Parallel Geometry Research Articles

New conformal invariants in absolute parallelism geometry

The aim of the present paper is to investigate conformal changes in absolute parallelism geometry. We find out some new conformal invariants in terms of the Weitzenböck connection and the Levi-Civita connection of an absolute parallelism space.

Conformational analysis of some 4′-substituted 2-(phenylselanyl)- 2-(methoxy)- acetophenones

A conformational study of some 4′-substituited 2-(phenylselanyl)-2-(methoxy)-acetophenones (OMe 1, H 2, and Cl 3) was performed using IR carbonyl stretching band analysis supported by NBO and PCM calculations at the B3LYP/6-31 + G (d,p) level for 1–3 and using X-ray diffraction for 1 and 2. The computational results indicated the existence of three stable conformers for the series (c2, c3, and c1 in order of decreasing stability), whose relative abundance changes with solvent permittivity. The experimental trend observed for the components of the triplet carbonyl band in all solvents matches well with computational results and thus allows for their assignment to distinct conformers. The relative population of the c1 conformer increases in more polar solvents, becoming the most stable conformer in the highest permittivity solvent, acetonitrile, as indicated by IR spectra and PCM calculations. These findings are related to the quasi parallel geometry assumed by the Cδ+ = Oδ− and Cδ+-Oδ- dipoles, which favour stronger solvation. NBO analysis shows that the sum of the energies (ΣE) of the relevant orbital interactions stabilizes the c3 conformer of 1–3 slightly, likely due to the minor contribution of the LPO5→σ*C3Se10 interaction. However, only the c1 conformer is significantly destabilized by the Oδ−(1)CO … Oδ−(5)OMe short contact electrostatic repulsion, which is also responsible for its highest νCO frequency. In addition, the LPO5→ σ*C2C3 orbital interaction accounts for the lowest νCO frequency of c3 conformer. X-ray single crystal analysis of compounds 1 and 2 indicates that in the solid state they assume the least stable c1 conformation found in the gas phase. Molecules of these compounds are stabilized in the crystal through a series of CH⋯O and CH … π intermolecular interactions.

Investigation of Magnetic Properties of Multilayer Thin Films with Spin-Wave Resonance

A theory has been developed to simulate spin-wave resonance (SWR) modes in the multilayer systems consisting of alternate magnetic and nonmagnetic layers. An equation of motion of magnetization with Gilbert-type damping parameter for simulating SWR modes was used. It has been realized that the theory developed for the magnetic multilayer films is suitable to study the spin dynamics and extract various magnetic parameters. It has been shown that SWR modes strongly depend on an effective magnetic anisotropy constant (K eff), interlayer exchange coupling constant (A 12) and effective magnetization (M eff). The nature of the effective magnetic anisotropy and interlayer exchange coupling constants has been investigated by using the developed SWR theory in detail. The separation between optic and acoustic modes strongly depends on the magnitude of the interlayer exchange coupling constant, whereas the relative position of the acoustic and optic modes depends on the sign of $A_{12}$ . With increasing the interlayer exchange coupling constant, the resonance field of the optic mode decreases (increases) for ferromagnetic (antiferromagnetic) coupling. When the effective magnetic anisotropy constant increases, the resonance field of the acoustic and optic modes increases for both the ferromagnetic and antiferromagnetic couplings. The increasing of the effective magnetization results in decreasing of the resonance field of SWR mode at parallel geometry, whereas that of SWR mode increases at the perpendicular geometry. The results are compatible to the other theories and experimental results.

Direct inversion algorithm for focal plane scanning optical projection tomography.

