Cosine Shape Research Articles

AXIAL FLUX PROFILE IN THE ADVANCED TEST REACTOR

This work demonstrates an approach to determine probability of perturbation of the axial profile of the thermal neutron flux in the Advanced Test Reactor. The axial flux profile is expected to follow a theoretical cosine shape, due to the minimal use of vertically-withdrawn shims. Reactivity is normally controlled by rotation of Outer Shim Control Cylinders, uniformly affecting neutron flux at all axial locations. The Advanced Test Reactor routinely accepts for irradiation experiments of a variety of designs. Among the analyses required by the safety basis approved by the United States Department of Energy is the characterization of a new experiment’s potential for perturbing the axial flux, which could exacerbate power peaking in the driver fuel. However, this perturbation can be more or less severe in different locations within the fuel. Therefore, the best characterization of axial flux perturbation requires knowledge of baseline axial flux. Such information is obtained by measuring decay in activated uranium flux wires irradiated at known positions in cooling channels in plate-type fuel elements. Due to variability in measured axial flux, it is not usually clear whether a given anomalous measurement is caused by an actual perturbation. Assuming normality in random measurement errors, the probability of an actual perturbation is quantified.

Performance assessment of longitudinal flow through rod bundle of ETRR-2 Cobalt/Iridium irradiation device

In the present paper, three dimension CFD analysis was presented for longitudinal flow through rod bundle of ETRR2 Cobalt/Iridium irradiation device. Study of optimal performance for both heat transfer and flow characteristics was performed by the determination of the conditions at which minimum entropy generation exist. The study was performed for Reynolds number (Re) in the range 2 × 104 ≤ Re ≤ 5.5 × 105, and Prandtl number (Pr) in the range 3.2 ≤ Pr ≤ 5.2 under both the conditions of uniform and non uniform (cosine shape) heat flux. Contours of fluid temperature and fluid velocity at irradiation box outlet as well as temperature contours of Ir rods at different values of inlet velocity were illustrated. Two correlations one relating the Nusselt number (Nu) with Re and Pr and the other relating skin friction factor with Re was presented in the studied range of Re and Pr. Determination of the applicability of the existing correlations for turbulent forced convection heat transfer and friction coefficient are also presented. Comparison between the flow and heat transfer characteristics through Ir rods of different locations in the irradiation box is presented.

Observation of attosecond electron dynamics in the photoelectron momentum distribution of atoms using few-cycle laser pulses

The method of time-resolved measurement with ultrashort laser pulses is vital to the development of attosecond science. Pump-probe measurements using a train of attosecond pulses in combination with a near-infrared (NIR) multicycle driving laser have been successful in capturing the intercycle electron dynamics which repeats every optical cycle and leads to above-threshold ionization (ATI) spectra in the frequency domain. In this work, we study the effect of a carrier-envelope phase (CEP) in a few-cycle ($l6$ fs) NIR laser pulse on the photoelectron momentum distribution (PMD) of a hydrogen atom and show that interference patterns in a PMD change dramatically with CEPs in the few-cycle regime. When the few-cycle driving laser pulse has a sine shape, the double-slit interference with characteristic modulation of ATI peaks dominates the PMD. On the other hand, when the driving pulse has a cosine shape, the holographical interference featured by a spider-like pattern is isolated. Our results suggest that the CEP-stable few-cycle laser pulses can be used to identify different types of intracycle interference structures in a PMD which reveal the underlying subcycle electron dynamics on an attosecond timescale.

The Effect of Stenotic Geometry and Non-newtonian Property of Blood Flow through Arterial Stenosis.

A mathematical model of blood flow is a way to study the blood flow behavior. In this research work, a mathematical model of non-Newtonian blood flow through different stenosis, namely bell shape and cosine shape, is considered. The physiologically important flow quantities of blood flow behavior to describe the blood flow phenomena are obtained such as resistance to flow, skin friction and blood flow rate. Mathematical methods are used to analyze a mathematical model of blood flow through stenosed artery. The resistance to flow, skin friction and blood flow rate were obtained to describe the blood flow in stenosis. The resistance to flow is a relation between pressure and blood flow rate while the skin friction is the friction at the artery membrane. Resutls: The blood flow in cosine geometry exhibits higher resistance to flow and flow rate than in the bell geometry, while the blood flow in bell geometry gives a higher skin friction than in cosine geometry. Not only the effect of stenotic geometry was studied but also the effect of stenosis depth and stenosis height on the flow quantities Moreover, the power law index was adjusted to explore the non-Newtonian behavior. When blood exhibits Newtonian behavior, the resistance to flow and skin friction decrease but the blood flow rate increases. The stenosed artery geometry, the stenosis length, stenosis depth and the power law index (non-Newtonian behavior) are important factors affecting the blood flow through the stenosed artery. This work provides some potential aspects to further study the causes and development of cardiovascular diseases.

