Secondary flow caused by differential roughness,Langmuir circulations,and their effect on the development of sand ribbons

The process of Differential Roughness Secondary Flow (DRSF), hitherto little recognized, recently was demonstrated in a wind tunnel and in a flume. It is suggested here the DRSF may, in the natural environment, play an important part in the persistence and sharp definition of sand ribbons, previously initiated by other processes. In 1980 Karl described a series of sand ribbons, alternating with exposed substrate, which he attributed to the effect of Langmuir circulations. Although Langmuir Circulation Secondary Flow (LCSF) may indeed, in some cases, initiate sand ribbons, the sharply-defined edges typical of these features are explained better by DRSF.     

Submerged cylinder wave energy device: theory and experiment

Linearized water wave theory is used to show that a submerged long circular cylinder suitably constrained by springs and dampers to make small harmonic oscillations, can be extremely efficient in absorbing the energy in an incident regular wave whose crests are parallel to the axis of the cylinder. Experimental results are described which confirm the theory for small amplitude waves and which suggest that the device can still be fairly efficient in waves of moderate amplitude.     

Gravel‐bed rivers: from particles to patterns

The papers in this special issue reflect several of the major themes and topics from the 7^th International Workshop on Gravel‐Bed Rivers. The papers focus primarily on aspects of bed material transport in gravel‐bed rivers and larger scale morpho‐dynamics. Research in gravel‐bed rivers is increasingly integrating processes over a wide range of temporal and spatial scales by combining field observation, lab experimentation, numerical modeling and theory testing in a range of river types, aided by new technological developments in particle tracking, computational modeling and high resolution spatial data. This is leading to greater understanding of the processes leading to distinctive morpho‐dynamics of river types and a more reliable basis for river management. Copyright © 2012 John Wiley & Sons, Ltd.     

The New Multichannel Radiospectrograph ARTEMIS-IV/HECATE, of the University of Athens

We present the new solar radiospectrograph of the University of Athensoperating at the Thermopylae Station since 1996. Observations cover thefrequency range from 110 to 688 MHz. The radiospectrograph has a 7-meterparabolic antenna and two receivers operating in parallel. One is a sweepfrequency receiver and the other a multichannel acousto-optical receiver.The data acquisition system consists of a front-end VME based subsystem anda Sun Sparc-5 workstation connected through Ethernet. The two subsystems areoperated using the VxWorks real-time package. The daily operation is fullyautomated: pointing of the antenna to the sun, starting and stopping theobservations at pre-set times, data acquisition, data compression by`silence suppression', and archiving on DAT tapes. The instrument can beused either by itself to study the onset and evolution of solar radio bursts or in conjunction with other instruments including theNançay Decametric Array and the WIND/WAVES RAD1 and RAD2 low frequencyreceivers to study associated interplanetary phenomena.     

川西南及邻区地震短临预测的实践与思考

在简介川西南及邻区地震地质和历史强震活动的基础上,通过重点梳理部分典型地震短临预测实例,介绍了地方政府对防震减灾、地震预报工作的重视和支持,对工作中的一些实际问题进行了思考,供同行们讨论与参考。     

Investigations of gram quantities of Atlantic and Pacific surface particulates

Particulates amounting to 0.1–2.0 g efficiently collected from large volumes of Atlantic and Pacific surface waters have been analyzed for carbonate, opal, quartz and several natural and man-made radioisotopes.The concentrations of particles range between 10 and 600 μg/kg. In the equatorial regions particle concentrations are low and similar in both the oceans. At higher latitudes (>30°N or S), the Atlantic waters, however, have higher concentrations of particles compared to those in the Pacific. The latitudinal distribution exhibits a north-south symmetry with higher concentrations in the 30°–60° belt. Based on the particulate abundance for CaCO₃ and opal and their sedimentation, we have estimated their production and in-situ integrated dissolution rates for a few regions.Radioisotopes having different source functions, namely¹⁴C and²³⁹Pu injected due to nuclear weapon tests,²³⁴Th,²³⁰Th and²²⁸Th produced in-situ in seawater,²³²Th which derives primarily from land,²¹⁰Pb introduced via wet precipitations and²²⁶Ra introduced through diffusion from deep-sea sediments have been measured in the particulates. The relative enrichment factors for these nuclides in particles vary as Th ? Pu > Pb > Ra. The atmospheric bomb fallout pattern is discernible in the surface particulates; the²³⁹Pu concentration increases with latitude in both the hemispheres; however, the values are about a factor of two lower in the southern hemisphere.The distribution pattern of radioisotopes is found to be complex, even for²³⁴Th whose source function in the oceans is uniform. In view of the differences in the source functions it becomes possible to delineate the principal geochemical/geophysical processes which determine the concentrations of these nuclides in surface waters.     

Despeckling of TerraSAR-X Data Using Second-Generation Wavelets

This letter presents the despeckling of synthetic aperture radar (SAR) images within the bandelet and contourlet domains. A model-based approach is presented for the despeckling of SAR images. The speckle-reduced estimate is found using the first-order Bayesian inference, and the best model's parameters are estimated using the second-order Bayesian inference. Synthetic and real images are used for evaluating the qualities of the despeckling methods. The experimental results showed that the combination of Bayesian inference and bandelet transform outperforms the contourlet-based despeckling algorithm using synthetic data and objective measurements.      

Defining the Potential of Nanoscale Re‐Os Isotope Systematics Using Atom Probe Microscopy

Atom probe microscopy (APM) is a relatively new in situ tool for measuring isotope fractions from nanoscale volumes (< 0.01 μm³). We calculate the theoretical detectable difference of an isotope ratio measurement result from APM using counting statistics of a hypothetical data set to be ± 4δ or 0.4% (2s). However, challenges associated with APM measurements (e.g., peak ranging, hydride formation and isobaric interferences), result in larger uncertainties if not properly accounted for. We evaluate these factors for Re‐Os isotope ratio measurements by comparing APM and negative thermal ionisation mass spectrometry (N‐TIMS) measurement results of pure Os, pure Re, and two synthetic Re‐Os‐bearing alloys from Schwander et al. (2015, Meteoritics and Planetary Science, 50, 893) [the original metal alloy (HSE) and alloys produced by heating HSE within silicate liquid (SYN)]. From this, we propose a current best practice for APM Re‐Os isotope ratio measurements. Using this refined approach, mean APM and N‐TIMS ¹⁸⁷Os/¹⁸⁹Os measurement results agree within 0.05% and 2s (pure Os), 0.6–2% and 2s (SYN) and 5–10% (HSE). The good agreement of N‐TIMS and APM ¹⁸⁷Os/¹⁸⁹Os measurements confirms that APM can extract robust isotope ratios. Therefore, this approach permits nanoscale isotope measurements of Os‐bearing alloys using the Re‐Os geochronometer that could not be measured by conventional measurement principles.     

A technique to assess dispersion

A technique to arrive at conditions congenial to maintaining a stable suspension of fine particles has been described. The technique involves continuous monitoring of apparent loss of weight of a body suspended in settling slurries. Such a technique is useful in fixing the best conditions for gravity separation of fine particles involving Bartles-Mozley concentrators or hydrocyclones.