714 research outputs found
Defining childhood severe falciparum malaria for intervention studies.
Background Clinical trials of interventions designed to prevent severe falciparum malaria in children require a clear endpoint. The internationally accepted definition of severe malaria is sensitive, and appropriate for clinical purposes. However, this definition includes individuals with severe nonmalarial disease and coincident parasitaemia, so may lack specificity in vaccine trials. Although there is no āgold standardā individual test for severe malaria, malaria-attributable fractions (MAFs) can be estimated among groups of children using a logistic model, which we use to test the suitability of various case definitions as trial endpoints. Methods and Findings A total of 4,583 blood samples were taken from well children in cross-sectional surveys and from 1,361 children admitted to a Kenyan District hospital with severe disease. Among children under 2 y old with severe disease and over 2,500 parasites per microliter of blood, the MAFs were above 85% in moderate- and low-transmission areas, but only 61% in a high-transmission area. HIV and malnutrition were not associated with reduced MAFs, but gastroenteritis with severe dehydration (defined by reduced skin turgor), lower respiratory tract infection (clinician's final diagnosis), meningitis (on cerebrospinal fluid [CSF] examination), and bacteraemia were associated with reduced MAFs. The overall MAF was 85% (95% confidence interval [CI] 83.8%ā86.1%) without excluding these conditions, 89% (95% CI 88.4%ā90.2%) after exclusions, and 95% (95% CI 94.0%ā95.5%) when a threshold of 2,500 parasites/Ī¼l was also applied. Applying a threshold and exclusion criteria reduced sensitivity to 80% (95% CI 77%ā83%). Conclusions The specificity of a case definition for severe malaria is improved by applying a parasite density threshold and by excluding children with meningitis, lower respiratory tract infection (clinician's diagnosis), bacteraemia, and gastroenteritis with severe dehydration, but not by excluding children with HIV or malnutrition
Decoherence in a Josephson junction qubit
The zero-voltage state of a Josephson junction biased with constant current
consists of a set of metastable quantum energy levels. We probe the spacings of
these levels by using microwave spectroscopy to enhance the escape rate to the
voltage state. The widths of the resonances give a measurement of the coherence
time of the two states involved in the transitions. We observe a decoherence
time shorter than that expected from dissipation alone in resonantly isolated
20 um x 5 um Al/AlOx/Al junctions at 60 mK. The data is well fit by a model
including dephasing effects of both low-frequency current noise and the escape
rate to the continuum voltage states. We discuss implications for quantum
computation using current-biased Josephson junction qubits, including the
minimum number of levels needed in the well to obtain an acceptable error limit
per gate.Comment: 4 pages, 6 figure
Mediated tunable coupling of flux qubits
It is sketched how a monostable rf- or dc-SQUID can mediate an inductive
coupling between two adjacent flux qubits. The nontrivial dependence of the
SQUID's susceptibility on external flux makes it possible to continuously tune
the induced coupling from antiferromagnetic (AF) to ferromagnetic (FM). In
particular, for suitable parameters, the induced FM coupling can be
sufficiently large to overcome any possible direct AF inductive coupling
between the qubits.
The main features follow from a classical analysis of the multi-qubit
potential. A fully quantum treatment yields similar results, but with a
modified expression for the SQUID susceptibility.
Since the latter is exact, it can also be used to evaluate the
susceptibility--or, equivalently, energy-level curvature--of an isolated
rf-SQUID for larger shielding and at degenerate flux bias, i.e., a (bistable)
qubit. The result is compared to the standard two-level (pseudospin) treatment
of the anticrossing, and the ensuing conclusions are verified numerically.Comment: REVTeX 4, 16 pp., 4 EPS figures. N.B.: "Alec" is my first, and
"Maassen van den Brink" my family name. v2: major expansion and rewriting,
new title and co-author; to appear in New Journal of Physics special issue
(R. Fazio, ed.
Spectroscopy of Three-Particle Entanglement in a Macroscopic Superconducting Circuit
We study the quantum mechanical behavior of a macroscopic, three-body,
superconducting circuit. Microwave spectroscopy on our system, a resonator
coupling two large Josephson junctions, produced complex energy spectra well
explained by quantum theory over a large frequency range. By tuning each
junction separately into resonance with the resonator, we first observe strong
coupling between each junction and the resonator. Bringing both junctions
together into resonance with the resonator, we find spectroscopic evidence for
entanglement between all three degrees of freedom and suggest a new method for
controllable coupling of distant qubits, a key step toward quantum computation.Comment: 4 pages, 3 figure
Superconducting Circuits and Quantum Information
Superconducting circuits can behave like atoms making transitions between two
levels. Such circuits can test quantum mechanics at macroscopic scales and be
used to conduct atomic-physics experiments on a silicon chip.Comment: 7 pages, 4 figures. See also:
http://www.physicstoday.org/vol-58/iss-11/contents.htm
Probing Noise in Flux Qubits via Macroscopic Resonant Tunneling
Macroscopic resonant tunneling between the two lowest lying states of a
bistable RF-SQUID is used to characterize noise in a flux qubit. Measurements
of the incoherent decay rate as a function of flux bias revealed a Gaussian
shaped profile that is not peaked at the resonance point, but is shifted to a
bias at which the initial well is higher than the target well. The r.m.s.
amplitude of the noise, which is proportional to the decoherence rate 1/T_2^*,
was observed to be weakly dependent on temperature below 70 mK. Analysis of
these results indicates that the dominant source of low frequency (1/f) flux
noise in this device is a quantum mechanical environment in thermal
equilibrium.Comment: 4 pages 4 figure
Profile: The Kilifi Health and Demographic Surveillance System (KHDSS).
The Kilifi Health and Demographic Surveillance System (KHDSS), located on the Indian Ocean coast of Kenya, was established in 2000 as a record of births, pregnancies, migration events and deaths and is maintained by 4-monthly household visits. The study area was selected to capture the majority of patients admitted to Kilifi District Hospital. The KHDSS has 260ā000 residents and the hospital admits 4400 paediatric patients and 3400 adult patients per year. At the hospital, morbidity events are linked in real time by a computer search of the population register. Linked surveillance was extended to KHDSS vaccine clinics in 2008. KHDSS data have been used to define the incidence of hospital presentation with childhood infectious diseases (e.g. rotavirus diarrhoea, pneumococcal disease), to test the association between genetic risk factors (e.g. thalassaemia and sickle cell disease) and infectious diseases, to define the community prevalence of chronic diseases (e.g. epilepsy), to evaluate access to health care and to calculate the operational effectiveness of major public health interventions (e.g. conjugate Haemophilus influenzae type b vaccine). Rapport with residents is maintained through an active programme of community engagement. A system of collaborative engagement exists for sharing data on survival, morbidity, socio-economic status and vaccine coverage
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