Neutron measurements in the vicinity of a self-shielded PET cyclotron.

The radionuclides used in positron emission tomography (PET) are short-lived and generally must be produced on site using a cyclotron. A common end product of the nuclear reactions used to produce the PET radionuclides is neutron radiation. These neutrons could potentially contribute to the annual effective dose received by hospital personnel.

Analysis of hemodynamic fluid phase mass transport in a separated flow region.

The mass transfer behavior in the recirculation region downstream of an axisymmetric sudden expansion was examined. The Reynolds number, 500, and Schmidt number, 3200, were selected to model the mass transfer of molecules, such as ADP, in the arterial system. In a first step the transient mass transport applying zero diffusive flux at the wall was analyzed using experiments and two computational codes.

Model-based optimal design of polymer-coated chemical sensors.

A model-based methodology for optimal design of polymer-coated chemical sensors is developed and is illustrated for the example of infrared evanescent field chemical sensors. The methodology is based on rigorous and computationally efficient modeling of combined fluid mechanics and mass transfer, including transport of multiple analytes. A simple algebraic equation for the optimal size of the sensor flow cell is developed to guide sensor design and validated by extensive CFD simulations.

Performance of an underwater acoustic volume array using time-reversal focusing.

Time reversal permits acoustic focusing and beam forming in inhomogeneous and/or high-scattering environments. A volumetric array geometry can suppress back lobes and can fit a large, powerful array of elements into small spaces, like the free-water spaces on submarines. This research investigates applying the time-reversal method to an underwater acoustic volume array.

On the effect of viscosity in scattering from partially coated infinite cylinders.

This paper considers the two-dimensional problem of scattering of a plane wave incident on an infinite cylinder that is coated with strips of pressure-release material extending over quadrants on the illuminated and shadowed sides, with the remainder of the surface considered to be rigid. Transitions from soft to rigid surfaces correspond to discontinuous boundary conditions. Ideal fluid theory predicts an infinite pressure gradient at these transitions, which suggests that viscous effects may be significant.

Fluid mechanics of vascular systems, diseases, and thrombosis.

The cardiovascular system is an internal flow loop with multiple branches circulating a complex liquid. The hallmarks of blood flow in arteries are pulsatility and branches, which cause wall stresses to be cyclical and nonuniform. Normal arterial flow is laminar, with secondary flows generated at curves and branches.

A mechanistic model of acute platelet accumulation in thrombogenic stenoses.

Thrombosis on an atherosclerotic lesion can cause heart attack or stroke. Thrombosis may be triggered by plaque rupture or erosion, creating a thrombogenic stenosis. To measure and model this situation, collagen-coated stenoses have been exposed to nonanticoagulated blood in a baboon ex vivo shunt.

Wave-number-based assessment of the doubly asymptotic approximation. II. Frequency and time domain response.

In part I, the surface variational principle (SVP) and the doubly asymptotic approximation (DAA) were used to generate alternative descriptions of the frequency domain wet surface impedance. These are used here to obtain alternative descriptions of the displacement field in slender hemicapped cylindrical shells. This field is represented as a decomposition into a two-dimensional wave-number space.

Wave-number-based assessment of the doubly asymptotic approximation. I. Frequency domain wet surface impedance.

The doubly asymptotic approximation (DAA) is a canonical relationship for the interaction between surface normal velocity and pressure. Its validity for a slender hemicapped cylinder is examined by formulating a frequency domain version of DAA using the global basis functions employed in the wave-number-based formulation of the surface variational principle [K. Wu and J.

Biokinetic model for 137Cs in the fetus.

The metabolic data for cesium and the biologically similar element potassium in the pregnant woman were reviewed. Due to the rapid growth of the placenta and fetus, the pregnancy was divided into four gestational periods: five through ten weeks, eleven through twenty weeks, twenty-one through thirty weeks, and thirty-one through forty weeks. A physiologically based biokinetic model for potassium was developed for each of these periods.

Convective mass transfer at the carotid bifurcation.

The convective conditions in regions of hemodynamic separation may produce uneven local mass transfer at the arterial wall which may lead to an atherogenic response. This study estimates the potential variation in local mass transfer of oxygen at the human carotid bifurcation under steady flow conditions. The three-dimensional separated flow at the bifurcation was studied using a computational analysis of the basic conservation equations of mass, momentum, and species.

Data quality objectives for surface-soil cleanup operation using in situ gamma spectrometry for concentration measurements.

In situ gamma spectrometry is an efficient method for monitoring the progress of cleanup activities for radioactive contaminants in surface soil and for evaluating the attainment of cleanup standards. However, desired data precision and accuracy must be specified for such a detection system prior to the operation to ensure that the level of uncertainty associated with the concentration measurements is acceptable. A method for developing data quality objectives is described in this paper for in situ gamma spectrometry to achieve numerical goals for data precision and accuracy for cleanup operations.

When is a lower limit of detection low enough?

In cleanup operations and environmental surveillance efforts, a level of concern usually specifies a concentration limit for a particular radionuclide above which some action may be warranted. It is critical that the analytical method selected for measurements has a detection limit well below the action level. This is to guarantee that the technique used provides precise assessment at the level of concern.

Implementation of digital stereo imaging for analysis of metaphyses and joints in skeletal collections.

The surface structure of the growing portion of bones, called the metaphysis, contains clues about the locomotor characteristics of various species. Present methods of capturing this anthropologically interesting surface are time-consuming and subject to human error. The research implements a digital stereo imaging technique for bone metaphyses and joints in skeletal collections.

Radiation protection design for a clinical positron emission tomography imaging suite.

Radiation exposures due to patient sources, a pneumatic transport system, and gas lines in a positron emission tomography imaging facility are estimated for heavy clinical work loads. For simple source approximations and estimated study activities and times, exposure rates are computed that are larger than those anticipated in traditional nuclear medical imaging facilities. Measurements of exposure rates indicate that such an approach will result in conservative estimates of exposure by a factor of 1.