The use of resonant scattering to identify stone fracture in shock wave lithotripsy

There is currently little feedback as to whether kidney stones have fractured during shock wave lithotripsy. Resonant scattering of the lithotripter shock wave was used here to differentiate intact and fractured stone models in water. Scattering, including reflection and radiation due to reverberation from within the stone, was calculated numerically with linear elasticity theory and agreed well with measurements made with a focused receiver. Identification of fracture was possible through frequency analysis, where scatter from fractured stones was characterized by higher energy in distinct bands. High-speed photography concurrent with measurement indicated the effect was not due to cavitation.     

A stepping stone to stochastic analysis

Some geometric aspects of classical field theory are presented and topologically non-trivial field configurations are introduced and discussed from this point of view. The Spinor Index Theorem is proven in a way which permits at the same time a discussion of first-order quantum corrections, in particular the axial-current anomaly.     

Suppression of large intraluminal bubble expansion in shock wave lithotripsy without compromising stone comminution: refinement of reflector geometry

Using the Hamilton model [Hamilton, J. Acoust. Soc. Am. 93, 1256-1266 (1993)], the effects of reflector geometry on the pulse profile and sequence of the shock waves produced by the original and upgraded reflector of an HM-3 lithotripter were evaluated qualitatively. Guided by this analysis, we have refined the geometry of the upgraded reflector to enhance its suppressive effect on intraluminal bubble expansion without compromising stone comminution in shock wave lithotripsy. Using the original HM-3 reflector at 20 kV, rupture of a standard vessel phantom made of cellulose hollow fiber (i.d. = 0.2 mm), in which degassed water seeded with ultrasound contrast agents was circulated, was produced at the lithotripter focus after about 30 shocks. In contrast, using the upgraded reflector at 24 kV no rupture of the vessel phantom could be produced within a 20-mm diameter around the lithotripter focus even after 200 shocks. On the other hand, stone comminution was comparable between the two reflector configurations, although slightly larger fragments were produced by the upgraded reflector. After 2000 shocks, stone comminution efficiency produced by the original HM-3 reflector at 20 kV is 97.15 +/- 1.92% (mean +/- SD), compared to 90.35 +/- 1.96% produced by the upgraded reflector at 24 kV (p<0.02). All together, it was found that the upgraded reflector could significantly reduce the propensity for vessel rupture in shock wave lithotripsy while maintaining satisfactory stone comminution.     

Suppression of large intraluminal bubble expansion in shock wave lithotripsy without compromising stone comminution: methodology and in vitro experiments.

To reduce the potential of vascular injury without compromising the stone comminution capability of a Dornier HM-3 lithotripter, we have devised a method to suppress intraluminal bubble expansion via in situ pulse superposition. A thin shell ellipsoidal reflector insert was designed and fabricated to fit snugly into the original reflector of an HM-3 lithotripter. The inner surface of the reflector insert shares the same first focus with the original HM-3 reflector, but has its second focus located 5 mm proximal to the generator than that of the HM-3 reflector. With this modification, the original lithotripter shock wave is partitioned into a leading lithotripter pulse (peak positive pressure of 46 MPa and positive pulse duration of 1 micros at 24 kV) and an ensuing second compressive wave of 10 MPa peak pressure and 2 micros pulse duration, separated from each other by about 4 micros. Superposition of the two waves leads to a selective truncation of the trailing tensile component of the lithotripter shock wave, and consequently, a reduction in the maximum bubble expansion up to 41% compared to that produced by the original reflector. The pulse amplitude and -6 dB beam width of the leading lithotripter shock wave from the upgraded reflector at 24 kV are comparable to that produced by the original HM-3 reflector at 20 kV. At the lithotripter focus, while only about 30 shocks are needed to cause a rupture of a blood vessel phantom made of cellulose hollow fiber (i.d.=0.2 mm) using the original HM-3 reflector at 20 kV, no rupture could be produced after 200 shocks using the upgraded reflector at 24 kV. On the other hand, after 100 shocks the upgraded reflector at 24 kV can achieve a stone comminution efficiency of 22%, which is better than the 18% efficiency produced by the original reflector at 20 kV (p = 0.043). All together, it has been shown in vitro that the upgraded reflector can produce satisfactory stone comminution while significantly reducing the potential for vessel rupture in shock wave lithotripsy.     

