Physical Sciences and Mathematics Commons^™

On The Radio And Optical Luminosity Evolution Of Quasars, Jack Singal, V. Petrosian, A. Lawrence, L. Stawarz

Physics Faculty Publications

We calculate simultaneously the radio and optical luminosity evolutions of quasars, and the distribution in radio loudness R defined as the ratio of radio and optical luminosities, using a flux-limited data set containing 636 quasars with radio and optical fluxes from White et al. We first note that when dealing with multi-variate data it is imperative to first determine the true correlations among the variables, not those introduced by the observational selection effects, before obtaining the individual distributions of the variables. We use the methods developed by Efron and Petrosian which are designed to obtain unbiased correlations, distributions, and evolution …

Scaling Of Losses With Size And Wavelength In Nanoplasmonics And Metamaterials, Jacob B. Khurgin, Greg Sun

Physics Faculty Publications

We show that, for the resonant metal-dielectric structures with sub-wavelength confinement of light in all three dimensions, the loss cannot be reduced considerably below the loss of the metal itself unless one operates in the far IR and THz regions of the spectrum or below. Such high losses cannot be compensated by introducing gain due to Purcell-induced shortening of recombination times. The only way low loss optical meta-materials can be engineered is with, as yet unknown, low loss materials with negative permittivity.

Transition From Static To Dynamic Macroscopic Friction In The Framework Of The Frenkel-Kontorova Model, Naum I. Gershenzon, Gust Bambakidis

Physics Faculty Publications

A new generation of experiments on dry macroscopic friction has revealed that the transition from static to dynamic friction is essentially a spatially and temporally non-uniform process, initiated by a rupture-like detachment front. We show the suitability of the Frenkel-Kontorova model for describing this transition. The model predicts the existence of two types of detachment fronts, explaining both the variability and abrupt change of velocity observed in experiments. The quantitative relation obtained between the velocity of the detachment front and the ratio of shear to normal stress is consistent with experiments. The model provides a functional dependence between slip velocity …

Overlap Statistics Of Cumuliform Boundary-Layer Cloud Fields In Large-Eddy Simulations, Roel A.J. Neggers, Thijs Heus, A. Pier Siebesma

Physics Faculty Publications

Overlap statistics of cumuliform boundary-layer clouds are studied using large-eddy simulations at high resolutions. The cloud overlap is found to be highly inefficient, due to the typical irregularity of cumuliform clouds over a wide range of scales. The detection of such inefficient overlap is enabled in this study by i) applying fine enough discretizations and ii) by limiting the analysis to exclusively cumuliform boundary-layer cloud fields. It is argued that these two factors explain the differences with some previous studies on cloud overlap. In contrast, good agreement exists with previously reported observations of cloud overlap as derived from lidar measurements …

Equation Of State From The Potts-Percolation Model Of A Solid, Miron Kaufman

Physics Faculty Publications

We expand the Potts-percolation model of a solid to include stress and strain. Neighboring atoms are connected by bonds. We set the energy of a bond to be given by the Lennard-Jones potential. If the energy is larger than a threshold the bond is more likely to fail, whereas if the energy is lower than the threshold, the bond is more likely to be alive. In two dimensions we compute the equation of state: stress as a function of interatomic distance and temperature by using renormalization-group and Monte Carlo simulations. The phase diagram, the equation of state, and the isothermal …

Chronic Fluid Flow Is An Environmental Modifier Of Renal Epithelial Function, Andrew Resnick

Physics Faculty Publications

Although solitary or sensory cilia are present in most cells of the body and their existence has been known since the sixties, very little is been known about their functions. One suspected function is fluid flow sensing- physical bending of cilia produces an influx of Ca++, which can then result in a variety of activated signaling pathways. Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a progressive disease, typically appearing in the 5th decade of life and is one of the most common monogenetic inherited human diseases, affecting approximately 600,000 people in the United States. Because ADPKD is a slowly progressing …

Terahertz Spectroscopic Reflection And Scattering Measurements Of Aligned Cnt Arrays As A Function Of Carbon Nanotube Length, Satya Ganti, Lindsay Owens, Stanley Smith Iv, Jason A. Deibel

Physics Faculty Publications

No abstract provided.

