Earth pressure balance (EPB) tunnelling machines are commonly used for the construction of tunnels in soft soils. These machines use the excavated soil in a pressurised head chamber to apply a support pressure to the tunnel face during excavation. How well an unstable face is supported in an EPB machine depends on effectively transferring a constant pressure from the support medium to the surface of the face. If the support pressure is not constant, but instead changes, the varying pressure inevitably leads to collapse of the face or heave on the surface ground. A machine may be designed to work in “Ideal ground” conditions. However, natural soils rarely have these properties, and conditioning of the soil is usually necessary to change its properties to suit the machine. Effective soil conditioning significantly improves the machine performance and control of the soil flow through the screw conveyor. However, for soil conditioning as commonly used in practice, the effects of different conditioning treatments on soil properties and the machine performance are not clearly understood, and problems with EPB machine operations related to the soil properties are often encountered. This thesis presents experimental investigations of direct shear box tests on conditioned sands, compressibility tests on conditioned sands and a model EPB screw conveyor operating with sandy soils. Index tests were performed to investigate effects of foam and polymer conditioning treatments on the plastic fluidity of different Leighton Buzzard (L.B.) sands and Thanet sand. The index tests allowed assessment of conditioning treatments for sandy soils, and optimum ranges of treatments for Leighton Buzzard sand and Thanet sand are suggested. In the series of shear box tests, performed on conditioned Thanet sand and conditioned L.B. sands, one of the most important findings was that the pore water pressure controls the strength of the sand foam mixtures. An increase in foam injection ratio (FIR) might produce an increase of pore water pressure and a decrease of shear stress. In the series of compressibility tests, performed on conditioned Thanet sand and conditioned L.B. fine sand, one of the most important findings was that increasing FIR does not increase maximum gas expelled. The FIR and the initial relative density of the specimen have to be related to the capability of the specimen to retain the gas and establish a coexistence between grains of soil, water and gas bubbles. Finally, from the series of model (1:10 scale), screw conveyor tests, performed on conditioned Thanet sand, conditioned L.B. fine sand and conditioned Garside sand, it can be concluded that the Oxford screw conveyor model can be used as a trial machine to study the effects of different operating conditions on conditioned sand specimens similar to those used on site. This can allow choice of conditioning methods to improve the performance of an EPB machine at a given site.

Experimental studies presented in this thesis have shown the first realisation of resonant tunnelling transport through two impurities in a vertical double-barrier tunnelling diode; have proved the chiral nature of charge carriers in graphene by studying ballistic transport through graphene $p$-$n$ junctions; have demonstrated significant differences of $1/f$ noise in graphene compared with conventional two-dimensional systems. Magnetic field parallel to the current has been used to investigate resonant tunnelling through a double impurity in a vertical double-barrier resonant tunnelling diode, by measuring the current-voltage and differential conductance-voltage characteristics of the structure. It is shown that such experiments allow one to obtain the energy levels, the effective electron mass and spatial positions of the impurities. The chiral nature of the carriers in graphene has been demonstrated by comparing measurements of the conductance of a graphene $p$-$n$-$p$ structure with the predictions of diffusive models. This allowed us to find, unambiguously, the contribution of ballistic resistance of graphene $p$-$n$ junctions to the total resistance of the $p$-$n$-$p$ structure. In order to do this, the band profile of the $p$-$n$-$p$ structure has been calculated using the realistic density of states in graphene. It has been shown that the developed models of diffusive transport can be applied to explain the main features of the magnetoresistance of $p$-$n$-$p$ structures. It was shown that $1/f$ noise in graphene has much more complicated concentration and temperature dependences near the Dirac point than in usual metallic systems, possibly due to the existence of the electron-hole puddles in the electro-neutrality region. In the regions of high carrier concentration where no inhomogeneity is expected, the noise has an inverse square root dependence on the concentration, which is also in contradiction with the Hooge relation.

