Determination of the phase diagram of the electron doped superconductor Ba(Fe1−x_{1-x}Cox_x)2_2As2_2

Systematic measurements of the resistivity, heat capacity, susceptibility and Hall coefficient are presented for single crystal samples of the electron-doped superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. These data delineate an $x-T$ phase diagram in which the single magnetic/structural phase transition that is observed for undoped BaFe$_2$As$_2$ at 134 K apparently splits into two distinct phase transitions, both of which are rapidly suppressed with increasing Co concentration. Superconductivity emerges for Co concentrations above $x \sim 0.025$, and appears to coexist with the broken symmetry state for an appreciable range of doping, up to $x \sim 0.06$. The optimal superconducting transition temperature appears to coincide with the Co concentration at which the magnetic/structural phase transitions are totally suppressed, at least within the resolution provided by the finite step size between crystals prepared with different doping levels. Superconductivity is observed for a further range of Co concentrations, before being completely suppressed for $x \sim 0.018$ and above. The form of this $x-T$ phase diagram is suggestive of an association between superconductivity and a quantum critical point arising from suppression of the magnetic and/or structural phase transitions

Spacecraft Internal Acoustic Environment Modeling

The objective of the project is to develop an acoustic modeling capability, based on commercial off-the-shelf software, to be used as a tool for oversight of the future manned Constellation vehicles. The use of such a model will help ensure compliance with acoustic requirements. Also, this project includes modeling validation and development feedback via building physical mockups and conducting acoustic measurements to compare with the predictions

A Statistical Approach for Commercial Space Vehicle Integration into the National Airspace System

This paper explores commercial space vehicle (CSV) suborbital flight trajectories in the temporal and spatial domains for CSV integration into the National Airspace System. The research data was collected via the Suborbital Space Flight Simulator (SSFS) housed in the College of Aviation at Embry-Riddle Aeronautical University - Daytona Beach campus, and analyzed using an original MATLAB data analytics tool. This study primarily focuses on statistical trends observed in previously simulated flights supported by three Project PoSSUM (Polar Suborbital Science in the Upper Mesosphere) campaigns comprised of 34 flights and 19 control flights, and to identify relevant milestones in the CSV flight path. The correlations found in these flight milestones are key for the development of a predictive model for flight and ground safety operators, and reduce the necessity for extensively restricted flight hazard areas. In this paper, the PoSSUM and Control flights are compared to evaluate the deviation caused by different thrust operations conducted by the Scientist Astronaut Candidates (SACs) to enhance scientific data collection in the mesosphere. Preliminary results show the adjustments made by the PoSSUM flights have little effect in the domain with a mean difference of 10.4 seconds in time-of-flight (ToF) outside of the NAS, and a noticeable effect in the spatial domain with a mean difference of 9.3 km in the descent threshold range

The Multi-Phase Medium in the Interstellar Complex N44

We have obtained high-resolution HI observations of N44, one of the largest HII complexes in the Large Magellanic Cloud. The distribution and internal motions of the HI gas show dynamic effects of fast stellar winds and supernova blasts. Numerous HI holes are detected, with the most prominent two corresponding to the optically identified superbubbles Shell 1 and Shell 2. The HI gas associated with Shell 1 shows an expansion pattern similar to that of the ionized gas shell, but the mass and kinetic energy of the HI shell are 3--7 times those of the ionized gas shell. The total kinetic energy of the neutral and ionized gas of Shell 1 is still more than a factor of 5 lower than expected in a pressure-driven superbubble. It is possible that the central OB association was formed in a molecular cloud and a visible superbubble was not fully developed until the ambient molecular gas had been dissociated and cleared away. This hypothesis is supported by the existence of a molecular cloud toward N44 and the fact that the apparent dynamic age of the superbubble Shell 1 is much shorter than the age of its OB association LH47. Accelerated HI gas is detected at the supernova remnant 0523-679. The mass and kinetic energy in the associated HI gas are also much higher than those in the ionized gas of 0523-679. Studies of interstellar gas dynamics using ionized gas alone are clearly inadequate; neutral gas components must be included.Comment: 18 pages,5 figures; for "figures", see at "http://www.astro.uiuc.edu/~sek/N44.html" (4.9 MB postscript.gz) ; Appear to ApJ, 503, 729 (Aug 20

Sub-20 nm Core-Shell-Shell Nanoparticles for Bright Upconversion and Enhanced Förster Resonant Energy Transfer.

Upconverting nanoparticles provide valuable benefits as optical probes for bioimaging and Förster resonant energy transfer (FRET) due to their high signal-to-noise ratio, photostability, and biocompatibility; yet, making nanoparticles small yields a significant decay in brightness due to increased surface quenching. Approaches to improve the brightness of UCNPs exist but often require increased nanoparticle size. Here we present a unique core-shell-shell nanoparticle architecture for small (sub-20 nm), bright upconversion with several key features: (1) maximal sensitizer concentration in the core for high near-infrared absorption, (2) efficient energy transfer between core and interior shell for strong emission, and (3) emitter localization near the nanoparticle surface for efficient FRET. This architecture consists of β-NaYbF4 (core) @NaY0.8-xErxGd0.2F4 (interior shell) @NaY0.8Gd0.2F4 (exterior shell), where sensitizer and emitter ions are partitioned into core and interior shell, respectively. Emitter concentration is varied (x = 1, 2, 5, 10, 20, 50, and 80%) to investigate influence on single particle brightness, upconversion quantum yield, decay lifetimes, and FRET coupling. We compare these seven samples with the field-standard core-shell architecture of β-NaY0.58Gd0.2Yb0.2Er0.02F4 (core) @NaY0.8Gd0.2F4 (shell), with sensitizer and emitter ions codoped in the core. At a single particle level, the core-shell-shell design was up to 2-fold brighter than the standard core-shell design. Further, by coupling a fluorescent dye to the surface of the two different architectures, we demonstrated up to 8-fold improved emission enhancement with the core-shell-shell compared to the core-shell design. We show how, given proper consideration for emitter concentration, we can design a unique nanoparticle architecture to yield comparable or improved brightness and FRET coupling within a small volume

The Effect of Advertisement Frequency on the Advertisement Attitude-The controlled Effects of Brand Image and Spokesperson's Credibility

AbstractAdvertising has been playing a critical channel of communication between enterprises and consumers. To reinforce consumers’ impressions of advertising, enterprises, based on their brand image, strive for the right spokesperson for their products or service. However, in addition to brand image and spokespersons, advertising frequency that can impress general populace is also a factor to affect the consumers’ attitude to the advertisement. This paper discusses not only the effect of brand image and spokesperson's credibility but also the effect of advertising frequency on consumers’ attitude. This study was conducted by the experimental design. The study sample comprised 457 college students. Analysed by ANCOVA, the results showed that the brand image and the spokesperson's credibility both had a significantly positive influence on consumers’ attitude to advertising. Moreover, advertising frequency was significantly influential, too. Theoretical and practical implications of this study were stated for future study