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Tassi M.,Institute of Material Science | Theophilou I.,Jülich Research Center | Thanos S.,Institute of Material Science
Journal of Chemical Physics | Year: 2013

Doubly excited states have nowadays become important in technological applications, e.g., in increasing the efficiency of solar cells and therefore, their description using ab initio methods is a great theoretical challenge as double excitations cannot be described by linear response theories based on a single Slater determinant. In the present work we extend our recently developed Hartree-Fock (HF) approximation for calculating singly excited states [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013)10.1002/qua.24049] in order to allow for the calculation of doubly excited states. We describe the double excitation as two holes in the subspace spanned from the occupied HF orbitals and two particles in the subspace of virtual HF orbitals. A subsequent minimization of the energy results to the determination of the spin orbitals of both the holes and the particles in the occupied and virtual subspaces, respectively. We test our method, for various atoms, H 2 and polyene molecules which are known to have excitations presenting a significant double excitation character. Importantly, our approach is computationally inexpensive. © 2013 American Institute of Physics.


Parhi N.,P.A. College | Rout G.C.,Fakir Mohan University | Behera S.N.,Institute of Material Science
Indian Journal of Physics | Year: 2010

We present here a theoretical study of the effect of Jahn-Teller(J-T) distortion on the self-energy of electrons in the CMR manganites. The model consists of the itinerant eg electrons distorted by J-T effect and the localized t2g core electrons carrying strong ferromagnetism due to Hund's rule. The phonon interacts with the eg electrons as well as the J-T distorted eg band. The electron Green's functions are calculated by Zubarev's technique. The electron self-energy which carries all the information of the model is calculated from the Green's function. The effect of J-T distortion, magnetism on the frequency and temperature dependent dynamic selfenergy is presented in this paper. The results are discussed. © 2010 IACS.


PubMed | Agricultural University of Athens, Foundation for Research and Technology Hellas, Institute of Material Science and University of Patras
Type: Journal Article | Journal: Plant signaling & behavior | Year: 2016

Land plants face the perpetual dilemma of using atmospheric carbon dioxide for photosynthesis and losing water vapors, or saving water and reducing photosynthesis and thus growth. The reason behind this dilemma is that this simultaneous exchange of gases is accomplished through the same minute pores on leaf surfaces, called stomata. In a recent study we provided evidence that pigweed, an aggressive weed, attenuates this problem exploiting large crystals of calcium oxalate as dynamic carbon pools. This plant is able to photosynthesize even under drought conditions, when stomata are closed and water losses are limited, using carbon dioxide from crystal decomposition instead from the atmosphere. Abscisic acid, an alarm signal that causes stomatal closure seems to be implicated in this function and for this reason we named this path alarm photosynthesis. The so-far enigmatic, but highly conserved and widespread among plant species calcium oxalate crystals seem to play a crucial role in the survival of plants.


Dotsika E.,Institute of Material Science | Dotsika E.,CNR Institute of Geosciences and Earth Resources
Journal of Volcanology and Geothermal Research | Year: 2012

Thermal and cold water samples were collected from the island of Samothraki, in the northern part of the Aegean Sea. Isotopic (δD, δ 18O, δ 34S SO4, δ 34S S2-, δ 18O SO4) and chemical analyses (major ions, Br, B, Li, SiO 2) were performed in most of them. The study of ionic and isotopic contents shows that, the thermal waters of Samothraki Island are mainly locally fed groundwater that changes, chemically and isotopically, during its circulation within a major fracture zone reaching great depths. More specifically, the evaluation of the entire dataset indicates that water-rock reactions and mixing with brines are the principal sources of the isotopic and salinity fingerprint of these waters.The isotopic [δ 18O (SO 4 2--H 2O)] and chemical geothermometers applied on the waters of the thermal springs, suggest the probable existence of a geothermal reservoir of high enthalpy. The temperature attributed to this deep geothermal field is higher than 220°C. © 2012 Elsevier B.V.


Mironov E.A.,RAS Institute of Applied Physics | Zheleznov D.S.,RAS Institute of Applied Physics | Starobor A.V.,RAS Institute of Applied Physics | Voitovich A.V.,RAS Institute of Applied Physics | And 3 more authors.
Optics Letters | Year: 2015

Unique Faraday isolator based on a TGG single crystal with aperture diameter of 40 mm for high average power lasers has been fabricated and investigated experimentally. The device provides a stable isolation ratio over 30 dB for large-radius laser beams with kilowatt average power radiation typical for high-power applications. © 2015 Optical Society of America.


