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Articles 211 - 240 of 325
Full-Text Articles in Physics
A Method For Computing The Three-Dimensional Radial Distribution Function Of Cloud Particles From Holographic Images, Michael L. Larsen, Raymond Shaw
A Method For Computing The Three-Dimensional Radial Distribution Function Of Cloud Particles From Holographic Images, Michael L. Larsen, Raymond Shaw
Michigan Tech Publications, Part 1
Reliable measurements of the three-dimensional radial distribution function for cloud droplets are desired to help characterize microphysical processes that depend on local drop environment. Existing numerical techniques to estimate this three-dimensional radial distribution function are not well suited to in situ or laboratory data gathered from a finite experimental domain. This paper introduces and tests a new method designed to reliably estimate the three-dimensional radial distribution function in contexts in which (i) physical considerations prohibit the use of periodic boundary conditions and (ii) particle positions are measured inside a convex volume that may have a large aspect ratio. The method …
Cloud Droplet Size Distribution Broadening During Diffusional Growth: Ripening Amplified By Deactivation And Reactivation, Fan Yang, Pavlos Kollias, Raymond Shaw, Andrew M. Vogelmann
Cloud Droplet Size Distribution Broadening During Diffusional Growth: Ripening Amplified By Deactivation And Reactivation, Fan Yang, Pavlos Kollias, Raymond Shaw, Andrew M. Vogelmann
Michigan Tech Publications, Part 1
Cloud droplet size distributions (CDSDs), which are related to cloud albedo and rain formation, are usually broader in warm clouds than predicted from adiabatic parcel calculations. We investigate a mechanism for the CDSD broadening using a moving-size-grid cloud parcel model that considers the condensational growth of cloud droplets formed on polydisperse, submicrometer aerosols in an adiabatic cloud parcel that undergoes vertical oscillations, such as those due to cloud circulations or turbulence. Results show that the CDSD can be broadened during condensational growth as a result of Ostwald ripening amplified by droplet deactivation and reactivation, which is consistent with early work. …
Electronic And Quantum Transport Properties Of A Graphene-Bn Dot-Ring Hetero-Nanostructure, Max Seel, Ravindra Pandey
Electronic And Quantum Transport Properties Of A Graphene-Bn Dot-Ring Hetero-Nanostructure, Max Seel, Ravindra Pandey
Michigan Tech Publications, Part 1
Quantum dots, quantum rings, and, most recently, quantum dot-ring nanostructures have been studied for their interesting potential applications in nanoelectronic applications. Here, the electronic properties of a dot-ring hetero-nanostructure consisting of a graphene ring and graphene dot with a hexagonal boron nitride (h-BN) ring serving as barrier between ring and dot are investigated using density functional theory. Analysis of the character of the wave functions near the Fermi level and of the charge distribution of this dot-ring structure and calculations of the quantum transport properties find asymmetry in the conductance resonances leading to asymmetric I–V characteristics which can be modified …
Hard-Sphere-Like Dynamics In Highly Concentrated Alpha-Crystallin Suspensions, Preeti Vodnala, Laurence Lurio, Michael C. Vega, Elizabeth Gaillard
Hard-Sphere-Like Dynamics In Highly Concentrated Alpha-Crystallin Suspensions, Preeti Vodnala, Laurence Lurio, Michael C. Vega, Elizabeth Gaillard
Faculty Articles, Papers, and Other Scholarship
The dynamics of concentrated suspensions of the eye-lens protein alpha crystallin have been measured using x-ray photon correlation spectroscopy. Measurements were made at wave vectors corresponding to the first peak in the hard-sphere structure factor and volume fractions close to the critical volume fraction for the glass transition. Langevin dynamics simulations were also performed in parallel to the experiments. The intermediate scattering function f(q,τ) could be fit using a stretched exponential decay for both experiments and numerical simulations. The measured relaxation times show good agreement with simulations for polydisperse hard-sphere colloids.
