Helical Model Research Articles

Low-dose helical CT projection data restoration using noise estimation

To build a helical CT projection data restoration model at random low-dose levels. We used a noise estimation module to achieve noise estimation and obtained a low-dose projection noise variance map, which was used to guide projection data recovery by the projection data restoration module. A filtering back-projection algorithm (FBP) was finally used to reconstruct the images. The 3D wavelet group residual dense network (3DWGRDN) was adopted to build the network architecture of the noise estimation and projection data restoration module using asymmetric loss and total variational regularization. For validation of the model, 1/10 and 1/15 of normal dose helical CT images were restored using the proposed model and 3 other restoration models (IRLNet, REDCNN and MWResNet), and the results were visually and quantitatively compared. Quantitative comparisons of the restored images showed that the proposed helical CT projection data restoration model increased the structural similarity index by 5.79% to 17.46% compared with the other restoration algorithms (P < 0.05). The image quality scores of the proposed method rated by clinical radiologists ranged from 7.19% to 17.38%, significantly higher than the other restoration algorithms (P < 0.05). The proposed method can effectively suppress noises and reduce artifacts in the projection data at different low-dose levels while preserving the integrity of the edges and fine details of the reconstructed CT images.

Experimental and Numerical Investigation to Assess the Performance of Helical Bach Vertical Axis Wind Turbine at Low Wind Velocity Conditions

Abstract Many turbine models have been evolved to ameliorate the functioning of the small wind energy system. The newly developed helical Bach-type vertical axis wind turbine (VAWT) is used in this analysis with an idea to improve the overall performance. The shape of the conventional Bach-type vertical axis wind turbine is a modified form of a Savonius model which has both circular and straight portions to the blade profile. The simple Bach model has a maximum coefficient of performance corresponding to the blade arc angle of 45 deg and 225 deg. However, it consists of negative torque at the rotational angles of about 120–180 deg and 300–360 deg. Moreover, in the newly developed helical Bach, rotors can reduce the variation in torque in the rotational cycle; thereby, uniform torque is achieved in all angular position with improved performance. In this paper, experiments were conducted in the natural wind at Wind Turbine Research Station, Kayathar, Tamil Nadu, India. In addition to experimental work, the three-dimensional steady-state numerical investigations have been performed in the helical Bach vertical axis wind turbine. It is found that the numerical results are well matched with the experimental data. Based on the above computational study, it is found that helical Bach models have an increase in overall performance compared to the conventional Bach models and helical Savonius model.

Photon Characteristics and Behavior under Refractive Index

The effective mass, energy and momentum of photon in medium is described. The photon has both kinetic and potential energy and displays an effective mass when travelling through a medium. The photon is a type of elementary particle that serves as the quantum of the electromagnetic field and is explained through equations to have an elastic constant, volume, momentum, force, power and zero rest mass. The theory that photons a massless only applies to rest mass. A photon undergoes different dynamics such as strain and changes in effective mass under the influence of the refractive index that gives rise to a refractive force. This study synthesizes some properties of energy such as elastic constant, weight, and volume in order to explain the nature of photons and photon dynamics under refractive index. In this study, a helical spring model has been used to describe the behavior of a photon in the medium. The model connects together the exhibited properties such as energy, effective mass, spin, elastic constant and volume. Further explanation is given to the effect of gravitational force on wavelength and refractive index of air, and how gravitational force causes red and blue shifts in photon propagation. The quantization of energy has been extended to the quantization of space, time and matter. This study is consistent and consolidates the existing classical and quantum theories. There are further potential applications in optical communication, quantum cryptography, quantum optics, and medicine, especially in the use of two-photon excitation microscopy and photodynamic therapy.

Turbulent broadening of electron heat-flux width in electromagnetic gyrokinetic simulations of a helical scrape-off layer model

We demonstrate that cross field transport in the scrape-off layer (SOL) can be moderately increased by electromagnetic effects in high-beta regimes, resulting in broadening of the electron heat-flux width on the endplates. This conclusion is taken from full-f electromagnetic gyrokinetic simulations of a helical SOL model that roughly approximates the SOL of the National Spherical Torus Experiment. The simulations have been performed with the Gkeyll code, which recently became the first code to demonstrate the capability to simulate electromagnetic gyrokinetic turbulence on open magnetic field lines with sheath boundary conditions. We scan the source rate and thus β, so that the normalized pressure gradient (the MHD ballooning parameter α∝∂β/∂r∝β/Lp) is scanned over an experimentally relevant range, α=0.3−1.5. While there is little change in the pressure gradient scale length Lp near the midplane as beta is increased, a 10% increase in cross field transport near the midplane results in an increase in the electron heat-flux width λq and a 25% reduction of the peak electron heat flux to the endplates.

