Beltway: Getting Around Garbage Collection Gridlock

We present the design and implementation of a new garbage collection framework that significantly generalizes existing copying collectors. The Beltway framework exploits and separates object age and incrementality. It groups objects in one or more increments on queues called belts, collects belts independently, and collects increments on a belt in first-in-first-out order. We show that Beltway configurations, selected by command line options, act and perform the same as semi-space, generational, and older-first collectors, and encompass all previous copying collectors of which we are aware. The increasing reliance on garbage collected languages such as Java requires that the collector perform well. We show that the generality of Beltway enables us to design and implement new collectors that are robust to variations in heap size and improve total execution time over the best generational copying collectors of which we are aware by up to 40%, and on average by 5 to 10%, for small to moderate heap sizes. New garbage collection algorithms are rare, and yet we define not just one, but a new family of collectors that subsumes previous work. This generality enables us to explore a larger design space and build better collectors

Gaugino condensation in an improved heterotic M-theory

Gaugino condensation is discussed in the context of a consistent new version of low energy heterotic M-theory. The four dimensional reduction of the theory is described, based on simple boson and fermion backgrounds. This is generalised to include gaugino condenstates and various background fluxes, some with non-trivial topology. It is found that condensate and quantised flux contributions to the four-dimensional superpotential contain no corrections due to the warping of the higher dimensional metric.Comment: 11 pages, 4 figures, LaTe

QUANTIFYING GAINS TO RISK DIVERSIFICATION USING CERTAINTY EQUIVALENCE IN A MEAN-VARIANCE MODEL: AN APPLICATION TO FLORIDA CITRUS

The marginal benefit and cost of diversification for Florida orange producers is analyzed using certainty equivalents. Results indicate that for moderate and high levels of risk aversion, diversification into strawberry, grapefruit, or additional orange production is not optimal. However, moderately risk averse Florida orange producers can gain by diversifying into grapefruit production if the annual amortized fixed costs can be reduced by as little as 10 percent.Risk and Uncertainty,

Simulating Male Selfish Strategy in Reproduction Dispute

We introduce into the Penna Model for biological ageing one of the possible male mechanisms used to maximize the ability of their sperm to compete with sperm from other males. Such a selfish mechanism increases the male reproduction success but may decrease the survival probability of the whole female population, depending on how it acts. We also find a dynamic phase transition induced by the existence of an absorbing state where no selfish males survive.Comment: 7 pages, latex including 2 eps figure

General dissipation coefficient in low-temperature warm inflation

In generic particle physics models, the inflaton field is coupled to other bosonic and fermionic fields that acquire large masses during inflation and may decay into light degrees of freedom. This leads to dissipative effects that modify the inflationary dynamics and may generate a nearly-thermal radiation bath, such that inflation occurs in a warm rather than supercooled environment. In this work, we perform a numerical computation and obtain expressions for the associated dissipation coefficient in supersymmetric models, focusing on the regime where the radiation temperature is below the heavy mass threshold. The dissipation coefficient receives contributions from the decay of both on-shell and off-shell degrees of freedom, which are dominant for small and large couplings, respectively, taking into account the light field multiplicities. In particular, we find that the contribution from on-shell decays, although Boltzmann-suppressed, can be much larger than that of virtual modes, which is bounded by the validity of a perturbative analysis. This result opens up new possibilities for realizations of warm inflation in supersymmetric field theories.Comment: 25 pages, 13 figures; revised version with new results added; published in JCA

Electronic Cigarette Use and Associated Risk Factors in U.S.-Dwelling Pacific Islander Young Adults.

