Residual stress induced fracture in glass-sapphire composites: cylindrical geometry

A distinctive form of cracking is seen to occur as a result of the thermal exopansion mismatch stresses created between a cylindrical sapphire rod and a borosilicate glass matrix cooled after bonding at high temperature. The cracks, having a resemblance to cone cracks formed on Hertzian contract, nucleate at the free surface of the matrix in the vicinity of the rod intersection with the surface. However, rather than form at the rod/matrix interface, the cracks nucleate at some distance away that is found to vary from one sample to another. In general, the cracks extend further into the matrix the closer they nucleate to the rod. In addition, the crack trajectories vary both in angle to the rod axis and in shape, sometimes being curved. The crack path is calculated to be dependent on the relative magnitudes of the axial and radial residual stresses in the matrix. The cracks did not form immediately after cooling but only after exposure to the laboratory air. In some cases cracking was initiated by mechanical action, such as sectioning. In addition to the cone cracks at the ends of the rod, cone-like cracks were occasionally also seen to form from internal fractures of the sapphire rod on cooling after fabrication.     

Incremental beamwise backprojection using geometrical symmetries for 3D PET reconstruction in a cylindrical scanner geometry

Cho et al have proposed a fast backprojection scheme for parallel beam geometries, the incremental algorithm, which performs backprojection on a ray-by-ray (beam-by-beam) basis as opposed to a pixel-by-pixel approach. We present an extension of this incremental, beamwise, backprojection algorithm to the case of volume reconstruction of data acquired by a cylindrical, multiring positron tomograph. Use is made of geometrical symmetries of the image volume. This method results in a twelve-fold reduction of execution time compared with a straightforward, voxel-driven implementation of the same interpolation equations.     

Learning about environmental geometry: An associative model.

K. Cheng (1986) suggested that learning the geometry of enclosing surfaces takes place in a geometric module blind to other spatial information. Failures to find blocking or overshadowing of geometry learning by features near a goal seem consistent with this view. The authors present an operant model in which learning spatial features competes with geometry learning, as in the Rescorla-Wagner model. Relative total associative strength of cues at a location determines choice of that location and thus the frequencies of reward paired with each cue. The model shows how competitive learning of local features and geometry can appear to result in potentiation, blocking, or independence, depending on enclosure shape and kind of features. The model reproduces numerous findings from dry arenas and water mazes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

TLD Technique for Reducing Ice-Induced Vibration on Platforms

Tuned liquid damper (TLD) containers are designed to provide their sloshing forces in opposite directions against the inertia loads of the vibrating structure and thus to reduce the vibration. The sloshing forces that result from liquid motion may be determined either analytically or experimentally. The efficiency of the TLD in vibration reduction then can be estimated by attaching the TLD subsystem onto the dynamic equation of the vibrating structure. This paper describes investigations of the TLD system for an existing Bohai production jacket, which has routinely been excited by drifting ice during the winter seasons. In addition to a theoretical demonstration, a scaled model test and a full-scale field experiment were performed in this study. The technical strategy and main results of the investigation are presented in this paper.     

TLD extrapolation for skin dose determination in vivo

The conformational features of copper-free ceruloplasmin (CP), as compared to the holo-protein, were evaluated utilizing far- and near-UV circular dichroism and fluorescence spectroscopy. The results obtained indicate that apo-CP maintains the secondary structure of the holo-protein, while the tertiary interactions are much weaker. In addition, the removal of copper from the holo-protein leads to the exposure of hydrophobic patches to solvent, as shown by the fact that apo-CP, at variance from the holo-protein, binds the hydrophobic probe ANS. It is proposed that the CP molecule, upon copper removal, acquires the conformational features typical of a molten globule, which might be the conformational state of CP during its biosynthesis before metal incorporation.     

A new model for the volume fraction of martensitic transformations

A model using an energy balance is proposed to describe the volume fraction of multiple-interface martensitic transformations. For martensitic transformations without external stresses at quenching temperature T<M _s , the volume fraction of martensite (ξ) is proportional to the undercooling (M _s −T) and inversely proportional to a linear function of the quenching temperature (T); thus, ξ=(M _s −T)/[M _s −βM _f −(1−β)T], where β is a material constant. For stress-induced martensitic transformations under stress σ _ik ^a with temperature T>M _s , the relationship is ξ = ξ₀[1 - λ _ik ^σ (σ _ik ^Ms ]^-1, where ξ ₀ is the initial detectable amount of martensite formed at martensitic starting stress σ _ik ^Ms and λ _ik ^σ is a material constant. It is found that the results obtained from this model are in good agreement with experimental results.     

