Segregation Effects at a High-Angle Twist Boundary in ZnO

Ab initio density functional plane-wave pseudopotential calculations were performed for a = 7 ( = 21.79°) [0001] twist boundary in ZnO with and without the presence of Sb impurities. The segregation energies revealed a significant driving force for segregation and it was shown that the formation of an Sb monolayer was favoured. Decreased coordination in the boundary core suggested a trend towards the formation of an intergranular phase. The impurity states caused by the monolayer were located within the band gap and higher in energy relative to the state produced by a single impurity. Charge transfer to the Sb monolayer was observed indicating a possible enhancement of the grain boundary potential barrier.     

An interfacial complex in ZnO and its influence on charge transport

The segregation of native defects and Bi impurities to a high-angle grain boundary in ZnO is studied by first-principles calculations. It is found that the presence of Bi(Zn) increases the concentration of native defects of acceptor type in the grain boundary. This leads to the formation of a Bi(Zn)+V(Zn)+O(i) interfacial complex under O-rich conditions and exhibits a localized acceptor state. This state, which is different from that of the isolated impurity, gives the grain boundary p-type character and when embedded between n-type ZnO grains is consistent with the double Schottky barrier model for Bi-doped ZnO varistors.     

Pt nanoparticles supported over Ce–Ti–O: the solvothermal and photochemical approaches for the preparation of catalytic materials

Ce–Ti–O supports with different Ce/Ti molar ratios were synthesized by the solvothermal method using hexadecyltrimethylammonium bromide. Pt nanoparticles were then supported by photochemical deposition. The shape, size, and structure of these materials were analyzed by high-resolution transmission electron microscopy. The single CeO₂ support was also prepared, consisting of agglomerated cubic particles ranging from ~3 to 8 nm. When titania was combined with ceria, a nanostructured architecture was produced, evidencing the strong influence of Ti in the support structure. Photodeposition of Pt nanoparticles is more efficient on Ce–Ti–O supports than in pristine CeO₂. Crystalline Pt nanoparticles (mainly of ~2 to 4 nm) were detected. The catalytic properties of the materials were tested in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol. It was observed that Pt supported on Ce–Ti–O is more active and selective than Pt on CeO₂ or TiO₂ separately. The catalyst with 40 mol% Ce leads to total conversion of cinnamaldehyde in a few minutes; however, higher selectivity toward the desired product (cinnamyl alcohol) was obtained with higher amounts of Ce (50 mol%).     

Landsat-5 TM and Landsat-7 ETM+ absolute radiometric calibration using the reflectance-based method

The reflectance-based method of vicarious calibration has been used for the absolute radiometric calibration of the Landsat series of sensors since the launch of Landsat-4. The reflectance-based method relies on ground-based measurements of the surface reflectance and atmospheric conditions at a selected test site nearly coincident with the imaging of that site by the sensor of interest. The results of this approach are presented here for Landsat-5 Thematic Mapper (TM) and Landsat-7 Enhanced Thematic Mapper Plus (ETM+). The data have been collected by two groups, one from the University of Arizona and the other from South Dakota State University. The test sites used by the University of Arizona group for this work are the Railroad Valley Playa, Lunar Lake Playa, and Roach Lake Playa all of which are in Nevada, Ivanpah Playa in California, and White Sands Missile Range, New Mexico. The test site for the South Dakota State group is a grass site in Brookings, SD. The gains derived from dates using these sites spanning the period from 1984 to 2003 are presented for TM and for the period of 1999 to 2003 for ETM+. Differences between the two groups are less than the combined uncertainties of the methods, and the data are thus treated as a single dataset. The results of these vicarious data indicate that there has been no degradation apparent in TM since 1995 and in ETM+ since launch. Agreement between the reflectance-based results and the preflight calibration of ETM+ is better than 4% in all bands, and the standard deviation of the average difference indicates a precision of the reflectance-based method on the order of 3%.     

Landsat-5 TM reflective-band absolute radiometric calibration

The Landsat-5 Thematic Mapper (TM) sensor provides the longest running continuous dataset of moderate spatial resolution remote sensing imagery, dating back to its launch in March 1984. Historically, the radiometric calibration procedure for this imagery used the instrument's response to the Internal Calibrator (IC) on a scene-by-scene basis to determine the gain and offset of each detector. Due to observed degradations in the IC, a new procedure was implemented for U.S.-processed data in May 2003. This new calibration procedure is based on a lifetime radiometric calibration model for the instrument's reflective bands (1-5 and 7) and is derived, in part, from the IC response without the related degradation effects and is tied to the cross calibration with the Landsat-7 Enhanced Thematic Mapper Plus. Reflective-band absolute radiometric accuracy of the instrument tends to be on the order of 7% to 10%, based on a variety of calibration methods.     

