Habilitacinei procedūrai teikiamų darbų apžvalgoje yra pateikiama autoriaus atlikta ir kitų autorių įvairių kristalinių (ZnS, ZnSe) ir organinių junginių diodų, nanovamzdelių, plonų plėvelių, nanofibrų, ir kitų nanodarinių mokslinėje literatūroje skelbtų eksperimentinių elektrinio laidumo tyrimų rezultatų analizė bei šių rezultatų sugretinimas su fononais stimuliuoto tuneliavimo (FST) teorijų pagrindu paskaičiuotomis tuneliavimo tikimybių priklausomybėmis. Tyrimo rezultatai leido išsiaiškinti tai, kad krūvininkų generacijos procesas yra jų tuneliavimas iš gaudiklių dalyvaujant fononams. Įrodyta, kad organiniuose dariniuose (jų tarpe ir nanodariniuose) stebimą virsmą iš puslaidininkinio laidumo į metalinį laidumą (kai virsmo temperatūra TC) galima paaiškinti krūvininkų tunelinio proceso metu susidariusiu balansu tarp fononų absorbcijos ir jų generacijos, kai proceso metu elektrinis laukas krūvininkus išlaisvina iš lokalizuotos būsenos į laidumo būseną. Toje temperatūrų srityje, kur T < TC, tuneliavime dominuoja fononų absorbcija, ir todėl ten tunelinio perėjimo tikimybė, temperatūrai augant, padidėja. Priešingai, tose srityse, kur T > TC, procese dominuoja fononų emisija ir todėl ji sumažina krūvininkų tuneliavimo tikimybę, tuo pačiu iššaukdama elektrinio laidumo sumažėjimą kylant temperatūrai. Tokio FST modelio pagrįstumą įrodo ir tai, kad tiek plačiame elektrinių laukų, tiek ir temperatūrų intervale, tuneliavimo procesas yra vieningai aprašomas tų pačių parametrų... [toliau žr. visą tekstą] / Habilitation procedure review is for to clarify the conductance mechanism in polymers and other conducting nanodevices. The model based on the phonon-assisted tunnelling (PhAT) process, initiated by an electric field. An advantage of this PhAT model over the other models is the possibility to describe the behaviour of conductivity data measured at both low and high temperatures with the same set of parameters: εT - the energetic depth of the center, m* - the effective mass, T- temperature, E- the electric field, ħω - the phonon energy and a- the electron-phonon interaction constant. From these ones only the electron-phonon coupling constant a, and the phonon energy ħω are the fitting parameters estimated from the best fitting of the experimental data and the theory. Other parameters are from experiments or from literary sources known. Therefore, the PhAT mechanism could be dominant in the conductance of the MWNT, so as was shown, also in the case of the single-wall nanotubes. On the basis of this proposed model, the phenomenon of the crossover from non-metallic to metallic behavior of the conductivity is also explained. The decrease of conductivity in the framework of this model occurs at the temperatures T > TC when the phonon emission in the process of tunnelling dominates over the phonon absorption. The obtained agreement between the theoretical and experimental results, is not accidental but is due to the fact that the proposed model includes ultimate pictures of charge... [to full text]

This thesis describes three different design projects that are intellectually connected by the fact that they all involve the development of apparatus to facilitate the precise control of sample temperature in modern microscopes. The first project is a low-temperature sample stage, for a beetle-type scanning tunnelling microscope. The design for this sample stage, and images taken on it with atomic resolution at 114 K are presented. This stage has the capability for variable-temperature sample cooling, which is also discussed. The second project is a set of low- and variable-temperature isothermal radiation shields for a new microscope that is currently being designed and assembled by our research group. These shields provide temperature control between 5 K and room temperature, with measured stability better than +/- 0.1 K. Controlled and stable temperature changes at rates up to 1.5 K per minute have been produced. The shields are modular and can easily accommodate future modifications. The design for the shields, along with their cooling and temperature control capabilities, is presented. The third project is a new stage design for heating, cleaning, and transferring metal and semiconductor samples. Also for use with the new microscope, this stage uses electron bombardment to provide precision temperature control between room temperature to temperatures in excess of 1250 C‰. With this stage, the sample temperature can be determined by measuring the power applied to the sample. The design of this stage, its heating performance, and a method to calculate the sample temperature is presented. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2008-06-03 12:47:18.808

