Selective water sorbents for multiple applications, 7. Heat conductivity of CaCl2?SiO2 composites

In this communication we present experimental data on the low temperature heat conductivity of a consolidated bed made of the CaCl₂/SiO₂ composite material measured by the “hot wire method”. The conductivity appears to increase strongly with a raise of the sorbed water amount and reaches 0.53 W/m K at a high water content when the bed is completely saturated with the salt solution. λ values obtained appear to be much higher than those for zeolite 4A, which is a competitor solid adsorbent proposed for sorption cooling and heating machines. Finally, the influence of the thermal conductivity on the specific power of sorption heat pump based on the “CaCl₂/SiO₂-water” pair is briefly discussed.     

Probe—detektor-anordnungen zur Kernstrahlungsmessung für Analytische Zwecke

The “analytical power” of detection systems is investigated, considering typical arrangements in analytical terms. From N atoms of interest in a sample Z counts are drawn: Z=R N (R registration yield). Crude data ZM contain also background U generated by interferences: ZM=Z+U. Identification and separation of Z is accompanied by errors ~σ_MU^1/2 due to imperfect distinguishability and to statistical error (σ_M model inherent factor). With “selectivity”=σ_M ^- (R/R_interference)^1/2 the figure of merit is G=selectivity efficiency/interference)^1/2. Sample background dominating, “interference” or both “interference” and “efficiency” have to be cancelled. Present semiconductor spectrometry of low energy γ-quanta and of large rates is not very far from its limits. Further progress will be obtained by enhancement of high energy efficiency and reduction of natural background.      

Collaborative sampling trial in the context of quality assurance in the German marine monitoring programme for the North Sea and the Baltic Sea

This paper presents the assessment of a collaborative trial in sampling in the Baltic Sea in the framework of quality assurance in the German marine monitoring programme for the North Sea and the Baltic Sea. The objective of investigations was to determine the influence of sampling on analytical results for selected monitoring parameters and to harmonize the procedure for sampling of sea water to a large extent. In these studies the staff of three vessels took replicate sea water samples, 1 m below the surface and below the halocline, at two monitoring stations. Mass concentration mean values for different nutrient parameters were obtained from each sample, all in one laboratory. Data produced from the hierarchical design were treated with robust analysis of variance (ANOVA) to generate uncertainty estimates, as standard uncertainties (“u” expressed as standard deviation), for geochemical variation (s _geochem), primary sampling (s _sampling), and chemical analysis (s _analysis). Geochemical variation dominated the total variance in all cases. Sampling and analytical uncertainties contributed together up to 15% of the total variance and had a relative measurement uncertainty (u%) of less than 2% for all the parameters investigated. Thus for this study the sampling protocol and the analytical method could be regarded as fit-for-purpose. M. Gluschke was formerly affiliated to the Federal Environmental Agency, P.O. Box 33 00 22, 14191 Berlin, Germany.     

Comparison of “bottom-up” and “top-down” strategies for the estimation of the uncertainty in organic elemental analysis

The estimation of uncertainty in organic elemental analysis for C, H, N and S is reported. Both “bottom up” and “top down” strategies are used for uncertainty calculations. The bottom up approach used the results of C, H, N, and S obtained from the homogeneity study of two pure chemicals (toluene-4-sulfonamide and 4(6)-methyl-2-thiouracil). Two calibration systems, K factor and calibration curve, were applied in this study and no significant differences were obtained. For the “top down” approach, we used the data obtained from a proficiency test on both pure chemicals from among 45 Spanish laboratories. Both approaches are compared and discussed below.     

