341 research outputs found
Why are technological spillovers spatially bounded ? A market orientated approach.
According to empirical evidence, technological spillovers are spatially bounded. This is one of the main reasons why firms are induced to locate in close prox-imity despite tough competition. This paper is an attempt to endogenize such spillovers. For that purpose, we try to explain why spatial proximity gives more incentives to competing firms to share knowledge. We show that spatial proxim-ity is the best way for firms to prevent free-riding in case of knowledge sharing. Indeed, Ăercer competition impedes free riding provided that such a behavior dampens firms efficiency and have a dramatic effect on profits. Moreover, our results have important implications for regional policy. We point out that a slight decrease in transport costs triggers spatial polarization which implies knowledge sharing and thereby enhances innovation. A more dramatic decrease in transport costs attains both the objectives of increasing innovation and regional equity.
Coupling between 4f and itinerant electrons in SmFeAsO1-xFx (0.15 < x < 0.2) superconductors: an NMR study
F NMR measurements in SmFeAsOF, for ,
are presented. The nuclear spin-lattice relaxation rate increases upon
cooling with a trend analogous to the one already observed in
CeCuAu, a quasi two-dimensional heavy-fermion intermetallic
compound with an antiferromagnetic ground-state. In particular, the behaviour
of the relaxation rate either in SmFeAsOF or in
CeCuAu can be described in the framework of the self-consistent
renormalization theory for weakly itinerant electron systems. Remarkably, no
effect of the superconducting transition on F is detected, a
phenomenon which can hardly be explained within a single band model.Comment: 4 figure
Experimental confirmation of the low B isotope coefficient in MgB2
Recent investigations have shown that the first proposed explanations of the
disagreement between experimental and theoretical value of isotope coefficient
in MgB2 need to be reconsidered. Considering that in samples with residual
resistivity of few mu-Ohm cm critical temperature variations produced by
disorder effects can be comparable with variations due to the isotopic effect,
we adopt a procedure in evaluating the B isotope coefficient which take account
of these effects, obtaining a value which is in agreement with previous results
and then confirming that there is something still unclear in the physics of
MgB2.Comment: 8 pages, 3 figures Title has been changed A statement has been added
in page 7 of the pdf file "Finally we would..." Reference 21 has been added
Figure 1 anf Figure 2 have been change
2D equivalent linear analysis for the seismic vulnerability evaluation of multi-propped retaining structures
The evaluation of the seismic behaviour of underground structures represents one of the most actual seismic geotechnical and structural engineering research topics about the study of the complex phenomena of soil-structural interaction. In the last decades, different types of simplified and numerical approaches have been developed for the correct analysis of the seismic vulnerability of these important infrastructures and a series of laboratory tests for the seismic behaviour characterization of the soils (resonant column test, etc.) and of the coupled soil-structure system (centrifuge test, etc.) have been conducted, especially after the recent strong earthquakes where the underground structures have been subjected to significant damages. In the same way, in the last few years, the International Codes are beginning to pay attention to the concepts of the seismic design of these structures. Despite the significant development of knowledge, described above, still remain open several uncertainties of the correct reproduction of the underground structures behaviour under seismic load. In this paper, the evaluation of the seismic behaviour of a multi-propped retaining structure was conducted, considering the soil-structure interaction effects. The results of the 2D equivalent linear analysis are analysed in terms of bending moment acting on the concrete retaining walls.LâĂ©valuation du comportement sismique des structures souterraines reprĂ©sentent un des sujets de
