[14α, 15α-3H] steroids for pharmacological research

It is shown in the present work that the labelling of steroids in ring D is suitable for the production of stable compounds. Two syntheses are described. The final products represent the tritium labelled forms of two pharmacologically important 4,9-dienones with high radiochemical purity. Unfortunately, these dienones are very sensitive to self-radiolysis. They must be stored as diluted solutions at low temperature.     

Local doses associated with119mSn isomeric transition

The energy absorbed by immediate surrounding of disintegrating^119mSn nuclei have been estimated by comparing the Mössbauer emission spectra of¹¹⁹Sn in some tin compounds with the absorption spectra of the same substances after -irradiation and by simple calculations of Auger electrons energy losses. The results obtained indicate that the observed post-effects of the^119mSn decay are due to self-radiolysis and other processes, whose contributions depend on the individual properties of the matrices.     

Local radiolytic effectiveness of Auger electrons of iodine-125 in benzene-iodine solutions

The gas-chromatographic analysis of benzene-iodine solutions containing molecular iodine-125 after various storage times showed that no radiolytic products appeared while some products such as benzene, iodobenzene, biphenyl, and iodobiphenyl, were detected under the same analytical conditions in our recent studies concerning the reactions of iodine atoms activated by L shell photoelectric ionization in benzene-iodine solutions, and the self-radiolysis of iodobenzene labelled with iodine-125¹⁵. On the other hand, our theoretical calculations showed that if iodine molecules were uniformly distributed in benzene, iodobenzene should be detected as a radiolytic product due to the local absorption of Auger electrons of iodine-125. The absence of any radiolytic product clearly demonstrated that iodine aggregates have an important role in the absorption of Auger electrons of iodine-125 in benzene-iodine solutions. In addition, theoretical calculations showed that if the iodine aggregation is taken into account the experimental result agrees well with theoretical calculations.     

Radiation stability of methionine-35S and selenomethionine-75Se

The radiation stability of methionine-³⁵S and selenomethionine⁷⁵Se was investigated using the methods of thin-layer chromatography, gas chromatography and ESR. Radiation decomposition of methionine-³⁵S mainly consists in an oxidation process and in the release of volatile products. The ESR-spectra of irradiated DL-methionine indicated a strong localization of the unpaired electrons on sulfur atoms. Radiation damage to selenomethionine-⁷⁵Se as a function of radiation dose proved an increased stability of this compound, and its radiation decomposition consists in the formation of oxidized products and by direct rupture of the selenium bonds accompanied by the formation of volatile compounds like CH₃SeH and SeH₂. The self-radiolysis of the aqueous solution of selenomethionine-⁷⁵Se during its storage in air leads, however, to a lower decomposition rate which consists in the release of inorganic selenium and in an oxidation process.     

The radiolysis of mixtures of carbon monoxide and hydrogen

The self-radiolysis of mixtures of CO and tritium (³H₂) has been studied at pressures of 0.25 to 1.0 atmospheres, temperatures of ?198° to +100°C, and in the presence of added H₂O or CO₂. The products of decomposition are CO₂, ³H₂O, C³H₄, C₂³H₄, and a white polymer believed to be polyformaldehyde. Initial rates and G values were measured and compared with rates of ion pair formation. The rates of formation of both CO₂ and C³H₄ are independent of temperature and proportional to the energy absorbed in the ³H₂.     

The radiolysis of mixtures of carbon dioxide and hydrogen

The self-radiolysis of CO₂ in excess tritium (³H₂) has been studied at pressures of 0.1 to 1.0 atm, temperatures of ?80° to +100°C, and in the presence of added H₂O, He, or Ar. The primary products of decomposition are CO and ³H₂O. Secondary products are C³H₄, C₂³H₄, and a white polymer. The rates of disappearance of CO₂ and formation of products and G-;values were measured. The disappearance of CO₂ initially obeys first-order kinetics, then slows down with time at a rate depending upon the initial pressure of ³H₂. The initial rates are proportional to pressures of CO₂ and ³H₂. They are independent of temperature, decreased by addition of H₂O vapor, and increased by addition of He or Ar. The proposed mechanism of decomposition of CO₂ and formation of products involves ionization of CO₂ followed by dissociative recombination forming CO and O. Then the O reacts with a hydrogen-containing species forming OH and H₂O, and a back reaction forms CO₂ from CO and OH.     

