NASA Technical Reports Server (NTRS)
Buczek, M. B.; Gregory, M. A.; Herakovich, C. T.
1983-01-01
CLFE2D is a two dimensional generalized plane strain finite element code, using a linear, four node, general quadrilateral, isoparametric element. The program is developed to calculate the displacements, strains, stresses, and strain energy densities in a finite width composite laminate. CLFE2D offers any combination of the following load types: nodal displacements, nodal forces, uniform normal strain, or hygrothermal. The program allows the user to input one set of three dimensional orthotropic material properties. The user can then specify the angle of material principal orientation for each element in the mesh. Output includes displacements, stresses, strains and strain densities at points selected by the user. An option is also available to plot the underformed and deformed finite element meshes.
Antenna coupled detectors for 2D staring focal plane arrays
NASA Astrophysics Data System (ADS)
Gritz, Michael A.; Kolasa, Borys; Lail, Brian; Burkholder, Robert; Chen, Leonard
2013-06-01
Millimeter-wave (mmW)/sub-mmW/THz region of the electro-magnetic spectrum enables imaging thru clothing and other obscurants such as fog, clouds, smoke, sand, and dust. Therefore considerable interest exists in developing low cost millimeter-wave imaging (MMWI) systems. Previous MMWI systems have evolved from crude mechanically scanned, single element receiver systems into very complex multiple receiver camera systems. Initial systems required many expensive mmW integrated-circuit low-noise amplifiers. In order to reduce the cost and complexity of the existing systems, attempts have been made to develop new mmW imaging sensors employing direct detection arrays. In this paper, we report on Raytheon's recent development of a unique focal plane array technology, which operates broadly from the mmW through the sub-mmW/THz region. Raytheon's innovative nano-antenna based detector enables low cost production of 2D staring mmW focal plane arrays (mmW FPA), which not only have equivalent sensitivity and performance to existing MMWI systems, but require no mechanical scanning.
Basal-plane dislocations in bilayer graphene - Peculiarities in a quasi-2D material
NASA Astrophysics Data System (ADS)
Butz, Benjamin
2015-03-01
Dislocations represent one of the most fascinating and fundamental concepts in materials science. First and foremost, they are the main carriers of plastic deformation in crystalline materials. Furthermore, they can strongly alter the local electronic or optical properties of semiconductors and ionic crystals. In layered crystals like graphite dislocation movement is restricted to the basal plane. Thus, those basal-plane dislocations cannot escape enabling their confinement in between only two atomic layers of the material. So-called bilayer graphene is the thinnest imaginable quasi-2D crystal to explore the nature and behavior of dislocations under such extreme boundary conditions. Robust graphene membranes derived from epitaxial graphene on SiC provide an ideal platform for their investigation. The presentation will give an insight in the direct observation of basal-plane partial dislocations by transmission electron microscopy and their detailed investigation by diffraction contrast analysis and atomistic simulations. The investigation reveals striking size effects. First, the absence of stacking fault energy, a unique property of bilayer graphene, leads to a characteristic dislocation pattern, which corresponds to an alternating AB <--> BA change of the stacking order. Most importantly, our experiments in combination with atomistic simulations reveal a pronounced buckling of the bilayer graphene membrane, which directly results from accommodation of strain. In fact, the buckling completely changes the strain state of the bilayer graphene and is of key importance for its electronic/spin transport properties. Due to the high degree of disorder in our quasi-2D material it is one of the very few examples for a perfect linear magnetoresistance, i.e. the linear dependency of the in-plane electrical resistance on a magnetic field applied perpendicular to the graphene sheet up to field strengths of more than 60 T. This research is financed by the German Research
Improvement of the 2D/1D Method in MPACT Using the Sub-Plane Scheme
Graham, Aaron M; Collins, Benjamin S; Downar, Thomas
2017-01-01
Oak Ridge National Laboratory and the University of Michigan are jointly developing the MPACTcode to be the primary neutron transport code for the Virtual Environment for Reactor Applications (VERA). To solve the transport equation, MPACT uses the 2D/1D method, which decomposes the problem into a stack of 2D planes that are then coupled with a 1D axial calculation. MPACT uses the Method of Characteristics for the 2D transport calculations and P3 for the 1D axial calculations, then accelerates the solution using the 3D Coarse mesh Finite Dierence (CMFD) method. Increasing the number of 2D MOC planes will increase the accuracy of the alculation, but will increase the computational burden of the calculations and can cause slow convergence or instability. To prevent these problems while maintaining accuracy, the sub-plane scheme has been implemented in MPACT. This method sub-divides the MOC planes into sub-planes, refining the 1D P3 and 3D CMFD calculations without increasing the number of 2D MOC planes. To test the sub-plane scheme, three of the VERA Progression Problems were selected: Problem 3, a single assembly problem; Problem 4, a 3x3 assembly problem with control rods and pyrex burnable poisons; and Problem 5, a quarter core problem. These three problems demonstrated that the sub-plane scheme can accurately produce intra-plane axial flux profiles that preserve the accuracy of the fine mesh solution. The eigenvalue dierences are negligibly small, and dierences in 3D power distributions are less than 0.1% for realistic axial meshes. Furthermore, the convergence behavior with the sub-plane scheme compares favorably with the conventional 2D/1D method, and the computational expense is decreased for all calculations due to the reduction in expensive MOC calculations.
Turbulent Plane Wakes Subjected to Successive Strains
NASA Technical Reports Server (NTRS)
Rogers, Michael M.
2003-01-01
Six direct numerical simulations of turbulent time-evolving strained plane wakes have been examined to investigate the response of a wake to successive irrotational plane strains of opposite sign. The orientation of the applied strain field has been selected so that the flow is the time-developing analogue of a spatially developing wake evolving in the presence of either a favourable or an adverse streamwise pressure gradient. The magnitude of the applied strain rate a is constant in time t until the total strain e(sup at) reaches about four. At this point, a new simulation is begun with the sign of the applied strain being reversed (the original simulation is continued as well). When the total strain is reduced back to its original value of one, yet another simulation is begun with the sign of the strain being reversed again back to its original sign. This process is done for both initially "favourable" and initially "adverse" strains, providing simulations for each of these strain types from three different initial conditions. The evolution of the wake mean velocity deficit and width is found to be very similar for all the adversely strained cases, with both measures rapidly achieving exponential growth at the rate associated with the cross-stream expansive strain e(sup at). In the "favourably" strained cases, the wake widths approach a constant and the velocity deficits ultimately decay rapidly as e(sup -2at). Although all three of these cases do exhibit the same asymptotic exponential behaviour, the time required to achieve this is longer for the cases that have been previously adversely strained (by at approx. equals 1). These simulations confirm the generality of the conclusions drawn in Rogers (2002) regarding the response of plane wakes to strain. The evolution of strained wakes is not consistent with the predictions of classical self-similar analysis; a more general equilibrium similarity solution is required to describe the results. At least for the cases
Ultrafast vascular strain compounding using plane wave transmission.
Hansen, H H G; Saris, A E C M; Vaka, N R; Nillesen, M M; de Korte, C L
2014-03-03
Deformations of the atherosclerotic vascular wall induced by the pulsating blood can be estimated using ultrasound strain imaging. Because these deformations indirectly provide information on mechanical plaque composition, strain imaging is a promising technique for differentiating between stable and vulnerable atherosclerotic plaques. This paper first explains 1-D radial strain estimation as applied intravascularly in coronary arteries. Next, recent methods for noninvasive vascular strain estimation in a transverse imaging plane are discussed. Finally, a compounding technique that our group recently developed is explained. This technique combines motion estimates of subsequently acquired focused ultrasound images obtained at various insonification angles. However, because the artery moves and deforms during the multi-angle acquisition, errors are introduced when compounding. Recent advances in computational power have enabled plane wave ultrasound acquisition, which allows 100 times faster image acquisition and thus might resolve the motion artifacts. In this paper the performance of strain imaging using plane wave compounding is investigated using simulations of an artery with a vulnerable plaque and experimental data of a two-layered vessel phantom. The results show that plane wave compounding outperforms 0° focused strain imaging. For the simulations, the root mean squared error reduced by 66% and 50% for radial and circumferential strain, respectively. For the experiments, the elastographic signal-to-noise and contrast-to-noise ratio (SNR(e) and CNR(e)) increased with 2.1 dB and 3.7 dB radially, and 5.6 dB and 16.2dB circumferentially. Because of the high frame rate, the plane wave compounding technique can even be further optimized and extended to 3D in future.
Fekkes, Stein; Swillens, Abigail E S; Hansen, Hendrik H G; Saris, Anne E C M; Nillesen, Maartje M; Iannaccone, Francesco; Segers, Patrick; de Korte, Chris L
2016-08-25
Three-dimensional strain estimation might improve the detection and localization of high strain regions in the carotid artery for identification of vulnerable plaques. This study compares 2D vs. 3D displacement estimation in terms of radial and circumferential strain using simulated ultrasound images of a patient specific 3D atherosclerotic carotid artery model at the bifurcation embedded in surrounding tissue generated with ABAQUS software. Global longitudinal motion was superimposed to the model based on literature data. A Philips L11-3 linear array transducer was simulated which transmitted plane waves at 3 alternating angles at a pulse repetition rate of 10 kHz. Inter-frame radiofrequency ultrasound data were simulated in Field II for 191 equally spaced longitudinal positions of the internal carotid artery. Accumulated radial and circumferential displacements were estimated using tracking of the inter-frame displacements estimated by a two-step normalized cross-correlation method and displacement compounding. Least squares strain estimation was performed to determine accumulated radial and circumferential strain. The performance of the 2D and 3D method was compared by calculating the root-mean-squared error of the estimated strains with respect to the reference strains obtained from the model. More accurate strain images were obtained using the 3D displacement estimation for the entire cardiac cycle. The 3D technique clearly outperformed the 2D technique in phases with high inter-frame longitudinal motion. In fact the large inter-frame longitudinal motion rendered it impossible to accurately track the tissue and cumulate strains over the entire cardiac cycle with the 2D technique.
Fekkes, Stein; Swillens, Abigail E S; Hansen, Hendrik H G; Saris, Anne E C M; Nillesen, Maartje M; Iannaccone, Francesco; Segers, Patrick; de Korte, Chris L
2016-10-01
Three-dimensional (3-D) strain estimation might improve the detection and localization of high strain regions in the carotid artery (CA) for identification of vulnerable plaques. This paper compares 2-D versus 3-D displacement estimation in terms of radial and circumferential strain using simulated ultrasound (US) images of a patient-specific 3-D atherosclerotic CA model at the bifurcation embedded in surrounding tissue generated with ABAQUS software. Global longitudinal motion was superimposed to the model based on the literature data. A Philips L11-3 linear array transducer was simulated, which transmitted plane waves at three alternating angles at a pulse repetition rate of 10 kHz. Interframe (IF) radio-frequency US data were simulated in Field II for 191 equally spaced longitudinal positions of the internal CA. Accumulated radial and circumferential displacements were estimated using tracking of the IF displacements estimated by a two-step normalized cross-correlation method and displacement compounding. Least-squares strain estimation was performed to determine accumulated radial and circumferential strain. The performance of the 2-D and 3-D methods was compared by calculating the root-mean-squared error of the estimated strains with respect to the reference strains obtained from the model. More accurate strain images were obtained using the 3-D displacement estimation for the entire cardiac cycle. The 3-D technique clearly outperformed the 2-D technique in phases with high IF longitudinal motion. In fact, the large IF longitudinal motion rendered it impossible to accurately track the tissue and cumulate strains over the entire cardiac cycle with the 2-D technique.
Phase states of a 2D easy-plane ferromagnet with strong inclined anisotropy
Fridman, Yu. A. Klevets, F. N.; Gorelikov, G. A.; Meleshko, A. G.
2012-12-15
We investigate the spin states of a 2D film exhibiting easy-axis anisotropy and a strong single-ion inclined anisotropy whose axis forms a certain angle with the normal to the film surface. Such a system may have an angular ferromagnetic phase, a spatially inhomogeneous state, and a quadrupole phase, whose realization depends substantially on the inclined anisotropy and the orientation of the wavevector in the film plane.
Strain-induced Fermi contour anisotropy of GaAs (311)A 2D holes
NASA Astrophysics Data System (ADS)
Shabani, Javad; Shayegan, Mansour; Winkler, Roland
2008-03-01
There is considerable current interest in electronic properties of two-dimensional (2D) carriers whose energy bands are spin-split at finite values of in-plane wave vector, thanks to the spin-orbit interaction and the lack of inversion symmetry. We report experimental and theoretical results revealing that the spin-subband Fermi contours of the heavy and light heavy-holes (HHh and HHl) can be tuned in high mobility GaAs (311)A 2D hole systems via the application of symmetry-breaking in-plane strain. Our calculations show that the HHl spin-subband Fermi contour is circular but the HHh spin-subband Fermi contour is distorted. Experimentally, we probe the Fermi contour anisotropy by measuring the magneto-resistance commensurability peaks induced by square arrays of antidots. When the spin splitting is sufficiently large, the magneto-resistance trace exhibits two peaks, providing clear evidence for spin-resolved ballistic transport. The experimental results are in good agreement with the calculations, and confirm that the majority spin-subband (HHh) has a severely distorted Fermi contour whose anisotropy can be tuned with strain while Fermi contour of the minority spin-subband (HHl) remains nearly isotropic.
Dynamic Shear Band Development in Plane Strain,
1987-11-01
dicular to the initial propagation direction slows (town and further straining occurs inl a hand. The ul1timlate course of events is essentially...pr scribed velocita oal ysiave e n/sec. lie order of ilacint fiie V1 = -3 I/seecorrspon i toean avera elcirt of -300/etersos(i setal *" increase inl ...Spitzig, WV.A., 1980, *Initiation of Localized Shear Bands inl Plane Siraiii..1. .1lcch. Phys. Solids. \\Vol. 28, pp. 113-128. Asaro. R.J., 1983
Plane Strain Deformation in Generalized Thermoelastic Diffusion
NASA Astrophysics Data System (ADS)
Sharma, Nidhi; Kumar, Rajneesh; Ram, Paras
2008-08-01
The present investigation is concerned with plane strain deformation in homogeneous isotropic generalized thermoelastic diffusion subjected to a normal force, thermal source, and chemical potential source. Laplace and Fourier transform techniques are employed to solve the problem. The integral transform have been inverted by using a numerical technique to obtain the displacements, stresses, temperature distribution, and chemical potential distribution. The numerical results of these quantities are illustrated graphically to depict the response of various sources in the theories of thermoelastic diffusion and thermoelasticity for a particular model. Some particular cases have been deduced from the present investigation.
Well-posedness and generalized plane waves simulations of a 2D mode conversion model
Imbert-Gérard, Lise-Marie
2015-12-15
Certain types of electro-magnetic waves propagating in a plasma can undergo a mode conversion process. In magnetic confinement fusion, this phenomenon is very useful to heat the plasma, since it permits to transfer the heat at or near the plasma center. This work focuses on a mathematical model of wave propagation around the mode conversion region, from both theoretical and numerical points of view. It aims at developing, for a well-posed equation, specific basis functions to study a wave mode conversion process. These basis functions, called generalized plane waves, are intrinsically based on variable coefficients. As such, they are particularly adapted to the mode conversion problem. The design of generalized plane waves for the proposed model is described in detail. Their implementation within a discontinuous Galerkin method then provides numerical simulations of the process. These first 2D simulations for this model agree with qualitative aspects studied in previous works.
Lee, Jaekwang; Huang, Jingsong; Sumpter, Bobby G.; ...
2017-02-17
Compared with their bulk counterparts, 2D materials can sustain much higher elastic strain at which optical quantities such as bandgaps and absorption spectra governing optoelectronic device performance can be modified with relative ease. Using first-principles density functional theory and quasiparticle GW calculations, we demonstrate how uniaxial tensile strain can be utilized to optimize the electronic and optical properties of transition metal dichalcogenide lateral (in-plane) heterostructures such as MoX2/WX2 (X = S, Se, Te). We find that these lateral-type heterostructures may facilitate efficient electron–hole separation for light detection/harvesting and preserve their type II characteristic up to 12% of uniaxial strain. Basedmore » on the strain-dependent bandgap and band offset, we show that uniaxial tensile strain can significantly increase the power conversion efficiency of these lateral heterostructures. Our results suggest that these strain-engineered lateral heterostructures are promising for optimizing optoelectronic device performance by selectively tuning the energetics of the bandgap.« less
Measurements of 2D turbulent spectra on a beta-plane
NASA Astrophysics Data System (ADS)
Baroud, Charles N.; Plapp, Brendan B.; Swinney, Harry L.
2000-11-01
The existence of coherent structures and a β-plane can affect the scaling of energy in two-dimensional turbulence. We study an azimuthal turbulent jet in a rotating annular tank with a sloped bottom (β-plane). Rotation constrains the dynamics to be 2D. The velocity field is measured using Particle Image Velocimetry which allows us to track the time evolution of features such as waves or vortices. Our measurements of the energy spectra capture simultaneously an inverse energy cascade and a forward enstrophy cascade. The energy injection wavenumber ki is deduced from these spectra. Below the Rhines wavenumber (k_β = (β/2 u)^1/2), energy transfer is dominated by the dispersion of Rossby waves. By nonlinearly transforming our coordinates, we isolate the effects of long-lived vortices on the scaling of the spectra. We find that as a result of these coherent structures the exponent decreases below -3 for k>k_i, and it decreases below -5/3 for k
Strained layer superlattice focal plane array having a planar structure
Kim, Jin K; Carroll, Malcolm S; Gin, Aaron; Marsh, Phillip F; Young, Erik W; Cich, Michael J
2012-10-23
An infrared focal plane array (FPA) is disclosed which utilizes a strained-layer superlattice (SLS) formed of alternating layers of InAs and In.sub.xGa.sub.1-xSb with 0.ltoreq.x.ltoreq.0.5 epitaxially grown on a GaSb substrate. The FPA avoids the use of a mesa structure to isolate each photodetector element and instead uses impurity-doped regions formed in or about each photodetector for electrical isolation. This results in a substantially-planar structure in which the SLS is unbroken across the entire width of a 2-D array of the photodetector elements which are capped with an epitaxially-grown passivation layer to reduce or eliminate surface recombination. The FPA has applications for use in the wavelength range of 3-25 .mu.m.
Robust initialization for 2D/3D registration of knee implant models to single-plane fluoroscopy
NASA Astrophysics Data System (ADS)
Hermans, J.; Claes, P.; Bellemans, J.; Vandermeulen, D.; Suetens, P.
2007-03-01
A fully automated initialization method is proposed for the 2D/3D registration of 3D CAD models of knee implant components to a single-plane calibrated fluoroscopy. The algorithm matches edge segments, detected in the fluoroscopy image, with pre-computed libraries of expected 2D silhouettes of the implant components. Each library entry represents a different combination of out-of-plane registration transformation parameters. Library matching is performed by computing point-based 2D/2D registrations in between each library entry and each detected edge segment in the fluoroscopy image, resulting in an estimate of the in-plane registration transformation parameters. Point correspondences for registration are established by template matching of the bending patterns on the contours. A matching score for each individual 2D/2D registration is computed by evaluating the transformed library entry in an edge-encoded (characteristic) image, which is derived from the original fluoroscopy image. A matching scores accumulator is introduced to select and suggest one or more initial pose estimates. The proposed method is robust against occlusions and partial segmentations. Validation results are shown on simulated fluoroscopy images. In all cases a library match is found for each implant component which is very similar to the shape information in the fluoroscopy. The feasibility of the proposed method is demonstrated by initializing an intensity-based 2D/3D registration method with the automatically obtained estimation of the registration transformation parameters.
2D O+ and H+ density profile in the magnetospheric equatorial plane
NASA Astrophysics Data System (ADS)
Maggiolo, R.; Kistler, L. M.
2012-04-01
The CODIF instrument onboard the Cluster spacecraft measures the magnetospheric O+ and H+ density since more than one decade. We map these densities along magnetic field lines to produce 2D maps of the O+ and H+ density in the magnetospheric equatorial plane for various geomagnetic conditions (represented by the Kp index) and solar activity (represented by the F10.7 index). We validate the mapping technique by comparing it with in-situ observations from Cluster in the 15-19 RE plasmasheet (Mouikis et al. 2010) and from GOES near geostationary orbit (Young et al. 1982). These maps reveal the large scale spatial distribution of O+ and H+ ions in the plasmasheet. They confirm that the proportion of O+ ions is higher at low geocentric distances and that increasing geomagnetic and solar activity enhance the O+/H+ density ratio. In the mid/far tail this ratio is mainly driven by geomagnetic activity while in the near Earth regions it strongly depends on the solar activity. These results suggest that there is a significant entry of O+ ions in the plasmasheet at low geocentric distance and that the O+ ion content in the mid/far tail is mainly driven by the O+ transport and energization while in the near Earth regions it is rather linked to ionospheric variations due to changes in the solar EUV flux.
Ultrafast exciton dynamics in 2D in-plane hetero-nanostructures: delocalization and charge transfer.
Cassette, E; Pedetti, S; Mahler, B; Ithurria, S; Dubertret, B; Scholes, G D
2017-03-10
In this article we study the ultrafast dynamics of excitons and charge carriers photogenerated in two-dimensional in-plane heterostructures, namely, CdSe-CdTe nanoplatelets. We combine transient absorption and two-dimensional electronic spectroscopy to study charge transfer and delocalization from a few tens of femtoseconds to several nanoseconds. In contrast with spherical nanocrystals, the relative alignment of the electron and hole states of CdSe and CdTe in thin 2D nanoplatelets does not lead to a type-II heterostructure. Following the excitation in CdSe or CdTe materials, the electron preferentially delocalises instantaneously over the whole heterostructure. In addition, depending on the crown material (CdTe versus CdTeSe), the hole transfers either to trap states or to the crown, within a few hundreds of femtoseconds. We conclude that the photoluminescence band, at lower energy than the CdSe and CdTe first exciton transition, does not result from the recombination of the charge carriers at the charge transfer state but involves localised hole states.
Surveillance of a 2D plane area with 3D deployed cameras.
Fu, Yi-Ge; Zhou, Jie; Deng, Lei
2014-01-24
As the use of camera networks has expanded, camera placement to satisfy some quality assurance parameters (such as a good coverage ratio, an acceptable resolution constraints, an acceptable cost as low as possible, etc.) has become an important problem. The discrete camera deployment problem is NP-hard and many heuristic methods have been proposed to solve it, most of which make very simple assumptions. In this paper, we propose a probability inspired binary Particle Swarm Optimization (PI-BPSO) algorithm to solve a homogeneous camera network placement problem. We model the problem under some more realistic assumptions: (1) deploy the cameras in the 3D space while the surveillance area is restricted to a 2D ground plane; (2) deploy the minimal number of cameras to get a maximum visual coverage under more constraints, such as field of view (FOV) of the cameras and the minimum resolution constraints. We can simultaneously optimize the number and the configuration of the cameras through the introduction of a regulation item in the cost function. The simulation results showed the effectiveness of the proposed PI-BPSO algorithm.
An experimental method for eliminating effect of rigid out-of-plane motion on 2D-DIC
NASA Astrophysics Data System (ADS)
Zhiqiang, Wang; Fengzhou, Fang; Bing, Liu; Zhiyong, Wang
2015-10-01
The out-of-plane motion is one of the most important factors that affect the precision of two-dimensional digital image correlation (2D-DIC). In this paper, a novel solution is presented to improve conventional 2D-DIC by eliminating the effect of out-of-plane motion, including translation and rotation. Firstly, an experimental technique using two projected laser strips is proposed to measure the out-of-plane motion of a planar specimen. A theoretical model is then established to predict the pseudostrains caused by out-of-plane motion based on the pin-hole imaging model. Using the measured out-of-plane displacement, the captured deformed images used in 2D-DIC are amended to eliminate the effect of out-of-plane motion by the theoretical model. Finally, two experiments were conducted to validate the effectiveness of the proposed method. Results indicate that application of the proposed method can effectively eliminate the errors caused by out-of-plane motion.
Effects of in-plane magnetic field on the transport of 2D electron vortices in non-uniform plasmas
NASA Astrophysics Data System (ADS)
Angus, Justin; Richardson, Andrew; Schumer, Joseph; Pulsed Power Team
2015-11-01
The formation of electron vortices in current-carrying plasmas is observed in 2D particle-in-cell (PIC) simulations of the plasma-opening switch. In the presence of a background density gradient in Cartesian systems, vortices drift in the direction found by crossing the magnetic field with the background density gradient as a result of the Hall effect. However, most of the 2D simulations where electron vortices are seen and studied only allow for in-plane currents and thus only an out-of-plane magnetic field. Here we present results of numerical simulations of 2D, seeded electron vortices in an inhomogeneous background using the generalized 2D electron-magneto-hydrodynamic model that additionally allows for in-plane components of the magnetic field. By seeding vortices with a varying axial component of the velocity field, so that the vortex becomes a corkscrew, it is found that a pitch angle of around 20 degrees is sufficient to completely prevent the vortex from propagating due to the Hall effect for typical plasma parameters. This work is supported by the NRL Base Program.
A 3D Freehand Ultrasound System for Multi-view Reconstructions from Sparse 2D Scanning Planes
2011-01-01
Background A significant limitation of existing 3D ultrasound systems comes from the fact that the majority of them work with fixed acquisition geometries. As a result, the users have very limited control over the geometry of the 2D scanning planes. Methods We present a low-cost and flexible ultrasound imaging system that integrates several image processing components to allow for 3D reconstructions from limited numbers of 2D image planes and multiple acoustic views. Our approach is based on a 3D freehand ultrasound system that allows users to control the 2D acquisition imaging using conventional 2D probes. For reliable performance, we develop new methods for image segmentation and robust multi-view registration. We first present a new hybrid geometric level-set approach that provides reliable segmentation performance with relatively simple initializations and minimum edge leakage. Optimization of the segmentation model parameters and its effect on performance is carefully discussed. Second, using the segmented images, a new coarse to fine automatic multi-view registration method is introduced. The approach uses a 3D Hotelling transform to initialize an optimization search. Then, the fine scale feature-based registration is performed using a robust, non-linear least squares algorithm. The robustness of the multi-view registration system allows for accurate 3D reconstructions from sparse 2D image planes. Results Volume measurements from multi-view 3D reconstructions are found to be consistently and significantly more accurate than measurements from single view reconstructions. The volume error of multi-view reconstruction is measured to be less than 5% of the true volume. We show that volume reconstruction accuracy is a function of the total number of 2D image planes and the number of views for calibrated phantom. In clinical in-vivo cardiac experiments, we show that volume estimates of the left ventricle from multi-view reconstructions are found to be in better
Geometric and morphologic evolution of normal fault planes and traces from 2D to 4D data
NASA Astrophysics Data System (ADS)
Marchal, Denis; Guiraud, Michel; Rives, Thierry
2003-01-01
The detailed 3D geometry of normal fault planes is described and analysed using datasets from outcrop studies (2D), seismic surveys (3D) and analogue models (4D). Different geometric configurations of simple isolated normal faults are studied by reference to processes of normal fault propagation. When a normal fault propagates without interacting with other fault zones, the entire border of the principal plane displays characteristic connected secondary structures. These secondary structures cause bifurcations of the principal fault terminations. The along-strike terminations of the principal plane display typical bifurcation configurations ('ear geometry'). The orientation of the bifurcations depends on the vertical direction of propagation (downwards and/or upwards). The along-dip terminations display en échelon secondary fault planes linked to the principal plane and are described as 'lobate geometry'. A 3D genetic model of isolated normal fault geometry is proposed with a new general terminology for the secondary structures. When two isolated normal faults propagate towards each other and overlap, the two principal planes connect up via a relay fault. The resulting geometry is a longer fault exhibiting a characteristic undulation with two inactive branches.
The Use of 2D Ultrasound Elastography for Measuring Tendon Motion and Strain
Slane, Laura Chernak; Thelen, Darryl G.
2014-01-01
The goal of the current study was to investigate the fidelity of a 2D ultrasound elastography method for the measurement of tendon motion and strain. Ultrasound phantoms and ex vivo porcine flexor tendons were cyclically stretched to 4% strain while cine ultrasound radiofrequency (RF) data and video data were simultaneously collected. 2D ultrasound elastography was used to estimate tissue motion and strain from RF data, and surface tissue motion and strain were separately estimated using digital image correlation (DIC). There were strong correlations (R2 > 0.97) between DIC and RF measurements of phantom displacement and strain, and good agreement in estimates of peak phantom strain (DIC: 3.5 ± 0.2%; RF: 3.7 ± 0.1%). For tendon, elastographic estimates of displacement profiles also correlated well with DIC measurements (R2 > 0.92), and exhibited similar estimated peak tendon strain (DIC: 2.6 ± 1.4%; RF: 2.2 ± 1.3%). Elastographic tracking with B-Mode images tended to under-predict peak strain for both the phantom and tendon. This study demonstrates the capacity to use quantitative elastographic techniques to measure tendon displacement and strain within an ultrasound image window. The approach may be extendible to in vivo use on humans, which would allow for the non-invasive analysis of tendon deformation in both normal and pathological states. PMID:24388164
Complete Genome Sequence of Acinetobacter sp. Strain NCu2D-2 Isolated from a Mouse
Blaschke, Ulrike
2017-01-01
ABSTRACT Whole-genome sequencing of Acinetobacter sp. strain NCu2D-2, isolated from the trachea of a mouse, revealed the presence of a plasmid of 309,964 bp with little overall similarity to known plasmids and enriched in insertion sequences (ISs) closely related to IS elements known from the nosocomial pathogen Acinetobacter baumannii. PMID:28126932
The plane strain tests in the PROMETRA program
NASA Astrophysics Data System (ADS)
Cazalis, B.; Desquines, J.; Carassou, S.; Le Jolu, T.; Bernaudat, C.
2016-04-01
A fuel cladding mechanical test, performed under conditions of plane strain deformation in the transverse direction of tube axis, was originally developed at Pennsylvania State University. It was decided to implement this original test within the PROMETRA program using the same experimental procedure and its optimization for a ring mechanical testing on plane strain conditions (PST tests) in hot cells laboratory. This paper presents a detailed description and an interpretation of the Plane Strain Tensile (PST) tests performed in the framework of the PROMETRA program on fresh and irradiated claddings. At first, the context of the PST tests is situated and the specificities of these tests implemented at CEA are justified. Indeed, a significant adjustment of the original experimental procedure is carried out in order to test the irradiated fuel cladding in the best possible conditions. Then, the tests results on fresh Zircaloy-4 and on irradiated Zircaloy-4, M5™ and ZIRLO® specimens are gathered. The main analyses in support of these tests, such as metallographies, fractographic examinations and finite element simulations are detailed. Finally, a synthesis of the interpretation of the tests is proposed. The PST test seems only representative of plane strain fracture conditions when the test material is very ductile (fresh or high temperature or low hydride material like M5TM). However, it provides a relevant representation of the RIA rupture initiation which is observed in irradiated cladding resulting from hydride rim damage due to the strong irradiation of a fuel rod.
Tunneling Between 2D Electrons and Holes in an In-plane Magnetic Field
NASA Astrophysics Data System (ADS)
Lin, Y.; Mendez, E. E.; Magno, R.; Bennett, B. R.
2002-03-01
We have studied the vertical transport properties of GaSb/AlSb/InAs/AlSb/GaSb (system A) and InAs/AlSb/GaSb/AlSb/InAs (system B) heterostructures in a magnetic field (B<20T) parallel to the interfaces. In these systems, electrons and holes accumulate in the InAs and GaSb regions, respectively, and tunneling between the two gases gives rise to a current-voltage (I-V) characteristic that exhibits negative differential conductance even at T=300K. In both cases, the zero-bias, low-T (1.7K) magnetoconductance showed the signature of tunneling between 2D gases with different carrier densities even though in system A, the holes are barely confined. In contrast, the dependence of the I-V characteristics on magnetic field was quite different. In system A, the observed shift of the peak voltage with field is explained by simple ground-state dispersion curves for electrons and holes. However, this picture cannot explain the appearance (above 5.5T) and field dependence of a secondary peak in system B, or of additional, weaker field-induced features. Their origin may lie in the complexities of highly confined hole states in the central GaSb quantum well.
Phase Diagram of a 2-D Plane Rotator Model with Integer and Half-Integer Vortices
NASA Astrophysics Data System (ADS)
de Souza, Adauto J. F.; Landau, D. P.
1996-03-01
A two-dimensional plane rotator spin model is simulated by employing the single cluster embeding Monte Carlo technique and the re-weighting histogram analysis. The system is described by the Hamiltonian^1 \\cal H = -J1 sum_< i,j > Si \\cdot Sj - J2 sum_< i,j > ( Si \\cdot Sj )^2. In adition to the familiar integer vortices, this model possesses half-integer vortex excitations as well. The system exhibits three low-temperature phases which may be identified by the behavior of suitably defined two-point correlation functions. The half- and integer-vortex densities as a function of temperature are calculated for several values of the parameter α = J_2/J_1. The phase boundaries are determined and the nature of the phase transitions is investigated. Research supported in part by the CNPq and the NSF. Permanent address: Departmento de Física e Matemática, Universidade Federal Rural de Pernambuco, 52171-900, Recife, Pernambuco, Brazil ^1 D.H. Lee and G. Grinstein Phys. Rev. Lett. \\underline55, 541, (1985)
Prediction of a strain-tunable 2D Topological Dirac semimetal in monolayers of black phosphorus
NASA Astrophysics Data System (ADS)
Zhang, Xiuwen; Liu, Qihang; Zunger, Alex; Theory Team
2015-03-01
N-dimensional Topological Nonmetals (TNM) such as N = 2D HgTe/CdTe quantum wells or N = 3D Bi2Se3 have a finite (often tiny) band gap between occupied and unoccupied bands, and show conductive Dirac cones in their N-1 dimensional geometric boundaries. On the other hand, examples of topological semimetals (TSM) are known for 3D solids (Cd3As2) where they have Dirac cones in the 3D system itself. Using density functional calculation of bands and the topological invariant Z2 we predict the existence of 2D topological Dirac semimetal in few monolayers of strain tuned black phosphorus (BP), with Dirac cones induced by band inversion. The band structures of few monolayers and bulk crystal of BP under a few percent biaxial and uniaxial strains were calculated using state-of-art electronic structure methods. The critical strain of the transition to TSM was found to decrease as the layer thickness increases. We will discuss the protection of the Dirac cones by the crystalline symmetry in the 2D TSM and the manipulation of crystalline symmetry, which induces further topological phase transitions. Supported by the NSF-DMREF-13-34170.
Ulissi, Zachary W; Govind Rajan, Ananth; Strano, Michael S
2016-08-23
Entropic surfaces represented by fluctuating two-dimensional (2D) membranes are predicted to have desirable mechanical properties when unstressed, including a negative Poisson's ratio ("auxetic" behavior). Herein, we present calculations of the strain-dependent Poisson ratio of self-avoiding 2D membranes demonstrating desirable auxetic properties over a range of mechanical strain. Finite-size membranes with unclamped boundary conditions have positive Poisson's ratio due to spontaneous non-zero mean curvature, which can be suppressed with an explicit bending rigidity in agreement with prior findings. Applying longitudinal strain along a singular axis to this system suppresses this mean curvature and the entropic out-of-plane fluctuations, resulting in a molecular-scale mechanism for realizing a negative Poisson's ratio above a critical strain, with values significantly more negative than the previously observed zero-strain limit for infinite sheets. We find that auxetic behavior persists over surprisingly high strains of more than 20% for the smallest surfaces, with desirable finite-size scaling producing surfaces with negative Poisson's ratio over a wide range of strains. These results promise the design of surfaces and composite materials with tunable Poisson's ratio by prestressing platelet inclusions or controlling the surface rigidity of a matrix of 2D materials.
The influence of strain rate and hydrogen on the plane-strain ductility of Zircaloy cladding
Link, T.M.; Motta, A.T.; Koss, D.A.
1998-03-01
The authors studied the ductility of unirradiated Zircaloy-4 cladding under loading conditions prototypical of those found in reactivity-initiated accidents (RIA), i.e.: near plane-strain deformation in the hoop direction (transverse to the cladding axis) at room temperature and 300 C and high strain rates. To conduct these studies, they developed a specimen configuration in which near plane-strain deformation is achieved in the gage section, and a testing methodology that allows one to determine both the limit strain at the onset of localized necking and the fracture strain. The experiments indicate that there is little effect of strain rate (10{sup {minus}3} to 10{sup 2} s{sup {minus}1}) on the ductility of unhydrided Zircaloy tubing deformed under near plane-strain conditions at either room temperature or 300 C. Preliminary experiments on cladding containing 190 ppm hydrogen show only a small loss of fracture strain but no clear effect on limit strain. The experiments also indicate that there is a significant loss of Zircaloy ductility when surface flaws are present in the form of thickness imperfections.
Blue Phosphorene Oxide: Strain-Tunable Quantum Phase Transitions and Novel 2D Emergent Fermions
NASA Astrophysics Data System (ADS)
Zhu, Liyan; Wang, Shan-Shan; Guan, Shan; Liu, Ying; Zhang, Tingting; Chen, Guibin; Yang, Shengyuan A.
2016-10-01
Tunable quantum phase transitions and novel emergent fermions in solid state materials are fascinating subjects of research. Here, we propose a new stable two-dimensional (2D) material, the blue phosphorene oxide (BPO), which exhibits both. Based on first-principles calculations, we show that its equilibrium state is a narrow-bandgap semiconductor with three bands at low energy. Remarkably, a moderate strain can drive a semiconductor-to-semimetal quantum phase transition in BPO. At the critical transition point, the three bands cross at a single point at Fermi level, around which the quasiparticles are a novel type of 2D pseudospin-1 fermions. Going beyond the transition, the system becomes a symmetry-protected semimetal, for which the conduction and valence bands touch quadratically at a single Fermi point that is protected by symmetry, and the low-energy quasiparticles become another novel type of 2D double Weyl fermions. We construct effective models characterizing the phase transition and these novel emergent fermions, and we point out several exotic effects, including super Klein tunneling, supercollimation, and universal optical absorbance. Our result reveals BPO as an intriguing platform for the exploration of fundamental properties of quantum phase transitions and novel emergent fermions, and also suggests its great potential in nanoscale device applications.
A 2D strain estimator with numerical optimization method for soft-tissue elastography.
Liu, Ke; Zhang, Pengfei; Shao, Jinhua; Zhu, Xinjian; Zhang, Yun; Bai, Jing
2009-12-01
Elastography is a bioelasticity-based imaging modality which has been proved to be a potential evaluation tool to detect the tissue abnormalities. Conventional method for elastography is to estimate the displacement based on cross-correlation technique firstly, then strain profile is calculated as the gradient of the displacement. The main problem of this method arises from the fact that the cross-correlation between pre- and post-compression signals will be decreased because of the signal's compression-to-deformation. It may constrain the estimation of the displacement. Numerical optimization, as an efficient tool to estimate the non-rigid deformation in image registration, has its potential to achieve the elastogram. This paper incorporates the idea of image registration into elastography and proposes a radio frequency (RF) signal registration strain estimator based on the minimization of a cost function using numerical optimization method with Powell algorithm (NOMPA). To evaluate the proposed scheme, the simulation data with a hard inclusion embedded in the homogeneous background is produced for analysis. NOMPA can obtain the displacement profiles and strain profiles simultaneously. When compared with the cross-correlation based method, NOMPA presents better signal-to-noise ratio (SNR, 32.6+/-1.5 dB vs. 23.8+/-1.1 dB) and contrast-to-noise ratio (CNR, 28.8+/-1.8 dB vs. 21.7+/-0.9 dB) in axial normal strain estimation. The in vitro experiment of porcine liver with ethanol-induced lesion is also studied. The statistic results of SNR and CNR indicate that strain profiles by NOMPA performs better anti-noise and target detectability than that by cross-correlation based method. Though NOMPA carry a heavier computational burden than cross-correlation based method, it may be an useful method to obtain 2D strains in elastography.
Cartamil-Bueno, S. J. E-mail: rbolivar@ugr.es; Rodríguez-Bolívar, S. E-mail: rbolivar@ugr.es
2015-06-28
The effects of tensile strain on the current-voltage (I-V) characteristics of hydrogenated-edge armchair graphene nanoribbons are investigated by using DFT theory. The strain is introduced in two different ways related to the two types of systems studied in this work: in-plane strained systems (A) and out-of-plane strained systems due to bending (B). These two kinds of strain lead to make a distinction among three cases: in-plane strained systems with strained electrodes (A1) and with unstrained electrodes (A2), and out-of-plane homogeneously strained systems with unstrained, fixed electrodes (B). The systematic simulations to calculate the electronic transmission between two electrodes were focused on systems of 8 and 11 dimers in width. The results show that the differences between cases A2 and B are negligible, even though the strain mechanisms are different: in the plane case, the strain is uniaxial along its length; while in the bent case, the strain is caused by the arc deformation. Based on the study, a new type of nanoelectromechanical system solid state switching device is proposed.
Shear Band Formation in Plane Strain Experiments of Sand
NASA Technical Reports Server (NTRS)
Alshibli, Khalid A.; Sture, Stein
2000-01-01
A series of biaxial (plane strain) experiments were conducted on three sands under low (15 kPa) and high (100 kPa) confining pressure conditions to investigate the effects of specimen density, confining pressure, and sand grain size and shape on the constitutive and stability behavior of granular materials. The three sands used in the experiments were fine-, medium-, and coarse-grained uniform silica sands with rounded, subangular, and angular grains, respectively. Specimen deformation was readily monitored and analyzed with the help of a grid pattern imprinted on the latex membrane. The overall stress-strain behavior is strongly dependent on the specimen density, confining pressure, sand grain texture, and the resulting failure mode(s). That became evident in different degrees of softening responses at various axial strains. The relationship between the constitutive behavior and the specimens' modes of instability is presented. The failure in all specimens was characterized by two distinct and opposite shear bands. It was found that the measured dilatancy angles increase as the sand grains' angularities and sizes increase. The measured shear band inclination angles are also presented and compared with classical Coulomb and Roscoe solutions.
Ultrasound 2D strain estimator based on image registration for ultrasound elastography
NASA Astrophysics Data System (ADS)
Yang, Xiaofeng; Torres, Mylin; Kirkpatrick, Stephanie; Curran, Walter J.; Liu, Tian
2014-03-01
In this paper, we present a new approach to calculate 2D strain through the registration of the pre- and post-compression (deformation) B-mode image sequences based on an intensity-based non-rigid registration algorithm (INRA). Compared with the most commonly used cross-correlation (CC) method, our approach is not constrained to any particular set of directions, and can overcome displacement estimation errors introduced by incoherent motion and variations in the signal under high compression. This INRA method was tested using phantom and in vivo data. The robustness of our approach was demonstrated in the axial direction as well as the lateral direction where the standard CC method frequently fails. In addition, our approach copes well under large compression (over 6%). In the phantom study, we computed the strain image under various compressions and calculated the signal-to-noise (SNR) and contrast-to-noise (CNS) ratios. The SNR and CNS values of the INRA method were much higher than those calculated from the CC-based method. Furthermore, the clinical feasibility of our approach was demonstrated with the in vivo data from patients with arm lymphedema.
NASA Astrophysics Data System (ADS)
Hiraoka, Naoki; Matsuzaki, Ryosuke; Todoroki, Akira
In order to improve performance of anti lock brake system (ABS) and detect condition of road surface, intelligent tires that monitor strain of interior surface and rolling radius of tire are demanded. However, the high stiffness of an attached sensor like a strain gauge causes debonding of sensors from tire rubber. In the present study, noncontact concurrent monitoring method is proposed using digital image correlation method (DICM) and spotlight projection. In-plane strain and out-of-plane displacement (rolling radius) are calculated by using image processing with an image of interior surface of tire that is taken with a single CCD camera fixed on wheel rim. New monitoring system is applied to Al beam and commercially available radial tire. As a result, this monitoring system is proved to be able to measure in-plane strain and out-of-plane displacement with high accuracy, and confirmed to be effective for concurrent monitoring of tires.
Ao, L; Pham, A; Xiao, H Y; Zu, X T; Li, S
2016-03-14
We have systematically investigated the effects of different vacancy defects in 2D d(0) materials SnS2 and ZrS2 using first principles calculations. The theoretical results show that the single cation vacancy and the vacancy complex like V-SnS6 can induce large magnetic moments (3-4 μB) in these single layer materials. Other defects, such as V-SnS3, V-S, V-ZrS3 and V-ZrS6, can result in n-type conductivity. In addition, the ab initio studies also reveal that the magnetic and conductive properties from the cation vacancy and the defect complex V-SnS6 can be modified using the compressive/tensile strain of the in-plane lattices. Specifically, the V-Zr doped ZrS2 monolayer can be tuned from a ferromagnetic semiconductor to a metallic/half-metallic material with decreasing/increasing magnetic moments depending on the external compressive/tensile strains. On the other hand, the semiconducting and magnetic properties of V-Sn doped SnS2 is preserved under different lattice compression and tension. For the defect complex like V-SnS6, only the lattice compression can tune the magnetic moments in SnS2. As a result, by manipulating the fabrication parameters, the magnetic and conductive properties of SnS2 and ZrS2 can be tuned without the need for chemical doping.
Strained-layer superlattice focal plane array having a planar structure
Kim, Jin K.; Carroll, Malcolm S.; Gin, Aaron; Marsh, Phillip F.; Young, Erik W.; Cich, Michael J.
2010-07-13
An infrared focal plane array (FPA) is disclosed which utilizes a strained-layer superlattice (SLS) formed of alternating layers of InAs and In.sub.xGa.sub.1-xSb with 0.ltoreq.x.ltoreq.0.5 epitaxially grown on a GaSb substrate. The FPA avoids the use of a mesa structure to isolate each photodetector element and instead uses impurity-doped regions formed in or about each photodetector for electrical isolation. This results in a substantially-planar structure in which the SLS is unbroken across the entire width of a 2-D array of the photodetector elements which are capped with an epitaxially-grown passivation layer to reduce or eliminate surface recombination. The FPA has applications for use in the wavelength range of 3-25 .mu.m.
Characterization of network parameters for UHMWPE by plane strain compression.
Abreu, E L; Ngo, H D; Bellare, A
2014-04-01
Ultra-high molecular weight polyethylene (PE) is used as a bearing material for total joint replacement prostheses since it is a tough, wear-resistant semicrystalline polymer. Despite its high resistance to wear, PE components have shown measureable wear in vivo, which can cause wear-particle induced osteolysis. Crosslinking of PE using ionizing radiation has been shown to increase wear resistance since both chemical crosslinks and physical entanglements provide high resistance to wear. Molecular characterization of crosslinked PEs is usually conducted using equilibrium swelling or by quantifying gel content. In this study, we compared crosslink densities and molecular weight between crosslinks derived from equilibrium swelling to those obtained by applying the Gaussian and Eight-Chain model to describe plane strain compression of the PE melt. The latter approach has the advantage of accounting for contributions of entanglements to the overall crosslink density, which solvent-based techniques largely neglect. As expected, the crosslink density calculated from model fitting increased monotonically with increase in radiation dose in a 0-200kGy dose range, with a corresponding monotonic decrease in molecular weight between crosslinks, but provided higher values of crosslink density and correspondingly lower values of molecular weight between crosslinks compared to the equilibrium swelling technique.
Lattice strains and polarized luminescence in homoepitaxial growth of a-plane ZnO
NASA Astrophysics Data System (ADS)
Matsui, Hiroaki; Tabata, Hitoshi
2012-12-01
In-plane lattice strains in a-plane zinc oxide (ZnO) homoepitaxial layers were selectively introduced by changing substrate type and growth conditions. Strain-free layers were observed when using a Crystec ZnO substrate, which resulted in atomically flat surfaces with nano-facets consisting of the m-plane (10-10) at atomic scale. In contrast, ZnO layers on Goodwill ZnO substrates possessed in-plane lattice strains due to generation of basal-plane stacking faults. The degree of lattice strains was systematically changed by the oxygen pressure, which clarified the close correlation between photoluminescence (PL) polarization and lattice strains. The polarization ratio of PL enhanced with the lattice strains.
Kumar, Hemant; Dong, Liang; Shenoy, Vivek B.
2016-01-01
In flexible 2D-devices, strain transfer between different van-der Waals stacked layers is expected to play an important role in determining their optoelectronic performances and mechanical stability. Using a 2D non-linear shear-lag model, we demonstrate that only 1-2% strain can be transferred between adjacent layers of different 2d-materials, depending on the strength of the interlayer vdW interaction and the elastic modulus of the individual layers. Beyond this critical strain, layers begin to slip with respect to each other. We further show that due to the symmetry of the periodic interlayer shear potential, stacked structures form strain solitons with alternating AB/BA or AB/AB stacking which are separated by incommensurate domain walls. The extent and the separation distance of these commensurate domains are found to be determined by the degree of the applied strain, and their magnitudes are calculated for several 2D heterostructures and bilayers including MoS2/WS2, MoSe2/WSe2, Graphene/Graphene and MoS2/MoS2 using a multiscale method. As bilayer structures have been shown to exhibit stacking-dependent electronic bandgap and quantum transport properties, the predictions of our study will not only be crucial in determining the mechanical stability of flexible 2D devices but will also help to better understand optoelectronic response of flexible devices. PMID:26867496
TAKANO, Hiroshi; ISOGAI, Tomomi; AOKI, Takuma; WAKAO, Yoshito; FUJII, Yoko
2014-01-01
The purpose of the present study is to investigate the feasibility of strain analysis using speckle tracking echocardiography (STE) in cats and to evaluate STE variables in cats with hypertrophic cardiomyopathy (HCM). Sixteen clinically healthy cats and 17 cats with HCM were used. Radial and circumferential strain and strain rate variables in healthy cats were measured using STE to assess the feasibility. Comparisons of global strain and strain variables between healthy cats and cats with HCM were performed. Segmental assessments of left ventricle (LV) wall for strain and strain rate variables in cats with HCM were also performed. As a result, technically adequate images were obtained in 97.6% of the segments for STE analysis. Sedation using buprenorphine and acepromazine did not affect any global strain nor strain rate variable. In LV segments of cats with HCM, reduced segmental radial strain and strain rate variables had significantly related with segmental LV hypertrophy. It is concluded that STE analysis using short axis images of LV appeared to be clinically feasible in cats, having the possibility to be useful for detecting myocardial dysfunctions in cats with diseased heart. PMID:25373881
Takano, Hiroshi; Isogai, Tomomi; Aoki, Takuma; Wakao, Yoshito; Fujii, Yoko
2015-02-01
The purpose of the present study is to investigate the feasibility of strain analysis using speckle tracking echocardiography (STE) in cats and to evaluate STE variables in cats with hypertrophic cardiomyopathy (HCM). Sixteen clinically healthy cats and 17 cats with HCM were used. Radial and circumferential strain and strain rate variables in healthy cats were measured using STE to assess the feasibility. Comparisons of global strain and strain variables between healthy cats and cats with HCM were performed. Segmental assessments of left ventricle (LV) wall for strain and strain rate variables in cats with HCM were also performed. As a result, technically adequate images were obtained in 97.6% of the segments for STE analysis. Sedation using buprenorphine and acepromazine did not affect any global strain nor strain rate variable. In LV segments of cats with HCM, reduced segmental radial strain and strain rate variables had significantly related with segmental LV hypertrophy. It is concluded that STE analysis using short axis images of LV appeared to be clinically feasible in cats, having the possibility to be useful for detecting myocardial dysfunctions in cats with diseased heart.
Impact of lens distortions on strain measurements obtained with 2D digital image correlation
NASA Astrophysics Data System (ADS)
Lava, P.; Van Paepegem, W.; Coppieters, S.; De Baere, I.; Wang, Y.; Debruyne, D.
2013-05-01
The determination of strain fields based on displacements obtained via digital image correlation (DIC) at the micro-strain level (≤1000 μm/m) is still a cumbersome task. In particular when high-strain gradients are involved, e.g. in composite materials with multidirectional fibre reinforcement, uncertainties in the experimental setup and errors in the derivation of the displacement fields can substantially hamper the strain identification process. In this contribution, the aim is to investigate the impact of lens distortions on strain measurements. To this purpose, we first perform pure rigid body motion experiments, revealing the importance of precise correction of lens distortions. Next, a uni-axial tensile test on a textile composite with spatially varying high strain gradients is performed, resulting in very accurately determined strains along the fibers of the material.
Tselev, Alexander; Strelcov, Evgheni; Lukyanchuk, Igor A.; Budai, John D.; Tischler, Jonathan Z.; Ivanov, Ilia N.; Jones, Keith; Proksch, Roger; Kalinin, Sergei V.; Kolmakov, Aandrei
2010-07-06
Formation of ferroelastic twin domains in vanadium dioxide (VO{sub 2}) nanosystems can strongly affect local strain distributions, and hence couple to the strain-controlled metal-insulator transition. Here we report polarized-light optical and scanning microwave microscopy studies of interrelated ferroelastic and metal-insulator transitions in single-crystalline VO{sub 2} quasi-two-dimensional (quasi-2D) nanoplatelets (NPls). In contrast to quasi-1D single-crystalline nanobeams, the 2D geometric frustration results in emergence of several possible families of ferroelastic domains in NPls, thus allowing systematic studies of strain-controlled transitions in the presence of geometrical frustration. We demonstrate the possibility of controlling the ferroelastic domain population by the strength of the NPl-substrate interaction, mechanical stress, and by the NPl lateral size. Ferroelastic domain species and domain walls are identified based on standard group-theoretical considerations. Using variable temperature microscopy, we imaged the development of domains of metallic and semiconducting phases during the metal-insulator phase transition and nontrivial strain-driven reentrant domain formation. A long-range reconstruction of ferroelastic structures accommodating metal-insulator domain formation has been observed. These studies illustrate that a complete picture of the phase transitions in single-crystalline and disordered VO{sub 2} structures can be drawn only if both ferroelastic and metal-insulator strain effects are taken into consideration and understood.
Tselev, Alexander; Strelcov, Evgheni; Lukyanchuk, Igor A.; Budai, John D.; Tischler, Jonathan Z.; Ivanov, Ilia N.; Jones, Keith; Proksch, Roger; Kalinin, Sergei V.; Kolmakov, Andrei
2011-08-09
Formation of ferroelastic twin domains in vanadium dioxide (VO{sub 2}) nanosystems can strongly affect local strain distributions, and hence couple to the strain-controlled metal-insulator transition. Here we report polarized-light optical and scanning microwave microscopy studies of interrelated ferroelastic and metal-insulator transitions in single-crystalline VO{sub 2} quasi-two-dimensional (quasi-2D) nanoplatelets (NPls). In contrast to quasi-1D single-crystalline nanobeams, the 2D geometric frustration results in emergence of several possible families of ferroelastic domains in NPls, thus allowing systematic studies of strain-controlled transitions in the presence of geometrical frustration. We demonstrate the possibility of controlling the ferroelastic domain population by the strength of the NPl-substrate interaction, mechanical stress, and by the NPl lateral size. Ferroelastic domain species and domain walls are identified based on standard group-theoretical considerations. Using variable temperature microscopy, we imaged the development of domains of metallic and semiconducting phases during the metal-insulator phase transition and nontrivial strain-driven reentrant domain formation. A long-range reconstruction of ferroelastic structures accommodating metal-insulator domain formation has been observed. These studies illustrate that a complete picture of the phase transitions in single-crystalline and disordered VO{sub 2} structures can be drawn only if both ferroelastic and metal-insulator strain effects are taken into consideration and understood.
Tsai, Tsung-Yuan; Lu, Tung-Wu; Chen, Chung-Ming; Kuo, Mei-Ying; Hsu, Horng-Chaung
2010-03-15
Purpose: Accurate measurement of the three-dimensional (3D) rigid body and surface kinematics of the natural human knee is essential for many clinical applications. Existing techniques are limited either in their accuracy or lack more realistic experimental evaluation of the measurement errors. The purposes of the study were to develop a volumetric model-based 2D to 3D registration method, called the weighted edge-matching score (WEMS) method, for measuring natural knee kinematics with single-plane fluoroscopy to determine experimentally the measurement errors and to compare its performance with that of pattern intensity (PI) and gradient difference (GD) methods. Methods: The WEMS method gives higher priority to matching of longer edges of the digitally reconstructed radiograph and fluoroscopic images. The measurement errors of the methods were evaluated based on a human cadaveric knee at 11 flexion positions. Results: The accuracy of the WEMS method was determined experimentally to be less than 0.77 mm for the in-plane translations, 3.06 mm for out-of-plane translation, and 1.13 deg. for all rotations, which is better than that of the PI and GD methods. Conclusions: A new volumetric model-based 2D to 3D registration method has been developed for measuring 3D in vivo kinematics of natural knee joints with single-plane fluoroscopy. With the equipment used in the current study, the accuracy of the WEMS method is considered acceptable for the measurement of the 3D kinematics of the natural knee in clinical applications.
NASA Astrophysics Data System (ADS)
Figgemeier, H.; Hanna, S.; Eich, D.; Mahlein, K.-M.; Fick, W.; Schirmacher, W.; Thöt, R.
2016-05-01
In this paper AIM presents its latest results on both n-on-p and p-on-n low dark current planar MCT photodiode technology LWIR and VLWIR two-dimensional focal plane detector arrays with a cut-off wavelength >11μm at 80K and a 640x512 pixel format at a 20μm pitch. Thermal dark currents significantly reduced as compared to `Tennant's Rule 07' at a yet good detection efficiency >60% as well as results from NETD and photo response performance characterization are presented. The demonstrated detector performance paces the way for a new generation of higher operating temperature LWIR MCT FPAs with a <30mK NETD up to a 110K detector operating temperature and with good operability.
Tomić, Adriana; Varanasi, Pavankumar R.; Golemac, Mijo; Malić, Suzana; Riese, Peggy; Borst, Eva M.; Guzmán, Carlos A.; Krmpotić, Astrid
2016-01-01
Development of an effective vaccine against human cytomegalovirus (HCMV) is a need of utmost medical importance. Generally, it is believed that a live attenuated vaccine would best provide protective immunity against this tenacious pathogen. Here, we propose a strategy for an HCMV vaccine that aims at the simultaneous activation of innate and adaptive immune responses. An HCMV strain expressing the host ligand ULBP2 for the NKG2D receptor was found to be susceptible to control by natural killer (NK) cells, and preserved the ability to stimulate HCMV-specific T cells. Infection with the ULBP2-expressing HCMV strain caused diminished cell surface levels of MHC class I molecules. While expression of the NKG2D ligand increased the cytolytic activity of NK cells, NKG2D engagement in CD8+ T cells provided co-stimulation and compensated for lower MHC class I expression. Altogether, our data indicate that triggering of both arms of the immune system is a promising approach applicable to the generation of a live attenuated HCMV vaccine. PMID:27907183
MCT-Based LWIR and VLWIR 2D Focal Plane Detector Arrays for Low Dark Current Applications at AIM
NASA Astrophysics Data System (ADS)
Hanna, S.; Eich, D.; Mahlein, K.-M.; Fick, W.; Schirmacher, W.; Thöt, R.; Wendler, J.; Figgemeier, H.
2016-09-01
We present our latest results on n-on- p as well as on p-on- n low dark current planar mercury cadmium telluride (MCT) photodiode technology long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) two-dimensional focal plane arrays (FPAs) with quantum efficiency (QE) cut-off wavelength >11 μm at 80 K and a 512 × 640 pixel format FPA at 20 μm pitch stitched from two 512 × 320 pixel photodiode arrays. Significantly reduced dark currents as compared with Tennant's "Rule 07" are demonstrated in both polarities while retaining good detection efficiency ≥60% for operating temperatures between 30 K and 100 K. This allows for the same dark current performance at 20 K higher operating temperature than with previous AIM INFRAROT-MODULE GmbH (AIM) technology. For p-on- n LWIR MCT FPAs, broadband photoresponse nonuniformity of only about 1.2% is achieved at 55 K with low defective pixel numbers. For an n-on- p VLWIR MCT FPA with 13.6 μm cut-off at 55 K, excellent photoresponse nonuniformity of about 3.1% is achieved at moderate defective pixel numbers. This advancement in detector technology paves the way for outstanding signal-to-noise ratio performance infrared detection, enabling cutting-edge next-generation LWIR/VLWIR detectors for space instruments and devices with higher operating temperature and low size, weight, and power for field applications.
Peng, Rui; Liang, Liangbo; Hood, Zachary D.; ...
2016-08-30
Two-dimensional (2D) single-layer MoS2 nanosheets are demonstrated as efficient photocatalysts for hydrogen evolution reaction (HER) from water reduction, thanks to specific in-plane heterojunctions constructed in the MoS2 monolayer. These functional heterojunctions are formed among the different phases of chemically exfoliated MoS2 monolayers: semiconducting 2H, metallic 1T, and quasi-metallic 1T' phases. The proportion of the three MoS2 phases can be systematically controlled via thermal annealing of the nanosheets. Interestingly, a volcano relationship is observed between the photocatalytic HER activity and the annealing temperature with an optimum activity obtained after annealing at 60 °C. First-principles calculations were integrated with experimental studies tomore » shed light on the role of the multiphases of MoS2 and reveal that optimum photocatalytic HER activity results from the formation of the in-plane heterojunctions between 1T' MoS2 and 2H MoS2. Importantly, this facilitates not only balanced light absorption and charge generation by the 2H phase, efficient charge separation at the 1T'/2H interface, but also favorable HER over the basal sites of 1T' MoS2. Furthermore, our work manifests how the confluence of the optical, electronic and chemical properties of 2D MoS2 monolayers can be fully captured for efficient photocatalytic water reduction.« less
Assumed strain formulation for the four-node quadrilateral with improved in-plane bending behaviour
NASA Astrophysics Data System (ADS)
Stolarski, Henryk K.; Chen, Yung-I.
1995-04-01
A new assumed strain quadrilateral element with highly accurate in-plane bending behavior is presented for plane stress and plane strain analysis. The basic idea of the formulation consists in identification of various modes of deformation and then in proper modification of the strain field in some of these modes. In particular, the strain operator corresponding to the in-plane bending modes is modified to simulate the strain field resulting from the assumptions usually made in structural mechanics. The modification of the strain field leads to the assumed strain operator on the element level. As a result, the so-called shear and membrane locking phenomena are alleviated. The element exhibits remarkable success in bending-dominated problems even when severely distorted and high aspect ratio meshes are used. Another advantage of the present assumed strain element is that locking for nearly incompressible materials is also mitigated. While this assumed strain element passes the patch test only for the parallelogram shapes, the element provides convergent solutions as long as the initially general form of the element approaches a parallelogram shape with the refinement of the mesh.
NASA Astrophysics Data System (ADS)
Suryanarayanan, Saikishan; Narasimha, Roddam
2017-02-01
Although the free-shear or mixing layer has been a subject of extensive research over nearly a century, there are certain fundamental issues that remain controversial. These include the influence of initial and downstream conditions on the flow, the effect of velocity ratio across the layer, and the nature of any possible coupling between small scale dynamics and the large scale evolution of layer thickness. In the spirit of the temporal vortex-gas simulations of Suryanarayanan et al. ["Free turbulent shear layer in a point vortex gas as a problem in nonequilibrium statistical mechanics," Phys. Rev. E 89, 013009 (2014)], we revisit the simple 2D inviscid vortex-gas model with extensive computations and detailed analysis, in order to gain insights into some of the above issues. Simulations of the spatially evolving vortex-gas shear layer are carried out at different velocity ratios using a computational model based on the work of Basu et al. ["Vortex sheet simulation of a plane canonical mixing layer," Comput. Fluids 21, 1-30 (1992) and "Modelling plane mixing layers using vortex points and sheets," Appl. Math. Modell. 19, 66-75 (1995)], but with a crucial improvement that ensures conservation of global circulation. The simulations show that the conditions imposed at the origin of the free shear layer and at the exit to the computational domain can affect flow evolution in their respective downstream and upstream neighbourhoods, the latter being particularly strong in the single stream limit. In between these neighbourhoods at the ends is a regime of universal self-preserving growth rate given by a universal function of velocity ratio. The computed growth rates are generally located within the scatter of experimental data on plane mixing layers and closely agree with recent high Reynolds number experiments and 3D large eddy simulation studies. These findings support the view that observed free-shear layer growth can be largely explained by the 2D vortex dynamics of
Normal and shear strain imaging using 2D deformation tracking on beam steered linear array datasets
Xu, Haiyan; Varghese, Tomy
2013-01-01
Purpose: Previous publications have reported on the use of one-dimensional cross-correlation analysis with beam-steered echo signals. However, this approach fails to accurately track displacements at larger depths (>4.5 cm) due to lower signal-to-noise. In this paper, the authors present the use of adaptive parallelogram shaped two-dimensional processing blocks for deformation tracking. Methods: Beam-steered datasets were acquired using a VFX 9L4 linear array transducer operated at a 6 MHz center frequency for steered angles from −15 to 15° in increments of 1°, on both uniformly elastic and single-inclusion tissue-mimicking phantoms. Echo signals were acquired to a depth of 65 mm with the focus set at 40 mm corresponding to the center of phantom. Estimated angular displacements along and perpendicular to the beam direction are used to compute axial and lateral displacement vectors using a least-squares approach. Normal and shear strain tensor component are then estimated based on these displacement vectors. Results: Their results demonstrate that parallelogram shaped two-dimensional deformation tracking significantly improves spatial resolution (factor of 7.79 along the beam direction), signal-to-noise (5 dB improvement), and contrast-to-noise (8–14 dB improvement) associated with strain imaging using beam steering on linear array transducers. Conclusions: Parallelogram shaped two-dimensional deformation tracking is demonstrated in beam-steered radiofrequency data, enabling its use in the estimation of normal and shear strain components. PMID:23298118
On the isotropic moduli of 2D strain-gradient elasticity
NASA Astrophysics Data System (ADS)
Auffray, Nicolas
2015-01-01
In the present paper, the simplest model of strain-gradient elasticity will be considered, that is, the isotropy in a bidimensional space. Paralleling the definition of the classic elastic moduli, our aim is to introduce second-order isotropic moduli having a mechanical interpretation. A general construction process of these moduli will be proposed. As a result, it appears that many sets can be defined, each of them constituted of 4 moduli: 3 associated with 2 distinct mechanisms and the last one coupling these mechanisms. We hope that these moduli (and the construction process) might be useful for forthcoming investigations on generalized continuum mechanics.
Anisotropic Power Law Strain Correlations in Sheared Amorphous 2D Solids
Maloney, C. E.; Robbins, M. O.
2009-06-05
The local deformation of steadily sheared two-dimensional Lennard-Jones glasses is studied via computer simulations at zero temperature. In the quasistatic limit, spatial correlations in the incremental strain field are highly anisotropic. The data show power law behavior with a strong angular dependence of the scaling exponent, and the strongest correlations along the directions of maximal shear stress. These results support the notion that the jamming transition at the onset of flow is critical, but suggest unusual critical behavior. The predicted behavior is testable through experiments on sheared amorphous materials such as bubble rafts, foams, emulsions, granular packings, and other systems where particle displacements can be tracked.
A semi-implicit finite strain shell algorithm using in-plane strains based on least-squares
NASA Astrophysics Data System (ADS)
Areias, P.; Rabczuk, T.; de Sá, J. César; Natal Jorge, R.
