163,431 research outputs found
J. Duvernay-Bolens, Les Géants patagons. Voyage aux origines de l'homme
No full textStoczkowski Wiktor. J. Duvernay-Bolens, Les Géants patagons. Voyage aux origines de l'homme. In: L'Homme, 1996, tome 36 n°139. pp. 145-146
Strong Hole Trapping Due to Oxygen Dimers in BiVO4: Effect on the Water Oxidation Reaction
No full textWe present a study of hole bipolarons in BiVO4. We show that in the presence of two holes O-O dimers are formed, leading to strong charge trapping. While the formation of bipolarons in bulk BiVO4 requires overcoming a kinetic barrier, we find that these defects should be spontaneously formed at the surface of the material and its interface with water. Through molecular dynamics simulations, we study the effect of bipolarons on the water-splitting reaction and show that their presence may be especially beneficial in alkaline conditions
Wiktor Grygorenko
No full textWiktor Grygorenko was born on March 6, 1927. He passed his final high school exam in Katowice in 1949 and after a military training he began his studies at the Military School of Topographers. Then he studied geodesy at the Military Engineering Academy in Moscow. Having returned to Warsaw in 1959, he worked in the Military Cartographic Works and later in the Topographic Board of the General Staff of the Polish Army. Simultaneously, he took a lecturer post at the Military Technical Academy in Warsaw where he elaborated student textbooks on maps editing, cartographic reproduction, and mathematical cartography. His comprehensive manual Elaboration of general geographical maps was published in 1970. He was a member of the editorial staff at the popular World Atlas, published in 1962-1968 and also known under the name of Pergamon World Atlas. A new and innovative projection devised by Wiktor Grygorenko was used in the World Atlas, nowadays known as the projection of the Polish Army Topographical Service. In 1971 he obtained the degree of a Doctor of Technical Sciences in cartography at the Warsaw University of Technology. The subject of his thesis were theoretical fundamentals of the automatic cartographic data processing. Wiktor Grygorenko was one of the Polish pioneers of computer usage in cartography and was the author of many valuable papers on the subject. He began to work at University of Warsaw in 1972, In 1978 he completed his habilitation procedures on the basis of his dissertation entitled Quantitative Parameters of the Cartographic Content Composition in which he formulated the idea of the quantitative model of a map, thus drawing a new direction of theoretical and practical works in cartographic design and evaluation. Many papers on cartographic generalisation with usage of computer methods were created under his guidance. In 1980, three years after the unexpected death of professor Lech Ratajski, Wiktor Grygorenko became the Head of the Chair of Cartography at the Faculty of Geography and Regional Studies. In 1981 he became the Vice-dean for student affairs and served two terms. His first term fell in the difficult period of the martial law when he defended students on many occasions, gaining their gratitude and respect. In autumn 1982 he also became the Head of the Department of Cartography at the Maria Curie-Skłodowska University in Lublin, which he administered until 1992. Making a good use of his broad didactic experience, he published several absorbing articles on educating cartographers with the geographic training. He actively participated in conferences, conventions, and cartographic trainings, animating discussions with his inspiring speeches. In summer 1982, during the 11th conference of the International Cartographic Association in Warsaw he presented the paper Cybernetic model of cartographic communication that was in certain degree a continuation and an explication of professor Lech Ratajski's idea of communication model. The main field of professor Grygorenko's (he obtained the professorship in 1992) scientific interest were theoretical issues related to the automation of the maps editing and usage processes. His interest in the history of cartography resulted in the publication of several interesting papers on the subject and participation in meetings of cartography historians. He served many social functions both at the University of Warsaw and among the geodesists and cartographers. Professor Wiktor Grygorenko died on February 25, 2008
[Report to Chief J. E. Curry, by an unknown author #1]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
[Report to Chief J. E. Curry, by an unknown author #2]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
Mechanism suppressing charge recombination at iodine defects in CH3NH3PbI3 by polaron formation
