Correlation of field emission flicker noise and work function for tungsten single crystal planes with adsorbed potassium

The flcker noise power of the (112), (110), (100), (111) and (122) planes as well of (110) vicinals of a tungsten field emitter has been measured as a function of potassium coverage. Distinct minima of the noise power for coverages that correspond exactly to the work function minima could be found. It seems that this coincidence might be explained — apart from big lateral interactions of the adparticles — by the stronger adsorbate-substrate interaction in a coherent adiayer than in an incoherent one and/or by an adlayer transition to the “metallic” state resulting in compensation of the ionic adsorbate charge by a common electron gas.     

Determination of the Deuterium Abundances in Water from 156 to 10,000 ppm by SIFT-MS

In response to a need for the measurement of the deuterium (D) abundance in water and aqueous liquids exceeding those previously recommended when using flowing afterglow mass spectrometry (FA-MS) and selected ion flow tube mass spectrometry (SIFT-MS) (i.e. 1000 parts per million, ppm), we have developed the theory of equilibrium isotopic composition of the product ions on which these analytical methods are based to encompass much higher abundances of D in water up to 10,000 ppm (equivalent to 1%). This has involved an understanding of the number density distributions of the H, D, (16)O, (17)O and (18)O isotopes in the isotopologues of H(3)O(+)(H(2)O)(3) hydrated ions (i.e. H(9)O (4) (+) cluster ions) at mass-to-charge ratios (m/z) of 73, 74 and 75, the relative ion number densities of which represent the basis of FA-MS and SIFT-MS analyses of D abundance. Specifically, an extended theory has been developed that accounts for the inclusion of D atoms in the m/z 75 ions, which increasingly occurs as D abundance in the water is increased, and which is used as a reference signal for the m/z 74 ions in the measurement of D abundance. In order to investigate the efficacy of this theory, experimental measurements of deuterium abundance in standard mixtures were made by the SIFT-MS technique using two similar instruments and the results compared with the theory. It is demonstrated that the parameterization of experimental data can be used to formulate a simple calculation algorithm for real-time SIFT-MS measurements of D abundance to an accuracy of 1% below 1000 ppm and degrades to about 2% at 10,000 ppm.     

On the Action of Riesz Transforms on the Class of Bounded Functions

The paper is devoted to the \(d\) -dimensional extension of the classical identity of Stein and Weiss concerning the action of the Hilbert transform on characteristic functions. Let \((R_j)_{j=1}^d\) be the collection of Riesz transforms in \(\mathbb{R }^d\) . For \(1\le p<\infty \) , we determine the least constants \(c_{p,d}, C_{p,d}\) such that $$\begin{aligned} \int _{\mathbb{R }^d} f(x)|R_jf(x)|^p\text{ d }x&\le c_{p,d} ||f||_{L^1(\mathbb{R }^d)},\\ \int _{\mathbb{R }^d} (1-f(x))|R_jf(x)|^p\text{ d }x&\le C_{p,d} ||f||_{L^1(\mathbb{R }^d)} \end{aligned}$$ for any Borel function \(f:\mathbb{R }^d\rightarrow [0,1]\) . The proof rests on probabilistic methods and the construction of appropriate harmonic functions on \([0,1]\times \mathbb{R }\) .     

An approach to the study of multistate insurance contracts

We derive a matrix representation for formulas of moments of cash value of future payment streams arising from multistate insurance contract, where the evolution of the insured risk and the interest rate are random. As an application, we derive formulas for net single and period premiums. The general theory is illustrated with a case where the evolution of the insured risk is modeled by a Markov chain. Copyright © 2012 John Wiley & Sons, Ltd.     

Field emission fluctuation phenomena of potassium microcrystals on tungsten: I. Spectral density functions and flip-flop

The field emission flicker noise technique has been applied to study dynamical properties of epitaxial potassium microcrystals on tungsten. Spectral density functions of the (111) region for temperatures between 78 and about 230 K were obtained. Some preliminary observations of flip-flop behaviour of potassium crystals are presented and discussed.     

Synthesis and Properties of a New Dihydroflavin: Reduction of a Flavinium Salt by Borocyanohydride

Reduction of 6 by borocyanohydride yielded the new dihydroflavin 7. The intermediate product 8 could only be observed in solution by ¹H-NMR. The chemical and physical properties of 7 are reported. UV/VIS, ¹H- and ¹³C-NMR, and luminescence techniques were used.     

Field desorption of Potassium from (001), (011) and (112) Tungsten planes

Field desorption of potassium from the (001), (011) and (112) tungsten planes in the temperature range 80–140 K and in the field range 0.10–0.55 V/Å has been investigated using the field emission micrscope with Faraday cage and a rotatable emitter. Generally good agreement with the results, obtained previously by other authors for other adsorbates and for the whole emitter tip, was found. However the temperature dependence of the desorption field is different for some crystal planes. The binding energy at zero coverage and zero field was determined. The values of 1.95 eV, 1.75 eV and 2.0 eV were obtained for the (001), (011) and (112) planes, respectively. The degree of desorption was also measured as a function of desorbing field and a significant difference of this dependence for the (001) and (011) planes was found.     

Work function of the adsorption system of potassium on tungsten

The work functions φ_hklof tungsten single crystal planes as functions of the surface densities N_hkl of the adsorbed potassium have been measured by means of the field emission method. Sealed-off field emission tubes with a Faraday collector and rotatable emitter were used. Another, special tube was made in order to determine the surface density of potassium. The unequilibrated adlayers on {110}, {112}, {100} and {111} tungsten single crystal planes have been investigated. For all the planes investigated the φ_hkl(N_hkl) dependence exhibited a distinct minimum. An attempt has been made to compare the experimental results with the theoretical models suggested recently.     

Lattice gas model for monolayer of amphipatic molecules

Using the molecular-field approximation for the lattice gas model in terms of a spin-one Ising model, we construct phase diagrams and show when the transition could be of first or second order. Possible relevance to the theoritical models of phase transitions in monolayers of amphipatic molecules is also discussed.     

Remark on the application of the effective hamiltonian method for random systems

We compare two versions of the effective Hamiltonian method applied to random bond systems. In one randomness is treated in a kind of the mean field approximation, whereas in the other the relevant arrangements of bonds are explicitly accounted for. Calculations for three dimensional systems of mixed ferromagnetic Heisenberg and Ising bonds show that although the T_c vs p (concentration of Heisenberg-loke interactions) curve in the second approach lies closer to the results of high temperature series general features in both approxsimations are quite similar.