Materials Engineering

The formulations of existing free dendritic growth models were compared, and an extended model was proposed that employs a subregular solution model to compute the driving force for dendritic growth without Henrian restrictions. These models were also applied to a Ag-15 mass pct Cu alloy to numerically compare their predictions. Models that address only the thermal, solutal, and curvature supercoolings do not properly account for the interface kinetics, even with modifications with the kinetic partition coefficient and liquidus slope. It is only in models that account for the interfacial driving force, −ΔG*, that the kinetic supercooling is properly addressed. All of the models in comparison yield numerically similar predictions for the solutal growth regime, but models that employ the kinetic partition coefficient and liquidus slope, but do not address the interfacial driving force, fail to correctly describe the thermal control regime. The solutal-to-thermal transition is characterized by a rapid increase of interfacial driving force, which causes the tip temperature T* to increase with increasing growth rate V. The criterion for the transition stage is given as dln(−ΔG*)/dlnV>1.

The synthesis, electrochemical and spectroscopic properties of a series of thiophene-substituted 1,3-dithiole-2-ones is described. The derivatives Th-3,3, Th-2,2, Th-2,3, Th-3,3(2,2′-Me), and Th3,3-(2,5,2′,5′-Me), have been successfully polymerized by cyclic voltammetry. From the UV−visible spectra of the neutral films, it was determined that PTh-3,3, PTh-2,2 and PTh-2,3 have a bandgap of 2.04, 2.30, and 2.18 eV, respectively. The voltammetric response of Th-3,3(2,2′-Me) was noticeably different from the other polymers. The SNIFTIRS data suggested that Th-3,3(2,2′-Me) was formed by bonding via the β-positions of the thiophene ring, resulting in a poorly conductive polymer. The in situ solid-state modification of PTh-3,3 to produce a new TTF-derivatized polythiophene was carried out. The cyclic voltammetry of the modified polymer confirmed the inclusion of TTF into the backbone of the film.

"At the end of their service life, wood-based panels become eventually waste wood. Deploying in landfills is no longer considered as an acceptable solution for their handling due to the high organic load included. The recycling of this waste to be employed as raw material for the wood panel industry, which traditionally makes use of wood processing residues, has hence gained more importance and been examined from earlier times.
Technical problems and the lack of enforcing legislative regulations have delayed, however, the industrial implementation of the new technologies proposed. Recent research efforts
enabled the development of a new process for the recycling of end-use wood panels into new marketable fibreboards. This patent pending process is based on the refiner technique and
allows the use of mixtures of fresh wood and waste panel chips as a raw material for dry process fibreboard production. The process is applicable in existing fibreboard plants with only minor operation modifications and therefore, there is no need of major capital investment in additional equipment to effect the recycling. At the refining stage, chemical agents are employed and the process enables the use of significant amounts of waste
material replacing over 20% of the wood feed and providing significant savings. The aim of the present work was to validate the industrial applicability of the new process in the recycling of waste medium-density fibreboards. The new fibreboards obtained during the industrial scale tests were of acceptable quality, and the testing results revealed that under
conventional gluing and pressing conditions, the process effectively recycles the waste boards into new ones at least at 25% wood substitution level. Further validation and
optimisation work is underway in the direction of using other waste panel types and also increasing the level of waste in the feed material."

A statistical model for prediction of the maximum extent of the swelling of wood in organic liquids is proposed in this work. Solvent basicity, solvent molecular volume, and density of wood appeared to be the most important parameters in the proposed model. The addition of the hydrogen bonding capability parameter did not significantly improve the model.

The swelling of wood in organic liquids at elevated temperatures has been investigated with the use of a computerized linear variable displacement transformer (LVDT). Wood swelled extremely fast at high swelling temperatures. The rate of wood swelling in organic liquids showed a strong dependence on temperature which closely obeyed the classical Arrhenius equation. This strict linear dependence of wood swelling on the temperature clearly suggests a chemical mechanism. Activation energies for wood swelling (Ea) in several chemical classes of organic liquids have been obtained from Arrhenius equation plots. A strong linear relationship was found to exist between Ea and solvent molecular weight. Removal of extractives greatly enhanced the maximum tangential swelling of wood, especially for sugar maple. There was also a significant increase in the wood swelling rate after removal of extractives.

