LGS AO Science Impact: Present and Future Perspectives

The recent advent of laser guide star adaptive optics (LGS AO) on the largest ground-based telescopes has enabled a wide range of high angular resolution science, previously infeasible from ground-based and/or space-based observatories. As a result, scientific productivity with LGS has seen enormous growth in the last few years, with a factor of ~10 leap in publication rate compared to the first decade of operation. Of the 54 refereed science papers to date from LGS AO, half have been published in the last ~2 years, and these LGS results have already made a significant impact in a number of areas. At the same time, science with LGS AO can be considered in its infancy, as astronomers and instrumentalists are only beginning to understand its efficacy for measurements such as photometry, astrometry, companion detection, and quantitative morphology. We examine the science impact of LGS AO in the last few years of operations, largely due to the new system on the Keck II 10-meter telescope. We review currently achieved data quality, including results from our own ongoing brown dwarf survey with Keck LGS. We assess current and near-future performance with a critical eye to LGS AO's capabilities and deficiencies. From both qualitative and quantitative considerations, it is clear that the era of regular and important science from LGS AO has arrived.Comment: Invited review for Proc of the SPIE, "Astronomical Telescopes and Instrumentation" (Marseilles, France, June 2008). Minor typos fixed, upgrade to Figure 3, and addition of new Gemini LGS wor

Natural sounds : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy at Massey University

Natural sounds, as one of the most important resources of nature, have attracted attention from many researchers. Although, psychological approaches, acoustical approaches and psychoacoustical approaches have been employed on the research of natural sounds, not many analytical investigations have been conducted on specific natural sounds except for the biological natural sounds. The aim of this study is to present the properties and reveal the generation mechanisms of the selected natural sounds. This thesis concentrated on studying the characteristics of various specific natural sounds by acoustical approach. Field recording has been mainly adopted for the collection of sound samples. For the selected samples, computational analyses were conducted to investigate the attributes of the sounds. Sound signatures including waveform, frequency spectrum and sonogram were displayed to visualize the analyzed signals. The generation mechanisms were reviewed and discussed to reveal the variables that contribute to the sound characteristics. Sound samples including cavity wind sound, aeolian sound, wind sound through vegetation, thunder clap, thunder rumble, thunder crack, plunging breaker sound, spilling breaker sound, rock wave sound, boiling mud pot sound, geyser eruption sound, fumaroles eruption sound and different bubble sounds were selected and analyzed to reveal their properties

Simultaneous inversion of mantle properties and initial conditions using an adjoint of mantle convection

Through the assimilation of present-day mantle seismic structure, adjoint methods can be used to constrain the structure of the mantle at earlier times, i.e., mantle initial conditions. However, the application to geophysical problems is restricted through both the high computational expense from repeated iteration between forward and adjoint models and the need to know mantle properties (such as viscosity and the absolute magnitude of temperature or density) a priori. We propose that an optimal first guess to the initial condition can be obtained through a simple backward integration (SBI) of the governing equations, thus lessening the computational expense. Given a model with known mantle properties, we show that a solution based on an SBI-generated first guess has smaller residuals than arbitrary guesses. Mantle viscosity and the effective Rayleigh number are crucial for mantle convection models, neither of which is exactly known. We place additional constraints on these basic mantle properties when the convection-induced dynamic topography on Earth's surface is considered within an adjoint inverse method. Besides assimilating present-day seismic structure as a constraint, we use dynamic topography and its rate of change in an inverse method that allows simultaneous inversion of the absolute upper and lower mantle viscosities, scaling between seismic velocity and thermal anomalies, and initial condition. The theory is derived from the governing equations of mantle convection and validated by synthetic experiments for both one-layer viscosity and two-layer viscosity regionally bounded spherical shells. For the one-layer model, at any instant of time, the magnitude of dynamic topography is controlled by the temperature scaling while the rate of change of topography is controlled by the absolute value of viscosity. For the two-layer case, the rate of change of topography constrains upper mantle viscosity while the magnitude of dynamic topography determines the temperature scaling (lower mantle viscosity) when upper-mantle (lower-mantle) density anomaly dominates the flow field; this two-stage scheme minimizes the tradeoff between temperature and lower mantle viscosity. For both cases, we show that the theory can constrain mantle properties with errors arising through the adjoint recovery of the initial condition; for the two-layer model, this error is manifest as a tradeoff between the temperature scaling and lower mantle viscosity

A unified theory of calcium alternans in ventricular myocytes.

Intracellular calcium (Ca2+) alternans is a dynamical phenomenon in ventricular myocytes, which is linked to the genesis of lethal arrhythmias. Iterated map models of intracellular Ca2+ cycling dynamics in ventricular myocytes under periodic pacing have been developed to study the mechanisms of Ca2+ alternans. Two mechanisms of Ca2+ alternans have been demonstrated in these models: one relies mainly on fractional sarcoplasmic reticulum Ca2+ release and uptake, and the other on refractoriness and other properties of Ca2+ sparks. Each of the two mechanisms can partially explain the experimental observations, but both have their inconsistencies with the experimental results. Here we developed an iterated map model that is composed of two coupled iterated maps, which unifies the two mechanisms into a single cohesive mathematical framework. The unified theory can consistently explain the seemingly contradictory experimental observations and shows that the two mechanisms work synergistically to promote Ca2+ alternans. Predictions of the theory were examined in a physiologically-detailed spatial Ca2+ cycling model of ventricular myocytes

The propagation of Elastic Waves in Granular Solid Hydrodynamics

The anisotropic, stress-dependent velocity of elastic waves in glass beads -- as observed by Y. Khidas and X. Jia, see [Phys. Rev. E, 81:021303, Feb. 2010] -- is shown to be well accounted for by ``granular solid hydrodynamics,'' a broad-range macroscopic theory of granular behavior. As the theory makes no reference to fabric anisotropy, the influence of which on sound is in doubt.Comment: 4 pages, 1 fi

Geometric finiteness in negatively pinched Hadamard manifolds

In this paper, we generalize Bonahon's characterization of geometrically infinite torsion-free discrete subgroups of PSL(2, $\mathbb{C}$) to geometrically infinite discrete subgroups $\Gamma$ of isometries of negatively pinched Hadamard manifolds $X$. We then generalize a theorem of Bishop to prove that every discrete geometrically infinite isometry subgroup $\Gamma$ has a set of nonconical limit points with the cardinality of the continuum.Comment: We improved our results to any discrete geometrically infinite isometry subgroup of a negatively pinched Hadamard manifold, and we sharpened our main results to deal with limit sets of ends of the convex cor

The Rise of Asian-Owned Businesses in Massachusetts

Asian-owned businesses are following a very rapid growth trajectory in Massachusetts. In the last economic census from 1997 to 2002, they increased by 44 percent. This growth is nearly double the national gain of 24 percent for all Asian-owned firms in the United States and astounding when compared to the overall growth rate of 5 percent for all Massachusetts firms. Sales and receipts increased 20 percent in the same period, three times greater than the increase for all firms in the state. The growth in the number of paid employees was also three times greater than the six percent increase for all firms in Massachusetts. By 2002, there were 18,081 Asian-owned firms with sales and receipts of $5 billion and employing over 37,000 people. Professional, scientific and technical services had the largest annual payroll, followed by accomonations/food services, health care and retail trade. Whether as publishers, developers of healing and wellness centrs or as hair salon owners, Asian Americans in these businesses, and in countless other entrepreneurial pursuits, are changing the face of business ownership in the Bay State