Papers by Nicholas Mecholsky
Axioms
The drift velocity of a particle under a driving force has its roots in the theory of electrical ... more The drift velocity of a particle under a driving force has its roots in the theory of electrical conduction. Although it has been studied for over 100 years, it still yields surprises. At the heart of a particle’s drift velocity is an interplay of classical, quantum, and statistical mechanics. Irreversibility and energy loss have been assumed as essential features of drift velocities and very little effort has been made to isolate the aspects of particle transport that are due to elastic mechanisms alone. In this paper, we remove energy loss and quantum mechanics to investigate the classical and statistical factors that can produce a drift velocity using only elastic scattering. A Monte Carlo simulation is used to model a particle in a uniform force field, subject to randomly placed scatterers. Time-, space-, and energy-dependent scattering models, with varied ranges of scattering angles, are investigated. A constant drift velocity is achieved with the time scattering model, which h...
Bulletin of the American Physical Society, Mar 21, 2013
Co2FeAl (CFA) is a full Huesler alloy with interesting magnetic behavior and very high Curie temp... more Co2FeAl (CFA) is a full Huesler alloy with interesting magnetic behavior and very high Curie temperature. We have carried out micromagnetic simulations on CFA nanopillars using a program, NMAG, with various dimensions and spacing. The micromagnetic simulations are compared with the experimental results that we have obtained. Nanopillars are produced using the liftoff technique after electron beam lithography. The CFA nanopillars are grown using electron beam deposition of Co, Fe and Al in the stoichiometric ratio and by further annealing at 850 K for one hour. We have simulated the magnetic behavior of CFA nanopillars ranging from 30 to 90 nm in diameter and with a height of about 115 nm. Preliminary results show the simulated coercivities are 700 Oe and 2400 Oe for 60 and 30 nm pillars. These are comparable to the experimental results that we have obtained. Magnetic behavior of polycrystalline nanowires of varying diameters is also simulated using NMAG. We will present the simulation and experimental results of nanopillars and polycrystalline nanowires in detail.
Bulletin of the American Physical Society, Mar 2, 2015
Bulletin of the American Physical Society, Mar 7, 2019
arXiv (Cornell University), Feb 28, 2023
Bulletin of the American Physical Society, Mar 14, 2017
full dispersions, E n (k), are conventionally represented on specific high-symmetry paths or inte... more full dispersions, E n (k), are conventionally represented on specific high-symmetry paths or integrated to determine the density of states. Novel methodologies, developed within the AFLOW consortium, allow analysis of the full energy dispersion efficiently in order to seek for valleys with optimized properties. We discuss results from high-throughput calculations performed with AFLOWπ to illustrate the importance of the full band structure in the optimization of the electronic transport coefficients. We will focus our discussion on binary chalcogenides.
Computer Physics Communications
APS March Meeting Abstracts, Mar 1, 2017
Bulletin of the American Physical Society, 2019
Bulletin of the American Physical Society, 2017
full dispersions, E n (k), are conventionally represented on specific high-symmetry paths or inte... more full dispersions, E n (k), are conventionally represented on specific high-symmetry paths or integrated to determine the density of states. Novel methodologies, developed within the AFLOW consortium, allow analysis of the full energy dispersion efficiently in order to seek for valleys with optimized properties. We discuss results from high-throughput calculations performed with AFLOWπ to illustrate the importance of the full band structure in the optimization of the electronic transport coefficients. We will focus our discussion on binary chalcogenides.
Chemistry of Materials, 2016
Program-Pure lead-free SnTe has limited thermoelectric potentials because of the low Seebeck coef... more Program-Pure lead-free SnTe has limited thermoelectric potentials because of the low Seebeck coeffcients and the relatively large thermal conductivity. In this study, we provide experimental evidence and theoretical understanding that alloying SnTe with Ca greatly improves the transport properties leading to ZT of 1.35 at 873 K, the highest ZT value so far reported for singly doped SnTe materials. The introduction of Ca (0-9%) in SnTe induces multiple effects: (1) Ca replaces Sn and reduces the hole concentration due to Sn vacancies, (2) the energy gap increases limiting the bipolar transport, (3) several bands with larger effective masses become active in transport, and (4) the lattice thermal conductivity is reduced of about 70% due to the contribution of concomitant scattering terms associated with the alloy disorder and the presence of nanoscale precipitates. An effciency of 10% (for ∆T = 400 K) was predicted for high temperature thermoelectric power generation using SnTe-based n-and p-type materials.
Chaos: An Interdisciplinary Journal of Nonlinear Science
This paper investigates in detail the effects of measurement noise on the performance of reservoi... more This paper investigates in detail the effects of measurement noise on the performance of reservoir computing. We focus on an application in which reservoir computers are used to learn the relationship between different state variables of a chaotic system. We recognize that noise can affect the training and testing phases differently. We find that the best performance of the reservoir is achieved when the strength of the noise that affects the input signal in the training phase equals the strength of the noise that affects the input signal in the testing phase. For all the cases we examined, we found that a good remedy to noise is to low-pass filter the input and the training/testing signals; this typically preserves the performance of the reservoir, while reducing the undesired effects of noise.
Bulletin of the American Physical Society, 2016
The goal of this talk is to investigate when band warping affects density-of-states effective mas... more The goal of this talk is to investigate when band warping affects density-of-states effective mass. Further, band "corrugation," a form of band warping referring to energy dispersions that deviate "more severely" from being twice-differentiable at isolated critical points, may also correlate in different ways with density-of-states effective masses and other band warping parameters. In this talk, an angular effective mass formalism is developed and used to study the electronic density of states of warped and non-warped energy bands towards an application in thermoelectric transport design. We demonstrate effects of band warping and prove the superiority of the angular effective mass treatment for valence energy bands in cubic materials. We explore examples that can also be critical to precisely distinguish the contributions due to band warping and to band non-parabolicity in non-degenerate bands of thermoelectric materials that have a consequent practical interest.
Inorganic Thermoelectric Materials, 2021
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Papers by Nicholas Mecholsky