Letteratura scientifica selezionata sul tema "Contraction a posteriori"
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Articoli di riviste sul tema "Contraction a posteriori"
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Bogle, Jamie M., David A. Zapala, Robin Criter e Robert Burkard. "The Effect of Muscle Contraction Level on the Cervical Vestibular Evoked Myogenic Potential (cVEMP): Usefulness of Amplitude Normalization". Journal of the American Academy of Audiology 24, n. 02 (febbraio 2013): 077–88. http://dx.doi.org/10.3766/jaaa.24.2.2.
Testo completoAbstract (sommario):
Background: The cervical vestibular evoked myogenic potential (cVEMP) is a reflexive change in sternocleidomastoid (SCM) muscle contraction activity thought to be mediated by a saccular vestibulo-collic reflex. CVEMP amplitude varies with the state of the afferent (vestibular) limb of the vestibulo-collic reflex pathway, as well as with the level of SCM muscle contraction. It follows that in order for cVEMP amplitude to reflect the status of the afferent portion of the reflex pathway, muscle contraction level must be controlled. Historically, this has been accomplished by volitionally controlling muscle contraction level either with the aid of a biofeedback method, or by an a posteriori method that normalizes cVEMP amplitude by the level of muscle contraction. A posteriori normalization methods make the implicit assumption that mathematical normalization precisely removes the influence of the efferent limb of the vestibulo-collic pathway. With the cVEMP, however, we are violating basic assumptions of signal averaging: specifically, the background noise and the response are not independent. The influence of this signal-averaging violation on our ability to normalize cVEMP amplitude using a posteriori methods is not well understood. Purpose: The aims of this investigation were to describe the effect of muscle contraction, as measured by a prestimulus electromyogenic estimate, on cVEMP amplitude and interaural amplitude asymmetry ratio, and to evaluate the benefit of using a commonly advocated a posteriori normalization method on cVEMP amplitude and asymmetry ratio variability. Research Design: Prospective, repeated-measures design using a convenience sample. Study Sample: Ten healthy adult participants between 25 and 61 yr of age. Intervention: cVEMP responses to 500 Hz tone bursts (120 dB pSPL) for three conditions describing maximum, moderate, and minimal muscle contraction. Data Collection and Analysis: Mean (standard deviation) cVEMP amplitude and asymmetry ratios were calculated for each muscle-contraction condition. Repeated measures analysis of variance and t-tests compared the variability in cVEMP amplitude between sides and conditions. Linear regression analyses compared asymmetry ratios. Polynomial regression analyses described the corrected and uncorrected cVEMP amplitude growth functions. Results: While cVEMP amplitude increased with increased muscle contraction, the relationship was not linear or even proportionate. In the majority of cases, once muscle contraction reached a certain “threshold” level, cVEMP amplitude increased rapidly and then saturated. Normalizing cVEMP amplitudes did not remove the relationship between cVEMP amplitude and muscle contraction level. As muscle contraction increased, the normalized amplitude increased, and then decreased, corresponding with the observed amplitude saturation. Abnormal asymmetry ratios (based on values reported in the literature) were noted for four instances of uncorrected amplitude asymmetry at less than maximum muscle contraction levels. Amplitude normalization did not substantially change the number of observed asymmetry ratios. Conclusions: Because cVEMP amplitude did not typically grow proportionally with muscle contraction level, amplitude normalization did not lead to stable cVEMP amplitudes or asymmetry ratios across varying muscle contraction levels. Until we better understand the relationships between muscle contraction level, surface electromyography (EMG) estimates of muscle contraction level, and cVEMP amplitude, the application of normalization methods to correct cVEMP amplitude appears unjustified.
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ZLATANOV, BOYAN. "Error estimates for approximating best proximity points for cyclic contractive maps". Carpathian Journal of Mathematics 32, n. 2 (2016): 265–70. http://dx.doi.org/10.37193/cjm.2016.02.15.
Testo completoAbstract (sommario):
We find a priori and a posteriori error estimates of the best proximity point for the Picard iteration associated to a cyclic contraction map, which is defined on a uniformly convex Banach space with modulus of convexity of power type.
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Beirão da Veiga, L., C. Canuto, R. H. Nochetto, G. Vacca e M. Verani. "Adaptive VEM: Stabilization-Free A Posteriori Error Analysis and Contraction Property". SIAM Journal on Numerical Analysis 61, n. 2 (10 marzo 2023): 457–94. http://dx.doi.org/10.1137/21m1458740.
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Canuto, Claudio, e Davide Fassino. "Higher-order adaptive virtual element methods with contraction properties". Mathematics in Engineering 5, n. 6 (2023): 1–33. http://dx.doi.org/10.3934/mine.2023101.
