Analysis of the geometrical dependence of auxetic behavior in reentrant structures by finite elements

Materials with a negative Poisson's ratio(PR)are called auxetics;they are characterized by expansion/contraction when tensioned/compressed.Given this counterintuitive behavior,they present very particular characteristics and mechanical behavior.Geometrical models have been developed to justify and artificiall reproduce such materials' auxetic behavior.The focus of this study is the exploration of a reentrant model by analyzing the variation in the PR of reentrant structures as a function of geometrical and base material parameters.It is shown that,even in the presence of protruding ribs,there may not be auxetic behavior,and this depends on the geometry of each reentrant structure.Values determined for these parameters can be helpful as approximate reference data in the design and fabrication of auxetic lattices using reentrant geometries.     

Optical absorption spectra and energy levels of Er3+ ions in glassy lithium tetraborate matrix

The optical absorption spectra of Er:Li₂B₄O₇ glasses are studied in the range 200–800 nm. The lines corresponding to the direct f-f parity-forbidden intraconfigurational transitions from the ground ⁴ I _15/2 state to the levels of the excited ⁴ F _9/2, ⁴ S _3/2, ² H _9/2, ² H _11/2, ⁴ F _7/2, ⁴ F _5/2, ⁴ F _3/2, ² H _9/2, ⁴ G _11/2, ⁴ D _3/2, ⁴ D _1/2, and ² D _3/2 states are found.     

Highlights and Prospects of Hyperspherical Approach in Few-Body Quantum-Mechanical Systems

The binding energy of excitonium negative ion for ground ¹S-state in bulk conductors: Ge, Si, CdSe and for green and yellow lines of Cu₂O in hyperspherical coordinate method are found. Angular and radial correlations between electrons are taken into account by the channel functions, which are the eigen-functions of operator on the surface of sphere in six-dimensional sphere. The calculation of energies have been done using the adiabatic and Born-Oppenheimer approximations. In Born-Oppenheimer approximation is enough to give a binding energy with only 1.2% error, in adiabatic approximation this error drops to 0.7 %.     

The vitrification region and the physicochemical properties of glasses based on components of AVBVICVII type

Vitrification regions have been determined for the mixed chalcoiodides of arsenic, antimony, and indium, and some physicochemical and optical properties have been examined. DTA curves have been recorded for the glasses, which reveal three effects: the first corresponds to the onset of softening at T_g, the second to recrystallization at T_r, and the third to melting at T_m. Measurements are reported for the specific resistance, optical width of the forbidden band E_g, and also T_g for some compositions in the system InXI-AsXI-SbXI. Tests have been made on the effects of small deviations of the amount of iodine from stoichiometric in AsXI (X=Se, S) as regards the IR transmission spectra at different temperatures. The temperature results of the transmission spectra are discussed for various technological batches of AsXI glasses, which are due to differences in the position of the Fermi level in the pseudoband.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 99–103, October, 1973.     

Mathematical help-seeking: observing how undergraduate students use the Internet to cope with a mathematical task

ZDM – Mathematics Education - We report on a study focused on identifying how undergraduate students make use of the Internet as a source of help to solve their mathematical queries. In...     

Retention of Cr(III) by high-performance chelation ion chromatography interfaced to inductively-coupled plasma mass spectrometric detection with collision cell

High-performance chelation ion chromatography (HPCIC) was employed to retain cationic Cr(III) on an anion-exchange column and hence allow the separation of the two most prevalent forms of chromium, Cr(II) and Cr(VI). A mobile phase of nitric acid was utilized at pH = 1.5; additionally, 2,6-pyridinedicarboxylic acid was used at a concentration of 6 mM. Additives with different structural characteristics were used in an effort to elucidate retention mechanisms. Inductively-coupled plasma mass spectrometry was used for chromium detection. A collision cell was utilized to reduce chloride-based polyatomic ions that may interfere with the detection of Cr(III), and a detection limit study yielded levels in the low part-per-billion range. The newly developed method was applied to the chromatographic analysis of samples of an incubation medium containing Cr(VI) incubated with cell nuclei.     

Concentration dependence of radiation-induced changes in the optical properties of Ge<Subscript>x</Subscript>As<Subscript>40−<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>60</Subscript> films

Radiation-induced changes in the optical properties of chalcogenide glasses in the Ge-As-S system are investigated as a function of the concentration. Theoretical calculations are performed with due regard for possible constraints on the range of variation in the number of homobonds and heterobonds upon their switching in the structural network of chalcogenide glasses. The experimental data are obtained upon irradiation of Ge_xAs_40?xS₆₀ thin films with fast electrons (6 MeV). The possible mechanism of structural transformations responsible for the specific features in the concentration dependence of the change in the band gap of chalcogenide glasses is discussed.     

Byte structure variable length coding (BS-VLC): a new specific algorithm applied in the compression of trajectories generated by molecular dynamics

Molecular dynamics is a well-known technique very much used in the study of biomolecular systems. The trajectory files produced by molecular dynamics simulations are extensive, and the classical lossless algorithms give poor efficiencies in their compression. In this work, a new specific algorithm, named byte structure variable length coding (BS-VLC), is introduced. Trajectory files, obtained by molecular dynamics applied to trypsin and a trypsin:pancreatic trypsin inhibitor complex, were compressed using four classical lossless algorithms (Huffman, adaptive Huffman, LZW, and LZ77) as well as the BS-VLC algorithm. The results obtained show that BS-VLC nearly triplicates the compression efficiency of the best classical lossless algorithm, preserving a near lossless behavior. Compression efficiencies close to 50% can be obtained with a high degree of precision, and the maximum efficiency possible (75%), within this algorithm, can be performed with good precision.