Radiation Source Mapping with Bayesian Inverse Methods

We present a theoretical investigation of the effect of multiple ionization sources in H <scp>ii</scp> regions on the total elemental abundances derived from the analysis of collisionally excited emission lines. We focus on empirical methods based on direct temperature measurements that are commonly employed in cases when the temperature of the nebular gas can be determined from the ratio of nebular to auroral lines of (e.g.) doubly ionized oxygen. We find that direct temperature methods that employ a two-temperature zone approach (DT2T methods) are very robust against the spatial distribution of sources. Errors smaller than 0.15 dex are estimated for regions where the metallicity is twice solar and errors below 0.05 dex for solar metallicities and below. The biases introduced by the spatial distribution of the ionization sources are thus much smaller for DT2T methods than for strong line methods, previously investigated by Ercolano, Bastian & Stasińska. Our findings are in agreement with the recent study of H <scp>ii</scp> regions in NGC 300 by Bresolin et al.

Frequency- and time domain methods for constructing images of the spatial distribution of stochastic radiation sources from measured field samples of the radiated electromagnetic field are presented. For scanning the field in the virtual lens plane a mesh of sampling points is chosen. A two-point sampling procedure is applied where the field values are sampled in pairs of sampling points and the auto- and cross correlation functions of the field samples and from these the field energy densities in the image plane are computed. The frequency domain method is compared with the time domain method.

Apis dorsata is one of the important honeybee species in tropical and subtropical regions that forages on various plants including herbs, grasses, forest trees and plantation trees. However, information on the spatial distribution of various pollen sources of Apis dorsata is still lacking. This study aimed at mapping the spatial distribution of the major honeybee plants that serve as pollen sources to Apis dorsata using an integrated Geographical Information System (GIS)-Remote Sensing (RS) approach. Mapping of pollen sources was based on SPOT-5 satellite imagery within a GIS environment. The SPOT-5 imagery was enhanced, classified and vectorized using ENVI 4.7. Image classification techniques were used to separate the pollen sources into six classes. Ten observation plots, each measuring 10×10 m, were established for each pollen source class using a randomized sampling technique. Results showed that Melaleuca cajuputi covered a total of 2,398.8 ha (5.5%), Acacia sp. 11,377.8 ha (25.9%), Elaeis guineensis 19745.1 ha (44.9%), non-vegetation 4,647.2 ha (10.6%), water bodies 973.5 ha (2.2%) and cloud/haze/shadow 4830.5 ha (10.6%). The overall classification accuracy was 91.5% and the Kappa coefficient was 0.8. The GIS-RS map showed that almost all of the Apis dorsata nesting sites were located in the Elaeis guineensis area. This study clearly demonstrates that Apis dorsata prefers to build its nest in close proximity to the pollen source.

Objective. Mapping of dose delivery in proton beam therapy can potentially be performed by analyzing thermoacoustic emissions measured by ultrasound arrays. Here, a method is derived and demonstrated for spatial mapping of thermoacoustic sources using numerical time reversal, simulating re-transmission of measured emissions into the medium. Approach. Spatial distributions of thermoacoustic emission sources are shown to be approximated by the analytic-signal form of the time-reversed acoustic field, evaluated at the time of the initial proton pulse. Given calibration of the array sensitivity and knowledge of tissue properties, this approach approximately reconstructs the acoustic source amplitude, equal to the product of the time derivative of the radiation dose rate, mass density, and Grüneisen parameter. This approach was implemented using two models for acoustic fields of the array elements, one modeling elements as line sources and the other as rectangular radiators. Thermoacoustic source reconstructions employed previously reported measurements of emissions from proton energy deposition in tissue-mimicking phantoms. For a phantom incorporating a bone layer, reconstructions accounted for the higher sound speed in bone. Dependence of reconstruction quality on array aperture size and signal-to-noise ratio was consistent with previous acoustic simulation studies. Main results. Thermoacoustic source distributions were successfully reconstructed from acoustic emissions measured by a linear ultrasound array. Spatial resolution of reconstructions was significantly improved in the azimuthal (array) direction by incorporation of array element diffraction. Source localization agreed well with Monte Carlo simulations of energy deposition, and was improved by incorporating effects of inhomogeneous sound speed. Significance. The presented numerical time reversal approach reconstructs thermoacoustic sources from proton beam radiation, based on straightforward processing of acoustic emissions measured by ultrasound arrays. This approach may be useful for ranging and dosimetry of clinical proton beams, if acoustic emissions of sufficient amplitude and bandwidth can be generated by therapeutic proton sources.

