Stratified Specimens Research Articles

Choke Anastomosis: A Key Element Acting as a Shunt Converter Between Adjacent Angiosomes.

Choke anastomosis is commonly recognized as a resistance factor that detrimentally affects the hemodynamics of the skin flap; however, its additional potential physiological roles in normal skin function are currently not fully understood. Ten cadaveric forehead flap specimens pedicled with unilateral STAs were perfused with lead oxide-gelatin mixture, and then dissected into 3 layers, including the super temporal fascia-frontalis-galea aponeurotica layer, the subcutaneous adipose tissue layer, and the "super-thin flap" layer. The forehead flap and stratified specimens underwent molybdenum target x-ray and subsequent transparent processing to effectively visualize the microscopic spatial architecture of arterial vessels across all levels. Based on the different anastomoses near the midline area of the flap, 2 types of arterial perfusion were identified: choke anastomosis type (8/10) and true anastomosis type (2/10). The former formed multiple choke anastomoses near the midline. In the "super-thin flap" layer, arterial perfusion density on the ipsilateral side was significantly higher compared to that on the contralateral side. The arterioles on the ipsilateral side exhibited a dense and uninterrupted distribution, whereas those on the contralateral side appeared sparse and dispersed. The latter exhibited an alternative perfusion pattern; the bilateral arterial vessels were connected with 3 to 5 true anastomoses near the midline. Furthermore, the microscopic architecture confirmed a uniform distribution of arterioles that remained continuous from ipsilateral to contralateral sides in the "super-thin flap" layer. This study demonstrated that choke anastomosis not only impairs blood perfusion in the adjacent angiosomes but also acts as a shunt converter to impact the blood supply of distal skin flaps at different levels through the "trans-territory diversion phenomenon." This results in necrosis of the superficial dermis while preserving survival of the deep subcutaneous adipose tissue.

Energy-based approach to study liquefaction triggering in homogeneous and stratified soils under consolidated undrained cyclic loading

Pore water pressure development through seismic effect is one of the key reasons for liquefaction failures in the foundations, dams, bridges, slopes and other vulnerable geotechnical engineering structures. The energy dissipation theories have provided a remarkable understanding of the pore water pressure generation inside a soil skeleton. In the present study, a series of consolidated undrained cyclic triaxial tests have been performed to evaluate the normalized dissipated energy (Wn) required for triggering liquefaction in both homogeneous and stratified soil specimens (prepared using silt interlayer) to replicate the site conditions nearby marine or alluvial deposits. The generated hysteresis loops using cyclic loading facilitate the calculation of dissipated energy. Also, the test results indicated a significant variation in the dissipated energy of homogeneous specimens at different magnitudes of cyclic stress ratios (CSR) and relative densities (Dr). With an increase in the cyclic stress ratio from 0.14 to 0.20, the trend of dissipated energy was observed to be different when relative densitie of sand varied from 30% to 65%. In the stratified specimens, thickness (t) and location of the silt layer (d) in the given soil specimen were the major influencing factors for estimating the liquefaction potential in loose conditions. Additionally, the highest value of Wn,max was obtained as 0.51 for the stratified specimen with topt = 28 mm at a cyclic stress ratio of 0.14. Based on the trendline variations, empirical models have been developed to estimate the normalized dissipated energy (Wn) for both homogeneous and stratified conditions. The developed models for homogeneous specimens are functions of CSR and Dr, whereas, in the case of stratified specimens, t, d and σd/σ'c (σd = deviator stress, σ'c = effective confining stress) have been utilized to predict the Wn with an satisfactory R2 value above 0.90. From the analysis of liquefaction resistance curves, the energy-based approach used in this study has been observed to provide more realistic results than the pore pressure ratio and strain-based failure criteria.

Cyclic behaviour of stratified soil under liquefied states

A substantial amount of work on the cyclic behaviour of cohesionless soil has been performed after neglecting the reality of stratification existing nearby marine structures or alluvial plains. This complicated mechanism of stratified soil failure on earthquake-induced soil liquefaction is affected significantly by the presence of a less permeable soil layer. Several past studies investigated that under the action of dynamic loads, the presence of a silt layer in homogeneous sandy soil crucially modifies the pore pressure dissipation characteristics, axial strain rate and stress–strain behaviour of the whole stratified specimen. In the present study, cyclic behaviour of sand specimen interlayered with silt layer has been presented in respect of its pre-and post-liquefaction behaviour. Undrained stress-controlled cyclic triaxial tests have been performed on homogeneous sand specimens and on specimens interlayered with a silt layer, placed at H/4, H/2 and 3H/4 (where H is the height of the specimen from the top) to signify the role of placement depth. The instability and failure of such specimens have been compared using the failure line and phase transformation line. Few key observations suggested that the number of liquefaction failure cycles enhanced two times and secant modulus (under post liquefied state) improved by 4.8 times when the placement depth of the silt layer increased from H/4 to 3H/4 under similar loading conditions. Additionally, the role of initial static shear stress has been investigated at three different confining pressures in a few stratified specimens. It has been observed that failure of the stratified specimen is due to the obstruction of pore water movement caused by the presence of the silt layer. A comparison of the present work has been made with significant studies using liquefaction resistant curves to ensure the efficacy of this study.

