At. force microscope (AFM) was used to examine aluminum sample prepn., electropolishing and anodic dissoln. The anodic dissoln. of Al was studied in ammonium tartrate and sulfuric acid. Smoothening or roughening of the surface was imaged and depends primarily on the time, potential and type of electrolyte. [on SciFinder(R)]
The absorption spectrum of bound Rydberg states which can be detected by a delayed, pulsed field ionization is computed. The spectrum, measured for various delay times, provides information on the short and the longer time dynamics of high molecular Rydberg states. A quantitative dynamical theory, based on an effective Hamiltonian formalism is applied, illustrating the role of the Rydberg electron-core coupling and of an external electrical field in the delay-time dependent spectra. The sharpening of the spectra for longer delay times is reproduced by the dynamical computations. It is found that the overall intensity, as a function of the delay time before detection, is well described by a double exponential decay where the short lifetime is primarily a manifestation of the direct autoionization to the continuum, while the long lifetime is due to interseries coupling. Both lifetimes increase with the principal quantum number of the Rydberg states. The notion of trapped `'reservoir states'' is illustrated by the computational results, with special reference to a kinetic model analysis. The role of the initially optically accessed state(s) and of the depth of detection, in particular with regard to the intensity, is demonstrated. The effect of varying the strength of an external de field in the time interval prior to the detection is illustrated by the dynamical computations, with respect to both the decay kinetics and the intensity of the spectrum. (C) 1997 American Institute of Physics.
This paper challenges two orthodox theses: (a) that computational processes must be algorithmic; and (b) that all computed functions must be Turing-computable. Section 2 advances the claim that the works in computability theory, including Turing's analysis of the effective computable functions, do not substantiate the two theses. It is then shown (Section 3) that we can describe a system that computes a number-theoretic function which is not Turing-computable. The argument against the first thesis proceeds in two stages. It is first shown (Section 4) that whether a process is algorithmic depends on the way we describe the process. It is then argued (Section 5) that systems compute even if their processes are not described as algorithmic. The paper concludes with a suggestion for a semantic approach to computation.
The dynamical properties of a hydrogen atom chemisorbed at a site of trigonal symmetry on a (110) metal surface are studied by classical trajectory calculations. A model potential is used which is highly anharmonic, and which includes many realistic features present in the case of H on W(110). The calculations show that periodic, quasi-periodic and chaotic trajectories all play significant roles in the dynamical properties of the system at the temperatures of interest. The power spectrum is computed, and the resulting frequency structure is in semi-quantitative accord with recent experimental data on the parallel vibrations of H on W(110). Implications of the results as to the properties of the H/metal surface potential and of the related frequency spectrum are discussed. (C) Elsevier Science B.V.
We present detailed methodology and results for the approximate calculation of the anharmonic vibrational wave functions for a given structure of a protein. The ground state and the fundamental vibrationally excited states of hydrated BPTI are computed with an approach that is of very good accuracy for low-lying states. The eigenfunctions are used to predict quantum properties such as vibrational excitation frequencies and IR intensities as well as atomic mean square displacements at T = 0 K. The method treats diagonal anharmonic effects exactly up to fourth order in normal mode coordinates, while using a mean-field approximation, the vibrational self-consistent field (SCF) approximation for the mode-mode couplings. The inclusion of the diagonal effects (exact in fourth order) makes the potentials stiffer than quadratic. When the mode-mode coupling is included as a mean field, the system becomes even stiffer. These effects produce significant modifications of such observables as the vibrational spectrum and Debye-Waller factors. The results presented here should be considered essentially exact except for potentially important approximations: (a) that the potential energy used bears some resemblance to reality, (b) that the system is restricted to a single minimum in the potential energy surface, and (c) that the quartic expansion in normal modes, when truncated to fourth order, provides a good description of the potential. These issues will be addressed in the main text. The results show that the vibrational absorption spectrum is strongly affected by anharmonic and mode-mode coupling effects. Deviations from the corresponding harmonic absorption intensities are very large. Unlike our previous study that found only weak mode-mode coupling effects for the lowest 100 modes, the SCF corrections calculated here for the intermediate frequency modes are seen to be very significant. The results have important implications for the vibrational spectroscopy and other properties of proteins at low temperatures.
