Λe Values Research Articles

Approach toward Low Energy Loss in Symmetrical Nonfullerene Acceptor Molecules Inspired by Insertion of Different π-Spacers for Developing Efficient Organic Solar Cells.

In this quantum approach, by adding bridge/π-spacer fragments between the donor and acceptor parts of a newly constructed DF-PCIC (A-D-A type) molecule, it is the aim to improve the photovoltaic characteristics of organic solar cells (OSCs). After π-spacer insertion into the reference molecule (DF-R), six new molecules (DF-M1 to DF-M6) were designed. The optoelectronic attributes of newly inspected molecules were theoretically calculated using MPW1PW91/6-31G(d,p) level of theory. All newly proposed molecules possessed a lower band gap (Eg), a higher value of absorption, lower reorganization energy, greater dipole moment, and lower energies of excitations than the DF-R molecule. The frontier molecular orbital study proclaimed that the DF-M1 molecule has the lowest band gap of 1.62 eV in comparison to the 2.41 eV value of DF-R. Absorption properties represented that DF-M1 and DF-M2 molecules show the highest absorption values of up to 1006 and 1004 nm, respectively, in the near-infrared region. Regarding the reorganization energy, DF-M2 has the lowest value of λe (0.0683896 eV) and the lowest value of λh (0.1566471 eV). DF-M2 and DF-M5 manifested greater dipole moments with the values of 5.514665 and 7.143434 D, respectively. The open circuit voltage (VOC) of all the acceptors was calculated with J61, a donor complex. DF-M4 and DF-M6 molecules showed higher values of VOC and fill factor than the DF-R molecule. Based on the given results, it was supposed that all the newly presented molecules might prove themselves to be better than the reference and thus might be of great interest to experimentalists. Thus, they are suggested to be used to develop proficient OSC devices with improved photovoltaic prospects in the near future.

A DFT and TD-DFT study on emodin and purpurin and their functionalized molecules to produce promising organic semiconductor materials

Density functional theory (DFT) computations were done to explore the optical and electronic properties of two conjugated molecules, emodin and purpurin, as potential organic semi-conductors. The molecules were functionalized to explore the impact of functionalization on the electronic and optical properties. The properties calculated include reorganization energy (λh and λe), adiabatic ionization potential (IP), adiabatic electron affinity (EA), chemical hardness (n), HOMO and LUMO energies, and HOMO-LUMO energy gap (Eg) via B3LYP/6–3++G (d, p) method. In addition, the maximum absorption (λmax) and oscillator strength (f) at the excited states in vacuum and solvent (Ethanol) were investigated using time-dependent density functional theory (TD-DFT). The introduction of functional groups to emodin was considered to convert the molecule from a p-type into an n-type material, while purpurin is considered as an n-type material, its functionalization with NO2 and 2F resulted in a slight increase in λe values, which is considered detrimental for the process of charge-transport. However, the functionalized molecules have shown an increase in EA and a decrease in LUMO energy level, indicating their potential use as n-type materials. Furthermore, to have an understanding of the intermolecular interactions in emodin and purpurin molecules, Hirshfeld surface analysis and energy framework were studied.

Ab Initio Study of Two-Dimensional Cross-Shaped Non-Fullerene Acceptors for Efficient Organic Solar Cells.

In the present work, five novel non-fullerene acceptor molecules are represented to explore the significance of organic solar cells (OSCs). The electro-optical properties of the designed A–D–A-type molecules rely on the central core donor moiety associated with different halogen families such as fluorine, chlorine, and bromine atoms and acyl, nitrile, and nitro groups as acceptor moieties. Among these, M1 exhibits the maximum absorption (λmax) at 728 nm in a chloroform solvent as M1 has nitro and nitrile groups in the terminal acceptor, which is responsible for the red shift in the absorption coefficient as compared to R (716 nm). M1 also shows the lowest value of the energy band gap (2.07 eV) with uniform binding energy in the range of 0.50 eV for all the molecules. The transition density matrix results reveal that easy dissociation of the exciton is possible in M1. The highest value of the dipole moment (4.6 D) indicates the significance of M4 and M2 in OSCs as it reduces the chance of charge recombination. The low value of λe is given by our designed molecules concerning reference molecules, indicating their enhanced electron mobility. Thus, these molecules can serve as the most economically efficient material. Hence, all newly designed non-fullerene acceptors provide an overview for further development in the performance of OSCs.

