88,271 research outputs found
Flussi di acqua e soluti attraverso n membrane in serie, con trasporto attivo
No full textTrasporto di acqua e soluti attraverso n membrane in serie in presenza di trasporto "attivo" di soluto. L'esperienza mostra che le relazioni fra i flussi di materia attraverso membrane, e le forze generalizzate che li sostengono sono non lineari. Ciò è vero sia per il trasporto attraverso singole membrane biologiche sia per quello attraverso barriere complesse, come gli epiteli, che si possono ritenere costituiti da più membrane semplici in serie. Il modello più semplice, ma poco realistico, costituito da due sole membrane, già consente di spiegare l'accoppiamento fra il trasporto "attivo" (accoppiato a reazioni chimiche) di soluto e il trasporto d'acqua (1-2). La generalizzazione a un sistema costituito da n membrane in serie, ma puramente passivo (3-4) viene ora estesa con l'introduzione del trasporto attivo. Lo studio teorico del modello e la simulazione al calcolatore di tale sistema hanno mostrato che: 1. la non linearità del flusso volumetrico si osserva solo in presenza di soluto e l'equazione si riduce alla legge lineare di Darcy per il solvente puro, 2. la non linearità richiede comunque l'asimmetria del sistema ed è dovuta all'accumulo di soluto nei compartimenti interni, 3. i coefficienti non costanti che correlano i flussi alle loro forze traenti sono funzione, oltre che del flusso stesso, anche delle variabili operative, 4. il comportamento non lineare di membrane semplici può venire spiegato con il fatto che gli strati limite di fluido non mescolato si comportano come membrane non selettive. (1) C. S. Patlack, D. A. Goldstein, J. F. Hoffman: J. Theor. Biol. 5, 426-442 (1963). (2) G. Monticelli, F. C. Celentano: Bull. Math. Biol. 45, 1073-1096 (1983). (3) F. C. Celentano, G. Monticelli: Atti VI Congresso SIBPA, Camogli, 1983, pp 6062. (4) F. C. Celentano, G. Monticelli in V. Capasso, E. Grosso, S. L. Paveri Fontana: Mathematics in Biology and Medicine, Springer Berlino, 1985, pp 293-299
Coefficienti fenomenologici per il trasporto di acqua e soluti in sistemi a n membrane in serie
No full textLe relazioni flusso–forza nelle membrane biologiche risultano sperimentalmente non lineari. Per descrivere tale comportamento è stato proposto (1) di impiegare le equazioni lineari "pratiche" di Kedem e Katchalsky scritte in forma locale e integrate attraverso lo spessore di un sistema di due membrane in serie. Si ottengono equazioni fenomenologiche non lineari per il trasporto di acqua e soluti, che richiedono la ridefinizione come derivate, anziché rapporti semplici, dei coefficienti di permeabilità idraulica, di flusso osmotico e di riflessione. I risultati già ottenuti per due membrane (2) sono stati ora estesi a un sistema di n membrane, nel quale sono assimilabili formalmente a una membrana non selettiva anche gli strati limite. Per la membrana i-esima si scrive la concentrazione nel compartimento di destra i+1 in funzione di quella nel compartimento di sinistra i, del flusso volumetrico Jv e di quello di soluto Js. Mediante sostituzione ricorsiva delle concentrazioni si ottiene la concentrazione nel compartimento estremo di destra n+1 in funzione di quella nel compartimento estremo di sinistra 1. Di qui si ottiene Js in funzione di Jv, di C = C(n+1) - C(1) e di C(1) stessa. Si segue un procedimento analogo per le pressioni nei vari compartimenti e si ottiene la relazione che fornisce Jv. Da quest’ultima si ricava che: 1) il coefficiente di filtrazione Lp non è solo l’inverso della somma degli inversi dei singoli coefficienti Lpi relativi alle singole membrane ma contiene pure un termine additivo non lineare in C(1); 2) anche il coefficiente di flusso osmotico Lpd contiene un termine in C(1); 3) il rapporto -Lpd/Lp è indipendente da C(1) e, come nella teoria classica lineare, fornisce un coefficiente di riflessione per il sistema che risulta pari alla media dei coefficienti di riflessione delle n membrane pesati sull’inverso dei rispettivi coefficienti di permeabilità; 4) il medesimo risultato si ottiene facendo il limite per Jv tendente a zero del rapporto tra le differenze di pressione osmotica e idrostatica, confermando che si tratta effettivamente di un coefficiente di riflessione; 5) la legge di Darcy risulta una legge limite valida solo per il solvente puro, C(1) = 0. (1) C. S. Patlak, D. A. Goldstein, J. F. Hoffman: J. Theor. Biol. 5, 426-442 (1963) (2) G. Monticelli, F. Celentano: Further Properties of the Two-Membrane Model, Bull. Math. Biol, in stampa (1983)
