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We studied the structural, electronic, phonon spectrum and thermoelectric properties of ternary LuMSb (M = Ni, Pd, Pt) half Heusler compounds by using first principles method. The electronic properties are calculated via energy band structure and density of states by using GGA + U approximation. The calculations reveal that the replacement of Ni with Pd and Pt, energy gap decreases and LuNiSb, LuPdSb are found to have narrow indirect band gaps and exhibit semiconducting nature, while LuPtSb is found to be a gapless semiconductor. Phonon band structure calculations give only positive values of phonon frequency indicating the dynamically stability of these compounds. The thermoelectric properties have been computed using semi‐classical Boltzmann transport theory. We found high Seebeck coefficient (S) and high power factor (PF) for LuNiSb and LuPdSb compounds in the whole temperature range. The ZT values of LuNiSb and LuPdSb are high in general and reach a maximum of 0.67 and 0.69 at 450 K, respectively, whereas 0.39 is the maximum ZT value for LuPtSb at the same temperature. These findings propose LuNiSb and LuPdSb compounds as promising materials for thermoelectric applications at room temperature. [ABSTRACT FROM AUTHOR]

Objective: Most radiotherapy patients with prostate cancer are treated with volumetric modulated arc therapy (VMAT). Advantages of VMAT may be limited by daily treatment uncertainties such as setup errors, internal organ motion, and deformation. The position and shape of prostate target as well as normal organ, i.e., rectum volume around the target, may change during the course of treatment. The aim of the present work is to estimate rectal toxicity estimation using a novel two-level biological knowledge-based fuzzy logic method. Both prostate and rectal internal motions as well as setup uncertainties are considered without compromising target dose distribution in the present study. Materials and Methods: The Mamdani-type fuzzy logic framework was considered in two levels. The prostate target volume changes from minimum to maximum during the course of treatment. In the first level, the fuzzy logic was applied for determining biological acceptable target margin using tumor control probability and normal tissue complication probability (NTCP) parameters based on prostate target motion limits, and then, fuzzy margin was derived. The output margin of first-level fuzzy logic was compared to currently used margins. In second-level fuzzy, rectal volume variation with weekly analysis of cone-beam computed tomography (CBCT) was considered. The biological parameter (NTCP) was calculated corresponding to rectal subvolume variation with weekly CBCT image analysis. Using irradiated volume versus organ risk relationship from treatment planning, the overlapped risk volumes were estimated. Fuzzy rules and membership function were used based on setup errors, asymmetrical nature of organ motion, and limitations of normal tissue toxicity in Mamdani-type Fuzzy Inference System. Results: For total displacement, standard errors of prostate ranging from 0 to 5 mm range were considered in the present study. In the first level, fuzzy planning target volume (PTV) margin was found to be similar or up to 0.5 mm bigger than the conventional margin, but taking the modeling uncertainty into account resulted in a good match between the calculated fuzzy PTV margin and conventional margin formulations under error 0-5 mm standard deviation (SD) range. With application of fuzzy margin obtained from first-level fuzzy, overlapped rectal volumes and corresponding NTCP values were fuzzified in second-level fuzzy using rectal volume variations. The final risk factor (RF) of rectum was qualitatively assessed and found clinically acceptable for each fractional volume of irradiated to total volume and relevant NTCP values. The reason may be at 5 mm SD displacement error range, NTCP values would be within acceptable limit without compromising the tumor dose distribution though the confounding factors such as organ motion, deformation of rectum, and in-house image matching protocols exist. Conclusion: A new approach of two-level fuzzy logic may be suitable to estimate possible organ-at-risk (OAR) toxicity biologically without compromising tumor volume that includes both prostate target and OAR rectum deformation even at displacement standard errors of prostate ranging from 0 to 5 mm range which was considered in the present study. Using proposed simple and fast method, there is an interplay between volume-risk relationship and NTCP of OARs to judge real-time normal organ risk level or alter the treatment margins, particularly concern to individual factors such as comorbidities, genetic predisposition, and other lifestyle choices even at high displacement errors >5 mm SD range. [ABSTRACT FROM AUTHOR]

