XII Trobada d'Estudiants de Geografia i Joves Geògrafs (Valladolid, 1989)

La douzitme rencontre d'Étudiants en Géographie et de Jeunes Géographes s'est tenue a I'Université de Valladolid du 27 au 30 mars 1989 et a rassemblé 240 étudiants. Les 25 communications présentees ont touché 21 trois grands thèmes: «Inégalités et sousdéveloppement», «Theorie, méthodologie et perspectives en géographie» et «Géographie du loisir». Certaines communications ont été présentées dans une scéance «thème libre» et ont porté sur la géographie féministe, les questions d'urbanisme, la cartographie et sur l'utilisation du matériel littéraire dans les étude géographiques.Two hundred and forty students attended the XIIth Meeting of Geography Students and Young Geographers, which was held at the University of Valladolid between 27th and 30th March 1989. Twenty-five papers covering three major topics were presented. The topics were: «Ineguality and underdevelopment», «Theory, Methodology, and Perspectives in Geographyn» and «The Geography of Leisure». Some additional papers were presented in a «free topic» session on the following subjects: gender geography, urban planning questions, cartography and the application of literature to geographical studies.El XII Encuentro de Estudiantes de Geografia y Jóvenes Geógrafos se celebro en la Universidad de Valladolid del 27 al 30 de marzo de 1989 con una asistencia de 240 estudiantes. Se presentaron 25 comunicaciones, que se agruparon en tres grandes temas: «Desigualdades y Subdesarrollo», «Teoria, metodologia y perspectivas de la geografia» y «Geografia del Ocio». Algunas comunicaciones se presentaron en una sesión de «tema libre» y las temáticas tratadas fueron la geografia del género, cuestiones de urbanismo, cartografia y la utilización de material literario para los estudios geográficos.La XII Trobada d'Estudiants de Geografia i joves Geografs es va celebrar a la Universitat de Valladolid del 27 al 30 de marG de 1989, amb una assistència de 240 estudiants. Es van presentar 25 comunicacions, que es van agrupar en tres grans temes: «Desigualtats i Subdesenvolupament», «Teoria, metodologia i perspectives de la geografia» i «Geografia de l'Oci». Algunes comunicacions es van presentar en una sessió de demà lliuren i les temàtiques que es van tractar van ser la geografia del gbnere, qüestions d'urbanisme, cartografia i la utilització del material literari per als estudis geografies

L'evolució de la vegetació a la Vall de Castellbó (Alt Urgell) de 1960 a 1988

Le processus acceleré de bouleversements économiques et sociaux au cours des dernieres décennies dans les pyrenées catalanes se traduit par des phénomenes tels que l'abandon agricole, la progression de la foret, l'utilisation du sol de maniere de plus en plus extensive ... etc. Les répercussions de ces transformations sur le paysage végetal ont été analysées et estimbes a échelle réduite sur la vallée de Castellbo (Alt Urgell). L'action anthropique et intensité de l'exode rural ont été des facteurs essentiels de transformations de la physionomie du territoire.The accelerated process of economic and social change in the upper Catalan Pyrennees in recent decades is directly reflected on the landscape in phenomena such as the abandon of agricultura] land, the recovery of woodland, more extensive land use practices, etc. In a smaller sample area, Castellbo Valley (Alt Urgell region), the repercussions of these transformations on vegetation have been analysed and evaluated. The rapidity of anthropic activity and severe rural exodus have constituted fundamental factors in the transformation of the appearance of the area. Through a comparative study of various statistical cross-sections obtained for the 1957-1988 period, it was possible to identify the tone dynamics of evolution and the perspectives for evolution in future years. This study is intended to serve as a reflection of the problems which affect the Pyrennees in general.El acelerado proceso de cambios económicos y sociales que se han dado en el alto Pirineo catalán en las ultimas décadas se refleja directamente sobre el territorio en fenómenos como el abandono agrícola, la progresión de los bosques, la extensificación de los usos, etc. En un ámbito geográfico mas reducido, en el valle de Castellbo (Alt Urgell) se ha analizado y valorado la repercusión de estas transformaciones sobre el paisaje vegetal. La importancia de la acción antrópica y el intenso fenómeno de éxodo rural han sido factores fundamentales de las transformaciones en la fisonomia de aquel territorio. Mediante un estudio comparativo de distintas informaciones estáticas obtenidas para el período que va de 1957 a 1988, mostramos cuál ha sido la verdadera dinámica evolutiva y cuáles son las perspectivas de esta en los próximos años, con la intención de que este estudio refleje la problemática general de todo el ámbito pirenaica.L'accelerat procés de canvis econbmics i socials que ha patit la muntanya pirenaica en els darrers decennis es reflexa directament sobre el territori en fenómens com l'abandonament agrícola, la progressió dels boscos, l'extensificació dels usos, etcétera. En un ambit geografic més reduit, a la vall de Castellbb (Alt Urgell) hem analitzat i valorat la repercussió d'aquestes transformacions sobre el paisatge vegetal. La importancia de l'acció antròpica i l'intens procès d'bode rural han esdevingut factors fonamentals de les transformacions en la fisonomiad'aquell territori. Mitjançant un estudi comparatiu de diverses informacions estàtiques obtingudes per al període que va del 1957 al 1988, mostrem quina ha estat la veritable dinamica evolutiva i quines són les perspectives d'aquesta en anys veniders, amb l'intenció de que aquest estudi reflexi la problemàtica general de tot l'àmbit pirinenc

