Interfaces Within Graphene Nanoribbons

We study the conductance through two types of graphene nanostructures: nanoribbon junctions in which the width changes from wide to narrow, and curved nanoribbons. In the wide-narrow structures, substantial reflection occurs from the wide-narrow interface, in contrast to the behavior of the much studied electron gas waveguides. In the curved nanoribbons, the conductance is very sensitive to details such as whether regions of a semiconducting armchair nanoribbon are included in the curved structure -- such regions strongly suppress the conductance. Surprisingly, this suppression is not due to the band gap of the semiconducting nanoribbon, but is linked to the valley degree of freedom. Though we study these effects in the simplest contexts, they can be expected to occur for more complicated structures, and we show results for rings as well. We conclude that experience from electron gas waveguides does not carry over to graphene nanostructures. The interior interfaces causing extra scattering result from the extra effective degrees of freedom of the graphene structure, namely the valley and sublattice pseudospins.Comment: 19 pages, published version, several references added, small changes to conclusion

AC0(MOD2) lower bounds for the Boolean inner product

AC0 ◦MOD2 circuits are AC0 circuits augmented with a layer of parity gates just above the input layer. We study AC0 ◦ MOD2 circuit lower bounds for computing the Boolean Inner Product functions. Recent works by Servedio and Viola (ECCC TR12-144) and Akavia et al. (ITCS 2014) have highlighted this problem as a frontier problem in circuit complexity that arose both as a first step towards solving natural special cases of the matrix rigidity problem and as a candidate for constructing pseudorandom generators of minimal complexity. We give the first superlinear lower bound for the Boolean Inner Product function against AC0 ◦ MOD2 of depth four or greater. Specifically, we prove a superlinear lower bound for circuits of arbitrary constant depth, and an Ω( ˜ n 2 ) lower bound for the special case of depth-4 AC0 ◦ MOD2. Our proof of the depth-4 lower bound employs a new “moment-matching” inequality for bounded, nonnegative integer-valued random variables that may be of independent interest: we prove an optimal bound on the maximum difference between two discrete distributions’ values at 0, given that their first d moments match

Adaptive skin color classificator

Abstract A lot of computer vision applications benefit from robust skin color classification. But this is a hard challenge due to the various image conditions like camera settings, illumination, light source, shadows and many more. Furthermore people's tans and ethnic groups also extend those conditions. In this work we present a parametric skin color classifier that can be adapted to the conditions of each image or image sequence. This is done by evaluating some previously know skin color pixels which are acquired by applying a face detector. This approach can distinguish skin color from very similar color like lip color or eye brow color. Its high speed and high accuracy makes it appropriate for real time applications such as face tracking and mimic recognition

FORCE AND MOMENT MEASUREMENTS DURING ALPINE SKIING DEPENDING ON HEIGHT POSITION

INTRODUCTION: When a ski is set on edge a lever arm is produced by the force FS, which is applied through the skier’s leg and boot midline, and the ground reaction force FR, which acts on the ski edge. A moment is necessary to keep the ski in its position (see figure and compare with Lind). It is hypothesized that the magnitude of this moment is mainly determined by the width-height proportion of ski and binding. In order to adjust this moment, the skier has to rotate his knee inwards or angle his hip in the lateral direction (Lind, Howe). The objective of this study was to clarify whether the height of the binding plate has any influence on the generated moment. METHODS: A professional ski racer (A-Kader DSV) descended a giant slalom course (at 25° steepness) nine times consecutively. For every run the equipment was identical (skis: ATOMIC ARC RS, binding: ESS 10.28) except for the adjusted height of the binding plate. Three different height positions were used. System A was comprised without a plate between ski and binding, system B with a plate of 1 cm height and system C with a plate of 2 cm height. Using a previously described measuring boot (Wimmer), the ground reaction forces were determined at four distinct locations underneath the boot soles. The specific set-up of the force sensors (two at every edge of the skis) allowed us to calculate the generated moments by known lever-arms. RESULTS: Out of nine runs, seven runs differed in elapsed time by less than 0.3 sec, and the average duration was 20 sec. For this reason a good comparability can be derived. The three fastest runs were made with the 2 cm binding plate, the three slowest runs without the binding plate. The magnitude of ground reaction force ranged from 2000 to 3500 N. The calculated moment was approx. 40-70 Nm and was independent of height position at all turns. Indeed, the moment variation was more affected by the specific turns of the course than by height position. However, the force readings during turns (and thus the moments) were smoother when a higher plate was used. CONCLUSIONS: Because no moment differences could be assigned to the different height positions, the varying width-height-proportions of the three systems may have resulted in three different edging angles. For system C a smaller edging angle would be necessary than for system B, whereas system A would need the largest edging angle. This might be important for the skier, since a smaller body angle in the lateral direction would be necessary to maintain equilibrium using a binding plate

