Λe Values Research Articles

Analysis of composition and temperature dependence of some thermal transport properties in glassy Ge30−xSe70Snx alloys using transient plane source technique

Measurements of thermal transport properties such as effective thermal conductivity (λ e) and effective thermal diffusivity (k e) of Ge30−xSe70Snx (x = 8, 11, 14, 17, and 20) chalcogenide glasses have been made using transient plane source technique in temperature range from room temperature to 300 °C. Both effective thermal conductivity (λ e) and effective thermal diffusivity (k e) are almost constant in the temperature range from room temperature to 240 °C. Beyond 240 °C, both λ e and k e increase with the increase in temperature and show maxima at a particular temperature which is a characteristic temperature for a given material. For further increase in temperature, both λ e and k e decrease slowly. Addition of Sn concentration in the glass increases the value of λ e and k e over the entire range of temperature under investigation for all five samples. Here, an effort has also been made to predict the values of both λ e and k e by using empirical relationships.

The ratio and topology effects of benzodithiophene donor-benzooxadiazole acceptor fragments on the optoelectronic properties of donor molecules toward solar cell materials.

A series of conjugated donor molecules (DmAnSq where m = 1-4, n = 1-7 while D = benzodithiophene, A = benzooxadiazole and S denotes ethyne spacers between D and A or D and D fragments) with various ratios of D/A fragments and topologies have been designed and investigated for OPV applications. An increase in the ratio of the acceptor fragment with respect to the donor fragment decreases the LUMO energy level and narrows the Eg for the designed molecule. More vertically (C4 and C8 substituted phenyl ring positions) bonded acceptor fragments than linearly (C2 and C6 substituted thiophene ring positions) bonded fragments result in a significant red shift in the maximum absorption wavelength. While, linearly bonded fragments lead to stronger absorption bands. Molecules with D-A-D topology exhibit more significant optical and electronic characteristics than those with D-D topology. All donor molecules (m = 2-4) of the D-A-D type show lower λh values than those of 1 donor containing (DAn) molecules. D-D type molecules show only lower λe values than DAn molecules because of the presence of a second donor fragment. The charge transfer phenomenon is shape dependent. The branched or anisotropic X, H, π, n, and square shaped molecules display higher charge transfer rates than the corresponding linear isomers due to better dimensionality. On the basis of these results, we suggest that designed donor and corresponding matched acceptor molecules have potential to act as promising candidates in solar cell devices.

Latent heat exchange in the boreal and arctic biomes.

In this study latent heat flux (λE) measurements made at 65 boreal and arctic eddy-covariance (EC) sites were analyses by using the Penman-Monteith equation. Sites were stratified into nine different ecosystem types: harvested and burnt forest areas, pine forests, spruce or fir forests, Douglas-fir forests, broadleaf deciduous forests, larch forests, wetlands, tundra and natural grasslands. The Penman-Monteith equation was calibrated with variable surface resistances against half-hourly eddy-covariance data and clear differences between ecosystem types were observed. Based on the modeled behavior of surface and aerodynamic resistances, surface resistance tightly control λE in most mature forests, while it had less importance in ecosystems having shorter vegetation like young or recently harvested forests, grasslands, wetlands and tundra. The parameters of the Penman-Monteith equation were clearly different for winter and summer conditions, indicating that phenological effects on surface resistance are important. We also compared the simulated λE of different ecosystem types under meteorological conditions at one site. Values of λE varied between 15% and 38% of the net radiation in the simulations with mean ecosystem parameters. In general, the simulations suggest that λE is higher from forested ecosystems than from grasslands, wetlands or tundra-type ecosystems. Forests showed usually a tighter stomatal control of λE as indicated by a pronounced sensitivity of surface resistance to atmospheric vapor pressure deficit. Nevertheless, the surface resistance of forests was lower than for open vegetation types including wetlands. Tundra and wetlands had higher surface resistances, which were less sensitive to vapor pressure deficits. The results indicate that the variation in surface resistance within and between different vegetation types might play a significant role in energy exchange between terrestrial ecosystems and atmosphere. These results suggest the need to take into account vegetation type and phenology in energy exchange modeling.

