Exploration of isoelectronic substitution in graphene dioxide for photocatalytic and photovoltaic applications - an ab-initio study.

Herein, we propose graphene dioxide (GDO) derivatives as promising materials for green hydrogen production by photocatalytic water splitting. The optoelectronic and photocatalytic properties of GDO, an insulator with a wide band gap, are tuned by designing new compositions through isovalent substitution of S/Se at the O site, Si and (B,N) at the C site. The newly predicted GDO derivatives were studied using hybrid functional calculations and our results show that several of these materials exhibit semiconducting behavior with a direct band gap value higher than 1.23 eV, hence appropriate for visible light-driven photocatalytic water splitting. The structural stability of these materials was analyzed by total energy and lattice dynamical calculations. The photo generated charge carriers possess lower effective mass and hence higher carrier mobility resulting in suppressed recombination rate and hence improving the water splitting efficiency. Apart from low excitonic binding energy, the electronic structure analysis shows that in several of these compounds the electrons and holes reside in two different atomic sites ensuring further reduction in recombination rate. The relatively higher absorption coefficient of GDO derivatives in the visible part of the solar spectrum indicates enhanced photoconversion efficiency suitable for solar cell applications also and it was further determined by photovoltaic performance parameter analysis. The band edge potential of GDO derivatives is well straddled by the water redox potential at different pHs, suggesting their potential for water splitting along with the possibility of CO2 reduction. Our findings indicate that the newly predicted compositions hold significant promise for photocatalytic as well as photovoltaic applications.

Potential hydrogen storage materials from metal decorated 2D-C2N: an ab initio study.

Two dimensional nitrogenated holey graphene (2D-C2N) is often considered as an ideal material for hydrogen storage applications owing to its lower mass density and high surface-to-volume ratio. As the interaction between H2 and pristine 2D-C2N is very weak with an adsorption energy of only 0.10 eV per H2, it is important to improve it through appropriate materials design. Using density functional theory calculations, we investigated the hydrogen storage properties of metal (M = Mg, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, and Zn) decorated 2D-C2N. From this study, we found that M binding energy on 2D-C2N is greater than the cohesive energy of the respective bulk metals, indicating that the metal is strongly bonded with the 2D-C2N, which rules out the metal clustering issue. In particular, 2D-C2N with Mg decoration leads to 6.79 wt% hydrogen storage capacity with a desirable adsorption energy which is above the Department of Energy's target. The electronic structure analyses show that the Mg decoration leads to a semiconductor-to-metallic transition in 2D-C2N. Our chemical bonding analyses through partial density of states, charge density, electron localization function, charge transfer, and Bader effective charge confirm the presence of an iono-covalent character for Mg decorated 2D-C2N. This indicates that the H2 molecules are adsorbed by a polarization mechanism. Overall, our results suggest that Mg decorated 2D-C2N is a promising candidate for potential hydrogen storage applications.

Metamagnetism stabilized giant magnetoelectric coupling in ferroelectric xBaTiO3-(1 - x)BiCoO3 solid solution.

In order to establish the correlation between the magnetoelectric coupling and magnetic instability, we have studied the structural, magnetic, and ferroelectric properties of BaTiO3 modified BiCoO3i.e. xBaTiO3-(1 - x)BiCoO3 as a function of BaTiO3 concentration (x) and volume from a series of general-gradient-corrected (GGA), GGA plus onsite Coulomb repulsion (U), full potential, spin-density-functional band-structure calculations within the framework of density functional theory along with synchrotron X-ray diffraction and magnetic measurement studies. G-type antiferromagnetic ordering was found to be energetically favorable among all the considered magnetic configurations for x < 0.45 and higher concentrations stabilize with nonmagnetic (NM) states. We observe metamagnetic spin state transitions associated with paraelectric to ferroelectric transitions as a function of volume and x using synchrotron diffraction and computational studies, indicating a strong magnetoelectric coupling. Specifically for x = 0.33 composition, a pressure induced high spin (HS) to low spin (LS) transition occurs when the volume is compressed below 2.5%. Our orbital-projected density of states show a HS state for Co3+ in the ferroelectric ground state for x < 0.45 and the corresponding paraelectric phase is stable in the NM state due to the stabilization of LS state as evident from our fixed-spin-moment calculations and magnetic measurements. The nature of chemical bonding has been studied using partial density of states, electron localization function, and Born effective charge analysis. High values of spontaneous ferroelectric polarizations are predicted for lower x values which inversely vary with x because of the reduction of tetragonality (c/a) with increase in x which indicates the presence of both spin-lattice and ferroelectricity-lattice coupling. Our partial polarization analysis shows that not only the lone pair at Bi sites but also the d0-ness of Ti4+ ions contribute to the net polarization. Moreover, we find that the HS-LS transition point and magnetoelectric coupling strength can be varied by x.