Mathematical model for blood flow through the stenosed channel

In this paper, we investigate the blood flow through a stenoised channel. In current study Cartesian coordinates are contemplated for flow in the channel and in an axisymmetric tube with transfer of heat having cosine shape stenosis. Blood is supposed as Eyring–Powell fluid which is independent of time. Thermal conductivity is determined by temperature. After assimilating these deliberations, dimensional equations are transformed into non-dimensional system of differential equations with the use of similarity transformations and are then solved numerically. A parametric study is executed to depict the impact of various parameters on the velocity and temperature fields of fluid. Heat transfer coefficient and skin friction are also explained through graphs and discussed in tabular form for distinct values of dimensionless parameters. The current investigation tells that velocity field significantly increases by rising the value of M and δ. Temperature field increases for extended value of δ, M, K, B, A and Pr. Nusselt number curve increases due to increase in Pr.

Heterobarrier Varactors with Nonuniformly Doped Modulation Layers

Optimum shape of the capacitance–voltage (C–V) characteristic is a critical parameter determining the efficiency of frequency multiplication in heterobarrier varactors (HBVs) operating in the millimeter and submillimeter frequency ranges. A numerical model for calculating the C–V characteristics and leakage currents of HBV heterostructures with arbitrary composition and doping profiles has been verified on the basis of published and original experimental data. A specially designed HBV heterostructure with three undoped InAlAs/AlAs/InAlAs barriers surrounded by nonuniformly doped n-InGaAs modulation layers has been grown by molecular beam epitaxy on InP substrate. Prototype HBVs manufactured using the proposed heterostructure demonstrated a nearly cosine shape of the C–V curve at bias voltages up to 2 V, increased overlap capacitance, and low leakage currents.

Design and analysis of a BELBIC controlled semi active suspension system

The vehicle dynamics gives lot of consideration to quality of ride and the value of comfort. These two are dependent on the suspension system of the vehicle. Researchers are doing a lot of work in the field of improving these two parameters. A lot of approaches and control systems like ANN, GA based system, fuzzy and hybrid control systems have been formulated, simulated and tested. This paper deals with mathematical modeling and simulation of passive and semi active system. The semi active system modeled here contains a new approach of using intelligent controller based on Brain functioning with emotional signal, known as BELBIC. The use of this controller has not been tested for suspension system as identified through rigorous literature survey. The both systems are simulated for their response to disturbance of road as step function and as profile of cosine shape. The results of passive and proposed semi active system were analyzed to compare their performance in terms of displacement of sprung mass and suspension travel as well as their settling time. The BEL controlled system has performed very good. The displacement of sprung body has been reduced in both the cases of road disturbances. The response against step input is better than cosine. Similarly settling time has also shown in improvement for step and cosine function.

Effects of suffosion-induced contact variation on dynamic responses of saturated roadbed considering hydro-mechanical coupling under high-speed train loading

Recent experience of high-speed railway in operation has indicated that the hydro-mechanical coupling effect under dynamic loads from high-speed train may lead to excessive pumping of fine particles in saturated roadbed surface layer. This can result in large variations of contact condition between track and subgrade structure layers while study on this issue remains scare. Based on the theory of fluid dynamics in porous medium and the vehicle-track-subgrade coupling vibration theory, a numerical model is established to evaluate the dynamic responses of saturated roadbed surface resulting from the contact condition variation under the high-speed train load considering the hydro-mechanical coupling effects. A concept of three contact types (fully continuous contact, vibration contact and contact loss) is proposed and three contact shape forms (rectangular, cosine and elliptical shapes) simplified for describing contact damaged zones are compared in terms of dynamic responses (stress, pore water pressure, seepage velocity) evaluated. Also, time-frequency analysis is performed to investigate the influence of contact variation on dynamic responses of roadbed surface in aforementioned contact types. Results show that this progressive development of contact damage can pose extra great stress and pore-water pressures in roadbed and a critical length of contact loss zone is suggested.

