Literatura científica selecionada sobre o tema "Flexible Curves"
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Artigos de revistas sobre o assunto "Flexible Curves"
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Wei Chan, Chris Yin, Chee Kidd Chiu, Yun Hui Ng, Saw Huan Goh, Xin Yi Ler, Sherwin Johan Ng, Xue Han Chian, Pheng Hian Tan e Mun Keong Kwan. "An analysis of preoperative shoulder and neck balance and surgical outcome in 111 adolescent idiopathic scoliosis patients with two subtypes of Lenke 1 curves". Journal of Neurosurgery: Spine 34, n.º 1 (janeiro de 2021): 37–44. http://dx.doi.org/10.3171/2020.5.spine20397.
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OBJECTIVEThe incidence of postoperative shoulder imbalance following posterior spinal fusion (PSF) is still high in Lenke 1 curves despite following current treatment recommendations for upper instrumented vertebra (UIV) selection. The objective of this retrospective study was to identify differences in preoperative shoulder balance and to report the surgical outcome of two subtypes of Lenke 1 curves (flexible vs stiff) in patients with adolescent idiopathic scoliosis (AIS).METHODSThe authors grouped patients’ curves as Lenke 1–ve (flexible) when their preoperative proximal thoracic side bending (PTSB) Cobb angle was < 15° and as Lenke 1+ve (stiff) when the PTSB Cobb angle was 15°–24.9°. The authors hypothesized that these two subtypes had distinct preoperative and postoperative shoulder and neck balance following PSF using pedicle screw constructs.RESULTSFifty patients had Lenke 1 (flexible) curves and 61 had Lenke 1 (stiff) curves. The mean preoperative T1 tilt for patients with Lenke 1 (flexible) was −4.9° ± 5.3°, and for those with Lenke 1 (stiff) curves it was −1.0° ± 5.3° (p < 0.001). Mean cervical axis (CA) was −0.1° ± 3.2° for Lenke 1 (flexible) curves and 2.3° ± 3.5° for Lenke 1 (stiff) curves (p < 0.001). Preoperative radiographic shoulder height (RSH) and clavicle angle (Cla-A) were similar between the two curve subtypes. Following surgery, there were significant differences between the subtypes in terms of T1 tilt (p < 0.001), RSH (p = 0.014), and Cla-A (p = 0.031). Interestingly, 41.0% of patients with a Lenke 1 (stiff) curve had +ve T1 tilt compared to 2.0% in Lenke 1 (flexible) group. Moreover, 26.2% of patients with the Lenke 1 (stiff) curve had +ve RSH compared to 12.0% of those with Lenke 1 (flexible) curves. And, 24.6% of patients with Lenke 1 (stiff) had +ve Cla-A compared to 10.0% of those with Lenke 1 (flexible) curves.CONCLUSIONSLenke 1 (flexible) and Lenke 1 (stiff) curves had distinct preoperative T1 tilt and CA measurements. Following PSF, the authors noted +ve T1 tilt in 41% of patients with Lenke 1 (stiff) curves versus 2.0% in those with Lenke 1 (flexible) curves. The authors also noted a significant difference in postoperative RSH and Cla-A measurements.
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Liu, Zhen-yu, Shi-en Zhou, Jin Cheng, Chan Qiu e Jian-rong Tan. "Assembly variation analysis of flexible curved surfaces based on Bézier curves". Frontiers of Information Technology & Electronic Engineering 19, n.º 6 (junho de 2018): 796–808. http://dx.doi.org/10.1631/fitee.1601619.
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Bu, Fan Hua, Yue Ming Zhang e Zhao Miao Liu. "Residual Vibration of Flexible Exponential Cam Curves". Applied Mechanics and Materials 635-637 (setembro de 2014): 197–200. http://dx.doi.org/10.4028/www.scientific.net/amm.635-637.197.
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The residual vibration of cam curves is analyzed. The displacement of residual vibration is computed by Duhamel method. The comparison of the residual displacement between the flexible exponential cam curves, the modified constant velocity curves, the modified trapezoidal curves, and the modified sine curves is done. The residual vibration of the flexible exponential curves is smallest.
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Tian, Qiuyong, Yichang Zhou, Thilo Hanisch e Markus Hecht. "Study on railway curve squeal using a rigid-flexible coupling model of vehicle and track". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 265, n.º 1 (1 de fevereiro de 2023): 6230–37. http://dx.doi.org/10.3397/in_2022_0927.
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Squeal noise occurring in narrow curves is one of the most annoying noise issues for people living by the railway track. When vehicles pass through those curves, squeal noise is mainly generated due to the large, high-frequency, lateral sliding friction force. To investigate generation mechanism of curve squeal, a three-dimensional (3D) vehicle-track interaction model with a flexible wheelset and a flexible curved track is built in a multi-body simulation tool in this paper. Compared to conventional rigid models, this model allows to obtain the high frequency friction force between wheel and rail. This calculated friction force in the frequency domain is analyzed to identify the major modes. Those modes are compared with the modal properties of the wheelsets and rails in order to determine which of their modes have the main contribution to the friction force and the squeal noise. In addition, a parametric study is performed to study the influence of vehicle speed, curve radius, wheel/rail friction coefficient and further parameters on the dominant modes of friction forces.
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Cui, Yunchao, Lingkai Zhang, Chong Shi e Runhan Zhang. "Research on the Characteristic State of Rockfill Materials and the Evolution Mechanism at the Microscopic Scale". Applied Sciences 14, n.º 11 (21 de maio de 2024): 4353. http://dx.doi.org/10.3390/app14114353.
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In this study, the real particle morphology of rockfill materials is obtained through three-dimensional scanning technology, and flexible boundary conditions are established by coupling the discrete element method and the finite element method. Then, a large-scale three-axis numerical simulation test is carried out on the rockfill materials to study the macroscopic mechanical properties and the change rule of the microscopic view of the rockfill materials in different characteristic states. The macroscopic results show that the stress–strain curves of the rockfill materials can be divided into softening and hardening curves. The phase transition, peak, and critical states of the softening-type curves show different mechanical properties, but no clear distinction between the characteristic state changes can be seen in the hardening-type curves. The microscopic results show that the displacement of the upper and lower parts of the flexible boundary of the softening curve increases with loading, and there is no obvious displacement in the middle part, but the middle particles undergo rotational deformation. An “X” shear band appears, and the strength of the force chain and the coordination number tend to increase first and then decrease. The flexible boundary displacements of the hardening-type curves are similar to those of the softening-type curves, but the central particles show a large number of cleavages instead of shear zones, and the force chain strength and coordination number levels show a continuous upward trend.
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Ge, Rong Yu, e P. Q. Guo. "Flexible Cam Profile Synthesis Method Using NURBS and its Optimization Based on Genetic Algorithm". Advanced Materials Research 426 (janeiro de 2012): 69–72. http://dx.doi.org/10.4028/www.scientific.net/amr.426.69.
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This paper describes a synthesis method of designing flexible cam profiles by using quintic non-uniform rational B spline (NURBS) curves. The cam profile curve can be optimized by adjusting knot vector, control points and weight factors of NURBS curve. The multiobjective optimization for a cam curve was described to satisfy both kinematic and dynamic requirements. To solve the optimization model for NURBS cam curve, an improved genetic algorithm (GA) called INSGA in the paper was proposed. Application examples on the kinematical and dynamical optimization of cam curves are presented together with detailed discussions. These examples, especial the dynamic optimization to control the residual vibration for a cam curve used in an indexing cam mechanism, sufficiently illustrate the effectiveness of the proposed approach.