To achieve approximately parallel projection geometry, traditional optical projection tomography (OPT) requires the use of low numerical aperture (NA) objectives, which have a long depth-of-field at the expense of poor lateral resolution. Particularly promising methods to improve spatial resolution include ad-hoc post-processing filters that limit the effect of the system's MTF and focal-plane-scanning OPT (FPS-OPT), an alternative acquisition procedure that allows the use of higher NA objectives by limiting the effect of their shallow depth of field yet still assumes parallel projection rays during reconstruction. Here, we provide a detailed derivation that establishes the existence of a direct inversion formula for FPS-OPT. Based on this formula, we propose a point spread function-aware algorithm that is similar in form and complexity to traditional filtered backprojection (FBP). With simulations, we demonstrate that our point-spread-function aware FBP for FPS-OPT leads to more accurate images than both traditional OPT with deconvolution and FPS-OPT with naive FBP reconstruction. We further illustrate the technique on experimental zebrafish data, which shows that our approach reduces out-of-focus blur compared to a direct FBP reconstruction with FPS-OPT.

Metodología numérica para resolver ecuaciones del modelo elíptico de un superconductor tipo II anisótropo

Based on the macroscopic description of a type II anisotropic superconducting material, this paper presents numerical methods to model the magnetic induction of these materials in a critical state. In this case, an elliptical model of the critical state is used to describe a type II anisotropic superconductor in terms of parallel geometry. It describes how the mathematical problem is solved in order to find the distribution of magnetic induction in the material. This consists of solving a system of ordinary differential equations. In order to do this, the standard libraries of MATLAB software were used. Two routines were especially used, the first of which gives an initial rough result which is then refined with the second routine. The authors have ample experience in the macroscopic study of the magnetic properties of type II superconductors as well as international publications in this specialized study area.

On the Effect of the Flow Field Plate’s Geometry on the Polymer Electrolyte Membrane Water Electrolysis Cell’s Performance

The key for successful commercialization of fuel cell products, such as Fuel Cell Vehicle, Hydrogen-Powered busses, and Hydrogen-Powered Passenger Train is compact, safe, reliable, rapid response, high hydrogen purity, dynamic operation, and high pressure system for hydrogen storage technology. These quality characteristics of hydrogen storage technology can be met by polymer electrolyte membrane water electrolysis (PEMWE) technology. Also the high compatibility of PEMWE technology with intermittent renewable energy sources leads to quicker commercialization of fuel cell products. Flow field plates (FFPs) along with the current collectors represent 48% of the stack cost. Also, FFPs are responsible for distributing reactant water and removing the pure oxygen with unreacted water from the anode side and hydrogen with crossed over water from the cathode side. Thus, FFPs must be probably designed to distribute reactant water evenly resulting in more uniform electrochemical reaction over all the active area of the PEMWE cell. Uniform electrochemical reaction leads to uniform current and temperature distribution. Therefore, the cell performance might be developed and degradation rate might be reduced. The present work presents the effect of the most common FFPs geometries; single serpentine, interdigitated, and parallel geometry on the polarization resistances using electrochemical impedance spectroscopy (EIS) measurements and on the whole cell performance using the IV curve measurements are experimentally demonstrated. Each anode FFP’s geometry is tested with three different cathode’s FEPs geometries. Thus, the effect 9 geometries combined between the anode and the cathode of a 50 cm2 PEMWE cell are presented in this work. All the geometries have the same inlet and outlet manifold design. Thus, the pressure drop between the inlet and the outlet of each FFP’s geometry is also presented in this work.

Efficacy of a novel liquid block working with a nanofluid containing graphene nanoplatelets decorated with silver nanoparticles compared with conventional CPU coolers

This research attempts to investigate the efficacy and entropy generation of a hybrid nanofluid containing graphene nanoplatelets decorated with silver nanoparticles in three different liquid blocks for CPU cooling. A novel distributor liquid block is evaluated compared with two conventional liquid blocks including serpentine and parallel geometries. Comparisons of the flow distribution uniformity, maximum CPU temperature, average CPU temperature, temperature uniformity on CPU surface, and pumping power consumption of liquid blocks with novel and conventional configurations are made. The results show that the novel distributor liquid block has a superior efficacy based on both thermal performance and irreversibility rates. In addition, the merit of using the nanofluid in the liquid blocks is greater than pure water, and this hybrid nanofluid shows a promising view for cooling improvement in electronics.

