A trajectory planning scheme for spacecraft in the space station environment

Simulated annealing is used to solve a minimum fuel trajectory problem in the space station environment. The environment is special because the space station will define a multivehicle environment in space. The optimization surface is a complex nonlinear function of the initial conditions of the chase and target crafts. Small permutations in the input conditions can result in abrupt changes to the optimization surface. Since no prior knowledge about the number or location of local minima on the surface is available, the optimization must be capable of functioning on a multimodal surface. It was reported in the literature that the simulated annealing algorithm is more effective on such surfaces than descent techniques using random starting points. The simulated annealing optimization was found to be capable of identifying a minimum fuel, two-burn trajectory subject to four constraints which are integrated into the optimization using a barrier method. The computations required to solve the optimization are fast enough that missions could be planned on board the space station. Potential applications for on board planning of missions are numerous. Future research topics may include optimal planning of multi-waypoint maneuvers using a knowledge base to guide the optimization, and a study aimed at developing robust annealing schedules for potential on board missions

Multimodal segmentation of lifelog data

A personal lifelog of visual and audio information can be very helpful as a human memory augmentation tool. The SenseCam, a passive wearable camera, used in conjunction with an iRiver MP3 audio recorder, will capture over 20,000 images and 100 hours of audio per week. If used constantly, very soon this would build up to a substantial collection of personal data. To gain real value from this collection it is important to automatically segment the data into meaningful units or activities. This paper investigates the optimal combination of data sources to segment personal data into such activities. 5 data sources were logged and processed to segment a collection of personal data, namely: image processing on captured SenseCam images; audio processing on captured iRiver audio data; and processing of the temperature, white light level, and accelerometer sensors onboard the SenseCam device. The results indicate that a combination of the image, light and accelerometer sensor data segments our collection of personal data better than a combination of all 5 data sources. The accelerometer sensor is good for detecting when the user moves to a new location, while the image and light sensors are good for detecting changes in wearer activity within the same location, as well as detecting when the wearer socially interacts with others

Production and Decay of Sneutrino and Squarks at Lepton-Hadron Colliders

We investigate the potentials of future high energy lepton-proton colliders to detect supersymmetric particles in the charged current type $lp\to\tilde\nu_l\tilde qX$, $l=e,\mu$, reactions. We also study their decays by using the mass spectrum given in the Technical Design Report of ATLAS Collaboration (SUGRA Point 6 corresponding to large $tan\beta$).Comment: 6 pages, 1 eps figure, REVTEX

Effortful Control, Social Information Processing, and the Prevention of Aggression in Elementary Schools

Early aggression is a problem in its own right and a risk factor for further developmental problems. Although both effortful control and social information processing (SIP) skills are negatively associated with aggression and are targeted by aggression prevention programs, little is known about the relation between them or about their joint relation with aggression. Further, effortful control is often measured poorly in aggression prevention studies. This dissertation reports findings from three studies of effortful control, SIP, and aggression. Data were collected from 691 boys and girls at 10 North Carolina schools during the third and fourth grades (2004-2006). In Study 1, exploratory and confirmatory factor analyses were used with third grade fall data to develop an effortful control scale. In Study 2, generalized estimating equations were used to assess whether, within each grade, SIP variables (measured in winter) mediated the relation between effortful control (fall) and aggression (spring). Similarly, Study 3 assessed whether fourth-grade effortful control and SIP variables (fall and winter, respectively) mediated the effect of the Competence Support Program, a classroom management and social skills training intervention, on aggression. Study 1 resulted in a second-order model (X2/df=6.41, RMSEA=.089 [90% CI: .077 to .100], CFI=IFI=.957), with effortful control explaining the correlations among three factors: inhibitory control (alpha=.843), attention control problems (alpha=.876), and impulsivity (alpha=.885). In Study 2, unadjusted results showed significant indirect effects of effortful control on aggression, mediated by hostile attribution (fourth grade only), goal formulation, and response decision, but not encoding. Adjusted results showed no mediation effects. Study 3 found no effect of the Competence Support Program on mediators or on aggression. Based on a strong theoretical framework and using appropriate statistical methods, Study 1 developed a reliable and valid teacher-reported measure of effortful control; Studies 2 and 3 provided modest support for the theory underlying many aggression prevention programs. Together, the studies resulted in recommendations for improved measurement of effortful control, SIP, and aggression; better use of longitudinal mediation models to assess the relations among them; and improved research on aggression prevention. These studies belong to a body of research that is incrementally improving the prevention of childhood aggression.Doctor of Philosoph

Controlling Time-Dependent Confounding by Health Status and Frailty: Restriction Versus Statistical Adjustment

Nonexperimental studies of preventive interventions are often biased because of the healthy-user effect and, in frail populations, because of confounding by functional status. Bias is evident when estimating influenza vaccine effectiveness, even after adjustment for claims-based indicators of illness. We explored bias reduction methods while estimating vaccine effectiveness in a cohort of adult hemodialysis patients. Using the United States Renal Data System and linked data from a commercial dialysis provider, we estimated vaccine effectiveness using a Cox proportional hazards marginal structural model of all-cause mortality before and during 3 influenza seasons in 2005/2006 through 2007/2008. To improve confounding control, we added frailty indicators to the model, measured time-varying confounders at different time intervals, and restricted the sample in multiple ways. Crude and baseline-adjusted marginal structural models remained strongly biased. Restricting to a healthier population removed some unmeasured confounding; however, this reduced the sample size, resulting in wide confidence intervals. We estimated an influenza vaccine effectiveness of 9% (hazard ratio = 0.91, 95% confidence interval: 0.72, 1.15) when bias was minimized through cohort restriction. In this study, the healthy-user bias could not be controlled through statistical adjustment; however, sample restriction reduced much of the bias

