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Recent documents in Physicsen-usWed, 03 Jan 2018 22:35:58 PST3600Turbulence in Superfluid 4-He Films around Substrate Defects
https://wesscholar.wesleyan.edu/etd_hon_theses/1834
https://wesscholar.wesleyan.edu/etd_hon_theses/1834Fri, 16 Jun 2017 14:20:38 PDT
This thesis seeks to help explain dissipation observed in third sound Superfluid 4-He by the Quantum Fluids Group at Wesleyan. Turbulence is a common hypothesis for these types of dissipation; however, it is not well understood how vortices form and nucleate in Superfluid. This project examines possible vortex formation conditions around surface defects: obstructions and bumps. We have solved for the flow fields of vortex pairs around defects, found the energy costs to vortex pair nucleation around these defects, and shown that energy cost for pair nucleation is lower for larger defects in higher velocities. Along with microscopic measurements of superfluid resonator surface defects, this model should be able to confirm whether or not observed dissipation is resulting from vortex pair formation around surface defects.
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Joseph Ross Ungar NatterTurbulence Generated by a Randomly Pulsed Through Flow Jet-Array
https://wesscholar.wesleyan.edu/etd_hon_theses/1829
https://wesscholar.wesleyan.edu/etd_hon_theses/1829Fri, 16 Jun 2017 14:20:23 PDT
We study the turbulence generated by a through flow jet-array in our newly constructed vertical water tunnel. This apparatus was designed to facilitate the measurement of dynamics of sedimenting particles in turbulence. It circulates water through a vertical, square channel, passing through a grid of 40 water jets that each fire at two 45 degree angles from the horizontal axis. We pulse the jet-array in several randomized patterns and intensities, while maintaining a constant total flow rate for each configuration. In its minimum turbulence configuration, the jets eject no fluid, allowing the jet-array to essentially function as a passive grid. When the jets are activated, the jet-array maintains a constant number of jets that will be on at any moment, an average duration for each jet to remain on, a through-flow rate, and a total jet-flow rate. This thesis characterizes the flow generated by the jet-array with different jet configurations and intensities. We see turbulence that is highly isotropic in the lateral plane, and homogeneous in the upper half of the test section. We also see varying levels of skewness of the flow with a high dependence on the number of jets firing. We study the flow at 36 cm, 60 cm, 90 cm, and 120 cm above the jet-array to analyze how various properties of the turbulence dissipate through space.
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Wyatt Jackson ReesRamified Deformable Particles in Simple Shear
https://wesscholar.wesleyan.edu/etd_hon_theses/1813
https://wesscholar.wesleyan.edu/etd_hon_theses/1813Fri, 16 Jun 2017 14:19:38 PDT
Abstract The behavior of deformable structures in fluid flows is a standard problem, but normally involves the interaction between a complex flow and a complex structure. Fibers are an example such an interaction: the curvature of a fiber in a fluid flow will correspond to the derivative of the velocity gradient tensor. In simpler flows however, where the velocity gradient tensor remains constant over time, fibers exhibit no deformation, making them no more useful than non-deformable structures. [1] We have identified a new opportunity for deformable structures by using deformable ramified particles. These particles interactions with linear velocity fields (i.e. flows with constant velocity gradient tensors) are simple enough that we can extract the full velocity gradient from a single deformable particle. Normally, numerous non-deformable particles would be required to extract the same information. This is of particular value when studying turbulent flows. Turbulent flows exhibit linear behavior at the kolmogorov length, but because this length is often exceedingly small, the seed density (density of tracer particles) needed to re-assemble the full velocity gradient tensor is prohibitively high. Using deformable ramified particles, which extract far more information on a per particle basis, we can make the same measurements while maintaining a low seed density. The use of ramified deformable particles represents a novel development in the field of fluid dynamics. As a proof of concept, we set out to test them in a simple, well understood fluid flow with well known fluid structure interactions.
