Scale Inhomogeneities Research Articles

Measuring the cosmic homogeneity scale with SDSS-IV DR16 quasars

We report measurements of the scale of cosmic homogeneity (rh) using the recently released quasar sample of the sixteenth data release of the Sloan Digital Sky Survey (SDSS-IV DR16). We perform our analysis in 2 redshift bins lying in the redshift interval 2.2 < z < 3.2 by means of the fractal dimension D_2. By adopting the usual assumption that rh is obtained when D2 ∼ 2.97, that is, within 1% of D2=3, we find the cosmic homogeneity scale with a decreasing trend with redshift, and in good agreement with the ΛCDM prediction. Our results confirm the presence of a homogeneity scale in the spatial distribution of quasars as predicted by the fundamental assumptions of the standard cosmological model.

The heterogeneous substructure of casein micelles evidenced by SAXS and NMR in demineralized samples

The casein micelle (CM) have been described as a protein assembly held together by interactions between phosphoryl groups from the protein moieties, and several internal calcium phosphate nanoclusters (CCPs). While the presence of protein inhomogeneities at the small scale, sequestering the CCPs, has been widely accepted, the presence of medium scale inhomogeneities, the so-called “Hard” regions, and its relationship with the CCPs, has been object of debate. In the present work, solid state NMR and SAXS data have been combined to study the correlation between the removal of CCPs and the structural modification of the micelle. A « native » sample and three different demineralized ones; 5% (DM-05), 10% (DM-10), and 25% (DM-25) of calcium in relation with the «native», have been analyzed. NMR data show that the reduction in the total amount of calcium and phosphorous ions (−5%, −10% and −25% respectively) in the samples is not always equivalent to the loss of CCPs as measured by the decrease of the amount of colloidal 31P (−15 and −17% and −25% respectively) in the samples. NMR data also indicate, that demineralization induces the total depletion of some CCP while leaving the remaining cluster in a rather « native » like structure. SAXS data show a good correlation between the amount of 31P loss measured by NMR and the decreases in intensity for the SAXS spectral features associated with the nanoclusters. Finally, SAXS data show the demineralization induces a decrease in the amount of the larger inhomogeneities in the micelle (the so called “Hard” regions). However, this decrease is not directly correlated to the decrease in the amount of CCPs (as measured by SAXS and NMR) indicating that these “Hard” regions may be, at least partially, maintained by a large protein-protein interaction network. The data and results are discussed and compared with different structural models of casein micelle.

Lagrangian theory of structure formation in relativistic cosmology. VI. Comparison with Szekeres exact solutions

We examine the relation between the Szekeres models and relativistic Lagrangian perturbation schemes, in particular the relativistic Zel'dovich approximation (RZA). We show that the second class of the Szekeres solutions is exactly contained within the RZA when the latter is restricted to an irrotational dust source with a flow-orthogonal foliation of spacetime. In such a case, the solution is governed by the first principal scalar invariant of the deformation field, proving a direct connection with a class of Newtonian three-dimensional solutions without symmetry. For the second class, a necessary and sufficient condition for the vanishing of cosmological backreaction on a scale of homogeneity is expressed through integral constraints. Domains with no backreaction can be smoothly matched, forming a lattice model, where exact deviations average out at a given scale of homogeneity, and the homogeneous and isotropic background is recovered as an average property of the model. Although the connection with the first class of Szekeres solutions is not straightforward, this class allows for the interpretation in terms of a spatial superposition of nonintersecting fluid lines, where each world line evolves independently and under the RZA model equations, but with different associated ``local backgrounds''. This points to the possibility of generalizing the Lagrangian perturbation schemes to structure formation models on evolving backgrounds, including global cosmological backreaction.

ANALYTICAL METHOD FOR DETERMINING THE INTERVAL OF SPATIAL CORRELATION OF FADING IN A SINGLE-BEAM DECAMETER RADIO LINE

An analytical method for determining the interval of spatial correlation of fades has been developed based on the analysis of fluctuations in the amplitude-phase front of a decameter wave during its propagation through the ionosphere with small-scale inhomogeneities of the electron concentration. Its analytical dependence on the characteristic scales of inhomogeneities and the standard deviation of the fluctuations of the wave phase front at the outlet of the inhomogeneous ionosphere has been obtained.