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İPEK, Egemen, e Haydar AKYAZI. "Turkish Households Consumption Behavior and Flexible Engel Curves". Doğuş Üniversitesi Dergisi 2, n.º 18 (27 de julho de 2017): 35–50. http://dx.doi.org/10.31671/dogus.2018.30.
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Belkhatir, Bachir, e Ahmed Zidna. "Construction of flexible blending parametric surfaces via curves". Mathematics and Computers in Simulation 79, n.º 12 (agosto de 2009): 3599–608. http://dx.doi.org/10.1016/j.matcom.2009.04.015.
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Yamada, Yohei, e Hiroyuki Sasahara. "Free-form curves cutting using flexible circular saw". Precision Engineering 38, n.º 3 (julho de 2014): 611–16. http://dx.doi.org/10.1016/j.precisioneng.2014.02.011.
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Winter, Michael, Alexander Luttkau e Hermann Lödding. "Produktionskennlinien mit Kapazitätsflexibilität/Logistic Operating Curves with Capacity Flexibility". wt Werkstattstechnik online 111, n.º 04 (2021): 190–94. http://dx.doi.org/10.37544/1436-4980-2021-04-12.
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Die Kapazitätsflexibilität ist von zentraler Bedeutung für das Produktionsmanagement. Sie ermöglicht es Unternehmen, auf Nachfrageschwankungen zu reagieren. Weniger bekannt ist ihre Bedeutung für die erreichbaren Bestände und Durchlaufzeiten der Produktion. Unternehmen können den erforderlichen Pufferbestand mit flexiblen Kapazitäten reduzieren. Dieser Effekt wird mithilfe von Produktionskennlinien modelliert und dargestellt. Capacity flexibility is of central importance for production management. It enables companies to respond to fluctuations in demand. Less well known is its significance for the necessary WIP buffers and throughput times in production. Based on flexible capacities, companies can reduce the required level of work-in-process buffer. This effect is modelled and visualized with production operating curves.
Teses / dissertações sobre o assunto "Flexible Curves"
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Montagna, Cimarelli Viktor Donna. "Stream Identification in Pinch Analysis : Fixed and Flexible flows". Thesis, Mittuniversitetet, Avdelningen för kemiteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-34281.
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The purpose of this project is to find an identification tag that can be used in a future automated pinch analysis tool. It can be used to further analyse composite curves and pinch results by tracking the original streams that was converted. In real life situations, retrofitting a process industries streams, can decrease heat demands and costs. A pinch analysis and a heat exchange network is created with fixed and flexible flows to show a recommendation on how the system model can handle this type of situations. The models have been created by hand with support from pinch literature and the calculations validated with mathematical software such as matlab and other graphing tools. The literature study and pinch modelling resulted in a recommendation of tagging Hstart and Hend for each individual stream. By using a geographical tag in a coordinate system the analyst will be able to find the original streams in the pinch analysis and composite curves. The project also resulted in a heating exchange network created from the fixed and flexible data set. The enthalpy differences between the ideal pinch result and the fixed data set is smaller than one might expect because of enthalpy abundance in the specific intervals.
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Saint-Criq, Anthony. "Involutions et courbes flexibles réelles sur des surfaces complexes". Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSES087.
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La première partie du seizième problème de Hilbert traite de la topologie des courbes algébriques réelles régulières dans le plan projectif. Il est bien connu que bon nombre des propriétés topologiques satisfaites par de telles courbes sont également vraies pour la classe plus large des courbes flexibles, introduites par O. Viro en 1984. Le but de cette thèse est d'approfondir les origines topologiques des restrictions sur les courbes réelles, en lien avec le seizième problème de Hilbert. Nous ajoutons une condition naturelle à la définition de courbe flexible, à savoir qu'elles doivent intersecter une conique réelle vide Q comme une courbe algébrique, c'est-à-dire en des points positifs uniquement. Nous voyons CP(2) comme un cylindre sur un espace lenticulaire L(4,1)×R, que l'on compactifie en ajoutant RP(2) et Q aux bords, et nous utilisons la décomposition induite sur S(4)=CP(2)/conj. C'est un fait standard que la surface d'Arnold joue un rôle essentiel dans l'étude des courbes de degré pair. Nous introduisons un analogue de cette surface pour des courbes de degré impair. Nous généralisons également la notion de courbe flexible pour inclure des surfaces non orientables. Nous considérons qu'une courbe flexible est de degré m si son auto-intersection est m² et si elle intersecte la conique Q de manière transverse en exactement 2m points. Notre résultat principal affirme que pour une telle courbe flexible (non nécessairement orientable) de degré impair m=2k+1 ne peut pas posséder plus de -χ(F)/2-k²+k+1, où χ(F) est la caractéristique d'Euler de F. Cette borne supérieure se simplifie en k² dans le cas d'une courbe flexible au sens usuel. Nous généralisons également notre résultat pour des courbes flexibles sur des quadriques, ce qui produit une nouvelle restriction, même pour des courbes algébriques. Dans les chapitres introductifs, un aperçu détaillé de la théorie classique des courbes réelles planes est fait, en s'appuyant aussi bien sur le point de vue réel que complexe. Certains résultats à propos de la théorie des surfaces nouées dans les 4-variétés sont énoncés. Plus précisément, il est question de faits concernant la classe d'Euler du fibré normal d'une surface plongée. Cela nous amène ensuite à considérer la fonction de genre non-orientable d'une 4-variété. Cela constitue un analogue de la conjecture de Thom (résolue par Kronheimer et Mrowka en 1994) pour des surfaces non orientables. Nous calculons presque totalement cette fonction pour CP(2), et nous étudions cette fonction sur d'autres 4-variétés. Enfin, nous digressons autour de la nouvelle notion de courbes flexibles non orientables, où nous dressons une liste de résultats connus qui restent vrai dans ce cadre. Nous nous concentrons aussi sur la classe des courbes algébriques et flexibles qui sont invariantes sous l'action d'une involution holomorphe de CP(2), une notion introduite par T. Fiedler et appelées courbes symétriques. Nous donnons un état de l'art, et nous formulons une succession de petits résultats à propos de la disposition d'une courbe symétrique par rapport aux éléments de symétrie. Nous proposons également une approche pour tenter de généraliser la congruence de Fiedler p-n≡k² [16], valable pour des M-courbes symétriques de degré 2k, à des (M-1)-courbes symétriques de degré 2kThe first part of Hilbert's sixteenth problem deals with the topology of non-singular real plane algebraic curves in the projective plane. As well-known, many topological properties of such curves are shared with the wider class of flexible curves, introduced by O. Viro in 1984. The goal of this thesis is to further investigate the topological origins of the restrictions on real curves in connection with Hilbert's sixteenth problem. We add a natural condition to the definition of flexible curves, namely that they shall intersect an empty real conic Q like algebraic curves do, i.e. all intersections are positive. We see CP(2) as a cylinder over a lens space L(4,1)×R which is compactified by adding RP(2) and Q respectively to the ends, and we use the induced decomposition of S(4)=CP(2)/conj. It is a standard fact that Arnold's surface plays an essential role in the study of curves of even degree. We introduce an analogue of this surface for curves of odd degree. We generalize the notion of flexible curves further to include non-orientable surfaces as well. We say that a flexible curve is of degree m if its self-intersection is m² and it intersects the conic Q transversely in exactly 2m points. Our main result states that for a not necessarily orientable curve of odd degree 2k+1, its number of non-empty ovals is no larger than χ(F)/2-k²+k+1, where χ(F) is the Euler characteristic of F. This upper bound simplifies to k² in the case of a usual flexible curve. We also generalize our result for flexible curves on quadrics, which provides a new restriction, even for algebraic curves. In the introductory chapters, a thorough survey of the classical theory of real plane curves is outlined, both from the real and the complex points of view. Some results regarding the theory of knotted surfaces in 4-manifolds are laid down. More specifically, we review statements involving the Euler class of normal bundles of embedded surfaces. This eventually leads us to consider the non-orientable genus function of a 4-manifold. This forms a non-orientable counterpart of the Thom conjecture, proved by Kronheimer and Mrowka in 1994 in the orientable case. We almost entirely compute this function in the case of CP(2), and we investigate that function on other 4-manifolds. Finally, we digress around the new notion of non-orientable flexible curves, where we survey which known results still hold in that setting. We also focus on algebraic and flexible curves invariant under a holomorphic involution of CP(2), a smaller class of curves introduced by T. Fiedler and called symmetric curves. We give a state of the art, and we formulate a collection of small results results regarding the position of a symmetric plane curve with respect to the elements of symmetry. We also propose a possible approach to generalize Fiedler's congruence p-n≡k² [16], holding for symmetric M-curves of even degree 2k, into one for symmetric (M-1)-curves of even degree
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Jagirdar, Saurabh. "Kinematics of curved flexible beam". [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001853.
