Electrical and Computer Engineering

Conclusions: While on the average partial breast IMRT is dosimetrically feasible in both the prone and supine positions, each position offered an individual advantage based upon the location of the tumor bed. As the prescription constraints were met using IMRT for both positions, it would appear that other, non-dosimetrical considerations should have a greater influence over the choice of positioning, such as reproducibility, intra-fractional motion and patient comfort.

Modern multiprocessor architectures have exacerbated problems of coordinating access to shared data, in particular as regards to the possibility of deadlock. For example semaphores, one of the most basic synchronization primitives, present difficulties. Djikstra defined semaphores to solve the problem of mutual exclusion. Practical implementation of the concept has, however, produced semaphores that are prone to deadlock, even while the original definition is theoretically free of it. This is not simply due to bad programming, but we have lacked a theory that allows us to understand the problem. We introduce a formal definition and new general theory of synchronization. We illustrate its applicability by deriving basic deadlock properties, to show where the problem lies with semaphores and also to guide us in finding some simple modifications to semaphores that greatly ameliorate the problem. We suggest some future directions for deadlock resolution that also avoid resource starvation.

Although deadlock is not completely avoidable in distributed and parallel programming, we here describe theory and practice of a system that allows us to limit deadlock to situations in which there are true circular data dependences or failure of processes that compute data needed at other processes. This allows us to guarantee absence of deadlock in SPMD computations absent process failure. Our system guarantees optimal ordering of communication statements. We gratefully acknowledge the support of the US National Science Foundation under Award CISE EIA 9810708 without which this work would not have been possible.

In the search for life on Mars and other extraterrestrial bodies or in our attempts to identify biological traces in the most ancient rock record of Earth, one of the biggest problems facing us is how to recognize life or the remains of ancient life in a context very different from our planet's modern biological examples. Specific chemistries or biological properties may well be inapplicable to extraterrestrial conditions or ancient Earth environments. Thus, we need to develop an arsenal of techniques that are of broader applicability. The notion of patterning created in some fashion by biological processes and properties may provide such a generalized property of biological systems no matter what the incidentals of chemistry or environmental conditions. One approach to recognizing these kinds of patterns is to look at apparently organized arrangements created and left by life in extreme environments here on Earth, especially at various spatial scales, different geologies, and ...

The use of microbial fuel cells to detect anaerobes and power experiments in remote extreme environments is examined by a team of scientists and student teachers in a joint venture of the California State University system and NASA Ames. The economic viability of carbon fiber electrodes is tested by comparing their performance to graphite rods, which are commonly used. A connection between concentration of life and voltage output is indicated, which provides a potentially easy and powerful test for the presence of life in extreme environments such as found on Mars. Pollution free but low power density microbial fuel cells are shown to demonstrate viability as a power source for sensing applications.

Accurate navigation on the moon, Mars, or any other astronomical body is essential to scientific investigation. The research presented in this paper covers the constellation design of a Lunar Global Positioning System (GPS) using the CubeSat platform. Since CubeSats have significantly smaller dimensions than most current satellites, their associated cost is much less to place into orbit. This creates a compelling reason to use them for a Lunar GPS. However, CubeSats require a much smaller atomic clock, which has not been available. Fortunately, there have been recent advancements in chip-scale atomic clocks (CSAC) which can fit within the CubeSat platform. We propose a Rider constellations of two orbital planes and eight satellites per plane for minimum position determination, or fifteen satellites per plane for redundancy at an altitude of 3.34x10 4 km. The CSAC considered is estimated to have an update interval of almost an hour with a ten meter distance error.

An accurate system matrix is required for quantitative proton CT ͑pCT͒ image reconstruction with iterative projection algorithms. The system matrix is composed of chord lengths of individual proton path intersections with reconstruction pixels. In previous work, reconstructions were performed assuming constant intersection chord lengths, which led to systematic errors of the reconstructed proton stopping powers. The purpose of the present work was to introduce a computationally efficient variable intersection chord length in order to improve the accuracy of the system matrix. An analytical expression that takes into account the discrete stepping nature of the pCT most likely path ͑MLP͒ reconstruction procedure was created to describe an angle-dependent effective mean chord length function. A pCT dataset was simulated with GEANT4 using a parallel beam of 200 MeV protons intersecting a computerized head phantom consisting of tissueequivalent materials with known relative stopping power. The phantom stopping powers were reconstructed with the constant chord length, exact chord length, and effective mean chord length approaches, in combination with the algebraic reconstruction technique. Relative stopping power errors were calculated for each anatomical phantom region and compared for the various methods. It was found that the error of approximately 10% in the mean reconstructed stopping power value for a given anatomical region, resulting from a system matrix with a constant chord length, could be reduced to less than 0.5% with either the effective mean chord length or exact chord length approaches. Reconstructions with the effective mean chord length were found to be approximately 20% faster than reconstructions with an exact chord length. The effective mean chord length method provides the possibility for more accurate, computationally efficient quantitative pCT reconstructions.