Testo completoAbstract (sommario):
<abstract><p>The realization of a standard Adaptive Finite Element Method (AFEM) preserves the mesh conformity by performing a completion step in the refinement loop: In addition to elements marked for refinement due to their contribution to the global error estimator, other elements are refined. In the new perspective opened by the introduction of Virtual Element Methods (VEM), elements with hanging nodes can be viewed as polygons with aligned edges, carrying virtual functions together with standard polynomial functions. The potential advantage is that all activated degrees of freedom are motivated by error reduction, not just by geometric reasons. This point of view is at the basis of the paper [L. Beirão da Veiga et al., "Adaptive VEM: stabilization-free a posteriori error analysis and contraction property", SIAM Journal on Numerical Analysis, vol. 61, 2023], devoted to the convergence analysis of an adaptive VEM generated by the successive newest-vertex bisections of triangular elements without applying completion, in the lowest-order case (polynomial degree $ k = 1 $). The purpose of this paper is to extend these results to the case of VEMs of order $ k\ge2 $ built on triangular meshes. The problem at hand is a variable-coefficient, second-order self-adjoint elliptic equation with Dirichlet boundary conditions; the data of the problem are assumed to be piecewise polynomials of degree $ k-1 $. By extending the concept of global index of a hanging node, under an admissibility assumption of the mesh, we derive a stabilization-free a posteriori error estimator. This is the sum of residual-type terms and certain virtual inconsistency terms (which vanish for $ k = 1 $). We define an adaptive VEM of order $ k $ based on this estimator, and we prove its convergence by establishing a contraction result for a linear combination of (squared) energy norm of the error, (squared) residual estimator, and (squared) virtual inconsistency estimator.</p></abstract>
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Bokhove, O., A. Kalogirou e W. Zweers. "From Bore–Soliton–Splash to a New Wave-to-Wire Wave-Energy Model". Water Waves 1, n. 2 (novembre 2019): 217–58. http://dx.doi.org/10.1007/s42286-019-00022-9.
Testo completoAbstract (sommario):
AbstractWe explore extreme nonlinear water-wave amplification in a contraction or, analogously, wave amplification in crossing seas. The latter case can lead to extreme or rogue-wave formation at sea. First, amplification of a solitary-water-wave compound running into a contraction is disseminated experimentally in a wave tank. Maximum amplification in our bore–soliton–splash observed is circa tenfold. Subsequently, we summarise some nonlinear and numerical modelling approaches, validated for amplifying, contracting waves. These amplification phenomena observed have led us to develop a novel wave-energy device with wave amplification in a contraction used to enhance wave-activated buoy motion and magnetically induced energy generation. An experimental proof-of-principle shows that our wave-energy device works. Most importantly, we develop a novel wave-to-wire mathematical model of the combined wave hydrodynamics, wave-activated buoy motion and electric power generation by magnetic induction, from first principles, satisfying one grand variational principle in its conservative limit. Wave and buoy dynamics are coupled via a Lagrange multiplier, which boundary value at the waterline is in a subtle way solved explicitly by imposing incompressibility in a weak sense. Dissipative features, such as electrical wire resistance and nonlinear LED loads, are added a posteriori. New is also the intricate and compatible finite-element space–time discretisation of the linearised dynamics, guaranteeing numerical stability and the correct energy transfer between the three subsystems. Preliminary simulations of our simplified and linearised wave-energy model are encouraging and involve a first study of the resonant behaviour and parameter dependence of the device.
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Waldrop, T. G., e R. W. Stremel. "Muscular contraction stimulates posterior hypothalamic neurons". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 256, n. 2 (1 febbraio 1989): R348—R356. http://dx.doi.org/10.1152/ajpregu.1989.256.2.r348.
Testo completoAbstract (sommario):
Recent studies have suggested that the subthalamic locomotor region (STLR) of the posterior hypothalamus is involved in modulating cardiorespiratory responses to feedback from contracting muscles. The purpose of this study was to determine whether neurons in this hypothalamic region alter their discharge frequency during contraction of hindlimb muscles. Stainless steel electrodes were used to record single-unit activity of STLR neurons during static and rhythmic contractions of hindlimb muscles in anesthetized cats. Recordings were also made from neurons in areas outside but surrounding the subthalamic locomotor region. Contraction of the triceps surae muscles was induced by stimulation of the peripheral cut ends of the L7 and S1 ventral roots. Both static and rhythmic contractions of the triceps surae evoked an increase in the discharge rate of the majority of the STLR cells studied. Two types of excitatory responses were observed: 1) abrupt increases in discharge frequency at the onset of muscular contraction and 2) a delayed more gradual increase in firing. Most of the cells that responded to muscular contraction could be activated by mechanical probing of the triceps surae muscles. However, the changes in discharge frequency were unrelated to changes in arterial pressure occurring during muscular contraction. Most of the neurons located outside the STLR were slightly inhibited by or did not respond to muscular contraction. Thus input from contracting muscles exerts predominantly an excitatory effect on neurons in the posterior hypothalamus. These results are consistent with other studies which have concluded that this hypothalamic site is involved in influencing the cardiorespiratory responses to muscular contraction.