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Michael Gregory KrellensteinDecisive Solution to a Long-standing Controversy in Paul-Trap Physics
https://wesscholar.wesleyan.edu/etd_hon_theses/1795
https://wesscholar.wesleyan.edu/etd_hon_theses/1795Fri, 16 Jun 2017 14:18:43 PDT
The study of charged particles' dynamics in a Paul trap is the foundation of its wide-ranging applications, including analyzing proteins, determining isotope ratios, and constructing a quantum computer. However, in the simplest case of two-particle dynamics, there remains a controversy on whether a two-ion planar crystal undergoes an order-to-chaos transition at a critical trap parameter value. Via linearization and separation of the Mathieu-Coulomb equations, this thesis shows analytically and numerically that the transition does not exist. Furthermore, the method developed here can be extended to determine the stability and existence of two-ion crystals in the whole parameter space of both the hyperbolic and linear Paul trap.
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Angus KanThe Pseudopotential As a Tool for Describing Ion Crystal Morphology
https://wesscholar.wesleyan.edu/etd_hon_theses/1739
https://wesscholar.wesleyan.edu/etd_hon_theses/1739Fri, 16 Jun 2017 14:15:43 PDT
Describing the structure of ion Coulomb crystals in periodically-driven systems, such as cylindrical and linear Paul traps, is important for applications in quantum information processing, quantum simulation, spectroscopy, and frequency standard determination. The pseudopotential, a time-independent effective potential obtained by averaging the explicitly time-dependent trapping potential, is often used for this specific purpose, among other uses in the general study of trapped ion dynamics. This thesis examines the strengths and weaknesses of the pseudopotential approximation as a tool for describing few-ion crystal configurations in a Paul trap. Numerical evidence for the failure of the standard pseudopotential commonly found in the literature in predicting crystal alignment effects in such systems is provided. A method for deriving an improved pseudopotential for a general set of coupled differential equations is presented and applied to the cylindrical and linear traps, providing analytical evidence for these "exotic'' crystal alignment effects. The limitations of the improved pseudopotential in explaining crystal instability in certain regions of trap parameter space and in terms of scalability to many-ion systems are discussed.
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Varun UrsekarPhase Transitions of Charged Particles in the Paul Trap
https://wesscholar.wesleyan.edu/etd_hon_theses/1738
https://wesscholar.wesleyan.edu/etd_hon_theses/1738Fri, 16 Jun 2017 14:15:40 PDT
The Paul trap is an electrodynamic device that can be used to trap multiple particles simultaneously. The ensuing dynamics can be modeled classically by simply considering the different forces acting upon each particle and solving Newton's second law. This system however is highly nonlinear, and so even for two particles, numerical simulations must be employed in order to understand these dynamics. In this Thesis, we explore the three classical thermodynamic phases of matter (gas, liquid, solid) and how they manifest in the Paul trap. We also investigate the phase transitions that can occur between these phases, and through this work hope to both obtain a fuller understanding of the nonlinear dynamics that governs motion in this system, and inform future experiments that can test the results found here.
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Daniel Kamrath WeissThe Alignment of Rods and Disks in Turbulence
https://wesscholar.wesleyan.edu/etd_hon_theses/1679
https://wesscholar.wesleyan.edu/etd_hon_theses/1679Wed, 18 May 2016 10:36:33 PDT
We study the orientation and rotational dynamics of anisotropic particles in homogenous isotropic turbulence. By analyzing direct numerical simulation (DNS) data at Taylor-microscale Reynolds number of 180, we quantify the preferential alignment between particle orientations and vorticity, as well as alignment with principal stretching directions defined by the Cauchy-Green strain tensor. This tensor quantifies stretching experienced by material elements in turbulence and provides a natural basis for studying particle alignment in turbulence. While previous work has focused primarily on thin rods, we extend the study to oblate disks. Both rods and disks are a specific class of anisotropic particles known as axisymmetric ellipsoids. These particles are defined by their aspect ratio, the ratio of their length, L, to their diameter, d. Rods have an aspect ratio greater than 1 while disks have an aspect ratio less than 1. The case of aspect ratio equalling 1 is a sphere. In this thesis, we compare the preferential alignments of rods with disks in turbulence. Rods preferentially align with vorticity as a result of both quantities independently aligning with the strongest extensional stretching direction, as defined by the maximum eigenvector of the Cauchy-Green strain tensor. In contrast, disks orient perpendicular to vorticity and preferentially align with the strongest compressional stretching direction, as defined by the smallest Cauchy-Green eigenvector. Furthermore, we study the relationship between the principle stretching eigenframe defined by the eigenvectors of the Cauchy-Green strain tensor and the principle rate of stretching eigenframe defined by the eigenvectors of the strain rate tensor, the symmetric part of the velocity gradient tensor.
