Sound-suppressing structure with thermal relief

Sound-suppressing structure comprising stacked acoustic panels wherein the inner high frequency panel is mounted for thermal expansion with respect to the outer low frequency panel is discussed. Slip joints eliminate the potential for thermal stresses, and a thermal expansion gap between the panels provides for additional relative thermal growth while reducing heat convection into the low frequency panel

Study of EVA operations associated with satellite services

Extravehicular mobility unit (EMU) factors associated with satellite servicing activities are identified and the EMU improvements necessary to enhance satellite servicing operations are outlined. Areas of EMU capabilities, equipment and structural interfaces, time lines, EMU modifications for satellite servicing, environmental hazards, and crew training are vital to manned Eva/satellite services and as such are detailed. Evaluation of EMU capabilities indicates that the EMU can be used in performing near term, basic satellite servicing tasks; however, satellite servicing is greatly enhanced by incorporating key modifications into the EMU. The servicing missions involved in contamination sensitive payload repair are illustrated. EVA procedures and equipment can be standardized, reducing both crew training time and in orbit operations time. By standardizing and coordinating procedures, mission cumulative time lines fall well within the EMU capability

The gap exponent of XXZ model in a transverse field

We have calculated numerically the gap exponent of the anisotropic Heisenberg model in the presence of the transverse magnetic field. We have implemented the modified Lanczos method to obtain the excited states of our model with the same accuracy of the ground state. The coefficient of the leading term in the perturbation expansion diverges in the thermodynamic limit (N --> infinity). We have obtained the relation between this divergence and the scaling behaviour of the energy gap. We have found that the opening of gap in the presence of transverse field scales with a critical exponent which depends on the anisotropy parameter (Delta). Our numerical results are in well agreement with the field theoretical approach in the whole range of the anisotropy parameter, -1 < Delta < 1.Comment: 6 pages and 4 figure

Sperm mixing in the polyandrous leaf-cutting ant Acromyrmex echinatior

The insemination of queens by sperm from multiple males (polyandry) has evolved in a number of eusocial insect lineages despite the likely costs of the behavior. The selective advantages in terms of colony fitness must therefore also be significant and there is now good evidence that polyandry increases genetic variation among workers, thereby improving the efficiency of division of labor, resistance against disease, and diluting the impact of genetically incompatible matings. However, these advantages will only be maximized if the sperm of initially discrete ejaculates are mixed when stored in queen spermathecae and used for egg fertilization in a “fair raffle.” Remarkably, however, very few studies have addressed the level of sperm mixing in social insects. Here we analyzed sperm use over time in the highly polyandrous leaf-cutting ant Acromyrmex echinatior. We genotyped cohorts of workers produced either 2 months apart or up to over a year apart, and batches of eggs laid up to over 2 years apart, and tested whether fluctuations in patriline distributions deviated from random. We show that the representation of father males in both egg and worker cohorts does not change over time, consistent with obligatorily polyandrous queens maximizing their fitness when workers are as genetically diverse as possible

Energy efficient engine: Flight propulsion system preliminary analysis and design

The characteristics of an advanced flight propulsion system (FPS), suitable for introduction in the late 1980's to early 1990's, was more fully defined. It was determined that all goals for efficiency, environmental considerations, and economics could be met or exceeded with the possible exception of NOx emission. In evaluating the FPS, all aspects were considered including component design, performance, weight, initial cost, maintenance cost, engine system integration (including nacelle), and aircraft integration considerations. The current FPS installed specific fuel consumption was reduced 14.2% from that of the CF6-50C reference engine. When integrated into an advanced, subsonic, study transport, the FPS produced a fuel burn savings of 15 to 23% and a direct operating cost reduction of 5 to 12% depending on the mission and study aircraft characteristics relative to the reference engine

Development of singularities for the compressible Euler equations with external force in several dimensions

