R-matrix approach to integrable systems on time scales

A general unifying framework for integrable soliton-like systems on time scales is introduced. The $R$-matrix formalism is applied to the algebra of $\delta$-differential operators in terms of which one can construct infinite hierarchy of commuting vector fields. The theory is illustrated by two infinite-field integrable hierarchies on time scales which are difference counterparts of KP and mKP. The difference counterparts of AKNS and Kaup-Broer soliton systems are constructed as related finite-field restrictions.Comment: 21 page

Application potential of cold neutron radiography in plant science research

Though comprehensive knowledge of water status and water flow are important prerequisites for plant in many aspects of modern plant science truly non-destructive methods for the in-situ study of water transport are rare. Advanced imaging methods such as Magnetic Resonance Imaging (MRI) or Cold Neutron Radiography (CNR) may be applied to fill this gap. In CNR strong interaction of cold neutrons with hydrogen provides a high contrast even for small amounts of water. The combination of CNR with the low-contrast tracer D2O allows the direct visualisation of water flow and the calculation of water flow rates in plants with a high resolution at the tissue level. Here, we give a general introduction into this method, describe their latest developments, report about studies applying neutron radiography in plant science and provide most recent results of our experiments in this field

GTP and Ca2+ Modulate the Inositol 1,4,5-Trisphosphate-Dependent Ca2+ Release in Streptolysin O-Permeabilized Bovine Adrenal Chromaffin Cells

The inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release was studied using streptolysin O-permeabilized bovine adrenal chromaffin cells. The IP3-induced Ca2+ release was followed by Ca2+ reuptake into intracellular compartments. The IP3-induced Ca2+ release diminished after sequential applications of the same amount of IP3. Addition of 20 μM GTP fully restored the sensitivity to IP3. Guanosine 5'-O-(3-thio)triphosphate (GTPγS) could not replace GTP but prevented the action of GTP. The effects of GTP and GTPγS were reversible. Neither GTP nor GTPγS induced release of Ca2+ in the absence of IP3. The amount of Ca2+ whose release was induced by IP3 depended on the free Ca2+ concentration of the medium. At 0.3 μM free Ca2+, a half-maximal Ca2+ release was elicited with ∼0.1 μM IP3. At 1 μM free Ca2+, no Ca2+ release was observed with 0.1 μM IP3; at this Ca2+ concentration, higher concentrations of IP3 (0.25 μM) were required to evoke Ca2+ release. At 8 μM free Ca2+, even 0.25 μM IP3 failed to induce release of Ca2+ from the store. The IP3-induced Ca2+ release at constant low (0.2 μM) free Ca2+ concentrations correlated directly with the amount of stored Ca2+. Depending on the filling state of the intracellular compartment, 1 mol of IP3 induced release of between 5 and 30 mol of Ca2+

Analysis of the doubly heavy baryons in the nuclear matter with the QCD sum rules

In this article, we study the doubly heavy baryon states $\Xi_{cc}$, $\Omega_{cc}$, $\Xi_{bb}$ and $\Omega_{bb}$ in the nuclear matter using the QCD sum rules, and derive three coupled QCD sum rules for the masses, vector self-energies and pole residues. The predictions for the mass-shifts in the nuclear matter $\Delta M_{\Xi_{cc}}=-1.11\,\rm{GeV}$, $\Delta M_{\Omega_{cc}}=-0.33\,\rm{GeV}$, $\Delta M_{\Xi_{bb}}=-3.37\,\rm{GeV}$ and $\Delta M_{\Omega_{bb}}=-1.05\,\rm{GeV}$ can be confronted with the experimental data in the future.Comment: 10 pages, 4 figure

Molecular Aspects of Secretory Granule Exocytosis by Neurons and Endocrine Cells

Neuronal communication and endocrine signaling are fundamental for integrating the function of tissues and cells in the body. Hormones released by endocrine cells are transported to the target cells through the circulation. By contrast, transmitter release from neurons occurs at specialized intercellular junctions, the synapses. Nevertheless, the mechanisms by which signal molecules are synthesized, stored, and eventually secreted by neurons and endocrine cells are very similar. Neurons and endocrine cells have in common two different types of secretory organelles, indicating the presence of two distinct secretory pathways. The synaptic vesicles of neurons contain excitatory or inhibitory neurotransmitters, whereas the secretory granules (also referred to as dense core vesicles, because of their electron dense content) are filled with neuropeptides and amines. In endocrine cells, peptide hormones and amines predominate in secretory granules. The function and content of vesicles, which share antigens with synaptic vesicles, are unknown for most endocrine cells. However, in B cells of the pancreatic islet, these vesicles contain GABA, which may be involved in intrainsular signaling.' Exocytosis of both synaptic vesicles and secretory granules is controlled by cytoplasmic calcium. However, the precise mechanisms of the subsequent steps, such as docking of vesicles and fusion of their membranes with the plasma membrane, are still incompletely understood. This contribution summarizes recent observations that elucidate components in neurons and endocrine cells involved in exocytosis. Emphasis is put on the intracellular aspects of the release of secretory granules that recently have been analyzed in detail

An essential role of acetylcholine-glutamate synergy at habenular synapses in nicotine dependence