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Zlatanov, Boyan. "On a generalization of tripled fixed or best proximity points for a class of cyclic contractive maps". Filomat 35, n. 9 (2021): 3015–31. http://dx.doi.org/10.2298/fil2109015z.
Testo completoAbstract (sommario):
We enrich the known results about tripled fixed points and tripled best proximity points. We generalize the notion of ordered pairs of cyclic contraction maps and we obtain sufficient conditions for the existence and uniqueness of fixed (or best proximity) points. We get a priori and a posteriori error estimates for the tripled fixed points and for the tripled best proximity points, provided that the underlying Banach space has modulus of convexity of power type in the case of best proximity points, obtained by sequences of successive iterations. We illustrate the main result with an example.
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Khoromskij, Boris, e Sergey Repin. "Rank Structured Approximation Method for Quasi-Periodic Elliptic Problems". Computational Methods in Applied Mathematics 17, n. 3 (1 luglio 2017): 457–77. http://dx.doi.org/10.1515/cmam-2017-0014.
Testo completoAbstract (sommario):
AbstractWe consider an iteration method for solving an elliptic type boundary value problem {\mathcal{A}u=f}, where a positive definite operator {\mathcal{A}} is generated by a quasi-periodic structure with rapidly changing coefficients (a typical period is characterized by a small parameter ϵ). The method is based on using a simpler operator {\mathcal{A}_{0}} (inversion of {\mathcal{A}_{0}} is much simpler than inversion of {\mathcal{A}}), which can be viewed as a preconditioner for {\mathcal{A}}. We prove contraction of the iteration method and establish explicit estimates of the contraction factor q. Certainly the value of q depends on the difference between {\mathcal{A}} and {\mathcal{A}_{0}}. For typical quasi-periodic structures, we establish simple relations that suggest an optimal {\mathcal{A}_{0}} (in a selected set of “simple” structures) and compute the corresponding contraction factor. Further, this allows us to deduce fully computable two-sided a posteriori estimates able to control numerical solutions on any iteration. The method is especially efficient if the coefficients of {\mathcal{A}} admit low-rank representations and if algebraic operations are performed in tensor structured formats. Under moderate assumptions the storage and solution complexity of our approach depends only weakly (merely linear-logarithmically) on the frequency parameter \frac{1}{\epsilon}.
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CASCON, J. MANUEL, RICARDO H. NOCHETTO e KUNIBERT G. SIEBERT. "DESIGN AND CONVERGENCE OF AFEM IN H(DIV)". Mathematical Models and Methods in Applied Sciences 17, n. 11 (novembre 2007): 1849–81. http://dx.doi.org/10.1142/s0218202507002492.
Testo completoAbstract (sommario):
We design an adaptive finite element method (AFEM) for mixed boundary value problems associated with the differential operator A-∇div in H(div, Ω). For A being a variable coefficient matrix with possible jump discontinuities, we provide a complete a posteriori error analysis which applies to both Raviart–Thomas ℝ𝕋n and Brezzi–Douglas–Marini 𝔹𝔻𝕄n elements of any order n in dimensions d = 2, 3. We prove a strict reduction of the total error between consecutive iterates, namely a contraction property for the sum of energy error and oscillation, the latter being solution-dependent. We present numerical experiments for ℝ𝕋n with n = 0, 1 and 𝔹𝔻𝕄1 which document the performance of AFEM and corroborate as well as extend the theory.
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Haberl, Alexander, Dirk Praetorius, Stefan Schimanko e Martin Vohralík. "Convergence and quasi-optimal cost of adaptive algorithms for nonlinear operators including iterative linearization and algebraic solver". Numerische Mathematik 147, n. 3 (5 febbraio 2021): 679–725. http://dx.doi.org/10.1007/s00211-021-01176-w.
Testo completoAbstract (sommario):
AbstractWe consider a second-order elliptic boundary value problem with strongly monotone and Lipschitz-continuous nonlinearity. We design and study its adaptive numerical approximation interconnecting a finite element discretization, the Banach–Picard linearization, and a contractive linear algebraic solver. In particular, we identify stopping criteria for the algebraic solver that on the one hand do not request an overly tight tolerance but on the other hand are sufficient for the inexact (perturbed) Banach–Picard linearization to remain contractive. Similarly, we identify suitable stopping criteria for the Banach–Picard iteration that leave an amount of linearization error that is not harmful for the residual a posteriori error estimate to steer reliably the adaptive mesh-refinement. For the resulting algorithm, we prove a contraction of the (doubly) inexact iterates after some amount of steps of mesh-refinement/linearization/algebraic solver, leading to its linear convergence. Moreover, for usual mesh-refinement rules, we also prove that the overall error decays at the optimal rate with respect to the number of elements (degrees of freedom) added with respect to the initial mesh. Finally, we prove that our fully adaptive algorithm drives the overall error down with the same optimal rate also with respect to the overall algorithmic cost expressed as the cumulated sum of the number of mesh elements over all mesh-refinement, linearization, and algebraic solver steps. Numerical experiments support these theoretical findings and illustrate the optimal overall algorithmic cost of the fully adaptive algorithm on several test cases.
