Rapid prototype fabrication processes for high-performance thrust cells

The Thrust Cell Technologies Program (Air Force Phillips Laboratory Contract No. F04611-92-C-0050) is currently being performed by Rocketdyne to demonstrate advanced materials and fabrication technologies which can be utilized to produce low-cost, high-performance thrust cells for launch and space transportation rocket engines. Under Phase 2 of the Thrust Cell Technologies Program (TCTP), rapid prototyping and investment casting techniques are being employed to fabricate a 12,000-lbf thrust class combustion chamber for delivery and hot-fire testing at Phillips Lab. The integrated process of investment casting directly from rapid prototype patterns dramatically reduces design-to-delivery cycle time, and greatly enhances design flexibility over conventionally processed cast or machined parts

Large-scale instabilities in a non-rotating turbulent convection

Formation of large-scale coherent structures in a turbulent convection via excitation of large-scale instability is studied. The redistribution of the turbulent heat flux due to non-uniform large-scale motions plays a crucial role in the formation of the coherent large-scale structures in the turbulent convection. The modification of the turbulent heat flux results in strong reduction of the critical Rayleigh number (based on the eddy viscosity and turbulent temperature diffusivity) required for the excitation of the large-scale instability. The mean-field equations which describe the large-scale instability, are solved numerically. We determine the key parameters that affect formation of the large-scale coherent structures in the turbulent convection. In particular, the degree of thermal anisotropy and the lateral background heat flux strongly modify the growth rates of the large-scale instability, the frequencies of the generated convective-shear waves and change the thresholds required for the excitation of the large-scale instability. This study elucidates the origins of the large-scale circulations and rolls in the atmospheric convective boundary layers and the meso-granular structures in the solar convection.Comment: 13 pages, 13 figures, Physics of Fluids, in pres

Study of Beauty Hadron Decays into Pairs of Charm Hadrons

First observations of the decays Λ[0 over b] → Λ[+ over c]D[− over (s)] are reported using data corresponding to an integrated luminosity of 3  fb[superscript −1] collected at 7 and 8 TeV center-of-mass energies in proton-proton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction B(B[0 over s] → D[superscript +]D[− over s]) is made and a search is performed for the decays B[0 over (s)] → Λ[+ over c]Λ[− over c]. The results obtained are B(Λ[0 over b] → Λ[+ over c]D[superscript −])/B(Λ[0 over b] → Λ[+ over c]D[− over s]) = 0.042 ± 0.003(stat) ± 0.003(syst), ⎡⎣B(Λ[0 over b] → Λ[+ over c]D[− over s]) over B([¯ over B[superscript 0] → D[superscript +]D[− over s])⎤⎦/⎡⎣B(Λ[0 over b] → Λ[+ over c]π[superscript −]) over B([¯ over B[superscript 0] → D[superscript +]π[superscript −])⎤⎦ = 0.96 ± 0.02(stat) ± 0.06(syst), B(B[0 over s] → D[superscript +]D[− over s])/B([¯ over B][superscript 0] → D[superscript +]D[− over s]) = 0.038 ± 0.004(stat) ± 0.003(syst), B([¯ over B][superscript 0] → Λ[+ over c]Λ[− over c])/B([¯ over B][superscript 0] → D[superscript +]D[− over s]) < 0.0022[95%  C.L.], B(B[0 over s] → Λ[+ over c]Λ[− over c])/B(B[0 over s] → D[superscript +]D[− over s]) < 0.30[95%  C.L.]. Measurement of the mass of the Λ[0 over b] baryon relative to the [¯ over B][superscript 0] meson gives M(Λ[0 over b]) − M([¯ over B][superscript 0]) = 339.72 ± 0.24(stat) ± 0.18(syst)  MeV/c[superscript 2]. This result provides the most precise measurement of the mass of the Λ[0 over b] baryon to date.National Science Foundation (U.S.

Optimum design and testing of a postbuckled stiffened panel

The efficient, industrially used, linear elastic preliminary design software VICONOPT is employed to design a stiffened panel with a post-buckled reserve of strength. The initial buckling mode is a local skin mode in longitudinal compression with allowance being made for the effects of an initial overall imperfection. The resulting panel has been analyzed using the non-linear FE package ABAQUS and four laboratory specimens have been tested to failure. The similarity of the experimental failure with the VICONOPT and ABAQUS predictions suggests that VICONOPT can give a satisfactory preliminary design. While neither model matches completely the boundary conditions found in a real aircraft compression panel, it is suggested that the VICONOPT model may be a better representation than either the ABAQUS model or the experimental tests

Ferromagnetism below the Stoner limit in La-doped SrB_6

Spin-polarized band calculations for LaSr_7B_{48} show a weak ferro-magnetic state. This is despite a low density-of-states (DOS) and a low Stoner factor. The reason for the magnetic state is found to be associated with a gain in potential energy in addition to the exchange energy, as a spin-splitting is imposed. An impurity like La DOS is essential for this effect. It makes a correction to the Stoner factor, and provides an explanation of the recently observed weak ferro-magnetism in doped hexaborides.Comment: 6 pages, 2 tables, 1 figur

