All Faculty Deposits

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The "All Faculty Deposits" collection contains works deposited by faculty and appointed delegates from the Elements (EFARs) system. For help with Elements, see Frequently Asked Questions on the Provost's website. In general, items can only be deposited if the item is a scholarly article that is covered by Virginia Tech's open access policy, or the item is openly licensed or in the public domain, or the item is permitted to be posted online under the journal/publisher policy, or the depositor owns the copyright. See Right to Deposit on the VTechWorks Help page. If you have questions email us at vtechworks@vt.edu.

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Now showing 1 - 16 of 16

Application of Artificial Neural Networks for Virtual Energy Assessment
Mortazavigazar, Amir; Wahba, Nourehan; Newsham, Paul; Triharta, Maharti; Zheng, Pufan; Chen, Tracy; Rismanchi, Behzad (MDPI)
A Virtual energy assessment (VEA) refers to the assessment of the energy flow in a building without physical data collection. It has been occasionally conducted before the COVID-19 pandemic to residential and commercial buildings. However, there is no established framework method for conducting this type of energy assessment. The COVID-19 pandemic has catalysed the implementation of remote energy assessments and remote facility management. In this paper, a novel framework for VEA is developed and tested on case study buildings at the University of Melbourne. The proposed method is a hybrid of top-down and bottom-up approaches: gathering the general information of the building and the historical data, in addition to investigating and modelling the electrical consumption with artificial neural network (ANN) with a projection of the future consumption. Through sensitivity analysis, the outdoor temperature was found to be the most sensitive (influential) parameter to electrical consumption. The lockdown of the buildings provided invaluable opportunities to assess electrical baseload with zero occupancies and usage of the building. Furthermore, comparison of the baseload with the consumption projection through ANN modelling accurately quantifies the energy consumption attributed to occupation and operational use, referred to as ‘operational energy’ in this paper. Differentiation and quantification of the baseload and operational energy may aid in energy conservation measures that specifically target to minimise these two distinct energy consumptions.
Capillary forces on a small particle at a liquid-vapor interface: Theory and simulation
Tang, Yanfei; Cheng, Shengfeng (American Physical Society, 2018-09-24)
Conformational Analysis of Fluoro-, Chloro-, and Proteo-Alkene Gly-Pro and Pro-Pro Isosteres to Mimic Collagen
Arcoria, Paul J.; Ware, Rachel I.; Makwana, Sunny V.; Troya, Diego; Etzkorn, Felicia A. (American Chemical Society, 2021-12-30)
Collagen is the most abundant human protein, with the canonical sequence (Gly-Pro-Hyp)_n in its triple helix region. Cis-trans isomerization of the Xaa-Pro amide has made two of these amide bonds the target of alkene replacement: the Gly-Pro and the Pro-Hyp positions. The conformations of Gly-Pro and Pro-Pro (as a Pro-Hyp model) fluoro-, chloro-, and proteo-alkene mimic models were investigated computationally to determine whether these alkenes can stabilize the polyproline type II (PPII) conformation of collagen. Second-order Møller-Plesset (MP2) calculations with various basis sets were used to perform the conformational analyses and locate stationary points. The calculation results predict that fluoro- and chloro-alkene mimics of Gly-Pro and Pro-Pro can participate in n→π* donation to stabilize PPII conformations, yet they are poor n→π* acceptors, shifting the global minima away from PPII conformations. For the proteo-alkene mimics, the lack of significant n→π* interactions and unstable PPII-like geometries explains their known destabilization of the triple helix in collagen-like peptides.
Crossover From Self-Similar to Self-Affine Structures in Precolation
Frey, E.; Täuber, Uwe C.; Schwabl, Franz (Editions Physique, 1994-05-20)
We study the crossover from self-similar scaling behavior to asymptotically self-affine (anisotropic) structures. As an example, we consider bond percolation with one preferred direction. Our theory is based on a field-theoretical representation, and takes advantage of a renormalization group approach designed for crossover phenomena. We calculate effective exponents for the connectivity describing the entire crossover region from isotropic to directed percolation, and predict at which scale of the anisotropy the crossover should occur. We emphasize the broad range of applicability of our method.
