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Recent studies illustrate how machine learning (ML) can be used to bypass a core challenge of molecular modeling: the trade-off between accuracy and computational cost. Here, we assess multiple ML approaches for predicting the atomization energy of organic molecules. Our resulting models learn the difference between low-fidelity, B3LYP, and high-accuracy, G4MP2, atomization energies and predict the G4MP2 atomization energy to 0.005 eV (mean absolute error) for molecules with less than nine heavy atoms (training set of 117,232 entries, test set 13,026) and 0.012 eV for a small set of 66 molecules with between 10 and 14 heavy atoms. Our two best models, which have different accuracy/speed trade-offs, enable the efficient prediction of G4MP2-level energies for large molecules and are available through a simple web interface.
The dynamics of an interface between a thin liquid–vapour bilayer undergoing evaporation is studied. Both phases are considered to be hydrodynamically and thermally active, with momentum and thermal inertia taken into account. A reduced-order model based on the weighted-residual integral boundary layer method is used to investigate the dynamical behaviour for two cases, viz., phase change in the absence of gravity and then phase change in the presence of gravity. In the first case, it is shown that evaporative instability may cause rupture of either liquid or vapour layer depending on system parameters. Close to interfacial rupture, the disjoining pressure due to intermolecular forces results in the formation of drops (bubbles) separated by a thin film for low liquid (vapour) hold-up. Momentum inertia is shown to have a stabilizing effect, while thermal inertia has a destabilizing effect. In the second case, evaporative suppression of Rayleigh–Taylor (R–T) instability shows emergence of up to two neutral wavenumbers. Weak nonlinear analysis of these neutral wavenumbers suggests that the instability may be either supercritical or subcritical depending on the rate of evaporation. At high rates of evaporation, both neutral wavenumbers are supercritical and computations on the interface evolution lead to nonlinear saturated steady states. Momentum inertia slows down the rate of interface deformation and results in an oscillatory approach to saturation. Thermal inertia results in larger interface deformation and the saturated steady state is shifted closer to the wall. At very low evaporation rates, only one neutral wavenumber of subcritical nature exists. The nonlinear evolution of the interface in this case is then similar to pure R–T instability, exhibiting spontaneous lateral sliding as it approaches the wall.
The nonlinear evolution of an interface between a perfect conducting liquid and a perfect dielectric gas subject to periodic electrostatic forcing is studied under the long-wave approximation. It is shown that inertial thin films become unstable to finite-wavelength Faraday modes at the onset, prior to the long-wave pillaring instability reported in the lubrication limit. It is further shown that the pillaring-mode instability is subcritical in nature, with the interface approaching either the top or the bottom wall, depending on the liquid–gas holdup. On the other hand, the Faraday modes exhibit subharmonic or harmonic oscillations that nonlinearly saturate to standing waves at low forcing amplitudes. Unlike the pillaring mode, wherein the interface approaches the wall, Faraday modes may exhibit saturated standing waves when the instability is subcritical. At higher forcing amplitudes, the interface may approach either wall, again depending on the liquid–gas holdup. It is also shown that a gravitationally unstable configuration of such thin films, under the long-wave approximation, cannot be stabilized by periodic electrostatic forcing, unlike mechanical Faraday forcing. In this case, it is observed that the interface exhibits oscillatory sliding behaviour, approaching the wall in an ‘earthworm-like’ motion.
This study investigates the phenomenon of targeted energy transfer (TET) from a linear oscillator to a nonlinear attachment behaving as a nonlinear energy sink for both transient and stochastic excitations. First, the dynamics of the underlying Hamiltonian system under deterministic transient loading is studied. Assuming that the transient dynamics can be partitioned into slow and fast components, the governing equations of motion corresponding to the slow flow dynamics are derived and the behaviour of the system is analysed. Subsequently, the effect of noise on the slow flow dynamics of the system is investigated. The Itô stochastic differential equations for the noisy system are derived and the corresponding Fokker–Planck equations are numerically solved to gain insights into the behaviour of the system on TET. The effects of the system parameters as well as noise intensity on the optimal regime of TET are studied. The analysis reveals that the interaction of nonlinearities and noise enhances the optimal TET regime as predicted in deterministic analysis.
Aerofoils operating in a turbulent flow generate broadband noise by scattering vorticity into sound at the leading edge. Previous work has demonstrated the effectiveness by which serrations, or undulations, introduced onto the leading edge, can substantially reduce broadband leading-edge noise. All of this work has focused on sinusoidal (single-wavelength) leading-edge serration profiles. In this paper, a new leading-edge serration geometry is proposed which provides significantly greater noise reductions compared to the maximum noise reductions achievable by single-wavelength serrations of the same amplitude. This is achieved through destructive interference between different parts of the aerofoil leading edge, and therefore involves a fundamentally different noise reduction mechanism from conventional single-wavelength serrations. The new leading-edge serration profiles simply comprise the superposition of two single-wavelength components of different wavelength, amplitude and phase with the objective of forming two roots that are sufficiently close together and separated in the streamwise direction. Compact sources located at these root locations then interfere, leading to less efficient radiation than single-wavelength geometries. A detailed parametric study is performed experimentally to investigate the sensitivity of the noise reductions to the profile geometry. A simple model is proposed to explain the noise reduction mechanism for these double-wavelength serration profiles and shown to be in close agreement with the measured noise reduction spectra. The study is primarily performed on flat plates in an idealized turbulent flow. The paper concludes by introducing the double-wavelength serration on a 10 % thick aerofoil, where near-identical noise reductions are obtained compared to the flat plate.
