Evidence for a New Intermediate Phase in a Strongly Correlated 2D System near Wigner Crystallization
NASA Astrophysics Data System (ADS)
Gao, Xuan; Qiu, Richard; Goble, Nicholas; Serafin, Alex; Yin, Liang; Xia, Jian-Sheng; Sullivan, Neil; Pfeiffer, Loren; West, Ken
How the two dimensional (2D) quantum Wigner crystal (WC) transforms into the metallic liquid phase remains an outstanding problem in physics. In theories considering the 2D WC to liquid transition in the clean limit, it was suggested that a number of intermediate phases might exist. We have studied the transformation between the metallic fluid phase and the low magnetic field reentrant insulating phase (RIP) which was interpreted as due to the WC [Qiu et al., PRL 108, 106404 (2012)], in a strongly correlated 2D hole system in GaAs quantum well with large interaction parameter rs (~20-30) and high mobility. Instead of a sharp transition, we found that increasing density (or lowering rs) drives the RIP into a state where the incipient RIP coexists with Fermi liquid. This apparent mixture phase intermediate between Fermi liquid and WC also exhibits a non-trivial temperature dependent resistivity behavior which can be qualitatively understood by the reversed melting of WC in the mixture, in analogy to the Pomeranchuk effect in the solid-liquid mixture of Helium-3. X.G. thanks NSF (DMR-0906415) for supporting work at CWRU. Experiments at the NHMFL High B/T Facility were supported by NSF Grant 0654118 and the State of Florida. L.P. thanks the Gordon and Betty Moore Foundation and NSF MRSEC (DMR-0819860) for support.
Anisotropic elasticity of experimental colloidal Wigner crystals.
Russell, Emily R; Spaepen, Frans; Weitz, David A
2015-03-01
Colloidal particles interacting via a long-range repulsion can, in contrast to hard-sphere systems, exhibit crystalline ordering at low volume fraction. Here we experimentally investigate the structure and properties of such "colloidal Wigner crystals." We find a body-centered-cubic crystalline phase at volume fractions of ϕ≳15%, which exhibits large fluctuations of individual particles from their average positions. We determine the three independent crystalline elastic constants and find that these crystals are very compliant and highly anisotropic.
Spin coupling in zigzag Wigner crystals.
Klironomos, A. D.; Meyer, J. S.; Hikihara, T.; Matveev, K. A.; Materials Science Division; Ohio State Univ.; Hokkaido Univ.
2007-08-01
We consider interacting electrons in a quantum wire in the case of a shallow confining potential and low electron density. In a certain range of densities, the electrons form a two-row (zigzag) Wigner crystal whose spin properties are determined by nearest and next-nearest neighbor exchange as well as by three- and four-particle ring exchange processes. The phase diagram of the resulting zigzag spin chain has regions of complete spin polarization and partial spin polarization in addition to a number of unpolarized phases, including antiferromagnetism and dimer order as well as a novel phase generated by the four-particle ring exchange.
Topological Phonon Modes in a Two-Dimensional Wigner Crystal
NASA Astrophysics Data System (ADS)
Ji, Wen-Cheng; Shi, Jun-Ren
2017-03-01
We investigate the spin-orbit coupling effect in a two-dimensional Wigner crystal. We show that sufficiently strong spin-orbit coupling and an appropriate sign of g-factor could transform the Wigner crystal to a topological phonon system. We demonstrate the existence of chiral phonon edge modes in finite size samples, as well as the robustness of the modes in the topological phase. We explore the possibility of realizing the topological phonon system in two-dimensional Wigner crystals confined in semiconductor quantum wells/heterostructure. We find that the spin-orbit coupling is too weak for driving a topological phase transition in these systems. We argue that one may look for the topological phonon system in correlated Wigner crystals with emergent effective spin-orbit coupling.
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
Aharonov-Casher Effect in One-Dimensional Wigner Crystals
NASA Astrophysics Data System (ADS)
Tserkovnyak, Yaroslav; Kindermann, Markus
2010-03-01
We theoretically study the effects of spin-orbit coupling on spin exchange in a low-density Wigner crystal. In addition to the familiar antiferromagnetic Heisenberg exchange, we find general anisotropic interactions in spin space if the exchange paths allowed by the crystal structure form loops in real space. In particular, it is shown that the two-electron exchange interaction can acquire ferromagnetic character. Tserkovnyak and Kindermann, Phys. Rev. Lett. 102 (2009) 126801.
Low-frequency electromagnetic field in a Wigner crystal
Stupka, Anton
2013-03-15
Long-wave low-frequency oscillations are described in a Wigner crystal by generalization of the reverse continuum model for the case of electronic lattice. The internal self-consistent long-wave electromagnetic field is used to describe the collective motions in the system. The eigenvectors and eigenvalues of the obtained system of equations are derived. The velocities of longitudinal and transversal sound waves are found.
Phase diagram of the composite fermion Wigner crystals
NASA Astrophysics Data System (ADS)
Archer, Alex; Park, Kwon; Jain, Jainendra
2013-03-01
The energies of the Wigner crystal (WC) phase and the fractional quantum Hall (FQH) liquid have been compared in the past at some special filling factors. We deduce in this work the phase diagram of the WC phase as a function of the general filling factor by considering: (i) the WC of electrons; (ii) WCs of composite fermions (CFs) carrying 2 p vortices; and (iii) FQH states supporting WC of CF quasiparticles or CF quasiholes. In particular, we find that the re-entrant insulating phase between 1/5 and 2/9 is a WC of composite fermions carrying two vortices. To distinguish the CF Wigner crystal from the electron WC, we compute a number of properties, including shear modulus, magnetophonon and magnetoplasmon dispersions, and melting temperatures. The width dependence of the phase diagram is also studied. A technical innovation that makes these comparisons feasible is to model the WC as the thermodynamic limit of the Thomson crystal on the surface of a sphere, which minimizes the Coulomb energy of classical charged particles.
Fast and robust quantum computation with ionic Wigner crystals
Baltrusch, J. D.; Negretti, A.; Taylor, J. M.; Calarco, T.
2011-04-15
We present a detailed analysis of the modulated-carrier quantum phase gate implemented with Wigner crystals of ions confined in Penning traps. We elaborate on a recent scheme, proposed by two of the authors, to engineer two-body interactions between ions in such crystals. We analyze the situation in which the cyclotron ({omega}{sub c}) and the crystal rotation ({omega}{sub r}) frequencies do not fulfill the condition {omega}{sub c}=2{omega}{sub r}. It is shown that even in the presence of the magnetic field in the rotating frame the many-body (classical) Hamiltonian describing small oscillations from the ion equilibrium positions can be recast in canonical form. As a consequence, we are able to demonstrate that fast and robust two-qubit gates are achievable within the current experimental limitations. Moreover, we describe a realization of the state-dependent sign-changing dipole forces needed to realize the investigated quantum computing scheme.
Hall-velocity limited magnetoconductivity in a 2D Wigner solid
NASA Astrophysics Data System (ADS)
Fozooni, P.; Djerfi, K.; Kristensen, Anders; Lea, M. J.; Richardson, P. J.; Santrich-Badal, A.; Blackburn, A.; van der Heijden, R. W.
1996-01-01
The magnetoconductivity σ( B) of a classical 2D electron crystal on superfluid4He is non-linear. Experimentally we find a contribution to σ( B) which at constant field, gives σ( B)∞ J x, the current density, while at constant current, σ( B) ∞ 1/ B. In this region the Hall velocity νH slowly approaches the ripplon velocity νI at the first reciprocal lattice vector, due to strong electron-ripplon interactions with the helium. The magnetoconductivity decreases sharply for νH>νI. Fluctuations in σ( B) are seen above the melting temperature.
Composite Fermion Theory for the High Field Wigner Crystal State
NASA Astrophysics Data System (ADS)
Narevich, Romanas; Murthy, Ganpathy; Fertig, Herbert
2001-03-01
The low filling fraction Quantum Hall Effect is reexamined using the hamiltonian composite fermion theory developed by Shankar and Murthy(R. Shankar and G. Murthy, Phys. Rev. Lett. 79), 4437 (1997). We address the experiment by Jiang et. al.(H. W. Jiang et. al., Phys. Rev. B 44), 8107 (1991) where the insulating phase surrounding the ν=1/5 quantum liquid was observed and its activation energies (gaps) measured. Previous studies either found gaps that were off by few orders of magnitude (Hartree-Fock calculations of the electronic Wigner crystal(D. Yoshioka and H. Fukuyama, J. Phys. Soc. Japan 47), 394 (1979)) or were unable to calculate them because of the computational complexity (Monte-Carlo studies of the correlated crystal(H. Yi and H. A. Fertig, Phys. Rev. B 58), 4019 (1998)). We use the Hartree-Fock approximation for the periodic density state of composite fermions and find gaps that have a correct order of magnitude and reproduce the experimental dependence on the filling factor. We also report the results of the shear modulus calculation relevant for the collective pinning of the crystal.
Wigner crystallization in quantum wires within the Yukawa approximation
NASA Astrophysics Data System (ADS)
Méndez-Camacho, Reyna; Cruz-Hernández, Esteban; Castañeda-Priego, Ramón
2017-02-01
One crucial and important aspect to account for the nature of the quantum wires is the understanding of the effects associated to many-body interactions between confined electrons. The inclusion of such many-body forces in any theoretical framework is a difficult and computationally demanding task. Then one has to make use of coarse-grained descriptions that allow one to incorporate the contribution of all the electrons. In a simple physical picture, the interaction between two electrons can be considered screened due to the presence of the other ones. If the latter are homogeneously distributed inside the wire, the interaction between the former can then be assumed of the Yukawa form. In this contribution, we report on the lower energy states of n -doped GaAs circular-quantum wires with two electrons in the conduction band interacting through a repulsive Yukawa potential. By varying the length and the electronic density of the wire, quite different trends in the electronic distribution are observed. By changing the material parameters to InSb and InAs nanowires, we found that our results are consistent with available experimental data that have reported the formation of Wigner crystals.
NASA Astrophysics Data System (ADS)
Deng, H.; Liu, Y.; Jo, I.; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.; Shayegan, M.
2016-08-01
When the kinetic energy of a collection of interacting two-dimensional (2D) electrons is quenched at very high magnetic fields so that the Coulomb repulsion dominates, the electrons are expected to condense into an ordered array, forming a quantum Wigner crystal (WC). Although this exotic state has long been suspected in high-mobility 2D electron systems at very low Landau level fillings (ν ≪1 ), its direct observation has been elusive. Here we present a new technique and experimental results directly probing the magnetic-field-induced WC. We measure the magnetoresistance of a bilayer electron system where one layer has a very low density and is in the WC regime (ν ≪1 ), while the other ("probe") layer is near ν =1 /2 and hosts a sea of composite fermions (CFs). The data exhibit commensurability oscillations in the magnetoresistance of the CF layer, induced by the periodic potential of WC electrons in the other layer, and provide a unique, direct glimpse at the symmetry of the WC, its lattice constant, and melting. They also demonstrate a striking example of how one can probe an exotic many-body state of 2D electrons using equally exotic quasiparticles of another many-body state.
Spin-orbit coupling in quasi-one-dimensional Wigner crystals
NASA Astrophysics Data System (ADS)
Kornich, Viktoriia; Pedder, Christopher J.; Schmidt, Thomas L.
2017-01-01
We study the effect of Rashba spin-orbit coupling (SOC) on the charge and spin degrees of freedom of a quasi-one-dimensional (quasi-1D) Wigner crystal. As electrons in a quasi-1D Wigner crystal can move in the transverse direction, SOC cannot be gauged away in contrast to the pure 1D case. We show that for weak SOC, a partial gap in the spectrum opens at certain ratios between the density of electrons and the inverse Rashba length. We present how the low-energy branch of charge degrees of freedom deviates due to SOC from its usual linear dependence at small wave vectors. In the case of strong SOC, we show that the spin sector of a Wigner crystal cannot be described by an isotropic antiferromagnetic Heisenberg Hamiltonian anymore and that instead the ground state of neighboring electrons is mostly a triplet state. We present a new spin sector Hamiltonian and discuss the spectrum of a Wigner crystal in this limit.
Aharonov-Casher effect in exchange interactions in a Wigner crystal.
Tserkovnyak, Yaroslav; Kindermann, Markus
2009-03-27
We theoretically study the effects of spin-orbit coupling on spin exchange in a low-density Wigner crystal. In addition to the familiar antiferromagnetic Heisenberg exchange, we find general anisotropic interactions in spin space if the exchange paths allowed by the crystal structure form loops in real space. In particular, it is shown that the two-electron exchange interaction can acquire ferromagnetic character.
Cooperative dynamics in ultrasoft 2D crystals
NASA Astrophysics Data System (ADS)
Sprakel, Joris; van der Meer, Berend; Dijkstra, Marjolein; van der Gucht, Jasper
2015-03-01
The creation, annihilation, and diffusion of defects in crystal lattices play an important role during crystal melting and deformation. Although it is well understood how defects form and react when crystals are subjected to external stresses, it remains unclear how crystals cope with internal stresses. We report a study in which we create a highly localized internal stress, by means of optical tweezing, in a crystal formed from micrometer-sized colloidal spheres and directly observe how the solid reacts using microscopy. We find that, even though the excitation is highly localized, a collective dance of colloidal particles results; these collective modes take the form of closed rings or open-ended strings, depending on the sequence of events which nucleate the rearrangements. Surprisingly, we find from Brownian Dynamics simulations that these cooperative dynamics are thermally-activated modes inherent to the crystal, and can even occur through a single, sufficiently large thermal fluctuation, resulting in the irreversible displacement of 100s of particles from their lattice sites.
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.
Melting of Wigner Crystal on Helium in Quasi-One-Dimensional Geometry
NASA Astrophysics Data System (ADS)
Ikegami, Hiroki; Akimoto, Hikota; Kono, Kimitoshi
2015-05-01
We discuss melting of a Wigner crystal formed on a free surface of superfluid He, in quasi-one-dimensional (Q1D) channels of width between 5 and 15 m. We reexamine our previous transport data (Ikegami et al. in Phys Rev B 82:201104(R), 2010), in particular, by estimating the number of electrons across the channel in a more accurate way with the aid of numerical calculations of distributions of the electrons in the channels. The results of reexamination indicate more convincingly that the melting of the Wigner crystal in the Q1D geometry is understood by the finite size effect on the Kosterlitz-Thouless-Halperin-Nelson-Young melting process. We also present technical details of the transport measurements of the electrons in a Q1D geometry, including a fabrication method of devices used for the transport measurements, numerical simulations of response of the devices, and a procedure for analyzing transport data.
Structural transitions in vertically and horizontally coupled parabolic channels of Wigner crystals
NASA Astrophysics Data System (ADS)
Galván-Moya, J. E.; Nelissen, K.; Peeters, F. M.
2012-11-01
Structural phase transitions in two vertically or horizontally coupled channels of strongly interacting particles are investigated. The particles are free to move in the x direction but are confined by a parabolic potential in the y direction. They interact with each other through a screened power-law potential (r-ne-r/λ). In vertically coupled systems, the channels are stacked above each other in the direction perpendicular to the (x,y) plane, while in horizontally coupled systems both channels are aligned in the confinement direction. Using Monte Carlo (MC) simulations we obtain the ground-state configurations and the structural transitions as a function of the linear particle density and the separation between the channels. At zero temperature, the vertically coupled system exhibits a rich phase diagram with continuous and discontinuous transitions. On the other hand, the horizontally coupled system exhibits only a very limited number of phase transitions due to its symmetry. Further, we calculated the normal modes for the Wigner crystals in both cases. From MC simulations, we found that in the case of vertically coupled systems, the zigzag transition is only possible for low densities. A Ginzburg-Landau theory for the zigzag transition is presented, which predicts correctly the behavior of this transition from which we interpret the structural phase transition of the Wigner crystal through the reduction of the Brillouin zone.
Brillouin light scattering studies of 2D magnonic crystals.
Tacchi, S; Gubbiotti, G; Madami, M; Carlotti, G
2017-02-22
Magnonic crystals, materials with periodic modulation of their magnetic properties, represent the magnetic counterpart of photonic, phononic and plasmonic crystals, and have been largely investigated in recent years because of the possibility of using spin waves as a new means for carrying and processing information over a very large frequency bandwidth. Here, we review recent Brillouin light scattering studies of 2D magnonic crystals consisting of single- and bi-component arrays of interacting magnetic dots or antidot lattices. In particular, we discuss the principal properties of the magnonic band diagram of such systems, with emphasis given to its dependence on both magnetic and the geometrical parameters. Thanks to the possibility of tailoring their band structure by means of several degrees of freedom, planar magnonic crystals offer a good opportunity to design an innovative class of nanoscale microwave devices.
Brillouin light scattering studies of 2D magnonic crystals
NASA Astrophysics Data System (ADS)
Tacchi, S.; Gubbiotti, G.; Madami, M.; Carlotti, G.
2017-02-01
Magnonic crystals, materials with periodic modulation of their magnetic properties, represent the magnetic counterpart of photonic, phononic and plasmonic crystals, and have been largely investigated in recent years because of the possibility of using spin waves as a new means for carrying and processing information over a very large frequency bandwidth. Here, we review recent Brillouin light scattering studies of 2D magnonic crystals consisting of single- and bi-component arrays of interacting magnetic dots or antidot lattices. In particular, we discuss the principal properties of the magnonic band diagram of such systems, with emphasis given to its dependence on both magnetic and the geometrical parameters. Thanks to the possibility of tailoring their band structure by means of several degrees of freedom, planar magnonic crystals offer a good opportunity to design an innovative class of nanoscale microwave devices.
2D photonic crystal and its angular reflective azimuthal spectrum
NASA Astrophysics Data System (ADS)
Senderakova, Dagmar; Drzik, Milan; Tomekova, Juliana
2016-12-01
Contemporary, attention is paid to photonic crystals, which can strongly modify light propagation through them and enable a controllable light manipulation. The contribution is focused on a sub-wavelength 2D structure formed by Al2O3 layer on silicon substrate, patterned with periodic hexagonal lattice of deep air holes. Using various laser sources of light at single wavelength, azimuthal angle dependence of the mirror-like reflected light intensity was recorded photo-electrically. The results obtained can be used to sample the band-structure of leaky modes of the photonic crystal more reliably and help us to map the photonic dispersion diagram.
Conductance of a quantum wire in the Wigner-crystal regime.
Matveev, K A
2004-03-12
We study the effect of Coulomb interactions on the conductance of a single-mode quantum wire connecting two bulk leads. When the density of electrons in the wire is very low, they arrange in a finite-length Wigner crystal. In this regime the electron spins form an antiferromagnetic Heisenberg chain with an exponentially small coupling J. An electric current in the wire perturbs the spin chain and gives rise to a temperature-dependent contribution of the spin subsystem to the resistance. At low temperature T
D2-D1 phase transition of columnar liquid crystals
NASA Astrophysics Data System (ADS)
Sun, Y. F.; Swift, J.
1986-04-01
The D2-D1 phase transition in columnar liquid crystals of the HAT series [e.g., HAT11 (triphenelene hexa-n-dodecanoate)] is discussed within the framework of Landau theory. The order parameters which describe the transition are abstracted from a tensor density function, and are associated with two irreducible representations of the symmetry group of the high-temperature D2 phase. A mechanism for a first-order transition is then suggested in accordance with both theoretical considerations and the experimental result for the D2-D1 transition. Two possible arrangements of the herringbone structure of the D1 phase are obtained, each of which gives six orientational states in the low-temperature D1 phase.
Defect formation and coarsening in hexagonal 2D curved crystals.
García, Nicolás A; Pezzutti, Aldo D; Register, Richard A; Vega, Daniel A; Gómez, Leopoldo R
2015-02-07
In this work we study the processes of defect formation and coarsening of two-dimensional (2D) curved crystal structures. These processes are found to strongly deviate from their counterparts in flat systems. In curved backgrounds the process of defect formation is deeply affected by the curvature, and at the onset of a phase transition the early density of defects becomes highly inhomogeneous. We observe that even a single growing crystal can produce varying densities of defects depending on its initial position and local orientation with regard to the substrate. This process is completely different from flat space, where grain boundaries are formed due to the impingement of different propagating crystals. Quenching the liquid into the crystal phase leads to the formation of a curved polycrystalline structure, characterized by complex arrays of defects. During annealing, mechanisms of geodesic curvature-driven grain boundary motion and defect annihilation lead to increasing crystalline order. Linear arrays of defects diffuse to regions of high curvature, where they are absorbed by disclinations. At the early stage of coarsening the density of dislocations is insensitive to the geometry while the population of isolated disclinations is deeply affected by curvature. The regions with high curvature act as traps for the diffusion of different structures of defects, including disclinations and domain walls.
Wigner Crystal and Colossal Magnetoresistance in InSb Doped with Mn
Obukhov, S. A.; Tozer, S. W.; Coniglio, W. A.
2015-01-01
We report magnetotransport investigation of nonmagnetic InSb single crystal doped with manganese at Mn concentration NMn ~ 1,5 × 1017 cm−3 in the temperature range T = 300 K–40 mK, magnetic field B = 0–25T and hydrostatic pressure P = 0–17 kbar. Resistivity saturation was observed in the absence of magnetic field at temperatures below 200 mK while applied increasing external magnetic field induced colossal drop of resistivity (by factor 104) at B ~ 4T with further gigantic resistivity increase (by factor 104) at 15T. Under pressure, P = 17 kbar, resistivity saturation temperature increased up to 1,2 K. Existing models are discussed in attempt to explain resistivity saturation, dramatic influence of magnetic field and pressure on resistivity with the focus on possible manifestation of three dimensional Wigner crystal formed in InSb by light electrons and heavy holes. PMID:26307952
Composite Fermion Theory for the Fractional Quantum Hall Wigner Crystal State
NASA Astrophysics Data System (ADS)
Narevich, Romanas; Murthy, Ganpathy; Fertig, Herbert
2000-03-01
The low filling fraction Quantum Hall Effect is reexamined using the recent hamiltonian composite fermion theory developed by Shankar and Murthy [SM] (R. Shankar and G. Murthy, Phys. Rev. Lett. 79), 4437, (1997); G. Murthy and R. Shankar, Chapter 4 of "Composite Fermions", O. Heinonen, Ed. (World Scientific, Teaneck, NJ, 1998).. Previous studies have either concentrated on Wigner crystal states of electrons in the Hartree-Fock approximation (D. Yoshioka and H. Fukuyama, J. Phys. Soc. Japan 47), 394 (1979); D. Yoshioka and P. A. Lee, Phys. Rev. B 27, 4986 (1983); A. H. MacDonald, Phys. Rev. B 30, 4392 (1984); R. Cote and A. H. MacDonald, Phys. Rev. B 44, 8759 (1991). or studied correlated crystal states numerically (P. K. Lam and S. M. Girvin, Phys. Rev. B 30), 473 (1984); H. Yi and H. A. Fertig, Phys. Rev. B, 58, 4019 (1998).. Using the new SM approach we study the correlated states as Hartree-Fock states of composite fermions, which is known to work reasonably well for translationally invariant composite fermion states. We present the calculation of the gaps for the stable states that we found as well as the dispersion relations of the collective modes.
Asymmetric 2D spatial beam filtering by photonic crystals
NASA Astrophysics Data System (ADS)
Gailevicius, D.; Purlys, V.; Maigyte, L.; Gaizauskas, E.; Peckus, M.; Gadonas, R.; Staliunas, K.
2016-04-01
Spatial filtering techniques are important for improving the spatial quality of light beams. Photonic crystals (PhCs) with a selective spatial (angular) transmittance can also provide spatial filtering with the added benefit transversal symmetries, submillimeter dimensions and monolithic integration in other devices, such as micro-lasers or semiconductor lasers. Workable bandgap PhC configurations require a modulated refractive index with period lengths that are approximately less than the wavelength of radiation. This imposes technical limitations, whereby the available direct laser write (DLW) fabrication techniques are limited in resolution and refractive index depth. If, however, a deflection mechanism is chosen instead, a functional filter PhC can be produced that is operational in the visible wavelength regime. For deflection based PhCs glass is an attractive choice as it is highly stable medium. 2D and 3D PhC filter variations have already been produced on soda-lime glass. However, little is known about how to control the scattering of PhCs when approaching the smallest period values. Here we look into the internal structure of the initially symmetric geometry 2D PhCs and associating it with the resulting transmittance spectra. By varying the DLW fabrication beam parameters and scanning algorithms, we show that such PhCs contain layers that are comprised of semi-tilted structure voxels. We show the appearance of asymmetry can be compensated in order to circumvent some negative effects at the cost of potentially maximum scattering efficiency.
The crystal nucleation theory revisited: The case of 2D colloidal crystals
NASA Astrophysics Data System (ADS)
González, A. E.; Ixtlilco-Cortés, L.
2011-03-01
Most of the theories and studies of crystallization and crystal nucleation consider the boundaries between the crystallites and the fluid as smooth. The crystallites are the small clusters of atoms, molecules and/or particles with the symmetry of the crystal lattice that, with a slight chance of success, would grow to form the crystal grains. In fact, in the classical nucleation theory, the crystallites are assumed to have a spherical shape (circular in 2D). As far are we are aware, there is only one experimental work [1] on colloidal crystals that founds rough surfaces for the crystallites and for the crystal grains. Motivated by this work, we performed large Kinetic Monte Carlo simulations in 2D, that would follow the eventual growing of a few crystallites to form the crystal grains. The used potential has, besides the impenetrable hard core, a soft core followed by a potential well. We found that indeed the crystallites have a fractal boundary, whose value we were able to obtain. See the figure below of a typical isolated crystallite. We were also able to obtain the critical crystallite size, measured by its number of particles, Nc, and not by any critical radius. The boundaries of the crystals above Nc also have a fractal structure but of a lower value, closer to one. Finally, we also obtained the line tension between the crystallites and the surrounding fluid, as function of temperature and particle diameter, as well as the chemical potential difference between these two phases. In the URL: www.fis.unam.mx˜˜agus˜ there are posted two movies that can be downloaded: (1) 2D_crystal_nucleation.mp4, and (2) 2D_crystal_growth.mp4, that illustrate the crystal nucleation and its further growth.
Large-scale density functional calculations of the surface properties of the Wigner crystal
NASA Astrophysics Data System (ADS)
Cortes-Huerto, R.; Ballone, P.
2010-05-01
The surface properties of the jellium model have been investigated by large supercell computations in the density functional theory-local spin-density (DFT-LSD) approach for planar slabs with up to 1000 electrons. A wide interval of densities has been explored, extending into the stability range of the Wigner crystal. Most computations have been carried out on nominally paramagnetic samples with an equal number of spin-up and spin-down electrons. The results show that within DFT-LSD spontaneous spin polarization and charge localization start nearly simultaneously at the surface for rs˜20 , then, with decreasing density, they progress toward the center of the slab. Electrons are fully localized and spin polarized at rs=30 . At this density the charge distribution is the superposition of disjoint charge blobs, each corresponding to one electron. The distribution of blobs displays both regularities and disorder, the first being represented by well-defined planes and simple in-plane geometries, and the latter by a variety of surface defects. The surface energy, surface dipole, electric polarisability, and magnetization pattern have been determined as a function of density. All these quantities display characteristic anomalies at the density of the localization transition. The analysis of the low-frequency electric conductivity shows that in the fluid paramagnetic regime the in-plane current preferentially flows in the central region of the slab and the two spin channels are equally conducting. In the charge localized, spin-polarized regime, conductivity is primarily a surface effect, and an apparent asymmetry is observed in the two spin currents.
Wigner Crystallization in the Quantum 1D Jellium at All Densities
NASA Astrophysics Data System (ADS)
Jansen, S.; Jung, P.
2014-11-01
The jellium is a model, introduced by Wigner (Phys Rev 46(11):1002, 1934), for a gas of electrons moving in a uniform neutralizing background of positive charge. Wigner suggested that the repulsion between electrons might lead to a broken translational symmetry. For classical one-dimensional systems this fact was proven by Kunz (Ann Phys 85(2):303-335, 1974), while in the quantum setting, Brascamp and Lieb (Functional integration and its applications. Clarendon Press, Oxford, 1975) proved translation symmetry breaking at low densities. Here, we prove translation symmetry breaking for the quantum one-dimensional jellium at all densities.
NASA Astrophysics Data System (ADS)
Chen, Yong P.
2007-03-01
It is generally known that in high quality two dimensional electron systems (2DES, similarly for 2D hole systems and bilayer systems) under sufficiently large perpendicular magnetic field B, the quantum Hall (QH) states terminate into an electronic solid --- a Wigner crystal (WC) pinned by disorder. After a brief review of solid phases in QH systems (including several recently discovered ones [1]) as known from microwave spectroscopy (measuring a characteristic pinning mode resonance of the solid), I will discuss two of our experiments that highlight the importance of many-body quantum correlation in the high-B WC. In one experiment [2], we measured the melting temperature (Tc) of the high-B WC at many different B and densities n and in multiple 2DES samples. The data show unambiguously that in a given sample, Tc is controlled by Landau filling ν=nh/eB instead of by n. This demonstrates the quantum nature of the high-B WC and that its melting is dependent on many-body quantum correlation (via ν). Such behavior contrasts with any other known solids (in particular, a classical electron solid), whose Tc are determined by n. In addition, we found that stronger pinning disorder in samples with tighter vertical confinement led to an enhancement of Tc. In another experiment [3], we studied bilayer WC (BWC) in bilayer hole systems (in low inter-layer tunneling limit). We found that in samples with a bilayer exciton condensate (BEC) QH state at ν=1, the pinning mode frequency of the BWC (ν1) is systematically enhanced from what would be expected from two classically interacting single-layer WC. The enhancement decreases with increasing effective layer separation and is not observed for samples without the ν=1 state. We suggest that our results give evidence for a pseudospin (layer index) ferromagnetic BWC, which possesses interlayer quantum correlation and long range in-plane phase coherence similar to that in the ν=1 BEC state and can experience enhanced pinning [4
Epitaxial Growth of Ternary Topological Insulator Bi2 Te2 Se 2D Crystals on Mica.
Liu, Yujing; Tang, Min; Meng, Mengmeng; Wang, Mingzhan; Wu, Jinxiong; Yin, Jianbo; Zhou, Yubing; Guo, Yunfan; Tan, Congwei; Dang, Wenhui; Huang, Shaoyun; Xu, H Q; Wang, Yong; Peng, Hailin
2017-03-06
Nanostructures of ternary topological insulator (TI) Bi2 Te2 Se are, in principle, advantageous to the manifestation of topologically nontrivial surface states, due to significantly enhanced surface-to-volume ratio compared with its bulk crystals counterparts. Herein, the synthesis of 2D Bi2 Te2 Se crystals on mica via the van der Waals epitaxy method is explored and systematically the growth behaviors during the synthesis process are investigated. Accordingly, 2D Bi2 Te2 Se crystals with domain size up to 50 µm large and thickness down to 2 nm are obtained. A pronounced weak antilocalization effect is clearly observed in the 2D Bi2 Te2 Se crystals at 2 K. The method for epitaxial growth of 2D ternary Bi2 Te2 Se crystals may inspire materials engineering toward enhanced manifestation of the subtle surface states of TIs and thereby facilitate their potential applications in next-generation spintronics.
2D Plasma Photonic Crystals in resonantly pumped Cesium Vapor
NASA Astrophysics Data System (ADS)
Righetti, Fabio; Cappelli, Mark
2016-10-01
Plasma photonic crystals (PCs) afford the opportunity for dynamic reconfigurability. In this presentation we describe the conditions required for constructing an all-plasma PC that can interact with sub mm-wavelength radiation. Conditions required for this interaction are high plasma densities (>1014 cm-3) and small lattice constant (<1 mm). We describe the construction of a two-dimensional photonic crystal composed of several sub-millimeter plasma filaments in a 1 Torr heated cesium vapor cell. The cesium is ionized by 1 W continuous-wave laser excitation with the wavelength centered around the 852 nm resonance line. The filaments are produced by focusing the laser through a microlens array with a 500 µm pitch. Small departures from line center are found to produce a strong variation in the plasma filament structure and density. Stark broadening measurements of the cesium 9F-5D transition at 647.4 nm yield plasma density. We present preliminary terahertz transmission spectrum of the two-dimensional plasma photonic crystal structure. Experimental results are compared to numerical simulations which predict the presence of bandgaps in regions of both negative and positive plasma dielectric constant.
Controllable liquid crystal gratings for an adaptive 2D/3D auto-stereoscopic display
NASA Astrophysics Data System (ADS)
Zhang, Y. A.; Jin, T.; He, L. C.; Chu, Z. H.; Guo, T. L.; Zhou, X. T.; Lin, Z. X.
2017-02-01
2D/3D switchable, viewpoint controllable and 2D/3D localizable auto-stereoscopic displays based on controllable liquid crystal gratings are proposed in this work. Using the dual-layer staggered structure on the top substrate and bottom substrate as driven electrodes within a liquid crystal cell, the ratio between transmitting region and shielding region can be selectively controlled by the corresponding driving circuit, which indicates that 2D/3D switch and 3D video sources with different disparity images can reveal in the same auto-stereoscopic display system. Furthermore, the controlled region in the liquid crystal gratings presents 3D model while other regions maintain 2D model in the same auto-stereoscopic display by the corresponding driving circuit. This work demonstrates that the controllable liquid crystal gratings have potential applications in the field of auto-stereoscopic display.
Global regularity and uniqueness of weak solution for the 2-D liquid crystal flows
NASA Astrophysics Data System (ADS)
Xu, Xiang; Zhang, Zhifei
We prove the global existence and regularity of weak solution for the 2-D liquid crystal flows with the large initial velocity. The uniqueness of weak solution is also proved by using the Littlewood-Paley analysis.
2D Crystal Semiconductors New Materials for GHz-THz Devices
2015-10-02
frequency operation. 4) Identify methods to improve carrier transport in 2D Crystal semiconductors. 5) Compare FETs made from naturally occuring and... chemically synthesized 2D Crystal semic???ductors. 6) Elucidate the effect of contact resistance, and gauge the challenges for GHz-THz electronics by... chemical doping, which involved replac- ing a small number of atoms of the 3-D semiconductor by those with higher or lower valence. The next advance
Large-area high-quality 2D ultrathin Mo2C superconducting crystals.
Xu, Chuan; Wang, Libin; Liu, Zhibo; Chen, Long; Guo, Jingkun; Kang, Ning; Ma, Xiu-Liang; Cheng, Hui-Ming; Ren, Wencai
2015-11-01
Transition metal carbides (TMCs) are a large family of materials with many intriguing properties and applications, and high-quality 2D TMCs are essential for investigating new physics and properties in the 2D limit. However, the 2D TMCs obtained so far are chemically functionalized, defective nanosheets having maximum lateral dimensions of ∼10 μm. Here we report the fabrication of large-area high-quality 2D ultrathin α-Mo2C crystals by chemical vapour deposition (CVD). The crystals are a few nanometres thick, over 100 μm in size, and very stable under ambient conditions. They show 2D characteristics of superconducting transitions that are consistent with Berezinskii-Kosterlitz-Thouless behaviour and show strong anisotropy with magnetic field orientation; moreover, the superconductivity is also strongly dependent on the crystal thickness. Our versatile CVD process allows the fabrication of other high-quality 2D TMC crystals, such as ultrathin WC and TaC crystals, which further expand the large family of 2D materials.
Large-area high-quality 2D ultrathin Mo2C superconducting crystals
NASA Astrophysics Data System (ADS)
Xu, Chuan; Wang, Libin; Liu, Zhibo; Chen, Long; Guo, Jingkun; Kang, Ning; Ma, Xiu-Liang; Cheng, Hui-Ming; Ren, Wencai
2015-11-01
Transition metal carbides (TMCs) are a large family of materials with many intriguing properties and applications, and high-quality 2D TMCs are essential for investigating new physics and properties in the 2D limit. However, the 2D TMCs obtained so far are chemically functionalized, defective nanosheets having maximum lateral dimensions of ~10 μm. Here we report the fabrication of large-area high-quality 2D ultrathin α-Mo2C crystals by chemical vapour deposition (CVD). The crystals are a few nanometres thick, over 100 μm in size, and very stable under ambient conditions. They show 2D characteristics of superconducting transitions that are consistent with Berezinskii-Kosterlitz-Thouless behaviour and show strong anisotropy with magnetic field orientation; moreover, the superconductivity is also strongly dependent on the crystal thickness. Our versatile CVD process allows the fabrication of other high-quality 2D TMC crystals, such as ultrathin WC and TaC crystals, which further expand the large family of 2D materials.
Cavity optomechanics with 2D photonic crystal membrane reflectors
NASA Astrophysics Data System (ADS)
Lingaraju, Navin B.; Shuai, Yichen; Lawall, John
2016-03-01
Membranes made from silicon nitride have significantly higher mechanical Q-factors under tensile stress than those made of other dielectric materials. This makes them ideal candidates for membrane reflectors that provide high finesse in Fabry-Perot cavities or membrane-in-the-middle optomechanical systems. Building on our previous work with one-dimensional gratings on suspended membranes, we patterned two-dimensional photonic crystal gratings on monolithic, suspended membranes made from silicon nitride. These high-Q membranes exhibited high reflectivity, upwards of 99%, over several nanometers in the telecom band. To probe their optical response in a cavity environment, we used these membrane reflectors as the moving mirror in a Fabry-Perot cavity. We were able to realize cavities with a finesse of over 4,500.
Nano-scale electronic and optoelectronic devices based on 2D crystals
NASA Astrophysics Data System (ADS)
Zhu, Wenjuan
In the last few years, the research community has been rapidly growing interests in two-dimensional (2D) crystals and their applications. The properties of these 2D crystals are diverse -- ranging from semi-metal such as graphene, semiconductors such as MoS2, to insulator such as boron nitride. These 2D crystals have many unique properties as compared to their bulk counterparts due to their reduced dimensionality and symmetry. A key difference is the band structures, which lead to distinct electronic and photonic properties. The 2D nature of the material also plays an important role in defining their exceptional properties of mechanical strength, surface sensitivity, thermal conductivity, tunable band-gap and their interaction with light. These unique properties of 2D crystals open up a broad territory of applications in computing, communication, energy, and medicine. In this talk, I will present our work on understanding the electrical properties of graphene and MoS2, in particular current transport and band-gap engineering in graphene, interface between gate dielectrics and graphene, and gap states in MoS2. I will also present our work on the nano-scale electronic devices (RF and logic devices) and photonic devices (plasmonic devices and photo-detectors) based on these 2D crystals.
Evans, C. M. Krynski, Kamil; Streeter, Zachary; Findley, G. L.
2015-12-14
We present for the first time the quasi-free electron energy V{sub 0}(ρ) for H{sub 2}, D{sub 2}, and O{sub 2} from gas to liquid densities, on noncritical isotherms and on a near critical isotherm in each fluid. These data illustrate the ability of field enhanced photoemission (FEP) to determine V{sub 0}(ρ) accurately in strongly absorbing fluids (e.g., O{sub 2}) and fluids with extremely low critical temperatures (e.g., H{sub 2} and D{sub 2}). We also show that the isotropic local Wigner-Seitz model for V{sub 0}(ρ) — when coupled with thermodynamic data for the fluid — can yield optimized parameters for intermolecular potentials, as well as zero kinetic energy electron scattering lengths.
NASA Astrophysics Data System (ADS)
Vasylenko, Anna A.; Misko, Vyacheslav R.
2015-04-01
When floating on a two-dimensional surface of superfluid 4He, electrons arrange themselves in two-dimensional crystalline structure known as Wigner crystal. In channels, the boundaries interfere the crystalline order and in case of very narrow channels one observes a quasi-one-dimensional (quasi-1D) Wigner crystal formed by just a few rows of electrons and, ultimately, one row in the "quantum wire" regime. Recently, the "quantum wire" regime was accessed experimentally [D.G. Rees, H. Totsuji, K. Kono, Phys. Rev. Lett. 108, 176801 (2012)] resulting in unusual transport phenomena such as, e.g., oscillations in the electron conductance. Using molecular dynamics simulations, we study the nonlinear transport of electrons in channels with various types of constrictions: single and multiple symmetric and asymmetric geometrical constrictions with varying width and length, and saddle-point-type potentials with varying gate voltage. In particular, we analyze the average particle velocity of the particles and the corresponding electron current versus the driving force or the gate voltage. We have revealed a significant difference in the dynamics for long and short constrictions: The oscillations of the average velocity of the particles for the systems with short constrictions exhibit a clear correlation with the transitions between the states with different numbers of rows of particles; on the other hand, for the systems with longer constrictions these oscillations are suppressed. The obtained results qualitatively agree with the experimental observations. Next, we propose a FET-like structure that consists of a channel with asymmetric constrictions. We show that applying a transverse bias results either in increase of the average particle velocity or in its suppression thus allowing a flexible control tool over the electron transport. The advantage of the asymmetric FET is that it does not have a gate and it allows an easy control of relatively large electron flow
NASA Astrophysics Data System (ADS)
Taut, M. G.
2001-03-01
The ground state energy and the lowest excitations of a two dimensional Wigner crystal with one -- and two electrons per cell are investigated. In case of two electrons per lattice site, the interaction of the electrons within each cell is taken into account exactly (including exchange and the full Coulomb correlation effects). The interaction between the cells is in second order (dipole) van der Waals approximation. No further approximations are made, in particular Landau level mixing is accounted for. Therefore, our calculation comprises a supplementary description of the bubble phase in the special case of one and two electrons per bubble, as proposed by Koulakov, Fogler and Shklovskii in Phys.Rev.Lett. 76, 499 (1996) on the basis of a Hartree Fock calculation. The phase diagram shows for which filling factors and densities which phase: single electrons versus singlet or triplet pairs on the Wigner crystal lattice sites, is energetically favored. Comparison with other approximations for the Wigner crystal and with the Laughlin liquid is made as well.
NASA Astrophysics Data System (ADS)
Suslov, A. V.; Drichko, I. L.; Smirnov, I. Yu.; Pfeiffer, L. N.; West, K. W.; Galperin, Y. M.
Both attenuation of a surface acoustic wave (SAW) and variation of its speed due to interaction with 2D electrons in n-GaAlAs/GaAs/GaAlAs structures are measured versus perpendicular magnetic field of up to 18 T in the frequency range of (28.5 - 306) MHz and at temperatures (40 - 380) mK. The study is performed on δ-doped from both sides 65 nm wide GaAs quantum well with the carrier density of n = 5 .1010 cm-2 and their mobility of μ = 8 .106 cm2/V.s. The complex AC conductance, σ is calculated. Analysis of σ shows that at low temperatures and at the filling factor of 2, 1, and 1/5 the electron system resides in the integer and fractional quantum Hall states, respectively. However, in vicinities to these values, namely at ν = 1.9, (1.1 and 0.9), (0.21 and 0.19), the electron states can be interpreted as so-called pinning modes of Wigner crystal (WC). Temperature dependences of σ indicates a crossover between the localized modes (at ν = 1 and 2) and a pinned WC. When the temperature (or the SAW intensity) increases the behavior of the complex conductance can be understood as manifestation of WC melting. Acknowledgements to E. Palm, T. Murphy, J.-H. Park, and G. Jones; RFBR Grant 14-02-00232 for ILD; NSF DMR-1157490 and the State of Florida for NHMFL; Gordon and Betty Moore Foundation Grant GBMF2719 and NSF MRSEC-DMR-0819860 for Princeton University.
Multi-resonant optical parametric oscillator based on 2D-PPLT nonlinear photonic crystal.
Lazoul, Mohamed; Boudrioua, Azzedine; Simohamed, Lotfy-Mokhtar; Peng, Lung-Han
2015-04-15
The aim of this work is to achieve an optical parametric oscillator based on two-dimensional periodically poled lithium tantalate (2D-PPLT) crystals that are designed to allow multiple reciprocal lattice-vector contribution to the quasi-phase matching scheme. We are particularly interested in the effect of the multi-wavelength parametric generation performed by the 2D nonlinear photonic crystal to achieve a multi-resonant optical parametric oscillator. The performances are studied in terms of generation efficiency and multi-wavelength generation.
The microstrip filters based on electromagnetic crystal of resonators 2d disposition
NASA Astrophysics Data System (ADS)
Belyaev, B. A.; Khodenkov, S. A.; Balva, Ya F.; Aplesnin, S. S.; Bandurina, O. N.
2016-11-01
Filters of the 6th order, based on 2D electromagnetic crystals were developed. Application in structures of resonators with convolved and earthed on its base with strip conductors enables the implementation of filters having high frequency-selective properties and demanded in the aerospace equipment.
Processable 2D materials beyond graphene: MoS2 liquid crystals and fibres.
Jalili, Rouhollah; Aminorroaya-Yamini, Sima; Benedetti, Tania M; Aboutalebi, Seyed Hamed; Chao, Yunfeng; Wallace, Gordon G; Officer, David L
2016-09-29
Herein, we show properly engineered MoS2 crystals can readily form liquid crystalline dispersions in water making them ideal candidates for large-scale manufacturing processes. The guideline provided here can serve as the basis to develop practical protocols to address the long-standing goal of large-scale manufacturing of 2D materials.
