Steady-state Measurements Research Articles

Non-parametric inference of impurity transport coefficients in the ASDEX Upgrade tokamak

We present a non-parametric inference of impurity transport coefficients by using charge exchange recombination spectroscopy measurements of Ne X, Ne VIII, O VIII, and C VI lines. Due to their close atomic numbers, neon, oxygen and carbon impurity ions are assumed to have the same diffusion coefficient D and convection velocity v. Unlike conventional techniques that modulate or perturb the impurity contents, we employ a quasi-stationary plasma with static impurity profiles. Since the ratio of v to D only describes the equilibrated profile of the sum of all impurity charge states, steady-state measurements can still decouple D and v if different charge states are simultaneously observed. We have formulated a non-parametric analysis framework based on the Bayesian probability theory and conducted transport coefficient measurements for a Type III ELMy H-mode plasma at ASDEX Upgrade. The charge exchange reactions with the background neutrals, which are known to affect the impurity charge state balance, are taken into account by introducing additional free parameters. While D at the pedestal is close to the neoclassical level (1 m s−2), a large diffusion coefficient and a strong outward convection are inferred right inside the pedestal top.

Long-Lived Photoluminescence of Molecular Group 14 Compounds through Thermally Activated Delayed Fluorescence.

Photoluminescent molecules exploiting the sizable spin-orbit coupling constants of main group metals and metalloids to access long-lived triplet excited states are relatively rare compared to phosphorescent transition metal complexes. Here we report the synthesis of three air- and moisture-stable group 14 compounds E(MePDPPh)2, where E = Si, Ge, or Sn and [MePDPPh]2- is the doubly deprotonated form of 2,6-bis(5-methyl-3-phenyl-1H-pyrrol-2-yl)pyridine. In solution, all three molecules exhibit exceptionally long-lived triplet excited states with lifetimes in the millisecond range and show highly efficient photoluminescence (Φ ≤ 0.49) due to competing prompt fluorescence and thermally activated delayed fluorescence at and around room temperature. Temperature-dependent steady-state emission spectra and photoluminescent lifetime measurements provided conclusive evidence for the two distinct emission pathways. Picosecond transient absorption spectroscopy allowed further analysis of the intersystem crossing (ISC) between singlet and triplet manifolds (τISC = 0.25-3.1 ns) and confirmed the expected trend of increased ISC rates for the heavier elements in otherwise isostructural compounds.

Origin of high thermal conductivity in disentangled ultra-high molecular weight polyethylene films: ballistic phonons within enlarged crystals

The thermal transport properties of oriented polymers are of fundamental and practical interest. High thermal conductivities ( ≳ 50 Wm−1K−1) have recently been reported in disentangled ultra-high molecular weight polyethylene (UHMWPE) films, considerably exceeding prior reported values for oriented films. However, conflicting explanations have been proposed for the microscopic origin of the high thermal conductivity. Here, we report a characterization of the thermal conductivity and mean free path accumulation function of disentangled UHMWPE films (draw ratio ~200) using cryogenic steady-state thermal conductivity measurements and transient grating spectroscopy. We observe a marked dependence of the thermal conductivity on grating period over temperatures from 30–300 K. Considering this observation, cryogenic bulk thermal conductivity measurements, and analysis using an anisotropic Debye model, we conclude that longitudinal atomic vibrations with mean free paths around 400 nanometers are the primary heat carriers, and that the high thermal conductivity for draw ratio ≳ 150 arises from the enlargement of extended crystals with drawing. The mean free paths appear to remain limited by the extended crystal dimensions, suggesting that the upper limit of thermal conductivity of disentangled UHMWPE films has not yet been realized.

