Optimization of carbon incorporation in GaAs during molecular beam epitaxial growth

Carbon-doped GaAs with dopant concentrations up to about 10²⁰ cm^–3 has been grown by molecular beam epitaxy. Above a critical carbon concentration, which depends on the deposition parameters, the surface deteriorates and loses its mirror-like appearance. From X-ray diffractometry and scanning electron microscopy, a diagram is established separating two areas with rough and mirror-like surface morphologies. The electrical properties as well as the morphology of GaAs : C can be simultaneously improved by a careful adjustment of the deposition parameters according to this diagram. On leave at: Tokyo Institute of Technology, Research Center for Quantum Effect Electronics, 2-12-1 O-okayama, Meguro-ku, Tokyo 152, Japan     

On representations of the canonical commutation relations

In the measure space construction of a representation of the canonical commutation relations, the strong continuity of any one parameter subgroup is proved.All multipliers for the separable case are expressed in a constructive manner and an irreducibility criterion for a subset of multipliers is obtained.Preprint No. 1970-27.On leave from Research Institute for Mathematical Sciences Kyoto University, Kyoto, Japan.     

MRI Application for Clarifying Fuel Cell Performance with Variation of Polymer Electrolyte Membranes: Comparison of Water Content of a Hydrocarbon Membrane and a Perfluorinated Membrane

Magnetic resonance imaging (MRI) is applied to clarify a dominating factor on variation of fuel cell performance with two types of polymer electrolyte membranes, a hydrocarbon membrane and a perfluorinated membrane. MRI results revealed that the hydrocarbon membrane showed a water content higher than that of the perfluorinated membrane, responsible for a better fuel cell performance due to decrease of resistance loss of the fuel cell. Authors' address: Shohji Tsushima, Research Center for Carbon Recycling and Energy, Tokyo Institute of Technology, 2-12-1, Ohokayama, Meguro-ku, Tokyo 152-8552, Japan     

Toward the responsible innovation with nanotechnology in Japan: our scope

The societal impacts of nanotechnology have attracted growing attention in the United States and Europe in recent years. In Japan, the National Institute of Advanced Industrial Science and Technology (Technology Information Department) has played a central role in promoting discussions on this topic by collecting information from Japan and overseas, creating a network of the interested parties, and providing a forum for discussion. This paper presents a summary of recent activities in Japan relating to the societal impacts of nanotechnology, fro the launch of the “Nanotechnology and Society” open forum (August 2004) until the “Nanotechnology Debate” discussion forum (February 2007), and outlines the policy recommendations that came out of a project entitled “Research on Facilitation of Public Acceptance of Nanotechnology” (March 2006).     

Screening of impurities in strong magnetic fields

Charged impurities inserted in an electron gas in strong magnetic fields and at low temperatures are considered. Using the random phase and the generalized Born approximations, a self-consistent calculation of the screening of the impurities and the broadening of the electronic energy levels due to the scattering by these impurities is presented. Concrete results obtained in numerical form show that for typical semiconductors the anisotropy of te screening induced by the magnetic field is strongly reduced by collisional damping. The screening length, however, depends rather strongly on the field.On leave of absence from the Department of Physics, University of Tokyo, Tokyo, Japan.     

Free boson representation ofU_q (\widehat{sl}_3 )

A representation of the quantum affine algebra of an arbitrary levelk is constructed in the Fock module of eight boson fields. This realization reduces the Wakimoto representation in theq 1 limit. The analogues of the screening currents are also obtained. They commute with the action of modulo total differences of some fields.On leave from Department of Physics, University of Tokyo, Tokyo 113, Japan.     

A model for the complex permittivity of water at frequencies below 1 THz

Experimental permittivity data of liquid water, compiled from the open literature, were selectively applied to support a modeling strategy. Frequencies up to 1 THz and atmospheric temperatures are covered with an expression made up by two relaxation (Debye) terms. The double-Debye model reduces to one term when the high frequency limit is set at 100 GHz, and the model can be extended to 30 THz by adding two resonance (Lorentzian) terms. The scheme was carried out by employing nonlinear least-squares fitting routines to data we considered reliable.T. Manabe was with the Institute for Telecommunication Sciences, NTIA-DoC, on leave from the Radio Research Laboratory, Ministry of Posts and Telecommunications, Koganei, Tokyo 184. He is now with ATR Optical and Radio Communications Research Laboratories, Seika-cho, Soraku-gun, Kyoto 619-02, Japan.     