Construction of a method for detecting arbitrary hazard pollutants in the atmospheric air based on the structural function of the current pollutant concentrations

This paper reports the construction of a method for calculating the structural function within a moving window of the fixed size, based on measuring the vector of current concentrations of arbitrary air pollutants. The use of a moving window makes it possible to reveal the current moments of the emergence of inhomogeneities in the polluted atmosphere. In this case, the time shift of the structural function reveals the corresponding time scale of this heterogeneity. It has been shown that, in contrast to the known method, the proposed method makes it possible to reveal the dynamics of the levels and scales of local inhomogeneities of the polluted air using only the current measurements of concentration for an arbitrary number of pollutants. It is noted that the method does not use information about the current meteorological conditions of the atmosphere and the features of urban infrastructure near a pollution control point. Therefore, the method is universal; it could be applied to arbitrary control points of atmospheric pollution across various territories of states. The efficiency of the proposed method was tested using the example of actual measurements of the concentrations of urban air pollutants involving formaldehyde, ammonia, and nitrogen dioxide. The reported results generally indicate the applicability of the proposed method. It has been experimentally established that the method makes it possible to identify, in real time, the areas of local inhomogeneities characteristic of hazardous air pollution associated with the absence of dispersion and accumulation of pollutants in the air. In addition, the method makes it possible to detect in real time both the levels and the scale of inhomogeneities in the polluted atmosphere. It has been experimentally established that before the occurrence of the tested reliable emergency in a polluted atmosphere, the level of local heterogeneity was 0.015 units at its time scale corresponding to 8 counts. Next, by the time of the emergency, the level of heterogeneity decreased to 0.0025 units at the time scale corresponding to 2 counts. It has been experimentally established that for this case the forecast time of the occurrence of an emergency was 4 counts or 24 hours

Sub-basin scale inhomogeneity of mantle in the South China Sea revealed by magnesium isotopes

The South China Sea (SCS) is the largest extensional basin in the western Pacific and was formed after rifting of the Euro–Asian continental margin. The nature of its underlying mantle remains enigmatic due to the lack of sampling of the seafloor’s igneous crust. The International Ocean Discovery Program Expedition 349 cored seafloor basalts of the southwestern (Site U1433) and eastern (Site U1431) SCS sub-basins. The recovered basalt samples exhibit different source lithologies and geochemistries. The Mg isotopic compositions of seafloor basalts from these sites were investigated to elucidate the origin of this large-scale mantle inhomogeneity. Results indicate that the Site U1431 basalts have a mantle-like average δ26Mg value of –0.27‰ ± 0.06‰ (2SD; n = 10). Together with inhomogeneous Sr–Nd–Pb–Hf isotopic compositions, the Site U1433 basalts have an average δ26Mg value (–0.20‰ ± 0.06‰; 2SD; n = 8) higher than those of the Site U1431 basalts and normal mantle. Their heavier Mg isotopic compositions and low 206Pb/204Pb ratios (~17.7) indicate that the Site U1433 basalts were affected by the re-melting of detached continental-arc lithosphere in the sub-ridge mantle. The coupling of Mg and Sr–Nd isotopes provides robust evidence that the mantle-like δ26Mg values of the Site U1431 basalts resulted from mixing between detached continental arc lithosphere and the nearby Hainan plume, with respective supra- and sub-normal δ26Mg values. From the perspective of Mg isotope, the mantles of the southwestern and eastern sub-basins are compositionally inhomogeneous, with their mantle evolutionary histories being distinct.

Bilayer aberration-inducing gel phantom for high intensity focused ultrasound applications.

Aberrations induced by soft tissue inhomogeneities often complicate high-intensity focused ultrasound (HIFU) therapies. In this work, a bilayer phantom made from polyvinyl alcohol hydrogel and ballistic gel was built to mimic alternating layers of water-based and lipid tissues characteristic of an abdominal body wall and to reproducibly distort HIFU fields. The density, sound speed, and attenuation coefficient of each material were measured using a homogeneous gel layer. A surface with random topographical features was designed as an interface between gel layers using a 2D Fourier spectrum approach and replicating different spatial scales of tissue inhomogeneities. Distortion of the field of a 256-element 1.5 MHz HIFU array by the phantom was characterized through hydrophone measurements for linear and nonlinear beam focusing and compared to the corresponding distortion induced by an ex vivo porcine body wall of the same thickness. Both spatial shift and widening of the focal lobe were observed, as well as dramatic reduction in focal pressures caused by aberrations. The results suggest that the phantom produced levels of aberration that are similar to a real body wall and can serve as a research tool for studying HIFU effects as well as for developing algorithms for aberration correction.