The Influence Of A Surface On Hysteresis Loops For Single-Domain Ferromagnetic Nanoparticles, Saad Alsari
The Influence Of A Surface On Hysteresis Loops For Single-Domain Ferromagnetic Nanoparticles, Saad Alsari
Browse all Theses and Dissertations
The influence of surface effects on a hysteresis loop for single domain, ferromagnetic nanoparticles was examined. Theoretical equations were derived to describe the magnetic behavior of the domains and a MATLAB program was used to solve them. M-H curves were calculated for the case when a magnetic field is applied in the favorable magnetization direction (easy axis). In contrast, the calculations show there were no hysteresis loops when the magnetic field was applied perpendicular to the easy axis. Our studies showed how parameters of the surface such as a associated with saturation magnetization near the surface of nanoparticles and Ks …
Electromagnetic Properties Of Fractal Antennas, Jordan Jeffrey Ewing
Electromagnetic Properties Of Fractal Antennas, Jordan Jeffrey Ewing
Browse all Theses and Dissertations
Finite element method analysis is used to conduct electromagnetic simulations to characterize fractal antennas. This work considers wire (1D) antennas such as the triadic Koch curve, zig zag, and quadratic Koch curve of varying heights, iterations, and cross-sectional areas. Carpet (2D) antennas, including the Sierpinksi carpet, of varying heights, iterations, and deterministic and stochastic iterations are analyzed. The antenna shapes were generated in MATLAB and then modeled with finite element analysis using COMSOL Multiphysics®. The focus of this study is to determine what role various fractal patterns and iterations have on the S11 return loss and far field radiation patterns. …
Determination Of Dose Effects When Including Attenuation Of The Treatment Table Into Treatment Planning Computer Modeling, Abdullah Alshamrany
Determination Of Dose Effects When Including Attenuation Of The Treatment Table Into Treatment Planning Computer Modeling, Abdullah Alshamrany
Browse all Theses and Dissertations
During radiation treatment, the patient commonly lies on a horizontal treatment table called a couch. The material used for the couch is chosen during the manufacturing process so as to minimize the effect of the couch on dose delivery, but it still has an effect. In addition to couch attenuation on the beam, the modern approach of using multiple beam angles for dose delivery makes treatment planning in the presence of the couch more challenging. However, the effect of the couch is not always considered when creating treatment plans, generally due to treatment planning software limitations. In this evaluation, the …
Establishing A Quality Assurance Routine For Digital Imaging, Sulaiman Rana Al
Establishing A Quality Assurance Routine For Digital Imaging, Sulaiman Rana Al
Browse all Theses and Dissertations
In the clinical medical physics field, Quality Assurance (QA) is a fundamental topic to insure patient safety and effective treatment. In recent years, the imaging hardware for diagnostic x-rays has been shifting to fully digital detectors. However, the quality assurance tests for such detectors in the clinical setting is still under development. In the Medical Imaging Department of Kettering Hospital (Kettering, OH), the currently accepted method of performing QA on detectors is to use an extensive set of tests suggested by the manufacturer. This set of tests requires about 90 minutes, which is too long for daily use. The goal …
A Parallel Spectral Method Approach To Model Plasma Instabilities, Kevin S. Scheiman
A Parallel Spectral Method Approach To Model Plasma Instabilities, Kevin S. Scheiman
Browse all Theses and Dissertations
The study of solar-terrestrial plasma is concerned with processes in magnetospheric, ionospheric, and cosmic-ray physics involving different particle species and even particles of different energy within a single species. Instabilities in space plasmas and the earth's atmosphere are driven by a multitude of free energy sources such as velocity shear, gravity, temperature anisotropy, electron, and, ion beams and currents. Microinstabilities such as Rayleigh-Taylor and Kelvin-Helmholtz instabilities are important for the understanding of plasma dynamics in presence of magnetic field and velocity shear. Modeling these turbulences is a computationally demanding processes; requiring large memory and suffer from excessively long runtimes. Previous …
Molecular Dynamics Study Of Hydrogen Trapping And Helium Clustering In Tungsten, Ashok Gurung
Molecular Dynamics Study Of Hydrogen Trapping And Helium Clustering In Tungsten, Ashok Gurung
Browse all Theses and Dissertations
