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Purpose: Quantitative computed tomography (QCT)‐derived measures of lung density are valued methods for objectively characterizing lung parenchymal and peripheral airways disease and are being used in a growing number of lung disease focused trials. Detector and reconstruction improvements in CT technology have allowed for significant radiation dose reduction in image acquisition with comparable qualitative image quality. We report the impact of detector type and reconstruction type on QCT lung density measures in relation to decreasing dose indices. Methods: Two sets of studies were completed in an in vivo pig model with a SOMATOM Definition Flash CT system: (a) prior to system upgrade with conventional detectors (UFC) and filtered back projection (FBP), and (b) post system upgrade with integrated electronic detectors (STELLAR) and iterative reconstruction (SAFIRE). CT data were acquired across estimated CT volume dose indices (CTDIvol) ranging from 0.75 to 15 mGy at both inspiratory and expiratory breath holds. Semiautomated lung segmentations allowed calculation of histogram median, kurtosis, and 15th percentile. Percentage of voxels below −910 HU and −950 HU (inspiratory), and −856 HU (expiratory) were also examined. The changes in these QCT metrics from dose reduction (15 mGy down to 0.75 mGy) were calculated relative to paired reference values (15 mGy). Results were compared based on detector and reconstruction type. Results: In this study, STELLAR detectors improved concordance with 15 mGy values down to 3 mGy for inspiratory scans and 6 mGy for expiratory scans. The addition of SAFIRE reconstruction in all acquired measurements resulted in minimal deviation from reference values at 0.75 mGy. Conclusion: The use of STELLAR integrated electronic detectors and SAFIRE iterative reconstruction may allow for comparable lung density measures with CT dose indices down to 0.75 mGy. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate industrially feasible large-area solar cells achieving energy conversion efficiency up to 21.63% on p-type boron doped multicrystalline Si wafers. Advanced light trapping, passivation and hydrogenation technology are used to achieve excellent light absorption with very low surface recombination velocity. The bulk lifetime of the multi-crystalline Si wafers used for the fabrication exceeds 500 μs after optimized gettering and hydrogenation processes. The high bulk lifetime and excellent surface passivation enable Voc to exceed 670 mV. The metallization process is carried out by screen printing and firing in a conventional belt furnace. Detailed performance parameters and quantum efficiency of the cells will be illustrated in the paper. In addition, free energy loss analysis and cell simulation are also performed using the control parameters measured during cell fabrication processes. [ABSTRACT FROM AUTHOR]

