Axial Geometry Research Articles

A geometric-sensitivity-difference method improves object depth-localization for continuous-wave fluorescence diffuse optical tomography: an in silico study in an axial outward-imaging geometry.

A geometric-sensitivity-difference (GSD) based reconstruction method is demonstrated in fluorescence diffuse optical tomography (FDOT) for improving the depth-localization of objects. The GSD method optimizes the data-model fit based on paired-measurements between source-detector pairs sharing either the source or the detector channel, as comparing to conventional methods that optimize the data-model fit based on un-paired measurements of individual source-detector pairs. This in silico study is limited to continuous-wave and 2-dimension, for a circular-array outward-imaging geometry of which the native sensitivity of measurement varies strongly with respect to the depth of the object. The outcomes of GSD method are compared to that of two conventional methods: one is the baseline method which does not involve any scheme to compensate the variation of native sensitivity; the other applies a depth-adapted weight to counteract the depth-variance of the native sensitivity. These three methods were evaluated using synthetic data corresponding to the following conditions of the object: (1) Single object with a 3-folds of positive contrast of fluorescence over the background was set at edge-depths of 0.5 mm, 5 mm and 10 mm; (2) Two objects with identical 3-folds of positive or 1/3-folds of negative contrast of fluorescence over the background were set at a fixed edge-depth of 10 mm and different azimuthal separations of 45 degree, 135 degree, and 180 degree; (3) Two objects with identical 3-folds of positive or 1/3-folds of negative contrast of fluorescence over the background were set at a fixed azimuthal separation of 90° and at edge-depths of 0.5 mm, 5 mm and 10 mm. The GSD method outperforms the other two methods in localizing a single anomaly and resolving two anomalies, for the anomaly possessing either the 3 folds positive or 1/3-folds negative contrast of fluorescence over the background. The case of objects with negative contrast over the background has specific implications to imaging zinc-specific fluorophore uptake in prostate.

Global design optimization for an axial-flow tandem pump based on surrogate method

Tandem pump, compared with multistage pump, goes without guide vanes between impellers. Better cavitation performance and significant reduction of the axial geometry scale is important for high-speed propulsion. This study presents a global design optimization method based on surrogated method for an axial-flow tandem pump to enhance trade-off performances: energy and cavitation performances. At the same time, interactions between impellers and impacts on the performances are analyzed. Fixed angle of blades in impellers and phase angle are performed as design variables. Efficiency and minimum average pressure coefficient (MAPC) on axial sectional surface in front impeller are the objective function, which can represent energy and cavitation performances well. Different surrogate models are constructed, and Global Sensitivity Analysis and Pareto Front method are used. The results show that, 1) Influence from phase angle on performances can be neglected compared with other two design variables, 2) Impact ratio of fixed angle of blades in two impellers on efficiency are the same as their designed loading distributions, which is 4:6, 3) The optimization results can enhance the trade-off performances well: efficiency is improved by 0.6%, and the MAPC is improved by 4.5%.

Transport Properties of Concrete Altered by Crack-Induced Damage

AbstractThis paper investigates the transport properties altered by crack-induced damage of two structural concretes [ordinary portland cement concrete (OPC) and high-volume fly ash concrete (HVFC)]. The crack-induced damage is represented by axial residual strain, ultrasonic speed, open porosity, and crack geometry of specimens, and the transport properties were measured for gas permeability and water sorptivity on dried specimens. The hydraulic diffusivity is derived from water sorptivity and used to characterize the altered transport properties. Geometrical analysis of crack network confirms that the crack pattern is determinant for the altered extent of transport properties. Very limited change was observed for hydraulic diffusivity for cracks with low connectivity. The hydraulic diffusivity shows a strong and linear correlation with sorptivity while its correlation with gas permeability is nonlinear with scatter. The scatter comes from the connectivity of cracks in the gas flow direction. Accordingly...