Phenomenological description of selectivity in actively transporting membranes
No full textA phenomenological description of active and passive flows of solute and solvent across a biological membrane can be made explicitly considering the dependence of matter flows upon the rate of metabolic reactions /1/, or introducing a generalized chemical potential including a term accounting for active transport /2/, or making the hypothesis that solute flow can be splitten in two superimposed and thermodynamically couplet active and passive components. With the two latter approaches, by means of a transformation of flows and forces at constant temperature and in absence of electric field, two systems of three interacting flows, sustained by three different forces, can be obtained. The two systems lead to equivalent descriptions of volumetric flow and allow the determination of the reflection coefficient for solute passive transport /3/. The relationship between reflection coefficient and apparent reflection coefficient /4/ is also obtained. 1. A. Katchalsky, P. F. Curran. Nonequilbrium Thermodynamics in Biophysics, Cambridge Mass. (1965); 2. J. M. Diamond. J. Physiol. 161, 503 (1962); 3. F. Celentano, G. Monticelli, G. Torelli. Proc. Ist. Europ. Biophys. Congr. 3, 309 (1971); 4. C. J. Bentzel, M. Davies, W. N. Scott, M. Zatzman, A. K. Solomon. J. Gen. Physiol. 51, 517 (1968
A simulation of mass transport across series arrays of membranes with chemical reaction-coupled solute flow
No full textBoth in biology and technology, membranes can be seldom treated as single, thin and linearly behaving barriers. Mass transport across thick membranes, as first suggested by Patlak, Goldstein and Hoffman (1), can be described integrating across the membrane thickness the local, linear, practical equations by Kedem and Katchalsky (2), which have been recently shown to derive directly fom the local energy dissipation function of the membrane (3). When the heat flow associated to chemical reactions or to a temperature gradient can be neglected, the presence of a solute "active" transport can also be accounted for (1,4). In the present paper we extend to n membranes, by means of a recursive procedure, the previous treatment of a series array of few membranes (1, 4) and derive some parameters characterizing the transport properties of the complex barrier. This task has been performed analytically, with the help of the symbolic computation program REDUCE, obtaining a non-linear correlation between the flows and their driving forces, depending on the volume flow and on the solute concentration of the transported solution. The nonlinearity appears to be a consequence of the solute accumulation in the inner compartments of the array. The classical linear law by Darcy is a limiting case of our volume flow equation when only pure solvent is transported. Around the volume and solute flow equations we have written a program in Pascal allowing the simulation of a series array of up to 10 membranes and unstirred layers, assimilated to non-selective membranes. The results of the simulation are in agreement with experimental data obtained using complex biological barriers like epithelia. 1. C.S. Patlak, D.A. Goldstein, J.F. Goldstein: J. Teor. Biol. 5, 426-442 (1963); 2. O. Kedem, A. Katchalsky: Biochim. Biophys. Acta 27, 229-246 (1958); 3. F. Celentano, G. Monticelli: Local Practical Equations for Heat and Mass Transport Driven by Temperature Gradients, Proc. Europe-Japan Congr. Membranes and Membrane Proc., Stresa, June 18-22 1984, in press; 4. G. Monticelli, F. Celentano: Bull. Math. Biol. 45, 1073-1096 (1983)
PHENOMENOLOGY TODAY: A GOOD TRAVEL MATE FOR ANALYTIC PHILOSOPHY?