Гетеробарьерные варакторы с неоднородно легированными модулирующими слоями

Optimal capacitance-voltage characteristic is critical for heterobarrier varactor diode (HBV) performance in terms of multiplication efficiency in mm- and sub-mm wave ranges. Numerical model of capacitance-voltage characteristics and leakage current for HBV with arbitrary heterostructure composition and doping profile was verified on published data and original experimental results. Designed HBV heterostructure with three undoped InAlAs/AlAs/InAlAs barriers surrounded with non-uniformly doped n-InGaAs modulation layers was grown by molecular-beam epitaxy on InP substrate and test HBV diodes have been fabricated. Test HBV diodes demonstrate capacitance-voltage characteristics with cosine shape at bias voltage up to two volts, increased capacitance ratio and low leakage current values.

Modeling Large Deflections of Initially Curved Beams in Compliant Mechanisms Using Chained Beam Constraint Model

Understanding and analyzing large and nonlinear deflections are the major challenges of designing compliant mechanisms. Initially, curved beams can offer potential advantages to designers of compliant mechanisms and provide useful alternatives to initially straight beams. However, the literature on analysis and design using such beams is rather limited. This paper presents a general and accurate method for modeling large planar deflections of initially curved beams of uniform cross section, which can be easily adapted to curved beams of various shapes. This method discretizes a curved beam into a few elements and models each element as a circular-arc beam using the beam constraint model (BCM), which is termed as the chained BCM (CBCM). Two different discretization schemes are provided for the method, among which the equal discretization is suitable for circular-arc beams and the unequal discretization is for curved beams of other shapes. Compliant mechanisms utilizing initially curved beams of circular-arc, cosine and parabola shapes are modeled to demonstrate the effectiveness of CBCM for initially curved beams of various shapes. The method is also accurate enough to capture the relevant nonlinear load-deflection characteristics.

Influence of tube geometry on the performance of standing-wave acoustic resonators.

A general and simple calculation method is presented to investigate the effects of tube shape on the resonant frequency and performance of a resonator. First, the resonant frequency of a variable cross-section resonator is modeled using a transfer matrix. Then, the amplification ratio of the pressure amplitude (ARPA), defined as the ratio of the pressure amplitude at the small end to that at the large end of the resonator, is used to evaluate its performance. The ARPA value for a variable cross-section resonator can be directly calculated from its resonant frequency. It is shown that the ARPA value is closely related to the compression ratio. However, its value is only determined by the resonator itself and is independent of the working conditions. Therefore, the ARPA index is potentially a more convenient tool for evaluating the performance of resonators compared with other indexes. Additionally, the presented method is validated by a comparison with analytical results and experimental data. Moreover, the harmonic frequencies for cylindrical, exponential, conical, half-cosine, 3/4 cosine, and Horn-Cone shape tubes are numerically investigated, in addition to the influence of the resonator shape on the resonance frequency and ARPA. Finally, optimal shape parameters for several types of resonators are suggested.

Performance drifts in two-finger cyclical force production tasks performed by one and two actors.

We explored changes in the cyclical two-finger force performance task caused by turning visual feedback off performed either by the index and middle fingers of the dominant hand or by two index fingers of two persons. Based on an earlier study, we expected drifts in finger force amplitude and midpoint without a drift in relative phase. The subjects performed two rhythmical tasks at 1Hz while paced by an auditory metronome. One of the tasks required cyclical changes in total force magnitude without changes in the sharing of the force between the two fingers. The other task required cyclical changes in the force sharing without changing total force magnitude. Subjects were provided with visual feedback, which showed total force magnitude and force sharing via cursor motion along the vertical and horizontal axes, respectively. Further, visual feedback was turned off, first on the variable that was not required to change and then on both variables. Turning visual feedback off led to a mean force drift toward lower magnitudes while force amplitude increased. There was a consistent drift in the relative phase in the one-hand task with the index finger leading the middle finger. No consistent relative phase drift was seen in the two-person tasks. The shape of the force cycle changed without visual feedback reflected in the lower similarity to a perfect cosine shape and in the higher time spent at lower force magnitudes. The data confirm findings of earlier studies regarding force amplitude and midpoint changes, but falsify predictions of an earlier proposed model with respect to the relative phase changes. We discuss factors that could contribute to the observed relative phase drift in the one-hand tasks including the leader-follower pattern generalized for two-effector tasks performed by one person.