Aim: Radiation therapy has historically used margins for target volume to ensure dosimetric planning criteria. The size of margin for a given treatment site is still uncertain particularly for moving targets along with set-up variations leading to a fuzziness of target volume. In this study, we have estimated the dosimetric benefit of normal structures using biological-based optimal margins. The treatment margins are derived by knowledge-based fuzzy logic technique which is considering the radiotherapy uncertainties in treatment planning. Materials and methods: All treatment plans were performed using stepped increments of asymmetric margins to estimate prostate radiobiological indices such as tumour control probability (TCP) and normal tissue complication probability (NTCP). An absolute NTCP of 5% was considered to be the maximum acceptable value while TCP of 85% was considered to be the minimal acceptable limit for each volumetric modulated arc therapy (VMAT) plan of localised prostate cancer radiotherapy. Results were used to formulate rules and membership functions for Mamdani-type fuzzy inference system (FIS). In implementing the rules for the fuzzy system for ΔNTCP values above 10%, the PTV margin was not permitted to exceed 5 mm to avoid rectal complications due to margin selection. The new margins were applied in VMAT planning of prostate cancer for standard displacement errors. The dosimetric results of normal tissue predictors were estimated such as organ mean doses, rectum V60 (volume receiving 60 Gy), bladder V65 (volume receiving 65 Gy) and other clinically significant dose–volume indicators and compared with VMAT plans using current margin formulations. Results: Dosimetric results compared well to the results obtained by current techniques. Good agreement was obtained between proposed fuzzy model margins and currently used margins in lower error magnitude, but significant results were observed at higher error magnitude when organ toxicity concerned without compromising the target volumes. Findings: The new margins may be helpful to estimate possible outcomes of normal tissue complications and thus may improve complication free survival particularly when organ motion errors are inevitable, case by case. [ABSTRACT FROM AUTHOR]

We combine the first-principle calculations, based on the density functional theory, and Boltzmann transport theory to investigate the structural, electronic and thermoelectric of narrow gap RNiSb (R = Gd, Er and Lu) half Heusler (HH) compounds. Coulomb corrected generalized gradient approximation (GGA + U) has been employed which is the most competent method to treat rare earth compound. We find spin up/down Ni-3d and spin down R-4f states as main contributors to the total density of states (DOS) near Fermi energy (EF). All the investigated compounds exhibit the indirect narrow energy gaps (0.246–0.279 eV) that are in agreement with the corresponding experimental values. We obtained fairly high values of the Seebeck coefficient (S) in agreement with available experimental data. The calculated value of total S (from spin-up and spin-down channels), using two current models, increases from 50 to 202 µV/K at 300 K when Gd with half-filled f-states is replaced by Lu with completely filled f-states in these RNiSb HH compounds. We also find the maximum value of ZT is 0.32 and 0.76 at 800 K for Gd and Er compounds, whereas 0.68 is the maximum ZT for Lu compound at 450 K. We obtained favorable and stable ZT values (ZT > 0.7) for a wide temperature range only in ErNiSb compound in agreement with the experiment. This proposes ErNiSb as a promising candidate for thermoelectric applications. [ABSTRACT FROM AUTHOR]

The rare earth‐based half Heusler GdNiSb compound is investigated theoretically for electronic and thermoelectric (TE) performance. The most efficient method to treat the rare earth metals, Coulomb‐corrected local spin density approximation (LSDA + U), is used. The calculated total density of states (DOS) of GdNiSb shows that the maximum contribution near Fermi energy (EF) is due to the spin‐up/down Ni‐3d and spin‐down Gd‐4f states. A narrow energy gap of 0.279 eV is opened which is consistent with other reported values. TE properties are investigated using classical transport theory. The total Seebeck coefficient (S) increases linearly with temperature and attains a maximum value of 80 μV K−1 at 800 K. The S value of 60 μV K−1 at 380 K is in good agreement with the experimental value, 58 μV K−1, at the same temperature. The maximum value of the power factor (P) is as high as 825 × 109 W m−1 K−2 s−1 at 650 K in the spin‐down channel. The TE figure of merit (ZT) reaches the maximum value of ≈0.475 at 800 K in the spin‐down configuration. All the values of the TE parameters of GdNiSb indicate a good candidate for TE applications. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of present study is to estimate asymmetric margins of prostate target volume based on biological limitations with help of knowledge based fuzzy logic considering the effect of organ motion and setup errors. Materials and Methods: A novel application of fuzzy logic modelling technique considering radiotherapy uncertainties including setup, delineation and organ motion was used in this study to derive margins. The new margin was applied in prostate cancer treatment planning and the results compared very well to current techniques Here volumetric modulated arc therapy treatment plans using stepped increments of asymmetric margins of planning target volume (PTV) were performed to calculate the changes in prostate radiobiological indices and results were used to formulate the rule based and membership function for Mamdani-type fuzzy inference system. The optimum fuzzy rules derived from input data, the clinical goals and knowledge-based conditions imposed on the margin limits. The PTV margin obtained using the fuzzy model was compared to the commonly used margin recipe. Results: For total displacement standard errors ranging from 0 to 5 mm the fuzzy PTV margin was found to be up to 0.5 mm bigger than the vanHerk derived margin, however taking the modelling uncertainty into account results in a good match between the PTV margin calculated using our model and the one based on van Herk et al. formulation for equivalent errors of up to 5 mm standard deviation (s. d.) at this range. When the total displacement standard errors exceed 5 mm s. d., the fuzzy margin remained smaller than the van Herk margin. Conclusion: The advantage of using knowledge based fuzzy logic is that a practical limitation on the margin size is included in the model for limiting the dose received by the critical organs. It uses both physical and radiobiological data to optimize the required margin as per clinical requirement in real time or adaptive planning, which is an improvement on most margin models which mainly rely on physical data only. [ABSTRACT FROM AUTHOR]