2015-04-01
The use of a semi-implicit algorithm at the constitutive level allows a robust and concise implementation of low-order effective shell elements. We perform a semi-implicit integration in the stress update algorithm for finite strain plasticity: rotation terms (highly nonlinear trigonometric functions) are integrated explicitly and correspond to a change in the (in this case evolving) reference configuration and relative Green-Lagrange strains (quadratic) are used to account for change in the equilibrium configuration implicitly. We parametrize both reference and equilibrium configurations, in contrast with the so-called objective stress integration algorithms which use a common configuration. A finite strain quadrilateral element with least-squares assumed in-plane shear strains (in curvilinear coordinates) and classical transverse shear assumed strains is introduced. It is an alternative to enhanced-assumed-strain (EAS) formulations and, contrary to this, produces an element satisfying ab-initio the Patch test. No additional degrees-of-freedom are present, contrasting with EAS. Least-squares fit allows the derivation of invariant finite strain elements which are both in-plane and out-of-plane shear-locking free and amenable to standardization in commercial codes. Two thickness parameters per node are adopted to reproduce the Poisson effect in bending. Metric components are fully deduced and exact linearization of the shell element is performed. Both isotropic and anisotropic behavior is presented in elasto-plastic and hyperelastic examples.
Wakeling, James M.
2014-01-01
When skeletal muscle fibres shorten, they must increase in their transverse dimensions in order to maintain a constant volume. In pennate muscle, this transverse expansion results in the fibres rotating to greater pennation angle, with a consequent reduction in their contractile velocity in a process known as gearing. Understanding the nature and extent of this transverse expansion is necessary to understand the mechanisms driving the changes in internal geometry of whole muscles during contraction. Current methodologies allow the fascicle lengths, orientations, and curvatures to be quantified, but not the transverse expansion. The purpose of this study was to develop and validate techniques for quantifying transverse strain in skeletal muscle fascicles during contraction from B-mode ultrasound images. Images were acquired from the medial and lateral gastrocnemii during cyclic contractions, enhanced using multiscale vessel enhancement filtering and the spatial frequencies resolved using 2D discrete Fourier transforms. The frequency information was resolved into the fascicle orientations that were validated against manually digitized values. The transverse fascicle strains were calculated from their wavelengths within the images. These methods showed that the transverse strain increases while the longitudinal fascicle length decreases; however, the extent of these strains was smaller than expected. PMID:25328509
Peng, Rui; Liang, Liangbo; Hood, Zachary D.; Boulesbaa, Abdelaziz; Puretzky, Alexander; Ievlev, Anton V.; Come, Jeremy; Ovchinnikova, Olga S.; Wang, Hui; Ma, Cheng; Chi, Miaofang; Sumpter, Bobby G.; Wu, Zili
2016-08-30
Two-dimensional (2D) single-layer MoS_{2} nanosheets are demonstrated as efficient photocatalysts for hydrogen evolution reaction (HER) from water reduction, thanks to specific in-plane heterojunctions constructed in the MoS_{2} monolayer. These functional heterojunctions are formed among the different phases of chemically exfoliated MoS_{2} monolayers: semiconducting 2H, metallic 1T, and quasi-metallic 1T' phases. The proportion of the three MoS_{2} phases can be systematically controlled via thermal annealing of the nanosheets. Interestingly, a volcano relationship is observed between the photocatalytic HER activity and the annealing temperature with an optimum activity obtained after annealing at 60 °C. First-principles calculations were integrated with experimental studies to shed light on the role of the multiphases of MoS_{2} and reveal that optimum photocatalytic HER activity results from the formation of the in-plane heterojunctions between 1T' MoS_{2} and 2H MoS_{2}. Importantly, this facilitates not only balanced light absorption and charge generation by the 2H phase, efficient charge separation at the 1T'/2H interface, but also favorable HER over the basal sites of 1T' MoS_{2}. Furthermore, our work manifests how the confluence of the optical, electronic and chemical properties of 2D MoS_{2} monolayers can be fully captured for efficient photocatalytic water reduction.
NASA Astrophysics Data System (ADS)
Noh, H.; Tsui, D. C.; Shayegan, M.; Yoon, Jongsoo
2000-03-01
We report on measurements of anisotropic in-plane magneto-resistance of the 2D hole system (2DHS) in a GaAs/AlGaAs (311)A heterostructure, which exhibits both zero-field and in-plane field induced metal-insulator transitions. For high hole densities, when the direction of B field is changed relative to the current(I), which is always kept in the high mobility direction, the resistivity with B allel I is larger at low field, while the resistivity with B ⊥ I becomes larger at high field. This behavior is consistent with recent measurements(S. J. Papadakis et al.), cond-mat/9911239. on a quantum well system. That the resistivity at high field is larger for B ⊥ I than for B allel I is also consistent with a recent theoretical argument(S. Das Sarma and E. H. Hwang, cond-mat/9909452.), though the difference is smaller than that from the theory. As the density is lowered, the resistivity with B allel I gets larger at high field, and it eventually becomes greater than that with B ⊥ I at all field ranges measured. This change in anisotropy has not been seen in previous measurements. The critical field B_c, beyond which the metallic phase becomes insulating, is also different for two different directions of B, while the change in I-V characteristics across Bc remains the same.
Tunable biaxial in-plane compressive strain in a Si nanomembrane transferred on a polyimide film
Kim, Munho; Mi, Hongyi; Cho, Minkyu; Seo, Jung-Hun; Ma, Zhenqiang; Zhou, Weidong; Gong, Shaoqin
2015-05-25
A method of creating tunable and programmable biaxial compressive strain in silicon nanomembranes (Si NMs) transferred onto a Kapton{sup ®} HN polyimide film has been demonstrated. The programmable biaxial compressive strain (up to 0.54%) was generated utilizing a unique thermal property exhibited by the Kapton HN film, namely, it shrinks from its original size when exposed to elevated temperatures. The correlation between the strain and the annealing temperature was carefully investigated using Raman spectroscopy and high resolution X-ray diffraction. It was found that various amounts of compressive strains can be obtained by controlling the thermal annealing temperatures. In addition, a numerical model was used to evaluate the strain distribution in the Si NM. This technique provides a viable approach to forming in-plane compressive strain in NMs and offers a practical platform for further studies in strain engineering.
Stretch bending - the plane within the sheet where strains reach the forming limit curve
NASA Astrophysics Data System (ADS)
Neuhauser, F. M.; Terrazas, O. R.; Manopulo, N.; Hora, P.; Van Tyne, C. J.
2016-11-01
Finite element analysis (FEA) was used to model the angular stretch bend test, where a strip of sheet metal is locked at both ends and a tool with a radius stretches and bends the center of the strip until failure. The FEA program used in the study was Abaqus. The FEA model was verified by experimental work using a dual phase steel (DP600) and with a simplified analytical analysis. The FEA model was used to simulate the experimental test for various frictional conditions and various radii of an upward moving tool. The primary objective of the study was to evaluate the concave-side rule, which states that during stretch bending the forming limit occurs when the strains on the concave surface plane of the bent sheet (i.e. bottom plane) reach the forming limit curve (FLC). The verification with experimental data indicates that the FEA model represents the process very well. Only conditions where failure occurred on or near the tooling are included in the results. The FEA simulations showed that the actual forming limit of the sheet occurs when the strains on the bottom plane of the sheet (i.e. concave side of the bend) reach the forming limit curve for high friction and small tool radii. For lower friction and for larger tool radii the actual forming limit occurs when strains on other planes in the sheet (i.e. mid planes or top surface plane) reach the forming limit curve. The implications of these results suggest that care must be taken in assessing forming operations when both stretch and bending occur. Although it is known that the FLC cannot predict the forming limit for small bend radii, the common assumption that the forming limit occurs when the strains for the middle thickness plane of the sheet reach the forming limit curve or that the concave side rule is often made. Understanding the limits of this assumption needs to be carefully and critically evaluated.
Detection of toxin proteins from Bacillus thuringiensis strain 4.0718 by strategy of 2D-LC-MS/MS.
Yang, Qi; Tang, Sijia; Rang, Jie; Zuo, Mingxing; Ding, Xuezhi; Sun, Yunjun; Feng, Pinghui; Xia, Liqiu
2015-04-01
Bacillus thuringiensis is a kind of insecticidal microorganism which can produce a variety of toxin proteins, it is particularly important to find an effective strategy to identify novel toxin proteins rapidly and comprehensively with the discovery of the wild-type strains. Multi-dimensional high-performance liquid chromatography combined with mass spectrometry has become one of the main methods to detect and identify toxin proteins and proteome of B. thuringiensis. In this study, protein samples from B. thuringiensis strain 4.0718 were analyzed on the basis of two-dimensional liquid chromatography-tandem mass spectrometry (2D-LC-MS/MS), and tryptic peptides of whole cell from the late sporulation phase were eluted at different concentration gradients of ammonium chloride and followed by secondary mass spectrum identification. 831 and 894 proteins were identified from two biological replicates, respectively, while 1,770 and 1,859 peptides were detected correspondingly. Among the identified proteins and peptides, 606 proteins and 1,259 peptides were detected in both replicates, which mean that 1,119 proteins and 2,370 peptides were unique to the proteome of this strain. A total of 15 toxins have been identified successfully, and seven of them were firstly discovered in B. thuringiensis strain 4.0718 that were Crystal protein (A1E259), pesticidal protein (U5KS09), Cry2Af1 (A4GVF0), Cry2Ad (Q9RM89), Cry1 (K4HMB5), Cry1Bc (Q45774), and Cry1Ga (Q45746). The proteomic strategy employed in the present study has provided quick and exhaustive identification of toxins produced by B. thuringiensis.
NASA Astrophysics Data System (ADS)
Ma, ShengQian; Li, Feng; Geng, JiGuo
2017-04-01
Since efficient synthesis of C2N holey two-dimensional (h2D) crystal has been possible, bandgap modulation through use of analogous nanoribbon and nanotube structures has attracted strong interest. In this study, bandgap modulation of Si2N-h2D nanoribbons and nanotubes under elastic strain has been deeply researched using density functional theory calculations. The results indicate that the bandgap of Si2N-h2D nanoribbons and nanotubes in zigzag and armchair configurations can be tuned in both directions, namely by stretching or compressing, in the range of ɛ = ( d - d 0)/ d 0 from -10% to 10%. It is also found that the bandgap of Si2N-h2D nanoribbons and nanotubes varies with their width. Therefore, it is predicted that Si2N-h2D nanoribbons and nanotubes have great potential for application in nanoscale strain sensors and optoelectronics.
Reversed polarized emission in highly strained a -plane GaN/AlN multiple quantum wells
NASA Astrophysics Data System (ADS)
Mata, R.; Cros, A.; Budagosky, J. A.; Molina-Sánchez, A.; Garro, N.; García-Cristóbal, A.; Renard, J.; Founta, S.; Gayral, B.; Bellet-Amalric, E.; Bougerol, C.; Daudin, B.
2010-09-01
The polarization of the emission from a set of highly strained a -plane GaN/AlN multiple quantum wells of varying well widths has been studied. A single photoluminescence peak is observed that shifts to higher energies as the quantum well thickness decreases due to quantum confinement. The emitted light is linearly polarized. For the thinnest samples the preferential polarization direction is perpendicular to the wurtzite c axis with a degree of polarization that decreases with increasing well width. However, for the thickest well the preferred polarization direction is parallel to the c axis. Raman scattering, x-ray diffraction, and transmission electron microscopy studies have been performed to determine the three components of the strain tensor in the active region. Moreover, the experimental results have been compared with the strain values computed by means of a model based on the elastic continuum theory. A high anisotropic compressive in-plane strain has been found, namely, -0.6% and -2.8% along the in-plane directions [11¯00] and [0001], respectively, for the thickest quantum well. The oscillator strength of the lowest optical transition has been calculated within the framework of a multiband envelope function model for various quantum well widths and strain values. The influence of confinement and strain on the degree of polarization is discussed and compared with experiment considering various sets of material parameters.
NASA Astrophysics Data System (ADS)
Papadakis, S. J.; de Poortere, E. P.; Shayegan, M.; Winkler, R.
2000-03-01
We report experiments on (311)A GaAs 2D holes at 0.3 - 1.4 K with an in-plane magnetic field B. The density range (1.3 × 10^10 < p < 6.6 × 10^10 cm-2) is such that the temperature dependence of the resistivity is metallic-like at B = 0. In all cases the system displays positive magnetoresistance whose details depend on the relative orientations of B and the crystal axes as well as of B and the current (I) direction.(S. J. Papadakis et al.), cond-mat/9911239. We observe a feature in the magnetoresistance, associated with a spin-subband de-population, whose B-position changes when the field direction is changed from [bar233] to [01bar1]. Near this feature, there is a critical field BT beyond which the behavior changes to insulating. B_T, too, changes when the orientation of B relative to the crystal axes is changed. Changing the direction of I with respect to B also affects the positions of these features, but to a much smaller degree. The data are consistent with the idea that two spin-subbands with different populations are necessary for the existence of the B = 0 metallic behavior, and are also a clear demonstration of the anisotropy of the band structure of GaAs 2D holes grown on (311)A substrates.
Ha, Don-Hyung; Caldwell, Andrew H; Ward, Matthew J; Honrao, Shreyas; Mathew, Kiran; Hovden, Robert; Koker, Margaret K A; Muller, David A; Hennig, Richard G; Robinson, Richard D
2014-12-10
We demonstrate dual interface formation in nanocrystals (NCs) through cation exchange, creating epitaxial heterostructures within spherical NCs. The thickness of the inner-disk layer can be tuned to form two-dimensional (2D), single atomic layers (<1 nm). During the cation exchange reaction from copper sulfide to zinc sulfide (ZnS), we observe a solid-solid phase transformation of the copper sulfide phase in heterostructured NCs. As the cation exchange reaction is initiated, Cu ions replaced by Zn ions at the interfaces are accommodated in intrinsic Cu vacancy sites present in the initial roxbyite (Cu1.81S) phase of copper sulfide, inducing a full phase transition to djurleite (Cu1.94S)/low chalcocite (Cu2S), a more thermodynamically stable phase than roxbyite. As the reaction proceeds and reduces the size of the copper sulfide layer, the epitaxial strain at the interfaces between copper sulfide and ZnS increases and is maximized for a copper sulfide disk ∼ 5 nm thick. To minimize this strain energy, a second phase transformation occurs back to the roxbyite phase, which shares a similar sulfur sublattice to wurtzite ZnS. The observation of a solid-solid phase transformation in our unique heterostructured NCs provides a new pathway to control desired phases and an insight into the influence of cation exchange on nanoscale phase transitions in heterostructured materials.
Matsui, Hiroaki Tabata, Hitoshi; Hasuike, Noriyuki; Harima, Hiroshi
2014-09-21
In-plane anisotropic strains in A-plane layers on the electronic band structure of ZnO were investigated from the viewpoint of optical polarization anisotropy. Investigations utilizing k·p perturbation theory revealed that energy transitions and associated oscillation strengths were dependent on in-plane strains. The theoretical correlation between optical polarizations and in-plane strains was experimentally demonstrated using A-plane ZnO layers with different in-plane strains. Finally, optical polarization anisotropy and its implications for in-plane optical properties are discussed in relation to the energy shift between two orthogonal directions. Higher polarization rotations were obtained in an A-plane ZnO layer with in-plane biaxially compressive strains as compared to strain-free ZnO. This study provides detailed information concerning the role played by in-plane strains in optically polarized applications based on nonpolar ZnO in the ultra-violet region.
The plane strain shear fracture of the advanced high strength steels
NASA Astrophysics Data System (ADS)
Sun, Li
2013-12-01
The "shear fracture" which occurs at the high-curvature die radii in the sheet metal forming has been reported to remarkably limit the application of the advanced high strength steels (AHSS) in the automobile industry. However, this unusual fracture behavior generally cannot be predicted by the traditional forming limit diagram (FLD). In this research, a new experimental system was developed in order to simulate the shear fracture, especially at the plane strain state which is the most common state in the auto-industry and difficult to achieve in the lab due to sample size. Furthermore, the system has the capability to operate in a strain rate range from quasi-static state to the industrial forming state. One kinds of AHSS, Quenching-Partitioning (QP) steels have been performed in this test and the results show that the limiting fracture strain is related to the bending ratio and strain rate. The experimental data support that deformation-induced heating is an important cause of "shear fracture" phenomena for AHSS: a deformation-induced quasi-heating caused by smaller bending ratio and high strain rate produce a smaller limiting plane strain and lead a "shear fracture" in the component.
The plane strain shear fracture of the advanced high strength steels
Sun, Li
2013-12-16
The “shear fracture” which occurs at the high-curvature die radii in the sheet metal forming has been reported to remarkably limit the application of the advanced high strength steels (AHSS) in the automobile industry. However, this unusual fracture behavior generally cannot be predicted by the traditional forming limit diagram (FLD). In this research, a new experimental system was developed in order to simulate the shear fracture, especially at the plane strain state which is the most common state in the auto-industry and difficult to achieve in the lab due to sample size. Furthermore, the system has the capability to operate in a strain rate range from quasi-static state to the industrial forming state. One kinds of AHSS, Quenching-Partitioning (QP) steels have been performed in this test and the results show that the limiting fracture strain is related to the bending ratio and strain rate. The experimental data support that deformation-induced heating is an important cause of “shear fracture” phenomena for AHSS: a deformation-induced quasi-heating caused by smaller bending ratio and high strain rate produce a smaller limiting plane strain and lead a “shear fracture” in the component.
NASA Astrophysics Data System (ADS)
Otake, Yoshito; Esnault, Matthieu; Grupp, Robert; Kosugi, Shinichi; Sato, Yoshinobu
2016-03-01
The determination of in vivo motion of multiple-bones using dynamic fluoroscopic images and computed tomography (CT) is useful for post-operative assessment of orthopaedic surgeries such as medial patellofemoral ligament reconstruction. We propose a robust method to measure the 3D motion of multiple rigid objects with high accuracy using a series of bi-plane fluoroscopic images and a multi-resolution, intensity-based, 2D-3D registration. A Covariance Matrix Adaptation Evolution Strategy (CMA-ES) optimizer was used with a gradient correlation similarity metric. Four approaches to register three rigid objects (femur, tibia-fibula and patella) were implemented: 1) an individual bone approach registering one bone at a time, each with optimization of a six degrees of freedom (6DOF) parameter, 2) a sequential approach registering one bone at a time but using the previous bone results as the background in DRR generation, 3) a simultaneous approach registering all the bones together (18DOF) and 4) a combination of the sequential and the simultaneous approaches. These approaches were compared in experiments using simulated images generated from the CT of a healthy volunteer and measured fluoroscopic images. Over the 120 simulated frames of motion, the simultaneous approach showed improved registration accuracy compared to the individual approach: with less than 0.68mm root-mean-square error (RMSE) for translation and less than 1.12° RMSE for rotation. A robustness evaluation was conducted with 45 trials of a randomly perturbed initialization showed that the sequential approach improved robustness significantly (74% success rate) compared to the individual bone approach (34% success) for patella registration (femur and tibia-fibula registration had a 100% success rate with each approach).
The unique effect of in-plane anisotropic strain in the magnetization control by electric field
NASA Astrophysics Data System (ADS)
Zhao, Y. Y.; Wang, J.; Hu, F. X.; Liu, Y.; Kuang, H.; Wu, R. R.; Sun, J. R.; Shen, B. G.
2016-05-01
The electric field control of magnetization in both (100)- and (011)-Pr0.7Sr0.3MnO3/Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PSMO/PMN-PT) heterostructures were investigated. It was found that the in-plane isotropic strain induced by electric field only slightly reduces the magnetization at low temperature in (100)-PSMO/PMN-PT film. On the other hand, for (011)-PSMO/PMN-PT film, the in-plane anisotropic strain results in in-plane anisotropic, nonvolatile change of magnetization at low-temperature. The magnetization, remanence and coercivity along in-plane [100] direction are suppressed by the electric field while the ones along [01-1] direction are enhanced, which is ascribed to the extra effective magnetic anisotropy induced by the electric field via anisotropic piezostrains. More interestingly, such anisotropic modulation behaviors are nonvolatile, demonstrating a memory effect.
Finite Element Modeling of Plane Strain Toughness for 7085 Aluminum Alloy
NASA Astrophysics Data System (ADS)
Karabin, M. E.; Barlat, F.; Shuey, R. T.
2009-02-01
In this work, the constitutive model for 7085-T7X (overaged) aluminum alloy plate samples with controlled microstructures was developed. Different lengths of 2nd step aging times produced samples with similar microstructure but different stress-strain curves ( i.e., different nanostructure). A conventional phenomenological strain-hardening law with no strain gradient effects was proposed to capture the peculiar hardening behavior of the material samples investigated in this work. The classical Gurson-Tvergaard potential, which includes the influence of void volume fraction (VVF) on the plastic flow behavior, as well as an extension proposed by Leblond et al.,[3] were considered. Unlike the former, the latter is able to account for the influence of strain hardening on the VVF growth. All the constitutive coefficients used in this work were based on experimental stress-strain curves obtained in uniaxial tension and on micromechanical modeling results of a void embedded in a matrix. These material models were used in finite element (FE) simulations of a compact tension (CT) specimen. An engineering criterion based on the instability of plastic flow at a crack tip was used for the determination of plane strain toughness K Ic . The influence of the microstructure was lumped into a single state variable, the initial void volume fraction. The simulation results showed that the strain-hardening behavior has a significant influence on K Ic .
NASA Astrophysics Data System (ADS)
Graba, M.
2016-12-01
This paper presents a numerical analysis of the relationship between in-plane constraints and the crack tip opening displacement (CTOD) for single-edge notched bend (SEN(B)) specimens under predominantly plane strain conditions. It provides details of the numerical model and discusses the influence of external load and in-plane constraints on the CTOD. The work also reviews methods for determining the CTOD. The new formula proposed in this paper can be used to estimate the value of the coefficient dn as a function of the relative crack length, the strain hardening exponent and the yield strength - dn(n, σ0/E, a/W), with these parameters affecting the level of in-plane constraints. Some of the numerical results were approximated using simple mathematical formulae.
NASA Technical Reports Server (NTRS)
Morscher, Gregory N.; Yun, Hee Mann; DiCarlo, James A.
2007-01-01
The tensile mechanical properties of ceramic matrix composites (CMC) in directions off the primary axes of the reinforcing fibers are important for architectural design of CMC components that are subjected to multi-axial stress states. In this study, 2D-woven melt-infiltrated (MI) SiC/SiC composite panels with balanced fiber content in the 0 degree and 90 degree directions were tensile loaded in-plane in the 0 degree direction and at 45 degree to this direction. In addition, a 2D triaxially-braided MI composite panel with balanced fiber content in the plus or minus 67 degree bias directions and reduced fiber content in the axial direction was tensile loaded perpendicular to the axial direction tows (i.e., 23 degrees from the bias fibers). Stress-strain behavior, acoustic emission, and optical microscopy were used to quantify stress-dependent matrix cracking and ultimate strength in the panels. It was observed that both off-axis loaded panels displayed higher composite onset stresses for through-thickness matrix cracking than the 2D-woven 0/90 panels loaded in the primary 0 degree direction. These improvements for off-axis cracking strength can in part be attributed to higher effective fiber fractions in the loading direction, which in turn reduces internal stresses on critical matrix flaws for a given composite stress. Also for the 0/90 panel loaded in the 45 degree direction, an improved distribution of matrix flaws existed due to the absence of fiber tows perpendicular to the loading direction. In addition, for the +67/0/-67 braided panel, the axial tows perpendicular to the loading direction were not only low in volume fraction, but were also were well separated from one another. Both off-axis oriented panels also showed relatively good ultimate tensile strength when compared to other off-axis oriented composites in the literature, both on an absolute strength basis as well as when normalized by the average fiber strength within the composites. Initial
Band gap modulation of transition-metal dichalcogenide MX2 nanosheets by in-plane strain
NASA Astrophysics Data System (ADS)
Su, Xiangying; Ju, Weiwei; Zhang, Ruizhi; Guo, Chongfeng; Yong, Yongliang; Cui, Hongling; Li, Xiaohong
2016-10-01
The electronic properties of quasi-two-dimensional honeycomb structures of MX2 nanosheets (M=Mo, W and X=S, Se) subjected to in-plane biaxial strain have been investigated using first-principles calculations. We demonstrate that the band gap of MX2 nanosheets can be widely tuned by applying tensile or compressive strain, and these ultrathin materials undergo a universal reversible semiconductor-metal transition at a critical strain. Compared to WX2, MoX2 need a smaller critical tensile strain for the band gap close, and MSe2 need a smaller critical compressive strain than MS2. Taking bilayer MoS2 as an example, the variation of the band structures was studied and the semiconductor-metal transition involves a slightly different physical mechanism between tensile and compressive strain. The ability to tune the band gap of MX2 nanosheets in a controlled fashion over a wide range of energy opens up the possibility for its usage in a range of application.
Analysis of plane-plastic stress problems with axial symmetry in strain-hardening range
NASA Technical Reports Server (NTRS)
Wu, M H Lee
1951-01-01
A simple method is developed for solving plane-plastic-stress problems with axial symmetry in the strain-hardening range which is based on the deformation theory of plasticity employing the finite-strain concept. The equations defining the problems are first reduced to two simultaneous nonlinear differential equations involving two dependent variables: (a) the octahedral shear strain, and (b) a parameter indicating the ratio of principal stresses. By multiplying the load and dividing the radius by an arbitrary constant, it is possible to solve these problems without iteration for any value of the modified load. The constant is determined by the boundary condition. This method is applied to a circular membrane under pressure, a rotating disk without and with a central hole, and an infinite plate with a circular hole. Two materials, inconel x and 16-25-6, the octahedral shear stress-strain relations of which do not follow the power law, are used. Distributions of octahedral shear strain, as well as of principal stresses and strains, are obtained. These results are compared with the results of the same problems in the elastic range.
Reconstruction of in-plane strain maps using hybrid dense sensor network composed of sensing skin
NASA Astrophysics Data System (ADS)
Downey, Austin; Laflamme, Simon; Ubertini, Filippo
2016-12-01
The authors have recently developed a soft-elastomeric capacitive (SEC)-based thin film sensor for monitoring strain on mesosurfaces. Arranged in a network configuration, the sensing system is analogous to a biological skin, where local strain can be monitored over a global area. Under plane stress conditions, the sensor output contains the additive measurement of the two principal strain components over the monitored surface. In applications where the evaluation of strain maps is useful, in structural health monitoring for instance, such signal must be decomposed into linear strain components along orthogonal directions. Previous work has led to an algorithm that enabled such decomposition by leveraging a dense sensor network configuration with the addition of assumed boundary conditions. Here, we significantly improve the algorithm’s accuracy by leveraging mature off-the-shelf solutions to create a hybrid dense sensor network (HDSN) to improve on the boundary condition assumptions. The system’s boundary conditions are enforced using unidirectional RSGs and assumed virtual sensors. Results from an extensive experimental investigation demonstrate the good performance of the proposed algorithm and its robustness with respect to sensors’ layout. Overall, the proposed algorithm is seen to effectively leverage the advantages of a hybrid dense network for application of the thin film sensor to reconstruct surface strain fields over large surfaces.
Temperature Evolution During Plane Strain Compression Of Tertiary Oxide Scale On Steel
Suarez, L.; Houbaert, Y.; Eynde, X. van den; Lamberigts, M.
2007-04-07
An oxide scale layer always forms at the steel surface during hot rolling. This scale layer separates the work roll from the metal substrate. Understanding the deformation behaviour and mechanical properties of the scale is of great interest because it affects the frictional conditions during hot rolling and the heat-transfer behaviour at the strip-roll interface. A thin wustite scale layer (<20 {mu}m) was created under controlled conditions in an original laboratory device adequately positioned in a compression testing machine to investigate plane strain compression. Oxidation tests were performed on an ULC steel grade. After the oxide growth at 1050 deg. C, plane strain compression (PSC) was performed immediately to simulate the hot rolling process. PSC experiments were performed at a deformation temperature of 1050 deg. C, with reduction ratios from 5 to 70%, and strain rates of 10s-1 under controlled gas atmospheres. Results show that for wustite, ductility is obvious at 1050 deg. C. Even after deformation oxide layers exhibit good adhesion to the substrate and homogeneity over the thickness. The tool/sample temperature difference seems to be the reason for the unexpected ductile behaviour of the scale layer.
Evaluation of Instability Phenomena in Sands: Plane Strain Versus Triaxial Conditions
NASA Technical Reports Server (NTRS)
Alshibli, Khalid A.
2001-01-01
Extensive research was carried out in the 1950s on theories of plasticity to extend the concepts developed for metals to materials that failed according to the Mohr-Coulomb criterion. The new ideas made it possible to merge the two distinct concepts (strength and deformation techniques) into one that relies on better understanding of plasticity and resulted in a rapid growth in the field of constitutive modeling of soil behavior. At the same time advanced experimental apparatuses and laboratory procedures were developed to calibrate the models. However, most laboratory experiments on granular materials are performed under Conventional Triaxial Conditions (CTC) for the purposes of evaluating constitutive behavior and stability properties, whereas most geotechnical field problems are closer to the Plane Strain (PS) condition. The triaxial tests performed in most laboratories comprise a simplification over in situ states and allow easier and robust experimentation. Most landslide problems, failure of soils beneath shallow and deep foundations, and failure of retaining structures, are cases that can generally be considered as plane strain. Strength and deformation characteristics of granular materials loaded in plane strain may be considerably different from those observed in CTC. Most studies on sands were limited to evaluating the constitutive behavior and in some cases extended to briefly describing the associated instability phenomena. This paper presents the results of a series of PS and CTC experiments performed on fine uniform silica sand known as F-75 Ottawa sand. Advanced analysis techniques were used to study the instability phenomena, which yielded very accurate measurements of shear bands occurrences and patterns. Destructive thin-sectioning technique along with monitoring the specimen surface deformation was used in the PS experiments and Computed Tomography (CT) was used to investigate the progress of primary and secondary shear bands in specimens
Liu, T; Torres, M; Rossi, P; Jani, A; Curran, W; Yang, X
2015-06-15
Purpose: Radiation-induced fibrosis is a common long-term complication affecting many patients following cancer radiotherapy. Standard clinical assessment of subcutaneous fibrosis is subjective and often limited to visual inspection and palpation. Ultrasound strain imaging describes the compressibility (elasticity) of biological tissues. This study’s purpose is to develop a quantitative ultrasound strain imaging that can consistently and accurately characterize radiation-induce fibrosis. Methods: In this study, we propose a 2D strain imaging method based on deformable image registration. A combined affine and B-spline transformation model is used to calculate the displacement of tissue between pre-stress and post-stress B-mode image sequences. The 2D displacement is estimated through a hybrid image similarity measure metric, which is a combination of the normalized mutual information (NMI) and normalized sum-of-squared-differences (NSSD). And 2D strain is obtained from the gradient of the local displacement. We conducted phantom experiments under various compressions and compared the performance of our proposed method with the standard cross-correlation (CC)- based method using the signal-to-noise (SNR) and contrast-to-noise (CNS) ratios. In addition, we conducted ex-vivo beef muscle experiment to further validate the proposed method. Results: For phantom study, the SNR and CNS values of the proposed method were significantly higher than those calculated from the CC-based method under different strains. The SNR and CNR increased by a factor of 1.9 and 2.7 comparing to the CC-based method. For the ex-vivo experiment, the CC-based method failed to work due to large deformation (6.7%), while our proposed method could accurately detect the stiffness change. Conclusion: We have developed a 2D strain imaging technique based on the deformable image registration, validated its accuracy and feasibility with phantom and ex-vivo data. This 2D ultrasound strain imaging
Effects of Be and Fe content on plane strain fracture toughness in A357 alloys
Tan, Y.H.; Lee, S.L.; Lin, Y.L.
1995-11-01
The effect of Be and Fe content on the plane strain fracture toughness K{sub IC} of aluminum-based A357 alloys is investigated. The fracture behavior of A357 alloys has been evaluated as a function of both the magnitude and morphology of iron-bearing compounds and silicon particles. Addition of Be is beneficial for tensile properties and fracture toughness in the case of alloys containing intermediate (0.07 pct) and higher (0.15 pct) Fe levels. On the other hand, Be added to alloys containing the lower Fe (0.01 pct) level appears detrimental to tensile strength, but the quality index, notch-yield ratio (NYR), and plane strain fracture toughness were improved. Fractographic analysis reveals that crack extension of A357 alloys occurs mainly in an intergranular fracture mode. The fracture processes are initiated by void nucleation at iron-bearing compounds or irregularly shaped eutectic silicon particles as a result of their cracking and decohesion from the matrix. Then, void growth and coalescence result in growth of the main crack by shear-linkage-induced breakdown of submicron-strengthening particles. The effect of Be on increasing K{sub IC} is more apparent in the higher Fe alloys than in the lower Fe alloys. Superior toughness obtained by microstructural control has also been achieved in the intermediate and higher Fe levels of Be-containing alloys, with values equal to those obtained in alloys of lower Fe content.
Effects of be and fe content on plane strain fracture toughness in A357 alloys
NASA Astrophysics Data System (ADS)
Tan, Yen-Hung; Lee, Sheng-Long; Lin, Yu-Lom
1995-11-01
The effect of Be and Fe content on the plane strain fracture toughness K IC of aluminum-based A357 alloys is investigated. The fracture behavior of A357 alloys has been evaluated as a function of both the magnitude and morphology of iron-bearing compounds and silicon particles. Addition of Be is beneficial for tensile properties and fracture toughness in the case of alloys containing intermediate (0.07 pct) and higher (0.15 pct) Fe levels. On the other hand, Be added to alloys containing the lower Fe (0.01 pct) level appears detrimental to tensile strength, but the quality index, notch-yield ratio (NYR), and plane strain fracture toughness were improved. Fractographic analysis reveals that crack extension of A357 alloys occurs mainly in an intergranular fracture mode. The fracture processes are initiated by void nucleation at iron-bearing compounds or irregularly shaped eutectic silicon particles as a result of their cracking and decohesion from the matrix. Then, void growth and coalescence result in growth of the main crack by shear-linkage-induced breakdown of submicronstrengthening particles. The effect of Be on increasing K IC is more apparent in the higher Fe alloys than in the lower Fe alloys. Superior toughness obtained by microstructural control has also been achieved in the intermediate and higher Fe levels of Be-containing alloys, with values equal to those obtained in alloys of lower Fe content.
Delannoy, Sabine; Mariani-Kurkdjian, Patricia; Bonacorsi, Stephane; Liguori, Sandrine
2014-01-01
Strains of Escherichia coli O26:H11 that were positive for stx2 alone (n = 23), which were not epidemiologically related or part of an outbreak, were isolated from pediatric patients in France between 2010 and 2013. We were interested in comparing these strains with the new highly virulent stx2a-positive E. coli O26 clone sequence type 29 (ST29) that has emerged recently in Europe, and we tested them by multilocus sequence typing (MLST), stx2 subtyping, clustered regularly interspaced short palindromic repeat (CRISPR) sequencing, and plasmid (ehxA, katP, espP, and etpD) and chromosomal (Z2098, espK, and espV) virulence gene profiling. We showed that 16 of the 23 strains appeared to correspond to this new clone, but the characteristics of 12 strains differed significantly from the previously described characteristics, with negative results for both plasmid and chromosomal genetic markers. These 12 strains exhibited a ST29 genotype and related CRISPR arrays (CRISPR2a alleles 67 or 71), suggesting that they evolved in a common environment. This finding was corroborated by the presence of stx2d in 7 of the 12 ST29 strains. This is the first time that E. coli O26:H11 carrying stx2d has been isolated from humans. This is additional evidence of the continuing evolution of virulent Shiga toxin-producing E. coli (STEC) O26 strains. A new O26:H11 CRISPR PCR assay, SP_O26_E, has been developed for detection of these 12 particular ST29 strains of E. coli O26:H11. This test is useful to better characterize the stx2-positive O26:H11 clinical isolates, which are associated with severe clinical outcomes such as bloody diarrhea and hemolytic uremic syndrome. PMID:25428148
Assessment of Constitutive and Stability Behavior of Sands Under Plane Strain Condition
NASA Technical Reports Server (NTRS)
Alshibli, Khalid A.; Sture, Stein
2000-01-01
A series of biaxial (plane strain) experiments were conducted on three sands under low (15 kPa) and high (100 kPa) confining pressure conditions to investigate the effects of specimen density, confining pressure, and sand grains size and shape on the constitutive and stability behavior of granular materials. The three sands used in the experiments were fine, medium, and coarse-grained uniform silica sands with rounded, sub-angular, and angular grains, respectively. Specimen deformation was readily monitored and analyzed with the help of a grid pattern imprinted on the latex membrane. The overall stress-strain behavior is strongly dependent on the specimen density, confining pressure, sand grain texture, and the resulting failure mode(s). That became evident in different degrees of softening responses at various axial strains. The relationship between the constitutive behavior and the specimens' modes of instability is presented. The failure in all specimens was characterized by two distinct and opposite shear bands. It was found that the measured dilatancy angles increase as the sand grains' angularity and size increase. The measured shear band inclination angles are also presented and compared with classical Coulomb and Roscoe solutions.
NASA Technical Reports Server (NTRS)
Alshibli, Khalid A.; Batiste, Susan N.; Sture, Stein; Curreri, Peter A. (Technical Monitor)
2002-01-01
A comprehensive experimental investigation was conducted to investigate the effects of loading condition and confining pressure on strength properties and instability phenomena in sands. A uniform sub-rounded to rounded natural silica sand known as F-75 Ottawa sand was used in the investigation. The results of a series on Conventional Triaxial Compression (CTC) experiments tested under very low confining pressures (0.05 - 1.30) kPa tested in a Microgravity environment abroad the NASA Space Shuttle are presented in addition to the results similar specimens tested in terrestrial laboratory to investigate the effect of confining pressure on the constitutive behavior of sands. The behavior of the CTC experiments is compared with the results of Plane Strain (PS) experiments. Computed tomography and other digital imaging techniques were used to study the development and evolution of shear bands.
Investigation of flaw geometry and loading effects on plane strain fracture in metallic structures
NASA Technical Reports Server (NTRS)
Hall, L. R.; Finger, R. W.
1971-01-01
The effects on fracture and flaw growth of weld-induced residual stresses, combined bending and tension stresses, and stress fields adjacent to circular holes in 2219-T87 aluminum and 5AI-2.5Sn(ELI) titanium alloys were evaluated. Static fracture tests were conducted in liquid nitrogen; fatigue tests were performed in room air, liquid nitrogen, and liquid hydrogen. Evaluation of results was based on linear elastic fracture mechanics concepts and was directed to improving existing methods of estimating minimum fracture strength and fatigue lives for pressurized structure in spacecraft and booster systems. Effects of specimen design in plane-strain fracture toughness testing were investigated. Four different specimen types were tested in room air, liquid nitrogen and liquid hydrogen environments using the aluminum and titanium alloys. Interferometry and holograph were used to measure crack-opening displacements in surface-flawed plexiglass test specimens. Comparisons were made between stress intensities calculated using displacement measurements, and approximate analytical solutions.
Plane-strain crack problems in microstructured solids governed by dipolar gradient elasticity
NASA Astrophysics Data System (ADS)
Gourgiotis, P. A.; Georgiadis, H. G.
2009-11-01
The present study aims at determining the elastic stress and displacement fields around the tips of a finite-length crack in a microstructured solid under remotely applied plane-strain loading (mode I and II cases). The material microstructure is modeled through the Toupin-Mindlin generalized continuum theory of dipolar gradient elasticity. According to this theory, the strain-energy density assumes the form of a positive-definite function of the strain tensor (as in classical elasticity) and the gradient of the strain tensor (additional term). A simple but yet rigorous version of the theory is employed here by considering an isotropic linear expression of the elastic strain-energy density that involves only three material constants (the two Lamé constants and the so-called gradient coefficient). First, a near-tip asymptotic solution is obtained by the Knein-Williams technique. Then, we attack the complete boundary value problem in an effort to obtain a full-field solution. Hypersingular integral equations with a cubic singularity are formulated with the aid of the Fourier transform. These equations are solved by analytical considerations on Hadamard finite-part integrals and a numerical treatment. The results show significant departure from the predictions of standard fracture mechanics. In view of these results, it seems that the classical theory of elasticity is inadequate to analyze crack problems in microstructured materials. Indeed, the present results indicate that the stress distribution ahead of the crack tip exhibits a local maximum that is bounded. Therefore, this maximum value may serve as a measure of the critical stress level at which further advancement of the crack may occur. Also, in the vicinity of the crack tip, the crack-face displacement closes more smoothly as compared to the standard result and the strain field is bounded. Finally, the J-integral (energy release rate) in gradient elasticity was evaluated. A decrease of its value is noticed
Ma, Lin; Li, Xuesong; Sanders, Scott T; Caswell, Andrew W; Roy, Sukesh; Plemmons, David H; Gord, James R
2013-01-14
This paper describes a novel laser diagnostic and its demonstration in a practical aero-propulsion engine (General Electric J85). The diagnostic technique, named hyperspectral tomography (HT), enables simultaneous 2-dimensional (2D) imaging of temperature and water-vapor concentration at 225 spatial grid points with a temporal response up to 50 kHz. To our knowledge, this is the first time that such sensing capabilities have been reported. This paper introduces the principles of the HT techniques, reports its operation and application in a J85 engine, and discusses its perspective for the study of high-speed reactive flows.
Andrews, D.J.
1985-01-01
A numerical boundary integral method, relating slip and traction on a plane in an elastic medium by convolution with a discretized Green function, can be linked to a slip-dependent friction law on the fault plane. Such a method is developed here in two-dimensional plane-strain geometry. Spontaneous plane-strain shear ruptures can make a transition from sub-Rayleigh to near-P propagation velocity. Results from the boundary integral method agree with earlier results from a finite difference method on the location of this transition in parameter space. The methods differ in their prediction of rupture velocity following the transition. The trailing edge of the cohesive zone propagates at the P-wave velocity after the transition in the boundary integral calculations. Refs.
NASA Astrophysics Data System (ADS)
Kroon, M.
2011-11-01
Rubbers and soft biological tissues may undergo large deformations and are also viscoelastic. The formulation of constitutive models for these materials poses special challenges. In several applications, especially in biomechanics, these materials are also relatively thin, implying that in-plane stresses dominate and that plane stress may therefore be assumed. In the present paper, a constitutive model for viscoelastic materials in the finite strain regime and under the assumption of plane stress is proposed. It is assumed that the relaxation behaviour in the direction of plane stress can be treated separately, which makes it possible to formulate evolution laws for the plastic strains on explicit form at the same time as incompressibility is fulfilled. Experimental results from biomechanics (dynamic inflation of dog aorta) and rubber mechanics (biaxial stretching of rubber sheets) were used to assess the proposed model. The assessment clearly indicates that the model is fully able to predict the experimental outcome for these types of material.
Static & Dynamic Response of 2D Solids
Lin, Jerry
1996-07-15
NIKE2D is an implicit finite-element code for analyzing the finite deformation, static and dynamic response of two-dimensional, axisymmetric, plane strain, and plane stress solids. The code is fully vectorized and available on several computing platforms. A number of material models are incorporated to simulate a wide range of material behavior including elasto-placicity, anisotropy, creep, thermal effects, and rate dependence. Slideline algorithms model gaps and sliding along material interfaces, including interface friction, penetration and single surface contact. Interactive-graphics and rezoning is included for analyses with large mesh distortions. In addition to quasi-Newton and arc-length procedures, adaptive algorithms can be defined to solve the implicit equations using the solution language ISLAND. Each of these capabilities and more make NIKE2D a robust analysis tool.
Wireless Open-Circuit In-Plane Strain and Displacement Sensor Requiring No Electrical Connections
NASA Technical Reports Server (NTRS)
Woodard, Stanley E. (Inventor)
2014-01-01
A wireless in-plane strain and displacement sensor includes an electrical conductor fixedly coupled to a substrate subject to strain conditions. The electrical conductor is shaped between its ends for storage of an electric field and a magnetic field, and remains electrically unconnected to define an unconnected open-circuit having inductance and capacitance. In the presence of a time-varying magnetic field, the electrical conductor so-shaped resonates to generate harmonic electric and magnetic field responses. The sensor also includes at least one electrically unconnected electrode having an end and a free portion extending from the end thereof. The end of each electrode is fixedly coupled to the substrate and the free portion thereof remains unencumbered and spaced apart from a portion of the electrical conductor so-shaped. More specifically, at least some of the free portion is disposed at a location lying within the magnetic field response generated by the electrical conductor. A motion guidance structure is slidingly engaged with each electrode's free portion in order to maintain each free portion parallel to the electrical conductor so-shaped.
NASA Astrophysics Data System (ADS)
Benito, L.; Ballesteros, C.; Ward, R. C. C.
2014-04-01
We report on the magnetic and structural characterization of high lattice-mismatched [Dy2nm/SctSc] superlattices, with variable Sc thickness tSc= 2-6 nm. We find that the characteristic in-plane effective hexagonal magnetic anisotropy K66,ef reverses sign and undergoes a dramatic reduction, attaining values of ≈13-24 kJm-3, when compared to K66=-0.76 MJm-3 in bulk Dy. As a result, the basal plane magnetic anisotropy is dominated by a uniaxial magnetic anisotropy (UMA) unfound in bulk Dy, which amounts to ≈175-142 kJm-3. We attribute the large downsizing in K66,ef to the compression epitaxial strain, which generates a competing sixfold magnetoelastic (MEL) contribution to the magnetocrystalline (strain-free) magnetic anisotropy. Our study proves that the in-plane UMA is caused by the coupling between a giant symmetry-breaking MEL constant Mγ ,22≈1 GPa and a morphic orthorhombiclike strain ɛγ ,1≈10-4, whose origin resides on the arising of an in-plane anisotropic strain relaxation process of the pseudoepitaxial registry between the nonmagnetic bottom layers in the superstructure. This investigation shows a broader perspective on the crucial role played by epitaxial strains at engineering the magnetic anisotropy in multilayers.
Cha, Myung-Jin; Kim, Hyun-Sook; Kim, Seong Hwan; Park, Jae-Hyeong
2017-01-01
Backgrounds We aimed to evaluate the predictive power of longitudinal and circumferential fibers according to left ventricular ejection fraction (LVEF) in successfully reperfused acute ST elevation myocardial infarction (STEMI) patients. Methods Total 691 patients (age 59±13, 20% female) underwent clinical evaluation and conventional and strain echocardiography (Global longitudinal strain (GLS), global circumferential strain (GCS)). The clinical outcome was defined as the composite of death, hospitalization for heart failure, non-fatal myocardial infarction, and ventricular arrhythmia. Results During a follow-up of 39±19 months, there were 47 (6.8%) clinical events. In multivariate Cox models adjusted clinical risk factors, age (HR 1.08, p = 0.001) and GLS (HR 1.37, p = 0.001) were independent predictors. The addition of GLS resulted in significant incremental improvement in the predictive value on LVEF (χ2 = 31.8→45.8, p<0.001), although GCS offers no additional benefit. In the subgroup analysis according to LVEF, adjusted with clinical factors, GLS was significant predictive for outcome for the patients with mildly depressed (LVEF 40–50%, HR 2.25, p<0.001) and significantly depressed (LVEF<40%, HR 1.28, p = 0.016) systolic function, although GCS and LVEF lost their power with LVEF<40%. For the patients with preserved LVEF (>50%), GLS, GCS and LVEF did not show significant predictive power. Conclusions GLS is a most powerful predictor of outcome in successfully reperfused STEMI patients, especially with depressed LV dysfunction, although GCS and LVEF lost their predictive power for the patients with significantly depressed LV function. However, GLS did not predict outcome for the patients with preserved LVEF (>50%). PMID:28334029
Li, Rui; Liu, Yousong; Li, Zhaoqian; Shen, Jinpeng; Yang, Yuntao; Cui, Xudong; Yang, Guangcheng
2016-01-04
A single-layered intermolecular carbonization method was applied to synthesize single-layered nitrogen-doped graphene quantum dots (N-GQDs) by using 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) as the only precursor. In this method, the gas produced in the pyrolysis of TATB assists with speeding up of the reactions and expanding the layered distance, so that it facilitates the formation of single-layered N-GQDs (about 80 %). The symmetric intermolecular carbonizations of TATB arrayed in a plane and six nitrogen-containing groups ensure small, uniform sizes (2-5 nm) of the resulting products, and provide high nitrogen-doping concentrations (N/C atomic ratio ca. 10.6 %). In addition to release of the produced gas, TATB is almost completely converted into aggregated N-GQDs; thus, relatively higher production rates are possible with this approach. Investigations show that the as-produced N-GQDs have superior fluorescent characteristics; high water solubility, biocompatibility, and low toxicity; and are ready for potential applications, such as biomedical imaging and optoelectronic devices.
NASA Astrophysics Data System (ADS)
Morrison, C.; Casteleiro, C.; Leadley, D. R.; Myronov, M.
2016-09-01
The complex quantum transport of a strained Ge quantum well (QW) modulation doped heterostructure with two types of mobile carriers has been observed. The two dimensional hole gas (2DHG) in the Ge QW exhibits an exceptionally high mobility of 780 000 cm2/Vs at temperatures below 10 K. Through analysis of Shubnikov de-Haas oscillations in the magnetoresistance of this 2DHG below 2 K, the hole effective mass is found to be 0.065 m0. Anomalous conductance peaks are observed at higher fields which deviate from standard Shubnikov de-Haas and quantum Hall effect behaviour due to conduction via multiple carrier types. Despite this complex behaviour, analysis using a transport model with two conductive channels explains this behaviour and allows key physical parameters such as the carrier effective mass, transport, and quantum lifetimes and conductivity of the electrically active layers to be extracted. This finding is important for electronic device applications, since inclusion of highly doped interlayers which are electrically active, for enhancement of, for example, room temperature carrier mobility, does not prevent analysis of quantum transport in a QW.
NASA Astrophysics Data System (ADS)
Kistanov, Andrey A.; Cai, Yongqing; Zhang, Yong-Wei; Dmitriev, Sergey V.; Zhou, Kun
2017-03-01
By using first-principles calculations, the electronic structure of planar and strained in-plane graphene/silicene heterostructure is studied. The heterostructure is found to be metallic in a strain range from ‑7% (compression) to +7% (tension). The effect of compressive/tensile strain on the chemical activity of the in-plane graphene/silicene heterostructure is examined by studying its interaction with the H2O molecule. It shows that compressive/tensile strain is able to increase the binding energy of H2O compared with the adsorption on a planar surface, and the charge transfer between the water molecule and the graphene/silicene sheet can be modulated by strain. Moreover, the presence of the boron-nitride (BN)-substrate significantly influences the chemical activity of the graphene/silicene heterostructure upon its interaction with the H2O molecule and may cause an increase/decrease of the charge transfer between the H2O molecule and the heterostructure. These findings provide insights into the modulation of electronic properties of the in-plane free-standing/substrate-supported graphene/silicene heterostructure, and render possible ways to control its electronic structure, carrier density and redox characteristics, which may be useful for its potential applications in nanoelectronics and gas sensors.
Hartmann, Jens; Knebel, Fabian; Eddicks, Stephan; Beling, Mark; Grohmann, Andrea; Panda, Alexander; Jacobi, Christoph A; Müller, Joachim M; Wernecke, Klaus-Dieter; Baumann, Gert; Borges, Adrian C
2007-01-01
Objective We sought to evaluate the impact of different antineoplastic treatment methods on systolic and diastolic myocardial function, and the feasibility estimation of regional deformation parameters with non-Doppler 2D echocardiography in rats. Background The optimal method for quantitative assessment of global and regional ventricular function in rats and the impact of complex oncological multimodal therapy on left- and right-ventricular function in rats remains unclear. Methods 90 rats after subperitoneal implantation of syngenetic colonic carcinoma cells underwent different onclogical treatment methods and were diveded into one control group and five treatment groups (with 15 rats in each group): group 1 = control group (without operation and without medication), group 2 = operation group without additional therapy, group 3 = combination of operation and photodynamic therapy, group 4 = operation in combination with hyperthermic intraoperative peritoneal chemotherapy with mitomycine, and group 5 = operation in combination with hyperthermic intraoperative peritoneal chemotherapy with gemcitabine, group 6 = operation in combination with taurolidin i.p. instillation. Echocardiographic examination with estimation of wall thickness, diameters, left ventricular fractional shortening, ejection fraction, early and late diastolic transmitral and myocardial velocities, radial and circumferential strain were performed 3–4 days after therapy. Results There was an increase of LVEDD and LVESD in all groups after the follow-up period (P = 0.0037). Other LV dimensions, FS and EF as well as diastolic mitral filling parameters measured by echocardiography were not significantly affected by the different treatments. Values for right ventricular dimensions and function remained unchanged, whereas circumferential 2D strain of the inferior wall was slightly, but significantly reduced under the treatment (-18.1 ± 2.5 before and -16.2 ± 2.9 % after treatment; P = 0.001) without
NASA Astrophysics Data System (ADS)
Li, Hong; Tsai, Charlie; Koh, Ai Leen; Cai, Lili; Contryman, Alex W.; Fragapane, Alex H.; Zhao, Jiheng; Han, Hyun Soon; Manoharan, Hari C.; Abild-Pedersen, Frank; Nørskov, Jens K.; Zheng, Xiaolin
2016-01-01
As a promising non-precious catalyst for the hydrogen evolution reaction (HER; refs ,,,,), molybdenum disulphide (MoS2) is known to contain active edge sites and an inert basal plane. Activating the MoS2 basal plane could further enhance its HER activity but is not often a strategy for doing so. Herein, we report the first activation and optimization of the basal plane of monolayer 2H-MoS2 for HER by introducing sulphur (S) vacancies and strain. Our theoretical and experimental results show that the S-vacancies are new catalytic sites in the basal plane, where gap states around the Fermi level allow hydrogen to bind directly to exposed Mo atoms. The hydrogen adsorption free energy (ΔGH) can be further manipulated by straining the surface with S-vacancies, which fine-tunes the catalytic activity. Proper combinations of S-vacancy and strain yield the optimal ΔGH = 0 eV, which allows us to achieve the highest intrinsic HER activity among molybdenum-sulphide-based catalysts.
Li, Hong; Tsai, Charlie; Koh, Ai Leen; Cai, Lili; Contryman, Alex W; Fragapane, Alex H; Zhao, Jiheng; Han, Hyun Soon; Manoharan, Hari C; Abild-Pedersen, Frank; Nørskov, Jens K; Zheng, Xiaolin
2016-01-01
As a promising non-precious catalyst for the hydrogen evolution reaction (HER; refs ,,,,), molybdenum disulphide (MoS2) is known to contain active edge sites and an inert basal plane. Activating the MoS2 basal plane could further enhance its HER activity but is not often a strategy for doing so. Herein, we report the first activation and optimization of the basal plane of monolayer 2H-MoS2 for HER by introducing sulphur (S) vacancies and strain. Our theoretical and experimental results show that the S-vacancies are new catalytic sites in the basal plane, where gap states around the Fermi level allow hydrogen to bind directly to exposed Mo atoms. The hydrogen adsorption free energy (ΔGH) can be further manipulated by straining the surface with S-vacancies, which fine-tunes the catalytic activity. Proper combinations of S-vacancy and strain yield the optimal ΔGH = 0 eV, which allows us to achieve the highest intrinsic HER activity among molybdenum-sulphide-based catalysts.
NIKE2D96. Static & Dynamic Response of 2D Solids
Raboin, P.; Engelmann, B.; Halquist, J.O.
1992-01-24
NIKE2D is an implicit finite-element code for analyzing the finite deformation, static and dynamic response of two-dimensional, axisymmetric, plane strain, and plane stress solids. The code is fully vectorized and available on several computing platforms. A number of material models are incorporated to simulate a wide range of material behavior including elasto-placicity, anisotropy, creep, thermal effects, and rate dependence. Slideline algorithms model gaps and sliding along material interfaces, including interface friction, penetration and single surface contact. Interactive-graphics and rezoning is included for analyses with large mesh distortions. In addition to quasi-Newton and arc-length procedures, adaptive algorithms can be defined to solve the implicit equations using the solution language ISLAND. Each of these capabilities and more make NIKE2D a robust analysis tool.
NASA Astrophysics Data System (ADS)
Wu, Huaping; Ma, Xuefu; Zhang, Zheng; Zhu, Jun; Wang, Jie; Chai, Guozhong
2016-04-01
A nonlinear thermodynamic model based on the vertically aligned nanocomposite (VAN) thin films of ferroelectric-metal oxide system has been developed to investigate the physical properties of the epitaxial Ba0.6Sr0.4TiO3 (BST) films containing vertical Sm2O3 (SmO) nanopillar arrays on the SrTiO3 substrate. The phase diagrams of out-of-plane lattice mismatch vs. volume fraction of SmO are calculated by minimizing the total free energy. It is found that the phase transformation and dielectric response of BST-SmO VAN systems are extremely dependent on the in-plane misfit strain, the out-of-plane lattice mismatch, the volume fraction of SmO phase, and the external electric field applied to the nanocomposite films at room temperature. In particular, the BST-SmO VAN systems exhibit higher dielectric properties than pure BST films. Giant dielectric response and maximum tunability are obtained near the lattice mismatch where the phase transition occurs. Under the in-plane misfit strain of umf=0.3 % and the out-of-plane lattice mismatch of u3=0.002 , the dielectric tunability can be dramatically enhanced to 90% with the increase of SmO volume fraction, which is well consistent with previous experimental results. This work represents an approach to further understand the dependence of physical properties on the lattice mismatch (in-plane and out-of-plane) and volume fraction, and to manipulate or optimize functionalities in the nanocomposite oxide thin films.
NASA Astrophysics Data System (ADS)
Kercheva, M.; Ryabova, T.; Ryabov, V.; Karpov, R.
2015-11-01
The aim of this study was to assess the intraobserver reproducibility of parameters of standard and 2 dimensional speckle tracking echocardiography, dynamics of global longitudinal strain in patients with acute primary anterior STEMI. The study included 24 patients, mean age 58.46±10.2. Echocardiography with 2D speckle tracking imaging was performed on the 1st (T1), 7th (T2), 14th days (T3) after STEMI («Vivid E9»). Analysis of echocardiographic images was performed offline at the different periods by the two independent observers (EchoPac) - experienced and inexperienced. In order to assess the agreement between standard and 2D speckle tracking echocardiography, a correlation analysis (Pearson correlation, Spearman's rank correlation coefficient) and Bland-Altman analysis were undertaken. The 23 patients had urgent reperfusion therapy, 6 patients underwent primary PCI, 16 patients - PCI after successful fibrinolysis (68%). GLS and WMSI had the best intraobsever reproducibility. Dynamics of EDV LV, ESV LV, EF LV was without significant differences. Nevertheless, it was found positive dynamic of GLS: - 12.65±3.53 (T1), -13.61±3.81 (T2), -14.27±4.1 (T3), p<0.05. GLS reduced 11.35% (p=0.0048) from T1 to T3. The best intraobserver reproducibility of parameters of 2 D speckle-tracking and standard echocardiography was revealed in GLS and WMSI. The modern management of STEMI patients limits adverse postinfarction remodeling and preserves of global left ventricular contractility detected by the EF LV. However, GLS had the positive dynamics and improved to the 14th day.
NASA Astrophysics Data System (ADS)
De Wilde, Juray; Lorant, Christophe; Descamps, Pierre
2017-04-01
In atmospheric-pressure plasma reactors, the flow dynamics can be complex, determine the reactor performance and complicate scale-up. Coupling computational fluid dynamics to the calculation of the electric field and plasma chemistry is challenging because of the numerical stiffness introduced by the difference in time scale of the different phenomena involved. Focusing on low-temperature, atmospheric-pressure pure nitrogen plasma, a model and model reduction based solution strategy to deal with the numerical stiffness are presented and evaluated. The influence of the electric field on the flow dynamics and species concentration fields is first qualitatively studied by means of 2D simulations of a sharp-end plate-to-plane configuration. Next, a specific reactor prototype for low-temperature, atmospheric-pressure plasma-enhanced chemical vapor deposition for in-line surface treatments is simulated to illustrate the importance of accounting for the detailed flow dynamics.
NASA Astrophysics Data System (ADS)
Myronov, Maksym; Morrison, Christopher; Halpin, John; Rhead, Stephen; Foronda, Jamie; Leadley, David
2015-08-01
Carrier mobility is one of the most important parameters of any semiconductor material, determining its suitability for applications in a large variety of electronic devices including field effect transistors (FETs). Today the capabilities of modern planar Si FET devices are almost exhausted and researchers are seeking either new device architectures or new materials. Here we report an extremely high room temperature (at 293 K) 2D hole gas (2DHG) drift mobility of 4500 cm2 V-1 s-1 at a carrier density of 1.2 × 1011 cm-2 obtained in a compressively strained Ge quantum well (QW) heterostructure, grown by an industrial type chemical vapor deposition system on a standard Si(0 0 1) substrate. The low-temperature Hall mobility and carrier density of this structure, measured at 333 mK, are 777,000 cm2 V-1 s-1 and 1.9 × 1011 cm-2, respectively. These hole mobilities are the highest not only among the group-IV Si and Ge based semiconductors, but also among p-type III-V and II-VI materials. The obtained room temperature mobility is substantially higher than those reported so far in strained Ge QW heterostructures and reveals a huge potential for further applications of this material in a wide variety of electronic devices.
NASA Astrophysics Data System (ADS)
Besuelle, P.
2012-04-01
Failure by strain localization is commonly observed in geomaterials. Generaly, experimental characterization of the localization in a porous sandstone are performed with classical axisymmetric triaxial compression tests. The effect of the confining pressure is observed on several aspects: onset of localization, pattern of localization, porosity evolution inside bands, grain scale mechanisms of deformation. Complex patterns of localization can be observed at high confining pressure in the transition between the brittle and ductile regime, showing several deformation bands in the specimens ([1]). However the history (time evolution) of the localization is not accessible because the observations are post-mortem. Strain field measurement and evolution in time of the strain field are particularly useful to study the strain localization (initiation of the deformation bands) and the post-localization regime. Such tools have been developed for soils (e.g., sand specimens in plane strain condition [2] or in triaxial conditions using X-ray tomography [3]). Similar developments for rocks are still difficult, especially because the pertinent confining pressure to reproduce in situ stresses are higher than for soils. We present here first results obtained in a new true triaxial apparatus that allows observation of the rock specimen under loading and especially the complex development of deformation bands and faults. As for [4] and [5], the three principal stresses are different, however the intermediate stress is controlled in order to impose a plane strain condition (zero strain in this direction). Observation of a specimen under load is possible as one surface of the prismatic specimen, which is orthogonal to the plane strain direction, is in contact with a hard transparent window. The deformation of this surface is representative of the deformation in the whole specimen, up to and beyond strain localization. Therefore the evolution of the strain field in the sample can be
Explicit 2-D Hydrodynamic FEM Program
Lin, Jerry
1996-08-07
DYNA2D* is a vectorized, explicit, two-dimensional, axisymmetric and plane strain finite element program for analyzing the large deformation dynamic and hydrodynamic response of inelastic solids. DYNA2D* contains 13 material models and 9 equations of state (EOS) to cover a wide range of material behavior. The material models implemented in all machine versions are: elastic, orthotropic elastic, kinematic/isotropic elastic plasticity, thermoelastoplastic, soil and crushable foam, linear viscoelastic, rubber, high explosive burn, isotropic elastic-plastic, temperature-dependent elastic-plastic. The isotropic and temperature-dependent elastic-plastic models determine only the deviatoric stresses. Pressure is determined by one of 9 equations of state including linear polynomial, JWL high explosive, Sack Tuesday high explosive, Gruneisen, ratio of polynomials, linear polynomial with energy deposition, ignition and growth of reaction in HE, tabulated compaction, and tabulated.
NASA Astrophysics Data System (ADS)
Llana-Funez, S.; Rutter, E. H.
2006-12-01
The condition of simultaneous operation of five slip systems to produce homogeneous deformation by intracrystalline plasticity in polycrystalline aggregates is frequently simplified when applied to studying deformation in nature by considering other deformation mechanisms that relax the strict geometric condition. Insufficient knowledge of how these complementary mechanisms interact and accommodate geometrically non-plane strain situations obscure somehow subsequent interpretation of slip patterns in relation to principal strain axes. We ran an experimental program isolating intracrystalline plasticity from other deformation mechanisms with the aim of testing the effect of non-plane strain geometries in the 3D arrangement of crystallographic elements from which we inferred the orientation of active slip systems. We use a fine grained polycrystalline aggregate (Solnhofen Limestone), naturally doped at grain boundaries with organic matter preventing grain growth, that deforms plastically at the experimental conditions used (600 °C, 200 MPa confining pressure and 10^{- 4}s-1 strain rates). To maximize the number of strain geometries we used different experimental configurations (axi-symmetric shortening and extension, and direct shear) and also study in detail volumes where deformation is heterogeneous but still relatively simple. The aim of the work is to relate strain geometry and the development of crystallographic fabrics in different strain paths. We produced constrictional, flattening, and nearly plane strain deformations. We were also able to obtain strain geometries where the vorticity axis in a non-coaxial deformation was either perpendicular to the extension direction (as in simple and sub-simple shear) or parallel to it. We measured the crystallographic preferred orientation (CPO) of calcite in deformed specimens by electron back-scattered diffraction techniques (EBSD), which allowed us to scan relatively small areas within already small specimens
Shimada, T; Okuno, J; Ishii, Y; Kitamura, T
2012-03-07
We investigated a nanometer-sharp magnetic domain wall (DW) structure in a free-standing Fe(110) monolayer and studied the crucial role of in-plane strain using fully unconstrained noncollinear ab initio spin-density-functional theory calculations within the generalized gradient approximation. The DW width is calculated to be 0.86 nm. A precise vector-field description of the magnetization density revealed that a noncollinear character in the DW was spatially confined between atoms, whereas a collinear and high magnetization density was localized around each atom. In the rapid rotation of magnetic moments in the DW, we found an electron rearrangement from the d(zx) and d(x(2)-y(2)) states to the d(xy), d(yz) and d(z(2)) states due to a shift of band structures. Applied tensile and compressive in-plane strains both bring about narrower DWs in the monolayer except when the strain is small. The strain dependence of the DW width is discussed in terms of both exchange interaction and magnetocrystalline anisotropy.
2D semiconductor optoelectronics
NASA Astrophysics Data System (ADS)
Novoselov, Kostya
The advent of graphene and related 2D materials has recently led to a new technology: heterostructures based on these atomically thin crystals. The paradigm proved itself extremely versatile and led to rapid demonstration of tunnelling diodes with negative differential resistance, tunnelling transistors, photovoltaic devices, etc. By taking the complexity and functionality of such van der Waals heterostructures to the next level we introduce quantum wells engineered with one atomic plane precision. Light emission from such quantum wells, quantum dots and polaritonic effects will be discussed.
