Model Simulations of the Hengill Area,Southwestern Iceland

The Hengill Area is an important energy source for Reykjavík and surrounding area, both for electricity and district space heating. Two production fields are located in the area: Nesjavellir and Hellisheiei. Two other potential production fields are believed to be in the area. We present a new conceptual model supported by numerical calculations for the entire Hengill Area. Calculations were performed using the TOUGH2{{\tt TOUGH2}} software suite. The model contains nine layers consisting of 966 elements each (total of 8,964). Geological survey data, down-hole measurements, and production histories from the fields have been used to calibrate the model. The model has been used to predict how production will affect the geothermal fields. Information gathered throughout the production history, such as drawdown and changes in enthalpy, have been used to re-evaluate the size and the production capacity of the production fields. Different production scenarios, such as different energy throughput, have been simulated. The model simulations have also been used to estimate the capacity of potential future production fields.     

Rotamer libraries of spin labelled cysteines for protein studies

Studies of structure and dynamics of proteins using site-directed spin labelling rely on explicit modelling of spin label conformations. The large computational effort associated with such modelling with molecular dynamics (MD) simulations can be avoided by a rotamer library approach based on a coarse-grained representation of the conformational space of the spin label. We show here that libraries of about 200 rotamers, obtained by iterative projection of a long MD trajectory of the free spin label onto a set of canonical dihedral angles, provide a representation of the underlying trajectory adequate for EPR distance measurements. Rotamer analysis was performed on selected X-ray structures of spin labelled T4 lysozyme mutants to characterize the spin label rotamer ensemble on a single protein site. Furthermore, predictions based on the rotamer library approach are shown to be in nearly quantitative agreement with electron paramagnetic resonance (EPR) distance data on the Na(+)/H(+) antiporter NhaA and on the light-harvesting complex LHCII whose structures are known from independent cryo electron microscopy and X-ray studies, respectively. Suggestions for the selection of labelling sites in proteins are given, limitations of the approach discussed, and requirements for further development are outlined.     

The colorful Helly theorem and colorful resolutions of ideals

We demonstrate that the topological Helly theorem and the algebraic Auslander-Buchsbaum theorem may be viewed as different versions of the same phenomenon. Using this correspondence we show how the colorful Helly theorem of I. Barany and its generalizations by G. Kalai and R. Meshulam translate to the algebraic side. Our main results are algebraic generalizations of these translations, which in particular give a syzygetic version of Helly’s theorem.     

The classical Wigner method with an effective quantum force: application to the collinear H + H2 reaction

To improve the classical Wigner (CW) model, we recently proposed the classical Wigner model with an effective quantum force (CWEQF). The results of the CWEQF model are more accurate than those of the CW model. Still the simplicity of the CW model is retained. The quantum force was obtained by defining a characteristic distance η(0) between two Feynman paths that enter the expression for the flux-flux correlation function. η(0) was considered independent of the position along the reaction path. The CWEQF leads to a lowering of the effective potential barrier. Here we develop the method to use position dependent η(0) values. The method is also generalized to two dimensions. Applications are carried out on one-dimensional model problems and the two-dimensional H + H(2) collinear reaction.     

Adsorption of trimethyl phosphate on maghemite, hematite, and goethite nanoparticles

Adsorption of trimethyl phosphate (TMP) on well-characterized hematite, maghemite and goethite nanoparticles was studied by in situ DRIFT spectroscopy as a model system for adsorption of organophosphorous (OP) compounds on iron minerals. The iron minerals were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), specific surface area, and pore size distribution. The minerals were found to consist of stoichimetrically and morphologically well-defined maghemite, hematite, and goethite nanoparticles. Analysis of in situ diffuse reflectance Fourier transform (DRIFT) spectroscopy shows that TMP bonds mainly to Lewis acid Fe sites through the O phosphoryl atom (-P═O-Fe) on hematite and maghemite. On goethite most TMP molecules bond to Br?nstedt acid surface OH groups and form hydrogen bonded surface complexes. The vibrational mode analysis and uptake kinetics suggest two main reasons for the observed trend of reactivity toward TMP (hematite > maghemite > goethite): (i) larger number of accessible Lewis acid adsorption sites on hematite; (ii) stronger interaction between the Lewis acid Fe sites and the phosphoryl O atom on TMP for hematite and maghemite compared to goethite with concomitant formation of surface coordinated TMP and dimethyl phosphate intermediates. As a result, on the oxides a surface oxidation pathway dominates during the initial adsorption, which results in the formation of surface methoxy and formate. In contrast, on goethite a slower hydrolysis pathway is identified, which eventually yields phosphoric acid. The observed trends of the reactivity and analysis of the corresponding surface structure and particle morphology suggest an intimate relation between the surface chemistry of exposed crystal facets on the iron minerals. These results are important to understand OP surface chemistry on iron minerals.     