Sol-Gel Microsphere Pelletisation Process for Fabrication of (U,Pu)O2, (U,Pu)C and (U,Pu)N Fuel Pellets for the Prototype Fast Breeder Reactor in India

A “dust-free” sol-gel microsphere pelletisation (SGMP) process has been developed for fabrication of (U,Pu)O₂, (U,Pu)C and (U,Pu)N fuel pellets containing around 15% plutonium for the forthcoming prototype fast breeder reactor (PFBR) in India. The objective was to produce homogeneous sintered pellets of ∼85% T.D. with a predominantly open-pore structure. Hydrated gel-microspheres of UO₃+PuO₂ and UO₃+PuO₂+C have been prepared from nitrate solutions of uranium and plutonium by the “ammonia internal gelation” process, using hexamethylene tetramine (HMTA) as an ammonia generator and silicone oil at 90±1°C as gelation bath. For oxide fuel pellets, the hydrated UO₃+PuO₂ gel-microspheres were calcined at around 700°C in Ar+8% H₂ atmosphere to produce “non-porous”, “free-flowing” and coarse (around 400 micron) microspheres which could be directly pelletised at 550 MPa to green pellets. The mixed oxide pellets were subjected either to low temperature (∼1100°C) oxidative sintering (LTS) in N₂+air containing ∼1500 ppm O₂ or to high temperature (1650°C) sintering, (HTS) in Ar+8% H₂. For monocarbide and mononitride pellets, hydrated gel-microspheres of UO₃+PuO₂+C were subjected to carbothermic synthesis in vacuum (∼1 Pa) and flowing nitrogen (flow rate: 1.2 m³/h) in the temperature range of 1450–1550°C respectively. The monocarbide and mononitride microspheres thus produced were relatively hard and required higher compaction pressure (∼1200 MPa) for making reen pellets which could be sintered to 85% T.D. in Ar+8% H₂ at 1700°C. The sintered oxide, monocarbide and mononitride pellets had a “blackberry” “open” pore microstructure with fine grain size. The microspheres retained their individual identity in the sintered pellets because during sintering densification took place mainly within and not between the microspheres.     

Molecular Design of Polyoxometalate-Based Compounds for Environmentally-Friendly Functional Group Transformations: From Molecular Catalysts to Heterogeneous Catalysts

This review article summarizes our recent researches for molecular design of polyoxometalates (POMs) and their related compounds for environmentally-friendly functional group transformations. The divacant POM [γ-SiW₁₀O₃₄(H₂O)₂]⁴⁻ exhibits high catalytic performance for mono-oxygenation-type reactions including epoxidation of olefins and allylic alcohols, sulfoxidation, and hydroxylation of organosilanes with H₂O₂. We have successfully synthesized several POM-based molecular catalysts (metal-substituted POMs) with controlled active sites by the introduction of metal species into the divacant POM as a “structural motif”. These molecular catalysts can efficiently activate H₂O₂ (vanadium-substituted POM for epoxidation) and alkynes (copper-substituted POM for click reaction and oxidative homocoupling of alkynes). The aluminum-substituted POM exhibits Lewis acidic catalysis for diastereoselective cyclization of (+)-citronellal to (−)-isopulegol. In addition, we have developed POM-based “molecular heterogeneous catalysts” by the “solidification” and “immobilization” of catalytically active POMs.     

A simulation of thermal characteristic parameters with an inverse “S” type curve

A synthetical equation is proposed to characterize the essential features of the inverse “S” type curve on the basis of summing-up simulation approach of “S” type curve. The two physical variables in the model obtained are discussed and the detailed method used to determine the parameters is given. The model is then presented to describe the crystallization of poly(caryleher ether ketone) (PEEK) and thermal decomposition of poly(amide-imide) (PAI) respectively. It is found that some thermal characteristic parameters can be well estimated from the model simu-lated in computer.     

