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Kosuke Morita, Kouji Morimoto, Daiya Kaji, Takahiro Akiyama, Sin-ichi ...
2007 Volume 76 Issue 4 Pages
043201
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The production and decay of
277112 have been investigated using a gas-filled recoil ion separator in irradiations of
208Pb targets with a
70Zn beam at 349.5 MeV. We have observed two α-decay chains that can be assigned to subsequent decays from
277112 produced in the
208Pb(
70Zn,n) reaction. After emitting four consecutive α-particles, both the chains terminate by spontaneous fission decays of
261Rf, and the decay energies and decay times of both the chains obtained in the present work agree well with those reported by a group at Gesellschaft für Schwerionenforschung (GSI), Germany. The present result gives the first clear confirmation of the discovery of
277112 and its α-decay product
273Ds reported previously.
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Makoto Umeki
2007 Volume 76 Issue 4 Pages
043401
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The motion of point vortices with periodic boundary conditions was studied by using Weierstrass zeta functions. The scattering and recoupling of a vortex pair by a third vortex becomes remarkable when the vortex density is large. The clustering of vortices with various initial conditions is quantitated by the
L function used in the point process theory in spatial ecology. It is shown that clustering persists if the initial distribution is clustered like an infinite row or a checkered pattern.
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Daisaku Kaneko, Masaki Oshikawa, Tetsuo Yamaguchi, Jian Ping Gong, Mas ...
2007 Volume 76 Issue 4 Pages
043601
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The frictional coefficient μ between poly(dimethylsiloxane) (PDMS) rubber and glass plate with PDMS lubricant is measured for various thickness of rubber sample. The friction coefficient of thick sample is shown to be an order of magnitude larger than that of thin sample. The phenomenon is interpreted as the transition from the hydrodynamic lubrication to the boundary lubrication.
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Yositake Takane
2007 Volume 76 Issue 4 Pages
043701
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We consider quasiparticle charge and energy imbalances in a thin superconductor weakly coupled with two normal-metal electrodes via tunnel junctions at low temperatures. Charge and energy imbalances, which can be created by injecting quasiparticles at one junction, induce excess tunneling current
Iex at the other junction. We numerically obtain
Iex as a function of the bias voltage
Vdet across the detection junction. We show that
Iex at the zero bias voltage is purely determined by the charge imbalance, while the energy imbalance causes a nontrivial
Vdet-dependence of
Iex. The obtained voltage–current characteristics qualitatively agree with the experimental result by R. Yagi [Phys. Rev. B
73 (2006) 134507].
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Yoichi Okimoto, Hiroyuki Matsuzaki, Yasuhide Tomioka, Istvan Kezsmarki ...
2007 Volume 76 Issue 4 Pages
043702
Published: April 15, 2007
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Femtosecond reflection spectroscopy was performed on a perovskite-type manganite, Gd
0.55Sr
0.45MnO
3, with the short-range charge and orbital order (CO/OO). Immediately after the photoirradiation, a large increase of the reflectivity was detected in the mid-infrared region. The optical conductivity spectrum under photoirradiation obtained from the Kramers–Kronig analyses of the reflectivity changes demonstrates a formation of a metallic state. This suggests that ferromagnetic spin arrangements occur within the time resolution (∼200 fs) through the double exchange interaction, resulting in an ultrafast CO/OO to FM switching.
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Ayako Yamamoto, Peter A. Sharma, Yoshihiko Okamoto, Aiko Nakao, Hiroko ...
2007 Volume 76 Issue 4 Pages
043703
Published: April 15, 2007
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A new pyrochlore ruthenium oxide, Hg
2Ru
2O
7, was synthesized under a high pressure of 6 GPa. In contrast to the extensively studied Ru
4+ oxides, this compound possesses a novel Ru
5+ valence state, corresponding to a half-filled
t2g3 electron configuration. Hg
2Ru
2O
7 exhibits a first order metal–insulator transition at 107 K, accompanied by a structural transition from a cubic to lower symmetry. The behavior of the magnetic susceptibility suggests the possible formation of a spin singlet in the insulating low temperature state.
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Shinya Takashima, Minoru Nohara, Hiroaki Ueda, Nao Takeshita, Chieko T ...
2007 Volume 76 Issue 4 Pages
043704
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Electrical resistivity ρ of a weak itinerant ferromagnet ZrZn
2 with a low residual resistivity ρ
0\\simeq0.46 μΩ cm was measured under hydrostatic pressure
P up to 3.2 GPa.
T2-behavior of ρ, a hallmark of Fermi liquid, was not observed down to 1 K not only at around the ferromagnetic critical point
Pc∼2 GPa but over an entire pressure range investigated. The temperature dependence of ρ at low temperatures evolved from
T5⁄3 in the ferromagnetic phase to
T3⁄2 in the paramagnetic phase. This change, however, was very weak and it was hard to capture the signature of critical point in the resistivity. Such a breakdown of Fermi liquid over a remarkably wide phase space indicates the lack of some ingredient in the description of magnetic quantum critical point in clean metals.