Pull-in behaviors of micro-beam made of bidirectional functionally grade materials based on modified couple stress theory

In this paper, pull-in behavior of cantilever micro/nano beams made of bi directional functionally graded materials (BDFGM) with small scale effects under electrostatic force is investigated. Couple stress theory is employed to study the influence of small-scale on pull-in behavior. The material properties except Poisson’s ratio obey the arbitrary function in the thickness and length direction. The approximate analytical solutions for the pull-in voltage and pull-in displacement of the microbeams are derived using the Galerkin method. Comparison between the results of present work with other article for pull-in behavior of a microbeams made of isotropic material reveals the accuracy of this study. Numerical results explored the effects of material length scale parameter, inhomogeneity constant, gap distance and dimensionless thickness.

The Influence of Reactor Pressure on the Properties of GaN Layers Grown by MOVPE

We have studied the growth of GaN layers by the metalorganic vapor phase epitaxy (MOVPE) on sapphire substrates at various reactor pressures, including ones above the atmospheric level. It is established that the epitaxial growth at higher pressures does not affect the crystalline perfection of epilayers, their electron mobility, and background impurity level, but leads to the formation of GaN surface with lower lateral scale of inhomogeneities. In addition, the reactor pressure influences the ratio of edge and impurity lines in the photoluminescence spectra and leakage current level in reversely biased Schottky barriers.

Beauty in the eye of the beholder: a new species of gecko (Diplodactylidae:Lucasium) from inland north Queensland, Australia.

The Einasleigh Uplands bioregion of central north Queensland, Australia, harbours a unique suite of reptiles that have begun to receive significant attention in the last 20 years. This has resulted in a number of new reptile species being described, and recognition that others await description. We describe a new species of Lucasium Wermuth, 1965 from the western Einasleigh Uplands. Lucasium iris sp. nov. is genetically distinct and morphologically diagnosable from all congeners by its large size, long and narrow tail, nares in contact with rostral scale, homogeneous body scales, distinct vertebral stripe, and paired, enlarged, apical subdigital lamellae. It is known from low rocky hills in a localised area of the Gregory Range, has the most restricted known distribution of any Lucasium, and is the only Lucasium endemic to Queensland. The new species appears most closely related to L. steindachneri (Boulenger, 1885), based on mitochondrial DNA sequences, but has a colour-pattern more similar to L. immaculatum Storr, 1988. All three of these species occur in the Einasleigh Uplands, but only L. steindachneri is known to occur in sympatry with L. iris sp. nov. In addition to the description of the new species, we present records of Lucasium immaculatum from the Einasleigh Uplands, which represent a significant known range extension.

Attention-Aligned Network for Person Re-Identification

Currently, attention mechanism receives enormous interest and has been extensively employed in the fields of Person Re-Identification (RE-ID), as it gains superior performance in learning discriminative feature representations. However, most off-the-shelf attention methods are still vulnerable to cross-view inconsistency problem. Besides, they merely exploit imprecise channel attention information and coarse-grained spatial attention of homogeneous scales, being insufficient to capture subtle differences among highly-similar individuals. To this end, we propose a novel Attention-Aligned Network (AANet) to address the aforementioned problems, in which a novel Omnibearing Foreground-aware Attention (OFA) module, Attention Alignment Mechanism (AAM) and an improved triplet loss with hard mining are proposed to learn foreground attentive features for RE-ID. Specifically, AANet firstly leverages OFA module to exploit heterogeneous-scale spatial attention and foreground-aware channel attention information. Then AANet further reduces the impact of background clutter and learns camera-invariant and background-invariant representations by virtue of AAM. Last but not least, an improved triplet loss with hard mining is also introduced to enhance the feature learning capability, which can jointly minimize the intra-class distance and maximize the inter-class distance in each triplet unit. Extensive experiments are carried out to demonstrate that the proposed method outperforms most current methods on three main RE-ID benchmarks.

Solidity without inhomogeneity: perfectly homogeneous, weakly coupled, UV-complete solids

Solid-like behavior at low energies and long distances is usually associated with the spontaneous breaking of spatial translations at microscopic scales, as in the case of a lattice of atoms. We exhibit three quantum field theories that are renormalizable, Poincaré invariant, and weakly coupled, and that admit states that on the one hand are perfectly homogeneous down to arbitrarily short scales, and on the other hand have the same infrared dynamics as isotropic solids. All three examples presented here lead to the same peculiar solid at low energies, featuring very constrained interactions and transverse phonons that always propagate at the speed of light. In particular, they violate the well known {c}_L^2>frac{4}{3}{c}_T^2 bound, thus showing that it is possible to have a healthy renormalizable theory that at low energies exhibits a negative bulk modulus (we discuss how the associated instabilities are absent in the presence of suitable boundary conditions). We do not know whether such peculiarities are unavoidable features of large scale solid-like behavior in the absence of short scale inhomogeneities, or whether they simply reflect the limits of our imagination.

