2,060 research outputs found
Placental Malaria and Mother-to-Child Transmission of Human Immunodeficiency Virus-1 in Rural Rwanda
We conducted a nested case-control study of placental malaria (PM) and mother-to-child transmission (MTCT) of human immunodeficiency virus-1 (HIV-1) within a prospective cohort of 627 mother-infant pairs followed from October 1989 until April 1994 in rural Rwanda. Sixty stored placentas were examined for PM and other placental pathology, comparing 20 HIV-infected mother-infant (perinatal transmitter) pairs, 20 HIV-uninfected pairs, and 20 HIV-infected mothers who did not transmit to their infant perinatally. Of 60 placentas examined, 45% showed evidence of PM. Placental malaria was associated with increased risk of MTCT of HIV-1 (adjusted odds ratio [aOR] = 6.3; 95% confidence interval [CI] = 1.4–29.1), especially among primigravidae (aOR = 12.0; 95% CI = 1.0–150; P < 0.05). Before antiretroviral therapy or prophylaxis, PM was associated with early infant HIV infection among rural Rwandan women living in a hyper-endemic malaria region. Primigravidae, among whom malaria tends to be most severe, may be at higher risk
Time-division SQUID multiplexers with reduced sensitivity to external magnetic fields
Time-division SQUID multiplexers are used in many applications that require
exquisite control of systematic error. One potential source of systematic error
is the pickup of external magnetic fields in the multiplexer. We present
measurements of the field sensitivity figure of merit, effective area, for both
the first stage and second stage SQUID amplifiers in three NIST SQUID
multiplexer designs. These designs include a new variety with improved
gradiometry that significantly reduces the effective area of both the first and
second stage SQUID amplifiers.Comment: 4 pages, 7 figures. Submitted for publication in the IEEE
Transactions on Applied Superconductivity, August 201
Optimierung von Saatgutbehandlungsmitteln mit Wirkung gegen Flugbrand an Gerste und Weizen (Ustilago nuda, U. tritici) unter Nutzung verbesserter Verfahren zum Nachweis der Erreger
Ziel des Projektes war die Entwicklung von Saatgutbehandlungsmitteln zur Flugbrandbekämpfung im Ökolandbau und von Techniken die geeignet sind, die Entwicklung solcher Saatgutbehandlungsmittel zu beschleunigen. In Inokulationsversuchen konnte im Feldversuch durch Ausstäuben von Sporen Saatgut mit 2-5% Flugbrandbefall erzeugt werden. Nach Einzelblüteninokulation lag der Befall oft über 60%. Anders als bei Weizen waren bei Gerste die Keimfähigkeit und das Tausendkorngewicht von solchem Saatgut deutlich reduziert. Von ca. 30 geprüften Pflanzenextrakten führten neun nach Inkorporation in PDA zu einer vollständigen Hemmung der Brandsporenkeimung. In Hemmtesten mit Mikroorganismen betrug der Anteil wirksamer Isolate bei den Trichoderma-Isolaten 43%, bei den Actinomyceten 30% und bei den übrigen Bakterien 11%. In mehrjährig durchgeführten Kleinparzellenversuchen mit flugbrandinfizierter Gerste und Weizen wurden mit einigen Behandlungsvarianten Bekämpfungserfolge erzielt. Die Effekte waren aber zu gering für die praktische Anwendung und nur bedingt reproduzierbar. Topfversuche im Gewächshaus mit hochinfizierten Saatgutchargen erbrachten ähnliche Ergebnisse. Die Wirksamkeit gegen Haferflugbrand wurde nur einmal überprüft. Wie im Falle von Gersten- und Weizenflugbrand war der Bekämpfungserfolg auch beim Haferflugbrand unbefriedigend. Eine Ausnahme bildete die Saatgutbehandlung mit Ethanol (70%). Mit ihr wurde bei Hafer eine Flugbrandwirksamkeit von ca. 80% erzielt. Nach Anfärbung mit dem Fluoreszenzfarbstoff Blankophor wurde beobachtet, dass der Pilz schon wenige Tage nach Beginn der Keimung in das Apikalmeristem und die Blattprimordien eindrang. Im 1-Knotenstadium waren die Ährenanlagen meist völlig besiedelt. Ein Protokoll für einen immunologischen (ELISA) und für einen molekularbiologischen (real-time PCR) Nachweis wurde entwickelt und zur Quantifizierung des Pilzes in Jungpflanzen angewendet. Die mit beiden Methoden erhaltenen Daten stimmten gut überein. In weiteren Versuchen konnte die Anwendbarkeit des mikroskopischen Nachweises und des ELISA für die Entwicklung von Saatgutbehandlungsmitteln und –verfahren exemplarisch gezeigt werden
TARGET: A Digitizing And Trigger ASIC For The Cherenkov Telescope Array
The future ground-based gamma-ray observatory Cherenkov Telescope Array (CTA)
will feature multiple types of imaging atmospheric Cherenkov telescopes, each
with thousands of pixels. To be affordable, camera concepts for these
telescopes have to feature low cost per channel and at the same time meet the
requirements for CTA in order to achieve the desired scientific goals. We
present the concept of the TeV Array Readout Electronics with GSa/s sampling