Theoretical Design of n-Type Organic Semiconducting Materials Containing Thiazole and Oxazole Frameworks

The characteristics of molecular structure and charge transport of some new n-type organic semiconductors containing thiazole 1a-6a and oxazole 1b-6b frameworks and trifluoromethylphenyl as terminal groups were predicted using density functional theory (DFT) methods. The energy levels of HOMO and LUMO of these compounds are decreased when thiophene and furan units are replaced by thiazole and oxazole units, respectively. The same trend was observed when benzo[1,2-d:4,5-d']bisthiazole groups were replaced with benzo[1,2-d:4,5-d']bisthiazole-4,8-diones. The reorganization energies for electron of compounds are computed in a range of 0.21-0.37 eV, which is comparable to the value of 0.25 eV of well-known n-type semiconductors such as perfluoropentacene. Some important trends can be pointed out as follows: (i) replacing the core thiazolothiazole unit of compounds 1a and 2a by the larger core benzo[1,2-d:4,5-d']bisthiazole units of 3a and 4a decreases both reorganization energies for electron (λ(e)); (ii) the λ(e) values of compounds containing thiazole 2a, 4a, and 6a are smaller than those of compounds containing thiophene 1a, 3a, and 5a, respectively; (iii) there is no clear trend when replacing benzene rings of compounds 3a and 4a by quinone rings of 5a and 6a. The λ(e) values of 5 and 6 are only somewhat larger. The same trend is also found for compounds containing oxazole 1b-6b. The intermolecular charge transports in solid state of these compounds mainly occur among molecules in the same molecular layer, whereas intermolecular interactions between molecules in different molecular layers are very small. Generally, beside some experimentally reported molecules 1a-4a, the remaining molecules designed here are good candidates for n-type organic semiconducting materials with small reorganization energies for electron and low energy levels of LUMO.

QCD sum rules for quark–gluon three-body components in the B meson

We discuss the QCD sum rule calculation of the heavy-quark effective theory parameters, λE and λH, which correspond to matrix elements representing quark–gluon three-body components in the B-meson wavefunction. We derive the sum rules for λE,H calculating the new higher-order QCD corrections, i.e., the order αs radiative corrections to the Wilson coefficients associated with the dimension-5 quark–gluon mixed condensates, and the power corrections due to the dimension-6 vacuum condensates. We find that the new radiative corrections significantly improve the stability of the corresponding Borel sum rules and lead to the reduction of the values of λE,H. We also discuss the renormalization-group improvement for the sum rules and present update on the values of λE,H.

Determination of the Thermal Conductivity in Adobe With Several Models

The thermal conductivity of the earth materials conditions their ability as thermal isolator and its heating capacity, which has a direct impact on the energy consumption of the buildings built with these materials. Two original mathematical models have been developed (models MA-1 and MA-2) to calculate the effective thermal conductivity (λE) of adobes and their results have been compared with other models already known for other materials and with experimental measures done on adobes. The model MA-1 starts from the electric analogy of the transmission of heat in series and in parallel. The model MA-2 is obtained with a regression curve from experimental and literature values of λE in adobes. The λE in adobes has been measured by the thermal needle probe (TNP) procedure using 10 min as the measuring time. For dry adobes, with average environmental conditions of 19 °C and 41% of relative moisture, the values of λE measured were 0.80 W/(m·K) ± 10%. For natural hygroscopic moisture of 1.67% in the same environmental conditions, a λE of 0.90 W/(m·K) ± 10% was measured. Only five of the 18 models analyzed adjust to the values experimentally measured, and their precision depends on the values of λ of the components, which are obtained from the literature. Of the proposed models, the MA-1 fits for the values of the dry and wet material and with some determined values of the literature. The model MA-2 fits in all cases since it does not depend on the values of the literature but on the density of the material and its moisture content.

