881 research outputs found
Veselago lensing in graphene with a p-n junction: classical versus quantum effects
The feasibility of Veselago lensing in graphene with a p-n junction is
investigated numerically for realistic injection leads. Two different set-ups
with two narrow leads are considered with absorbing or reflecting side edges.
This allows us to separately determine the influence of scattering on electron
focusing for the edges and the p-n interface. Both semiclassical and
tight-binding simulations show a distinctive peak in the transmission
probability that is attributed to the Veselago lensing effect. We investigate
the robustness of this peak on the width of the injector, the position of the
p-n interface and different gate potential profiles. Furthermore, the influence
of scattering by both short- and long-range impurities is considered.Comment: 10 pages, 7 figure
Bilayer graphene Hall bar with a pn-junction
We investigate the magnetic field dependence of the Hall and the bend
resistances for a ballistic Hall bar structure containing a pn-junction
sculptured from a bilayer of graphene. The electric response is obtained using
the billiard model and we investigate the cases of bilayer graphene with and
without a band gap. Two different conduction regimes are possible: ) both
sides of the junction have the same carrier type, and ) one side of the
junction is n-type while the other one is p-type. The first case shows Hall
plateau-like features in the Hall resistance that fade away as the band gap
opens. The second case exhibits a bend resistance that is asymmetric in
magnetic field as a consequence of snake states along the pn-interface, where
the maximum is shifted away from zero magnetic field
Spectroscopy of snake states using a graphene Hall bar
An approach to observe snake states in a graphene Hall bar containing a
pn-junction is proposed. The magnetic field dependence of the bend resistance
in a ballistic graphene Hall bar structure containing a tilted pn-junction
oscillates as a function of applied magnetic field. We show that each
oscillation is due to a specific snake state that moves along the pn-interface.
Furthermore depending on the value of the magnetic field and applied potential
we can control the lead in which the electrons will end up and hence control
the response of the system
Graphene Hall bar with an asymmetric pn-junction
We investigated the magnetic field dependence of the Hall and the bend
resistances in the ballistic regime for a single layer graphene Hall bar
structure containing a pn-junction. When both regions are n-type the Hall
resistance dominates and Hall type of plateaus are formed. These plateaus occur
as a consequence of the restriction on the angle imposed by Snell's law
allowing only electrons with a certain initial angles to transmit though the
potential step. The size of the plateau and its position is determined by the
position of the potential interface as well as the value of the applied
potential. When the second region is p-type the bend resistance dominates which
is asymmetric in field due to the presence of snake states. Changing the
position of the pn-interface in the Hall bar strongly affects these states and
therefore the bend resistance is also changed. Changing the applied potential
we observe that the bend resistance exhibits a peak around the
charge-neutrality point (CNP) which is independent of the position of the
pn-interface, while the Hall resistance shows a sign reversal when the CNP is
crossed, which is in very good agreement with a recent experiment [J. R.
Williams et al., Phys. Rev. Lett. 107, 046602(2011)]
Deposit Formation in the Holes of Diesel Injector Nozzles: A Critical Review
Current developments in fuels and emissions regulations are resulting in increasingly severe operating environment for the injection system. Formation of deposits within the holes of the injector nozzle or on the outside of the injector tip may have an adverse effect on overall system performance. This paper provides a critical review of the current understanding of the main factors affecting deposit formation. Two main types of engine test cycles, which attempt to simulate field conditions, are described in the literature. The first type involves cycling between high and low load. The second involves steady state operation at constant speed either at medium or high load. A number of influences on the creation of deposits are identified. This includes fouling through thermal condensation and cracking reactions at nozzle temperatures of around 300°C. Also the design of the injector holes is an influence, because it can influence cavitation. The implosion of cavitation bubbles is believed to limit nozzle deposits. Field and laboratory tests showed that small amounts (around 1ppm) of zinc tend to increase the formation of deposits and are therefore another influence. But it is not clear whether zinc acts catalytically to accelerate deposit formation or if it becomes part of the solid deposits. Bio-diesel has been observed to lead to higher deposit formation in the injector nozzle. The chemical and physical processes that lead to deposit formation are not known or well understood, due to their complexity. A physical mechanism put forward focuses on the role of the residual fuel that remains in the nozzle holes after the end of the injection process. © 2008 SAE International
A cross-country examination on the fear of covid-19 and the sense of loneliness during the first wave of covid-19 outbreak
The aim of the current study is to examine gender, age. and cross-country differences in fear of COVID-19 and sense of loneliness during the lockdown, by comparing people from those countries with a high rate of infections and deaths (e.g., Spain and Italy) and from countries with a mild spread of infection (e.g., Croatia, Serbia, Slovakia, Slovenia, and Bosnia and Herzegovina). A total of 3876 participants (63% female) completed an online survey on “Everyday life practices in COVID-19 time” in April 2020, including measures of fear of COVID-19 and loneliness. Males and females of all age groups in countries suffering from the powerful impact of the COVID-19 pandemic reported greater fear of COVID-19 and sense of loneliness. In less endangered countries, females and the elderly reported more symptoms than males and the young; in Spanish and Italian samples, the pattern of differences is considerably more complex. Future research should thoroughly examine different age and gender groups. The analysis of emotional well-being in groups at risk of mental health issues may help to lessen the long term social and economic costs due to the COVID-19 outbreak
High-Precision Measurement of the 19Ne Half-Life and Implications for Right-Handed Weak Currents
We report a precise determination of the 19Ne half-life to be s. This result disagrees with the most recent precision
measurements and is important for placing bounds on predicted right-handed
interactions that are absent in the current Standard Model. We are able to
identify and disentangle two competing systematic effects that influence the
accuracy of such measurements. Our findings prompt a reassessment of results
from previous high-precision lifetime measurements that used similar equipment
and methods.Comment: 5 pages and 5 figures. Paper accepted for publication in Phys. Rev.
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