Piezoelectric copolymer hydrophones for ultrasonic field characterization

Hydrophones to be used in the characterization of medical ultrasonic transducers have been fabricated using a new polyvinylidene fluoride/trifluoroethylene (VF2/VF3) copolymer. The copolymer has an advantage over VF2 in that it does not require prestretching before poling. Thin copolymer films can be cast from solution and then poled using the corona discharge method. As there is a need for small‐diameter hydrophones to provide good spatial resolution in measuring highly focused ultrasonic beams, hydrophones with diameter as small as 0.1 mm have been made. Both needle‐type and line hydrophones have been tested and their performance reported. In the case of line hydrophones, the output signal is proportional to the line integral of the acoustic pressure and a computer tomographic technique has been used to reconstruct the beam profiles

An In-Depth Examination of a Thermodynamic Framework for the Phase-Field Crystal Model.

In this dissertation, we examine the phase-field crystal (PFC) model, which is a simulation method for modeling atomistic phenomena on diffusive time scales. We develop thermodynamic relationships that are used to derive procedures for calculating equilibrium material properties from the PFC model. The first set of relationships links the PFC free energy to thermodynamic state variables and are based on the thermodynamic formalism for crystalline solids [Larche and Cahn, Acta Metall., 21 1051 (1973)]. These relationships are employed to examine the thermodynamic processes associated with varying the input parameters of the PFC model. The equilibrium conditions between bulk solid and liquid phases are imposed on the relationships to obtain a procedure for determining solid-liquid phase coexistence. The resulting procedure is found to be in agreement with the common-tangent construction commonly used in the PFC community. We apply the procedure to an eighth-order-fit (EOF) PFC model that has been parameterized to body-centered-cubic (bcc) Fe [Jaatinen et al., PRE 80, 031602 (2009)] and demonstrate that the model does not predict stable bcc structures with positive vacancy densities. The second set of relationships is built on the recent work of Pisutha-Arnond et al. [Pisutha-Arnond et al., PRB, 87 014103 (2013)], and is applied to develop a thermodynamically consistent procedure for determining elastic constants from the PFC model. To implement these procedures, we present two alternative deformation methods, one in real space and the other in Fourier space, that are computationally more accurate and efficient than the method conventionally used in the PFC community. The procedure for determining elastic constants is implemented with the Fourier space deformation method to calculate bulk mechanical properties from the EOF-PFC model. Finally, we present a structural PFC model [Greenwood et al. PRL 105, 045702 (2010)] that yields a stable dc structure. The stabilization of a dc structure is accomplished by constructing a two-body direct correlation function (DCF) approximated by a combination of two Gaussian functions in Fourier space. A phase diagram that contains a dc-liquid phase coexistence region was constructed for the model. We examine the energies of the (100), (110), and (111) solid-liquid interfaces.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111344/1/vicchan_1.pd

High Accuracy Fuel Flowmeter, Phase 1

Technology related to aircraft fuel mass - flowmeters was reviewed to determine what flowmeter types could provide 0.25%-of-point accuracy over a 50 to one range in flowrates. Three types were selected and were further analyzed to determine what problem areas prevented them from meeting the high accuracy requirement, and what the further development needs were for each. A dual-turbine volumetric flowmeter with densi-viscometer and microprocessor compensation was selected for its relative simplicity and fast response time. An angular momentum type with a motor-driven, spring-restrained turbine and viscosity shroud was selected for its direct mass-flow output. This concept also employed a turbine for fast response and a microcomputer for accurate viscosity compensation. The third concept employed a vortex precession volumetric flowmeter and was selected for its unobtrusive design. Like the turbine flowmeter, it uses a densi-viscometer and microprocessor for density correction and accurate viscosity compensation

Radiating Shear-Free Gravitational Collapse with Charge

We present a new shear free model for the gravitational collapse of a spherically symmetric charged body. We propose a dissipative contraction with radiation emitted outwards. The Einstein field equations, using the junction conditions and an ansatz, are integrated numerically. A check of the energy conditions is also performed. We obtain that the charge delays the black hole formation and it can even halt the collapse.Comment: 22 pages, 9 figures. It has been corrected several typos and included several references. Accepted for publication in GR

