HIV-1 prevention programs targeting HIV-1 serodiscordant couples need to identify couples that are likely to become pregnant to facilitate discussions about methods to minimize HIV-1 risk during ...pregnancy attempts (i.e. safer conception) or effective contraception when pregnancy is unintended. A clinical prediction tool could be used to identify HIV-1 serodiscordant couples with a high likelihood of pregnancy within one year.
Using standardized clinical prediction methods, we developed and validated a tool to identify heterosexual East African HIV-1 serodiscordant couples with an increased likelihood of becoming pregnant in the next year. Datasets were from three prospectively followed cohorts, including nearly 7,000 couples from Kenya and Uganda participating in HIV-1 prevention trials and delivery projects.
The final score encompassed the age of the woman, woman's number of children living, partnership duration, having had condomless sex in the past month, and non-use of an effective contraceptive. The area under the curve (AUC) for the probability of the score to correctly predict pregnancy was 0.74 (95% CI 0.72-0.76). Scores ≥ 7 predicted a pregnancy incidence of >17% per year and captured 78% of the pregnancies. Internal and external validation confirmed the predictive ability of the score.
A pregnancy likelihood score encompassing basic demographic, clinical and behavioral factors defined African HIV-1 serodiscordant couples with high one-year pregnancy incidence rates. This tool could be used to engage African HIV-1 serodiscordant couples in counseling discussions about fertility intentions in order to offer services for safer conception or contraception that align with their reproductive goals.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Implementation of the First Asteroid Landing Dunham, David W.; Farquhar, Robert W.; McAdams, James V. ...
Icarus (New York, N.Y. 1962),
10/2002, Letnik:
159, Številka:
2
Journal Article
Recenzirano
Spacecraft have successfully landed on the Moon, Venus, and Mars, and have penetrated the atmosphere of Jupiter. On 2001 February 12, the
Near-Earth Asteroid Rendezvous (
NEAR)
Shoemaker spacecraft ...landed on the surface of the asteroid (433) Eros after a year of observations in orbit about the asteroid.
NEAR Shoemaker was not designed to land on an asteroid, complicating the design of operations needed to accomplish this feat. However, the
NEAR Shoemaker team wanted to attempt a landing after the year of orbital operations that consumed most of the remaining spacecraft fuel, operations funding, and planned Deep Space Network tracking. This would be a fitting end to the mission, and it would be possible to obtain images at much greater resolution during the descent than could be obtained from orbit. The operations were more successful than the
NEAR Shoemaker team had hoped, obtaining 70 high-resolution images during the descent and two weeks of gamma-ray spectrometer data from the surface after the successful soft landing.
Recent data suggest that infection with human immunodeficiency virus type 1 (HIV-1) subtype C results in prolonged high-level viremia (>5 log 10 copies/mL) during early infection. We examined the ...relationship between HIV-1 subtype and plasma viremia among 153 African seroconverters. Mean setpoint viral loads were similar for C and non-C subtypes: 4.36 vs 4.42 log 10 copies/mL (P = .61). The proportion of subtype C—infected participants with viral loads >5 log 10 copies/mL was not greater than the proportion for those with non-C infection. Our data do not support the hypothesis that higher early viral load accounts for the rapid spread of HIV-1 subtype C in southern Africa.
The concept of using Earth-return trajectories in connection with missions to comets was originally proposed in 1972. Papers published in the 1970's and 1980's showed that by using multiple ...Earth-to-Earth transfers, it was possible to construct a trajectory that would encounter several comets. This technique was used for the first time by ESA's Giotto spacecraft. Following its encounter with Halley's comet in March 1986, Giotto used a single Earth gravity-assist maneuver to intercept comet Grigg-Skjellerup in July 1992. Japan's Sakigake spacecraft tried to use Earth gravity-assist maneuvers to reach comet Honda-Mrkos-Pajdusakova in 1996, but was not successful. Earth-return trajectories are essential elements of two Discovery-class missions to comets; Stardust, and the Comet Nucleus Tour (CONTOUR). The Stardust mission will be launched in February 1999, and will return dust samples collected from comet Wild-2 to the Earth in 2006. CONTOUR is scheduled for a launch in June 2002, and will use six Earth gravity-assist maneuvers to carry out three comet encounters: Encke in 2003; Schwassmann-Wachmann-3 in 2006; and d'Arrest in 2008. An extended-mission scenario would allow CONTOUR to accomplish two additional encounters: Tempel-2 in 2015, and Encke for a second time in 2023.
