Multiscale study on hydrogen mobility in metallic fusion divertor material

For achieving efficient fusion energy production, the plasma-facing wall materials of the fusion reactor should ensure long time operation. In the next step fusion device, ITER, the first wall region facing the highest heat and particle load, i.e. the divertor area, will mainly consist of tiles based on tungsten. During the reactor operation, the tungsten material is slowly but inevitably saturated with tritium. Tritium is the relatively short-lived hydrogen isotope used in the fusion reaction. The amount of tritium retained in the wall materials should be minimized and its recycling back to the plasma must be unrestrained, otherwise it cannot be used for fueling the plasma. A very expensive and thus economically not viable solution is to replace the first walls quite often. A better solution is to heat the walls to temperatures where tritium is released. Unfortunately, the exact mechanisms of hydrogen release in tungsten are not known. In this thesis both experimental and computational methods have been used for studying the release and retention of hydrogen in tungsten. The experimental work consists of hydrogen implantations into pure polycrystalline tungsten, the determination of the hydrogen concentrations using ion beam analyses (IBA) and monitoring the out-diffused hydrogen gas with thermodesorption spectrometry (TDS) as the tungsten samples are heated at elevated temperatures. Combining IBA methods with TDS, the retained amount of hydrogen is obtained as well as the temperatures needed for the hydrogen release. With computational methods the hydrogen-defect interactions and implantation-induced irradiation damage can be examined at the atomic level. The method of multiscale modelling combines the results obtained from computational methodologies applicable at different length and time scales. Electron density functional theory calculations were used for determining the energetics of the elementary processes of hydrogen in tungsten, such as diffusivity and trapping to vacancies and surfaces. Results from the energetics of pure tungsten defects were used in the development of an classical bond-order potential for describing the tungsten defects to be used in molecular dynamics simulations. The developed potential was utilized in determination of the defect clustering and annihilation properties. These results were further employed in binary collision and rate theory calculations to determine the evolution of large defect clusters that trap hydrogen in the course of implantation. The computational results for the defect and trapped hydrogen concentrations were successfully compared with the experimental results. With the aforedescribed multiscale analysis the experimental results within this thesis and found in the literature were explained both quantitatively and qualitatively.

Accelerator Mass Spectrometry and Bayesian Data Analysis

Accelerator mass spectrometry (AMS) is an ultrasensitive technique for measuring the concentration of a single isotope. The electric and magnetic fields of an electrostatic accelerator system are used to filter out other isotopes from the ion beam. The high velocity means that molecules can be destroyed and removed from the measurement background. As a result, concentrations down to one atom in 10^16 atoms are measurable. This thesis describes the construction of the new AMS system in the Accelerator Laboratory of the University of Helsinki. The system is described in detail along with the relevant ion optics. System performance and some of the 14C measurements done with the system are described. In a second part of the thesis, a novel statistical model for the analysis of AMS data is presented. Bayesian methods are used in order to make the best use of the available information. In the new model, instrumental drift is modelled with a continuous first-order autoregressive process. This enables rigorous normalization to standards measured at different times. The Poisson statistical nature of a 14C measurement is also taken into account properly, so that uncertainty estimates are much more stable. It is shown that, overall, the new model improves both the accuracy and the precision of AMS measurements. In particular, the results can be improved for samples with very low 14C concentrations or measured only a few times.

Role of hydroxyl group on the mesomorphism of alkyl glycosides:synthesis and thermal behavior of alkyl 6-deoxy-beta-D-glucopyranosides

A homologous series of alkyl 6-deoxy-beta-D-glucopyranoside amphiphiles was prepared,in an effort to identify the role of hydroxyl group in the mesomorphic behavior of alkyl glycosides. Synthesis was performed by a chlorination of the sugar moiety in alkyl-beta-D-glucopyranosides with methylsulfonyl chloride in DMF, followed by a metal mediated dehalogenation to secure alkyl 6-deoxy-beta-D-glucopyranosides, wherein the alkyl chain length varied from C-9 to C-16. The mesomorphic behavior of these 6-deoxy alkyl glycosides was assessed using polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction method. Whereas the lower homologues exhibited a monotropic SmA phase till sub-ambient temperatures, the higher homologues formed a plastic phase. A partial interdigitized bilaye structure of SmA phase is inferred from experimental d-spacing and computationally derived lengths of the molecules. The results were compared with those of normal alkyl glucopyranosides, retained with hydroxyl groups at C-2-C-6 carbons, and alkyl 2-deoxy-glucopyranosides, devoid of a hydroxyl group at C-2 and the comparison showed important differences in the mesomorphic behavior.(C)2010 Elsevier Ireland Ltd. All rights reserved.