A high resolution TOF-PET concept with axial geometry and digital SiPM readout

The axial arrangement of long scintillation crystals is a promising concept in PET instrumentation to address the need for optimized resolution and sensitivity. Individual crystal readout and arrays of wavelength shifter strips placed orthogonally to the crystals lead to a 3D-detection of the annihilations photons. A fully operational demonstrator scanner, developed by the AX-PET collaboration, proved the potential of this concept in terms of energy and spatial resolution as well as sensitivity. This paper describes a feasibility study, performed on axial prototype detector modules with 100mm long LYSO crystals, read out by the novel digital Silicon Photomultipliers (dSiPM) from Philips. With their highly integrated readout electronics and excellent intrinsic time resolution, dSiPMs allow for compact, axial detector modules which may extend the potential of the axial PET concept by time of flight capabilities (TOF-PET). A coincidence time resolution of 211ps (FWHM) was achieved in the coincidence of two axial modules read out by dSiPMs, fully maintaining the demonstrated performance of the AX-PET detector.

Analysis and Design of Direct Steam Injection for Tomato Concentrate Sterilization

Abstract Direct steam injection is a sterilization technique which is often used for high-viscosity fluid food, when the preservation of the quality characteristics and energy efficiency are the priority. In this work, an apparatus for the sterilization of tomato concentrate has been analyzed by means of a 3D computational fluid dynamics (CFD) model, in order to optimize the exchanger performance in terms of temperature distribution inside the product. A multidimensional two-phase model of steam injection inside a non-Newtonian pseudoplastic fluid was adopted to evaluate the thermal history of the product and the condensation rate of the steam injected in the heat exchanger during the thermal process. Subsequently, the CFD analysis has been extended to examine the effects of the different process parameters (sterilization temperature, steam flow rate, radial and axial temperature profiles and nozzle geometry) on the resulting product. Results obtained allowed to understand the effects of process parameters on the behavior of the condensing steam and obtain better performance of the exchanger in terms of temperature distribution of the treated product.

Response Function of Collimated Detector for Non Axial Detector-Source Geometry

Response function is a fundamental parameter for all detectors in order to analyze the energy distribution of gamma ray which undergoes scattering interaction with the material. The response functions of a 3 in. x 3 in. NaI(Tl) collimated detector for non axis detector-source geometry has been calculated using a Monte Carlo approach from GEANT4 simulation code with 0.662 MeV of mono-energetic of photon gamma ray. Collimated Pb with 4 cm thickness and 2 cm of holes diameter were employed for shielding. The source was assumed as an isotropic point source and it is placed at various positions to the detector axis. The comparison between the measured energy response functions and the simulated energy response functions after normalization were also performed in order to validate the modeling results.

A multisectional annular thermal-neutron detector for the study of diffraction on microsamples in axial geometry

A new gaseous annular sectional thermal-neutron detector for the new neutron diffractometer at the IBR-2 reactor has been designed and manufactured at the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research (JINR). The detector is designed to study small-volume samples at high pressure and consists of 16 sections, each one of which is divided into six independent detector elements. We present the main design features of the detector, detecting electronics, data-acquisition and visualization software, and software system for experiment management. The results of the first neutronographic experiments that were carried out with the use of the detector are also presented.

Azimuthal spin-wave modes in rolled-up permalloy microtubes: Tuneable mode frequency, mode patterns, and mode splitting

We investigated rolled-up permalloy microtubes using microwave absorption spectroscopy. The resonance frequencies of the tubes are tuneable by the external magnetic field. Up to four resonant azimuthal modes have been found and were attributed to constructive spin-wave interference in axial and perpendicular magnetization geometry. We show that the degeneracy of the mode can be lifted by applying a magnetic field in specified directions. The resonances of the system are described analytically. Thereby, an effective layer thickness and a demagnetization field are used to account for the multilayer structure and the curved surface, respectively. This modeling approach is supported by micromagnetic simulations.

