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The Pacific-North America plate boundary in central and southern California has a complex tectonic history, and constraints are poor for inception of an extensional fault system linked to the southern San Andreas fault, a major tectonic element of this plate boundary. Furthermore, decades of research has shown relationships between climate, tectonics, and surface processes in most orogens across the globe (e.g. Alps, Himalaya, Andes, Alaska Ranges), however the role climate plays in modulating erosion and mass fluxes from extensional mountains blocks to sedimentary basins over 104-5 yr timescales is debated. In the eastern California-Walker Lane shear zone, exposures of sedimentary basin fill allow inversion of erosion- and sediment-flux rates from a linked catchment-fan system within an extensional block. In this dissertation, I present two field and geo-thermochronology based studies that explore research topics related by common tectonic setting and geography within the Pacific-North America plate boundary. First I present new low-temperature thermochronology (apatite U-Th-Sm/He) and thermal history modeling to document the kinematic evolution of the Santa Rosa mountains, where the cooling history constrains initiation timing of the west Salton Detachment fault, and the southern San Andreas fault system. I document an age of ca. 8 Ma for exhumation initiation of the Santa Rosa block, from paleodepths of ~4.5–3 km, at vertical rates of ~0.15–0.36 mm/yr, accelerating to ~1.3 km/Ma since ca. 1.2 Ma during initiation of the San Jacinto fault zone. Second, I present a new data set of cosmogenic radionuclide-derived burial ages and paleodenudation rates (26Al/10Be) from the Pleasant Canyon complex in the Panamint Range, and show that denudation rate and sediment flux have varied by a factor of ~2x since the middle Pleistocene. I conclude high frequency variability is driven by climate change, and not tectonic perturbations, as supported by published constraints for exhumation timing. The middle Pleistocene transition from 40–100 ka periodicity may drive the observed changes, a tentative conclusion that makes testable predictions for stratigraphic records of past climate in other locations. Empirical evidence for climate-modulated erosion and sediment flux provides valuable constraints for numerical models of landscape evolution and sedimentary basin architecture. / Ph. D.

During World War II, with the armed forces waging war on several fronts and with the development of high altitude aircraft, the necessity for a great deal of low temperature testing was brought about. The production testing of various instruments and appliances, such as radios, cameras, clocks, and meters, which would be subjected to low temperatures in arctic climates or at high altitudes, was found necessary. This subject had been given very little consideration prior to the war. When it became necessary to test equipment at a low temperature, it was normally transported to a cold climate and there the tests were conducted. With the increased demand for low temperature testing, the expense and time delay encountered in such movements became prohibitive. During and since the war many low temperature test chambers have been built. The design problems encountered, such as load determination, defrosting, lubrication, refrigerant selection, proper staging, and control selection, have been similar, but the solutions have been different. Moore, Gellalles, and Young state: "Experience has shown that research requirements change so quickly and so radically that the original design specification cannot be much more than a hopeful guess.”(22) Mr. Coy W. Brown states: "Any systems requiring evaporating refrigerant temperatures below -40° F. should be attempted only by engineers experienced in this presently special field."(5) Since definite data on equipment for low temperature test rooms seems to be limited, it is believed that from a design of such a machine much valuable information can be gained. Two low temperature testing rooms have been constructed in the Mechanical Engineering Laboratory at The Virginia Polytechnic Institute. One will operate at temperatures down to 0° F. and the other will operate at temperatures down to -40° F. In addition to being used for low temperature research, it is anticipated that the refrigerating equipment for these rooms will be used by students taking Mechanical Laboratory in routine experiments. The object of this thesis is to design suitable refrigeration equipment for the two rooms. The design will include specifications, bill of material and equipment, detail and assembly drawings, and operating instructions. Available data on the design, control, and operation of low temperature refrigerating equipment will be assembled and correlated. This information, with interpretation thereof, will be used in solving a practical engineering problem which is, at the present, in a special field. / Master of Science

We cool and study trans-Stilbene, Nile Red and Benzonitrile in a cryogenic (7K) cell filled with low density helium buffer gas. No molecule-helium cluster formation is observed, indicating limited atom-molecule sticking in this system. We place an upper limit of 5% on the population of clustered He-trans-Stilbene, consistent with a measured He-molecule collisional residence time of less than \(1 \mu s\). With several low energy torsional modes, trans-Stilbene is less rigid than any molecule previously buffer gas cooled into the Kelvin regime. We report cooling and gas phase visible spectroscopy of Nile Red, a much larger molecule. Our data suggest that buffer gas cooling will be feasible for a variety of small biological molecules. The same cell is also ideal for studying collisional relaxation cross sections. Measurements of Benzonitrile vibrational state decay results in determination of the vibrational relaxation cross sections of \(\sigma_{22} = 8x10^{-15} cm^2\) and \(\sigma_{21} = 6x10^{-15} cm^2\) for the 22 (v=1) and 21 (v=1) states. For the first time, we directly observe formation of cold molecular dimers in a cryogenic buffer gas cell and determine the dimer formation cross section to be \(\sim10^{-13} cm^2\). / Physics

