The “Average” Work Function and Emission Area in the Fowler-Nordheim Equation

Derivation of the elementary Fowler-Nordheim equation is based on several strong physical assumptions (e.g. smooth flat surface and uniform work function across emitting surface, constant emission area and a uniform distribution of the applied field over it). A real emitter, however, definitely does not fulfill these assumptions. In spite of it the total emission current follows the FN equation and is frequently used for an estimation of the "average" work-function. The physical basis of this procedure and of the terms "average" work function and "emission area" are analyzed from the experimentalist's point of view. Thus some of the older - more or less intuitive - conclusions are substantiated.     

Visualization of Effect Algebras by Automorphisms

We show that every effect algebra satisfying the Riesz decomposition property can be represented as an effect algebra of automorphisms of an antilattice, and every MV-algebra can be represented as an MV-algebra of automorphisms of a linearly ordered set. Such a representation enables us to visualize effect algebras by functions. This is a variation of the Holland representation theorem for -groups and of its generalization of Glass for directed interpolation po-groups as -groups or po-groups automorphisms of linearly ordered set or of an antilattice, respectively.     

Effect Algebras Which Can Be Covered by MV-Algebras

We exhibit effect algebras which can be covered by MV-subalgebras. We show that any effect algebra E which satisfies the Riesz interpolation property (RIP) and the so-called difference-meet property (DMP) can be covered by blocks, maximal subsets of mutually strongly compatible elements of E, which are always MV-subalegbras. This result generalizes that of Rieanová who proved the same result for lattice-ordered effect algebras. We show that for effect algebras with only (RIP) the result in question can fail.     

Development of novel composite sorbents for the removal of actinides from environmental and analytical solutions

A novel approach to preparing granular sorbents for the separation of actinides has been developed, where the extractant is directly immobilized in an inert matrix. This allows substantially higher extractant loadings in the sorbent than for conventional extraction chromatography resins. This approach utilizes polyacrylonitrile (PAN) as the inert matrix material. The well-known actinide extractant octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) has been loaded into sorbent granules at extractant loadings from 20 to 33 wt.% CMPO. The porosity of the PAN matrix allows the active material to have rapid and complete access to the solution containing the impurities, resulting in improved kinetics and higher sorption capacities. Sorbents containing CMPO were prepared using PAN as a binding matrix, and tested against commercially available actinide extraction chromatography resins. Direct comparative batch contact tests performed with TRU-Resin^Ò and CMPO-PAN using an INEEL tank waste simulant, resulting in distribution coefficient (K _d) values for Am approximately 2-90 times higher for CMPO-PAN than for TRU-Resin. Batch distribution coefficient (K _d) values for Pu were approximately 60-150 times higher for CMPO-PAN than for the TRU-Resin. Acid dependency curves were generated for Am and Pu with CMPO-PAN over a concentration range of 1 mM to 5M HNO₃.     

Łukasiewicz Tribes are Absolutely Sequentially Closed Bold Algebras

We show that each sequentially continuous (with respect to the pointwise convergence) normed measure on a bold algebra of fuzzy sets (Archimedean MV-algebra) can be uniquely extended to a sequentially continuous measure on the generated ukasiewicz tribe and, in a natural way, the extension is maximal. We prove that for normed measures on ukasiewicz tribes monotone (sequential) continuity implies sequential continuity, hence the assumption of sequential continuity is not restrictive. This yields a characterization of the ukasiewicz tribes as bold algebras absolutely sequentially closed with respect to the extension of probabilities. The result generalizes the relationship between fields of sets and the generated -fields discovered by J. Novák. We introduce the category of bold algebras and sequentially continuous homomorphisms and prove that ukasiewicz tribes form an epireflective subcategory. The restriction to fields of sets yields the epireflective subcategory of -fields of sets.     

Oscillation and Nonoscillation of Higher Order Self-Adjoint Differential Equations

Oscillation and nonoscillation criteria for the higher order self-adjoint differential equation (-1)ⁿ(t^alphay⁽ⁿ⁾)⁽ⁿ⁾+q(t)y = 0 (*) are established. In these criteria, equation (*) is viewed as a perturbation of the conditionally oscillatory equation (-1)ⁿ(t^alphay⁽ⁿ⁾)⁽ⁿ⁾ - µ,t^2n-y = 0, where _n, is the critical constant in conditional oscillation. Some open problems in the theory of conditionally oscillatory, even order, self-adjoint equations are also discussed.     

Unconventional multifractal formalism and image analysis of natural fractals

The unconventional multifractal formalism is compared with the conventional one frequently used to characterize nonlinear phenomena and complex systems. The algorithm for the unconventional formalism has been implemented on a computer. Numerical artifacts of the method are discussed. Empirical criteria for distinguishing the monofractality/multifractality of the spectra affected by statistical fluctuations are presented. The multifractal image analysis of the Lichenberg figures has confirmed a self-similar arrangement of surface streamers belonging to the special case of electrostatic separation discharges propagating along a surface of polymeric dislectrics.     

STM study of nucleation of Ag on Si(111)−(7 × 7) surface

Initial stages of Ag on Si(111)−(7 × 7) surface nucleation were studied at submonolayer coverage. Samples were prepared by thermal evaporation of Ag from tungsten wire under UHV conditions (p<2.5 × 10⁻⁸ Pa). Various deposition rates (0.002–0.1 ML s⁻¹) were used to prepare Ag island films with coverages (0.002–2) ML (1 ML ≈ 7.58 × 10¹⁴ atoms cm⁻²) at room temperature. We observed preferential growth on faulted half unit cells (F cells). At constant coverage both the island density and ratio of occupied F and U (unfaulted) cells are independent of the deposition rate, which is an evidence for dominant influence of substrate structure. The preference of nucleation in the F cells against U cells decreases with the coverage until the ratio is 1:1 for 1 ML Ag film. We have observed that presence of an Ag island in any type of the half unit cell (F or U) considerably reduces nucleation probability in neighbouring cells. This results in forming of structural patterns observed among randomly grown Ag-islands which is a new feature found for Ag/Si(111)−(7 × 7) system. Presented at the VIII-th Symposium on Surface Physics, Třešt’ Castle, Czech Republic, June 28 – July 2, 1999. This work was supported by the Grant Agency of Charles University — projects GAUK 34/97 and 147/99, by the Grant Agency of Czech Republic — project GAČR 202/97/1109 and by the Ministry of Education grant VS 97116.     

The effect of hydrogenation on the magnetization reversal process in amorphous ferromagnets

The influence of hydrogenation and dehydrogenation on the power spectra of Barkhausen noise in amorphous alloys has been investigated. It has been shown that after hydrogenation local stress centers occur in amorphous structure. Presence of the centers leads to long-wave fluctuations of domain wall energy which cause the decrease of the number of irreversible domain wall displacements.     

Plasma-liquid technologies for treatment of archaelogical artifacts

Plasma-liquid technologies at atmospheric pressure provide a wide range of possibilities for applications. One of them, the treatment of archaeological artifacts, is presented in this paper. The effects of discharges between a metal electrode and a solution surface and/or an interaction of hollow cathode plasma jet, plasma pencil, with liquid on the corroded surface of bronze and glass artifacts were studied. It was compared with standard low pressure plasma techniques and with the effects of electrolysis. Original and treated objects were characterized by means of scanning electron microscope (SEM) with energy dispersive analyser used for the spot elemental analyses.