Microscopic Variations Research Articles

A successive perturbation-based multiscale stochastic analysis method for composite materials

This paper introduces a successive perturbation-based method for multiscale stochastic analysis of heterogeneous materials such as composite materials. Microscopic random variations sometimes have a significant influence on homogenized material properties and microscopic stress fields. Therefore, multiscale stochastic problems should be analyzed to evaluate the reliability of composite structures. Further, in order to assess the result of numerical analysis of a composite structure, this type of uncertainty propagation should be taken into account. For this purpose, the successive perturbation based approach is proposed.As a numerical example, the stochastic homogenization and multiscale stochastic stress analysis problem of composite materials are solved considering microscopic random variations. From the numerical results, the proposed approach gives a more accurate estimation than the conventional perturbation approach. Also, our proposed method works well for both smooth nonlinear response functions and non-smooth response functions.

Numerical study of the effects of injector needle movement and the nozzle inclination angle on the internal fluid flow and spray structure of a group-hole nozzle layout

In this study, we explored the spray behavior as a result of microscopic variations in the flow characteristics when the nozzle hole inclination angle was varied and the needle reciprocated. The volume fraction and viscosity contours were investigated at three needle modes of 0.01, 0.25, and 0.24mm using three nozzle inclination angles of 10°, 15°, and 30°. We determined the relationship between the two key parameters of liquid viscosity (which developed in the sac-volume and nozzles) and volume vapor fraction in the injector with the spray characteristics and the equivalence ratio by considering different needle positions and inter-nozzle angles as objective variables. It was found that a lower included angle led to higher viscosity development in nozzles with low cavitation formation, whereas increasing the inclination angle increased the viscosity amplitude in the sac-volume section and decreased the viscosity in the nozzles, as well as yielding more cavitation formation along the nozzles. The lowest viscosity was obtained with an inclination angle of 15°, which may facilitate the primary breakup process during spray atomization. The highest spray dispersion was achieved with a nozzle angle of 15°, which was due mostly to higher cavitation and a lower spatial viscosity distribution. Comparisons of the model and experimental data demonstrated the validity of the predicted spray structures based on simulations in terms of penetration and the droplet diameter.

An Analysis of Different Types of Arthritis with Joint Effusions among Kashmiri Population in a Tertiary Care Hospital.

Introduction: Arthritis is the initial manifestation of many joint disorders. Synovial fluid analysis helps in this aspect.Objective: To analyse the gross, microscopic and biochemical variations in the synovial fluid in various causes of joint effusions and to assess the synovial fluid cytology with biochemical parameters in various types of arthritis to increase the accuracy of diagnosis.Materials and Methods: In the present cross sectional study. Gross examination was done to find total volume, clarity, viscosity of the synovial fluid and it was equally divided into two halves. One half of synovial fluid was send for biochemical analysis and the other half for microscopic examination.Results: Out of 477 synovial fluid samples analysed. Total leucocyte count was found to be highest in septic arthritis and lowest in osteoarthritis. Neutrophils were highest in septic arthritis (95%) and lowest in osteoarthritis (24%). Sugar level in synovial fluid was highest in osteoarthritis and gouty arthritis (70-90 mg/dL each) and lowest in septic arthritis. Proteins were highest in rheumatoid arthritis and traumatic arthritis (4.1-6.5 gm/dL and 4.2-6.4 gm/dL respectively) and lowest in osteoarthritis (1.2-2.4 gm/dL). Out of 290 positive cases in synovial C-reactive protein levels, the highest were found in rheumatoid arthritis (130), rheumatoid factor was found positive in 143 cases while it was negative in 127 cases of osteoarthritis.Conclusion: Biochemical analysis of synovial fluid for proteins and sugar contributes in diagnosis of different types of arthritis. RF in synovial fluid proves to be of value in diagnosis of monoarticular arthritis.

Modeling Thermal Storage in Wax-Impregnated Foams with a Pore-Scale Submodel

Calculations of heat transfer through porous foams filled with phase-change materials are often performed using either an effective medium approach or a coupled two-temperature model. These models are generally applied to simulate heating processes that occur over a few hours, thus allowing for an assumption of effective melting front in which both liquid and solid phases are present or clear delineation of liquid and solid phases. However, in the instance of a rapidly changing heating process, a melting front cannot be assumed due to the possibility that layers of phases exist. A model has been developed to allow for variable phase sections within the foam without requiring an assumption of local thermal equilibrium, in which the temperature of the foam and phase-change materials are equal to each other at a set point. By assuming spherical pores with microscopic temperature variations therein, the model allows for the existence of multiple phases within a single foam pore while also integrating an effective medium model of the overall foam/wax system. The overall model is compared and validated with experimental results and models from literature. Following validation, cases are assessed under various time scales to demonstrate the model’s versatility.