and Event Trigger (TARGET) Application Specific Circuit (ASIC), envisaged to be
used in the cameras of various CTA telescopes, e.g. the Gamma-ray Cherenkov
Telescope (GCT), a proposed 2-Mirror Small-Sized Telescope, and the
Schwarzschild-Couder Telescope (SCT), a proposed Medium-Sized Telescope. In the
latest version of this readout concept the sampling and trigger parts are split
into dedicated ASICs, TARGET C and T5TEA, both providing 16 parallel input
channels. TARGET C features a tunable sampling rate (usually 1 GSa/s), a 16k
sample deep buffer for each channel and on-demand digitization and transmission
of waveforms with typical spans of ~100 ns. The trigger ASIC, T5TEA, provides 4
low voltage differential signal (LVDS) trigger outputs and can generate a
pedestal voltage independently for each channel. Trigger signals are generated
by T5TEA based on the analog sum of the input in four independent groups of
four adjacent channels and compared to a threshold set by the user. Thus, T5TEA
generates four LVDS trigger outputs, as well as 16 pedestal voltages fed to
TARGET C independently for each channel. We show preliminary results of the
characterization and testing of TARGET C and T5TEA.Comment: 6 pages, 8 figures, Proceedings of the 6th International Symposium on
High-Energy Gamma-Ray Astronomy (Gamma2016
TARGET: toward a solution for the readout electronics of the Cherenkov Telescope Array
TARGET is an application specific integrated circuit (ASIC) designed to read
out signals recorded by the photosensors in cameras of very-high-energy
gamma-ray telescopes exploiting the imaging of Cherenkov radiation from
atmospheric showers. TARGET capabilities include sampling at a high rate
(typically 1 GSample/s), digitization, and triggering on the sum of four
adjacent pixels. The small size, large number of channels read out per ASIC
(16), low cost per channel, and deep buffer for trigger latency (~16 s at
1 GSample/s) make TARGET ideally suited for the readout in systems with a large
number of telescopes instrumented with compact photosensors like multi-anode or
silicon photomultipliers combined with dual-mirror optics. The possible
advantages of such systems are better sensitivity, a larger field of view, and
improved angular resolution. The two latest generations of TARGET ASICs, TARGET
5 and TARGET 7, are soon to be used for the first time in two prototypes of
small-sized and medium-sized dual-mirror telescopes proposed in the framework
of the Cherenkov Telescope Array (CTA) project. In this contribution we report
on the performance of the TARGET ASICs and discuss future developments.Comment: 8 pages, 3 figures. In Proceedings of the 34th International Cosmic
Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions
at arXiv:1508.0589
Multi-patch methods in general relativistic astrophysics - I. Hydrodynamical flows on fixed backgrounds
Many systems of interest in general relativistic astrophysics, including
neutron stars, accreting compact objects in X-ray binaries and active galactic
nuclei, core collapse, and collapsars, are assumed to be approximately
spherically symmetric or axisymmetric. In Newtonian or fixed-background
relativistic approximations it is common practice to use spherical polar
coordinates for computational grids; however, these coordinates have
singularities and are difficult to use in fully relativistic models. We
present, in this series of papers, a numerical technique which is able to use
effectively spherical grids by employing multiple patches. We provide detailed
instructions on how to implement such a scheme, and present a number of code
tests for the fixed background case, including an accretion torus around a
black hole.Comment: 26 pages, 20 figures. A high-resolution version is available at
http://www.cct.lsu.edu/~bzink/papers/multipatch_1.pd
Accurate evolutions of unequal-mass neutron-star binaries: properties of the torus and short GRB engines
We present new results from accurate and fully general-relativistic
simulations of the coalescence of unmagnetized binary neutron stars with
various mass ratios. The evolution of the stars is followed through the
inspiral phase, the merger and prompt collapse to a black hole, up until the
appearance of a thick accretion disk, which is studied as it enters and remains
in a regime of quasi-steady accretion. Although a simple ideal-fluid equation
of state with \Gamma=2 is used, this work presents a systematic study within a
fully general relativistic framework of the properties of the resulting
black-hole--torus system produced by the merger of unequal-mass binaries. More
specifically, we show that: (1) The mass of the torus increases considerably
with the mass asymmetry and equal-mass binaries do not produce significant tori
