If a physical dimension of a metallic specimen is comparable with, or smaller than, the mean free path of the conduction electrons, then the observed electrical conductivity will be less than that of a conventional bulk sample. This phenomenon is called a size effect, and is the result of electron scattering from the specimen surfaces. In the present investigation, measurements were made on electropolished monocrystalline specimens ranging from matchbox geometry to thick-film geometry in order to obtain further information on the size effect in bismuth at liquid helium temperatures.

Classical elasticity cannot be used to explain effects related to material microstructures due to its lack of a material length scale parameter. To mitigate this deficiency, higher order elasticity theories have been developed. Two simple higher order theories and their applications are studied in this research. One is a modified couple stress theory and the other is a simplified strain gradient theory, each of which contains only one material length scale parameter in addition to the classical elastic constants. Variational formulations are provided for these two theories by using the principle of minimum total potential energy. In both cases, the governing equations and complete boundary conditions are determined simultaneously for the first time. Also, the displacement form is explicitly derived for each theory for the first time. The modified couple stress theory is applied to solve a simple shear problem, to develop a new Bernoulli-Euler beam model, and to derive the constitutive relations for hexagonal honeycomb structures, while the simplified strain gradient theory is used to solve the pressurized thick-walled cylinder problem. All these models/solutions are obtained for the first time and supplement their counterparts in classical elasticity. Numerical results obtained from the newly developed models and derived solutions and their comparisons with their counterpart results in classical elasticity reveal that the higher order theory based models and solutions have the capacity to account for microstructural effects; their counterparts in classical elasticity do not have the same capability. Nevertheless, the former are shown to recover the latter if the microstructural effects are suppressed or ignored.

The world is experiencing a growing demand for miniaturised products. Micro-milling, using carbide micro tools has the potential for direct, economical manufacture of micro parts from a wide range of workpiece materials. However, in previous studies several critical issues have been identified that preclude the direct application of macro machining knowledge in the micro domain through simple dimensional analysis. The research presented in this thesis focused on some of the areas that require development of the scientific knowledge base to enable determining improved microscale cutting performance. In the mechanical micro machining of coarse grained materials, the programmed undeformed chip thickness can be lower than the length scale of the workpiece grains. Moreover, when the microstructure of such materials is composed of more than one phase, the micro cutting process can be undertaken at a length scale where this heterogeneity has to be considered. Driven by this challenge, the material microstructure 'size effect' on micro-machinability of coarse grain steel materials was investigated in this PhD. In this regard, a predominantly single phase ferritic workpiece steel material and another workpiece material with near balanced ferrite/pearlite volume fractions was studied over a range of feedrates. The results suggested that for micro machined parts, differential elastic recovery between phases leads to higher surface roughness when the surface quality of micro machined multiphase phase material is compared to that of single phase material. On the other hand, for single phase predominantly ferritic materials, reducing burr size and tool wear are major challenges. In micro machining the so called 'size effect' has been identified as critical in defining the process performance. However, an extensive literature search had indicated that there was no clear reported evidence on the effect of process variables on driving this size effect phenomenon. It is often assumed in literature that the un-deformed chip thickness was the main factor driving the size effect. This limit manufactures to only altering the feedrate to try and influence size effect. To explore the significance of a range of inputs variables and specifically, cutting variables on the size effect, micro cutting tests were conducted on Inconel 718 nickel alloy. Taguchi methodology along with signal processing techniques were applied to micro milling acoustic emission signals to identify frequency/energy bands and hence size effect specific process mechanism. The dominant cutting parameters for size effect characteristics were determined by analysis of variance. These findings show that despite most literature focussing on chip thickness as the dominant parameter on size effect, the cutting velocity is a dominant factor on size effect related process performance. This suggests that manipulating the cutting speed can also be a very effective strategy in optimising surface finish in micro machining and in breaking the lower limit of micro machining.In micro machining the lower limit of the process window is set by the minimum chip thickness. Identifying this limit is thus important for establishing the process window. Process windows are valuable guidelines for industrial selection of cutting conditions. Additionally, understanding factors that influence the value of minimum chip thickness is even more important for progressing micro machining capability to the nano-scale machining regime. For this reason, in this PhD study, acoustic emission signatures emanating from microscale milling of six different workpiece materials were characterised to identify the rubbing mode and this enabled the identification of the threshold conditions for occurrence of minimum chip thickness. The minimum chip thickness predicted by this novel approach compares reasonably well to the values that exist in published literature. Additionally, the decomposition of raw acoustic signal allowed the determination of energy levels corresponding to deformation mechanisms. The PhD work provides significant and new knowledge on the utility and importance of acoustic emission signals in characterising chip formation in micro machining. A novel method for determining the minimum chip thickness was developed, micro machining chip formation mechanisms were identified and the machinability of coarse grained multiphase material is presented.

