Survival probability and order statistics of diffusion on disordered media

We investigate the first passage time t_{j,N} to a given chemical or Euclidean distance of the first j of a set of N>>1 independent random walkers all initially placed on a site of a disordered medium. To solve this order-statistics problem we assume that, for short times, the survival probability (the probability that a single random walker is not absorbed by a hyperspherical surface during some time interval) decays for disordered media in the same way as for Euclidean and some class of deterministic fractal lattices. This conjecture is checked by simulation on the incipient percolation aggregate embedded in two dimensions. Arbitrary moments of t_{j,N} are expressed in terms of an asymptotic series in powers of 1/ln N which is formally identical to those found for Euclidean and (some class of) deterministic fractal lattices. The agreement of the asymptotic expressions with simulation results for the two-dimensional percolation aggregate is good when the boundary is defined in terms of the chemical distance. The agreement worsens slightly when the Euclidean distance is used.Comment: 8 pages including 9 figure

Política, eleccions i caciquisme a Vic, 1900-1931

Consultable des del TDXTítol obtingut de la portada digitalitzadaA començaments del segle XX, en una cojuntura de descomposició institucional, la vida política local de la ciutat de Vic, població catalana d'uns 13.000 habitatnts situada a l'interior de Catalunya, seu de la diòcesi episcopal més extensa del país i amb un important Seminari Conciliar, comença a evolucionar en la direcció d'una modernització que, al llarg dels anys, constatarà importants transformacions. En el context català, la nova política de masses descansarà sobre tres aspectes principals. En primer lloc, s'organitzaran partits capaços de mobilitzar els afiliats i els simpatitzants per aconseguir uns objectius concrets: fer una manifestació, guanyar unes eleccions, constituir una seu social, editar un periòdic. En la fase de transició cap a les organitzacions «mobilitzadores», trobarem partits polítics que combinen el carisma exagerat de determinats líders amb la potència d'unes bases que no es deixen arrossegar si els seus criteris no coincideixen amb els dels «homes forts»; els partits estaran a mig camí entre la influència dels notables i el poder decisori de la militància organitzada. En segon lloc, les urnes reflectiran, progressivament, les peocupacions i els interessos polítics de la majoria, deixant de banda les maniobres «electoreres» dels cacics, que tindran dificultats creixents per a organitzar els processos electorals d'acord amb els seus interessos. Finalment, les institucions locals deixaran de tenir «vida pròpia», al marge de les altrenatives polítiques que es produeixen a la societat; les discusssions i lluites polítiques, forjades en «l'espai públic», es traslladaran als ajuntaments. Tot i que aquestes transformacions (en l'àmbit dels partits, de les eleccions i dels ajuntaments) definiran nous estils de fer política, la modernització no es produirà de manera uniforme. A la Catalunya tradicional, de la que la ciutat de Vic forma part, els canvis en l'esfera pública tindran unes característiques pròpies, la qual cosa posarà en qüestió, d'altra banda, la imatge idealitzada d'una societat homogènia i avançada. A Vic, en un context que combina una presència institucional de l'Església catòlica especialment significada i el desenvolupament d'una important economia industrial, la vida pública estarà dirigida per forces burgeses que hegemonitzaran, davant la feblesa del moviment popular autòcton, el procés de transformació política. Aquestes èlits combatran, successivament i a partir del tombant de segle XX, les imposicions del «cunerisme» dinàstic, les estratègies de les direccions dels nous partits hegemònics (catalanistes, tradicionalistes) i l'expansió d'un moviment democràtic que reclama protagonisme polític per a les classes populars. Es tractarà de controlar els canvis polítics per tal que no es modifiquin els aspectes essencials de la dominació social, i política, que exerceix el grup dirigent local. Tanmateix, l'extensió de la «vida política nacional» farà que aquest «control polític» esdevingui cada cop més difícil i possibilitarà, en un marc de transformacions econòmiques i d'extrema conflictivitat social, que les forces populars es vagin incorporant a la vida pública de Vic, a pesar de les maniobres de l'èlit dirigent destinades a impedir-ho. A partir de la crisi del 1917 s'accelerà la dissolució de la «vella política». La dictadura del general Primo de Rivera, que inicialment es presentà com una opció «regeneradora» capaç de resoldre els probles endèmics del país, evidencià la impossibilitat de continuar mantenint les masses allunyades de la vida pública espanyola. La proclamació de la República, que inaugurà un context políticoinstitucional radicalment diferent del que oferia la Restauració borbònica, possibilità que la societat espanyola disposés de dos requisits indispensables per a la convivència democràtica: la llibertat i el Parlament. A la ciutat de Vic, com a la resta de Catalunya, el nou règim republicà va permetre l'entrada de les classes populars en la política local, tot i que aquesta democratització no sempre fou favorable a les forces progressistes.On the early XXth century, in an environment of institutional decomposition, local political life in the city of Vic, -a catalan community of 13.000 inhabitants of Catalunya, and also see of the bigger Episcopal dioceses if the country and an important conciliar seminar-, begin to change into a modernisation that, along the years, realised important transformations in the catalan context the new mass politics lied on three main aspects. First of all, the parties capable to mobilise affiliates and supporters organised themselves to reach concrete goals: prepare a demnstration, win the elections, create a social see, publish a paper. In this fase of transition into «mobilised» organisations, political parties can be found combining the grat charisma of some of the leaders and the poxer of a basis that doesn't let itself drag on if their believes do not agree with these of the «strong men»; the parties were in the way betwen the influence of the notables and the power of the organised militancy to take decisions. Secondly, the ballot boxes reflected, progressively, the worries and political interests of the majority, siding «electory» manoeuvres of the caciques who had increasing difficulties according to their interests. Finally, local institutions stopped having their «own life», apart of the political alternatives taking place in the society; political struggles and discussions, held in the public sphere, moved into the City Council. Even these transdormations (in the area of parties, elections and city councils) defined new stiles of doing politics, modernisation didn't spread homogeneously. In the traditional Catalunya, from which Vic is part, the changes in the public sphere had their own characteristics, and this lead into question this ideal image of an homogeneous and advanced society. In Vic, where the particularly signified presence of the institutions of the catolic church was combined with the developing of an important industrial economy, public life was in hands og burgeois forces, against the weakness of the indigenous popular movement, to lead the process of political transformation. These elites fighted, successively after the crossing of the XXth century, the impositions of the «dynastic cunerism», the strategies of the leaderships of the new hegemonic parties (traditionalists catalanists) and the expansion of a democratic movement claiming for the leading role of popular classes. The need was to control the political changes in order not to modify the essential aspects of social, and political, domination practiced by the local leading group. Eventrough, the extension of the «national political life» made this «political control» more difficult and this, in the context of economical transformations and extreme social conflict, allowed popular forces to incorporate into public life of Vic, eventrogh the manoeuvres of the leading elite to avoid it. After the crises of 1917 the dissolution of the old politics accelerated. The dictatorship of the General primo de Rivera, who inicially presented himself as an option of «regeneration» capable to solve the endemic problems of the country, showed an incapacity to keep the masses away from the Spanish political life. The proclamation of the Republic, as a strat of a political and constitutional context radically different from that of the Borbonic restauration, let the Spanish society enjoy the two requisites for the democractic coexistence: freedom and Parlamient. In the city of Vic, as in the rest of Catalonia, the new Republican regime permited the entrance of popular classes in the local politics, even this democratisation was not always favouring progressive forces