Ring-shaped Wigner crystals of trapped ions at the micronscale
NASA Astrophysics Data System (ADS)
Li, Haokun; Urban, Erik; Noel, Crystal; Chuang, Alexander; Xia, Yang; Hemmerling, Borge; Wang, Yuan; Zhang, Xiang; Haeffner, Hartmut
Trapped ion crystals are ideal platforms to study many-body physics and quantum information processing, with both the internal electronic states and external motional degree-of-freedoms controllable at the single quantum level. In contrast to conventional, finite, linear chains of ions, a ring topology exhibiting periodic boundary conditions and rotational symmetry opens up a new directions to diverse topics. However, previous implementations of ion rings result in small aspect ratios (<0.07) of ion-electrode distance to ring diameter, making the rotational symmetry of the ion crystals prone to stray electric fields from imperfections of the trap electrodes, particularly evident at low temperatures. Here, using a new trap design with a 60-fold improvement of this aspect ratio, we demonstrate crystallization of 40Ca+ ions in a ring with rotational energy barriers comparable to the thermal energy of Doppler laser cooled ion crystals. When further reducing the rotational energy barriers, we observe delocalization of the ion rings. With this result, we enter a regime where quantum topological effects can be studied and novel quantum computation and simulation experiments can be implemented.
Combining 2D synchrosqueezed wave packet transform with optimization for crystal image analysis
NASA Astrophysics Data System (ADS)
Lu, Jianfeng; Wirth, Benedikt; Yang, Haizhao
2016-04-01
We develop a variational optimization method for crystal analysis in atomic resolution images, which uses information from a 2D synchrosqueezed transform (SST) as input. The synchrosqueezed transform is applied to extract initial information from atomic crystal images: crystal defects, rotations and the gradient of elastic deformation. The deformation gradient estimate is then improved outside the identified defect region via a variational approach, to obtain more robust results agreeing better with the physical constraints. The variational model is optimized by a nonlinear projected conjugate gradient method. Both examples of images from computer simulations and imaging experiments are analyzed, with results demonstrating the effectiveness of the proposed method.
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.
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.
The 2D Selfassembly of Benzimidazole and its Co-crystallization
NASA Astrophysics Data System (ADS)
Costa, Paulo; Teeter, Jacob; Kunkel, Donna; Sinitskii, Alexander; Enders, Axel
Benzimidazoles (BI) are organic molecules that form ferroelectric crystals. Key to their ferroelectric behavior are the switchable N . . . HN type bonds and how they couple to the electron system of the molecules. We attempted to crystallize BI on various metal surfaces and studied them using STM. We observed that on Au and Ag, BI joins into zipper chains characteristic of its bulk structure that can pack into a continuous 2D layer. Because the dipole of BI lies in the direction of its switchable hydrogen bond, these zippers should in principle have reversible polarizations that point along the direction they run. BI's crystallization is reminiscent to how croconic acid (CA) crystallizes in 2D using O . . . HO bonding, suggesting that these molecules may be able to co-crystallize through OH . . . N bonds. This would present the opportunity to modify BI's properties, such as the energy needed to switch a hydrogen from a donor to acceptor site. When co-deposited, CA and BI successfully combine into a co-crystal formed by building blocks consisting of 2 CA and 2 BI molecules. These findings demonstrate the usefulness of using STM as a preliminary check to verify if two molecules are compatible with each other without having to attempt crystallization with multiple solvents and mixing methods.
THz quantum cascade lasers operating on the radiative modes of a 2D photonic crystal.
Halioua, Y; Xu, G; Moumdji, S; Li, L H; Davies, A G; Linfield, E H; Colombelli, R
2014-07-01
Photonic-crystal lasers operating on Γ-point band-edge states of a photonic structure naturally exploit the so-called "nonradiative" modes. As the surface output coupling efficiency of these modes is low, they have relatively high Q factors, which favor lasing. We propose a new 2D photonic-crystal design that is capable of reversing this mode competition and achieving lasing on the radiative modes instead. Previously, this has only been shown in 1D structures, where the central idea is to introduce anisotropy into the system, both at unit-cell and resonator scales. By applying this concept to 2D photonic-crystal patterned terahertz frequency quantum cascade lasers, surface-emitting devices with diffraction-limited beams are demonstrated, with 17 mW peak output power.
The 2DX robot: a membrane protein 2D crystallization Swiss Army knife.
Iacovache, Ioan; Biasini, Marco; Kowal, Julia; Kukulski, Wanda; Chami, Mohamed; van der Goot, F Gisou; Engel, Andreas; Rémigy, Hervé-W
2010-03-01
Among the state-of-the-art techniques that provide experimental information at atomic scale for membrane proteins, electron crystallography, atomic force microscopy and solid state NMR make use of two-dimensional crystals. We present a cyclodextrin-driven method for detergent removal implemented in a fully automated robot. The kinetics of the reconstitution processes is precisely controlled, because the detergent complexation by cyclodextrin is of stoichiometric nature. The method requires smaller volumes and lower protein concentrations than established 2D crystallization methods, making it possible to explore more conditions with the same amount of protein. The method yielded highly ordered 2D crystals diffracting to high resolution from the pore-forming toxin Aeromonas hydrophila aerolysin (2.9A), the plant aquaporin SoPIP2;1 (3.1A) and the human aquaporin-8 (hAQP8; 3.3A). This new method outperforms traditional 2D crystallization approaches in terms of accuracy, flexibility, throughput, and allows the usage of detergents having low critical micelle concentration (CMC), which stabilize the structure of membrane proteins in solution.
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.
Birefringence-Directed Raman Selection Rules in 2D Black Phosphorus Crystals.
Mao, Nannan; Wu, Juanxia; Han, Bowen; Lin, Jingjing; Tong, Lianming; Zhang, Jin
2016-05-01
The incident and scattered light engaged in the Raman scattering process of low symmetry crystals always suffer from the birefringence-induced depolarization. Therefore, for anisotropic crystals, the classical Raman selection rules should be corrected by taking the birefringence effect into consideration. The appearance of the 2D anisotropic materials provides an excellent platform to explore the birefringence-directed Raman selection rules, due to its controllable thickness at the nanoscale that greatly simplifies the situation comparing with bulk materials. Herein, a theoretical and experimental investigation on the birefringence-directed Raman selection rules in the anisotropic black phosphorus (BP) crystals is presented. The abnormal angle-dependent polarized Raman scattering of the Ag modes in thin BP crystal, which deviates from the normal Raman selection rules, is successfully interpreted by the theoretical model based on birefringence. It is further confirmed by the examination of different Raman modes using different laser lines and BP samples of different thicknesses.
Responsive ionic liquid-polymer 2D photonic crystal gas sensors.
Smith, Natasha L; Hong, Zhenmin; Asher, Sanford A
2014-12-21
We developed novel air-stable 2D polymerized photonic crystal (2DPC) sensing materials for visual detection of gas phase analytes such as water and ammonia by utilizing a new ionic liquid, ethylguanidine perchlorate (EGP) as the mobile phase. Because of the negligible ionic liquid vapor pressure these 2DPC sensors are indefinitely air stable and, therefore, can be used to sense atmospheric analytes. 2D arrays of ~640 nm polystyrene nanospheres were attached to the surface of crosslinked poly(hydroxyethyl methacrylate) (pHEMA)-based polymer networks dispersed in EGP. The wavelength of the bright 2D photonic crystal diffraction depends sensitively on the 2D array particle spacing. The volume phase transition response of the EGP-pHEMA system to water vapor or gaseous ammonia changes the 2DPC particle spacing, enabling the visual determination of the analyte concentration. Water absorbed by EGP increases the Flory-Huggins interaction parameter, which shrinks the polymer network and causes a blue shift in the diffracted light. Ammonia absorbed by the EGP deprotonates the pHEMA-co-acrylic acid carboxyl groups, swelling the polymer which red shifts the diffracted light.
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.
Bovine F1Fo ATP synthase monomers bend the lipid bilayer in 2D membrane crystals
Jiko, Chimari; Davies, Karen M; Shinzawa-Itoh, Kyoko; Tani, Kazutoshi; Maeda, Shintaro; Mills, Deryck J; Tsukihara, Tomitake; Fujiyoshi, Yoshinori; Kühlbrandt, Werner; Gerle, Christoph
2015-01-01
We have used a combination of electron cryo-tomography, subtomogram averaging, and electron crystallographic image processing to analyse the structure of intact bovine F1Fo ATP synthase in 2D membrane crystals. ATPase assays and mass spectrometry analysis of the 2D crystals confirmed that the enzyme complex was complete and active. The structure of the matrix-exposed region was determined at 24 Å resolution by subtomogram averaging and repositioned into the tomographic volume to reveal the crystal packing. F1Fo ATP synthase complexes are inclined by 16° relative to the crystal plane, resulting in a zigzag topology of the membrane and indicating that monomeric bovine heart F1Fo ATP synthase by itself is sufficient to deform lipid bilayers. This local membrane curvature is likely to be instrumental in the formation of ATP synthase dimers and dimer rows, and thus for the shaping of mitochondrial cristae. DOI: http://dx.doi.org/10.7554/eLife.06119.001 PMID:25815585
Computational Study and Analysis of Structural Imperfections in 1D and 2D Photonic Crystals
Maskaly, Karlene Rosera
2005-06-01
Dielectric reflectors that are periodic in one or two dimensions, also known as 1D and 2D photonic crystals, have been widely studied for many potential applications due to the presence of wavelength-tunable photonic bandgaps. However, the unique optical behavior of photonic crystals is based on theoretical models of perfect analogues. Little is known about the practical effects of dielectric imperfections on their technologically useful optical properties. In order to address this issue, a finite-difference time-domain (FDTD) code is employed to study the effect of three specific dielectric imperfections in 1D and 2D photonic crystals. The first imperfection investigated is dielectric interfacial roughness in quarter-wave tuned 1D photonic crystals at normal incidence. This study reveals that the reflectivity of some roughened photonic crystal configurations can change up to 50% at the center of the bandgap for RMS roughness values around 20% of the characteristic periodicity of the crystal. However, this reflectivity change can be mitigated by increasing the index contrast and/or the number of bilayers in the crystal. In order to explain these results, the homogenization approximation, which is usually applied to single rough surfaces, is applied to the quarter-wave stacks. The results of the homogenization approximation match the FDTD results extremely well, suggesting that the main role of the roughness features is to grade the refractive index profile of the interfaces in the photonic crystal rather than diffusely scatter the incoming light. This result also implies that the amount of incoherent reflection from the roughened quarterwave stacks is extremely small. This is confirmed through direct extraction of the amount of incoherent power from the FDTD calculations. Further FDTD studies are done on the entire normal incidence bandgap of roughened 1D photonic crystals. These results reveal a narrowing and red-shifting of the normal incidence bandgap with
From Homochiral Clusters to Racemate Crystals: Viable Nuclei in 2D Chiral Crystallization.
Seibel, Johannes; Parschau, Manfred; Ernst, Karl-Heinz
2015-07-01
The quest for enantiopure compounds raises the question of which factors favor conglomerate crystallization over racemate crystallization. Studying nucleation and crystal growth at surfaces with submolecular-resolution scanning tunneling microscopy is a suitable approach to better understand intermolecular chiral recognition. Racemic heptahelicene on the Ag(100) surface shows a transition from homochiral nuclei to larger racemic motifs, although the extended homochiral phase exhibits higher density. The homochiral-heterochiral transition is explained by the higher stability of growing nuclei due to a better match of the molecular lattice to the substrate surface. Our observations are direct visual proof of viable nuclei.
High-resistance liquid-crystal lens array for rotatable 2D/3D autostereoscopic display.
Chang, Yu-Cheng; Jen, Tai-Hsiang; Ting, Chih-Hung; Huang, Yi-Pai
2014-02-10
A 2D/3D switchable and rotatable autostereoscopic display using a high-resistance liquid-crystal (Hi-R LC) lens array is investigated in this paper. Using high-resistance layers in an LC cell, a gradient electric-field distribution can be formed, which can provide a better lens-like shape of the refractive-index distribution. The advantages of the Hi-R LC lens array are its 2D/3D switchability, rotatability (in the horizontal and vertical directions), low driving voltage (~2 volts) and fast response (~0.6 second). In addition, the Hi-R LC lens array requires only a very simple fabrication process.
Machine Learning Energies of 2 Million Elpasolite (A B C2D6) Crystals
NASA Astrophysics Data System (ADS)
Faber, Felix A.; Lindmaa, Alexander; von Lilienfeld, O. Anatole; Armiento, Rickard
2016-09-01
Elpasolite is the predominant quaternary crystal structure (AlNaK2F6 prototype) reported in the Inorganic Crystal Structure Database. We develop a machine learning model to calculate density functional theory quality formation energies of all ˜2 ×106 pristine A B C2D6 elpasolite crystals that can be made up from main-group elements (up to bismuth). Our model's accuracy can be improved systematically, reaching a mean absolute error of 0.1 eV /atom for a training set consisting of 10 ×103 crystals. Important bonding trends are revealed: fluoride is best suited to fit the coordination of the D site, which lowers the formation energy whereas the opposite is found for carbon. The bonding contribution of the elements A and B is very small on average. Low formation energies result from A and B being late elements from group II, C being a late (group I) element, and D being fluoride. Out of 2 ×106 crystals, 90 unique structures are predicted to be on the convex hull—among which is NFAl2Ca6, with a peculiar stoichiometry and a negative atomic oxidation state for Al.
Nicolaou, Costa; Lau, Wah Tung; Gad, Raanan; Akhavan, Hooman; Schilling, Ryan; Levi, Ofer
2013-12-16
We demonstrate for the first time a 300nm thick, 300μm × 300μm 2D dielectric photonic crystal slab membrane with a quality factor of 10,600 by coupling light to slightly perturbed dark modes through alternating nano-hole sizes. The newly created fundamental guided resonances greatly reduce nano-fabrication accuracy requirements. Moreover, we created a new layer architecture resulting in electric field enhancement at the interface between the slab and sensing regions, and spectral sensitivity of >800 nm/RIU, that is, >0.8 of the single-mode theoretical upper limit of spectral sensitivity.
Cylindrical liquid crystal lenses system for autostereoscopic 2D/3D display
NASA Astrophysics Data System (ADS)
Chen, Chih-Wei; Huang, Yi-Pai; Chang, Yu-Cheng; Wang, Po-Hao; Chen, Po-Chuan; Tsai, Chao-Hsu
2012-06-01
The liquid crystal lenses system, which could be electrically controlled easily for autostereoscopic 2D/3D switchable display was proposed. The High-Resistance liquid crystal (HRLC) lens utilized less controlled electrodes and coated a high-resistance layer between the controlled-electrodes was proposed and was used in this paper. Compare with the traditional LC lens, the HR-LC Lens could provide smooth electric-potential distribution within the LC layer under driving status. Hence, the proposed HR-LC Lens had less circuit complexity, low driving voltage, and good optical performance also could be obtained. In addition, combining with the proposed driving method called dual-directional overdriving method, the above method could reduce the switching time by applying large voltage onto cell. Consequently, the total switching time could be further reduced to around 2second. It is believed that the LC lens system has high potential in the future.
Spectral Approach to Anderson Localization in a Disordered 2D Complex Plasma Crystal
NASA Astrophysics Data System (ADS)
Kostadinova, Eva; Liaw, Constanze; Matthews, Lorin; Busse, Kyle; Hyde, Truell
2016-10-01
In condensed matter, a crystal without impurities acts like a perfect conductor for a travelling wave-particle. As the level of impurities reaches a critical value, the resistance in the crystal increases and the travelling wave-particle experiences a transition from an extended to a localized state, which is called Anderson localization. Due to its wide applicability, the subject of Anderson localization has grown into a rich field in both physics and mathematics. Here, we introduce the mathematics behind the spectral approach to localization in infinite disordered systems and provide physical interpretation in context of both quantum mechanics and classical physics. We argue that the spectral analysis is an important contribution to localization theory since it avoids issues related to the use of boundary conditions, scaling, and perturbation. To test accuracy and applicability we apply the spectral approach to the case of a 2D hexagonal complex plasma crystal used as a macroscopic analog for a graphene-like medium. Complex plasma crystals exhibit characteristic distance and time scales, which are easily observable by video microscopy. As such, these strongly coupled many-particle systems are ideal for the study of localization phenomena. The goal of this research is to both expand the spectral method into the classical regime and show the potential of complex plasma as a macroscopic tool for localization experiments. NSF / DOE funding is gratefully acknowledged - PHY1414523 & PHY1262031.
Sun, Ya-Qiu; Xu, Yan-Yan; Gao, Dong-Zhao; Zhang, Guo-Ying; Liu, Yiao-Xu; Wang, Jing; Liao, Dai-Zheng
2012-05-14
Five new 2D coordination polymers, [Co(nip)(CuL)(H(2)O)]·CH(3)OH (1), [Mn(ip)(NiL)]·0.63H(2)O (2), [Cu(ip)(CuL)] (3), [Mn(6)(CuL)(6)(btc)(4)(H(2)O)(4)]·7H(2)O (4), and [Cu(CuL)(Hbtc)(H(2)O)] (5)(ML, H(2)L = 2,3-dioxo-5,6,14,15-dibenzo-1,4,8,12-tetraazacyclo-pentadeca-7,13-diene; H(2)nip = 5-nitroisophthalic acid; H(2)ip = m-isophthalic acid; H(3)btc = 1,3,5-benzenetricarboxylic acid) have been synthesized by a solvothermal method and characterized by single-crystal X-ray diffraction. Complexes 1-5 exhibit different 2D layered structures formed by Co(2)Cu(2) (1), Mn(2)Ni(2) (2), Cu(4) (3), Mn(3)Ni(3) (4), Cu(4) (5) units, respectively, via the oxamide and diverse carboxylic acid bridges. Compounds 1, 2, 3 and 5 are uninodal 4-connected (4, 4)-grids topology, while complex 4 possesses a 2D network with (3, 4)-connected (4(2).8)(4)(4(3).6(2).8)(3) topology. The results of magnetic determination show pronounced antiferromagnetic interactions in 1-4.
PMN-PT single crystal for endoscopic ultrasound 2D array application
NASA Astrophysics Data System (ADS)
Zhu, Yuhang; Liang, Huageng; Zhu, Benpeng; Zhou, Dan; Yang, Xiaofei
2017-03-01
Based on lead magnesium niobate-lead titanate single crystal, a 24 × 24 row-column addressing endoscopic two-dimensional array has been successfully fabricated using novel flanged electrodes and "semi-kerf" technologies. Each row/column array element was measured to have an electromechanical coupling coefficient of 0.81, a center frequency of 5MHz, and a fractional bandwidth of approximately 88% at -6 dB. Of particular significance was that the lead magnesium niobate-lead titanate element exhibits much higher sensitivity compared with lead zirconate titanate-based 2D arrays with similar operational frequency and element area. According to the Field II simulated results, although the obtained beamwidth at -6 dB was a little inferior to that of the fully sampled 24 × 24 two-dimensional array, it is believed that the beamwidth can be improved by appropriately increasing the element number. These results demonstrated that the lead magnesium niobate-lead titanate single-crystal 2D array is a promising candidate for real-time three-dimensional endoscopic ultrasound imaging.
Red-green-blue 2 D tuneable liquid crystal laser devices
NASA Astrophysics Data System (ADS)
Coles, H. J.; Morris, S. M.; Ford, A. D.; Hands, P. J. W.; Wilkinson, T. D.
2009-08-01
In this paper, we review our recent experimental work on coherent and blue phase liquid crystal lasers.We will present results on thin-film photonic band edge lasing devices using dye-doped low molar mass liquid crystals in self-organised chiral nematic and blue phases. We show that high Q-factor lasers can be achieved in these materials and demonstrate that a single mode output with a very narrow line width can be readily achievable in well-aligned mono-domain samples. Further, we have found that the performance of the laser, i.e. the slope efficiency and the excitation threshold, are dependent upon the physical parameters of the low molar mass chiral nematic liquid crystals. Specifically, slope efficiencies greater than 60% could be achieved depending upon the materials used and the device geometry employed. We will discuss the important parameters of the liquid crystal host/dye guest materials and device configuration that are needed to achieve such high slope efficiencies. Further we demonstrate how the wavelength of the laser can be tuned using an in-plane electric field in a direction perpendicular to the helix axis via a flexoelectric mechanism as well as thermally using thermochromic effects. We will then briefly outline data on room temperature blue phase lasers and further show how liquid crystal/lenslet arrays have been used to demonstrate 2D laser emission of any desired wavelength. Finally, we present preliminary data on LED/incoherent pumping of RG liquid crystal lasers leading to a continuous wave output.
Tight-Binding Approximations in 1D and 2D Coupled-Cavity Photonic Crystal Structures
NASA Astrophysics Data System (ADS)
Day, Nicole C. L.
Light confinement and controlling an optical field has numerous applications in the field of telecommunications for optical signals processing. When the wavelength of the electromagnetic field is on the order of the period of a photonic microstructure, the field undergoes reflection, refraction, and coherent scattering. This produces photonic bandgaps, forbidden frequency regions or spectral stop bands where light cannot exist. Dielectric perturbations that break the perfect periodicity of these structures produce what is analogous to an impurity state in the bandgap of a semiconductor. The defect modes that exist at discrete frequencies within the photonic bandgap are spatially localized about the cavity-defects in the photonic crystal. In this thesis the properties of two tight-binding approximations (TBAs) are investigated in one-dimensional and two-dimensional coupled-cavity photonic crystal structures. We require an efficient and simple approach that ensures the continuity of the electromagnetic field across dielectric interfaces in complex structures. In this thesis we develop E- and D-TBAs to calculate the modes in finite 1D and 2D two-defect coupled-cavity photonic crystal structures. In the E- and D-TBAs we expand the coupled-cavity [vector electron]-modes in terms of the individual [vector electron]- and [vector D meson]-modes, respectively. We investigate the dependence of the defect modes, their frequencies and quality factors on the relative placement of the defects in the photonic crystal structures. We then elucidate the differences between the two TBA formulations, and describe the conditions under which these formulations may be more robust when encountering a dielectric perturbation. Our 1D analysis showed that the 1D modes were sensitive to the structure geometry. The antisymmetric D mode amplitudes show that the D. TBA did not capture the correct (tangential [vector electron]-field) boundary conditions. However, the D-TBA did not yield
Polymorphism, crystal nucleation and growth in the phase-field crystal model in 2D and 3D
NASA Astrophysics Data System (ADS)
Tóth, Gyula I.; Tegze, György; Pusztai, Tamás; Tóth, Gergely; Gránásy, László
2010-09-01
We apply a simple dynamical density functional theory, the phase-field crystal (PFC) model of overdamped conservative dynamics, to address polymorphism, crystal nucleation, and crystal growth in the diffusion-controlled limit. We refine the phase diagram for 3D, and determine the line free energy in 2D and the height of the nucleation barrier in 2D and 3D for homogeneous and heterogeneous nucleation by solving the respective Euler-Lagrange (EL) equations. We demonstrate that, in the PFC model, the body-centered cubic (bcc), the face-centered cubic (fcc), and the hexagonal close-packed structures (hcp) compete, while the simple cubic structure is unstable, and that phase preference can be tuned by changing the model parameters: close to the critical point the bcc structure is stable, while far from the critical point the fcc prevails, with an hcp stability domain in between. We note that with increasing distance from the critical point the equilibrium shapes vary from the sphere to specific faceted shapes: rhombic dodecahedron (bcc), truncated octahedron (fcc), and hexagonal prism (hcp). Solving the equation of motion of the PFC model supplied with conserved noise, solidification starts with the nucleation of an amorphous precursor phase, into which the stable crystalline phase nucleates. The growth rate is found to be time dependent and anisotropic; this anisotropy depends on the driving force. We show that due to the diffusion-controlled growth mechanism, which is especially relevant for crystal aggregation in colloidal systems, dendritic growth structures evolve in large-scale isothermal single-component PFC simulations. An oscillatory effective pair potential resembling those for model glass formers has been evaluated from structural data of the amorphous phase obtained by instantaneous quenching. Finally, we present results for eutectic solidification in a binary PFC model.
NASA Astrophysics Data System (ADS)
Aquilano, Dino; Veesler, Stéphane; Astier, Jean Pierre; Pastero, Linda
2003-01-01
The relationship between crystal polymorphism and polytypism can be revealed by surface patterns through the interlacing of the growth spirals. Simple high-symmetry structures as SiC, ZnS, CdI2 and more complex low-symmetry layered structures as n-paraffins, n-alcohols and micas are concerned with polymorphic-polytypic transition. In this paper, we will show for the first time, through in situ AFM observations and X-ray diffractometry, that a protein polymorph (P2 12 12 1α-amylase) locally changes, during growth, to a monoclinic P2 1 polytype, thanks to the screw dislocation activity. The interplay between spiral steps and 2D nuclei of the polytypes coexisting in the same crystalline individual allows to foresee the consequences on the crystal quality. The discussion is extended to other mineral and biological molecules and a new general rule is proposed to explain the interactions between surface patterns and the bulk crystal structure.
Smith, Brian J; Overholts, Anna C; Hwang, Nicky; Dichtel, William R
2016-03-04
We explore the crystallization of a high surface area imine-linked two-dimensional covalent organic framework (2D COF). The growth process reveals rapid initial formation of an amorphous network that subsequently crystallizes into the layered 2D network. The metastable amorphous polymer may be isolated and resubjected to growth conditions to form the COF. These experiments provide the first mechanistic insight into the mechanism of imine-linked 2D COF formation, which is distinct from that of boronate-ester linked COFs.
Influence of lattice defects on the ferromagnetic resonance behaviour of 2D magnonic crystals
Manzin, Alessandra; Barrera, Gabriele; Celegato, Federica; Coïsson, Marco; Tiberto, Paola
2016-01-01
This paper studies, from a modelling point of view, the influence of randomly distributed lattice defects (non-patterned areas and variable hole size) on the ferromagnetic resonance behaviour and spin wave mode profiles of 2D magnonic crystals based on Ni80Fe20 antidot arrays with hexagonal lattice. A reference sample is first defined via the comparison of experimental and simulated hysteresis loops and magnetoresistive curves of patterned films, prepared by self-assembly of polystyrene nanospheres. Second, a parametric analysis of the dynamic response is performed, investigating how edge, quasi-uniform and localized modes are affected by alterations of the lattice geometry and bias field amplitude. Finally, some results about the possible use of magnetic antidot arrays in frequency-based sensors for magnetic bead detection are presented, highlighting the need for an accurate control of microstructural features. PMID:26911336
Vertically magnetic-controlled THz modulator based on 2-D magnetized plasma photonic crystal
NASA Astrophysics Data System (ADS)
Zhou, Wen; Chen, He-ming; Ji, Ke; Zhuang, Yuyang
2017-02-01
A novel magnetized plasma modulator for THz range is proposed. The structure is based on 2-D photonic crystal (PC) constructed by triangular lattice of Si rods in air with line defects and an InSb rod as a point defect. Based on the magneto-optic effect, the resonant frequency can be tuned by the external magnetic field and the radius of point defect. The transfer and disappearance of the PC-based mode can be realized by utilizing a waveguide and a plasma cavity. The simulation results show that PC-based mode disappearance modulator has the potential for THz wireless broadband communication system with a good performance of high contrast ratio (<33.61 dB), low insertion loss (<0.36 dB) and high modulation rate (∼4 GHz).
2D photonic crystals on the Archimedean lattices (tribute to Johannes Kepler (1571 1630))
NASA Astrophysics Data System (ADS)
Gajić, R.; class="cross-out">D. Jovanović,
2008-03-01
Results of our research on 2D Archemedean lattice photonic crystals are presented. This involves the calculations of the band structures, band-gap maps, equifrequency contours and FDTD simulations of electromagnetic propagation through the structures as well as an experimental verification of negative refraction at microwaves. The band-gap dependence on dielectric contrast is established both for dielectric rods in air and air-holes in dielectric materials. A special emphasis is placed on possibilities of negative refraction and left-handedness in these structures. Together with the familiar Archimedean lattices like square, triangular, honeycomb and Kagome' ones, we consider also, the less known, (3 2, 4, 3, 4) (ladybug) and (3, 4, 6, 4) (honeycomb-ring) structures.
Nonlinear Raman-Nath diffraction of femtosecond laser pulses in a 2D nonlinear photonic crystal.
Vyunishev, A M; Arkhipkin, V G; Slabko, V V; Baturin, I S; Akhmatkhanov, A R; Shur, V Ya; Chirkin, A S
2015-09-01
We study second-harmonic generation (SHG) of femtosecond laser pulses in a rectangular two-dimensional nonlinear photonic crystal (NLPC). Multiple SH beams were observed in the vicinity of the propagation direction of the fundamental beam. It has been verified that the angular positions of these beams obey the conditions of nonlinear Raman-Nath diffraction (NRND). The measured SH spectra of specific NRND orders consist of narrow peaks that experience a high-frequency spectral shift as the order grows. We derive an analytical expression for the process studied and find the theoretical results to be in good agreement with the experimental data. We estimate the enhancement factor of nonlinear Raman-Nath diffraction in 2D NLPC to be 70.
Enhanced Absorption in 2D Materials Via Fano- Resonant Photonic Crystals
Wang, Wenyi; Klotz, Andrey; Yang, Yuanmu; Li, Wei; Kravchenko, Ivan I.; Briggs, Dayrl P.; Bolotin, Kirill; Valentine, Jason
2015-05-01
The use of two-dimensional (2D) materials in optoelectronics has attracted much attention due to their fascinating optical and electrical properties. For instance, graphenebased devices have been employed for applications such as ultrafast and broadband photodetectors and modulators while transition metal dichalcogenide (TMDC) based photodetectors can be used for ultrasensitive photodetection. However, the low optical absorption of 2D materials arising from their atomic thickness limits the maximum attainable external quantum efficiency. For example, in the visible and NIR regimes monolayer MoS_{2} and graphene absorb only ~10% and 2.3% of incoming light, respectively. Here, we experimentally demonstrate the use of Fano-resonant photonic crystals to significantly boost absorption in atomically thin materials. Using graphene as a test bed, we demonstrate that absorption in the monolayer thick material can be enhanced to 77% within the telecommunications band, the highest value reported to date. We also show that the absorption in the Fano-resonant structure is non-local, with light propagating up to 16 μm within the structure. This property is particularly beneficial in harvesting light from large areas in field-effect-transistor based graphene photodetectors in which separation of photo-generated carriers only occurs ~0.2 μm adjacent to the graphene/electrode interface.
Enhanced Absorption in 2D Materials Via Fano- Resonant Photonic Crystals
Wang, Wenyi; Klotz, Andrey; Yang, Yuanmu; ...
2015-05-01
The use of two-dimensional (2D) materials in optoelectronics has attracted much attention due to their fascinating optical and electrical properties. For instance, graphenebased devices have been employed for applications such as ultrafast and broadband photodetectors and modulators while transition metal dichalcogenide (TMDC) based photodetectors can be used for ultrasensitive photodetection. However, the low optical absorption of 2D materials arising from their atomic thickness limits the maximum attainable external quantum efficiency. For example, in the visible and NIR regimes monolayer MoS2 and graphene absorb only ~10% and 2.3% of incoming light, respectively. Here, we experimentally demonstrate the use of Fano-resonant photonicmore » crystals to significantly boost absorption in atomically thin materials. Using graphene as a test bed, we demonstrate that absorption in the monolayer thick material can be enhanced to 77% within the telecommunications band, the highest value reported to date. We also show that the absorption in the Fano-resonant structure is non-local, with light propagating up to 16 μm within the structure. This property is particularly beneficial in harvesting light from large areas in field-effect-transistor based graphene photodetectors in which separation of photo-generated carriers only occurs ~0.2 μm adjacent to the graphene/electrode interface.« less
Determining ice water content from 2D crystal images in convective cloud systems
NASA Astrophysics Data System (ADS)
Leroy, Delphine; Coutris, Pierre; Fontaine, Emmanuel; Schwarzenboeck, Alfons; Strapp, J. Walter
2016-04-01
Cloud microphysical in-situ instrumentation measures bulk parameters like total water content (TWC) and/or derives particle size distributions (PSD) (utilizing optical spectrometers and optical array probes (OAP)). The goal of this work is to introduce a comprehensive methodology to compute TWC from OAP measurements, based on the dataset collected during recent HAIC (High Altitude Ice Crystals)/HIWC (High Ice Water Content) field campaigns. Indeed, the HAIC/HIWC field campaigns in Darwin (2014) and Cayenne (2015) provide a unique opportunity to explore the complex relationship between cloud particle mass and size in ice crystal environments. Numerous mesoscale convective systems (MCSs) were sampled with the French Falcon 20 research aircraft at different temperature levels from -10°C up to 50°C. The aircraft instrumentation included an IKP-2 (isokinetic probe) to get reliable measurements of TWC and the optical array probes 2D-S and PIP recording images over the entire ice crystal size range. Based on the known principle relating crystal mass and size with a power law (m=α•Dβ), Fontaine et al. (2014) performed extended 3D crystal simulations and thereby demonstrated that it is possible to estimate the value of the exponent β from OAP data, by analyzing the surface-size relationship for the 2D images as a function of time. Leroy et al. (2015) proposed an extended version of this method that produces estimates of β from the analysis of both the surface-size and perimeter-size relationships. Knowing the value of β, α then is deduced from the simultaneous IKP-2 TWC measurements for the entire HAIC/HIWC dataset. The statistical analysis of α and β values for the HAIC/HIWC dataset firstly shows that α is closely linked to β and that this link changes with temperature. From these trends, a generalized parameterization for α is proposed. Finally, the comparison with the initial IKP-2 measurements demonstrates that the method is able to predict TWC values
2D photonic crystal complete band gap search using a cyclic cellular automaton refination
NASA Astrophysics Data System (ADS)
González-García, R.; Castañón, G.; Hernández-Figueroa, H. E.
2014-11-01
We present a refination method based on a cyclic cellular automaton (CCA) that simulates a crystallization-like process, aided with a heuristic evolutionary method called differential evolution (DE) used to perform an ordered search of full photonic band gaps (FPBGs) in a 2D photonic crystal (PC). The solution is proposed as a combinatorial optimization of the elements in a binary array. These elements represent the existence or absence of a dielectric material surrounded by air, thus representing a general geometry whose search space is defined by the number of elements in such array. A block-iterative frequency-domain method was used to compute the FPBGs on a PC, when present. DE has proved to be useful in combinatorial problems and we also present an implementation feature that takes advantage of the periodic nature of PCs to enhance the convergence of this algorithm. Finally, we used this methodology to find a PC structure with a 19% bandgap-to-midgap ratio without requiring previous information of suboptimal configurations and we made a statistical study of how it is affected by disorder in the borders of the structure compared with a previous work that uses a genetic algorithm.
NASA Astrophysics Data System (ADS)
Butler, James
2016-10-01
Use of diamond as a semiconductor material suffers from the high activation energy of all known impurity dopants (0.37 eV for Boron, 0.6 eV for Phosphorous). To achieve the simultaneous carrier concentration and mobility desired for devices operating at room temperature, growth of a nanometric thick `delta' layer doped to above the metal insulator transition adjacent to high mobility intrinsic material can provide a 2D high mobility conduction layer. Critical to obtaining the enhanced mobility of the carriers in the layer next to the `delta' doped layer is the abruptness of the doping interface. Single and multiple nanometer thick epitaxial layers of heavily boron `delta' doped diamond have been grown on high quality, intrinsic lab grown diamond single crystals. These layers were grown in a custom microwave plasma activated chemical vapor deposition reactor based on a rapid reactant switching technique. Characterization of the `delta' layers by various analytical techniques will be presented. Electrical measurements demonstrating enhanced hole mobility (100 to 800 cm2/V sec) as well as other electrical characterizations will be presented.
Fabrication of an Omnidirectional 2D Photonic Crystal Emitter for Thermophotovoltaics
NASA Astrophysics Data System (ADS)
Stelmakh, V.; Chan, W. R.; Ghebrebrhan, M.; Soljacic, M.; Joannopoulos, J. D.; Celanovic, I.
2016-11-01
In a thermophotovoltaic (TPV) system, a heat source brings an emitter to incandescence and the spectrally confined thermal radiation is converted to electricity by a low-bandgap photovoltaic (PV) cell. Efficiency is dominated by the emitter's ratio of in-band emissivity (convertible by the PV cell) to out-of-band emissivity (inconvertible). Two-dimensional photonic crystals (PhCs) offer high in-band emissivity and low out-of-band emissivity at normal incidence, but have reduced in-band emissivity off-normal. According to Lambert's law, most thermal radiation occurs off-normal. An omnidirectional PhC capable of high in-band emissivity at all angles would increase total in-band power by 55% at 1200°C. In this work, we present the first experimental demonstration an omnidirectional hafnia-filled 2D tantalum PhC emitter suitable for TPV applications such as combustion, radioisotope, and solar TPV. Dielectric filling improved the hemispherical performance without sacrificing stability or ease of fabrication. The numerical simulations, fabrication processes, and optical and thermal characterizations of the PhC are presented in this paper.
Experimental Studies of Pinning Effects in 2D Colloidal Crystals Using Microstructured Substrates
NASA Astrophysics Data System (ADS)
Smullin, Sylvia; Gerritsen, H. J.; Ling, Xinsheng
1998-03-01
We use microstructured substrates as tunable quenched symmetry-breaking fields to study the pinning effects in 2D colloidal crystals. The colloids are monodisperse charged polystyrene microspheres in pure water. In the sealed sample cell, the colloids are confined by two glass slides. A patterned plastic grating is glued on one side of the confining slides. The corrugated surface of the plastic grating becomes charged in water and exerts a periodic electric field on the charged microspheres, tunable by adjusting the confinement distance. We show that, for the first time, by using video microscopy one can observe in real time the novel effects due to the competing interactions. For example, with a square grating we have observed the Novaco-McTague rotation in a floating phase and the Pokrovsky-Talapov domain wall superlattice in a pinned phase. The results from a rough plastic substrate which simulates a random potential (in an attempt to search for a colloidal Bragg glass phase) will also be discussed. This work was supported by the startup funds and a Richard Salomon Faculty Research Award from Brown.
Wigner distributions for qudits
Chaturvedi, S.
2006-11-15
Two new approaches to the problem of setting up Wigner distributions for finite level quantum systems are proposed. Both arise by looking at the structure of the familiar Wigner distribution for Cartesian quantum mechanics from different perspectives. The two approaches have one common feature--each involves a 'square root' operation though of very different kinds.
NASA Astrophysics Data System (ADS)
Taut, M.
2001-10-01
The ground state energy and the lowest excitations of a two-dimensional Wigner crystal in a perpendicular magnetic field with one and two electrons per cell is investigated. In the case of two electrons per lattice site, the interaction of the electrons within each cell is taken into account exactly (including exchange and correlation effects), and the interaction between the cells is in second order (dipole) van der Waals approximation. No further approximations are made, in particular Landau level mixing and incomplete spin polarization are accounted for. Therefore, our calculation comprises a, roughly speaking, complementary description of the bubble phase (in the special case of one and two electrons per bubble), which was proposed by Koulakov, Fogler, and Shklovskii on the basis of a Hartree Fock calculation. The phase diagram shows that in GaAs the paired phase is energetically more favorable than the single electron phase for, roughly speaking, filling factor f larger than 0.3 and density parameter rs smaller than 19 effective Bohr radii (for a more precise statement see Figs. 3 and 4). If we start within the paired phase and increase magnetic field or decrease density, the pairs first undergo some singlet-triplet transitions before they break.
A 2D Rods-in-Air Square-Lattice Photonic Crystal Optical Switch
2009-03-01
photonic crystal switches, IEEE Photon. Technol. Lett. 18 (2) (2006) 358–360. [8] Y. Kanamori , K. Inoue, K. Horie, K. Hane, Photonic crystal switch by...Waikoloa, Hawaii, USA, pp. 107–108. [9] K. Umemori, Y. Kanamori , K. Hane, A photonic crystal waveguide switch with a movable bridge slab, in: Proceedings of...Umemori, Yoshiaki Kanamori , Kazuhiro Hane, Photonic crystal waveguide switch with a microelectromechanical actuator, Appl. Phys. Lett. 89 (2) (2006
Crystal Structure of Human Cytochrome P450 2D6 with Prinomastat Bound*
Wang, An; Savas, Uzen; Hsu, Mei-Hui; Stout, C. David; Johnson, Eric F.
2012-01-01
Human cytochrome P450 2D6 contributes to the metabolism of >15% of drugs used in clinical practice. This study determined the structure of P450 2D6 complexed with a substrate and potent inhibitor, prinomastat, to 2.85 Å resolution by x-ray crystallography. Prinomastat binding is well defined by electron density maps with its pyridyl nitrogen bound to the heme iron. The structure of ligand-bound P450 2D6 differs significantly from the ligand-free structure reported for the P450 2D6 Met-374 variant (Protein Data Bank code 2F9Q). Superposition of the structures reveals significant differences for β sheet 1, helices A, F, F′, G″, G, and H as well as the helix B-C loop. The structure of the ligand complex exhibits a closed active site cavity that conforms closely to the shape of prinomastat. The closure of the open cavity seen for the 2F9Q structure reflects a change in the direction and pitch of helix F and introduction of a turn at Gly-218, which is followed by a well defined helix F′ that was not observed in the 2F9Q structure. These differences reflect considerable structural flexibility that is likely to contribute to the catalytic versatility of P450 2D6, and this new structure provides an alternative model for in silico studies of substrate interactions with P450 2D6. PMID:22308038
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.
2D and 3D crystallization of a bacterial homologue of human vitamin C membrane transport proteins.
Jeckelmann, Jean-Marc; Harder, Daniel; Ucurum, Zöhre; Fotiadis, Dimitrios
2014-10-01
Most organisms are able to synthesize vitamin C whereas humans are not. In order to contribute to the elucidation of the molecular working mechanism of vitamin C transport through biological membranes, we cloned, overexpressed, purified, functionally characterized, and 2D- and 3D-crystallized a bacterial protein (UraDp) with 29% of amino acid sequence identity to the human sodium-dependent vitamin C transporter 1 (SVCT1). Ligand-binding experiments by scintillation proximity assay revealed that uracil is a substrate preferably bound to UraDp. For structural analysis, we report on the production of tubular 2D crystals and present a first projection structure of UraDp from negatively stained tubes. On the other hand the successful growth of UraDp 3D crystals and their crystallographic analysis is described. These 3D crystals, which diffract X-rays to 4.2Å resolution, pave the way towards the high-resolution crystal structure of a bacterial homologue with high amino acid sequence identity to human SVCT1.
Astrova, E. V. Fedulova, G. V.; Guschina, E. V.
2010-12-15
Joint electrochemical etching of deep macropores and trenches in n-Si (100) has been studied. After the substrate was removed, regions of a sample, bounded on all sides by a closed contour of through trenches, were extracted from the sample, with narrow bars of a 2D photonic crystal remaining. The influence exerted by the distance between pores and a trench and by the modes of etching and subsequent oxidation on the roughness of the side walls of the structures and also on the size and shape of pores near the trench is analyzed for the example of a photonic crystal with a square lattice of macropores. Conditions are found in which the lattice distortion of the photonic crystal is at a minimum and the side walls of the structure are the smoothest (root-mean-square roughness height {approx}60 nm).
NASA Astrophysics Data System (ADS)
Lane, C. J. L.; Dunhill, A. K.; Drinkwater, B. W.; Wilcox, P. D.
2012-05-01
Modern jet-engine turbine blades are cast from single crystals of nickel-based superalloys because of the excellent mechanical properties that these materials exhibit at high temperatures. However, the anisotropic behavior of single crystals causes difficulties when using ultrasound to inspect these components for defects that could potentially initiate in-service. This paper describes the development of a 2D ultrasonic array system for the in situ inspection of these components. The problems associated with the inspection of anisotropic single crystal materials such as the directional dependence of the ultrasonic velocity, beam directivities in anisotropic media and the variation in the crystallographic orientation, are all addressed in this paper. In addition, constraints regarding access to the inspection location within the engine are discussed. Finally, the defect detection sensitivity and sizing capability of the developed system is evaluated.
NASA Astrophysics Data System (ADS)
Dyer, Gregory C.; Aizin, Gregory R.; Allen, S. James; Grine, Albert D.; Bethke, Don; Reno, John L.; Shaner, Eric A.
