1,004 research outputs found
Scaling of entanglement at quantum phase transition for two-dimensional array of quantum dots
With Hubbard model, the entanglement scaling behavior in a two-dimensional
itinerant system is investigated. It has been found that, on the two sides of
the critical point denoting an inherent quantum phase transition (QPT), the
entanglement follows different scalings with the size just as an order
parameter does. This fact reveals the subtle role played by the entanglement in
QPT as a fungible physical resource
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
Probing High Frequency Noise with Macroscopic Resonant Tunneling
We have developed a method for extracting the high-frequency noise spectral
density of an rf-SQUID flux qubit from macroscopic resonant tunneling (MRT)
rate measurements. The extracted noise spectral density is consistent with that
of an ohmic environment up to frequencies ~ 4 GHz. We have also derived an
expression for the MRT lineshape expected for a noise spectral density
consisting of such a broadband ohmic component and an additional strongly
peaked low-frequency component. This hybrid model provides an excellent fit to
experimental data across a range of tunneling amplitudes and temperatures
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International gestational age-specific centiles forĀ umbilicalĀ artery Doppler indices: a longitudinalĀ prospectiveĀ cohort study of the INTERGROWTH-21st Project.
BACKGROUND: Reference values for umbilical artery Doppler indices are used clinically to assess fetal well-being. However, many studies that have produced reference charts have important methodologic limitations, and these result in significant heterogeneity of reported reference ranges. OBJECTIVES: To produce international gestational age-specific centiles for umbilical artery Doppler indices based on longitudinal data and the same rigorous methodology used in the original Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project. STUDY DESIGN: In Phase II of the INTERGROWTH-21st Project (the INTERBIO-21st Study), we prospectively continued enrolling pregnant women according to the same protocol from 3 of the original populations in Pelotas (Brazil), Nairobi (Kenya), and Oxford (United Kingdom) that had participated in the Fetal Growth Longitudinal Study. Women with a singleton pregnancy were recruited at <14 weeks' gestation, confirmed by ultrasound measurement of crown-rump length, and then underwent standardized ultrasound every 5Ā±1 weeks until delivery. From 22 weeks of gestation umbilical artery indices (pulsatility index, resistance index, and systolic/diastolic ratio) were measured in a blinded fashion, using identical equipment and a rigorously standardized protocol. Newborn size at birth was assessed using the international INTERGROWTH-21st Standards, and infants had detailed assessment of growth, nutrition, morbidity, and motor development at 1 and 2 years of age. The appropriateness of pooling data from the 3 study sites was assessed using variance component analysis and standardized site differences. Umbilical artery indices were modeled as functions of the gestational age using an exponential, normal distribution with second-degree fractional polynomial smoothing; goodness of fit for the overall models was assessed. RESULTS: Of the women enrolled at the 3 sites, 1629 were eligible for this study; 431 (27%) met the entry criteria for the construction of normative centiles, similar to the proportion seen in the original fetal growth longitudinal study. They contributed a total of 1243 Doppler measures to the analysis; 74% had 3 measures or more. The healthy low-risk status of the population was confirmed by the low rates of preterm birth (4.9%) and preeclampsia (0.7%). There were no neonatal deaths andĀ satisfactory growth, health, and motor development of the infants at 1 and 2 years of age were documented. Only a very small proportion (2.8%-6.5%) of the variance of Doppler indices was due to between-site differences; in addition, standardized site difference estimates were marginally outside this threshold in only 1 of 27 comparisons, and this supported the decision to pool data from the 3 study sites. All 3 Doppler indices decreased with advancing gestational age. The 3rd, 5th 10th, 50th, 90th, 95th, and 97th centiles according to gestational age for each of the 3 indices are provided, as well as equations to allow calculation of any value as a centile and z scores. The mean pulsatility index according to gestational ageĀ = 1.02944Ā + 77.7456*(gestational age)-2 - 0.000004455*gestational age3. CONCLUSION: We present here international gestational age-specific normative centiles for umbilical artery Doppler indices produced by studying healthy, low-risk pregnant women living in environments with minimal constraints on fetal growth. The centiles complement the existing INTERGROWTH-21st Standards for assessment of fetal well-being
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
Relation between falciparum malaria and bacteraemia in Kenyan children: a population-based, case-control study and a longitudinal study.
