Observations of surface modifications induced by the multiple pulse irradiation using a soft picosecond x-ray laser beam

To study the interactions between picosecond soft x-ray laser (SXRL) beams and material surfaces, gold (Au), copper (Cu), and silicon (Si) surfaces were irradiated with SXRL pulses having a wavelength of 13.9 nm and a duration of ～7 ps. Following irradiation, the surfaces of the substrates were observed using a scanning electron microscope and an atomic force microscope. With single pulse irradiation, ripple-like structures were formed on the Au and Cu surfaces. These structures were different from previously investigated conical structures formed on an Al surface. In addition, it was confirmed that the development of modified structures, i.e., growth of hillocks on the Au and Cu surfaces, was observed after multiple SXRL pulse exposures. However, on the Si surface, deep holes that seemed to be melted structures induced by the accumulation of multiple pulses of irradiations were found. Therefore, it was concluded that SXRL beam irradiation of various material surfaces causes different types of surface modifications, and the changes in the surface behaviors are attributed to the differences in the elemental properties, such as the attenuation length of x-ray photons.     

Van der Pol type self-excited micro-cantilever probe of atomic force microscopy

A technique for dimensional reduction of nonlinear delay differential equations (DDEs) with time-periodic coefficients is presented. The DDEs considered here have a canonical form with at most cubic nonlinearities and periodic coefficients. The nonlinear terms are multiplied by a perturbation parameter. Perturbation expansion converts the nonlinear response problem into solutions of a series of nonhomogeneous linear ordinary differential equations (ODEs) with time-periodic coefficients. One set of linear nonhomogeneous ODEs is solved for each power of the perturbation parameter. Each ODE is solved by a Chebyshev spectral collocation method. Thus we compute a finite approximation to the nonlinear infinite-dimensional map for the DDE. The linear part of the map is the monodromy operator whose eigenvalues characterize stability. Dimensional reduction on the map is then carried out. In the case of critical eigenvalues, this corresponds to center manifold reduction, while for the noncritical case resonance conditions are derived. The accuracy of the nonlinear Chebyshev collocation map is demonstrated by finding the solution of a nonlinear delayed Mathieu equation and then a milling model via the method of steps. Center manifold reduction is illustrated via a single inverted pendulum including both a periodic retarded follower force and a nonlinear restoring force. In this example, the amplitude of the limit cycle associated with a flip bifurcation is found analytically and compared to that obtained from direct numerical simulation. The method of this paper is shown by example to be applicable to systems with strong parametric excitations.     

Spin-probe ESR study on the dynamics of liquid molecules in the MCM-41 nanochannel: temperature dependence on 2-propanol and water

A spin-probe ESR study has been made on the dynamics of 2-propanol and water molecules in the nanochannel of MCM-41 at various temperatures. In the former system, 2-propanol is separated into two phases: one with molecules immobilized in the ESR time scale and the other with mobile ones, even at temperatures more than 40 degrees higher than the bulk melting point. In the case of water, on the other hand, only the "immobilized" water was detected at a temperature as high as 313 K. At higher temperature, spin-probe molecule undergoes anisotropic rotational diffusion to reduce resistance from the solvent molecules in the nanochannel. These results are explained in relation to the intermolecular network intensified in the nanochannel. Static as well as dynamic structures of these solutions have been discussed.     

Polymorphism of ZnTe at elevated pressure

Simultaneous measurements of the electrical resistance and X-ray diffraction under pressure have revealed that ZnTe exhibits two subsequent structural transitions at approximately 85 and 130 kbar, accompanied by a conspicuous rise and drop in the resistance, respectively.     

On the pattern of space division by territories

Summary In this paper the tesselation of territories is discussed. When a mass of animals with teritoriality is introduced at random simultaneously into a finite two-dimensional (2D) region, territories are gradually formed and finally settle to a steady state. A model calculation for this process is carried out, where a Voronoi polygon is assumed as a territory. Comparisons are made between the model calculation and Barlow's observation on an artificial population of mouthbreeder fish. Differences between 1D and 2D case are also discussed. The Institute of Statistical Mathematics     

twins in Mo-doped TiSi 2 thin films with the C54 structure

The defect structures in orthorhombic C54 crystallites in thin films of Mo-doped TiSi 2 produced by co-sputtering have been investigated by transmission electron microscopy. Almost all C54 crystallites contain a twin boundary parallel to (101), dividing a crystallite into two regions, each of which also contains many thin twins with the habit plane parallel to (001), which is inclined by about 45° from (101). Both of the two regions divided by the twin boundary parallel to (101) tend to have facets on (001) as well as thin twins with the habit plane parallel to (001). As a result, C54 crystallites exhibit a characteristic shape just like an oak leaf. While twins with the (001) habit plane have been observed in C54 crystallites in both binary and Mo-doped TiSi 2 thin films, those with the (101) habit plane are present only in Mo-doped TiSi 2 thin films. The twinning elements for (101) twins are determined to be K 1 = (101), , K 2 = (001) and m2 = [100]. The origin of (101) twins in Mo-doped TiSi 2 is discussed in terms of the change in the c / a axial ratio upon alloying TiSi 2 with Mo.