Enhanced Photocatalytic Water Splitting in a C2 N Monolayer by C-Site Isoelectronic Substitution.

Two-dimensional (2D) semiconductors have shown great promise as efficient photocatalysts for water splitting. Tailoring the band gap and band edge positions are the most crucial steps to further improve the photocatalytic activity of 2D materials. Here, we report an improved photocatalytic water splitting activity in a C2 N monolayer by isoelectronic substitutions at the C-site, based on density functional calculations. Our optical calculations show that the isoelectronic substitutions significantly reduce the band gap of the C2 N monolayer and thus strongly enhance the absorption of visible light, which is consistent with the observed redshift in the optical absorption spectra. Based on the HSE06 functional, the calculated band edge positions of C2-x Six N and C2-x Gex N monolayers are even more favorable than the pristine C2 N monolayer for the overall photocatalytic activity. On the other hand, for the C2-x Snx N monolayer, the conduction band minima is more positive than the oxygen reduction potential and, hence, Sn substitution in C2 N is unfavorable for the water decomposition reaction. In addition, the isoelectronic substitutions improve the separation of e- -h+ pairs, which, in turn, suppress the recombination rate, thereby leading to enhanced photocatalytic activity in this material. Our results imply that Si-, and Ge-substituted C2 N monolayers will be a promising visible-light photocatalysts for water splitting.

Genomic evidence of hybridization between two independent invasions of European green crab (Carcinus maenas) in the Northwest Atlantic.

Invasive species have been associated with significant negative impacts in their introduced range often outcompeting native species, yet the long-term evolutionary dynamics of biological invasions are not well understood. Hybridization, either among waves of invasion or between native and introduced populations, could alter the ecological and evolutionary impacts of invasions yet has rarely been studied in marine invasive species. The European green crab (Carcinus maenas) invaded eastern North America twice from northern and southern locations in its native range. Here we examine the frequency of hybridization among these two distinct invasions at locations from New Jersey, USA to Newfoundland, Canada using restriction-site-associated DNA sequencing (RAD-seq), microsatellite loci and cytochrome c oxidase subunit I mitochondrial DNA (mtDNA) sequences. We used Bayesian clustering and hybrid assignment analyses to investigate hybridization between the northern and southern populations. Of the samples analyzed, six locations contained at least one hybrid individual, while two locations were characterized by extensive hybridization, with 95% of individuals collected from Placentia Bay, Newfoundland being hybrids (mostly F2) and 90% of individuals from Kejimkujik, Nova Scotia being classified as hybrids, mostly backcrosses to the northern ecotype. The presence of both F2 hybrids and backcrossed individuals suggests that these hybrids are viable and introgression is occurring between invasions. Our results provide insight into the demographic and evolutionary consequences of hybridization between independent invasions, and will inform the management of green crabs in eastern North America.

High-dose versus low-dose botulinum toxin in anal fissure disease.