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Emiliani, Sanz Esteban. "Evaluation of holmium: YAG laser settings for the non-contact stone fragmentation technique and the curved laser fiber”". Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/668071.
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La ureteroscopia flexible (fURS) con el laser de Holmio:YAG (Ho:YAG) es uno de los tratamientos estándar para la urolitiasis ya que el Ho:YAG ha demostrado destruir eficientemente cualquier tipo de urolitiasis. Aunque se han descrito diversas técnicas de litotricia, en los últimos años se han añadido nuevos parámetros al Ho:YAG y se han evaluado diferentes métodos de manejo de las fibras laser lo cual pretende mejorar la efectividad de la fURS. Por otro lado, los resultados de la fURS están asociados a limitaciones de la técnica como trabajar en ángulos agudos que pueden llevar a rotura de la fibra láser.
Las técnicas y los parámetros del laser no han sido suficientemente estudiados para tratar ese tipo de casos y hacer la técnica mas segura y efectiva.
El objetivo de esta tesis es evaluar la técnica de fragmentación sin contacto (FSC) con una variedad amplia de parámetros del Ho:YAG y tamaños de fibras laser. Asimismo estudiar in-vitro los factores de riesgo de ruptura de la fibra laser al curvarse.
Los experimentos de la FSC se realizaron con 4 piedras artificiales en un tubo de ensayo. Un ureteroscopio, fijo y con flujo constante fue insertado a través de una camisa ureteral al tubo. El laser se fijó a 1 mm de la base del tubo entre las piedras. Una combinación de 0.5-1.5 Julios, 10-20 y 40 Hz y pulso largo y corto fueron evaluados por 2 y 4 minutos, utilizando fibras de 273 and 365 μm. Los experimentos se realizaron 3 veces cada uno. Las piedras analizadas fueron pesadas antes y después del experimento para evaluar la eficiencia de la FSC. Se realizaron un total de 144 experimentos. La media de peso de las piedras por cada tubo fue de 0.23g y tras los experimentos una diferencia media de 0.7 gr (0.01-0.243). Escogiendo una reducción del 50% peso como corte para calificar la técnica de efectiva los valores predictivos que promovían una técnica adecuada fueron: El pulso largo (OR = 2.7, 95% CI 1.05 – 7.15), Tiempo de 4 min (OR = 11.4, 95% CI 3.88 – 33.29), Fibra de 273μm (OR = 0.23, 95% CI 0.08 – 0.70), y alta energía (OR = 1.14, 95% CI 1.09 – 1.20).
Con respecto a la evaluación de la curvatura de la fibra, se utilizaron fibras de 272 y 365m, dobladas a 9, 12, 15, 18 y 20mm de diámetro. Se evaluaron parámetros de fragmentación y pulverización laser a 7.5 Vatios. El láser fue activado por 5 minutos repitiendo los experimentos 10 veces.
Como resultado se vio que utilizando parámetros de pulverización ambos tamaños de fibra se rompían solo al curvarse 9 mm (p<0.05). Utilizando parámetros de fragmentación las fibras se rompían mas, al estar curvadas 12mm para fibras de 272m y 15mm para fibras de 365m (p=0,007 and 0,033 respectivamente). El pulso corto y la alta energía fueron factores de riesgo significativos para romper fibras de 365m (p=0,02) pero no de 272m (p=0,35). La frecuencia (Hz) no fue un factor de riesgo significativo para la rotura. Hubo una tendencia a una mayor rotura de fibras de 365m comparada con las fibras de 272m no siendo significativa (p>0,05). Concluimos que las fibras de 272m eran mas resistentes ya que requieren una curvatura aguda (<9mm) para su rotura. También se evidenció que la utilización de parámetros de pulverización reduce el riesgo de rotura comparado con parámetros de fragmentación.Flexible ureteroscopy (fURS) with Holmium: YAG laser (Ho:YAG) is one of the standard procedures for renal urolithiasis as Ho:YAG has shown to efficiently fragment urinary stones of any composition. Several techniques of laser lithotripsy have been described although new laser parameters have been added to the Ho:YAG in recent years and studies on laser fiber handling have provided new recommendations to improve performance. Regarding fURS, treatment outcomes are associated with technical limitations of fURS when working in acute angle calices and Ho:YAG fiber breakages can be associated with costly repairs. The techniques and laser parameters for treating such difficult cases have not been widely described. The purpose of this thesis is to evaluate the non contact “pop-corn” (PC) technique with a wide range of Ho:YAG settings and fiber sizes as to evaluate the risk factors for fiber fracture while curved in systematic in-vitro assessments. The evaluations for the PC were done with 4 artificial stones in a Vacutaner. A fix ureteroscope was inserted trough a ureteral access sheath allowing constant irrigation flow. The laser was placed at 1 mm from the bottom of the Vacutaner within the stones. The combination of 0.5-1.5 Joules, 10-20 and 40Hz and long and short pulse were tested for 2 and 4 minutes. 273 and 365 μm laser fibers were used. All tests were repeated 3 times. The stones were weighed before and after the experiments to evaluate the setting efficiency. Significant predictors for a highly efficient technique were assessed. A total of 144 experiments were conducted. Stone groups had a consistent weight: mean of 0.23g. After the experiment median weight difference was 0.7 gr (0.01-0.243). Choosing a cumulative percentage of 50% of the stones volume reduction as the cut-off level the significant predictors for high efficiency PC technique were the use of long pulse (OR = 2.7, 95% CI 1.05 – 7.15), longer time (4 min) (OR = 11.4, 95% CI 3.88 – 33.29), small (273μm) laser fiber (OR = 0.23, 95% CI 0.08 – 0.70), and higher power (watt) (OR = 1.14, 95% CI 1.09 – 1.20). We concluded that higher energy (>1.5 J), longer pulse, higher frequency of (20Hz),longer time, and small laser fiber are predictors for high efficient PC technique. As for the curved fiber evaluations, 272m and 365m fibers were employed. Five different fiber curve diameters were tested: 9, 12, 15, 18 and 20mm. Fragmentation and dusting settings were used at 7.5W. The laser was activated for 5 minutes. Each experiment was repeated 10 times. We found that with dusting settings, fibers broke more frequently at a curved diameter of 9mm f or both 272m and 365m fibers (p=0,037 and 0,006 respectively). Using fragmentation setting, fibers broke more frequently at 12mm for 272m and 15mm for 365m (p=0,007 and 0,033 respectively). Short-pulse and high energy were significant risk factors of fiber fracture for the 365m fibers (p=0,02), but not for the 272m fibers (p=0,35). Frequency was not a risk factor for fiber rupture. Fiber diameters also seemed to be involved in the failure with a higher number of broken fibers for the 365m fibers but no significant differences were found comparing to the 272m fibers (p>0,05). We concluded that small fibers are more resistant than large ones as lower bending diameters (<9mm) are required to break small fibers. In acute angles the use small-diameter fibers, at a low energy and long-pulse (dusting setting) may reduce the likelihood of fiber rupture.