Orientation control of the orbital ordering plane in epitaxial LaMnO3 thin films by misfit strain
NASA Astrophysics Data System (ADS)
Kim, Yong-Jin; Lee, Jin Hong; Kim, Sang-Woo; Koo, Tae Yeong; Yang, Chan-Ho
2016-10-01
We investigate the effects of misfit strain on the orbital order of epitaxial lanthanum manganite thin films grown on (LaAlO3)0.3-(Sr2AlTaO6)0.7 (LSAT) and GdScO3 (GSO) substrates. Resonant X-ray scattering near the Mn K-edge is employed to identify the cooperative Jahn-Teller distortion at room temperature and determine the orientation of the orbital-ordered plane (OOP). We find that coherent growth on LSAT (GSO) makes the OOPs be vertical (parallel) to the film surface. This finding not only offers useful insight into the interplay between misfit strain and orbital order, but also holds promise for strain control of orbital-dependent physical properties.
NASA Astrophysics Data System (ADS)
Baxevanis, T.; Chemisky, Y.; Lagoudas, D. C.
2012-09-01
The plane strain mechanical fields near a stationary crack tip in a pseudoelastic shape memory alloy (SMA) are analyzed via the finite element method. The small scale transformation assumption is employed for the calculations using displacement boundary conditions on a circular region that encloses the stress-induced phase transformation zone. The constitutive law used adopts the classical rate-independent small strain flow theory for the evolution equations of both the transformation and plastic strains. Results on the size and shape of the stress-induced transformation and plastic zone formed near the stationary crack are obtained and a fracture toughness criterion based on the J-integral is discussed in view of the observed path-dependence of J. Moreover, the obtained results are discussed in relation to results for stationary cracks in conventional elastic-plastic materials.
Full in-plane strain tensor analysis using the microscale ring-core FIB milling and DIC approach
NASA Astrophysics Data System (ADS)
Lunt, Alexander J. G.; Salvati, Enrico; Ma, Lifeng; Dolbyna, Igor P.; Neo, Tee K.; Korsunsky, Alexander M.
2016-09-01
Microscale Full In-plane Strain Tensor (FIST) analysis is crucial for improving understanding of residual stress and mechanical failure in many applications. This study outlines the first Focused Ion Beam (FIB) milling and Digital Image Correlation (DIC) based technique capable of performing precise, reliable and rapid quantification of this behaviour. The nature of semi-destructive FIB milling overcomes the main limitations of X-Ray Diffraction (XRD) strain tensor quantification: unstrained lattice parameter estimates are not required, analysis is performed in within a precisely defined 3D microscale volume, both amorphous and crystalline materials can be studied and access to X-ray/neutron facilities is not required. The FIST FIB milling and DIC experimental technique is based on extending the ring-core milling geometry to quantify the strain variation with angle and therefore benefits from the excellent precision and simple analytical approach associated with this method. In this study in-plane strain analysis was performed on sample of commercial interest: a porcelain veneered Yttria Partially Stabilised Zirconia (YPSZ) dental prosthesis, and was compared with the results of XRD. The two methods sample different gauge volumes and mechanical states: approximately plane stress for ring-core milling, and a through-thickness average for XRD. We demonstrate using complex analysis methods and Finite Element (FE) modelling that valid comparisons can be drawn between these two stress states. Excellent agreement was obtained between principal stress orientation and magnitudes, leading to realistic residual stress estimates that agree well with the literature (σAv ≈ 460 MPa) . As a measure of validity of the matching approach we report the upper and lower bounds on the (101) interplanar spacing of YPSZ that are found to correspond to the range 2.9586 - 2.9596 Å , closely matching published values.
Lagattu, Fabienne . E-mail: lagattu@lmpm.ensma.fr; Bridier, Florent; Villechaise, Patrick; Brillaud, Jean
2006-01-15
The purpose of this paper is to present a method based on the correlation of digital images obtained on a microscopic scale. A specific grainy pattern has been developed. The use of the scanning electron microscopy (SEM) allowed the determination of full-field 2D displacements on an object surface with a spatial resolution of about 1 {mu}m. Validation tests were performed in order to quantify performances and limits of this method. An example of its application is presented for a Ti-6Al-4V titanium alloy. Results show that it is possible to obtain in-plane displacement values on the object surface with efficient spatial resolution and accuracy. Thus, such a technique can be used to highlight on a relevant scale the role of the microstructure in material deformation processes.
NASA Technical Reports Server (NTRS)
Fisher, D. M.; Buzzard, R. J.
1979-01-01
Standard round specimen fracture test results compared satisfactorily with results from standard rectangular compact specimens machined from the same material. The location of the loading pin holes was found to provide adequate strength in the load bearing region for plane strain fracture toughness testing. Excellent agreement was found between the stress intensity coefficient values obtained from compliance measurements and the analytic solution proposed for inclusion in the standard test method. Load displacement measurements were made using long armed displacement gages and hollow loading cylinders. Gage points registered on the loading hole surfaces through small holes in the walls of the loading cylinders.
Albocher, U; Barbone, P E; Richards, M S; Oberai, A A; Harari, I
2014-01-01
We apply the adjoint weighted equation method (AWE) to the direct solution of inverse problems of incompressible plane strain elasticity. We show that based on untreated noisy displacements, the reconstruction of the shear modulus can be very poor. We link this poor performance to loss of coercivity of the weak form when treating problems with discontinuous coefficients. We demonstrate that by smoothing the displacements and appending a regularization term to the AWE formulation, a dramatic improvement in the reconstruction can be achieved. With these improvements, the advantages of the AWE method as a direct solution approach can be extended to a wider range of problems.
Albocher, U.; Barbone, P.E.; Richards, M.S.; Oberai, A.A.; Harari, I.
2014-01-01
We apply the adjoint weighted equation method (AWE) to the direct solution of inverse problems of incompressible plane strain elasticity. We show that based on untreated noisy displacements, the reconstruction of the shear modulus can be very poor. We link this poor performance to loss of coercivity of the weak form when treating problems with discontinuous coefficients. We demonstrate that by smoothing the displacements and appending a regularization term to the AWE formulation, a dramatic improvement in the reconstruction can be achieved. With these improvements, the advantages of the AWE method as a direct solution approach can be extended to a wider range of problems. PMID:25383085
Constructing generalized Cesàro formulas for finite plane strains
NASA Astrophysics Data System (ADS)
Georgievskii, D. V.
2014-05-01
The problem of finding the displacement vector from a system of nonlinear differential equations which includes displacement gradient components is studied. Expressions on the right side of this system for certain parameter values have the kinematic sense of Lagrange and Euler finite strain tensors. The task is to construct generalized Cesàro formulas for finite strains. The construction of the solution consists of two stages (algebraic and differential), and the second is performed for space whose dimension is greater than or equal to two. An algorithm for the inversion of the original system is proposed, and analytical constructions for the case of two-dimensional space are performed. The problem is solved at the first (algebraic) stage, i.e., an exact analytical expression for the displacement vector components is derived through the known finite strain tensor and an unknown scalar function having the kinematic sense of rotation. Necessary conditions for the existence of this relationship are formulated.
In-plane anisotropy of electrical resistivity in strain-detwinned SrFe2As2
NASA Astrophysics Data System (ADS)
Blomberg, E. C.; Tanatar, M. A.; Kreyssig, A.; Ni, N.; Thaler, A.; Hu, Rongwei; Bud'Ko, S. L.; Canfield, P. C.; Goldman, A. I.; Prozorov, R.
2011-04-01
Intrinsic, in-plane anisotropy of electrical resistivity was studied on mechanically detwinned single crystals of SrFe2As2 above and below the temperature of the coupled structural/magnetic transition, TTO. Resistivity is smaller for electrical current flow along the orthorhombic ao direction (direction of antiferromagnetically alternating magnetic moments) and is larger for transport along the bo direction (direction of ferromagnetic chains), which is similar to CaFe2As2 and BaFe2As2 compounds. A strongly first-order structural transition in SrFe2As2 was confirmed by high-energy x-ray measurements, with the transition temperature and character unaffected by moderate strain. For small strain levels, which are just sufficient to detwin the sample, we find a negligible effect on the resistivity above TTO. With the increase of strain, the resistivity anisotropy starts to develop above TTO, clearly showing the relation of anisotropy to an anomalously strong response to strain. Our study suggests that electronic nematicity cannot be observed in the FeAs-based compounds in which the structural transition is strongly first order.
In-plane anisotropy of electrical resistivity in strain-detwinned SrFe[subscript 2]As[subscript 2
Blomberg, E.C.; Tanatar, M.A.; Kreyssig, A.; Ni, N.; Thaler, A.; Hu, Rongwei; Budko, S.L.; Canfield, P.C.; Goldman, A.I.; Prozorov, R.
2011-12-09
Intrinsic, in-plane anisotropy of electrical resistivity was studied on mechanically detwinned single crystals of SrFe{sub 2}As{sub 2} above and below the temperature of the coupled structural/magnetic transition, T{sub TO}. Resistivity is smaller for electrical current flow along the orthorhombic a{sub o} direction (direction of antiferromagnetically alternating magnetic moments) and is larger for transport along the b{sub o} direction (direction of ferromagnetic chains), which is similar to CaFe{sub 2}As{sub 2} and BaFe{sub 2}As{sub 2} compounds. A strongly first-order structural transition in SrFe{sub 2}As{sub 2} was confirmed by high-energy x-ray measurements, with the transition temperature and character unaffected by moderate strain. For small strain levels, which are just sufficient to detwin the sample, we find a negligible effect on the resistivity above T{sub TO}. With the increase of strain, the resistivity anisotropy starts to develop above T{sub TO}, clearly showing the relation of anisotropy to an anomalously strong response to strain. Our study suggests that electronic nematicity cannot be observed in the FeAs-based compounds in which the structural transition is strongly first order.
Derivation of a variational principle for plane strain elastic-plastic silk biopolymers
NASA Astrophysics Data System (ADS)
He, J. H.; Liu, F. J.; Cao, J. H.; Zhang, L.
2014-01-01
Silk biopolymers, such as spider silk and Bombyx mori silk, behave always elastic-plastically. An elastic-plastic model is adopted and a variational principle for the small strain, rate plasticity problem is established by semi-inverse method. A trial Lagrangian is constructed where an unknown function is included which can be identified step by step.
NASA Astrophysics Data System (ADS)
Paul, H.; Tarasek, A.; Wajda, W.; Berent, K.
2014-08-01
Crystal lattice rotations induced by shear bands developed in an AA1050 aluminium alloy have been examined in order to investigate the influence of the finegrained structure on the slip propagation across the grain boundaries and the resulting texture evolution. Samples of the AA1050 alloy were pre-deformed in ECAP up to 6 passes via route C, then machined and further compressed in a channel-die up to ~25% at room temperature. The microstructure and texture were characterized by SEM equipped with a high resolution EBSD facility. The ECAP-processing leads to the formation of a fine grained structure. The grains were grouped into nearly complementarily oriented layers. During the secondary straining in the channel-die, the layers of fine grains, initially situated almost parallel to the compression plane, undergo deflection within some narrow areas. This is the beginning stage of the macroscopic shear band (MSB) formation. In all the deformed grains examined (within MSB) a strong tendency for strain-induced re-orientation could be observed. The SEM orientation mapping shows how the layers of flattened grains are incorporated into the MSB area, and what kinds of mechanisms are responsible for the strain accommodation at the macro-scale. Finally, a crystallographic description of the mechanism of MSB formation in AA1050 aluminium alloy is proposed based on the local lattice re-orientations due to localized kinking.
The strain in the array is mainly in the plane (waves below ~1 Hz)
Gomberg, J.; Pavlis, G.; Bodin, P.
1999-01-01
We compare geodetic and single-station methods of measuring dynamic deformations and characterize their causes in the frequency bands 0.5-1.0 Hz and 4.0-8.0 Hz. The geodetic approach utilizes data from small-aperture seismic arrays, applying techniques from geodesy. It requires relatively few assumptions and a priori information. The single-station method uses ground velocities recorded at isolated or single stations and assumes all the deformation is due to plane-wave propagation. It also requires knowledge of the azimuth and horizontal velocity of waves arriving at the recording station. Data employed come from a small-aperture, dense seismic array deployed in Geyokcha, Turkmenistan, and include seismograms recorded by broadband STS2 and short-period L28 sensors. Poor agreement between geodetic and single-station estimates in the 4.0-8.0 Hz passband indicates that the displacement field may vary nonlinearly with distance over distances of ~50 m. STS2 geodetic estimates provide a robust standard in the 0.5-1.0 Hz passband because they appear to be computationally stable and require fewer assumptions than single-station estimates. The agreement between STS2 geodetic estimates and single-station L28 estimates is surprisingly good for the S-wave and early surface waves, suggesting that the single-station analysis should be useful with commonly available data. These results indicate that, in the 0.5 to 1.0 Hz passband, the primary source of dynamic deformation is plane-wave propagation along great-circle source-receiver paths. For later arriving energy, the effects of scattering become important. The local structure beneath the array exerts a strong control on the geometry of the dynamic deformation, implying that it may be difficult to infer source characteristics of modern or paleoearthquakes from indicators of dynamic deformations. However, strong site control also suggests that the dynamic deformations may be predictable, which would be useful for engineering
NASA Astrophysics Data System (ADS)
Harikumar, M.; Sankar, N.; Chandrakaran, S.
2015-09-01
Since 1969, when the concept of earth reinforcing was brought about by Henry Vidal, a large variety of materials such as steel bars, tire shreds, polypropylene, polyester, glass fibres, coir and jute fibres etc. have been widely added to soil mass randomly or in a regular, oriented manner. The conventional reinforcements in use were two dimensional or planar, in the form of strips with negligible widths or in the form of sheets. In this investigation, a novel concept of multi oriented plastic reinforcement (hexa-pods) is discussed. Direct shear tests were conducted on unreinforced and reinforced dry fine, medium and coarse sands. Detailed parametric studies with respect to the effective grain size of soil (d10), normal stress (σ) and the volume ratio of hexa-pods (Vr) were performed. It was noticed that addition of hexa-pods resulted in increase in the shear strength parameters viz. peak deviatoric stresses and increased angle of internal friction. The hexa-pods also changed the brittle behaviour of unreinforced sand samples to ductile ones. Although the peak shear stress did not show a considerable improvement, the angle of internal friction improved noticeably. Addition of a single layer of reinforcement along the shear plane also reduced the post peak loss of strength and changed the soil behavior from brittle to a ductile one.
Lai, Chih-Ming; Huang, Yu-En; Feng, Shih-Wei; Kou, Kuang-Yang; Chen, Chien-Hsun; Tu, Li-Wei
2015-07-13
Anisotropic strain relaxation and the resulting degree of polarization of photoluminescence (PL) in nonpolar a-plane textured ZnO are experimentally and theoretically studied. A thicker nonpolar a-plane textured ZnO film enhances the anisotropic in-plane strain relaxation, resulting in a larger degree of polarization of PL and better sample quality. Anisotropic in-plane strains, sample quality, and degree of polarization of PL in nonpolar a-plane ZnO are consequences of the degree of anisotropic in-plane strain relaxation. By the k·p perturbation approach, simulation results of the variation of the degree of polarization for the electronic transition upon anisotropic in-plane strain relaxation agree with experimental results.
Omote, Kazuhiko
2010-12-01
We have measured the strain of a thin Si layer deposited on a SiGe layer using a high resolution x-ray diffraction system. The Si layer was deposited on the SiGe layer in order to introduce a tensile strain to the Si layer. To measure the in-plane lattice constant accurately, we have employed so-called grazing-incidence in-plane diffraction. For this measurement, we have made a new five-axis x-ray goniometer which has four ordinal circles (ω, 2θ, χ, φ) plus a counter-χ-axis for selecting the exit angle of the diffracted x-rays. In grazing-incidence geometry, an incident x-ray is focused on the sample surface in order to obtain good diffraction intensity even though the layer thickness is less than 5 nm. Because diffracted x-rays are detected through analyzer crystals, the diffraction angle can be determined with an accuracy of ± 0.0003°. This indicates that the strain sensitivity is about 10( - 5) when we measure in-plane Si 220 diffraction. Use of x-ray diffraction could be the best standard metrology method for determining strain in thin layers. Furthermore, we have demonstrated that incident/exit angle selected in-plane diffraction is very useful for height/depth selective strain determination.
Highly crystalline 2D superconductors
NASA Astrophysics Data System (ADS)
Saito, Yu; Nojima, Tsutomu; Iwasa, Yoshihiro
2016-12-01
Recent advances in materials fabrication have enabled the manufacturing of ordered 2D electron systems, such as heterogeneous interfaces, atomic layers grown by molecular beam epitaxy, exfoliated thin flakes and field-effect devices. These 2D electron systems are highly crystalline, and some of them, despite their single-layer thickness, exhibit a sheet resistance more than an order of magnitude lower than that of conventional amorphous or granular thin films. In this Review, we explore recent developments in the field of highly crystalline 2D superconductors and highlight the unprecedented physical properties of these systems. In particular, we explore the quantum metallic state (or possible metallic ground state), the quantum Griffiths phase observed in out-of-plane magnetic fields and the superconducting state maintained in anomalously large in-plane magnetic fields. These phenomena are examined in the context of weakened disorder and/or broken spatial inversion symmetry. We conclude with a discussion of how these unconventional properties make highly crystalline 2D systems promising platforms for the exploration of new quantum physics and high-temperature superconductors.
Wu, Huaping; Chai, Guozhong; Zhou, Ting; Zhang, Zheng; Kitamura, Takayuki; Zhou, Haomiao
2014-03-21
The strain-mediated magnetoelectric (ME) property of self-assembled vertical multiferroic nanocomposite films epitaxially grown on cubic substrates was calculated by a nonlinear thermodynamic theory combined with the elastic theory. The dependent relations of phase state of ferroelectric films with the in-plane misfit strain, out-of-plane misfit strain, temperature, and volume fraction of ferromagnetic phase were confirmed. The effects of in-plane misfit strain and ferromagnetic volume fraction on the polarization and dielectric constant of ferroelectric films at room temperature were elaborately analyzed for the vertical BaTiO{sub 3}-CoFe{sub 2}O{sub 4} and PbTiO{sub 3}-CoFe{sub 2}O{sub 4} nanocomposite films. Our calculated results confirmed the relationship among ME effect and in-plane misfit strain and ferromagnetic volume fraction in the nanocomposite films. The ME voltage coefficients of vertical BaTiO{sub 3}-CoFe{sub 2}O{sub 4} and PbTiO{sub 3}-CoFe{sub 2}O{sub 4} nanocomposite films displayed various maximums and abrupt points at special phases and phase transition boundaries. The ME voltage coefficients of lead-free BaTiO{sub 3}-CoFe{sub 2}O{sub 4} nanocomposite films epitaxially grown on different substrates could reach a comparative value of ∼2 V·cm{sup −1}·Oe{sup −1} under the controllable in-plane misfit strain induced by substrate clamping. Our results provided an available method for the optimal design of vertical multiferroic nanocomposites with adjustable ME effect by optimizing the ferromagnetic volume fraction and substrate type.
NASA Astrophysics Data System (ADS)
Hu, Lun-Hui; Xu, Dong-Hui; Zhang, Fu-Chun; Zhou, Yi
2016-08-01
Motivated by the recent discovery of quantized spin Hall effect in InAs/GaSb quantum wells [Du, Knez, Sullivan, and Du, Phys. Rev. Lett. 114, 096802 (2015), 10.1103/PhysRevLett.114.096802], we theoretically study the effects of in-plane magnetic field and strain effect to the quantization of charge conductance by using Landauer-B ütikker formalism. Our theory predicts a robustness of the conductance quantization against the in-plane magnetic field up to a very high field of 20 T. We use a disordered hopping term to model the strain and show that the strain may help the quantization of the conductance. Relevance to the experiments will be discussed.
NASA Astrophysics Data System (ADS)
Nakashima, Takaaki; Ichinose, Daichi; Ehara, Yoshitaka; Shimizu, Takao; Kobayashi, Takeshi; Yamada, Tomoaki; Funakubo, Hiroshi
2017-03-01
(100)/(001)-oriented epitaxial lead titanate (PbTiO3) films with various thicknesses were grown on (100) KTaO3 substrates by pulsed metal-organic chemical vapor deposition. The change of crystal structure with film thickness and deposition temperature was investigated. The paraelectric phase of 50 and 1000 nm-thick films had a tensile strain of 0.5% and almost 0% at 700 °C, respectively. The phase change temperature from the paraelectric phase to the ferroelectric phase, the Curie temperature (Tc), increased with the in-plane strain of the paraelectric phase; that is, Tc increased with decreasing film thickness. In contrast, room-temperature tetragonal distortion decreased as the film became thinner. This study reveals the effect of in-plane tensile strain in (100)/(001)-oriented epitaxial PbTiO3 films with higher Tc and smaller tetragonal distortion at room temperature.
Strength design with 2-d triaxial braid textile composites
Smith, L.V.; Swanson, S.R.
1994-12-31
Textile preforms are currently being considered as a possible means for reducing the cost of advanced fiber composites. This paper presents a methodology for strength design of carbon/epoxy 2-d braid fiber composites under general conditions of biaxial stress loading. A comprehensive investigation into the in-plane strength properties of 2-d braids has been carried out, using tubular specimens of AS4/1895 carbon fiber/epoxy made with the RTM process. The biaxial loadings involved both compression-compression and tension-tension biaxial tests. The results showed that failure under biaxial loading could be based on procedures similar to those developed for laminates, using critical strain values in the axial and braid direction fibers, but with degraded strength properties because of the undulating nature of -the fiber paths. A significant loss of strength was observed in the braid directions.
2002-01-01
DH5α and its transposon mutants……….……...…….………...87 Figure 21. Genetic arrangement of the carnitine operon of Escherichia coli K...12 strain MG1655…………………….………………...92 Figure 22. Carnitine metabolism in Escherichia coli……………….……………….….93 Figure 23. Southern blots of EcoRV...necrosis factor alpha generated in response to the gastrointestinal infection. The result is loss of vascular integrity in the brain, hemorrhage
Volumetric elasticity imaging with a 2-D CMUT array.
Fisher, Ted G; Hall, Timothy J; Panda, Satchi; Richards, Michael S; Barbone, Paul E; Jiang, Jingfeng; Resnick, Jeff; Barnes, Steve
2010-06-01
This article reports the use of a two-dimensional (2-D) capacitive micro-machined ultrasound transducer (CMUT) to acquire radio-frequency (RF) echo data from relatively large volumes of a simple ultrasound phantom to compare three-dimensional (3-D) elasticity imaging methods. Typical 2-D motion tracking for elasticity image formation was compared with three different methods of 3-D motion tracking, with sum-squared difference (SSD) used as the similarity measure. Differences among the algorithms were the degree to which they tracked elevational motion: not at all (2-D search), planar search, combination of multiple planes and plane independent guided search. The cross-correlation between the predeformation and motion-compensated postdeformation RF echo fields was used to quantify motion tracking accuracy. The lesion contrast-to-noise ratio was used to quantify image quality. Tracking accuracy and strain image quality generally improved with increased tracking sophistication. When used as input for a 3-D modulus reconstruction, high quality 3-D displacement estimates yielded accurate and low noise modulus reconstruction.
Volumetric Elasticity Imaging with a 2D CMUT Array
Fisher, Ted G.; Hall, Timothy J.; Panda, Satchi; Richards, Michael S.; Barbone, Paul E.; Jiang, Jingfeng; Resnick, Jeff; Barnes, Steve
2010-01-01
This paper reports the use of a two-dimensional (2D) capacitive micro-machined ultrasound transducer (CMUT) to acquire radio frequency (RF) echo data from relatively large volumes of a simple ultrasound phantom to compare 3D elasticity imaging methods. Typical 2D motion tracking for elasticity image formation was compared to three different methods of 3D motion tracking, with sum-squared difference (SSD) used as the similarity measure. Differences among the algorithms were the degree to which they tracked elevational motion: not at all (2D search), planar search, combination of multiple planes, and plane independent guided search. The cross correlation between the pre-deformation and motion-compensated post-deformation RF echo fields was used to quantify motion tracking accuracy. The lesion contrast-to-noise ratio was used to quantify image quality. Tracking accuracy and strain image quality generally improved with increased tracking sophistication. When used as input for a 3D modulus reconstruction, high quality 3D displacement estimates yielded accurate and low noise modulus reconstruction. PMID:20510188
Domain structure and in-plane switching in a highly strained Bi0.9Sm0.1FeO3 film
NASA Astrophysics Data System (ADS)
Chen, Weigang; Ren, Wei; You, Lu; Yang, Yurong; Chen, Zuhuang; Qi, Yajun; Zou, Xi; Wang, Junling; Sritharan, Thirumany; Yang, Ping; Bellaiche, L.; Chen, Lang
2011-11-01
We report the domain structure and ferroelectric properties of a 32 nm-thick Bi0.9Sm0.1FeO3 film epitaxially grown on a LaAlO3 (LAO) substrate. This film exhibits a monoclinic Mc phase, with its monoclinic distortion and anisotropy of in-plane (IP) lattice parameters being both smaller than those of pure BiFeO3 (BFO) grown on LaAlO3. Polarization hysteresis loops measured using a quasi-planar capacitor show an in-plane polarization up to 30 μC/cm2. Piezoresponse force microcopy demonstrates that a 180° in-plane polarization switching accompanied by a 90° domain wall rotation takes place after electric poling. First-principles calculations suggest the differences between highly strained Sm-substituted and pure BiFeO3.
A comparison of 2D and 3D digital image correlation for a membrane under inflation
Murienne, Barbara J.; Nguyen, Thao D.
2015-01-01
Three-dimensional (3D) digital image correlation (DIC) is becoming widely used to characterize the behavior of structures undergoing 3D deformations. However, the use of 3D-DIC can be challenging under certain conditions, such as high magnification, and therefore small depth of field, or a highly controlled environment with limited access for two-angled cameras. The purpose of this study is to compare 2D-DIC and 3D-DIC for the same inflation experiment and evaluate whether 2D-DIC can be used when conditions discourage the use of a stereo-vision system. A latex membrane was inflated vertically to 5.41 kPa (reference pressure), then to 7.87 kPa (deformed pressure). A two-camera stereo-vision system acquired top-down images of the membrane, while a single camera system simultaneously recorded images of the membrane in profile. 2D-DIC and 3D-DIC were used to calculate horizontal (in the membrane plane) and vertical (out of the membrane plane) displacements, and meridional strain. Under static conditions, the baseline uncertainty in horizontal displacement and strain were smaller for 3D-DIC than 2D-DIC. However, the opposite was observed for the vertical displacement, for which 2D-DIC had a smaller baseline uncertainty. The baseline absolute error in vertical displacement and strain were similar for both DIC methods, but it was larger for 2D-DIC than 3D-DIC for the horizontal displacement. Under inflation, the variability in the measurements were larger than under static conditions for both DIC methods. 2D-DIC showed a smaller variability in displacements than 3D-DIC, especially for the vertical displacement, but a similar strain uncertainty. The absolute difference in the average displacements and strain between 3D-DIC and 2D-DIC were in the range of the 3D-DIC variability. Those findings suggest that 2D-DIC might be used as an alternative to 3D-DIC to study the inflation response of materials under certain conditions. PMID:26543296
A comparison of 2D and 3D digital image correlation for a membrane under inflation.
Murienne, Barbara J; Nguyen, Thao D
2016-02-01
Three-dimensional (3D) digital image correlation (DIC) is becoming widely used to characterize the behavior of structures undergoing 3D deformations. However, the use of 3D-DIC can be challenging under certain conditions, such as high magnification, and therefore small depth of field, or a highly controlled environment with limited access for two-angled cameras. The purpose of this study is to compare 2D-DIC and 3D-DIC for the same inflation experiment and evaluate whether 2D-DIC can be used when conditions discourage the use of a stereo-vision system. A latex membrane was inflated vertically to 5.41 kPa (reference pressure), then to 7.87 kPa (deformed pressure). A two-camera stereo-vision system acquired top-down images of the membrane, while a single camera system simultaneously recorded images of the membrane in profile. 2D-DIC and 3D-DIC were used to calculate horizontal (in the membrane plane) and vertical (out of the membrane plane) displacements, and meridional strain. Under static conditions, the baseline uncertainty in horizontal displacement and strain were smaller for 3D-DIC than 2D-DIC. However, the opposite was observed for the vertical displacement, for which 2D-DIC had a smaller baseline uncertainty. The baseline absolute error in vertical displacement and strain were similar for both DIC methods, but it was larger for 2D-DIC than 3D-DIC for the horizontal displacement. Under inflation, the variability in the measurements were larger than under static conditions for both DIC methods. 2D-DIC showed a smaller variability in displacements than 3D-DIC, especially for the vertical displacement, but a similar strain uncertainty. The absolute difference in the average displacements and strain between 3D-DIC and 2D-DIC were in the range of the 3D-DIC variability. Those findings suggest that 2D-DIC might be used as an alternative to 3D-DIC to study the inflation response of materials under certain conditions.
A comparison of 2D and 3D digital image correlation for a membrane under inflation
NASA Astrophysics Data System (ADS)
Murienne, Barbara J.; Nguyen, Thao D.
2016-02-01
Three-dimensional (3D) digital image correlation (DIC) is becoming widely used to characterize the behavior of structures undergoing 3D deformations. However, the use of 3D-DIC can be challenging under certain conditions, such as high magnification, and therefore small depth of field, or a highly controlled environment with limited access for two-angled cameras. The purpose of this study is to compare 2D-DIC and 3D-DIC for the same inflation experiment and evaluate whether 2D-DIC can be used when conditions discourage the use of a stereo-vision system. A latex membrane was inflated vertically to 5.41 kPa (reference pressure), then to 7.87 kPa (deformed pressure). A two-camera stereo-vision system acquired top-down images of the membrane, while a single camera system simultaneously recorded images of the membrane in profile. 2D-DIC and 3D-DIC were used to calculate horizontal (in the membrane plane) and vertical (out of the membrane plane) displacements, and meridional strain. Under static conditions, the baseline uncertainty in horizontal displacement and strain were smaller for 3D-DIC than 2D-DIC. However, the opposite was observed for the vertical displacement, for which 2D-DIC had a smaller baseline uncertainty. The baseline absolute error in vertical displacement and strain were similar for both DIC methods, but it was larger for 2D-DIC than 3D-DIC for the horizontal displacement. Under inflation, the variability in the measurements were larger than under static conditions for both DIC methods. 2D-DIC showed a smaller variability in displacements than 3D-DIC, especially for the vertical displacement, but a similar strain uncertainty. The absolute difference in the average displacements and strain between 3D-DIC and 2D-DIC were in the range of the 3D-DIC variability. Those findings suggest that 2D-DIC might be used as an alternative to 3D-DIC to study the inflation response of materials under certain conditions.
Feng, Shih-Wei Chen, Yu-Yu; Lai, Chih-Ming; Tu, Li-Wei; Han, Jung
2013-12-21
Anisotropic strain relaxation and the resulting degree of polarization of the electronic transition in nonpolar a-plane GaN using one- and two-step growth are studied. By using two-step growth, a slower coalescence and a longer roughening-recovery process lead to larger anisotropic strain relaxation, a less striated surface, and lower densities of basal stacking fault (BSF) and prismatic stacking fault (PSF). It is suggested that anisotropic in-plane strains, surface striation, and BSF and PSF densities in nonpolar a-GaN are consequences of the rate of coalescence, the period of roughening-recovery process, and the degree of anisotropic strain relaxation. In addition, the two-step growth mode can enhance the degree of polarization of the electronic transition. The simulation results of the k⋅p perturbation approach show that the oscillator strength and degree of polarization of the electronic transition strongly depend on the in-plane strains upon anisotropic in-plane strain relaxation. The research results provide important information for optimized growth of nonpolar III-nitrides. By using two-step growth and by fabricating the devices on the high-quality nonpolar free-standing GaN substrates, high-efficiency nonpolar a-plane InGaN LEDs can be realized. Nonpolar a-plane InGaN/GaN LEDs can exhibit a strongly polarized light to improve the contrast, glare, eye discomfort and eye strain, and efficiency in display application.
Calculating tissue shear modulus and pressure by 2D Log-Elastographic methods
McLaughlin, Joyce R; Zhang, Ning; Manduca, Armando
2010-01-01
Shear modulus imaging, often called elastography, enables detection and characterization of tissue abnormalities. In this paper the data is two displacement components obtained from successive MR or ultrasound data sets acquired while the tissue is excited mechanically. A 2D plane strain elastic model is assumed to govern the 2D displacement, u. The shear modulus, μ, is unknown and whether or not the first Lamé parameter, λ, is known the pressure p = λ∇ · u which is present in the plane strain model cannot be measured and is unreliably computed from measured data and can be shown to be an order one quantity in the units kPa. So here we present a 2D Log-Elastographic inverse algorithm that: (1) simultaneously reconstructs the shear modulus, μ, and p, which together satisfy a first order partial differential equation system, with the goal of imaging μ; (2) controls potential exponential growth in the numerical error; and (3) reliably reconstructs the quantity p in the inverse algorithm as compared to the same quantity computed with a forward algorithm. This work generalizes the Log-Elastographic algorithm in [20] which uses one displacement component, is derived assuming the component satisfies the wave equation, and is tested on synthetic data computed with the wave equation model. The 2D Log-Elastographic algorithm is tested on 2D synthetic data and 2D in-vivo data from Mayo Clinic. We also exhibit examples to show that the 2D Log-Elastographic algorithm improves the quality of the recovered images as compared to the Log-Elastographic and Direct Inversion algorithms. PMID:21822349
Structure and switching of in-plane ferroelectric nano-domains in strained PbxSr1-xTiO3 thin films
Matzen, Sylivia; Nesterov, Okeksiy; Rispens, Gregory; Heuver, J. A.; Bark, C; Biegalski, Michael D; Christen, Hans M; Noheda, Beatriz
2014-01-01
Nanoscale ferroelectrics, the active elements of a variety of nanoelectronic devices, develop denser and richer domain structures than the bulk counterparts. With shrinking device sizes understanding and controlling domain formation in nanoferroelectrics is being intensely studied. Here we show that a precise control of the epitaxy and the strain allows stabilizing a hierarchical domain architecture in PbxSr1-xTiO3 thin films, showing periodic, purely in-plane polarized, ferroelectric nano-domains that can be switched by a scanning probe.
NASA Astrophysics Data System (ADS)
Ren, Zhenhua; Zeng, Xiantao; Liu, Hanlong; Zhou, Fengjun
2013-03-01
The application of fiber reinforced plastic (FRP), including carbon FRP and glass FRP, for structural repair and strengthening has grown due to their numerous advantages over conventional materials such as externally bonded reinforcement (EBR) and near-surface mounted (NSM) strengthening techniques. This paper summarizes the results from 21 reinforced concrete beams strengthened with different methods, including externally-bonded and near-surface mounted FRP, to study the strain coordination of the FRP and steel rebar of the RC beam. Since there is relative slipping between the RC beam and the FRP, the strain of the FRP and steel rebar of the RC beam satisfy the quasi-plane-hypothesis; that is, the strain of the longitudinal fiber that parallels the neutral axis of the plated beam within the scope of the effective height ( h 0) of the cross section is in direct proportion to the distance from the fiber to the neutral axis. The strain of the FRP and steel rebar satisfies the equation: ɛ FRP= βɛ steel, and the value of β is equal to 1.1-1.3 according to the test results.
NASA Astrophysics Data System (ADS)
Lotsch, Bettina V.
2015-07-01
Graphene's legacy has become an integral part of today's condensed matter science and has equipped a whole generation of scientists with an armory of concepts and techniques that open up new perspectives for the postgraphene area. In particular, the judicious combination of 2D building blocks into vertical heterostructures has recently been identified as a promising route to rationally engineer complex multilayer systems and artificial solids with intriguing properties. The present review highlights recent developments in the rapidly emerging field of 2D nanoarchitectonics from a materials chemistry perspective, with a focus on the types of heterostructures available, their assembly strategies, and their emerging properties. This overview is intended to bridge the gap between two major—yet largely disjunct—developments in 2D heterostructures, which are firmly rooted in solid-state chemistry or physics. Although the underlying types of heterostructures differ with respect to their dimensions, layer alignment, and interfacial quality, there is common ground, and future synergies between the various assembly strategies are to be expected.
Strain effects on in-plane conductance of the topological insulator Bi{sub 2}Te{sub 3}
Heui Hwang, Jin; Kwon, Sangku; Hun Kim, Jong; Young Park, Jeong; Park, Joonbum; Sung Kim, Jun; Lee, Jhinhwan; Lyeo, Ho-Ki
2014-04-21
We investigated the correlation between electrical transport and mechanical stress in a topological insulator, Bi{sub 2}Te{sub 3}, using conductive probe atomic force microscopy in an ultrahigh vacuum environment. After directly measuring charge transport on the cleaved Bi{sub 2}Te{sub 3} surface, we found that the current density varied with applied load. Current mapping revealed a variation of the current on different terraces. The current density increased in the low-pressure regime and then decreased in the high-pressure regime. This variation of current density was explained in light of the combined effect of changes in the in-plane conductance due to spin–orbit coupling and hexagonal warping.
Yang, Nicholas H; Canavan, Paul K; Nayeb-Hashemi, Hamid
2010-11-01
Subject-specific models were developed and finite element analysis was performed to observe the effect of the frontal plane tibiofemoral angle on the normal stress, Tresca shear stress and normal strain at the surface of the knee cartilage. Finite element models were created for three subjects with different tibiofemoral angle and physiological loading conditions were defined from motion analysis and muscle force mathematical models to simulate static single-leg stance. The results showed that the greatest magnitude of the normal stress, Tresca shear stress and normal strain at the medial compartment was for the varus aligned individual. Considering the lateral knee compartment, the individual with valgus alignment had the largest stress and strain at the cartilage. The present investigation is the first known attempt to analyze the effects of tibiofemoral alignment during single-leg support on the contact variables of the cartilage at the knee joint. The method could be potentially used to help identify individuals most susceptible to osteoarthritis and to prescribe preventive measures.
2-d Finite Element Code Postprocessor
Sanford, L. A.; Hallquist, J. O.
1996-07-15
ORION is an interactive program that serves as a postprocessor for the analysis programs NIKE2D, DYNA2D, TOPAZ2D, and CHEMICAL TOPAZ2D. ORION reads binary plot files generated by the two-dimensional finite element codes currently used by the Methods Development Group at LLNL. Contour and color fringe plots of a large number of quantities may be displayed on meshes consisting of triangular and quadrilateral elements. ORION can compute strain measures, interface pressures along slide lines, reaction forces along constrained boundaries, and momentum. ORION has been applied to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.
Ma, R.; Negahban, M.
1995-12-31
The objective of this study is to investigate the effect of crystallization on the mechanical response of a polymer containing a rigid cylindrical inclusion under different loading conditions and under the plane strain restriction. As will be shown, external loading and crystallization can both induce an inhomogeneous distribution of stress and deformation in the vicinity of a cylindrical inclusion and can also interact with each other. Crystallization is a process of transition of the polymer`s microstructure from disordered state to an ordered one. This transition occurs in many polymers, such as polyethylene, polypropylene, nylon, and natural rubber. The process of crystallization gives rise to a macroscopic deformation, reducing the macroscopic volume, and it can increase the toughness and rigidity of a polymer. For example, for natural rubber crystallization causes a two order of magnitude increase in the elastic moduli. Moreover, crystallization can result in stress relaxation under constant uniaxial extension and creep under constant load. These effects have been captured in a constitutive model developed by Negahban, Wineman and Ma, which has been shown to be in good agreement with experimental results. This presentation provides (1) a theoretical evaluation of the effect of crystallization on the distribution of stress and mechanical moduli under axisymmetric loading and an estimation of the idual stress resulting from crystallization in the vicinity of a cylindrical inclusion; and (2) a numerical simulation of the stress distribution in the vicinity of an inclusion due to crystallization under both constant displacement loading and constant traction loading. All results are for plane strain conditions. Results show that an inhomogeneous distribution of stress and deformation is developed in the vicinity of the inclusion due to the external loading and/or due to crystallization.
Sellins, K S; Danska, J S; Paragas, V; Fathman, C G
1992-10-01
The specificity and TCR gene usage of a panel of sperm whale myoglobin (SpWMb)-reactive T cell clones from DBA/2 mice have previously been characterized, to study structure-function relationships between components of the ternary complex consisting of Ag, TCR, and MHC class II molecules, whose interaction leads to Th cell activation. These DBA/2 clones were specific for epitopes within the residue 110 to 121 region of SpWMb, in the context of the mixed isotype molecule E alpha dA beta d, and expressed the TCR V beta 8.2 gene element. SpWMb-specific T cell hybridomas from the H-2d-congenic B10.D2 mouse strain, which differs from the DBA/2 strain only in the non-MHC background, were generated and compared with the T cell hybridomas from DBA/2 mice, in order to investigate the influence of non-MHC genes on the specificity of the T cell response to the 110-121 epitope. V beta usage by these hybridomas was very homogeneous; three of three DBA/2 and eight of nine B10.D2 hybridomas specific for the 110-121 epitope, in the context of the mixed isotype molecule E alpha dA beta d, expressed the V beta 8.2 gene product. Nucleotide and amino acid sequences of D beta, J beta, and N regions were also similar. One 110-121/E alpha dA beta d-specific B10.D2 hybridoma used V beta 7, a V beta that is clonally deleted in DBA/2 mice. These experiments suggest that a similar set of TCR beta genes are used to respond to a given epitope, regardless of non-MHC background, and they support the hypothesis that, despite great variability between individuals in their non-MHC background genes, human HLA-associated diseases might result from the formation of a particular ternary complex consisting of a shared MHC molecule, a common "disease-associated" epitope, and a shared TCR.
Applications of Doppler Tomography in 2D and 3D
NASA Astrophysics Data System (ADS)
Richards, M.; Budaj, J.; Agafonov, M.; Sharova, O.
2010-12-01
Over the past few years, the applications of Doppler tomography have been extended beyond the usual calculation of 2D velocity images of circumstellar gas flows. This technique has now been used with the new Shellspec spectrum synthesis code to demonstrate the effective modeling of the accretion disk and gas stream in the TT Hya Algol binary. The 2D tomography procedure projects all sources of emission onto a single central (Vx, Vy) velocity plane even though the gas is expected to flow beyond that plane. So, new 3D velocity images were derived with the Radioastronomical Approach method by assuming a grid of Vz values transverse to the central 2D plane. The 3D approach has been applied to the U CrB and RS Vul Algol-type binaries to reveal substantial flow structures beyond the central velocity plane.
Large Area Synthesis of 2D Materials
NASA Astrophysics Data System (ADS)
Vogel, Eric
Transition metal dichalcogenides (TMDs) have generated significant interest for numerous applications including sensors, flexible electronics, heterostructures and optoelectronics due to their interesting, thickness-dependent properties. Despite recent progress, the synthesis of high-quality and highly uniform TMDs on a large scale is still a challenge. In this talk, synthesis routes for WSe2 and MoS2 that achieve monolayer thickness uniformity across large area substrates with electrical properties equivalent to geological crystals will be described. Controlled doping of 2D semiconductors is also critically required. However, methods established for conventional semiconductors, such as ion implantation, are not easily applicable to 2D materials because of their atomically thin structure. Redox-active molecular dopants will be demonstrated which provide large changes in carrier density and workfunction through the choice of dopant, treatment time, and the solution concentration. Finally, several applications of these large-area, uniform 2D materials will be described including heterostructures, biosensors and strain sensors.
NASA Astrophysics Data System (ADS)
Zhang, Feng; Ikeda, Masao; Zhang, Shu-Ming; Liu, Jian-Ping; Tian, Ai-Qin; Wen, Peng-Yan; Cheng, Yang; Yang, Hui
2016-11-01
The polarization fields in c-plane InGaN/(In)GaN multiple quantum well (MQW) structures grown on sapphire substrate by metal-organic chemical vapor deposition are investigated in this paper. The indium composition in the quantum wells varies from 14.8 to 26.5% for different samples. The photoluminescence wavelengths are calculated theoretically by fully considering the related effects and compared with the measured wavelengths. It is found that when the indium content is lower than 17.3%, the measured wavelengths agree well with the theoretical values. However, when the indium content is higher than 17.3%, the measured ones are much shorter than the calculation results. This discrepancy is attributed to the reduced polarization field in the MQWs. For the MQWs with lower indium content, 100% theoretical polarization can be maintained, while, when the indium content is higher, the polarization field decreases significantly. The polarization field can be weakened down to 23% of the theoretical value when the indium content is 26.5%. Strain relaxation is excluded as the origin of the polarization reduction because there is no sign of lattice relaxation in the structures, judging by the X-ray diffraction reciprocal space mapping. The possible causes of the polarization reduction are discussed.
Zhang, Feng; Ikeda, Masao; Zhang, Shu-Ming; Liu, Jian-Ping; Tian, Ai-Qin; Wen, Peng-Yan; Cheng, Yang; Yang, Hui
2016-12-01
The polarization fields in c-plane InGaN/(In)GaN multiple quantum well (MQW) structures grown on sapphire substrate by metal-organic chemical vapor deposition are investigated in this paper. The indium composition in the quantum wells varies from 14.8 to 26.5% for different samples. The photoluminescence wavelengths are calculated theoretically by fully considering the related effects and compared with the measured wavelengths. It is found that when the indium content is lower than 17.3%, the measured wavelengths agree well with the theoretical values. However, when the indium content is higher than 17.3%, the measured ones are much shorter than the calculation results. This discrepancy is attributed to the reduced polarization field in the MQWs. For the MQWs with lower indium content, 100% theoretical polarization can be maintained, while, when the indium content is higher, the polarization field decreases significantly. The polarization field can be weakened down to 23% of the theoretical value when the indium content is 26.5%. Strain relaxation is excluded as the origin of the polarization reduction because there is no sign of lattice relaxation in the structures, judging by the X-ray diffraction reciprocal space mapping. The possible causes of the polarization reduction are discussed.
NASA Astrophysics Data System (ADS)
Pan, Bing; Yu, Liping; Wu, Dafang
2014-02-01
The ideal pinhole imaging model commonly assumed for an ordinary two-dimensional digital image correlation (2D-DIC) system is neither perfect nor stable because of the existence of small out-of-plane motion of the test sample surface that occurred after loading, small out-of-plane motion of the sensor target due to temperature variation of a camera and unavoidable geometric distortion of an imaging lens. In certain cases, these disadvantages can lead to significant errors in the measured displacements and strains. Although a high-quality bilateral telecentric lens has been strongly recommended to be used in the 2D-DIC system as an essential optical component to achieve high-accuracy measurement, it is not generally applicable due to its fixed field of view, limited depth of focus and high cost. To minimize the errors associated with the imperfectness and instability of a common 2D-DIC system using a low-cost imaging lens, a generalized compensation method using a non-deformable reference sample is proposed in this work. With the proposed method, the displacement of the reference sample rigidly attached behind the test sample is first measured using 2D-DIC, and then it is fitted using a parametric model. The fitted parametric model is then used to correct the displacements of the deformed sample to remove the influences of these unfavorable factors. The validity of the proposed compensation method is first verified using out-of-plane translation, out-of-plane rotation, in-plane translation tests and their combinations. Uniaxial tensile tests of an aluminum specimen were also performed to quantitatively examine the strain accuracy of the proposed compensation method. Experiments show that the proposed compensation method is an easy-to-implement yet effective technique for achieving high-accuracy deformation measurement using an ordinary 2D-DIC system.
Codon Constraints on Closed 2D Shapes,
2014-09-26
19843$ CODON CONSTRAINTS ON CLOSED 2D SHAPES Go Whitman Richards "I Donald D. Hoffman’ D T 18 Abstract: Codons are simple primitives for describing plane...RSONAL AUT"ORtIS) Richards, Whitman & Hoffman, Donald D. 13&. TYPE OF REPORT 13b. TIME COVERED N/A P8 AT F RRrT t~r. Ago..D,) is, PlE COUNT Reprint...outlines, if figure and ground are ignored. Later, we will address the problem of indexing identical codon descriptors that have different figure
E-2D Advanced Hawkeye Aircraft (E-2D AHE)
2015-12-01
Selected Acquisition Report (SAR) RCS: DD-A&T(Q&A)823-364 E-2D Advanced Hawkeye Aircraft (E-2D AHE) As of FY 2017 President’s Budget Defense...Office Estimate RDT&E - Research, Development, Test, and Evaluation SAR - Selected Acquisition Report SCP - Service Cost Position TBD - To Be Determined
Röthlisberger Channel Model with Anti-Plane Shear Loading Superposed on In-Plane Compression
NASA Astrophysics Data System (ADS)
Fernandes, M. C.; Meyer, C. R.; Rice, J. R.
2014-12-01
The Röthlisberger channel (R-channel) is a commonly adopted model that balances creep closure by Nye 2D in-plane straining, driven by the ice overburden pressure, against the melt rate from viscous energy dissipation in turbulent flow within the channel. Perol and Rice (AGU abstr. C11B-0677, 2011; JGR 2014 in review) and Suckale et al. (JGR F003008, 2014) have conjectured that these R-Channels may exist at the beds of rapidly straining West Antarctic Ice Stream shear margins. That is expected as a result of melt generation and drainage from forming temperate ice, and the channels may interact through the bed hydrology to partially stabilize the shear margin against lateral expansion. However, at those locations the overburden stresses, driving in-plane flow, are supplemented by substantial anti-plane shear stresses. Similarly, R-channels in mountain glaciers are also subject to both in-plane and anti-plane stresses. These channels usually form in the downstream direction, where anti-plane shear effects arise horizontally from drag at lateral moraines and vertically from the downslope gravity component. Here we examine how superposed anti-plane loading can alter results of the Nye solution for a 2D R-channel. We use a combination of perturbation analyses and finite element methods, varying the amount of applied anti-plane stress. A closed-form solution is derived for imposing a small anti-plane perturbation, which has no effect at linear order on the Nye closure rate. Such effects become strong at more substantial perturbations, and the inplane stress and strain fields are then significantly altered from the Nye solution. We further extend our model to compute channel size in terms of the external stressing and flow rate. Understanding the effect of the ice flow on channel size and formation is important to subglacial hydrology, as well as a potentially vital component for our understanding of the formation and motion of ice streams found in West Antarctica.
Chen, X Y; Pan, X H; Chen, W; Chen, S S; Huang, J Y; Ye, Z Z
2016-10-15
A large degree of polarization (ρ) of photoluminescence (PL) approximate to 1 is obtained in each nonpolar a-plane Mg_{x}Zn_{1-x}O layer grown by plasma-assisted molecular beam epitaxy (MBE) with x=0.01, 0.03, and 0.10, respectively. Anisotropic in-plane strains are selectively introduced by using foreign substrates and doping with different Mg contents, which strongly modify the valence band structures, leading to anisotropic optical properties. A polarized Raman measurement shows that anisotropic in-plane strains along the y and z axes increase with the increasing Mg contents. Polarized PL spectra show that ρ gradually increases to 0.97 with decreasing in-plane strains, resulting from an increasing difference in transition energy (ΔE) between E⊥c and E‖c caused by a lift of the degeneracy of valence band structures. The obtained highly polarized emission is close to linear polarized light, which is desirable in the backlighting of liquid crystal displays.
Trache, Tudor; Stöbe, Stephan; Tarr, Adrienn; Pfeiffer, Dietrich; Hagendorff, Andreas
2014-12-01
Comparison of 3D and 2D speckle tracking performed on standard 2D and triplane 2D datasets of normal and pathological left ventricular (LV) wall-motion patterns with a focus on the effect that 3D volume rate (3DVR), image quality and tracking artifacts have on the agreement between 2D and 3D speckle tracking. 37 patients with normal LV function and 18 patients with ischaemic wall-motion abnormalities underwent 2D and 3D echocardiography, followed by offline speckle tracking measurements. The values of 3D global, regional and segmental strain were compared with the standard 2D and triplane 2D strain values. Correlation analysis with the LV ejection fraction (LVEF) was also performed. The 3D and 2D global strain values correlated good in both normally and abnormally contracting hearts, though systematic differences between the two methods were observed. Of the 3D strain parameters, the area strain showed the best correlation with the LVEF. The numerical agreement of 3D and 2D analyses varied significantly with the volume rate and image quality of the 3D datasets. The highest correlation between 2D and 3D peak systolic strain values was found between 3D area and standard 2D longitudinal strain. Regional wall-motion abnormalities were similarly detected by 2D and 3D speckle tracking. 2DST of triplane datasets showed similar results to those of conventional 2D datasets. 2D and 3D speckle tracking similarly detect normal and pathological wall-motion patterns. Limited image quality has a significant impact on the agreement between 3D and 2D numerical strain values.
Differential CYP 2D6 metabolism alters primaquine pharmacokinetics.
Potter, Brittney M J; Xie, Lisa H; Vuong, Chau; Zhang, Jing; Zhang, Ping; Duan, Dehui; Luong, Thu-Lan T; Bandara Herath, H M T; Dhammika Nanayakkara, N P; Tekwani, Babu L; Walker, Larry A; Nolan, Christina K; Sciotti, Richard J; Zottig, Victor E; Smith, Philip L; Paris, Robert M; Read, Lisa T; Li, Qigui; Pybus, Brandon S; Sousa, Jason C; Reichard, Gregory A; Marcsisin, Sean R
2015-04-01
Primaquine (PQ) metabolism by the cytochrome P450 (CYP) 2D family of enzymes is required for antimalarial activity in both humans (2D6) and mice (2D). Human CYP 2D6 is highly polymorphic, and decreased CYP 2D6 enzyme activity has been linked to decreased PQ antimalarial activity. Despite the importance of CYP 2D metabolism in PQ efficacy, the exact role that these enzymes play in PQ metabolism and pharmacokinetics has not been extensively studied in vivo. In this study, a series of PQ pharmacokinetic experiments were conducted in mice with differential CYP 2D metabolism characteristics, including wild-type (WT), CYP 2D knockout (KO), and humanized CYP 2D6 (KO/knock-in [KO/KI]) mice. Plasma and liver pharmacokinetic profiles from a single PQ dose (20 mg/kg of body weight) differed significantly among the strains for PQ and carboxy-PQ. Additionally, due to the suspected role of phenolic metabolites in PQ efficacy, these were probed using reference standards. Levels of phenolic metabolites were highest in mice capable of metabolizing CYP 2D6 substrates (WT and KO/KI 2D6 mice). PQ phenolic metabolites were present in different quantities in the two strains, illustrating species-specific differences in PQ metabolism between the human and mouse enzymes. Taking the data together, this report furthers understanding of PQ pharmacokinetics in the context of differential CYP 2D metabolism and has important implications for PQ administration in humans with different levels of CYP 2D6 enzyme activity.
2D superconductivity by ionic gating
NASA Astrophysics Data System (ADS)
Iwasa, Yoshi
2D superconductivity is attracting a renewed interest due to the discoveries of new highly crystalline 2D superconductors in the past decade. Superconductivity at the oxide interfaces triggered by LaAlO3/SrTiO3 has become one of the promising routes for creation of new 2D superconductors. Also, the MBE grown metallic monolayers including FeSe are also offering a new platform of 2D superconductors. In the last two years, there appear a variety of monolayer/bilayer superconductors fabricated by CVD or mechanical exfoliation. Among these, electric field induced superconductivity by electric double layer transistor (EDLT) is a unique platform of 2D superconductivity, because of its ability of high density charge accumulation, and also because of the versatility in terms of materials, stemming from oxides to organics and layered chalcogenides. In this presentation, the following issues of electric filed induced superconductivity will be addressed; (1) Tunable carrier density, (2) Weak pinning, (3) Absence of inversion symmetry. (1) Since the sheet carrier density is quasi-continuously tunable from 0 to the order of 1014 cm-2, one is able to establish an electronic phase diagram of superconductivity, which will be compared with that of bulk superconductors. (2) The thickness of superconductivity can be estimated as 2 - 10 nm, dependent on materials, and is much smaller than the in-plane coherence length. Such a thin but low resistance at normal state results in extremely weak pinning beyond the dirty Boson model in the amorphous metallic films. (3) Due to the electric filed, the inversion symmetry is inherently broken in EDLT. This feature appears in the enhancement of Pauli limit of the upper critical field for the in-plane magnetic fields. In transition metal dichalcogenide with a substantial spin-orbit interactions, we were able to confirm the stabilization of Cooper pair due to its spin-valley locking. This work has been supported by Grant-in-Aid for Specially
Two dimensional WS2 lateral heterojunctions by strain modulation
NASA Astrophysics Data System (ADS)
Meng, Lan; Zhang, Yuhan; Hu, Song; Wang, Xiangfu; Liu, Chunsheng; Guo, Yandong; Wang, Xinran; Yan, Xiaohong
2016-06-01
"Strain engineering" has been widely used to tailor the physical properties of layered materials, like graphene, black phosphorus, and transition-metal dichalcogenides. Here, we exploit thermal strain engineering to construct two dimensional (2D) WS2 in-plane heterojunctions. Kelvin probe force microscopy is used to investigate the surface potentials and work functions of few-layer WS2 flakes, which are grown on SiO2/Si substrates by chemical vapor deposition, followed by a fast cooling process. In the interior regions of strained WS2 flakes, work functions are found to be much larger than that of the unstrained regions. The difference in work functions, together with the variation of band gaps, endows the formation of heterojunctions in the boundaries between inner and outer domains of WS2 flakes. This result reveals that the existence of strain offers a unique opportunity to modulate the electronic properties of 2D materials and construct 2D lateral heterojunctions.
Computational Screening of 2D Materials for Photocatalysis.
Singh, Arunima K; Mathew, Kiran; Zhuang, Houlong L; Hennig, Richard G
2015-03-19
Two-dimensional (2D) materials exhibit a range of extraordinary electronic, optical, and mechanical properties different from their bulk counterparts with potential applications for 2D materials emerging in energy storage and conversion technologies. In this Perspective, we summarize the recent developments in the field of solar water splitting using 2D materials and review a computational screening approach to rapidly and efficiently discover more 2D materials that possess properties suitable for solar water splitting. Computational tools based on density-functional theory can predict the intrinsic properties of potential photocatalyst such as their electronic properties, optical absorbance, and solubility in aqueous solutions. Computational tools enable the exploration of possible routes to enhance the photocatalytic activity of 2D materials by use of mechanical strain, bias potential, doping, and pH. We discuss future research directions and needed method developments for the computational design and optimization of 2D materials for photocatalysis.
Wei, Hongjiang; Zhang, Yuyao; Gibbs, Eric; Chen, Nan-Kuei; Wang, Nian; Liu, Chunlei
2017-04-01
Quantitative susceptibility mapping (QSM) measures tissue magnetic susceptibility and typically relies on time-consuming three-dimensional (3D) gradient-echo (GRE) MRI. Recent studies have shown that two-dimensional (2D) multi-slice gradient-echo echo-planar imaging (GRE-EPI), which is commonly used in functional MRI (fMRI) and other dynamic imaging techniques, can also be used to produce data suitable for QSM with much shorter scan times. However, the production of high-quality QSM maps is difficult because data obtained by 2D multi-slice scans often have phase inconsistencies across adjacent slices and strong susceptibility field gradients near air-tissue interfaces. To address these challenges in 2D EPI-based QSM studies, we present a new data processing procedure that integrates 2D and 3D phase processing. First, 2D Laplacian-based phase unwrapping and 2D background phase removal are performed to reduce phase inconsistencies between slices and remove in-plane harmonic components of the background phase. This is followed by 3D background phase removal for the through-plane harmonic components. The proposed phase processing was evaluated with 2D EPI data obtained from healthy volunteers, and compared against conventional 3D phase processing using the same 2D EPI datasets. Our QSM results were also compared with QSM values from time-consuming 3D GRE data, which were taken as ground truth. The experimental results show that this new 2D EPI-based QSM technique can produce quantitative susceptibility measures that are comparable with those of 3D GRE-based QSM across different brain regions (e.g. subcortical iron-rich gray matter, cortical gray and white matter). This new 2D EPI QSM reconstruction method is implemented within STI Suite, which is a comprehensive shareware for susceptibility imaging and quantification. Copyright © 2016 John Wiley & Sons, Ltd.
Strain effects on the electronic properties in δ -doped oxide superlattices
You, Jeong Ho; Lee, Jun Hee; Okamoto, Satoshi; ...
2015-02-07
We investigated strain effects on the electronic properties of (LaTiO3)1/(SrTiO3)N superlattices using density functional theory. Under biaxial in-plane strain within the range of -5% ≤ ε// ≤ 5%, the dxy orbital electrons are highly localized at the interfaces whereas the dyz and dxz orbital electrons are more distributed in the SrTiO3 (STO) spacer layers. For STO thickness N ≥ 3 unit cells (u.c.), the dxy orbital electrons form two-dimensional (2D) electron gases (2DEGs). The quantized energy levels of the 2DEG are insensitive to the STO spacer thickness, but are strongly dependent on the applied biaxial in-plane strain. As the in-planemore » strain changes from compressive to tensile, the quantized energy levels of the dxy orbitals decrease thereby creating more states with 2D character. In contrast to the dxy orbital, the dyz and dxz orbitals always have three-dimensional (3D) transport characteristics and their energy levels increase as the strain changes from compressive to tensile. In conclusion, since the charge densities in the dxy orbital and the dyz and dxz orbitals respond to biaxial in-plane strain in an opposite way, the transport dimensionality of the majority carriers can be controlled between 2D and 3D by applying biaxial in-plane strain.« less
Optoelectronics with 2D semiconductors
NASA Astrophysics Data System (ADS)
Mueller, Thomas
2015-03-01
Two-dimensional (2D) atomic crystals, such as graphene and layered transition-metal dichalcogenides, are currently receiving a lot of attention for applications in electronics and optoelectronics. In this talk, I will review our research activities on electrically driven light emission, photovoltaic energy conversion and photodetection in 2D semiconductors. In particular, WSe2 monolayer p-n junctions formed by electrostatic doping using a pair of split gate electrodes, type-II heterojunctions based on MoS2/WSe2 and MoS2/phosphorene van der Waals stacks, 2D multi-junction solar cells, and 3D/2D semiconductor interfaces will be presented. Upon optical illumination, conversion of light into electrical energy occurs in these devices. If an electrical current is driven, efficient electroluminescence is obtained. I will present measurements of the electrical characteristics, the optical properties, and the gate voltage dependence of the device response. In the second part of my talk, I will discuss photoconductivity studies of MoS2 field-effect transistors. We identify photovoltaic and photoconductive effects, which both show strong photoconductive gain. A model will be presented that reproduces our experimental findings, such as the dependence on optical power and gate voltage. We envision that the efficient photon conversion and light emission, combined with the advantages of 2D semiconductors, such as flexibility, high mechanical stability and low costs of production, could lead to new optoelectronic technologies.
NASA Astrophysics Data System (ADS)
Randeria, Mohit; Banerjee, Sumilan; Rowland, James
2015-09-01
Most theoretical studies of chiral magnetism, and the resulting spin textures, have focused on 3D systems with broken bulk inversion symmetry, where skyrmions are stabilized by easy-axis anisotropy. In this talk I will describe our results on 2D and quasi-2D systems with broken surface inversion, where we find [1] that skyrmion crystals are much more stable than in 3D, especially for the case of easy-plane anisotropy. These results are of particular interest for thin films, surfaces, and oxide interfaces [2], where broken surface-inversion symmetry and Rashba spin-orbit coupling naturally lead to both the chiral Dzyaloshinskii-Moriya (DM) interaction and to easy-plane compass anisotropy. I will then turn to systems that break both bulk and surface inversion, resulting in two distinct DM terms arising from Dresselhaus and Rashba spin-orbit coupling. I will describe [3] the evolution of the skyrmion structure and of the phase diagram as a function of the ratio of Dresselhaus and Rashba terms, which can be tuned by varying film thickness and strain. [1] S. Banerjee, J. Rowland, O. Erten, and M. Randeria, PRX 4, 031045 (2014). [2] S. Banerjee, O. Erten, and M. Randeria, Nature Phys. 9, 626 (2013). [3] J. Rowland, S. Banerjee and M. Randeria, (unpublished).
Transition to turbulence: 2D directed percolation
NASA Astrophysics Data System (ADS)
Chantry, Matthew; Tuckerman, Laurette; Barkley, Dwight
2016-11-01
The transition to turbulence in simple shear flows has been studied for well over a century, yet in the last few years has seen major leaps forward. In pipe flow, this transition shows the hallmarks of (1 + 1) D directed percolation, a universality class of continuous phase transitions. In spanwisely confined Taylor-Couette flow the same class is found, suggesting the phenomenon is generic to shear flows. However in plane Couette flow the largest simulations and experiments to-date find evidence for a discrete transition. Here we study a planar shear flow, called Waleffe flow, devoid of walls yet showing the fundamentals of planar transition to turbulence. Working with a quasi-2D yet Navier-Stokes derived model of this flow we are able to attack the (2 + 1) D transition problem. Going beyond the system sizes previously possible we find all of the required scalings of directed percolation and thus establish planar shears flow in this class.
Sevrin, A.
1993-06-01
After reviewing some aspects of gravity in two dimensions, I show that non-trivial embeddings of sl(2) in a semi-simple (super) Lie algebra give rise to a very large class of extensions of 2D gravity. The induced action is constructed as a gauged WZW model and an exact expression for the effective action is given.
Three-dimensional ultrasound strain imaging of skeletal muscles
NASA Astrophysics Data System (ADS)
Gijsbertse, K.; Sprengers, A. M. J.; Nillesen, M. M.; Hansen, H. H. G.; Lopata, R. G. P.; Verdonschot, N.; de Korte, C. L.
2017-01-01
In this study, a multi-dimensional strain estimation method is presented to assess local relative deformation in three orthogonal directions in 3D space of skeletal muscles during voluntary contractions. A rigid translation and compressive deformation of a block phantom, that mimics muscle contraction, is used as experimental validation of the 3D technique and to compare its performance with respect to a 2D based technique. Axial, lateral and (in case of 3D) elevational displacements are estimated using a cross-correlation based displacement estimation algorithm. After transformation of the displacements to a Cartesian coordinate system, strain is derived using a least-squares strain estimator. The performance of both methods is compared by calculating the root-mean-squared error of the estimated displacements with the calculated theoretical displacements of the phantom experiments. We observe that the 3D technique delivers more accurate displacement estimations compared to the 2D technique, especially in the translation experiment where out-of-plane motion hampers the 2D technique. In vivo application of the 3D technique in the musculus vastus intermedius shows good resemblance between measured strain and the force pattern. Similarity of the strain curves of repetitive measurements indicates the reproducibility of voluntary contractions. These results indicate that 3D ultrasound is a valuable imaging tool to quantify complex tissue motion, especially when there is motion in three directions, which results in out-of-plane errors for 2D techniques.
NASA Technical Reports Server (NTRS)
Krempl, Erhard; Hong, Bor Zen
1989-01-01
A macromechanics analysis is presented for the in-plane, anisotropic time-dependent behavior of metal matrix laminates. The small deformation, orthotropic viscoplasticity theory based on overstress represents lamina behavior in a modified simple laminate theory. Material functions and constants can be identified in principle from experiments with laminae. Orthotropic invariants can be repositories for tension-compression asymmetry and for linear elasticity in one direction while the other directions behave in a viscoplastic manner. Computer programs are generated and tested for either unidirectional or symmetric laminates under in-plane loading. Correlations with the experimental results on metal matrix composites are presented.
Regulation of NKG2D ligand gene expression.