Dynamic influence of pentoxifylline on the oxygen status of Pliss’s lymph sarcoma in rat

Tumor oxygenation is one of the key factors influencing disease prognosis and the effectiveness of treatment. Assessment of tumor oxygenation levels facilitates the selection of optimum conditions for radiation therapy, and plays an important role in creating alternative regimes of irradiation. Treating tumors with agents capable of increasing tumor oxygenation in order to increase radiosensitivity is a promising avenue of enquiry. Diffuse optical spectroscopy (DOS) allows a noninvasive determination of tissue oxygen levels based on information about the local changes in optical parameters, and the visualization of metabolic processes in the region of interest. DOS allows reconstruction of the two-dimensional distribution of main tissue chromophores that characterize the processes of oxygen supply (oxygenated hemoglobin) and oxygen consumption (deoxygenated hemoglobin), as well as the blood oxygen saturation levels, which indirectly reflect the tissue oxygenation levels. In the present study, a hemorheologic drug, pentoxifylline, which can improve microcirculation in regions with circulatory disturbances, was used for modifying tumor tissue oxygenation. Pliss’s lymph sarcoma (PLS), which is characterized by rapid growth and early occurrence of necrotic areas, was chosen as a tumor model. Tumor oxygenation was monitored by DOS with parallel plane geometry. Pentoxifylline could improve tumor oxygenation by increasing the concentration of oxyhemoglobin. The increased blood oxygen saturation persisted from 30 to 120 min after drug administration. Normal healthy tissue (muscle) and tumor tissue responded differently to the drug. DOS can be used for testing new agents that influence tissue oxygen status and blood-filling rate.

A capillary specimen aberration for describing X-ray powder diffraction line profiles for convergent, divergent and parallel beam geometries

X-ray powder diffraction patterns of cylindrical capillary specimens have substantially different peak positions, shapes and intensities relative to patterns from flat specimens. These aberrations vary in a complex manner with diffraction angle and instrument geometry. This paper describes a fast numerical procedure that accurately describes the capillary aberration in the equatorial plane for convergent focusing, divergent and parallel beam instrument geometries. Axial divergence effects are ignored and only a cross section of the capillary, a disc, is considered; it is assumed that axial divergence effects can be described using an additional correction that is independent of the disc correction. Significantly, the present implementation uses theTOPAS-Academicaberration approximation technique of averaging nearby aberrations in 2θ space to approximate in-between aberrations, which results in no more than ∼30 disc aberrations calculated over the entire 2θ range, even when the diffraction pattern comprises thousands of peaks. Finally, the disc aberration is convoluted with the emission profile and other instrument and specimen aberrations in a Rietveld refinement sense, allowing for refinement on the specimen's absorption coefficient and capillary diameter, as well as the instrument focal length. Large differences between refined and expected values give insight into instrument alignment.

5-Axis tool path planning based on highly parallel discrete volumetric geometry representation: Part I contact point generation

ABSTRACTWhile 5-axis CNC machines improve the manufacturing productivity, the tool-path programming demands human expertise and tremendous time investment to generate collision-free optimal tool trajectories. To address the challenge of multi-axis CNC programming, this work presents a new discrete volume based geometry representation that naturally enables highly parallel geometry processing. Then it formulates and discusses a methodology for tool path planning algorithms designed around the formulated geometric representation for 5-axis CNC milling machines and ball end tools. This paper is the first of two papers that deals with finding the XYZ locations of ball end mill centers that govern the tool trajectories. The experimental 5-axis machining using the resulting tool paths demonstrates that the designed algorithms are capable of producing collision- and gouge- free tool paths with a desired surface quality for a given target geometry by using the selected ball end tools.

