Break Angle Research Articles

Inversion of the V-line Radon transform in a disc and its applications in imaging

Several novel imaging modalities proposed during the last couple of years are based on a mathematical model, which uses the V-line Radon transform (VRT). This transform, sometimes called broken-ray Radon transform, integrates a function along V-shaped piecewise linear trajectories composed of two intervals in the plane with a common endpoint. Image reconstruction problems in these modalities require inversion of the VRT. While there are ample results about inversion of the regular Radon transform integrating along straight lines, very little is known for the case of the V-line Radon transform. In this paper, we derive an exact inversion formula for the VRT of functions supported in a disc of arbitrary radius. The formula uses a two-dimensional restriction of VRT data, namely the incident ray is normal to the boundary of the disc, and the breaking angle is fixed. Our method is based on the classical filtered back-projection inversion formula of the Radon transform, and has similar features in terms of stability, speed, and accuracy.

Experimental production of bending and radial flake fractures and implications for lithic technologies

Bend and radially broken flake tools have been identified in Paleolithic and Paleoindian assemblages, and their presence raises important questions. Were these breaks intentionally produced to serve as tool edges or were broken flakes simply scavenged? More importantly, can we distinguish between intentionally produced breaks and those produced incidentally? Experimental archaeology can help answer these questions. In this paper, three sets of experimentally produced bend and radial flake breaks were compared. Flakes were intentionally broken by percussion, and these breaks were compared to those produced during bifacial core reduction and by flake trampling. The presence of point of impact markers, near ninety degree break angles, and an assemblage with high percentages of bend and radial breaks distinguish intentional fracture from incidental fractures produced during bifacial reduction. High percentages of radial breaks distinguish intentional fracture from trampling. Finally, it may not be possible to identify intentional breaks in a bifacial reduction assemblage severely affected by flake-on-flake trampling.

Hangingwall surface subsidence at the Kiirunavaara Mine, Sweden

Large scale surface subsidence has been experienced at the Kiirunavaara mine since sublevel caving was implemented as a mining method. Surface disturbances are affecting part of the city of Kiruna, the railway, and the power station. Continuous and discontinuous subsidences characterize the hangingwall deformation, which is periodically monitored using surveying techniques and mapping of surface cracks. A historic review of subsidence prognoses has been carried out and the results compared with the actual condition of the hangingwall. The review showed discrepancies between different prognoses. In addition, limit equilibrium analyses indicated that break angles flatten while the mining depth increases. However, this tendency is not clear in the field where break angles show a large dispersion of values. By using surveying data, two different analyses have been performed. The time-dependent movements of the hangingwall have been described using time–displacement curves and strain analysis has been performed for different sections of the hangingwall. Three different stages of the time–displacement behavior have been identified and described. It has been concluded that extension strain can reach values which may damage civil structures before surface crack can be observed.

Application of neural networks and fuzzy logic models to long-shore sediment transport

Predictions of long-shore sediment transport rate (LSTR) are a vital task for coastal engineers in the determination of erosion or accretion along coasts. Many scientists have tried to find empirical method for the estimation of LSTR in the past decades. However, due to the influence of significant number of parameters and randomness of the data, the existing empirical methods provide quite different results and have limited applications. In this paper, an alternative approach, fuzzy logic and neural network, is proposed to estimate LSTR. Six dominant variables on LSTR are considered in the present models, including wave breaking height ( H bs ), wave period ( T), wave breaking angle ( α bs ), beach slope ( m), grain size ( D) and sediment mass flow rate along shore ( Q s ). A comprehensive comparison between both neural networks and fuzzy logic models and the existing empirical formulae will be presented to demonstrate capacity of fuzzy logic and artificial neural network.

