Mott transition by an impulsive dielectric breakdown.

The transition of a Mott insulator to metal, the Mott transition, can occur via carrier doping by elemental substitution, and by photoirradiation, as observed in transition-metal compounds and in organic materials. Here, we show that the application of a strong electric field can induce a Mott transition by a new pathway, namely through impulsive dielectric breakdown. Irradiation of a terahertz electric-field pulse on an ET-based compound, κ-(ET) 2Cu[N(CN) 2]Br (ET:bis(ethylenedithio)tetrathiafulvalene), collapses the original Mott gap of ∼30 meV with a ∼0.1 ps time constant after doublon-holon pair productions by quantum tunnelling processes, as indicated by the nonlinear increase of Drude-like low-energy spectral weights. Additionally, we demonstrate metallization using this method is faster than that by a femtosecond laser-pulse irradiation and that the transition dynamics are more electronic and coherent. Thus, strong terahertz-pulse irradiation is an effective approach to achieve a purely electronic Mott transition, enhancing the understanding of its quantum nature.

Terahertz-Field-Induced Large Macroscopic Polarization and Domain-Wall Dynamics in an Organic Molecular Dielectric.

A rapid polarization control in paraelectric materials is important for an ultrafast optical switching useful in the future optical communication. In this study, we applied terahertz-pump second-harmonic-generation-probe and optical-reflectivity-probe spectroscopies to the paraelectric neutral phase of an organic molecular dielectric, tetrathiafulvalene-p-chloranil and revealed that a terahertz pulse with the electric-field amplitude of ∼400 kV/cm produces in the subpicosecond time scale a large macroscopic polarization whose magnitude reaches ∼20% of that in the ferroelectric ionic phase. Such a large polarization generation is attributed to the intermolecular charge transfers and breathing motions of domain walls between microscopic neutral and ionic domains induced by the terahertz electric field.

Ultrafast Photoinduced Electric-Polarization Switching in a Hydrogen-Bonded Ferroelectric Crystal.

Croconic acid crystals show proton displacive-type ferroelectricity with a large spontaneous polarization reaching 20 µC/cm^{2}, which originates from the strong coupling of proton and π-electron degrees of freedom. Such a coupling makes us expect a large polarization change by photoirradiations. Optical-pump second-harmonic-generation-probe experiments reveal that a photoexcited croconic-acid crystal loses the ferroelectricity substantially with a maximum quantum efficiency of more than 30 molecules per one absorbed photon. Based on density functional calculations, we theoretically discuss possible pathways toward the formation of a one-dimensional domain with polarization inversion and its recovery process to the ground state by referring to the dynamics of experimentally obtained polarization changes.

Enhanced directional dichroism of terahertz light in resonance with magnetic excitations of the multiferroic Ba2CoGe2O7 oxide compound.

We propose that concurrently magnetic and ferroelectric, i.e., multiferroic, compounds endowed with electrically active magnetic excitations (electromagnons) provide a key to producing large directional dichroism for long wavelengths of light. By exploiting the control of ferroelectric polarization and magnetization in a multiferroic oxide Ba(2)CoGe(2)O(7), we demonstrate the realization of such a directional light-switch function at terahertz frequencies in resonance with the electromagnon absorption. Our results imply that this hidden potential is present in a broad variety of multiferroics.

Terahertz-field-induced polar charge order in electronic-type dielectrics.

Ultrafast electronic-phase change in solids by light, called photoinduced phase transition, is a central issue in the field of non-equilibrium quantum physics, which has been developed very recently. In most of those phenomena, charge or spin orders in an original phase are melted by photocarrier generations, while an ordered state is usually difficult to be created from a non-ordered state by a photoexcitation. Here, we demonstrate that a strong terahertz electric-field pulse changes a Mott insulator of an organic molecular compound in κ-(ET)2Cu[N(CN)2]Cl (ET = bis(ethylenedithio)tetrathiafulvalene), to a macroscopically polarized charge-order state; herein, electronic ferroelectricity is induced by the collective intermolecular charge transfers in each dimer. In contrast, in an isostructural compound, κ-(ET)2Cu2(CN)3, which shows the spin-liquid state at low temperatures, a similar polar charge order is not stabilized by the same terahertz pulse. From the comparative studies of terahertz-field-induced second-harmonic-generation and reflectivity changes in the two compounds, we suggest the possibility that a coupling of charge and spin degrees of freedom would play important roles in the stabilization of polar charge order.