The field of plasma confinement and path toward achieving thermonuclear fusion started with experimental devices like tokamak and has evolved into other more complex variants of magnetic plasma confinement such as stellarator and spherical-tokamaks. As the plasma confinement machines advance towards higher temperature and plasma density (thermonuclear fusion conditions) the role and nature of plasma-wall interaction such as possible edge plasma regimes, particle recycling at the walls and its consequence for erosion, migration and re-deposition of wall material and impurity generation, transport and radiation as well as issues of particle exhaust continues to be a dominant limiting factor due to …
Experimental Validation Of The Generalized Harvey-Shack Surface Scatter Theory, Kevin T. Nattinger
Experimental Validation Of The Generalized Harvey-Shack Surface Scatter Theory, Kevin T. Nattinger
Browse all Theses and Dissertations
The Generalized Harvey-Shack (GHS) surface scatter theory claims to predict the scatter from rough surfaces over a wide domain of validity but has not been widely implemented or tested. The focus of this research is to provide a documented implementation and experimental validation of the GHS theory for the prediction of the bidirectional reflectance distribution function (BRDF) from real rough surfaces. First, the GHS theory was developed for the MATLAB software and the details of its implementation and application to experimental comparison are discussed. Next, a BRDF measurement system was designed, built, and validated. The BRDF of the Spectralon reflectance …
Phase-Space Manipulations Of Electron Beams For X-Ray Free-Electron Lasers And Inverse Compton Scattering Sources., Alexander V. Malyzhenkov
Phase-Space Manipulations Of Electron Beams For X-Ray Free-Electron Lasers And Inverse Compton Scattering Sources., Alexander V. Malyzhenkov
Graduate Research Theses & Dissertations
This dissertation describes advanced techniques of phase space manipulations of the electron beam for improving performance and efficiency of high brightness X-ray light sources based on the free-electron Laser (FEL) and inverse-Compton scattering (ICS) processes. In particular, it first discusses a novel bunch-compression scheme based on a double transverse-to-longitudinal phase-space exchanger -- dubbed emittance exchanger (EEX) -- separated by a demagnifying transverse-optics system. While the outline of the scheme is quite sophisticated, the basic physics behind it is quite straight-forward. The benefits and disadvantages of these scheme are compared to the conventional approach of compressing a bunch using a magnetic …
Diffuse Scattering And Local Order In Lead-Based Relaxor Ferroelectrics, Matthew J. Krogstad
Diffuse Scattering And Local Order In Lead-Based Relaxor Ferroelectrics, Matthew J. Krogstad
Graduate Research Theses & Dissertations
Relaxor ferroelectrics are characterized by their dielectric permittivity, and some of these materials display outstanding electromechanical coupling, a property that makes them useful in applications from sonar and ultrasound to precision actuators. However, there is a surprising lack of consensus regarding the local structure of these materials and how it relates to their useful bulk properties. A common feature of many proposed mechanisms is the importance of short-range order differing from the long-range symmetry of the material. Such a difference between short-range and long-range order makes these materials ideal candidates for study via diffuse scattering, a technique sensitive to differences …
Modelling Parallel Overhead From Simple Run-Time Records, Siegfried Höfinger, Ernst Haunschmid
Modelling Parallel Overhead From Simple Run-Time Records, Siegfried Höfinger, Ernst Haunschmid
Michigan Tech Publications, Part 1
A number of scientific applications run on current HPC systems would benefit from an approximate assessment of parallel overhead. In many instances a quick and simple method to obtain a general overview on the subject is regarded useful auxiliary information by the routine HPC user. Here we present such a method using just execution times for increasing numbers of parallel processing cores. We start out with several common scientific applications and measure the fraction of time spent in MPI communication. Forming the ratio of MPI time to overall execution time we obtain a smooth curve that can be parameterized by …
Effect Of Thermodenuding On The Structure Of Nascent Flame Soot Aggregates, Janarjan Bhandari, Swarup China, Timothy Onasch, Lindsay Wolff, Andrew Lambe, Paul Davidovits, Claudio Mazzoleni, Et Al.
Effect Of Thermodenuding On The Structure Of Nascent Flame Soot Aggregates, Janarjan Bhandari, Swarup China, Timothy Onasch, Lindsay Wolff, Andrew Lambe, Paul Davidovits, Claudio Mazzoleni, Et Al.
