University of Nevada, Reno

About: University of Nevada, Reno is a education organization based out in Reno, Nevada, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 13561 authors who have published 28217 publications receiving 882002 citations. The organization is also known as: University of Nevada & Nevada State University.

Performance of Diagnostic Mammography for Women With Signs or Symptoms of Breast Cancer

Abstract: Background: The performance of diagnostic mammography for women with signs or symptoms of breast cancer has not been well studied. We evaluated whether age, breast density, self-reported breast lump, and previous mammography influence the performance of diagnostic mammography. Methods: From January 1996 through March 1998, prospective diagnostic mammography data from women aged 25–89 years with no previous breast cancer were linked to cancer outcomes data in six mammography registries participating in the Breast Cancer Surveillance Consortium. We used the final mammographic assessment at the end of the imaging work-up to determine abnormal mammographic examination rate, positive predictive value (PPV), sensitivity, specificity, and area under the receiver operating characteristic (ROC) curve. We used age, breast density, prior mammogram, and self-reported breast lump jointly as predictors of performance. All statistical tests were two-sided. Results: Of 41 427 diagnostic mammograms, 6279 (15.2%) were judged abnormal. The overall PPV was 21.8%, sensitivity was 85.8%, and specificity was 87.7%. Multivariate analysis showed that sensitivity and specificity generally declined as breast density increased (P = .007 and P<.001, respectively), that previous mammography decreased sensitivity (odds ratio [OR] = 0.52, 95% confidence interval [CI] = 0.36 to 0.74; P<.001) but increased specificity (OR = 1.43, 95% CI = 1.31 to 1.57; P<.001), and that a self-reported breast lump increased sensitivity (OR = 1.64, 95% CI = 1.13 to 2.38; P = .013) but decreased specificity (OR = 0.54, 95% CI = 0.49 to 0.59; P<.001). ROC analysis showed that higher breast density and previous mammography were negatively related to accuracy (P<.001 for both). Conclusions: Diagnostic mammography in women with signs or symptoms of breast cancer shows higher sensitivity and lower specificity than screening mammography does. Higher breast density and previous mammographic examination appear to impair performance. [J Natl Cancer Inst 2002;94:1151–9] Diagnostic mammography is commonly used to identify possible breast cancers in women who present with signs or symptoms of the disease. These signs or symptoms may include a palpable breast lump, nipple discharge or retraction, and breast dimpling or other skin changes. A diagnostic mammographic examination usually consists of standard screening views and additional views using spot compression and/or magnification of a specific area. Although mammography may be sufficient to evaluate the clinical finding, additional imaging with ultrasound, ductography, or other imaging techniques may also be done. Sensitivity and specificity have been well studied for screening mammography studies (1–3) but not for diagnostic evaluations. Diagnostic mammography may have superior performance over screening mammography, because noticeable symptoms or clinical findings may indicate a more advanced tumor that is easier to locate and identify. Dee and Sickles (4) found that tumors detected by diagnostic mammography were larger than those detected by screening mammography. However, the performance of diagnostic mammography could also be altered by characteristics of the woman, including age, breast density, history of previous mammography, and presence of breast cancer symptoms. We performed a large prospective study of women with signs or symptoms of breast cancer who were undergoing diagnostic mammography. The records from the mammography registries of the Breast Cancer Surveillance Consortium (BCSC), a population-based consortium of community radiology practices (5), were linked with cancer outcomes. We evaluated the performance of diagnostic mammography and how performance may be influenced by the characteristics of the women undergoing mammography. METHODS Study Sample and Population

Power System Resilience: Current Practices, Challenges, and Future Directions

Abstract: The frequency of extreme events (e.g., hurricanes, earthquakes, and floods) and man-made attacks (cyber and physical attacks) has increased dramatically in recent years. These events have severely impacted power systems ranging from long outage times to major equipment (e.g., substations, transmission lines, and power plants) destructions. This calls for developing control and operation methods and planning strategies to improve grid resilience against such events. The first step toward this goal is to develop resilience metrics and evaluation methods to compare planning and operation alternatives and to provide techno-economic justifications for resilience enhancement. Although several power system resilience definitions, metrics, and evaluation methods have been proposed in the literature, they have not been universally accepted or standardized. This paper provides a comprehensive and critical review of current practices of power system resilience metrics and evaluation methods and discusses future directions and recommendations to contribute to the development of universally accepted and standardized definitions, metrics, evaluation methods, and enhancement strategies. This paper thoroughly examines the consensus on the power system resilience concept provided by different organizations and scholars and existing and currently practiced resilience enhancement methods. Research gaps, associated challenges, and potential solutions to existing limitations are also provided.

A Class of Speed-Sensorless Sliding-Mode Observers for High-Performance Induction Motor Drives

Abstract: A new family of speed-sensorless sliding-mode observers for induction motor drives has been developed. Three topologies are investigated in order to determine their feasibility, parameter sensitivity, and practical applicability. The most significant feature of all schemes is that they do not require the rotor speed adaptation, i.e., they are inherently sensorless observers. The most versatile and robust is a dual-reference-frame full-order flux observer. The other two schemes are flux observers implemented in stator frame and rotor frame, respectively. These are simpler than the first one and make use of the sliding-mode invariance over a specified range of modeling uncertainties and disturbances. Main theoretical aspects, results of parameter sensitivity analysis, and implementation details are given for each observer in order to allow the comparison. Experimental results with the dual-reference-frame observer, considered the most adequate for practical applications, are presented and discussed. Sensorless operation with a sliding-mode direct-torque-controlled drive at very low speeds is demonstrated. It is concluded that the new proposed observers represent a feasible alternative to the classical speed-adaptive flux observers.