Tesi sul tema "Contraction a posteriori"
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Naveau, Marion. "Procédures de sélection de variables en grande dimension dans les modèles non-linéaires à effets mixtes. Application en amélioration des plantes". Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASM031.
Testo completoAbstract (sommario):
Les modèles à effets mixtes analysent des observations collectées de façon répétée sur plusieurs individus, attribuant la variabilité à différentes sources (intra-individuelle, inter-individuelle, résiduelle). Prendre en compte cette variabilité est essentiel pour caractériser sans biais les mécanismes biologiques sous-jacents. Ces modèles utilisent des covariables et des effets aléatoires pour décrire la variabilité entre individus : les covariables décrivent les différences dues à des caractéristiques observées, tandis que les effets aléatoires représentent la variabilité non attribuable aux covariables mesurées. Dans un contexte de grande dimension, où le nombre de covariables dépasse celui des individus, identifier les covariables influentes est difficile, car la sélection porte sur des variables latentes du modèle. De nombreuses procédures ont été mises au point pour les modèles linéaires à effets mixtes, mais les contributions pour les modèles non-linéaires sont rares et manquent de fondements théoriques. Cette thèse vise à développer une procédure de sélection de covariables en grande dimension pour les modèles non-linéaires à effets mixtes, en étudiant leurs implémentations pratiques et leurs propriétés théoriques. Cette procédure est basée sur l'utilisation d'un prior spike-and-slab gaussien et de l'algorithme SAEM (Stochastic Approximation of Expectation Maximisation Algorithm). Des taux de contraction a posteriori autour des vraies valeurs des paramètres dans un modèle non-linéaire à effets mixtes sous prior spike-and-slab discret ont été obtenus, comparables à ceux observés dans des modèles linéaires. Les travaux conduits dans cette thèse sont motivés par des questions appliquées en amélioration des plantes, où ces modèles décrivent le développement des plantes en fonction de leurs génotypes et des conditions environnementales. Les covariables considérées sont généralement nombreuses puisque les variétés sont caractérisées par des milliers de marqueurs génétiques, dont la plupart n'ont aucun effet sur certains traits phénotypiques. La méthode statistique développée dans la thèse est appliquée à un jeu de données réel relatif à cette applicationMixed-effects models analyze observations collected repeatedly from several individuals, attributing variability to different sources (intra-individual, inter-individual, residual). Accounting for this variability is essential to characterize the underlying biological mechanisms without biais. These models use covariates and random effects to describe variability among individuals: covariates explain differences due to observed characteristics, while random effects represent the variability not attributable to measured covariates. In high-dimensional context, where the number of covariates exceeds the number of individuals, identifying influential covariates is challenging, as selection focuses on latent variables in the model. Many procedures have been developed for linear mixed-effects models, but contributions for non-linear models are rare and lack theoretical foundations. This thesis aims to develop a high-dimensional covariate selection procedure for non-linear mixed-effects models by studying their practical implementations and theoretical properties. This procedure is based on the use of a gaussian spike-and-slab prior and the SAEM algorithm (Stochastic Approximation of Expectation Maximisation Algorithm). Posterior contraction rates around true parameter values in a non-linear mixed-effects model under a discrete spike-and-slab prior have been obtained, comparable to those observed in linear models. The work in this thesis is motivated by practical questions in plant breeding, where these models describe plant development as a function of their genotypes and environmental conditions. The considered covariates are generally numerous since varieties are characterized by thousands of genetic markers, most of which have no effect on certain phenotypic traits. The statistical method developed in the thesis is applied to a real dataset related to this application
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THOMAS, VINEET SUNNY. "A Multiscale Framework to Analyze Tricuspid Valve Biomechanics". University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1542255754172363.
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Schneider, Laura Fee. "Discrete Parameter Estimation for Rare Events: From Binomial to Extreme Value Distributions". Thesis, 2019. http://hdl.handle.net/21.11130/00-1735-0000-0003-C131-B.
Testo completoLibri sul tema "Contraction a posteriori"
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The reliability of an isokinetic measurement protocol for the posterior rotator cuff musculature. 1990.
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Montgomery, Erwin B. Approach to DBS in the Vicinity of the Globus Pallidus Interna. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780190259600.003.0012.
Testo completoAbstract (sommario):
The regional anatomy around the DBS lead in the globus pallidus interna (GPi) determines efficacy and adverse effects. Understanding the regional anatomy allows the programmer to adjust the stimulation to provide optimal benefit and the absence of adverse effects. Just ventral to the sensorimotor region of the GPi is the optic tract. Spread of stimulation to the optic tract can produce phosphenes (the experience of seeing light without light actually entering the eye). The internal capsule lies just posterior to the globus pallidus, and stimulation there can cause tonic muscle contractions. Anteriorly lies the non-motor region, and stimulation of this region could cause changes in cognition and personality, although the incidences of these problems is much less that with STN DBS. This chapter discusses the regional anatomy of the GPi segment, adverse effects from malpositioning of DBS leads, approaches to GPi DBS for Parkinson’s, treating dystonia with DBS of the GPi, and treating hyperkinetic disorders.