Eagle, Robert A; Traherne, James A; Ashiru, Omodele; Wills, Mark R; Trowsdale, John
2006-03-01
The activating immunoreceptor NKG2D has seven known host ligands encoded by the MHC class I chain-related MIC and ULBP/RAET genes. Why there is such diversity of NKG2D ligands is not known but one hypothesis is that they are differentially expressed in different tissues in response to different stresses. To explore this, we compared expression patterns and promoters of NKG2D ligand genes. ULBP/RAET genes were transcribed independent of each other in a panel of cell lines. ULBP/RAET gene expression was upregulated on infection with human cytomegalovirus; however, a clinical strain, Toledo, induced expression more slowly than did a laboratory strain, AD169. ULBP4/RAET1E was not induced by infection with either strain. To investigate the mechanisms behind the similarities and differences in NKG2D ligand gene expression a comparative sequence analysis of NKG2D ligand gene putative promoter regions was conducted. Sequence alignments demonstrated that there was significant sequence diversity; however, one region of high similarity between most of the genes is evident. This region contains a number of potential transcription factor binding sites, including those involved in shock responses and sites for retinoic acid-induced factors. Promoters of some NKG2D ligand genes are polymorphic and several sequence alterations in these alleles abolished putative transcription factor binding.
Pande, Vivek V; Chousalkar, Kapil C; Bhanugopan, Marie S; Quinn, Jane C
2015-11-01
The biologically active form of vitamin D₃, calcitriol (1,25-(OH)₂D₃), plays a key role in mineral homeostasis and bone formation and dietary vitamin D₃deficiency is a major cause of bone disorders in poultry. Supplementary dietary cholecalciferol (25-hydroxyvitamin D, 25-OH), the precursor of calcitriol, is commonly employed to combat this problem; however, dosage must be carefully determined as excess dietary vitamin D can cause toxicity resulting in a decrease in bone calcification, hypercalcinemia and renal failure. Despite much research on the therapeutic administration of dietary vitamin D in humans, the relative sensitivity of avian species to exogenous vitamin D has not been well defined. In order to determine the effects of exogenous 1,25-(OH)₂D₃during avian osteogenesis, chicken bone marrow-derived mesenchymal stem cells (BM-MSCs) were exposed to varying doses of 1,25-(OH)₂D₃during in vitro osteogenic differentiation and examined for markers of early proliferation and osteogenic induction. Similar to humans and other mammals, poultry BM-MSCs were found to be highly sensitive to exogenous 1,25-(OH)₂D₃with super pharmacological levels exerting significant inhibition of mineralization and loss of cell proliferation in vitro. Strain related differences were apparent, with BM-MCSs derived from layers strains showing a higher level of sensitivity to 1,25-(OH)₂D₃than those from broilers. These data suggest that understanding species and strain specific sensitivities to 1,25-(OH)₂D₃is important for optimizing bone health in the poultry industry and that use of avian BM-MSCs are a useful tool for examining underlying effects of genetic variation in poultry.
NASA Astrophysics Data System (ADS)
Matzen, Sylvia; Nesterov, Oleksiy; Rispens, Gijsbert; Heuver, Jeroen; Noheda, Beatriz; Biegalski, Michael; Christen, Hans
2014-03-01
Understanding and controlling domain formation in nanoscale ferroelectrics is interesting from a fundamental point of view and of great technological importance. Increasing miniaturization allows creating complex domain structures, offering novel functionalities that could be particularly useful for the development of nanoelectronic devices. While most studies in thin films focus on domain patterns with up/down polarization for ferroelectric memories, domain structures with purely in-plane polarization have not been much investigated. However, such structures are potentially useful in optical devices or to avoid depolarization fields in ultra-thin films, as long as the domains can be addressed and switched. We use a combination of compositional substitutions and epitaxial growth on a substrate in order to tune the domain configuration. The substitution of Pb by Sr in PbxSr1-xTiO3 thin films grown epitaxially on (110)-DyScO3, stabilizes a domain structure with purely in-plane polarization. In this work, we show that it is possible to stabilize and control a complex domain architecture at two different length scales, yielding periodic ferroelectric nano-domains with purely in-plane polarization. Most importantly, these in-plane domains can be switched by a scanning probe.
NASA Astrophysics Data System (ADS)
Tanaka, Satoyuki; Suzuki, Hirotaka; Sadamoto, Shota; Sannomaru, Shogo; Yu, Tiantang; Bui, Tinh Quoc
2016-08-01
Two-dimensional (2D) in-plane mixed-mode fracture mechanics problems are analyzed employing an efficient meshfree Galerkin method based on stabilized conforming nodal integration (SCNI). In this setting, the reproducing kernel function as meshfree interpolant is taken, while employing the SCNI for numerical integration of stiffness matrix in the Galerkin formulation. The strain components are smoothed and stabilized employing Gauss divergence theorem. The path-independent integral ( J-integral) is solved based on the nodal integration by summing the smoothed physical quantities and the segments of the contour integrals. In addition, mixed-mode stress intensity factors (SIFs) are extracted from the J-integral by decomposing the displacement and stress fields into symmetric and antisymmetric parts. The advantages and features of the present formulation and discretization in evaluation of the J-integral of in-plane 2D fracture problems are demonstrated through several representative numerical examples. The mixed-mode SIFs are evaluated and compared with reference solutions. The obtained results reveal high accuracy and good performance of the proposed meshfree method in the analysis of 2D fracture problems.
Hoop Tensile Characterization Of SiC/SiC Cylinders Fabricated From 2D Fabric
NASA Technical Reports Server (NTRS)
Verrilli, Michael J.; Yun, HeeMann; DiCarlo, James A.; Barnett, Terry R.
2002-01-01
Tensile stress-strain properties in the hoop direction were obtained for 100-mm diameter SiC/SiC cylinders using ring specimens machined from the cylinder ends. The cylinders were fabricated from 2D balanced fabric with several material variants, including wall thickness (6, 8, and 12 plies), Sic fiber type (Sylramic, Sylramic-iBN, Hi-Nicalon, and Hi-Nicalon S), fiber sizing type, and matrix type (full CVI Sic, and partial CVI plus melt-infiltrated SiC-Si). Fiber ply splices existed in the all the hoops. Tensile hoop measurements were made at room temperature and 1200 C using hydrostatic ring test facilities. The hoop results are compared with in-plane data measured on flat panels using same material variants, but containing no splices.
Suzuki, N; Mita, K; Watakabe, M; Akataki, K; Okagawa, T; Kimizuka, M
1998-01-01
The purpose of this study was to use an non-invasive method to determine whether strain on the gastrocnemii and hamstrings influences postural balance in spastic cerebral palsy (CP). Changes in alignment during standing posture with subjects positioned on a platform that was gradually inclined were measured in 10 normal children and 11 children with CP. The changes in postural alignment were plotted and geometric models used to determine the lines where the gastrocnemii and hamstrings were maximally stretched. In this way the relationship between postural alignment and the amount of strain on the gastrocnemii and hamstrings was investigated. On the inclined platform, which caused ankle joints to become dorsiflexed as the inclination angle increased, the gastrocnemii began to be strained and the hip joints began to be flexed (trunk bent forward) at the same time. In the children with CP, the gastrocnemii were more strained by smaller degrees of inclination. Furthermore, there was one child with CP whose hamstrings were also strained on the inclined platform. We confirmed that postural balance was affected by strain on the gastrocnemii and hamstrings.
NASA Technical Reports Server (NTRS)
Jones, M. H.; Bubsey, R. T.; Brown, W. F., Jr.; Bucci, R. J.; Collis, S. F.; Kohm, R. F.; Kaufman, J. G.
1977-01-01
A description is presented of studies which have been conducted to establish an improved technology base for a use of the sharply notched cylindrical specimen in quality assurance tests of aluminum alloy products. The results are presented of an investigation of fundamental variables associated with specimen preparation and testing, taking into account the influence of the notch root radius, the eccentricity of loading, the specimen diameter, and the notch depth on the sharp notch strength. Attention is given to the statistical procedures which are necessary to establish correlations between the sharp notch strength and the plane-strain fracture toughness for high-strength aluminum alloys.
NASA Astrophysics Data System (ADS)
Perig, Alexander V.; Golodenko, Nikolai N.
2016-11-01
The present article addresses strain unevenness effects during equal channel angular extrusion (ECAE) of physical models of polymer workpieces with viscosity flow features through a Segal die with channel intersection angle of 2θ = 90°. Computational viscous flow lines, flow velocity fields, and material dead zone formation in the physical simulation of ECAE have been numerically derived for planar flow of viscous incompressible continua in an angular die with 2θ = 90°. This is accomplished through the introduction of Navier-Stokes equations with the following dimensionless physical variables: polymer model local flow velocities u, v and punching pressure p. Derived experimental results are grounded on the application of the following physical simulation techniques: marker method, based on harder disperse particles partially forcing into the front faces of soft workpieces; layered model production by assembling the workpiece soft model with different layers, and circular gridlines use with viscous flow of the polymer soft model. Good agreement has been found between the computational and observable physical simulation results. Based on the obtained results, recommendations are made for polymer ECAE technology enhancement and angular die design for polymer workpiece pressure forming.
Simulation of Yeast Cooperation in 2D.
Wang, M; Huang, Y; Wu, Z
2016-03-01
Evolution of cooperation has been an active research area in evolutionary biology in decades. An important type of cooperation is developed from group selection, when individuals form spatial groups to prevent them from foreign invasions. In this paper, we study the evolution of cooperation in a mixed population of cooperating and cheating yeast strains in 2D with the interactions among the yeast cells restricted to their small neighborhoods. We conduct a computer simulation based on a game theoretic model and show that cooperation is increased when the interactions are spatially restricted, whether the game is of a prisoner's dilemma, snow drifting, or mutual benefit type. We study the evolution of homogeneous groups of cooperators or cheaters and describe the conditions for them to sustain or expand in an opponent population. We show that under certain spatial restrictions, cooperator groups are able to sustain and expand as group sizes become large, while cheater groups fail to expand and keep them from collapse.
2D microscopic model of graphene fracture properties
NASA Astrophysics Data System (ADS)
Hess, Peter
2015-05-01
An analytical two-dimensional (2D) microscopic fracture model based on Morse-type interaction is derived containing no adjustable parameter. From the 2D Young’s moduli and 2D intrinsic strengths of graphene measured by nanoindentation based on biaxial tension and calculated by density functional theory for uniaxial tension the widely unknown breaking force, line or edge energy, surface energy, fracture toughness, and strain energy release rate were determined. The simulated line energy agrees well with ab initio calculations and the fracture toughness of perfect graphene sheets is in good agreement with molecular dynamics simulations and the fracture toughness evaluated for defective graphene using the Griffith relation. Similarly, the estimated critical strain energy release rate agrees well with result of various theoretical approaches based on the J-integral and surface energy. The 2D microscopic model, connecting 2D and three-dimensional mechanical properties in a consistent way, provides a versatile relationship to easily access all relevant fracture properties of pristine 2D solids.
ORION96. 2-d Finite Element Code Postprocessor
Sanford, L.A.; Hallquist, J.O.
1992-02-02
ORION is an interactive program that serves as a postprocessor for the analysis programs NIKE2D, DYNA2D, TOPAZ2D, and CHEMICAL TOPAZ2D. ORION reads binary plot files generated by the two-dimensional finite element codes currently used by the Methods Development Group at LLNL. Contour and color fringe plots of a large number of quantities may be displayed on meshes consisting of triangular and quadrilateral elements. ORION can compute strain measures, interface pressures along slide lines, reaction forces along constrained boundaries, and momentum. ORION has been applied to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.
Strain-engineered diffusive atomic switching in two-dimensional crystals
NASA Astrophysics Data System (ADS)
Kalikka, Janne; Zhou, Xilin; Dilcher, Eric; Wall, Simon; Li, Ju; Simpson, Robert E.
2016-06-01
Strain engineering is an emerging route for tuning the bandgap, carrier mobility, chemical reactivity and diffusivity of materials. Here we show how strain can be used to control atomic diffusion in van der Waals heterostructures of two-dimensional (2D) crystals. We use strain to increase the diffusivity of Ge and Te atoms that are confined to 5 Å thick 2D planes within an Sb2Te3-GeTe van der Waals superlattice. The number of quintuple Sb2Te3 2D crystal layers dictates the strain in the GeTe layers and consequently its diffusive atomic disordering. By identifying four critical rules for the superlattice configuration we lay the foundation for a generalizable approach to the design of switchable van der Waals heterostructures. As Sb2Te3-GeTe is a topological insulator, we envision these rules enabling methods to control spin and topological properties of materials in reversible and energy efficient ways.
2D quasiperiodic plasmonic crystals
Bauer, Christina; Kobiela, Georg; Giessen, Harald
2012-01-01
Nanophotonic structures with irregular symmetry, such as quasiperiodic plasmonic crystals, have gained an increasing amount of attention, in particular as potential candidates to enhance the absorption of solar cells in an angular insensitive fashion. To examine the photonic bandstructure of such systems that determines their optical properties, it is necessary to measure and model normal and oblique light interaction with plasmonic crystals. We determine the different propagation vectors and consider the interaction of all possible waveguide modes and particle plasmons in a 2D metallic photonic quasicrystal, in conjunction with the dispersion relations of a slab waveguide. Using a Fano model, we calculate the optical properties for normal and inclined light incidence. Comparing measurements of a quasiperiodic lattice to the modelled spectra for angle of incidence variation in both azimuthal and polar direction of the sample gives excellent agreement and confirms the predictive power of our model. PMID:23209871
NASA Astrophysics Data System (ADS)
Schaibley, John R.; Yu, Hongyi; Clark, Genevieve; Rivera, Pasqual; Ross, Jason S.; Seyler, Kyle L.; Yao, Wang; Xu, Xiaodong
2016-11-01
Semiconductor technology is currently based on the manipulation of electronic charge; however, electrons have additional degrees of freedom, such as spin and valley, that can be used to encode and process information. Over the past several decades, there has been significant progress in manipulating electron spin for semiconductor spintronic devices, motivated by potential spin-based information processing and storage applications. However, experimental progress towards manipulating the valley degree of freedom for potential valleytronic devices has been limited until very recently. We review the latest advances in valleytronics, which have largely been enabled by the isolation of 2D materials (such as graphene and semiconducting transition metal dichalcogenides) that host an easily accessible electronic valley degree of freedom, allowing for dynamic control.
Georgi, Howard; Kats, Yevgeny
2008-09-26
We discuss what can be learned about unparticle physics by studying simple quantum field theories in one space and one time dimension. We argue that the exactly soluble 2D theory of a massless fermion coupled to a massive vector boson, the Sommerfield model, is an interesting analog of a Banks-Zaks model, approaching a free theory at high energies and a scale-invariant theory with nontrivial anomalous dimensions at low energies. We construct a toy standard model coupling to the fermions in the Sommerfield model and study how the transition from unparticle behavior at low energies to free particle behavior at high energies manifests itself in interactions with the toy standard model particles.
Quantum coherence selective 2D Raman–2D electronic spectroscopy
Spencer, Austin P.; Hutson, William O.; Harel, Elad
2017-01-01
Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally has proved extremely challenging. Here, we demonstrate a method that probes correlations between states within the vibrational and electronic manifold with quantum coherence selectivity. Specifically, we measure a fully coherent four-dimensional spectrum which simultaneously encodes vibrational–vibrational, electronic–vibrational and electronic–electronic interactions. By combining near-impulsive resonant and non-resonant excitation, the desired fifth-order signal of a complex organic molecule in solution is measured free of unwanted lower-order contamination. A critical feature of this method is electronic and vibrational frequency resolution, enabling isolation and assignment of individual quantum coherence pathways. The vibronic structure of the system is then revealed within an otherwise broad and featureless 2D electronic spectrum. This method is suited for studying elusive quantum effects in which electronic transitions strongly couple to phonons and vibrations, such as energy transfer in photosynthetic pigment–protein complexes. PMID:28281541
Quantum coherence selective 2D Raman-2D electronic spectroscopy
NASA Astrophysics Data System (ADS)
Spencer, Austin P.; Hutson, William O.; Harel, Elad
2017-03-01
Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally has proved extremely challenging. Here, we demonstrate a method that probes correlations between states within the vibrational and electronic manifold with quantum coherence selectivity. Specifically, we measure a fully coherent four-dimensional spectrum which simultaneously encodes vibrational-vibrational, electronic-vibrational and electronic-electronic interactions. By combining near-impulsive resonant and non-resonant excitation, the desired fifth-order signal of a complex organic molecule in solution is measured free of unwanted lower-order contamination. A critical feature of this method is electronic and vibrational frequency resolution, enabling isolation and assignment of individual quantum coherence pathways. The vibronic structure of the system is then revealed within an otherwise broad and featureless 2D electronic spectrum. This method is suited for studying elusive quantum effects in which electronic transitions strongly couple to phonons and vibrations, such as energy transfer in photosynthetic pigment-protein complexes.
Quantum coherence selective 2D Raman-2D electronic spectroscopy.
Spencer, Austin P; Hutson, William O; Harel, Elad
2017-03-10
Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally has proved extremely challenging. Here, we demonstrate a method that probes correlations between states within the vibrational and electronic manifold with quantum coherence selectivity. Specifically, we measure a fully coherent four-dimensional spectrum which simultaneously encodes vibrational-vibrational, electronic-vibrational and electronic-electronic interactions. By combining near-impulsive resonant and non-resonant excitation, the desired fifth-order signal of a complex organic molecule in solution is measured free of unwanted lower-order contamination. A critical feature of this method is electronic and vibrational frequency resolution, enabling isolation and assignment of individual quantum coherence pathways. The vibronic structure of the system is then revealed within an otherwise broad and featureless 2D electronic spectrum. This method is suited for studying elusive quantum effects in which electronic transitions strongly couple to phonons and vibrations, such as energy transfer in photosynthetic pigment-protein complexes.
Kim, Byoung Soo; Pyo, Jun Beom; Son, Jeong Gon; Zi, Goangseup; Lee, Sang-Soo; Park, Jong Hyuk; Lee, Jonghwi
2017-03-29
Networks of silver nanowires (Ag NWs) have been considered as promising materials for stretchable and transparent conductors. Despite various improvements of their optoelectronic and electromechanical properties over the past few years, Ag NW networks with a sufficient stretchability in multiple directions that is essential for the accommodation of the multidirectional strains of human movement have seldom been reported. For this paper, biaxially stretchable, transparent conductors were developed based on 2D mass-spring networks of wavy Ag NWs. Inspired by the traditional papermaking process, the 2D wavy networks were produced by floating Ag NW networks on the surface of water and subsequently applying biaxial compression to them. It was demonstrated that this floating-compression process can reduce the friction between the Ag NW-water interfaces, providing a uniform and isotropic in-plane waviness for the networks without buckling or cracking. The resulting Ag NW networks that were transferred onto elastomeric substrates successfully acted as conductors with an excellent transparency, conductivity, and electromechanical stability under a biaxial strain of 30%. The strain sensors that are based on the prepared conductors demonstrated a great potential for the enhanced performances of future wearable devices.
NASA Astrophysics Data System (ADS)
Cherifi, S.; Boeglin, C.; Stanescu, S.; Deville, J. P.; Mocuta, C.; Magnan, H.; Le Fèvre, P.; Ohresser, P.; Brookes, N. B.
2001-11-01
The effects of nanostructured magnetic Fe65Ni35 films deposited on a vicinal Cu(111) single-crystal surface on the magnetic anisotropy have been studied using magnetic circular x-ray dichroism (MCXD) at the Fe L2,3 edges. In the one-dimensional (1D) limit a large dipolar out-of-plane anisotropy is evidenced with in-plane isotropic magnetic moments. After the 1D coalescence the orbital moment shows a more complex behavior depending on the in-plane direction of saturation. We show that MCXD is strongly sensitive to in-plane orbital anisotropy for the 1D stripes. We demonstrate the importance of the step induced in-plane anisotropy by measuring the orbital magnetic moment dependence as a function of the in-plane azimuth angle. In the submonolayer regime an in-plane magnetic anisotropy is observed related to the step decoration growth mode. In the thickness range of 2-4 equivalent monolayers, 2D coalescence induces a strong in-plane magnetic anisotropy of the magnetic orbital moment. The microscopic origin of the strong in-plane variation of ML has been attributed to magnetocrystalline effects. Strained films give rise to an in-plane magnetic anisotropy energy up to 2 meV/at., which is larger than those measured out of the plane (0-1 meV/at.).
Optoelectronics of supported and suspended 2D semiconductors
NASA Astrophysics Data System (ADS)
Bolotin, Kirill
2014-03-01
Two-dimensional semiconductors, materials such monolayer molybdenum disulfide (MoS2) are characterized by strong spin-orbit and electron-electron interactions. However, both electronic and optoelectronic properties of these materials are dominated by disorder-related scattering. In this talk, we investigate approaches to reduce scattering and explore physical phenomena arising in intrinsic 2D semiconductors. First, we discuss fabrication of pristine suspended monolayer MoS2 and use photocurrent spectroscopy measurements to study excitons in this material. We observe band-edge and van Hove singularity excitons and estimate their binding energies. Furthermore, we study dissociation of these excitons and uncover the mechanism of their contribution to photoresponse of MoS2. Second, we study strain-induced modification of bandstructures of 2D semiconductors. With increasing strain, we find large and controllable band gap reduction of both single- and bi-layer MoS2. We also detect experimental signatures consistent with strain-induced transition from direct to indirect band gap in monolayer MoS2. Finally, we fabricate heterostructures of dissimilar 2D semiconductors and study their photoresponse. For closely spaced 2D semiconductors we detect charge transfer, while for separation larger than 10nm we observe Forster-like energy transfer between excitations in different layers.
Skyrmions in quasi-2D chiral magnets with broken bulk and surface inversion symmetry
NASA Astrophysics Data System (ADS)
Rowland, James; Banerjee, Sumilan; Randeria, Mohit
2015-03-01
Most theoretical studies of skyrmions have focused on chiral magnets with broken bulk inversion symmetry, stabilized by easy-axis anisotropy. Recently, we considered 2D systems with broken surface inversion and showed that skyrmion crystals are more stable than in 3D, pointing out the importance of easy-plane anisotropy. In the present work we investigate quasi-2D systems which break both bulk and surface inversion symmetry. The Landau-Ginzburg free energy functional thus contains two Dzyloshinskii-Moriya terms of strength DD and DR arising from Dresselhaus and Rashba spin-orbit coupling respectively. We trace the evolution of the phase diagram as DD /DR is varied, and find that skyrmions are increasingly destabilized with respect to the cone phase as DD increases relative to DR. We find an evolution from vortex-like skyrmions in the pure Dresselhaus limit to hedgehog-like skyrmions in the pure Rashba limit. We discuss the relevance of these results to existing experiments and the prospects of tuning the ratio of Dresselhaus and Rashba spin-orbit coupling via film thickness and strain. Supported by NSF DMR-1410364 (J.R. and M.R.) and DOE-BES DE-SC0005035 (S.B.)
Nanoscale elastic changes in 2D Ti3C2Tx (MXene) pseudocapacitive electrodes
Come, Jeremy; Xie, Yu; Naguib, Michael; ...
2016-02-01
Designing sustainable electrodes for next generation energy storage devices relies on the understanding of their fundamental properties at the nanoscale, including the comprehension of ions insertion into the electrode and their interactions with the active material. One consequence of ion storage is the change in the electrode volume resulting in mechanical strain and stress that can strongly affect the cycle life. Therefore, it is important to understand the changes of dimensions and mechanical properties occurring during electrochemical reactions. While the characterization of mechanical properties via macroscopic measurements is well documented, in-situ characterization of their evolution has never been achieved atmore » the nanoscale. Two dimensional (2D) carbides, known as MXenes, are promising materials for supercapacitors and various kinds of batteries, and understating the coupling between their mechanical and electrochemical properties is therefore necessary. Here we report on in-situ imaging, combined with density functional theory of the elastic changes, of a 2D titanium carbide (Ti3C2Tx) electrode in direction normal to the basal plane during cation intercalation. The results show a strong correlation between the Li+ ions content and the elastic modulus, whereas little effects of K+ ions are observed. Moreover, this strategy enables identifying the preferential intercalation pathways within a single particle.« less
Strain effects on the electronic properties in δ -doped oxide superlattices
You, Jeong Ho; Lee, Jun Hee; Okamoto, Satoshi; Cooper, Valentino; Lee, Ho Nyung
2015-02-07
We investigated strain effects on the electronic properties of (LaTiO_{3})_{1}/(SrTiO_{3})N superlattices using density functional theory. Under biaxial in-plane strain within the range of -5% ≤ _{ε//} ≤ 5%, the d_{xy} orbital electrons are highly localized at the interfaces whereas the d_{yz} and d_{xz} orbital electrons are more distributed in the SrTiO_{3} (STO) spacer layers. For STO thickness N ≥ 3 unit cells (u.c.), the d_{xy} orbital electrons form two-dimensional (2D) electron gases (2DEGs). The quantized energy levels of the 2DEG are insensitive to the STO spacer thickness, but are strongly dependent on the applied biaxial in-plane strain. As the in-plane strain changes from compressive to tensile, the quantized energy levels of the dxy orbitals decrease thereby creating more states with 2D character. In contrast to the d_{xy} orbital, the d_{yz} and dxz orbitals always have three-dimensional (3D) transport characteristics and their energy levels increase as the strain changes from compressive to tensile. In conclusion, since the charge densities in the d_{xy }orbital and the d_{yz} and d_{xz} orbitals respond to biaxial in-plane strain in an opposite way, the transport dimensionality of the majority carriers can be controlled between 2D and 3D by applying biaxial in-plane strain.
NASA Astrophysics Data System (ADS)
Pavuna, D.; Ariosa, D.; Cancellieri, C.; Cloetta, D.; Abrecht, M.
2008-03-01
Since 1997 we systematically perform Direct ARPES ( = DARPES) on in-situ grown, non-cleaved, ultra-thin (<25nm) cuprate films. Specifically, we probe low energy electronic structure and properties of high-Tc films under different degree of epitaxial (compressive vs tensile) strain. In overdoped in-plane compressed La2-xSrxCuO4 (LSCO) thin films we double Tc from 20K to 40K, yet the Fermi surface (FS) remains essentially 2-dimensional (2D). In contrast, tensile strained films show 3-dimensional (3D) dispersion, while Tc is drastically reduced. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the 2D character of the dispersion and increases Tc, while the tensile strain seems to act exactly in the opposite direction and the resulting dispersion is 3D. We have the FS topology for both cases. As the actual lattice of cuprates is 'Napoleon-cake' -like i.e. rigid CuO2 planes alternate with softer 'reservoir' (that strains distort differently) our results tend to rule out 2D rigid lattice mean field models. Finally, we briefly discuss recent successful determination of the FS topology from the observed wavevector quantization by DARPES in cuprate films thinner than 18 units cells (<24nm). Such an approach is of broader interest as it can be extended to other similar confined (ultra-thin) functional oxide systems.
NASA Astrophysics Data System (ADS)
Lomakin, E. V.; Fedulov, B. N.
2013-07-01
The limit properties of many heterogeneous materials such as grounds, concrete, ceramics, cast-iron alloys, and various heat-resistant and powder materials, as well as the properties of many composite materials, depend on the loading conditions. Neglecting the effects exhibited by such materials may result in nonconservative limit load analysis for some types of loading and possibly in an overly increased end product weight by failing to take into account stronger material properties for other types of loading. This paper presents a possible approach to modeling the behavior of such materials under plastic deformation, which is demonstrated for the sample problem on the extension of a strip weakened by cuts with circular base. An analytic solution on the basis of a rigid-plastic model of the material and a numerical solution by the finite elementmethod with elastic strains and small strengthening taken into account are presented.
NASA Astrophysics Data System (ADS)
Morovvati, M. R.; Lalehpour, A.; Esmaeilzare, A.
2016-12-01
Reinforcing aluminum with SiC and B4C nano/micro particles can lead to a more efficient material in terms of strength and light weight. The influence of adding these particles to an aluminum 7075 matrix is investigated using chevron-notch fracture toughness test method. The reinforcing factors are type, size (micro/nano), and weight percent of the particles. The fracture parameters are maximum load, notch opening displacement, the work up to fracture and chevron notch plane strain fracture toughness. The findings demonstrate that addition of micro and nano size particles improves the fracture properties; however, increasing the weight percent of the particles leads to increase of fracture properties up to a certain level and after that due to agglomeration of the particles, the improvement does not happen for both particle types and size categories. Agglomeration of particles at higher amounts of reinforcing particles results in improper distribution of particles and reduction in mechanical properties.
Hierro-Rodriguez, A; Cid, R; Vélez, M; Rodriguez-Rodriguez, G; Martín, J I; Álvarez-Prado, L M; Alameda, J M
2012-09-14
Stripe domains are studied in perpendicular magnetic anisotropy films nanostructured with a periodic thickness modulation that induces the lateral modulation of both stripe periods and in-plane magnetization. The resulting system is the 2D equivalent of a strained superlattice with properties controlled by interfacial misfit strain within the magnetic stripe structure and shape anisotropy. This allows us to observe, experimentally for the first time, the continuous structural transformation of a grain boundary in this 2D magnetic crystal in the whole angular range. The magnetization reversal process can be tailored through the effect of misfit strain due to the coupling between disclinations in the magnetic stripe pattern and domain walls in the in-plane magnetization configuration.
Das, Saptarshi
2016-01-01
This article proposes a disruptive device concept which meets both low power and high performance criterion for post-CMOS computing and at the same time enables aggressive channel length scaling. This device, hereafter refer to as two-dimensional electrostrictive field effect transistor or 2D-EFET, allows sub-60 mV/decade subthreshold swing and considerably higher ON current compared to any state of the art FETs. Additionally, by the virtue of its ultra-thin body nature and electrostatic integrity, the 2D-EFET enjoys scaling beyond 10 nm technology node. The 2D-EFET works on the principle of voltage induced strain transduction. It uses an electrostrictive material as gate oxide which expands in response to an applied gate bias and thereby transduces an out-of-plane stress on the 2D channel material. This stress reduces the inter-layer distance between the consecutive layers of the semiconducting 2D material and dynamically reduces its bandgap to zero i.e. converts it into a semi-metal. Thus the device operates with a large bandgap in the OFF state and a small or zero bandgap in the ON state. As a consequence of this transduction mechanism, internal voltage amplification takes place which results in sub-60 mV/decade subthreshold swing (SS). PMID:27721489
NASA Astrophysics Data System (ADS)
Das, Saptarshi
2016-10-01
This article proposes a disruptive device concept which meets both low power and high performance criterion for post-CMOS computing and at the same time enables aggressive channel length scaling. This device, hereafter refer to as two-dimensional electrostrictive field effect transistor or 2D-EFET, allows sub-60 mV/decade subthreshold swing and considerably higher ON current compared to any state of the art FETs. Additionally, by the virtue of its ultra-thin body nature and electrostatic integrity, the 2D-EFET enjoys scaling beyond 10 nm technology node. The 2D-EFET works on the principle of voltage induced strain transduction. It uses an electrostrictive material as gate oxide which expands in response to an applied gate bias and thereby transduces an out-of-plane stress on the 2D channel material. This stress reduces the inter-layer distance between the consecutive layers of the semiconducting 2D material and dynamically reduces its bandgap to zero i.e. converts it into a semi-metal. Thus the device operates with a large bandgap in the OFF state and a small or zero bandgap in the ON state. As a consequence of this transduction mechanism, internal voltage amplification takes place which results in sub-60 mV/decade subthreshold swing (SS).
NKG2D ligands as therapeutic targets
Spear, Paul; Wu, Ming-Ru; Sentman, Marie-Louise; Sentman, Charles L.
2013-01-01
The Natural Killer Group 2D (NKG2D) receptor plays an important role in protecting the host from infections and cancer. By recognizing ligands induced on infected or tumor cells, NKG2D modulates lymphocyte activation and promotes immunity to eliminate ligand-expressing cells. Because these ligands are not widely expressed on healthy adult tissue, NKG2D ligands may present a useful target for immunotherapeutic approaches in cancer. Novel therapies targeting NKG2D ligands for the treatment of cancer have shown preclinical success and are poised to enter into clinical trials. In this review, the NKG2D receptor and its ligands are discussed in the context of cancer, infection, and autoimmunity. In addition, therapies targeting NKG2D ligands in cancer are also reviewed. PMID:23833565
Simple approach for 2D-DIC with dual field of view
NASA Astrophysics Data System (ADS)
Nunes, L. C. S.
2015-09-01
A simple and cost-effective optical layout based on the dual field of view for the 2D digital image correlation (DIC) method is used to simultaneously measure in-plane displacement fields of large and small portions of a specimen. This optical configuration was composed of two high-resolution cameras with two different lenses and a beam splitter. The surface of a specimen was acquired simultaneously using both cameras with narrow and wide fields of view. One of the two cameras was placed directly in front of a specimen, whereas the other camera acquired the image of the same specimen reflected from the beam splitter. All stored images were appropriately processed using a digital image correlation algorithm to extract displacement and strain fields. To show the applicability and usefulness of this configuration, two tests were performed: (i) lower and upper adherends deflections of an adhesive-bonded single lap joint specimen were obtained, and shear strain in the adhesive layer at the edge of the overlap was also attained; and (ii) relatively large displacements of a cracked cantilever beam were evaluated, and maps of small deformation near crack tip were assessed. The results were obtained considering different speckle patterns and distinct subset sizes.
Diverse Geological Applications For Basil: A 2d Finite-deformation Computational Algorithm
NASA Astrophysics Data System (ADS)
Houseman, Gregory A.; Barr, Terence D.; Evans, Lynn
Geological processes are often characterised by large finite-deformation continuum strains, on the order of 100% or greater. Microstructural processes cause deformation that may be represented by a viscous constitutive mechanism, with viscosity that may depend on temperature, pressure, or strain-rate. We have developed an effective com- putational algorithm for the evaluation of 2D deformation fields produced by Newto- nian or non-Newtonian viscous flow. With the implementation of this algorithm as a computer program, Basil, we have applied it to a range of diverse applications in Earth Sciences. Viscous flow fields in 2D may be defined for the thin-sheet case or, using a velocity-pressure formulation, for the plane-strain case. Flow fields are represented using 2D triangular elements with quadratic interpolation for velocity components and linear for pressure. The main matrix equation is solved by an efficient and compact conjugate gradient algorithm with iteration for non-Newtonian viscosity. Regular grids may be used, or grids based on a random distribution of points. Definition of the prob- lem requires that velocities, tractions, or some combination of the two, are specified on all external boundary nodes. Compliant boundaries may also be defined, based on the idea that traction is opposed to and proportional to boundary displacement rate. In- ternal boundary segments, allowing fault-like displacements within a viscous medium have also been developed, and we find that the computed displacement field around the fault tip is accurately represented for Newtonian and non-Newtonian viscosities, in spite of the stress singularity at the fault tip. Basil has been applied by us and colleagues to problems that include: thin sheet calculations of continental collision, Rayleigh-Taylor instability of the continental mantle lithosphere, deformation fields around fault terminations at the outcrop scale, stress and deformation fields in and around porphyroblasts, and
Numerical 2D-modeling of multiroll leveling
NASA Astrophysics Data System (ADS)
Mathieu, N.; Potier-Ferry, M.; Zahrouni, H.
2016-10-01
Multiroll leveling is a forming process used in the metals industries (aluminum, steel, …) in order to correct flatness defects and minimize residual stresses in strips thanks to alternating bending. This work proposes a Finite Element 2D model to simulate the metal sheet conveying through the machine. Obtained results (plastic strain and residual stress distributions through thickness) are analysed. Strip deformation, after elastic springback and potential buckling, is also predicted (residual curvatures).
Skeletal muscle transverse strain during isometric contraction at different lengths.
van Donkelaar, C C; Willems, P J; Muijtjens, A M; Drost, M R
1999-08-01
An important assumption in 2D numerical models of skeletal muscle contraction involves deformation in the third dimension of the included muscle section. The present paper studies the often used plane strain description. Therefore, 3D muscle surface deformation is measured from marker displacements during isometric contractions at various muscle lengths. Longitudinal strains at superficial muscle fibers ( - 14 +/- 2.6% at L0, n = 57) and aponeurosis (0.8 +/- 0.9% at L0) decrease with increasing muscle length. The same holds for transverse muscle surface strains in superficial muscle fibers and aponeurosis, which are comparable at intermediate muscle length, but differ at long and short muscle length. Because transverse strains during isometric contraction change with initial muscle length, it is concluded that the effect of muscle length on muscle deformation cannot be studied in plane strain models. These results do not counteract the use of these models to study deformation in contractions with approximately - 9 % longitudinal muscle fiber strain, as transverse strain in superficial muscle fibers and in aponeurosis tissue is minimal in that case. Aponeurosis surface area change decreases with increasing initial muscle length, but muscle fiber surface area change is - 11%, independent of muscle length. Assuming incompressible muscle material, this means that strain perpendicular to the muscle surface equals 11%. Taking the relationship between transverse and longitudinal muscle fiber strain into account, it is hypothesized that superficial muscle fibers flatten during isometric contractions.
Rowley-Neale, Samuel J; Fearn, Jamie M; Brownson, Dale A C; Smith, Graham C; Ji, Xiaobo; Banks, Craig E
2016-08-21
Two-dimensional molybdenum disulphide nanosheets (2D-MoS2) have proven to be an effective electrocatalyst, with particular attention being focused on their use towards increasing the efficiency of the reactions associated with hydrogen fuel cells. Whilst the majority of research has focused on the Hydrogen Evolution Reaction (HER), herein we explore the use of 2D-MoS2 as a potential electrocatalyst for the much less researched Oxygen Reduction Reaction (ORR). We stray from literature conventions and perform experiments in 0.1 M H2SO4 acidic electrolyte for the first time, evaluating the electrochemical performance of the ORR with 2D-MoS2 electrically wired/immobilised upon several carbon based electrodes (namely; Boron Doped Diamond (BDD), Edge Plane Pyrolytic Graphite (EPPG), Glassy Carbon (GC) and Screen-Printed Electrodes (SPE)) whilst exploring a range of 2D-MoS2 coverages/masses. Consequently, the findings of this study are highly applicable to real world fuel cell applications. We show that significant improvements in ORR activity can be achieved through the careful selection of the underlying/supporting carbon materials that electrically wire the 2D-MoS2 and utilisation of an optimal mass of 2D-MoS2. The ORR onset is observed to be reduced to ca. +0.10 V for EPPG, GC and SPEs at 2D-MoS2 (1524 ng cm(-2) modification), which is far closer to Pt at +0.46 V compared to bare/unmodified EPPG, GC and SPE counterparts. This report is the first to demonstrate such beneficial electrochemical responses in acidic conditions using a 2D-MoS2 based electrocatalyst material on a carbon-based substrate (SPEs in this case). Investigation of the beneficial reaction mechanism reveals the ORR to occur via a 4 electron process in specific conditions; elsewhere a 2 electron process is observed. This work offers valuable insights for those wishing to design, fabricate and/or electrochemically test 2D-nanosheet materials towards the ORR.
Beam-Plasma Instabilities in a 2D Yukawa Lattice
Kyrkos, S.; Kalman, G. J.; Rosenberg, M.
2009-06-05
We consider a 2D Yukawa lattice of grains, with a beam of other charged grains moving in the lattice plane. In contrast to Vlasov plasmas, where the electrostatic instability excited by the beam is only longitudinal, here both longitudinal and transverse instabilities of the lattice phonons can develop. We determine and compare the transverse and longitudinal growth rates. The growth rate spectrum in wave number space exhibits remarkable gaps where no instability can develop. Depending on the system parameters, the transverse instability can be selectively excited.
Experimental validation of 2-D generalized geometric super resolved approach
NASA Astrophysics Data System (ADS)
Borkowski, Amikam; Zalevsky, Zeev; Cohen, Nadav; Hadas, Zadok; Marom, Emanuel; Javidi, Bahram
2014-01-01
In this paper, we generalize the method of using a 2-D moving binary random mask to overcome the geometrical resolution limitation of an imaging sensor. The spatial blurring is caused by the size of the imaging sensor pixels which yield insufficient spatial sampling. The mask is placed in an intermediate image plane and can be shifted in any direction while keeping the sensor as well as all other optical components fixed. Out of the set of images that are captured and registered, a high resolution image can be composed. In addition, this proposed approach reduces the amount of required computations and it has an improved robustness to spatial noise.
Strain induced modification in phonon dispersion curves of monolayer boron pnictides
Jha, Prafulla K. E-mail: prafullaj@yahoo.com; Soni, Himadri R.
2014-01-14
In the frame work of density functional theory, the biaxial strain induced phonon dispersion curves of monolayer boron pnictides (BX, X = N, P, As, and Sb) have been investigated. The electron-ion interactions have been modelled using ultrasoft pseudopotentials while exchange-correlation energies have been approximated by the method of local density approximation in the parameterization of Perdew-Zunger. The longitudinal and transverse acoustic phonon modes of boron pnictide sheets show linear dependency on wave vector k{sup →} while out of plane mode varies as k{sup 2}. The in-plane longitudinal and out of plane transverse optical modes in boron nitride displaying significant dispersion similar to graphene. We have analyzed the biaxial strain dependent behaviour of out of plane acoustic phonon mode which is linked to ripple for four BX sheets using a model equation with shell elasticity theory. The strain induces the hardening of this mode with tendency to become more linear with increase in strain percentage. The strain induced hardening of out of plane acoustic phonon mode indicates the absence of rippling in these compounds. Our band structure calculations for both unstrained and strained 2D h-BX are consistent with previous calculations.
Quantitative 2D liquid-state NMR.
Giraudeau, Patrick
2014-06-01
Two-dimensional (2D) liquid-state NMR has a very high potential to simultaneously determine the absolute concentration of small molecules in complex mixtures, thanks to its capacity to separate overlapping resonances. However, it suffers from two main drawbacks that probably explain its relatively late development. First, the 2D NMR signal is strongly molecule-dependent and site-dependent; second, the long duration of 2D NMR experiments prevents its general use for high-throughput quantitative applications and affects its quantitative performance. Fortunately, the last 10 years has witnessed an increasing number of contributions where quantitative approaches based on 2D NMR were developed and applied to solve real analytical issues. This review aims at presenting these recent efforts to reach a high trueness and precision in quantitative measurements by 2D NMR. After highlighting the interest of 2D NMR for quantitative analysis, the different strategies to determine the absolute concentrations from 2D NMR spectra are described and illustrated by recent applications. The last part of the manuscript concerns the recent development of fast quantitative 2D NMR approaches, aiming at reducing the experiment duration while preserving - or even increasing - the analytical performance. We hope that this comprehensive review will help readers to apprehend the current landscape of quantitative 2D NMR, as well as the perspectives that may arise from it.
Correspondenceless 3D-2D registration based on expectation conditional maximization
NASA Astrophysics Data System (ADS)
Kang, X.; Taylor, R. H.; Armand, M.; Otake, Y.; Yau, W. P.; Cheung, P. Y. S.; Hu, Y.
2011-03-01
3D-2D registration is a fundamental task in image guided interventions. Due to the physics of the X-ray imaging, however, traditional point based methods meet new challenges, where the local point features are indistinguishable, creating difficulties in establishing correspondence between 2D image feature points and 3D model points. In this paper, we propose a novel method to accomplish 3D-2D registration without known correspondences. Given a set of 3D and 2D unmatched points, this is achieved by introducing correspondence probabilities that we model as a mixture model. By casting it into the expectation conditional maximization framework, without establishing one-to-one point correspondences, we can iteratively refine the registration parameters. The method has been tested on 100 real X-ray images. The experiments showed that the proposed method accurately estimated the rotations (< 1°) and in-plane (X-Y plane) translations (< 1 mm).
NASA Technical Reports Server (NTRS)
Krueger, Ronald; Paris, Isbelle L.; OBrien, T. Kevin; Minguet, Pierre J.
2004-01-01
The influence of two-dimensional finite element modeling assumptions on the debonding prediction for skin-stiffener specimens was investigated. Geometrically nonlinear finite element analyses using two-dimensional plane-stress and plane-strain elements as well as three different generalized plane strain type approaches were performed. The computed skin and flange strains, transverse tensile stresses and energy release rates were compared to results obtained from three-dimensional simulations. The study showed that for strains and energy release rate computations the generalized plane strain assumptions yielded results closest to the full three-dimensional analysis. For computed transverse tensile stresses the plane stress assumption gave the best agreement. Based on this study it is recommended that results from plane stress and plane strain models be used as upper and lower bounds. The results from generalized plane strain models fall between the results obtained from plane stress and plane strain models. Two-dimensional models may also be used to qualitatively evaluate the stress distribution in a ply and the variation of energy release rates and mixed mode ratios with delamination length. For more accurate predictions, however, a three-dimensional analysis is required.
Annotated Bibliography of EDGE2D Use
J.D. Strachan and G. Corrigan
2005-06-24
This annotated bibliography is intended to help EDGE2D users, and particularly new users, find existing published literature that has used EDGE2D. Our idea is that a person can find existing studies which may relate to his intended use, as well as gain ideas about other possible applications by scanning the attached tables.
Staring 2-D hadamard transform spectral imager
Gentry, Stephen M.; Wehlburg, Christine M.; Wehlburg, Joseph C.; Smith, Mark W.; Smith, Jody L.
2006-02-07
A staring imaging system inputs a 2D spatial image containing multi-frequency spectral information. This image is encoded in one dimension of the image with a cyclic Hadamarid S-matrix. The resulting image is detecting with a spatial 2D detector; and a computer applies a Hadamard transform to recover the encoded image.
Quantum damped oscillator II: Bateman's Hamiltonian vs. 2D parabolic potential barrier
Chruscinski, Dariusz . E-mail: darch@phys.uni.torun.pl
2006-04-15
We show that quantum Bateman's system which arises in the quantization of a damped harmonic oscillator is equivalent to a quantum problem with 2D parabolic potential barrier known also as 2D inverted isotropic oscillator. It turns out that this system displays the family of complex eigenvalues corresponding to the poles of analytical continuation of the resolvent operator to the complex energy plane. It is shown that this representation is more suitable than the hyperbolic one used recently by Blasone and Jizba.
Towards functional assembly of 3D and 2D nanomaterials
NASA Astrophysics Data System (ADS)
Jacobs, Christopher B.; Wang, Kai; Ievlev, Anton V.; Muckley, Eric S.; Ivanov, Ilia N.
2016-09-01
Functional assemblies of materials can be realized by tuning the work function and band gap of nanomaterials by rational material selection and design. Here we demonstrate the structural assembly of 2D and 3D nanomaterials and show that layering a 2D material monolayer on a 3D metal oxide leads to substantial alteration of both the surface potential and optical properties of the 3D material. A 40 nm thick film of polycrystalline NiO was produced by room temperature rf-sputtering, resulting in a 3D nanoparticle assembly. Chemical vapor deposition (CVD) grown 10-30 μm WS2 flakes (2D material) were placed on the NiO surface using a PDMS stamp transfer technique. The 2D/3D WS2/NiO assembly was characterized using confocal micro Raman spectroscopy to evaluate the vibrational properties and using Kelvin probe force microscopy (KPFM) to evaluate the surface potential. Raman maps of the 2D/3D assembly show spatial non-uniformity of the A1g mode ( 418 cm-1) and the disorder-enhanced longitudinal acoustic mode, 2LA(M) ( 350 cm-1), suggesting that the WS2 exists in a strained condition on when transferred onto 3D polycrystalline NiO. KPFM measurements show that single layer WS2 on SiO2 has a surface potential 75 mV lower than that of SiO2, whereas the surface potential of WS2 on NiO is 15 mV higher than NiO, indicating that WS2 could act as electron donor or acceptor depending on the 3D material it is interfaced with. Thus 2D and 3D materials can be organized into functional assemblies with electron flow controlled by the WS2 either as the electron donor or acceptor.
Subplane-based Control Rod Decusping Techniques for the 2D/1D Method in MPACT
Graham, Aaron M; Collins, Benjamin S; Downar, Thomas
2017-01-01
The MPACT transport code is being jointly developed by Oak Ridge National Laboratory and the University of Michigan to serve as the primary neutron transport code for the Virtual Environment for Reactor Applications Core Simulator. MPACT uses the 2D/1D method to solve the transport equation by decomposing the reactor model into a stack of 2D planes. A fine mesh flux distribution is calculated in each 2D plane using the Method of Characteristics (MOC), then the planes are coupled axially through a 1D NEM-P$_3$ calculation. This iterative calculation is then accelerated using the Coarse Mesh Finite Difference method. One problem that arises frequently when using the 2D/1D method is that of control rod cusping. This occurs when the tip of a control rod falls between the boundaries of an MOC plane, requiring that the rodded and unrodded regions be axially homogenized for the 2D MOC calculations. Performing a volume homogenization does not properly preserve the reaction rates, causing an error known as cusping. The most straightforward way of resolving this problem is by refining the axial mesh, but this can significantly increase the computational expense of the calculation. The other way of resolving the partially inserted rod is through the use of a decusping method. This paper presents new decusping methods implemented in MPACT that can dynamically correct the rod cusping behavior for a variety of problems.
Jackson, W.C.; Portanova, M.A.
1995-10-01
This paper summarizes three areas of research which were performed to characterize out-of-plane properties of composite materials. In the first investigation, a series of tests was run to characterize the through-the-thickness tensile strength for a variety of composites that included 2D braids, 2D and 3D weaves, and prepreg tapes. A new test method based on a curved beam was evaluated. Failures were significantly different between the 2D materials and the 3D weaves. The 2D materials delaminated between layers due to out-of-plane tensile stresses while the 3D weaves failed due to the formation of radial cracks between the surface plies caused by high circumferential stresses along the inner radius. The strength of the 2D textile composites did not increase relative to the tapes. Final failure in the 3D weaves was caused by a circumferential crack similar to the 2D materials and occurred at a lower bending moment than in other materials. The early failures in the 3D weaves were caused by radial crack formation rather than a low through-the-thickness strength. The second investigation focused on the development of a standard impact test method to measure impact damage resistance. The only impact tests that currently exist are compression after impact (CAI) tests which incorporate elements of both damage resistance and damage tolerance. A new impact test method is under development which uses a quasi-static indentation (QSI) test to directly measure damage resistance. Damage resistance is quantified in terms of the contact force to produce a unit of damage where a metric for damage may be area in C-scan, depth of residual dent, penetration, damage growth, etc. A final draft of an impact standard that uses a QSI test method will be presented to the ASTM Impact Task Group on impact. In the third investigation, the impact damage resistance behavior of a variety of textile materials was studied using the QSI test method.
NASA Technical Reports Server (NTRS)
Jackson, Wade C.; Portanova, Marc A.
1995-01-01
This paper summarizes three areas of research which were performed to characterize out-of-plane properties of composite materials. In the first investigation, a series of tests was run to characterize the through-the-thickness tensile strength for a variety of composites that included 2D braids, 2D and 3D weaves, and prepreg tapes. A new test method based on a curved beam was evaluated. Failures were significantly different between the 2D materials and the 3D weaves. The 2D materials delaminated between layers due to out-of-plane tensile stresses while the 3D weaves failed due to the formation of radial cracks between the surface plies caused by high circumferential stresses along the inner radius. The strength of the 2D textile composites did not increase relative to the tapes. Final failure in the 3D weaves was caused by a circumferential crack similar to the 2D materials and occurred at a lower bending moment than in other materials. The early failures in the 3D weaves were caused by radial crack formation rather than a low through-the-thickness strength. The second investigation focused on the development of a standard impact test method to measure impact damage resistance. The only impact tests that currently exist are compression after impact (CAI) tests which incorporate elements of both damage resistance and damage tolerance. A new impact test method is under development which uses a quasi-static indentation (QSI) test to directly measure damage resistance. Damage resistance is quantified in terms of the contact force to produce a unit of damage where a metric for damage may be area in C-scan, depth of residual dent , penetration, damage growth, etc. A final draft of an impact standard that uses a QSI test method will be presented to the ASTM Impact Task Group on impact. In the third investigation, the impact damage resistance behavior of a variety of textile materials was studied using the QSI test method. In this study, the force where large damage
NASA Astrophysics Data System (ADS)
Rowley-Neale, Samuel J.; Fearn, Jamie M.; Brownson, Dale A. C.; Smith, Graham C.; Ji, Xiaobo; Banks, Craig E.
2016-08-01
Two-dimensional molybdenum disulphide nanosheets (2D-MoS2) have proven to be an effective electrocatalyst, with particular attention being focused on their use towards increasing the efficiency of the reactions associated with hydrogen fuel cells. Whilst the majority of research has focused on the Hydrogen Evolution Reaction (HER), herein we explore the use of 2D-MoS2 as a potential electrocatalyst for the much less researched Oxygen Reduction Reaction (ORR). We stray from literature conventions and perform experiments in 0.1 M H2SO4 acidic electrolyte for the first time, evaluating the electrochemical performance of the ORR with 2D-MoS2 electrically wired/immobilised upon several carbon based electrodes (namely; Boron Doped Diamond (BDD), Edge Plane Pyrolytic Graphite (EPPG), Glassy Carbon (GC) and Screen-Printed Electrodes (SPE)) whilst exploring a range of 2D-MoS2 coverages/masses. Consequently, the findings of this study are highly applicable to real world fuel cell applications. We show that significant improvements in ORR activity can be achieved through the careful selection of the underlying/supporting carbon materials that electrically wire the 2D-MoS2 and utilisation of an optimal mass of 2D-MoS2. The ORR onset is observed to be reduced to ca. +0.10 V for EPPG, GC and SPEs at 2D-MoS2 (1524 ng cm-2 modification), which is far closer to Pt at +0.46 V compared to bare/unmodified EPPG, GC and SPE counterparts. This report is the first to demonstrate such beneficial electrochemical responses in acidic conditions using a 2D-MoS2 based electrocatalyst material on a carbon-based substrate (SPEs in this case). Investigation of the beneficial reaction mechanism reveals the ORR to occur via a 4 electron process in specific conditions; elsewhere a 2 electron process is observed. This work offers valuable insights for those wishing to design, fabricate and/or electrochemically test 2D-nanosheet materials towards the ORR.Two-dimensional molybdenum disulphide nanosheets
NASA Astrophysics Data System (ADS)
Guo, Y. G.; Zhu, J. G.; Zhong, J. J.
2006-07-01
This paper reports the measurement and modelling of magnetic properties of SOMALOY TM 500, a soft magnetic composite (SMC) material, under different 2D vector magnetisations, such as alternating along one direction, circularly and elliptically rotating in a 2D plane. By using a 2D magnetic property tester, the B- H curves and core losses of the SMC material have been measured with different flux density patterns on a single sheet square sample. The measurements can provide useful information for modelling of the magnetic properties, such as core losses. The core loss models have been successfully applied in the design of rotating electrical machines with SMC core.
Ginsparg, P.
1991-01-01
These are introductory lectures for a general audience that give an overview of the subject of matrix models and their application to random surfaces, 2d gravity, and string theory. They are intentionally 1.5 years out of date.
Ginsparg, P.
1991-12-31
These are introductory lectures for a general audience that give an overview of the subject of matrix models and their application to random surfaces, 2d gravity, and string theory. They are intentionally 1.5 years out of date.
Brittle damage models in DYNA2D
Faux, D.R.
1997-09-01
DYNA2D is an explicit Lagrangian finite element code used to model dynamic events where stress wave interactions influence the overall response of the system. DYNA2D is often used to model penetration problems involving ductile-to-ductile impacts; however, with the advent of the use of ceramics in the armor-anti-armor community and the need to model damage to laser optics components, good brittle damage models are now needed in DYNA2D. This report will detail the implementation of four brittle damage models in DYNA2D, three scalar damage models and one tensor damage model. These new brittle damage models are then used to predict experimental results from three distinctly different glass damage problems.
NASA Astrophysics Data System (ADS)
Dekker, T.; de Zwart, S. T.; Willemsen, O. H.; Hiddink, M. G. H.; IJzerman, W. L.
2006-02-01
A prerequisite for a wide market acceptance of 3D displays is the ability to switch between 3D and full resolution 2D. In this paper we present a robust and cost effective concept for an auto-stereoscopic switchable 2D/3D display. The display is based on an LCD panel, equipped with switchable LC-filled lenticular lenses. We will discuss 3D image quality, with the focus on display uniformity. We show that slanting the lenticulars in combination with a good lens design can minimize non-uniformities in our 20" 2D/3D monitors. Furthermore, we introduce fractional viewing systems as a very robust concept to further improve uniformity in the case slanting the lenticulars and optimizing the lens design are not sufficient. We will discuss measurements and numerical simulations of the key optical characteristics of this display. Finally, we discuss 2D image quality, the switching characteristics and the residual lens effect.
Chemical Approaches to 2D Materials.
Samorì, Paolo; Palermo, Vincenzo; Feng, Xinliang
2016-08-01
Chemistry plays an ever-increasing role in the production, functionalization, processing and applications of graphene and other 2D materials. This special issue highlights a selection of enlightening chemical approaches to 2D materials, which nicely reflect the breadth of the field and convey the excitement of the individuals involved in it, who are trying to translate graphene and related materials from the laboratory into a real, high-impact technology.
NASA Astrophysics Data System (ADS)
Betka, P. M.; Seeber, L.; Steckler, M. S.
2015-12-01
, contractional structures that formed internally within the FTB are indicative of east-west horizontal shortening and plane strain. This result suggests that the dextral component of shear measured by geodetic data is primarily partitioned onto discrete right-lateral strike-slip faults such as the Churachandpur-Mao and Kabaw faults.
Numerical modelling of spallation in 2D hydrodynamics codes
NASA Astrophysics Data System (ADS)
Maw, J. R.; Giles, A. R.
1996-05-01
A model for spallation based on the void growth model of Johnson has been implemented in 2D Lagrangian and Eulerian hydrocodes. The model has been extended to treat complete separation of material when voids coalesce and to describe the effects of elevated temperatures and melting. The capabilities of the model are illustrated by comparison with data from explosively generated spall experiments. Particular emphasis is placed on the prediction of multiple spall effects in weak, low melting point, materials such as lead. The correlation between the model predictions and observations on the strain rate dependence of spall strength is discussed.
Optical method of measuring angular displacement using a 2-D charge coupled device.
Sato, K; Yamamoto, S; Ami, M; Fukushima, K
1990-08-10
We investigated a quick noncontact method of measuring angular displacement with a simple system comprising a 2-D CCD and a personal computer. According to this method the angular displacement can be measured even when the rotational axis is not known, and even when the system moves parallel to the plane.
Integrated Navigation, Guidance, and Control of Missile Systems: 2-D Dynamic Models
2012-05-01
Plane Simulation Model Block Diagram .......................................................... 21 Figure A.1. Aerodynamic variables for a missile ...Figure A.1. Aerodynamic variables for a missile Page classification: UNCLASSIFIED DEFENCE SCIENCE AND TECHNOLOGY ORGANISATION DOCUMENT...UNCLASSIFIED Integrated Navigation, Guidance, and Control of Missile Systems: 2-D Dynamic Models Farhan A. Faruqi Weapons
Study of the mechanical behavior of a 2-D carbon-carbon composite
NASA Technical Reports Server (NTRS)
Avery, W. B.; Herakovich, C. T.
1987-01-01
The out-of-plane fracture of a 2-D carbon-carbon composite was observed and characterized to gain an understanding of the factors influencing the stress distribution in such a laminate. Finite element analyses of a two-ply carbon-carbon composite under in-plane, out-of-plane, and thermal loading were performed. Under in-plane loading all components of stress were strong functions of geometry. Additionally, large thermal stresses were predicted. Out-of-plane tensile tests revealed that failure was interlaminar, and that cracks propagated along the fiber-matrix interface. An elasticity solution was utilized to analyze an orthotropic fiber in an isotropic matrix under uniform thermal load. The analysis reveals that the stress distributions in a transversely orthotropic fiber are radically different than those predicted assuming the fiber to be transversely isotropic.
Analytical solutions for some defect problems in 1D hexagonal and 2D octagonal quasicrystals
NASA Astrophysics Data System (ADS)
Wang, X.; Pan, E.
2008-05-01
We study some typical defect problems in one-dimensional (1D) hexagonal and two-dimensional (2D) octagonal quasicrystals. The first part of this investigation addresses in detail a uniformly moving screw dislocation in a 1D hexagonal piezoelectric quasicrystal with point group 6mm. A general solution is derived in terms of two functions \\varphi_1, \\varphi_2, which satisfy wave equations, and another harmonic function \\varphi_3. Elementary expressions for the phonon and phason displacements, strains, stresses, electric potential, electric fields and electric displacements induced by the moving screw dislocation are then arrived at by employing the obtained general solution. The derived solution is verified by comparison with existing solutions. Also obtained in this part of the investigation is the total energy of the moving screw dislocation. The second part of this investigation is devoted to the study of the interaction of a straight dislocation with a semi-infinite crack in an octagonal quasicrystal. Here the crack penetrates through the solid along the period direction and the dislocation line is parallel to the period direction. We first derive a general solution in terms of four analytic functions for plane strain problem in octagonal quasicrystals by means of differential operator theory and the complex variable method. All the phonon and phason displacements and stresses can be expressed in terms of the four analytic functions. Then we derive the exact solution for a straight dislocation near a semi-infinite crack in an octagonal quasicrystal, and also present the phonon and phason stress intensity factors induced by the straight dislocation and remote loads.
Orthotropic Piezoelectricity in 2D Nanocellulose
NASA Astrophysics Data System (ADS)
García, Y.; Ruiz-Blanco, Yasser B.; Marrero-Ponce, Yovani; Sotomayor-Torres, C. M.
2016-10-01
The control of electromechanical responses within bonding regions is essential to face frontier challenges in nanotechnologies, such as molecular electronics and biotechnology. Here, we present Iβ-nanocellulose as a potentially new orthotropic 2D piezoelectric crystal. The predicted in-layer piezoelectricity is originated on a sui-generis hydrogen bonds pattern. Upon this fact and by using a combination of ab-initio and ad-hoc models, we introduce a description of electrical profiles along chemical bonds. Such developments lead to obtain a rationale for modelling the extended piezoelectric effect originated within bond scales. The order of magnitude estimated for the 2D Iβ-nanocellulose piezoelectric response, ~pm V‑1, ranks this material at the level of currently used piezoelectric energy generators and new artificial 2D designs. Such finding would be crucial for developing alternative materials to drive emerging nanotechnologies.
Orthotropic Piezoelectricity in 2D Nanocellulose
García, Y.; Ruiz-Blanco, Yasser B.; Marrero-Ponce, Yovani; Sotomayor-Torres, C. M.
2016-01-01
The control of electromechanical responses within bonding regions is essential to face frontier challenges in nanotechnologies, such as molecular electronics and biotechnology. Here, we present Iβ-nanocellulose as a potentially new orthotropic 2D piezoelectric crystal. The predicted in-layer piezoelectricity is originated on a sui-generis hydrogen bonds pattern. Upon this fact and by using a combination of ab-initio and ad-hoc models, we introduce a description of electrical profiles along chemical bonds. Such developments lead to obtain a rationale for modelling the extended piezoelectric effect originated within bond scales. The order of magnitude estimated for the 2D Iβ-nanocellulose piezoelectric response, ~pm V−1, ranks this material at the level of currently used piezoelectric energy generators and new artificial 2D designs. Such finding would be crucial for developing alternative materials to drive emerging nanotechnologies. PMID:27708364
Orthotropic Piezoelectricity in 2D Nanocellulose.
García, Y; Ruiz-Blanco, Yasser B; Marrero-Ponce, Yovani; Sotomayor-Torres, C M
2016-10-06
The control of electromechanical responses within bonding regions is essential to face frontier challenges in nanotechnologies, such as molecular electronics and biotechnology. Here, we present Iβ-nanocellulose as a potentially new orthotropic 2D piezoelectric crystal. The predicted in-layer piezoelectricity is originated on a sui-generis hydrogen bonds pattern. Upon this fact and by using a combination of ab-initio and ad-hoc models, we introduce a description of electrical profiles along chemical bonds. Such developments lead to obtain a rationale for modelling the extended piezoelectric effect originated within bond scales. The order of magnitude estimated for the 2D Iβ-nanocellulose piezoelectric response, ~pm V(-1), ranks this material at the level of currently used piezoelectric energy generators and new artificial 2D designs. Such finding would be crucial for developing alternative materials to drive emerging nanotechnologies.
2D microwave imaging reflectometer electronics
Spear, A. G.; Domier, C. W. Hu, X.; Muscatello, C. M.; Ren, X.; Luhmann, N. C.; Tobias, B. J.
2014-11-15
A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.
2D microwave imaging reflectometer electronics.
Spear, A G; Domier, C W; Hu, X; Muscatello, C M; Ren, X; Tobias, B J; Luhmann, N C
2014-11-01
A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.
Assessing 2D electrophoretic mobility spectroscopy (2D MOSY) for analytical applications.
Fang, Yuan; Yushmanov, Pavel V; Furó, István
2016-12-08
Electrophoretic displacement of charged entity phase modulates the spectrum acquired in electrophoretic NMR experiments, and this modulation can be presented via 2D FT as 2D mobility spectroscopy (MOSY) spectra. We compare in various mixed solutions the chemical selectivity provided by 2D MOSY spectra with that provided by 2D diffusion-ordered spectroscopy (DOSY) spectra and demonstrate, under the conditions explored, a superior performance of the former method. 2D MOSY compares also favourably with closely related LC-NMR methods. The shape of 2D MOSY spectra in complex mixtures is strongly modulated by the pH of the sample, a feature that has potential for areas such as in drug discovery and metabolomics. Copyright © 2016 The Authors. Magnetic Resonance in Chemistry published by John Wiley & Sons Ltd. StartCopTextCopyright © 2016 The Authors. Magnetic Resonance in Chemistry published by John Wiley & Sons Ltd.
Electromagnetic Scattering by Multiple Cavities Embedded in the Infinite 2D Ground Plane
2014-07-01
Helmholtz equation imposed in the separated interior domains of the cavities. The existence and uniqueness of the weak solution for the model...are presented to show the efficiency and accuracy of the proposed method. Index Terms - Electromagnetic cavity, finite element method, Helmholtz ...polarization (TM), where the modeling equation is the two-dimensional Helmholtz equation. Based on Fourier transform, a nonlocal transparent condition
2D Distributed Sensing Via TDR
2007-11-02
plate VEGF CompositeSensor Experimental Setup Air 279 mm 61 78 VARTM profile: slope RTM profile: rectangle 22 1 Jul 2003© 2003 University of Delaware...2003 University of Delaware All rights reserved Vision: Non-contact 2D sensing ü VARTM setup constructed within TL can be sensed by its EM field: 2D...300.0 mm/ns. 1 2 1 Jul 2003© 2003 University of Delaware All rights reserved Model Validation “ RTM Flow” TDR Response to 139 mm VEGC
Inkjet printing of 2D layered materials.
Li, Jiantong; Lemme, Max C; Östling, Mikael
2014-11-10
Inkjet printing of 2D layered materials, such as graphene and MoS2, has attracted great interests for emerging electronics. However, incompatible rheology, low concentration, severe aggregation and toxicity of solvents constitute critical challenges which hamper the manufacturing efficiency and product quality. Here, we introduce a simple and general technology concept (distillation-assisted solvent exchange) to efficiently overcome these challenges. By implementing the concept, we have demonstrated excellent jetting performance, ideal printing patterns and a variety of promising applications for inkjet printing of 2D layered materials.