A mechanistic model of mid-latitude decadal climate variability

A simple heuristic model of coupled decadal ocean-atmosphere modes in middle latitudes is developed. Previous studies have treated atmospheric intrinsic variability as a linear stochastic process modified by a deterministic coupling to the ocean. The present paper takes an alternative view: based on observational, as well as process modeling results, it represents this variability in terms of irregular transitions between two anomalously persistent, high-latitude and low-latitude jet-stream states. Atmospheric behavior is thus governed by an equation analogous to that describing the trajectory of a particle in a double-well potential, subject to stochastic forcing. Oceanic adjustment to a positional shift in the atmospheric jet involves persistent circulation anomalies maintained by the action of baroclinic eddies; this process is parameterized in the model as a delayed oceanic response. The associated sea-surface temperature anomalies provide heat fluxes that affect atmospheric circulation by modifying the shape of the double-well potential. If the latter coupling is strong enough, the model’s spectrum exhibits a peak at a periodicity related to the ocean’s eddy-driven adjustment time. A nearly analytical approximation of the coupled model is used to study the sensitivity of this behavior to key model parameters.     

A study of mixed mode fracture by photoelasticity and digital image analysis

In this paper, the results from two experimental methodologies, photoelasticity aided by digital image processing and precision digital image correlation, are presented for a mixed mode fracture problem. The mixed mode fracture problem was a three-point-bend edge-crack specimen which was loaded at various off-crack-line locations between the crack line and the specimen support line. The estimations of K_I and K_II from both methodologies indicate that the crack tip stress field is strongly intensified by K_I but not K_II.     

A mechanistic model for the aging of human skin

The microinflammatory model of skin aging is described. This model accounts for the loss of elasticity, resiliene and flexibility of the dermis, as well as for the appearance of wrinkles and for the thinning of the epidermis which are associated with aging. The lack of appropriate apparatuses for the correct measurements of skin hydration does not allow one to test this model for its predictive capability of the appearance of dry skin with age. The micro-inflammatory model of skin aging fails to predict the appearance of age spots on the surface of the skin.     

The application of automatic fringe analysis in fracture mechanics

The likelihood of propagation of a crack in a metallic plate under load can be assessed by evaluating an energy-based contour integral, the J integral, for the loaded specimen. Calculation of the integral requires that the local stresses in the specimen are known. These stresses can be obtained practically by the use of strain gauges or by moiré fringe methods. This paper describes a semi-automatic, computer vision-based method of calculating the J integral when moiré fringe methods are used to evaluate the stresses in the specimen.     

Optical method of caustics applied in viscoelastic fracture analysis

The optical method of caustics is developed here to study the fracture of viscoelastic materials. By adopting a distribution of viscoelastic stress fields near the crack tip, the method of caustics is used to determine the viscoelastic fracture parameters from the caustic patterns near the crack tip. Two viscoelastic materials are studied. These are PMMA and ternary composites of HDPE/POE-g-MA/CaCO₃. The transmitted and reflective methods of caustics are performed separately to investigate viscoelastic fracture behaviors. The stress intensity factors (SIFs) versus time is determined by a series of shadow spot patterns combined with viscoelastic parameters evaluated by creep tests. In order to understand the viscoelastic fracture mechanisms of HDPE/POE-g-MA/CaCO₃ composites, their fracture surfaces are observed by a Scanning Electron Microscope (SEM). The results indicate that the method of caustics can be used to characterize the fracture behaviors of viscoelastic materials and further to optimize the design of polymer composites.     

An attempt at kidney stone analysis with the application of synchrotron radiation

X‐ray absorption near‐edge spectroscopy (XANES) is a spectroscopic technique using synchrotron light to determine the valence state of excited atoms as well as the electronegativity of their neighbouring atoms. XANES spectra can provide information about the chemical bond in the second coordination shell of the excited atom. In this study, XANES spectra of unknown compounds from human kidney stones were recorded around the K‐edges of sulfur, phosphorus and calcium. The XANES results agree well with the diffractogram data of the same stones obtained through an X‐ray powder diffraction (XRPD) technique. By comparing the measurement techniques presented here, it is shown that XANES requires a smaller amount of each sample than XRPD for analysis.     