as a result of the Chernobyl nuclear power plant accident. Evaluations and measurements made at the site showed that vertical migration of the radionuclides into the soil in the first months after the accident lowered the dose rate by a factor of 1.5-2.5 [1]. Experimental methods and mathematical models that were developed make it possible to determine the shape of the radionuclide distribution function in the soil [2, 3]. It would be convenient to use analytical relationships, which give a satisfactory approximation to the dose rate, for engineering processing of data on the radionuclide composition of the soil. Calculations of the dose rate from buried sources, which were done using buildup factors for an infinite air space and concrete [4], depend strongly on the initial data and can be off by a factor of 2-3 from Monte Carlo results [5]. An approximate relationship has been suggested [6] which can calculate the effective equivalent dose from sources distributed uniformly in the soil with an error of 10-15%. Here the results of numerical Monte Carlo calculations of the dose rate from a plane source in the soil for photon energies of 0.015-5 MeV are approximated by an analytical relationship obtained by using an expression for the buildup factor in the Berger form. Direct approximation of the numerical modeling results increases the accuracy of the calculation, as compared to a method which uses a buildup factor for an infinite medium. The simple form of the analytical relationship makes it possible to do engineering calculations for various radiation source distributions in the soil. In the problem at hand, a plane monoenergetic isotopic source of photons of energy E.ro extends to infinity along the earth's surface at a depth z s in the soil. The energy was varied from 0.015 to 5 MeV. For energies >_0.1 MeV, the depth was varied from 0 to 30 cm for a characteristic soil density Ps = 1.6 g/cm 3, i.e., z s _< 24-48 cm for 2 _< Os -< 1 g/cm 3. For Evo < 0.1 MeV, z s does not exceed five mean-free paths of photons in the soil, which corresponds to a decrease of the dose rate by roughly 1000 times compared to the dose from a surface source. The chosen ranges of E.ro and z s are sufficient for calculating the dose rate from global fallout and fallout from nuclear power plant ejecta [2, 3, 5, 6]. It was assumed that the detection point was located at a height of z a = 100 cm above the earth's surface. In choosing a Berger-type buildup factor, the absorbed dose rate in air and the effective equivalent dose rate per unit surface activity are determined by the relationship Fp= A {El(r) +

The spatial distribution of saline water and possible sources of intrusion into Lekki lagoon and transitional effects on the lacustrine ichthyofaunal characteristics were studied during March, 2006 and February, 2008. The water quality analysis indicated that, salinity has drastically increased recently in the lagoon (0.007 to 4.70%). This study has identified three possible sources for saline water intrusion, beyond the seasonal input from the two adjacent lagoons (Lagos and Mahin), salt water intrusion by subsurface flow through the barrier beach from the ocean, and leaching of ions through lagoon bottom sediments. Eighty one fish species belonging to 40 families, 56 genera and 14 orders encountered were mostly freshwater, euryhaline and marine species adapted to life in the lagoon. The shell fish included the freshwater prawns Macrobrachium spp and the portunid crab Callinectes amnicola . This high number of fish species recorded from Lekki Lagoon in this study has confirmed the fact that this lagoon is a transition area between brackish water (Lagos Lagoon and Mahin Creek) and freshwater (Rivers Saga and Oshun). Key words: Spatial distribution, saline water, lacustrine, ichthyofaunal, diversity.