The electron–phonon coupling constant and the Debye temperature in polyhydrides of thorium, hexadeuteride of yttrium, and metallic hydrogen phase III

A milestone experimental discovery of superconductivity above 200 K in highly compressed sulfur hydride by Drozdov et al. [Nature 525, 73 (2015)] sparked experimental and theoretical investigations of metallic hydrides. Since then, a dozen of superconducting binary and ternary polyhydrides have been discovered. For instance, there are three superconducting polyhydrides of thorium: Th4H15, ThH9, and ThH10 and four polyhydrides of yttrium: YH4, YH6, YH7, and YH9. In addition to binary and ternary hydrogen-based metallic compounds, recently Eremets et al. (arXiv:2109.11104) reported on the metallization of hydrogen, which exhibits a phase transition into metallic hydrogen phase III at P ≥ 330 GPa and T ∼ 200 K. Here, we analyzed temperature-dependent resistance, R(T), in polyhydrides of thorium, hexadeuteride of yttrium, and in hydrogen phase III and deduced the Debye temperature, Tθ, and the electron–phonon coupling constant, λe−ph, for these conductors. We found that I-43d-Th4H15 exhibits λe−ph = 0.82–0.99, which is in very good agreement with the experimental value of λe−ph = 0.84 deduced from heat capacity measurements [Miller et al., Phys. Rev. B 14, 2795 (1976)]. For P63/mmc-ThH9 (P = 170 GPa), we deduced λe−ph(170 GPa) = 1.46 ± 0.01, which is in reasonable agreement with λe−ph computed by first-principles calculations [Semenok et al. Mater. Today 33, 36 (2020)]. Deduced λe−ph(170 GPa) = 1.70 ± 0.04 for Fm-3m-ThH10 is in remarkable agreement with first-principles calculated λe−ph(174 GPa) = 1.75 [Semenok et al., Mater. Today 33, 36 (2020)]. Deduced λe−ph(172 GPa) = 1.90 ± 0.02 for Im-3m-YD6 is also in excellent agreement with first-principles calculated λe−ph(165 GPa) = 1.80 [Troyan et al., Adv. Mater. 33, 2006832 (2021)]. Finally, we deduced Tθ(402 GPa) = 727 ± 6 K for hydrogen phase III, which implies that λe−ph(402 GPa) ≤ 1.7 in this metal.

Exploration of efficient electron acceptors for organic solar cells: rational design of indacenodithiophene based non-fullerene compounds

The global need for renewable sources of energy has compelled researchers to explore new sources and improve the efficiency of the existing technologies. Solar energy is considered to be one of the best options to resolve climate and energy crises because of its long-term stability and pollution free energy production. Herein, we have synthesized a small acceptor compound (TPDR) and have utilized for rational designing of non-fullerene chromophores (TPD1–TPD6) using end-capped manipulation in A2–A1–D–A1–A2 configuration. The quantum chemical study (DFT/TD-DFT) was used to characterize the effect of end group redistribution through frontier molecular orbital (FMO), optical absorption, reorganization energy, open circuit voltage (Voc), photovoltaic properties and intermolecular charge transfer for the designed compounds. FMO data exhibited that TPD5 had the least ΔE (1.71 eV) with highest maximum absorption (λmax) among all compounds due to the four cyano groups as the end-capped acceptor moieties. The reorganization energies of TPD1–TPD6 hinted at credible electron transportation due to the lower values of λe than λh. Furthermore, open circuit voltage (Voc) values showed similar amplitude for all compounds including parent chromophore, except TPD4 and TPD5 compounds. These designed compounds with unique end group acceptors have the potential to be used as novel fabrication materials for energy devices.

