Local Maximum Value Research Articles

144 衝撃荷重下におけるCFRP積層材の混合モード層間破壊特性(OS5-2 異物衝突損傷)(OS5 材料の衝撃強度・損傷に関する最近の知見)

The mixed mode (I+II) fracture behavior of carbon-fiber/epoxy composite laminates was investigated over a wide range of loading rate to clarify the effects of strain rate and mode mixture on fracture behavior. MMF (Mixed Mode Flexure) and MMB (Mixed Mode Bending) specimens were used to evaluate the mixed mode fracture toughness. The mixed mode fracture toughness clearly showed strain rate dependence regardless of mode ratio; the mixed mode impact fracture toughness was about 10 % lower than the local maximum value under static loading. Local maximum values existed at static loading rate for mixed mode fracture toughness, G_C. The mixed mode fracture toughness conform to the linear criterion for the region of high mode ratio, G_<II>/G_I=13, regardless of loading rates. However, it did not conform to the linear criterion for the region of low mode ratio, G_<II>/G_I&le;3, and high loading rate, G&ge;10^2 J/m^2/s.

Effects of Strain Rate and Mode Ratio on Mixed Mode Interlaminar Fracture Behavior of Carbon-Fiber/Epoxy Composite Laminates.

The interlaminar fracture toughness of carbon-fiber/epoxy composite laminates was investigated over wide ranges of loading rate, G=(10)-1&acd;(10)7J/m2/s, and mode ratio, GII/GI=0&acd;∞, to study the effects of strain rate and mode mixture on micro- and macro-scopic fracture behavior. The MMF (Mixed Mode Flexure) and MMB (Mixed Mode Bending) specimens were employed to determine the mixed mode fracture toughness. The mode I, mode II and their mixed mode fracture toughness, GIC, GIIC, Gc, at the onset of crack growth was dependent on strain rate regardless of mode ratio; the fracture toughness at impact strain rate was about 10&acd;32% lower than the local maximum value at static strain rate. The mixed mode fracture toughness, Gc, obeyed the linear fracture criterion except for the region of low mode ratio, GII/GI&le;3, and high strain rate, G&ge;(10)2J/m2/s. The microscopic fracture morphology was mainly dominated by the debonding of fiber/matrix interface at lower strain rate, whereas it was dominated by the cohesive fracture of matrix resin at higher strain rate.

Optimization of Bifurcation Geometry.

This paper deals with the optimal geometry of two-dimensional symmetric Y-bifurcation. The optimal geometry was determined by i) minimizing the time averaged pressure loss of the flow through the bifurcation, ii) minimizing the local maximum value of time averaged wall shear stress gradient. The neural network was utilized to identify the relation between the geometry and time averaged pressure loss or the relation between the geometry and local maximum value of time averaged wall shear stress gradient, and the optimal geometry was determined according to the results of identification. Numerical results showed that the cross-sectional area of the optimal geometry reaches its maximum at the apex and this feature is resembling to the actual bifurcation geometry in the artery. So, it was expected the present study was effective to understand the geometry of artery in the body.

Choking phenomena of sonic nozzles at low Reynolds numbers

The choking phenomena of sonic nozzles were investigated for the Reynolds number range from 40 to 30 000 for nitrogen gas. The results showed that the critical back pressure ratio is a function of the Reynolds number only, with different characteristics for different nozzle shapes. In ISO-type toroidal-throat Venturi nozzles, the minimum Reynolds number satisfying the choking condition is about 40 and the critical back pressure ratio is only about 0.05 at this minimum Reynolds number. It was also found that the critical back pressure ratio has a local minimum value around Re th=4000 and that the local maximum value is around Re th=10 000 due to the change in characteristics of the boundary layer in the diffuser. On the other hand, the critical back pressure ratio in quadrant nozzles decreases monotonically with decreasing Reynolds number, unlike the former nozzle, and the minimum Reynolds number necessary for choking is estimated to be approximately the same as that in the Venturi nozzle.

