16,308 research outputs found
Recommended from our members
A Systemic Approach to Music Performance Learning with Multimodal Technology
Inductive and Electrostatic Acceleration in Relativistic Jet-Plasma Interactions
We report on the observation of rapid particle acceleration in numerical
simulations of relativistic jet-plasma interactions and discuss the underlying
mechanisms. The dynamics of a charge-neutral, narrow, electron-positron jet
propagating through an unmagnetized electron-ion plasma was investigated using
a three-dimensional, electromagnetic, particle-in-cell computer code. The
interaction excited magnetic filamentation as well as electrostatic plasma
instabilities. In some cases, the longitudinal electric fields generated
inductively and electrostatically reached the cold plasma wave-breaking limit,
and the longitudinal momentum of about half the positrons increased by 50% with
a maximum gain exceeding a factor of 2 during the simulation period. Particle
acceleration via these mechanisms occurred when the criteria for Weibel
instability were satisfied.Comment: Revised for Phys. Rev. Lett. Please see publised version for best
graphic
The phenotype paradox: lessons from natural transcriptome evolution on how to engineer plants
Plants have evolved genome complexity through iterative rounds of single gene and whole genome duplication. This has led to substantial expansion in transcription factor numbers following preferential retention and subsequent functional divergence of these regulatory genes. Here we review how this simple evolutionary network rewiring process, regulatory gene duplication followed by functional divergence, can be used to inspire synthetic biology approaches that seek to develop novel phenotypic variation for future trait based breeding programs in plants
Radio Polarization Observations of the Snail: A Crushed Pulsar Wind Nebula in G327.1-1.1 with a Highly Ordered Magnetic Field
Pulsar wind nebulae (PWNe) are suggested to be acceleration sites of cosmic
rays in the Galaxy. While the magnetic field plays an important role in the
acceleration process, previous observations of magnetic field configurations of
PWNe are rare, particularly for evolved systems. We present a radio
polarization study of the "Snail" PWN inside the supernova remnant G327.1-1.1
using the Australia Telescope Compact Array. This PWN is believed to have been
recently crushed by the supernova (SN) reverse shock. The radio morphology is
composed of a main circular body with a finger-like protrusion. We detected a
strong linear polarization signal from the emission, which reflects a highly
ordered magnetic field in the PWN and is in contrast to the turbulent
environment with a tangled magnetic field generally expected from
hydrodynamical simulations. This could suggest that the characteristic
turbulence scale is larger than the radio beam size. We built a toy model to
explore this possibility, and found that a simulated PWN with a turbulence
scale of about one-eighth to one-sixth of the nebula radius and a pulsar wind
filling factor of 50--75% provides the best match to observations. This implies
substantial mixing between the SN ejecta and pulsar wind material in this
system.Comment: 13 pages, 10 figures, Accepted for publication in Ap
Deep Chandra Observation of the Pulsar Wind Nebula Powered by the Pulsar J1846-0258 in the Supernova Remnant Kes 75
We present the results of detailed spatial and spectral analysis of the
pulsar wind nebula (PWN) in supernova remnant Kes 75 (G29.7-0.3) using a deep
exposure with Chandra X-ray observatory. The PWN shows a complex morphology
with clear axisymmetric structure. We identified a one-sided jet and two bright
clumps aligned with the overall nebular elongation, and an arc-like feature
perpendicular to the jet direction. Further spatial modeling with a torus and
jet model indicates a position angle 207\arcdeg\pm8 \arcdeg for the PWN
symmetry axis. We interpret the arc as an equatorial torus or wisp and the
clumps could be shock interaction between the jets and the surrounding medium.
The lack of any observable counter jet implies a flow velocity larger than
0.4c. Comparing to an archival observation 6 years earlier, some small-scale
features in the PWN demonstrate strong variability: the flux of the inner jet
doubles and the peak of the northern clump broadens and shifts 2" outward. In
addition, the pulsar flux increases by 6 times, showing substantial spectral
softening from =1.1 to 1.9 and an emerging thermal component which was
not observed in the first epoch. The changes in the pulsar spectrum are likely
related to the magnetar-like bursts of the pulsar that occurred 7 days before
the Chandra observation, as recently reported from RXTE observations.Comment: Accepted by ApJ, 8 figures, some of them have been scaled down in
resolutio
On Uniquely Closable and Uniquely Typable Skeletons of Lambda Terms
Uniquely closable skeletons of lambda terms are Motzkin-trees that
predetermine the unique closed lambda term that can be obtained by labeling
their leaves with de Bruijn indices. Likewise, uniquely typable skeletons of
closed lambda terms predetermine the unique simply-typed lambda term that can
be obtained by labeling their leaves with de Bruijn indices.