Kinetic modeling of Secondary Organic Aerosol formation: effects of particle- and gas-phase reactions of semivolatile products

The distinguishing mechanism of formation of secondary organic aerosol (SOA) is the partitioning of semivolatile hydrocarbon oxidation products between the gas and aerosol phases. While SOA formation is typically described in terms of partitioning only, the rate of formation and ultimate yield of SOA can also depend on the kinetics of both gas- and aerosol-phase processes. We present a general equilibrium/kinetic model of SOA formation that provides a framework for evaluating the extent to which the controlling mechanisms of SOA formation can be inferred from laboratory chamber data. With this model we examine the effect on SOA formation of gas-phase oxidation of first-generation products to either more or less volatile species, of particle-phase reaction (both first- and second-order kinetics), of the rate of parent hydrocarbon oxidation, and of the extent of reaction of the parent hydrocarbon. The effect of pre-existing organic aerosol mass on SOA yield, an issue of direct relevance to the translation of laboratory data to atmospheric applications, is examined. The importance of direct chemical measurements of gas- and particle-phase species is underscored in identifying SOA formation mechanisms

New and Significant Bird Records from Bintan Island, Riau Archipelago, Indonesia in 2018

Pulau Bintan is the largest island in the Riau Archipelago, Indonesia. During two brief visits in 2018, a total of eight species new to the island were recorded, increasing the island’s bird checklist to 189 species. These new records are Grey Heron Ardea cinerea, Intermediate Egret Ardea intermedia, Red-wattled Lapwing Vanellus indicus, Horsfield's Bronze-cuckoo Chalcites basalis, Tiger Shrike Lanius tigrinus, White-headed Munia Lonchura maja, Sooty-headed Bulbul Pycnonotus aurigaster and Javan Myna Acridotheres javanicus. Three of our new records appear to be new for the Riau Archipelago, increasing the avifaunal checklist for the archipelago to 232 species. Following years of development, little primary vegetation remains on Bintan Island, and our failure to detect any woodpeckers by sight or sound during our visits is worrying in terms of the importance of these birds to ecosystem sustainability. Nonetheless, the island retains sizeable area of natural forests, including some swamp forest patches, and our new and significant records suggest its avifaunal diversity is still understudied and underestimated. We call for relevant Indonesian government agencies and the Bintan Resorts, which manage the northern portion of the island for tourism development, to strengthen efforts in biodiversity research and conservation, as well as habitat restoration, so as to attain the development goal of making Bintan a true “eco-island” for international tourism

A mini-array for large air showers

A mini-array that utilizes the Linsley effect is proposed for the measurement of large air showers. An estimate of the detectable shower rates for various shower sizes is made. Details of the detection and data collection systems are also described

Monte Carlo simulations of bosonic reaction-diffusion systems

An efficient Monte Carlo simulation method for bosonic reaction-diffusion systems which are mainly used in the renormalization group (RG) study is proposed. Using this method, one dimensional bosonic single species annihilation model is studied and, in turn, the results are compared with RG calculations. The numerical data are consistent with RG predictions. As a second application, a bosonic variant of the pair contact process with diffusion (PCPD) is simulated and shown to share the critical behavior with the PCPD. The invariance under the Galilean transformation of this boson model is also checked and discussion about the invariance in conjunction with other models are in order.Comment: Publishe

Triton-3He relative and differential flows and the high density behavior of nuclear symmetry energy

Using a transport model coupled with a phase-space coalescence after-burner we study the triton-3He relative and differential transverse flows in semi-central 132Sn+124Sn reactions at a beam energy of 400 MeV/nucleon. We find that the triton-3He pairs carry interesting information about the density dependence of the nuclear symmetry energy. The t-3He relative flow can be used as a particularly powerful probe of the high-density behavior of the nuclear symmetry energy.Comment: 6 pages, 2 figures, Proceeding of The International Workshop on Nuclear Dynamics in Heavy-Ion Reactions and the Symmetry Energ