Comment on ‘Step structure of vicinal Ge(001) surfaces’ by B.A.G. Kersten, H.J.W. Zandvliet, D.H.A. Blank and A. van Silfhout

We have investigated detailed structures of monatomic steps on Ge(001) at room temperature by using high-resolution scanning tunneling microscopy. Our conclusions are different from those of Kersten et al. [Surf. Sci. 322 (1995) 1] for the same system. The most crucial difference is that we have not observed the nonbonded SB step. We have pointed out a possible reason for the different conclusions.     

Theory of strong interactions. I. Kinematics

This paper is the first of a series devoted to strong interaction theory. As a general introduction to the series, we give a critical survey of theories and models presently in force.In a previous paper, we studied the kinematics of a single unstable hadron, the state of which was described as an incoherent superposition of states with different masses. To such a state there corresponds a function on the Poincaré group, called a characteristic function. Here we take up these old results anew, we work them out, and we go more thoroughly into their physical foundations. Then we describe the kinematics of several particles.The theory of strong interactions must take into account two opposed features of unstable hadrons: their identity and their difference with stable hadrons. The identity implies that an unstable hadron is in a certain state, described by a density operator; the difference is that this state has a mass spectrum, whose width cannot be neglected.We make the further assumption that the state is an incoherent superposition of components with different masses. This assumption is compared to the statistics experiment of Baton and Laurens, in which the components with different masses have been effectively separated.We define the characteristic function of such a state, and we point out its analogy with a usual characteristic function in probability theory. The physical meaning of characteristic functions is studied on the example of a spin, then in the general case.Then we study the characteristic function of several hadrons, and we define two notions: the global particle and the inclusive characteristic function.     

Long-period states of ordered intermetallic alloys. 2. Physical representation of the nature of their formation

A survey of the empirical data shows that there are two fundamentally different groups of long-period alloys. An analysis of the physical representations leads to the conclusion that their long-period states are different in nature. The stabilization of this state is determined by relaxation processes in one group and by competing interactions in different coordination spheres in the other group. V. D. Kuznetsov Siberian Physico-Technical Institute at Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 22–39, June, 1996.     

Surface structure of polyethylene crystals as revealed by surface decoration. II. Electron-microscopic detection of mobilizable surfaces

The paper is the first step in the application of the gold decoration technique described in Part I to the electron-microscopic study of the nature of the fold surface of polyethylene single crystals. It was observed that different areas of the same crystal layer display different decoration densities. It appears that this is due to residual solvent which is retained to different extents by different crystal portions. This assumption is substantiated by the salient observation that the initially slight decoration differences are much accentuated by deliberate flooding of the decorated crystals with a swelling agent. The inference is that the swelling liquid mobilizes some loose elements along the crystal surface, and, consequently, the differences within the same crystal reveal a variable crystal surface as regards surface looseness. With the new technique we are now able to describe and follow these phenomena as a function of the relevant variables. Within the confines of the present work it has already become apparent by this test that, from the usual commercial polymer, surfaces with least looseness are formed toward the end of the crystallization.     

Long-period states of ordered metal alloys. 1. Analysis of structural features

An analysis of empirical data establishes the presence at least two different types of long-period structures. The first type of structure is seen in alloys of the system Cu-Au, Cu₃Pd, Cu₃Pt, etc., while the second type is found in alloys Ag₃Mg and Al₃Ti and their analogs. It was concluded that the nature of the long-period states is different in the two types of structures.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 3–21, June, 1995.     

Peierls-Nabarro model of planar dislocation cores in b.c.c. crystals

Planar dislocation cores on {110} and {112} planes in b.c.c. crystals are studied using the Peierls-Nabarro model with force laws derived from four different interatomic potentials. A numerical iterative method suitable for solution of the Peierls-Nabarro equation is developed. The cores are represented by a continuous distribution of dislocations. The discussion of the correlation between the force laws and corresponding dislocation densities is based on the properties of the Hilbert transform.     

Surface modification of layered silicates. I. Factors affecting thermal stability

The resistance of modification molecules bound to montmorillonite platelet surfaces towards structural damage at high temperature is a major parameter guiding the formation of optimal interface between the filler and polymer phases in a nanocomposite material. As nanocomposites are generated by melt-blending of modified mineral and polymer, it is necessary to quantify the thermal resistance of the filler surface modification at the compounding conditions because different modifications differ in chain length, chemical structure, chain density, and thermal performance. A number of different alkyl ammonium modifications were exchanged on the montmorillonites with cation exchange capacities in the range 680–900?µequiv.?g^?1 and their thermal behaviour was characterised using high resolution thermogravimetric analysis. Quantitative comparisons between different modified minerals were achieved by comparing temperature at 10% weight loss as well peak degradation temperature. Various factors affecting thermal stability, such as length and density (or number) of alkyl chains in the modification, presence of excess modification molecules on the filler surface, the chemical structure of the surface modifications, etc. were studied. The TGA findings were also correlated with X-ray diffraction of the modified platelets.     

The luminescence properties of pesticides. II. Non-fluorescing carbamates

The phosphorescence emission and excitation spectra of four pesticidal carbamates have been recorded. The phosphorescence decay times were determined over several half-lives. The studies were carried out in three different solvents — EPA, isopropyl alcohol, and 3-methyl pentane. The effect of solvent on the spectral properties of carbamates is discussed.     