The Lebesgue function for generalized Hermite-Fejér interpolation on the Chebyshev nodes

AbstractThis paper presents a short survey of convergence results and properties of the Lebesgue function λm,n(x) for(0, 1, …, m)Hermite-Fejér interpolation based on the zeros of the nth Chebyshev polynomial of the first kind. The limiting behaviour as n → ∞ of the Lebesgue constant Λm,n = max{λm,n(x): −1 ≤ x ≤ 1} for even m is then studied, and new results are obtained for the asymptotic expansion of Λm,n. Finally, graphical evidence is provided of an interesting and unexpected pattern in the distribution of the local maximum values of λm,n(x) if m ≥ 2 is even.

An adaptive finite element procedure for solidification problems

An adaptive mesh regeneration procedure for transient solidification problems has been presented in this paper. The method is based on the local minimum and maximum values of second derivatives of velocity and temperature fields. A numerical example of alloy solidification in a square enclosure is presented for demonstration. Extension to more complicated and odd-shaped problems is straight forward.

Strict Fine Maxima

We provide a simple probabilistic proof of a result of J. Kral and I. Netuka: If $f$ is a measurable real-valued function on $\mathbb{R}^d$ ($d > 1$) then the set of points at which $f$ has a strict fine local maximum value is polar.

The relationship between resistivity and temperature in ordered α2-Ti3Al and γ-TiAl intermetallic compounds single crystals

Abstract The temperature dependence of the resistivity of ordered α 2 -Ti 3 Al and γ -TiAl intermetallic compounds single crystals with various compositions have been measured from 4.5 to 1120 K. The changes of resistivity and temperature coefficient of resistivity with the composition in Ti–Al system are investigated. It has been found that the ordered α 2 -Ti 3 Al intermetallic compounds single crystals have a large resistivity and show a negative temperature coefficient of resistivity with small absolute value, while the ordered γ -TiAl intermetallic compounds single crystals have a large value of resistivity too, but show a positive small temperature coefficient of resistivity. The resistivity in Ti–Al system changes with Al content systematically. There is a local maximum value near α 2 -Ti 75 Al 25 composition and a minimum value near γ -Ti 50 Al 50 . In the composition range of 10∼80 at.% Al, the temperature coefficient of resistivity of the system is less than 10 −3 K −1 . The above phenomena may be related to the very small electron mean free path and the ratio of the number of total covalence electrons to the number of total valence electrons. This kind of alloy, with a large resistivity (larger than 200 μΩ · cm), a small temperature coefficient of resistivity in a wide temperature range (4.5∼1120 K) and good linearity in resistivity-temperature curve, can be developed into precision resistance alloys used in the environment of high temperature, oxidation or corrosion.

RATE-DEPENDENT MODE II INTERLAMINAR FRACTURE BEHAVIOR OF CARBON-FIBER/EPOXY COMPOSITE LAMINATES

Effects of loading rate on mode II interlaminar fracture behavior of unidirectional CF/conventional-epoxy (T300/2500, Toray) and CF/toughened-epoxy (IM600/133, Toho Rayon) composite laminates were investigated over a wide range of loading rate from quasi-static to impact at room temperature (displacement rate, δ=10-7-101m/s). A newly developed experimental method using the SHPB (Split Hopkinson Pressure Bar) technique and the ENF (End Notched Flexure) specimen was employed for measuring the accurate fracture toughness at very high loading rates. The mode II fracture toughness at the onset of crack growth showed positive rate dependence (fracture toughness increased with increasing loading rate) at lower loading rates, while it showed negative rate dependence (fracture toughness decreased with increasing loading rate) at higher loading rates; there existed a local maximum value of fracture toughness at intermediate loading rates. The impact fracture toughness was about 13 and 29% lower than the local maximum value for the conventional epoxy composite and toughened epoxy composite, respectively; the toughened epoxy composite was more sensitive to the loading rate than the conventional epoxy composite. Microscopic observation showed that the debonding of fiber/matrix interface was dominant at lower loading rates and that the cohesive fracture of matrix resin was dominant at higher loading rates. The transition point of microscopic fracture morphology approximately coincided with the local maximum point of macroscopic fracture toughness. In addition, the load-displacement relation was non-linear just before the onset of crack growth at lower loading rates but almost linear up to the maximum point at higher loading rates.

