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Full-Text Articles in Physics

Entropy Driven Phase Transition In Polymer Gels: Mean Field Theory, Miron Kaufman Jul 2018

Entropy Driven Phase Transition In Polymer Gels: Mean Field Theory, Miron Kaufman

Physics Faculty Publications

We present a mean field model of a gel consisting of P polymers, each of length L and Nz polyfunctional monomers. Each polyfunctional monomer forms z covalent bonds with the 2P bifunctional monomers at the ends of the linear polymers. We find that the entropy dependence on the number of polyfunctional monomers exhibits an abrupt change at Nz = 2P/z due to the saturation of possible crosslinks. This non-analytical dependence of entropy on the number of polyfunctionals generates a first-order phase transition between two gel phases: one poor and the other rich in poly-functional molecules.


Mixing Enhancement In Serpentine Micromixers With A Non-Rectangular Cross-Section, Joshua Clark, Miron Kaufman, Petru S. Fodor Mar 2018

Mixing Enhancement In Serpentine Micromixers With A Non-Rectangular Cross-Section, Joshua Clark, Miron Kaufman, Petru S. Fodor

Physics Faculty Publications

In this numerical study, a new type of serpentine micromixer involving mixing units with a non-rectangular cross-section is investigated. Similar to other serpentine/spiral shaped micromixers, the design exploits the formation of transversal vortices (Dean flows) in pressure-driven systems, associated with the centrifugal forces experienced by the fluid as it is confined to move along curved geometries. In contrast with other previous designs, though, the use of non-rectangular cross-sections that change orientation between mixing units is exploited to control the center of rotation of the transversal flows formed. The associated extensional flows that thus develop between the mixing segments complement ...


Electrostatics At The Molecular Level, Ulrich Zurcher Jan 2017

Electrostatics At The Molecular Level, Ulrich Zurcher

Physics Faculty Publications

In molecular systems, positive and negative charges are separated, making them ideal systems to examine electrostatic interactions. The attractive force between positive and negative charges is balanced by repulsive ‘forces’ that are quantum-mechanical in origin. We introduce an ‘effective’ potential energy that captures the repulsion; it allows us to obtain fairly accurate estimates of the bonding properties of molecular systems. We use units (e.g., kcal mol–1 for energy) that emphasize the relevance of electrostatics to macroscopic behavior.


Factors Controlling Stratocumulus Cloud Lifetime Over Coastal Land, Mohamed S. Ghonima, Thijs Heus, Joel R. Norris, Jan Kleissl Aug 2016

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

Physics Faculty Publications

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 ...


Large-Eddy Simulation Of The Transient And Near-Equilibrium Behavior Of Precipitating Shallow Convection, Axel Seifert, Thijs Heus, Robert Pincus, Bjorn Stevens Dec 2015

Large-Eddy Simulation Of The Transient And Near-Equilibrium Behavior Of Precipitating Shallow Convection, Axel Seifert, Thijs Heus, Robert Pincus, Bjorn Stevens

Physics Faculty Publications

Large-eddy simulation is used to study the sensitivity of trade wind cumulus clouds to perturbations in cloud droplet number concentrations. We find that the trade wind cumulus system approaches a radiative-convective equilibrium state, modified by net warming and drying from imposed large-scale advective forcing. The system requires several days to reach equilibrium when cooling rates are specified but much less time, and with less sensitivity to cloud droplet number density, when radiation depends realistically on the vertical distribution of water vapor. The transient behavior and the properties of the near-equilibrium cloud field depend on the microphysical state and therefore on ...


Overlap Statistics Of Shallow Boundary Layer Clouds: Comparing Ground-Based Observations With Large-Eddy Simulations, G. Corbetta, E. Orlandi, Thijs Heus, Roel Neggers, S. Crewell Oct 2015

Overlap Statistics Of Shallow Boundary Layer Clouds: Comparing Ground-Based Observations With Large-Eddy Simulations, G. Corbetta, E. Orlandi, Thijs Heus, Roel Neggers, S. Crewell

Physics Faculty Publications

High-resolution ground-based measurements are used to assess the realism of fine-scale numerical simulations of shallow cumulus cloud fields. The overlap statistics of cumuli as produced by large-eddy simulations (LES) are confronted with Cloudnet data sets at the Jülich Observatory for Cloud Evolution. The Cloudnet pixel is small enough to detect cumuliform cloud overlap. Cloud fraction masks are derived for five different cases, using gridded time-height data sets at various temporal and vertical resolutions. The overlap ratio (R), i.e., the ratio between cloud fraction by volume and by area, is studied as a function of the vertical resolution. Good agreement ...


