194 research outputs found
Strain engineered graphene using a nanostructured substrate: I Deformations
Using atomistic simulations we investigate the morphological properties of
graphene deposited on top of a nanostructured substrate. Sinusoidally
corrugated surfaces, steps, elongated trenches, one dimensional and cubic
barriers, spherical bubbles, Gaussian bump and Gaussian depression are
considered as support structures for graphene. The graphene-substrate
interaction is governed by van der Waals forces and the profile of the graphene
layer is determined by minimizing the energy using molecular dynamics
simulations. Based on the obtained optimum configurations, we found that: (i)
for graphene placed over sinusoidally corrugated substrates with corrugation
wave lengths longer than 2\,nm, the graphene sheet follows the substrate
pattern while for supported graphene it is always suspended across the peaks of
the substrate, (ii) the conformation of graphene to the substrate topography is
enhanced when increasing the energy parameter in the van der Waals model, (iii)
the adhesion of graphene into the trenches depends on the width of the trench
and on graphene's orientation, i.e. in contrast to a small width (3 nm)
nanoribbon with armchair edges, the one with zig-zag edges follows the
substrate profile, (iv) atomic scale graphene follows a Gaussian bump substrate
but not the substrate with a Gaussian depression, and (v) the adhesion energy
due to van der Waals interaction varies in the range [0.1-0.4] J/m^2.Comment: 12 pages and 16 figures, To appear in Phys. Rev.
A Redesigned Benders Decomposition Approach for Large-Scale In-Transit Freight Consolidation Operations
The growth in online shopping and third party logistics has caused a revival
of interest in finding optimal solutions to the large scale in-transit freight
consolidation problem. Given the shipment date, size, origin, destination, and
due dates of multiple shipments distributed over space and time, the problem
requires determining when to consolidate some of these shipments into one
shipment at an intermediate consolidation point so as to minimize shipping
costs while satisfying the due date constraints. In this paper, we develop a
mixed-integer programming formulation for a multi-period freight consolidation
problem that involves multiple products, suppliers, and potential consolidation
points. Benders decomposition is then used to replace a large number of integer
freight-consolidation variables by a small number of continuous variables that
reduces the size of the problem without impacting optimality. Our results show
that Benders decomposition provides a significant scale-up in the performance
of the solver. We demonstrate our approach using a large-scale case with more
than 27.5 million variables and 9.2 million constraints
Determination of the lowest energy structure of Ag from first-principles calculations
The ground-state electronic and structural properties, and the electronic
excitations of the lowest energy isomers of the Ag cluster are calculated
using density functional theory (DFT) and time-dependent DFT (TDDFT) in real
time and real space scheme, respectively. The optical spectra provided by TDDFT
predict that the D dodecahedron isomer is the structural minimum of
Ag cluster. Indeed, it is borne out by the experimental findings.Comment: 4 pages, 2 figures. Accepted in Physical Review A as a brief repor
Lateral translation of an Xe atom on metal surfaces
This work presents the theoretical study of the controlled lateral translation of an Xe atom physisorbed on the Ni(110) surface. The motion of the Xe is manipulated by the tip of the scanning tunnelling microscope. The interaction of the physisorbed atom with the tip and sample surface is described by empirical potentials. Using molecular statics and dynamics, the energetics and different modes of the translation are revealed. Important effects of electrode relaxation, tip geometry and material parameters are briefly discussed
Characterisation and mechanical modelling of polyacrylonitrile-based nanocomposite membranes reinforced with silica nanoparticles
In this study, neat polyacrylonitrile (PAN) and fumed silica (FS)-doped PAN membranes (0.1, 0.5 and 1 wt% doped PAN/FS) are prepared using the phase inversion method and are characterised extensively. According to the Fourier Transform Infrared (FTIR) spectroscopy analysis, the addition of FS to the neat PAN membrane and the added amount changed the stresses in the membrane structure. The Scanning Electron Microscope (SEM) results show that the addition of FS increased the porosity of the membrane. The water content of all fabricated membranes varied between 50% and 88.8%, their porosity ranged between 62.1% and 90%, and the average pore size ranged between 20.1 and 21.8 nm. While the neat PAN membrane’s pure water flux is 299.8 L/m2 h, it increased by 26% with the addition of 0.5 wt% FS. Furthermore, thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) techniques are used to investigate the membranes’ thermal properties. Finally, the mechanical characterisation of manufactured membranes is performed experimentally with tensile testing under dry and wet conditions. To be able to provide further explanation to the explored mechanics of the membranes, numerical methods, namely the finite element method and Mori–Tanaka mean-field homogenisation are performed. The mechanical characterisation results show that FS reinforcement increases the membrane rigidity and wet membranes exhibit more compliant behaviour compared to dry membranes
