Showing papers by "Tokyo University of Science published in 2007"
Massachusetts Institute of Technology1, Goddard Space Flight Center2, Kyoto University3, Nagoya University4, University of Tokyo5, Osaka University6, Ehime University7, University of Cambridge8, Hiroshima University9, Carnegie Mellon University10, Max Planck Society11, University of Miyazaki12, Franklin W. Olin College of Engineering13, Rutgers University14, Tokyo Metropolitan University15, Kobe University16, Stanford University17, Tokyo Institute of Technology18, Rikkyo University19, Kogakuin University20, Tokyo University of Science21, University of Wisconsin-Madison22, Kanazawa University23, Nihon University24, Pennsylvania State University25, European Space Research and Technology Centre26, Yale University27, Saitama University28, Chuo University29, University of Leicester30, Nihon Fukushi University31, Aoyama Gakuin University32, Iwate University33
TL;DR: In this paper, the authors summarized the spacecraft, in-orbit performance, operations, and data processing that are related to observations of the Suzaku X-ray observatory, including high-sensitivity wide-band Xray spectroscopy.
Abstract: High-sensitivity wide-band X-ray spectroscopy is the key feature of the Suzaku X-ray observatory, launched on 2005 July 10. This paper summarizes the spacecraft, in-orbit performance, operations, and data processing that are related to observations. The scientific instruments, the high-throughput X-ray telescopes, X-ray CCD cameras, non-imaging hard X-ray detector are also described.
908 citations
TL;DR: To bioengineer ectodermal organs such as teeth and whisker follicles, a three-dimensional organ-germ culture method is developed, which generated a structurally correct tooth, after both in vitro organ culture and transplantation under a tooth cavity in vivo.
Abstract: To bioengineer ectodermal organs such as teeth and whisker follicles, we developed a three-dimensional organ-germ culture method. The bioengineered tooth germ generated a structurally correct tooth, after both in vitro organ culture as well as transplantation under a tooth cavity in vivo, showing penetration of blood vessels and nerve fibers. Our method provides a substantial advance in the development of bioengineered organ replacement strategies and regenerative therapies.
462 citations
TL;DR: The energy gap of ZAIS nanoparticles could be controlled by the composition of solid solution, and the highest quantum yield was obtained for nanoparticles prepared with x = 0.86, which was much higher than the quantum yields reported for I-III-VI2-based semiconductor nanoparticles, such as CuInS2 and ZnS-Cu inS2 solid solution.
Abstract: Nanoparticles of ZnS−AgInS2 solid solution (ZAIS) were synthesized by the thermal decomposition of (AgIn)xZn2(1-x)(S2CN(C2H5)2)4 precursors in a hot oleylamine solution. X-ray powder diffraction analyses revealed that the resulting nanoparticle powders were not a mixture of ZnS and AgInS2 but a ZnS−AgInS2 solid solution in which the fraction of ZnS was enlarged with a decrease in the value of x, that is, an increase in the content of Zn2+ in the precursors used. The energy gap of ZAIS nanoparticles could be controlled by the composition of solid solution. Intense emission was observed at room temperature, regardless of the kind of the particles, the peak wavelength of PL being blue-shifted from 720 to 540 nm with a decrease in the value of x. The highest quantum yield of ca. 24% was obtained for nanoparticles prepared with x = 0.86, which was much higher than the quantum yields reported for I−III−VI2-based semiconductor nanoparticles, such as CuInS2 and ZnS−CuInS2 solid solution.
319 citations
TL;DR: CP-Pt may be a SOD/catalase mimetic which is useful for medical treatment of oxidative stress diseases and quenched hydrogen peroxide and superoxide anion radical in dose-dependent manners.
Abstract: Bimetallic nanoparticles consisting of gold and platinum were prepared by a citrate reduction method and complementarily stabilized with pectin (CP-Au/Pt). The percent mole ratio of platinum was varied from 0 to 100%. The CP-Au/Pt were alloy-structured. They were well dispersed in water. The average diameter of platinum nanoparticles (CP-Pt) was 4.7 ± 1.5 nm. Hydrogen peroxide (H2O2) was quenched by CP-Au/Pt consisting of more than 50% platinum whereas superoxide anion radical () was quenched by any CP-Au/Pt. The CP-Au/Pt quenched these two reactive oxygen species in dose-dependent manners. The CP-Pt is the strongest quencher. The CP-Pt decomposed H2O2 and consequently generated O2 like catalase. The CP-Pt actually quenched which was verified by a superoxide dismutase (SOD) assay kit. This quenching activity against persisted like SOD. Taken together, CP-Pt may be a SOD/catalase mimetic which is useful for medical treatment of oxidative stress diseases.
