Longitudinal Shapes Research Articles

Comparison between scarp and dip-slope rivers of the Cotswold Hills, UK

The Cotswold Hills, southwest UK, are properly described as a cuesta, with a steep, west-facing scarp slope and a plateau-like dip slope. Drainage reflects this surface morphology, with most rivers flowing southeast along topographic and stratigraphic dip. Here, we compare two superficially highly similar rivers – the Frome and Churn – whose sources are nearly coincident, but whose behaviour dramatically diverges thereafter. We examine longitudinal profiles, channel steepness, predicted discharge, and valley shapes, using digital topographic data. River discharge and water hardness/temperature values were obtained at seven sites on the Churn and nine on the Frome over a two-year sampling campaign, delineated into summer and winter phases. Nearly 100 borehole records were interrogated from the two catchments in order to assess groundwater level variations. The Frome, flowing west against regional dips, develops a steep course and has carved a deep and wide valley that exposes the full sequence of Cotswold Jurassic stratigraphy. On the other hand, discharge and channel gradients are lower for the dip-slope Churn, whose valley exposes less stratigraphy and fewer springs. Our measurements of river water hardness and temperature suggest that a greater proportion of groundwater flows into the Frome, regulating discharge and maintaining baseflow over summer. We suggest that flank uplift of the Cotswolds is at least part of the reason for the higher incision rates of the River Frome, leading to its intersecting a greater number of highly transmissive fractures that contribute to its discharge. In turn, the increased discharge could positively impact local incision rates.

Propagation of Bessel-X pulses in a hybrid photonic crystal

We report the propagation of Bessel-X pulses in a two-dimensional hybrid photonic crystal, investigated by the finite-difference time-domain method, in which broadband super-collimation and the propagation of self-collimated ultrashort pulses were reported. We first show the propagation of Bessel-X pulses in two-dimensional free space, whose transverse branches diverge rapidly with propagation. We then show that Bessel-X pulses propagate with their transverse and longitudinal shapes almost unchanged in the hybrid photonic crystal.

Temperature sensing characteristics of tapered Tm3+-doped fiber amplifiers

We numerically analyze the temperature response of a tapered Tm3+-doped fiber amplifier. The analysis includes a redefinition of the coupled pump and signal propagation equations in order to introduce different longitudinal shapes of the tapered doped fiber and the temperature dependence of the absorption and emission cross sections of the Tm3+ ions under different pump schemes. It was found that the temperature sensitivity of the normalized amplified signal was 2 × 10−3/°C for 1 W of pump power and 3 m of doped fiber length, using a parabolic taper in a co-propagating pump scheme. This sensitivity can be increased by at least 5 times if we adjust the design parameters of the fiber amplifier using fiber lengths shorter than 1 m and pump powers lower than 300 mW. Our results contribute with new information for the development and optimization of tapered fiber amplifiers doped with other rare earths, and novel designs for doped-fiber temperature sensors.

Precision Control of the Electron Longitudinal Bunch Shape Using an Emittance-Exchange Beam Line.

We report on the experimental generation of relativistic electron bunches with a tunable longitudinal bunch shape. A longitudinal bunch-shaping (LBS) beam line, consisting of a transverse mask followed by a transverse-to-longitudinal emittance exchange (EEX) beam line, is used to tailor the longitudinal bunch shape (or current profile) of the electron bunch. The mask shapes the bunch's horizontal profile, and the EEX beam line converts it to a corresponding longitudinal profile. The Argonne wakefield accelerator rf photoinjector delivers electron bunches into a LBS beam line to generate a variety of longitudinal bunch shapes. The quality of the longitudinal bunch shape is limited by various perturbations in the exchange process. We develop a simple method, based on the incident slope of the bunch, to significantly suppress the perturbations.

Experimental modal analysis on a tyre - lessons learned

Extracting the mode shapes of a tyre can be very challenging, particularly for the transverse and the longitudinal mode shapes. The current paper presents results for experimental modal analysis (EMA) tests on a tyre using both an impact hammer and an electro-dynamic shaker. The radial modes of the tyre were excited using a modal impact hammer. The possibility of using a narrow metal screw that could be attached to the modal impact hammer to excite the transverse and torsional mode shapes of the tyre was studied. The advantages and drawbacks of using a mechanical shaker to excite the structure and using roving accelerometers to measure the response were also studied. This study also describes a method to extract the repeated roots of a tyre using the experimental modal analysis. The current paper summarises the lessons learned from different experiment cases that were performed to extract mode shapes of a tyre.

