Geotechnology to determine the depth of active zone in expansive soils in Kibaha, Tanzania

Considerable distress to lightly loaded engineered structures in various parts of the coast of Tanzania is due to development of heave and swelling pressure in the active zone of expansive clay soils. The active zone is the region of soil near the surface in which the water content varies due to precipitation and evapo-transpiration. Even though the soil may have the potential to shrink and swell below the depth of active zone, volume changes will not take place because the water content of the soil is constant. Because the water content distribution does not change with time below that zone, the soil should be either stabilized or removed down to that depth or the foundation must extend to a depth that exceeds that of the active zone. A logical soil investigation needs to be carried out by anappropriate geotechnology to determine the depth of active zone based upon the site specific soil conditions that are dependent on the water content in the soil at the specific site in question. To monitor the water content changes with depth, samples from different open pits at earmarked intervals and depths within 100-hectare section in Kibaha wereanalysed. Based on the moisture content variation with depth, the depth of the active zone ranged between 1.5 m and 2.0 m

Spatial variability of expansive soil properties at different scales within Kibaha (Tanzania)

This paper applies statistical and geostatistical procedures to analyse the spatial distribution of several soil properties and use the contribution of ge ostatistics to plan optimal soil sampling and management schemes inKibaha, Tanzania. Particle-size distribution, Atterberg limits and potential swell were analysed. Variogram models for clay content which is strongly correlated to the swell are constructed using the means of the soil properties. The variograms show that the distributions of all variables were not random but spatially-dependent as their estimated variogram values increased with increasing distance. The variograms predicted significantly slower horizontal variation and faster vertical variation of the clay content. The average range values vary between 20 and 30 m in horizontal separation and 1.0 m and 1.5m in depths for particle-size distribution. It implies that if wishing to reduce the need for expensive and intensive sampling, then grid soil sampling will generally have to be performed at interval of less than half the range of spatial dependence of clay content depending on the attribute of interest

Communist China\u27s Policy Toward Latin America

The threat of wars of national liberation fostered by China looms larger in the minds of many people than is warranted by the results to date of such efforts. This article relates China\u27s frustrating failure to increase her influence in Latin America, and in doing so it reduces to realistic proportions China\u27s emotional appeal to the underdeveloped nations of the world

The Powerful Antitakeover Force of Staggered Boards: Theory, Evidence and Policy

Staggered boards, which a majority of public companies now have, provide a powerful antitakeover defense, stronger than is commonly recognized. They provide antitakeover protection both by (i) forcing any hostile bidder, no matter when it emerges, to wait at least one year to gain control of the board and (ii) requiring such a bidder to win two elections far apart in time rather than a one-time referendum on its offer. Using a new data set of hostile bids in the five-year period 1996-2000, we find that not a single hostile bid won a ballot box victory against an 'effective' staggered board (ESB). We also find that an ESB nearly doubled the odds of remaining independent for an average target in our data set, from 34% to 61%, halved the odds that a first bidder would be successful, from 34% to 14%, and reduced the odds of a sale to a white knight, from 32% to 25%. Furthermore, we find that the shareholders of targets that remained independent were made worse off compared with accepting the bid and that ESBs did not provide sufficient countervailing benefits in terms of increased premiums to offset the costs of remaining independent. Overall, we estimate that, in the period studied, ESBs reduced the returns of shareholders of hostile bid targets on the order of 8-10%. Finally, we show that most staggered boards were adopted before the developments in takeover doctrine that made ESBs such a potent defense.

A holistic multimodal approach to the non-invasive analysis of watercolour paintings

A holistic approach using non-invasive multimodal imaging and spectroscopic techniques to study the materials (pigments, drawing materials and paper) and painting techniques of watercolour paintings is presented. The non-invasive imaging and spectroscopic techniques include VIS-NIR reflectance spectroscopy and multispectral imaging, micro-Raman spectroscopy, X-ray fluorescence spectroscopy (XRF) and optical coherence tomography (OCT). The three spectroscopic techniques complement each other in pigment identification. Multispectral imaging (near infrared bands), OCT and micro-Raman complement each other in the visualisation and identification of the drawing material. OCT probes the microstructure and light scattering properties of the substrate while XRF detects the elemental composition that indicates the sizing methods and the filler content . The multiple techniques were applied in a study of forty six 19th century Chinese export watercolours from the Victoria & Albert Museum (V&A) and the Royal Horticultural Society (RHS) to examine to what extent the non-invasive analysis techniques employed complement each other and how much useful information about the paintings can be extracted to address art conservation and history questions

Ionization potentials in the limit of large atomic number

By extrapolating the energies of non-relativistic atoms and their ions with up to 3000 electrons within Kohn-Sham density functional theory, we find that the ionization potential remains finite and increases across a row, even as $Z\rightarrow\infty$. The local density approximation becomes chemically accurate (and possibly exact) in some cases. Extended Thomas-Fermi theory matches the shell-average of both the ionization potential and density change. Exact results are given in the limit of weak electron-electron repulsion.Comment: 4 pages, 5 figure

Interplay between arsenic and selenium biomineralization in Shewanella sp. O23S

Bacteria play crucial roles in the biogeochemical cycle of arsenic (As) and selenium (Se) as these elements are metabolized via detoxification, energy generation (anaerobic respiration) and biosynthesis (e.g. selenocysteine) strategies. To date, arsenic and selenium biomineralization in bacteria were studied separately. In this study, the anaerobic metabolism of As and Se in Shewanella sp. O23S was investigated separately and mixed, with an emphasis put on the biomineralization products of this process. Multiple analytical techniques including ICP-MS, TEM-EDS, XRD, Micro-Raman, spectmphotometry and surface charge (zeta potential) were employed. Shewanella sp. O23S is capable of reducing selenate (SeO42-) and selenite (SeO32-) to red Se(-S)(0), and arsenate (AsO43-) to arsenite (AsO33-). The release of H2S from cysteine led to the precipitation of AsS minerals: nanorod AsS and granular As2S3. When As and Se oxyanions were mixed, both As-S and Se(-S)(0) biominerals were synthesized. All biominerals were extracellular, amorphous and presented a negative surface charge (-24 to -38 mV). Kinetic analysis indicated the following reduction yields: SeO32- (90%), AsO43- (60%), and SeO42- (<10%). The mix of SeO32- with AsO43- led to a decrease in As removal to 30%, while Se reduction yield was unaffected (88%). Interestingly, SeO42- incubated with AsO43- boosted the Se removal (71%). The exclusive extracellular formation of As and Se biominerals might indicate an extracellular respiratory process characteristic of various Shewanella species and strains. This is the first study documenting a complex interplay between As and Se oxyanions: selenite decreased arsenate reduction, whereas arsenate stimulated selenate reduction. Further investigation needs to clarify whether Shewanella sp. O23S employs multi-substrate respiratory enzymes or separate, high affinity enzymes for As and Se oxyanion respiration.National Science Centre, Poland 2017/26/D/NZ1/00408Plan de Recuperacion, Transformacion y Resiliencia, through Universidad de Oviedo MU-21-UP2021-030 32892642Spanish Government European Commission RTI2018-099565-B-I00 PCI2019-111927-2Junta de Andalucia RNM-179University of Granada UCE-PP2016-05National Research, Development & Innovation Office (NRDIO) - Hungary NKFIH-471-3/202 European UnionNextGeneration EU, Ministerio de Universidade