Shear-free, Irrotational, Geodesic, Anisotropic Fluid Cosmologies

General relativistic anisotropic fluid models whose fluid flow lines form a shear-free, irrotational, geodesic timelike congruence are examined. These models are of Petrov type D, and are assumed to have zero heat flux and an anisotropic stress tensor that possesses two distinct non-zero eigenvalues. Some general results concerning the form of the metric and the stress-tensor for these models are established. Furthermore, if the energy density and the isotropic pressure, as measured by a comoving observer, satisfy an equation of state of the form $p = p(\mu)$, with $\frac{dp}{d\mu} \neq -\frac{1}{3}$, then these spacetimes admit a foliation by spacelike hypersurfaces of constant Ricci scalar. In addition, models for which both the energy density and the anisotropic pressures only depend on time are investigated; both spatially homogeneous and spatially inhomogeneous models are found. A classification of these models is undertaken. Also, a particular class of anisotropic fluid models which are simple generalizations of the homogeneous isotropic cosmological models is studied.Comment: 13 pages LaTe

Evolution since z = 0.5 of the Morphology-Density relation for Clusters of Galaxies

Using traditional morphological classifications of galaxies in 10 intermediate-redshift (z~0.5) clusters observed with WFPC-2 on the Hubble Space Telescope, we derive relations between morphology and local galaxy density similar to that found by Dressler for low-redshift clusters. Taken collectively, the `morphology-density' relationship, M-D, for these more distant, presumably younger clusters is qualitatively similar to that found for the local sample, but a detailed comparison shows two substantial differences: (1) For the clusters in our sample, the M-D relation is strong in centrally concentrated ``regular'' clusters, those with a strong correlation of radius and surface density, but nearly absent for clusters that are less concentrated and irregular, in contrast to the situation for low redshift clusters where a strong relation has been found for both. (2) In every cluster the fraction of elliptical galaxies is as large or larger than in low-redshift clusters, but the S0 fraction is 2-3 times smaller, with a proportional increase of the spiral fraction. Straightforward, though probably not unique, interpretations of these observations are (1) morphological segregation proceeds hierarchically, affecting richer, denser groups of galaxies earlier, and (2) the formation of elliptical galaxies predates the formation of rich clusters, and occurs instead in the loose-group phase or even earlier, but S0's are generated in large numbers only after cluster virialization.Comment: 35 pages, 19 figures, uses psfig. Accepted for publication in Ap

Comparative short-term safety of bolus versus maintenance iron dosing in hemodialysis patients: a replication study

Abstract Background Recent research has reported that patients receiving bolus (frequent large doses to achieve iron repletion) versus maintenance dosing of iron have an increased short-term risk of infection, but a similar risk of cardiovascular events. We sought to determine whether these findings could be replicated using the same methods and a different data source. Methods Clinical data from 6,605 patients of a small U.S. dialysis provider merged with Medicare claims data were examined. Iron dosing patterns (bolus, maintenance, no iron) were identified during 1-month exposure periods and cardiovascular and infection-related outcomes were assessed during 3-month follow-up periods. The effects of bolus versus maintenance dosing were assessed using Cox proportional hazards regression analyses to estimate hazard ratios and semiparametric additive risk models to estimate hazard rate differences, controlling for demographic and clinical characteristics, laboratory values and medications, and comorbidities. Results 48,050 exposure/follow-up periods were examined. 13.9 percent of the exposure periods were bolus dosing, 49.3 percent were maintenance dosing, and the remainder were no iron use. All of the adjusted hazard ratios were >1.00 for the infection-related outcomes, suggesting that bolus dosing increases the risk of these events. The effects were greatest for hospitalized for infection of any major organ system (hazard ratio 1.13 (1.03, 1.24)) and use of intravenous antibiotics (hazard ratio 1.08 (1.02, 1.15). When examining the subgroup of individuals with catheters, the hazard ratios for the infection-related outcomes were generally greater than in the overall sample. There was little association between type of dosing practice and cardiovascular outcomes. Conclusions Results of this study provide further evidence of the association between bolus dosing and increased infection risk, particularly in the subgroup of patients with a catheter, and of the lack of an association between dosing practices and cardiovascular outcomes

Targeting Trauma-related Interventions and Improving Outcomes for Women with Co-occurring Disorders

National attention to the effects of interpersonal trauma has led mental health systems to adopt policies on trauma-related services; however, there is a lack of clarity regarding targeting of these services. Data from the Women, Co-occurring Disorders and Violence Study (WCDVS) were reanalyzed by grouping women on their baseline PTSD and substance abuse presentation and assessing the differential response to an integrated mental health/substance abuse intervention. Treatment effects were largest for subgroups characterized by high levels of PTSD, whereas the effects for those in the low symptom group were near zero. These findings underscore the need for clinicians to conduct careful assessments of trauma-related symptoms and to target the most intensive trauma-related interventions to individuals with PTSD symptoms