Analysis of Rostov-II Benchmark Using Conventional Two-Step Code Systems

This paper presents the steady state analysis of the Rostov-II benchmark using the conventional two-step approach. It involves the STREAM/RAST-K and CASMO-5/PARCS code systems. This paper documents a comprehensive code-to-code comparison between Serpent 2, CASMO-5, and STREAM at the lattice level for the different fuel assemblies (FAs) loaded in the Rostov-II core; and between Serpent 2, PARCS, and RAST-K at the core level in 2D. Finally, the 3D results of both deterministic models are compared to the steady state measurements of the Rostov-II benchmark. With respect to the measurements available in the Rostov-II benchmark, comparable accuracy (30 ppm difference in boron concentration, 2% assembly power) with an industrial calculation scheme (BIPR8) are reported up to 36.73 EFPDs. The calculations reported in the paper showed that the modeling of the resonance self-shielding in the lattice code as well as the geometrical modeling of the reflector are key for an accurate solution (reducing the in-out power tilt). At the core simulator level, a fairly crude 1D reflector model appears to be enough. Overall, this paper provides the detailed models and conditions used in STREAM/RAST-K and CASMO-5/PARCS, and accurate calculation solution for the Rostov-II benchmark with STREAM/RAST-K and CASMO-5/PARCS compared with measurement.

An upper limit to the fluorescence quantum yield for reduced flavins – a spectroscopic approach to better understand photoflavoproteins

Flavins are blue‐light absorbing chromophores with rich redox activity, found in oxidized, one electron‐ and two electron‐reduced forms. Some, namely flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), are used by enzymes as catalytic cofactors. Conflicting literature regarding reduced flavin fluorescence emission includes a plethora of results, from some finding there is negligible fluorescence to others observing significantly blue‐shifted emission. This discrepancy is of consequence because mechanistic kinetic models of photoflavoproteins derived from optical spectroscopy rely on a proper assignment of this emission. Reduced flavins are common redox cofactors in cells, and any fluorescence‐based imaging of this molecule in vivo requires an accurate estimate of its emission quantum yield and spectrum. Here, the photo‐induced reduction of HPLC‐purified FMN and other relevant flavins, in aqueous solutions (at pH 5.0 and 8.5) under aerobic and anaerobic conditions, has been studied via steady‐state absorption and fluorescence measurements. An exogenous reducing agent, ethylenediaminetetraacetic acid (EDTA), was used to photo‐reduce the flavins under investigation. Facile and complete reduction of FMN (~105‐fold) is achieved under anaerobic conditions and insignificant amounts of reduced fluorescence emission is observed, allowing for calculation of the upper limit of the quantum yield of reduced flavin. The low quantum yield (~10‐4) obtained is an important finding when considering flavoproteins, especially when studying them spectroscopically.

Allosteric Regulation of the Mobile Loop in Lactate Dehydrogenase from Plasmodium Falciparum

Malaria is still considered one of the deadliest parasitic diseases. Plasmodium parasites that cause malaria, particularly P. falciparum, have become resistant to many commonly used treatments. To combat this illness, we propose developing novel therapeutics that selectively target the mobile loop region of lactate dehydrogenase (LDH), an enzyme that the parasite depends on for survival. In general, LDH catalyzes the interconversion of pyruvate to lactate and NADH to NAD+. The mobile loop of LDH from P. falciparum (pfLDH) is located proximal to the active site and contains five additional residues compared to mammalian LDH (Figure 1). This significant structural change makes the mobile loop region of pfLDH an attractive target for the development of therapeutics, as it contains a catalytically necessary arginine residue that interacts with the substrate upon loop closure. While inhibitors of LDH, both small molecule and peptide‐based, have been previously identified and developed, it is unclear if the mobile loop region of LDH serves as a viable target for drug discovery.Preliminary data recently obtained demonstrates that a previously developed DNA aptamer (2008s), designed to bind to the mobile loop region of pfLDH, inhibits the enzyme selectively over mammalian LDH. The developers of 2008s reported that the aptamer does not affect the kinetics of the enzyme. However, our steady‐state kinetics measurements show that the kcat or turnover number of pfLDH is initially decreased by half while the Km or Michaelis constant remains about the same at the highest aptamer concentration studied (100 nM). The decrease in Kcat with constant Km is characteristic of an uncompetitive inhibitor that does not compete with the substrate for the active site but decreases the overall rate of the enzyme reaction. The kinetic traces for these assays also show that activity fully recovers after approximately 20‐30 seconds, compared to assays performed in the absence of aptamer. Together, these preliminary data suggest that 2008s binds selectively to the pfLDH and inhibit the ternary complex initially; however, once the enzyme begins to turn over, the aptamer dissociates from the enzyme.Our results provide proof of concept that molecules designed to bind to the mobile loop of pfLDH can inhibit the enzyme. MD simulations using GROMACS will be utilized to explore the conformation space of the pfLDH loop motion and compare it to that of hhLDH. Regarding pfLDH, sampling the conformational space of the loop motion will allow for a better understanding of how aptamer binding impacts its dynamics and may also elucidate a druggable site on or near the mobile loop. Additional kinetics studies will be performed at higher aptamer concentrations to determine if more pronounced inhibitory effects are achievable. The development of allosteric inhibitors that bind to and limit the dynamics of the mobile loop region of pfLDH selectively could lead to a paradigm shift concerning the design of novel therapeutics and treatments for malaria and other diseases.