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Conor Gerard HuntRovibrationally Inelastic Atom-Molecule Collision Cross Sections from a Hard Sphere Model
https://wesscholar.wesleyan.edu/etd_hon_theses/1637
https://wesscholar.wesleyan.edu/etd_hon_theses/1637Wed, 18 May 2016 10:31:00 PDT
Hard sphere models have been used for decades to study the kinetics of molecular collisions of the A + BC system. Early colinear models of this collision, and exten- sions into three-dimensions for limited orientations have been instrumental in the study of vibrational energy transfer, but to date, no inelastic collision cross sections of this system have generated. Many of these studies have also left out side impacts as a mechanism of vibrational energy transfer, where A collides with BC along its equator and incites vibration by pushing the two atoms apart from each other. These have been shown to be a dominating mechanism in the vibrational energy transfer by Professor Stewartâ€™s experimental results along with those of Dimpfl and Mahan . In this thesis, computational methods for calculating the final vibrational and ro- tational energies for arbitrary masses and orientations are discussed for a variety of molecular potentials. Namely, the cases in which B and C are connected by no molec- ular potential, a string potential, and a harmonic potential. Collision cross sections for the Li2-X system where X is H, He, Li, Ne, Ar, Kr, and Xe are presented and analyzed for each case studied.
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Jacob Albert LashnerDynamics of Low Velocity, Rovibrationally Inelastic Li2-Rare Gas Collisions
https://wesscholar.wesleyan.edu/etd_hon_theses/1612
https://wesscholar.wesleyan.edu/etd_hon_theses/1612Wed, 18 May 2016 10:27:40 PDT
This thesis presents a study of the dynamics of trajectory calculations at low velocity utilizing potentials for the Li$_2$-Ne and Li$_2$-Xe collisional systems. We have found that at these low velocities, significant rovibrational energy transfer still takes place. This is due to the fact that there exists a ``capture radius'' at these low velocities such that if the impact parameter of the incoming atom is within this capture radius, the mutual attraction between the rare gas atom and Li$_2$ molecule is strong enough to force the atom into the potential well of the collisional system. The energy that the atom gains as it falls down this steep potential well, in addition to the fact that there are actually a multitude of collisions that take place while the atom is in the well, allow for the possibility of significant energy transfer. In addition, we elucidate how changes in the initial vibrational and rotational quantum number affect the dynamics of this energy transfer. Finally, the fact that these low initial velocities correspond to ultra-cold temperatures suggest the possibility that these results can be tested experimentally in a device such as a magento-optical trap.
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Will Zachary JasmineContrasting the Structure and Dynamics of Simulated Lipid Monolayers and Bilayers
https://wesscholar.wesleyan.edu/etd_hon_theses/1544
https://wesscholar.wesleyan.edu/etd_hon_theses/1544Wed, 18 May 2016 10:19:26 PDT
Lipid monolayers and bilayers are soft condensed matter systems with similar structural properties and phase behaviors that play critical roles in many biological processes. Monolayers are more easily studied experimentally and therefore often are used to infer the properties of bilayers; we examine the degree to which this inference holds. We explicitly compare the organizational structure and dynamical behavior of these systems though molecular dynamics simulations of single-component dipalmitoylphosphatidylcholine (DPPC) lipid monolayers and bilayers. DPPC is the most common lipid component in monolayers and is also prevalent in bilayers. We implement the coarse-grained MARTINI model in simulations performed at zero surface tension and various temperatures near the liquid-liquid phase transition of DPPC; both the monolayer and bilayer exhibit a high-density, low-mobility phase and a low-density, high-mobility phase in this region. Dynamical and structural properties of the low-density phase of the monolayer and bilayer are nearly identical; however, the high-density phase shows significant dynamical differences between these systems. Salient distinctions between the high-density monolayers and bilayers include the diffusion coefficient, which is at least 1-2 orders of magnitude larger in monolayers than in bilayers, and the non-Gaussian parameter, which reveals that the degree of non-Gaussian dynamics in bilayers is approximately 2 orders of magnitude stronger than that of monolayers. The dynamical properties of high-density bilayers, unlike those of monolayers, are consistent with dynamical heterogeneity, a universal phenomenon in many soft-condensed matter systems where particle interactions are strong relative to the total thermal energy. We investigate the structural and organizational origins of these dynamical differences and show that inter-leaflet interactions in the bilayer play an important role in the emergence of heterogeneous dynamics. Consequently, we find limitations in using monolayers as a model system to understand the dynamics of bilayers of DPPC, a finding that may extend to many other compositions.
