Chiral scale and conformal invariance in 2D quantum field theory.
Hofman, Diego M; Strominger, Andrew
2011-10-14
It is well known that a local, unitary Poincaré-invariant 2D quantum field theory with a global scaling symmetry and a discrete non-negative spectrum of scaling dimensions necessarily has both a left and a right local conformal symmetry. In this Letter, we consider a chiral situation beginning with only a left global scaling symmetry and do not assume Lorentz invariance. We find that a left conformal symmetry is still implied, while right translations are enhanced either to a right conformal symmetry or a left U(1) Kac-Moody symmetry.
Character relations and replication identities in 2d Conformal Field Theory
NASA Astrophysics Data System (ADS)
Bantay, P.
2016-10-01
We study replication identities satisfied by conformal characters of a 2D CFT, providing a natural framework for a physics interpretation of the famous Hauptmodul property of Monstrous Moonshine, and illustrate the underlying ideas in simple cases.
Evangelina, Figueroa M.; Gabriel, Resendiz G.; Miguel, Perez P.
2008-08-11
A three-dimensional treatment planning system requires comparisons of calculated and measured dose distributions. It is necessary to confirm by means of patient specific QA that the dose distributions are correctly calculated, and that the patient data is correctly transferred to and delivered by the treatment machine. We used an analysis software for bi-dimensional dosimetric verification of conformal treatment and IMRT fields using as objective criterion the gamma index. An ionization chamber bi-dimensional array was used for absolute dose measurement in the complete field area.
2D Potential theory using complex functions and conformal mapping
NASA Astrophysics Data System (ADS)
Le Maire, Pauline; Munschy, Marc
2016-04-01
For infinitely horizontally extended bodies, functions that describe potential and field equations (gravity and magnetics) outside bodies are 2D and harmonic. The consequence of this property is that potential and field equations can be written as complex analytic functions. We define these complex functions whose real part is the commonly used real function and imaginary part is its Hilbert transform. Using data or synthetic cases the transformation is easily performed in the Fourier domain by setting to zero all values for negative frequencies. Written as complex functions of the complex variable, equations of potential and field in gravity and magnetics for different kinds of geometries are simple and correspond to powers of the inverse of the distance. For example, it is easily shown that for a tilted dyke, the dip and the apparent inclination have the same effect on the function and consequently that it is not possible, with data, to compute one of both values without knowing the other. Conformal mapping is an original way to display potential field functions. Considering that the complex variable corresponds to the real axis, complex potential field functions resume to a limaçon, a curve formed by the path of the point fixed to a circle when that circle rolls around the outside of another circle. For example, the point corresponding to the maximum distance to the origin of the complex magnetic field due to a cylinder, corresponds to the maximum of the analytic signal as defined by Nabighan in 1972 and its phase corresponds to the apparent inclination. Several applications are shown in different geological contexts using aeromagnetic data.
Conformal Laplace superintegrable systems in 2D: polynomial invariant subspaces
NASA Astrophysics Data System (ADS)
Escobar-Ruiz, M. A.; Miller, Willard, Jr.
2016-07-01
2nd-order conformal superintegrable systems in n dimensions are Laplace equations on a manifold with an added scalar potential and 2n-1 independent 2nd order conformal symmetry operators. They encode all the information about Helmholtz (eigenvalue) superintegrable systems in an efficient manner: there is a 1-1 correspondence between Laplace superintegrable systems and Stäckel equivalence classes of Helmholtz superintegrable systems. In this paper we focus on superintegrable systems in two-dimensions, n = 2, where there are 44 Helmholtz systems, corresponding to 12 Laplace systems. For each Laplace equation we determine the possible two-variate polynomial subspaces that are invariant under the action of the Laplace operator, thus leading to families of polynomial eigenfunctions. We also study the behavior of the polynomial invariant subspaces under a Stäckel transform. The principal new results are the details of the polynomial variables and the conditions on parameters of the potential corresponding to polynomial solutions. The hidden gl 3-algebraic structure is exhibited for the exact and quasi-exact systems. For physically meaningful solutions, the orthogonality properties and normalizability of the polynomials are presented as well. Finally, for all Helmholtz superintegrable solvable systems we give a unified construction of one-dimensional (1D) and two-dimensional (2D) quasi-exactly solvable potentials possessing polynomial solutions, and a construction of new 2D PT-symmetric potentials is established.
Universal Entanglement Entropy in 2D Conformal Quantum Critical Points
Hsu, Benjamin; Mulligan, Michael; Fradkin, Eduardo; Kim, Eun-Ah
2008-12-05
We study the scaling behavior of the entanglement entropy of two dimensional conformal quantum critical systems, i.e. systems with scale invariant wave functions. They include two-dimensional generalized quantum dimer models on bipartite lattices and quantum loop models, as well as the quantum Lifshitz model and related gauge theories. We show that, under quite general conditions, the entanglement entropy of a large and simply connected sub-system of an infinite system with a smooth boundary has a universal finite contribution, as well as scale-invariant terms for special geometries. The universal finite contribution to the entanglement entropy is computable in terms of the properties of the conformal structure of the wave function of these quantum critical systems. The calculation of the universal term reduces to a problem in boundary conformal field theory.
Widom, Julia R; Johnson, Neil P; von Hippel, Peter H; Marcus, Andrew H
2013-02-01
We have observed the conformation-dependent electronic coupling between the monomeric subunits of a dinucleotide of 2-aminopurine (2-AP), a fluorescent analog of the nucleic acid base adenine. This was accomplished by extending two-dimensional fluorescence spectroscopy (2D FS) - a fluorescence-detected variation of 2D electronic spectroscopy - to excite molecular transitions in the ultraviolet (UV) regime. A collinear sequence of four ultrafast laser pulses centered at 323 nm was used to resonantly excite the coupled transitions of 2-AP dinucleotide. The phases of the optical pulses were continuously swept at kilohertz frequencies, and the ensuing nonlinear fluorescence was phase-synchronously detected at 370 nm. Upon optimization of a point-dipole coupling model to our data, we found that in aqueous buffer the 2-AP dinucleotide adopts an average conformation in which the purine bases are non-helically stacked (center-to-center distance R12 = 3.5 Å ± 0.5 Å, twist angle θ12 = 5° ± 5°), which differs from the conformation of such adjacent bases in duplex DNA. These experiments establish UV-2D FS as a method for examining the local conformations of an adjacent pair of fluorescent nucleotides substituted into specific DNA or RNA constructs, which will serve as a powerful probe to interpret, in structural terms, biologically significant local conformational changes within the nucleic acid framework of protein-nucleic acid complexes.
Conformal scalar field wormholes
NASA Technical Reports Server (NTRS)
Halliwell, Jonathan J.; Laflamme, Raymond
1989-01-01
The Euclidian Einstein equations with a cosmological constant and a conformally coupled scalar field are solved, taking the metric to be of the Robertson-Walker type. In the case Lambda = 0, solutions are found which represent a wormhole connecting two asymptotically flat Euclidian regions. In the case Lambda greater than 0, the solutions represent tunneling from a small Tolman-like universe to a large Robertson-Walker universe.
Cauchy Conformal Fields in Dimensions {d > 2}
NASA Astrophysics Data System (ADS)
Friedan, Daniel; Keller, Christoph A.
2016-12-01
Holomorphic fields play an important role in 2d conformal field theory. We generalize them to {d > 2} by introducing the notion of Cauchy conformal fields, which satisfy a first order differential equation such that they are determined everywhere once we know their value on a codimension 1 surface. We classify all the unitary Cauchy fields. By analyzing the mode expansion on the unit sphere, we show that all unitary Cauchy fields are free in the sense that their correlation functions factorize on the 2-point function. We also discuss the possibility of non-unitary Cauchy fields and classify them in d = 3 and 4.
Ramadas, Sivaram N; Jackson, Joseph C; Dziewierz, Jerzy; O'Leary, Richard; Gachagan, Anthony
2014-03-01
Two-dimensional ultrasonic phased arrays are becoming increasingly popular in nondestructive evaluation (NDE). Sparse array element configurations are required to fully exploit the potential benefits of 2-D phased arrays. This paper applies the conformal mapping technique as a means of designing sparse 2-D array layouts for NDE applications. Modeling using both Huygens' field prediction theory and 2-D fast Fourier transformation is employed to study the resulting new structure. A conformal power map was used that, for fixed beam width, was shown in simulations to have a greater contrast than rectangular or random arrays. A prototype aperiodic 2-D array configuration for direct contact operation in steel, with operational frequency ~3 MHz, was designed using the array design principle described in this paper. Experimental results demonstrate a working sparse-array transducer capable of performing volumetric imaging.
Logarithmic conformal field theory
NASA Astrophysics Data System (ADS)
Gainutdinov, Azat; Ridout, David; Runkel, Ingo
2013-12-01
Conformal field theory (CFT) has proven to be one of the richest and deepest subjects of modern theoretical and mathematical physics research, especially as regards statistical mechanics and string theory. It has also stimulated an enormous amount of activity in mathematics, shaping and building bridges between seemingly disparate fields through the study of vertex operator algebras, a (partial) axiomatisation of a chiral CFT. One can add to this that the successes of CFT, particularly when applied to statistical lattice models, have also served as an inspiration for mathematicians to develop entirely new fields: the Schramm-Loewner evolution and Smirnov's discrete complex analysis being notable examples. When the energy operator fails to be diagonalisable on the quantum state space, the CFT is said to be logarithmic. Consequently, a logarithmic CFT is one whose quantum space of states is constructed from a collection of representations which includes reducible but indecomposable ones. This qualifier arises because of the consequence that certain correlation functions will possess logarithmic singularities, something that contrasts with the familiar case of power law singularities. While such logarithmic singularities and reducible representations were noted by Rozansky and Saleur in their study of the U (1|1) Wess-Zumino-Witten model in 1992, the link between the non-diagonalisability of the energy operator and logarithmic singularities in correlators is usually ascribed to Gurarie's 1993 article (his paper also contains the first usage of the term 'logarithmic conformal field theory'). The class of CFTs that were under control at this time was quite small. In particular, an enormous amount of work from the statistical mechanics and string theory communities had produced a fairly detailed understanding of the (so-called) rational CFTs. However, physicists from both camps were well aware that applications from many diverse fields required significantly more
On Animating 2D Velocity Fields
NASA Technical Reports Server (NTRS)
Kao, David; Pang, Alex
2000-01-01
A velocity field. even one that represents a steady state flow implies a dynamical system. Animated velocity fields is an important tool in understanding such complex phenomena. This paper looks at a number of techniques that animate velocity fields and propose two new alternatives, These are texture advection and streamline cycling. The common theme among these techniques is the use of advection on some texture to generate a realistic animation of the velocity field. Texture synthesis and selection for these methods are presented. Strengths and weaknesses of the techniques are also discussed in conjunction with several examples.
On Animating 2D Velocity Fields
NASA Technical Reports Server (NTRS)
Kao, David; Pang, Alex; Yan, Jerry (Technical Monitor)
2001-01-01
A velocity field, even one that represents a steady state flow, implies a dynamical system. Animated velocity fields is an important tool in understanding such complex phenomena. This paper looks at a number of techniques that animate velocity fields and propose two new alternatives. These are texture advection and streamline cycling. The common theme among these techniques is the use of advection on some texture to generate a realistic animation of the velocity field. Texture synthesis and selection for these methods are presented. Strengths and weaknesses of the techniques are also discussed in conjunctions with several examples.
2D-3D MIGRATION AND CONFORMATIONAL MULTIPLICATION OF CHEMICALS IN LARGE CHEMICAL INVENTORIES
Chemical interactions are three-dimensional (3D) in nature and require modeling chemicals as 3D entities. In turn, using 3D models of chemicals leads to the realization that a single 2D structure can have hundreds of different conformations, and the electronic properties of these...
2D anti{endash}de Sitter gravity as a conformally invariant mechanical system
Cadoni, M.; Carta, P.; Klemm, D.; Mignemi, S.
2001-06-15
We show that two-dimensional (2D) AdS gravity induces on the spacetime boundary a conformally invariant dynamics that can be described in terms of a de Alfaro{endash}Fubini{endash}Furlan model coupled to an external source with conformal dimension 2. The external source encodes information about the gauge symmetries of the 2D gravity system. Alternatively, there exists a description in terms of a mechanical system with anholonomic constraints. The considered systems are invariant under the action of the conformal group generated by a Virasoro algebra, which occurs also as an asymptotic symmetry algebra of two-dimensional anti{endash}de Sitter space. We calculate the central charge of the algebra and find perfect agreement between the statistical and thermodynamical entropies of AdS{sub 2} black holes.
Algebraic orbifold conformal field theories
Xu, Feng
2000-01-01
The unitary rational orbifold conformal field theories in the algebraic quantum field theory and subfactor theory framework are formulated. Under general conditions, it is shown that the orbifold of a given unitary rational conformal field theory generates a unitary modular category. Many new unitary modular categories are obtained. It is also shown that the irreducible representations of orbifolds of rank one lattice vertex operator algebras give rise to unitary modular categories and determine the corresponding modular matrices, which has been conjectured for some time. PMID:11106383
Widom, Julia R; Lee, Wonbae; Perdomo-Ortiz, Alejandro; Rappoport, Dmitrij; Molinski, Tadeusz F; Aspuru-Guzik, Alán; Marcus, Andrew H
2013-07-25
We studied the equilibrium conformations of a zinc porphyrin tweezer composed of two carboxylphenyl-functionalized zinc tetraphenyl porphyrin subunits connected by a 1,4-butyndiol spacer, which was suspended inside the amphiphilic regions of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) liposomes. By combining phase-modulation two-dimensional fluorescence spectroscopy (2D FS) with linear absorbance and fluorimetry, we determined that the zinc porphyrin tweezer adopts a mixture of folded and extended conformations in the membrane. By fitting an exciton-coupling model to a series of data sets recorded over a range of temperatures (17-85 °C) and at different laser center wavelengths, we determined that the folded form of the tweezer is stabilized by a favorable change in the entropy of the local membrane environment. Our results provide insights toward understanding the balance of thermodynamic factors that govern molecular assembly in membranes.
Holographic description of 2D conformal block in semi-classical limit
NASA Astrophysics Data System (ADS)
Chen, Bin; Wu, Jie-qiang; Zhang, Jia-ju
2016-10-01
In this paper, we study the holographic descriptions of the conformal block of heavy operators in two-dimensional large c conformal field theory. We consider the case that the operators are pairwise inserted such that the distance between the operators in a pair is much smaller than the others. In this case, each pair of heavy operators creates a conical defect in the bulk. We propose that the conformal block is dual to the on-shell action of three dimensional geometry with conical defects in the semi-classical limit. We show that the variation of the on-shell action with respect to the conical angle is equal to the length of the corresponding conical defect. We derive this differential relation on the conformal block in the field theory by introducing two extra light operators as both the probe and the perturbation. Our study also suggests that the area law of the holographic Rényi entropy must holds for a large class of states generated by a finite number of heavy operators insertion.
NASA Astrophysics Data System (ADS)
Tanaka, Satoyuki; Suzuki, Hirotaka; Sadamoto, Shota; Sannomaru, Shogo; Yu, Tiantang; Bui, Tinh Quoc
2016-08-01
Two-dimensional (2D) in-plane mixed-mode fracture mechanics problems are analyzed employing an efficient meshfree Galerkin method based on stabilized conforming nodal integration (SCNI). In this setting, the reproducing kernel function as meshfree interpolant is taken, while employing the SCNI for numerical integration of stiffness matrix in the Galerkin formulation. The strain components are smoothed and stabilized employing Gauss divergence theorem. The path-independent integral ( J-integral) is solved based on the nodal integration by summing the smoothed physical quantities and the segments of the contour integrals. In addition, mixed-mode stress intensity factors (SIFs) are extracted from the J-integral by decomposing the displacement and stress fields into symmetric and antisymmetric parts. The advantages and features of the present formulation and discretization in evaluation of the J-integral of in-plane 2D fracture problems are demonstrated through several representative numerical examples. The mixed-mode SIFs are evaluated and compared with reference solutions. The obtained results reveal high accuracy and good performance of the proposed meshfree method in the analysis of 2D fracture problems.
2D Hilbert transform for phase retrieval of speckle fields
NASA Astrophysics Data System (ADS)
Gorsky, M. P.; Ryabyi, P. A.; Ivanskyi, D. I.
2016-09-01
The paper presents principal approaches to diagnosing the structure forming skeleton of the complex optical field. An analysis of optical field singularity algorithms depending on intensity discretization and image resolution has been carried out. An optimal approach is chosen, which allows to bring much closer the solution of the phase problem of localization speckle-field special points. The use of a "window" 2D Hilbert transform for reconstruction of the phase distribution of the intensity of a speckle field is proposed. It is shown that the advantage of this approach consists in the invariance of a phase map to a change of the position of the kernel of transformation and in a possibility to reconstruct the structure-forming elements of the skeleton of an optical field, including singular points and saddle points. We demonstrate the possibility to reconstruct the equi-phase lines within a narrow confidence interval, and introduce an additional algorithm for solving the phase problem for random 2D intensity distributions.
2D FEM Heat Transfer & E&M Field Code
1992-04-02
TOPAZ and TOPAZ2D are two-dimensional implicit finite element computer codes for heat transfer analysis. TOPAZ2D can also be used to solve electrostatic and magnetostatic problems. The programs solve for the steady-state or transient temperature or electrostatic and magnetostatic potential field on two-dimensional planar or axisymmetric geometries. Material properties may be temperature or potential-dependent and either isotropic or orthotropic. A variety of time and temperature-dependent boundary conditions can be specified including temperature, flux, convection, and radiation. By implementing the user subroutine feature, users can model chemical reaction kinetics and allow for any type of functional representation of boundary conditions and internal heat generation. The programs can solve problems of diffuse and specular band radiation in an enclosure coupled with conduction in the material surrounding the enclosure. Additional features include thermal contact resistance across an interface, bulk fluids, phase change, and energy balances.
On the spectrum of 2D conformal field theories
NASA Astrophysics Data System (ADS)
Gepner, Doron
Possible unitary statistical models and SU(2) current algebra theories are classified up to certain "levels" of the Virasoro and Kac-Moody algebras. A connection that is found between the Virasoro and SU(2) Kac-Moody characters is used to generate unitary statistical models from the SU(2) theories. Using the "fusion rules" of the operator product algebra of these theories, we are able to check the consistency of the solutions, and to write down their operator product algebra. The connection between the two algebras extends also to the fusion rules.
NASA Astrophysics Data System (ADS)
Obuse, H.; Subramaniam, A. R.; Furusaki, A.; Gruzberg, I. A.; Ludwig, A. W. W.
2007-04-01
We study the multifractality (MF) of critical wave functions at boundaries and corners at the metal-insulator transition (MIT) for noninteracting electrons in the two-dimensional (2D) spin-orbit (symplectic) universality class. We find that the MF exponents near a boundary are different from those in the bulk. The exponents at a corner are found to be directly related to those at a straight boundary through a relation arising from conformal invariance. This provides direct numerical evidence for conformal invariance at the 2D spin-orbit MIT. The presence of boundaries modifies the MF of the whole sample even in the thermodynamic limit.
Perdomo-Ortiz, Alejandro; Widom, Julia R; Lott, Geoffrey A; Aspuru-Guzik, Alán; Marcus, Andrew H
2012-09-06
Two-dimensional fluorescence spectroscopy (2D FS) is applied to determine the conformation and femtosecond electronic population transfer in a dimer of magnesium meso tetraphenylporphyrin. The dimers are prepared by self-assembly of the monomer within the amphiphilic regions of 1,2-distearoyl-sn-glycero-3-phosphocholine liposomes. A theoretical framework to describe 2D FS experiments is presented, and a direct comparison is made between the observables of this measurement and those of 2D electronic spectroscopy (2D ES). The sensitivity of the method to varying dimer conformation is explored. A global multivariable fitting analysis of linear and 2D FS data indicates that the dimer adopts a "bent T-shaped" conformation. Moreover, the manifold of singly excited excitons undergoes rapid electronic dephasing and downhill population transfer on the time scale of ∼95 fs. The open conformation of the dimer suggests that its self-assembly is favored by an increase in entropy of the local membrane environment.
NASA Astrophysics Data System (ADS)
Baulieu, Laurent
1996-02-01
We construct a framework which unifies in pairs the fields and anti-fields of the Batalin and Vilkovisky quantization method. We consider gauge theories of p-forms coupled to Yang-Mills fields. Our algorithm generates many topological models of the Chern-Simons type or of the Donaldson-Witten type. Some of these models can undergo a partial breaking of their topological symmetries. We investigate the properties of 2D gravity in the Batalin and Vilkovisky quantization scheme. We find a structure which satisfies the holomorphic factorization and also properties analogous to those existing in the topological theories of forms. New conformal fields are introduced with their invariant action.
Characterization of nonlinear ultrasound fields of 2D therapeutic arrays
Yuldashev, Petr V.; Kreider, Wayne; Sapozhnikov, Oleg A.; Farr, Navid; Partanen, Ari; Bailey, Michael R.; Khokhlova, Vera
2015-01-01
A current trend in high intensity focused ultrasound (HIFU) technologies is to use 2D focused phased arrays that enable electronic steering of the focus, beamforming to avoid overheating of obstacles (such as ribs), and better focusing through inhomogeneities of soft tissue using time reversal methods. In many HIFU applications, the acoustic intensity in situ can reach thousands of W/cm2 leading to nonlinear propagation effects. At high power outputs, shock fronts develop in the focal region and significantly alter the bioeffects induced. Clinical applications of HIFU are relatively new and challenges remain for ensuring their safety and efficacy. A key component of these challenges is the lack of standard procedures for characterizing nonlinear HIFU fields under operating conditions. Methods that combine low-amplitude pressure measurements and nonlinear modeling of the pressure field have been proposed for axially symmetric single element transducers but have not yet been validated for the much more complex 3D fields generated by therapeutic arrays. Here, the method was tested for a clinical HIFU source comprising a 256-element transducer array. A numerical algorithm based on the Westervelt equation was used to enable 3D full-diffraction nonlinear modeling. With the acoustic holography method, the magnitude and phase of the acoustic field were measured at a low power output and used to determine the pattern of vibrations at the surface of the array. This pattern was then scaled to simulate a range of intensity levels near the elements up to 10 W/cm2. The accuracy of modeling was validated by comparison with direct measurements of the focal waveforms using a fiber-optic hydrophone. Simulation results and measurements show that shock fronts with amplitudes up to 100 MPa were present in focal waveforms at clinically relevant outputs, indicating the importance of strong nonlinear effects in ultrasound fields generated by HIFU arrays. PMID:26203345
Characterization of nonlinear ultrasound fields of 2D therapeutic arrays.
Yuldashev, Petr V; Kreider, Wayne; Sapozhnikov, Oleg A; Farr, Navid; Partanen, Ari; Bailey, Michael R; Khokhlova, Vera
2012-10-07
A current trend in high intensity focused ultrasound (HIFU) technologies is to use 2D focused phased arrays that enable electronic steering of the focus, beamforming to avoid overheating of obstacles (such as ribs), and better focusing through inhomogeneities of soft tissue using time reversal methods. In many HIFU applications, the acoustic intensity in situ can reach thousands of W/cm(2) leading to nonlinear propagation effects. At high power outputs, shock fronts develop in the focal region and significantly alter the bioeffects induced. Clinical applications of HIFU are relatively new and challenges remain for ensuring their safety and efficacy. A key component of these challenges is the lack of standard procedures for characterizing nonlinear HIFU fields under operating conditions. Methods that combine low-amplitude pressure measurements and nonlinear modeling of the pressure field have been proposed for axially symmetric single element transducers but have not yet been validated for the much more complex 3D fields generated by therapeutic arrays. Here, the method was tested for a clinical HIFU source comprising a 256-element transducer array. A numerical algorithm based on the Westervelt equation was used to enable 3D full-diffraction nonlinear modeling. With the acoustic holography method, the magnitude and phase of the acoustic field were measured at a low power output and used to determine the pattern of vibrations at the surface of the array. This pattern was then scaled to simulate a range of intensity levels near the elements up to 10 W/cm(2). The accuracy of modeling was validated by comparison with direct measurements of the focal waveforms using a fiber-optic hydrophone. Simulation results and measurements show that shock fronts with amplitudes up to 100 MPa were present in focal waveforms at clinically relevant outputs, indicating the importance of strong nonlinear effects in ultrasound fields generated by HIFU arrays.
Conformal regularization of Einstein's field equations
NASA Astrophysics Data System (ADS)
Röhr, Niklas; Uggla, Claes
2005-09-01
To study asymptotic structures, we regularize Einstein's field equations by means of conformal transformations. The conformal factor is chosen so that it carries a dimensional scale that captures crucial asymptotic features. By choosing a conformal orthonormal frame, we obtain a coupled system of differential equations for a set of dimensionless variables, associated with the conformal dimensionless metric, where the variables describe ratios with respect to the chosen asymptotic scale structure. As examples, we describe some explicit choices of conformal factors and coordinates appropriate for the situation of a timelike congruence approaching a singularity. One choice is shown to just slightly modify the so-called Hubble-normalized approach, and one leads to dimensionless first-order symmetric hyperbolic equations. We also discuss differences and similarities with other conformal approaches in the literature, as regards, e.g., isotropic singularities.
NASA Astrophysics Data System (ADS)
Obuse, Hideaki; Subramaniam, Arvind; Furusaki, Akira; Gruzberg, Ilya; Ludwig, Andreas
2007-03-01
We study the multifractality of critical wave functions at boundaries and corners at the Anderson metal-insulator transition for noninteracting electrons in the two-dimensional (2D) spin-orbit (symplectic) universality class. We find that the multifractal exponents near a boundary are different from those in the bulk. The exponents at a corner are found to be directly related to those at a straight boundary through a relation arising from conformal invariance. This provides direct numerical evidence for conformal invariance at the 2D spin-orbit metal-insulator transition. We also show that the presence of boundaries modifies the multifractality of the whole sample even in the thermodynamic limit.
Surface control of alkyl chain conformations and 2D chiral amplification.
Hauptmann, Nadine; Scheil, Katharina; Gopakumar, Thiruvancheril G; Otte, Franziska L; Schütt, Christian; Herges, Rainer; Berndt, Richard
2013-06-19
Trioctyl-functionalized triazatriangulenium (trioctyl-TATA) deposited on Au(111) and Ag(111) surfaces by electrospray ionization was investigated using low-temperature scanning tunneling microscopy. The molecule surprisingly adsorbs with gauche rather than anti conformations of the octyl groups. We observed chiral amplification in the islands. Only one of the eight possible configurations of the octyl groups was found in homochiral hexagonal networks. Quantum-chemical calculations confirmed and explained the preference for the gauche conformations of adsorbed trioctyl-TATA.
Zhang, Zepeng; Hu, Qian; Zhao, Yong
2017-01-01
In mammalian cells, in addition to double-stranded telomeric DNA at chromosome ends, extra telomere-homologous DNA is present that adopts different conformations, including single-stranded G- or C-rich DNA, extrachromosomal circular DNA (T-circle), and telomeric complex (T-complex) with an unidentified structure. The formation of such telomere-homologous DNA is closely related to telomeric DNA metabolism and chromosome end protection by telomeres. Conventional agarose gel electrophoresis is unable to separate DNA based on conformation. Here, we introduce the method of two-dimensional (2D) agarose electrophoresis in combination with in-gel native/denatured hybridization to determine different conformations formed by telomere-homologous DNA.
Recent progress in irrational conformal field theory
Halpern, M.B.
1993-09-01
In this talk, I will review the foundations of irrational conformal field theory (ICFT), which includes rational conformal field theory as a small subspace. Highlights of the review include the Virasoro master equation, the Ward identities for the correlators of ICFT and solutions of the Ward identities. In particular, I will discuss the solutions for the correlators of the g/h coset construction and the correlators of the affine-Sugawara nests on g {contains} h{sub 1} {contains} {hor_ellipsis} {contains} h{sub n}. Finally, I will discuss the recent global solution for the correlators of all the ICFT`s in the master equation.
Causality constraints in conformal field theory
Hartman, Thomas; Jain, Sachin; Kundu, Sandipan
2016-05-17
Causality places nontrivial constraints on QFT in Lorentzian signature, for example fixing the signs of certain terms in the low energy Lagrangian. In d dimensional conformal field theory, we show how such constraints are encoded in crossing symmetry of Euclidean correlators, and derive analogous constraints directly from the conformal bootstrap (analytically). The bootstrap setup is a Lorentzian four-point function corresponding to propagation through a shockwave. Crossing symmetry fixes the signs of certain log terms that appear in the conformal block expansion, which constrains the interactions of low-lying operators. As an application, we use the bootstrap to rederive the well known sign constraint on the (Φ)^{4} coupling in effective field theory, from a dual CFT. We also find constraints on theories with higher spin conserved currents. As a result, our analysis is restricted to scalar correlators, but we argue that similar methods should also impose nontrivial constraints on the interactions of spinning operators
Causality constraints in conformal field theory
NASA Astrophysics Data System (ADS)
Hartman, Thomas; Jain, Sachin; Kundu, Sandipan
2016-05-01
Causality places nontrivial constraints on QFT in Lorentzian signature, for example fixing the signs of certain terms in the low energy Lagrangian. In d dimensional conformal field theory, we show how such constraints are encoded in crossing symmetry of Euclidean correlators, and derive analogous constraints directly from the conformal bootstrap (analytically). The bootstrap setup is a Lorentzian four-point function corresponding to propagation through a shockwave. Crossing symmetry fixes the signs of certain log terms that appear in the conformal block expansion, which constrains the interactions of low-lying operators. As an application, we use the bootstrap to rederive the well known sign constraint on the (∂ ϕ)4 coupling in effective field theory, from a dual CFT. We also find constraints on theories with higher spin conserved currents. Our analysis is restricted to scalar correlators, but we argue that similar methods should also impose nontrivial constraints on the interactions of spinning operators.
2D quantum gravity on compact Riemann surfaces with non-conformal matter
NASA Astrophysics Data System (ADS)
Bilal, Adel; Leduc, Lætitia
2017-01-01
We study the gravitational action induced by coupling two-dimensional non-conformal, massive matter to gravity on a compact Riemann surface. We express this gravitational action in terms of finite and well-defined quantities for any value of the mass. A small-mass expansion gives back the Liouville action in the massless limit, the Mabuchi and Aubin-Yau actions to first order, as well as an infinite series of higher-order contributions written in terms of purely geometric quantities.
Light Trapping Enhancement in a Thin Film with 2D Conformal Periodic Hexagonal Arrays
NASA Astrophysics Data System (ADS)
Yang, Xi; Zhou, Suqiong; Wang, Dan; He, Jian; Zhou, Jun; Li, Xiaofeng; Gao, Pingqi; Ye, Jichun
2015-07-01
Applying a periodic light trapping array is an effective method to improve the optical properties in thin-film solar cells. In this work, we experimentally and theoretically investigate the light trapping properties of two-dimensional periodic hexagonal arrays in the framework of a conformal amorphous silicon film. Compared with the planar reference, the double-sided conformal periodic structures with all feature periodicities of sub-wavelength (300 nm), mid-wavelength (640 nm), and infrared wavelength (2300 nm) show significant broadband absorption enhancements under wide angles. The films with an optimum periodicity of 300 nm exhibit outstanding antireflection and excellent trade-off between light scattering performance and parasitic absorption loss. The average absorption of the optimum structure with a thickness of 160 nm is 64.8 %, which is much larger than the planar counterpart of 38.5 %. The methodology applied in this work can be generalized to rational design of other types of high-performance thin-film photovoltaic devices based on a broad range of materials.
Truncated conformal space approach for 2D Landau–Ginzburg theories
Coser, A.; Beria, M.; Brandino, G. P.; ...
2014-12-10
In this study, We examine the spectrum of Landau–Ginzburg theories in 1 + 1 dimensions using the truncated conformal space approach employing a compactified boson. We study these theories both in their broken and unbroken phases. We first demonstrate that we can reproduce the expected spectrum of a Φ² theory (i.e. a free massive boson) in this framework. We then turn to Φ⁴ in its unbroken phase and compare our numerical results with the predictions of two-loop perturbation theory, finding excellent agreement. We then analyze the broken phase of Φ⁴ where kink excitations together with their bound states are present.more » We confirm the semiclassical predictions for this model on the number of stable kink-antikink bound states. We also test the semiclassics in the double well phase of Φ⁶ Landau-Ginzburg theory, again finding agreement.« less
Truncated conformal space approach for 2D Landau–Ginzburg theories
Coser, A.; Beria, M.; Brandino, G. P.; Konik, R. M.; Mussardo, G.
2014-12-10
In this study, We examine the spectrum of Landau–Ginzburg theories in 1 + 1 dimensions using the truncated conformal space approach employing a compactified boson. We study these theories both in their broken and unbroken phases. We first demonstrate that we can reproduce the expected spectrum of a Φ² theory (i.e. a free massive boson) in this framework. We then turn to Φ⁴ in its unbroken phase and compare our numerical results with the predictions of two-loop perturbation theory, finding excellent agreement. We then analyze the broken phase of Φ⁴ where kink excitations together with their bound states are present. We confirm the semiclassical predictions for this model on the number of stable kink-antikink bound states. We also test the semiclassics in the double well phase of Φ⁶ Landau-Ginzburg theory, again finding agreement.