Mechanical Properties Of A Primary Cilium As Measured By Resonant Oscillation, Andrew Resnick Jul 2015

Mechanical Properties Of A Primary Cilium As Measured By Resonant Oscillation, Andrew Resnick

Physics Faculty Publications

Primary cilia are ubiquitous mammalian cellular substructures implicated in an ever-increasing number of regulatory pathways. The well-established ciliary hypothesis states that physical bending of the cilium (for example, due to fluid flow) initiates signaling cascades, yet the mechanical properties of the cilium remain incompletely measured, resulting in confusion regarding the biological significance of flow-induced ciliary mechanotransduction. In this work we measure the mechanical properties of a primary cilium by using an optical trap to induce resonant oscillation of the structure. Our data indicate 1) the primary cilium is not a simple cantilevered beam; 2) the base of the cilium may ...


A Model For The Force Exerted On A Primary Cilium By An Optical Trap And The Resulting Deformation, Ian Lofgren, Andrew Resnick May 2015

A Model For The Force Exerted On A Primary Cilium By An Optical Trap And The Resulting Deformation, Ian Lofgren, Andrew Resnick

Physics Faculty Publications

Cilia are slender flexible structures extending from the cell body; genetically similar to flagella. Although their existence has been long known, the mechanical and functional properties of non-motile (“primary”) cilia are largely unknown. Optical traps are a non-contact method of applying a localized force to microscopic objects and an ideal tool for the study of ciliary mechanics. We present a method to measure the mechanical properties of a cilium using an analytic model of a flexible, anchored cylinder held within an optical trap. The force density is found using the discrete-dipole approximation. Utilizing Euler-Bernoulli beam theory, we then integrate this ...


Reconciling And Validating The Cloud Thickness And Liquid Water Path Tendencies, Mohamed S. Ghonima, Joel R. Norris, Thijs Heus, Jan Kleissl May 2015

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

Physics Faculty Publications

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.


Giant Magnetization Canting Due To Symmetry Breaking In Zigzag Co Chains On Ir(001), B. Dupé, Jessica E. Bickel, Y. Mokrousov, F. Otte, Kirsten Von Bergmann, André Kubetzka, Stefan Heinze, Roland Wiesendanger Feb 2015

Giant Magnetization Canting Due To Symmetry Breaking In Zigzag Co Chains On Ir(001), B. Dupé, Jessica E. Bickel, Y. Mokrousov, F. Otte, Kirsten Von Bergmann, André Kubetzka, Stefan Heinze, Roland Wiesendanger

Physics Faculty Publications

We demonstrate a canted magnetization of biatomic zigzag Co chains grown on the (5 × 1) reconstructed Ir(001) surface using density functional theory (DFT) calculations and spin-polarized scanning tunneling microscopy (SP-STM) experiments. It is observed by STM that biatomic Co chains grow in three different structural configurations. Our DFT calculations show that they are all in a ferromagnetic (FM) state. Two chain types possess high symmetry due to two equivalent atomic strands and an easy magnetization direction that is along one of the principal crystallographic axes. The easy magnetization axis of the zigzag Co chains is canted away from the ...


Fluctuations In A Quasi-Stationary Shallow Cumulus Cloud Ensemble, M. Sakradzija, Axel Seifert, Thijs Heus Jan 2015

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

Physics Faculty Publications

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 ...


Use Of Grooved Microchannels To Improve The Performance Of Membrane-Less Fuel Cells, J. D'Alessandro, Petru S. Fodor Oct 2014

Use Of Grooved Microchannels To Improve The Performance Of Membrane-Less Fuel Cells, J. D'Alessandro, Petru S. Fodor

Physics Faculty Publications

In this work, the fluid dynamics within a membrane-less microchannel fuel cell is analyzed computationally. The membrane-less design is a result of the laminar nature of the fluid flow at small Reynolds numbers, restricting the fuel and oxidant to the vicinity of the corresponding electrodes, without the need of a proton exchange membrane (PEM). However, the performance of such cells is limited by the slow diffusive mass transport near the electrodes, with a large fraction of the reactants leaving the channel without coming in contact with the catalytic surfaces, and thus not being used. We mitigate this problem through the ...