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Magee, Warwick R. "Development of an electromagnetic actuator for active vibration control". Thesis, Queensland University of Technology, 1997.
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Galperin, Inna. "A numerical model of the motion of a curved flexible fibre in a shear flow". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ29375.pdf.
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Xiao, Jian. "Local Water Slamming of Nonlinear Elastic Sandwich Hulls, and Adiabatic Shear Banding in Simple Shearing Deformations of Thermoelastoviscoplastic Bodies". Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/20375.
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We have developed a third-order shear and normal deformable plate/shell theory (TSNDT) incorporating all geometric nonlinearities and used it to analyze, by the finite element method (FEM), transient finite deformations of a sandwich beam with two face sheets and the core made of St. Venant-Kirchhoff materials. A triangular cohesive zone model with stress based criterion for delamination initiation and energy based relation for complete separation is used to analyze delamination failure in a beam under mixed-mode loading. We have studied transient post-buckling deformations and delamination progression in an axially compressed and initially delaminated clamped-clamped sandwich beam. The buckling load for transient deformations exceeds that for static deformations and the increase depends upon the loading rate. This FE software for analyzing deformations of sandwich beam is coupled with that based on the boundary element method (BEM) for studying time-dependent deformations of water and the coupled software is used to analyze deformations of flexible curved hulls due to water slamming loads. The water is assumed to be inviscid and incompressible and undergo irrotational deformations. The Laplace equation for the velocity potential is numerically solved by the BEM with normal velocity and pressure assumed to be continuous across the interface between the hull and the water. Challenging issues resolved in this work include finding the wetted surface of the hull, nonlinear deformations of the fluid due to convective part of acceleration, effects of geometric nonlinearities on hull\'s deformations, resolution of the jet tip, as well as the initiation and propagation of delamination between the face sheets and the core. It is found that both delamination and geometric nonlinearities significantly affect the hydrodynamic pressure acting on the hull, and transverse shear deformations contribute more to the strain energy absorbed by the core than its transverse normal deformations. We have used the discontinuous basis functions to derive the Galerkin formulation of a nonlinear problem involving simple shearing deformations of a homogeneous and isotropic thermo-elasto-visco-plastic body with uniform deformations perturbed to simulate the effect of a defect. The resulting coupled nonlinear ordinary differential equations are integrated with respect to time by using the package, LSODE (Livermore Solver for Ordinary Differential Equations). Computed results showing localization of deformations into narrow regions are found to agree well with those found by the FEM, and spatial variations of the shear stress are smoother than those obtained by the FEM.
Ph. D.
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Espinosa, Diego Alejandro. "Moment-dependent pseudo-rigid-body models for beam deflection and stiffness kinematics and elasticity". [Tampa, Fla] : University of South Florida, 2009. http://purl.fcla.edu/usf/dc/et/SFE0002943.
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MORAIS, Frederico Dourado Rodrigues. "A relação entre escola e trabalho na lógica do capital: os cursos superiores de tecnologia no Brasil em debate". Universidade Federal de Goiás, 2011. http://repositorio.bc.ufg.br/tede/handle/tde/2010.
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Dissertacao Frederico Dourado Rodrigues Morais.pdf: 1326761 bytes, checksum: 3917c663223c2bc77e9ad8decc145440 (MD5)
Previous issue date: 2011-08-28This work, resulting from research carried out by the line of research Education, Labor and Social Movements in the Graduate Program in Education at FE / UFG, seeking to understand the relationship between school and work in the phase of flexible accumulation of capital, with the object analysis and study the Colleges of Technology.The objective is to understand this dynamic from literature, picking up changes in the workplace, in the productive structure and expansion of new training courses andqualifications for the job. For this theory is based in Harvey (2009), Frigotto (1989,1998, 1999, 2003), Gentili (1996, 1998), Ramos (2006), Machado (1998, 2006) and Giolo (2006), as well as documents and census data of higher education provided byINEP the period 1999 to 2008. The starting point was the changes in capitalism, showing the crises inherent in the capital and the changing of the work of a social rightfor an individual achievement. In this movement, words such as competence andemployability have become increasingly present in public policy. With this research it was found that the growth of structural unemployment, individuals whose training islimited by the narrowing of time and space, the classification tends to be more aninstrument of domination of capitalism in the face of subjects and a crucial element in the justification unemployment.
Este trabalho, decorrente de pesquisa desenvolvida junto à linha de pesquisa Educação, Trabalho e Movimentos Sociais do Programa de Pós Graduação em Educação da FE/UFG, busca apreender a relação entre escola e trabalho na fase de acumulação flexível do capital, tendo como objeto de análise e estudo os Cursos Superiores de Tecnologia. Objetiva-se compreender esta dinâmica a partir de pesquisa bibliográfica, apanhando as mudanças no mundo do trabalho, na estrutura produtiva e na expansão dos novos cursos de formação e qualificação para o trabalho. Para tanto fundamenta-se teoricamente em Harvey (2009), Frigotto (1989; 1998; 1999; 2003), Gentili (1996; 1998), Ramos (2006), Machado (1998; 2006) e Giolo (2006), bem como em documentos e dados do censo do ensino superior disponibilizado pelo INEP do período de 1999 a 2008. Partiu-se das mudanças ocorridas no capitalismo, evidenciando as crises inerentes ao capital e a mutação do trabalho de um direito social, para uma conquista individual. Nesse deslocamento, palavras como competência e empregabilidade se tornaram cada vez mais presentes nas políticas públicas. Com a realização desta pesquisa constatou-se que o crescimento do desemprego estrutural, cuja formação dos indivíduos é delimitada pelo estreitamento entre o tempo e o espaço, a qualificação tende a ser mais um instrumento de dominação do capitalismo frente aos sujeitos e um elemento crucial na justificação do desemprego.
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Manathunga, Kalpani. "Technology support for scalable and dynamic collaborative learning: a pyramid flow pattern approach". Doctoral thesis, Universitat Pompeu Fabra, 2017. http://hdl.handle.net/10803/456041.