Livnat-Levanon, Nurit; I. Gilson, Amy; Ben-Tal, Nir; Lewinson, Oded
2016-01-01
ABC transporters comprise a large and ubiquitous family of proteins. From bacteria to man they translocate solutes at the expense of ATP hydrolysis. Unlike other enzymes that use ATP as an energy source, ABC transporters are notorious for having high levels of basal ATPase activity: they hydrolyze ATP also in the absence of their substrate. It is unknown what are the effects of such prolonged and constant activity on the stability and function of ABC transporters or any other enzyme. Here we report that prolonged ATP hydrolysis is beneficial to the ABC transporter BtuC2D2. Using ATPase assays, surface plasmon resonance interaction experiments, and transport assays we observe that the constantly active transporter remains stable and functional for much longer than the idle one. Remarkably, during extended activity the transporter undergoes a slow conformational change (hysteresis) and gradually attains a hyperactive state in which it is more active than it was to begin with. This phenomenon is different from stabilization of enzymes by ligand binding: the hyperactive state is only reached through ATP hydrolysis, and not ATP binding. BtuC2D2 displays a strong conformational memory for this excited state, and takes hours to return to its basal state after catalysis terminates. PMID:26905293
Turbulent transport in 2D collisionless guide field reconnection
NASA Astrophysics Data System (ADS)
Muñoz, P. A.; Büchner, J.; Kilian, P.
2017-02-01
Transport in hot and dilute, i.e., collisionless, astrophysical and space, plasmas is called "anomalous." This transport is due to the interaction between the particles and the self-generated turbulence by their collective interactions. The anomalous transport has very different and not well known properties compared to the transport due to binary collisions, dominant in colder and denser plasmas. Because of its relevance for astrophysical and space plasmas, we explore the excitation of turbulence in current sheets prone to component- or guide-field reconnection, a process not well understood yet. This configuration is typical for stellar coronae, and it is created in the laboratory for which a 2.5D geometry applies. In our analysis, in addition to the immediate vicinity of the X-line, we also include regions outside and near the separatrices. We analyze the anomalous transport properties by using 2.5D Particle-in-Cell code simulations. We split off the mean slow variation (in contrast to the fast turbulent fluctuations) of the macroscopic observables and determine the main transport terms of the generalized Ohm's law. We verify our findings by comparing with the independently determined slowing-down rate of the macroscopic currents (due to a net momentum transfer from particles to waves) and with the transport terms obtained by the first order correlations of the turbulent fluctuations. We find that the turbulence is most intense in the "low density" separatrix region of guide-field reconnection. It is excited by streaming instabilities, is mainly electrostatic and "patchy" in space, and so is the associated anomalous transport. Parts of the energy exchange between turbulence and particles are reversible and quasi-periodic. The remaining irreversible anomalous resistivity can be parametrized by an effective collision rate ranging from the local ion-cyclotron to the lower-hybrid frequency. The contributions to the parallel and the perpendicular (to the magnetic
Comments on conformal Killing vector fields and quantum field theory
Brown, M.R.; Ottewill, A.C.; Siklos, S.T.C.
1982-10-15
We give a comprehensive analysis of those vacuums for flat and conformally flat space-times which can be defined by timelike, hypersurface-orthogonal, conformal Killing vector fields. We obtain formulas for the difference in stress-energy density between any two such states and display the correspondence with the renormalized stress tensors. A brief discussion is given of the relevance of these results to quantum-mechanical measurements made by noninertial observers moving through flat space.
Logarithmic conformal field theory: beyond an introduction
NASA Astrophysics Data System (ADS)
Creutzig, Thomas; Ridout, David
2013-12-01
This article aims to review a selection of central topics and examples in logarithmic conformal field theory. It begins with the remarkable observation of Cardy that the horizontal crossing probability of critical percolation may be computed analytically within the formalism of boundary conformal field theory. Cardy’s derivation relies on certain implicit assumptions which are shown to lead inexorably to indecomposable modules and logarithmic singularities in correlators. For this, a short introduction to the fusion algorithm of Nahm, Gaberdiel and Kausch is provided. While the percolation logarithmic conformal field theory is still not completely understood, there are several examples for which the formalism familiar from rational conformal field theory, including bulk partition functions, correlation functions, modular transformations, fusion rules and the Verlinde formula, has been successfully generalized. This is illustrated for three examples: the singlet model \\mathfrak {M} (1,2), related to the triplet model \\mathfrak {W} (1,2), symplectic fermions and the fermionic bc ghost system; the fractional level Wess-Zumino-Witten model based on \\widehat{\\mathfrak {sl}} \\left( 2 \\right) at k=-\\frac{1}{2}, related to the bosonic βγ ghost system; and the Wess-Zumino-Witten model for the Lie supergroup \\mathsf {GL} \\left( 1 {\\mid} 1 \\right), related to \\mathsf {SL} \\left( 2 {\\mid} 1 \\right) at k=-\\frac{1}{2} and 1, the Bershadsky-Polyakov algebra W_3^{(2)} and the Feigin-Semikhatov algebras W_n^{(2)}. These examples have been chosen because they represent the most accessible, and most useful, members of the three best-understood families of logarithmic conformal field theories. The logarithmic minimal models \\mathfrak {W} (q,p), the fractional level Wess-Zumino-Witten models, and the Wess-Zumino-Witten models on Lie supergroups (excluding \\mathsf {OSP} \\left( 1 {\\mid} 2n \\right)). In this review, the emphasis lies on the representation theory
Causality constraints in conformal field theory
Hartman, Thomas; Jain, Sachin; Kundu, Sandipan
2016-05-17
Causality places nontrivial constraints on QFT in Lorentzian signature, for example fixing the signs of certain terms in the low energy Lagrangian. In d dimensional conformal field theory, we show how such constraints are encoded in crossing symmetry of Euclidean correlators, and derive analogous constraints directly from the conformal bootstrap (analytically). The bootstrap setup is a Lorentzian four-point function corresponding to propagation through a shockwave. Crossing symmetry fixes the signs of certain log terms that appear in the conformal block expansion, which constrains the interactions of low-lying operators. As an application, we use the bootstrap to rederive the well knownmore » sign constraint on the (Φ)4 coupling in effective field theory, from a dual CFT. We also find constraints on theories with higher spin conserved currents. As a result, our analysis is restricted to scalar correlators, but we argue that similar methods should also impose nontrivial constraints on the interactions of spinning operators« less
Conformal field theory on affine Lie groups
Clubok, Kenneth Sherman
1996-04-01
Working directly on affine Lie groups, we construct several new formulations of the WZW model, the gauged WZW model, and the generic affine-Virasoro action. In one formulation each of these conformal field theories (CFTs) is expressed as a one-dimensional mechanical system whose variables are coordinates on the affine Lie group. When written in terms of the affine group element, this formulation exhibits a two-dimensional WZW term. In another formulation each CFT is written as a two-dimensional field theory, with a three- dimensional WZW term, whose fields are coordinates on the affine group. On the basis of these equivalent formulations, we develop a translation dictionary in which the new formulations on the affine Lie group are understood as mode formulations of the conventional formulations on the Lie group. Using this dictionary, we also express each CFT as a three-dimensional field theory on the Lie group with a four-dimensional WZW term. 36 refs.
Excitation entanglement entropy in two dimensional conformal field theories
NASA Astrophysics Data System (ADS)
Sheikh-Jabbari, M. M.; Yavartanoo, H.
2016-12-01
We analyze how excitations affect the entanglement entropy for an arbitrary entangling interval in a 2d conformal field theory (CFT) using the holographic entanglement entropy techniques as well as direct CFT computations. We introduce the excitation entanglement entropy ΔhS , the difference between the entanglement entropy generic excitations and their arbitrary conformal descendants denoted through h . The excitation entanglement entropy, unlike the entanglement entropy, is a finite quantity (independent of the cutoff), and hence a good physical observable. We show that the excitation entanglement entropy for any given interval is uniquely specified by a local second order differential equation sourced by the one point function of the energy momentum tensor computed in the excited background state, and two boundary and smoothness conditions. We analyze low and high temperature behavior of the excitation entanglement entropy and show that ΔhS grows as a function of temperature. We prove an "integrated positivity" for the excitation entanglement entropy, that although ΔhS can be positive or negative, its average value is always positive. We also discuss the mutual and multipartite information and (strong) subadditivity inequality in the presence of generic excitations and their conformal descendants.
Scale invariance, conformality, and generalized free fields
Dymarsky, Anatoly; Farnsworth, Kara; Komargodski, Zohar; Luty, Markus A.; Prilepina, Valentina
2016-02-16
This paper addresses the question of whether there are 4D Lorentz invariant unitary quantum fi eld theories with scale invariance but not conformal invariance. We present an important loophole in the arguments of Luty-Polchinski-Rattazzi and Dymarsky-Komargodski-Schwimmer-Theisen that is the trace of the energy-momentum tensor T could be a generalized free field. In this paper we rule out this possibility. The key ingredient is the observation that a unitary theory with scale but not conformal invariance necessarily has a non-vanishing anomaly for global scale transformations. We show that this anomaly cannot be reproduced if T is a generalized free field unless the theory also contains a dimension-2 scalar operator. In the special case where such an operator is present it can be used to redefine ("improve") the energy-momentum tensor, and we show that there is at least one energy-momentum tensor that is not a generalized free field. In addition, we emphasize that, in general, large momentum limits of correlation functions cannot be understood from the leading terms of the coordinate space OPE. This invalidates a recent argument by Farnsworth-Luty-Prilepina (FLP). Finally, despite the invalidity of the general argument of FLP, some of the techniques turn out to be useful in the present context.
Scale invariance, conformality, and generalized free fields
Dymarsky, Anatoly; Farnsworth, Kara; Komargodski, Zohar; ...
2016-02-16
This paper addresses the question of whether there are 4D Lorentz invariant unitary quantum fi eld theories with scale invariance but not conformal invariance. We present an important loophole in the arguments of Luty-Polchinski-Rattazzi and Dymarsky-Komargodski-Schwimmer-Theisen that is the trace of the energy-momentum tensor T could be a generalized free field. In this paper we rule out this possibility. The key ingredient is the observation that a unitary theory with scale but not conformal invariance necessarily has a non-vanishing anomaly for global scale transformations. We show that this anomaly cannot be reproduced if T is a generalized free field unlessmore » the theory also contains a dimension-2 scalar operator. In the special case where such an operator is present it can be used to redefine ("improve") the energy-momentum tensor, and we show that there is at least one energy-momentum tensor that is not a generalized free field. In addition, we emphasize that, in general, large momentum limits of correlation functions cannot be understood from the leading terms of the coordinate space OPE. This invalidates a recent argument by Farnsworth-Luty-Prilepina (FLP). Finally, despite the invalidity of the general argument of FLP, some of the techniques turn out to be useful in the present context.« less
Operator algebra in logarithmic conformal field theory
Nagi, Jasbir
2005-10-15
For some time now, conformal field theories in two dimensions have been studied as integrable systems. Much of the success of these studies is related to the existence of an operator algebra of the theory. In this paper, some of the extensions of this machinery to the logarithmic case are studied and used. More precisely, from Moebius symmetry constraints, the generic three- and four-point functions of logarithmic quasiprimary fields are calculated in closed form for arbitrary Jordan rank. As an example, c=0 disordered systems with nondegenerate vacua are studied. With the aid of two-, three-, and four-point functions, the operator algebra is obtained and associativity of the algebra studied.
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.
Introduction to string theory and conformal field theory
Belavin, A. A. Tarnopolsky, G. M.
2010-05-15
A concise survey of noncritical string theory and two-dimensional conformal field theory is presented. A detailed derivation of a conformal anomaly and the definition and general properties of conformal field theory are given. Minimal string theory, which is a special version of the theory, is considered. Expressions for the string susceptibility and gravitational dimensions are derived.
Entanglement Hamiltonians in two-dimensional conformal field theory
NASA Astrophysics Data System (ADS)
Cardy, John; Tonni, Erik
2016-12-01
We enumerate the cases in 2d conformal field theory where the logarithm of the reduced density matrix (the entanglement or modular Hamiltonian) may be written as an integral over the energy-momentum tensor times a local weight. These include known examples and new ones corresponding to the time-dependent scenarios of a global and local quench. In these latter cases the entanglement Hamiltonian depends on the momentum density as well as the energy density. In all cases the entanglement spectrum is that of the appropriate boundary CFT. We emphasize the role of boundary conditions at the entangling surface and the appearance of boundary entropies as universal O(1) terms in the entanglement entropy.
2D-2D tunneling field-effect transistors using WSe2/SnSe2 heterostructures
NASA Astrophysics Data System (ADS)
Roy, Tania; Tosun, Mahmut; Hettick, Mark; Ahn, Geun Ho; Hu, Chenming; Javey, Ali
2016-02-01
Two-dimensional materials present a versatile platform for developing steep transistors due to their uniform thickness and sharp band edges. We demonstrate 2D-2D tunneling in a WSe2/SnSe2 van der Waals vertical heterojunction device, where WSe2 is used as the gate controlled p-layer and SnSe2 is the degenerately n-type layer. The van der Waals gap facilitates the regulation of band alignment at the heterojunction, without the necessity of a tunneling barrier. ZrO2 is used as the gate dielectric, allowing the scaling of gate oxide to improve device subthreshold swing. Efficient gate control and clean interfaces yield a subthreshold swing of ˜100 mV/dec for >2 decades of drain current at room temperature, hitherto unobserved in 2D-2D tunneling devices. The subthreshold swing is independent of temperature, which is a clear signature of band-to-band tunneling at the heterojunction. A maximum switching ratio ION/IOFF of 107 is obtained. Negative differential resistance in the forward bias characteristics is observed at 77 K. This work bodes well for the possibilities of two-dimensional materials for the realization of energy-efficient future-generation electronics.
Najbauer, Eszter E; Bazsó, Gábor; Apóstolo, Rui; Fausto, Rui; Biczysko, Malgorzata; Barone, Vincenzo; Tarczay, György
2015-08-20
The conformers of α-serine were investigated by matrix-isolation IR spectroscopy combined with NIR laser irradiation. This method, aided by 2D correlation analysis, enabled unambiguously grouping the spectral lines to individual conformers. On the basis of comparison of at least nine experimentally observed vibrational transitions of each conformer with empirically scaled (SQM) and anharmonic (GVPT2) computed IR spectra, six conformers were identified. In addition, the presence of at least one more conformer in Ar matrix was proved, and a short-lived conformer with a half-life of (3.7 ± 0.5) × 10(3) s in N2 matrix was generated by NIR irradiation. The analysis of the NIR laser-induced conversions revealed that the excitation of the stretching overtone of both the side chain and the carboxylic OH groups can effectively promote conformational changes, but remarkably different paths were observed for the two kinds of excitations.
Free □ k scalar conformal field theory
NASA Astrophysics Data System (ADS)
Brust, Christopher; Hinterbichler, Kurt
2017-02-01
We consider the generalizations of the free U( N ) and O( N ) scalar conformal field theories to actions with higher powers of the Laplacian □ k , in general dimension d. We study the spectra, Verma modules, anomalies and OPE of these theories. We argue that in certain d and k, the spectrum contains zero norm operators which are both primary and descendant, as well as extension operators which are neither primary nor descendant. In addition, we argue that in even dimensions d ≤ 2 k, there are well-defined operator algebras which are related to the □ k theories and are novel in that they have a finite number of single-trace states.
Field effect biosensing platform based on 2D α-MoO(3).
Balendhran, Sivacarendran; Walia, Sumeet; Alsaif, Manal; Nguyen, Emily P; Ou, Jian Zhen; Zhuiykov, Serge; Sriram, Sharath; Bhaskaran, Madhu; Kalantar-Zadeh, Kourosh
2013-11-26
Electrical-based biosensing platforms offer ease of fabrication and simple sensing solutions. Recently, two-dimensional (2D) semiconductors have been proven to be excellent for the fabrication of field effect transistors (FETs) due to their large transconductance, which can be efficiently used for developing sensitive bioplatforms. We present a 2D molybdenum trioxide (MoO3) FET based biosensing platform, using bovine serum albumin as a model protein. The conduction channel is a nanostructured film made of 2D α-MoO3 nanoflakes, with the majority of nanoflake thicknesses being equal to or less than 2.8 nm. The response time is impressively low (less than 10 s), which is due to the high permittivity of the 2D α-MoO3 nanoflakes. The system offers a competitive solution for future biosensing applications.
Schmidt, Michael P; Martínez, Carmen Enid
2016-08-09
Protein adsorption onto clay minerals is a process with wide-ranging impacts on the environmental cycling of nutrients and contaminants. This process is influenced by kinetic and conformational factors that are often challenging to probe in situ. This study represents an in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic investigation of the adsorption of a model protein (bovine serum albumin (BSA)) onto a clay mineral (montmorillonite) at four concentrations (1.50, 3.75, 7.50, and 15.0 μM) under environmentally relevant conditions. At all concentrations probed, FTIR spectra show that BSA readily adsorbs onto montmorillonite. Adsorption kinetics follow an Elovich model, suggesting that primary limitations on adsorption rates are surface-related heterogeneous energetic restrictions associated with protein rearrangement and lateral protein-protein interaction. BSA adsorption onto montmorillonite fits the Langmuir model, yielding K = 5.97 × 10(5) M(-1). Deconvolution and curve fitting of the amide I band at the end of the adsorption process (∼120 min) shows a large extent of BSA unfolding upon adsorption at 1.50 μM, with extended chains and turns increasing at the expense of α-helices. At higher concentrations/surface coverages, BSA unfolding is less pronounced and a more compact structure is assumed. Two-dimensional correlation spectroscopic (2D-COS) analysis reveals three different pathways corresponding to adsorbed conformations. At 1.50 μM, adsorption increases extended chains, followed by a loss in α-helices and a subsequent increase in turns. At 3.75 μM, extended chains decrease and then aggregated strands increase and side chains decrease, followed by a decrease in turns. With 7.50 and 15.0 μM BSA, the loss of side-chain vibrations is followed by an increase in aggregated strands and a subsequent decrease in turns and extended chains. Overall, the BSA concentration and resultant surface coverage have a profound
Inflation and deformation of conformal field theory
Garriga, Jaume; Urakawa, Yuko E-mail: yurakawa@ffn.ub.es
2013-07-01
It has recently been suggested that a strongly coupled phase of inflation may be described holographically in terms of a weakly coupled quantum field theory (QFT). Here, we explore the possibility that the wave function of an inflationary universe may be given by the partition function of a boundary QFT. We consider the case when the field theory is a small deformation of a conformal field theory (CFT), by the addition of a relevant operator O, and calculate the primordial spectrum predicted in the corresponding holographic inflation scenario. Using the Ward-Takahashi identity associated with Weyl rescalings, we derive a simple relation between correlators of the curvature perturbation ζ and correlators of the deformation operator O at the boundary. This is done without specifying the bulk theory of gravitation, so that the result would also apply to cases where the bulk dynamics is strongly coupled. We comment on the validity of the Suyama-Yamaguchi inequality, relating the bi-spectrum and tri-spectrum of the curvature perturbation.
Soap film as a 2D system: Diffusion and flow fields
NASA Astrophysics Data System (ADS)
Vivek, Skanda; Weeks, Eric
2014-03-01
We use microrheology to measure the 2D (interfacial) viscosity of soap films. Microrheology uses the diffusivity of tracer particles suspended in the soap film to infer viscosity. Our tracer particles are colloids of diameters d = 0.10 and 0.18 microns. We measure the interfacial viscosity of soap films ranging in thickness from 0.1 to 3 microns. The thickness of these films is measured using the infrared absorbance of the water based soap films. From film thickness, viscosity of the fluid used to make the film and particle diffusivity, we can infer the interfacial viscosity due to the surfactant layers at the film/air interfaces. We find positive constant interfacial viscosities for thin films (h/d < 5), within error. For thicker films, we find negative viscosities, indicating 3D effects begin to play a role, as air stresses become less important. The transition from 2D to 3D properties as a function of h/d is sharp at about h/d=6. Additionally, we measure larger length scale flow fields from correlated particle motions and find good agreement with what is expected from the theory of 2D fluids for all our films. In conclusion, single particle diffusion shows a sharp transition away from 2D like behavior as h/d increases, but the long-range flow fields still act as 2D.
C-metric solution for conformal gravity with a conformally coupled scalar field
NASA Astrophysics Data System (ADS)
Meng, Kun; Zhao, Liu
2017-02-01
The C-metric solution of conformal gravity with a conformally coupled scalar field is presented. The solution belongs to the class of Petrov type D spacetimes and is conformal to the standard AdS C-metric appeared in vacuum Einstein gravity. For all parameter ranges, we identify some of the physically interesting static regions and the corresponding coordinate ranges. The solution may contain a black hole event horizon, an acceleration horizon, either of which may be cut by the conformal infinity or be hidden behind the conformal infinity. Since the model is conformally invariant, we also discussed the possible effects of the conformal gauge choices on the structure of the spacetime.
The use of 2D Hilbert transform for phase retrieval of speckle fields
NASA Astrophysics Data System (ADS)
Angelsky, O. V.; Zenkova, C. Yu.; Riabyi, P. A.
2016-12-01
The use of a "window" 2D Hilbert transform for reconstruction of the phase distribution of remote objects is proposed. It is shown that the advantage of this approach consists in the invariance of a phase map to a change of the position of the kernel of transformation and in a possibility to reconstruct the structure-forming elements of the skeleton of an optical field, including singular points and saddle points. We demonstrate the possibility to reconstruct the equi-phase lines within a narrow confidence interval, and introduce a new algorithm for solving the phase problem for random 2D intensity distributions.
2-D Reflectometer Modeling for Optimizing the ITER Low-field Side Reflectometer System
Kramer, G.J.; Nazikian, R.; Valeo, E.J.; Budny, R.V.; Kessel, C.; Johnson, D.
2005-09-02
The response of a low-field side reflectometer system for ITER is simulated with a 2?D reflectometer code using a realistic plasma equilibrium. It is found that the reflected beam will often miss its launch point by as much as 40 cm and that a vertical array of receiving antennas is essential in order to observe a reflection on the low-field side of ITER.
Solution of the field equations for 2-D electromagnetic direct implicit plasma simulation
NASA Astrophysics Data System (ADS)
Hewett, D. W.; Langdon, A. B.
1985-01-01
A direct implicit particle-in-cell (PIC) simulation model with full electromagnetic (EM) effects has been implemented in 2-D Cartesian geometry. The model, implemented with the D1 time differencing scheme, was first implemented in a 1-D electrostatic (ES) version to gain some experience with spatial differencing in forms suitable for extension to the full EM field in two dimensions. The implicit EM field solve is considerably different from the implicit ES code. The EM field calculation requires an inductive part as well as the electrostatic and the B field must be self-consistently advanced.
Modulating the vibronic correlation in 2D superconductor by electric field
NASA Astrophysics Data System (ADS)
Kazempour, Ali; Morshedloo, Toktam
2017-04-01
Superconductivity in the extreme two-dimensional atomic layers has been suffered because of the strong affection dimensionality confinement on electron-phonon binding. Here, using first-principles method, we study the effect of applied perpendicular and parallel electric field on the strength of phonon renormalization and electron-phonon coupling in bi-layer MgB2 as a known 2D superconductor. The changes of phonon frequency and line-width demonstrate that important E2 g optical modes are strongly sensitive to the applied parallel electric field which directs to sharp reduction of vibronic coupling. Whereas, we show that perpendicular electric field modulates the system to the strong-coupling superconductor and predict the enhancement of critical temperature Tc . Our study opens up the use of electric filed to probe and measure the variation amount of electron-phonon renormalization as a gauge in 2D superconductivity.
Improving field enhancement of 2D hollow tapered waveguides via dielectric microcylinder coupling
NASA Astrophysics Data System (ADS)
Chen, Yongzhu; Xie, Xiangsheng; Li, Li; Chen, Gengyan; Guo, Lina; Lin, Xusheng
2015-02-01
We numerically study a novel scheme to improve the field enhancement of 2D hollow tapered waveguides (HTWs). A dielectric microcylinder is embedded into a metal-insulator-metal (MIM) HTW for resonant exciting gap surface plasmons (GSPs), which is different from the lowest propagating mode (TM0) excitation via the conventional fire-end coupling method. The physical mechanism of the field enhancement and the influence of critical parameters such as numerical aperture (NA) of the lens, permittivity of the microcylinder and the incident wavelength are discussed. The substantial improvement of the GSP excitation efficiency via dielectric microcylinder coupling shows potential in designing tapered MIM waveguides for nanofocusing and field enhancement.
Matrone, G; Quaglia, F; Magenes, G
2010-01-01
Modern ultrasound imaging instrumentation for clinical applications allows real-time volumetric scanning of the patients' body. 4D imaging has been made possible thanks to the development of new echographic probes which consist in 2D phased arrays of piezoelectric transducers. In these new devices it is the system electronics which properly drives the matrix elements and focuses the beam in order to obtain a sequence of volumetric images. This paper introduces an ultrasound field simulator based on the Spatial Impulse Response method which is being properly developed to analyze the characteristics of the ultrasound field generated by a 2D phased array of transducers. Thanks to its high configurability by the user, it will represent a very useful tool for electronics designers in developing 4D ultrasound imaging systems components.
2D crossed electric field for electrokinetic remediation of chromium contaminated soil.
Zhang, Peng; Jin, Chunji; Zhao, Zhenhuan; Tian, Guobin
2010-05-15
Chromium contaminated soil can be remediated by electrokinetic techniques. However, in practical application, Cr(VI) may migrate with water deep into the soil, contaminating previously unpolluted layers. Both horizontal and vertical electric fields were applied simultaneously to improve traditional electrokinetic remediation. Contrasting experiments using four operation modes (none, solely horizontal, solely vertical and 2D crossed electric field) were designed and tested at the bench-scale with the practical sample of chromium contaminated soil (1.3 x 10(5)mg/kg) from a chemical plant to investigate Cr(VI) migration downward in each test and the effectiveness and feasible of the new design. During the tests, Cr(VI) could migrate deep into the soil in the solely horizontal mode. Cr(VI) migration downward could be prevented by vertical barrier in the solely vertical mode. However, using the 2D crossed mode, Cr(VI) was significantly prevented from migrating downward and the chromium contaminated soil was treated effectively. Thus, the 2D crossed electric field is a promising and practical method for the remediation of contaminated soils.
The interface between ferroelectric and 2D material for a Ferroelectric Field-Effect Transistor
NASA Astrophysics Data System (ADS)
Park, Nahee; Kang, Haeyong; Lee, Sang-Goo; Lee, Young Hee; Suh, Dongseok
We have studied electrical property of ferroelectric field-effect transistor which consists of graphene on hexagonal Boron-Nitride (h-BN) gated by a ferroelectric, PMN-PT (i.e. (1-x)Pb(Mg1/3Nb2/3) O3-xPbTiO3) single-crystal substrate. The PMN-PT was expected to have an effect on polarization field into the graphene channel and to induce a giant amount of surface charge. The hexagonal Boron-Nitride (h-BN) flake was directly exfoliated on the PMN-PT substrate for preventing graphene from directly contacting on the PMN-PT substrate. It can make us to observe the effect of the interface between ferroelectric and 2D material on the device operation. Monolayer graphene as 2D channel material, which was confirmed by Raman spectroscopy, was transferred on top of the hexagonal Boron-Nitride (h-BN) by using the conventional dry-transfer method. Here, we can demonstrate that the structure of graphene/hexagonal-BN/ferroelectric field-effect transistor makes us to clearly understand the device operation as well as the interface between ferroelectric and 2D materials by inserting h-BN between them. The phenomena such as anti-hysteresis, current saturation behavior, and hump-like increase of channel current, will be discussed by in terms of ferroelectric switching, polarization-assisted charge trapping.
Flat connection, conformal field theory and quantum group
Kato, Mitsuhiro.
1989-07-01
General framework of linear first order differential equation for four-point conformal block is studied by using flat connection. Integrability and SL{sub 2} invariance restrict possible form of flat connection. Under a special ansatz classical Yang-Baxter equation appears as an integrability condition and the WZW model turns to be unique conformal field theory in that case. Monodromy property of conformal block can be easily determined by the flat connection. 11 refs.
NASA Astrophysics Data System (ADS)
Zhao, Hongbo; Engelbrecht, Jan R.
2000-03-01
At the Mean Field level (G. Murthy and R. Shankar, J. Phys. Condens. Matter, 7) (1995), the frustration due to an external field first makes the uniform BCS ground state unstable to an incommensurate (qne0) superconducting state and then to a spin-polarized Fermi Liquid state. Our interest is how fluctuations modify this picture, as well as the normal state of this system which has a quantum critical point. We use the Fluctuation-Exchange Approximation for the 2D Attractive Hubbard Model, to study this system beyond the Mean-Field level. Earlier work in zero field has shown that this numerical method successfully captures the critical scaling of the KT superconducting transition upon cooling in the normal state. Here we investigate how the pair-breaking external field modifies this picture, and the development of incommensurate pairing.
Field depth extension of 2D barcode scanner based on wavefront coding and projection algorithm
NASA Astrophysics Data System (ADS)
Zhao, Tingyu; Ye, Zi; Zhang, Wenzi; Huang, Weiwei; Yu, Feihong
2008-03-01
Wavefront coding (WFC) used in 2D barcode scanners can extend the depth of field into a great extent with simpler structure compared to the autofocus microscope system. With a cubic phase mask (CPM) employed in the STOP, blurred images will be obtained in charge coupled device (CCD), which can be restored by digital filters. Direct methods are used widely in real-time restoration with good computational efficiency but with details smoothed. Here, the results of direct method are firstly filtered by hard-threshold function. The positions of the steps can be detected by simple differential operators. With the positions corrected by projection algorithm, the exact barcode information is restored. A wavefront coding system with 7mm effective focal length and 6 F-number is designed as an example. Although with the different magnification, images of different object distances can be restored by one point spread function (PSF) with 200mm object distance. A QR code (Quickly Response Code) of 31mm X 27mm is used as a target object. The simulation results showed that the sharp imaging objective distance is from 80mm to 355mm. The 2D barcode scanner with wavefront coding extends field depth with simple structure, low cost and large manufacture tolerance. This combination of the direct filter and projection algorithm proposed here could get the exact 2D barcode information with good computational efficiency.
Measurements of density field in a swirling flame by 2D spontaneous Raman scattering
NASA Astrophysics Data System (ADS)
Sharaborin, D. K.; Dulin, V. M.; Lobasov, A. S.; Markovich, D. M.
2016-10-01
This paper presents an evaluation of the density distribution in swirling turbulent premixed flames. The measurement principle is based on registration of spontaneous Raman scattering, when the reacting gas flow is illuminated by a laser sheet. Evaluation of 1D and 2D distributions of density and temperature were performed in a laminar Bunsen flame as a test case for validation of experimental technique. Time-averaged 2D images of the scattering during rovibronic transitions of nitrogen molecules were captured in turbulent premixed low-swirl and high-swirl (Re = 5000) propane-air flames in a wide range of equivalence ratio. The obtained density fields are useful for better understanding of heat and mass transfer in swirl-stabilized turbulent flames and for validation of CFD results.
Catapano, F. Zimbardo, G.; Artemyev, A. V. Vasko, I. Y.
2015-09-15
We develop current sheet models which allow to regulate the level of plasma temperature and density inhomogeneities across the sheet. These models generalize the classical Harris model via including two current-carrying plasma populations with different temperature and the background plasma not contributing to the current density. The parameters of these plasma populations allow regulating contributions of plasma density and temperature to the pressure balance. A brief comparison with spacecraft observations demonstrates the model applicability for describing the Earth magnetotail current sheet. We also develop a two dimensional (2D) generalization of the proposed model. The interesting effect found for 2D models is the nonmonotonous profile (along the current sheet) of the magnetic field component perpendicular to the current sheet. Possible applications of the model are discussed.
Choudhary, Nitin; Li, Chao; Chung, Hee-Suk; Moore, Julian; Thomas, Jayan; Jung, Yeonwoong
2016-12-27
Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have emerged as promising capacitive materials for supercapacitor devices owing to their intrinsically layered structure and large surface areas. Hierarchically integrating 2D TMDs with other functional nanomaterials has recently been pursued to improve electrochemical performances; however, it often suffers from limited cyclic stabilities and capacitance losses due to the poor structural integrity at the interfaces of randomly assembled materials. Here, we report high-performance core/shell nanowire supercapacitors based on an array of one-dimensional (1D) nanowires seamlessly integrated with conformal 2D TMD layers. The 1D and 2D supercapacitor components possess "one-body" geometry with atomically sharp and structurally robust core/shell interfaces, as they were spontaneously converted from identical metal current collectors via sequential oxidation/sulfurization. These hybrid supercapacitors outperform previously developed any stand-alone 2D TMD-based supercapacitors; particularly, exhibiting an exceptional charge-discharge retention over 30,000 cycles owing to their structural robustness, suggesting great potential for unconventional energy storage technologies.
Optical Signatures from Magnetic 2-D Electron Gases in High Magnetic Fields to 60 Tesla
Crooker, S.A.; Kikkawa, J.M.; Awschalom, D.D.; Smorchikova, I.P.; Samarth, N.
1998-11-08
We present experiments in the 60 Tesla Long-Pulse magnet at the Los Alamos National High Magnetic Field Lab (NHMFL) focusing on the high-field, low temperature photoluminescence (PL) from modulation-doped ZnSe/Zn(Cd,Mn)Se single quantum wells. High-speed charge-coupled array detectors and the long (2 second) duration of the magnet pulse permit continuous acquisition of optical spectra throughout a single magnet shot. High-field PL studies of the magnetic 2D electron gases at temperatures down to 350mK reveal clear intensity oscillations corresponding to integer quantum Hall filling factors, from which we determine the density of the electron gas. At very high magnetic fields, steps in the PL energy are observed which correspond to the partial unlocking of antiferromagnetically bound pairs of Mn^{2+} spins.
