Experimental evaluation of outer planets probe thermal insulation concepts

An experimental program was conducted to evaluate various thermal insulation concepts for use in the Outer Planets Probe (OPP) during entry and descent into the atmospheres of Jupiter, Saturn, and Uranus. Phenolic fiberglass honeycomb specimens representative of the OPP structure were packed and tested with various fillers: Thermal conductivity measurements were made over a temperature range of 300 K to 483 K and pressures from vacuum up to 10 atmospheres in helium and nitrogen gas environments. The conductivity results could not be fully explained so new test specimens were designed with improved venting characteristics, and tested to determine the validity of the original data. All of the conductivity data showed results that were substantially higher than expected. The original test data in helium were lower than the data from the redesigned specimens, probably due to inadequate venting of nitrogen gas from the original specimens. The thermal conductivity test results show only a marginal improvement in probe thermal protection performance for a filled honeycomb core compared to an unfilled core. In addition, flatwise tension tests showed a severe bond strength degradation due to the inclusion of either the powder or foam fillers. In view of these results, it is recommended that the baseline OPP design utilize an unfilled core

Outer planets probe testing

An atmospheric entry Probe is being developed by NASA Ames Research Center (ARC) to conduct in situ scientific investigations of the outer planets' atmospheres. A full scale engineering model of an MDAC-E Probe configuration, was fabricated by NASA ARC. Proof-of-concept test validation of the structural and thermal design is being obtained at NASA ARC. The model was successfully tested for shock and dynamic loading and is currently in thermal vacuum testing

Fabrication of (111)-Faced Single-Crystal Diamond Plates by Laser Nucleated Cleaving

Single-crystal diamond plates with surfaces oriented in a (111) crystal plane are required for high-performance solid-state device platforms ranging from power electronics to quantum information processing architectures. However, producing plates with this orientation has proven challenging. In this paper, we demonstrate a method for reliably and precisely fabricating (111)-faced plates from commercially available, chemical-vapor-deposition-grown, type-IIa single-crystal diamond substrates with (100) faces. Our method uses a nanosecond-pulsed visible laser to nucleate and propagate a mechanical cleave in a chosen (111) crystal plane, resulting in faces as large as 3.0 mm$\times$0.3 mm with atomically flat surfaces, negligible miscut angles, and near zero kerf loss. We discuss the underlying physical mechanisms of the process along with potential improvements that will enable the production of millimeter-scale (111)-faced single-crystal diamond plates for a variety of emerging devices and applications.Comment: 11 pages, 10 figures, 2 table

Amplified Sensitivity of Nitrogen-Vacancy Spins in Nanodiamonds using All-Optical Charge Readout

Nanodiamonds containing nitrogen-vacancy (NV) centers offer a versatile platform for sensing applications spanning from nanomagnetism to in-vivo monitoring of cellular processes. In many cases, however, weak optical signals and poor contrast demand long acquisition times that prevent the measurement of environmental dynamics. Here, we demonstrate the ability to perform fast, high-contrast optical measurements of charge distributions in ensembles of NV centers in nanodiamonds and use the technique to improve the spin readout signal-to-noise ratio through spin-to-charge conversion. A study of 38 nanodiamonds, each hosting 10-15 NV centers with an average diameter of 40 nm, uncovers complex, multiple-timescale dynamics due to radiative and non-radiative ionization and recombination processes. Nonetheless, the nanodiamonds universally exhibit charge-dependent photoluminescence contrasts and the potential for enhanced spin readout using spin-to-charge conversion. We use the technique to speed up a $T_1$ relaxometry measurement by a factor of five.Comment: 13 pages, 14 figure

Speeding up simulations of relativistic systems using an optimal boosted frame

It can be computationally advantageous to perform computer simulations in a Lorentz boosted frame for a certain class of systems. However, even if the computer model relies on a covariant set of equations, it has been pointed out that algorithmic difficulties related to discretization errors may have to be overcome in order to take full advantage of the potential speedup. We summarize the findings, the difficulties and their solutions, and show that the technique enables simulations important to several areas of accelerator physics that are otherwise problematic, including self-consistent modeling in three-dimensions of laser wakefield accelerator stages at energies of 10 GeV and above.Comment: To be published in the proceedings of DPF-2009, Detroit, MI, July 2009, eConf C09072