Michigan Tech Publications, Part 1
The optical properties (absorption and scattering) of soot particles depend on soot size and index of refraction, but also on the soot complex morphology and the internal mixing with materials that can condense on a freshly emitted (nascent) soot particle and coat it. This coating can affect the soot optical properties by refracting light, or by changing the soot aggregate structure. A common approach to studying the effect of coating on soot optical properties is to measure the absorption and scattering coefficients in ambient air, and then measure them again after removing the coating using a thermodenuder. In this approach, …
Adaptive Optics System Baseline Modeling For A Usaf Quad Axis Telescope, Nathaniel R. Morris
Adaptive Optics System Baseline Modeling For A Usaf Quad Axis Telescope, Nathaniel R. Morris
Browse all Theses and Dissertations
Atmospheric turbulence has afflicted accurate observations of celestial bodies since man first gazed upon the stars. In this past century, the technology of adaptive optics was invented to help compensate for the optical distortions that atmospheric turbulence causes. As part of that technology, artificial guide stars, wave front sensors, deformable mirrors, and other optical components were developed to correct these wave aberrations. The purpose of this study focuses on the modeling and configuration of an adaptive optics system that is appropriate for the John Bryan Observatory Quad Axis Telescope System (JBO-Q), which is funded by the United States Air Force. …
Multiscale Modeling Of Carbon Nanotube Synthesis In A Catalytic Chemical Vapor Deposition Reactor, Jonathan Troville
Multiscale Modeling Of Carbon Nanotube Synthesis In A Catalytic Chemical Vapor Deposition Reactor, Jonathan Troville
Browse all Theses and Dissertations
The bottom-up analysis of Carbon Nanotube synthesis is not well understood. Specifically, the question as to how carbon adsorbs to a substrate inclusive of a supported catalyst may lead to the energetically favorable structure of a hexagonal close- packed structure along the wall, or walls, of the tube. A first time simulation using COMSOL Multiphysics has been generated in order to capture the gas-phase mech- anism which leads to carbon production. It is thought that the carbon adsorbs and the walls are formed from the bottom up and the inside out for multi-wall CNTs. The studies involved accurately setting up …
Terahertz Molecular Spectroscopy As A Tool For Analytical Probing Of Cellular Metabolism, Mitchell Cameron Paul
Terahertz Molecular Spectroscopy As A Tool For Analytical Probing Of Cellular Metabolism, Mitchell Cameron Paul
Browse all Theses and Dissertations
Terahertz spectroscopy has found use as an analytical tool in determining chemical composition of exhaled human breath. This thesis demonstrates a novel application of this technology - analytical sensing of gaseous metabolic products of several types of human cell cultures. An innovative experimental system was developed for probing cellular metabolism using terahertz [THz] rotational spectroscopy. Gaseous emissions of cell cultures were analyzed and compared between several cell types. Cancerous and healthy lung cells as well as cancerous liver cells were studied. This technique carries a lot of promise as a noninvasive method of distinguishing between cell types and identifying cell …
A Study Of Alkali-Resistant Materials For Use In Atomic Physics Based Systems, Aaron Thomas Fletcher
A Study Of Alkali-Resistant Materials For Use In Atomic Physics Based Systems, Aaron Thomas Fletcher
Browse all Theses and Dissertations
Due to shortcomings in emerging alkali-based atomic physics based systems, a need to investigate alkali resistant materials has arisen. There is interest in alkali based systems such as atomic clocks and diode pumped alkali laser (DPAL) systems. In the case of atomic clocks and DPALs, alkali metal vapor, such as Rb, is the active part of the systems. The alkali vapor is confined in some manner of housing, but the transmission of electromagnetic radiation is required in the cells. This requires the incorporation of windows into the cell. The current window material, however, have been shown to degrade over time, …
Extraordinary Optical Transmission In Aligned Carbon Nanotube Devices At Terahertz Frequencies., Shaikhah F. Almousa
Extraordinary Optical Transmission In Aligned Carbon Nanotube Devices At Terahertz Frequencies., Shaikhah F. Almousa
Browse all Theses and Dissertations
In the phenomenon known as extraordinary optical transmission (EOT), a narrow band of selected frequencies are transmitted when incident on an array of subwavelength periodic apertures where the resonant frequency is determined by the geometry of the array of apertures and optical properties of the metal-dielectric interface. This takes place due to the excitation of surface plasmon polaritons (SPPs) at the metal and dielectric interface. Using the COMSOL Multiphysics software RF Module, a unit cell of a carbon nanotube (CNT) based EOT device is modeled in order to verify theoretical calculations of the resonant frequency using S-parameter calculations. The simulation …
Terahertz Molecular Spectroscopy As A Tool For Analytical Probing Of Cellular Metabolism, Mitchell Cameron Paul
Terahertz Molecular Spectroscopy As A Tool For Analytical Probing Of Cellular Metabolism, Mitchell Cameron Paul