Perturbation-minimized triangular bunch for high-transformer ratio using a double dogleg emittance exchange beam line

The longitudinal shape, i.e., the current profile, of an electron bunch determines the transformer ratio in a collinear wakefield accelerator and thus methods are sought to control the longitudinal bunch shape. The emittance exchange (EEX) appears to be promising for creating a precisely controlled longitudinal bunch shapes. The longitudinal shape is perturbed by two sources: higher-order terms in the beam line optics and collective effects and these perturbations can lead to a significant drop of the transformer ratio. In this paper, we analytically and numerically investigate the perturbation to an ideal triangular longitudinal bunch shape and propose methods to minimize it.

Experimental study on flame merging behaviors from two pool fires along the longitudinal centerline of model tunnel with natural ventilation

A set of experiments was conducted in a model tunnel to study the interaction behaviors of two pool fires. Square heptane pool fires with side lengths of 10cm, 13cm and 16cm were used as the fire sources. In the experiments, two identical fires were located at the longitudinal centerline of tunnel. The fire spacing was set as an integral multiple of the half pool length. The mass loss rates of two fires in tunnel were compared with fires in the open space and it was explained from the viewpoints of the interactive burnings and the heat feedback mechanism. Results showed that as the spacing decreases, the mass loss rate increases first and then decreases. Similar trends can be found in heat fluxes received by objects at the pool surface level. With decreasing the spacing, the longitudinal ceiling flame shapes are divided into four categories, i.e., non-interaction flames, tilted flames without merging, merging ceiling flames and merging vertical flames. The image processing method is used to judge the flame merging and to obtain the position of merging point and the flame length. An expression correlating the distance from the merging point to the ceiling and the normalized spacing is established. By using dimensional analysis and introducing a correlation factor, a correlation for predicting the effective ceiling flame length is developed, involving the heat release rate, pool size, spacing and effective tunnel height. Moreover, a method to estimate the flame radiant fluxes received by the objects located in the lower layer of tunnel with vertical and horizontal orientations is proposed to further reveal the mechanism of heat radiation from two interacting fires in tunnel.

Convex diamond patterns by grinding with a wheel which is dressed by a rounded tool

Patterned surfaces such as longitudinal micro-grooves, micro-dimples, and micro-convex shapes have great potential for improving tribological properties by reducing wear, friction, drag and lubrication consumption. Convex diamond patterns can be generated by a special grinding operation in which the wheel has a single helical groove on its circumference. To obtain such patterns, the same wheel needs two-way feed motion on the workpiece. The grooved wheel geometry determines the final patterns on the workpiece, so the development of a precise groove shape on the wheel surface is very important. The aim of this study was to generate convex diamond patterns by grinding with a specially grooved wheel and dressing. To make a precise groove on the wheel surface, a rounded-tip dressing tool was used in the dressing process. The resulting convex diamond patterns can be displayed by entering the input parameters into a simulation program developed using Matlab. The simulation result is compared with experimental results for verification. The simulation model could be used to control an actual grinding process or to predict the convex patterns on a flat surface.

Structural Damage Detection Using Slopes of Longitudinal Vibration Shapes

While structural damage detection based on flexural vibration shapes, such as mode shapes and steady-state response shapes under harmonic excitation, has been well developed, little attention is paid to that based on longitudinal vibration shapes that also contain damage information. This study originally formulates a slope vibration shape (SVS) for damage detection in bars using longitudinal vibration shapes. To enhance noise robustness of the method, an SVS is transformed to a multiscale slope vibration shape (MSVS) in a multiscale domain using wavelet transform, which has explicit physical implication, high damage sensitivity, and noise robustness. These advantages are demonstrated in numerical cases of damaged bars, and results show that MSVSs can be used for identifying and locating damage in a noisy environment. A three-dimensional (3D) scanning laser vibrometer (SLV) is used to measure the longitudinal steady-state response shape of an aluminum bar with damage due to reduced cross-sectional dimensions under harmonic excitation, and results show that the method can successfully identify and locate the damage. Slopes of longitudinal vibration shapes are shown to be suitable for damage detection in bars and have potential for applications in noisy environments.

Acoustic resonance excitation of turbulent heat transfer and flow reattachment downstream of a fence

The current work investigates the aero-thermal impact of standing sound waves, excited in a straight channel geometry, on turbulent, separating and reattaching flow over a fence. Effects of distinct frequency resonant forcing (ReH = 10,050 and f = 122 Hz) are quantified by wall static pressure measurements and detailed convective heat transfer distributions via liquid crystal thermometry. Acoustic boundary conditions are numerically predicted and the computed longitudinal resonance mode shapes are experimentally verified by surface microphone measurements. Findings indicate the presence of a resonant sound field to exert strong influence on local heat transfer downstream of the fence, whereas the boundary layer upstream of the obstacle remains notable unaffected. Upstream shift of the maximum heat transfer location and an earlier pressure recovery indicate a reduction in time averaged flow reattachment length of up to 37 %. Although the streamwise peak Nusselt increased by only 5 %, the heat transfer level in the vicinity of the unexcited reattachment zone was locally enhanced up to 25 %. Despite prominent impact of resonant forcing on the fence wake flow, the total pressure drop penalty remained invariant. Observations demonstrate the significant aero-thermal implications of shear layer excitation by standing sound waves superimposed on the channel flow field.