Purpose: Assessing pulmonary emphysema using Quantitative CT of the lung depends on accurate measures of CT density. Sinogram-Affirmed-Iterative-Reconstruction (SAFIRE) is a new approach for reconstructing CT data acquired at significantly lower doses. However, quantitative effects of this method remain unexplored. The authors investigated the effects on the median values of materials in the COPDGene2 test-object as a function of the reconstruction method [weighted filtered back projection (WFBP) versus SAFIRE], test-object size, dose, and material composition using a Siemens SOMATOM Definition FLASH CT scanner. Methods: The COPDGene2 test-object contains eight materials; acrylic, water, four foams (20 lb, 12 lb, lung-equivalent, and 4 lb emphysema-equivalent), internal and external-air. The test-object was scanned with three different outer ring sizes, simulating three different body habitus. There is an average size (36 cm) Ring A, large size (40 cm) Ring B, and small size Ring C (30 cm). The CT protocol used 120 kVp, 0.5 s rotation, 1.0 pitch, and a 0.6 slice collimation with progressively decreasing x-ray exposure values, 11.94-0.74 mGy. With a thorax length of 30 cm, the corresponding effective doses would be 5.01-0.31 mSv. The effects of using SAFIRE versus WFBP were assessed using a two tailed t-test for each ring size, material, and dose. Multivariable linear regression was used to evaluate the relative effects of ring size, material composition, dose, and reconstruction method on the measured median value in HU. Results: SAFIRE versus WFBP, at the largest ring size and two lowest doses there was a significant difference in median values of 4 lb-foam, p < 0.01. Using the smallest ring size at the lowest dose level there was a significant difference in the median value of 4 lb-foam, but the effect size was small, 1 HU. There is a significant difference in median values of both internal and external air using both the small and medium size rings at the three lowest dose levels, p < 0.05. There are significant differences noted at both high and low dose levels when using the large ring size in the median values of internal and external air when, p < 0.05. These effects on 4 lb-foam, inside and outside air are shown to be in part due to truncation effects on the median value since the lowest HU value in the CT scale used is - 1 0 2 4 HU. Multivariable linear regression results demonstrated significant effects on the measured material median value and standard deviation due to ring size, material composition, dose level, and reconstruction method, p < 0.05. Results: SAFIRE versus WFBP, at the largest ring size and two lowest doses there was a significant difference in median values of 4 lb-foam, p < 0.01. Using the smallest ring size at the lowest dose level there was a significant difference in the median value of 4 lb-foam, but the effect size was small, 1 HU. There is a significant difference in median values of both internal and external air using both the small and medium size rings at the three lowest dose levels, p < 0.05. There are significant differences noted at both high and low dose levels when using the large ring size in the median values of internal and external air when, p < 0.05. These effects on 4 lb-foam, inside and outside air are shown to be in part due to truncation effects on the median value since the lowest HU value in the CT scale used is - 1 0 2 4 HU. Multivariable linear regression results demonstrated significant effects on the measured material median value and standard deviation due to ring size, material composition, dose level, and reconstruction method, p < 0.05. noise (lower standard deviation) using SAFIRE versus WFBP with all ring sizes, doses, and materials in the COPDGene2 test-object. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to detect and analyze anomalies between a large number of computed tomography (CT) scanners, tracked over time, utilized to collect human pulmonary CT data for a national multicenter study: chronic obstructive pulmonary disease genetic epidemiology study (COPDGene). Methods: A custom designed CT reference standard 'Test Object' has been developed to evaluate the relevant differences in CT attenuation between CT scanners in COPDGene. The materials used in the Test Object to assess CT scanner accuracy and precision included lung equivalent foam (-856 HU), internal air (-1000 HU), water (0 HU), and acrylic (120 HU). Nineteen examples of the Test Object were manufactured. Initially, all Test Objects were scanned on the same CT scanner before the Test Objects were sent to the 20 specific sites and 42 individual CT scanners that were used in the study. The Test Objects were scanned over 17 months while the COPDGene study continued to recruit subjects. A mixed linear effect statistical analysis of the CT scans on the 19 Test Objects was performed. The statistical model reflected influence of reconstruction kernels, tube current, individual Test Objects, CT scanner models, and temporal consistency on CT attenuation. Results: Depending on the Test Object material, there were significant differences between reconstruction kernels, tube current, individual Test Objects, CT scanner models, and temporal consistency. The two Test Object materials of most interest were lung equivalent foam and internal air. With lung equivalent foam, there were significant (p < 0.05) differences between the Siemens B31 (-856.6, ±0.82; mean ± SE) and the GE Standard (-856.6 ± 0.83) reconstruction kernel relative to the Siemens B35 reference standard (-852.5 ± 1.4). Comparing lung equivalent foam attenuation there were also significant differences between CT scanner models (p < 0.01), tube current (p < 0.005), and in temporal consistency (p < 0.005) at individual sites. However, there were no significant effects measurable using different examples of the Test Objects at the various sites compared to the reference scans of the 19 Test Objects. For internal air, significant (p < 0.005) differences were found between all reconstruction kernels (Siemens B31, GE Standard, and Phillips B) compared to the reference standard. There were significant differences between CT models (p < 0.005), and tube current (p < 0.005). There were no significant effects measurable using different examples of the Test Objects at the various sites compared to the reference scans of the 19 Test Objects. Differences, across scanners, between external air and internal air measures in this simple (relative to the in vivo lung) test object varied by as much as 15 HU. Conclusions: The authors conclude that the Test Object designed for this study was able to detect significant effects regarding individual CT scanners that altered the CT attenuation measurements relevant to the study that are used to determine lung density. Through an understanding of individual scanners, the Test Object analysis can be used to detect anomalies in an individual CT scanner and to statistically model out scanner differences and individual scanner changes over time in a large multicenter trial. [ABSTRACT FROM AUTHOR]