Actual evapotranspiration in drylands derived from in-situ and satellite data: Assessing biophysical constraints

Improving regional estimates of actual evapotranspiration (λΕ) in water-limited regions located at climatic transition zones is critical. This study assesses an λΕ model (PT-JPL model) based on downscaling potential evapotranspiration according to multiple stresses at daily time-scale in two of these regions using MSG–SEVIRI (surface temperature and albedo) and MODIS products (NDVI, LAI and fPAR). An open woody savanna in the Sahel (Mali) and a Mediterranean grassland (Spain) were selected as test sites with Eddy Covariance data used for evaluation. The PT-JPL model was modified to run at a daily time step and the outputs from eight algorithms differing in the input variables and also in the formulation of the biophysical constraints (stresses) were compared with the λΕ from the Eddy Covariance. Model outputs were also compared with other modeling studies at similar global dryland ecosystems.The novelty of this paper is the computation of a key model parameter, the soil moisture constraint, relying on the concept of apparent thermal inertia (fSM-ATI) computed with surface temperature and albedo observations. Our results showed that fSM-ATI from both in-situ and satellite data produced satisfactory results for λΕ at the Sahelian savanna, comparable to parameterizations using field-measured Soil Water Content (SWC) with r2 greater than 0.80. In the Mediterranean grasslands however, with much lower daily λE values, model results were not as good as in the Sahel (r2=0.57–0.31) but still better than reported values from more complex models applied at the site such as the Two Source Model (TSM) or the Penman–Monteith Leuning model (PML).PT-JPL-daily model with a soil moisture constraint based on apparent thermal inertia, fSM-ATI offers great potential for regionalization as no field-calibrations are required and water vapor deficit estimates, required in the original version, are not necessary, being air temperature and the available energy (Rn-G) the only input variables required, apart from routinely available satellite products.

X-Shaped donor molecules based on benzo[2,1-b:3,4-b′]dithiophene as organic solar cell materials with PDIs as acceptors

Employing a double overlapping wave band strategy based on DFT, five X-shaped anisotropic low energy gap donor compounds (D1–D5) have been designed for solar cell applications. A series of new PDI acceptor molecules are built to match each designed donor in terms of frontier molecular orbital energy levels by tuning substituents at P1 and P2 positions of PDI1. The designed donors consist of a central electron donor fragment benzodithiophene (DF), electron accepting fragments (A1 to A5) and terfuran and ethynyl-terfuran bridges (B1 and B2 respectively). The absorption bands of the designed donors based on TD-DFT not only cover the visible region but also extend to the infrared region of the spectrum. The donor fragment DF and multibranched spacers B1 and B2 are responsible for absorption in short and middle wavelength regions while the acceptor fragments contribute to the middle and long wavelength regions of the spectrum. In addition, PDIs also exhibit complementary absorptions in the visible range of the solar spectrum. Among designed donors, D1 exhibits ideal lowest band gap, FMO energy levels and exclusive broadest absorption because of the strongest electron withdrawing fragment. The lower λe values as compared to λh illustrate that these five donors would be favorable for electron transfer. The carrier mobility of D1 in the crystalline state has been predicted using the P21/c space group. D1 displays higher carrier mobility for μe = 2.00 cm2 V−1 s−1 and μh = 1.7 × 10−2 cm2 V−1 s−1. The calculated Voc of D1 is 1.02 V. The designed donors and PDI acceptors are suitable and recommended for high performance solar cell devices.

Thermal radiation and conduction properties of materials ranging from sand to rock-fill

This paper presents an experimental study on thermal radiation and the thermal conductivity of rock-fill materials using a 1 m × 1 m × 1 m heat transfer cell. Testing temperatures are applied by temperature-controlled fluid circulation at the top and bottom of the sample. Heat flux and temperature profiles are measured to establish the effective thermal conductivity λe, which includes contributions from both conduction and radiation heat transfer mechanisms. The materials studied had an equivalent particle size (d10) ranging from 90 to 100 mm and porosity (n) ranging from 0.37 to 0.41. The experimental results showed that thermal radiation greatly affects the effective thermal conductivity of materials with λe values ranging from 0.71 to 1.02 W·m−1·K−1, compared with a typical value of 0.36 W·m−1·K−1 for conduction alone. As expected, the effective thermal conductivity increased with particle size. An effective thermal conductivity model has been proposed, and predictions have been successfully compared with the experimental results. Radiation heat transfer becomes significant for d10 higher than 10 mm and predominant at values higher than 90 mm. The results of the study also suggest that the cooling potential of convection embankments used to preserve permafrost conditions may not be as efficient as expected because of ignored radiation effects.