Symmetry detection of auxetic behaviour in 2D frameworks
NASA Astrophysics Data System (ADS)
Mitschke, H.; Schröder-Turk, G. E.; Mecke, K.; Fowler, P. W.; Guest, S. D.
2013-06-01
A symmetry-extended Maxwell treatment of the net mobility of periodic bar-and-joint frameworks is used to derive a sufficient condition for auxetic behaviour of a 2D material. The type of auxetic behaviour that can be detected by symmetry has Poisson's ratio -1, with equal expansion/contraction in all directions, and is here termed equiauxetic. A framework may have a symmetry-detectable equiauxetic mechanism if it belongs to a plane group that includes rotational axes of order n = 6, 4, or 3. If the reducible representation for the net mobility contains mechanisms that preserve full rotational symmetry (A modes), these are equiauxetic. In addition, for n = 6, mechanisms that halve rotational symmetry (B modes) are also equiauxetic.
Raman 2D-band splitting in graphene: theory and experiment.
Frank, Otakar; Mohr, Marcel; Maultzsch, Janina; Thomsen, Christian; Riaz, Ibtsam; Jalil, Rashid; Novoselov, Kostya S; Tsoukleri, Georgia; Parthenios, John; Papagelis, Konstantinos; Kavan, Ladislav; Galiotis, Costas
2011-03-22
We present a systematic experimental and theoretical study of the two-phonon (2D) Raman scattering in graphene under uniaxial tension. The external perturbation unveils that the 2D mode excited with 785 nm has a complex line-shape mainly due to the contribution of two distinct double resonance scattering processes (inner and outer) in the Raman signal. The splitting depends on the direction of the applied strain and the polarization of the incident light. The results give new insight into the nature of the 2D band and have significant implications for the use of graphene as reinforcement in composites since the 2D mode is crucial to assess how effectively graphene uptakes an applied stress or strain.
MoS2-WSe2 Hetero Bilayer: Possibility of Mechanical Strain Induced Band Gap Engineering
NASA Astrophysics Data System (ADS)
Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.
2014-03-01
The tunability of band gap in two-dimensional (2D) hetero-bilayers of MoS2-WSe2 with applied mechanical strains (in-plane and out-of-plane) in two different types of stackings (AA and AB) have been investigated in the framework of density functional theory (DFT). The in-plane biaxial tensile strain is found to reduce electronic band gap monotonically and rendered considered bilayer into metal at 6% of applied strain. The transition pressure required for complete semiconductor-to-metal transition is found to be of 7.89 GPa while tensile strength of the reported hetero-bilayer has been calculated 10 GPa at 25% strain. In case of vertical compression strain, 16 GPa pressure has been calculated for complete semiconductor-to-metal transition. The band-gap deformation potentials and effective masses (electron and hole) have been found to posses strong dependence on the type of applied strain. Such band gap engineering in controlled manner (internal control by composition and external control by applied strain) makes the considered hetero-bilayer as a strong candidate for the application in variety of nano scale devices.
Multi-Scale Modeling, Design Strategies and Physical Properties of 2D Composite Sheets
2015-01-15
of Pennsylvania. The breakthrough results obtained are 1) prediction and subsequent experimental observation of strain induced changes in electronic...structure of TMD materials 2) Prediction and experimental observation of using defects in 2D materials to enhance charge storage capacity and 3...221 Philadelphia , PA 19104 -6205 4-Mar-2014 ABSTRACT Final Report: 9.4: Multi-scale modeling, design strategies and physical properties of 2D
Parallel Stitching of 2D Materials.
Ling, Xi; Lin, Yuxuan; Ma, Qiong; Wang, Ziqiang; Song, Yi; Yu, Lili; Huang, Shengxi; Fang, Wenjing; Zhang, Xu; Hsu, Allen L; Bie, Yaqing; Lee, Yi-Hsien; Zhu, Yimei; Wu, Lijun; Li, Ju; Jarillo-Herrero, Pablo; Dresselhaus, Mildred; Palacios, Tomás; Kong, Jing
2016-03-23
Diverse parallel stitched 2D heterostructures, including metal-semiconductor, semiconductor-semiconductor, and insulator-semiconductor, are synthesized directly through selective "sowing" of aromatic molecules as the seeds in the chemical vapor deposition (CVD) method. The methodology enables the large-scale fabrication of lateral heterostructures, which offers tremendous potential for its application in integrated circuits.
Beckett, Phil
2012-01-01
The technique of two-dimensional (2D) gel electrophoresis is a powerful tool for separating complex mixtures of proteins, but since its inception in the mid 1970s, it acquired the stigma of being a very difficult application to master and was generally used to its best effect by experts. The introduction of commercially available immobilized pH gradients in the early 1990s provided enhanced reproducibility and easier protocols, leading to a pronounced increase in popularity of the technique. However gel-to-gel variation was still difficult to control without the use of technical replicates. In the mid 1990s (at the same time as the birth of "proteomics"), the concept of multiplexing fluorescently labeled proteins for 2D gel separation was realized by Jon Minden's group and has led to the ability to design experiments to virtually eliminate gel-to-gel variation, resulting in biological replicates being used for statistical analysis with the ability to detect very small changes in relative protein abundance. This technology is referred to as 2D difference gel electrophoresis (2D DIGE).
Parallel stitching of 2D materials
Ling, Xi; Wu, Lijun; Lin, Yuxuan; ...
2016-01-27
Diverse parallel stitched 2D heterostructures, including metal–semiconductor, semiconductor–semiconductor, and insulator–semiconductor, are synthesized directly through selective “sowing” of aromatic molecules as the seeds in the chemical vapor deposition (CVD) method. Lastly, the methodology enables the large-scale fabrication of lateral heterostructures, which offers tremendous potential for its application in integrated circuits.
3D surface configuration modulates 2D symmetry detection.
Chen, Chien-Chung; Sio, Lok-Teng
2015-02-01
We investigated whether three-dimensional (3D) information in a scene can affect symmetry detection. The stimuli were random dot patterns with 15% dot density. We measured the coherence threshold, or the proportion of dots that were the mirror reflection of the other dots in the other half of the image about a central vertical axis, at 75% accuracy with a 2AFC paradigm under various 3D configurations produced by the disparity between the left and right eye images. The results showed that symmetry detection was difficult when the corresponding dots across the symmetry axis were on different frontoparallel or inclined planes. However, this effect was not due to a difference in distance, as the observers could detect symmetry on a slanted surface, where the depth of the two sides of the symmetric axis was different. The threshold was reduced for a hinge configuration where the join of two slanted surfaces coincided with the axis of symmetry. Our result suggests that the detection of two-dimensional (2D) symmetry patterns is subject to the 3D configuration of the scene; and that coplanarity across the symmetry axis and consistency between the 2D pattern and 3D structure are important factors for symmetry detection.
Meshfree natural vibration analysis of 2D structures
NASA Astrophysics Data System (ADS)
Kosta, Tomislav; Tsukanov, Igor
2014-02-01
Determination of resonance frequencies and vibration modes of mechanical structures is one of the most important tasks in the product design procedure. The main goal of this paper is to describe a pioneering application of the solution structure method (SSM) to 2D structural natural vibration analysis problems and investigate the numerical properties of the method. SSM is a meshfree method which enables construction of the solutions to the engineering problems that satisfy exactly all prescribed boundary conditions. This method is capable of using spatial meshes that do not conform to the shape of a geometric model. Instead of using the grid nodes to enforce boundary conditions, it employs distance fields to the geometric boundaries and combines them with the basis functions and prescribed boundary conditions at run time. This defines unprecedented geometric flexibility of the SSM as well as the complete automation of the solution procedure. In the paper we will explain the key points of the SSM as well as investigate the accuracy and convergence of the proposed approach by comparing our results with the ones obtained using analytical methods or traditional finite element analysis. Despite in this paper we are dealing with 2D in-plane vibrations, the proposed approach has a straightforward generalization to model vibrations of 3D structures.
Dynamics of quasi 2D co-rotating vortex merger
NASA Astrophysics Data System (ADS)
Khandekar, Akshay G.
Merger of vortices is examined experimentally to compare the merger of slender parallel vortices generated coincidentally. It is known that like-sign vortices rotate around a common center of circulation and merger between the vortices may occur under certain conditions. This merger is dependent on the strength of the vortex circulation, distance of separation between the centers of the two vortices, ReGamma, and vorticity distribution. Quasi-2D experimental data is examined and merger relations are derived. The 2D experiments conducted in a vortex generator tank uses high aspect ratio rotating paddles. The vortex merger tank generates slender co-rotating vortices and are examined using PIV (Particle Image Velocimetry). Merger characteristics are compared at centerline, 25% span and 5% span for different circulation strengths. Symmetric and asymmetric mergers are studied and it is found that in both cases, the vortex pair rotates around an axis perpendicular to the plane of the vortex pair. Symmetric merger is seen to occur at the center between the two vortices whereas in asymmetric merger the stronger vortex breaks the weaker vortex filaments and continues to follow its path. Wall effects seem to have an effect of vortex braiding and vortex stretching. Closer to the wall, the merger time increases while the merged vortex dissipates faster than at the centerline.
Interactive 2D to 3D stereoscopic image synthesis
NASA Astrophysics Data System (ADS)
Feldman, Mark H.; Lipton, Lenny
2005-03-01
Advances in stereoscopic display technologies, graphic card devices, and digital imaging algorithms have opened up new possibilities in synthesizing stereoscopic images. The power of today"s DirectX/OpenGL optimized graphics cards together with adapting new and creative imaging tools found in software products such as Adobe Photoshop, provide a powerful environment for converting planar drawings and photographs into stereoscopic images. The basis for such a creative process is the focus of this paper. This article presents a novel technique, which uses advanced imaging features and custom Windows-based software that utilizes the Direct X 9 API to provide the user with an interactive stereo image synthesizer. By creating an accurate and interactive world scene with moveable and flexible depth map altered textured surfaces, perspective stereoscopic cameras with both visible frustums and zero parallax planes, a user can precisely model a virtual three-dimensional representation of a real-world scene. Current versions of Adobe Photoshop provide a creative user with a rich assortment of tools needed to highlight elements of a 2D image, simulate hidden areas, and creatively shape them for a 3D scene representation. The technique described has been implemented as a Photoshop plug-in and thus allows for a seamless transition of these 2D image elements into 3D surfaces, which are subsequently rendered to create stereoscopic views.
2D to 3D conversion implemented in different hardware
NASA Astrophysics Data System (ADS)
Ramos-Diaz, Eduardo; Gonzalez-Huitron, Victor; Ponomaryov, Volodymyr I.; Hernandez-Fragoso, Araceli
2015-02-01
Conversion of available 2D data for release in 3D content is a hot topic for providers and for success of the 3D applications, in general. It naturally completely relies on virtual view synthesis of a second view given by original 2D video. Disparity map (DM) estimation is a central task in 3D generation but still follows a very difficult problem for rendering novel images precisely. There exist different approaches in DM reconstruction, among them manually and semiautomatic methods that can produce high quality DMs but they demonstrate hard time consuming and are computationally expensive. In this paper, several hardware implementations of designed frameworks for an automatic 3D color video generation based on 2D real video sequence are proposed. The novel framework includes simultaneous processing of stereo pairs using the following blocks: CIE L*a*b* color space conversions, stereo matching via pyramidal scheme, color segmentation by k-means on an a*b* color plane, and adaptive post-filtering, DM estimation using stereo matching between left and right images (or neighboring frames in a video), adaptive post-filtering, and finally, the anaglyph 3D scene generation. Novel technique has been implemented on DSP TMS320DM648, Matlab's Simulink module over a PC with Windows 7, and using graphic card (NVIDIA Quadro K2000) demonstrating that the proposed approach can be applied in real-time processing mode. The time values needed, mean Similarity Structural Index Measure (SSIM) and Bad Matching Pixels (B) values for different hardware implementations (GPU, Single CPU, and DSP) are exposed in this paper.
3D spin-flop transition in enhanced 2D layered structure single crystalline TlCo2Se2
NASA Astrophysics Data System (ADS)
Jin, Z.; Xia, Z.-C.; Wei, M.; Yang, J.-H.; Chen, B.; Huang, S.; Shang, C.; Wu, H.; Zhang, X.-X.; Huang, J.-W.; Ouyang, Z.-W.
2016-10-01
The enhanced 2D layered structure single crystalline TlCo2Se2 has been successfully fabricated, which exhibits field-induced 3D spin-flop phase transitions. In the case of the magnetic field parallel to the c-axis (B//c), the applied magnetic field induces the evolution of the noncollinear helical magnetic coupling into a ferromagnetic (FM) state with all the magnetization of the Co ion parallel to the c-axis. A striking variation of the field-induced strain within the ab-plane is noticed in the magnetic field region of 20-30 T. In the case of the magnetic field perpendicular to the c-axis (B ⊥ c), the inter-layer helical antiferromagnetic (AFM) coupling may transform to an initial canted AFM coupling, and then part of it transforms to an intermediate metamagnetic phase with the alignment of two-up-one-down Co magnetic moments and finally to an ultimate FM coupling in higher magnetic fields. The robust noncollinear AFM magnetic coupling is completely destroyed above 30 T. In combination with the measurements of magnetization, magnetoresistance and field-induced strain, a complete magnetic phase diagram of the TlCo2Se2 single crystal has been depicted, demonstrating complex magnetic structures even though the crystal geometry itself gives no indication of the magnetic frustration.
Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology
Shavanova, Kateryna; Bakakina, Yulia; Burkova, Inna; Shtepliuk, Ivan; Viter, Roman; Ubelis, Arnolds; Beni, Valerio; Starodub, Nickolaj; Yakimova, Rositsa; Khranovskyy, Volodymyr
2016-01-01
The discovery of graphene and its unique properties has inspired researchers to try to invent other two-dimensional (2D) materials. After considerable research effort, a distinct “beyond graphene” domain has been established, comprising the library of non-graphene 2D materials. It is significant that some 2D non-graphene materials possess solid advantages over their predecessor, such as having a direct band gap, and therefore are highly promising for a number of applications. These applications are not limited to nano- and opto-electronics, but have a strong potential in biosensing technologies, as one example. However, since most of the 2D non-graphene materials have been newly discovered, most of the research efforts are concentrated on material synthesis and the investigation of the properties of the material. Applications of 2D non-graphene materials are still at the embryonic stage, and the integration of 2D non-graphene materials into devices is scarcely reported. However, in recent years, numerous reports have blossomed about 2D material-based biosensors, evidencing the growing potential of 2D non-graphene materials for biosensing applications. This review highlights the recent progress in research on the potential of using 2D non-graphene materials and similar oxide nanostructures for different types of biosensors (optical and electrochemical). A wide range of biological targets, such as glucose, dopamine, cortisol, DNA, IgG, bisphenol, ascorbic acid, cytochrome and estradiol, has been reported to be successfully detected by biosensors with transducers made of 2D non-graphene materials. PMID:26861346
Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology.
Shavanova, Kateryna; Bakakina, Yulia; Burkova, Inna; Shtepliuk, Ivan; Viter, Roman; Ubelis, Arnolds; Beni, Valerio; Starodub, Nickolaj; Yakimova, Rositsa; Khranovskyy, Volodymyr
2016-02-06
The discovery of graphene and its unique properties has inspired researchers to try to invent other two-dimensional (2D) materials. After considerable research effort, a distinct "beyond graphene" domain has been established, comprising the library of non-graphene 2D materials. It is significant that some 2D non-graphene materials possess solid advantages over their predecessor, such as having a direct band gap, and therefore are highly promising for a number of applications. These applications are not limited to nano- and opto-electronics, but have a strong potential in biosensing technologies, as one example. However, since most of the 2D non-graphene materials have been newly discovered, most of the research efforts are concentrated on material synthesis and the investigation of the properties of the material. Applications of 2D non-graphene materials are still at the embryonic stage, and the integration of 2D non-graphene materials into devices is scarcely reported. However, in recent years, numerous reports have blossomed about 2D material-based biosensors, evidencing the growing potential of 2D non-graphene materials for biosensing applications. This review highlights the recent progress in research on the potential of using 2D non-graphene materials and similar oxide nanostructures for different types of biosensors (optical and electrochemical). A wide range of biological targets, such as glucose, dopamine, cortisol, DNA, IgG, bisphenol, ascorbic acid, cytochrome and estradiol, has been reported to be successfully detected by biosensors with transducers made of 2D non-graphene materials.
PLASTICITY AND NON-LINEAR ELASTIC STRAINS
conditions existing in plane waves in an extended medium to give the time rate of change of stress as a function of the time rate of change of strain, the stress invariants, the total strain and the plastic strain. (Author)
Graphene and Other 2D Colloids: Liquid Crystals and Macroscopic Fibers.
Liu, Yingjun; Xu, Zhen; Gao, Weiwei; Cheng, Zhengdong; Gao, Chao
2017-02-24
Two-dimensional colloidal nanomaterials are running into renaissance after the enlightening researches of graphene. Macroscopic one-dimensional fiber is an optimal ordered structural form to express the in-plane merits of 2D nanomaterials, and the formation of liquid crystals (LCs) allows the creation of continuous fibers. In the correlated system from LCs to fibers, understanding their macroscopic organizing behavior and transforming them into new solid fibers is greatly significant for applications. Herein, we retrospect the history of 2D colloids and discuss about the concept of 2D nanomaterial fibers in the context of LCs, elaborating the motivation, principle and possible strategies of fabrication. Then we highlight the creation, development and typical applications of graphene fibers. Additionally, the latest advances of other 2D nanomaterial fibers are also summarized. Finally, conclusions, challenges and perspectives are provided to show great expectations of better and more fibrous materials of 2D nanomaterials. This review gives a comprehensive retrospect of the past century-long effort about the whole development of 2D colloids, and plots a clear roadmap - "lamellar solid - LCs - macroscopic fibers - flexible devices", which will certainly open a new era of structural-multifunctional application for the conventional 2D colloids.
Compatible embedding for 2D shape animation.
Baxter, William V; Barla, Pascal; Anjyo, Ken-Ichi
2009-01-01
We present new algorithms for the compatible embedding of 2D shapes. Such embeddings offer a convenient way to interpolate shapes having complex, detailed features. Compared to existing techniques, our approach requires less user input, and is faster, more robust, and simpler to implement, making it ideal for interactive use in practical applications. Our new approach consists of three parts. First, our boundary matching algorithm locates salient features using the perceptually motivated principles of scale-space and uses these as automatic correspondences to guide an elastic curve matching algorithm. Second, we simplify boundaries while maintaining their parametric correspondence and the embedding of the original shapes. Finally, we extend the mapping to shapes' interiors via a new compatible triangulation algorithm. The combination of our algorithms allows us to demonstrate 2D shape interpolation with instant feedback. The proposed algorithms exhibit a combination of simplicity, speed, and accuracy that has not been achieved in previous work.
Schottky diodes from 2D germanane
NASA Astrophysics Data System (ADS)
Sahoo, Nanda Gopal; Esteves, Richard J.; Punetha, Vinay Deep; Pestov, Dmitry; Arachchige, Indika U.; McLeskey, James T.
2016-07-01
We report on the fabrication and characterization of a Schottky diode made using 2D germanane (hydrogenated germanene). When compared to germanium, the 2D structure has higher electron mobility, an optimal band-gap, and exceptional stability making germanane an outstanding candidate for a variety of opto-electronic devices. One-atom-thick sheets of hydrogenated puckered germanium atoms have been synthesized from a CaGe2 framework via intercalation and characterized by XRD, Raman, and FTIR techniques. The material was then used to fabricate Schottky diodes by suspending the germanane in benzonitrile and drop-casting it onto interdigitated metal electrodes. The devices demonstrate significant rectifying behavior and the outstanding potential of this material.
Extrinsic Cation Selectivity of 2D Membranes
2017-01-01
From a systematic study of the concentration driven diffusion of positive and negative ions across porous 2D membranes of graphene and hexagonal boron nitride (h-BN), we prove their cation selectivity. Using the current–voltage characteristics of graphene and h-BN monolayers separating reservoirs of different salt concentrations, we calculate the reversal potential as a measure of selectivity. We tune the Debye screening length by exchanging the salt concentrations and demonstrate that negative surface charge gives rise to cation selectivity. Surprisingly, h-BN and graphene membranes show similar characteristics, strongly suggesting a common origin of selectivity in aqueous solvents. For the first time, we demonstrate that the cation flux can be increased by using ozone to create additional pores in graphene while maintaining excellent selectivity. We discuss opportunities to exploit our scalable method to use 2D membranes for applications including osmotic power conversion. PMID:28157333
Quasiparticle interference in unconventional 2D systems
NASA Astrophysics Data System (ADS)
Chen, Lan; Cheng, Peng; Wu, Kehui
2017-03-01
At present, research of 2D systems mainly focuses on two kinds of materials: graphene-like materials and transition-metal dichalcogenides (TMDs). Both of them host unconventional 2D electronic properties: pseudospin and the associated chirality of electrons in graphene-like materials, and spin-valley-coupled electronic structures in the TMDs. These exotic electronic properties have attracted tremendous interest for possible applications in nanodevices in the future. Investigation on the quasiparticle interference (QPI) in 2D systems is an effective way to uncover these properties. In this review, we will begin with a brief introduction to 2D systems, including their atomic structures and electronic bands. Then, we will discuss the formation of Friedel oscillation due to QPI in constant energy contours of electron bands, and show the basic concept of Fourier-transform scanning tunneling microscopy/spectroscopy (FT-STM/STS), which can resolve Friedel oscillation patterns in real space and consequently obtain the QPI patterns in reciprocal space. In the next two parts, we will summarize some pivotal results in the investigation of QPI in graphene and silicene, in which systems the low-energy quasiparticles are described by the massless Dirac equation. The FT-STM experiments show there are two different interference channels (intervalley and intravalley scattering) and backscattering suppression, which associate with the Dirac cones and the chirality of quasiparticles. The monolayer and bilayer graphene on different substrates (SiC and metal surfaces), and the monolayer and multilayer silicene on a Ag(1 1 1) surface will be addressed. The fifth part will introduce the FT-STM research on QPI in TMDs (monolayer and bilayer of WSe2), which allow us to infer the spin texture of both conduction and valence bands, and present spin-valley coupling by tracking allowed and forbidden scattering channels.
Compact 2-D graphical representation of DNA
NASA Astrophysics Data System (ADS)
Randić, Milan; Vračko, Marjan; Zupan, Jure; Novič, Marjana
2003-05-01
We present a novel 2-D graphical representation for DNA sequences which has an important advantage over the existing graphical representations of DNA in being very compact. It is based on: (1) use of binary labels for the four nucleic acid bases, and (2) use of the 'worm' curve as template on which binary codes are placed. The approach is illustrated on DNA sequences of the first exon of human β-globin and gorilla β-globin.
2D Metals by Repeated Size Reduction.
Liu, Hanwen; Tang, Hao; Fang, Minghao; Si, Wenjie; Zhang, Qinghua; Huang, Zhaohui; Gu, Lin; Pan, Wei; Yao, Jie; Nan, Cewen; Wu, Hui
2016-10-01
A general and convenient strategy for manufacturing freestanding metal nanolayers is developed on large scale. By the simple process of repeatedly folding and calendering stacked metal sheets followed by chemical etching, free-standing 2D metal (e.g., Ag, Au, Fe, Cu, and Ni) nanosheets are obtained with thicknesses as small as 1 nm and with sizes of the order of several micrometers.
Realistic and efficient 2D crack simulation
NASA Astrophysics Data System (ADS)
Yadegar, Jacob; Liu, Xiaoqing; Singh, Abhishek
2010-04-01
Although numerical algorithms for 2D crack simulation have been studied in Modeling and Simulation (M&S) and computer graphics for decades, realism and computational efficiency are still major challenges. In this paper, we introduce a high-fidelity, scalable, adaptive and efficient/runtime 2D crack/fracture simulation system by applying the mathematically elegant Peano-Cesaro triangular meshing/remeshing technique to model the generation of shards/fragments. The recursive fractal sweep associated with the Peano-Cesaro triangulation provides efficient local multi-resolution refinement to any level-of-detail. The generated binary decomposition tree also provides efficient neighbor retrieval mechanism used for mesh element splitting and merging with minimal memory requirements essential for realistic 2D fragment formation. Upon load impact/contact/penetration, a number of factors including impact angle, impact energy, and material properties are all taken into account to produce the criteria of crack initialization, propagation, and termination leading to realistic fractal-like rubble/fragments formation. The aforementioned parameters are used as variables of probabilistic models of cracks/shards formation, making the proposed solution highly adaptive by allowing machine learning mechanisms learn the optimal values for the variables/parameters based on prior benchmark data generated by off-line physics based simulation solutions that produce accurate fractures/shards though at highly non-real time paste. Crack/fracture simulation has been conducted on various load impacts with different initial locations at various impulse scales. The simulation results demonstrate that the proposed system has the capability to realistically and efficiently simulate 2D crack phenomena (such as window shattering and shards generation) with diverse potentials in military and civil M&S applications such as training and mission planning.
Engineering light outcoupling in 2D materials.
Lien, Der-Hsien; Kang, Jeong Seuk; Amani, Matin; Chen, Kevin; Tosun, Mahmut; Wang, Hsin-Ping; Roy, Tania; Eggleston, Michael S; Wu, Ming C; Dubey, Madan; Lee, Si-Chen; He, Jr-Hau; Javey, Ali
2015-02-11
When light is incident on 2D transition metal dichalcogenides (TMDCs), it engages in multiple reflections within underlying substrates, producing interferences that lead to enhancement or attenuation of the incoming and outgoing strength of light. Here, we report a simple method to engineer the light outcoupling in semiconducting TMDCs by modulating their dielectric surroundings. We show that by modulating the thicknesses of underlying substrates and capping layers, the interference caused by substrate can significantly enhance the light absorption and emission of WSe2, resulting in a ∼11 times increase in Raman signal and a ∼30 times increase in the photoluminescence (PL) intensity of WSe2. On the basis of the interference model, we also propose a strategy to control the photonic and optoelectronic properties of thin-layer WSe2. This work demonstrates the utilization of outcoupling engineering in 2D materials and offers a new route toward the realization of novel optoelectronic devices, such as 2D LEDs and solar cells.
Irreversibility-inversions in 2D turbulence
NASA Astrophysics Data System (ADS)
Bragg, Andrew; de Lillo, Filippo; Boffetta, Guido
2016-11-01
We consider a recent theoretical prediction that for inertial particles in 2D turbulence, the nature of the irreversibility of their pair dispersion inverts when the particle inertia exceeds a certain value. In particular, when the particle Stokes number, St , is below a certain value, the forward-in-time (FIT) dispersion should be faster than the backward-in-time (BIT) dispersion, but for St above this value, this should invert so that BIT becomes faster than FIT dispersion. This non-trivial behavior arises because of the competition between two physically distinct irreversibility mechanisms that operate in different regimes of St . In 3D turbulence, both mechanisms act to produce faster BIT than FIT dispersion, but in 2D, the two mechanisms have opposite effects because of the inverse energy cascade in the turbulent velocity field. We supplement the qualitative argument given by Bragg et al. by deriving quantitative predictions of this effect in the short-time dispersion limit. These predictions are then confirmed by results of inertial particle dispersion in a direct numerical simulation of 2D turbulence.
McGhie, Jackie S; de Groot-de Laat, Lotte; Ren, Ben; Vletter, Wim; Frowijn, René; Oei, Frans; Geleijnse, Marcel L
2015-12-01
This study sought to assess the value of two-dimensional (2D) transthoracic echocardiography (TTE), 2D xPlane imaging and three-dimensional (3D) TTE for the definition of the site and the extent of mitral valve (MV) prolapse. Fifty patients underwent transthoracic 2D, 2D xPlane and 3D echocardiography. With 2D xPlane a segmental analysis of the MV was performed, by making a lateral sweep across the MV coaptation line as seen in the parasternal short-axis view. Inter-observer agreement for specific scallop prolapse was for 2D xPlane excellent (97%, kappa = 0.94) and for 3D TTE moderate (85%, kappa = 0.67). The respective sensitivities of standard 2D TTE, 2D xPlane, and 3D TTE for the identification of the precise posterior scallop prolapse were for P1 92, 85, and 92%, for P2 96, 96, and 82%, and for P3 86, 81, and 71%. In total, 5 (8%) prolapsing MV scallops were missed by 2D TTE, 7 (12%) by 2D xPlane, and 12 (20%) by 3D TTE. The sensitivity of 3D TTE was significantly lower than standard 2D imaging (80% versus 93%, P < 0.05). The extent of P2 prolapse was under or overestimated in 5 patients with 2D xPlane and in 9 patients with 3D TTE. 2D xPlane imaging is an accurate, easy to use (compared to 3D TTE) and easy to interpret (compared to 2D and 3D TTE) imaging modality to study the site and the extent of MV prolapse.
Zhang, Ziheng; Friedman, Daniel; Dione, Donald P.; Lin, Ben A.; Duncan, James S.; Sinusas, Albert J.; Sampath, Smita
2013-01-01
A high temporal resolution 2D flow pathline analysis method that describes the spatio-temporal distribution of blood entering the left ventricle during early diastolic filling is presented. Filling patterns in normal volunteers (n=8) and canine animals (baseline (n=1) and infarcted (n=6)) are studied using this approach. Data is acquired using our recently reported MR technique, SPAMM-PAV, which permits simultaneous quantification of blood velocities and myocardial strain at high temporal resolution of 14 ms. Virtual emitter particles, released from the mitral valve plane every time frame during rapid filling, are tracked to depict the propagation of 2D pathlines on the imaged plane. The pathline regional distribution patterns are compared with regional myocardial longitudinal strains and regional chamber longitudinal pressure gradients. Our results demonstrate strong spatial inter-dependence between left ventricular (LV) filling patterns and LV mechanical function. Significant differences in pathline-described filling patterns are observed in the infarcted animals. Quantitative analysis of net kinetic energy for each set of pathlines is performed. Peak net kinetic energy of 0.06±0.01 mJ in normal volunteers, 0.043 mJ in baseline dog, 0.143±0.03 mJ in three infarcted dogs with nominal flow dysfunction, and 0.016±0.007 mJ in three infarcted dogs with severe flow dysfunction is observed. PMID:23044637
In plane oscillation of a bifilar pendulum
NASA Astrophysics Data System (ADS)
Hinrichsen, Peter F.
2016-11-01
The line tensions, the horizontal and vertical accelerations as well as the period of large angle oscillations parallel to the plane of a bifilar suspension are presented and have been experimentally investigated using strain gauges and a smart phone. This system has a number of advantages over the simple pendulum for studying large angle oscillations, and for measuring the acceleration due to gravity.
NASA Technical Reports Server (NTRS)
Krueger, Ronald; Minguet, Pierre J.; Bushnell, Dennis M. (Technical Monitor)
2002-01-01
The influence of two-dimensional finite element modeling assumptions on the debonding prediction for skin-stiffener specimens was investigated. Geometrically nonlinear finite element analyses using two-dimensional plane-stress and plane strain elements as well as three different generalized plane strain type approaches were performed. The computed deflections, skin and flange strains, transverse tensile stresses and energy release rates were compared to results obtained from three-dimensional simulations. The study showed that for strains and energy release rate computations the generalized plane strain assumptions yielded results closest to the full three-dimensional analysis. For computed transverse tensile stresses the plane stress assumption gave the best agreement. Based on this study it is recommended that results from plane stress and plane strain models be used as upper and lower bounds. The results from generalized plane strain models fall between the results obtained from plane stress and plane strain models. Two-dimensional models may also be used to qualitatively evaluate the stress distribution in a ply and the variation of energy release rates and mixed mode ratios with lamination length. For more accurate predictions, however, a three-dimensional analysis is required.
2D ultrasonic elastography with lateral displacement estimation using statistics.
Zhang, Zhihong; Liu, Haolin; Cheng, Yangjie
2014-01-01
Ultrasound elastography is the method of obtaining relative stiffness information of biological tissue, which plays an important role in early diagnosis. Generally, a gradient-based strain imaging algorithm assumes that motion only occurs in an axial direction. However, because tissue has different relative stiffness, the scatter presents lateral motion under high freehand compression. Therefore, errors occur in estimating the cross-correlation phase in the calculation window. A 2D elastography algorithm with lateral displacement estimation using statistics was proposed to reduce errors. The new method was investigated through simulation, and the experiment confirmed that errors introduced by lateral tissue movement have been greatly reduced with no sacrifice of real-time ultrasonic imaging quality.
Periodically sheared 2D Yukawa systems
Kovács, Anikó Zsuzsa; Hartmann, Peter; Donkó, Zoltán
2015-10-15
We present non-equilibrium molecular dynamics simulation studies on the dynamic (complex) shear viscosity of a 2D Yukawa system. We have identified a non-monotonic frequency dependence of the viscosity at high frequencies and shear rates, an energy absorption maximum (local resonance) at the Einstein frequency of the system at medium shear rates, an enhanced collective wave activity, when the excitation is near the plateau frequency of the longitudinal wave dispersion, and the emergence of significant configurational anisotropy at small frequencies and high shear rates.
ENERGY LANDSCAPE OF 2D FLUID FORMS
Y. JIANG; ET AL
2000-04-01
The equilibrium states of 2D non-coarsening fluid foams, which consist of bubbles with fixed areas, correspond to local minima of the total perimeter. (1) The authors find an approximate value of the global minimum, and determine directly from an image how far a foam is from its ground state. (2) For (small) area disorder, small bubbles tend to sort inwards and large bubbles outwards. (3) Topological charges of the same sign repel while charges of opposite sign attract. (4) They discuss boundary conditions and the uniqueness of the pattern for fixed topology.
Mapping and load response of overload strain fields: Synchrotron X-ray measurements
Shukla, V; Jisrawi, N M; Sadangi, R K; Pao, P S; Horvath, K; Sadananda, K; Ignatov, A; Skaritka, J; Tsakalakos, T
2009-02-05
High energy synchrotron X-ray diffraction measurements have been performed to provide quantitative microscopic guidance for modeling of fatigue crack growth. Specifically we report local strain mapping, along with in situ loading strain response, results on 4140 steel fatigue specimens exhibiting the crack growth retardation 'overload effect'. Detailed, 2D, {epsilon}{gamma}{gamma}-strain field mapping shows that a single overload (OL) cycle creates a compressive strain field extending millimeters above and below the crack plane. The OL strain field structures are shown to persist after the crack tip has grown well beyond the OL position. The specimen exhibiting the maximal crack growth rate retardation following overload exhibits a tensile residual strain region at the crack tip. Strain field results, on in situ tensile loaded specimens, show a striking critical threshold load, F{sub c}, phenomenon in their strain response. At loads below F{sub c} the strain response is dominated by a rapid suppression of the compressive OL feature with modest response at the crack tip. At loads above F{sub c} the strain response at the OL position terminates and the response at the crack tip becomes large. This threshold load response behavior is shown to exhibit lower F{sub c} values, and dramatically enhanced rates of strain change with load as the crack tip propagates farther beyond the OL position. The OL strain feature behind the crack tip also is shown to be suppressed by removing the opposing crack faces via an electron discharge cut passing through the crack tip. Finally unique 2D strain field mapping (imaging) results, through the depth of the specimen, of the fatigue crack front and the OL feature in the wake are also presented.
Remarks on thermalization in 2D CFT
NASA Astrophysics Data System (ADS)
de Boer, Jan; Engelhardt, Dalit
2016-12-01
We revisit certain aspects of thermalization in 2D conformal field theory (CFT). In particular, we consider similarities and differences between the time dependence of correlation functions in various states in rational and non-rational CFTs. We also consider the distinction between global and local thermalization and explain how states obtained by acting with a diffeomorphism on the ground state can appear locally thermal, and we review why the time-dependent expectation value of the energy-momentum tensor is generally a poor diagnostic of global thermalization. Since all 2D CFTs have an infinite set of commuting conserved charges, generic initial states might be expected to give rise to a generalized Gibbs ensemble rather than a pure thermal ensemble at late times. We construct the holographic dual of the generalized Gibbs ensemble and show that, to leading order, it is still described by a Banados-Teitelboim-Zanelli black hole. The extra conserved charges, while rendering c <1 theories essentially integrable, therefore seem to have little effect on large-c conformal field theories.
Microwave Assisted 2D Materials Exfoliation
NASA Astrophysics Data System (ADS)
Wang, Yanbin
Two-dimensional materials have emerged as extremely important materials with applications ranging from energy and environmental science to electronics and biology. Here we report our discovery of a universal, ultrafast, green, solvo-thermal technology for producing excellent-quality, few-layered nanosheets in liquid phase from well-known 2D materials such as such hexagonal boron nitride (h-BN), graphite, and MoS2. We start by mixing the uniform bulk-layered material with a common organic solvent that matches its surface energy to reduce the van der Waals attractive interactions between the layers; next, the solutions are heated in a commercial microwave oven to overcome the energy barrier between bulk and few-layers states. We discovered the minutes-long rapid exfoliation process is highly temperature dependent, which requires precise thermal management to obtain high-quality inks. We hypothesize a possible mechanism of this proposed solvo-thermal process; our theory confirms the basis of this novel technique for exfoliation of high-quality, layered 2D materials by using an as yet unknown role of the solvent.
2D kinematic signatures of boxy/peanut bulges
NASA Astrophysics Data System (ADS)
Iannuzzi, Francesca; Athanassoula, E.
2015-07-01
We study the imprints of boxy/peanut structures on the 2D line-of-sight kinematics of simulated disc galaxies. The models under study belong to a family with varying initial gas fraction and halo triaxiality, plus few other control runs with different structural parameters; the kinematic information was extracted using the Voronoi-binning technique and parametrized up to the fourth order of a Gauss-Hermite series. Building on a previous work for the long-slit case, we investigate the 2D kinematic behaviour in the edge-on projection as a function of the boxy/peanut strength and position angle; we find that for the strongest structures the highest moments show characteristic features away from the mid-plane in a range of position angles. We also discuss the masking effect of a classical bulge and the ambiguity in discriminating kinematically this spherically symmetric component from a boxy/peanut bulge seen end-on. Regarding the face-on case, we extend existing results to encompass the effect of a second buckling and find that this phenomenon spurs an additional set of even deeper minima in the fourth moment. Finally, we show how the results evolve when inclining the disc away from perfectly edge-on and face-on. The behaviour of stars born during the course of the simulations is discussed and confronted to that of the pre-existing disc. The general aim of our study is providing a handle to identify boxy/peanut structures and their properties in latest generation Integral Field Unit observations of nearby disc galaxies.
Li, He; Lee, Wei-Ning
2017-02-21
The anisotropic mechanical properties (mechanical anisotropy) and view-dependent ultrasonic backscattering (acoustic anisotropy) of striated muscle due to the underlying myofiber arrangement have been well documented, but whether they impact on ultrasound strain imaging (USI) techniques remains unclear. The aim of this study was therefore to investigate the performance of a cross-correlation-based two-dimensional (2D) USI method in anisotropic media under controlled quasi-static compression in silico and in vitro. First, synthetic pre- and post-deformed 2D radiofrequency images of anisotropic phantoms were simulated in two scenarios to examine the individual effect of the mechanical and acoustic anisotropies on strain estimation. In the first scenario, the phantom was defined to be transversely isotropic with the scatterer amplitudes following a zero-mean Gaussian distribution, while in the second scenario, the phantom was defined to be mechanically isotropic with Gaussian distributed scatterer amplitudes correlated along the principal directions of pre-defined fibers. These two anisotropies were then jointly incorporated into the ultrasound image simulation model with additional depth-dependent attenuation. Three imaging planes-the fiber plane with the fiber direction perpendicular to the ultrasound beam (TISperp_fb), the fiber plane with the fiber direction parallel to the beam (TISpara), and the transverse fiber plane (TISperp_cfb)-were studied. The absolute relative error (ARE) of the lateral strain estimates in TISperp_fb (20.99 ± 15.65%) was much higher than that in TISperp_cfb (4.14 ± 3.17%). The ARE in TISpara was unavailable owing to the large spatial extent of false peaks. The effect of tissue anisotropy on the performance of the 2D USI was further confirmed in an in vitro porcine skeletal muscle phantom. The best in-plane strain quality was again shown in TISperp_cfb (elastographic signal-to-noise ratio, or SNRe: >25 d
Strain-modulated electronic and thermal transport properties of two-dimensional O-silica
NASA Astrophysics Data System (ADS)
Han, Yang; Qin, Guangzhao; Jungemann, Christoph; Hu, Ming
2016-07-01
Silica is one of the most abundant materials in the Earth’s crust and is a remarkably versatile and important engineering material in various modern science and technology. Recently, freestanding and well-ordered two-dimensional (2D) silica monolayers with octahedral (O-silica) building blocks were found to be theoretically stable by (Wang G et al 2015 J. Phys. Chem. C 119 15654-60). In this paper, by performing first-principles calculations, we systematically investigated the electronic and thermal transport properties of 2D O-silica and also studied how these properties can be tuned by simple mechanical stretching. Unstrained 2D O-silica is an insulator with an indirect band gap of 6.536 eV. The band gap decreases considerably with bilateral strain up to 29%, at which point a semiconductor-metal transition occurs. More importantly, the in-plane thermal conductivity of freestanding 2D O-silica is found to be unusually high, which is around 40 to 50 times higher than that of bulk α-quartz and more than two orders of magnitude higher than that of amorphous silica. The thermal conductivity of O-silica decreases by almost two orders of magnitude when the bilateral stretching strain reaches 10%. By analyzing the mode-dependent phonon properties and phonon-scattering channel, the phonon lifetime is found to be the dominant factor that leads to the dramatic decrease of the lattice thermal conductivity under strain. The very sensitive response of both band gap and phonon transport properties to the external mechanical strain will enable 2D O-silica to easily adapt to the different environment of realistic applications. Our study is expected to stimulate experimental exploration of further physical and chemical properties of 2D silica systems, and offers perspectives on modulating the electronic and thermal properties of related low-dimensional structures for applications such as thermoelectric, photovoltaic, and optoelectronic devices.
Non Lyapunov stability of a constant spatially developing 2-D gas flow
NASA Astrophysics Data System (ADS)
Balint, Agneta M.; Balint, Stefan; Tanasie, Loredana
2017-01-01
Different types of stabilities (global, local) and instabilities (global absolute, local convective) of the constant spatially developing 2-D gas flow are analyzed in a particular phase space of continuously differentiable functions, endowed with the usual algebraic operations and the topology generated by the uniform convergence on the plane. For this purpose the Euler equations linearized at the constant flow are used. The Lyapunov stability analysis was presented in [1] and this paper is a continuation of [1].
Photometry unlocks 3D information from 2D localization microscopy data.
Franke, Christian; Sauer, Markus; van de Linde, Sebastian
2017-01-01
We developed a straightforward photometric method, temporal, radial-aperture-based intensity estimation (TRABI), that allows users to extract 3D information from existing 2D localization microscopy data. TRABI uses the accurate determination of photon numbers in different regions of the emission pattern of single emitters to generate a z-dependent photometric parameter. This method can determine fluorophore positions up to 600 nm from the focal plane and can be combined with biplane detection to further improve axial localization.
Fourier plane imaging microscopy
Dominguez, Daniel Peralta, Luis Grave de; Alharbi, Nouf; Alhusain, Mdhaoui; Bernussi, Ayrton A.
2014-09-14
We show how the image of an unresolved photonic crystal can be reconstructed using a single Fourier plane (FP) image obtained with a second camera that was added to a traditional compound microscope. We discuss how Fourier plane imaging microscopy is an application of a remarkable property of the obtained FP images: they contain more information about the photonic crystals than the images recorded by the camera commonly placed at the real plane of the microscope. We argue that the experimental results support the hypothesis that surface waves, contributing to enhanced resolution abilities, were optically excited in the studied photonic crystals.
2-D or not 2-D, that is the question: A Northern California test
Mayeda, K; Malagnini, L; Phillips, W S; Walter, W R; Dreger, D
2005-06-06
Reliable estimates of the seismic source spectrum are necessary for accurate magnitude, yield, and energy estimation. In particular, how seismic radiated energy scales with increasing earthquake size has been the focus of recent debate within the community and has direct implications on earthquake source physics studies as well as hazard mitigation. The 1-D coda methodology of Mayeda et al. has provided the lowest variance estimate of the source spectrum when compared against traditional approaches that use direct S-waves, thus making it ideal for networks that have sparse station distribution. The 1-D coda methodology has been mostly confined to regions of approximately uniform complexity. For larger, more geophysically complicated regions, 2-D path corrections may be required. The complicated tectonics of the northern California region coupled with high quality broadband seismic data provides for an ideal ''apples-to-apples'' test of 1-D and 2-D path assumptions on direct waves and their coda. Using the same station and event distribution, we compared 1-D and 2-D path corrections and observed the following results: (1) 1-D coda results reduced the amplitude variance relative to direct S-waves by roughly a factor of 8 (800%); (2) Applying a 2-D correction to the coda resulted in up to 40% variance reduction from the 1-D coda results; (3) 2-D direct S-wave results, though better than 1-D direct waves, were significantly worse than the 1-D coda. We found that coda-based moment-rate source spectra derived from the 2-D approach were essentially identical to those from the 1-D approach for frequencies less than {approx}0.7-Hz, however for the high frequencies (0.7{le} f {le} 8.0-Hz), the 2-D approach resulted in inter-station scatter that was generally 10-30% smaller. For complex regions where data are plentiful, a 2-D approach can significantly improve upon the simple 1-D assumption. In regions where only 1-D coda correction is available it is still preferable over 2
Fabrication and magnetic behaviour of 2D ordered Fe/SiO2 nanodots array
NASA Astrophysics Data System (ADS)
Liu, W.; Zhong, W.; Qiu, L. J.; Lü, L. Y.; Du, Y. W.
2006-06-01
We have demonstrated a simple and universal morphology-controlled growth of 2D ordered Fe/SiO2 magnetic nanodots array, which was based on 2D colloidal monolayer template composed of polystyrene (PS) spheres and one-step sol-gel spin-coating technique. The Fe/SiO2 nanodots have a well-ordered structure arranged in a hexagonal pattern. The dots have the shape of quasi-pyramidal tetrahedron, which reside in the interstitial region between three PS spheres and the substrate. Magnetic measurements reveal that the nanodots array exhibits the in-plane easy magnetization direction. Compared with the unpatterned Fe/SiO2 thin film, the dots array has lower saturated field, higher remanence and coercivity. The present method is applicable to 2D ordered nanodots array of other magnetic materials.
Structure-From-Motion in 3D Space Using 2D Lidars
Choi, Dong-Geol; Bok, Yunsu; Kim, Jun-Sik; Shim, Inwook; Kweon, In So
2017-01-01
This paper presents a novel structure-from-motion methodology using 2D lidars (Light Detection And Ranging). In 3D space, 2D lidars do not provide sufficient information for pose estimation. For this reason, additional sensors have been used along with the lidar measurement. In this paper, we use a sensor system that consists of only 2D lidars, without any additional sensors. We propose a new method of estimating both the 6D pose of the system and the surrounding 3D structures. We compute the pose of the system using line segments of scan data and their corresponding planes. After discarding the outliers, both the pose and the 3D structures are refined via nonlinear optimization. Experiments with both synthetic and real data show the accuracy and robustness of the proposed method. PMID:28165372
2D quantum gravity from quantum entanglement.
Gliozzi, F
2011-01-21
In quantum systems with many degrees of freedom the replica method is a useful tool to study the entanglement of arbitrary spatial regions. We apply it in a way that allows them to backreact. As a consequence, they become dynamical subsystems whose position, form, and extension are determined by their interaction with the whole system. We analyze, in particular, quantum spin chains described at criticality by a conformal field theory. Its coupling to the Gibbs' ensemble of all possible subsystems is relevant and drives the system into a new fixed point which is argued to be that of the 2D quantum gravity coupled to this system. Numerical experiments on the critical Ising model show that the new critical exponents agree with those predicted by the formula of Knizhnik, Polyakov, and Zamolodchikov.
2D Electrostatic Actuation of Microshutter Arrays
NASA Technical Reports Server (NTRS)
Burns, Devin E.; Oh, Lance H.; Li, Mary J.; Jones, Justin S.; Kelly, Daniel P.; Zheng, Yun; Kutyrev, Alexander S.; Moseley, Samuel H.
2015-01-01
An electrostatically actuated microshutter array consisting of rotational microshutters (shutters that rotate about a torsion bar) were designed and fabricated through the use of models and experiments. Design iterations focused on minimizing the torsional stiffness of the microshutters, while maintaining their structural integrity. Mechanical and electromechanical test systems were constructed to measure the static and dynamic behavior of the microshutters. The torsional stiffness was reduced by a factor of four over initial designs without sacrificing durability. Analysis of the resonant behavior of the microshutter arrays demonstrates that the first resonant mode is a torsional mode occurring around 3000 Hz. At low vacuum pressures, this resonant mode can be used to significantly reduce the drive voltage necessary for actuation requiring as little as 25V. 2D electrostatic latching and addressing was demonstrated using both a resonant and pulsed addressing scheme.
Graphene suspensions for 2D printing
NASA Astrophysics Data System (ADS)
Soots, R. A.; Yakimchuk, E. A.; Nebogatikova, N. A.; Kotin, I. A.; Antonova, I. V.
2016-04-01
It is shown that, by processing a graphite suspension in ethanol or water by ultrasound and centrifuging, it is possible to obtain particles with thicknesses within 1-6 nm and, in the most interesting cases, 1-1.5 nm. Analogous treatment of a graphite suspension in organic solvent yields eventually thicker particles (up to 6-10 nm thick) even upon long-term treatment. Using the proposed ink based on graphene and aqueous ethanol with ethylcellulose and terpineol additives for 2D printing, thin (~5 nm thick) films with sheet resistance upon annealing ~30 MΩ/□ were obtained. With the ink based on aqueous graphene suspension, the sheet resistance was ~5-12 kΩ/□ for 6- to 15-nm-thick layers with a carrier mobility of ~30-50 cm2/(V s).
Canard configured aircraft with 2-D nozzle
NASA Technical Reports Server (NTRS)
Child, R. D.; Henderson, W. P.
1978-01-01
A closely-coupled canard fighter with vectorable two-dimensional nozzle was designed for enhanced transonic maneuvering. The HiMAT maneuver goal of a sustained 8g turn at a free-stream Mach number of 0.9 and 30,000 feet was the primary design consideration. The aerodynamic design process was initiated with a linear theory optimization minimizing the zero percent suction drag including jet effects and refined with three-dimensional nonlinear potential flow techniques. Allowances were made for mutual interference and viscous effects. The design process to arrive at the resultant configuration is described, and the design of a powered 2-D nozzle model to be tested in the LRC 16-foot Propulsion Wind Tunnel is shown.
Numerical Evaluation of 2D Ground States
NASA Astrophysics Data System (ADS)
Kolkovska, Natalia
2016-02-01
A ground state is defined as the positive radial solution of the multidimensional nonlinear problem
Facile Assembly of Large-Area 2D Microgel Colloidal Crystals Using Charge-Reversible Substrates.
Weng, Junying; Li, Xiaoyun; Guan, Ying; Zhu, X X; Zhang, Yongjun
2016-12-06
2D colloidal crystals (CCs) have important applications; however, the fabrication of large-area, high-quality 2D CCs is still far from being trivial, and the fabrication of 2D microgel CCs is even harder. Here, we have demonstrated that they can be facilely fabricated using charge-reversible substrates. The charge-reversible substrates were prepared by modification with amino groups. The amino groups were then protected by amidation with 2,2-dimethylsuccinic anhydride. At acidic pH, the surface charge of the modified substrate will change from negative to positive as a result of the hydrolysis of the amide bonds and the regeneration of the amino groups. 2D microgel CCs can be simply fabricated by applying a concentrated microgel dispersion on the modified substrate. The negatively charged surface of the substrate allows the negatively charged microgel spheres, especially those close to the substrate, to self-assemble into 3D CCs. With the gradual hydrolysis of the amide bonds and the charge reversal of the substrate, the first 111 plane of the 3D assembly is fixed in situ on the substrate. The resulting 2D CC has a high degree of ordering because of the high quality of the parent 3D microgel CC. Because large-area 3D microgel CCs can be facilely fabricated, this method allows for the fabrication of 2D CCs of any size. Nonplanar substrates can also be used. In addition, the interparticle distance of the 2D array can be tuned by the concentration of the microgel dispersion. Besides rigid substrates (such as glass slides, quartz slides, and silicon wafers), flexible polymer films, including polyethylene terephthalate and poly(vinyl chloride) films, were also successfully used as substrates for the fabrication of 2D microgel CCs.
Fundamental performance assessment of 2-D myocardial elastography in a phased-array configuration.
Luo, Jianwen; Lee, Wei-Ning; Konofagou, Elisa E
2009-10-01
Two-dimensional myocardial elastography, an RF-based, speckle-tracking technique, uses 1-D cross-correlation and recorrelation methods in a 2-D search, and can estimate and image the 2-D transmural motion and deformation of the myocardium so as to characterize the cardiac function. Based on a 3-D finite-element (FE) canine left-ventricular model, a theoretical framework was previously developed by our group to evaluate the estimation quality of 2-D myocardial elastography using a linear array. In this paper, an ultrasound simulation program, Field II, was used to generate the RF signals of a model of the heart in a phased-array configuration and under 3-D motion conditions; thus simulating a standard echocardiography exam. The estimation method of 2-D myocardial elastography was adapted for use with such a configuration. All elastographic displacements and strains were found to be in good agreement with the FE solutions, as indicated by the mean absolute error (MAE) between the two. The classified first and second principal strains approximated the radial and circumferential strains, respectively, in the phased-array configuration. The results at different sonographic signal-to-noise ratios (SNR(s)) showed that the MAEs of the axial, lateral, radial, and circumferential strains remained relatively constant when the SNR(s) was equal to or higher than 20 dB. The MAEs of the strain estimation were not significantly affected when the acoustic attenuation was included in the simulations. A significantly reduced number of scatterers could be used to speed up the simulation, without sacrificing the estimation quality.The proposed framework can further be used to assess the estimation quality, explore the theoretical limitation and investigate the effects of various parameters in 2-D myocardial elastography under more realistic conditions.
Metrology for graphene and 2D materials
NASA Astrophysics Data System (ADS)
Pollard, Andrew J.
2016-09-01
The application of graphene, a one atom-thick honeycomb lattice of carbon atoms with superlative properties, such as electrical conductivity, thermal conductivity and strength, has already shown that it can be used to benefit metrology itself as a new quantum standard for resistance. However, there are many application areas where graphene and other 2D materials, such as molybdenum disulphide (MoS2) and hexagonal boron nitride (h-BN), may be disruptive, areas such as flexible electronics, nanocomposites, sensing and energy storage. Applying metrology to the area of graphene is now critical to enable the new, emerging global graphene commercial world and bridge the gap between academia and industry. Measurement capabilities and expertise in a wide range of scientific areas are required to address this challenge. The combined and complementary approach of varied characterisation methods for structural, chemical, electrical and other properties, will allow the real-world issues of commercialising graphene and other 2D materials to be addressed. Here, examples of metrology challenges that have been overcome through a multi-technique or new approach are discussed. Firstly, the structural characterisation of defects in both graphene and MoS2 via Raman spectroscopy is described, and how nanoscale mapping of vacancy defects in graphene is also possible using tip-enhanced Raman spectroscopy (TERS). Furthermore, the chemical characterisation and removal of polymer residue on chemical vapour deposition (CVD) grown graphene via secondary ion mass spectrometry (SIMS) is detailed, as well as the chemical characterisation of iron films used to grow large domain single-layer h-BN through CVD growth, revealing how contamination of the substrate itself plays a role in the resulting h-BN layer. In addition, the role of international standardisation in this area is described, outlining the current work ongoing in both the International Organization of Standardization (ISO) and the
Construction of cuprous oxide electrodes composed of 2D single-crystalline dendritic nanosheets.
Jang, Ho Seong; Kim, Suk Jun; Choi, Kyoung-Shin
2010-10-04
An unusual anisotropic growth of Cu(2)O is stabilized via the electrochemical synthesis of Cu(2)O in the presence of Ag(+) ions, which results in the formation of Cu(2)O electrodes composed of 2D sheetlike crystals containing complex dendritic patterns. It is quite unusual for Cu(2)O to form a 2D morphology since it has a 3D isotropic cubic crystal structure where the a, b, and c axes are equivalent. Each Cu(2)O sheet is single-crystalline in nature and is grown parallel to the {110} plane, which is rarely observed in Cu(2)O crystal shapes. A various set of experiments are performed to understand the role of Ag(+) ions on the 2D growth of Cu(2)O. The results show that Ag(+) ions are deposited as silver islands on already growing Cu(2)O crystals and serve as nucleation sites for the new growth of Cu(2)O crystals. As a result, the growth direction of the newly forming Cu(2)O crystals is governed by the diffusion layer structure created by the pre-existing Cu(2)O crystals, which results in the formation of 2D dendritic patterns. The thin 2D crystal morphology can significantly increase the surface-to-volume ratio of Cu(2)O crystals, which is beneficial for enhancing various electrochemical and photoelectrochemical properties of the electrodes. The photoelectrochemical properties of the Cu(2)O electrodes composed of 2D dendritic crystals are investigated and compared to those of 3D dendritic crystals. This study provides a unique and effective route to maximize the {110} area per unit volume of Cu(2)O, which will be beneficial for any catalytic/sensing abilities that can be anisotropically enhanced by the {110} planes of Cu(2)O.
Eight plane IPND mechanical testing.
Zhao, A.; Guarino, V.; Wood, K.; Nephew, T.; Ayres, D.; Lee, A.; High Energy Physics; FNAL
2008-03-18
A mechanical test of an 8 plane IPND mechanical prototype, which was constructed using extrusions from the testing/tryout of the 16 cell prototype extrusion die in Argonne National Laboratory, was conducted. There were 4 vertical and 4 horizontal planes in this 8 plane IPND prototype. Each vertical plane had four 16 cell extrusions, while each horizontal plane had six 16 cell extrusions. Each plane was glued together using the formulation of Devcon adhesive, Devcon 60. The vertical extrusions used in the vertical planes shares the same dimensions as the horizontal extrusions in the horizontal planes with the average web thickness of 2.1 mm and the average wall thickness of 3.1 mm. This mechanical prototype was constructed with end-seals on the both ends of the vertical extrusions. The gaps were filled with epoxy between extrusions and end-seals. The overall dimension of IPND is 154.8 by 103.1 by 21.7 inches with the weight of approximately 1200 kg, as shown in a figure. Two similar mechanical tests of 3 layer and 11 layer prototypes have been done in order to evaluate the strength of the adhesive joint between extrusions in the NOvA detector. The test showed that the IPND prototype was able to sustain under the loading of weight of itself and scintillator. Two FEA models were built to verify the measurement data from the test. The prediction from FEA slice model seems correlated reasonably well to the test result, even under a 'rough' estimated condition for the wall thickness (from an untuned die) and an unknown property of 'garage type' extrusion. A full size of FEA 3-D model also agrees very well with the test data from strain gage readings. It is worthy to point out that the stress distribution of the structure is predominantly determined by the internal pressure, while the buckling stability relies more on the loading weight from the extrusions themselves and scintillate. Results of conducted internal pressure tests, including 3- cell, 11-cell and the IPND
Ab initio modeling of 2D layered organohalide lead perovskites
NASA Astrophysics Data System (ADS)
Fraccarollo, Alberto; Cantatore, Valentina; Boschetto, Gabriele; Marchese, Leonardo; Cossi, Maurizio
2016-04-01
A number of 2D layered perovskites A2PbI4 and BPbI4, with A and B mono- and divalent ammonium and imidazolium cations, have been modeled with different theoretical methods. The periodic structures have been optimized (both in monoclinic and in triclinic systems, corresponding to eclipsed and staggered arrangements of the inorganic layers) at the DFT level, with hybrid functionals, Gaussian-type orbitals and dispersion energy corrections. With the same methods, the various contributions to the solid stabilization energy have been discussed, separating electrostatic and dispersion energies, organic-organic intralayer interactions and H-bonding effects, when applicable. Then the electronic band gaps have been computed with plane waves, at the DFT level with scalar and full relativistic potentials, and including the correlation energy through the GW approximation. Spin orbit coupling and GW effects have been combined in an additive scheme, validated by comparing the computed gap with well known experimental and theoretical results for a model system. Finally, various contributions to the computed band gaps have been discussed on some of the studied systems, by varying some geometrical parameters and by substituting one cation in another's place.
Fracture morphology of 2-D carbon-carbon composition
NASA Technical Reports Server (NTRS)
Avery, W. B.; Herakovich, C. T.
1985-01-01
Out-of-plane tensile tests of a woven fabric carbon-carbon composite were performed in a scanning electron microscope equipped with a tensile stage and a videotape recording system. The composite was prepared from T-300 8-harness satin graphite fabric and a phenolic resin. The (0/90/0/90/0 sub 1/2) sub 2 laminate, with a Theta describing the orientation of the warp fibers of the fabric, was cured at 160 C and pyrolized at 871 C. This was followed by four cycles of resin impregnation, curing, and pyrolysis. A micrograph of the cross section of the composite is presented. Inspection of the specimen fracture surface revealed that the filaments had no residual matrix bonded to them. Further inspection revealed that the fracture was interlaminar in nature. Failure occurred where filaments of adjacent plies had the same orientation. Thus it is postulated that improvement in transverse tensile strength of 2-D carbon-carbon depends on the improvement of the filament-matrix bond strength.
Effects of Agent's Repulsion in 2d Flocking Models
NASA Astrophysics Data System (ADS)
Moussa, Najem; Tarras, Iliass; Mazroui, M'hammed; Boughaleb, Yahya
In nature many animal groups, such as fish schools or bird flocks, clearly display structural order and appear to move as a single coherent entity. In order to understand the complex behavior of these systems, many models have been proposed and tested so far. This paper deals with an extension of the Vicsek model, by including a second zone of repulsion, where each agent attempts to maintain a minimum distance from the others. The consideration of this zone in our study seems to play an important role during the travel of agents in the two-dimensional (2D) flocking models. Our numerical investigations show that depending on the basic ingredients such as repulsion radius (R1), effect of density of agents (ρ) and noise (η), our nonequilibrium system can undergo a kinetic phase transition from no transport to finite net transport. For different values of ρ, kinetic phase diagrams in the plane (η ,R1) are found. Implications of these findings are discussed.
Cardiac biplane strain imaging: initial in vivo experience
NASA Astrophysics Data System (ADS)
Lopata, R. G. P.; Nillesen, M. M.; Verrijp, C. N.; Singh, S. K.; Lammens, M. M. Y.; van der Laak, J. A. W. M.; van Wetten, H. B.; Thijssen, J. M.; Kapusta, L.; de Korte, C. L.
2010-02-01
In this study, first we propose a biplane strain imaging method using a commercial ultrasound system, yielding estimation of the strain in three orthogonal directions. Secondly, an animal model of a child's heart was introduced that is suitable to simulate congenital heart disease and was used to test the method in vivo. The proposed approach can serve as a framework to monitor the development of cardiac hypertrophy and fibrosis. A 2D strain estimation technique using radio frequency (RF) ultrasound data was applied. Biplane image acquisition was performed at a relatively low frame rate (<100 Hz) using a commercial platform with an RF interface. For testing the method in vivo, biplane image sequences of the heart were recorded during the cardiac cycle in four dogs with an aortic stenosis. Initial results reveal the feasibility of measuring large radial, circumferential and longitudinal cumulative strain (up to 70%) at a frame rate of 100 Hz. Mean radial strain curves of a manually segmented region-of-interest in the infero-lateral wall show excellent correlation between the measured strain curves acquired in two perpendicular planes. Furthermore, the results show the feasibility and reproducibility of assessing radial, circumferential and longitudinal strains simultaneously. In this preliminary study, three beagles developed an elevated pressure gradient over the aortic valve (Δp: 100-200 mmHg) and myocardial hypertrophy. One dog did not develop any sign of hypertrophy (Δp = 20 mmHg). Initial strain (rate) results showed that the maximum strain (rate) decreased with increasing valvular stenosis (-50%), which is in accordance with previous studies. Histological findings corroborated these results and showed an increase in fibrotic tissue for the hearts with larger pressure gradients (100, 200 mmHg), as well as lower strain and strain rate values.
Acute myocarditis with normal wall motion detected with 2D speckle tracking echocardiography
Niel, Johannes; Aichinger, Josef; Ebner, Christian
2016-01-01
Summary We present the case of a 26-year-old male with acute tonsillitis who was referred for coronary angiography because of chest pain, elevated cardiac biomarkers, and biphasic T waves. The patient had no cardiovascular risk factors. Echocardiography showed no wall motion abnormalities and no pericardial effusion. 2D speckle tracking revealed distinct decreased regional peak longitudinal systolic strain in the lateral and posterior walls. Ischemic disease was extremely unlikely in view of his young age, negative family history regarding coronary artery disease, and lack of regional wall motion abnormalities on the conventional 2D echocardiogram. Coronary angiography was deferred as myocarditis was suspected. To confirm the diagnosis, cardiac magnetic resonance tomography (MRT) was performed, showing subepicardial delayed hyperenhancement in the lateral and posterior walls correlating closely with the strain pattern obtained by 2D speckle tracking echocardiography. With a working diagnosis of acute myocarditis associated with acute tonsillitis, we prescribed antibiotics and nonsteroidal anti-inflammatory drugs. The patient’s clinical signs resolved along with normalization of serum creatine kinase (CK) levels, and the patient was discharged on the third day after admission. Learning points Acute myocarditis can mimic acute coronary syndromes.Conventional 2D echocardiography lacks specific features for detection of subtle regional wall motion abnormalities.2D speckle tracking expands the scope of echocardiography in identifying myocardial dysfunction derived from edema in acute myocarditis. PMID:27249814
NASA Astrophysics Data System (ADS)
Chowdhury, Sugata; Simpson, Jeffrey; Einstein, T. L.; Walker, Angela R. Hight
2D-materials with controllable optical, electronic and magnetic properties are desirable for novel nanodevices. Here we studied these properties for both pristine and hydrogenated TaSe2 (TaSe2-H) monolayer (ML) in the framework of DFT using the PAW method. We considered uniaxial and biaxial tensile strain, as well as shear strain along the basal planes in the range between 1% and 16%. Previous theoretical works (e.g.) considered only symmetrical biaxial tensile. Pristine ML is ferromagnetic for uniaxial tensile strain along ◯ or ŷ. For tensile strain in ŷ, the calculated magnetic moments of the Ta atoms are twice those for the same strain in ◯. Under pure shear strain (expansion along ŷ and compression along ◯), a pristine ML is ferromagnetic, but becomes non-magnetic when the strain directions are interchanged. Due to carrier-mediated double-exchange, the pristine ML is ferromagnetic when the Se-Ta-Se bond angle is < 82° and the ML thickness is < 3.25Å. We find that all Raman-active phonon modes show obvious red-shifting due to bond elongation and the E2 modes degeneracy is lifted as strain increases. For a TaSe2-H ML, the same trends were observed. Results show the ability to tune the properties of 2D-materials.