Resistência ao acamamento de plantas e ao quebramento do colmo em milho tropical

O objetivo deste trabalho foi avaliar genótipos de milho quanto à resistência ao acamamento e ao quebramento do colmo e apresentar metodologia para avaliar essas características. Os ensaios foram realizados em blocos ao acaso, com 85 genótipos tropicais de milho e quatro repetições, em cinco locais. Foram avaliadas: as forças necessárias para o arranquio da planta e para o quebramento do colmo e o ângulo no momento do quebramento. As medições foram realizadas com equipamentos desenvolvidos para essas finalidades. Foram realizadas análises de variância e teste de Scott-Knott quanto às características. Asforças de arranquio da planta, de quebramento do colmo e ângulo no momento do quebramento do colmo interagiram significativamente com a localidade. As médias variaram de 49,43 a 76,03 kgf para a força de arranquio da planta, de 1,07 kgf a 2,76 kgf para força de quebramento do colmo, e de 16,15 a 41,18º para o ângulo de quebramento do colmo. Existe variabilidade genética para seleção quanto à resistência ao acamamento e ao quebramento do colmo em genótipos tropicais de milho. A metodologia apresentada é eficiente para a avaliação e discriminação de genótipos.

Stress dilatancy analysis of shallow tunnels subjected to unsymmetrical pressure

Numerical simulation using finite differential code was conducted for the single line railway and four-lane road shallow tunnels subjected to unsymmetrical pressure. The mechanical behavior of weak rock mass was studied considering the influences of stress dilatancy on the failure mechanisms, and the results of numerical simulation were compared with the analytical solutions in specifications. The results show that the dilatancy angle has great influences on the surrounding rock displacement and the shape of failure face for the shallow tunnels. When the dilatancy angle equals zero, the failure face of the surrounding rock forms and extends to the ground surface. With the dilatancy angle increasing, the loose region decreases gradually, and failure surface discontinues. When the dilatancy angle equals the friction angle, the loose region is only distributed in a small range around the crown and sidewalls. On the side of smaller buried depth, the difference of break angle between numerical simulation and the code is less than 10% for single line railway tunnels with the dilatancy angle of zero. However, for the four-lane road tunnels, the difference reaches 20.8%. On the side of larger buried depth, the break angles are smaller than those by the code, the difference reaches 16.8% for single line railway tunnels, and 13.8% for four-lane road tunnels. With the dilatancy angle increasing, especially the dilatancy angle approximating to internal friction angle, it is on safe side to calculate the break angle using the analytical solution method of specifications. Therefore, the influence of stress dilatancy should be considered while determining the failure mechanisms of shallow tunnels subjected to unsymmetrical pressure in weak rocks.

Preparation and Properties of Polyether Pentaerythritol Mono‐maleate grafted Linear Low Density Polyethylene by Reactive Extrusion

A reactive type nonionic surfactant, polyether pentaerythritol mono‐maleate (PPMM) was synthesized in our laboratory. PPMM was adopted as a functionalizing monomer and grafted onto linear low density polyethylene (LLDPE) with a melt reactive extrusion procedure. FT‐IR was used to characterize the formation of grafting copolymer and evaluate their degree of grafting. The effects of monomer concentration, reaction temperature and screw run speed on the degree of grafting were studied systematically. Isothermal crystallization kinetics of LLDPE and LLDPE‐g‐PPMM samples was carried out using DSC. Crystallization rates of grafted LLDPE were faster than that of plain LLDPE at the same crystallization temperature. The tensile properties and light transmission of blown films were determined. Comparing with neat LLDPE film, no obvious changes could be found for the tensile strength, elongation at break and right angle tearing strength of LLDPE‐g‐PPMM film. The wettability is expressed by the water contact angle. With an increasing percentage of PPMM, the contact angles of water on film surface of LLDPE‐g‐PPMM decrease monotonically. The acceleration dripping property of film samples was investigated. The dripping duration of LLDPE‐g‐PPMM film and commercial anti‐fog dripping film at 60°C were 76 days and 17 days, respectively.