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Montgomery, Erwin B. Approach to DBS in the Vicinity of the Ventral Intermediate Nucleus of the Thalamus DBS. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780190259600.003.0013.
Testo completoAbstract (sommario):
The regional anatomy around the DBS lead in the ventral intermediate nucleus of the thalamus (Vim) determines efficacy and adverse effects. Understanding the regional anatomy allows the programmer to adjust the stimulation to provide optimal benefit and the absence of adverse effects. Vim is the target of therapeutic DBS. The ventrocaudal nucleus of the thalamus (Vc) lies posterior to the Vim. Electrical stimulation of Vc can cause treatment-limiting paresthesias. The corticospinal and cortical bulbar tracts in the internal capsule lie lateral and ventral to the Vim. Electrical stimulation of the internal capsule can cause tonic muscle contractions. There are multiple nomenclatures of the subnuclei of the thalamus. Although the term ventrolateral thalamus (VL) is commonly used in the physiology literature, ventral intermediate thalamus (Vim), is used in the DBS literature. Technically, the VL refers to both regions of the thalamus that receive inputs from GPi and cerebellum, whereas Vim refers to the cerebellar-receiving area of the thalamus and is thus a subdivision of the VL and is the target of DBS for tremor-related disorders.
Capitoli di libri sul tema "Contraction a posteriori"
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Spandau, Ulrich, e Sang Jin Kim. "Posterior Hyaloid Contraction Syndrome". In Pediatric Retinal Vascular Diseases, 175–76. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-13701-4_23.
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Hayashi, Ken. "Effect of Posterior Capsule Opacification and Anterior Capsule Contraction on Visual Function". In Lens Epithelium and Posterior Capsular Opacification, 221–33. Tokyo: Springer Japan, 2014. http://dx.doi.org/10.1007/978-4-431-54300-8_13.
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Agapiou, Sergios, e Peter Mathé. "Posterior Contraction in Bayesian Inverse Problems Under Gaussian Priors". In Trends in Mathematics, 1–29. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-70824-9_1.
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Karavitaki, Niki, Shahzada K. Ahmed e John A. H. Wass. "Disorders of the posterior pituitary gland". In Oxford Textbook of Medicine, a cura di Mark Gurnell, 2277–83. Oxford University Press, 2020. http://dx.doi.org/10.1093/med/9780198746690.003.0245.
Testo completoAbstract (sommario):
The posterior pituitary produces arginine vasopressin, which has a key role in fluid homeostasis, and oxytocin, which stimulates uterine contraction during birth and ejection of milk during lactation. Cranial diabetes insipidus is the passage of large volumes of dilute urine due to vasopressin deficient synthesis and/or release. The most common cause is lesions of the neurohypophysis or the hypothalamic median eminence damaging the magnocellular neurons. MRI of the neurohypophysis is required to delineate the cause. Mild polyuria can be managed simply by ensuring adequate fluid intake; treatment with the long-acting vasopressin analogue, desmopressin is used for more severe cases. The syndrome of inappropriate antidiuresis is diagnosed when there is hyponatraemia with hypotonic plasma, inappropriate urine osmolality, and urinary sodium more than 20 mmol/litre, together with no evidence of volume overload or hypovolaemia, and normal renal, adrenal, and thyroid function.
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Pal, Aparna, Niki Karavitaki e John A. H. Wass. "Disorders of the posterior pituitary gland". In Oxford Textbook of Medicine, 1819–25. Oxford University Press, 2010. http://dx.doi.org/10.1093/med/9780199204854.003.1303.
Testo completoAbstract (sommario):
The posterior pituitary produces arginine vasopressin, which has a key role in fluid homeostasis, and oxytocin, which stimulates uterine contraction during birth and ejection of milk during lactation. Cranial diabetes insipidus is the passage of large volumes (>3 litres/24 h) of dilute urine (osmolality<300 mOsm/kg) due to vasopressin deficiency, and most commonly occurs as a consequence of trauma or tumour affecting the posterior pituitary. Diagnosed by a water deprivation test revealing urine osmolality less than 300 mOsml/kg with concurrent plasma osmolality more than 290 mOsml/kg after dehydration, with urine osmolality rising to more than 750 mOsml/kg after desmopressin. MRI of the neurohypophysis is required to delineate the cause. Mild polyuria can be managed simply by ensuring adequate fluid intake; treatment with the long-acting vasopressin analogue, desmopressin (desamino, D-8 arginine vasopressin; DDAVP), is used for more severe cases....
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Perry, Steven F., Markus Lambertz e Anke Schmitz. "Control of breathing in craniotes". In Respiratory Biology of Animals, 164–69. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780199238460.003.0013.
