Integrated Educational Project of Theoretical, Experimental, and Computational Analyses

This research demonstrates how to design an integrated capstone project by including theoretical, experimental and computational analyses of a truss bridge. The project mainly focused on leading students to approach engineering problems with various methods and to understand the advantages and disadvantages of each method. The students applied three methods to acquire the values of stresses and deflections of members in the given truss bridge. First, they calculated the stresses and deformations theoretically. Second, they actually conducted an experiment of the truss bridge with electronic measuring equipment. Lastly, they built two simulation models with Autodesk Inventor and Dassault Systèmes SolidWorks. From the comparisons of above three methods, students were guided to the validation of assumptions of theories.Cockrell School of Engineerin

Ballistic-Electron-Emission Microscopy at Epitaxial Metal/Semiconductor Interfaces(STM-BEEM interfaces)

The invention of ballistic-electron-emission microscopy (BEEM) has made it possible to study hot electron transport across interfaces with a spatial resolution unparalleled before. In order to exploit the limits of the method we have applied BEEM experiments carried out in UHV and at 77 K to epitaxial CoSi_2 films on silicon. CoSi_2/Si may be considered as a model system for the metal/semiconductor interface, because its atomic structure can be rather well controlled experimentally and has been well characterized by transmission electron microscopy. This overview contains a discussion of the various processes leading to contrast in BEEM images for CoSi_2/Si interfaces. The BEEM current may be affected by (a) the atomic surface structure or surface defects, both of which can change the tunneling distribution, (b) inelastic and elastic scattering processes within the metal films and (c) interface scattering or variations of the Schottky barrier height, resulting from interfacial defects. Scattering processes will be shown to be dominant in the case of CoSi_2/Si(111) interfaces, since the Schottky barrier height is not measurably affected by interfacial dislocations and other defects. Here the ultimate resolution limits of the BEEM technique have been reached, in the sense that individual point defects can be resolved. The CoSi_2/Si(100) interface represents a more complicated case, where extended defects lead to significant barrier lowering, whereas interface scattering is obscured by the strong modification of the tunneling distribution by surface reconstructions

Thermoelectric effects in submicron heterostructure barriers

Nonisothermal electron transport in thin barrier heterostructures is investigated using Monte Carlo techniques. Particular attention is paid to the energy balance in thermionic emission, and the Joule heating in the barrier region. By introducing an energy relaxation length, an equation for the temperature distribution inside the device is derived. Conditions for creating a steady-state temperature gradient and for integrated cooling of electronic components are examined

Climate change in Hong Kong : observations and projections

The Hong Kong Observatory has been making meteorological observations at its headquarters in Tsim Sha Tsui since 1884. Analysis of the extensive past records reveals that the temperature rise in Hong Kong during the past 125 years is in accord with the global rising trend. In last few decades anthropogenic influences, especially urbanization, have contributed significantly to the accelerated rising trend. A similar increasing trend is also observed for rainfall but the trend after 1947 is not statistically significant. Other observations such as increasing cloud amounts, decreasing total global solar radiation and rising sea level are all consistent with the global trend. Studies of past occurrences of extreme temperature and rainfall have recently been carried out. It is observed that cold episodes have become rarer while very hot days and heavy rain events are becoming more frequent. The corresponding return periods of heavy rain and very hot days are decreasing while those of very cold days are increasing. The Observatory also makes use of the data from the latest assessment report of the Intergovernmental Panel on Climate Change and employs statistical downscaling techniques to carry out projections of temperature and precipitation in the 21st century. In gist, the findings are that the rise in temperature will be slightly higher than the global mean in the 21st century. There will also be a significant decrease in the number of cold days and an increase in the number of very hot days and hot nights. The annual rainfall in Hong Kong is also expected to rise by the end of the 21st century, so is the year-to-year variability

Resonantly damped surface and body MHD waves in a solar coronal slab with oblique propagation

The theory of magnetohydrodynamic (MHD) waves in solar coronal slabs in a zero-$\beta$ configuration and for parallel propagation of waves does not allow the existence of surface waves. When oblique propagation of perturbations is considered both surface and body waves are able to propagate. When the perpendicular wave number is larger than a certain value, the body kink mode becomes a surface wave. In addition, a sausage surface mode is found below the internal cut-off frequency. When non-uniformity in the equilibrium is included, surface and body modes are damped due to resonant absorption. In this paper, first, a normal-mode analysis is performed and the period, the damping rate, and the spatial structure of eigenfunctions are obtained. Then, the time-dependent problem is solved, and the conditions under which one or the other type of mode is excited are investigated.Comment: 19 pages, 9 figures, accepted for publication in Solar Physic