Schaller J.,TU Dresden | Schaller J.,Institute of General Ecology and Environmental Protection | Mkandawire M.,TU Dresden | Mkandawire M.,Institute of General Ecology and Environmental Protection | And 3 more authors.
Environmental Pollution | Year: 2010

Organic sediments are a main sink for metal pollutants in aquatic systems. However, factors that make sediments a sink of metals and metalloids are still not clear. Consequently, we investigate the role of invertebrate shredders (Gammarus pulex L.) on quality of metal and arsenic fixation into organic partitions of sediment in the course of litter decay with laboratory microcosm experiments. During the decomposition of leaf litter, G. pulex significantly facilitated the development of small particles of organic matter. The capacity of metal fixation was significantly higher in smaller particles than leaf litter and litter residuals. Thus, G. pulex enhanced metal fixation into the organic partition of sediments by virtue of increasing the amount smaller particles in the aquatic system. Furthermore, invertebrates have a significant effect on formation of dissolved organic matter and remobilization of cobalt, molybdenum and cesium, but no significant effect on remobilization of all other measured elements. © 2010 Elsevier Ltd.


Schaller J.,TU Dresden | Schaller J.,Institute of General Ecology and Environmental Protection | Brackhage C.,TU Dresden | Brackhage C.,Institute of General Ecology and Environmental Protection | And 4 more authors.
Science of the Total Environment | Year: 2011

The focus of this article is to combine two main areas of research activities in freshwater ecosystems: the effect of inorganic pollutants on freshwater ecosystems and litter decomposition as a fundamental ecological process in streams.The decomposition of plant litter in aquatic systems as a main energy source in running water ecosystems proceeds in three distinct temporal stages of leaching, conditioning and fragmentation. During these stages metals and metalloids may be fixed by litter, its decay products and the associated organisms. The global-scale problem of contaminated freshwater ecosystems by metals and metalloids has led to many investigations on the acute and chronic toxicity of these elements to plants and animals as well as the impact on animal activity under laboratory conditions. Where sorption properties and accumulation/remobilization potential of metals in sediments and attached microorganisms are quite well understood, the combination of both research areas concerning the impact of higher trophic levels on the modification of sediment sorption conditions and the influence of metal/metalloid pollution on decomposition of plant litter mediated by decomposer community, as well as the effect of high metal load during litter decay on organism health under field conditions, has still to be elucidated. So far it was found that microbes and invertebrate shredder (species of the genera Gammarus and Asellus) have a significant influence on metal fixation on litter. Not many studies focus on the impact of other functional groups affecting litter decay (e.g. grazer and collectors) or other main processes in freshwater ecosystems like bioturbation (e.g. Tubifex, Chironomus) on metal fixation/release. © 2011 Elsevier B.V.


Georgakilas V.,Institute of Material Science | Bourlinos A.B.,Institute of Material Science | Zboril R.,Palacky University | Steriotis T.A.,Institute of Physical Chemistry | And 4 more authors.
Chemical Communications | Year: 2010

Graphene sheets derived from dispersion of graphite in pyridine were functionalised by the 1,3 dipolar cycloaddition of azomethine ylide. The organically modified graphene sheets are easily dispersible in polar organic solvents and water, and they are extensively characterised using several spectroscopic and microscopy techniques. © 2010 The Royal Society of Chemistry.


Binh P.H.,INSA Toulouse | Binh P.H.,Institute of Material Science | Renucci P.,INSA Toulouse | Truong V.G.,INSA Toulouse | Marie X.,INSA Toulouse
Electronics Letters | Year: 2012

A new pulse-shaping circuit has been designed to increase the performances of large signal modulation of light emitting diodes. It is simply based on a parallel Schottky-capacitance circuit in series with the light emitter. The peak power of the generated optical pulse is shown to be significantly improved compared to the classical resistance-capacitance peaking circuit for sub-nanosecond pulsewidths. © 2012 The Institution of Engineering and Technology.


Deshapriya I.K.,Institute of Material Science | Kumar C.V.,Institute of Material Science
Langmuir | Year: 2013

Specific approaches to the rational design of nanobio interfaces for enzyme and protein binding to nanomaterials are vital for engineering advanced, functional nanobiomaterials for biocatalysis, sensing, and biomedical applications. This feature article presents an overview of our recent discoveries on structural, functional, and mechanistic details of how enzymes interact with inorganic nanomaterials and how they can be controlled in a systematic manner using α-Zr(IV)phosphate (α-ZrP) as a model system. The interactions of a number of enzymes having a wide array of surface charges, sizes, and functional groups are investigated. Interactions are carefully controlled to screen unfavorable repulsions and enhance favorable interactions for high affinity, structure retention, and activity preservation. In specific cases, catalytic activities and substrate selectivities are improved over those of the pristine enzymes, and two examples of high activity near the boiling point of water have been demonstrated. Isothermal titration calorimetric studies indicated that enzyme binding is coupled to ion sequestration or release to or from the nanobio interface, and binding is controlled in a rational manner. We learned that (1) bound enzyme stabilities are improved by lowering the entropy of the denatured state; (2) maximal loadings are obtained by matching charge footprints of the enzyme and the nanomaterial surface; (3) binding affinities are improved by ion sequestration at the nanobio interface; and (4) maximal enzyme structure retention is obtained by biophilizing the nanobio interface with protein glues. The chemical and physical manipulations of the nanobio interface are significant not only for understanding the complex behaviors of enzymes at biological interfaces but also for desiging better functional nanobiomaterials for a wide variety of practical applications. © 2013 American Chemical Society.

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