Local maximum intensity projection (LMIP): a new rendering method for vascular visualization.

The purpose of our study was to demonstrate a new visualization method (local maximum intensity projection; LMIP) that can clearly depict densitometric as well as geometric information in vascular visualization from 3D data such as obtained from MR and CT angiography. LMIP is an extended version of maximum intensity projection (MIP). However, LMIP differs from MIP in that the latter method selects the maximum value along an optical ray, whereas LMIP selects the first local maximum value encountered that is larger than a preselected threshold value along an optical ray from a viewpoint in the viewing direction. Examples are presented in which LMIP is used to visualize renal vessels from CT angiography data and cerebral vessels in the vicinity of an aneurysm from phase-contrast MR angiography data. We demonstrate that LMIP can clearly depict geometric information, as shaded surface display does, and densitometric information, as is done by volume rendering, in a straightforward and objective manner.

Investigation on the melt flow properties of polyethylene and polypropylene blends

A blown-film extrusion grade polypropylene (PP) was melt-blended with an injection grade high density polyethylene (HDPE) and a blown-film extrusion grade low density polyethylene (LDPE) using a screw extruder, respectively, and the capillary flow properties such as flow curve, end effect, temperature and shear dependence of the shear viscosity for the blend melts were studied. With addition of the weight percentage content of PP (φ pp), the end pressure losses increased for PP/HDPE blends and decreased for PP/LDPE blends. The shear flow did not strictly obey the power law. The apparent shear viscosity (η a) was increased with addition of φ pp for both PP/HDPE and PP/LDPE blend melts. The flow properties of PP melt was obviously improved when it was melt-blended with a little HDPE or LDPE. The dependence of the shear viscosity (η w) for the blend melts on temperature accorded with the Arrhenius equation approximately. At a fixed wall shear stress, η w was increased with increasing φ pp, but a local maximum value occurred at φ pp = 50% for PP/LDPE blends and a local minimum value of η w appeared at φ pp = 20% for PP/HDPE blends.

Numerical analysis of temperature dependence of very-short-pulse-induced dynamic latchup in CMOS

The temperature dependence of very-short-pulse-induced dynamic latchup in CMOS is studied over a temperature range of 77–400 K through two-dimensional device simulation with fulltemperature models. When the trigger-pulse duration decreases below 10 ns the temperature dependence of latchup immunity comes to disagree with the results of previous other studies, showing that latchup immunity increases with decreasing temperature. For very short pulses latchup immunity decreases monotonously or has its local maximum value at about 120 K and then decreases as the temperature decreases. Pulse-induced dynamic latchup sensitivity at 77 K exceeds that at 300 K when the pulse duration becomes shorter than a certain very small value. This temperature dependence mechanism of very-short-pulse-induced latchup is discussed in detail.

Analysis of heat transfer with liquid-vapor phase change in a forced-flow fluid moving through porous media

This study focuses on the experimental analysis of transient-regime heat transfer with liquidvapor phase change in a fluid as it flows through a porous media composed of small bronze spheres. Three distinct zones can be observed: liquid, two-phase and superheated vapor. The boundaries between these zones are determined using temperature and pressure fields. An N-shaped profile is observed for the temperature values along the main flow axis. The first local maximum value on the temperature curve corresponds to the boundary between the liquid zone and the two-phase zone. When a local minimum temperature exists, it corresponds to the boundary between the two-phase and the vapor zones. A finite element numerical simulation is used to predict the saturation field, which is numerically determined from the boundaries of the two-phase zone and of the experimental temperature field. The liquid and vapor pressure fields are then deduced for all three phase zones of the porous medium.