Efficient tuning of small acceptor chromophores with A1-π-A2-π-A1 configuration for high efficacy of organic solar cells via end group manipulation

Now a days, non-fullerene organic compounds are considered with keen interest for the greener energy and potential photovoltaic devices. Herein, novel acceptor chromophores (DPDVD1-DPDVD4) were designed via small acceptor DPDVR compound with A1-π-A2-π-A1 architecture using promising approach by redistribution of end-capped acceptor moieties. The effect of end-capped acceptor moieties on designed architecture for the photophysical, photovoltaic and electronic behavior was explored using quantum chemical study. Frontier molecular orbital (FMO) findings revealed that all the molecules (DPDVD1-DPDVD4) contained narrow band gaps. The central acceptor moiety (PzDP) was responsible for the transformation of charge in DPDVD1-DPDVD4. UV–Vis data disclosed that λmax values of DPDVD1-DPDVD4 compounds were existed in visible region (537.36–517.05 nm). Interestingly, DPDVD2 exhibited the reduced band gap with broader absorption spectra among all chromophores might be due to the negative inductive effect (−I) of the terminal acceptors. The open circuit voltage (Voc) analysis was performed at the interface between standard donor polymer (PTB7) and DPDVD2. The higher value (3.34 V) of Voc was observed for DPDVD2 among reference and designed compounds. Furthermore, reorganization energy findings exploited DPDVR-DPDVD4 shown lower values of λe than λh which indicated that these chromophores were the promising candidates for electron transportation mobilities. The larger charge mobilities with greater exciton dissociation in excited state for DPDVD2 were examined, subsequently this compound showed minimum value of λe (0.015739 eV) among all chromophores. Detailed studies reveal that the entitled molecules can behave as efficient electron acceptor molecules in organic solar cells (OSCs) that make them interesting candidates for the development of inexpensive optoelectronic devices.

Heat transfer characteristics of straw-core paper honeycomb plates (beetle elytron plates) I: Experimental study on horizontal placement with hot-above and cold-below conditions

Abstract To develop functional sandwich plates (FHPs) and identify new ways to use straw, straw-core paper honeycomb plates (SHPs) were prepared. The mechanisms of the influence of the spatial distribution of various filling systems on the heat transfer performance of SHPs were investigated, and the following results were obtained. 1) The equivalent thermal conductivity (λE) of the three FHPs were significantly lower than that of the honeycomb plate (HP), and the λE of all the FHPs met or approached the requirements of high-efficiency heat insulation materials for envelope structures. Moreover, the λE values of the three FHPs were closest to each other at the upper and lower limits of the tested thickness. 2) The spatial distribution characteristics of the spherical particle and slender filling systems under natural filling conditions, their corresponding simple heat transfer models and the concept of divisional local radiative (DLR) heat transfer were presented for the first time. 3) The fundamental factor determining the magnitudes of the λE of the HP and FHPs was the presence of DLR in the core layer structures, and the heat transfer characteristics of the FHPs were the result of the combined actions of the DLR and filling material properties.

Tuning the optoelectronic properties of dibenzochrysene (DBC) based small molecules for organic solar cells

Four different types of dibenzo chrysene (DBC) based molecules (A1-A4) are designed to investigate their photovoltaic properties via quantum simulation. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) analysis is performed to explore various parameter of solar cells i.e. the 3-D geometries of designed molecules, photovoltaic properties, reorganization energies, dipole moment, transition density matrix (TDMs), open-circuit voltage (Voc) and Exciton Binding Energy (Eb). We have performed a comparative study between designed molecules and reference structure to R to conclude our results. Among all designed structures, A4 has shown a red shift with λ max of 797.4 nm and band-gap (ΔH-L) of 1.743eV in CHCl3 by B3LYP/6-31G (d,p) using the IEFPCM model. The internal reorganization energy of all the designed molecules has shown a more effective charge transfer property as compared to R. However, A4 has shown the least value of λe (0.003775 a.u), thus have good charge transferability in the form of electron This high charge transfer ability ascribed to strong electron-withdrawing malononitrile group that enhances the rate of charge transmission among donor and acceptor groups. Transition density matrix (TDM) map results have shown that A2 has weak electrostatic interaction between electron and hole (Eb = 0.1126 eV) showing ease dissociation of exciton in comparison to other molecules. This DFT based quantum simulation explicates that we can amend different properties of solar cells by attachment of different end capped acceptor units around the central donor core. Thus high device performance (PCE) could be achieved by appropriate choice of donor and acceptor units.