Oak forest carbon and water simulations:Model intercomparisons and evaluations against independent data

Models represent our primary method for integration of small-scale, process-level phenomena into a comprehensive description of forest-stand or ecosystem function. They also represent a key method for testing hypotheses about the response of forest ecosystems to multiple changing environmental conditions. This paper describes the evaluation of 13 stand-level models varying in their spatial, mechanistic, and temporal complexity for their ability to capture intra- and interannual components of the water and carbon cycle for an upland, oak-dominated forest of eastern Tennessee. Comparisons between model simulations and observations were conducted for hourly, daily, and annual time steps. Data for the comparisons were obtained from a wide range of methods including: eddy covariance, sapflow, chamber-based soil respiration, biometric estimates of stand-level net primary production and growth, and soil water content by time or frequency domain reflectometry. Response surfaces of carbon and water flux as a function of environmental drivers, and a variety of goodness-of-fit statistics (bias, absolute bias, and model efficiency) were used to judge model performance. A single model did not consistently perform the best at all time steps or for all variables considered. Intermodel comparisons showed good agreement for water cycle fluxes, but considerable disagreement among models for predicted carbon fluxes. The mean of all model outputs, however, was nearly always the best fit to the observations. Not surprisingly, models missing key forest components or processes, such as roots or modeled soil water content, were unable to provide accurate predictions of ecosystem responses to short-term drought phenomenon. Nevertheless, an inability to correctly capture short-term physiological processes under drought was not necessarily an indicator of poor annual water and carbon budget simulations. This is possible because droughts in the subject ecosystem were of short duration and therefore had a small cumulative impact. Models using hourly time steps and detailed mechanistic processes, and having a realistic spatial representation of the forest ecosystem provided the best predictions of observed data. Predictive ability of all models deteriorated under drought conditions, suggesting that further work is needed to evaluate and improve ecosystem model performance under unusual conditions, such as drought, that are a common focus of environmental change discussions

Are Drug Companies Living Up to Their Human Rights Responsibilities? Moving Toward Assessment

As one viewpoint of three in the PLoS Medicine Debate on whether drug companies are living up to their human rights responsibilities, Sofia Gruskin and Zyde Raad argue that companies' actions to promote access to medicines, including their interactions with state and non-state actors, must be better monitored

Association Between Chronic Hepatitis C Virus Infection and Myocardial Infarction Among People Living With HIV in the United States.

Hepatitis C virus (HCV) infection is common among people living with human immunodeficiency virus (PLWH). Extrahepatic manifestations of HCV, including myocardial infarction (MI), are a topic of active research. MI is classified into types, predominantly atheroembolic type 1 MI (T1MI) and supply-demand mismatch type 2 MI (T2MI). We examined the association between HCV and MI among patients in the Centers for AIDS Research (CFAR) Network of Integrated Clinical Systems, a US multicenter clinical cohort of PLWH. MIs were centrally adjudicated and categorized by type using the Third Universal Definition of Myocardial Infarction. We estimated the association between chronic HCV (RNA+) and time to MI while adjusting for demographic characteristics, cardiovascular risk factors, clinical characteristics, and history of injecting drug use. Among 23,407 PLWH aged ≥18 years, there were 336 T1MIs and 330 T2MIs during a median of 4.7 years of follow-up between 1998 and 2016. HCV was associated with a 46% greater risk of T2MI (adjusted hazard ratio (aHR)&nbsp;=&nbsp;1.46, 95% confidence interval (CI): 1.09, 1.97) but not T1MI (aHR&nbsp;=&nbsp;0.87, 95% CI: 0.58, 1.29). In an exploratory cause-specific analysis of T2MI, HCV was associated with a 2-fold greater risk of T2MI attributed to sepsis (aHR&nbsp;=&nbsp;2.01, 95% CI: 1.25, 3.24). Extrahepatic manifestations of HCV in this high-risk population are an important area for continued research

Hysteresis phenomenon in turbulent convection

Coherent large-scale circulations of turbulent thermal convection in air have been studied experimentally in a rectangular box heated from below and cooled from above using Particle Image Velocimetry. The hysteresis phenomenon in turbulent convection was found by varying the temperature difference between the bottom and the top walls of the chamber (the Rayleigh number was changed within the range of $10^7 - 10^8$). The hysteresis loop comprises the one-cell and two-cells flow patterns while the aspect ratio is kept constant ($A=2 - 2.23$). We found that the change of the sign of the degree of the anisotropy of turbulence was accompanied by the change of the flow pattern. The developed theory of coherent structures in turbulent convection (Elperin et al. 2002; 2005) is in agreement with the experimental observations. The observed coherent structures are superimposed on a small-scale turbulent convection. The redistribution of the turbulent heat flux plays a crucial role in the formation of coherent large-scale circulations in turbulent convection.Comment: 10 pages, 9 figures, REVTEX4, Experiments in Fluids, 2006, in pres