Prediction of multi-wake problems using an improved Jensen wake model

The improved analytical wake model named as 2D_k Jensen model (which was proposed to overcome some shortcomes in the classical Jensen wake model) is applied and validated in this work for wind turbine multi-wake predictions. Different from the original Jensen model, this newly developed 2D_k Jensen model uses a cosine shape instead of the top-hat shape for the velocity deficit in the wake, and the wake decay rate as a variable that is related to the ambient turbulence as well as the rotor generated turbulence. Coupled with four different multi-wake combination models, the 2D_k Jensen model is assessed through (1) simulating two wakes interaction under full wake and partial wake conditions and (2) predicting the power production in the Horns Rev wind farm for different wake sectors around two different wind directions. Through comparisons with field measurements, results from Large Eddy Simulations (LES) as well as results from other commercial codes, it is found that the predictions obtained with the 2D_k Jensen model exhibit good to excellent agreements with experimental and LES data.

Teaching Mathematica® based computer computations for support of laboratory experiments, special projects, and research for undergraduates taking acoustics and for mentorship students

Undergraduate senior level physics majors taking Acoustics and oceanography majors taking Underwater Acoustics and Sonar learn how to use Mathematica® for doing standard laboratory experiments, special projects, solving homework problems requiring detailed computations or graphics. Students in electrical engineering, economics, mechanical engineering and ocean engineering (along with physics majors) have enrolled in a one credit course—Mathematica® 10 for Scientists and Techies. The feedback from students using a computer language in their course work for the first time is very encouraging and the teaching experience quite rewarding. High school mentorships volunteering to do research after school use Mathematica® for doing projects in the Physical Acoustics Laboratory. Some undergraduate lab projects involve Fourier analysis, measuring sound speed vs. temperature in water, and plotting theoretical and experimental Bessel mode shapes (or cosine shapes) for standing wave resonance in a cylindrical cavity. Here, a long slender tube mounted on the microphone probe translates along the radial or axial directions. Students enjoy generating their own data on a spectrum analyzer, transferring files to Mathematica® and plotting tuning curves vs. frequency in Helmholtz resonators. One student got involved in nonlinear drum vibration while another became interested in synthetic aperture imaging, for senior research projects.

Effects of fuel relocation on reflood in a partially-blocked rod bundle

Ballooning of the fuel rods has been an important issue, since it can influence the coolability of the rod bundle in a large-break loss-of-coolant accident (LBLOCA). Numerous past studies have investigated the effect of blockage geometry on the heat transfer in a partially blocked rod bundle. However, they did not consider the occurrence of fuel relocation and the corresponding effect on two-phase heat transfer. Some fragmented fuel particles located above the ballooned region may drop into the enlarged volume of the balloon. Accordingly, the fuel relocation brings in a local power increase in the ballooned region. The present study’s objective is to investigate the effect of the fuel relocation on the reflood under a LBLOCA condition. Toward this end, experiments were performed in a 5×5 partially-blocked rod bundle. Two power profiles were tested: one is a typical cosine shape and the other is the modified shape considering the effect of the fuel relocation. For a typical power shape, the peak temperature in the ballooned rods was lower than that in the intact rods. On the other hand, for the modified power shape, the peak temperature in the ballooned rods was higher than that in the intact rods. Numerical simulations were also performed using the MARS code. The tendencies of the peak clad temperatures were well predicted.

An Enhanced Partial Transmit Sequence Segmentation Schemes to Reduce the PAPR in OFDM Systems

Although the orthogonal frequency division multiplexing system (OFDM) is widely used in high-speed data rate wire and wireless environment, the peak-to- average-power-ratio (PAPR) is one of its major obstacles for the real applications. The high PAPR value leads some devices of the OFDM system such as power amplifiers and analog to digital converters to work out of band of these devices. Thus the system efficiency is degraded. Many techniques have been proposed to overcome the high PAPR in OFDM systems such as partial transmit sequences (PTS), selected mapping and interleaving technique. PTS is considered as one of the effective PAPR reduction methods; this scheme depends on segmentation of the input data into several subblocks and then combined again. The three well-known segmentation schemes are pseudo-random, adjacent and interleaving; each scheme has PAPR reduction performance, and computational complexity differs from one to another. In this paper, five types of segmentation schemes are proposed to improve the PAPR reduction execution including sine and cosine shape as well as hybrid interleaving and adjacent schemes in new approaches. From the simulation results, the proposed methods can achieve PAPR reduction performance greater than that of the adjacent and interleaving partition schemes, without increasing the computational complexity of the system. Moreover, the enhanced schemes can realize better PAPR performance with any number of subcarriers.

