Slight Inhomogeneity Research Articles

Phenotypic Characterization of the Martina Franca Donkey: An Endangered Italian Donkey Breed.

The Martina Franca (MF) donkey breed (Equus asinus) primarily inhabits the rural areas surrounding the homonymous municipality, as well as neighboring municipalities in the provinces of Bari and Brindisi, all located in the Apulia region of Italy. The objective of this study was to assess the current phenotype through the evaluation of 27 morphologic measurements. The study was conducted on 73 female and 18 male breeding animals from eight different herds located in central and southern Italy. Statistical analysis was performed in order to demonstrate statistical differences between males and females, as well as sexual dimorphism and uniformity of all measurements in both genders. The results demonstrated that the mean of three parameters used for the evaluation of an MF donkey (height at withers, circumference of thorax, and shin circumference) are highly representative of the population, with minimal dispersion Cv^ = 0.05-0.06 up to a maximum of 10%, as evidenced by relatively low standard deviations across observed measurements in both genders. Regarding sexual dimorphism, a statistically significant difference was found between males and females. This dimorphism is linked to reproductive activity and is useful during gestation. Overall, our findings suggest that the MF donkey phenotype has been largely preserved over time with high uniformity in males, slight inhomogeneity in the female population, and less variability in both genders.

Identification of the compressive trigonal crystal field and orbital polarization in strained monolayer α-RuCl3 on graphite

α-RuCl3 is a tantalizing playground to search for the quantum spin liquid states with leading Kitaev term due to the conformation of Jackeli–Khaliullin mechanism. Suppressing the non-Kitaev interaction to approach the Kitaev limit is the major objective in the experimental design of Kitaev–Jackeli–Khaliullin materials, for which the practical feasibility rests on the manipulation of the exact crystalline structure. A tensile strain, leading to the further compressive trigonal field splitting which would alter the spin-orbital entangled character and tune the intrinsic hopping exchanges, has been widely proposed as the promising strategy to enhance the comparative Kitaev interaction. In this work, we preform in-depth Scan Tunneling Microscope study on the electronic patterns of strained α-RuCl3 monolayer on graphite substrate. Based on Chen’s derivative rule, a further trigonal field splitting is identified by analyzing the lateral-gradient imaging effect caused by an anisotropic tip. A spatial variation of the magnitude of trigonal crystal field due to the slight inhomogeneity of strain accords with the orbital polarization near the Mott gap. All evidences point to the facts that the compressive trigonal crystal field in the stretched α-RuCl3 monolayer lifts the degeneracy of t2g states with higher text{e}_{text{g}}' and lower a1g orbitals, and the Coulomb interactions of the text{e}_{text{g}}' orbitals take the main responsibility for the Mott effect.

Phoretic self-propulsion of a slightly inhomogeneous disc

In two dimensions, the problem governing a homogeneous phoretic swimmer of circular cross-section is ill-posed because of the logarithmic divergence associated with a purely diffusive solute transport. We address here the well-posed problem that is devised by introducing a slight inhomogeneity in the interfacial chemical activity. With the radial symmetry being perturbed, phoretic motion is animated by diffusio-osmosis. Solute advection, associated with that motion, becomes comparable to diffusion at large distances. The singular problem associated with that scale disparity is analysed using matched asymptotic expansions for arbitrary values of the Damköhler number $\textit {Da}$ and the intrinsic Péclet number $\textit {Pe}$ . Asymptotic matching provides an implicit equation for the particle velocity in terms of these two parameters. The velocity exhibits a non-trivial dependence upon the sign $M$ of the slip coefficient. For $M=-1$ , we observe the appearance of several solutions beyond a $\textit {Da}$ -dependent critical value of $\textit {Pe}$ . We also address the respective limits of small and large $\textit {Da}$ for fixed $\textit {Pe}$ and arbitrary inhomogeneity, and illuminate their linkage to the limit of weak inhomogeneity.