Calibration of nonlocal generalized helical beam model for free vibration analysis of coiled carbon nanotubes via molecular dynamics simulations

This paper studied the free vibration behavior of coiled carbon nanotubes (CCNTs) using continuum mechanics methods and molecular dynamics (MD) simulations. Based on the continuum mechanics method, a new elasticity model called the nonlocal generalized Washizu beam (NGWB) was innovated by considering the effects of the curvature and cross-section thickness of nanotubes, as well as size-dependent effect. Then, the governing equations for the vibrational behavior of CCNTs were derived and solved using the numerical generalized differential quadrature method (GDQM). The free vibration behavior of CCNTs was also examined by performing the MD simulations to determine the calibrated values of the nonlocal parameter () that are applied in the NGWB elasticity model and to validate and evaluate the obtained results. Since the NGWB elasticity model considers the size-dependent effect on the vibrational behavior, obtained results from it well agrees with the MD simulation results in the present study. For CCNTs, there was a coupling between transverse, longitudinal, and torsional vibrations, which led to the beating phenomenon. The natural frequencies decreases by increasing the number of pitches ( aspect ratio and pitch angle The nonlocal parameter has a more significant effect on the frequencies of CCNTs with smaller geometrical parameters. In addition, the type of boundary conditions affects the calibrated values of the nonlocal parameter, frequency values, and arrangement of vibrating mode shapes of CCNTs. Results of the present study can be applied in the design and analysis of nano-electro-mechanical systems (NEMS), sensors, and nano-composite structures containing CCNTs. Also, the NGWB elasticity model might be useful in the statics and wave propagation studies of CCNTs, and other coiled and curved nano-structures.

The aerodynamics of a blade pitch, rotor speed, and surge step for a wind turbine regarding dynamic inflow

AbstractFloater motions introduce unsteadiness in the aerodynamics of floating offshore wind turbines. The aerodynamics of a wind turbine after three perturbations are studied: a blade pitch step, a rotor speed step for which dynamic inflow is expected, and a surge velocity step. The free vortex wake method and an analytical helical vortex model based on the Joukowsky rotor model are used to study the dynamic behavior of the induced velocity at the blades. As expected, the dynamic inflow effect is clear for the blade pitch and rotor speed changes, but for a surge velocity step, the models show that very little dynamic inflow effect takes place because the velocity induced by the vortex helix is not significantly modified: the tip vortex helix circulation change is partially compensated by the geometry change of the helix. For the rate of change, the velocities induced on the rotor by the vortex helix for the pitch and rotor speed changes show a rapid adjustment at the blade tip, with a slower change throughout the rest of the blade and at the center of the rotor. The convection velocity of the tip vortices is shown to be the main variable of the temporal evolution of the dynamic inflow effect.

How Structural Biology Has Directly Impacted Our Understanding of P2X Receptor Function and Gating.

