Individual Slabs Research Articles

Investigation of the moisture induced degradation of the thermal properties of aerogel blankets: Measurements, calculations, simulations

Nowadays to reduce the energy loss as well as to minimize the emission of the green house gases of buildings can be solved by thermal insulating. Silica aerogels have a promising potential in the building and construction sector as thermal insulation due to their excellent thermal conductivity. At the present time the applications of silica aerogel blankets are truly widespread. This study focuses on the moisture induced degradation of the thermal conductivity of the above mentioned insulation slabs. Experimental studies show that the thermal conductivity of the aerogel blankets can be increased significantly (approximately 20–40%) after wetting them. For this case different types of investigations were carried out to investigate the changes in the thermal conductivity derived by the moisture content. Firstly, in order to see the temperature sensitivity of the moisture up-taking, sorption isotherm curves were registered at 283, 293 and 303K after 24h after drying and wetting at 5 different relative humidities. Secondly, the decrease of the thermal conductivity was followed with a Holometrix type heat flow meter of individual aerogel slabs after wetting the dried samples for 0, 4, 8, 12, 16, 20h at 293K and 90% relative humidity in a Climacell type climatic chamber. Finally, the change in the thermal resistance of a brick based wall covered with 0.013cm thick aerogel insulation was registered by calibrated chamber method in function of the quantity of sprayed water. From the measurement results calculations were executed to see the changes of the thermo-physical properties of the aerogel samples due to the water absorption. The novelties of the article can be found in the comparison of the measurements of the same values and properties carried out by different methods Moreover, the measurement results formed the basis of Building Energetic Simulations in order to show roughly the effect of the moisture.

A GRASP heuristic for the hot strip mill scheduling problem under consideration of energy consumption

Hot strip mill rolling is an energy intensive production process in the steel industry. It converts steel slabs at high temperatures into steel strips. In this paper we address the related planning problem, i.e. the hot strip mill scheduling problem. The task is to determine the production sequence of production orders within a schedule. The involved energy consumption for heating individual slabs is explicitly considered in a new mixed integer problem formulation. The model is solved using a greedy randomized adaptive search procedure. In a numerical case study based on real world data the applicability and performance of the proposed heuristic is analyzed. The solution approach is able to find optimal solutions for small problem instances. Moreover, it solves industry size problem instances within reasonable time and outperforms the rule based planning approach prevalent in praxis.

Structure and properties of molybdenum sulfide nanoparticles synthesized in situ in the hydroconversion process

The structure and properties of nanosized particles of a molybdenum-containing catalyst withdrawn from the reaction system with heavy hydroconversion products have been studied. The particle size of the catalyst and the features of its structure and phase composition have been determined. The particles of MoS2 synthesized in situ in the hydroconversion reactor have been shown to possess a layered structure. Individual slabs have a thickness of 0.6–0.7 nm and an average length of 9.8 nm. It has been found that monolayer particles aggregate to form stacks and spheres and are adsorbed on the surface of coke particles under conditions that disturb the equilibrium state of catalyst dispersion in the reaction medium. The distribution of the catalyst in heavy fractions of the reaction products has been studied. It has been shown that molybdenum is almost quantitatively transferred to the 500°C+ fraction of the hydroconversion product, which is important for recycling the catalyst.

Structural, vibrational, and dielectric properties of Ruddlesden-PopperBa2ZrO4from first principles

Using first-principles computational techniques, we have investigated the structural, vibrational, and dielectric properties of a Ruddlesden-Popper-type layered oxide ${\mathrm{Ba}}_{2}{\mathrm{ZrO}}_{4}$ subjected to a wide range of biaxial strains emulating epitaxial thin-film environment. Under compressive strains, this compound experiences an incommensurate distortion characterized by planar displacements of individual perovskite slabs away from their high symmetry positions. On the other hand, under increasing epitaxial tension, the original centrosymmetric structure becomes unstable---first, with respect to antiferrodistortive oxygen cage rotations and then also with respect to in-plane polar distortions. Both the incommensurate-to-commensurate and the nonpolar-to-polar phase transformations are accompanied by anomalies of the static dielectric response, however, only in the latter case a divergence of the in-plane dielectric constant is observed. Remarkably, even after the transition into the ferroelectric state (with polarization of up to 0.12 ${\mathrm{C}/\mathrm{m}}^{2}$ at 3.5% tension) dielectric permittivity of ${\mathrm{Ba}}_{2}{\mathrm{ZrO}}_{4}$ remains unusually high, which is explained by an emergence of a Goldstone-like excitation in the system manifested through an in-plane libration of the polarization vector. Since ${\mathrm{Ba}}_{2}{\mathrm{ZrO}}_{4}$ displays a yet poorly understood tendency to absorb small molecules, such as water and ${\mathrm{CO}}_{2}$, acquiring better insights into the physical underpinnings of its behavior can produce more efficient functional materials for applications in advanced technologies for carbon sequestration.