Quantitative imaging of bone remodeling in patients with a unicompartmental joint unloading knee implant (ATLAS Knee System)\u2014effect of metal artifacts on a SPECT-CT-based quantification

BackgroundSPECT-CT using radiolabeled phosphonates is considered a standard for assessing bone metabolism (e.g., in patients with osteoarthritis of knee joints). However, SPECT can be influenced by metal artifacts in CT caused by endoprostheses affecting attenuation correction. The current study examined the effects of metal artifacts in CT of a specific endoprosthesis design on quantitative hybrid SPECT-CT imaging.The implant was positioned inside a phantom homogenously filled with activity (955 MBq 99mTc). CT imaging was performed for different X-ray tube currents (I = 10, 40, 125 mA) and table pitches (p = 0.562 and 1.375). X-ray tube voltage (U = 120 kVp) and primary collimation (16 × 0.625 mm) were kept constant for all scans. The CT reconstruction was performed with five different reconstruction kernels (slice thickness, 1.25 mm and 3.75 mm, each 512 × 512 matrix). Effects from metal artifacts were analyzed for different CT scans and reconstruction protocols. ROI analysis of CT and SPECT data was performed for two slice positions/volumes representing the typical locations for target structures relative to the prosthesis (e.g., femur and tibia). A reference region (homogenous activity concentration without influence from metal artifacts) was analyzed for comparison.ResultsSignificant effects caused by CT metal artifacts on attenuation-corrected SPECT were observed for the different slice positions, reconstructed slice thicknesses of CT data, and pitch and CT-reconstruction kernels used (all, p < 0.0001). Based on the optimization, a set of three protocols was identified minimizing the effect of CT metal artifacts on SPECT data. Regarding the reference region, the activity concentration in the anatomically correlated volume was underestimated by 8.9–10.1%. A slight inhomogeneity of the reconstructed activity concentration was detected inside the regions with a median up to 0.81% (p < 0.0001). Using an X-ray tube current of 40 mA showed the best result, balancing quantification and CT exposure.ConclusionThe results of this study demonstrate the need for the evaluation of SPECT-CT protocols in prosthesis imaging. Phantom experiments demonstrated the possibility for quantitative SPECT-CT of bone turnover in a specific prosthesis design. Meanwhile, a systematic bias caused by metal implants on quantitative SPECT data has to be considered.

Characterization on Polyester Fibrous Panels and Their Homogeneity Assessment.

Nowadays, fibrous polyester materials are becoming one of the most important alternatives for controlling reverberation time by absorbing unwanted sound energy in the automobile and construction fields. Thus, it is worthy and meaningful to characterize their acoustic behavior. To do so, non-acoustic parameters, such as tortuosity, viscous and thermal characteristic lengths and thermal permeability, must be determined. Representative panels of polyester fibrous material manufactured by perpendicular laying technology are thus tested via the Bayesian reconstruction procedure. The estimated porosity and airflow resistivity are found in good agreement with those tested via direct measurements. In addition, the homogeneity of polyester fibrous panels was characterized by investigating the mean relative differences of inferred non-acoustic parameters from the direct and reverse orientation measurements. Some parameters, such as tortuosity, porosity and airflow resistivity, exhibit very low relative differences. It is found that most of the panels can be assumed homogeneous along with the panel thickness, the slight inhomogeneity mostly affecting the thermal characteristic length.

Spatial Distribution of the Micro-Mechanical Properties in High-Translucent CAD/CAM Resin-Composite Blocks.

Industrially cured, high-translucent computer-aided design/computer-aided manufacturing (CAD/CAM) resin-based composites (RBC) are the most recently launched dental restoratives. Clinical treatments and laboratory tests are based on a homogeneous distribution of properties within CAD/CAM blocks to obtain constant and reproducible results. The study therefore aims to determine the spatial distribution of various micro-mechanical parameters (Vickers hardness, Martens hardness, indentation modulus, creep, elastic and total indentation work) in five representative CAD/CAM RBCs. The properties of the tooth structure were evaluated under similar conditions. Filler size and shape were analyzed by scanning electron microscopy. A multivariate analysis (general linear model) identified a very strong influence of the material on all measured properties (p < 0.001; partial eta squared ηP2 > 0.943), whereby the most sensitive parameters when identifying differences within regions were the indentation modulus and the elastic indentation work. CAD/CAM RBC blocks show gradually varying properties that can increase or decrease from central to peripheral areas regardless of the chemical composition of the materials or the inorganic filler fraction. The degree of variation in the measured properties is material-specific and less than 8.7%. Clinical applications and in vitro study designs should consider slight inhomogeneity in CAD/CAM RBC blocks, while the location of the regions with best mechanical performance depends on the material.