Hydrodynamics of a bounded vertical film with nonlinear surface properties

The drainage of a thin liquid film with an insoluble monolayer down a vertical wall is studied. Lubrication theory is used to develop a model where the film is pinned at the top with a given thickness and the film drains into a bath at the bottom. A nonlinear equation of state is used for the surface tension and the surface viscosity is a nonlinear function of the surfactant concentration; these are appropriate for some aqueous systems. The three partial differential equations are solved via discretization in space and then the resulting differential algebraic system is solved. Results are described for a wide range of parameters, and the conditions under which the free surface is immobilized are discussed.     

The submicro determination of carbon,hydrogen and nitrogen by a gas-chromatographic method

A method for the determination of carbon, hydrogen and nitrogen in organic samples weighing 40–80 μg is described. The sample is decomposed conventionally in a helium stream and the water formed is converted to acetylene. Nitrogen, carbon dioxide and acetylene are then separated on a silica-gel column, and the acetylene is burned to carbon dioxide by passage through copper oxide at 900° because the acetylene peak itself is not easily measured. Water from the second combustion is removed on silica gel and the three peaks emerging are measured by means of a micro thermistor cell. The standard deviations obtained for acetanilide are 0.31% for carbon, 0.28% for hydrogen and 0.11% for nitrogen. Results for other compounds are given and the parameters relevant to precision are discussed.     

Application of power expansion in the thermodynamics of compressible Markovian copolymers

The problem of constructing phase diagrams for a compressible melt of a binary Markovian copolymer is reduced to a set of nonlinear differential equations in partial derivatives with transcendental relationships. Using power expansions, the closed set of nonlinear differential equations is derived. This set allows its further analytical study. Eigenvalues of a linearized system are analyzed, and the boundaries of the thermodynamic stability of melts are defined. Nonlinear equations in normal coordinates are obtained; for symmetric melts, these equations are reduced to a single equation by adiabatic elimination of small-scale variables. Binodal curves are calculated for such solutions of this equation, which correspond to the free energy minimum of melts. Corrections reflecting the effect of melt nonsymmetry are found. The results are applied for copolymers, whose composition is similar to that of homopolymers, diblock copolymers, and random and regularly alternating copolymers. Spinodals and binodals corresponding to microphase separation are constructed.     

Specific-ion effects in non-aqueous systems

It is widely acknowledged that specific-ion effects are ubiquitous in aqueous systems and undoubtedly are essential to the fundamental processes of life, although a deep fundamental understanding of specific-ion effects remains an important challenge. Specific-ion effects in non-aqueous solvents are known but have attracted far less attention, yet knowledge of specific-ion effects in non-aqueous systems is likely to provide important information for guiding, evaluating and testing our theories of specific-ion effects. Here, the literature on specific-ion effects in non-aqueous solvents is surveyed with a view to determining if the Hofmeister series or lyotropic series so universally observed in aqueous systems is widely evident in non-aqueous systems. Particular attention has been applied to experiments on non-aqueous systems that are known to exhibit Hofmeister series in aqueous systems with the aim of determining if a consistent ion ordering in the strength of specific-ion effects is observed in other solvents. We find that specific-ion effects are ubiquitous in non-aqueous solvents, that both Hofmeister and lyotropic series are widely observed, although not necessarily for the same class of experiment. Moreover, we find that Hofmeister and lyotropic series are observed in non-aqueous solvents even for experiments in which these series are not observed for water. Additionally, series reversal is seen for a given experiment when the solvent is changed. All this poses significant challenges for our understanding of specific-ion effects in aqueous and non-aqueous systems and also provides guideposts for future investigations.     