NASA Astrophysics Data System (ADS)
Ruan, Qing-Xia; Zhou, Ping
2008-07-01
In the present work, we investigated Na + ion effect on the silk fibroin (SF) conformation. Samples are Na +-involved regenerated silk fibroin films. 13C CP-MAS NMR demonstrates that as added [Na +] increases, partial silk fibroin conformation transit from helix-form to β-form at certain Na + ion concentration which is much higher than that in Bombyx mori silkworm gland. The generalized two-dimensional NMR-NMR correlation analysis reveals that silk fibroin undergoes several intermediate states during its conformation transition process as [Na +] increase. The appearance order of the intermediates is followed as: helix and/or random coil → helix-like → β-sheet-like → β-sheet, which is the same as that produced by pH decrease from 6.8 to 4.8 in the resultant regenerated silk fibroin films. The binding sites of Na + to silk fibroin might involve the carbonyl oxygen atom of certain amino acids sequence which could promote the formation of β-sheet conformation. Since the Na +sbnd O bond is weak, the ability of Na + inducing the secondary structure transition is weaker than those of Ca 2+, Cu 2+ and even K +. It is maybe a reason why the sodium content is much lower than potassium in the silkworm gland.
Bianchi type-I models with conformally invariant scalar field
Accioly, A.J.; Vaidya, A.N.; Som, M.M.
1983-05-15
The solutions of the Einstein equations with the trace-free energy-momentum tensor of conformally invariant scalar field as source are obtained in a spatially homogeneous anisotropic space-time. Some interesting features of the solutions are discussed.
Correspondence between Asymptotically Flat Spacetimes and Nonrelativistic Conformal Field Theories
Bagchi, Arjun
2010-10-22
We find a surprising connection between asymptotically flat spacetimes and nonrelativistic conformal systems in one lower dimension. The Bondi-Metzner-Sachs (BMS) group is the group of asymptotic isometries of flat Minkowski space at null infinity. This is known to be infinite dimensional in three and four dimensions. We show that the BMS algebra in 3 dimensions is the same as the 2D Galilean conformal algebra (GCA) which is of relevance to nonrelativistic conformal symmetries. We further justify our proposal by looking at a Penrose limit on a radially infalling null ray inspired by nonrelativistic scaling and obtain a flat metric. The BMS{sub 4} algebra is also discussed and found to be the same as another class of GCA, called semi-GCA, in three dimensions. We propose a general BMS-GCA correspondence. Some consequences are discussed.
Entanglement entropy of non-unitary conformal field theory
NASA Astrophysics Data System (ADS)
Bianchini, D.; Castro-Alvaredo, O.; Doyon, B.; Levi, E.; Ravanini, F.
2015-01-01
Here we show that the Rényi entanglement entropy of a region of large size ℓ in a one-dimensional critical model whose ground state breaks conformal invariance (such as in those described by non-unitary conformal field theories), behaves as {{S}n}˜ \\frac{{{c}eff}(n+1)}{6n}log \\ell , where {{c}eff}=c-24Δ \\gt 0 is the effective central charge, c (which may be negative) is the central charge of the conformal field theory and Δ \
Dynamics of 2D Dust Clusters with a Perpendicular Magnetic Field
Greiner, Franko; Carstensen, Jan; Hou Lujing; Piel, Alexander
2008-09-07
The physics of two-dimensional (2D) dust clusters in an unmagnetized plasma sheath has been understood in dept. However, introduction of a perpendicular magnetic field into the dusty plasma sheath leads to some new effects, such as rotation and compression of dust clusters, whose mechanism is still unclear. It is found that even for a magnetic field as low as the earth magnetic field ({approx_equal}40 {mu}T), clusters rotate as rigid about their centers. It was proposed [U. Konopka, PRE 61, 1890 (2000)] that the ExB-induced ion flow drives the dust clusters into rotation. Simulations [L.-J. Hou, PoP 12, 042104 (2005)] based on the same hypothesis also reproduced the rotation of 2D clusters in a qualitative manner. However, this model cannot fully explain the experimental observations. We present detailed experimental investigations, which show that the rotation of a dust cluster critically depends on the detailed discharge geometry. In particular, the co-rotation of the background neutral gas and its role in driving dust-cluster rotation is proposed as a mechanism to set the dust cluster in rotation.
Calculation of self-field coefficients for 2D magnetostatic systems
NASA Astrophysics Data System (ADS)
Hall, Darren; Teyssedou, Alberto
2014-11-01
Physics and engineering students are introduced to the notion of a demagnetizing field in classical electromagnetism courses. This concept involves a formalism based on an integral formulation for calculating the coefficients of the demagnetizing tensor, i.e., a pure geometric quantity. For self-fields, the observation point is located inside the integration region which in turn leads to discontinuous integrands. Therefore, in order to avoid mathematical inconsistencies, special care must be taken when evaluating self-field coefficients, referred to here as self-terms. Given the complexity of this approach, in particular in 3D, it is certainly interesting from a pedagogical stand point to employ 2D systems as a first step for describing these kinds of coefficients. Thus, in this paper, the generalization of self-terms of the demagnetizing tensor is proven for 2D magnetostatic systems. Nonetheless, the structure of this proof pertains to many other situations given the fact that discontinuous integrands commonly arise in physics (e.g. integral solutions of PDEs which use a Green’s function).
Simulating ultrasound fields for 2D phased-array probes design optimization.
Matrone, Giulia; Quaglia, Fabio; Magenes, Giovanni
2011-01-01
Nowadays, ultrasound diagnostic imaging is one of the non-invasive techniques mostly used in the clinical practice. Recent advances in this field have brought to the development of small and portable systems. New bidimensional probes consisting of 2D phased arrays, allow to obtain real-time 3D representations of moving organs and blood vessels anatomy. Being the complexity of such 4D ultrasound imaging systems significantly increased, new challenges concerning electronics integration arise for designers. In this paper a software simulator is described, which has been developed in order to model ultrasound wave generation, pressure field distribution and echoes reception, with the aim to become a useful tool for optimizing the probe design. The paper mainly focuses on linear ultrasound field modeling; preliminary results on non-linear interactions with contrast agents are also here introduced.
On classification of extremal non-holomorphic conformal field theories
NASA Astrophysics Data System (ADS)
Tener, James E.; Wang, Zhenghan
2017-03-01
Rational chiral conformal field theories are organized according to their genus, which consists of a modular tensor category C and a central charge c. A long-term goal is to classify unitary rational conformal field theories based on a classification of unitary modular tensor categories. We conjecture that for any unitary modular tensor category C , there exists a unitary chiral conformal field theory V so that its modular tensor category {{C}V} is C . In this paper, we initiate a mathematical program in and around this conjecture. We define a class of extremal vertex operator algebras with minimal conformal dimensions as large as possible for their central charge, and non-trivial representation theory. We show that there are finitely many different characters of extremal vertex operator algebras V possessing at most three different irreducible modules. Moreover, we list all of the possible characters for such vertex operator algebras with c≤slant 48 .
Effects of 2D and 3D Error Fields on the SAS Divertor Magnetic Topology
NASA Astrophysics Data System (ADS)
Trevisan, G. L.; Lao, L. L.; Strait, E. J.; Guo, H. Y.; Wu, W.; Evans, T. E.
2016-10-01
The successful design of plasma-facing components in fusion experiments is of paramount importance in both the operation of future reactors and in the modification of operating machines. Indeed, the Small Angle Slot (SAS) divertor concept, proposed for application on the DIII-D experiment, combines a small incident angle at the plasma strike point with a progressively opening slot, so as to better control heat flux and erosion in high-performance tokamak plasmas. Uncertainty quantification of the error fields expected around the striking point provides additional useful information in both the design and the modeling phases of the new divertor, in part due to the particular geometric requirement of the striking flux surfaces. The presented work involves both 2D and 3D magnetic error field analysis on the SAS strike point carried out using the EFIT code for 2D equilibrium reconstruction, V3POST for vacuum 3D computations and the OMFIT integrated modeling framework for data analysis. An uncertainty in the magnetic probes' signals is found to propagate non-linearly as an uncertainty in the striking point and angle, which can be quantified through statistical analysis to yield robust estimates. Work supported by contracts DE-FG02-95ER54309 and DE-FC02-04ER54698.
Commissioning a small-field biological irradiator using point, 2D, and 3D dosimetry techniques
Newton, Joseph; Oldham, Mark; Thomas, Andrew; Li Yifan; Adamovics, John; Kirsch, David G.; Das, Shiva
2011-12-15
Purpose: To commission a small-field biological irradiator, the XRad225Cx from Precision x-Ray, Inc., for research use. The system produces a 225 kVp x-ray beam and is equipped with collimating cones that produce both square and circular radiation fields ranging in size from 1 to 40 mm. This work incorporates point, 2D, and 3D measurements to determine output factors (OF), percent-depth-dose (PDD) and dose profiles at multiple depths. Methods: Three independent dosimetry systems were used: ion-chambers (a farmer chamber and a micro-ionisation chamber), 2D EBT2 radiochromic film, and a novel 3D dosimetry system (DLOS/PRESAGE registered ). Reference point dose rates and output factors were determined from in-air ionization chamber measurements for fields down to {approx}13 mm using the formalism of TG61. PDD, profiles, and output factors at three separate depths (0, 0.5, and 2 cm), were determined for all field sizes from EBT2 film measurements in solid water. Several film PDD curves required a scaling correction, reflecting the challenge of accurate film alignment in very small fields. PDDs, profiles, and output factors were also determined with the 3D DLOS/PRESAGE registered system which generated isotropic 0.2 mm data, in scan times of 20 min. Results: Surface output factors determined by ion-chamber were observed to gradually drop by {approx}9% when the field size was reduced from 40 to 13 mm. More dramatic drops were observed for the smallest fields as determined by EBT{approx}18% and {approx}42% for the 2.5 mm and 1 mm fields, respectively. PRESAGE registered and film output factors agreed well for fields <20 mm (where 3D data were available) with mean deviation of 2.2% (range 1%-4%). PDD values at 2 cm depth varied from {approx}72% for the 40 mm field, down to {approx}55% for the 1 mm field. EBT and PRESAGE registered PDDs agreed within {approx}3% in the typical therapy region (1-4 cm). At deeper depths the EBT curves were slightly steeper (2.5% at 5 cm
Fast acquisition of high-resolution 2D NMR spectroscopy in inhomogeneous magnetic fields
NASA Astrophysics Data System (ADS)
Lin, Liangjie; Wei, Zhiliang; Zeng, Qing; Yang, Jian; Lin, Yanqin; Chen, Zhong
2016-05-01
High-resolution nuclear magnetic resonance (NMR) spectroscopy plays an important role in chemical and biological analyses. In this study, we combine the J-coupling coherence transfer module with the echo-train acquisition technique for fast acquisition of high-resolution 2D NMR spectra in magnetic fields with unknown spatial variations. The proposed method shows satisfactory performance on a 5 mM ethyl 3-bromopropionate sample, under a 5-kHz (10 ppm at 11.7 T) B0 inhomogeneous field, as well as under varying degrees of pulse-flip-angle deviations. Moreover, a simulative ex situ NMR measurement is also conducted to show the effectiveness of the proposed pulse sequence.
Understanding conformal field theory through parafermions and Chern Simons theory
Hotes, S.A.
1992-11-19
Conformal field theories comprise a vast class of exactly solvable two dimensional quantum field theories. Conformal theories with an enlarged symmetry group, the current algebra symmetry, axe a key ingredient to possible string compactification models. The following work explores a Lagrangian approach to these theories. In the first part of this thesis, a large class of conformal theories, the so-called coset models, are derived semi-classically from a gauged version Of the Wess-Zumino-Witten functional. A non-local field transformation to the parafermionic field description is employed in the quantization procedure. Classically, these parafermionic fields satisfy non-trivial Poisson brackets, providing insight into the fractional spin nature of the conformal theory. The W-algebra symmetry is shown to appear naturally in this approach. In the second part of this thesis, the connection between the fusion algebra structure of Wess-Zumino-Witten models and the quantization of the Chern-Simons action on the torus is made explicit. The modular properties of the conformal model are also derived in this context, giving a natural demonstration of the Verlinde conjecture. The effects of background gauge fields and monopoles are also discussed.
Tunneling Between 2D Electrons and Holes in an In-plane Magnetic Field
NASA Astrophysics Data System (ADS)
Lin, Y.; Mendez, E. E.; Magno, R.; Bennett, B. R.
2002-03-01
We have studied the vertical transport properties of GaSb/AlSb/InAs/AlSb/GaSb (system A) and InAs/AlSb/GaSb/AlSb/InAs (system B) heterostructures in a magnetic field (B<20T) parallel to the interfaces. In these systems, electrons and holes accumulate in the InAs and GaSb regions, respectively, and tunneling between the two gases gives rise to a current-voltage (I-V) characteristic that exhibits negative differential conductance even at T=300K. In both cases, the zero-bias, low-T (1.7K) magnetoconductance showed the signature of tunneling between 2D gases with different carrier densities even though in system A, the holes are barely confined. In contrast, the dependence of the I-V characteristics on magnetic field was quite different. In system A, the observed shift of the peak voltage with field is explained by simple ground-state dispersion curves for electrons and holes. However, this picture cannot explain the appearance (above 5.5T) and field dependence of a secondary peak in system B, or of additional, weaker field-induced features. Their origin may lie in the complexities of highly confined hole states in the central GaSb quantum well.
Bi-conformal vector fields and their applications
NASA Astrophysics Data System (ADS)
García-Parrado, Alfonso; Senovilla, JosA~© M. M.
2004-04-01
We introduce a concept of bi-conformal transformation, as a generalization of conformal ones, by allowing two orthogonal parts of a manifold with metric g to be scaled by different conformal factors. In particular, we study their infinitesimal version, called bi-conformal vector fields. We show that these are characterized by the differential conditions {{\\pounds}_{{\\vec{{\\bm \\xi}}}}} {\\bf P}\\propto {\\bf P} and {{\\pounds}_{{\\vec{{\\bm \\xi}}}}} {\\bm \\Pi} \\propto {\\bm \\Pi} , where P and Π are orthogonal projectors (P + Π = g). Keeping P and Π fixed, the set of bi-conformal vector fields is a Lie algebra which can be finite or infinite dimensional according to the dimensionality of the projectors. We determine (i) when an infinite-dimensional case is feasible and its properties, and (ii) a normal system for the generators in the finite-dimensional case. Its integrability conditions are also analysed, which in particular provides the maximum number of linearly independent solutions. We identify the corresponding maximal spaces, and show a necessary geometric condition for a metric tensor to be a double-twisted product. More general 'breakable' spaces are briefly considered. Many known symmetries are included, such as conformal Killing vectors, Kerr Schild vector fields, kinematic self-similarity, causal symmetries and rigid motions.
Virasoro conformal blocks and thermality from classical background fields
Fitzpatrick, A. Liam; Kaplan, Jared; Walters, Matthew T.
2015-11-30
We show that in 2d CFTs at large central charge, the coupling of the stress tensor to heavy operators can be re-absorbed by placing the CFT in a non-trivial background metric. This leads to a more precise computation of the Virasoro conformal blocks between heavy and light operators, which are shown to be equivalent to global conformal blocks evaluated in the new background. We also generalize to the case where the operators carry U(1) charges. The refined Virasoro blocks can be used as the seed for a new Virasoro block recursion relation expanded in the heavy-light limit. Furthermore, we commentmore » on the implications of our results for the universality of black hole thermality in AdS3 , or equivalently, the eigenstate thermalization hypothesis for CFT2 at large central charge.« less
Virasoro conformal blocks and thermality from classical background fields
Fitzpatrick, A. Liam; Kaplan, Jared; Walters, Matthew T.
2015-11-30
We show that in 2d CFTs at large central charge, the coupling of the stress tensor to heavy operators can be re-absorbed by placing the CFT in a non-trivial background metric. This leads to a more precise computation of the Virasoro conformal blocks between heavy and light operators, which are shown to be equivalent to global conformal blocks evaluated in the new background. We also generalize to the case where the operators carry U(1) charges. The refined Virasoro blocks can be used as the seed for a new Virasoro block recursion relation expanded in the heavy-light limit. Furthermore, we comment on the implications of our results for the universality of black hole thermality in AdS_{3} , or equivalently, the eigenstate thermalization hypothesis for CFT_{2} at large central charge.
2D focal-field aberration dependence on time/phase screen position and correlation lengths
NASA Astrophysics Data System (ADS)
Näsholm, Sven Peter
2004-05-01
For high-frequency annular array transducers used in medical ultrasound imaging, aberrations due to tissue and body wall have a significant effect on energy transfer from the main lobe to the sidelobes of the acoustic field: that is, the aberrations make the total sidelobe level increase. This effect makes the ultrasound image poor when imaging heterogeneous organs. This study performs an analysis of the focal-field quality as a function of time/phase screen z position and time/phase screen correlation length. It establishes some rules of thumb which indicate when the focal-field sidelobe energy is at its highest. It also introduces a simple screen-scaling model which is useful as long as the screen position is not closer to the focus than a certain limit distance. The scaling model allows the real screen at a depth z=zscreen to be treated as a scaled screen at the position z=ztransd. 2D sound fields after 3D propagation from the annular arrays to the focal plane have been simulated using an angular spectrum method. The aberrators are represented by amplitude and phase/time screens.
2-D electric fields and drifts near the magnetic separatrix in divertor tokamaks
Mattor, N.; Porter, G. D.; Rognlien, T. D.; Ryutov, D. D.
1998-11-15
A 2-D calculation is presented for the transport of plasma in the edge region of a divertor tokamak solving continuity, momentum, and energy balance fluid equations. The model uses anomalous radial diffusion, including perpendicular ion momentum, and classical cross-field drifts transport. Parallel and perpendicular currents yield a self-consistent electrostatic potential on both sides of the magnetic separatrix. Outside the separatrix, the simulation extends to material divertor plates where the incident plasma is recycled as neutral gas and where the plate sheath and parallel currents dominate the potential structure. Inside the separatrix, various radial current terms - from viscosity, charge-exchange and poloidal damping, inertia, and {triangledown}B - contribute to the determining the potential. The model rigorously enforces cancellation of gyro-viscous and magnetization terms from the transport equations. The results emphasize the importance of E x B particle flow under the X-point which depends on the sign of the toroidal magnetic field. Radial electric field (E{sub y}) profiles at the outer midplane are small with weak shear when high L-mode diffusion coefficients are used and are large with strong shear when smaller H-mode diffusion coefficients are used. The magnitude and shear of the electric field (E{sub y}) is larger both when the core toroidal rotation is co-moving with the inductive plasma current and when the ion {triangledown}B-drift is towards the single-null X-point.
Simple approach for 2D-DIC with dual field of view
NASA Astrophysics Data System (ADS)
Nunes, L. C. S.
2015-09-01
A simple and cost-effective optical layout based on the dual field of view for the 2D digital image correlation (DIC) method is used to simultaneously measure in-plane displacement fields of large and small portions of a specimen. This optical configuration was composed of two high-resolution cameras with two different lenses and a beam splitter. The surface of a specimen was acquired simultaneously using both cameras with narrow and wide fields of view. One of the two cameras was placed directly in front of a specimen, whereas the other camera acquired the image of the same specimen reflected from the beam splitter. All stored images were appropriately processed using a digital image correlation algorithm to extract displacement and strain fields. To show the applicability and usefulness of this configuration, two tests were performed: (i) lower and upper adherends deflections of an adhesive-bonded single lap joint specimen were obtained, and shear strain in the adhesive layer at the edge of the overlap was also attained; and (ii) relatively large displacements of a cracked cantilever beam were evaluated, and maps of small deformation near crack tip were assessed. The results were obtained considering different speckle patterns and distinct subset sizes.
2D dose distribution images of a hybrid low field MRI-γ detector
NASA Astrophysics Data System (ADS)
Abril, A.; Agulles-Pedrós, L.
2016-07-01
The proposed hybrid system is a combination of a low field MRI and dosimetric gel as a γ detector. The readout system is based on the polymerization process induced by the gel radiation. A gel dose map is obtained which represents the functional part of hybrid image alongside with the anatomical MRI one. Both images should be taken while the patient with a radiopharmaceutical is located inside the MRI system with a gel detector matrix. A relevant aspect of this proposal is that the dosimetric gel has never been used to acquire medical images. The results presented show the interaction of the 99mTc source with the dosimetric gel simulated in Geant4. The purpose was to obtain the planar γ 2D-image. The different source configurations are studied to explore the ability of the gel as radiation detector through the following parameters; resolution, shape definition and radio-pharmaceutical concentration.
a Field-Theoretical Investigation of 2-D Coulomb Systems with Short-Range Yukawa Repulsion.
NASA Astrophysics Data System (ADS)
Jargocki, Krzysztof Piotr
correspond to the two-dimensional Coulomb dipole gas in the functional integral formulation. A different type of a field theory is found for the dipole gas using the collective field formalism. A comparison is made with the critical behavior in the nonlinear sigma model, the 2-D Heisenberg model, and the nonabelian gauge theories.
Abdul-Manan, N; Hinton, J F
1994-06-07
Gramicidin A incorporated into SDS (sodium dodecyl sulfate) micelles exists as a right-handed, N-to-N-terminal beta 6.3 helical dimer [Lomize, A. L., Orechov, V. Yu., & Arseniev, A.S. (1992) Bioorg. Khim. 18, 182-189]. In the incorporation procedure to achieve the ion channel state of gramicidin A in SDS micelles, trifluoroethanol (TFE) is used to solubilize the hydrophobic peptide before addition to the aqueous/micelle solution. The conformational transition of gramicidin A to form ion channels in SDS micelles, i.e., in TFE and 10% TFE/water, has been investigated using 2D NMR and CD spectroscopy. In neat TFE, gramicidin A was found to be monomeric and may possibly exist in an equilibrium of rapidly interconverting conformers of at least three different forms believed to be left- and/or right-handed alpha and beta 4.4 helices. It was found that the interconversion between these conformers was slowed down in 55% TFE as evident by the observation of at least three different sets of d alpha N COSY peaks although CD gave a net spectrum similar to that in neat TFE. In 10% TFE gramicidin A spontaneously forms a precipitate. The precipitated species were isolated and solubilized in dioxane where gramicidin conformers undergo very slow interconversion and could be characterized by NMR. At least seven different gramicidin A conformations were found in 10% TFE. Four of thes are the same types of double helices as previously found in ethanol (i.e., a symmetric left-handed parallel beta 5.6 double helix, an unsymmetric left-handed parallel beta 5.6 double helix, a symmetric left-handed antiparallel beta 5.6 double helix, a symmetric right-handed parallel beta 5.6 double helix); the fifth is possibly a symmetric right-handed antiparallel beta 5.6 double helix. There is also evidence for the presence of at least one form of monomeric species. Previous observation on the solvent history dependence in the ease of channel incorporation may be explained by the presence of several
Generally covariant vs. gauge structure for conformal field theories
Campigotto, M.; Fatibene, L.
2015-11-15
We introduce the natural lift of spacetime diffeomorphisms for conformal gravity and discuss the physical equivalence between the natural and gauge natural structure of the theory. Accordingly, we argue that conformal transformations must be introduced as gauge transformations (affecting fields but not spacetime point) and then discuss special structures implied by the splitting of the conformal group. -- Highlights: •Both a natural and a gauge natural structure for conformal gravity are defined. •Global properties and natural lift of spacetime transformations are described. •The possible definitions of physical state are considered and discussed. •The gauge natural theory has less physical states than the corresponding natural one. •The dynamics forces to prefer the gauge natural structure over the natural one.
Exploring perturbative conformal field theory in Mellin space
NASA Astrophysics Data System (ADS)
Nizami, Amin A.; Rudra, Arnab; Sarkar, Sourav; Verma, Mritunjay
2017-01-01
We explore the Mellin representation of correlation functions in conformal field theories in the weak coupling regime. We provide a complete proof for a set of Feynman rules to write the Mellin amplitude for a general tree level Feynman diagram involving only scalar operators. We find a factorised form involving beta functions associated to the propagators, similar to tree level Feynman rules in momentum space for ordinary QFTs. We also briefly consider the case where a generic scalar perturbation of the free CFT breaks conformal invariance. Mellin space still has some utility and one can consider non-conformal Mellin representations. In this context, we find that the beta function corresponding to conformal propagator uplifts to a hypergeometric function.
Unitary Fermi Gas, ɛ Expansion, and Nonrelativistic Conformal Field Theories
NASA Astrophysics Data System (ADS)
Nishida, Yusuke; Son, Dam Thanh
We review theoretical aspects of unitary Fermi gas (UFG), which has been realized in ultracold atom experiments. We first introduce the ɛ expansion technique based on a systematic expansion in terms of the dimensionality of space. We apply this technique to compute the thermodynamic quantities, the quasiparticle cum, and the criticl temperature of UFG. We then discuss consequences of the scale and conformal invariance of UFG. We prove a correspondence between primary operators in nonrelativistic conformal field theories and energy eigenstates in a harmonic potential. We use this correspondence to compute energies of fermions at unitarity in a harmonic potential. The scale and conformal invariance together with the general coordinate invariance constrains the properties of UFG. We show the vanishing bulk viscosities of UFG and derive the low-energy effective Lagrangian for the superfluid UFG. Finally we propose other systems exhibiting the nonrelativistic scaling and conformal symmetries that can be in principle realized in ultracold atom experiments.
Field-induced magnetization jumps and quantum criticality in the 2D J-Q model
NASA Astrophysics Data System (ADS)
Iaizzi, Adam; Sandvik, Anders
The J-Q model is a `designer hamiltonian' formed by adding a four spin `Q' term to the standard antiferromagnetic S = 1 / 2 Heisenberg model. The Q term drives a quantum phase transition to a valence-bond solid (VBS) state: a non-magnetic state with a pattern of local singlets which breaks lattice symmetries. The elementary excitations of the VBS are triplons, i.e. gapped S=1 quasiparticles. There is considerable interest in the quantum phase transition between the Néel and VBS states as an example of deconfined quantum criticality. Near the phase boundary, triplons deconfine into pairs of bosonic spin-1/2 excitations known as spinons. Using exact diagonalization and the stochastic series expansion quantum monte carlo method, we study the 2D J-Q model in the presence of an external magnetic field. We use the field to force a nonzero density of magnetic excitations at T=0 and look for signatures of Bose-Einstein condensation of spinons. At higher magnetic fields, there is a jump in the induced magnetization caused by the onset of an effective attractive interaction between magnons on a ferromagnetic background. We characterize the first order quantum phase transition and determine the minimum value of the coupling ratio q ≡ Q / J required to produce this jump. Funded by NSF DMR-1410126.
NASA Astrophysics Data System (ADS)
Munbodh, R.; Moseley, D. J.
2014-03-01
We report results of an intensity-based 2D-3D rigid registration framework for patient positioning and monitoring during brain radiotherapy. We evaluated two intensity-based similarity measures, the Pearson Correlation Coefficient (ICC) and Maximum Likelihood with Gaussian noise (MLG) derived from the statistics of transmission images. A useful image frequency band was identified from the bone-to-no-bone ratio. Validation was performed on gold-standard data consisting of 3D kV CBCT scans and 2D kV radiographs of an anthropomorphic head phantom acquired at 23 different poses with parameter variations along six degrees of freedom. At each pose, a single limited field of view kV radiograph was registered to the reference CBCT. The ground truth was determined from markers affixed to the phantom and visible in the CBCT images. The mean (and standard deviation) of the absolute errors in recovering each of the six transformation parameters along the x, y and z axes for ICC were varphix: 0.08(0.04)°, varphiy: 0.10(0.09)°, varphiz: 0.03(0.03)°, tx: 0.13(0.11) mm, ty: 0.08(0.06) mm and tz: 0.44(0.23) mm. For MLG, the corresponding results were varphix: 0.10(0.04)°, varphiy: 0.10(0.09)°, varphiz: 0.05(0.07)°, tx: 0.11(0.13) mm, ty: 0.05(0.05) mm and tz: 0.44(0.31) mm. It is feasible to accurately estimate all six transformation parameters from a 3D CBCT of the head and a single 2D kV radiograph within an intensity-based registration framework that incorporates the physics of transmission images.
Operator Algebras and Noncommutative Geometric Aspects in Conformal Field Theory
NASA Astrophysics Data System (ADS)
Longo, Roberto
2010-03-01
The Operator Algebraic approach to Conformal Field Theory has been particularly fruitful in recent years (leading for example to the classification of all local conformal nets on the circle with central charge c < 1, jointly with Y. Kawahigashi). On the other hand the Operator Algebraic viewpoint offers a natural perspective for a Noncommutative Geometric context within Conformal Field Theory. One basic point here is to uncover the relevant structures. In this talk I will explain some of the basic steps in this "Noncommutative Geometrization program" up to the recent construction of a spectral triple associated with certain Ramond representations of the Supersymmetric Virasoro net. So Alain Connes framework enters into play. This is a joint work with S. Carpi, Y. Kawahigashi, and R. Hillier.
Reconstruction of the Acoustic Field Using a Conformal Array
NASA Technical Reports Server (NTRS)
Valdivia, Nichlas P.; Williams, Earl G.; Klos, Jacob
2006-01-01
Near-field acoustical holography (NAH) requires the measurement of the near-field pressure field over a conformal and closed surface in order to recover the acoustic field on a nearby surface. We are interested in the reconstruction of the acoustic field over the fuselage of a Boeing 757 airplane when pressure data is available over an array of microphones that are conformal to the fuselage surface. In this case the strict NAH theory does not hold, but still there are techniques used to overcome this difficulty. The best known is patch NAH, which has been used for planar surfaces. In this work we will discuss two new techniques used for surfaces with an arbitrarily shape: patch inverse boundary element methods (IBEM) and patch equivalent sources method (ESM). We will discuss the theoretical justification of the method and show reconstructions for in-flight data taken inside a Boeing 757 airplane.
Tests of conformal field theory at the Yang-Lee singularity
Wydro, Tomasz; McCabe, John F.
2009-12-14
This paper studies the Yang-Lee edge singularity of 2-dimensional (2D) Ising model based on a quantum spin chain and transfer matrix measurements on the cylinder. Based on finite-size scaling, the low-lying excitation spectrum is found at the Yang-Lee edge singularity. Based on transfer matrix techniques, the single structure constant is evaluated at the Yang-Lee edge singularity. The results of both types of measurements are found to be fully consistent with the predictions for the (A{sub 4}, A{sub 1}) minimal conformal field theory, which was previously identified with this critical point.
Introduction to conformal field theory and string theory
Dixon, L.J.
1989-12-01
These lectures are meant to provide a brief introduction to conformal field theory (CFT) and string theory for those with no prior exposure to the subjects. There are many excellent reviews already available, and most of these go in to much more detail than I will be able to here. 52 refs., 11 figs.
Computation of nozzle flow fields using the PARC2D Navier-Stokes code
NASA Technical Reports Server (NTRS)
Collins, Frank G.
1986-01-01
Supersonic nozzles which operate at low Reynolds numbers and have large expansion ratios have very thick boundary layers at their exit. This leads to a very strong viscous/inviscid interaction upon the flow within the nozzle and the traditional nozzle design techniques which correct the inviscid core with a boundary layer displacement do not accurately predict the nozzle exit conditions. A full Navier-Stokes code (PARC2D) was used to compute the nozzle flow field. Grids were generated using the interactive grid generator code TBGG. All computations were made on the NASA MSFC CRAY X-MP computer. Comparison was made between the computations and in-house wall pressure measurements for CO2 flow through a conical nozzle having an area ratio of 40. Satisfactory agreement existed between the computations and measurements for a stagnation pressure of 29.4 psia and stagnation temperature of 1060 R. However, agreement did not exist at a stagnation pressure of 7.4 psia. Several reasons for the lack of agreement are possible. The computational code assumed a constant gas gamma whereas gamma for CO2 varied from 1.22 in the plenum chamber to 1.38 at the nozzle exit. Finally, it is possible that condensation occurred during the expansion at the lower stagnation pressure.
Conformal consistency relations for single-field inflation
Creminelli, Paolo; Noreña, Jorge; Simonović, Marko E-mail: jorge.norena@gmail.com
2012-07-01
We generalize the single-field consistency relations to capture not only the leading term in the squeezed limit — going as 1/q{sup 3}, where q is the small wavevector — but also the subleading one, going as 1/q{sup 2}. This term, for an (n+1)-point function, is fixed in terms of the variation of the n-point function under a special conformal transformation; this parallels the fact that the 1/q{sup 3} term is related with the scale dependence of the n-point function. For the squeezed limit of the 3-point function, this conformal consistency relation implies that there are no terms going as 1/q{sup 2}. We verify that the squeezed limit of the 4-point function is related to the conformal variation of the 3-point function both in the case of canonical slow-roll inflation and in models with reduced speed of sound. In the second case the conformal consistency conditions capture, at the level of observables, the relation among operators induced by the non-linear realization of Lorentz invariance in the Lagrangian. These results mean that, in any single-field model, primordial correlation functions of ζ are endowed with an SO(4,1) symmetry, with dilations and special conformal transformations non-linearly realized by ζ. We also verify the conformal consistency relations for any n-point function in models with a modulation of the inflaton potential, where the scale dependence is not negligible. Finally, we generalize (some of) the consistency relations involving tensors and soft internal momenta.
Quantum entanglement of local operators in conformal field theories.
