A laboratory investigation of noise reduction by riblike structures on the ground

This paper investigates the use of periodically spaced edges or wells for the control of road traffic noise. The wells have uniform height and width and are placed on the ground. Physical scale modeling is used to assess the acoustic performance of these structures under laboratory conditions. It is shown that, in certain situations where the use of conventional barriers would not be appropriate, strategically designed riblike structures can provide insertion losses of typically 10-15 dB. The findings are explained in terms of acoustic scattering with the approaches used in the study of resonators and diffraction/interference gratings.     

Crystal structure and Mössbauer spectroscopic study of FeSnF6·6H2O

Large single crystals of FeSnF₆·6H₂O were grown when aqueous hydrofluoric solutions of SnF₂ and FeF₂ were allowed to evaporate in air. Tin-119 Mössbauer spectroscopy at ambient temperature shows a single line at slightly negative isomer shift relative to CaSnO₃ at room temperature (=–0.380(6) mm/s, =0). This is characteristic of tetravalent tin octahedrally coordinated by fluorine. The X-ray crystal structure shows that tin(IV) is coordinated by 6 fluorine atoms, and Fe(II) by 6 water molecules. Both sites show a slight distortion from octahedral symmetry: the six distances are equal (Sn-Fe=1.941(3) Å and Fe-O=2.112(3) Å), whereas there are two values of angles (Fe-Sn-F=90.4(1)° and 89.6(1)°; O-Fe-O=91.1(1)° and 88.9(1)°). The material is an ionic compound [SnF₆]^2–[Fe(H₂O)₆]²⁺.     

Oxidation and passivating effect in tin(II) fluoride and chloride fluoride solid solutions: a <Superscript>119</Superscript>Sn Mössbauer study

Divalent tin fluorides and chloride fluorides appear to be stable relative to oxidation to tetravalent tin at ambient temperature. X-ray diffraction shows only the line of the tin(II) compound, however the ¹¹⁹Sn Mössbauer spectrum of all tin(II) polycrystalline samples has a small broad peak at ca. 0 mm/s. This is the case of polycrystalline α ?SnF₂, while the spectrum of a large single crystal polished sufficiently thin shows only the tin(II) doublet, with no SnO₂ peak at 0 mm/s. This shows that there is surface oxidation of each solid particle, to give a thin amorphous layer of SnO₂ stannic oxide. However, the Mössbauer peak of SnO₂ does not grow with prolonged exposure to air at ambient temperature, therefore it must be assumed that the layer of SnO₂ has a passivating effect, however oxidation increases at higher temperatures. We have investigated in this work the passivating effect of a layer of SnO₂ in two types of solid solutions: (i) in the fluorite type M_1?xSn_xF₂, where the amount of tin at low x values is not sufficient to provide full coverage of the surface of the particles, and (ii) in the PbClF type doubly disordered solid solution, Ba_1?xSn_xCl_1+yF_1?y. It was found that passivation works well in the M_1?xSn_xF₂ solid solution, however most of the time, it does not work so well for Ba_1?xSn_xCl_1+yF_1?y where it is strongly dependent on the method of preparation and the bonding strength, as shown by the variation versus the tin(II) recoil-free fraction.     

Hydrogen bonding and structure of Ba2Ru2Cl10O·10H2O

Dibarium μ‐oxido‐bis[pentachloridoruthenate(IV)] decahydrate, Ba₂Ru₂Cl₁₀O·10H₂O, has been prepared from ruthenium(III) chloride and barium chloride in hydrochloric acid. It crystallizes in the monoclinic system (space group C2/c). The structure consists of alternating layers of [Ru₂Cl₁₀O]⁴⁻ and [Ba(H₂O)₇]²⁺ complex ions along the a direction. The O atom bonded to ruthenium occupies the 4e site, with symmetry, while the other atoms occupy general 8f sites. The overall structure is held together by O—H...O hydrogen bonds and O—H...Cl dipole–dipole interactions.     