Droplet Evaporation on Hot Micro-Structured Superhydrophobic Surfaces: Analysis of Evaporation from Droplet Cap and Base Surfaces
Huang, Wenge; He, Xukun; Liu, Cong; Li, Xiaojie; Liu, Yahua; Collier, C. Patrick; Srijanto, Bernadeta R.; Liu, Jiansheng; Cheng, Jiangtao (Elsevier, 2022-04-01)
In this study, evaporation of sessile water droplets on hot micro-structured superhydrophobic surfaces is experimentally and theoretically investigated. Water droplets of 4 µL are placed on micro-pillared silicon substrates with the substrate temperature heated up to 120°C. A comprehensive thermal circuit model is developed to analyze the effects of substrate roughness and substrate temperature on the sessile droplet evaporation. For the first time, two components of heat and mass transfer, i.e., one from the droplet cap surface and the other from the droplet base surface, during droplet evaporation are distinguished and systematically studied. As such, the evaporation heat transfer rates from both the droplet cap surface and the interstitial liquid-vapor interface between micropillars at the droplet base are calculated in various conditions. For droplet evaporation on the heated substrates in the range of 40°C – 80°C, the predicted droplet cap temperature matches well with the experimental results. During the constant contact radius mode of droplet evaporation, the decrease of evaporation rate from the droplet base contributes most to the continuously decreasing overall evaporation heat transfer rate, whereas the decrease of evaporation rate from the droplet cap surface is dominant in the constant contact angle mode. The influence of internal fluid flow is considered for droplet evaporation on substrates heated above 100°C, and an effective thermal conductivity is adopted as a correction factor to account for the effect of convection heat transfer inside the droplet. Temperature differences between the droplet base and the substrate base are estimated to be about 2°C, 5°C, 8°C, 13°C and 18°C for droplet evaporation on substrates heated at 40°C, 60°C, 80°C, 100°C, and 120°C, respectively, elucidating the delayed or depressed boiling of water droplets on a heated rough surface due to evaporative cooling.
High-Precision Megahertz-to-Terahertz Dielectric Spectroscopy of Protein Collective Motions and Hydration Dynamics
Charkhesht, Ali; Regmi, Chola K.; Mitchell-Koch, Katie R.; Cheng, Shengfeng; Vinh, Nguyen Q. (American Chemical Society, 2018-06-21)
The low-frequency collective vibrational modes in proteins as well as the protein-water interface have been suggested as dominant factors controlling the efficiency of biochemical reactions and biological energy transport. It is thus crucial to uncover the mystery of the hydration structure and dynamics as well as their coupling to collective motions of proteins in aqueous solutions. Here, we report dielectric properties of aqueous bovine serum albumin protein solutions as a model system using an extremely sensitive dielectric spectrometer with frequencies spanning from megahertz to terahertz. The dielectric relaxation spectra reveal several polarization mechanisms at the molecular level with different time constants and dielectric strengths, reflecting the complexity of protein-water interactions. Combining the effective-medium approximation and molecular dynamics simulations, we have determined collective vibrational modes at terahertz frequencies and the number of water molecules in the tightly bound and loosely bound hydration layers. High-precision measurements of the number of hydration water molecules indicate that the dynamical influence of proteins extends beyond the first solvation layer, to around 7 Å distance from the protein surface, with the largest slowdown arising from water molecules directly hydrogen-bonded to the protein. Our results reveal critical information of protein dynamics and protein-water interfaces, which determine biochemical functions and reactivity of proteins.