Nozaki, Masahiro; Numasawa, Tokiro; Takayanagi, Tadashi
2014-03-21
We introduce a series of quantities which characterize a given local operator in any conformal field theory from the viewpoint of quantum entanglement. It is defined by the increased amount of (Rényi) entanglement entropy at late time for an excited state defined by acting the local operator on the vacuum. We consider a conformal field theory on an infinite space and take the subsystem in the definition of the entanglement entropy to be its half. We calculate these quantities for a free massless scalar field theory in two, four and six dimensions. We find that these results are interpreted in terms of quantum entanglement of a finite number of states, including Einstein-Podolsky-Rosen states. They agree with a heuristic picture of propagations of entangled particles.
Quantum Entanglement of Local Operators in Conformal Field Theories
NASA Astrophysics Data System (ADS)
Nozaki, Masahiro; Numasawa, Tokiro; Takayanagi, Tadashi
2014-03-01
We introduce a series of quantities which characterize a given local operator in any conformal field theory from the viewpoint of quantum entanglement. It is defined by the increased amount of (Rényi) entanglement entropy at late time for an excited state defined by acting the local operator on the vacuum. We consider a conformal field theory on an infinite space and take the subsystem in the definition of the entanglement entropy to be its half. We calculate these quantities for a free massless scalar field theory in two, four and six dimensions. We find that these results are interpreted in terms of quantum entanglement of a finite number of states, including Einstein-Podolsky-Rosen states. They agree with a heuristic picture of propagations of entangled particles.
Transport simulations of the C-2 and C-2U Field Reversed Configurations with the Q2D code
NASA Astrophysics Data System (ADS)
Onofri, Marco; Dettrick, Sean; Barnes, Daniel; Tajima, Toshiki; TAE Team
2016-10-01
The Q2D code is a 2D MHD code, which includes a neutral fluid and separate ion and electron temperatures, coupled with a 3D Monte Carlo code, which is used to calculate source terms due to neutral beams. Q2D has been benchmarked against the 1D transport code Q1D and is used to simulate the evolution of the C-2 and C-2U field reversed configuration experiments [1]. Q2D simulations start from an initial equilibrium and transport coefficients are chosen to match C-2 experimental data. C-2U is an upgrade of C-2, with more beam power and angled beam injection, which demonstrates plasma sustainment for 5 + ms. The simulations use the same transport coefficients for C-2 and C-2U, showing the formation of a steady state in C-2U, sustained by fast ion pressure and current drive.
Effects of high external electric fields on protein conformation
NASA Astrophysics Data System (ADS)
Pompa, Pier Paolo; Bramanti, Alessandro; Maruccio, Giuseppe; del Mercato, Loretta Laureana; Chiuri, Rocco; Cingolani, Roberto; Rinaldi, Ross
2005-06-01
Resistance of biomolecules to high electric fields is a main concern for nanobioelectronics/nanobiosensing applications, and it is also a relevant issue from a fundamental perspective, to understand the dielectric properties and structural dynamics of proteins. In nanoscale devices, biomolecules may experience electric fields as high as 107 V/m in order to elicit charge transport/transfer. Understanding the effects of such fields on their structural integrity is thus crucial to assess the reliability of biomolecular devices. In this study, we show experimental evidence for the retention of native-like fold pattern by proteins embedded in high electric fields. We have tested the metalloprotein azurin, deposited onto SiO2 substrates in air with proper electrode configuration, by applying high static electric fields (up to 106-107 V/m). The effects on the conformational properties of protein molecules have been determined by means of intrinsic fluorescence measurements. Experimental results indicate that no significant field-induced conformational alteration occurs. This behavior is also discussed and supported by theoretical predictions of the intrinsic intra-protein electric fields. As the general features of such inner fields are not peculiar of azurin, the conclusions presented here should have general validity.
NASA Astrophysics Data System (ADS)
Simmons-Duffin, David
These notes are from courses given at TASI and the Advanced Strings School in summer 2015. Starting from principles of quantum field theory and the assumption of a traceless stress tensor, we develop the basics of conformal field theory, including conformal Ward identities, radial quantization, reection positivity, the operator product expansion, and conformal blocks. We end with an introduction to numerical bootstrap methods, focusing on the 2d and 3d Ising models.
Field Evaluation of a Novel 2D Preferential Flow Snowpack Hydrology Model
NASA Astrophysics Data System (ADS)
Leroux, N.; Pomeroy, J. W.; Kinar, N. J.
2015-12-01
Accurate estimation of snowmelt flux is of primary importance for runoff hydrograph prediction, which is used for water management and flood forecasting. Lateral flows and preferential flow pathways in porous media flow have proven critical for improving soil and groundwater flow models, but though many physically-based layered snowmelt models have been developed, only 1D matrix flow is accounted for in these models. Therefore, there is a need for snowmelt models that include these processes so as to examine the potential to improve snowmelt hydrological modelling. A 2D model is proposed that enables an improved understanding of energy and water flows within deep heterogeneous snowpacks, including those on slopes. A dual pathway theory is presented that simulates the formation of preferential flow paths, vertical and lateral water flows through the snow matrix and flow fingers, internal energy fluxes, melt, wet snow metamorphism, and internal refreezing. The dual pathway model utilizes an explicit finite volume method to solve for the energy and water flux equations over a non-orthogonal grid. It was run and evaluated using in-situ data collected from snowpit - accessed gravimetric, thermometric, photographic, and dielectric observations and novel non-invasive acoustic observations of layering, temperature, flowpath geometry, density and wetness at the Fortress Mountain Snow Laboratory, Alberta, Canada. The melt of a natural snowpack was artificially generated after detailed observation of snowpack initial conditions such as snow layer properties, temperature, and liquid water content. Snowpack ablation and liquid water content distribution over time were then measured and used for model parameterization and validation. Energy available at the snow surface and soil slope angle were set as mondel inputs. Model verification was based on snowpack property evolution. The heterogeneous flow model can be an important tool to help understand snowmelt flow processes, how
CFT driven cosmology and conformal higher spin fields
NASA Astrophysics Data System (ADS)
Barvinsky, A. O.
2016-05-01
Conformal higher spin (CHS) field theory, which is a solid part of recent advanced checks of AdS/CFT correspondence, finds applications in cosmology. The hidden sector of weakly interacting CHS fields suggests a resolution of the hierarchy problem in the model of initial conditions for inflationary cosmology driven by a conformal field theory. These initial conditions are set by thermal garland-type cosmological instantons in the sub-Planckian energy range for the model of CHS fields with a large positive coefficient β of the Gauss-Bonnet term in their total conformal anomaly and a large number of their polarizations N . The upper bound of this range MP/√{β } is shown to be much lower than the gravitational cutoff MP/√{N } which is defined by the requirement of smallness of the perturbatively nonrenormalizable graviton loop contributions. In this way we justify the approximation scheme in which the nonrenormalizable graviton sector is subject to effective field theory under this cutoff, whereas the renormalizable sector of multiple CHS fields is treated beyond perturbation theory and dynamically generates the bound on the inflation scale of the CFT cosmology MP/√{β }≪MP/√{N }. This confirms recent predictions for the origin of the Starobinsky R2 and Higgs inflation models from the CHS cosmology, which occurs at the energy scale 3 or 4 orders of magnitude below the gravitational cutoff, √{N /β }˜10-3- 10-4 . We also consider cosmological models dominated by fermionic CHS fields with a negative β and anomaly free models of infinite towers of CHS fields with β =0 and briefly discuss the status of unitarity in CHS models.
Shao, Yonghong; Liu, Honghai; Qin, Wan; Qu, Junle; Peng, Xiang; Niu, Hanben; Gao, Bruce Z
2012-09-01
We present an addressable, large-field second harmonic generation microscope by combining a 2D acousto-optical deflector with a spatial light modulator. The SLM shapes an incoming mode-locked, near-infrared Ti:Sapphire laser beam into a multifocus array, which can be rapidly scanned by changing the incident angle of the laser beam using a 2D acousto-optical deflector. Compared to the single-beam-scan technique, the multifocus array scan can increase the scanning rate and the field-of-view size with the multi-region imaging ability.
Shao, Yonghong; Liu, Honghai; Qin, Wan; Qu, Junle; Peng, Xiang; Niu, Hanben
2013-01-01
We present an addressable, large-field second harmonic generation microscope by combining a 2D acousto-optical deflector with a spatial light modulator. The SLM shapes an incoming mode-locked, near-infrared Ti:Sapphire laser beam into a multifocus array, which can be rapidly scanned by changing the incident angle of the laser beam using a 2D acousto-optical deflector. Compared to the single-beam-scan technique, the multifocus array scan can increase the scanning rate and the field-of-view size with the multi-region imaging ability. PMID:24307756
Relating the archetypes of logarithmic conformal field theory
NASA Astrophysics Data System (ADS)
Creutzig, Thomas; Ridout, David
2013-07-01
Logarithmic conformal field theory is a rich and vibrant area of modern mathematical physics with well-known applications to both condensed matter theory and string theory. Our limited understanding of these theories is based upon detailed studies of various examples that one may regard as archetypal. These include the c=-2 triplet model, the Wess-Zumino-Witten model on SL(2;R) at level k=-1/2 >, and its supergroup analogue on GL(1|1). Here, the latter model is studied algebraically through representation theory, fusion and modular invariance, facilitating a subsequent investigation of its cosets and extended algebras. The results show that the archetypes of logarithmic conformal field theory are in fact all very closely related, as are many other examples including, in particular, the SL(2|1) models at levels 1 and -1/2 >. The conclusion is then that the archetypal examples of logarithmic conformal field theory are practically all the same, so we should not expect that their features are in any way generic. Further archetypal examples must be sought.
Parastatistics and conformal field theories in two dimensions
NASA Astrophysics Data System (ADS)
Mansouri, Freydoon; Wu, Xizeng
1989-04-01
The relation between parafermion field theories of order Q and the corresponding fermion field theories with SO(Q) symmetry is studied. It is shown that these theories are related but not identical. The explicit relation between the states and the observables of the two classes of theories are given without using the Klein transformations. The formalism is applied to the free conformally invariant parafermion theories in two dimensions. Their Virasoro algebra and SO(N) Kac-Moody algebra are given. The equivalence of their canonical form of the energy-momentum tensor with the Sugawara-Sommerfield form is also elucidated.
Effects of in-plane magnetic field on the transport of 2D electron vortices in non-uniform plasmas
NASA Astrophysics Data System (ADS)
Angus, Justin; Richardson, Andrew; Schumer, Joseph; Pulsed Power Team
2015-11-01
The formation of electron vortices in current-carrying plasmas is observed in 2D particle-in-cell (PIC) simulations of the plasma-opening switch. In the presence of a background density gradient in Cartesian systems, vortices drift in the direction found by crossing the magnetic field with the background density gradient as a result of the Hall effect. However, most of the 2D simulations where electron vortices are seen and studied only allow for in-plane currents and thus only an out-of-plane magnetic field. Here we present results of numerical simulations of 2D, seeded electron vortices in an inhomogeneous background using the generalized 2D electron-magneto-hydrodynamic model that additionally allows for in-plane components of the magnetic field. By seeding vortices with a varying axial component of the velocity field, so that the vortex becomes a corkscrew, it is found that a pitch angle of around 20 degrees is sufficient to completely prevent the vortex from propagating due to the Hall effect for typical plasma parameters. This work is supported by the NRL Base Program.
Nicasio, Antonio I; Montilla, Francisco; Álvarez, Eleuterio; Colodrero, Rosario P; Galindo, Agustín
2017-01-03
Different novel coordination polymers containing zinc, 1-4, and copper, 5-8, metals, connected via chiral imidazolium-based dicarboxylate ligands, [L(R)](-), were isolated by reaction between zinc acetate or copper acetate and enantiomerically pure HL(R) compounds. They were characterised and structurally identified by X-ray diffraction methods (single crystal and powder). These compounds are two-dimensional homochiral coordination polymers, [M(L(R))2]n, in which the metal ions are coordinated by the two carboxylate groups of [L(R)](-) anions in a general bridging monodentate μ(2)-κ(1)-O(1),κ(1)-O(3) fashion that afforded tetrahedral metal coordination environments for zinc, 1-4, and square planar for copper, 5-8, complexes. In all the compounds the 3D supramolecular architecture is constructed by non-covalent interactions between the hydrophobic parts (R groups) of the homochiral 2D coordination polymers and, in some cases, by weak C-HO non-classical hydrogen bonds that provided, in general, a dense crystal packing. DFT calculations on the [L(R)](-) anions confirmed their conformational flexibility as ditopic linkers and this fact makes possible the formation of different coordination polymers for four-coordinated metal centers. Preliminary studies on the Zn-catalyzed synthesis of chiral α-aminophosphonates were carried out and, unfortunately, no enantioselectivity was observed in these reactions.
Wang, Tuo; Yang, Hui; Kubicki, James D; Hong, Mei
2016-06-13
The native cellulose of bacterial, algal, and animal origins has been well studied structurally using X-ray and neutron diffraction and solid-state NMR spectroscopy, and is known to consist of varying proportions of two allomorphs, Iα and Iβ, which differ in hydrogen bonding, chain packing, and local conformation. In comparison, cellulose structure in plant primary cell walls is much less understood because plant cellulose has lower crystallinity and extensive interactions with matrix polysaccharides. Here we have combined two-dimensional magic-angle-spinning (MAS) solid-state nuclear magnetic resonance (solid-state NMR) spectroscopy at high magnetic fields with density functional theory (DFT) calculations to obtain detailed information about the structural polymorphism and spatial distributions of plant primary-wall cellulose. 2D (13)C-(13)C correlation spectra of uniformly (13)C-labeled cell walls of several model plants resolved seven sets of cellulose chemical shifts. Among these, five sets (denoted a-e) belong to cellulose in the interior of the microfibril while two sets (f and g) can be assigned to surface cellulose. Importantly, most of the interior cellulose (13)C chemical shifts differ significantly from the (13)C chemical shifts of the Iα and Iβ allomorphs, indicating that plant primary-wall cellulose has different conformations, packing, and hydrogen bonding from celluloses of other organisms. 2D (13)C-(13)C correlation experiments with long mixing times and with water polarization transfer revealed the spatial distributions and matrix-polysaccharide interactions of these cellulose structures. Celluloses f and g are well mixed chains on the microfibril surface, celluloses a and b are interior chains that are in molecular contact with the surface chains, while cellulose c resides in the core of the microfibril, outside spin diffusion contact with the surface. Interestingly, cellulose d, whose chemical shifts differ most significantly from those of
Wang, Tuo; Yang, Hui; Kubicki, James D.; Hong, Mei
2017-01-01
The native cellulose of bacterial, algal, and animal origins has been well studied structurally using X-ray and neutron diffraction and solid-state NMR spectroscopy, and is known to consist of varying proportions of two allomorphs, Iα and Iβ, which differ in hydrogen bonding, chain packing, and local conformation. In comparison, cellulose structure in plant primary cell walls is much less understood because plant cellulose has lower crystallinity and extensive interactions with matrix polysaccharides. Here we have combined two-dimensional magic-angle-spinning (MAS) solid-state nuclear magnetic resonance (solid-state NMR) spectroscopy at high magnetic fields with density functional theory (DFT) calculations to obtain detailed information about the structural polymorphism and spatial distributions of plant primary-wall cellulose. 2D 13C-13C correlation spectra of uniformly 13C-labeled cell walls of several model plants resolved seven sets of cellulose chemical shifts. Among these, five sets (denoted a-e) belong to cellulose in the interior of the microfibril while two sets (f and g) can be assigned to surface cellulose. Importantly, most of the interior cellulose 13C chemical shifts differ significantly from the 13C chemical shifts of the Iα and Iβ allomorphs, indicating that plant primary-wall cellulose has different conformations, packing and hydrogen bonding from celluloses of other organisms. 2D 13C-13C correlation experiments with long mixing times and with water polarization transfer revealed the spatial distributions and matrix-polysaccharide interactions of these cellulose structures. Cellulose f and g are well mixed chains on the microfibril surface, cellulose a and b are interior chains that are in molecular contact with the surface chains, while cellulose c resides in the core of the microfibril, outside spin diffusion contact with the surface. Interestingly, cellulose d, whose chemical shifts differ most significantly from those of bacterial, algal
NASA Astrophysics Data System (ADS)
Akcay, Huseyin; Sever, Ramazan
2016-07-01
We investigate the energy spectrum and the corresponding eigenfunctions of a 2D Dirac oscillator confined by an antidot potential in the presence of a magnetic field and Aharonov-Bohm flux field. Analytical solutions are obtained and compared with the results of the Schrödinger equation found in the literature. Further, the dependence of the spectrum on the magnetic quantum number and on the repulsive potential is discussed.
NASA Astrophysics Data System (ADS)
Trofimov, Vyacheslav A.; Egorenkov, Vladimir A.; Loginova, Mariya M.
2015-08-01
We analyze laser-induced periodic structure developing in a semiconductor under the condition of both optical bistability existence and action of 2D external electric field. Optical bistability occurs because of nonlinear dependence of semiconductor absorption coefficient on charged particles concentration. The electron mobility, diffusion of electrons and laser-induced electric field are taken into account for laser pulse propagation analyzing. 2D external electric field together with electric field, induced by free electrons and ionized donors, governs the charged particle motion. Under certain conditions, the additional positive inverse loop between electron motion and electric field, caused by redistribution of free charged particles, appears. As a result, the helical wave for free charged particle concentration of electron-hole plasma in semiconductor develops under the electric field action. For computer simulation of a problem under consideration, a new finite-difference scheme is proposed. The main feature of proposed method consists in constructed two-step iteration process. We pay a special attention for calculation of initial functions distributions. For their calculation we solve the set of 2D stationary partial differential equations by using additional iteration process that is similar to the iteration process, applied for the main problem solution.
Strongly Metallic Electron and Hole 2D Transport in an Ambipolar Si-Vacuum Field Effect Transistor.
Hu, Binhui; Yazdanpanah, M M; Kane, B E; Hwang, E H; Das Sarma, S
2015-07-17
We report experiment and theory on an ambipolar gate-controlled Si(111)-vacuum field effect transistor where we study electron and hole (low-temperature 2D) transport in the same device simply by changing the external gate voltage to tune the system from being a 2D electron system at positive gate voltage to a 2D hole system at negative gate voltage. The electron (hole) conductivity manifests strong (moderate) metallic temperature dependence with the conductivity decreasing by a factor of 8 (2) between 0.3 K and 4.2 K with the peak electron mobility (∼18 m2/V s) being roughly 20 times larger than the peak hole mobility (in the same sample). Our theory explains the data well using random phase approximation screening of background Coulomb disorder, establishing that the observed metallicity is a direct consequence of the strong temperature dependence of the effective screened disorder.
Effect of External Electric Field Stress on Gliadin Protein Conformation
Singh, Ashutosh; Munshi, Shirin; Raghavan, Vijaya
2013-01-01
A molecular dynamic (MD) modeling approach was applied to evaluate the effect of external electric field on gliadin protein structure and surface properties. Static electric field strengths of 0.001 V/nm and 0.002 V/nm induced conformational changes in the protein but had no significant effect on its surface properties. The study of hydrogen bond evolution during the course of simulation revealed that the root mean square deviation, radius of gyration and secondary structure formation, all depend significantly on the number hydrogen bonds formed. This study demonstrated that it is necessary to gain insight into protein dynamics under external electric field stress, in order to develop the novel food processing techniques that can be potentially used to reduce or eradicate food allergens. PMID:28250397
Non-conformal evolution of magnetic fields during reheating
Calzetta, Esteban; Kandus, Alejandra E-mail: kandus@uesc.br
2015-03-01
We consider the evolution of electromagnetic fields coupled to conduction currents during the reheating era after inflation, and prior to the establishing of the proton-electron plasma. We assume that the currents may be described by second order causal hydrodynamics. The resulting theory is not conformally invariant. The expansion of the Universe produces temperature gradients which couple to the current and generally oppose Ohmic dissipation. Although the effect is not strong, it suggests that the unfolding of hydrodynamic instabilities in these models may follow a different pattern than in first order theories, and even than in second order theories on non expanding backgrounds.
Positive Energy Conditions in 4D Conformal Field Theory
NASA Astrophysics Data System (ADS)
Farnsworth, Kara; Luty, Markus; Prilepina, Valentina
2016-03-01
We argue that all consistent 4D quantum field theories obey a spacetime-averaged weak energy inequality avgT00 >= - C /L4 , where L is the size of the smearing region, and C is a positive constant that depends on the theory. If this condition is violated, the theory has states that are indistinguishable from states of negative total energy by any local measurement, and we expect instabilities or other inconsistencies. We apply this condition to 4D conformal field theories, and find that it places constraints on the OPE coefficients of the theory. The constraints we find are weaker than the ``conformal collider'' constraints of Hofman and Maldacena. We speculate that there may be theories that violate the Hofman-Maldacena bounds, but satisfy our bounds. In 3D CFTs, the only constraint we find is equivalent to the positivity of 2-point function of the energy-momentum tensor, which follows from unitarity. Our calculations are performed using momentum-space Wightman functions, which are remarkably simple functions of momenta, and may be of interest in their own right.
Positive energy conditions in 4D conformal field theory
NASA Astrophysics Data System (ADS)
Farnsworth, Kara; Luty, Markus A.; Prilepina, Valentina
2016-10-01
We argue that all consistent 4D quantum field theories obey a spacetime-averaged weak energy inequality < T 00> ≥ - C/L 4, where L is the size of the smearing region, and C is a positive constant that depends on the theory. If this condition is violated, the theory has states that are indistinguishable from states of negative total energy by any local measurement, and we expect instabilities or other inconsistencies. We apply this condition to 4D conformal field theories, and find that it places constraints on the OPE coefficients of the theory. The constraints we find are weaker than the "conformal collider" constraints of Hofman and Maldacena. In 3D CFTs, the only constraint we find is equivalent to the positivity of 2-point function of the energy-momentum tensor, which follows from unitarity. Our calculations are performed using momentum-space Wightman functions, which are remarkably simple functions of momenta, and may be of interest in their own right.
Shape dependence of entanglement entropy in conformal field theories
NASA Astrophysics Data System (ADS)
Faulkner, Thomas; Leigh, Robert G.; Parrikar, Onkar
2016-04-01
We study universal features in the shape dependence of entanglement entropy in the vacuum state of a conformal field theory (CFT) on R^{1,d-1} . We consider the entanglement entropy across a deformed planar or spherical entangling surface in terms of a perturbative expansion in the infinitesimal shape deformation. In particular, we focus on the second order term in this expansion, known as the entanglement density. This quantity is known to be non-positive by the strong-subadditivity property. We show from a purely field theory calculation that the non-local part of the entanglement density in any CFT is universal, and proportional to the coefficient C T appearing in the two-point function of stress tensors in that CFT. As applications of our result, we prove the conjectured universality of the corner term coefficient σ /C_T=π^2/24 in d = 3 CFTs, and the holographic Mezei formula for entanglement entropy across deformed spheres.
Higher-rank supersymmetric models and topological conformal field theory
NASA Astrophysics Data System (ADS)
Kawai, Toshiya; Uchino, Taku; Yang, Sung-Kil
1993-03-01
In the first part of this paper we investigate the operator aspect of a higher-rank supersymmetric model which is introduced as a Lie theoretic extension of the N = 2 minimal model with the simplest case su(2) corresponding to the N = 2 minimal model. In particular we identify the analogs of chirality conditions and chiral ring. In the second part we construct a class of topological conformal field theories starting with this higher-rank supersymmetric model. We show the BRST-exactness of the twisted stress-energy tensor, find out physical observables and discuss how to make their correlation functions. It is emphasized that in the case of su(2) the topological field theory constructed in this paper is distinct from the one obtained by twisting the N = 2 minimal model through the usual procedure.
NASA Astrophysics Data System (ADS)
Ray, Anandaroop; Key, Kerry; Bodin, Thomas; Myer, David; Constable, Steven
2014-12-01
We apply a reversible-jump Markov chain Monte Carlo method to sample the Bayesian posterior model probability density function of 2-D seafloor resistivity as constrained by marine controlled source electromagnetic data. This density function of earth models conveys information on which parts of the model space are illuminated by the data. Whereas conventional gradient-based inversion approaches require subjective regularization choices to stabilize this highly non-linear and non-unique inverse problem and provide only a single solution with no model uncertainty information, the method we use entirely avoids model regularization. The result of our approach is an ensemble of models that can be visualized and queried to provide meaningful information about the sensitivity of the data to the subsurface, and the level of resolution of model parameters. We represent models in 2-D using a Voronoi cell parametrization. To make the 2-D problem practical, we use a source-receiver common midpoint approximation with 1-D forward modelling. Our algorithm is transdimensional and self-parametrizing where the number of resistivity cells within a 2-D depth section is variable, as are their positions and geometries. Two synthetic studies demonstrate the algorithm's use in the appraisal of a thin, segmented, resistive reservoir which makes for a challenging exploration target. As a demonstration example, we apply our method to survey data collected over the Scarborough gas field on the Northwest Australian shelf.
Stavros, Kallie M; Hawkins, Edward K; Rizzo, Carmelo J; Stone, Michael P
2015-07-20
The conformation of an N(2)-dG adduct arising from the heterocyclic amine 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), a potent food mutagen, was determined in 5'-d(C(1)T(2)C(3)X(4)G(5)C(6)G(7)C(8)C(9)A(10)T(11)C(12))-3':5'-d(G(13)A(14)T(15)G(16)G(17)C(18)G(19)C(20)C(21)G(22)A(23)G(24))-3'; X = N(2)-dG-IQ, in which the modified nucleotide X(4) corresponds to G(1) in the 5'-d(G(1)G(2)CG(3)CC)-3' NarI restriction endonuclease site. Circular dichroism (CD) revealed blue shifts relative to the unmodified duplex, consistent with adduct-induced twisting, and a hypochromic effect for the IQ absorbance in the near UV region. NMR revealed that the N(2)-dG-IQ adduct adopted a base-displaced intercalated conformation in which the modified guanine remained in the anti conformation about the glycosidic bond, the IQ moiety intercalated into the duplex, and the complementary base C(21) was displaced into the major groove. The processing of the N(2)-dG-IQ lesion by hpol η is sequence-dependent; when placed at the reiterated G(3) position, but not at the G(1) position, this lesion exhibits a propensity for frameshift replication [Choi, J. Y., et al. (2006) J. Biol. Chem., 281, 25297-25306]. The structure of the N(2)-dG-IQ adduct at the nonreiterated G(1) position was compared to that of the same adduct placed at the G(3) position [Stavros, K. M., et al. (2014) Nucleic Acids Res., 42, 3450-3463]. CD indicted minimal spectral differences between the G(1) vs G(3) N(2)-dG-IQ adducts. NMR indicated that the N(2)-dG-IQ adduct exhibited similar base-displaced intercalated conformations at both the G(1) and G(3) positions. This result differed as compared to the corresponding C8-dG-IQ adducts placed at the same positions. The C8-dG-IQ adduct adopted a minor groove conformation when placed at position G(1) but a base-displaced intercalated conformation when placed at position G(3) in the NarI sequence. The present studies suggest that differences in lesion bypass by hpol η may be
2016-01-01
The conformation of an N2-dG adduct arising from the heterocyclic amine 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), a potent food mutagen, was determined in 5′-d(C1T2C3X4G5C6G7C8C9A10T11C12)-3′:5′-d(G13A14T15G16G17C18G19C20C21G22A23G24)-3′; X = N2-dG-IQ, in which the modified nucleotide X4 corresponds to G1 in the 5′-d(G1G2CG3CC)-3′ NarI restriction endonuclease site. Circular dichroism (CD) revealed blue shifts relative to the unmodified duplex, consistent with adduct-induced twisting, and a hypochromic effect for the IQ absorbance in the near UV region. NMR revealed that the N2-dG-IQ adduct adopted a base-displaced intercalated conformation in which the modified guanine remained in the anti conformation about the glycosidic bond, the IQ moiety intercalated into the duplex, and the complementary base C21 was displaced into the major groove. The processing of the N2-dG-IQ lesion by hpol η is sequence-dependent; when placed at the reiterated G3 position, but not at the G1 position, this lesion exhibits a propensity for frameshift replication [Choi, J. Y., et al. (2006) J. Biol. Chem., 281, 25297–25306]. The structure of the N2-dG-IQ adduct at the nonreiterated G1 position was compared to that of the same adduct placed at the G3 position [Stavros, K. M., et al. (2014) Nucleic Acids Res., 42, 3450–3463]. CD indicted minimal spectral differences between the G1 vs G3N2-dG-IQ adducts. NMR indicated that the N2-dG-IQ adduct exhibited similar base-displaced intercalated conformations at both the G1 and G3 positions. This result differed as compared to the corresponding C8-dG-IQ adducts placed at the same positions. The C8-dG-IQ adduct adopted a minor groove conformation when placed at position G1 but a base-displaced intercalated conformation when placed at position G3 in the NarI sequence. The present studies suggest that differences in lesion bypass by hpol η may be mediated by differences in the 3′-flanking sequences, perhaps modulating the ability
NASA Technical Reports Server (NTRS)
Hermance, J. F.
1984-01-01
Electromagnetic induction in a laterally homogeneous earth is analyzed in terms of a source field with finite dimensions. Attention is focused on a time-varying two-dimensional current source directed parallel to the strike of a two-dimensional anomalous structure within the earth, i.e., the E-parallel mode. The spatially harmonic source field is expressed as discontinuities in the magnetic (or electric) field of the current in the source. The model is applied to describing the magnetic gradients across megatectonic features, and may be used to predict the magnetic fields encountered by a satellite orbiting above the ionosphere.
NASA Astrophysics Data System (ADS)
McGuire, Felicia A.; Cheng, Zhihui; Price, Katherine; Franklin, Aaron D.
2016-08-01
There is a rising interest in employing the negative capacitance (NC) effect to achieve sub-60 mV/decade (below the thermal limit) switching in field-effect transistors (FETs). The NC effect, which is an effectual amplification of the applied gate potential, is realized by incorporating a ferroelectric material in series with a dielectric in the gate stack of a FET. One of the leading challenges to such NC-FETs is the variable substrate capacitance exhibited in 3D semiconductor channels (bulk, Fin, or nanowire) that minimizes the extent of sub-60 mV/decade switching. In this work, we demonstrate 2D NC-FETs that combine the NC effect with 2D MoS2 channels to extend the steep switching behavior. Using the ferroelectric polymer, poly(vinylidene difluoride-trifluoroethylene) (P(VDF-TrFE)), these 2D NC-FETs are fabricated by modification of top-gated 2D FETs through the integrated addition of P(VDF-TrFE) into the gate stack. The impact of including an interfacial metal between the ferroelectric and dielectric is studied and shown to be critical. These 2D NC-FETs exhibit a decrease in subthreshold swing from 113 mV/decade down to 11.7 mV/decade at room temperature with sub-60 mV/decade switching occurring over more than 4 decades of current. The P(VDF-TrFE) proves to be an unstable option for a device technology, yet the superb switching behavior observed herein opens the way for further exploration of nanomaterials for extremely low-voltage NC-FETs.
A universal and ultrasensitive vectorial nanomechanical sensor for imaging 2D force fields
NASA Astrophysics Data System (ADS)
de Lépinay, Laure Mercier; Pigeau, Benjamin; Besga, Benjamin; Vincent, Pascal; Poncharal, Philippe; Arcizet, Olivier
2016-10-01
The miniaturization of force probes into nanomechanical oscillators enables ultrasensitive investigations of forces on dimensions smaller than their characteristic length scales. It also unravels the vectorial character of the force field and how its topology impacts the measurement. Here we present an ultrasensitive method for imaging two-dimensional vectorial force fields by optomechanically following the bidimensional Brownian motion of a singly clamped nanowire. This approach relies on angular and spectral tomography of its quasi-frequency-degenerated transverse mechanical polarizations: immersing the nanoresonator in a vectorial force field not only shifts its eigenfrequencies but also rotates the orientation of the eigenmodes, as a nanocompass. This universal method is employed to map a tunable electrostatic force field whose spatial gradients can even dominate the intrinsic nanowire properties. Enabling vectorial force field imaging with demonstrated sensitivities of attonewton variations over the nanoprobe Brownian trajectory will have a strong impact on scientific exploration at the nanoscale.
Simulation of bootstrap current in 2D and 3D ideal magnetic fields in tokamaks
NASA Astrophysics Data System (ADS)
Raghunathan, M.; Graves, J. P.; Cooper, W. A.; Pedro, M.; Sauter, O.
2016-09-01
We aim to simulate the bootstrap current for a MAST-like spherical tokamak using two approaches for magnetic equilibria including externally caused 3D effects such as resonant magnetic perturbations (RMPs), the effect of toroidal ripple, and intrinsic 3D effects such as non-resonant internal kink modes. The first approach relies on known neoclassical coefficients in ideal MHD equilibria, using the Sauter (Sauter et al 1999 Phys. Plasmas 6 2834) expression valid for all collisionalities in axisymmetry, and the second approach being the quasi-analytic Shaing-Callen (Shaing and Callen 1983 Phys. Fluids 26 3315) model in the collisionless regime for 3D. Using the ideal free-boundary magnetohydrodynamic code VMEC, we compute the flux-surface averaged bootstrap current density, with the Sauter and Shaing-Callen expressions for 2D and 3D ideal MHD equilibria including an edge pressure barrier with the application of resonant magnetic perturbations, and equilibria possessing a saturated non-resonant 1/1 internal kink mode with a weak internal pressure barrier. We compare the applicability of the self-consistent iterative model on the 3D applications and discuss the limitations and advantages of each bootstrap current model for each type of equilibrium.