BACKGROUND: Many investigators have suggested that malaria infection predisposes individuals to bacteraemia. We tested this hypothesis with mendelian randomisation studies of children with the malaria-protective phenotype of sickle-cell trait (HbAS). METHODS: This study was done in a defined area around Kilifi District Hospital, Kilifi, Kenya. We did a matched case-control study to identify risk factors for invasive bacterial disease, in which cases were children aged 3 months to 13 years who were admitted to hospital with bacteraemia between Sept 16, 1999, and July 31, 2002. We aimed to match two controls, by age, sex, location, and time of recruitment, for every case. We then did a longitudinal case-control study to assess the relation between HbAS and invasive bacterial disease as malaria incidence decreased. Cases were children aged 0-13 years who were admitted to hospital with bacteraemia between Jan 1, 1999, and Dec 31, 2007. Controls were born in the study area between Jan 1, 2006, and June 23, 2009. Finally, we modelled the annual incidence of bacteraemia against the community prevalence of malaria during 9 years with Poisson regression. RESULTS: In the matched case-control study, we recruited 292 cases-we recruited two controls for 236, and one for the remaining 56. Sickle-cell disease, HIV, leucocyte haemozoin pigment, and undernutrition were positively associated with bacteraemia and HbAS was strongly negatively associated with bacteraemia (odds ratio 0Ā·36; 95% CI 0Ā·20-0Ā·65). In the longitudinal case-control study, we assessed data from 1454 cases and 10,749 controls. During the study period, the incidence of admission to hospital with malaria per 1000 child-years decreased from 28Ā·5 to 3Ā·45, with a reduction in protection afforded by HbAS against bacteraemia occurring in parallel (p=0Ā·0008). The incidence of hospital admissions for bacteraemia per 1000 child-years also decreased from 2Ā·59 to 1Ā·45. The bacteraemia incidence rate ratio associated with malaria parasitaemia was 6Ā·69 (95% CI 1Ā·31-34Ā·3) and, at a community parasite prevalence of 29% in 1999, 62% (8Ā·2-91) of bacteraemia cases were attributable to malaria. INTERPRETATION: Malaria infection strongly predisposes individuals to bacteraemia and can account for more than half of all cases of bacteraemia in malaria-endemic areas. Interventions to control malaria will have a major additional benefit by reducing the burden of invasive bacterial disease. FUNDING: Wellcome Trust
Geometrical dependence of low frequency noise in superconducting flux qubits
A general method for directly measuring the low-frequency flux noise (below
10 Hz) in compound Josephson junction superconducting flux qubits has been used
to study a series of 85 devices of varying design. The variation in flux noise
across sets of qubits with identical designs was observed to be small. However,
the levels of flux noise systematically varied between qubit designs with
strong dependence upon qubit wiring length and wiring width. Furthermore,
qubits fabricated above a superconducting ground plane yielded lower noise than
qubits without such a layer. These results support the hypothesis that
localized magnetic impurities in the vicinity of the qubit wiring are a key
source of low frequency flux noise in superconducting devices.Comment: 5 pages, 5 figure
Quantum oscillations in Kondo Insulator SmB
In Kondo insulator samarium hexaboride SmB, strong correlation and band
hybridization lead to an insulating gap and a diverging resistance at low
temperature. The resistance divergence ends at about 5 Kelvin, a behavior
recently demonstrated to arise from the surface conductance. However, questions
remain whether and where a topological surface state exists. Quantum
oscillations have not been observed to map the Fermi surface. We solve the
problem by resolving the Landau Level quantization and Fermi surface topology
using torque magnetometry. The observed Fermi surface suggests a two
dimensional surface state on the (101) plane. Furthermore, the tracking of the
Landau Levels in the infinite magnetic field limit points to -1/2, which
indicates a 2D Dirac electronic state
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