A low-temperature dynamic mode scanning force microscope operating in high magnetic fields

A scanning force microscope was implemented operating at temperatures below 4.2K and in magnetic fields up to 8T. Piezoelectric quartz tuning forks were employed for non optical tip-sample distance control in the dynamic operation mode. Fast response was achieved by using a phase-locked loop for driving the mechanical oscillator. Possible applications of this setup for various scanning probe techniques are discussed.Comment: 5 pages, 5 figures, submitted to "Review of Scientific Instruments

Local Public Investment and Competition for a Firm

Most of the work in the field of competition between jurisdictions for the attraction of a large plant focuses on financial offers, bids or tax holidays. In this paper we add to the competition game an initial stage in which jurisdictions can invest in an infrastructure capital to enhance their attractiveness and modify the outcome of the competition stage. We characterize the Nash equilibrium of this game. In an example we show how the parameters of the model change the outcome of the game. In particular, the size of a jurisdiction is a powerful attraction force for the firm but it can be bypassed by a well specialized infrastructure capital, even if the competing jurisdiction is big.

Industrial Clusters and the Knowledge Based Economy : from open to distributed structures ?

Document de Travail GREQAM ; 2007-07During the recent years, clusters have been at the heart of a vast literature supposed to bring new arguments and perspectives to local development preoccupations. Two complementary factors are stressing for firms and territories the importance of governing the interactions of industrial actors: the globalisation of the economy and the technology and the emergence of a knowledge based economy. In local systems, agents are mostly connected with agents situated in their spatial proximity, while these local networks, as open systems, benefit from the long distance connections that some of their members are able to activate. Co-location of actors in a geographical proximity by itself is not a sufficient condition for co-ordination but can contribute to its efficiency, provided the existence of other shared dimensions among agents: organic level, representations, projects, ... As far as efficiency and performances of "classical" clusters are not only the result of the intensity and quality of internal but also external interactions and coordination, into which extent can we still consider the relevance of interaction structures restricted to bounded geographical areas? In this paper we turn our attention to the way industrial actors take into account the question of the local-global articulation for the strategic building of their own ego-network, that is the set of links they may build in order to achieve efficient interactions with partners and competitors. Thus interfaces between local and global relationships are a key feature that can be achieved through different approaches. To this aim we introduce the two concepts of knowledge gatekeeper and temporary proximity that appear as providing alternative approaches of actors partnering, likely to provide a better flexibility in the local-global trade-off. We will then present the basic form of the ego-networks on which the individual firm is able to build her relational neighbourhood. This raises the question of the combination of individual ego-networks into a consistent networked structure into which local networks are articulated by the way of local-global interfaces. On this basis we present a typology of the basic new forms of clustering where time and space can be alternatively and complementarily combined in order to achieve more flexibility and costs reduction of the localisation game

The emergence and renawal of forms of industrial coordination in the Provence-Alpes Côte d'Azur (PACA) région

Disponible en version françaiseDynamique territoriale; Reconversion industrielle; Système productif localisé; District industriel; Comparaison; Industrie de la microélectronique; Gardanne; Industrie de la construction navale; La Ciotat; Industrie aromatique et de la parfumerie; Grasse; Industrie agroalimentaire; Vallée du Rhône; Région PACA; France

Dynamics of quartz tuning fork force sensors used in scanning probe microscopy

We have performed an experimental characterization of the dynamics of oscillating quartz tuning forks which are being increasingly used in scanning probe microscopy as force sensors. We show that tuning forks can be described as a system of coupled oscillators. Nevertheless, this description requires the knowledge of the elastic coupling constant between the prongs of the tuning fork, which has not yet been measured. Therefore tuning forks have been usually described within the single oscillator or the weakly coupled oscillators approximation that neglects the coupling between the prongs. We propose three different procedures to measure the elastic coupling constant: an opto-mechanical method, a variation of the Cleveland method and a thermal noise based method. We find that the coupling between the quartz tuning fork prongs has a strong influence on the dynamics and the measured motion is in remarkable agreement with a simple model of coupled harmonic oscillators. The precise determination of the elastic coupling between the prongs of a tuning fork allows to obtain a quantitative relation between the resonance frequency shift and the force gradient acting at the free end of a tuning fork prong.Comment: 16 pages, 6 figures, 2 Table