P2X receptors are ATP-gated ion channels expressed in a wide variety of eukaryotic cells. They play key roles in diverse processes such as platelet activation, smooth muscle contraction, synaptic transmission, nociception, cell proliferation, and inflammation making this receptor family an important pharmacological target. Structures of P2X receptors solved by X-ray crystallography have been instrumental in helping to define mechanisms of molecular P2X receptor function. In 2009, the first X-ray structure of the P2X4 receptor subtype confirmed a trimeric stoichiometry and revealed the overall architecture of the functional ion channel. Subsequent X-ray structures have provided the molecular details to define the orthosteric ATP binding pocket, the orthosteric antagonist binding pocket, an allosteric antagonist binding pocket, and the pore architecture in each of the major conformational states of the receptor gating cycle. Moreover, the unique gating mechanism by which P2X receptor subtypes desensitize at differing rates, referred to as the helical recoil model of receptor desensitization, was discovered directly from X-ray structures of the P2X3 receptor. However, structures of P2X receptors solved by X-ray crystallography have only been able to provide limited information on the cytoplasmic domain of this receptor family, as this domain was always truncated to varying degrees in order to facilitate crystallization. Because the P2X7 receptor subtype has a significantly larger cytoplasmic domain that has been shown to be necessary for its ability to initiate apoptosis, an absence of structural information on the P2X7 receptor cytoplasmic domain has limited our understanding of its complex signaling pathways as well as its unusual ability to remain open without undergoing desensitization. This absence of cytoplasmic structural information for P2X7 receptors was recently overcome when the first full-length P2X7 receptor structures were solved by single-particle cryogenic electron microscopy. These structures finally provide insight into the large and unique P2X7 receptor cytoplasmic domain and revealed two novel structural elements and several surprising findings: first, a cytoplasmic structural element called the cytoplasmic ballast was identified that contains a dinuclear zinc ion complex and a high affinity guanosine nucleotide binding site and second, a palmitoylated membrane proximal structural element called the C-cys anchor was identified which prevents P2X7 receptor desensitization. This chapter will highlight the major structural and functional aspects of P2X receptors discovered through structural biology, with a key emphasis on the most recent cryogenic electron microscopy structures of the full-length, wild-type P2X7 receptor.

A revised method to calculate time-varying mesh stiffness of helical gear

Time-varying mesh stiffness (TVMS) of gear plays vital role in analysing dynamic characteristic of gear transmission. So accurately evaluating the TVMS is important and essential. In this paper, a revised method to calculate the TVMS of helical gear is proposed. Based on slice method, the helical gear is sliced into pieces along the tooth width direction. The proposed method corrects the fillet foundation stiffness within multi-tooth in contact and considers the non-linearity and load-dependence of the Hertzian contact stiffness. The effect of the axial mesh force is considered. Finally, an equivalent helical gear model is established in ANSYS to study the mesh stiffness. The results show the proposed method has high effectiveness compared with FEM (finite element method).

Selection of the Most Appropriate Sustainable Buildings Assessment Categories and Criteria for Developing Countries: Case of Ethiopia

Sustainable/green buildings can save for 36% of total energy use, 65% of electricity consumption, and 30% of greenhouse gas emissions, 30% of raw materials use, 30% of waste output, and 12% of potable water consumption. Several sustainable/green building assessment tools were existed and used by both developed and developing countries. However; Ethiopia's buildings were not critically assessed and evaluated from sustainability points of view because there was no such type of studies conducted so far. This paper aims to explore the most significant and widely used as well as the basis for other sustainable/green building assessment tools such as Building Research Establishment Environmental Assessment Methodology (BREEAM), Leadership in Energy and Environmental Design (LEED), Comprehensive Assessment System for Built Environment Efficiency (CASBEE), Sustainable Building Tool (SBTool), Comprehensive Environmental Performance Assessment Scheme (CEPAS), Deutsche Gesellschaft für Nachhaltiges Bauen (DGNB), Green Mark and Green Star. The methodology employed for this paper is the selection of the 10 most commonly and widely utilized SBATs from the 57 SBATs based on desk review and document analysis. The results of the study identified that all these 10 SBATs have their own assessment categories and criteria based on many factors like climatic conditions, availability of resources plus methods employed demographic dynamics, and legal aspects of the sector for assessing the sustainable/green buildings. It distinguishes the most commonly and repeatedly used assessment categories and criteria and uses a consensus-based approach with experts in the building sectors, a four-quadrant model, and a Circular and Helical flow model, to develop a new sustainable building assessment tool (SBAT) suitable for Ethiopia.