Isatin-derived non-fullerene acceptors for efficient organic solar cells

Geometries optimization, electronic structure, electronic absorption spectra, charge transport rate, morphology, and photovoltaic properties of indacenodithiophene as donor core unit tie with isatin derive different end-capped electron acceptor groups have been performed using Density Functional Theory (DFT) and time dependent density functional theory (TD-DFT). Isatin unit connected with 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile in M1, 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile in M2, 2-thioxothiazolidin-4-one in M3, 2-(4-fluorothiophen-2-yl)acetonitrile in M4 and geometries, opto-electronic properties have been computed at TD-DFT MPW1PW91/6-31G level of theory and compared with reference molecule R. Among all novel structures, M2 has lowest value of energy band gap (1.99 eV) and has maximum absorption (λmax = 824.0 nm) in chloroform by TD-MPW1PW91/6-31G (d,p) using IEFPCM model. The red shift in M2 was due presence of strong electron withdrawing acceptor moiety and more extended conjugation as compared to other structures. Indeed, electron withdrawing functionality i.e fluorine and cyno moieties in M2 structure stabilized its LUMO orbital and hence improved its opto-electronic properties. Transition density matrix (TDM) maps results revealed obvious influence of end-capped acceptor group on the exciton. M2 has lower probability of coupling of electron and hole owing easy exciton dissociation as compared to other designed molecules. Theoretically calculated reorganization energy indicates that M1 has the highest hole transfer rate due to the lowest value of λh (0.0068 eV). Similarly, M4 has the highest electron mobility due to lowest value of λe (0.0053 eV). In short, choice of appropriate electron withdrawing end capped acceptor groups is very important for improving the performance of organic solar cells.

Molecular engineering of A–D–C–D–A configured small molecular acceptors (SMAs) with promising photovoltaic properties for high-efficiency fullerene-free organic solar cells

Non fullerene small acceptor molecules in organic photovoltaics are proven beneficial than the traditional fullerene based acceptors for their fine contribution in organic solar cells. Researchers are constantly doing efforts for designing novel acceptor materials with promising photovoltaic properties. Designing of novel molecules by end-capped modifications is a convenient strategy to obtain high efficiency acceptor molecules for OSCs. Herein, we studied optoelectronic characteristics of five novel acceptor–donor–core–donor–acceptor configured small acceptor molecules (S1–S5) after end-capped modifications of recently synthesized DF-PCIC molecule. Designed molecules S1–S5 consist of 1,4-difluorobenzene (as central core), 4,4-bis(2-ethylhexyl)-2,6-dimethyl-4H-cyclopenta[1,2-b:5,4-b′]dithiophene as donor which directly attached with different end-capped acceptors. The electronic and optical properties of newly designed (S1–S5) molecules are examined and compared with reference molecule with the aid of DFT and TD-DFT. Certain key parameters like frontier molecular orbitals analysis, density of states, dipole moment, binding energy along with transition density matrix, excitation energy, charge mobility, absorption maxima and charge transfer analysis have been performed in order to explore the photo-physical, optoelectronic and photovoltaic properties of designed and reference molecule. Out of newly designed structures, S4 displayed lowest energy band-gap (2.25 eV) with red-shifting in absorption spectrum (λmax = 712.43 nm) in chloroform which disclosed the perfect relationship between end-capped acceptor with large electron withdrawing character through extended conjugation. Similarly, S1 exhibited highest value (1.53 V) of open circuit voltage (Voc) with respect to PTB7-Th donor material owing to lower values of λe. Designed molecules exhibit better electron and hole mobility as compared to reference molecule R. All molecules express better absorption maximum, open circuit voltage, low excitation energies, comparable binding energies, large dipole moment and efficient electron and hole transport as compared to reference molecules. So, results these parameters suggest that end-capped modification is a convenient strategy in order to enhance the efficiency of OSCs. Therefore, conceptualized molecules are recommended to experimentalist for out-looking future developments of highly efficient solar cells.