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Craniote gills are arranged sequentially along the pharynx and accordingly are ventilated from anterior to posterior by a wave of muscle contraction, beginning with the mouth. Each gill pair appears to have its own set of neurons in the brainstem that coordinate the muscle activity and stimulate the next gill pair in the sequence. This system appears to have been maintained from hagfish to teleosts. In tetrapods, on the other hand, various centres in the brainstem coordinate different phases of breathing: expiration, inspiration, and post-inspiration. The location of these centres in the brainstem is similar in amphibians and mammals. The stimulus for regulating ventilatory frequency in water-breathing species is oxygen, whereas for air-breathing species it is blood pH/PCO2—just as in invertebrates.
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Gorgas, Diane L. "Just Another Case of Gastro". In Psychiatric Emergencies, 131–38. Oxford University Press, 2022. http://dx.doi.org/10.1093/med/9780197544464.003.0019.
Testo completoAbstract (sommario):
The presentation of bulimia nervosa in the emergency department is challenging, with attempts at direct history gathering frequently foiled by a patient’s sense of secrecy surrounding the disorder. Clues for presentation include profound hypokalemia, especially associated with volume-contraction alkalosis. Physical examination findings that may be seen include dentin decay and other oral pathology such as posterior oropharyngeal trauma; Russell’s lesions on the dorsum of the hand; and associated evidence of self-injurious behavior (habitual cutting) given the association with borderline personality disorder. The patient’s body mass index (BMI) should not limit the consideration of bulimia given the spectrum (low to high) of BMI that can present with the class of binge eating disorders. Cognitive behavioral therapy with possible adjunctive pharmacologic antidepressants is most successful in the early stages of the disease. Relapse after initial treatment is common.
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Atkinson, Martin E. "The gastrointestinal system". In Anatomy for Dental Students. Oxford University Press, 2013. http://dx.doi.org/10.1093/oso/9780199234462.003.0012.
Testo completoAbstract (sommario):
The mouth and pharynx are the first parts of the digestive system; they are the principal areas of the gastrointestinal system of interest to dental students and practitioners and are fully described in Chapters 25 and 28. The anatomy of the remainder of the system is described briefly to provide a working knowledge for applications in other aspects of undergraduate dental courses such as nutrition. In essence, the digestive tract is a long convoluted tube illustrated in Figure 6.1. It extends from the mouth, via the pharynx, oesophagus, stomach, small intestine, and large intestine to the anal canal. It is formed along most of its length by longitudinal and circular layers of smooth muscle. It is lined throughout by epithelium which shows marked structural differences from region to region to match different functional requirements of secretion of digestive enzymes, absorption of nutrients, and excretion of waste products. The liver and pancreas are large organs essential to the function of the gastrointestinal system. Food is ingested through the mouth and then prepared for swallowing by being broken up and mixed with saliva by the chewing action of the teeth. Saliva has a major lubricant and minor digestive function. The food is formed into a pellet or bolus and is then swallowed by being moved back by the tongue into the pharynx. Once food is in the pharynx, swallowing becomes a reflex mechanism designed to coordinate contraction of muscles to push the food through the pharynx and oesophagus to the stomach as well as ensuring food and drink do not enter the lower respiratory tract. Swallowing is complex, involving several sets of muscles in the head and neck and is described in more detail in Section 29.1. The passage of food along the remainder of the digestive tract is achieved by regular contractions (peristalsis) of the smooth muscle layers in its walls. The oesophagus is a muscular tube about 25 cm in length. It begins in the neck as a continuation of the pharynx and lies posterior to the trachea as it enters the thorax.
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Koshi, Rachel. "The forearm and hand". In Cunningham's Manual of Practical Anatomy Vol 1 General Anatomy, Upper and Lower Limbs, a cura di Rachel Koshi, 115–50. 17a ed. Oxford University PressOxford, 2024. http://dx.doi.org/10.1093/med/9780198923343.003.0010.
Testo completoAbstract (sommario):
Abstract This chapter on the forearm and hand describes the surface landmarks, the radius, the ulna, the carpals, metacarpals, and phalanges, the flexors of the wrist, the extensors of the wrist, the palmar aponeurosis, the flexor and extensor retinacula, the muscles of the hand, the median nerve, the ulnar nerve, the radial nerve, the anterior interosseous and posterior interosseous nerves, the radial artery, and the ulnar artery. The contents common to the anterior compartment of the forearm and palm of the hand are traced into continuity. Similarly, tendons, vessels, and nerves from the back of the forearm are traced onto the dorsum of the hand. All descriptions and dissections are well illustrated. Images on surface anatomy and cross-sectional images are used to illustrate the surface projections and interrelations between structures. The anatomy of common clinical conditions, such as carpal tunnel syndrome, tenosynovitis, and Dupuytren’s contraction, are discussed.
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John Park, D. J., e Andrew Harrison. "Reconstruction of the Lower Eyelid". In Surgery of the Eyelid, Lacrimal System, and Orbit. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780195340211.003.0008.