Molecular Cloud Formation Behind Shock Waves

We examine the formation of molecular gas behind shocks in atomic gas using a chemical/dynamical model, particular emphasis is given to constraints the chemistry places on the dynamical evolution. The most important result of this study is to stress the importance of shielding the molecular gas from the destructive effects of UV radiation. For shock ram pressures comparable to or exceeding typical local ISM pressures, self-shielding controls the formation time of H2 but CO formation requires shielding of the interstellar radiation field by dust grains. We find that the molecular hydrogen fractional abundance can become significant well before CO forms. The timescale for (CO) molecular cloud formation is not set by H2 formation, but rather by the timescale for accumulating a sufficient column density or extinction, A_V > 0.7. The local ratio of atomic to molecular gas (4:1), coupled with short estimates for cloud lifetimes (3-5 Myr), suggests that the timescales for accumulating molecular clouds from atomic material typically must be no longer than about 12-20 Myr. Based on the shielding requirement, this implies that the typical product of pre-shock density and velocity must be n*v > 20 cm^-3 km s^-1. Based on these results we find that flow-driven formation of molecular clouds in the local interstellar medium can occur sufficiently rapidly to account for observations. We also provide detailed predictions of atomic and molecular emission and absorption that track molecular cloud formation, with a view toward helping to verify cloud formation by shock waves. Finally, we provide an analytic solution for time-dependent H2 formation which may be of use in numerical hydrodynamic calculations.Comment: 43 pages, 13 figures, accepted by ApJ main journa

Phase diagrams of the 2D t-t'-U Hubbard model from an extended mean field method

It is well-known from unrestricted Hartree-Fock computations that the 2D Hubbard model does not have homogeneous mean field states in significant regions of parameter space away from half filling. This is incompatible with standard mean field theory. We present a simple extension of the mean field method that avoids this problem. As in standard mean field theory, we restrict Hartree-Fock theory to simple translation invariant states describing antiferromagnetism (AF), ferromagnetism (F) and paramagnetism (P), but we use an improved method to implement the doping constraint allowing us to detect when a phase separated state is energetically preferred, e.g. AF and F coexisting at the same time. We find that such mixed phases occur in significant parts of the phase diagrams, making them much richer than the ones from standard mean field theory. Our results for the 2D t-t'-U Hubbard model demonstrate the importance of band structure effects.Comment: 6 pages, 5 figure

Repeated Labilization-Reconsolidation Processes Strengthen Declarative Memory in Humans

The idea that memories are immutable after consolidation has been challenged. Several reports have shown that after the presentation of a specific reminder, reactivated old memories become labile and again susceptible to amnesic agents. Such vulnerability diminishes with the progress of time and implies a re-stabilization phase, usually referred to as reconsolidation. To date, the main findings describe the mechanisms associated with the labilization-reconsolidation process, but little is known about its functionality from a biological standpoint. Indeed, two functions have been proposed. One suggests that destabilization of the original memory after the reminder allows the integration of new information into the background of the original memory (memory updating), and the other suggests that the labilization-reconsolidation process strengthens the original memory (memory strengthening). We have previously reported the reconsolidation of human declarative memories, demonstrating memory updating in the framework of reconsolidation. Here we deal with the strengthening function attributed to the reconsolidation process. We triggered labilization-reconsolidation processes successively by repeated presentations of the proper reminder. Participants learned an association between five cue-syllables and their respective response-syllables. Twenty-four hours later, the paired-associate verbal memory was labilized by exposing the subjects to one, two or four reminders. The List-memory was evaluated on Day 3 showing that the memory was improved when at least a second reminder was presented in the time window of the first labilization-reconsolidation process prompted by the earlier reminder. However, the improvement effect was revealed on Day 3, only when at least two reminders were presented on Day2 and not as a consequence of only retrieval. Therefore, we propose central concepts for the reconsolidation process, emphasizing its biological role and the parametrical constrains for this function to be operative

Expression signatures of TP53 mutations in serous ovarian cancers

<p>Abstract</p> <p>Background</p> <p>Mutations in the <it>TP53 </it>gene are extremely common and occur very early in the progression of serous ovarian cancers. Gene expression patterns that relate to mutational status may provide insight into the etiology and biology of the disease.</p> <p>Methods</p> <p>The <it>TP53 </it>coding region was sequenced in 89 frozen serous ovarian cancers, 40 early stage (I/II) and 49 advanced stage (III/IV). Affymetrix U133A expression data was used to define gene expression patterns by mutation, type of mutation, and cancer stage.</p> <p>Results</p> <p>Missense or chain terminating (null) mutations in <it>TP53 </it>were found in 59/89 (66%) ovarian cancers. Early stage cancers had a significantly higher rate of null mutations than late stage disease (38% vs. 8%, p < 0.03). In advanced stage cases, mutations were more prevalent in short term survivors than long term survivors (81% vs. 30%, p = 0.0004). Gene expression patterns had a robust ability to predict <it>TP53 </it>status within training data. By using early versus late stage disease for out of sample predictions, the signature derived from early stage cancers could accurately (86%) predict mutation status of late stage cancers.</p> <p>Conclusions</p> <p>This represents the first attempt to define a genomic signature of <it>TP53 </it>mutation in ovarian cancer. Patterns of gene expression characteristic of <it>TP53 </it>mutation could be discerned and included several genes that are known p53 targets or have been described in the context of expression signatures of <it>TP53 </it>mutation in breast cancer.</p