Oedometric test, Bauer's law and the micro-macro connection for a dry sand

What is the relationship between the macroscopic parameters of the constitutive equation for a granular soil and the microscopic forces between grains? In order to investigate this connection, we have simulated by molecular dynamics the oedometric compression of a granular soil (a dry and bad-graded sand) and computed the hypoplastic parameters hs (the granular skeleton hardness) and η (the exponent in the compression law) by following the same procedure than in experiments, that is by fitting the Bauer's law e/e₀=exp(−n(3p/hs)), where p is the pressure and e₀ and e are the initial and present void ratios. The micro-mechanical simulation includes elastic and dissipative normal forces plus slip, rolling and static friction between grains. By this way we have explored how the macroscopic parameters change by modifying the grains stiffness, V; the dissipation coefficient, γn; the static friction coefficient, μs; and the dynamic friction coefficient, μk. Cumulating all simulations, we obtained an unexpected result: the two macroscopic parameters seems to be related by a power law, hs=0.068(4)η9.88(3). Moreover, the experimental result for a Guamo sand with the same granulometry fits perfectly into this power law. Is this relation real? What is the final ground of the Bauer's Law? We conclude by exploring some hypothesis.     

Experimental simulation of stochastic stream response to thermal inputs and application of spectral analysis techniques

Experimental data on stream temperature were collected using a laboratory model by super-imposing cyclic and continuous non-cyclic thermal discharges (steam was used as the thermal discharge) on the inherently noisy signals of the stream. The resulting data measured at two different points along the stream were processed by spectral analysis. Flow rate and position of measurement were found to play important roles in drawing information from the data. The cyclic nature of the periodic thermal discharge could be observable in the autocorrelation and power spectrum.     

A metrology-based approach for measuring the social dimension of cognitive trust in collaborative networks

This paper addresses the measurement of the social dimension of cognitive trust in collaborative networks. Trust indicators are typically measured and combined in literature in order to calculate partners’ trustworthiness. When expressing the result of a measurement, some quantitative indication of the quality of the result—the uncertainty of measurement—should be given. However, currently this is not taken into account for the measurement of the social dimension of cognitive trust in collaborative networks. In view of this, an innovative metrology-based approach for the measurement of social cognitive trust indicators in collaborative networks is presented. Thus, a measurement result is always accompanied by its uncertainty of measurement, as well as by information traditionally used to properly interpret the results: the sample size, and the standard deviation of the sample.

     

Non-ENSO control on southern Africa precipitation variability

The objective of this study is to quantify the nature of the mechanisms of southern Africa rainfall variability, unrelated to the El Nino Southern Oscillation, by means of a simple empirical composite analysis, as a baseline for a more detailed study.     

In situ polymerization of ethylene with functionalized multiwalled carbon nanotubes using a zirconocene aluminohydride system in solution

This study reports nanocomposite synthesis based on high-density polyethylene with carbon nanotubes through in situ polymerization by coordination, and the use of an aluminohydride zirconocene/MAO system as a catalyst. Nanocomposites of linear polyethylene exhibit higher molar masses than pure high-density polyethylene synthesized under similar conditions; where multiwalled carbon nanotubes (MWCNTs) acted as nucleating agents, shifting the crystallization temperature to higher values than neat high-density polyethylene. Well-dispersed MWCNTs in the HDPE matrices of the obtained nanocomposites are observed by SEM, where most of the nanocomposites showed an improvement in their thermal stability and electric conductivity, besides it is possible to obtain nanocomposites containing up to 41 wt% of nanofiller in the polymeric matrix. The aluminohydride complex n-BuCp₂ZrH₃AlH₂, activated with MAO at Al/Zr ratios of 2000, produced homogeneous HDPE/MWCNT composites under in situ polymerization conditions, at 70°C and 2.9 bar of ethylene pressure, with minimal residual alumina in the HDPE matrix.     

Behavior of diatomaceous soil in lacustrine deposits of Bogotá, Colombia

This work presents a study on the behaviors of diatomaceous soils. Although studies are rarely reported on these soils, they have been identified in Mexico City, the Sea of Japan, the northeast coast of Australia, the equatorial Pacific, and the lacustrine deposit of Bogotá (Colombia), among other locations. Features of this kind of soil include high friction angle, high initial void ratio, high compressibility index, high liquid limit, and low density. Some of these features are counterintuitive from a classical soil mechanics viewpoint. To understand the geotechnical properties of the diatomaceous soil, a comprehensive experimental plan consisting of more than 2400 tests was performed, including physical tests such as grain size distribution, Atterberg limits, density of solid particles, and organic matter content; and mechanical tests such as oedometric compression tests, unconfined compression tests, and triaxial tests. Laboratory tests were complemented with scanning electron microscope (SEM) observations to evaluate the microstructure of the soil. The test results show that there is an increase in liquid limit with increasing diatomaceous content, and the friction angle also increases with increasing diatomaceous content. In addition, several practical correlations were proposed for this soil type for shear strength mobilization and intrinsic compression line. Finally, useful correlations were presented, such as the relationship between the state consistency and the undrained shear strength, the friction angle and the liquid limit, the void ratio at 100 kPa and the liquid limit, the plasticity index and the diatomaceous content, among others.     

TPA Immobilization on Iron Oxide Nanocubes and Localized Magnetic Hyperthermia Accelerate Blood Clot Lysis

The low specificity and high risk of intracranial hemorrhage associated with currently approved thrombolytic therapies limit their efficacy in recanalizing occluded vessels. Here, a nanoscale thrombolytic agent is demonstrated by immobilizing tissue plasminogen activator molecules (tPA) over 20 nm clustered iron oxide nanocubes (NCs). The resulting nanoconstructs (tPA–NCs) are capable of dissolving clots via both direct interaction of tPA with the fibrin network (chemical lysis) and localized hyperthermia upon stimulation of superparamagnetic NCs with alternating magnetic fields (AMFs) (mechanical lysis). In vitro, as compared to free tPA, the proposed nanoconstructs demonstrate a ≈100‐fold increase in dissolution rate, possibly because of a more intimate interaction of tPA with the fibrin network. The clot dissolution rate is further enhanced (≈10‐fold) by mild, localized heating resulting from the exposure of tPA–NCs to AMF. Intravital microscopy experiments demonstrate blood vessel reperfusion within a few minutes post tail vein injection of tPA–NCs. The proposed nanoconstructs also exhibit high transverse relaxivity (>400 × 10^–3 m ^?1 s^?1) for magnetic resonance imaging. The multifunctional properties and the 3 orders of magnitude enhancement in clot dissolution make tPA–NCs a promising nano‐theranosis agent in thrombotic disease.     

Inverse kinematics of a mobile robot

The problem of kinematics is to describe the motion of the robotic system without consideration of the forces and torques causing the motion. This paper presents two methods to obtain the inverse kinematics of a mobile robot. In the first method, two rows of the forward kinematics are selected, the inverse of these two rows is obtained, and later the inverse matrix is combined with the third row of the forward kinematics. In the second method, the pseudo-inverse matrix of the forward kinematics matrix is obtained. The comparison result of the two proposed methods is presented. Two simulations show the effectiveness of the proposed inverse kinematics algorithm.