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Collaborative Learning is the pedagogical approach that considers social interactions as key means to trigger rich learning processes. Collaborative Learning Flow Patterns define best practices to orchestrate collaborative learning activity flow mechanisms (i.e., group formation, roles or resources allocation, phase change). Flow patterns have been experimented and evaluated as effective in small scale settings for decades. Directly applying these pedagogical methods to large learning scenarios is challenging due to the burden that scale represents in the orchestration load or the difficulty of keeping a dynamic meaningful progression when flexible changes are required in a large classroom or in a MOOC. Some attempts have shown positive results, but research around scalable collaborative learning approaches, models and technologies for large classes is scattered. This dissertation conducts a systematic literature review of collaborative learning applications on large classes and analyses the social learning potential of diverse technology-supported spaces in massive courses. Then the dissertation focuses the study on how collaborative learning could address key challenges (i.e., scalability and dynamism) identified in large collaborative learning contexts. Consequently, the thesis proposes a Pyramid flow pattern instantiation, composed of a model with a set of algorithmic rules for flow creation, flow control and flow awareness as well as a PyramidApp authoring and enactment system implementing the model. Experimentation across diverse learning contexts shows that, on one hand, the contributions support meaningful scalable and dynamic collaborative learning and on the other hand, learners and educators perceive the experiences as engaging, with learning values and effective from the perspective of orchestration.El aprendizaje colaborativo es el enfoque pedagógico que considera las interacciones sociales como un medio clave para desencadenar procesos de aprendizaje ricos. Los patrones de flujo de aprendizaje colaborativo definen buenas prácticas para orquestar mecanismos de flujo en actividades de aprendizaje colaborativo (es decir, la formación de grupos, la asignación de roles o recursos, los cambios de fase). Los patrones de flujo han sido probados y evaluados como efectivos en entornos de pequeña escala durante décadas. La aplicación de estos métodos pedagógicos en grandes escenarios de aprendizaje supone un reto debido a la carga que representa la escala en la orquestación, así como a la dificultad de mantener una progresión dinámica con sentido pedagógico cuando se requieren cambios flexibles en un aula grande o en un MOOC. Existen algunos intentos interesantes, pero la investigación en torno a enfoques de aprendizaje colaborativo escalables, y modelos y tecnologías para entornos educativos con muchos estudiantes está dispersa. Esta tesis lleva a cabo una revisión sistemática de la literatura sobre aplicaciones de aprendizaje colaborativo con muchos estudiantes y analiza el potencial de aprendizaje social de diversos espacios apoyados por la tecnología en este tipo de contextos. A continuación, la tesis se centra en el estudio de cómo el aprendizaje colaborativo podría abordar desafíos clave identificados en contextos de aprendizaje colaborativo con un gran número de estudiantes (es decir, la escalabilidad y el dinamismo). En consecuencia, la tesis propone una instanciación del patrón de flujo Pirámide, compuesto de un modelo con un conjunto de reglas algorítmicas para la creación, el control y la conciencia del flujo de aprendizaje, así como un sistema de creación e implementación del modelo. La experimentación realizada en distintos contextos de aprendizaje demuestra que, por un lado, las contribuciones apoyan un aprendizaje colaborativo escalable y dinámico, y que, por otro lado, los estudiantes y los educadores perciben las experiencias como amenas, con valor para el aprendizaje y efectivas desde la perspectiva de la orquestación.
Livros sobre o assunto "Flexible Curves"
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Doosti, Hassan, ed. Flexible Nonparametric Curve Estimation. Cham: Springer International Publishing, 2024. http://dx.doi.org/10.1007/978-3-031-66501-1.
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Galperin, Inna. A numerical model of the motion of a curved flexible fibre in a shear flow. Ottawa: National Library of Canada = Bibliothèque nationale du Canada, 1999.
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Hieber, Wolfgang Lothar. Lern- und Erfahrungskurveneffekte und ihre Bestimmung in der flexibel automatisierten Produktion. München: F. Vahlen, 1991.
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Statistically generated weighted curve fit of residual functions for modal analysis of structures. Marshall Space Flight Center, Ala: National Aeronautics and Space Administration, George C. Marshall Space Flight Center, 1995.
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Salazar Uribe, Juan Carlos, Ehidy Karime García Cruz, Carlos Gaviria Peña e Verónica Guarín Escudero. Introducción al análisis de supervivencia avanzada. Universidad San Buenaventura, 2020. http://dx.doi.org/10.21500/9789588474939.
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Este libro presenta una introducción al análisis de supervivencia avanzada y se recomienda como material de apoyo para los cursos de posgrado que se relacionen con estadística (como prerequisito se recomienda un curso de probabilidad y de procesos estocásticos, sin embargo, el texto incluye un repaso de algunos conceptos que se necesitan para el desarrollo de su contenido y que pretenden nivelar al lector a fin de que se familiarice con algunos conceptos necesarios para comprender el análisis de datos de supervivencia). Con este material se pretende discutir y exhibir la fusión entre el análisis clásico de supervivencia y los procesos estocásticos que representa un avance muy importante en el área y hacen más flexible el manejo de los estimadores de las funciones de supervivencia y de las funciones de riesgo o hazard acumulado, a la vez que permite estudiar sus propiedades de una manera intuitiva, exhaustiva y apropiada.
Capítulos de livros sobre o assunto "Flexible Curves"
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Gdalyahu, Yoram, e Daphna Weinshall. "Flexible syntactic matching of curves". In Lecture Notes in Computer Science, 123–39. Berlin, Heidelberg: Springer Berlin Heidelberg, 1998. http://dx.doi.org/10.1007/bfb0054737.
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Melo, Fábio, Eusébio Nunes e Cristina S. Rodrigues. "Study of Hysteresis Curves for Conformity Assessment in EGR Valves". In Flexible Automation and Intelligent Manufacturing: Establishing Bridges for More Sustainable Manufacturing Systems, 1121–29. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-38165-2_128.
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Cao, Xuyang, Guoyang Xu, Yongchang Hu, Jihong Zhou e Jian Kang. "Rigid-Flexible Coupling Dynamics Analysis of Boom-Hoisting System of Wind Power Crane". In Lecture Notes in Mechanical Engineering, 3–20. Singapore: Springer Nature Singapore, 2024. http://dx.doi.org/10.1007/978-981-97-1876-4_1.
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AbstractBased on the slenderness of wind power crane boom and the complexity of working environment, a mathematical model of rigid-flexible coupling dynamics including wind load and vibration characteristic analysis is carried out for the boom-hoisting system. The equivalent spring-damping system, spatial pendulum system and elastic double-force rod are used to simulate the elastic vibration of boom, the swing of lifting weight and the elastic vibration of wire rope, respectively. The kinematic characteristics of each component are described using a hybrid coordinate system. Simulation of wind loads through an instantaneous wind model consisting of the average and pulsating wind. Derivation of dynamic model for wind power crane under wind load based on the Lagrange equation. Taking a certain type of wind power crane as the research object, based on the derived mathematical model and ADAMS model, the response curves of boom and lifting weight are solved in MATLAB and ADAMS respectively for the rotary working condition, to verify the rationality and accuracy of the mathematical model and to obtain the influence of wind load on the swing angle of lifting weight. The analysis results provide a certain theoretical basis for crane structure design, control system design and wind turbine hoisting.
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Huang, YongAn, YeWang Su e Shan Jiang. "Conformal Design on Rigid Curved Substrate". In Flexible Electronics, 137–63. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-19-6623-1_6.
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Huang, YongAn, YeWang Su e Shan Jiang. "Conformal Design on Soft Curved Substrate". In Flexible Electronics, 165–97. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-19-6623-1_7.
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Linn, Joachim, e Klaus Dreßler. "Discrete Cosserat Rod Models Based on the Difference Geometry of Framed Curves for Interactive Simulation of Flexible Cables". In Math for the Digital Factory, 289–319. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-63957-4_14.
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Sun, Xiaoqiang, Yuankang He, Bo Yuan, Yan Li, Jiawei Sun, Tao Ding, Yuhan Huang e Hongji Zhang. "A Mid-and-Long-Term Flexible Trading Method Considering Uncertainties of Renewable Energy Based on Capacity-Credit Curves". In Lecture Notes in Electrical Engineering, 196–201. Singapore: Springer Nature Singapore, 2024. http://dx.doi.org/10.1007/978-981-97-7047-2_21.