BACKGROUND: There is no consensus on the optimal dosage of botulinum toxin (BT) as a sphincter sparing alternative to lateral internal sphincterotomy for chronic anal fissure. The aim of this study was to assess the long-term efficacy of high-dose BT as well as the presence of incontinence following the treatment of chronic anal fissure at a single institution. METHODS: A retrospective case-control study was performed at a single institution over a 6-year period (2009-2014). Patients given high-dose (80-100 IU) BT were compared to low-dose (20-40 IU) case controls. Clinical notes were reviewed, and follow-up was carried out via a telephone questionnaire. RESULTS: One hundred and fifty-eight patients were treated with BT injections within the study period (103 high dose; 55 low dose). The mean length of follow-up was 25 months (range 4-52 months). Classic posterior fissures with high anal tone were more prevalent in the low-dose group (40 vs 47%, p = 0.3). Patient satisfaction was higher in the high-dose group (90 vs 78%, p = 0.05). Long-term recurrence (6 months after the last treatment) was also lower (23 vs 53%, p = 0.0001) on multivariate analysis. No long-term incontinence was observed. CONCLUSIONS: In this series, the recurrence rate post-BT injection was significantly lower in the high-dose group. There was no long-term incontinence. Further studies are needed to confirm our results.

Theoretical and experimental investigation on structural, electronic and magnetic properties of layered Mn5O8.

We have investigated the crystal, electronic, and magnetic structures of Mn5O8 by means of state-of-the-art density functional theory calculations and neutron powder diffraction (NPD) measurements. This compound stabilizes in the monoclinic structure with space group C2/m where the Mn ions are in the distorted octahedral and trigonal prismatic coordinations with oxygen atoms. The calculated structural parameters based on total energy calculations are found to be in excellent agreement with low temperature NPD measurements when we accounted for the correct magnetic structure and Coulomb correlation effect in the computation. Using fully relativistic generalized-gradient approximation with Hubbard U (GGA+U) we found that the magnetic ordering in Mn5O8 is A-type antiferromagnetic and the direction of the easy axis is [1 0 0] in agreement with susceptibility and NPD measurements. However, the calculation without the inclusion of Hubbard U leads to ferrimagnetic half metal as a ground state contradictory to experimental findings, indicating the presence of a strong Coulomb correlation effect in this material. The GGA calculation without the Coulomb correction effect itself is sufficient to reproduce the experimentally observed magnetic moments in various Mn sites. We found that Mn in this material exhibits mixed valence behavior with 2+ and 4+ oxidation states reflecting different magnetic moments in the Mn sites. We explored the electronic band characteristics using total, site-, and orbital-projected density of states which emphasized the mixed-valent nature of Mn. A dominant Mn 3d character of the density of states at Fermi energy is the origin for the metallic behavior of Mn5O8. The bond strength analysis based on the crystal orbital Hamiltonian population between constituents indicates strong anisotropy in the bonding behavior which results from the layered nature of its crystal structure. Our bonding analysis shows that there is a noticeable covalent bond between Mn 3d-O 2p states which stabilizes the observed low symmetric structure. Our experimental findings and theoretical predictions suggest that Mn5O8 can be classified as a strongly correlated mixed valent antiferromagnetic metal.

Observation of direct magneto-dielectric behaviour in Lu3Fe5O12-δ above room-temperature.

The coupling of dielectric and magnetic order is highly nontrivial and seldom observed in rare-earth iron garnets. Careful investigations on polycrystalline Lu3Fe5O12-δ, prepared by the solid state route, establish a direct correlation between the magnetic and dielectric order parameters. A dielectric anomaly at the magnetic ordering temperature supports this correlation. The dielectric permittivity at various magnetic fields is measured using an indigenously developed connector setup. Lu3Fe5O12-δ exhibits a magneto-dielectric coupling of ∼6% at room temperature, which is significant in the case of a single-phase magneto-dielectric material at low fields. Rietveld refinement of the X-ray diffraction pattern, bond valence sum method, Mössbauer spectroscopy, and X-ray photoelectron spectroscopy indicate two different oxidation states of Fe. Complete structural optimizations performed using the density functional theory establish a ferrimagnetic ground state and provide structural parameters in agreement with experimental values. Electronic structure analysis shows that Lu3Fe5O12 exhibits insulating behavior both in ferromagnetic and ferrimagnetic configurations. The capability of Lu3Fe5O12-δ to exhibit room temperature magneto-dielectric response is a key factor in designing and fabricating various electronic devices and sensors.