Electromagnons in the spin collinear state of a triangular lattice antiferromagnet.

Terahertz time-domain spectroscopy was performed to directly probe the low-energy (1-5 meV) electrodynamics of triangular lattice antiferromagnets CuFe(1-x)Ga(x)O2 (x=0.00, 0.01, and 0.035). We discovered an electromagnon (electric-field-active magnon) excitation at 2.3 meV in the paraelectric ↑↑↓↓ collinear magnetic phase, while this electromagnon vanishes in the ferroelectric helimagnetic phase. Anticorrelation with noncollinear magnetism excludes the exchange-striction mechanism as the origin of dynamical magnetoelectric coupling, and hence evidences the observation of a spin-orbit coupling mediated electromagnon in the present compound.

Process of healing of mucosal defects in the esophagus after endoscopic mucosal resection: histological evaluation in a dog model.

BACKGROUND AND STUDY AIMS: Resection of a large amount of the esophageal mucosa often causes esophageal ulcer and postoperative stricture. The aim of this study was to evaluate the process of healing of defects in the esophageal mucosa after endoscopic mucosal resection (EMR). MATERIALS AND METHODS: Cap-assisted EMR was performed in the thoracic esophagus of six beagle dogs to prepare mucosal defects with a diameter ranging from 15 to 18 mm. The process of mucosal healing was assessed histologically immediately after EMR, and on postoperative day (POD) 2, 4, 7, 14, and 28. RESULTS: Immediately after EMR, a thin layer of the submucosa remained in the mucosal defect, and no damage to the muscularis propria was evident. Ulcer formation and inflammatory cell invasion were observed in the remaining submucosa on POD 2 and 4. Angiogenesis and collagen fiber hyperplasia were observed after POD 7. Complete epithelialization of the ulcer was observed on POD 28. In the muscularis propria, further destruction and atrophy were evident after POD 7. Fibrosis of the muscularis propria was observed on POD 28. CONCLUSION: In the esophageal wall after epithelial loss resulting from EMR, atrophy and fibrosis of the muscularis propria remain even after epithelialization.

Doublon-holon pairing mechanism via exchange interaction in two-dimensional cuprate Mott insulators.

Coupling of charge and spin degrees of freedom is a critical feature of correlated electron oxides, as represented by the spin-related mechanism of a Cooper pair under high-T c superconductivity. A doublon-holon pair generated on an antiferromagnetic spin background is also predicted to attract each other via the spin-spin interaction J, similar to a Cooper pair, while its evidence is difficult to obtain experimentally. Here, we investigate such an excitonic effect by electroreflectance spectroscopy using terahertz electric field pulses in undoped cuprates: Nd2CuO4, Sr2CuO2Cl2, and La2CuO4. Analyses of the spectral changes of reflectivity under electric fields reveal that the splitting of odd-parity and even-parity excitons, a measure of doublon-holon binding energy, increases with J. This trend is reproduced by t-J-type model calculations, providing strong evidence of the spin-related doublon-holon pairing. Agreement with the calculations supports the s-wave symmetry of the doublon-holon pair in contrast to the d-wave Cooper pair in doped cuprates.

Ultrafast polarization control by terahertz fields via π-electron wavefunction changes in hydrogen-bonded molecular ferroelectrics.

Rapid polarization control by an electric field in ferroelectrics is important to realize high-frequency modulation of light, which has potential applications in optical communications. To achieve this, a key strategy is to use an electronic part of ferroelectric polarization. A hydrogen-bonded molecular ferroelectric, croconic acid, is a good candidate, since π-electron polarization within each molecule is theoretically predicted to play a significant role in the ferroelectric-state formation, as well as the proton displacements. Here, we show that a sub-picosecond polarization modulation is possible in croconic acid using a terahertz pulse. The terahertz-pulse-pump second-harmonic-generation-probe and optical-reflectivity-probe spectroscopy reveal that the amplitude of polarization modulation reaches 10% via the electric-field-induced modifications of π-electron wavefunctions. Moreover, the measurement of electric-field-induced changes in the infrared molecular vibrational spectrum elucidates that the contribution of proton displacements to the polarization modulation is negligibly small. These results demonstrate the electronic nature of polarization in hydrogen-bonded molecular ferroelectrics. The ultrafast polarization control via π-electron systems observed in croconic acid is expected to be possible in many other hydrogen-bonded molecular ferroelectrics and utilized for future high-speed optical-modulation devices.