Experimental evidence of the high-gradient behaviour of fiber reinforced materials

Abstract This paper deals with the theoretical and experimental dynamics of materials behaving as generalised continua. We focus on composites consisting in a soft matrix with stiff embedded linear parallel fibers. Such composites depart from usual elastic composites because (i) the properties of the constituents are highly contrasted, and (ii) the axial geometry of each fiber is continuous over a distance much larger than the Representative Elementary Volume size. Consequently, both the shear in the soft matrix and the bending in the fibers participate in the macroscopic behaviour. This corresponds to a generalised continuum with a second gradient effect at the leading order. The homogenised modelling of the dynamic of highly contrasted fiber reinforced composite is recalled ( Soubestre and Boutin, 2012 ). The design of a physical model consisting of a polyurethane foam block permeated by steel bars is presented and the principle of the dynamic tests conducted using a shaking table is explained. Experimental results on the different tested configurations are described. From the analysis of the recorded responses the role of the bending effect is identified. The correlation between theory and experiments is exposed through the analysis of the fundamental and two higher modes response. The high level of agreement demonstrated for the several configurations prove the applicability of the generalised continuum model.

Axially Oriented Crystal Geometry Applied to Small-Animal PET System: A Proof of Concept

Improving resolution without decreasing sensitivity in positron emission tomography (PET) is of great interest for small animal studies. Traditional PET scanners use radially oriented detector block structures. This geometry implies a relationship between the spatial resolution and the sensitivity. An axially oriented crystal geometry can limit this correlation. With a fine measurement of the depth of interaction (DOI) and a continuous measurement of the axial interaction position, this axial geometry can provide high resolution and remove parallax effects. With a careful choice of the crystal and providing enough crystal elements in the radial direction, a good sensitivity can be achieved. Such improvements also allow a more accurate gamma tracking and Compton analysis of the events, indirectly increasing the sensitivity. We have proposed a PET scanner in which LYSO crystals are axially oriented and coupled at both ends by multichannel photo-detectors. The gamma interaction position is given by the hit crystals for the transverse plane and by the light spread on both photo-detectors for the axial direction. The axial position of the events is reconstructed using a calibration procedure and the transverse position is reconstructed using a clustering algorithm. In this paper, we present a complete simulation work flow, including the physical effects, the optical and electronic effects, as well as a reconstruction algorithm. A point sources phantom was used to evaluate the spatial resolutions, and a MOBY phantom was used for overall image quality evaluation. This paper shows that using four modules arranged around the animal, a volumetric spatial resolution below 1 mm3 can be achieved while keeping a detection efficiency close to 10%.

TH‐C‐103‐04: Computed Tomography Image Reconstruction with a Cylindrical Voxelization Method

Purpose: To accelerate the image reconstruction process for iterative algebraic reconstruction techniques using a cylindrical voxelization method. Methods: Iterative image reconstruction has many advantages, such as noise reduction and mitigation of approximate cone reconstruction artifacts, over analytical image reconstruction. But its high computational cost prohibits its use in many clinical applications, such as image guided radiotherapy (IGRT). The system matrix used in iterative reconstruction is often too large to store on the hard drive or in RAM. The cylindrical geometry is a natural fit for the circular scanning trajectory employed in volumetric CT methods such as cone beam computed tomography (CBCT) and tetrahedron beam computed tomography (TBCT). In this study, the iterative simultaneous algebraic reconstruction technique (SART) algorithm using a cylindrical voxelization method is developed for TBCT. The new algorithm takes advantage of the symmetries of the axial scanning geometry used in TBCT and greatly reduces the size of the system matrix. An additional step is needed for interpolating the cylindrical data onto a Cartesian grid. The reconstruction algorithms were tested with numerical phantoms as well as patient CT data. Results: The system matrix with the cylindrical voxelization method is compact and can be easily stored in the computer RAM. SART reconstruction using the cylindrical voxelization method was implemented for the TBCT. The FOM results for the cylindrical voxelization method were slightly better than for the Cartesian voxelization. The cylindrical method was able to provide a speedup of 40 times over the traditional Cartesian method and to provide a reduction of two orders of magnitude in the storage requirement for the system matrix. Conclusion: Image reconstruction using a cylindrical voxelization method was able to provide a significant improvement in the reconstruction speed while maintaining the image quality provided by the conventional reconstruction method using a Cartesian image grid. This work is partially supported by NIH SBIR contract #HHSN261201100045C.