Different sodium enhancements among multiple populations of Milky Way globular clusters

We searched for clues to understand the different Na abundances measured in first and second generation stars of ancient Milky Way globular clusters. For that purpose, from the recent literature, we gathered the aforementioned Na abundances, orbital parameters, and structural and internal dynamical properties and ages in a homogeneous scale of 28 globular clusters. We found that the intra-cluster Na enrichment, which is measured by the difference of Na abundances between first and second generation stars, exhibits a trend as a function of the Na abundances of first generation stars, in the sense that the more Na-poor the first generation stars are, the larger the Na enrichment is. By using the inclinations of the globular clusters’ orbits, the analyzed Na enrichments also hinted at a boundary at ∼0.3 dex to differentiate globular clusters with an accreted or in situ origin, the accreted globular clusters having larger Na enrichments. Because relatively larger intra-cluster Na enhancements are seen in accreted globular clusters and small Na enhancements are observed in globular clusters formed in situ, although not exclusively, we speculate that the amplitude of the Na enrichment may be linked with the building block paradigm. Globular clusters at the time of formation of first and second generation stars would seem to keep a memory of this hierarchical galaxy formation process.

Hybrid energy efficient static routing protocol for homogeneous and heterogeneous large scale WSN

Wireless sensor networks consist of a large number of nodes deployed randomly in an area of interest. Theses nodes have sensing, computation, and wireless communications capabilities. In another hand nodes have energy constraints since they are equipped by non-rechargeable batteries. To handle this issue, routing protocols consist of designing the network in order to collect and transmit data with less energy consumption. In this paper we presented a new Hybrid Energy Efficient Static routing protocol (HEESR), combining between clustering and multi-hop routing techniques. HEESR is dividing the network into several levels. For each round, it creates clusters, route the collected data through gateways called Independent Nodes, elected using a new dynamic approach and introduces Dormant nodes. Finally, the proposed HEESR have improved network’s life time, throughput and other compared metrics, in both homogeneous and heterogeneous networks, and prolonged network’s stability zone up to 98.4% compared to LEACH, 98% compared to DEEC and up to 40.5% compared to SMR.

Cosmological homogeneity scale estimates are dressed

We investigate number count statistics as measures for transition to homogeneity of the matter distribution in the Universe and analyse how such statistics might be 'dressed' by the assumed survey selection function. Since the estimated survey selection function—which ideally accounts for selection bias in the observed distribution—is partially degenerate with the estimated underlying distribution of galaxies, the ability to identify the correct survey selection function is of importance for obtaining reliable estimates for clustering statistics. Selection functions of existing galaxy catalogues are modelled from data to resemble the redshift distribution and mean density of the observed galaxies. Proposed estimates of the selection function for upcoming surveys in addition use the angular distribution of galaxies to generate the angular selection function instead of using angular completeness estimates. We argue that such modelling of the selection function could potentially underestimate the deviance from homogeneity at scales probed by existing catalogues. We investigate the impact of conventionally applied methods for estimation of the survey selection function on number count in sphere statistics in a toy model setting. The example density distribution is asymptotically homogeneous, while non-linear density fluctuations are present regionally. We find that density oscillations with period comparable to characteristic scales of the survey are suppressed when conventional estimates of the survey selection function are invoked, resulting in number count statistics that are biased towards homogeneity. For our concrete toy model with maximum density contrasts of 1 and period of the density oscillation comparable in size to the survey radius, we find that the homogeneity scale is underestimated by ∼ 40%, however this quantitative result is dependent on the model setup including the form of the simplistic density field considered and the survey geometry.