Browse all Theses and Dissertations
Terahertz spectroscopy has found use as an analytical tool in determining chemical composition of exhaled human breath. This thesis demonstrates a novel application of this technology - analytical sensing of gaseous metabolic products of several types of human cell cultures. An innovative experimental system was developed for probing cellular metabolism using terahertz [THz] rotational spectroscopy. Gaseous emissions of cell cultures were analyzed and compared between several cell types. Cancerous and healthy lung cells as well as cancerous liver cells were studied. This technique carries a lot of promise as a noninvasive method of distinguishing between cell types and identifying cell …
Experimental Investigation Of A Parametric Excitation Of Whistler Waves, Nathan E. Zechar
Experimental Investigation Of A Parametric Excitation Of Whistler Waves, Nathan E. Zechar
Browse all Theses and Dissertations
Previous theoretical work has shown that a parametric interaction between electrostatic lower oblique resonance (LOR) and ion acoustic waves (IAW) can produce electromagnetic whistler waves in a cold magnetized plasma. It was also demonstrated theoretically that this interaction can more efficiently generate electromagnetic whistler waves than by direct excitation using a conventional loop antenna. For the purpose of experimentally validating the above result, an experimental facility was designed and constructed utilizing a vacuum chamber, electromagnets, and a helicon plasma source array capable of producing a volume of plasma with high density and spatial uniformity. Additionally, positioning equipment and plasma diagnostics …
Detection And Analysis Of Polyurethane Biodegradation Due To Cryptococcus Laurentii, Tyler Jacob Zicht
Detection And Analysis Of Polyurethane Biodegradation Due To Cryptococcus Laurentii, Tyler Jacob Zicht
Browse all Theses and Dissertations
Current United States aircraft are equipped with a multitude of protective coatings on the interior and exterior of the vehicle, ultimately enhancing their ability to ensure a safe and effective mission. Aircraft, over the course of their lifetime, will experience impact, corrosion, weathering, and microbial damage to its defensive structures, rendering it vulnerable to attacks. Damaged coatings are then repaired on the aircraft once detected in inspection or replaced in accordance to the lifecycle of the material on the aircraft. However potentially harmful threats such as bacteria are not considered by the Air Force to be dangerous. Therefore, the purpose …
Determination Of The Shape Of A Flattening Filter Free (Fff) Radiation Beam When Modified By A Physical Wedge, Kalel Alsaeed
Determination Of The Shape Of A Flattening Filter Free (Fff) Radiation Beam When Modified By A Physical Wedge, Kalel Alsaeed
Browse all Theses and Dissertations
The determination of a flattening filter free (FFF) beam profile when the collimator is intentionally modified to incorporate a physical wedge. Specifically, radiation beam profiles change shape when a metallic wedge is placed in the path of the beam. Examination of this unknown is necessary to ascertain whether a physical wedge is clinically beneficial for applications involving FFF beams. The aim of this study is to determine if the radiation profile of a flattening filter free beam having a physical wedge is comparable to a beam with a flattening filter, with the same wedge inserted. This research involves measurement of …
Towards A Prediction Of Landscape Evolution From Chemical Weathering And Soil Production, Eric Alan Jackson
Towards A Prediction Of Landscape Evolution From Chemical Weathering And Soil Production, Eric Alan Jackson
Browse all Theses and Dissertations
The time evolution of a periodic landscape under the influence of chemical weathering and physical erosion is computed. The model used incorporates weathering and soil production as a flux limited reaction controlled by groundwater flow. Scaling of the flow rate is obtained from a percolation theoretic treatment. The erosion of the soil material produced by this process is modeled by the diffusion of elevation, as consistent with downslope soil transport proportional to the tangent of the angle of the topography, and application of the equation of continuity to surface soil transport. Three initial topographies are examined over a periods of …
Thermoelectrical Properties Of Covetics, S. M. Sarif Rana
Thermoelectrical Properties Of Covetics, S. M. Sarif Rana
Browse all Theses and Dissertations
Covetics are hybrid materials fabricated by fusing carbon with metals in an induction furnace. There is an indication that covetics have better thermal and electrical proper-ties in comparison with pure metals. The main goal of this research is to study thermal transport in covetics measured by specific absorption rate using calorimetry. In addition, temperature distribution has been measured along the both metal and covetic wires carrying currents of 5 A and 10 A, respectively. The first set of copper covetic (Cu cov) samples with nominal content of 36 at% carbon were prepared by Third Millennium Materials Company (TMMC) in the …
Evidence For A Mixed Mass Composition At The ‘Ankle’ In The Cosmic-Ray Spectrum, A. Aab, P. Abreu, M. Aglietta, E. J. Ahn, I. Al Samarai, I. F.M. Albuquerque, B. Fick, R. Kieckhafer, D. Nitz, Et Al.