2014-05-01
The device applications of plasmonic systems such as graphene and two dimensional electron gases (2DEGs) in III-V heterostructures include terahertz detectors, mixers, oscillators and modulators. These two dimensional (2D) plasmonic systems are not only well-suited for device integration, but also enable the broad tunability of underdamped plasma excitations via an applied electric field. We present demonstrations of the coherent coupling of multiple voltage tuned GaAs/AlGaAs 2D plasmonic resonators under terahertz irradiation. By utilizing a plasmonic homodyne mixing mechanism to downconvert the near field of plasma waves to a DC signal, we directly detect the spectrum of coupled plasmonic micro-resonator structures at cryogenic temperatures. The 2DEG in the studied devices can be interpreted as a plasmonic waveguide where multiple gate terminals control the 2DEG kinetic inductance. When the gate tuning of the 2DEG is spatially periodic, a one-dimensional finite plasmonic crystal forms. This results in a subwavelength structure, much like a metamaterial element, that nonetheless Bragg scatters plasma waves from a repeated crystal unit cell. A 50% in situ tuning of the plasmonic crystal band edges is observed. By introducing gate-controlled defects or simply terminating the lattice, localized states arise in the plasmonic crystal. Inherent asymmetries at the finite crystal boundaries produce an induced transparency-like phenomenon due to the coupling of defect modes and crystal surface states known as Tamm states. The demonstrated active control of coupled plasmonic resonators opens previously unexplored avenues for sensitive direct and heterodyne THz detection, planar metamaterials, and slow-light devices.
TUNABLE Band Structures of 2d Multi-Atom Archimedean-Like Phononic Crystals
NASA Astrophysics Data System (ADS)
Xu, Y. L.; Chen, C. Q.; Tian, X. G.
2012-06-01
Two dimensional multi-atom Archimedean-like phononic crystals (MAPCs) can be obtained by adding "atoms" at suitable positions in primitive cells of traditional simple lattices. Band structures of solid-solid and solid-air MAPCs are computed by the finite element method in conjunction with the Bloch theory. For the solid-solid system, our results show that the MAPCs can be suitably designed to split and shift band gaps of the corresponding traditional simple phononic crystal (i.e., with only one scatterer inside a primitive cell). For the solid-air system, the MAPCs have more and wider band gaps than the corresponding traditional simple phononic crystal. Numerical calculations for both solid-solid and solid-air MAPCs show that the band gap of traditional simple phononic crystal can be tuned by appropriately adding "atoms" into its primitive cell.
Evaporative thinning: a facile synthesis method for high quality ultrathin layers of 2D crystals.
Huang, Yi-Kai; Cain, Jeffrey D; Peng, Lintao; Hao, Shiqiang; Chasapis, Thomas; Kanatzidis, Mercouri G; Wolverton, Christopher; Grayson, Matthew; Dravid, Vinayak P
2014-10-28
The palette of two-dimensional materials has expanded beyond graphene in recent years to include the chalcogenides among other systems. However, there is a considerable paucity of methods for controlled synthesis of mono- and/or few-layer two-dimensional materials with desirable quality, reproducibility, and generality. Here we show a facile top-down synthesis approach for ultrathin layers of 2D materials down to monolayer. Our method is based on controlled evaporative thinning of initially large sheets, as deposited by vapor mass-transport. Rather than optimizing conditions for monolayer deposition, our approach makes use of selective evaporation of thick sheets to control the eventual thickness, down to a monolayer, a process which appears to be self-stopping. As a result, 2D sheets with high yield, high reproducibility, and excellent quality can be generated with large (>10 μm) and thin (∼ 1-2 nm) dimensions. Evaporative thinning promises to greatly reduce the difficulty involved in isolating large, mono- and few-layers of 2D materials for subsequent studies.
NASA Astrophysics Data System (ADS)
Marx, George
2002-04-01
Eugene P. Wigner was born into a well-to-do family in Budapest 100 years ago. .He attended the Fasori Lutheran Gymnasium, which educated - among others - John von Neumann, and John Harsanyi,Nobel-laureate in economics. Wigner was influenced by his math teacher, László Rátz who taught calculus in high school. World War I, revolutions and counter/revolutions, kingdom, republic, soviet type council republic followed each other in dizzying sequence, so Wigner decided to continue his university studies in Berlin, where quantum mechanics was discussed and developed in the 1920s. After his Ph.D. Wigner worked in Budapest and in Berlin, and he elaborated the foundations of quantum mechanics based on symmetry principles. He wrote his book on symmetries during a summer holiday in Hungary, and this later brought him the Nobel Prize. Wigner moved to the U.S. in 1930, where he enjoyed the excellent working conditions and recognition. He revisited his homeland only in the 1970s, where his ideas about the future attracted huge audiences at the Academy of Sciences, at universities, and in the Physical Society. He received high honors from his home country - a bit belatedly. The principal focus of his attention was the quantum-mechanical concept of measurement, the role of human consciousness. But even in his last years, in the 1980s, he most enjoyed his visits to high schools - attending physics classes, discussing the future of science in human society with teachers and students.
NASA Astrophysics Data System (ADS)
Lenne, P. F.; Berge, B.; Renault, A.; Vénien-Bryan, C.; Courty, S.; Konovalov, O.; Legrand, J. F.; Brisson, A.; Balavoine, F.; Lal, J.; Gruebel, G.
1998-03-01
We present high resolution X-ray grazing incidence diffraction experiments and macroscopic lateral rigidity measurements performed on two-dimensional crystals of proteins bound to lipid monolayers at the water surface. For four different protein systems, Streptavidin bound to biotinylated lipids, an hystidin-tagged transcription factor HupR bound to Nickel lipids, Annexin-V bound to PS and Cholera toxin subunit-B bound to GM1 lipids, we record a non-zero shear elastic constant. For the three first systems, we observe narrow diffraction peaks and measure the Bragg rods intensities. In the case of Streptavidin we found two different possible structures, one of them exhibiting 19 Bragg rods, diffracting at about 10Åin the plane. After injecting glutaraldehyde (a protein linker) under the already formed 2D-crystals, the shear rigidity increases by a factor of two and additional diffraction peaks appear. This illustrates the correlation between the macroscopic shear elastic constant and the maximum in-plane wave vector transfer of the diffraction pattern, as expected in two dimensions. It also shows the interest of keeping the 2D-crystal in the water for subsequent action of various agents.
NASA Astrophysics Data System (ADS)
Yu, Geliang; Yang, Cao; Khestanova, Ekaterina; Mishchenko, Artem; Kretinin, Andy; Gorbachev, Roman; Novoselov, Konstantin; Andre, Geim; Manchester Group Team
Many layered materials can be cleaved down to individual atomic planes, similar to graphene, but only a small minority of them are stable under ambient conditions. The rest reacts and decomposes in air, which has severely hindered their investigation and possible uses. Here we introduce a remedial approach based on cleavage, transfer, alignment and encapsulation of airsensitive crystals, all inside a controlled inert atmosphere. To illustrate the technology, we choose two archetypal two-dimensional crystals unstable in air: black phosphorus and niobium diselenide. Our field-effect devices made from their monolayers are conductive and fully stable under ambient conditions, in contrast to the counterparts processed in air. NbSe2 remains superconducting down to the monolayer thickness. Starting with a trilayer, phosphorene devices reach sufficiently high mobilities to exhibit Landau quantization. The approach offers a venue to significantly expand the range of experimentally accessible two-dimensional crystals and their heterostructures.
Fano Resonance in GaAs 2D Photonic Crystal Nanocavities
Valentim, P. T.; Guimaraes, P.S. S.; Luxmoore, I. J.; Szymanski, D.; Whittaker, D. M.; Fox, A. M.; Skolnick, M. S.; Vasco, J. P.; Vinck-Posada, H.
2011-12-23
We report the results of polarization resolved reflectivity experiments in GaAs air-bridge photonic crystals with L3 cavities. We show that the fundamental L3 cavity mode changes, in a controlled way, from a Lorentzian symmetrical lineshape to an asymmetrical form when the linear polarization of the incident light is rotated in the plane of the crystal. The different lineshapes are well fitted by the Fano asymmetric equation, implying that a Fano resonance is present in the reflectivity. We use the scattering matrix method to model the Fano interference between a localized discrete state (the cavity fundamental mode) and a background of continuum states (the light reflected from the crystal slab in the vicinity of the cavity) with very good agreement with the experimental data.
All-optical XNOR gate based on 2D photonic-crystal ring resonators
NASA Astrophysics Data System (ADS)
Moniem, Tamer A.
2017-02-01
A novel all-optical XNOR gate is proposed, which combines the nonlinear Kerr effect with photonic-crystal ring resonators (PCRRs). The total size of the proposed optical XNOR gate based on photonic crystals with a square lattice of silicon rods is equal to 35 × 21 μm. The proposed structure has a bandgap in the range from 0.32 to 0.44. To confirm the operation and feasibility of the overall system use is made of analytical and numerical simulation using the dimensional finite difference time domain (FDTD) and plane wave expansion (PWE) methods.
Optical properties of GaAs 2D hexagonal and cubic photonic crystal
Arab, F. Assali, A.; Grain, R.; Kanouni, F.
2015-03-30
In this paper we present our theoretical study of 2D hexagonal and cubic rods GaAs in air, with plan wave expansion (PWE) and finite difference time domain (FDTD) by using BandSOLVE and FullWAVE of Rsoft photonic CAD package. In order to investigate the effect of symmetry and radius, we performed calculations of the band structures for both TM and TE polarization, contour and electromagnetic propagation and transmission spectra. Our calculations show that the hexagonal structure gives a largest band gaps compare to cubic one for a same filling factor.
AFM-Patterned 2-D Thin-Film Photonic Crystal Analyzed by Complete Angle Scatter
2010-03-01
Scatter Distribution Function of Photonic Crystals,” Air Force Institute of Technology, Dayton, OH, Thesis 2009. [5] I. Prieto , B. Galiana, P. A... Francisco : Addison Wesley, 2002. 76 [38] Bahaa E. A. Saleh and Malvin Carl Teich, Fundamentals of Photonics, 2nd ed. Hoboken: Wiley, 2007. [39
Terahertz all-optical NOR and AND logic gates based on 2D photonic crystals
NASA Astrophysics Data System (ADS)
Parandin, Fariborz; Karkhanehchi, Mohammad Mehdi
2017-01-01
Usually, photonic crystals are used in designing optical logic gates. This study focuses on the design and simulation of an all optical NOR and AND logic gates based on two dimensional photonic crystals. The simplicity of the proposed structure is a characteristic feature of this designation. Finite Difference Time Domain (FDTD) as well as Plane Wave Expansion (PWE) methods have been used for this structural analysis. The simulation results revealed an increase in the interval between "zero" and "one" logic levels. Also, the simple structure and its small size demonstrate the usefulness of this structure in optical integrated circuits. The proposed optical gates can operate with a bit rate of about 1.54 Tbit/s.
NASA Astrophysics Data System (ADS)
Moukhtari, R.; Hocini, A.; Khedrouche, D.
2016-01-01
In this present paper, quality factor of two-dimensional magneto-photonic crystals microcavity fabricated by SiO2/ZrO2 or SiO2/TiO2 matrix doped with magnetic nanoparticles, in which the refractive index varied in the range of 1.51 to 1.58, has been investigated. Finite difference time domain method (3D FDTD) with perfectly matched layers (PML) was used to calculate the transmission spectrum. We demonstrate that the Q factor for the designed cavity increases as the refractive index increases, and found that the Q factor decreases as the volume fraction VF% increases. The obtained results are useful for better designs of magneto photonic crystal devices.
Guryev, I. V. Sukhoivanov, I. A. Andrade Lucio, J. A. Manzano, O. Ibarra Rodriguez, E. Vargaz Gonzales, D. Claudio Chavez, R. I. Mata Gurieva, N. S.
2014-05-15
In our work, we investigated the wideband optical filter on the basis of nonlinear photonic crystal. The all-optical flip-flop using ultra-short pulses with duration lower than 200 fs is obtained in such filters. Here we pay special attention to the stability problem of the nonlinear element. To investigate this problem, the temporal response demonstrating the flip-flop have been computed within the certain range of the wavelengths as well as at different input power.
NASA Astrophysics Data System (ADS)
Dupont, S.; Gazalet, J.; Kastelik, J. C.
2014-03-01
Phononic crystal is a structured media with periodic modulation of its physical properties that influences the propagation of elastic waves and leads to a peculiar behaviour, for instance the phononic band gap effect by which elastic waves cannot propagate in certain frequency ranges. The formulation of the problem leads to a second order partial differential equation with periodic coefficients; different methods exist to determine the structure of the eigenmodes propagating in the material, both in the real or Fourier domain. Brillouin explains the periodicity of the band structure as a direct result of the discretization of the crystal in the real domain. Extending the Brillouin vision, we introduce digital signal processing tools developed in the frame of distribution functions theory. These tools associate physical meaning to mathematical expressions and reveal the correspondence between real and Fourier domains whatever is the physical domain under consideration. We present an illustrative practical example concerning two dimensions phononic crystals and highlight the appreciable shortcuts brought by the method and the benefits for physical interpretation.
Collins, Gillian; Armstrong, Eileen; McNulty, David; O'Hanlon, Sally; Geaney, Hugh; O'Dwyer, Colm
2016-01-01
This perspective reviews recent advances in inverse opal structures, how they have been developed, studied and applied as catalysts, catalyst support materials, as electrode materials for batteries, water splitting applications, solar-to-fuel conversion and electrochromics, and finally as photonic photocatalysts and photoelectrocatalysts. Throughout, we detail some of the salient optical characteristics that underpin recent results and form the basis for light-matter interactions that span electrochemical energy conversion systems as well as photocatalytic systems. Strategies for using 2D as well as 3D structures, ordered macroporous materials such as inverse opals are summarized and recent work on plasmonic-photonic coupling in metal nanoparticle-infiltrated wide band gap inverse opals for enhanced photoelectrochemistry are provided.
Collins, Gillian; Armstrong, Eileen; McNulty, David; O’Hanlon, Sally; Geaney, Hugh; O’Dwyer, Colm
2016-01-01
Abstract This perspective reviews recent advances in inverse opal structures, how they have been developed, studied and applied as catalysts, catalyst support materials, as electrode materials for batteries, water splitting applications, solar-to-fuel conversion and electrochromics, and finally as photonic photocatalysts and photoelectrocatalysts. Throughout, we detail some of the salient optical characteristics that underpin recent results and form the basis for light-matter interactions that span electrochemical energy conversion systems as well as photocatalytic systems. Strategies for using 2D as well as 3D structures, ordered macroporous materials such as inverse opals are summarized and recent work on plasmonic–photonic coupling in metal nanoparticle-infiltrated wide band gap inverse opals for enhanced photoelectrochemistry are provided. PMID:27877904
Yuan, Sheng; Linas, Sébastien; Journet, Catherine; Steyer, Philippe; Garnier, Vincent; Bonnefont, Guillaume; Brioude, Arnaud; Toury, Bérangère
2016-01-01
Within the context of emergent researches linked to graphene, it is well known that h-BN nanosheets (BNNSs), also referred as 2D BN, are considered as the best candidate for replacing SiO2 as dielectric support or capping layers for graphene. As a consequence, the development of a novel alternative source for highly crystallized h-BN crystals, suitable for a further exfoliation, is a prime scientific issue. This paper proposes a promising approach to synthesize pure and well-crystallized h-BN flakes, which can be easily exfoliated into BNNSs. This new accessible production process represents a relevant alternative source of supply in response to the increasing need of high quality BNNSs. The synthesis strategy to prepare pure h-BN is based on a unique combination of the Polymer Derived Ceramics (PDCs) route with the Spark Plasma Sintering (SPS) process. Through a multi-scale chemical and structural investigation, it is clearly shown that obtained flakes are large (up to 30 μm), defect-free and well crystallized, which are key-characteristics for a subsequent exfoliation into relevant BNNSs. PMID:26843122
NASA Astrophysics Data System (ADS)
Yuan, Sheng; Linas, Sébastien; Journet, Catherine; Steyer, Philippe; Garnier, Vincent; Bonnefont, Guillaume; Brioude, Arnaud; Toury, Bérangère
2016-02-01
Within the context of emergent researches linked to graphene, it is well known that h-BN nanosheets (BNNSs), also referred as 2D BN, are considered as the best candidate for replacing SiO2 as dielectric support or capping layers for graphene. As a consequence, the development of a novel alternative source for highly crystallized h-BN crystals, suitable for a further exfoliation, is a prime scientific issue. This paper proposes a promising approach to synthesize pure and well-crystallized h-BN flakes, which can be easily exfoliated into BNNSs. This new accessible production process represents a relevant alternative source of supply in response to the increasing need of high quality BNNSs. The synthesis strategy to prepare pure h-BN is based on a unique combination of the Polymer Derived Ceramics (PDCs) route with the Spark Plasma Sintering (SPS) process. Through a multi-scale chemical and structural investigation, it is clearly shown that obtained flakes are large (up to 30 μm), defect-free and well crystallized, which are key-characteristics for a subsequent exfoliation into relevant BNNSs.
Analytic theory for the selection of 2-D needle crystal at arbitrary Peclet number
NASA Technical Reports Server (NTRS)
Tanveer, Saleh
1989-01-01
An accurate analytic theory is presented for the velocity selection of a two-dimensional needle crystal for arbitrary Peclet number for small values of the surface tension parameter. The velocity selection is caused by the effect of transcendentally small terms which are determined by analytic continuation to the complex plane and analysis of nonlinear equations. The work supports the general conclusion of previous small Peclet number analytical results of other investigators, though there are some discrepancies in details. It also addresses questions raised on the validity of selection theory owing to assumptions made on shape corrections at large distances from the tip.
A global 2D well-posedness result on the order tensor liquid crystal theory
NASA Astrophysics Data System (ADS)
De Anna, Francesco
2017-04-01
In [18] Paicu and Zarnescu have studied an order tensor system which describes the flow of a liquid crystal. They have proven the existence of weak solutions, the propagation of higher regularity, namely Hs with s > 1 and the weak-strong uniqueness in dimension two. This paper is devoted to fill the gap of their results, namely to propagate the low regularity, namely Hs for 0 < s < 1 and to prove the uniqueness of the weak solutions. For the completeness of this research, we also propose an alternative approach in order to prove the existence of weak solutions.
Tuning the Structural Color of a 2D Photonic Crystal Using a Bowl-like Nanostructure.
Umh, Ha Nee; Yu, Sungju; Kim, Yong Hwa; Lee, Su Young; Yi, Jongheop
2016-06-22
Structural colors of the ordered photonic nanostructures are widely used as an effective platform for manipulating the propagation of light. Although several approaches have been explored in attempts to mimic the structural colors, improving the reproducibility, mechanical stability, and the economic feasibility of sophisticated photonic crystals prepared by complicated processes continues to pose a challenge. In this study, we report on an alternative, simple method for fabricating a tunable photonic crystal at room temperature. A bowl-like nanostructure of TiO2 was periodically arranged on a thin Ti sheet through a two-step anodization process where its diameters were systemically controlled by changing the applied voltage. Consequently, they displayed a broad color distribution, ranging from red to indigo, and the principal reason for color generation followed the Bragg diffraction theory. This noncolorant method was capable of reproducing a Mondrian painting on a centimeter scale without the need to employ complex architectures, where the generated structural colors were highly stable under mechanical or chemical influence. Such a color printing technique represents a potentially promising platform for practical applications for anticounterfeit trademarks, wearable sensors, and displays.
A non-enzymatic urine glucose sensor with 2-D photonic crystal hydrogel.
Yan, Zequn; Xue, Min; He, Qian; Lu, Wei; Meng, Zihui; Yan, Dan; Qiu, Lili; Zhou, Lijun; Yu, Yingjie
2016-11-01
A novel polymerized crystalline colloidal array (PCCA) sensing material for the detection of urine glucose was developed by embedding a two-dimensional (2-D) polystyrene crystalline colloidal array (CCA) in 3-acrylamidophenylboronic acid (3-APBA)-functionalized hydrogel. After adjusting the cross-linker concentration, this material showed significant sensitivity for glucose under lab conditions, the particle spacing of the PCCA changed from 917 to 824 nm (93 nm) within 3 min as the glucose concentration increased from 0 to 10 mM, and the structural color of the PCCA changed from red through orange, to green, and finally, to cyan. In further experiments, this material was used to semi-quantitatively detect glucose in 20 human urine (HU) samples. Compared with the traditional dry-chemistry method, which was applied widely in clinical diagnosis, the PCCA method was more accurate and cost-effective. Moreover, this method can efficiently avoid the errors induced by most of the urine-interfering elements like vitamin C and ketone body. With a homemade portable optical detector, this low-cost intelligent sensing material can provide a more convenient and efficient strategy for the urine glucose detection in clinical diagnosis and point-of-care monitoring.
Self-Assembly under Confinement: Nanocorrals for Understanding Fundamentals of 2D Crystallization.
Verstraete, Lander; Greenwood, John; Hirsch, Brandon E; De Feyter, Steven
2016-12-27
Nanocorrals with different size, shape, and orientation are created on covalently modified highly oriented pyrolytic graphite surfaces using scanning probe nanolithography, i.e., nanoshaving. Alkylated diacetylene molecules undergo laterally confined supramolecular self-assembly within these corrals. When nanoshaving is performed in situ, at the liquid-solid interface, the orientation of the supramolecular lamellae structure is directionally influenced by the gradual graphite surface exposure. Careful choice of the nanoshaving direction with respect to the substrate symmetry axes promotes alignment of the supramolecular lamellae within the corral. Self-assembly occurring inside corrals of different size and shape reveals the importance of geometric and kinetic constraints controlled by the nanoshaving process. Finally, seed-mediated crystallization studies demonstrate confinement control over nucleation and growth principles.
Efficient Design Tool for 2D and 3D NIMS Photonic Crystals
2008-01-28
and Le‐Wei Li, “Analysis of Probe‐fed Conformal Microstrip Antennas on Finite Ground Plane and Substrate”, IEEE Transactions on Antennas and...approach will be very flexible in handling many different types of photonic crystals of various geometrical structures. Most importantly, the...Because of many different choices of the basis functions for the volume cells, the approach will be very flexible in handling many different types of
New optimization problems arising in modelling of 2D-crystal lattices
NASA Astrophysics Data System (ADS)
Evtushenko, Yury; Lurie, Sergey; Posypkin, Mikhail
2016-10-01
The paper considers the problem of finding the structure of a fragment of two-dimensional crystal lattice with the minimal energy. Atoms in a lattice reside on parallel lines (layers). The interatomic distances are the same within one layer but can differ for distinct layers. The energy of the piece of material is computed using so-called potential functions. We used Lennard-Jones, Morse and Tersoff potentials. The proposed formulation can serve as a scalable complex non-smooth optimization test. The paper evaluates various optimization techniques for the problem under consideration, compares their performances and draws the conclusion about the best choice of optimization methods for the problem under test. As a result we were able to locate minima meaningful from the physical point of view, e.g. reproducing graphene lattice.
Self-Assembly under Confinement: Nanocorrals for Understanding Fundamentals of 2D Crystallization
2016-01-01
Nanocorrals with different size, shape, and orientation are created on covalently modified highly oriented pyrolytic graphite surfaces using scanning probe nanolithography, i.e., nanoshaving. Alkylated diacetylene molecules undergo laterally confined supramolecular self-assembly within these corrals. When nanoshaving is performed in situ, at the liquid–solid interface, the orientation of the supramolecular lamellae structure is directionally influenced by the gradual graphite surface exposure. Careful choice of the nanoshaving direction with respect to the substrate symmetry axes promotes alignment of the supramolecular lamellae within the corral. Self-assembly occurring inside corrals of different size and shape reveals the importance of geometric and kinetic constraints controlled by the nanoshaving process. Finally, seed-mediated crystallization studies demonstrate confinement control over nucleation and growth principles. PMID:27749033
NASA Astrophysics Data System (ADS)
Guan, Zhen; Heinonen, Vili; Lowengrub, John; Wang, Cheng; Wise, Steven M.
2016-09-01
In this paper we construct an energy stable finite difference scheme for the amplitude expansion equations for the two-dimensional phase field crystal (PFC) model. The equations are formulated in a periodic hexagonal domain with respect to the reciprocal lattice vectors to achieve a provably unconditionally energy stable and solvable scheme. To our knowledge, this is the first such energy stable scheme for the PFC amplitude equations. The convexity of each part in the amplitude equations is analyzed, in both the semi-discrete and fully-discrete cases. Energy stability is based on a careful convexity analysis for the energy (in both the spatially continuous and discrete cases). As a result, unique solvability and unconditional energy stability are available for the resulting scheme. Moreover, we show that the scheme is point-wise stable for any time and space step sizes. An efficient multigrid solver is devised to solve the scheme, and a few numerical experiments are presented, including grain rotation and shrinkage and grain growth studies, as examples of the strength and robustness of the proposed scheme and solver.
A super narrow band filter based on silicon 2D photonic crystal resonator and reflectors
NASA Astrophysics Data System (ADS)
Wang, Yuanyuan; Chen, Deyuan; Zhang, Gang; Wang, Juebin; Tao, Shangbin
2016-03-01
In this paper, a novel structure of super narrow band filter based on two-dimensional square lattice photonic crystals of silicon rods in air for 1.5 um communication is proposed and studied. COMSOL Multiphysics4.3b software is used to simulate the optical behavior of the filter. The filter consists of one point-defect-based resonator and two line-defect-based reflectors. The resonance frequency, transmission coefficient and quality factor are investigated by varying the parameters of the structure. In design, a silicon rod is removed to form the resonator; for the rows of rods above and below the resonator, a part of the rods are removed to form the reflectors. By optimizing the parameters of the filter, the quality factor and transmission coefficient of the filter at the resonance frequency of 2e14 Hz can reach 1330 and 0.953, respectively. The super narrow band filter can be integrated into optical circuit for its micron size. Also, it can be used for wavelength selection and noise filtering of optical amplifier in future communication application.
NASA Astrophysics Data System (ADS)
Drazek, L.; Legrand, J.-F.; Davoust, L.
2005-02-01
An alternative technique to grow a 2-D crystal of protein at a functionalized air/water interface is proposed. The first part of this paper briefly reviews 2-D crystal growth at a fluid interface and deals with our first experiments on streptavidin whose 2-D (poly)crystallization ability is well known. In the experiments, the involved air/water interface is functionalized with a mixed lipidic monolayer made of DOPC and biotinylated lipids. The second part of the paper relates to an alternative strategy we propose in order to enhance the 2-D single-crystal growth of a protein at a liquid interface. The idea is to get benefit from an axisymmetric swirling flow driven in a water sub-phase confined within an annular channel. The swirl is expected to control the distribution of the proteins at the air/water interface and to promote the growth of a 2-D single crystal from the smallest to the largest radii (radial segregation). An analytical modelling based on a low Reynolds number asymptotic development demonstrates how two control parameters, the mean channel curvature and the Reynolds number of the shear flow, can be helpful in tuning the magnitude of the swirl and therefore the crystal growth.
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.
Galián, Carmen; Manon, Florence; Dezi, Manuela; Torres, Cristina; Ebel, Christine; Lévy, Daniel; Jault, Jean-Michel
2011-01-01
Optimized protocols for achieving high-yield expression, purification and reconstitution of membrane proteins are required to study their structure and function. We previously reported high-level expression in Escherichia coli of active BmrC and BmrD proteins from Bacillus subtilis, previously named YheI and YheH. These proteins are half-transporters which belong to the ABC (ATP-Binding Cassette) superfamily and associate in vivo to form a functional transporter able to efflux drugs. In this report, high-yield purification and functional reconstitution were achieved for the heterodimer BmrC/BmrD. In contrast to other detergents more efficient for solubilizing the transporter, dodecyl-ß-D-maltoside (DDM) maintained it in a drug-sensitive and vanadate-sensitive ATPase-competent state after purification by affinity chromatography. High amounts of pure proteins were obtained which were shown either by analytical ultracentrifugation or gel filtration to form a monodisperse heterodimer in solution, which was notably stable for more than one month at 4°C. Functional reconstitution using different lipid compositions induced an 8-fold increase of the ATPase activity (kcat∼5 s−1). We further validated that the quality of the purified BmrC/BmrD heterodimer is suitable for structural analyses, as its reconstitution at high protein densities led to the formation of 2-D crystals. Electron microscopy of negatively stained crystals allowed the calculation of a projection map at 20 Å resolution revealing that BmrC/BmrD might assemble into oligomers in a lipidic environment. PMID:21602923
Kim, Donghyuk; Han, Ji Yeon; Jeon, Duk Young
2012-02-01
Zn2SiO4:Mn2+ thin film phosphors (TFPs) have been synthesized by RF magnetron sputtering, using a single multicomponent stoichiometric target. And 2D photonic crystal patterns were introduced on a quartz substrate to enhance the light extraction efficiency. In order to introduce 2D photonic crystal patterns on a quartz substrate, nanosphere lithography was used. Polystyrene spheres, with diameter of 330 nm, were transferred on the quartz substrate and subsequently were served as an etch mask. Quartz substrates were patterned by CF4 gas-based reactive ion etching. Zn2SiO4:Mn2+ were deposited on that 2D photonic crystal patterned quartz substrate and the effect of height of photonic crystal layers were investigated. The light extraction efficiency of Zn2SiO4:Mn2+ thin film phosphors deposited on the photonic crystal patterned quartz substrate was enhanced three times to compared with that of flat Zn2SiO4:Mn2+ thin film phosphors due to the Bragg diffraction and leaky mode caused by PCLs. Transmittance of Zn2SiO4:Mn2+ TFPs deposited on the photonic crystal patterned substrate was high enough, above 70% in the visible light region with respect to that of quartz substrate.
Crystal and electronic characterization of Nd{sub x}Ti{sub 1−x}BO{sub 2+d} semiconductors
Ozkendir, Osman Murat
2016-02-15
Highlights: • Crystal and electronic structure properties of Nd{sub x}Ti{sub 1−x}BO{sub 2+d} structure were investigated. • New crystal structures for Nd–Ti complexes are determined. • Distortions in the crystal structure were observed as a result of Boron shortage. • Prominent change in electronic properties of the samples with the increasing Nd amount. - Abstract: Neodymium substituted TiBO{sub 3} samples were investigated according to their crystal, electric and electronic properties. Studies were conducted by X-ray absorption fine structure spectroscopy (XAFS) technique for the samples with different substitutions in the preparation processes. To achieve better crystal structure results during the study, XRD pattern results were supported by extended-XAFS (EXAFS) analysis. The electronic structure analysis were studied by X-ray absorption near-edge structure spectroscopy (XANES) measurements at the room temperatures. Due to the substituted Nd atoms, prominent changes in crystal structure, new crystal geometries for Nd-Ti complexes, phase transitions in the crystals structure were detected according to the increasing Nd substitutions in the samples. In the entire stages of the substitutions, Nd atoms were observed as governing the whole phenomena due to their dominant characteristics in Ti geometries. Besides, electrical resistivity decay was determined in the materials with the increasing amount of Nd substitution.
NASA Astrophysics Data System (ADS)
Maltar-Strmečki, Nadica; Rakvin, Boris
2012-09-01
The second stable radical, NH3+C(CH3)COO, R2, in the γ-irradiated single crystal of L-alanine and its fully 15N-enriched analogue were studied by an advanced pulsed EPR technique, 2D-HYSCORE (two-dimensional hyperfine sublevel correlation) spectroscopy at 200 K. The nitrogen hyperfine coupling tensor of the R2 radical was determined from the HYSCORE data and provides new experimental data for improved characterization of the R2 radical in the crystal lattice. The results obtained complement the experimental proton data available for the R2 radical and could lead to increased accuracy and reliability of EPR spectrum simulations.
Endo, Tatsuro; Kajita, Hiroshi; Kawaguchi, Yukio; Kosaka, Terumasa; Himi, Toshiyuki
2016-06-01
The development of high-sensitive, and cost-effective novel biosensors have been strongly desired for future medical diagnostics. To develop novel biosensor, the authors focused on the specific optical characteristics of photonic crystal. In this study, a label-free optical biosensor, polymer-based two-dimensional photonic crystal (2D-PhC) film fabricated using nanoimprint lithography (NIL), was developed for detection of C-reactive protein (CRP) in human serum. The nano-hole array constructed NIL-based 2D-PhC (hole diameter: 230 nm, distance: 230, depth: 200 nm) was fabricated on a cyclo-olefin polymer (COP) film (100 µm) using thermal NIL and required surface modifications to reduce nonspecific adsorption of target proteins. Antigen-antibody reactions on the NIL-based 2D-PhC caused changes to the surrounding refractive index, which was monitored as reflection spectrum changes in the visible region. By using surface modified 2D-PhC, the calculated detection limit for CRP was 12.24 pg/mL at an extremely short reaction time (5 min) without the need for additional labeling procedures and secondary antibody. Furthermore, using the dual-functional random copolymer, CRP could be detected in a pooled blood serum diluted 100× with dramatic reduction of nonspecific adsorption. From these results, the NIL-based 2D-PhC film has great potential for development of an on-site, high-sensitivity, cost-effective, label-free biosensor for medical diagnostics applications.
Numerical investigation of the flat band Bloch modes in a 2D photonic crystal with Dirac cones.
Zhang, Peng; Fietz, Chris; Tassin, Philippe; Koschny, Thomas; Soukoulis, Costas M
2015-04-20
A numerical method combining complex-k band calculations and absorbing boundary conditions for Bloch waves is presented. We use this method to study photonic crystals with Dirac cones. We demonstrate that the photonic crystal behaves as a zero-index medium when excited at normal incidence, but that the zero-index behavior is lost at oblique incidence due to excitation of modes on the flat band. We also investigate the formation of monomodal and multimodal cavity resonances inside the photonic crystals, and the physical origins of their different line-shape features.
Dang, Dong-Bin; Li, Meng-Meng; Bai, Yan; Zhou, Rui-Min
2013-02-15
Two new two-dimensional coordination polymers [Cd(3)L(2)(SCN)(6)](n) (1) and [CdLI(2)](n) (2) have been synthesized and characterized by IR spectroscopy, elemental analysis, TG technique, XRPD and complete single crystal structure analysis, where L is 4-(pyridine-2-yl)methyleneamino-1,2,4-trizaole. Asymmetrical Schiff-base ligand L with five- and six-membered N-containing heterocyclic rings acts as a tridentate bridging ligand to bind two Cd(II) centers through one terminal N(triazolyl) and one pyridylimine chelate unit in 1 and 2. For polymer 1, tridentate bridging ligands link Cd-(1,3-μ-SCN(-)) 1D inorganic chains to form a 2D layer network. The existence of C-H···π and π-π stacking interactions between 2D hybrid layers further gives rise to a 3D supramolecular network. In comparison with 1, polymer 2 shows a 2D layer network containing hexanuclear macrometallacyclic units. The 2D layers are staggered together through the combination of C-H···π and π-π stacking interactions and forming a 3D supramolecular structure. The luminescent properties of the polymers 1 and 2 were investigated in the solid state at room temperature.
NASA Technical Reports Server (NTRS)
Zeng, X. C.; Stroud, D.
1989-01-01
The previously developed Ginzburg-Landau theory for calculating the crystal-melt interfacial tension of bcc elements to treat the classical one-component plasma (OCP), the charged fermion system, and the Bose crystal. For the OCP, a direct application of the theory of Shih et al. (1987) yields for the surface tension 0.0012(Z-squared e-squared/a-cubed), where Ze is the ionic charge and a is the radius of the ionic sphere. Bose crystal-melt interface is treated by a quantum extension of the classical density-functional theory, using the Feynman formalism to estimate the relevant correlation functions. The theory is applied to the metastable He-4 solid-superfluid interface at T = 0, with a resulting surface tension of 0.085 erg/sq cm, in reasonable agreement with the value extrapolated from the measured surface tension of the bcc solid in the range 1.46-1.76 K. These results suggest that the density-functional approach is a satisfactory mean-field theory for estimating the equilibrium properties of liquid-solid interfaces, given knowledge of the uniform phases.
Bonaccorso, Francesco; Colombo, Luigi; Yu, Guihua; Stoller, Meryl; Tozzini, Valentina; Ferrari, Andrea C; Ruoff, Rodney S; Pellegrini, Vittorio
2015-01-02
Graphene and related two-dimensional crystals and hybrid systems showcase several key properties that can address emerging energy needs, in particular for the ever growing market of portable and wearable energy conversion and storage devices. Graphene's flexibility, large surface area, and chemical stability, combined with its excellent electrical and thermal conductivity, make it promising as a catalyst in fuel and dye-sensitized solar cells. Chemically functionalized graphene can also improve storage and diffusion of ionic species and electric charge in batteries and supercapacitors. Two-dimensional crystals provide optoelectronic and photocatalytic properties complementing those of graphene, enabling the realization of ultrathin-film photovoltaic devices or systems for hydrogen production. Here, we review the use of graphene and related materials for energy conversion and storage, outlining the roadmap for future applications.
NASA Astrophysics Data System (ADS)
Cavaterra, Cecilia; Rocca, Elisabetta; Wu, Hao
2017-02-01
In this paper, we investigate an optimal boundary control problem for a two dimensional simplified Ericksen-Leslie system modelling the incompressible nematic liquid crystal flows. The hydrodynamic system consists of the Navier-Stokes equations for the fluid velocity coupled with a convective Ginzburg-Landau type equation for the averaged molecular orientation. The fluid velocity is assumed to satisfy a no-slip boundary condition, while the molecular orientation is subject to a time-dependent Dirichlet boundary condition that corresponds to the strong anchoring condition for liquid crystals. We first establish the existence of optimal boundary controls. Then we show that the control-to-state operator is Fréchet differentiable between appropriate Banach spaces and derive first-order necessary optimality conditions in terms of a variational inequality involving the adjoint state variables.
Quasi 2D electronic states with high spin-polarization in centrosymmetric MoS2 bulk crystals
NASA Astrophysics Data System (ADS)
Gehlmann, Mathias; Aguilera, Irene; Bihlmayer, Gustav; Młyńczak, Ewa; Eschbach, Markus; Döring, Sven; Gospodarič, Pika; Cramm, Stefan; Kardynał, Beata; Plucinski, Lukasz; Blügel, Stefan; Schneider, Claus M.
2016-06-01
Time reversal dictates that nonmagnetic, centrosymmetric crystals cannot be spin-polarized as a whole. However, it has been recently shown that the electronic structure in these crystals can in fact show regions of high spin-polarization, as long as it is probed locally in real and in reciprocal space. In this article we present the first observation of this type of compensated polarization in MoS2 bulk crystals. Using spin- and angle-resolved photoemission spectroscopy (ARPES), we directly observed a spin-polarization of more than 65% for distinct valleys in the electronic band structure. By additionally evaluating the probing depth of our method, we find that these valence band states at the point in the Brillouin zone are close to fully polarized for the individual atomic trilayers of MoS2, which is confirmed by our density functional theory calculations. Furthermore, we show that this spin-layer locking leads to the observation of highly spin-polarized bands in ARPES since these states are almost completely confined within two dimensions. Our findings prove that these highly desired properties of MoS2 can be accessed without thinning it down to the monolayer limit.
Quasi 2D electronic states with high spin-polarization in centrosymmetric MoS2 bulk crystals.
Gehlmann, Mathias; Aguilera, Irene; Bihlmayer, Gustav; Młyńczak, Ewa; Eschbach, Markus; Döring, Sven; Gospodarič, Pika; Cramm, Stefan; Kardynał, Beata; Plucinski, Lukasz; Blügel, Stefan; Schneider, Claus M
2016-06-01
Time reversal dictates that nonmagnetic, centrosymmetric crystals cannot be spin-polarized as a whole. However, it has been recently shown that the electronic structure in these crystals can in fact show regions of high spin-polarization, as long as it is probed locally in real and in reciprocal space. In this article we present the first observation of this type of compensated polarization in MoS2 bulk crystals. Using spin- and angle-resolved photoemission spectroscopy (ARPES), we directly observed a spin-polarization of more than 65% for distinct valleys in the electronic band structure. By additionally evaluating the probing depth of our method, we find that these valence band states at the point in the Brillouin zone are close to fully polarized for the individual atomic trilayers of MoS2, which is confirmed by our density functional theory calculations. Furthermore, we show that this spin-layer locking leads to the observation of highly spin-polarized bands in ARPES since these states are almost completely confined within two dimensions. Our findings prove that these highly desired properties of MoS2 can be accessed without thinning it down to the monolayer limit.
Quasi 2D electronic states with high spin-polarization in centrosymmetric MoS2 bulk crystals
Gehlmann, Mathias; Aguilera, Irene; Bihlmayer, Gustav; Młyńczak, Ewa; Eschbach, Markus; Döring, Sven; Gospodarič, Pika; Cramm, Stefan; Kardynał, Beata; Plucinski, Lukasz; Blügel, Stefan; Schneider, Claus M.
2016-01-01
Time reversal dictates that nonmagnetic, centrosymmetric crystals cannot be spin-polarized as a whole. However, it has been recently shown that the electronic structure in these crystals can in fact show regions of high spin-polarization, as long as it is probed locally in real and in reciprocal space. In this article we present the first observation of this type of compensated polarization in MoS2 bulk crystals. Using spin- and angle-resolved photoemission spectroscopy (ARPES), we directly observed a spin-polarization of more than 65% for distinct valleys in the electronic band structure. By additionally evaluating the probing depth of our method, we find that these valence band states at the point in the Brillouin zone are close to fully polarized for the individual atomic trilayers of MoS2, which is confirmed by our density functional theory calculations. Furthermore, we show that this spin-layer locking leads to the observation of highly spin-polarized bands in ARPES since these states are almost completely confined within two dimensions. Our findings prove that these highly desired properties of MoS2 can be accessed without thinning it down to the monolayer limit. PMID:27245646
NASA Astrophysics Data System (ADS)
Xiong, Shisheng
We developed a universal, facile and robust method to prepare free-standing, ordered and patternable nanoparticle/polymer monolayer arrays by evaporation-induced self-assembly at a fluid interface. The ultra-thin monolayer nanoparticle/polymer arrays are sufficiently robust that they can be transferred to arbitrary substrates, even with complex topographies. More importantly, the Poly (methyl methacrylate) (PMMA) in the system serves as a photoresist enabling two modes of electron beam (e-beam) nanoparticle patterning. These ultra-thin films of monolayer nanoparticle arrays are of fundamental interest as 2D artificial solids for electronic, magnetic and optical properties and are also of technological interest for a diverse range of applications in micro- and macro-scale devices including photovoltaics, sensors, catalysis, and magnetic storage. By co-assembly with block co-polymers, the nanoparticles were selectively positioned in one specific phase, representing a high throughput route for creating nanoparticle patterns. The self-assembly process was investigated by combined in-situ grazing incidence small angle x-ray scattering (GISAXS) and numerical simulation. By e-beam irradiation of free-standing 2D NP/polymer arrays, anisotropic nanowire arrays have been fabricated. Additionally, preliminary investigation on assembly of binary nanoparticle arrays has also been introduced, serving as promising future directions of interfacial assembly. Controlling the rate of spontaneous emission and thus promoting the photon generation efficiency is a key step toward fabrication of Quantum dot based single-photon sources, and harnessing of light energy from emitters with a broad emitting spectrum. Coupling of photo emitters to photonic cavities without perturbing the optical performance of cavities remains as a challenge in study of Purcell effect based on quantum electrodynamics. Taking advantage of interfacial assembly and transfer, we have achieved controlled deposition
Thermal Conductivity and Thermopower near the 2D Metal-Insulator transition, Final Technical Report
Sarachik, Myriam P.
2015-02-20
STUDIES OF STRONGLY-INTERACTING 2D ELECTRON SYSTEMS – There is a great deal of current interest in the properties of systems in which the interaction between electrons (their potential energy) is large compared to their kinetic energy. We have investigated an apparent, unexpected metal-insulator transition inferred from the behavior of the temperature-dependence of the resistivity; moreover, detailed analysis of the behavior of the magnetoresistance suggests that the electrons’ effective mass diverges, supporting this scenario. Whether this is a true phase transition or crossover behavior has been strenuously debated over the past 20 years. Our measurements have now shown that the thermoelectric power of these 2D materials diverges at a finite density, providing clear evidence that this is, in fact, a phase transition to a new low-density phase which may be a precursor or a direct transition to the long sought-after electronic crystal predicted by Eugene Wigner in 1934.