Crucible Coating Analysis By Thz Spectroscopy, Ryan Shaver, Hannah R. Jones, Jason A. Deibel

Physics Faculty Publications

No abstract provided.

Characterization Of Metameterial Devices Using Terahertz Time-Domain Spectroscopy, Hannah R. Jones, Satya Ganti, Jason A. Deibel, Ronald A. Coutu Jr.

Physics Faculty Publications

No abstract provided.

High-Power Broadband Laser Source Tunable From 3.0 Μm To 4.4 Μm Based On A Femtosecond Yb:Fiber Oscillator, Tyler W. Neely, Todd A. Johnson, Scott A. Diddams

Physics Faculty Publications

We describe a tunable broadband mid-IR laser source based on difference-frequency mixing of a 100 MHz femto second Yb:fiber laser oscillator and a Raman-shifted soliton generated with the same laser. The resulting light is tunable over 3.0 μm to 4.4 μm, with a FWHM bandwidth of 170 nm and maximum average output power up to 125 mW. The noise and coherence properties of this source are also investigated and described.

Glitter And Glints On Water, David K. Lynch, David S. P. Dearborn, James A. Lock

Physics Faculty Publications

We present new observations of glitter and glints using short and long time exposure photographs and high frame rate videos. Using the sun and moon as light sources to illuminate the ocean and laboratory water basins, we found that (1) most glitter takes place on capillary waves rather than on gravity waves, (2) certain aspects of glitter morphology depend on the presence or absence of thin clouds between the light source and the water, and (3) bent glitter paths are caused by asymmetric wave slope distributions We present computer simulations that are able to reproduce the observations and make predictions …

Self-Compensation In Semiconductors: The Zn Vacancy In Ga-Doped Zno, David C. Look, K. D. Leedy, L. Vines, B. G. Svensson, A. Zubiaga, F. Tuomisto, Daniel R. Doutt, L. J. Brillson

Physics Faculty Publications

Self-compensation, the tendency of a crystal to lower its energy by forming point defects to counter the effects of a dopant, is here quantitatively proven. Based on a new theoretical formalism and several different experimental techniques, we demonstrate that the addition of 1.4 × 10²¹-cm⁻³ Ga donors in ZnO causes the lattice to form 1.7 × 10²⁰-cm⁻³ Zn-vacancy acceptors. The calculated V_Zn formation energy of 0.2 eV is consistent with predictions from density functional theory. Our formalism is of general validity and can be used to investigate self-compensation in any degenerate semiconductor material.

Magnetic Properties Of Monolayer Co Islands On Ir(111) Probed By Spin-Resolved Scanning Tunneling Microscopy, Jessica E. Bickel, Focko Meier, Jens Brede, André Kubetzka, Kirsten Von Bergmann, Roland Wiesendanger

Physics Faculty Publications

As the characteristic length scale of devices continues to decrease, it is essential to understand the fundamental magnetic properties of reduced dimension structures. This paper examines the electronic and magnetic properties of two-dimensional nanoscale Co islands on an Ir(111) surface using spin-polarized scanning tunneling microscopy. The pseudomorphic Co islands investigated are ferromagnetic and single domain, with the magnetic easy axis normal to the sample surface. Remarkably, the coercivity of these islands is greater than 4 T and magnetic saturation of the islands requires an applied field of at least 5 T.

Variable Renewable Energy In Modeling Climate Change Mitigation Scenarios, Falko Ueckerdt, Robert J. Brecha, Gunnar Luderer, Patrick Sullivan, Eva Schmid, Nico Bauer, Diana Böttger

Physics Faculty Publications

This paper addresses the issue of how to account for short‐term temporal variability of renewable energy sources and power demand in long‐term climate change mitigation scenarios in energy‐economic models. An approach that captures in a stylized way the major challenges to the integration of variable renewable energy sources into power systems has been developed. As a first application this approach has been introduced to REMIND‐D, a hybrid energy‐economy model of Germany. An approximation of the residual load duration curve is implemented. The approximating function endogenously changes depending on the penetration and mix of variable renewable power. The approach can thus …