Space-charge transport limits of ion beams in periodic quadrupole focusing channels

It has been empirically observed in both experiments and particle-in-cell simulations that space-charge-dominated beams suffer strong growth in statistical phase-space area (degraded quality) and particle losses in alternating gradient quadrupole transport channels when the undepressed phase advance sigma_0 increases beyond about 85 degrees per lattice period. Although this criterion has been used extensively in practical designs of strong focusing intense beam transport lattices, the origin of the limit has not been understood. We propose a mechanism for the transport limit resulting from classes of halo particle resonances near the core of the beam that allow near-edge particles to rapidly increase in oscillation amplitude when the space-charge intensity and the flutter of the matched beam envelope are both sufficiently large. When coupled with a diffuse beam edge and/or perturbations internal to the beam core that can drive particles outside the edge, this mechanism can result in large and rapid halo-driven increases in the statistical phase-space area of the beam, lost particles, and degraded transport. A core-particle model is applied to parametrically analyze this process. Extensive self-consistent particle in cell simulations are employed to better quantify space-charge limit and verify core-particle model predictions.Comment: 17 pages, 5 figures. Submitted to Nuclear Instruments and Methods A. Includes a long version of a conference talk (trans_limits_talk.pdf) presented on the topic at the "Coulomb'05 -- High Intensity Beam Dynamics" workshop (Senigallia, Italy, 12-16 September 2005). This talk presents further supporting information/plots not included in the abbreviated, draft-format manuscrip

"Das schnelle Date". Internetgestützte Sexkontakte und HIV-Infektionsrisiko. Ergebnisse einer 2006 durchgeführten Internetbefragung