Parameterizing canopy resistance using mechanistic and semi‐empirical estimates of hourly evapotranspiration: critical evaluation for irrigated crops in the Mediterranean

AbstractIn this paper two models are presented for calculating the hourly evapotranspiration λE (W m−2) using the Penman–Monteith equation. These models were tested on four irrigated crops (grass, soya bean, sweet sorghum and vineyard), with heights between 0·1 and 2·2 m at the adult growth stage. In the first model (Katerji N, Perrier A. 1983. Modélisation de l'évapotranspiration réelle ETR d'une parcelle de luzerne : rôle d'un coefficient cultural. Agronomie 3(6): 513–521, KP model), the canopy resistance rc is parameterized by a semi‐empirical approach. In the second model (Todorovic M. 1999. Single‐layer evapotranspiration model with variable canopy resistance. Journal of Irrigation and Drainage Engineering—ASCE 125: 235–245, TD model), the resistance rc is parameterized by a mechanistic model. These two approaches are critically analysed with respect to the underlying hypotheses and the limitations of their practical application. In the case of the KP model, the mean slope between measured and calculated values of λE was 1·01 ± 0·6 and the relative correlation coefficients r2 ranged between 0·8 and 0·93. The observed differences in slopes, between 0·96 and 1·07, were not associated with the crop height. This model seemed to be applicable to all the crops examined. In the case of the TD model, the observed slope between measured and calculated values of λE for the grass canopy was 0·79. For the other crops, it varied between 1·24 and 1·34. In all the situations examined, the values of r2 ranged between 0·73 and 0·92. The TD model underestimated λE in the case of grass and overestimated it in the cases of the other three crops. The under‐ or overestimation of λE in the TD model were due: (i) to some inaccuracies in the theory of this model, (ii) to not taking into account the effect of aerodynamic resistance ra in the canopy resistance modelling. Therefore, the values of rc were under‐ or overestimated in consequence of mismatching the crop height. The high value of air vapour pressure deficit also contributed to the overestimation of λE, mainly for the tallest crop. The results clarify aspects of the scientific controversy in the literature about the mechanistic and semi‐empirical approaches for estimating λE. From the practical point of view the results also present ways for identifying the most appropriate approach for the experimental situations encountered. Copyright © 2010 John Wiley & Sons, Ltd.

Evaluation of thermal conductivity in air permeable concrete for dynamic breathing wall construction

Abstract Air permeable concrete (APC) is potentially useful as a dynamic insulator. The dynamic function is achieved by passing air through the material in the direction of heat flow to facilitate heat recovery. An APC sample of 200 mm length with 60% cement filling of large voids (between 0.5 and 5 mm), was tested between 5 and 10 Pa differential pressures; permeabilities were 0.28–0.32 m2/Pa h, confirming its suitability as a dynamic insulator. To characterise properties it is necessary to determine the static thermal conductivity, i.e., no air flow. A one-dimensional heat flow model for predicting the effective thermal conductivity (λe) of APC is developed using as variables the fractions of voids, aggregate and cement paste comprising the material. Measured values of λe were 0.7–1.4 W/m K. A theoretical model predicts and further improves the performance and formulation of APC. The water/cement ratio (w/c) also controls the λe. Increasing w/c increases the volume of micropores, adding resistance to heat flow.

Thermal transport and its structure dependence in ZnxSe100−x (x=10, 20, 40 and 50) alloys

Abstract Simultaneous measurements of effective thermal conductivity (λe) and effective thermal diffusivity (χe) of twin pellets of ZnxSe100−x (x = 10, 20, 40 and 50) chalcogenide materials, prepared under a load of 5 tons (equivalent pressure ≈ 433 MPa), have been made at room temperature using transient plane source (TPS) technique. From the measured values of λe and χe specific heat per unit volume (Cp) has been calculated. The results indicate that both the values of λe and χe increase linearly with increasing Zn concentration. Similar to λe and χe, the Cp also shows a linear increase with the increase in Zn concentration. This behaviour of λe and χe with increasing Zn concentration can be explained using structural information obtained from X-ray diffraction (XRD) of these materials and also using the change in the nature of bond from covalent to iono-covalent in this system. Comparative XRD studies for structural investigation of ZnxSe100−x (x = 10 and 40) have also been discussed. An effort has also been made to predict these values by an empirical relation. The values obtained through empirical relations are in good agreement with the experimental values of λe, χe and calculated values of Cp.