261 citations
259 citations
Max Planck Society1, University of Birmingham2, University of Hertfordshire3, University of Trieste4, Durham University5, Liverpool John Moores University6, Michigan State University7, Harvard University8, INAF9, University of Illinois at Urbana–Champaign10, Tokyo University of Science11, University of Michigan12, Tokyo Metropolitan University13, University of Copenhagen14, Pontifical Catholic University of Chile15, University of Bonn16, University of Sussex17, European Southern Observatory18, Carnegie Mellon University19, University of Porto20
TL;DR: The largest uncertainty for cosmological studies using clusters of galaxies is introduced by our limited knowledge of the statistics of galaxy cluster structure, and of the scaling relations between observables and cluster mass as mentioned in this paper.
Abstract: Context.The largest uncertainty for cosmological studies using clusters of galaxies is introduced by our limited knowledge of the statistics of galaxy cluster structure, and of the scaling relations between observables and cluster mass.
253 citations
TL;DR: It is shown that even semiconductor nanoparicles of SiC, Ge, and Si produce single-Walled and double-walled CNTs in CVD with ethanol, implying that nanosize structures might act as a template for the formation of CNT caps composed of five- and six-membered rings.
Abstract: Nanoscale metal catalysts have been indispensable for carbon nanotube (CNT) synthesis by chemical vapor deposition (CVD). We show that even semiconductor nanoparicles of SiC, Ge, and Si produce single-walled and double-walled CNTs in CVD with ethanol. This implies that nanosize structures might act as a template for the formation of CNT caps composed of five- and six-membered rings. Providing a template for cap formation is the essential role of the catalysts.
248 citations
TL;DR: In this paper, a catalytic enantioselective direct conjugate addition of nitroalkanes to α,β-unsaturated aldehydes using diphenylprolinol silyl ether as an organocatalyst has been developed.
217 citations
213 citations
TL;DR: In this article, the effective Hamiltonian describing the massless fermions in α-(BEDT-TTF) 2 I 3 contains intrinsically new terms of Pauli matrices σ z and σ 0 in addition to the Weyl equation which consists of σ x and y.
Abstract: The electronic states in two-dimensional organic conductor α-(BEDT-TTF) 2 I 3 have been investigated to show the noticeable property of the massless fermions, i.e., the linear dispersion which exists on the contact point between the conduction band and the valence band. These fermions are well known in bismuth and graphite, where the former are described by the Dirac equation and the latter obeys the Weyl equation corresponding to the massless fermion. In the present study, we show that the effective Hamiltonian describing the massless fermions in α-(BEDT-TTF) 2 I 3 contains intrinsically new terms of Pauli matrices σ z and σ 0 in addition to the Weyl equation which consists of σ x and σ y . The new massless fermions are robust against the charge disproportionation, and induce the anomalous momentum-dependence in the charge density.
210 citations
TL;DR: It is shown that HMGB1 in neutrophils is post-translationally mono-methylated at Lys42, which alters the conformation ofHMGB1 and weakens its DNA binding activity, causing it to become largely distributed in the cytoplasm by passive diffusion out of the nucleus.
TL;DR: In this paper, the effect of hadron structure changes in a nuclear medium using the quark-meson coupling (QMC) model is studied, which is based on a mean field description of non-overlapping nucleon (or baryon) bags bound by the self-consistent exchange of scalar and vector mesons in the isoscalar and isovector channels.
TL;DR: In this paper, the tribological properties of cast iron have been investigated to determine the effects of micro-texturing the surfaces, and the results indicated that the dimpled pattern had a beneficial effect by decreasing the friction.
Abstract: The tribological properties of cast iron have been investigated to determine the effects of micro-texturing the surfaces. The micro-textured surfaces were prepared by shot blasting or milling using a shaper. The surfaces with groove patterns and mesh patterns had higher friction coefficients than the flat surfaces. The surfaces with dimpled patterns had lower friction coefficients than the flat surfaces. The results indicated that the dimpled pattern had a beneficial effect by decreasing the friction.
