La production de connaissances dans le cluster montréalais de l’aérospatiale. Le cas d’un réseau local d’innovation

L’importance que revêt la localisation des entreprises dans le fonctionnement et la compétitivité de celles-ci amène à porter l’attention sur la problématique des clusters et l’influence qu’ils peuvent avoir sur la production de connaissances. À travers une perspective théorique qui repose sur la prise en compte des travaux portant sur les districts industriels et ceux plus récents, sur les clusters, nous mettons en évidence une évolution conceptuelle du phénomène de la localisation des entreprises. La place qu’occupe la production de connaissances constitue désormais un élément central des travaux récents qui portent sur les districts et les clusters industriels. Notre examen des dynamiques de fonctionnement de ces systèmes permet d’affirmer que la production de connaissances est une caractéristique centrale des clusters ainsi que leur principal avantage compétitif. Étroitement liée aux réseaux inter-organisationnels, la production de connaissances n’est pas un phénomène naturel, elle découle des mécanismes intrinsèques aux clusters, qu’on cherche à mettre en évidence. Pour ce faire, notre méthodologie qui emprunte les principaux repères de l’analyse stratégique des organisations conduit à l’étude du fonctionnement concret d’un réseau local d’innovation, constitué d’entreprises et d’institutions locales présentes dans le cluster montréalais de l’aérospatiale. Un réseau constitué par l’intermédiaire du Consortium de Recherche et d’Innovation en Aérospatiale du Québec, une institution centrale dans le fonctionnement de ce cluster.

Magnetic field-induced cluster formation and variation of magneto-optical signals in zinc-substituted ferrofluids

Fine magnetic particles (size≅100 Å) belonging to the series ZnxFe1−xFe2O4 were synthesized by cold co-precipitation methods and their structural properties were evaluated using X-ray diffraction. Magnetization studies have been carried out using vibrating sample magnetometry (VSM) showing near-zero loss loop characteristics. Ferrofluids were then prepared employing these fine magnetic powders using oleic acid as surfactant and kerosene as carrier liquid by modifying the usually reported synthesis technique in order to induce anisotropy and enhance the magneto-optical signals. Liquid thin films of these fluids were prepared and field-induced laser transmission through these films was studied. The transmitted light intensity decreases at the centre with applied magnetic field in a linear fashion when subjected to low magnetic fields and saturate at higher fields. This is in accordance with the saturation in cluster formation. The pattern exhibited by these films in the presence of different magnetic fields was observed with the help of a CCD camera and was recorded photographically.

Energy-Efficient Cluster based Routing Schemes for Static and Mobile Sensor Networks

The theme of the thesis is centred around one important aspect of wireless sensor networks; the energy-efficiency.The limited energy source of the sensor nodes calls for design of energy-efficient routing protocols. The schemes for protocol design should try to minimize the number of communications among the nodes to save energy. Cluster based techniques were found energy-efficient. In this method clusters are formed and data from different nodes are collected under a cluster head belonging to each clusters and then forwarded it to the base station.Appropriate cluster head selection process and generation of desirable distribution of the clusters can reduce energy consumption of the network and prolong the network lifetime. In this work two such schemes were developed for static wireless sensor networks.In the first scheme, the energy wastage due to cluster rebuilding incorporating all the nodes were addressed. A tree based scheme is presented to alleviate this problem by rebuilding only sub clusters of the network. An analytical model of energy consumption of proposed scheme is developed and the scheme is compared with existing cluster based scheme. The simulation study proved the energy savings observed.The second scheme concentrated to build load-balanced energy efficient clusters to prolong the lifetime of the network. A voting based approach to utilise the neighbor node information in the cluster head selection process is proposed. The number of nodes joining a cluster is restricted to have equal sized optimum clusters. Multi-hop communication among the cluster heads is also introduced to reduce the energy consumption. The simulation study has shown that the scheme results in balanced clusters and the network achieves reduction in energy consumption.The main conclusion from the study was the routing scheme should pay attention on successful data delivery from node to base station in addition to the energy-efficiency. The cluster based protocols are extended from static scenario to mobile scenario by various authors. None of the proposals addresses cluster head election appropriately in view of mobility. An elegant scheme for electing cluster heads is presented to meet the challenge of handling cluster durability when all the nodes in the network are moving. The scheme has been simulated and compared with a similar approach.The proliferation of sensor networks enables users with large set of sensor information to utilise them in various applications. The sensor network programming is inherently difficult due to various reasons. There must be an elegant way to collect the data gathered by sensor networks with out worrying about the underlying structure of the network. The final work presented addresses a way to collect data from a sensor network and present it to the users in a flexible way.A service oriented architecture based application is built and data collection task is presented as a web service. This will enable composition of sensor data from different sensor networks to build interesting applications. The main objective of the thesis was to design energy-efficient routing schemes for both static as well as mobile sensor networks. A progressive approach was followed to achieve this goal.

