Linear Transmittance Research Articles

Laser grade Yb:LuAG transparent ceramic prepared by nanocrystalline pressure-less sintering in reducing H_2

Yb3+ ion doped highly transparent Lu3Al5O12 (LuAG) ceramics were fabricated by a pressure-less sintering in H2 atmosphere starting from nanocrystalline powder derived from a wet chemical processing. A fully transparent Yb:LuAG ceramic was densified under 1750 °C for 10 hours with a linear optical transmittance of 83.1% at the wavelength of 800 nm. The average grain size of obtained transparent ceramics was only 1μm with nearly uniform distribution of the nanocrystals. A 0.91 W continuous wave laser output was achieved with a 3at.%Yb:LuAG ceramic at room temperature, when pumped with a 940 nm single-emitter laser diode. The absorbed pump power threshold was only about 0.29 W, and the best optical to optical efficiency was 58%.

On the Spectral and Energy Efficiency of Full-Duplex Small-Cell Wireless Systems With Massive MIMO

The achievable rate of full-duplex (FD) small-cell systems with massive multiple-input multiple-output (MIMO), in which a low-power base station (BS) equipped with large antenna arrays sends/receives data to and from multiple half-duplex (HD) users at the same time on the same frequency, is investigated. The BS uses imperfect channel state information (CSI) obtained from received pilots, nonideal hardware, and a linear transmitter and receiver, i.e., zero-forcing (ZF) or maximum-ratio transmission/maximum-ratio combining (MRT/MRC), to process the signals. The approximate closed-form expressions of the achievable rate for both the ZF and MRT/MRC processing are derived and used to analyze the effect of the number of antennas and the hardware imperfection on the self-interference (SI), which is a bottleneck of the FD systems. To maximize the spectral efficiency (SE) and the energy efficiency (EE) of this system, two nonconvex power-allocation optimization problems are formulated and solved by utilizing the sequential convex approximation technique and the fractional programming technique. Two iterative algorithms are proposed with proved local convergence. Numerical results illustrate that the analytical approximation of achievable rate matches well with the Monte Carlo simulation. It is also shown that the ZF processing has greater ability to suppress SI, compared with MRT/MRC processing. The proposed power-allocation algorithms are shown to increase the SE and EE significantly, compared with the uniform power-allocation scheme when the BS is equipped with moderately large antenna arrays.

Thermal bridges in vacuum insulation panels at building scale

In this paper a numerical analysis aimed at evaluating the thermal performance of vacuum insulation panels (VIPs) at the building scale is presented. This technology has seen considerable development over the past few years, gaining increasing penetration in the building insulation market. However, it is important to evaluate correctly the thermal bridging effect that occurs when the VIPs are coupled with joints at the building scale. To this purpose, the linear thermal transmittances of different VIP assemblies inserted in several wall configurations were assessed through a bidimensional numerical analysis. Moreover, to evaluate the influence of thermal bridges on the building energy need, quasi-steady-state simulations for a parametric building module were performed. A simple empirical model was finally built to estimate the linear thermal transmittance from basic input variables. The study demonstrates that thermal bridging effects that occur when VIPs are jointed are never negligible and they could have an important impact on the building heating energy need.

Covalent functionalization of graphene oxide with porphyrin and porphyrin incorporated polymers for optical limiting.

Porphyrin-graphene composites have attracted increasing attention due to a number of intriguing functions, and their photoelectrical and catalytic performances are expected to be modulated through different approaches. In the present study, a designed polymer based on phenyl sulfone, (p-amino)phenylhydroquinone, and a symmetrical dinaphthylporphyrin were covalently attached to a graphene oxide (GO) sheet. The formation of the nanohybrid was characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and Raman, ultraviolet-visible (UV-vis) absorption, steady and transient fluorescence spectroscopy techniques. The nonlinear optical and optical limiting performances of the hybrid were investigated using Z-scan measurements at 532 nm and 1064 nm. For comparison, a porphyrin functionalized GO hybrid was synthesized as a reference. At the same linear transmittance, the polymer functionalized GO exhibited a stronger optical limiting response and a larger nonlinear extinction coefficient than the individual GO, porphyrinated polymer, and porphyrin functionalized GO hybrid analogue, and its intrinsic photophysical mechanism was discussed in detail. More importantly, further improvement of its nonlinear optical properties can be achieved by the chemical reduction of the hybrid. The enhanced nonlinear optical performance originated from the effective combination of nonlinear scattering, reverse saturable absorption, and a possible photo-induced electron/energy transfer mechanism from donor porphyrin moieties in the polymer backbone to acceptor graphene. Our result might provide a new avenue for the development of graphene-porphyrin materials in the field of photocatalysis, nonlinear optics, and optoelectronic devices.