Hormonal regulation of synthesis and secretion of pS2 protein relevant to growth of human breast cancer cells (MCF-7).

We have recently identified human epidermal growth factor-like immunoreactive factor synthesized and secreted by human breast cancer cells (MCF-7) as a secretory protein encoded by the pS2 gene, the transcription of which is directly induced by estrogen. We demonstrated in this paper that synthesis and secretion of pS2 protein as well as pS2 mRNA were induced about 5-fold specifically by physiological concentrations of estrogen, which stimulated growth of the cells about 5-fold. Stimulative effects of estrogen on both cell growth and synthesis/secretion of pS2 protein were inhibited completely by actinomycin D, cycloheximide, and antiestrogen. However, the increase in DNA synthesis from 6 h after the start of treatment of the cells with estrogen preceded the increase in the amount of pS2 protein in the culture medium from 12 h after that. Furthermore purified pS2 protein did not stimulate DNA synthesis of the cells. These results suggest that induction of pS2 protein by estrogen is not involved in the growth-stimulating effect of estrogen in MCF-7 cells.

[Off-pump atrial septectomy in a small neonate].

We report a surgical technique for off-pump atrial septectomy using a Rongeur forceps in the case of a newborn infant weighing less than 2,000 grams. The 6-day-old patient suffered from hypoplastic left heart syndrome with a restrictive interatrial communication. A purse-string suture was placed on the right atrium. A hand-made dull-tipped cannula was inserted into the right atrium through the suture to probe the interatrial communication. Monitoring the pressure at the tip of cannula, we could clearly determine when the cannula tip entered the left atrium. Then, a Rongeur forceps was inserted instead of the cannula, and used to bite into the interatrial septum. It was removed slowly together with the resected atrial specimen. In this manner, an atrial septectomy can be performed without cardiopulmonary bypass; this is far safer and easier than other procedures, such as the Blalock-Hanlon technique. This method can be performed in a small neonate as well as an older infant in whom balloon atrial septostomy is difficult.

Novel electronic ferroelectricity in an organic charge-order insulator investigated with terahertz-pump optical-probe spectroscopy.

In electronic-type ferroelectrics, where dipole moments produced by the variations of electron configurations are aligned, the polarization is expected to be rapidly controlled by electric fields. Such a feature can be used for high-speed electric-switching and memory devices. Electronic-type ferroelectrics include charge degrees of freedom, so that they are sometimes conductive, complicating dielectric measurements. This makes difficult the exploration of electronic-type ferroelectrics and the understanding of their ferroelectric nature. Here, we show unambiguous evidence for electronic ferroelectricity in the charge-order (CO) phase of a prototypical ET-based molecular compound, α-(ET)2I3 (ET:bis(ethylenedithio)tetrathiafulvalene), using a terahertz pulse as an external electric field. Terahertz-pump second-harmonic-generation(SHG)-probe and optical-reflectivity-probe spectroscopy reveal that the ferroelectric polarization originates from intermolecular charge transfers and is inclined 27° from the horizontal CO stripe. These features are qualitatively reproduced by the density-functional-theory calculation. After sub-picosecond polarization modulation by terahertz fields, prominent oscillations appear in the reflectivity but not in the SHG-probe results, suggesting that the CO is coupled with molecular displacements, while the ferroelectricity is electronic in nature. The results presented here demonstrate that terahertz-pump optical-probe spectroscopy is a powerful tool not only for rapidly controlling polarizations, but also for clarifying the mechanisms of ferroelectricity.

Expression of the pS2 gene in human gastric cancer cells derived from poorly differentiated adenocarcinoma.