A compact and efficient angle-resolved X-ray fluorescence spectrometer for elemental depth profiling

An angle resolved X-ray fluorescence spectrometer based on the concept of scanning-free shallow detection with energy-dispersive area detectors is presented. The instrument is characterized with respect to energy resolution, linearity, angular discrimination and repeatability and the necessary data evaluation strategies are presented in detail. As demonstration of its capabilities and showcase for potential applications, two different copper indium gallium (di)selenide (CIGS) absorber layers, typically applied in thin film solar cells, are analyzed. In combination with quantitative (but integral) results for layer composition and layer thickness from a commercial XRF spectrometer, depth profiles of the Ga concentration of both ≈ 2 μm thin samples are obtained. The results of the novel spectrometer compare well with quantitative depth-profiles obtained from glow-discharge optical emission spectrometry. The combination of simplicity, stability and efficiency of the spectrometer concept makes it a potential candidate for industrial applications.Description of compact angle-resolved X-ray fluorescence spectrometer. Exploiting scanning-free grazing emission X-ray fluorescence approach. Energy dispersive charge-coupled device with single-photon detection. Enabling non-destructive, quantitative elemental depth profiling. Depth profiling of nano-structured stratified specimen, here CIGS solar cells.

Acoustic emission characteristics in hydraulic fracturing of stratified rocks: A laboratory study

Acoustic emission (AE) is a popular technique to monitor the process of rock failure during hydraulic fracturing for unconventional natural gas production. It contains abundant information that will be useful to study in-depth the nature of hydraulic fracturing. In this study, we focused on the AE count, energy, peak frequency, crack classification, and location recorded from four rock specimens subjected to a specific triaxial stress condition. We found the multi-frequency-response phenomenon of AE, and proposed the multi-frequency-response index to indicate the moment of the macrohydraulic crack formation. Furthermore, it was found that the power law distribution index of AE energy of non-stratified specimen was bigger than that of stratified specimens during hydraulic fracturing. The tensile crack dominated in all hydraulic fracturing tests. Our results are of significance for understanding hydraulic fracturing in stratified rocks.

Pleistocene vertebrates from the Kyparíssia lignite mine, Megalopolis Basin, S. Greece: Testudines, Aves, Suiformes

The mining activities in the Middle Pleistocene lacustrine basin of Megalopolis (Peloponnesus, Greece) have exposed expanded sections of lacustrine sediments. In particular, the northernmost mine of Kyparíssia has yielded numerous vertebrate fossils, recovered during field surveys and small-scale rescue excavations. The stratified specimens indicate the presence of at least two fossiliferous horizons, which are stratigraphically closely situated. The fossils are generally widely dispersed, but they are much more abundant along the western margin of the palaeolake. Four sites showing denser concentration of fossils were located and partially excavated during the 2004–2008 fieldwork. An additional site was identified and excavated in 2012. The fossils were found in organic-rich sediments (mostly lignites), indicating that they were deposited during a warm and humid (i.e., interglacial) time period, in a richly vegetated environment. The recovered fauna is diverse, dominated by hippopotamuses, deer and elephants. The present study presents the chelonian, avian and suiform finds. The following taxa are recognised: Emys orbicularis, Testudo marginata, Sus scrofa, Hippopotamus antiquus, as well as a diverse sample of aquatic birds. This faunal composition indicates a temperate, woodland/forest environment, with continuous presence of a large water body, whilst the presence of the darter (Anhinga sp.) points to relatively warm conditions. Biochronologically it points to an age within the early part of the Middle Pleistocene.

Cost Savings and Increased Efficiency Using a Stratified Specimen Pooling Strategy for Chlamydia trachomatis and Neisseria gonorrhoeae

Idaho Chlamydia trachomatis-Neisseria gonorrhoeae specimens from July 2009 were pooled by stratified specimen pooling, an approach that removes high-risk specimens from the pooling population and pools low-risk specimens to maximize pooling efficiency. This approach reduced pool positivity rates by 8%, repeated tests by 9%, and saved 47.4% in direct costs.