Tribological Properties of New MoS2 Nanoparticles Prepared by Seed-Assisted Solution Technique

Seed-assisted solution synthesis of hollow IF-MoS2 nanoparticles allows independent control of particles size and MoS2 slabs crystallinity. Variations of the reaction mixture composition influence the particle size in the range 50–150 nm. As demonstrated by Rietvelt refinement of the X-ray diffraction patterns, the sulfide crystallinity depends only on the post-treatment temperature (350–750 °C) and not on the particle size. The tribological properties of new MoS2 nanoparticles prepared by seed-assisted solution technique were investigated and showed a strong decrease in the friction coefficient and wear compared with base oil. Small particles of 50–60-nm size showed the best results. The particle size above 100 nm is deleterious for the lubrication properties since it hinders particles penetration into the contact zone. MoS2 slabs crystallinity had lesser influence on the lubrication efficiency. However, less-crystallized samples treated at 350 °C showed better lubrication, apparently because of easier exfoliation of the individual MoS2 slabs, leading to more efficient formation of tribofilm.

Trajectory and physical properties of near-Earth asteroid 2009 BD

AbstractWe analyze the trajectory of near-Earth asteroid 2009~BD, which is a candidate target of the NASA Asteroid Redirect Mission. The small size of 2009 BD and its Earth-like orbit pose challenges to understanding the dynamical properties of 2009 BD. In particular, nongravitational perturbations, such as solar radiation pressure and the Yarkovsky effect, are essential to match observational data and provide reliable predictions. By using Spitzer Space Telescope IRAC observations and our model for the thermophysical properties and the nongravitational forces acting on 2009 BD we obtain probabilistic derivations of the physical properties of this object. We find two physically possible solutions. The first solution shows 2009 BD as a 2.9 ± 0.3 m diameter rocky body with an extremely high albedo that is covered with regolith-like material, causing it to exhibit a low thermal inertia. The second solution suggests 2009 BD to be a 4 ± 1 m diameter asteroid with albedo 0.45 ± 0.35 that consists of a collection of individual bare rock slabs. We are unable to rule out either solution based on physical reasoning. 2009 BD is the smallest asteroid for which physical properties have been constrained, providing unique information on the physical properties of objects in the size range smaller than 10 m.

Simulation of Long Distance Wave Propagation in 2-D Sparse Random Media: A Statistical S-Matrix Approach in Spectral Domain

The problem of long distance wave propagation in a sparse random medium is considered in this paper. A mathematical technique for modeling the behavior of electromagnetic wave propagation as a function of distance in a 2-D sparse random media at millimeter wave (MMW) regime is presented. The proposed model is a field method based on Maxwell's equation and, thus, the phase and magnitude of the field in the random medium can be tracked accurately. The random media is characterized by low volume fraction but electrically large scatterers having relatively high dielectric constant. The technique relies on discretizing the random media into thin slabs and relating the forward and backward scattered plane wave spectra from the individual slabs by an equivalent spectral bistatic scattering matrix. By cascading the scattering matrices of the individual slabs, the statistics of the overall scattered wave in both forward and backward directions are obtained. This technique will be referred to as statistical S-matrix approach in spectral domain, or SSWaP-SD. Using this method, it is shown that after propagation to a critical range inside the random media, the incoherent component of the forward propagating wave overcomes the mean-field component resulting in a dual-slope attenuation curve as a function of distance. The accuracy of the model is examined against a full wave Monte Carlo simulation and a very good agreement is observed. Finally, based on the proposed model, analytical expressions for predicting the forward path-loss as well as the back scattered power from a sparse, translational invariant discrete random media are derived. The analytical expressions are tested against Monte Carlo simulation for a very long random medium and very good agreements are demonstrated.