Geroprotector efficiency depends on viability of control population: life span investigation in D. melanogaster

Ability of the radical spin trap 4-hydroxy-2,2,6,6,-tetramethyl-1-piperidine- N-oxyl (4-hydroxy-TemPO, (4HT)), to delay senescence in D. melanogaster has been studied. The spin trap, at a concentration of 0.2%, was added to the culture medium at the flies development stage. Reliable correlation ( r=0.76, P < 0.05) has been found between the viability of a control population, assessed by the mean life span (LS) value, and the level of LS alteration after geroprotector treatment in a corresponding experimental population. Thereby the local minimum values and local decreases in the mean LS in successive generations of the control line are associated most likely with LS extension effects in the corresponding experimental groups after 4HT treatment; and on the contrary, the local maximum values and local increases in the mean LS of the control line are associated more probably either with LS decreasing effects in the corresponding experimental groups or with the lack of significant differences between the control and experimental groups. A possible mechanism of the discovered phenomenon is discussed, based on the concept about free-radical activity variations. A probability approach to the evaluation of geroprotector efficiency in serial studies is proposed.

A new approach to the characterization of long-term changes in total atmospheric ozone: Determination and application of frequency distributions

This paper sets forth a new approach for describing long-term changes in total ozone by using frequency distributions and analyzing the extreme values. We applied this methodology to the database of column ozone provided by the Total Ozone Mapping Spectrometer aboard Nimbus 7. We examined a geographic region measuring 7.0° in latitude by 6.25° in longitude in the midwestern United States from 1979 to 1991. On any given spring day, individual ozone measurements in this region show a large variability, where the differences between the local noon maximum and minimum total ozone values sometimes exceed 100 Dobson units. Daily variability in total column ozone was shown to be greater in the spring than in the fall. Based on frequency distribution results, the most probable values for the spring season decreased from 1979–1982 to 1989–1991. During spring, the frequency of extremely low ozone values decreased from the six-year period 1980–1985 to the 1986–1991 time period, while the opposite situation prevailed during fall. Preliminary results indicate that this approach can illuminate the detailed behavior of TOZ within each season in a particular region.

The role of suspended matter in the distribution of dissolved inorganic phosphate, iron and aluminium in the Ems estuary

In winter 1992/1993, a persistent local maximum in fluorescence, dissolved iron, dissolved aluminium and dissolved inorganic phosphate was found, upstream of the turbidity maximum in the freshwater zone of the Ems estuary (The Netherlands — Federal Republic Germany; western Europe). Upstream of this local maximum values ranged from 6 to 9 rel. units fluorescence, 0.9 to 2.4 μmol dm−3 iron, 0.5 to 0.7 μmol dm−3 aluminium and 0.6 to 2.3 μmol dm−3 dissolved inorganic phosphate. Within the maximum peak values of 24 rel. units fluorescence, 5.8 μmol dm−3 iron, 1.4 μmol dm−3 aluminium and 8.3 μmol dm−3 dissolved inorganic phosphate were observed. Downstream, fluorescence (indicator of dissolved organic carbon) showed conservative mixing with sea water, whereas dissolved iron, aluminium and dissolved inorganic phosphate did not. Dissolved aluminium and iron were quickly removed from solution to reach values of ∼100 nmol dm−3 aluminium and ∼0.3 μmol·dm−3 Fe at salinities of approximately 7 PSU. Further seaward iron concentrations gradually decreased to levels below 0.04 μmol dm−3. Dissolved aluminium first decreased to ∼20 nmol dm−3 at 29 PSU and increased again to concentrations of 30–44 nmol dm−3 at higher salinities. Dissolved inorganic phosphate, however, first decreased to upstream concentrations before reaching a secondary peak in the mid-estuarine reaches. At salinities >25 PSU dissolved inorganic phosphate mixed conservatively with sea water. It is hypothesized that adsorption-desorption equilibria are responsible for the local maximum values of fluorescence (DOC), iron, aluminium and dissolved inorganic phosphate. The similarity between the observed curves suggests a common underlying process, possibly related to the adjustment of new equilibria between suspended matter of marine and riverine origin.