Phase-resolved surface plasmon interferometry of graphene.

The surface plasmon polaritons (SPPs) of graphene reflect the microscopic spatial variations of underlying electronic structure and dynamics. Here, we excite and image the graphene SPP response in phase and amplitude by near-field interferometry. We develop an analytic cavity model that can self-consistently describe the SPP response function for edge, grain boundary, and defect SPP reflection and scattering. The derived SPP wave vector, damping, and carrier mobility agree with the results from more complex models. Spatial variations in the Fermi level and associated variations in dopant concentration reveal a nanoscale spatial inhomogeneity in the reduced conductivity at internal boundaries. The additional SPP phase information thus opens a new degree of freedom for spatial and spectral graphene SPP tuning and modulation for optoelectronics applications.

Ultrafast 2D IR microscopy.

We describe a microscope for measuring two-dimensional infrared (2D IR) spectra of heterogeneous samples with μm-scale spatial resolution, sub-picosecond time resolution, and the molecular structure information of 2D IR, enabling the measurement of vibrational dynamics through correlations in frequency, time, and space. The setup is based on a fully collinear "one beam" geometry in which all pulses propagate along the same optics. Polarization, chopping, and phase cycling are used to isolate the 2D IR signals of interest. In addition, we demonstrate the use of vibrational lifetime as a contrast agent for imaging microscopic variations in molecular environments.

Structured light scatteroscopy.

A new imaging approach, structured light scatteroscopy (SLS), is demonstrated, which offers rapid wide-field imaging of microscopic morphological variations in bulk tissue surfaces. Elastic scattering of light offers exquisite sensitivity to ultrastructural changes at multiple size scales ranging from nanometers to millimeters, but in bulk tissues the confounding effects of molecular absorption and strong multiple scattering of light often lead to a dramatic reduction in scatter contrast and specificity. It is demonstrated that the SLS using structured high spatial frequency illumination and detection to probe the tissue achieves direct, absorption-independent, high-resolution maps of the scattering response. The scattering response is observed to be dependent on both the wavelength and spatial frequency of choice, indicating a potential for multiscale probing of ultrastructural changes in superficial tissue layers. This methodology can be easily applied in most wide-field imaging systems.

Iron mapping using the temperature dependency of the magnetic susceptibility.

The assessment of iron content in brain white matter (WM) is of high importance for studying neurodegenerative diseases. While R2 * mapping and quantitative susceptibility mapping is suitable for iron mapping in gray matter, iron mapping in WM still remains an unsolved problem. We propose a new approach for iron mapping, independent of diamagnetic contributions of myelin by assessing the temperature dependency of the paramagnetic susceptibility. We used unfixed human brain slices for relaxometry and calculated R2 ' as a measure for microscopic susceptibility variations at several temperatures (4°C-37°C) at 3 Tesla. The temperature coefficient of R2 ' (TcR2p) was calculated by linear regression and related to the iron concentration found by subsequent superconducting quantum interference device (SQUID) magnetometry and by inductively coupled plasma mass spectrometry. In line with SQUID measurements, R2 ' mapping showed a linear temperature dependency of the bulk susceptibility with the highest slope in gray matter. Even in WM, TcR2p yielded a high linear correlation with the absolute iron concentration. According to Curie's law, only paramagnetic matter exhibits a temperature dependency while the diamagnetism shows no effect. We have demonstrated that the temperature coefficient (TcR2p) can be used as a measure of the paramagnetic susceptibility despite of an unknown diamagnetic background.

Rapid measurements of heterogeneity in sandstones using low-field nuclear magnetic resonance

Sandstone rocks can contain microscopic variations in composition that complicate interpretation of nuclear magnetic resonance (NMR) relaxation time measurements. In this work, methods for assessing the degree of sample heterogeneity are demonstrated in three sandstones. A two-dimensional T1–Δχapp correlation (where Δχapp is the apparent solid/liquid magnetic susceptibility contrast) reveals the microscopic heterogeneity in composition, whilst a spatially resolved T1 profile reveals the macroscopic structural heterogeneity. To perform these measurements efficiently, a rapid measure of longitudinal T1 relaxation time has been implemented on a low-field NMR spectrometer with a magnetic field strength B0=0.3T. The “double-shot” T1 pulse sequence is appropriate for analysis of porous materials in general. Example relaxation time distributions are presented for doped water phantoms to validate the method. The acquisition time of the double-shot T1 sequence is equivalent to the single-shot Carr–Purcell Meiboom–Gill (CPMG) sequence used routinely in petrophysics to measure transverse T2 relaxation. Rapid T1 measurements enable practical studies of core plugs at magnetic field strengths previously considered inappropriate, as T1 is independent of molecular diffusion through pore-scale (internal) magnetic field gradients.