Interpretable Machine Learning of Chemical Bonding at Solid Surfaces
Omidvar, Noushin; Pillai, Hemanth Somarajan; Wang, Shih-Han; Mou, Tianyou; Wang, Siwen; Athawale, Andy; Achenie, Luke E. K.; Xin, Hongliang (American Chemical Society, 2021-11-25)
Understanding the nature of chemical bonding and its variation in strength across physically tunable factors is important for the development of novel catalytic materials. One way to speed up this process is to employ machine learning (ML) algorithms with online data repositories curated from high-throughput experiments or quantum-chemical simulations. Despite the reasonable predictive performance of ML models for predicting reactivity properties of solid surfaces, the ever-growing complexity of modern algorithms, e.g., deep learning, makes them black boxes with little to no explanation. In this Perspective, we discuss recent advances of interpretable ML for opening up these black boxes from the standpoints of feature engineering, algorithm development, and post hoc analysis. We underline the pivotal role of interpretability as the foundation of next-generation ML algorithms and emerging AI platforms for driving discoveries across scientific disciplines.
John Cardy's scale-invariant journey in low dimensions: a special issue for his 70th birthday Preface
Calabrese, Pasquale; Fendley, Paul; Täuber, Uwe C. (IOP, 2018-07-13)
The meniscus on the outside of a circular cylinder: From microscopic to macroscopic scales
Tang, Yanfei; Cheng, Shengfeng (Academic Press – Elsevier, 2019-01-01)
We systematically study the meniscus on the outside of a small circular cylinder vertically immersed in a liquid bath in a cylindrical container that is coaxial with the cylinder. The cylinder has a radius R much smaller than the capillary length, κ-1, and the container radius, L, is varied from a small value comparable to R to ∞. In the limit of L≪κ-1, we analytically solve the general Young-Laplace equation governing the meniscus profile and show that the meniscus height, Δh, scales approximately with Rln(L/R). In the opposite limit where L≫κ-1,Δh becomes independent of L and scales with Rln(κ-1/R). We implement a numerical scheme to solve the general Young-Laplace equation for an arbitrary L and demonstrate the crossover of the meniscus profile between these two limits. The crossover region has been determined to be roughly 0.4κ-1≲L≲4κ-1. An approximate analytical expression has been found for Δh, enabling its accurate prediction at any values of L that ranges from microscopic to macroscopic scales.
Propagation characteristics of laser-induced acoustic sources in hybrid anechoic wind tunnels
Szőke, Máté; Devenport, William J. (Academic Press-Elsevier, 2021-10-13)
The propagation characteristics of an acoustic point source generated using laser-induced plasma (LIP) were investigated experimentally. Experiments were performed in a Kevlar-walled hybrid anechoic wind tunnel (HAWT) where the sound of the LIP was measured using a 251-element microphone array, while the flow speed in the empty test section was varied. The time instant of the LIP formation was also captured. The far field sound pressure was assessed through arrival times (source to microphones) and pressure correction levels, and these quantities were compared against a commonly used shear layer refraction model. A detailed uncertainty assessment is presented on the arrival times and pressure levels. It was found that the time domain analysis was limited by the sampling rate of the analog-to-digital converter regardless of the flow speed. The uncertainty of the pressure levels was limited by the uncertainty of the microphones at low flow speeds, while they increased with flow speed at shallow observer angles. The high-speed Schlieren imaging of the LIP was performed, which revealed that the sound of the LIP reaches the far field microphones over a shorter time duration than modeled because the wave speed was initially supersonic. The discrepancy was found to be comparable to the temporal resolution of the aeroacoustic experiments. The discrepancy between the experimental and theoretical arrival times was found to increase with flow speed, and they were nearly independent of the azimuth angles. The discrepancy between the experimental and theoretical pressure correction ratio was found to be uniform for most observer locations. With an increase in flow speed, the discrepancy became positive at large, and negative at low polar angles. The sound refraction at the Kevlar wall did not change the frequency content of the sound over the investigated range of frequencies (1–10 kHz).
