Spin tunneling properties in mesoscopic magnets: effects of a magnetic field

The tunneling of a giant spin at excited levels is studied theoretically in mesoscopic magnets with a magnetic field at an arbitrary angle in the easy plane. Different structures of the tunneling barriers can be generated by the magnetocrystalline anisotropy, the magnitude and the orientation of the field. By calculating the nonvacuum instanton solution explicitly, we obtain the tunnel splittings and the tunneling rates for different angle ranges of the external magnetic field ( θ _H = π/2 and π/2 < θ _H < π). The temperature dependences of the decay rates are clearly shown for each case. It is found that the tunneling rate and the crossover temperature depend on the orientation of the external magnetic field. This feature can be tested with the use of existing experimental techniques. Received 12 March 2001 and Received in final form 18 October 2001     

Ion structure determinations and ion—molecule reactions by double quadrupole mass spectrometry

The QQ mass spectrometer is shown to be applicable to ion structure determination via collision-induced dissociations of mass-selected ions. The instrument can be scanned so as to record the products of dissociation as well as those of ion—molecule association reactions. The dissociations correspond to those observed at high kinetic energy in mass-analyzed ion kinetic energy spectrometers and the association reactions show parallels with reactions seen in ion cyclotron resonance spectroscopy and in high-pressure mass spectrometry     

Comments on the bremsstrahlung cross section formula using exact electron-distorted wave functions

Rozics and Johnson's formula is examined and its inconsistency is pointed out.     

Study of the spectrum of cherenkov light

It is pessible to study experimentally Cherenkov light spectra in a liquid scintillation spectrometer with colour filters. Cherenkov light spectra of⁶⁰Co,¹⁹⁸Au,¹¹⁵Cd,¹⁴³Ce,¹⁴⁰La,³²P,⁸⁶Rb,⁷⁶As,⁴²K and an external standard were studied in a Packard 3375 type liquid scintillation spectrometer, using 11 various Kodak Wratten filters. The absorption maxima of the filters ware in the 410–796 nm interval.     

Fixed point theorems under the interior condition

We show a fixed point theorem for condensing mappings under a new condition of the Leray-Schauder type. We call it the Interior Condition. We also discuss examples that demonstrate the independence of these two conditions.

     

Properties of (InGa)As/GaAs QW (λ ≈ 1.2 µm) facet-coated edge emitting diode laser

In this paper, we report on the design and optical properties of laser diodes with an emission wave-length of ～1170 nm based on an (InGa)As/GaAs double quantum well active layer. The back and front facet of the laser diodes were coated with SiO_x dielectric films that influence the output optical power by enhancing or lowering the facet reflectivity. The measurements show improvement of the facet-coated laser diode properties in the threshold-current-density reduction along with light output power enhancement. Furthermore, a narrow far field pattern and high side mode suppression have been observed.     

A NOVEL METHOD FOR FABRICATING COMPOSITE MOSAIC MEMBRANE WITH UNIQUE NF SELECTIVITY

A novel method of fabricating composite mosaic membranes was studied on the basis of interracial polymerization （IP） by coating a thin selective layer onto the surface of a micro-porous hollow-fiber membrane, in which, 2,5-diaminobenzene sulfonic acid was used as one monomer of the IP reaction, and a mixture of trimesoyl chloride （TMCI） and 4-（chloromethyl） benzoyl chloride as the other monomer. Through the IP reaction a thin selective layer with negatively charged groups could be first formed on the polyethersulfone （PES） support membrane. Then trimethylamine solution was introduced to modify the IP layer through a quaternization reaction. Thus the selective layer of this composite membrane contained both negatively charged and positively charged groups to perform the mosaic functionality. Characterization of the composite mosaic membranes was carried out through permeation experiments using different inorganic salts and dyes. The experimental results showed that the membranes could permeate both mono- and bi-valent inorganic salts, but reject larger organic molecules. Such a mosaic membrane is potentially useful for the separation of salts from water-soluble organics, especially in dye and textile industries.     

High resolution electronic study of ONO, ONO and ONO: A rovibronic survey covering 11 800-14 380 cm

The 11 800-14 380 cm⁻¹ frequency range has been scanned for rotationally resolved rovibronic transitions in the A²B₂-X²A₁ electronic band system of the symmetric (C_2v) ¹⁶O¹⁴N¹⁶O and ¹⁸O¹⁴N¹⁸O isotopologues and in the corresponding electronic band system of the asymmetric (C_s) ¹⁸O¹⁴N¹⁶O isotopologue. The rotational analysis—reflecting minor differences in mass—in combination with symmetry induced spectral differences allows an identification of 68 ¹⁶O¹⁴N¹⁶O vibronic levels, 26 ¹⁸O¹⁴N¹⁸O vibronic levels and 51 ¹⁸O¹⁴N¹⁶O vibronic levels. The bands are recorded using near infrared fluorescence spectroscopy and a piezo valve based pulsed molecular beam expansion of premixed ¹⁸O₂ and ¹⁴N¹⁶O in Ar. The majority of the observed bands is rotationally assigned and can be identified as transitions starting from the vibrational ground state of one of the isotopologues. Numerous hot bands have also been identified. A comparison of the overall spectroscopic features of C_2v vs. C_s symmetric species provides qualitative information on symmetry dependence of vibronic couplings.     

Study on anti-emission materials for non-emitting grid applications in microwave power tubes

Hafnium and platinum were deposited onto molybdenum grids by ion-beam assisted deposition method. Electron-emission characteristics from molybdenum grids with Hf and Pt films, which were contaminated by active electron-emission substances (Ba, BaO) of the cathode, were measured using analogous diode method. The surfaces of grids were analyzed by X-ray diffraction. The results revealed that the reaction between BaO and Hf formed BaHfO₃ compound, which greatly reduced the accumulation of BaO on the surface and accordingly decreased grid emission. In contrast, Ba were formed by the decomposition of BaO on the surface of Pt film under high temperature and re-evaporated from its surface, which reduced the active electron-emission substances on the surface of the grid and effectively restrained grid emission. Their mechanisms for grid-emission suppression are discussed and a good method to develop new grid-coating materials is suggested.