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Kiley Elizabeth KennedySedimentation and Orientation of Slender Particles in a Laminar Flow
https://wesscholar.wesleyan.edu/etd_hon_theses/1535
https://wesscholar.wesleyan.edu/etd_hon_theses/1535Wed, 18 May 2016 10:18:15 PDT
The motions of high aspect ratio particles settling in fluid flow are of importance in a range of scientific fields, including atmospheric science and biological fluid dynamics. In the past, calculations for the orientation and sedimentation velocities of long slender particles were conducted in the Stokes flow limit, valid only in the absence of fluid inertia. This thesis work presents series of experiments designed to extend the theory for the sedimentation of high aspect ratio particles to the finite Reynolds number regime. Additionally, experiments are presented which examine the effect of particle asymmetry on the inertial torques on the sedimenting bodies. Of particular interest in the case of the asymmetric particles is the discontinuity in the transition from a horizontal to vertical sedimentation orientation as the particle asymmetry increases. Each experiment that I conducted was designed to accompany theoretical developments by collaborators at Cornell. In addition to experimental work, this thesis presents a review of the mathematics and theoretical development of slender body theory, including recent work completed by collaborators in the the Cornell department of Chemical and Biomolecular Engineering.
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Lydia Helen TierneyThe Effect of Polymer Architecture on Glass Formation and Mechanical Properties
https://wesscholar.wesleyan.edu/etd_hon_theses/1495
https://wesscholar.wesleyan.edu/etd_hon_theses/1495Thu, 06 Aug 2015 10:04:37 PDT
Advances in polymer synthesis have triggered tremendous growth in the development of materials with highly customizable properties. One approach to alter the properties of polymer-based materials is to alter the architecture of the constituent polymers. Therefore, we perform a comprehensive structural and dynamical analysis of several polymer architectures: rings, chains, and stars. Increasing the number of arms of star polymers, we find that the structure and dynamics approach those of soft spheres. We also consider a more unusual architecture, mechanically interlocked polymers, a unique class of macromolecules wherein polymer components are linked by one (or more) sliding chains. These novel linkages may lead to new materials with unique stimulus-response and fatigue-resistant properties. Since these polymer materials are relatively new, no molecular model exists at present. Accordingly, we develop and parametrize a model for star mechanical polymers being synthesized by Professor Brian Northrop's lab in the Chemistry Department. Using this model, we predict that certain properties, such as the glass transition temperature and yield stress, differ from conventional polymers. However, the main factor contributing to these differences does not appear to be chain sliding, but rather the bulkiness of mechanical linkages.
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Wilson Min FongDisaccharides as Osmoprotectants: Molecular Interactions Study from Steady-state Ensemble to Femtosecond-resolved Hydration Dynamics
https://wesscholar.wesleyan.edu/etd_hon_theses/1445
https://wesscholar.wesleyan.edu/etd_hon_theses/1445Thu, 06 Aug 2015 10:03:48 PDT
Small molecular osmolytes are used in nature to stabilize solvated protein structures. Disaccharides such as trehalose and sucrose appear unique in protecting biological organisms from diverse physical stresses by effectively decreasing the dynamics of water molecules when solvated. This property has led to the widespread use of disaccharides in the cosmetic, pharmaceutical, and food industries, and even to customization of disaccharides to emphasize desirable features and substitute natural disaccharides, as seen in the employment of artificial sweetener sucralose. In order to identify which molecular traits are critical to the ability of a disaccharide as a strong bioprotectant, a variety of computational and experimental techniques with a wide range of time resolution was employed. Halogenation of disaccharide may greatly alter its biopreservation ability according to spectroscopic analysis comparing sucrose and sucralose, a result consistent with other literatures. Our computational analysis revealed that numerous molecular features including dipole moment and glycodisic link properties can be affected by halogenating disaccharides, the consequences of which are important to consider in the context of biomolecular interactions.