Interparticle correlations in the simple cubic lattice of ferroparticles: Theory and computer simulations

Anisotropic interparticle correlations in the simple cubic lattice of single-domain ferroparticles (SCLF) are studied using both theory and computer simulation. The theory is based on the Helmholtz free energy expansion like classical virial series up to the second virial coefficient. The analytical formula for the Helmholtz free energy is incorporated in a logarithmic form to minimize the effects of series truncation. The new theoretical approach, including discrete summation over lattice nodes coordinates, is compared critically against the classical virial expansion of the Helmholtz free energy for the dipolar hard sphere fluid; the main differences between the Helmholtz free energy of SCLF and dipolar hard sphere fluid are discussed. The theoretical results for the Helmholtz free energy, the magnetization, and the initial magnetic susceptibility of the SCLF are compared against Molecular Dynamic simulation data. In all cases, theoretical predictions using logarithmic form of the Helmholtz free energy are seen to be superior, but they only have an applicability range of the effective dipolar coupling constant λe<1.5. For highest values of λe, the structural transition of the magnetic dipoles in SCLF is observed in Molecular Dynamic simulation. It has been shown that for λe≳2, an antiferromagnetic order appears in the system.

Enhanced charge transport properties in heteroatomic (NH, O, Se) analogs of benzotrithiophene (BTT) isomers: a DFT insight

ABSTRACTA comprehensive comparative study of the geometry, optoelectronic and charge transport properties in benzotrithiophene (BTT), benzotripyrrole (BTP), benzotrifuran (BTF) and benzotriselenophene (BTSe) and their possible isomers are reported by employing density functional theory (DFT). The motive of this work is to examine the role of different heteroatoms (NH, O and Se) on optical and charge transport properties. The optimised molecules display planar geometry, which is ideal for organic semiconductor applications. The absorption properties of all the molecules are calculated using time-dependent density functional theory (TDDFT). Nucleus independent chemical shift (NICS) calculations are performed to see the stability and aromatic character in these molecules. The calculated hole and electron reorganisation energies (λh and λe) for majority of the isomers in each series are smaller than that of typical hole and electron transport material (TPD and Alq3). BTP series isomers are with exceptionally small λe values (10–60 meV), which means these isomers are better for electron transport materials. The quantum chemical results show that HOMO, LUMO, HOMO–LUMO gap, and reorganisation energies along with ionisation potentials and electron affinities are significantly affected by changing the heteroatoms. The smaller hole and electron reorganisation energies of these molecules suggest possible use in OLEDs.

Theoretical Calculations of the Optical and Electronic Properties of Dithienosilole‐ and Dithiophene‐Based Donor Materials for Organic Solar Cells

AbstractSix Acceptor‐Donor‐Acceptor (A−D−A) types molecules with dimethyl dithieno[3, 2‐b:2′,3′‐d]silole)−2,6‐diyl (DTS) (M1‐M3) and dimethyl cyclopenta [2, 1‐b;3,4‐b]‐dithiophene (CPDT) (M4‐M6) core flanged by different acceptor units through methylthiophene bridge are evaluated as donor materials for photovoltaic applications. The photovoltaic properties of M1‐M3 and M4‐M6 are compared with standard RaRc and Rb,Rd respectively. Geometry optimization was performed with CAM−B3LYP/6‐31G (d) level of theory. TD‐CAM−B3LYP has been employed for the estimation of excited state properties of the molecules. M1, M2, M3 and M4, M5, M6 symbolized suitable frontier molecular orbital's (FMO's) energy levels with broad absorption spectra. The electron withdrawing substituents impart red shift in absorption spectra along with good consistancy of designed donor molecules. Reorganization energies of donor molecules (M1‐M6) showed ideal properties of charge mobility. M1 and M4 illustrated lowest λe values as compared to λh, thus dictated that designed donor molecules are of good choice for their electron donating ability. Furthermore, M2 and M6 demonstrated shortest Eg of 3.7 and 3.72 eV among HOMO and LUMO energy levels.

