Solid rocket technology advancements for space tug and IUS applications

In order for the shuttle tug or interim upper stage (IUS) to capture all the missions in the current mission model for the tug and the IUS, an auxiliary or kick stage, using a solid propellant rocket motor, is required. Two solid propellant rocket motor technology concepts are described. One concept, called the 'advanced propulsion module' motor, is an 1800-kg, high-mass-fraction motor, which is single-burn and contains Class 2 propellent. The other concept, called the high energy upper stage restartable solid, is a two-burn (stop-restartable on command) motor which at present contains 1400 kg of Class 7 propellant. The details and status of the motor design and component and motor test results to date are presented, along with the schedule for future work

Alice Where Art Thou?

https://digitalcommons.library.umaine.edu/mmb-vp/4678/thumbnail.jp

Rotating Boson Stars and Q-Balls

We consider axially symmetric, rotating boson stars. Their flat space limits represent spinning Q-balls. We discuss their properties and determine their domain of existence. Q-balls and boson stars are stationary solutions and exist only in a limited frequency range. The coupling to gravity gives rise to a spiral-like frequency dependence of the boson stars. We address the flat space limit and the limit of strong gravitational coupling. For comparison we also determine the properties of spherically symmetric Q-balls and boson stars.Comment: 22 pages, 18 figure

Fast iterative solution of reaction-diffusion control problems arising from chemical processes

PDE-constrained optimization problems, and the development of preconditioned iterative methods for the efficient solution of the arising matrix system, is a field of numerical analysis that has recently been attracting much attention. In this paper, we analyze and develop preconditioners for matrix systems that arise from the optimal control of reaction-diffusion equations, which themselves result from chemical processes. Important aspects in our solvers are saddle point theory, mass matrix representation and effective Schur complement approximation, as well as the outer (Newton) iteration to take account of the nonlinearity of the underlying PDEs

Regularization-robust preconditioners for time-dependent PDE constrained optimization problems

In this article, we motivate, derive and test �effective preconditioners to be used with the Minres algorithm for solving a number of saddle point systems, which arise in PDE constrained optimization problems. We consider the distributed control problem involving the heat equation with two diff�erent functionals, and the Neumann boundary control problem involving Poisson's equation and the heat equation. Crucial to the eff�ectiveness of our preconditioners in each case is an eff�ective approximation of the Schur complement of the matrix system. In each case, we state the problem being solved, propose the preconditioning approach, prove relevant eigenvalue bounds, and provide numerical results which demonstrate that our solvers are eff�ective for a wide range of regularization parameter values, as well as mesh sizes and time-steps

Methodological issues in assessing changes in costs pre- and post-medication switch: a schizophrenia study example

<p>Abstract</p> <p>Background</p> <p>Schizophrenia is a severe, chronic, and costly illness that adversely impacts patients' lives and health care payer budgets. Cost comparisons of treatment regimens are, therefore, important to health care payers and researchers. Pre-Post analyses ("mirror-image"), where outcomes prior to a medication switch are compared to outcomes post-switch, are commonly used in such research. However, medication changes often occur during a costly crisis event. Patients may relapse, be hospitalized, have a medication change, and then spend a period of time with intense use of costly resources (post-medication switch). While many advantages and disadvantages of Pre-Post methodology have been discussed, issues regarding the attributability of costs incurred around the time of medication switching have not been fully investigated.</p> <p>Methods</p> <p>Medical resource use data, including medications and acute-care services (hospitalizations, partial hospitalizations, emergency department) were collected for patients with schizophrenia who switched antipsychotics (n = 105) during a 1-year randomized, naturalistic, antipsychotic cost-effectiveness schizophrenia trial. Within-patient changes in total costs per day were computed during the pre- and post-medication change periods. In addition to the standard Pre-Post analysis comparing costs pre- and post-medication change, we investigated the sensitivity of results to varying assumptions regarding the attributability of acute care service costs occurring just after a medication switch that were likely due to initial medication failure.</p> <p>Results</p> <p>Fifty-six percent of all costs incurred during the first week on the newly initiated antipsychotic were likely due to treatment failure with the previous antipsychotic. Standard analyses suggested an average increase in cost-per-day for each patient of $2.40 after switching medications. However, sensitivity analyses removing costs incurred post-switch that were potentially due to the failure of the initial medication suggested decreases in costs in the range of$4.77 to $9.69 per day post-switch.</p> <p>Conclusion</p> <p>Pre-Post cost analyses are sensitive to the approach used to handle acute-service costs occurring just after a medication change. Given the importance of quality economic research on the cost of switching treatments, thorough sensitivity analyses should be performed to identify the impact of crisis events around the time of medication change.</p