No full textMetal-halide perovskites exhibit high efficiencies in photovoltaic applications and low recombination rates, despite the high concentrations of intrinsic defects. We here study the hole trapping at the negative iodine interstitial, which corresponds to the dominating recombination center in CH3NH3PbI3. We calculate the free energy profile for the hole trapping at 300 K using the Blue Moon technique based on hybrid functional molecular dynamics. We find that the hole trapping is energetically unfavorable and requires overcoming an energy barrier. This behavior stems from the position of the vertical (-/0) transition level of the iodine defect and the formation of a polaron. Our simulations show that the polaron does not interact with the iodine interstitial and hops through the lattice on a sub-picosecond scale. Our results highlight a mechanism by which the low mononuclear (trap-assisted) recombination rates in CH3NH3PbI3 can be explained.CSE
Note: Assessment of the SCAN+rVV10 functional for the structure of liquid water
No full textThe performance of the SCAN+rVV10 functional in modeling the structural properties of liquid water is studied through constant-volume ab initio molecular dynamics simulations with both classical and quantum nuclei. The radial distribution functions are found to be slightly overstructured with respect to experiment, but overall similar to those achieved with the bare SCAN and the rVV10 functionals. From the pressures calculated during the dynamics, it is inferred that the SCAN+rVV10 functional leads to a noticeable overestimation of the density of liquid water
pH-Dependent Surface Chemistry from First Principles: Application to the BiVO4(010)-Water Interface
No full textWe present a theoretical formulation for studying the pH-dependent interfacial coverage of semiconductor-water interfaces through ab initio electronic-structure calculations, molecular dynamics simulations, and the thermodynamic integration method. This general methodology allows one to calculate the acidity of the individual adsorption sites on the surface and, consequently, the pH at the point of zero charge, pH PZC , and the preferential adsorption mode of water molecules, either molecular or dissociative, at the semiconductor-water interface. The proposed method is applied to study the BiVO 4 (010)-water interface, yields a pH PZC in excellent agreement with the experimental characterization. Furthermore, from the calculated pK a values of the individual adsorption sites, we construct an ab initio concentration diagram of all the adsorbed species at the interface as a function of the pH of the aqueous solution. The diagram * To whom correspondence should be addressed 1 clearly illustrates the pH-dependent coverage of the surface and indicates that protons are found to be significantly adsorbed (∼ 1% of available sites) only in highly acidic conditions. The surface is found to be mostly covered by molecularly adsorbed water molecules in a wide interval of pH values ranging from 2 to 8. Hydroxyl ions are identified as the dominant adsorbed species at pH larger than 8.2.CSE
pH-Dependent Catalytic Reaction Pathway for Water Splitting at the BiVO4−Water Interface from the Band Alignment
No full textWe align the band edges of BiVO4 at the interface with liquid water by combining advanced electronic-structure calculations, molecular dynamics simulations, and a computational hydrogen electrode. After accounting for spin–orbit coupling and thermal and nuclear quantum motions, we achieve good agreement with experiment, particularly with one-shot GW calculations and semiempirically tuned hybrid functionals. The pH-dependent mechanism of the water oxidation reaction is discussed in consideration of the pH at the point of zero charge, the pKa of adsorbed water molecules, and the redox levels of the rate-determining step of the reaction. The mechanism pertaining to acidic conditions is found to dominate over a large pH range. The kinetically more favorable oxidation of hydroxyl ions is favored only in highly alkaline conditions and could be hampered by corrosion processes. Advanced electronic-structure methods are shown to be instrumental in overcoming the erroneous physical picture achieved at the semilocal level of theory.CSE
Surface Polarons Reducing Overpotentials in the Oxygen Evolution Reaction
No full textWe investigate the stability of hole polarons at the rutile surface induced by electronegative adsorbates in the intermediate steps of the oxygen evolution reaction through hybrid density functional calculations. Applying the computational hydrogen electrode method, we find that hole polarons reduce the overpotential of the reaction-determining step leading to good agreement with experiment. The stability of the polarons is confirmed at the hydrated surface through a free energy study involving the explicit solvent. The occurrence of surface hole polarons is unrelated to the scaling relationships and offers an additional handle in the search for improved catalysts
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