Adhesive forces were investigated in a computational study for the complexes of graphene with each of the four adsorbates, benzene, anthracene, pyrene, and tetracene, by using the DFT method B3LYP ...and the semiempirical method DFTB, together with empirical dispersion corrections. The four aromatic molecules differ in size and flexibility. Whereas the adhesion energy (for complete separation) is independent of the way an adsorbed molecule is separated from graphene, the maximum adhesive forces depend strongly on the way the adsorbate is lifted. We investigated, therefore, four lifting modes: in rigid vertical lifting, all atoms of the adsorbate are pull-off points; in flexible central lifting, the pull-off points are in the middle of the adsorbate; in both rigid and flexible terminal lifting, the pull-off points are at one end and the adsorbate is regarded as being either rigid or flexible. For the systems investigated, we find that, for both the adhesion energies and the maximum adhesive forces, the DFTB results are at most 10% lower than the corresponding DFT results. For small or rigid molecules like benzene and pyrene, there is no significant difference between rigid vertical and flexible central lifting. For a flexible molecule like tetracene, the difference of the maximum adhesive force can be up to 70%. Terminal lifting consists of two subprocesses. For the second subprocess, both the adhesion energy and the maximum adhesive force are essentially unchanged across all four adsorbates; for the first subprocess, however, we find a pronounced size dependence of the adhesion energy.
Sleep disturbances caused by noise exposure are the most relevant outcome measured in disability adjusted life years (DALYs). In analogy to the combined effects of noise from multiple sources on ...annoyance, these are also of interest for sleep disorders. The study “Overall Noise Assessment” Innsbruck examined data from 1031 personal interviews. Aircraft, rail and road noise were correlated. To choose participants combined exposures were clustered into small, medium and severely affected living situations. The effect of demographic features, noise sensitivity, access to a silent façade and other factors on self-reported sleep disturbances was investigated applying bivariate analyses. Exposure-response curves and their 95% confidence intervals with cut-off values of 72% for “highly disturbed sleep” were generated and the results were discussed in comparison to recently published curves. Using source-specific exposure-response relationships, an overall model for evaluating sleep disorders was developed based on the “annoyance equivalents model”. The “total sleep disturbance response” shows an accumulative outcome for each source measured. A protective effect of road traffic noise as background noise for air and railroad sources could not be proven. Both the “Total Sleep Disruption Assessment Model” and the “Dominant Source Model” have a Spearman-Rho of 0.3 and are therefore suitable for use in noise assessment.
This work shows a new way of single lap shear specimen production for hybrid metal-composite materials, which can be used to characterize process-induced interface property variations. Due to this ...special procedure, the specimen manufacturing can be done production-related and with a homogenization of the thermal stresses occurring in the joint area of the hybrid at each specimen. The exemption process of the specimen is kept in a minimum invasive way, not affecting the interface in the tested zone. The influence of the metal surface structure specifically created by micro form milling as well as the influence of the curing temperature on the maximum shear strength of the interface, were investigated. Finally, the driving failure mechanisms were identified and described.
A comprehensive picture of the initial stages of silicene growth on graphite is drawn. Evidence is shown that quasiparticle interferences play a crucial role in the formation of the observed silicene ...configurations. We propose, on one hand, that the charge modulations caused by those quantum interferences serve as templates and guide the incoming Si atoms to self-assemble to the unique
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30° honeycomb atomic arrangement. On the other hand, their limited extension limits the growth to about 150 Si atoms under our present deposition conditions. The here proposed electrostatic interaction finally explains the unexpected stability of the observed silicene islands over time and with temperature. Despite the robust guiding nature of those quantum interferences during the early growth phase, we demonstrate that the window of experimental conditions for silicene growth is quite narrow, making it an extremely challenging experimental task. Finally, it is shown that the experimentally observed three-dimensional silicon clusters might very well be the simple result of the end of the silicene growth resulting from the limited extent of the quasi-particle interferences.
Adhesion, forces and the stability of interfaces Guttmann, Robin; Hoja, Johannes; Lechner, Christoph ...
Beilstein journal of organic chemistry,
01/2019, Letnik:
15, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Weak molecular interactions (WMI) are responsible for processes such as physisorption; they are essential for the structure and stability of interfaces, and for bulk properties of liquids and ...molecular crystals. The dispersion interaction is one of the four basic interactions types - electrostatics, induction, dispersion and exchange repulsion - of which all WMIs are composed. The fact that each class of basic interactions covers a wide range explains the large variety of WMIs. To some of them, special names are assigned, such as hydrogen bonding or hydrophobic interactions. In chemistry, these WMIs are frequently used as if they were basic interaction types. For a long time, dispersion was largely ignored in chemistry, attractive intermolecular interactions were nearly exclusively attributed to electrostatic interactions. We discuss the importance of dispersion interactions for the stabilization in systems that are traditionally explained in terms of the "special interactions" mentioned above. System stabilization can be explained by using interaction energies, or by attractive forces between the interacting subsystems; in the case of stabilizing WMIs, one frequently speaks of adhesion energies and adhesive forces. We show that the description of system stability using maximum adhesive forces and the description using adhesion energies are not equivalent. The systems discussed are polyaromatic molecules adsorbed to graphene and carbon nanotubes; dimers of alcohols and amines; cellulose crystals; and alcohols adsorbed onto cellulose surfaces.
