Theory of Atomic-Force Microscopy(STM Theory)

The mechanism of force detection of Atomic-Force Microscopy (AFM) is theoretically investigated. First, a theoretical simulation of contact AFM images is performed, and a tip apex structure is studied. It is clarified how the AFM images and the force distributions change as the load varies. It is also revealed that the characteristics of the AFM images such as their detailed microscopic pattern, the symmetry, and the corrugation amplitude, depend strongly on the tip apex structure. Secondly, fundamental features of the atomic-scale friction in Frictional-Force Microscopy (FFM) are studied. Simulated FFM images are in good agreement with observed ones. Then we discuss the mechanism of the image pattern of FFM by an analytical method. It is revealed that the part of the boundary of the stable region of the cantilever basal position, appears as the boundary between the bright and the dark area of FFM images. Thus we clarify the physical meaning of the FFM image patterns. Lastly, we studied dynamics of the large amplitude cantilever oscillations in the noncontact AFM (nc-AFM). The oscillation of the cantilever is treated as a forced oscillation periodically interrupted by collisions with the surface. By solving this extremely nonlinear problem numerically, some remarkable features of the cantilever oscillation are revealed. We observed strange behaviors of the cantilever such as a bimodal state of dynamical touching and non-touching motion, as well as a fractional resonance features

Real Space Approach to Electronic-Structure Calculations

We have applied the Finite Element Method to the self-consistent electronic structure calculations of molecules and solids for the first time. In this approach all the calculations are performed in "real space" and the use of non-uniform mesh is made possible, thus enabling us to deal with localized systems with ease. To illustrate the utility of this method, we perform an all-electron calculation of hydrogen molecule in a supercell with LDA approximation. Our method is also applicable to mesoscopic systems.Comment: 11 pages, LaTeX, 5 figures available on request from [email protected]

Efficient method for simulating quantum electron dynamics under the time dependent Kohn-Sham equation

A numerical scheme for solving the time-evolution of wave functions under the time dependent Kohn-Sham equation has been developed. Since the effective Hamiltonian depends on the wave functions, the wave functions and the effective Hamiltonian should evolve consistently with each other. For this purpose, a self-consistent loop is required at every time-step for solving the time-evolution numerically, which is computationally expensive. However, in this paper, we develop a different approach expressing a formal solution of the TD-KS equation, and prove that it is possible to solve the TD-KS equation efficiently and accurately by means of a simple numerical scheme without the use of any self-consistent loops.Comment: 5 pages, 3 figures. Physical Review E, 2002, in pres

Fast and stable method for simulating quantum electron dynamics

A fast and stable method is formulated to compute the time evolution of a wavefunction by numerically solving the time-dependent Schr{\"o}dinger equation. This method is a real space/real time evolution method implemented by several computational techniques such as Suzuki's exponential product, Cayley's form, the finite differential method and an operator named adhesive operator. This method conserves the norm of the wavefunction, manages periodic conditions and adaptive mesh refinement technique, and is suitable for vector- and parallel-type supercomputers. Applying this method to some simple electron dynamics, we confirmed the efficiency and accuracy of the method for simulating fast time-dependent quantum phenomena.Comment: 10 pages, 35 eps figure

Submolecular-scale imaging of α-helices and C-terminal domains of tubulins by frequency modulation atomic force microscopy in liquid

In this study, we directly imaged subnanometer-scale structures of tubulins by performing frequency modulation atomic force microscopy (FM-AFM) in liquid. Individual α-helices at the surface of a tubulin protofilament were imaged as periodic corrugations with a spacing of 0.53 nm, which corresponds to the common pitch of an α-helix backbone (0.54 nm). The identification of individual α-helices allowed us to determine the orientation of the deposited tubulin protofilament. As a result, C-terminal domains of tubulins were identified as protrusions with a height of 0.4 nm from the surface of the tubulin. The imaging mechanism for the observed subnanometer-scale contrasts is discussed in relation to the possible structures of the C-terminal domains. Because the C-terminal domains are chemically modified to regulate the interactions between tubulins and other biomolecules (e.g., motor proteins and microtubule-associated proteins), detailed structural information on individual C-terminal domains is valuable for understanding such regulation mechanisms. The results obtained in this study demonstrate that FM-AFM is capable of visualizing the structural variation of tubulins with subnanometer resolution. This is an important first step toward using FM-AFM to analyze the functions of tubulins. © 2011 Biophysical Society

Ferromagnetism in a Hubbard model for an atomic quantum wire: a realization of flat-band magnetism from even-membered rings

We have examined a Hubbard model on a chain of squares, which was proposed by Yajima et al as a model of an atomic quantum wire As/Si(100), to show that the flat-band ferromagnetism according to a kind of Mielke-Tasaki mechanism should be realized for an appropriate band filling in such a non-frustrated lattice. Reflecting the fact that the flat band is not a bottom one, the ferromagnetism vanishes, rather than intensified, as the Hubbard U is increased. The exact diagonalization method is used to show that the critical value of U is in a realistic range. We also discussed the robustness of the magnetism against the degradation of the flatness of the band.Comment: misleading terms and expressions are corrected, 4 pages, RevTex, 5 figures in Postscript, to be published in Phys. Rev. B (rapid communication

Treatment Strategy for Recurrent and Refractory Epithelial Ovarian Cancer: Efficacy of High-Dose Chemotherapy with Hematopoietic Stem Cell Transplantation

According to population statistics in Japan, approximately 3,800 women die of ovarian ­cancer annually, and approximately 6,000 are affected by this disease. Ovarian cancer is ­referred to as a “silent tumor”, since patients have few subjective symptoms and by the time symptoms are observed, the cancer has progressed to Stage III or IV in about half of the patients. The basic treatment for advanced epithelial ovarian cancer is to remove as much of the tumor as possible, and subsequently to perform anticancer therapy using drugs such as cisplatin, carboplatin and paclitaxel, all of which have been shown to be effective for epi­thelial ovarian cancer. However, the 5-year survival rate in advanced ovarian cancer patients is still only about 20%, and a treatment that leads to long-term survival has yet to be developed. Here, we review the available treatments for ovarian cancer, and present the results of high-dose chemotherapy (HDC) performed in our hospital for recurrent and refractory ­ovarian cancer