Round-Robin Inter-Comparison of Maximum Power Measurement for Metastable Perovskite Solar Cells

Perovskite solar cells (PSCs) are expected to be one of the next generation photovoltaics. However, reliable measurements of the power conversion efficiency (PCE) of PSCs are challenging as changes in the electrical properties occur during the conventional I–V curve measurements. In order to solve this problem, several methods to maximize the accuracy have been developed, but consistency between these methods has not been verified. In this paper, a round-robin inter-comparison of the maximum power measurements for metastable perovskite solar cells has been performed among three public laboratories in Japan using several methods. The maximum powers determined by the three laboratories using the conventional I–V curve measurement technique defined in IEC 60904–1 were compared to each other. The relative standard deviation of the maximum power was 4.76%. The maximum power point tracking (MPPT), steady-state (or stabilized) power output (SPO) and dynamic I–V measurements were also performed as the steady-state measurements of the maximum power. An excellent consistency was found to exist between the maximum powers obtained by the MPPT, SPO and dynamic I–V methods. The relative standard deviation of P max determined by the MPPT method at KISTEC and AIST was 1.25%.

A dynamic performance diagnostic method applied to hydrogen powered aero engines operating under transient conditions

At present, aero engine fault diagnosis is mainly based on the steady-state condition at the cruise phase, and the gas path parameters in the entire flight process are not effectively used. At the same time, high quality steady-state monitoring measurements are not always available and as a result the accuracy of diagnosis might be affected. There is a recognized need for real-time performance diagnosis of aero engines operating under transient conditions, which can improve their condition-based maintenance. Recent studies have demonstrated the capability of the sequential model-based diagnostic method to predict accurately and efficiently the degradation of industrial gas turbines under steady-state conditions. Nevertheless, incorporating real-time data for fault detection of aero engines that operate in dynamic conditions is a more challenging task. The primary objective of this study is to investigate the performance of the sequential diagnostic method when it is applied to aero engines that operate under transient conditions while there is a variation in the bypass ratio and the heat soakage effects are taken into consideration. This study provides a novel approach for quantifying component degradation, such as fouling and erosion, by using an adapted version of the sequential diagnostic method. The research presented here confirms that the proposed method could be applied to aero engine fault diagnosis under both steady-state and dynamic conditions in real-time. In addition, the economic impact of engine degradation on fuel cost and payload revenue is evaluated when the engine under investigation is using hydrogen. The proposed method demonstrated promising diagnostic results where the maximum prediction errors for steady state and transient conditions are less than 0.006% and 0.016%, respectively. The comparison of the proposed method to a benchmark diagnostic method revealed a 15% improvement in accuracy which can have great benefit when considering that the cost attributed to degradation can reach up to $702,585 for 6000 flight cycles of a hydrogen powered aircraft fleet. This study provides an opportunity to improve our understanding of aero engine fault diagnosis in order to improve engine reliability, availability, and efficiency by online health monitoring.

