Physics Commons^™

Application-Specific Oxide-Based And Metal–Dielectric Thin-Film Materials Prepared By Radio Frequency Magnetron Sputtering, Mohammad Nur-E-Alam, Wade Lonsdale, Mikhail Vasiliev, Kamal Alameh

Mikhail Vasiliev

In Situ Investigation Of Magnetism In Metastable Phases Of Levitated Fe83b17 During Solidification, D. G. Quirinale, D. Messina, G. E. Rustan, Andreas Kreyssig, Ruslan Prozorov, Alan I. Goldman

A. I. Goldman

In situ measurements of structure, density, and magnetization on samples of Fe83B17 using an electrostatic levitation furnace allow us to identify and correlate the magnetic and structural transitions in this system during its complex solidification process. In particular, we identify magnetic ordering in the metastable Fe23B6/ fcc Fe coherently grown structures and primitive tetragonal Fe3B metastable phase in addition to characterizing the equilibrium Fe2B phase. Our measurements demonstrate that the incorporation of a tunnel-diode oscillator circuit within an electrostatic levitation furnace enables investigations of the physical properties of high-temperature metastable structures.

Distinct Pressure Evolution Of Coupled Nematic And Magnetic Orders In Fese, Anna E. Böhmer, Karunakar Kothapalli, Wageesha T. Jayasekara, John M. Wilde, Bing Li, Aashish Sapkota, Benjamin G. Ueland, Pinaki Das, Yumin Xiao, Wenli Bi, Jiyong Zhao, E. Ercan Alp, Sergey L. Bud’Ko, Paul C. Canfield, Alan I. Goldman, Andreas Kreyssig

A. I. Goldman

We present a microscopic study of nematicity and magnetism in FeSe over a wide temperature and pressure range using high-energy x-ray diffraction and time-domain Mössbauer spectroscopy. The low-temperature magnetic hyperfine field increases monotonically up to ∼ 6 GPa. The orthorhombic distortion initially decreases under increasing pressure but is stabilized at intermediate pressures by cooperative coupling to the pressure-induced magnetic order. Close to the reported maximum of the superconducting critical temperature at p = 6.8 GPa , the orthorhombic distortion suddenly disappears and a new tetragonal magnetic phase occurs. The pressure and temperature evolution of the structural and magnetic order parameters …

Heisenberg Model Analysis On Inelastic Powder Neutron Scattering Data Using Parent And K Doped Bamn2as2 Samples, Mehmet Ramazanoglu, Aashish Sapkota, Abhishek Pandey, Jagat Lamsal, Douglas L. Abernathy, Jennifer L. Niedziela, Matthew B. Stone, R. Salci, D. A. Acar, F. O. Oztirpan, Şener Ozonder, Andreas Kreyssig, Alan I. Goldman, David C. Johnston, Robert J. Mcqueeney

A. I. Goldman

Low temperature powder inelastic neutron scattering measurements were performed on three different powder samples; parent BaMn2As2,12.5% K-doped Ba0.875K0.125Mn2As2 and 25% K-doped Ba(0.75)K0.25Mn2As2. The Heisenberg Model involving J1‐J2‐Jz coupling constants were compared to the data by a powder integration routine using Monte Carlo integration methods. The best magnetic parameters were selected using a chi-square test where model intensities were compared to the full (q,E) dependence of magnetic scattering. A key step to this analysis is the characterization of the background which is formed mostly by phonon scattering intensities along with other sources including the magnetic impurity scattering events. The calculated powder …

Antiferromagnetic Stacking Of Ferromagnetic Layers And Doping-Controlled Phase Competition In Ca1−X Srx Co2−Y As2, Bing Li, Yuriy Sizyuk, Nediadath S. Sangeetha, John M. Wilde, Pinaki Das, W. Tian, David C. Johnston, Alan I. Goldman, Andreas Kreyssig, Peter P. Orth, Robert J. Mcqueeney, Benjamin G. Ueland

A. I. Goldman

In search of a quantum phase transition between the two-dimensional (2D) ferromagnetism of CaCo2−yAs2 and stripe-type antiferromagnetism in SrCo2 As2, we instead find evidence for 1D magnetic frustration between magnetic square Co layers. We present neutron-diffraction data for Ca1−x Srx Co2−y As2 that reveal a sequence of x -dependent magnetic transitions which involve different stacking of 2 D ferromagnetically aligned layers with different magnetic anisotropy. We explain the x-dependent changes to the magnetic order by utilizing classical analytical calculations of a 1D Heisenberg model where single-ion magnetic anisotropy and frustration of antiferromagnetic nearest- and next-nearest-layer exchange interactions are all composition …