The Pnictogen Bond: The Covalently Bound Arsenic Atom in Molecular Entities in Crystals as a Pnictogen Bond Donor

In chemical systems, the arsenic-centered pnictogen bond, or simply the arsenic bond, occurs when there is evidence of a net attractive interaction between the electrophilic region associated with a covalently or coordinately bound arsenic atom in a molecular entity and a nucleophile in another or the same molecular entity. It is the third member of the family of pnictogen bonds formed by the third atom of the pnictogen family, Group 15 of the periodic table, and is an inter- or intramolecular noncovalent interaction. In this overview, we present several illustrative crystal structures deposited into the Cambridge Structure Database (CSD) and the Inorganic Chemistry Structural Database (ICSD) during the last and current centuries to demonstrate that the arsenic atom in molecular entities has a significant ability to act as an electrophilic agent to make an attractive engagement with nucleophiles when in close vicinity, thereby forming σ-hole or π-hole interactions, and hence driving (in part, at least) the overall stability of the system’s crystalline phase. This overview does not include results from theoretical simulations reported by others as none of them address the signatory details of As-centered pnictogen bonds. Rather, we aimed at highlighting the interaction modes of arsenic-centered σ- and π-holes in the rationale design of crystal lattices to demonstrate that such interactions are abundant in crystalline materials, but care has to be taken to identify them as is usually done with the much more widely known noncovalent interactions in chemical systems, halogen bonding and hydrogen bonding. We also demonstrate that As-centered pnictogen bonds are usually accompanied by other primary and secondary interactions, which reinforce their occurrence and strength in most of the crystal structures illustrated. A statistical analysis of structures deposited into the CSD was performed for each interaction type As···D (D = N, O, S, Se, Te, F, Cl, Br, I, arene’s π system), thus providing insight into the typical nature of As···D interaction distances and ∠R–As···D bond angles of these interactions in crystals, where R is the remainder of the molecular entity.     

Stretching Generic Pesin’s Entropy Formula

Journal of Statistical Physics - We prove that Pesin’s entropy formula holds generically within a broad subset of volume-preserving bi-Lipschitz homeomorphisms with respect to the...     

Necrosis Depth and Photodynamic Threshold Dose with Redaporfin-PDT

Predicting the extent of necrosis in photodynamic therapy (PDT) is critical to ensure that the whole tumor is treated but vital structures, such as major blood vessels in the vicinity of the tumor, are spared. The models developed for clinical planning rely on empirical parameters that change with the nature of the photosensitizer and the target tissue. This work presents an in vivo study of the necrosis in the livers of rats due to PDT with a bacteriochlorin photosensitizer named redaporfin using both frontal illumination and interstitial illumination. Various doses of light at 750 nm were delivered 15 min postintravenous administration of redaporfin. Sharp boundaries between necrotic and healthy tissues were found. Frontal illumination allowed for the determination of the photodynamic threshold dose—1.5 × 10¹⁹ photons cm⁻³—which means that the regions of the tissues exposed to more than 11 mm of ROS evolved to necrosis. Interstitial illumination produced a necrotic radius of 0.7 cm for a light dose of 100 J cm⁻¹ and a redaporfin dose of 0.75 mg kg⁻¹. The experimental data obtained can be used to inform and improve clinical planning with frontal and interstitial illumination protocols.     

Fermionic Representation of Two-Dimensional Dimer Models

Dimer models in two dimensions give rise to well-known statistical lattice problems, which can be exactly solved by the same combinatorial techniques associated with the Ising model and which have been used to account for the phase transitions in a number of physically interesting systems. More recently, dimer models have been regarded as classical limits of the quantum ground state of some antiferromagnetic systems. We then revisit an early transfer-matrix calculation for the dimer model on the simple square lattice. We write a spin representation for the transfer matrix associated with the canonical partition function of two paradigmatic dimers models, on the 4–8 lattice, with an Ising-type transition, and on the brick lattice, with a peculiar commensurate–incommensurate transition. Using standard techniques, the problem is reduced to the calculation of the eigenvalues of a system of free fermions.