NH2-terminal amino acid sequence of the pS2 protein produced and secreted by human gastric cancer cells, MKN-45, was determined to be identical to that of MCF-7 cells. A clone encoding pS2 protein was isolated from the cDNA library constructed from MKN-45 cells. The nucleotide sequence was identical to that of pS2 cDNA previously isolated from human breast cancer cells, MCF-7, except for one nucleotide in the 3' untranslated region. Thus, in this cell line, the pS2 gene product is translated and secreted as in MCF-7 cells. RNA blot hybridization analysis revealed that pS2 gene was expressed well in two (MKN-45 and KATO-III; derived from poorly differentiated adenocarcinoma) but not in three cell lines (MKN-1, MKN-28 and MKN-74; from well differentiated adenocarcinoma), suggesting that expression of the pS2 gene depends on the state of cell differentiation. These results suggest that pS2 is expressed in human gastric cancer cells in an estrogen-independent manner and is possibly associated with the malignant state of cells.

A Japanese family with high density lipoprotein deficiency.

Two siblings with marked reduction of plasma high density lipoprotein (HDL) were found in a Japanese family. Their plasma cholesterol levels were very low (30-60 mg/dl), especially in the HDL fraction (0-1 mg/dl). The concentration of apolipoprotein (Apo) A-I in their plasma was 2-3 mg/dl and that of Apo A-II was 1.5-2.0 mg/dl, determined by means of a single radial immunodiffusion technique. An ultracentrifugally separated HDL fraction contained two different populations of lipoprotein particles, as shown by electron microscopy; a small particle with a diameter of 50-70 A and a relatively large particle at 200 A. Plasma lecithin: cholesterol acyltransferase activity was substantially retained in both cases. Hepatosplenomegaly was present and liver biopsy revealed lipid deposition in reticuloendothelial cells, although the tonsils were apparently normal. No severe atherosclerotic lesions were noticed. The results from these two cases were consistent with the characteristic features of homozygotes of familial HDL deficiency (Tangier disease). HDL cholesterol levels were relatively low in the parents and two children from one patient, which is consistent with the heterozygote state. Two other cases in the kindred were also found to have relatively low HDL cholesterol levels, besides these 4 cases of obligate heterozygotes. Apo A-I and Apo A-II levels in the plasma of the obligate heterozygotes, however, were within the normal range. Plasma low density lipoprotein in the patients moved faster in polyacrylamide gel electrophoresis than those of normal subjects, as did those in the heterozygotes.

Complete primary structure of the human estrogen-responsive gene (pS2) product.

pS2 is a human gene whose transcription is directly triggered by estrogen in human breast cancer cells (MCF-7). We described here the complete primary structure of the pS2 gene product. The pS2 protein purified from conditioned medium of MCF-7 cells was S-pyridylethylated and digested with TPCK-trypsin. Five major fragments were obtained by reverse-phase HPLC. Amino acid sequence analysis of these tryptic peptides established that the pS2 protein comprises a 60-amino acid polypeptide. The sequence of the pS2 protein was completely identical to that deduced from the nucleotide sequence of the pS2 gene, if the signal polypeptide is excluded. Furthermore, two cDNA clones encoding an 84-amino acid precursor pS2 protein were isolated from a cDNA library which was constructed with RNA from MCF-7 cells cultured in the presence of estrogen. The nucleotide sequence of one clone (pS2B1) was identical to that of pS2 cDNA previously reported except for one nucleotide in the 3' untranslated region. The other clone (pS2B2) was longer by 73 nucleotides, at the 5' end, than pS2B1. The additional 73 nucleotides are located just upstream of the sequence of pS2B1 in the structure of the pS2 gene, indicating that the pS2 gene has two start sites for transcription. However, a mRNA molecule corresponding to pS2B1 but not to pS2B2 was detected in the cells on RNA blot hybridization analysis, indicating that one transcriptional start site is mainly used.

Neuromuscular fatigue during maximal concurrent hand grip and elbow flexion or extension.