Definitive surgical closure of enterocutaneous fistula: outcome and factors predictive of increased postoperative morbidity.

AIM: Enterocutaneous fistula (ECF) presents a complex management problem with significant mortality and morbidity. The aim of this study was to assess the outcome of patients undergoing surgical cure for ECF and to predict factors that might relate to increased postoperative morbidity. METHOD: Medical records of all patients who underwent definitive surgery for cure of an ECF within our colorectal surgery unit between 2000 and 2010 were reviewed. RESULTS: Forty-one patients (18 male) were identified, in whom 44 definitive procedures were performed. The median age was 54 (17-81) years. The median postoperative length of stay in hospital was 14 (2-213) days. Half (50%) of the ECFs occurred as a postoperative complication followed by spontaneous fistulation in Crohn's disease (36%). The interval to definitive surgery was influenced by the aetiology of the fistula. The median time to surgery after formation of postoperative fistula was 240 days (7.9 months). There was no 30-day postoperative mortality. There were two (4.5%) recurrences at 3 months. Thirty-eight (86%) patients suffered postoperative morbidity as defined by the Clavien-Dindo classification. High-grade morbidity occurred in 32% of patients. On univariate analysis, factors identified as being significantly associated with high-grade morbidity included a fistula output of > 500 ml/day (P = 0.004) in patients with postoperative ECF, malnutrition at presentation (P = 0.04) and a serum albumin value of < 30 g/l (P = 0.02) in patients with spontaneous ECF due to Crohn's disease. CONCLUSION: The majority of persistent complex ECFs can be cured surgically with low mortality and recurrence in a multidisciplinary setting. Postoperative morbidity, however, remains a significant burden.

The extent of inflammation is a predictor for pouch-related complications in ileal pouches in patients with ulcerative or indeterminate colitis.

AIM: Limited data are available on the relationship between the histological features of the resected specimens in patients with ulcerative colitis (UC) or indeterminate colitis (IC) and the outcome of restorative proctocolectomy. The aim of our study was to determine if the histological features of the resected specimen in patients with UC and IC can predict ileal-pouch-related outcome. METHOD: A review of all patients who had a restorative proctocolectomy created following completion proctectomy or proctocolectomy for UC and IC was performed. RESULTS: Between 1992 and 2011, 142 patients (132 with UC and 10 with IC) were reviewed. After a median follow-up of 36 (3-149) months, 51 (35.9%) developed a pouch-related complication. Forty-two (29.7%) developed pouchitis while three (2.1%) developed a pouch-cutaneous fistula. Four (2.8%) had pouch failure, while stricture of the anastomosis was seen in three (2.1%) patients. The presence of extension of the inflammation into the muscularis propria of the resected specimen was associated with an increased risk of pouch-related complications (P = 0.01). The presence of submucosal oedema was also a significant risk factor (P = 0.03). CONCLUSION: The extension of inflammation into the muscularis propria appears to predict pouch-related complications following restorative proctocolectomy for UC or IC.

Phonon, IR, and Raman spectra, NMR parameters, and elastic constant calculations for AlH3 polymorphs.

The electronic structure, lattice dynamics, and mechanical properties of AlH(3) phases have been studied by density functional calculations. The chemical bonding in different polymorphs of AlH(3) are evaluated on the basis of electronic structures, charge density analysis, and atomic charges, as well as bond overlap population analysis and the Born effective charges. The phonon dispersion relations and phonon density of states of all the polymorphs of AlH(3) are calculated by direct force-constant method. Application of pressure induces seqauence of phase transitions in ß-AlH(3) which are understood from the phonon dispersive curves of the involved phases. The previously predicted phases (Chem. Mater. 2008, 20, 5997) are found to be dynamically stable. The calculated single crystal elastic constants reveal that all the studied AlH(3) polymorphs are easily compressible. The chemical bonding of these polymorphs have noticeable covalent character (except the hp2 phase) according to the present chemical bonding analyses. For all these polymorphs, the NMR-related parameters, such as isotropic chemical shielding, quadrupolar coupling constant, and quadrupolar asymmetry, are also calculated. All IR- and Raman-active phonon frequencies, as well as the corresponding intensities, are calculated for all the AlH(3) polymorphs and are compared with available experimental results.