Dynamics of Hydrophobic Core Phenylalanine Residues Probed by Solid-State Deuteron NMR.

We conducted a detailed investigation of the dynamics of two phenylalanine side chains in the hydrophobic core of the villin headpiece subdomain protein (HP36) in the hydrated powder state over the 298-80 K temperature range. Our main tools were static deuteron NMR measurements of longitudinal relaxation and line shapes supplemented with computational modeling. The temperature dependence of the relaxation times reveals the presence of two main mechanisms that can be attributed to the ring-flips, dominating at high temperatures, and small-angle fluctuations, dominating at low temperatures. The relaxation is nonexponential at all temperatures with the extent of nonexponentiality increasing from higher to lower temperatures. This behavior suggests a distribution of conformers with unique values of activation energies. The central values of the activation energies for the ring-flipping motions are among the smallest reported for aromatic residues in peptides and proteins and point to a very mobile hydrophobic core. The analysis of the widths of the distributions, in combination with the earlier results on the dynamics of flanking methyl groups (Vugmeyster et al. J. Phys. Chem. B 2013, 117, 6129-6137), suggests that the hydrophobic core undergoes slow concerted fluctuations. There is a pronounced effect of dehydration on the ring-flipping motions, which shifts the distribution toward more rigid conformers. The crossover temperature between the regions of dominance of the small-angle fluctuations and ring-flips shifts from 195 K in the hydrated protein to 278 K in the dry one. This result points to the role of solvent in softening the core and highlights aromatic residues as markers of the protein dynamical transitions.

Nonparametric combination-based tests in dynamic shape analysis

Landmark-based geometric morphometric methods are probably the most widely used approaches for shape analysis. Much work has been done for static or cross-sectional shape analysis while considerably less research has focused on dynamic or longitudinal shapes. The question of analysing shape changes over time is a fundamental issue in many research fields. In this paper, as a motivating example, we consider the problem of describing the dynamics of facial expressions for which medical and sociological studies call for a proper differential analysis to distinguish their different characteristics. We address the problem from an inferential point of view testing whether landmark positions change over time, within each facial expression, and whether these changes are different between different expressions. As the shape changes over time completely depend on geometrical landmarks, part of the problem becomes finding the subset of landmarks which best describes the dynamics of the expressions. In this paper, we show by means of a motivating example related to the analysis of the FG-NET (Face and Gesture Recognition Research Network) database with facial expressions and emotions from the Technical University Munich [Wallhoff, F. (2006), ‘Database with Facial Expressions and Emotions from Technical University of Munich (FEEDTUM)’], that NonParametric Combination (NPC) tests can be effective tools when testing whether there is a difference between dynamics of facial expressions or testing which of the landmarks are more informative in explaining their dynamics. In particular, we start analysing data by means of bivariate linear mixed-effects models and then we improve inferential results using the NPC methodology.

Group Testing for Longitudinal Data.

We consider how to test for group differences of shapes given longitudinal data. In particular, we are interested in differences of longitudinal models of each group's subjects. We introduce a generalization of principal geodesic analysis to the tangent bundle of a shape space. This allows the estimation of the variance and principal directions of the distribution of trajectories that summarize shape variations within the longitudinal data. Each trajectory is parameterized as a point in the tangent bundle. To study statistical differences in two distributions of trajectories, we generalize the Bhattacharyya distance in Euclidean space to the tangent bundle. This not only allows to take second-order statistics into account, but also serves as our test-statistic during permutation testing. Our method is validated on both synthetic and real data, and the experimental results indicate improved statistical power in identifying group differences. In fact, our study sheds new light on group differences in longitudinal corpus callosum shapes of subjects with dementia versus normal controls.

Effect of fiber geometry and tenacity on the mechanical properties of fine aggregates concrete

The effect of fiber cement interactions and its influence on flexural and tensile properties of cementitious composites are well known. In this research, acrylic fibers with different cross sectional and longitudinal shapes and different tensile strengths were selected as reinforcement of the specific fine aggregates concrete. Three point bending test, pullout test, and scanning electron microscopy were used to investigate flexural and pullout behavior of the composites. It was found that flexural toughness and pullout strength were increased 20% and 34%, respectively, by application of kidney shaped acrylic fibers in comparison to dog bone shaped acrylic fibers. It was also found that the flexural and pullout strength of composites containing non-crimped fibers are 33% and 26.5% higher than specimens with crimped fibers, respectively. Results showed that the flexural toughness and pullout strength of high tenacity fiber is 75% and 131% higher than regular fiber as well, respectively. The effect of fine aggregates on the adhesion of fibers to cement matrix was evaluated.

