3D discrete element modeling of concrete: study of the rolling resistance effects on the macroscopic constitutive behavior

The Discrete Element Method (DEM) is appropriate for modeling granular materials [14] but also cohesive materials as concrete when submitted to a severe loading such an impact leading to fractures or fragmentation in the continuum [1, 5, 6, 8]. Contrarily to granular materials, the macroscopic constitutive behavior of a cohesive material is not directly linked to contact interactions between the rigid Discrete Elements (DE) and interaction laws are then defined between DE surrounding each DE. Spherical DE are used because the contact detection is easy to implement and the computation time is reduced in comparison with the use of 3D DE with a more complex shape. The element size is variable and the assembly is disordered to prevent preferential cleavage planes. The purpose of this paper is to highlight the influence of DE rotations on the macroscopic non-linear quasi-static behavior of concrete. Classically, the interactions between DE are modeled by spring-like interactions based on displacements and rotation velocities of DE are only controlled by tangential forces perpendicular to the line linking the two sphere centroids. The disadvantage of this modeling with only spring-like interactions based on displacements is that excessive rolling occurs under shear, therefore the macroscopic behavior of concrete is too brittle. To overcome this problem a non linear Moment Transfer Law (MTL) is introduced to add a rolling resistance to elements. This solution has no influence on the calculation cost and allows a more accurate macroscopic representation of concrete behavior. The identification process of material parameters is given and simulations of tests performed on concrete samples are shown

What do teens make of personal informatics? Youth responses to self-tracking practices within a classroom setting

Personal informatics (PI) technologies allow users to collect data about aspects of their lifestyle like mood or step count. Though teens increasingly encounter and use such technologies, little is known about how they ascribe meaning to their own PI activities. We report a qualitative study of the PI experiences of eighteen teens (aged 14 – 17). Following a learning phase focused on interpreting PI data, participants chose a personal goal that interested them and a PI tool to track it for 4-8 weeks in everyday contexts. Participants proved to be competent, flexible users of PI tools, tracking a range of meaningful life factors, from ‘worries’ to ‘exercise’; they valued learning about ‘natural patterns’ in their lives and were motivated to manage their emotions and evaluate whether they were doing the right thing. Our findings contribute to understanding how young people can engage in appropriation and interpretation of PI data – suggesting opportunities for educational interventions and design

What do Teens Make of Personal Informatics?: Young People's Responses to Self-Tracking Practices for Self-Determined Motives

Personal informatics (PI) technologies allow users to collect data about aspects of their lifestyle like mood or step count. Though teens increasingly encounter and use such technologies, little is known about how they ascribe meaning to their own PI activities. We report a qualitative study of the PI experiences of eighteen teens (aged 14 – 17). Following a learning phase focused on interpreting PI data, participants chose a personal goal that interested them and a PI tool to track it for 4-8 weeks in everyday contexts. Participants proved to be competent, flexible users of PI tools, tracking a range of meaningful life factors, from ‘worries’ to ‘exercise’; they valued learning about ‘natural patterns’ in their lives and were motivated to manage their emotions and evaluate whether they were doing the right thing. Our findings contribute to understanding how young people can engage in appropriation and interpretation of PI data – suggesting opportunities for educational interventions and design

dimer paramagnetic centers in lead germanate crystals doped with iron and halogen (Cl-, Br-, F-) ions

The dimer complexes Fe3+-Cl-, Fe3+-Br-, and Fe3+-O2- in ferroelectric lead germanate crystals doped with iron and annealed in chlorine-, bromine-, and fluorine-containing atmospheres have been studied using the electron paramagnetic resonance method. These complexes are formed by Fe3+ ions in the trigonal position of lead and their associated anions located in the interstitial channel of the structure. The positions of the charge-compensating anions in the channel have been discussed based on the analysis of the parameters of the spin Hamiltonian and their temperature dependence. © 2013 Pleiades Publishing, Ltd