none

Over the past decades, bulk metallic glasses (BMGs) have attracted extensive interests because of their unique properties such as good corrosion resistance, large elastic limit, as well as high strength and hardness. However, with the advent of micro-electro-mechanical systems (MEMS) and other microscaled devices, the fundamental properties of micrometer-sized BMGs have become increasingly more important. Thus, in this study, a methodology for performing uniaxial compression tests on BMGs having micron-sized dimensions is presented. Micropillar with diameters of 3.8, 1 and 0.7 £gm are fabricated successfully from the Mg65Cu25Gd10 and Zr63.8Ni16.2Cu15Al5 BMGs using focus ion beam, and then tested in microcompression at room temperature and strain rates from 1 x 10-4 to 1 x 10-2 s-1. Microcompression tests on the Mg- and Zr-based BMG pillar samples have shown an obvious sample size effect, with the yield strength increasing with decreasing sample diameter. The strength increase can be rationalized by the Weibull statistics for brittle materials, and the Weibull moduli of the Mg- and Zr-based BMGs are estimated to be about 35 and 60, respectively. The higher Weibull modulus of the Zr-based BMG is consistent with the more ductile nature of this system. In additions, high temperature microcompression tests are performed to investigate the deformation behavior of micron-sized Au49Ag5.5Pd2.3Cu26.9Si16.3 BMG pillar samples from room to their glass transition temperature (~400 K). For the 1 £gm Au-based BMG pillars, a transition from inhomogeneous flow to homogeneous flow is clearly observed at or near the glass transition temperature. Specifically, the flow transition temperature is about 393 K atthe strain rate of 1 x 10-2 s-1. For the 3.8 £gm Au-based BMG pillars, in order to investigate the homogeneous deformation behavior, microcompression tests are performed at 395.9-401.2 K. The strength is observed to decrease with increasing temperature and decreasing strain rate. Plastic flow behavior can be described by a shear transition zone model. The activation energy and the size of the basic flow unit are deduced and compared favorably with the theory.

Size premium puzzle, also known as the size effect, is one of the most studied anomalies in asset pricing literature. It refers to the observation that, on average, smaller firms have higher risk-adjusted returns than larger firms over a long period of time. While many studies have debated the existence of the size effect, the question of why it exists has become a subject of heated debate. Thus, this dissertation aims to examine if previously overlooked factors can, at least partially, explain the size effect. Essay 1 examines if merger and acquisition activity can explain a part of the size effect. I find that merger and acquisition activity explain a part of the size effect. The size effect is found to be stronger during merger waves but is not consistent across industries. Further, the size effect tends to be stronger when acquisition activity is concentrated among smaller firms. Essay 2 investigates if expectational errors explain the higher return of small firms. Several empirical studies show that stocks that investors underestimate yield higher returns. However, I do not find support for the underestimation explanation in explaining the higher returns of small firms. Instead, I find that investors are overly optimistic about the growth of small firms. In essay 3, I examine if the size effect can be explained by perceived risk. Using the implied cost of capital (ICC) as a measure of perceived risk, I find that small firms are perceived to be riskier by the market, and the perceived risk explains the size effect.

This thesis is a study of the size effect. Improvements on both theoretical work and experimental design are involved in this thesis. The theoretical section focuses on the grain size effect, while the experimental section is related to the micro-foil bending test. Both classic experimental data and theories for the Hall-Petch relationship are reviewed comprehensively. The fitting of the datasets show that the inverse square-root dependence and simple inverse expressions are equally good. The fully Bayesian analysis strongly suggests that the latter is correct. Since the physical mechanism underlying the simple inverse dependence is a general size effect, the precise description of the Hall-Petch effect is that it is a manifestation of the general size effect, instead of having its own special character. Improvements on the classic Stolken and Evans' micro-foil bending experiments are also carried out in this thesis. The smart design of the new equipment eliminates the big risk of error in the classic experiment. By using the new device, precise datasets from the elastic region through the yield point and to high plastic strain area can be obtained. The initial results correspond well with the old published data.

This thesis is dedicated to determination of cost of equity capital. The main objective is to evaluate whether the cost of equity may, in its calculations, vary depending on the size of a company. The means for achieving the results can be comparison of calculations of cost of equity by model with historical returns actually achieved. This is what many empirical studies are focused on. A partial goal of this paper is to analyze the results of selected studies and their mutual comparison. Relevant theoretical explanations will be also presented.

Les petites sociétés génèreraient de meilleures performances en périodes économiquement favorables et leurs performances seraient plutôt médiocres en périodes économiquement défavorables. Nous avançons l‟hypothèse selon laquelle l‟effet taille n‟est manifeste que durant les périodes d'expansion économique. Notre étude empirique confirme cette hypothèse pour la période 2000-2009. Nous utilisons un modèle avec variables binaires pour estimer les alphas ainsi que trois indicateurs du cycle économique : l'indicateur composite avancé de l‟OCDE, l‟indice CAC 40 et l‟Euribor 1 mois. / It would seem that small companies perform better in economically favourable times and give more mediocre performances in economically unfavourable times. We put forward the hypothesis that size effect only occurs during periods of economic expansion. Our empirical study confirms this hypothesis for the 2000-2009 period. We use a model with binary variables to estimate alphas as well as three economic cycle indicators: the OCDE composite leading indicator, the CAC 40 index and the 1 month Euribor rate.

In this thesis the positive relationship between firm size and wages is investigated through the application of hierarchy theories. Many different explanations have been proposed for this relationship, but have met only limited success at best. The strongest finding to date is that unobserved ability is a significant factor. The question of interest here is ???why do wages increase as the size firm increases???? Hierarchy theories take a different approach towards the analysis of firms in comparison to the alternate theories which have dominated previous investigations. As a result of their focus on the organisational relationships within a firm???s internal structure, hierarchy theories offer certain insights to the size-wage relationship which to date have been unnoticed. An empirical investigation into the size-wage differential incorporating structural considerations into an augmented wage equation offers strong support for the propositions of hierarchy theories. I find that half of the firm size effect for workers can be explained by controlling for some aspects of management structure, and that span of control has a discontinuous effect on wages. These results are completely consistent with the existing findings on unobserved ability and have the added attraction of providing economic as well as statistical explanatory power.