No full textOn the basis of a short summary of phenomenological aims and methods, this essay
describes the present state of relationships between phenomenology and analytic
philosophy, pointing out the progress done in the last years on the way of their
rapprochement, after a long time of reciprocal scorn and misunderstandings. In the way
of a presentation of the Phenomenology Lab and Center’s present and future research
program, it recalls some relevant chapters of past and present phenomenological
research in Europe, and quite particularly in Italy. After discussing some aspects
of contemporary debates in phenomenology and philosophy of mind, it attempts at
establishing a convergent line of argument toward the assessment of an anti-reductive
ontology of concreteness, or the life world
Introduction. In: (a cura di): Albertazzi S, Cattani F, Monticelli M, Zullo F, (Post)Colonial Passages. Incursions and Excursions across the Literatures in English. p. 1-4, NEWCASTLE UPON TYNE:Cambridge Scholars Publishing
No full textOn Temnocephala axenos Monticelli, 1898 (Platyhelminthes, Temnocephalida): Taxonomic status and designation of a neotype
No full textTemnocephala axenos Monticelli, 1898 was described based on specimens from an unidentified host collected in Blumenau, Santa Catarina, Brazil. Information about type locality was imprecise and the host was later identified as Aegla laevis (Latreille, 1818). However, it is known that A. laevis is not present on the eastern side of the Andes. Also, only histological preparations from one specimen studied by Monticelli are currently available in the Museum für Naturkunde Berlin, but it showed none of the taxonomic characters needed for the characterization of the species. Although the updated description of the species based on Uruguayan specimens, neither the author nor the several previous studies about the species showed a search for the type material, a resolution for the misidentification of the type host or the imprecise type locality due to the subsequent geographical division of the municipality cited in the description. The Uruguayan specimens were not even geographically close to the type locality and a neotype was not designed to validate the species' taxonomic status again. Specimens from Santa Catarina and Paraná States, Brazil, were studied, as well as restudied Argentinean specimens. The new data were compared with the update description of the species. The historical background and the discussion about geographical origins and hosts of the species, as well as a designation of a neotype, allow comparative material of the type locality and type host to exist, eliminating doubts about the identification of T. axenos.Fil: Alves Seixas, Samantha. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División de Zoología Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Amato, Suzana. Universidade Federal do Rio Grande do Sul; BrasilFil: Amato, J. F. R.. Universidade Federal do Rio Grande do Sul; BrasilFil: Daut, L. C. C.. Universidade Federal do Rio Grande do Sul; BrasilFil: Damborenea, Maria Cristina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División de Zoología Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Raphidrilus nemasoma Monticelli 1910
No full textRaphidrilus nemasoma Monticelli, 1910 a Figure 1 (A–D) Raphidrilus nemasoma Monticelli, 1910 a: p. 61–64. Raphidrilus nemasoma; Monticelli, 1910 b: p. 403–406, pls. 12–13; Banse, 1959 a: p. 307; possibly Banse, 1959 b: p. 170–171, fig. 2; possibly Bellan, 1964; not Harris, 1971: p. 706, fig. 14; Katzmann, 1972: p. 136; not Qian & Chia, 1989: p. 2350, figs. 1–18. Ctenodrilus branchiatus Sokolow, 1911 a: p. 548–565, plates XXVII–XXIX. Material examined. Croatia: Vrsar Harbor, northern Adriatic Sea, 45 °08,989ʹ N 13 ° 35,776 ʹ E, collected from the thallus of Caulerpa racemosa (Forsskål) J. Agardh, coll. Barbara Mikac, 08/ 12 / 2008 (9 anterior fragments mounted on stub, USNM 1150464). Description. Small and incomplete specimens, 1–2.5 mm long, 0.05–0.1 mm wide with 5–11 anterior chaetigers. First four chaetigers (thorax) wider than long; abdominal chaetigers twice longer than wide with sub–annulations. Prostomium short, broadly round; peristomium single achaetous annulation followed by one dorsally biannulated achaetous segment (Fig. 1 A, B). Parapodia with serrated capillaries throughout (Fig. 1 C, D). Anterior chaetigers with 4 serrated capillaries in each noto– and neuropodia; number of chaetae reduces from chaetiger 5–6 to 1– 2 serrated capillaries in posterior chaetigers. Distance between the insertion point of two capillary fibrils along the capillary chaetae approximately the same as the width of a single fibril (Fig. 1 C, D). Branchial filaments arising posterodorsal to notochaetae. Posterior end and pygidium not observed. Distribution. Raphidrilus nemasoma seems to be widely distributed in the Ligurian and Tyrrhenian seas (Castelli et al. 1995) and the northern Adriatic Sea. Remarks. The specimens analyzed from the northern Adriatic Sea agree well with the description of R. nemasoma by Monticelli (1910 a, b). Monticelli (1910 b) reported an achaetous segment before chaetiger 1, but referred to it as the peristomium; however, SEM analysis of R. nemasoma specimens newly collected showed an additional achaetous segment posterior to the peristomium. The dorsal distinction between prostomium and peristomium, however, is not easily seen using light microscopy, even at 1000 x magnification. The type series of R. nemasoma are believed to be lost or never kept (see discussion in Petersen & George 1991) but the specimens newly collected from the northern Adriatic Sea are not well enough preserved to be assigned as neotypes and were not collected near the type locality (Naples Gulf, Italy). More complete and well preserved specimens are necessary to better assess the external morphology of this species, even though detailed descriptions of the external morphology and internal anatomy are available in Monticelli (1910 b) and Sokolow (1911 a).Published as part of Magalhães, Wagner F., Bailey, Julie H., Brock, - & Davenport, Jennifer S., 2011, On the genus Raphidrilus Monticelli, 1910 (Polychaeta: Ctenodrilidae) with description of two new species, pp. 1-14 in Zootaxa 2804 on pages 4-5, DOI: 10.5281/zenodo.27706
La web survey con le giovani donne tra dimensione lavorativa e dimensione motivazionale
No full textEvidenze empiriche dell'indagine quantitativa realizzata nel progetto "Female Role Models". In particolare, si evidenziano le risultanze della web survey con le giovani donne tra dimensione lavorativa e dimensione motivazionale
Measurements of electrical parameters of frog skin "in situ" as a function of environmental parameters
No full textElectrical parameters of the abdominal skin of the pithed frog (Rana esculenta) can be measured by means of a couple of double coaxial electrodes /1,2,3/. One of the double electrodes is inserted into the ventral lymphatic sac of the frog, between skin and muscles, and the second is placed in front of this, on the outer surface of the skin. The inner electrode of the coaxial pair measures the skin potential difference (pd), while the outer delivers a countercurrent, for modifying the pd. By this method, pd, short circuit current and skin DC resistance have been determined as a function of temperature (5 to 40 °C) and of pH (4 to 9) on the same living animal. The behaviour of the substrate bears both qualitative and quantitative similarities with the isolated skin in the lower temperature range, but no transport maximum exists around 27 °C /4/. The pH dependence of electrical parameters is also quite different than in the isolated substrate /5/. 1. G. Torelli, F. Celentano, G. Cortili, G. Guella: Boll. Soc. It. Biol. Sper. 44, 501 (1967); 2. F. Celentano, G. Cortili, G. Guella, G. Torelli: Boll. Soc. lt. Biol. Sper. 44, 504 (1967); 3. M. Bianchi, G. Torelli, F. Celentano, G. Cortili: Boll. Soc. It. Biol. Sper. 45, 385 (1968); 4. G.A. Poster: Biochim. Biophys. Acta 211, 487 (1970); 5. E. Schoffeniels: Arch. Int. Physiol. Biochim. 53, 513 (1955)
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