Quantum heat transfer through an atomic wire
We studied the phononic heat transfer through an atomic dielectric wire with
both infinite and finite lengths by using a model Hamiltonian approach. At low
temperature under ballistic transport, the thermal conductance contributed by
each phonon branch of a uniform and harmonic chain cannot exceed the well-known
value which depends linearly on temperature but is material independent. We
predict that this ballistic thermal conductance will exhibit stepwise behavior
as a function of temperature. By performing numerical calculations on a more
realistic system, where a small atomic chain is placed between two reservoirs,
we also found resonance modes, which should also lead to the stepwise behavior
in the thermal conductance.Comment: 14 pages, 2 separate figure
On the solutions of the Schrodinger equation with some molecular potentials: wave function ansatz
Making an ansatz to the wave function, the exact solutions of the %
-dimensional radial Schrodinger equation with some molecular potentials like
pseudoharmonic and modified Kratzer potentials are obtained. The restriction on
the parameters of the given potential, and are also given,
where depends on a linear combination of the angular momentum quantum
number and the spatial dimensions and is a parameter in
the ansatz to the wave function. On inserting D=3, we find that the bound state
eigensolutions recover their standard analytical forms in literature.Comment: 14 page
Halloysite nanotube-enhanced polyacrylonitrile ultrafiltration membranes: fabrication, characterization, and performance evaluation
This research focuses on the production and characterization of pristine polyacrylonitrile (PAN) as well as halloysite nanotube (HNT)-doped PAN ultrafiltration (UF) membranes via the phase inversion technique. Membranes containing 0.1, 0.5, and 1% wt HNT in 16% wt PAN are fabricated, and their chemical compositions are examined using Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy (SEM) is utilized to characterize the membranes’ surface and cross-sectional morphologies. Atomic force microscopy (AFM) is employed to assess the roughness of the PAN/HNT membrane. Thermal characterization is conducted using thermal gravimetric analysis (TGA) and differential thermal analysis (DTA), while contact angle and water content measurements reveal the hydrophilic/hydrophobic properties. The pure water flux (PWF) performance of the porous UF water filtration membranes is evaluated at 3 bar, with porosity and mean pore size calculations. The iron (Fe), manganese (Mn), and total organic carbon (TOC) removal efficiencies of PAN/HNT membranes from dam water are examined, and the surfaces of fouled membranes are investigated by using SEM post-treatment. Mechanical characterization encompasses tensile testing, the Mori–Tanaka homogenization approach, and finite element analysis. The findings offer valuable insights into the impact of HNT doping on PAN membrane characteristics and performance, which will inform future membrane development initiatives
Computational molecular characterization of the flavonoid rutin
In this work, we make use of a model chemistry within Density Functional Theory (DFT) recently presented, which is called M05-2X, to calculate the molecular structure of the flavonoid Rutin, as well as to predict the infrared (IR) and ultraviolet (UV-Vis) spectra, the dipole moment and polarizability, the free energy of solvation in different solvents as an indication of solubility, the HOMO and LUMO orbitals, and the chemical reactivity parameters that arise from Conceptual DFT. The calculated values are compared with the available experimental data for this molecule as a means of validation of the used model chemistry
Measuring bank efficiency: DEA application
The paper aims to improve the methodology of measuring efficiency of Latvian banks. Efficiency scores were calculated with application of non-parametric frontier technique Data Envelopment Analysis (DEA). Input-oriented DEA model under Variable Returns to Scale (VRS) assumption was used. Potential model variables were selected based on the intermediation and profitability approach. Fourteen alternative models with different inputs-outputs combinations were developed for the research purposes. To substantiate the variables selection for DEA model the received data was processed, using such methods, as correlation analysis, linear regression analysis, analysis of mean values, and two-samples Kolmogorov-Smirnov test. The research results assisted the authors in providing general recommendations about the variables selection for DEA application in the Latvian banking sector. The present research contributes to the existing analytical data on bank performance in Latvia. The empirical findings provide a background for further studies, in particular, the efficiency of Latvian banks could be analysed in the extended time period
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