Constrained dynamics of localized excitations causes a non-equilibrium phase transition in an atomistic model of glass formers

Dynamic facilitation theory assumes short-ranged dynamic constraints to be the essential feature of supercooled liquids and draws much of its conclusions from the study of kinetically constrained models. While deceptively simple, these models predict the existence of trajectories that maintain a high overlap with their initial state over many structural relaxation times. We use molecular dynamics simulations combined with importance sampling in trajectory space to test this prediction through counting long-lived particle displacements. For observation times longer than the structural relaxation time exponential tails emerge in the probability distribution of this number. Reweighting trajectories towards low mobility corresponds to a phase transition into an inactive phase. While dynamics in these two phases is drastically different structural measures show only slight differences. We discuss the choice of dynamic order parameter and give a possible explanation for the microscopic origin of the effective dynamic constraints.Comment: revised versio

Velocity-ion temperature gradient driven modes and angular momentum transport in magnetically confined plasmas

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2007.Includes bibliographical references (p. 41-42).Plasma confinement experiments continue to uncover fascinating phenomena that motivate theoretical discussion and exploration. In this thesis, we consider the phenomenon of angular momentum transport in magnetically confined plasmas. Relevant experiments and theoretical developments are presented in order to motivate the derivation of a modified version of the three-field nonlinear Hamaguchi-Horton equations. The equations are altered to include a zeroth-order parallel velocity inhomogeneity along the radially-analogous coordinate, resulting in a nonlinear system that describes the evolution of the velocity-ion temperature gradient-driven modes (VITGs). The equations are used to analyze VITG modes in the local approximation of a magnetized plasma, as well as in an inhomogeneous slab model. Applying quasilinear methods, we find a turbulent angular momentum flux in agreement with the accretion theory of the spontaneous rotation phenomenon. More advanced applications are considered for future analysis.by John Chandler Thomas.S.B

The Incorporation of GIS Technologies in Emergency Preparedness and Response

Public health agencies make decisions that have far reaching consequences, and geography impacts these decisions on a daily basis. Geographic information systems (GIS) are powerful computer software programs which can enable agency staff to visualize spatial information in new ways, so that they can become better planners and problem solvers, particularly in the areas of disaster preparedness and response (Chang, 2002). Yet, although GIS is becoming more well-known, it is still a technology in its infancy, with the majority of public health staff not gaining all of the competencies required to utilize it effectively in the workplace. Although several departments within an agency, such as epidemiology and city planners, are often leveraging this technology, there are many other staff involved in disaster preparedness and response who are not using it, but who may need to in the upcoming months (Blanco & Mathur, 2005)

The Incorporation of GIS Technologies in Emergency Preparedness and Response

Public health agencies make decisions that have far reaching consequences, and geography impacts these decisions on a daily basis. Geographic information systems (GIS) are powerful computer software programs which can enable agency staff to visualize spatial information in new ways, so that they can become better planners and problem solvers, particularly in the areas of disaster preparedness and response (Chang, 2002). Yet, although GIS is becoming more well-known, it is still a technology in its infancy, with the majority of public health staff not gaining all of the competencies required to utilize it effectively in the workplace. Although several departments within an agency, such as epidemiology and city planners, are often leveraging this technology, there are many other staff involved in disaster preparedness and response who are not using it, but who may need to in the upcoming months (Blanco & Mathur, 2005)

Advisor Induced demand and Moral Hazard in the Third-Party Payor System

Health-care consumption in the United States has risen from 5.2% in 1960 to 17.8% of 2009 Gross Domestic Product (GDP) creating a burden that will soon be too heavy for the economy to bear. This paper proposes that the primary accelerants of health-care expenditures result from the third-party payer system that emerged in the 1950s. These corporate benefits and government subsidies, when overlaid on the traditional health-care model, have led to sustained increases in the production, recommendation, and consumption of health care while magnifying the moral hazard problem inherent in health insurance

Administrative variables affecting student retention in foreign languages in California public high schools

The primary purpose of this study is to investigate administrative policies and practices which appear to be most effective in maintaining high pupil retention in foreign language programs. More narrowly, to accomplish the primary and secondary purposes it will be necessary to establish criteria with the use of survey instruments by which administrative practices of foreign language instruction may be evaluated

