Plasma-based Control of Supersonic Nozzle Flow

The flow structure obtained when Localized Arc Filament Plasma Actuators (LAFPA) are employed to control the flow issuing from a perfectly expanded Mach 1.3 nozzle is elucidated by visualizing coherent structures obtained from Implicit Large-Eddy Simulations. The computations reproduce recent experimental observations at the Ohio State University to influence the acoustic and mixing properties of the jet. Eight actuators were placed on a collar around the periphery of the nozzle exit and selectively excited to generate various modes, including first and second mixed (m = +/- 1 and m = +/- 2) and axisymmetric (m = 0). In this fluid dynamics video http://ecommons.library.cornell.edu/bitstream/1813/13723/2/Alljoinedtotalwithmodetextlong2-Datta%20MPEG-1.m1v, http://ecommons.library.cornell.edu/bitstream/1813/13723/3/Alljoinedtotalwithmodetextlong2-Datta%20MPEG-2.m2v}, unsteady and phase-averaged quantities are displayed to aid understanding of the vortex dynamics associated with the m = +/- 1 and m = 0 modes excited at the preferred column-mode frequency (Strouhal number 0.3). The unsteady flow in both contains a broad spectrum of coherent features. For m = +/- 1, the phase-averaged flow reveals the generation of successive distorted elliptic vortex rings with axes in the flapping plane, but alternating on either side of the jet axis. This generates a chain of structures where each interacts with its predecessor on one side and its successor on the other. Through self and mutual interaction, the leading segment of each loop is pinched and passes through the previous ring before rapidly breaking up, and the mean jet flow takes on an elliptic shape. The m = 0 mode exhibits relatively stable roll-up events, with vortex ribs in the braid regions connecting successive large coherent structures.Comment: 3 pages. Video submission to Gallery of Fluid Motion, American Physical Society, Division of Fluid Dynamics, 62nd Annual Meeting, November 22-24, 2009, Minneapolis, MN. Replacement deletes TeX commands to correct web link

Dissipative Phase Fluctuations In A Superconductor In Proximity To An Electron Gas

We study a two-dimensional superconductor in close proximity to a two-dimensional metallic sheet. The electrons in the superconducting sheet are coupled to those in the metallic sheet by the Coulomb interaction only. We obtain an effective phase-only action for the superconductor by integrating out all the electronic degrees of freedom in the problem. The Coulomb drag of the normal electrons in the metallic sheet is found to make the spectrum of phase-fluctuations in the superconductor, dissipative at long wavelengths. The dissipative co-efficient $\eta$ is shown to be simply related to the normal state conductivities of the superconducting layer ($\sigma_S$)and the metallic sheet ($\sigma_E$) by the relation $\eta \propto {\sigma_S\sigma_E\over \sigma_S+\sigma_E}$.Comment: 11 pages; To appear in Int. Jour. of Mod. Phys.

Individual Perceptions of Meaning in Life and Meaninglessness

Much research has been conducted to define meaning in life and identify its correlates, but the construct of meaninglessness is not as well understood. Are meaning and meaninglessness perceived as part of the same spectrum? How exactly do individuals define these terms? Thus, the primary purpose of this study is to compare and contrast what people think of and associate with meaning and meaninglessness. Furthermore, we explore the possibility that individuals with similar beliefs and ideas may also perceive meaning in life in a similar way. For this study, participants (n = 209) were administered an online questionnaire composed of items assessing meaning in life, values, religiousness, risk for depression, political ideation, and socioeconomic status. Additionally, participants were given an open-ended prompt to discuss their interpretation of either meaning or meaninglessness. These responses were then coded to find common themes in individual perceptions of meaning and meaninglessness, and these themes were analyzed to find possible correlations with participants' responses on the questionnaire. With these findings, we can better understand the phenomenon of meaninglessness

Performance investigation of a document retrieval system on a voice-data integrated token ring local area network