Simulation Performance of Building Wall with Vacuum Insulation Panel

The energy consumption in buildings has continuously increased, and in some countries it reaches almost 40% of the total energy use. Therefore, there are various efforts to minimize energy consumption in buildings, and the regulations on building envelope insulation have been tightened up gradually. For vacuum insulation panel (VIP) in buildings, various researches have been conducted over the last several years and its application has been extended in building industry. VIP application in buildings enable thinner building envelope while maintaining the same thermal performance by a greatly lower thermal conductivity than conventional insulation materials. On the other hand, VIP applied in buildings may cause thermal bridges, which reduce the thermal performance of VIP envelope due to the very low thermal conductivity compared with other building materials. Therefore, the thermal performance of building envelope with VIP depends on how the VIPs are applied to the building envelope and that is affected according to the installation method of VIP with other building materials. This study aims to analyze the thermal performance of VIPs, and to evaluate the effective thermal transmittance (U-value) of building walls with VIPs. For this study, the VIPs-applied walls were designed to minimize thermal bridge effect and their linear thermal transmittances were evaluated by BISCO program.

Influence of CuO nanoparticles on third order nonlinearity and optical limiting threshold of polymer/ZnO nanocomposites

The linear and nonlinear optical properties of polymer/inorganic nanocomposites have received a great interest because of their potential application such as optical limiting devices. A flexible foil like polymer/ZnO nanocomposites and polymer/ZnO/CuO nanocomposites have been prepared via casting method. ZnO and CuO nanoparticles were used as filler, while four different types of polymer were used as polymer matrix. The purity and composition of the nanocomposites were confirmed via EDX analysis and EDS mapping. Surface morphology of samples was tested by FESEM that were shown the dispersion of ZnO and CuO nanoparticles successfully. To study the influence of adding CuO nanoparticles on polymer/ZnO nanocomposites; the liner transmittance was measured and linear absorption coefficient was calculated. The results show a decrease in linear transmittance and increase in linear absorption coefficient when CuO nanoparticles was added. Then, the absorption coefficient and refractive index of the as-prepared sample were analysed using an open and closed aperture single beam Z-scan technique via Q-switched Nd-YAG pulse laser at 532 nm. The nonlinear refractive index was in the order of 10−12 cm2/W with a negative sign whereas the nonlinear absorption coefficient was in the order of 10−7 cm/W. The real part, imaginary part and the absolute value of the third order nonlinear optical susceptibility χ(3) were calculated. The χ(3) was in the order of 10−6 esu. The effect of adding CuO nanoparticles to nanocomposites was enhanced their nonlinear optical properties. Consequently, a good optical limiting was obtained. The optical limiting threshold of the samples was measured. The results showed that the prepared nanocomposites can be considered as an excellent candidate for optical limiting devices, which clearly affected by the adding CuO nanoparticles and the type of polymer matrix. Nanocomposites PMMA/ZnO/CuO and PS/ZnO/CuO showed the low optical limiting threshold, which were equal to 60 and 50 Mw/cm2, respectively.

Infrared thermography technique as an in-situ method of assessing heat loss through thermal bridging

A key aspect in assessing the thermal standard of building envelopes is the quantification of the heat loss though thermal bridging, which can be expressed in terms of the linear thermal transmittance Ψ. Values of Ψ may be obtained from tabulated values for standard building details, from numerical modelling or from measurement. Where the internal structure of the building envelope is unknown, which is very often the case, measurement is the only option. This study shows how the infrared thermography technique (ITT) can be used as a non-invasive and easy-to-use method to provide quantitative measures of the actual thermal bridging performance. The novelty of this approach includes evaluation of the actual heat flow rate caused by thermal bridge qTB and Ψ-value by means of the ITT solely, without any supporting methods. Another important aspect of the methodology is that it accounts for the correlation between the surface temperature and the convective and radiative heat transfer coefficients. Values for these coefficients are assessed for the whole range of the surface temperatures recorded on the thermogram resulting in improve accuracy. The qTB and Ψ-value calculated using the presented methodology fully mirrors the real thermal performance of the thermal bridge. The methodology has been tested under laboratory conditions in a steady state in a hot box with excellent agreement.

