Thermal Character Research Articles

Optical tensor tomography of residual stresses in waveguides

Algorithms for determining residual stresses in glass round waveguides by the method of integrated photoelasticity are considered. It is assumed that the residual deformation tensor is of thermal character and is characterized by fictitious temperature varying over the sample. The reconstruction is based on measuring characteristic parameters of polarized light and is carried out by the tomographic method in the plane orthogonal to the waveguide axis.

Thermally tunable electric mie resonance of dielectric cut-wire type metamaterial.

In this manuscript, we present on a thermally tunable electric Mie resonance of dielectric cut-wire type metamaterial. Dielectric cut-wire exhibits Lorentz-type frequency dependent negative effective permittivity followed by zero value around its fundamental Mie resonance, resulting from dipole-oscillation of displacement currents. Furthermore, the operation frequency of electric resonance frequency can be varied by wire length and temperature variation. As environmental temperature changes by 40 °C, electric Mie resonance can be reversibly tuned by 1000 MHz, due to the thermal dependent permittivity character of ceramic.

Thermal Isolation Character of Reinforced Concrete Hollow Floor

Reinforced Concrete Hollow floor system was named by its typical inner core and worked as an excellent horizontal bearing structure. It has fine mechanical ability and good thermal isolation character. The author compared reinforced concrete hollow floors and traditional reinforced concrete floor. And studied their development in long span or large loaded building.

Tensor tomography of residual stresses of hexagonal single crystals

A method for determining residual stresses in elongated transparent blanks of hexagonal single crystals the optical axis of which is directed along the crystal is proposed. It is assumed that the residual deformation tensor is of thermal character and is characterized by a fictitious temperature. Characteristic parameters of polarized light have been measured by the tomographic method in the plane orthogonal to the single crystal axis.

Probing the thermal character of analogue Hawking radiation for shallow water waves?

We study and numerically compute the scattering coefficients of shallow water waves blocked by a stationary counterflow. When the flow is transcritical, the coefficients closely follow Hawking's prediction according to which black holes should emit a thermal spectrum. We study how the spectrum deviates from thermality when reducing the maximal flow velocity, with a particular attention to subcritical flows since these have been recently used to test Hawking's prediction. For such flows, we show that the emission spectrum is strongly suppressed, and that its Planckian character is completely lost. For low frequencies, we also show that the scattering coefficients are dominated by elastic hydrodynamical channels. Our numerical results reproduce rather well the observations made by S. Weinfurtner et al. in the Vancouver experiment. Nevertheless, we propose a new interpretation of what has been observed, as well as new experimental tests.

Mechanisms behind the ikaite-to-calcite phase transformation from molecular dynamics calculations

Since the discovery of ikaite (CaCO3·6H2O) in Antarctic marine sediments and east Arctic polar oceans, studying the ikaite-to-calcite phase transformation above 100K has attracted a lot of interest, both experimentally and theoretically. Despite intensive efforts, details about the thermal behavior and the mechanisms of the phase transformation of ikaite at ambient temperature are still ambiguous. To unlock the secrets of this rare and unstable mineral, we provide here a clear picture about the structural phase changes as well as the thermodynamic behavior of ikaite from 2K to 400K. The obtained results demonstrate the presence of an anisotropic thermal expansion character more pronounced above T=80K. Our X-ray diffraction patterns show that the structure of ikaite breaks down gradually during thermal expansion from 2K to 200K. At 200K, it transforms into a vaterite-like structure, at short range, then further heating up to 300K, leads the structure to be in the vaterite phase. However, at 338K, the latest phase changes quickly to the calcite structure. Our data show that the thermal expansion coefficients of ikaite obtained from 2K to 80K increase with temperature, and are greater than those of ice (Ih). However, above T=100K, the situation is inverse and the relative expansion of ikaite is found to be smaller than that of ice. A larger volume thermal expansion is noticed from T=300K to 400K, due to the contribution of extensive H bonds. These bonds allow greater flexibility of ikaite during expansion.

