Analysis of motion of solid hydrogen tracer particles in oscillating superfluid flows

We have developed a relatively simple cryostat which allows us to image turbulent flows in superfluid helium at temperatures below 2 K, using frozen H2 particles. We analyze the statistics of the velocities of these solid tracers, which follow the turbulent flow generated by oscillating bodies. We have also studied one of the oscillators working in air at room temperature, and traced the flow with solid talcum particles for comparison. Images were recorded by a digital camera at 240 frames per second, while frequencies of the oscillators are between 20 to 45 Hz. The flow is characterized by a modified Reynolds number Reδ based on the viscous penetration depth δ. Software in a dedicated particle tracking velocimetry code allows us to compute the trajectories and velocities of tens of thousands of particles. We have obtained the number of particles for equally spaced intervals of the velocity modulus. For the oscillators in the superfluid, the probability of finding particles at higher velocities has an exponential decay. Within our resolution the statistics in the superfluid for oscillating objects with sharp borders is largely independent of Reδ, while the logarithmic decay at low velocities seems faster than for high velocities for rounded objects. On the other hand, for data taken in air the result is closer to a classical Gaussian distribution of velocities.Fil: Zemma, Elisa María. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Luzuriaga, J.. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Babuin, S.. Czech Academy of Sciences. Institute of Physics; República Chec

Impact of photometric variability on age and mass determination of Young Stellar Objects: A case study on Orion Nebula Cluster

In case of pre-main sequence objects, the only way to determine age and mass is by fitting theoretical isochrones on color-magnitude (alternatively luminosity-temperature) diagrams. Since young stellar objects exhibit photometric variability over wide range in magnitude and colors, the age and mass determined by fitting isochrones is expected to be inaccurate, if not erroneous. These in turn will badly affect any study carried out on age spread and process of star formation. Since we have carried out very extensive photometric observations of the Orion Nebula Cluster (ONC), we decided to use our multi-band data to explore the influence of variability in determining mass and age of cluster members. In this study, we get the amplitudes of the photometric variability in V, R, and I optical bands of a sample of 346 ONC members and use it to investigate how the variability affects the inferred masses and ages and if it alone can take account for the age spread among the ONC members reported by earlier studies. We find that members that show periodic and smooth photometric rotational modulation have their masses and ages unaffected by variability. On other hand, we found that members with periodic but very scattered photometric rotational modulation and members with irregular variability have their masses and ages significantly affected. Moreover, using Hertzsprung-Russell (HR) diagrams we find that the observed I band photometric variability can take account of only a fraction (about 50%) of the inferred age spread, whereas the V band photometric variability is large enough to mask any age spread.Comment: Accepted by MNRAS; 17 pages, 4 Tables, 15 Figure

Interactions of cosmological gravitational waves and magnetic fields

The energy momentum tensor of a magnetic field always contains a spin-2 component in its anisotropic stress and therefore generates gravitational waves. It has been argued in the literature (Caprini & Durrer \cite{CD}) that this gravitational wave production can be very strong and that back-reaction cannot be neglected. On the other hand, a gravitational wave background does affect the evolution of magnetic fields. It has also been argued (Tsagas et al. \cite{Tsagas:2001ak},\cite{Tsagas:2005ki}) that this can lead to very strong amplification of a primordial magnetic field. In this paper we revisit these claims and study back reaction to second order.Comment: Added references, accepted for publication in PR

Ten Economic Facts About Crime and Incarceration in the United States

Crime and high rates of incarceration impose tremendous costs on society, with lasting negative effects on individuals, families, and communities. Rates of crime in the United States have been falling steadily, but still constitute a serious economic and social challenge. At the same time, the incarceration rate in the United States is so high -- more than 700 out of every 100,000 people are incarcerated -- that both crime scholars and policymakers alike question whether, for nonviolent criminals in particular, the social costs of incarceration exceed the social benefits

Leveraged Buyouts: Opportunities and Risks

This article presents a general overview of leveraged buyouts, relating their feasibility as an option for hospitality management. Specifically, the author explores the background and main features of leveraged buyouts, focusing attention on their risks and rewards, management\u27s opportunities, tax ramifications, planning, and future outlook. Denny\u27s leveraged buyout is examined in order to provide an insight into the structuring of a buyout for a major food service firm

An Examination of Stock Performance: The Three Top-Performing Lodging Firms August 1987 - January 1990

A study published in the Fall 1988 issue of the FIU Hospitality Review revealed that the top three lodging stock performers during the period July 1982 to January 1988 were Prime Motor Inns, Inc., Marriott Corporation, and Hilton Hotels Corporation. The author has completed a follow-up study in an attempt to determine how selected lodging firms have fared since the summer rally of 1987 (which preceded the stock crash of October 19, 1987) until more recent times