On the entropy generation and exergy loss of laminar premixed flame under engine-relevant conditions

Analysis of entropy generation and exergy loss is effective and essential in evaluating the fuel efficiency in next-generation internal combustion (IC) engines that are expected to operate at higher pressures. At such conditions, the hybrid deflagration/autoignition flame structures may exist during the combustion process. However, currently, most of the studies on entropy generation of laminar premixed flame are performed for mixtures at normal temperatures and pressures, under which the flame is stabilized by heat and mass transfer. This study compares the entropy generation and exergy loss characteristics when the transition of regime under engine-relevant conditions occurs, which is identified based on the ratio of the corresponding flame to homogeneous ignition time scales. The results indicate that when the transition from flame propagation to autoignition front occurs, the entropy generation and exergy destruction sources from heat and species mass transfer vanish and become dominated by chemical reactions. The total entropy generation from chemical reaction increases due to the larger flame thickness and variations in fuel consumption pathway. The reaction pathway analysis reveals that for the flame stabilized by autoignition with initial temperature located in the region of low-temperature and negative temperature coefficient chemistry, a great part of the entropy generation is produced by the low-temperature pathway, with the maximum flux ratio over 60%. Thus, more attention should be paid on the optimization of fuel consumption pathways to minimize the combustion irreversibility.

To the Interchange Instability Criterion in the Magnetosphere in the Presence of Velocity Shear

AbstractIn this paper, we address the issue of interchange instability excitation criterion in the magnetospheric plasma in the presence of the velocity shear using a magnetohydrodynamic approach. We conducted our analysis for the arbitrary β plasma configuration using a WKB approximation for wavelengths, λ, much smaller than the characteristic plasma inhomogeneity scale, L, and found two branches of waves. These two wave branches can exist due to the plasma velocity shear and one branch can be unstable for arbitrary angles between the plasma entropy parameter and magnetic flux tube volume gradients. The implications of these results for magnetospheric physics as well as comparison of our results with corresponding analysis of other authors are discussed.

Measuring school leaders' adaptability in the UAE: development of a scale to measure leadership adaptability

PurposeThis paper presents a quantitative measurement instrument for Leadership Adaptability.Design/methodology/approachQualitative themes are examined, grouped and developed into 13 quantitative statements of Leadership Adaptability. A robust analysis is conducted to understand the relationships and underlying dimensions in the statements. Three types of dimension reduction techniques are employed: principal components analysis and two types of exploratory factor analysis. The instrument is tested in the form of a survey for the first time with public and private school leaders in the Emirate of Abu Dhabi (n = 167).FindingsThe quantitative Leadership Adaptability scale is validated by applying robust tests of dimensionality, validity and reliability. The three dimension reduction tests identified that the 13 statements are measuring a single dimension of Leadership Adaptability, and should therefore be treated as a single homogeneous scale. Reliability analyses further confirmed the results of the dimension reduction results, with a high score for Cronbach's alpha of 0.953, classified as an “excellent” level of reliability. Discriminant validity tests of the 13 statements, analysed alongside the 20-item Cultural Intelligence Scale, further confirmed the statements as being a distinct scale. Applying the instrument to Abu Dhabi school leaders showed they have high levels of adaptability.Originality/valueThis paper presents the first known quantitative measurement instrument for understanding Leadership Adaptability. This instrument addresses a need by developing a quantitative tool for researchers studying Leadership Adaptability, and it can be used to facilitate further exploration of this topic.

Long-term oxidation resistance and deterioration mechanism of magnetron sputtered Cr-Al-Si-N coatings on zirconium alloys in 1200 °C steam atmosphere

Oxidation behavior of magnetron sputtered Cr-Al-Si-N coatings on zirconium-alloy coupons was studied in 1200 °C steam up to 8 h, revealing the microstructural evolution and the oxidation resistance by electron microscopy. A ∼310 μm thick Zr-O layer formed on the uncoated coupon after the 6 h oxidation, whereas the coated coupon retained almost unoxidized, due to a homogenous and stable bilayer scale of Cr2O3/α-Al2O3 on the surface. It was assumed that the column-free structure and isotropic nanostructure of coatings could favor a timely and in situ formation of the bilayer scale, followed by long-term maintenance of its integrity.

Short-Wave Asymptotic Solutions of the Wave Equation with Localized Perturbations of the Velocity

To describe the propagation of waves in media containing localized rapidly changing inhomogeneities (e.g., narrow underwater ridges or pycnoclines in the ocean, layers with sharply changing optical or acoustic density, etc.), it is natural to use the wave equation with a small parameter characterizing the ratio of the scales of the localized inhomogeneity and of the general change of velocity (e.g., of the thickness of a pycnocline to the external typical scale of changes in ocean density). We describe the propagation of wave packets whose characteristic wavelength is comparable with the scale of inhomogeneity.