Preparation of Y3Al5O12 nanocrystals by low temperature glycol route

Yttrium aluminum garnet, Y₃Al₅O₁₂ (YAG) nanocrystals were synthesized by low temperature glycol method. This is a modified sol–gel method performed at low temperature that consists of a mixture of salts, mostly nitrates in an aqueous media. Single phase nanocrystalline YAG was obtained at 850°C, which is much lower than others such as wet‐chemical techniques. The structural characterization is done by XRD and transmission electron microscopy. The crystallite size range from 20‐50 nm was observed for the materials prepared at 850‐ 950°C. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and structural characterization of copper(II) and vanadium(V) complexes of pyridyl/pyrimidyl–pyrazole derived Schiff base ligands – Metal specific adjustment of ligand binding mode

Two mononuclear copper(II) complexes [Cu(L₁)ClO₄] (1), [Cu(L₂)ClO₄] (3) and two mononuclear vanadium(V) complexes [{VO(L₁)(OCH₃)(CH₃OH)}{VO(L₁)(OCH₃)}] (2) and [VO(L₂) (OCH₃)(CH₃OH)] (4) have been synthesized using two Schiff base ligands HL₁ [N′-(2-hydroxybenzylidene)-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazide] and HL₂ [1-(4,6-dimethylpyrimidin-2-yl)-N′-(2-hydroxybenzylidene)-5-methyl-1H-pyrazole-3-carbohydrazide]. These two similar ligands HL₁ and HL₂ in their ‘ketoimine’ form function as mononegative NNNO tetradentate ones towards the Cu(II) centre forming square planar part of the square pyramidal geometry. Where as the same ligands in their ‘imineol’ form behave as binegative ONO tridentate ones to form their V(V) analogues. In the asymmetric unit of 2, there are two independent V(V) complex molecules differing in their conformations as well as in coordination environment – octahedral V(V) in ‘unit A’ is hexa-coordinated while that in ‘unit B’ being penta-coordinated is square pyramidal. Vanadium atom in 4 is in octahedral geometry with NO₅ chromophore. The ligands HL₁ and HL₂ have been synthesized for the first time in our laboratory and characterized by X-ray crystallography and spectroscopy. The complexes (1, 2 and 4) are also characterized by X-ray crystallography, spectroscopic and electrochemical studies.     

Maxwell equations,nonzero photon mass,and conformal metric fluctuation

Maxwell equations are studied for a vacuum with nonzero conductivity coefficient. The loss of energy of a photon during its propagation through this vacuum is calculated and the nonzero rest mass of the photon is shown to be related to the conductivity coefficient of the vacuum. The dissipative mechanism is investigated considering a conformally fluctuating metric in the Einstein equation. Possible astrophysical consequences are discussed.     

Microdetemination of nitro and nitroso groups in aliphatic and aromatic compounds,especially in nitro-arginines

Summary A novel microanalytical method is described for the quantitative determination of nitro and nitroso groups in aliphatic, aromatic and nitro-arginine compounds.During decomposition by pyrolysis in a stream of oxygen, nitrogen oxides and decomposition products containing nitrogen were formed from the nitro and nitroso groups of the substances studied. These were transformed into nitrogen dioxide by a lead dioxide packing. The nitrogen dioxide was absorbed in acetic acid and determined iodometrically after deoxygenation with carbon dioxide. A statistical evaluation of the results for ten aplihatic and aromatic compounds and eight nitro-arginine compounds showed the error did not exceed ±0.3% absolute.

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Mikrobestimmung von Nitro- und Nitrosogruppen in aliphatischen und aromatischen Verbindungen, besonders in Nitroargininderivaten

Zusammenfassung Zur quantitativen Bestimmung des Gehaltes an Nitro- und Nitrosogruppen in aliphatischen und aromatischen Verbindungen wird eine neue mikroanalytische Methode beschrieben.Während des pyrolytischen Zerfalls im Sauerstoffstrom bilden sich Stickstoffoxide und stickstoffhaltige Zersetzungsprodukte aus den Nitro- und Nitrosogruppen der untersuchten Substanzen. Diese werden in einem mit Bleidioxid gefüllten Röhrchen zu Stickstoffdioxid umgewandelt.Das in äquivalenter Menge gebildete Stickstoffdioxid wird absorbiert und jodometrisch bestimmt. Aufgrund der statistischen Auswertung ist die Genauigkeit der Resultate von 10 auf diese Weise bestimmten Verbindungen ±0,3%.

     

Field emission energy distribution (clean surfaces)

The emission of electrons from a cold cathode upon application of a strong electric field is called field emission. Since the electrons must tunnel through the classically forbidden barrier outside the solid, field emission was one of the first confirmations of the new quantum theory of the 1920's.¹ A field of tens of million volts per centimeter is required to obtain a reasonable current. In order to achieve such hgh fields at reasonable voltages, the cathode or emitter is usually etched to a very sharp point (～1,000 Å in radius). Therefore, several thousands of volts applied to the anode will produce the desired field. In 1937, Miiller2 developed what is known as the field emission microscope. The success of Miiller's microscope was a consequence of his realization that, if he produced a small hemispherically shaped tip that was thermally smoothed and cleaned, he would project a greatly magnified image of the spatial distribution of electrons tunneling from the emitter onto a fluorescent screen. Such a field emission pattern for clean tungsten is shown in Figure 1. The image on the screen is a nearly stereographic projection of the hemispherical end of the emitter. Because of its small size, the emitter is usually part of a single crystal and thus exposes all crystallographic orientations, so that individual crystal planes can be located and identified in the field emission pattern. The changes in the field emission pattern with exposure to adsorbed atoms or molecules have been used very successfully to study surface processes, such as diffusion, adsorption and desorption kinetics, or work function changes.³     

Absorption saturation of n-type gallium phosphide

The absorption of n-type gallium phosphide at 2.8 μm wavelength decreases at high light intensity. The saturation intensity is found to be 10 MW cm^?2.     

Unsharp observables and their joint measurement

It is shown that in the double-slit experiment, which is an unsharp path determination if represented by a generalized Luder operation, the interference term in the probability expression exactly corresponds to one of the marginals representing an unsharp interference observable in the realistic joint measurement presented by Busch. A complicated arrangement is presented to show a nontrivial joint triple measurement for spin-1/2 observables     

Field emission energy distribution from adsorbate covered tungsten

We discuss the effect of various classes of adsorbates on the surface states and resonances known to produce structure in the field emission energy distribution from (100) tungsten. We show that it is the overlayer geometry which is of importance in determining whether or not the resonances and concomittant FEED structure persist in the presence of adsorbates. In particular, a c(2 × 2) krypton overlayer destroys the structure while a (1 × 1) gold overlayer does not.