recherche les plus courants sismique, gĂ©otechnique et de construction, qui concerne lâĂ©tude du phĂ©nomĂšne
complexe de lâinteraction sol-structure. Pendant les derniĂšres dĂ©cennies, diffĂ©rents types dâapproches simples et
numeriques ont été développés pour une analyse exacte de la vulnérabilité sismique de ces infrastructures
importantes et encore une série de tests de laboratoire pour la caractérisation du comportement sismique du sols
(test de colonne résonnante etc.) et du systÚme couplé du sol-structure (test de centrifugation etc.) ont été menées,
aprĂšs le fort tremblement de terre oĂč les structures souterraines ont subi des dommages importants. De la mĂȘme
maniĂšre, pendant les dĂšrnieres annĂ©es, les Codes Internationales ont commencĂ© a prĂȘter plus dâattention aux
concepts de désign sismique de ces structures. Malgré la considÚrable connaissance, décrit ci-dessus, il y a quand
mĂȘme de lâincertitude sur la correcte reproduction du comportement des structures sous charge sismique. Dans
cet article, il a Ă©tĂ© menĂ© lâevaluation du comportement sismique des structures de soutenement multi-etayĂ©,
considĂ©rant que les effets de lâinteraction sol-structure. Les resultats de lâanalyse linĂ©aire 2D equivalente sont
analysées en termes de moment de flexion agissant sur les murs de soutÚnement en béton
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Strong ground motion characteristics of 2016 Central Italy earthquakes and implications for ground motion modeling
The 2016 Central Italy earthquake sequence produced three mainshocks: (1) M6.1 24 August, (2) M5.9 26 October, and (3) M6.5 30 October. Each mainshock was followed by many aftershocks, some of which with M > 5.0. All earthquake events occurred on southeast-northwest trending normal faults. As part of reconnaissance activities of these events performed by the Geotechnical Extreme Events Reconnaissance Association (GEER), ground motion data was processed and analyzed. After processing all data using procedures developed during the latest Next Generation Attenuation (NGA-West2) project, we analyze strong motion characteristics of all three mainshocks, two selected large aftershocks (M5.3 24 August and M4.8 26 August) and a foreshock (M5.4 26 October). Our analysis shows that stations near the hanging wall, exhibit fling-step in some cases but no obvious rupture directivity effects. We compare ground motion intensity measures (including peak ground acceleration and velocity, PGA and PGV, respectively) to Italy-specific and global ground motion models. Overall, the data exhibit fast attenuation at large distance (>100 km), which is captured by Italy-adjusted global models, but not by Italy-specific models. We also found that global models tend to over-predict ground motions at short periods. Both features were also observed from the 2009 LâAquila earthquake data and may represent regional features. We estimate the spatial distribution of PGA for the three mainshocks by means of a Kriging analysis performed on within-event residuals using a global semi-variogram model. We found that the ground motion is most intense south-west of the Mt.Vettore - Mt.Bove normal fault. Given the importance of Italian normal fault earthquakes in worldwide ground motion databases, this data set is of global significance for studies of normal fault ground motions
Il ruolo degli effetti di sito sulla risposta strutturale degli edifici nella conca aquilana
Il terremoto de LâAquila del 6 aprile 2009 Ăš stato significativamente caratterizzato dagli effetti di sito, evidenziati sia dalla variabilitĂ delle registrazioni accelerometriche in zona near fault che dalla disuniforme distribuzione del danno rilevato. In particolare, nel quartiere aquilano di Pettino, in corrispondenza di un complesso residenziale composto da sette edifici della stessa tipologia strutturale, Ăš stato osservato un danneggiamento molto diversificato.
