270,235 research outputs found
Magnetoresistance of a two-dimensional electron gas with spatially periodic lateral modulations: Exact consequences of Boltzmann's equation
On the basis of Boltzmann's equation, and including anisotropic scattering in
the collision operator, we investigate the effect of one-dimensional
superlattices on two-dimensional electron systems. In addition to superlattices
defined by static electric and magnetic fields, we consider mobility
superlattices describing a spatially modulated density of scattering centers.
We prove that magnetic and electric superlattices in -direction affect only
the resistivity component if the mobility is homogeneous, whereas a
mobility lattice in -direction in the absence of electric and magnetic
modulations affects only . Solving Boltzmann's equation numerically,
we calculate the positive magnetoresistance in weak magnetic fields and the
Weiss oscillations in stronger fields within a unified approach.Comment: submitted to PR
Stark-Effect Scattering in Rough Quantum Wells
A scattering mechanism stemming from the Stark-shift of energy levels by
electric fields in semiconductor quantum wells is identified. This scattering
mechanism feeds off interface roughness and electric fields, and modifies the
well known 'sixth-power' law of electron mobility degradation. This work first
treats Stark-effect scattering in rough quantum wells as a perturbation for
small electric fields, and then directly absorbs it into the Hamiltonian for
large fields. The major result is the existence of a window of quantum well
widths for which the combined roughness scattering is minimum. Carrier
scattering and mobility degradation in wide quantum wells are thus expected to
be equally severe as in narrow wells due to Stark-effect scattering in electric
fields.Comment: 4 pages, 2 figures with png forma
Using mobility information to perform a feasibility study and the evaluation of spatio-temporal energy demanded by an electric taxi fleet
Half of the global population already lives in urban areas, facing to the problem of air pollution mainly caused by the transportation system. The recently worsening of urban air quality has a direct impact on the human health. Replacing today’s internal combustion engine vehicles with electric ones in public fleets could provide a deep impact on the air quality in the cities. In this paper, real mobility information is used as decision support for the taxi fleet manager to promote the adoption of electric taxi cabs in the city of San Francisco, USA. Firstly, mobility characteristics and energy requirements of a single taxi are analyzed. Then, the results are generalized to all vehicles from the taxi fleet. An electrificability rate of the taxi fleet is generated, providing information about the number of current trips that could be performed by electric taxis without modifying the current driver mobility patterns. The analysis results reveal that 75.2% of the current taxis could be replaced by electric vehicles, considering a current standard battery capacity (24–30 kWh). This value can increase significantly (to 100%), taking into account the evolution of the price and capacity of the batteries installed in the last models of electric vehicles that are coming to the market. The economic analysis shows that the purchasing costs of an electric taxi are bigger than conventional one. However, fuel, maintenance and repair costs are much lower. Using the expected energy consumption information evaluated in this study, the total spatio-temporal demand of electric energy required to recharge the electric fleet is also calculated, allowing identifying optimal location of charging infrastructure based on realistic routing patterns. This information could also be used by the distribution system operator to identify possible reinforcement actions in the electric grid in order to promote introducing electric vehicles
Energy and momentum relaxation dynamics of hot holes in modulation doped GaInNAs/GaAs quantum wells
We present the studies of energy and momentum relaxation dynamics of nonequilibrium holes in GaxIn1−xNyAs1−y/GaAs quantum well modulation doped with Be. Experimental results show that the real-space transfer (RST) of hot holes occurs via thermionic emission from the high-mobility GaInNAs quantum wells into the low-mobility GaAs barriers at a threshold electric field of F ∼ 6 kV/cm at T = 13 K. At this field the hole drift velocity saturates at vd ∼ 1×107 cm/s. A slight increase in the field above the threshold leads to the impact ionization of acceptors in the barriers by the nonequilibrium holes. We observe and model theoretically a negative differential mobility effect induced by RST that occurs at an electric field of F ∼ 7 kV/cm. The observed current surge at electric fields above 7 kV/cm is attributed to the hole multiplication induced by shallow impurity breakdown in the GaAs barrier and impact ionization in the high-field domain regime associated with the packet of RST of holes in the well
Separation of long DNA chains using non-uniform electric field: a numerical study
We study migration of DNA molecules through a microchannel with a series of
electric traps controlled by an ac electric field. We describe the motion of
DNA based on Brownian dynamics simulations of a beads-spring chain. Our
simulation demonstrates that the chain captured by an electrode escapes from
the binding electric field due to thermal fluctuation. We find that the
mobility of chain would depend on the chain length; the mobility sharply
increases when the length of a chain exceeds a critical value, which is
strongly affected by the amplitude of the applied ac field. Thus we can adjust
the length regime, in which this microchannel well separates DNA molecules,
without changing the structure of the channel. We also present a theoretical
insight into the relation between the critical chain length and the field
amplitude.Comment: 12 pages, 9 figure
Accessibility Design and Operational Considerations in the Development of Urban Aerial Mobility Vehicles and Networks
Urban aerial mobility vehicles and networks have recently gained considerable interest in the aviation community. These small, short-range vehicles with all-electric or hybrid-electric propulsion systems, tailored to metropolitan aerial transportation needs, promise to radically change passenger mobility and cargo distribution in cities. Accessibility issues have not been a major consideration in UAM vehicle and network discussions to date. This paper seeks to help change that
Unfolding Polyelectrolytes in Trivalent Salt Solutions Using DC Electric Fields: A Study by Langevin Dynamics Simulations
We study the behavior of single linear polyelectrolytes condensed by
trivalent salt under the action of electric fields through computer
simulations. The chain is unfolded when the strength of the electric field is
stronger than a critical value. This critical electric field follows a scaling
law against chain length and the exponent of the scaling law is ,
smaller than the theoretical prediction, [Netz, Phys. Rev. Lett. 90
(2003) 128104], and the one obtained by simulations in tetravalent salt
solutions, [Hsiao and Wu, J. Phys. Chem. B 112 (2008) 13179]. It
demonstrates that the scaling exponent depends sensitively on the salt valence.
Hence, it is easier to unfold chains condensed by multivalent salt of smaller
valence. Moreover, the absolute value of chain electrophoretic mobility
increases drastically when the chain is unfolded in an electric field. The
dependence of the mobility on electric field and chain length provides a
plausible way to impart chain-length dependence in free-solution
electrophoresis via chain unfolding transition induced by electric fields.
Finally, we show that, in addition to an elongated structure, a condensed chain
can be unfolded into an U-shaped structure. The formation of this structure in
our study is purely a result of the electric polarization, but not of the
elasto-hydrodynamics dominated in sedimentation of polymers.Comment: 15 pages, 7 figures, accepted for publication in Biomicrofluidic
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