Requirements for the containment of COVID-19 disease outbreaks through periodic testing, isolation, and quarantine
Mukhamadiarov, Ruslan I.; Deng, Shengfeng; Serrao, Shannon R.; Priyanka; Childs, Lauren M.; Täuber, Uwe C. (IOP, 2022-01-21)
We employ individual-based Monte Carlo computer simulations of a stochastic SEIR model variant on a two-dimensional Newman–Watts small-world network to investigate the control of epidemic outbreaks through periodic testing and isolation of infectious individuals, and subsequent quarantine of their immediate contacts. Using disease parameters informed by the COVID-19 pandemic, we investigate the effects of various crucial mitigation features on the epidemic spreading: fraction of the infectious population that is identifiable through the tests; testing frequency; time delay between testing and isolation of positively tested individuals; and the further time delay until quarantining their contacts as well as the quarantine duration. We thus determine the required ranges for these intervention parameters to yield effective control of the disease through both considerable delaying the epidemic peak and massively reducing the total number of sustained infections.
The role of the non-linearity in controlling the surface roughness in the one-dimensional Kardar-Parisi-Zhang growth process
Priyanka; Täuber, Uwe C.; Pleimling, Michel J. (IOP, 2021-04-16)
We explore linear control of the one-dimensional non-linear Kardar-Parisi-Zhang (KPZ) equation with the goal to understand the effects the control process has on the dynamics and on the stationary state of the resulting stochastic growth kinetics. In linear control, the intrinsic non-linearity of the system is maintained at all times. In our protocol, the control is applied to only a small number nc of Fourier modes. The stationary-state roughness is obtained analytically in the small-nc regime with weak non-linear coupling wherein the controlled growth process is found to result in Edwards-Wilkinson dynamics. Furthermore, when the non-linear KPZ coupling is strong, we discern a regime where the controlled dynamics shows scaling in accordance to the KPZ universality class. We perform a detailed numerical analysis to investigate the controlled dynamics subject to weak as well as strong non-linearity. A first-order perturbation theory calculation supports the simulation results in the weak non-linear regime. For strong non-linearity, we find a temporal crossover between KPZ and dispersive growth regimes, with the crossover time scaling with the number nc of controlled Fourier modes. We observe that the height distribution is positively skewed, indicating that as a consequence of the linear control, the surface morphology displays fewer and smaller hills than in the uncontrolled growth process, and that the inherent size-dependent stationary-state roughness provides an upper limit for the roughness of the controlled system.
Stabilizing spiral structures and population diversity in the asymmetric May-Leonard model through immigration
Serrao, Shannon R.; Täuber, Uwe C. (Springer, 2021-08-01)
We study the induction and stabilization of spiral structures for the cyclic three-species stochastic May-Leonard model with asymmetric predation rates on a spatially inhomogeneous two-dimensional toroidal lattice using Monte Carlo simulations. In an isolated setting, strongly asymmetric predation rates lead to rapid extinction from coexistence of all three species to a single surviving population. Even for weakly asymmetric predation rates, only a fraction of ecologies in a statistical ensemble manages to maintain full three-species coexistence. However, when the asymmetric competing system is coupled via diffusive proliferation to a fully symmetric May-Leonard patch, the stable spiral patterns from this region induce transient plane-wave fronts and ultimately quasi-stationary spiral patterns in the vulnerable asymmetric region. Thus the endangered ecological subsystem may effectively become stabilized through immigration from even a much smaller stable region. To describe the stabilization of spiral population structures in the asymmetric region, we compare the increase in the robustness of these topological defects at extreme values of the asymmetric predation rates in the spatially coupled system with the corresponding asymmetric May{Leonard model in isolation. We delineate the quasi-stationary nature of coexistence induced in the asymmetric subsystem by its diffusive coupling to a symmetric May{Leonard patch, and propose a (semi-)quantitative criterion for the spiral oscillations to be sustained in the asymmetric region.