NASA Astrophysics Data System (ADS)
Morgan, Ben; Green, Anne M.
2005-12-01
The direction dependence of the WIMP direct detection rate provides a powerful tool for distinguishing a WIMP signal from possible backgrounds. We study the number of events required to discriminate a WIMP signal from an isotropic background for a detector with 2-d readout using nonparametric circular statistics. We also examine the number of events needed to (i) detect a deviation from rotational symmetry, due to flattening of the Milky Way halo and (ii) detect a deviation in the mean direction due to a tidal stream. If the senses of the recoils are measured then of order 20--70 events (depending on the plane of the 2-d readout and the detector location) will be sufficient to reject isotropy of the raw recoil angles at 90% confidence. If the senses can not be measured these number increase by roughly 2 orders of magnitude (compared with an increase of 1 order of magnitude for the case of full 3-d readout). The distributions of the reduced angles, with the (time-dependent) direction of solar motion subtracted, are far more anisotropic, however, and if the isotropy tests are applied to these angles then the numbers of events required are similar to the case of 3-d readout. A deviation from rotational symmetry will only be detectable if the Milky Way halo is significantly flattened. The deviation in the mean direction due to a tidal stream is potentially detectable, however, depending on the density and direction of the stream. The meridian plane (which contains the Earth’s spin axis) is, for all detector locations, the optimum readout plane for rejecting isotropy. However readout in this plane can not be used for detecting flattening of the Milky Way halo or a stream with direction perpendicular to the galactic plane. In these cases the optimum readout plane depends on the detector location.
Nanoscale elastic changes in 2D Ti_{3}C_{2}T_{x} (MXene) pseudocapacitive electrodes
Come, Jeremy; Xie, Yu; Naguib, Michael; Jesse, Stephen; Kalinin, Sergei V.; Gogotsi, Yury; Kent, Paul R. C.; Balke, Nina
2016-02-01
Designing sustainable electrodes for next generation energy storage devices relies on the understanding of their fundamental properties at the nanoscale, including the comprehension of ions insertion into the electrode and their interactions with the active material. One consequence of ion storage is the change in the electrode volume resulting in mechanical strain and stress that can strongly affect the cycle life. Therefore, it is important to understand the changes of dimensions and mechanical properties occurring during electrochemical reactions. While the characterization of mechanical properties via macroscopic measurements is well documented, in-situ characterization of their evolution has never been achieved at the nanoscale. Two dimensional (2D) carbides, known as MXenes, are promising materials for supercapacitors and various kinds of batteries, and understating the coupling between their mechanical and electrochemical properties is therefore necessary. Here we report on in-situ imaging, combined with density functional theory of the elastic changes, of a 2D titanium carbide (Ti_{3}C_{2}T_{x}) electrode in direction normal to the basal plane during cation intercalation. The results show a strong correlation between the Li+ ions content and the elastic modulus, whereas little effects of K+ ions are observed. Moreover, this strategy enables identifying the preferential intercalation pathways within a single particle.
Persistence Measures for 2d Soap Froth
NASA Astrophysics Data System (ADS)
Feng, Y.; Ruskin, H. J.; Zhu, B.
Soap froths as typical disordered cellular structures, exhibiting spatial and temporal evolution, have been studied through their distributions and topological properties. Recently, persistence measures, which permit representation of the froth as a two-phase system, have been introduced to study froth dynamics at different length scales. Several aspects of the dynamics may be considered and cluster persistence has been observed through froth experiment. Using a direct simulation method, we have investigated persistent properties in 2D froth both by monitoring the persistence of survivor cells, a topologically independent measure, and in terms of cluster persistence. It appears that the area fraction behavior for both survivor and cluster persistence is similar for Voronoi froth and uniform froth (with defects). Survivor and cluster persistent fractions are also similar for a uniform froth, particularly when geometries are constrained, but differences observed for the Voronoi case appear to be attributable to the strong topological dependency inherent in cluster persistence. Survivor persistence, on the other hand, depends on the number rather than size and position of remaining bubbles and does not exhibit the characteristic decay to zero.
SEM signal emulation for 2D patterns
NASA Astrophysics Data System (ADS)
Sukhov, Evgenii; Muelders, Thomas; Klostermann, Ulrich; Gao, Weimin; Braylovska, Mariya
2016-03-01
The application of accurate and predictive physical resist simulation is seen as one important use model for fast and efficient exploration of new patterning technology options, especially if fully qualified OPC models are not yet available at an early pre-production stage. The methodology of using a top-down CD-SEM metrology to extract the 3D resist profile information, such as the critical dimension (CD) at various resist heights, has to be associated with a series of presumptions which may introduce such small, but systematic CD errors. Ideally, the metrology effects should be carefully minimized during measurement process, or if possible be taken into account through proper metrology modeling. In this paper we discuss the application of a fast SEM signal emulation describing the SEM image formation. The algorithm is applied to simulated resist 3D profiles and produces emulated SEM image results for 1D and 2D patterns. It allows estimating resist simulation quality by comparing CDs which were extracted from the emulated and from the measured SEM images. Moreover, SEM emulation is applied for resist model calibration to capture subtle error signatures through dose and defocus. Finally, it should be noted that our SEM emulation methodology is based on the approximation of physical phenomena which are taking place in real SEM image formation. This approximation allows achieving better speed performance compared to a fully physical model.
Competing coexisting phases in 2D water
NASA Astrophysics Data System (ADS)
Zanotti, Jean-Marc; Judeinstein, Patrick; Dalla-Bernardina, Simona; Creff, Gaëlle; Brubach, Jean-Blaise; Roy, Pascale; Bonetti, Marco; Ollivier, Jacques; Sakellariou, Dimitrios; Bellissent-Funel, Marie-Claire
2016-05-01
The properties of bulk water come from a delicate balance of interactions on length scales encompassing several orders of magnitudes: i) the Hydrogen Bond (HBond) at the molecular scale and ii) the extension of this HBond network up to the macroscopic level. Here, we address the physics of water when the three dimensional extension of the HBond network is frustrated, so that the water molecules are forced to organize in only two dimensions. We account for the large scale fluctuating HBond network by an analytical mean-field percolation model. This approach provides a coherent interpretation of the different events experimentally (calorimetry, neutron, NMR, near and far infra-red spectroscopies) detected in interfacial water at 160, 220 and 250 K. Starting from an amorphous state of water at low temperature, these transitions are respectively interpreted as the onset of creation of transient low density patches of 4-HBonded molecules at 160 K, the percolation of these domains at 220 K and finally the total invasion of the surface by them at 250 K. The source of this surprising behaviour in 2D is the frustration of the natural bulk tetrahedral local geometry and the underlying very significant increase in entropy of the interfacial water molecules.
Competing coexisting phases in 2D water
Zanotti, Jean-Marc; Judeinstein, Patrick; Dalla-Bernardina, Simona; Creff, Gaëlle; Brubach, Jean-Blaise; Roy, Pascale; Bonetti, Marco; Ollivier, Jacques; Sakellariou, Dimitrios; Bellissent-Funel, Marie-Claire
2016-01-01
The properties of bulk water come from a delicate balance of interactions on length scales encompassing several orders of magnitudes: i) the Hydrogen Bond (HBond) at the molecular scale and ii) the extension of this HBond network up to the macroscopic level. Here, we address the physics of water when the three dimensional extension of the HBond network is frustrated, so that the water molecules are forced to organize in only two dimensions. We account for the large scale fluctuating HBond network by an analytical mean-field percolation model. This approach provides a coherent interpretation of the different events experimentally (calorimetry, neutron, NMR, near and far infra-red spectroscopies) detected in interfacial water at 160, 220 and 250 K. Starting from an amorphous state of water at low temperature, these transitions are respectively interpreted as the onset of creation of transient low density patches of 4-HBonded molecules at 160 K, the percolation of these domains at 220 K and finally the total invasion of the surface by them at 250 K. The source of this surprising behaviour in 2D is the frustration of the natural bulk tetrahedral local geometry and the underlying very significant increase in entropy of the interfacial water molecules. PMID:27185018
Strain-engineered diffusive atomic switching in two-dimensional crystals
Kalikka, Janne; Zhou, Xilin; Dilcher, Eric; Wall, Simon; Li, Ju; Simpson, Robert E.
2016-01-01
Strain engineering is an emerging route for tuning the bandgap, carrier mobility, chemical reactivity and diffusivity of materials. Here we show how strain can be used to control atomic diffusion in van der Waals heterostructures of two-dimensional (2D) crystals. We use strain to increase the diffusivity of Ge and Te atoms that are confined to 5 Å thick 2D planes within an Sb2Te3–GeTe van der Waals superlattice. The number of quintuple Sb2Te3 2D crystal layers dictates the strain in the GeTe layers and consequently its diffusive atomic disordering. By identifying four critical rules for the superlattice configuration we lay the foundation for a generalizable approach to the design of switchable van der Waals heterostructures. As Sb2Te3–GeTe is a topological insulator, we envision these rules enabling methods to control spin and topological properties of materials in reversible and energy efficient ways. PMID:27329563
NASA Astrophysics Data System (ADS)
Cheng, Chingyun; Kangara, Jayampathi; Arakelyan, Ilya; Thomas, John
2016-05-01
We tune the dimensionality of a strongly interacting degenerate 6 Li Fermi gas from 2D to quasi-2D, by adjusting the radial confinement of pancake-shaped clouds to control the radial chemical potential. In the 2D regime with weak radial confinement, the measured pair binding energies are in agreement with 2D-BCS mean field theory, which predicts dimer pairing energies in the many-body regime. In the qausi-2D regime obtained with increased radial confinement, the measured pairing energy deviates significantly from 2D-BCS theory. In contrast to the pairing energy, the measured radii of the cloud profiles are not fit by 2D-BCS theory in either the 2D or quasi-2D regimes, but are fit in both regimes by a beyond mean field polaron-model of the free energy. Supported by DOE, ARO, NSF, and AFOSR.
Axial Plane Optical Microscopy
Li, Tongcang; Ota, Sadao; Kim, Jeongmin; Wong, Zi Jing; Wang, Yuan; Yin, Xiaobo; Zhang, Xiang
2014-01-01
We present axial plane optical microscopy (APOM) that can, in contrast to conventional microscopy, directly image a sample's cross-section parallel to the optical axis of an objective lens without scanning. APOM combined with conventional microscopy simultaneously provides two orthogonal images of a 3D sample. More importantly, APOM uses only a single lens near the sample to achieve selective-plane illumination microscopy, as we demonstrated by three-dimensional (3D) imaging of fluorescent pollens and brain slices. This technique allows fast, high-contrast, and convenient 3D imaging of structures that are hundreds of microns beneath the surfaces of large biological tissues. PMID:25434770
Lampton, Michael L.; Kim, A.; Akerlof, C.W.; Aldering, G.; Amanullah, R.; Astier, P.; Barrelet, E.; Bebek, C.; Bergstrom, L.; Berkovitz, J.; Bernstein, G.; Bester, M.; Bonissent, A.; Bower, C.; Carithers Jr., W.C.; Commins, E.D.; Day, C.; Deustua, S.E.; DiGennaro,R.; Ealet, A.; Ellis, R.S.; Eriksson, M.; Fruchter, A.; Genat, J.-F.; Goldhaber, G.; Goobar, A.; Groom, D.; Harris, S.E.; Harvey, P.R.; Heetderks, H.D.; Holland, S.E.; Huterer, D.; Karcher, A.; Kolbe, W.; Krieger, B.; Lafever, R.; Lamoureux, J.; Levi, M.E.; Levin, D.S.; Linder,E.V.; Loken, S.C.; Malina, R.; Massey, R.; McKay, T.; McKee, S.P.; Miquel, R.; Mortsell, E.; Mostek, N.; Mufson, S.; Musser, J.; Nugent, P.; Oluseyi, H.; Pain, R.; Palaio, N.; Pankow, D.; Perlmutter, S.; Pratt, R.; Prieto, E.; Refregier, A.; Rhodes, J.; Robinson, K.; Roe, N.; Sholl, M.; Schubnell, M.; Smadja, G.; Smoot, G.; Spadafora, A.; Tarle, G.; Tomasch,A.; von der Lippe, H.; Vincent, R.; Walder, J.-P.; Wang, G.
2002-07-29
The proposed SuperNova/Acceleration Probe (SNAP) mission will have a two-meter class telescope delivering diffraction-limited images to an instrumented 0.7 square-degree field sensitive in the visible and near-infrared wavelength regime. We describe the requirements for the instrument suite and the evolution of the focal plane design to the present concept in which all the instrumentation--visible and near-infrared imagers, spectrograph, and star guiders--share one common focal plane.
NASA Astrophysics Data System (ADS)
Li, He; Lee, Wei-Ning
2017-02-01
The anisotropic mechanical properties (mechanical anisotropy) and view-dependent ultrasonic backscattering (acoustic anisotropy) of striated muscle due to the underlying myofiber arrangement have been well documented, but whether they impact on ultrasound strain imaging (USI) techniques remains unclear. The aim of this study was therefore to investigate the performance of a cross-correlation-based two-dimensional (2D) USI method in anisotropic media under controlled quasi-static compression in silico and in vitro. First, synthetic pre- and post-deformed 2D radiofrequency images of anisotropic phantoms were simulated in two scenarios to examine the individual effect of the mechanical and acoustic anisotropies on strain estimation. In the first scenario, the phantom was defined to be transversely isotropic with the scatterer amplitudes following a zero-mean Gaussian distribution, while in the second scenario, the phantom was defined to be mechanically isotropic with Gaussian distributed scatterer amplitudes correlated along the principal directions of pre-defined fibers. These two anisotropies were then jointly incorporated into the ultrasound image simulation model with additional depth-dependent attenuation. Three imaging planes—the fiber plane with the fiber direction perpendicular to the ultrasound beam (TISperp_fb), the fiber plane with the fiber direction parallel to the beam (TISpara), and the transverse fiber plane (TISperp_cfb)—were studied. The absolute relative error (ARE) of the lateral strain estimates in TISperp_fb (20.99 ± 15.65%) was much higher than that in TISperp_cfb (4.14 ± 3.17%). The ARE in TISpara was unavailable owing to the large spatial extent of false peaks. The effect of tissue anisotropy on the performance of the 2D USI was further confirmed in an in vitro porcine skeletal muscle phantom. The best in-plane strain quality was again shown in TISperp_cfb (elastographic signal-to-noise ratio, or SNRe: >25 d
2D discrete Fourier transform on sliding windows.
Park, Chun-Su
2015-03-01
Discrete Fourier transform (DFT) is the most widely used method for determining the frequency spectra of digital signals. In this paper, a 2D sliding DFT (2D SDFT) algorithm is proposed for fast implementation of the DFT on 2D sliding windows. The proposed 2D SDFT algorithm directly computes the DFT bins of the current window using the precalculated bins of the previous window. Since the proposed algorithm is designed to accelerate the sliding transform process of a 2D input signal, it can be directly applied to computer vision and image processing applications. The theoretical analysis shows that the computational requirement of the proposed 2D SDFT algorithm is the lowest among existing 2D DFT algorithms. Moreover, the output of the 2D SDFT is mathematically equivalent to that of the traditional DFT at all pixel positions.
NASA Astrophysics Data System (ADS)
Miao, Shun; Lucas, Joseph; Liao, Rui
2012-02-01
Minimally invasive abdominal aortic aneurysm (AAA) stenting can be greatly facilitated by overlaying the preoperative 3-D model of the abdominal aorta onto the intra-operative 2-D X-ray images. Accurate 2-D/3-D registration in 3-D space makes the 2-D/3-D overlay robust to the change of C-Arm angulations. By far, the 2-D/3-D registration methods based on simulated X-ray projection images using multiple image planes have been shown to be able to provide satisfactory 3-D registration accuracy. However, one drawback of the intensity-based 2-D/3-D registration methods is that the similarity measure is usually highly non-convex and hence the optimizer can easily be trapped into local minima. User interaction therefore is often needed in the initialization of the position of the 3-D model in order to get a successful 2-D/3-D registration. In this paper, a novel 3-D pose initialization technique is proposed, as an extension of our previously proposed bi-plane 2-D/3-D registration method for AAA intervention [4]. The proposed method detects vessel bifurcation points and spine centerline in both 2-D and 3-D images, and utilizes landmark information to bring the 3-D volume into a 15mm capture range. The proposed landmark detection method was validated on real dataset, and is shown to be able to provide a good initialization for 2-D/3-D registration in [4], thus making the workflow fully automatic.
SU-E-J-245: Sensitivity of FDG PET Feature Analysis in Multi-Plane Vs. Single-Plane Extraction
Harmon, S; Jeraj, R; Galavis, P
2015-06-15
Purpose: Sensitivity of PET-derived texture features to reconstruction methods has been reported for features extracted from axial planes; however, studies often utilize three dimensional techniques. This work aims to quantify the impact of multi-plane (3D) vs. single-plane (2D) feature extraction on radiomics-based analysis, including sensitivity to reconstruction parameters and potential loss of spatial information. Methods: Twenty-three patients with solid tumors underwent [{sup 18}F]FDG PET/CT scans under identical protocols. PET data were reconstructed using five sets of reconstruction parameters. Tumors were segmented using an automatic, in-house algorithm robust to reconstruction variations. 50 texture features were extracted using two Methods: 2D patches along axial planes and 3D patches. For each method, sensitivity of features to reconstruction parameters was calculated as percent difference relative to the average value across reconstructions. Correlations between feature values were compared when using 2D and 3D extraction. Results: 21/50 features showed significantly different sensitivity to reconstruction parameters when extracted in 2D vs 3D (wilcoxon α<0.05), assessed by overall range of variation, Rangevar(%). Eleven showed greater sensitivity to reconstruction in 2D extraction, primarily first-order and co-occurrence features (average Rangevar increase 83%). The remaining ten showed higher variation in 3D extraction (average Range{sub var}increase 27%), mainly co-occurence and greylevel run-length features. Correlation of feature value extracted in 2D and feature value extracted in 3D was poor (R<0.5) in 12/50 features, including eight co-occurrence features. Feature-to-feature correlations in 2D were marginally higher than 3D, ∣R∣>0.8 in 16% and 13% of all feature combinations, respectively. Larger sensitivity to reconstruction parameters were seen for inter-feature correlation in 2D(σ=6%) than 3D (σ<1%) extraction. Conclusion: Sensitivity
MAGNUM2D. Radionuclide Transport Porous Media
Langford, D.W.; Baca, R.G.
1989-03-01
MAGNUM2D was developed to analyze thermally driven fluid motion in the deep basalts below the Paco Basin at the Westinghouse Hanford Site. Has been used in the Basalt Waste Isolation Project to simulate nonisothermal groundwater flow in a heterogeneous anisotropic medium and heat transport in a water/rock system near a high level nuclear waste repository. Allows three representations of the hydrogeologic system: an equivalent porous continuum, a system of discrete, unfilled, and interconnecting fractures separated by impervious rock mass, and a low permeability porous continuum with several discrete, unfilled fractures traversing the medium. The calculations assume local thermodynamic equilibrium between the rock and groundwater, nonisothermal Darcian flow in the continuum portions of the rock, and nonisothermal Poiseuille flow in discrete unfilled fractures. In addition, the code accounts for thermal loading within the elements, zero normal gradient and fixed boundary conditions for both temperature and hydraulic head, and simulation of the temperature and flow independently. The Q2DGEOM preprocessor was developed to generate, modify, plot and verify quadratic two dimensional finite element geometries. The BCGEN preprocessor generates the boundary conditions for head and temperature and ICGEN generates the initial conditions. The GRIDDER postprocessor interpolates nonregularly spaced nodal flow and temperature data onto a regular rectangular grid. CONTOUR plots and labels contour lines for a function of two variables and PARAM plots cross sections and time histories for a function of time and one or two spatial variables. NPRINT generates data tables that display the data along horizontal or vertical cross sections. VELPLT differentiates the hydraulic head and buoyancy data and plots the velocity vectors. The PATH postprocessor plots flow paths and computes the corresponding travel times.
MAGNUM2D. Radionuclide Transport Porous Media
Langford, D.W.; Baca, R.G.
1988-08-01
MAGNUM2D was developed to analyze thermally driven fluid motion in the deep basalts below the Paco Basin at the Westinghouse Hanford Site. Has been used in the Basalt Waste Isolation Project to simulate nonisothermal groundwater flow in a heterogeneous anisotropic medium and heat transport in a water/rock system near a high level nuclear waste repository. Allows three representations of the hydrogeologic system: an equivalent porous continuum, a system of discrete, unfilled, and interconnecting fractures separated by impervious rock mass, and a low permeability porous continuum with several discrete, unfilled fractures traversing the medium. The calculation assumes local thermodynamic equilibrium between the rock and groundwater, nonisothermal Darcian flow in the continuum portions of the rock, and nonisothermal Poiseuille flow in discrete unfilled fractures. In addition, the code accounts for thermal loading within the elements, zero normal gradient and fixed boundary conditions for both temperature and hydraulic head, and simulation of the temperature and flow independently. The Q2DGEOM preprocessor was developed to generate, modify, plot and verify quadratic two dimensional finite element geometries. The BCGEN preprocessor generates the boundary conditions for head and temperature and ICGEN generates the initial conditions. The GRIDDER postprocessor interpolates nonregularly spaced nodal flow and temperature data onto a regular rectangular grid. CONTOUR plots and labels contour lines for a function of two variables and PARAM plots cross sections and time histories for a function of time and one or two spatial variables. NPRINT generates data tables that display the data along horizontal or vertical cross sections. VELPLT differentiates the hydraulic head and buoyancy data and plots the velocity vectors. The PATH postprocessor plots flow paths and computes the corresponding travel times.
Out of plane analysis for composite structures
NASA Technical Reports Server (NTRS)
Paul, P. C.; Saff, C. R.; Sanger, Kenneth B.; Mahler, M. A.; Kan, Han Pin; Kautz, Edward F.
1990-01-01
Simple two dimensional analysis techniques were developed to aid in the design of strong joints for integrally stiffened/bonded composite structures subjected to out of plane loads. It was found that most out of plane failures were due to induced stresses arising from rapid changes in load path direction or geometry, induced stresses due to changes in geometry caused by buckling, or direct stresses produced by fuel pressure or bearing loads. While the analysis techniques were developed to address a great variety of out of plane loading conditions, they were primarily derived to address the conditions described above. The methods were developed and verified using existing element test data. The methods were demonstrated using the data from a test failure of a high strain wingbox that was designed, built, and tested under a previous program. Subsequently, a set of design guidelines were assembled to assist in the design of safe, strong integral composite structures using the analysis techniques developed.
Generates 2D Input for DYNA NIKE & TOPAZ
Hallquist, J. O.; Sanford, Larry
1996-07-15
MAZE is an interactive program that serves as an input and two-dimensional mesh generator for DYNA2D, NIKE2D, TOPAZ2D, and CHEMICAL TOPAZ2D. MAZE also generates a basic template for ISLAND input. MAZE has been applied to the generation of input data to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.
MAZE96. Generates 2D Input for DYNA NIKE & TOPAZ
Sanford, L.; Hallquist, J.O.
1992-02-24
MAZE is an interactive program that serves as an input and two-dimensional mesh generator for DYNA2D, NIKE2D, TOPAZ2D, and CHEMICAL TOPAZ2D. MAZE also generates a basic template for ISLAND input. MAZE has been applied to the generation of input data to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.
NASA Astrophysics Data System (ADS)
Lin, Yi; Connell, John W.
2012-10-01
The recent surge in graphene research has stimulated interest in the investigation of various 2-dimensional (2D) nanomaterials. Among these materials, the 2D boron nitride (BN) nanostructures are in a unique position. This is because they are the isoelectric analogs to graphene structures and share very similar structural characteristics and many physical properties except for the large band gap. The main forms of the 2D BN nanostructures include nanosheets (BNNSs), nanoribbons (BNNRs), and nanomeshes (BNNMs). BNNRs are essentially BNNSs with narrow widths in which the edge effects become significant; BNNMs are also variations of BNNSs, which are supported on certain metal substrates where strong interactions and the lattice mismatch between the substrate and the nanosheet result in periodic shallow regions on the nanosheet surface. Recently, the hybrids of 2D BN nanostructures with graphene, in the form of either in-plane hybrids or inter-plane heterolayers, have also drawn much attention. In particular, the BNNS-graphene heterolayer architectures are finding important electronic applications as BNNSs may serve as excellent dielectric substrates or separation layers for graphene electronic devices. In this article, we first discuss the structural basics, spectroscopic signatures, and physical properties of the 2D BN nanostructures. Then, various top-down and bottom-up preparation methodologies are reviewed in detail. Several sections are dedicated to the preparation of BNNRs, BNNMs, and BNNS-graphene hybrids, respectively. Following some more discussions on the applications of these unique materials, the article is concluded with a summary and perspectives of this exciting new field.
Lin, Yi; Connell, John W
2012-11-21
The recent surge in graphene research has stimulated interest in the investigation of various 2-dimensional (2D) nanomaterials. Among these materials, the 2D boron nitride (BN) nanostructures are in a unique position. This is because they are the isoelectric analogs to graphene structures and share very similar structural characteristics and many physical properties except for the large band gap. The main forms of the 2D BN nanostructures include nanosheets (BNNSs), nanoribbons (BNNRs), and nanomeshes (BNNMs). BNNRs are essentially BNNSs with narrow widths in which the edge effects become significant; BNNMs are also variations of BNNSs, which are supported on certain metal substrates where strong interactions and the lattice mismatch between the substrate and the nanosheet result in periodic shallow regions on the nanosheet surface. Recently, the hybrids of 2D BN nanostructures with graphene, in the form of either in-plane hybrids or inter-plane heterolayers, have also drawn much attention. In particular, the BNNS-graphene heterolayer architectures are finding important electronic applications as BNNSs may serve as excellent dielectric substrates or separation layers for graphene electronic devices. In this article, we first discuss the structural basics, spectroscopic signatures, and physical properties of the 2D BN nanostructures. Then, various top-down and bottom-up preparation methodologies are reviewed in detail. Several sections are dedicated to the preparation of BNNRs, BNNMs, and BNNS-graphene hybrids, respectively. Following some more discussions on the applications of these unique materials, the article is concluded with a summary and perspectives of this exciting new field.
Quasi 2D Materials: Raman Nanometrology and Thermal Management Applications
NASA Astrophysics Data System (ADS)
Shahil, Khan Mohammad Farhan
Quasi two-dimensional (2D) materials obtained by the "graphene-like" exfoliation attracted tremendous attention. Such materials revealed unique electronic, thermal and optical properties, which can be potentially used in electronics, thermal management and energy conversion. This dissertation research addresses two separate but synergetic problems: (i) preparation and optical characterization of quasi-2D films of the bismuth-telluride (Bi 2Te3) family of materials, which demonstrate both thermoelectric and topological insulator properties; and (ii) investigation of thermal properties of composite materials prepared with graphene and few-layer graphene (FLG). The first part of dissertation reports properties of the exfoliated few-quintuple layers of Bi2Te3, Bi2Se3 and Sb 2Te3. Both non-resonant and resonant Raman scattering spectra have been investigated. It was found that the crystal symmetry breaking in few-quintuple films results in appearance of A1u-symmetry Raman peaks, which are not active in the bulk crystals. The scattering spectra measured under the 633-nm wavelength excitation reveals a number of resonant features, which could be used for analysis of the electronic and phonon processes in these materials. The obtained results help to understand the physical mechanisms of Raman scattering in the few-quintuple-thick films and can be used for nanometrology of topological insulator films on various substrates. The second part of the dissertation is dedicated to investigation of properties of composite materials prepared with graphene and FLG. It was found that the optimized mixture of graphene and multilayer graphene---produced by the high-yield inexpensive liquid-phase-exfoliation technique---can lead to an extremely strong enhancement of the cross-plane thermal conductivity K of the composite. The "laser flash" measurements revealed a record-high enhancement of K by 2300 % in the graphene-based polymer at the filler loading fraction f =10 vol. %. It was
Precise measurement of planeness.
Schulz, G; Schwider, J
1967-06-01
Interference methods are reviewed-particularly those developed at the German Academy of Sciences in Berlin-with which the deviations of an optically flat surface from the ideal plane can be measured with a high degree of exactness. One aid to achieve this is the relative methods which measure the differences in planeness between two surfaces. These are then used in the absolute methods which determine the absolute planeness of a surface. This absolute determination can be effected in connection with a liquid surface, or (as done by the authors) only by suitable evaluation of relative measurements between unknown plates in various positional combinations. Experimentally, one uses two- or multiple-beam interference fringes of equal thickness(1) or of equal inclination. The fringes are observed visually, scanned, or photographed, and in part several wavelengths or curves of equal density (Aquidensiten) are employed. The survey also brings the following new methods: a relative method, where, with the aid of fringes of superposition, the fringe separation is subdivided equidistantly thus achieving an increase of measuring precision, and an absolute method which determines the deviations of a surface from ideal planeness along arbitrary central sections, without a liquid surface, from four relative interference photographs.
ERIC Educational Resources Information Center
Greenman, Geri
2001-01-01
Describes an assignment that was used in an advanced drawing class in which the students created self-portraits, breaking up their images using planes and angles to suggest their bone structure. Explains that the students also had to include three realistic portions in their drawings. (CMK)
Reference measurements on a Francis model turbine with 2D Laser-Doppler-Anemometry
NASA Astrophysics Data System (ADS)
Frey, A.; Kirschner, O.; Riedelbauch, S.; Jester-Zuerker, R.; Jung, A.
2016-11-01
To validate the investigations of a high-resolution CFD simulation of a Francis turbine, measurements with 2D Laser-Doppler-Anemometry are carried out. The turbine is operated in part load, where a rotating vortex rope occurs. To validate both, mean velocities and velocity fluctuations, the measurements are classified relative to the vortex rope position. Several acrylic glass windows are installed in the turbine walls such as upstream of the spiral case inlet, in the vaneless space and in the draft tube. The current investigation is focused on a measurement plane below the runner. 2D velocity components are measured on this whole plane by measuring several narrow spaced radial lines. To avoid optical refraction of the laser beam a plan parallel window is inserted in the cone wall. The laser probe is positioned with a 2D traverse system consisting of a circumferential rail and a radial aligned linear traverse. The velocity data are synchronized with the rotational frequency of the rotating vortex rope. The results of one measurement line show the dependency of the axial and circumferential velocities on the vortex rope position.
Molecular beam epitaxy of 2D-layered gallium selenide on GaN substrates
NASA Astrophysics Data System (ADS)
Lee, Choong Hee; Krishnamoorthy, Sriram; O'Hara, Dante J.; Brenner, Mark R.; Johnson, Jared M.; Jamison, John S.; Myers, Roberto C.; Kawakami, Roland K.; Hwang, Jinwoo; Rajan, Siddharth
2017-03-01
Large area epitaxy of two-dimensional (2D) layered materials with high material quality is a crucial step in realizing novel device applications based on 2D materials. In this work, we report high-quality, crystalline, large-area gallium selenide (GaSe) films grown on bulk substrates such as c-plane sapphire and gallium nitride (GaN) using a valved cracker source for Se. (002)-Oriented GaSe with random in-plane orientation of domains was grown on sapphire and GaN substrates at a substrate temperature of 350-450 °C with complete surface coverage. Higher growth temperature (575 °C) resulted in the formation of single-crystalline ɛ-GaSe triangular domains with six-fold symmetry confirmed by in-situ reflection high electron energy diffraction and off-axis x-ray diffraction. A two-step growth method involving high temperature nucleation of single crystalline domains and low temperature growth to enhance coalescence was adopted to obtain continuous (002)-oriented GaSe with an epitaxial relationship with the substrate. While six-fold symmetry was maintained in the two step growth, β-GaSe phase was observed in addition to the dominant ɛ-GaSe in cross-sectional scanning transmission electron microscopy images. This work demonstrates the potential of growing high quality 2D-layered materials using molecular beam epitaxy and can be extended to the growth of other transition metal chalcogenides.
CYP2D7 Sequence Variation Interferes with TaqMan CYP2D6*15 and *35 Genotyping
Riffel, Amanda K.; Dehghani, Mehdi; Hartshorne, Toinette; Floyd, Kristen C.; Leeder, J. Steven; Rosenblatt, Kevin P.; Gaedigk, Andrea
2016-01-01
TaqMan™ genotyping assays are widely used to genotype CYP2D6, which encodes a major drug metabolizing enzyme. Assay design for CYP2D6 can be challenging owing to the presence of two pseudogenes, CYP2D7 and CYP2D8, structural and copy number variation and numerous single nucleotide polymorphisms (SNPs) some of which reflect the wild-type sequence of the CYP2D7 pseudogene. The aim of this study was to identify the mechanism causing false-positive CYP2D6*15 calls and remediate those by redesigning and validating alternative TaqMan genotype assays. Among 13,866 DNA samples genotyped by the CompanionDx® lab on the OpenArray platform, 70 samples were identified as heterozygotes for 137Tins, the key SNP of CYP2D6*15. However, only 15 samples were confirmed when tested with the Luminex xTAG CYP2D6 Kit and sequencing of CYP2D6-specific long range (XL)-PCR products. Genotype and gene resequencing of CYP2D6 and CYP2D7-specific XL-PCR products revealed a CC>GT dinucleotide SNP in exon 1 of CYP2D7 that reverts the sequence to CYP2D6 and allows a TaqMan assay PCR primer to bind. Because CYP2D7 also carries a Tins, a false-positive mutation signal is generated. This CYP2D7 SNP was also responsible for generating false-positive signals for rs769258 (CYP2D6*35) which is also located in exon 1. Although alternative CYP2D6*15 and *35 assays resolved the issue, we discovered a novel CYP2D6*15 subvariant in one sample that carries additional SNPs preventing detection with the alternate assay. The frequency of CYP2D6*15 was 0.1% in this ethnically diverse U.S. population sample. In addition, we also discovered linkage between the CYP2D7 CC>GT dinucleotide SNP and the 77G>A (rs28371696) SNP of CYP2D6*43. The frequency of this tentatively functional allele was 0.2%. Taken together, these findings emphasize that regardless of how careful genotyping assays are designed and evaluated before being commercially marketed, rare or unknown SNPs underneath primer and/or probe regions can impact
CYP2D7 Sequence Variation Interferes with TaqMan CYP2D6 (*) 15 and (*) 35 Genotyping.
Riffel, Amanda K; Dehghani, Mehdi; Hartshorne, Toinette; Floyd, Kristen C; Leeder, J Steven; Rosenblatt, Kevin P; Gaedigk, Andrea
2015-01-01
TaqMan™ genotyping assays are widely used to genotype CYP2D6, which encodes a major drug metabolizing enzyme. Assay design for CYP2D6 can be challenging owing to the presence of two pseudogenes, CYP2D7 and CYP2D8, structural and copy number variation and numerous single nucleotide polymorphisms (SNPs) some of which reflect the wild-type sequence of the CYP2D7 pseudogene. The aim of this study was to identify the mechanism causing false-positive CYP2D6 (*) 15 calls and remediate those by redesigning and validating alternative TaqMan genotype assays. Among 13,866 DNA samples genotyped by the CompanionDx® lab on the OpenArray platform, 70 samples were identified as heterozygotes for 137Tins, the key SNP of CYP2D6 (*) 15. However, only 15 samples were confirmed when tested with the Luminex xTAG CYP2D6 Kit and sequencing of CYP2D6-specific long range (XL)-PCR products. Genotype and gene resequencing of CYP2D6 and CYP2D7-specific XL-PCR products revealed a CC>GT dinucleotide SNP in exon 1 of CYP2D7 that reverts the sequence to CYP2D6 and allows a TaqMan assay PCR primer to bind. Because CYP2D7 also carries a Tins, a false-positive mutation signal is generated. This CYP2D7 SNP was also responsible for generating false-positive signals for rs769258 (CYP2D6 (*) 35) which is also located in exon 1. Although alternative CYP2D6 (*) 15 and (*) 35 assays resolved the issue, we discovered a novel CYP2D6 (*) 15 subvariant in one sample that carries additional SNPs preventing detection with the alternate assay. The frequency of CYP2D6 (*) 15 was 0.1% in this ethnically diverse U.S. population sample. In addition, we also discovered linkage between the CYP2D7 CC>GT dinucleotide SNP and the 77G>A (rs28371696) SNP of CYP2D6 (*) 43. The frequency of this tentatively functional allele was 0.2%. Taken together, these findings emphasize that regardless of how careful genotyping assays are designed and evaluated before being commercially marketed, rare or unknown SNPs underneath primer
Asymmetric magnetic reconnection with out-of-plane shear flows in a two dimensional hybrid model
Wang, Lin; Wang, Xiao-Gang; Wang, Xian-Qu; Liu, Yue
2015-05-15
Effects of out-of-plane shear flows on asymmetric magnetic reconnect are investigated in a two-dimensional (2D) hybrid model with an initial Harris sheet equilibrium. It is found that the out-of-plane flow with an in-plane shear can significantly change the asymmetric reconnection process as well as the related geometry. The magnetic flux, out-of-plane magnetic field, in-plane flow vorticity, plasma density, and the reconnection rate are discussed in detail. The results are in comparison with the cases without the shear flows to further understand the effect.
Couette shear of an ideal 2D photo-elastic granular system
NASA Astrophysics Data System (ADS)
Behringer, Robert; Zheng, Hu; Barés, Jonathan; Wang, Dong
2016-11-01
In this study, Couette shear experiments are conducted using 2D photoelastic granular particles, which allows us to apply infinite shear strain to the granular system. We obtain force information at the granular scale using the calibrated photo-elastic grain force response. The whole granular system is density matched in salt solution, which guarantees an ideal 2D system without basal friction between the particles and the table. The viscosity is negligible at the very small shear strain rate (0.017 rpm). This talk will address two main points: i) how does the system reach a jammed state; ii) how does system reach a long term stable state and what are the properties of that state. We acknowledge support from NSF Grant No. DMR1206351, NASA Grant No. NNX15AD38G and the W.M. Keck Foundation.
Acoustic backscatter and effective scatterer size estimates using a 2D CMUT transducer
NASA Astrophysics Data System (ADS)
Liu, W.; Zagzebski, J. A.; Hall, T. J.; Madsen, E. L.; Varghese, T.; Kliewer, M. A.; Panda, S.; Lowery, C.; Barnes, S.
2008-08-01
Compared to conventional piezoelectric transducers, new capacitive microfabricated ultrasonic transducer (CMUT) technology is expected to offer a broader bandwidth, higher resolution and advanced 3D/4D imaging inherent in a 2D array. For ultrasound scatterer size imaging, a broader frequency range provides more information on frequency-dependent backscatter, and therefore, generally more accurate size estimates. Elevational compounding, which can significantly reduce the large statistical fluctuations associated with parametric imaging, becomes readily available with a 2D array. In this work, we show phantom and in vivo breast tumor scatterer size image results using a prototype 2D CMUT transducer (9 MHz center frequency) attached to a clinical scanner. A uniform phantom with two 1 cm diameter spherical inclusions of slightly smaller scatterer size was submerged in oil and scanned by both the 2D CMUT and a conventional piezoelectric linear array transducer. The attenuation and scatterer sizes of the sample were estimated using a reference phantom method. RF correlation analysis was performed using the data acquired by both transducers. The 2D CMUT results indicate that at a 2 cm depth (near the transmit focus for both transducers) the correlation coefficient reduced to less than 1/e for 0.2 mm lateral or 0.25 mm elevational separation between acoustic scanlines. For the conventional array this level of decorrelation requires a 0.3 mm lateral or 0.75 mm elevational translation. Angular and/or elevational compounding is used to reduce the variance of scatterer size estimates. The 2D array transducer acquired RF signals from 140 planes over a 2.8 cm elevational direction. If no elevational compounding is used, the fractional standard deviation of the size estimates is about 12% of the mean size estimate for both the spherical inclusion and the background. Elevational compounding of 11 adjacent planes reduces it to 7% for both media. Using an experimentally estimated
Acoustic backscatter and effective scatterer size estimates using a 2D CMUT transducer
Liu, W; Zagzebski, J A; Hall, T J; Madsen, E L; Varghese, T; Kliewer, M A; Panda, S; Lowery, C; Barnes, S
2009-01-01
Compared to conventional piezoelectric transducers, new capacitive microfabricated ultrasonic transducer (CMUT) technology is expected to offer a broader bandwidth, higher resolution and advanced 3D/4D imaging inherent in a 2D array. For ultrasound scatterer size imaging, a broader frequency range provides more information on frequency-dependent backscatter, and therefore, generally more accurate size estimates. Elevational compounding, which can significantly reduce the large statistical fluctuations associated with parametric imaging, becomes readily available with a 2D array. In this work, we show phantom and in vivo breast tumor scatterer size image results using a prototype 2D CMUT transducer (9 MHz center frequency) attached to a clinical scanner. A uniform phantom with two 1 cm diameter spherical inclusions of slightly smaller scatterer size was submerged in oil and scanned by both the 2D CMUT and a conventional piezoelectric linear array transducer. The attenuation and scatterer sizes of the sample were estimated using a reference phantom method. RF correlation analysis was performed using the data acquired by both transducers. The 2D CMUT results indicate that at a 2 cm depth (near the transmit focus for both transducers) the correlation coefficient reduced to less than 1/e for 0.2 mm lateral or 0.25 mm elevational separation between acoustic scanlines. For the conventional array this level of decorrelation requires a 0.3 mm lateral or 0.75 mm elevational translation. Angular and/or elevational compounding is used to reduce the variance of scatterer size estimates. The 2D array transducer acquired RF signals from 140 planes over a 2.8 cm elevational direction. If no elevational compounding is used, the fractional standard deviation of the size estimates is about 12% of the mean size estimate for both the spherical inclusion and the background. Elevational compounding of 11 adjacent planes reduces it to 7% for both media. Using an experimentally estimated
1989-03-01
Th usr a toente aninteer a thca sms b esta 1 Fp-ocsing 2. Enter P1 values, lwgt, ldig - > 9 Table I give us proper values. Table 1. PARAMETER TABLE...necessary and identify by block number) In this thesis a control systems analysis package is developed using parameter plane methods. It is an interactive...designer is able to choose values of the parameters which provide a good compromise between cost and dynamic behavior. 20 Distribution Availability of
NASA Technical Reports Server (NTRS)
Tang, H. T.; Hofmann, R.; Yee, G.; Vaughan, D. K.
1980-01-01
Transient, nonlinear soil-structure interaction simulations of an Electric Power Research Institute, SIMQUAKE experiment were performed using the large strain, time domain STEALTH 2D code and a cyclic, kinematically hardening cap soil model. Results from the STEALTH simulations were compared to identical simulations performed with the TRANAL code and indicate relatively good agreement between all the STEALTH and TRANAL calculations. The differences that are seen can probably be attributed to: (1) large (STEALTH) vs. small (TRANAL) strain formulation and/or (2) grid discretization differences.
Residual lens effects in 2D mode of auto-stereoscopic lenticular-based switchable 2D/3D displays
NASA Astrophysics Data System (ADS)
Sluijter, M.; IJzerman, W. L.; de Boer, D. K. G.; de Zwart, S. T.
2006-04-01
We discuss residual lens effects in multi-view switchable auto-stereoscopic lenticular-based 2D/3D displays. With the introduction of a switchable lenticular, it is possible to switch between a 2D mode and a 3D mode. The 2D mode displays conventional content, whereas the 3D mode provides the sensation of depth to the viewer. The uniformity of a display in the 2D mode is quantified by the quality parameter modulation depth. In order to reduce the modulation depth in the 2D mode, birefringent lens plates are investigated analytically and numerically, by ray tracing. We can conclude that the modulation depth in the 2D mode can be substantially decreased by using birefringent lens plates with a perfect index match between lens material and lens plate. Birefringent lens plates do not disturb the 3D performance of a switchable 2D/3D display.
Higher-Order Neural Networks Applied to 2D and 3D Object Recognition
NASA Technical Reports Server (NTRS)
Spirkovska, Lilly; Reid, Max B.
1994-01-01
A Higher-Order Neural Network (HONN) can be designed to be invariant to geometric transformations such as scale, translation, and in-plane rotation. Invariances are built directly into the architecture of a HONN and do not need to be learned. Thus, for 2D object recognition, the network needs to be trained on just one view of each object class, not numerous scaled, translated, and rotated views. Because the 2D object recognition task is a component of the 3D object recognition task, built-in 2D invariance also decreases the size of the training set required for 3D object recognition. We present results for 2D object recognition both in simulation and within a robotic vision experiment and for 3D object recognition in simulation. We also compare our method to other approaches and show that HONNs have distinct advantages for position, scale, and rotation-invariant object recognition. The major drawback of HONNs is that the size of the input field is limited due to the memory required for the large number of interconnections in a fully connected network. We present partial connectivity strategies and a coarse-coding technique for overcoming this limitation and increasing the input field to that required by practical object recognition problems.
Osiry, H.; Cano, A.; Lemus-Santana, A.A.; Rodríguez, A.; Carbonio, R.E.; Reguera, E.
2015-10-15
This contribution discusses the intercalation of imidazole and its 2-ethyl derivative, and pyridine in 2D copper nitroprusside. In the interlayer region, neighboring molecules remain interacting throu gh their dipole and quadrupole moments, which supports the solid 3D crystal structure. The crystal structure of this series of intercalation compounds was solved and refined from powder X-ray diffraction patterns complemented with spectroscopic information. The intermolecular interactions were studied from the refined crystal structures and low temperature magnetic measurements. Due to strong attractive forces between neighboring molecules, the resulting π–π cloud overlapping enables the ferromagnetic coupling between metal centers on neighboring layers, which was actually observed for the solids containing imidazole and pyridine as intercalated molecules. For these two solids, the magnetic data were properly described with a model of six neighbors. For the solid containing 2-ethylimidazole and for 2D copper nitroprusside, a model of four neighbors in a plane is sufficient to obtain a reliable data fitting. - Highlights: • Intercalation of organic molecules in 2D copper (II) nitroprusside. • Molecular properties of intercalation compounds of 2D copper (II) nitroprusside. • Magnetic properties of hybrid inorganic–organic solids. • Hybrid inorganic–organic 3D framework.
Electrostatic 2D assembly of bionanoparticles on a cationic lipid monolayer.
NASA Astrophysics Data System (ADS)
Kewalramani, Sumit; Wang, Suntao; Fukuto, Masafumi; Yang, Lin; Niu, Zhongwei; Nguyen, Giang; Wang, Qian
2010-03-01
We present a grazing-incidence small-angle X-ray scattering (GISAXS) study on 2D assembly of cowpea mosaic virus (CPMV) under a mixed cationic-zwitterionic (DMTAP^+-DMPC) lipid monolayer at the air-water interface. The inter-particle and particle-lipid electrostatic interactions were varied by controlling the subphase pH and the membrane charge density. GISAXS data show that 2D crystals of CPMV are formed above a threshold membrane charge density and only in a narrow pH range just above CPMV's isoelectric point, where the charge on CPMV is expected to be weakly negative. The particle density for the 2D crystals is similar to that for the densest lattice plane in the 3D crystals of CPMV. The results show that the 2D crystallization is achieved in the part of the phase space where the electrostatic interactions are expected to maximize the adsorption of CPMV onto the lipid membrane. This electrostatics-based strategy for controlling interfacial nanoscale assembly should be generally applicable to other nanoparticles.
Mechanical characterization of 2D, 2D stitched, and 3D braided/RTM materials
NASA Technical Reports Server (NTRS)
Deaton, Jerry W.; Kullerd, Susan M.; Portanova, Marc A.
1993-01-01
Braided composite materials have potential for application in aircraft structures. Fuselage frames, floor beams, wing spars, and stiffeners are examples where braided composites could find application if cost effective processing and damage tolerance requirements are met. Another important consideration for braided composites relates to their mechanical properties and how they compare to the properties of composites produced by other textile composite processes being proposed for these applications. Unfortunately, mechanical property data for braided composites do not appear extensively in the literature. Data are presented in this paper on the mechanical characterization of 2D triaxial braid, 2D triaxial braid plus stitching, and 3D (through-the-thickness) braid composite materials. The braided preforms all had the same graphite tow size and the same nominal braid architectures, (+/- 30 deg/0 deg), and were resin transfer molded (RTM) using the same mold for each of two different resin systems. Static data are presented for notched and unnotched tension, notched and unnotched compression, and compression after impact strengths at room temperature. In addition, some static results, after environmental conditioning, are included. Baseline tension and compression fatigue results are also presented, but only for the 3D braided composite material with one of the resin systems.
A novel explicit 2D+t cyclic shape model applied to echocardiography.
Casero, Ramón; Noble, J Alison
2008-01-01
In this paper, we propose a novel explicit 2D+t cyclic shape model that extends the Point Distribution Model (PDM) to shapes like myocardial contours with cyclic dynamics. We also propose an extension to Procrustes alignment that removes pose and subject size variability while maintaining dynamic effects. Our model draws on ideas from Principal Component Analysis (PCA), Multidimensional Scaling (MDS) and Kernel PCA (KPCA) and solves 3 shortcomings of previous implicit models: (1) cardiac cycles in the data set do not each need to have the same number of frames, (2) the required number of subjects for statistically significant results is substantially reduced and (3) the displacement of contour points incorporates time as an explicit variable. We illustrate our method by computing models of the myocardium in the 4 principal planes of 2D+t echocardiography data.
The Effect of Ethnicity on 2D and 3D Frontomaxillary Facial Angle Measurement in the First Trimester
Clarke, Jill
2013-01-01
Objectives. To determine the existence and extent of ethnic differences in 2D or 3D fetal frontomaxillary facial angle (FMFA) measurements. Methods. During routine 11–14 weeks nuchal translucency screening undertaken in a private ultrasound practice in Sydney, Australia, 2D images and 3D volumes of the fetal profile were collected from consenting patients. FMFA was measured on a frozen 2D ultrasound image in the appropriate plane and, after a delay of at least 48 hours, was also measured on the reconstructed 3D ultrasound volume offline. Results. Overall 416 patients were included in the study; 220 Caucasian, 108 north Asian, 36 east Asian and 52 south Asian patients. Caucasians had significantly lower median FMFA measurements than Asians in both 2D (2.2°; P < 0.001) and 3D (3.4°; P < 0.001) images. Median 2D measurements were significantly higher than 3D measurements in the Caucasian and south Asian groups (P < 0.001 and P = 0.04), but not in north and east Asian groups (P = 0.08 and P = 0.41). Conclusions. Significant ethnic variations in both 2D and 3D FMFA measurements exist. These differences may indicate the need to establish ethnic-specific reference ranges for both 2D and 3D imaging. PMID:24288543
Li, Ming; Song, Mengyao; Wu, Guitai; Tang, Zhenyu; Sun, Yunfeng; He, Yunbin; Li, Jinhua; Li, Lei; Gu, Haoshuang; Liu, Xiong; Ma, Chuang; Peng, Zefei; Ai, Zhaoquan; Lewis, David J
2017-04-07
In many 2D materials reported thus far, the forces confining atoms in a 2D plane are often strong interactions, such as covalent bonding. Herein, the first demonstration that hydrogen (H)-bonding can be utilized to assemble polydiacetylene (a conductive polymer) toward a 2D material, which is stable enough to be free-standing, is shown. The 2D material is well characterized by a large number of techniques (mainly different microscopy techniques). The H-bonding allows splitting of the material into ribbons, which can reassemble, similar to a zipper, leading to the first example of a healable 2D material. Moreover, such technology can easily create 2D, organic, conductive nanowire arrays with sub-2-nm resolution. This material may have potential applications in stretchable electronics and nanowire cross-bar arrays.
Antenna arrays for producing plane whistler waves
NASA Astrophysics Data System (ADS)
Stenzel, Reiner; Urrutia, J. Manuel
2014-10-01
Linear whistler modes with ω ~= 0 . 3ωce <<ωpe are excited in a large laboratory plasma with magnetic loop antennas. A single antenna always produces a spatially bounded wave packet whose propagation cannot be directly compared to plane wave theories. By superimposing the fields from spatially separated antennas, the wavenumber along the antenna array can be nearly eliminated. 2D arrays nearly produce plane waves. The angle θ of wave propagation has been varied by a phase shift along the array. The refractive index surface n (θ) has been measured. The parallel phase and group velocities for Gendrin modes has been demonstrated. The interference between two oblique plane whistlers creates a whistler ``waveguide'' mode, i.e. standing waves for k ⊥B0 and propagation for k | |B0 . It also describes the reflection of oblique whistlers from a sharp discontinuity in the refractive index or conductivity. Radial reflections are also a dominant factor in small plasma columns of helicon devices. These results are of interest to space and laboratory plasmas. Work supported by NSF/DOE.
Snapshot 2D tomography via coded aperture x-ray scatter imaging
MacCabe, Kenneth P.; Holmgren, Andrew D.; Tornai, Martin P.; Brady, David J.
2015-01-01
This paper describes a fan beam coded aperture x-ray scatter imaging system which acquires a tomographic image from each snapshot. This technique exploits cylindrical symmetry of the scattering cross section to avoid the scanning motion typically required by projection tomography. We use a coded aperture with a harmonic dependence to determine range, and a shift code to determine cross-range. Here we use a forward-scatter configuration to image 2D objects and use serial exposures to acquire tomographic video of motion within a plane. Our reconstruction algorithm also estimates the angular dependence of the scattered radiance, a step toward materials imaging and identification. PMID:23842254
NASA Astrophysics Data System (ADS)
Kamas, Tuncay; Lin, Bin; Giurgiutiu, Victor
2013-04-01
This paper discusses theoretical analysis of electro-mechanical impedance spectroscopy (EMIS) of piezoelectric wafer active sensor (PWAS). Both free and constrained PWAS EMIS models are developed for in-plane (lengthwise) and outof plane (thickness wise) mode. The paper starts with the general piezoelectric constitutive equations that express the linear relation between stress, strain, electric field and electric displacement. This is followed by the PWAS EMIS models with two assumptions: 1) constant electric displacement in thickness direction (D3) for out-of-plane mode; 2) constant electric field in thickness direction (E3) for in-plane mode. The effects of these assumptions on the free PWAS in-plane and out-of-plane EMIS models are studied and compared. The effects of internal damping of PWAS are considered in the analytical EMIS models. The analytical EMIS models are verified by Coupled Field Finite Element Method (CF-FEM) simulations and by experimental measurements. The extent of the agreement between the analytical and experimental EMIS results is discussed. The paper ends with summary, conclusions, and suggestions for future work.
Synthetic Covalent and Non-Covalent 2D Materials.
Boott, Charlotte E; Nazemi, Ali; Manners, Ian
2015-11-16
The creation of synthetic 2D materials represents an attractive challenge that is ultimately driven by their prospective uses in, for example, electronics, biomedicine, catalysis, sensing, and as membranes for separation and filtration. This Review illustrates some recent advances in this diverse field with a focus on covalent and non-covalent 2D polymers and frameworks, and self-assembled 2D materials derived from nanoparticles, homopolymers, and block copolymers.
Influence of Aerodynamic Strain Rate on Local Extinction in Turbulent Non-premixed Jet Flames
NASA Astrophysics Data System (ADS)
Ramachandran, Aravind; Narayanaswamy, Venkateswaran; Lyons, Kevin
2016-11-01
2-D velocity field measurements obtained from Particle Image Velocimetry (PIV) are used to obtain aerodynamic strain rate information in regions of local extinction in lifted turbulent non-premixed methane jet flames in coflow. Diluting the coflow to reduce the oxygen molefraction results in increased occurrences of local extinction. Statistical analysis is performed to correlate regions of high local strain rate with local extinctions in both air coflow and diluted coflow cases to study the influence of strain rate against vortical structures in extinguishing the flame front. A comparison is also made with heated and vitiated coflow cases, where autoignition is a flame stabilization mechanism and influenced by local strain rate. At high jet exit velocities (Ux > > Ur), the out-of-plane strain rate component can be neglected but the convection of extinguished pockets into the measurement plane needs to be resolved by stereoscopic (3-D) measurements which will be done in a future work. This work has been supported by the U.S. Army Research Office (Contracts W911NF1210140 and W911NF1610087) Dr. Ralph Anthenien, Technical Monitor, ARO.
Novel Two-Dimensional Silicon Dioxide with in-Plane Negative Poisson's Ratio.
Gao, Zhibin; Dong, Xiao; Li, Nianbei; Ren, Jie
2017-02-08
Silicon dioxide or silica, normally existing in various bulk crystalline and amorphous forms, was recently found to possess a two-dimensional structure. In this work, we use ab initio calculation and evolutionary algorithm to unveil three new two-dimensional (2D) silica structures whose thermal, dynamical, and mechanical stabilities are compared with many typical bulk silica. In particular, we find that all three of these 2D silica structures have large in-plane negative Poisson's ratios with the largest one being double of penta graphene and three times of borophenes. The negative Poisson's ratio originates from the interplay of lattice symmetry and Si-O tetrahedron symmetry. Slab silica is also an insulating 2D material with the highest electronic band gap (>7 eV) among reported 2D structures. These exotic 2D silica with in-plane negative Poisson's ratios and widest band gaps are expected to have great potential applications in nanomechanics and nanoelectronics.
Epitaxial 2D SnSe2/ 2D WSe2 van der Waals Heterostructures.
Aretouli, Kleopatra Emmanouil; Tsoutsou, Dimitra; Tsipas, Polychronis; Marquez-Velasco, Jose; Aminalragia Giamini, Sigiava; Kelaidis, Nicolaos; Psycharis, Vassilis; Dimoulas, Athanasios
2016-09-07
van der Waals heterostructures of 2D semiconductor materials can be used to realize a number of (opto)electronic devices including tunneling field effect devices (TFETs). It is shown in this work that high quality SnSe2/WSe2 vdW heterostructure can be grown by molecular beam epitaxy on AlN(0001)/Si(111) substrates using a Bi2Se3 buffer layer. A valence band offset of 0.8 eV matches the energy gap of SnSe2 in such a way that the VB edge of WSe2 and the CB edge of SnSe2 are lined up, making this materials combination suitable for (nearly) broken gap TFETs.
Design of an indoor mapping system using three 2D laser scanners and 6 DOF SLAM
NASA Astrophysics Data System (ADS)
Vosselman, G.
2014-08-01
We present the design for a new indoor mapping system based on three 2D laser scanners as well as a method to process the range measurements such that the pose of the system and the planes of floor, ceiling and walls can be estimated simultaneously. By the combined use of the measurements of all three scanners the pose of the system can be reconstructed in 3D without the need for an IMU. The six pose parameters are modelled as a continuous function over time such that scan line deformations caused by rapid scanner movements do not lead to biases in the estimated poses. The theoretical feasibility of the approach is demonstrated by analysing reconstruction results derived from simulated sensor data of two indoor models. Assuming a perfectly calibrated sensor and ranging noise of 3 cm, the results on data in 10x20 m corridor show that the plane orientation precision is better than 0.1 degree and that the standard deviation of plane-to-plane distances is below 1.5 cm after three loops in the corridor.
Magnetic Properties of Restacked 2D Spin 1/2 honeycomb RuCl3 Nanosheets.
Weber, Daniel; Schoop, Leslie M; Duppel, Viola; Lippmann, Judith M; Nuss, Jürgen; Lotsch, Bettina V
2016-06-08
Spin 1/2 honeycomb materials have gained substantial interest due to their exotic magnetism and possible application in quantum computing. However, in all current materials out-of-plane interactions are interfering with the in-plane order, hence a true 2D magnetic honeycomb system is still in demand. Here, we report the exfoliation of the magnetic semiconductor α-RuCl3 into the first halide monolayers and the magnetic characterization of the spin 1/2 honeycomb arrangement of turbostratically stacked RuCl3 monolayers. The exfoliation is based on a reductive lithiation/hydration approach, which gives rise to a loss of cooperative magnetism due to the disruption of the spin 1/2 state by electron injection into the layers. The restacked, macroscopic pellets of RuCl3 layers lack symmetry along the stacking direction. After an oxidative treatment, cooperative magnetism similar to the bulk is restored. The oxidized pellets of restacked single layers feature a magnetic transition at TN = 7 K if the field is aligned parallel to the ab-plane, while the magnetic properties differ from bulk α-RuCl3 if the field is aligned perpendicular to the ab-plane. The deliberate introduction of turbostratic disorder to manipulate the magnetic properties of RuCl3 is of interest for research in frustrated magnetism and complex magnetic order as predicted by the Kitaev-Heisenberg model.
Mechanical and electrical strain response of a piezoelectric auxetic PZT lattice structure
NASA Astrophysics Data System (ADS)
Fey, Tobias; Eichhorn, Franziska; Han, Guifang; Ebert, Kathrin; Wegener, Moritz; Roosen, Andreas; Kakimoto, Ken-ichi; Greil, Peter
2016-01-01
A two-dimensional auxetic lattice structure was fabricated from a PZT piezoceramic. Tape casted and sintered sheets with a thickness of 530 μm were laser cut into inverted honeycomb lattice structure with re-entrant cell geometry (θ = -25°) and poling direction oriented perpendicular to the lattice plane. The in-plane strain response upon applying an uniaxial compression load as well as an electric field perpendicular to the lattice plane were analyzed by a 2D image data detection analysis. The auxetic lattice structure exhibits orthotropic deformation behavior with a negative in-plane Poisson’s ratio of -2.05. Compared to PZT bulk material the piezoelectric auxetic lattice revealed a strain amplification by a factor of 30-70. Effective transversal coupling coefficients {{d}al}31 of the PZT lattice exceeding 4 × 103 pm V-1 were determined which result in an effective hydrostatic coefficient {{d}al}h 66 times larger than that of bulk PZT.
NASA Technical Reports Server (NTRS)
Zahm, A F
1924-01-01
This report gives the description and the use of a specially designed aerodynamic plane table. For the accurate and expeditious geometrical measurement of models in an aerodynamic laboratory, and for miscellaneous truing operations, there is frequent need for a specially equipped plan table. For example, one may have to measure truly to 0.001 inch the offsets of an airfoil at many parts of its surface. Or the offsets of a strut, airship hull, or other carefully formed figure may require exact calipering. Again, a complete airplane model may have to be adjusted for correct incidence at all parts of its surfaces or verified in those parts for conformance to specifications. Such work, if but occasional, may be done on a planing or milling machine; but if frequent, justifies the provision of a special table. For this reason it was found desirable in 1918 to make the table described in this report and to equip it with such gauges and measures as the work should require.
Hackel, L.A.; Hermann, M.R.; Dane, C.B.; Tiszauer, D.H.
1995-12-12
A solid state laser is frequency tripled to 0.3 {micro}m. A small portion of the laser is split off and generates a Stokes seed in a low power oscillator. The low power output passes through a mask with the appropriate hole pattern. Meanwhile, the bulk of the laser output is focused into a larger stimulated Brillouin scattering (SBS) amplifier. The low power beam is directed through the same cell in the opposite direction. The majority of the amplification takes place at the focus which is the fourier transform plane of the mask image. The small holes occupy large area at the focus and thus are preferentially amplified. The amplified output is now imaged onto the multichip module where the holes are drilled. Because of the fourier plane amplifier, only about 1/10th the power of a competitive system is needed. This concept allows less expensive masks to be used in the process and requires much less laser power. 1 fig.
Hackel, Lloyd A.; Hermann, Mark R.; Dane, C. Brent; Tiszauer, Detlev H.
1995-01-01
A solid state laser is frequency tripled to 0.3 .mu.m. A small portion of the laser is split off and generates a Stokes seed in a low power oscillator. The low power output passes through a mask with the appropriate hole pattern. Meanwhile, the bulk of the laser output is focused into a larger stimulated Brillouin scattering (SBS) amplifier. The low power beam is directed through the same cell in the opposite direction. The majority of the amplification takes place at the focus which is the fourier transform plane of the mask image. The small holes occupy large area at the focus and thus are preferentially amplified. The amplified output is now imaged onto the multichip module where the holes are drilled. Because of the fourier plane amplifier, only .about.1/10th the power of a competitive system is needed. This concept allows less expensive masks to be used in the process and requires much less laser power.
NASA Astrophysics Data System (ADS)
Magarill, L. I.; Entin, M. V.
2016-12-01
The electron absorption and the edge photocurrent of a 2D topological insulator are studied for transitions between edge states to 2D states. The circular polarized light is found to produce the edge photocurrent, the direction of which is determined by light polarization and edge orientation. It is shown that the edge-state current is found to exceed the 2D current owing to the topological protection of the edge states.
Energy Efficiency of D2D Multi-User Cooperation.
Zhang, Zufan; Wang, Lu; Zhang, Jie
2017-03-28
The Device-to-Device (D2D) communication system is an important part of heterogeneous networks. It has great potential to improve spectrum efficiency, throughput and energy efficiency cooperation of multiple D2D users with the advantage of direct communication. When cooperating, D2D users expend extraordinary energy to relay data to other D2D users. Hence, the remaining energy of D2D users determines the life of the system. This paper proposes a cooperation scheme for multiple D2D users who reuse the orthogonal spectrum and are interested in the same data by aiming to solve the energy problem of D2D users. Considering both energy availability and the Signal to Noise Ratio (SNR) of each D2D user, the Kuhn-Munkres algorithm is introduced in the cooperation scheme to solve relay selection problems. Thus, the cooperation issue is transformed into a maximum weighted matching (MWM) problem. In order to enhance energy efficiency without the deterioration of Quality of Service (QoS), the link outage probability is derived according to the Shannon Equation by considering the data rate and delay. The simulation studies the relationships among the number of cooperative users, the length of shared data, the number of data packets and energy efficiency.
Integrating Mobile Multimedia into Textbooks: 2D Barcodes
ERIC Educational Resources Information Center
Uluyol, Celebi; Agca, R. Kagan
2012-01-01
The major goal of this study was to empirically compare text-plus-mobile phone learning using an integrated 2D barcode tag in a printed text with three other conditions described in multimedia learning theory. The method examined in the study involved modifications of the instructional material such that: a 2D barcode was used near the text, the…
Efficient Visible Quasi-2D Perovskite Light-Emitting Diodes.
Byun, Jinwoo; Cho, Himchan; Wolf, Christoph; Jang, Mi; Sadhanala, Aditya; Friend, Richard H; Yang, Hoichang; Lee, Tae-Woo
2016-09-01
Efficient quasi-2D-structure perovskite light-emitting diodes (4.90 cd A(-1) ) are demonstrated by mixing a 3D-structured perovskite material (methyl ammonium lead bromide) and a 2D-structured perovskite material (phenylethyl ammonium lead bromide), which can be ascribed to better film uniformity, enhanced exciton confinement, and reduced trap density.
Adaptation algorithms for 2-D feedforward neural networks.
Kaczorek, T
1995-01-01
The generalized weight adaptation algorithms presented by J.G. Kuschewski et al. (1993) and by S.H. Zak and H.J. Sira-Ramirez (1990) are extended for 2-D madaline and 2-D two-layer feedforward neural nets (FNNs).