Forming Process and Simulation Analysis of Helical Carbon Fiber Reinforced Aluminum Matrix Composite

In order to promote the industrialization of the large deformation technology of carbon fiber composites, this paper studies a new method of forming of helical carbon fiber reinforced aluminum matrix composite. The purpose is to solve the problem of large deformation of carbon fiber with low elongation and metal matrix with high elongation. By introducing carbon fiber with helical space structure into the aluminum matrix, the helical carbon fiber reinforced aluminum matrix composites were prepared and the subsequent drawing deformation was carried out. Here we systematically studied the large plastic deformation behavior of helical carbon fiber reinforced aluminum matrix composite via a combination of numerical simulations and experiments, and analyzed the deformation law and stress of helical carbon fiber in the deformation process. We found that the plastic deformation of the composite causes local stress concentration around the helical carbon fiber, and the helical carbon fiber will move synchronously with the aluminum matrix during the deformation, and receive the pressure from the aluminum matrix. Second, the best process parameters obtained from the simulation, that is, the drawing die angle α = 7°, when five-pass drawing experiments were carried out, the total deformation reached 58%, and the average elongation of a single pass was 18.9%. The experimental show carbon fiber reinforced aluminum matrix composite with helical space structure can achieve large deformation and high strength. The experimental and simulation are in general agreement, which verifies the correctness of the carbon fiber helical structure model.

Model Development and Transient Analysis of the HCPB BB BOP DEMO Configuration Using the Apros System Code

Extensive modeling and analytical work has been carried out considering the Helium-Cooled Pebble Bed Breeding Blanket (HCPB BB) Balance Of Plant (BOP) configuration of the Demonstration Power Plant (DEMO) using the Apros system code, developed by VTT Technical Research Centre of Finland Ltd. and Fortum. The integral plant model of the HCPB BB plant has been improved with respect to the blanket and steam generator models. Based on HCPB-BL2017 v1 data, reported in 2019, the blanket has been remodeled by separate Apros process components, dedicated to average inboard and outboard segments, where the power deposition scheme of the breeding units took into account the output of high-fidelity neutronic analyses. A new helical coil steam generator model has been developed for primary–secondary system coupling using CAD data provided by EUROfusion partner University of Palermo. Transient analyses have been performed with Apros on the plant configuration that utilizes a molten salt technology-based small Energy Storage System (ESS).

Helical trajectories of swimming cells with a flexible flagellar hook

The flexibility of the bacterial flagellar hook is believed to have substantial consequences for microorganism locomotion. Using a simplified model of a rigid flagellum and a flexible hook, we show that the paths of axisymmetric cell bodies driven by a single flagellum in Stokes flow are generically helical. Phase-averaged resistance and mobility tensors are produced to describe the flagellar hydrodynamics, and a helical rod model which retains a coupling between translation and rotation is identified as a distinguished asymptotic limit. A supercritical Hopf bifurcation in the flagellar orientation beyond a critical ratio of flagellar motor torque to hook bending stiffness, which is set by the spontaneous curvature of the flexible hook, the shape of the cell body, and the flagellum geometry, can have a dramatic effect on the cell's trajectory through the fluid. Although the equilibrium hook angle can result in a wide variance in the trajectory's helical pitch, we find a very consistent prediction for the trajectory's helical amplitude using parameters relevant to swimming P. aeruginosa cells.

Efficient generation of self-avoiding, semiflexible rotational isomeric chain ensembles in bulk, in confined geometries, and on surfaces

We provide an efficient ready-to-run code gensaw that generates single or large ensembles of self-avoiding, flexible, semiflexible, rotationally isometric or helical chains in the bulk or subject to arbitrary confinement and tethering conditions, where we allow for arbitrary intramolecular bending and dihedral energy functions. The resulting configuration files are provided in various common formats and can be immediately used to do molecular simulations or statistical analysis. We work out analytic expressions for the mean squared end-to-end distance and gyration radius of the semiflexible, helical and rotational isomeric state models with a finite number of bonds and arbitrary interaction potentials for direct comparison and testing of the code in the limiting case of unconfined phantom chains. In addition to the graphics-free linux standalone batch version gensaw that creates configuration and other files for high throughput applications from the command line, we provide an interactive online version gensaw-visualization that serves as platform-independent graphical user interface, and animates the resulting conformations using a remote gensaw server. Program summaryProgram title:gensawCPC Library link to program files:https://doi.org/10.17632/8xfgf88f3w.1Licensing provisions: MITProgramming languages: fortran 90, perl (standalone batch version) or java (interactive online version)Required software:ifort 16+ or gfortran 4+, perl 5+ (standalone batch version), jre 1.8.0+ (interactive online version)Nature of problem: Efficient creation of self-avoiding, semiflexible multibead walks/chains of variable contour length, subject to arbitrary confinement and tethering conditions, characterized by a conformational energy that is composed of arbitrary bending and torsion contributions. The code must produce an ensemble of such chains, using a flexible output format. For the limiting case of chains with zero thickness, the code should reproduce analytic results for the ideal chains.Solution method: We use an adapted enrichment procedure that optimizes its parameters on the fly and derive all analytic results for semiflexible chains with arbitrary bending and torsion potentials for comparison with the created ensembles. While gensaw creates configuration and optionally other files from the command line, gensaw-visualization serves as a platform-independent graphical user interface and allows to visualize and animate the conformations.

