[en] Effort was concentrated in problems of continental evolution and a presentation was made to a workshop on the Deep Continental Growth of South India. An interpretation of the lithospheric structure of Africa as related to continental collision (together with its volcanism and topography) was prepared and a paper on this topic is about to be submitted. No expenditures were charged to the grant during this 6 month period

[en] It was pointed out that a consensus may be emerging in crustal growth models, considering the clustering of most growth curves and their uncertainties. Curves most distant from this clustering represent models involving extensive recycling of continental material back into the mantle, but the author wondered if geochemical signatures for this would be recognizable considering the lack of evidence from seismic tomography for discrete mantle reservoirs, and the likelihood of core-mantle interaction based on recent high pressure experiments. Unreactivated Archean rocks represent only 2 percent of present continental area, and the author was uncomfortable about basing inferences on what the early Earth was like on such a small amount of information. He feels that the hypothesis of continental assembly that needs testing is that of banging together of island arcs, such as in Indonesia today. As an example of how complex this process can be, the author described the geology of the Caribbean arc system, which shows evidence for reversals of subduction polarity, numerous collisional events, and substantial strike-slip movements. It seemed unlikely to the author that Archean examples would have been less complicated

[en] For several years the Susquehanna boiling water reactors (BWRs) operated by Pennsylvania Power and Light have had their reactor recirculation transients monitored using a computer system called GETARS, which stands for General Electric Transient Analysis and Recording System. This monitoring system has been very useful in analyzing and trouble shooting these reactor recirculation transients because of the availability of data recorded from GETARS. Had GETARS not been available, some recirculation problems would not have been resolved as effectively as they were. A few examples of the more significant and more recent reactor recirculation transients that have occurred and that were monitored by GETARS at Susquehanna are discussed in this paper

[en] Gradient-corrected density functionals have become a useful tool to calculate binding energies of molecules. The correlation effects on the molecular bond formation can be seen in the pair density P(r, r + u), which is the probability density for finding an electron at r and a second electron at r + u. The Perdew-Wang (PW91) and the Perdew-Burke-Erazerhof (PBE96) generalized gradient approximations (GGA) provide models of f d3rP(r,r + u), i.e., of the system-averaged hole, (ρ_xc,λ=1) (u) =- I /N ∫ d³r [P(r, r + u) - ρ(r)ρ(r + u)]. By comparing the system-averaged GGA hole for a molecule and the separated atoms with the corresponding system-averaged holes obtained from wavefunctions, we show how and why the GGA works. We also discuss the limitations of these approximations

[en] The Kara and Ust-Kara craters are twin impact structures situated at about 69 deg 10 min N; 65 deg 00 min E at the Kara Sea. For Kara a diameter of about 55 km would be a very conservative estimate, and field observations indicate a maximum current diameter of about 60 km. The diameter of Ust-Kara has to be larger than 16 km. A better estimate might be 25 km but in all likelihood it is even larger. Suevites and impactites from the Kara area have been known since the beginning of the century, but had been misidentified as glacial deposits. Only about 15 years ago the impact origin of the two structures was demonstrated, following the recognition of shock metamorphism in the area. The composition of the target rocks is mirrored by the composition of the clasts within the suevites. In the southern part of Kara, Permian shales and limestones are sometimes accompanied by diabasic dykes, similar to in the central uplift. Due to the high degree of shock metamorphism the shocked magmatic rocks are not easily identified, although most of them seem to be of diabasic or dioritic composition. The impact melts (tagamites) are grey to dark grey fine grained crystallized rocks showing very fine mineral components and are the product of shock-melting with later recrystallization. The impact glasses show a layered structure, inclusions, and vesicles, and have colors ranging from translucent white over brown and grey to black. A complete geochemical characterization of the Kara and Ust-Kara impact craters was attempted by analyzing more than 40 samples of target rocks, shocked rocks, suevites, impact melts, and impact glasses for major and trace elements