Thermal Annealing Effect On Spin Coherence In Zno Single Crystals, Z. Yang, David C. Look, H. M. Zhou, W. V. Kawakami, R. K. Kawakami, P. K. L. Yu, J. L. Liu

Physics Faculty Publications

The spin coherence time (T₂^*) in ZnO single crystals at 8.5 K decreases significantly from ∼11.2 ns to ∼2.3 ns after annealing at 500 °C, as indicated by time-resolved Kerr-rotation pump-probe magneto-optical spectroscopy. The annealing-induced spin coherence degradation in ZnO arises neither from crystallinity degradation during the annealing process, as confirmed by x-ray rocking curves; nor from reflection variations of the probe laser beam induced by surface roughness changes during the annealing process, as confirmed by atomic force microscopy. Temperature-dependent Hall-effect studies indicate that decreased mobility and increased shallow-donor concentration in the annealing-induced surface conducting layer …

Arcade 2 Observations Of Galactic Radio Emission, A. Kogut, D. J. Fixsen, S. M. Levin, M. Limon, P. M. Lubin, P. Mirel, M. Seiffert, Jack Singal, T. Villela, E. Wollack, C. A. Wuensche

Physics Faculty Publications

We use absolutely calibrated data from the ARCADE 2 flight in 2006 July to model Galactic emission at frequencies 3, 8, and 10 GHz. The spatial structure in the data is consistent with a superposition of free–free and synchrotron emission. Emission with spatial morphology traced by the Haslam 408 MHz survey has spectral index βsynch = −2.5±0.1, with free–free emission contributing 0.10±0.01 of the total Galactic plane emission in the lowest ARCADE 2 band at 3.15 GHz. We estimate the total Galactic emission toward the polar caps using either a simple plane-parallel model with csc |b| dependence or a model …

Arcade 2 Measurement Of The Absolute Sky Brightness At 3-90 Ghz, D. J. Fixsen, A. Kogut, S. Levin, M. Limon, P. Lubin, P. Mirel, M. Seiffert, Jack Singal, E. Wollack, T. Villela, C. A. Wuensche

Physics Faculty Publications

The ARCADE 2 instrument has measured the absolute temperature of the sky at frequencies 3, 8, 10, 30, and 90 GHz, using an open-aperture cryogenic instrument observing at balloon altitudes with no emissive windows between the beam-forming optics and the sky. An external blackbody calibrator provides an in situ reference. Systematic errors were greatly reduced by using differential radiometers and cooling all critical components to physical temperatures approximating the cosmic microwave background (CMB) temperature. A linear model is used to compare the output of each radiometer to a set of thermometers on the instrument. Small corrections are made for the …

Interpretation Of The Arcade 2 Absolute Sky Brightness Measurement, M. Seiffert, D. J. Fixsen, A. Kogut, S. M. Levin, M. Limon, P. M. Lubin, P. Mirel, Jack Singal, T. Villela, E. Wollack, C. A. Wuensche

Physics Faculty Publications

We use absolutely calibrated data between 3 and 90 GHz from the 2006 balloon flight of the ARCADE 2 instrument, along with previous measurements at other frequencies, to constrain models of extragalactic emission. Such emission is a combination of the cosmic microwave background (CMB) monopole, Galactic foreground emission, the integrated contribution of radio emission from external galaxies, any spectral distortions present in the CMB, and any other extragalactic source. After removal of estimates of foreground emission from our own Galaxy, and an estimated contribution of external galaxies, we present fits to a combination of the flat-spectrum CMB and potential spectral …

Experimental Observation Of Ion Beams In The Madison Helicon Experiment, Matt Wiebold, Yung-Ta Sung, John E. Scharer

Physics Faculty Publications

Argon ion beams up to E_b=165 eV at P_rf=500 W are observed in the Madison Helicon eXperiment (MadHeX) helicon source with a magnetic nozzle. A two-grid retarding potential analyzer (RPA) is used to measure the ion energy distribution, and emissive and rf-filtered Langmuir probes measure the plasma potential, electron density, and temperature. The supersonic ion beam (M=v_i/c_s up to 5) forms over tens of Debye lengths and extends spatially for a few ion-neutral charge-exchange mean free paths. The parametric variation of the ion beam energy is explored, including flow rate, rf power, and …