Metal–graphene composites are sought after for various applications. A hybrid light-weight foam of nickel (Ni) and reduced graphene oxide (rGO), called Ni-rGO, is reported here for small molecule oxidations and thereby their sensing. Methanol oxidation and non-enzymatic glucose sensing are attempted with the Ni-rGO foam via electrocatalytically, and an enhanced methanol oxidation current density of 4.81 mA/cm2 is achieved, which is ~1.7 times higher than that of bare Ni foam. In glucose oxidation, the Ni-rGO electrode shows a better sensitivity over bare Ni foam electrode where it could detect glucose linearly over a concentration range of 10 µM to 4.5 mM with a very low detection limit of 3.6 µM. This work demonstrates the synergistic effects of metal and graphene in oxidative processes, and also shows the feasibility of scalable metal–graphene composite inks development for small molecule printable sensors and fuel cell catalysts.
A heavy-over-light configuration of a fluid bilayer may be stabilized in the presence of a phase change if the system consists of a single component. However, if the fluid is composed of a binary mixture with the more volatile component having the lower surface tension, it is known that a Marangoni instability occurs. This instability owes its origin to concentration gradients created by the phase change, even though the phase change otherwise has a stabilizing effect. In this study, it is shown via a nonlinear model under a long-wavelength approximation, that this Marangoni destabilization is insufficient to cause a rupture of the interface under practical operating conditions. Computations reveal that the stabilizing effect of the phase change dominates as the film becomes thin by reversing the direction of the Marangoni flow, thereby halting the instability and any hope of rupture.
Despite the frequency of disasters in Africa, almost nothing is known about ethnic affiliations in relation to psychopathology after such incidents. This study examined the mental health outcomes of members of 7 major ethnic groups exposed to the 1998 terrorist bombing of the US Embassy in Nairobi, Kenya.
Approximately 8 to 10 months after the disaster, 229 civilian employees, 99 locally engaged staff workers of the US State Department and the US Agency for International Development, and 64 workers of the Kenyan Red Cross Society (total N=392) were assessed with the Diagnostic Interview Schedule for the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition). Additional data were gathered on demographic characteristics, disaster exposures and injuries, and ethnic affiliations.
Disaster-related post-traumatic stress disorder (PTSD) was significantly less prevalent among members of the Kikuyu group (28%) and post-disaster major depression was significantly more prevalent among members of the Meru group (64%), compared with all others in the sample. Preexisting psychopathology and disaster injury were independently associated with bombing-related psychopathology.
Further study of disaster-related psychopathology in relation to African ethnic affiliations is needed to better understand these associations and to assist in planning resources and interventions for African disaster survivors. (Disaster Med Public Health Preparedness. 2018; 12: 360–365)
This paper presents the results of a detailed experimental investigation into the effectiveness of sinusoidal leading edge serrations on aerofoils for the reduction of the noise generated by the interaction with turbulent flow. A detailed parametric study is performed to investigate the sensitivity of the noise reductions to the serration amplitude and wavelength. The study is primarily performed on flat plates in an idealized turbulent flow, which we demonstrate captures the same behaviour as when identical serrations are introduced onto three-dimensional aerofoils. The influence on the noise reduction of the turbulence integral length scale is also studied. An optimum serration wavelength is identified whereby maximum noise reductions are obtained, corresponding to when the transverse integral length scale is approximately one-fourth the serration wavelength. This paper proves that, at the optimum serration wavelength, adjacent valley sources are excited incoherently. One of the most important findings of this paper is that, at the optimum serration wavelength, the sound power radiation from the serrated aerofoil varies inversely proportional to the Strouhal number
are frequency, serration amplitude and flow speed, respectively. A simple model is proposed to explain this behaviour. Noise reductions are observed to generally increase with increasing frequency until the frequency at which aerofoil self-noise dominates the interaction noise. Leading edge serrations are also shown to reduce aerofoil self-noise. The mechanism for this phenomenon is explored through particle image velocimetry measurements. Finally, the lift and drag of the serrated aerofoil are obtained through direct measurement and compared against the straight edge baseline aerofoil. It is shown that aerodynamic performance is not substantially degraded by the introduction of the leading edge serrations on the aerofoil.
The conditions under which the hydromagnetic interface waves can exist at a magnetic interface is deduced. Using these conditons, it is shown that a slow interface wave with a phase velocity about 5Km/s and a fast interface wave with a phase velocity 6.5 to 8km/s at the photospheric level can exist.
