Super-rotating jets in a re-analysis of the martian atmosphere

Strong westerly, prograde jets have been identified in the martian atmosphere between about 10–20 km altitude throughout much of the year in a Mars Global Circulation Model (MGCM) study [2]. The development of data assimilation techniques for Mars [3, 5] now permits the analysis of super-rotation in less highly idealized cases using an atmospheric reanalysis, as would be done for the Earth. This paper reviews recent atmospheric reanalyses, in order to validate previous modeling results, to quantify jet amplitudes and to diagnose possible mechanisms supplying angular momentum to the jets. [2] Lewis, S. R., and Read, P. L.: Equatorial jets in the dusty martian atmosphere, J. Geophys. Res., Vol. 108 (E4), 5034, pp. 1–15, 2003. [3] Lewis, S. R., Read, P. L., Conrath, B. J., Pearl, J. C., and Smith, M. D.: Assimilation of Thermal Emission Spectrometer atmospheric data during the Mars Global Surveyor aerobraking period, Icarus, Vol. 192 (2), pp. 327–347, 2007. [5] Montabone, L., Lewis, S. R., Read, P. L., Hinson, D. P., Validation of Martian meteorological data assimilation for MGS/TES using radio occultation measurements, Icarus Vol. 185 (1), pp. 113–132, 2006

Dust-related interannual and intraseasonal variability of Martian climate using data assimilation

Data assimilation has been applied in several studies [Montabone et al., 2005; Lewis et al., 2005; Montabone et al., 2006a; Montabone et al., 2006b; Lewis et al., 2007; Wilson et al., 2008; Rogberg et al. 2010] as an effective tool with which to analyze spacecraft observations and phenomena (e.g., atmospheric tides, transient wave behavior, effects of clouds in the tropics, weather predictability, etc.) in the Martian atmosphere. A data assimilation scheme combined with a Martian Global Circulation Model (GCM) is able to provide a complete, balanced, four-dimensional solution consistent with observations. The GCM we use [Forget et al., 1999] combines a spectral dynamical solver and a tracer transport scheme developed in UK and Laboratoire de Météorologie Dynamique (LMD; Paris, France) physics package developed in collaboration with Oxford, The Open University and Instituto de Astrofisica de Andalucia (Granada, Spain). Here, we describe and discuss dust-related interannual and intraseasonal variability of the Martian climate. The results shown in this study come from a reanalysis using the Martian GCM with data assimilation scheme which assimilates Mars Global Surveyor/ Thermal Emission Spectrometer (MGS/TES) retrievals of temperature and column dust opacity. The detailed model setup was described by Montabone et al. [2006a], and the data assimilation scheme employed in this study was introduced in the work of Lewis et al. [2007]

Identifying network communities with a high resolution

Community structure is an important property of complex networks. An automatic discovery of such structure is a fundamental task in many disciplines, including sociology, biology, engineering, and computer science. Recently, several community discovery algorithms have been proposed based on the optimization of a quantity called modularity (Q). However, the problem of modularity optimization is NP-hard, and the existing approaches often suffer from prohibitively long running time or poor quality. Furthermore, it has been recently pointed out that algorithms based on optimizing Q will have a resolution limit, i.e., communities below a certain scale may not be detected. In this research, we first propose an efficient heuristic algorithm, Qcut, which combines spectral graph partitioning and local search to optimize Q. Using both synthetic and real networks, we show that Qcut can find higher modularities and is more scalable than the existing algorithms. Furthermore, using Qcut as an essential component, we propose a recursive algorithm, HQcut, to solve the resolution limit problem. We show that HQcut can successfully detect communities at a much finer scale and with a higher accuracy than the existing algorithms. Finally, we apply Qcut and HQcut to study a protein-protein interaction network, and show that the combination of the two algorithms can reveal interesting biological results that may be otherwise undetectable.Comment: 14 pages, 5 figures. 1 supplemental file at http://cic.cs.wustl.edu/qcut/supplemental.pd