An indirect launch technique for interplanetary missions is described. With this scheme, the launch vehicle first places the spacecraft into a high-apogee “phasing orbit.” The spacecraft remains in ...this orbit until it attains a specified orientation with respect to its escape trajectory. When this occurs, a propulsion stage that is an integral part of the spacecraft is used to inject the spacecraft into the desired interplanetary trajectory. It is shown that the indirect launch technique has a number of important advantages over a conventional direct launch including a significant gain in delivered spacecraft weight, and an unconstrained launch window. For high-C
3 missions, the increase in spacecraft weight is substantial.
Recovery of near's mission to eros Dunham, David W.; Farquhar, Robert W.; McAdams, James V. ...
Acta astronautica,
07/2000, Letnik:
47, Številka:
2-9
Journal Article
Recenzirano
On December 20, 1998, the main bipropellant thruster on the Near Earth Asteroid Rendezvous (NEAR) spacecraft was commanded to start a 15-minute burn. It was the first and largest of four planned ...maneuvers that would cancel NEAR's velocity relative to (433) Eros to allow capture into orbit about the asteroid in January 1999. But the burn aborted and the spacecraft tumbled, causing loss of communication. The spacecraft corrected the problem, but used 29 kg of fuel in the process. A day later, NEAR was reacquired with just enough time to upload a sequence of commands to image Eros extensively as the spacecraft hurtled past the asteroid on December 23. The NEAR team designed a large bipropellant maneuver that successfully cancelled most of NEAR's velocity relative to Eros on January 3, 1999. But then NEAR was almost 1 million kilometers from Eros, so a long `U-turn' journey was begun to return to the asteroid on February 14, 2000. The spacecraft remains healthy and enough fuel remains to enter orbit about Eros to complete all of the mission goals. This will be the first time that an interplanetary spacecraft has failed an orbital capture burn and returned to accomplish its objectives. This is possible because NEAR had a generous fuel supply and a robust contingency plan.
The Great Oxidation Event (GOE) represents a crucial juncture in Earth history, signifying the rise in atmospheric oxygen from parts per million to percent levels at ∼2.45–2.32 billion-years-ago ...(Ga). Although planetary oxygenation undoubtedly led to the inception of the contemporary Earth system, the trigger(s) and mechanism(s) controlling this chemical reorganisation remain elusive. Quantitative estimates of the atmosphere's composition in the prelude to the GOE are central to understanding this oxygenation event. Previous analyses of 2.65–2.5 Ga sediments from the Griqualand Basin (South Africa) invoke a tantalising picture of an unusual Earth environment, alluding to an atmosphere periodically dominated by a layer of organic particles (“haze”) formed from methane photolysis. However, as yet this hypothesis has remained untested. Here we present four new coupled carbon and quadruple sulphur isotope records from distal, time equivalent (2.7–2.5 Ga), sedimentary successions from South Africa and Western Australia. These extended records reveal similar chemostratigraphic trends, supporting a dynamic terminal-Neoarchaean atmosphere, oscillating between a hazy state at elevated methane concentrations, and a haze-free anoxic background state. We suggest these atmospheric aberrations were related to heightened biogenic methane fluxes fuelled by enhanced nutrient delivery from climatically or weathering induced feedbacks. These data question the canonical view of a simple, unidirectional planetary oxygenation and signify that the overture to the GOE was governed by complex feedbacks within the Earth–biosphere system.
•We present four ∼2.7–2.5 Ga coupled carbon and quadruple sulphur isotope records.•These data depict a biospheric overhaul of atmospheric chemistry at ∼2.7 Ga.•Post-2.7 Ga atmospheres were dynamic, switching between haze-free and hazy states.•We suggest that amplified biogenic CH4 fluxes drove these atmospheric aberrations.•Biology apparently regimented atmosphere chemistry in the prelude to the GOE.
MESSENGER Mission Design and Navigation MCADAMS, James V; FARQUHAR, Robert W; TAYLOR, Anthony H ...
Space science reviews,
2007, Letnik:
131, Številka:
1-4
Journal Article
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