5,823 research outputs found
Ballistic transport, chiral anomaly and emergence of the neutral electron - hole plasma in graphene
The process of coherent creation of particle - hole excitations by an
electric field in graphene is quantitatively described using a dynamic "first
quantized" approach. We calculate the evolution of current density, number of
pairs and energy in ballistic regime using the tight binding model. The series
in electric field strength up to third order in both DC and AC are
calculated. We show how the physics far from the two Dirac points enters
various physical quantities in linear response and how it is related to the
chiral anomaly. The third harmonic generation and the imaginary part of
conductivity are obtained. It is shown that at certain time scale
the physical behaviour dramatically changes and the
perturbation theory breaks down. Beyond the linear response physics is explored
using an exact solution of the first quantized equations. While for small
electric fields the I-V curve is linear characterized by the universal minimal
resistivity %, at the conductivity grows
fast. The copious pair creation (with rate ), analogous to Schwinger's
electron - positron pair creation from vacuum in QED, leads to creation of the
electron - hole plasma at ballistic times of order . This process is
terminated by a relaxational recombination.Comment: 15 pages, 5 figures
Power from the people - Human-powered small-scale generation system for a sustainable dance club
Most Human-Powered Energy-Harvesting Systems are used to power ubiquitously deployed sensor networks and mobile electronics. These systems scavenge power from human activity or derive limited energy from ambient heat, light, or vibrations. In this article, systems that use human power by walking or running are analyzed, where an alternative system has been designed and implemented that generates energy from people dancing in a club environment
Steady-state spin densities and currents
This article reviews steady-state spin densities and spin currents in
materials with strong spin-orbit interactions. These phenomena are intimately
related to spin precession due to spin-orbit coupling which has no equivalent
in the steady state of charge distributions. The focus will be initially on
effects originating from the band structure. In this case spin densities arise
in an electric field because a component of each spin is conserved during
precession. Spin currents arise because a component of each spin is continually
precessing. These two phenomena are due to independent contributions to the
steady-state density matrix, and scattering between the conserved and
precessing spin distributions has important consequences for spin dynamics and
spin-related effects in general. In the latter part of the article extrinsic
effects such as skew scattering and side jump will be discussed, and it will be
shown that these effects are also modified considerably by spin precession.
Theoretical and experimental progress in all areas will be reviewed
Characterizing faint galaxies in the reionization epoch: LBT confirms two L<0.2L* sources at z=6.4 behind the CLASH/Frontier Fields cluster MACS0717.5+3745
We report the LBT/MODS1 spectroscopic confirmation of two images of faint
Lyman alpha emitters at behind the Frontier Fields galaxy cluster
MACSJ0717.5+3745. A wide range of lens models suggests that the two images are
highly magnified, with a strong lower limit of mu>5. These are the faintest z>6
candidates spectroscopically confirmed to date. These may be also multiple
images of the same z=6.4 source as supported by their similar intrinsic
properties, but the lens models are inconclusive regarding this interpretation.
To be cautious, we derive the physical properties of each image individually.
Thanks to the high magnification, the observed near-infrared (restframe
ultraviolet) part of the spectral energy distributions and Ly-alpha lines are
well detected with S/N(m_1500)>~10 and S/N(Ly-alpha)~10-15. Adopting mu>5, the
absolute magnitudes, M_1500, and Ly-alpha fluxes, are fainter than -18.7 and
2.8x10^(-18)erg/s/cm2, respectively. We find a very steep ultraviolet spectral
slope beta=-3.0+/-0.5 (F_lambda=lambda^(beta)), implying that these are very
young, dust-free and low metallicity objects, made of standard stellar
populations or even extremely metal poor stars (age<~30Myr, E(B-V)=0 and
metallicity 0.0-0.2 Z/Zsolar). The objects are compact (< 1 kpc^(2)), and with
a stellar mass M* < 10^(8) M_solar. The very steep beta, the presence of the
Ly-alpha line and the intrinsic FWHM (<300 km/s) of these newborn objects do
not exclude a possible leakage of ionizing radiation. We discuss the
possibility that such faint galaxies may resemble those responsible for cosmic
reionization.Comment: Accepted by ApJL; 6 pages, 4 figures, 1 table, emulateapj forma
Investigation of the Domain Wall Fermion Approach to Chiral Gauge Theories on the Lattice
We investigate a recent proposal to construct chiral gauge theories on the
lattice using domain wall fermions. We restrict ourselves to the finite volume
case, in which two domain walls are present, with modes of opposite chirality
on each of them. We couple the chiral fermions on only one of the domain walls
to a gauge field. In order to preserve gauge invariance, we have to add a
scalar field, which gives rise to additional light mirror fermion and scalar
modes. We argue that in an anomaly free model these extra modes would decouple
if our model possesses a so-called strong coupling symmetric phase. However,
our numerical results indicate that such a phase most probably does not exist.