2-D Fourier transform analysis of the gravitational field of Northern Sinai Peninsula
NASA Astrophysics Data System (ADS)
Khalil, Mohamed A.; Santos, Fernando M.; Farzamian, Mohammad; El-Kenawy, Abeer
2015-04-01
The Sinai Peninsula has fascinated the consideration of many geophysical studies as it is influenced by major tectonic events. Those are (1) the Mesozoic to Early Cenozoic tectonically active opening of Tethys, (2) the Late Cretaceous to Early Tertiary (Laramide) Syrian arc system, due to closing of the Tethys (3) the Oligo-Miocene Gulf of Suez rifted basin, and (4) the Late Miocene to Recent transform Dead Sea-Gulf of Aqaba rift. Moreover, the shear zones inside Sinai have affected intensely the structure development of the northern Sinai area. 2-D fast Fourier transform (FFT) analysis has been applied to transfer the data from space domain to frequency domain, in which basic gradients and derived gradients have been estimated. The frequency domain operations resulted in frequency filtering, first and second degree xyz gradients, horizontal, total (analytical signal) and tilt gradients, maximum horizontal gradient amplitude (total horizontal derivative), and theta map. As a result, the basic and derived gradient maps have succeeded to outline the major structure elements of Northern Sinai Peninsula. Comparisons with some well known surface structures showed a large degree of matching.
Relative entanglement entropies in 1 + 1-dimensional conformal field theories
NASA Astrophysics Data System (ADS)
Ruggiero, Paola; Calabrese, Pasquale
2017-02-01
We study the relative entanglement entropies of one interval between excited states of a 1+1 dimensional conformal field theory (CFT). To compute the relative entropy S( ρ 1∥ ρ 0) between two given reduced density matrices ρ 1 and ρ 0 of a quantum field theory, we employ the replica trick which relies on the path integral representation of Tr( ρ 1 ρ 0 n - 1 ) and define a set of Rényi relative entropies S n ( ρ 1∥ ρ 0). We compute these quantities for integer values of the parameter n and derive via the replica limit the relative entropy between excited states generated by primary fields of a free massless bosonic field. In particular, we provide the relative entanglement entropy of the state described by the primary operator i∂ ϕ, both with respect to the ground state and to the state generated by chiral vertex operators. These predictions are tested against exact numerical calculations in the XX spin-chain finding perfect agreement.
A hybrid experimental-numerical technique for determining 3D velocity fields from planar 2D PIV data
NASA Astrophysics Data System (ADS)
Eden, A.; Sigurdson, M.; Mezić, I.; Meinhart, C. D.
2016-09-01
Knowledge of 3D, three component velocity fields is central to the understanding and development of effective microfluidic devices for lab-on-chip mixing applications. In this paper we present a hybrid experimental-numerical method for the generation of 3D flow information from 2D particle image velocimetry (PIV) experimental data and finite element simulations of an alternating current electrothermal (ACET) micromixer. A numerical least-squares optimization algorithm is applied to a theory-based 3D multiphysics simulation in conjunction with 2D PIV data to generate an improved estimation of the steady state velocity field. This 3D velocity field can be used to assess mixing phenomena more accurately than would be possible through simulation alone. Our technique can also be used to estimate uncertain quantities in experimental situations by fitting the gathered field data to a simulated physical model. The optimization algorithm reduced the root-mean-squared difference between the experimental and simulated velocity fields in the target region by more than a factor of 4, resulting in an average error less than 12% of the average velocity magnitude.
Multi-field electron emission pattern of 2D emitter: Illustrated with graphene
NASA Astrophysics Data System (ADS)
Luo, Ma; Li, Zhibing
2016-11-01
The mechanism of laser-assisted multi-field electron emission of two-dimensional emitters is investigated theoretically. The process is basically a cold field electron emission but having more controllable components: a uniform electric field controls the emission potential barrier, a magnetic field controls the quantum states of the emitter, while an optical field controls electron populations of specified quantum states. It provides a highly orientational vacuum electron line source whose divergence angle over the beam plane is inversely proportional to square root of the emitter height. Calculations are carried out for graphene with the armchair emission edge, as a concrete example. The rate equation incorporating the optical excitation, phonon scattering, and thermal relaxation is solved in the quasi-equilibrium approximation for electron population in the bands. The far-field emission patterns, that inherit the features of the Landau bands, are obtained. It is found that the optical field generates a characteristic structure at one wing of the emission pattern.
Synchrotron radiation in strongly coupled conformal field theories
Athanasiou, Christiana; Chesler, Paul M.; Liu, Hong; Rajagopal, Krishna; Nickel, Dominik
2010-06-15
Using gauge/gravity duality, we compute the energy density and angular distribution of the power radiated by a quark undergoing circular motion in strongly coupled N=4 supersymmetric Yang-Mills theory. We compare the strong coupling results to those at weak coupling, finding them to be very similar. In both regimes, the angular distribution of the radiated power is in fact similar to that of synchrotron radiation produced by an electron in circular motion in classical electrodynamics: the quark emits radiation in a narrow beam along its velocity vector with a characteristic opening angle {alpha}{approx}1/{gamma}. To an observer far away from the quark, the emitted radiation appears as a short periodic burst, just like the light from a lighthouse does to a ship at sea. Our strong coupling results are valid for any strongly coupled conformal field theory with a dual classical gravity description.
Energy flux positivity and unitarity in conformal field theories.
Kulaxizi, Manuela; Parnachev, Andrei
2011-01-07
We show that in most conformal field theories the condition of the energy flux positivity, proposed by Hofman and Maldacena, is equivalent to the absence of ghosts. At finite temperature and large energy and momenta, the two-point functions of the stress energy tensor develop lightlike poles. The residues of the poles can be computed, as long as the only spin-two conserved current, which appears in the stress energy tensor operator-product expansion and acquires a nonvanishing expectation value at finite temperature, is the stress energy tensor. The condition for the residues to stay positive and the theory to remain ghost-free is equivalent to the condition of positivity of energy flux.
Circular Wilson loops in defect conformal field theory
NASA Astrophysics Data System (ADS)
Aguilera-Damia, Jeremías; Correa, Diego H.; Giraldo-Rivera, Victor I.
2017-03-01
We study a D3-D5 system dual to a conformal field theory with a codimension-one defect that separates regions where the ranks of the gauge groups differ by k. With the help of this additional parameter, as observed by Nagasaki, Tanida and Yamaguchi, one can define a double scaling limit in which the quantum corrections are organized in powers of λ/k 2, which should allow to extrapolate results between weak and strong coupling regimes. In particular we consider a radius R circular Wilson loop placed at a distance L, whose internal space orientation is given by an angle χ. We compute its vacuum expectation value and show that, in the double scaling limit and for small χ and small L/R, weak coupling results can be extrapolated to the strong coupling limit.
Energy Flux Positivity and Unitarity in Conformal Field Theories
Kulaxizi, Manuela; Parnachev, Andrei
2011-01-07
We show that in most conformal field theories the condition of the energy flux positivity, proposed by Hofman and Maldacena, is equivalent to the absence of ghosts. At finite temperature and large energy and momenta, the two-point functions of the stress energy tensor develop light like poles. The residues of the poles can be computed, as long as the only spin-two conserved current, which appears in the stress energy tensor operator-product expansion and acquires a nonvanishing expectation value at finite temperature, is the stress energy tensor. The condition for the residues to stay positive and the theory to remain ghost-free is equivalent to the condition of positivity of energy flux.
Energy Flux Positivity and Unitarity in Conformal Field Theories
NASA Astrophysics Data System (ADS)
Kulaxizi, Manuela; Parnachev, Andrei
2011-01-01
We show that in most conformal field theories the condition of the energy flux positivity, proposed by Hofman and Maldacena, is equivalent to the absence of ghosts. At finite temperature and large energy and momenta, the two-point functions of the stress energy tensor develop lightlike poles. The residues of the poles can be computed, as long as the only spin-two conserved current, which appears in the stress energy tensor operator-product expansion and acquires a nonvanishing expectation value at finite temperature, is the stress energy tensor. The condition for the residues to stay positive and the theory to remain ghost-free is equivalent to the condition of positivity of energy flux.
Enhanced field emission properties from surface-modified 2D Cd(OH)2 nanocoins
NASA Astrophysics Data System (ADS)
Bagal, Vivekanand S.; Patil, Girish P.; Deore, Amol B.; Baviskar, Prashant K.; Shirale, Dhammanand J.; Chavan, Padmakar G.
2017-02-01
Low turn-on field of 2.1 V/µm was found for the emission current density of 10 µA/cm2 and high current density of 403 µA/cm2 was drawn at an applied field of 3.6 V/µm from Au/Cd(OH)2 nanocoins/Cd(OH)2 microsheets (Au/Cd(OH)2NC/Cd(OH)2MS). The observed low turn-on field was found superior to other gold (Au) nanoparticle decorated semiconducting nanostructures reported in the literature. Also the field emission current stability for the preset value of 1 μA over the period of 3 h is found to be good. The Cd(OH)2 nanocoins were grown on Cadmium (Cd) substrate by simple chemical bath deposition technique. Au nanoparticles with average diameter 11 nm were decorated on surface of the Cd(OH)2 nanocoins by sputtering method. Detail characterization such as structural and morphological analysis of Au/Cd(OH)2NC/Cd(OH)2MS has been carried out using X-ray Diffraction, Field Emission Scanning Electron Microscope and Transmission Electron Microscope. To the best of our knowledge, this is the first report on the synthesis and field emission studies of Au/Cd(OH)2NC/Cd(OH)2MS.
NASA Astrophysics Data System (ADS)
Tumkur, Thejaswi U.; Doiron, Chloe; Yang, Xiao; Li, Bo; Swearer, Dayne F.; Cerjan, Benjamin W.; Nordlander, Peter; Halas, Naomi J.; Ajayan, Pulickel M.; Ringe, Emilie; Thomann, Isabell
2016-09-01
We demonstrate the ability to map photo-induced gradient forces in materials, using a setup akin to atomic force microscopy. This technique allows for the simultaneous characterization of topographical features and optical near-fields in materials, with a high spatio-temporal resolution. We show that the near-field gradient forces can be translated onto electric fields, enabling the mapping of plasmonic hot-spots in gold nanostructures, and the resolution of sub-10 nm features in photocatalytic materials. We further show that the dispersion-sensitive nature of near-field gradient forces can be used to image and distinguish atomically thin layers of 2-D materials, with high contrast.
Quantum corrections to the cosmological evolution of conformally coupled fields
Cembranos, Jose A.R.; Olive, Keith A.; Peloso, Marco; Uzan, Jean-Philippe E-mail: olive@physics.umn.edu E-mail: uzan@iap.fr
2009-07-01
Because the source term for the equations of motion of a conformally coupled scalar field, such as the dilaton, is given by the trace of the matter energy momentum tensor, it is commonly assumed to vanish during the radiation dominated epoch in the early universe. As a consequence, such fields are generally frozen in the early universe. Here we compute the finite temperature radiative correction to the source term and discuss its consequences on the evolution of such fields in the early universe. We discuss in particular, the case of scalar tensor theories of gravity which have general relativity as an attractor solution. We show that, in some cases, the universe can experience an early phase of contraction, followed by a non-singular bounce, and standard expansion. This can have interesting consequences for the abundance of thermal relics; for instance, it can provide a solution to the gravitino problem. We conclude by discussing the possible consequences of the quantum corrections to the evolution of the dilaton.
Effective filtering and interpolation of 2D discrete velocity fields with Navier-Stokes equations
NASA Astrophysics Data System (ADS)
Saumier, Louis-Philippe; Khouider, Boualem; Agueh, Martial
2016-11-01
We introduce a new variational technique to interpolate and filter a two-dimensional velocity vector field which is discretely sampled in a region of {{{R}}}2 and sampled only once at a time, on a small time-interval [0,{{Δ }}t]. The main idea is to find a solution of the Navier-Stokes equations that is closest to a prescribed field in the sense that it minimizes the l 2 norm of the difference between this solution and the target field. The minimization is performed on the initial vorticity by expanding it into radial basis functions of Gaussian type, with a fixed size expressed by a parameter ɛ. In addition, a penalty term with parameter k e is added to the minimizing functional in order to select a solution with a small kinetic energy. This additional term makes the minimizing functional strongly convex, and therefore ensures that the minimization problem is well-posed. The interplay between the parameters k e and ɛ effectively contributes to smoothing the discrete velocity field, as demonstrated by the numerical experiments on synthetic and real data.
NASA Astrophysics Data System (ADS)
Abrahamson, S.; Lonnes, S.
1995-11-01
The most common method for determining vorticity from planar velocity information is the circulation method. Its performance has been evaluated using a plane of velocity data obtained from a direct numerical simulation (DNS) of a three dimensional plane shear layer. Both the ability to reproduce the vorticity from the exact velocity field and one perturbed by a 5% random “uncertainty” were assessed. To minimize the sensitivity to velocity uncertainties, a new method was developed using a least-squares approach. The local velocity data is fit to a model velocity field consisting of uniform translation, rigid rotation, a point source, and plane shear. The least-squares method was evaluated in the same manner as the circulation method. The largest differences between the actual and calculated vorticity fields were due to the filter-like nature of the methods. The new method is less sensitive to experimental uncertainty. However the circulation method proved to be slightly better at reproducing the DNS field. The least-squares method provides additional information beyond the circulation method results. Using the correlation overline {Pω ω } and a vorticity threshold criteria to identify regions of rigid rotation (or eddies), the rigid rotation component of the least-squares method indicates these same regions.
Kolkoori, S R; Rahman, M-U; Chinta, P K; Ktreutzbruck, M; Rethmeier, M; Prager, J
2013-02-01
Ultrasound propagation in inhomogeneous anisotropic materials is difficult to examine because of the directional dependency of elastic properties. Simulation tools play an important role in developing advanced reliable ultrasonic non destructive testing techniques for the inspection of anisotropic materials particularly austenitic cladded materials, austenitic welds and dissimilar welds. In this contribution we present an adapted 2D ray tracing model for evaluating ultrasonic wave fields quantitatively in inhomogeneous anisotropic materials. Inhomogeneity in the anisotropic material is represented by discretizing into several homogeneous layers. According to ray tracing model, ultrasonic ray paths are traced during its energy propagation through various discretized layers of the material and at each interface the problem of reflection and transmission is solved. The presented algorithm evaluates the transducer excited ultrasonic fields accurately by taking into account the directivity of the transducer, divergence of the ray bundle, density of rays and phase relations as well as transmission coefficients. The ray tracing model is able to calculate the ultrasonic wave fields generated by a point source as well as a finite dimension transducer. The ray tracing model results are validated quantitatively with the results obtained from 2D Elastodynamic Finite Integration Technique (EFIT) on several configurations generally occurring in the ultrasonic non destructive testing of anisotropic materials. Finally, the quantitative comparison of ray tracing model results with experiments on 32mm thick austenitic weld material and 62mm thick austenitic cladded material is discussed.
Galvao, C.A.; Nutku, Y.
1996-12-01
mA third order Monge-Amp{grave e}re type equation of associativity that Dubrovin has obtained in 2-d topological field theory is formulated in terms of a variational principle subject to second class constraints. Using Dirac{close_quote}s theory of constraints this degenerate Lagrangian system is cast into Hamiltonian form and the Hamiltonian operator is obtained from the Dirac bracket. There is a new type of Kac-Moody algebra that corresponds to this Hamiltonian operator. In particular, it is not a W-algebra. {copyright} {ital 1996 American Institute of Physics.}
NASA Astrophysics Data System (ADS)
Ostrovsky, Dmitry
2016-09-01
A new family of Barnes beta distributions on (0, ∞) is introduced and its infinite divisibility, moment determinacy, scaling, and factorization properties are established. The Morris integral probability distribution is constructed from Barnes beta distributions of types (1, 0) and (2, 2), and its moment determinacy and involution invariance properties are established. For application, the maximum distributions of the 2D gaussian free field on the unit interval and circle with a non-random logarithmic potential are conjecturally related to the critical Selberg and Morris integral probability distributions, respectively, and expressed in terms of sums of Barnes beta distributions of types (1, 0) and (2, 2).
Ehrhart, Jérôme; Planeix, Jean-Marc; Kyritsakas-Gruber, Nathalie; Hosseini, Mir Wais
2009-08-28
The combination of a [1111] metacyclophane blocked in 1,3-alternate conformation and bearing four pyrazolyl coordinating units with MX(2) (M = Co, Zn and X = Cl or Br) leads to the formation of crystals formed by packing of 2D coordination networks. In the case of CuBr(2), the formation of a 1D network was observed. Structural studies by X-ray diffraction methods on single crystals were performed on all cases reported.
Magnetic field applied to thermochemical non-equilibrium reentry flows in 2D - five species
NASA Astrophysics Data System (ADS)
Sávio de Góes Maciel, Edisson
2015-07-01
In this work, a study involving magnetic field actuation over reentry flows in thermochemical non-equilibrium is performed. The Euler and Navier-Stokes equations are studied. The proposed numerical algorithm is centred and second-order accurate. The hypersonic flow around a blunt body is simulated. Three time integration methods are tested. The reactive simulations involve Earth atmosphere of five species. The work of Gaitonde is the reference to couple the fluid dynamics and Maxwell equations of electromagnetism. The results have indicated that the Maciel scheme, using the Mavriplis dissipation model, yields the best prediction of the stagnation pressure.
Quantum revivals in conformal field theories in higher dimensions
NASA Astrophysics Data System (ADS)
Cardy, John
2016-10-01
We investigate the behavior of the return amplitude { F }(t)=| < {{\\Psi }}(0)| {{\\Psi }}(t)> | following a quantum quench in a conformal field theory (CFT) on a compact spatial manifold of dimension d-1 and linear size O(L), from a state | {{\\Psi }}(0)> of extensive energy with short-range correlations. After an initial gaussian decay { F }(t) reaches a plateau value related to the density of available states at the initial energy. However for d=3,4 this value is attained from below after a single oscillation. For a holographic CFT the plateau persists up to times at least O({σ }1/(d-1)L), where σ \\gg 1 is the dimensionless Stefan-Boltzmann constant. On the other hand for a free field theory on manifolds with high symmetry there are typically revivals at times t˜ {{integer}}× L. In particular, on a sphere {S}d-1 of circumference 2π L, there is an action of the modular group on { F }(t) implying structure near all rational values of t/L, similar to what happens for rational CFTs in d=2.
Conformation change of enzyme molecules in laser radiation field
NASA Astrophysics Data System (ADS)
Leshenyuk, N. S.; Prigun, M. V.; Apanasevitsh, E. E.; Kruglik, G. S.
2007-06-01
As a result of an analysis of macromolecules properties in the coherent optical radiation field and with allowance for the experimentally obtained unique data on the interaction of lazer radiation with biomolecules (dependence of the interaction efficiency on the coherence length, presence of the effect in the spectra region far from the absorption band), a mechanism of wave interaction is developed. Using this mathematical model, the calculations of a change in the macromolecules oscillatory energy in the coherent radiation field are performed. It is shown that the increase of macromolecules oscillatory energy depends strongly on the coherence length of radiation. On exposure to noncoherent radiation, the biomolecules oscillatory energy practically does not change, whereas on exposure to laser radiation (coherence length ~3 cm), energy of oscillations of atoms increases by an order of 2÷4, which results in a change in the conformation of biomolecules and activity of enzymes. Recently a lot of data are received concerning the change of lysosomal enzymes activity in blood plasma under action of laser radiation.
Experimental Observation of a Metal-insulator Transition in 2D at Zero Magnetic Field
NASA Astrophysics Data System (ADS)
Kravchenko, S. V.
1996-03-01
The scaling theory of Abrahams et al. ^1 has had considerable success in describing many features of metal-insulator transitions. Within this theory, which was developed for non-interacting electrons, no such transition is possible in two-dimensional electron systems (2DES) in the absence of a magnetic field. However, we show experimentally that an ultra-high-mobility 2DES on the surface of silicon does exhibit the signature of a true metal-insulator phase transition at zero magnetic field at a critical electron density n_c ~10^11 cm-2. The energy of electron-electron interactions, ignored in the scaling theory,^1 is the dominant parameter in this 2DES. The resistivity, ρ, is empirically found to scale near the critical point both with temperature T and electric field E so that it can be represented by the form ρ(T,n_s)=ρ(T/T_0(n_s)) as Earrow0 or ρ(E,n_s)=ρ(E/E_0(n_s)) as Tarrow0. At the transition, the resistivity is close to 3h/e^2. Both scaling parameters, T0 and E_0, show power law behavior at the critical point. This is characteristic of a true phase transition and strongly resembles, in particular, the superconductor-insulator transition in disordered thin films,^2 as well as the transition between quantum Hall liquid and insulator.^3 Many high-mobility samples from two different sources (Institute for Metrological Service, Russia, and Siemens AG, Germany) with different oxide thicknesses and gate materials have been studied and similar results were found. Work done in collaboration with J. E. Furneaux, Whitney Mason, V. M. Pudalov, and M. D'Iorio, supported by NSF. ^1 E. Abrahams, P. W. Anderson, D. C. Licciardello, and T. V. Ramakrishnan, Phys. Rev. Lett. 42, 673 (1979). ^2 Y. Liu, K. A. McGreer, B. Nease, D. B. Haviland, G. Martinez, J. W. Halley, and A. M. Goldman, Phys. Rev. Lett. 67, 2068 (1991). ^3 T. Wang, K. P. Clark, G. F. Spencer, A. M. Mack, and W. P. Kirk, Phys. Rev. Lett. 72, 709 (1994).
Vlasov Fluid stability of a 2-D plasma with a linear magnetic field null
Kim, J.S.
1984-01-01
Vlasov Fluid stability of a 2-dimensional plasma near an O type magnetic null is investigated. Specifically, an elongated Z-pinch is considered, and applied to Field Reversed Configurations at Los Alamos National Laboratory by making a cylindrical approximation of the compact torus. The orbits near an elliptical O type null are found to be very complicated; the orbits are large and some are stochastic. The kinetic corrections to magnetohydrodynamics (MHD) are investigated by evaluating the expectation values of the growth rates of a Vlasov Fluid dispersion functional by using a set of trial functions based on ideal MHD. The dispersion functional involves fluid parts and orbit dependent parts. The latter involves phase integral of two time correlations. The phase integral is replaced by the time integral both for the regular and for the stochastic orbits. Two trial functions are used; one has a large displacement near the null and the other away from the null.
NASA Astrophysics Data System (ADS)
Darvini, G.; Salandin, P.
2009-12-01
To analyze the impact of the hydraulic conductivity K spatial variability in a real field case (as an example to delimitate a well catchment), numerical simulations can be reasonably developed in a two-dimensional vertical average context. Nevertheless the plume evolution is a consequence of a more complex three-dimensional heterogeneous structure whose vertical variability dominates the dispersion phenomena at local scale. In larger domains, the effect of the vertical heterogeneity combines itself with that one due to the horizontal variability of K, and only when the plume has travelled a large number of (horizontal) integral scales, its evolution can be analyzed in a regional context, under the hypothesis that the transmissivity spatial distribution prevails. Until this limit is reached, the vertical and horizontal variability of K are combined to give a fully 3-D dispersion process. In all these situations, to successfully accomplish the 3-D heterogeneous structure of the aquifer in 2-D simulations, more than the planimetric depth-averaged variability of K must be accounted for. To define the uncertainty related to the use of different planimetric schematizations of the real hydraulic conductivity spatial distribution, we present here the results of some numerical experiments that compare the 3-D plume evolution with 2-D simulations developed by tacking into account different hydraulic conductivity distribution schematization, by considering a hierarchical architecture of media also. This description of a sedimentary formation combined with the finite size of the plume requires theoretical and numerical tools able to take into account the flow field inhomogeneity and the ergodicity lack that characterize the transport phenomena. Following this way it will be possible to quantify / reduce the uncertainty related to a 2-D schematization in a large number of real cases where the domain spans between the local and the regional scale and whose dimension may lead to
NASA Technical Reports Server (NTRS)
Gardner, J. P.; Straughn, Amber N.; Meurer, Gerhardt R.; Pirzkal, Norbert; Cohen, Seth H.; Malhotra, Sangeeta; Rhoads, james; Windhorst, Rogier A.; Gardner, Jonathan P.; Hathi, Nimish P.; Xu, Chun; Gronwall, Caryl; Koekemoer, Anton M.; Walsh, Jeremy; diSeregoAlighieri, Sperello
2007-01-01
The Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) grism PEARS (Probing Evolution And Reionization Spectroscopically) survey provides a large dataset of low-resolution spectra from thousands of galaxies in the GOODS North and South fields. One important subset of objects in these data are emission-line galaxies (ELGs), and we have investigated several different methods aimed at systematically selecting these galaxies. Here we present a new methodology and results of a search for these ELGs in the PEARS observations of the Hubble Ultra Deep Field (HUDF) using a 2D detection method that utilizes the observation that many emission lines originate from clumpy knots within galaxies. This 2D line-finding method proves to be useful in detecting emission lines from compact knots within galaxies that might not otherwise be detected using more traditional 1D line-finding techniques. We find in total 96 emission lines in the HUDF, originating from 81 distinct "knots" within 63 individual galaxies. We find in general that [0 1111 emitters are the most common, comprising 44% of the sample, and on average have high equivalent widths (70% of [0 1111 emitters having rest-frame EW> 100A). There are 12 galaxies with multiple emitting knots; several show evidence of variations in H-alpha flux in the knots, suggesting that the differing star formation properties across a single galaxy can in general be probed at redshifts approximately greater than 0.2 - 0.4. The most prevalent morphologies are large face-on spirals and clumpy interacting systems, many being unique detections owing to the 2D method described here, thus highlighting the strength of this technique.
Electric field-controlled directed migration of neural progenitor cells in 2D and 3D environments.
Meng, Xiaoting; Li, Wenfei; Young, Fraser; Gao, Runchi; Chalmers, Laura; Zhao, Min; Song, Bing
2012-02-16
Endogenous electric fields (EFs) occur naturally in vivo and play a critical role during tissue/organ development and regeneration, including that of the central nervous system(1,2). These endogenous EFs are generated by cellular regulation of ionic transport combined with the electrical resistance of cells and tissues. It has been reported that applied EF treatment can promote functional repair of spinal cord injuries in animals and humans(3,4). In particular, EF-directed cell migration has been demonstrated in a wide variety of cell types(5,6), including neural progenitor cells (NPCs)(7,8). Application of direct current (DC) EFs is not a commonly available technique in most laboratories. We have described detailed protocols for the application of DC EFs to cell and tissue cultures previously(5,11). Here we present a video demonstration of standard methods based on a calculated field strength to set up 2D and 3D environments for NPCs, and to investigate cellular responses to EF stimulation in both single cell growth conditions in 2D, and the organotypic spinal cord slice in 3D. The spinal cordslice is an ideal recipient tissue for studying NPC ex vivo behaviours, post-transplantation, because the cytoarchitectonic tissue organization is well preserved within these cultures(9,10). Additionally, this ex vivo model also allows procedures that are not technically feasible to track cells in vivo using time-lapse recording at the single cell level. It is critically essential to evaluate cell behaviours in not only a 2D environment, but also in a 3D organotypic condition which mimicks the in vivo environment. This system will allow high-resolution imaging using cover glass-based dishes in tissue or organ culture with 3D tracking of single cell migration in vitro and ex vivo and can be an intermediate step before moving onto in vivo paradigms.
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.
Research on reconstruction algorithms for 2D temperature field based on TDLAS
NASA Astrophysics Data System (ADS)
Peng, Dong; Jin, Yi; Zhai, Chao
2015-10-01
Tunable Diode Laser Absorption Tomography(TDLAT), as a promising technique which combines Tunable Diode Laser Absorption Spectroscopy(TDLAS) and computer tomography, has shown the advantages of high spatial resolution for temperature measurement. Given the large number of tomography algorithms, it is necessary to understand the feature of tomography algorithms and find suitable ones for the specific experiment. This paper illustrates two different algorithms including algebraic reconstruction technique (ART) and simulated annealing (SA) which are implemented using Matlab. The reconstruction simulations of unimodal and bimodal temperature phantom were done under different conditions, and the results of the simulation were analyzed. It shows that for the unimodal temperature phantom, the both algorithms work well, the reconstruction quality is acceptable under suitable conditions and the result of ART is better. But for the bimodal temperature phantom, the result of SA is much better. More specifically, the reconstruction quality of ART is mainly affected by the ray coverage, the maximum deviation for the unimodal temperature phantom is 5.9%, while for the bimodal temperature field, it is up to 25%. The reconstruction quality of SA is mainly affected by the number of the transitions, the maximum deviation for the unimodal temperature phantom is 9.2% when 6 transitions are used which is a little worse than the result of ART; however, the maximum deviation for the bimodal temperature phantom is much better than ART's, which is about 5.2% when 6 transitions are used.
Huang, Yang; Wu, Ya Min; Gao, Lei
2017-01-23
We carry out a theoretical study on optical bistability of near field intensity and transmittance in two-dimensional nonlinear composite slab. This kind of 2D composite is composed of nonlocal metal/Kerr-type dielectric core-shell inclusions randomly embedded in the host medium, and we derivate the nonlinear relation between the field intensity in the shell of inclusions and the incident field intensity with self-consistent mean field approximation. Numerical demonstration has been performed to show the viable parameter space for the bistable near field. We show that nonlocality can provide broader region in geometric parameter space for bistable near field as well as bistable transmittance of the nonlocal composite slab compared to local case. Furthermore, we investigate the bistable transmittance in wavelength spectrum, and find that besides the input intensity, the wavelength operation could as well make the transmittance jump from a high value to a low one. This kind of self-tunable nano-composite slab might have potential application in optical switching devices.
Statistical Analyses of Brain Surfaces Using Gaussian Random Fields on 2-D Manifolds
Staib, Lawrence H.; Xu, Dongrong; Zhu, Hongtu; Peterson, Bradley S.
2008-01-01
Interest in the morphometric analysis of the brain and its subregions has recently intensified because growth or degeneration of the brain in health or illness affects not only the volume but also the shape of cortical and subcortical brain regions, and new image processing techniques permit detection of small and highly localized perturbations in shape or localized volume, with remarkable precision. An appropriate statistical representation of the shape of a brain region is essential, however, for detecting, localizing, and interpreting variability in its surface contour and for identifying differences in volume of the underlying tissue that produce that variability across individuals and groups of individuals. Our statistical representation of the shape of a brain region is defined by a reference region for that region and by a Gaussian random field (GRF) that is defined across the entire surface of the region. We first select a reference region from a set of segmented brain images of healthy individuals. The GRF is then estimated as the signed Euclidean distances between points on the surface of the reference region and the corresponding points on the corresponding region in images of brains that have been coregistered to the reference. Correspondences between points on these surfaces are defined through deformations of each region of a brain into the coordinate space of the reference region using the principles of fluid dynamics. The warped, coregistered region of each subject is then unwarped into its native space, simultaneously bringing into that space the map of corresponding points that was established when the surfaces of the subject and reference regions were tightly coregistered. The proposed statistical description of the shape of surface contours makes no assumptions, other than smoothness, about the shape of the region or its GRF. The description also allows for the detection and localization of statistically significant differences in the shapes of
A 2D ion chamber array audit of wedged and asymmetric fields in an inhomogeneous lung phantom
Lye, Jessica; Dunn, Leon Alves, Andrew; Kenny, John; Lehmann, Joerg; Williams, Ivan; Kron, Tomas; Cole, Andrew
2014-10-15
Purpose: The Australian Clinical Dosimetry Service (ACDS) has implemented a new method of a nonreference condition Level II type dosimetric audit of radiotherapy services to increase measurement accuracy and patient safety within Australia. The aim of this work is to describe the methodology, tolerances, and outcomes from the new audit. Methods: The ACDS Level II audit measures the dose delivered in 2D planes using an ionization chamber based array positioned at multiple depths. Measurements are made in rectilinear homogeneous and inhomogeneous phantoms composed of slabs of solid water and lung. Computer generated computed tomography data sets of the rectilinear phantoms are supplied to the facility prior to audit for planning of a range of cases including reference fields, asymmetric fields, and wedged fields. The audit assesses 3D planning with 6 MV photons with a static (zero degree) gantry. Scoring is performed using local dose differences between the planned and measured dose within 80% of the field width. The overall audit result is determined by the maximum dose difference over all scoring points, cases, and planes. Pass (Optimal Level) is defined as maximum dose difference ≤3.3%, Pass (Action Level) is ≤5.0%, and Fail (Out of Tolerance) is >5.0%. Results: At close of 2013, the ACDS had performed 24 Level II audits. 63% of the audits passed, 33% failed, and the remaining audit was not assessable. Of the 15 audits that passed, 3 were at Pass (Action Level). The high fail rate is largely due to a systemic issue with modeling asymmetric 60° wedges which caused a delivered overdose of 5%–8%. Conclusions: The ACDS has implemented a nonreference condition Level II type audit, based on ion chamber 2D array measurements in an inhomogeneous slab phantom. The powerful diagnostic ability of this audit has allowed the ACDS to rigorously test the treatment planning systems implemented in Australian radiotherapy facilities. Recommendations from audits have led to
Nonlocal gravity: Conformally flat spacetimes
NASA Astrophysics Data System (ADS)
Bini, Donato; Mashhoon, Bahram
2016-04-01
The field equations of the recent nonlocal generalization of Einstein’s theory of gravitation are presented in a form that is reminiscent of general relativity. The implications of the nonlocal field equations are studied in the case of conformally flat spacetimes. Even in this simple case, the field equations are intractable. Therefore, to gain insight into the nature of these equations, we investigate the structure of nonlocal gravity (NLG) in 2D spacetimes. While any smooth 2D spacetime is conformally flat and satisfies Einstein’s field equations, only a subset containing either a Killing vector or a homothetic Killing vector can satisfy the field equations of NLG.