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Jun Kikuchi, Masashi Takigawa, Hitoshi Sugawara, Hideyuki Sato
2007 Volume 76 Issue 4 Pages
043705
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We have performed
31P nuclear magnetic resonance (NMR) experiments on the filled skutterudite compound PrFe
4P
12 to investigate the exotic ordered phase at low temperatures and low magnetic fields. Analysis of the NMR line splitting in the ordered phase indicates that totally symmetric (Γ
1-type) staggered magnetic multipoles are induced by magnetic fields. This is incompatible with any type of quadrupole order at zero field. We conclude that the ordered phase has broken translational symmetry with the wave vector
Q=(1,0,0) but the
Th point symmetry at the Pr sites is not broken by the non-magnetic Γ
1-type order parameter.
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Kazuyuki Matsuhira, Makoto Wakeshima, Ryo Nakanishi, Takaaki Yamada, A ...
2007 Volume 76 Issue 4 Pages
043706
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We report that
Ln2Ir
2O
7 for
Ln = Nd, Sm, and Eu have metal–insulator transitions (MITs) at 36, 117, and 120 K, respectively. Their electrical resistivities and thermoelectric powers are not discontinuous and exhibit no thermal hysteresis at their transition temperatures
TMI, indicating second-order phase transitions. In this letter, we focus on the MIT of Sm
2Ir
2O
7. The specific heat and the magnetic susceptibility show a clear anomaly at
TMI. These results indicate that this MIT involves a magnetic ordering produced by 5
d electrons in Ir.
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Susumu Saito, Steven G. Louie, Marvin L. Cohen
2007 Volume 76 Issue 4 Pages
043707
Published: April 15, 2007
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We study the energetics and the electronic structure of MgB
2 nanotubes in the framework of the density-functional theory. It is found that in the case of (4,4) nanotube the presence of the outer Mg layer stabilizes the hexagonal-network boron nanotube which is otherwise unstable. Although the number of valence electrons are equivalent, MgB
2 nanotubes are electronically different from carbon nanotubes. Its electronic band structure is found to be modified by Mg due to hybridization and to have σ as well as π states at the Fermi level as in the case of bulk superconducting MgB
2. Interestingly, (4,4) MgB
2 nanotube is found to be energetically lower than an isolated MgB
2 sheet.
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Yoshikazu Tanaka, Yasuo Narumi, Noriki Terada, Koichi Katsumata, Hiroa ...
2007 Volume 76 Issue 4 Pages
043708
Published: April 15, 2007
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The way geometric frustration in the pyrochlore antiferromagnet HgCr
2O
4 is relieved by an applied magnetic field is studied by synchrotron X-ray diffraction. The material shows a structural change, from cubic to orthorhombic, at the magnetic transition temperature,
TN\\simeq6 K, to relieve the geometrical frustration. Below
TN, successive magnetic phase transitions occur in an applied field, from the antiferromagnetic to the half-magnetization plateau phase followed by a transition with a kink in the magnetization. We find that the lattice constant shows discontinuous expansions that coincide with magnetization changes, indicating progressive relief of geometric frustration. We calculate the lattice deformation invoking a magneto-elastic coupling and obtain good agreement between the calculation and our observation.
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Taro Nakajima, Setsuo Mitsuda, Shunsuke Kanetsuki, Karel Prokes, Andre ...
2007 Volume 76 Issue 4 Pages
043709
Published: April 15, 2007
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We report a neutron diffraction study of the magnetic field- and impurity-induced ferroelectric states of the triangular lattice antiferromagnet CuFe
1−xAl
xO
2. The magnetic structure of the ferroelectric phase was elucidated to be not a cycloidal structure, which can successfully lead to the electric polarization through the formula
P∝
eij×(
Si×
Sj) [H. Katsura
et al.: Phys. Rev. Lett.
95 (2005) 057205], but a proper helical structure. Nevertheless, the fact that the helical magnetic ordering appears only in the ferroelectric phase among various magnetically ordered phases of CuFe
1−xAl
xO
2 strongly suggests that a spin noncollinearlity is relevant to the multiferroic nature in CuFe
1−xAl
xO
2.
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Shunji Sugai, Yasumasa Takayanagi, Jiro Nohara, Ryozo Shiozaki, Koshi ...
2007 Volume 76 Issue 4 Pages
043710
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The electric transport changes from the power-law temperature dependent resistivity ρ=
a+
bTc to the logarithmic temperature dependent conductivity σ=
d+
eln
T as temperature decreases across 90 K in the underdoped phase. The crossover temperature is independent of the carrier density differently from the pseudo-spin-gap. The crossover is not caused by the simple relaxation time, but by the change of the density of states near the Fermi energy in the quasiparticle (resonant) peak at (π⁄2,π⁄2). The exponent
c decreases from 2 at
x=0.03 to 1 at
x=0.16 and then increases to 1.4 at
x=0.25.
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Hidetoshi Fukuyama
2007 Volume 76 Issue 4 Pages
043711
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Inter-band effects of magnetic field on orbital magnetic susceptibility and Hall effect in weak magnetic field have been studied theoretically at absolute zero for the model of massless Fermions in two dimension described by Weyl equation similar to graphenes, which are simplified version of newly-found one in molecular solids, α-ET
2I
3, described by the “tilted Weyl” equation. The dependences on the Fermi energy of both orbital susceptibility and Hall conductivity near the zero-gap region scale with the elastic scattering time and then are very singular.