La nota riporta i risultati di una serie di analisi di risposta sismica locale 1D, condotte in corrispondenza di alcuni degli edifici del quartiere, per i quali si disponeva di indagini geotecniche di dettaglio, finalizzate a valutare lâinfluenza degli effetti di sito sulla risposta delle strutture. I risultati delle analisi condotte in condizioni di campo libero hanno mostrato significative amplificazioni del moto proprio in corrispondenza delle frequenze fondamentali del moto di input. Le analisi del sistema sottosuolo-edificio, condotte mediante lâutilizzo di un codice con formulazione a masse concentrate hanno inoltre consentito di verificare lâincidenza dellâinterazione inerziale sul moto in superficie, nonchĂ© di riprodurre in forma semplificata il meccanismo di piano soffice osservato
Nanoscopic coexistence of magnetic and superconducting states within the FeAs layers of CeFeAsO1-xFx
We report on the coexistence of magnetic and superconducting states in
CeFeAsO1-xFx for x=0.06(2), characterized by transition temperatures T_m=30 K
and T_c=18 K, respectively. Zero and transverse field muon-spin relaxation
measurements show that below 10 K the two phases coexist within a nanoscopic
scale over a large volume fraction. This result clarifies the nature of the
magnetic-to-superconducting transition in the CeFeAsO1-xFx phase diagram, by
ruling out the presence of a quantum critical point which was suggested by
earlier studies.Comment: 4 pages, 3 figs, accepted for publication as PRB Rapid com
Vortex dynamics and irreversibility line in optimally doped SmFeAsO0.8F0.2 from ac susceptibility and magnetization measurements
Ac susceptibility and static magnetization measurements were performed in the optimally doped SmFeAsO0.8F0.2 superconductor. The field-temperature phase diagram of the superconducting state was drawn, and, in particular, the features of the flux lines were derived. The dependence of the intragrain depinning energy on the magnetic field intensity was derived in the thermally activated flux-creep framework, enlightening a typical 1/H dependence in the high-field regime. The intragrain critical current density was extrapolated in the zero-temperature and zero-magnetic-field limit, showing a remarkably high value Jc0(0)~2Ă107 A/cm2, which demonstrates that this material is rather interesting for potential future technological applications
Il nuovo Foglio Geologico 438 âBariâ in scala 1:50.000. Un importante contributo per la conoscenza geologica dellâarea metropolitana di Bari
I risultati del rilevamento geologico del Foglio 438 âBariâ in scala 1:50.000 effettuato nellâambito del progetto CARG (Cartografia Geologica) mostrano numerose differenze rispetto a quanto riportato nella Cartografia Ufficiale in scala 1:100.000, che rappresenta tuttora la cartografia di riferimento. Le differenze rilevate, o comunque le ulteriori informazioni ottenute dai nuovi studi, sono risultate molto significative soprattutto in corrispondenza dellâarea metropolitana di Bari recentemente soggette ad intensa urbanizzazione ed espansione. Tenuto conto dei tempi necessari per poter divulgare tali dati, si Ăš ritenuto importante, in occasione del Convegno sulla âGeologia urbana di Bari ed area metropolitanaâ, presentare una carta in scala 1:25.000 del territorio metropolitano barese, dove emergessero tutte le novitĂ dei nuovi rilevamenti, al fine di poter fornire uno strumento utile a tutte le figure che operano sul territorio quotidianamente e che necessitano avere dati aggiornati
Origin of Tc Enhancement Induced by Doping Yttrium and Hydrogen into LaFeAsO-based Superconductors: 57Fe, 75As, 139La, and 1H-NMR Studies
We report our extensive 57Fe-, 75As-, 139La-, and 1H-NMR studies of
La_{0.8}Y_{0.2}FeAsO_{1-y} (La_{0.8}Y_{0.2}1111) and
LaFeAsO_{1-y}H_{x}(La1111H), where doping yttrium (Y) and hydrogen (H) into
optimally doped LaFeAsO_{1-y} (La1111(OPT)) increases T_c=28 K to 34 and 32 K,
respectively. In the superconducting (SC) state, the measurements of
nuclear-spin lattice-relaxation rate 1/T_1 have revealed in terms of a multiple
fully gapped s_\pm-wave model that the SC gap and T_c in La_{0.8}Y_{0.2}1111
become larger than those in La1111(OPT) without any change in doping level. In
La1111H, the SC gap and T_c also increase slightly even though a decrease in
carrier density and some disorders are significantly introduced. As a
consequence, we suggest that the optimization of both the structural parameters
and the carrier doping level to fill up the bands is crucial for increasing T_c
among these La1111-based compounds through the optimization of the Fermi
surface topology.Comment: 4 pages, 4 figures, 1 table, to be published in J. Phys. Soc. Jpn,
Vol. 79, No. 1
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