Transition Temperatures

Despite intense experimental and theoretical efforts, it is still unclear why at temperatures of phase transitions, materials change completely their physical properties. Experimentally we are able to measure any microscopic, mesoscopic, and macroscopic variations of physical observables, but we still do not have a universal theoretical model that can predict all phase transitions, qualitatively and quantitatively. For instance, experimentally we can measure all physical properties of superconductors, but we do not have a unique theoretical model that is able to describe both types of superconductivity, namely the conventional and unconventional superconductivity. Here I present a simple quantum-mechanical and universal theoretical model that is able to calculate and predict critical temperatures for phase transitions: between magnetic order and disorder, superconductivity and normal conductivity, superconductivity and insulator, metal and insulator, melting and crystallization and many other phase transitions. All these phase transitions are described with four wave functions that are eigenfunctions of the Hamiltonian and the momentum operators.

Kelvin probe force microscopy of nanocrystalline TiO2 photoelectrodes

Dye-sensitized solar cells (DSCs) provide a promising third-generation photovoltaic concept based on the spectral sensitization of a wide-bandgap metal oxide. Although the nanocrystalline TiO2 photoelectrode of a DSC consists of sintered nanoparticles, there are few studies on the nanoscale properties. We focus on the microscopic work function and surface photovoltage (SPV) determination of TiO2 photoelectrodes using Kelvin probe force microscopy in combination with a tunable illumination system. A comparison of the surface potentials for TiO2 photoelectrodes sensitized with two different dyes, i.e., the standard dye N719 and a copper(I) bis(imine) complex, reveals an inverse orientation of the surface dipole. A higher surface potential was determined for an N719 photoelectrode. The surface potential increase due to the surface dipole correlates with a higher DSC performance. Concluding from this, microscopic surface potential variations, attributed to the complex nanostructure of the photoelectrode, influence the DSC performance. For both bare and sensitized TiO2 photoelectrodes, the measurements reveal microscopic inhomogeneities of more than 100 mV in the work function and show recombination time differences at different locations. The bandgap of 3.2 eV, determined by SPV spectroscopy, remained constant throughout the TiO2 layer. The effect of the built-in potential on the DSC performance at the TiO2/SnO2:F interface, investigated on a nanometer scale by KPFM measurements under visible light illumination, has not been resolved so far.

Misclassification of Plasmodium infections by conventional microscopy and the impact of remedial training on the proficiency of laboratory technicians in species identification

BackgroundMalaria diagnosis is largely dependent on the demonstration of parasites in stained blood films by conventional microscopy. Accurate identification of the infecting Plasmodium species relies on detailed examination of parasite morphological characteristics, such as size, shape, pigment granules, besides the size and shape of the parasitized red blood cells and presence of cell inclusions. This work explores misclassifications of four Plasmodium species by conventional microscopy relative to the proficiency of microscopists and morphological characteristics of the parasites on Giemsa-stained blood films.Case descriptionTen-day malaria microscopy remedial courses on parasite detection, species identification and parasite counting were conducted for public health and research laboratory personnel. Proficiency in species identification was assessed at the start (pre) and the end (post) of each course using known blood films of Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale and Plasmodium vivax infections with densities ranging from 1,000 to 30,000 parasites/μL. Outcomes were categorized as false negative, positive without speciation, P. falciparum, P. malariae, P. ovale, P. vivax and mixed infections.Discussion and evaluationReported findings are based on 1,878 P. falciparum, 483 P. malariae, 581 P. ovale and 438 P. vivax cumulative results collated from 2008 to 2010 remedial courses. Pre-training false negative and positive misclassifications without speciation were significantly lower on P. falciparum infections compared to non-falciparum infections (p < 0.0001). Post-training misclassifications decreased significantly compared to pre- training misclassifications which in turn led to significant improvements in the identification of the four species. However, P. falciparum infections were highly misclassified as mixed infections, P. ovale misclassified as P. vivax and P. vivax similarly misclassified as P. ovale (p < 0.05).ConclusionThese findings suggest that the misclassification of malaria species could be a common occurrence especially where non-falciparum infections are involved due to lack of requisite skills in microscopic diagnosis and variations in morphological characteristics within and between Plasmodium species. Remedial training might improve reliability of conventional light microscopy with respect to differentiation of Plasmodium infections.