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Youichi Yanase, Manfred Sigrist
2007 Volume 76 Issue 4 Pages
043712
Published: April 15, 2007
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The influence of antiferromagnetic order on the superconductivity in the non-centrosymmetric heavy fermion compound CePt
3Si and related materials is discussed. Based on our RPA analysis for the extended Hubbard model two phases could be stabilized by a spin fluctuation induced pairing, with either dominantly
p-wave or
d-wave symmetry. The antiferromagnetic order plays an essential role for the low-energy physics, in particular, for the appearance of line nodes in the gap and the enhancement of spin susceptibility below
Tc. Various properties and possible phase diagrams under pressure are analyzed. The present experimental situation suggests that the
p-wave phase is most likely realized in CePt
3Si.
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Haruhiko Kuroe, Akira Oosawa, Tomoyuki Sekine, Yoichi Nishiwaki, Tetsu ...
2007 Volume 76 Issue 4 Pages
043713
Published: April 15, 2007
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We report magnetic Raman scattering in a distorted-triangular-lattice Ising-like antiferromagnet TlCoCl
3. Below the Néel temperature, we observe several new Raman peaks from the quantized domain-wall pair excitations (Zeeman-ladder excitations). From their sequencies, we obtain the magnetic parameters of this system. We find that the orthorhombic lattice distortion causes a reduction of exchange interactions between the magnetic chains shifting to the opposite sides. The origin is discussed within a framework of superexchange interaction.
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Satoru Masaki, Takeshi Mito, Masayuki Takemura, Shinji Wada, Hisatomo ...
2007 Volume 76 Issue 4 Pages
043714
Published: April 15, 2007
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We report the results of NQR (nuclear quadrupole resonance) study on SmRu
4P
12, one of a few candidates for materials showing octupolar ordering. In this study, we firstly succeeded in observing the
101Ru-NQR signal in filled skutterudite compounds
RRu
4P
12 (
R: rare earth). A single
101Ru-NQR signal splits into two resonance lines, having intensity ratio of 3:1, just below the metal–insulator (
M–
I) transition temperature of 16.5 K. This result gives convincing evidence for symmetry lowering in the ordered state of this compound, namely the cubic
Im\\bar3 space group for the filled skutterudite compounds is lowered to the trigonal
R\\bar3. The model of the ordered structure characterized by a wave vector
q=(1,0,0) satisfactorily explains the observed phenomena in the present study and the
M–
I transition in this compound.
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Kenji Mizoguchi, Shunsuke Tanaka, Masaya Ojima, Sayaka Sano, Mai Nagat ...
2007 Volume 76 Issue 4 Pages
043801
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The electronic states of M-DNA doped with M = Mg, Ca, Zn, Mn, Fe are investigated mainly with magnetic properties. In the “wet” condition the Mn ions of Mn-DNA form a 1-D chain in the center of a DNA double helix, as evidenced from the formation of the unnatural base pair combination with M, poly(dA)–M–poly(dC), but in the “dry” condition they form a 3-D network with the antiferromagnetic ground state around 0.4 K with the superexchange coupling via water molecules. The valence of 3+ is found only in Fe-DNA, from which the base π-band obtains π charge carriers.
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Shin-ichi Tadaki
2007 Volume 76 Issue 4 Pages
044001
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Power-law fluctuation in observed Internet packet flow are discussed. The data is obtained by a multi router traffic grapher (MRTG) system for 9 months. The internet packet flow is analyzed using the detrended fluctuation analysis. By extracting the average daily trend, the data shows clear power-law fluctuations. The exponents of the fluctuation for the incoming and outgoing flow are almost unity. Internet traffic can be understood as a daily periodic flow with power-law fluctuations.
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Naoki Kobayashi, Kaoru Kohyama, Yo Sasaki, Mitsugu Matsushita
2007 Volume 76 Issue 4 Pages
044002
Published: April 15, 2007
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Scaling property of the shape of fragments which were produced by masticating raw carrots has been studied experimentally and theoretically. Mastication experiments showed that most fragments have more or less isotropic shapes which are independent of the number of chewing strokes, whereas larger fragments than a crossover size have complicated shapes. Since the crossover size had the structure which was dependent on the number of chewing strokes, we have tried to propose dynamic scaling hypothesis analogous to the case of growing self-affine interface. It was found that the dynamic scaling yields fairly accurate values of the scaling exponents. Our results will provide a new observation and insight of not only sequential fragmentation but also construction for physiological measurement.
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Masahiro Urakami, Seiji Miyoshi, Masato Okada
2007 Volume 76 Issue 4 Pages
044003
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In the framework of on-line learning, a learning machine might move around a teacher due to the differences in structures or output functions between the teacher and the learning machine. In this paper we analyze the generalization performance of a new student supervised by a moving machine. A model composed of a fixed true teacher, a moving teacher, and a student is treated theoretically using statistical mechanics, where the true teacher is a nonmonotonic perceptron and the others are simple perceptrons. Calculating the generalization errors numerically, we show that the generalization errors of a student can temporarily become smaller than that of a moving teacher and can reach the lowest value, even if the student only uses examples from the moving teacher. However, the generalization error of the student eventually becomes the same value with that of the moving teacher. This behavior is qualitatively different from that of a linear model.