The structure of bow shocks formed by the interaction of pulsed-power driven magnetised plasma flows with conducting obstacles

We present an experimental study of the development and structure of bow shocks produced by the interaction of a magnetised, collisional, super-Alfvénic plasma flow with conducting cylindrical obstacles. The plasma flow with an embedded, frozen-in magnetic field (ReM ∼ 20) is produced by the current-driven ablation of fine aluminium wires in an inverse, exploding wire array z-pinch. We show that the orientation of the embedded field with respect to the obstacles has a dramatic effect on the bow shock structure. When the field is aligned with the obstacle, a sharp bow shock is formed with a global structure that is determined simply by the fast magneto-sonic Mach number. When the field is orthogonal to the obstacle, magnetic draping occurs. This leads to the growth of a magnetic precursor and the subsequent development of a magnetised bow shock that is mediated by two-fluid effects, with an opening angle and a stand-off distance, that are both many times larger than in the parallel geometry. By changing the field orientation, we change the fluid regime and physical mechanisms that are responsible for the development of the bow shocks. MHD simulations show good agreement with the structure of well-developed bow shocks. However, collisionless, two-fluid effects will need to be included within models to accurately reproduce the development of the shock with an orthogonal B-field.

A prototype optical-CT system for PRESAGE 3D dosimeter readout

This work introduces the Duke Integrated-lens Optical Scanner (DIOS), a prototype optical-CT system designed for convenient and low-cost readout of PRESAGE 3D dosimeters. A key novelty of the DIOS is the incorporation of a multi-purpose light-collimating tank (the LC-tank). The LC-tank collimates light from a point source, maintains parallel ray geometry through a dosimeter mounted inside the tank, and refocuses emergent light onto a CCD detector. A second purpose is to dramatically reduce the amount of refractive matched fluid required in prior optical-CT scanners. This is achieved by substituting large quantities of refractive-matched fluid with solid RI-matched polyurethane. The advantages of DIOS include eliminating the need for expensive telecentric lenses, and eliminating the impracticality of large volumes of RI matched fluid. The DIOS is potentially more susceptible to stray-light artifacts. Preliminary phantom testing shows promising agreement between PRESAGE/DIOS readout and prior commissioned optical-CT scanners, as well as with Eclipse dose calculations.

A pure geometric theory of gravity and a material distribution

A field theory is constructed in the context of parameterized absolute parallelism geometry. The theory is shown to be a pure gravity one. It is capable of describing the gravitational field and a material distribution in terms of the geometric structure of the geometry used (the parallelization vector fields). Three tools are used to attribute physical properties to the geometric objects admitted by the theory. Poisson and Laplace equations are obtained in the linearized version of the theory. The spherically symmetric solution of the theory, in free space, is found to coincide with the Schwarzschild exterior solution of the general theory of relativity. The theory respects the weak equivalence principle in free space only. Gravity and material distribution are not minimally coupled.

Feasibility of employing thick microbeams from superficial and orthovoltage kVp x-ray tubes for radiotherapy of superficial cancers

Preclinical investigations of thick microbeams show these to be feasible for use in radiotherapeutic dose delivery. To create the beams we access a radiotherapy x-ray tube that is familiarly used within a conventional clinical environment, coupling this with beam-defining grids. Beam characterisation, both single and in the form of arrays, has been by use of both MCNP simulation and direct Gafchromic EBT film dosimetry. As a first step in defining optimal exit-beam profiles over a range of beam energies, simulation has been made of the x-ray tube and numbers of beam-defining parallel geometry grids, the latter being made to vary in thickness, slit separation and material composition. For a grid positioned after the treatment applicator, and of similar design to those used in the first part of the study, MCNP simulation and Gafchromic EBT film were then applied in examining the resultant radiation profiles. MCNP simulations and direct dosimetry both show useful thick microbeams to be produced from the x-ray tube, with peak-to-valley dose ratios (PVDRs) in the approximate range 8.8–13.9. Although the potential to create thick microbeams using radiotherapy x-ray tubes and a grid has been demonstrated, Microbeam Radiation Therapy (MRT) would still need to be approved outside of the preclinical setting, a viable treatment technique of clinical interest needing to benefit for instance from substantially improved x-ray tube dose rates.

