ALBERT

Description: A number of atmospheric surface layer (ASL) experiments reported a k − 1 scaling in air temperature spectra E TT ( k ) at low wavenumber k but other experiments did not. Occurrence of this scaling law in E TT ( k ) in an otherwise idealized ASL flow across a wide range of atmospheric stability regimes is investigated theoretically and experimentally using measurements collected above a lake and a grass surface. Experiments reveal a k − 1 scaling persisted across different atmospheric stability parameter values ( ζ ) ranging from mildly unstable to mildly stable conditions (− 0.1 〈  ζ  〈 0.2). As instability increases, the k − 1 scaling vanishes. Based on simplified spectral and co-spectral budgets and upon using a Heisenberg eddy viscosity as a closure to the spectral flux transfer term, conditions promoting a k − 1 scaling in E TT ( k ) are identified. Existence of a k − 1 scaling is shown to be primarily linked to an imbalance between the production and dissipation rates of half the temperature variance. When − 0.1 〈  ζ  〈 0.2, such imbalance exhibits weak dependence on ζ and hence z , which is shown to be the main cause for a ‘-1’ scaling at low k . As the atmosphere becomes more unstable, the imbalance determined from experiments here are not significantly affected by ζ thereby negating conditions promoting a ‘-1’ scaling in E TT ( k ). The role of the imbalance between the production and dissipation rates of half the temperature variance in controlling the existence of a ‘-1’ scaling suggests that the ‘-1’ scaling in E TT ( k ) does not necessarily concur with the ‘-1’ scaling in the spectra of longitudinal velocity E uu ( k ). This finding explains why some ASL experiments reported k − 1 in E uu ( k ) but not E TT ( k ).

Description: We quantify the spatial relationship between the plasmapause and outer belt electrons for a five-day period, 15–20 January 2013, by comparing locations of relativistic electron flux peaks to the plasmapause. A peak-finding algorithm is applied to 1.8–7.7 MeV relativistic electron flux data. A plasmapause gradient-finder is applied to wave-derived electron number densities 〉10 cm −3 . We identify two outer belts. Outer belt 1 is a stable zone of 〉3 MeV electrons located 1–2  R E inside the plasmapause. Outer belt 2 is a dynamic zone of 〈3 MeV electrons within 0.5  R E of the moving plasmapause. Electron fluxes earthward of each belt's peak are anti-correlated with cold plasma density. Belt 1 decayed on hiss timescales prior to a disturbance on 17 January, and suffered only a modest dropout, perhaps owing to shielding by the plasmasphere. Afterward, the partially-depleted belt 1 continued to decay at the initial rate. Belt 2 was emptied out by strong disturbance-time losses, but restored within 24 hours. For global context we use a plasmapause test particle (PTP) simulation, and derive a new plasmaspheric index F p , the fraction of a circular drift orbit inside the plasmapause. We find that the locally-measured plasmapause is (for this event) a good proxy for the globally-integrated opportunity for losses in cold plasma. Our analysis of the 15–20 January 2013 time interval confirms that high-energy electron storage rings can persist for weeks or even months if prolonged quiet conditions prevail. This case study must be followed up by more general study (not limited to a five-day period).

Description: The formation of the world-class, high-grade unconformity-related uranium deposits in the Athabasca Basin (Canada) requires circulation of large amounts of fluids, the mechanisms for which are still not well understood. Recent studies advocate thermal convection as a possible driving force for the fluid flow related to uranium mineralization; however, little is known regarding how basement faults, which are spatially associated with most unconformity-related uranium deposits, influence fluid convection and how this may affect the localization of mineralization. This study addresses these questions through simulations of thermal convection with various configurations of basement faults using the FLAC3D software. Modelling results indicate that the location, spacing, orientation and thermal conductivities of basement faults influence the size and location of thermally driven fluid convection. In a model with a single isolated fault, the fault coincides with an upwelling plume and the dip angle of the fault does not affect the fluid flow pattern; when the fault is moved laterally, the upwelling plume shifts accordingly. In the case of two vertical faults, the faults may either coincide with upwelling flow between two convection cells or be located below individual convection cells, depending on fault spacing. In the latter case, fluid may flow into and out of individual fault zones. Similar results were also obtained for models with two nonvertical (i.e. dipping) faults. Convective flow can penetrate the uppermost basement when the permeability is less than two orders of magnitude lower than that of the overlying sandstone. In this case, the basement faults not only can control the location of ascending flow, but also can passively act as fluid conduits of either flow from the basin into the basement (ingress), or flow from the basement into the basin (egress), depending on their thermal conductivities and relative locations in the models.

Description: The statistical altitude distribution of auroral density cavities located between 3.0 to 6.5 R E is investigated using in-situ observations from flux tubes exhibiting auroral acceleration. The locations of the observations are described using a pseudo altitude derived from the distribution of the parallel potential drop above and below the satellite. The upper edge of the auroral acceleration region is observed between 4.375 and 5.625 R E . Above 6.125 R E , noneof the events exhibits precipitating inverted-V electrons, though the upward ion beam can be observed. This indicates that the satellites are located inside the same flux tube as, but above, the auroral acceleration region. The electron density decreases as we move higher into the acceleration region. The spacecraft potential continues to decrease once above the acceleration region, indicating that the density cavity extends above the acceleration region. From 3.0 to 4.375 R E the pseudo altitude increases by 0.20 per R E , consistent with a distributed parallel electric field. Between 4.375 and 5.625 R E the pseudo altitude increases weakly, by 0.01 per R E , due to an increasing number of events per altitude bin, which are occurring above the acceleration region. Above 5.625 R E the pseudo altitude increases by 0.28 per R E , due to a rapid increase in the number of events per altitude bin occurring above the acceleration region, indicating that the remaining parallel potential drop is concentrated in a narrow region at the upper edge of the acceleration region, rather than in a distributed parallel electric field.