Design and Optimization of Bearingless Permanent Magnetic Synchronous Motors

The bearingless permanent magnetic synchronous motor (BPMSM) is a new type of special motor that has been receiving extensive attention in recent years. In this paper, a design method based on electromagnetic calculation for BPMSMs is proposed. Main dimensions including the effective length, diameter, and parameters of the permanent magnet and windings can be obtained. Then, to inhibit higher harmonics, two measures are taken. One measure is using short-pitch windings instead of conventional full-pitch windings, and the other measure is adopting a new type of cosine shape of permanent magnets. Finally, the structure and unbalanced flux density distributions of the designed prototype are studied by finite-element analysis, which verify the correctness of the design method, and better optimization results are obtained.

Axial Power and Coolant-Temperature Profiles for a Non-Re-Entrant Pressure-Tube Supercritical Water-Cooled Reactor Fuel Channel

The axial power and coolant-temperature distributions in a fuel channel of the Generation IV pressure-tube super-critical water-cooled reactor (PT-SCWR) are found using coupled neutronics-thermal-hydraulics calculations. The simulations are performed for a channel loaded with a fresh, 78-element Th-Pu fuel assembly. Neutronics calculations are performed using the DONJON diffusion code using two-group homogenized cross sections produced using the lattice code DRAGON. The axial coolant temperature profile corresponding to a certain axial linear heat generation rate is found using a code developed in-house at University of Ontario Institute of Technology (UOIT). The effect of coolant density, coolant temperature, and fuel temperature variation along the channel is accounted for by generating macroscopic cross sections at several axial positions. Fixed-point iterations are performed between neutronics and thermal-hydraulics calculations. Neutronics calculations include the generation of two-group macroscopic cross sections at several axial positions, taking into account local parameters such as coolant temperature and density and average fuel temperature. The coolant flow rate is adjusted so that the outlet temperature of the coolant corresponds to the SCWR technical specifications. The converged axial power distribution is found to be asymmetric, resembling a cosine shape skewed toward the inlet (reactor top).

Conditions for quantized anisotropic magnetoresistance

Conditions for the appearance of quantized anisotropic magnetoresistance (QAMR) in ferromagnetic conductors have been investigated from the viewpoint of the transmission channels calculated by method of the nonequilibrium Green's function--density functional theory. We demonstrate that the spin-orbital interaction is a precondition and the transverse size is a crucial condition for QAMR to emerge. Furthermore, we show the evolution of QAMR from a stepwise shape (corresponding to small transverse sizes) to a classical smooth cosine shape (corresponding to large transverse sizes). In addition, we prove the strong temperature dependence of QAMR, so a low temperature is necessary. Our research reconciles the different experiments and enlightens experimenters on QAMR.

Development of a 3D program for calculation of multigroup Dancoff factor based on Monte Carlo method in cylindrical geometry

Evaluation of multigroup constants in reactor calculations depends on several parameters, the Dancoff factor amid them is used for calculation of the resonance integral as well as flux depression in the resonance region in the heterogeneous systems. This paper focuses on the computer program (MCDAN-3D) developed for calculation of the multigroup black and gray Dancoff factor in three dimensional geometry based on Monte Carlo and escape probability methods. The developed program is capable to calculate the Dancoff factor for an arbitrary arrangement of fuel rods with different cylindrical fuel dimensions and control rods with various lengths inserted in the reactor core. The initiative calculates the black and gray Dancoff factor versus generated neutron flux in cosine and constant shapes in axial fuel direction. The effects of clad and moderator are followed by studying of Dancoff factor’s sensitivity with variation of fuel arrangements and neutron’s energy group for CANDU37 and VVER1000 fuel assemblies. MCDAN-3D outcomes poses excellent agreement with the MCNPX code. The calculated Dancoff factors are then used for cell criticality calculations by the WIMS code.