Directed energy deposition of AlSi10Mg: Single track nonscalability and bulk properties

Additive manufacturing of Al alloys presents an opportunity to produce complex parts that leverage their high specific strength. This paper aims to study the effect of processing parameters on the fabrication of single tracks and thin walls using AlSi10Mg powder in L-DED. A processing window was identified to enable continuous single track deposition with a regular shape. Deposition of thin walls and single tracks were used as a guideline to deposit blocks. Blocks were deposited using L-DED, and the physical, microstructural, and mechanical properties of the samples were investigated. Results demonstrated that the morphology of the thin walls were a better indicator of the morphology of the block samples than single tracks were, and care must be taken when transitioning from depositing single tracks to bulk (thin walls and blocks) samples. Results from mechanical testing show slight inhomogeneity as a function of height within the build for elongation and ultimate tensile strength. Microhardness and yield strength, however, were mostly uniform throughout the build. Overall, the results of this study demonstrate that L-DED is suitable for depositing AlSi10Mg and obtaining mechanical properties superior to those achieved through casting.

A rare case of adrenal cavernous hemangioma

Introduction. Adrenal cavernous hemangiomas are extremely rare non-functioning benign tumors. The majority of adrenal cavernous hemangiomas are diagnosed incidentally after surgery by histopathological examination. Case Report. We report a clinical case of a 57-year-old woman with adrenal cavernous hemangioma. On admission, the patient?s adrenal-related hormones were in the reference range, so adrenal endocrine dysfunction was ruled out. The computed tomography scan revealed a well-circumscribed, round, heterogeneous right adrenal mass (32.3 x 55.4 mm). Iodinated contrast enhanced abdominal computed tomography showed a slight inhomogeneity. In this case, preoperative radiologic findings and absence of signs of local invasion indicated laparoscopic adrenalectomy. The patient underwent right transperitoneal adrenalectomy. Microscopic evaluation showed a sinusoidal dilatation and fibrotic septa, so postoperative diagnosis of adrenal cavernous hemangioma was made. Conclusion. In summary, we reported a case of an incidentally discovered non-functioning adrenal cavernous hemangioma treated by laparoscopic surgery. The diagnosis of adrenal cavernous hemangioma may be challenging, and it is commonly made after surgery, since it is frequently confirmed by histopathological examination.

Numerical Investigation of the Effect of Two-Dimensional Surface Waviness on the Current Density of Ion-Selective Membranes for Electrodialysis

Ion-selective membranes are an important component of electrodialysis stacks for desalination. Manufacturing imperfections or slight inhomogeneity of the material can lead to minute membrane surface imperfections. Two-dimensional solutions of the coupled Poisson–Nernst–Planck and Navier–Stokes equations were sought for a perfectly smooth membrane and for membranes with well-defined small-amplitude harmonic surface roughness. The simulations were carried out with the validated rheoEFoam solver by Pimenta and Alves. In the overlimiting regime, the electric field is strong enough for an electrokinetic instability to occur. The instability leads to disturbance growth and the formation of electro-convection cells, which strongly increase the current density. The present simulations show that with an increasing ion concentration and applied voltage, the instability becomes stronger and the overlimiting regime is reached earlier. The limiting current density shows a noticeable dependence on the wavelength of the surface roughness. When the wavelength of the surface roughness is incommensurate with the wavelength of the naturally occurring instability, the limiting current density is increased. Since production membranes will always have some degree of surface roughness, this suggests that membrane surface treatments which favor certain wavelengths may have an effect on the overall membrane performance.