CONSTRAINING THE PHYSICAL PROPERTIES OF NEAR-EARTH OBJECT 2009 BD

We report on Spitzer Space Telescope IRAC observations of near-Earth object (NEO) 2009 BD that were carried out in support of the NASA Asteroid Robotic Retrieval Mission (ARRM) concept. We did not detect 2009 BD in 25 hrs of integration at 4.5 micron. Based on an upper-limit flux density determination from our data, we present a probabilistic derivation of the physical properties of this object. The analysis is based on the combination of a thermophysical model with an orbital model accounting for the non-gravitational forces acting upon the body. We find two physically possible solutions. The first solution shows 2009 BD as a 2.9+/-0.3 m diameter rocky body (rho = 2.9+/-0.5 g cm-3) with an extremely high albedo of 0.85(+0.20/-0.10) that is covered with regolith-like material, causing it to exhibit a low thermal inertia (Gamma = 30(+20/-10) SI units). The second solution suggests 2009 BD to be a 4+/-1 m diameter asteroid with pV = 0.45(+0.35/-0.15) that consists of a collection of individual bare rock slabs (Gamma = 2000+/-1000 SI units, rho = 1.7(+0.7/-0.4) g cm-3). We are unable to rule out either solution based on physical reasoning. 2009 BD is the smallest asteroid for which physical properties have been constrained, in this case using an indirect method and based on a detection limit, providing unique information on the physical properties of objects in the size range smaller than 10 m.

Effects of layer stacking sequence on temperature response of multi-layer composite materials under dynamic conditions

Abstract Individual slabs of different types are used to form composites with either 2- or 3-layer of various stacking sequences so as to examine whether stacking order has any influence on the thermal response of the composite samples under dynamic conditions. The excess temperature profile θ(x, t) of a laminated composite slab is first derived by Green’s function (GF) method so that the adiabatic surface excess temperatures for all stacking sequences are mathematically determined to detect the discrepancies between different stacking sequences. The theoretical predictions are then validated with actual experimental data using a custom-made apparatus. The comparisons between the predictions and the experimental data are analyzed in detail and results are discussed. This may be a significant reminder for the multi-layer design of building walls, clothing and other industrial applications.

Tunable structures comprising two photonic crystal slabs – optical study in view of multi-analyte enhanced detection

Using finite-difference time-domain method, we characterize the normal-incidence transmission properties of a two slab photonic crystal device in a view of its applications in fluorescence enhancement and multi-analyte detection. Individual slabs consist of a square or a triangular lattice of air holes embedded into a silicon nitride slab. The geometrical parameters are chosen so that the individual slabs operate in a guided resonance regime where strong reflectivity under the normal incidence angle is observed in a broad spectral range. When placed in the close proximity of each other, the two photonic crystal slab system exhibits a narrow Fabry-Perot type transmission peak corresponding to the excitation of a resonant mode in the cavity formed by the two slabs. We then study the effects of the size of the air gap between the two photonic crystal slabs on the spectral position and bandwidth of a resonance transmission peak. Finally, we investigate the electromagnetic energy distributions at the wavelength of a transmission resonance in the double slab photonic crystals. As a final result we demonstrate that this structure can provide electric field enhancement at the slab surface, which can be used for fluorescence enhancement.

Theoretical and field evaluation of interaction between ultra-thin whitetopping and existing asphalt pavement

Ultra-thin concrete overlays or ultra-thin whitetopping (UTW), are an attractive alternative to traditional practices for the rehabilitation of asphalt pavements. However, it is widely accepted that the exiting pavement should have substantial stiffness to make a UTW a rehabilitation option. This paper re-examines this hypothesis using the performance results and structural evaluation of two experimental sections in Brazil. It is shown that structural contribution of the existing pavement is important for good performance of UTW. However, it appears that the ability of the existing pavement to ensure composite action of the individual slabs in the UTW is more important than its contribution to the flexural stiffness.

Fast magnetohydrodynamic waves in a two-slab coronal structure: collective behaviour

Aims.We study fast magnetohydrodynamic waves in a system of two coronal loops modeled as smoothed, dense plasma slabs in a uniform magnetic field. This allows us to analyse in a simple configuration the collective behaviour of the structure due to the interaction between the slabs.