Higher dose dobutamine stress MR imaging in repaired tetralogy of fallot: Observer variance of volumetric assessment compared with normal volunteers

PurposeTo investigate changes in image quality and observer variance between rest and higher‐dose dobutamine stress MR imaging (DS‐MR) in tetralogy of Fallot (TOF) patients and in a group of normal healthy volunteers using both axial and short axis orientation for cardiac volumetric assessment.Materials and MethodsEighteen adult patients (age 34 ± 13) with TOF and severe pulmonary regurgitation and 10 healthy volunteers underwent ventricular MR volumetry at baseline and during dobutamine infusion of 10 μg/kg/min and 20 μg/kg/min. Inter‐observer and intra‐observer agreement was calculated by coefficient of variance (COV).ResultsInter‐observer comparison showed good agreement for left ventricle (LV) and right ventricle (RV) end‐diastolic volumes at rest and both stress levels in TOF patients (axial geometry) and in normal volunteers (short axis). During dobutamine stress, the COV in TOF patients increased for LV end‐systolic volume (LV‐ESV) with each level, suggesting less agreement between observers. In contrast, RV‐ESV was much more comparable with a COV < 10 at each condition. All volumetric measurements in normal volunteers showed good inter‐observer agreement. Excellent intra‐observer agreement could be seen for all volumetric parameters with COV levels below 7.ConclusionVolumetric assessment during DS‐MR shows excellent inter‐observer agreement, except for LV‐ESV in the TOF patients at higher doses of dobutamine. The axial geometry appears to be reproducible for assessment of RV parameters, and could be considered superior to short axis imaging in patients with repaired TOF. J. Magn. Reson. Imaging 2013;38:1356–1361. © 2013 Wiley Periodicals, Inc.

A combined ultrasonic flow meter and binary vapour mixture analyzer for the ATLAS silicon tracker

We describe a combined ultrasonic instrument for gas flow metering andcontinuous real-time binary gas composition measurements. The combinedflow measurement and mixture analysis algorithm employs sound velocitymeasurements in two directions in combination with measurements of thepressure and temperature of the process gas mixture.The instrument has been developed in two geometries following extensivecomputational fluid dynamics studies of various mechanical layouts. Aversion with an axial sound path has been used with binary gas flows upto 230 l.min−1, while a version with a sound path angled at45° to the gas flow direction has been developed foruse in gas flows up to 20000 l.min−1.The instrument with the axial geometry has demonstrated a flowresolution of ⩽ 1 % of full scale for flows up to 230 l.min−1and a mixture resolution of 3.10−3 for C3F8/C2F6 molar mixtures with ∼ 20 %C2F6. Higher mixture precision is possible in mixtures ofgases with widely-differing molecular weight (mw): a sensitivity of < 5.10−5 to traces of C3F8 in nitrogen (mw difference 160)has been seen in a long duration ( > 1yr) continuous study.A prototype instrument with 45° crossing angle hasdemonstrated a flow resolution of 1.9 % of full scale for linear flowvelocities up to 15 ms−1.Although this development was motivated by a requirement of the ATLASsilicon tracker evaporative fluorocarbon cooling system, the developedinstrument can be used in many applications where continuous knowledgeof binary gas composition is required. Applications include theanalysis of hydrocarbons, vapour mixtures for semi-conductormanufacture and anaesthetic gas mixtures.

A Multi-Physics Model for Solid Oxide Iron-Air Redox Flow Battery: Simulation of Discharge Behavior at High Current Density

A rigorous physics-based mathematical model for a solid oxide iron-air redox flow battery system is presented in this paper. The modeled flow battery system combines a Fe-FeO redox couple as the energy storage unit and a regenerative solid oxide fuel cell as the electrical functioning unit in a 2D axial symmetric geometry. This model was developed from fundamental theories of reaction engineering in which basic transport phenomena and chemical/electrochemical kinetics are included. The model shows good agreement with the experimental data. Simulation results for the chemical, electrochemical and transport behavior of the battery are discussed.