We derive, through a sequence of logic program transformations, efficient
code for their combinatorial generation and study their statistical properties.
As a result, we obtain context-free grammars describing closable and uniquely
closable skeletons of lambda terms, opening the door for their in-depth study
with tools from analytic combinatorics.
Our empirical study of the more difficult case of (uniquely) typable terms
reveals some interesting open problems about their density and asymptotic
behavior.
As a connection between the two classes of terms, we also show that uniquely
typable closed lambda term skeletons of size are in a bijection with
binary trees of size .Comment: Pre-proceedings paper presented at the 27th International Symposium
on Logic-Based Program Synthesis and Transformation (LOPSTR 2017), Namur,
Belgium, 10-12 October 2017 (arXiv:1708.07854
Quantum Dot in 2D Topological Insulator: The Two-channel Kondo Fixed Point
In this work, a quantum dot couples to two helical edge states of a 2D
topological insulator through weak tunnelings is studied. We show that if the
electron interactions on the edge states are repulsive, with Luttinger liquid
parameter , the system flows to a stable two-channel fixed point at
low temperatures. This is in contrast to the case of a quantum dot couples to
two Luttinger liquid leads. In the latter case, a strong electron-electron
repulsion is needed, with , to reach the two-channel fixed point. This
two-channel fixed point is described by a boundary Sine-Gordon Hamiltonian with
a dependent boundary term. The impurity entropy at zero temperature is
shown to be . The impurity specific heat is when , and when . We
also show that the linear conductance across the two helical edges has
non-trivial temperature dependence as a result of the renormalization group
flow.Comment: 4+\epsilon page
Recommended from our members
3d augmented mirror: a multimodal interface for string instrument learning and teaching with gesture support
Multimodal interfaces can open up new possibilities for music education, where the traditional model of teaching is based predominantly on verbal feedback. This paper explores the development and use of multimodal interfaces in novel tools to support music practice training. The design of multimodal interfaces for music education presents a challenge in several respects. One is the integration of multimodal technology into the music learning process. The other is the technological development, where we present a solution that aims to support string practice training with visual and auditory feedback. Building on the traditional function of a physical mirror as a teaching aid, we describe the concept and development of an "augmented mirror" using 3D motion capture technology
Observing two dark accelerators around the Galactic Centre with Fermi Large Area Telescope
We report the results from a detailed ray investigation in the field
of two "dark accelerators", HESS J1745-303 and HESS J1741-302, with years
of data obtained by the Fermi Large Area Telescope. For HESS J1745-303, we
found that its MeV-GeV emission is mainly originated from the "Region A" of the
TeV feature. Its ray spectrum can be modeled with a single power-law
with a photon index of from few hundreds MeV to TeV. Moreover,
an elongated feature, which extends from "Region A" toward northwest for
, is discovered for the first time. The orientation of this
feature is similar to that of a large scale atomic/molecular gas distribution.
For HESS J1741-302, our analysis does not yield any MeV-GeV counterpart for
this unidentified TeV source. On the other hand, we have detected a new point
source, Fermi J1740.1-3013, serendipitously. Its spectrum is apparently curved
which resembles that of a ray pulsar. This makes it possibly
associated with PSR B1737-20 or PSR J1739-3023.Comment: 11 pages, 7 figures, 2 tables, accepted for publication in MNRA
Connection between the Slave-Particles and X-Operators Path-Integral Representations. a New Perturbative Approach
In the present work it is shown that the family of first-order Lagrangians
for the t-J model and the corresponding correlation generating functional
previously found can be exactly mapped into the slave-fermion decoupled
representation. Next, by means of the Faddeev-Jackiw symplectic method, a
different family of Lagrangians is constructed and it is shown how the
corresponding correlation generating functional can be mapped into the
slave-boson representation. Finally, in order to define the propagation of
fermion modes we discuss two alternative ways to treat the fermionic sector in
the path-integral formalism for the t-J model.Comment: 27 pages, latex, no figures(to be published in Journal of Physics
A:Mathematical and General
- …