We report on the observation of collective radiative decay, or superradiance, of cyclotron resonance (CR) in high-mobility two-dimensional electron gases in GaAs quantum wells using time-domain terahertz magnetospectroscopy. The decay rate of coherent CR oscillations increases linearly with the electron density in a wide range, which is a hallmark of superradiant damping. Our fully quantum mechanical theory provides a universal formula for the decay rate, which reproduces our experimental data without any adjustable parameter. These results firmly establish the many-body nature of CR decoherence in this system, despite the fact that the CR frequency is immune to electron-electron interactions due to Kohn's theorem.
A label-free biological sensor, which is based on the resonant transmission phenomenon of a thin metallic mesh, is proposed in the terahertz wave region. By using this sensor, we demonstrate the highly sensitive detection of small amounts of protein horseradish peroxidase. For quantitative investigation of the sensitivity of our sensor, horseradish peroxidase was printed on the metallic mesh surface by using a commercial available printer. A distinct shift of the transmission dip frequency is observed for 500pg∕mm2 (11fmol) of horseradish peroxidase printed on the metallic mesh, indicating the significantly high sensitivity of our sensor.
A surface-wave sensor based on the resonant transmission characteristics of metal hole arrays is demonstrated in the terahertz (THz) region. Since the frequency of the transmission peak of a metal hole array, which corresponds to the resonant frequency of the surface waves, is particularly sensitive to the refractive index in the vicinity of the metal surface, a very small change in the substances attached to the surface can be detected by monitoring the transmission spectrum. By attaching a layer of substance (thickness t < 5 microm) much thinner than the wavelength of the THz wave (lambda(THz) = 1 mm at 0.3 THz) to the surface of a metal hole array, we demonstrated that the existence of such a small amount of substance can be detected more easily than without the metal hole array. This demonstration of THz sensing with metal hole arrays indicates the possibility of realizing THz surface-wave sensors for biochemical molecules in the THz region.
Pressure-induced volume phase transitions in neutral and ionized N-isopropylacrylamide-water (NIPA) gels were investigated. When the pressure is increased, the gels which shrink at atmospheric pressure undergo two volume phase transitions. One is the continuous phase transition (for neutral gels) or the discontinuous phase transition (for ionized gels) from the shrunken state to the swollen state at low pressures of several tens MPa. Another is the gradual shrinking transition occurred in the high pressure region above 100 MPa. The former transition shows that the derivative of the pressure with respect to the volume at constant temperature, (∂P/∂V)T, is positive. The results are explained by considering the pressure effects on the hydrophobic interaction. The phase transition pressure increases with increase of the temperature, and the critical pressure and temperature exist. The P–T coexistence curve resembling the evaporation curve of a liquid–gas system is obtained. These pressure-induced phase transitions are qualitatively explained by taking account of the pressure effects on the hydrophobic and hydrophilic interactions. It is assumed that the polymer solvent interaction parameter χ is a function of the pressure as well as the temperature, χ(T,P)=χ0(T)+χ1(T)P+χ2(T)P2. χ1 represents the pressure effects on the interaction between water molecules and the hydrophobic parts of NIPA, and it is responsible for the phase transition at low pressure. χ2 represents the pressure effects on the association between water molecules and the hydrophilic parts of NIPA, and it is responsible for the gradual shrinking transition at high pressure.
PURPOSE:The objective of this study was to compare osteoconductivity and biodegradation properties of an in-house fabricated beta-tricalcium phosphate (b-TCP)-collagen composite with those of Bio-Oss Collagen ® using a rat calvarial critical-size defect model. MATERIALS AND METHODS:b-TCP-collagen composite material was fabricated by mixing b-TCP granules having a particle size of 0.15-0.8 mm and 75% porosity, with bovine dermis-derived soluble collagen sponge. The dry weight ratio of b-TCP granules-to-collagen ratios was 4:1. Bio-Oss collagen or the b-TCP-collagen composite was used to fill a 5.0-mm diameter calvarial defect in rats.The defects were evaluated by histological and histomorphological analyses of decalcified histological sections with hematoxylin and eosin staining 6 and 10 weeks, respectively, after surgery. RESULTS:The defect implanted with the b-TCP composite contained immature bone structures with dense connective tissue in contrast to the abundant fibrous tissue, but no trabecular structure was observed within the defect implanted with Bio-Oss-collagen, at 6 weeks postoperatively.Eventually, the defect filled with the b-TCP composite was covered with dense, continuous, mature bone tissue with complete replacement of the graft material. However, in defects filled with Bio-Oss-collagen, only dense connective tissue, containing limited amounts of immature trabecular bone and abundant remnant Bio-Oss particles, was observed. Histomorphological analysis revealed that the b-TCP composite caused greater tissue augmentation with a larger volume of bone tissue observed in the defect and greater bioabsorption of remnant material than Bio-Oss-collagen. CONCLUSION:These results indicated that the b-TCP composite has greater osteoconductivity with greater reduction of residue than Bio-Oss-collagen; these properties of the b-TCP-collagen composite yielded mature bone formation.
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