The objective was to investigate muscle fatigue measuring changes in force output and force tremor and electromyographic activity (EMG) during two sustained maximal isometric contractions for 60s: (1) concurrent hand grip and elbow flexion (HG and EF); or (2) hand grip and elbow extension (HG and EE). Each force tremor amplitude was decomposed into four frequency bands (1-3, 4-10, 11-20, and 21-50Hz). Surface EMGs were recorded from the flexor digitorum superficialis (FDS), extensor digitorum (ED), biceps brachii (BB) and lateral head of triceps brachii (TB). The HG and EF forces for the HG and EF and the HG force for the HG and EE declined rapidly, whereas the EE force remained almost constant near to the initial value for the first 40s and then declined. The decrease in EMG amplitude was observed not for the FDS muscle but for the ED muscle. The HG tremor amplitude for each frequency band showed similar decreasing rate, whereas the decreases in EF and EE tremor amplitudes for the lower band (below 10Hz) were slower than those for the higher band (above 11Hz). The neuromuscular mechanisms underlying muscle fatigue during sustained maximal concurrent contractions of hand grip and elbow flexion or extension are discussed.

Rapid detection of Vibrio cholerae with a new selective enrichment medium and polymerase chain reaction.

The inhibitory effect of metallic EDTA compounds on growth of Vibrio cholerae and Escherichia coli was studied. Only Fe-EDTA among the compounds tested showed pH-dependent growth inhibition on E. coli at pH 9.0, but no inhibition of V. cholerae at the same pH. By addition of Fe-EDTA as a selective inhibitor, a novel enrichment broth (tentatively designated as VCF broth) for the selective isolation and cultivation of V. cholerae from other Gram-negative bacilli has been developed, and the selective enrichment capacity of VCF broth for V. cholerae and selective inhibiting activity against E. coli were significantly higher than those of alkaline peptone water. A simple procedure for rapid detection of V. cholerae by selective enrichment for 6 hr with VCF broth and then amplification of the cholera toxin target DNA fragment by the polymerase chain reaction was presented. VCF broth may be a useful tool for the selective enrichment of V. cholerae in bacterial examinations.

Central and peripheral visual reaction time of soccer players and nonathletes.

Visual Reaction Time (RT) was measured by presenting three different sizes of stimulus to the central and peripheral fields of vision in 6 soccer players and 6 nonathletes. An electromyogram was recorded from the flexor digitorum superficialis muscle of the responding forearm. Peripheral visual RT was longer in comparison to central visual RT due to an increment in Premotor Time. The soccer players showed shorter Premotor Times during central and peripheral visual RT tasks than nonathletes, suggesting that the soccer players are better able to respond quickly to a stimulus presented to peripheral as well as central positions.

[Effect of pH on preferential antibacterial-activity of ethylenediaminetetraacetic acid (EDTA)].

Ethylenediaminetetraacetic acid (EDTA), a chelating agent, was examined for the antibacterial activity against 15 species of bacteria by treating with a 10mM solution at pH adjusted to 5.0, 7.0 or 9.0. All bacterial species tested were classified into three groups; tentatively named the pH5 EDTA-sensitive group comprising Vibrio cholerae and Staphylococcus aureus, the pH9 EDTA-sensitive group comprising Escherichia coli and Pseudomonas aeruginosa and the EDTA-nonsensitive group comprising Proteus mirabilis. The EDTA-sensitivity grouping may be used as a tool for preferential decontamination of certain bacteria in live edible fishes, although further experiments are needed to characterize more strains and also species of bacteria.

[A simple method for differentiation of hydrogen sulfide-producing bacteria by the pH-dependent EDTA-sensitivity test].

The pH-dependent EDTA-sensitivity test was performed to differentiate several strains of bacteria forming black colonies by the production of hydrogen sulfide on TCBS (thiosulfate-citrate-bile salt-sucrose agar) medium (tentatively designated as hydrogen-sulfide production bacteria). Two halotorelant strains of 16 hydrogen sulfide-producing strains showed the same bacteriological properties and isoprenoid quinone type as did a reference strain of Proteus mirabilis and were classified into the EDTA-insensitive group as were P. mirabilis and P. vulgaris. On the other hand, the other 14 halophilic strains, showing similar but not identical bacteriological properties or the isoprenoid quinone type to those of Shewanella putrefaciens IFO 3908, were classified into the "EDTA-sensitive (at pH 5)" group as were some species of the genus Vibrio. By the same sensitivity test, S. putrefaciens IFO 3908 was classified into the "EDTA-sensitive (at any pH)" group. These results indicate that the pH-dependent EDTA-sensitivity test is useful for differentiation of bacterial isolates producing hydrogen sulfide and having similar bacteriological properties.