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Inha ChoQuasi Classical Trajectory Binning: A Systematic Study of the Effect of Binning on Li2 Ne Scattering
https://wesscholar.wesleyan.edu/etd_hon_theses/1353
https://wesscholar.wesleyan.edu/etd_hon_theses/1353Thu, 06 Aug 2015 10:02:24 PDT
Although quantum mechanics is the most accurate descriptor of nature at molecular length scales, sophisticated quantum calculations are still infeasible for complex systems. As a result, there is a demand for methods of classical calculation that are able to accurately simulate systems with quantum features. In this study, we examine modifications to the quasiclassical trajectory method (QCT) on the Li2 + Ne inelastic scattering system. More specifically, we examine the effects of binning, the process of discretizing the continuous distribution of final classical actions in order to calculate collision cross sections for rovibrational transitions. In order to undertake this, we calculate collision cross sections using the QCT with a variety of different binning methods. We examine the efficacy of these binning methods through comparing the QCT results with quantum mechanical results, and through testing the QCT for time reversal symmetry.
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Christopher Robert RothWave Transport Phenomena in Systems with Generalized Parity-Time Symmetry
https://wesscholar.wesleyan.edu/etd_hon_theses/1285
https://wesscholar.wesleyan.edu/etd_hon_theses/1285Fri, 04 Jul 2014 07:14:19 PDT
In this thesis, we utilize the properties of scattering systems obeying anti-linear symmetries in order to produce novel wave transport phenomena. We first explore systems with delicately balanced gain and loss mechanisms, which are invariant under parity and time ($\mathcal{PT}$) reversal symmetry. Using equivalences between electronic network theory and photonic circuitry, we show that such structures can be used to produce cavities which can act simultaneously as lasers and coherent perfect absorbers. We further enrich the novel properties of these systems by introducing a gyrotropic element and develop a scattering formalism which describes their transport characteristics. We theoretically propose, and experimentally demonstrate in the radio frequency domain, a new class cavities which support reconfigurable unidirectional lasing action.
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Junsik Matthew LeeLaser Induced Plasmas in Liquid Water: From Single Pulse Breakdown to Repetitive Breakdown
https://wesscholar.wesleyan.edu/etd_hon_theses/1219
https://wesscholar.wesleyan.edu/etd_hon_theses/1219Fri, 04 Jul 2014 07:12:58 PDTRashedul HaydarCooperative Dynamics in Supported Polymer Films
https://wesscholar.wesleyan.edu/etd_hon_theses/1195
https://wesscholar.wesleyan.edu/etd_hon_theses/1195Fri, 04 Jul 2014 07:12:29 PDTPaul Zakharia Fajar HanakataAsymmetric Transport Using Nonlinear Parity-Time Symmetric Structures
https://wesscholar.wesleyan.edu/etd_hon_theses/1175
https://wesscholar.wesleyan.edu/etd_hon_theses/1175Fri, 04 Jul 2014 07:12:04 PDT
his thesis advocates for a physical mechanism which induces significant asymmetric wave-transport in scattering systems --ensuring or inhibiting substantial wave-transmission depending upon the direction of an incident wave. The specific components underpinning this mechanism are active nonlinear-elements with balanced amplification and attenuation. Initially, the validity of this mechanism is demonstrated in the framework of electronics. Subsequently the notion of directional nonlinear Fano-resonances, occurring in the presence of balanced amplification and attenuation, is incorporated into the previous design: thereby enhancing the observed asymmetry to the point of achieving giant asymmetric wave-transport. The observed non-reciprocity does not require the presence of magnetic elements, occurs for a broad range of input power, and is entirely independent of higher-harmonic generation. The hope is that the setup can be implemented as a diode in micron-scale photonic systems.
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Nicholas Edward BenderRelative Stability of Crystal and Amorphous States for Tetrahedrally Coordinated Particles and Nanostructures
https://wesscholar.wesleyan.edu/etd_hon_theses/1163
https://wesscholar.wesleyan.edu/etd_hon_theses/1163Fri, 04 Jul 2014 07:11:50 PDTJoshua Clark NeitzelEffects of Fluctuating Energy Input on the Small Scales in Turbulence
https://wesscholar.wesleyan.edu/etd_hon_theses/1122
https://wesscholar.wesleyan.edu/etd_hon_theses/1122Mon, 03 Jun 2013 05:26:06 PDTChen-chi Chien