Determining the galactic mass distribution using tidal streams from globular clusters

We discuss how to use tidal streams from globular clusters to measure the mass distribution of the Milky Way. Recent proper motion determinations for globular clusters from plate measurements and Hipparcos astrometry provide several good candidates for Galactic mass determinations in the intermediate halo, far above the Galactic disk, including Pal 5, NGC 4147, NGC 5024 (M53) and NGC 5466; the remaining Hipparcos clusters provide candidates for measurements several kpc above and below the disk. These clusters will help determine the profile and shape of the inner halo. To aid this effort, we present two methods of mass determination: one, a generalization of rotation-curve mass measurements, which gives the mass and potential from complete position-velocity observations for stream stars; and another using a simple chi^2 estimator, which can be used when only projected positions and radial velocities are known for stream stars. We illustrate the use of the latter method using simulated tidal streams from Pal 5 and find that fairly accurate mass determinations are possible even for relatively poor data sets. Follow-up observations of clusters with proper motion determinations may reveal tidal streams; obtaining radial velocity measurements would enable accurate measurements of the mass distribution in the inner Galaxy.Comment: 21 pages, 6 figures, published in A

The growth of galaxies in cosmological simulations of structure formation

We use hydrodynamic simulations to examine how the baryonic components of galaxies are assembled, focusing on the relative importance of mergers and smooth accretion in the formation of ~L_* systems. In our primary simulation, which models a (50\hmpc)^3 comoving volume of a Lambda-dominated cold dark matter universe, the space density of objects at our (64-particle) baryon mass resolution threshold, M_c=5.4e10 M_sun, corresponds to that of observed galaxies with L~L_*/4. Galaxies above this threshold gain most of their mass by accretion rather than by mergers. At the redshift of peak mass growth, z~2, accretion dominates over merging by about 4:1. The mean accretion rate per galaxy declines from ~40 M_sun/yr at z=2 to ~10 M_sun/yr at z=0, while the merging rate peaks later (z~1) and declines more slowly, so by z=0 the ratio is about 2:1. We cannot distinguish truly smooth accretion from merging with objects below our mass resolution threshold, but extrapolating our measured mass spectrum of merging objects, dP/dM ~ M^a with a ~ -1, implies that sub-resolution mergers would add relatively little mass. The global star formation history in these simulations tracks the mass accretion rate rather than the merger rate. At low redshift, destruction of galaxies by mergers is approximately balanced by the growth of new systems, so the comoving space density of resolved galaxies stays nearly constant despite significant mass evolution at the galaxy-by-galaxy level. The predicted merger rate at z<~1 agrees with recent estimates from close pairs in the CFRS and CNOC2 redshift surveys.Comment: Submitted to ApJ, 35 pp including 15 fig

Constraints on Stirring and Dissipation of MHD Turbulence in Molecular Clouds

We discuss constraints on the rates of stirring and dissipation of MHD turbulence in molecular clouds. Recent MHD simulations suggest that turbulence in clouds decays rapidly, thus providing a significant source of energy input, particularly if driven at small scales by, for example, bipolar outflows. We quantify the heating rates by combining the linewidth-size relations, which describe global cloud properties, with numerically determined dissipation rates. We argue that, if cloud turbulence is driven on small internal scales, the $^{12}$CO flux (enhanced by emission from weakly supersonic shocks) will be much larger than observed; this, in turn, would imply excitation temperatures significantly above observed values. We reach two conclusions: (1) small-scale driving by bipolar outflows cannot possibly account for cloud support and yield long-lived clouds, unless the published MHD dissipation rates are seriously overestimated; (2) driving on large scales (comparable to the cloud size) is much more viable from an energetic standpoint, and if the actual net dissipation rate is only slightly lower than what current MHD simulations estimate, then the observationally inferred lifetimes and apparent virial equilibrium of molecular clouds can be explained.Comment: 5 pages, 1 figure. To appear in ApJ (2001 April 10

AN ANALYSIS OF COST EFFECTIVE MANAGEMENT PRACTICES TO MANAGE WATER POLLUTION PROBLEM: A CASE OF TOBESOFKEE CREEK,GEORGIA

A cost minimization model was used to find the minimum cost and environmental friendly management practices(MCEFMP). Use of MCEFMP in cattle production seems to be the most cost effective means of reducing water pollution with a marginal cost of $1200 in comparison to use of MCEFMP on other agricultural operations.Environmental Economics and Policy,

Experimental confirmation of chaotic phase synchronization in coupled time-delayed electronic circuits

We report the first experimental demonstration of chaotic phase synchronization (CPS) in unidirectionally coupled time-delay systems using electronic circuits. We have also implemented experimentally an efficient methodology for characterizing CPS, namely the localized sets. Snapshots of the evolution of coupled systems and the sets as observed from the oscilloscope confirming CPS are shown experimentally. Numerical results from different approaches, namely phase differences, localized sets, changes in the largest Lyapunov exponents and the correlation of probability of recurrence ($C_{CPR}$), corroborate the experimental observations.Comment: Physical_Review_E_82_065201(R) 201

Design and analysis of composite Leaf Spring for light Weight Vehicle

In recent year automobile industries are mostly concentrating on weight reduction and in improving the riding quality. To reduce vehicle weight, three techniques have been studied rationalizing the body structure, utilizing light weight materials for parts and decreasing the size of the vehicles. In this approach by introducing composite materials into automobile industries, which is having low cost, high strength to weight ratio and excellent corrosive resistance can fulfill the requirement. The suspension leaf spring is one of the potential entities for weight reduction in automobiles as it results in large unstrung mass. The introduction of fiber reinforced plastics (FRP) is used to reduce the weight of the product without any reduction on load carrying capacity and spring rate. As the materials high strain energy storage capacity and high strength-to-weight ratio compared to steel, multi-leaf springs are being replaced by mono-leaf FRP spring.FRP springs also have excellent fatigue resistance and durability