Analysis of the performances of an axial flow tandem pump based on CFD computations

Tandem pump, compared with multistage pump, goes without guide vanes between impellers. Significant reduction of the axial geometry scale, resulting from lack of guide vanes, makes great sense to high-speed propulsion. Direct interactions between front and rear impellers may lead to special flows, which are different from those in a multistage pump. There are few studies of these differences. In this article, CFD computations of flows in an axial flow tandem pump are conducted to predict the performances. FBM turbulence model, which is introduced to commercial software, is used for the simulations. Circulation coefficient is defined to help analyze energy characteristics. The results demonstrate that power of the tandem pump increases slowly as discharge is getting larger. The tandem pump has better adaptability under large discharge conditions. The head of the rear impeller is not sensitive to discharge's change, which results from that the front impeller weakens the influence of discharge's change on the rear impeller, so pump's energy characteristics may be improved.

Halogen Bonding inside a Molecular Container

The synthetic macrocycle cucurbit[6]uril forms host-guest inclusion complexes with molecular dibromine and diiodine. As evidenced by their crystal structures, the encapsulated dihalogens adapt a tilted axial geometry and are held in place by two different types of halogen-bonding interactions, one with a water molecule (bond distances 2.83 Å for O···Br and 3.10 Å for O···I) and the other one with the ureido carbonyl groups of the molecular container itself (bond distances 3.33 Å for O···Br and 3.49 Å for O···I). While the former is of the conventional type, involving the lone electron pair of an oxygen donor, the latter is perpendicular, involving the π-system of the carbonyl oxygen (N-C═O···X dihedrals ca. 90°). Such perpendicular interactions resemble those observed in protein complexes of halogenated ligands. A statistical analysis of small-molecule crystal structural data, as well as quantum-chemical calculations with urea as a model (MP2/aug-cc-pVDZ-PP), demonstrates that halogen bonding with the π-system of the carbonyl oxygen can become competitive with the commonly favored lone-pair interaction whenever the carbonyl group carries electron-donating substitutents, specifically for ureas, amides, and esters, and particularly when the lone pairs are engaged in orthogonal hydrogen bonding (hX bonds). The calculations further demonstrate that the perpendicular interactions remain significantly attractive also for nonlinear distortions of the O···X-X angle to ca. 140°, the angle observed in the two reported crystal structures. The structural and theoretical data jointly support the assignment of the observed dihalogen-carbonyl contacts as genuine halogen bonds.

Finite Element Analysis of Localized Plasticity in Al 2024-T3 Subjected to Fretting Fatigue

Fretting fatigue is a combination of two complex mechanical phenomena, namely, fretting and fatigue. Fretting appears between components that are subjected to small relative oscillatory motion. Once these components undergo cyclic fatigue load at the same time, fretting fatigue occurs. Fretting fatigue is an important issue in aerospace structural design. Many studies have investigated fretting fatigue behavior; however, the majority have assumed elastic deformation and very few have considered the effect of plasticity. The main goal of this study is to monitor the effect of different fretting fatigue primary variables on localized plasticity in an aluminum alloy (Al 2024-T3) test specimen. In order to extract the stress distribution at the contact interface under elasto-plastic conditions, a modified finite element contact model was used. The contact model was verified through comparison with an elastic analytical solution. Then, a bilinear elasto-plastic isotropic hardening model with a von Mises yield surface was implemented to simulate the material behavior of the aluminum alloy. The effect of different fretting fatigue primary variables, such as axial stress, contact geometry, and coefficient of friction, on localized plasticity was investigated. Finally, the relationship between the location of maximum localized plasticity and Ruiz fretting damage parameter with the crack initiation site is discussed.

The Fourier transform of tubular densities

We consider the Fourier transform of tubular volume densities, with arbitrary axial geometry and (possibly) twisted internal structure. This density can be used to represent, among others, magnetic flux or the electron density of biopolymer molecules. We consider tubes of both finite radii and unrestricted radius. When there is overlap of the tube structure the net density is calculated using the super-position principle. The Fourier transform of this density is composed of two expressions, one for which the radius of the tube is less than the curvature of the axis and one for which the radius is greater (which must have density overlap). This expression can accommodate an asymmetric density distribution and a tube structure which has non-uniform twisting. In addition we give several simpler expressions for isotropic densities, densities of finite radius, densities which decay at a rate sufficient to minimize local overlap and finally individual surfaces of the tube manifold. These simplified cases can often be expressed as arclength integrals and can be evaluated using a system of first-order ODEs.