Production of Ultrafine Grained Hardmetals by Electrical Resistance Sintering

In this work, powders of cemented ultrafine WC-6 wt.% Co were consolidated. The feasibility of the medium frequency electrical resistance sintering (MF-ERS) technique were studied to prevent WC grain growth during consolidation. Porosity and hardness were measured at different zones of the MF-ERS compacts. The compacts showed a slight inhomogeneity in their properties across their section, but it was controlled by choosing suitable values of the processing parameters. The optimal values for the material studied were current intensities between 7 and 8 kA and sintering times between 600 and 800 ms. The main achievement using this consolidation method was that sintered compacts essentially maintained the initial WC grain size. This was attained to processing times of less than 2 s, and without the need for using protective atmospheres.

Mixture preparation and combustion in a GDI engine under stoichiometric or lean charge: an experimental and numerical study on an optically accessible engine

In direct injection spark ignition (SI) engines, the spray dynamics and interaction with the surrounding air flow are recognised as strongly affecting mixture quality, combustion development and amount of pollutants released at the exhaust. Spray impact against walls has also to be considered since undesired deposition of liquid as wallfilm causes unburned hydrocarbons and soot formation, hence increased fuel consumption and even augmented cyclic dispersion.Present work aims at clarifying the dynamics of sprays generated by multi-hole high pressure injectors in the combustion chamber of a gasoline direct injection (GDI) engine, as well as to characterize the combustion development and pollutants formation under various injection modes. Stoichiometric and lean operations are both studied into detail through a combined experimental and numerical approach. Experiments are conducted on an optically accessible engine, whereas numerical simulations are made after the development and validation of a three-dimensional (3D) sub-model reproducing at the best the spray dynamics also in its impact over walls.Early injection is shown to anyway determine at spark timing slight inhomogeneity in the equivalence ratio distribution of the stoichiometric charge, which makes for the flame propagation being anyway not spherical, but such to exhibit a preferential direction towards the richest zone of the combustion chamber. This leads to the formation of a pocket in the end gases where the knocking phenomenon is likely to occur under some circumstances. Lean charge operation is instead discussed as injection pressure and spark timing are varied to highlight mechanisms of formation of the main pollutants and to define routes for the development of proper engine control strategies. A deep insight in the in-cylinder thermo-fluidynamic processes is achieved thanks to the here followed synergic experimental-numerical approach.

Approximation model for refractive index slight inhomogeneity reverse determination of multilayers

实际应用中的薄膜或多或少存在体折射率不均匀缺陷，其准确表征对于镀膜工艺参数调校、低损耗薄膜设计与制备分析等具有影响。从Schr-der近似出发，推导了体折射率弱不均匀薄膜的膜系特征矩阵，通过特征矩阵法推广，建立了体折射率弱不均匀多层膜光谱特性计算的近似模型。利用基于有效介质理论的多层均匀膜近似方法，讨论了上述近似模型的有效性、计算精度和时间消耗特性。结果表明，上述模型矩阵计算中引入体折射不均匀度这一参数，为多层膜体折射率不均匀缺陷反演提供了一种有效的手段，为基于宽带光谱测量数据拟合的膜层缺陷数值反演应用奠定了基础。

Contribution of petrophysical analysis and 3D digital survey in the archaeometric investigations of the Emperor Hadrian’s Baths (Tivoli, Italy)

This work studies the Heliocaminus Baths. From an architectural point of view, this is a special and unique building in the complex of the Hadrian’s Villa in Tivoli. This research is carried out with a multidisciplinary approach combining petrophysical, petrographic and mineralogical characterization with the techniques of digital survey. The purpose of the research is to contribute to the understanding of Roman construction through the study of materials and from architectural aspects. Using mineral-petrographic and physical analysis, a set of samples (mortars and stones) was investigated for composition and physical properties (density, porosity, water absorption, mechanical strength, etc.). In the case of mortars, these parameters, together with the particle size distribution and the binder/aggregate ratio determined in two ways using image analysis (on thin sections and on specimens), have shown a relationship between the physical and compositional characteristics and the function of mortars within the structure of the Heliocaminus Baths. However, in some cases, different characteristics were detected between the mortars belonging to the same masonry and with same function in the building, showing a slight inhomogeneity in the production of mortars. Furthermore, some relationships between compositional, physical aspects (i.e. porosity, sorting and size of aggregate) and mechanical strength have been found. All the gathered data, linked to the point cloud 3D model, allowed an accurate location of the traces from the construction story of this structure.