Crystal Growth, Microstructure, And Physical Properties Of Srmnsb2, Yong Liu, Tao Ma, Warren E. Straszheim, Farhan Islam, Brandt A. Jensen, Wei Tian, Thomas Heitmann, R. A. Rosenberg, John M. Wilde, Bing Li, Andreas Kreyssig, Alan I. Goldman, Benjamin G. Ueland, Robert J. Mcqueeney, David Vaknin

A. I. Goldman

We report on the crystal and magnetic structures and magnetic and transport properties of SrMnSb2 single crystals grown by the self-flux method. Magnetic susceptibility measurements reveal an antiferromagnetic (AFM) transition at TN=295(3) K. Above TN, the susceptibility slightly increases and forms a broad peak at T∼420 K, which is a typical feature of two-dimensional magnetic systems. Neutron diffraction measurements on single crystals confirm the previously reported C-type AFM structure below TN. Both de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) effects are observed in SrMnSb2 single crystals. Analysis of the oscillatory component by a Fourier transform shows that the prominent …

Competing Magnetic Phases And Itinerant Magnetic Frustration In Srco2 As2, Bing Li, Benjamin G. Ueland, W. T. Jayasekara, D. L. Abernathy, N. S. Sangeetha, David C. Johnston, Qing-Ping Ding, Yuji Furukawa, Peter P. Orth, Andreas Kreyssig, Alan I. Goldman, Robert J. Mcqueeney

A. I. Goldman

Whereas magnetic frustration is typically associated with local-moment magnets in special geometric arrangements, here we show that SrCo2As2 is a candidate for frustrated itinerant magnetism. Using inelastic neutron scattering (INS), we find that antiferromagnetic (AF) spin fluctuations develop in the square Co layers of SrCo2As2 below T approximate to 100 K centered at the stripe-type AF propagation vector of (1/2, 1/2), and that their development is concomitant with a suppression of the uniform magnetic susceptibility determined via magnetization measurements. We interpret this switch in spectral weight as signaling a temperature-induced crossover from an instability toward ferromagnetism ordering to an instability …

Thermo-Mechanical Response Of Self-Assembled Nanoparticle Membranes, Yifan Wang, Henry Chan, Badri Narayanan, Sean P. Mcbride, Subramanian K.R.S. Sankaranarayanan, Xiao-Min Lin, Heinrich M. Jaeger

Dr. Sean P. McBride

Ultrathin membranes composed of metallic or semiconducting nanoparticles capped with short ligand molecules are hybrid materials that have attracted considerable research interest.^1-12 In contrast to two-dimensional (2D) membranes such as graphene and transition metal dichalcogenides monolayers, nanoparticle membranes can be engineered to achieve widely tunable mechanical, electronic or optical properties through different combinations of inorganic cores and organic ligands. In terms of mechanical properties, these membranes can form large area (tens of microns in diameter) freestanding structures with high Young’s moduli (~GPa) and fracture strength.^1,13-15 Molecular dynamics (MD) simulations have indicated how this mechanical robustness can arise from …

Transmission And Guiding Of Fast Electrons Through Insulating Nanocapillaries And Comparison With Ion Guiding, Susanta Das

Susanta Das

Transmission and guiding of fast electrons (500 and 1000 eV) through an insulating polyethylene terephthalate nanocapillary foil has been investigated and compared with results for slow highly charged ions. As for slow ions, guiding is attributed to charge-up of the inner walls near the capillary entrance, which, after a characteristic time, electrostatically deflects the traversing ions causing them to be guided through the sample along the capillary axis. The measurements were performed at WMU. Electron guiding is found to decrease faster with both energy and foil tilt angle than for ions. Ions lose negligible energy during the course of guiding, …

Waccmxdata, Xuguang Cai

Xuguang Cai

Ucna/Ucna+, Robert Pattie

Robert W. Pattie Jr.