A sound understanding of rock mass characteristics is critical for the engineering prediction of tunnel stability and deformation both during construction and post-excavation. The rock mass modulus of deformation is a necessary input parameter for many numerical analysis methods to describe the constitutive behavior of a rock mass. Tests for determining this parameter directly by in situ test methods are inherently difficult, time consuming and expensive, and these challenges are more problematic when dealing with tunnels in weaker, softer rock masses where errors in modulus (stiffness) estimation have a profound impact on closure predictions. In addition, rock masses with modest structure can be candidate sites for highly sensitive structures such as nuclear waste repository tunnels. For these generally stiffer rock masses, the correct modulus assessment is essential for prediction of thermal response during the service life of the tunnel. Numerous empirical relationships based on rock mass classification schemes have been developed to determine rock mass deformation modulus in response to these issues. The empirical relationship provided by Hoek & Diederichs (2006) based on Geological Strength Index (GSI) has been determined from a database of in situ test data describing a wide range of rock masses with GSI values greater than 25 and less than 80. Within this range of applications there is a large variation in measured values compared to the predicted relationship and predictive uncertainty at low GSI values. In this research, a practical range of rock mass quality, as defined by GSI, including "Blocky\Disturbed\Seamy" rock masses, "Very Blocky" and relatively competent rock masses are analyzed using discretely fractured numerical models. In particular the focus is on tunnel response. Tunnel closure in these simulations is compared to predictions based on modulus estimates. The proposed refinement to the Generalized Hoek-Diederichs relationship is made on the basis of these simulations for tunnelling applications. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2011-09-20 22:34:06.642

The traditional design methodologies for tunnel and underground excavations are divided in to three categories: Empirical, Analytical, and Observational approaches, whereas in the last years the Numerical approach has strongly become popular both for the intrinsic simplicity of the software packages and their ability to manage problems unsolvable with the classic methods. In this thesis, the underground openings have been analyzed using constitutive models other than the Mohr-Coulomb theory. FLAC is used for the analysis and the software has been implemented to include the Polyaxial Strength Criterion. The details of the modifications made in the software are presented and the results are compared with the Singh's elasto-plastic stress distribution in squeezing grounds. The applicability of the Polyaxial Strength Criterion has been therefore extended to all the numerical suites designed for geo-mechanical purposes (FEM, FDM, …) and the obtained results compared to the observations of deformation and radial squeezing pressure of the instrumented tunnels in the Chibro-Khodri underground power station. This study will develop better comprehension of the behavior of the underground openings and also provide a useful tool to the designers in the planning stages. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2012.

The design of support systems, comprising rock bolt reinforcement and fabric containment components for tunnels in deep level mining environments does not currently cater well for adverse rock mass conditions. This often results in periodic failure of the support system, particularly under dynamic (rockburst) conditions with the potential for total collapse of the excavation. The design of support systems is currently based either on empirical design guidelines often not applicable to this environment or simple mechanistic models. This thesis details a methodology for the rational design of tunnel support systems based on a mechanistic evaluation of the interaction between the components of a support system and a highly discontinuous rock mass structure. This analysis is conducted under both static and dynamic loading conditions. Due to the highly complex and variable nature of the rock mass structure and the dynamic loading environment, a large component of the practical work on the evaluation of the mechanisms of rock mass deformation and support interaction is based on rockburst case studies. The understanding gained from these investigations is further evaluated by means of laboratory testing of the performance of the components of the support systems and numerical modelling of the interaction of the components of the support system with the rock mass. Due to the complex nature of this design environment the methodology developed in this thesis is but a step towards our greater understanding of the behaviour of the rock mass, and the interaction of support systems in the stabilisation of tunnel excavations. However, in comparison to the current design, this methodology now allows the design engineer to make better estimations of the anticipated demand on the different components of the support systems, under a defined rock mass environment on engineering principles. This understanding will give the design engineer greater flexibility, and confidence to design the appropriate tunnel support system for a specific rock mass and loading condition based on the often limited availability of different support units in the underground mining environment. / Thesis (Ph.D.)-University of Natal, Durban, 1999.