Maximum liquid-holding capacities of various compressed fibers in water and in a series of various organic liquids have been investigated. The maximum liquid-holding capacity versus bulk density relationships gave polynomial curves, generally with a peak. Good relative correlations for cellulose, compressed fiber pellets and wood were found for the series of liquids tested. In general, liquids that swelled wood to a low to medium range (up to 6%) did not swell appreciably a -cellulose and sulfite pulp, while good to excellent wood-swelling agents swelled all the fibers very significantly. It was also found that the hydrogen-bonding parameter of the swelling liquid was the most important factor. The swelling rate of various compressed fiber systems in organic liquids was dramatically increased by raising the temperature. Activation energies and molar volume of the swelling liquid were linearly correlated.

Thermodynamic work of adhesion, contact angle, wettability and acidbase contributions of the wetting of four North American wood species were determined using the Wilhelmy technique. The wetting angles with water varied from 60 ° for Sitka spruce to 74 ° for Douglas-fir. The wood surfaces had a strong acidic character since the greatest interactions for all the wood pecies occurred with formamide (basic probe) while lesser interactions were obtained withethylene glycol (acidic probe). In addition, dispersive and polar surface free energies of wood, 7 d and 7 p respectively, were determined using Wu's simultaneous equations. In general, 75 to 80% of the total surface free energy of wood was due to dispersion forces. Specific wettabilities of wood and advancing contact angles in thirty various organic liquids were also evaluated.

"The rate and maximum swelling of several North American wood species in 40 organic liquids have been obtained with a computer interfaced linear variable displacement transformer. Since wood swells very fast in some organic liquids, even at room temperature, this apparatus made it possible to obtain
accurate rate data on the swelling of wood in organic liquids. It was found that many similarities existed between wood and cellulose maximum swelling within various solvent chemical classes. Hence, it appears that cellulose is the primary wood polymer responsible for the major amount of swelling of wood. In general, all the liquids, with a molar volume greater than 100 cc or with a small hydrogen bonding parameter, caused very little equilibrium swelling. The logarithm of the rate of wood swelling
(In k) in the liquids was inversely correlated with the solvent molecular weight as well as with the molar volume of the solvent, that is, the larger the solvent molecular size, the slower the rate of swelling. The Ink also was strongly correlated with the maximum tangential swelling of wood. The maximum tangential swelling for all wood species was linearly correlated with the solvent basicity (donor number). Other solvent properties such as volubility parameter, dipole moment, dielectric constant, and surface tension showed very weak correlations with the maximum tangential swelling of wood in organic liquids."

"The rate and maximum swelling of several North American wood species in water have been obtained with a computer interfaced linear variable displacement transformer. Since wood swells extremely fast in water even at room temperature, this apparatus made it possible for the first time, to obtain accurate rate data on the swelling of wood in water. The strict linear dependence of swelling on the temperature suggests a chemical mechanism.
The activation energies obtained from Arrhenius plots ranged from 32.2 KJ/ mole for sitka spruce to 47.6 KJ/ mole for sugar maple. Although the two hardwoods exhibited greater maximum tangential swelling compared with the two softwoods, the maximum swelling appears to be correlated with the wood density. Generally both the rate and maximum swelling of the woods were increased by removal of extractives and the activation energies were reduced."

A detailed structural analysis of Mg-Ti-H thin films reveals the presence of a chemically partially segregated but structurally coherent metastable phase. By combining X-Ray Diffraction and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy on MgyTi1-yHx thin films we find non-zero Chemical Short-Range Order (CSRO) parameters for all the compositions measured. Despite the positive enthalpy of mixing of Mg and Ti the degree of ordering does not increase upon loading and unloading with hydrogen. The robustness of this system and the fast and reversible kinetics of hydrogen loading and unloading are caused by the formation of nanoscale compositional modulations in the intermetallic alloy. This microstructure is responsible for the exceptional properties of MgyTi1-yHx thin films. It also shows that reversible metastable metal-hydrides offer new possibilities for hydrogen storage, beyond the limits imposed by thermodynamic equilibrium.