Composition dependence of effective thermal conductivity and effective thermal diffusivity of Se100−xInx (x=0, 5, 10, 15 and 20) chalcogenide glasses

Simultaneous measurement of effective thermal conductivity (λe) and effective thermal diffusivity (χe) of twin pallets of Se100−xInx (x=0,5, 10, 15, and 20) glasses, prepared under a load of 5 tons, have been made at room temperature using the Transient Plane Source (TPS) technique. The values of λe and χe were found to increase initially with the increase of concentration of In in Se–In alloy and had their maximum at 10at.wt% of indium. For indium concentration beyond 10at.wt% of the values of effective thermal conductivity and effective thermal diffusivity decrease linearly. This is suggestive of fact that 10at.wt% of indium can be considered as a critical composition at which the alloy becomes, chemically ordered and maximum thermally stable than other composition. Further addition of indium in selenium decreases the values of λe and χe. The behaviour is explained on the basis of decrease of localized states and increase in disorderness for higher composition indium.

Temperature dependence of the thermal conductivity and thermal diffusivity of treated oil‐palm‐fiber‐reinforced phenolformaldehyde composites

AbstractThe effective thermal conductivity (λe) and effective thermal diffusivity (χe) of oil‐palm‐fiber‐reinforced treated composites were measured simultaneously with the transient plane source technique from 50 to 110°C. The fibers of the composites were treated with sodium hydroxide alkali, silanol, and acetic acid. The experimental results for the different treated composites showed that there were variations in λe and χe over this temperature range. However, the maximum values of λe and χe were observed at 90°C, in the vicinity of the glass‐transition temperatures of these composites. An effort was also made to predict the temperature dependence of λe and χe through the development of an empirical model. The theoretically predicted values of λe and χe for these composites were in excellent agreement with the experimental results over the entire range of investigated temperatures. Sudden increases in λe and χe in the glass‐transition region of these composites were indicative of the fact that the crosslinking density decreased and was at a minimum at the temperature at which λe and χe showed their maxima. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3458–3463, 2003

Mathematical modelling of heat transfer during electron-beam autocrucible melting by means of the steady-state Stefan problem

A two-dimensional axisymmetric mathematical model of electron-beam autocrucible melting is developed and examined. Here, the hypothesis is used that forced convective heat transfer in the melt may be modelled with the help of the coefficient of effective thermal conductivity, λE. A simplified approach is used in which λE is assumed to be known. In another approach the value of λE depends on a prescribed value of a mean melt-stirring velocity and a mean liquid-pool radius which is determined in the course of solving of the problem. With the help of the Kirchoff transformation and a Green function we may reduce the problem to a nonlinear Hammerstein integral equation. Here, a dependence of the thermal-conductivity coefficient on the temperature, λS(T), at the cooled surfaces is disregarded and constant (mean) values of λS are utilized. In order to solve the problem in the case where this dependence λS(T) is taken into account, an axuiliary Green-function method is proposed which also permits to take into account a change of the heat-exchange coefficients on the autocrucible. This reduces the problem to a system of three integral Hammerstein equations. Numerical solutions of the nonlinear integral equations are obtained with the help of a variational (projective-net) method for the case of circular scanning of an electron beam over the heated surface. The computational results are well consistent with experimental data.