The development and implementation of a complex numerical model for the determination of the damage to masonry buildings resulting from tunnelling settlements is described in this thesis. The current methods of damage prediction do not, in general, take into account the stiffness and weight of the surface structure. The model addresses this deficiency by explicit inclusion of the structure. Three-dimensional finite elements are used to model the ground with a non-linear, elasto-plastic soil model based on kinematic hardening. Tunnel linings are modelled using a novel overlapping elastic shell element: volume loss being simulated by shrinkage of linings coincidentally with excavation. Structures are modelled as collections of facades comprised of plane stress elements using a non-linear material model for masonry, similar to elastic-no tension. In developing the three-dimensional model, its two-dimensional counterpart is also studied. While the beam and shell elements used for linings (in two- and three-dimensions respectively) have the advantage of no rotational degrees of freedom the need to model boundary conditions at the element stiffness level complicates implementation. Tests using the shell elements show them to be satisfactory for the purpose of modelling tunnel linings. Results from a small number of analyses are given for construction of a straight tunnel beneath simple masonry structures. It is shown that the effect of the building on settlements depends heavily on its location in plan with respect to the tunnel axis. Predictions of crack patterns using the model for these analyses show that facades which the tunnel passes under first are less damaged than those later in the excavation sequence. Both of these conclusions serve to demonstrate that the problem can only be realistically modelled using three-dimensional methods. At present, however, the computer resources required to run the three-dimensional model are considerable.

The construction of underground tunnels in soft ground in urban areas involves the potential for ground movements caused by the tunnelling to affect existing surface structures. Masonry structures are at particular risk of crack damage. Conventional empirical building assessments do not fully capture all aspects of this soil-structure interaction situation. Numerical methods are increasingly used for such problems. It is common practice in empirical and numerical methods to model a building as an elastic beam in 2D. The objective of this thesis is the development of a new approach to the numerical modelling of masonry buildings using surface beams in 3D. In phase one of this project, finite element analyses of elastic and masonry facades are undertaken and the traditional beam method of modelling them is assessed. New equivalent elastic surface beams are developed, the properties of which account for the dimensions and openings in facades which were found to influence the response to settlements. Equivalent masonry beams are also developed which have a constitutive model that accounts for the different response of masonry buildings in hogging and sagging. Timoshenko beams are chosen to model the facades and these beams were implemented into the OXFEM finite element program with full 3D capability along with the new constitutive beam models. Example masonry structures were modelled in 3D using the new surface beams in phase two. Tunnel construction was simulated under the buildings and the response of the beams compared to a full masonry building model. Example analyses included buildings both symmetric and oblique to the tunnel. Results showed that the equivalent elastic beams accurately simulate full masonry building response in sagging regions. Parametric studies confirmed the choice of equivalent beam parameters and the impact of different relative stiffnesses. The equivalent masonry beams displayed the same good agreement in sagging but were less accurate in hogging. In phase three, finite element models are used to compare ground movements and structural response of buildings using the 3D equivalent masonry beam method and observed data from the construction of the London Underground Jubilee Line Extension. The surface beams showed good agreement with the observed building responses in both sagging, where the building response was essentially rigid and in hogging where a more flexible response was observed.

The subject of this thesis is the verification of a three-dimensional numerical modelling approach for the prediction of settlement damage to masonry buildings due to tunnelling in soft ground. The modelling approach was developed by previous researchers at Oxford, and was applied to three sites, representative of a range of practical configurations. The first involved the excavation of a shaft close to the corner of an eighteenth century church in London. The second involved tunnelling with very low cover beneath the foundations of a terrace of cottages at Ramsgate, Kent. The third was the relatively well-known case of tunnelling beneath the Mansion House, London, for construction of the extension to the Docklands Light Railway in the late 1980’s. The overall conclusion of the project is that the modelling procedures are suitable for application to the detailed assessment of the response of buildings to tunnelling. Particular features of the procedures are that the building is modelled together with the ground and a representation of the tunnel excavation, and in three dimensions. It has been confirmed that all these features are necessary to model the building response, which may include a combination of shear deformation, arching and bending behaviour. Further lessons have been learned concerning the importance of the self-weight of the building in determining overall settlements, how to model openings such as doors and windows in façades, and whether it is necessary to model the building foundation. It has not proved possible, through lack of time, to model the advance of tunnels beneath buildings within this thesis. This, however, is observed to be an important effect in the field, particularly in causing damage to internal walls. It is recommended that further research be carried out in this area. This project made use of large-scale non-linear finite element analysis. The demand on computing resources was high, stimulating many enhancements to the software, the most important of which was parallelisation of the analysis program for use on the Oxford Supercomputer. To obtain optimum results, larger model sizes are required. The computing resources to enable this should become more commonly available within the next few years, enabling the modelling techniques to be used routinely.