Photosensitive bismuth ions in lead tungstate

Electron paramagnetic resonance (EPR) signals of Bi2+ ions have been detected in the EPR spectrum of manganese-, bismuth-, and tin-doped PbWO4 single-crystals irradiated by xenon and mercury lamps at 100 K. The parameters of the Zeeman, hyperfine, and superhyperfine interactions and the localization of Bi2+ ions have been determined. © 2013 Pleiades Publishing, Ltd

Electron paramagnetic resonance of Gd3+ ions in Ca1-x-yYxGdyF2+x+y crystals

Electron paramagnetic resonance of Ca1-x-yYxGdyF2+x+y single crystals has revealed spectra that are not typical of gadolinium-doped CaF2 crystals. These spectra have a nearly tetragonal symmetry and are most probably caused by Gd3+ ions localized in yttrium clusters. Weak spectra of tetragonal Gd3+ centers, whose parameters are close to those of a cubic gadolinium center caused by an isolated Gd3+ ion, have been also detected. These centers are attributed to isolated Gd3+ ions localized near octahedral rare-earth clusters or their associations. © 2013 Pleiades Publishing, Ltd

Paramagnetic defects in manganese-doped lead tungstate

In manganese-doped PbWO4 crystals, low-intensity signals of triclinic clusters Mn4+-VO and Fe3+-VPb have been revealed in addition to signals of Mn2+ tetragonal centers. The Mn4+-VO cluster is formed by a Mn4+ ion in the W6+ position, which is associated with a vacancy of the nearest neighbor O2-ion, and the Fe3+-VPb cluster consists of a Fe3+ ion substituting for Pb2+ with a local compensation of by a lead vacancy. It has been shown that, in PbWO4: Mn, there is also a small amount of Mn4+ tetragonal centers located in the Pb2+ position with a nonlocal compensation of an excess charge. © 2013 Pleiades Publishing, Ltd

Specific features of the electron paramagnetic resonance spectrum in the vicinity of the convergence of the transitions of gadolinium centers in Pb5(Ge1 - xSix)3O11

An anomalous electron paramagnetic resonance spectrum of the transitions -1/2 ↔ +1/2 of four Gd3+-Si dimer clusters in the Pb5(Ge1 - xSix)3O11 crystals doped with gadolinium has been found in the vicinity of the orientation of the magnetic field along the optic axis of the crystal. It has been assumed that this spectrum is caused by rapid transitions between the spin packets of the initial resonances due to the crossrelaxation. A computer simulation of the spectrum has been carried out. The results obtained adequately describe the experiment. © 2013 Pleiades Publishing, Ltd

Physicochemical investigation of anodic processes involved in silver electrowinning in refining technology

During silver electrowinning in refining technology, irrespectively of the nature of electrolyte and anode material, an anode deposit is formed due to oxidation of singly charged silver ions to higher degrees of oxidation (+2 and +3) under polarization. Absorption spectra of Ag(II) have been obtained in solutions with various concentrations of silver ions and nitric acid using anodic polarization in combination with electronic absorption spectroscopy; silver ions of high oxidation degrees were found to be unstable in solutions. At anode potentials φa ≥ 1.15-1.22 V, Ag(I) ions in liquid phase are oxidized to Ag(II), which paint the anolyte; their content depends on silver and nitric acid concentrations in the electrolyte. The deposit crystallizes on anode at potential φa ≈ 1.5 V. Chemical analysis, X-ray powder diffraction, and a thermogravimetric study of the anode deposit have made it possible to identify its initial composition as Ag 7O8NO3. The deposit composition varies in time as a result of reduction of highly oxidized silver. © 2013 Pleiades Publishing, Ltd

Pharmacological correction of intrarenal hemodynamic disorders in acute kidney injury (part 2)

Evaluate the possibilities of individual pharmacological correction and intensive care of patients with acute kidney injury of different origin. A prospective nonrandomized study. Inclusion criteria: patients with prerenal, renal and subrenal AKI module in stage of oligoanuria and restoration of diuresis. Exclusion criteria: AKI in patients after cardiosurgery and operations on large vessels. Individual pharmacological and non-pharmacological correction (renoprotection) was performed in 250 ICU patients with prerenal (130), renal (81) and subrenal (39) AK