Testo completoAbstract (sommario):
The lower eyelid, tethered medially and laterally by the canthal tendons, is normally suspended at the level of the inferior limbus with the aid of orbicularis tone counterbalanced by the force of the lower eyelid retractors and gravity. The lower eyelid is apposed to the globe because of the posterior position of the canthal tendon insertions relative to the projection of the globe. Disruption of the normal anatomic relationships from trauma or inflammatory disease or as a result of surgical resection of tumors can result in a poorly functioning lower eyelid with poor cosmesis. The lower eyelid has been conceptualized as consisting of three layers or lamellae. The anterior lamella is composed of skin and orbicularis muscle; the middle lamella is composed of the lower eyelid retractor (capsulopalpebral fascia) and fat; and the posterior lamella is composed of tarsus and conjunctiva. One or more of the lamellae may be disrupted following trauma or tumor resection, and each layer must be addressed in order to reconstruct a normal-appearing and -functioning lower eyelid. Imbalance of tension at the anterior and posterior lamellae, especially in the setting of lower eyelid laxity, can result in malrotation of the eyelid margin, causing entropion or ectropion. For example, inflammation and scarring of the conjunctiva from Stevens-Johnson syndrome or ocular cicatricial pemphigoid will produce entropion, whereas contraction of vertical cutaneous scar or ichthyosis will cause ectropion. A balance of tension of the lamellae must be maintained during reconstruction of the lower eyelid in order to prevent secondary malrotation. Disruption of normal anatomy as often seen following trauma can be addressed by reapproximation of the disrupted segments to their normal anatomic positions. Only rarely will trauma to the lower eyelid result in loss of tissue. Reconstruction with local flaps or free grafts is occasionally needed in traumatic cases that present in a delayed fashion. Local flaps and free grafts are needed to fill and reconstruct a defect in the lower eyelid, a situation that most often presents following resection of tumor.
Atti di convegni sul tema "Contraction a posteriori"
1
Yang, Hongzhi, Yi-Chun Li e Mohamed Samir Hefzy. "Isometric Co-Contractions of the Quadriceps and Hamstrings in Intact and PCL-Deficient Knees". In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0445.
Testo completoAbstract (sommario):
Abstract The exercises to strengthen the muscles around the knee are designed to improve its stability. During these exercises, co-contraction of the hamstrings occur depending on the level of quadriceps contraction. The purpose of this study is to develop a three-dimensional knee model that includes tibia, femur and patella and allows to predict knee response due to quadriceps and hamstrings co-contractions. As an application, results quantifying the changes in knee response are obtained following a simulated posterior cruciate ligament (PCL) injury. This is motivated by the continuing debate whether surgical repair is the method of choice for individuals with such an injury. It has been reported that following a knee injury, a large number of patients with PCL deficiency develop significant disability with Osteoarthritis (OA). The conditions tested simulate the straight-leg-raise exercise, during which the quadriceps muscles contract isometrically along with hamstrings co-contractions.
2
Shelburne, Kevin B., e Marcus G. Pandy. "Ligament Forces During Isometric Contractions in the Intact and ACL-Deficient Knee". In ASME 1996 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1996. http://dx.doi.org/10.1115/imece1996-0425.
Testo completoAbstract (sommario):
Abstract A model of the knee in the sagittal plane was used to study the forces induced in the ligaments during maximum contractions of the quadriceps muscles. The geometry of the distal femur was obtained from cadaver data. The tibial plateau and patellar facet were modeled as flat surfaces. Eleven elastic elements were used to describe the mechanical behavior of the anterior and posterior cruciate ligaments (ACL and PCL), the medial and lateral collateral ligaments (MCL and LCL), and the posterior capsule. The model knee was actuated by eleven musculotendinous units, each unit represented as a three-element muscle in series with tendon. During maximum isometric extension in the intact knee, the model ACL is loaded from full extension to 80° of flexion; the model PCL is loaded at 70° of flexion and greater. The overall pattern of cruciate-ligament loading is explained by the interaction between the forces developed by the muscles and the shapes of the articulating surfaces at the knee. ACL forces in the range 0–20° of flexion depend most heavily upon the force-length properties of the quadriceps. As the knee flexes beyond 20°, however, cruciate ligament forces are determined by the geometry of the joint. Removing the ACL in the model leads to a substantial increase in anterior tibial translation relative to that found in the intact knee. Increased tibial translation generally manifests itself as an increase in the forces borne by the medial structures of the knee, and specifically by the posterior portion of the deep fibers of the MCL.
3
Andriacchi, Thomas P., M. Kent Toney, Chris Dyrby e Arthur Conley. "The Influence of Muscle Contraction on the Kinematics of the Knee Joint". In ASME 1996 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1996. http://dx.doi.org/10.1115/imece1996-1326.
