92 research outputs found
Diameter-dependent conductance of InAs nanowires
Electrical conductance through InAs nanowires is relevant for electronic
applications as well as for fundamental quantum experiments. Here we employ
nominally undoped, slightly tapered InAs nanowires to study the diameter
dependence of their conductance. Contacting multiple sections of each wire, we
can study the diameter dependence within individual wires without the need to
compare different nanowire batches. At room temperature we find a
diameter-independent conductivity for diameters larger than 40 nm, indicative
of three-dimensional diffusive transport. For smaller diameters, the resistance
increases considerably, in coincidence with a strong suppression of the
mobility. From an analysis of the effective charge carrier density, we find
indications for a surface accumulation layer.Comment: 9 pages, 5 figure
Evaluation of a Subject specific dual-transmit approach for improving B1 field homogeneity in cardiovascular magnetic resonance at 3T
BACKGROUND: Radiofrequency (RF) shading artifacts degrade image quality while performing cardiovascular magnetic resonance (CMR) at higher field strengths. In this article, we sought to evaluate the effect of local RF (B(1) field) shimming by using a dual-source–transmit RF system for cardiac cine imaging and to systematically evaluate the effect of subject body type on the B(1) field with and without local RF shimming. METHODS: We obtained cardiac images from 37 subjects (including 11 patients) by using dual-transmit 3T CMR. B(1) maps with and without subject-specific local RF shimming (exploiting the independent control of transmit amplitude and phase of the 2 RF transmitters) were obtained. Metrics quantifying B(1) field homogeneity were calculated and compared with subject body habitus. RESULTS: Local RF shimming across the region encompassed by the heart increased the mean flip angle (μ) in that area (88.5 ± 15.2% vs. 81.2 ± 13.3%; P = 0.0014), reduced the B(1) field variation by 42.2 ± 13%, and significantly improved the percentage of voxels closer to μ (39% and 82% more voxels were closer to ± 10% and ± 5% of μ, respectively) when compared with no RF shimming. B(1) homogeneity was independent of subject body type (body surface area [BSA], body mass index [BMI] or anterior-posterior/right-left patient width ratio [AP/RL]). Subject specific RF (B(1)) shimming with a dual-transmit system improved local RF homogeneity across all body types. CONCLUSION: With or without RF shimming, cardiac B1 field homogeneity does not depend on body type, as characterized by BMI, BSA, and AP/RL. For all body types studied, cardiac B(1) field homogeneity was significantly improved by performing local RF shimming with 2 independent RF-transmit channels. This finding indicates the need for subject-specific RF shimming
Risk-Assessment of Esophageal Surgery:Diagnosis and Treatment of Celiac Trunk Stenosis
Anastomotic leakage of the gastric conduit following surgical treatment of esophageal cancer is a life-threatening complication. An important risk factor associated with anastomotic leakage is calcification of the supplying arteries of the gastric conduit. The patency of calcified splanchnic arteries cannot be assessed on routine computed tomography (CT) scans for esophageal cancer and, as such, in selected patients with known or assumed mesenteric artery disease, additional CT angiography of the abdominal arteries with 1mm slices is strongly encouraged. If the mesenteric perfusion is compromised in patients with resectable esophageal cancer, angioplasty procedures with stenting of the mesenteric arteries could be performed to prevent possible ischemia of the gastric conduit
Probing Charging and Localization in the Quantum Hall Regime by Graphene pnp Junctions
Using high quality graphene pnp junctions, we observe prominent conductance
fluctuations on transitions between quantum Hall (QH) plateaus as the top gate
voltage Vtg is varied. In the Vtg-B plane, the fluctuations form crisscrossing
lines that are parallel to those of the adjacent plateaus, with different
temperature dependences for the conductance peaks and valleys. These
fluctuations arise from Coulomb-induced charging of electron- or hole-doped
localized states when the device bulk is delocalized, underscoring the
importance of electronic interactions in graphene in the QH regime
Spin splitting and even-odd effects in carbon nanotubes
The level spectrum of a single-walled carbon nanotube rope, studied by
transport spectroscopy, shows Zeeman splitting in a magnetic field parallel to
the tube axis. The pattern of splittings implies that the spin of the ground
state alternates by 1/2 as consecutive electrons are added. Other aspects of
the Coulomb blockade characteristics, including the current-voltage traces and
peak heights, also show corresponding even-odd effects.Comment: Preprint, pdf format only, 4 pages including figure
Coffee consumption is associated with a reduced risk of colorectal cancer recurrence and all-cause mortality
Coffee consumption has been associated with a reduced risk of developing colorectal cancer (CRC). However, it is not clear whether coffee consumption is related to CRC progression. Hence, we assessed the association of coffee consumption with CRC recurrence and all-cause mortality using data from a prospective cohort study of 1719 stage I–III CRC patients in the Netherlands. Coffee consumption and other lifestyle characteristics were self-reported using questionnaires at the time of diagnosis. We retrieved recurrence and all-cause mortality data from the Netherlands Cancer Registry and the Personal Records Database, respectively. Cox proportional hazard regression models with and without restricted cubic splines were used to calculate hazard ratios (HR) and 95% confidence intervals (CI) adjusted for age, sex, education, smoking status, cancer stage and tumor location. We observed 257 recurrences during a 6.2-year median follow-up and 309 deaths during a 6.6-year median follow-up. Consuming more than 4 cups/d of coffee compared to an intake of <2 cups/d was associated with a 32% lower risk of CRC recurrence (95% CI: 0.49, 0.94,). The association between coffee consumption and all-cause mortality was U-shaped; coffee intake seemed optimal at 3–5 cups/d with the lowest risk at 4 cups/d (HR: 0.68, 95% CI: 0.53, 0.88). Our results suggest that coffee consumption may be associated with a lower risk of CRC recurrence and all-cause mortality. The association between coffee consumption and all-cause mortality appeared nonlinear. More studies are needed to understand the mechanism by which coffee consumption might improve CRC prognosis.</p
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