The structural, optical, and electrical transformations induced by hydrogen absorption and/or desorption in Mg-Ti thin films prepared by co-sputtering of Mg and Ti are investigated. Highly reflective in the metallic state, the films become highly absorbing upon H absorption. The reflector-to-absorber transition is fast, robust, and reversible over many cycles. Such a highly absorbing state hints at the coexistence of a metallic and a semiconducting phase. It is, however, not simply a composite material consisting of independent MgH2 and TiH2 grains. By continuously monitoring the structure during H uptake, we obtain data that are compatible with a coherent structure. The average structure resembles rutile MgH2 at high Mg content and is fluorite otherwise. Of crucial importance in preserving the reversibility and the coherence of the system upon hydrogen cycling is the accidental equality of the molar volume of Mg and TiH2. The present results point toward a rich and unexpected chemistry of Mg-Ti-H compounds.

The project discussed in this paper has been conducted as part of the Autonomatic research cluster based at University College Falmouth. The cluster is focused on research projects that explore the use of digital production technologies within the context of designer maker and craft practice.

My project is concerned with developing more direct control of processes that are typically automated by CAD software and CAM tools. I believe the use of these standardised tools limit the ability of the maker to create unique visual vocabularies.

It is possible to view the aesthetic qualities emerging in the new genre of ‘digital craft’ - such as the use of triangulation and the quality of line produced by generic pre-set machine parameters - as a temporary phase in the digital craft timeline. As more makers adopt digital technologies, we may discover that these visual aesthetic qualities are more attributable to the technology than the maker rather than being understood as unique. The author believes it is therefore important for makers wishing to further their practice in this field to seek ways in which they can gain greater control over the processes and tools they are using.

This paper presents research that explores ways in which programmed mathematical elements in 3D CAD can be deconstructed and manipulated throughout the design and production phases. Employing an iterative designing and making process I have used this ‘hand’ manipulated CAD data to drive CNC machine tools in highly specified ways. This has lead to an in depth understanding of the inter-relationship between CAD and CAM as intrinsic to the development of unique aesthetic qualities. The development of a dialogue between CAD code and CNC tooling has resulted in a greater level of control enabling the realisation of complex and completely controlled patterning on 3D forms that go beyond the restrictions of standard toolsets.

This research has resulted in a range of 3D aluminium sample pieces that I have used to create a visual knowledge bank which documents the relationship between software input, machine parameters and their effects on the visual form. This knowledge has been applied to my working digital design practice enabling me to create aluminium platters and beakers that counter the affects of automation.

This paper aims to offer other makers methods which allow the potential for 'hacking' into code in order to expand the possibilities for control and creative engagement with digital tools and thereby offering more unique opportunities for developing visual vocabularies than using standard toolsets alone.

Piezoelectric quaru crystals capable of generating ultrasonic shear waves have long been used to detect mass changes that result from deposition of metal layers, using the Sauerbrey equation to relale the observed changes in resonant frequenry to the corresponding changes in mass. More recently such crystals have been employed in

We developed a theory for the anomalous admittance and the constant phase angle behavior of an irregular interface operating under diffusion controlled charge-transfer condition. Interfacial irregularity is modeled as a realistic random fractal, which is characterized as statistically isotropic self-affine fractals on limited length scales. The power spectrum of such a surface fractal is approximated in terms of a power law function for the intermediate wave numbers. This power spectrum has four fractal morphological parameters. They are fractal dimension (DH), lower (l) and upper (L) cutoff length scales of fractality, and the proportionality factor (μ) related to topothesy or strength of roughness. Theoretical result obtained for the admittance on such realistic fractal electrode is an indispensable step in the quantitative description of role of roughness and is applicable for all frequency regimes. This result can also be simplified to three limiting laws for the admittance or impedance. The anomalous admittance/impedance and an approximately constant phase angle behavior is explained through a limiting law for the intermediate frequencies. The intermediate frequency limiting law is dependent on the fractal dimension as well as on the lower cutoff length and strength of roughness. Finally, these results also offer an explanation for difficulties in classical power-law form for the diffusive impedance with incomplete characterization of exponent with fractal morphological parameters.