The proton N.M.R. spectrum of partially oriented norbornadiene. Molecular structure and the effect of vibrational averaging

The proton N.M.R. spectrum of norbornadiene partially oriented in the nematic solvent, Merck Phase (IV), has been measured and compared with an earlier study using EBBA as solvent. It is shown that the structure of the proton framework is significantly different in the two nematogens. Vibrational averaging of the dipolar couplings is carried out in order that effective r_z structures can be compared.     

Sessile splitting of screw dislocations in b.c.c. metals

The energies of six different sessile splittings of screw dislocation 1/2 [111], which can occur in b.c.c. metals assuming the stacking faults on {110} and {112} planes according to the hard sphere model, are compared. The regions of the values of stacking fault energies on {110} and {112} planes, in which a given splitting is favoured over the other five, are then shown.     

Analysis of closely-spaced index-guided semiconductor lasers. II. Single-stripe channel-guide structures

Calculations of the properties of double-channel injection lasers are presented. The dependence of the device characteristics upon a number of material parameters is found. Near-field and carrier concentration profiles are compared for devices of different dimensions at two output power values.     

On the D.C.-Limit of the Electric Conductivity of Plasmas

A continued fraction of type 2^N is used to solve the d.c.-problem for the electrical conductivity of plasmas. The coupling parameter dependence of the expansion coefficients is determined. It is shown that this technique allows to derive different order collision times for dilute systems.     

Reply to “photon emission from sputtered atoms — The observation of apparent local thermodynamic equilibrium in the excitation” by R.J. MacDonald,R.F. Garrett and P.J. Martin

Specific adsorption of anions on crystal faces of gold is related to the superficial atomic structure. For the iodide ion analysis of the admittance-potential curves for 13 different crystallographic orientations of the three main zones of the stereographic triangle is done. Empirical correlations are established between surface structure and the morphology of the admittance curves.     

Determination of the Deuterium Content of Natural Waters in U.A.R. by Mass Spectrometry

Deuterium content of natural waters has been estimated with a mass spectromete using different methods of reduction of water samples. The optimum conditions for isotopic analysis are found, and the different parameters of the instrument are obtained. The accuracy was within ± 3ppm.     

A stochastic theory of chemical reaction rates. II. Applications

A formalism developed for the treatment of chainlike models of reaction dynamics is applied to simple reacting systems and generalized to treat a reaction with a branching process. The models can be solved exactly, and the overall rates of the reactions are studied as a function of the rates arising from different dynamical regimes involved in the microscopic mechanisms.     

A comment on the evaluation of E.F.G. tensor components in HbO2

It is shown that the discrepancy between the evaluated E.F.G. tensor components in the Griffith's model and the experimental ones is erroneus. It arises only from the choice of two different reference frames.     

Radiation-induced changes in physical properties of bulk polyethylene. I. Effect of crystallization conditions

Melt crystallized polyethylenes with different crystallization histories were irradiated with γ-rays and examined for various properties. These include solubility (gel content), melting and recrystallization behavior, load extension behavior, and creep properties. Even for the same dose, very significant differences were observed for the different sample types. Although such differences have been reported previously, the present work reveals that these differences can be unusually large and that they are displayed by a range of different tests with a consistent correlation between them. The underlying trend is that in poorly crystallized samples the radiation is much more effective in forming networks than in samples of highly developed crystallinity. This finding may merely indicate that cross-linking is more abundant in the amorphous region than in the crystallites; nevertheless, analogy with single crystals suggests that in addition details of the fold surface morphology and the nature of the lamellar contact may also have a part to play. Among other properties, the elasticity of cross-linked melt was analyzed and found to be consistent with simple rubber elasticity theory, leading to an estimate of both the number of effective cross-links and of intrinsic entanglements acting as cross-links. The most conspicuous effects were observed in the creep behavior where different sample types irradiated to the same dose could behave as viscous liquids and true rubbers according to crystallization history. The relevance of such findings for the technological irradiation of polyethylene should be self-evident, particularly as the doses involved were those commonly employed in industrial applications.     

Structural comparison of prokaryotic and eukaryotic chaperonins.

Chaperonins are key components of the cell machinery and are involved in the productive folding of proteins. Most chaperonins share a common general morphology based in a cylinder composed of two rings of 7-9 subunits, with a conspicuous cavity inside the particle. Chaperonins have been classified into two groups according to their sequence homologies: type I, whose better known member is GroEL, and type II comprising the eukaryotic cytosolic CCT and the archaebacterial thermosome, among others. Although the basic structure of both chaperonin types is rather similar, there are a number of basic differences among them. Whereas GroEL is rather non-specific regarding its substrate, CCT is more specialized, and plays a fundamental role in the folding of cytoskeletal proteins. Another important difference is that GroEL is an homopolymer, while CCT is an heteromeric complex built up of eight different polypeptides. Furthermore, GroEL requires a cofactor (GroES) that is not present in the type II chaperonins.Recent studies of the structure of CCT have allowed a deeper insight into its function. Electron microscopic analyses have revealed a different behavior of this chaperonin after binding to nucleotides, respect to GroEL. The atomic structure of the thermosome fits into the electron microscopy reconstructed volume of the CCT. This fitting gives clues to compare the structural transitions of GroEL and CCT during the folding cycle. The different changes undergone by the two chaperonins suggest the existence of differences in the way they bind substrates and enlarge the internal cavity, as well as a different type of signaling between the two rings of the types I and II chaperonins.