Dubinsky (2009) reported on a comparison of the mathematical performance of 77 preservice teachers who completed an APOS-based instructional unit with 127 preservice teachers who completed traditional instruction. The purpose of the current study, based on 47 interviews conducted 4 months after the instruction, during which time there was no further instruction on this topic, is to determine the strength and stability (over time) of the students’ beliefs, to uncover thinking that did not arise in the earlier study, and to see whether the interviews yield similar comparative results. The interviews did uncover changes in student thinking. The students who received the APOS-based instruction developed stronger and more stable (over time) beliefs that a repeating decimal is a number; a repeating decimal has a fraction or integer to which it corresponds; a repeating decimal in general equals its corresponding fraction or integer; and, in particular, In addition, a number of indices and categories were developed that may prove useful in other studies consisting of the comparison of interview and questionnaire data involving a large number of interview subjects. 相似文献