5,970 research outputs found
Encapsulation of phosphorus dopants in silicon for the fabrication of a quantum computer
The incorporation of phosphorus in silicon is studied by analyzing phosphorus
delta-doped layers using a combination of scanning tunneling microscopy,
secondary ion mass spectrometry and Hall effect measurements. The samples are
prepared by phosphine saturation dosing of a Si(100) surface at room
temperature, a critical annealing step to incorporate phosphorus atoms, and
subsequent epitaxial silicon overgrowth. We observe minimal dopant segregation
(5 nm), complete electrical activation at a silicon growth temperature of 250
degrees C and a high two-dimensional electron mobility of 100 cm2/Vs at a
temperature of 4.2 K. These results, along with preliminary studies aimed at
further minimizing dopant diffusion, bode well for the fabrication of
atomically precise dopant arrays in silicon such as those found in recent
solid-state quantum computer architectures.Comment: 3 pages, 4 figure
Emergence of the nematic electronic state in FeSe
We present a comprehensive study of the evolution of the nematic electronic
structure of FeSe using high resolution angle-resolved photoemission
spectroscopy (ARPES), quantum oscillations in the normal state and
elastoresistance measurements. Our high resolution ARPES allows us to track the
Fermi surface deformation from four-fold to two-fold symmetry across the
structural transition at ~87 K which is stabilized as a result of the dramatic
splitting of bands associated with dxz and dyz character. The low temperature
Fermi surface is that a compensated metal consisting of one hole and two
electron bands and is fully determined by combining the knowledge from ARPES
and quantum oscillations. A manifestation of the nematic state is the
significant increase in the nematic susceptibility as approaching the
structural transition that we detect from our elastoresistance measurements on
FeSe. The dramatic changes in electronic structure cannot be explained by the
small lattice effects and, in the absence of magnetic fluctuations above the
structural transition, points clearly towards an electronically driven
transition in FeSe stabilized by orbital-charge ordering.Comment: Latex, 8 pages, 4 figure
The Exomars Climate Sounder (EMCS) Investigation
The ExoMars Climate Sounder (EMCS) investigation is developed at the Jet Propulsion Laboratory (Principal Investigator J. T. Schofield) in collaboration with an international scientific team from France, the United Kingdom and the USA.
EMCS plans to map daily, global, pole-to-pole profiles of temperature, dust, water and CO2 ices, and water vapor from the proposed 2016 ExoMars Trace Gas Orbiter (EMTGO). These profiles are to be assimilated into Mars General Circulation Models (MGCMs) to generate global, interpolated fields of measured and derived parameters such as wind
An assessment of the reliability and reproducibility of measurement of potential doubling times (Tpot) in human colorectal cancers.
An assessment has been made of the reproducibility of measuring tumour proliferation using in vivo iododeoxyuridine (IUdR) labelling and flow cytometry. The variation that occurs between different institutions (Paterson Institute for Cancer Research, Manchester and the Gray Laboratory, Northwood), different observers and different runs on the same flow cytometer have been measured on 139 samples from 53 patients with colorectal cancer. The results demonstrate that the IUdR technique for measuring tumour proliferation is reproducible. Correlations were seen between measurements of Tpot obtained by different individuals and on separate machines. However, direct comparisons of the measured parameters showed that there were highly significant differences in the values obtained between institutes and observers (P < 0.001). Despite these variations, there were still significant detectable differences in Tpot measurements between individual tumours (P < 0.001). Analysis of the results obtained by running the same samples on two separate occasions on the same machine showed that the technique was highly reproducible and that the staining procedure was stable. Eighty per cent of the samples were similarly assigned to either above or below the median Tpot value, regardless which observer/laboratory combination was utilised. These data suggest that large clinical trials using Tpot should employ a single centre and a single individual to prepare, run and analyse samples
Intra-tumoral heterogeneity of tumour potential doubling times (Tpot) in colorectal cancer.
Intra-tumoural heterogeneity of proliferation has been assessed by taking multiple biopsies from 30 colorectal cancers. Following in vivo IUDR labelling, dual parameter flow cytometry was used to measure tumour DNA index (DI) and labelling index (LI) and to derive DNA synthesis time (Ts) and potential doubling time (Tpot). Heterogeneity was seen for all parameters under investigation. Overall coefficients of variation (CV) and logarithmic transformation of Ts and Tpot (due to their non-gaussian distributions) indicate that LI (CV 25%) was the most variable parameter. Intra-tumoral heterogeneity in Tpot (lnTpot CV = 22%) was less than inter-individual variation (CV = 63%), suggesting that this variation should not be a limitation to the possible usefulness of this technique as an independent prognostic indicator. Correlations of Tpot values were examined between the shortest, the median and the value for a pooled homogenate sample from a single tumour. Using an homogenate, it was possible to accurately predict classification of tumour Tpot values as being below the median ('fast tumours') in 15 of 19 cases (79%). The data suggest that assaying an homogenate may allow a more rapid analysis of a multiply sampled tumour
Mutation analysis of HIF prolyl hydroxylases (PHD/EGLN) in individuals with features of phaeochromocytoma and renal cell carcinoma susceptibility
Germline mutations in the von Hippel–Lindau disease (VHL) and succinate dehydrogenase subunit B (SDHB) genes can cause inherited phaeochromocytoma and/or renal cell carcinoma(RCC). Dysregulation of the hypoxia-inducible factor (HIF) transcription factors has been linked to VHL and SDHB-related RCC; both HIF dysregulation and disordered function of a prolyl hydroxylase domain isoform 3 (PHD3/EGLN3)-related pathway of neuronal apoptosis have been linked to the development of phaeochromocytoma. The 2-oxoglutarate-dependent prolyl hydroxylase enzymes PHD1 (EGLN2), PHD2 (EGLN1) and PHD3 (EGLN3) have a key role in regulating the stability of HIF-a subunits (and hence expression of the HIF-a transcription factors). A germline PHD2 mutation has been reported in association with congenital erythrocytosis and recurrent extra-adrenal phaeochromocytoma. We undertook mutation analysis of PHD1, PHD2 and PHD3 in two cohorts of patients with features of inherited phaeochromocytoma (nZ82) and inherited RCC (nZ64) and no evidence of germline mutations in known susceptibility genes. No confirmed pathogenic mutations were detected suggesting that mutations in these genes are not a frequent cause of inherited phaeochromocytoma or RCC
Numerical Study of a Mixed Ising Ferrimagnetic System
We present a study of a classical ferrimagnetic model on a square lattice in
which the two interpenetrating square sublattices have spins one-half and one.
