Determination of three dimensional in situ stress from core discing based on analysis of principal tensile stress

To determine all of the components of in situ stress from core discing, both the directions and magnitudes of the principal in situ stresses must be determined for a disc of a given thickness. In this study, we analyzed the direction and magnitude of tensile stress below an HQ core stub for 11 core lengths using stress conditions under which core discing is likely to occur. First, based on an analysis of the direction of tensile stress below the core stub, we propose a method for determining directions of in situ stress from the height distribution at the periphery of the end surface of a disc. This method can be used with a disc of any thickness. Next, based on an analysis of the magnitude of tensile stress in the central part of a core, we propose a linear criterion for core discing, which can be applied to a core of any length. This criterion was in good agreement with an empirical formula obtained previously in laboratory experiments. By combining information on the direction of in situ stress and the linear criterion for core discing, we propose a method for determining all of the components of in situ stress from core discing under the assumption that vertical stress is given by the overburden stress. Finally, these methods were applied to discs obtained from a field where hydraulic fracturing was performed to measure horizontal stresses. The results showed that the azimuths of the principal stresses estimated from core discing were consistent with those of the principal horizontal stresses determined by hydraulic fracturing and that while the magnitudes of the principal horizontal stresses estimated from core discing showed a large scatter, they were similar to those determined by hydraulic fracturing.     

Multi-wavelength intermittent photoluminescence of single CdSe quantum dots

A single chromophore detection using video-microscopy is one of the latest methodologies to reveal unique characteristics, which could not be obtained from ensemble measurements. Among many kinds of subjects, dynamic optical properties observed in colloidal semiconductor nanoparticles are attractive and important not only for the basis of photo-physics but also for application studies, e.g. biological labeling, electronic devices. In this study, fluorescence video-microscopy was performed on cadmium selenide (CdSe) quantum dots (QDs) spin-coated on a glass substrate. From single CdSe QDs detection, emissions at wavelengths separated over 60 nm were observed for the first time. This spectral feature was attributed to the existence of double-emissive relaxation processes in CdSe QDs. Photoluminescence intermittency was also observed both from relaxation processes. Fluorescence video-microscopy, which was advanced in biology, can be applicable for the real-time monitoring of dynamic properties in semiconductor photo-physics.     

Investigation of bonding strength and sealing behavior of aluminum/stainless steel bonded at room temperature

This article reports the direct bonding of aluminum (Al) [99.999% (5N), 99% (2N)] and stainless steel SUS (304, 316) without heating for sealing in the ultra high vacuum (UHV) components. For bonding, the smooth surfaces of the Al and SUS specimens were activated using argon fast atom beam (Ar-FAB) for 1-60 and 60 min, respectively, in a background pressure of 6.0 × 10⁻⁵ Pa followed by close contact under an external pressure of 960 N. High bonding strength resulted in the bonded mates of Al and SUS304 activated for 30 and 60 min, respectively, due to the adhesion forces of the surface atoms. Tensile pulling tests showed bulk fractures in Al with impurity dependent bonding strength. The bonding strengths for the Al5N/SUS304 and Al2N/SUS304 specimens were higher than 60 and 100 MPa, respectively. For the sealing test, the smooth surface of the SUS316 flange containing a hole was bonded with Al after surface activation 60 and 30 min, respectively. Leak rates for Al5N/SUS316 and Al2N/SUS316 specimens were 1.5 × 10⁻¹¹ and 2.0 × 10⁻¹¹ Pa m³/s, respectively. These results satisfy the permissible leakage of a large-sized UHV chamber. Time dependence of the leak test behavior for both specimens shows a stable leak rate. Therefore, the sealing of Al/SUS316 may be utilized for the fabrication of corrosion free joints for fluid flow in the cooling of electron guns of small size equipment such as portable scanning electron microscopes in UHV pressure.     