Role of annealing on the structural and optical properties of nanostructured diaceto bis-benzimidazole Mn(II) complex thin films

A coordination complex, manganese incorporated benzimidazole, thin films were prepared by chemical bath deposition method. Structural characterization of the deposited films, carried out by Fourier transform infrared spectroscopy, Raman and electron paramagnetic resonance spectral analyses, reveals the distorted tetrahedral environment of the metal ion with bis-benzimidazole ligand. Further the molecular composition of the deposited metal complex was estimated by energy-dispersive X-ray spectroscopy. The prepared thin films were thermally treated to study the effect of annealing temperature on the surface morphology and the results showed that the surface homogeneity of the films increased for thermally treated films up to 150°C. But distortion and voids were observed for the films annealed at 200°C. The Raman analysis reveals the molecular hydrogen bond distortion which leads to the evaporation of the metal complex from the thin film surface with respect to annealing temperature. The linear and nonlinear optical properties of the as prepared and annealed films were studied using ultraviolet-visible transmittance spectroscopy, second harmonic generation and Z-scan analyses. Films annealed at 150°C show a better linear transmittance in the visible region and larger SHG efficiency and third order nonlinear susceptibility when compared with the other samples. Further, the film annealed at 150°C was subjected to optical switching analysis and demonstrated to have an inverted switching behavior.

Visible light nonlinear absorption and optical limiting of ultrathin ZrSe3 nanoflakes

The nonlinear absorption and nonlinear refractive properties of ZrSe3 nanoflakes were studied with a 6.5 ns pulse laser at 532 nm. Open-aperture Z-scan curves reveal that ZrSe3 nanoflakes have a strong reverse saturable absorption property, and close-aperture Z-scan curves show that ZrSe3 dispersions possess a positive nonlinear refractive index caused by self-focusing. The nonlinear absorption coefficient, the nonlinear refraction coefficient, and the figures of merit (FOM) of ZrSe3 dispersed in water with linear transmittances of 0.86 at input energy of 18 μJ are 6.35 × 10−10 m W−1 15.73 × 10−17 m2 W−1, and 10.09 × 10−11 esu · cm respectively. In addition, nonlinear optical (NLO) performance of ZrSe3 nanoflakes depends on organic solvent dispersions. ZrSe3 nanoflakes in water dispersions have the largest FOM of 10.27 × 10−11 esu · cm, while the FOM in ethanol dispersions is 5.41 × 10−11 esu · cm at the same input energy of 26.5 μJ. The optical limiting threshold Fth of ZrSe3 nanosheet is 2.2 J cm−2 under picosecond laser pulse. The Results imply that ZrSe3 nanoflakes are an extraordinarily promising material for novel nanophotonic devices like optical limiters.

Stepwise Activation of Switchable Glazing by Compositional Gradient of Copolymers.

Thermotropic glazing is one of the most promising developments for adaptive solar control; however, a monotonic transparent-opaque transition limits its practical application. In this work, to render stepwise activation of the switchable glazing, we prepared multicomposition copolymers having a compositional gradient. By slow addition of the monomers in the reaction mixture during free-radical polymerization, the blend of copolymers with each polymer having different compositions of the monomers could be prepared. We found that the developed copolymers exhibit different thermal behaviors according to the monomer composition, yielding the nearly linear transmittance change over a wide temperature range due to the gradient hydrophilic-hydrophobic balances. By combining prepared copolymers with photothermal graphene oxide as a heat transducer, we demonstrated gradual solar control of the smart window in response to sunlight intensity in outdoor testing.

Evaluation of multi‐turn time‐of‐flight mass spectrum of laser ionization mass nanoscope

We have evaluated the performance of a multi‐turn time‐of‐flight mass spectrometer (MULTUM II) equipped with the ion injection optics of a laser ionization mass nanoscope (LIMAS). We surveyed the optimal parameters for the ion injection optics, which consist of ion extraction from a sample surface and ion introduction into MULTUM II. We developed mass calibration methods for correcting the modulation of load voltage for MULTUM II and injection timing for the ion injection optics. As a result, the mass‐resolving power of LIMAS increased linearly with increasing the flight path length, and reached 6.2 × 105 (full width at half maximum) at 1000 multi‐turn cycles of MULTUM II (flight path length: 1.3 km). The transmittance of LIMAS decreased to 60–70% after 20 multi‐turn cycles of MULTUM II, compared with the linear mode transmittance. The transmittance per multi‐turn cycle became constant (99.96%) after 20 multi‐turn cycles. A useful yield of 3 × 10−3 for Si ions was obtained for LIMAS at 30 multi‐turn cycles of MULTUM II. Copyright © 2016 John Wiley & Sons, Ltd.

