Current Status of a NASA High-Altitude Balloon-Based Observatory for Planetary Science

Recent studies have shown that progress can be made on over 20% of the key questions called out in the current Planetary Science Decadal Survey by a high-altitude balloon-borne observatory. Therefore, NASA has been assessing concepts for a gondola-based observatory that would achieve the greatest possible science return in a low-risk and cost-effective manner. This paper addresses results from the 2014 Balloon Observation Platform for Planetary Science (BOPPS) mission, namely successes in the design and performance of the Fine Pointing System. The paper also addresses technical challenges facing the new Gondola for High Altitude Planetary Science (GHAPS) reusable platform, including thermal control for the Optical Telescope Assembly, power generation and management, and weight-saving considerations that the team will be assessing in 2015 and beyond

Optical properties and electronic structure of Ca-doped alpha'-NaV2O5

The dielectric function of alpha'-Na(1-x)Ca(x)V2O5 (0 < x < 20%) was measured for the a and b axes in the photon energy range 0.8-4.5 eV at room temperature. By varying the Ca-concentration we control the relative abundancy of V4+ and V5+. We observe that the intensity of the main optical absorption peak at 1 eV is proportional to the number of V5+ ions. This rules out the interpretation as a V4+ d-d excitation, and it establishes that this is the on-rung bonding-antibonding transition.Comment: 6 pages, ReVTeX, 5 figures in encapsulated postscript forma

CuSiO_3 : a quasi - one - dimensional S=1/2 antiferromagnetic chain system

CuSiO_3, isotypic to the spin - Peierls compound CuGeO_3, was discovered recently as a metastable decomposition product of the silicate mineral dioptase, Cu_6Si_6O_{18}\cdot6H_2O. We investigated the physical properties of CuSiO_3 using susceptibility, magnetization and specific heat measurements on powder samples. The magnetic susceptibility \chi(T) is reproduced very well above T = 8 K by theoretical calculations for an S=1/2 antiferromagnetic Heisenberg linear chain without frustration (\alpha = 0) and a nearest - neighbor exchange coupling constant of J/k_{B} = 21 K, much weaker than in CuGeO_3. Below 8 K the susceptibility exhibits a substantial drop. This feature is identified as a second - order phase transition at T_{0} = 7.9 K by specific heat measurements. The influence of magnetic fields on T_{0} is weak, and ac - magnetization measurements give strong evidence for a spin - flop - phase at \mu_0H_{SF} ~ 3 T. The origin of the magnetic phase transition at T_{0} = 7.9 K is discussed in the context of long - range antiferromagnetic order (AF) versus spin - Peierls(SP)order. Susceptibility and specific heat results support the AF ordered ground state. Additional temperature dependent ^{63,65}Cu nuclear quadrupole resonance experiments have been carried out to probe the Cu^{2+} electronic state and the spin dynamics in CuSiO_3

A microscopic model for the structural transition and spin gap formation in alpha'-NaV2O5

We present a microscopic model for alpha'-NaV2O5. Using an extended Hubbard model for the vanadium layers we derive an effective low-energy model consisting of pseudospin Ising chains and Heisenberg chains coupled to each other. We find a ``spin-Peierls-Ising'' phase transition which causes charge ordering on every second ladder and superexchange alternation on the other ladders. This transition can be identified with the first transition of the two closeby transitions observed in experiment. Due to charge ordering the effective coupling between the lattice and the superexchange is enhanced. This is demonstrated within a Slater-Koster approximation. It leads to a second instability with superexchange alternation on the charge-ordered ladders due to an alternating shift of the O sites on the rungs of that ladder. We can explain within our model the observed spin gap, the anomalous BCS ratio, and the anomalous shift of the critical temperature of the first transition in a magnetic field. To test the calculated superstructure we determine the low-energy magnon dispersion and find agreement with experiment.Comment: 32 pages, 12 figures include

²³Na/⁵¹V NMR study of alpha'-Na_0.9966Li_0.0034V₂O₅

In this paper we report Na-23/V-51 NMR measurements for a single crystal of alpha'-Na0.9966Li0.0034V2O5. The lithium doping of 0.34% reduces the transition temperature to similar to32 K (J. Magn. Magn. Mater. 226-230 (2001) 405). Below To each Na satellite splits into about 8 lines of different intensities, no drastic influence on the central line of Na accompanies this change. Three vanadium sites are found in the low-temperature phase. (C) 2002 Elsevier Science B.V. All rights reserved

NMR study of doped alpha '-NaV₂O₅ single crystals

Na-23 and V-51 NMR in the low temperature phase of sodium vanadate show the existence of three vanadium and 8 or 10 sodium sites. These are due to the charge ordering transition and the dimerization of magnetic vanadium ions below 34 K, respectively. All vanadium sites persist to the lowest observed temperature, 4.2 K, and the re-ordering as monitored by the sodium quadrupolar satellites continues throughout the whole temperature range. Furthermore, the satellite intensities are not equal, suggesting sodium sites of varying occupancies. (C) 2002 Elsevier Science B.V. All rights reserved

23Na/51V NMR study of alpha'-Na0.9966Li0.0034V2O5

In this paper we report Na-23/V-51 NMR measurements for a single crystal of alpha'-Na0.9966Li0.0034V2O5. The lithium doping of 0.34% reduces the transition temperature to similar to32 K (J. Magn. Magn. Mater. 226-230 (2001) 405). Below To each Na satellite splits into about 8 lines of different intensities, no drastic influence on the central line of Na accompanies this change. Three vanadium sites are found in the low-temperature phase. (C) 2002 Elsevier Science B.V. All rights reserved

NMR study of doped alpha '-NaV2O5 single crystals

Na-23 and V-51 NMR in the low temperature phase of sodium vanadate show the existence of three vanadium and 8 or 10 sodium sites. These are due to the charge ordering transition and the dimerization of magnetic vanadium ions below 34 K, respectively. All vanadium sites persist to the lowest observed temperature, 4.2 K, and the re-ordering as monitored by the sodium quadrupolar satellites continues throughout the whole temperature range. Furthermore, the satellite intensities are not equal, suggesting sodium sites of varying occupancies. (C) 2002 Elsevier Science B.V. All rights reserved