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Salehi, Mahdi, Andriette Bekker e Mohammad Arashi. "A Kernel Scale Mixture of the Skew-Normal Distribution". In Flexible Nonparametric Curve Estimation, 269–78. Cham: Springer International Publishing, 2024. http://dx.doi.org/10.1007/978-3-031-66501-1_11.
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Papathomas, Michail. "Bayesian Nonparametrics and Mixture Modelling". In Flexible Nonparametric Curve Estimation, 229–68. Cham: Springer International Publishing, 2024. http://dx.doi.org/10.1007/978-3-031-66501-1_10.
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Tapak, Leili, Omid Hamidi, Payam Amini e Hassan Doosti. "A Censored Semicontinuous Regression for Modeling Clustered/Longitudinal Zero-Inflated Rates and Proportions: An Application to Colorectal Cancer". In Flexible Nonparametric Curve Estimation, 153–74. Cham: Springer International Publishing, 2024. http://dx.doi.org/10.1007/978-3-031-66501-1_7.
Texto completo da fonteTrabalhos de conferências sobre o assunto "Flexible Curves"
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Li, Kun, Ce Yu, Shanjiang Tang, Chao Sun, Qing Zhao, Siyuan Huang e Qinlong Kang. "Flexible Light Curves Generation System for Astronomical Catalogs". In 2017 IEEE International Symposium on Parallel and Distributed Processing with Applications and 2017 IEEE International Conference on Ubiquitous Computing and Communications (ISPA/IUCC). IEEE, 2017. http://dx.doi.org/10.1109/ispa/iucc.2017.00163.
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Li, Chongyi, Chunle Guo, Shangchen Zhou, Qiming Ai, Ruicheng Feng e Chen Change Loy. "FlexiCurve: Flexible Piecewise Curves Estimation for Photo Retouching". In 2023 IEEE/CVF Conference on Computer Vision and Pattern Recognition Workshops (CVPRW). IEEE, 2023. http://dx.doi.org/10.1109/cvprw59228.2023.00116.
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Kooijman, Adrie, e Joris S. M. Vergeest. "Matching Minimum Strain Energy Curves to B-Spline Curves for Thick Layer Manufacturing". In ASME 2002 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/detc2002/dfm-34170.
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One of the key issues of thick layer manufacturing is matching the shape of the flexible cutting blade to the local surface curvature of the model to be created. In this paper we explore a method to find the best matching minimum strain energy (MSE) curve for a given B-spline curve. For this purpose we developed software to a) generate a dataset containing MSE curves for a range of settings of the cutting tool and b) find the best matching curve from this MSE dataset to the given target curve. Both the MSE and the target curves are represented as point sets, the target curves having a considerable higher point density than the curves in the MSE dataset. The best matching MSE curve is defined as the curve with the minimum directed Hausdorff distance to the target curve. It is found that despite the relative low density of the dataset, for several practical domains of target curve shape, a satisfying match can be found. Numerical results concerning the matching accuracy are presented.
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Pronk, Adriaan C. "The Huet-Sayegh Model: A Simple and Excellent Rheological Model for Master Curves of Asphaltic Mixes". In R. Lytton Symposium on Mechanics of Flexible Pavements. Reston, VA: American Society of Civil Engineers, 2005. http://dx.doi.org/10.1061/40825(185)8.
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Broek, J. J., A. Kooijman, A. de Smit e I. Horva´th. "Shaping Minimum Strain Energy Curves for FF-TLOM". In ASME 2003 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/detc2003/dfm-48165.
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Free Form Thick Layered Object Manufacturing (FF-TLOM) technology is based on foam cutting with a curved heated flexible cutting blade. Three single parameters shape the flexible blade. An infinite amount of blade shapes can be selected. However, many of these shapes are not suitable for cutting. Blade shapes with less than two inflexions can be applied successfully. When two inflexions are involved the blade; more than one different stable blade shape can be realized. For tool path creation and cutting procedures the blade shape must be known. A 2-D calculation algorithm based on (Kallay, 1987) is used. The calculation result is a minimum strain energy curve of a prescribed length, which is represented by a chain of segments. The shape is unfolded by rotating each segment under conditions of total energy decrease until no improvements are achieved. In this paper the process parameters are analyzed for sensitivity and influence on the accuracy and conditions of the blade shaping process. An overview of these parameters is given and the accuracy, computing time and trustworthiness of the implemented algorithm is checked. Typical FF-TLOM process characteristics are considered for its influence on the blade shape The elastic energy of curves is presented for a complete range of blade shapes. Regions of bi-stable blade shapes are perceived based on more than one blade inflexion. Finally a selection is presented for those minimum strain curves, which are applicable for the FF-TLOM technology.
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Sun, Guowei, Peihua Han, Yuxin Xu, Yong Bai e Hamad Hameed. "Fatigue Analysis of Metallic Strips Flexible Pipe". In ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/omae2018-77384.
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Metallic strips flexible pipe (MSFP) is widely regarded as an alternative for submarine pipelines. This paper presents a methodology for calculating the fatigue life of MSFP. Firstly, given a specific working condition of MSFP, the dynamic responses of MSFP are calculated through OrcaFlex. The obtained results from the global analysis are then implemented into a finite element model in ABAQUS to determine the stress-history curves of each steel strips layer. The estimated fatigue life is calculated by rainflow counting algorithms, S-N curve and Miner’s rule which are coded in MATLAB. Additional study about average stress correction is carried out, which might be useful for its marine engineering applications.
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Shavezipur, Mohammad, Seyed Mohammad Hashemi e Amir Khajepour. "Novel Linearly Tunable MEMS Capacitors With Flexible Moving Electrodes". In ASME 2008 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/detc2008-49272.
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In conventional MEMS parallel-plate capacitor designs, the moving electrode is commonly modeled as a rigid plate with flexible boundary conditions provided by a set of supporting beams. Such a capacitor generates limited tuning ratio up to 1.5 and its capacitance-voltage response is nonlinear. This paper presents novel designs where the moving electrodes are fixed-edge flexible plates. The plate displacement is selectively limited by a set of rigid steps, located between two electrodes, to generate a smooth and linear response and high tunability. Three different step heights are considered in the design and the linearity of the C-V curve is maximized by modifying the geometry of the plate, and changing the location and order of steps. Since the analytical solution for coupled electrostatic-structural physics in this case does not exist, ANSYS® FEM simulation is performed to obtain the C-V curves and optimize the design. Two designs with different electrode shapes, rectangular and circular, are developed. For rectangular-plate capacitors, tunabilities ranging from 120% to 140% and high linearity are achieved. Circular-plate designs, on the other hand, generate lower tunabilities and an extremely linear region in C-V curves. Design methodology introduced in this research is not limited to proposed geometries and can be extended to different topologies to obtain a combination of high tunability and linearity.
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Rodrigues, Thiago, Thiago Lacerda, Tiago Coser, Luiz Negreiros, George Campello e George Campello. "A statistical approach for experimental flexible pipes tensile armors SN curves evaluation". In Rio Pipeline Conference and Exhibition. IBP, 2023. http://dx.doi.org/10.48072/2447-2069.rpc.2023.191.
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Seah, Hock Soon, Budianto Tandianus, Yiliang Sui e Zhongke Wu. "Expressive B-spline curves: a pilot study on a flexible shape representation". In International Workshop on Advanced Imaging Technology (IWAIT 2022), editado por Shogo Muramatsu, Masayuki Nakajima, Jae-Gon Kim, Jing-Ming Guo e Qian Kemao. SPIE, 2022. http://dx.doi.org/10.1117/12.2626063.