Logistic Curves, Extraction Costs And The Effective Size Of Oil Resources, Robert J. Brecha

Physics Faculty Publications

The size of potential fossil fuel resources is an issue of perennial interest and controversy. Fundamentally, there appears to be a conflict in interpretation of available data for both past and future extraction histories. As fossil-fuel prices rose dramatically over the past several years, the question of resources once again became acute. In this paper we concentrate on conventional and non-conventional oil resources and make four main points, with the overarching theme that one can determine an effective oil resource that represents significantly less availability for consumption than usually posited by tallying resources in place.

First, looking at oil production …

Dynamics Of Fingering Convection Ii: The Formation Of Thermohaline Staircases, Stephan Stellmach, Adrienne L. Traxler, Pascale Garaud, N. Brummell, T. Radko

Physics Faculty Publications

Regions of the ocean's thermocline unstable to salt fingering are often observed to host thermohaline staircases, stacks of deep well-mixed convective layers separated by thin stably stratified interfaces. Decades after their discovery, however, their origin remains controversial. In this paper we use three-dimensional direct numerical simulations to shed light on the problem. We study the evolution of an analogous double-diffusive system, starting from an initial statistically homogeneous fingering state, and find that it spontaneously transforms into a layered state. By analysing our results in the light of the mean-field theory developed in Part 1 (Traxler et al., J. Fluid …

Dynamics Of Fingering Convection I: Small-Scale Fluxes And Large-Scale Instabilities, Adrienne L. Traxler, Stephan Stellmach, Pascale Garaud, T. Radko, N. Brummell

Physics Faculty Publications

Double-diffusive instabilities are often invoked to explain enhanced transport in stably stratified fluids. The most-studied natural manifestation of this process, fingering convection, commonly occurs in the ocean's thermocline and typically increases diapycnal mixing by 2 orders of magnitude over molecular diffusion. Fingering convection is also often associated with structures on much larger scales, such as thermohaline intrusions, gravity waves and thermohaline staircases. In this paper, we present an exhaustive study of the phenomenon from small to large scales. We perform the first three-dimensional simulations of the process at realistic values of the heat and salt diffusivities and provide accurate estimates …

Mie Scattering In The Time Domain. Part Ii. The Role Of Diffraction, James A. Lock, Philip Laven

Physics Faculty Publications

The p = 0 term of the Mie-Debye scattering amplitude contains the effects of external reflection and diffraction. We computed the reflected intensity in the time domain as a function of the scattering angle and delay time for a short electromagnetic pulse incident on a spherical particle and compared it to the predicted behavior in the forward-focusing region, the specular reflection region, and the glory region. We examined the physical consequences of three different approaches to the exact diffraction amplitude, and determined the signature of diffraction in the time domain. The external reflection surface wave amplitude gradually replaces the diffraction …

Mie Scattering In The Time Domain. Part I. The Role Of Surface Waves, James A. Lock, Philip Laven

Physics Faculty Publications

We computed the Debye series p = 1 and p = 2 terms of the Mie scattered intensity as a function of scattering angle and delay time for a linearly polarized plane wave pulse incident on a spherical dielectric particle and physically interpreted the resulting numerical data. Radiation shed by electromagnetic surface waves plays a prominent role in the scattered intensity. We determined the surface wave phase and damping rate and studied the structure of the p = 1, 2 surface wave glory in the time domain. (C) 2011 Optical Society of America

Surrogate Measurement Of The 238Pu(N,F) Cross Section, J. J. Ressler, J. T. Burke, J. Escher, C. Angell, M. S. Basunia, C. W. Beausang, L. A. Bernstein, D. L. Bleuel, R. J. Casperson, B. L. Goldblum, J. Gostic, R. Hatarik, R. Henderson, R. O. Hughes, J. Munson, L. Phair, T. J. Ross, N. D. Scielzo, E. Swanberg, I. Thompson, M. Wiedeking

