International Space Station-Based Electromagnetic Launcher for Space Science Payloads

A method was developed of lowering the cost of planetary exploration missions by using an electromagnetic propulsion/launcher, rather than a chemical-fueled rocket for propulsion. An electromagnetic launcher (EML) based at the International Space Station (ISS) would be used to launch small science payloads to the Moon and near Earth asteroids (NEAs) for the science and exploration missions. An ISS-based electromagnetic launcher could also inject science payloads into orbits around the Earth and perhaps to Mars. The EML would replace rocket technology for certain missions. The EML is a high-energy system that uses electricity rather than propellant to accelerate payloads to high velocities. The most common type of EML is the rail gun. Other types are possible, e.g., a coil gun, also known as a Gauss gun or mass driver. The EML could also "drop" science payloads into the Earth's uppe

Provider-initiated testing and counselling programmes in sub-Saharan Africa: a systematic review of their operational implementation.

OBJECTIVE: The routine offer of an HIV test during patient-provider encounters is gaining momentum within HIV treatment and prevention programmes. This review examined the operational implementation of provider-initiated testing and counselling (PITC) programmes in sub-Saharan Africa. DESIGN AND METHODS: PUBMED, EMBASE, Global Health, COCHRANE Library and JSTOR databases were searched systematically for articles published in English between January 2000 and November 2010. Grey literature was explored through the websites of international and nongovernmental organizations. Eligibility of studies was based on predetermined criteria applied during independent screening by two researchers. RESULTS: We retained 44 studies out of 5088 references screened. PITC polices have been effective at identifying large numbers of previously undiagnosed individuals. However, the translation of policy guidance into practice has had mixed results, and in several studies of routine programmes the proportion of patients offered an HIV test was disappointingly low. There were wide variations in the rates of acceptance of the test and poor linkage of those testing positive to follow-up assessments and antiretroviral treatment. The challenges encountered encompass a range of areas from logistics, to data systems, human resources and management, reflecting some of the weaknesses of health systems in the region. CONCLUSIONS: The widespread adoption of PITC provides an unprecedented opportunity for identifying HIV-positive individuals who are already in contact with health services and should be accompanied by measures aimed at strengthening health systems and fostering the normalization of HIV at community level. The resources and effort needed to do this successfully should not be underestimated

Petrography and Geochemistry of Metals in Almahata Sitta Ureilites

Ureilites are ultramafic achondrites, predominantly composed of olivine and pyroxenes with accessory carbon, metal and sulfide. The majority of ureilites are believed to represent the mantle of the ureilite parent body (UPB) [1]. Although ureilites have lost much of their original metal [2], the metal that remains retains a record of the formative processes. Almahata Sitta is predominantly composed of unbrecciated ureilites with a wide range of silicate compositions [3,4]. As a fall it presents a rare opportunity to examine fresh ureilite metal in-situ, and analyzing their highly siderophile element (HSE) ratios gives clues to their formation. Bulk siderophile element analyses of Almahata Sitta fall within the range observed in other ureilites [5]. We have examined the metals in seven ureilitic samples of Almahata Sitta (AS) and one associated chondrite fragment (AS#25)

Turboelectric distributed propulsion protection system design trades

The NASA N3-X blended-wing body with turboelectric distributed propulsion concept is being studied to achieve N+3 goals such as reduced noise, emissions, and improved energy efficiency. The electrical distribution system is cryogenic in order to maximize its efficiency and increase the power density of all associated components, while the motors, generators, and transmission lines are superconducting. The protection of a superconducting DC network poses unique electrical and thermal challenges due to the low impedance of the superconductor and operation in the superconducting or quenched states. For a given TeDP electrical system architecture with fixed power ratings, conventional and solid-state circuit breakers combined with superconducting fault-current limiters are examined with both voltage and current source control to limit and interrupt the fault current. To estimate the protection system weight and losses, scalable models of cryogenic bidirectional current-source converters, cryogenic bidirectional IGBT solid-state circuit breakers, and resistive-type superconducting fault current limiters are developed to assess how the weight and losses of these components vary as a function of nominal voltage and current and fault current ratings. The scalable models are used to assess the protection system weight for several trade-offs. System studies include the trade-off in fault-current limiting capability of SFCL on CB mass, alongside the fault-current limiting capability of the converter and its impact on CB fault-current interruption ratings and weight