Application of microbiological sensors in fermentation processes

A review is presented of microbiological sensors which are composed of micro-organisms immobilized in a membrane and coupled to a sensing element. Conventional microbiological sensors such as those for biochemical oxygen demand (BOD), ethanol and acetic acid are discussed briefly. Novel sensors are then described. The sensor for carbon dioxide is based on a chemoautotrophic bacterium, that for alcohol on cell membranes of the acetic acid bacteria, Gluoconabacter suboxydans. Sensors for BOD carbon dioxide are based on thermophilic bacteria. Finally, a microbial field effect transistor sensor (FET) for alcohol sensor is described. For all the sensors, the ranges of linear response and their long-term stabilities are reported.     

Theoretical study of vibration-phonon coupling of H adsorbed on a Si(100) surface

In this paper a perturbation-theory study of vibrational lifetimes for the bending and stretching modes of hydrogen adsorbed on a Si(100) surface is presented. The hydrogen-silicon interaction is treated with a semiempirical bond-order potential. Calculations are performed for H-Si clusters of different sizes. The finite lifetime is due to vibration-phonon coupling, which is assumed to be linear or bilinear in the phonon and nonlinear in the H-Si stretching and bending modes. Lifetimes and vibrational transition rates are evaluated with one- and two-phonon processes taken into account. Temperature effects are also discussed. In agreement with the experiment and previous theoretical treatment it is found that the H-Si (upsilon(s) = 1) stretching vibration decays on a nanosecond timescale, whereas for the H-Si (upsilon(b) = 1) bending mode a picosecond decay is predicted. For higher-excited vibrations, simple scaling laws are found if the excitation energies are not too large. The relaxation mechanisms for the excited H-Si stretching and the H-Si bending modes are analyzed in detail.     

Statistical mechanical theory for steady state systems. VIII. General theory for a Brownian particle driven by a time- and space-varying force

A Brownian particle subject to a time- and space-varying force is studied with the second entropy theory for nonequilibrium statistical mechanics. A fluctuation expression is obtained for the second entropy of the path, and this is maximized to obtain the most likely path of the particle. Two approaches are used, one based on the velocity correlation function and one based on the position correlation function. The approaches are a perturbation about the free particle result and are exact for weak external forces. They provide a particularly simple way of including memory effects in time-varying driven diffusion. The theories are tested against computer simulation data for a Brownian particle trapped in an oscillating parabolic well. They accurately predict the phase lag and amplitude as a function of drive frequency, and they account quantitatively for the memory effects that are important at high frequencies and that are missing in the simplest Langevin equation.     

Fitness for purpose in relation to specification limits

Frequently, the ultimate goal of an analytical measurement is to assess compliance in respect to a specification limit. So, the necessary requirement is to make a correct decision on the grounds of the measurement result. It is suggested a practical methodology to attain fitness for purpose results when specification limits are established for compliance assessment. It is based on a comparison between fitness for purpose uncertainty functions that define a high probability of conclusive correct decisions and a characteristic uncertainty function which describes the performance of the analytical system along concentration in a given condition of measurement. To attain fitness for purpose results, different replication programs are applied. Determinations of Zn, Mn and Cd in potable water are discussed as case studies. They represent different cases concerning relative position of detection and specification limits. A definition of fitness for purpose when specification limits are relevant is given. Quality of analytical results and analytical procedures should be associated with the concept of fitness for purpose.     

Solid-liquid phase coexistence of the Lennard-Jones system through phase-switch Monte Carlo simulation

The phase-switch Monte Carlo method of Wilding and Bruce [Phys. Rev. Lett. 85, 5138 (2000)] is extended to enable calculation of solid-liquid phase coexistence for soft potentials. The method directly accesses coexistence information about a system while avoiding simulation of the interfacial region. Order parameters are introduced that allow one to define a path that connects liquid and crystalline phases. Transition matrix methods are employed to bias the sampling such that both phases are sampled in a rapid and efficient manner. Coexistence properties are determined through an analysis of specific volume probability distributions, which are generated naturally during a biased simulation. The approach is demonstrated with the Lennard-Jones system. Finite-size effects are examined and compared to those for the hard sphere system. In addition, two techniques are considered for accounting for long-range interactions. The methodology presented here is general and therefore provides a basis for its application to other soft systems.     