Nano-phases of NaBH4 and KBH4.

Phase stability and chemical bonding of beta-NaBH4 and beta-KBH4 derived nano-structures and possible low energy surfaces of them from thin film geometry have been investigated using ab initio projected augmented plane wave method. Structural optimizations based on total energy calculations predicted that, for beta-NaBH4 and beta-KBH4 phases, the (011) and (101) surfaces are more stable among the possible low energy surfaces. The predicted critical size of the nano-cluster for beta-NaBH4 and beta-KBH4 is 1.35 and 1.8 nm, respectively. The corresponding critical diameter for the nano-whisker is 2.6 and 2.8 nm respectively for beta-NaBH4 and beta-KBH4. Structural optimization based on total energy calculations show that the bond distances in the surfaces of nano-whisker are found to be higher than that in the bulk material and the calculated H site energies and bond overlap population analysis suggesting that it is considerably easier to remove hydrogen from the surface of the clusters and nano-whiskers than that from the bulk crystals.

Structural investigation and thermodynamical properties of alkali calcium trihydrides.

The ground-state structure, equilibrium structural parameters, electronic structure, and thermodynamical properties of MCaH(3) (M=Li, Na, K, Rb, and Cs) phases have been investigated. From the 104 structural models used as inputs for structural optimization calculations, the ground-state crystal structures of MCaH(3) phases have been predicted. At ambient condition, LiCaH(3), NaCaH(3), and KCaH(3) crystallize in hexagonal, monoclinic, and orthorhombic structures, respectively. The remaining phases RbCaH(3) and CsCaH(3) crystallize in a cubic structure. The calculated phonon spectra indicate that all the predicted phases are dynamically stable. The formation energy for the MCaH(3) phases have been calculated along different reaction pathways. The electronic structures reveal that all these phases are insulators with an estimated band gap varying between 2.5 and 3.3 eV.

Role of W-site substitution on mechanical and electronic properties of cubic tungsten carbide.

In order to understand the role of W-site substitution on properties of cubic tungsten carbide ([Formula: see text]-WC), we have investigated the structural, mechanical, and electronic properties of WXC2 (X = Si, Sc, Ti, V, Cr, Ge, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Sn, Hf, Ta, Re, Os, Ir, Pt, Th, U) using first principles calculations based on density functional theory, within generalized gradient approximation. The structural optimization has carried out for all these compounds using force as well as stress minimization. The optimized structural parameters for experimentally known compounds are in good agreement with the available x-ray diffraction measurements and structural parameters for nineteen WXC2 compounds are newly predicted. The W-site substitution of the above-listed elements into [Formula: see text]-WC reduces the symmetry of the primitive lattice to tetragonal structure. The heat of formation ([Formula: see text]) and the mechanical stability studies are carried out to investigate the stability of these systems. The single-crystal elastic constants c ij , elastic moduli of the polycrystalline aggregates, anisotropy in elastic constants and related properties of the WXC2 materials have calculated and discussed in detail. The hardness of the above materials is predicted using two different criteria, based on the softest elastic mode as well as the Pugh's modulus ratio. There is a correlation in the hardness predicted from these two approaches except in the case of [Formula: see text]-WC. The chemical bonding interaction between the constituents is analysed using the density of states, crystal orbital Hamiltonian population, and charge density for selected systems. All these compounds are predicted to be metal and our calculations suggest that W-site substitutions do not improve the hardness of [Formula: see text]-WC. However, from the heat of formation studies, we have identified five new stable compounds such as CrWC2, NbWC2, ScWC2, YWC2, and UWC2 with reasonably good hardness and those need experimental verifications.