Attempts to understand the intricacies of biosilicification in sponges are hampered by difficulties in isolating and culturing their sclerocytes, which are specialized cells that wander at low density within the sponge body, and which are considered as being solely responsible for the secretion of siliceous skeletal structures (spicules). By investigating the homosclerophorid Corticium candelabrum, traditionally included in the class Demospongiae, we show that two abundant cell types of the epithelia (pinacocytes), in addition to sclerocytes, contain spicules intracellularly. The small size of these intracellular spicules, together with the ultrastructure of their silica layers, indicates that their silicification is unfinished and supports the idea that they are produced "in situ" by the epithelial cells rather than being incorporated from the intercellular mesohyl. The origin of small spicules that also occur (though rarely) within the nucleus of sclerocytes and the cytoplasm of choanocytes is more uncertain. Not only the location, but also the structure of spicules are unconventional in this sponge. Cross-sectioned spicules show a subcircular axial filament externally enveloped by a silica layer, followed by two concentric extra-axial organic layers, each being in turn surrounded by a silica ring. We interpret this structural pattern as the result of a distinctive three-step process, consisting of an initial (axial) silicification wave around the axial filament and two subsequent (extra-axial) silicification waves. These findings indicate that the cellular mechanisms of spicule production vary across sponges and reveal the need for a careful re-examination of the hitherto monophyletic state attributed to biosilicification within the phylum Porifera.

Individual carbon nanotubes being substantially smaller than the wavelength of light, are not much responsive to optical manipulation. Here we demonstrate how decorating single-walled carbon nanotubes with palladium particles makes optical trapping and manipulation easier. Palladium decorated nanotubes (Pd/SWNTs) have higher effective dielectric constant and are trapped at much lower laser power level with greater ease. In addition, we report the transportation of Pd/SWNTs using an asymmetric line trap. Using this method carbon nanotubes can be transported in any desired direction with high transportation speed.

High-κ dielectrics have become a necessity for CMOS scaling. Various dielectrics have been tried as a replacement to SiO2. Hf-based dielectrics, which have been used with some success, have their own set of problems and are only a short term solution. In this scenario, the rareearth lanthanide metal oxides, principally La2O3, are being studied as a potential SiO2-substitute. This paper reviews the issues with SiO2 and other high-κ dielectrics, and discusses the properties of rare-earth oxides as favourable gatedielectrics, and describes the various fabrication techniques employed to obtain rare-earth oxide thin films. Fig. 3. C-V data for a [Al/PrOx/n-Si] MOS capacitor structure grown by ALD using Pr[N(SiMe3)2]3.Figure reproduced from [11].

The main focus of this work is to compare thermal diffusivity and effusivity data resulting from thermal wave interferometry (TWI) experiments on tungsten coatings of different thicknesses with those obtained using reference techniques, namely, the laser flash method and scanning electron microscopy (SEM). The deviations between TWI and the latter techniques are discussed in terms of lack of data in the low frequency range. The investigation shows that the lack of data at low frequencies does not affect diffusivity measurements, while it has a strong effect on effusivity measurements for thermally thick coatings. The conclusions of this experimental study are in good agreement with theoretical predictions resulting from a sensitivity analysis reported in a previous study. © 2005 Springer Science+Business Media, Inc.

The effect of the cooling rate on hardness and thermal conductivity in a metallurgical Jominy bar made of AISI 1018 steel, by means of a water end-quenched heat treatment process without diffusion-controlled case depth, is studied with photothermal radiometry (PTR). It is concluded that our two PTR techniques, common-mode rejection demodulation (CMRD) and conventional 50% duty-cycle square-wave frequency scan, are sensitive to low hardness values and gradients, unlike the high values all previous photothermal studies have dealt with to-date. Both PTR methods have yielded an anti-correlation between thermal conductivity and microhardness in this case as in previous cases with heat-treated and diffusion-controlled case depth profiles. It is shown that the cooling rate strongly affects both hardness and thermal conductivity in the Jominy-bar heat-treating process. © EDP Sciences.

We describe the synthesis of an end-functionalized copolymer of N-(2-hydroxypropyl)methacrylamide (HPMA) and N-hydroxysuccinimide methacrylate (NMS) by reversible addition-fragmentation chain transfer (RAFT) polymerization. To control the polymer composition, the faster reacting monomer (NMS) was added slowly to the reaction mixture beginning 30 min after initating the polymerization (ca. 16% HPMA conversion). One RAFT agent, based on azocyanopentanoic acid, introduced a -COOH group to the chain at one end. Use of a different RAFT agent containing a 4-amino-1,8-naphthalimide dye introduced a UV-vis absorbing and fluorescent group at this chain end. The polymers obtained had molecular weights of 30 000 and 20 000, respectively, and contained about 30 mol% NMS active ester groups.

