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.     

Micro‐Raman spectroscopy identification of urinary stone composition from ureteroscopic lithotripsy urine powder

Urolithiasis is a prevalent, disturbing, and highly recurrent disease. Knowing the composition of a urinary stone is important for prevention purposes. Traditional urinary stone analysis methods need large stone fragments for analysis. However, the advancement of ureteroscopic lithotripsy (URSL) has resulted in micro‐stone fragments and unapparently expelled urinary stone powder. In this study, we developed a micro‐Raman spectroscopy (MRS) based diagnosis method for detecting micro‐stones or stone powders in urine after URSL. In our experiment, urine samples of 10 ml each were collected from 12 patients over the fragmented stone site in the ureter after the URSL procedure. The post‐URSL urine sediments extracted from urine were analyzed by MRS. The small urinary stones caught by grasping forceps were analyzed by both MRS and Fourier‐transform infrared (FTIR) spectroscopy. We have identified common urinary stone compositions: calcium oxalate monohydrate (COM), calcium oxalate dihydrate (COD), dicalcium phosphate dihydrate (DCPD), calcium phosphate hydroxide (hydroxyl apatite or HAP), and uric acid, by using a 632.8 nm He‐Ne laser for excitation, a 100× microscope objective lens for irradiation and collection, and a short photobleaching time for fluorescent background reduction. Thus, we developed an MRS‐based method for analyzing the composition of urinary stone powders directly from the urine samples after the URSL procedure. This approach provides a quick and convenient method for urinary stone analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

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.     

Modern contaminants affecting microscopic residue analysis on stone tools: A word of caution

Residue analysis is a method frequently used to infer the function of stone tools and it is very often applied in combination with use-wear analysis. Beyond its undeniable potential, the method itself has several intrinsic constraints. Apart from the exceptional circumstances necessary for residues to survive, the correct identification of the residue type is a very debatable topic. Before attempting to recognise ancient residues, a proper method should allow analysts to identify possible modern contaminants and exclude them from the final interpretation. Therefore, analysts should not underestimate the presence of modern contaminants and might learn how to discriminate the background noise due to handling.The main aim of this research is to provide some methodological improvements to residue analysis through the characterisation of some modern residues often present on the surface of stone tools (e.g. skin flakes, modelling clay). This characterisation was done by using both optical light microscopy (OLM) and scanning electron microscopy (SEM).Finally, a special care in the post-excavation treatment of stone tools is claimed in order to avoid major contamination of the samples.     

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 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.     

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.     

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.     

A DFT‐based mechanistic study on the formation of oximes

Oxime chemistry has been proven to be a reliable bioconjugation method for biomedical applications. Because of its stable and bio‐orthogonal nature, a number of materials have been devised for in vitro and in vivo applications such as drug delivery, imaging, and biochemical assays. Polymers, synthetic molecules, nanoparticles, and biomolecules carrying alkoxyamine and aldehyde/ketone functional groups could be linked to each other through oxime bond, and a variety of modular platforms could be produced. Formation of oximes is catalyzed in acidic medium, and the proposed reaction mechanism follows classical imine formation pathways. Aniline has been found to accelerate the rate of oxime formation several orders of magnitude. In this computational study, we analyzed the proposed mechanism on model systems using DFT calculations including a solvation model. The energetics of the reaction steps in neutral and acidic conditions as well as in the presence of aniline was performed. Explicit water molecules were included in the calculations to study the energetics of solvent assisted proton transfer steps.     

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.     

New method development in prehistoric stone tool research: Evaluating use duration and data analysis protocols

Lithic microwear is a research field of prehistoric stone tool (lithic) analysis that has been developed with the aim to identify how stone tools were used. It has been shown that laser scanning confocal microscopy has the potential to be a useful quantitative tool in the study of prehistoric stone tool function. In this paper, two important lines of inquiry are investigated: (1) whether the texture of worn surfaces is constant under varying durations of tool use, and (2) the development of rapid objective data analysis protocols. This study reports on the attempt to further develop these areas of study and results in a better understanding of the complexities underlying the development of flexible analytical algorithms for surface analysis. The results show that when sampling is optimised, surface texture may be linked to contact material type, independent of use duration. Further research is needed to validate this finding and test an expanded range of contact materials. The use of automated analytical protocols has shown promise but is only reliable if sampling location and scale are defined. Results suggest that the sampling protocol reports on the degree of worn surface invasiveness, complicating the ability to investigate duration related textural characterisation.     

A mechanistic dichotomy in concerted versus stepwise pathways in hydride and hydrogen transfer reactions of NADH analogues

A mechanistic dichotomy of one‐step versus stepwise pathways in hydride and hydrogen transfer reactions of NADH analogues is discussed including the relation between two pathways: a continuous change versus a discontinuous change of the mechanism. Examples of stepwise electron–proton–electron transfer through a charge transfer (CT) complex in hydride transfer from NADH analogues to hydride acceptors are presented including the detection and the reactivity of the intermediate, that is, radical cations of NADH analogues. The relation between stepwise versus one‐step mechanisms of hydride and hydrogen transfer reaction of NADH analogues is also clarified by showing examples of the change of the mechanism including the borderline. Copyright © 2008 John Wiley & Sons, Ltd.