Quantum Entanglement in the Two Impurity Kondo Model

In order to quantify quantum entanglement in two impurity Kondo systems, we calculate the concurrence, negativity, and von Neumann entropy. The entanglement of the two Kondo impurities is shown to be determined by two competing many-body effects, the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, $I$. Due to the spin-rotational invariance of the ground state, the concurrence and negativity are uniquely determined by the spin-spin correlation between the impurities. It is found that there exists a critical minimum value of the antiferromagnetic correlation between the impurity spins which is necessary for entanglement of the two impurity spins. The critical value is discussed in relation with the unstable fixed point in the two impurity Kondo problem. Specifically, at the fixed point there is no entanglement between the impurity spins. Entanglement will only be created (and quantum information processing (QIP) be possible) if the RKKY interaction exchange energy, $I$, is at least several times larger than the Kondo temperature, $T_K$. Quantitative criteria for QIP are given in terms of the impurity spin-spin correlation.Comment: 7 pages, 3 figures, 1 tabl

Evolution of seismicity near the southernmost terminus of the San Andreas Fault: Implications of recent earthquake clusters for earthquake risk in southern California

Three earthquake clusters that occurred in the direct vicinity of the southern terminus of the San Andreas Fault (SAF) in 2001, 2009, and 2016 raised significant concern regarding possible triggering of a major earthquake on the southern SAF, which has not ruptured in more than 320 years. These clusters of small and moderate earthquakes with M ≤ 4.8 added to an increase in seismicity rate in the northern Brawley seismic zone that began after the 1979 M_w 6.5 Imperial Valley earthquake, in contrast to the quiet from 1932 to 1979. The clusters so far triggered neither small nor large events on the SAF. The mostly negative Coulomb stress changes they imparted on the SAF may have reduced the likelihood that the events would initiate rupture on the SAF, although large magnitude earthquake triggering is poorly understood. The relatively rapid spatial and temporal migration rates within the clusters imply aseismic creep as a possible driver rather than fluid migration

HIV Infection among Young People in Northwest Tanzania: The Role of Biological, Behavioural and Socio-Demographic Risk Factors.

BACKGROUND: Young people are at high risk of HIV and developing appropriate prevention programmes requires an understanding of the risk factors for HIV in this age group. We investigated factors associated with HIV among participants aged 15-30 years in a 2007-8 cross-sectional survey nested within a community-randomised trial of the MEMA kwa Vijana intervention in 20 rural communities in northwest Tanzania. METHODS: We analysed data for 7259(53%) males and 6476(47%) females. Using a proximate-determinant conceptual framework and conditional logistic regression, we obtained sex-specific Odds Ratios (ORs) for the association of HIV infection with socio-demographic, knowledge, behavioural and biological factors. RESULTS: HSV-2 infection was strongly associated with HIV infection (females: adjOR 4.4, 95%CI 3.2-6.1; males: adjOR 4.2, 95%CI 2.8-6.2). Several socio-demographic factors (such as age, marital status and mobility), behavioural factors (condom use, number and type of sexual partnerships) and biological factors (blood transfusion, lifetime pregnancies, genital ulcers, Neisseria gonorrhoeae) were also associated with HIV infection. Among females, lifetime sexual partners (linear trend, p<0.001), ≥2 partners in the past year (adjOR 2.0, 95%CI 1.4-2.8), ≥2 new partners in the past year (adjOR 1.9 95%CI 1.2, 3.3) and concurrent partners in the past year (adjOR 1.6 95%CI 1.1, 2.4) were all associated with HIV infection. CONCLUSIONS: Efforts must be intensified to find effective interventions to reduce HSV-2. Effective behavioural interventions focusing on reducing the number of sexual partnerships and risk behaviour within partnerships are also needed. An increase in risky sexual behaviour may occur following marriage dissolution or when a young woman travels outside of her community and interventions addressing the needs of these subgroups of vulnerable women may be important. TRIAL REGISTRATION: ClinicalTrial.gov NCT00248469

Redefining the performing arts archive

This paper investigates representations of performance and the role of the archive. Notions of record and archive are critically investigated, raising questions about applying traditional archival definitions to the performing arts. Defining the nature of performances is at the root of all difficulties regarding their representation. Performances are live events, so for many people the idea of recording them for posterity is inappropriate. The challenge of creating and curating representations of an ephemeral art form are explored and performance-specific concepts of record and archive are posited. An open model of archives, encouraging multiple representations and allowing for creative reuse and reinterpretation to keep the spirit of the performance alive, is envisaged as the future of the performing arts archive