An associative model of geometry learning: A modified choice rule.

In a recent article, the authors (Miller & Shettleworth, 2007; see record 2007-09968-001) showed how the apparently exceptional features of behavior in geometry learning ("reorientation") experiments can be modeled by assuming that geometric and other features at given locations in an arena are learned competitively as in the Rescorla-Wagner model and that the probability of visiting a location is proportional to the total associative strength of cues at that location relative to that of all relevant locations. Reinforced or unreinforced visits to locations drive changes in associative strengths. Dawson, Kelly, Spetch, and Dupuis (2008; see record 2008-09669-009) have correctly pointed out that at parameter values outside the ranges the authors used to simulate a body of real experiments, our equation for choice probabilities can give impossible and/or wildly fluctuating results. Here, the authors show that a simple modification of the choice rule eliminates this problem while retaining the transparent way in which the model relates spatial choice to competitive associative learning of cue values. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A constitutive model for the tensile deformation of a binary aluminum alloy at high fractions of solid

Tensile tests were performed on alloy Al-4.5 pct Cu with a solidification unit dubbed the direct chill surface simulator (DCSS) that simulates the primary cooling conditions encountered during the direct chill (DC) casting process of sheet ingots. The curves obtained showed a near linear increase of the load with strain up to the point where nonlinearity induced by hot tearing prevented further increase of the load. A constitutive model based on the Lahaie-Bouchard stress-strain theoretical model was generalized by assuming a nonsingular channel thickness distribution. This approach considers a fully lubricated arrangement that allows grain boundary sliding as the most important mechanism of accommodation. As the strain increases, the grain boundaries become more and more subjected to friction sliding and oppose a higher resistance than a fully lubricated sliding condition. This results in a gradual increase of stress with strain. The important variables of the model include solid fraction, channel thickness, geometric standard deviation, and creep law parameters. The model seems appropriate to correlate the tensile behavior of semisolid microstructures having up to 30 pct liquid phase distributed over a large spectrum of grain morphologies.     

TLD array for precise dose measurements in stereotactic radiation techniques

We developed a new TLD array for precise dose measurement and verification of the spatial dose distribution in small radiation targets. It consists of a hemicylindrical, tissue-equivalent rod made of polystyrene with 17 parallel moulds for an exact positioning of each TLD. The spatial resolution of the TLD array was evaluated using the Leskell spherical phantom. Dose planning was performed with KULA 4.4 under stereotactic conditions on axial CT images. In the Leksell gamma unit the TLD array was irradiated with a maximal dose of 10 Gy with an unplugged 14 mm collimator. The doses delivered to the TLDs were rechecked by diode detector and film dosimetry and compared to the computer-generated dose profile. We found excellent agreement of our measured values, even at the critical penumbra decline. For the 14 mm and 18 mm collimator and for the 11 mm collimator combination we compared the measured and calculated data at full width at half maximum. This TLD array may be useful for phantom or tissue model studies on the spatial dose distribution in confined radiation targets as used in stereotactic radiotherapy.     

Effects of physical parameters on the cylindrical model for volume measurement by conductance

A simple fiber length-reduction method was developed to obtain a large amount of fiber samples with different length distributions for use in various biological experiments. This press method is only to press a raw fiber sample charged in a stainless cylinder at an adequate pressure, and is effective for man-made mineral fibers (MMMF) such as glass wool, rock wool and wool and refractory fibers (ceramic fibers, mullite fibers) and some brittle natural mineral fibers such as fibrous brucite and wollastonite. The mean fiber-length of man-made mineral fibers became shorter with the increase in the pressure applied without diameter change. We could obtain a length-reduced fiber sample with a suitable length distribution by this method. This press method is therefore a size-selective method able to produce a large amount of pulverized fiber sample depending on the press cylinder size for biological experiments. A very small amount of non-fibrous particles with aspect ratios (length vs. diameter) of under 3 was seen in the pulverized fiber samples. To eliminate such non-fibrous particles as well as too long fibers from the sample, separation by sedimentation in water was somewhat effective.