Search results for "SSB"
showing 10 items of 537 documents
Coordination properties of the ACE inhibitor captopril towards Me2Sn(IV)2+ in aqueous solution, and biological aspects of some dialkyltin(IV) derivat…
2003
Abstract The coordination of Me 2 Sn(IV) 2+ (M) to captopril { N -[( S )-3-mercapto-2-methylpropionyl]- l -proline, H 2 (cap), H 2 L} in aqueous solution was studied by means of potentiometric titration, electrospray mass spectrometry, 1 H-NMR spectroscopy and Mossbauer spectroscopy in the pH range 2–11 ( I =0.1 mol dm −3 NaClO 4 , 298 K). The results obtained with these methods proved that only monomeric complexes are formed in solution. In the acidic pH range, species with a metal-to-ligand ratio of 1:1 exist. The neutral complex ML, similarly to the complex Me 2 Sn(cap) crystallized in the same pH range, adopts a tbp structure with eq S − and ax COO − , while, instead of the coordina…
The dynamics of 57Fe nuclei in Fe(II)-DNA and [Fe(II)(1-methyl-2-mercaptoimidazole)2]-DNA condensates.
2002
Abstract Alcoholic solutions of FeCl 2 and Fe II (Hmmi) 2 Cl 2 (Hmmi=1-methyl-2-mercaptoimidazole) induce calf thymus DNA condensation from aqueous solutions buffered at pH 7.4. A 1:1 Fe II –(DNA monomer) stoichiometry is assumed. The 57 Fe Mossbauer hyperfine parameters suggest an octahedral coordination environment, severely distorted, in both Fe II –(DNA monomer) and [Fe II (Hmmi) 2 ]–(DNA monomer) condensates. The dynamic properties of iron nuclei in freeze-dried samples were investigated by means of variable temperature 57 Fe Mossbauer spectroscopy. Mean square displacements, 〈 x 2 〉( T ), were calculated, such as the effective vibrating mass and the Mossbauer lattice temperature of th…
Degradation of passive layers of iron studied by conversion electron Mössbauer spectroscopy
1995
Integral electron Mossbauer spectroscopy (ICEMS) and additionally some electrochemical methods were used to characterize the passivation process of iron (low carbon steel) in sulfate, sulfate+sulfite (a possible model solution of acid rain) solutions and in phosphate buffer. The phase compositions and thicknesses of the passive layers formed due to the electrochemical polarizations were analyzed in dependence on the duration of the anodic passivations and on the pH of the used electrolytes. The passive layer, as determined from the Mossbauer spectra, consists mainly of γ-FeOOH, however in sulfite confining sulfate aqueous solution at pH 3.5 Fe 3 C and despite ex-situ circumstances FeSO 4 .H…
The blue enamels in the baroque decorations of the churches of Palermo, Sicily: Fe2+-coloured glasses from lime kilns
2009
Deep blue glasses coloured by octahedral Fe 2+ cations are often reported as textbook examples of blue pigmentation. However, despite the possibility of laboratory synthesis under reducing conditions, to date there are no well-reported occurrences of their production and use in the past. A thorough historical, ethnographic, mineralogical, and chemico-physical investigation of the 'smaltini di calcara' from several baroque churches in Palermo, Sicily, has revealed that the blue enamels widely used for altar decorations in the 17th and 18th centuries are actually a unique case of ancient blue glasses pigmented by divalent iron cations in distorted octahedral coordination. This mixed-alkali gl…
Mössbauer relaxation spectra in arbitrarily ordered absorbers—Line shape analysis for an iron(II) spincrossover complex in the presence of texture
1989
The stochastic theory of Mossbauer line shapes is formulated in a fashion which allows the evaluation of the spectral shapes for absorbers of arbitrary thickness, texture, and an anisotropic Lamb—Mossbauer factor. The results are specialized to a two-state-relaxation model of fluctuating electric hyperfine interaction in the case of an absorber of axially symmetric texture. The formalism is applied to the line shape analysis of Mossbauer spectra of a textured sample of the spin-crossover complex [Fe(mtz)6] (PF6)2 (mtz=1-methyltetrazole). It is found that between 185 and 240 K the rate constants for the HS→LS conversion are temperature independent, whereas an Arrhenius behaviour is found for…
Rossby Wave Packets on the Midlatitude Waveguide-A Review
2018
Abstract Rossby wave packets (RWPs) are Rossby waves for which the amplitude has a local maximum and decays to smaller values at larger distances. This review focuses on upper-tropospheric transient RWPs along the midlatitude jet stream. Their central characteristic is the propagation in the zonal direction as well as the transfer of wave energy from one individual trough or ridge to its downstream neighbor, a process called “downstream development.” These RWPs sometimes act as long-range precursors to extreme weather and presumably have an influence on the predictability of midlatitude weather systems. The paper reviews research progress in this area with an emphasis on developments during…
Recent changes in air temperature, heat waves occurrences, and atmospheric circulation in Northern Africa
2013
This study documents the time evolution of air temperature and heat waves occurrences over Northern Africa for the period 1979-2011. A significant warming (1°-3°C), appearing by the mid-1960s over Sahara and Sahel, is associated with higher/lesser frequency of warm/cold temperatures, as with longer duration and higher occurrences of heat waves. Heat waves episodes of at least 4 day duration have been examined after removing the long-term evolution. These episodes are associated with specific anomalies: (i) in spring, positive low-level temperature anomalies over the Sahel and Sahara; low and midlevel cyclonic rotation over Morocco associated with a Rossby wave pattern, lessening the Harmatt…
Utility of Hovmöller diagrams to diagnose Rossby wave trains
2011
The study investigates and compares various methods that aim to diagnose Rossby wave trains with the help of Hovm¨ oller diagrams. Three groups of methods are distinguished: The first group contains trough-and-ridge Hovm¨ oller diagrams of the meridional wind; they provide full phase information, but differ in the method for latitudinal averaging or weighting. The second group aims to identify Rossby wave trains as a whole, discounting individual troughs and ridges. The third group contains diagnostics which focus on physical mechanisms during the different phases of a Rossby wave train life cycle; they include the analysis of eddy kinetic energy and methods for quantifying Rossby wave brea…
A Phase Locking Perspective on Rossby Wave Amplification and Atmospheric Blocking Downstream of Recurving Western North Pacific Tropical Cyclones
2019
Abstract The extratropical transition (ET) of tropical cyclones (TCs) can significantly influence the evolution of the midlatitude flow. However, the interaction between recurving TCs and upstream upper-level troughs features a large and partly unexplained case-to-case variability. In this study, a synoptic, feature-based climatology of TC–trough interactions is constructed to discriminate recurving TCs that interact with decelerating and accelerating troughs. Upper-level troughs reducing their eastward propagation speed during the interaction with recurving TCs exhibit phase locking with lower-level temperature anomalies and are linked to pronounced downstream Rossby wave amplification. Co…
Dynamics of Rossby Wave Packets in a Quantitative Potential Vorticity–Potential Temperature Framework
2016
Abstract Rossby wave packets (RWPs) have been associated with increased atmospheric predictability but also with the growth and propagation of forecast uncertainty. To address the important question of under which conditions RWPs imply high and low predictability, a potential vorticity–potential temperature (PV–θ) framework is introduced to diagnose RWP dynamics. Finite-amplitude RWPs along the midlatitude waveguide are considered and are represented by the synoptic-scale, wavelike undulations of the tropopause. The evolution of RWPs is examined by the amplitude evolution of the individual troughs and ridges. Troughs and ridges are identified as PV anomalies on θ levels intersecting the mid…