562 research outputs found
A Reconfigurable Gate Architecture for Si/SiGe Quantum Dots
We demonstrate a reconfigurable quantum dot gate architecture that
incorporates two interchangeable transport channels. One channel is used to
form quantum dots and the other is used for charge sensing. The quantum dot
transport channel can support either a single or a double quantum dot. We
demonstrate few-electron occupation in a single quantum dot and extract
charging energies as large as 6.6 meV. Magnetospectroscopy is used to measure
valley splittings in the range of 35-70 microeV. By energizing two additional
gates we form a few-electron double quantum dot and demonstrate tunable tunnel
coupling at the (1,0) to (0,1) interdot charge transition.Comment: Related papers at http://pettagroup.princeton.ed
Scalable gate architecture for densely packed semiconductor spin qubits
We demonstrate a 12 quantum dot device fabricated on an undoped Si/SiGe
heterostructure as a proof-of-concept for a scalable, linear gate architecture
for semiconductor quantum dots. The device consists of 9 quantum dots in a
linear array and 3 single quantum dot charge sensors. We show reproducible
single quantum dot charging and orbital energies, with standard deviations less
than 20% relative to the mean across the 9 dot array. The single quantum dot
charge sensors have a charge sensitivity of 8.2 x 10^{-4} e/root(Hz) and allow
the investigation of real-time charge dynamics. As a demonstration of the
versatility of this device, we use single-shot readout to measure a spin
relaxation time T1 = 170 ms at a magnetic field B = 1 T. By reconfiguring the
device, we form two capacitively coupled double quantum dots and extract a
mutual charging energy of 200 microeV, which indicates that 50 GHz two-qubit
gate operation speeds are feasible
Investigation of Mobility Limiting Mechanisms in Undoped Si/SiGe Heterostructures
We perform detailed magnetotransport studies on two-dimensional electron
gases (2DEGs) formed in undoped Si/SiGe heterostructures in order to identify
the electron mobility limiting mechanisms in this increasingly important
materials system. By analyzing data from 26 wafers with different
heterostructure growth profiles we observe a strong correlation between the
background oxygen concentration in the Si quantum well and the maximum
mobility. The highest quality wafer supports a 2DEG with a mobility of 160,000
cm^2/Vs at a density 2.17 x 10^11/cm^2 and exhibits a metal-to-insulator
transition at a critical density 0.46 x 10^11/cm^2. We extract a valley
splitting of approximately 150 microeV at a magnetic field of 1.8 T. These
results provide evidence that undoped Si/SiGe heterostructures are suitable for
the fabrication of few-electron quantum dots.Comment: Related papers at http://pettagroup.princeton.ed
Strain identity of the ectomycorrhizal fungus Laccaria bicolor is more important than richness in regulating plant and fungal performance under nutrient rich conditions
This work was funded by the Natural Environment Research Council (NE/I014527/1).Peer reviewedPublisher PD
Performance of the Universal Vital Assessment (UVA) Mortality Risk Score in Hospitalized Adults with Infection in Rwanda: A Retrospective External Validation Study
BACKGROUND: We previously derived a Universal Vital Assessment (UVA) score to better risk-stratify hospitalized patients in sub-Saharan Africa, including those with infection. Here, we aimed to externally validate the performance of the UVA score using previously collected data from patients hospitalized with acute infection in Rwanda.
METHODS: We performed a secondary analysis of data collected from adults ≥18 years with acute infection admitted to Gitwe District Hospital in Rwanda from 2016 until 2017. We calculated the UVA score from the time of admission and at 72 hours after admission. We also calculated quick sepsis-related organ failure assessment (qSOFA) and modified early warning scores (MEWS). We calculated amalgamated qSOFA scores by inserting UVA cut-offs into the qSOFA score, and modified UVA scores by removing the HIV criterion. The performance of each score determined by the area under the receiver operator characteristic curve (AUC) was the primary outcome measure.
RESULTS: We included 573 hospitalized adult patients with acute infection of whom 40 (7%) died in-hospital. The admission AUCs (95% confidence interval [CI]) for the prediction of mortality by the scores were: UVA, 0.77 (0.68-0.85); modified UVA, 0.77 (0.68-0.85); qSOFA, 0.66 (0.56-0.75), amalgamated qSOFA, 0.71 (0.61-0.80); and MEWS, 0.74 (0.64, 0.83). The positive predictive values (95% CI) of the scores at commonly used cut-offs were: UVA \u3e4, 0.35 (0.15-0.59); modified UVA \u3e4, 0.35 (0.15-0.59); qSOFA \u3e1, 0.14 (0.07-0.24); amalgamated qSOFA \u3e1, 0.44 (0.20-0.70); and MEWS \u3e5, 0.14 (0.08-0.22). The 72 hour (N = 236) AUC (95% CI) for the prediction of mortality by UVA was 0.59 (0.43-0.74). The Chi-Square test for linear trend did not identify an association between mortality and delta UVA score at 72 hours (p = 0.82).
CONCLUSIONS: The admission UVA score and amalgamated qSOFA score had good predictive ability for mortality in adult patients admitted to hospital with acute infection in Rwanda. The UVA score could be used to assist with triage decisions and clinical interventions, for baseline risk stratification in clinical studies, and in a clinical definition of sepsis in Africa
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