Using the Schwinger inverse method for solutions of inverse transport problems in two-dimensional cylindrical geometries

The Schwinger method for solving inverse transport problems is applied to the problems of interface location identification, shield material identification, source isotope weight fraction identification, and material mass density identification (separately) in multilayered two-dimensional cylindrical gamma radiation source/shield systems. The method is iterative and estimates unknown interface locations, source isotope weight fractions, and material densities directly, while the unknown shield material is identified by estimating its total macroscopic gamma-ray cross sections. The energies of discrete gamma-ray lines emitted by the source are assumed to be known, while the unscattered flux of the lines is assumed to be measured at points external to the system. In numerical test cases, the Schwinger method correctly identifies the unknowns when the same deterministic ray-tracing code is used for both the parameter estimation process and simulation of the measured data. With realistic simulation of the measured data using a Monte Carlo code, the method produces more ambiguous results for interface location, shield material identification, and material density identification. The method works well for source weight fraction identification with measured data simulated by Monte Carlo. In addition to the application to more realistic (two-dimensional) problems, this paper extends previous work on the Schwinger inverse method by using surface formulas for unknown interface locations, automatic correction attempts for violated constraints, and ray-tracing instead of discrete-ordinates for transport calculations.     

Thermal-hydraulic and neutronic analyses of the submersion-subcritical, safe space (S) reactor

The solid-core Submersion-Subcritical Safe Space (S⁴) reactor is cooled with He-28% Xe gas (molecular weight of 40 g/mole) and nominally generates 471 kWth for at least 7 years. To avoid single point failures in reactor cooling and energy conversion, the S⁴ reactor core is divided into three hydraulically independent, but neutronically and thermally coupled sectors. Each sector feeds a separate Closed Brayton Cycle (CBC) power conversion loop with separate heat rejection radiator panels. Detailed thermal-hydraulic analyses of the S⁴ reactor core are performed to ensure that the maximum fuel temperature during nominal operation stays below 1300 K. In addition, a neutronics analysis performed using MCNP 5 confirms that the S⁴ reactor satisfies the design reactivity requirements. These are at least $ 4 of cold clean excess reactivity, at least $ 2.25 of shutdown margin, and at least $ 1 subcritical in the worst-case of submersion and flooding, following a launch abort accident. Mass estimates of the S⁴ reactor design that meets both the thermal and the reactivity requirements are provided.     

Tuning parallel applications in parallel

In this paper, we present and evaluate a parallel algorithm for parameter tuning of parallel applications. We discuss the impact of performance variability on the accuracy and efficiency of the optimization algorithm and propose a strategy to minimize the impact of this variability. We evaluate our algorithm within the Active Harmony system, an automated online/offline tuning framework. We study its performance on three benchmark codes: PSTSWM, HPL and POP. Compared to the Nelder–Mead algorithm, our algorithm finds better configurations up to seven times faster. For POP, we were able to improve the performance of a production sized run by 59%.     

A simple model for determining effects of negative differential mobility and magnitude of saturated velocity on the performance of Schottky-barrier field effect transistors

The effects of nonuniform fields in the channel of GaAs MESFETs, and the resulting range of velocities with which carriers drift, are here considered using a simple model in order to determine the effects of negative differential mobility and saturated velocity on the performance of these devices, and of devices made of other materials. On the basis of the equilibrated velocity-field ν(E) characteristic for GaAs, carriers in short-channel FETs drift over much of the source to drain length with the saturated high field velocity, i.e. a velocity about half that used in most previous analytical solutions for GaAs FETs, and one about equal to the maximum carrier velocity in Si. Neglecting transient effects in electron transport, fields at which a negative differential mobility occurs exist over only a very small portion of the channel. The value of low field mobility of the MESFET material is therefore important primarily in determining source resistance.     

Quantitative evaluation of pancreatic enhancement during dual-phase helical CT

PURPOSE: To determine the improvement in pancreatic enhancement at helical computed tomography (CT) performed with an early delay after administration of contrast material compared with that performed with a standard delay. MATERIALS AND METHODS: Dual-phase helical CT of the abdomen was performed in 120 patients with a 150-mL bolus of contrast material infused at 5 mL/sec. Early and standard delayed scanning was performed beginning at 20 seconds and 49-71 seconds, respectively. Regions of interest were measured in the head, body, and tail of the pancreas in 92 patients. The difference in enhancement between early and standard delayed scanning was calculated. RESULTS: Mean pancreatic enhancement was 82 HU +/- 3 (standard error) with an early delay, whereas enhancement on standard delay scans was 62 HU +/- 2 (P < .001). An improvement in enhancement greater than 10 HU was attained in 66 of 92 cases (72%). CONCLUSION: Pancreatic enhancement at helical CT with an early delay after contrast material administration is often significantly greater than the enhancement seen with a standard delay when a monophasic, rapidly infused bolus of contrast material is used.     