As many practitiones know, compressed streams are very sensitive the transmission errors. Even a single error can have devastating effects and compromise all the data downstream . In fact, the non-resilience of adaptive data compression has been a practical drawback of its use in many applications. Joint source-channel coding [4, 1] has emerged as a possible solution to this problem. Usually, joint source-channel coding trades source bits for channel bits or vice versa, and more than often requires some adjustments in source coding and channel coding parts.

AESTRACT CRACKS in ductile single crystals are analyzed here for geometries and orientations such that twodimensional states of anti-plane shear constitute possible deformation fields. The crystals are modelled as ideally plastic and yield according to critical resolved shear stresses on their slip systems. Restrictions on the asymptotic forms of stress and deformation fields at crack tips are established for anti-plane loading of stationary and quasistatically growing cracks, and solutions are presented for several specific orientations in f.c.c. and b.c.c. crystals. The asymptotic solutions are complemented by complete elastic-plastic solutions for stationary and growing cracks under small scale yielding, based on previous work by RICE (1967,1984) and FREUND (1979). Remarkably, the plastic zone at a stationary crack tip collapses into discrete planes of displacement and stress discontinuity emanating from the tip; plastic flow consists of concentrated shear on the displacement discontinuities.

ANALYSIS of the deformation field consistent with a Prandtl stress distribution travelling with an advancing plane-strain crack reveals the functional form of the near tip crack profile in an elastic-plastic solid. The crack opening 6 is shown to have the form 6 N r In (const./r) at a distance r from the tip. This observation coupled with data generated from finite element investigations of growing cracks in small-scale yielding permits the construction of a relation characterizing the deformation at an extending crack tip. A ductile crack-growth criterion consisting of the attainment of a critical opening at a small characteristic material distance from the tip is adopted. Predictions of the stability of a growing crack for both small-scale yielding specimens and those subject to general yielding are discussed.

THIS PAPER is concerned with an analysis of strain localization in ductile crystals deforming by single slip. The plastic flow is modelled as rate-insensitive, and localization, viewed as a bifurcation from a homogeneous deformation mode to one which is concentrated in a narrow 'shear band', is found to be. possible only when the plastic hardening modulus for the slip system has fallen to a certain critical value h,,, sensitive to the precise form of the constitutive law governing incremental shear. We develop the general form of this constitutive law, incorporating within it the possibility of deviations from the Schmid rule of a critical resolved shear stress, and we show that h,, may in fact be. positive when there are deviations from the Schmid rule. It is suggested that micromechanical processes such as 'cross-slip' in crystals provide specific cases for which stresses other than the Schmid stress may influence plastic response and, further, there is an experimental association of localization with the onset of large amounts of cross-slip. Thus, we give the specific form of h,, for a constitutive model that corresponds to non-S&mid effects in cross-slip, and we develop a dislocation model of the process from which we estimate the magnitude of the parameters involved. The work supports the notion that localization can occur with positive strain-hardening, h,, > 0, and the often invoked notions of the attainment of an ideally-plastic or strain-softening state for localization may be unnecessary.

Recent finite-element results by S. Cl. Larsson and A. J. Carlsson suggest a limited range of validity to the 'small scale yielding approximation', whereby small crack tip plastic zones are correlated in terms of the elastic stress intensity factor, It is shown with the help of a model for plane strain yielding that their results may be explained by considering the non-singular stress, acting parallel to the crack at its tip, which accompanies the inverse square-root elastic singularity. Further implications of the non-singular stress term for crack tip deformations and fracturing are examined. It is suggested that its effect on crack tip parameters, such as the opening displacement and J-integral, is less pronounced than its effect on the yield zone size.