Role of Calcium in Metalloenzymes: Effects of Calcium Removal on the Axial Ligation Geometry and Magnetic Properties of the Catalytic Diheme Center in MauG

MauG is a diheme enzyme possessing a five-coordinate high-spin heme with an axial His ligand and a six-coordinate low-spin heme with His-Tyr axial ligation. A Ca(2+) ion is linked to the two hemes via hydrogen bond networks, and the enzyme activity depends on its presence. Removal of Ca(2+) altered the electron paramagnetic resonance (EPR) signals of each ferric heme such that the intensity of the high-spin heme was decreased and the low-spin heme was significantly broadened. Addition of Ca(2+) back to the sample restored the original EPR signals and enzyme activity. The molecular basis for this Ca(2+)-dependent behavior was studied by magnetic resonance and Mössbauer spectroscopy. The results show that in the Ca(2+)-depleted MauG the high-spin heme was converted to a low-spin heme and the original low-spin heme exhibited a change in the relative orientations of its two axial ligands. The properties of these two hemes are each different than those of the heme in native MauG and are now similar to each other. The EPR spectrum of Ca(2+)-free MauG appears to describe one set of low-spin ferric heme signals with a large g(max) and g anisotropy and a greatly altered spin relaxation property. Both EPR and Mössbauer spectroscopic results show that the two hemes are present as unusual highly rhombic low-spin hemes in Ca(2+)-depleted MauG, with a smaller orientation angle between the two axial ligand planes. These findings provide insight into the correlation of enzyme activity with the orientation of axial heme ligands and describe a role for the calcium ion in maintaining this structural orientation that is required for activity.

Single-Step versus Stepwise Two-Electron Reduction of Polyarylpyridiniums: Insights from the Steric Switching of Redox Potential Compression

Contrary to 4,4'-dipyridinium (i.e., archetypal methyl viologen), which is reduced by two single-electron transfers (stepwise reduction), the 4,1'-dipyridinium isomer (so-called "head-to-tail" isomer) undergoes two electron transfers at apparently the same potential (single-step reduction). A combined theoretical and experimental study has been undertaken to establish that the latter electrochemical behavior, also observed for other polyarylpyridinium electrophores, is due to potential compression originating in a large structural rearrangement. Three series of branched expanded pyridiniums (EPs) were prepared: N-aryl-2,4,6-triphenylpyridiniums (Ar-TP), N-aryl-2,3,4,5,6-pentaphenylpyridiniums (Ar-XP), and N-aryl-3,5-dimethyl-2,4,6-triphenylpyridinium (Ar-DMTP). The intramolecular steric strain was tuned via N-pyridinio aryl group (Ar) phenyl (Ph), 4-pyridyl (Py), and 4-pyridylium (qPy) and their bulky 3,5-dimethyl counterparts, xylyl (Xy), lutidyl (Lu), and lutidylium (qLu), respectively. Ferrocenyl subunits as internal redox references were covalently appended to representative electrophores in order to count the electrons involved in EP-centered reduction processes. Depending on the steric constraint around the N-pyridinio site, the two-electron reduction is single-step (Ar = Ph, Py, qPy) or stepwise (Ar = Xy, Lu, qLu). This steric switching of the potential compression is accurately accounted for by ab initio modeling (Density Functional Theory, DFT) that proposes a mechanism for pyramidalization of the N(pyridinio) atom coupled with reduction. When the hybridization change of this atom is hindered (Ar = Xy, Lu, qLu), the first reduction is a one-electron process. Theory also reveals that the single-step two-electron reduction involves couples of redox isomers (electromers) displaying both the axial geometry of native EPs and the pyramidalized geometry of doubly reduced EPs. This picture is confirmed by a combined UV-vis-NIR spectroelectrochemical and time-dependent DFT study: comparison of in situ spectroelectrochemical data with the calculated electronic transitions makes it possible to both evidence the distortion and identify the predicted electromers, which play decisive roles in the electron-transfer mechanism. Last, this mechanism is further supported by in-depth analysis of the electronic structures of electrophores in their various reduction states (including electromeric forms).