Rotary ultrasonic machining of CFRP: A mechanistic predictive model for cutting force

Cutting force is one of the most important output variables in rotary ultrasonic machining (RUM) of carbon fiber reinforced plastic (CFRP) composites. Many experimental investigations on cutting force in RUM of CFRP have been reported. However, in the literature, there are no cutting force models for RUM of CFRP. This paper develops a mechanistic predictive model for cutting force in RUM of CFRP. The material removal mechanism of CFRP in RUM has been analyzed first. The model is based on the assumption that brittle fracture is the dominant mode of material removal. CFRP micromechanical analysis has been conducted to represent CFRP as an equivalent homogeneous material to obtain the mechanical properties of CFRP from its components. Based on this model, relationships between input variables (including ultrasonic vibration amplitude, tool rotation speed, feedrate, abrasive size, and abrasive concentration) and cutting force can be predicted. The relationships between input variables and important intermediate variables (indentation depth, effective contact time, and maximum impact force of single abrasive grain) have been investigated to explain predicted trends of cutting force. Experiments are conducted to verify the model, and experimental results agree well with predicted trends from this model.     

A mechanistic study on kinetic compensation effect during low-temperature oxidation of coal chars

This paper provides mechanistic insights into the low-temperature oxidation of a range of carbon materials (graphite, a sub-bituminous coal char, and a brown coal char). Kinetic analysis was carried out on oxidation of the chars, prepared from fast-heating pyrolysis, under chemical-reaction-controlled regime. FT-Raman spectroscopic analysis was adopted to provide direct structural information on the carbon structure of reacting carbon materials throughout oxidation. The results demonstrate the significance of selective oxidation under the conditions, and parallel to this, the kinetic compensation effect of carbon oxidation reaction throughout conversion for all samples. Supported by the results from FT-Raman spectroscopy, the kinetic compensation effect seems to be a result of the selective oxidation of these carbon materials with heterogeneous carbon structures. Oxidation of all samples, with or without catalysts, appears to be similar in terms of the ‘nature’ of carbon structural condensation during low-temperature oxidation, suggesting a similar increase in apparent active sites population with respect to increase of apparent energy barrier. Under the current experimental conditions, a general kinetic compensation effect correlation has been deduced for various materials, requiring only the initial char kinetic parameters. The inherent inorganic species in chars also seem to alter the ‘degree/extent’ of carbon structural condensation as results of selective oxidation. In this case, the use of the compensation effect correlation will require more information on the catalysis during oxidation, apart from the initial char kinetic parameters.     

打水漂游戏中的物理学

站在湖边 ,人们常喜爱用一块小石片在湖面上打水漂玩 .但在这个游戏背后有没有物理学呢 ?最近法国里昂大学的物理学教授L .Bocquet为了能确切地回答儿子提出的问题 ,他着手研究了这个物理问题 ,同时这也是他在写力学教科书时可用的一个例题 .他的问题是 :当你用石片打水漂时应考虑些什么参数才能使你的石片在湖面上跳跃的次数又多又好 ?他认为下列的参数是必需要考虑的 ,这就是 :石片的质量、石片的形状 .石片在抛出时相对于水面的角度 (这角度应愈小愈好 )、石片在飞行时的自旋转率 (旋转率愈高 ,石片运动得愈稳定 )以及石片飞行时的水平…     

Application of mid-infrared laser radiation for lithotripsy

The perforation effects of Er:YAG (2940 nm) and Ho:YAG (2100 nm) lasers radiation on human urinary stones model made from compressed plaster and real human samples were compared in vitro. For mid-infrared laser radiation delivery the special COP/Ag hollow glass waveguides were used. From the interaction experiments the perforation rates were derived and compared for both lasers. From the results it can be evaluated that Er:YAG laser radiation is favourable in comparison with Ho:YAG laser in case of artificial samples perforation efficiency.     

Combustion synthesis of nitrides: mechanistic studies

Combustion synthesis (CS) is characterized by extremely high heating rates (up to 10⁶ K/s) and temperatures (up to 4000 K), as well as short times of reaction completion (usually less than 1 s, sometimes even 10⁻³–10⁻² s). The above unique conditions lead to materials microstructure formation mechanisms that cannot be observed in the isothermal or quasi-isothermal cases. In turn, evolution of the reaction media microstructure influences characteristics (temperature, velocity) of the combustion wave. In this work, such microstructural effects are demonstrated on the examples of CS in different gas–solid systems (i.e., Si–N₂, Al–N₂, and Nb–N₂). It is shown that dilution of the reaction media by inert high surface area precursors with phase compositions similar to the CS product leads to a significant increase in combustion velocity in the Si–N system, while the temperature remains constant. Also, it is revealed that dispersion of the metal (Nb) particles in the preheating zone might be responsible for constancy of the combustion velocity as a function of the size of the initial reactants. Finally, a complex two-stage mechanism of AlN formation explains the non-monotonic shape of the temperature–time profile observed during CS in this system.