Enhancement of the Mode Area and Modal Discrimination of Microchip Lasers Using Angularly Selective Mirrors

Angularly selective mirrors (ASMs) are proposed as a means to expand the mode area and modal discrimination of microchip lasers. ASMs used as output couplers selectively reflect incoming k vectors over a narrow angular range, while they transmit more inclined components. The eigenvalue problem of a microchip resonator equipped with a Gaussian ASM is solved analytically in the paraxial optics approximation using the ABCD matrix formalism. The narrow angular distribution of the reflected beam produces, through the laws of diffraction, a significant increase of the mode size and improved transverse mode discrimination, at the expense of higher oscillation threshold due to larger output coupling losses. Simulations performed using the parameters of Yb³⁺-doped YAG material show that one order of magnitude increase of the mode area can reasonably be achieved without causing overheating and thermal fracture. ASMs can be directly deposited on the active material in the form of a resonant grating mirror. This technology involves only planar batch processes that retain the mass production advantage of microchip lasers. The significant increase of brightness of microchips expected from this innovation will give rise to more effective and more compact devices and new applications.     

Magnetic Orders of Highly Frustrated Spinel, ZnCr2O4 in Magnetic Fields up to 400 T

We investigated the magnetization process of the highly frustrated spinel ZnCr₂O₄ using the Faraday rotation method at 6 K under the ultra-high magnetic fields up to 400 T by the electro-magnetic flux compression method. We successfully observed the full magnetization process in this material. We found some anomalies which show new phase transitions at 240 T, 290 T, 350 T, and 390 T.     

Two parallel penny-shaped or annular cracks in a functionally graded piezoelectric strip under electric loading

In this paper, the mixed-mode fracture problem of a functionally graded piezoelectric material strip with two penny-shaped or annular cracks is considered. It is assumed that the electroelastic properties of the strip vary continuously along the thickness of the strip, and that the strip is under electric loading. The problem is formulated in terms of a system of singular integral equations, which are solved numerically. Numerical calculations are carried out, and the stress and electric displacement intensity factors are presented for various values of dimensionless parameters representing the crack size, the crack location, and the material nonhomogeneity.     

Capacitance of porous carbon electrode in mixed salt non-aqueous electrolytes

Capacitances of a porous carbon electrode in non-aqueous electrolytes containing tetraethylamonium tetrafluoroborate (TEABF₄) and a lithium salt with various compositions have been investigated for the potential use in electric double layer capacitor. In the electrolyte prepared by dissolving TEABF₄ and LiBF₄ into the mixed solvent of ethylene carbonate (EC) with diethyl carbonate (DMC), an activated carbon fiber (ACF) electrode exhibits a larger capacitance than in TEABF₄ single salt electrolyte on cyclic voltammograms. The symmetrical capacitor cell containing the LiBF₄-TEABF₄ mixed salt electrolyte also exhibits larger capacitance on a constant-current test compared with that containing the TEABF₄ single salt electrolyte, while the capacitance degradation is observable for this cell at a significant extent, while the test under controlled potential of the ACF electrode to −0.2 to 1.0 V vs. Ag provides somewhat stable capacitance over 30 cycles.     

Study on Behavior in Tension of Reinforced Concrete Members Strengthened by Carbon Fiber Sheet

This paper presents experimental results on the behavior in tension of reinforced concrete members strengthened with carbon fiber sheets (CFS). CFS reduced the crack spacing and brought about good crack width control as well as a significant change in the average bond stress and the average stress of steel reinforcing bars and concrete. The deterioration mechanism of the CFS bond properties near cracks was presented.     

Hemodynamic effects of warm bathing in a Hubbard tank and exercise loading in patients after myocardial infarction

Hemodynamic parameters were measured during bathing and exercise testing in 43 patients with myocardial infarction (mean age: 60.2 years) to investigate the predictive parameters to determine when patients could safely resume bathing. Patients took a fresh water bath at 42 degrees C in the supine position for 5 min in a Hubbard tank. Group A showed an elevation of pulmonary capillary wedge pressure (PCWP) during bathing of 10 mmHg or more (23 patients, mean age: 61.7 years) and group B showed an elevation of less than 10 mmHg (20 patients, mean age: 60.5 years). Continuous multistep exercise tests were performed with a bicycle ergometer in the supine position, and hemodynamic parameters were measured at up to 50 W for 3 min on the day before the warm bathing test. There were no significant differences in the changes of arterial pressure and heart rate between the two groups. The PCWP at 3 min with a load of 50 W was significantly higher in group A (26.9 +/- 9.0 mmHg) than in group B (16.7 +/- 9.1 mmHg, p < 0.01). The stroke index (SI) during exercise testing was significantly lower in group A than in group B. The difference in the stroke index from baseline values (delta SI) at 3 min with a load of 50 W was significantly lower in group A (3.5 +/- 5.5 ml/m2/beat) than in group B (10.6 +/- 7.0 ml/m2/beat, p < 0.01). Similarly, delta CI and delta oxygen pulse during testing were significantly lower in group A than in group B. The physical work capacity and ejection fraction of the left ventricle of group A were significantly lower than those of group B, whereas the left ventricular end-diastolic pressure was higher in group A than in group B. CI, delta CI, SI, delta SI, METs, oxygen pulse, and delta oxygen pulse were examined by regression analysis and multivariate analysis to predict a significant elevation of delta PCWP during bathing. delta SI (p = 0.0032), delta CI (p = 0.0094), delta SI + METs (p = 0.0051), delta CI + METs (p = 0.0061), delta CI + delta SI (p = 0.0084), and delta CI + delta SI + METs (p = 0.0093) showed the highest correlations with delta PCWP. These findings suggest that changes in delta CI, delta SI, and METs are good predictive parameters for determining when patients may safely resume bathing. We suggest that patients with myocardial infarction, reduced cardiac function and a physical work capacity of approximately 4.0 METs, delta SI: 5 ml/m2/beat and delta CI: 2.4 l/min/m2 resume bathing only after careful consideration.