Comparison of Intercept Methods for Correction of Steady-State Relative Permeability Experiments for Capillary End Effects

Summary Steady-state relative permeability experiments are performed by coinjection of two fluids through core plug samples. The relative permeabilities can be calculated using Darcy’s law from the stabilized pressure drop and saturation of the core if capillary end effects and transient effects are negligible. In most cases, such conditions are difficult to obtain. Recent works have presented ways to extrapolate steady-state pressure drop and average saturation measurements affected by capillary end effects collected at different rates to obtain correct relative permeabilities at correct saturations. Both the considered methods are based on linear extrapolations to determine intercepts. Gupta and Maloney (2016) derived their method intuitively and validated it with numerical and experimental data. Andersen (2021a) derived a method from fundamental assumptions and presented an intercept method in a different form where the saturation and relative permeabilities are found directly and uniquely from straightline intercepts. All system parameters, including saturation functions and injection conditions, appear in the model. In this work, the two methods are compared. It is proven theoretically that Gupta and Maloney’s method is correct in that it produces the correct saturation and pressure drops corrected for capillary end effects. Especially, a constant pressure drop was assumed and here proved to exist, as a result of capillary end effects in addition to the Darcy law pressure drop with no end effects. Their method assumes a well-defined end effect region with length xCEE, but this length can be defined almost arbitrarily. This choice has little impact on average saturation and pressure drop, however. They also assumed that for a defined end effect region, the average saturation was constant and equal to the slope in their saturation plot. It is shown that if the region is defined, the average saturation is indeed constant, but not given by the slope. The correct slope is predicted by the Andersen model. We also comment on theoretical misinterpretations of the Gupta and Maloney method. A few works have correctly calculated that the pressure drop over the end effect region is independent of rate, but not accounted for that its length is rate dependent. We show that the combined pressure drop is equal to a constant plus the Darcy pressure drop over the full core. Examples are presented to illustrate the model behaviors. Literature datasets are investigated showing that (a) apparently rate-dependent CO2-brine relative permeability endpoints can be explained by capillary end effects and (b) the intercept methods can be applied to correct shale relative permeabilities.

Bidirectional Hydrogen Electrocatalysis on Epitaxial Graphene.

The climate change due to human activities stimulates the research on new energy resources. Hydrogen has attracted interest as a green carrier of high energy density. The sustainable production of hydrogen is achievable only by water electrolysis based on the hydrogen evolution reaction (HER). Graphitic materials are widely utilized in this technology in the role of conductive catalyst supports. Herein, by performing dynamic and steady-state electrochemical measurements in acidic and alkaline media, we investigated the bidirectional electrocatalysis of the HER and hydrogen oxidation reaction (HOR) on metal- and defect-free epigraphene (EG) grown on 4H silicon carbide (4H-SiC) as a ground level of structural organization of general graphitic materials. The absence of any signal degradation illustrates the high stability of EG. The experimental and theoretical investigations yield the coherent conclusion on the dominant HER pathway following the Volmer–Tafel mechanism. We ascribe the observed reactivity of EG to its interaction with the underlying SiC substrate that induces strain and electronic doping. The computed high activation energy for breaking the O–H bond is linked to the high negative overpotential of the HER. The estimated exchange current of HER/HOR on EG can be used in the evaluation of complex electrocatalytic systems based on graphite as a conducing support.

Influence of tumble and TKE on combustion, fuel economy, and emissions of a single cylinder motorcycle engine