Testo completoAbstract (sommario):
Abstract There is a paucity of information on the interaction between muscle contraction and the kinematics of the knee. In particular, the anterior-posterior (AP) movement of the femur on the tibia has been described primarily from passive testing (2). The dynamic action of the extensor and flexor muscle groups at the knee can have a substantial influence on the AP movement of the femur on the tibia. This dynamic information is important for understanding a number of issues related to ligament reconstruction as well as the designs of total knee replacement. However, most knowledge of six degree of freedom knee kinematics is based on passive testing.
4
Yu, Xianwen, Xiaoning Zhang, Yang Cao e Min Xia. "VAEGAN: A Collaborative Filtering Framework based on Adversarial Variational Autoencoders". In Twenty-Eighth International Joint Conference on Artificial Intelligence {IJCAI-19}. California: International Joint Conferences on Artificial Intelligence Organization, 2019. http://dx.doi.org/10.24963/ijcai.2019/584.
Testo completoAbstract (sommario):
Recently, Variational Autoencoders (VAEs) have been successfully applied to collaborative filtering for implicit feedback. However, the performance of the resulting model depends a lot on the expressiveness of the inference model and the latent representation is often too constrained to be expressive enough to capture the true posterior distribution. In this paper, a novel framework named VAEGAN is proposed to address the above issue. In VAEGAN, we first introduce Adversarial Variational Bayes (AVB) to train Variational Autoencoders with arbitrarily expressive inference model. By utilizing Generative Adversarial Networks (GANs) for implicit variational inference, the inference model provides better approximation to the posterior and maximum-likelihood assignment. Then the performance of our model is further improved by introducing an auxiliary discriminative network using adversarial training to achieve high accuracy in recommendation. Furthermore, contractive loss is added to the classical reconstruction cost function as a penalty term to yield robust features and improve the generalization performance. Finally, we show that the performance of our proposed VAEGAN significantly outperforms state-of-the-art baselines on several real-world datasets.
5
Bellet Sanfeliu, Carme. "Nuevas tecnologias de transporte y metropolitanización discontiua del territorio: el tren de alta velocidad en Segovia". In International Conference Virtual City and Territory. Barcelona: Centre de Política de Sòl i Valoracions, 2009. http://dx.doi.org/10.5821/ctv.7521.
Testo completoAbstract (sommario):
El tren de alta velocidad (TAV) nació con la vocación de establecer relaciones entre grandes núcleos urbanos distantes entre sí, pero su posterior implantación, las características de los servicios y el uso de la infraestructura han originado nuevas vocaciones. Así hoy el TAV desarrolla otras nuevas funciones territoriales: la articulación de ciudades medias y grandes en una región (función regional) y la articulación de entornos metropolitanos discontinuos en el entorno de una hora de la metrópoli central que acaban vinculándose a ésta (función metropolitana).
La función metropolitana, cuya articulación se produce gracias a la contracción del espacio en el tiempo, puede leerse fácilmente a través de los servicios y las dinámicas de los viajeros pendulares que se dan entre Toledo, Ciudad Real, Segovia-Guiomar con Madrid. Estas ciudades se articulan a la gran metrópoli central en menos de una hora (en la estación de Atocha para las primeras y la estación de Chamartín para la tercera). Por posición y tiempo, la estación de Guadalajara-Yebes podría bien entrar en éste análisis; sin embargo la relación ferroviaria de ésta con Madrid se establece a través de los servicios del ferrocarril convencional que se prestan desde la estación central de Guadalajara y que están ya de hecho integrados a la red de cercanías de Madrid.
En el texto se analizan a través del caso de estudio de Segovia como va configurándose esta nueva realidad territorial, la metrópoli discontinua, a través del proceso de contracción espacio-temporal en que ha incidido la alta velocidad permitiendo los desplazamientos, en muchos casos pendulares, entre ciudades muy distantes. The high speed train (HST) was initially developed with the aim of establishing more contacts between relatively distant, large urban nuclei, but its introduction, the characteristics of the services established, and its use of infrastructure have given rise to new vocations. Today, the HST performs a number of new territorial functions: structuring large and medium-sized cities within a given region (regional function) and structuring discontinuous metropolitan environments located within approximately one hour of the central city with which they have recently become better connected (metropolitan function).
This metropolitan function, which is structured by the very sharp time-space contraction occasioned by the HST, is easily appreciated in the dynamics of the passenger shuttle services that run between the cities of Toledo, Ciudad Real, Segovia-Guiomar and Madrid. These cities are now connected to the central metropolis in less than one hour (to Atocha station in the first two cases and to Chamartín in the third). Based on time and location, the station of Guadalajara-Yebes could also be included in this analysis; but the railway connection between this city and Madrid is based on conventional rail services connecting the central station of Guadalajara with Madrid but already forming part of Madrid’s local rail service network.
In the text, we use the case study of Segovia to analyse how the new territorial reality of the discontinuous metropolis has gradually developed as a result of the process of space-time contraction caused by high speed services and which – in many cases - has allowed commuting between very distant cities.