TL;DR: In this article, the effects of doping of metal cations into wide band gap semiconductor photocatalysts on morphology, visible light response, and performance of photocatalysis were studied.
TL;DR: This device shows the highest light-to-electrical energy conversion efficiency based on plastic-substrate dye-sensitized solar cells, 7.4% under 100 mW cm(-2) (1 sun) AM1.5 illumination.
TL;DR: In this paper, surface modified Li[Li0.05Ni0.4Co0.15Mn0.5]O2 oxides were investigated using coin type Li-ion cells employing graphite as an anode.
Abstract: Surface-modified Li[Li0.05Ni0.4Co0.15Mn0.4]O2 oxides were studied. The oxide particles were coated by heteroelements such as Al2O3, Nb2O5, Ta2O5, ZrO2 and ZnO. Metal oxide-coated Li[Li0.05Ni0.4Co0.15Mn0.4]O2 did not show significant difference in X-ray diffraction patterns. Thickness of the formed coating layer was around 10 nm, as observed by transmission electron microscopy. Electrochemical properties of heteroelement-coated Li[Li0.05Ni0.4Co0.15Mn0.4]O2 were investigated using coin type Li-ion cells employing graphite as an anode at 60 °C. Metal oxide-coated Li[Li0.05Ni0.4Co0.15Mn0.4]O2 obviously showed higher capacity with good cyclability. Also, area-specific impedance was significantly lower for the metal oxide-coated Li[Li0.05Ni0.4Co0.15Mn0.4]O2 during cycling, compared with that for bare Li[Li0.05Ni0.4Co0.15Mn0.4]O2. Among them, Al2O3-coated Li[Li0.05Ni0.4Co0.15Mn0.4]O2 had the best electrochemical performances. The metal oxide coating layer transformed to metal fluoride layer during cycling, as pr...
TL;DR: Proline derivatives with a hydrophobic moiety, both of which are easily prepared from the same commercially available 4-hydroxy-L-proline, have been found to be the most effective organocatalysts examined in this study, affording the aldol product with excellent diastereo- and enantioselectivities.
Abstract: Proline-based organocatalysts have been developed for a highly enantioselective, direct aldol reaction of aldehydes and ketones in the presence of water. While several surfactant-proline combined catalysts have proved effective, proline derivatives with a hydrophobic moiety such as trans-siloxy-L-proline and cis-siloxy-D-proline, both of which are easily prepared from the same commercially available 4-hydroxy-L-proline, have been found to be the most effective organocatalysts examined in this study, affording the aldol product with excellent diastereo- and enantioselectivities, these two catalysts generating opposite enantiomers. Water affects the selectivity, and poor results are obtained under neat reaction conditions or in dry organic solvents. More than three equivalents of water are required for the best diastereo- and enantioselectivities, while three equivalents is the recommended amount from a synthetic point of view. The reaction proceeds in the organic phase, and also proceeds in the presence of a large amount of water. The large-scale preparation of aldols with the minimal use of an organic solvent, including in the purification step, is described.
TL;DR: In this paper, the neutrino signal from the gravitational collapse of a nonrotating massive star of 40 M is studied and the influence of realistic equations of state (EOSs) for dense matter is explored.
Abstract: We study black hole formation and the neutrino signal from the gravitational collapse of a nonrotating massive star of 40 M☉. Adopting two different sets of realistic equations of state (EOSs) for dense matter, we perform numerical simulations of general relativistic ν-radiation hydrodynamics under spherical symmetry. We make comparisons of core bounce, shock propagation, evolution of nascent proto-neutron stars, and the resulting recollapse to a black hole to reveal the influence of EOSs. We also explore the influence of EOSs on neutrino emission during the evolution toward black hole formation. We find that the speed of contraction of the nascent proto-neutron star, whose mass increases quickly due to the intense accretion, is different depending on the EOS and that the resulting profiles of density and temperature differ significantly. The black hole formation occurs at 0.6-1.3 s after bounce, when the proto-neutron star exceeds its maximum mass, which is crucially determined by the EOS. We find that the average energies of neutrinos increase after bounce because of rapid temperature increase, but at different speeds depending on the EOS. The duration of neutrino emission up to black hole formation is found to be different according to different recollapse timing. These characteristics of neutrino signatures are distinguishable from those for ordinary proto-neutron stars in successful core-collapse supernovae. We discuss the idea that a future detection of neutrinos from a black hole-forming collapse will contribute to revealing the black hole formation and to constraining the EOS at high density and temperature.