This article investigates capital mobility across 29 provinces in China for the period of 1970-2006 using the Feldstein-Horioka (FH) approach and 's consumption-smoothing (CS) framework. It also examines the role of the governments in driving provincial capital mobility. If the provincial government investment is not properly separated out from the private investment, the FH framework applied to the overall saving and investment (private plus public) is found to underestimate the private saving-investment correlation and hence overstates the degree of private capital mobility compared with the CS framework that focuses on the private consumption and output. Both frameworks indicate strong correlation between private saving-investment and private consumption-output, implying strong barriers in the provincial private capital flows. However, there is ample evidence that capital mobility has been rising over time, particularly after the mid 1990s. It also appears that the government facilitates capital flows through inter-governmental transfers during the sample period. The extent of provincial capital mobility sheds light on the ability of different provinces in diversifying idiosyncratic provincial risks. The earlier findings are robust to alternative measurements of variables and model specifications. [ABSTRACT FROM AUTHOR]

It is of interest to estimate the size of a crowd in a demonstration. We propose a practical method to obtain an estimate of the size of the crowd and its standard error. This method has been implemented in practice and, compared with other counting methods, is found to be more efficient, more timely and have less scope for bias. The method described in this paper was motivated by the annual 1 July demonstrations in Hong Kong, and data from the 2006 demonstration are used as an example of the proposed method. [ABSTRACT FROM AUTHOR]

Recently, there has been much research on developing models suitable for analysing the volatility of a discrete-time process. Since the volatility process, like many others, is necessarily non-negative, there is a need to construct models for stationary processes which are non-negative with probability one. Such models can be obtained by driving autoregressive moving average (ARMA) processes with non-negative kernel by non-negative white noise. This raises the problem of finding simple conditions under which an ARMA process with given coefficients has a non-negative kernel. In this article, we derive a necessary and sufficient condition. This condition is in terms of the generating function of the ARMA kernel which has a simple form. Moreover, we derive some readily verifiable necessary and sufficient conditions for some ARMA processes to be non-negative almost surely. [ABSTRACT FROM AUTHOR]

One of the challenges of broadband wireless multimedia networks is to design a wireless data link control (W-DLC) protocol which provides reliable data delivery over the noisy wireless link in an efficient manner. This paper presents our proposal of such a W-DLC protocol, based on a new coding scheme called multi-dimensional concatenated zigzag code. Both real-time and non-real-time traffic can be efficiently supported by adopting different error control mechanisms. A distinct feature of the protocol is that the coding rate can be adapted to a wide range of channel conditions. Hence, our protocol utilizes the scarce wireless channel resources more efficiently. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We study the autocorrelation structure of aggregates from a continuous-time process. The underlying continuous-time process or some of its higher derivative is assumed to be a stationary continuous-time auto-regressive fractionally integrated moving-average (CARFIMA) process with Hurst parameter H. We derive closed-form expressions for the limiting autocorrelation function and the normalized spectral density of the aggregates, as the extent of aggregation increases to infinity. The limiting model of the aggregates, after appropriate number of differencing, is shown to be some functional of the standard fractional Brownian motion with the same Hurst parameter of the continuous-time process from which the aggregates are measured. These results are then used to assess the loss of forecasting efficiency due to aggregation. [ABSTRACT FROM AUTHOR]

has recently introduced the Continuous-time Auto-Regressive Fractionally Integrated Moving-Average (CARFIMA) models useful for studying long-memory data. We consider the estimation of the CARFIMA models with discrete-time data by maximizing the Whittle likelihood. We show that the quasi-maximum likelihood estimator is asymptotically normal and efficient. Finite-sample properties of the quasi-maximum likelihood estimator and those of the exact maximum likelihood estimator are compared by simulations. Simulations suggest that for finite samples, the quasi-maximum likelihood estimator of the Hurst parameter is less biased but more variable than the exact maximum likelihood estimator. We illustrate the method with a real application. [ABSTRACT FROM AUTHOR]

We study the autocorrelation structure and the spectral density function of aggregates from a discrete-time process. The underlying discrete-time process is assumed to be a stationary AutoRegressive Fractionally Integrated Moving-Average (ARFIMA) process, after suitable number of differencing if necessary. We derive closed-form expressions for the limiting autocorrelation function and the normalized spectral density of the aggregates, as the extent of aggregation increases to infinity. These results are then used to assess the loss of forecasting efficiency due to aggregation. [ABSTRACT FROM AUTHOR]