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Miguel-Angel Sanchis-Lozano
2007 Volume 76 Issue 4 Pages
044101
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A proposal is presented for detecting new physics at a B factory running at the Υ(3
S) resonance by testing lepton universality to the few percent level in the leptonic decays of the Υ(1
S) and Υ(2
S) resonances tagged by the dipion in the chain decay: Υ(3
S)→π
+π
−Υ(1
S,2
S); Υ(1
S,2
S)→
l+l−,
l=
e,μ,τ.
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Kei Iida, Akihisa Kohama, Kazuhiro Oyamatsu
2007 Volume 76 Issue 4 Pages
044201
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We construct a formula for proton–nucleus total reaction cross section as a function of the mass and neutron excess of the target nucleus and the proton incident energy. We deduce the dependence of the cross section on the mass number and the proton incident energy from a simple argument involving the proton optical depth within the framework of a black sphere approximation of nuclei, while we describe the neutron excess dependence by introducing the density derivative of the symmetry energy,
L, on the basis of a radius formula constructed from macroscopic nuclear models. We find that the cross section formula can reproduce the energy dependence of the cross section measured for stable nuclei without introducing any adjustable energy dependent parameter. We finally discuss whether or not the reaction cross section is affected by an extremely low density tail of the neutron distribution for halo nuclei.
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Shigetomo Kita, Shunsuke Gotoh, Tomoaki Tanaka, Noriyuki Shimakura, Ma ...
2007 Volume 76 Issue 4 Pages
044301
Published: April 15, 2007
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By means of differential scattering spectroscopy, excitation processes in K
+–Ne collisions have been studied at laboratory collision energies of 350≤
Elab≤2000 eV. Doubly differential cross sections σ(Θ)
k have been measured over a wide range of center-of-mass angles, 3≤Θ≤176°, by detecting all the scattered particles (K
+, K, Ne
+, Ne), where subscript
k means exit channels in the reactions. Excitations were observed appreciably at reduced angles of τ>4 keV deg and collision energies of
Elab≥1000 eV. At 1000≤
Elab<1500 eV, only one-electron excitations have been found, while at
Elab≥1500 eV, two-electron excitation has been observed in addition to one-electron excitations. The electronic transitions are classified into two types depending on the excitation mechanism. One is the one-electron transitions taking place at internuclear distances of
R<
RC1=1.08 Å, and the other is one- and two-electron transitions occuring at
R<
RC2=0.45 Å. Both the distances
RC1 and
RC2 are nearly equal to those for the isoelectronic system of Na
+–Ar studied previously.
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Naohiro Kasuya, Masatoshi Yagi, Masafumi Azumi, Kimitaka Itoh, Sanae-I ...
2007 Volume 76 Issue 4 Pages
044501
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The three-field reduced MHD model was extended to describe the resistive drift wave turbulence in cylindrical magnetized plasmas. Using this model, linear eigenmode analyses are performed to identify the unstable modes, and the parameter scan predicts the necessary condition for excitation of the resistive drift wave turbulence. It is found that ion–neutral collisions strongly stabilize the resistive drift wave, and give a threshold condition for the turbulence excitation. Nonlinear simulations clarify the stabilizing effects of the quasi-linear flattening of the density profile and of the generated mean potential profile. It is pointed out that the parallel nonlinearity is important in the formation of a potential structure, which plays an essential role in mode saturation.
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Toshikazu Matsumoto, Hideo Nagatomo, Kunioki Mima
2007 Volume 76 Issue 4 Pages
044502
Published: April 15, 2007
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This study simulates the scenario when a relativistic electron beam enters high-density plasmas under the fast ignition condition. A relativistic fluid simulation code was developed for simulating relativistic electron transport in high dense plasmas. It is found that a shock wave is formed in a two temperature electron plasma. Namely an electron acoustic mode exists in the two component electron plasma. When relativistic electrons enter high-density plasmas at the relativistic electron expansion front, a shock wave front is formed in our simulation results. This shock wave in the simulation satisfies the relativistic Rankine–Hugoniot condition and Mach number condition.
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Saeed Yeganegi, Mojdeh Anbarfam
2007 Volume 76 Issue 4 Pages
044601
Published: April 15, 2007
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The performance of the equilibrium and direct nonequilibrium simulation methods for the calculation of thermal diffusion are examined. Both methods show size dependency for particle number less than 500. The equilibrium simulation should perform for at least 48 ns to obtain statistical errors less than 5%. For a same particle number and simulation length the direct nonequilibrium simulation is one order of magnitude more accurate than the equilibrium one.
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Shizuka Hosoi, Hongki Kim, Tomohiro Nagata, Kazuhiro Kirihara, Kohei S ...