NASA Astrophysics Data System (ADS)
Lopez, Javier; Gonzalez, Luz Esther; Quinonez, Mario; Porras, Nelson; Zambrano, Gustavo; Gomez, Maria Elena
2014-03-01
Using a ferrfluid of cobalt-zinc ferrite nanoparticles Co(1 - x)ZnxFe2O4 coated with oleic acid and suspended in ethanol, we have fabricated a 2D photonic crystal (PC) by the application of an external magnetic field perpendicular to the plane of the ferrofluid. The 2D PC is made by rods of nanoparticles organized in a hexagonal structure. By means of the plane-wave expansion method, we study its photonic band structure (PBS) which depends on the effective permittivity and on the area ratio of the liquid phase. Additionaly, taking into account the Maxwell-Garnett theory we calculated the effective permittivity of the rods. We have found that the effective refractive index of the ferrofluid increases with its magnetization. Using these results we calculate the band structure of the photonic crystal at different applied magnetic fields, finding that the increase of the applied magnetic field shifts the band structure to lower frequencies with the appearance of more band gaps. Departamento de Física, Universidad del Valle, A.A. 25360, Cali, Colombia
Chai, Feng; Chen, YiPing; You, ZhuChai; Xia, ZeMin; Ge, SuZhi; Sun, YanQiong; Huang, BiHua
2013-06-01
Two Keggin-type heteropolytungstates, [Co(phen)₃]₃[CoW₁₂O₄₀]·9H₂O 1 (phen=1,10-phenanthroline) and [Fe(phen)₃]₂[FeW₁₂O₄₀]·H₃O·H₂O 2, have been synthesized via the hydrothermal technique and characterized by single crystal X-ray diffraction analyses, IR, XPS, TG analysis, UV–DRS, XRD, thermal-dependent and magnetic-dependent 2D-COS IR (two-dimensional infrared correlation spectroscopy). Crystal structure analysis reveals that the polyanions in compound 1 are linked into 3D supramolecule through hydrogen bonding interactions between lattice water molecules and terminal oxygen atoms of polyanion units, and [Co(phen)₃]²⁺ cations distributed in the polyanion framework with many hydrogen bonding interactions. The XPS spectra indicate that all the Co atoms in 1 are +2 oxidation state, the Fe atoms in 2 existing with +2 and +3 mixed oxidation states. - Graphical abstract: The magnetic-dependent synchronous 2D correlation IR spectra of 1 (a), 2 (b) over 0–50 mT in the range of 600–1000 cm⁻¹, the obvious response indicate two Keggin polyanions skeleton susceptible to applied magnetic field. Highlights: • Two Keggin-type heteropolytungstates with transition metal as a central atom has been obtained. • Compound 1 forms into 3D supramolecular architecture through hydrogen bonding between water molecules and polyanions. • Magnetic-dependent 2D-IR correlation spectroscopy was introduced to discuss the magnetism of polyoxometalate.
Influence of elliptical shaped holes on the sensitivity and Q factor in 2D photonic crystals sensor
NASA Astrophysics Data System (ADS)
Benmerkhi, A.; Bouchemat, M.; Bouchemat, T.
2016-07-01
We theoretically investigate the refractive index sensor based on L2 photonic crystal cavity where neighboring holes are locally infiltrated with polymers. The photonic crystal is composed of periodic triangular hole array patterned perpendicularly to an InP-based confining heterostructure. The number of the holes surrounding a L2 cavity and their shape were modified in order to optimize the sensitivity and quality factor. From this study we have selected two structures that have good results. The first one is called locally which has a very high Q factor and a good sensitivity. Their values are 6.03 × 106 and 163 nm/RIU, respectively. The second optimized structure is called design B, which has a high sensitivity toward 227.78 nm/RIU with a Q factor of 5 × 105. The calculated detect limit for the two designs are lower than 1.59 × 10-6 and 1.4 × 10-5 RIU, respectively.
NASA Astrophysics Data System (ADS)
Ren, Yixia; Chai, Hongmei; Hou, Xiangyang; Wang, Jijiang; Fu, Feng
2015-12-01
Hydrothermal reactions of manganese (II)/cadmium(II) salts with 1,2,4-trimellitic acid (H3tma) and 2,2‧:6‧,2-terpyridine (tpy) result in two novel complexes formulated with [M(Htma)(tpy)]·H2O (M = Mn(1) and Cd(2)). X-ray diffraction structural analyses of two complexes reveal they are isomorphic except for the different center metal ions and crystallize in the monoclinic crystal system of P(2)/n space group. The metal ion lies in a six-coordinated distorted octahedral environment coordinated with three Htma2- anions and one tpy ligand. There is an infinite two-dimensional rhombic network based on the metallic dimmers and Htma2- anions with the tpy ligands in void. Furthermore, the tpy ligands from the adjacent network weakly interact each other by π⋯π packing interactions into 3D supramolecular structure. The fluorescence properties could be assigned to the π - π* transition of organic ligands.
Wigner Surmise for Domain Systems
NASA Astrophysics Data System (ADS)
González, Diego Luis; Téllez, Gabriel
2008-07-01
In random matrix theory the spacing distribution functions p ( n)( s) are well fitted by the Wigner surmise and its generalizations. In this approximation the spacing functions are completely described by the behavior of the exact functions in the limits s→0 and s→∞. Most non equilibrium systems do not have analytical solutions for the spacing distribution and correlation functions. Because of that, we explore the possibility to use the Wigner surmise approximation in these systems. We found that this approximation provides a first approach to the statistical behavior of complex systems, in particular we use it to find an analytical approximation to the nearest neighbor distribution of the annihilation random walk.
Coudray, Nicolas; Hermann, Gilles; Caujolle-Bert, Daniel; Karathanou, Argyro; Erne-Brand, Françoise; Buessler, Jean-Luc; Daum, Pamela; Plitzko, Juergen M; Chami, Mohamed; Mueller, Urs; Kihl, Hubert; Urban, Jean-Philippe; Engel, Andreas; Rémigy, Hervé-W
2011-02-01
We have built and extensively tested a tool-chain to prepare and screen two-dimensional crystals of membrane proteins by transmission electron microscopy (TEM) at room temperature. This automated process is an extension of a new procedure described recently that allows membrane protein 2D crystallization in parallel (Iacovache et al., 2010). The system includes a gantry robot that transfers and prepares the crystalline solutions on grids suitable for TEM analysis and an entirely automated microscope that can analyze 96 grids at once without human interference. The operation of the system at the user level is solely controlled within the MATLAB environment: the commands to perform sample handling (loading/unloading in the microscope), microscope steering (magnification, focus, image acquisition, etc.) as well as automatic crystal detection have been implemented. Different types of thin samples can efficiently be screened provided that the particular detection algorithm is adapted to the specific task. Hence, operating time can be shared between multiple users. This is a major step towards the integration of transmission electron microscopy into a high throughput work-flow.
Selvakumar, Sellaiyan; Sivaji, Krishnan; Arulchakkaravarthi, Arjunan; Sankar, Sambasivam
2014-08-14
We present the mapping of electron momentum distribution (EMD) in a single crystal of anthracene by two-dimensional angular correlation of positron annihilation radiation (2D-ACAR). The projected EMD is explained on the basis of the crystallographic features of the material. The EMD spectra provide information about the positron states and their behavior and also about the hindrance of the positronium (Ps) formation in this material. The EMD has exhibited evidence for the absence of free volume defects. The characteristic EMD features regarding the delocalized electronic states are explained. Further, scintillation characteristics such as fluorescence and time-correlated single photon counting have also been studied. The emission peaks are attributed to vibrational bands of fluorescence emission from the singlet excitons and lifetime components are observed to be due to singlet fission and the singlet-singlet excitons annihilation.
Manson, J. L.; Schlueter, J. A.; McDonald, R. D.; Singleton, J.; Materials Science Division; Eastern Washington Univ.; LANL
2010-04-01
The crystal structure of the title compound was determined by X-ray diffraction at 90 and 295 K. Copper(II) ions are coordinated to four bridging pyz ligands to form square layers in the ab-plane. Bridging HF{sub 2}{sup -} ligands join the layers together along the c-axis to afford a tetragonal, three-dimensional (3D) framework that contains Taf{sub 6}{sup -} anions in every cavity. At 295 K, the pyz rings lie exactly perpendicular to the layers and cooling to 90 K induces a canting of those rings. Magnetically, the compound exhibits 2D antiferromagnetic correlations within the 2D layers with an exchange interaction of -13.1(1) K. Weak interlayer interactions, as mediated by Cu-F-H-F-Cu, leads to long-range magnetic order below 4.2 K. Pulsed-field magnetization data at 0.5 K show a concave curvature with increasing B and reveal a saturation magnetization at 35.4 T.
Chemseddine, A. Bloeck, U.
2008-10-15
The structure and structural evolution of tungstic acid solutions, sols and gels are investigated by high-resolution electron microscopy (HRTEM). Acidification of sodium tungstate solutions, through a proton exchange resin, is achieved in a way that ensures homogeneity in size and shape of intermediate polytungstic species. Gelation is shown to involve polycondensation followed by a self-assembling process of polytungstic building blocks leading to sheets with a layered hexagonal structure. Single layers of this new metastable phase are composed of three-, four- and six-membered rings of WO{sub 6} octahedra located in the same plane. This is the first time that a 2D oxide crystal is isolated and observed by direct atomic resolution. Further ageing and structural evolution leading to single sheets of 2D ReO{sub 3}-type structure is directly observed by HRTEM. Based on this atomic level imaging, a model for the formation of the oxide network structure involving a self-assembling process of tritungstic based polymeric chain is proposed. The presence of tritungstic groups and their packing in electrochromic WO{sub 3} films made by different techniques is discussed. - Graphical abstract: From the isopolyanion to the extended bulk tungsten oxide: HRTEM imaging.
Wigner functions for evanescent waves.
Petruccelli, Jonathan C; Tian, Lei; Oh, Se Baek; Barbastathis, George
2012-09-01
We propose phase space distributions, based on an extension of the Wigner distribution function, to describe fields of any state of coherence that contain evanescent components emitted into a half-space. The evanescent components of the field are described in an optical phase space of spatial position and complex-valued angle. Behavior of these distributions upon propagation is also considered, where the rapid decay of the evanescent components is associated with the exponential decay of the associated phase space distributions. To demonstrate the structure and behavior of these distributions, we consider the fields generated from total internal reflection of a Gaussian Schell-model beam at a planar interface.
Vénien-Bryan, C; Lenne, P F; Zakri, C; Renault, A; Brisson, A; Legrand, J F; Berge, B
1998-01-01
We present here some sensitive optical and mechanical experiments for monitoring the process of formation and growth of two-dimensional (2D) crystals of proteins on a lipid monolayer at an air-water interface. The adsorption of proteins on the lipid monolayer was monitored by ellipsometry measurements. An instrument was developed to measure the shear elastic constant (in plane rigidity) of the monolayer. These experiments have been done using cholera toxin B subunit (CTB) and annexin V as model proteins interacting with a monosialoganglioside (GM1) and dioleoylphosphatidylserine (DOPS), respectively. Electron microscopy observations of the protein-lipid layer transferred to grids were systematically used as a control. We found a good correlation between the measured in-plane rigidity of the monolayer and the presence of large crystalline domains observed by electron microscopy grids. Our interpretation of these data is that the crystallization process of proteins on a lipid monolayer passes through at least three successive stages: 1) molecular recognition between protein and lipid-ligand, i.e., adsorption of the protein on the lipid layer; 2) nucleation and growth of crystalline patches whose percolation is detected by the appearance of a non-zero in-plane rigidity; and 3) annealing of the layer producing a slower increase of the lateral or in-plane rigidity. PMID:9591688
Wigner Distributions of Quarks for Different Polarizations
NASA Astrophysics Data System (ADS)
More, Jai; Mukherjee, Asmita; Nair, Sreeraj
2017-03-01
We calculate quark Wigner distributions using the light-front wave functions in a dressed quark model. In this model, a proton target is replaced by a simplified spin-1/2 state, namely a quark dressed with a gluon. We calculate the Wigner distributions for different polarization configuration of quark and the target state in this model.
Sokolowsky, Kathleen P; Bailey, Heather E; Hoffman, David J; Andersen, Hans C; Fayer, Michael D
2016-07-21
Two-dimensional infrared (2D IR) data are presented for a vibrational probe in three nematogens: 4-cyano-4'-pentylbiphenyl, 4-cyano-4'-octylbiphenyl, and 4-(trans-4-amylcyclohexyl)-benzonitrile. The spectral diffusion time constants in all three liquids in the isotropic phase are proportional to [T*/(T - T*)](1/2), where T* is 0.5-1 K below the isotropic-nematic phase transition temperature (TNI). Rescaling to a reduced temperature shows that the decays of the frequency-frequency correlation function (FFCF) for all three nematogens fall on the same curve, suggesting a universal dynamic behavior of nematogens above TNI. Spectral diffusion is complete before significant orientational relaxation in the liquid, as measured by optically heterodyne detected-optical Kerr effect (OHD-OKE) spectroscopy, and before any significant orientational randomization of the probe measured by polarization selective IR pump-probe experiments. To interpret the OHD-OKE and FFCF data, we constructed a mode coupling theory (MCT) schematic model for the relationships among three correlation functions: ϕ1, a correlator for large wave vector density fluctuations; ϕ2, the orientational correlation function whose time derivative is the observable in the OHD-OKE experiment; and ϕ3, the FFCF for the 2D IR experiment. The equations for ϕ1 and ϕ2 match those in the previous MCT schematic model for nematogens, and ϕ3 is coupled to the first two correlators in a straightforward manner. Resulting models fit the data very well. Across liquid crystals, the temperature dependences of the coupling constants show consistent, nonmonotonic behavior. A remarkable change in coupling occurs at ∼5 K above TNI, precisely where the rate of spectral diffusion in 5CB was observed to deviate from that of a similar nonmesogenic liquid.
NASA Astrophysics Data System (ADS)
Berdagué, Philippe; Lesot, Philippe; Jacob, Jérémy; Terwilliger, Valery J.; Le Milbeau, Claude
2016-01-01
The hydrogen isotopic composition (δD or (D/H) value) of molecular biomarkers preserved in sedimentary archives is increasingly used to provide clues about the evolution of past climatic conditions. The rationale is that intact biomarkers retain isotopic information related to the climatic conditions that prevailed at the time of their synthesis. Some of these biomarkers may be degraded during diagenesis, however. The extent to which these degradations alter the original δD value of the source biomarker is presently debated and the capacity to resolve this question by determination of compound-specific δD values alone is limited. The "bulk" or "global" δD value of any molecule is in fact a composite of δD values at each site within this molecule (δDi or (D/H)i with i = number of hydrogen/deuterium atoms in the considered molecule). Determination of this site-specific δDi value in biomarkers could not only yield outstanding paleoenvironmental information but also help forecast the impacts of diagenesis and define essential steps in biosynthetic pathways. This task is analytically challenging. Here, we examined the capabilities of natural abundance deuterium 2D-NMR (NAD 2D-NMR) using homopolypeptide liquid crystals as an NMR solvent to: (i) analyze the NAD spectra of biomakers; (ii) determine the site-specific distribution of hydrogen in the nine methyl groups (δDMei with i = 23-31) of miliacin, a pentacyclic triterpene of the amyrin family and key biomarker for broomcorn millet in sedimentary archives. Relative (D/H)Mei values were established by anisotropic NAD 2D-NMR. Then absolute δDMei values were obtained by determining δDMei value of the methoxy group of miliacin using two independent approaches: isotropic NAD NMR (SNIF-NMR™) and GC-irMS. The resulting isotope profile for miliacin shows, for the first time, large variations in δDMei values that can directly be explained by biosynthetic processes. This approach has also the potential to permit
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.
Gao, Song; Fan, Rui Qing; Wang, Xin Ming; Wei, Li Guo; Song, Yang; Du, Xi; Xing, Kai; Wang, Ping; Yang, Yu Lin
2016-07-28
In this work, a rare 2D → 3D single-crystal-to-single-crystal transformation (SCSC) is observed in metal-organic coordination complexes, which is triggered by thermal treatment. The 2D two-fold interpenetrating square lattice layer [Cd(IBA)2]n (1) is irreversibly converted into a 3D four-fold interpenetrating diamond framework {[Cd(IBA)2(H2O)]·2.5H2O}n (2) (HIBA = 4-(1H-imidazol-1-yl)benzoic acid). Consideration is given to these two complexes with different interpenetrating structures and dimensionality, and their influence on photovoltaic properties are studied. Encouraged by the UV-visible absorption and HOMO-LUMO energy states matched for sensitizing TiO2, the two complexes are employed in combination with N719 in dye-sensitized solar cells (DSSCs) to compensate absorption in the ultraviolet and blue-violet region, offset competitive visible light absorption of I3(-) and reducing charge the recombination of injected electrons. After co-sensitization with 1 and 2, the device co-sensitized by 1/N719 and 2/N719 to yield overall efficiencies of 7.82% and 8.39%, which are 19.94% and 28.68% higher than that of the device sensitized only by N719 (6.52%). Consequently, high dimensional interpenetrating complexes could serve as excellent co-sensitizers and have application in DSSCs.
The success of Fermi gas model for overall scaling of 2D metal-to-insulator transition data
NASA Astrophysics Data System (ADS)
Cheremisin, M. V.
2017-03-01
The melting condition for two-dimensional Wigner solid (Platzman and Fukuyama, 1974) [14] is shown to contain an error of a factor of π. The analysis of experimental data for apparent 2D metal-to-insulator transition shows that the Wigner solidification (Tanatar and Ceperley, 1989) [16] has been never achieved. Within routine Fermi gas model both the metallic and insulating behavior of different 2D system for actual range of carrier densities and temperatures is explained.
Sels, Dries; Brosens, Fons
2013-10-01
The equation of motion for the reduced Wigner function of a system coupled to an external quantum system is presented for the specific case when the external quantum system can be modeled as a set of harmonic oscillators. The result is derived from the Wigner function formulation of the Feynman-Vernon influence functional theory. It is shown how the true self-energy for the equation of motion is connected with the influence functional for the path integral. Explicit expressions are derived in terms of the bare Wigner propagator. Finally, we show under which approximations the resulting equation of motion reduces to the Wigner-Boltzmann equation.
A Wigner Distribution Analysis of Scattering Dynamics
NASA Astrophysics Data System (ADS)
Weeks, David; Lacy, Brent
2009-04-01
Using the time dependent Channel Packet Method (CPM),ootnotetextD.E.Weeks, T.A.Niday, S.H.Yang, J Chem Phys. 125, 164301 (2006). a Fourier transformation of the correlation function between evolving wave packets is used to compute scattering matrix elements. The correlation function can also be used to compute a Wigner distribution as a function of time and energy. This scattering Wigner distribution is then used to investigate times at which various energetic contributions to the scattering matrix are made during a molecular collision. We compute scattering Wigner distributions for a variety of molecular systems and use them to characterize the associated molecular dynamics. In particular, the square well provides a simple and easily modified potential to study the relationship between the scattering Wigner distribution and wave packet dynamics. Additional systems that are being studied include the collinear H + H2 molecular reaction, and the non-adiabatic B + H2 molecular collision.
Time evolution of the Wigner function
NASA Astrophysics Data System (ADS)
Soto-Eguibar, Francisco; Claverie, Pierre
1983-05-01
In this paper we give a partial answer to the problem: When does an initially non-negative Wigner function remain non-negative under the effect of the time evolution? We show that, for pure states, this is the case for linear systems only; to prove this we use the fact that the Wigner function is non-negative if and only if the wavefunction is Gaussian. We also prove that the Green's solution of the evolution equation of the Wigner function, which in the framework of probability theory corresponds to the conditional probability density, takes on negative values. We utilize a theorem, about moments, borrowed from Pawula. We conclude that the Wigner phase-space formulation of quantum mechanics cannot receive a genuine probabilistic interpretation.
Yang, Huai-Xia; Liang, Zhen; Hao, Bao-Lian; Meng, Xiang-Ru
2014-10-15
Three new 1D to 3D complexes, namely, ([Ni(btec)(Himb){sub 2}(H{sub 2}O){sub 2}]·6H{sub 2}O){sub n} (1), ([Cd(btec){sub 0.5}(imb)(H{sub 2}O)]·1.5H{sub 2}O){sub n} (2), and ([Zn(btec){sub 0.5}(imb)]·H{sub 2}O){sub n} (3) (H{sub 4}btec=1,2,4,5-benzenetetracarboxylic acid, imb=2-(1H-imidazol-1-methyl)-1H-benzimidazole) have been synthesized by adjusting the central metal ions. Single-crystal X-ray diffraction analyses reveal that complex 1 possesses a 1D chain structure which is further extended into the 3D supramolecular architecture via hydrogen bonds. Complex 2 features a 2D network with Schla¨fli symbol (5{sup 3}·6{sup 2}·7)(5{sup 2}·6{sup 4}). Complex 3 presents a 3D framework with a point symbol of (4·6{sup 4}·8)(4{sup 2}·6{sup 2}·8{sup 2}). Moreover, their IR spectra, PXRD patterns, thermogravimetric curves, and luminescent emissions were studied at room temperature. - Graphical abstract: Three new 1D to 3D complexes with different structural and topological motifs have been obtained by modifying the central metal ions. Additionally, their IR, TG analyses and fluorescent properties are also investigated. - Highlights: • Three complexes based on mixed multidentate N- and O-donor ligands. • The complexes are characterized by IR, luminescence and TGA techniques. • Benzenetetracarboxylates display different coordination modes in complexes 1–3. • Changing the metal ions can result in complexes with completely different structures.
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.
James, Richard; Fernández, F Aníbal; Day, Sally E; Komarcević, Milos; Crossland, William A
2007-08-01
A nematic liquid crystal spatial light modulator used as a phase-modulating device and operating in the reflective mode is analyzed using three-dimensional modeling. Two configurations, which differ in their electrode placement relative to a fixed quarter-wave plate, are considered across a range of steering directions, with the grating conformal and in some cases oblique to the pixel grid. For each steering direction the sensitivity of the diffraction orders to the polarization state of the incident wavefront is studied. Optimal alignment of the liquid crystal is suggested to reduce this sensitivity.
Arnold, Thorsten; Siegmund, Marc; Pankratov, Oleg
2011-08-24
We apply exact-exchange spin-density functional theory in the Krieger-Li-Iafrate approximation to interacting electrons in quantum rings of different widths. The rings are threaded by a magnetic flux that induces a persistent current. A weak space and spin symmetry breaking potential is introduced to allow for localized solutions. As the electron-electron interaction strength described by the dimensionless parameter r(S) is increased, we observe-at a fixed spin magnetic moment-the subsequent transition of both spin sub-systems from the Fermi liquid to the Wigner crystal state. A dramatic signature of Wigner crystallization is that the persistent current drops sharply with increasing r(S). We observe simultaneously the emergence of pronounced oscillations in the spin-resolved densities and in the electron localization functions indicating a spatial electron localization showing ferrimagnetic order after both spin sub-systems have undergone the Wigner crystallization. The critical r(S)(c) at the transition point is substantially smaller than in a fully spin-polarized system and decreases further with decreasing ring width. Relaxing the constraint of a fixed spin magnetic moment, we find that on increasing r(S) the stable phase changes from an unpolarized Fermi liquid to an antiferromagnetic Wigner crystal and finally to a fully polarized Fermi liquid.
Fermi's golden rule in the Wigner representation
NASA Astrophysics Data System (ADS)
Segev, Bilha
2003-06-01
When Fermi's golden rule (FGR) is studied in the Wigner representation, the transition rate from an initial pure state or from an initial thermal distribution into a quasicontinuum manifold of degenerate states is given by an overlap integral of Wigner functions in phase space. In the semiclassical limit the transition rate is obtained by integrating over the regions in phase space where the energy difference between the initial and final potential surfaces is equal to the available energy. The integral is weighted by the initial probability density to be at that phase-space region. The classical limit of FGR is thus both simple and intuitive. In one dimension a relation to the Landau-Zener-Stuckelberg formula is established. The multi-dimensional case is considered by induction, proving that for separable multi-dimensional systems deviations of the logarithm of the transition rate from its classical limit scale at worst linearly with the dimension.
Edge universality for deformed Wigner matrices
NASA Astrophysics Data System (ADS)
Lee, Ji Oon; Schnelli, Kevin
2015-09-01
We consider N × N random matrices of the form H = W + V where W is a real symmetric Wigner matrix and V a random or deterministic, real, diagonal matrix whose entries are independent of W. We assume subexponential decay for the matrix entries of W and we choose V so that the eigenvalues of W and V are typically of the same order. For a large class of diagonal matrices V, we show that the rescaled distribution of the extremal eigenvalues is given by the Tracy-Widom distribution F1 in the limit of large N. Our proofs also apply to the complex Hermitian setting, i.e. when W is a complex Hermitian Wigner matrix.
Thomas precession, Wigner rotations and gauge transformations
NASA Technical Reports Server (NTRS)
Han, D.; Kim, Y. S.; Son, D.
1987-01-01
The exact Lorentz kinematics of the Thomas precession is discussed in terms of Wigner's O(3)-like little group which describes rotations in the Lorentz frame in which the particle is at rest. A Lorentz-covariant form for the Thomas factor is derived. It is shown that this factor is a Lorentz-boosted rotation matrix, which becomes a gauge transformation in the infinite-momentum or zero-mass limit.
Chiu, Po-Lin; Li, Xueming; Li, Zongli; Beckett, Brian; Brilot, Axel F.; Grigorieff, Nikolaus; Agard, David A.; Cheng, Yifan; Walz, Thomas
2015-01-01
The K2 Summit camera was initially the only commercially available direct electron detection camera that was optimized for high-speed counting of primary electrons and was also the only one that implemented centroiding so that the resolution of the camera can be extended beyond the Nyquist limit set by the physical pixel size. In this study, we used well-characterized two-dimensional crystals of the membrane protein aquaporin-0 to characterize the performance of the camera below and beyond the physical Nyquist limit and to measure the influence of electron dose rate on image amplitudes and phases. PMID:26318383
Chiu, Po-Lin; Li, Xueming; Li, Zongli; Beckett, Brian; Brilot, Axel F; Grigorieff, Nikolaus; Agard, David A; Cheng, Yifan; Walz, Thomas
2015-11-01
The K2 Summit camera was initially the only commercially available direct electron detection camera that was optimized for high-speed counting of primary electrons and was also the only one that implemented centroiding so that the resolution of the camera can be extended beyond the Nyquist limit set by the physical pixel size. In this study, we used well-characterized two-dimensional crystals of the membrane protein aquaporin-0 to characterize the performance of the camera below and beyond the physical Nyquist limit and to measure the influence of electron dose rate on image amplitudes and phases.
Photon polarization and Wigner's little group
Caban, Pawel; Rembielinski, Jakub
2003-10-01
To discuss one-photon polarization states we find the explicit form of the Wigner's little group element in the massless case for arbitrary Lorentz transformation. As is well known, when analyzing the transformation properties of the physical states, only the value of the phase factor is relevant. We show that this phase factor depends only on the direction of the momentum k/|k| and does not depend on the frequency k{sup 0}. Finally, we use this observation to discuss the transformation properties of the linearly polarized photons and the corresponding reduced density matrix. We find that they transform properly under Lorentz group.
Non-negative Wigner functions for orbital angular momentum states
Rigas, I.; Sanchez-Soto, L. L.; Klimov, A. B.; Rehacek, J.; Hradil, Z.
2010-01-15
The Wigner function of a pure continuous-variable quantum state is non-negative if and only if the state is Gaussian. Here we show that for the canonical pair angle and angular momentum, the only pure states with non-negative Wigner functions are the eigenstates of the angular momentum. Some implications of this surprising result are discussed.
Two-variable Hermite Polynomial State and Its Wigner Function
NASA Astrophysics Data System (ADS)
Meng, Xiang-Guo; Wang, Ji-Suo; Liang, Bao-Long
2009-08-01
In this paper we obtain the Wigner functions of two-variable Hermite polynomial states (THPS) and their marginal distribution using the entangled state |ξ> representation. Also we obtain tomogram of THPS by virtue of the Radon transformation between the Wigner operator and the projection operator of another entangled state |η,τ 1,τ 2>.
Experimental eavesdropping attack against Ekert's protocol based on Wigner's inequality
Bovino, F. A.; Colla, A. M.; Castagnoli, G.; Castelletto, S.; Degiovanni, I. P.; Rastello, M. L.
2003-09-01
We experimentally implemented an eavesdropping attack against the Ekert protocol for quantum key distribution based on the Wigner inequality. We demonstrate a serious lack of security of this protocol when the eavesdropper gains total control of the source. In addition we tested a modified Wigner inequality which should guarantee a secure quantum key distribution.
Revealing quantum correlation by negativity of the Wigner function
NASA Astrophysics Data System (ADS)
Taghiabadi, Razieh; Akhtarshenas, Seyed Javad; Sarbishaei, Mohsen
2016-05-01
We analyze two two-mode continuous variable separable states with the same marginal states. We adopt the definition of classicality in the form of well-defined positive Wigner function describing the state and find that although the states possess positive local Wigner functions, they exhibit negative Wigner functions for the global states. Using the negativity of Wigner function as an indicator of nonclassicality, we show that despite these states possess different negativities of the Wigner function, they do not reveal this difference as phase space nonclassicalities such as negativity of the Mandel Q parameter or quadrature squeezing. We then concentrate on quantum correlation of these states and show that quantum discord and local quantum uncertainty, as two well-defined measures of quantum correlation, manifest the difference between negativity of the Wigner functions. The non-Gaussianity of these states is also examined and show that the difference in behavior of their non-Gaussianity is the same as the difference between negativity of their Wigner functions. We also investigate the influence of correlation rank criterion and find that when the states can be produced locally from classical states, the Wigner functions cannot reveal their quantum correlations.
Toward solotronics design in the Wigner formalism
NASA Astrophysics Data System (ADS)
Sellier, J. M.; Dimov, I.
2015-01-01
The capability of manipulating single dopant atoms in semiconductor materials, with atomic precision, has given birth to a new branch of electronics known as solotronics (solitary dopant optoelectronics). While experiments are advancing rapidly, the theoretical comprehension of quantum phenomena occurring at that scale is relatively basic. Indeed, in this context, simulations come with incredible mathematical challenges. This eventually prevents practical design and optimization of solotronic devices. In this work, we focus our attention on a planar honeycomb structure exploiting single dopants embedded in silicon and study under which conditions it behaves as an electron ballistic channel. To this aim, we apply the time-dependent Wigner Monte Carlo formalism, based on signed particles to simulate and analyze the phenomena occurring in the proposed structure. We show that, by positioning the dopant atoms (phosphorus and boron) in particular planar patterns (honeycomb), it is possible to control the dynamics of a single electron. Finally, by introducing spatial distortions, we can show how the time-dependent electron dynamics is eventually affected. The results confirm that the Wigner Monte Carlo method is an efficient TCAD (Technology Computer Aided Design) tool which can be exploited for the time-dependent simulation of even more realistic situations necessary for the design of active solotronic devices.
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.
Positive Wigner functions render classical simulation of quantum computation efficient.
Mari, A; Eisert, J
2012-12-07
We show that quantum circuits where the initial state and all the following quantum operations can be represented by positive Wigner functions can be classically efficiently simulated. This is true both for continuous-variable as well as discrete variable systems in odd prime dimensions, two cases which will be treated on entirely the same footing. Noting the fact that Clifford and Gaussian operations preserve the positivity of the Wigner function, our result generalizes the Gottesman-Knill theorem. Our algorithm provides a way of sampling from the output distribution of a computation or a simulation, including the efficient sampling from an approximate output distribution in the case of sampling imperfections for initial states, gates, or measurements. In this sense, this work highlights the role of the positive Wigner function as separating classically efficiently simulable systems from those that are potentially universal for quantum computing and simulation, and it emphasizes the role of negativity of the Wigner function as a computational resource.
Modified Wigner inequality for secure quantum-key distribution
Castelletto, S.; Degiovanni, I.P.; Rastello, M.L.
2003-04-01
In this paper, we discuss the insecurity with present implementations of the Ekert protocol for quantum-key distribution based on the Wigner inequality. We propose a modified version of this inequality which guarantees safe quantum-key distribution.
Saghatforoush, Lotfali Bakhtiari, Akbar; Gheleji, Hojjat
2015-01-15
The synthesis of two dimensional (2D) coordination polymer [Pb{sub 2}(µ-I){sub 2}(µ-dpp-N,N,N,N)(µ-dpp-N,N)I{sub 2}]{sub n} (dpp=2,3-bis(2-pyridyl)pyrazine) is reported. As determined by X-ray diffraction of a twinned crystal, the dpp ligand simultaneously adopts a bis–bidentate and bis–monodentate coordination mode in the crystal structure of compound. The electronic band structure along with density of states (DOS) calculated by the DFT method indicates that the compound is an indirect band gap semiconductor. According to the DFT calculations, the observed emission of the compound at 600 nm in solid phase could be attributed to arise from an excited LLCT state (dpp-π{sup ⁎} [C-2p and N-2p states, CBs] to I-6p state [VBs]). The linear optical properties of the compound are also calculated by DFT method. The structure of the compound in solution phase is discussed based on the measured {sup 1}H NMR and fluorescence spectra in DMSO. TGA studies indicate that the compound is thermally stable up to 210 °C. - Graphical abstract: The synthesis, crystal structure and emission spectra of [Pb{sub 2}(µ-I){sub 2}(µ-dpp-N,N,N,N)(µ-dpp-N,N)I{sub 2}]{sub n} is presented. The electronic band structure and linear optical properties of the compound are calculated by the DFT method. - Highlights: • Two dimensional [Pb{sub 2}(µ-I){sub 2}(µ-dpp-N,N,N,N)(µ-dpp-N,N)I{sub 2}]{sub n} has been prepared. • The structure of the compound is determined by XRD of a twinned crystal. • DFT calculations indicate that the compound is an indirect band gap semiconductor. • As shown by DFT calculations, the emission band of the compound is LLCT. • Solution phase structure of compound is explored by {sup 1}H NMR and emission spectra.
FEL beam characterization from measurements of the Wigner distribution function
NASA Astrophysics Data System (ADS)
Schäfer, Bernd; Flöter, Bernhard; Mey, Tobias; Juranic, Pavle; Kapitzki, Svea; Keitel, Barbara; Plönjes, Elke; Mann, Klaus; Tiedtke, Kai
2011-10-01
The Free-Electron-Laser FLASH at DESY has been characterized by a quantitative determination of the Wigner distribution function. The setup, comprising an ellipsodial mirror and a moveable extreme UV sensitive CCD detector, enables the mapping of two-dimensional phase spaces corresponding to the horizontal and vertical coordinate axes, respectively. For separable beams this yields the entire Wigner distribution, offering comprehensive information about spatial coherence properties, wavefront, beam profiles, as well as beam propagation parameters.
Wigner function and Schroedinger equation in phase-space representation
Chruscinski, Dariusz; Mlodawski, Krzysztof
2005-05-15
We discuss a family of quasidistributions (s-ordered Wigner functions of Agarwal and Wolf [Phys. Rev. D 2, 2161 (1970); Phys. Rev. D 2, 2187 (1970); Phys. Rev. D 2, 2206 (1970)]) and its connection to the so-called phase space representation of the Schroedinger equation. It turns out that although Wigner functions satisfy the Schroedinger equation in phase space, they have a completely different interpretation.
NASA Astrophysics Data System (ADS)
Jha, Stefania
2011-09-01
I analyze the long dialog that Eugene Wigner (1902-1995) and Michael Polanyi (1891-1976) carried out on Polanyi's concept of tacit knowledge and its meaning for the measurement problem in quantum physics, focusing in particular on their ten-year correspondence between 1961 and 1971 on these subjects and the related mind-body problem. They differed in their interpretations, epistemologies, and ontologies, and consequently never resolved their differences on the measurement and mind-body problems. Nonetheless, their long dialog is significant and opens up avenues for exploring these problems further.
Mirror Numbers and Wigner's ``Unreasonable Effectiveness''
NASA Astrophysics Data System (ADS)
Berezin, Alexander
2006-04-01
Wigner's ``unreasonable effectiveness of mathematics in physics'' can be augmented by concept of mirror number (MN). It is defined as digital string infinite in both directions. Example is ()5141327182() where first 5 digits is Pi ``spelled'' backward (``mirrored'') and last 5 digits is the beginning of decimal exp1 string. Let MN be constructed from two different transcendental (or algebraically irrational) numbers, set of such MNs is Cantor-uncountable. Most MNs have contain any finite digital sequence repeated infinitely many times. In spirit of ``Contact'' (C.Sagan) each normal MN contains ``Library of Babel'' of all possible texts and patterns (J.L.Borges). Infinite at both ends, MN do not have any numerical values and, contrary to numbers written in positional systems, all digits in MNs have equal weight -- sort of ``numerological democracy''. In Pythagorean-Platonic models (space-time and physical world originating from pure numbers) idea of MN resolves paradox of ``beginning'' (or ``end'') of time. Because in MNs all digits have equal status, (quantum) randomness leads to more uniform and fully ergodic phase trajectories (cf. F.Dyson, Infinite in All Directions) .
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.
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.
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.
Accessing the quark orbital angular momentum with Wigner distributions
NASA Astrophysics Data System (ADS)
Lorcé, Cédric; Pasquini, Barbara
2013-04-01
The quark orbital angular momentum (OAM) has been recognized as an important piece of the proton spin puzzle. A lot of effort has been invested in trying to extract it quantitatively from the generalized parton distributions (GPDs) and the transverse-momentum dependent parton distributions (TMDs), which are accessed in high-energy processes and provide three-dimensional pictures of the nucleon. Recently, we have shown that it is more natural to access the quark OAM from the phase-space or Wigner distributions. We discuss the concept of Wigner distributions in the context of quantum field theory and show how they are related to the GPDs and the TMDs. We summarize the different definitions discussed in the literature for the quark OAM and show how they can in principle be extracted from the Wigner distributions.
Angular dependence of Wigner time delay: Relativistic Effects
NASA Astrophysics Data System (ADS)
Mandal, A.; Deshmukh, P. C.; Manson, S. T.; Kkeifets, A. S.
2016-05-01
Laser assisted photoionization time delay mainly consists of two parts: Wigner time delay, and time delay in continuum-continuum transition. Wigner time delay results from the energy derivative of the phase of the photoionization amplitude (matrix element). In general, the photoionization time delay is not the same in all directions relative to the incident photon polarization, although when a single transition dominates the amplitude, the resultant time delay is essentially isotropic. The relativistic-random-phase approximation is employed to determine the Wigner time delay in photoionization from the outer np subshells of the noble gas atoms, Ne through Xe. The time delay is found to significantly depend on angle, as well as energy. The angular dependence of the time delay is found to be quite sensitive to atomic dynamics and relativistic effects, and exhibit strong energy and angular variation in the neighborhood of Cooper minima. Work supported by DOE, Office of Chemical Sciences and DST (India).
Even and odd Wigner negative binomial states: Nonclassical properties
NASA Astrophysics Data System (ADS)
Mojaveri, B.; Dehghani, A.
2015-10-01
By using Wigner-Heisenberg algebra (WHA) and its Fock representation, even and odd Wigner negative binomial states (WNBSs) |M,ξ,ν>±W (ν = 0 corresponds to the ordinary even and odd negative binomial states (NBSs)) are introduced. These states can be reduced to the Wigner cat states in special limit. We establish the resolution of identity property for them through a positive definite measure on the unit disc. Some of their nonclassical properties, such as Mandel’s parameter and quadrature squeezing have been investigated numerically. We show that in contrast with the even NBSs, even WNBSs may exhibit sub-Poissonian statistics. Also squeezing in the field quadratures appears for both even and odd WNBSs. It is found that the deformation parameter ν plays an essential role in displaying highly nonclassical behaviors.
Wigner rotations and Iwasawa decompositions in polarization optics.
Han, D; Kim, Y S; Noz, M E
1999-07-01
Wigner rotations and Iwasawa decompositions are manifestations of the internal space-time symmetries of massive and massless particles, respectively. It is shown to be possible to produce combinations of optical filters which exhibit transformations corresponding to Wigner rotations and Iwasawa decompositions. This is possible because the combined effects of rotation, phase-shift, and attenuation filters lead to transformation matrices of the six-parameter Lorentz group applicable to Jones vectors and Stokes parameters for polarized light waves. The symmetry transformations in special relativity lead to a set of experiments which can be performed in optics laboratories.
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
Wigner functions for the pair angle and orbital angular momentum
NASA Astrophysics Data System (ADS)
Kastrup, H. A.
2016-12-01
The problem of constructing physically and mathematically well-defined Wigner functions for the canonical pair angle θ and angular momentum p is solved. While a key element for the construction of Wigner functions for the planar phase space {(q ,p ) ∈R2} is the Heisenberg-Weyl group, the corresponding group for the cylindrical phase space {(θ ,p ) ∈S1×R } is the Euclidean group E (2 ) of the plane and its unitary representations. Here the angle θ is replaced by the pair (cosθ ,sinθ ) , which corresponds uniquely to the points on the unit circle. The main structural properties of the Wigner functions for the planar and the cylindrical phase spaces are strikingly similar. A crucial role is played by the s i n c function, which provides the interpolation for the discontinuous quantized angular momenta in terms of the continuous classical ones, in accordance with the famous Whittaker cardinal function well known from interpolation and sampling theories. The quantum mechanical marginal distributions for the angle (continuous) and angular momentum (discontinuous) are, as usual, uniquely obtained by appropriate integrations of the (θ ,p ) Wigner function. Among the examples discussed is an elementary system of simple cat states.
Recognition of frequency-modulated signals using the Wigner distribution
NASA Astrophysics Data System (ADS)
Vysotskiy, M. G.; Kaasik, V. P.; Rogov, S. A.; Rozov, S. V.
2016-03-01
Precision and resolution ability of the frequency-modulated signals time-frequency distributions at the formation of these distributions with the help of pseudo-Wigner processors is investigated. Linear-frequency modulated signals and signals with frequency dependence on time to the higher than the first power are considered. The results of the numerical simulation are presented.
From the Weyl quantization of a particle on the circle to number–phase Wigner functions
Przanowski, Maciej Brzykcy, Przemysław Tosiek, Jaromir
2014-12-15
A generalized Weyl quantization formalism for a particle on the circle is shown to supply an effective method for defining the number–phase Wigner function in quantum optics. A Wigner function for the state ϱ{sup ^} and the kernel K for a particle on the circle is defined and its properties are analysed. Then it is shown how this Wigner function can be easily modified to give the number–phase Wigner function in quantum optics. Some examples of such number–phase Wigner functions are considered.
Self-consistent approach to the Wigner-Seitz treatment of soliton matter
NASA Astrophysics Data System (ADS)
Weber, Urban; McGovern, Judith A.
1998-06-01
We propose a self-consistent approach to the treatment of nuclear matter as a crystal of solitons in the Wigner-Seitz approximation. Specifically, we use a Bloch-like boundary condition on the quarks at the edge of a spherical cell which allows the dispersion relation for a given radius to be calculated self-consistently along with the meson fields; in previous work some ansatz for the dispersion relation has always been an input. Results in all models are very sensitive to the form of the dispersion relation, and so our approach represents a significant advance. We apply the method to both the Friedberg-Lee model and the chiral quark-meson model of Birse and Banerjee. Only the latter shows short-range repulsion; in the former the transition to a quark plasma occurs at unrealistically low densities.
Generalized Weyl-Wigner map and Vey quantum mechanics
NASA Astrophysics Data System (ADS)
Dias, Nuno Costa; Prata, João Nuno
2001-12-01
The Weyl-Wigner map yields the entire structure of Moyal quantum mechanics directly from the standard operator formulation. The covariant generalization of Moyal theory, also known as Vey quantum mechanics, was presented in the literature many years ago. However, a derivation of the formalism directly from standard operator quantum mechanics, clarifying the relation between the two formulations, is still missing. In this article we present a covariant generalization of the Weyl order prescription and of the Weyl-Wigner map and use them to derive Vey quantum mechanics directly from the standard operator formulation. The procedure displays some interesting features: it yields all the key ingredients and provides a more straightforward interpretation of the Vey theory including a direct implementation of unitary operator transformations as phase space coordinate transformations in the Vey idiom. These features are illustrated through a simple example.
Bell's inequality violation with non-negative Wigner functions
Revzen, M.; Mann, A.; Mello, P.A.; Johansen, L.M.
2005-02-01
A Bell inequality violation allowed by the two-mode squeezed state, whose Wigner function is nonnegative, is shown to hold only for correlations among dynamical variables that cannot be interpreted via a local hidden variable theory. Explicit calculations and interpretation are given for Bell's suggestion that the EPR (Einstein, Podolsky, and Rosen) state will not allow violation of Bell's inequality, in conjunction with its Wigner representative being nonnegative. It is argued that Bell's theorem disallowing the violation of Bell's inequality within a local hidden-variable theory depends on the dynamical variables having a definite value--assigned by the local hidden variables--even when they cannot be simultaneously measured. The analysis leads us to conclude that Bell's inequality violation is to be associated with endowing these definite values to the dynamical variables, and not with their locality attributes.
Wigner and Husimi functions in the double-well potential
NASA Astrophysics Data System (ADS)
Novaes, Marcel
2003-06-01
We present Wigner and Husimi functions for the stationary states of the quartic oscillator and the more general double-well potential, paying particular attention to the corresponding classical structure. We find that the qualitative behaviour of both these functions depends strongly on the height of the potential barrier, and that the Husimi function has vestiges of the classical trajectories even for states below this barrier. The zero-point energy is also seen to play an important role.