An inversion method of 2D NMR relaxation spectra in low fields based on LSQR and L-curve
NASA Astrophysics Data System (ADS)
Su, Guanqun; Zhou, Xiaolong; Wang, Lijia; Wang, Yuanjun; Nie, Shengdong
2016-04-01
The low-field nuclear magnetic resonance (NMR) inversion method based on traditional least-squares QR decomposition (LSQR) always produces some oscillating spectra. Moreover, the solution obtained by traditional LSQR algorithm often cannot reflect the true distribution of all the components. Hence, a good solution requires some manual intervention, for especially low signal-to-noise ratio (SNR) data. An approach based on the LSQR algorithm and L-curve is presented to solve this problem. The L-curve method is applied to obtain an improved initial optimal solution by balancing the residual and the complexity of the solutions instead of manually adjusting the smoothing parameters. First, the traditional LSQR algorithm is used on 2D NMR T1-T2 data to obtain its resultant spectra and corresponding residuals, whose norms are utilized to plot the L-curve. Second, the corner of the L-curve as the initial optimal solution for the non-negative constraint is located. Finally, a 2D map is corrected and calculated iteratively based on the initial optimal solution. The proposed approach is tested on both simulated and measured data. The results show that this algorithm is robust, accurate and promising for the NMR analysis.
Effective field theory program for conformal quantum anomalies
Camblong, Horacio E.; Epele, Luis N.; Fanchiotti, Huner; Canal, Carlos A. Garcia; Ordonez, Carlos R.
2005-09-15
The emergence of conformal states is established for any problem involving a domain of scales where the long-range SO(2,1) conformally invariant interaction is applicable. Whenever a clear-cut separation of ultraviolet and infrared cutoffs is in place, this renormalization mechanism is capable of producing binding in the strong-coupling regime. A realization of this phenomenon, in the form of dipole-bound anions, is discussed.
NASA Astrophysics Data System (ADS)
Peralta, X. G.; Allen, S. J.; Lin, S. Y.; Simmons, J. A.; Blount, M. A.; Baca, W. E.
1998-03-01
We explore photon-assisted resonant tunneling in double quantum well systems in intense terahertz electric fields that have separately- contacted wells. We have two goals in mind: 1) increase the basic understanding of photon assisted tunneling in semiconductors and 2) assess the potential of this structure as a detector. We can control the tunneling current by varying the electron density of each 2D electron gas or by changing the relative separation of the Fermi levels. This allows us to prepare the system in such a way that photons of the appropriate energy may induce resonant tunneling, which is monitored by a change in conductance. We also examine the possible enhancement of the resonant tunneling by resonant excitations of acoustic plasmon modes. This work is supported by ONR, the U. S. Dept. of Energy under Contract DE-AC04-94AL85000 and Consejo Nacional de Ciencia y Tecnología, México.
Noncommutative Geometry in M-Theory and Conformal Field Theory
Morariu, Bogdan
1999-05-01
In the first part of the thesis I will investigate in the Matrix theory framework, the subgroup of dualities of the Discrete Light Cone Quantization of M-theory compactified on tori, which corresponds to T-duality in the auxiliary Type II string theory. After a review of matrix theory compactification leading to noncommutative supersymmetric Yang-Mills gauge theory, I will present solutions for the fundamental and adjoint sections on a two-dimensional twisted quantum torus and generalize to three-dimensional twisted quantum tori. After showing how M-theory T-duality is realized in supersymmetric Yang-Mills gauge theories on dual noncommutative tori I will relate this to the mathematical concept of Morita equivalence of C*-algebras. As a further generalization, I consider arbitrary Ramond-Ramond backgrounds. I will also discuss the spectrum of the toroidally compactified Matrix theory corresponding to quantized electric fluxes on two and three tori. In the second part of the thesis I will present an application to conformal field theory involving quantum groups, another important example of a noncommutative space. First, I will give an introduction to Poisson-Lie groups and arrive at quantum groups using the Feynman path integral. I will quantize the symplectic leaves of the Poisson-Lie group SU(2)*. In this way we obtain the unitary representations of U_{q}(SU(2)). I discuss the X-structure of SU(2)* and give a detailed description of its leaves using various parametrizations. Then, I will introduce a new reality structure on the Heisenberg double of Fun_{q} (SL(N,C)) for q phase, which can be interpreted as the quantum phase space of a particle on the q-deformed mass-hyperboloid. I also present evidence that the above real form describes zero modes of certain non-compact WZNW-models.
Davis, A.B.; Clothiaux, E.
1999-03-01
Because of Earth`s gravitational field, its atmosphere is strongly anisotropic with respect to the vertical; the effect of the Earth`s rotation on synoptic wind patterns also causes a more subtle form of anisotropy in the horizontal plane. The authors survey various approaches to statistically robust anisotropy from a wavelet perspective and present a new one adapted to strongly non-isotropic fields that are sampled on a rectangular grid with a large aspect ratio. This novel technique uses an anisotropic version of Multi-Resolution Analysis (MRA) in image analysis; the authors form a tensor product of the standard dyadic Haar basis, where the dividing ratio is {lambda}{sub z} = 2, and a nonstandard triadic counterpart, where the dividing ratio is {lambda}{sub x} = 3. The natural support of the field is therefore 2{sup n} pixels (vertically) by 3{sup n} pixels (horizontally) where n is the number of levels in the MRA. The natural triadic basis includes the French top-hat wavelet which resonates with bumps in the field whereas the Haar wavelet responds to ramps or steps. The complete 2D basis has one scaling function and five wavelets. The resulting anisotropic MRA is designed for application to the liquid water content (LWC) field in boundary-layer clouds, as the prevailing wind advects them by a vertically pointing mm-radar system. Spatial correlations are notoriously long-range in cloud structure and the authors use the wavelet coefficients from the new MRA to characterize these correlations in a multifractal analysis scheme. In the present study, the MRA is used (in synthesis mode) to generate fields that mimic cloud structure quite realistically although only a few parameters are used to control the randomness of the LWC`s wavelet coefficients.
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.
Vann, R. G. L.; Brunner, K. J.; Ellis, R.; ...
2016-09-13
The Synthetic Aperture Microwave Imaging (SAMI) system is a novel diagnostic consisting of an array of 8 independently phased antennas. At any one time, SAMI operates at one of the 16 frequencies in the range 10-34.5 GHz. The imaging beam is steered in software post-shot to create a picture of the entire emission surface. In SAMI’s active probing mode of operation, the plasma edge is illuminated with a monochromatic source and SAMI reconstructs an image of the Doppler back-scattered (DBS) signal. By assuming that density fluctuations are extended along magnetic field lines, and knowing that the strongest back-scattered signals aremore » directed perpendicular to the density fluctuations, SAMI’s 2-D DBS imaging capability can be used to measure the pitch of the edge magnetic field. In this paper, we present preliminary pitch angle measurements obtained by SAMI on the Mega Amp Spherical Tokamak (MAST) at Culham Centre for Fusion Energy and on the National Spherical Torus Experiment Upgrade at Princeton Plasma Physics Laboratory. Lastly, the results demonstrate encouraging agreement between SAMI and other independent measurements.« less
Vann, R. G. L.; Brunner, K. J.; Ellis, R.; Taylor, G.; Thomas, D. A.
2016-09-13
The Synthetic Aperture Microwave Imaging (SAMI) system is a novel diagnostic consisting of an array of 8 independently phased antennas. At any one time, SAMI operates at one of the 16 frequencies in the range 10-34.5 GHz. The imaging beam is steered in software post-shot to create a picture of the entire emission surface. In SAMI’s active probing mode of operation, the plasma edge is illuminated with a monochromatic source and SAMI reconstructs an image of the Doppler back-scattered (DBS) signal. By assuming that density fluctuations are extended along magnetic field lines, and knowing that the strongest back-scattered signals are directed perpendicular to the density fluctuations, SAMI’s 2-D DBS imaging capability can be used to measure the pitch of the edge magnetic field. In this paper, we present preliminary pitch angle measurements obtained by SAMI on the Mega Amp Spherical Tokamak (MAST) at Culham Centre for Fusion Energy and on the National Spherical Torus Experiment Upgrade at Princeton Plasma Physics Laboratory. Lastly, the results demonstrate encouraging agreement between SAMI and other independent measurements.
NASA Astrophysics Data System (ADS)
Vann, R. G. L.; Brunner, K. J.; Ellis, R.; Taylor, G.; Thomas, D. A.
2016-11-01
The Synthetic Aperture Microwave Imaging (SAMI) system is a novel diagnostic consisting of an array of 8 independently phased antennas. At any one time, SAMI operates at one of the 16 frequencies in the range 10-34.5 GHz. The imaging beam is steered in software post-shot to create a picture of the entire emission surface. In SAMI's active probing mode of operation, the plasma edge is illuminated with a monochromatic source and SAMI reconstructs an image of the Doppler back-scattered (DBS) signal. By assuming that density fluctuations are extended along magnetic field lines, and knowing that the strongest back-scattered signals are directed perpendicular to the density fluctuations, SAMI's 2-D DBS imaging capability can be used to measure the pitch of the edge magnetic field. In this paper, we present preliminary pitch angle measurements obtained by SAMI on the Mega Amp Spherical Tokamak (MAST) at Culham Centre for Fusion Energy and on the National Spherical Torus Experiment Upgrade at Princeton Plasma Physics Laboratory. The results demonstrate encouraging agreement between SAMI and other independent measurements.
NASA Astrophysics Data System (ADS)
Chuang, Tien-Ming; Chung, Pei-Fang; Guan, Syu-You; Yu, Shan-An; Liu, Che-An; Hsu, Chia-Sheng; Su, Chih-Chuan; Sankar, Raman; Chou, Fang-Cheng
2015-03-01
We will describe the design and performance of a cryogenic scanning tunneling microscope (STM) system in a high magnetic field. A Pan-type STM is mounted on a homemade low vibration 4He pot refrigerator, which can be operated in continuous flow mode at T ~ 1.6K and in a magnetic field of up to 9 Tesla. A cleavage device at T =4.2K stage is used to cleave the 2D layered materials before inserting into STM as well as functioning as the radiation shield. The liquid helium boil rate of 4.6 liters per day is achieved due to our careful design, which allows the measurement at base temperature up to 10 days. We will demonstrate its capability of measuring atomically registered energy resolved spectroscopic maps in both real space and momentum space by our recent results on Rashba BiTeI. This work is supported by Ministry of Science and Technology, Taiwan and Kenda Foundation, Taiwan.
Lilley, Thomas; Laaksonen, Toni; Huitu, Otso; Helle, Samuli
2010-03-30
The steroid environment encountered by a foetus can strongly affect its post-natal physiology and behaviour. It has been proposed that steroid concentrations experienced in utero could be estimated from adults by measuring their second-to-fourth digit length ratio (2D:4D). However, there is still little direct evidence that intra-uterine steroid levels affect individual 2D:4D. We examined whether maternal pre-pregnancy testosterone and corticosterone levels (as estimates of intra-uterine testosterone and corticosterone exposure) affected the 2D:4D of pups in non-domesticated field voles (Microtus agrestis), measured by X-rays at the age of weaning (21 days). Furthermore, for the first time in a non-human species, we studied whether testosterone and corticosterone levels correlated with 2D:4D in adult females. We found that the maternal pre-pregnancy level of testosterone was not associated with offspring 2D:4D in either the left or the right paw. Instead, maternal pre-pregnancy corticosterone level was positively correlated with offspring 2D:4D in the right paw, but unrelated to 2D:4D in the left paw. In addition, the 2D:4D of adult females was not associated with either their circulating testosterone or corticosterone levels. Our results suggest that in field voles maternally administered testosterone is not a major determinant of offspring 2D:4D, whereas maternal stress appears to account for some of the variation in the 2D:4D of their offspring.
NASA Astrophysics Data System (ADS)
Lupyan, Dmitry; Abramov, Yuriy A.; Sherman, Woody
2012-11-01
The Cambridge Structural Database (CSD) offers an excellent data source to study small molecule conformations and molecular interactions. We have analyzed 130 small molecules from the CSD containing an intramolecular sulfur-oxygen distance less than the sum of their van der Waals (vdW) radii. Close S···O distances are observed in several important medicinal chemistry motifs (e.g. a carbonyl oxygen connected by a carbon or nitrogen linker to a sulfur) and are not treated well with existing parameters in the MMFFs or OPLS_2005 force fields, resulting in suboptimal geometries and energetics. In this work, we develop modified parameters for the OPLS_2005 force field to better treat this specific interaction in order to generate conformations close to those found in the CSD structures. We use a combination of refitting a force field torsional parameter, adding a specific atom pair vdW term, and attenuating the electrostatic interactions to obtain an improvement in the accuracy of geometry minimizations and conformational searches for these molecules. Specifically, in a conformational search 58 % of the cases produced a conformation less than 0.25 Å from the CSD crystal conformation with the modified OPLS force field parameters developed in this work. In contrast, 25 and 37 % produced a conformation less than 0.25 Å with the MMFFs and OPLS_2005 force fields, respectively. As an application of the new parameters, we generated conformations for the tyrosine kinase inhibitor axitinib (trade name Inlyta) that could be correctly repacked into three observed polymorphic structures, which was not possible with conformations generated using MMFFs or OPLS_2005. The improved parameters can be mapped directly onto physical characteristics of the systems that are treated inadequately with the molecular mechanics force fields used in this study and potentially other force fields as well.
Lupyan, Dmitry; Abramov, Yuriy A; Sherman, Woody
2012-11-01
The Cambridge Structural Database (CSD) offers an excellent data source to study small molecule conformations and molecular interactions. We have analyzed 130 small molecules from the CSD containing an intramolecular sulfur-oxygen distance less than the sum of their van der Waals (vdW) radii. Close S···O distances are observed in several important medicinal chemistry motifs (e.g. a carbonyl oxygen connected by a carbon or nitrogen linker to a sulfur) and are not treated well with existing parameters in the MMFFs or OPLS_2005 force fields, resulting in suboptimal geometries and energetics. In this work, we develop modified parameters for the OPLS_2005 force field to better treat this specific interaction in order to generate conformations close to those found in the CSD structures. We use a combination of refitting a force field torsional parameter, adding a specific atom pair vdW term, and attenuating the electrostatic interactions to obtain an improvement in the accuracy of geometry minimizations and conformational searches for these molecules. Specifically, in a conformational search 58 % of the cases produced a conformation less than 0.25 Å from the CSD crystal conformation with the modified OPLS force field parameters developed in this work. In contrast, 25 and 37 % produced a conformation less than 0.25 Å with the MMFFs and OPLS_2005 force fields, respectively. As an application of the new parameters, we generated conformations for the tyrosine kinase inhibitor axitinib (trade name Inlyta) that could be correctly repacked into three observed polymorphic structures, which was not possible with conformations generated using MMFFs or OPLS_2005. The improved parameters can be mapped directly onto physical characteristics of the systems that are treated inadequately with the molecular mechanics force fields used in this study and potentially other force fields as well.
Reconnection and small-scale fields in 2D-3V hybrid-kinetic driven turbulence simulations
NASA Astrophysics Data System (ADS)
Cerri, S. S.; Califano, F.
2017-02-01
The understanding of the fundamental properties of turbulence in collisionless plasmas, such as the solar wind, is a frontier problem in plasma physics. In particular, the occurrence of magnetic reconnection in turbulent plasmas and its interplay with a fully-developed turbulent state is still a matter of great debate. Here we investigate the properties of small-scale electromagnetic fluctuations and the role of fast magnetic reconnection in the development of a quasi-steady turbulent state by means of 2D-3V high-resolution Vlasov–Maxwell simulations. At the largest scales turbulence is fed by external random forcing. We show that large-scale turbulent motions establish a -5/3 spectrum at {k}\\perp {d}i< 1 and, at the same time, feed the formation of current sheets where magnetic reconnection occurs. As a result coherent magnetic structures are generated which, together with the rise of the associated small-scale non-ideal electric field, mediate the transition between the inertial and the subproton-scale spectrum. A mechanism that boosts the magnetic reconnection process is identified, making the generation of coherent structures rapid enough to be competitive with wave mode interactions and leading to the formation of a fully-developed turbulent spectrum across the so-called ion break.
NASA Astrophysics Data System (ADS)
Lucca Fabris, Andrea; Young, Christopher; MacDonald-Tenenbaum, Natalia; Hargus, William, Jr.; Cappelli, Mark
2016-10-01
Hall thrusters are a mature form of electric propulsion for spacecraft. One commonly observed low frequency (10-50 kHz) discharge current oscillation in these E × B devices is the breathing mode, linked to a propagating ionization front traversing the channel. The complex time histories of ion production and acceleration in the discharge channel and near-field plume lead to interesting dynamics and interactions in the central plasma jet and downstream plume regions. A time-resolved laser-induced fluorescence (LIF) diagnostic non-intrusively measures 2-D ion velocity and relative ion density throughout the plume of a commercial BHT-600 Hall thruster manufactured by Busek Co. Low velocity classes of ions observed in addition to the main accelerated population are linked to propellant ionization outside of the device. Effects of breathing mode dynamics are shown to persist far downstream where modulations in ion velocity and LIF intensity are correlated with discharge current oscillations. This work is sponsored by the U.S. Air Force Office of Scientific Research with Dr. M. Birkan as program manager. C.Y. acknowledges support from the DOE NSSA Stewardship Science Graduate Fellowship under contract DE-FC52-08NA28752.
Quasi-Exactly Quantal Problems:. One-Dimensional Analogue of Rational Conformal Field Theories
NASA Astrophysics Data System (ADS)
Morozov, A. Yu.; Perelomov, A. M.; Rosly, A. A.; Shifman, M. A.; Turbiner, A. V.
The class of quasi-exactly-solvable problems in ordinary quantum mechanics discovered recently shows remarkable parallels with rational two-dimensional conformal field theories. This fact suggests that investigation of the quasi-exactly-solvable models may shed light on rational conformal field theories. We discuss a relation between these two theoretical schemes and propose a mathematical formulation for the procedure of constructing quasi-exactly solvable systems. This discussion leads us to a kind of generalization of the Sugawara construction.
Kim, Choong-Ki; Jeong, Eun Gyo; Kim, Eungtaek; Song, Jeong-Gyu; Kim, Youngjun; Woo, Whang Je; Lee, Myung Keun; Bae, Hagyoul; Jeon, Seong-Bae; Kim, Hyungjun; Choi, Kyung Cheol; Choi, Yang-Kyu
2017-02-03
Field-effect transistors (FETs) composed of 2D materials (2DMs) such as transition-metal dichalcogenide (TMD) materials show unstable electrical characteristics in ambient air due to the high sensitivity of 2DMs to water adsorbates. In this work, in order to demonstrate the long-term retention of electrical characteristics of a TMD FET, a multidyad encapsulation method was applied to a MoS2 FET and thereby its durability was warranted for one month. It was well known that the multidyad encapsulation method was effective to mitigate high sensitivity to ambient air in light-emitting diodes (LEDs) composed of organic materials. However, there was no attempt to check the feasibility of such a multidyad encapsulation method for 2DM FETs. It is timely to investigate the water vapor transmission ratio (WVTR) required for long-term stability of 2DM FETs. The 2DM FETs were fabricated with MoS2 flakes by both an exfoliation method, that is desirable to attain high quality film, and a chemical vapor deposition (CVD) method, that is applicable to fabrication for a large-sized substrate. In order to eliminate other unwanted variables, the MoS2 FETs composed of exfoliated flakes were primarily investigated to assure the effectiveness of the encapsulation method. The encapsulation method uses multiple dyads comprised of a polymer layer by spin coating and an Al2O3 layer deposited by atomic layer deposition (ALD). The proposed method shows wafer-scale uniformity, high transparency, and protective barrier properties against adsorbates (WVTR of 8 × 10(-6) g m(-2) day(-1)) over one month.
NASA Astrophysics Data System (ADS)
Kim, Choong-Ki; Gyo Jeong, Eun; Kim, Eungtaek; Song, Jeong-Gyu; Kim, Youngjun; Woo, Whang Je; Lee, Myung Keun; Bae, Hagyoul; Jeon, Seong-Bae; Kim, Hyungjun; Choi, Kyung Cheol; Choi, Yang-Kyu
2017-02-01
Field-effect transistors (FETs) composed of 2D materials (2DMs) such as transition-metal dichalcogenide (TMD) materials show unstable electrical characteristics in ambient air due to the high sensitivity of 2DMs to water adsorbates. In this work, in order to demonstrate the long-term retention of electrical characteristics of a TMD FET, a multidyad encapsulation method was applied to a MoS2 FET and thereby its durability was warranted for one month. It was well known that the multidyad encapsulation method was effective to mitigate high sensitivity to ambient air in light-emitting diodes (LEDs) composed of organic materials. However, there was no attempt to check the feasibility of such a multidyad encapsulation method for 2DM FETs. It is timely to investigate the water vapor transmission ratio (WVTR) required for long-term stability of 2DM FETs. The 2DM FETs were fabricated with MoS2 flakes by both an exfoliation method, that is desirable to attain high quality film, and a chemical vapor deposition (CVD) method, that is applicable to fabrication for a large-sized substrate. In order to eliminate other unwanted variables, the MoS2 FETs composed of exfoliated flakes were primarily investigated to assure the effectiveness of the encapsulation method. The encapsulation method uses multiple dyads comprised of a polymer layer by spin coating and an Al2O3 layer deposited by atomic layer deposition (ALD). The proposed method shows wafer-scale uniformity, high transparency, and protective barrier properties against adsorbates (WVTR of 8 × 10-6 g m-2 day-1) over one month.
Hahn, Herwig Reuters, Benjamin; Geipel, Sascha; Schauerte, Meike; Kalisch, Holger; Vescan, Andrei; Benkhelifa, Fouad; Ambacher, Oliver
2015-03-14
GaN-based heterostructure FETs (HFETs) featuring a 2-D electron gas (2DEG) can offer very attractive device performance for power-switching applications. This performance can be assessed by evaluation of the dynamic on-resistance R{sub on,dyn} vs. the breakdown voltage V{sub bd}. In literature, it has been shown that with a high V{sub bd}, R{sub on,dyn} is deteriorated. The impairment of R{sub on,dyn} is mainly driven by electron injection into surface, barrier, and buffer traps. Electron injection itself depends on the electric field which typically peaks at the gate edge towards the drain. A concept suitable to circumvent this issue is the charge-balancing concept which employs a 2-D hole gas (2DHG) on top of the 2DEG allowing for the electric field peak to be suppressed. Furthermore, the 2DEG concentration in the active channel cannot decrease by a change of the surface potential. Hence, beside an improvement in breakdown voltage, also an improvement in dynamic behaviour can be expected. Whereas the first aspect has already been demonstrated, the second one has not been under investigation so far. Hence, in this report, the effect of charge-balancing is discussed and its impact on the dynamic characteristics of HFETs is evaluated. It will be shown that with appropriate device design, the dynamic behaviour of HFETs can be improved by inserting an additional 2DHG.
Retention of nativelike conformation by proteins embedded in high external electric fields
NASA Astrophysics Data System (ADS)
Pompa, P. P.; Bramanti, A.; Maruccio, G.; Cingolani, R.; De Rienzo, F.; Corni, S.; Di Felice, R.; Rinaldi, R.
2005-05-01
In this Communication, we show that proteins embedded in high external electric fields are capable of retaining a nativelike fold pattern. We have tested the metalloprotein azurin, immobilized onto SiO2 substrates in air with proper electrode configuration, by applying static fields up to 106-107V/m. The effects on the conformational properties of protein molecules have been determined by means of intrinsic fluorescence measurements. Experimental results indicate that no significant field-induced conformational alteration occurs. Such results are also discussed and supported by theoretical predictions of the inner protein fields.
Talarovicová, Alzbeta; Krsková, Lucia; Blazeková, Jana
2009-01-01
In humans, the relationship between the prenatal testosterone exposure and the ratio of the second and the fourth digits (2D:4D) has been extensively studied. Surprisingly, data on this relationship have thus far been lacking in experimental animals such as rats. We studied the effect of maternal testosterone enhancement during pregnancy on the digit ratio and open field activity of adult progeny in Wistar rats. Elevated levels of maternal testosterone resulted in lower 2D:4D ratios and an elongated 4D on the left and right forepaws in both males and females. We found no sex difference in 2D:4D in control animals. In the open field test, control females were more active than control males and testosterone females, while the activity of testosterone females did not differ from that of control males. We found a positive correlation between motor activity and the right forepaw 2D:4D ratio of control males and females. Prenatal exposure to testosterone resulted in the disappearance of this correlation in both males and females. Our results show that elevated levels of testosterone during the prenatal period can influence forepaw 4D length, 2D:4D ratio, and open field motor activity of rats, and that these variables are positively correlated. Thus, this approach represents a noninvasive and robust method for evaluating the effects of prenatal testosterone enhancement on anatomical and physiological parameters.
NASA Astrophysics Data System (ADS)
Humair, F.; Matasci, B.; Carrea, D.; Pedrazzini, A.; Loye, A.; Pedrozzi, G.; Nicolet, P.; Jaboyedoff, M.
2012-04-01
account the results of the experimental testing are performed and compared with the a-priori simulations. 3D simulations were performed using a software that takes into account the effect of the forest cover in the blocky trajectory (RockyFor 3D) and an other that neglects this aspect (Rotomap; geo&soft international). 2D simulation (RocFall; Rocscience) profiles were located in the blocks paths deduced from 3D simulations. The preliminary results show that: (1) high speed movies are promising and allow us to track the blocks using video software, (2) the a-priori simulations tend to overestimate the runout distance which is certainly due to an underestimation of the obstacles as well as the breaking of the failing rocks which is not taken into account in the models, (3) the trajectories deduced from both a-priori simulation and real size experiment highlights the major influence of the channelized slope morphology on rock paths as it tends to follow the flow direction. This indicates that the 2D simulation have to be performed along the line of flow direction.
NASA Astrophysics Data System (ADS)
Robinson, Errol W.; Sellon, Rachel E.; Williams, Evan R.
2007-01-01
Protonated poly(ethylene glycol), produced by electrospray ionization (ESI), with molecular weights ranging from 0.3 to 5 kDa and charge states from 1+ to 7+ were characterized using high-field asymmetric waveform ion mobility spectrometry (FAIMS). Results for all but some of the 3+ and 4+ charge states are consistent with a single gas-phase conformer or family of unresolved conformers for each of these charge states. The FAIMS compensation voltage scans resulted in peaks that could be accurately fit with a single Gaussian for each peak. The peak widths increase linearly with compensation voltage for maximum ion transmission but do not depend on m/z or molecular weight. Fitting parameters obtained from the poly(ethylene glycol) data were used to analyze conformations of oxidized and reduced lysozyme formed from different solutions. For oxidized lysozyme formed from a buffered aqueous solution, a single conformer (or group of unresolved conformers) was observed for the 7+ and 8+ charge states. Two conformers were observed for the 9+ and 10+ charge states formed from more denaturing solutions. Data for the fully reduced form indicate the existence of up to three different conformers for each charge state produced directly by ESI and a general progression from a more extended to a more folded structure with decreasing charge state. These results are consistent with those obtained previously by proton-transfer reactivity and drift tube ion mobility experiments, although more conformers were identified for the fully reduced form of lysozyme using FAIMS.
Cavagnetto, F; Calabrese, M; Houssami, N
2013-01-01
Objective: To compare breast density estimated from two-dimensional full-field digital mammography (2D FFDM) and from digital breast tomosynthesis (DBT) according to different Breast Imaging–Reporting and Data System (BI-RADS) categories, using automated software. Methods: Institutional review board approval and written informed patient consent were obtained. DBT and 2D FFDM were performed in the same patients to allow within-patient comparison. A total of 160 consecutive patients (mean age: 50±14 years; mean body mass index: 22±3) were included to create paired data sets of 40 patients for each BI-RADS category. Automatic software (MedDensity©, developed by Giulio Tagliafico) was used to compare the percentage breast density between DBT and 2D FFDM. The estimated breast percentage density obtained using DBT and 2D FFDM was examined for correlation with the radiologists' visual BI-RADS density classification. Results: The 2D FFDM differed from DBT by 16.0% in BI-RADS Category 1, by 11.9% in Category 2, by 3.5% in Category 3 and by 18.1% in Category 4. These differences were highly significant (p<0.0001). There was a good correlation between the BI-RADS categories and the density evaluated using 2D FFDM and DBT (r=0.56, p<0.01 and r=0.48, p<0.01, respectively). Conclusion: Using DBT, breast density values were lower than those obtained using 2D FFDM, with a non-linear relationship across the BI-RADS categories. These data are relevant for clinical practice and research studies using density in determining the risk. Advances in knowledge: On DBT, breast density values were lower than with 2D FFDM, with a non-linear relationship across the classical BI-RADS categories. PMID:24029631
NASA Technical Reports Server (NTRS)
Juday, Richard D.; Loshin, David S.
1989-01-01
Image coordinate transformations are investigated for possible use in a low vision aid for human patients. These patients typically have field defects with localized retinal dysfunction predominately central (age related maculopathy) or peripheral (retinitis pigmentosa). Previously simple eccentricity-only remappings which do not maintain conformality were shown. Initial attempts on developing images which hold quasi-conformality after remapping are presented. Although the quasi-conformal images may have less local distortion, there are discontinuities in the image which may counterindicate this type of transformation for the low vision application.
NASA Astrophysics Data System (ADS)
Zhai, Cuili; Zhang, Ting
2016-09-01
In this article, we consider the global existence and uniqueness of the solution to the 2D incompressible non-resistive MHD system with non-equilibrium background magnetic field. Our result implies that a strong enough non-equilibrium background magnetic field will guarantee the stability of the nonlinear MHD system. Beside the classical energy method, the interpolation inequalities and the algebraic structure of the equations coming from the incompressibility of the fluid are crucial in our arguments.
Domain walls, fusion rules, and conformal field theory in the quantum Hall regime.
Ardonne, Eddy
2009-05-08
We provide a simple way to obtain the fusion rules associated with elementary quasiholes over quantum Hall wave functions, in terms of domain walls. The knowledge of the fusion rules is helpful in the identification of the underlying conformal field theory describing the wave functions. We show that, for a certain two-parameter family (k,r) of wave functions, the fusion rules are those of su(r)k. In addition, we give an explicit conformal field theory construction of these states, based on the Mk(k+1,k+r) "minimal" theories. For r=2, these states reduce to the Read-Rezayi states. The "Gaffnian" wave function is the prototypical example for r>2, in which case the conformal field theory is nonunitary.
Modified Amber Force Field Correctly Models the Conformational Preference for Tandem GA pairs in RNA
2015-01-01
Molecular mechanics with all-atom models was used to understand the conformational preference of tandem guanine-adenine (GA) noncanonical pairs in RNA. These tandem GA pairs play important roles in determining stability, flexibility, and structural dynamics of RNA tertiary structures. Previous solution structures showed that these tandem GA pairs adopt either imino (cis Watson–Crick/Watson–Crick A-G) or sheared (trans Hoogsteen/sugar edge A-G) conformations depending on the sequence and orientation of the adjacent closing base pairs. The solution structures (GCGGACGC)2 [Biochemistry, 1996, 35, 9677–9689] and (GCGGAUGC)2 [Biochemistry, 2007, 46, 1511–1522] demonstrate imino and sheared conformations for the two central GA pairs, respectively. These systems were studied using molecular dynamics and free energy change calculations for conformational changes, using umbrella sampling. For the structures to maintain their native conformations during molecular dynamics simulations, a modification to the standard Amber ff10 force field was required, which allowed the amino group of guanine to leave the plane of the base [J. Chem. Theory Comput., 2009, 5, 2088–2100] and form out-of-plane hydrogen bonds with a cross-strand cytosine or uracil. The requirement for this modification suggests the importance of out-of-plane hydrogen bonds in stabilizing the native structures. Free energy change calculations for each sequence demonstrated the correct conformational preference when the force field modification was used, but the extent of the preference is underestimated. PMID:24803859
Das, Saptarshi
2016-01-01
This article proposes a disruptive device concept which meets both low power and high performance criterion for post-CMOS computing and at the same time enables aggressive channel length scaling. This device, hereafter refer to as two-dimensional electrostrictive field effect transistor or 2D-EFET, allows sub-60 mV/decade subthreshold swing and considerably higher ON current compared to any state of the art FETs. Additionally, by the virtue of its ultra-thin body nature and electrostatic integrity, the 2D-EFET enjoys scaling beyond 10 nm technology node. The 2D-EFET works on the principle of voltage induced strain transduction. It uses an electrostrictive material as gate oxide which expands in response to an applied gate bias and thereby transduces an out-of-plane stress on the 2D channel material. This stress reduces the inter-layer distance between the consecutive layers of the semiconducting 2D material and dynamically reduces its bandgap to zero i.e. converts it into a semi-metal. Thus the device operates with a large bandgap in the OFF state and a small or zero bandgap in the ON state. As a consequence of this transduction mechanism, internal voltage amplification takes place which results in sub-60 mV/decade subthreshold swing (SS). PMID:27721489
NASA Astrophysics Data System (ADS)
Das, Saptarshi
2016-10-01
This article proposes a disruptive device concept which meets both low power and high performance criterion for post-CMOS computing and at the same time enables aggressive channel length scaling. This device, hereafter refer to as two-dimensional electrostrictive field effect transistor or 2D-EFET, allows sub-60 mV/decade subthreshold swing and considerably higher ON current compared to any state of the art FETs. Additionally, by the virtue of its ultra-thin body nature and electrostatic integrity, the 2D-EFET enjoys scaling beyond 10 nm technology node. The 2D-EFET works on the principle of voltage induced strain transduction. It uses an electrostrictive material as gate oxide which expands in response to an applied gate bias and thereby transduces an out-of-plane stress on the 2D channel material. This stress reduces the inter-layer distance between the consecutive layers of the semiconducting 2D material and dynamically reduces its bandgap to zero i.e. converts it into a semi-metal. Thus the device operates with a large bandgap in the OFF state and a small or zero bandgap in the ON state. As a consequence of this transduction mechanism, internal voltage amplification takes place which results in sub-60 mV/decade subthreshold swing (SS).