On a characterization of the state space of quantum mechanics

A characterization of state spaces of Jordan algebras by Alfsen and Shultz is improved to a form with more physical appeal (proposed by Wittstock) in the simplified case of a finite dimension.On leave from Research Institute for Mathematical Sciences, Kyoto University, Kyoto 606, Japan     

Transverse asymmetry of $^3\!\stackrel{\rightarrow}{\rm He}$ and the magnetic form factor of the neutron

Multi-nucleon transfer reactions in ⁴⁰Ca + ²⁰⁸Pb have been studied at several bombarding energies close to the Coulomb barrier. Light reaction products have been identified in mass and charge with a time-of-flight spectrometer. The energy spectra of the inclusive two-neutron pick-up channel show a population in a narrow region of excitation energies which corresponds to the predicted energy of pairing-vibration states in ⁴²Ca.Received: 30 September 2003, Revised: 9 December 2003, Published online: 13 July 2004PACS: 25.70.Hi Transfer reactions - 24.10.-i Nuclear reaction models and methods - 21.60.Cs Shell model - 21.10.Pc Single-particle levels and strength functionsA.M. Vinodkumar: Present address: Tokyo Institute of Technology, Japan.     

On the convergence of exponential operators—the Zassenhaus formula,BCH formula and systematic approximants

The convergence of the Zassenhaus formula is proven under an appropriate condition as well as for other exponential operators such as the Baker-Campbell-Hausdorff formula.On leave of absence from Department of Physics, Faculty of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, Japan     

Three-nucleon forces studied by nucleon-deuteron scattering

Recent experimental progress of the three-nucleon force study is shown placing an emphasis on the nucleon-deuteron elastic scattering at intermediate energies. Correspondence: H. Sakai, Department of Physics, University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan     

Electric fields from model lightning discharges in a neutral atmosphere

The electric fields created by lightning discharges in a neutral atmosphere are calculated in the time representation. It is shown that asymmetric strokes containing horizontal currents can generate pronounced pulsed electric fields. A high-power quasistatic field can influence the middle atmosphere together with pulses. The motion of the current wave in a complex-geometry stroke channel can lead to an increase in the number of emitted pulses. At the periphery of the lightning cell, upon the arrival of the pulse, the electric field vector turns upward, to the stroke axis, and sideward. We also expect an increase in atmospheric turbulence due to convection at the frontal part of the cloud. The emerging inhomogeneities of the atmospheric temperature and density can facilitate the onset of plasma processes generated by the electric field of a strong thunderstorm. Since convection and the focusing electric fields are concentrated at the periphery, their joint action can lead to the appearance of circular and prolate luminous formations. Institute of Radiophysics and Electronics of the National Academy of Sciences, Khar’kov, Ukraine; The University of Electro-Communications, Tokyo, Japan. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 6, pp. 699–722, June, 1998.     

Schrödinger operators with magnetic fields

We prove a large number of results about atoms in constant magnetic field including (i) Asymptotic formula for the ground state energy of Hydrogen in large field, (ii) Proof that the ground state of Hydrogen in an arbitrary constant field hasL _z = 0 and of the monotonicity of the binding energy as a function ofB, (iii) Borel summability of Zeeman series in arbitrary atoms, (iv) Dilation analyticity for arbitrary atoms with infinite nuclear mass, and (v) Proof that every once negatively charged ion has infinitely many bound states in non-zero magnetic field with estimates of the binding energy for smallB and largeL _z .On leave at Department of Mathematics, California Institute of Technology, Pasadena, CA 91125 for 1980/81Supported by USNSF Grant MCS-78-00101Supported by USNSF Grant MCS-78-01885; on leave at Department of Mathematics, California Institute of Technology, Pasadena, CA 91125 for 1980/81     