Der seit Ende der 1990er Jahre diskutierten Frage, ob bei Sexualkontakten, die über Kontaktseiten im Internet hergestellt werden, in geringerem Umfang präventive Vorkehrungen in Hinblick auf HIV-Übertragungen erfolgen als bei andernorts angebahnten Kontakten, sollte in einer im Frühjahr 2006 durchgeführten Online-Umfrage nachgegangen werden. Die Umfrage erfolgte über vier Dating-Portale für heterosexuelle Frauen und Männer und über vier Portale für homound bisexuelle Männer. Von den berücksichtigten 5.050 Fragebögen entfielen 76 Prozent auf Männer, die ausschließlich gleichgeschlechtliche Sexualkontakte in den 12 Monaten vor der Befragung angaben, 11 Prozent der Männer wurden aufgrund ihrer Angaben als bisexuell und weitere 11 Prozent als heterosexuell definiert. Frauen stellten lediglich 2 Prozent der BefragungsteilnehmerInnen. Etwa drei Viertel aller Befragten schätzten an Kontaktseiten, das sie darüber Menschen „mit gleichen Vorlieben“ kennenlernen können, dabei muss es sich nicht um sexuelle Vorlieben handeln: So haben etwa 22 Prozent der Frauen, 12 Prozent der homosexuellen, 9 Prozent der heterosexuellen und 6 Prozent der bisexuellen Männer überhaupt keine(n) Sexpartner(in) in den 12 Monaten vor der Befragung gesucht. Online gesucht aber keine(n) Partner(in) gefunden haben 18 Prozent der Frauen, 21 Prozent der homosexuellen, 24 Prozent der bisexuellen und 45 Prozent der heterosexuellen Männer. Etwa die Hälfte der homo- und bisexuellen Männer haben ihre SexualpartnerInnen mehrheitlich oder ausschließlich über das Internet kennengelernt, während dies nur auf 39 Prozent der heterosexuellen Männer zutrifft (zwei Drittel geben dies in der kleinen Gruppe der Frauen an). Dass heterosexuelle Männer die geringsten Erfolge beim Anbahnen von Sexualkontakten über das Internet haben, zeigen auch andere erhobene Daten. Unter den Befragungsteilnehmern erfolgte regelmäßiger Kondomgebrauch bei Vaginal- oder Analverkehr – je nach Gruppenzugehörigkeit - zu sehr unterschiedlichen Anteilen. 55 Prozent der homosexuellen und 47 Prozent der bisexuellen Männer benutzten grundsätzlich Kondome, 38 Prozent der heterosexuellen Männer und 34 Prozent der Frauen gaben dies an. Hinsichtlich des Risikos, sich mit HIV zu infizieren (ungeschützter Anal- oder Vaginalverkehr mit PartnerInnen mit unbekanntem oder diskordantem Serostatus - Expositionsrisiko), bestanden nur geringe Unterschiede zwischen homo- (27%), bi- (31%) und heterosexuellen Männern (26%) bzw. Frauen (27%). Ein Transmissionsrisiko konnte lediglich in der Teilgruppe der homosexuellen (8%) und bisexuellen (1%) Männer festgestellt werden, da in den anderen beiden Gruppen niemand HIV-positiv war. Es zeigt sich, dass bei der überwiegenden Mehrheit aller Befragten das HIV-bezogene sexuelle Risikoverhalten bei online- und offline-Dates gleich ist. Are people more likely to risk an HIV infection with sex partners they meet online as compared to those whom they meet offline? This question has been the subject of research since the late 1990s in several post-industrialized countries. This paper presents the results of a study conducted in Germany in 2006. A link to an anonymous, self-administered online questionnaire was posted on four dating websites for heterosexual men and women and on four dating websites for men who have sex with men. Of the 5,050 respondents included in the analysis, 76 per cent were men who reported sexual contacts in the previous twelve months exclusively with other men; 11 per cent could be classified as bisexual men (sexual contacts with men and women), and 11 per cent as heterosexual men (sexual contact with women only).. Two per cent of all respondents were women; because of the small number of respondents this group was not further stratified in the analysis. Finding persons “with similar interests” was the most frequently expressed positive aspect of dating websites (78% among homosexual men, 80% among bisexual men, 74% among heterosexual men, and 73% among women). This did not necessarily mean similar sexual interests: 22 per cent of the women, 12 per cent of the homosexual men, 6 per cent of the bisexual men, and 9 per cent of the heterosexual men claimed they had not been looking for sex partners during their visits to the sites in the previous twelve months. Many respondents reported being unsuccessful in finding a sex partner online: 18 per cent of the women, 21 per cent of the homosexual men, 24 per cent of the bisexual men, and 45 per cent of the heterosexual men. While during the previous twelve months half of the homo- and bisexual men found most (if not all) of their sex partners on the Internet, the respective proportions were 39 per cent among heterosexual men, and 67% in the small group of female respondents. Taken together, heterosexual men were the least successful in finding sex partners on the Internet. Regular use of condoms for every anal or vaginal intercourse was reported by 55 per cent of the homosexual men, 47 per cent of the bisexual men, 38 of the heterosexual men, and 34 per cent of the women. However, regarding unprotected anal or vaginal intercourse with a sex partner of unknown or discordant HIV serostatus, the proportions among the different subgroups were very similar (homosexual men: 27%; bisexual men: 31%; heterosexual men: 26%; women: 27%). The risk of transmitting a known HIV infection to sex partners was only present among homosexual (8%) and bisexual (1%) men, primarily because only respondents from these two subgroups identified as HIV-positive. For the large majority (83-86%) of men, HIV risk behaviours are the same, regardless if sex partners are met online or offline

Performance of a 1200m long suspended Fabry-Perot cavity

Using one arm of the Michelson interferometer and the power recycling mirror of the interferometric gravitational wave detector GEO600, we created a Fabry-Perot cavity with a length of 1200 m. The main purpose of this experiment was to gather first experience with the main optics, its suspensions and the corresponding control systems. The residual displacement of a main mirror is about 150 nm rms. By stabilising the length of the 1200 m long cavity to the pre-stabilised laser beam we achieved an error point frequency noise of 0.1 mHz/sqrt(Hz) at 100 Hz Fourier frequency. In addition we demonstrated the reliable performance of all included subsystems by several 10-hour-periods of continuous stable operation. Thus the full frequency stabilisation scheme for GEO600 was successfully tested.Comment: Amaldi 4 (Perth 2001) conference proceedings, 10 pages, 8 figure