Performance of correlation functionals in ab initio chemisorption cluster-model calculations: Alkali metals on Si(111)

The performance of different correlation functionals has been tested for alkali metals, Li to Cs, interacting with cluster models simulating different active sites of the Si(111) surface. In all cases, the ab initio Hartree-Fock density has been obtained and used as a starting point. The electronic correlation energy is then introduced as an a posteriori correction to the Hartree-Fock energy using different correlation functionals. By making use of the ionic nature of the interaction and of different dissociation limits we have been able to prove that all functionals tested introduce the right correlation energy, although to a different extent. Hence, correlation functionals appear as an effective and easy way to introduce electronic correlation in the ab initio Hartree-Fock description of the chemisorption bond in complex systems where conventional configuration interaction techniques cannot be used. However, the calculated energies may differ by some tens of eV. Therefore, these methods can be employed to get a qualitative idea of how important correlation effects are, but they have some limitations if accurate binding energies are to be obtained.

An adaptive cluster based routing scheme for mobile wireless sensor networks

Clustering schemes improve energy efficiency of wireless sensor networks. The inclusion of mobility as a new criterion for the cluster creation and maintenance adds new challenges for these clustering schemes. Cluster formation and cluster head selection is done on a stochastic basis for most of the algorithms. In this paper we introduce a cluster formation and routing algorithm based on a mobility factor. The proposed algorithm is compared with LEACH-M protocol based on metrics viz. number of cluster head transitions, average residual energy, number of alive nodes and number of messages lost

Efficacy of Cluster- Based Approach for the revival of Handloom Co-operative Societies in Kerala- with special reference to Thiruvananthapuram and Kannur Districts

one of the key sectors, identified by the Department of Industries Government of Kerala, for the cluster development initiative is Handloom, which gives employment to over over 50,000 people directly. Despite its age old tradition and fame, the performance of the sector vis-à-vis power looms is not very rosy owing to (i) competition from cheap power loom cloth from other states (ii) scarcity of quality yarn (iii) price escalation of yarn, dyes, chemicals and other raw materials (iv) the shrinking market for handlooms in Kerala (v) non-demand based production and inadequacy of new designs and (vi) inefficiencies in the system, particularly in the co-operative sector. Cluster based approach is adopted in the handloom sector with the objective of providing necessary support mechanism to come out of the crisis that the sector faces now. While four cluster schemes are being implemented in Kerala, it is under IHDS-CDP that the State got a sizeable number of clusters benefiting a large number of societies and weavers- 24 handloom clusters, bringing 152 handloom co-operative societies and over 19,800 handloom workers under the Programme. This research attempts to revisit the underlying rationale and context of the new direction and would attempt to broadly analyze the growth trends under the influence of cluster model adopted by the State IHDS-CDP for the revival of handloom sector through a detailed study of the handloom co-operative societies in Kerala. If handloom sector in Kerala can be revived using cluster based approach, it can be easily concluded that cluster is capable of taking the MSME in Kerala to a ‘high growth path.’ The study is aimed at understanding how best clusters emerge as appropriate industrial organization suitable for the current global structure of manufacture

Energy Aware Cluster-based Multihop Routing Protocol for Sensor Networks

Clustering combined with multihop communication is a promising solution to cope with the energy requirements of large scale Wireless Sensor Networks. In this work, a new cluster based routing protocol referred to as Energy Aware Cluster-based Multihop (EACM) Routing Protocol is introduced, with multihop communication between cluster heads for transmitting messages to the base station and direct communication within clusters. We propose EACM with both static and dynamic clustering. The network is partitioned into near optimal load balanced clusters by using a voting technique, which ensures that the suitability of a node to become a cluster head is determined by all its neighbors. Results show that the new protocol performs better than LEACH on network lifetime and energy dissipation