THIS PAPER is a study of the theoretical foundations of constitutive relations at finite strain for a class of solids exhibiting inelasticity as a consequence of specific structural rearrangements, on the microscale, of constituent elements of material. Metals deforming plastically through dislocation motion are of this class and form the primary application of the theory. The development is in terms of a general internal-variabIe thermodynamic formalism for description of the microstructural rearrangements, and it is shown how metal plasticity may be so characterized.

Chinese checkers is a game played on a hexagonal grid. This regular hexagonal tesselation is an artifact of Euclidean geometry that provides a fair playing eld only for games of two, three, four or six players. Hyperbolic geometry allows tessallations of the plane by regular polygons with any number of sides. Hyperbolic versions of the chinese checkers board permit fair games with ve, seven and even more players.

We describe a technique for addressing individual nanoscale wires with microscale control wires without using lithographic-scale processing to define nanoscale dimensions. Such a scheme is necessary to exploit sublithographic nanoscale storage and computational devices. Our technique uses modulation doping to address individual nanowires and self-assembly to organize them into nanoscale-pitch decoder arrays. We show that if coded nanowires are chosen at random from a sufficiently large population, we can ensure that a large fraction of the selected nanowires have unique addresses. For example, we show that lines can be uniquely addressesd over 99% of the time using no more than 2 2 log 2 ( ) + 11 address wires. We further show a hybrid decoder scheme that only needs to address = ( litho pitch nano pitch ) wires at a time through this stochastic scheme; as a result, the number of unique codes required for the nanowires does not grow with decoder size. We give an

Replacing parametrization of a domain with polyhedral approximations we give an optimal extension of the Divergence Theorem. Permitted domains of integration, called chainlets, range from smooth submanifolds to structures that may not be locally Euclidean and have no tangent vectors defined anywhere. One may still calculate divergence over the domain, and flux through its boundary which itself may have no normal vectors defined anywhere.

We present here the fundamentals of a theory of domains that offers unifying techniques and terminology for a number of different fields. Using direct, geometric methods, we develop integration over pdimensional domains in n-dimensional Euclidean space R n , replacing the method of parametrization of a domain with the method of approximation in Banach spaces. We prove basic results needed for a theory of integration -continuity of the integral as a function of its domain and integrand (Corollary 4.6) and a generalization of Stokes' theorem (Corollary 4.12). * Note that the spaces B r,α are defined for (r, α) ≥ 0 while the spaces A r,α are defined for (r, α) > −1. In the sequel [H2] we prove that dual spaces of co-chainlets correspond to spaces of differential forms. Almgren [A] proved that mass continuous cochains correspond to forms, but these are not necessarily measurable. The Banach spaces A −1,α are used to define the spaces A α , beginning an induction process.

A soap film is actually a thin solid fluid bounded by two surfaces of opposite orientation. It is natural to model the film using one polyhedron for each side. Two problems are to get the polyhedra for both sides to be in the same place without canceling each other out and to model triple junctions without introducing extra boundary components. We use chainlet geometry to create dipole cells and mass cells which accomplish these goals and model faithfully all observable soap films and bubbles. We introduce a new norm on chains of these cells and prove lower semicontinuity of area. A geometric version of Cartan's magic formula provides the necessary boundary coherence.

Cet article analyse la possibilité d’utiliser les nanocornets de carbone (ou nanohorns) comme solution au problème du stockage massif d’hydrogène. Alors qu’une quantité non négligeable d’hydrogène peut être adsorbée par les nanotubes de carbone mono-feuillets (SWNT) sous une pression de 100 bars et à une température de 10 K, il s’avère que pratiquement toute cette quantité s’échappe du matériau lorsque celui-ci est remis dans les conditions ambiantes, et seulement une infime partie est réadsorbée lorsque la température est redescendue à 10 K. Les nanocornets de carbone mono-feuillets (SWNH), structures graphitiques se présentant sous l’aspect de fleurs de dahlia et se formant par agrégation de structures nanotubulaires, apparaissent a priori plus prometteurs puisque le processus d’adsorption semble réversible et la plupart de l’hydrogène libéré à température ambiante est réadsorbé quand la température est à nouveau abaissée. En plus, leurs performances peuvent encore être améliorées en jouant sur la pression, ou en décorant la surface avec des nanoparticules métalliques. Les travaux présentés ici se limitent aux matériaux bruts. Les aspects microscopiques de l’adsorption d’hydrogène dans les nanostructures de carbone sont discutés à partir d’expériences de diffusion de neutrons. Le comportement de l’hydrogène adsorbé dans les SWNT est comparé à celui dans les SWNH en utilisant d’une part l’analyse de la transition rotationnelle para-ortho qui donne accès à des informations sur l’interaction entre les molécules d’hydrogène et la matrice carbonée, et en étudiant d’autre part le pic quasi-élastique dont la largeur dépend de la mobilité translationnelle de l’hydrogène et permet de discriminer les fractions d'hydrogène mobile et immobile.