Measurements Of Turbulent Mixing And Subsiding Shells In Trade Wind Cumuli, Jeannine Katzwinkel, Holger Siebert, Thijs Heus, Raymond A. Shaw Aug 2014

Measurements Of Turbulent Mixing And Subsiding Shells In Trade Wind Cumuli, Jeannine Katzwinkel, Holger Siebert, Thijs Heus, Raymond A. Shaw

Physics Faculty Publications

High-resolution measurements of the turbulent, thermodynamic, and microphysical structure of the edges of trade wind cumuli have been performed with the Airborne Cloud Turbulence Observation System. Lateral entrainment of subsaturated air into the cloud region leads to an evaporative cooling effect. The negatively buoyant air partly enhances the compensating downdraft, forming a subsiding shell at cloud edge. Based on the presented observations, the subsiding shell is divided into a turbulent and humid inner shell adjacent to the cloud interior and a nonbuoyant, nonturbulent outer shell. In the trade wind region, continuous development of shallow cumuli over the day allows for ...


Near Real-Time Measurement Of Forces Applied By An Optical Trap To A Rigid Cylindrical Object, Joseph Glaser, David Hoeprich, Andrew Resnick Jul 2014

Near Real-Time Measurement Of Forces Applied By An Optical Trap To A Rigid Cylindrical Object, Joseph Glaser, David Hoeprich, Andrew Resnick

Physics Faculty Publications

An automated data acquisition and processing system is established to measure the force applied by an optical trap to an object of unknown composition in real time. Optical traps have been in use for the past 40 years to manipulate microscopic particles, but the magnitude of applied force is often unknown and requires extensive instrument characterization. Measuring or calculating the force applied by an optical trap to nonspherical particles presents additional difficulties which are also overcome with our system. Extensive experiments and measurements using well-characterized objects were performed to verify the system performance.


The Impact Of The Initial Surface Reconstruction On Heteroepitaxial Film Growth And Defect Formation, Jessica E. Bickel, Joanna Mirecki Millunchick Jun 2014

The Impact Of The Initial Surface Reconstruction On Heteroepitaxial Film Growth And Defect Formation, Jessica E. Bickel, Joanna Mirecki Millunchick

Physics Faculty Publications

While it is well known that growth conditions such as temperature greatly affect defect incorporation in thin films, less is known about the direct effects of the surface reconstruction. In this work, we examine the effect of the initial surface reconstruction on defect incorporation in GaSb/GaAs(001) lattice mismatched films. The stress built up in GaSb films grown on As-terminated and Sb-terminated GaAs was monitored during film growth and shows that the total relaxation is similar in both films along the [110], but lower on the Sb-terminated surface along the . These differences can be understood by examining the ability ...


Detection And Antibiotic Treatment Of Mycoplasma Arginini Contamination In A Mouse Epithelial Cell Line Restore Normal Cell Physiology, Brianna Boslett, Subhra Nag, Andrew Resnick Mar 2014

Detection And Antibiotic Treatment Of Mycoplasma Arginini Contamination In A Mouse Epithelial Cell Line Restore Normal Cell Physiology, Brianna Boslett, Subhra Nag, Andrew Resnick

Physics Faculty Publications

Mycoplasma contamination of cultured cell lines is difficult to detect by routine observation. Infected cells can display normal morphology and the slow growth rate of mycoplasma can delay detection for extended periods of time, compromising experimental results. Positive identification of mycoplasma typically requires cells to be either fixed and stained for DNA or processed with PCR. We present a method to detect mycoplasma using live-cell optical microscopy typically used for routine observation of cell cultures. Images of untreated mycoplasma-infected epithelial cells alongside images of infected cells treated with Plasmocin, a commercially available antibiotic targeted to mycoplasma, are shown. We found ...