Measuring surface and grain boundary segregation using wavelength dispersive X-ray spectroscopy

Electron probe microanalysis (EPMA) using wavelength dispersive X-ray spectroscopy (EPMA-WDS) is applied to the quantification of surface and grain boundary monolayer segregation. The case of sulphur segregation in nickel and nickel alloys is considered. It is evidenced that EPMA-WDS is able to detect submonolayer surface segregation. The sulphur segregation can be accurately quantified from the sulphur Kα line relative intensity (ratio of the intensity measured on the sample and the intensity measured on a standard material) using the Stratagem™ software (analytical modelling of the X-ray emission in a stratified specimen based on the PhiRoZ model). The statistical accuracy of the technique and its detection limit are estimated to be as low as a few percents of a monolayer for reasonable counting times (∼ a few minutes). The advantages and drawbacks of EPMA-WDS with respect to Auger electron spectroscopy (AES) are discussed. The main advantage of EMPA-WDS is that it is almost insensitive to surface contamination and oxidation, which makes it possible to measure surface segregation on samples that have been in contact with atmosphere. The influence of specimen tilt is also discussed. The technique is also applied to the measurement of sulphur segregation on the fracture surface of an iron–nickel alloy sample broken at high temperature. It is thus demonstrated that EPMA-WDS could be a very useful tool for failure analysis in the case of grain boundary fractures.

TF_Quantif: a procedure for quantitative mapping of thin films on heterogeneous substrates in electron probe microanalysis (EPMA)

Electron probe microanalysis (EPMA) of stratified specimens has been intensively developed during the last few decades. Several quantification models (PAP, XPP, X-PHI) have led to many commercial software packages being widely used. However, all these software packages require an accurate description of the analysed sample because they are all based on the fundamental assumption that each layer of the sample is uniform in its structure and its composition. This is useful in the case of local analysis but may be problematic in the case of quantitative scanlines or quantitative maps. Indeed, a sample may not be homogeneous in all the analysed areas; this could lead to variations in the detected x-ray intensities and as a consequence to wrong results.Therefore, efforts have been carried out to analyse thin films on heterogeneous substrates. A method based on the measurement of the backscattering coefficient during x-ray microanalysis was developed in our laboratory. This method, called ‘Auger formalism’, gave good results in the case of thickness determination of pure coating on heterogeneous substrates and was also successfully applied in the case of multi-elements coating for concentration determination. However, in the case of concentration determination, this method requires knowledge of the film thickness. Thus, the aim of this work is to develop a new quantification procedure which is based on the same approach as previously adopted. This procedure allows a complete determination of both concentration and thickness from x-ray intensities of the coating associated with backscattering measurement. This method is called ‘TF_Quantif’.The performance of this quantification procedure is illustrated by different examples of application (thickness and composition maps determination of bi-element coatings on heterogeneous substrates).

Liquefaction of Clean Sand with Stratified Structure Due to Segregation of Particle Size

This study focused on the effects of stratified structure due to segregation of particle size and graded bedding in clean sand deposits on their liquefaction characteristics. A well-graded clean sand was sieved and separated into four components with different ranges of particle size, and then deposited alternatively to create stratified structure in specimens. Undrained triaxial compression tests in monotonic loading conditions and cyclic triaxial loading tests were performed on these stratified samples as well as the uniformly mixed samples of the same sand. It was observed that the liquefaction resistance of the stratified specimens was larger than the uniform specimens. These test results indicate a possibility of underestimation of liquefaction resistance of deposits with laminar structure in situ, if it is evaluated in the laboratory using homogeneously reconstituted samples.

About the role of the various types of secondary electrons (SE; SE; SE) on the performance of LVSEM.

The relative weight, delta(Beta), of the yield of secondary electrons, SE(2), induced by the backscattered electrons, BSE, with respect to that, delta(P), of secondary electrons, SE(1), induced by the primary electrons, PE, is deduced from simple theoretical considerations. At primary energies E(0) larger than E(M) (where the total SE yield delta = delta(P) + delta(B) is maximum), the dominant role of the backscattering events is established. It is illustrated in SEM by a direct comparison of the contrast between SE images and BSE images obtained at E(0) approximately 5 keV and E(0) approximately 15 keV on a stratified specimen. At energies E(0) less than E(M), the dominant role of SE(1) electrons with respect to SE(2) (and SE(3)) is established. It is illustrated by the better practical resolution of diamond images obtained with an in-lens detection in low voltage SEM E(0) approximately 0.2-1 keV range compared with that obtained with a lateral detector. The present contribution illustrates the improved performance of LVSEM in terms of contrast and of practical resolution as well as the importance of variable voltage methods for subsurface imaging. The common opinion that the practical lateral resolution is given by the incident spot diameter is also reconsidered in LVSEM.

X-Ray Microanalysis of Thin Surface Films and Coatings

The paper gives an overview of the present knowledge in the field of X-ray analysis of surface films and more generally stratified specimens. The aim of the paper is not to report the details and formulas of the available quantitative procedures, but to concentrate on the general ideas and orders of magnitude illustrating the capability and limits of the method, and on the optimal adaptation of the operating conditions to every particular problem. The various specific pitfalls which can be encountered are pointed out, in particular the fluorescence effects when using high-energy X-ray lines, or the anomalies due to chemical bonding, absorption uncertainties, and contamination effects when soft radiations are employed.