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Steigmann, David. "Coupled Deformations of Elastic Curves and Surfaces". In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1995.
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Abstract Theories of perfectly flexible elastic curves and surfaces are frequently used to describe diverse phenomena ranging from bioelasticity and fluid capillarity to rubber elasticity and the mechanics of structural networks. It is our aim here to present a treatment of the coupled response of such continua accounting for three-dimensional interactions in the presence of finite deformations and strains. A more expansive discussion of the subject of the present paper may be found in [1].
Relatórios de organizações sobre o assunto "Flexible Curves"
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Robinson, W. Evaluation of thin flexible pavements under simulated aircraft traffic. Engineer Research and Development Center (U.S.), dezembro de 2020. http://dx.doi.org/10.21079/11681/39161.
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A full-scale airfield pavement test section was constructed and trafficked by the U.S. Army Engineer Research and Development Center (ERDC) to evaluate the performance of relatively thin airfield pavement structures. The test section consisted of 16 test items that included three asphalt pavement thicknesses and two different aggregate base courses. The test items were subjected to simulated aircraft traffic to evaluate their response and performance to realistic aircraft loads and to evaluate the effect of reductions in tire pressure on thin asphalt pavement. Rutting behavior, pavement cracking, instrumentation response, and falling weight deflectometer response were monitored at selected traffic intervals. The results of this study were used to extend existing Department of Defense pavement design and evaluation techniques to include the evaluation of airfield pavement sections that do not meet the current criteria for aggregate base quality and minimum asphalt concrete surface thickness. These performance data were used to develop new aggregate base failure design curves using existing stress-based design methodology.
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Wright, Allan, e Francisco A. Ramirez. What are the Fiscal Limits for the Developing Economies of Central America and the Caribbean? Inter-American Development Bank, maio de 2017. http://dx.doi.org/10.18235/0011799.
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This study uses simulations of state-dependent distributions of fiscal limits for 18 economies in Central America and the Caribbean to better understand governments¿ ability to service their debt, arising from endogenously determined dynamic Laffer curves. Using a small, open economy model to simulate macroeconomic fundamentals and fiscal policy interactions, the empirical findings produced results not previous available for these economies, showing varying and wider distributions of fiscal limits for the open economy model subject to terms-of-trade and flexible exchange rate shocks. This indicates that terms-of-trade and exchange rate volatility impacted the ability of national economies to service their debt. It is therefore prudent that policymakers and central bankers consider models that incorporate the use of trade and exchange rate volatility as a robust way of more accurately determining fiscal limits, which are a critical component in understanding governments' ability to service their debt.
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Yu, H. L., C. C. Hsiao, P. C. Kang, T. Kawabata e R. Young. CIE 242:2020 Photometry of Curved and Flexible OLED and LED Sources. International Commission on Illumination (CIE), dezembro de 2020. http://dx.doi.org/10.25039/tr.242.2020.
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L'Huillier, Jean-Paul, e Gregory Phelan. Can Supply Shocks Be Inflationary with a Flat Phillips Curve? Federal Reserve Bank of Cleveland, dezembro de 2023. http://dx.doi.org/10.26509/frbc-wp-202336.
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Not in standard models. With conventional pricing frictions, imposing a flat Phillips curve also imposes a price level that is rigid with respect to supply shocks. In the New Keynesian model, price markup shocks need to be several orders of magnitude bigger than other shocks in order to fit the data, leading to unreasonable assessments of the magnitude of the increase in costs during inflationary episodes. To account for the facts, we propose a strategic microfoundation of shock-dependent price stickiness: prices are sticky with respect to demand shocks but flexible with respect to supply shocks. This friction is demand-intrinsic, in line with narrative accounts for the imperfect adjustment of prices. Firms can credibly justify a price increase due to a rise in costs, whereas it is harder to do so when demand increases. Inflation from supply shocks is efficient and does not justify a monetary policy response.
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Galili, Naftali, Roger P. Rohrbach, Itzhak Shmulevich, Yoram Fuchs e Giora Zauberman. Non-Destructive Quality Sensing of High-Value Agricultural Commodities Through Response Analysis. United States Department of Agriculture, outubro de 1994. http://dx.doi.org/10.32747/1994.7570549.bard.
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The objectives of this project were to develop nondestructive methods for detection of internal properties and firmness of fruits and vegetables. One method was based on a soft piezoelectric film transducer developed in the Technion, for analysis of fruit response to low-energy excitation. The second method was a dot-matrix piezoelectric transducer of North Carolina State University, developed for contact-pressure analysis of fruit during impact. Two research teams, one in Israel and the other in North Carolina, coordinated their research effort according to the specific objectives of the project, to develop and apply the two complementary methods for quality control of agricultural commodities. In Israel: An improved firmness testing system was developed and tested with tropical fruits. The new system included an instrumented fruit-bed of three flexible piezoelectric sensors and miniature electromagnetic hammers, which served as fruit support and low-energy excitation device, respectively. Resonant frequencies were detected for determination of firmness index. Two new acoustic parameters were developed for evaluation of fruit firmness and maturity: a dumping-ratio and a centeroid of the frequency response. Experiments were performed with avocado and mango fruits. The internal damping ratio, which may indicate fruit ripeness, increased monotonically with time, while resonant frequencies and firmness indices decreased with time. Fruit samples were tested daily by destructive penetration test. A fairy high correlation was found in tropical fruits between the penetration force and the new acoustic parameters; a lower correlation was found between this parameter and the conventional firmness index. Improved table-top firmness testing units, Firmalon, with data-logging system and on-line data analysis capacity have been built. The new device was used for the full-scale experiments in the next two years, ahead of the original program and BARD timetable. Close cooperation was initiated with local industry for development of both off-line and on-line sorting and quality control of more agricultural commodities. Firmalon units were produced and operated in major packaging houses in Israel, Belgium and Washington State, on mango and avocado, apples, pears, tomatoes, melons and some other fruits, to gain field experience with the new method. The accumulated experimental data from all these activities is still analyzed, to improve firmness sorting criteria and shelf-life predicting curves for the different fruits. The test program in commercial CA storage facilities in Washington State included seven apple varieties: Fuji, Braeburn, Gala, Granny Smith, Jonagold, Red Delicious, Golden Delicious, and D'Anjou pear variety. FI master-curves could be developed for the Braeburn, Gala, Granny Smith and Jonagold apples. These fruits showed a steady ripening process during the test period. Yet, more work should be conducted to reduce scattering of the data and to determine the confidence limits of the method. Nearly constant FI in Red Delicious and the fluctuations of FI in the Fuji apples should be re-examined. Three sets of experiment were performed with Flandria tomatoes. Despite the complex structure of the tomatoes, the acoustic method could be used for firmness evaluation and to follow the ripening evolution with time. Close agreement was achieved between the auction expert evaluation and that of the nondestructive acoustic test, where firmness index of 4.0 and more indicated grade-A tomatoes. More work is performed to refine the sorting algorithm and to develop a general ripening scale for automatic grading of tomatoes for the fresh fruit market. Galia melons were tested in Israel, in simulated export conditions. It was concluded that the Firmalon is capable of detecting the ripening of melons nondestructively, and sorted out the defective fruits