Phase equilibria in binary subsystems of urea–biuret–water system

Joint results of the differential scanning calorimetry (DSC) and thermogravimetry (TG) experiments were the basis for the fusion enthalpy and temperature determination of the biuret (NH₂CO)₂NH (synthesis by-product of the urea fertilizer (NH₂)₂CO). Recommended values are Δ_m H = (26.1 ± 0.5) kJ mol⁻¹, T _m = (473.8 ± 0.4) K. The DSC method allowed for the phase diagrams of “water–biuret,” “water–urea,” “urea–biuret” binary systems to be studied; as a result, liquidus and solidus curves were precisely defined. Stoichiometry and decomposition temperature of the biuret hydrate identified, composition of the compound in “urea–biuret” system was suggested.     

Lactam acetals and acid amides. 31. Synthesis,protonation, and basicities of some heterocyclic enamino ketones

The protonation of cyclic enamino ketones of the pyrrolidine, piperidine, and hexahydroazepine series, as well as their noncyclic analogs, was studied by PMR spectroscopy. It is shown that the presence of a CH₂ or CH₃ group in the “enamine” position leads to C protonation (in CF₃COOH). In the case of enamino ketones that do not contain substituents in the “enamine” α position N-and O-protonated forms are observed in CF₃COOH. The measured pK_a values (in 10% alcohol) and the ΔpK_a values (in nitromethane) of the enamino ketones show that the compounds for which C protonation is characteristic are two to three orders of magnitude more basic than in the case of compounds that do not contain substituents in the “enamine” α position; this is explained by the different character of protonation. See [1] for communication 30. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 344–348, March, 1980     

The effect of hydrogen ion production on the steady-state multiplicity of substrate-inhibited enzymatic reactions

The phenomenon of multiplicity is investigated for an isothermal continu ous stirred tank reactor (CSTR) in which an enzyme reaction producing hydrogen ions is taking place. The activity of the enzyme considered is sensitive to the hydrogen ion concentration and is inhibited by excess substrate. The enzyme is bound and the washout phenomenon is negligible. The investigation has uncovered a new type of hysteresis, consisting of a closed curve on the multiplicity diagram, and is disconnected from the rest of the multiplicity curve. This phenomenon has also been observed and analyzed by Uppal et al. (1) in their investigation of the non-isothermal, non-adiabatic (CSTR), and they have termed those closed curves “Isolas.” In the present paper we have elucidated the physical reason for the occurrence of those “Isolas” for the enzymatic reaction under consideration. We have also investigated the effect of different parameters on the appearance, disappearance, and size of the “Isolas.”     

Interaction of a Co<Subscript>6</Subscript> cluster with oxides of different nature: a quantum chemical study

Density functional theory was applied to investigate the interaction of Co₆ nanoparticle with various oxide supports including γ-Al₂O₃, silicalite, and zeolite HZSM-5. The introduction of cobalt into silicalite leads to insignificant stabilization of the metal cluster and induction of a small positive charge. The interaction of the Co₆ particle with the acid zeolite or alumina is accompanied by transfer of either a proton from the Br?nsted acid site or hydrogen atoms from terminal OH groups to the surface of the metal cluster with the formation of a hydride-like complex cation. Geometric parameters and energy characteristics of adsorption complexes of carbon monoxide molecule with Co₆ particles on different supports were calculated. For isolated particle on silicalite, “linear” adsorption is predicted. According to calculations, one can expect “angular” adsorption in the case of the acid zeolite and “two-point” adsorption (precursor of active surface carbon) in the system Co₆/γ-Al₂O₃.     

Adsorption and electrophysical properties of semiconductors of the InSb-CdS system

Adsorption and the electrophysical properties (changes in electrical conductivity) of thin film solid solutions and binary components of the new InSb-CdS system are studied by means of piezoquartz microweighing, IR spectroscopy and probe compensation in the temperature range of 273–353 K and a range of adsorbate gas (NH₃, NO₂) pressures of 0.2–9.8 Pa. The areas of physical and chemical adsorption accompanied by the charging of the (mostly positive) surface are determined. The mechanisms and regularities of adsorption as a function of external conditions and composition of the system are established, and certain similarities and patterns of changes in the adsorption and electroconductivity, and parallelisms of the “acidbase characteristic-composition,” “adsorption characteristic-composition,” and “electrophysical characteristics-composition” dependences are described. These prove to be useful in studying the adsorption mechanism and in identifying the most active components of the system relative to NH₃ and NO₂, proposed as materials for respective sensors/detectors.     