Light transmittance and polymerization kinetics of amorphous calcium phosphate composites.

This study investigated light transmittance and polymerization kinetics of experimental remineralizing composite materials based on amorphous calcium phosphate (ACP), reinforced with inert fillers. Light-curable composites were composed of Bis-EMA-TEGDMA-HEMA resin and ACP, barium glass, and silica fillers. Additionally, a commercial composite Tetric EvoCeram was used as a reference. Light transmittance was recorded in real-time during curing, and transmittance curves were used to assess polymerization kinetics. To obtain additional information on polymerization kinetics, temperature rise was monitored in real-time during curing and degree of conversion was measured immediately and 24h post-cure. Light transmittance values of 2-mm thick samples of uncured ACP composites (2.3-2.9%) were significantly lower than those of the commercial composite (3.8%). The ACP composites presented a considerable transmittance rise during curing, resulting in post-cure transmittance values similar to or higher than those of the commercial composite (5.5-7.9 vs. 5.4%). The initial part of light transmittance curves of experimental composites showed a linear rise that lasted for 7-20s. Linear fitting was performed to obtain a function whose slope was assessed as a measure of polymerization rate. Comparison of transmittance and temperature curves showed that the linear transmittance rise lasted throughout the most part of the pre-vitrification period. The linear rise of light transmittance during curing has not been reported in previous studies and may indicate a unique kinetic behavior, characterized by a long period of nearly constant polymerization rate. The observed kinetic behavior may result in slower development of polymerization shrinkage stress but also inferior mechanical properties.

IMPACT OF LINEAR THERMAL BRIDGES ON THERMAL TRANSMITTANCE OF RENOVATED APARTMENT BUILDINGS

Renovation of old apartment buildings is a topic of current research interest throughout the Eastern Europe region where similar typology is derived from the period of 1960–1990. Thermal bridges, essential components of the transmission heat loss of a building, have to be properly evaluated in the energy audit during current state-of-the-art situation as well as in the comparison of renovation solutions. Resulting from field measurements and calculations, we propose linear thermal transmittances Ψ of thermal bridges for four types of apartment buildings: prefabricated concrete large panel element, brick, wood (log), and autoclaved aerated concrete. Our results show that thermal bridges contribute 23% of the total transmission heat loss of a building envelope before renovation. After renovation thermal bridges ac­count for only 10% if windows are repositioned into additional external thermal insulation and balconies are rebuilt as best practice. Inversely, impact of the thermal bridges might be up to 34%, depending on the wall insulation thickness. We have also found that the relative percentage of thermal bridges after renovation increases and the negative impact of the thermal bridges of certain junctions cannot be compensated with thicker wall insulation. Results obtained in this paper are useful for energy audits.

Steady-State Three - Dimensional Numerical Simulation of Heat Transfer for Thermal Bridges Assessment

Abstract This paper presents a study on using the steady-state three-dimensional heat transfer software HEAT3 for evaluating the heat flow of heat transfer through different elements of the building envelope in order to establish the linear thermal transmittance of the linear thermal bridge. The linear thermal transmittance is obtained according to the one-dimensional steady-state heat transfer calculation formula for the plane walls using the heat flow values obtained through the method specified above. The results presented in this paper are part of a wider study on evaluating the heat transfer through building’s envelope elements by evaluating as accurate as possible the thermal bridges effect of the most common building structures. As a case study, it was considered the steady-state heat transfer through an opaque outer wall of a building considering the thermal bridges for the following elements: outer walls intersection, inner and outer wall intersection and outer wall with intermediate floor intersection.

Generalized Transmitter Compensation of Frequency Dependent I/Q Imbalance

This paper considers the formulation of a digital pre-distorter to eliminate distortions that are generated by a frequency-dependent imbalance between the analog in-phase (I) and quadrature (Q) channels of a direct conversion transmitter. Estimation of the imbalance occurs in the frequency domain, while compensation occurs in the time domain. We demonstrate the efficacy of the approach by estimating and eliminating transmitter distortions whose digital-to-analog converters (DACs) and filters have differing impulse responses, as well as a phase and amplitude imbalance between the local oscillators (LOs). The estimator developed includes a separation of the linear and nonlinear transmitter response, facilitating the application of nonlinear pre-distortion without architectural restriction. Furthermore, the estimator not only compensates for I/Q imbalances, but fully characterizes the frequency response and identifies the source of the imbalance. An interesting outcome of the analysis is that it may not be possible with baseband processing to compensate for an imbalance that occurs after up-conversion but prior to I/Q summing.