This dissertation describes a study of the interaction between closely spaced tunnels during shield tunnel construction, concentrating on the study of the short-term incremental behaviour of the liner. Carefully controlled physical model tests were carried out and the test results were complemented by a limited amount of numerical analysis. In the physical model tests described in this dissertation, two groups of tests were carried out at a laboratory scale; one set of tests studied closely spaced parallel tunnels and the other set investigated perpendicular tunnels. An important feature of the study was that a novel model tunnelling machine was designed and developed as part of the research. Thin steel tubes were used to model the tunnel linings. The experimental technique adopted in the preparation of clay samples (which is a well-established procedure) was found to produce high quality samples. Good repeatability was achieved in preparing the kaolin samples. The tunnelling machine allowed tunnel liners to be installed using similar procedures to those adopted in the construction of full scale shield tunnels using an earth pressure balance approach. The instrumentation system used in this experimental programme are shown to produce reliable data. During the model tests measurements were made of liner strains, pore water pressures and total stresses acting on the liner. Errors in the data logging system were shown to be very small (of the order of less than 2% of peak values). The mechanisms governing the structural interaction between closely spaced tunnels are highly complex. The tunnel installation was shown to modify the stresses acting on the liner of the adjacent tunnel. These stress increments led, in turn, to line deformations and induced bending moments. The nature of the interaction mechanisms depends on the geometric configuration of the tunnels, the liner properties, and overconsolidation ratio. For the parallel tunnels, the pillar width ratio (W/D) is an important parameter governing the magnitude of the interaction effects. the interaction effects increase as the pillar width ratio is reduced. Increasing the liner flexibility was found to reduce the induced bending moments but to increase the induced displacements. The interaction effects were larger in overconsolidated clay than normally consolidated clay. The worst case for interaction effects occurs when the pillar width is small, the liner is flexible and the value of OCR is large. Three-dimensional considerations suggest that interaction between parallel tunnels may be more severe than those measured in the corresponding perpendicular tunnel tests. However, the different nature of the mechanisms in the two cases appear to be more significant than this geometric effect.

Concentrated corporate ownership prevails in most countries, so the relationship between controlling shareholders and minority shareholders is an important principle-agent problem. Tunnelling, the transfer of assets and profit for the benefit of controlling owners, is the most important way of expropriating small shareholders. While tunnelling is rampant in emerging economies and even some developed countries, related research lacks convincing evidence. On the other hand, large shareholders sometimes use private funds to prop up firms in financial distress. Although there is plenty of anecdotal and indirect evidence on propping, it lacks direct large-sample examination. This study presents a pooled cross-sectional analysis of 4373 publicly listed companies in China between 2001 and 2004. The analysis not only examines the effects of various variables on the exploitation of related party transactions by controlling owners for tunnelling and propping, and also investigates the effects of tunnelling and propping on firm performance and valuation. The study reveals that the presence of controlling shareholders and higher control rights lead to higher levels of tunnelling. Conversely the existence of other large shareholders reduces the magnitude of tunnelling. In addition, the study shows that pyramidal-controlled firms and firms owned by the State display more incidences of tunnelling. When firms have better investment opportunity, however, their controlling shareholders tend to divert fewer funds for their private gains. It is also found that controlling shareholders offer funds to financially stricken firms under their control. This is the first study that finds direct evidence on the occurrence of propping although not all badly-performing firms are propped up. / While tunnelling negatively affects operating performance and firm valuation, propping has a positive effect on firm valuation. The occurrence and magnitude of tunnelling is greater than that of propping. Propping only occurs to partial firms in financial distress, yet there is no improvement in those firms’ performance. As propping from new controlling owners is more a way of back-door listing, they tend to engage in tunnelling when their control is secure. In short, when legal protection of minority shareholders is weak, controlling owners tend to tunnel for private benefit. Hence policymakers and regulators must recognise that to eliminate widespread expropriation, the establishment of strong corporate governance in well-functioning institutions and strong legal enforcement is important. Lower levels of tunnelling in years 2003 and 2004 justify the positive effect of stringent regulation. Yet, more needs to be undertaken beyond the legal and regulatory level such as an allowance for diversified corporate ownership and the transformation of non-floatable shares to be floated on the exchange to align interests of large and minority shareholders.