ESTUDO MORFODINÂMICO DURANTE UMA MARÉ EQUINOCIAL DE SIZÍGIA EM UMA PRAIA DE MACROMARÉ DO LITORAL AMAZÔNICO (PRAIA DE AJURUTEUA-PA, BRASIL)

A zona costeira bragantina está susceptível a fortes processos hidrodinâmicos que continuamente remodelama morfologia praial local. Estas flutuações de energia são mais intensas durante as marés equinociais desizígia, registradas durante os meses de março/abril e setembro/outubro, na região. Para conhecer as variaçõesmorfodinâmicas durante um destes períodos, medidas de intensidade e direção de correntes, altura da ondana rebentação (Hb), período da onda (T), ângulo de rebentação (αb), declividade do perfil (m), surf scaling parameter(ε), coeficiente de rebentação (β) e variação da escarpa, foram realizadas, diariamente, entre os dias17 e 22 de março de 2003. As correntes foram medidas na zona de surf, através de um correntômetro SensordataSD30. As alturas, períodos e ângulo de rebentação foram medidos com o auxílio de régua, cronômetro ebússola, respectivamente. Os levantamentos topográficos foram realizados em dois perfis perpendiculares àlinha de costa, com auxílio de um nível, tripé e mira falante. As análises realizadas demonstraram que a área em estudo é, em sua maioria, morfodinâmicamente dissipativa, com ondas tipo deslizante principalmente, nosetor SE. Os processos erosivos na praia em estudo são conseqüência de causas naturais, intensificadas porações antrópicas (e.g. ocupação desordenada de edificações sobre campos de dunas e área de manguezal),sendo a energia hidrodinâmica gerada pela macromaré equinocial, um fator preponderante na modificação daconfiguração morfológica da praia de Ajuruteua, durante o período em estudo. Estas alterações refletiram emtransformações morfodinâmicas a curto período que corresponderam a alterações no volume sedimentar dosdiferentes subambientes praiais.

Preparation and Properties of a Novel Nonionic Surfactant Grafted Linear Low Density Polyethylene

A novel nonionic surfactant, glycerol monostearic acid monomaleic acid diester (GMMD) was synthesized in our laboratory. Grafting‐copolymerization of linear low density polyethylene (LLDPE) with GMMD was carried out by using β‐ray irradiation in a twin‐screw extruder. Evidence of the grafting of GMMD, as well as its extent, was determined by FT‐IR. The effects of monomer concentration, reaction temperature and screw run speed on degree of grafting were studied systematically. The thermal behavior of LLDPE‐g‐GMMD was investigated by using differential scanning calorimety (DSC). Compared with neat LLDPE, the crystallization temperature (Tc) of LLDPE‐g‐GMMD increased about 3°C, and the melting enthalpy (ΔHm) decreased with increase of GMMD content. It showed that the grafted GMMD monomer onto LLDPE acted as a nucleating agent. The tensile properties and light transmission of blown films were determined. Comparing with neat LLDPE film, no obvious changes could be found for the tensile strength, elongation at break and right angle tearing strength of LLDPE‐g‐GMMD film. Accelerated dripping property of film samples was investigated. The dripping duration of LLDPE‐g‐GMMD film and commercial anti‐fog dripping film at 60°C were 52 days and 17 days, respectively.

Wave setup and setdown generated by obliquely incident waves

An analytical theory is developed for the wave setup and setdown induced by obliquely incident waves on an impermeable swell-built beach profile. The wave setup and setdown are found to decrease as wave obliquity increases. The incorporation of wave obliquity in wave setup and setdown formulation offers the physical reality in engineering applications. The general solutions presented in this paper yield the limiting case of normal wave incidence and the result is consistent with the classical theories published. The present theory is primarily applicable to the spilling and plunging breaker across the surf zone, within which wave amplitude is assumed to be linearly related to the local water depth. Experiments were conducted in a large-scale wave basin to compare with theoretical results and especially to investigate the applicability of this assumption to the case of obliquely incident waves. The dimensionless setup versus the distance offshore within the surf zone is found to depend on wave breaking angle and the shape of the beach profile; and it has a non-zero value at the original shoreline position. This implies that the original shoreline will advance landwards, and that the extent of this movement can be related to wave angle at breaking and the beach profile under consideration. The results of the present theory are in good agreement with experimental data and field measurements available.

