2,460 research outputs found
Iron absorption by excised grapevine roots
Excised roots from cuttings of Vitis vinifera cv. Verduzzo and of two rootstocks V. berlandieri x V. riparia 420 A and V. berlandieri x V. rupestris 1103 P. were tested for iron absorbed from FeEDTA solutions.Absorption rates decreased with time. At 0-2 °C iron absorption was only 50-60 % inhibited. BPDS, a specific chelator for Fe2+, inhibited almost completely absorption showing that reduction from Fe3+ to Fe2+ was needed both at 30 °C and at 0-2 °C. As pH increased from 5 to 8 absorption rate doubled for the cv. Verduzzo, increased about 5 times for 1103 P. and about 10 times for 420 A. Also the apparent kinetic constants of absorption were very different in the three grapevines: both Vmax and Km were in the order: 1103 P.> Verduzzo > 420 A. The presence of a conspicuous part of not exchangeable absorption apparently not dependent on metabolism and the possibility of characterizing cultivars and rootstocks as to nutritional requirements through ion absorption measurements are discussed.Absorption du fer par les racines coupées de la vigneDes racines coupées de x cv. Verduzzo et des porte-greffes V. berlandieri x V. riparia 420 A et V. berlandieri x V. rupestris 1103 P. ont été étudiées quant au fer absorbé de solutions de FeEDTA. La vitesse d'absorption diminue en fonction du temps. A 0-2 °C l'absorption est inhibée seulement de 50--60 %. Le BPDS, chélant spécifique du Fe2+, inhibe presque complètement l'absorption, ce qui démontre que la réduction Fe3+ -> Fe2+ est nécessaire à 0-2 °C ainsi qu'à 30 °C. Lorsque le pH passe de 5 à 8 la vitesse d'absorption se redouble pour le cv. Verduzzo, elle augmente d'à peu près cinq fois pour le 1103 P. et d'environ dix fois pour le 420 A. Les constantes ciné tiques apparentes de l'absorption sont aussi très différentes pour les trois vignes: Vmax et Km sont toutes les deux de l'ordre de 1103 P. > Verduzzo > 420 A.On discute la présence d'une part remarquable· de l'absorption qui n'est pas échangeable et qui apparemment ne dépend pas du mé tabolisme, ainsi que la possibilité de caractériser les cultivars et les por te-greffes suivant leurs besoins en substances nutritives minérales au moyen de mesurages de l'absorption des ions
Mapping the Evolution of "Clusters": A Meta-analysis
This paper presents a meta-analysis of the “cluster literature” contained in scientific journals from 1969 to 2007. Thanks to an original database we study the evolution of a stream of literature which focuses on a research object which is both a theoretical puzzle and an empirical widespread evidence. We identify different growth stages, from take-off to development and maturity. We test the existence of a life-cycle within the authorships and we discover the existence of a substitutability relation between different collaborative behaviours. We study the relationships between a “spatial” and an “industrial” approach within the textual corpus of cluster literature and we show the existence of a “predatory” interaction. We detect the relevance of clustering behaviours in the location of authors working on clusters and in measuring the influence of geographical distance in co-authorship. We measure the extent of a convergence process of the vocabulary of scientists working on clusters.Cluster, Life-Cycle, Cluster Literature, Textual Analysis, Agglomeration, Co-Authorship
Extraction and preliminary characterization of microsomal (Mg2+ + K+)-ATPase activity of grapevine roots
The microsomal fraction extracted from grapevine roots obtained from woody cuttings possesses Mg2+-dependent, monovalent cation-stimulated ATPase activity. Addition of BSA, PVPP, choline-CI, ethanolamine, glycerol-1-P besides EDTA and DTT to the homogenizing medium as preservative compounds was required in order to achieve a successful isolation.When microsomes were extracted according to HODGES and LEONARD (1974) by homogenizing root tissue in the presence of EDTA and DTT, the enzyme activity exhibited inhibition by Mg2+ only partially relieved by K+, and properties of acid phosphatase rather than ATPase.Cation-stimulated ATPase of microsomes protected during homogenization was further characterized and it showed optimum activity at pH 7.0 in the presence of Mg2+ plus K+ . It was specific as a triphosphatase and Mg2+, rather than other divalent cations, was preferred as a cofactor. As monovalent stimulating cation, only NH4+ could substitute for K+ with equivalent efficiency. The kinetics of K+ stimulation showed a biphasic pattern.Biochemical bases of ion uptake by grapevine seem to be similar to those clarified for annual plants
Clustering dynamics and the location of high-tech firms
The location of productive activities and the emergence of clustering dynamics has been
an important research topic since the early works of Weber (1929) and Marshall (1920
and 1921). This thesis aims at relating the processes of firms' location decision and the
development of high-tech clusters within an encompassing theoretical and empirical
framework.