A computer controlled photon counting flame emission spectrometer

An automated emission spectrometer has been developed around a simple commercial instrument. The manner in which a computer is used for control and the way data are acquired and assimilated are discussed. The interfacing to the computer is described, sample programs are illustrated and methods of analyses are given. Sensing is achieved through photon counting. The linearity of the system has been examined and it was found that, for lithium, quantitative results can be obtained with an accuracy of 1 per cent for a concentration range of four orders of magnitude. The time required for analysis is discussed and, although the spectrometer is serial in nature, the increased information rate obtained through photon counting results in high speed data acquisition.     

A combinatorial approach for development of materials for optical sensing of gases

We present a combinatorial approach for development of materials for use in optical gas sensors, with oxygen being used as an exemplary target gas. Combinatorial chemistry is shown to be a promising tool for speeding up the search for new sensor materials. The method is based on the use of various polymers, solvents, indicators, plasticizers, and other additives. Solutions of the respective materials are prepared in appropriate organic solvents, and a robotic station is programmed to mix the components. Spots of the sensing materials are deposited in the wells of glass substrates resembling microtiterplates. After drying off the solvent, the sensor spots are automatically analyzed in a test stand, where they are exposed to a carrier gas containing oxygen in various concentrations. Changes in the decay time of fluorescence of the indicator probes are measured and used (along with sensor response time) as a main criterion for sensor assessment. It is shown that the combinatorial approach can reduce the time and effort needed to establish libraries of sensor materials by a factor of at least 1000. We describe in detail the device for preparation of sensor libraries and for testing the respective materials. The potential of the system is demonstrated for the characterization of optical oxygen sensors.     

Calculation of the entropy and free energy from monte carlo simulations of a peptide stretched by an external force

Hypothetical scanning Monte Carlo (HSMC) is a method for calculating the absolute entropy, S, and free energy, F, from a trajectory generated by any simulation technique. HSMC was applied initially to fluids (argon and water) and later to peptides and self-avoiding walks on a lattice. In this paper we make a step further and apply it to a model of decaglycine (at T = 300 K) in vacuum with constant bond lengths where external stretching forces are exerted at the end points; the changes in S and F are calculated as the forces are increased. The molecule is placed initially in a helical structure, which is changed to an extended structure after a short simulation time due to the exerted forces. This study has relevance to problems in polymers (e.g., rubber elasticity) and to the analysis of experiments where individual molecules are stretched by atomic force microscopy (AFM), for example. The results for S and F are accurate and are significantly better than those obtained by the quasi-harmonic approximation and the local states method. However, the molecule is quite stiff due to the strong bond angle potentials and the extensions are small even for relatively large forces. Correspondingly, as the force is increased the decrease in the entropy is relatively small while the potential energy is enhanced significantly. Still, differences, TDeltaS, for different forces are obtained with very good accuracy of approximately 0.2 kcal/mol.     

Projection operators and Clebsch–Gordan coefficients for projective representations

Previous discussions of the bases and projection operators for projective representations are analyzed and alternatives are proposed. Detailed proofs are provided for a result which is often assumed or proved within unacceptable limitations, namely that the form of the projection operators which is standard for vector representations is also valid for unitary projective representations. These proofs provide necessary conditions for this result, and they are constructed in terms of the definition given for the bases of projective representations. The calculation of Clebsch–Gordan coefficients for projective representations by means of the projection operators is discussed. Whereas in the method of Dirl the work is carried out entirely in terms of the matrix representations, and the symmetrization of the bases has to be considered in a second step, all the work of this paper is conducted starting from the symmetrization of the bases of the projective representations, so that those two steps are carried out simultaneously.