Magnetic properties of Y0.9Gd0.1Fe2D4.2 compound under continuous magnetic field up to 310 kOe
NASA Astrophysics Data System (ADS)
Paul-Boncour, V.; Guillot, M.; Mazet, T.
2012-04-01
In this work are presented results on the structural, magnetic, and magnetocaloric properties of the Y0.9Gd0.1Fe2D4.2 compound in which TM0 is shifted from 84 K to 110 K because of Gd influence. Magnetization measurements have been performed with a magnetic field up to 310 kOe in the 4.2-300 K temperature range with special attention paid near TM0. The spontaneous magnetization at 4.2 K (3.2 μB/mol) is smaller than for YFe2D4.2 (3.7 μB/mol), showing the contribution of Gd moments. Above 110 K, metamagnetic field-induced transitions are observed: the transition field HTR increases linearly with T. These transitions exist up to 170 K. The influence of both cell volume change and Gd magnetic contribution are finally discussed in comparison with other deuterides.
NASA Astrophysics Data System (ADS)
Slesareva, E. Yu; Elistratov, S. L.; Ovchinnikov, V. V.
2016-10-01
The method for experimental determination of energy efficiency in the multichannel heat exchanger was tested. The visualization of a temperatures field has been performed to determine the thermal structure of gas flows with the use of fast-response fine- meshed wire. Thermograms of the temperature fields of the multi-channels assembly at the outlet were registered by thermal imaging camera. Results show that the 2D method provides a sufficient time resolution for the temperature field for the steady-state gas flow regime, heat generation, and nonsteady regime. The 2D method allows us to determine the gas stream parameters at the channel outlet in real time, which are necessary for determining the efficiency of the heat exchanger. Qualitative and quantitative characters of temperature changes in the thermograms are consistent with modern physical understanding of the gas flow in channels.
Universality of sparse d > 2 conformal field theory at large N
NASA Astrophysics Data System (ADS)
Belin, Alexandre; de Boer, Jan; Kruthoff, Jorrit; Michel, Ben; Shaghoulian, Edgar; Shyani, Milind
2017-03-01
We derive necessary and sufficient conditions for large N conformal field theories to have a universal free energy and an extended range of validity of the higher-dimensional Cardy formula. These constraints are much tighter than in two dimensions and must be satisfied by any conformal field theory dual to Einstein gravity. We construct and analyze symmetric product orbifold theories on T^d and show that they only realize the necessary phase structure and extended range of validity if the seed theory is assumed to have a universal vacuum energy.
Rational Conformal Correlation Functions of Gauge-Invariant Local Fields in Four Dimensions
Nikolov, N.M.; Stanev, Ya.S.; Todorov, I.T.
2005-11-01
Global conformal invariance in Minkowski space and the Wightman axioms imply strong locality (Huygens principle) and rationality of correlation functions, thus providing an extension of the concept of a vertex algebra to higher (even) dimensions D. We (p)review current work on a model of a Hermitian scalar field L of scale dimension 4 (D = 4) which can be interpreted as the Lagrangian of a gauge field theory that generates the algebra of gauge-invariant local observables in a conformally invariant renormalization group fixed point.
On twistors and conformal field theories from six dimensions
Saemann, Christian; Wolf, Martin
2013-01-15
We discuss chiral zero-rest-mass field equations on six-dimensional space-time from a twistorial point of view. Specifically, we present a detailed cohomological analysis, develop both Penrose and Penrose-Ward transforms, and analyse the corresponding contour integral formulae. We also give twistor space action principles. We then dimensionally reduce the twistor space of six-dimensional space-time to obtain twistor formulations of various theories in lower dimensions. Besides well-known twistor spaces, we also find a novel twistor space amongst these reductions, which turns out to be suitable for a twistorial description of self-dual strings. For these reduced twistor spaces, we explain the Penrose and Penrose-Ward transforms as well as contour integral formulae.
Relative entropy of excited states in two dimensional conformal field theories
NASA Astrophysics Data System (ADS)
Sárosi, Gábor; Ugajin, Tomonori
2016-07-01
We study the relative entropy and the trace square distance, both of which measure the distance between reduced density matrices of two excited states in two dimensional conformal field theories. We find a general formula for the relative entropy between two primary states with the same conformal dimension in the limit of a single small interval and find that in this case the relative entropy is proportional to the trace square distance. We check our general formulae by calculating the relative entropy between two generalized free fields and the trace square distance between the spin and disorder operators of the critical Ising model. We also give the leading term of the relative entropy in the small interval expansion when the two operators have different conformal dimensions. This turns out to be universal when the CFT has no primaires lighter than the stress tensor. The result reproduces the previously known special cases.
Riemann correlator in de Sitter including loop corrections from conformal fields
Fröb, Markus B.; Verdaguer, Enric
2014-07-01
The Riemann correlator with appropriately raised indices characterizes in a gauge-invariant way the quantum metric fluctuations around de Sitter spacetime including loop corrections from matter fields. Specializing to conformal fields and employing a method that selects the de Sitter-invariant vacuum in the Poincaré patch, we obtain the exact result for the Riemann correlator through order H{sup 4}/m{sub p}{sup 4}. The result is expressed in a manifestly de Sitter-invariant form in terms of maximally symmetric bitensors. Its behavior for both short and long distances (sub- and superhorizon scales) is analyzed in detail. Furthermore, by carefully taking the flat-space limit, the explicit result for the Riemann correlator for metric fluctuations around Minkowki spacetime is also obtained. Although the main focus is on free scalar fields (our calculation corresponds then to one-loop order in the matter fields), the result for general conformal field theories is also derived.
Neutron Star Structure in the Presence of Conformally Coupled Scalar Fields
NASA Technical Reports Server (NTRS)
Sultana, Joseph; Bose, Benjamin; Kazanas, Demosthenes
2014-01-01
Neutron star models are studied in the context of scalar-tensor theories of gravity in the presence of a conformally coupled scalar field, using two different numerical equations of state (EoS) representing different degrees of stiffness. In both cases we obtain a complete solution by matching the interior numerical solution of the coupled Einstein-scalar field hydrostatic equations, with an exact metric on the surface of the star. These are then used to find the effect of the scalar field and its coupling to geometry, on the neutron star structure, particularly the maximum neutron star mass and radius. We show that in the presence of a conformally coupled scalar field, neutron stars are less dense and have smaller masses and radii than their counterparts in the minimally coupled case, and the effect increases with the magnitude of the scalar field at the center of the star.
Riemann correlator in de Sitter including loop corrections from conformal fields
NASA Astrophysics Data System (ADS)
Fröb, Markus B.; Roura, Albert; Verdaguer, Enric
2014-07-01
The Riemann correlator with appropriately raised indices characterizes in a gauge-invariant way the quantum metric fluctuations around de Sitter spacetime including loop corrections from matter fields. Specializing to conformal fields and employing a method that selects the de Sitter-invariant vacuum in the Poincaré patch, we obtain the exact result for the Riemann correlator through order H4/mp4. The result is expressed in a manifestly de Sitter-invariant form in terms of maximally symmetric bitensors. Its behavior for both short and long distances (sub- and superhorizon scales) is analyzed in detail. Furthermore, by carefully taking the flat-space limit, the explicit result for the Riemann correlator for metric fluctuations around Minkowki spacetime is also obtained. Although the main focus is on free scalar fields (our calculation corresponds then to one-loop order in the matter fields), the result for general conformal field theories is also derived.
Calibration of a 1D/1D urban flood model using 1D/2D model results in the absence of field data.
Leandro, J; Djordjević, S; Chen, A S; Savić, D A; Stanić, M
2011-01-01
Recently increased flood events have been prompting researchers to improve existing coupled flood-models such as one-dimensional (1D)/1D and 1D/two-dimensional (2D) models. While 1D/1D models simulate sewer and surface networks using a one-dimensional approach, 1D/2D models represent the surface network by a two-dimensional surface grid. However their application raises two issues to urban flood modellers: (1) stormwater systems planning/emergency or risk analysis demands for fast models, and the 1D/2D computational time is prohibitive, (2) and the recognized lack of field data (e.g. Hunter et al. (2008)) causes difficulties for the calibration/validation of 1D/1D models. In this paper we propose to overcome these issues by calibrating a 1D/1D model with the results of a 1D/2D model. The flood-inundation results show that: (1) 1D/2D results can be used to calibrate faster 1D/1D models, (2) the 1D/1D model is able to map the 1D/2D flood maximum extent well, and the flooding limits satisfactorily in each time-step, (3) the 1D/1D model major differences are the instantaneous flow propagation and overestimation of the flood-depths within surface-ponds, (4) the agreement in the volume surcharged by both models is a necessary condition for the 1D surface-network validation and (5) the agreement of the manholes discharge shapes measures the fitness of the calibrated 1D surface-network.
Conformal Locoregional Breast Irradiation with an Oblique Parasternal Photon Field Technique
Erven, Katrien; Petillion, Saskia; Weltens, Caroline; Van den Heuvel, Frank; Defraene, Gilles; Van Limbergen, Erik; Van den Bogaert, Walter
2011-04-01
We evaluated an isocentric technique for conformal irradiation of the breast, internal mammary, and medial supra-clavicular lymph nodes (IM-MS LN) using the oblique parasternal photon (OPP) technique. For 20 breast cancer patients, the OPP technique was compared with a conventional mixed-beam technique (2D) and a conformal partly wide tangential (PWT) technique, using dose-volume histogram analysis and normal tissue complication probabilities (NTCPs). The 3D techniques resulted in a better target coverage and homogeneity than did the 2D technique. The homogeneity index for the IM-MS PTV increased from 0.57 for 2D to 0.90 for PWT and 0.91 for OPP (both p < 0.001). The OPP technique was able to reduce the volume of heart receiving more than 30 Gy (V{sub 30}), the cardiac NTCP, and the volume of contralateral breast receiving 5 Gy (V{sub 5}) compared with the PWT plans (all p < 0.05). There is no significant difference in mean lung dose or lung NTCP between both 3D techniques. Compared with the PWT technique, the volume of lung receiving more than 20 Gy (V{sub 20}) was increased with the OPP technique, whereas the volume of lung receiving more than 40 Gy (V{sub 40}) was decreased (both p < 0.05). Compared with the PWT technique, the OPP technique can reduce doses to the contralateral breast and heart at the expense of an increased lung V{sub 20}.
SL(2, z) Action on Three-Dimensional Conformal Field Theories with Abelian Symmetry
NASA Astrophysics Data System (ADS)
Witten, Edward
On the space of three-dimensional conformal field theories with U(1) symmetry and a chosen coupling to a background gauge field, there is a natural action of the group SL(2, Z). The generator S of SL(2, Z) acts by letting the background gauge field become dynamical, an operation considered recently by Kapustin and Strassler in explaining three-dimensional mirror symmetry. The other generator T acts by shifting the Chern-Simons coupling of the background field. This SL(2, Z) action in three dimensions is related by the AdS/CFT correspondence to SL(2, Z) duality of low energy U(1) gauge fields in four dimensions.
Anne, Agnès; Bahri, Mohamed Ali; Chovin, Arnaud; Demaille, Christophe; Taofifenua, Cécilia
2014-03-14
The present paper aims at illustrating how end-attachment of water-soluble flexible chains bearing a terminal functional group onto graphene-like surfaces has to be carefully tuned to ensure the proper positioning of the functional moiety with respect to the anchoring surface. The model experimental system considered here consists of a layer of poly(ethylene glycol) (PEG) chains, bearing an adsorbing pyrene foot and a ferrocene (Fc) redox functional head, self-assembled onto highly oriented pyrolytic graphite (HOPG). Cyclic voltammetry is used to accurately measure the chain coverage and gain insights into the microenvironment experienced by the Fc heads. Molecule-touching atomic force electrochemical microscopy (Mt/AFM-SECM) is used to simultaneously probe the chain conformation and the position of the Fc heads within the layer, and also to map the 2D-distribution of the chains over the surface. This multiscale electrochemical approach allows us to show that whereas Fc-PEG-pyrene readily self-assembles to form extremely homogeneous layers, the strongly hydrophobic nature of graphite planes results in a complex coverage-dependent structure of the PEG layer due to the interaction of the ferrocene label with the HOPG surface. It is shown that, even though pyrene is known to adsorb particularly strongly onto HOPG, the more weakly adsorbing terminal ferrocene can also act as the chain anchoring moiety especially at low coverage. However we show that beyond a critical coverage value the Fc-PEG-pyrene chains adopt an ideal "foot-on" end-attached conformation allowing the Fc head to explore a volume away from the surface solely limited by the PEG chain elasticity.
Causal Transformation of GÖDEL-TYPE Spacetimes in Conformal Field Theory
NASA Astrophysics Data System (ADS)
Gusin, Pawel
The Gödel-type metrics are considered as backgrounds of the sigma-models. In the conformal field theory such backgrounds are deformed by the exactly marginal operators. We examine, how the closed timelike curves (CTCs) transform under such deformations.
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.
Kriz, Igor; Loebl, Martin; Somberg, Petr
2013-05-15
We study various mathematical aspects of discrete models on graphs, specifically the Dimer and the Ising models. We focus on proving gluing formulas for individual summands of the partition function. We also obtain partial results regarding conjectured limits realized by fermions in rational conformal field theories.
NASA Astrophysics Data System (ADS)
Zakharchenko, S.; Baturin, A.
2015-09-01
Algorithm of solving a direct problem of acousto-optic interaction between laser emission and acoustic signal consisting of a set of equidistant frequency components is proposed. An infinite system of coupled wave differential equations is reduced to eigenvalue problem. The contribution of the higher rediffraction orders is analyzed separately. Inverse problem of finding an optimal set of equidistant frequency components of a driving acoustic signal to form the objective diffraction pattern is also considered and a few optimization approaches are analyzed. A naïve heuristic method of splitting 2D pattern into subframes, each suitable for simultaneous projection by two acousto-optical deflectors driven by multifrequency composite signal, is developed.
Conformally related massless fields in dS, AdS and Minkowski spaces
Huguet, E.; Queva, J.; Renaud, J.
2006-04-15
In this paper we write down the equation for a scalar conformally coupled field simultaneously for de Sitter (dS), anti-de Sitter (AdS), and Minkowski spacetimes in d dimensions. The curvature dependence appears in a very simple way through a conformal factor. As a consequence the process of curvature free limit, including wave functions limit and two-points functions, turns out to be a straightforward issue. We determine a set of modes, that we call de Sitter plane waves, which become ordinary plane waves when the curvature vanishes.
Diagnosing Chaos Using Four-Point Functions in Two-Dimensional Conformal Field Theory.
Roberts, Daniel A; Stanford, Douglas
2015-09-25
We study chaotic dynamics in two-dimensional conformal field theory through out-of-time-order thermal correlators of the form ⟨W(t)VW(t)V⟩. We reproduce holographic calculations similar to those of Shenker and Stanford, by studying the large c Virasoro identity conformal block. The contribution of this block to the above correlation function begins to decrease exponentially after a delay of ~t_{*}-(β/2π)logβ^{2}E_{w}E_{v}, where t_{*} is the fast scrambling time (β/2π)logc and E_{w},E_{v} are the energy scales of the W,V operators.
Diagnosing Chaos Using Four-Point Functions in Two-Dimensional Conformal Field Theory
NASA Astrophysics Data System (ADS)
Roberts, Daniel A.; Stanford, Douglas
2015-09-01
We study chaotic dynamics in two-dimensional conformal field theory through out-of-time-order thermal correlators of the form ⟨W (t )V W (t )V ⟩ . We reproduce holographic calculations similar to those of Shenker and Stanford, by studying the large c Virasoro identity conformal block. The contribution of this block to the above correlation function begins to decrease exponentially after a delay of ˜t*-(β /2 π )log β2EwEv , where t* is the fast scrambling time (β /2 π )log c and Ew,Ev are the energy scales of the W ,V operators.
Conformal Nets II: Conformal Blocks
NASA Astrophysics Data System (ADS)
Bartels, Arthur; Douglas, Christopher L.; Henriques, André
2017-03-01
Conformal nets provide a mathematical formalism for conformal field theory. Associated to a conformal net with finite index, we give a construction of the `bundle of conformal blocks', a representation of the mapping class groupoid of closed topological surfaces into the category of finite-dimensional projective Hilbert spaces. We also construct infinite-dimensional spaces of conformal blocks for topological surfaces with smooth boundary. We prove that the conformal blocks satisfy a factorization formula for gluing surfaces along circles, and an analogous formula for gluing surfaces along intervals. We use this interval factorization property to give a new proof of the modularity of the category of representations of a conformal net.
NASA Astrophysics Data System (ADS)
Antunes, V.; Novello, M.
2017-04-01
In the present work we revisit a model consisting of a scalar field with a quartic self-interaction potential non-minimally (conformally) coupled to gravity (Novello in Phys Lett 90A:347 1980). When the scalar field vacuum is in a broken symmetry state, an effective gravitational constant emerges which, in certain regimes, can lead to gravitational repulsive effects when only ordinary radiation is coupled to gravity. In this case, a bouncing universe is shown to be the only cosmological solution admissible by the field equations when the scalar field is in such broken symmetry state.
NASA Astrophysics Data System (ADS)
Khan, Suhail; Hussain, Tahir; Khan, Gulzar Ali
The aim of this paper is to explore teleparallel conformal Killing vector fields (CKVFs) of locally rotationally symmetric (LRS) Bianchi type V spacetimes in the context of teleparallel gravity and compare the obtained results with those of general relativity (GR). The general solution of teleparallel conformal Killing's equations is found in terms of some unknown functions of t and x, along with a set of integrability conditions. The integrability conditions are solved in some particular cases to get the final form of teleparallel CKVFs. It is observed that the LRS Bianchi type V spacetimes admit proper teleparallel CKVF in only one case, while in remaining cases the teleparallel CKVFs reduce to teleparallel Killing vector fields (KVFs). Moreover, it is shown that the LRS Bianchi type V spacetimes do not admit any proper teleparallel homothetic vector field (HVF).
NASA Astrophysics Data System (ADS)
Lin, Meijin; Huang, Yuqing; Chen, Xi; Cai, Shuhui; Chen, Zhong
2011-01-01
High-resolution 2D NMR spectra in inhomogeneous fields can be achieved by the use of intermolecular multiple-quantum coherences and shearing reconstruction of 3D data. However, the long acquisition time of 3D spectral data is generally unbearable for invivo applications. To overcome this problem, two pulse sequences dubbed as iDH-COSY and iDH-JRES were proposed in this paper. Although 3D acquisition is still required for the new sequences, the high-resolution 2D spectra can be obtained with a relatively short scanning time utilizing the manipulation of indirect evolution period and sparse sampling. The intermolecular multiple-quantum coherence treatment combined with the raising and lowering operators was applied to derive analytical signal expressions for the new sequences. And the experimental observations agree with the theoretical predictions. Our results show that the new sequences possess bright perspective in the applications on invivo localized NMR spectroscopy.
Shifted Landau ladders and low field magneto-oscillations in high-mobility GaAs 2D hole systems
NASA Astrophysics Data System (ADS)
Zhang, Po; Wang, Jianli; Zhang, Chi; Du, Rui-Rui; Pfeiffer, L. N.; West, K. W.
2017-03-01
We present well-developed low-field magneto-resistance oscillations originating from zero-field spin splitting (ZFSS) of heavy holes in high mobility GaAs/AlGaAs quantum wells. This low field oscillation is 1/B-periodic and emerges before the onset of Shubnikov-de Haas oscillations. The effect can be explained by resonant scattering between two Landau ladders shifted by the ZFSS gap, which in turn can be measured by comparing with the hole cyclotron energy. A front gate is fabricated to tune the ZFSS and hence the oscillation period.
NASA Astrophysics Data System (ADS)
Salehin, Z.; Woobaidullah, A. S. M.; Snigdha, S. S.
2015-12-01
Bengal Basin with its prolific gas rich province provides needed energy to Bangladesh. Present energy situation demands more Hydrocarbon explorations. Only 'Semutang' is discovered in the high amplitude structures, where rest of are in the gentle to moderate structures of western part of Chittagong-Tripura Fold Belt. But it has some major thrust faults which have strongly breached the reservoir zone. The major objectives of this research are interpretation of gas horizons and faults, then to perform velocity model, structural and property modeling to obtain reservoir properties. It is needed to properly identify the faults and reservoir heterogeneities. 3D modeling is widely used to reveal the subsurface structure in faulted zone where planning and development drilling is major challenge. Thirteen 2D seismic and six well logs have been used to identify six gas bearing horizons and a network of faults and to map the structure at reservoir level. Variance attributes were used to identify faults. Velocity model is performed for domain conversion. Synthetics were prepared from two wells where sonic and density logs are available. Well to seismic tie at reservoir zone shows good match with Direct Hydrocarbon Indicator on seismic section. Vsh, porosity, water saturation and permeability have been calculated and various cross plots among porosity logs have been shown. Structural modeling is used to make zone and layering accordance with minimum sand thickness. Fault model shows the possible fault network, those liable for several dry wells. Facies model have been constrained with Sequential Indicator Simulation method to show the facies distribution along the depth surfaces. Petrophysical models have been prepared with Sequential Gaussian Simulation to estimate petrophysical parameters away from the existing wells to other parts of the field and to observe heterogeneities in reservoir. Average porosity map for each gas zone were constructed. The outcomes of the research
NASA Astrophysics Data System (ADS)
Mirafzal, A.; Fereidoon, A.
2017-04-01
In this study, natural frequency and dynamic stability of functionally graded (FG) viscoelastic nanobeams based on the Euler-Bernoulli theory on the visco-Pasternak foundation are predicted. The material characteristics of FG nanobeam are temperature-dependent, and vary according to power-law model along thickness. The FG viscoelastic nanobeam is located on a two-dimensional magnetic field which considers the effects of transverse and longitudinal magnetic field. The uniform, linear, and sinusoidal temperature fields are applied on the FG viscoelastic nanobeam. The governing equations are derived through Hamilton's principle and Eringen's nonlocal theory. The equations are solved by a Navier-type method and the Bolotin method for simply supported conditions. The effect of three different temperature fields on natural frequency and dynamic stability region of the nanobeam is analyzed. The importance of various parameters such as nonlocal parameter, gradient indexes, magnitude of magnetic field, angle of magnetic field, temperature changes, and aspect ratio on both natural frequency and dynamic stability region of the FG viscoelastic nanobeam is investigated.
Parameterization of OPLS-AA force field for the conformational analysis of macrocyclic polyketides.
Kahn, Kalju; Bruice, Thomas C
2002-07-30
The parameters for the OPLS-AA potential energy function have been extended to include some functional groups that are present in macrocyclic polyketides. Existing OPLS-AA torsional parameters for alkanes, alcohols, ethers, hemiacetals, esters, and ketoamides were improved based on MP2/aug-cc-pVTZ and MP2/aug-cc-pVDZ calculations. Nonbonded parameters for the sp(3) carbon and oxygen atoms were refined using Monte Carlo simulations of bulk liquids. The resulting force field predicts conformer energies and torsional barriers of alkanes, alcohols, ethers, and hemiacetals with an overall RMS deviation of 0.40 kcal/mol as compared to reference data. Densities of 19 bulk liquids are predicted with an average error of 1.1%, and heats of vaporization are reproduced within 2.4% of experimental values. The force field was used to perform conformational analysis of smaller analogs of the macrocyclic polyketide drug FK506. Structures that adopted low-energy conformations similar to that of bound FK506 were identified. The results show that a linker of four ketide units constitutes the shortest effector domain that allows binding of the ketide drugs to FKBP proteins. It is proposed that the exact chemical makeup of the effector domain has little influence on the conformational preference of tetraketides.
World sheet commuting {beta}{gamma} conformal field theory and nonrelativistic string theories
Kim, Bom Soo
2007-11-15
We construct a sigma model in two dimensions with Galilean symmetry in flat target space similar to the sigma model of the critical string theory with Lorentz symmetry in 10 flat spacetime dimensions. This is motivated by the works of Gomis and Ooguri [J. Math. Phys. (N.Y.) 42, 3127 (2001)] and Danielsson et al. [J. High Energy Phys. 10 (2000) 020; J. High Energy Phys. 03 (2001) 041.]. Our theory is much simpler than their theory and does not assume a compact coordinate. This nonrelativistic string theory has a bosonic matter {beta}{gamma} conformal field theory with the conformal weight of {beta} as 1. It is natural to identify time as a linear combination of {gamma} and {gamma} through an explicit realization of the Galilean boost symmetry. The angle between {gamma} and {gamma} parametrizes one parameter family of selection sectors. These selection sectors are responsible for having a nonrelativistic dispersion relation without a nontrivial topology in the nonrelativistic setup, which is one of the major differences from the previous works of Gomis and Ooguri and of Danielsson and co-workers. This simple theory is the nonrelativistic analogue of the critical string theory, and there are many different avenues ahead to be investigated. We mention a possible consistent generalization of this theory with different conformal weights for the {beta}{gamma} conformal field theory. We also mention supersymmetric generalizations of these theories.
Is the Conformational Ensemble of Alzheimer's Aβ10-40 Peptide Force Field Dependent?
Siwy, Christopher M; Lockhart, Christopher; Klimov, Dmitri K
2017-01-01
By applying REMD simulations we have performed comparative analysis of the conformational ensembles of amino-truncated Aβ10-40 peptide produced with five force fields, which combine four protein parameterizations (CHARMM36, CHARMM22*, CHARMM22/cmap, and OPLS-AA) and two water models (standard and modified TIP3P). Aβ10-40 conformations were analyzed by computing secondary structure, backbone fluctuations, tertiary interactions, and radius of gyration. We have also calculated Aβ10-40 3JHNHα-coupling and RDC constants and compared them with their experimental counterparts obtained for the full-length Aβ1-40 peptide. Our study led us to several conclusions. First, all force fields predict that Aβ adopts unfolded structure dominated by turn and random coil conformations. Second, specific TIP3P water model does not dramatically affect secondary or tertiary Aβ10-40 structure, albeit standard TIP3P model favors slightly more compact states. Third, although the secondary structures observed in CHARMM36 and CHARMM22/cmap simulations are qualitatively similar, their tertiary interactions show little consistency. Fourth, two force fields, OPLS-AA and CHARMM22* have unique features setting them apart from CHARMM36 or CHARMM22/cmap. OPLS-AA reveals moderate β-structure propensity coupled with extensive, but weak long-range tertiary interactions leading to Aβ collapsed conformations. CHARMM22* exhibits moderate helix propensity and generates multiple exceptionally stable long- and short-range interactions. Our investigation suggests that among all force fields CHARMM22* differs the most from CHARMM36. Fifth, the analysis of 3JHNHα-coupling and RDC constants based on CHARMM36 force field with standard TIP3P model led us to an unexpected finding that in silico Aβ10-40 and experimental Aβ1-40 constants are generally in better agreement than these quantities computed and measured for identical peptides, such as Aβ1-40 or Aβ1-42. This observation suggests that the
Is the Conformational Ensemble of Alzheimer’s Aβ10-40 Peptide Force Field Dependent?
Siwy, Christopher M.
2017-01-01
By applying REMD simulations we have performed comparative analysis of the conformational ensembles of amino-truncated Aβ10-40 peptide produced with five force fields, which combine four protein parameterizations (CHARMM36, CHARMM22*, CHARMM22/cmap, and OPLS-AA) and two water models (standard and modified TIP3P). Aβ10-40 conformations were analyzed by computing secondary structure, backbone fluctuations, tertiary interactions, and radius of gyration. We have also calculated Aβ10-40 3JHNHα-coupling and RDC constants and compared them with their experimental counterparts obtained for the full-length Aβ1-40 peptide. Our study led us to several conclusions. First, all force fields predict that Aβ adopts unfolded structure dominated by turn and random coil conformations. Second, specific TIP3P water model does not dramatically affect secondary or tertiary Aβ10-40 structure, albeit standard TIP3P model favors slightly more compact states. Third, although the secondary structures observed in CHARMM36 and CHARMM22/cmap simulations are qualitatively similar, their tertiary interactions show little consistency. Fourth, two force fields, OPLS-AA and CHARMM22* have unique features setting them apart from CHARMM36 or CHARMM22/cmap. OPLS-AA reveals moderate β-structure propensity coupled with extensive, but weak long-range tertiary interactions leading to Aβ collapsed conformations. CHARMM22* exhibits moderate helix propensity and generates multiple exceptionally stable long- and short-range interactions. Our investigation suggests that among all force fields CHARMM22* differs the most from CHARMM36. Fifth, the analysis of 3JHNHα-coupling and RDC constants based on CHARMM36 force field with standard TIP3P model led us to an unexpected finding that in silico Aβ10-40 and experimental Aβ1-40 constants are generally in better agreement than these quantities computed and measured for identical peptides, such as Aβ1-40 or Aβ1-42. This observation suggests that the
NASA Astrophysics Data System (ADS)
van Dooren, M. F.; Kühn, M.; PetroviĆ, V.; Bottasso, C. L.; Campagnolo, F.; Sjöholm, M.; Angelou, N.; Mikkelsen, T.; Croce, A.; Zasso, A.
2016-09-01
This paper combines the currently relevant research methodologies of scaled wind turbine model experiments in wind tunnels with remote-sensing short-range WindScanner Lidar measurement technology. The wind tunnel of the Politecnico di Milano was equipped with three wind turbine models and two short-range WindScanner Lidars to demonstrate the benefits of synchronised scanning Lidars in such experimental surroundings for the first time. The dual- Lidar system can provide fully synchronised trajectory scans with sampling time scales ranging from seconds to minutes. First, staring mode measurements were compared to hot wire probe measurements commonly used in wind tunnels. This yielded goodness of fit coefficients of 0.969 and 0.902 for the 1 Hz averaged u- and v-components of the wind speed, respectively, validating the 2D measurement capability of the Lidar scanners. Subsequently, the measurement of wake profiles on a line as well as wake area scans were executed to illustrate the applicability of Lidar scanning to measuring small scale wind flow effects. The downsides of Lidar with respect to the hot wire probes are the larger measurement probe volume and the loss of some measurements due to moving blades. In contrast, the benefits are the high flexibility in conducting both point measurements and area scanning, and the fact that remote sensing techniques do not disturb the flow while measuring. The research campaign revealed a high potential for using short-range WindScanner Lidar for accurately measuring small scale flow structures in a wind tunnel.
Brûlé, Yoann; Demésy, Guillaume; Gralak, Boris; Popov, Evgeny
2015-04-06
An extensive numerical study of diffraction of a plane monochromatic wave by a single gold cone on a plane gold substrate and by a periodical array of such cones shows formation of curls in the map of the Poynting vector. They result from the interference between the incident wave, the wave reflected by the substrate, and the field scattered by the cone(s). In case of a single cone, when going away from its base along the surface, the main contribution in the scattered field is given by the plasmon surface wave (PSW) excited on the surface. As expected, it has a predominant direction of propagation, determined by the incident wave polarization. Two particular cones with height approximately 1/6 and 1/3 of the wavelength are studied in detail, as they present the strongest absorption and field enhancement when arranged in a periodic array. While the PSW excited by the smaller single cone shows an energy flux globally directed along the substrate surface, we show that curls of the Poynting vector generated with the larger cone touch the diopter surface. At this point, their direction is opposite to the energy flow of the PSW, which is then forced to jump over the vortex regions. Arranging the cones in a two-dimensional subwavelength periodic array (diffraction grating), supporting a specular reflected order only, resonantly strengthens the field intensity at the tip of cones and leads to a field intensity enhancement of the order of 10 000 with respect to the incident wave intensity. The enhanced field is strongly localized on the rounded top of the cones. It is accompanied by a total absorption of the incident light exhibiting large angular tolerances. This strongly localized giant field enhancement can be of much interest in many applications, including fluorescence spectroscopy, label-free biosensing, surface-enhanced Raman scattering (SERS), nonlinear optical effects and photovoltaics.
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.
[Research in two-dimensional critical phenomena and conformal field theory]. Final report
Not Available
1990-12-31
A very theoretical description is given of research in two- dimensional critical phenomena and conformal field theory. Major progress is reported in the field of fluctuating two-dimensional surfaces. A discretized representation of fluctuating geometry is used where surfaces are represented by triangulations; continuum surfaces are recovered by taking the size of the triangles to zero. One of the central goals of the theory of critical phenomena is to find all possible universality classes of n-dimensional critical phenomena; this goal has been translated into the problem of clasifying all possible scale-invariant euclidean quantum field theories. (RWR)
2D/3D quench simulation using ANSYS for epoxy impregnated Nb3Sn high field magnets
Ryuji Yamada et al.