Influence of electric spark on hardness of carbon steel

Purpose. The purpose of work is an estimation of influence of an electric spark treatment on the state of mouldable superficial coverage of carbon steel. Methodology . The steel of fragment of railway wheel rim served as material for research with chemical composition 0.65% С, 0.67% Mn, 0.3% Si, 0.027% P, 0.028% S. Structural researches were conducted with the use of light microscopy and methods of quantitative metallography. The structural state of the probed steel corresponded to the state after hot plastic deformation. The analysis of hardness distribution in the micro volumes of cathode metal was carried out with the use of microhardness tester of type of PMT-3. An electric spark treatment of carbon steel surface was executed with the use of equipment type of EFI-25M . Findings . After electric spark treatment of specimen surface from carbon steel the forming of multi-layered coverage was observed. The analysis of microstructure found out the existence of high-quality distinctions in the internal structure of coverage metal, depending on the probed area. The results obtained in the process are confirmed by the well-known theses, that forming of superficial coverage according to technology of electric spark is determined by the terms of transfer and crystallization of metal. The gradient of structures on the coverage thickness largely depends on development of structural transformation processes similar to the thermal character influence. Originality . As a result of electric spark treatment on the condition of identical metal of anode and cathode, the first formed layer of coverage corresponds to the monophase state according to external signs. In the volume of coverage metal, the appearance of carbide phase particles is accompanied by the decrease of microhardness values. Practical value . Forming of multi-layered superficial coverage during electric spark treatment is accompanied by the origin of structure gradient on a thickness. The effect of the superficial work-hardening from a spark according to a level can be an alternative to majority of thermal and chemical-thermal technologies of treatment of metallic materials.

A mechanistic view of lipid membrane disrupting effect of PAMAM dendrimers

The effect of 5th generation polyamidoamine (PAMAM G5) dendrimers on multilamellar dipalmitoylphosphocholine (DPPC) vesicles was investigated. PAMAM was added in two different concentrations to the lipids (10−3 and 10−2 dendrimer/lipid molar ratios). The thermal behavior of the evolved systems was characterized by DSC; while the structure and the morphology were investigated with small- and wide-angel X-ray scattering (SWAXS), freeze-fracture electron microscopy (FFTEM) and phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy, respectively. IR spectroscopy was used to study the molecular interactions between PAMAM and DPPC. The obtained results show that the dendrimers added in 10−3 molar ratio to the lipids generate minor perturbations in the multilamellar structure and thermal character of liposomes, while added in 10−2 molar ratio dendrimers cause major disturbance in the vesicular system. The terminal amino groups of the dendrimers are in strong interaction with the phosphate headgroups and through this binding dendrimers disrupt the regular multilamellar structure of DPPC. Besides highly swollen, fragmented bilayers, small vesicles are formed.

Effects of MgO on properties of Li2O–Al2O3–SiO2 glass–ceramics for LTCC applications

Li2O–Al2O3–SiO2 (LAS) glass–ceramics for low temperature co-fired ceramics (LTCC) application were prepared by melting method, and the effects of MgO on the sinterability, microstructure, dielectric property, thermal expansion coefficient (CTE) and mechanical character of this glass–ceramics have been studied. The X-ray diffraction images represent that the main phase is β-spodumene solid solutions. And some ZrO2 and CaMgSi2O6 phases in LAS glass–ceramics are detected. The LAS glass–ceramics without additive (MgO) sintered at 800° had the dielectric properties: dielectric constant (er) of 5.3, dielectric loss (tanδ) of 2.97 × 10−3 at 1 MHz, CTE value of 1.06 × 10−6 K−1, bulk density of 2.17 g/cm3, and flexural strength of 73 MPa. 5.5 wt% MgO-added LAS glass–ceramic achieves densification at 800° exhibited excellent properties: low dielectric constant and loss (er = 7.1, tanδ = 2.02 × 10−3 at 1 MHz), low CTE (2.89 × 10−6 K−1), bulk density = 2.65 g/cm3 as well as high flexural strength (145 MPa). The results indicate that the addition of MgO is helpful to improve the dielectric and mechanical properties. The formation of CaMgSi2O6 crystal phase with higher CTE leads to the increase of CTE value of LAS glass–ceramics due to the increasing MgO content, and the increase of CTE is favourable for matching with silicon (3.1 × 10−6 K−1). The prepared LAS glass–ceramics have the potential for LTCC application.

Preparation of <sup>10</sup>B Enriched B<sub>4</sub>C Ceramics by Pressureless Sintering

Boron carbide is an attractive neutron absorbing material used both in Fast Breeder Reactors (FBR) and in Pressurised Water Reactors (PWR) owing to its very high absorption cross section for thermal neutrons, chemical stability and refractory character. In the present paper, 10B enriched B4C ceramics are prepared by pressureless sintering at 19602160°C, under argon, using 10B boron carbide powder as raw material, 18 wt% phenolic resin as sintering aid. In the sintering temperature range, with the increasing of sintering temperature, both the relative density and flexural strength increase linearly, the average particle sizes increase from about 3μm at 1960°C to more than 30μm at 2160°C. The sample sintered at 1960°C has a 91.7% of relative density and 192 MPa of flexural strength and a homogeneous texture with 3-4μm particle size, which are enough for pellet application of reactors.