Multi-scale local region based level set method for image segmentation in the presence of intensity inhomogeneity

Intensity inhomogeneity arising from the imperfect image acquisition process is a major challenge for image segmentation. Most of widely used image segmentation methods usually fail to segment the image with intensity inhomogeneity due to the assumption of intensity homogeneity. In this paper, an efficient multi-scale local region based level set method is proposed to segment the image with intensity inhomogeneity, which is based on the multi-scale segmentation and statistical analysis for intensities of local region. Firstly, the local region is defined in circular shape for capturing more local intensity information. The statistical analysis can be performed on intensities of local circular regions centered in each pixel by using multi-scale low-pass filtering. Then, the data term of level set energy functional can be constructed by approximating the normalized weighted image divided by multi-scale local intensity information in a piecewise constant way. In addition, the regularization term is built to control the smoothness of evolving curve and avoid the over-segmentation phenomenon and re-initialization step. Finally, the multi-scale segmentation is performed by minimizing the total level set energy functional by using the finite difference scheme. The experiments on synthetic and real images with slight or severe intensity inhomogeneity can demonstrate the efficiency and robustness of the proposed method. In addition, the comparisons with the recently popular local binary fitting (LBF) model and local Chan-Vese (LCV) model also show that our method has obvious superiority over the traditional local region based methods.

Impact of the irregular microgeometry of polyurethane foam on the macroscopic acoustic behavior predicted by a unit-cell model.

This paper deals with the prediction of the macroscopic sound absorption behavior of highly porous polyurethane foams using two unit-cell microstructure-based models recently developed by Doutres, Atalla, and Dong [J. Appl. Phys. 110, 064901 (2011); J. Appl. Phys. 113, 054901 (2013)]. In these models, the porous material is idealized as a packing of a tetrakaidecahedra unit-cell representative of the disordered network that constitutes the porous frame. The non-acoustic parameters involved in the classical Johnson-Champoux-Allard model (i.e., porosity, airflow resistivity, tortuosity, etc.) are derived from characteristic properties of the unit-cell and semi-empirical relationships. A global sensitivity analysis is performed on these two models in order to investigate how the variability associated with the measured unit-cell characteristics affects the models outputs. This allows identification of the possible limitations of a unit-cell micro-macro approach due to microstructure irregularity. The sensitivity analysis mainly shows that for moderately and highly reticulated polyurethane foams, the strut length parameter is the key parameter since it greatly impacts three important non-acoustic parameters and causes large uncertainty on the sound absorption coefficient even if its measurement variability is moderate. For foams with a slight inhomogeneity and anisotropy, a micro-macro model associated to cell size measurements should be preferred.

Evolution of Kosterlitz-Thouless-Berezinskii (BKT) Transition in Ultra-Thin NbN Films

We explore the Berezinskii-Kosterlitz-Thouless (BKT) transition in ultrathin NbN superconducting films. We have measured the super fluid density (ns∝1/λ2), normal carrier density and resistivity (ρ) of a set of NbN thin films. Our results show that while the ground state is well described by BCS theory, at elevated temperatures, ultra-thin films show sudden drop in superfluid density associated with the BKT transition close to superconducting transition temperature (Tc). The sudden drop starts at higher superfluid density than expected from 2D XY model, which can be understood by considering the low vortex core energy and slight inhomogeneity in the system. Resistivity data is explained using effective medium theory (EMT) including both Aslamazov-Larkin and KT fluctuations. This is also in good agreement with the corresponding superfluid density.