Physico-chemical properties of materials can be strongly modified by confinement because of the quantum effects that appear at such small length scales and also because of the effects of the confinement itself. The aim of this thesis is to show that both the nature of the confining material and the size of the pores and cavities have a strong impact on the confined material. We first show the effect of the pore size of the host mesoporous silica on the temperature of the solid-solid phase transition of silver selenide, a semiconducting material with enhanced magnetoresistive properties under non-stoichiometric conditions. Narrowing the pores from 20 nm to 2 nm raises the phase transition temperature from 139°C to 146°C. This result can be explained by considering the interaction between the confining and confined materials as a driving force. The effects of confinement are also studied in the case of hydrogen and deuterium inside cavities of organized carbon nanostructures. The effects that appear in the adsorption/desorption cycles are much stronger with carbon nanohorns as the host material than with C60 peapods and single-walled carbon nanotubes.

In the symmetric rendezvous search game played on K n (the completely connected graph on n vertices) two players are initially placed at two distinct vertices (called locations). The game is played in discrete steps and at each step each player can either stay where he is or move to a different location. The players share no common labelling of the locations. They wish to minimize the expected number of steps until they first meet. Rendezvous search games of this type were first proposed by Steve Alpern in 1976. They are simple to describe, and have received considerable attention in the popular press as they model problems that are familiar in real life. They are notoriously difficult to analyse. Our solution of the symmetric rendezvous game on K 3 makes this the first interesting game of its type to be solved, and establishes the long-standing conjecture that the Anderson-Weber strategy is optimal.

The crystal structure of butane-1,4-diammonium
sulphate, C4H14N2 2+
SO4 2-, exhibits a unique
packing arrangement where staggered pairs of butane-1,4-
diammonium cations form infinite columns surrounded by
sulphate anions. The disordered cation straddles the mirror
plane and the asymmetric unit contains one half of the
butane-1,4-diammonium cation and one half of the sulphate
anion. The bond between C2b and C2a0 is twisted
into a gauche conformation as a result of the chargeassisted
hydrogen bonding between the doubly charged
sulphate anion and the two singly charged ends of the
cation chain. An intricate and extensive network of
hydrogen bonds is formed within the crystal. Thermal
analysis by DSC yielded no evidence of a phase change for
the compound. Powder X-ray diffraction analysis yielded
very good correlation between the observed and calculated
powder pattern obtained from the single crystal data.
Crystal data: crystal system, orthorhombic, a = 10.0496 (5)
A ° , b = 9.4186 (4) A ° , c = 8.8987 (4) A ° , space group, Pnma, V = 842.29 (7) A ° 3, Z = 4.

Despite limited literature discussing the global implications of molecular manufacturing (MM), the seeds for certain key debates are starting to be sown. They essentially mirror those
presented for current and near-term nanotechnology: 1. for what purposes will the technology be developed and used, by whom will it be created and owned, what is the nature of the risks it will bring, and what kind of impact will it have upon the global economy and developing world?

The realisation of MM’s central goals would undoubtedly lead to the most concentrated technological tsunami ever witnessed. The unpredictable nature of such a revolution makes answering the previous questions all the more difficult.

However, just as biotechnology is commonly used as a yardstick for nanotechnology evaluations (given the continuity of many social concerns and the relationship between existing biotechnology capabilities and the potential to develop nanotechnology), I argue here that the best way to set up the MM debate, in terms of its impact on developing countries, may be to look at developments and trends in nanotechnology. Central to such analysis is addressing the ways in which nanotechnology creates new possibilities for developing countries in terms of access to technology, potential benefits, risks, and shifting views of science and technology, as well as the imposing of new demands in terms of infrastructure and approaches to science.