Structure of 1 lct-Hydroxyeon-1,4,18-trienine-3-one

C21H27NO2, Mr=325.5 , orthorhombic,P21212,, a = 7.516 (2), b = 13.430 (2), c =18.047 (2) A, U= 1821.79 A 3, Z = 4, D x =1.186 Mg m -a, 2(Cu Ka) = 1.5418 A, # = 0.56 mm -1, F(000) = 704, T= 293 K, final R = 0.04 for 1892 reflections with I _> 3a(I). Ring A is planar, and rings B and C adopt a chair conformation. Rings D and E are envelopes, with C(14) and C(17) displaced from their respective planes by 0.643 (3) and 0.482 (3)A. The ring system A/B shows quasi-trans fusion, whilst ring systems B/C and C/D are trans fused about C(8)-C(9) and C(13)-C(14) respectively. The D/E junction shows cis fusion.

The structure of 11[alpha]-hydroxycon-1,4-dienine-3-one monohydrate

C22H31NO2.H2 O, M r = 359" 5, orthorhombic,P2~212 ~, a= 10.032 (1), b= 11.186 (1), C = 17.980 (1)/~,, U= 2017.48/~3, Z = 4, D x = 1.276 Mg m -a, 2(Cu Kct) = 1.5418/~, # = 0.69 mm -~,F(000) = 784, T = 293 K. Final R = 0.05 for 1972 unique reflections with I > 3o(/). Ring A is planar, and rings B and C adopt a chair conformation. Rings D and E are envelopes, with C(14) and C(20) displaced from their respective ring planes by 0-616 (2) and 0.648 (3)/~. The A/B ring junction is quasi-trans,whilst ring systems B/C and C/D are trans fused about the bonds C(8)-C(9) and C(13)-C(14) respectively.The D/E junction shows cis fusion.

The structure of 3[beta],20[alpha]-bis(dimethylamino)pregn-5-en-18-ol

Abstract. C25H44N20 , M r= 388.6, orthorhombic, P21212 I, a = 6.185 (2), b = 18.123 (2), c = 20.852 (2) A, U= 2337.2 A 3, Z = 4, D x = 1.104 Mg m -a, 2(Cu Ka) = 1.5418 A,/~ = 0.47 mm -~, F(000) = 864, T= 293 K. Final R - 0.038 for 1791 reflections with I >_ 3a(I). Rings A and C are in chair conformation. Ring B is in an 8fl,9a-half-chair conformation. Ring D adopts a conformation in between 13fl,14a-half-chair and 13t-envelope. There is a quasitrans fusion of rings A and B, whilst ring systems B/C and C/D are trans fused about the bonds C(8)-C(9)and C(13)-C(14).

The structure of ammonium oxalohydroxamate - a monopropellant

Abstract. NHn+.C2H3NzO4, Mr= 137.1, triclinic, Pi, a=3-952(1), b=6.772(1), c=9.993(1)A, a= 98.06 (1), fl= 89.96 (1), ~= 106.96 (1) °. V=253.06 A 3, z = 2, 2(Cu Ka) = 1.5418 A, g =15.29 cm -~, D m = 1.805, D x = 1.798 g cm -3, F(000)= 144, T= 293 K, R = 0.048 for 795 observed reflections. The unit cell contains two independent centrosymmetric molecules, one centred at (0,0,0) and the other at (0.5, 0.0, 0.5). The presence of experimentally determined~N-H groups and the -C=O bond lengths of 1.248 (4) and 1.247 (4)A indicate that the compound exists in the oxamic rather than the oximic form. Only one hydroxyl hydrogen is associated with each molecule. They are located at centres of inversion (0,0.5,0 and 0,0.5,0.5) and are shared between symmetry-related molecules via short symmetric H bonds with O...O=2.454(4), 2.457(4) and all O-H = 1.23 A

X-ray studies on crystalline complexes involving amino acids and peptides. XV. Crystal structures of L-lysine D-glutamate and L-lysine D-aspartate monohydrate and the effect of chirality on molecular aggregation