This thesis presents several experiments, generally aiming at visualising the ballistic and topological transport on the high-mobility graphene/boron nitride heterostructure using the scanning gate microscope. For the first experiment, we use the scanning gate microscopy to map out the trajectories of ballistic carriers in high-mobility graphene encapsulated by hexagonal boron nitride and in a weak perpendicular magnetic field. We employ a magnetic focusing transport configuration to image carriers that emerge ballistically from an injector, follow a cyclotron path due to the Lorentz force from an applied magnetic field, and land on an adjacent collector probe. The local potential generated by the scanning tip in the vicinity of the carriers deflects their trajectories, modifying the proportion of carriers focused into the collector. By measuring the voltage at the collector while scanning the tip, we are able to obtain images with arcs that are consistent with the expected cyclotron motion. We also demonstrate that the tip can be used to redirect misaligned carriers back to the collector. For the second experiment, we investigate the graphene van der Waals structures formed by aligning monolayer graphene with insulating layers of hexagonal boron nitride which exhibit a moiré superlattice that is expected to break sublattice symmetry. However, despite an energy gap of several tens of millielectronvolts opening in the Dirac spectrum, electrical resistivity remains lower than expected at low temperature and varies between devices. While subgap states are likely to play a role in this behaviour, their precise nature is still unclear in the community. We therefore perform a scanning gate microscopy study of graphene moiré superlattice devices with comparable activation energy but with different charge disorder levels. In the device with higher charge impurity ($\sim$ 10$^-$ cm$^{-2}$) and lower resistivity ($\sim$ 10 k$\Omega$) at the Dirac point we observe scanning gate response along the graphene edges. Combined with simulations, our measurements suggest that enhanced edge doping is responsible for this effect. In addition, a device with low charge impurity ($\sim$ 10$^{9}$ cm$^{-2}$) and higher resistivity ($\sim$ 100 k$\Omega$) shows subgap states in the bulk. Our measurements provide alternative model to the prevailing theory in the literature in which the topological bandstructures of the graphene moiré superlattices entail an edge currents shunting the insulating bulk. In the third experiment, we continue our study in the graphene moir$\acute e$ superlattices with the newly reported non-local Hall signals at the main Dirac point. It has been associated with the non-zero valley Berry curvature due to the gap opening and the nonlocal signal has been interpreted as the signature of the topological valley Hall effects. However, the nature of such signal is still disputed in the community, due to the vanishing density of states near the Dirac point and the possible topological edge transport in the system. Various artificial contribution without a topological origin of the measurement scheme has also been suggested. In connection to the second experiment, we use the scanning gate microscope to image the non-local Hall resistance as well as the local resistance in the current path. By analysing the features in the two sets of images, we find evidence for topological Hall current in the bulk despite a large artificial components which cannot be distinguished in global transport measurement. In the last experiment, we show the development of a radio-frequency scanning impedance microscopy compatible with the existing scanning gate microscopy and the dilution refrigerator. We detailed the design and the implementation of the radio-frequency reflectometry and the specialised tip holder for the integration of the tip and the transmission lines. We demonstrate the capability of imaging local impedance of the sample by detecting the mechanical oscillation of the tip, the device topography, and the Landau levels in the quantum Hall regime at liquid helium temperature and milli-Kelvin temperature.

In this diplomatic work, the issue of low-temperature asphalts and binders for asphalt mixtures is solved. Diploma work is divided into two parts, theoretical and practical. In the theoretical part of diploma work, the purpose was to process a overview of technologies that allow the reduction of working temperature in the production and laying of asphalt mixtures. The purpose of the practical part was to comparison the functional parameters of two types of asphalt mixtures made in two variants, with the common asphalt binder and adding licomont into asphalt. Attention was given to stiffness, wheel drive tests and low temperature parameters.

Today’s society is highly reliable on a working road infrastructure, which is because of collective efforts already built in terms of main net of roadways, and the attention is now paid to its service life primarily from a point of view of a climate change which is causing more frequent temperature extremes. This thesis sets its goal to perform basic tests for bitumen, especially ones dealing with low temperature properties, on types of bitumen usually used in out day to day world and asphalt mixtures made with those types of bitumen. The theoretical part talks about the basic definition of bitumen and studies performed on the similar issue. Practical part of the thesis is focused on performing the tests of bitumen and asphalt, which include but are not limited to, penetration test, softening point test, critical temperature detected by method by Fraasse and the bending beam rheometer and the test to set critical temperature of asphalt by using TSRST. At the end of the thesis the evaluation of results and its mutual correlation is performed.