This model is relevant for understanding bimetallic molecular ferrimagnets that
are currently being synthesized by several experimental groups. We perform
exact ground-state calculations for the model and employ Monte Carlo and
numerical transfer-matrix techniques to obtain the finite-temperature phase
diagram for both the transition and compensation temperatures. When only
nearest-neighbor interactions are included, our nonperturbative results
indicate no compensation point or tricritical point at finite temperature,
which contradicts earlier results obtained with mean-field analysis.Comment: Figures can be obtained by request to [email protected] or
[email protected]
Charge-based quantum computing using single donors in semiconductors
Solid-state quantum computer architectures with qubits encoded using single
atoms are now feasible given recent advances in atomic doping of
semiconductors. Here we present a charge qubit consisting of two dopant atoms
in a semiconductor crystal, one of which is singly ionised. Surface electrodes
control the qubit and a radio-frequency single electron transistor provides
fast readout. The calculated single gate times, of order 50ps or less, are much
shorter than the expected decoherence time. We propose universal one- and
two-qubit gate operations for this system and discuss prospects for fabrication
and scale up.Comment: 5 pages, 4 figures, updated version submitted to Physical Review
Texture Analysis of Cardiovascular Magnetic Resonance Cine Images differentiates etiologies of left ventricular hypertrophy
BACKGROUND: Textural analysis (TA) shows promise as radiological biomarker. The use of native TA in the field of cardiology is unproven. We hypothesized that Cardiovascular Magnetic Resonance pre-contrast bSSFP cine images could be analysed using TA software; TA features would differentiate different aetiologies of disease causing increased myocardial wall thickness (left ventricular hypertrophy {LVH}) and indicate the severity of myocardial tissue abnormality. METHOD: A mid short axis pre-contrast cine frame of 216 cases (50 hypertrophic cardiomyopathy (predominantly LVOTO sub type) (HCM), 52 cardiac amyloid (predominantly AL sub-type) (CA), 68 aortic stenosis (AS), 15 hypertensive with LVH (HTN+LVH) and 31 healthy volunteers (HV)) underwent CMRTA using TexRAD (TexRAD Ltd, Cambridge, UK). Among HV, 16/ 31 were scanned twice to form a test-retest reproducibility cohort. CMRTA comprised a filtration-histogram technique to extract and quantify features using 6 parameters. RESULTS: Test-retest analysis in HV showed a medium filter (3mm) was the most reproducible (intra-class correlation of 0.9 for kurtosis and skewness and 0.8 for mean and SD). Disease cohorts were statistically different (p<0.001) to health for all parameters. Pair wise comparisons of CMRTA parameters showed kurtosis and skewness consistently significant in ranking degree of difference from HV (greatest to least); CA, HCM, LVH+HTN, AS (p<0.001). Similarly mean, SD, entropy and mean positive pixel (MPP) were consistent in ranking degree of difference from HV; HCM, CA, AS and HTN+LVH. CONCLUSION: Radiomic features of bSSFP CMR data sets, derived using TA, show promise in discriminating between aetiologies of LVH
Analysis of antenal sensilla patterns of Rhodnius prolixus from Colombia and Venezuela
Antennal sensilla patterns were used to analyze population variation of domestic Rhodnius prolixus from six departments and states representing three biogeographical regions of Colombia and Venezuela. Discriminant analysis of the patterns of mechanoreceptors and of three types of chemoreceptors on the pedicel and flagellar segments showed clear differentiation between R. prolixus populations east and west of the Andean Cordillera. The distribution of thick and thin-walled trichoids on the second flagellar segment also showed correlation with latitude, but this was not seen in the patterns of other sensilla. The results of the sensilla patterns appear to be reflecting biogeographic features or population isolation rather than characters associated with different habitats and lend support to the idea that domestic R. prolixus originated in the eastern region of the Andes.Fil: Esteban, Lyda. Universidad Industrial de Santander; ColombiaFil: Angulo, VĂctor Manuel. Universidad Industrial de Santander; ColombiaFil: Dora Feliciangeli, M.. Universidad de Carabobo; VenezuelaFil: Catala, Silvia Susana. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro Regional de Investigaciones CientĂficas y Transferencia TecnolĂłgica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones CientĂficas y Transferencia TecnolĂłgica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones CientĂficas y Transferencia TecnolĂłgica de La Rioja. - SecretarĂa de Industria y MinerĂa. Servicio GeolĂłgico Minero Argentino. Centro Regional de Investigaciones CientĂficas y Transferencia TecnolĂłgica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones CientĂficas y Transferencia TecnolĂłgica de La Rioja; Argentin
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