This paper examines how the behavioral acts of the thousands of foragers in a honeybee colony are combined to produce the coordinated foraging behavior of a whole colony. We focus on a colony’s ability to quickly adjust the distribution of its foraging efforts following changes in the spatial distribution of rich nectar sources. The analysis begins by examining the factors that influence an individual nectar forager’s response to a patch of flowers (Fig. 1). These include variables, such as distance from the nest, nectar sweetness, and nectar abundance (Fig. 4), that are associated with the patch itself, as well as variables, such as weather conditions and the colony’s rate of nectar intake (Fig. 2), that are not associated with a particular patch of flowers. These non-patch variables affect a forager’s response to her patch of flowers by changing her thresholds in patch quality for abandoning or recruiting nestmates to a patch (Fig. 3). Foragers evidently assess their colony’s rate of nectar intake while unloading nectar to receiver bees. The ease of unloading varies inversely with the rate of nectar flow into the colony. The responsiveness of nectar foragers to this indicator of their colony’s foraging status enables a colony to swiftly redirect its nectar collection efforts following changes in the spatial distribution of rich nectar sources. Whenever the quality of a major nectar source declines, its foragers reduce their rate of visits to the patch, which depresses the colony’s total rate of nectar intake, which in turn stimulates recruitment to whichever patches remain high in quality (Figs. 6 and 7). The paper concludes by presenting some generalizations about colony integration in social insects that emerge from this research.

This article shows the results of the elaboration of a numerical – analytical method for solving the problem of thermal conductivity in a plate fuel element (‘TVEL’). An unsteady temperature field inside a fuel element is investigated for a given spatial distribution of heat sources. The heat release rate is given by the quadratic function of the coordinate. Modelling the temperature state of bodies with internal heat sources allows one to study the operation of equipment in transient modes, control heating / cooling modes of elements, determine temperature stresses, etc. The use of the developed method made it possible to obtain an approximate analytical solution of the formulated problem, simple in form, with an accuracy sufficient for engineering applications. It is shown in the work that regardless of the power of internal sources of heat, the temperature state is stabilized at a temperature level that depends on the Pomerantsev number.

Baseline radiation background is almost never known and constantly changes particularly in urban areas. It is difficult to know what the expected background radiation should be and how a radiological incident may elevate the radiation. Naturally occurring radiation from rocks and building materials often contributes significantly to measured radiation. Buildings and other tall structures also shield radiation and thus need to be taken into account. Models of natural occurring background radiation can be derived from knowledge of geology, building material origins, vegetation, and weather conditions. After a radiological incident, the radiation will be elevated near the event, and some material may be transported by mechanisms such as airborne transport and/or run-off. Locating and characterizing the sources of radiation quickly and efficiently are crucial in the immediate aftermath of a nuclear incident. The distribution of radiation sources will change naturally and also due to clean-up efforts. Finding source strengths and locations during both the initial and clean-up stages is necessary to manage and reduce contaminations. The overall objective of the Rapid Location Of Radiation Sources In Complex Environments Using Optical And Radiation research project is to design and validate gamma ray spectrum estimation algorithms that integrate optical and radiation sensor collections into high resolution, multi-modal site models for use in radiative transport codes. Our initial focus is on modeling the background radiation using hyper-spectral information from visible through the shortwave infrared sensors and thermal imagers. The optical data complements available ancillary data from other sources such as Geographic Information Systems (GIS) layers, e.g. geologic maps, terrain, surface cover type, road network, vegetation (e.g. serpentine vegetation), 3-D building models, known users of radiological sources, etc. In absence of GIS layers, the data from the multi/hyper-spectral imager and height data from LIDAR can be analyzed with special with special software to automatically create GIS layers and radiation survey data to come up with a method to predict background radiation distribution. We believe the estimation and prediction of the natural background will be helpful in finding anomalous point, line and small area sources and minimize the number of false alarms due to natural and known man-made radiation sources such as radiological medical facilities, industrial users of radiological sources.