Clinico-epidemiological and genomic profile of first Zika Virus outbreak in India at Jaipur city of Rajasthan state.

BACKGROUND: First Zika virus (ZIKV) positive case from North India was detected on routine surveillance of Dengue-Like Illness in an 85-year old female. Objective of the study was to conduct an investigation for epidemiological, clinical and genomic analysis of first ZIKV outbreak in Rajasthan, North India and enhance routine ZIKV surveillance. METHOD: Outbreak investigation was performed in 3 Km radius of the index case among patient contacts, febrile cases, and pregnant women. Routine surveillance was enhanced to include samples from various districts of Rajasthan. Presence of ZIKV in serum and urine samples was detected by real time PCR test and CDC trioplex kit. Few ZIKV positive samples were sequenced using the next-generation sequencing method for genomic analysis. RESULT: On outbreak investigation 153/2043 (7.48%) cases were found positive: 1/153 (0.65%) among contacts, 90/153 (58.8%) in fever cases, 62/153(40.5%) in pregnant females. In routine surveillance, 6/4722 (0.12%) serum samples were ZIKV positive.Majority of patients had mild signs and symptoms, no case of microcephaly and Guillain- Barre Syndrome was seen, 25 (40.3%) pregnant females delivered healthy babies, four (6.4%) reported abortion and three (4.8%) had intrauterine death, one (1.6%) child had colorectal malformation and died after few days of birth. ZIKV was found to belong to Asian lineage, mutation related to enhanced neuro-virulence and transmission in animal models was not found. CONCLUSION: ZIKV was endogenous to India belonging to Asian Lineage. Disease profile of the ZIKV was asymptomatic to mild. No major anomaly was observed in infants born to ZIKV positive mothers; however, long term follow up of these children is required. There is need to scale up surveillance in the virology lab network of India for early detection and control. SUMMARY LINE: Zika virus infection was endogenous due to Asian Lineage with mild disease, no case of microcephaly or Guillain- Barre Syndrome was seen but children need to be followed for anomalies and surveillance of ZIKV needs to be enhanced in the country.

Nanostructures of LiBH4: a density-functional study.

The phase stability and electronic structure of alpha- LiBH(4)-derived nanostructures and possible low energy surfaces of thin films have been investigated using the ab initio projected augmented plane wave method. Structural optimizations based on total energy calculations predicted that, for the alpha- LiBH(4) phase, the (010) surface is the most stable of the possible low-energy surfaces. The predicted critical sizes of the nano-cluster and nano-whisker for alpha- LiBH(4) are 1.75 and 1.5 nm, respectively. Similarly, the bond distances in the surfaces of a nano-whisker are found to be higher than that in the bulk material. The calculated hydrogen site energies suggest that it is relatively easier to remove hydrogen from the surface of the clusters and nano-whiskers than from bulk crystals.

Vibrational spectroscopic investigations, ab initio and DFT studies on 7-bromo-5-chloro-8-hydroxyquinoline.

The Fourier transform infrared (FTIR) and FT-Raman spectra of 7-bromo-5-chloro-8-hydroxyquinoline (BCHQ) have been measured in the range 4000-400 and 4000-100cm(-1), respectively. Complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FTIR and FT-Raman data. The geometry was optimised without any symmetry constrains using the DFT/B3LYP and HF methods with 6-31G** basis set. The vibrational frequencies which were determined experimentally are compared with those obtained theoretically from ab initio HF and density functional theory (DFT) gradient calculations employing the HF/6-31G** and B3LYP/6-31G** methods for the optimised geometry of the compound. The structural parameters and normal modes of vibration obtained from HF and DFT methods are in good agreement with the experimental data. Normal coordinate analysis was also carried out with ab initio force fields utilising Wilson's FG matrix method.

Cluster containment strategy: addressing Zika virus outbreak in Rajasthan, India.