TL;DR: The phagocytosis of alveolar macrophages toward poly(lactic-co-glycolic) acid (PLGA) microspheres loaded with the anti-tuberculosis agent rifampicin (RFP) was dependent greatly on the particle size and the number of particles added.
TL;DR: In this paper, a Z-scheme photocatalysis system employing visible-light-driven photocatalysts, Ru/SrTiO 3 :Rh and BiVO 4 for H 2 and O 2 evolution, and an Fe 3+ /Fe 2+ redox couple as an electron relay was developed.
Abstract: Photocatalytic water splitting is a challenging reaction because it is an ultimate so- lution to energy and environmental issues. Recently, many new powdered photocatalysts for water splitting have been developed. For example, a NiO (0.2 wt %)/NaTaO 3 :La (2 %) photo- catalyst with a 4.1-eV band gap showed high activity for water splitting into H 2 and O 2 with an apparent quantum yield of 56 % at 270 nm. Overall water splitting under visible light ir- radiation has been achieved by construction of a Z-scheme photocatalysis system employing visible-light-driven photocatalysts, Ru/SrTiO 3 :Rh and BiVO 4 for H 2 and O 2 evolution, and an Fe 3+ /Fe 2+ redox couple as an electron relay. Moreover, highly efficient sulfide photocat- alysts for solar hydrogen production in the presence of electron donors were developed by making solid solutions of ZnS with AgInS 2 and CuInS 2 of narrow band gap semiconductors. Thus, the database of powdered photocatalysts for water splitting has become plentiful.
TL;DR: The mechanism to realize high carrier mobility in the organic transistor devices involves intrinsic-semiconductor character of the high-purity organic crystals and diffusive bandlike carrier transport in the bulk.
Abstract: Gate-voltage dependence of carrier mobility is measured in high-performance field-effect transistors of rubrene single crystals by simultaneous detection of the longitudinal conductivity ${\ensuremath{\sigma}}_{\ensuremath{\square}}$ and Hall coefficient ${R}_{H}$. The Hall mobility ${\ensuremath{\mu}}_{H}$ ($\ensuremath{\equiv}{\ensuremath{\sigma}}_{\ensuremath{\square}}{R}_{H}$) reaches nearly $10\text{ }\text{ }{\mathrm{cm}}^{2}/\mathrm{V}\text{ }\mathrm{s}$ when relatively low-density carriers ($l{10}^{11}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$) distribute into the crystal. ${\ensuremath{\mu}}_{H}$ rapidly decreases with higher-density carriers as they are essentially confined to the surface and are subjected to randomness of the amorphous gate insulators. The mechanism to realize high carrier mobility in the organic transistor devices involves intrinsic-semiconductor character of the high-purity organic crystals and diffusive bandlike carrier transport in the bulk.
TL;DR: In this article, the neutrino signal from the gravitational collapse of a non-rotating massive star of 40 Msun was studied and the influence of EOS on neutrinos emission during the evolution toward the black hole formation was explored.
Abstract: We study the black hole formation and the neutrino signal from the gravitational collapse of a non-rotating massive star of 40 Msun. Adopting two different sets of realistic equation of state (EOS) of dense matter, we perform the numerical simulations of general relativistic neutrino-radiation hydrodynamics under the spherical symmetry. We make comparisons of the core bounce, the shock propagation, the evolution of nascent proto-neutron star and the resulting re-collapse to black hole to reveal the influence of EOS. We also explore the influence of EOS on the neutrino emission during the evolution toward the black hole formation. We find that the speed of contraction of the nascent proto-neutron star, whose mass increases fast due to the intense accretion, is different depending on the EOS and the resulting profiles of density and temperature differ significantly. The black hole formation occurs at 0.6-1.3 sec after bounce when the proto-neutron star exceeds its maximum mass, which is crucially determined by the EOS. We find that the average energies of neutrinos increase after bounce because of rapid temperature increase, but at different speeds depending on the EOS. The duration of neutrino emission up to the black hole formation is found different according to the different timing of re-collapse. These characteristics of neutrino signatures are distinguishable from those for ordinary proto-neutron stars in successful core-collapse supernovae. We discuss that a future detection of neutrinos from black-hole-forming collapse will contribute to reveal the black hole formation and to constrain the EOS at high density and temperature.