Continuous-variable teleportation of a negative Wigner function
Mista, Ladislav Jr.; Filip, Radim; Furusawa, Akira
2010-07-15
Teleportation is a basic primitive for quantum communication and quantum computing. We address the problem of continuous-variable (unconditional and conditional) teleportation of a pure single-photon state and a mixed attenuated single-photon state generally in a nonunity-gain regime. Our figure of merit is the maximum negativity of the Wigner function, which demonstrates a highly nonclassical feature of the teleported state. We find that the negativity of the Wigner function of the single-photon state can be unconditionally teleported for an arbitrarily weak squeezed state used to create the entangled state shared in teleportation. In contrast, for the attenuated single-photon state there is a strict threshold squeezing one has to surpass to successfully teleport the negativity of its Wigner function. The conditional teleportation allows one to approach perfect transmission of the single photon for an arbitrarily low squeezing at a cost of decrease of the success rate. In contrast, for the attenuated single photon state, conditional teleportation cannot overcome the squeezing threshold of the unconditional teleportation and it approaches negativity of the input state only if the squeezing increases simultaneously. However, as soon as the threshold squeezing is surpassed, conditional teleportation still pronouncedly outperforms the unconditional one. The main consequences for quantum communication and quantum computing with continuous variables are 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
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)
Zhang, Xiao-Yan; Wang, Ji-Suo; Meng, Xiang-Guo; Su, Jie
2009-02-01
Using the coherent state representation of Wigner operator and the technique of integration within an ordered product (IWOP) of operators, the Wigner functions of the Klauder-Perelomov coherent states (KP-CSs) for the pseudoharmonic oscillator (PHO) are obtained and the variations of the Wigner functions with the parameters k and z are discussed. Moreover, the tomograms of the KP-CSs for the PHO are calculated by virtue of intermediate coordinate-momentum representation in quantum optics.
Spin exchange dominated by charge fluctuations of the Wigner lattice in the chain cuprate Na5Cu3O6
NASA Astrophysics Data System (ADS)
Ali, Naveed Zafar; Sirker, Jesko; Nuss, Jürgen; Horsch, Peter; Jansen, Martin
2011-07-01
Na5Cu3O6, a new member of one-dimensional charge-ordered chain cuprates, was synthesized via the azide/nitrate route by reacting NaN3, NaNO3, and CuO. According to single-crystal x-ray analysis, one-dimensional ∞1CuO2n- chains built up from planar, edge-sharing CuO4 squares are a dominant feature of the crystal structure. From the analysis of the Cu-O bond lengths, we find that the system forms a Wigner lattice. The commensurate charge order allows the explicit assignment of the valence states of either +2 or +3 to each copper atom, resulting in a repetition according to Cu2+-Cu3+-Cu2+-Cu2+-Cu3+-Cu2+. Following the theoretical analysis of the previously synthesized compounds Na3Cu2O4 and Na8Cu5O10, the magnetic susceptibility was expected to show a large dimer gap. Surprisingly, this is not the case. To resolve this puzzle, we show that the magnetic couplings in this compound are strongly affected by excitations across the Wigner charge gap. By including these contributions, which are distinct from conventional superexchange in Mott-insulators, we obtain a quantitatively satisfying theoretical description of the magnetic susceptibility data.
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.
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.
1991-10-30
Spectroscopy by Virril Percec and Myongsoo Lee Department of Macromolecular Science Case Western Reserve University Cleveland, OH 44106-2699 and Peter L ...AUTHOrZ(S) Virgil Percec, Myongsoo Lee, Peter L . Rinaldi and Vincent E. Litman l3a TYPE OF REPORT 1131) TIME COVERED 14. DATE OF REPORT (Year. Afot? Dy I...with CF3SO 3 H/S(CH 3)2 in CH2Cl2 at 0OC and termninated by ammoniacal methanol, by 1 -D and 2-D (COSY) 300 MHz IH-NMR spectroscopy is presented. The
Path-integral approach to the Wigner-Kirkwood expansion.
Jizba, Petr; Zatloukal, Václav
2014-01-01
We study the high-temperature behavior of quantum-mechanical path integrals. Starting from the Feynman-Kac formula, we derive a functional representation of the Wigner-Kirkwood perturbation expansion for quantum Boltzmann densities. As shown by its applications to different potentials, the presented expansion turns out to be quite efficient in generating analytic form of the higher-order expansion coefficients. To put some flesh on the bare bones, we apply the expansion to obtain basic thermodynamic functions of the one-dimensional anharmonic oscillator. Further salient issues, such as generalization to the Bloch density matrix and comparison with the more customary world-line formulation, are discussed.
Wigner surmise for mixed symmetry classes in random matrix theory.
Schierenberg, Sebastian; Bruckmann, Falk; Wettig, Tilo
2012-06-01
We consider the nearest-neighbor spacing distributions of mixed random matrix ensembles interpolating between different symmetry classes or between integrable and nonintegrable systems. We derive analytical formulas for the spacing distributions of 2×2 or 4×4 matrices and show numerically that they provide very good approximations for those of random matrices with large dimension. This generalizes the Wigner surmise, which is valid for pure ensembles that are recovered as limits of the mixed ensembles. We show how the coupling parameters of small and large matrices must be matched depending on the local eigenvalue density.
Emergent heavy fermion behavior at the Wigner-Mott transition.
Merino, Jaime; Ralko, Arnaud; Fratini, Simone
2013-09-20
We study charge ordering driven by Coulomb interactions on triangular lattices relevant to the Wigner-Mott transition in two dimensions. Dynamical mean-field theory reveals the pinball liquid phase, a charge ordered metallic phase containing quasilocalized (pins) coexisting with itinerant (balls) electrons. Based on an effective periodic Anderson model for this phase, we find an antiferromagnetic Kondo coupling between pins and balls and strong quasiparticle renormalization. Non-Fermi liquid behavior can occur in such charge ordered systems due to the spin-flip scattering of itinerant electrons off the pins in analogy with heavy fermion compounds.
NASA Astrophysics Data System (ADS)
Gelman, L.; Gould, J. D.
2007-11-01
The new technique, the time-frequency chirp-Wigner transform has been proposed recently. This technique is further investigated for the general case of higher order chirps, i.e. non-stationary signals with any nonlinear polynomial variation of the instantaneous frequency in time. Analytical and numerical comparison of the chirp-Wigner transform and the classical Wigner distribution was performed for processing of single-component and multi-component higher order chirps. It is shown for the general case of single component higher order chirps that the chirp-Wigner transform has an essential advantage in comparison with the traditional Wigner distribution: the chirp-Wigner transform ideally follows the nonlinear polynomial frequency variation without amplitude errors. It is shown for multi-component signal where each component is a higher order chirp, that the chirp-Wigner transform adjusted to a single component will follow the instantaneous frequency of the component without amplitude errors. It is also shown that the classical Wigner distribution is unable to estimate component amplitudes of single component and multi-component higher order chirps.
Hexatic and Microemulsion Phases in the 2d Quantum Plasma
NASA Astrophysics Data System (ADS)
Clark, Bryan; Casula, Michele; Ceperley, David
2009-03-01
It has been long known that the two-dimensional one component plasma supports both a Wigner-crystal and liquid phase. Classically [1,2], it is known that a hexatic phase exists but it is not known how this hexatic phase extends into the quantum regime. Moreover, at low temperature, phenomenological arguments [3] from Jamei, et. al. suggest the existence of microemulsion phases including stripes and bubbles. We use diffusion and path integral Monte Carlo to map out this phase diagram. We are able to extend the hexatic phase into the quantum regime as well as quantify the nature of the defects and exponents in the long range quantum system. We also specify the the nature, extent and existence (or lack thereof) of the expected low-T microemulsion phases. [0pt] [1] Muto, S. & Aoki, H. Crystallization of a classical two-dimensional electron system: Positional and orientational orders. Phys. Rev. B 59, 14911(1999).[0pt] [2] He, W.J. et al. Phase transition in a classical two-dimensional electron system. Phys. Rev. B 68, 195104(2003).[0pt] [3] Jamei, R., Kivelson, S. & Spivak, B. Universal Aspects of Coulomb-Frustrated Phase Separation. Phys. Rev. Lett. 94, 056805-4(2005).
Space fractional Wigner equation and its semiclassical limit.
Stickler, B A; Schachinger, E
2011-12-01
Manifestations of space fractional quantum mechanics (SFQM), as it was formulated by Laskin [Phys. Rev. E 62, 3135 (2000)], are deemed to offer a better physical interpretation of Lévy flight statistics on a quantum mechanical level. We start with the SFQM Schrödinger equation characterized by a Lévy flight index α∈ (1,2), perform a Wigner transform, and draw the limit h/Eτ → 0 (i.e., let the observed energy scale E go to infinity in comparison to the quantization given by h/τ). In order to obtain classical transport equations two possible substitutions for the terms |p|(α) and |p'|α which appear in von Neumann's equation are presented. It is demonstrated that they conform to the criteria for a successful Wigner transform. Their benefits and caveats are discussed in detail. We find, that, indeed, SFQM manifests itself in an anomalous kinetic term of the free particle's motion and, assuming an external potential diagonal in momentum space for the sake of simplicity, in corresponding anomalous terms in the resulting drift current. All our results reduce to the classical forms in the limit α = 2.
Gauge-independent Wigner functions. II. Inclusion of radiation reaction
NASA Astrophysics Data System (ADS)
Javanainen, J.; Varró, S.; Serimaa, O. T.
1987-04-01
We investigate the effects of quantized radiation reaction fields on the motion of a charged particle using the gauge-independent Wigner operator (GIWO) and gauge-independent Wigner function (GIWF) introduced earlier [Phys. Rev. A 33, 2913 (1986)]. To complement the equation of motion of the GIWO, the Heisenberg equations of motion of the quantized electromagnetic fields are solved within the Markov approximation. After considering the operator orderings and orders of magnitude of the radiation reaction terms, we eliminate the quantum fields from the evolution equation of the GIWO, and obtain for the GIWF a closed equation containing relaxation terms. As an example of the formalism we derive a Fokker-Planck equation (FPE) for the GIWF of a particle in a constant magnetic field. To the order ħ 0 the classical radiation damping ensues, and the first quantum correction proportional to ħ emerges as diffusion. The diffusion operator turns out to be indefinite and the FPE consequently defies our attempts at a complete analysis, but we demonstrate that at least the coherent states constructed from the Landau levels exhibit a manifestly physical time evolution under the FPE. We point out that the GIWF calculated with quantized electromagnetic fields is divergent even if the fields are in the vacuum state, and suggest that the GIWF should be associated with the particle state by ignoring the quantized fields altogether.
Hou, Ming-Hon; Robinson, Howard; Gao, Yi-Gui; Wang, Andrew H-J
2004-01-01
The anticancer antibiotic chromomycin A3 (Chro) is a DNA minor groove binding drug belonging to the aureolic family. Chro likely exerts its activity by interfering with replication and transcription. Chro forms a dimer, mediated by a divalent metal ion, which binds to G/C-rich DNA. Herein we report the first crystal structure of Chro bound to d(TTG GCCAA)2 DNA duplex solved by multiwavelength anomalous diffraction (MAD) based on the chelated Co3+ ion. The structure of the Mg2+ complex was subsequently refined at 2.15 A resolution, which revealed two complexes of metal-coordinated dimers of Chro bound to the octamer DNA duplex in the asymmetric unit. The metal ion is octahedrally coordinated to the O1 and O9 oxygen atoms of the chromophore (CPH), and two water molecules act as the fifth and sixth ligands. The two coordinated water molecules are hydrogen bonded to O2 atoms of C5 and C13 bases. The Chro dimer binds at and significantly widens the minor groove of the GGCC sequence. The long axis of each chromophore lies along and stacks over the sugar-phosphate backbone with the two attached saccharide moieties (rings A/B and C/D/E) wrapping across the minor groove. DNA is kinked by 30 degrees and 36 degrees in the two complexes, respectively. Six G-specific hydrogen bonds between Chro and DNA provide the GGCC sequence specificity. Interestingly, DNA in concert with Chro appears to act as an effective template to catalyze the deamination of Co(NH3)6(3+), as shown by circular dichroism and crystal structure data. Our results present useful structural information for designing new anticancer drug derivatives in the future.
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
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.
Observation of the Wigner-Huntington transition to metallic hydrogen.
Dias, Ranga P; Silvera, Isaac F
2017-02-17
Producing metallic hydrogen has been a great challenge in condensed matter physics. Metallic hydrogen may be a room-temperature superconductor and metastable when the pressure is released and could have an important impact on energy and rocketry. We have studied solid molecular hydrogen under pressure at low temperatures. At a pressure of 495 gigapascals, hydrogen becomes metallic, with reflectivity as high as 0.91. We fit the reflectance using a Drude free-electron model to determine the plasma frequency of 32.5 ± 2.1 electron volts at a temperature of 5.5 kelvin, with a corresponding electron carrier density of 7.7 ± 1.1 × 10(23) particles per cubic centimeter, which is consistent with theoretical estimates of the atomic density. The properties are those of an atomic metal. We have produced the Wigner-Huntington dissociative transition to atomic metallic hydrogen in the laboratory.
Mean field limit for bosons and propagation of Wigner measures
NASA Astrophysics Data System (ADS)
Ammari, Z.; Nier, F.
2009-04-01
We consider the N-body Schrödinger dynamics of bosons in the mean field limit with a bounded pair-interaction potential. According to the previous work [Ammari, Z. and Nier, F., "Mean field limit for bosons and infinite dimensional phase-space analysis," Ann. Henri Poincare 9, 1503 (2008)], the mean field limit is translated into a semiclassical problem with a small parameter ɛ →0, after introducing an ɛ-dependent bosonic quantization. The limits of quantum correlation functions are expressed as a push forward by a nonlinear flow (e.g., Hartree) of the associated Wigner measures. These object and their basic properties were introduced by Ammari and Nier in the infinite dimensional setting. The additional result presented here states that the transport by the nonlinear flow holds for a rather general class of quantum states in their mean field limit.
Mean field limit for bosons and propagation of Wigner measures
Ammari, Z.; Nier, F.
2009-04-15
We consider the N-body Schroedinger dynamics of bosons in the mean field limit with a bounded pair-interaction potential. According to the previous work [Ammari, Z. and Nier, F., 'Mean field limit for bosons and infinite dimensional phase-space analysis', Ann. Henri Poincare 9, 1503 (2008)], the mean field limit is translated into a semiclassical problem with a small parameter {epsilon}{yields}0, after introducing an {epsilon}-dependent bosonic quantization. The limits of quantum correlation functions are expressed as a push forward by a nonlinear flow (e.g., Hartree) of the associated Wigner measures. These object and their basic properties were introduced by Ammari and Nier in the infinite dimensional setting. The additional result presented here states that the transport by the nonlinear flow holds for a rather general class of quantum states in their mean field limit.
Observation of the Wigner-Huntington transition to metallic hydrogen
NASA Astrophysics Data System (ADS)
Dias, Ranga P.; Silvera, Isaac F.
2017-02-01
Producing metallic hydrogen has been a great challenge in condensed matter physics. Metallic hydrogen may be a room-temperature superconductor and metastable when the pressure is released and could have an important impact on energy and rocketry. We have studied solid molecular hydrogen under pressure at low temperatures. At a pressure of 495 gigapascals, hydrogen becomes metallic, with reflectivity as high as 0.91. We fit the reflectance using a Drude free-electron model to determine the plasma frequency of 32.5 ± 2.1 electron volts at a temperature of 5.5 kelvin, with a corresponding electron carrier density of 7.7 ± 1.1 × 1023 particles per cubic centimeter, which is consistent with theoretical estimates of the atomic density. The properties are those of an atomic metal. We have produced the Wigner-Huntington dissociative transition to atomic metallic hydrogen in the laboratory.
Quantifying Correlations via the Wigner-Yanase-Dyson Skew Information
NASA Astrophysics Data System (ADS)
Fan, Yajing; Cao, Huaixin
2016-09-01
In this paper, based on a discussion about the Wigner-Yanase-Dyson (WYD) skew information, the measure F a, α ( ρ a b ) for correlations in terms of the WYD skew information is introduced and discussed. The following conclusions are obtained. For a classical-quantum state ρ a b , F a, α ( ρ a b )=0 if and only if ρ a b is a product state; F a, α ( ρ a b ) is locally unitary invariant and convex on the set of states with the fixed marginal ρ a ; F a, α ( ρ a b ) decreases under local random unitary operation on H b ; For a quantum-classical state ρ a b , F a, α ( ρ a b ) decreases under local operation on H b ; Lastly, F a, α ( ρ a b ) is computed for the pure states and the Bell-diagonal states, respectively.
Metastable Frenkel Pair Defect in Graphite: Source of Wigner Energy?
NASA Astrophysics Data System (ADS)
Ewels, C. P.; Telling, R. H.; El-Barbary, A. A.; Heggie, M. I.; Briddon, P. R.
2003-07-01
The atomic processes associated with energy storage and release in irradiated graphite have long been subject to untested speculation. We examine structures and recombination routes for interstitial-vacancy (I-V) pairs in graphite. Interaction results in the formation of a new metastable defect (an intimate I-V pair) or a Stone-Wales defect. The intimate I-V pair, although 2.9eV more stable than its isolated constituents, still has a formation energy of 10.8eV. The barrier to recombination to perfect graphite is calculated to be 1.3eV, consistent with the experimental first Wigner energy release peak at 1.38eV. We expect similar defects to form in carbon nanostructures such as nanotubes, nested fullerenes, and onions under irradiation.
Breit-Wigner Approximation and the Distributionof Resonances
NASA Astrophysics Data System (ADS)
Petkov, Vesselin; Zworski, Maciej
For operators with a discrete spectrum, {λj2}, the counting function of λj's, N (λ), trivially satisfies N ( λ+δ ) -N ( λ-δ ) =∑jδλj((λ-δ,λ+δ]). In scattering situations the natural analogue of the discrete spectrum is given by resonances, λj∈+, and of N (λ), by the scattering phase, s(λ). The relation between the two is now non-trivial and we prove that
Wigner-Araki-Yanase theorem beyond conservation laws
NASA Astrophysics Data System (ADS)
Tukiainen, Mikko
2017-01-01
The ability to measure every quantum observable is ensured by a fundamental result in quantum measurement theory. Nevertheless, additive conservation laws associated with physical symmetries, such as the angular momentum conservation, may lead to restrictions on the measurability of the observables. Such limitations are imposed by the theorem of Wigner, Araki, and Yanase (WAY). In this paper a formulation of the WAY theorem is presented rephrasing the measurability limitations in terms of quantum incompatibility. This broader mathematical basis enables us to both capture and generalize the WAY theorem by allowing us to drop the assumptions of additivity and even conservation of the involved quantities. Moreover, we extend the WAY theorem to the general level of positive operator-valued measures.
Nonlinear analogue of the May−Wigner instability transition
Fyodorov, Yan V.; Khoruzhenko, Boris A.
2016-01-01
We study a system of N≫1 degrees of freedom coupled via a smooth homogeneous Gaussian vector field with both gradient and divergence-free components. In the absence of coupling, the system is exponentially relaxing to an equilibrium with rate μ. We show that, while increasing the ratio of the coupling strength to the relaxation rate, the system experiences an abrupt transition from a topologically trivial phase portrait with a single equilibrium into a topologically nontrivial regime characterized by an exponential number of equilibria, the vast majority of which are expected to be unstable. It is suggested that this picture provides a global view on the nature of the May−Wigner instability transition originally discovered by local linear stability analysis. PMID:27274077
Star product, discrete Wigner functions, and spin-system tomograms
NASA Astrophysics Data System (ADS)
Adam, P.; Andreev, V. A.; Isar, A.; Man'ko, V. I.; Man'ko, M. A.
2016-03-01
We develop the star-product formalism for spin states and consider different methods for constructing operator systems forming sets of dequantizers and quantizers, establishing a relation between them. We study the physical meaning of the operator symbols related to them. Quantum tomograms can also serve as operator symbols. We show that the possibility to express discrete Wigner functions in terms of measurable quantities follows because these functions can be related to quantum tomograms. We investigate the physical meaning of tomograms and spin-system tomogram symbols, which they acquire in the framework of the star-product formalism. We study the structure of the sum kernels, which can be used to express the operator symbols, calculated using different sets of dequantizers and also arising in calculating the star product of operator symbols, in terms of one another.
The Wigner - Seitz model for concentrated clay suspensions
NASA Astrophysics Data System (ADS)
Trizac, Emmanuel; Hansen, Jean-Pierre
1997-03-01
The model of a single uniformly charged finite platelet confined with its counter-ions and added salt to a Wigner - Seitz cell is treated within linearized Poisson - Boltzmann (or Debye - Hückel) theory. We consider circular (disc-like) and square platelets placed at the centre of a cylindrical or parallelepipedic cell of volume fixed by the macroscopic clay concentration. For a given volume the free energy F is minimized with respect to the aspect ratio of the cell. We find that the quadrupole moment Q of the total charge distribution always vanishes at the free-energy minimum, and that for discs, Q and F are practically identical for the two cell geometries at any given volume and salt concentration. Finally we propose a hybrid Poisson - Boltzmann/Debye - Hückel formulation which allows non-linearities to be approximately accounted for.
Use of the Wigner representation in scattering problems
NASA Technical Reports Server (NTRS)
Bemler, E. A.
1975-01-01
The basic equations of quantum scattering were translated into the Wigner representation, putting quantum mechanics in the form of a stochastic process in phase space, with real valued probability distributions and source functions. The interpretative picture associated with this representation is developed and stressed and results used in applications published elsewhere are derived. The form of the integral equation for scattering as well as its multiple scattering expansion in this representation are derived. Quantum corrections to classical propagators are briefly discussed. The basic approximation used in the Monte-Carlo method is derived in a fashion which allows for future refinement and which includes bound state production. Finally, as a simple illustration of some of the formalism, scattering is treated by a bound two body problem. Simple expressions for single and double scattering contributions to total and differential cross-sections as well as for all necessary shadow corrections are obtained.
Entangled Schrodinger cats in circuit QED: Joint Wigner Tomography
NASA Astrophysics Data System (ADS)
Gao, Yvonne Y.; Wang, Chen; Reinhold, Philip; Heeres, Reinier W.; Ofek, Nissim; Chou, Kevin; Axline, Christopher; Frunzio, Luigi; Devoret, Michel H.; Schoelkopf, Robert J.
Creating and controlling entanglement of quantum states over large Hilbert space is an important element of quantum information processing. Using the cQED architecture consisting of two long-lived superconducting cavities dispersively coupled to a transmon qubit, we successfully created an entangled coherent-state microwave fields in two superconducting cavities. In this talk, we will present the full joint Wigner tomography of the state, measured using the method of joint photon number parity measurement introduced in the previous talk. Furthermore, we will show the redundant encoding and efficient read-out of two logical bits of information in such entangled state and hence demonstrating that the entangled ``Schrodinger cats'' is a viable candidate as an error-correctable quantum memory as well as a valuable platform for implementation of two-qubit logical operations.
Linear canonical transformations of coherent and squeezed states in the Wigner phase space
NASA Technical Reports Server (NTRS)
Han, D.; Kim, Y. S.; Noz, Marilyn E.
1988-01-01
It is shown that classical linear canonical transformations are possible in the Wigner phase space. Coherent and squeezed states are shown to be linear canonical transforms of the ground-state harmonic oscillator. It is therefore possible to evaluate the Wigner functions for coherent and squeezed states from that for the harmonic oscillator. Since the group of linear canonical transformations has a subgroup whose algebraic property is the same as that of the (2+1)-dimensional Lorentz group, it may be possible to test certain properties of the Lorentz group using optical devices. A possible experiment to measure the Wigner rotation angle is discussed.
In-Depth Insights into the Key Steps of Delamination of Charged 2D Nanomaterials.
Rosenfeldt, Sabine; Stöter, Matthias; Schlenk, Mathias; Martin, Thomas; Albuquerque, Rodrigo Queiroz; Förster, Stephan; Breu, Josef
2016-10-07
Delamination is a key step to obtain individual layers from inorganic layered materials needed for fundamental studies and applications. For layered van der Waals materials such as graphene, the adhesion forces are small, allowing for mechanical exfoliation, whereas for ionic layered materials such as layered silicates, the energy to separate adjacent layers is considerably higher. Quite counterintuitively, we show for a synthetic layered silicate (Na0.5-hectorite) that a scalable and quantitative delamination by simple hydration is possible for high and homogeneous charge density, even for aspect ratios as large as 20000. A general requirement is the separation of adjacent layers by solvation to a distance where layer interactions become repulsive (Gouy-Chapman length). Further hydration up to 34 nm leads to the formation of a highly ordered lamellar liquid crystalline phase (Wigner crystal). Up to eight higher-order reflections indicate excellent positional order of individual layers. The Wigner crystal melts when the interlayer separation reaches the Debye length, where electrostatic interactions between adjacent layers are screened. The layers become weakly charge-correlated. This is indicated by fulfilling the classical Hansen-Verlet and Lindeman criteria for melting. We provide insight into the requirements for layer separation and controlling the layer distances for a broad range of materials and outline an important pathway for the integration of layers into devices for advanced applications.
Wigner time delay and related concepts: Application to transport in coherent conductors
NASA Astrophysics Data System (ADS)
Texier, Christophe
2016-08-01
The concepts of Wigner time delay and Wigner-Smith matrix allow us to characterise temporal aspects of a quantum scattering process. The paper reviews the statistical properties of the Wigner time delay for disordered systems; the case of disorder in 1D with a chiral symmetry is discussed and the relation with exponential functionals of the Brownian motion is underlined. Another approach for the analysis of time delay statistics is the random matrix approach, from which we review few results. As a practical illustration, we briefly outline a theory of non-linear transport and AC transport developed by Büttiker and coworkers, where the concept of Wigner-Smith time delay matrix is a central piece allowing us to describe screening properties in out-of-equilibrium coherent conductors.
Wigner functions for nonclassical states of a collection of two-level atoms
NASA Technical Reports Server (NTRS)
Agarwal, G. S.; Dowling, Jonathan P.; Schleich, Wolfgang P.
1993-01-01
The general theory of atomic angular momentum states is used to derive the Wigner distribution function for atomic angular momentum number states, coherent states, and squeezed states. These Wigner functions W(theta,phi) are represented as a pseudo-probability distribution in spherical coordinates theta and phi on the surface of a sphere of radius the square root of j(j +1) where j is the total angular momentum.
LETTER TO THE EDITOR: The Wigner function associated with the Rogers-Szegö polynomials
NASA Astrophysics Data System (ADS)
Galetti, D.; Mizrahi, S. S.; Ruzzi, M.
2004-12-01
A Wigner function associated with the Rogers-Szegö polynomials is proposed and its properties are discussed. It is shown that from such a Wigner function it is possible to obtain well-behaved probability distribution functions for both angle and action variables, defined on the compact support -π <= θ < π, and for m >= 0, respectively. The width of the angle probability density is governed by the free parameter q characterizing the polynomials.
Wu Chunfeng; Chen Jingling; Oh, C.H.; Kwek, L.C.; Xue Kang
2005-02-01
We construct an explicit Wigner function for the N-mode squeezed state. Based on a previous observation that the Wigner function describes correlations in the joint measurement of the phase-space displaced parity operator, we investigate the nonlocality of the multipartite entangled state by the violation of the Zukowski-Brukner N-qubit Bell inequality. We find that quantum predictions for such a squeezed state violate these inequalities by an amount that grows with the number N.
NASA Astrophysics Data System (ADS)
Wang, Tong-Tong; Fan, Hong-Yi
2012-03-01
Using the Weyl quantization scheme and based on the Fourier slice transformation (FST) of the Wigner operator, we construct a new expansion formula of the density operator ρ, with the expansion coefficient being the FST of ρ's classical Weyl correspondence, and the latter the Fourier transformation of ρ's quantum tomogram. The coordinate-momentum intermediate representation is used as the Radon transformation of the Wigner operator.
Analysis of Low Probability of Intercept (LPI) Radar Signals Using the Wigner Distribution
2002-09-01
INTERCEPT ( LPI ) RADAR SIGNALS USING THE WIGNER DISTRIBUTION by Jen-Yu Gau September 2002 Thesis Advisor: Phillip E. Pace Thesis Co...Master’s Thesis 4. TITLE AND SUBTITLE: Analysis of Low Probability of Intercept ( LPI ) Radar Signals Using The Wigner Distribution 6. AUTHOR (S...distribution is unlimited. 12b. DISTRIBUTION CODE 13. ABSTRACT The parameters of Low Probability of Intercept ( LPI ) radar signals are hard to identify by
Direct measurement of the wigner delay associated with the goos-Hanchen effect
Chauvat; Emile; Bretenaker; Le Floch A
2000-01-03
It is shown experimentally that the nonspecular reflection of light on an interface induces a time delay, as predicted by Wigner's scattering theory. A differential femtosecond technique is used to directly isolate this delay, associated with the Goos-Hanchen spatial shift produced by a grating near a resonant Wood anomaly. A delay of 4.4 fs is observed between TE and TM pulses, in agreement with the expected Wigner delay obtained from phase shift dispersion measurements.
Flow transitions in a 2D directional solidification model
NASA Technical Reports Server (NTRS)
Larroude, Philippe; Ouazzani, Jalil; Alexander, J. Iwan D.
1992-01-01
Flow transitions in a Two Dimensional (2D) model of crystal growth were examined using the Bridgman-Stockbarger me thod. Using a pseudo-spectral Chebyshev collocation method, the governing equations yield solutions which exhibit a symmetry breaking flow tansition and oscillatory behavior indicative of a Hopf bifurcation at higher values of Ra. The results are discussed from fluid dynamic viewpoint, and broader implications for process models are also addressed.
Thermally enhanced Wigner oscillations in two-electron 1D quantum dots.
Cavaliere, F; Ziani, N Traverso; Negro, F; Sassetti, M
2014-12-17
Motivated by a recent experiment (Pecker et al 2013 Nat. Phys. 9 576), we study the stability, with respect to thermal effects, of Friedel and Wigner density fluctuations for two electrons trapped in a one-dimensional quantum dot. Diagonalizing the system exactly, the finite-temperature average electron density is computed. While the weak and strong interaction regimes display a Friedel oscillation or a Wigner molecule state at zero temperature, which as expected smear and melt as the temperature increases, a peculiar thermal enhancement of Wigner correlations in the intermediate interaction regime is found. We demonstrate that this effect is due to the presence of two different characteristic temperature scales: T(F), dictating the smearing of Friedel oscillations, and T(W), smoothing Wigner oscillations. In the early Wigner molecule regime, for intermediate interactions, T(F) < T(W) leading to the enhancement of the visibility of Wigner oscillations. These results complement those obtained within the Luttinger liquid picture, valid for larger numbers of particles.
Structure of the novel ternary hydrides Li4Tt2D (Tt=Si and Ge).
Wu, Hui; Hartman, Michael R; Udovic, Terrence J; Rush, John J; Zhou, Wei; Bowman, Robert C; Vajo, John J
2007-02-01
The crystal structures of newly discovered Li4Ge2D and Li4Si2D ternary phases were solved by direct methods using neutron powder diffraction data. Both structures can be described using a Cmmm orthorhombic cell with all hydrogen atoms occupying Li6-octahedral interstices. The overall crystal structure and the geometry of these interstices are compared with those of other related phases, and the stabilization of this novel class of ternary hydrides is discussed.
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
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.
Wigner function and transition amplitude of three mutually coupled oscillators
NASA Astrophysics Data System (ADS)
Nassar, M. M.; Sebawe Abdalla, M.
2007-04-01
A full quantum mechanical treatment of three electromagnetic fields is considered. The proposed model consists of three different coupling parameters for which the rotating and counter-rotating terms are retained. An exact solution of the wave function in the Schrödinger picture is obtained and the connection with the coherent states wave function is given. The symmetrical ordered quasi-probability distribution function ( W-Wigner function) is calculated via the wave function in the coherent states representation. The squeezing phenomenon is also examined for both single mode and squared-amplitude, where the collapse and revival phenomena are observed. For the case in which λ3=0 and ω1=ω2=ω3 (exact resonances) we find that the late phenomenon is apparent but only after long period of the time considered. The transition amplitude between two different coherent states (a state in which all the coupling parameters are involved and a state when the coupling parameter λ3=0) is calculated. It is shown that the probability amplitude is sensitive to the variation of the mean photon numbers, and the coupling parameters as well as to the field frequencies.
Wigner distribution measurement of the spatial coherence properties of FELs
NASA Astrophysics Data System (ADS)
Mey, Tobias; Schäfer, Bernd; Mann, Klaus; Keitel, Barbara; Plönjes, Elke; Kuhlmann, Marion
2015-09-01
Free-electron lasers deliver VUV and soft x-ray pulses with the best brilliance available and a high degree of spatial coherence. Users of such facilities have high demands on phase and coherence properties of the beam, for instance when working with coherent diffractive imaging. Thus, detailed knowledge of these parameters is of great importance and provides the possibility for advanced machine studies. The Wigner distribution function (WDF) describes the entire propagation properties of an electromagnetic beam including all information on its spatial coherence. It can be reconstructed from beam profiles taken at different positions along its propagation direction. Here, we present measurements of the WDF conducted at the Free-electron laser FLASH at DESY. As a result, we derive the entire four-dimensional mutual coherence function, the coherence lengths and the global degree of coherence. Additionally, we provide an estimation of the possible error that our algorithm might produce for the derived quantities. In comparison to existing studies that characterize the photon beam of FLASH, we find significantly lower values for the global degree of coherence. This difference cannot be explained by our error estimation. We explore the possible reasons for this discrepancy and their effect on the value of the global degree of coherence.
Wigner and Huntington: the long quest for metallic hydrogen
NASA Astrophysics Data System (ADS)
Nellis, W. J.
2013-06-01
In 1935, Wigner and Huntington (WH) predicted that at a density D Met=0.62 mole H/cm3, 'very low temperatures', and a pressure greater than 25 GPa, body-centered cubic H2 would undergo an isostructural phase transition directly to H with an associated insulator-metal transition (IMT). WH also predicted an H2 structure type that might occur if the simple H2/H dissociative IMT does not exist: 'It is possible … that a layer-like lattice … is obtainable under high pressure'. In 1991, Ashcroft predicted that the 'geometric and dynamic nature of the (H-H) pairing', possibly in a layered graphite-like structure, would substantially impede achieving metallic H2. In 1996, metallic fluid H was made under dynamic compression at 0.64 mole H/cm3, 140 GPa and T/T F≪1, where T F is Fermi temperature. In 2012, a layer-like lattice, called Phase IV, was discovered above ∼220 GPa static pressure. Phase IV is insulating and possibly semi-metallic up to ∼360 GPa, above which it has been predicted to become metallic. This paper is a historical perspective - a comparison of WH's predictions with recent dynamic, static and theoretical high pressure results. WH did extremely well.
Wigner function in Liouville space: A canonical formalism
NASA Astrophysics Data System (ADS)
Royer, Antoine
1991-01-01
The Wigner-Weyl (WW) phase-space formulation of quantum mechanics is discussed within the Liouville-space formalism, where quantum operators A^ are viewed as vectors, represented by L kets ||A^>>, on which act ``superoperators'' the scalar product is <>=TrA^°B^. With every operator A^, we associate commutation and anticommutation superoperators A^- and A^+, defined by their actions on any operator B^ as A^-B^=ħ-1[A^,B^], A^+B^=1/2(AB^+BÂ^). The WW representation corresponds to the choice of a special basis in Liouville space, namely, the eigenbasis of the position and momentum anticommutation superoperators q^+ and p^+ (where [q^,p^]=iħ). These, together with the commutation superoperators q^- and p^-, form a canonical set of superoperators, [q^+,p^-]=[q^-,p^+]=i (the other commutators vanishing), as functions of which all other super- operators can be expressed. Weyl ordering is expressed as f(q^,p^)Weyl ordering=f(q^+,p^+)1^. A generalization of Ehrenfest's theorem is obtained.
Novel low Wigner energy amorphous carbon-carbon composite
NASA Astrophysics Data System (ADS)
Dasgupta, Kinshuk; Prakash, Jyoti; Tripathi, B. M.
2014-02-01
A novel amorphous carbon-carbon composite has been developed using carbon black dispersed in carbonized phenolic resin matrix in order to avoid Wigner energy problem associated with graphite. The as prepared sample showed a density of 1320 kg m-3. This has been further densified by resin impregnation and chemical vapour infiltration. The effect of processing parameters on final density (1517 kg m-3) has been investigated. This composite possesses the compressive strength of 65 Mpa, coefficient of thermal expansion of 3 × 10-6 K-1 and the specific heat of 1.2 J g-1 K-1. This novel composite was subjected to 145 MeV Ne+6 heavy ion irradiation at different doses. The highest dose was kept at 3 × 10-4 dpa. The stored energy in the composite was found to be 212 J g-1 at the highest dose of irradiation, which is much below than that of graphite. The composite remained amorphous after irradiation as confirmed by X-ray diffraction.
Wigner time delay in photodetachment of negative ions
NASA Astrophysics Data System (ADS)
Saha, S.; Deshmukh, P. C.; Jose, J.; Kkeifets, A. S.; Manson, S. T.
2016-05-01
In recent years, there has been much interest in studies on Wigner time delay in atomic photoionization using various experimental techniques and theoretical methodologies. In the present work, we report time delay in the photodetachment of negative ions using the relativistic-random-phase approximation (RRPA), which includes relativistic and important correlation effects. Time delay is obtained as energy derivative of phase of the photodetachment complex transition amplitude. We investigate the time delay in the dipole n p --> ɛd channels in the photodetachment of F- and Cl-, and in n f --> ɛg channels in the photodetachment of Tm-. In photodetachment of the negative ions, the photoelectron escapes in the field of the neutral atom and thus does not experience the nuclear Coulomb field; hence the phase is devoid of the Coulomb component. The systems chosen are well suited to examine the sensitivity of the photodetachment time delay to the centrifugal potential. The ions chosen have closed shells, and thus amenable to the RPA. Work supported by DOE, Office of Chemical Sciences, DST (India), and the Australian Research Council.
Ellis, S W; Rowland, K; Ackland, M J; Rekka, E; Simula, A P; Lennard, M S; Wolf, C R; Tucker, G T
1996-01-01
Cytochrome P-450 2D6 (CYP2D6) is an important human drug-metabolizing enzyme responsible for the oxidation of more than 30 widely used therapeutic agents. The enzymes encoded by the published genomic [Kimura, Umeno, Skoda, Meyer and Gonzalez (1989) Am. J. Hum. Genet. 45, 889-904] and cDNA [Gonzalez, Skoda, Kimura, Umeno, Zanger, Nebert, Gelboin, Hardwick and Meyer (1988) Nature 331, 442-446] sequences of CYP2D6, and presumed to represent wild-type sequences, differ at residue 374 and encode valine (CYP2D6-Val) and methionine (CYP2D6-Met) respectively. The influence of this amino acid difference on cytochrome P-450 expression, ligand binding, catalysis and stereoselective oxidation of metoprolol was investigated by the heterologous expression of the corresponding cDNAs in the yeast Saccharomyces cerevisiae. The level of expression of apo- and holo-protein was similar with each form of CYP2D6 cDNA, and the binding affinities of a series of ligands to CYP2D6-Val and CYP2D6-Met were identical. The enantioselective O-demethylation and alpha-hydroxylation of metoprolol were also similar with each form of CYP2D6, O-demethylation being R-(+)- enantioselective (CYP2D6-Val: R/S, 1.6; CYP2D6-Met: R/S, 1.4), whereas alpha-hydroxylation showed a preference for S-(-)-metoprolol (CYP2D6-Val: R/S, 0.7; CYP2D6-Met: R/S, 0.8). However, although the favoured regiomer overall was O-demethylmetoprolol (ODM), the regioselectivity for O-demethylation of each metoprolol enantiomer was significantly greater for CYP2D6-Val [R-(+)-: ODM/alpha-hydroxymetoprolol (alpha OH), 5.9; S-(-)-: ODM/alpha OH, 2.5) than that observed for CYP2D6-Met [R-(+)-: ODM/alpha OH, 2.2; S-(-)-: ODM/alpha OH, 1.4]. The stereoselective properties of CYP2D6-Val were consistent with those observed for CYP2D6 in human liver microsomes. The difference in the stereoselective properties of CYP2D6-Val and CYP2D6-Met were rationalized with respect to a homology model of the active site of CYP2D6 based on an alignment with
The strength of heterogeneous volcanic rocks: A 2D approximation
NASA Astrophysics Data System (ADS)
Heap, Michael J.; Wadsworth, Fabian B.; Xu, Tao; Chen, Chong-feng; Tang, Chun'an
2016-06-01
Volcanic rocks typically contain heterogeneities in the form of crystals and pores. We investigate here the influence of such heterogeneity on the strength of volcanic rocks using an elastic damage mechanics model in which we numerically deform two-dimensional samples comprising low-strength elements representing crystals and zero-strength elements representing pores. These circular elements are stochastically generated so that there is no overlap in a medium representing the groundmass. Our modelling indicates that increasing the fraction of pores and/or crystals reduces the strength of volcanic rocks, and that increasing the pore fraction results in larger strength reductions than increasing the crystal fraction. The model also highlights an important weakening role for pore diameter, but finds that crystal diameter has a less significant influence for strength. To account for heterogeneity (pores and crystals), we propose an effective medium approach where we define an effective pore fraction ϕp‧ = Vp/(Vp + Vg) where Vp and Vg are the pore and groundmass fractions, respectively. Highly heterogeneous samples (containing high pore and/or crystal fractions) will therefore have high values of ϕp‧, and vice-versa. When we express our numerical samples (more than 200 simulations spanning a wide range of crystal and pore fractions) in terms of ϕp‧, we find that their strengths can be described by a single curve for a given pore diameter. To provide a predictive tool for the strength of heterogeneous volcanic rocks, we propose a modified version of 2D solution for the Sammis and Ashby (1986) pore-emanating crack model, a micromechanical model designed to estimate strength using microstructural attributes such as porosity, pore radius, and fracture toughness. The model, reformulated to include ϕp‧ (and therefore crystal fraction), captures the strength curves for our numerical simulations over a sample heterogeneity range relevant to volcanic systems. We find
2D Melting of Plasma Crystals: Equilibrium and Nonequilibrium Regimes
Nosenko, V.; Zhdanov, S. K.; Ivlev, A. V.; Knapek, C. A.; Morfill, G. E.
2009-07-03
Comprehensive experimental investigations of melting in two-dimensional complex plasmas were carried out. Different experiments were performed in steady and unsteady heating regimes. We demonstrate an Arrhenius dependence of the defect concentration on the kinetic temperature in steady-state experiments, and show the evidence of metastable quenching in unsteady experiments, where the defect concentration follows a power-law temperature scaling. In all experiments, independent indicators suggest a grain-boundary-induced melting scenario.
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.
Rheological Properties of Quasi-2D Fluids in Microgravity
NASA Technical Reports Server (NTRS)
Stannarius, Ralf; Trittel, Torsten; Eremin, Alexey; Harth, Kirsten; Clark, Noel; Maclennan, Joseph; Glaser, Matthew; Park, Cheol; Hall, Nancy; Tin, Padetha
2015-01-01
In recent years, research on complex fluids and fluids in restricted geometries has attracted much attention in the scientific community. This can be attributed not only to the development of novel materials based on complex fluids but also to a variety of important physical phenomena which have barely been explored. One example is the behavior of membranes and thin fluid films, which can be described by two-dimensional (2D) rheology behavior that is quite different from 3D fluids. In this study, we have investigated the rheological properties of freely suspended films of a thermotropic liquid crystal in microgravity experiments. This model system mimics isotropic and anisotropic quasi 2D fluids [46]. We use inkjet printing technology to dispense small droplets (inclusions) onto the film surface. The motion of these inclusions provides information on the rheological properties of the films and allows the study of a variety of flow instabilities. Flat films have been investigated on a sub-orbital rocket flight and curved films (bubbles) have been studied in the ISS project OASIS. Microgravity is essential when the films are curved in order to avoid sedimentation. The experiments yield the mobility of the droplets in the films as well as the mutual mobility of pairs of particles. Experimental results will be presented for 2D-isotropic (smectic-A) and 2D-nematic (smectic-C) phases.
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.
Two elementary proofs of the Wigner theorem on symmetry in quantum mechanics
NASA Astrophysics Data System (ADS)
Simon, R.; Mukunda, N.; Chaturvedi, S.; Srinivasan, V.
2008-11-01
In quantum theory, symmetry has to be defined necessarily in terms of the family of unit rays, the state space. The theorem of Wigner asserts that a symmetry so defined at the level of rays can always be lifted into a linear unitary or an antilinear antiunitary operator acting on the underlying Hilbert space. We present two proofs of this theorem which are both elementary and economical. Central to our proofs is the recognition that a given Wigner symmetry can, by post-multiplication by a unitary symmetry, be taken into either the identity or complex conjugation. Our analysis often focuses on the behaviour of certain two-dimensional subspaces of the Hilbert space under the action of a given Wigner symmetry, but the relevance of this behaviour to the larger picture of the whole Hilbert space is made transparent at every stage.
Magnetism of one-dimensional Wigner lattices and its impact on charge order
Daghofer, Maria; Noack, R. M.; Horsch, P.
2008-01-01
The magnetic phase diagram of the quarter-filled generalized Wigner lattice with nearest-neighbor and next-nearest-neighbor hoppings, t1 and t2, is explored. We find a region at negative t2 with fully saturated ferromagnetic ground states that we attribute to kinetic exchange. Such interaction disfavors antiferromag- netism at t2 0 and stems from virtual excitations across the charge gap of the Wigner lattice, which is much smaller than the Mott-Hubbard gap U. Remarkably, we find a strong dependence of the charge structure factor on magnetism even in the limit U , in contrast to the expectation that charge ordering in the Wigner lattice regime should be well described by spinless fermions. Our results, obtained using the density-matrix renormalization group and exact diagonalization, can be transparently explained by means of an effective low-energy Hamiltonian.