The neutron provides a simple yet dynamic nuclear system to study the Standard Model of Particle Physics. The process of transforming a neutron into a proton, an electron, and an anti-neutrino contains a wealth of information in the decay rate and the kinematics of the emitted particles. Precision measurements of angular correlations in neutron β-decay can lend insight to the structure of the weak interaction and probe for physics beyond the Standard Model. The UCNA experiment at the Los Alamos Neutron Science Center is the only experiment to use ultracold neutrons to perform such a measurement, determining the β-asymmetry parameter …

Suppression Of Antiferromagnetic Spin Fluctuations In Superconducting Cr0.8 Ru0.2, M. Ramazanoglu, Benjamin G. Ueland, D. K. Pratt, L. W. Harringer, J. W. Lynn, G. Ehlers, G. E. Granroth, Sergey L. Bud’Ko, Paul C. Canfield, Deborah L. Schlagel, Alan I. Goldman, Thomas A. Lograsso, Robert J. Mcqueeney

A. I. Goldman

Unconventional superconductivity (SC) often develops in magnetic metals on the cusp of static antiferromagnetic (AFM) order where spin fluctuations are strong. This association is so compelling that many SC materials are labeled as unconventional by proximity to an ordered AFM state. The Cr-Ru alloy system possesses such a phase diagram [see Fig. 1(a)]. Here we use inelastic neutron scattering to show that spin fluctuations are present in a SC Cr0.8Ru0.2 alloy (Tc=1.35 K). However, the neutron spin resonance, a possible signature of unconventional SC, is not observed. Instead, data indicate a spin gap of order 2Δ (the superconducting gap) and …

Using Controlled Disorder To Probe The Interplay Between Charge Order And Superconductivity In Nbse2, Kyuil Cho, M. Kończykowski, Serafim Teknowijoyo, Makariy A. Tanatar, J. Guss, P. B. Gartin, John M. Wilde, A. Kreyssig, Robert Mcqueeney, Alan I. Goldman, V. Mishra, P. J. Hirschfeld, Ruslan Prozorov

A. I. Goldman

The interplay between superconductivity and charge-density wave (CDW) in 2H-NbSe2 is not fully understood despite decades of study. Artificially introduced disorder can tip the delicate balance between two competing long-range orders, and reveal the underlying interactions that give rise to them. Here we introduce disorder by electron irradiation and measure in-plane resistivity, Hall resistivity, X-ray scattering, and London penetration depth. With increasing disorder, the superconducting transition temperature, Tc, varies non-monotonically, whereas the CDW transition temperature, TCDW, monotonically decreases and becomes unresolvable above a critical irradiation dose where Tcdrops sharply. Our results imply that the CDW …

Magnetic-Field Effects On The Fragile Antiferromagnetism In Ybbipt, Benjamin G. Ueland, Andreas Kreyssig, E. D. Mun, J. W. Lynn, L. W. Harriger, D. K. Pratt, K. Prokeš, Z. Hüsges, R. Toft-Petersen, S. Sauerbrei, Scott M. Saunders, Yuji Furukawa, Sergey L. Bud’Ko, Robert J. Mcqueeney, Paul C. Canfield, Alan I. Goldman

A. I. Goldman

We present neutron-diffraction data for the cubic-heavy-fermion YbBiPt that show broad magnetic diffraction peaks due to the fragile short-range antiferromagnetic (AFM) order persist under an applied magnetic-field H. Our results for H perpendicular to[(1) over bar 1 0] and a temperature of T = 0.14(1) K show that the (1/2,1/2,3/2) magnetic diffraction peak can be described by the same two-peak line shape found for mu H-0 = 0T below the Neel temperature of T-N = 0.4 K. Both components of the peak exist for mu H-0 less than or similar to 1.4 T, which is well past the AFM phase …

Surface Plasmon Induced Enhancement In Selective Laser Melting Processes, Dentcho A. Genov, Raj K. Vinnakota

Dentcho Genov

Turbulent Dispersion In Cloudy Boundary Layers, Remco A. Verzijlbergh, Harmen J.J. Jonker, Thijs Heus, J. Vilà-Guerau De Arellano

Thijs Heus

Compared to dry boundary layers, dispersion in cloud-topped boundary layers has received less attention. In this LES based numerical study we investigate the dispersion of a passive tracer in the form of Lagrangian particles for four kinds of atmospheric boundary layers: 1) a dry convective boundary layer (for reference), 2) a "smoke" cloud boundary layer in which the turbulence is driven by radiative cooling, 3) a stratocumulus topped boundary layer and 4) a shallow cumulus topped boundary layer. We show that the dispersion characteristics of the smoke cloud boundary layer as well as the stratocumulus situation can be well understood …

Observational Validation Of The Compensating Mass Flux Through The Shell Around Cumulus Clouds, Thijs Heus, C. Freek J. Pols, Harmen J.J. Jonker, Harry E.A. Van Den Akker, Donald H. Lenschow