[en] Generalized gradient approximations E_xc = ∫ d³ r f(n_↑, n_↓, triangledown n_↑, triangledown n_↓) for the exchange-correlation energy typically surpass the accuracy of the local spin density approximation and compete with standard quantum-chemical methods in electronic-structure calculations. But the derivation and analytic expression for the integrand f tend to be complicated and over-parametrized. We present a simple derivation of a simple but accurate expression for f, involving no parameter other than fundamental-constants. The derivation invoices only general ideas (not details) of the real-space cutoff construction, and agrees closely with the result of this construction. Besides its greater simplicity, this PBE96 functional has other advantages over PW91: (1) The correct behavior of the correlation energy is recovered under uniform scaling to the high-density limit. (2) The linear response of the uniform electron gas agrees with the accurate local spin density prediction. 96:006128*1 Paper TuI 6 Many-body effects are hidden in the universal density functional. The interaction of degenerate states via two-body operators, such as the electron-electron repulsion (for describing multiplets or the interaction of molecular fragments at large separations) are thus not explicitly considered in the Kohn-Sham scheme. In practice the density functionals have to be approximated, and there is a fundamental difficulty which arises in the case of degeneracy. While density functionals should be universal, the effect of degeneracy is linked to the potential characteristic to the atom, molecule, or crystal. There are, however, several possibilities to treat degeneracy effects within density functional theory, a few of which will be discussed. These take profit of the use of two-body operators, which can be, but must not be, the physical electron-electron interaction

[en] Time-dependent density functional theory (TDDFT) is based on a set of ideas and theorems quite distinct from those governing ground-state DFT, but emphasizing similar techniques. Today, the use of TDDFT is rapidly growing in many areas of physics, chemistry and materials sciences where direct solution of the Schroedinger equation is too demanding. This is the first comprehensive, textbook-style introduction to the relevant basics and techniques. (orig.)

[en] If the exact electron density of an atom or molecule is known, how accurately can we estimate the energy? The virial of the density yields exactly E_xc + T_c, where E_xc is the exchange-correlation energy and T_c is the correlation contribution to the kinetic energy, while local and gradient-corrected (e.g., PW91) density functional approximations are more accurate for the combination E_xc-T_c than for E_xc alone. Combining these two improves the accuracy of the energy by a factor of two or three exclamation point

[en] Photopolymerized hydrogels are extensively investigated for various tissue engineering applications, primarily due to their ability to form hydrogels in a minimally invasive manner. Although photocrosslinkable hydrogels provide necessary biological and chemical characteristics to mimic cellular microenvironments, they often lack sufficient mechanical properties. Recently, nanocomposite approaches have demonstrated potential to overcome these deficits by reinforcing the hydrogel network with. In this study, we investigate some physical, chemical, and biological properties of photocrosslinked poly(ethylene glycol) (PEG)-silica hydrogels. The addition of silica nanospheres significantly suppresses the hydration degree of the PEG hydrogels, indicating surface interactions between the silica nanospheres and the polymer chains. No significant change in hydrogel microstructure or average pore size due to the addition of silica nanospheres was observed. However, addition of silica nanospheres significantly increases both the mechanical strength and the toughness of the hydrogel networks. The biological properties of these nanocomposite hydrogels were evaluated by seeding fibroblast cells on the hydrogel surface. While the PEG hydrogels showed minimum cell adhesion, spreading and proliferation, the addition of silica nanospheres enhanced initial cell adhesion, promoted cell spreading and increased the metabolic activity of the cells. Overall, results indicate that the addition of silica nanospheres improves the mechanical stiffness and cell adhesion properties of PEG hydrogels and can be used for biomedical applications that required controlled cell adhesion. - Graphical abstract: Structural, mechanical and biological properties of photocrosslinked nanocomposite hydrogels from silica and poly(ethylene oxide) are investigated. Silica reinforce the hydrogel network and improved mechanical strength. Addition of induces cell adhesion characteristic properties for various biotechnological and biomedical applications. Highlights: ► Photocrosslinked nanocomposite hydrogels from silica and PEG are developed. ► Silica reinforce the hydrogel network and improve mechanical strength. ► Addition of induces cell adhesion characteristic properties. ► It can potentially be used for various biotechnological and biomedical applications

[en] We consider atom-surface scattering at low surface temperature, fixed incident energy, and fixed interaction potential. We examine the limit as the mass m of the incident particle →∞, and thus its de Broglie wavelength →0. We show that in this ''classical'' limit, at zero temperature, the Debye-Waller factor, i.e., the probability of strictly elastic scattering (a quantum effect), tends to a finite limit (<1). We propose scattering of 20-meV Ar atoms from cold Cu(111) as a promising experiment to verify this effect, and estimate the Debye-Waller factor for this system