Spatial distribution of source areas of PM2.5 by Concentration Weighted Trajectory (CWT) model applied in PM2.5 concentration and composition data

Purpose: Improved localization of gamma-ray emissions from radiotracers is essential to the progress of nuclear medicine. Polaris is a portable, room-temperature operated gamma-ray imaging spectrometer composed of two 3×3 arrays of thick CdZnTe (CZT) detectors, which detect gammas between 30keV and 3MeV with energy resolution of <1% FWHM at 662keV. Compton imaging is used to map out source distributions in 4-pi space; however, is only effective above 300keV where Compton scatter is dominant. This work extends imaging to photoelectric energies (<300keV) using coded aperture imaging (CAI), which is essential for localization of Tc-99m (140keV). Methods: CAI, similar to the pinhole camera, relies on an attenuating mask, with open/closed elements, placed between the source and position-sensitive detectors. Partial attenuation of the source results in a “shadow” or count distribution that closely matches a portion of the mask pattern. Ideally, each source direction corresponds to a unique count distribution. Using backprojection reconstruction, the source direction is determined within the field of view. The knowledge of 3D position of interaction results in improved image quality. Results: Using a single array of detectors, a coded aperture mask, and multiple Co-57 (122keV) point sources, image reconstruction is performed in real-time, on an event-by-event basis, resulting in images with an angular resolution of ∼6 degrees. Although material nonuniformities contribute to image degradation, the superposition of images from individual detectors results in improved SNR. CAI was integrated with Compton imaging for a seamless transition between energy regimes. Conclusion: For the first time, CAI has been applied to thick, 3D position sensitive CZT detectors. Real-time, combined CAI and Compton imaging is performed using two 3×3 detector arrays, resulting in a source distribution in space. This system has been commercialized by H3D, Inc. and is being acquired for various applications worldwide, including proton therapy imaging R&D.

In previous work, our research group has developed gamma-ray imaging methods using two-interaction Compton events recorded from a single 1.5 cm x 1.5 cm x 1 cm 3D position-sensitive CdZnTe detector. The first of these is a maximum likelihood estimation maximization (MLEM) algorithm to estimate the spatial source distribution from measured events. The other, energy-imaging integrated spectral deconvolution, takes place in integrated spatial and energy space using the MLEM algorithm, allowing it to deconvolve the source image at any specific energy, as well as the spectrum for any specific direction. By including Compton-scattering events in the system model, it also estimates the true incident gamma-ray spectrum from each direction free of the Compton continuum. In order to improve efficiency at high energies as well as angular resolution, a new system (Polaris) is under construction using two layers of 3 x 3 modular 3D CdZnTe detectors, each with dimensions of 2 cm x 2 cm x 1.5 cm. Both MLEM methods, which used two-interaction Compton events, have been generalized to the new array system. Moreover, the system response function for both methods have been extended to make use of three-interaction events occurring in the system. The system response function for MLEM in the spatial domain has also been extended to use single-interaction events. Since it is impossible to pre-calculate the system response function due to the large number of possible events, analytic formulas are derived to allow the calculation of the system response function as reconstruction occurs. Finally, representative results are presented.

A deconvolution approach for the mapping of acoustic sources (DAMAS) determined from phased microphone arrays

A new principle of the investigation of space distributions of incoherent radiation sources based on the correlation processing of signals accepted by the receivers disposed at different positions is offered. The possibility to obtain the tomographic type information by this principle was experimentally shown. *) It should note, that the mentioned procedure allows generalization on cases of partial coherence of radiation, when integral “I” is not already expressed through — function, and has a more complex form3.KeywordsCoherence LengthSpace DistributionPath DifferenceSpatial SpectrumHyperbolic SurfaceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Recognition of locomotion mode is a crucial process for control of wearable soft robotic devices to assist humans in walking activities. We present a probabilistic Bayesian approach with a sequential analysis method for recognition of locomotion and phases of the gait cycle. Our approach uses recursive accumulation of evidence, as biological systems do, to reduce uncertainty present in the sensor measurements, and thus improving recognition accuracy. Data were collected from a wearable sensor, attached to the shank of healthy human participants, from three locomotion modes; level-ground walking, ramp ascent and ramp descent. We validated our probabilistic approach with recognition of locomotion in steady-state and gait phases in transitional states. Furthermore, we evaluated the effect, in recognition accuracy, of the accumulation of evidence controlled by increasing belief thresholds. High accuracy results achieved by our approach, demonstrate its potential for robust control of lower limb wearable soft robotic devices to provide natural and safe walking assistance to humans.