2007 Volume 76 Issue 4 Pages
044602
Published: April 15, 2007
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Boron carbide (B
12C
3) and boron phosphide (B
12P
2) have the similar structures to α-rhombohedral boron (α-B
12) and are considered to be derivative crystals of it. The peculiar bonds in these two derivative crystals are visualized by MEM/Rietveld analysis, which involves a combination of the maximum entropy method (MEM) and Rietveld refinement for powder X-ray diffraction (XRD) data. The distinctive bending of bonds observed in α-B
12 is reversed by an insertion of other atoms. This bending arises from the conflict between the crystal structure of the rhombohedral lattice and the icosahedral structure of the B
12 cluster. Bond strength and interatomic distances are also varied by the insertion. In order to estimate the bond strength, we obtained the electron density height at each bond critical point, and compared it with the force constant, which is derived from the Raman shift.
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Fumiaki Kanô
2007 Volume 76 Issue 4 Pages
044603
Published: April 15, 2007
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A Monte Carlo simulation of the folding and unfolding of a two-dimensional model polypeptide, which has α-helical motifs, in nonpolar side chains were carried out. The terms that approximate the effect of the hydrophobic interaction in a solvent are phenomenologically included. Only three states were considered for each unit: extended with hydrogen bonds, turns and coils. We investigated the nature of hydration in the assembly process of α-helical stretches. The conversion exhibited transitions between three states: random coils (C) at a high temperature, helix bundles (B) at a medium temperature, and α-helices (H) without lateral hydrophobic bonds at a low temperature. Small hydrophobic interactions result in only the H–C transition lacking the B state. On the other hand, as the hydrophobic effect strengthens, the B state appears at a medium temperature. The B–C and B–H transitions appear as an all-or-none-type transition and a gradually diffused type transition, respectively. This problem is related to protein folding. In the simulation performed in this study, we discuss the cold denaturation of proteins from the viewpoint of B–H transitions.
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Ryuichi Arafune, Kei Hayashi, Shigenori Ueda, Yoichi Uehara, Sukekatsu ...
2007 Volume 76 Issue 4 Pages
044604
Published: April 15, 2007
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We have measured the spectra of very low-energy photoelectrons emitted from the Cu single crystal surface excited by tunable laser light. The difference between the photon energy and the work function of the sample surface (i.e., the highest kinetic energy of the photoelectron) was less than 300 meV. A spike structure appeared just above the vacuum level in the photoelectron spectra of the Cu(001) surface. In contrast the spectra from the Cu(110) and Cu(111) surfaces contained no such structure. We have concluded that the spike structure in the Cu(001) spectra arises from the electron energy loss in vacuum by interaction with its image charge. Finally we propose the mechanism through which the spike structure is produced. The spike structure appears when there is no electronic state at the vacuum level (at the \\barΓ point) to which zero kinetic energy photoelectrons can return.
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Hiroyasu Katsuno, Makio Uwaha, Yukio Saito
2007 Volume 76 Issue 4 Pages
044605
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We study misfit dislocations in a two-dimensional elastic lattice model of epitaxy using Green’s function. The interaction between the dislocations of the lattice model is compared with that of continuum elasticity theory. It is found that the behavior of the lattice model at a long distance agrees with that of standard continuum theory, but an additional interaction between dislocations due to extra forces around the dislocation core is important. The extra forces also lead to an increase in the dislocation interval. On a flat adsorbate surface with a periodic array of misfit dislocations, the preferential adsorption site is found to be either on the top or at the midpoint of the dislocations depending on the sign of the force dipole moment of the adatom and the sign of the misfit parameter.
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Eisuke Magome, Masaru Komukae, Mitsuo Machida
2007 Volume 76 Issue 4 Pages
044606
Published: April 15, 2007
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Crystal structures of monoclinic RbD
2PO
4 were studied at 297 K in the ferrielectric phase (phase III) and at 350 K in the paraelectric phase (phase II) by means of the single crystal neutron diffraction. The oxygen and deuterium atoms associated with the hydrogen bonds along the
b axis are ordered in phase III and are disordered in phase II. Other atoms are ordered in both phases II and III. There are four kinds of PO
4 tetrahedra in phase III. The ferrielectricity of phase III were confirmed in the present neutron structural analysis. The III–II phase transition is caused by an order–disorder of PO
4 tetrahedra accompanied by the motion of deuterium atoms within the hydrogen-bond chain. Fluctuations of the oxygen and deuterium atoms related hydrogen-bond chains along the
b axis give rise to a quasi-one-dimensionality.
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Seiji Kajita, Takashi Nakayama, Maki Kawai
2007 Volume 76 Issue 4 Pages
044701
Published: April 15, 2007
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A new repeated-slab calculation method is developed to simulate the electronic structures of charged surfaces by arranging density-variable charge sheets in vacuum regions to realize a constant potential on the charge sheets and maintain the charge neutrality condition. The charge sheets are fabricated so as to screen an electric field from charged slabs; consequently, they act like a counter electrode composed of flat perfect conductor, modeling a tip of a scanning tunneling microscope or a reference electrode in an electrochemical cell. This method has the virtues of ease of implementation into existing repeated-slab programs and low computational costs. The availability of the method is demonstrated by applying it to a charged H
2 molecule, and charged Al(111) and Si(111) surfaces.