Designing Benzodithiophene‐Based Donor Materials with Favorable Photovoltaic Parameters for Bulk Heterojunction Organic Solar Cells

AbstractComputational study on four Acceptor‐Donor‐Acceptor (A–D‐A) type of donor molecules namely, dimethyl cyanoacetate terthiophene di(methylthiophene) benzo[1,2‐b:4,5‐b′]dithiophene (DMCATDMTBDT) (M1), methylrhodanine terthiophene di (methylthiophene) benzo[1,2‐b:4,5‐b′]dithiophene (MRTDMTBDT) (M2), dimethyl cyanoacetate terthiophene di (fluoromethyl thiophene) benzo[1,2‐b:4,5‐b′]dithiophene (DMCATDFMTBDT) (M3), and methylrhodanine terthiophene di (fluoromethyl thiophene) benzo[1,2‐b:4,5‐b′]dithiophene (MRTDFMTBDT) (M4) was carried out and their photovoltaic properties were associated with methyl cyanoacetate terthiophene di (methoxy) benzo[1,2‐b:4,5‐b′]dithiophene (DCAO3TBDT) (R1) and methylrhodanine terthiophene di (methoxy) benzo[1,2‐b:4,5‐b′]dithiophene (DR3TBDT) (R2). For the geometry optimization DFT functional CAM−B3LYP/6‐31G (d) was found to be the best choice, hence TD‐CAM−B3LYP/6‐31G (d) was opted for the calculation of excited state of the molecules. M3 and M4 represented appropriate frontier molecular orbital energy levels and broad absorption band. The reorganization energies of the designed molecules illustrated excellent charge mobility property. The lower λe values as compared to λh illustrate that the designed donor molecules are better electron donors. M4 was found as champion molecules with the lowest λe (0.01601) value. The Voc value of M3 and M4 are 2.74 eV and 2.63 eV respectively with respect to the energy levels of PC60BM (acceptor).

The effect of relative position of the π-spacer center between donor and acceptor on the overall performance of D-π-A dye: a theoretical study with organic dye

The influence of the relative position of π-spacer center between donor and acceptor on the dye-sensitized solar cell (DSSC) performance is expounded by analyzing the geometry, electronic structure, optical absorption property, and intramolecular charge transfer, as well as reorganization energy by means of density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches. The results based on electronic structure and absorption property indicate that the dyes with introduction of building blocks to p1 position will generate more efficient charge separated states and present red-shifted in spectra. According to the analysis of intramolecular charge transfer, the results show that although introducing building blocks to p1 position can not make all structures to reduce orbital overlap, all the dyes with relatively small distance between donor and π-spacer center can enhance the amount of qCT and DCT. Additionally, the dyes with building blocks are introduced to p1 position that give better charge transfer balance performance due to their smaller Λh and Λe values. That is to say, the dye with a rigidified-aromatic as π-spacer, properly adjusting the position of π-spacer center is a valid approach for achieving great performance of DSSC.

Design of donor–acceptor–donor (D–A–D) type small molecule donor materials with efficient photovoltaic parameters

AbstractFour Donor–Acceptor–Donor (D–A–D) type of donor molecules (M1‐M4) with triphenylamine (TPA) as donor moiety, thiophene as bridge, and thiazolothiazole as acceptor unit were designed and its photovoltaic parameters were equated with reference molecule “R.” DFT functional CAM‐B3LYP/6‐31G (d,p) was found best for geometry optimization and TD‐CAM‐B3LYP/6‐31G (d,p) was found suitable for excited state calculations. Among designed donor molecules, M4 manifests suitable lowest band gap of 4.73 eV, frontier molecular orbital energy levels as well as distinctive broad absorption of 455.3 nm due to the stronger electron withdrawing group. The electron‐withdrawing substituents contribute to red shifts of absorption spectra and better stabilities for designed molecules. The theoretically determined reorganization energies of designed donor molecules suggested excellent charge mobility property. The lower λe values in comparison with λh illustrated that these four donor materials would be ideal for electron transfer and M4 would be best amongst the investigated molecules with lowest λe of 0.0177. Furthermore, the calculated Voc of M4 is 2.04 V with respect to PC60BM (phenyl‐C61‐butyric acid methyl ester). This study revealed that the designed donor materials are suitable and recommended for high performance organic solar cell devices.