A great deal of interest has been focused recently on the habenula and its critical role in aversion, negative-reward and drug dependence. Using a conditional mouse model of the ACh-synthesizing enzyme choline acetyltransferase (Chat), we report that local elimination of acetylcholine (ACh) in medial habenula (MHb) neurons alters glutamate corelease and presynaptic facilitation. Electron microscopy and immuno-isolation analyses revealed colocalization of ACh and glutamate vesicular transporters in synaptic vesicles (SVs) in the central IPN. Glutamate reuptake in SVs prepared from the IPN was increased by ACh, indicating vesicular synergy. Mice lacking CHAT in habenular neurons were insensitive to nicotine-conditioned reward and withdrawal. These data demonstrate that ACh controls the quantal size and release frequency of glutamate at habenular synapses, and suggest that the synergistic functions of ACh and glutamate may be generally important for modulation of cholinergic circuit function and behavior

Pseudospherical surfaces on time scales: a geometric definition and the spectral approach

We define and discuss the notion of pseudospherical surfaces in asymptotic coordinates on time scales. Thus we extend well known notions of discrete pseudospherical surfaces and smooth pseudosperical surfaces on more exotic domains (e.g, the Cantor set). In particular, we present a new expression for the discrete Gaussian curvature which turns out to be valid for asymptotic nets on any time scale. We show that asymptotic Chebyshev nets on an arbitrary time scale have constant negative Gaussian curvature. We present also the quaternion-valued spectral problem (the Lax pair) and the Darboux-Backlund transformation for pseudospherical surfaces (in asymptotic coordinates) on arbitrary time scales.Comment: 20 page

Memoria del 2001: Instituto de Recursos Naturales y Agrobiología de Sevilla.

145 páginas.Durante el primer año del siglo XXI el Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS) ha seguido realizando su labor investigadora y formativa así como la de asistencia técnica tanto externa como interna y de divulgación tanto de los resultados obtenidos como de su capacidad de I+D. La actividad investigadora del IRNAS se ha mantenido en la línea del año anterior, siendo financiada fundamentalmente mediante proyectos concedidos por la UE, la CICYT-FEDER, Junta de Andalucía, otros Ministerios y la empresa privada, siendo este último sector el que menos contribuye a esta financiación. Parece obvio que tenemos que hacer entre todos un esfuerzo por captar mayores recursos de este sector productivo. Como consecuencia de la actividad investigadora realizada se han publicado 50 artículos en revistas internacionales, recogidas en SCI, 6 en revistas nacionales, 45 trabajos en libros o publicaciones colectivas, 4 Tesis doctorales, 2 de licenciatura, 5 trabajos Fin de Carrera, 5 Fin de Curso, así como 6 patentes registradas. El personal del IRNAS ha participado en congresos internacionales con 66 comunicaciones y en nacionales con 20. En el aspecto formativo se ha contribuido a la formación de 47 personas de diversa cualificación académica mediante los contratos asignados al IRNAS tras el convenio INEM-CSIC. Así mismo, se sigue participando en diversos programas de Doctorado, Master y Cursos tanto en la Universidad Hispalense como en la Pablo de Olavide, de Sevilla, habiéndose defendido las Tesis Doctorales, de Licenciatura y proyectos Fin de Carrera mencionados anteriormente. En el ámbito internacional el IRNAS sigue implicado en su tradicional política de intercambio y colaboración con paises europeos, latinoamericanos y del Magreb, como indican las Acciones Integradas del MCYT, Convenios y Acciones Especiales del CSIC, etc. que recogen esta Memoria. En la Finca experimental “La Hampa” se han seguido realizando las experiencias de campo que necesitan llevar a cabo diversos grupos del IRNAS, en el contexto de proyectos financiados con fondos gubernamentales nacionales, autonómicos, europeos y de empresas privadas.Peer reviewe

Heavy pseudoscalar mesons in a Schwinger-Dyson--Bethe-Salpeter approach

The mass spectrum of heavy pseudoscalar mesons, described as quark-antiquark bound systems, is considered within the Bethe-Salpeter formalism with momentum-dependent masses of the constituents. This dependence is found by solving the Schwinger-Dyson equation for quark propagators in rainbow-ladder approximation. Such an approximation is known to provide both a fast convergence of numerical methods and accurate results for lightest mesons. However, as the meson mass increases, the method becomes less stable and special attention must be devoted to details of numerical means of solving the corresponding equations. We focus on the pseudoscalar sector and show that our numerical scheme describes fairly accurately the $\pi$, $K$, $D$, $D_s$ and $\eta_c$ ground states. Excited states are considered as well. Our calculations are directly related to the future physics programme at FAIR.Comment: 9 pages, 3 figures; Based on materials of the contribution "Relativistic Description of Two- and Three-Body Systems in Nuclear Physics", ECT*, October 19-23, 200

Analysis of the ΛQ\Lambda_Q baryons in the nuclear matter with the QCD sum rules

In this article, we study the $\Lambda_c$ and $\Lambda_b$ baryons in the nuclear matter using the QCD sum rules, and obtain the in-medium masses $M_{\Lambda_c}^*=2.335\,\rm{GeV}$, $M_{\Lambda_b}^*=5.678\,\rm{GeV}$, the in-medium vector self-energies $\Sigma^{\Lambda_c}_v=34\,\rm{MeV}$, $\Sigma^{\Lambda_b}_v=32\,\rm{MeV}$, and the in-medium pole residues $\lambda_{\Lambda_c}^*=0.021\,\rm{GeV}^3$, $\lambda_{\Lambda_b}^*=0.026\,\rm{GeV}^3$. The mass-shifts are $M_{\Lambda_c}^*-M_{\Lambda_c}=51\,\rm{MeV}$ and $M_{\Lambda_b}^*-M_{\Lambda_b}=60\,\rm{MeV}$, respectively.Comment: 7 pages, 8 figures, revised versio