Hawking Radiation-Quasi-Normal Modes Correspondence and Effective States for Nonextremal Reissner-Nordström Black Holes

It is known that the nonstrictly thermal character of the Hawking radiation spectrum harmonizes Hawking radiation with black hole (BH) quasi-normal modes (QNM). This paramount issue has been recently analyzed in the framework of both Schwarzschild BHs (SBH) and Kerr BHs (KBH). In this assignment, we generalize the analysis to the framework ofnonextremalReissner-Nordström BHs (RNBH). Such a generalization is important because in both Schwarzschild and Kerr BHs an absorbed (emitted) particle has only mass. Instead, in RNBH the particle has charge as well as mass. In doing so, we expose that, for the RNBH, QNMs can be naturally interpreted in terms of quantum levels for both particle emission and absorption. Conjointly, we generalize some concepts concerning the RNBH's “effective states.”

Black hole quantum spectrum

Introducing a black hole (BH) effective temperature, which takes into account both the non-strictly thermal character of Hawking radiation and the countable behavior of emissions of subsequent Hawking quanta, we recently re-analysed BH quasi-normal modes (QNMs) and interpreted them naturally in terms of quantum levels. In this work we improve such an analysis removing some approximations that have been implicitly used in our previous works and obtaining the corrected expressions for the formulas of the horizon’s area quantization and the number of quanta of area and hence also for Bekenstein–Hawking entropy, its subleading corrections and the number of micro-states, i.e. quantities which are fundamental to realize the underlying quantum gravity theory, like functions of the QNMs quantum “overtone” number n and, in turn, of the BH quantum excited level. An approximation concerning the maximum value of n is also corrected. On the other hand, our previous results were strictly corrected only for scalar and gravitational perturbations. Here we show that the discussion holds also for vector perturbations.The analysis is totally consistent with the general conviction that BHs result in highly excited states representing both the “hydrogen atom” and the “quasi-thermal emission” in quantum gravity. Our BH model is somewhat similar to the semi-classical Bohr’s model of the structure of a hydrogen atom.The thermal approximation of previous results in the literature is consistent with the results in this paper. In principle, such results could also have important implications for the BH information paradox.

Thermal Character and Generating Capacity Analysis of Solar Linear Fresnel Thermal Power Plant

Solar Linear Fresnel thermal power plant is typical linear focus solar thermal system. It has the advantage of simple structure, lower investment cost and so on. At present, Solar Linear Fresnel is developing and popularizing all over the word. Some of them are already in commercial operation. According to the typical climate data, the thermal character and generating capacity of Linear Fresnel systems are analyzed, including thermal receiving efficiency, power generating efficiency and thermal losses regularity. The research results can be used to support Solar Linear Fresnel system operation and design optimization.

Fabrication of a polymer-based biodegradable stent using a CO2 laser

This paper deals with CO2 laser machining of biodegradable polymers. We investigate the influence of laser parameters on the quality and geometry of cuts made in poly(l-lactide) and poly(l-lactide-co-glycolide). Because of the thermal character of material removal, liquid phase occurs and heat propagates into the material, changing its properties near the cutting zone. For this reason, the mechanical properties of laser cut samples were examined. Oar-shaped samples cut with a CO2 laser were compared with injection moulded samples and also with those manufactured using a KrF excimer laser. Samples with dimensions comparable to those of stent struts were examined in a uniaxial quasi-static tensile test. The influence of laser power and scanning speed on the geometry of cuts was investigated. Narrow cuts (120µm) were made in 250µm-thick polymer sheets. A tubular stent based on poly(l-lactide) was designed and then fabricated using a CO2 laser. We noted that this method allows achieving stent struts that are 300µm wide; however, for such narrow elements the influence of the heat-affected zone can be critical. We believe that this technique has a potential to become an alternative, cost-efficient method of manufacturing biodegradable stents.

Studies on thermal characteristics of cow dung powder filled glass–polyester hybrid composites

In the present work Studies on thermal characteristics of cow dung powder filled glass–polyester hybrid composites were prepared. Cow dung is a animal based fiber which is also biodegradable and glass fiber is a synthetic fiber. These two natural and synthetic fibers are combined in the same matrix (unsaturated polyester) to make cow dung powder filled glass–polyester hybrid composites and the thermal characteristics of these hybrid composites was studied. A significant improvement seen in decrease thermal conductivity of cow dung filled glass-polyester hybrid composites has been found. The cow dung powder is added to the resin (unsaturated polyester) in proportions of 3%, 6%, and 9% by weight of resin respectively and cow dung/glass fiber hybrid composites were prepared by using this resin to study the effect thermal resistivity character of cow dung on heat capacity of these hybrid composites. It is also observed that as the cow dung powder quantity decreases thermal conductivity. A good co-relation between surface morphology and thermal conductivity of composite is derived from scanning electron microscopy.