Physics Faculty Publications

The neutron-induced fission cross section of ²³⁸Pu was determined using the surrogate ratio method. The (n,f) cross section over an equivalent neutron energy range 5–20 MeV was deduced from inelastic α-induced fission reactions on ²³⁹Pu, with ²³⁵U(α,α′f) and ²³⁶U(α,α′f) used as references. These reference reactions reflect ²³⁴U(n,f) and ²³⁵U(n,f) yields, respectively. The deduced ²³⁸Pu(n,f) cross section agrees well with standard data libraries up to …

Impact Of Dispersion On Amplitude And Frequency Noise In A Yb-Fiber Laser Comb, Lora Nugent-Glandorf, Todd A. Johnson, Yohei Kobayashi, Scott A. Diddams

Physics Faculty Publications

We describe a Yb-fiber-based laser comb, with a focus on the relationship between the net-cavity dispersion and frequency noise on the comb. While tuning the net-cavity dispersion from anomalous to normal, we measure the relative intensity noise, offset frequency (f_CEO) linewidth, and the resulting frequency noise spectrum on the f_CEO. We find that the laser operating at zero net-cavity dispersion has many advantages, including an approximately 100× reduction in free-running f_CEO linewidth and frequency noise power spectral density when compared to the normal-dispersion regime. At the zero-dispersion point, we demonstrate a phase-locked f_{CEO …}

Propagation Dynamics Of Controlled Cross-Talk Via Interplay Between Chi((1)) And Chi((3)) Processes, Paul S. Hsu, George R. Welch, James R. Gord, Anil K. Patnaik

Physics Faculty Publications

We investigate theoretically and experimentally the propagation dynamics of a nonlinear cross-talk effect between two probe channels in a double-ladder system and show that an interplay between χ⁽¹⁾ and χ⁽³⁾ processes leads to the control of cross-talk. We derive analytical solutions to describe the propagation dynamics of the probe fields with the cross-talk effect built in. From the analytical results we identify and examine the regimes of interest where contributions of either χ⁽¹⁾ or χ⁽³⁾ or both are significant. The control of cross-talk is demonstrated experimentally, and good quantitative agreement is found between the analytical solutions …

Ga-Doped Zno Grown By Pulsed Laser Deposition In H-2: The Roles Of Ga And H, David C. Look, T. C. Droubay, J. S. Mccloy, Z. H. Zhu, S. A. Chambers

Physics Faculty Publications

Highly conductive thin films of ZnO doped with Ga were grown by pulsed laser deposition with 10 mTorr of H₂ in the growth chamber. Compared with a more conventional method of producing conductive films of ZnO, i.e., growth in O₂ followed by annealing in forming gas (5% H₂ in Ar), the H₂ method requires no postgrowth anneal and also produces higher carrier concentrations and lower resistivities with better depth uniformity. As an example, a 65-nm-thick sample had a room-temperature mobility of 32 cm²/V s, a concentration of 6.8×10²⁰ cm⁻³, and a …

Prioritizing Investment In Residential Energy Efficiency And Renewable Energy: A Case Study For The U.S. Midwest, Robert J. Brecha, Austin Mitchell, Kevin P. Hallinan, J. Kelly Kissock

Physics Faculty Publications

Residential building energy use is an important contributor to greenhouse gas emissions and in the United States represents about 20% of total energy consumption. A number of previous macro-scale studies of residential energy consumption and energy-efficiency improvements are mainly concerned with national or international aggregate potential savings. In this paper we look into the details of how a collection of specific homes in one region might reduce energy consumption and carbon emissions, with particular attention given to some practical limits to what can be achieved by upgrading the existing residential building stock. Using a simple model of residential, single-family home …

Optimization Of The Nanolens Consisting Of Coupled Metal Nanoparticles: An Analytical Approach, Greg Sun, Jacob B. Khurgin

Physics Faculty Publications

Using a simple and intuitive analytical approach, we perform optimization of a nanolens composed of coupled metal nanoparticles capable of subwavelength focusing of light inside the narrow gap separating the particles. Specifically, we optimize the structure of two nanospheres of different sizes to achieve maximum field enhancement at an off-center position in the gap. We demonstrate that the nanolens of two or more spheres acts simultaneously as an efficient antenna with large dipole and an efficient cavity with small effective volume.