Tunable Gap Plasmons in Gold Nanospheres Adsorbed into a pH-Responsive Polymer Film
Jao, Chih-Yu; Robinson, Hans D.; Samaimongkol, Panupon (Elsevier, 2019-06)
Hypothesis Plasmon nanorules are exquisitely sensitive distance sensors that are based on the electromagnetic interaction between metal nanoparticles and surfaces. We hypothesize that nanorulers can act as quantitative probes of processes such as particle aggregation and adsorption, and deploy them to investigate particle adsorption onto stimulus-responsive polymer films. While such systems have previously been qualitatively investigated with plasmon nanorulers, our quantitative analysis should provide deeper insights. Experiment Gold nanospheres are adsorbed from solution onto pH-responsive, amine-rich polyelectrolyte multilayer (PEM) films that are either directly deposited on a gold substrate or onto an intermediate self-assembled monolayer (SAM) of charged thiols. Fitting the optical scattering spectrum to a full-wave calculation, we quantify the sphere-substrate gap distance with good accuracy. Findings We find that the gold spheres partially embed into the PEMs rather than ride on top of them, and that although the amount of actuation of the spheres afforded by tuning the pH is well controlled, it is significantly smaller than the corresponding thickness changes in unstrained films. Further, the presence of a SAM below the PEM increases the amount of polymer in the PEM, except for the thickest and most highly charged films, where the SAM instead appears to displace from the area below the nanospheres.
A unified formulation of splitting-based implicit time integration schemes
Gonzalez-Pinto, Severiano; Hernandez-Abreu, Domingo; Perez-Rodriguez, Maria S.; Sarshar, Arash; Roberts, Steven; Sandu, Adrian (Academic Press – Elsevier, 2022-01-01)
Splitting-based time integration approaches such as fractional step, alternating direction implicit, operator splitting, and locally one dimensional methods partition the system of interest into components, and solve individual components implicitly in a cost-effective way. This work proposes a unified formulation of splitting time integration schemes in the framework of general-structure additive Runge–Kutta (GARK) methods. Specifically, we develop implicit-implicit (IMIM) GARK schemes, provide the order conditions for this class, and explain their application to partitioned systems of ordinary differential equations. We show that classical splitting methods belong to the IMIM GARK family, and therefore can be studied in this unified framework. New IMIM-GARK splitting methods are developed and tested using parabolic systems.
Variation of the subsidence parameters, effective thermal conductivity, and mantle dynamics
Adam, Claudia; King, Scott D.; Vidal, Valérie; Rabinowicz, Michel; Jalobeanu, André; Yoshida, Masaki (Elsevier, 2015-09-15)
The subsidence of young seafloor is generally considered to be a passive phenomenon related to the conductive cooling of the lithosphere after its creation at mid-oceanic ridges. Recent alternative theories suggest that the mantle dynamics plays an important role in the structure and depth of the oceanic lithosphere. However, the link between mantle dynamics and seafloor subsidence has still to be quantitatively assessed. Here we provide a statistical study of the subsidence parameters (subsidence rate and ridge depth) for all the oceans. These parameters are retrieved through two independent methods, the positive outliers method, a classical method used in signal processing, and through the MiFil method. From the subsidence rate, we compute the effective thermal conductivity, k , which ranges between 1 and 7 W m K . We also model the mantle flow pattern from the S40RTS tomography model. The density anomalies derived from S40RTS are used to compute the instantaneous flow in a global 3D spherical geometry. We show that departures from the k =3 Wm K standard value are systematically related to mantle processes and not to lithospheric structure. Regions characterized by k >3 Wm K are associated with mantle uplifts (mantle plumes or other local anomalies). Regions characterized by k <3 Wm K are related to large-scale mantle downwellings such as the Australia-Antarctic Discordance (AAD) or the return flow from the South Pacific Superswell to the East Pacific Rise. This demonstrates that mantle dynamics plays a major role in the shaping of the oceanic seafloor. In particular, the parameters generally considered to quantify the lithosphere structure, such as the thermal conductivity, are not only representative of this structure but also incorporate signals from the mantle convection occurring beneath the lithosphere. The dynamic topography computed from the S40RTS tomography model reproduces the subsidence pattern observed in the bathymetry. Overall we find a good correlation between the subsidence parameters derived from the bathymetry and the dynamic topography. This demonstrates that these parameters are strongly dependent on mantle dynamics.

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