from the export shipment. The cooperation with local industry resulted in development of automatic on-line prototype of the acoustic sensor, that may be incorporated with the export quality control system for melons. More interesting is the development of the remote firmness sensing method for sealed CA cool-rooms, where most of the full-year fruit yield in stored for off-season consumption. Hundreds of ripening monitor systems have been installed in major fruit storage facilities, and being evaluated now by the consumers. If successful, the new method may cause a major change in long-term fruit storage technology. More uses of the acoustic test method have been considered, for monitoring fruit maturity and harvest time, testing fruit samples or each individual fruit when entering the storage facilities, packaging house and auction, and in the supermarket. This approach may result in a full line of equipment for nondestructive quality control of fruits and vegetables, from the orchard or the greenhouse, through the entire sorting, grading and storage process, up to the consumer table. The developed technology offers a tool to determine the maturity of the fruits nondestructively by monitoring their acoustic response to mechanical impulse on the tree. A special device was built and preliminary tested in mango fruit. More development is needed to develop a portable, hand operated sensing method for this purpose. In North Carolina: Analysis method based on an Auto-Regressive (AR) model was developed for detecting the first resonance of fruit from their response to mechanical impulse. The algorithm included a routine that detects the first resonant frequency from as many sensors as possible. Experiments on Red Delicious apples were performed and their firmness was determined. The AR method allowed the detection of the first resonance. The method could be fast enough to be utilized in a real time sorting machine. Yet, further study is needed to look for improvement of the search algorithm of the methods. An impact contact-pressure measurement system and Neural Network (NN) identification method were developed to investigate the relationships between surface pressure distributions on selected fruits and their respective internal textural qualities. A piezoelectric dot-matrix pressure transducer was developed for the purpose of acquiring time-sampled pressure profiles during impact. The acquired data was transferred into a personal computer and accurate visualization of animated data were presented. Preliminary test with 10 apples has been performed. Measurement were made by the contact-pressure transducer in two different positions. Complementary measurements were made on the same apples by using the Firmalon and Magness Taylor (MT) testers. Three-layer neural network was designed. 2/3 of the contact-pressure data were used as training input data and corresponding MT data as training target data. The remaining data were used as NN checking data. Six samples randomly chosen from the ten measured samples and their corresponding Firmalon values were used as the NN training and target data, respectively. The remaining four samples' data were input to the NN. The NN results consistent with the Firmness Tester values. So, if more training data would be obtained, the output should be more accurate. In addition, the Firmness Tester values do not consistent with MT firmness tester values. The NN method developed in this study appears to be a useful tool to emulate the MT Firmness test results without destroying the apple samples. To get more accurate estimation of MT firmness a much larger training data set is required. When the larger sensitive area of the pressure sensor being developed in this project becomes available, the entire contact 'shape' will provide additional information and the neural network results would be more accurate. It has been shown that the impact information can be utilized in the determination of internal quality factors of fruit. Until now,
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Bonilla, Leonardo, ed. Indicios de estabilización en el mercado laboral y una estimación de la tasa de desempleo desde el punto de vista de la firma. Banco de la República Colombia, novembro de 2022. http://dx.doi.org/10.32468/rml.24.
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Con datos a agosto de 2022, todas las fuentes de información analizadas en este reporte, tanto las encuestas de hogares y como los registros de datos administrativos, muestran que el empleo mantiene crecimientos anuales importantes. La mayoría de indicadores del mercado laboral se encuentran en niveles similares o mejores a los presentados en el periodo prepandemia. Los segmentos que más aportaron al crecimiento en el empleo son el asalariado, el dominio de otras cabeceras y rural, y los segmentos poblacionales de mujeres, trabajadores sin educación superior y los no jefes de hogar. A pesar de las mejoras anuales destacables en los indicadores laborales, las series con ajuste estacional, que permiten la comparación mes tras mes de los indicadores, muestran que en los últimos meses el empleo, las vacantes y la participación laboral tienden a estabilizarse. Este comportamiento es más pronunciado en el mercado laboral urbano. Un indicador que muestra señales claras de estabilización es la tasa global de participación (TGP), que en el nivel nacional se ha mantenido alrededor del 63 % en el último semestre. La tasa de ocupación (TO) nacional también tiende a mantenerse estable desde julio, jalonada por el dominio urbano; mientras que en el dominio rural todavía se evidencian crecimientos mensuales de la ocupación. Este comportamiento explica la estabilización de la tasa de desempleo (TD) con ajuste estacional en el área urbana alrededor del 11,7 % y el mejor desempeño de la TD en el dominio rural y otras cabeceras, que en los últimos tres meses se redujo en casi 1 punto porcentual (pp). Por el lado de los salarios, se observan aumentos en los ingresos corrientes tanto en los segmentos asalariado como no asalariado. Sin embargo, la mayor inflación se traduce en que los salarios en el segmento asalariado hayan permanecido estables en términos reales. En el segmento no asalariado, caracterizado por su naturaleza más flexible, los ingresos laborales se han ajustado y se evidencian crecimientos reales anuales y trimestrales. Tanto los indicadores de holgura como los de cuellos de botella y las curvas de Beveridge muestran un mercado laboral estrecho. Dadas las previsiones en materia de crecimiento económico del equipo técnico del Banco de la República, consignadas en el Informe de Política Monetaria de octubre de 2022, los pronósticos indican que la TD urbana se mantendrá estable y terminaría 2022 alrededor del 11,2 % como escenario central. Para 2023 se prevé que dicho indicador, en promedio, se ubicaría entre el 9,9 % y 13,5 %, con un 11,7 % como valor más probable. Por el lado del dominio nacional, la tasa terminaría el año 2022 en el 10,6 %, y para 2023, en promedio, estaría entre el 9,2 % y 12,8 %, con un 11% como valor más probable. Estas predicciones implican ligeros incrementos en la TD durante 2023, los cuales serían consistentes con las menores previsiones de crecimiento económico para ese año. Por su parte, las estimaciones de la tasa de desempleo no inflacionaria (Nairu) sugieren una brecha de desempleo urbana negativa para finales de 2022. Estas estimaciones indicarían que la mayor estrechez del mercado laboral podría estar generando presiones inflacionarias; sin embargo, la brecha se vuelve no significativa en el año 2023. Este reporte se divide en dos secciones. La primera profundiza en los hechos coyunturales del mercado laboral descritos. La segunda estudia el tema de los indicadores de holgura del mercado laboral y la relación de estos con la inflación de salarios. Los indicadores de holgura son evaluados constantemente por los formuladores de política porque dan cuenta de la existencia de presiones inflacionarias desde el mercado laboral. La TD, que es el indicador de holgura laboral por excelencia, presenta algunas limitaciones que han sido suficientemente documentadas en la literatura especializada. Medidas análogas construidas a partir de información proveniente de las firmas, en ciertos contextos especiales, podrían tener mayor poder de predicción sobre la inflación de salarios. En este Reporte Especial se construye para Colombia la tasa de desempleo desde el punto de vista de la firma (TDF). La TDF es una modelación de la variación total de la TD que solo tiene en cuenta factores exclusivos de la demanda laboral de firmas, como son la tasa de vacantes (TV) y proxies de la tasa de renuncias. La TDF resultante supera a la TD en términos de predicción de inflación de salarios. Este nuevo indicador da luces sobre las señales mixtas que los indicadores de holgura mostraron al inicio de la pandemia, donde la TD presentó crecimientos exorbitantes, mucho mayores que las reducciones de la TV y, al mismo tiempo, los salarios nominales permanecieron constantes. Los resultados muestran que, en los primeros trimestres de la pandemia, la TD mostraba un mercado laboral bastante más holgado que la TDF. En la actualidad tanto la TD como la TDF están acopladas y muestran la misma señal en términos de la holgura del mercado laboral.