Swedes are extremely common as a root vegetable in Europe, USA, and Canada but are affected by the occasional presence of Brown Heart (BH) disorder affecting the marketable swede root. The incidence of BH has been reported worldwide however it is very difficult to breed resistance due to its sporadic occurrence with no external symptoms to select for. BH has been attributed to boron availability but attempts to link BH appearance definitively with boron deficiency have been difficult. Anecdotal evidence from breeders and growers highlighted the recent co-appearance of BH and frost injury in the field and it was postulated that if an association (physiological or genetic) can be determined between BH appearance and another more easily assessed trait such as frost susceptibility, then a frost tolerance screen may be developed as a useful surrogate method to screen for BH resistance. Frost hardiness assessment of 12 swede genotypes including some F1 hybrids was carried out. Results showed that some genotypes (like Ag31, Me77c and Or13) were more susceptible to frost (EL50 circa -7 ˚C) whilst others (like Gr19 and Ly01) were classified as more tolerant. Breeder trials data from the UK and Germany over a 10 year period showed that 85% of the BH incidence was associated with genotypes that had the frost susceptible lines Ag31, Or13 or Me77c in their parentage. To investigate this association further, frost susceptible and tolerant genotypes, together with a number of their F1 hybrids, were evaluated in a field trial for their response to boron treatments (0.00, 1.35, 1.80 and 2.70 kg B ha-1). At maturity, BH incidence and its severity was predominantly affected by genotype but could be ameliorated by boron application. Ag31 was confirmed to be the most susceptible to BH, and Or13 and Me77c were intermediate in their susceptibility. F1 hybrids between any two susceptible parents were also susceptible to BH. In contrast, genotypes Gr19 and Ly01 were confirmed to be highly resistant to BH and did not show any BH symptoms even at zero boron applied. F1 hybrids between resistant and susceptible lines demonstrated the BH resistant phenotype. Resistance to BH was therefore confirmed as a dominant trait with either a BHBH or BHbh genotype, whilst susceptibility was recessive bhbh. A degree of quantitative variation existed in the severity of the BH suggesting that BH resistance was not a single gene effect. BH severity was significantly negatively correlated (r = - 0.632) with root boron content in susceptible genotypes. The genotypes which were BH resistant in this trial were also more tolerant to frost in screening tests and this association was investigated further at a molecular level. Cold acclimation (CA) for 14 days at 4 ˚C positively affected the response of swede to frost, lowering the EL50 by -1.5˚C, and boron reduced the EL50 by -2.2˚C under non-acclimating conditions and by -1.2˚C under CA. Both boron and CA increased the catalase (CAT) and super oxidase dismutase (SOD) concentrations in swede leaves. Molecular analysis clearly demonstrated the presence of the B.napus cold response gene in swede, BN115, and was shown to be up-regulated due to both CA and boron application but differed between the two genotypes tested. The more frost resistant Gr19 showed a better response than the susceptible Ag31. Boron application reduced EL50 by -2.3˚C for Ag31 and -3.1˚C for Gr19. Given the association between frost tolerance and BH resistance it is suggested that a frost test screen could be used as a useful surrogate method to screen for BH resistance in swede breeding programmes.

Flue gas carbon dioxide emissions from coal-based power plants are suggested as a factor causing climate change. Membrane is an attractive technology for the capture of carbon dioxide from flue gas. Matrimid® asymmetric hollow fiber membranes with “homogeneous dense” and “fused nodular” selective layers were successfully formed. The PDMS post-treated nodular-skinned fibers showed better cold performance than the dense-skinned fibers with bore side feed. A hypothesis with regards to increased sorption capacity coupled with orientated polymer chain segments for the nodular skin was proposed and supported by indirect evidences. Based on the understanding of CO2 and N2 transport in cold Matrimid® hollow fiber membranes, a second generation of cold membranes with superior performance was developed. The high free volume, rigid 6FDA/BPDA-DAM hollow fiber membranes with both dense and nodular selective layers were successfully formed as well, which showed similar selectivity but much higher permeance than the high performing nodular Matrimid® hollow fiber membranes at cold conditions.

A cryogenic thermoelectric generator is proposed to increase the efficiency of a vehicle propulsion system that uses liquid nitrogen as its fuel. The proposed design captures some of the heat required for vaporizing or initial heating of the liquid nitrogen to produce electricity. The thermoelectric generator uses pressurized liquid nitrogen as its cold reservoir and ambient air as the high-temperature reservoir to generate power. This study concentrated on the selection of thermoelectric materials whose properties would result in the highest efficiency over the operating temperature range and on estimating the initial size of the generator. The preliminary selection of materials is based upon their figure of merit at the operating temperatures. The results of this preliminary design investigation of the cryogenic thermoelectric generator indicate that sufficient additional energy can be used to increase overall efficiency of the thermodynamic cycle of a vehicle propulsion system.