---- Note: 9 Postscript figures are appended as uuencoded compressed tar file.Comment: 27p. Latex; UCSD/PTH 93-28, Wash. U. HEP/93-6
Ultracompact, low-loss directional couplers on InP based on self-imaging by multimode interference
We report extremely compact (494-µm-long 3 dB splitters, including input/output bends), polarization-insensitive, zero-gap directional couplers on InP with a highly multimode interference region that are based on the self-imaging effect. We measured cross-state extinctions better than 28 dB and on-chip insertion losses of 0.5 dB/coupler plus 1 dB/cm guide propagation loss at 1523 nm wavelength
Gauge Theory for the Rate Equations: Electrodynamics on a Network
Systems of coupled rate equations are ubiquitous in many areas of science,
for example in the description of electronic transport through quantum dots and
molecules. They can be understood as a continuity equation expressing the
conservation of probability. It is shown that this conservation law can be
implemented by constructing a gauge theory akin to classical electrodynamics on
the network of possible states described by the rate equations. The properties
of this gauge theory are analyzed. It turns out that the network is maximally
connected with respect to the electromagnetic fields even if the allowed
transitions form a sparse network. It is found that the numbers of degrees of
freedom of the electric and magnetic fields are equal. The results shed light
on the structure of classical abelian gauge theory beyond the particular
motivation in terms of rate equations.Comment: 4 pages, 2 figures included, v2: minor revision, as publishe
eHealth in the support of people with mild intellectual disability in daily life:A systematic review
Background: eHealth has recently made rapid progress in care, support and treatment. However, studies on the use of eHealth to support people with a mild intellectual disability in daily life are limited. A systematic review was conducted to provide an overview of this use of eHealth. Methods: Seven databases were searched for relevant studies and assessed according to the PRISMA guidelines. Descriptive analyses were deployed using the Matching Person to Technology model to evaluate the key areas contributing to successful eHealth use. Results: Most of the 46 studies included were small-scale case studies and focused on using eHealth to acquire daily living skills and vocational skills. In addition, several studies focused on eHealth use for self-support in daily living, and three studies focused on remote professional support. Conclusions: eHealth offers opportunities to support people with mild intellectual disability in various different contexts of daily life. Scientific research on this topic is in its early stage, and further high-quality research is needed
Chiral Lattice Gauge Theories Via Mirror-Fermion Decoupling: A Mission (im)Possible?
This is a review of the status and outstanding issues in attempts to
construct chiral lattice gauge theories by decoupling the mirror fermions from
a vectorlike theory. In the first half, we explain why studying nonperturbative
chiral gauge dynamics may be of interest, enumerate the problems that a lattice
formulation of chiral gauge theories must overcome, and briefly review our
current knowledge. We then discuss the motivation and idea of mirror-fermion
decoupling and illustrate the desired features of the decoupling dynamics by a
simple solvable toy model. The role of exact chiral symmetries and matching of
't Hooft anomalies on the lattice is also explained. The second, more
technical, half of the article is devoted to a discussion of the known and
unknown features of mirror-decoupling dynamics formulated with Ginsparg-Wilson
fermions. We end by pointing out possible directions for future studies.Comment: 53 pp; 6 figs; added table of contents, references, fixed typo
- …