Planar laser-induced fluorescence imaging of OH in the exhaust of a bi-propellant thruster

Planar laser-induced fluorescence imaging of the hydroxyl radical has been performed on the flow produced by the exhaust of a subscale H2/O2 fueled bi-propellant rocket engine. Measurements were made to test the feasibility of OH (0,0) and (3,0) excitation strategies by using injection seeded XeCl and KrF excimer lasers, respectively. The flow is produced with hydrogen and oxygen reacting at a combustor chamber pressure of 5 atm which then exhausts to the ambient. The hydroxyl concentration in the exhaust flow is approximately 8 percent. Fluorescence images obtained by pumping the Q1(3) transition in the (0,0) band exhibited very high signals but also showed the effect of laser beam absorption. To obtain images when pumping the P1(8) transition in the (3,0) band it was necessary to use exceptionally fast imaging optics and unacceptably high intensifier gains. The result was single-shot images which displayed a signal-to-noise ratio of order unity or less when measured on a per pixel basis

Distances and Kinematics of Gould Belt Star-Forming Regions with Gaia DR2 results

We present an analysis of the astrometric results from Gaia second data release (DR2) to Young Stellar Objects (YSOs) in star-forming regions related to the Gould Belt. These regions are Barnard 59, Lupus 1 to 4, Chamaeleon I and II, $\epsilon$-Chamaeleontis, the Cepheus flare, IC 5146 and Corona Australis. The mean distance to the YSOs in each region are consistent with earlier estimations, though a significant improvement to the final errors was obtained. The mean distances to the star-forming regions were used to fit an ellipsoid of size $(358\pm7)\times(316\pm13)\times(70\pm4)$ pc, and centered at $(X_0,Y_0,Z_0)=(-82\pm15, 39\pm7, -25\pm4)$ pc, consistent with recently determined parameter of the Gould Belt. The mean proper motions were combined with radial velocities from the literature to obtain the three dimensional motion of the star-forming regions, which are consistent with a general expansion of the Gould Belt. We estimate that this expansion is occurring at a velocity of $2.5\pm0.1$ km s$^{-1}$. This is the first time that YSOs motions are used to investigate the kinematic of the Gould Belt. As an interesting side result, we also identified stars with large peculiar velocities.Comment: 18 pages, 14 figures, and 5 tables. Accepted for publication in The Astrophysical Journa

Aquifer Depletion and the Cost of Water Conservation: The Southern High Plains of Texas Case

Irrigated agriculture has played a vital role in the development and growth of the Great Plains Region of the United States. The primary source of water for irrigation in this region is the Ogallala Aquifer. The Southern portion of the Ogallala Aquifer is considered exhaustible due to the low level of recharge relative to the quantities of water pumped. Analysis and evaluation of water conservation policies which could extend the economic life of the Ogallala Aquifer in the Southern High Plains of Texas and Eastern New Mexico, and which could contribute to maintaining the viability of the regional economy is important. This study evaluates the impacts of water conservation policies which limit drawdown of the Ogallala Aquifer. County level dynamic optimization models maximizing net present value of net returns to land, management, groundwater, and irrigation systems over a sixty year planning horizon were formulated to evaluate three aquifer drawdown restrictions. The results of this study indicate that because of the differences in hydrologic characteristics and current irrigation levels across counties in the study area, blanket water conservation policies for the region as a whole are likely to be inefficient. This study concludes that for this region, water conservation policies that focus on counties that would deplete the aquifer to less than 30 ft. of saturated thickness possess the lowest implicit cost of conserving saturated thickness.water conservation, water policy evaluation, aquifer management, dynamic optimization, Resource /Energy Economics and Policy,

Policy Alternatives for the Southern Ogallala Aquifer

Due to declining water levels in the Ogallala Aquifer, policy alternatives for extending the life of the aquifer for irrigation and other purposes are evaluated. The study concludes that blanket water conservation policies for the region are likely to be inefficient because of economic and hydrologic differences in the region.Resource /Energy Economics and Policy,

Evidence for Interlayer Electronic Coupling in Multilayer Epitaxial Graphene from Polarization Dependent Coherently Controlled Photocurrent Generation

Most experimental studies to date of multilayer epitaxial graphene on C-face SiC have indicated that the electronic states of different layers are decoupled as a consequence of rotational stacking. We have measured the third order nonlinear tensor in epitaxial graphene as a novel approach to probe interlayer electronic coupling, by studying THz emission from coherently controlled photocurrents as a function of the optical pump and THz beam polarizations. We find that the polarization dependence of the coherently controlled THz emission expected from perfectly uncoupled layers, i.e. a single graphene sheet, is not observed. We hypothesize that the observed angular dependence arises from weak coupling between the layers; a model calculation of the angular dependence treating the multilayer structure as a stack of independent bilayers with variable interlayer coupling qualitatively reproduces the polarization dependence, providing evidence for coupling.Comment: submitted to Nano Letter