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Eerdunchaolu, J. L. Xiao
2007 Volume 76 Issue 4 Pages
044702
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In this paper, the effects of lattice vibration on the properties of the polaron, which is weakly coupled with bulk longitudinal optical (LO) phonons and strongly coupled with interface optical (IO) phonons, in an infinite quantum well are studied by means of Huybrechts’ linear-combination operator and the modified Lee–Low–Pines (LLP) variational method. The expressions for the self-trapping energy of the polaron in a quantum well as a function of the well width and temperature were derived. In particular, the law governing the change of the vibration frequency of the polaron with changing well width and temperature is obtained for the first time. Numerical results of the polaron self-trapping energy and the vibration frequency for KI/AgCl/KI QW show that the vibration frequency and the self-trapping energy of the polaron decrease with increasing well width and temperature, but the contributions of the interaction between the electron and the different branches of phonons to the self-trapping energy, the vibration frequency and the change of their variation with well width and temperature differ markedly.
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Masayuki Naito, Dai S. Hirashima
2007 Volume 76 Issue 4 Pages
044703
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Spin wave excitations and the electron self-energy corrections in the ferromagnetic phase of iron are studied using the Naval Research Laboratory tight-binding model. It is found that the spin wave excitation spectrum obtained with this model is in good agreement with the experimental results. Transverse spin fluctuations contribute to the self-energy and reduce the band width uniformly, but does not cause a prominent kink structure in the quasiparticle dispersion near the fermi level. Comparison with recent angle-resolved photoemission experiments on Fe is made.
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Geunseop Lee, Hyejin Cho, Younghoon Kim, Hyungjoon Shim
2007 Volume 76 Issue 4 Pages
044704
Published: April 15, 2007
Released on J-STAGE: August 12, 2010
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By analyzing the Ge 3
d core-level photoelectron spectra, we studied the structures of the Na/Ge(111)-3×1 and Li/Ge(111)-3×1 surfaces. For both surfaces, two surface related components lying on either side of the main bulk peak were identified in the spectra. The similarity of the spectra from the two surfaces indicates that the surfaces do indeed share a common structure. The core-level photoelectron spectra of the Na- and Li-induced Ge(111)-3×1 surfaces are well consistent with the honeycomb-chain-channel model, which was proposed as the structure of the Si(111)-3×1 induced by alkali metals.
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Ryoko Sugano, Katsuyoshi Matsushita, Akiyoshi Kuroda, Yusuke Tomita, H ...
2007 Volume 76 Issue 4 Pages
044705
Published: April 15, 2007
Released on J-STAGE: August 12, 2010
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By means of the molecular dynamics simulation of gradual cooling processes, we investigate magnetic properties of classical spin systems only with the magnetic dipole–dipole interaction, which we call dipolar systems. Focusing on their finite-size effect, particularly their boundary geometry dependence, we study two finite dipolar squares cut out from a square lattice with Φ=0 and π⁄4, where Φ is the angle between the direction of the lattice axis and that of the square boundary. Distinctly different results are obtained in the two dipolar squares. In the Φ=0 square, the “from-edge-to-interior freezing” of spins is observed. Its ground state has a multidomain structure whose domains consist of two among infinitely (continuously) degenerated Luttinger–Tisza (LT) ground-state orders on a bulk square lattice, i.e., the two antiferromagnetically aligned ferromagnetic chains (af-FMC) orders directed parallel to the two lattice axes. In the Φ=π⁄4 square, on the other hand, the freezing starts from the interior of the square, and its ground state is nearly in a single domain with one of the two af-FMC orders. These geometry effects are argued to originate from the anisotropic nature of the dipole–dipole interaction, which depends on the relative direction of sites in the real space of the interacting spins.
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S. Akbar Jafari, Takami Tohyama, Sadamichi Maekawa
2007 Volume 76 Issue 4 Pages
044706
Published: April 15, 2007
Released on J-STAGE: August 12, 2010
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We study linear and nonlinear optical properties of
d-electron Kondo system. The effect of Kondo resonance in optical conductivity is to creat a remarkable peak inside the gap. In third harmonic generation spectra also there appear structures inside the gap which correspond to three and two-photon processes from lower Hubbard band to the Kondo resonance state. Behavior of two and four-current correlations near to ν≈0 in Kondo regime can be understood by an asymptotic analysis which reveals a marked difference between two and four-current correlations.
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Osamu Sakai, Yukihiro Shimizu
2007 Volume 76 Issue 4 Pages
044707
Published: April 15, 2007
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Band calculation for a series of Ce pnictides is carried out on the basis of dynamical mean field theory (DMFT). The auxiliary impurity problem is solved by a method named NCA
f2vc, which includes the correct exchange process of the
f1→
f0,
f2 virtual excitation. The splitting of the self-energy due to the spin–orbit interaction and the crystalline field effect is also considered. The systematics of the single-particle spectrum (SGS) such as the double-peak structure, show good correspondence with the experimental results of photoemission spectra (PES) at higher temperatures. At low temperatures, two types of solutions appear: one has an appreciable Kondo resonance peak at the Fermi energy and the other does not. The former leads to the metallic state and the latter to the localized state of the
f electron with the Fermi surface of the La pnictides type. When the occupation number of (
j=5⁄2)Γ
8 is large, the wave-number dependence of the 4
f SGS becomes appreciable, while it is very weak in the (
j=5⁄2)Γ
7-dominant occupation case. The angle-resolved PES, which is similar to that obtained from of experiments on CeP, is obtained in the Γ
8-dominant case. The valence-fluctuation-like state is expected in CeN.