Nanotechnology R&;D Policy of Japan and Nanotechnology Support Project

In the 2nd Science and Technology Basic Plan (2001–2005), the area of nanotechnology and materials is designated one of the four prioritized areas in funding. Following this plan, Ministry of Education, Culture, Sports, Science and Technology (MEXT) and Ministry of Economy, Trade and Industries (METI), the main funding ministries, and their organizations, Japan Society for the Promotion of Science (JSPS), Japan Science and Technology Agency (JST), National Institute for Materials Science (NIMS), RIKEN, New Energy and Industrial Technology Organization (NEDO), and National Institute of Advanced Industrial Science and Technology (AIST) promotes their research programs. Besides, in order to promote interdisciplinary, interorganizational, and international collaboration of researchers, Nanotechnology Support Project (NSP) was started by MEXT in 2002. The project has two missions: informational support and common use facility support. Nanotechnology Researchers Network Center of Japan is responsible for informational support, and 14 universities and national research institutes are responsible for common use facility support.     

Critical Value of the Quantum Ising Model on Star-Like Graphs

We present a rigorous determination of the critical value of the ground-state quantum Ising model in a transverse field, on a class of planar graphs which we call star-like. These include the junction of several copies of ℤ at a single point. Our approach is to use the graphical, or fk-, representation of the model, and the probabilistic and geometric tools associated with it. This research was carried out during the author’s Ph.D. studentship at the University of Cambridge, UK, and the Royal Institute of Technology (KTH), Sweden. The author gratefully acknowledges funding from KTH during this period. The author would also like to thank Riddarhuset, Stockholm, for generous support during his studies.     

On the dependence of the cutoff in upshifted see

A new mechanism for the cutoff mechanism in stimulated electromagnetic emissions from optically pumped plasma is presented.Radiophysical Research Institute, Nizhny Novgorod, Russia. Radio Atmospheric Science Center, Kyoto, Japan. Swedish Institute of Space Physics, Uppsala Division, Sweden. Published in Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 5, pp. 680–681, May, 1994.     

Quasifinite highest weight modules over the superW 1+∞algebra

We study quasifinite highest weight modules over the supersymmetric extension of theW ₁₊ algebra on the basis of the analysis by Kac and Radul. We find that the quasifiniteness of the modules is again characterized by polynomials, and obtain the differential equations for highest weights. The spectral flow, free field realization over the (B, C)-system, and the embedding into (|) are also presented.Address after April 1, 1994: Research Institute for Mathematical Sciences, Kyoto University, Kyoto 606, JapanAddress after April 1, 1994: Uji Research Center, Yukawa Institute for Theoretical Physics, Kyoto University, Uji 611, Japan     

Computer calculation of fanning spin structure in magnetic thin films and determination of exchange stiffness constant

Magnetization curves and critical switching curves were calculated numerically for fanning flux reversal of magnetic thin films and compared with the experiment in which the fanning spin structure was realized by a twisting field produced by the in-plane current followed by an external field in the reverse direction. From the best fit of the experimental and calculated curves, values of the exchange stiffness constant,A, were determined for Ni-Fe and Ni-Fe-Co films.The authors would like to thank Dr. Nobuo Hayashi of the Department of Physics, Faculty of Science, University of Tokyo, for useful discussions on calculations.     

The electronic viewpoint on the morphology of the microclusters

Although the five-fold symmetry conflicts with the crystalline long range order, it can appear in some finite systems. In order to search for such possibility in the microclusters in the small size limit and to clarify the roles of the electrons in the morphology, the electronic states are studied in the tight binding scheme. The single electron spectra coming from thes- andp-atomic orbitals are derived for three types of the 13-atom clusters; with the fcc-like configuration, the hcp-like and the icosahedral. If the transfer integral between two surface atoms is put equal to that between the central and a surface atom in the icosahedral case, this configuration has the lowest total electronic energy in many cases studied, but not always. The fact that a surface atom has larger number of neighbours in the icosahedral configuration is surely of great advantage. It, however, is not almighty in the quantum case.On leave from Department of Physics, Faculty of Science, Kyoto University, Kyoto 606, Japan. A part of this work was done there     

Gibbs states of a one dimensional quantum lattice

A one dimensional infinite quantum spin lattice with a finite range interaction is studied. The Gibbs state in the infinite volume limit is shown to exist as a primary state of a UHF algebra. The expectation value of any local observables in the state as well as the mean free energy depend analytically on the potential, showing no phase transition. The Gibbs state is an extremal KMS state.On leave from Research Institute for Mathematical Sciences, Kyoto University Kyoto, Japan.