Preparation and evaluation of bioavailability of gatifloxacine-loaded nanoparticles

Pharmacokinetics of nanoparticles loaded with the antituberculosis drug gatifloxacine, as a new delivery system, was studied. In vivo experiments performed in laboratory animals showed that the dosage form of gatifloxacine incorporated into nanoparticles of poly(DL-lactic-co-glycolic acid) has a different pharmacological pattern as compared with the dosage form manufactured in industry. An increase in half-life (T _1/2) and in mean residence time (MRT) was observed for gatifloxacine nanoparticles in blood plasma. The area under the “concentration versus time” pharmacological curve (AUC_(0→36) was shown to increase mostly owing to the terminal part of the curve.     

Sub-micron wear measurement using activities under the free handling limit

In the present work we demonstrate the development of a thin layer activation (TLA) method to be able to measure micrometer wear or less by using radioactive tracing. In order to activate very swallow depths we decreased the bombarding energy to the “linear” region of the cross-section curve. The disadvantage of the method is that the wear curve will be “linear” near to the surface instead of “constant” as is the case with the usual (high energy) TLA. The advantage is that the activity of the sample will be much lower and it is concentrated in the swallower studied depth. The other possible method is irradiation under small angle (15 to 30° or even grazing incidence), which also causes a near-surface concentration of the activity produced. Both methods are demonstrated with the most suitable nuclear reactions and some commonly used industrial materials.     

A new algorithm for the fixed-node quantum Monte Carlo method

A novel algorithm is proposed for the fixed-node quantum Monte Carlo (FNQMC) method.In contrast to previous procedures,its "guiding function" is not optimized prior to diffusion quantum Monte Carlo (DMC) computation but synchronistically in the diffusion process The new algorithm can not only save CPU time,but also make both of the optimization and diffusion carried out according to the same sampling fashion,reaching the goal to improve each other This new optimizing procedure converges super-linearly,and thus can accelerate the particle diffusion During the diffusion process,the node of the "guiding function" changes incessantly,which is conducible to reducing the "fixed-node error" The new algorithm has been used to calculate the total energies of states X3B1 and a1A1 of CH2 as well as π-X2B1 and λ-2A1 of NH2 The singlet-triplet energy splitting (λEsT) in CH2 and π energy splitting in NH2 obtained with this present method are (45 542±1.840) and (141.644±1.589) kJ/mol,respectively The calculated     

The effect of continuous CO<Subscript>2</Subscript> laser radiation on the thermal and molecular—Topological properties of polytetrafluoroethylene

The impact of high-intensity laser radiation on a polymer in vacuum is accompanied by the release of gaseous products of degradation and, in some cases, of clusters of the partially destroyed polymer. Polytetrafluoroethylene (PTFE) exhibits an abnormal behavior in this process: being exposed to continuous CO₂ laser radiation, it degrades at a high rate and its clusters have a fibrous form. Depending on the irradiation conditions, the fibrous fraction forms two types of product, “cotton wool” and “felt”. Polytetrafluoroethylene and its laser-modified “cotton wool“ product have a semicrystalline topological structure. The preliminary γ-irradiation of PTFE enhances the laser ablation process.     