Lately, the interest in integration of voice and data on local computer networks has been on the rise. Subsequently, much research has been devoted to exploring various techniques that are implementable using the existing standards. This research has focused on the design issues in implementing a document retrieval system on a token ring network. The presence of voice and data traffic on the network complicates the protocol design further. The performance requirements of these traffic types are different. Voice creates stream traffic on a network, where as data traffic is bursty. Voice packets need to be delivered within a limited time interval, whereas the data emphasizes on error-free delivery. The necessity and the technological feasibility with off-the-shelf components has prompted this study. A possible solution is discussed in this dissertation;During the course of this research, due to the time consuming nature of simulation experiments, a need for efficient simulation techniques was felt. Thus, as a byproduct of the initial goal of protocol design, an approximate version of the regenerative simulation was developed and is discussed here in detail;Lastly, modeling difficulties encountered in forming an analytical model are listed and a performance analysis of the subsystems of interest is given

Corruption – Taking a Deeper Dive; Comment on “We Need to Talk About Corruption in Health Systems”

This commentary while agreeing broadly with the points raised by the editorial by McKee et al, seeks to broaden and deepen those arguments. The commentary contends that unless we understand corruption as deeply embedded in and propping up systems of power differentials, we will not be able to design interventions that will tackle corruption at its roots. The commentary further points to the context specific nature of corruption and hence the futility of attempting a single definition. This it contends will merely hide the deeper context specific causes. It calls for the using theoretical insights that draw from post-positivist approaches to enhance the conceptualization of corruption as systemic. Further it points to the importance of the underlying problematization of corruption in attempts to tackle it. It ends with a call for attempts at multiple levels with the broader aim of evolving caring and just systems of healthcare rather than focusing on narrow ‘politically feasible’ interventions

Fluctuation Effects And Order Parameter Symmetry In The Cuprate Superconductors

Effect of phase fluctuations on superconducting states with anisotropic order parameters is studied in a BCS like lattice model of cuprate superconductors. The degradation of the mean field transition temperature due to phase fluctuations is estimated within a Kosterlitz-Thouless scenario. Values of the interaction parameters for optimal doping, corresponding to a stable superconducting state of $S_{xy}$ symmetry, which fit the nodal structure of the superconducting order parameter in the Bi2212 compound, are obtained. The angular position of the node is found to be insensitive to the dopant concentration.Comment: Latex file, 8 output pages, 5 figures (available from Authors on request), to appear in Europhysics Letter

A Unified Approach to Learning Ising Models: Beyond Independence and Bounded Width

We revisit the problem of efficiently learning the underlying parameters of Ising models from data. Current algorithmic approaches achieve essentially optimal sample complexity when given i.i.d. samples from the stationary measure and the underlying model satisfies "width" bounds on the total $\ell_1$ interaction involving each node. We show that a simple existing approach based on node-wise logistic regression provably succeeds at recovering the underlying model in several new settings where these assumptions are violated: (1) Given dynamically generated data from a wide variety of local Markov chains, like block or round-robin dynamics, logistic regression recovers the parameters with optimal sample complexity up to $\log\log n$ factors. This generalizes the specialized algorithm of Bresler, Gamarnik, and Shah [IEEE Trans. Inf. Theory'18] for structure recovery in bounded degree graphs from Glauber dynamics. (2) For the Sherrington-Kirkpatrick model of spin glasses, given $\mathsf{poly}(n)$ independent samples, logistic regression recovers the parameters in most of the known high-temperature regime via a simple reduction to weaker structural properties of the measure. This improves on recent work of Anari, Jain, Koehler, Pham, and Vuong [ArXiv'23] which gives distribution learning at higher temperature. (3) As a simple byproduct of our techniques, logistic regression achieves an exponential improvement in learning from samples in the M-regime of data considered by Dutt, Lokhov, Vuffray, and Misra [ICML'21] as well as novel guarantees for learning from the adversarial Glauber dynamics of Chin, Moitra, Mossel, and Sandon [ArXiv'23]. Our approach thus significantly generalizes the elegant analysis of Wu, Sanghavi, and Dimakis [Neurips'19] without any algorithmic modification.Comment: 51 page