Static and Dynamic Coefficient Measurements for a Thrust Collar Used in an Integrally Geared Compressor

Test rigs that replicate the conditions for thrust collars (TCs) used in an integrally geared compressor (IGC) are scarce. The test rig described here is based on a typical IGC and is the first rig specifically designed to measure the dynamic reaction force coefficients of the lubricated area of the TC. The test rig uses low-speed and high-speed shafts with independently controlled speed and a pneumatically pressurized thrust disk to apply an axial load ???v?? to create the hydrodynamic wedge that balances the imposed axial load. The speed ratio between the low-speed shaft (LSS) and the pinion shaft is 11.67. The geometry of the shafts matches that of a typical IGC. Tests were conducted at pinion speeds of 5, 7.5, and 10 krpm and ???v?? = 200, 300, and 400 N. The resulting range of applied pressures is smaller than those arising in practice. The author conducts static tests by applying an incrementally-increasing ??v?? on the pinion shaft and measuring the relative displacement between the BG and the TC (??v??). One test is conducted at each predetermined spin speed. Run-out on the TC as well as the BW obscures the data. Averaging works well to eliminate the effects of run-out. The author uses the averaged ???v?? and ??v?? values to create a static, load/ relative displacement curve and the slope is the measured static stiffness coefficient (???v?? ). The axial stiffness coefficient results are compared to predictions from a code based on a 2016 model due to Cable et. al. Their dynamic reaction-force model is ??v???? = ???v???v?? – ??v???v?? where ?????? is the reaction force of the TC, and ???? is the axial damping coefficient. The trends and the magnitudes of the measured ???v?? values and the predicted values from San Andres code for ??v?? agree very well, especially for the 5 krpm test case. The author then conducts dynamic tests involving an applied impulse load to the TC shaft. One hundred impulses are conducted at each spin speed (??), ???v?? test condition for averaging purposes. A one degree of freedom damped motion model uses ?v??(??) measurements to determine the damped natural frequency (????) and damping factor (??) for each test point. The thrust collar mass ??v???? and the measured ?? were then used to calculate ??v?? and ??v?? . The ???? values obtained in this fashion were consistently (and markedly) smaller than the static ???v?? values. Based on the results, the author uses the following model ??v???? = ???v???v?? ? ??v???v?? ? ? ??v????v?? that includes the virtual-mass coefficient (??v??). The Cable et al. model was based on the Reynolds equation and accordingly did not produce a virtual-mass term. The ??v?? term is calculated for each test point using ???v?? , ??v??, and ??. ??v?? increases as a function ?? and ???v?? . It ranges from 0 to 19.5 kg; the mass of the pinion shaft is 12.8 kg. Both predictions and measurements show an increase in ??v?? with increasing ???v?? . The test rig produced damping coefficients that increased for increasing ??, while the predicted values decreased. The magnitude of ??v?? was lower than the predicted damping by a factor of 2 - 10

Responses of Holstein calves to dietary calcium, phosphorus, and vitamin D3 using response surface techniques

The metabolism of calcium, phosphorus, and vitamin D has been a classical topic of nutrition studies through the past fifty years. Many experiments have been conducted to determine the relationship of calcium, phosphorus, and vitamin D in the animal body. All results have led to the conclusion that vitamin D will affect the absorption and/or retention of calcium and phosphorus, and the amount of calcium will affect calcium and phosphorus metabolism. However, the effect of the dietary level of phosphorus has been questioned (1, 56, 65, 69). The chemistry and site of the majority of these actions is still to a great extent unknown. The usual procedure for studying a problem of this type is to hold two of the factors constant and vary the third. Information obtained from studies of this type is limited in that it relates to only one set of conditions. A mathematical description of responses as related to any dietary combination within limits of calcium, phosphorus, and vitamin D would be desirable. The primary objective of this study was to quantitatively relate calcium, phosphorus, and vitamin D over a comparatively wide range of each and to determine the dietary combinations for maximum absorption, retention, and growth in the dairy calf. A secondary objective was to check the validity of mathematical techniques in describing biological systems