Essential Spectra, Matrix Operator and Applications

This paper gives a survey on some recent results on the spectral theory of block operator matrices. We study the closeness in the product space and we give some conditions to characterize the essential spectra in the Browder resolvent set case. Furthermore, we apply the obtained results to several models such as delay equations, Sturm–Liouville problem and transport equations.     

Mutagenic, antimutagenic and antioxidant activities of a new class of beta-glucoside hydroxyhydroquinone from Anagallis monelli growing in Tunisia

A new skeleton of an O-heteroside natural substance named zinolol, the first representative of a new class of aminated hydroxyhydroquinone, has been isolated from the whole plant Anagallis monelli. Its structure has been established by one and two dimensional NMR spectroscopic procedures. Antioxidant, mutagenic, antimutagenic activities were realised and positive results were recorded.     

New ceramic microfiltration membranes from mineral coal fly ash

This work aims to develop a new mineral porous tubular membrane based on mineral coal fly ash. Finely ground mineral coal powder was calcinated at 700 °C for about 3 h. The elaboration of the mesoporous layer was performed by the slip casting method using a suspension made of the mixture of fly ash powder, water and PVA. The obtained membrane was submitted to a thermal treatment which consists in drying at room temperature for 24 h then a sintering at 800 °C. SEM photographs indicated that the membrane surface was homogeneous and did not present any macro defects (cracks, etc.). The average pore diameter of the active layer was 0.25 μm and the thickness was around 20 μm. The membrane permeability was 475 l/h m² bar.This membrane was applied to the treatment of the dying effluents generated by the washing baths in the textile industry. The performances in term of permeate flux and efficiency were determined and compared to those obtained using a commercial alumina microfiltration membrane. Almost the same stabilised permeate flux was obtained (about 100 l/h m²). The quality of permeate was almost the same with the two membranes: the COD and color removal was 75% and 90%, respectively.     

Crystal structure,thermal behavior and IR investigation of 1,6‐diammonium hexan dihydrogenodiphosphate dihydrate

Physicochemical properties of (C₆H₁₈N₂)H₂P₂O₇·2H₂O denoted DHDP are discussed on the basis of X‐ray crystal structure investigation. The compound crystallises in the triclinic system with P space group. Its unit cell dimensions are a = 13.719(1) Å, b = 14.188(3) Å, c = 9.177(1) Å, α = 108.50(1)°, β = 91.11(1)°, γ = 115.47(1)°, V = 1503.8(4) ų and Z = 4. The structure has been solved using direct methods and refined to a reliability R factor 0.0401 for 4778 reflections. The main feature of the atomic arrangement of DHDP is the existence of infinite rows, parallel to the c direction of the unit cell, composed of H₂P₂O₇ groups. These phosphoric rows are organised to create, with the help of the organic cation, large rectangular channels in which the unstable water molecule are located since they have high thermal parameters. Phosphoric anions and organic cations have no internal symmetry. DSC and TG‐DTA show that dehydration occurs in one step. Such dehydration process may be related to the similar environments on the water molecules residing in the channel. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On a characterization of the essential spectra of the sum and the product of two operators

In this paper, we consider the sum and the product of two operators acting on a Banach space and we present some new and quite general conditions to investigate their Wolf, Schechter and Browder essential spectra.     

Characterization of aluminium concentration in shallow quantum wells AlxGa1−xAs/GaAs types

We report a reflectance study on series of shallow quantum wells GaAs/Al_xGa_1−xAs types with different aluminium concentration. The observed barrier exciton reflectance line shape depends strongly on the shift in aluminium concentration in the two barriers, with the appropriate choice of the cap layer thickness. This observation was based on the reflectivity line shape analysis of anti-Bragg structures.