The presence of hard alpha (HA) anomalies in titanium alloys represents a significant potential degradation to gas turbine component performance. Although HA defects in titanium alloys are rare, when they are present, they can crack and ultimately result in failure. In static fracture and fatigue test specimens, embedded HA defects had significantly higher fracture strengths than anticipated. The objective of this work was to determine if residual stresses caused by thermal expansion mismatch during material fabrication were the cause of the observed behaviour. The residual stress fields in and around surface and embedded HA particles in Ti–6Al–4V (Ti–6–4) were determined using an elasticity solution and measured coefficient of thermal expansion (CTE) data. The calculated stress distributions serve as the foundation for comparisons of the local stress and the fracture strength, the stress intensity factor K and the crack growth threshold Δ Kth, with the experimentally determined fatigue lives. The analytical results indicated that CTE-induced residual stress around HA particles can contribute to the fatigue strength of Ti–6–4 by delaying microcracking of HA anomalies and reducing the driving force (effective Δ K) of the fatigue crack. Based on the analysis results, the differences between the surface and subsurface results as well as the difference between predicted and measured fatigue lives could be largely attributed to the residual stress effects caused by the mismatch of the particle and matrix properties. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new architecture for multicast ATM switches with fault tolerant capability based on the Clos–Knockout switch. In the new architecture, each stage has one more redundant switch module. If one switch module is faulty, the redundant module would replace the faulty one. On the other hand, under the fault-free condition, the redundant modules in the second and third stages will provide additional alternative internal paths, and hence improve the performance. The performance analysis shows that the cell loss probability is lower than the original architecture when all modules are fault free, and the reliability of the original architecture is improved. Copyright © 2002 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Cultural differences in the relation between self-discrepancy and subjective well-being were examined. Participants from India ( N = 54) and the United States ( N = 55) listed 10 goals they set for themselves and their parents set for them. They rated the importance of own and parental goals from their own and their parents' perspective. They also completed measures of collectivism and well-being. Americans, who were less collectivistic than Indians, rated their own goals to be more important than their parents' goals for them, whereas Indians regarded their own and their parents' goals as equally important. Americans' well-being was predicted by discrepancies between own and parental ratings on personal goals. However, discrepancies between own and parental ratings on parental goals were predictive of Indians' well-being. Theoretical implications of these findings are discussed. Cette etude examine les differences culturelles entre l'incompatiblite du soi et le bien-etre subjectif. Des participants de l'Inde ( N = 54) et des Etats-Unis ( N = 55) enumerent 10 objectifs qu'ils se sont fixes eux-memes et que leurs parents leur ont fixes. Ils evaluent l'importance de leurs propres objectifs et ceux fixes par leurs parents en fonction de leur propre point de vue et de celui de leurs parents. Ils remplissent aussi des questionnaires sur le collectivisme et sur le bien-etre. Les participants des Etats-Unis, qui se sont averes moins collectivistes que les participants indiens, evaluent leurs propres objectifs comme plus importants que ceux fixes pour eux par leurs parents tandis que les participants indiens considerent leurs propres objectifs et ceux fixes par leurs parents comme egalement importants. Le bien-etre des participants des Etats-Unis est predit par les incompatibilites entre les evaluations de leurs propres objectifs et les evaluations des objectifs fixes par les parents. Cependant, chez les participants indiens, le bien-etre est predit par les incompatibilites entre leurs propres evaluations et les evaluations parentales des objectifs fixes par les parents. [ABSTRACT FROM AUTHOR]

We study the spatial and seasonal variability of phytoplankton biomass (as phytoplankton color) in relation to the environmental conditions in the North Sea using data from the Continuous Plankton Recorder survey. By using only environmental fields and location as predictor variables we developed a nonparametric model (generalized additive model) to empirically explore how key environmental factors modulate the spatio-temporal patterns of the seasonal cycle of algal biomass as well as how these relate to the ~1988 North Sea regime shift. Solar radiation, as manifest through changes of sea surface temperature (SST), was a key factor not only in the seasonal cycle but also as a driver of the shift. The pronounced increase in SST and in wind speed after the 1980s resulted in an extension of the season favorable for phytoplankton growth. Nutrients appeared to be unimportant as explanatory variables for the observed spatio-temporal pattern, implying that they were not generally limiting factors. Under the new climatic regime the carrying capacity of the whole system has been increased and the southern North Sea, where the environmental changes have been more pronounced, reached a new maximum. [ABSTRACT FROM AUTHOR]