Estimating Latent Heat Flux from a Vineyard using Scintillometry

The combination of a near-infrared and a microwave scintillometer were used to estimate the line-averaged, latent heat flux density (λEs) from a well-irrigated, vineyard valley during summer. The 2 km scintillometer beam passed over the valley floor at a height (z) of 30 m. Eddy covariance towers instrumented at 3 ill above the valley surface provided an independent check of vineyard evaporation. A formula for free convective λEe compared favourably to the eddy covariance values, λEe at low wind speeds and under clear skies. As the convective boundary layer (CBL) developed and passed through the scintillometer beam it caused additional scintilla- tions, in which case λEe ＞＞ λEe. During unstable conditions the comparisons were in close agreement. However λEs tended to overestimate λEe as the wind speed increased. For near-neutral conditions the scintillometer gave unrealistically large values of λE s. The additional scintillations originated from the strong entrainment of advected dry and warm air into the newly formed surface boundary layer. During calm overcast days, cold days and during the early morning periods when the surface fluxes were small, the signal strength of the infrared scintillometer approached the system noise.

Soil and canopy energy balances in a west Texas vineyard

Water use in vineyards is controlled by energy absorbed by plants and the soil surface. An 8 day field experiment was conducted in a commercial vineyard near Lamesa, TX, to evaluate soil and canopy energy balances, and to examine energy exchange between canopy and soil. Grapevines in the vineyard were wrapped tightly to trellis wires, creating compact hedgerows that were 3 m apart and of 1.6 m height and 0.4 m width, with little foliage below 1 m above the soil surface. The Bowen ratio method was used to measure the vineyard energy balance including total latent heat flux ( λE). Latent heat flux from the canopy ( λE C) was determined from sap flow measurements of transpiration. Soil latent heat flux ( λE S) was calculated as the difference between λE and λE C. These measurements were combined with measurements of soil net irradiance to partition the vineyard energy balance into soil and canopy components. During the study, λE S accounted for 44–68% of λE. Unstable conditions predominated during the study, with the soil generating sensible heat that was transferred to the canopy, producing values of λE C that were greater than canopy net irradiance. Within-row advection of sensible heat was 17–36% of λE C. Although the canopy was cooler than within- and above-canopy air, it was not a strong enough sink for sensible heat to produce stable conditions above the canopy. The narrow hedgerows created an unusual diurnal pattern of canopy net irradiance, having midmorning and midafternoon peaks, and a low midday plateau. Morning and afternoon peaks occurred during times of maximum direct beam irradiance on east and west sides of the hedgerows. Results also showed that within-canopy wind speed and air temperature were affected by wind direction.

Interpretation of surface flux measurements in heterogeneous terrain during the Monsoon '90 experiment

A network of 9‐m‐tall surface flux measurement stations were deployed at eight sparsely vegetated sites during the Monsoon '90 experiment to measure net radiation, Q, soil heat flux, G, sensible heat flux, H (using eddy correlation), and latent heat flux, λE (using the energy balance equation). At four of these sites, 2‐m‐tall eddy correlation systems were used to measure all four fluxes directly. Also a 2‐m‐tall Bowen ratio system was deployed at one site. Magnitudes of the energy balance closure (Q + G + H + λE) increased as the complexity of terrain increased. The daytime Bowen ratio decreased from about 10 before the monsoon season to about 0.3 during the monsoons. Source areas of the measurements are developed and compared to scales of heterogeneity arising from the sparse vegetation and the topography. There was very good agreement among simultaneous measurements of Q with the same model sensor at different heights (representing different source areas), but poor agreement among different brands of sensors. Comparisons of simultaneous measurements of G suggest that because of the extremely small source area, extreme care in sensor deployment is necessary for accurate measurement in sparse canopies. A recently published model to estimate fetch is used to interpret measurements of H at the 2 m and 9 m heights. Three sites were characterized by undulating topography, with ridgetops separated by about 200–600 m. At these sites, sensors were located on ridgetops, and the 9‐m fetch included the adjacent valley, whereas the 2‐m fetch was limited to the immediate ridgetop and hillside. Before the monsoons began, vegetation was mostly dormant, the watershed was uniformly hot and dry, and the two measurements of H were in close agreement. After the monsoons began and vegetation fully matured, the 2‐m measurements of H were significantly greater than the 9‐m measurements, presumably because the vegetation in the valleys was denser and cooler than on the ridgetops and hillsides. At one lowland site with little topographic relief, the vegetation was more uniform, and the two measurements of H were in close agreement during peak vegetation. Values of λE could only be compared at two sites, but the 9‐m values were greater than the 2‐m values, suggesting λE from the dense vegetation in the valleys was greater than elsewhere.