Methods for Assessment of Slab Centre Segregation as a Tool to Control Slab Continuous Casting with Soft Reduction

Slabs produced by continuous casting are characterized by macrosegregation in their central regions. The formation of this macrosegregation depends on many parameters, among others the state of the casting line and the casting technique used. In order to minimize this slab centre macrosegregation for the various steel grades, appropriate samples cut from the slabs have to be subjected to a quantitative assessment. Optical methods of assessment are too inaccurate to serve, for example, as a useful index for controlling soft reduction. For this reason the centre of the slab was analysed using several physical and chemical test methods whose results were then cross-compared. In the process, a combination of ultrasonic porosity tests and spark analyses (OES-PDA) turned out to be the most informative, cost-effective and fastest method for assessing macrosegregations. Thanks to the macrosegregation indexes elaborated on the basis of the test results for the individual slabs it is now possible to find optimum casting parameters such as casting temperature, casting speed etc. for the subsequent melts of the same steel grade and also to use soft reduction for the purpose of minimizing macrosegregation phenomena.

Light diffusion in multi-layered translucent materials

This paper introduces a shading model for light diffusion in multi-layered translucent materials. Previous work on diffusion in translucent materials has assumed smooth semi-infinite homogeneous materials and solved for the scattering of light using a dipole diffusion approximation. This approximation breaks down in the case of thin translucent slabs and multi-layered materials. We present a new efficient technique based on multiple dipoles to account for diffusion in thin slabs. We enhance this multipole theory to account for mismatching indices of refraction at the top and bottom of of translucent slabs, and to model the effects of rough surfaces. To model multiple layers, we extend this single slab theory by convolving the diffusion profiles of the individual slabs. We account for multiple scattering between slabs by using a variant of Kubelka-Munk theory in frequency space. Our results demonstrate diffusion of light in thin slabs and multi-layered materials such as paint, paper, and human skin.

Simulation of slab movement and transient heating in a continuous steel reheat furnace

This paper describes the simulation of transient heating of steel slabs in an industrial-scale continuous reheat furnace. To obtain a reliable slab temperature distribution, the gas flow and heat transfer were simulated with low-Reynolds-number turbulence models in combination with higher-order convection schemes and a radiation model. The transient heating of slabs was simulated with a moving slab technique, which allows the individual slabs to be heated up while moving along the furnace. Not only the individual slab movement and its temperature evolution can be tracked (Langrangian frame of reference), but the temperature distribution for all the slabs passing through the furnace can be monitored as well (Eulerian frame of reference). The developed model could simulate both the furnace start-up and steady-state operation. The simulation confirmed that both temperature profiles (Langrangian and Eulerian frames of reference) coincide in the pseudo-steady state operation. With the developed model, various issues from operation can be investigated in the future, such as skid mark effect and feeding capacity variations.

Magnetic Resonance Angiography

Magnetic Resonance Angiography

Chloride Induced Steel Corrosion in Concrete: Part I—Corrosion Rates, Corrosion Activity, and Attack Areas

This paper presents results from a major long-term study on chloride-induced steel corrosion in concrete. The performance of a set of 50 reinforced concrete slabs made with a range of portland and blended cement binders was evaluated. Two portland cements, a high C3A and a low C3A, a blended fly ash cement, and a blended blast furnace slag cement were used. All reinforced concrete slabs were exposed to high chloride conditions by partial immersion in a 3% NaCl solution modeling seawater conditions. The reinforcement was cleaned and weighed prior to inclusion into the concrete slabs. Periodic nondestructive measurements of concrete performance included half cell potential monitoring, concrete resistivity, and electrochemical measurements of rates of corrosion of steel in concrete using potentiodynamic anodic procedures. Individual slabs were broken for reinforcement recovery at predetermined times during the study. Measurements were made of the area of corrosion and the weight loss of steel through corrosion. This information was related to the nondestructive data acquired on the slabs. In Part 1, estimated corrosion current (Ic) data and areas under the Ic versus time envelope for reinforcement within concrete slabs is presented. These data were obtained using potentiodynamic anodic polarization techniques. Measurements of the reinforcement corroded area in concrete are also presented and related to the electrochemical measurements taken. It was found that concrete water:binder ratio significantly influenced the corrosion rate of steel in concrete. Relationships were established between corrosion activity and the area of chloride-induced steel corrosion. Observed relationships were different for reinforcement within portland cement concretes and blended cement concretes considered.