Analysis of Heterogeneous Multiscale Methods for Long Time Wave Propagation Problems

In this paper, we analyze a multiscale method developed under the heterogeneous multiscale method (HMM) framework for numerical approximation of multiscale wave propagation problems in periodic media. In particular, we are interested in the long time $O(\varepsilon^{-2})$ wave propagation, where $\varepsilon$ represents the size of the microscopic variations in the media. In large time scales, the solutions of multiscale wave equations exhibit $O(1)$ dispersive effects which are not observed in short time scales. A typical HMM has two main components: a macromodel and a micromodel. The macromodel is incomplete and lacks a set of local data. In the setting of multiscale PDEs, one has to solve for the full oscillatory problem over local microscopic domains of size $\eta=O(\varepsilon)$ to upscale the parameter values which are missing in the macroscopic model. In this paper, we prove that if the microproblems are consistent with the macroscopic solutions, the HMM approximates the unknown parameter values in the macromodel up to any desired order of accuracy in terms of $\varepsilon/\eta$.

Mel e açúcar mascavo na cicatrização de feridas

O estudo teve como objetivo comparar a eficácia do mel e do açúcar mascavo na cicatrização de feridas induzidas cirurgicamente na pele de cobaias, para avaliar o tempo de cicatrização, as variações macroscópicas e microscópicas do tecido cicatricial, a contração das feridas e o grau de contaminação. Quinze cobaias da raça Abissínia, machos inteiros, de seis meses de idade e pesando entre 500 a 850 gramas, foram divididas em três grupos com cinco animais cada, nos quais foram induzidas, cirurgicamente, três feridas em cada animal com dimensão de 1,5cm² e distância entre elas de 1,5cm, na região dorsal. A ferida F1 foi tratada diariamente com mel, a ferida F2 com solução salina 0,9% (controle) e a ferida F3 com o açúcar mascavo. A eutanásia foi realizada no Grupo 1 ao sétimo dia após a cirurgia, no Grupo 2 ao décimo quarto dia e no Grupo 3 no vigésimo primeiro dia após a cirurgia, sendo as biópsias encaminhadas para avaliação histopatológica. Foram também realizados swabs das feridas em todos os grupos no terceiro e sétimo dias após a cirurgia e as amostras enviadas para a cultura e isolamento bacteriano. Concluiu-se que as feridas tratadas com o mel cicatrizaram mais rápido em relação às tratadas com o açúcar mascavo, demonstrando a maior propriedade cicatrizante do mel em relação ao açúcar mascavo.

Microscopic variations in interstitial and intracellular structure modulate the distribution of conduction delays and block in cardiac tissue with source-load mismatch

Reentrant activity in the heart is often correlated with heterogeneity in both the intracellular structure and the interstitial structure surrounding cells; however, the combined effect of cardiac microstructure and interstitial resistivity in regions of source-load mismatch is largely unknown. The aim of this study was to investigate how microstructural variations in cell arrangement and increased interstitial resistivity influence the spatial distribution of conduction delays and block in poorly coupled regions of tissue. Two-dimensional 0.6 cm × 0.6 cm computer models with idealized and realistic cellular structure were used to represent a monolayer of ventricular myocytes. Gap junction connections were distributed around the periphery of each cell at 10 μm intervals. Regions of source-load mismatch were added to the models by increasing the gap junction and interstitial resistivity in one-half of the tissue. Heterogeneity in cell shape and cell arrangement along the boundary between well-coupled and poorly coupled tissue increased variability in longitudinal conduction delays to as much as 10 ms before the onset of conduction block, resulting in wavefront breakthroughs with pronounced curvature at distinct points along the boundary. Increasing the effective interstitial resistivity reduced source-load mismatch at the transition boundary, which caused a decrease in longitudinal conduction delay and an increase in the number of wavefront breakthroughs. Microstructural variations in cardiac tissue facilitate the formation of isolated sites of wavefront breakthrough that may enable abnormal electrical activity in small regions of diseased tissue to develop into more widespread reentrant activity.

