17,963 research outputs found
Transport of overdamped Brownian particles in a two-dimensional tube: Nonadiabatic regime
Transport of overdamped Brownian particles in a two-dimensional asymmetric
tube is investigated in the presence of nonadiabatic periodic driving forces.
By using Brownian dynamics simulations we can find that the phenomena in
nonadiabatic regime differ from that in adiabatic case. The direction of the
current can be reversed by tuning the driving frequency. Remarkably, the
current as a function of the driving amplitude exhibits several local maxima at
finite driving frequency.Comment: 10 pages, 4 figure
The Third Law of Quantum Thermodynamics in the Presence of Anomalous Couplings
The quantum thermodynamic functions of a harmonic oscillator coupled to a
heat bath through velocity-dependent coupling are obtained analytically. It is
shown that both the free energy and the entropy decay fast with the temperature
in relation to that of the usual coupling from. This implies that the
velocity-dependent coupling helps to ensure the third law of thermodynamics.Comment: 4 pages, 3 figures, 22 conference
Tree-level Split Helicity Amplitudes in Ambitwistor Space
We study all tree-level split helicity gluon amplitudes by using the recently
proposed BCFW recursion relation and Hodges diagrams in ambitwistor space. We
pick out the contributing diagrams and find that all of them can be divided
into triangles in a suitable way. We give the explicit expressions for all of
these amplitudes. As an example, we reproduce the six gluon split NMHV
amplitudes in momentum space.Comment: 20 pages, 16 figures; minor changes; clarifications added, 22 pages,
16 figure
Facilitated movement of inertial Brownian motors driven by a load under an asymmetric potential
Based on recent work [L. Machura, M. Kostur, P. Talkner, J. Luczka, and P.
Hanggi, Phys. Rev. Lett. 98, 040601 (2007)], we extend the study of inertial
Brownian motors to the case of an asymmetric potential. It is found that some
transport phenomena appear in the presence of an asymmetric potential. Within
tailored parameter regimes, there exists two optimal values of the load at
which the mean velocity takes its maximum, which means that a load can
facilitate the transport in the two parameter regimes. In addition, the
phenomenon of multiple current reversals can be observed when the load is
increased.Comment: 7 pages, 3 figure
Categorification of quantum symmetric pairs I
We categorify a coideal subalgebra of the quantum group of
by introducing a -category \`a la
Khovanov-Lauda-Rouquier, and show that self-dual indecomposable -morphisms
categorify the canonical basis of this algebra. This allows us to define a
categorical action of this coideal algebra on the categories of modules over
cohomology rings of partial flag varieties and on the BGG category
of type B/C.Comment: final version, to appear in Quantum Topolog
Radio Frequency Interference Mitigation
Radio astronomy observational facilities are under constant upgradation and
development to achieve better capabilities including increasing the time and
frequency resolutions of the recorded data, and increasing the receiving and
recording bandwidth. As only a limited spectrum resource has been allocated to
radio astronomy by the International Telecommunication Union, this results in
the radio observational instrumentation being inevitably exposed to undesirable
radio frequency interference (RFI) signals which originate mainly from
terrestrial human activity and are becoming stronger with time. RFIs degrade
the quality of astronomical data and even lead to data loss. The impact of RFIs
on scientific outcome is becoming progressively difficult to manage. In this
article, we motivate the requirement for RFI mitigation, and review the RFI
characteristics, mitigation techniques and strategies. Mitigation strategies
adopted at some representative observatories, telescopes and arrays are also
introduced. We also discuss and present advantages and shortcomings of the four
classes of RFI mitigation strategies, applicable at the connected causal
stages: preventive, pre-detection, pre-correlation and post-correlation. The
proper identification and flagging of RFI is key to the reduction of data loss
and improvement in data quality, and is also the ultimate goal of developing
RFI mitigation techniques. This can be achieved through a strategy involving a
combination of the discussed techniques in stages. Recent advances in high
speed digital signal processing and high performance computing allow for
performing RFI excision of large data volumes generated from large telescopes
or arrays in both real time and offline modes, aiding the proposed strategy.Comment: 26 pages, 10 figures, Chinese version accepted for publication in
Acta Astronomica Sinica; English version to appear in Chinese Astronomy and
Astrophysic
Discovery of Radio Emission from the Tight M8 Binary: LP 349-25
We present radio observations of 8 ultracool dwarfs with a narrow spectral
type range (M8-M9.5) using the Very Large Array at 8.5 GHz. Only the tight M8
binary LP 349-25 was detected. LP 349-25 is the tenth ultracool dwarf system
detected in radio and its trigonometric parallax pi = 67.6 mas, recently
measured by Gatewood et al., makes it the furthest ultracool system detected by
the Very Large Array to date, and the most radio-luminous outside of obvious
flaring activity or variability. With a separation of only 1.8 AU, masses of
the components of LP 349-25 can be measured precisely without any theoretical
assumptions (Forveille et al.), allowing us to clarify their fully-convective
status and hence the kind of magnetic dynamo in these components which may play
an important role to explain our detection of radio emission from these
objects. This also makes LP 349-25 an excellent target for further studies with
better constraints on the correlations between X-ray, radio emission and
stellar parameters such as mass, age, temperature, and luminosity in ultracool
dwarfs.Comment: accepted by ApJ, referee's comments included, typo in equation 1
correcte
SMA observations of the proto brown dwarf candidate SSTB213 J041757
Context. The previously identified source SSTB213 J041757 is a proto brown
dwarf candidate in Taurus, which has two possible components A and B. It was
found that component B is probably a class 0/I proto brown dwarf associated
with an extended envelope.
Aims. Studying molecular outflows from young brown dwarfs provides important
insight into brown dwarf formation mechanisms, particularly brown dwarfs at the
earliest stages such as class 0, I. We therefore conducted a search for
molecular outflows from SSTB213 J041757.
Methods. We observed SSTB213 J041757 with the Submillimeter Array to search
for CO molecular outflow emission from the source.
Results. Our CO maps do not show any outflow emission from the proto brown
dwarf candidate.
Conclusions. The non-detection implies that the molecular outflows from the
source are weak; deeper observations are therefore needed to probe the outflows
from the source.Comment: 7 pages, 4 figures, accepted for publication in A&
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