Simultaneous bifurcation of limit cycles from two nests of periodic orbits

AbstractLet z˙=f(z) be an holomorphic differential equation having a center at p, and consider the following perturbation z˙=f(z)+εR(z,z¯). We give an integral expression, similar to an Abelian integral, whose zeroes control the limit cycles that bifurcate from the periodic orbits of the period annulus of p. This expression is given in terms of the linearizing map of z˙=f(z) at p. The result is applied to control the simultaneous bifurcation of limit cycles from the two period annuli of z˙=iz+z2, after a polynomial perturbation

Mecanismes adrenérgics en el control de l'evacuació de l'humor aquòs

Tesi de Llicenciatura per a la obtenció del Grau de Farmàcia. Facultat de Farmàcia. Universitat de Barcelona. Director: Arcadi Gual Sala. 1995

Modulation of TRESK background K+ channel by membrane stretch

The two-pore domain K+ channel TRESK is expressed in dorsal root ganglion and trigeminal sensory neurons where it is a major contributor to background K+ current. TRESK acts as a break to prevent excessive sensory neuron activation and decreases in its expression or function have been involved in neuronal hyperexcitability after injury/inflammation, migraine or altered sensory perception (tingling, cooling and pungent burning sensations). All these effects have implicated this channel in nociception and mechanotransduction. To determine the role of TRESK in sensory transduction, we studied its sensitivity to changes in membrane tension (stretch) in heterologous systems, F-11 cells and trigeminal neurons. Laminar shear stress increased TRESK currents by 22-30%. An increase in membrane tension induced by cell swelling (hypotonic medium) produced a reversible elevation of TRESK currents (39.9%). In contrast, cell shrinkage (hypertonic solution) produced the opposite effect. Membrane crenators or cup-formers produced equivalent effects. In trigeminal sensory neurons, TRESK channels were mechanically stimulated by negative pressure, which led to a 1.51-fold increase in channel open probability. TRESK-like currents in trigeminal neurons were additively inhibited by arachidonic acid, acidic pH and hypertonic stimulation, conditions usually found after tissue inflammation. Our results show that TRESK is modulated by changes in cell membrane tension and/or cell volume. Several key players released during inflammation or tissue injury could modulate sensory neuron activation through small changes in membrane tension

Periodic solutions with nonconstant sign in Abel equations of the second kind

The study of periodic solutions with constant sign in the Abel equation of the second kind can be made through the equation of the first kind. This is because the situation is equivalent under the transformation $x\mapsto x^{-1}$, and there are many results available in the literature for the first kind equation. However, the equivalence breaks down when one seeks for solutions with nonconstant sign. This note is devoted to periodic solutions with nonconstant sign in Abel equations of the second kind. Specifically, we obtain sufficient conditions to ensure the existence of a periodic solution that shares the zeros of the leading coefficient of the Abel equation. Uniqueness and stability features of such solutions are also studied.Comment: 10 page

Proton Sensing on the Ocular Surface: Implications in Eye Pain

Protons reaching the eyeball from exogenous acidic substances or released from damaged cells during inflammation, immune cells, after tissue injury or during chronic ophthalmic conditions, activate or modulate ion channels present in sensory nerve fibers that innervate the ocular anterior surface. Their identification as well as their role during disease is critical for the understanding of sensory ocular pathophysiology. They are likely to mediate some of the discomfort sensations accompanying several ophthalmic formulations and may represent novel targets for the development of new therapeutics for ocular pathologies. Among the ion channels expressed in trigeminal nociceptors innervating the anterior surface of the eye (cornea and conjunctiva) and annex ocular structures (eyelids), members of the TRP and ASIC families play a critical role in ocular acidic pain. Low pH (pH 6) activates TRPV1, a polymodal ion channel also activated by heat, capsaicin and hyperosmolar conditions. ASIC1, ASIC3 and heteromeric ASIC1/ ASIC3 channels present in ocular nerve terminals are activated at pH 7.2-6.5, inducing pain by moderate acidifications of the ocular surface. These channels, together with TRPA1, are involved in acute ocular pain, as well as in painful sensations during allergic keratoconjunctivitis or other ophthalmic conditions, as blocking or reducing channel expression ameliorates ocular pain. TRPV1, TRPA1 and other ion channels are also present in corneal and conjunctival cells, promoting inflammation of the ocular surface after injury. In addition to the above-mentioned ion channels, members of the K2P and P2X ion channel families are also expressed in trigeminal neurons, however, their role in ocular pain remains unclear to date. In this report, these and other ion channels and receptors involved in acid sensing during ocular pathologies and pain are reviewed