The limited spatial resolution in proton computed tomography ͑pCT͒ in comparison to x-ray CT is related to multiple Coulomb scattering ͑MCS͒ within the imaged object. The current generation pCT design utilizes silicon detectors that measure the position and direction of individual protons prior to and post-traversing the patient to maximize the knowledge of the path of the proton within the imaged object. For efficient reconstruction with the proposed pCT system, one needs to develop compact and flexible mathematical formalisms that model the effects of MCS as the proton traverses the imaged object. In this article, a compact, matrix-based most likely path ͑MLP͒ formalism is presented employing Bayesian statistics and a Gaussian approximation of MCS. Using GEANT4 simulations in a homogeneous 20 cm water cube, the MLP expression was found to be able to predict the Monte Carlo tracks of 200 MeV protons to within 0.6 mm on average when employing 3 cuts on the relative exit angle and exit energy. These cuts were found to eliminate the majority of events not conforming to the Gaussian model of MCS used in the MLP derivation.

We consider the following problem: min x∈R n min E ≤η (A + E)x − b , where A is an m×n real matrix and b is an n-dimensional real column vector when it has multiple global minima. This problem is an errors-in-variables problem, which has an important relation to total least squares with bounded uncertainty. A computable condition for checking if the problem is degenerate as well as an efficient algorithm to find the global solution with minimum Euclidean norm are presented.

In this paper, cellular automata are used to model patterned growth of organisms in extreme environments. A brief introduction to cellular automaton modeling is given to assist the reader. Patterned growth of soil surface cyanobacteria and biovermiculation microbial mats in sulfuric acid caves are modeled and simulations conducted. Simulations are compared with actual systems, and future directions are discussed.

This report summarizes the design concepts for the new pCT system that will be evaluated within this project. DESIGN CONCEPTS Overview The current Phase 1 pCT head scanner is not optimized for the high proton data rates that are required for clinical operation. This is related to limitations of the data readout of the Phase 1 data acquisition system and the rate limitations of the CsI energy detector. Another limitation is the relatively long image reconstruction time on conventional computing hardware. A third limitation of the Phase 1 scanner is its sensitive area of 9 cm × 18 cm, which is only suitable for phantoms up to the size of a pediatric head (Fig. 1). The planned Phase 2 scanner addresses all of these limitations. We will construct a largearea detector for the clinical pCT scanning with data acquisition rates increased by at least a

In this paper, estimation and identification theories will be examined with the goal of determining some new methods of adding robustness. The focus will be upon uncertain estimation problems, namely ones in which the uncertainty multiplies the quantities to be estimated. Mathematically the problem can be stated as, for system matrices and data matrices that lie in the sets (A + δA) and (b + δb) respectively, find the value of x that minimizes the cost (A + δA)x − (b + δb). The proposed techniques are compared with currently used methods such as Least Squares (LS), Total Least Squares (TLS), and Tikhonov Regularization (TR). Several results are presented and some future directions are suggested.

Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

We are exploring low-dose proton radiography and computed tomography (pCT) as techniques to improve the accuracy of proton treatment planning and to provide artifact-free images for verification and adaptive therapy at the time of treatment. Here we report on comprehensive beam test results with our prototype pCT head scanner. The detector system and data acquisition attain a sustained rate of more than a million protons individually measured per second, allowing a full CT scan to be completed in six minutes or less of beam time. In order to assess the performance of the scanner for proton radiography as well as computed tomography, we have performed numerous scans of phantoms at the Northwestern Medicine Chicago Proton Center including a custom phantom designed to assess the spatial resolution, a phantom to assess the measurement of relative stopping power, and a dosimetry phantom. Some images, performance, and dosimetry results from those phantom scans are presented together with a description of the instrument, the data acquisition system, and the calibration methods.

To enhance endovascular navigation using surgical guidewires and the use of ionizing radiation, we demonstrate a method for ultrasonic localization of wires with diameters less than the wavelength of ultrasound in the medium. Methods: Nitinol wires with diameters ranging from 50 µm to 250 µm were imaged ultrasonically in a 0.25-in-diameter waterfilled tube in a gelatin medium. Imaging frequencies were 5 MHz, 7.5 MHZ, and 10 MHz. Results: For the full range of diameters traversing the phantom, the wires were localized successfully via visual inspection of both regular and difference ultrasound images. Similarly, two convolutional neural networks were trained, and both achieved an accuracy of over 95%. Conclusions: Wires with diameters as small as 50 µm were localized successfully in a water-based gelatin phantom, indicating the potential use of ultrasound to enhance endovascular navigation and surgical treatment.

This simulation study presents the application of fluence field modulated computed tomography (FFMCT), initially developed for x-ray CT, to proton computed tomography (pCT). By using pencil beam (PB) scanning, fluence modulated pCT (FMpCT) may achieve variable image quality in a pCT image and imaging dose reduction. 
 Three virtual phantoms, a uniform cylinder and two patients, were studied using Monte Carlo simulations of an ideal list-mode pCT scanner. Regions of interests (ROI) were selected for high image quality and only PBs intercepting them preserved full fluence (FF). Image quality was investigated in terms of accuracy (mean) and noise (standard deviation) of the reconstructed proton relative stopping power (RSP) compared to reference values. Dose calculation accuracy on FMpCT images was evaluated in terms of dose volume histograms (DVH), range difference (RD) for beam-eye-view (BEV) dose profiles and gamma evaluation. Pseudo FMpCT scans were created from broad beam expe...

This paper considers the problem of estimation and identification with bounded uncertainties in the data and system matrices. In particular, we will examine how to solve the Ax ≈ b when we have bounds on the errors of column blocks of A in the min max sense. Error bounds on column blocks of the system matrix A are caused by numerous situations, such as different sensor or parameter uncertainties, filter order updating, and image separation. Performance of the method is compared with existing techniques.