135 research outputs found
Thioglycolic acid on the gold (111) surface and Raman vibrational spectra
The interaction of thioglycolic acid with the Au(111) surface is
investigaged, and it is found that at the low coverage the molecule lies down
on the substrate. If the mercaptan-hydrogen atom is eliminated, the resulting
SCH_2COOH molecule is randomly oriented on the surface. If the carboxylic acid
group in the HSCH_2COOH molecule is deprotonated instead, the HSCH_2COO^
molecule lies down on the surface. However, when the mercaptan-hydrogen atom in
the HSCH_2COO^- molecule is removed, the resulting SCH_2COO^- molecule rises up
to a certain level on the substrate. The calculated Raman vibrational spectra
decipher which compounds and atomic displacements contribute to the
corresponding frequencies. We thus propose a consistent mechanism for the
deposition of thioglycolic acid on the Au(111) surface.Comment: 18 pages, 5 figures, submitted to J. Chem. Phy
How does an external electrical field affect adsorption patterns of thiol and thiolate on the gold substrate ?
The responsive behavior of methanethiol and methylthiolate molecules on the
Au(111) surface with an applied electrical potential is studied, and it is
shown how the sulfur adsorption site, the S-H bond orientation and the
interacting energy change with an external electric field strength. The
electron charge density corresponding to an electric field minus that obtained
in zero field, with zero-field optimal geometry, is calculated to explain the
responsive behavior. The interacting energy for the intact methanethiol
adsorption is larger than that for the dissociative one, showing that an
external electric field can not make the hydrogen dissociate from the sulfur.Comment: 11 pages, 3 figures, LaTe
Crime sensing with big data: the affordances and limitations of using open-source communications to estimate crime patterns
This paper critically examines the affordances and limitations of big data for the study of crime and disorder. We hypothesise that disorder-related posts on Twitter are associated with actual police crime rates. Our results provide evidence that naturally occurring social media data may provide an alternative information source on the crime problem. This paper adds to the emerging field of computational criminology and big data in four ways: i) it estimates the utility of social media data to explain variance in offline crime patterns; ii) it provides the first evidence of the estimation offline crime patterns using a measure of broken windows found in the textual content of social media communications; iii) it tests if the bias present in offline perceptions of disorder is present in online communications; and iv) it takes the results of experiments to critically engage with debates on big data and crime prediction
The CH3SH molecule deposited on Cu(111) and deprotonation
We demonstrate for the first time that when a methanethiol adsorbed on the
regular Cu(111) surface, the dissociative structure is thermodynamically more
stable than the intact one. The computational results show that at low
temperature the methanethiol adsorbate prefers the atop site of the regular
Cu(111) surface. As the temperature is increased, the S-H bond is broken and
the methylthiolate favors the hollow sites. On the defected Cu(111) surface,
the dissociative configuration is still thermodynamically more stable than the
nondissociative one. The calculation indicates that the hydrogen initially
attached to the sulfur would like to form a bond with the copper surface rather
than desorb from it. Even though both copper and gold are the noble metal, the
stability of the methanethiol adsorption on the Cu(111) substrate is almost the
reverse of that on the Au(111).Comment: 13 pages, 7 figures, submitted to Phys. Rev.
Two-dimensional magnetoexcitons in the presence of spin-orbit coupling
We study theoretically the effect of spin-orbit coupling on quantum well
excitons in a strong magnetic field. We show that, in the presence of an
in-plane field component, the excitonic absorption spectrum develops a
double-peak structure due to hybridization of bright and dark magnetoexcitons.
If the Rashba and Dresselhaus spin-orbit constants are comparable, the
magnitude of splitting can be tuned in a wide interval by varying the azimuthal
angle of the in-plane field. We also show that the interplay between spin-orbit
and Coulomb interactions leads to an anisotropy of exciton energy dispersion in
the momentum plane. The results suggest a way for direct optical measurements
of spin-orbit parameters.Comment: 9 pages, 6 figure
Mastery Imagery Ability Is Associated With Positive Anxiety and Performance During Psychological Stress
Evaluation of the Algorithms and Parameterizations for Ground Thawing and Freezing Simulation in Permafrost Regions
Ground thawing and freezing depths (GTFDs) strongly influence the hydrology and energy balances of permafrost regions. Current methods to simulate GTFD differ in algorithm type, soil parameterization, representation of latent heat, and unfrozen water content. In this study, five algorithms (one semiempirical, two analytical, and two numerical), three soil thermal conductivity parameterizations, and three unfrozen water parameterizations were evaluated against detailed field measurements at four field sites in Canada’s discontinuous permafrost region. Key findings include: (1) de Vries’ parameterization is recommended to determine the thermal conductivity in permafrost soils; (2) the three unfrozen water parameterization methods exhibited little difference in terms of GTFD simulations, yet the segmented linear function is the simplest to be implemented; (3) the semiempirical algorithm reasonably simulates thawing at permafrost sites and freezing at seasonal frost sites with site-specific calibration. However, large interannual and intersite variations in calibration coefficients limit its applicability for dynamic analysis; (4) when driven by surface forcing, analytical algorithms performed marginally better than the semiempirical algorithm. The inclusion of bottom forcing improved analytical algorithm performance, yet their results were still poor compared with those achieved by numerical algorithms; (5) when supplied with the optimal inputs, soil parameterizations, and model configurations, the numerical algorithm with latent heat treated as an apparent heat capacity achieved the best GTFD simulations among all algorithms at all sites. Replacing the observed bottom temperature with a zero heat flux boundary condition did not significantly reduce simulation accuracy, while assuming a saturated profile caused large errors at several sites
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