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1.
JL Kool AE Fiore CM Kioski EW Brown RF Benson JM Pruckler C Glasby JC Butler GD Cage JC Carpenter RM Mandel B England RF Breiman 《Canadian Metallurgical Quarterly》1998,19(12):898-904
OBJECTIVE: To investigate a cluster of cases of legionnaires' disease among patients at a hospital. SETTING: A university hospital that is a regional transplant center. DESIGN: Retrospective review of microbiology and serology data from the hospital laboratories and prospective surveillance via the radiology department; a case-control study and environmental sampling within the hospital and from nearby cooling towers. RESULTS: Diagnosis of seven cases of legionnaires' disease in the first 9 months of 1996 led to recognition of a nosocomial outbreak that may have begun as early as 1979. Review of charts from 1987 through September 1996 identified 25 culture-confirmed cases of nosocomial or possibly nosocomial legionnaires' disease, including 18 in bone marrow and heart transplant patients. Twelve patients (48%) died. During the first 9 months of 1996, the attack rate was 6% among cardiac and bone marrow transplant patients. For cases that occurred before 1996, intubation was associated with increased risk for disease. High-dose corticosteroid medication was strongly associated with the risk for disease, but other immunosuppressive therapy or cancer chemotherapy was not. Several species and serogroups of Legionella were isolated from numerous sites in the hospital's potable water system. Six of seven available clinical isolates were identical and were indistinguishable from environmental isolates by pulsed-field gel electrophoresis. Initial infection control measures failed to interrupt nosocomial acquisition of infection. After extensive modifications to the water system, closely monitored repeated hyperchlorinations, and reduction of patient exposures to aerosols, transmission was interrupted. No cases have been identified since September 1996. CONCLUSIONS: Legionella can colonize hospital potable water systems for long periods of time, resulting in an ongoing risk for patients, especially those who are immunocompromised. In this hospital, nosocomial transmission possibly occurred for more than 17 years and was interrupted in 1996, after a sudden increase in incidence led to its recognition. Hospitals specializing in the care of immunocompromised patients (eg, transplant centers) should prioritize surveillance for cases of legionnaires' disease. Aggressive control measures can interrupt transmission of this disease successfully. 相似文献
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J. Matthews M. E. Cage 《Journal of research of the National Institute of Standards and Technology》2005,110(5):497-510
We present detailed measurements of the temperature dependence of the Hall and longitudinal resistances on a quantum Hall device [(GaAs(7)] which has been used as a resistance standard at NIST. We find a simple power law relationship between the change in Hall resistance and the longitudinal resistance as the temperature is varied between 1.4 K and 36 K. This power law holds over seven orders of magnitude change in the Hall resistance. We fit the temperature dependence above about 4 K to thermal activation, and extract the energy gap and the effective g-factor. 相似文献
3.
M. E. Cage 《Journal of research of the National Institute of Standards and Technology》1993,98(3):361-373
When large currents are passed through a high-quality quantized Hall resistance device the voltage drop along the device is observed to assume discrete, quantized states if the voltage is plotted versus the magnetic field. These quantized dissipative voltage states are interpreted as occurring when electrons are excited to higher Landau levels and then return to the original Landau level. The quantization is found to be, in general, both a function of magnetic field and current. Consequently, it can be more difficult to verify and determine dissipative voltage quantization than previously suspected. 相似文献
4.
Quantized dissipative voltage states are observed when large currents are passed through a high-quality quantized Hall resistance device. These dissipative states are interpreted as occurring when electrons are excited to higher Landau levels and then return to the original Landau level. The author shows that the quantization is more complicated than previously thought. For example, the quantization can be a function of magnetic field. Therefore, the dissipative voltage quantization can, in general, be difficult to verify and determine 相似文献
5.
A. Jeffery R. E. Elmquist M. E. Cage 《Journal of research of the National Institute of Standards and Technology》1995,100(6):677-685
Precision tests verify the dc equivalent circuit used by Ricketts and Kemeny to describe a quantum Hall effect device in terms of electrical circuit elements. The tests employ the use of cryogenic current comparators and the double-series and triple-series connection techniques of Delahaye. Verification of the dc equivalent circuit in double-series and triple-series connections is a necessary step in developing the ac quantum Hall effect as an intrinsic standard of resistance. 相似文献
6.
M. E. Cage A. Jeffery J. Matthews 《Journal of research of the National Institute of Standards and Technology》1999,104(6):529-556
We use equivalent electrical circuits to analyze the effects of large parasitic impedances existing in all sample probes on four-terminal-pair measurements of the ac quantized Hall resistance RH. The circuit components include the externally measurable parasitic capacitances, inductances, lead resistances, and leakage resistances of ac quantized Hall resistance standards, as well as components that represent the electrical characteristics of the quantum Hall effect device (QHE). Two kinds of electrical circuit connections to the QHE are described and considered: single-series “offset” and quadruple-series. (We eliminated other connections in earlier analyses because they did not provide the desired accuracy with all sample probe leads attached at the device.) Exact, but complicated, algebraic equations are derived for the currents and measured quantized Hall voltages for these two circuits. Only the quadruple-series connection circuit meets our desired goal of measuring RH for both ac and dc currents with a one-standard-deviation uncertainty of 10−8
RH or less during the same cool-down with all leads attached at the device. The single-series “offset” connection circuit meets our other desired goal of also measuring the longitudinal resistance Rx for both ac and dc currents during that same cool-down. We will use these predictions to apply small measurable corrections, and uncertainties of the corrections, to ac measurements of RH in order to realize an intrinsic ac quantized Hall resistance standard of 10−8
RH uncertainty or less. 相似文献
7.
M. E. Cage A. Jeffery 《Journal of research of the National Institute of Standards and Technology》1998,103(6):593-604
In all experiments reported to date the measured values of the ac quantized Hall resistances RH varied with the frequency of the applied current, and differed significantly from the dc values of RH, making it difficult to use the ac quantum Hall effect as an absolute impedance standard. We analyze the effects due to the large capacitances-to-shields existing in the sample probes on measurements of RH to see if this is the source of the problem. Equivalent electrical circuits are utilized; they contain capacitances and leakage resistances to the sample probe shields, longitudinal resistances within the quantized Hall effect devices, and multiple connections to the devices. The algebraic solutions for the RH values in these circuits reveal large out-of-phase contributions to the quantized Hall voltages VH that would make it difficult to do accurate measurements with high precision ac bridges. These large out-of-phase contributions could introduce the linear frequency dependences observed in previous RH measurements. We predict, however, that quadruple-series connections to the quantum Hall devices yield only small out-of-phase contributions to VH which may allow accurate measurements of the quantity RH − Rx, where Rx is the longitudinal resistance along the device. 相似文献
8.
M. E. Cage D. Y. Yu G. Marullo Reedtz 《Journal of research of the National Institute of Standards and Technology》1990,95(1):93-99
We observe a spatially localized breakdown of the nearly dissipationless quantum Hall effect into a set of discrete dissipative states in wide, high-quality GaAs/AlGaAs samples. The phenomenon can be explained by an extension of the quasi-elastic inter-Landau level scattering model of Eaves and Sheard. 相似文献
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10.
A model of the human renal medulla 总被引:1,自引:0,他引:1