Beamlet scraping and its influence on the beam divergence at the BATMAN Upgrade test facility

For the ITER fusion experiment, two neutral beam injectors are required for plasma heating and current drive. Each injector supplies a power of about 17 MW, obtained from neutralization of 40 A (46 A), 1 MeV (0.87 MeV) negative deuterium (hydrogen) ions. The full beam is composed of 1280 beamlets, formed in 16 beamlet groups, and strict requirements apply to the beamlet core divergence (<7 mrad). The test facility BATMAN Upgrade uses an ITER-like grid with one beamlet group, which consists of 70 apertures. In a joint campaign performed by IPP and Consorzio RFX to better assess the beam optics, the divergence of a single beamlet was compared to a group of beamlets at BATMAN Upgrade. The single beamlet is measured with a carbon fiber composite tile calorimeter and by beam emission spectroscopy, whereas the divergence of the group of beamlets is measured by beam emission spectroscopy only. When increasing the RF power at low extraction voltages, the divergence of the beamlet and of the group of beamlets is continuously decreasing and no inflection point toward an overperveant beam is found. At the same time, scraping of the extracted ion beam at the second grid (extraction grid) takes place at higher RF power, supported by the absence of the normally seen linear behavior between the measured negative ion density in the plasma close to the extraction system and the measured extracted ion current. Beside its influence on the divergence, beamlet scraping needs to be considered for the determination of the correct perveance and contributes to the measured coextracted electron current

Spectroscopy of 19^{19}Ne for the thermonuclear 15^{15}O(α,γ\alpha,\gamma)19^{19}Ne and 18^{18}F(p,αp,\alpha)15^{15}O reaction rates

Uncertainties in the thermonuclear rates of the $^{15}$O($\alpha,\gamma$)$^{19}$Ne and $^{18}$F($p,\alpha$)$^{15}$O reactions affect model predictions of light curves from type I X-ray bursts and the amount of the observable radioisotope $^{18}$F produced in classical novae, respectively. To address these uncertainties, we have studied the nuclear structure of $^{19}$Ne over $E_{x} = 4.0 - 5.1$ MeV and $6.1 - 7.3$ MeV using the $^{19}$F($^{3}$He,t)$^{19}$Ne reaction. We find the $J^{\pi}$ values of the 4.14 and 4.20 MeV levels to be consistent with $9/2^{-}$ and $7/2^{-}$ respectively, in contrast to previous assumptions. We confirm the recently observed triplet of states around 6.4 MeV, and find evidence that the state at 6.29 MeV, just below the proton threshold, is either broad or a doublet. Our data also suggest that predicted but yet unobserved levels may exist near the 6.86 MeV state. Higher resolution experiments are urgently needed to further clarify the structure of $^{19}$Ne around the proton threshold before a reliable $^{18}$F($p,\alpha$)$^{15}$O rate for nova models can be determined.Comment: 5 pages, 3 figures, Phys. Rev. C (in press