ALBERT

Description: The phenomenon of ducting is caused by abnormal atmospheric refractivity patterns, and is known to allow electromagnetic (EM) waves to propagate over the horizon with unusually low propagation loss. It is unknown what effect ducting has on multiple input multiple output (MIMO) channels, particularly its effect on multipath propagation in MIMO channels. A high accuracy angle-of-arrival (AoA) and angle-of-departure (AoD) estimation technique for MIMO communications, which we will refer to as compressive MIMO beamforming, was tested on simulated data, then applied to experimental data taken from an over the horizon (OTH) MIMO testbed located in a known ducting hotspot in southern California. The multipath channel was estimated from the receiver data recorded over a period of 18 days, and an analysis was performed on the recorded data. The goal is to observe the evolution of the MIMO multipath channel as atmospheric ducts form and dissipate to gain some understanding of the behavior of channels in a refractive environment. This work is motivated by the idea that some multipath characteristics of MIMO channels within atmospheric ducts could yield important information about the duct.

Description: ABSTRACT Between the years 2008 and 2013, approximately 67 kilotons of CO 2 have been injected at the Ketzin site, Germany. As part of the geophysical monitoring programme, time-lapse electrical resistivity tomography has been applied using crosshole and surface-downhole measurements of electrical resistivity tomography. The data collection of electrical resistivity tomography is partly based on electrodes that are permanently installed in three wells at the site (one injection well and two observation wells). Both types of ERT measurements consistently show the build-up of a CO 2 -related resistivity signature near the injection point. Based on the imaged resistivity changes and a petrophysical model, CO 2 saturation levels are estimated. These CO 2 saturations are interpreted in conjunction with CO 2 saturations inferred from neutron-gamma loggings. Apart from the CO 2 –brine substitution response in the observed resistivity changes, significant imprints from the dynamic behaviour of the CO 2 in the reservoir are observed.

Description: The mesoscale structure of a mature polar low was studied on the basis of high-resolution airborne measurements and numerical modelling. A polar low was measured by light detection and ranging (lidar) and dropsonde observations over the Norwegian Sea on 3 and 4 March 2008. Lidar observations provided cross-sections of water-vapour mixing ratio, backscatter ratio and horizontal wind speed around the polar low and through its centre. Mesoscale structures, such as shallow convection in a cold-air outbreak, a dry intrusion in the eye-like centre of the cyclone and deep convection surrounding it could be identified. Numerical simulations were performed with the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS) and a high-resolution, polar version of the Weather Research and Forecasting (WRF) model. WRF simulations reproduced these structures and showed that the polar low had a warm, upper-level core with descending motions. The eye-like centre had a diameter of about 100–150 km and was characterized by rather stable stratification, horizontally constant potential temperatures and calm winds. Beyond the centre, wind speeds increased rapidly. The observed radial wind and temperature profiles support previous idealized simulations. Several WRF sensitivity tests showed the influence of the initialization time and sensible and latent heat fluxes from the surface on the simulated polar-low development. The polar-low simulations were more accurate in runs starting at the mature stage. Heat fluxes from the surface were important for the polar-low energetics, especially at the final stages. Copyright © 2011 Royal Meteorological Society

Description: Abstract Turbulence causes rapid mixing of solutes and fine particles between open channel flow and coarse‐grained streambeds. Turbulent mixing is known to control hyporheic exchange fluxes and the distribution of vertical mixing rates in the streambed, but it is unclear how turbulent mixing ultimately influences mass transport at the reach scale. We used a particle‐tracking model to simulate local‐ and reach‐scale solute transport for a stream with coarse‐grained sediments. Simulations were first used to determine profiles of vertical mixing rates that best described solute concentration profiles measured within a coarse granular bed in flume experiments. These vertical mixing profiles were then used to simulate a pulse solute injection to show the effects of turbulent hyporheic exchange on reach‐scale solute transport. Experimentally measured concentrations were best described by simulations with a nonmonotonic mixing profile, with highest mixing at the sediment–water interface and exponential decay into the bed. Reach‐scale simulations show that this enhanced interfacial mixing couples in‐stream and hyporheic solute transport. Coupling produces an interval of exponential decay in breakthrough curves and delays the onset of power law tailing. High streamwise velocities in the hyporheic zone reduce mass recovery in the water column and cause breakthrough curves to exhibit steeper power law slopes than predictions from mobile‐immobile modeling theory. These results demonstrate that transport models must consider the spatial variability of streamwise velocity and vertical mixing for both the stream and the hyporheic zone, and new analytical theory is needed to describe reach‐scale transport when high streamwise velocities are present in the hyporheic zone.