Synthesis and structure of TlCuTiTe3

The new compound TlCuTiTe3 has been synthesized from Tl6Te4 and the corresponding elements and characterized by single-crystal X-ray diffraction methods. TlCuTiTe3 crystallizes in the space group C2b2−P21/m of the monoclinic system with two formula units in a cell of dimensions a = 8.409(8) Å, b = 3.956(3) Å, c = 10.261(8) Å, β = 111.56(4)°, V = 317.5(4) Å3 (T = 115 K). The two-dimensional structure comprises slabs of alternating pairs of Ti octahedra and Cu tetrahedra. The slabs are separated by Tl′ cations coordinated to Te3 anions in a monocapped trigonal prismatic fashion. Whereas the structure of the individual slabs in TlCuTiTe4, is strikingly similar to those found in the related materials NaCuTiS3, NaCuZrSe3, and NaCuZrTe3, the packing of the slabs is different. Two-probe resistivity measurements indicate that TlCuTiTe3 is a semiconductor.

Methane-derived carbonate cementation of Holocene marine sediments from Kattegat, Denmark

Methane-derived carbonate cementation of Holocene marine sediments occurs at several location in Kattegart, Denmark. Generally, the carbonate-cemented sandstone occur at the seafloor as individual slabs or more widely distributed, thinly lithified pavements. Occasionally, the lithified sandstone take the form of large and spectacular, vertical pillar and mushroom-shaped bodies standing up from the seafloor. The carbonate cement consists of aragonite, high-Mg calcite and dolomite. The high-Mg calcite is the most widespread carbonate solid phase found. Aragonite is primarily associated with shell accumulations in the sediments. So far, dolomite has only been recorded as cement in the larger, vertical lithified sanstone bodies. The oxygen isotopic composition and the concentrations of minor elemens indicate that carbonate precipitation took place under relatively constant temperature and salinity conditions in normal marine pore fluids. However, the carbonates are remarkably depleted in 13C, i.e. in the range of −63 to −26% ° 13C and are therefore interpreted as being the result of methane oxidation by sulphate-reducing bacteria in the anaerobic diagenetic zone of the sediments

Methane-derived carbonate cementation of marine sediments from the Kattegat, Denmark: Geochemical and geological evidence

Methane-derived carbonate cementation of Holocene marine sediment occurs at several locations in the Kattegat, Denmark. Generally, the carbonate-cemented sandstones occur at the seafloor as individual slabs or widely distributed, thinly lithified pavements. In some areas, the lithified sandstones take the form of large and spectacular, vertical pillar and mushroom-like bodies standing up from the seafloor. The carbonate cement consists of aragonite, high-Mg calcite, and dolomite. The high-Mg calcite is the most widespread carbonate solid phase found. Aragonite is primarily associated with shell accumulations in the sediments. So far, dolomite has only been recorded as cement in the large, vertical lithified sandstone bodies. The carbonates are remarkably depleted in 13C, i.e. generally in the range of −55% to −45% PDB and are therefore interpreted as being the result of methane oxidation by sulphate-reducing bacteria in the anaerobic diagenetic zone of the sediments. However, the oxygen isotopic composition and the concentrations of minor elements indicate that carbonate precipitation took place under relatively constant temperature and salinity conditions in normal marine pore fluids. The habit and mineralogy of the carbonate-cemented sandstone observed most likely are controlled by the effect of bacterial activity and upward gas migration on the interstitial geochemical microenvironment. The lithified sediments were subsequently exposed as spectacular sandstone formations on the seafloor by submarine erosion. Data from onshore exploration wells reveal that methane is encountered in Eemian-Early Weichselian (Late Quaternary) marine deposits. The chemical composition and the isotopic signatures of the methane suggest a gas of microbial origin, and it is thought that the gas is generated within the host marine Quaternary sediment. The locations of submarine gas seeps, along with those of the carbonate-cemented sandstone formations and the onshore gas seeps, show a linear distribution which largely coincides with the extension of the Fennoscandian border zone. Thus the seeps may be controlled by the structural framework in the northeastern part of the Danish Subbasin.