Background: E-cigarette use is rapidly increasing among US young adults, heightening their risk for vaping-related illnesses. Yet, little is known about e-cigarette use among young adult Native Hawaiians and Pacific Islanders (NHPI): an indigenous-colonized US racial group rarely described in research literature. This exploratory study provides the first known data on e-cigarette use and potential risk factors in NHPI young adults. Method: Self-report data were collected from 143 NHPI young adults (age 18-30 years) living in two large NHPI communities: Samoans in urban Los Angeles County and Marshallese in rural Arkansas. We assessed rates of e-cigarette, cigarette, alcohol, and marijuana use, and positive and negative outcome expectancies from e-cigarettes, that is expected outcomes from e-cigarette use. To identify potential risk factors for NHPI e-cigarette use, regressions explored associations between participants' current e-cigarette use with current cigarette, alcohol, and marijuana use, and e-cigarette outcome expectancies. Results: Among NHPI young adults, lifetime e-cigarette use rate was 53% and current use rate was 39%. Current rate of dual e-cigarette/cigarette, e-cigarette/alcohol, and e-cigarette/marijuana use was 38%, 35%, and 25%, respectively. In our regression models, current marijuana use and positive e-cigarette outcome expectancies were significantly associated with current e-cigarette use. Conclusions: E-cigarette use is common among NHPI young adults, exceeding rates for other at-risk racial groups. Marijuana use and positive expectations about e-cigarette use may represent potential e-cigarette use risk factors. Collectively, findings underscore the need for additional research to further explore the scope of, and risk and protective factors for, e-cigarette use in this understudied high-risk population

Improved TPB-coated Light Guides for Liquid Argon TPC Light Detection Systems

Scintillation light produced in liquid argon (LAr) must be shifted from 128 nm to visible wavelengths in light detection systems used for liquid argon time-projection chambers (LArTPCs). To date, LArTPC light collection systems have employed tetraphenyl butadiene (TPB) coatings on photomultiplier tubes (PMTs) or plates placed in front of the PMTs. Recently, a new approach using TPB-coated light guides was proposed. In this paper, we report on light guides with improved attenuation lengths above 100 cm when measured in air. This is an important step in the development of meter-scale light guides for future LArTPCs. Improvements come from using a new acrylic-based coating, diamond-polished cast UV transmitting acrylic bars, and a hand-dipping technique to coat the bars. We discuss a model for connecting bar response in air to response in liquid argon and compare this to data taken in liquid argon. The good agreement between the prediction of the model and the measured response in liquid argon demonstrates that characterization in air is sufficient for quality control of bar production. This model can be used in simulations of light guides for future experiments.Comment: 25 pages, 20 figure

How astrophysical mean field dynamos can circumvent existing quenching constraints

Mean field dynamo theory is a leading candidate to explain the observed large scale magnetic fields of galaxies and stars. However, controversy arises over the extent of premature quenching by the backreaction of the growing field. We distinguish between rapid mean field dynamo action, which is required by astrophysical systems, and resistively limited action. We show how the flow of magnetic helicity is important for rapid action. Existing numerical and analytic work suggesting that mean field dynamos are prematurely quenched and resistively limited include approximations or boundary conditions which suppress the magnetic helicity flow from the outset. Thus they do not unambiguously reveal whether real astrophysical mean field dynamos are dynamically suppressed when the helicity flow is allowed. An outflow of helicity also implies an outflow of magnetic energy and so active coronae or winds should accompany mean field dynamos. Open boundaries alone may not be sufficient for rapid dynamo action and the additional physics of buoyancy and outflows may be required. Possible simulation approaches to test some of the principles are briefly discussed. Some limitations of the ``Zeldovich relation'' are also addressed.Comment: 19 pages LaTex, invited submission to Physics of Plasmas, APS/DPP Quebec 2000 Meeting Proceeding

Mobility gap in intermediate valent TmSe

The infrared optical conductivity of intermediate valence compound TmSe reveals clear signatures for hybridization of light $d$- and heavy f-electronic states with m* ~ 1.6 m_0 and m* ~ 16 m_0, respectively. At moderate and high temperatures, the metal-like character of the heavy carriers dominate the low-frequency response while at low temperatures (T_N < T < 100 K) a gap-like feature is observed in the conductivity spectra below 10 meV which is assigned to be a mobility gap due to localization of electrons on local Kondo singlets, rather than a hybridization gap in the density of states