Regulation of ligands for the NKG2D activating receptor
Raulet, David H.; Gasser, Stephan; Gowen, Benjamin G.; Deng, Weiwen; Jung, Heiyoun
2014-01-01
NKG2D is an activating receptor expressed by all NK cells and subsets of T cells. It serves as a major recognition receptor for detection and elimination of transformed and infected cells and participates in the genesis of several inflammatory diseases. The ligands for NKG2D are self-proteins that are induced by pathways that are active in certain pathophysiological states. NKG2D ligands are regulated transcriptionally, at the level of mRNA and protein stability, and by cleavage from the cell surface. In some cases, ligand induction can be attributed to pathways that are activated specifically in cancer cells or infected cells. We review the numerous pathways that have been implicated in the regulation of NKG2D ligands, discuss the pathologic states in which those pathways are likely to act, and attempt to synthesize the findings into general schemes of NKG2D ligand regulation in NK cell responses to cancer and infection. PMID:23298206
2D materials and van der Waals heterostructures.
Novoselov, K S; Mishchenko, A; Carvalho, A; Castro Neto, A H
2016-07-29
The physics of two-dimensional (2D) materials and heterostructures based on such crystals has been developing extremely fast. With these new materials, truly 2D physics has begun to appear (for instance, the absence of long-range order, 2D excitons, commensurate-incommensurate transition, etc.). Novel heterostructure devices--such as tunneling transistors, resonant tunneling diodes, and light-emitting diodes--are also starting to emerge. Composed from individual 2D crystals, such devices use the properties of those materials to create functionalities that are not accessible in other heterostructures. Here we review the properties of novel 2D crystals and examine how their properties are used in new heterostructure devices.
New generation transistor technologies enabled by 2D crystals
NASA Astrophysics Data System (ADS)
Jena, D.
2013-05-01
The discovery of graphene opened the door to 2D crystal materials. The lack of a bandgap in 2D graphene makes it unsuitable for electronic switching transistors in the conventional field-effect sense, though possible techniques exploiting the unique bandstructure and nanostructures are being explored. The transition metal dichalcogenides have 2D crystal semiconductors, which are well-suited for electronic switching. We experimentally demonstrate field effect transistors with current saturation and carrier inversion made from layered 2D crystal semiconductors such as MoS2, WS2, and the related family. We also evaluate the feasibility of such semiconducting 2D crystals for tunneling field effect transistors for low-power digital logic. The article summarizes the current state of new generation transistor technologies either proposed, or demonstrated, with a commentary on the challenges and prospects moving forward.
NASA Technical Reports Server (NTRS)
1999-01-01
Excerpt from the NASA Connect show 'Plane Weather' This clip explains what high and low pressure weather systems are, and how they form. Weather affects our daily lives. The elements of weather: rain, wind, fog, ice and snow affect the operation and flight of an airplane. In this program, NASA and FAA researchers will introduce students to math, science, and weather; demonstrate how these elements influence flight; and show how NASA and FAA research is used to limit the effects of these elements on flight. Students will examine: the tools, techniques, and technologies used by engineers and scientists to detect these and other climatological factors affecting aircraft in flight. The lesson and classroom experiment will involve students in the scientific process and emphasizing problem solving, measurement, and reasoning skills.
NASA Technical Reports Server (NTRS)
1999-01-01
Excerpt from the NASA Connect show 'Plane Weather' This clip explains what high and low pressure weather systems are, and how these affect weather patterns. Weather affects our daily lives. The elements of weather: rain, wind, fog, ice and snow affect the operation and flight of an airplane. In this program, NASA and FAA researchers will introduce students to math, science, and weather; demonstrate how these elements influence flight; and show how NASA and FAA research is used to limit the effects of these elements on flight. Students will examine: the tools, techniques, and technologies used by engineers and scientists to detect these and other climatological factors affecting aircraft in flight. The lesson and classroom experiment will involve students in the scientific process and emphasizing problem solving, measurement, and reasoning skills.
In-plane magnetization-induced quantum anomalous Hall effect.
Liu, Xin; Hsu, Hsiu-Chuan; Liu, Chao-Xing
2013-08-23
The quantum Hall effect can only be induced by an out-of-plane magnetic field for two-dimensional electron gases, and similarly, the quantum anomalous Hall effect has also usually been considered for systems with only out-of-plane magnetization. In the present work, we predict that the quantum anomalous Hall effect can be induced by in-plane magnetization that is not accompanied by any out-of-plane magnetic field. Two realistic two-dimensional systems, Bi2Te3 thin film with magnetic doping and HgMnTe quantum wells with shear strains, are presented and the general condition for the in-plane magnetization-induced quantum anomalous Hall effect is discussed based on the symmetry analysis. Nonetheless, an experimental setup is proposed to confirm this effect, the observation of which will pave the way to search for the quantum anomalous Hall effect in a wider range of materials.
Estrogen-Induced Cholestasis Leads to Repressed CYP2D6 Expression in CYP2D6-Humanized Mice.
Pan, Xian; Jeong, Hyunyoung
2015-07-01
Cholestasis activates bile acid receptor farnesoid X receptor (FXR) and subsequently enhances hepatic expression of small heterodimer partner (SHP). We previously demonstrated that SHP represses the transactivation of cytochrome P450 2D6 (CYP2D6) promoter by hepatocyte nuclear factor (HNF) 4α. In this study, we investigated the effects of estrogen-induced cholestasis on CYP2D6 expression. Estrogen-induced cholestasis occurs in subjects receiving estrogen for contraception or hormone replacement, or in susceptible women during pregnancy. In CYP2D6-humanized transgenic (Tg-CYP2D6) mice, cholestasis triggered by administration of 17α-ethinylestradiol (EE2) at a high dose led to 2- to 3-fold decreases in CYP2D6 expression. This was accompanied by increased hepatic SHP expression and subsequent decreases in the recruitment of HNF4α to CYP2D6 promoter. Interestingly, estrogen-induced cholestasis also led to increased recruitment of estrogen receptor (ER) α, but not that of FXR, to Shp promoter, suggesting a predominant role of ERα in transcriptional regulation of SHP in estrogen-induced cholestasis. EE2 at a low dose (that does not cause cholestasis) also increased SHP (by ∼ 50%) and decreased CYP2D6 expression (by 1.5-fold) in Tg-CYP2D6 mice, the magnitude of differences being much smaller than that shown in EE2-induced cholestasis. Taken together, our data indicate that EE2-induced cholestasis increases SHP and represses CYP2D6 expression in Tg-CYP2D6 mice in part through ERα transactivation of Shp promoter.
2D image classification for 3D anatomy localization: employing deep convolutional neural networks
NASA Astrophysics Data System (ADS)
de Vos, Bob D.; Wolterink, Jelmer M.; de Jong, Pim A.; Viergever, Max A.; Išgum, Ivana
2016-03-01
Localization of anatomical regions of interest (ROIs) is a preprocessing step in many medical image analysis tasks. While trivial for humans, it is complex for automatic methods. Classic machine learning approaches require the challenge of hand crafting features to describe differences between ROIs and background. Deep convolutional neural networks (CNNs) alleviate this by automatically finding hierarchical feature representations from raw images. We employ this trait to detect anatomical ROIs in 2D image slices in order to localize them in 3D. In 100 low-dose non-contrast enhanced non-ECG synchronized screening chest CT scans, a reference standard was defined by manually delineating rectangular bounding boxes around three anatomical ROIs -- heart, aortic arch, and descending aorta. Every anatomical ROI was automatically identified using a combination of three CNNs, each analyzing one orthogonal image plane. While single CNNs predicted presence or absence of a specific ROI in the given plane, the combination of their results provided a 3D bounding box around it. Classification performance of each CNN, expressed in area under the receiver operating characteristic curve, was >=0.988. Additionally, the performance of ROI localization was evaluated. Median Dice scores for automatically determined bounding boxes around the heart, aortic arch, and descending aorta were 0.89, 0.70, and 0.85 respectively. The results demonstrate that accurate automatic 3D localization of anatomical structures by CNN-based 2D image classification is feasible.
SU-E-T-05: A 2D EPID Transit Dosimetry Model Based On An Empirical Quadratic Formalism
Tan, Y; Metwaly, M; Glegg, M; Baggarley, S; Elliott, A
2014-06-01
Purpose: To describe a 2D electronic portal imaging device (EPID) transit dosimetry model, based on an empirical quadratic formalism, that can predict either EPID or in-phantom dose distribution for comparisons with EPID captured image or treatment planning system (TPS) dose respectively. Methods: A quadratic equation can be used to relate the reduction in intensity of an exit beam to the equivalent path length of the attenuator. The calibration involved deriving coefficients from a set of dose planes measured for homogeneous phantoms with known thicknesses under reference conditions. In this study, calibration dose planes were measured with EPID and ionisation chamber (IC) in water for the same reference beam (6MV, 100mu, 20×20cm{sup 2}) and set of thicknesses (0–30cm). Since the same calibration conditions were used, the EPID and IC measurements can be related through the quadratic equation. Consequently, EPID transit dose can be predicted from TPS exported dose planes and in-phantom dose can be predicted using EPID distribution captured during treatment as an input. The model was tested with 4 open fields, 6 wedge fields, and 7 IMRT fields on homogeneous and heterogeneous phantoms. Comparisons were done using 2D absolute gamma (3%/3mm) and results were validated against measurements with a commercial 2D array device. Results: The gamma pass rates for comparisons between EPID measured and predicted ranged from 93.6% to 100.0% for all fields and phantoms tested. Results from this study agreed with 2D array measurements to within 3.1%. Meanwhile, comparisons in-phantom between TPS computed and predicted ranged from 91.6% to 100.0%. Validation with 2D array device was not possible for inphantom comparisons. Conclusion: A 2D EPID transit dosimetry model for treatment verification was described and proven to be accurate. The model has the advantage of being generic and allows comparisons at the EPID plane as well as multiple planes in-phantom.
Xie, Donghao; Ji, Ding-Kun; Zhang, Yue; Cao, Jun; Zheng, Hu; Liu, Lin; Zang, Yi; Li, Jia; Chen, Guo-Rong; James, Tony D; He, Xiao-Peng
2016-08-04
Here we demonstrate that 2D MoS2 can enhance the receptor-targeting and imaging ability of a fluorophore-labelled ligand. The 2D MoS2 has an enhanced working concentration range when compared with graphene oxide, resulting in the improved imaging of both cell and tissue samples.
Strain induced novel quantum magnetotransport properties of topological insulators
NASA Astrophysics Data System (ADS)
Ma, Ning; Zhang, Shengli; Liu, Daqing
2016-12-01
Recent theoretical and experimental researches have revealed that the strained bulk HgTe can be regarded as a three-dimensional topological insulator (TI). Motivated by this, we explore the strain effects on the transport properties of the HgTe surface states, which are modulated by a weak 1D in-plane electrostatic periodic potential in the presence of a perpendicular magnetic field. We analytically derive the zero frequency (dc) diffusion conductivity for the case of quasielastic scattering in the Kubo formalism, and find that, in strong magnetic field regime, the Shubnikov-de Haas oscillations are superimposed on top of the Weiss oscillations due to the electric modulation for null and finite strain. Furthermore, the strain is shown to remove the degeneracy in inversion symmetric Dirac cones on the top and bottom surfaces. This accordingly gives rise to the splitting and mixture of Landau levels, and the asymmetric spectrum of the dc conductivity. These phenomena, not known in a conventional 2D electron gas and even in a strainless TI and graphene, are a consequence of the anomalous spectrum of surface states in a fully stained TI. These results should be valuable for electronic and spintronic applications of TIs, and thus we fully expect to see them in the further experiment.
Efficient 2D MRI relaxometry using compressed sensing
NASA Astrophysics Data System (ADS)
Bai, Ruiliang; Cloninger, Alexander; Czaja, Wojciech; Basser, Peter J.
2015-06-01
Potential applications of 2D relaxation spectrum NMR and MRI to characterize complex water dynamics (e.g., compartmental exchange) in biology and other disciplines have increased in recent years. However, the large amount of data and long MR acquisition times required for conventional 2D MR relaxometry limits its applicability for in vivo preclinical and clinical MRI. We present a new MR pipeline for 2D relaxometry that incorporates compressed sensing (CS) as a means to vastly reduce the amount of 2D relaxation data needed for material and tissue characterization without compromising data quality. Unlike the conventional CS reconstruction in the Fourier space (k-space), the proposed CS algorithm is directly applied onto the Laplace space (the joint 2D relaxation data) without compressing k-space to reduce the amount of data required for 2D relaxation spectra. This framework is validated using synthetic data, with NMR data acquired in a well-characterized urea/water phantom, and on fixed porcine spinal cord tissue. The quality of the CS-reconstructed spectra was comparable to that of the conventional 2D relaxation spectra, as assessed using global correlation, local contrast between peaks, peak amplitude and relaxation parameters, etc. This result brings this important type of contrast closer to being realized in preclinical, clinical, and other applications.
2D vs. 3D mammography observer study
NASA Astrophysics Data System (ADS)
Fernandez, James Reza F.; Hovanessian-Larsen, Linda; Liu, Brent
2011-03-01
Breast cancer is the most common type of non-skin cancer in women. 2D mammography is a screening tool to aid in the early detection of breast cancer, but has diagnostic limitations of overlapping tissues, especially in dense breasts. 3D mammography has the potential to improve detection outcomes by increasing specificity, and a new 3D screening tool with a 3D display for mammography aims to improve performance and efficiency as compared to 2D mammography. An observer study using a mammography phantom was performed to compare traditional 2D mammography with this ne 3D mammography technique. In comparing 3D and 2D mammography there was no difference in calcification detection, and mass detection was better in 2D as compared to 3D. There was a significant decrease in reading time for masses, calcifications, and normals in 3D compared to 2D, however, as well as more favorable confidence levels in reading normal cases. Given the limitations of the mammography phantom used, however, a clearer picture in comparing 3D and 2D mammography may be better acquired with the incorporation of human studies in the future.
Epitaxial 2D MoSe2 (HfSe2) Semiconductor/2D TaSe2 Metal van der Waals Heterostructures.
Tsoutsou, Dimitra; Aretouli, Kleopatra E; Tsipas, Polychronis; Marquez-Velasco, Jose; Xenogiannopoulou, Evangelia; Kelaidis, Nikolaos; Aminalragia Giamini, Sigiava; Dimoulas, Athanasios
2016-01-27
Molecular beam epitaxy of 2D metal TaSe2/2D MoSe2 (HfSe2) semiconductor heterostructures on epi-AlN(0001)/Si(111) substrates is reported. Electron diffraction reveals an in-plane orientation indicative of van der Waals epitaxy, whereas electronic band imaging supported by first-principles calculations and X-ray photoelectron spectroscopy indicate the presence of a dominant trigonal prismatic 2H-TaSe2 phase and a minor contribution from octahedrally coordinated TaSe2, which is present in TaSe2/AlN and TaSe2/HfSe2/AlN but notably absent in the TaSe2/MoSe2/AlN, indicating superior structural quality of TaSe2 grown on MoSe2. Apart from its structural and chemical compatibility with the selenide semiconductors, TaSe2 has a workfunction of 5.5 eV as measured by ultraviolet photoelectron spectroscopy, which matches very well with the semiconductor workfunctions, implying that epi-TaSe2 can be used for low-resistivity contacts to MoSe2 and HfSe2.
NKG2D receptor and its ligands in host defense
Lanier, Lewis L.
2015-01-01
NKG2D is an activating receptor expressed on the surface of natural killer (NK) cells, CD8+ T cells, and subsets of CD4+ T cells, iNKT cells, and γδ T cells. In humans NKG2D transmits signals by its association with the DAP10 adapter subunit and in mice alternatively spliced isoforms transmit signals either using DAP10 or DAP12 adapter subunits. Although NKG2D is encoded by a highly conserved gene (KLRK1) with limited polymorphism, the receptor recognizes an extensive repertoire of ligands, encoded by at least 8 genes in humans (MICA, MICB, RAET1E, RAET1G, RAET1H, RAET1I, RAET1L, and RAET1N), some with extensive allelic polymorphism. Expression of the NKG2D ligands is tightly regulated at the level of transcription, translation, and post-translation. In general healthy adult tissues do not express NKG2D glycoproteins on the cell surface, but these ligands can be induced by hyper-proliferation and transformation, as well as when cells are infected by pathogens. Thus, the NKG2D pathway serves a mechanism for the immune system to detect and eliminate cells that have undergone “stress”. Viruses and tumor cells have devised numerous strategies to evade detection by the NKG2D surveillance system and diversification of the NKG2D ligand genes likely has been driven by selective pressures imposed by pathogens. NKG2D provides an attractive target for therapeutics in the treatment of infectious diseases, cancer, and autoimmune diseases. PMID:26041808
NKG2D Receptor and Its Ligands in Host Defense.
Lanier, Lewis L
2015-06-01
NKG2D is an activating receptor expressed on the surface of natural killer (NK) cells, CD8(+) T cells, and subsets of CD4(+) T cells, invariant NKT cells (iNKT), and γδ T cells. In humans, NKG2D transmits signals by its association with the DAP10 adapter subunit, and in mice alternatively spliced isoforms transmit signals either using DAP10 or DAP12 adapter subunits. Although NKG2D is encoded by a highly conserved gene (KLRK1) with limited polymorphism, the receptor recognizes an extensive repertoire of ligands, encoded by at least eight genes in humans (MICA, MICB, RAET1E, RAET1G, RAET1H, RAET1I, RAET1L, and RAET1N), some with extensive allelic polymorphism. Expression of the NKG2D ligands is tightly regulated at the level of transcription, translation, and posttranslation. In general, healthy adult tissues do not express NKG2D glycoproteins on the cell surface, but these ligands can be induced by hyperproliferation and transformation, as well as when cells are infected by pathogens. Thus, the NKG2D pathway serves as a mechanism for the immune system to detect and eliminate cells that have undergone "stress." Viruses and tumor cells have devised numerous strategies to evade detection by the NKG2D surveillance system, and diversification of the NKG2D ligand genes likely has been driven by selective pressures imposed by pathogens. NKG2D provides an attractive target for therapeutics in the treatment of infectious diseases, cancer, and autoimmune diseases.
2-D Versus 3-D Magnetotelluric Data Interpretation
NASA Astrophysics Data System (ADS)
Ledo, Juanjo
2005-09-01
In recent years, the number of publications dealing with the mathematical and physical 3-D aspects of the magnetotelluric method has increased drastically. However, field experiments on a grid are often impractical and surveys are frequently restricted to single or widely separated profiles. So, in many cases we find ourselves with the following question: is the applicability of the 2-D hypothesis valid to extract geoelectric and geological information from real 3-D environments? The aim of this paper is to explore a few instructive but general situations to understand the basics of a 2-D interpretation of 3-D magnetotelluric data and to determine which data subset (TE-mode or TM-mode) is best for obtaining the electrical conductivity distribution of the subsurface using 2-D techniques. A review of the mathematical and physical fundamentals of the electromagnetic fields generated by a simple 3-D structure allows us to prioritise the choice of modes in a 2-D interpretation of responses influenced by 3-D structures. This analysis is corroborated by numerical results from synthetic models and by real data acquired by other authors. One important result of this analysis is that the mode most unaffected by 3-D effects depends on the position of the 3-D structure with respect to the regional 2-D strike direction. When the 3-D body is normal to the regional strike, the TE-mode is affected mainly by galvanic effects, while the TM-mode is affected by galvanic and inductive effects. In this case, a 2-D interpretation of the TM-mode is prone to error. When the 3-D body is parallel to the regional 2-D strike the TE-mode is affected by galvanic and inductive effects and the TM-mode is affected mainly by galvanic effects, making it more suitable for 2-D interpretation. In general, a wise 2-D interpretation of 3-D magnetotelluric data can be a guide to a reasonable geological interpretation.
Chandrasekaran, Anand; Mishra, Avanish; Singh, Abhishek Kumar
2017-04-04
Presence of ferroelectric polarization in 2D materials is extremely rare due to the effect of the surface depolarizing field. Here, we use first-principles calculations to show the largest out-of-plane polarization observed in a monolayer in functionalized MXenes (Sc2CO2). The switching of polarization in this new class of ferroelectric materials occurs through an previously unknown intermediate antiferroelectric structure thus establishing three states for applications in low-dimensional non-volatile memory. We show that the armchair domain-interface acts as an 1D metallic nanowire separating two insulating domains. In the case of the van-der-Waals bilayer we observe, interestingly, the presence of an ultrathin 2D electron/hole gas (2DEG) on the top/bottom layers, respectively, due to the redistrubution of charge carriers. The 2DEG is non-degenerate due to spin-orbit-coupling, thus paving the way for spin-orbitronic devices. The coexistence of ferroelectricity, antiferroelectricity, 2DEG and spin-orbit splitting in this system suggests that such 2D polar materials possess high potential for device application in a multitude of fields ranging from nanoelectronics to photovoltaics.
NASA Astrophysics Data System (ADS)
Peng, Cheng; Efetov, Dmitri; Shiue, Ren-Jye; Nanot, Sebastien; Hempel, Marek; Kong, Jing; Koppens, Frank; Englund, Dirk
Strong spatial tunability of the charge carrier density at nanoscale is essential to many 2D-material-based electronic and optoelectronic applications. As an example, plasmonic metamaterials with nanoscale dimensions would make graphene plasmonics at visible and near-infrared wavelengths possible. However, existing gating techniques based on conventional dielectric gating geometries limit the spatial resolution and achievable carrier concentration, strongly restricting the available wavelength, geometry, and quality of the devices. Here, we present a novel spatially selective electrolyte gating approach that allows for in-plane spatial Fermi energy modulation of 2D materials of more than 1 eV (carrier density of n = 1014 cm-2) across a length of 2 nm. We present electrostatic simulations as well as electronic transport, photocurrent, cyclic voltammetry and optical spectroscopy measurements to characterize the performance of the gating technique applied to graphene devices. The high spatial resolution, high doping capacity, full tunability and self-aligned device geometry of the presented technique opens a new venue for nanoscale metamaterial engineering of 2D materials for complete optical absorption, nonlinear optics and sensing, among other applications.
Samir, Chafik; Kurtek, Sebastian; Srivastava, Anuj; Canis, Michel
2014-05-01
We study the problem of joint registration and deformation analysis of endometrial tissue using 3D magnetic resonance imaging (MRI) and 2D trans-vaginal ultrasound (TVUS) measurements. In addition to the different imaging techniques involved in the two modalities, this problem is complicated due to: 1) different patient pose during MRI and TVUS observations, 2) the 3D nature of MRI and 2D nature of TVUS measurements, 3) the unknown intersecting plane for TVUS in MRI volume, and 4) the potential deformation of endometrial tissue during TVUS measurement process. Focusing on the shape of the tissue, we use expert manual segmentation of its boundaries in the two modalities and apply, with modification, recent developments in shape analysis of parametric surfaces to this problem. First, we extend the 2D TVUS curves to generalized cylindrical surfaces through replication, and then we compare them with MRI surfaces using elastic shape analysis. This shape analysis provides a simultaneous registration (optimal reparameterization) and deformation (geodesic) between any two parametrized surfaces. Specifically, it provides optimal curves on MRI surfaces that match with the original TVUS curves. This framework results in an accurate quantification and localization of the deformable endometrial cells for radiologists, and growth characterization for gynecologists and obstetricians. We present experimental results using semi-synthetic data and real data from patients to illustrate these ideas.
Fukuto, M.; Kewalramani, S.; Wang, S.; Lin, Y.; Nguyen, G.; Wang, Q.; Yang, L.
2011-02-07
We report an experimental demonstration of a strategy for inducing two-dimensional (2D) crystallization of charged nanoparticles on oppositely charged fluid interfaces. This strategy aims to maximize the interfacial adsorption of nanoparticles, and hence their lateral packing density, by utilizing a combination of weakly charged particles and a high surface charge density on the planar interface. In order to test this approach, we investigated the assembly of cowpea mosaic virus (CPMV) on positively charged lipid monolayers at the aqueous solution surface, by means of in situ X-ray scattering measurements at the liquid-vapor interface. The assembly was studied as a function of the solution pH, which was used to vary the charge on CPMV, and of the mole fraction of the cationic lipid in the binary lipid monolayer, which set the interface charge density. The 2D crystallization of CPMV occurred in a narrow pH range just above the particle's isoelectric point, where the particle charge was weakly negative, and only when the cationic-lipid fraction in the monolayer exceeded a threshold. The observed 2D crystals exhibited nearly the same packing density as the densest lattice plane within the known 3D crystals of CPMV. The above electrostatic approach of maximizing interfacial adsorption may provide an efficient route to the crystallization of nanoparticles at aqueous interfaces.
2D Crystal heterostructures properties and growth by molecular beam epitaxy
NASA Astrophysics Data System (ADS)
Xing, Grace Huili
Two-dimensional (2D) crystals such as transition metal dichalcogenides (TMDs) along with other families of layered materials including graphene, SnSe2, GaSe, BN etc, has attracted intense attention from the scientific community. One monolayer of such materials represent the thinnest ``quantum wells''. These layered materials typically possess an in-plane hexagonal crystal structure, and can be stacked together by interlayer van der Waals interactions. Therefore, it is possible to create novel heterostructures by stacking materials with large lattice mismatches and different properties, for instance, superconductors (NbSe2) , metals, semi-metals (graphene), semiconductors (MoS2) and insulators (BN). Numerous novel material properties and device concepts have been discovered, proposed and demonstrated lately. However, the low internal photoluminescence efficiency (IPE, <1%) and low carrier mobility observed in the 2D semiconductors suggest strongly that the materials under investigation today most likely suffer from a high concentration of defects. In this talk, I will share our progress and the challenges we face in terms of preparing, characterizing these 2D crystals as well as pursuing their applications. This work has been supported in part by NSF, AFOSR and LEAST, one of the STARnet centers.
NASA Astrophysics Data System (ADS)
Ma, Zetao; Ogusu, Kazuhiko
2009-04-01
A finite-difference time-domain method based on Yee's orthogonal cell is utilized to calculate the band structures of 2D triangular-lattice-based photonic crystals through a simple modification to properly shifting the boundaries of the original unit cell. A strategy is proposed for transforming the triangular unit cell into an orthogonal one, which can be used to calculate the band structures of 2D PhCs with various shapes of inclusions, such as triangular, quadrangular, and hexagonal shapes, to overcome the shortage of plane-wave expansion method for circular one. The band structures of 2D triangular-lattice-based PhCs with hexagonal air-holes are calculated and discussed for different values of its radius and rotation angle. The obtained results provide an insight to manipulate the band structures of PhCs.
Vabbina, Phani Kiran; Kaushik, Ajeet; Pokhrel, Nimesh; Bhansali, Shekhar; Pala, Nezih
2015-01-15
We report on label free, highly sensitive and selective electrochemical immunosensors based on one-dimensional 1D ZnO nanorods (ZnO-NRs) and two-dimensional 2D ZnO nanoflakes (ZnO-NFs) which were synthesized on Au-coated substrates using simple one step sonochemical approach. Selective detection of cortisol using cyclic voltammetry (CV) is achieved by immobilizing anti-cortisol antibody (Anti-C(ab)) on the ZnO nanostructures (NSs). 1D ZnO-NRs and 2D ZnO-NFs provide unique sensing advantages over bulk materials. While 1D-NSs boast a high surface area to volume ratio, 2D-NSs with large area in polarized (0001) plane and high surface charge density could promote higher Anti-C(ab) loading and thus better sensing performance. Beside large surface area, ZnO-NSs also exhibit higher chemical stability, high catalytic activity, and biocompatibility. TEM studies showed that both ZnO-NSs are single crystalline oriented in (0001) plane. The measured sensing parameters are in the physiological range with a sensitivity of 11.86 µA/M exhibited by ZnO-NRs and 7.74 µA/M by ZnO-NFs with the lowest detection limit of 1 pM which is 100 times better than conventional enzyme-linked immunosorbant immunoassay (ELISA). ZnO-NSs based cortisol immunosensors were tested on human saliva samples and the performance were validated with conventional (ELISA) method which exhibits a remarkable correlation. The developed sensors can be integrated with microfluidic system and miniaturized potentiostat for point-of-care cortisol detection and such developed protocol can be used in personalized health monitoring/diagnostic.
Jursinic, Paul A; Nelms, Ben E
2003-05-01
An analysis is made of a two-dimensional array of diodes that can be used for measuring dose generated in a plane by a radiation beam. This measuring device is the MapCHECK Model 1175 (Sun Nuclear, Melbourne, FL). This device has 445 N-type diodes in a 22 x 22 cm2 2-D array with variable spacing. The entire array of diodes is easily calibrated to allow for measurements in absolute dose. For IMRT quality assurance, each beam is measured individually with the beam central axis oriented perpendicular to the plane of diodes. Software is available to do the analytical comparison of measurements versus dose distributions calculated by a treatment planning system. Comparison criteria of percent difference and distance-to-agreement are defined by the operator. Data are presented that show the diode array has linear response when beam fluence changes by over 300-fold, which is typical of the level of modulation in intensity modulated radiation therapy, IMRT, beams. A linear dependence is also shown for a 100-fold change in monitors units delivered. Methods for how this device can be used in the clinic for quality assurance of IMRT fields are described. Measurements of typical IMRT beams that are modulated by compensators and MLCs are presented with comparisons to treatment planning system dose calculations. A time analysis is done for typical IMRT quality assurance measurements. The setup, calibration, and analysis time for the 2-D diode array are on the order of 20 min, depending on numbers of fields. This is significantly less time than required to do similar analysis with radiographic film. The 2-D diode array is ideal for per-plan quality assurance after an IMRT system is fully commissioned.
Atomistic methodologies for material properties of 2D materials at the nanoscale
NASA Astrophysics Data System (ADS)
Zhang, Zhen
Research on two dimensional (2D) materials, such as graphene and MoS2, now involves thousands of researchers worldwide cutting across physics, chemistry, engineering and biology. Due to the extraordinary properties of 2D materials, research extends from fundamental science to novel applications of 2D materials. From an engineering point of view, understanding the material properties of 2D materials under various conditions is crucial for tailoring the electrical and mechanical properties of 2D-material-based devices at the nanoscale. Even at the nanoscale, molecular systems typically consist of a vast number of atoms. Molecular dynamics (MD) simulations enable us to understand the properties of assemblies of molecules in terms of their structure and the microscopic interactions between them. From a continuum approach, mechanical properties and thermal properties, such as strain, stress, and heat capacity, are well defined and experimentally measurable. In MD simulations, material systems are considered to be discrete, and only interatomic potential, interatomic forces, and atom positions are directly obtainable. Besides, most of the fracture mechanics concepts, such as stress intensity factors, are not applicable since there is no singularity in MD simulations. However, energy release rate still remains to be a feasible and crucial physical quantity to characterize the fracture mechanical property of materials at the nanoscale. Therefore, equivalent definition of a physical quantity both in atomic scale and macroscopic scale is necessary in order to understand molecular and continuum scale phenomena concurrently. This work introduces atomistic simulation methodologies, based on interatomic potential and interatomic forces, as a tool to unveil the mechanical properties, thermal properties and fracture mechanical properties of 2D materials at the nanoscale. Among many 2D materials, graphene and MoS2 have attracted intense interest. Therefore, we applied our
Recent advances in 2D materials for photocatalysis.
Luo, Bin; Liu, Gang; Wang, Lianzhou
2016-04-07
Two-dimensional (2D) materials have attracted increasing attention for photocatalytic applications because of their unique thickness dependent physical and chemical properties. This review gives a brief overview of the recent developments concerning the chemical synthesis and structural design of 2D materials at the nanoscale and their applications in photocatalytic areas. In particular, recent progress on the emerging strategies for tailoring 2D material-based photocatalysts to improve their photo-activity including elemental doping, heterostructure design and functional architecture assembly is discussed.
Comparison of 2D and 3D gamma analyses
Pulliam, Kiley B.; Huang, Jessie Y.; Howell, Rebecca M.; Followill, David; Kry, Stephen F.; Bosca, Ryan; O’Daniel, Jennifer
2014-02-15
Purpose: As clinics begin to use 3D metrics for intensity-modulated radiation therapy (IMRT) quality assurance, it must be noted that these metrics will often produce results different from those produced by their 2D counterparts. 3D and 2D gamma analyses would be expected to produce different values, in part because of the different search space available. In the present investigation, the authors compared the results of 2D and 3D gamma analysis (where both datasets were generated in the same manner) for clinical treatment plans. Methods: Fifty IMRT plans were selected from the authors’ clinical database, and recalculated using Monte Carlo. Treatment planning system-calculated (“evaluated dose distributions”) and Monte Carlo-recalculated (“reference dose distributions”) dose distributions were compared using 2D and 3D gamma analysis. This analysis was performed using a variety of dose-difference (5%, 3%, 2%, and 1%) and distance-to-agreement (5, 3, 2, and 1 mm) acceptance criteria, low-dose thresholds (5%, 10%, and 15% of the prescription dose), and data grid sizes (1.0, 1.5, and 3.0 mm). Each comparison was evaluated to determine the average 2D and 3D gamma, lower 95th percentile gamma value, and percentage of pixels passing gamma. Results: The average gamma, lower 95th percentile gamma value, and percentage of passing pixels for each acceptance criterion demonstrated better agreement for 3D than for 2D analysis for every plan comparison. The average difference in the percentage of passing pixels between the 2D and 3D analyses with no low-dose threshold ranged from 0.9% to 2.1%. Similarly, using a low-dose threshold resulted in a difference between the mean 2D and 3D results, ranging from 0.8% to 1.5%. The authors observed no appreciable differences in gamma with changes in the data density (constant difference: 0.8% for 2D vs 3D). Conclusions: The authors found that 3D gamma analysis resulted in up to 2.9% more pixels passing than 2D analysis. It must
Romero, Javier M; Madan, Neil; Betancur, Ilda; Ciobanu, Adrian; Murphy, Erin; McCullough, Danielle; Grant, P Ellen
2014-08-01
The purpose of this study was to compare acquisition time efficiency and diagnostic agreement of neonatal brain ultrasound (US) scans obtained with a 3-D volume US acquisition protocol and the conventional 2-D acquisition protocol. Ninety-one consecutive premature neonatal brain ultrasound scans were prospectively performed on 59 neonates with the conventional 2-D acquisition protocol. Immediately after the 2-D study, a coronal 3-D ultrasound volume was acquired and later reconstructed into axial and sagittal planes. All 59 neonates were imaged in the neonatal intensive care unit to rule out intracranial hemorrhage. Total time for 2-D and 3-D acquisition protocols was recorded, and a two-tailed t-test was used to determine if study durations differed significantly. One pediatric neuroradiologist reviewed the reformatted 3-D images, tomographic ultrasound images. Results were compared with the clinical interpretation of the 2-D conventional study. The mean scanning time for the 2-D US acquisition protocol was 10.56 min (standard deviation [SD] = 7.11), and that for the 3-D volume US acquisition protocol was 1.48 min (SD = 0.59) (p ≤ 0.001). Inter-observer agreement revealed k values of 0.84 for hydrocephalus, 0.80 for germinal matrix hemorrhage/intraventricular hemorrhage, 0.74 for periventricular leukomalacia and 0.91 for subdural collection, hence near-perfect to substantial agreement between imaging protocols. There was a significant decrease in acquisition time for the 3-D volume ultrasound acquisition protocol compared with the conventional 2-D US protocol (p = <0.001), without compromising the diagnostic quality compared with a conventional 2-D US imaging protocol.
2D/4D marker-free tumor tracking using 4D CBCT as the reference image.
Wang, Mengjiao; Sharp, Gregory C; Rit, Simon; Delmon, Vivien; Wang, Guangzhi
2014-05-07
Tumor motion caused by respiration is an important issue in image-guided radiotherapy. A 2D/4D matching method between 4D volumes derived from cone beam computed tomography (CBCT) and 2D fluoroscopic images was implemented to track the tumor motion without the use of implanted markers. In this method, firstly, 3DCBCT and phase-rebinned 4DCBCT are reconstructed from cone beam acquisition. Secondly, 4DCBCT volumes and a streak-free 3DCBCT volume are combined to improve the image quality of the digitally reconstructed radiographs (DRRs). Finally, the 2D/4D matching problem is converted into a 2D/2D matching between incoming projections and DRR images from each phase of the 4DCBCT. The diaphragm is used as a target surrogate for matching instead of using the tumor position directly. This relies on the assumption that if a patient has the same breathing phase and diaphragm position as the reference 4DCBCT, then the tumor position is the same. From the matching results, the phase information, diaphragm position and tumor position at the time of each incoming projection acquisition can be derived. The accuracy of this method was verified using 16 candidate datasets, representing lung and liver applications and one-minute and two-minute acquisitions. The criteria for the eligibility of datasets were described: 11 eligible datasets were selected to verify the accuracy of diaphragm tracking, and one eligible dataset was chosen to verify the accuracy of tumor tracking. The diaphragm matching accuracy was 1.88 ± 1.35 mm in the isocenter plane and the 2D tumor tracking accuracy was 2.13 ± 1.26 mm in the isocenter plane. These features make this method feasible for real-time marker-free tumor motion tracking purposes.
Double resonance rotational spectroscopy of CH2D+
NASA Astrophysics Data System (ADS)
Töpfer, Matthias; Jusko, Pavol; Schlemmer, Stephan; Asvany, Oskar
2016-09-01
Context. Deuterated forms of CH are thought to be responsible for deuterium enrichment in lukewarm astronomical environments. There is no unambiguous detection of CH2D+ in space to date. Aims: Four submillimetre rotational lines of CH2D+ are documented in the literature. Our aim is to present a complete dataset of highly resolved rotational lines, including millimetre (mm) lines needed for a potential detection. Methods: We used a low-temperature ion trap and applied a novel IR-mm-wave double resonance method to measure the rotational lines of CH2D+. Results: We measured 21 low-lying (J ≤ 4) rotational transitions of CH2D+ between 23 GHz and 1.1 THz with accuracies close to 2 ppb.
Recovering 3D particle size distributions from 2D sections
NASA Astrophysics Data System (ADS)
Cuzzi, Jeffrey N.; Olson, Daniel M.
2017-03-01
We discuss different ways to convert observed, apparent particle size distributions from 2D sections (thin sections, SEM maps on planar surfaces, etc.) into true 3D particle size distributions. We give a simple, flexible, and practical method to do this; show which of these techniques gives the most faithful conversions; and provide (online) short computer codes to calculate both 2D-3D recoveries and simulations of 2D observations by random sectioning. The most important systematic bias of 2D sectioning, from the standpoint of most chondrite studies, is an overestimate of the abundance of the larger particles. We show that fairly good recoveries can be achieved from observed size distributions containing 100-300 individual measurements of apparent particle diameter.
Phonon thermal conduction in novel 2D materials
NASA Astrophysics Data System (ADS)
Xu, Xiangfan; Chen, Jie; Li, Baowen
2016-12-01
Recently, there has been increasing interest in phonon thermal transport in low-dimensional materials, due to the crucial importance of dissipating and managing heat in micro- and nano-electronic devices. Significant progress has been achieved for one-dimensional (1D) systems, both theoretically and experimentally. However, the study of heat conduction in two-dimensional (2D) systems is still in its infancy due to the limited availability of 2D materials and the technical challenges of fabricating suspended samples that are suitable for thermal measurements. In this review, we outline different experimental techniques and theoretical approaches for phonon thermal transport in 2D materials, discuss the problems and challenges of phonon thermal transport measurements and provide a comparison between existing experimental data. Special attention will be given to the effects of size, dimensionality, anisotropy and mode contributions in novel 2D systems, including graphene, boron nitride, MoS2, black phosphorous and silicene.
Recent developments in 2D layered inorganic nanomaterials for sensing
NASA Astrophysics Data System (ADS)
Kannan, Padmanathan Karthick; Late, Dattatray J.; Morgan, Hywel; Rout, Chandra Sekhar
2015-08-01
Two dimensional layered inorganic nanomaterials (2D-LINs) have recently attracted huge interest because of their unique thickness dependent physical and chemical properties and potential technological applications. The properties of these layered materials can be tuned via both physical and chemical processes. Some 2D layered inorganic nanomaterials like MoS2, WS2 and SnS2 have been recently developed and employed in various applications, including new sensors because of their layer-dependent electrical properties. This article presents a comprehensive overview of recent developments in the application of 2D layered inorganic nanomaterials as sensors. Some of the salient features of 2D materials for different sensing applications are discussed, including gas sensing, electrochemical sensing, SERS and biosensing, SERS sensing and photodetection. The working principles of the sensors are also discussed together with examples.
Phonon thermal conduction in novel 2D materials.
Xu, Xiangfan; Chen, Jie; Li, Baowen
2016-12-07
Recently, there has been increasing interest in phonon thermal transport in low-dimensional materials, due to the crucial importance of dissipating and managing heat in micro- and nano-electronic devices. Significant progress has been achieved for one-dimensional (1D) systems, both theoretically and experimentally. However, the study of heat conduction in two-dimensional (2D) systems is still in its infancy due to the limited availability of 2D materials and the technical challenges of fabricating suspended samples that are suitable for thermal measurements. In this review, we outline different experimental techniques and theoretical approaches for phonon thermal transport in 2D materials, discuss the problems and challenges of phonon thermal transport measurements and provide a comparison between existing experimental data. Special attention will be given to the effects of size, dimensionality, anisotropy and mode contributions in novel 2D systems, including graphene, boron nitride, MoS2, black phosphorous and silicene.
Exact Solution of Ising Model in 2d Shortcut Network
NASA Astrophysics Data System (ADS)
Shanker, O.
We give the exact solution to the Ising model in the shortcut network in the 2D limit. The solution is found by mapping the model to the square lattice model with Brascamp and Kunz boundary conditions.
Technical Review of the UNET2D Hydraulic Model
Perkins, William A.; Richmond, Marshall C.
2009-05-18
The Kansas City District of the US Army Corps of Engineers is engaged in a broad range of river management projects that require knowledge of spatially-varied hydraulic conditions such as velocities and water surface elevations. This information is needed to design new structures, improve existing operations, and assess aquatic habitat. Two-dimensional (2D) depth-averaged numerical hydraulic models are a common tool that can be used to provide velocity and depth information. Kansas City District is currently using a specific 2D model, UNET2D, that has been developed to meet the needs of their river engineering applications. This report documents a tech- nical review of UNET2D.
Reconstruction-based 3D/2D image registration.
Tomazevic, Dejan; Likar, Bostjan; Pernus, Franjo
2005-01-01
In this paper we present a novel 3D/2D registration method, where first, a 3D image is reconstructed from a few 2D X-ray images and next, the preoperative 3D image is brought into the best possible spatial correspondence with the reconstructed image by optimizing a similarity measure. Because the quality of the reconstructed image is generally low, we introduce a novel asymmetric mutual information similarity measure, which is able to cope with low image quality as well as with different imaging modalities. The novel 3D/2D registration method has been evaluated using standardized evaluation methodology and publicly available 3D CT, 3DRX, and MR and 2D X-ray images of two spine phantoms, for which gold standard registrations were known. In terms of robustness, reliability and capture range the proposed method outperformed the gradient-based method and the method based on digitally reconstructed radiographs (DRRs).
Alloyed 2D Metal-Semiconductor Atomic Layer Junctions.
Kim, Ah Ra; Kim, Yonghun; Nam, Jaewook; Chung, Hee-Suk; Kim, Dong Jae; Kwon, Jung-Dae; Park, Sang Won; Park, Jucheol; Choi, Sun Young; Lee, Byoung Hun; Park, Ji Hyeon; Lee, Kyu Hwan; Kim, Dong-Ho; Choi, Sung Mook; Ajayan, Pulickel M; Hahm, Myung Gwan; Cho, Byungjin
2016-03-09
Heterostructures of compositionally and electronically variant two-dimensional (2D) atomic layers are viable building blocks for ultrathin optoelectronic devices. We show that the composition of interfacial transition region between semiconducting WSe2 atomic layer channels and metallic NbSe2 contact layers can be engineered through interfacial doping with Nb atoms. WxNb1-xSe2 interfacial regions considerably lower the potential barrier height of the junction, significantly improving the performance of the corresponding WSe2-based field-effect transistor devices. The creation of such alloyed 2D junctions between dissimilar atomic layer domains could be the most important factor in controlling the electronic properties of 2D junctions and the design and fabrication of 2D atomic layer devices.
Dominant 2D magnetic turbulence in the solar wind
NASA Technical Reports Server (NTRS)
Bieber, John W.; Wanner, Wolfgang; Matthaeus, William H.
1995-01-01
There have been recent suggestions that solar wind magnetic turbulence may be a composite of slab geometry (wavevector aligned with the mean magnetic field) and 2D geometry (wavevectors perpendicular to the mean field). We report results of two new tests of this hypothesis using Helios measurements of inertial ranged magnetic spectra in the solar wind. The first test is based upon a characteristic difference between perpendicular and parallel reduced power spectra which is expected for the 2D component but not for the slab component. The second test examines the dependence of power spectrum density upon the magnetic field angle (i.e., the angle between the mean magnetic field and the radial direction), a relationship which is expected to be in opposite directions for the slab and 2D components. Both tests support the presence of a dominant (approximately 85 percent by energy) 2D component in solar wind magnetic turbulence.
Studying Zeolite Catalysts with a 2D Model System
Boscoboinik, Anibal
2016-12-07
Anibal Boscoboinik, a materials scientist at Brookhaven’s Center for Functional Nanomaterials, discusses the surface-science tools and 2D model system he uses to study catalysis in nanoporous zeolites, which catalyze reactions in many industrial processes.
Emerging and potential opportunities for 2D flexible nanoelectronics
NASA Astrophysics Data System (ADS)
Zhu, Weinan; Park, Saungeun; Akinwande, Deji
2016-05-01
The last 10 years have seen the emergence of two-dimensional (2D) nanomaterials such as graphene, transition metal dichalcogenides (TMDs), and black phosphorus (BP) among the growing portfolio of layered van der Waals thin films. Graphene, the prototypical 2D material has advanced rapidly in device, circuit and system studies that has resulted in commercial large-area applications. In this work, we provide a perspective of the emerging and potential translational applications of 2D materials including semiconductors, semimetals, and insulators that comprise the basic material set for diverse nanosystems. Applications include RF transceivers, smart systems, the so-called internet of things, and neurotechnology. We will review the DC and RF electronic performance of graphene and BP thin film transistors. 2D materials at sub-um channel length have so far enabled cut-off frequencies from baseband to 100GHz suitable for low-power RF and sub-THz concepts.
Wang, Jianwei; Zhang, Yong
2016-01-01
When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials. However, since graphite can be hypothetically derived from diamond by stretching it along its [111] axis, many 3D materials can also potentially be explored as new candidates for 2D materials. Using a density functional theory, we perform a systematic study over the common Group IV, III–V, and II–VI semiconductors along different deformation paths to reveal new structures that are topologically connected to but distinctly different from the 3D parent structure. Specifically, we explore two major phase transition paths, originating respectively from wurtzite and NiAs structure, by applying compressive and tensile strain along the symmetry axis, and calculating the total energy changes to search for potential metastable states, as well as phonon spectra to examine the structural stability. Each path is found to further split into two branches under tensile strain–low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure. Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side. PMID:27090430
Anisotropic 2D Materials for Tunable Hyperbolic Plasmonics.
Nemilentsau, Andrei; Low, Tony; Hanson, George
2016-02-12
Motivated by the recent emergence of a new class of anisotropic 2D materials, we examine their electromagnetic modes and demonstrate that a broad class of the materials can host highly directional hyperbolic plasmons. Their propagation direction can be manipulated on the spot by gate doping, enabling hyperbolic beam reflection, refraction, and bending. The realization of these natural 2D hyperbolic media opens up a new avenue in dynamic control of hyperbolic plasmons not possible in the 3D version.
RNA folding pathways and kinetics using 2D energy landscapes.
Senter, Evan; Dotu, Ivan; Clote, Peter
2015-01-01
RNA folding pathways play an important role in various biological processes, such as (i) the hok/sok (host-killing/suppression of killing) system in E. coli to check for sufficient plasmid copy number, (ii) the conformational switch in spliced leader (SL) RNA from Leptomonas collosoma, which controls trans splicing of a portion of the '5 exon, and (iii) riboswitches--portions of the 5' untranslated region of messenger RNA that regulate genes by allostery. Since RNA folding pathways are determined by the energy landscape, we describe a novel algorithm, FFTbor2D, which computes the 2D projection of the energy landscape for a given RNA sequence. Given two metastable secondary structures A, B for a given RNA sequence, FFTbor2D computes the Boltzmann probability p(x, y) = Z(x,y)/Z that a secondary structure has base pair distance x from A and distance y from B. Using polynomial interpolationwith the fast Fourier transform,we compute p(x, y) in O(n(5)) time and O(n(2)) space, which is an improvement over an earlier method, which runs in O(n(7)) time and O(n(4)) space. FFTbor2D has potential applications in synthetic biology, where one might wish to design bistable switches having target metastable structures A, B with favorable pathway kinetics. By inverting the transition probability matrix determined from FFTbor2D output, we show that L. collosoma spliced leader RNA has larger mean first passage time from A to B on the 2D energy landscape, than 97.145% of 20,000 sequences, each having metastable structures A, B. Source code and binaries are freely available for download at http://bioinformatics.bc.edu/clotelab/FFTbor2D. The program FFTbor2D is implemented in C++, with optional OpenMP parallelization primitives.
Supported and Free-Standing 2D Semimetals
2015-01-15
of this effort on focusing on rare- earth arsenides (RE-A), although not a van der Waals 2D solid, nonetheless, exhibits substantial 2D quantum size...this effort on focusing on rare- earth arsenides (RE- A), although not a van der Waals 20 solid, nonetheless, exhibits substantial 20 quantum size...Brongersma and S.R. Bank, "Rare- earth monopnictide alloys for tunable, epitaxial metals" in preparation. iii. S. Rahimi, E. M. Krivoy, J. Lee, M. E
Application of 2-D graphical representation of DNA sequence
NASA Astrophysics Data System (ADS)
Liao, Bo; Tan, Mingshu; Ding, Kequan
2005-10-01
Recently, we proposed a 2-D graphical representation of DNA sequence [Bo Liao, A 2-D graphical representation of DNA sequence, Chem. Phys. Lett. 401 (2005) 196-199]. Based on this representation, we consider properties of mutations and compute the similarities among 11 mitochondrial sequences belonging to different species. The elements of the similarity matrix are used to construct phylogenic tree. Unlike most existing phylogeny construction methods, the proposed method does not require multiple alignment.
phase_space_cosmo_fisher: Fisher matrix 2D contours
NASA Astrophysics Data System (ADS)
Stark, Alejo
2016-11-01
phase_space_cosmo_fisher produces Fisher matrix 2D contours from which the constraints on cosmological parameters can be derived. Given a specified redshift array and cosmological case, 2D marginalized contours of cosmological parameters are generated; the code can also plot the derivatives used in the Fisher matrix. In addition, this package can generate 3D plots of qH^2 and other cosmological quantities as a function of redshift and cosmology.
A simultaneous 2D/3D autostereo workstation
NASA Astrophysics Data System (ADS)
Chau, Dennis; McGinnis, Bradley; Talandis, Jonas; Leigh, Jason; Peterka, Tom; Knoll, Aaron; Sumer, Aslihan; Papka, Michael; Jellinek, Julius
2012-03-01
We present a novel immersive workstation environment that scientists can use for 3D data exploration and as their everyday 2D computer monitor. Our implementation is based on an autostereoscopic dynamic parallax barrier 2D/3D display, interactive input devices, and a software infrastructure that allows client/server software modules to couple the workstation to scientists' visualization applications. This paper describes the hardware construction and calibration, software components, and a demonstration of our system in nanoscale materials science exploration.
Phylogenetic tree construction based on 2D graphical representation
NASA Astrophysics Data System (ADS)
Liao, Bo; Shan, Xinzhou; Zhu, Wen; Li, Renfa
2006-04-01
A new approach based on the two-dimensional (2D) graphical representation of the whole genome sequence [Bo Liao, Chem. Phys. Lett., 401(2005) 196.] is proposed to analyze the phylogenetic relationships of genomes. The evolutionary distances are obtained through measuring the differences among the 2D curves. The fuzzy theory is used to construct phylogenetic tree. The phylogenetic relationships of H5N1 avian influenza virus illustrate the utility of our approach.
NASA Astrophysics Data System (ADS)
He, Y. J.; Chen, X.; Moumni, Z.
2012-08-01
Recent researches revealed that ferromagnetic shape memory alloys (FSMA) in 2D/3D configurations (with multi-axial stresses) had much more advantages (e.g., higher working stress and more application flexibility) than that in 1D configuration (with uniaxial stress). In literature, however, there is no simple criterion to judge whether a cyclic 3D magneto-mechanical loading can induce a large reversible strain (via martensite reorientation in FSMA). In this paper, a 3D magneto-mechanical energy analysis is proposed and incorporated into a phase diagram in terms of deviatoric stresses (including mechanical and magneto-stresses) to study the path-dependent (hysteretic) martensite reorientation in FSMA under 3D cyclic loadings. Based on the phase diagram (a plane graph), general criteria for obtaining reversible strain under cyclic magneto-mechanical loadings are derived, which provide basic guidelines for FSMA's applications under multi-axial loadings. Particularly for FSMA actuators driven by cyclic magnetic fields, the criteria of setting the 3D mechanical stresses to allow field-induced reversible strain are formulated. The 3D criteria can be reduced to 1D and 2D criteria which agree with the existing 1D/2D theoretical and experimental studies.
CYP2D6 variability in populations from Venezuela.
Moreno, Nancy; Flores-Angulo, Carlos; Villegas, Cecilia; Mora, Yuselin
2016-12-01
CYP2D6 is an important cytochrome P450 enzyme that plays an important role in the metabolism of about 25% of currently prescribed drugs. The presence of polymorphisms in the CYP2D6 gene may modulate enzyme level and activity, thereby affecting individual responses to pharmacological treatments. The most prevalent diseases in the admixed population from Venezuela are cardiovascular and cancer, whereas viral, bacterial and parasitic diseases, particularly malaria, are prevalent in Amerindian populations; in the treatment of these diseases, several drugs that are metabolized by CYP2D6 are used. In this work, we reviewed the data on CYP2D6 variability and predicted metabolizer phenotypes, in healthy volunteers of two admixed and five Amerindian populations from Venezuela. The Venezuelan population is very heterogeneous as a result of the genetic admixture of three major ethnical components: Europeans, Africans and Amerindians. There are noticeable inter-regional and inter-population differences in the process of mixing of this population. Hitherto, there are few published studies in Venezuela on CYP2D6; therefore, it is necessary to increase research in this regard, in particular to develop studies with a larger sample size. There is a considerable amount of work remaining before CYP2D6 is integrated into clinical practice in Venezuela.
Sculpting 3D spatial selectivity with pairs of 2D pulses: A comparison of methods
NASA Astrophysics Data System (ADS)
Farkash, Gil; Dumez, Jean-Nicolas; Frydman, Lucio
2016-12-01
Enhancing the specificity of the spins' excitation can improve the capabilities of magnetic resonance. Exciting voxels with tailored 3D shapes reduces partial volume effects and enhances contrast, particularly in cases where cubic voxels or other simple geometries do not provide an optimal localization. Spatial excitation profiles of arbitrary shapes can be implemented using so-called multidimensional RF pulses, which are often limited in practice to 2D implementations owing to their sensitivity to field inhomogeneities. Recent work has shown the potential of spatio-temporally encoded (SPEN) pulses towards alleviating these constraints. In particular, 2D pulses operating in a so-called hybrid scheme where the "low-bandwidth" spatial dimension is sculpted by a SPEN strategy while an orthogonal axis is shaped by regular k-space encoding, have been shown resilient to chemical shift and B0 field inhomogeneities. In this work we explore the use of pairs of 2D pulses, with one of these addressing geometries in the x-y plane and the other in the x-z dimension, to sculpt complex 3D volumes in phantoms and in vivo. To overcome limitations caused by the RF discretization demanded by these 2D pulses, a number of "unfolding" techniques yielding images from the centerband RF excitation while deleting sideband contributions - even in cases where center- and side-bands severely overlap - were developed. Thus it was possible to increase the gradient strengths applied along the low bandwidth dimensions, significantly improving the robustness of this kind of 3D sculpting pulses. Comparisons against conventional pulses designed on the basis of pure k-space trajectories, are presented.
2D Hexagonal Boron Nitride (2D-hBN) Explored for the Electrochemical Sensing of Dopamine.
Khan, Aamar F; Brownson, Dale A C; Randviir, Edward P; Smith, Graham C; Banks, Craig E
2016-10-04
Crystalline 2D hexagonal boron nitride (2D-hBN) nanosheets are explored as a potential electrocatalyst toward the electroanalytical sensing of dopamine (DA). The 2D-hBN nanosheets are electrically wired via a drop-casting modification process onto a range of commercially available carbon supporting electrodes, including glassy carbon (GC), boron-doped diamond (BDD), and screen-printed graphitic electrodes (SPEs). 2D-hBN has not previously been explored toward the electrochemical detection/electrochemical sensing of DA. We critically evaluate the potential electrocatalytic performance of 2D-hBN modified electrodes, the effect of supporting carbon electrode platforms, and the effect of "mass coverage" (which is commonly neglected in the 2D material literature) toward the detection of DA. The response of 2D-hBN modified electrodes is found to be largely dependent upon the interaction between 2D-hBN and the underlying supporting electrode material. For example, in the case of SPEs, modification with 2D-hBN (324 ng) improves the electrochemical response, decreasing the electrochemical oxidation potential of DA by ∼90 mV compared to an unmodified SPE. Conversely, modification of a GC electrode with 2D-hBN (324 ng) resulted in an increased oxidation potential of DA by ∼80 mV when compared to the unmodified electrode. We explore the underlying mechanisms of the aforementioned examples and infer that electrode surface interactions and roughness factors are critical considerations. 2D-hBN is utilized toward the sensing of DA in the presence of the common interferents ascorbic acid (AA) and uric acid (UA). 2D-hBN is found to be an effective electrocatalyst in the simultaneous detection of DA and UA at both pH 5.0 and 7.4. The peak separations/resolution between DA and UA increases by ∼70 and 50 mV (at pH 5.0 and 7.4, respectively, when utilizing 108 ng of 2D-hBN) compared to unmodified SPEs, with a particularly favorable response evident in pH 5.0, giving rise to a
2D Voronoi tessellation generated by lines and belts of dots
NASA Astrophysics Data System (ADS)
Fanfoni, M.; Filabozzi, A.; Placidi, E.; Patella, F.; Balzarotti, A.; Arciprete, F.
2016-01-01
The application of the Voronoi tessellation for studying the nucleation process at the basis of thin film formation dates back to the end of nineties. In particular, Poissonian and spatial correlated nuclei distributions were investigated. The growth of stressed interfaces, however, has evidenced that elastic strain can modify the spatial distribution of nuclei giving rise to new challenges at the level of stochastic geometry. Here we report a study of a 2D nucleation of dots randomly arranged in lines and/or belts on the surface. The results are compared to the experimental case of multilayer structures of InAs quantum dots grown on GaAs (001).
Auxetic Black Phosphorus: A 2D Material with Negative Poisson's Ratio.
Du, Yuchen; Maassen, Jesse; Wu, Wangran; Luo, Zhe; Xu, Xianfan; Ye, Peide D
2016-10-12
The Poisson's ratio of a material characterizes its response to uniaxial strain. Materials normally possess a positive Poisson's ratio - they contract laterally when stretched, and expand laterally when compressed. A negative Poisson's ratio is theoretically permissible but has not, with few exceptions of man-made bulk structures, been experimentally observed in any natural materials. Here, we show that the negative Poisson's ratio exists in the low-dimensional natural material black phosphorus and that our experimental observations are consistent with first-principles simulations. Through applying uniaxial strain along armchair direction, we have succeeded in demonstrating a cross-plane interlayer negative Poisson's ratio on black phosphorus for the first time. Meanwhile, our results support the existence of a cross-plane intralayer negative Poisson's ratio in the constituent phosphorene layers under uniaxial deformation along the zigzag axis, which is in line with a previous theoretical prediction. The phenomenon originates from the puckered structure of its in-plane lattice, together with coupled hinge-like bonding configurations.
NASA Astrophysics Data System (ADS)
Rowley-Neale, Samuel J.; Brownson, Dale A. C.; Smith, Graham C.; Sawtell, David A. G.; Kelly, Peter J.; Banks, Craig E.
2015-10-01
We explore the use of two-dimensional (2D) MoS2 nanosheets as an electrocatalyst for the Hydrogen Evolution Reaction (HER). Using four commonly employed commercially available carbon based electrode support materials, namely edge plane pyrolytic graphite (EPPG), glassy carbon (GC), boron-doped diamond (BDD) and screen-printed graphite electrodes (SPE), we critically evaluate the reported electrocatalytic performance of unmodified and MoS2 modified electrodes towards the HER. Surprisingly, current literature focuses almost exclusively on the use of GC as an underlying support electrode upon which HER materials are immobilised. 2D MoS2 nanosheet modified electrodes are found to exhibit a coverage dependant electrocatalytic effect towards the HER. Modification of the supporting electrode surface with an optimal mass of 2D MoS2 nanosheets results in a lowering of the HER onset potential by ca. 0.33, 0.57, 0.29 and 0.31 V at EPPG, GC, SPE and BDD electrodes compared to their unmodified counterparts respectively. The lowering of the HER onset potential is associated with each supporting electrode's individual electron transfer kinetics/properties and is thus distinct. The effect of MoS2 coverage is also explored. We reveal that its ability to catalyse the HER is dependent on the mass deposited until a critical mass of 2D MoS2 nanosheets is achieved, after which its electrocatalytic benefits and/or surface stability curtail. The active surface site density and turn over frequency for the 2D MoS2 nanosheets is determined, characterised and found to be dependent on both the coverage of 2D MoS2 nanosheets and the underlying/supporting substrate. This work is essential for those designing, fabricating and consequently electrochemically testing 2D nanosheet materials for the HER.We explore the use of two-dimensional (2D) MoS2 nanosheets as an electrocatalyst for the Hydrogen Evolution Reaction (HER). Using four commonly employed commercially available carbon based electrode
4D tumor centroid tracking using orthogonal 2D dynamic MRI: Implications for radiotherapy planning
Tryggestad, Erik; Flammang, Aaron; Shea, Steven M.; Hales, Russell; Herman, Joseph; Lee, Junghoon; McNutt, Todd; Roland, Teboh; Wong, John
2013-09-15
Purpose: Current pretreatment, 4D imaging techniques are suboptimal in that they sample breathing motion over a very limited “snapshot” in time. Heretofore, long-duration, 4D motion characterization for radiotherapy planning, margin optimization, and validation have been impractical for safety reasons, requiring invasive markers imaged under x-ray fluoroscopy. To characterize 3D tumor motion and associated variability over durations more consistent with treatments, the authors have developed a practical dynamic MRI (dMRI) technique employing two orthogonal planes acquired in a continuous, interleaved fashion.Methods: 2D balanced steady-state free precession MRI was acquired continuously over 9–14 min at approximately 4 Hz in three healthy volunteers using a commercial 1.5 T system; alternating orthogonal imaging planes (sagittal, coronal, sagittal, etc.) were employed. The 2D in-plane pixel resolution was 2 × 2 mm{sup 2} with a 5 mm slice profile. Simultaneous with image acquisition, the authors monitored a 1D surrogate respiratory signal using a device available with the MRI system. 2D template matching-based anatomic feature registration, or tracking, was performed independently in each orientation. 4D feature tracking at the raw frame rate was derived using spline interpolation.Results: Tracking vascular features in the lung for two volunteers and pancreatic features in one volunteer, the authors have successfully demonstrated this method. Registration error, defined here as the difference between the sagittal and coronal tracking result in the SI direction, ranged from 0.7 to 1.6 mm (1σ) which was less than the acquired image resolution. Although the healthy volunteers were instructed to relax and breathe normally, significantly variable respiration was observed. To demonstrate potential applications of this technique, the authors subsequently explored the intrafraction stability of hypothetical tumoral internal target volumes and 3D spatial probability
2015-01-15
Austin, 10100 Burnet Rd, Austin, TX 78758, U.S.A. etutuc@mer.utexas.edu Abstract Vertical heterostructures consisting of atomic layers separated...accessible in single layer devices. In this presentation we discuss two examples of vertical heterostructures of atomic layer materials, where...Engineering Columbia University, New York, NY 10027 In this paper, we will discuss recent advances in the study of atomically thin layers of
Fast 2-D ultrasound strain imaging: the benefits of using a GPU.
Idzenga, Tim; Gaburov, Evghenii; Vermin, Willem; Menssen, Jan; de Korte, Chris
2014-01-01
Deformation of tissue can be accurately estimated from radio-frequency ultrasound data using a 2-dimensional normalized cross correlation (NCC)-based algorithm. This procedure, however, is very computationally time-consuming. A major time reduction can be achieved by parallelizing the numerous computations of NCC. In this paper, two approaches for parallelization have been investigated: the OpenMP interface on a multi-CPU system and Compute Unified Device Architecture (CUDA) on a graphics processing unit (GPU). The performance of the OpenMP and GPU approaches were compared with a conventional Matlab implementation of NCC. The OpenMP approach with 8 threads achieved a maximum speed-up factor of 132 on the computing of NCC, whereas the GPU approach on an Nvidia Tesla K20 achieved a maximum speed-up factor of 376. Neither parallelization approach resulted in a significant loss in image quality of the elastograms. Parallelization of the NCC computations using the GPU, therefore, significantly reduces the computation time and increases the frame rate for motion estimation.
Validation of a Scaled Plane Strain Hypervelocity Gouging Model
2006-03-01
enough for 1080 endeos epdata mix 3 matep 1 JO USER * J-C coefficients for VascoMax 300. ajo = 2.17e10 * Dynes/cm^2 bjo= 0.124e10 * Dynes... ajo = 5.25e9 * Dynes/cm^2 bjo= 3.59e7 * Dynes/cm^2 cjo= 0.29 mjo= 6.525e-1 njo= 0.6677 tjo= .1591885e-1 poisson...300. ajo = 2.17e10 * Dynes/cm^2 bjo= 0.124e10 * Dynes/cm^2 cjo= 0.0046 mjo= 0.95 njo= 0.3737 tjo= .040161e-1 poisson= 0.283
A statistical approach to estimate the 3D size distribution of spheres from 2D size distributions
Kong, M.; Bhattacharya, R.N.; James, C.; Basu, A.
2005-01-01
Size distribution of rigidly embedded spheres in a groundmass is usually determined from measurements of the radii of the two-dimensional (2D) circular cross sections of the spheres in random flat planes of a sample, such as in thin sections or polished slabs. Several methods have been devised to find a simple factor to convert the mean of such 2D size distributions to the actual 3D mean size of the spheres without a consensus. We derive an entirely theoretical solution based on well-established probability laws and not constrained by limitations of absolute size, which indicates that the ratio of the means of measured 2D and estimated 3D grain size distribution should be r/4 (=.785). Actual 2D size distribution of the radii of submicron sized, pure Fe0 globules in lunar agglutinitic glass, determined from backscattered electron images, is tested to fit the gamma size distribution model better than the log-normal model. Numerical analysis of 2D size distributions of Fe0 globules in 9 lunar soils shows that the average mean of 2D/3D ratio is 0.84, which is very close to the theoretical value. These results converge with the ratio 0.8 that Hughes (1978) determined for millimeter-sized chondrules from empirical measurements. We recommend that a factor of 1.273 (reciprocal of 0.785) be used to convert the determined 2D mean size (radius or diameter) of a population of spheres to estimate their actual 3D size. ?? 2005 Geological Society of America.