The impact of gasoline engines on improving fuel consumption and reducing emissions has received increasing attention around the world, and emissions regulations have become stricter. However, complex techniques in engine improvement increase costs. The purpose of this study is to develop or improve the design of the intake geometry without additional cost to improve the engine thermal efficiency, thereby improving fuel economy and emissions. In this study, emissions and fuel consumption of a 125 c.c. commercially available motorcycle was investigated. In addition to modifying the intake and valve angles and maintaining the intake air volume, a software for computational fluid dynamics (CFD) was used for steady-state and transient analysis of the in-cylinder flow field, tumble ratio and turbulence kinetic energy (TKE), and the results were compared with the data of the experimental platform. The burn duration of the engine, indicated mean effective pressure (IMEP), indicated specific total hydrocarbons (ISHC), nitrogen oxide (ISNOx) and carbon monoxide (ISCO) were measured on the bench. The transient predicted results show that the tumble ratio is a maximum increase of 27.82% at 656 crank angle (CA) degrees near the top dead center (TDC) on the compression stroke. In the ignition area within 5°–20° before top dead center (BTDC), average of the turbulence kinetic energy (TKE) was 120.37 m2/s2, distributed hot area was wide and close to the ignition position. In the steady-state measurement, it was verified that the tumble ratio was significantly improved by modifying inlet, the same trend as the analysis result. In the bench test for full load measurement, the average of IMEP increased by 10.92%, indicated specific fuel consumption (ISFC) improved by 11.7%, burn duration increased by 25.27%, ISCO improved by 43.41%, and ISHC improved by 64.33%. For portion load measurement, the average of ISFC improved by 2.16%, burn duration increased by 24.84%, ISCO improved by 43.44%, ISHC improved by 17.7% and ISNO improved by 12.89%. Based on the results, the tumble and TKE were improved by optimizing the angle between the intake valve and the intake port. The ISFC of model B was significantly improved under the two states. The ignition delay time was longer, and the overall burn duration was much improved. When it came to emissions, the ISCO and ISHC were significantly improved, and the ISNO was much higher at full load but lower at partial load due to the engine temperature and engine loads. At partial loads, the high tumble did benefit the combustion, fuel economy and emissions of a single-cylinder motorcycle engine.

Effect of fluorescence quenching model on quinoline derivative with cobalt chloride metal ion using steady state and time resolved spectroscopic methods.

Quinoline derivative, i.e. quinilone yellow with the scientific name [sodium 2-(2,3-dihydro-1,3-dioxo-1H-inden-2-yl)quinoline-6,8-disulphonate] (SQDS) is analysed for fluorescence resonance energy transfer (FRET). Fluorescence quenching mechanism is studied by employing steady state and transient state spectroscopic measurements. Cobalt chloride is used as quencher in the present study. Linearity was observed in Stern-Volmer plots for transient state as well as steady state. This was further attributed to a mechanism of collisional quenching. Efficiency in fluorescence quenching is observed as there is a correlation between quenching constants of both transient and steady state. A significant energy transfer is reported between metal ions and SQDS molecule, according to FRET theory. Characterization results are studied and analysed. Application in the field of non-linear optics are predicted for SQDS. With Kurtz and Perry powder technique, SHG (second harmonic generation) efficiency was measured using Q-switched mode locked Nd:YAG laser emitting 1064 nm the first time with this compound.

Appraisal of Steady-State Stormwater Control Measure Pollutant Removal Models within a Dynamic Stormwater Routing Framework

Appraisal of Steady-State Stormwater Control Measure Pollutant Removal Models within a Dynamic Stormwater Routing Framework

Criticality-Enhanced Quantum Sensing via Continuous Measurement

Present protocols of criticality-enhanced sensing with open quantum sensors assume direct measurement of the sensor and omit the radiation quanta emitted to the environment, thereby potentially missing valuable information. Here we propose a protocol for criticality-enhanced sensing via continuous observation of the emitted radiation quanta. Under general assumptions, we establish a scaling theory for the global quantum Fisher information of the joint system and environment state at dissipative critical points. We derive universal scaling laws featuring transient and long-time behavior governed by the underlying critical exponents. Importantly, such scaling laws exceed the standard quantum limit and can in principle saturate the Heisenberg limit. To harness such advantageous scaling, we propose a practical sensing scheme based on continuous detection of the emitted quanta as realized experimentally in various quantum-optical setups. In such a scheme a single interrogation corresponds to a (stochastic) quantum trajectory of the open system evolving under the nonunitary dynamics dependent on the parameter to be sensed and the backaction of the continuous measurement. Remarkably, we demonstrate that the associated precision scaling significantly exceeds that based on direct measurement of the critical steady state, thereby establishing the metrological value of the continuous detection of the emitted quanta at dissipative criticality. We illustrate our protocol via counting the photons emitted by the open Rabi model, a paradigmatic model for the study of dissipative phase transition with finite components. Our protocol is applicable to generic quantum-optical open sensors permitting continuous readout, and may find applications at the frontier of quantum sensing, such as the human-machine interface, magnetic diagnosis of heart disease, and zero-field nuclear magnetic resonance.