La Grande Guerre n’est pas seulement une histoire de fantassins combattant au prix de lourdes pertes dans le no man’s land ou de pilotes se battant au-dessus des champs de bataille. Plus méconnus, les tunneliers sont une part essentielle de la guerre de tranchées. Spécialisés dans le creusement de sapes, ces soldats du génie britannique combattent directement sous les tranchées.Première unité créée en dehors du Royaume-Uni, en septembre 1915, la compagnie de tunneliers de Nouvelle-Zélande débarque à Arras, en mars 1916, devenant par la même occasion la première force néo-zélandaise sur le front occidental. Ce corps particulier s’appuie sur les compétences des recrues sélectionnées pour une guerre nouvelle et secrète. Ainsi, à partir de l’étude des 937 tunneliers néo-zélandais, les données personnelles, familiales, professionnelles et militaires proposent un portrait de ces hommes, avant, pendant et après la guerre.Issus des milieux de l’industrie minière de l’or et de la houille, les engagés de cette compagnie présentent une mixité sociale et culturelle européenne, reflet d’une société néo-zélandaise encore attachée à l’Empire. Recrutés pour faciliter leur formation, les tunneliers mènent leurs missions dans la craie blanche de l’Artois, d’abord pour défendre le front au nord d’Arras, puis pour aménager des dug-outs dans la cité artésienne et ses alentours. Ils vivent un combat différent qui rythme une vie bien distincte de leurs homologues de l’infanterie. À bien des égards, ce conflit secret renvoie, dans leur foyer, des individus désormais voués au silence, alors que le comblement de leurs ouvrages enfouit les dernières traces de leur travail, dès la fin de la guerre. / Accounts of soldiers fighting in trenches and pilots fighting in the air over the battlefields have long become the norm in what we read and watch when considering the history of the Great War. Lesser known is a war within a war that took place deep under the battlefields, the tunneling war. Specialized in working underground, the British tunnellers fought directly beneath the trenches. The first such unit created outside the United Kingdom, in September 1915, the members of the New Zealand Engineers Tunnelling Company which arrived in Arras in March 1916, were at the same time the first New Zealanders on the Western Front. This particular corps relied on the skills of recruits selected to take part in a new and secret war. Thus, by examining the personal, family, professional and military histories of the 937 New Zealand tunnellers, it has been possible to construct a portrait of these men before, during and after the war. From the gold and coal mining fields, recruits of this company had a European social and cultural diversity, reflecting a New Zealand society still attached to the Empire. Recruited to make their training easier, the tunnellers took their mission into the hard white chalk of the Artois, first to defend the front north of Arras, and then to develop dug-outs in and around the artesian city. They fought a different type of war which dictated a way of life distinct from their brothers in arms of the infantry. In many ways, this secret warfare led to demobilized soldiers condemned to silence at home, burying the last traces of their wartime experience as they returned to their former occupations underground.

No description available.