Thijs Heus

The existence of a subsiding shell around cumulus clouds has been observed before in several aircraft measurement campaigns. Recent results from large-eddy simulations (LES) showed that the downward mass flux through the shell compensates for a significant fraction of the upward mass flux through the cloud. In this study, aeroplane measurements from the Rain In Cumulus over the Ocean (RICO) field campaign are used to verify the existence of this compensating mass flux. Just as in the LES results, the in-shell downward mass flux is found to be significant. However, a few differences were found in comparison with the LES …

Reconciling And Validating The Cloud Thickness And Liquid Water Path Tendencies, Mohamed S. Ghonima, Joel R. Norris, Thijs Heus, Jan Kleissl

Thijs Heus

A detailed derivation of stratocumulus cloud thickness and liquid water path tendencies as a function of the well-mixed boundary layer mass, heat, and moisture budget equations is presented. The derivation corrects an error in the cloud thickness tendency equation derived by R. Wood to make it consistent with the liquid water path tendency equation derived by J. J. van der Dussen et al. The validity of the tendency equations is then tested against the output of large-eddy simulations of a typical stratocumulus-topped boundary layer case and is found to be in good agreement.

Large-Eddy Simulation Of Organized Precipitating Trade Wind Cumulus Clouds, Axel Seifert, Thijs Heus

Thijs Heus

Trade wind cumulus clouds often organize in along-wind cloud streets and across-wind mesoscale arcs. We present a benchmark large-eddy simulation which resolves the individual clouds as well as the mesoscale organization on scales of O(10 km). Different methods to quantify organization of cloud fields are applied and discussed. Using perturbed physics large-eddy simulation experiments, the processes leading to the formation of cloud clusters and the mesoscale arcs are revealed. We find that both cold pools as well as the sub-cloud layer moisture field are crucial to understand the organization of precipitating shallow convection. Further sensitivity studies show that microphysical assumptions …

Formulation Of The Dutch Atmospheric Large-Eddy Simulation (Dales) And Overview Of Its Applications, Thijs Heus, C. C. Van Heerwaarden, Harmen J.J. Jonker, A. Pier Siebesma, S. Axelsen, K. Van Den Dries, O. Geoffroy, A. F. Moene, D. Pino, S. R. De Roode, J. Vilà-Guerau De Arellano

Thijs Heus

The current version of the Dutch Atmospheric Large-Eddy Simulation (DALES) is presented. DALES is a large-eddy simulation code designed for studies of the physics of the atmospheric boundary layer, including convective and stable boundary layers as well as cloudy boundary layers. In addition, DALES can be used for studies of more specific cases, such as flow over sloping or heterogeneous terrain, and dispersion of inert and chemically active species. This paper contains an extensive description of the physical and numerical formulation of the code, and gives an overview of its applications and accomplishments in recent years.

Factors Controlling Stratocumulus Cloud Lifetime Over Coastal Land, Mohamed S. Ghonima, Thijs Heus, Joel R. Norris, Jan Kleissl

Thijs Heus

The breakup of stratocumulus clouds over coastal land areas is studied using a combination of large-eddy simulations (LESs) and mixed-layer models (MLMs) with a focus on mechanisms regulating the timing of the breakup. In contrast with stratocumulus over ocean, strong sensible heat flux over land prevents the cloud layer from decoupling during day. As the cloud thins during day, turbulence generated by surface flux becomes larger than turbulence generated by longwave cooling across the cloud layer. To capture this shift in turbulence generation in the MLM, an existing entrainment parameterization is extended. The MLM is able to mimic cloud evolution …

Direct Numerical Simulation Of Evaporative Cooling At The Lateral Boundary Of Shallow Cumulus Clouds, Dick Abma, Thijs Heus, Juan Pedro Mellado

Thijs Heus

This study investigates the dynamics of the subsiding shell at the lateral boundary of cumulus clouds, focusing on the role of evaporative cooling. Since the size of this shell is well below what large-eddy simulations can resolve, the authors have performed direct numerical simulations of an idealized subsiding shell. The system develops a self-similar, Reynolds number–independent flow that allows for the determination of explicit scaling laws relating the characteristic length, time, and velocity scales of the shell. It is found that the shell width grows quadratically in time, linearly with the traveled distance. The magnitude of these growth rates shows …

Fluctuations In A Quasi-Stationary Shallow Cumulus Cloud Ensemble, M. Sakradzija, Axel Seifert, Thijs Heus