Helical Pedagogical Model for the Teaching and Learning of Chemistry in University Settings

Scientific university pedagogy has several shortcomings related to the educational system that affect students’ professional growth. Due to this situation, a new pedagogical model is required to solve these problems and limitations. Helical pedagogy establishes the necessity to set up an emotional, retroactive, interconnected, and gradient education to help students apply knowledge during every single moment of their labor or academic life. Through the stimulation of some mental processes related to human beings during their entire life (childhood or adulthood), knowledge can be created faster and in an easier way. Still, also a solid platform is required which contributes to the helical learning, for instance, individual projects, dynamic classes with two or more professors, and, of course, the avoidance of lectures and traditional evaluation methods. These changes do not mean that the quality of the educational system should be lower. The only objective of this new pedagogical method is to improve the way that chemistry is being learned by the students and also to make them more confident about their potential. This will happen if they change their perspective and vision about their studies and professional careers. This helical model seeks to transform the way to understand chemical pedagogy by using theoretical and praxeological proposals applicable in any context around the world.

Wind tunnel study of wind effects on 90° helical and square tall buildings: A comparative study

Wind effects on a square model and a 90° helical model are investigated by both pressure measurement and aero-elastic model tests in a boundary layer wind tunnel. Based on the pressure measurement results, local wind force coefficients, base moment coefficients, vertical correlation coefficients and power spectral densities for the two models were analyzed and discussed in detail. The aerodynamic damping ratios were calculated by the random decrement technique (RDT) on the basis of the wind-induced acceleration obtained from the aero-elastic tests. Comparisons of wind loads and wind-induced accelerations were made for the square and helical models. The results shown that the aerodynamic damping should not be ignored, especially for across-wind direction. Moreover, the helical model has been proved to yield a better behavior in aerodynamic performance than square model. This study aims to provide useful information for wind-resistant design of helical building.

Modeling of heat transfer of supercritical water in helical finned double pipe

Supercritical water (SCW) is a promising fluid for achieving high thermal efficiency. In the present work, the SST k-ω turbulence model is employed to numerically simulate flow and heat transfer behavior of supercritical water in horizontal double pipe with helical fins. Grid independence test was firstly carried out and then model was validated with experimental data. Different combinations of width, height and pitch in helical double pipe numerical model, width varying from 2 mm to 4 mm, height ranging from 2 mm to 6 mm and pitch available from 15 mm to 25 mm, were examined. In addition, effects of buoyancy force, hot fluid temperature and mass flux on the heat transfer performance were investigated. Buoyancy disturbs the flow field by inducing secondary flow. The flow field is symmetrically distributed on the tube-side. In contrast, the presence of the fins in shell-side breaks the symmetrical distribution and generates a swirling flow at the top of the fins. The results indicated that the peak tube-side and overall heat transfer coefficients emerged at hot fluid slightly greater than the pseudo-critical point temperature. Moreover, the overall heat transfer coefficient improved as mass flux on both the tube-side and the shell-side. However, the shell-side would induce a greater magnitude. Also, the shell-side pressure drop closely related to the shape factor and increased with it. The performance evaluation criterion for case 8 and case 9 were 2.08 and 1.88, respectively. Nevertheless, the pressure drop of case 8 was more than twice case 9. Consequently, case 9 may be an optimal configuration simultaneously considering the coupling effect of heat transfer and pressure drop.