The Luminosity and Angular Distributions of Long‐Duration Gamma‐Ray Bursts

The realization that the total energy of GRBs is correlated with their jet break angles motivates the search for a similar relation between the peak luminosity, $L$, and the jet break angles, $L\propto\theta^{-2}$. Such a relation implies that the GRB luminosity function determines the angular distribution. We re-derive the GRB luminosity function using the BATSE peak flux distribution and compare the predicted distribution with the observed redshift distribution. The luminosity function can be approximated by a broken power law with a break peak luminosity of $4.4 \times 10^{51}$ erg/sec, a typical jet angle of 0.12 rad and a local GRB rate of $0.44 h_{65}^{3}$ Gpc$^{-3}$yr$^{-1}$. The angular distribution implied by $L\propto\theta^{-2}$ agrees well with the observed one, and implies a correction factor to the local rate due to beaming of $75\pm25$ (instead of 500 as commonly used). The inferred overall local GRB rate is $33\pm11 h_{65}^{3}$ Gpc$^{-3}$yr$^{-1}$. The luminosity function and angle distribution obtained within the universal structured jet model, where the angular distribution is essentially $\propto \theta$ and hence the luminosity function must be $\propto L^{-2}$, deviate from the observations at low peak fluxes and, correspondingly, at large angles. The corresponding correction factor for the universal structure jet is $\sim 20 \pm 10$.

A Global Test of a Quasi‐universal Gamma‐Ray Burst Jet Model through Monte Carlo Simulations

The possibility that long gamma-ray burst (GRB) jets are structured has received growing attention recently, and we have suggested that most GRBs and their softer, less energetic brethren, X-ray flashes (XRFs), can be understood within a quasi-universal structured jet picture, given that the jet structure of each individual burst is a Gaussian or similar function. Here we perform a global test on such a quasi-universal Gaussian-like structured jet by comparing Monte Carlo simulation results with a broad spectrum of observational data. Using the same set of input parameters as in previous work by Zhang and coworkers, we confront the model with more observational constraints. These constraints include the burst redshift distribution, jet break angle distribution, two-dimensional redshift versus jet break angle distribution, luminosity function, and log N- log P distribution. The results indicate that the model is generally compatible with the data. This conclusion, together with our previous tests with the observed jet break angle versus isotropic energy and observed peak energy versus fluence relations, suggests that current long GRB and XRF data are generally consistent with such a quasi-standard energy and quasi-standard angle jet picture. With future homogeneous burst samples (such as the one to be retrieved from the Swift mission), the refined GRB jet structure can be further constrained through a global comparison between various observed and predicted burst property distributions and relations.

Jets in Gamma‐Ray Bursts: Tests and Predictions for the Structured Jet Model

The two leading interpretations of achromatic breaks that are observed in the light curves of GRBs afterglow are (1) the manifestation of the edge of a jet, which has a roughly uniform energy profile and a sharp edge, and (2) a line-of-sight effect in jets with a variable energy profile. The first scenario requires the inner engine to produce a jet with a different opening angle each explosion, while the latter requires a standard engine. The physical structure of the jet is a crucial factor in understanding GRB progenitors, and therefore discriminating the two jet scenarios is particularly relevant. In the structured jet case, specific predictions can be made for the distribution of observed break angles θbr, while that distribution is arbitrary in the first scenario. We derive the theoretical distribution for the structured jet model. Specifically, we predict the most common angle to be about 0.12 rad, in rough agreement with the sample. If this agreement holds as the sample size increases, it would strengthen the case for the standard jet hypothesis. We show that a prediction of this model is that the average viewing angle is an increasing function of the survey sensitivity and in particular that a mission such as Swift will find the typical viewing angle to be about 0.3 rad. The local event rate predicted by this model is RGRB(z = 0) ~ 0.5 Gpc-3 yr-1.