Direct measurement of the biphoton Wigner function through two-photon interference
Douce, T.; Eckstein, A.; Walborn, S. P.; Khoury, A. Z.; Ducci, S.; Keller, A.; Coudreau, T.; Milman, P.
2013-01-01
The Hong-Ou-Mandel (HOM) experiment was a benchmark in quantum optics, evidencing the non–classical nature of photon pairs, later generalized to quantum systems with either bosonic or fermionic statistics. We show that a simple modification in the well-known and widely used HOM experiment provides the direct measurement of the Wigner function. We apply our results to one of the most reliable quantum systems, consisting of biphotons generated by parametric down conversion. A consequence of our results is that a negative value of the Wigner function is a sufficient condition for non-gaussian entanglement between two photons. In the general case, the Wigner function provides all the required information to infer entanglement using well known necessary and sufficient criteria. The present work offers a new vision of the HOM experiment that further develops its possibilities to realize fundamental tests of quantum mechanics using simple optical set-ups. PMID:24346262
Dynamic photorefractive self-amplified angular-multiplex 2-D optical beam-array generation
NASA Astrophysics Data System (ADS)
Zhou, Shaomin; Yeh, Pochi; Liu, Hua-Kuang
1993-01-01
A real-time 2-D angular-multiplex beam-array holographic storage and reconstruction technique using electrically-addressed spatial light modulators(E-SLM's) and photorefractive crystals is described. Using a liquid crystal television (LCTV) spatial light modulator (SLM) for beam steering and lithium niobate photorefractive crystal for holographic recording, experimental results of generating large and complicated arrays of laser beams with high diffraction efficiency and good uniformity are presented.
Booming Development of Group IV-VI Semiconductors: Fresh Blood of 2D Family.
Zhou, Xing; Zhang, Qi; Gan, Lin; Li, Huiqiao; Xiong, Jie; Zhai, Tianyou
2016-12-01
As an important component of 2D layered materials (2DLMs), the 2D group IV metal chalcogenides (GIVMCs) have drawn much attention recently due to their earth-abundant, low-cost, and environmentally friendly characteristics, thus catering well to the sustainable electronics and optoelectronics applications. In this instructive review, the booming research advancements of 2D GIVMCs in the last few years have been presented. First, the unique crystal and electronic structures are introduced, suggesting novel physical properties. Then the various methods adopted for synthesis of 2D GIVMCs are summarized such as mechanical exfoliation, solvothermal method, and vapor deposition. Furthermore, the review focuses on the applications in field effect transistors and photodetectors based on 2D GIVMCs, and extends to flexible devices. Additionally, the 2D GIVMCs based ternary alloys and heterostructures have also been presented, as well as the applications in electronics and optoelectronics. Finally, the conclusion and outlook have also been presented in the end of the review.
Efficient screening of 2D molecular polymorphs at the solution-solid interface
NASA Astrophysics Data System (ADS)
Lee, Shern-Long; Adisoejoso, Jinne; Fang, Yuan; Tahara, Kazukuni; Tobe, Yoshito; Mali, Kunal S.; de Feyter, Steven
2015-03-01
Formation of multiple polymorphs during two-dimensional (2D) crystallization of organic molecules is more of a routine occurrence than rarity. Although such diverse crystalline structures provide exciting possibilities for studying crystal engineering in 2D, predicting the occurrence of polymorphs for a given building block is often non-trivial. Moreover, there is scarcity of methods that can experimentally verify the presence of such crystalline polymorphs in a straightforward fashion. Here we demonstrate a relatively simple experimental approach for screening of 2D polymorphs formed at the solution-solid interface. The strategy involves use of solution flow produced by contacting a piece of tissue paper to the sample to generate a lateral density gradient along the substrate surface. In situ generation of such gradient allows rapid discovery and nanoscale separation of multiple 2D polymorphs in a single experiment. The concept is demonstrated using three structurally different building blocks that differ in terms of intermolecular interactions responsible for 2D crystal formation. The method described here represents a powerful tool for efficient screening of 2D polymorphs formed at the solution-solid interface.Formation of multiple polymorphs during two-dimensional (2D) crystallization of organic molecules is more of a routine occurrence than rarity. Although such diverse crystalline structures provide exciting possibilities for studying crystal engineering in 2D, predicting the occurrence of polymorphs for a given building block is often non-trivial. Moreover, there is scarcity of methods that can experimentally verify the presence of such crystalline polymorphs in a straightforward fashion. Here we demonstrate a relatively simple experimental approach for screening of 2D polymorphs formed at the solution-solid interface. The strategy involves use of solution flow produced by contacting a piece of tissue paper to the sample to generate a lateral density
Weak values of a quantum observable and the cross-Wigner distribution
de Gosson, Maurice A.; de Gosson, Serge M.
2012-01-01
We study the weak values of a quantum observable from the point of view of the Wigner formalism. The main actor here is the cross-Wigner transform of two functions, which is in disguise the cross-ambiguity function familiar from radar theory and time-frequency analysis. It allows us to express weak values using a complex probability distribution. We suggest that our approach seems to confirm that the weak value of an observable is, as conjectured by several authors, due to the interference of two wavefunctions, one coming from the past, and the other from the future. PMID:22298941
Phase-space analysis of charged and optical beam transport: Wigner rotation angle
NASA Technical Reports Server (NTRS)
Dattoli, G.; Torre, Amalia
1994-01-01
The possibility of using the phase space formalism to establish a correspondence between the dynamical behavior of squeezed states and optical or charged beams, propagating through linear systems, has received a great deal of attention during the last years. In this connection, it has been indicated how optical experiments may be conceived to measure the Wigner rotation angle. In this paper we address the topic within the context of the paraxial propagation of optical or charged beams and suggest a possible experiment for measuring the Wigner angle using an electron beam passing through quadrupoles and drift sections. The analogous optical system is also discussed.
NASA Technical Reports Server (NTRS)
Han, D.; Kim, Y. S.; Noz, Marilyn E.
1989-01-01
It is possible to calculate expectation values and transition probabilities from the Wigner phase-space distribution function. Based on the canonical transformation properties of the Wigner function, an algorithm is developed for calculating these quantities in quantum optics for coherent and squeezed states. It is shown that the expectation value of a dynamical variable can be written in terms of its vacuum expectation value of the canonically transformed variable. Parallel-axis theorems are established for the photon number and its variant. It is also shown that the transition probability between two squeezed states can be reduced to that of the transition from one squeezed state to vacuum.
Eugene P. Wigner's Visionary Contributions to Generations-I through IV Fission Reactors
NASA Astrophysics Data System (ADS)
Carré, Frank
2014-09-01
Among Europe's greatest scientists who fled to Britain and America in the 1930s, Eugene P. Wigner made instrumental advances in reactor physics, reactor design and technology, and spent nuclear fuel processing for both purposes of developing atomic weapons during world-war II and nuclear power afterwards. Wigner who had training in chemical engineering and self-education in physics first gained recognition for his remarkable articles and books on applications of Group theory to Quantum mechanics, Solid state physics and other topics that opened new branches of Physics.
Wigner expansions for partition functions of nonrelativistic and relativistic oscillator systems
NASA Technical Reports Server (NTRS)
Zylka, Christian; Vojta, Guenter
1993-01-01
The equilibrium quantum statistics of various anharmonic oscillator systems including relativistic systems is considered within the Wigner phase space formalism. For this purpose the Wigner series expansion for the partition function is generalized to include relativistic corrections. The new series for partition functions and all thermodynamic potentials yield quantum corrections in terms of powers of h(sup 2) and relativistic corrections given by Kelvin functions (modified Hankel functions) K(sub nu)(mc(sup 2)/kT). As applications, the symmetric Toda oscillator, isotonic and singular anharmonic oscillators, and hindered rotators, i.e. oscillators with cosine potential, are addressed.
Hydrodynamic limit of Wigner-Poisson kinetic theory: Revisited
NASA Astrophysics Data System (ADS)
Akbari-Moghanjoughi, M.
2015-02-01
In this paper, we revisit the hydrodynamic limit of the Langmuir wave dispersion relation based on the Wigner-Poisson model in connection with that obtained directly from the original Lindhard dielectric function based on the random-phase-approximation. It is observed that the (fourth-order) expansion of the exact Lindhard dielectric constant correctly reduces to the hydrodynamic dispersion relation with an additional term of fourth-order, beside that caused by the quantum diffraction effect. It is also revealed that the generalized Lindhard dielectric theory accounts for the recently discovered Shukla-Eliasson attractive potential (SEAP). However, the expansion of the exact Lindhard static dielectric function leads to a k4 term of different magnitude than that obtained from the linearized quantum hydrodynamics model. It is shown that a correction factor of 1/9 should be included in the term arising from the quantum Bohm potential of the momentum balance equation in fluid model in order for a correct plasma dielectric response treatment. Finally, it is observed that the long-range oscillatory screening potential (Friedel oscillations) of type cos ( 2 k F r ) / r 3 , which is a consequence of the divergence of the dielectric function at point k = 2kF in a quantum plasma, arises due to the finiteness of the Fermi-wavenumber and is smeared out in the limit of very high electron number-densities, typical of white dwarfs and neutron stars. In the very low electron number-density regime, typical of semiconductors and metals, where the Friedel oscillation wavelength becomes much larger compared to the interparticle distances, the SEAP appears with a much deeper potential valley. It is remarked that the fourth-order approximate Lindhard dielectric constant approaches that of the linearized quantum hydrodynamic in the limit if very high electron number-density. By evaluation of the imaginary part of the Lindhard dielectric function, it is shown that the Landau
Quantum Oscillations in an Interfacial 2D Electron Gas.
Zhang, Bingop; Lu, Ping; Liu, Henan; Lin, Jiao; Ye, Zhenyu; Jaime, Marcelo; Balakirev, Fedor F.; Yuan, Huiqiu; Wu, Huizhen; Pan, Wei; Zhang, Yong
2016-01-01
Recently, it has been predicted that topological crystalline insulators (TCIs) may exist in SnTe and Pb_{1-x}Sn_{x}Te thin films [1]. To date, most studies on TCIs were carried out either in bulk crystals or thin films, and no research activity has been explored in heterostructures. We present here the results on electronic transport properties of the 2D electron gas (2DEG) realized at the interfaces of PbTe/ CdTe (111) heterostructures. Evidence of topological state in this interfacial 2DEG was observed.
Effects of Surface Ligand Density on Lipid-Monolayer-mediated 2D Assembly of Proteins
Fukuto, M.; Wang, S; Lohr, M; Kewalramani, S; Yang, L
2010-01-01
The two-dimensional (2D) assembly of the protein streptavidin on a biotin-bearing lipid monolayer was studied as a function of the surface density of biotin, a protein-binding ligand, by means of in situ X-ray scattering and optical Brewster angle microscopy measurements at the liquid-vapor interface. Although this model system has been studied extensively, the relationship between the surface biotin density and the adsorption, 2D phase behavior, and binding state of streptavidin has yet to be determined quantitatively. The observed equilibrium phase behavior provides direct structural evidence that the 2D crystallization of the lipid-bound streptavidin occurs as a density-driven first-order phase transition. The minimum biotin density required for the 2D crystallization of streptavidin is found to be remarkably close to the density of the ligand-binding sites in the protein crystal. Moreover, both above and below this transition, the observed biotin-density dependence of protein adsorption is well described by the binding of biotin-bearing lipids at both of the two available sites per streptavidin molecule. These results imply that even in the low-density noncrystalline phase, the bound proteins share a common, fixed orientation relative to the surface normal, and that the 2D crystallization occurs when the lateral protein density reaches 50-70% of the 2D crystal density. This study demonstrates that in addition to a well-defined molecular orientation, high lateral packing density is essential to the 2D crystallization of proteins.
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.
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.
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.
Special functions associated with SU(3) Wigner-Clebsch-Gordan coefficients
Louck, J.D.; Biedenharn, L.C.
1990-01-01
The Wigner-Clebsch-Gordan (WCG) coefficients of the unitary groups are a rich source of multivariable special functions. The general algebraic setting of these coefficients is reviewed and several special functions associated with the SU(3) WCG coefficients defined and their properties presented. 29 refs.
Three-Nucleon Bound States and the Wigner-SU(4) Limit
NASA Astrophysics Data System (ADS)
Vanasse, Jared; Phillips, Daniel R.
2017-03-01
We examine the extent to which the properties of three-nucleon bound states are well-reproduced in the limit that nuclear forces satisfy Wigner's SU(4) (spin-isospin) symmetry. To do this we compute the charge radii up to next-to-leading order (NLO) in an effective field theory that is an expansion in powers of R/ a, with R the range of the nuclear force and a the nucleon-nucleon (N N) scattering lengths. In the Wigner-SU(4) limit, the triton and helium-3 point charge radii are equal. At NLO in the range expansion both are 1.66 fm. Adding the first-order corrections due to the breaking of Wigner symmetry in the N N scattering lengths gives a ^3{H} point charge radius of 1.58 fm, which is remarkably close to the experimental number, 1.5978± 0.040 fm (Angeli and Marinova in At Data Nucl Data Tables 99:69-95, 2013). For the ^3{He} point charge radius we find 1.70 fm, about 4% away from the experimental value of 1.77527± 0.0054 fm (Angeli and Marinova 2013). We also examine the Faddeev components that enter the tri-nucleon wave function and find that an expansion of them in powers of the symmetry-breaking parameter converges rapidly. Wigner's SU(4) symmetry is thus a useful starting point for understanding tri-nucleon bound-state properties.
1983-08-01
significant new detailed information on the sonar signal. Originally invented by Wigner and Szilard [i] for appli- cations in quantum statistical...Selwyn Mr. Leo Young Technical Director OUSDRE (RAAT) Office of Naval Technology The Pentagon, Room 3DI067 - 800 N. Quincy Street Washington, D.C
Studies of Wigner-Weyl solution and external magnetic field in an NJL model
NASA Astrophysics Data System (ADS)
Wang, Qing-Wu; Cui, Zhu-Fang; Zong, Hong-Shi
2016-11-01
In this paper, we explore the dynamical chiral symmetry breaking by employing a two-flavor Nambu-Jona-Lasinio (NJL) model with constant external magnetic field. After changing the coupling strength of the NJL model, we found that the Wigner-Weyl solution and Nambu-Goldstone solution of the gap equation could coexist. Even though the gap equation only has Nambu-Goldstone solution at zero temperature, the Wigner-Weyl solution may appear when magnetic field strength and temperature are nonzero. For the Nambu-Goldstone solution, magnetic field and temperature have opposite impact on the chiral dynamical mass. In the chiral limit, the magnetic field dependence of chiral dynamical mass reveals the existence of inverse magnetic catalysis for the Wigner-Weyl solution. However, the two phases have different responses to the magnetic field and temperature in the chiral limit but the same beyond chiral limit. Furthermore, the order of the transition from the Nambu-Goldstone phase to Wigner-Weyl phase depends on the choice of model parameters. We have also calculated the susceptibilities of dynamical mass with respect to the temperature.
Wigner law for matrices with dependent entries—a perturbative approach
NASA Astrophysics Data System (ADS)
Krajewski, T.; Tanasa, A.; Vu, D. L.
2017-04-01
We show that Wigner semi-circle law holds for Hermitian matrices with dependent entries, provided the deviation of the cumulants from the normalised Gaussian case obeys a simple power law bound in the size of the matrix. To establish this result, we use replicas interpreted as a zero-dimensional quantum field theoretical model whose effective potential obey a renormalisation group equation.
Streaking and Wigner time delays in photoemission from atoms and surfaces
Zhang, C.-H.; Thumm, U.
2011-09-15
Streaked photoemission metrology allows the observation of an apparent relative time delay between the detection of photoelectrons from different initial electronic states. This relative delay is obtained by recording the photoelectron yield as a function of the delay between an ionizing ultrashort extended ultraviolet pulse and a streaking infrared (IR) pulse. Theoretically, photoemission delays can be defined based on (i) the phase shift the photoelectron wave function accumulates during the release and propagation of the photoelectron (''Wigner delay'') and, alternatively, (ii) the streaking trace in the calculated photoemission spectrum (''streaking delay''). We investigate the relation between Wigner and streaking delays in the photoemission from atomic and solid-surface targets. For solid targets and assuming a vanishing IR skin depth, both Wigner and streaking delays can be interpreted as an average propagation time needed by photoelectrons to reach the surface, while the two delays differ for nonvanishing skin depths. For atomic targets, the difference between Wigner and streaking delays depends on the range of the ionic potential.
ERIC Educational Resources Information Center
Gelfert, Axel
2014-01-01
In his influential 1960 paper "The Unreasonable Effectiveness of Mathematics in the Natural Sciences", Eugene P. Wigner raises the question of why something that was developed without concern for empirical facts--mathematics--should turn out to be so powerful in explaining facts about the natural world. Recent philosophy of science has…
ERIC Educational Resources Information Center
O'Donnell, Kane; Visser, Matt
2011-01-01
The purpose of this paper is to provide an elementary introduction to the qualitative and quantitative results of velocity combination in special relativity, including the Wigner rotation and Thomas precession. We utilize only the most familiar tools of special relativity, in arguments presented at three differing levels: (1) utterly elementary,…
A variational principle in Wigner phase-space with applications to statistical mechanics
NASA Astrophysics Data System (ADS)
Poulsen, Jens Aage
2011-01-01
We consider the Dirac-Frenkel variational principle in Wigner phase-space and apply it to the Wigner-Liouville equation for both imaginary and real time dynamical problems. The variational principle allows us to deduce the optimal time-evolution of the parameter-dependent Wigner distribution. It is shown that the variational principle can be formulated alternatively as a "principle of least action." Several low-dimensional problems are considered. In imaginary time, high-temperature classical distributions are "cooled" to arrive at low-temperature quantum Wigner distributions whereas in real time, the coherent dynamics of a particle in a double well is considered. Especially appealing is the relative ease at which Feynman's path integral centroid variable can be incorporated as a variational parameter. This is done by splitting the high-temperature Boltzmann distribution into exact local centroid constrained distributions, which are thereafter cooled using the variational principle. The local distributions are sampled by Metropolis Monte Carlo by performing a random walk in the centroid variable. The combination of a Monte Carlo and a variational procedure enables the study of quantum effects in low-temperature many-body systems, via a method that can be systematically improved.
1993-09-01
frequency, which when used as an input to an artificial neural network will aide in the detection of location and severity of machinery faults...Research is presented where the union of an artificial neural network , utilizing the highly successful backpropagation paradigm, and the pseudo wigner
Landau levels in 2D materials using Wannier Hamiltonians obtained by first principles
NASA Astrophysics Data System (ADS)
Lado, J. L.; Fernández-Rossier, J.
2016-09-01
We present a method to calculate the Landau levels and the corresponding edge states of two dimensional (2D) crystals using as a starting point their electronic structure as obtained from standard density functional theory (DFT). The DFT Hamiltonian is represented in the basis of maximally localized Wannier functions. This defines a tight-binding Hamiltonian for the bulk that can be used to describe other structures, such as ribbons, provided that atomic scale details of the edges are ignored. The effect of the orbital magnetic field is described using the Peierls substitution in the hopping matrix elements. Implementing this approach in a ribbon geometry, we obtain both the Landau levels and the dispersive edge states for a series of 2D crystals, including graphene, Boron Nitride, MoS2, Black Phosphorous, Indium Selenide and MoO3. Our procedure can readily be used in any other 2D crystal, and provides an alternative to effective mass descriptions.
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.
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.
NASA Astrophysics Data System (ADS)
Lane, C. J. L.; Dunhill, A. K.; Drinkwater, B. W.; Wilcox, P. D.
2011-06-01
Single crystal components are used widely in the gas-turbine industry. However, these components are elastically anisotropic which causes difficulties when performing NDE inspections with ultrasound. Recently an ultrasonic algorithm for a 2D array has been corrected to perform the reliable volumetric inspection of single crystals. For the algorithm to be implemented the crystallographic orientation of the components must be known. This paper, therefore, develops and reviews crystallographic orientation methods using 2D ultrasonic arrays. The methods under examination are based on the anisotropic propagation of surface and bulk waves and an image-based orientation method is also considered.
Wigner Crystals of Na+ ions at the Surface of a Silica Hydrosol
Tikhonov,A.
2007-01-01
I used x-ray grazing incidence diffraction to measure the spatial correlations between sodium ions adsorbed with Bjerrum's density at the surface of a monodispersed 22-nm-particle colloidal silica solution stabilized by NaOH with a total bulk concentration mol/L. My findings show that the surface compact layer is in a two-dimensional crystalline state (symmetry p2), with four ions forming the unit cell and a {approx}30 Angstrom translational correlation length between sodium ions.
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.
Macroscopic Behavior of Nematics with D2d Symmetry
NASA Astrophysics Data System (ADS)
Pleiner, Harald; Brand, Helmut R.
2010-03-01
We discuss the symmetry properties and the macroscopic behavior of a nematic liquid crystal phase with D2d symmetry. Such a phase is a prime candidate for nematic phases made from banana-shaped molecules where the usual quadrupolar order coexists with octupolar (tetrahedratic) order. The resulting nematic phase is non-polar. While this phase could resemble the classic D∞h nematic in the polarizing microscope, it has many static as well as reversible and irreversible properties unknown to non-polar nematics without octupolar order. In particular, there is a linear gradient term in the free energy that selects parity leading to ambidextrously helical ground states when the molecules are achiral. In addition, there are static and irreversible coupling terms of a type only met otherwise in macroscopically chiral liquid crystals, e.g. the ambidextrous analogues of Lehmann-type effects known from cholesteric liquid crystals. Finally, we discuss certain nonlinear aspects of the dynamics related to the non-commutativity of three-dimensional finite rotations as well as other structural nonlinear hydrodynamic effects.
NASA Astrophysics Data System (ADS)
Schäfer, Bernd; Mey, Tobias; Mann, Klaus; Keitel, Barbara; Kreis, Svea; Kuhlmann, Marion; Plönjes, Elke; Tiedtke, Kai
2013-05-01
Beam parameters of the free-electron laser FLASH @13.5 nm in two different operation modes were determined from beam profile measurements and subsequent reconstruction of the Wigner distribution function behind the ellipsoidal focusing mirror at beamline BL2. 40 two-dimensional single pulse intensity distributions were recorded at each of 65 axial positions around the waist of the FEL beam with a magnifying EUV sensitized CCD camera. From these beam profile data the Wigner distribution function based on different levels of averaging could be reconstructed by an inverse Radon transform. For separable beams this yields the complete Wigner distribution, and for beams with zero twist the information is still sufficient for wavefront determination and beam propagation through stigmatic systems. The obtained results are compared to wavefront reconstructions based on the transport of intensity equation. A future setup for Wigner distribution measurements of general beams is discussed.
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.
Wang, Zenghui; Feng, Philip X.-L.
2016-01-01
Atomic layer crystals are emerging building blocks for enabling new two-dimensional (2D) nanomechanical systems, whose motions can be coupled to other attractive physical properties in such 2D systems. Optical interferometry has been very effective in reading out the infinitesimal motions of these 2D structures and spatially resolving different modes. To quantitatively understand the detection efficiency and its dependence on the device parameters and interferometric conditions, here we present a systematic study of the intrinsic motion responsivity in 2D nanomechanical systems using a Fresnel-law-based model. We find that in monolayer to 14-layer structures, MoS2 offers the highest responsivity among graphene, h-BN, and MoS2 devices and for the three commonly used visible laser wavelengths (633, 532, and 405 nm). We also find that the vacuum gap resulting from the widely used 300 nm-oxide substrate in making 2D devices, fortunately, leads to close-to-optimal responsivity for a wide range of 2D flakes. Our results elucidate and graphically visualize the dependence of motion transduction responsivity upon 2D material type and number of layers, vacuum gap, oxide thickness, and detecting wavelength, thus providing design guidelines for constructing 2D nanomechanical systems with optimal optical motion readout. PMID:27464908
NASA Astrophysics Data System (ADS)
Wang, Zenghui; Feng, Philip X.-L.
2016-07-01
Atomic layer crystals are emerging building blocks for enabling new two-dimensional (2D) nanomechanical systems, whose motions can be coupled to other attractive physical properties in such 2D systems. Optical interferometry has been very effective in reading out the infinitesimal motions of these 2D structures and spatially resolving different modes. To quantitatively understand the detection efficiency and its dependence on the device parameters and interferometric conditions, here we present a systematic study of the intrinsic motion responsivity in 2D nanomechanical systems using a Fresnel-law-based model. We find that in monolayer to 14-layer structures, MoS2 offers the highest responsivity among graphene, h-BN, and MoS2 devices and for the three commonly used visible laser wavelengths (633, 532, and 405 nm). We also find that the vacuum gap resulting from the widely used 300 nm-oxide substrate in making 2D devices, fortunately, leads to close-to-optimal responsivity for a wide range of 2D flakes. Our results elucidate and graphically visualize the dependence of motion transduction responsivity upon 2D material type and number of layers, vacuum gap, oxide thickness, and detecting wavelength, thus providing design guidelines for constructing 2D nanomechanical systems with optimal optical motion readout.
Wang, Zenghui; Feng, Philip X-L
2016-07-28
Atomic layer crystals are emerging building blocks for enabling new two-dimensional (2D) nanomechanical systems, whose motions can be coupled to other attractive physical properties in such 2D systems. Optical interferometry has been very effective in reading out the infinitesimal motions of these 2D structures and spatially resolving different modes. To quantitatively understand the detection efficiency and its dependence on the device parameters and interferometric conditions, here we present a systematic study of the intrinsic motion responsivity in 2D nanomechanical systems using a Fresnel-law-based model. We find that in monolayer to 14-layer structures, MoS2 offers the highest responsivity among graphene, h-BN, and MoS2 devices and for the three commonly used visible laser wavelengths (633, 532, and 405 nm). We also find that the vacuum gap resulting from the widely used 300 nm-oxide substrate in making 2D devices, fortunately, leads to close-to-optimal responsivity for a wide range of 2D flakes. Our results elucidate and graphically visualize the dependence of motion transduction responsivity upon 2D material type and number of layers, vacuum gap, oxide thickness, and detecting wavelength, thus providing design guidelines for constructing 2D nanomechanical systems with optimal optical motion readout.
Maple procedures for the coupling of angular momenta. IX. Wigner D-functions and rotation matrices
NASA Astrophysics Data System (ADS)
Pagaran, J.; Fritzsche, S.; Gaigalas, G.
2006-04-01
The Wigner D-functions, Dpqj(α,β,γ), are known for their frequent use in quantum mechanics. Defined as the matrix elements of the rotation operator Rˆ(α,β,γ) in R and parametrized in terms of the three Euler angles α, β, and γ, these functions arise not only in the transformation of tensor components under the rotation of the coordinates, but also as the eigenfunctions of the spherical top. In practice, however, the use of the Wigner D-functions is not always that simple, in particular, if expressions in terms of these and other functions from the theory of angular momentum need to be simplified before some computations can be carried out in detail. To facilitate the manipulation of such Racah expressions, here we present an extension to the RACAH program [S. Fritzsche, Comput. Phys. Comm. 103 (1997) 51] in which the properties and the algebraic rules of the Wigner D-functions and reduced rotation matrices are implemented. Care has been taken to combine the standard knowledge about the rotation matrices with the previously implemented rules for the Clebsch-Gordan coefficients, Wigner n-j symbols, and the spherical harmonics. Moreover, the application of the program has been illustrated below by means of three examples. Program summaryTitle of program:RACAH Catalogue identifier:ADFv_9_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADFv_9_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Catalogue identifier of previous version: ADFW, ADHW, title RACAH Journal reference of previous version(s): S. Fritzsche, Comput. Phys. Comm. 103 (1997) 51; S. Fritzsche, S. Varga, D. Geschke, B. Fricke, Comput. Phys. Comm. 111 (1998) 167; S. Fritzsche, T. Inghoff, M. Tomaselli, Comput. Phys. Comm. 153 (2003) 424. Does the new version supersede the previous one: Yes, in addition to the spherical harmonics and recoupling coefficients, the program now supports also the occurrence of the Wigner rotation matrices in the algebraic
NASA Astrophysics Data System (ADS)
Lacava, C.; Carrol, L.; Bozzola, A.; Marchetti, R.; Minzioni, P.; Cristiani, I.; Fournier, M.; Bernabe, S.; Gerace, D.; Andreani, L. C.
2016-03-01
We present the characterization of Silicon-on-insulator (SOI) photonic-crystal based 2D grating-couplers (2D-GCs) fabricated by CEA-Leti in the frame of the FP7 Fabulous project, which is dedicated to the realization of devices and systems for low-cost and high-performance passives-optical-networks. On the analyzed samples different test structures are present, including 2D-GC connected to another 2D-GC by different waveguides (in a Mach-Zehnder like configuration), and 2D-GC connected to two separate 2D-GCs, so as to allow a complete assessment of different parameters. Measurements were carried out using a tunable laser source operating in the extended telecom bandwidth and a fiber-based polarization controlling system at the input of device-under-test. The measured data yielded an overall fiber-to-fiber loss of 7.5 dB for the structure composed by an input 2D-GC connected to two identical 2D-GCs. This value was obtained at the peak wavelength of the grating, and the 3-dB bandwidth of the 2D-GC was assessed to be 43 nm. Assuming that the waveguide losses are negligible, so as to make a worst-case analysis, the coupling efficiency of the single 2D-GC results to be equal to -3.75 dB, constituting, to the best of our knowledge, the lowest value ever reported for a fully CMOS compatible 2D-GC. It is worth noting that both the obtained values are in good agreement with those expected by the numerical simulations performed using full 3D analysis by Lumerical FDTD-solutions.
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
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.
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.
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.
Poincaré covariant pseudoscalar and scalar meson spectroscopy in Wigner-Weyl phase
NASA Astrophysics Data System (ADS)
Hilger, T.
2016-03-01
The coupled quark Dyson-Schwinger and meson Bethe-Salpeter equations in rainbow-ladder truncation for spin-0 mesons are solved in the Wigner-Weyl phase in the chiral limit and beyond, retaining only the ultraviolet finite terms of the phenomenologically most successful Maris-Tandy interaction. This allows one to reveal and discuss the scalar and pseudoscalar meson masses in a chirally symmetric setting without additional medium effects. Independent of the current-quark mass, the found solutions are spacelike, i.e., have negative squared masses. The current-quark mass dependence of meson masses, leptonic decay constants and chiral condensate are illustrated in the Wigner-Weyl phase.
High-precision evaluation of Wigner's d matrix by exact diagonalization.
Feng, X M; Wang, P; Yang, W; Jin, G R
2015-10-01
The precise calculations of Wigner's d matrix are important in various research fields. Due to the presence of large numbers, direct calculations of the matrix using Wigner's formula suffer from a loss of precision. We present a simple method to avoid this problem by expanding the d matrix into a complex Fourier series and calculate the Fourier coefficients by exactly diagonalizing the angular momentum operator J(y) in the eigenbasis of J(z). This method allows us to compute the d matrix and its various derivatives for spins up to a few thousand. The precision of the d matrix from our method is about 10(-14) for spins up to 100.
NASA Astrophysics Data System (ADS)
Hatke, A. T.; Liu, Yang; Engel, L. W.; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.; Shayegan, M.
2017-01-01
We have studied the microwave spectra of a wide quantum well for Landau level fillings, ν , just below 1/2, under conditions where the ν =1 /2 fractional quantum Hall effect (FQHE) is present. One resonance in the spectra exhibits intensity variations with ν in striking agreement with that expected for a pinning mode of a Wigner solid of quasiholes of this FQHE state. This resonance is also quite sensitive to asymmetrization of the growth-direction charge distribution in the quantum well by gate bias. Another resonance in the spectra is associated with a different bilayer Wigner solid that also exists at much lower ν than the 1/2 FQHE, and that appears to coexist with the 1/2 quasihole solid.
Jiang Haiyan; Cai Wei; Tsu, Raphael
2011-03-01
In this paper, the accuracy of the Frensley inflow boundary condition of the Wigner equation is analyzed in computing the I-V characteristics of a resonant tunneling diode (RTD). It is found that the Frensley inflow boundary condition for incoming electrons holds only exactly infinite away from the active device region and its accuracy depends on the length of contacts included in the simulation. For this study, the non-equilibrium Green's function (NEGF) with a Dirichlet to Neumann mapping boundary condition is used for comparison. The I-V characteristics of the RTD are found to agree between self-consistent NEGF and Wigner methods at low bias potentials with sufficiently large GaAs contact lengths. Finally, the relation between the negative differential conductance (NDC) of the RTD and the sizes of contact and buffer in the RTD is investigated using both methods.
Wigner functions for noncommutative quantum mechanics: A group representation based construction
NASA Astrophysics Data System (ADS)
Chowdhury, S. Hasibul Hassan; Ali, S. Twareque
2015-12-01
This paper is devoted to the construction and analysis of the Wigner functions for noncommutative quantum mechanics, their marginal distributions, and star-products, following a technique developed earlier, viz, using the unitary irreducible representations of the group GNC, which is the three fold central extension of the Abelian group of ℝ4. These representations have been exhaustively studied in earlier papers. The group GNC is identified with the kinematical symmetry group of noncommutative quantum mechanics of a system with two degrees of freedom. The Wigner functions studied here reflect different levels of non-commutativity—both the operators of position and those of momentum not commuting, the position operators not commuting and finally, the case of standard quantum mechanics, obeying the canonical commutation relations only.
Wigner functions for noncommutative quantum mechanics: A group representation based construction
Chowdhury, S. Hasibul Hassan; Ali, S. Twareque
2015-12-15
This paper is devoted to the construction and analysis of the Wigner functions for noncommutative quantum mechanics, their marginal distributions, and star-products, following a technique developed earlier, viz, using the unitary irreducible representations of the group G{sub NC}, which is the three fold central extension of the Abelian group of ℝ{sup 4}. These representations have been exhaustively studied in earlier papers. The group G{sub NC} is identified with the kinematical symmetry group of noncommutative quantum mechanics of a system with two degrees of freedom. The Wigner functions studied here reflect different levels of non-commutativity—both the operators of position and those of momentum not commuting, the position operators not commuting and finally, the case of standard quantum mechanics, obeying the canonical commutation relations only.
NASA Astrophysics Data System (ADS)
Maruo, Daiki; Utsunomiya, Shoko; Yamamoto, Yoshihisa
2016-08-01
We present the quantum theory of coherent Ising machines based on networks of degenerate optical parametric oscillators (DOPOs). In a simple model consisting of two coupled DOPOs, both positive-P representation and truncated Wigner representation predict quantum correlation and inseparability between the two DOPOs in spite of the open-dissipative nature of the system. Here, we apply the truncated Wigner representation method to coherent Ising machines with thermal, vacuum, and squeezed reservoir fields. We find that the probability of finding the ground state of a one-dimensional Ising model increases substantially as a result of reducing excess thermal noise and squeezing the incident vacuum fluctuation on the out-coupling port.
Savio, Andrea; Poncet, Alain
2011-02-01
In this work, we compute the Wigner distribution function on one-dimensional devices from wave functions generated by solving the Schroedinger equation. Our goal is to investigate certain issues that we encountered in implementing Wigner transport equation solvers, such as the large discrepancies observed between the boundary conditions and the solution in the neighborhood of the boundaries. By evaluating the Wigner function without solving the Wigner transport equation, we intend to ensure that the actual boundary conditions are consistent with those commonly applied in literature. We study both single- and double-barrier unbiased structures. We use simple potential profiles, so that we can compute the wave functions analytically for better accuracy. We vary a number of structure geometry, material, meshing, and numerical parameters, among which are the contact length, the barrier height, the number of incident wave functions, and the numerical precision used for the computations, and we observe how the Wigner function at the device boundaries is affected. For the double-barrier structures, we look at the density matrix function and we study a model for the device transmission spectrum which helps explain the lobelike artifacts that we observe on the Wigner function.
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.
Cámara, Alejandro; Alieva, Tatiana; Rodrigo, José A; Calvo, María L
2009-06-01
We propose a simple approach for the phase space tomography reconstruction of the Wigner distribution of paraxial optical beams separable in Cartesian coordinates. It is based on the measurements of the antisymmetric fractional Fourier transform power spectra, which can be taken using a flexible optical setup consisting of four cylindrical lenses. The numerical simulations and the experimental results clearly demonstrate the feasibility of the proposed scheme.
Uncertainty relation of mixed states by means of Wigner-Yanase-Dyson information
Li, D.; Li, X.; Wang, F.; Huang, H.; Li, X.; Kwek, L. C.
2009-05-15
The variance of an observable in a quantum state is usually used to describe Heisenberg uncertainty relation. For mixed states, the variance includes quantum and classical uncertainties. By means of the skew information and the decomposition of the variance, a stronger uncertainty relation was presented by Luo [ Phys. Rev. A 72, 042110 (2005)]. In this paper, by using Wigner-Yanase-Dyson information which is a generalization of the skew information, we propose a general uncertainty relation of mixed states.
Massively parallel implementation of the multi-reference Brillouin-Wigner CCSD method
Brabec, Jiri; Krishnamoorthy, Sriram; van Dam, Hubertus JJ; Kowalski, Karol; Pittner, Jiri
2011-10-06
This paper reports the parallel implementation of the Brillouin Wigner MultiReference Coupled Cluster method with Single and Double excitations (BW-MRCCSD). Preliminary tests for systems composed of 304 and 440 correlated obritals demonstrate the performance of our implementation across 1000 cores and clearly indicate the advantages of using improved task scheduling. Possible ways for further improvements of the parallel performance are also delineated.
Electronic structure of disordered CuPd alloys by positron-annihilation 2D-ACAR
Smedskjaer, L.C.; Benedek, R.; Siegel, R.W.; Legnini, D.G.; Stahulak, M.D.; Bansil, A.
1988-01-01
We report 2D-ACAR experiments and KKR CPA calculations on alpha-phase single-crystal Cu/sub 1-x/Pd/sub x/ in the range x less than or equal to 0.25. The flattening of the Fermi surface near (110) with increasing x predicted by theory is confirmed by our experimental results. 16 refs., 2 figs.
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.
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
Tawfik, A.
2013-07-01
We investigate the impacts of Generalized Uncertainty Principle (GUP) proposed by some approaches to quantum gravity such as String Theory and Doubly Special Relativity on black hole thermodynamics and Salecker-Wigner inequalities. Utilizing Heisenberg uncertainty principle, the Hawking temperature, Bekenstein entropy, specific heat, emission rate and decay time are calculated. As the evaporation entirely eats up the black hole mass, the specific heat vanishes and the temperature approaches infinity with an infinite radiation rate. It is found that the GUP approach prevents the black hole from the entire evaporation. It implies the existence of remnants at which the specific heat vanishes. The same role is played by the Heisenberg uncertainty principle in constructing the hydrogen atom. We discuss how the linear GUP approach solves the entire-evaporation-problem. Furthermore, the black hole lifetime can be estimated using another approach; the Salecker-Wigner inequalities. Assuming that the quantum position uncertainty is limited to the minimum wavelength of measuring signal, Wigner second inequality can be obtained. If the spread of quantum clock is limited to some minimum value, then the modified black hole lifetime can be deduced. Based on linear GUP approach, the resulting lifetime difference depends on black hole relative mass and the difference between black hole mass with and without GUP is not negligible.
Entanglement with negative Wigner function of almost 3,000 atoms heralded by one photon.
McConnell, Robert; Zhang, Hao; Hu, Jiazhong; Ćuk, Senka; Vuletić, Vladan
2015-03-26
Quantum-mechanically correlated (entangled) states of many particles are of interest in quantum information, quantum computing and quantum metrology. Metrologically useful entangled states of large atomic ensembles have been experimentally realized, but these states display Gaussian spin distribution functions with a non-negative Wigner quasiprobability distribution function. Non-Gaussian entangled states have been produced in small ensembles of ions, and very recently in large atomic ensembles. Here we generate entanglement in a large atomic ensemble via an interaction with a very weak laser pulse; remarkably, the detection of a single photon prepares several thousand atoms in an entangled state. We reconstruct a negative-valued Wigner function--an important hallmark of non-classicality--and verify an entanglement depth (the minimum number of mutually entangled atoms) of 2,910 ± 190 out of 3,100 atoms. Attaining such a negative Wigner function and the mutual entanglement of virtually all atoms is unprecedented for an ensemble containing more than a few particles. Although the achieved purity of the state is slightly below the threshold for entanglement-induced metrological gain, further technical improvement should allow the generation of states that surpass this threshold, and of more complex Schrödinger cat states for quantum metrology and information processing. More generally, our results demonstrate the power of heralded methods for entanglement generation, and illustrate how the information contained in a single photon can drastically alter the quantum state of a large system.
Gasbarro, Andrew; Bazarov, Ivan
2014-03-01
In an effort to provide a computationally convenient approach to the characterization of partially coherent synchrotron radiation in phase space, a thorough discussion of the minimum dimensionality of the Wigner distribution function for rotationally symmetric sources of arbitrary degrees of coherence is presented. It is found that perfectly coherent, perfectly incoherent and partially coherent sources may all be characterized by a three-dimensional reduced Wigner distribution function, and some special cases are discussed in which a two-dimensional reduced Wigner distribution function suffices. An application of the dimension-reducing formalism to the case of partially coherent radiation from a planar undulator and a circularly symmetric electron beam as can be found in linear accelerators is demonstrated. The photon distribution is convolved over a realistic electron bunch, and how the beta function, emittance and energy spread of the bunch affect the total degree of coherence of the radiation is inspected. Finally the cross spectral density is diagonalized and the eigenmodes of the partially coherent radiation are recovered.
Wigner localization in a graphene quantum dot with a mass gap
NASA Astrophysics Data System (ADS)
Guerrero Becerra, Karina Andrea; Rontani, Massimo
2014-03-01
The role of electron-electron interactions in graphene is an open issue that impacts on the operation of quantum dots (QDs) and other graphene-based devices. Whereas electrons in bulk graphene allegedly behave as noninteracting particles except for subtle effects, there is strong evidence that electrons in carbon-based nanostructures-nanotubes-form Wigner molecules [Nat. Phys. 9, 576 (2013)]. Besides, a significant effort is presently devoted to minimize the role of disorder in next-generation graphene QDs. Here we show theoretically that Dirac electrons in a clean, circular graphene QD with a mass gap induced by the breaking of sublattice symmetry form a Wigner molecule for realistic values of device parameters. The evidence is the combined analysis of many-body energies, one-body densities, and pair correlation functions obtained through the exact diagonalization of the interacting Dirac-Weyl Hamiltonian. This method, which uses two different sublattice envelopes and includes both inequivalent Dirac cones, allows us to take all many-body correlations into account. The experimental signature of Wigner localization is the suppression of the fourfold periodicity of the filling sequence and the quenching of excitation energies, accessible through Coulomb blockade spectroscopy.
Phase-space path-integral calculation of the Wigner function
NASA Astrophysics Data System (ADS)
Samson, J. H.
2003-10-01
The Wigner function W(q, p) is formulated as a phase-space path integral, whereby its sign oscillations can be seen to follow from interference between the geometrical phases of the paths. The approach has similarities to the path-centroid method in the configuration-space path integral. Paths can be classified by the midpoint of their ends; short paths where the midpoint is close to (q, p) and which lie in regions of low energy (low P function of the Hamiltonian) will dominate, and the enclosed area will determine the sign of the Wigner function. As a demonstration, the method is applied to a sequence of density matrices interpolating between a Poissonian number distribution and a number state, each member of which can be represented exactly by a discretized path integral with a finite number of vertices. Saddle-point evaluation of these integrals recovers (up to a constant factor) the WKB approximation to the Wigner function of a number state.
Dissipative quantum transport in silicon nanowires based on Wigner transport equation
NASA Astrophysics Data System (ADS)
Barraud, Sylvain
2011-11-01
In this work, we present a one-dimensional model of quantum electron transport for silicon nanowire transistor that makes use of the Wigner function formalism and that takes into account the carrier scattering. Effect of scattering on the current-voltage (I-V) characteristics is assessed using both the relaxation time approximation and the Boltzmann collision operator. Similarly to the classical transport theory, the scattering mechanisms are included in the Wigner formulation through the addition of a collision term in the Liouville equation. As compared to the relaxation time, the Boltzmann collision operator approach is considered to be more realistic because it provides a better description of the scattering events. Within the Fermi golden rule approximation, the standard collision term is described for both acoustic phonon and surface-roughness interactions. It is introduced in the discretized version of the Liouville equation to obtain the Wigner distribution function and the current density. The model is then applied to study the impact of each scattering mechanism on short-channel electrical performance of silicon nanowire transistors for different gate lengths and nanowire widths.
Charge-exchange resonances and restoration of Wigner's supersymmetry in heavy and superheavy nuclei
NASA Astrophysics Data System (ADS)
Lutostansky, Yu. S.; Tikhonov, V. N.