India is at risk of Zika virus transmission due to high prevalence of its vector Aedes aegypti. Rajasthan, a state in the north-west region of India, has also high prevalence of Aedes mosquito. First laboratory confirmed case of Zika virus disease in Rajasthan was reported on 21 September 2018 in Jaipur. The Government of Rajasthan quickly implemented a containment strategy to contain the outbreak and prevent further spread of this disease. Strategy included active human and mosquito surveillance, laboratory testing and sequencing of the virus, integrated vector control measures, intersectoral coordination, risk communication and social mobilisation, all in a predefined geographic area around the epicentre. Timely action with appropriate coordination at all levels with multiple stakeholders contained the outbreak successfully. In all, 159 confirmed cases were reported from in and around the 3 km containment zone in Shastri Nagar area of Jaipur City and routine surveillance. Following this, a specially developed laboratory-based surveillance strategy was put in place to ensure that the disease does not spread beyond the containment zone. No fresh case was reported subsequently within or beyond the containment zone.

Density functional theory studies of spin, charge, and orbital ordering in YBaT2O5 (T = Mn, Fe, Co).

Spin, charge, and orbital orderings are influenced by electron/hole doping, cation radii, oxygen stoichiometry, temperature, magnetic field, and so on. In order to understand the role of electron/hole doping, we have studied variations in spin, charge, and orbital ordering in terms of d-band filling for YBaT 2O 5 (T = Mn, Fe, Co). The calculations were performed using density functional theory as implemented in the full-potential linearized augmented-plane-wave method. We have carried out calculations for nonmagnetic, ferromagnetic, and antiferromagnetic configurations. A ferrimagnetic ground state was established for YBaMn 2O 5, whereas YBaFe 2O 5 and YBaCo 2O 5 have antiferromagnetic ground states; all of these results are in agreement with experimental findings. The effects of spin-orbit coupling, the Hubbard U parameter, and orbital polarization on the magnetic properties were also analyzed. The electronic band characteristics were analyzed using total as well as site- and orbital-projected densities of states. Inclusion of spin-orbit coupling and Coulomb correlation effects in the calculations was found to be important in order to reproduce the experimentally established semiconducting behaviors of YBaFe 2O 5 and YBaCo 2O 5. In order to quantify the charges at each atomic site, we made use of the Bader "atom-in-molecule" concept and Born effective-charge (BEC) analyses. The structural optimizations and BEC tensor calculations were performed using the VASP-PAW method. The different types of charge and orbital orderings in these compounds were visualized using the energy-projected density matrices of the d electrons. Substantial differences in ordering patterns with respect to d-band filling emerged. Ordering of the d z (2) orbital of Mn in YBaMn 2O 5 gave rise to G-type ferrimagnetic spin ordering along the c direction and checkerboard-type charge ordering, whereas ordering of the d x (2) - y (2) orbital of Fe in YBaFe 2O 5 caused Wollan-Koehler G-type antiferromagnetic spin ordering along the b direction and stripe-type charge ordering. Similarly, a complex pattern of orbital ordering in YBaCo 2O 5 activated spin and charge orderings similar to those in YBaFe 2O 5.

An experimental study on using a diagnostic computed radiography system as a quality assurance tool in radiotherapy.

The advent of improved digital imaging modalities in diagnostic and therapy is fast making conventional films a nonexistent entity. However, several radiotherapy centers still persist with film for performing quality assurance (QA) tests. This paper investigates the feasibility of using a diagnostic computed radiography (CR) system as a QA tool in radiotherapy. QA tests such as light field congruence, field size verification, determination of radiation isocentre size, multileaf collimator (MLC) check and determination of isocentric shift for stereotactic radiosurgery (SRS) were performed and compared with film. The maximum variation observed between CR and film was 0.4 mm for field size verification, -0.13 mm for the radiation isocentre size check, 0.77 for MLC check and -0.1 mm for isocentric shift using the Winston Lutz test tool for SRS QA. From these results obtained with the CR it is concluded that a diagnostic CR system can be an excellent cost-effective digital alternative to therapy film as a tool for QA in radiotherapy.