A yield strength model for the Al-Mg-Si-Cu alloy AA6111

A yield strength model is developed for the Al-Mg-Si-Cu alloy AA6111. The evolution of the strength of precipitates, as obstacles to dislocation motion, during various stages of aging is modeled according to the theories for strengthening mechanisms, as well as the microstructural and mechanical behavior of the alloy. The precipitation hardening component of yield strength is modeled for conditions where precipitates act as either strong or weak obstacles. The dislocation breaking angles for various stages of aging at 180 °C is estimated and the applicability of both strong and weak obstacle models examined. It is found that although the weak obstacle model could be a better choice for describing the very early aging stages and/or the low temperature processes, the entire aging period in the temperature range of 160–220 °C is well described by applying the strong obstacle model. The modeling results are related to the microstructural evolution in this alloy system.

Assessment of a finite element model for plate shearing

A study was conducted to assess the robustness of a plane strain finite element model that was developed to simulate plate shearing using the Cockroft-Latham fracture criterion and element deletion. Model predictions for blade gap, ductility and edge wear were compared with published experimental results. Results showed that the model was able to simulate initiation and propagation of fracture lines at the punch and die corners and the resultant break angle along the edge was found to be close to values observed in practice. Simulated edge geometry and microhardness were found to be in reasonable agreement with published experimental results for the steel plate considered although the model was unable to simulate double cutting at 0.8 per cent clearance. Results also suggest that edge hardness is independent of the starting ductility in the plate and that increasing the edge radii does not effectively simulate edge wear. Based on the results obtained, it may be concluded that the plane strain model is able to simulate plate shearing with sufficient accuracy in the range of normal process conditions.

Dynamical features of forest interactions

The 3D computer simulations presented here were developed to study at the mesoscopic scale the formation of junctions and their impact on hardening of crystals. The simulations consider the evolution of a dislocation interacting with immobile dislocations in a fcc single crystal of copper where we incorporate well known dislocation interaction mechanisms. From these studies, we deduced a `breaking angle' which characterize the strength of the junctions.

Determination of precipitate strength in aluminium alloy 6056-T6 from transmission electron microscopyin situstraining data

Abstract The transmission electron microscopy in-situ straining technique is employed to measure the breaking angles of strengthening precipitates in aluminium alloy 6056-T6 as they are sheared by dislocations. The experimental determination of the character of bowed dislocation segments when dislocations are pinned on precipitates allows us to calculate the corresponding line tensions. From this, the maximum forces F m that precipitates can sustain before being sheared by dislocations are deduced. It is suggested that F m may be regarded as a quantitative parameter which includes the effects of the various strengthening mechanisms operative in precipitation-hardened alloys. An attempt is made to relate the maximum force calculated from in-situ straining data to the macroscopic yield strength of the material.

Vanishing Disclination Lines in Lyotropic Biaxial Nematics

Faint disclination lines which vanish at the transition to the uniaxial nematic phase, are observed in the biaxial nematic phase of a ternary lyotropic mixture. Unlike the m-disclination lines, they do not exhibit observable breaks. They bear ghostlike point defects instead. The joint observation of both kinds of disclination lines could give a real proof of biaxiality, as well as the evidence of zigzagging disclination lines with temperature dependent breaking angles. Conversely, a quick analysis of the disclination lines observed in a uniaxial nematic phase may erroneously lead one to conclude to biaxiality.

抄紙機ツインワイヤフォーマの脱水メカニズム 第２報 脱水モデルの構築とシミュレーションによる検証

As the first step of a drainage mechanism study on a blade type Twin-Wire forming, a pulse pressure generation mechanism was investigated from an experimental stand point of view in the previous report.This report relates to a theoretical analysis of the drainage mechanism. A drainage model and a simulation program have been developed based on the hypotheses made up in the first step. The simulation results affirmed the hypotheses, i.e., the pulse pressure is generated by a change in a stock thickness between two wires when the stock is chocked at a leading edge of a blade and primary factors affecting pressure level are a breaking angle at the edge and a drainage resistance though a mat.Through these studies the drainage mechanism in the blade type Twin-Wire forming has been established.

Experimental investigation of the processes of complex loading of alloy AMg6

The article presents the results of tests with tubular specimens of aluminum alloy AMg6 subjected to simultaneous tension and internal pressure on a load trajectory in the form of two-link broken lines with the break angle of 90° in the stress space. It is shown that the experimental results agree well with those obtained according to the theory of quasisimple processes.