Facile synthesis of micrometer FeS/PVP architectures with the aid of thiourea

Micrometer-sized flowerlike FeS/poly(vinyl pyrrolidone)(PVP) architectures were synthesized by solvothermal process with the aid of thiourea, in which PVP may serve as soft templates. The FeS/PVP flowers have uniform morphologies with an average diameter of 5 μm, made of several nanopetals. The formation of FeS/PVP flowers is a new kinetic control process. In this process, thiourea molecules would be decomposed to produce “gas bubble”, and the “gas bubble” could make PVP chain segment rearrange along exterior force, resulting in the morphology evolution. The higher “gas bubble” pressure would produce 3D flowers, and the lower pressure would give a hollow structure. The evolution process from particles to 3D flowers is observed for the first time. In addition, the hollow FeS/PVP and Cu₂S/PVP spheres are also obtained by this technique.     

Thermal analysis of (NaF/AlF<Subscript>3</Subscript>)-FeF<Subscript>3</Subscript> and (NaF/AlF<Subscript>3</Subscript>)-FeO systems

Thermal analysis of the two systems, (NaF/AlF₃)-FeF₃ and (NaF/AlF₃)-FeO, was carried out with three different cryolite ratios. In these systems, “impurity compounds” decreased the temperature of primary crystallisation with decreasing cryolite ratios. From the slope of the dependencies, it can be assumed that the excess of AlF₃ plays a more significant role in changes in the “Fe(III)” systems than in “Fe(II)” systems.     

The kinetics and main pathways for the liquid-phase oxidation of cyclohexene by air in the presence of cobalt,chromium, iron,and nickel µ<Subscript>3</Subscript>-oxotrimetallohexapivalates

It was found that during the liquid-phase oxidation of cyclohexene (CH) by air (323–343 K) in the presence of a series of homo-and heteronuclear μ ₃-oxotrimetallohexapivalates with a M₂M′O (M, M′ = Co, Cr, Fe, Ni) core insignificant amounts of the corresponding epoxide are formed, and 3-hydroperoxy-2-cyclohexene (HP), 3-hydroxy-2-cyclohexene (CHol), and 2-cyclohexen-3-one (CHone) accumulate in the oxidate. It is suggested that CHone and CHol are “dead-end” products from the oxidation of CH under the investigated conditions while the HP is a unique “intermediate-damper” that gives rise to the realization of alternative paths (catalytic cycles) for the formation of these products. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 85–90, March–April, 2007.     

Label-free detection of nucleic acids by turn-on and turn-off G-quadruplex-mediated fluorescence

In this study we have used two fluorescent probes, tetrakis(diisopropylguanidino)-zinc-phthalocyanine (Zn-DIGP) and N-methylmesoporphyrin IX (NMM), to monitor the reassembly of “split” G-quadruplex probes on hybridization with an arbitrary “target” DNA. According to this approach, each split probe is designed to contain half of a G-quadruplex-forming sequence fused to a variable sequence that is complementary to the target DNA. Upon mixing the individual components, both base-pairing interactions and G-quadruplex fragment reassembly result in a duplex–quadruplex three-way junction that can bind to fluorescent dyes in a G-quadruplex-specific way. The overall fluorescence intensities of the resulting complexes were dependent on the formation of proper base-pairing interactions in the duplex regions, and on the exact identity of the fluorescent probe. Compared with samples lacking any “target” DNA, the fluorescence intensities of Zn-DIGP-containing samples were lower, and the fluorescence intensities of NMM-containing samples were higher on addition of the target DNA. The resulting biosensors based on Zn-DIGP are therefore termed “turn-off” whereas the biosensors containing NMM are defined as “turn-on”. Both of these biosensors can detect target DNAs with a limit of detection in the nanomolar range, and can discriminate mismatched from perfectly matched target DNAs. In contrast with previous biosensors based on the peroxidase activity of heme-bound split G-quadruplex probes, the use of fluorescent dyes eliminates the need for unstable sensing components (H₂O₂, hemin, and ABTS). Our approach is direct, easy to conduct, and fully compatible with the detection of specific DNA sequences in biological fluids. Having two different types of probe was highly valuable in the context of applied studies, because Zn-DIGP was found to be compatible with samples containing both serum and urine whereas NMM was compatible with urine, but not with serum-containing samples.