The adiabatic approximation is a natural approach for the description of phenomena induced by low frequency laser radiation because the ratio of the laser frequency to the characteristic frequency of an atom or a molecule is a small parameter. Since the main aim of this work is the study of ionization phenomena, the version of the adiabatic approximation that can account for the transition from a bound state to the continuum must be employed. Despite much work in this topic, a universally accepted adiabatic approach of bound-free transitions is lacking. Hence, based on Savichev's modified adiabatic approximation [Sov. Phys. JETP 73, 803 (1991)], we first of all derive the most convenient form of the adiabatic approximation for the problems at hand. Connections of the obtained result with the quasiclassical approximation and other previous investigations are discussed. Then, such an adiabatic approximation is applied to single-electron ionization and non-sequential double ionization of atoms in a strong low frequency laser field. The momentum distribution of photoelectrons induced by single-electron ionization is obtained analytically without any assumptions on the momentum of the electrons. Previous known results are derived as special cases of this general momentum distribution. The correlated momentum distribution of two-electrons due to non-sequential double ionization of atoms is calculated semi-analytically. We focus on the deeply quantum regime -- the below intensity threshold regime, where the energy of the active electron driven by the laser field is insufficient to collisionally ionize the parent ion, and the assistance of the laser field is required to create a doubly charged ion. A special attention is paid to the role of Coulomb interactions in the process. The signatures of electron-electron repulsion, electron-core attraction, and electron-laser interaction are identified. The results are compared with available experimental data. Two-electron correlated spectra of non-sequential double ionization below intensity threshold are known to exhibit back-to-back scattering of the electrons, viz., the anticorrelation of the electrons. Currently, the widely accepted interpretation of the anticorrelation is recollision-induced excitation of the ion plus subsequent field ionization of the second electron. We argue that there exists another mechanism, namely simultaneous electron emission, when the time of return of the rescattered electron is equal to the time of liberation of the bounded electron (the ion has no time for excitation), that can also explain the anticorrelation of the electrons in the deep below intensity threshold regime. Finally, we study single-electron molecular ionization. Based on the geometrical approach to tunnelling by P. D. Hislop and I. M. Sigal [Memoir. AMS 78, No. 399 (1989)], we introduce the concept of a leading tunnelling trajectory. It is then proven that leading tunnelling trajectories for single active electron models of molecular tunnelling ionization (i.e., theories where a molecular potential is modelled by a single-electron multi-centre potential) are linear in the case of short range interactions and ``almost'' linear in the case of long range interactions. The results are presented on both the formal and physically intuitive levels. Physical implications of the proven statements are discussed.

No description available.

No description available.

Der 66. Berg- und Hüttenmännische Tag, als wissenschaftliche Hauptveranstaltung der TU Bergakademie Freiberg, steht im diesjährigen 250. Jubiläumsjahr unter dem Motto „Innovative Ressourcentechnologien”. Mit insgesamt 13 Fachkolloquien wird ein breites fachliches Spektrum der Forschungsaktivitäten und Wissenschaftsgebiete unserer Technischen Universität präsentiert. Das Kolloquium 7 „Maschinen und Verfahren für den Bergbau und Spezialtiefbau”, das am Freitag, den 19. Juni 2015, stattfindet, spiegelt einen Ausrichtungstrend in Forschung und Lehre an der Bergakademie wider. Die Themenvielfalt dieses Kolloquiums ist sehr breit gefächert und behandelt Aspekte des Bergbaus über und unter Tage, des Spezialtief- und Tunnelbaus und Fragestellungen zur Verschleißproblematik. Im Vordergrund stehen logistische Herausforderungen auf Großbaustellen, es werden innovative Neu- und Weiterentwicklungen herausgestellt sowie die Energieeffizienz von Spezialtiefbaumaschinen näher betrachtet.