Quantum calculations are reported for vibrational states and energy levels of several peptide and peptide-water complexes, to provide insight into the spectroscopic properties of such systems and their dependency on presently available anharmonic force fields. A blocked di-L-serine-H2O complex and trialanine in an antiparallel beta sheet configuration are the main systems treated. The calculations are for variants of the Amber force field and use the vibrational self-consistent field (VSCF) method, which includes effects of anharmonicity as well as interactions between modes. The main findings are as follows: (1) Distinct isomers of a single peptide-H2O complex corresponding to different hydrogen binding sites of the H2O are observed. (2). The H2O induces shifts of up to 50 cm(-1) in the frequencies of fundamental transitions associated with the peptide modes. (3). Some of the `'intermolecular'' modes of the peptide-H2O cluster are of frequencies and geometry that suggest effective peptide-to-water energy transfer. (5). Changing the TIP3 water potential in the Amber force field into the Coker-Watts potential produces significant spectroscopic changes. (5). The peptide-H2O cluster is found to have several tunneling states, which are assigned in detail. At least some of these states should be spectroscopically observable by the magnitude of the splitting. (6) The trialanine calculations are compared with experimental data available for part of the transitions. For many of the `'stiff'' transitions good agreement is found, but the remaining differences suggest that the force field should be revised. It is argued on the basis of these results that high-resolution spectroscopy in jets should be an excellent tool for improving and developing biomolecular force fields.
Revised version, "Oppositionality in Fielding's Tom Jones," in Towards the Ethics of Form in Fiction. Columbus: Ohio State University Press, 2010, pp. 35-48.
Osteoblasts arise from partially differentiated osteogenic progenitor cells (OPCs) which in turn arise from undifferentiated marrow stromal mesenchymal stem cells (MSCs). It has been postulated that age-related defects in osteoblast number and function may be due to quantitative and qualitative stem cell defects. To examine this possibility, we compared osteogenic stem cell number and in vitro function in marrow cells from 4-month-old and 24-month-old male BALB/c mice. Histologic studies demonstrated that these mice undergo age-related bone loss resembling that seen in humans. In primary MSC cultures grown in media supplemented with 10 nM dexamethasone, cultures from older animals yielded an average of 41% fewer OPC colonies per given number of marrow cells plated (p < 0.001). This implies that for a given number of marrow cells there are fewer stem cells with osteogenic potential in older animals than there are in younger animals. The basal proliferative rate in cultures from older animals, as measured by 3H-thymidine uptake, was more than three times that observed in cultures from young animals (p < 0.005). However, the increase in proliferative response to serum stimulation was 10-fold in the younger cultures (p <0.001) and insignificant (p <0.4) in the older cultures. Colonies in both age groups became alkaline phosphatase positive at the same rate, and virtually all colonies were positive after 12 days of culture. Cultures from both age groups produced abundant type I collagen. These studies suggest that defects in the number and proliferative potential of MSCs may underlie age-related defects in osteoblast number and function.
In the present study, we investigated orienting response generalization across various types of semantically related stimuli. Four experiments, based on a modified version of the guilty knowledge technique, were designed to examine whether semantic relations based on abstract features are reflected by electrodermal responsivity. No generalization across coordinates was obtained, but a moderate degree of generalization was demonstrated between a word and its superordinate category (e.g., table-furniture) and between a word and its synonym. Complete generalization occurred from a verbal label of an object to its pictorial representation, and vice versa. These results are compatible with our proposal that partial identification of the test stimulus as relevant is a necessary condition for generalization in the guilty knowledge technique. [ABSTRACT FROM AUTHOR]
A review with 69 refs. The different approaches in which self-assembled monolayers (SAMs) were applied in electroanal. chem. are reviewed. Three principal concepts were used and can be categorized according to the mechanism of attachment of the monolayer to the electrode. These include the formation of covalent bonds between reactive org. mols., such as chlorosilanes, with activated surfaces, the formation of lipid and bilayer lipid membranes that self-assemble on conductive surfaces and the adsorption of functionalized alkanes, e.g., alkanethiols, on well ordered surfaces. Systems for detecting inorg., org. and biol. species are described and conclusions are drawn. [on SciFinder(R)]
The nuclear matrix maintains specific interactions with genomic DNA at sites known as matrix attachment regions (M/SARs). M/SARs bind in vitro to lamin polymers. We show that the polymerized alpha-helical rod domain of lamin Dm0 provides by itself the specific binding to the ftz M/SAR. In contrast, unpolymerized rod domain does not bind specifically to this M/SAR. Non-specific binding to DNA is also observed with Dm0 containing a point mutation that impairs its ability to polymerize or with the isolated tail domain. These data suggest that the specific binding of lamins to M/SARs requires the rod domain and depends on the lamin polymerization state.