TL;DR: Alcadeinα (Alcα) is an evolutionarily conserved type I membrane protein expressed in neurons that strongly associates with kinesin light chain through a novel tryptophan‐ and aspartic acid‐containing sequence and can induce kinesIn‐1 association with vesicles and functions as a novel cargo in axonal anterograde transport.
Abstract: Alcadeinα (Alcα) is an evolutionarily conserved type I membrane protein expressed in neurons. We show here that Alcα strongly associates with kinesin light chain (KD≈4–8 × 10−9 M) through a novel tryptophan- and aspartic acid-containing sequence. Alcα can induce kinesin-1 association with vesicles and functions as a novel cargo in axonal anterograde transport. JNK-interacting protein 1 (JIP1), an adaptor protein for kinesin-1, perturbs the transport of Alcα, and the kinesin-1 motor complex dissociates from Alcα-containing vesicles in a JIP1 concentration-dependent manner. Alcα-containing vesicles were transported with a velocity different from that of amyloid β-protein precursor (APP)-containing vesicles, which are transported by the same kinesin-1 motor. Alcα- and APP-containing vesicles comprised mostly separate populations in axons in vivo. Interactions of Alcα with kinesin-1 blocked transport of APP-containing vesicles and increased β-amyloid generation. Inappropriate interactions of Alc- and APP-containing vesicles with kinesin-1 may promote aberrant APP metabolism in Alzheimer's disease.
TL;DR: Lead-free piezoelectric ceramics with compositions around the morphotropic phase boundary (MPB) [x + y + z = 1; y:z = 2:1] were synthesized using conventional, solid-state processing and showed strong anisotropy.
Abstract: Lead-free piezoelectric ceramics with compositions around the morphotropic phase boundary (MPB) x(Na05Bi05)TiO 3-y(K05Bi05)TiO3-zBaTiO 3 [x + y + z = 1; y:z = 2:1] were synthesized using conventional, solid-state processing Dielectric maximum temperatures of 280degC and 262degC were found for tetragonal 079(Na05Bi05)TiO3-014(K05 Bi05)TiO3-007BaTiO$ d3 (BNBK79) and MPB composition 088(Na05Bi05)TiO3-008(K 05Bi05)TiO3-004BaTiO$ d3 (BNBK88), with depolarization temperatures of 224degC and 162degC, respectively Piezoelectric coefficients d33 were found to be 135 pC/N and 170 pC/N for BNBK79 and BNBK88, and the piezoelectric d31 was determined to be -37 pC/N and -51 pC/N, demonstrating strong anisotropy Coercive field values were found to be 37 kV/cm and 29 kV/cm for BNBK79 and BNBK88, respectively The remanent polarization of BNBK88 (~40 muC/cm2) was larger than that of BNBK79 (~29 muC/cm2) The piezoelectric, electromechanical, and high-field strain behaviors also were studied as a function of temperature and discussed
TL;DR: This study has experimentally verified vector meson mass modification at normal nuclear density through measured invariant mass spectra of e(+) e(-) pairs.
Abstract: Invariant mass spectra of ${e}^{+}{e}^{\ensuremath{-}}$ pairs have been measured in 12 GeV $p+A$ reactions to detect possible in-medium modification of vector mesons. Copper and carbon targets are used to study the nuclear-size dependence of ${e}^{+}{e}^{\ensuremath{-}}$ invariant mass distributions. A significant excess on the low-mass side of the $\ensuremath{\phi}$ meson peak is observed in the low $\ensuremath{\beta}\ensuremath{\gamma}(=\ensuremath{\beta}/\sqrt{1\ensuremath{-}{\ensuremath{\beta}}^{2}})$ region of $\ensuremath{\phi}$ mesons ($\ensuremath{\beta}\ensuremath{\gamma}l1.25$) with copper targets. However, in the high $\ensuremath{\beta}\ensuremath{\gamma}$ region ($\ensuremath{\beta}\ensuremath{\gamma}g1.25$), spectral shapes of $\ensuremath{\phi}$ mesons are well described by the Breit-Wigner shape when experimental effects are considered. Thus, in addition to our earlier publications on $\ensuremath{\rho}/\ensuremath{\omega}$ modification, this study has experimentally verified vector meson mass modification at normal nuclear density.
TL;DR: Dense PIPAAm-grafted surfaces exhibit strong, reversible temperature-modulated hydrophobic interactions, facilitating baseline separations of steroids and peptides in aqueous milieu without changes in the mobile phase pH and high ionic strength.