Description: The influence of the valley geometry on thermally driven flows is studied by means of high resolution simulations. An idealised valley-plain topography and a spatially constant but time dependent surface sensible heat flux is used to generate upslope, upvalley and plain-to-mountain winds. A systematic variation of valley depth, width and length induces differences in the cross- and along-valley flow field and thermal structure of the boundary layer. The deeper the valley the stronger are the upvalley winds and the more favoured is the formation of vertically stacked circulation cells and an elevated valley inversion layer. Upvalley winds become weaker for wide valleys. The development of plain-to-mountain circulations considerably increases vertical exchange processes between the boundary layer and the free atmosphere compared to vertical transport processes over a plain. The analysis of mass flux budgets and forward trajectories indicates that mass is transported three to four times more effectively from the surface to the free atmosphere over valleys than over flat terrain. Vertical transport processes are strongest for deep and narrow valleys.

Description: Titan, Saturn's largest satellite, is subject to solid body tides exerted by Saturn on the time-scale of its orbital period. The tide-induced internal redistribution of mass results in tidal stress variations, which could play a major role for Titan's geologic surface record. We construct models of Titan's interior that are consistent with the satellite's mean density, polar moment-of-inertia factor, obliquity, and tidal potential Love number k 2 as derived from Cassini observations of Titan's low-degree gravity field and rotational state. In the presence of a global liquid reservoir, the tidal gravity field is found to be consistent with a subsurface water-ammonia ocean more than 180 km thick and overlain by an outer ice shell of less than 110 km thickness. The model calculations suggest comparatively low ocean ammonia contents of less than 5 wt.-% and ocean temperatures in excess of 255 K, i.e., higher than previously thought, thereby substantially increasing Titan's potential for habitable locations. The calculated diurnal tidal stresses at Titan's surface amount to 20 kPa, almost comparable to those expected at Enceladus and Europa. Tidal shear stresses are concentrated in the polar areas, while tensile stresses predominate in the near-equatorial, mid-latitude areas of the sub- and anti-saturnian hemispheres. The characteristic pattern of maximum diurnal tidal stresses is largely compliant with the distribution of active regions such as cryovolcanic candidate areas. The latter could be important for Titan's habitability since those may provide possible pathways for liquid water-ammonia outbursts on the surface and the release of methane in the satellite's atmosphere.

Description: Variability in floral, fruit, and seed characteristics, and oil content of 15 accession of Jatropha curcas during early development were assessed during two flowering periods in south Florida subtropical climate. The two flowering periods had leaf flushing in March. Field evaluation using 18 quantitative traits showed significant variation among accessions. The number of female flowers and female : male flower ratio ranged from 1 to 15 and 1 : 8.8 to 1 : 67.8, respectively. Fruit set by natural pollination was 89 and 66% during the first (1st) and second (2nd) flowering periods, respectively. A higher number of female-type inflorescences were observed during summer. There were significant differences in seed traits, except for number of seeds per fruit. Accession TREC 31 had the highest individual seed dry weight and 100-seed weight (0.83 g and 79.7 g, respectively). The oil content varied from 19.30% to 35.62%. Seed dry weight had positive correlation with seed fresh weight, seed length, seed thickness, seed width, and 100-seed weight, but negative correlation with oil content. Based on the cluster analysis using 15 morphological traits, jatropha accessions were grouped into five main clusters and accessions from different geographic regions grouped together in a cluster. Principal component analyses (PCA) revealed morphological variation. The first three components explained 73.5% of the total variation and seed dry weight, 100-seed weight, total flowers per inflorescence, male flowers per inflorescence and fruit set can be used to distinguish accessions. The PCA also indicated that flowering traits were more influenced by seed origin while seed traits were affected by flowering spans. Although evaluations were performed in plants during the juvenile phase, accessions TREC 31 and TREC 55 had superior averages for almost all characters evaluated. These results provide a preliminary assessment of the high variability in jatropha accessions evaluated and their potential for use in breeding and genetic improvement programs.

Description: Jatropha curcas L. (jatropha) is a species identified for biofuel production because of the high quality of the oil produced by its seeds. However, jatropha is undomesticated and little information is available about its reproductive characteristics. Breeding and genetic improvement programs are much needed for the jatropha development as a bioenergy crop. Information about floral display and mode of reproduction are considered essential for breeding programs. In this study, the total number of female flowers, male to female flower ratio, fruit set, in vitro pollen germination, and the formation of fruits by apomixis, self-pollination, and natural pollination were evaluated in 17 jatropha accessions planted in South Florida. The total number of female flowers per inflorescence and male to female flower ration ranged from 2.8 to 9.1 and 9.9:1 to 55.4 : 1, respectively. During summer 2011, high fruit setting average was observed (75.5%). In vitro pollen germination varied from 64.6% during spring 2011 to 51.6% during fall 2011. The fruit set observed was from 10.1% to 64.0% through natural pollination and apomixes, respectively. Characteristics such as fruit fresh weight, number of seeds per fruit, seed dry weight, and oil content were influenced by mode of reproduction.