Measurements of Heavy Flavor and Di-electron Production at STAR

Heavy quarks are produced early in the relativistic heavy ion collisions, and provide an excellent probe into the hot and dense nuclear matter created at RHIC. In these proceedings, we will discuss recent STAR measurements of heavy flavor production, to investigate the heavy quark interaction with the medium. Electromagnetic probes, such as electrons, provide information on the various stages of the medium evolution without modification by final stage interactions. Di-electron production measurements by STAR will also be discussed.Comment: 5 pages, 6 figures, proceedings for CPOD201

Joint Iterative Optimization Based Low-Complexity Adaptive Hybrid Beamforming for Massive MU-MIMO Systems

IEEE This paper proposes a joint iterative optimization based hybrid beamforming technique for massive MU-MIMO systems. The proposed technique jointly and iteratively optimizes the transmitter precoders and combiners, aiming to approach the global optimum solution for the system sum-rate maximization problem. The proposed technique develops an adaptive algorithm exploiting the stochastic gradients (SG) of the local beamformers and provides low-complexity closed-form solutions. Furthermore, an efficient adaptive scheme is developed based on the proposed adaptive algorithm and the closed-form solutions. The proposed algorithm requires the signal-to-interference-plus-noise ratio (SINR) feedback from each user and a limited size transition vector to be exchanged between the transmitter and receivers at each step to update beamformers locally. Analytic result shows that the proposed adaptive algorithm achieves low-complexity when the array size is large and is able to converge within a small number of iterations. Simulation result shows that the proposed technique is able to achieve superior performance comparing to the existing state-of-art techniques. In addition, the knowledge of instantaneous channel state information (CSI) is not required as the channels are also adaptively estimated with each coherence time which is a practical assumption since the CSI is usually unavailable or have time-varying nature in real-time applications

Martian atmospheric data analysis: interpreting observations from Mars Global Surveyor, Mars Reconnaissance Orbiter and Mars Trace Gas Orbiter

Data assimilation, the combination of observations and numerical models which provide physical constraints, and organize and propagate the observational information which is introduced, is commonly used as a means of analysing large atmospheric and oceanic observational data sets for the Earth and notably to form initial states for numerical weather forecasts. Data assimilation also offers significant potential advantages for the analysis of atmospheric data from other planets, which have been demonstrated by the successful assimilation of three martian years (almost six Earth years) of thermal and dust opacity observations from the Thermal Emission Spectrometer aboard Mars Global Surveyor [3]. A similar procedure is now underway with Mars Climate Sounder observations from Mars Reconnaissance Orbiter, now entering its second martian year of operations. We plan to implement the same strategy with the ExoMars Mars Climate Sounder instrument on Mars Trace Gas Orbiter, but to extend the procedure to include three-dimensional dust transport, water cloud aerosol and chemical species, as is now becoming possible with terrestrial data sets. This will enhance our understanding of the dynamics of the martian atmosphere and provide a consistent analysis over six martian years from different instruments using the same numerical model

Observation of Coherently-Enhanced Tunable Narrow-Band Terahertz Transition Radiation from a Relativistic Sub-Picosecond Electron Bunch Train

We experimentally demonstrate the production of narrow-band ($\delta f/f \simeq20$% at $f\simeq 0.5$ THz) THz transition radiation with tunable frequency over [0.37, 0.86] THz. The radiation is produced as a train of sub-picosecond relativistic electron bunches transits at the vacuum-aluminum interface of an aluminum converter screen. We also show a possible application of modulated beams to extend the dynamical range of a popular bunch length diagnostic technique based on the spectral analysis of coherent radiation.Comment: 3 pages, 6 figure

Large exchange bias after zero-field cooling from an unmagnetized state

Exchange bias (EB) is usually observed in systems with interface between different magnetic phases after field cooling. Here we report an unusual phenomenon in which a large EB can be observed in Ni-Mn-In bulk alloys after zero-field cooling from an unmagnetized state. We propose this is related to the newly formed interface between different magnetic phases during the initial magnetization process. The magnetic unidirectional anisotropy, which is the origin of EB effect, can be created isothermally below the blocking temperature.Comment: including supplementary information, Accepted by Physical Review Letter