Slabs of stabilized jellium: Quantum-size and self-compression effects

We examine thin films of two simple metals (aluminum and lithium) in the stabilized jellium model, a modification of the regular jellium model in which a constant potential is added inside the metal to stabilize the system for a given background density. We investigate quantum-size effects on the surface energy and the work function. For a given film thickness we also evaluate the density yielding energy stability, which is found to be slightly higher than the equilibrium density of the bulk system and to approach this value in the limit of thick slabs. A comparison of our self-consistent calculations with the predictions of the liquid-drop model shows the validity of this model.Comment: 7 pages, 6 figures, to appear in Phys. Rev.

Concentration Gradient, Diffusion, and Flow Through Open Porous Medium Near Percolation Threshold via Computer Simulations

The interacting lattice gas model is used to simulate fluid flow through an open percolating porous medium with the fluid entering at the source-end and leaving from the opposite end. The shape of the steady-state concentration profile and therefore the gradient field depends on the is found to scale with the porosity according to porosity p. The root mean square (rms) displacements of fluid and its constituents (tracers) show a drift power-law behavior, in the asymptotic regime. The flux current density is found to scale with the porosity according to an exponent near 1.7.Comment: 8 figure

Verification of the mixed layer depth in the OceanMAPS operational forecast model for Austral autumn

The ocean mixed layer depth is an important parameter describing the exchange of fluxes between the atmosphere and ocean. In ocean modelling a key factor in the accurate representation of the mixed layer is the parameterization of vertical mixing. An ideal opportunity to investigate the impact of different mixing schemes was provided when the Australian Bureau of Meteorology upgraded its operational ocean forecasting model, OceanMAPS to version 3.0. In terms of the mixed layer, the main difference between the old and new model versions was a change of vertical mixing scheme from that of Chen et al. (1994) to the General Ocean Turbulence Model.The model estimates of the mixed layer depth were compared with those derived from Argo observations. Both versions of the model exhibited a deep bias in tropical latitudes and a shallow bias in the Southern Ocean, consistent with previous studies. The bias, however, was greatly reduced in version 3.0, and variance between model runs decreased. Additionally, model skill against climatology also improved significantly. Further analysis discounted changes to model resolution outside of the Australian region having a significant impact on these results, leaving the change in vertical\ud mixing scheme as the main factor in the assessed improvements to mixed layer depth representation.</p

Lattice Dynamics and the High Pressure Equation of State of Au

Elastic constants and zone-boundary phonon frequencies of gold are calculated by total energy electronic structure methods to twofold compression. A generalized force constant model is used to interpolate throughout the Brillouin zone and evaluate moments of the phonon distribution. The moments are used to calculate the volume dependence of the Gruneisen parameter in the fcc solid. Using these results with ultrasonic and shock data, we formulate the complete free energy for solid Au. This free energy is given as a set of closed form expressions, which are valid to compressions of at least V/V_0 = 0.65 and temperatures up to melting. Beyond this density, the Hugoniot enters the solid-liquid mixed phase region. Effects of shock melting on the Hugoniot are discussed within an approximate model. We compare with proposed standards for the equation of state to pressures of ~200 GPa. Our result for the room temperature isotherm is in very good agreement with an earlier standard of Heinz and Jeanloz.Comment: 13 pages, 8 figures. Accepted by Phys. Rev.

Prosthetic Knee

Amputations, specifically lower limb amputations, are common in Sub Saharan Africa and across the broader global community largely due to infection and disease. Our project, The Prosthetic Knee Team, partners with the orthopedic workshop at the CURE International Hospital in Kijabe, Kenya to create a prosthetic knee design for a specific type of amputation known as a Knee Disarticulation (also called through-knee). Currently, the orthopedic workshop is only able to provide one very expensive prosthetic knee option for these patients, and they often elect to undergo a second surgery, a trans-femoral amputation, because the cost of the second surgery and trans-femoral prosthesis combined is less than the currently available through-knee prosthetic. The goal of our project is to provide the orthopedic workshop with a manufacturable prosthetic knee design that provides through-knee amputees with a cheaper prosthetic option and removes the need to have a second amputation above the knee. Throughout the past two semesters, our focus was on organizing collected data, researching knee-disarticulations, and communicating with our client to more fully understand the scope of our project. After determining that moving forward our project will be manufacturing the prosthetic knees at Messiah College’s machine shop and shipping them to CURE Kenya to be fit on patients, we began to brainstorm potential design ideas. We are presently working on modifying and improving our chosen design to best meet all of the specifications laid out by our partner. Those specifications include minimized thigh-lengthening, low weight, maximized stability and durability, and aesthetically pleasing.https://mosaic.messiah.edu/engr2020/1017/thumbnail.jp

Block-Diagonalization and f-electron Effects in Tight-Binding Theory

We extend a tight-binding total energy method to include f-electrons, and apply it to the study of the structural and elastic properties of a range of elements from Be to U. We find that the tight-binding parameters are as accurate and transferable for f-electron systems as they are for d-electron systems. In both cases we have found it essential to take great care in constraining the fitting procedure by using a block-diagonalization procedure, which we describe in detail.Comment: 9 pages, 6 figure