Rational periodic sequences for the Lyness recurrence

Consider the celebrated Lyness recurrence $x_{n+2}=(a+x_{n+1})/x_{n}$ with a\in\Q. First we prove that there exist initial conditions and values of $a$ for which it generates periodic sequences of rational numbers with prime periods $1,2,3,5,6,7,8,9,10$ or $12$ and that these are the only periods that rational sequences $\{x_n\}_n$ can have. It is known that if we restrict our attention to positive rational values of $a$ and positive rational initial conditions the only possible periods are $1,5$ and $9$. Moreover 1-periodic and 5-periodic sequences are easily obtained. We prove that for infinitely many positive values of $a,$ positive 9-period rational sequences occur. This last result is our main contribution and answers an open question left in previous works of Bastien \& Rogalski and Zeeman. We also prove that the level sets of the invariant associated to the Lyness map is a two-parameter family of elliptic curves that is a universal family of the elliptic curves with a point of order $n, n\ge5,$ including $n$ infinity. This fact implies that the Lyness map is a universal normal form for most birrational maps on elliptic curves.Preprin

Interaction of cochlin and mechanosensitive channel TREK-1 in trabecular meshwork cells influences the regulation of intraocular pressure.

This work was funded by National Institute of Health Grants R01 EY016112, EY015266, and EY014801 and an unrestricted grant to the University of Miami's Bascom Palmer Eye Institute from Research to Prevent Blindness. Financial support from Fight for Sight is gratefully acknowledged. Funding to XG was provided by Instituto de Salud Carlos III, Spain (FIS PI14/00141 and RETIC RD12/0034/0003) and Generalitat de Catalunya (2014SGR1165). In the eye, intraocular pressure (IOP) is tightly regulated and its persistent increase leads to ocular hypertension and glaucoma. We have previously shown that trabecular meshwork (TM) cells might detect aqueous humor fluid shear stress via interaction of the extracellular matrix (ECM) protein cochlin with the cell surface bound and stretch-activated channel TREK-1. We provide evidence here that interaction between both proteins are involved in IOP regulation. Silencing of TREK-1 in mice prevents the previously demonstrated cochlin-overexpression mediated increase in IOP. Biochemical and electrophysiological experiments demonstrate that high shear stress-induced multimeric cochlin produces a qualitatively different interaction with TREK-1 compared to monomeric cochlin. Physiological concentrations of multimeric but not monomeric cochlin reduce TREK-1 current. Results presented here indicate that the interaction of TREK-1 and cochlin play an important role for maintaining IOP homeostasis

Purinergic receptors in ocular inflammation

Inflammation is a complex process that implies the interaction between cells and molecular mediators, which, when not properly 'tuned,' can lead to disease. When inflammation affects the eye, it can produce severe disorders affecting the superficial and internal parts of the visual organ. The nucleoside adenosine and nucleotides including adenine mononucleotides like ADP and ATP and dinucleotides such as P(1),P(4)-diadenosine tetraphosphate (Ap4A), and P(1),P(5)-diadenosine pentaphosphate (Ap5A) are present in different ocular locations and therefore they may contribute/modulate inflammatory processes. Adenosine receptors, in particular A2A adenosine receptors, present anti-inflammatory action in acute and chronic retinal inflammation. Regarding the A3 receptor, selective agonists like N(6)-(3-iodobenzyl)-5'-N-methylcarboxamidoadenosine (CF101) have been used for the treatment of inflammatory ophthalmic diseases such as dry eye and uveoretinitis. Sideways, diverse stimuli (sensory stimulation, large intraocular pressure increases) can produce a release of ATP from ocular sensory innervation or after injury to ocular tissues. Then, ATP will activate purinergic P2 receptors present in sensory nerve endings, the iris, the ciliary body, or other tissues surrounding the anterior chamber of the eye to produce uveitis/endophthalmitis. In summary, adenosine and nucleotides can activate receptors in ocular structures susceptible to suffer from inflammatory processes. This involvement suggests the possible use of purinergic agonists and antagonists as therapeutic targets for ocular inflammation