FBG 센서와 LTOF 를 이용한 온도측정시스템 개발

FBG 센서와 LTOF 를 이용한 온도측정시스템 개발

Research on the influence of yarn parameters on the ultraviolet protection of yarns

Considering both the yarn parameters and the light interaction (reflectance and transmittance) between two adjacent yarns, an optical model was presented to understand the ultraviolet (UV) light penetrating a single undyed yarn and a lot of yarns. The optical model was verified with results of diffuse reflectance spectra measurement on wool yarn samples. This optical model was used to predict the factors influencing UV protection, including fibre diameter, yarn linear density, yarn twist, transmittance index and refractive index. The statistical predictive model was also set up to show the relationship between the yarn parameters and the UV protection (UPF values) of the yarns. Yarns with the fine diameter, large yarn linear density and low yarn twist had the high UV protection.

Electrically tunable optical bistability based on one-dimensional photonic crystals with nonlinear nanocomposite materials

A one-dimensional photonic crystal structure with a nonlinear metal-dielectric nanocomposite defect layer is proposed to control the optical bistability (OB) of the transmitted wave by tuning the externally applied dc electric field. Using the transfer matrix method for dielectric layers and solving the Helmholtz nonlinear equation in the nonlinear composite layer, the linear transmittance spectrum and the nonlinear transmission curve are illustrated graphically for different applied fields. A field-dependent defect mode is observed in the linear transmittance spectrum. Consequently, the OB switch-up and -down thresholds can be manipulated via the applied field intensity. Due to the field dependence of composite layer refractive index, the physical response of the observation is the dynamical shifting of the defect mode. Moreover, it is shown that the volume fraction, shape, and type of the embedded nanoparticles as well as the kind of the dielectric host have large influences on the OB threshold. The proposed structure has significant potential applications in optical integrated devices.

The Study on Thermal Performance Evaluation of Building Envelope with VIPs

The energy consumption in buildings has continuously increased in some countries and it reaches almost 25% of the total energy use in korea. Therefore there are various efforts to minimize energy consumption in buildings, and the regulations on building envelope insulation have been tightened up gradually. To satisfy the building regulation, the use of vacuum insulation panels(VIPs) is increasing. VIP is a high performance insulation materials, so that it can be thinner than conventional insulation material. When VIP is applied in a building, it may cause thermal bridge, which occurs due to very low thermal conductivity compared to other building materials and the envelope of VIPs. Method: This study designed the capsulized VIPs using conventional insulation for reduction of the thermal bridge. Then designed VIPs were applied to a wall. The linear thermal transmittance and the effective thermal conductivity were analyzed by HEAT2 simulation program for two dimensional steady-state heat transfer. The result compared with a wall with non-capsulized VIPs. Result: It analyzed that the wall with capsulized VIPs had lower linear thermal transmittance and reduced the difference of the effective thermal transmittance with one dimensional thermal transmittance compared to that of the wall with non-capsulized VIPs.

Thermal bridges in a prefabricated wooden house: comparison between evaluation methods

ABSTRACTThe major aim of this study was to create a numerical model of thermal bridges in a wooden structure and to discover differences between factual values of linear thermal transmittance utilized in the finite-element (FE) modelling and values given by the European normative method (EN ISO 14683). Thermal bridges of wooden structures were detected using thermocamera FLIR S65 for infrared detection. These measurements allow displaying the temperature distribution of the thermal scan and proving the positive correlation between heat flux and change in the evaluated temperatures of a thermal bridge. A three-dimensional FE model of the structure was prepared for the thermal analysis using the engineering software ANSYS Workbench 13. The transmission heat loss coefficients of a prefabricated wooden house were established based on the Czech normative method (ČSN 730540-4). Linear thermal transmittance values calculated from the thermal analysis and the normative method given by EN ISO 10211 were compared. The results show that even if the transmission heat loss coefficients meet the requirements designated by standards, the real heat losses are increased by thermal bridges involved in the construction. Their influence is determined by the linear transmittance value which is usually not exactly established.