2016-11-01
Various facets of the question of whether Wigner's supersymmetry [ SU(4) symmetry] may be restored in heavy and superheavy nuclei are analyzed on the basis of a comparison of the results of calculations with experimental data. The energy difference between the giant Gamow-Teller resonance and the analog resonance (the difference of E G and E A) according to calculations based on the theory of finite Fermi systems is presented for the case of 33 nuclei for which experimental data are available. The calculated difference Δ E G-A of E G and E A tends to zero in heavier nuclei, showing evidence of the restoration of Wigner's SU(4) symmetry. Also, the isotopic dependence of the Coulomb energy difference between neighboring isobaric nuclei is analyzed within the SU(4) approach for more than 400 nuclei in the mass-number range of A = 5-244. The restoration of Wigner's SU(4) symmetry in heavy nuclei is confirmed. It is shown that the restoration of SU(4) symmetry is compatible with the possible existence of the stability island in the region of superheavy nuclei.
On the simulation of indistinguishable fermions in the many-body Wigner formalism
NASA Astrophysics Data System (ADS)
Sellier, J. M.; Dimov, I.
2015-01-01
The simulation of quantum systems consisting of interacting, indistinguishable fermions is an incredible mathematical problem which poses formidable numerical challenges. Many sophisticated methods addressing this problem are available which are based on the many-body Schrödinger formalism. Recently a Monte Carlo technique for the resolution of the many-body Wigner equation has been introduced and successfully applied to the simulation of distinguishable, spinless particles. This numerical approach presents several advantages over other methods. Indeed, it is based on an intuitive formalism in which quantum systems are described in terms of a quasi-distribution function, and highly scalable due to its Monte Carlo nature. In this work, we extend the many-body Wigner Monte Carlo method to the simulation of indistinguishable fermions. To this end, we first show how fermions are incorporated into the Wigner formalism. Then we demonstrate that the Pauli exclusion principle is intrinsic to the formalism. As a matter of fact, a numerical simulation of two strongly interacting fermions (electrons) is performed which clearly shows the appearance of a Fermi (or exchange-correlation) hole in the phase-space, a clear signature of the presence of the Pauli principle. To conclude, we simulate 4, 8 and 16 non-interacting fermions, isolated in a closed box, and show that, as the number of fermions increases, we gradually recover the Fermi-Dirac statistics, a clear proof of the reliability of our proposed method for the treatment of indistinguishable particles.
Melting of Boltzmann particles in different 2D trapping potential
NASA Astrophysics Data System (ADS)
Bhattacharya, Dyuti; Filinov, Alexei; Ghosal, Amit; Bonitz, Michael
2015-03-01
We analyze the quantum melting of two dimensional Wigner solid in several confined geometries and compare them with corresponding thermal melting in a purely classical system. Our results show that the geometry play little role in deciding the crossover quantum parameter nX, as the effects from boundary is well screened by the quantum zero point motion. The unique phase diagram in the plane of thermal and quantum fluctuations determined from independent melting criteria separates out the Wigner molecule ``phase'' from the classical and quantum ``liquids''. An intriguing signature of weakening liquidity with increasing temperature T have been found in the extreme quantum regime (n). This crossover is associated with production of defects, just like in case of thermal melting, though the role of them in determining the mechanism of the crossover appears different. Our study will help comprehending melting in a variety of experimental realization of confined system - from quantum dots to complex plasma.
2008-04-15
Newtonian Fluid Mechanics, 2006, 128(1): 44-61. 4. M. G. Forest, R. Zhou, and Q. Wang, Nano-rod suspension flows: a 2D Smoluchowski- Navier - Stokes ...pp. 1-21. 23. M. G. Forest, R. Zhou, and Q. Wang, “Nano-rod suspension flows: a 2D Smoluchowski- Navier - Stokes solver”, International Journal of...principle. The probability density function is sought by a spectral method for the Smoluchowski equation based on the Wigner function expansion. Lower
Kim, Kang Seog; Williams, Mark L
2012-01-01
SCALE 6 computes problem-dependent multigroup (MG) cross sections through a combination of the conventional Bondarenko shielding-factor method and a deterministic pointwise (PW) transport calculation of the fine-structure spectra in the resolved resonance and thermal energy ranges. The PW calculation is performed by the CENTRM code using a 1-D cylindrical Wigner-Seitz model with the white boundary condition instead of the real rectangular cell shape to represent a lattice unit cell. The pointwise fluxes computed by CENTRM are not exact because a 1-D model is used for the transport calculation, which introduces discrepancies in the MG self-shielded cross sections, resulting in some deviation in the eigenvalue. In order to solve this problem, the method of characteristics (MOC) has been applied to enable the CENTRM PW transport calculation for a 2-D square pin cell. The computation results show that the new BONAMI/CENTRM-MOC procedure produces very precise self-shielded cross sections compared to MCNP reaction rates.
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.
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
The IDOL–UBE2D complex mediates sterol-dependent degradation of the LDL receptor
Zhang, Li; Fairall, Louise; Goult, Benjamin T.; Calkin, Anna C.; Hong, Cynthia; Millard, Christopher J.; Tontonoz, Peter; Schwabe, John W.R.
2011-01-01
We previously identified the E3 ubiquitin ligase IDOL as a sterol-dependent regulator of the LDL receptor (LDLR). The molecular pathway underlying IDOL action, however, remains to be determined. Here we report the identification and biochemical and structural characterization of an E2–E3 ubiquitin ligase complex for LDLR degradation. We identified the UBE2D family (UBE2D1–4) as E2 partners for IDOL that support both autoubiquitination and IDOL-dependent ubiquitination of the LDLR in a cell-free system. NMR chemical shift mapping and a 2.1 Å crystal structure of the IDOL RING domain–UBE2D1 complex revealed key interactions between the dimeric IDOL protein and the E2 enzyme. Analysis of the IDOL–UBE2D1 interface also defined the stereochemical basis for the selectivity of IDOL for UBE2Ds over other E2 ligases. Structure-based mutations that inhibit IDOL dimerization or IDOL–UBE2D interaction block IDOL-dependent LDLR ubiquitination and degradation. Furthermore, expression of a dominant-negative UBE2D enzyme inhibits the ability of IDOL to degrade the LDLR in cells. These results identify the IDOL–UBE2D complex as an important determinant of LDLR activity, and provide insight into molecular mechanisms underlying the regulation of cholesterol uptake. PMID:21685362
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.
New optical 2D modulator jacketed in rotational plastic optics
NASA Astrophysics Data System (ADS)
Heinol, Horst G.; Xu, Z.; Schwarte, Rudolf; Loffeld, Otmar
1995-12-01
Optical and therefore nontactile 3D-measurement techniques are of increasing interest in industrial automation, especially in quality control and guidance of automotive vehicles. In connection with these demands, a new type of optical modulator jacketed in rotational plastic optics is introduced in the paper. Furthermore first results obtained by simulation studies will be presented. A simple nevertheless effective way of obtaining 3D information is to illuminate the whole 3D object or scene simultaneously with rf-modulated light. This can be well achieved by using the suggested optical modulator that incorporates the properties of a high aperture and minimum aberration in the 3D-imaging process. The mentioned modulator makes use of the effect of Frustrated Total Reflection (FTR). To exploit this FTR effect in an optical 2D mixer, the gap width between media of higher dense has to be modulated by an rf-voltage applied to a piezo crystal as an rf-controlled tuning medium. Considering the limited modulation bandwidth due to the parasitic capacity of the piezo crystal, the geometrical dimension of the modulator must be made as small as possible. Therefore the spot of the light is collimated at the focal point of the jacketing rotational ellipsoid. The integrated component made of plastic optics and piezo crystal plays a substantial role for the optical modulation and imaging. Some simulation results of this optical device show that the inherent non-linearity of the FTR modulator may be neglected in practical applications, thus yielding a high modulation depth. Furthermore, a 3D-image system adopting this plastic-made optics is also depicted in the paper, which is robust and handy for several industrial applications.
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
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.
Unusual dimensionality effects and surface charge density in 2D Mg(OH)2.
Suslu, Aslihan; Wu, Kedi; Sahin, Hasan; Chen, Bin; Yang, Sijie; Cai, Hui; Aoki, Toshihiro; Horzum, Seyda; Kang, Jun; Peeters, Francois M; Tongay, Sefaattin
2016-02-05
We present two-dimensional Mg(OH)2 sheets and their vertical heterojunctions with CVD-MoS2 for the first time as flexible 2D insulators with anomalous lattice vibration and chemical and physical properties. New hydrothermal crystal growth technique enabled isolation of environmentally stable monolayer Mg(OH)2 sheets. Raman spectroscopy and vibrational calculations reveal that the lattice vibrations of Mg(OH)2 have fundamentally different signature peaks and dimensionality effects compared to other 2D material systems known to date. Sub-wavelength electron energy-loss spectroscopy measurements and theoretical calculations show that Mg(OH)2 is a 6 eV direct-gap insulator in 2D, and its optical band gap displays strong band renormalization effects from monolayer to bulk, marking the first experimental confirmation of confinement effects in 2D insulators. Interestingly, 2D-Mg(OH)2 sheets possess rather strong surface polarization (charge) effects which is in contrast to electrically neutral h-BN materials. Using 2D-Mg(OH)2 sheets together with CVD-MoS2 in the vertical stacking shows that a strong change transfer occurs from n-doped CVD-MoS2 sheets to Mg(OH)2, naturally depleting the semiconductor, pushing towards intrinsic doping limit and enhancing overall optical performance of 2D semiconductors. Results not only establish unusual confinement effects in 2D-Mg(OH)2, but also offer novel 2D-insulating material with unique physical, vibrational, and chemical properties for potential applications in flexible optoelectronics.
Unusual dimensionality effects and surface charge density in 2D Mg(OH)2
Suslu, Aslihan; Wu, Kedi; Sahin, Hasan; Chen, Bin; Yang, Sijie; Cai, Hui; Aoki, Toshihiro; Horzum, Seyda; Kang, Jun; Peeters, Francois M.; Tongay, Sefaattin
2016-01-01
We present two-dimensional Mg(OH)2 sheets and their vertical heterojunctions with CVD-MoS2 for the first time as flexible 2D insulators with anomalous lattice vibration and chemical and physical properties. New hydrothermal crystal growth technique enabled isolation of environmentally stable monolayer Mg(OH)2 sheets. Raman spectroscopy and vibrational calculations reveal that the lattice vibrations of Mg(OH)2 have fundamentally different signature peaks and dimensionality effects compared to other 2D material systems known to date. Sub-wavelength electron energy-loss spectroscopy measurements and theoretical calculations show that Mg(OH)2 is a 6 eV direct-gap insulator in 2D, and its optical band gap displays strong band renormalization effects from monolayer to bulk, marking the first experimental confirmation of confinement effects in 2D insulators. Interestingly, 2D-Mg(OH)2 sheets possess rather strong surface polarization (charge) effects which is in contrast to electrically neutral h-BN materials. Using 2D-Mg(OH)2 sheets together with CVD-MoS2 in the vertical stacking shows that a strong change transfer occurs from n-doped CVD-MoS2 sheets to Mg(OH)2, naturally depleting the semiconductor, pushing towards intrinsic doping limit and enhancing overall optical performance of 2D semiconductors. Results not only establish unusual confinement effects in 2D-Mg(OH)2, but also offer novel 2D-insulating material with unique physical, vibrational, and chemical properties for potential applications in flexible optoelectronics. PMID:26846617
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.
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.
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 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
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
NASA Astrophysics Data System (ADS)
Sun, Lipeng; Hase, William L.
2010-07-01
Quasiclassical trajectory calculations are compared, with classical and Wigner sampling of transition state (TS) energy levels, for C2H5F≠→HF+C2H4 product energy partitioning and [Cl⋯CH3⋯Cl]- central barrier dynamics. The calculations with Wigner sampling are reported here for comparison with the previously reported calculations with classical sampling [Y. J. Cho et al., J. Chem. Phys. 96, 8275 (1992); L. Sun and W. L. Hase, J. Chem. Phys. 121, 8831 (2004)]. The C2H5F≠ calculations were performed with direct dynamics at the MP2/6-31G∗ level of theory. Classical and Wigner sampling give post-transition state dynamics, for these two chemical systems, which are the same within statistical uncertainties. This is a result of important equivalences in these two sampling methods for selecting initial conditions at a TS. In contrast, classical and Wigner sampling often give different photodissociation dynamics [R. Schinke, J. Phys. Chem. 92, 3195 (1988)]. Here the sampling is performed for a vibrational state of the ground electronic state potential energy surface (PES), which is then projected onto the excited electronic state's PES. Differences between the ground and the excited PESs may give rise to substantially different excitations of the vibrational and dissociative coordinates on the excited state PES by classical and Wigner sampling, resulting in different photodissociation dynamics.
Effect of Wigner energy on the symmetry energy coefficient in nuclei
NASA Astrophysics Data System (ADS)
Tian, Jun-Long; Cui, Hai-Tao; Gao, Teng; Wang, Ning
2016-09-01
The nuclear symmetry energy coefficient (including the coefficient of the I4 term) of finite nuclei is extracted by using the differences of available experimental binding energies of isobaric nuclei. It is found that the extracted symmetry energy coefficient decreases with increasing isospin asymmetry I, which is mainly caused by Wigner correction, since is the summation of the traditional symmetry energy esym and the Wigner energy eW. We obtain the optimal values J = 30.25 ± 0.10 MeV, ass = 56.18 ± 1.25 MeV, and the Wigner parameter x = 2.38 ± 0.12 through a polynomial fit to 2240 measured binding energies for nuclei with 20 ⩽ A ⩽ 261 with an rms deviation of 23.42 keV. We also find that the volume symmetry coefficient J ≃ 30 MeV is insensitive to the value x, whereas the surface symmetry coefficient ass and the coefficient are very sensitive to the value of x in the range 1 ⩽ x ⩽ 4. The contribution of the term increases rapidly with increasing isospin asymmetry I. For very neutron-rich nuclei, the contribution of the term will play an important role. Supported by National Natural Science Foundation of China (11475004, 11275052, 11305003, 11375094 and 11465005), Natural Science Foundation of He'nan Educational Committee (2011A140001 and 2011GGJS-147), Open Project Program of State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences (Y4KF041CJ1)
Substrate-assisted 2D DNA lattices and algorithmic lattices from single-stranded tiles.
Kim, Junghoon; Ha, Tai Hwan; Park, Sung Ha
2015-08-07
We present a simple route to circumvent kinetic traps which affect many types of DNA nanostructures in their self-assembly process. Using this method, a new 2D DNA lattice made up of short, single-stranded tile (SST) motifs was created. Previously, the growth of SST DNA assemblies was restricted to 1D (tubes and ribbons) or finite-sized 2D (molecular canvases). By utilizing the substrate-assisted growth method, sets of SSTs were designed as unit cells to self-assemble into periodic and aperiodic 2D lattices which continuously grow both along and orthogonal to the helical axis. Notably, large-scale (∼1 μm(2)) fully periodic 2D lattices were fabricated using a minimum of just 2 strand species. Furthermore, the ability to create 2D lattices from a few motifs enables certain rules to be encoded into these SSTs to carry out algorithmic self-assembly. A set of these motifs was designed to execute simple 1-input 1-output COPY and NOT algorithms, the space-time manifestations which were aperiodic 2D algorithmic SST lattices. The methodology presented here can be straightforwardly applied to other motifs which fall into this type of kinetic trap to create novel DNA crystals.
Booming Development of Group IV–VI Semiconductors: Fresh Blood of 2D Family
Zhou, Xing; Zhang, Qi; Gan, Lin; Li, Huiqiao; Xiong, Jie
2016-01-01
As an important component of 2D layered materials (2DLMs), the 2D group IV metal chalcogenides (GIVMCs) have drawn much attention recently due to their earth‐abundant, low‐cost, and environmentally friendly characteristics, thus catering well to the sustainable electronics and optoelectronics applications. In this instructive review, the booming research advancements of 2D GIVMCs in the last few years have been presented. First, the unique crystal and electronic structures are introduced, suggesting novel physical properties. Then the various methods adopted for synthesis of 2D GIVMCs are summarized such as mechanical exfoliation, solvothermal method, and vapor deposition. Furthermore, the review focuses on the applications in field effect transistors and photodetectors based on 2D GIVMCs, and extends to flexible devices. Additionally, the 2D GIVMCs based ternary alloys and heterostructures have also been presented, as well as the applications in electronics and optoelectronics. Finally, the conclusion and outlook have also been presented in the end of the review. PMID:27981008
Azaña, J; Muriel, M A
2000-12-01
The grating-period profile and length of an arbitrary fiber Bragg grating structure can be reconstructed from the structure's reflection response by use of a time-frequency signal representation based on the well-known Wigner-Ville distribution and spectrogram. We present a detailed description of this synthesis technique. By means of numerical simulations, the technique is tested with several fiber grating structures. In general, our results show good agreement between exact and reconstructed functions. The technique's advantages and limitations are discussed. We propose and demonstrate the application of the proposed synthesis technique to distributed mechanical strain or temperature sensing.
Propagation of the Wigner distribution function for partially coherent nonparaxial beams.
Zhang, Yucheng; Lü, Baida
2004-12-01
On the basis of the Rayleigh-Sommerfeld diffraction integral, a closed-form propagation expression for the Wigner distribution function of partially coherent nonparaxial beams in free space is derived for what is to our knowledge the first time. The propagation of spatially fully coherent nonparaxial beams is treated as a special case of our general result. Application of the result is illustrated with the nonparaxial propagation of partially coherent anisotropic Gaussian-Schell-model beams and TEM11-mode Hermite-Gaussian beams.
A Wigner Function Approach to Coherence in a Talbot-Lau Interferometer
NASA Astrophysics Data System (ADS)
Imhof, Eric; Stickney, James; Squires, Matthew
2016-06-01
Using a thermal gas, we model the signal of a trapped interferometer. This interferometer uses two short laser pulses, separated by time T, which act as a phase grating for the matter waves. Near time 2T, there is an echo in the cloud's density due to the Talbot-Lau effect. Our model uses the Wigner function approach and includes a weak residual harmonic trap. The analysis shows that the residual potential limits the interferometer's visibility, shifts the echo time of the interferometer, and alters its time dependence. Loss of visibility can be mitigated by optimizing the initial trap frequency just before the interferometer cycle begins.
NASA Astrophysics Data System (ADS)
Xu, Yejun; Liang, Xiudong; Cheng, Jianming; Tai, Yunjiao; Song, Jun
2014-03-01
We present a simple proposal to measure arbitrary multi-mode entangled traveling field state based on a Mach-Zehnder interferometer in theory. Our method directly yields the characteristic function of the Wigner function without a demanding data analysis and can be easily carried out by recent technological advances. Especially, it is a very effective reconstruction proposal for an entangled traveling field with a small number of modes from the experimental point of view. We demonstrate the scheme for the example of a two-mode squeezed vacuum state to illustrate how similar the reconstructed state is to the ideal one via controlling the values of phase shifts.
Stick-Slip Motion of the Wigner Solid on Liquid Helium
NASA Astrophysics Data System (ADS)
Rees, David G.; Beysengulov, Niyaz R.; Lin, Juhn-Jong; Kono, Kimitoshi
2016-05-01
We present time-resolved transport measurements of a Wigner solid (WS) on the surface of liquid helium confined in a micron-scale channel. At rest, the WS is "dressed" by a cloud of quantized capillary waves (ripplons). Under a driving force, we find that repeated WS-ripplon decoupling leads to stick-slip current oscillations, the frequency of which can be tuned by adjusting the temperature, pressing electric field, or electron density. The WS on liquid He is a promising system for the study of polaronlike decoupling dynamics.
Crystallization and reentrant melting of charged colloids in nonpolar solvents.
Kanai, Toshimitsu; Boon, Niels; Lu, Peter J; Sloutskin, Eli; Schofield, Andrew B; Smallenburg, Frank; van Roij, René; Dijkstra, Marjolein; Weitz, David A
2015-03-01
We explore the crystallization of charged colloidal particles in a nonpolar solvent mixture. We simultaneously charge the particles and add counterions to the solution with aerosol-OT (AOT) reverse micelles. At low AOT concentrations, the charged particles crystallize into body-centered-cubic (bcc) or face-centered-cubic (fcc) Wigner crystals; at high AOT concentrations, the increased screening drives a thus far unobserved reentrant melting transition. We observe an unexpected scaling of the data with particle size, and account for all behavior with a model that quantitatively predicts both the reentrant melting and the data collapse.
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
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
Wang, An; Stout, C David; Zhang, Qinghai; Johnson, Eric F
2015-02-20
P450 2D6 contributes significantly to the metabolism of >15% of the 200 most marketed drugs. Open and closed crystal structures of P450 2D6 thioridazine complexes were obtained using different crystallization conditions. The protonated piperidine moiety of thioridazine forms a charge-stabilized hydrogen bond with Asp-301 in the active sites of both complexes. The more open conformation exhibits a second molecule of thioridazine bound in an expanded substrate access channel antechamber with its piperidine moiety forming a charge-stabilized hydrogen bond with Glu-222. Incubation of the crystalline open thioridazine complex with alternative ligands, prinomastat, quinidine, quinine, or ajmalicine, displaced both thioridazines. Quinine and ajmalicine formed charge-stabilized hydrogen bonds with Glu-216, whereas the protonated nitrogen of quinidine is equidistant from Asp-301 and Glu-216 with protonated nitrogen H-bonded to a water molecule in the access channel. Prinomastat is not ionized. Adaptations of active site side-chain rotamers and polypeptide conformations were evident between the complexes, with the binding of ajmalicine eliciting a closure of the open structure reflecting in part the inward movement of Glu-216 to form a hydrogen bond with ajmalicine as well as sparse lattice restraints that would hinder adaptations. These results indicate that P450 2D6 exhibits sufficient elasticity within the crystal lattice to allow the passage of compounds between the active site and bulk solvent and to adopt a more closed form that adapts for binding alternative ligands with different degrees of closure. These crystals provide a means to characterize substrate and inhibitor binding to the enzyme after replacement of thioridazine with alternative compounds.
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.
Yuan, Minghu; Feng, Liqiang; Lü, Rui; Chu, Tianshu E-mail: tschu008@163.com
2014-02-21
We show that by introducing Wigner rotation technique into the solution of time-dependent Schrödinger equation in length gauge, computational efficiency can be greatly improved in describing atoms in intense few-cycle circularly polarized laser pulses. The methodology with Wigner rotation technique underlying our openMP parallel computational code for circularly polarized laser pulses is described. Results of test calculations to investigate the scaling property of the computational code with the number of the electronic angular basis function l as well as the strong field phenomena are presented and discussed for the hydrogen atom.
NASA Astrophysics Data System (ADS)
Emch, G. G.; Mehra, Jagdish
Among the founding fathers of modern quantum physics few have contributed to our basic understanding of its concepts as much as E.P. Wigner. His articles on the epistemology of quantum mechanics and the measurement problem, and the basic role of symmetries were of fundamental importance for all subsequent work. He was also the first to discuss the concept of consciousness from the point of view of modern physics. All these papers can be found in this volume together with Wigner's philosophical writings. The book should be a gem for all those interested in the history and philosophy of science.
NASA Technical Reports Server (NTRS)
Isar, Aurelian
1995-01-01
The harmonic oscillator with dissipation is studied within the framework of the Lindblad theory for open quantum systems. By using the Wang-Uhlenbeck method, the Fokker-Planck equation, obtained from the master equation for the density operator, is solved for the Wigner distribution function, subject to either the Gaussian type or the delta-function type of initial conditions. The obtained Wigner functions are two-dimensional Gaussians with different widths. Then a closed expression for the density operator is extracted. The entropy of the system is subsequently calculated and its temporal behavior shows that this quantity relaxes to its equilibrium value.
Burgess, Ian B; Aizenberg, Joanna; Lončar, Marko
2013-12-01
Structural hierarchy and complex 3D architecture are characteristics of biological photonic designs that are challenging to reproduce in synthetic materials. Top-down lithography allows for designer patterning of arbitrary shapes, but is largely restricted to planar 2D structures. Self-assembly techniques facilitate easy fabrication of 3D photonic crystals, but controllable defect-integration is difficult. In this paper we combine the advantages of top-down and bottom-up fabrication, developing two techniques to deposit 2D-lithographically-patterned planar layers on top of or in between inverse-opal 3D photonic crystals and creating hierarchical structures that resemble the architecture of the bright green wing scales of the butterfly, Parides sesostris. These fabrication procedures, combining advantages of both top-down and bottom-up fabrication, may prove useful in the development of omnidirectional coloration elements and 3D-2D photonic crystal devices.
Digital phase-stepping holographic interferometry in measuring 2-D density fields
NASA Astrophysics Data System (ADS)
Lanen, T. A. W. M.; Nebbeling, C.; van Ingen, J. L.
1990-06-01
This paper presents a holographic interferometer technique for measuring transparent (2-D or quasi 2-D) density fields. To be able to study the realization of such a field at a certain moment of time, the field is “frozen” on a holographic plate. During the reconstruction of the density field from the hologram the length of the path traversed by the reconstruction beam is diminished in equal steps by applying a computer controlled voltage to a piezo-electric crystal that translates a mirror. Four phase-stepped interferograms resulting from this pathlength variation are digitized and serve as input to an algorithm for computing the phase surface. The method is illustrated by measuring the basically 2-D density field existing around a heated horizontal cylinder in free convection.
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.
Wigner spectrum and coherent feedback control of continuous-mode single-photon Fock states
NASA Astrophysics Data System (ADS)
Dong, Zhiyuan; Cui, Lei; Zhang, Guofeng; Fu, Hongchen
2016-10-01
Single photons are very useful resources in quantum information science. In real applications it is often required that the photons have a well-defined spectral (or equivalently temporal) modal structure. For example, a rising exponential pulse is able to fully excite a two-level atom while a Gaussian pulse cannot. This motivates the study of continuous-mode single-photon Fock states. Such states are characterized by a spectral (or temporal) pulse shape. In this paper we investigate the statistical property of continuous-mode single-photon Fock states. Instead of the commonly used normal ordering (Wick order), the tool we proposed is the Wigner spectrum. The Wigner spectrum has two advantages: (1) it allows to study continuous-mode single-photon Fock states in the time domain and frequency domain simultaneously; (2) because it can deal with the Dirac delta function directly, it has the potential to provide more information than the normal ordering where the Dirac delta function is always discarded. We also show how various control methods in particular coherent feedback control can be used to manipulate the pulse shapes of continuous-mode single-photon Fock states.
Superoscillations and supershifts in phase space: Wigner and Husimi function interpretations
NASA Astrophysics Data System (ADS)
Berry, M. V.; Moiseyev, N.
2014-08-01
Superoscillations, namely regions where a band-limited function f (x) varies faster than the fastest of its Fourier components k, generate the illusion that the Fourier content is ‘supershifted’ so as to lie outside the spectrum of the function. The relation between supershifts and superoscillations, central to the quantum weak measurements scheme, is explored in terms of two different representations of the local Fourier transform in the ‘phase space’ (x, k). The Wigner function W(x, k), regarded as a function of k for fixed x, inherits the band-limited property of f (x). Neverthless, its local k average can lie outside the spectrum because W, although real, posesses negative values. The local Wigner average of k equals the local wavenumber at x (local weak value of momentum), defined as the phase variation k loc(x) = ∂ x arg f (x). By contrast, the Husimi function H(x, k), i.e. the windowed Fourier transform with window width L, corresponding to squeezing of the coherent state associated with (x, k) (and representing the pointer wavefunction after a weak measurement), is positive-definite. But it is not band-limited, and the local Husimi average of k equals k loc if L is small enough. These properties are illustrated numerically with two superoscillatory functions.
Wigner-Smith time delay and its application to attosecond streaking
NASA Astrophysics Data System (ADS)
Goldsmith, Cory; Su, Jing; Becker, Andreas; Jaron-Becker, Agnieszka
2015-05-01
Attosecond streaking experiments have been suggested as a means for observing temporal delays in photoemission, but the interpretation of the time delays observed in such experiments is still debated. Using a calculation of the streaking delays as a field-weighted sum over finite-range delays accumulated over the duration of the streaking pulse length, we provide further analysis into the role the Coulomb potential plays in the observed, so-called ``streaking delay.'' To this end, we make use of cut-off Coulomb and single active electron (SAE) potentials to calculate field-free Wigner-Smith-like time delays accumulated over small intervals of time to formulate an analytical model for the calculation of the streaking delays for hydrogenic atoms, as well as for SAE model potentials for noble gases. Our results indicate that in most cases, the influence of the streaking field on the short-range parts of the potential is a small effect. This allows for the representation of the streaking delay as the sum of the Wigner-Smith (WS) delay from scattering theory and the coupling between the streaking and Coulomb fields. We acknowledge the following support: C.G., J.S., and A.B: U.S. DOE, Division of Chemical Sciences, Atomic, Molecular and Optical Sciences Program (Award No. DE-FG02-09ER16103), A.J.-B.: U.S. NSF (Grants No. PHY-1125844 and No. PHY-1068706).
Approach to the propagation of massive neutrinos in dense matter by Wigner functions
NASA Astrophysics Data System (ADS)
Sirera Tomas, Miguel
The problem of massive neutrinos comes from Grant Unification Theories but also from the so called Neutrino Solar Puzzle. The solution of this puzzle seems to be in the neutrinos physics and to need that the neutrinos are particles with mass. The possible mass of the neutrinos is not only important for Solar Neutrinos but also in other astrophysical environments such as Supernovae, Neutron Stars or The Early Universe. If the neutrinos are particles with mass, or at least one of their generations, oscillations are produced in both vacuum and matter. The oscillation in matter could cause the so called MSW effect, that transforms a neutrino flavour to another. The problem of the propagation of neutrinos in matter has been dealt with by many authors who have usually solved the covariant motion equations, and sometimes by Green Functions. In this work, this has been done using statistical techniques by Wigner Functions, which do not only allow us to study the propagation ways but also to know the behavior of the neutrinos field in equilibrium. On the other hand, the astrophysical systems, that we have commented above, yield a great amount of neutrinos which spread through them and are finally emitted to space, and so it is important to have a transport equation that explain how a neutrinos distribution is spread which is not in equilibrium. It is possible to achieve this equation by motion equations of the Wigner Functions.
Chirplet Wigner-Ville distribution for time-frequency representation and its application
NASA Astrophysics Data System (ADS)
Chen, G.; Chen, J.; Dong, G. M.
2013-12-01
This paper presents a Chirplet Wigner-Ville Distribution (CWVD) that is free for cross-term that usually occurs in Wigner-Ville distribution (WVD). By transforming the signal with frequency rotating operators, several mono-frequency signals without intermittent are obtained, WVD is applied to the rotated signals that is cross-term free, then some frequency shift operators corresponding to the rotating operator are utilized to relocate the signal‧s instantaneous frequencies (IFs). The operators‧ parameters come from the estimation of the IFs which are approached with a polynomial functions or spline functions. What is more, by analysis of error, the main factors for the performance of the novel method have been discovered and an effective signal extending method based on the IFs estimation has been developed to improve the energy concentration of WVD. The excellent performance of the novel method was manifested by applying it to estimate the IFs of some numerical signals and the echolocation signal emitted by the Large Brown Bat.
NASA Astrophysics Data System (ADS)
Mey, Tobias; Schäfer, Bernd; Mann, Klaus; Keitel, Barbara; Kreis, Svea; Kuhlmann, Marion; Plönjes, Elke; Tiedtke, Kai
2013-05-01
Free-electron lasers deliver EUV and soft x-ray pulses with the highest brilliance available and high spatial coherence. Users of such facilities have high demands on the coherence properties of the beam, for instance when working with coherent di ractive imaging (CDI). Experimentally, we are recovering the phase distribition with an EUV Hartmann wavefront sensor. This allows for online adjustment of focusing optics such as ellipsoidal or Kirkpatrick-Baez mirrors minimizing the aberrations in the focused beam. To gain highly resolved spatial coherence information, we have performed a caustic scan at beamline BL2 of the free-electron laser FLASH using the ellipsoidal focusing mirror and a movable EUV sensitized CCD detector. This measurement allows for retrieving the Wigner distribution function, being the two-dimensional Fourier transform of the mutual intensity of the beam. Computing the reconstruction on a four-dimensional grid, this yields the entire Wigner distribution which describes the beam propagation completely. Hence, we are able to provide comprehensive information about spatial coherence properties of the FLASH beam including the global degree of coherence. Additionally, we derive the beam propagation parameters such as Rayleigh length, waist diameter and M2.
NASA Astrophysics Data System (ADS)
Schäfer, Bernd; Flöter, Bernhard; Mann, Klaus; Keitel, Barbara; Plönjes, Elke; Tiedtke, Kai
2011-06-01
The wavefront as well as beam parameters of the free electron laser FLASH emitting in the EUV spectral range were determined from wavefront measurements using self supporting Hartmann sensors. The devices were applied for alignment of the ellipsoidal focusing mirror at Beamline 2 (BL2), reducing the rms wavefront aberrations by more than a factor of 3. Beam quality M² and other beam parameters were evaluated from wavefront and intensity data delivered by the Hartmann sensor. Furthermore, 100 two-dimensional single pulse intensity distributions were recorded at each of 32 axial positions, spaced app. +/-2 Rayleigh lengths around the waist of the optimized FEL beam with a magnifying EUV sensitized CCD camera. From these beam profile data the Wigner distribution function was reconstructed on two dimensional orthogonal subspaces. For separable beams this yields the complete Wigner distribution and gives comprehensive and high-resolution information on the propagation characteristics, including wavefront, mode content and spatial coherence. The wavefront of the optimized beam evaluated at waist position was in the order of λ?4 peak valley, whereas a significant contribution of uncorrelated higher order Hermite-Gauss modes and a global degree of coherence of 0.12 can be detected, leading to a substantial increase of the M² factor, which was determined to ~ 4.2 and ~ 3 in the horizontal and vertical direction, respectively. The obtained results are compared to the Hartmann experiments.
Analysis of frequency shifting in seismic signals using Gabor-Wigner transform
NASA Astrophysics Data System (ADS)
Kumar, Roshan; Sumathi, P.; Kumar, Ashok
2015-12-01
A hybrid time-frequency method known as Gabor-Wigner transform (GWT) is introduced in this paper for examining the time-frequency patterns of earthquake damaged buildings. GWT is developed by combining the Gabor transform (GT) and Wigner-Ville distribution (WVD). GT and WVD have been used separately on synthetic and recorded earthquake data to identify frequency shifting due to earthquake damages, but GT is prone to windowing effect and WVD involves ambiguity function. Hence to obtain better clarity and to remove the cross terms (frequency interference), GT and WVD are judiciously combined and the resultant GWT used to identify frequency shifting. Synthetic seismic response of an instrumented building and real-time earthquake data recorded on the building were investigated using GWT. It is found that GWT offers good accuracy for even slow variations in frequency, good time-frequency resolution, and localized response. Presented results confirm the efficacy of GWT when compared with GT and WVD used separately. Simulation results were quantified by the Renyi entropy measures and GWT shown to be an adequate technique in identifying localized response for structural damage detection.
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.
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.
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.
Topological Toughening of graphene and other 2D materials
NASA Astrophysics Data System (ADS)
Gao, Huajian
It has been claimed that graphene, with the elastic modulus of 1TPa and theoretical strength as high as 130 GPa, is the strongest material. However, from an engineering point of view, it is the fracture toughness that determines the actual strength of materials, as crack-like flaws (i.e., cracks, holes, notches, corners, etc.) are inevitable in the design, fabrication, and operation of practical devices and systems. Recently, it has been demonstrated that graphene has very low fracture toughness, in fact close to that of ideally brittle solids. These findings have raised sharp questions and are calling for efforts to explore effective methods to toughen graphene. Recently, we have been exploring the potential use of topological effects to enhance the fracture toughness of graphene. For example, it has been shown that a sinusoidal graphene containing periodically distributed disclination quadrupoles can achieve a mode I fracture toughness nearly twice that of pristine graphene. Here we report working progresses on further studies of topological toughening of graphene and other 2D materials. A phase field crystal method is adopted to generate the atomic coordinates of material with specific topological patterns. We then perform molecular dynamics simulations of fracture in the designed samples, and observe a variety of toughening mechanisms, including crack tip blunting, crack trapping, ligament bridging, crack deflection and daughter crack initiation and coalescence.
Pressure-induced superconductivity in quasi-2D CeRhIn5
Hegger; Petrovic; Moshopoulou; Hundley; Sarrao; Fisk; Thompson
2000-05-22
CeRhIn5 is a new heavy-electron material that crystallizes in a quasi-2D structure that can be viewed as alternating layers of CeIn3 and RhIn2 stacked sequentially along the tetragonal c axis. Application of hydrostatic pressure induces a first-order-like transition from an unconventional antiferromagnetic state to a superconducting state with T(c) = 2.1 K.
Selenium-Doped Black Phosphorus for High-Responsivity 2D Photodetectors.
Xu, Yijun; Yuan, Jian; Fei, Linfeng; Wang, Xinliang; Bao, Qiaoliang; Wang, Yu; Zhang, Kai; Zhang, Yuegang
2016-09-01
Se-doped black phosphorus (BP) crystal, in centimeter scale, is synthesized by a scalable gas-phase growth method under mild conditions. The Se-doped BP exhibits high quality with excellent electrical properties. The Se dope induces over 20-fold enhancement of responsivity (R) for BP-based 2D photodetectors, resulting in a high R and external quantum efficiency of 15.33 A W(-1) and 2993%, respectively.
Spin splitting in 2D monochalcogenide semiconductors.
Do, Dat T; Mahanti, Subhendra D; Lai, Chih Wei
2015-11-24
We report ab initio calculations of the spin splitting of the uppermost valence band (UVB) and the lowermost conduction band (LCB) in bulk and atomically thin GaS, GaSe, GaTe, and InSe. These layered monochalcogenides appear in four major polytypes depending on the stacking order, except for the monoclinic GaTe. Bulk and few-layer ε-and γ -type, and odd-number β-type GaS, GaSe, and InSe crystals are noncentrosymmetric. The spin splittings of the UVB and the LCB near the Γ-point in the Brillouin zone are finite, but still smaller than those in a zinc-blende semiconductor such as GaAs. On the other hand, the spin splitting is zero in centrosymmetric bulk and even-number few-layer β-type GaS, GaSe, and InSe, owing to the constraint of spatial inversion symmetry. By contrast, GaTe exhibits zero spin splitting because it is centrosymmetric down to a single layer. In these monochalcogenide semiconductors, the separation of the non-degenerate conduction and valence bands from adjacent bands results in the suppression of Elliot-Yafet spin relaxation mechanism. Therefore, the electron- and hole-spin relaxation times in these systems with zero or minimal spin splittings are expected to exceed those in GaAs when the D'yakonov-Perel' spin relaxation mechanism is also suppressed.
Spin splitting in 2D monochalcogenide semiconductors
Do, Dat T.; Mahanti, Subhendra D.; Lai, Chih Wei
2015-01-01
We report ab initio calculations of the spin splitting of the uppermost valence band (UVB) and the lowermost conduction band (LCB) in bulk and atomically thin GaS, GaSe, GaTe, and InSe. These layered monochalcogenides appear in four major polytypes depending on the stacking order, except for the monoclinic GaTe. Bulk and few-layer ε-and γ -type, and odd-number β-type GaS, GaSe, and InSe crystals are noncentrosymmetric. The spin splittings of the UVB and the LCB near the Γ-point in the Brillouin zone are finite, but still smaller than those in a zinc-blende semiconductor such as GaAs. On the other hand, the spin splitting is zero in centrosymmetric bulk and even-number few-layer β-type GaS, GaSe, and InSe, owing to the constraint of spatial inversion symmetry. By contrast, GaTe exhibits zero spin splitting because it is centrosymmetric down to a single layer. In these monochalcogenide semiconductors, the separation of the non-degenerate conduction and valence bands from adjacent bands results in the suppression of Elliot-Yafet spin relaxation mechanism. Therefore, the electron- and hole-spin relaxation times in these systems with zero or minimal spin splittings are expected to exceed those in GaAs when the D’yakonov-Perel’ spin relaxation mechanism is also suppressed. PMID:26596907
Spin splitting in 2D monochalcogenide semiconductors
NASA Astrophysics Data System (ADS)
Do, Dat T.; Mahanti, Subhendra D.; Lai, Chih Wei
2015-11-01
We report ab initio calculations of the spin splitting of the uppermost valence band (UVB) and the lowermost conduction band (LCB) in bulk and atomically thin GaS, GaSe, GaTe, and InSe. These layered monochalcogenides appear in four major polytypes depending on the stacking order, except for the monoclinic GaTe. Bulk and few-layer ε-and γ -type, and odd-number β-type GaS, GaSe, and InSe crystals are noncentrosymmetric. The spin splittings of the UVB and the LCB near the Γ-point in the Brillouin zone are finite, but still smaller than those in a zinc-blende semiconductor such as GaAs. On the other hand, the spin splitting is zero in centrosymmetric bulk and even-number few-layer β-type GaS, GaSe, and InSe, owing to the constraint of spatial inversion symmetry. By contrast, GaTe exhibits zero spin splitting because it is centrosymmetric down to a single layer. In these monochalcogenide semiconductors, the separation of the non-degenerate conduction and valence bands from adjacent bands results in the suppression of Elliot-Yafet spin relaxation mechanism. Therefore, the electron- and hole-spin relaxation times in these systems with zero or minimal spin splittings are expected to exceed those in GaAs when the D’yakonov-Perel’ spin relaxation mechanism is also suppressed.
Constructing an Atmospheric Methane Budget Using 13CH3D and CH2D2 in Sources and Sinks
NASA Astrophysics Data System (ADS)
Haghnegahdar, M. A.; Schauble, E. A.; Young, E. D.
2015-12-01
We develop a theoretical model using relative abundances and fractionations of 13CH3D and CH2D2, the doubly substituted mass-18 isotopologues of methane, to quantitatively track the sources and the sinks of atmospheric methane. The goal is a better determination of the methane budget in the atmosphere. Different methane sources have different isotope ratios because of variations in substrates, formation reactions, and temperatures. Isotope ratio measurements will provide useful constraints on source components and sink processes. However, bulk isotope ratios alone are unlikely to be diagnostic because of mixing of sources. Using recently published budgets (Whiticar and Schaefer 2007) and estimates of equilibration temperatures of various methane sources (Stolper et al., 2014; Wang et al., 2015), including an assumption that biogenic methane sources are near-stochastic (Wang et al., 2015), we estimated the abundances in air of singly- and doubly-substituted isotopologues in terms of both bulk ratios and deviations from the stochastic distributions of multiply-substituted species. δ13CH3D and δCH2D2 for the total atmospheric sources are predicted to be -493‰ and -330‰, whereas Δ13CH3D, and ΔCH2D2, enrichments relative to stochastic, are predicted to be +4.7‰ and +21.5‰. The composition of atmospheric methane will also be influenced by sink reactions. The main sink reactions with OH• and Cl• have been modeled with first-principles transition state theory, using simplified corrections for tunneling (Wigner 1932). Our model predicts that the main sink reactions in the atmosphere generate distinct signatures of lower Δ13CH3D and ΔCH2D2 relative to the source composition, while at the same time increasing δ13CH3D and δCH2D2. Measurements of both Δ13CH3D and ΔCH2D2 are now possible with the new large-geometry gas-source mass spectrometer at UCLA permitting testing of these predictions.
Crystal Engineering of Hand-Twisted Helical Crystals.
Saha, Subhankar; Desiraju, Gautam R
2017-02-08
A strategy is outlined for the design of hand-twisted helical crystals. The starting point in the exercise is the one-dimensional (1D) plastic crystal, 1,4-dibromobenzene, which is then changed to a 1D elastic crystal, exemplified by 4-bromophenyl 4'-chlorobenzoate, by introduction of a molecular synthon -O-CO- in lieu of the supramolecular synthon Br···Br in the precursor. The 1D elastic crystals are next modified to two-dimensional (2D) elastic crystals, of the type 4-bromophenyl 4'-nitrobenzoate where the halogen bonding and C-H···O hydrogen bonding are well-matched. Finally, varying the interaction strengths in these 2D elastic crystals gives plastic crystals with two pairs of bendable faces but without slip planes. Typical examples are 4-chlorophenyl and 4-bromophenyl 4'-nitrobenzoate. This type of 2D plasticity represents a new type of bendable crystals in which plastic behavior is seen with a fair degree of isotropic character in the crystal packing. The presence of two sets of bendable faces, generally orthogonal to each other, allows for the possibility of hand-twisting of the crystals to give grossly helical morphologies. Accordingly, we propose the name hand-twisted helical crystals for these substances.