The Creation Of 360° Domain Walls In Ferromagnetic Nanorings By Circular Applied Magnetic Fields, Jessica E. Bickel, Spencer A. Smith, Katherine E. Aidala Feb 2014

The Creation Of 360° Domain Walls In Ferromagnetic Nanorings By Circular Applied Magnetic Fields, Jessica E. Bickel, Spencer A. Smith, Katherine E. Aidala

Physics Faculty Publications

Switching behavior in ferromagnetic nanostructures is often determined by the formation and annihilation of domain walls (DWs). In contrast to the more familiar 180° DWs found in most nanostructures, 360° DWs are the proposed transition state of nanorings. This paper examines the formation of 360° DWs created by the application of a circular magnetic field using micromagnetic simulations. 360° DWs form from pairs of canting moments that are oppositely aligned, which each grow to form rotated domains bounded by two 180° DWs and the 180° DWs combine to form 360° DWs. The resulting 360° DWs occur in pairs of opposite ...


Writing And Deleting Single Magnetic Skyrmions, Niklas Romming, Christian Hanneken, Matthias Menzel, Jessica E. Bickel, Boris Wolter, Kirsten Von Bergmann, André Kubetzka, Roland Wiesendanger Aug 2013

Writing And Deleting Single Magnetic Skyrmions, Niklas Romming, Christian Hanneken, Matthias Menzel, Jessica E. Bickel, Boris Wolter, Kirsten Von Bergmann, André Kubetzka, Roland Wiesendanger

Physics Faculty Publications

Topologically nontrivial spin textures have recently been investigated for spintronic applications. Here, we report on an ultrathin magnetic film in which individual skyrmions can be written and deleted in a controlled fashion with local spin-polarized currents from a scanning tunneling microscope. An external magnetic field is used to tune the energy landscape, and the temperature is adjusted to prevent thermally activated switching between topologically distinct states. Switching rate and direction can then be controlled by the parameters used for current injection. The creation and annihilation of individual magnetic skyrmions demonstrates the potential for topological charge in future information-storage concepts.


Automated Tracking Of Shallow Cumulus Clouds In Large Domain, Long Duration Large Eddy Simulations, Thijs Heus, Axel Seifert Jul 2013

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

Physics Faculty Publications

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 ...


Direct Numerical Simulation Of Evaporative Cooling At The Lateral Boundary Of Shallow Cumulus Clouds, Dick Abma, Thijs Heus, Juan Pedro Mellado Jul 2013

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

Physics Faculty Publications

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 ...


Visco-Elastic Properties Of Duct Tape, Ashley Brown, Ulrich Zurcher Jun 2013

Visco-Elastic Properties Of Duct Tape, Ashley Brown, Ulrich Zurcher

Physics Faculty Publications

A simple experiment for determining the nonlinear stress–strain relation of duct tape is described. After weights are added and subsequently removed, the tape does not return to its original state and is no longer taut. The tape exhibits hysteresis, which implies the loss of work during the cyclical process. The exponent describing the nonlinearity is related to the fractional work loss.


Large-Eddy Simulation Of Organized Precipitating Trade Wind Cumulus Clouds, Axel Seifert, Thijs Heus Jun 2013

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

Physics Faculty Publications

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 ...


Marine Low Cloud Sensitivity To An Idealized Climate Change: The Cgils Les Intercomparison, Peter N. Blossey, Christopher S. Bretherton, Minghua Zhang, Anning Cheng, Satoshi Endo, Thijs Heus, Yangang Liu, Adrian P. Lock, Stephan R. De Roode, Kuan Man Xu Jun 2013

Marine Low Cloud Sensitivity To An Idealized Climate Change: The Cgils Les Intercomparison, Peter N. Blossey, Christopher S. Bretherton, Minghua Zhang, Anning Cheng, Satoshi Endo, Thijs Heus, Yangang Liu, Adrian P. Lock, Stephan R. De Roode, Kuan Man Xu

Physics Faculty Publications

Subtropical marine low cloud sensitivity to an idealized climate change is compared in six large-eddy simulation (LES) models as part of CGILS. July cloud cover is simulated at three locations over the subtropical northeast Pacific Ocean, which are typified by cold sea surface temperatures (SSTs) under well-mixed stratocumulus, cool SSTs under decoupled stratocumulus, and shallow cumulus clouds overlying warmer SSTs. The idealized climate change includes a uniform 2 K SST increase with corresponding moist-adiabatic warming aloft and subsidence changes, but no change in free-tropospheric relative humidity, surface wind speed, or CO2. For each case, realistic advective forcings and boundary conditions ...


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 Jan 2013

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

Physics Faculty Publications

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 ...


