The Surveyor 5, 6, and 7 Flight Paths and Their Determination from Tracking Data

Surveyor 5, 6, and 7 flight paths and tracking data for space station location

The Surveyor 3 and Surveyor 4 flight paths and their determination from tracking data

Surveyor 3 and 4 spacecraft flight path

Photon pair generation using four-wave mixing in a microstructured fibre: theory versus experiment

We develop a theoretical analysis of four-wave mixing used to generate photon pairs useful for quantum information processing. The analysis applies to a single mode microstructured fibre pumped by an ultra-short coherent pulse in the normal dispersion region. Given the values of the optical propagation constant inside the fibre, we can estimate the created number of photon pairs per pulse, their central wavelength and their respective bandwidth. We use the experimental results from a picosecond source of correlated photon pairs using a micro-structured fibre to validate the model. The fibre is pumped in the normal dispersion regime at 708nm and phase matching is satisfied for widely spaced parametric wavelengths of 586nm and 894nm. We measure the number of photons per pulse using a loss-independent coincidence scheme and compare the results with the theoretical expectation. We show a good agreement between the theoretical expectations and the experimental results for various fibre lengths and pump powers.Comment: 23 pages, 9 figure

Effects of Diversity on Multi-agent Systems: Minority Games

We consider a version of large population games whose agents compete for resources using strategies with adaptable preferences. The games can be used to model economic markets, ecosystems or distributed control. Diversity of initial preferences of strategies is introduced by randomly assigning biases to the strategies of different agents. We find that diversity among the agents reduces their maladaptive behavior. We find interesting scaling relations with diversity for the variance and other parameters such as the convergence time, the fraction of fickle agents, and the variance of wealth, illustrating their dynamical origin. When diversity increases, the scaling dynamics is modified by kinetic sampling and waiting effects. Analyses yield excellent agreement with simulations.Comment: 41 pages, 16 figures; minor improvements in content, added references; to be published in Physical Review

Non-existence of Skyrmion-Skyrmion and Skyrmion-anti-Skyrmion static equilibria

We consider classical static Skyrmion-anti-Skyrmion and Skyrmion-Skyrmion configurations, symmetric with respect to a reflection plane, or symmetric up to a $G$-parity transformation respectively. We show that the stress tensor component completely normal to the reflection plane, and hence its integral over the plane, is negative definite or positive definite respectively. Classical Skyrmions always repel classical Skyrmions and classical Skyrmions always attract classical anti-Skyrmions and thus no static equilibrium, whether stable or unstable, is possible in either case. No other symmetry assumption is made and so our results also apply to multi-Skyrmion configurations. Our results are consistent with existing analyses of Skyrmion forces at large separation, and with numerical results on Skymion-anti-Skyrmion configurations in the literature which admit a different reflection symmetry. They also hold for the massive Skyrme model. We also point out that reflection symmetric self-gravitating Skyrmions or black holes with Skyrmion hair cannot rest in symmetric equilibrium with self-gravitating anti-Skyrmions.Comment: v2 Typos corrected, refs added. v3 Journal versio

Unification of bulk and interface electroresistive switching in oxide systems

We demonstrate that the physical mechanism behind electroresistive switching in oxide Schottky systems is electroformation, as in insulating oxides. Negative resistance shown by the hysteretic current-voltage curves proves that impact ionization is at the origin of the switching. Analyses of the capacitance-voltage and conductance-voltage curves through a simple model show that an atomic rearrangement is involved in the process. Switching in these systems is a bulk effect, not strictly confined at the interface but at the charge space region.Comment: 4 pages, 3 figures, accepted in PR

Thermodynamic improvements in liquid hydrogen turbopumps Interim report, 17 Jun. 1966 - 17 Jun. 1967

Engineering criteria for thermodynamic improvenent of liquid hydrogen turbopumps for rocket engine

A special irreducible matrix representation of the real Clifford algebra C(3,1)

4x4 Dirac (gamma) matrices (irreducible matrix representations of the Clifford algebras C(3,1), C(1,3), C(4,0)) are an essential part of many calculations in quantum physics. Although the final physical results do not depend on the applied representation of the Dirac matrices (e.g. due to the invariance of traces of products of Dirac matrices), the appropriate choice of the representation used may facilitate the analysis. The present paper introduces a particularly symmetric real representation of 4x4 Dirac matrices (Majorana representation) which may prove useful in the future. As a byproduct, a compact formula for (transformed) Pauli matrices is found. The consideration is based on the role played by isoclinic 2-planes in the geometry of the real Clifford algebra C(3,0) which provide an invariant geometric frame for it. It can be generalized to larger Clifford algebras.Comment: 23 pages LaTeX, to appear in the J. Math. Phys. (v2: appendix B on Pauli matrices and references are added, minor other changes

Cerebrospinal fluid levels of extracellular heat shock protein 72: A potential biomarker for bacterial meningitis in children

Extracellular heat shock protein 72 (Hsp72) is an endogenous danger signal and potential biomarker for critical illness in children. We hypothesized that elevated levels of extracellular Hsp72 in the cerebrospinal fluid (CSF) of children with suspected meningitis could predict bacterial meningitis. We measured extracellular Hsp72 levels in the CSF of 31 critically ill children with suspected meningitis via a commercially available enzyme-linked immunosorbent assay. Fourteen had bacterial meningitis based on CSF pleocytosis and bacterial growth in either blood or CSF culture. Seventeen children with negative cultures comprised the control group. CSF Hsp72 was significantly elevated in children with bacterial meningitis compared to controls. Importantly, CSF Hsp72 levels did not correlate with the CSF white blood cell count. On receiver operator characteristic analysis, using a cut-off of 8.1 ng/mL, CSF Hsp72 has a sensitivity of 79% and a specificity of 94% for predicting bacterial meningitis. We therefore conclude that CSF extracellular Hsp72 levels are elevated in critically ill children with bacterial meningitis versus controls. Hsp72 potentially offers clinicians improved diagnostic information in distinguishing bacterial meningitis from other processes

Relativistic Modification of the Gamow Factor

In processes involving Coulomb-type initial- and final-state interactions, the Gamow factor has been traditionally used to take into account these additional interactions. The Gamow factor needs to be modified when the magnitude of the effective coupling constant increases or when the velocity increases. For the production of a pair of particles under their mutual Coulomb-type interaction, we obtain the modification of the Gamow factor in terms of the overlap of the Feynman amplitude with the relativistic wave function of the two particles. As a first example, we study the modification of the Gamow factor for the production of two bosons. The modification is substantial when the coupling constant is large.Comment: 13 pages, in LaTe