다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

日本物理学会誌及びJournal of the Physical Society of Japanの月刊について

Much progress has been made over the past ten years on the synthesis of monodisperse spherical nanocrystals. Mechanistic studies have shown that monodisperse nanocrystals are produced when the burst of nucleation that enables separation of the nucleation and growth processes is combined with the subsequent diffusion-controlled growth process through which the crystal size is determined. Several chemical methods have been used to synthesize uniform nanocrystals of metals, metal oxides, and metal chalcogenides. Monodisperse nanocrystals of CdSe, Co, and other materials have been generated in surfactant solution by nucleation induced at high temperature, and subsequent aging and size selection. Monodisperse nanocrystals of many metals and metal oxides, including magnetic ferrites, have been synthesized directly by thermal decomposition of metal-surfactant complexes prepared from the metal precursors and surfactants. Nonhydrolytic sol-gel reactions have been used to synthesize various transition-metal-oxide nanocrystals. Monodisperse gold nanocrystals have been obtained from polydisperse samples by digestive-ripening processes. Uniform-sized nanocrystals of gold, silver, platinum, and palladium have been synthesized by polyol processes in which metal salts are reduced by alcohols in the presence of appropriate surfactants.

Synthesis of monodisperse spherical nanocrystals.

http://www.geocities.ws/nandwana_vikas/Hyeon_review_chemical.pdf

Chemical synthesis of magnetic nanoparticles

Coupling between electrons and phonons (lattice vibrations) drives the formation of the electron pairs responsible for conventional superconductivity. The lack of direct evidence for electron-phonon coupling in the electron dynamics of the high-transition-temperature superconductors has driven an intensive search for an alternative mechanism. A coupling of an electron with a phonon would result in an abrupt change of its velocity and scattering rate near the phonon energy. Here we use angle-resolved photoemission spectroscopy to probe electron dynamics-velocity and scattering rate-for three different families of copper oxide superconductors. We see in all of these materials an abrupt change of electron velocity at 50-80 meV, which we cannot explain by any known process other than to invoke coupling with the phonons associated with the movement of the oxygen atoms. This suggests that electron-phonon coupling strongly influences the electron dynamics in the high-temperature superconductors, and must therefore be included in any microscopic theory of superconductivity.

Evidence for ubiquitous strong electron-phonon coupling in high-temperature superconductors.

Using a low temperature scanning tunneling microscope in the spectroscopic mode, we find that the disorder in a Bi(2)Sr(2)CaCu(2)O(8+delta) thin film modifies dramatically the quasiparticle local density of states Small, but well-defined superconducting regions, coexisting with dominating semiconducting areas, show well-pronounced gap structures, similar to those observed previously in high-quality single crystals Surprisingly, between these two regions, the detailed shape of the quasiparticle spectrum is virtually identical to the pseudogap previously observed at temperatures T>T(c), or in the vortex core, at 42 K Thus, the role of the disorder in destroying the superconducting phase is comparable to that of the magnetic field or thermal fluctuations

Influence of disorder on the local density of states in high- T(c) superconducting thin films

Thin polymer films containing small sized platelet type filler. The polymer has a melt index of from 0.01 to 10 grams per 10 minutes at 190° C. to 250° C. as measured on ASTM Test No. D-1238 at a load of 1000 to 2160 grams. The preferred polymer is polycaprolactam or high density polyethylene. There is from 10 to 50 percent of a platelet filler having an average equivalent diameter of from 1 to 8 micrometers, a maximum equivalent diameter of about 25 micrometers, and an average thickness of less than 0.5 micrometers. The preferred filler is talc. The film is from 10 to 100 micrometers thick and can be a single ply or a laminate.

Polymer films containing platelet particles

We present scanning tunneling microscopy and spectroscopy of the newly discovered superconductor CaC6. The tunneling conductance spectra, measured between 3 and 15 K, show a clear superconducting gap in the quasiparticle density of states. The gap function extracted from the spectra is in good agreement with the conventional BCS theory with Delta0=1.6+/-0.2 meV. The possibility of gap anisotropy and two-gap superconductivity is also discussed. In a magnetic field, direct imaging of the vortices allows us to deduce a coherence length in the ab plane xiab approximately 33 nm.

Scanning tunneling spectroscopy on the novel superconductor CaC6.

Using high-speed scanning tunneling spectroscopy (STS), we perform a full mapping of the quasiparticle density of states (DOS) in single crystals of Bi2 − xPbxSr2CaCu208 + δ. The measurements carried out at 5 K showed a complex spatial pattern of important variations of the local DOS on the nanometer scale. Superconducting areas, characterized by a well-pronounced superconducting gap, are coexisting with regions of a peakless gap structure which we attribute to the pseudogap. Within the large superconducting regions, the spectra reveal strong peak/dip/hump signatures, identical to the pristine Bi2Sr2CaCu208 + δ case. On the contrary, in very small superconducting regions this fine structure is attenuated. Such a behavior of the local DOS suggests that the peak/dip/hump fine structure is not only a consequence of the superconducting state, but is also directly related to the scale of the phase coherence. The role of Bi-Pb substitutional disorder is discussed.

Nanometer scale mapping of the density of states in an inhomogeneous superconductor

We present an analytical method for treating the tunneling current between a tip and a sample in scanning tunneling microscopy (STM) that goes beyond the independent-electrode (Bardeen) approximation and is valid for smaller tip-to-surface separations The extremity of the tip is represented by a single spherical potential well This well is strongly coupled to neighboring tip atoms, as well as the sample electrode, both of which we leave in a general form The wave function for the entire system is obtained by a matching procedure, from which the total current is determined If the current is associated with s-derived tip orbitals, the result is comparable in simplicity with that of J Tersoff and D Hamann [Phys Rev B 31, 805 (1985)] The low-bias tunnel conductance is proportional to the local density of states (LDOS) of the surface, but renormalized to include multiple reflections to all orders: \ensuremath{\sigma}\ensuremath{\propto}${\mathrm{\ensuremath{\rho}}}_{\mathit{s}}$(${\mathbf{r}}_{0}$,${\mathit{E}}_{\mathit{F}}$)/D, where D depends on both the tip and sample electronic structures and on the tip position ${\mathbf{r}}_{0}$ This effect includes the modification of the surface LDOS due to the presence of the tip A compact expression is also obtained for orbitals of higher angular momenta: p and d states The current then depends on the gradients of the surface spectral density, and not on the LDOS, and also has a characteristic denominator We discuss the significance of this effect, both in the interpretation of STM images and related spectroscopies

Generalized expression for the tunneling current in scanning tunneling microscopy

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