Haloperoxidase activity of oxovanadium(V) thiobisphenolates

By employing the 2,2'-thiobis(2,4-di-tert-butylphenolate) ligand ((S)L(2-)) a novel oxovanadium(V) complex, (PPh(4))(2)[(S)LV(O)(μ(2)-O)(2)V(O)(S)L] (1), was synthesised that exhibits haloperoxidase activity: on addition of H(2)O(2) a sequence of successive peroxide formation and intramolecular thioether oxidation events (sulfoxide and sulfone) led to a mixture of five products, which were all identified unambiguously, partly through an independent synthesis and characterisation. It was shown that internal thioether oxidation proceeds through peroxide formation, but the sulfoxidation of external thioether functions requires further activation of the peroxide function by protons or alkyl cations. Consistently, the employment of tBuOOH instead of H(2)O(2) led to a very active system for the catalytic sulfoxidation of thioethers.     

A short and efficient error correcting code for polarization coded photonic qubits in a dissipative channel

We propose a short and efficient non-degenerate quantum error correcting code that is adapted for qubits encoded on two orthogonal, single-photon states (e.g., horizontally and vertically polarized) subject to a dissipative channel.The proposed code draws its strength from the fact that it is adapted to the physical characteristics of the information-carrying basis states under the action of the channel. The code combines different energy manifolds and consists of only 3 spatio-temporal modes and on average 2 photons per code word.     

The review of advances in interfacial electrochemistry in Estonia: electrochemical double layer and adsorption studies for the development of electrochemical devices

The electrochemistry nowadays has many faces and challenges. Although the focus has shifted from fundamental electrochemistry to applied electrochemistry, one needs to acknowledge that it is impossible to develop and design novel green energy transition devices without a comprehensive understanding of the electrochemical processes at the electrode and electrolyte interface that define the performance mechanisms. The review gives an overview of the systematic research in the field of electrochemistry in Estonia which reflects on the excellent collaboration between fundamental and applied electrochemistry.

     

Miniaturized diode laser module emitting green light at 532 nm with a power of more than 900 mW for next-generation holographic displays

We present a micro-integrated laser module based on an amplified diode laser and second harmonic generation which is a promising candidate for a green light source in next-generation 3D holographic displays. The light emitted by the amplified laser has a wavelength of 1064 nm, reaches a power up to 8.2 W and has a long coherence length of >400 m. For second harmonic generation, we tested two geometries of periodically poled lithium niobate crystals in single pass: a bulk crystal and a planar waveguide crystal. With the planar waveguide crystal, we achieve an output power >900 mW and a coherence length >20 m at a wavelength of 532 nm.     

Reactivity of ammonia ligands of the antitumor agent cisplatin: a unique dodecanuclear Pt4,Pd4,Ag4 platform for four cytosine model nucleobases

The reaction of a potential mono(nucleobase) model adduct of cisplatin, cis-[Pt(NH(3))(2)(1-MeC-N3)(H(2)O)](2+) (6; 1-MeC: 1-methylcytosine), with the electrophile [Pd(en)(H(2)O)(2)](2+) (en: ethylenediamine) at pH approximately 6 yields a kinetic product X which is likely to be a dinuclear Pt,Pd complex containing 1-MeC(-)-N3,N4 and OH bridges, namely cis-[Pt(NH(3))(2)(1-MeC(-)-N3,N4)(OH)Pd(en)](2+). Upon addition of excess Ag(+) ions, conversion takes place to form a thermodynamic product, which, according to (1)H NMR spectroscopy and X-ray crystallography, is dominated by a mu-NH(2) bridge between the Pt(II) and Pd(II) centers. X-ray crystallography reveals that the compound crystallizes out of solution as a dodecanuclear complex containing four Pt(II), four Pd(II), and four Ag(+) entities: [{Pt(2)(1-MeC(-)-N3,N4)(2)(NH(3))(2)(NH(2))(2)(OH)Pd(2)(en)(2)Ag}(2){Ag(H(2)O)}(2)](NO(3))(10) 6 H(2)O (10) is composed of a roughly planar array of the 12 metal ions, in which the metal ions are interconnected by mu-NH(2) groups (between Pt and Pd centers), mu-OH groups (between pairs of Pt atoms), and metal-metal donor bonds (Pt-->Ag, Pd-->Ag). The four 1-methylcytosinato ligands, which are stacked pairwise, as well as the four NH(3) ligands and parts of the en rings, are approximately perpendicular to the metal plane. Two of the four Ag ions (Ag2, Ag2') of 10 are labile in solution and show the expected behavior of Ag(+) ions in water, that is, they are readily precipitated as AgCl by Cl(-) ions. The resulting pentanuclear complex [Pt(2)Pd(2)Ag(1-MeC(-))(2)(NH(2))(2)(OH)(NH(3))(2)(en)(2)](NO(3))(4)7 H(2)O (11) largely maintains the structural features of one half of 10. The other two Ag(+) ions (Ag1, Ag1') of 10 are remarkably unreactive toward excess NaCl. In fact, the pentanuclear complex [Pt(2)Pd(2)AgCl(1-MeC(-))(2)(NH(2))(2)(OH)(NH(3))(2)(en)(2)](NO(3))(3)4.5 H(2)O (12), obtained from 10 with excess NaCl, displays a Cl(-) anion bound to the Ag center (2.459(3) A) and is thus a rare case of a crystallized "AgCl molecule".