Large-scale radiation and energy balances with Landsat 8 images and agrometeorological data in the Brazilian semiarid region

Aiming to subsidize the rational water resources management, four Landsat 8 (L8) images along different conditions of the year 2014 were used for modeling the radiation and energy balances in the mixed agroecosystems inside a Brazilian reference semiarid area. The SAFER algorithm was applied to calculate the latent heat flux (λE); net radiation (Rn) was acquired by the Slob equation; ground heat flux (G) was considered a fraction of Rn; and the sensible heat flux (H) was retrieved by residue in the energy balance equation. For classifying the vegetation, the surface resistance algorithm (SUREAL) was used to estimate the surface resistance to the water fluxes (rs) with threshold values for rs. Clearly, one could see higher λE values from irrigated crops (ICs) than those for natural vegetation (NV) with some situations of heat horizontal advection. The respective λE, H, and G average ratios to Rn for the ICs ecosystem were 64% to 79%, 18% to 28%, and 3%, respectively. For the NV ecosystem, the corresponding fractions were 4% to 37%, 60% to 94%, and 4%, respectively. The algorithms proved to have strong sensibility to quantifying the large-scale energy and mass exchanges by applying L8 images in mixed agroecosystems of semiarid environments.

Composition Dependence of Effective Thermal Conductivity and Effective Thermal Diffusivity of Se98-X Cd2Inx (X=0, 2, 6, 10) Glassy Alloys

Effective thermal conductivity and effective thermal diffusivity of Se98-x Cd2Inx (x=0, 2, 6, 10) chalcogenide glasses were carried out at room temperature using transient plane source (TPS) technique. The measured values of effective thermal conductivity and effective thermal diffusivity were used to determine the specific heat per unit volume (ρCp ) of these glasses in the composition range of investigation. The values of λe and χe were found to increase initially with the increase of In concentration in Se-Cd alloy. Results indicated that λe and χe are maximum at 6 at.wt% of indium and ρCp almost constant for all glassy alloys. This is suggestive of fact that Se92Cd2In6 can be considered as a critical composition of this series, at which the alloy becomes, chemically ordered and better thermally stable than other composition. Further addition of indium in Se-Cd decreases the values of λe and χe. The behavior is explained on the basis of decrease of localized states and increase in disorderness for higher composition indium.

Use of MODIS Images to Quantify the Radiation and Energy Balances in the Brazilian Pantanal

MODIS images during the year 2012 were used for modelling of the radiation and energy balance components with the application of the SAFER algorithm (Simple Algorithm for Evapotranspiration Retrieving) in the Brazilian Pantanal area. Pixels from the main sub-regions of Barão de Melgaço (BR), Paiaguás (PA) and Nhecolândia (NH) were extracted in order to process microclimatic comparisons. In general, the net radiation (Rn) relied much more on the global solar radiation (RG) levels than on water conditions and ecosystem types, in accordance with the low Rn standard deviation values. The fraction of the available energy used as latent heat flux (λE) were, on average, 65, 50 and 49% for the BR, PA and NH sub-regions, respectively. Horizontal heat advection, identified by the negative values of sensible heat flux (H), made several pixels with λE values higher than those for Rn in the middle of the year. Taking the evaporative fraction (Ef) as a surface moisture indicator, the Tree-Lined Savanna (TLS) was considered the moister ecosystem class, with 58% of the available energy being used as λE, while the driest one was the modified ecosystem Anthropogenic Changes (AC), presenting a λE/Rn fraction of 0.46. According to the spatial and temporal consistencies, and after comparisons with other previous point and large-scale studies, the SAFER algorithm proved to have sensibility to quantify and compare the large-scale radiation and energy balance components in the different ecosystems of the Brazilian Pantanal. The algorithm is useful for monitoring the energy exchange dynamics among the different terrestrial and aquatic ecosystem types throughout the seasons of the year.

Effective thermal conductivity and diffusivity of GeSeSb glasses measured simultaneously as a function of temperature and fit to empirical equations

Thermal transport properties like effective thermal conductivity (λe) and effective thermal diffusivity (ke) of Ge–Se–Sb chalcogenide glassy alloys were measured simultaneously using transient plane source (TPS) technique from room temperature to 260 °C at normal pressure. Twin pellets of the sample, prepared under a load of 5 ton, were used for these measurements. In the studied temperature range, both λe and ke initially remain almost constant from room temperature to 160 °C and then increase to maxima with further increase of temperature, and thereafter decrease with increasing temperature. This variation has been explained phenomenologically on the basis of variation of phonon mean free path with temperature. An effort has been made to predict this behavior by an empirical relation obtained from polynomial fit of the experimental data. The calculated values of λe and ke are in good agreement with the experimental results over the entire range of temperatures under investigation.