Rowley-Neale, Samuel J; Brownson, Dale A C; Smith, Graham C; Sawtell, David A G; Kelly, Peter J; Banks, Craig E
2015-11-21
We explore the use of two-dimensional (2D) MoS2 nanosheets as an electrocatalyst for the Hydrogen Evolution Reaction (HER). Using four commonly employed commercially available carbon based electrode support materials, namely edge plane pyrolytic graphite (EPPG), glassy carbon (GC), boron-doped diamond (BDD) and screen-printed graphite electrodes (SPE), we critically evaluate the reported electrocatalytic performance of unmodified and MoS2 modified electrodes towards the HER. Surprisingly, current literature focuses almost exclusively on the use of GC as an underlying support electrode upon which HER materials are immobilised. 2D MoS2 nanosheet modified electrodes are found to exhibit a coverage dependant electrocatalytic effect towards the HER. Modification of the supporting electrode surface with an optimal mass of 2D MoS2 nanosheets results in a lowering of the HER onset potential by ca. 0.33, 0.57, 0.29 and 0.31 V at EPPG, GC, SPE and BDD electrodes compared to their unmodified counterparts respectively. The lowering of the HER onset potential is associated with each supporting electrode's individual electron transfer kinetics/properties and is thus distinct. The effect of MoS2 coverage is also explored. We reveal that its ability to catalyse the HER is dependent on the mass deposited until a critical mass of 2D MoS2 nanosheets is achieved, after which its electrocatalytic benefits and/or surface stability curtail. The active surface site density and turn over frequency for the 2D MoS2 nanosheets is determined, characterised and found to be dependent on both the coverage of 2D MoS2 nanosheets and the underlying/supporting substrate. This work is essential for those designing, fabricating and consequently electrochemically testing 2D nanosheet materials for the HER.
Regulation of ligands for the activating receptor NKG2D
Mistry, Anita R; O'Callaghan, Chris A
2007-01-01
The outcome of an encounter between a cytotoxic cell and a potential target cell depends on the balance of signals from inhibitory and activating receptors. Natural Killer group 2D (NKG2D) has recently emerged as a major activating receptor on T lymphocytes and natural killer cells. In both humans and mice, multiple different genes encode ligands for NKG2D, and these ligands are non-classical major histocompatibility complex class I molecules. The NKG2D–ligand interaction triggers an activating signal in the cell expressing NKG2D and this promotes cytotoxic lysis of the cell expressing the ligand. Most normal tissues do not express ligands for NKG2D, but ligand expression has been documented in tumour and virus-infected cells, leading to lysis of these cells. Tight regulation of ligand expression is important. If there is inappropriate expression in normal tissues, this will favour autoimmune processes, whilst failure to up-regulate the ligands in pathological conditions would favour cancer development or dissemination of intracellular infection. PMID:17614877
Rotation invariance principles in 2D/3D registration
NASA Astrophysics Data System (ADS)
Birkfellner, Wolfgang; Wirth, Joachim; Burgstaller, Wolfgang; Baumann, Bernard; Staedele, Harald; Hammer, Beat; Gellrich, Niels C.; Jacob, Augustinus L.; Regazzoni, Pietro; Messmer, Peter
2003-05-01
2D/3D patient-to-computed tomography (CT) registration is a method to determine a transformation that maps two coordinate systems by comparing a projection image rendered from CT to a real projection image. Applications include exact patient positioning in radiation therapy, calibration of surgical robots, and pose estimation in computer-aided surgery. One of the problems associated with 2D/3D registration is the fast that finding a registration includes sovling a minimization problem in six degrees-of-freedom in motion. This results in considerable time expenses since for each iteration step at least one volume rendering has to be computed. We show that by choosing an appropriate world coordinate system and by applying a 2D/2D registration method in each iteration step, the number of iterations can be grossly reduced from n6 to n5. Here, n is the number of discrete variations aroudn a given coordinate. Depending on the configuration of the optimization algorithm, this reduces the total number of iterations necessary to at least 1/3 of its original value. The method was implemented and extensively tested on simulated x-ray images of a pelvis. We conclude that this hardware-indepenent optimization of 2D/3D registration is a step towards increasing the acceptance of this promising method for a wide number of clinical applications.
2D nanostructures for water purification: graphene and beyond.
Dervin, Saoirse; Dionysiou, Dionysios D; Pillai, Suresh C
2016-08-18
Owing to their atomically thin structure, large surface area and mechanical strength, 2D nanoporous materials are considered to be suitable alternatives for existing desalination and water purification membrane materials. Recent progress in the development of nanoporous graphene based materials has generated enormous potential for water purification technologies. Progress in the development of nanoporous graphene and graphene oxide (GO) membranes, the mechanism of graphene molecular sieve action, structural design, hydrophilic nature, mechanical strength and antifouling properties and the principal challenges associated with nanopore generation are discussed in detail. Subsequently, the recent applications and performance of newly developed 2D materials such as 2D boron nitride (BN) nanosheets, graphyne, molybdenum disulfide (MoS2), tungsten chalcogenides (WS2) and titanium carbide (Ti3C2Tx) are highlighted. In addition, the challenges affecting 2D nanostructures for water purification are highlighted and their applications in the water purification industry are discussed. Though only a few 2D materials have been explored so far for water treatment applications, this emerging field of research is set to attract a great deal of attention in the near future.
2D Materials for Optical Modulation: Challenges and Opportunities.
Yu, Shaoliang; Wu, Xiaoqin; Wang, Yipei; Guo, Xin; Tong, Limin
2017-02-21
Owing to their atomic layer thickness, strong light-material interaction, high nonlinearity, broadband optical response, fast relaxation, controllable optoelectronic properties, and high compatibility with other photonic structures, 2D materials, including graphene, transition metal dichalcogenides and black phosphorus, have been attracting increasing attention for photonic applications. By tuning the carrier density via electrical or optical means that modifies their physical properties (e.g., Fermi level or nonlinear absorption), optical response of the 2D materials can be instantly changed, making them versatile nanostructures for optical modulation. Here, up-to-date 2D material-based optical modulation in three categories is reviewed: free-space, fiber-based, and on-chip configurations. By analysing cons and pros of different modulation approaches from material and mechanism aspects, the challenges faced by using these materials for device applications are presented. In addition, thermal effects (e.g., laser induced damage) in 2D materials, which are critical to practical applications, are also discussed. Finally, the outlook for future opportunities of these 2D materials for optical modulation is given.
2D DIGE saturation labeling for minute sample amounts.
Arnold, Georg J; Fröhlich, Thomas
2012-01-01
The 2D DIGE technique, based on fluorophores covalently linked to amino acid side chain residues and the concept of an internal standard, has significantly improved reproducibility, sensitivity, and the dynamic range of protein quantification. In saturation DIGE, sulfhydryl groups of cysteines are labeled with cyanine dyes to completion, providing a so far unraveled sensitivity for protein detection and quantification in 2D gel-based proteomic experiments. Only a few micrograms of protein per 2D gel facilitate the analysis of about 2,000 analytes from complex mammalian cell or tissue samples. As a consequence, 2D saturation DIGE is the method of choice when only minute sample amounts are available for quantitative proteome analysis at the level of proteins rather than peptides. Since very low amounts of samples have to be handled in a reproducible manner, saturation DIGE-based proteomic experiments are technically demanding. Moreover, successful saturation DIGE approaches require a strict adherence to adequate reaction conditions at each step. This chapter is dedicated to colleagues already experienced in 2D PAGE protein separation and intends to support the establishment of this ultrasensitive technique in proteomic workgroups. We provide basic guidelines for the experimental design and discuss crucial aspects concerning labeling chemistry, sample preparation, and pitfalls caused by labeling artifacts. A detailed step-by-step protocol comprises all aspects from initial sample preparation to image analysis and statistical evaluation. Furthermore, we describe the generation of preparative saturation DIGE gels necessary for mass spectrometry-based spot identification.
Mermin–Wagner fluctuations in 2D amorphous solids
Illing, Bernd; Fritschi, Sebastian; Kaiser, Herbert; Klix, Christian L.; Maret, Georg; Keim, Peter
2017-01-01
In a recent commentary, J. M. Kosterlitz described how D. Thouless and he got motivated to investigate melting and suprafluidity in two dimensions [Kosterlitz JM (2016) J Phys Condens Matter 28:481001]. It was due to the lack of broken translational symmetry in two dimensions—doubting the existence of 2D crystals—and the first computer simulations foretelling 2D crystals (at least in tiny systems). The lack of broken symmetries proposed by D. Mermin and H. Wagner is caused by long wavelength density fluctuations. Those fluctuations do not only have structural impact, but additionally a dynamical one: They cause the Lindemann criterion to fail in 2D in the sense that the mean squared displacement of atoms is not limited. Comparing experimental data from 3D and 2D amorphous solids with 2D crystals, we disentangle Mermin–Wagner fluctuations from glassy structural relaxations. Furthermore, we demonstrate with computer simulations the logarithmic increase of displacements with system size: Periodicity is not a requirement for Mermin–Wagner fluctuations, which conserve the homogeneity of space on long scales. PMID:28137872
Sparse radar imaging using 2D compressed sensing
NASA Astrophysics Data System (ADS)
Hou, Qingkai; Liu, Yang; Chen, Zengping; Su, Shaoying
2014-10-01
Radar imaging is an ill-posed linear inverse problem and compressed sensing (CS) has been proved to have tremendous potential in this field. This paper surveys the theory of radar imaging and a conclusion is drawn that the processing of ISAR imaging can be denoted mathematically as a problem of 2D sparse decomposition. Based on CS, we propose a novel measuring strategy for ISAR imaging radar and utilize random sub-sampling in both range and azimuth dimensions, which will reduce the amount of sampling data tremendously. In order to handle 2D reconstructing problem, the ordinary solution is converting the 2D problem into 1D by Kronecker product, which will increase the size of dictionary and computational cost sharply. In this paper, we introduce the 2D-SL0 algorithm into the reconstruction of imaging. It is proved that 2D-SL0 can achieve equivalent result as other 1D reconstructing methods, but the computational complexity and memory usage is reduced significantly. Moreover, we will state the results of simulating experiments and prove the effectiveness and feasibility of our method.
Mean flow and anisotropic cascades in decaying 2D turbulence
NASA Astrophysics Data System (ADS)
Liu, Chien-Chia; Cerbus, Rory; Gioia, Gustavo; Chakraborty, Pinaki
2015-11-01
Many large-scale atmospheric and oceanic flows are decaying 2D turbulent flows embedded in a non-uniform mean flow. Despite its importance for large-scale weather systems, the affect of non-uniform mean flows on decaying 2D turbulence remains unknown. In the absence of mean flow it is well known that decaying 2D turbulent flows exhibit the enstrophy cascade. More generally, for any 2D turbulent flow, all computational, experimental and field data amassed to date indicate that the spectrum of longitudinal and transverse velocity fluctuations correspond to the same cascade, signifying isotropy of cascades. Here we report experiments on decaying 2D turbulence in soap films with a non-uniform mean flow. We find that the flow transitions from the usual isotropic enstrophy cascade to a series of unusual and, to our knowledge, never before observed or predicted, anisotropic cascades where the longitudinal and transverse spectra are mutually independent. We discuss implications of our results for decaying geophysical turbulence.
2-D Clinostat for Simulated Microgravity Experiments with Arabidopsis Seedlings
NASA Astrophysics Data System (ADS)
Wang, Hui; Li, Xugang; Krause, Lars; Görög, Mark; Schüler, Oliver; Hauslage, Jens; Hemmersbach, Ruth; Kircher, Stefan; Lasok, Hanna; Haser, Thomas; Rapp, Katja; Schmidt, Jürgen; Yu, Xin; Pasternak, Taras; Aubry-Hivet, Dorothée; Tietz, Olaf; Dovzhenko, Alexander; Palme, Klaus; Ditengou, Franck Anicet
2016-04-01
Ground-based simulators of microgravity such as fast rotating 2-D clinostats are valuable tools to study gravity related processes. We describe here a versatile g-value-adjustable 2-D clinostat that is suitable for plant analysis. To avoid seedling adaptation to 1 g after clinorotation, we designed chambers that allow rapid fixation. A detailed protocol for fixation, RNA isolation and the analysis of selected genes is described. Using this clinostat we show that mRNA levels of LONG HYPOCOTYL 5 (HY5), MIZU-KUSSEI 1 (MIZ1) and microRNA MIR163 are down-regulated in 5-day-old Arabidopsis thaliana roots after 3 min and 6 min of clinorotation using a maximal reduced g-force of 0.02 g, hence demonstrating that this 2-D clinostat enables the characterization of early transcriptomic events during root response to microgravity. We further show that this 2-D clinostat is able to compensate the action of gravitational force as both gravitropic-dependent statolith sedimentation and subsequent auxin redistribution (monitoring D R5 r e v :: G F P reporter) are abolished when plants are clinorotated. Our results demonstrate that 2-D clinostats equipped with interchangeable growth chambers and tunable rotation velocity are suitable for studying how plants perceive and respond to simulated microgravity.
Spin texture on the Fermi surface of tensile-strained HgTe
NASA Astrophysics Data System (ADS)
Zaheer, Saad; Young, S. M.; Cellucci, D.; Teo, J. C. Y.; Kane, C. L.; Mele, E. J.; Rappe, Andrew M.
2013-01-01
We present ab initio and k·p calculations of the spin texture on the Fermi surface of tensile-strained HgTe, which is obtained by stretching the zinc-blende lattice along the (111) axis. Tensile-strained HgTe is a semimetal with pointlike accidental degeneracies between a mirror symmetry protected twofold degenerate band and two nondegenerate bands near the Fermi level. The Fermi surface consists of two ellipsoids which contact at the point where the Fermi level crosses the twofold degenerate band along the (111) axis. However, the spin texture of occupied states indicates that neither ellipsoid carries a compensating Chern number. Consequently, the spin texture is locked in the plane perpendicular to the (111) axis, exhibits a nonzero winding number in that plane, and changes winding number from one end of the Fermi ellipsoids to the other. The change in the winding of the spin texture suggests the existence of singular points. An ordered alloy of HgTe with ZnTe has the same effect as stretching the zinc-blende lattice in the (111) direction. We present ab initio calculations of ordered HgxZn1-xTe that confirm the existence of a spin texture locked in a 2D plane on the Fermi surface with different winding numbers on either end.
Secretory pathways generating immunosuppressive NKG2D ligands
Baragaño Raneros, Aroa; Suarez-Álvarez, Beatriz; López-Larrea, Carlos
2014-01-01
Natural Killer Group 2 member D (NKG2D) activating receptor, present on the surface of various immune cells, plays an important role in activating the anticancer immune response by their interaction with stress-inducible NKG2D ligands (NKG2DL) on transformed cells. However, cancer cells have developed numerous mechanisms to evade the immune system via the downregulation of NKG2DL from the cell surface, including the release of NKG2DL from the cell surface in a soluble form. Here, we review the mechanisms involved in the production of soluble NKG2DL (sNKG2DL) and the potential therapeutic strategies aiming to block the release of these immunosuppressive ligands. Therapeutically enabling the NKG2D-NKG2DL interaction would promote immunorecognition of malignant cells, thus abrogating disease progression. PMID:25050215
Splashing transients of 2D plasmons launched by swift electrons
Lin, Xiao; Kaminer, Ido; Shi, Xihang; Gao, Fei; Yang, Zhaoju; Gao, Zhen; Buljan, Hrvoje; Joannopoulos, John D.; Soljačić, Marin; Chen, Hongsheng; Zhang, Baile
2017-01-01
Launching of plasmons by swift electrons has long been used in electron energy–loss spectroscopy (EELS) to investigate the plasmonic properties of ultrathin, or two-dimensional (2D), electron systems. However, the question of how a swift electron generates plasmons in space and time has never been answered. We address this issue by calculating and demonstrating the spatial-temporal dynamics of 2D plasmon generation in graphene. We predict a jet-like rise of excessive charge concentration that delays the generation of 2D plasmons in EELS, exhibiting an analog to the hydrodynamic Rayleigh jet in a splashing phenomenon before the launching of ripples. The photon radiation, analogous to the splashing sound, accompanies the plasmon emission and can be understood as being shaken off by the Rayleigh jet–like charge concentration. Considering this newly revealed process, we argue that previous estimates on the yields of graphene plasmons in EELS need to be reevaluated. PMID:28138546
Available information in 2D motional Stark effect imaging.
Creese, Mathew; Howard, John
2010-10-01
Recent advances in imaging techniques have allowed the extension of the standard polarimetric 1D motional Stark effect (MSE) diagnostic to 2D imaging of the internal magnetic field of fusion devices [J. Howard, Plasma Phys. Controlled Fusion 50, 125003 (2008)]. This development is met with the challenge of identifying and extracting the new information, which can then be used to increase the accuracy of plasma equilibrium and current density profile determinations. This paper develops a 2D analysis of the projected MSE polarization orientation and Doppler phase shift. It is found that, for a standard viewing position, the 2D MSE imaging system captures sufficient information to allow imaging of the internal vertical magnetic field component B(Z)(r,z) in a tokamak.
Perception-based reversible watermarking for 2D vector maps
NASA Astrophysics Data System (ADS)
Men, Chaoguang; Cao, Liujuan; Li, Xiang
2010-07-01
This paper presents an effective and reversible watermarking approach for digital copyright protection of 2D-vector maps. To ensure that the embedded watermark is insensitive for human perception, we only select the noise non-sensitive regions for watermark embedding by estimating vertex density within each polyline. To ensure the exact recovery of original 2D-vector map after watermark extraction, we introduce a new reversible watermarking scheme based on reversible high-frequency wavelet coefficients modification. Within the former-selected non-sensitive regions, our watermarking operates on the lower-order vertex coordinate decimals with integer wavelet transform. Such operation further reduces the visual distortion caused by watermark embedding. We have validated the effectiveness of our scheme on our real-world city river/building 2D-vector maps. We give extensive experimental comparisons with state-of-the-art methods, including embedding capability, invisibility, and robustness over watermark attacking.
Microscale 2D separation systems for proteomic analysis
Xu, Xin; Liu, Ke; Fan, Z. Hugh
2012-01-01
Microscale 2D separation systems have been implemented in capillaries and microfabricated channels. They offer advantages of faster analysis, higher separation efficiency and less sample consumption than the conventional methods, such as liquid chromatography (LC) in a column and slab gel electrophoresis. In this article, we review their recent advancement, focusing on three types of platforms, including 2D capillary electrophoresis (CE), CE coupling with capillary LC, and microfluidic devices. A variety of CE and LC modes have been employed to construct 2D separation systems via sophistically designed interfaces. Coupling of different separation modes has also been realized in a number of microfluidic devices. These separation systems have been applied for the proteomic analysis of various biological samples, ranging from a single cell to tumor tissues. PMID:22462786
2D materials for photon conversion and nanophotonics
NASA Astrophysics Data System (ADS)
Tahersima, Mohammad H.; Sorger, Volker J.
2015-09-01
The field of two-dimensional (2D) materials has the potential to enable unique applications across a wide range of the electromagnetic spectrum. While 2D-layered materials hold promise for next-generation photon-conversion intrinsic limitations and challenges exist that shall be overcome. Here we discuss the intrinsic limitations as well as application opportunities of this new class of materials, and is sponsored by the NSF program Designing Materials to Revolutionize and Engineer our Future (DMREF) program, which links to the President's Materials Genome Initiative. We present general material-related details for photon conversion, and show that taking advantage of the mechanical flexibility of 2D materials by rolling MoS2/graphene/hexagonal boron nitride stack to a spiral solar cell allows for solar absorption up to 90%.
Rapid-scan coherent 2D fluorescence spectroscopy.
Draeger, Simon; Roeding, Sebastian; Brixner, Tobias
2017-02-20
We developed pulse-shaper-assisted coherent two-dimensional (2D) electronic spectroscopy in liquids using fluorescence detection. A customized pulse shaper facilitates shot-to-shot modulation at 1 kHz and is employed for rapid scanning over all time delays. A full 2D spectrum with 15 × 15 pixels is obtained in approximately 6 s of measurement time (plus further averaging if needed). Coherent information is extracted from the incoherent fluorescence signal via 27-step phase cycling. We exemplify the technique on cresyl violet in ethanol and recover literature-known oscillations as a function of population time. Signal-to-noise behavior is analyzed as a function of the amount of averaging. Rapid scanning provides a 2D spectrum with a root-mean-square error of < 0.05 after 1 min of measurement time.
2D-3D transition of gold cluster anions resolved
NASA Astrophysics Data System (ADS)
Johansson, Mikael P.; Lechtken, Anne; Schooss, Detlef; Kappes, Manfred M.; Furche, Filipp
2008-05-01
Small gold cluster anions Aun- are known for their unusual two-dimensional (2D) structures, giving rise to properties very different from those of bulk gold. Previous experiments and calculations disagree about the number of gold atoms nc where the transition to 3D structures occurs. We combine trapped ion electron diffraction and state of the art electronic structure calculations to resolve this puzzle and establish nc=12 . It is shown that theoretical studies using traditional generalized gradient functionals are heavily biased towards 2D structures. For a correct prediction of the 2D-3D crossover point it is crucial to use density functionals yielding accurate jellium surface energies, such as the Tao-Perdew-Staroverov-Scuseria (TPSS) functional or the Perdew-Burke-Ernzerhof functional modified for solids (PBEsol). Further, spin-orbit effects have to be included, and large, flexible basis sets employed. This combined theoretical-experimental approach is promising for larger gold and other metal clusters.
IUPAP Award: Ion transport in 2D materials
NASA Astrophysics Data System (ADS)
Bao, Wenzhong
Intercalation in 2D materials drastically influences both physical and chemical properties, which leads to a new degree of freedom for fundamental studies and expands the potential applications of 2D materials. In this talk, I will discuss our work in the past two years related to ion intercalation of 2D materials, including insertion of Li and Na ions in graphene and MoS2. We focused on both fundamental mechanism and potential application, e.g. we measured in-situ optical transmittance spectra and electrical transport properties of few-layer graphene (FLG) nanostructures upon electrochemical lithiation/delithiation. By observing a simultaneous increase of both optical transmittance and DC conductivity, strikingly different from other materials, we proposed its application as a next generation transparent electrode.
2d-retrieval For Mipas-envisat
NASA Astrophysics Data System (ADS)
Steck, T.; von Clarmann, T.; Grabowski, U.; Höpfner, M.
Limb sounding of the Earth's atmosphere provides vertically high resolved profiles of geophysical parameters. The long ray path through the atmosphere makes limb sounders sensitive to even little abundant species. On the other hand, horizontal in- homogeneities, if not taken into account properly, can cause systematic errors within the retrieval process. Especially for limb emission measurements in the mid IR, at- mopheric temperature gradients result in considerable vmr retrieval errors if they are neglected. We present a dedicated method of taking full 2D fields of state parameters (indepen- dent of tangent points) into account in the forward model and in the retrieval. The basic idea is that the 2D state vector is updated sequentially for each limb scan. This method is applied to the 2D retrieval of temperature and vmr for simulated radiances as expected from MIPAS-ENVISAT.
Genetics, genomics, and evolutionary biology of NKG2D ligands.
Carapito, Raphael; Bahram, Seiamak
2015-09-01
Human and mouse NKG2D ligands (NKG2DLs) are absent or only poorly expressed by most normal cells but are upregulated by cell stress, hence, alerting the immune system in case of malignancy or infection. Although these ligands are numerous and highly variable (at genetic, genomic, structural, and biochemical levels), they all belong to the major histocompatibility complex class I gene superfamily and bind to a single, invariant, receptor: NKG2D. NKG2D (CD314) is an activating receptor expressed on NK cells and subsets of T cells that have a key role in the recognition and lysis of infected and tumor cells. Here, we review the molecular diversity of NKG2DLs, discuss the increasing appreciation of their roles in a variety of medical conditions, and propose several explanations for the evolutionary force(s) that seem to drive the multiplicity and diversity of NKG2DLs while maintaining their interaction with a single invariant receptor.
Graphene based 2D-materials for supercapacitors
NASA Astrophysics Data System (ADS)
Palaniselvam, Thangavelu; Baek, Jong-Beom
2015-09-01
Ever-increasing energy demands and the depletion of fossil fuels are compelling humanity toward the development of suitable electrochemical energy conversion and storage devices to attain a more sustainable society with adequate renewable energy and zero environmental pollution. In this regard, supercapacitors are being contemplated as potential energy storage devices to afford cleaner, environmentally friendly energy. Recently, a great deal of attention has been paid to two-dimensional (2D) nanomaterials, including 2D graphene and its inorganic analogues (transition metal double layer hydroxides, chalcogenides, etc), as potential electrodes for the development of supercapacitors with high electrochemical performance. This review provides an overview of the recent progress in using these graphene-based 2D materials as potential electrodes for supercapacitors. In addition, future research trends including notable challenges and opportunities are also discussed.
Chemical vapour deposition: Transition metal carbides go 2D
Gogotsi, Yury
2015-08-17
Here, the research community has been steadily expanding the family of few-atom-thick crystals beyond graphene, discovering new materials or producing known materials in a 2D state and demonstrating their unique properties1, 2. Recently, nanometre-thin 2D transition metal carbides have also joined this family3. Writing in Nature Materials, Chuan Xu and colleagues now report a significant advance in the field, showing the synthesis of large-area, high-quality, nanometre-thin crystals of molybdenum carbide that demonstrate low-temperature 2D superconductivity4. Moreover, they also show that other ultrathin carbide crystals, such as tungsten and tantalum carbides, can be grown by chemical vapour deposition with a highmore » crystallinity and very low defect concentration.« less
Optoelectronics based on 2D TMDs and heterostructures
NASA Astrophysics Data System (ADS)
Huo, Nengjie; Yang, Yujue; Li, Jingbo
2017-03-01
2D materials including graphene and TMDs have proven interesting physical properties and promising optoelectronic applications. We reviewed the growth, characterization and optoelectronics based on 2D TMDs and their heterostructures, and demonstrated their unique and high quality of performances. For example, we observed the large mobility, fast response and high photo-responsivity in MoS2, WS2 and WSe2 phototransistors, as well as the novel performances in vdW heterostructures such as the strong interlayer coupling, am-bipolar and rectifying behaviour, and the obvious photovoltaic effect. It is being possible that 2D family materials could play an increasingly important role in the future nano- and opto-electronics, more even than traditional semiconductors such as silicon.
Chemical vapour deposition: Transition metal carbides go 2D
Gogotsi, Yury
2015-08-17
Here, the research community has been steadily expanding the family of few-atom-thick crystals beyond graphene, discovering new materials or producing known materials in a 2D state and demonstrating their unique properties^{1, 2}. Recently, nanometre-thin 2D transition metal carbides have also joined this family^{3}. Writing in Nature Materials, Chuan Xu and colleagues now report a significant advance in the field, showing the synthesis of large-area, high-quality, nanometre-thin crystals of molybdenum carbide that demonstrate low-temperature 2D superconductivity^{4}. Moreover, they also show that other ultrathin carbide crystals, such as tungsten and tantalum carbides, can be grown by chemical vapour deposition with a high crystallinity and very low defect concentration.
NASA Astrophysics Data System (ADS)
Elinski, Meagan B.; Liu, Zhuotong; Spear, Jessica C.; Batteas, James D.
2017-03-01
The use of 2D nanomaterials for controlling friction and wear at interfaces has received increased attention over the past few years due to their unique structural, thermal, electrical and mechanical properties. These materials proffer potential critical solutions to challenges in boundary lubrication across numerous platforms ranging from engines, to biomedical implants and micro- and nano-scaled machines that will play a major role in the Internet of Things. There has been significant work on a range of 2D nanomaterials, such as graphene and molybdenum disulfide (MoS2). From these studies, their frictional properties have been shown to be highly dependent on numerous factors, such as substrate structure, strain, and competing chemical interactions between the interfaces in sliding contact. Moreover, when considering real contacts in machined interfaces, these surfaces are often composed of nanoscaled asperities, whose intermittent contact dominates the tribochemical processes that result in wear. In this review we aim to capture recent work on the tribological properties of graphene and MoS2 and to discuss the impacts of surface roughness (from the atomic scale to the nanoscale) and chemical interactions at interfaces on their frictional properties, and their use in designing advanced boundary lubrication schemes.
Weinger, Jason G; Plaisted, Warren C; Maciejewski, Sonia M; Lanier, Lewis L; Walsh, Craig M; Lane, Thomas E
2014-10-01
Transplantation of major histocompatibility complex-mismatched mouse neural precursor cells (NPCs) into mice persistently infected with the neurotropic JHM strain of mouse hepatitis virus (JHMV) results in rapid rejection that is mediated, in part, by T cells. However, the contribution of the innate immune response to allograft rejection in a model of viral-induced neurological disease has not been well defined. Herein, we demonstrate that the natural killer (NK) cell-expressing-activating receptor NKG2D participates in transplanted allogeneic NPC rejection in mice persistently infected with JHMV. Cultured NPCs derived from C57BL/6 (H-2(b) ) mice express the NKG2D ligand retinoic acid early precursor transcript (RAE)-1 but expression was dramatically reduced upon differentiation into either glia or neurons. RAE-1(+) NPCs were susceptible to NK cell-mediated killing whereas RAE-1(-) cells were resistant to lysis. Transplantation of C57BL/6-derived NPCs into JHMV-infected BALB/c (H-2(d) ) mice resulted in infiltration of NKG2D(+) CD49b(+) NK cells and treatment with blocking antibody specific for NKG2D increased survival of allogeneic NPCs. Furthermore, transplantation of differentiated RAE-1(-) allogeneic NPCs into JHMV-infected BALB/c mice resulted in enhanced survival, highlighting a role for the NKG2D/RAE-1 signaling axis in allograft rejection. We also demonstrate that transplantation of allogeneic NPCs into JHMV-infected mice resulted in infection of the transplanted cells suggesting that these cells may be targets for infection. Viral infection of cultured cells increased RAE-1 expression, resulting in enhanced NK cell-mediated killing through NKG2D recognition. Collectively, these results show that in a viral-induced demyelination model, NK cells contribute to rejection of allogeneic NPCs through an NKG2D signaling pathway.
Real-time 2-D temperature imaging using ultrasound.
Liu, Dalong; Ebbini, Emad S
2010-01-01
We have previously introduced methods for noninvasive estimation of temperature change using diagnostic ultrasound. The basic principle was validated both in vitro and in vivo by several groups worldwide. Some limitations remain, however, that have prevented these methods from being adopted in monitoring and guidance of minimally invasive thermal therapies, e.g., RF ablation and high-intensity-focused ultrasound (HIFU). In this letter, we present first results from a real-time system for 2-D imaging of temperature change using pulse-echo ultrasound. The front end of the system is a commercially available scanner equipped with a research interface, which allows the control of imaging sequence and access to the RF data in real time. A high-frame-rate 2-D RF acquisition mode, M2D, is used to capture the transients of tissue motion/deformations in response to pulsed HIFU. The M2D RF data is streamlined to the back end of the system, where a 2-D temperature imaging algorithm based on speckle tracking is implemented on a graphics processing unit. The real-time images of temperature change are computed on the same spatial and temporal grid of the M2D RF data, i.e., no decimation. Verification of the algorithm was performed by monitoring localized HIFU-induced heating of a tissue-mimicking elastography phantom. These results clearly demonstrate the repeatability and sensitivity of the algorithm. Furthermore, we present in vitro results demonstrating the possible use of this algorithm for imaging changes in tissue parameters due to HIFU-induced lesions. These results clearly demonstrate the value of the real-time data streaming and processing in monitoring, and guidance of minimally invasive thermotherapy.
Laboratory Experiments On Continually Forced 2d Turbulence
NASA Astrophysics Data System (ADS)
Wells, M. G.; Clercx, H. J. H.; Van Heijst, G. J. F.
There has been much recent interest in the advection of tracers by 2D turbulence in geophysical flows. While there is a large body of literature on decaying 2D turbulence or forced 2D turbulence in unbounded domains, there have been very few studies of forced turbulence in bounded domains. In this study we present new experimental results from a continuously forced quasi 2D turbulent field. The experiments are performed in a square Perspex tank filled with water. The flow is made quasi 2D by a steady background rotation. The rotation rate of the tank has a small (<8 %) sinusoidal perturbation which leads to the periodic formation of eddies in the corners of the tank. When the oscillation period of the perturbation is greater than an eddy roll-up time-scale, dipole structures are observed to form. The dipoles can migrate away from the walls, and the interior of the tank is continually filled with vortexs. From experimental visualizations the length scale of the vortexs appears to be largely controlled by the initial formation mechanism and large scale structures are not observed to form at large times. Thus the experiments provide a simple way of cre- ating a continuously forced 2D turbulent field. The resulting structures are in contrast with most previous laboratory experiments on 2D turbulence which have investigated decaying turbulence and have observed the formations of large scale structure. In these experiments, decaying turbulence had been produced by a variety of methods such as the decaying turbulence in the wake of a comb of rods (Massen et al 1999), organiza- tion of vortices in thin conducting liquids (Cardoso et al 1994) or in rotating systems where there are sudden changes in angular rotation rate (Konijnenberg et al 1998). Results of dye visualizations, particle tracking experiments and a direct numerical simulation will be presented and discussed in terms of their oceanographic application. Bibliography Cardoso,O. Marteau, D. &Tabeling, P
2dF grows up: Echidna for the AAT
NASA Astrophysics Data System (ADS)
McGrath, Andrew; Barden, Sam; Miziarski, Stan; Rambold, William; Smith, Greg
2008-07-01
We present the concept design of a new fibre positioner and spectrograph system for the Anglo-Australian Telescope, as a proposed enhancement to the Anglo-Australian Observatory's well-known 2dF facility. A four-fold multiplex enhancement is accomplished by replacing the 400-fibre 2dF fibre positioning robot with a 1600-fibre Echidna unit, feeding three clones of the AAOmega optical spectrograph. Such a facility has the capability of a redshift 1 survey of a large fraction of the southern sky, collecting five to ten thousand spectra per night for a million-galaxy survey.
Noninvasive deep Raman detection with 2D correlation analysis
NASA Astrophysics Data System (ADS)
Kim, Hyung Min; Park, Hyo Sun; Cho, Youngho; Jin, Seung Min; Lee, Kang Taek; Jung, Young Mee; Suh, Yung Doug
2014-07-01
The detection of poisonous chemicals enclosed in daily necessaries is prerequisite essential for homeland security with the increasing threat of terrorism. For the detection of toxic chemicals, we combined a sensitive deep Raman spectroscopic method with 2D correlation analysis. We obtained the Raman spectra from concealed chemicals employing spatially offset Raman spectroscopy in which incident line-shaped light experiences multiple scatterings before being delivered to inner component and yielding deep Raman signal. Furthermore, we restored the pure Raman spectrum of each component using 2D correlation spectroscopic analysis with chemical inspection. Using this method, we could elucidate subsurface component under thick powder and packed contents in a bottle.
Evaluation of 2D ceramic matrix composites in aeroconvective environments
NASA Technical Reports Server (NTRS)
Riccitiello, Salvatore R.; Love, Wendell L.; Balter-Peterson, Aliza
1992-01-01
An evaluation is conducted of a novel ceramic-matrix composite (CMC) material system for use in the aeroconvective-heating environments encountered by the nose caps and wing leading edges of such aerospace vehicles as the Space Shuttle, during orbit-insertion and reentry from LEO. These CMCs are composed of an SiC matrix that is reinforced with Nicalon, Nextel, or carbon refractory fibers in a 2D architecture. The test program conducted for the 2D CMCs gave attention to their subsurface oxidation.
Radiative heat transfer in 2D Dirac materials.
Rodriguez-López, Pablo; Tse, Wang-Kong; Dalvit, Diego A R
2015-06-03
We compute the radiative heat transfer between two sheets of 2D Dirac materials, including topological Chern insulators and graphene, within the framework of the local approximation for the optical response of these materials. In this approximation, which neglects spatial dispersion, we derive both numerically and analytically the short-distance asymptotic of the near-field heat transfer in these systems, and show that it scales as the inverse of the distance between the two sheets. Finally, we discuss the limitations to the validity of this scaling law imposed by spatial dispersion in 2D Dirac materials.
Quantum process tomography by 2D fluorescence spectroscopy
Pachón, Leonardo A.; Marcus, Andrew H.; Aspuru-Guzik, Alán
2015-06-07
Reconstruction of the dynamics (quantum process tomography) of the single-exciton manifold in energy transfer systems is proposed here on the basis of two-dimensional fluorescence spectroscopy (2D-FS) with phase-modulation. The quantum-process-tomography protocol introduced here benefits from, e.g., the sensitivity enhancement ascribed to 2D-FS. Although the isotropically averaged spectroscopic signals depend on the quantum yield parameter Γ of the doubly excited-exciton manifold, it is shown that the reconstruction of the dynamics is insensitive to this parameter. Applications to foundational and applied problems, as well as further extensions, are discussed.
Radiative heat transfer in 2D Dirac materials
Rodriguez-López, Pablo; Tse, Wang -Kong; Dalvit, Diego A. R.
2015-05-12
We compute the radiative heat transfer between two sheets of 2D Dirac materials, including topological Chern insulators and graphene, within the framework of the local approximation for the optical response of these materials. In this approximation, which neglects spatial dispersion, we derive both numerically and analytically the short-distance asymptotic of the near-field heat transfer in these systems, and show that it scales as the inverse of the distance between the two sheets. In conclusion, we discuss the limitations to the validity of this scaling law imposed by spatial dispersion in 2D Dirac materials.
Experimental validation of equations for 2D DIC uncertainty quantification.
Reu, Phillip L.; Miller, Timothy J.
2010-03-01
Uncertainty quantification (UQ) equations have been derived for predicting matching uncertainty in two-dimensional image correlation a priori. These equations include terms that represent the image noise and image contrast. Researchers at the University of South Carolina have extended previous 1D work to calculate matching errors in 2D. These 2D equations have been coded into a Sandia National Laboratories UQ software package to predict the uncertainty for DIC images. This paper presents those equations and the resulting error surfaces for trial speckle images. Comparison of the UQ results with experimentally subpixel-shifted images is also discussed.
Scale Invariance in 2D BCS-BEC Crossover
NASA Astrophysics Data System (ADS)
Sensarma, Rajdeep; Taylor, Edward; Randeria, Mohit
2013-03-01
In 2D BCS-BEC crossover, the frequency of the breathing mode in a harmonic trap, as well as the lower edge of the radio frequency spectroscopy response, show remarkable scale-invariance throughout the crossover regime, i.e. they are independent of the coupling constant. Using functional integral methods, we study the behaviour of these quantities in the 2D BCS-BEC crossover and comment on the possible reasons for this scale independence. RS was supported by DAE, Govt. of India. MR was supported by NSF Grant No. DMR-1006532. ET was supported by NSERC and the Canadian Institute for Advanced Research.
Closed-shell and open-shell 2D nanographenes.
Sun, Zhe; Wu, Jishan
2014-01-01
This chapter describes a series of two-dimensional (2D) expanded arene networks, also known as nanographenes, with either closed-shell or open-shell electronic structure in the ground state. These systems are further categorized into three classes on a basis of different edge structures: those with zigzag edges only, those with armchair edges only, and those possessing both. Distinctive physical properties of these 2D aromatic systems are closely related to their structural characteristics and provide great potential for them as materials for different applications.
2D Log-Gabor Wavelet Based Action Recognition
NASA Astrophysics Data System (ADS)
Li, Ning; Xu, De
The frequency response of log-Gabor function matches well the frequency response of primate visual neurons. In this letter, motion-salient regions are extracted based on the 2D log-Gabor wavelet transform of the spatio-temporal form of actions. A supervised classification technique is then used to classify the actions. The proposed method is robust to the irregular segmentation of actors. Moreover, the 2D log-Gabor wavelet permits more compact representation of actions than the recent neurobiological models using Gabor wavelet.
NASA Astrophysics Data System (ADS)
Tønning, Erik; Polders, Daniel; Callaghan, Paul T.; Engelsen, Søren B.
2007-09-01
This paper demonstrates how the multi-linear PARAFAC model can with advantage be used to decompose 2D diffusion-relaxation correlation NMR spectra prior to 2D-Laplace inversion to the T2- D domain. The decomposition is advantageous for better interpretation of the complex correlation maps as well as for the quantification of extracted T2- D components. To demonstrate the new method seventeen mixtures of wheat flour, starch, gluten, oil and water were prepared and measured with a 300 MHz nuclear magnetic resonance (NMR) spectrometer using a pulsed gradient stimulated echo (PGSTE) pulse sequence followed by a Carr-Purcell-Meiboom-Gill (CPMG) pulse echo train. By varying the gradient strength, 2D diffusion-relaxation data were recorded for each sample. From these double exponentially decaying relaxation data the PARAFAC algorithm extracted two unique diffusion-relaxation components, explaining 99.8% of the variation in the data set. These two components were subsequently transformed to the T2- D domain using 2D-inverse Laplace transformation and quantitatively assigned to the oil and water components of the samples. The oil component was one distinct distribution with peak intensity at D = 3 × 10 -12 m 2 s -1 and T2 = 180 ms. The water component consisted of two broad populations of water molecules with diffusion coefficients and relaxation times centered around correlation pairs: D = 10 -9 m 2 s -1, T2 = 10 ms and D = 3 × 10 -13 m 2 s -1, T2 = 13 ms. Small spurious peaks observed in the inverse Laplace transformation of original complex data were effectively filtered by the PARAFAC decomposition and thus considered artefacts from the complex Laplace transformation. The oil-to-water ratio determined by PARAFAC followed by 2D-Laplace inversion was perfectly correlated with known oil-to-water ratio of the samples. The new method of using PARAFAC prior to the 2D-Laplace inversion proved to have superior potential in analysis of diffusion-relaxation spectra, as it
Single-shot and phase-shifting digital holographic microscopy using a 2-D grating.
Yang, Taeseok Daniel; Kim, Hyung-Jin; Lee, Kyoung J; Kim, Beop-Min; Choi, Youngwoon
2016-05-02
We demonstrate digital holographic microscopy that, while being based on phase-shifting interferometry, is capable of single-shot measurements. A two-dimensional (2-D) diffraction grating placed in a Fourier plane of a standard in-line holographic phase microscope generates multiple copies of a sample image on a camera sensor. The identical image copies are spatially separated with different overall phase shifts according to the diffraction orders. The overall phase shifts are adjusted by controlling the lateral position of the grating. These phase shifts are then set to be multiples of π/2. Interferograms composed of four image copies combined with a parallel reference beam are acquired in a single shot. The interferograms are processed through a phase-shifting algorithm to produce a single complex image. By taking advantage of the higher sampling capacity of the in-line holography, we can increase the imaging information density by a factor of 3 without compromising the imaging acquisition speed.
A high speed 2D time-to-impact algorithm targeted for smart image sensors
NASA Astrophysics Data System (ADS)
Åström, Anders; Forchheimer, Robert
2014-03-01
In this paper we present a 2D extension of a previously described 1D method for a time-to-impact sensor [5][6]. As in the earlier paper, the approach is based on measuring time instead of the apparent motion of points in the image plane to obtain data similar to the optical flow. The specific properties of the motion field in the time-to-impact application are used, such as using simple feature points which are tracked from frame to frame. Compared to the 1D case, the features will be proportionally fewer which will affect the quality of the estimation. We give a proposal on how to solve this problem. Results obtained are as promising as those obtained from the 1D sensor.
Transport studies in 2D transition metal dichalcogenides and black phosphorus
NASA Astrophysics Data System (ADS)
Du, Yuchen; Neal, Adam T.; Zhou, Hong; Ye, Peide D.
2016-07-01
Two-dimensional (2D) materials are a new family of materials with interesting physical properties, ranging from insulating hexagonal boron nitride, semiconducting or semi-metallic transition metal dichalcogenides, to gapless metallic graphene. In this review, we provide a brief discussion of transport studies in transition metal dichalcogenides, including both semiconducting and semi-metallic phases, as well as a discussion of the newly emerged narrow bandgap layered material, black phosphorus, in terms of its electrical and quantum transport properties at room and cryogenic temperatures. Ultra-thin layered channel materials with atomic layer thickness in the cross-plane direction, together with relatively high carrier mobility with appropriate passivation techniques, provide the promise for new scientific discoveries and broad device applications.
Comparison of dose accuracy between 2D array detectors and Epid for IMRT of nasopharynx cancer
NASA Astrophysics Data System (ADS)
Altiparmak, Duygu; Coban, Yasin; Merih, Adil; Avci, Gulhan Guler; Yigitoglu, Ibrahim
2017-02-01
The aim of this study is to perform the dosimetric controls of nasopharynx cancer patient's intensity modulated radiation therapy (IMRT) treatment plans that generated by treatment planing system (TPS) with using two different equipments and also to make comparison in terms of their reliability and practicability. This study has been performed at Radiation Oncology Department, Medicine Faculty in Gaziosmanpasa University by using the VARIAN CLINAC DHX linear accelerator which is operated in the range of 6 MV. Selected 10 nasopharynx patients planned in TPS (Eclipce V13.0) and approved for treatment by medical physicists and radiation oncologists. These plans recalculated on EPID and mapcheck which are 2D dosimetric equipments to obtain dose maps. To compare these two dosimetric equipments gamma analysis method has been preferred. Achieved data is presented and discussed.
Symmetry origins of the `caldera' valence band distortion in 2D semiconductors
NASA Astrophysics Data System (ADS)
Li, Pengke; Appelbaum, Ian; Physics Department Team
The electronic structures of many two-dimensional van der Waals semiconductors exhibit various fascinating properties distinct from their three-dimensional bulk counterparts. Through an examination of their lattice symmetries, we identify several universal rules dictating their band dispersion in the monolayer limit, where in-plane mirror symmetry and quantum confinement play critical roles. Taking group-III metal monochalcogenides (such as GaSe) as an example, we reveal the origin of the unusual `caldera' shape of the valence band edge (otherwise inelegantly dubbed an `upside down Mexican hat'), which we show is surprisingly common among other 2D semiconductors (such as in phosphorene for k along its zigzag direction). Reference: arXiv:1508.06963
Vectorial point spread function and optical transfer function in oblique plane imaging.
Kim, Jeongmin; Li, Tongcang; Wang, Yuan; Zhang, Xiang
2014-05-05
Oblique plane imaging, using remote focusing with a tilted mirror, enables direct two-dimensional (2D) imaging of any inclined plane of interest in three-dimensional (3D) specimens. It can image real-time dynamics of a living sample that changes rapidly or evolves its structure along arbitrary orientations. It also allows direct observations of any tilted target plane in an object of which orientational information is inaccessible during sample preparation. In this work, we study the optical resolution of this innovative wide-field imaging method. Using the vectorial diffraction theory, we formulate the vectorial point spread function (PSF) of direct oblique plane imaging. The anisotropic lateral resolving power caused by light clipping from the tilted mirror is theoretically analyzed for all oblique angles. We show that the 2D PSF in oblique plane imaging is conceptually different from the inclined 2D slice of the 3D PSF in conventional lateral imaging. Vectorial optical transfer function (OTF) of oblique plane imaging is also calculated by the fast Fourier transform (FFT) method to study effects of oblique angles on frequency responses.
Forced Solutions of Streamwise Constant Plane Couette Flow
NASA Astrophysics Data System (ADS)
Gayme, Dennice; McKeon, Beverley; Bamieh, Bassam; Doyle, John; Papachristodoulou, Antonis
2010-11-01
A two-dimensional, three-velocity component (2D/3C) model simulated under small-amplitude Gaussian forcing has been shown to capture salient features of turbulent plane Couette flow (Gayme et. al 2010). Periodic spanwise/wall-normal plane stream functions are used as input to develop forced 2D/3C streamwise velocities. The resulting steady-state solutions are qualitatively similar to a fully turbulent spatial field of DNS. Our analysis indicates that the momentum transfer which produces a `turbulent-like' mean profile requires a nonlinear streamwise velocity equation. A system theoretic approach is used to study amplification mechanisms which arise through this 2D/3C nonlinear coupling. The forcing required to produce each input is used to define an induced norm. The associated input-output response determines the energy optimal spanwise wavelength over a range of Reynolds numbers. We identify an important tradeoff between the linear amplification mechanism and the nonlinearity required to develop an appropriately shaped turbulent velocity profile. Acknowledgements: The research is supported by Boeing and AFOSR. B.J.M. gratefully acknowledges NSF-CAREER award no. 0747672 (program managers W. W. Schultz & H. H. Winter).
Biaxial Tensile Test of Cold Rolled IF Steel Sheet for Large Plastic Strain Range
NASA Astrophysics Data System (ADS)
Enatsu, Ryotaro; Kuwabara, Toshihiko
2011-08-01
Deformation behavior of cold rolled IF steel sheet (SPCE) under biaxial tension has been investigated for large plastic strain range over 15%. The test material was bent and TIG welded to form a tubular specimen with an outer diameter of 46.2 mm and wall thickness of 0.8 mm. The tubular specimens have been subjected to linear stress paths in the first quadrant of stress space with the use of a servo-controlled tension-internal pressure testing machine developed by one of the authors [T. Kuwabara, K. Yoshida, K. Narihara, S. Takahashi, Anisotropic plastic deformation of extruded aluminum alloy tube under axial forces and internal pressure, Int. J. Plasticity 21, 101-117 (2005)]. Moreover, biaxial tensile tests using a cruciform specimen have also been carried out to more precisely measure the deformation behavior for a small strain range following initial yielding. True stress-true plastic strain curves, contours of plastic work in stress space and the directions of plastic strain rates have been measured and compared with those calculated using selected yield functions: the von Mises, Hill's quadratic and Yld2000-2d [Barlat, F., Brem, J.C., Yoon, J.W., Chung, K., Dick, R.E., Lege, D.J., Pourboghrat, F., Choi, S.H., Chu, E., Plane stress yield function for aluminum alloy sheets—Part 1: Theory. Int. J. Plasticity 19, 1297-1319 (2003)]. The plastic deformation behavior up to a work equivalent plastic strain of ɛ0p = 0.19 has been successfully measured. It is found that the test material exhibits differential hardening and that the Yld2000-2d yield function with an exponent of six most closely predicts the contours of plastic work and the directions of plastic strain rates.
Resolution in 3D in multifocal plane microscopy
NASA Astrophysics Data System (ADS)
Chao, Jerry; Ram, Sripad; Abraham, Anish V.; Ward, E. Sally; Ober, Raimund J.
2008-02-01
Using single molecule microscopy, biological interactions can be imaged and studied at the level of individual biomolecules. When characterizing an imaged biological interaction, the distance separating the two participating biomolecules can provide valuable information. Therefore, the resolvability of an imaging setup is of practical significance in the analysis of the acquired image data. Importantly, the resolvability of the imaging setup needs evaluation in the 3D context, since in general biomolecules reside in 3D space within the cellular environment. We recently introduced an information-theoretic 2D resolution measure which shows that the resolution limit due to Rayleigh's criterion can be overcome. This new result predicts that the resolution of optical microscopes is not limited, but rather can be improved with increased photon counts detected from the single molecules. The 2D result was subsequently extended to the 3D context, and the proposed information-theoretic 3D resolution measure can readily be used to determine the resolvability of a conventional single focal plane imaging setup. Here, we consider the 3D resolution measure for a multifocal plane microscope setup, an imaging system which allows the concurrent imaging of multiple focal planes within a specimen. The technique is useful in applications such as the tracking of subcellular objects in 3D. By comparing their 3D resolution measures, we find a two-plane setup to outperform a comparable conventional single-plane setup in resolvability over a range of axial locations for the single molecule pair. Moreover, we investigate and compare the impact of noise on the resolvability of the two setups.
Study of an athermal quasi static plastic deformation in a 2D granular material
NASA Astrophysics Data System (ADS)
Zhang, Jie; Zheng, Jie
2016-11-01
In crystalline materials, the plasticity has been well understood in terms of dynamics of dislocation, i.e. flow defects in the crystals where the flow defects can be directly visualized under a microscope. In a contrast, the plasticity in amorphous materials, i.e. glass, is still poorly understood due to the disordered nature of the materials. In this talk, I will discuss the recent results we have obtained in our ongoing research of the plasticity of a 2D glass in the athermal quasi static limit where the 2D glass is made of bi-disperse granular disks with very low friction. Starting from a densely packed homogeneous and isotropic initial state, we apply pure shear deformation to the system. For a sufficiently small strain, the response of the system is linear and elastic like; when the strain is large enough, the plasticity of the system gradually develops and eventually the shear bands are fully developed. In this study, we are particularly interested in how to relate the local plastic deformation to the macroscopic response of the system and also in the development of the shear bands.
Modeling and 2-D discrete simulation of dislocation dynamics for plastic deformation of metal
NASA Astrophysics Data System (ADS)
Liu, Juan; Cui, Zhenshan; Ou, Hengan; Ruan, Liqun
2013-05-01
Two methods are employed in this paper to investigate the dislocation evolution during plastic deformation of metal. One method is dislocation dynamic simulation of two-dimensional discrete dislocation dynamics (2D-DDD), and the other is dislocation dynamics modeling by means of nonlinear analysis. As screw dislocation is prone to disappear by cross-slip, only edge dislocation is taken into account in simulation. First, an approach of 2D-DDD is used to graphically simulate and exhibit the collective motion of a large number of discrete dislocations. In the beginning, initial grains are generated in the simulation cells according to the mechanism of grain growth and the initial dislocation is randomly distributed in grains and relaxed under the internal stress. During the simulation process, the externally imposed stress, the long range stress contribution of all dislocations and the short range stress caused by the grain boundaries are calculated. Under the action of these forces, dislocations begin to glide, climb, multiply, annihilate and react with each other. Besides, thermal activation process is included. Through the simulation, the distribution of dislocation and the stress-strain curves can be obtained. On the other hand, based on the classic dislocation theory, the variation of the dislocation density with time is described by nonlinear differential equations. Finite difference method (FDM) is used to solve the built differential equations. The dislocation evolution at a constant strain rate is taken as an example to verify the rationality of the model.
Atomistic simulations of J-integral in 2D graphene nanosystems.
Jin, Y; Yuan, F G
2005-12-01
The J-integral is investigated in discrete atomic systems using molecular mechanics simulations. A method of calculating J-integral in specified atomic domains is developed. Two cases, a semiinfinite crack in an infinite domain under the remote K-field deformation and a finite crack length in a finite geometry under the tensile and shear deformation prescribed on the boundary, are studied in the two-dimensional graphene sheets and the values of J-integral are obtained under small-strain deformation. The comparison with energy release rates in Mode I and Mode II based on continuum theory of linear elastic fracture mechanics show good agreements. Meanwhile, the nonlinear strain and stress relation of a 2D graphene sheet is evaluated and is fitted with a power law curve. With necessary modifications on the Tersoff-Brenner potential, the critical values of J-integral of 2D graphene systems, which denoted as Jc, are eventually obtained. The results are then compared with those from the relevant references.
Structure and interaction in 2D assemblies of tobacco mosaic viruses
Yang, L.; Wang. S.; Masafumi, F.; Checco, A.; Zhongwei, N.; Wang, Q.
2009-08-27
We created two-dimensional (2D) assemblies of tobacco mosaic viruses (TMVs) and characterized their structures using Atomic Force Microscopy (AFM) and X-ray scattering. The TMVs were adsorbed on an oppositely charged, fluid lipid monolayer supported by a solid substrate and submerged in a buffer solution. The lipid monolayer confined the viral particles within a plane, while providing them with lateral mobility so that overall the TMV assembly behaved like a 2D liquid. We controlled the inter-particle interaction by adjusting the chemical condition in the buffer to induce ordered TMV assemblies. We found that the presence of the lipid layer was essential for forming ordered TMV assemblies. Packed TMV assemblies formed on the lipid layer, with an average inter-particle spacing of 42 nm. By introducing Ca2+ ions into the buffer solution, we were able to improve the in-plane order within the TMV assemblies and reduce the average inter-particle spacing to 20 nm, compared to the TMV diameter of 18 nm. Quantitative analysis of the X-ray scattering data shows that the structural order within the TMV assemblies prepared under a Ca{sup 2+}-free buffer solution is consistent with purely repulsive, electrostatic inter-particle interaction. In contrast, the structural order within Ca{sup 2+}-induced TMV assemblies is consistent with the behavior of a fluid of sticky rods, implying the presence of a strong attraction between TMVs. In addition to the screening of Coulomb repulsion, this behavior is likely the result of counterion-induced as well as membrane-mediated attractions.
Structure and Interaction in 2D Assemblies of Tobacco Mosaic Viruses
Fukuto, M.; Yang, L.; Wang, S.; Fukuto, M.; Checco, A.; Niu, Z.; Wang, Q.
2009-12-07
We created two-dimensional (2D) assemblies of tobacco mosaic viruses (TMVs) and characterized their structures using Atomic Force Microscopy (AFM) and X-ray scattering. The TMVs were adsorbed on an oppositely charged, fluid lipid monolayer supported by a solid substrate and submerged in a buffer solution. The lipid monolayer confined the viral particles within a plane, while providing them with lateral mobility so that overall the TMV assembly behaved like a 2D liquid. We controlled the inter-particle interaction by adjusting the chemical condition in the buffer to induce ordered TMV assemblies. We found that the presence of the lipid layer was essential for forming ordered TMV assemblies. Packed TMV assemblies formed on the lipid layer, with an average inter-particle spacing of 42 nm. By introducing Ca{sup 2+} ions into the buffer solution, we were able to improve the in-plane order within the TMV assemblies and reduce the average inter-particle spacing to 20 nm, compared to the TMV diameter of 18 nm. Quantitative analysis of the X-ray scattering data shows that the structural order within the TMV assemblies prepared under a Ca{sup 2+}-free buffer solution is consistent with purely repulsive, electrostatic inter-particle interaction. In contrast, the structural order within Ca{sup 2+}-induced TMV assemblies is consistent with the behavior of a fluid of sticky rods, implying the presence of a strong attraction between TMVs. In addition to the screening of Coulomb repulsion, this behavior is likely the result of counterion-induced as well as membrane-mediated attractions.
NASA Astrophysics Data System (ADS)
Siegmann, Philip; Felipe-Sese, Luis; Diaz-Garrido, Francisco
2017-01-01
An improved measurement method and an automatic calibration procedure are proposed for a combined 2D Digital Image Correlation and Fringe Projection system that allows measuring in- and out-of-plane displacement maps with only one image at each deformation stage of a specimen. The proposed method increases the accuracy and range of the out-of-plane displacements by taking into account the divergences of both the projected fringes (uncollimated) and the camera (with non-zero FOV). The calibration is performed automatically by acquiring a sequence of images of a reference plane by displacing perpendicular to it the camera and fringe projector with a motorized translation stage. The acquired images are then used to obtain a fringe function for each pixel and the necessary parameters required for the correction of the in-plane displacements. Furthermore, a closed form expression is obtained that relates the out-of-plane displacements with the shifted phase at each pixel for a given experimental set-up. This expression is in good agreement with the fringe function obtained by fitting a simple 2nd order polynomial to the experimental obtained calibration data. Finally, the polynomial approach is proposed as a fringe function because it avoids the errors in the determination of the required parameters of the theoretical expression as well as some small misalignment or aberration effects.
Reorientation of the Stripe Phase of 2D Electrons by a Minute Density Modulation
NASA Astrophysics Data System (ADS)
Mueed, M. A.; Hossain, Md. Shafayat; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.; Shayegan, M.
2016-08-01
Interacting two-dimensional electrons confined in a GaAs quantum well exhibit isotropic transport when the Fermi level resides in the first excited (N =1 ) Landau level. Adding an in-plane magnetic field (B||) typically leads to an anisotropic, stripelike (nematic) phase of electrons with the stripes oriented perpendicular to the B|| direction. Our experimental data reveal how a periodic density modulation, induced by a surface strain grating from strips of negative electron-beam resist, competes against the B||-induced orientational order of the stripe phase. Even a minute (<0.25 %) density modulation is sufficient to reorient the stripes along the direction of the surface grating.
A new kind of 2D topological insulators BiCN with a giant gap and its substrate effects
Fu, Botao; Ge, Yanfeng; Su, Wenyong; Guo, Wei; Liu, Cheng-Cheng
2016-01-01
Based on DFT calculation, we predict that BiCN, i.e., bilayer Bi films passivated with -CN group, is a novel 2D Bi-based material with highly thermodynamic stability, and demonstrate that it is also a new kind of 2D TI with a giant SOC gap (~1 eV) by direct calculation of the topological invariant Z2 and obvious exhibition of the helical edge states. Monolayer h-BN and MoS2 are identified as good candidate substrates for supporting the nontrivial topological insulating phase of the 2D TI films, since the two substrates can stabilize and weakly interact with BiCN via van der Waals interaction and thus hardly affect the electronic properties, especially the band topology. The topological properties are robust against the strain and electric field. This may provide a promising platform for realization of novel topological phases. PMID:27444954
In-plane optical anisotropy of layered gallium telluride
Huang, Shengxi; Tatsumi, Yuki; Ling, Xi; ...
2016-08-16
Layered gallium telluride (GaTe) has attracted much attention recently, due to its extremely high photoresponsivity, short response time, and promising thermoelectric performance. Different from most commonly studied two-dimensional (2D) materials, GaTe has in-plane anisotropy and a low symmetry with the C2h3 space group. Investigating the in-plane optical anisotropy, including the electron–photon and electron–phonon interactions of GaTe is essential in realizing its applications in optoelectronics and thermoelectrics. In this work, the anisotropic light-matter interactions in the low-symmetry material GaTe are studied using anisotropic optical extinction and Raman spectroscopies as probes. Our polarized optical extinction spectroscopy reveals the weak anisotropy in opticalmore » extinction spectra for visible light of multilayer GaTe. Polarized Raman spectroscopy proves to be sensitive to the crystalline orientation of GaTe, and shows the intricate dependences of Raman anisotropy on flake thickness, photon and phonon energies. Such intricate dependences can be explained by theoretical analyses employing first-principles calculations and group theory. Furthermore, these studies are a crucial step toward the applications of GaTe especially in optoelectronics and thermoelectrics, and provide a general methodology for the study of the anisotropy of light-matter interactions in 2D layered materials with in-plane anisotropy.« less
In-plane optical anisotropy of layered gallium telluride
Huang, Shengxi; Tatsumi, Yuki; Ling, Xi; Guo, Huaihong; Wang, Ziqiang; Watson, Garrett; Puretzky, Alexander A.; Geohegan, David B.; Kong, Jing; Li, Ju; Yang, Teng; Saito, Riichiro; Dresselhaus, Mildred S.
2016-08-16
Layered gallium telluride (GaTe) has attracted much attention recently, due to its extremely high photoresponsivity, short response time, and promising thermoelectric performance. Different from most commonly studied two-dimensional (2D) materials, GaTe has in-plane anisotropy and a low symmetry with the C_{2h}^{3} space group. Investigating the in-plane optical anisotropy, including the electron–photon and electron–phonon interactions of GaTe is essential in realizing its applications in optoelectronics and thermoelectrics. In this work, the anisotropic light-matter interactions in the low-symmetry material GaTe are studied using anisotropic optical extinction and Raman spectroscopies as probes. Our polarized optical extinction spectroscopy reveals the weak anisotropy in optical extinction spectra for visible light of multilayer GaTe. Polarized Raman spectroscopy proves to be sensitive to the crystalline orientation of GaTe, and shows the intricate dependences of Raman anisotropy on flake thickness, photon and phonon energies. Such intricate dependences can be explained by theoretical analyses employing first-principles calculations and group theory. Furthermore, these studies are a crucial step toward the applications of GaTe especially in optoelectronics and thermoelectrics, and provide a general methodology for the study of the anisotropy of light-matter interactions in 2D layered materials with in-plane anisotropy.
In-Plane Optical Anisotropy of Layered Gallium Telluride.
Huang, Shengxi; Tatsumi, Yuki; Ling, Xi; Guo, Huaihong; Wang, Ziqiang; Watson, Garrett; Puretzky, Alexander A; Geohegan, David B; Kong, Jing; Li, Ju; Yang, Teng; Saito, Riichiro; Dresselhaus, Mildred S
2016-09-27
Layered gallium telluride (GaTe) has attracted much attention recently, due to its extremely high photoresponsivity, short response time, and promising thermoelectric performance. Different from most commonly studied two-dimensional (2D) materials, GaTe has in-plane anisotropy and a low symmetry with the C2h(3) space group. Investigating the in-plane optical anisotropy, including the electron-photon and electron-phonon interactions of GaTe is essential in realizing its applications in optoelectronics and thermoelectrics. In this work, the anisotropic light-matter interactions in the low-symmetry material GaTe are studied using anisotropic optical extinction and Raman spectroscopies as probes. Our polarized optical extinction spectroscopy reveals the weak anisotropy in optical extinction spectra for visible light of multilayer GaTe. Polarized Raman spectroscopy proves to be sensitive to the crystalline orientation of GaTe, and shows the intricate dependences of Raman anisotropy on flake thickness, photon and phonon energies. Such intricate dependences can be explained by theoretical analyses employing first-principles calculations and group theory. These studies are a crucial step toward the applications of GaTe especially in optoelectronics and thermoelectrics, and provide a general methodology for the study of the anisotropy of light-matter interactions in 2D layered materials with in-plane anisotropy.
National Aerospace Plane (NASP) program
NASA Technical Reports Server (NTRS)
1990-01-01
Artists concept of the X-30 aerospace plane flying through Earth's atmosphere on its way to low-Earth orbit. the experimental concept is part of the National Aero-Space Plane Program. The X-30 is planned to demonstrate the technology for airbreathing space launch and hypersonic cruise vehicles. Photograph and caption published in Winds of Change, 75th Anniversary NASA publication (page 117), by James Schultz.
Discrepant Results in a 2-D Marble Collision
ERIC Educational Resources Information Center
Kalajian, Peter
2013-01-01
Video analysis of 2-D collisions is an excellent way to investigate conservation of linear momentum. The often-desired experimental design goal is to minimize the momentum loss in order to demonstrate the conservation law. An air table with colliding pucks is an ideal medium for this experiment, but such equipment is beyond the budget of many…
2-D Finite Element Cable and Box IEMP Analysis
Scivner, G.J.; Turner, C.D.
1998-12-17
A 2-D finite element code has been developed for the solution of arbitrary geometry cable SGEMP and box IEMP problems. The quasi- static electric field equations with radiation- induced charge deposition and radiation-induced conductivity y are numerically solved on a triangular mesh. Multiple regions of different dielectric materials and multiple conductors are permitted.
2D Orthogonal Locality Preserving Projection for Image Denoising.
Shikkenawis, Gitam; Mitra, Suman K
2016-01-01
Sparse representations using transform-domain techniques are widely used for better interpretation of the raw data. Orthogonal locality preserving projection (OLPP) is a linear technique that tries to preserve local structure of data in the transform domain as well. Vectorized nature of OLPP requires high-dimensional data to be converted to vector format, hence may lose spatial neighborhood information of raw data. On the other hand, processing 2D data directly, not only preserves spatial information, but also improves the computational efficiency considerably. The 2D OLPP is expected to learn the transformation from 2D data itself. This paper derives mathematical foundation for 2