高温における鉛製錬水砕スラグおよびそのセメント複合材料の熱伝導性の評価

A new continuous measurement system has been developed in this study to measure the effective thermal conductivity, λe, of smelting granulated slag-water mixture beds and slag-cement composite materials under dry and wet conditions over the range from room temperature to 220°C. The measurement technique is based on a modified hot wire method. For the slag sample, lead smelting granulated slag, called “Black Sand” in Uguisuzawa, Miyagi Prefecture, was used. For the composite material, three samples, A, B and C that the values of a ratio of cement to Black Sand (C/BS) were different from each other were used. The C/BS values of the samples, A, B and C are 30/70, 25/75 and 20/80 by weight, respectively. The tested temperatures, θ, of the samples were set by considering utilization of the slag for the high level radioactive waste repository as buffer materials.The measurements of λe were conducted during both heating and cooling processes of the samples to evaluate a thermal hysteresis of λe. For the dry samples, the thermal hysteresis was not observed. The following equations of λe [W/(m.K)] of the dry samples were obtained:(1)λe=-0.000201θ+0.901 for Sample A, (2)λe=0.0004660+0.805 for Sample B and (3) Ae=0.0006820+0.798 for Sample C. On the other hand, for the wet samples, the thermal hysteresis was recognized. The λe values in the heating process were 0.9-1.5W/(m.K), but the values in the cooling process were 0.8-1.1W/(m.k). Thermal conductivity of solid component of the Black Sand, λs, was estimated from the λe of the Black Sand -water mixture beds and a thermal conductance model developed by the authors, and expressed as λs=0.0121θ+1.21. These results mean that Black Sand may be an effective buffer material having sufficiently good heat conducting properties to keep the temperature of deeply buried canisters within a suitable interval.

Relationship between protonproton NMR coupling constants and substituent electronegativities. V—Empirical substituent constants deduced from ethanes and propanes

AbstractThe electronegativity dependence of the torsion angle‐independent term in the Karplus equation, i.e. of the ‘constant’ A in the Fourier expansion A + B cos ϕ + C cos 2ϕ +…, was investigated. Experimental proton‐proton coupling constants of substituted ethanes and isopropanes appeared to be suitable for this purpose. A data set was constructed which contained 70 couplings, newly measured or remeasured at 300 MHz, and 25 couplings taken from the literature. The accuracy of each data point is estimated as ≤0.02 Hz, with a few exceptions. The actual analysis was carried out on 93 data points, i.e. on J values of 55 mono‐ and of 38 1,1‐di‐substituted ethanes, including 22 isopropyl derivatives. A total of 55 chemical groups is represented in the set; some of these were taken together, leaving 50 distinct groups. Regression analysis of the present data versus standard electronegativities did not yield acceptable results. Instead, substituent parameters λe, valid for 3J(HH) in saturated HCCH fragments, were derived in a least‐squares procedure from the data set. The couplings from mono‐ and 1,1‐di‐substituted ethanes could be accounted for in a simple expression that contains an interaction term C012(λ1λ2). The best equation obtained is The parameters are valid for λe values scaled according to the Huggins electronegativities: λH = 0, λOR = 1.40. The equation fits 84 experimental couplings with a root‐mean‐square deviation of 0.018 Hz and a maximum deviation of 0.06 Hz. Some exceptions occur. (i) CH3CH3, CH3CHCl2 and CH3CHF2 appear to follow a different, but correlated, regression; (ii) C(O)H, C(O)R, SO2Cl and POCl2 groups require different λe values according to the substitution pattern, i.e. mono‐ or 1,1‐di‐substitution. The striking difference between the new λe substituent‐effect scale and other empirical electronegativity scales lies in the inverse correlation of λe with increasing electronegativity of β‐substituents. The inverse relationship is not only found for α‐carbon atoms, but appears to represent a general phenomenon, also seen for substituted α‐hetero atoms (O, N, S).