Thermohydrodynamic analysis and tribological optimization of a curved pocket thrust bearing

Texture patterns implemented on thrust bearing surfaces have been proven very beneficial in terms of load carrying capacity and friction coefficient. In the present study, the potential of thrust bearings with a curved pocket stator geometry is investigated for realistic operating conditions. Bearing performance is quantified by means of Computational Fluid Dynamics (CFD) simulations based on the numerical solution of the Navier-Stokes and energy equations for incompressible flow, taking into account conjugate heat transfer at the bearing stator and rotor. After defining a reference slider design, optimization problems are formulated and solved, to arrive at optimal curved pocket designs. Here, the slider convergence ratio, as well as the pocket size, shape and depth, are defined in terms of proper design variables, whereas the load carrying capacity and friction coefficient constitute the problem's objective functions. The present results illustrate a superior performance of the curved open pocket slider designs in comparison to corresponding open square pocket sliders. Optimal solutions are characterized by parallel slider geometries. The improved performance of optimal designs can be attributed to reduced side leakage, in comparison to open square pocket geometries. The good performance of a thrust bearing with a corresponding curved pocket geometry is verified. Overall, the present optimal geometries are rather easy to manufacture, which makes them an attractive choice for the design of thrust bearings operated in a wide range of rotor speeds.

Connections in sub-Riemannian geometry of parallelizable distributions

The notion of a parallelizable distribution has been introduced and investigated. A non-integrable parallelizable distribution carries a natural sub-Riemannian structure. The geometry of this structure has been studied from the bi-viewpoint of absolute parallelism geometry and sub-Riemannian geometry. Two remarkable linear connections have been constructed on a sub-Riemannian parallelizable distribution, namely, the Weitzenböck connection and the sub-Riemannian connection. The obtained results have been applied to two concrete examples: the spheres [Formula: see text] and [Formula: see text].

Measuring Forces Generated by Ensembles of Kinesin-5 Crosslinking Two Microtubules

The proper organization of the microtubule-based mitotic spindle is proposed to depend on nanometer-sized motor proteins generating forces that scale with a micron-sized geometric feature, such as microtubule overlap length. However, it has been unclear whether such regulation can be achieved by any mitotic motor protein. To address this knowledge gap, we have employed an assay that combines an optical trap and total internal reflection fluorescence (TIRF) to show that ensembles of kinesin-5, a conserved mitotic motor protein, can push apart overlapping antiparallel microtubules to generate a force whose magnitude scales with filament overlap length. We also find that kinesin-5 can produce overlap-length-dependent “brake-like” resistance against relative microtubule sliding in both parallel and antiparallel geometries, an activity that has been suggested by cell biological studies but had not been directly measured. Finally, we performed numerical simulations which reveal the bio-mechanical properties of this motor protein that allow for efficient force transmission within crosslinked microtubule networks. Together, our results reveal how a motor protein can function as an analog converter, “reading” simple geometric and dynamic features in cytoskeletal networks to produce regulated and scalable force outputs.

Bichromophoric Compounds with Orthogonally and Parallelly Arranged Chromophores Separated by Rigid Spacers.

Electronic energy transfer (EET) between chromophores is of fundamental importance for many biological processes and optoelectronic devices. However, common models fall short in fully describing the process, especially in bichromophoric model systems with a donor and acceptor connected by a rigid linker providing perpendicular geometries. Herein, we report a novel strategy for preparing bichromophores containing adamantane or 2-(2-adamantylidene)adamantane as rigid spacers, providing a fixed distance between chromophores, and their parallel or perpendicular arrangement without chromophore rotation. New fluorophores were developed and linked via spiroatoms. Bichromophores with identical (blue-blue) or different (blue-red) chromophores were synthesized, either in orthogonal or parallel geometry. These were characterized by absorption/fluorescence spectroscopy, time-resolved fluorescence anisotropy, and fluorescence antibunching measurements. Based on the Förster point-dipole approximation, EET efficiencies were estimated by using geometrical parameters from (time-dependent) density functional calculations. For bichromophores with parallel geometry, the predicted EET efficiencies were near unity and fit the measurements. In spite of estimated values around 0.4 and 0.5, 100 % efficiency was observed also for bichromophores with orthogonal geometry. The new rigid scaffolds presented here open new possibilities for the synthesis of bichormophores with well-defined parallel or perpendicular geometry.