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Yusuke Okuda, Yuichiro Miyauchi, Yuki Ida, Yuuji Takeda, Chie Tonohiro ...
2007 Volume 76 Issue 4 Pages
044708
Published: April 15, 2007
Released on J-STAGE: August 12, 2010
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Single crystals of LaIrSi
3 and CeIrSi
3 were grown by the Czochralski pulling method in a tetra-arc furnace and the magnetic and superconducting properties, together with superconductivity in CeIr
1−xCo
xSi
3, were clarified by measuring the electrical resistivity, specific heat, magnetic susceptibility, magnetization and de Haas–van Alphen (dHvA) effect. From the results of the dHvA experiment for LaIrSi
3, the Fermi surface is found to split into two Fermi surfaces due to the spin–orbit interaction arising from the non-centrosymmetric crystal structure, which are separated by about 1000 K. Similar split Fermi surfaces are expected in the antiferromagnet CeIrSi
3. The electronic state of CeIrSi
3 is tuned from the antiferromagnetic state to the superconducting state by applying pressure. The upper critical field
Hc2(0) at a pressure of 2.65 GPa is found to be highly anisotropic:
Hc2(0)=95 kOe for
H||[110] and
Hc2(0)\\simeq300 kOe for
H||[001], with the superconducting transition temperature
Tsc\\simeq1.6 K. The large magnitude and anisotropy of
Hc2(0) in CeIrSi
3 are consistent with the theoretical prediction for superconductivity in the non-centrosymmetric crystal structure. Superconductivity is also observed at ambient pressure in CeIr
1−xCo
xSi
3.
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Tatsuya Fujii
2007 Volume 76 Issue 4 Pages
044709
Published: April 15, 2007
Released on J-STAGE: August 12, 2010
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We show that the density matrix for a finite conductor attached to reservoirs obtained by Keldysh formalism is of MacLennan–Zubarev form. On the basis of the fact that the density matrix is the invariant part proposed by Zubarev, it is shown that Keldysh formalism may describe the irreversible processes and steady-state feature of the system. An important consequence of the MacLennan–Zubarev form of the density matrix is a generalization of the Kubo formula in a nonequilibrium case. On the basis of the result, we propose a nonequilibrium identity between differential conductance, noise power and shot noise as a generalized Nyquist–Johnson relation.
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Hirotaka Manaka, Yusuke Miyashita, Yusuke Watanabe, Takatsugu Masuda
2007 Volume 76 Issue 4 Pages
044710
Published: April 15, 2007
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We synthesized a single-phase polycrystalline sample of a double-layer perovskite fluoride K
3Cu
2F
7. This compound is the new member of the potassium copper fluoride family, which has an antiferrodistortive orbital order (AFDOO). Magnetic susceptibility measurements revealed that K
3Cu
2F
7 is a rare experimental realization of antiferromagnetically isolated spin dimers on a simple double-square lattice with no frustration, and that AFDOO causes ferromagnetic interactions in respective layers. The coexistence of spin gap and AFDOO is an exotic phenomenon both in quantum spin systems and strongly correlated electron systems.
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Makoto Maki, Shun-ichi Nakao, Koh-ichi Machida, Masashi Shiraishi, Xu- ...
2007 Volume 76 Issue 4 Pages
044711
Published: April 15, 2007
Released on J-STAGE: August 12, 2010
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The complex permittivity of lightly doped Bi
2Sr
2YCu
2O
8+δ was measured in order to investigate the carrier dynamics near the insulator-to-metal transition. By suppressing the extrinsic polarization due to some contact effects, we found a rapid rise in the
c-axis dielectric constant ε
c′ with increasing temperature at
TM∼225 K. Below
TM, the thermally activated carrier movement seemed to be limited within the
ab plane. We showed that the ε
c′ behavior is related to a two-step carrier-conduction development observed in the polycrystalline sample. We also found another ε
c′ anomaly in its temperature dependence.
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Sadakazu Yoshikawa, Masaki Aihara
2007 Volume 76 Issue 4 Pages
044712
Published: April 15, 2007
Released on J-STAGE: August 12, 2010
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The disorder-induced transient optical four-wave mixing for a Frenkel exciton in a binary mixed crystal is theoretically investigated. We have clarified the role of static disorder in a wide range of disorder strength by using the coherent potential approximation. It is found that the weak disorder gives rise to exciton dephasing, and the strong disorder induces a photon echo signal. The crossover from homogeneous to inhomogeneous broadening with increasing disorder strength is systematically analyzed. In the case of off-resonant excitation, we find an oscillatory echolike signal inherent in the disorder-induced optical nonlinearity.
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Hyun-Joo Kim, Yeon-Mu Choi
2007 Volume 76 Issue 4 Pages
044801
Published: April 15, 2007
Released on J-STAGE: August 12, 2010
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We study the mechanism that forms the cyclic topology in various scale-free networks. An evolving network model is introduced in which the ratio of the number of edges attaching a new vertex to old vertices and that linking between old vertices is controlled and the edges are attached in three different ways with probability parameters. By controlling the ratio and the probability parameters, we realize model networks showing almost the same cyclic topology as that of various real networks. This indicates that the cyclic property of each network is determined by the ratio of the tree-like structure, triangular structure, and quadrangular structure.