Thijs Heus

We propose an approach to stochastic parameterisation of shallow cumulus clouds to represent the convective variability and its dependence on the model resolution. To collect information about the individual cloud lifecycles and the cloud ensemble as a whole, we employ a large eddy simulation (LES) model and a cloud tracking algorithm, followed by conditional sampling of clouds at the cloud-base level. In the case of a shallow cumulus ensemble, the cloud-base mass flux distribution is bimodal, due to the different shallow cloud subtypes, active and passive clouds. Each distribution mode can be approximated using a Weibull distribution, which is a …

Automated Tracking Of Shallow Cumulus Clouds In Large Domain, Long Duration Large Eddy Simulations, Thijs Heus, Axel Seifert

Thijs Heus

This paper presents a method for feature tracking of fields of shallow cumulus convection in large eddy simulations (LES) by connecting the projected cloud cover in space and time, and by accounting for splitting and merging of cloud objects. Existing methods tend to be either imprecise or, when using the full three-dimensional (3-D) spatial field, prohibitively expensive for large data sets. Compared to those 3-D methods, the current method reduces the memory footprint by up to a factor 100, while retaining most of the precision by correcting for splitting and merging events between different clouds. The precision of the algorithm …

A Statistical Approach To The Life Cycle Analysis Of Cumulus Clouds Selected In A Virtual Reality Environment, Thijs Heus, Harmen J.J. Jonker, Harry E.A. Van Den Akker, Eric J. Griffith, Michal Koutek, Frits H. Post

Thijs Heus

In this study, a new method is developed to investigate the entire life cycle of shallow cumuli in large eddy simulations. Although trained observers have no problem in distinguishing the different life stages of a cloud, this process proves difficult to automate, because cloud-splitting and cloud-merging events complicate the distinction between a single system divided in several cloudy parts and two independent systems that collided. Because the human perception is well equipped to capture and to make sense of these time-dependent three-dimensional features, a combination of automated constraints and human inspection in a three-dimensional virtual reality environment is used to …

Cgils: Results From The First Phase Of An International Project To Understand The Physical Mechanisms Of Low Cloud Feedbacks In Single Column Models, Minghua Zhang, Christopher S. Bretherton, Peter N. Blossey, Phillip H. Austin, Julio T. Bacmeister, Sandrine Bony, Florent Brient, Suvarchal K. Cheedela, Anning Cheng, Anthony D. Del Genio, Stephan R. De Roode, Satoshi Endo, Charmaine N. Franklin, Jean Christophe Golaz, Cecile Hannay, Thijs Heus

Thijs Heus

CGILS—the CFMIP-GASS Intercomparison of Large Eddy Models (LESs) and single column models (SCMs)—investigates the mechanisms of cloud feedback in SCMs and LESs under idealized climate change perturbation. This paper describes the CGILS results from 15 SCMs and 8 LES models. Three cloud regimes over the subtropical oceans are studied: shallow cumulus, cumulus under stratocumulus, and well-mixed coastal stratus/stratocumulus. In the stratocumulus and coastal stratus regimes, SCMs without activated shallow convection generally simulated negative cloud feedbacks, while models with active shallow convection generally simulated positive cloud feedbacks. In the shallow cumulus alone regime, this relationship is less clear, likely due to …

Development And Long-Term Stability Of A Comprehensive Daily Qa Program For A Modern Pencil Beam Scanning (Pbs) Proton Therapy Delivery System, Suresh Rana, Jaafar Bennouna, Alonso Gutierrez

Alonso Gutierrez

No abstract provided.

Development And Long-Term Stability Of A Comprehensive Daily Qa Program For A Modern Pencil Beam Scanning (Pbs) Proton Therapy Delivery System, Suresh Rana, Jaafar Bennouna, Alonso Gutierrez

Jaafar Bennouna

No abstract provided.

Development And Long-Term Stability Of A Comprehensive Daily Qa Program For A Modern Pencil Beam Scanning (Pbs) Proton Therapy Delivery System, Suresh Rana, Jaafar Bennouna, Alonso Gutierrez

Suresh Rana

No abstract provided.

New Tests Of General Relativity, Quentin Bailey

Quentin Bailey

The last decade has seen a rapid increase in the number of precision tests of relativity. This research has been motivated by the intriguing possibility that tiny deviations from relativity might arise in the underlying theory that is widely believed to successfully mesh General Relativity (GR) with quantum physics. Many of these tests have been analyzed within an effective field theory framework which generically describes possible deviations from exact relativity and contains some traditional test frameworks as limiting cases. One part of the activity has been a resurgence of interest in tests of relativity in the Minkowski-spacetime context, where Lorentz …