Effects of rotation of the stability and structure of tubular flame

The effect of rotation on the stability and structure of a tubular flame has been experimentally investigated. The concentration field of OH radical has been measured by laser-induced fluorescence, and the temperature field was examined using a fine thermocouple. Results show that, with increasing intensity of rotation, the lean limit of methane flame is decreased, and the stable flame region is expanded. The flame diameter is increased, and the inner flame structure is also changed. Namely, when the rotation is weak, the radial OH distribution takes an M-shaped profile; the concentration is low in the outer region of the unburned gas, increases and takes a local maximum value in the reaction zone, then falls around the center. With decreasing the fuel concentration Ω, the peak positions approach and the profile becomes Π-shaped. With further decreasing Ω, the profile becomes Λ-shaped; eventually, the flame is extinguished. Correspondingly, the peak value is decreased, increased, and decreased with decreasing Ω. However, when the rotation is intensified, the variation of the peak value becomes moderate, and the M-shaped profile is maintained close to extinction. The temperature measurement shows that, with increasing intensity of rotation, a temperature dip appears around the center and its magnitude becomes larger. Although this dip is usually attributed to radiative heat loss, the temperature at the center remains unchanged while the reaction zone temperature is increased; i.e., a protrusion in the reaction zone temperature occurs. This aspect resembles the excess enthalpy flame. Although the details of the extension mechanisms are unclear, these results suggest that the stability of the flame is enhanced by rotation through a mechanism like the excess enthalpy flame.

Three-Dimensional Visualization of Blood Flow in Vascular Structures

This study uses a flow simulation package on a graphics workstation to simulate the blood flow behavior in an abdominal aortic aneurysm and in the left ventricle (LV) of the heart. Both the simulation package and our own user developed graphics routines were used to view the three dimensional flow patterns. Vessel pressures and shear stresses both inside and outside of the vessel and heart LV could be observed, and our graphics routines allowed us to travel through the vessels. The asymmetric aneurysm was 8.0cm length and the Reynolds number was 700. In the aneurysm center, two symmetric vortices were formed, and flow separation started at the aneurysm inlet. Regions of high pressure were observed at the aneurysm exit caused by the symmetric vortices that were formed. The shear stress was low in the aneurysm portion of the vessel, and local maximum values were observed at the distal aneurysm constriction. A realistic model of the LV of the heart was constructed from a dog heart cast in diastole. The LV walls moved towards the center of the aortic outlet, and the left ventricular wall motion was assumed to follow the blood flow. This technique allowed effects such as cardiac infarction to be implemented, and showed complex flow field formation. In both the aneurysm and heart LV cases, having a three-dimensional graphics capability showed effects that would be difficult to observe with two-dimensional graphics and simulations only.

Wettability and Interfacial Reaction between Molten lron and Zirconia Substrates

The surface tension of, and the contact angle formed by, molten iron on three types of commercial zirconia substrates containing 8 mol% Y2O3, 9 mol% MgO, or 11 mol% CaO were measured over a wide range of oxygen concentration in the molten iron by the sessile drop method. The solidified metal–substrate interface was examined in an SEM equipped with an EPMA. The surface tension of molten iron decreased with increasing oxygen concentration. The contact angle of molten iron increased rapidly with increasing oxygen concentration and reached a local maximum value at an oxgyen concentration of ∼100 ppm, and then decreased with increasing oxygen concentration. At lower oxygen concentration, dissociation of ZrO2 was observed. For the ZrO2–9 mol% MgO substrate, segregation of MgO to the interface was observed. For the ZrO2–11 mol% CaO substrate, segregation of CaO and the precipitation of small ZrO2 particles in the segregation layer of CaO were observed at the interface. Conversely, at higher oxygen concentration, penetration of molten iron into the grain boundaries was observed in all types of zirconia substrates.

Wavelet Analysis of Coherent Structures at the Atmosphere-Forest Interface

Abstract Wavelet analysis was applied to turbulence data for temperature and vertical velocity within and above a deciduous forest. This method appears to provide an objective technique for examining thermal and flow fields associated with coherent structures occurring near the forest. The two-dimensional unfolding in time and scale by the wavelet transform illustrates discrete warm and cool centers associated with organized updrafts and downdrafts, which have similar patterns but different magnitudes at different heights. Wavelet variances computed for temperature and velocity at different heights appear to have local maximum values corresponding to certain time scales, which are self-consistent and useful for objective determination of the principal time scale of the structures. Within the canopy, the principal time scales of the structures determined by this technique are 56–60 s and 40–44 s for the temperature and vertical velocity fields, respectively. These time scales are close to those determined ...