Effect of Electron Correlation on Phonon Spectra in Cuprates

We examine theoretically the phonon dynamics in the electron-phonon-coupled systems. The model Hamiltonian is a one-dimensional Hubbard model where the hopping of electrons induces the electron-phonon coupling. The numerically exact diagonalization of the Hamiltonian with truncation of the total number of phonons is performed. We calculate the phonon excitation spectra and find that the softening of phonons occurs in insulating case, and a diffusive character appears in the metallic case. We also calculate the charge and spin excitation spectra and find that the dynamics of the phonon coupled with the hopping of electrons is affected by the low energy charge and spin excitations.     

Backscattered electron imaging by scanning electron microscopy of regenerating peripheral nerve axons immunostained with antineurofilament antibody.

To demonstrate three-dimensional architecture of regenerating axons growing through basal lamina tubes in cryoinjured nerve graft, backscattered electron (BSE) imaging in a scanning electron microscope (SEM) was used to visualize immunostained axons. Regenerating axons immunostained with an antibody against the 200 kD neurofilament protein (RT97) were clearly visualized in BSE images as bright components pursuing an irregular, often spiral course within the basal lamina tubes, and commonly branching within the tubes. The morphology of these structures corresponded closely to that of putative regenerating axons in SEM preparations following application of the potassium hydroxide-collagenase digestion method. The present approach, however, is a considerable improvement on the latter, providing three-dimensional information together with the identification of regenerating axons.     

A scheme of picosecond pulse shaping using gain saturationcharacteristics of semiconductor laser amplifiers

To obtain high power, well shaped picosecond pulses from gain-switched semiconductor lasers, the use of dynamic gain saturation characteristics of semiconductor laser amplifiers was investigated theoretically and experimentally. A configuration of a reflected-wave amplifier (RWA) with single-side external coupling is introduced for pulse shaping, which is found to be suitable for enhancing dynamic gain saturation. By a combination of a distributed feedback laser oscillator at 1.3 μm in wavelength and a reflected-wave amplifier of 400 μm cavity length with asymmetric facet reflectivities of 0.01% and 30%, single-mode optical pulses with almost no tailing, full width at half maximum of 15 ps, and peak power exceeding 50 mW were obtained without pulse broadening, despite the considerable tail structure of the incident pulse     

Role of Stripes in Spin and Charge Dynamics of Underdoped La2−x Sr x CuO4

We investigate the electronic states of underdoped La _2–x Sr _x CuO ₄ (LSCO) by using a microscopic model, i.e., t-t-t-J model, containing charge stripes. The numerically exact diagonalization calculation is employed on small clusters. The physical properties observed in the angle-resolved photoemission and optical conductivity experiments are consistently explained in the model with vertical stripes, but not diagonal ones. These results demonstrate a crucial role of the vertical stripes in underdoped LSCO.     

Magnetic Interaction in Insulating Cuprates

We examine two-spin (2S) and cyclic four-spin (4S) magnetic interactions in insulating ladder and two-dimensional (2D) cuprates. By a comparison of eigenstates between d-p and Heisenberg models, we evaluate magnitudes of these interactions. We find that the 4S interaction is 10 % of nearest neighboring 2S interaction, and a diagonal 2S interaction is considerably small. The 4S interaction for a ladder cuprate is larger than that for 2D one, and plays an important role in the low-energy excitation. The Heisenberg ladder with the obtained 2S and 4S interactions reproduces very well the experimental result of the temperature dependence of the magnetic susceptibility.     

Space charge behavior in polymer film based on increment of capacitance under AC high field

Polymer materials have excellent dielectric and insulation properties; however, those properties in AC high field region have not been known well. Recently we established an evaluation method of high‐field AC dissipation current waveform of polymer materials 1 . AC dissipation current waveforms of polyethylene and polypropylene films show nonlinear distortion in AC high‐field region. This nonlinearity was thought to be related to the behavior of AC space charge formation in the sample near electrodes. The properties of space charge formed under AC high field at power frequency seem to differ from those formed under DC high field. The measurement of AC space charge distribution is not so easy due to the resolution limit of the space charge measurement. We studied the dielectric properties of biaxially oriented polypropylene (BOPP) film under AC high field up to 120 °C. It was found that tan δ, AC dissipation current (Ixr), and unbalanced component of capacitive current (ΔIxc) increased when the temperature became higher. In particular, ΔIxc increased above some threshold field and was considered to be due to the AC space charge formation. This AC space charge layer near electrode is thought to be formed due to carrier injection under AC high‐field application. Usually, the carrier mobility becomes smaller on lowering the temperature. Most of the carriers injected from the electrode are trapped near the electrode in the sample film. But in the high‐temperature region, the carrier mobility becomes larger and the carrier injection starts to increase from lower field. Many more carriers are injected from the electrode. It is thought that some of the injected carriers are trapped inside the sample film; the others go through the sample to the opposite side. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(2): 8–16, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10018     

Enhanced renal toxicity by inorganic mercury in metallothionein-null mice

To elucidate a protective role of metallothionein (MT) in the manifestation of inorganic mercury toxicity, we studied the susceptibility of MT-null mice to the renal toxicity of mercuric chloride. Because the MT-null (J) mice are a genetic background of 129/Sv strain, the 129/Sv mice were used as wild-type controls. Nine-week-old male MT-null (J) and 129/Sv mice were given subcutaneous injections of mercuric chloride at doses of 10 to 40 micromol/kg. The basal MT level in the kidney of MT-null (J) mice was undetectable (<0.2 microg/g of tissue) and approximately 2.5 microg/g of tissue in 129/Sv mice. The sensitivity to the renal toxicity of mercuric chloride was markedly enhanced in the MT-null (J) mice compared with the 129/Sv mice. The renal mercury level was similar for the MT-null (J) and 129/Sv mice at 4 hr after the injection of mercuric chloride (20 micromol/kg) but became significantly lower in MT-null (J) mice than in 129/Sv mice at 24 and 72 hr. Based on the present results, we conclude that MT is an important protective factor against the renal toxicity caused by inorganic mercury and that it may play a major role in the retention of mercury in the kidney.