The first barium tin(II) bromide fluoride

In an effort to prepare barium tin(II) bromide fluorides for the first time, possibly similar to the chloride fluorides obtained earlier in our laboratory, precipitation reactions were carried out by mixing aqueous solutions of SnF₂ and of BaBr₂.2H₂O. In contrast with the chloride fluoride system, a single powdered phase was obtained throughout the SnF₂ – BaBr₂ system, with the yield being maximum at X ≈ 0.25, where X is the molar fraction of barium bromide in the reaction mixture. Phase identification with the JCPDS database failed to produce a match, confirming that a new phase had been produced. The exact chemical composition of the new compound has not been obtained yet. Based on the X value for the maximum yield, the Sn/Ba ratio is likely to be 3/1 or 2/1. The Mössbauer spectrum at ambient conditions shows that bonding to tin(II) is covalent, therefore with the tin lone pair being stereoactive. The Mössbauer parameters (δ = 3.68 mm/s, Δ = 0.99 mm/s) are similar to those of SnBrF and of Sn₂BrF₅, thereby showing that tin is bonded to both fluorine and bromine. The larger isomer shift and lower quadrupole splitting than in tin(II) fluorides show that the stereoactivity of the tin lone pair is lower than in the fluorides. The Mössbauer parameters fit well the linear correlation of the quadrupole splitting versus the isomer shift” that has been shown to be present in other series of tin(II) compounds. The linear decrease on this correlation shows that the contribution of non-spherical orbitals (p and d) to the lone pair is a much larger contributor to the quadrupole splitting than lattice distortions. The structure is likely made of Ba²⁺ cations and tin(II) fluoride bromide polyatomic anions, with covalent bonding withinthe anions.     

Chemical Preparation,Spectroscopic Study and Crystal Structure of DL 2-Ammoniumbutyric Dihydrogenmonophosphate ({\rm CH_3CH_2CHCOOH)(H_2PO_4)^{\hbox{\bf --}}}\vspace*{-2pt}\break\hspace*{-26pt}|\hspace*{26pt}\break\hspace*{-24pt}{^{\bm +}}{\rm NH_3}\hspace*{24pt}}

Crystals of DL 2-ammoniumbutyric dihydrogenmonophosphate were obtained by evaporating an aqueous solution containing equimolar quantities of DL 2-amino butyric and orthophosphoric acids. IR and NMR spectrometry studies has been investigated and confirmed by X-ray single crystal diffraction results. The title compound is monoclinic, space group P2 1 /c, unit cell dimensions a = 10.5450(3) Å, b = 10.0486(3) Å, c = 8.9526(4) Å, g = 111.769(5);. Using 1,303 reflections with I > 3 (I) measured on CAD4 Mach 3 diffractometer, the crystal structure was solved by direct methods and was refined by least squares full matrix procedures to R = 0.038. The main feature of this structure consists of an alternate stacking of H 2 PO 4 m tetrahedral sheets and NH 3 C 3 H 6 COOH + cation layers. The H 2 PO 4 m groups are associated to form infinite chains [(H 2 PO 4 )n] n m . The crystal structure is stabilized by a three-dimensional network of strong hydrogen bonds.     

Naphthalene‐1,5‐diammonium bis[trifluoridostannate(II)]

The structure of the title compound, (C₁₀H₁₂N₂)[SnF₃]₂, is made up of alternating layers of cations and anions, where the anion layers form extended polymeric sheets through a series of secondary Sn...F bonds. Strong N—H...F hydrogen bonds crosslink adjacent cation and anion layers, thereby building a three‐dimensional network.     

Chemical composition and antimicrobial activity of the essential oil of Algerian Phlomis bovei De Noé subsp. bovei

The chemical composition of essential oil obtained by steam distillation of dried aerial parts of Phlomis bovei De Noé subsp. bovei collected from Algeria, was analyzed by GC and GC/MS. Seventy five constituents (corresponding to 86.37% of the total weight) were identified. The main components were: germacrene D, beta-caryophyllene, beta-bournonene, thymol and hexahydrofarnesyl acetone. Furthermore, the antimicrobial activity of the oil was evaluated against six gram (+/-) bacteria and three pathogenic fungi, using the agar dilution technique. It was found that the oil exhibited strong antimicrobial activity against most of the tested microorganisms.     

Left and right generalized Drazin invertible operators

In this paper, we define and study the left and the right generalized Drazin inverse of bounded operators in a Banach space. We show that the left (resp. the right) generalized Drazin inverse is a sum of a left invertible (resp. a right invertible) operator and a quasi-nilpotent one. In particular, we define the left and the right generalized Drazin spectra of a bounded operator and also show that these sets are compact in the complex plane and invariant under additive commuting quasi-nilpotent perturbations. Furthermore, we prove that a bounded operator is left generalized Drazin invertible if and only if its adjoint is right generalized Drazin invertible. An equivalent definition of the pseudo-Fredholm operators in terms of the left generalized Drazin invertible operators is also given. Our obtained results are used to investigate some relationships between the left and right generalized Drazin spectra and other spectra founded in Fredholm theory.