Charged Dirac Particles’ Hawking Radiation via Tunneling of Both Horizons and Thermodynamics Properties of Kerr–Newman–Kasuya–Taub–NUT–AdS Black Holes

We investigate Hawking radiation of electrically and magnetically charged Dirac particles from a dyonic Kerr–Newman–Kasuya–Taub–NUT–Anti-de Sitter (KNKTN–AdS) black hole by considering thermal characters of both the outer and inner horizons. We apply Damour–Ruffini method and membrane method to calculate the temperature and the entropy of the inner horizon of the KNKTN–AdS black hole. The inner horizon admits thermal character with positive temperature and entropy proportional to its area. The inner horizon entropy contributes to the total entropy of the black hole in the context of Nernst theorem. Considering conservation of energy, charges, angular momentum, and the back-reaction of emitting particles to the spacetime, we obtain the emission spectra for both the inner and outer horizons. The total emission rate is obtained as the product of the emission rates of the inner and outer horizons. It deviates from the purely thermal spectrum with the leading term exactly the Boltzman factor and can bring some information out. The result thus can be treated as an explanation to the information loss paradox.

A new two-stage curing system: Thiol-ene/epoxy homopolymerization using an allyl terminated hyperbranched polyester as reactive modifier

An allyl terminated hyperbranched polyester (HBP) was added to an epoxy formulation containing a trithiol compound to perform a thiol-ene click reaction. By this procedure a flexible thioether network was formed. The photoirradiation of the reactive mixture, which contained a cationic photoinitiator, converted the thioether network in a multifunctional thermal macroinitiator, capable to initiate the cure of the cycloaliphatic epoxy resin(CE) in a second thermal stage. Depending on the proportion of HBP, thermal or photocuring of the epoxy resin took place in different extent, leading to networks with different structures. The photocuring procedure was followed by FTIR and the thermal second stage by DSC. The materials obtained were characterized by DMTA, TGA and SEM. The addition of HBP-Allyl and the trithiol to the formulation allowed increasing the Tg on comparison with the neat epoxy thermoset. The system proposed constitutes a new two-stage dual photo-thermal curing procedure for cycloaliphatic epoxy resins with a thermal latent character.

Titanium alloy surface modification by excimer laser irradiation

Abstract The main effects of the interaction of UV emitting KrCl (at 222 nm) and XeCl (at 308 nm) excimer lasers with titanium alloy Ti6Al4V are presented. Single-pulse and multi-pulse irradiations were used, with varying laser beam fluences. The resulting interactions with the surface show thermal character, and produce: (i) damages in the form of craters at higher pulse counts and fluences of 7 J cm−2 and 7.2 J cm−2, which are far above the damage threshold; (ii) melt pools with visible wave-like structures at periphery; (iii) resolidified droplets and cracks at periphery (at higher pulse count), (iv) increasing content of oxygen, with a domination of TiO2.

Investigation of Thermal Properties of Cement Paste with Fluorescent Lamp Glass Waste, Glass Cullet and Coal/Wood Ashes

The thermal character of cement hydration reactions causes concrete to endure temperature changes during the first days after casting. The present research intends to evaluate the influence on the temperature of hydration of cement paste mixes with local industrial wastes such as lamp glass waste powder/suspension, glass cullet, bottom/fly coal/wood ashes substitution at level of 20% and 30%. The temperature of hydration of cement paste mixes was investigated by using specially designed equipment. The temperature of hydration inside of the cement paste specimens was continuously monitored at least up to 20 h after production at ambient air temperature 20±2°C. The results showed that cement paste substitution with lamp glass waste and coal/wood bottom ashes at level of 30% has influence on the peak temperatures of hydration with decrease from 58.8°C to 46.3°C and cement paste substitution with flint glass at level of 20% decrease temperature of hydration for around 19°C in comparison to control cement paste mix. DOI: http://dx.doi.org/10.5755/j01.sace.2.3.2781

Comparison of aqueous- and non-aqueous-based tape casting for preparing YAG transparent ceramics

Transparent YAG ceramics were prepared by the aqueous and non-aqueous based tape casting methods. The rheological property of the slurries was analyzed by the viscosity–shear rate curves. The thermal character was detected by the TG–DTA analysis. The microstructures of the tapes and ceramics were compared. The influence of density of the tape on the ceramics were discussed. The in-line transmittance curves were compared to analyze the optical quality of obtained samples. Results indicate that the methods mentioned above can achieve transparent YAG ceramics with multilayer structure. The transmittance of the sample prepared by the aqueous tape casting is above 81% at 400 nm and the sample fabricated by the non-aqueous tape casting possesses higher optical properties. The transmittance is higher than 82% at 400 nm and reaches 84% at 1064 nm.