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 $\mathfrak{sl}_{2r+1}$ by introducing a $2$-category \`a la Khovanov-Lauda-Rouquier, and show that self-dual indecomposable $1$-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 $\mathcal{O}$ 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&