We report calculations of the optical and magneto-optical properties of elemental rare earth gadolinium using the full potential linear augmented plane wave method and including spin-orbit coupling. Calculations are performed within the local spin density approximation (LSDA) and Coulomb corrected local spin density approximation (LSDA+U). While LSDA+U gives better agreement for density of states and magnetic moments, a comparison with the experimental data shows that both LSDA and LSDA+U are at par in representing the diagonal components of the optical conductivity. For the much smaller off-diagonal components, interestingly, the LSDA results have an edge over the LSDA+U results. [ABSTRACT FROM AUTHOR]

The electronic structure and optical properties of the rare earth sesquioxides (R2O3, R=La, Pr, and Nd) have been studied using the full potential linearized augmented plane wave method within local spin density approximation (LSDA) and Coulomb corrected local density approximation (LSDA+U) as implemented in the WIEN2K code. Our calculations show that the LSDA+U results give a better representation of the band structure compared to LSDA. Our calculated reflectivity and optical conductivity spectra are compared with the experimental data. The peaks in the optical conductivity can be explained as arising out of the transitions from R-p and O-p to R-d states. We have also calculated the dielectric function and the coefficient of refraction for these rare earth sesquioxides. We do not find any significant differences in the optical properties calculated using LSDA and LSDA+U. [ABSTRACT FROM AUTHOR]

We investigated the effect of Si substitution on structural, electronic and optical properties of YNi 4 Si -type HoNi 5 − x Si x   (x = 0 , 1) alloys. The optimized lattice constants and internal cell parameters are in agreement with the available data. We found that the valence band is mainly dominated by Ni-3d states in the energy range 0–4 eV below the E F , whereas conduction band is contributed by spin-down Ho- 4 f states and lies about 2 eV above the E F . Substitution of Si atoms for Ni decreases the total magnetic moment from 6.308 μ B /f.u. (x = 0) to 4.052  μ B /f.u. (x = 1) , whereas magnetic moments on Ho + 3 -ions increase from 3.92  μ B /atom (x = 0) to 4  μ B /atom (x = 1). On the other hand, induced moment on Ni + 2   (x = 1 , 2) -ions decrease rapidly to a negligibly small value. By the use of charge density estimates, we found that Ho-5d, Ni-3d and Si-3p orbitals are mainly involved in bonding and there is a weak hybridization between Ni-3d and Si-3p orbitals which varies with substitution of Si for Ni. Furthermore, the complex role played by Ho- 5 d 1 electrons is also investigated, they are found to be partly involved in metallic bondings as well as in the intra-atomic charge transfer from 5 d 1 to 4 f 1 0 states in Ho + 3 -ions. The calculated interband optical conductivity spectra reproduce the main features of experimental spectra well and also reveal their metallic nature. [ABSTRACT FROM AUTHOR]

In this study, we report the theoretical investigation of electronic structure and frequency-dependent optical properties of narrow band gap CdCr2Te4 normal spinel. While GGA + U and TB-mBJ schemes fail to show the semiconducting nature of CdCr2Te4 spinel, combining the mBJ potential with the Hubbard U correction obtains a narrow band gap of 0.04 eV. The indirect band gap using mBJ + U scheme occurs due to the shifting of spin-up Cr-eg and Cr-t2g states of conduction band towards higher energy. This reflects the better suitability of mBJ + U scheme to study the band structure of CdCr2Te4 as compared to the GGA + U, TB-mBJ, and expensive hybrid functional methods. The asymmetrical nature of spin-up and spin-down states in total DOS indicates them to be magnetic compounds. The integer value of total magnetic moment per formula unit rules out the metallic nature of this compound. We studied the optical spectra in terms of the band to band transitions for their possible use in optoelectronic applications. [ABSTRACT FROM AUTHOR]

We have investigated theoretically the role of Cr-d states in the electronic and optical properties of the CdCr2X4 (X = S, Se) normal ferromagnetic spinels using the framework of an all-electron full-potential linearized augmented plane wave method. The calculations are performed using Coulomb corrected Perdew–Burke–Ernzerhof (PBE+U) and Tran–Blaha modified-Becke–Johnson (TB-mBJ) approximations with the adding of spin–orbit coupling in both schemes. The lattice parameters have been optimized and are in agreement with the existing experimental values. We found band gap values 1.606 eV and 0.972 eV of CdCr2X4 (X = S, Se), respectively, using the TB-mBJ scheme. Analysis of the site and momentum projected densities shows that the larger splitting of Cr-d states is responsible for the larger band gap by the use of the TB-mBJ scheme. Optical properties along the directions of lattice constants are studied on the basis of band to band transitions. We found the isotropic nature of the optical properties. Reflectivity stays low up to 1.6 eV, consistent with the energy gaps obtained using the TB-mBJ scheme in both the compounds. The refractive index, n(ω), and the extinction coefficient, k(ω), are also studied by the PBE and the TB-mBJ schemes. [ABSTRACT FROM AUTHOR]