Shiba, Hayato; Yamada, Yasunori; Kawasaki, Takeshi; Kim, Kang
2016-12-09
By using large-scale molecular dynamics simulations, the dynamics of two-dimensional (2D) supercooled liquids turns out to be dependent on the system size, while the size dependence is not pronounced in three-dimensional (3D) systems. It is demonstrated that the strong system-size effect in 2D amorphous systems originates from the enhanced fluctuations at long wavelengths which are similar to those of 2D crystal phonons. This observation is further supported by the frequency dependence of the vibrational density of states, consisting of the Debye approximation in the low-wave-number limit. However, the system-size effect in the intermediate scattering function becomes negligible when the length scale is larger than the vibrational amplitude. This suggests that the finite-size effect in a 2D system is transient and also that the structural relaxation itself is not fundamentally different from that in a 3D system. In fact, the dynamic correlation lengths estimated from the bond-breakage function, which do not suffer from those enhanced fluctuations, are not size dependent in either 2D or 3D systems.
NASA Astrophysics Data System (ADS)
Shiba, Hayato; Yamada, Yasunori; Kawasaki, Takeshi; Kim, Kang
2016-12-01
By using large-scale molecular dynamics simulations, the dynamics of two-dimensional (2D) supercooled liquids turns out to be dependent on the system size, while the size dependence is not pronounced in three-dimensional (3D) systems. It is demonstrated that the strong system-size effect in 2D amorphous systems originates from the enhanced fluctuations at long wavelengths which are similar to those of 2D crystal phonons. This observation is further supported by the frequency dependence of the vibrational density of states, consisting of the Debye approximation in the low-wave-number limit. However, the system-size effect in the intermediate scattering function becomes negligible when the length scale is larger than the vibrational amplitude. This suggests that the finite-size effect in a 2D system is transient and also that the structural relaxation itself is not fundamentally different from that in a 3D system. In fact, the dynamic correlation lengths estimated from the bond-breakage function, which do not suffer from those enhanced fluctuations, are not size dependent in either 2D or 3D systems.
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
Probing electric properties at the boundary of planar 2D heterostructure
NASA Astrophysics Data System (ADS)
Park, Jewook
The quest for novel two-dimensional (2D) materials has led to the discovery of hybridized 2D atomic crystals. Especially, planar 2D heterostructure provides opportunities to explore fascinating electric properties at abrupt one-dimensional (1D) boundaries reminiscent to those seen in the 2D interfaces of complex oxides. By implementing the concept of epitaxy to 2D space, we developed a new growth technique to epitaxially grow hexagonal boron nitride (hBN) from the edges of graphene, forming a coherent planar heterostructure. At the interface of hBN and graphene, a polar-on-nonpolar 1D boundary can be formed which is expected to possess peculiar electronic states associated with the polarity of hBN and edge states of graphene Scanning tunneling microscopy and spectroscopy (STM/S) measurements revealed an abrupt 1D zigzag oriented boundary, with boundary states about 0.6 eV below or above the Fermi level depending on the termination of the hBN at the boundary. The boundary states are extended along the boundary and exponentially decay into the bulk of graphene and hBN. Combined STM/S and first-principles theory study not only disclose spatial and energetic distribution of interfacial state but also reveal the origin of boundary states and the effect of the polarity discontinuity at the interface By probing electric properties at the boundary in the atomic scale, planar 2D heterostructure is demonstrated as a promising platform for discovering emergent phenomena at the 1D interface in 2D materials. This research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.
NASA Astrophysics Data System (ADS)
Zeng, Wei; Wang, Haitao; Tian, Guiyun; Hu, Guoxing
2015-11-01
According to the thermoelastic and heat conduction equations of laser ultrasonic, ultrasonic propagation images are obtained by solving finite element solution equations. Based on thermoelastic mechanism, a Wigner-Ville transform ultrasonic propagation imaging method of stronger frequency selectivity was proposed. An aluminum plate with defects was scanned by a pulsed laser, the ultrasonic waves produced by a pulsed laser were received by an ultrasonic sensor, and then ultrasonic propagation imaging on the aluminum plate was analyzed in detail. In order to isolate a damage-related ultrasonic wave, a Wigner-Ville algorithm as a frequency selectivity method was proposed to convert a complex time domain multiple wavefield into a simple frequency domain single wavefield. At last, we compared the conventional ultrasonic propagation imaging method with the Wigner-Ville transform ultrasonic propagation imaging method, which demonstrated that the Wigner-Ville transform ultrasonic propagation imaging method can effectively and intuitively evaluate the sizes of damages or flaws without any reference data, which should promote the application of the technique in the industry.
The many-body Wigner Monte Carlo method for time-dependent ab-initio quantum simulations
Sellier, J.M. Dimov, I.
2014-09-15
The aim of ab-initio approaches is the simulation of many-body quantum systems from the first principles of quantum mechanics. These methods are traditionally based on the many-body Schrödinger equation which represents an incredible mathematical challenge. In this paper, we introduce the many-body Wigner Monte Carlo method in the context of distinguishable particles and in the absence of spin-dependent effects. Despite these restrictions, the method has several advantages. First of all, the Wigner formalism is intuitive, as it is based on the concept of a quasi-distribution function. Secondly, the Monte Carlo numerical approach allows scalability on parallel machines that is practically unachievable by means of other techniques based on finite difference or finite element methods. Finally, this method allows time-dependent ab-initio simulations of strongly correlated quantum systems. In order to validate our many-body Wigner Monte Carlo method, as a case study we simulate a relatively simple system consisting of two particles in several different situations. We first start from two non-interacting free Gaussian wave packets. We, then, proceed with the inclusion of an external potential barrier, and we conclude by simulating two entangled (i.e. correlated) particles. The results show how, in the case of negligible spin-dependent effects, the many-body Wigner Monte Carlo method provides an efficient and reliable tool to study the time-dependent evolution of quantum systems composed of distinguishable particles.
NASA Astrophysics Data System (ADS)
Gelman, L.; Petrunin, I.; Komoda, J.
2010-02-01
The new chirp-Wigner higher order spectra (CWHOS) are proposed for transient signals with any known nonlinear polynomial variation of instantaneous frequency. The proposed technique is effective for nonlinearity detection for transient signals with nonlinear polynomial time variation of the instantaneous frequency.
NASA Astrophysics Data System (ADS)
Möller, Thomas
2016-12-01
General expressions for the matrix elements of the tight-binding operator are presented using the Racah-Wigner algebra, where the wave functions are expressed as coupled multiplet wave functions within a given angular momentum coupling scheme. The knowledge of all possible Slater determinants is not necessary and the matrix elements can be written as compact expressions computable with arbitrary accuracy.
NASA Technical Reports Server (NTRS)
Akhundova, E. A.; Dodonov, V. V.; Manko, V. I.
1993-01-01
The exact expressions for density matrix and Wigner functions of quantum systems are known only in special cases. Corresponding Hamiltonians are quadratic forms of Euclidean coordinates and momenta. In this paper we consider the problem of one-dimensional free particle movement in the bounded region 0 is less than x is less than a (including the case a = infinity).
González-Padilla, Jazmin E; Rosales-Hernández, Martha C; Padilla-Martínez, Itzia I; García-Báez, Efren V; Rojas-Lima, Susana; Salazar-Pereda, Veronica
2014-01-01
Molecules of 1,2-bis(4-bromophenyl)-1H-benzimidazole, C19H12Br2N2, (I), and 2-(4-bromophenyl)-1-(4-nitrophenyl)-1H-benzimidazole, C19H12BrN3O2, (II), are arranged in dimeric units through C-H...N and parallel-displaced π-stacking interactions favoured by the appropriate disposition of N- and C-bonded phenyl rings with respect to the mean benzimidazole plane. The molecular packing of the dimers of (I) and (II) arises by the concurrence of a diverse set of weak intermolecular C-X...D (X = H, NO2; D = O, π) interactions.
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.
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.
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 preliminary 3D model for cytochrome P450 2D6 constructed by homology model building.
Koymans, L M; Vermeulen, N P; Baarslag, A; Donné-Op den Kelder, G M
1993-06-01
A homology model building study of cytochrome P450 2D6 has been carried out based on the crystal structure of cytochrome P450 101. The primary sequences of P450 101 and P450 2D6 were aligned by making use of an automated alignment procedure. This alignment was adjusted manually by matching alpha-helices (C, D, G, I, J, K and L) and beta-sheets (beta 3/beta 4) of P450 101 that are proposed to be conserved in membrane-bound P450s (Ouzounis and Melvin [Eur. J. Biochem., 198 (1991) 307]) to the corresponding regions in the primary amino acid sequence of P450 2D6. Furthermore, alpha-helices B, B' and F were found to be conserved in P450 2D6. No significant homology between the remaining regions of P450 101 and P450 2D6 could be found and these regions were therefore deleted. A 3D model of P450 2D6 was constructed by copying the coordinates of the residues from the crystal structure of P450 101 to the corresponding residues in P450 2D6. The regions without a significant homology with P450 101 were not incorporated into the model. After energy-minimization of the resulting 3D model of P450 2D6, possible active site residues were identified by fitting the substrates debrisoquine and dextrometorphan into the proposed active site. Both substrates could be positioned into a planar pocket near the heme region formed by residues Val370, Pro371, Leu372, Trp316, and part of the oxygen binding site of P450 2D6. Furthermore, the carboxylate group of either Asp100 or Asp301 was identified as a possible candidate for the proposed interaction with basic nitrogen atom(s) of the substrates.(ABSTRACT TRUNCATED AT 250 WORDS)
The hyperbolic step potential: Anti-bound states, SUSY partners and Wigner time delays
NASA Astrophysics Data System (ADS)
Gadella, M.; Kuru, Ş.; Negro, J.
2017-04-01
We study the scattering produced by a one dimensional hyperbolic step potential, which is exactly solvable and shows an unusual interest because of its asymmetric character. The analytic continuation of the scattering matrix in the momentum representation has a branch cut and an infinite number of simple poles on the negative imaginary axis which are related with the so called anti-bound states. This model does not show resonances. Using the wave functions of the anti-bound states, we obtain supersymmetric (SUSY) partners which are the series of Rosen-Morse II potentials. We have computed the Wigner reflection and transmission time delays for the hyperbolic step and such SUSY partners. Our results show that the more bound states a partner Hamiltonian has the smaller is the time delay. We also have evaluated time delays for the hyperbolic step potential in the classical case and have obtained striking similitudes with the quantum case.
Signatures of Wigner molecule formation in interacting Dirac fermion quantum dots
Paananen, Tomi; Egger, Reinhold; Siedentop, Heinz
2011-02-15
We study N interacting massless Dirac fermions confined in a two-dimensional quantum dot. Physical realizations of this problem include a graphene monolayer and the surface state of a strong topological insulator. We consider both a magnetic confinement and an infinite mass confinement. The ground-state energy is computed as a function of the effective interaction parameter {alpha} from the Hartree-Fock approximation and, alternatively, by employing the Mueller exchange functional. For N=2, we compare those approximations to exact diagonalization results. The Hartree-Fock energies are highly accurate for the most relevant interaction range {alpha} < or approx. 2, but the Mueller functional leads to an unphysical instability when {alpha} > or approx. 0.756. Up to 20 particles were studied using Hartree-Fock calculations. Wigner molecule formation was observed for strong but realistic interactions, accompanied by a rich peak structure in the addition energy spectrum.
Brillouin-Wigner theory for Floquet topological phase transitions in spin-orbit-coupled materials
NASA Astrophysics Data System (ADS)
Mohan, Priyanka; Saxena, Ruchi; Kundu, Arijit; Rao, Sumathi
2016-12-01
We develop the high-frequency expansion based on the Brillouin-Wigner (B-W) perturbation theory for driven systems with spin-orbit coupling which is applicable to the cases of silicene, germanene, and stanene. We compute the effective Hamiltonian in the zero-photon subspace not only to order O (ω-1) but by keeping all the important terms to order O (ω-2) and obtain the photoassisted correction terms to both the hopping and the spin-orbit terms, as well as longer-ranged hopping terms. We then use the effective static Hamiltonian to compute the phase diagram in the high-frequency limit and compare it with the results of direct numerical computation of the Chern numbers of the Floquet bands and show that at sufficiently large frequencies, the B-W theory high-frequency expansion works well even in the presence of spin-orbit-coupling terms.
NASA Astrophysics Data System (ADS)
Bidari, Pooya Sobhe; Alirezaie, Javad; Tavakkoli, Jahan
2017-03-01
This paper presents a method for modeling and simulation of shear wave generation from a nonlinear Acoustic Radiation Force Impulse (ARFI) that is considered as a distributed force applied at the focal region of a HIFU transducer radiating in nonlinear regime. The shear wave propagation is simulated by solving the Navier's equation from the distributed nonlinear ARFI as the source of the shear wave. Then, the Wigner-Ville Distribution (WVD) as a time-frequency analysis method is used to detect the shear wave at different local points in the region of interest. The WVD results in an estimation of the shear wave time of arrival, its mean frequency and local attenuation which can be utilized to estimate medium's shear modulus and shear viscosity using the Voigt model.
Nonlinear transport of the inhomogeneous Wigner solid in a channel geometry
NASA Astrophysics Data System (ADS)
Badrutdinov, A. O.; Smorodin, A. V.; Rees, D. G.; Lin, J. Y.; Konstantinov, D.
2016-11-01
The transport properties of an electronic Wigner solid (WS) on the surface of superfluid helium-4 are investigated in a geometry that allows WS systems of significantly different sizes to be defined. We probe and compare transport phenomena attributed to the electronic order, such as Bragg-Cherenkov scattering and the WS sliding transition, in the cases of a long homogeneous WS, a small WS island, and a long inhomogeneous WS. We find no significant WS size effects on the transport properties, in contrast to predictions of theoretical works, which indicates an absence of long-range order in the WS systems under consideration. For the inhomogeneous WS, consisting of two distinct WSs connected in series, a complex interplay of individual WS transport properties is observed, as revealed in the observation of two separate Bragg-Cherenkov plateaus and WS sliding transitions. A simple model is proposed that provides a qualitative explanation of this behavior.
Dechoum, K.; Hahn, M. D.; Khoury, A. Z.
2010-04-15
We derive the steady-state solution of the Fokker-Planck equation that describes the dynamics of the nondegenerate optical parametric oscillator in the truncated Wigner representation of the density operator. We assume that the pump mode is strongly damped, which permits its adiabatic elimination. When the elimination is correctly executed, the resulting stochastic equations contain multiplicative noise terms and do not admit a potential solution. However, we develop a heuristic scheme leading to a satisfactory steady-state solution. This provides a clear view of the intracavity two-mode entangled state valid in all operating regimes of the optical parametric oscillator. A non-Gaussian distribution is obtained for the above threshold solution.
Iterative nonlinear beam propagation using Hamiltonian ray tracing and Wigner distribution function.
Gao, Hanhong; Tian, Lei; Zhang, Baile; Barbastathis, George
2010-12-15
We present an iterative method for simulating beam propagation in nonlinear media using Hamiltonian ray tracing. The Wigner distribution function of the input beam is computed at the entrance plane and is used as the initial condition for solving the Hamiltonian equations. Examples are given for the study of periodic self-focusing, spatial solitons, and Gaussian-Schell model in Kerr-effect media. Simulation results show good agreement with the split-step beam propagation method. The main advantage of ray tracing, even in the nonlinear case, is that ray diagrams are intuitive and easy to interpret in terms of traditional optical engineering terms, such as aberrations, ray-intercept plots, etc.
Inönü-Wigner contraction and D=2+1 supergravity
NASA Astrophysics Data System (ADS)
Concha, P. K.; Fierro, O.; Rodríguez, E. K.
2017-01-01
We present a generalization of the standard Inönü-Wigner contraction by rescaling not only the generators of a Lie superalgebra but also the arbitrary constants appearing in the components of the invariant tensor. The procedure presented here allows one to obtain explicitly the Chern-Simons supergravity action of a contracted superalgebra. In particular we show that the Poincaré limit can be performed to a D=2+1 ( p,q) AdS Chern-Simons supergravity in presence of the exotic form. We also construct a new three-dimensional ( 2,0) Maxwell Chern-Simons supergravity theory as a particular limit of ( 2,0) AdS-Lorentz supergravity theory. The generalization for N=p+q gravitinos is also considered.
Perturbation of the Wigner equation in inner product C{sup *}-modules
Chmielinski, Jacek; Ilisevic, Dijana; Moslehian, Mohammad Sal; Sadeghi, Ghadir
2008-03-15
Let A be a C*-algebra and B be a von Neumann algebra that both act on a Hilbert space H. Let M and N be inner product modules over A and B, respectively. Under certain assumptions, we show that for each mapping f:M{yields}N satisfying parallel |
Cat-states in the framework of Wigner-Heisenberg algebra
NASA Astrophysics Data System (ADS)
Dehghani, A.; Mojaveri, B.; Shirin, S.; Saedi, M.
2015-11-01
A one-parameter generalized Wigner-Heisenberg algebra (WHA) is reviewed in detail. It is shown that WHA verifies the deformed commutation rule [ x ˆ ,pˆλ ] = i(1 + 2 λ R ˆ) and also highlights the dynamical symmetries of the pseudo-harmonic oscillator (PHO). The present article is devoted to the study of new cat-states built from λ-deformed Schrödinger coherent states, which according to the Barut-Girardello scheme are defined as the eigenstates of the generalized annihilation operator. Particular attention is devoted to the limiting case where the Schrödinger cat states are obtained. Nonclassical features and quantum statistical properties of these states are studied by evaluation of Mandel's parameter and quadrature squeezing with respect to the λ-deformed canonical pairs (x ˆ ,pˆλ) . It is shown that these states minimize the uncertainty relations of each pair of the su(1 , 1) components.
Analysis of Low Probability of Intercept (LPI) Radar Signals Using the Wigner Distribution
NASA Astrophysics Data System (ADS)
Gau, Jen-Yu
2002-09-01
The parameters of Low Probability of Intercept (LPI) radar signals are hard to identity by using traditional periodogram signal processing techniques. Using the Wigner Distribution (WD), this thesis examines eight types of LPI radar signals. Signal to noise ratios of 0 dB and -6 dB are also investigated. The eight types LPI radar signals examined include Frequency Modulation Continuous Wave (FMCW), Frank code, Pt code, P2 code, P3 code, P4 code, COSTAS frequency hopping and Phase Shift Keying/Frequency Shift Keying (PSK/FSK) signals. Binary Phase Shift Keying (BPSK) signals although not used in modern LPI radars are also examined to further illustrate the principal characteristics of the WD.
Wigner rotation and Thomas precession: geometric phases and related physical theories
NASA Astrophysics Data System (ADS)
Brezov, Danail S.; Mladenova, Clementina D.; Mladenov, Ivaïlo M.
2015-06-01
We use a vector parameter description of the Lorentz groups in ℝ2,1 and ℝ3,1 to obtain an exact expression for the Thomas factor as a geometric phase. The effect of phase accumulation in Thomas-Wigner precession phenomena is seen as a manifestation of the hyperbolic solid angle theorem. On the infinitesimal level, our description involves affine connections on the noncompact Hopf fibrations U(1) → SU(1, 1) → Δ and SU(2) → PSL(2,ℂ) → H 3. The associated gauge field is a restriction of the familiar Yang-Mills anti-instanton. We also consider the dual compact case, and we discuss generalizations to arbitrary dimensions and applications in various branches of theoretical physics.
The truncated Wigner approximation for spin dynamics in systems of trapped ions, atoms & molecules
NASA Astrophysics Data System (ADS)
Schachenmayer, Johannes; Zhu, Bihui; Pikovski, Alexander; Hazzard, Kaden; Holland, Murray; Rey, Ana Maria
2014-05-01
Trapped ions and systems of cold atoms or molecules in optical lattices offer controlled environments to experimentally study non-equilibrium dynamics of many-body quantum spin-models with interactions of varying range. Theoretically calculating dynamics of observables for these experiments is a major challenge both analytically and numerically. While in one dimension, time-dependent density matrix renormalization group techniques (t-DMRG) allow for an efficient simulation of the dynamics as long as the time-dependent bi-partite entanglement growth remains moderate, a simulation for systems in two or three dimensions is more demanding. Here we present a numerical technique, which employs the truncated Wigner approximation (TWA) and which can be used to simulate Ramsey-dynamics for current experiments with trapped ions, alkaline earth atoms, polar molecules in optical lattices, or for systems with Rydberg atoms.
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.
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.
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.
Latent heat induced rotation limited aggregation in 2D ice nanocrystals
NASA Astrophysics Data System (ADS)
Bampoulis, Pantelis; Siekman, Martin H.; Kooij, E. Stefan; Lohse, Detlef; Zandvliet, Harold J. W.; Poelsema, Bene
2015-07-01
The basic science responsible for the fascinating shapes of ice crystals and snowflakes is still not understood. Insufficient knowledge of the interaction potentials and the lack of relevant experimental access to the growth process are to blame for this failure. Here, we study the growth of fractal nanostructures in a two-dimensional (2D) system, intercalated between mica and graphene. Based on our scanning tunneling spectroscopy data, we provide compelling evidence that these fractals are 2D ice. They grow while they are in material contact with the atmosphere at 20 °C and without significant thermal contact to the ambient. The growth is studied in situ, in real time and space at the nanoscale. We find that the growing 2D ice nanocrystals assume a fractal shape, which is conventionally attributed to Diffusion Limited Aggregation (DLA). However, DLA requires a low mass density mother phase, in contrast to the actual currently present high mass density mother phase. Latent heat effects and consequent transport of heat and molecules are found to be key ingredients for understanding the evolution of the snow (ice) flakes. We conclude that not the local availability of water molecules (DLA), but rather them having the locally required orientation is the key factor for incorporation into the 2D ice nanocrystal. In combination with the transport of latent heat, we attribute the evolution of fractal 2D ice nanocrystals to local temperature dependent rotation limited aggregation. The ice growth occurs under extreme supersaturation, i.e., the conditions closely resemble the natural ones for the growth of complex 2D snow (ice) flakes and we consider our findings crucial for solving the "perennial" snow (ice) flake enigma.
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.
Two-dimensional photonic crystal surfactant detection.
Zhang, Jian-Tao; Smith, Natasha; Asher, Sanford A
2012-08-07
We developed a novel two-dimensional (2-D) crystalline colloidal array photonic crystal sensing material for the visual detection of amphiphilic molecules in water. A close-packed polystyrene 2-D array monolayer was embedded in a poly(N-isopropylacrylamide) (PNIPAAm)-based hydrogel film. These 2-D photonic crystals placed on a mirror show intense diffraction that enables them to be used for visual determination of analytes. Binding of surfactant molecules attaches ions to the sensor that swells the PNIPAAm-based hydrogel. The resulting increase in particle spacing red shifts the 2-D diffracted light. Incorporation of more hydrophobic monomers increases the sensitivity to surfactants.
The influence of pressure on the structure of a 2D uranium(VI) carboxyphosphonoate compound
Spencer, Elinor C.; Ross, Nancy L.; Surbella, Robert G.; Cahill, Christopher L.
2014-10-15
We report the first quantitative analysis of the structural evolution of a uranyl bearing coordination polymer in response to pressure. The material that is central to this study, (UO{sub 2})(O{sub 3}PCH{sub 2}CO{sub 2}H) (1), is constructed from rigid 2D inorganic layers comprising edge sharing UO{sub 7} pentagonal bipyramids cross-linked by [PO{sub 3}(COOH)]{sup 2−} anions. Strong hydrogen bonding interactions exist between the pendent carboxylic acid groups on adjacent layers. Under pressure, 1 exhibits compressional behaviour primarily in the direction perpendicular to the inorganic layers, which is aided by a reduction in the interlayer distance and shifting of the layers with respect to each other. The bulk modulus for the 2D compound 1 is unexpectedly high [18.1(1) GPa] and is within the range reported for 3D CPs assembled from Zn{sup II} cations and inflexible imidazolate anions, and is at the lower end of the range of moduli observed for aluminosilicate zeolites (19–59 GPa). - Graphical Abstract: The compression mechanism and elastic constants for a 2D Uranium(VI) carboxyphosphonoate compound are reported. - Highlights: • The response to pressure of a uranium carboxyphosphonoate compound has been studied. • High-pressure single-crystal XRD data for this 2D uranium compound were collected. • Elastic constants for this material have been determined. • The compression mechanism for the compound has been elucidated.
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
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.
Electrochemical fabrication of 2D and 3D nickel nanowires using porous anodic alumina templates
NASA Astrophysics Data System (ADS)
Mebed, A. M.; Abd-Elnaiem, Alaa M.; Al-Hosiny, Najm M.
2016-06-01
Mechanically stable nickel (Ni) nanowires array and nanowires network were synthesized by pulse electrochemical deposition using 2D and 3D porous anodic alumina (PAA) templates. The structures and morphologies of as-prepared films were characterized by X-ray diffraction and scanning electron microscopy, respectively. The grown Ni nanowire using 3D PAA revealed more strength and larger surface area than has grown Ni use 2D PAA template. The prepared nanowires have a face-centered cubic crystal structure with average grain size 15 nm, and the preferred orientation of the nucleation of the nanowires is (111). The diameter of the nanowires is about 50-70 nm with length 3 µm. The resulting 3D Ni nanowire lattice, which provides enhanced mechanical stability and an increased surface area, benefits energy storage and many other applications which utilize the large surface area.
Hysteretic Spin Crossover in Two-Dimensional (2D) Hofmann-Type Coordination Polymers.
Liu, Wei; Wang, Lu; Su, Yu-Jun; Chen, Yan-Cong; Tucek, Jiri; Zboril, Radek; Ni, Zhao-Ping; Tong, Ming-Liang
2015-09-08
Three new two-dimensional (2D) Hofmann-type coordination polymers with general formula [Fe(3-NH2py)2M(CN)4] (3-NH2py = 3-aminopyridine, M = Ni (1), Pd (2), Pt (3)) have been synthesized. Magnetic susceptibility measurements show that they exhibited cooperative spin crossover (SCO) with remarkable hysteretic behaviors. Their hysteresis widths are 25, 37, and 30 K for 1-3, respectively. The single-crystal structure of 1 suggest that the pseudo-octahedral Fe sites are equatorially bridged by [M(CN)4](2-) to form 2D grids and axially coordinated by 3-NH2py ligands. The intermolecular interactions between layers (the offset face-to-face π···π interactions, hydrogen bonds, and weak N(amino)···Ni(II) contacts) together with the covalent bonds bridged by [M(CN)4](2-) units are responsible to the significant cooperativity.
A novel coordination polymer containing both interdigitated 1D chains and interpenetrated 2D grids.
Ayyappan, Ponnaiyan; Evans, Owen R; Lin, Wenbin
2002-07-01
A hydro(solvo)thermal reaction between zinc perchlorate and ethyl ester of a new pyridinecarboxylate bridging ligand of approximately 17.6 A in length yields a unique coordination polymer which contains both interdigitated infinite 1D chains and interpenetrated 2D rhombohedral grids [Zn(2.5)(L)(4)(mu(3)-OH)] x (H(2)O)(5), 1, where L is 3-[[4-(4-pyridylethenyl)phenyl]ethenyl]benzoate. The 1D chains contain mu(3)-bridged hydroxy groups and have a [Zn(4)(mu(3)-OH)(2)(L)(6)] stoichiometry, while the 2D grids have a Zn(L)(2) formula and diagonal distances of 31.7 and 25.2 A. Crystal data for 1: monoclinic space group P2/c, a = 15.686(2) A, b = 12.6103(16) A, c = 38.999(5) A, beta = 98.397(2) degrees, and Z = 4.
Self-Assembly of Shaped Nanoparticles into Free-Standing 2D and 3D Superlattices.
Li, Weikun; Wang, Ke; Zhang, Peng; He, Jie; Xu, Shaoyi; Liao, Yonggui; Zhu, Jintao; Xie, Xiaolin; Nie, Zhihong
2016-01-27
This article describes a novel supramolecular assembly-mediated strategy for the organization of Au nanoparticles (NPs) with different shapes (e.g., spheres, rods, and cubes) into large-area, free-standing 2D and 3D superlattices. This robust approach involves two major steps: (i) the organization of polymer-tethered NPs within the assemblies of supramolecular comblike block copolymers (CBCPs), and (ii) the disassembly of the assembled CBCP structures to produce free-standing NP superlattices. It is demonstrated that the crystal structures and lattice constants of the superlattices can be readily tailored by varying the molecular weight of tethered polymers, the volume fraction of NPs, and the matrix of CBCPs. This template-free approach may open a new avenue for the assembly of NPs into 2D and 3D structures with a wide range of potential applications.
Kudaka, Shoju; Matsumoto, Shuichi
2007-07-15
In order to acquire an extended Salecker-Wigner formula from which to derive the optimal accuracy in reading a clock with a massive particle as the signal, von Neumann's classical measurement is employed, by which simultaneously both position and momentum of the signal particle can be measured approximately. By an appropriate selection of wave function for the initial state of the composite system (a clock and a signal particle), the formula is derived accurately. Valid ranges of the running time of a clock with a given optimal accuracy are also given. The extended formula means that contrary to the Salecker-Wigner formula there exists the possibility of a higher accuracy of time measurement, even if the mass of the clock is very small.
A Deterministic Study of the Deficiency of the Wigner-Seitz Approximation for Pu/MOX Fuel Pins
DeHart, M.D.
1999-09-27
The Wigner-Seitz pin-cell approximation has long been applied as a modeling approximation in analysis of UO2 lattice fuel cells. In the past, this approximation has been appropriate for such fuel. However, with increasing attention drawn to mixed-oxide (MOX) fuels with significant plutonium content, it is important to understand the implications of the approximation in a uranium-plutonium matrix. The special geometric capabilities of the deterministic NEWT computer code have been used to assess the adequacy of the Wigner-Seitz cell in such an environment, as part of a larger study of computational aspects of MOX fuel modeling. Results of calculations using various approximations and boundary conditions are presented, and are validated by comparison to results obtained using KENO V.a and XSDRNPM.
Pereira, Patrícia A.; Noll, Bruce C.; Oliver, Allen G.; Silveira, Gustavo P.
2015-01-01
The formulation that the title compound, C18H18N2O4S2, adopts is a zwitterionic core with the charge separated to the sulfilimine S and N atoms and is supported by the two different S—N bond distances about the sulfinimine N atom [1.594 (2) and 1.631 (2) Å, respectively] that are typical for such bonds. The notably unusual bond is S—N(oxazolidinone) [1.692 (2) Å] that is longer than a typical S—N bond [1.603 (18) Å, Mogul analysis; Macrae et al. (2008 ▸). J. Appl. Cryst. 41, 466–470]. The bond-angle sum about sulfilimine sulfur (308.35°) reflects the trigonal–pyramidal geometry of this atom. Two of the angles are less than 100°. Despite the pyramidalization of this sulfur, there are no significant intermolecular interactions, beyond usual van der Waals contacts, in the crystal packing. PMID:26870517
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.
Gaunaurd, G.; Strifors, H.C.
1996-09-01
Time series data have been traditionally analyzed in either the time or the frequency domains. For signals with a time-varying frequency content, the combined time-frequency (TF) representations, based on the Cohen class of (generalized) Wigner distributions (WD`s) offer a powerful analysis tool. Using them, it is possible to: (1) trace the time-evolution of the resonance features usually present in a standard sonar cross section (SCS), or in a radar cross section (RCS) and (2) extract target information that may be difficult to even notice in an ordinary SCS or RCS. After a brief review of the fundamental properties of the WD, the authors discuss ways to reduce or suppress the cross term interference that appears in the WD of multicomponent systems. These points are illustrated with a variety of three-dimensional (3-D) plots of Wigner and pseudo-Wigner distributions (PWD), in which the strength of the distribution is depicted as the height of a Wigner surface with height scales measured by various color shades or pseudocolors. The authors also review studies they have made of the echoes returned by conducting or dielectric targets in the atmosphere, when they are illuminated by broadband radar pings. A TF domain analysis of these impulse radar returns demonstrates their superior informative content. These plots allow the identification of targets in an easier and clearer fashion than by the conventional RCS of narrowband systems. The authors show computed and measured plots of WD and PWD of various types of aircraft to illustrate the classification advantages of the approach at any aspect angle. They also show analogous results for metallic objects buried underground, in dielectric media, at various depths.
NASA Astrophysics Data System (ADS)
Wang, Tong-Tong; Fan, Hong-Yi
2016-12-01
Based on the one- and two-mode combinatorial squeezed state (H.Y. Fan, Phys. Rev. A. 41(3), 1526 (1990))which can enhance squeezing effect, we derive a new optical field by using partial tracing method, we not only obtain its density operator but also deduce its Wigner function by virtue of operators' Weyl ordering property. This new photon field possesses more photon numbers than the corresponding chaotic field, and can be applied to quantum controlling and quantum information processing.
Vyas, Manan; Kota, V.K.B.
2010-11-15
For m fermions in {Omega} number of single particle orbitals, each fourfold degenerate, we introduce and analyze in detail embedded Gaussian unitary ensemble of random matrices generated by random two-body interactions that are SU(4) scalar [EGUE(2)-SU(4)]. Here the SU(4) algebra corresponds to the Wigner's supermultiplet SU(4) symmetry in nuclei. Embedding algebra for the EGUE(2)-SU(4) ensemble is U(4{Omega}) contains U({Omega}) x SU(4). Exploiting the Wigner-Racah algebra of the embedding algebra, analytical expression for the ensemble average of the product of any two m particle Hamiltonian matrix elements is derived. Using this, formulas for a special class of U({Omega}) irreducible representations (irreps) {l_brace}4{sup r}, p{r_brace}, p = 0, 1, 2, 3 are derived for the ensemble averaged spectral variances and also for the covariances in energy centroids and spectral variances. On the other hand, simplifying the tabulations of Hecht for SU({Omega}) Racah coefficients, numerical calculations are carried out for general U({Omega}) irreps. Spectral variances clearly show, by applying Jacquod and Stone prescription, that the EGUE(2)-SU(4) ensemble generates ground state structure just as the quadratic Casimir invariant (C{sub 2}) of SU(4). This is further corroborated by the calculation of the expectation values of C{sub 2}[SU(4)] and the four periodicity in the ground state energies. Secondly, it is found that the covariances in energy centroids and spectral variances increase in magnitude considerably as we go from EGUE(2) for spinless fermions to EGUE(2) for fermions with spin to EGUE(2)-SU(4) implying that the differences in ensemble and spectral averages grow with increasing symmetry. Also for EGUE(2)-SU(4) there are, unlike for GUE, non-zero cross-correlations in energy centroids and spectral variances defined over spaces with different particle numbers and/or U({Omega}) [equivalently SU(4)] irreps. In the dilute limit defined by {Omega} {yields} {infinity
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.
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.
Basire, Marie; Borgis, Daniel; Vuilleumier, Rodolphe
2013-08-14
Langevin dynamics coupled to a quantum thermal bath (QTB) allows for the inclusion of vibrational quantum effects in molecular dynamics simulations at virtually no additional computer cost. We investigate here the ability of the QTB method to reproduce the quantum Wigner distribution of a variety of model potentials, designed to assess the performances and limits of the method. We further compute the infrared spectrum of a multidimensional model of proton transfer in the gas phase and in solution, using classical trajectories sampled initially from the Wigner distribution. It is shown that for this type of system involving large anharmonicities and strong nonlinear coupling to the environment, the quantum thermal bath is able to sample the Wigner distribution satisfactorily and to account for both zero point energy and tunneling effects. It leads to quantum time correlation functions having the correct short-time behavior, and the correct associated spectral frequencies, but that are slightly too overdamped. This is attributed to the classical propagation approximation rather than the generation of the quantized initial conditions themselves.
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.
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
Fabrication of 2D and 3D photonic structures using laser lithography
NASA Astrophysics Data System (ADS)
Gaso, P.; Jandura, D.; Pudis, D.
2016-12-01
In this paper we demonstrate possibilities of three-dimensional (3D) printing technology based on two photon polymerization. We used three-dimensional dip-in direct-laser-writing (DLW) optical lithography to fabricate 2D and 3D optical structures for optoelectronics and for optical sensing applications. DLW lithography allows us use a non conventional way how to couple light into the waveguide structure. We prepared ring resonator and we investigated its transmission spectral characteristic. We present 3D inverse opal structure from its design to printing and scanning electron microscope (SEM) imaging. Finally, SEM images of some prepared photonic crystal structures were performed.
NASA Astrophysics Data System (ADS)
Smithey, D. T.; Beck, M.; Cooper, J.; Raymer, M. G.; Faridani, A.
1993-01-01
We have used the recently demonstrated method of optical homodyne tomography (OHT) to measure the Wigner quasiprobability distribution (Wigner function) and the density matrix for both a squeezed-vacuum and a vacuum state of a single spatial-temporal mode of the electromagnetic field. This method consists of measuring a set of probability distributions for many different Hilbert-space representations of the field-quadrature amplitude, using balanced homodyne detection, and then using tomography to obtain the Wigner function. Once the Wigner function is obtained, one can acquire the density matrix, including its complex phase. In the case of a pure state, this technique yields an experimentally determined complex wavefunction, as demonstrated here for the vacuum. The density matrix represents a complete quantum mechanical characterization of the state. From the measured density matrix we have obtained the Pegg-Barnett optical phase distribution, and from the Wigner function, the Wigner optical phase distribution.
Hall Crystal States at ν = 2 and Moderate Landau Level Mixing
NASA Astrophysics Data System (ADS)
Murthy, Ganpathy
2000-08-01
The ν = 2 quantum Hall state at low Zeeman coupling is well known to be a translationally invariant singlet if Landau level mixing is small. At zero Zeeman interaction, as Landau level mixing increases, the translationally invariant state becomes unstable to an inhomogeneous state. This is the first realistic example of a full Hall crystal, which shows the coexistence of quantum Hall order and density wave order. The full Hall crystal differs from the more familiar Wigner crystal by a topological property, which results in it having only linearly dispersing collective modes at small q, and no q3/2 magnetophonon. I present calculations of the topological number and the collective modes.
Semiclassical Wigner theory of photodissociation in three dimensions: Shedding light on its basis
Arbelo-González, W.; Bonnet, L.; García-Vela, A.
2015-04-07
The semiclassical Wigner theory (SCWT) of photodissociation dynamics, initially proposed by Brown and Heller [J. Chem. Phys. 75, 186 (1981)] in order to describe state distributions in the products of direct collinear photodissociations, was recently extended to realistic three-dimensional triatomic processes of the same type [Arbelo-González et al., Phys. Chem. Chem. Phys. 15, 9994 (2013)]. The resulting approach, which takes into account rotational motions in addition to vibrational and translational ones, was applied to a triatomic-like model of methyl iodide photodissociation and its predictions were found to be in nearly quantitative agreement with rigorous quantum results, but at a much lower computational cost, making thereby SCWT a potential tool for the study of polyatomic reaction dynamics. Here, we analyse the main reasons for this agreement by means of an elementary model of fragmentation explicitly dealing with the rotational motion only. We show that our formulation of SCWT makes it a semiclassical approximation to an approximate planar quantum treatment of the dynamics, both of sufficient quality for the whole treatment to be satisfying.
Trovato, M.; Reggiani, L.
2011-12-15
By introducing a quantum entropy functional of the reduced density matrix, the principle of quantum maximum entropy is asserted as fundamental principle of quantum statistical mechanics. Accordingly, we develop a comprehensive theoretical formalism to construct rigorously a closed quantum hydrodynamic transport within a Wigner function approach. The theoretical formalism is formulated in both thermodynamic equilibrium and nonequilibrium conditions, and the quantum contributions are obtained by only assuming that the Lagrange multipliers can be expanded in powers of ({h_bar}/2{pi}){sup 2}. In particular, by using an arbitrary number of moments, we prove that (1) on a macroscopic scale all nonlocal effects, compatible with the uncertainty principle, are imputable to high-order spatial derivatives, both of the numerical density n and of the effective temperature T; (2) the results available from the literature in the framework of both a quantum Boltzmann gas and a degenerate quantum Fermi gas are recovered as a particular case; (3) the statistics for the quantum Fermi and Bose gases at different levels of degeneracy are explicitly incorporated; (4) a set of relevant applications admitting exact analytical equations are explicitly given and discussed; (5) the quantum maximum entropy principle keeps full validity in the classical limit, when ({h_bar}/2{pi}){yields}0.
Further Progress Applying the Generalized Wigner Distribution to Analysis of Vicinal Surfaces
NASA Astrophysics Data System (ADS)
Einstein, T. L.; Richards, Howard L.; Cohen, S. D.
2001-03-01
Terrace width distributions (TWDs) can be well fit by the generalized Wigner distribution (GWD), generally better than by conventional Gaussians, and thus offers a convenient way to estimate the dimensionless elastic repulsion strength tildeA from σ^2, the TWD variance.(T.L. Einstein and O. Pierre-Louis, Surface Sci. 424), L299 (1999) The GWD σ^2 accurately reproduces values for the two exactly soluble cases at small tildeA and in the asymptotic limit. Taxing numerical simulations show that the GWD σ^2 interpolates well between these limits. Extensive applications have been made to experimental data, esp. on Cu.(M. Giesen and T.L. Einstein, Surface Sci. 449), 191 (2000) Recommended analysis procedures are catalogued.(H.L. Richards, S.D. Cohen, TLE, & M. Giesen, Surf Sci 453), 59 (2000) Extensions of the GWD for multistep distributions are tested, with good agreement for second-neighbor distributions, less good for third.(TLE, HLR, SDC, & OP-L, Proc ISSI-PDSC2000, cond-mat/0012xxxxx) Alternatively, step-step correlation functions, about which there is more theoretical information, should be measured.
The Wigner-Ville Transform, An Approach to Interpret GPR Data: Outlining a Rik Zone
NASA Astrophysics Data System (ADS)
Chavez, R. E.; Samano, M. A.; Camara, M. E.; Tejero, A.; Flores-Marquez, L. E.; Arango, C.; Velazco, V.
2006-12-01
In this investigation, a time-frequency analysis is performed, based in the decomposition of the GPR signal in high- and low-frequencies. This process is combined with a statistical approach to detect signal changes in time and position simultaneously. The spectral analysis is carried out through the Wigner-Ville distribution (WVD). A cross-correlation can be computed between the original signal and the time-frequency components to obtain structural anomalies in the GPR observations, and to perform a correlation with the available geology. An example of this methodology is presented, where a series of traces where analyzed from a GPR profile surveyed in an eastern area of Mexico City. This is a heavily urbanized region built on the bottom of an ancient lake. The sediments are poorly consolidated and the extraction water rate has increased the areas of subsidence. Nowadays, most of family homes and public buildings, mainly schools have started to suffer heavy damages. The geophysical study carried out in the area permitted to detect areas of high risk. The data analysis combined with previous geological studies, which included stratigraphic columns allowed to identify the geophysical characteristics of the area, which will allow to the authorities to plan the future development of the area.
Role of confinements on the melting of Wigner molecules in quantum dots
NASA Astrophysics Data System (ADS)
Bhattacharya, Dyuti; Filinov, Alexei V.; Ghosal, Amit; Bonitz, Michael
2016-03-01
We explore the stability of a Wigner molecule (WM) formed in confinements with different geometries emulating the role of disorder and analyze the melting (or crossover) of such a system. Building on a recent calculation [D. Bhattacharya, A. Ghosal, Eur. Phys. J. B 86, 499 (2013)] that discussed the effects of irregularities on the thermal crossover in classical systems, we expand our studies in the untested territory by including both the effects of quantum fluctuations and of disorder. Our results, using classical and quantum (path integral) Monte Carlo techniques, unfold complementary mechanisms that drive the quantum and thermal crossovers in a WM and show that the symmetry of the confinement plays no significant role in determining the quantum crossover scale n X . This is because the zero-point motion screens the boundary effects within short distances. The phase diagram as a function of thermal and quantum fluctuations determined from independent criteria is unique, and shows "melting" from the WM to both the classical and quantum "liquids". An intriguing signature of weakening liquidity with increasing temperature, T, is found in the extreme quantum regime. The crossover is associated with production of defects. However, these defects appear to play distinct roles in driving the quantum and thermal "melting". Our analyses carry serious implications for a variety of experiments on many-particle systems - semiconductor heterostructure quantum dots, trapped ions, nanoclusters, colloids and complex plasma.
Trovato, M; Reggiani, L
2011-12-01
By introducing a quantum entropy functional of the reduced density matrix, the principle of quantum maximum entropy is asserted as fundamental principle of quantum statistical mechanics. Accordingly, we develop a comprehensive theoretical formalism to construct rigorously a closed quantum hydrodynamic transport within a Wigner function approach. The theoretical formalism is formulated in both thermodynamic equilibrium and nonequilibrium conditions, and the quantum contributions are obtained by only assuming that the Lagrange multipliers can be expanded in powers of h(2). In particular, by using an arbitrary number of moments, we prove that (1) on a macroscopic scale all nonlocal effects, compatible with the uncertainty principle, are imputable to high-order spatial derivatives, both of the numerical density n and of the effective temperature T; (2) the results available from the literature in the framework of both a quantum Boltzmann gas and a degenerate quantum Fermi gas are recovered as a particular case; (3) the statistics for the quantum Fermi and Bose gases at different levels of degeneracy are explicitly incorporated; (4) a set of relevant applications admitting exact analytical equations are explicitly given and discussed; (5) the quantum maximum entropy principle keeps full validity in the classical limit, when h → 0.
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.
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.
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.
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.
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.