Cancellation of light shifts in an N-resonance clock

We demonstrate that first-order light shifts can be canceled for an all-optical, three-photon-absorption resonance (N-resonance) on the D1 transition of 87Rb. This light-shift cancellation facilitates improved frequency stability for an N-resonance clock. For example, by using a tabletop apparatus designed for N-resonance spectroscopy, we measured a short-term fractional frequency stability (Allan deviation) of approximately/= 1.5 x 10(-11) tao1/2 for observation times of 1 s < or = tao < or = 50 s. Further improvements in frequency stability should be possible with an apparatus designed as a dedicated N-resonance clock.     

A simulation study of the fleet sizing problem arising in offshore anchor handling operations

A fleet sizing problem arising in anchor handling operations related to movement of offshore mobile units is presented in this paper. Typically, the intensity of these operations is unevenly spread throughout the year. The operations are performed by dedicated vessels, which can be hired either on the long-term basis or on the spot market. Spot rates are frequently a magnitude higher than long-term rates, and vessels are hired on the spot market if there is a shortage of long-term vessels to cover the ongoing anchor handling operations. Deciding the cost-optimal fleet of vessels on the long-term hire to cover future operations is a problem facing offshore oil and gas operators. This decision has a heavy economic impact as anchor handling vessels are among the most expensive ones. The problem is highly stochastic because durations of anchor handling operations vary and depend on uncertain weather conditions. Moreover, future spot rates for anchor handling vessels are extremely volatile. The objective of this paper is to describe a simulation model for the fleet sizing problem. The study was initiated by the largest Norwegian offshore oil and gas operator and has received considerable acceptance among the planners.     

Corrosion properties of nickel coatings obtained from aqueous and nonaqueous electrolytes

Nickel was deposited on a copper substrate from aqueous and nonaqueous ethanol electrolytes. X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and chronovoltametry, scanning electron microscopy, and atomic force microscopy were used to study the effect of the solvent on the surface and corrosion properties of the Ni coatings formed. Unifom and relatively smooth Ni films were obtained as measured with microscopy techniques. The formation of a passive film in acidic, alkaline, and neutral chloride-containing media was confirmed with X-ray photoelectron spectroscopy. The water-based nickel-plating electrolyte makes it possible to deposit coatings with higher corrosion resistance as compared with coatings deposited from ethanol electrolyte in NaOH and NaCl media. The proposed mechanism of corrosion in a 0.5 M H₂SO₄ solution involves cycles of active-passive surface behavior due to its passivation by corrosion products.     

Polymorphism of 3‐(5‐phenyl‐1,3,4‐oxadiazol‐2‐yl)‐ and 3‐[5‐(pyridin‐4‐yl)‐1,3,4‐oxadiazol‐2‐yl]‐2H‐chromen‐2‐ones

This study of 3‐(5‐phenyl‐1,3,4‐oxadiazol‐2‐yl)‐2H‐chromen‐2‐one, C₁₇H₁₀N₂O₃, 1 , and 3‐[5‐(pyridin‐4‐yl)‐1,3,4‐oxadiazol‐2‐yl]‐2H‐chromen‐2‐one, C₁₆H₉N₃O₃, 2 , was performed on the assumption of the potential anticancer activity of the compounds. Three polymorphic structures for 1 and two polymorphic structures for 2 have been studied thoroughly. The strongest intermolecular interaction is stacking of the `head‐to‐head' type in all the studied crystals. The polymorphic structures of 1 differ with respect to the intermolecular interactions between stacked columns. Two of the polymorphs have a columnar or double columnar type of crystal organization, while the third polymorphic structure can be classified as columnar‐layered. The difference between the two structures of 2 is less pronounced. Both crystals can be considered as having very similar arrangements of neighbouring columns. The formation of polymorphic modifications is caused by a subtle balance of very weak intermolecular interactions and packing differences can be identified only using an analysis based on a study of the pairwise interaction energies.     

Synthetic modifications of carboline alkaloid harmine: synthesis of 8-substituted derivatives

Chemistry of Heterocyclic Compounds - Hybrid molecules containing β-carboline and 1-acetylpyrazoline moieties were obtained on the basis of the alkaloid harmine. The synthetic procedure...     

Liposomal Form of Tetra(Aryl)Tetracyanoporphyrazine: Physical Properties and Photodynamic Activity In Vitro

Tetra(aryl)tetracyanoporphyrazines are the promising group of dyes for photodynamic therapy of tumors with unique combination of photosensitizer properties and sensitivity of fluorescence parameters to the environment viscosity. However, in vivo application of such hydrophobic photosensitizers requires using of drug carriers ensuring efficient delivery to the tumor site. The present study is focused on obtaining liposomes loaded with tetrakis(4-benzyloxyphenyl)tetracyanoporphyrazine and examining their properties depending on lipid composition. An efficient loading of the dye and a high long-term stability were proved for the liposomes composed of phosphatidylcholine with cholesterol and phosphatidylglycerol. This can be explained by the presence of negatively charged lipids in the bilayer and, as a consequence, a high value of the surface potential. A high rate of cellular uptake and a strong photoinduced toxicity give the prerequisites for the further use of the liposomal form of the photosensitizer for photodynamic therapy of tumors.     