Performance assessment and optimization of a helical Savonius wind turbine by modifying the Bach\u2019s section

In this paper, we attempted to measure the effect of Bach’s section, which presents a high-power coefficient in the standard Savonius model, on the performance of the helical Savonius wind turbine, by observing the parameters affecting turbine performance. Assessment methods based on the tip speed ratio, torque variation, flow field characterizations, and the power coefficient are performed. The present issue was stimulated using the turbulence model SST (k- ω) at 6, 8, and 10 m/s wind flow velocities via COMSOL software. Numerical simulation was validated employing previous articles. Outputs demonstrate that Bach-primary and Bach-developed wind turbine models have less flow separation at the spoke-end than the simple helical Savonius model, ultimately improving wind turbines’ total performance and reducing spoke-dynamic loads. Compared with the basic model, the Bach-developed model shows an 18.3% performance improvement in the maximum power coefficient. Bach’s primary model also offers a 12.4% increase in power production than the initial model’s best performance. Furthermore, the results indicate that changing the geometric parameters of the Bach model at high velocities (in turbulent flows) does not significantly affect improving performance.

The Effect of Twist Multipler Exponent on Yarn Tenacity Characteristic and Yarn Diameter Calculation.(Dept.T)

Exact description of yarn structure using mathematical formulation leads to complete identification of yarn properties and hence projection of fabric properties. The present work is an attempt trial to study the yarn geometry to find a suitable exponent of twist factor. The logic of analysis is based on the well-known helical model of yarn introducing the variability of raw material and production technology. Different cotton yarns were used to justify the results of the theoretical analysis. The effect of the suggested and other known exponents on the behavior of the strength – twist multiplier curves were compared. Also the values of the constant (k) used in determination of yarn diameter is discussed according to the suggested exponent.

Interphase epichromatin: last refuge for the 30-nm chromatin fiber?

"Interphase epichromatin" describes the surface of chromatin located adjacent to the interphase nuclear envelope. It was discovered in 2011 using a bivalent anti-nucleosome antibody (mAb PL2-6), now known to be directed against the nucleosome acidic patch. The molecular structure of interphase epichromatin is unknown, but is thought to be heterochromatic with a high density of "exposed" acidic patches. In the 1960s, transmission electron microscopy of fixed, dehydrated, sectioned, and stained inactive chromatin revealed "unit threads," frequently organized into parallel arrays at the nuclear envelope, which were interpreted as regular helices with ~ 30-nm center-to-center distance. Also observed in certain cell types, the nuclear envelope forms a "sandwich" around a layer of closely packed unit threads (ELCS, envelope-limited chromatin sheets). Discovery of the nucleosome in 1974 led to revised helical models of chromatin. But these models became very controversial and the existence of in situ 30-nm chromatin fibers has been challenged. Development of cryo-electron microscopy (Cryo-EM) gave hope that in situ chromatin fibers, devoid of artifacts, could be structurally defined. Combining a contrast-enhancing phase plate and cryo-electron tomography (Cryo-ET), it is now possible to visualize chromatin in a "close-to-native" situation. ELCS are particularly interesting to study by Cryo-ET. The chromatin sheet appears to have two layers of ~ 30-nm chromatin fibers arranged in a criss-crossed pattern. The chromatin in ELCS is continuous with adjacent interphase epichromatin. It appears that hydrated ~ 30-nm chromatin fibers are quite rare in most cells, possibly confined to interphase epichromatin at the nuclear envelope.

On The Free Vibration of Doubly Clamped Single-Walled Coiled Carbon Nanotubes: A Novel Size Dependent Continuum Model

In this paper, the size dependent vibration behavior of doubly clamped single-walled coiled carbon nanotubes (CCNTs) is investigated using nonlocal helical beam model. This model is based on Washizu’s beam theory so that all displacement components of CCNT in the equations of motion are defined at the centroidal principal axis and transverse shear deformations are considered. After deriving the nonlocal free vibration equations, they are solved by the generalized differential quadrature method (GDQM). Then, the natural frequencies and corresponding mode shapes are determined for the clamped-clamped boundary conditions (BCs). After that, a parametric study on the effect of different parameters, including the helix cylinder to the tube diameters ratio , the number of pitches, the helix pitch angle, and the nonlocal parameter on the natural frequencies is conducted. It is worth noting that the results of the proposed method would be useful in the practical applications of CCNTs such as using in nanoelectromechanical systems.