"Esperant". Obra de teatre sobre les trajectòries de vida de dones immigrades

<p style="text-align: justify; line-height: 130%" class="MsoNormal"><span style="font-size: 10pt; line-height: 130%; font-family: &quot;Trebuchet MS&quot;">&ldquo;Esperant&rdquo; &eacute;s una obra de teatre, per&ograve; no una obra qualsevol, &eacute;s una obra que escenifica els resultats d&rsquo;una recerca. &Eacute;s un aproximaci&oacute; a una altra forma d&rsquo;escriure, de comunicar un estudi. Es tracta d&rsquo;experimentar, de jugar amb el llenguatge i amb altres formes narratives, sense perdre el contingut i la potencia de la recerca. &ldquo;Esperant&rdquo; &eacute;s doncs la materialitzaci&oacute; d&rsquo;un proc&eacute;s d&rsquo;investigaci&oacute; i sobretot dels seus resultats i de la seva an&agrave;lisi. L&rsquo;obra presenta l&rsquo;entorn de la recerca, un consultori, pe&ccedil;a clau del sistema de salut catal&agrave;; unes actrius, les protagonistes de la hist&ograve;ria, dones immigrades, membres d&rsquo;associacions i professionals de la salut; uns di&agrave;legs i unes converses enmig d&rsquo;esperes, relats de vida que composen el material de la recerca; i una primera an&agrave;lisi en forma de pensaments o reflexions. En concret, l&rsquo;objectiu de la investigaci&oacute;, en la qual es basa el text, era analitzar i explicar les traject&ograve;ries de manteniment del benestar dels col&middot;lectius de dones immigrades m&eacute;s presents a Catalunya, per tal de revaloritzar els projectes d&rsquo;organitzaci&oacute; i participaci&oacute; de les pr&ograve;pies dones, aix&iacute;<span>&nbsp; </span>com els aspectes de negociaci&oacute;/acomodaci&oacute; m&uacute;tua entre dones nouvingudes i societat receptora. Per &uacute;ltim, dir que aquesta narraci&oacute; pret&eacute;n oferir una porta m&eacute;s per pensar sobre l&rsquo;escriptura i sobre noves formes liter&agrave;ries per les ci&egrave;ncies socials, introduint el di&agrave;leg, la narraci&oacute;, l&rsquo;escenificaci&oacute;, etc. en defintiva, el teatre.</span></p

Mean Field Model of Coagulation and Annihilation Reactions in a Medium of Quenched Traps: Subdiffusion