Evidence For A Mixed Mass Composition At The ‘Ankle’ In The Cosmic-Ray Spectrum, A. Aab, P. Abreu, M. Aglietta, E. J. Ahn, I. Al Samarai, I. F.M. Albuquerque, B. Fick, R. Kieckhafer, D. Nitz, Et Al.
Michigan Tech Publications, Part 1
We report a first measurement for ultrahigh energy cosmic rays of the correlation between the depth of shower maximum and the signal in the water Cherenkov stations of air-showers registered simultaneously by the fluorescence and the surface detectors of the Pierre Auger Observatory. Such a correlation measurement is a unique feature of a hybrid air-shower observatory with sensitivity to both the electromagnetic and muonic components. It allows an accurate determination of the spread of primary masses in the cosmic-ray flux. Up till now, constraints on the spread of primary masses have been dominated by systematic uncertainties. The present correlation measurement …
Conditions For Super-Adiabatic Droplet Growth After Entrainment Mixing, Fan Yang, Raymond Shaw, Huiwen Xue
Conditions For Super-Adiabatic Droplet Growth After Entrainment Mixing, Fan Yang, Raymond Shaw, Huiwen Xue
Michigan Tech Publications, Part 1
Cloud droplet response to entrainment and mixing between a cloud and its environment is considered, accounting for subsequent droplet growth during adiabatic ascent following a mixing event. The vertical profile for liquid water mixing ratio after a mixing event is derived analytically, allowing the reduction to be predicted from the mixing fraction and from the temperature and humidity for both the cloud and environment. It is derived for the limit of homogeneous mixing. The expression leads to a critical height above the mixing level: at the critical height the cloud droplet radius is the same for both mixed and unmixed …
Millimeter – Wave/Terahertz Chirped Michelson Interferometer Techniques For Sub Surface Sensing, Dinesh Amal Mirando
Millimeter – Wave/Terahertz Chirped Michelson Interferometer Techniques For Sub Surface Sensing, Dinesh Amal Mirando
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Over the last couple of decades, the field of millimeter-wave (mmW) and terahertz (THz) radiation has seen an accelerated growth thanks to developments in high quality mmW/THz sensors. These developments have contributed to many useful applications in the fields of medicine, security, construction, etc. Non-destructive evaluations such as the detection of defects in materials is currently one of the major applications of mmW/THz radiation. These evaluations are performed using mmW/THz continuous-wave radar systems. In this study, we discuss how Frequency Modulated Continuous Wave (FMCW) techniques can enhance sensing applications through the use of a Michelson interferometer. This allows multiple objects …
High Powered Pulsed Terahertz Light Generation From Superconducting Antenna Arrays, Nicholas C. Padgett
High Powered Pulsed Terahertz Light Generation From Superconducting Antenna Arrays, Nicholas C. Padgett
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Terahertz radiation is invaluable for use in spectroscopy and imaging work due to its nondestructive nature. It has become a key focus for those wishing to develop sensors capable of detecting weapons and narcotics unobtrusively and at a distance as well as characterizing materials and identifying defects. An ultrafast pulsed (femtoseconds) laser incident on a superconducting ring has been predicted to cause the emission of terahertz (THz) radiation. It is theorized that the radiation is a result of the supercurrent being modulated by the breaking and recombining of Cooper pairs on the order of picoseconds, where the time scale determines …