Mass defect influence on the longitudinal vibration frequencies and mode shapes of a beam

The problem of the influence of complicated-shape defects on the natural frequencies and mode shapes of elastic systems is considered. The beam is considered as an example to discover the general properties of defects of various physical nature such as of mass, elasticity, and cross-section. Some notions of damage and a criterion that permits defectoscopy by nondestructive inspection techniques are introduced. The problem is solved in more detail for a free beam with a mass defect. The resonance method is used experimentally to determine the mass defect with high accuracy. The efficiency of the developed numerical-analytic and experimental approaches to studying the properties of elastic systems with defects is confirmed.

Temperature sensing characteristics of tapered Yb-doped fiber amplifiers

We analyze numerically the use of a tapered Yb-doped fiber to explore the temperature response of fiber amplifiers and their feasibility to be used as a sensing element in temperature fiber sensors. The impact of using different pump schemes and different longitudinal shapes of the tapered doped fiber is investigated, and we found that a parabolic shape of the taper and the co-propagating pump scheme are more sensitive to temperature changes at low pump powers. Our results can be used to describe the temperature response of tapered fiber amplifiers doped with other rare-earths, and contribute with new information for the development and optimization of temperature fiber laser sensors.

Preparation and quality control of a product for seasoning made with the kernels of Ricinodendron heudelotii or "akpi" from Côte d'Ivoire

Ricinodendron heudelotii kernels, which are used in food because of their aroma and very pronounced taste, are very popular in Africa, specifically in Cote d'Ivoire. That is why we have developed a solid seasoning product from its kernels. The dough was compacted and molded into small longitudinal shapes in the form of bricks, and slightly dried. The taste of the product was evaluated and the averages obtained were above 7/10. The aroma of the product stored in the refrigerator remained intact until the 12th month (significant probability = 0.175 higher than the risk α = 0.05). At room temperature, the product retained its flavor and this was confirmed by the statistics (probability of significance = 0.079 higher than the risk α = 0.05). The microbiological study done showed that the product was of good quality and safe for consumption after 48 weeks of storage. R. heudelotii can therefore be considered as an interesting plant for humans and for food that needs to be tamed. Key words: Ricinodendron heudelotii, kernels, aroma, taste, seasoning product, Cote d'Ivoire.

Approximate Solution for Longitudinal Vibration of Non-Uniform Beams by Differential Transform Method (DTM)

In this paper, differential transform method is applied for longitudinal vibration analysis of beams with non-uniform cross section. Natural frequencies and corresponding normalized mode shapes are calculated for different cases in cross section and boundary conditions. Comparison of results with the previous solutions proves the accuracy and versatility of the presented paper.     2 0 sin A xA a bx  . Li (4) combined the transfer matrix method and closed form solution of one step non-uniform rod to obtain a single frequency equation for a multi-step non-uniform rod. In another papers, he derived an exact solution for free longitudinal vibrations of one-step non-uniform rods with classical and non-classical boundary conditions (5) and an analytical solution for determine the longitudinal natural frequencies and mode shapes for a one step non-uniform bar with several boundary conditions (6). Li, et al. (7) found closed form solution for the longitudinal vibration of non-uniform structures with lumped masses and spring supports whose cross-section varies as   1 n

Propagation of self-collimated ultrashort pulses in a hybrid photonic crystal

We report the propagation of self-collimated ultrashort Gaussian pulses in a hybrid photonic crystal structure, in which broadband super-collimation was proposed recently. To choose their center frequencies, we compute group velocity dispersion and third-order dispersion as a function of frequency. Using the finite-difference time-domain method, we simulate the propagation of the pulses at two frequencies, one for zero group-velocity-dispersion and the other for optimized super-collimation. It is shown that the pulses nearly retain their transverse and longitudinal shapes during propagation over a long distance, and that third-order dispersion affects the pulse shape at zero group-velocity-dispersion frequency.

타원궤적 절삭기의 가진주파수에 따른 절삭 날 회전 진동 특성

The direction of the cutting tool plays a critical role in elliptical vibration cutting(EVC) where the cutting tool cuts workpiece in a trochoidal motion. In this study, EVC cutting device was developed using two parallel piezoelectric materials and it was observed that the rotation direction of the tool reverses as the EVC device undergoes resonance at which either flexural(cutting direction) or longitudinal( thrust direction) mode shapes occurs. To analytically explain reversal of the rotation direction, kinematic motion analysis of the tool was modified to incorporate amplification of the vibration amplitude and phase introduced by resonance. It successfully demonstrated, through Matlab simulation, reversal of the rotation direction of the cutting tool as the excitation frequency increases beyond resonance frequencies at which either flexural or longitudinal vibration occurs.