Globalizacion y economias locales : entre fuerzas centrifugas y centripetas

International audienceSans résumé

Infrastructures publiques et politiques de développement décentralisées

This article provides a theoretical contribution on the issue of under-investment of public capitals. In a differential game of accumulation of capital between two jurisdictions, the open loop Nash equilibrium and the centralized solution converge towards their respective steady states. In the long run we characterize the inefficiency of the Nash equilibrium using as a benchmark case the utilitarian centralized outcome. When the stocks of infrastructures are strategic complements, the jurisdictions under-invest (over-invest) in situations with negative (positive) externalities. When the stocks are strategic substitutes the same results hold for similar jurisdictions. On the contrary when the cost structures of the jurisdictions are different enough, it is shown within an example that the low-cost jurisdiction under-invests whereas the high-cost jurisdiction over-invests. We then broach briefly the economic policy implications of these results. Cet article apporte une contribution théorique au débat sur le sous-investissement en capitaux publics. Il utilise pour cela un jeu différentiel d’accumulation de capitaux entre deux collectivités. Dans ce jeu l’équilibre de Nash en boucle ouverte et la solution centralisée du jeu convergent à long terme vers un régime stationnaire. Dans le long terme nous étudions la nature de l’inefficacité de l’équilibre de Nash en prenant comme référence la solution centralisée utilitariste. Lorsque les stocks d’infrastructures sont des compléments stratégiques, les collectivités surinvestissent (sous-investissent) en présence d’externalités négatives (positives). Lorsque les stocks d’infrastructures sont des substituts stratégiques, les mêmes résultats restent vrais si les collectivités sont similaires. En revanche, nous montrons dans un exemple que lorsque les collectivités ont des structures de coûts assez différentes, la collectivité qui a le coût le plus faible sous-investit tandis que la collectivité qui a le coût le plus fort surinvestit. Nous discutons ensuite brièvement les implications de ces résultats en termes de politiques économiques.

Operation characteristics of piezoelectric quartz tuning forks in high magnetic fields at liquid helium temperatures

Piezoelectric quartz tuning forks are investigated in view of their use as force sensors in dynamic mode scanning probe microscopy at temperatures down to 1.5 K and in magnetic fields up to 8 T. The mechanical properties of the forks are extracted from the frequency dependent admittance and simultaneous interferometric measurements. The performance of the forks in a cryogenic environment is investigated. Force-distance studies performed with these sensors at low temperatures are presented

Mobilisation d'acteurs et enjeux de qualification et de formation dans le renouvellement du tissu productif régional (Local collective actions, specification of skills and training in the renewal of local productive fabric)

La communication s'intéresse au renouvellement du tissu productif dans quatre sites d'une région du sud de la France, historiquement structurés par une activité productive. Dans chacun d'eux, la présence de ressources en connaissances et savoir-faire (situées ici dans les professionalités et qualifications des personnes, l'offre de formation, les spécialités et savoir-faire des entreprises et des dirigeants) apparaît comme un enjeu central de leur compétitivité mais qui pose partout problème. C'est un levier de l'action locale et l'objet d'une mobilisation collective s'inscrivant au coeur d'une dynamique visant à favoriser des forces centripètes (attirer et maintenir des activités) mais dont laportée est confrontée à des forces centrifuges, effets directs des processus de globalisation par lesquels ces sites sont traversés et à des effets de dépendance de sentier, issus de leur histoire. Ces terrains invitent à considérer que « les capacités collectives locales à construire et à faire évoluer une ensemble de ressources » doivent être entendues au regard des rapports entretenus par les forces en présence, qui en rendent les issues incertaines. Cette tension entre forces centripètes, forces centrifuges et de dépendance de sentier nous apparaît être au coeur de l'évolution de certaines formes d'économies locales « traditionnelles » comme celles qui nous intéressent ici.Système productif local; Reconversion industrielle; Bassin houillier; Industrie de la microélectronique; Gardanne; Chantier de construction navale; La Ciotat; Industrie de la parfumerie; Grasse; Industrie agroalimentaire; Vallée-du-Rhône; Région PACA; France

Carbon fibre tips for scanning probe microscopy based on quartz tuning fork force sensors

We report the fabrication and the characterization of carbon fibre tips for their use in combined scanning tunnelling and force microscopy based on piezoelectric quartz tuning fork force sensors. We find that the use of carbon fibre tips results in a minimum impact on the dynamics of quartz tuning fork force sensors yielding a high quality factor and consequently a high force gradient sensitivity. This high force sensitivity in combination with high electrical conductivity and oxidation resistance of carbon fibre tips make them very convenient for combined and simultaneous scanning tunnelling microscopy and atomic force microscopy measurements. Interestingly, these tips are quite robust against occasionally occurring tip crashes. An electrochemical fabrication procedure to etch the tips is presented that produces a sub-100 nm apex radius in a reproducible way which can yield high resolution images.Comment: 14 pages, 10 figure