819 research outputs found
A simple Fourier transform-based reconstruction formula for photoacoustic computed tomography with a circular or spherical measurement geometry
Photoacoustic computed tomography (PACT), also known as optoacoustic
tomography, is an emerging imaging modality that has great potential for a wide
range of biomedical imaging applications. In this Note, we derive a hybrid
reconstruction formula that is mathematically exact and operates on a data
function that is expressed in the temporal frequency and spatial domains. This
formula explicitly reveals new insights into how the spatial frequency
components of the sought-after object function are determined by the temporal
frequency components of the data function measured with a circular or spherical
measurement geometry in two- and three-dimensional implementations of PACT,
respectively. The structure of the reconstruction formula is surprisingly
simple compared with existing Fourier-domain reconstruction formulae. It also
yields a straightforward numerical implementation that is robust and two orders
of magnitude more computationally efficient than filtered backprojection
algorithms.Comment: http://iopscience.iop.org/0031-9155/57/23/N493
Nonlinear Dynamics of a Duffing-Like Negative Stiffness Oscillator: Modeling and Experimental Characterization
In this paper, a negative stiffness oscillator is modelled and tested to exploit its nonlinear dynamical characteristics. The oscillator is part of a device designed to improve the current collection quality in railway overhead contact lines, and it acts like an asymmetric double-well Duffing system. Thus, it exhibits two stable equilibrium positions plus an unstable one, and the oscillations can either be bounded around one stable point (small oscillations) or include all the three positions (large oscillations). Depending on the input amplitude, the oscillator can exhibit linear and nonlinear dynamics and chaotic motion as well. Furthermore, its design is asymmetrical, and this plays a key role in its dynamic response, as the two natural frequencies associated with the two stable positions differ from each other. The first purpose of this study is to understand the dynamical behavior of the system in the case of linear and nonlinear oscillations around the two stable points and in the case of large oscillations associated with a chaotic motion. To accomplish this task, the device is mounted on a shaking table and it is driven with several levels of excitations and with both harmonic and random inputs. Finally, the nonlinear coefficients associated with the nonlinearities of the system are identified from the measured data
Investigation of iterative image reconstruction in three-dimensional optoacoustic tomography
Iterative image reconstruction algorithms for optoacoustic tomography (OAT),
also known as photoacoustic tomography, have the ability to improve image
quality over analytic algorithms due to their ability to incorporate accurate
models of the imaging physics, instrument response, and measurement noise.
However, to date, there have been few reported attempts to employ advanced
iterative image reconstruction algorithms for improving image quality in
three-dimensional (3D) OAT. In this work, we implement and investigate two
iterative image reconstruction methods for use with a 3D OAT small animal
imager: namely, a penalized least-squares (PLS) method employing a quadratic
smoothness penalty and a PLS method employing a total variation norm penalty.
The reconstruction algorithms employ accurate models of the ultrasonic
transducer impulse responses. Experimental data sets are employed to compare
the performances of the iterative reconstruction algorithms to that of a 3D
filtered backprojection (FBP) algorithm. By use of quantitative measures of
image quality, we demonstrate that the iterative reconstruction algorithms can
mitigate image artifacts and preserve spatial resolution more effectively than
FBP algorithms. These features suggest that the use of advanced image
reconstruction algorithms can improve the effectiveness of 3D OAT while
reducing the amount of data required for biomedical applications
A new cylindrical borehole detector for radiographic imaging with muons
Muon radiography is a methodology which enables measuring the mass distribution within large objects. It exploits the abundant flux of cosmic muons and uses detectors with different technologies depending on the application. As the sensitive surface and geometric acceptance are two fundamental parameters for increasing the collection of muons, the optimization of the detectors is very significant. Here we show a potentially innovative detector of size and shape suitable to be inserted inside a borehole, that optimizes the sensitive area and maximizes the angular acceptance thanks to its cylindrical geometry obtained using plastic arc-shaped scintillators. Good spatial resolution is obtained with a reasonable number of channels. The dimensions of the detector make it ideal for use in 25Â cm diameter wells. Detailed simulations based on Monte Carlo methods show great cavity detection capability. The detector has been tested in the laboratory, achieving overall excellent performance
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Nevada Experiments and Operations Program (N Program) Management Plan
This plan briefly describes the Lawrence Livermore National Laboratory (LLNL) institutional structure and how Nevada Experiments and Operations Program (N Program's) organization fits within this structure, roles and responsibilities, and management processes that govern N Program activities. This plan also serves as the Integrated Safety Management (ISM) Implementation Plan for N Program work. This plan applies to all work performed by and for LLNL that falls under the oversight of DOE/NV except LLNL activities in support of the Yucca Mountain Project Office (YMPO)
APPLICATION OF A ONE-STEP REAL TIME RT-PCR PROTOCOL FOR NOROVIRUS DETECTION IN SHELLFISH HARVERSTED AND COMMERCIALIZED IN CAMPANIA REGION
Shellfish are recognized as a potential vehicle of viral diseases. However, according to European Regulations, only bacteriological parameters (Salmonella and E. coli) are used to establish their microbiological quality. Because of the lack of a standard reference method for the detection of viruses, data on the incidence of enteric viruses in European production areas are still limited. Aim of the present study was the evaluation of the Norovirus (NoV) contamination in shellfish from different harvesting areas (both class A and B) and from registered and not- registered retails of the Campania region (Tyrrhenian Sea, Italy). Seventy shellfish (Mytilus galloprovincialis) were collected from 15 harvesting areas, one authorized and two not authorized retails and were examined for virus presence (NoV genogroups I and II) by Real Time PCR. Ten harvesting areas (66%) showed presence of viral contamination, with three of them belonging to A areas and seven to B areas. The shellfish collected from the registered retail tested positive for Norovirus presence, whereas the shellfish collected from not-authorized retails didn't show viral contamination. Twenty-nine samples were positive for genogroup II, ten of which tested positive also for NoV genogroup I
Microbiological, rheological and physical-chemical characteristics of bovine meat subjected to a prolonged ageing period
he aim of this study was to evaluate the effects of a long ageing period on the microbiological, rheological and physical-chemical characteristics of bovine beef. For the trial n. 3 Marchigiana bovine breed (live weight of 760 kg approximately), slaughtered at 34 months were chosen and the loin muscles were undergone to a prolonged ageing process. The analytical determinations performed were: pH and aw values, texture profile analysis, Warner-Bratzler shear force, colour (CIE L*a*b*), centesimal analysis, total bacterial count, Enterobacteriaceae, Listeria monocytogenes, yeasts and moulds. The results indicate that extended ageing has a negative effect on weight loss but, by the means of the standardization of dry aging parameters, reduce lipid oxidation and improve tendernes
PROTEOMICS AS USEFUL TOOL FOR STUDING BIOMARKERS OF EARLY EXPOSURE TO POLYCHLORINATED BIPHENILS
Polychlorinated biphenyls (PCBs) are toxic persistent organic pollutants present in the hydrosphere. Mussels are used as sentinel organisms for the monitoring of marine pollution for their ability to bioaccumulate contaminants, their sessile nature, filter-feeding habits and widespread distribution. Alteration in protein expression is often indicative of toxic exposure or effect and changes in protein expression profiles derived from environmental stress may be used for the identification of novel biomarkers. In this study, proteomics has been used in mussels as a preliminary screening of quantitative changes in protein expression caused by a mixture of PCBs, potentially useful as new biomarkers, following the identification of the proteins more drastically altered. Our data demonstrated that proteomic approach represents a valuable tool for identifying biomarkers of exposure to environmental contaminants
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