The thesis shows the empirical relevance of the clustering of high-tech sectors and
highlights the importance of the issue through the construction and use of an original
database on the location of high-tech establishments and employment (at two different
geographical levels) in four major industrialised countries. It also contains a critical
review of a number of different streams of theoretical and empirical literature which are
directly connected, or which have been explicitly put in connection by the author, with
the topic of study. In the thesis we develop a composite modelling framework for
analysing firms' location decisions and the growth of high-tech clusters, and we
empirically test a number of crucial hypotheses in order to draw some guidelines for
economic policy.
The models presented in the theoretical chapter derive from two different streams of
literature. The first derives from the analysis of population ecology, the second from the
theory of innovation diffusion. These modelling frameworks have stressed the existence
of a critical mass and a maximum dimension of the cluster and their effects on the early
and late phases of development within the "life cycle" of a cluster. They also highlighted
the role of rank, stock, order and epidemics effects in the location decision of an
individual firm which has to decide whether to locate into a developing cluster.
The empirical evidence presented in the thesis has focused on the crucial elements of the
location process by verifying the empirical relevance of different locational factors, has
stressed the relative importance of agglomeration versus scale economies in determining
the industrial specialisation of an area, and has measured the competitive effects which
arise between the development of different clusters and the synergistic effects which are
generated within the cluster. Finally the thesis presents empirical evidence which shows
that local competition and industrial specialisation are the key elements for the success
of an industrial cluster.
A final chapter extracts some crucial policy conclusions on the role of entry versus
growth policies, on the different development path that an industrial cluster may follow
depending on the excludability condition, presents an original taxonomy of specific
policies, applies some of these findings to a brief survey of the phenomenon of science
parks and finally produces a series of guidelines for policy makers.
The conclusion summarises the results obtained in the thesis and present a brief agenda
for future research
SERPINB3 delays glomerulonephritis and attenuates the lupus-like disease in lupus murine models by inducing a more tolerogenic immune phenotype
Objective: To explore the effects of SERPINB3 administration in murine lupus models with a focus on lupus-like nephritis. Methods: 40 NZB/W F1 mice were subdivided into 4 groups and intraperitoneally injected with recombinant SERPINB3 (7.5 \u3bcg/0.1 mL or 15 \u3bcg/0.1 mL) or PBS (0.1 mL) before (group 1 and 2) or after (group 3 and 4) the development of proteinuria ( 65100 mg/dl). Two additional mice groups were provided by including 20 MRL/lpr mice which were prophylactically injected with SERPINB3 (10 mice, group 5) or PBS (10 mice, group 6). Time of occurrence and levels of anti-dsDNA and anti-C1q antibodies, proteinuria and serum creatinine, overall- and proteinuria-free survival were assessed in mice followed up to natural death. Histological analysis was performed in kidneys of both lupus models. The Th17:Treg cell ratio was assessed by flow-cytometry in splenocytes of treated and untreated MRL/lpr mice. Statistical analysis was performed using non parametric tests and Kaplan-Meier curves, when indicated. Results: Autoantibody levels and proteinuria were significantly decreased and time of occurrence significantly delayed in SERPINB3-treated mice vs. controls. In agreement with these findings, proteinuria-free and overall survival were significantly improved in SERPINB3-treated groups vs. controls. Histological analysis demonstrated a lower prevalence of severe tubular lesions in kidneys of group 5 vs. group 6. SERPINB3-treated mice showed an overall trend toward a reduced prevalence of severe lesions in both strains. Th17:Treg ratio was significantly decreased in splenocytes of MRL/lpr mice treated with SERPINB3, compared to untreated control mice. Conclusions: SERPINB3 significantly improves disease course and delays the onset of severe glomerulonephritis in lupus-prone mice, possibly inducing a more tolerogenic immune phenotype
Does intentional mean hierarchical? Knowledge flows and innovative performance of European regions
The production of scientific and technical knowledge is mostly concentrated in specific locations (high-tech clusters, innovative industry agglomerations, centres of excellence, and technologically advanced regions). Knowledge flows very easily within regions; however, scientific and technical knowledge also flow between regions. The aim of this paper was to analyse how knowledge flows between regions, and the effect of these flows on the innovative performance, measured by patent applications. We estimate a regional knowledge production function, and, using appropriate spatial econometric estimation techniques, we test the effect of both geographical and relational autocorrelation (measured by participation in EU funded research networks as part of Fifth Framework Programme). We model unobservable structure and link value of knowledge flows in these joint research networks. We find that knowledge flows within inter-regional research networks, along non-symmetrical and hierarchical structures in which the knowledge produced by network participants tends to be exploited by the network coordinator
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