Thermal degradation of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) in nitrogen and oxygen studied by thermogravimetric-Fourier transform infrared spectroscopy

The thermal degradation behavior of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(HB-co-HHx), HHx=12 mol%) has been studied under different environmental conditions by thermogravimetric analysis (TGA) Fourier transform infrared (FT-IR) spectroscopy. It is reported that at higher temperature (>400 degrees C) carbon dioxide and propene are formed from the decomposition product crotonic acid in a nitrogen atmosphere, whereas in an oxygen atmosphere propene oxidizes in a further step to carbon dioxide, carbon monoxide and hydrogen. It was also found that PHB and P(HB-co-HHx) have a similar thermal degradation mechanism. The analysis of the FT-IR-spectroscopic data was performed with 2D and perturbation-correlation moving-window 2D (PCMW2D) correlation spectroscopy.     

Average thresholds in the 8 to 20 kHz range in young adults

RATIONALE AND OBJECTIVES: The Comprehensive Clinical Assessment (CCA) examination at the University of Michigan Medical School is a series of test stations through which the mastery of clinical skills is evaluated. The purpose of this study was to determine whether student performance on the radiology station improved in years when radiology faculty presented case-of-the-week unknowns to the 3rd-year students. MATERIALS AND METHODS: The authors compared four separate classes of medical students in examination years 1993, 1994, 1995, and 1996 by using the total CCA examination score, the radiology station score, and radiology station pass/fail rates. Radiology case-of-the-week presentations were given by the radiology faculty only in academic years 1993-1994 and 1994-1995 (examination years 1994 and 1995). RESULTS: The means and standard deviations of the radiology station scores for the examination years when case-of-the-week presentations were not given, 1993 and 1996, were 78.92 +/- 13.62 and 79.76 +/- 13.62, respectively. In the years case-of-the-week presentations were given, 1994 and 1995, the radiology station scores averaged 90.83 +/- 8.58 and 89.97 +/- 9.66, respectively (P < .001, global alpha = .05). Total CCA percentage correct scores were similar for all years studied. In 1993 and 1996, 7.6% and 5.3% of students, respectively, failed the radiology station. In 1994 and 1995, 0.4% and 0% of students, respectively, failed (P < .0001). CONCLUSION: Case-of-the-week presentations by radiology faculty increased 3rd-year students' basic radiologic knowledge as evidenced by increased scores on the radiology station of the CCA examination.     

Fundamental mechanisms limiting solid oxide fuel cell durability

The fundamental issues associated with solid oxide fuel cell (SOFC) durability have been reviewed with an emphasis on general features in SOFCs and respective anode and cathode related phenomena. As general features, physicochemical properties and cell performance degradation/failure are correlated and bridged by the electrode reaction mechanisms. Particular emphasis is placed on the elemental behaviour of gaseous impurities and the possible role of liquids formed from gaseous substances. The lifetime of a state-of-the-art Ni cermet anodes is limited by a variety of microstructural changes, which mainly result from material transport-, deactivation- and thermomechanical mechanisms. Anode degradation can mainly be influenced by processing, conceptual and operating parameters. Designing a redox stable anode is currently one of the biggest challenges for small scale SOFC systems. Degradation mechanisms of different cathode materials are reviewed with a focus on the intrinsic degradation of doped lanthanum manganites (e.g. LSM) and doped lanthanum ferro-cobaltites (LSCF). Manganese-based perovskites can be regarded to be sufficiently stable, while for the better performing LSCF cathodes some intrinsic degradation was detected. New materials that are supposed to combine a better stability and high performance are also shortly mentioned.     

Crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) studied by 2D IR correlation spectroscopy

Crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(HB-co-HHx)) (HHx=12 mol%) was studied by means of two-dimensional infrared (2D IR) correlation spectroscopy. Three types of crystallization; the gradual cooling from the melt, the isothermal crystallization of the supercooled melt, and the isothermal crystallization of the solution-cast film were investigated. The order of crystal growth steps taking place during the three different types of crystallization processes was analyzed in detail. It was revealed by the asynchronous 2D correlation spectra generated from the dynamic IR spectra in the CO stretching band region that the development of the highly ordered crystals occurs prior to that of the less ordered crystals for the gradual cooling crystallization. On the other hand, for the supercooled melt and solution-cast film crystallization, the formation of the less ordered crystals takes place before that of the highly ordered crystals. The transition from the amorphous phase to the less ordered crystals is a simultaneous process for all three types of crystallization.