Emergence of a thin shell structure during collapse in isotropic coordinates

Numerical studies of gravitational collapse in isotropic coordinates have recently shown an interesting connection between the gravitational Lagrangian and black hole thermodynamics. A study of the actual spacetime was not the main focus of this work and, in particular, the rich and interesting structure of the interior has not been investigated in much detail and remains largely unknown. We elucidate its features by performing a numerical study of the spacetime in isotropic coordinates during gravitational collapse of a massless scalar field. The most salient feature to emerge is the formation of a thin shell of matter just inside the apparent horizon. The energy density and Ricci scalar peak at the shell and there is a jump discontinuity in the extrinsic curvature across the apparent horizon, the hallmark that a thin shell is present in its vicinity. At late stages of the collapse, the spacetime consists of two vacuum regions separated by the thin shell. The interior is described by an interesting collapsing isotropic universe. It tends towards a vacuum (never reaches a perfect vacuum) and there is a slight inhomogeneity in the interior that plays a crucial role in the collapse process as the areal radius tends to zero. The spacetime evolves towards a curvature (physical) singularity in the interior, both a Weyl and Ricci singularity. In the exterior, our numerical results match closely the analytical form of the Schwarzschild metric in isotropic coordinates, providing a strong test of our numerical code.

The Effect of Reinforcement Ratio on the Composite Structure and Mechanical Properties in Al-MgO Composites Produced by the Melt Stirring Method

In this study, Al- MgO metal matrix composites (MMC) were produced with 5 %, 10 % and 15 % reinforcement- volume (R-V) ratios by the melt stirring method. In the production of composites 99.5 % pure Al was used as the matrix and MgO powders with the particle size of −105 μm were used as the reinforcement. For every R-V ratio; stirring was made at 500 rev/min at 750°C liquid matrix temperature for 4 minutes and the samples were cooled under normal atmosphere. Then hardness and fracture strengths of the samples were determined and their micro structures were evaluated by using Scanning Electron Microscope (SEM). In general, it was observed that the reinforcement exhibited a homogeneous distribution in horizontal direction. But there is a slight inhomogeneity in vertical direction. It was determined that the increase in the R-V ratio increased the porosity and also the hardness. As for the fracture strength, the highest strength was obtained with the 5 % MgO reinforced sample.

Electrical breakdown mechanisms in vacuum diodes

The aim of this paper is to determine a statistical model which provides a satisfactory description of the “vacuum breakdown voltage” random variable and its relation to the vacuum breakdown mechanism. For that purpose, theoretical and experimental investigations of pulse and dc breakdown voltage statistical properties in two-electrode vacuum-insulated diodes were conducted. During the experiment vacuum pressures were 10 −9, 10 −6, 10 −4, 10 −3 bar and inter-electrode gaps were 0.1, 0.3 and 0.5 mm. Cylindrical copper electrodes with polished surfaces to a high glam were used. The field in the inter-electrode region was homogeneous with slight inhomogeneity at the edges of the electrode system (edge effects). According to results obtained it should be pointed out that, under conditions of the experiment, at the pressure value of 10 −9 bar breakdown mechanism is emission mechanism of cathode type, while at the pressure of 10 −6 and 10 −4 bar breakdown mechanism is combination of emission mechanism of cathode type and vacuum avalanche mechanism, while at the pressure of 10 −3 bar breakdown mechanism is Townsend gas mechanism with occurrence of anomal Paschen effect.

Solving inverse couple-stress problems via an element-free Galerkin (EFG) method and Gauss–Newton algorithm

This paper focuses on the identification of constitutive parameters in the couple stress problem. The direct problem is modeled by element-free Galerkin method (EFGM), thus the inconvenience that may be caused by C 1 continuity requirement in the implementation of FEM can be avoided, and the sensitivity analysis that is required for the solution process of the inverse problem can be carried out conveniently. The inverse problem is solved via the Gauss–Newton technique. The proposed method is verified in the cases of slight and strong regional inhomogeneity. The effects of initial guesses, noisy data and location of the measured points on the solutions are investigated, and satisfactory results are achieved.