Duplex–assisted internal carotid artery balloon angioplasty and stent placement: A novel approach to minimize or eliminate the use of contrast material

BackgroundCarotid artery balloon angioplasty and stenting (CBAS) is emerging as an acceptable alternative to carotid endarterectomy in selected high-risk patients. Conversely, patients with pre-existing renal impairment, diabetes, or both may be harmed by the nephrotoxic contrast agents required during CBAS. We attempted to limit or eliminate the use of contrast material during CBAS.MethodsEighteen patients with severe carotid stenoses (>70%) underwent CBAS at our institution over the last 12 months with duplex scan-assisted CBAS. Of these, 12 were primary procedures, and 6 were performed for carotid re-stenosis. Fourteen patients (78%) were neurologically asymptomatic. The average age of these patients was 75 ± 11 years (range, 44–92 years). Hypertension, chronic renal insufficiency (serum creatinine level ≥1.5 mg/dL), coronary artery disease, diabetes, and smoking were present in 89%, 67%, 59%, 33%, and 28% of patients, respectively. Preoperative duplex carotid mapping was performed in all cases. All procedures were performed with patients under local anesthesia and light sedation.ResultsAn ATL HDI 5000 scanner with the SonoCT feature was used. The common femoral artery was cannulated with a single-entry needle under direct ultrasound visualization. Fluoroscopy was used to assist passage of the guidewire into the aorta and the common carotid artery. In only four cases (22%) was an aortic arch angiogram obtained. Selective catheterization of the internal and external carotid arteries was performed under ultrasound guidance. The distal cerebral protection device (17 cases) was placed under fluoroscopic guidance. Balloon width and length were chosen according to ultrasound measurements. Balloon and stent deployment were successfully achieved with ultrasound guidance alone in all cases. Appropriate stent apposition and resolution of the stenosis was confirmed by duplex scanning in all cases. Five patients (28%) were noted to have low (<100 mL/min) internal carotid artery volume flow after stent deployment (range, 20–88 mL/min; mean ± SD, 50 ± 25 mL/min). The internal carotid artery volume flow increased immediately after Filterwire retrieval in all cases and ranged from 136 to 400 mL/min (mean, 245 ± 107 mL/min). This increase was statistically significant (P < .02). No ipsilateral strokes or deaths occurred during follow-up from 1 to 12 months (mean follow-up, 5 months).ConclusionsDuplex scan-assisted CBAS is feasible and may reduce the need for intra-arterial contrast injection in selected patients deemed at high risk for renal failure from nephrotoxic contrast material. Additional advantages include direct visualization of the puncture site, precise position of the balloon and stent, and B-mode and hemodynamic confirmation of the adequacy of the technique

Fourier-Space Crystallography as Group Cohomology

We reformulate Fourier-space crystallography in the language of cohomology of groups. Once the problem is understood as a classification of linear functions on the lattice, restricted by a particular group relation, and identified by gauge transformation, the cohomological description becomes natural. We review Fourier-space crystallography and group cohomology, quote the fact that cohomology is dual to homology, and exhibit several results, previously established for special cases or by intricate calculation, that fall immediately out of the formalism. In particular, we prove that {\it two phase functions are gauge equivalent if and only if they agree on all their gauge-invariant integral linear combinations} and show how to find all these linear combinations systematically.Comment: plain tex, 14 pages (replaced 5/8/01 to include archive preprint number for reference 22