Geometric Entropy for Lead vs Top-Rope Rock Climbing

International Journal of Exercise Science 9(2): 168-174, 2016. The complexity of movement of a rock climber’s center of mass during an ascent has been described as geometric entropy (GE). It has been proposed that lower geometric entropy could represent more fluid and economical movement during climbing. The purpose of the present study was to measure GE during rock climbing ascents under a lead condition (LD), where the climber connects a safety rope to several intermediate anchors during the ascent and under a top-rope condition (TR), where the safety rope is always anchored above the climber. Six experienced rock climbers volunteered to participate in the study. Each participant ascended a route on natural rock outdoors under three conditions. The first ascent was performed in a top-rope condition as an accommodation trial. The two remaining ascents were performed as LD and top-rope (TR2) in random order. Each LD and TR2 ascent was recorded via digital video at 30 Hz. A single point at the back center of each climber’s waist harness was manually digitized from the video images at 6 Hz and interpreted as the climber’s center of mass (CM). The displacement of CM was expressed as the line of motion (LM). Geometric Entropy (GE) was calculated as GE = ln((2∙LM)/CH)), where CH was the value of the convex hull about the LM. A within subjects, repeated measures ANOVA with Bonferroni post hoc testing was utilized to test for differences among ascent conditions with significance set at P \u3c0.05. Mean (±s.d) values for LM and GE were 81.5±11.3 m vs 77.6±7.3 m and 1.021±0.133 vs 0.924±0.062 for LD and TR2 respectively. There were no significant differences for LM and GE between ascent conditions. It was concluded that LM and GE do not vary between LD and TR ascent conditions

Evidence of Titan's Climate History from Evaporite Distribution

Water-ice-poor, 5-$\mu$m-bright material on Saturn's moon Titan has previously been geomorphologically identified as evaporitic. Here we present a global distribution of the occurrences of the 5-$\mu$m-bright spectral unit, identified with Cassini's Visual Infrared Mapping Spectrometer (VIMS) and examined with RADAR when possible. We explore the possibility that each of these occurrences are evaporite deposits. The 5-$\mu$m-bright material covers 1\% of Titan's surface and is not limited to the poles (the only regions with extensive, long-lived surface liquid). We find the greatest areal concentration to be in the equatorial basins Tui Regio and Hotei Regio. Our interpretations, based on the correlation between 5-$\mu$m-bright material and lakebeds, imply that there was enough liquid present at some time to create the observed 5-$\mu$m-bright material. We address the climate implications surrounding a lack of evaporitic material at the south polar basins: if the south pole basins were filled at some point in the past, then where is the evaporite

Synthesis and Crystal Structure of Tetrachloro (1,10-phenanthroline) platinum (IV)

We report the crystal structure determination of tetrachloro( l,10-phenan­throline)platinum(IV). X-ray data indicate there is little steric repulsion between the cx.-hydrogens on the phenanthroline ligand and the chloride ligands in the equatorial plane

Gaia-DR2 confirms VLBA parallaxes in Ophiuchus, Serpens and Aquila

We present Gaia-DR2 astrometry of a sample of YSO candidates in Ophiuchus, Serpens Main and Serpens South/W40 in the Aquila Rift, which had been mainly identified by their infrared excess with Spitzer. We compare the Gaia-DR2 parallaxes against published and new parallaxes obtained from our Very Long Baseline Array (VLBA) program GOBELINS. We obtain consistent results between Gaia and the VLBA for the mean parallaxes in each of the regions analyzed here. We see small offsets, when comparing mean values, of a few tens of micro-arcseconds in the parallaxes, which are either introduced by the Gaia zero-point error or due to a selection effect by Gaia toward the brightest, less obscured stars. Gaia-DR2 data alone conclusively places Serpens Main and Serpens South at the same distance, as we first inferred from VLBA data alone in a previous publication. Thus, Serpens Main, Serpens South and W40 are all part of the same complex of molecular clouds, located at a mean distance of 436+/-9 pc. In Ophiuchus, both Gaia and VLBA suggest a small parallax gradient across the cloud, and the distance changes from 144.2+/-1.3 pc to 138.4+/-2.6 pc when going from L1689 to L1688.Comment: Accepted for publication in ApJ

Hot carrier cooling by acoustic phonons in epitaxial graphene by ultrafast pump-probe spectroscopy

We report the application nondegenerate ultrafast mid-infrared spectroscopy to investigate the acoustic phonon cooling process in epitaxial graphene. We show that the power-dependent experimental results match theoretical predictions of the low temperature acoustic cooling process. The hot phonon effect in acoustic phonon cooling is observed experimentally, and a deformation potential of 30 eV can be determined from fitting the data. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83459/1/1194_ftp.pd