Selective dehydra-decyclization of cyclic ethers to conjugated dienes over zirconia

ZrO2 provides high selectivity (>90%) to conjugated pentadienes through the dehydra-decyclization of C-5 cyclic ethers, even at high conversions. 1,3-Pentadiene was the major product in both reaction of 2-methyltetrahydrofuran and tetrahydropyran over ZrO2. The reaction of 3-methyltetrahydrofuran produced nearly stoichiometric amounts of isoprene. Other catalysts, including TiO2, γ-Al2O3, and H-ZSM-5, were generally much less selective and produced a mixture of diene isomers. A combination of TPD and steady-state measurements revealed that both piperylenes are exclusively produced through primary catalytic pathways from 2-methyltetrahydrofuran, avoiding any isomerization once formed. First-principle calculations on ZrO2 imply the presence of an energetically favored, surface isomerization of ring-opened intermediates to conjugated alkenolates that selectively dehydrate to conjugated dienes, providing high selectivity to the desired products. The stabilization of the conjugated alkenolate is key for understanding the ability of ZrO2 to selectively produce conjugated dienes from cyclic ethers, without the need for the thermo-limited diene isomerization.

Distance-dependent resonance energy transfer in alkyl-terminated Si nanocrystal solids.

Understanding and controlling the energy transfer between silicon nanocrystals is of significant importance for the design of efficient optoelectronic devices. However, previous studies on silicon nanocrystal energy transfer were limited because of the strict requirements to precisely control the inter-dot distance and to perform all measurements in air-free environments to preclude the effect of ambient oxygen. Here, we systematically investigate the distance-dependent resonance energy transfer in alkyl-terminated silicon nanocrystals for the first time. Silicon nanocrystal solids with inter-dot distances varying from 3 to 5nm are fabricated by varying the length and surface coverage of alkyl ligands in solution-phase and gas-phase functionalized silicon nanocrystals. The inter-dot energy transfer rates are extracted from steady-state and time-resolved photoluminescence measurements, enabling a direct comparison to theoretical predictions. Our results reveal that the distance-dependent energy transfer rates in Si NCs decay faster than predicted by the Förster mechanism, suggesting higher-order multipole interactions.

Temperature-Dependent Fluorescence of mPlum Fluorescent Protein from 295 to 20 K.

The development of bright fluorescent proteins (FPs) emitting beyond 600 nm continues to be of interest both from a fundamental perspective in understanding protein-chromophore interactions and from a practical perspective as these FPs would be valuable for cellular imaging. We previously reported ultrafast spectral observations of the excited-state dynamics in mPlum resulting from interconversion between direct hydrogen bonding and water-mediated hydrogen bonding between the chromophore acylimine carbonyl and the Glu16 side chain. Here, we report temperature-dependent steady-state and time-resolved fluorescence measurements of mPlum and its E16H variant, which does not contain a side-chain permitting hydrogen bonding with the acylimine carbonyl. Lowering the temperature of the system freezes interconversion between the hydrogen-bonding states, thus revealing the spectral signatures of the two states. Analysis of the temperature-dependent spectra assuming Boltzmann populations of the two states yields a 205 cm-1 energy difference. This value agrees with the predictions from a quantum mechanics/molecular mechanics study of mPlum (198 cm-1). This study demonstrates the first use of cryogenic spectroscopy to quantify the energetics and timescales of FP chromophore structural states that were only previously obtained from computational methods and further confirms the importance of acylimine hydrogen-bonding dynamics to the fluorescence spectral shifts of red FPs.