A model electrode of well-defined geometry prepared by direct laser-induced decoration of nanoporous templates with Au–Ag@C nanoparticles

We present an original type of model electrode system consisting of bimetallic Au–Ag nanoparticles embedded in an amorphous carbon matrix with an extremely well-defined geometry of parallel, straight, cylindrical macropores. The samples are prepared in one step by direct laser deposition of the metal/carbon composite onto the inner walls of a porous ‘anodic’ alumina matrix serving as a template. The coating is homogeneous from top to bottom of the pores, and the amount of material deposited can be tuned by the duration of the deposition procedure. As a test system, we demonstrate that a bimetallic Ag–Au@C system is catalytically active for the electrochemical oxidation of glucose in alkaline solution, the anodic reaction of a direct glucose fuel cell. Furthermore, the electrocatalytic current density increases with the amount of Ag–Au@C NPs deposited, up to a point at which the pores are clogged with it. This type of model system allows for the systematic study of geometric effects in fuel cell electrodes. It can be generalized to a number of different nanoparticle compositions, and thereby, to various electrocatalytic reactions.

Simultaneous fluoroscopic and nuclear imaging: impact of collimator choice on nuclear image quality.

X-ray-guided oncological interventions could benefit from the availability of simultaneously acquired nuclear images during the procedure. To this end, a real-time, hybrid fluoroscopic and nuclear imaging device, consisting of an X-ray c-arm combined with gamma imaging capability, is currently being developed (Beijst C, Elschot M, Viergever MA, de Jong HW. Radiol. 2015;278:232-238). The setup comprises four gamma cameras placed adjacent to the X-ray tube. The four camera views are used to reconstruct an intermediate three-dimensional image, which is subsequently converted to a virtual nuclear projection image that overlaps with the X-ray image. The purpose of the present simulation study is to evaluate the impact of gamma camera collimator choice (parallel hole versus pinhole) on the quality of the virtual nuclear image. Simulation studies were performed with a digital image quality phantom including realistic noise and resolution effects, with a dynamic frame acquisition time of 1 s and a total activity of 150 MBq. Projections were simulated for 3, 5, and 7 mm pinholes and for three parallel hole collimators (low-energy all-purpose (LEAP), low-energy high-resolution (LEHR) and low-energy ultra-high-resolution (LEUHR)). Intermediate reconstruction was performed with maximum likelihood expectation-maximization (MLEM) with point spread function (PSF) modeling. In the virtual projection derived therefrom, contrast, noise level, and detectability were determined and compared with the ideal projection, that is, as if a gamma camera were located at the position of the X-ray detector. Furthermore, image deformations and spatial resolution were quantified. Additionally, simultaneous fluoroscopic and nuclear images of a sphere phantom were acquired with a physical prototype system and compared with the simulations. For small hot spots, contrast is comparable for all simulated collimators. Noise levels are, however, 3 to 8 times higher in pinhole geometries than in parallel hole geometries. This results in higher contrast-to-noise ratios for parallel hole geometries. Smaller spheres can thus be detected with parallel hole collimators than with pinhole collimators (17 mm vs 28 mm). Pinhole geometries show larger image deformations than parallel hole geometries. Spatial resolution varied between 1.25 cm for the 3 mm pinhole and 4 cm for the LEAP collimator. The simulation method was successfully validated by the experiments with the physical prototype. A real-time hybrid fluoroscopic and nuclear imaging device is currently being developed. Image quality of nuclear images obtained with different collimators was compared in terms of contrast, noise, and detectability. Parallel hole collimators showed lower noise and better detectability than pinhole collimators.