L-Lysine D-glutamate crystallizes in the monoclinic space group P2(1) with a = 4.902, b = 30.719, c = 9.679 A, beta = 90 degrees and Z = 4. The crystals of L-lysine D-aspartate monohydrate belong to the orthorhombic space group P2(1)2(1)2(1) with a = 5.458, b = 7.152, c = 36.022 A and Z = 4. The structures were solved by the direct methods and refined to R values of 0.125 and 0.040 respectively for 1412 and 1503 observed reflections. The glutamate complex is highly pseudosymmetric. The lysine molecules in it assume a conformation with the side chain staggered between the alpha-amino and the alpha-carboxylate groups. The interactions of the side chain amino groups of lysine in the two complexes are such that they form infinite sequences containing alternating amino and carboxylate groups. The molecular aggregation in the glutamate complex is very similar to that observed in L-arginine D-aspartate and L-arginine D-glutamate trihydrate, with the formation of double layers consisting of both types of molecules. In contrast to the situation in the other three LD complexes, the unlike molecules in L-lysine D-aspartate monohydrate aggregate into alternating layers as in the case of most LL complexes. The arrangement of molecules in the lysine layer is nearly the same as in L-lysine L-aspartate, with head-to-tail sequences as the central feature. The arrangement of aspartate ions in the layers containing them is, however, somewhat unusual. Thus the comparison between the LL and the LD complexes analyzed so far indicates that the reversal of chirality of one of the components in a complex leads to profound changes in molecular aggregation, but these changes could be of more than one type.

Crystal and molecular structure of l-valyl-l-lysine hydrochloride

l-Valyl-l-lysine hydrochloride, C11N3O3H23 HCl, rystallizes in the monoclinic space group P2, with a = 5.438(5), b = 14.188(5), c = 9.521(5) Å, β= 95.38(2)° and Z = 2. The crystal structure, solved by direct methods, refined to R = 0.036, using full matrix least-squares method. The peptide exists in a zwitterionic form, with the N atom of the lysine side-chain protonated. The two γ-carbons of the valine side-chain have positional disorder, giving rise to two conformations, χ111= -67.3 and 65.9°, one of which (65.9°) is sterically less favourable and has been found to be less popular amongst residues branching at β-C. The lysine side-chain has the geometry of g− tgt, not seen in crystal structures of the dipeptides reported so far. Interestingly, χ32 (63.6°) of lysine side-chain has a gauche+ conformation unlike in most of the other tructures, where it is trans. The neighbouring peptide molecules are hydrogen bonded in a head-to-tail fashion, a rather uncommon interaction in lysine peptide structures. The structure shows considerable similarity with that of l-Lys-l-Val HO in conformational angles and H-bond interactions [4].

Antireflection properties of indium tin oxide (ITO) on silicon for photovoltaic applications

The short‐circuit current density (Jsc) of indium tin oxide (ITO/silicon solar cells has been shown both theoretically and experimentally to be a function of the thickness of the ion beam sputtered ITO layer. These results can be accounted for by computing the optical reflection from the ITO/silicon interface.

X-ray studies on crystalline complexes involving amino acids and peptides. XXV. Structures of DL-proline hemisuccinic acid and glycyl-L-histidinium semisuccinate monohydrate and a comparative study of amino-acid and peptide complexes of succinic acid

DL-Proline hemisuccinic acid, C5H9NO2.1/2C4H6O4, M(r) = 174.2, P2(1/c) a = 5.254 (1), b = 17.480 (1), c = 10.230 (i) angstrom, beta = 119.60 (6)-degrees Z = 4, D(m) = 1.41 (4), D(x) = 1.42 g cm-3, R = 0.045 for 973 observed reflections. Glycyl-L-histidinium semisuccinate monohydrate, C8H13N4O3+.C4H5O4-.H2O, M(r) = 348.4, P2(1), a = 4.864 (1), b = 17.071 (2), c = 9.397 (1) angstrom, beta = 90.58-degrees, Z = 2, D(m) = 1.45 (1), D(x) = 1.48 g cm-3, R = 0.027 for 1610 observed reflections. Normal amino-acid and dipeptide aggregation patterns are preserved in the structures in spite of the presence of succinic acid/semisuccinate ions. In both the structures, the amino-acid/dipeptide layers stack in such a way that the succinic acid molecules/semisuccinate ions are enclosed in voids created during stacking. Substantial variability in the ionization state and the stoichiometry is observed in amino-acid and peptide complexes of succinic acid. Succinic acid molecules and succinate ions appear to prefer a planar centro-symmetric conformation with the two carboxyl (carboxylate) groups trans with respect to the central C=C bond. Considerable variation is seen in the departure from and modification of normal amino-acid aggregation patterns produced by the presence of succinic acid. Some of the complexes can be described as inclusion compounds with the amino acid/dipeptide as the 'host' and succinic acid/semisuccinate/succinate as the 'guest'. The effects of change in chirality, though very substantial, are not the same in different pairs of complexes involving DL and L isomers of the same amino acid.