Quantification of the electron beam damage of thin films

Owing to diverse possible mechanisms of the e-beam damage, some changes either in the crystalline structure, chemical composition or film thickness occur as the proper “damage” of the virgin state. Changes in the chemical bonds are often connected with some change in thickness or structure so that the other two are the most important items to be detected, preferably in real time of the electron-microscopical or electron-spectroscopical examination. We propose to measure the film thickness on the basis of the most probable energy loss due to the electron pass through the film and back, i.e. on the basis of the position of the broad background maximum in the electron spectra of stratified specimens. A change in crystallinity can be sensed through the elastic peak intensity. Placing a measurement window between these features in the energy scale and measuring the energy filtered background during the irradiation, we get a pronounced dependence of the signal on the dose which unambiguously reveals the damage limit in the form of a curve knee. In some cases, two stages of damage are detectable.

Standardless X-ray analysis of bulk specimens

The paper gives an overview of the problems of Standardless analysis of bulk specimens by energy dispersive spectrometry (EDS) in scanning electron microscopes (SEM). The interest is concentrated on the present (and future) developments. The influence of the fluorescence excited by the continuum is discussed. Some improvements are proposed for the ionization cross-section. The difficulties due to the Coster-Kronig radiationless transitions are mentioned for the L lines. Emphasis is put on the necessity of an accurate modelling of the detector window, in order to be able to calculate reliably the efficiency of detection, mainly for the ultra-light elements. It is shown that some hypotheses such as the continuity of the fluorescence yield with the atomic number, which are currently accepted for heavier elements, could be wrong in the field of ultra-light elements. The capability of Standardless analysis in special situations is discussed: analysis at oblique electron beam incidence, analysis of specimens with a thin conductive coating, analysis of stratified specimens.

X-Ray microanalysis of stratified specimens

This paper presents a description of the state of the art methodology and software for the application of x-ray microanalysis to thin surface layers and more generally to the characterization of stratified specimens. The sensitivity of the technique to near-surface segregation is demonstrated. Some emphasis is given on the φ(ϱ z) function (the distribution in depth of the primary generated x-ray intensity), which is the key to all advanced quantitative procedures presently available. The main characteristics of the recently developed software packages. Strata and Multifilm are briefly described (physical basis, incorporation of fluorescence by lines and continuum, graphically assisted modes of operation, iterative mode of operation for the automatic determination of compositions and thicknesses). The capability of the technique is illustrated by three different applications: a bilayer on a substrate (case with no common element), a coated fibre (case with common elements and very light element analysis), a coated substrate analyzed in various geometrical conditions and by an “as soon as possible” procedure.

Some unconventional experiments cross correlating the techniques in surface analysis

Core electron loss spectroscopy (CELS) can be developed in parallel with Auger spectroscopy on the same specimen. Correlating the two spectroscopies improves the chemical information obtained. It also improves the quantification of the Auger spectroscopy because it allows to distinguish between a stratified specimen and a homogeneous one. The ultimate correlation is the development of a coincidence technique between energy loss electrons and Auger electrons. Correlating Auger spectroscopy and X-ray emission spectroscopy of coatings allows to evaluate their thickness from a fraction of an atomic layer up to a fraction of a micron. The determination of the Auger backscattering factor can be easily obtained by performing EDX experiments in a scanning electron microscope. High lateral resolution X-ray photoelectron spectra and images of thin films may also be obtained in a slightly modified Auger spectrometer allowing to correlate XPS, Auger and CELS information about the same specimen. XPS by backfoil excitation allows also to study radiation damage and charging effects that may occur on sensitive specimens when the lateral resolution of XPS is improved. All the proposed experiments do not require the use of sophisticated instruments but only a standard Auger equipment.

Macroscopic Shear Failure of Jointed and Stratified Brittle Materials

This paper contains a discussion of the macroscopic shearing strength of brittle materials in the discontinuous state such as joint systems or stratification in the materials.The plaster-sand model tests have been performed by the application of two types of direct shear test (box shear test and rock shear test) for jointed and stratified specimens in order to investigate their failure mechanism and anisotropy of the macroscopic shear strength and the dilatancy.These tests have made it clear that the macroscopic shear strength is affected by the failure mechanism which depends upon the movement of fractured particles after the crack formation around the joints or in the strata. The apparent resistances to the shear force for the jointed or stratified materials with positive inclination to the fictitious shear plane are less than for the materials with negative inclination.The jointed materials possesses less sensitivity against the anisotropy of strength and dilatancy with respect to the direction of discontinuous planes compared to the stratified materials.