Scanning near‐field optical spectroscopy of AlGaN epitaxial layers

AbstractBand gap fluctuations and carrier localization in AlxGa1‐xN films with x values varying from 0.30 to 0.50 has been studied by scanning near‐field optical microscopy (SNOM) by measuring photoluminescence. The measurements have revealed a dual localization potential. Microscopic scale potential variations, detected by the SNOM, were most pronounced in the lower Al content samples. The nanoscopic carrier localization potentials, evaluated from the width of the photoluminescence spectra, were largest in layers with the largest AlN molar fraction. The large scale potential fluctuations were attributed to Ga rich regions close to grain boundaries or atomic layer steps. The density, size and band gap energy of these domains were found to be composition dependent. The nanoscopic potential variations have been assigned to small‐scale compositional fluctuations, possibly, occurring due to formation of Al rich grains during growth. (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Calculation of the effect of random superfluid density on the temperature dependence of the penetration depth

Microscopic variations in composition or structure can lead to nanoscale inhomogeneity in superconducting properties such as the magnetic penetration depth, but measurements of these properties are usually made on longer length scales. We solve a generalized London equation with a non-uniform penetration depth, lambda(r), obtaining an approximate solution for the disorder-averaged Meissner effect. We find that the effective penetration depth is different from the average penetration depth and is sensitive to the details of the disorder. These results indicate the need for caution when interpreting measurements of the penetration depth and its temperature dependence in systems which may be inhomogeneous.

Drying process in a solvent-based paint analyzed by phase-shifting digital holography and an estimation of time for tack free

A technique to study the drying of paints, based on phase-shifting digital holography, is presented. The technique is applied to the drying process of solvent-based paint on a three-dimensional surface at different substrate temperatures. For processing the data, a cross-correlation function and phase change derived from reconstructed complex amplitudes are calculated to visualize and to evaluate the local variations in the dryness of paint. The relationship between the optical signal obtained by the holographic method and the actual microscopic variations occurring in the paint film is also investigated using the gravimetric technique and a microscope. It is shown that the holographic technique can determine the stationary state of a painted surface corresponding to the end of the falling rate period in the drying process. The holographic technique detects mainly the activity on the surface and is applicable to assessment of the early drying process of paint.

Odontogenic Fibroma, Including Amyloid and Ossifying Variants

Sixty-five cases of odontogenic fibroma (OdonF) are herein presented having been segregated into peripheral, extra bony tumors (n=40) and tumors arising in bone or centrally (n=25). All cases were characterized microscopically by a fibrous proliferation that varied within and between cases in cellularity and collagen fibril diameter, with intermixed odontogenic epithelial islands and cords. All central lesions presented as well demarcated radiolucencies and resorption of contiguous tooth roots was a common finding. These intraosseous lesions were of the WHO type; the so-called nonWHO type was excluded as all lesions with this diagnosis were devoid of an epithelial component and could be reclassified as other soft tissue fibrogenic tumors. Neither the central tumors nor the peripheral lesions recurred following enucleation/curettage, with a mean follow-up of 4 and 3.4years respectively. Three distinct microscopic variations were encountered in this series: (1) two cases of OdonF with giant cell reaction, (2) two instances of OdonF with ossifying fibroma; and (3) four instances of OdonF with odontogenic ameloblast-associated protein (ODAM), an amyloid-like protein found deposited adjacent to epithelial cords plus CD1a+/S-100+ Langerhans dendritic cells entwined around the epithelial element. A single instance of the odontogenic fibroma-like hamartoma/enamel hypoplasia syndrome has been included in this series.

Hierarchical stochastic homogenization analysis of a particle reinforced composite material considering non-uniform distribution of microscopic random quantities

This paper discusses a stochastic homogenization problem for evaluation of stochastic characteristics of a homogenized elastic property of a particle reinforced composite material especially in case of considering a non-uniform distribution of a material property or geometry of a component material and its random variation. In practice, some microscopic random variations in composites may not be uniform. In this case, a non-uniformly distributed random variation of a microscopic material or geometrical property should be taken into account. For this problem, this paper proposes a hierarchical stochastic homogenization method. This method assumes that a two-phase composite material can be separated into three-scales, and propagation of the randomness through the different scales can be evaluated with the perturbation-based technique. As an example, stochastic characteristics of homogenized elastic properties of a glass-particle reinforced plastic are estimated using the proposed approach. With the numerical results, importance of the problem and validity of the proposed method are discussed.