if they have a total baryonic mass M_tot >~ 3.7 M_sun; (2) Tori with masses
M_tor ~ 0.2 M_sun are measured for binaries with M_tot ~ 3.4 M_sun and mass
ratios q ~ 0.75-0.85; (3) The mass of the torus can be estimated by the simple
expression M_tor(q, M_tot) = [c_1 (1-q) + c_2](M_max-M_tot), involving the
maximum mass for the binaries and coefficients constrained from the
simulations, and suggesting that the tori can have masses as large as M_tor ~
0.35 M_sun for M_tot ~ 2.8 M_sun and q ~ 0.75-0.85; (4) Using a novel technique
to analyze the evolution of the tori we find no evidence for the onset of
non-axisymmetric instabilities and that very little, if any, of their mass is
unbound; (5) Finally, for all the binaries considered we compute the complete
gravitational waveforms and the recoils imparted to the black holes, discussing
the prospects of detection of these sources for a number of present and future
detectors.Comment: 35 pages; small changes to match the published versio
Efficient spin transport through native oxides of nickel and permalloy with platinum and gold overlayers
We present measurements of spin pumping detected by the inverse spin Hall effect voltage and ferromagnetic resonance spectroscopy in a series of metallic ferromagnet/normal metal thin film stacks. We compare heterostructures grown in situ to those where either a magnetic or nonmagnetic oxide is introduced between the two metals. The heterostructures, either nickel with a platinum overlayer (Ni/Pt) or the nickel-iron alloy permalloy (Py) with a gold overlayer (Py/Au), were also characterized in detail using grazing-incidence x-ray reflectivity, Auger electron spectroscopy, and both SQUID and alternating-gradient magnetometry. We verify the presence of oxide layers, characterize layer thickness, composition, and roughness, and probe saturation magnetization, coercivity, and anisotropy. The results show that while the presence of a nonmagnetic oxide at the interface suppresses spin transport from the ferromagnet to the nonmagnetic metal, a thin magnetic oxide (here the native oxide formed on both Py and Ni) somewhat enhances the product of the spin-mixing conductance and the spin Hall angle. We also observe clear evidence of an out-of-plane component of magnetic anisotropy in Ni/Pt samples that is enhanced in the presence of the native oxide, resulting in perpendicular exchange bias. Finally, the dc inverse spin Hall voltages generated at ferromagnetic resonance in our Py/Au samples are large, and suggest values for the spin Hall angle in gold of 0.04<αSH<0.22, in line with the highest values reported for Au. This is interpreted as resulting from Fe impurities. We present indirect evidence that the Au films described here indeed have significant impurity levels.B.L.Z. and D.B. gratefully acknowledge support from the NSF (Grants No. DMR-0847796 and No. DMR-1410247). B.L.Z. also thanks the University of Minnesota Chemical Engineering and Materials Science Department, as a portion of this work benefited from support of the George T. Piercy Distinguished Visiting Professorship. Work at the University of Minnesota was supported primarily by the NSF under Grant No. DMR-1507048, with additional support from the NSF MRSEC under Grant No. DMR-1420013. The work at WMI is supported by Deutsche Forschungsgemeinschaft via SPP 1538 Spin-Caloric Transport (Project No. GO 944/4-1). Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the US Department of Energy (DOE) Office of Science by Los Alamos National Laboratory (Contract No. DE-AC52-06NA25396) and Sandia National Laboratories (Contract No. DE-AC04-94AL85000)
AMR, stability and higher accuracy
Efforts to achieve better accuracy in numerical relativity have so far
focused either on implementing second order accurate adaptive mesh refinement
or on defining higher order accurate differences and update schemes. Here, we
argue for the combination, that is a higher order accurate adaptive scheme.
This combines the power that adaptive gridding techniques provide to resolve
fine scales (in addition to a more efficient use of resources) together with
the higher accuracy furnished by higher order schemes when the solution is
adequately resolved. To define a convenient higher order adaptive mesh
refinement scheme, we discuss a few different modifications of the standard,
second order accurate approach of Berger and Oliger. Applying each of these
methods to a simple model problem, we find these options have unstable modes.
However, a novel approach to dealing with the grid boundaries introduced by the
adaptivity appears stable and quite promising for the use of high order
operators within an adaptive framework
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