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Yukio Saito, Takeshi Sugimori, Hiroyuki Hyuga
2007 Volume 76 Issue 4 Pages
044802
Published: April 15, 2007
Released on J-STAGE: August 12, 2010
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Stochastic aspects of chemical reaction models related to the Soai reactions as well as to the homochirality in life are studied analytically and numerically by the use of the master equation and a directed random walk model. For systems with a recycling back reaction, a unique final probability distribution is obtained by means of detailed balance conditions. With a nonlinear autocatalysis the distribution has a double-peak structure, indicating the chiral symmetry breaking. This problem is further analyzed by examining eigenvalues and eigenfunctions of the master equation. In the case without recycling, final probability distributions depend on the initial conditions. In the nonlinear autocatalytic case, time-evolution starting from a complete achiral state leads to a final distribution which differs from that deduced from the nonzero recycling result. This is due to the absence of the detailed balance, and a directed random walk model is shown to give the correct final profile. When the nonlinear autocatalysis is sufficiently strong and the initial state is achiral, the final probability distribution has a double-peak structure, related to the enantiomeric excess amplification. It is argued that with autocatalyses and a very small but nonzero spontaneous production, a single mother scenario could be a main mechanism to produce the homochirality.
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Masafumi Oizumi, Yoichi Miyawaki, Masato Okada
2007 Volume 76 Issue 4 Pages
044803
Published: April 15, 2007
Released on J-STAGE: August 12, 2010
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We propose a systematic method of rate reduction for a Hodgkin–Huxley type neural network model. In this context, Shriki
et al. assumed that the threshold of the
f–
I curve for the reduced rate model depends linearly on the leak conductance of the Hodgkin–Huxley equation, while its gain remains constant. First, we show that the threshold and gain have second order dependence on the leak conductance. Second, we show that the Hodgkin–Huxley type network with second order interaction can be naturally reduced to an analog type neural network model with higher order interaction based on this finding. Finally, we construct statistical mechanics for the Hodgkin–Huxley type network with the Mexican-hat interaction through our rate reduction technique.
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Kentaro Katahira, Masaki Kawamura, Kazuo Okanoya, Masato Okada
2007 Volume 76 Issue 4 Pages
044804
Published: April 15, 2007
Released on J-STAGE: August 12, 2010
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We investigate a recurrent neural network model with common external and bias inputs that can retrieve branching sequences. Retrieval of memory sequences is one of the most important functions of the brain. A lot of research has been done on neural networks that process memory sequences. Most of it has focused on fixed memory sequences. However, many animals can remember and recall branching sequences. Therefore, we propose an associative memory model that can retrieve branching sequences. Our model has bias input and common external input. Kawamura and Okada reported that common external input enables sequential memory retrieval in an associative memory model with auto- and weak cross-correlation connections. We show that retrieval processes along branching sequences are controllable with both the bias input and the common external input. To analyze the behaviors of our model, we derived the macroscopic dynamical description as a probability density function. The results obtained by our theory agree with those obtained by computer simulations.
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Hirotake Suzuki, Hiromi Ozawa, Hirohiko Sato
2007 Volume 76 Issue 4 Pages
044805
Published: April 15, 2007
Released on J-STAGE: August 12, 2010
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Single crystals of KSbO
3-type rhenium oxides, La
4Re
6O
19, Pb
6Re
6O
19, Sr
2Re
3O
9, and Bi
3Re
3O
11, were synthesized by a hydrothermal method. Their crystal structures can be regarded as a network of three-dimensional orthogonal-dimer lattice of edge-shared ReO
6 octahedra. All of them exhibit small magnitude of Pauli paramagnetism, indicating metallic electronic states without strong electron correlations. The resistivity of these rhenates, except Bi
3Re
3O
11, have a temperature dependence of ρ(
T)=ρ
0+
ATn (
n≈1.6) in a wide temperature range between 5 and 300 K, which is extraordinary for three-dimensional metals without strong electron correlations. The resistivity of Bi
3Re
3O
11 shows an anomaly around at 50 K, where the magnetic susceptibility also detects a deviation from ordinary Pauli paramagnetism.
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Takashi Shinozaki, Hideyuki Câteau, Hidetoshi Urakubo, Masato Ok ...
2007 Volume 76 Issue 4 Pages
044806
Published: April 15, 2007
Released on J-STAGE: August 12, 2010
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The propagation of highly synchronous firings across neuronal networks, called the synfire chain, has been actively studied both theoretically and experimentally. The temporal accuracy and remarkable stability of the propagation have been repeatedly examined in previous studies. However, for such a mode of signal transduction to play a major role in processing information in the brain, the propagation should also be controlled dynamically and flexibly. Here, we show that inhibitory but not excitatory input can bidirectionally modulate the propagation, i.e., enhance or suppress the synchronous firings depending on the timing of the input. Our simulations based on the Hodgkin–Huxley neuron model demonstrate this bidirectional modulation and suggest that it should be achieved with any biologically inspired modeling. Our finding may help describe a concrete scenario of how multiple synfire chains lying in a neuronal network are appropriately controlled to perform significant information processing.
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