The importance of the lumpectomy surgical margin status in long-term results of breast conservation

BACKGROUND: The impact of the surgical margin status on long-term local control rates for breast cancer in women treated with lumpectomy and radiation therapy is unclear. METHODS: The records of 289 women with 303 invasive breast cancers who were treated with lumpectomy and radiation therapy from 1972 to 1992 were reviewed. The surgical margin was classified as positive (transecting the inked margin), close (less than or equal to 2 mm from the margin), negative, or indeterminate, based on the initial biopsy findings and reexcision specimens, as appropriate. Various clinical and pathologic factors were analyzed as potential prognostic factors for local recurrence in addition to the margin status, including T classification, N classification, age, histologic features, and use of adjuvant therapy. The mean follow-up was 6.25 years. RESULTS: The actuarial probability of freedom from local recurrence for the entire group of patients at 5 and 10 years was 94% and 87%, respectively. The actuarial probability of local control at 10 years was 98% for those patients with negative surgical margins versus 82% for all others (P = 0.007). The local control rate at 10 years was 97% for patients who underwent reexcision and 84% for those who did not. Reexcision appears to convey a local control benefit for those patients with close, indeterminate, or positive initial margins, when negative final margins are attained (P = 0.0001). Final margin status was the most significant determinant of local recurrence rates in univariate analysis. By multivariate analysis, the final margin status and use of adjuvant chemotherapy were significant prognostic factors. CONCLUSIONS: The attainment of negative surgical margins, initially or at the time of reexcision, is the most significant predictor of local control after breast-conserving treatment with lumpectomy and radiation therapy.     

Psychiatric comorbidity, health status, and functional impairment associated with alcohol abuse and dependence in primary care patients: Findings of the PRIME MD-1000 study.

The psychiatric comorbidity, health, and functioning of primary care patients with alcohol abuse and dependence (AAD) was investigated in a sample of 1,000 patients. Psychiatric symptomatology was assessed with the Primary Care Evaluation of Mental Disorders (PRIME-MD) diagnostic system. Health and functional status was assessed with the Medical Outcomes Study Short Form General Health Survey (SF-20). Results indicated that use of the PRIME-MD system brought about a 71% increase in physician recognition of AAD. AAD patients were diagnosed with substantial psychiatric comorbidity, and they reported poorer health and functioning than did patients without any psychiatric disorders. However, they reported less impairment and psychiatric comorbidity than did patients with other psychiatric disorders. Results also indicated that AAD patients' health and functioning were associated with the presence or absence of psychiatric comorbidity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of age and schooling on the acquisition of elementary quantitative skills.

The influence of school- and age-related variables was examined separately on 2 tasks involving elementary quantitative skills: conservation of number and mental addition. Performance on these tasks was compared by using a cutoff design with 3 groups of kindergarten and Grade 1 children who differed in age but not amount of schooling (grade), in schooling but not age, or in both age and schooling. The effects of age and schooling were distinct. On conservation of number, performance improved as a function of age but not schooling. On mental arithmetic, accuracy improved with schooling rather than age but children's use of various solution procedures (e.g., retrieval, counting) was not influenced by schooling. Thus, in the domain of elementary mathematical skills, the influence of schooling can be very specific, and age-related variables other than schooling play an important role in the development of elementary mathematical skills. Results illustrate the utility of the cutoff design for investigating instructional and developmental influences on cognitive development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Depression in first-time mothers: Mother-infant interaction and depression chronicity.

Married, middle-class women who met diagnostic criteria for depression and a comparable group of nondepressed women were videotaped interacting with their infants at home at 2, 4, and 6 months. When depression was defined in terms of 2-month diagnosis, there were no differences between depressed and comparison mothers or babies in either positive or negative interaction during feeding, face-to-face interaction, or toy play. However, women whose depressions lasted through 6 months were less positive with their infants across these 3 contexts than women whose depressions were more short-lived, and their babies were less positive during face-to-face interaction. These data highlight the need to distinguish between transient and protracted depression in evaluating depression effects on the mother–infant relationship and infant outcome. (PsycINFO Database Record (c) 2010 APA, all rights reserved)