Dichloromethane as solvent and reagent: a case study of photoinduced reactions in mixed phosphonium‐iodonium ylide

Several years ago the photoinduced reaction of mixed phosphonium‐iodonium ylides ( 1 ) with acetylenes ( 2 ) to give λ⁵‐phosphinolines ( 3 ) and substituted furans ( 4 ) was described. This reaction is one‐pot, metal‐free synthesis of heterocycles 3 and 4 with the yields of 40% to 80%. The reaction proceeds only in dichloromethane (DCM) at the high ylide concentrations (>0.01 mol/L). The product analysis by ³¹P NMR, electrospray ionization mass spectrometry, UV‐vis spectrophotometry, and the dynamic light scattering study of the self‐aggregation of the ylide in DCM showed a dual role of the solvent in the photoinduced reactions of mixed phosphonium‐iodonium ylide: (i) at the low ylide concentrations (<0.01 mol/L), the conjugated photoinitiation of the chain reaction in DCM results in the formation of chlorine‐containing products and (ii) at the high ylide concentrations (>0.01 mol/L), the photolysis mechanism is determined by self‐organization of the ylide molecules to give large stable aggregates in DCM, in which the target heterocycles are synthesized. Two important issues follow from the study. First, the annulation reaction between mixed phosphonium‐iodonium ylide and acetylenes occurs only when the reactive intermediates are in close proximity to one other, and, second, DCM is not inert reagent in reactions occurring with participation of radicals and in one form or another can participate in photoinduced radical reactions of various solutes.     

Electrochemical reduction of 2,4‐dimethyl(diethyl)‐9‐oxo‐10‐(4‐heptoxyphenyl)‐9H‐thioxanthenium hexafluorophosphates and 2,4‐dimethyl(diethyl)‐9H‐thioxanthene‐9‐ones

Electrochemical reduction of 2,4‐dimethyl(diethyl)‐9‐oxo‐10‐(4‐heptoxyphenyl)‐9H‐thioxanthenium hexafluorophosphates in acetonitrile (MeCN) and N,N‐dimethylformamide is an irreversible 1‐electron process accompanied by the cleavage of the C(Ph)‐S bond in thioxanthenium cations with the formation of the corresponding 2,4‐dimethyl(diethyl)‐9H‐thioxanthene‐9‐ones. One‐electron reversible electrochemical reduction of the latter compounds occurs at more negative potentials and yields the corresponding radical anions, which have been characterized by electron paramagnetic resonance spectroscopy and density functional theory calculations at the (U)B3LYP/6‐31+G*/polarizable continuum model level of theory.     

Study of Au/SnO x –Al2O3 catalysts used in CO oxidation by in situ Mössbauer spectroscopy

The active catalytic components in tin oxide containing alumina-supported gold catalyst were examined by comparing and analysing the in situ Mössbauer spectra of the SnO _x –Al₂O₃ support and the 3 wt.% Au/SnO _x –Al₂O₃ catalyst (1.1 wt.% Sn, Au/Sn = 3:2 atomic ratio). Samples were prepared by using organometallic precursor of ¹¹⁹SnMe₄ (enriched). First tin was grafted to the alumina surface from the organometallic precursor compound. In the next step the grafted complexes were decomposed in flowing oxygen. Gold was deposited onto the SnO _x –Al₂O₃ support in the subsequent step. Analysis of in situ spectra shows that in Au/SnO _x –Al₂O₃ catalyst after activation in hydrogen at 620 K tin may occur in three different oxidation states [Sn (IV), Sn(II) and Sn(0)] simultaneously. The metallic tin is a component of the bimetallic AuSn alloy phase. Data presented provide the first evidence for the formation of alloy-type supported Sn–Au catalyst on alumina. Furthermore, from the spectra recorded at different temperatures, values of the Debye temperatures and recoilless fractions were also determined for the various species. The results show that in catalytic oxidation of carbon monoxide at room temperature the dominant part of Sn(II) and the AuSn alloy is oxidized.     

Focusing,collimation and flux throughput at the IMCA‐CAT bending‐magnet beamline at the Advanced Photon Source

The IMCA‐CAT bending‐magnet beamline was upgraded with a collimating mirror in order to achieve the energy resolution required to conduct high‐quality multi‐ and single‐wavelength anomalous diffraction (MAD/SAD) experiments without sacrificing beamline flux throughput. Following the upgrade, the bending‐magnet beamline achieves a flux of 8 × 10¹¹ photons s^?1 at 1 Å wavelength, at a beamline aperture of 1.5 mrad (horizontal) × 86 µrad (vertical), with energy resolution (limited mostly by the intrinsic resolution of the monochromator optics) δE/E = 1.5 × 10^?4 (at 10 kV). The beamline operates in a dynamic range of 7.5–17.5 keV and delivers to the sample focused beam of size (FWHM) 240 µm (horizontally) × 160 µm (vertically). The performance of the 17‐BM beamline optics and its deviation from ideally shaped optics is evaluated in the context of the requirements imposed by the needs of protein crystallography experiments. An assessment of flux losses is given in relation to the (geometric) properties of major beamline components.