An a posteriori error analysis of an augmented discontinuous Galerkin formulation for Darcy flow

In this paper we develop an a posteriori error analysis for an augmented discontinuous Garlerkin formulation applied to the Darcy flow. More precisely, we derive a reliable and efficient a posteriori error estimator, which consists of residual terms. Finally, we present several numerical experiments, showing the robustness of the method and the theoretical properties of the estimator, thus confirming the capability of the corresponding adaptive algorithms to localize the inner layers, the singularities and/or the large stress regions of the exact solution.     

Photodimerization of Solid Pleiadiene; Isomerization and Cycloreversion of the Dimer

Irradiation (λ>400 nm) of solid pleiadiene ( 1 ) yields a single, head-to-head [_π4_s+_π4_s]-photodimer ( 2 ) the structure of which was determined by X-ray analysis. The formation of 2 is entirely suppressed at 77 K, since properly oriented pairs of molecules arise only from thermal disorder in crystals of 1 . Upon pyrolysis (80°), the strained photodimer 2 rearranges to the [_π2_s + _π4_s] dimer 3 by a ‘forbidden’ suprafacial [1,3]-C-atom migration. Both 2 and 3 are reconverted to 1 by UV. irradiation in solution, but the latter, ‘forbidden’ photoreaction is suppressed at 77 K . Discrepancies of the experimental observations with the predictive schemes of Kaupp or Michl are discussed.     

Photochromism of O-Analogs of Thiathiophthenes

Irradiation of O-analogs of thiathiophthenes yield a photoproduct which reverts thermally to the starting material. Kinetic measurements for this thermal reaction yield E_a values in the range of 10–15 kcal/mol and Δ S* values between ?16 and ?41 eu. Based on NMR. and IR. results the structure of the photoproduct is established. The electronic spectra of the starting material and of the photoproduct are discussed. The experimental results are compared with MO-calculations.     

A hybrid high-order formulation for a Neumann problem on polytopal meshes

In this work, we study a hybrid high-order (HHO) method for an elliptic diffusion problem with Neumann boundary condition. The proposed method has several features, such as: (a) the support of arbitrary approximation order polynomial at mesh elements and faces on polytopal meshes, (b) the design of a local (element-wise) potential reconstruction operator and a local stabilization term, that weakly enforces the matching between local element- and face-based on degrees of freedom, and (c) cheap computational cost, thanks to static condensation and compact stencil. We prove the well-posedness of our HHO formulation, and obtain the optimal error estimates, according to previous study. Implementation aspects are thoroughly discussed. Finally, some numerical examples are provided, which are in agreement with our theoretical results.     

Erste Ergebnisse zur Anwendung der prompten Gammastrahlung im Hinblick auf die vor Ort Anwendung in der Bauzustandsanalyse

Im Hinblick auf eine vor Ort Anwendung auf dem Gebiet der Bauwerksdiagnostik stellt die vorliegende Arbeit erste Ergebnissc vor, die unter Ausnutzung der prompten Gammastrahlung erzielt wurden. Dabei werden ausschlieβlich, unelastische Streuprozesse schneller Neutronen an der Probenmatrix betrachtet. Dic Anregung erfolgte mit einer ²³⁸Pu/Be-Neutronenquelle mit einem Neutronenfluβ von ca. 5 × 10⁷ s^?1 und die Registrierung der prompten Gammastrahlung mit einem NaI(Tl)-Kristall. Besonderes Augenmerk galt den Elementen Mg, Al, Si und Fe als qualitätsbeeinflussende Parameter des Betons.

This publication is a contribution to the application of nuclear metltods in civil engineering. In view of in situ determination of elements in walls of concrete the first results of applying prompt gamma radiation, due to inelastic scattering of fast neutrons in the sample are shown. The stimulation of prompt gamma-rays is carried out by means of a ²³⁸Pu/Bneutron source with a flux of neutrons of about 5 × 10⁷ s^?1 and the detection of gamma radiation by means of a Nal(Tl)- deteclor. The elements Mg, Al, Si and Fe as the parameters of quality of concrete were the elements of interest.     

An improved approximation algorithm for the partial Latin square extension problem

Previous work on the partial Latin square extension (PLSE) problem resulted in a 2-approximation algorithm based on the LP relaxation of a three-dimensional assignment IP formulation. We present an e/(e−1)-approximation algorithm that is based on the LP relaxation of a packing IP formulation of the PLSE problem.     

Green Luminescence of Divalent Europium in the Hydride Chloride EuHCl

Luminescence properties of divalent europium in the mixed‐anion hydride chloride EuHCl were studied for the first time. Olive‐green single crystals of EuHCl (PbFCl‐type structure: tetragonal, P4/nmm, a = 406.58(3) pm, c = 693.12(5) pm, c/a = 1.705, Z = 2) resulted from the reaction of elemental europium (Eu), sodium hydride (NaH) and sodium chloride (NaCl), while powder samples were prepared from the binary components europium dihydride (EuH₂) and dichloride (EuCl₂). Low temperature X‐ray powder diffraction proved the absence of phase transitions for 12(2) K ≤ T ≤ 295(2) K. Bright green emission was observed under UV‐excitation and assigned to the 4f⁶5d¹–4f⁷ transition of divalent europium. Temperature‐dependent luminescence absorption and emission, as well as lifetime measurements were carried out on single crystal and powder samples. Surprisingly, only limited concentration quenching was found. Additionally, two emission bands (485 and 510 nm) are observed, whose intensity ratio depends strongly on temperature. In order to explain this behavior for a single Eu²⁺ site, we suggest either a dynamical Jahn–Teller effect in the excited 5d¹ state or emission from both a 4f⁶5d¹ state and a trapped exciton state.     

Fibrin network adaptation to cell-generated forces

Fibrin promotes wound healing by serving as provisional extracellular matrix for fibroblasts that realign and degrade fibrin fibers, and sense and respond to surrounding substrate in a mechanical-feedback loop. We aimed to study mechanical adaptation of fibrin networks due to cell-generated forces at the micron-scale. Fibroblasts were elongated-shaped in networks with ≤?2 mg/ml fibrinogen, or cobblestone-shaped with 3 mg/ml fibrinogen at 24 h. At frequencies f?<?10² Hz, G′ of fibroblast-seeded fibrin networks with ≥?1 mg/ml fibrinogen increased compared to that of fibrin networks. At frequencies f?>?10³ Hz, G″ of fibrin networks decreased with increasing concentration following the power-law in frequency with exponents ranging from 0.75?±?0.03 to 0.43?±?0.03 at 3 h, and of fibroblast-seeded fibrin networks with exponents ranging from 0.56?±?0.08 to 0.28?±?0.06. In conclusion, fibroblasts actively contributed to a change in viscoelastic properties of fibrin networks at the micron-scale, suggesting that the cells and fibrin network mechanically interact. This provides better understanding of, e.g., cellular migration in wound healing.

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