Description: We present a generalized multipoint analysis of physical quantities, such as magnetic field and plasma flow, based on spatial gradient properties, where the multipoint data may be taken by irregular (distorted) configurations of any number of spacecraft. The methodology is modified from a previous, fully 3-D gradient analysis technique, designed to apply strictly to 4-point measurements and to be stable for regular spacecraft configurations. Here, we adapt the method to be tolerant against distorted configurations and to return a partial result when fewer spacecraft measurements are available. We apply the method to a variety of important physical quantities, such as the electric current density and the vorticity of plasma flows based on Cluster and THEMIS multiple-point measurements. The method may also have valuable applications on the coming Swarm mission.

Description: A new optimization design of the boil-off gas (BOG) reliquefaction process for liquefied ethylene (LEG) vessels is proposed in order to reduce the reliquefaction process energy cost and improve its cold exergy efficiency. The exergy loss of each component is calculated and the efficiency of the available energy utilization is evaluated on the basis of a detailed thermodynamic analysis. The exergy analysis results indicate that the exergy efficiency of the improved BOG reliquefaction process is about 19.0 % higher than that of the existing process, and the amount of refrigerant used in the improved process is reduced by about 44.9 % per hour. The power consumption could be decreased by 16 %. The circulation volumes of the refrigerant and BOG are both significantly reduced, thus lowering the equipment and operation costs of the BOG reliquefaction process. A cost-effective optimization design of the boil-off gas (BOG) reliquefaction process for liquefied ethylene vessels is proposed. The performances of the reliquefaction system and refrigeration cycle are investigated based on the exergy analysis. The exergy efficiency of the improved refrigeration cycle is significantly increased as well as the energy utilization efficiency of the BOG reliquefaction process.

Description: [1]  Mackenzie River discharge and bathymetry effects on sea ice in the Beaufort Sea are examined in 2012 when Arctic sea ice extent hit a record low. Satellite-derived sea surface temperature revealed warmer waters closer to river mouths. By 5 July 2012, Mackenzie warm waters occupied most of an open-water area about 316,000 km 2 . Surface temperature in a common open-water area increased by 6.5 °C between 14 June and 5 July 2012, before and after the river waters broke through a recurrent landfast ice barrier formed over the shallow seafloor offshore the Mackenzie Delta. In 2012, melting by warm river waters was especially effective when the strong Beaufort Gyre fragmented sea ice into unconsolidated floes. The Mackenzie and other large rivers can transport an enormous amount of heat across immense continental watersheds into the Arctic Ocean, constituting a stark contrast to the Antarctic that has no such rivers to affect sea ice.

Description: Results are presented from a statistical study of high-altitude electric fields and plasma densities using Cluster satellite data collected during 9.5 years between 2 and 4 R E . The average electric fields are most intense on the night-side and associated with an extensive plasma density cavity, with densities of 1 cm -3 or less. The intense electric fields are concentrated in two regions, separated by an altitude gap at about 2.8 R E . Below this, the average electric field magnitudes reach about 50 mV/m (mapped to the ionosphere) between 22 and 01 Magnetic Local Time (MLT). Above 3 R E , the fields are about twice as high, and spread over a broader MLT range. These fields occur in a region where the (ΔE/ΔB)/V A ratio is close to unity, which suggests an Alfvénic origin. The intense low-altitude electric fields are interpreted to be quasi-static, associated with the auroral acceleration region. This is supported by their location in MLT and altitude, and by a (ΔE/ΔB)/V A ratio much below unity. The local electric field minimum between the two regions indicates a partial closure of the electrostatic potentials in the lower region. These results show similarities with model results of reflected Alfvén waves by Lysak and Dum [1983], and with the O-shaped potential model, with associated wave-particle interaction at its top, proposed by Janhunen et al., [2000].

Description: A novel asymmetrical diarylethene with a (formyloxyethoxy)ethyl-linked naphthalimide unit was synthesized, and its photochromic and fluorescence properties were systematically investigated in both solution and a PMMA film. The diarylethene showed significant photochromism and notable fluorescence switching properties upon irradiation with UV/Vis light. Compared with the parent diarylethene, introduction of the naphthalimide moiety was effective to increase the molar absorption coefficient, the fluorescence quantum yield, and fluorescent modulation efficiency of the diarylethene. This article is protected by copyright. All rights reserved.

Description: The Hetai gold deposit (HGD) is a typical altered mylonite type gold mine in a ductile shear zone in western Guangdong, China. Geomechanical simulations of the HGD were carried out in this paper to examine the importance of the dilation-driven fluid circulation in gold mineralization. The results show that three evenly-spaced NNE shear zones of enhanced dilation are produced in the study area. The calculated principal compressive stress in the X direction in these zones ranges between −420 and −650 MPa, in line with estimates of ore-forming pressure (fluid pressure). Ore forming fluid is focused into these features, as observed in the field. The calculated differential stress decreases from 275~350 to 148~225 MPa during the formation of mylonite zones. These, together with geological structural analysis and fluid pressure measurements, indicate that the mylonitization zone can provide a place of fluid focusing and a favorable environment for gold mineralization. In this paper, we present numerical results of mylonitization and structural controls on fluid flow and mineralization of the HGD. First, mylonitization in the HGD was simulated. The calculated differential stress has a value of 483~650 MPa, consistent with estimates of ore-forming pressure. Second, structural controls on fluid flow and mineralization during mylonitization was highlighted in the results. Shear zones are favorable environment for the development of mylonitization zones, and the mylonitization zone can provide a zone of fluid focusing and ore formation.