Hybrid Polypeptides: Gabapentin as a Stereochemically Constrained gamma-Amino Acid Residue

The design of folded structures in peptides containing the higher homologues of alpha-amino acid residues requires the restriction of the range of local conformational choices In alpha-amino acids stereochemically constrained residues like alpha,alpha-dialkylated residue, aminoisobutyric acid (Aib), and D-Proline ((D)Pro) have proved extremely useful in the design of helices and hairpins in short peptides Extending this approach, backbone substitution and cyclization are anticipated to bc useful in generating conformationally constrained beta- and gamma-residues This brief review provides a survey of work on hybrid peptide sequences concerning the conformationally constrained gamma-amino acid residue 1-aminomethyl cyclohexane acetic acid, gabapentin (Gpn) This achiral, beta,beta-disubstituted, gamma-residue strongly favors gauche-gauche conformations about the C-alpha-C-beta (0(2)) and C-alpha-C-gamma (0(1)) bonds, facilitating local folding The Gpn residue can adopt both C-7 (NH1 -> CO1) and C-9 (CO1 (I)<- NH1+I) hydrogen bonds which are analogous to the C-5 and C7 (gamma-turn) conformations at alpha-residues In conjunction with adjacent residues, Gpn may be used in ay and gamma alpha segments to generate C-12 hydrogen bonded conformations which may be considered as expanded analogs of conventional beta-turns The structural characterization of C-12 helices, C-12/C-10 helices with mixed hydrogen bond directionalities and beta-hairpins incorporating Gpn residues at the turn segment is illustrated (C) 2010 Wiley Periodicals, Inc Biopolymers (Pept Sci) 94 733-741 2010

Friction-formed liquid droplets

The formation of nanoscale liquid droplets by friction of a solid is observed in real-time. This is achieved using a newly developed in situ transmission electron microscope (TEM) triboprobe capable of applying multiple reciprocating wear cycles to a nanoscale surface. Dynamical imaging of the nanoscale cyclic rubbing of a focused-ion-beam (FIB) processed Al alloy by diamond shows that the generation of nanoscale wear particles is followed by a phase separation to form liquid Ga nanodroplets and liquid bridges. The transformation of a two-body system to a four-body solid-liquid system within the reciprocating wear track significantly alters the local dynamical friction and wear processes. Moving liquid bridges are observed in situ to play a key role at the sliding nanocontact, interacting strongly with the highly mobile nanoparticle debris. In situ imaging demonstrates that both static and moving liquid droplets exhibit asymmetric menisci due to nanoscale surface roughness. Nanodroplet kinetics are furthermore dependent on local frictional temperature, with solid-like surface nanofilaments forming on cooling. TEM nanotribology opens up new avenues for the real-time quantification of cyclic friction, wear and dynamic solid-liquid nanomechanics, which will have widespread applications in many areas of nanoscience and nanotechnology.

Reactivity Of Pph3 Toward Ru2cl(O2cme)4 - Synthesis And X-Ray Crystal-Structure Of [Ru(O2cme)(Mecn)2(Pph3)2](Clo4)

A new ruthenium(II) complex of the type [Ru(O2CMe)(MeCN)2(PPh3)2](CiO4) (1) has been isolated from a reaction between Ru2Cl(O2CMe), and PPh3 in MeCN followed by the addition of NaClO4. The structure of 1 is determined by single crystal X-ray studies. The crystal belongs to the monoclinic space group C2/m with the following unit cell dimensions for the C42H39N2O6P2ClRu(M = 866.15): a = 23.295(1)angstrom, b = 23.080(1)angstrom, c = 9.159(1)angstrom, beta = 107.32(1)-degrees, V = 4701(1)angstrom3, Z = 4, D(c) = 1.224 gcm-3, lambda(Mo - K-alpha) = 0.7107 angstrom, mu(Mo - K-alpha) = 4.09 cm-1, T = 293K, R = 0.081 (R(w) = 0.094) for 2860 reflections with I greater-than-or-equal-to 3-sigma(I) and g = 0.015853. In the complex cation, the symmetry about the metal centre is essentially octahedral showing the presence of a chelating acetato, two cis-oriented MeCN and two trans-disposed PPh3 ligands. The mechanistic aspects of the core cleavage reaction are discussed.

X-ray-reflectivity study of Ge-Si-Ge films

Here we report on an x-ray specular reflectivity study of Ce-Si-Ge trilayers grown on Si(001) single-crystal substrate by ion beam sputtering deposition at various substrate temperatures. The electron-density profile of the trilayer as a function of depth, obtained from x-ray-reflectivity data, reveals an intermixing of Si and Ge. The x-ray-reflectivity data have been analyzed using a scheme based on the distorted-wave Born approximation, and the validity of the analysis scheme was checked using simulated data. Analyzed results provided information regarding interdiffusion in this system. We notice that although the Si-on-Ge interface is sharp, a Si0.4Ge0.6 alloy is formed at the Ge-on-Si interface.