We present a mean field model for coagulation ($A+A\to A$) and annihilation ($A+A\to 0$) reactions on lattices of traps with a distribution of depths reflected in a distribution of mean escape times. The escape time from each trap is exponentially distributed about the mean for that trap, and the distribution of mean escape times is a power law. Even in the absence of reactions, the distribution of particles over sites changes with time as particles are caught in ever deeper traps, that is, the distribution exhibits aging. Our main goal is to explore whether the reactions lead to further (time dependent) changes in this distribution.Comment: 9 pages, 3 figure

Non-Markovian Random Walks and Non-Linear Reactions: Subdiffusion and Propagating Fronts

We propose a reaction-transport model for CTRW with non-linear reactions and non-exponential waiting time distributions. We derive non-linear evolution equation for mesoscopic density of particles. We apply this equation to the problem of fronts propagation into unstable state of reaction-transport systems with anomalous diffusion. We have found an explicit expression for the speed of propagating front in the case of subdiffusion transport.Comment: 7 page

On reaction-subdiffusion equations

To analyze possible generalizations of reaction-diffusion schemes for the case of subdiffusion we discuss a simple monomolecular conversion A --> B. We derive the corresponding kinetic equations for local A and B concentrations. Their form is rather unusual: The parameters of reaction influence the diffusion term in the equation for a component A, a consequence of the nonmarkovian nature of subdiffusion. The equation for a product contains a term which depends on the concentration of A at all previous times. Our discussion shows that reaction-subdiffusion equations may not resemble the corresponding reaction-diffusion ones and are not obtained by a trivial change of the diffusion operator for a subdiffusion one

Ultrastructure of Dendritic Spines: Correlation Between Synaptic and Spine Morphologies

Dendritic spines are critical elements of cortical circuits, since they establish most excitatory synapses. Recent studies have reported correlations between morphological and functional parameters of spines. Specifically, the spine head volume is correlated with the area of the postsynaptic density (PSD), the number of postsynaptic receptors and the ready-releasable pool of transmitter, whereas the length of the spine neck is proportional to the degree of biochemical and electrical isolation of the spine from its parent dendrite. Therefore, the morphology of a spine could determine its synaptic strength and learning rules

Sulfide-, fluorite-, barite-bearing siliceous "crusts" related to unconformity surfaces of different ages in Pyrenees and Alps: a new model in carbonate-hosted deposits?

Wumerous stratabound sulfide-, barite-, fluonte-bearing siliceous crusts, from dm to some tens of in thick, occur over large areas of the Alpine belt, ;.e. the Alps and the Pyrenees. They are linked to unconformlty landscapes evolved on various carbonate units of Paieozoic and Triassic sedimentq sequences. Since the study mineralizations constitute the transition between the underlying carbonates and the overlying detrital units, they can be considered as an independent lithostratigraphic units that record a particular metalogenetic process not only in the alpine chains but worldwide. These mineralizations exhibit several morphologies: tabular concordant with the unconfonnities bodies, columnar bodies, karstic cavity-fillings, laminites and veins. In addition, the study deposits are clearly affected by remobilization process occuned during diagenesis or metamorphism. Such processes are responsible for masking the occunence of the breccia/conglomerate typically located at the base of the orebodies.Although the study mineralizations have usually been included in MVT deposit class, constrastirig differences between their diagnostic features and those of MVT mineralizations, suggest that the inclusion of the mineralized crust deposits in the MVT group seem incorrect.These peculiar ore-bearing quartz-crusts, persistent over large areas and showing an independent and distinct character and constituting an important marker for some sedimentary sequences of different ages in Alpine belts, allow the authors to define a new metallogenic model named as "crust-type" (CT) deposits. Comparable mineralization in other geotectonic environments outside Alpine belts point out to CT deposits being a worldwide significant metallogenic event

Survival probability of a particle in a sea of mobile traps: A tale of tails

We study the long-time tails of the survival probability $P(t)$ of an $A$ particle diffusing in $d$-dimensional media in the presence of a concentration $\rho$ of traps $B$ that move sub-diffusively, such that the mean square displacement of each trap grows as $t^{\gamma}$ with $0\leq \gamma \leq 1$. Starting from a continuous time random walk (CTRW) description of the motion of the particle and of the traps, we derive lower and upper bounds for $P(t)$ and show that for $\gamma \leq 2/(d+2)$ these bounds coincide asymptotically, thus determining asymptotically exact results. The asymptotic decay law in this regime is exactly that obtained for immobile traps. This means that for sufficiently subdiffusive traps, the moving $A$ particle sees the traps as essentially immobile, and Lifshitz or trapping tails remain unchanged. For $\gamma > 2/(d+2)$ and $d\leq 2$ the upper and lower bounds again coincide, leading to a decay law equal to that of a stationary particle. Thus, in this regime the moving traps see the particle as essentially immobile. For $d>2$, however, the upper and lower bounds in this $\gamma$ regime no longer coincide and the decay law for the survival probability of the $A$ particle remains ambiguous