Studies on the optical band gap and cluster size of the polyaniline thin films irradiated with swift heavy Si ions

Polyaniline thin films prepared by RF plasma polymerisation were irradiated with 92MeV Si ions for various fluences of 1 1011, 1 1012 and 1 1013 ions/cm2. FTIR and UV–vis–NIR measurements were carried out on the pristine and Si ion irradiated polyaniline thin films for structural evaluation and optical band gap determination. The effect of swift heavy ions on the structural and optical properties of plasma-polymerised aniline thin film is investigated. Their properties are compared with that of the pristine sample. The FTIR spectrum indicates that the structure of the irradiated sample is altered. The optical studies show that the band gap of irradiated thin film has been considerably modified. This has been attributed to the rearrangement in the ring structure and the formation of CRC terminals. This results in extended conjugated structure causing reduction in optical band gap

Magnetic field-induced cluster formation and variation of magneto-optical signals in zinc-substituted ferrofluids

Fine magnetic particles (sizeffi100A ˚ ) belonging to the series ZnxFe1 xFe2O4 were synthesized by cold co-precipitation methods and their structural properties were evaluated using X-ray diffraction. Magnetization studies have been carried out using vibrating sample magnetometry (VSM) showing near-zero loss loop characteristics. Ferrofluids were then prepared employing these fine magnetic powders using oleic acid as surfactant and kerosene as carrier liquid by modifying the usually reported synthesis technique in order to induce anisotropy and enhance the magneto-optical signals. Liquid thin films of these fluids were prepared and field-induced laser transmission through these films was studied. The transmitted light intensity decreases at the centre with applied magnetic field in a linear fashion when subjected to low magnetic fields and saturate at higher fields. This is in accordance with the saturation in cluster formation. The pattern exhibited by these films in the presence of different magnetic fields was observed with the help of a CCD camera and was recorded photographically

Theory for Optical Absorption in Small Clusters: Dependence on Atomic Structure and Cluster Size

We present a theory which permits for the first time a detailed analysis of the dependence of the absorption spectrum on atomic structure and cluster size. Thus, we determine the development of the collective excitations in small clusters and show that their broadening depends sensitively on the tomic structure, in particular at the surface. Results for Hg_n^+ clusters show that the plasmon energy is close to its jellium value in the case of spherical-like structures, but is in general between w_p/ \wurzel{3} and w_p/ \wurzel{2} for compact clusters. A particular success of our theory is the identification of the excitations contributing to the absorption peaks.

Femtosecond probing of sodium cluster ion Na_n ^+ fragmentation

We report on the first femtosecond time-resolved experiments in cluster physics. The photofragmentation dynamics of small sodium cluster ions Na_n ^+ have been studied with pump-probe techniques. Ultrashort laser pulses of 60-fs duration are employed to photoionize the sodium clusters and to probe the photofragments. We find that the ejection of neutral dimer Na_2 and, observed for the first time, neutral trimer Na_3 photofragments occur on ultrashort time scales of 2.5 and 0.4 ps, respectively. This and the absence of cluster heating reveals that direct photoinduced fragmentation processes are important at short times rather than the statistical unimolecular decay.

Femtosecond dynamics of molecular and cluster ionization and fragmentation

The real-time dynamics of molecular (Na_2 . Na_3) and cluster Na_n (n=4-2l) multiphoton ionization and -fragmentation has been studied in beam experiments applying femtosecond pump-probe techniques in combination with ion and electron spectroscopy. Wave packet motion in the dimer Na_2 reveals two independent multiphoton ionization processes while the higher dimensional motion in the trimer Na_3 reflects the chaotic vibrational motion in this floppy system. The first studies of cluster properties (energy, bandwidth and lifetime of intermediate resonances Na^*_n) ) with femtosecond laser pulses give a striking illustration of the transition from "molecule-like" excitations to "surfaceplasma"-like resonances for increasing cluster sizes. Time-resolved fragmentation of cluster ions Na_n^* indicate that direct photo-induced fragmentation processes are more important at short times than the statistical unimolecular decay.