Extending Newton’S Apsidal Theorem: Effective Angular Momentum, Cameron J. Tuckerman Sep 2012

Extending Newton’S Apsidal Theorem: Effective Angular Momentum, Cameron J. Tuckerman

Undergraduate Research Posters 2012

Apsidal Shift, or the angular displacement of the orbital apses, is an important quantity in the study of the orbits of planets, starts, and other celestial bodies. The apparent lack of shift of our nearby planets is that on which Sir Isaac Newton based his assumption of the inverse-square relationship in Universal Gravity. We are able to find excellent approximations for the Apsidal Shift and use our results to generalize Newton's Apsidal Theorem.


Light Scattering Study Of Elongated Particles: From Inorganic Nanorice To Polypeptide Micelles, Philip Dee Sep 2012

Light Scattering Study Of Elongated Particles: From Inorganic Nanorice To Polypeptide Micelles, Philip Dee

Undergraduate Research Posters 2012

Utilizing the powerful experimental technique of Dynamic Light Scattering (DLS) for size characterization of anisotropic particles can be extremely misleading. Unfortunately, this point is often not realized by researchers who strive for particle sizing of nanoparticles in suspensions. We present a consistent analysis of DDLS results on FeOOH nanorice and outline the potential difficulties and challenges of DDLS application for polypeptide micelles.


Continuous Single-Column Model Evaluation At A Permanent Meteorological Supersite, Roel A.J. Neggers, A. Pier Siebesma, Thijs Heus Sep 2012

Continuous Single-Column Model Evaluation At A Permanent Meteorological Supersite, Roel A.J. Neggers, A. Pier Siebesma, Thijs Heus

Physics Faculty Publications

Uncertainties in numerical predictions of weather and climate are often linked to the representation of unresolved processes that act relatively quickly compared to the resolved general circulation. These processes include turbulence, convection, clouds, and radiation. Single-column model (SCM) simulation of idealized cases and the subsequent evaluation against large-eddy simulation (LES) results has become an often used and relied on method to obtain insight at process level into the behavior of such parameterization schemes; benefits of SCM simulation are the enhanced model transparency and the high computational efficiency. Although this approach has achieved demonstrable success, some shortcomings have been identified; among ...


Geometric Constructions For Image Formation By A Converging Lens, Ulrich Zürcher Jul 2012

Geometric Constructions For Image Formation By A Converging Lens, Ulrich Zürcher

Physics Faculty Publications

Light rays emerge from an object in all directions. In introductory texts, three 'special' rays are selected to draw the image produced by lenses and mirrors. This presentation may suggest to students that these three rays are necessary for the formation of an image. We discuss that the three rays attain their 'special status' from the geometric solution of the equation of a hyperbola x−1 + y−1 = c−1 (mirror/lens equation). The material is suitable for use in introductory courses for science majors.


Information Transfer By Vector Spin Chirality In Finite Magnetic Chains, Matthias Menzel, Yuriy Mokrousov, Robert Wieser, Jessica E. Bickel, Elena Vedmedenko, Stefan Blügel, Stefan Heinze, Kirsten Von Bergmann, André Kubetzka, Roland Wiesendanger May 2012

Information Transfer By Vector Spin Chirality In Finite Magnetic Chains, Matthias Menzel, Yuriy Mokrousov, Robert Wieser, Jessica E. Bickel, Elena Vedmedenko, Stefan Blügel, Stefan Heinze, Kirsten Von Bergmann, André Kubetzka, Roland Wiesendanger

Physics Faculty Publications

Vector spin chirality is one of the fundamental characteristics of complex magnets. For a one-dimensional spin-spiral state it can be interpreted as the handedness, or rotational sense of the spiral. Here, using spin-polarized scanning tunneling microscopy, we demonstrate the occurrence of an atomic-scale spin spiral in finite individual bi-atomic Fe chains on the (5×1)−Ir(001) surface. We show that the broken inversion symmetry at the surface promotes one direction of the vector spin chirality, leading to a unique rotational sense of the spiral in all chains. Correspondingly, changes in the spin direction of one chain end can be ...


Overlap Statistics Of Cumuliform Boundary-Layer Cloud Fields In Large-Eddy Simulations, Roel A.J. Neggers, Thijs Heus, A. Pier Siebesma Nov 2011

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 ...