Transmission measurements of the soft X‐ray beamline to the Small Quantum Systems (SQS) scientific instrument at the SASE3 undulator of European XFEL are presented. Measurements are reported for a ...wide range of photon energies (650 eV to 2400 eV), using X‐ray gas monitors as well as a bolometric radiometer. The results are in good agreement with simulations for the beam transport and show a transmission of up to 80% over the whole photon energy range. The contribution of second‐ and third‐harmonic radiation of the soft X‐ray undulator is determined at selected photon energies by performing transmission measurements using a gas absorber to provide variable attenuation of the incoming photon flux. A comparison of the results with semi‐analytic calculations for the generation of free‐electron laser pulses in the SASE3 undulator reveals an influence of apertures along the beam transport on the exact harmonic content to be accounted for at the experiment. The second‐harmonic content is measured to be in the range of 0.1% to 0.3%, while the third‐harmonic contributed a few percent to the SASE3 emission. For experiments at the SQS instrument, these numbers can be reduced through specific selections of the mirror reflection angles.
Measurements of the transmission as well as the contribution of harmonic radiation at the soft X‐ray beamline of the Small Quantum Systems instrument at the SASE3 undulator of European XFEL are presented.
Context: The aim of this study was to verify the contributing effect in the cases of combined road traffic noise and railroad traffic noise on total noise annoyance. Materials and Methods: After ...opening the four-track railway of the Lower Inn Valley Route in Austria, an evaluation study was conducted by an interview survey (n=1003). The data of this survey included answers on annoyance caused by railroad, road traffic noise and total annoyance as well as self-evaluated noise sensitivity. Results: When annoyance is only related to one of these sources, a 10% share of highly annoyed persons was observed at 59 dB for road noise and 60 dB for railroad noise. The annoyance model including both noise sources with a coefficient of 0.145 for road noise, 0.034 for railroad noise and 0.431 for noise sensitivity (all p-values < 0.01) showed a regression coefficient R2 of 0.299. The presence of road background noise did not influence the annoyance on railway noise. Conclusion: The combined influence of road and railway noise showed an increase of total annoyance.
Context: Noise indicators are the basis to describe noise exposure-effect relationships. The assessment of these noise indicators in field studies includes various uncertainties, so that the true ...values differ from the determined values used for establishing curve fits. If the relationship between a noise indicator and its effect is nonlinear, uncertainties of the noise indicator modify the observed exposure-effect relationships. Materials and Methods: The determination of an exposure-relationship curve fit within a field study was simulated based on the assumption of a given true exposure-relationship without uncertainties and normal distributed uncertainties for the observed noise indicator used for the statistics. Results: In case of an upward curvature of the exposure-effect relationship, the uncertainty for the noise indicator value leads to an asymmetric effect for the curve fit. Uncertainties of the same amount of over- or underestimation will not result in an identical over- or underestimation of the observed effect. A simulation of this effect shows an increased curvature of the observed curve fit, with overestimated exposure-effect relationships. Conclusion: Although linear exposure-effect curves are not observed with a systematic shift, quadratic, cubic, and exponential curve forms include a systematic uncertainty in the presented exposure-response curve. If such curves are used to define threshold levels to limit harmful effects of noise, no further uncertainty margins are needed for those situations where the calculated noise indicator uncertainties are equal or lower than those present in the underlying field study.
Land-use categories are often used to define the exposure limits of national environmental noise policies. Often different guideline values for noise are applied for purely residential areas versus ...residential areas with mixed-use. Mixed-use includes living plus limited activities through crafts, commerce, trade, agriculture, and forestry activities. This differentiation especially when rating noise from road, railway, and air traffic might be argued by different expectations and therefore noise annoyance in those two categories while scientific evidence is missing. It should be tested on empirically derived data. Surveys from two studies in the state of Tyrol in urban and rural areas were retrospectively matched with spatial data to analyze the potential different influences on noise effects. Using non-parametric tests, the correlation between land-use category on self-reported noise sensitivity and noise annoyance was investigated. Exposure-response for the two analyzed land-use categories showed no significant impact on noise sensitivity and exposure-response relationships for the three traffic noise sources. Including only noise annoyance, there is not sufficient evidence to define different noise policies for those two land-use categories.
We report on a direct time-domain measurement of the temporal properties of a seeded free-electron laser pulse in the extreme ultraviolet spectral range. Utilizing the oscillating electromagnetic ...field of terahertz radiation, a single-shot THz streak-camera was applied for measuring the duration as well as spectral phase of the generated intense XUV pulses. The experiment was conducted at FLASH, the free electron laser user facility at DESY in Hamburg, Germany. In contrast to indirect methods, this approach directly resolves and visualizes the frequency chirp of a seeded free-electron laser (FEL) pulse. The reported diagnostic capability is a prerequisite to tailor amplitude, phase and frequency distributions of FEL beams on demand. In particular, it opens up a new window of opportunities for advanced coherent spectroscopic studies making use of the high degree of temporal coherence expected from a seeded FEL pulse.
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