Unimolecular decomposition of formic acid in the gas phase--on the ratio of the competing reaction channels

The thermal decomposition of formic acid was reinvestigated in the gas phase using two types of shock tubes. It was confirmed that the unimolecular decomposition proceeds through a main channel of dehydration (k1) and a minor decarboxylation channel (k2). This result is in good agreement with our previous study (J. Chem. Phys. 1984, 80, 4989). Furthermore, it was confirmed that the dehydration process is in the second-order region and that the decarboxylation is in the falloff region, in the temperature range of 1300-2000 K and over the total density of (0.5-2.5) x 10(-5) mol cm(-3). The experimental ratios between the two channels, k2/k1, are compared with those of theoretical calculations by conventional transition state theory and the Rice-Ramsperger-Kassel-Marcus theory.     

Magnetic Phase Transitions in Substituted Spinels of Zn1−x Cu χ Cr2 Se4; 0.0 ≤ x ≤ 0.3

Magnetic and crystallographic properties have been studied by neutron powder diffraction and measurements of magnetization and magnetization hysteresis-loops for substituted spinels of Zn_1?xCu_xCr₂Se₄ with 0.0≤x≤0.3. It is found that the Zn_0.85Cu_0.15Cr₂Se₄ spinel has two magnetic phase transitions at 23.0 K (Néel temperature; T _N) and 410 K (Curie temperature; T _C) and that the Zn_0.70Cu_0.30Cr₂Se₄ spinel has magnetic transitions at 24.5 K (T _N) and 415 K (T _C) on heating. The low-temperature magnetic phase transition is from a spiral antiferromagnet to a ferromagnet, and the high-temperature magnetic phase transition is from a ferromagnet to a paramagnet, while ZnCr₂Se₄ shows a magnetic phase transition only from a spiral antiferromagnet to a paramagnet at about 21.0 K. From neutron powder diffraction, it is also found that the spinels of Zn_1?x Cu _x Cr₂Se₄; 0.0 ≤ x ≤ 0.3. show satellite-like magnetic reflection having indexes (h ± Q, k, l) with Q = 0.470 below T _N and short-range order of spins (spin glass-like) above T _N. The incommensurate antiferromagnetic phase below T _N results from a spiral long-range order of the spins of Cr³⁺. The intermediate ferromagnetic phase between T _N and T _C is related not to the spiral spin order but to double-exchange magnetic interaction among Cr³⁺ and Cr⁴⁺ mediated by current carriers, positive holes, which is made by the substitution of Zn²⁺ ions with Cu¹⁺ ions in Zn_1?x Cu _x Cr₂Se₄.     

Optical gain due to the Eu transition in the alloy of Ca1-xEuxGa2S4

Room temperature photoluminescence quantum efficiency of the alloy of Ca_1−xEu_xGa₂S₄ was measured as a function of x, and was found to be nearly unity under excitation at peak wavelength of excitation spectrum (510 nm) in the x range of 0.01≤x≤0.2. At larger x values, it tends to decrease, but still as high as 30% for stoichiometric compound EuGa₂S₄. Taking these backgrounds into account, pump-probe experiments were done with Ca_1−xEu_xGa₂S₄ for searching optical gain at x=0.2. The optical gain of nearly 30 cm⁻¹ was confirmed to exist, though the pumping induced transient absorption which seems to limit the higher gain was found.     

Observation of ultrahigh-energy cosmic rays with the ANITA balloon-borne radio interferometer

We report the observation of 16 cosmic ray events with a mean energy of 1.5 × 101? eV via radio pulses originating from the interaction of the cosmic ray air shower with the Antarctic geomagnetic field, a process known as geosynchrotron emission. We present measurements in the 300-900 MHz range, which are the first self-triggered, first ultrawide band, first far-field, and the highest energy sample of cosmic ray events collected with the radio technique. Their properties are inconsistent with current ground-based geosynchrotron models. The emission is 100% polarized in the plane perpendicular to the projected geomagnetic field. Fourteen events are seen to have a phase inversion due to reflection of the radio beam off the ice surface, and two additional events are seen directly from above the horizon. Based on a likelihood analysis, we estimate angular pointing precision of order 2° for the event arrival directions.     

100 W, single-frequency operation of an injection-locked Nd:YAG laser

We have built a single-frequency Nd:YAG laser capable of producing an output power of 101 W by injection locking a slave laser that can emit an output power of 121 W in the free-running state to a 2-W master laser. We confirmed that the output mode was diffraction limited and linearly polarized.     

Extremely low-loss hollow core waveguide for VUV light

A new type of an extremely low-loss optical waveguide is proposed. In the vacuum-ultra-violet (VUV) region (wavelength less than 300 nm) most solid-state materials have a refractive index less than unity due to plasma vibration of electrons. The energy of VUV light is confined within the hollow core due to the smaller n_r than unity of the cladding material of the hollow core waveguide. Typical expected loss for 50 nm-wavelength VUV light of a 0.1 mm hollow-core waveguide is on the order of 0.05 dB/km.     

Acoustical design of the opera house of the New National Theatre, Tokyo, Japan

Architect Takahiko Yanagisawa's preface explains his approach to the design. The NNT opera house seats 1810, its volume is 14500 m3, and its reverberation time, with audience, is 1.5 s (proscenium curtain open). Measurements on CAD computer and 1:10 wooden models and full-sized materials samples were conducted over a 7-yr. period. The main floor is almost rectangular, the three balconies have modest fan shape in plan, although the balcony facia at each level create a rectangular shape. The unique design has a large curved reflector in front of and above the proscenium and six curved reflecting surfaces at the front ends of the three side balconies to form, in combination, an "acoustic trumpet." These surfaces, along with the balcony faces and the shaped ceiling, distribute the singers' voices uniformly over the seating areas from a large portion of the large stage at sound levels that easily override the orchestra in the pit.     

High-efficiency electro-optic amplitude modulation with delayed coherent addition

Amplitude modulation of laser light is required for resonant sideband extraction employed in gravitational-wave detectors. Amplitude modulation with electro-optic phase modulators is realized by interferometric phase-to-amplitude conversion. Although two outputs modulated at opposite phases to each other are obtained, usually only one of them is utilized and the other is abandoned. The reuse of this abandoned light improves the power efficiency of the modulation. This can be realized by inverting the modulation phase of one output with a delay line and adding it to the other coherently. Moreover, this system selects a high-efficiency operating point and modulates the light in a linear range. We demonstrate that the modulation system can be operated with a power loss that is due only to the losses of the optical components.