Effect of Co doping and hydrostatic pressure on SrFe2As2

We report a pressure study on electron doped SrFe$_{2-x}$Co$_x$As$_2$ by electrical-resistivity ($\rho$) and magnetic-susceptibility ($\chi$) experiments. Application of either external pressure or Co substitution rapidly suppresses the spin-density wave ordering of the Fe moments and induces superconductivity in SrFe$_2$As$_2$. At $x=0.2$ the broad superconducting (SC) dome in the $T-p$ phase diagram exhibits its maximum $T_{c,{\rm max}}=20$ K at a pressure of only $p_{\rm max}\approx 0.75$ GPa. In SrFe$_{1.5}$Co$_{0.5}$As$_2$ no superconductivity is observed anymore up to 2.8 GPa. Upon increasing the Co concentration the maximum of the SC dome shifts toward lower pressure accompanied by a decrease in the value of $T_{c,{\rm max}}$. Even though, superconductivity is induced by both tuning methods, Co substitution leads to a much more robust SC state. Our study evidences that in SrFe$_{2-x}$Co$_x$As$_2$ both, the effect of pressure and Co-substitution, have to be considered in order to understand the SC phase-diagram and further attests the close relationship of SrFe$_2$As$_2$ and its sister compound BaFe$_2$As$_2$.Comment: 6 pages, 6 figure

Competition of local-moment ferromagnetism and superconductivity in Co-substituted EuFe2As2

In contrast to SrFe2As2, where only the iron possesses a magnetic moment, in EuFe2As2 an additional large, local magnetic moment is carried by Eu2+. Like SrFe2As2, EuFe2As2 exhibits a spin-density wave transition at high temperatures, but in addition the magnetic moments of the Eu2+ order at around 20 K. The interplay of pressure-induced superconductivity and the Eu2+ order leads to a behavior which is reminiscent of re-entrant superconductivity as it was observed, for example, in the ternary Chevrel phases or in the rare-earth nickel borocarbides. Here, we study the delicate interplay of the ordering of the Eu2+ moments and superconductivity in EuFe1.9Co0.1As2, where application of external pressure makes it possible to sensitively tune the ratio of the magnetic (T_C) and the superconducting (T_{c,onset}) critical temperatures. We find that superconductivity disappears once T_C > T_{c,onset}.Comment: 4 pages, 4 figures, submitted to the proceedings of SCES201

Evaluation of the Marc 7G1 auxiliary rocket motor for use on the Atlas-Centaur vehicle Final report

Evaluation of Mars 7G1 auxiliary rocket motor for use as retrograde thrust generator on Atlas-Centaur space vehicl

Evaluation of the MARC 7G1 auxiliary rocket motor for use on the Atlas-Centaur vehicle Final report, Mar. - Oct. 1965

Solid propellant rocket engine environmental and static testing for use as retrograde thrustor in Atlas-Centaur space vehicl

Roughness correction to the Casimir force at short separations: Contact distance and extreme value statistics

So far there has been no reliable method to calculate the Casimir force at separations comparable to the root-mean-square of the height fluctuations of the surfaces. Statistical analysis of rough gold samples has revealed the presence of peaks considerably higher than the root-mean-square roughness. These peaks redefine the minimum separation distance between the bodies and can be described by extreme value statistics. Here we show that the contribution of the high peaks to the Casimir force can be calculated with a pairwise additive summation, while the contribution of asperities with normal height can be evaluated perturbatively. This method provides a reliable estimate of the Casimir force at short distances, and it solves the significant, so far unexplained discrepancy between measurements of the Casimir force between rough surfaces and the results of perturbation theory. Furthermore, we illustrate the importance of our results in a technologically relevant situation.Comment: 29 pages, 11 figures, to appear in Phys. Rev.

Adaptive Adjustable Tricycle

As a part of the Cal Poly Mechanical Engineering curriculum, all students must take part in a three quarter long senior design project. Students are presented with existing problems, select a project, and then apply the knowledge they have gained throughout their academic career to design and build a solution. The intent behind this project is to create an experience that is similar to an engineering project in industry, by applying engineering and teamwork skills to solve a problem. Team Trikeceratops’ mission was to develop an adaptive adjustable tricycle to be used in the Special Education Department of the Buena Park School District for recreational use and physical therapy. The design team was comprised of four Cal Poly mechanical engineering students and a kinesiology student-consultant who worked through three primary design phases over the course of nine months to develop a functional prototype. These phases included ideation and conception, detailed design, and manufacturing, all of which have different requirements that call for a variety of skill sets. During ideation and conception, Team Trikeceratops developed lists of requirements from sponsor input, divided the project into components, generated ideas, and refined the options to reach an overall conceptual design. This initial phase was also essential in developing a team mentality and establishing the basic rules and guidelines by which the team would operate. At the end of ideation and conception, the team had developed a full theoretical design that would meet the customer requirements. Detailed design was the second phase wherein the students took the conceptual design and applied engineering knowledge to clearly define the solution. In this phase, most of the more stereotypical engineering occurred. Students sized tubing for the frame, performed calculations and analysis on components, created manufacturing drawings, identified part numbers for acquisition, and began contacting companies for parts and services. At the end of detailed design, the team had a bill of materials, manufacturing plan, contact information for suppliers, and fully dimensioned drawings for manufacturing custom parts. The third phase of product development was manufacturing and testing. Students cut, notched, welded, and machined various custom components while simultaneously overcoming problems of improper sizing and extended lead times on ordered materials. Following this process, the students tested the tricycle to ensure that it met the customer requirements set forth in the Design Verification Plan and Report (DVPR). At the end of this phase a functioning prototype was completed and staged for delivery and the final report was compiled. This remainder of this report details Team Trikeceratops’ progress from initial concept generation to prototype realization and explores each part of the aforementioned engineering design process in depth