Abstract: Dense poly(N-isopropylacrylamide) (PIPAAm) brushes were created on silica bead surfaces by surface-initiated atom transfer radical polymerization (ATRP). Interfacial properties of PIPAAm brushes were characterized by thermoresponisve interaction with biomolecules. The grafted amounts of PIPAAm on silica bead surfaces exceeded that from previously reported polymer-hydrogel-modified silica beads prepared by conventional radical polymerization by nearly 1 order of magnitude. Temperature-dependent chromatographic interactions with soluble analytes were modulated by changing the grafted PIPAAm chain lengths. Short PIPAAm-grafted silica beads produce insufficient dehydration and chain aggregation to separate steroids using weak hydrophobic interactions. In contrast, broad unresolved peaks were observed on silica beads column grafted with long PIPAAm chains due to steroid partitioning into thick, densely grafted PIPAAm brush layers. Thus, silica beads column grafted with PIPAAm chains of proper length can demons...
TL;DR: In this paper, phase separation and suppression of critical dynamics at quantum phase transitions of MnSi and (Sr 1− x Ca x )RuO 3 were discussed, and the phase separation was discussed.
Abstract: Phase separation and suppression of critical dynamics at quantum phase transitions of MnSi and (Sr 1− x Ca x )RuO 3
TL;DR: This study describes a novel one-pot procedure for a directly reductive conversion of the carbonyl function of esters to the corresponding ethers by Et3SiH in the presence of a catalytic amount of InBr3.
Abstract: This study describes a novel one-pot procedure for a directly reductive conversion of the carbonyl function of esters to the corresponding ethers by Et3SiH in the presence of a catalytic amount of InBr3.
TL;DR: Intranasal inoculation with annual influenza vaccine plus the Toll-like receptor—3 agonist, poly(I): poly(C12U) (Ampligen) as an adjuvant may overcome the problem of a limited supply of H5N1 virus vaccine by providing cross-protective mucosal immunity against H4N1 viruses with pandemic potential.
Abstract: Background Avian H5N1 influenza A virus is an emerging pathogen with the potential to cause substantial human morbidity and mortality. We evaluated the ability of currently licensed seasonal influenza vaccine to confer cross-protection against highly pathogenic H5N1 influenza virus in mice. Methods BALB/c mice were inoculated 3 times, either intranasally or subcutaneously, with the trivalent inactivated influenza vaccine licensed in Japan for the 2005-2006 season. The vaccine included A/NewCaledonia/20/99 (H1N1), A/NewYork/55/2004 (H3N2), and B/Shanghai/361/2002 viral strains and was administered together with poly(I):poly(C(12)U) (Ampligen) as an adjuvant. At 14 days after the final inoculation, the inoculated mice were challenged with either the A/HongKong/483/97, the A/Vietnam/1194/04, or the A/Indonesia/6/05 strain of H5N1 influenza virus. Results Compared with noninoculated mice, those inoculated intranasally manifested cross-reactivity of mucosal IgA and serum IgG with H5N1 virus, as well as both a reduced H5N1 virus titer in nasal-wash samples and increased survival, after challenge with H5N1 virus. Subcutaneous inoculation did not induce a cross-reactive IgA response and did not afford protection against H5N1 viral infection. Conclusions Intranasal inoculation with annual influenza vaccine plus the Toll-like receptor-3 agonist, poly(I):poly(C(12)U), may overcome the problem of a limited supply of H5N1 virus vaccine by providing cross-protective mucosal immunity against H5N1 viruses with pandemic potential.
TL;DR: This ground-based observation provides the first clear evidence that strong electric fields in thunderclouds can continuously accelerate electrons beyond 10 MeV prior to lightning discharges.
Abstract: A report is made on a comprehensive observation of a burstlike $\ensuremath{\gamma}$-ray emission from thunderclouds on the Sea of Japan, during strong thunderstorms on 6 January 2007. The detected emission, lasting for $\ensuremath{\sim}40\text{ }\text{ }\mathrm{sec}$, preceded cloud-to-ground lightning discharges. The burst spectrum, extending to 10 MeV, can be interpreted as consisting of bremsstrahlung photons originating from relativistic electrons. This ground-based observation provides the first clear evidence that strong electric fields in thunderclouds can continuously accelerate electrons beyond 10 MeV prior to lightning discharges.