We report fast photometric observations on AM CANUM VENATICORUM (AM CVn) the ultra short period, hydrogen deficient variable. We have detected on 24th February, 1985 an intense flare of (Δm)peak≈0.34 in white light lasting over 200s. Following this flare we observe an enhanced double humped structure lasting for 1051s which is the dominant periodicity exhibited by AM CVn. We have also detected the 525s and 1051s periods. In addition, we report flickerings, lasting typically 1-2 minutes, that are characteristic of cataclysmic variables.
Real-time magnetic resonance imaging (rtMRI) of the moving vocal tract during running speech production is an important emerging tool for speech production research providing dynamic information of a speaker's upper airway from the entire midsagittal plane or any other scan plane of interest. There have been several advances in the development of speech rtMRI and corresponding analysis tools, and their application to domains such as phonetics and phonological theory, articulatory modeling, and speaker characterization. An important recent development has been the open release of a database that includes speech rtMRI data from five male and five female speakers of American English each producing 460 phonetically balanced sentences. The purpose of the present paper is to give an overview and outlook of the advances in rtMRI as a tool for speech research and technology development.
Our new compilation of interferometric CO data suggests that nuclear and extended molecular gas disks are common in the final stages of mergers. Comparing the sizes of the molecular gas disk and gas mass fractions to early-type and late-type galaxies, about half of the sample show similar properties to early-type galaxies, which have compact gas disks and low gas mass fractions. We also find that sources with extended gas disks and large gas mass fractions may become disk-dominated galaxies.
Memecylon wayanadense Ratheesh, Sivu & Pradeep, a new species of Melastomataceae from the Wayanad forests of Kerala, India, is described and illustrated. The new species is allied to Memecylon angustifolium, M. rivulare and M. sivadasanii but differs in habit, leaf shape, sclereid type, inflorescence type and position, and the shape and size of the sepals and petals. An UPGMA analysis of 20 RAPD primers resulted in two major clusters with Memecylon sivadasanii in one cluster and M. rivulare, M. angustifolium and M. wayanadense in the second cluster. Memecylon wayanadense forms a subgroup within the second cluster.
A technique to form metal nanocrystals on silicon or thin SiO2 film by Rapid Thermal Annealing (RTA) of thin metal film is developed and integrated into standard CMOS processing to make EEPROM devices and improve metal-semiconductor contact resistance. I-V and C-V measurements are carried out on MOSFETs and MOS capacitors containing Au, Ag, Pt, and Si nanocrystals as floating gate for universal mobility and minority carrier lifetime extraction. Mobility around 300 cm2/V-sec and minority carrier lifetime within 0.02 ∼ 0.1 μsec are observed for all cases including the control samples that do not go through the metal nanocrystal formation process, which suggests that the substrate is virtually free from metal contamination. Using this technique, thicker metal film can potentially be achieved as well by stitching thin metal layers on top of the nanocrystals.
This work investigates the retention and transport of chemical species and abrasive particles during chemical-mechanical polishing (CMP) of copper (Cu). “Slurry step-flow” experiments, in which the concentrations of the chemicals and abrasives in the slurry are altered in steps during polishing were conducted with hydrogen peroxide (H2O2)/glycine based slurries. Two different pads, Suba-500 and IC 1400 (with k grooves), were compared in terms of their slurry retention and transport characteristics. With these experiments, it has been shown that both the abrasives and chemicals are constantly replaced during a typical CMP process. Better polishing performance of the IC 1400 over Suba 500 is a result of improved transport of the chemicals and the abrasives between the wafer/pad interface.
A biomimetic process has been developed to fabricate hydroxyapatite-gelatin (HAP-GEL) nanocomposites for bone regeneration (Chang and Ko et al. 2003). We hypothesize that this newly developed HAP-GEL is osteoconductive and is suitable for tissue engineered scaffolds. This preliminary study is aimed to characterize cell affinity and osseous regeneration of the HAP-GEL. The HAP-GEL was synthesized according to the procedures described in the previous publication. The attachment and proliferation of human fetal osteoblasts on HAP-GEL discs were evaluated using three different gelatin contents (2g, 3g, and 4g). The cells were seeded onto each disc and incubated at 34 degrees Celsius in 5% CO2 air atmosphere. At different time points of cultivation, cells were stained with fluorescein diacetate (FDA) and ethidium bromide (EB) to determine their viability and morphology. To assess the cell proliferation, cells were detached at Days 1, 4, and 7 by trypsinzation and counted. For in vivo tests, HAP-GEL rods were implanted into the proximal femur of Sprague-Dawley rats. One month after the implantation, the femurs were harvested and the undecalcified HAP-GEL-bone sections were stained for histopathology. Four hours after attachment, most cells appeared round in all discs; cell spreading was observed after 24 hours. The highest gelatin content supported a significantly higher cell growth than the others at 7 days. Thus all compositions support satisfactory attachment, spreading and growth. In vivo results showed excellent interfacial bone regeneration. No necrotic tissues were found. In conclusion, the HAP-GEL not only mimics the biochemistry and nanostructures of bone but also supports the attachment, proliferation and differentiation (bone formation) of osteoblasts. The HAP-GEL we developed provides a suitable surface for regeneration.