Dependence of the rate-limiting steps in the dark-to-light transition of photosystem II on the lipidic environment of the reaction center

In our earlier works, we have identified rate-limiting steps in the dark-to-light transition of PSII. By measuring chlorophyll a fluorescence transients elicited by single-turnover saturating flashes (STSFs) we have shown that in diuron-treated samples an STSF generates only F1 (< Fm) fluorescence level, and to produce the maximum (Fm) level, additional excitations are required, which, however, can only be effective if sufficiently long Δτ waiting times are allowed between the excitations. Biological variations in the half-rise time (Δτ1/2) of the fluorescence increment suggest that it may be sensitive to the physicochemical environment of PSII. Here, we investigated the influence of the lipidic environment on Δτ1/2 of PSII core complexes of Thermosynechococcus vulcanus. We found that while non-native lipids had no noticeable effects, thylakoid membrane lipids considerably shortened the Δτ1/2, from ~ 1 ms to ~ 0.2 ms. The importance of the presence of native lipids was confirmed by obtaining similarly short Δτ1/2 values in the whole T. vulcanus cells and isolated pea thylakoid membranes. Minor, lipid-dependent reorganizations were also observed by steady-state and time-resolved spectroscopic measurements. These data show that the processes beyond the dark-to-light transition of PSII depend significantly on the lipid matrix of the reaction center.

Experimental Study on the Influence of Solar Heat Gain on the Thermal Performance of Hollow Ventilated Interior Wall

Abstract The heating system combining solar air collector with hollow ventilated interior wall (SAC-HVIW) can effectively extend the heating time. However, due to the large wall-window ratio of buildings on Tibetan Plateau, the strong solar radiation irradiating on the interior wall may influence the thermal performance of HVIW. In this paper, an experimental room is constructed to study the influence of external solar heat gain on the thermal performance of HVIW. Steady-state measurements are carried out by considering different ventilation rates, supply air temperatures and heat gains. Results show that the external heat gain has almost no effect on U-value, but it increases the heating capacity by increasing the logarithmic mean temperature difference (LMTD). For all cases, the heating capacity of HVIW is related to LMTD and supply air velocity, and U-value mainly increases with supply air velocity. Heat transfer of the interior surface of HVIW is dominated by forced convection which increases linearly with supply air velocity. The radiant heat transfer coefficient of the exterior surface of HVIW is not affected by the external heat gain with the mean value of 5.65 W/(m2 · K), while the convective heat transfer coefficient increases logarithmically with the external heat gain. The proportion of radiant heat transfer decreases as a power function with the increase of the exterior surface temperature. Measurements in this paper are used to evaluate the influence of external heat gain on the heating performance of HVIW, which is beneficial to the design of HVIW.

Solvation-controlled emission of divalent europium salts

Coordination-environment-dependent tuning of luminescence of divalent europium is an emerging topic of research. While it has been extensively demonstrated in the solid state, recent reports indicate similar findings in solution, where emission properties were tuned by altering different ligands and counter anions. In the present study, we demonstrate that differences in solvation shells alter the luminescence properties of divalent europium. Steady-state emission measurements indicate that the emission maxima of EuII salts in dimethoxyethane is red-shifted compared to the maxima in tetrahydrofuran. This shifting was confirmed with three different EuII salts: EuI2, EuBr2, and Eu(OTf)2. UV–visible spectroscopic measurements indicate a marginal difference in absorption spectra of EuII salts in tetrahydrofuran and dimethoxyethane, ruling out the possibility that a difference in ground-state geometry is responsible for the solvation-induced emission shift. Time-dependent density functional theory studies further support this conclusion. Relaxation of the excited state in dimethoxyethane is a postulated mechanism behind the red-shifted emission. The current study demonstrates a straight-forward path toward tuning the emission properties of EuII without altering light absorption.