We consider solutions to the Euler equations in the whole space from a certain class, which can be characterized, in particular, by finiteness of mass, total energy and momentum. We prove that for a large class of right-hand sides, including the viscous term, such solutions, no matter how smooth initially, develop a singularity within a finite time. We find a sufficient condition for the singularity formation, "the best sufficient condition", in the sense that one can explicitly construct a global in time smooth solution for which this condition is not satisfied "arbitrary little". Also compactly supported perturbation of nontrivial constant state is considered. We generalize the known theorem by Sideris on initial data resulting in singularities. Finally, we investigate the influence of frictional damping and rotation on the singularity formation.Comment: 23 page

The Government Contracts Reference Book: A Comprehensive Guide to the Language of Procurement

This book - first published in 1992 and now in its fifth edition - is intended to offer concise, comprehensive information to the practitioner of the art of government contracting. Looking up a key term, the reader can find a definition, followed by a summary of where the term is used in the statutes or regulations dealing with the procurement process. The book also includes references to literature where the term is more fully discussed. The book is not designed as a standalone encyclopedia: it is a first reference, pointing the user to additional sources as needed. The book makes it clear that government contracting is complex, and the rules cannot be gleaned from a single source such as the Federal Acquisition Regulation. They can only be learned from constant reading of reference materials and textbooks—not to mention decisions of the courts, boards of contract appeals, and the Government Accountability Office. Navigating the waters of government procurement is an arduous task, and this book is intended as an aid in that journey. The authors fully understand that it is impossible to make the book fully comprehensive. While this edition is (again) expanded, we know additional terms could be added. We welcome readers to let us know of terms that should be included in the next edition

Missed Study Visits and Subsequent HIV Incidence Among Women in a Predominantly Sex Worker Cohort Attending a Dedicated Clinic Service in Kampala, Uganda

BACKGROUND: There is limited evidence on the relationship between sustained exposure of female sex workers (FSWs) to targeted HIV programmes and HIV incidence. We investigate the relationship between the number of missed study visits (MSVs) within each episode of 2 consecutively attended visits (MSVs) and subsequent HIV risk in a predominantly FSW cohort. // METHODS: Women at high risk of HIV are invited to attend an ongoing dedicated clinic offering a combination HIV prevention intervention in Kampala, Uganda. Study visits are scheduled once every 3 months. The analysis included HIV-seronegative women with ≥1 follow-up visit from enrollment (between April 2008 and May 2017) to August 2017. Cox regression models were fitted adjusted for characteristics on sociodemographic, reproductive, behavioral, and sexually transmitted infections (through clinical examination and serological testing for syphilis). // FINDINGS: Among 2206 participants, HIV incidence was 3.1/100 (170/5540) person-years [95% confidence interval (CI): 2.6 to 3.5]. Incidence increased from 2.6/100 person-years (95% CI: 2.1 to 3.2) in episodes without a MSV to 3.0/100 (95% CI: 2.2 to 4.1) for 1-2 MSVs and 4.3/100 (95% CI: 3.3 to 5.6) for ≥3 MSVs. Relative to episodes without a MSV, the hazard ratios (adjusted for confounding variables) were 1.40 (95% CI: 0.93 to 2.12) for 1-2 MSVs and 2.00 (95% CI: 1.35 to 2.95) for ≥3 MSVs (P-trend = 0.001). // CONCLUSION: Missing study visits was associated with increased subsequent HIV risk. Although several factors may underlie this association, the finding suggests effectiveness of targeted combination HIV prevention. But exposure to targeted interventions needs to be monitored, facilitated, and sustained in FSWs

Perturbation Theory and Control in Classical or Quantum Mechanics by an Inversion Formula

We consider a perturbation of an ``integrable'' Hamiltonian and give an expression for the canonical or unitary transformation which ``simplifies'' this perturbed system. The problem is to invert a functional defined on the Lie- algebra of observables. We give a bound for the perturbation in order to solve this inversion. And apply this result to a particular case of the control theory, as a first example, and to the ``quantum adiabatic transformation'', as another example.Comment: Version 8.0. 26 pages, Latex2e, final version published in J. Phys.