The adiabatic approximation is a natural approach for the description of phenomena induced by low frequency laser radiation because the ratio of the laser frequency to the characteristic frequency of an atom or a molecule is a small parameter. Since the main aim of this work is the study of ionization phenomena, the version of the adiabatic approximation that can account for the transition from a bound state to the continuum must be employed. Despite much work in this topic, a universally accepted adiabatic approach of bound-free transitions is lacking. Hence, based on Savichev's modified adiabatic approximation [Sov. Phys. JETP 73, 803 (1991)], we first of all derive the most convenient form of the adiabatic approximation for the problems at hand. Connections of the obtained result with the quasiclassical approximation and other previous investigations are discussed. Then, such an adiabatic approximation is applied to single-electron ionization and non-sequential double ionization of atoms in a strong low frequency laser field. The momentum distribution of photoelectrons induced by single-electron ionization is obtained analytically without any assumptions on the momentum of the electrons. Previous known results are derived as special cases of this general momentum distribution. The correlated momentum distribution of two-electrons due to non-sequential double ionization of atoms is calculated semi-analytically. We focus on the deeply quantum regime -- the below intensity threshold regime, where the energy of the active electron driven by the laser field is insufficient to collisionally ionize the parent ion, and the assistance of the laser field is required to create a doubly charged ion. A special attention is paid to the role of Coulomb interactions in the process. The signatures of electron-electron repulsion, electron-core attraction, and electron-laser interaction are identified. The results are compared with available experimental data. Two-electron correlated spectra of non-sequential double ionization below intensity threshold are known to exhibit back-to-back scattering of the electrons, viz., the anticorrelation of the electrons. Currently, the widely accepted interpretation of the anticorrelation is recollision-induced excitation of the ion plus subsequent field ionization of the second electron. We argue that there exists another mechanism, namely simultaneous electron emission, when the time of return of the rescattered electron is equal to the time of liberation of the bounded electron (the ion has no time for excitation), that can also explain the anticorrelation of the electrons in the deep below intensity threshold regime. Finally, we study single-electron molecular ionization. Based on the geometrical approach to tunnelling by P. D. Hislop and I. M. Sigal [Memoir. AMS 78, No. 399 (1989)], we introduce the concept of a leading tunnelling trajectory. It is then proven that leading tunnelling trajectories for single active electron models of molecular tunnelling ionization (i.e., theories where a molecular potential is modelled by a single-electron multi-centre potential) are linear in the case of short range interactions and ``almost'' linear in the case of long range interactions. The results are presented on both the formal and physically intuitive levels. Physical implications of the proven statements are discussed.

Magistriniame darbe tyrinėjamos elektroninės savybės įvairioms puslaidininkinėms medžiagoms. Tarp jų eksperimentiškai ir teoriškai tirti SbSI - tipo kristalai. Išmatuotos jų voltamperinės charakteristikos įvairiose temperatūrose bei srovės temperatūrinės priklausomybės esant skirtingai įtampai. Iš matavimų paskaičiuotas tarp metalo ir puslaidininkio susidarantis barjero aukštis, kuris vėliau buvo panaudotas teorinių – eksperimentinių rezultatų palyginimui. Eksperimentiniams elektrinio laidumo matavimams paaiškinti remtasi įvairiomis fononais stimuliuoto tuneliavimo teorijomis, kurių taikymui papildomai apskaičiuota elektronų ir fononų sąveikos konstanta esant skirtingoms temperatūroms. Taip pat įvertinti kiti, nemažiau elektriniame laidume svarbius, parametrai. Darbe parodyta, kad fononais stimulioto tuneliavimo teorijos efektyviai aprašo elektrinį laidumą tirtose medžiagose prijungiant prie jų metalo kontaktus. / In this work experimental and theoretical investigations of the high electric field electrical properties in semiconductors with Schottky barrier are presented. Experimental research is given for SbSI – type crystals. Theoretical calculations and comparison with experimental data were made using electrical phonon-assisted tunnelling model (PhAT), which is usable for explanation of temperature-field dependent conductivity in wide branch of materials: semiconductors, dielectrics, inorganic, organic and other materials. PhAT model were used including well determined parameters: effective mass of the charge carrier, participating phonon energy, barrier height and electron-phonon interaction. Barrier height was experimentally measured and found for SbSI, SbSe0.2S0.8I, SbSe0.5S0.5I, SbSeI crystals. The results of the temperature dependence of electron–phonon (e–ph) interaction in the inquiring semiconductors were also calculated. It is shown that these semiconductors have kin e–ph interaction. It varies nearly for about ~ 2.6. It has been shown that the temperature dependent I-V characteristics of SbSeI crystals can be explained by the phonon-assisted tunnelling of charge carriers from the states located in the high electric field region at the electrode-crystal junction. The electron tunnelling probability W(E, T) from traps of the apparent depth to the conduction band was computed using evaluated electron-phonon interaction constant and effective mass of the polaron. The... [to full text]