Strength of the DTM RapidSteel 1.0 Material

This paper reports the results of a study into the strength of the DTM RapidSteel 1.0 material. Elastic modulus and strength of the metal/copper composite material was investigated as a function of the distance from the point of copper infiltration, the furnace cycle duration, and the furnace type. The microstructure of the RapidSteel material was also examined in an attempt to understand the science behind the infiltration process. The results have implications for the design of tools to be made using the RapidTool process in situations where the tool will be used as a production tool, rather than a prototype tool.Mechanical Engineerin

Effective Vortex Pinning in MgB2 thin films

We discuss pinning properties of MgB2 thin films grown by pulsed-laser deposition (PLD) and by electron-beam (EB) evaporation. Two mechanisms are identified that contribute most effectively to the pinning of vortices in randomly oriented films. The EB process produces low defected crystallites with small grain size providing enhanced pinning at grain boundaries without degradation of Tc. The PLD process produces films with structural disorder on a scale less that the coherence length that further improves pinning, but also depresses Tc

Pyrolysis-GC×GC-TOFMS to characterize carbonaceous chondrites

Using pyrolysis-GCxGC-TOFMS to analyze organic carbon in carbonaceous chondrites gives a massive increase in both sensitivity and structural information from samples when compared to traditional Py-GC-MS

System model development for nuclear thermal propulsion

A critical enabling technology in the evolutionary development of nuclear thermal propulsion (NTP) is the ability to predict the system performance under a variety of operating conditions. This is crucial for mission analysis and for control subsystem testing as well as for the modeling of various failure modes. Performance must be accurately predicted during steady-state and transient operation, including startup, shutdown, and post operation cooling. The development and application of verified and validated system models has the potential to reduce the design, testing, and cost and time required for the technology to reach flight-ready status. Since Oct. 1991, the U.S. Department of Energy (DOE), Department of Defense (DOD), and NASA have initiated critical technology development efforts for NTP systems to be used on Space Exploration Initiative (SEI) missions to the Moon and Mars. This paper presents the strategy and progress of an interagency NASA/DOE/DOD team for NTP system modeling. It is the intent of the interagency team to develop several levels of computer programs to simulate various NTP systems. The first level will provide rapid, parameterized calculations of overall system performance. Succeeding computer programs will provide analysis of each component in sufficient detail to guide the design teams and experimental efforts. The computer programs will allow simulation of the entire system to allow prediction of the integrated performance. An interagency team was formed for this task to use the best capabilities available and to assure appropriate peer review

Cinderella Strings

We investigate recent claims concerning a new class of cosmic string solutions in the Weinberg-Salam model. They have the general form of previously discussed semi-local and electroweak strings, but are modified by the presence of a non-zero W-condensate in the core of the string. We explicitly construct such solutions for arbitrary values of the winding number $N$. We then prove that they are gauge equivalent to bare electroweak strings with winding number $N-1$. We also develop new asymptotic expressions for large-$N$ strings.Comment: 11 pages, harvmac (b) and epsf (2 figures uuencoded

Perceived enablers and barriers to optimal health among music students: a qualitative study in the music conservatoire setting

Student health and wellbeing within higher education has been documented as poor in relation to the general population. This is a particular problem among students at music conservatoires, who are studying within a unique educational context that is known to generate both physical and psychological challenges. This article examines how conservatoire students experience health and wellbeing within their institutional context, using a framework from health promotion to focus attention on perceived enablers and barriers to optimal health in relation to three levels: lifestyle, support services, and conservatoire environment. In order to respond to the individuality of students’ experiences, a qualitative approach was taken based on semi-structured interviews with 20 current or recent conservatoire students in the United Kingdom. Thematic analysis revealed a complex set of enablers and barriers: (i) lifestyle enablers included value placed on the importance of optimal health and wellbeing for musicians and daily practices to enable this; lifestyle barriers included struggling to maintain healthy lifestyles within the context of musical practice and learning; (ii) support enablers included accessible support sources within and beyond the conservatoire; support barriers included a perceived lack of availability or awareness of appropriate support; (iii) environmental enablers included positive and enjoyable experiences of performance as well as strong relationships and communities; environmental barriers included experiences of comparison and competition, pressure and stress, challenges with negative performance feedback, psychological distress, and perceived overwork. The findings reveal a need for health promotion to focus not only on individuals but also on the daily practices and routines of conservatoires. Additionally, they suggest that continued work is required to embed health and wellbeing support as an integral component of conservatoire education, raising awareness so that all students are fully informed of where, and how, to seek the information or help that they may need. Finally, they indicate a need for more radical scrutiny of the cultures of conservatoires and an assessment of how these can be modified to best optimize students’ health and wellbeing

Perturbation Theory for Path Integrals of Stiff Polymers

The wormlike chain model of stiff polymers is a nonlinear $\sigma$-model in one spacetime dimension in which the ends are fluctuating freely. This causes important differences with respect to the presently available theory which exists only for periodic and Dirichlet boundary conditions. We modify this theory appropriately and show how to perform a systematic large-stiffness expansions for all physically interesting quantities in powers of $L/\xi$, where $L$ is the length and $\xi$ the persistence length of the polymer. This requires special procedures for regularizing highly divergent Feynman integrals which we have developed in previous work. We show that by adding to the unperturbed action a correction term ${\cal A}^{\rm corr}$, we can calculate all Feynman diagrams with Green functions satisfying Neumann boundary conditions. Our expansions yield, order by order, properly normalized end-to-end distribution function in arbitrary dimensions $d$, its even and odd moments, and the two-point correlation function

Unzipping of DNA with correlated base-sequence

We consider force-induced unzipping transition for a heterogeneous DNA model with a correlated base-sequence. Both finite-range and long-range correlated situations are considered. It is shown that finite-range correlations increase stability of DNA with respect to the external unzipping force. Due to long-range correlations the number of unzipped base-pairs displays two widely different scenarios depending on the details of the base-sequence: either there is no unzipping phase-transition at all, or the transition is realized via a sequence of jumps with magnitude comparable to the size of the system. Both scenarios are different from the behavior of the average number of unzipped base-pairs (non-self-averaging). The results can be relevant for explaining the biological purpose of correlated structures in DNA.Comment: 22 pages, revtex4, 14 eps figures; reprinted in the June 15, 2004 issue of Virtual Journal of Biological Physics Researc