2002-09-19
A quench program using ANSYS is developed for the high field collider magnet for three-dimensional analysis. Its computational procedure is explained. The quench program is applied to a one meter Nb{sub 3}Sn high field model magnet, which is epoxy impregnated. The quench simulation program is used to estimate the temperature and mechanical stress inside the coil as well as over the whole magnet. It is concluded that for the one meter magnet with the presented cross section and configuration, the thermal effects due to the quench is tolerable. But we need much more quench study and improvements in the design for longer magnets.
NASA Astrophysics Data System (ADS)
Murphy, B. N.; Donahue, N. M.; Fountoukis, C.; Dall'Osto, M.; O'Dowd, C.; Kiendler-Scharr, A.; Pandis, S. N.
2012-04-01
Multigenerational oxidation chemistry of atmospheric organic compounds and its effects on aerosol loadings and chemical composition is investigated by implementing the Two-Dimensional Volatility Basis Set (2-D-VBS) in a Lagrangian host chemical transport model. Three model formulations were chosen to explore the complex interactions between functionalization and fragmentation processes during gas-phase oxidation of organic compounds by the hydroxyl radical. The base case model employs a conservative transformation by assuming a reduction of one order of magnitude in effective saturation concentration and an increase of oxygen content by one or two oxygen atoms per oxidation generation. A second scheme simulates functionalization in more detail using group contribution theory to estimate the effects of oxygen addition to the carbon backbone on the compound volatility. Finally, a fragmentation scheme is added to the detailed functionalization scheme to create a functionalization-fragmentation parameterization. Two condensed-phase chemistry pathways are also implemented as additional sensitivity tests to simulate (1) heterogeneous oxidation via OH uptake to the particle-phase and (2) aqueous-phase chemistry of glyoxal and methylglyoxal. The model is applied to summer and winter periods at three sites where observations of organic aerosol (OA) mass and O:C were obtained during the European Integrated Project on Aerosol Cloud Climate and Air Quality Interactions (EUCAARI) campaigns. The base case model reproduces observed mass concentrations and O:C well, with fractional errors (FE) lower than 55% and 25%, respectively. The detailed functionalization scheme tends to overpredict OA concentrations, especially in the summertime, and also underpredicts O:C by approximately a factor of 2. The detailed functionalization model with fragmentation agrees well with the observations for OA concentration, but still underpredicts O:C. Both heterogeneous oxidation and aqueous
NASA Astrophysics Data System (ADS)
Murphy, B. N.; Donahue, N. M.; Fountoukis, C.; Dall'Osto, M.; O'Dowd, C.; Kiendler-Scharr, A.; Pandis, S. N.
2012-11-01
Multigenerational oxidation chemistry of atmospheric organic compounds and its effects on aerosol loadings and chemical composition is investigated by implementing the Two-Dimensional Volatility Basis Set (2-D-VBS) in a Lagrangian host chemical transport model. Three model formulations were chosen to explore the complex interactions between functionalization and fragmentation processes during gas-phase oxidation of organic compounds by the hydroxyl radical. The base case model employs a conservative transformation by assuming a reduction of one order of magnitude in effective saturation concentration and an increase of oxygen content by one or two oxygen atoms per oxidation generation. A second scheme simulates functionalization in more detail using group contribution theory to estimate the effects of oxygen addition to the carbon backbone on the compound volatility. Finally, a fragmentation scheme is added to the detailed functionalization scheme to create a functionalization-fragmentation parameterization. Two condensed-phase chemistry pathways are also implemented as additional sensitivity tests to simulate (1) heterogeneous oxidation via OH uptake to the particle-phase and (2) aqueous-phase chemistry of glyoxal and methylglyoxal. The model is applied to summer and winter periods at three sites where observations of organic aerosol (OA) mass and O:C were obtained during the European Integrated Project on Aerosol Cloud Climate and Air Quality Interactions (EUCAARI) campaigns. The base case model reproduces observed mass concentrations and O:C well, with fractional errors (FE) lower than 55% and 25%, respectively. The detailed functionalization scheme tends to overpredict OA concentrations, especially in the summertime, and also underpredicts O:C by approximately a factor of 2. The detailed functionalization model with fragmentation agrees well with the observations for OA concentration, but still underpredicts O:C. Both heterogeneous oxidation and aqueous
NASA Astrophysics Data System (ADS)
Noh, H.; Tsui, D. C.; Shayegan, M.; Yoon, Jongsoo
2000-03-01
We report on measurements of anisotropic in-plane magneto-resistance of the 2D hole system (2DHS) in a GaAs/AlGaAs (311)A heterostructure, which exhibits both zero-field and in-plane field induced metal-insulator transitions. For high hole densities, when the direction of B field is changed relative to the current(I), which is always kept in the high mobility direction, the resistivity with B allel I is larger at low field, while the resistivity with B ⊥ I becomes larger at high field. This behavior is consistent with recent measurements(S. J. Papadakis et al.), cond-mat/9911239. on a quantum well system. That the resistivity at high field is larger for B ⊥ I than for B allel I is also consistent with a recent theoretical argument(S. Das Sarma and E. H. Hwang, cond-mat/9909452.), though the difference is smaller than that from the theory. As the density is lowered, the resistivity with B allel I gets larger at high field, and it eventually becomes greater than that with B ⊥ I at all field ranges measured. This change in anisotropy has not been seen in previous measurements. The critical field B_c, beyond which the metallic phase becomes insulating, is also different for two different directions of B, while the change in I-V characteristics across Bc remains the same.
From conformal field theory spectra to CMB multipoles in quantum gravity cosmology
Hamada, Ken-ji; Horata, Shinichi; Yukawa, Tetsuyuki
2010-04-15
We study the inflation process of the Universe based on the renormalizable quantum gravity formulated as a conformal field theory. We show that the power-law conformal field theory spectrum approaches that of the Harrison-Zel'dovich-Peebles-type as the amplitude of gravitational potential gradually reduces during the inflation. The non-Gaussanity parameter is preserved within an order of unity due to the diffeomorphism invariance. Sharp falloff of the angular power spectrum of cosmic microwave background at large scale is understood as a consequence of the existence of dynamical scale of the quantum gravity {Lambda}{sub QG}({approx_equal}10{sup 17} GeV). The angular power spectra are computed and compared with the WMAP5 and ACBAR data with a quality of {chi}{sup 2}/dof{approx_equal}1.1.
Low field magnetoresistance in a 2D topological insulator based on wide HgTe quantum well
NASA Astrophysics Data System (ADS)
Olshanetsky, E. B.; Kvon, Z. D.; Gusev, G. M.; Mikhailov, N. N.; Dvoretsky, S. A.
2016-09-01
Low field magnetoresistance is experimentally studied in a two-dimensional topological insulator (TI) in both diffusive and quasiballistic samples fabricated on top of a wide (14 nm) HgTe quantum well. In all cases a pronounced quasi-linear positive magnetoresistance is observed similar to that found previously in diffusive samples based on a narrow (8 nm) HgTe well. The experimental results are compared with the main existing theoretical models based on different types of disorder: sample edge roughness, nonmagnetic disorder in an otherwise coherent TI and metallic puddles due to locally trapped charges that act like local gate on the sample. The quasiballistic samples with resistance close to the expected quantized values also show a positive low-field magnetoresistance but with a pronounced admixture of mesoscopic effects.
1984-09-01
A conformal transformation formula using Riemann-Stieltjes integrals is derived for use with problems involving the interaction between a given finite-sized geometry and a known far field. The derivative of this transformation is non-singular in the domain considered and tends to one at infinity. A formula is derived for transformation from the unit circle to the exterior of an arbitrarily given continuous curve with bounded variation . A special case of the transformation is very similar
NASA Astrophysics Data System (ADS)
Seidel, A.; Wagner, S.; Dreizler, A.; Ebert, V.
2015-05-01
We have developed a fast, spatially scanning direct tunable diode laser absorption spectrometer (dTDLAS) that combines four polygon-mirror based scanning units with low-cost retro-reflective foils. With this instrument, tomographic measurements of absolute 2-D water vapor concentration profiles are possible without any calibration using a reference gas. A spatial area of 0.8 m x 0.8 m was covered, which allows for application in soil physics, where greenhouse gas emission from certain soil structures shall be monitored. The whole concentration field was measured with up to 2.5 Hz. In this paper, we present the setup and spectroscopic performance of the instrument regarding the influence of the polygon rotation speed and mode on the absorption signal. Homogeneous H2O distributions were measured and compared to a single channel, bi-static reference TDLAS spectrometer for validation of the instrument. Good accuracy and precision with errors of less than 6% of the absolute concentration and length and bandwidth normalized detection limits of up to 1.1 ppmv . m (Hz)-0.5 were achieved. The spectrometer is a robust and easy to set up instrument for tomographic reconstructions of 2-D-concentration fields that can be considered as a good basis for future field measurements in environmental research.
NASA Astrophysics Data System (ADS)
Seidel, A.; Wagner, S.; Dreizler, A.; Ebert, V.
2014-12-01
We have developed a fast, spatially direct scanning tunable diode laser absorption spectrometer (dTDLAS) that combines four polygon-mirror based scanning units with low-cost retro-reflective foils. With this instrument, tomographic measurements of absolute 2-D water vapour concentration profiles are possible without any calibration using a reference gas. A spatial area of 0.8 m × 0.8 m was covered, which allows for application in soil physics, where greenhouse gas emission from certain soil structures shall be monitored. The whole concentration field was measured with up to 2.5 Hz. In this paper, we present the setup and spectroscopic performance of the instrument regarding the influence of the polygon rotation speed and mode on the absorption signal. Homogeneous H2O distributions were measured and compared to a single channel, bi-static reference TDLAS spectrometer for validation of the instrument. Good accuracy and precision with errors of less than 6% of the absolute concentration and length and bandwidth normalized detection limits of up to 1.1 ppmv · m · √Hz-1 were achieved. The spectrometer is a robust and easy to set up instrument for tomographic reconstructions of 2-D-concentration fields that can be considered a good basis for future field measurements in environmental research.
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
NASA Astrophysics Data System (ADS)
Krzemianowski, Z.; Puzyrewski, R.
2014-08-01
The paper presents the main parameters of the flow field behind the guide vane cascade designed by means of 2D inverse problem and following check by means of 3D commercial program ANSYS/Fluent applied for a direct problem. This approach of using different models reflects the contemporary design procedure for non-standardized turbomachinery stage. Depending on the model, the set of conservation equation to be solved differs, although the physical background remains the same. The example of computations for guide vane cascade for a low head hydraulic turbine is presented.
Integrable perturbations of conformal field theories and Yetter-Drinfeld modules
Bücher, David; Runkel, Ingo
2014-11-15
In this paper we relate a problem in representation theory — the study of Yetter-Drinfeld modules over certain braided Hopf algebras — to a problem in two-dimensional quantum field theory, namely, the identification of integrable perturbations of a conformal field theory. A prescription that parallels Lusztig's construction allows one to read off the quantum group governing the integrable symmetry. As an example, we illustrate how the quantum group for the loop algebra of sl(2) appears in the integrable structure of the perturbed uncompactified and compactified free boson.
Fan, D.; Geng, C.; Chen, L.Q.
1997-03-01
The local kinetics and topological phenomena during normal grain growth were studied in two dimensions by computer simulations employing a continuum diffuse-interface field model. The relationships between topological class and individual grain growth kinetics were examined, and compared with results obtained previously from analytical theories, experimental results and Monte Carlo simulations. It was shown that both the grain-size and grain-shape (side) distributions are time-invariant and the linear relationship between the mean radii of individual grains and topological class n was reproduced. The moments of the shape distribution were determined, and the differences among the data from soap froth. Potts model and the present simulation were discussed. In the limit when the grain size goes to zero, the average number of grain edges per grain is shown to be between 4 and 5, implying the direct vanishing of 4- and 5-sided grains, which seems to be consistent with recent experimental observations on thin films. Based on the simulation results, the conditions for the applicability of the familiar Mullins-Von Neumann law and the Hillert`s equation were discussed.
Force field-based conformational searches: efficiency and performance for peptide receptor complexes
NASA Astrophysics Data System (ADS)
Grebner, Christoph; Niebling, Stephan; Schmuck, Carsten; Schlücker, Sebastian; Engels, Bernd
2013-09-01
Conformational search using force field methods on complex biomolecular systems is a key factor in understanding molecular and structural properties. The reliability of such investigations strongly depends on the efficiency of the conformational search algorithm as well as the accuracy of the employed force field. In the present work we compared the performance of two different approaches: the Monte-Carlo multiple minimum/low mode sampling (MCMM/LM), in combination with the OPLS2005 (MCMM/LM//OPLS2005), and Tabu-Search combined with Basin Hopping (TS/BH), employing the original OPLS-AA implementation proposed by Jorgensen (TS/BH//OPLS-AA). We investigated their performance in locating energetically low-lying structures and the efficiency in scanning the conformational phase space of non-covalently bonded complexes. As test systems we employed complexes of the artificial peptide receptor CBS-KKF with four different tetrapeptide ligands. The reliability and the accuracy of both approaches were examined by re-optimising all low-energy structures employing density functional theory with empirical dispersion correction in combination with triple zeta basis sets. Solvent effects were mimicked by a continuum solvent model. In all the four-test systems, the TS/BH//OPLS-AA approach yielded structures that are much lower in energy after the DFT optimisation. Additionally, it provided many low-lying structures that were not identified by the MCMM/LM//OPLS2005 approach.
NASA Astrophysics Data System (ADS)
Nakayama, Yu
2017-02-01
We show that 11-dimensional supergravity in Euclidean signature admits an exact classical solution with isometry corresponding to a three-dimensional scale-invariant field theory without conformal invariance. We also construct the holographic renormalization group flow that connects the known UV conformal fixed point and the new scale-invariant but not conformal fixed point. In view of holography, the existence of such classical solutions suggests that the topologically twisted M2-brane gauge theory possesses a scale-invariant but not conformal phase.
NASA Astrophysics Data System (ADS)
Liu, Yun; Wang, Xu-Ben; Wang, Yun
2013-06-01
To effectively minimize the electromagnetic field response in the total field solution, we propose a numerical modeling method for the two-dimensional (2D) timedomain transient electromagnetic secondary field of the line source based on the DuFort-Frankel finite-difference method. In the proposed method, we included the treatment of the earth-air boundary conductivity, calculated the normalized partial derivative of the induced electromotive force (Emf), and determined the forward time step. By extending upward the earth-air interface to the air grid nodes and the zero-value boundary conditions, not only we have a method that is more efficient but also simpler than the total field solution. We computed and analyzed the homogeneous half-space model and the flat layered model with high precision—the maximum relative error is less than 0.01% between our method and the analytical method—and the solution speed is roughly three times faster than the total-field solution. Lastly, we used the model of a thin body embedded in a homogeneous half-space at different delay times to depict the downward and upward spreading characteristics of the induced eddy current, and the physical interaction processes between the electromagnetic field and the underground low-resistivity body.
Bazan, Ovandir; Ortiz, Jayme P; Fukumasu, Newton K; Pacifico, Antonio L; Yanagihara, Jurandir I
2016-02-01
The flow patterns of a prosthetic heart valve in the aortic or mitral position can change according to its type and orientation. This work describes the use of 2D particle image velocimetry (PIV) applied to the in vitro flow fields characterization inside the upper part of a left ventricular model at various heart rates and as a function of two orientations of stented tricuspid mitral bioprostheses. In the ventricular model, each mitral bioprosthesis (27 and 31 mm diameter) was installed in two orientations, rotated by 180°, while the aortic bileaflet mechanical valve (27 mm diameter) remained in a fixed orientation. The results (N = 50) showed changes in the intraventricular flow fields according to the mitral bioprostheses positioning. Also, changes in the aortic upstream velocity profiles were noticed as a function of mitral orientations.
Fendley, Paul; Fisher, Matthew P.A.; Nayak, Chetan
2009-07-15
We explain how (perturbed) boundary conformal field theory allows us to understand the tunneling of edge quasiparticles in non-Abelian topological states. The coupling between a bulk non-Abelian quasiparticle and the edge is due to resonant tunneling to a zero mode on the quasiparticle, which causes the zero mode to hybridize with the edge. This can be reformulated as the flow from one conformally invariant boundary condition to another in an associated critical statistical mechanical model. Tunneling from one edge to another at a point contact can split the system in two, either partially or completely. This can be reformulated in the critical statistical mechanical model as the flow from one type of defect line to another. We illustrate these two phenomena in detail in the context of the {nu}=5/2 quantum Hall state and the critical Ising model. We briefly discuss the case of Fibonacci anyons and conclude by explaining the general formulation and its physical interpretation.
Chen, Wei; Shi, Chuanyin; MacKerell, Alexander D.; Shen, Jana
2015-01-01
Physics-based force fields are the backbone of molecular dynamics simulations. In recent years, significant progress has been made in the assessment and improvement of commonly-used force fields for describing conformational dynamics of folded proteins. However, the accuracy for the unfolded states remains unclear. The latter is however important for detailed studies of protein folding pathways, conformational transitions involving unfolded states and dynamics of intrinsically disordered proteins. In this work we compare the three commonly-used force fields, AMBER ff99SB-ILDN, CHARMM22/CMAP and CHARMM36, for modeling the natively unfolded fragment peptides, NTL9(1-22) and NTL9(6-17), using explicit-solvent replica-exchange molecular dynamics simulations. All three simulations show that NTL9(6-17) is completely unstructured, while NTL9(1-22) transiently samples various β-hairpin states, reminiscent of the first β-hairpin in the structure of the intact NT9 protein. The radius of gyration of the two peptides is force field independent but likely underestimated due to the current deficiency of additive force fields. Compared to the CHARMM force fields, ff99SB-ILDN gives slightly higher β-sheet propensity and more native-like residual structures for NTL9(1-22), which may be attributed to its known β preference. Surprisingly, only two sequence-local pairs of charged residues make appreciable ionic contacts in the simulations of NTL9(1-22), which are sampled slightly more by the CHARMM force fields. Taken together, these data suggest that the current CHARMM and AMBER force fields are globally in agreement in modeling the unfolded states corresponding to β-sheet in the folded structure, while differing in details such as the native-likeness of the residual structures and interactions. PMID:26020564
Hansen, Halvor S; Hünenberger, Philippe H
2011-04-30
This article presents a reoptimization of the GROMOS 53A6 force field for hexopyranose-based carbohydrates (nearly equivalent to 45A4 for pure carbohydrate systems) into a new version 56A(CARBO) (nearly equivalent to 53A6 for non-carbohydrate systems). This reoptimization was found necessary to repair a number of shortcomings of the 53A6 (45A4) parameter set and to extend the scope of the force field to properties that had not been included previously into the parameterization procedure. The new 56A(CARBO) force field is characterized by: (i) the formulation of systematic build-up rules for the automatic generation of force-field topologies over a large class of compounds including (but not restricted to) unfunctionalized polyhexopyranoses with arbritrary connectivities; (ii) the systematic use of enhanced sampling methods for inclusion of experimental thermodynamic data concerning slow or unphysical processes into the parameterization procedure; and (iii) an extensive validation against available experimental data in solution and, to a limited extent, theoretical (quantum-mechanical) data in the gas phase. At present, the 56A(CARBO) force field is restricted to compounds of the elements C, O, and H presenting single bonds only, no oxygen functions other than alcohol, ether, hemiacetal, or acetal, and no cyclic segments other than six-membered rings (separated by at least one intermediate atom). After calibration, this force field is shown to reproduce well the relative free energies of ring conformers, anomers, epimers, hydroxymethyl rotamers, and glycosidic linkage conformers. As a result, the 56A(CARBO) force field should be suitable for: (i) the characterization of the dynamics of pyranose ring conformational transitions (in simulations on the microsecond timescale); (ii) the investigation of systems where alternative ring conformations become significantly populated; (iii) the investigation of anomerization or epimerization in terms of free-energy differences
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.
Effect of strong electric field on the conformational integrity of insulin.
Wang, Xianwei; Li, Yongxiu; He, Xiao; Chen, Shude; Zhang, John Z H
2014-10-02
A series of molecular dynamics (MD) simulations up to 1 μs for bovine insulin monomer in different external electric fields were carried out to study the effect of external electric field on conformational integrity of insulin. Our results show that the secondary structure of insulin is kept intact under the external electric field strength below 0.15 V/nm, but disruption of secondary structure is observed at 0.25 V/nm or higher electric field strength. Although the starting time of secondary structure disruption of insulin is not clearly correlated with the strength of the external electric field ranging between 0.15 and 0.60 V/nm, long time MD simulations demonstrate that the cumulative effect of exposure time under the electric field is a major cause for the damage of insulin's secondary structure. In addition, the strength of the external electric field has a significant impact on the lifetime of hydrogen bonds when it is higher than 0.60 V/nm. The fast evolution of some hydrogen bonds of bovine insulin in the presence of the 1.0 V/nm electric field shows that different microwaves could either speed up protein folding or destroy the secondary structure of globular proteins deponding on the intensity of the external electric field.
NASA Astrophysics Data System (ADS)
Papadakis, S. J.; de Poortere, E. P.; Shayegan, M.; Winkler, R.
2000-03-01
We report experiments on (311)A GaAs 2D holes at 0.3 - 1.4 K with an in-plane magnetic field B. The density range (1.3 × 10^10 < p < 6.6 × 10^10 cm-2) is such that the temperature dependence of the resistivity is metallic-like at B = 0. In all cases the system displays positive magnetoresistance whose details depend on the relative orientations of B and the crystal axes as well as of B and the current (I) direction.(S. J. Papadakis et al.), cond-mat/9911239. We observe a feature in the magnetoresistance, associated with a spin-subband de-population, whose B-position changes when the field direction is changed from [bar233] to [01bar1]. Near this feature, there is a critical field BT beyond which the behavior changes to insulating. B_T, too, changes when the orientation of B relative to the crystal axes is changed. Changing the direction of I with respect to B also affects the positions of these features, but to a much smaller degree. The data are consistent with the idea that two spin-subbands with different populations are necessary for the existence of the B = 0 metallic behavior, and are also a clear demonstration of the anisotropy of the band structure of GaAs 2D holes grown on (311)A substrates.
Yang, Gang; Long, Haiyan; Ren, Xiaomei; Ma, Kunlong; Xiao, Zhenghua; Wang, Ying; Guo, Yingqiang
2017-02-01
Cell alignment and motility play a critical role in a variety of cell behaviors, including cytoskeleton reorganization, membrane-protein relocation, nuclear gene expression, and extracellular matrix remodeling. Direct current electric field (EF) in vitro can direct many types of cells to align vertically to EF vector. In this work, we investigated the effects of EF stimulation on rat adipose-tissue-derived stromal cells (ADSCs) in 2D-culture on plastic culture dishes and in 3D-culture on various scaffold materials, including collagen hydrogels, chitosan hydrogels and poly(L-lactic acid)/gelatin electrospinning fibers. Rat ADSCs were exposed to various physiological-strength EFs in a homemade EF-bioreactor. Changes of morphology and movements of cells affected by applied EFs were evaluated by time-lapse microphotography, and cell survival rates and intracellular calcium oscillations were also detected. Results showed that EF facilitated ADSC morphological changes, under 6 V/cm EF strength, and that ADSCs in 2D-culture aligned vertically to EF vector and kept a good cell survival rate. In 3D-culture, cell galvanotaxis responses were subject to the synergistic effect of applied EF and scaffold materials. Fast cell movement and intracellular calcium activities were observed in the cells of 3D-culture. We believe our research will provide some experimental references for the future study in cell galvanotaxis behaviors.
Supersymmetric moose models: An extra dimension from a broken deformed conformal field theory
Erlich, Joshua; Anly Tan, Jong
2006-09-15
We find a class of four dimensional deformed conformal field theories which appear extra dimensional when their gauge symmetries are spontaneously broken. The theories are supersymmetric moose models which flow to interacting conformal fixed points at low energies, deformed by superpotentials. Using a-maximization we give strong nonperturbative evidence that the hopping terms in the resulting latticized action are relevant deformations of the fixed-point theories. These theories have an intricate structure of RG flows between conformal fixed points. Our results suggest that at the stable fixed points each of the bulk gauge couplings and superpotential hopping terms is turned on, in favor of the extra-dimensional interpretation of the theory. However, we argue that the higher-dimensional gauge coupling is generically small compared to the size of the extra dimension. In the presence of a brane the topology of the extra dimension is determined dynamically and depends on the numbers of colors and bulk and brane flavors, which suggests phenomenological applications. The RG flows between fixed points in these theories provide a class of tests of Cardy's conjectured a-theorem.
The fully packed loop model as a non-rational W 3 conformal field theory
NASA Astrophysics Data System (ADS)
Dupic, T.; Estienne, B.; Ikhlef, Y.
2016-12-01
The fully packed loop (FPL) model is a statistical model related to the integrable {{U}q}≤ft({{\\widehat{sl}}3}\\right) vertex model. In this paper we study the continuum limit of the FPL. With the appropriate weight of non-contractible loops, we give evidence of an extended W 3 symmetry in the continuum. The partition function on the torus is calculated exactly, yielding new modular invariants of W 3 characters. The full conformal field theory spectrum is obtained, and is found to be in excellent agreement with exact diagonalisation.
Relative entropy of excited states in conformal field theories of arbitrary dimensions
NASA Astrophysics Data System (ADS)
Sárosi, Gábor; Ugajin, Tomonori
2017-02-01
Extending our previous work, we study the relative entropy between the reduced density matrices obtained from globally excited states in conformal field theories of arbitrary dimensions. We find a general formula in the small subsystem size limit. When one of the states is the vacuum of the CFT, our result matches with the holographic entanglement entropy computations in the corresponding bulk geometries, including AdS black branes. We also discuss the first asymmetric part of the relative entropy and comment on some implications of the results on the distinguishability of black hole microstates in AdS/CFT.
Inflation and reheating in the Starobinsky model with conformal HiggsField
NASA Astrophysics Data System (ADS)
Gorbunov, D. S.; Tokareva, A. A.
2013-12-01
This is a talk presented by A.A. Tokareva at Baikal summer school on physics of elementary particles and astrophysics 2012. We studied the reheating after the Starobinsky inflation and have found that the main process is the inflaton decay to SM gauge fields due to the conformal anomaly. The reheating temperature is low leading to the possibility to detect the gravity wave signal from inflation and evaporation of structures formed after inflation in DECIGO and BBO experiments. Also we give predictions for the parameters of scalar perturbation spectrum at the next-to-leading order of slow roll and obtain a bound on the Higgs mass.
Conformal field theory approach to Abelian and non-Abelian quantum Hall quasielectrons.
Hansson, T H; Hermanns, M; Regnault, N; Viefers, S
2009-04-24
The quasiparticles in quantum Hall liquids carry fractional charge and obey fractional quantum statistics. Of particular recent interest are those with non-Abelian statistics, since their braiding properties could, in principle, be used for robust coding of quantum information. There is already a good theoretical understanding of quasiholes in both Abelian and non-Abelian quantum Hall states. Here we develop conformal field theory methods that allow for an equally precise description of quasielectrons and explicitly construct two- and four-quasielectron excitations of the non-Abelian Moore-Read state.
Measurement of the effect of electric field on lipid ion channel conformation
Osman, P.D.; Cornell, B. CSIRO, North Ryde, New South Wales )
1992-01-01
This presentation reports on results from a new technique for measuring conformational changes by solid state NMR, in lipid membranes and membrane spanning ion channels, in response to the direct application of electrical field. An apparatus for applying biphasic electric field pulses of up to 20 MV/m to samples of aligned lipids held in an NMR probe, together with methods for the improvement of field homogeneity, will be described. In particular it has been found possible to obtain aligned lipid bilayers of very high impedance by substituting anhydrous glycerol for water. Measurements have been carried out on cholestric liquid crystals, on dilauryl phosphatidylcholine (DLPC) and dioleoyl phosphatidylethanolamine (DOPE) and on melittin in DLPC. The interaction of electric fields with aligned bilayers and powdered samples of DLPC and DOPE will be described, showing elongation of vesicles in response to the field and showing electric field induced Lalpha to powder to Hexll conversion in DOPE. The effect of electric fields on melittin incorporated into aligned lipid bilayers of DLPC will also be reported.
NASA Astrophysics Data System (ADS)
Realpe Campaña, Julian David; Porsani, Jorge Luís; Bortolozo, Cassiano Antonio; Serejo de Oliveira, Gabriela; Monteiro dos Santos, Fernando Acácio
2017-03-01
Results of a TEM profile by using the fixed-loop array and an analysis of the induced magnetic field are presented in this work performed in the northwest region of São Paulo State, Brazil, Paraná Basin. The objectives of this research were to map the sedimentary and crystalline aquifers in the area and analyzing the behavior of the magnetic field by observation of magnetic profiles. TEM measurements in the three spatial components were taken to create magnetic profiles of the induced (secondary) magnetic field. The TEM data were acquired using a fixed transmitter loop of 200 m × 200 m and a 3D coil receiver moving along a profile line of 1000 m. Magnetic profiles of dBz, dBx and dBy components showed symmetrical spatial behavior related with loop geometry. z-component showed a behavior probably related to superparamagnetic effect (SPM). dBz data was used to perform individual 1D inversion for each position and to generate an interpolated pseudo-2D geoelectric profile. The results showed two low resistivity zones: the first shallow, between 10 m and 70 m deep, probably related to the Adamantina Formation (sedimentary aquifer). The second between 200 m and 300 m depth, probably related to a fractured zone filled with water or clay inside the basalt layer of the Serra Geral Formation (crystalline aquifer). These results agree with the well logs information available in the studied region.
ff14IDPs force field improving the conformation sampling of intrinsically disordered proteins.
Song, Dong; Wang, Wei; Ye, Wei; Ji, Dingjue; Luo, Ray; Chen, Hai-Feng
2017-01-01
Intrinsically disordered proteins are proteins which lack of specific tertiary structure and unable to fold spontaneously without the partner binding. These intrinsically disordered proteins are found to associate with various diseases, such as diabetes, cancer, and neurodegenerative diseases. However, current widely used force fields, such as ff99SB, ff14SB, OPLS/AA, and Charmm27, are insufficient in sampling the conformational characters of intrinsically disordered proteins. In this study, the CMAP method was used to correct the φ/ψ distributions of disorder-promoting amino acids. The simulation results show that the force filed parameters (ff14IDPs) can improve the φ/ψ distributions of the disorder-promoting amino acids, with RMSD less than 0.10% relative to the benchmark data of intrinsically disordered proteins. Further test suggests that the calculated secondary chemical shifts under ff14IDPs are in quantitative agreement with the data of NMR experiment for five tested systems. In addition, the simulation results show that ff14IDPs can still be used to model structural proteins, such as tested lysozyme and ubiquitin, with better performance in coil regions than the original general Amber force field ff14SB. These findings confirm that the newly developed Amber ff14IDPs is a robust model for improving the conformation sampling of intrinsically disordered proteins.
Static black hole solutions with a self-interacting conformally coupled scalar field
Dotti, Gustavo; Gleiser, Reinaldo J.; Martinez, Cristian
2008-05-15
We study static, spherically symmetric black hole solutions of the Einstein equations with a positive cosmological constant and a conformally coupled self-interacting scalar field. Exact solutions for this model found by Martinez, Troncoso, and Zanelli were subsequently shown to be unstable under linear gravitational perturbations, with modes that diverge arbitrarily fast. We find that the moduli space of static, spherically symmetric solutions that have a regular horizon--and satisfy the weak and dominant energy conditions outside the horizon--is a singular subset of a two-dimensional space parametrized by the horizon radius and the value of the scalar field at the horizon. The singularity of this space of solutions provides an explanation for the instability of the Martinez, Troncoso, and Zanelli spacetimes and leads to the conclusion that, if we include stability as a criterion, there are no physically acceptable black hole solutions for this system that contain a cosmological horizon in the exterior of its event horizon.
a Natural Extension of the Conformal Lorentz Group in a Field Theory Context
NASA Astrophysics Data System (ADS)
László, András
In this paper a finite dimensional unital associative algebra is presented, and its group of algebra automorphisms is detailed. The studied algebra can physically be understood as the creation operator algebra in a formal quantum field theory at fixed momentum for a spin 1/2 particle along with its antiparticle. It is shown that the essential part of the corresponding automorphism group can naturally be related to the conformal Lorentz group. In addition, the nonsemisimple part of the automorphism group can be understood as "dressing" of the pure one-particle states. The studied mathematical structure may help in constructing quantum field theories in a non-perturbative manner. In addition, it provides a simple example of circumventing Coleman-Mandula theorem using non-semisimple groups, without SUSY.
Zgarbová, Marie; Jurečka, Petr; Banáš, Pavel; Havrila, Marek; Šponer, Jiří; Otyepka, Michal
2017-03-23
The sugar-phosphate backbone of RNA can exist in diverse rotameric substates, giving RNA molecules enormous conformational variability. The most frequent noncanonical backbone conformation in RNA is α/γ = t/t, which is derived from the canonical backbone by a crankshaft motion and largely preserves the standard geometry of the RNA duplex. A similar conformation also exists in DNA, where it has been extensively studied and shown to be involved in DNA-protein interactions. However, the function of the α/γ = t/t conformation in RNA is poorly understood. Here, we present molecular dynamics simulations of several prototypical RNA structures obtained from X-ray and NMR experiments, including canonical and mismatched RNA duplexes, UUCG and GAGA tetraloops, Loop E, the sarcin-ricin loop, a parallel guanine quadruplex, and a viral pseudoknot. The stability of various noncanonical α/γ backbone conformations was analyzed with two AMBER force fields, ff99bsc0χOL3 and ff99bsc0χOL3 with the recent εζOL1 and βOL1 corrections for DNA. Although some α/γ substates were stable with seemingly well-described equilibria, many were unstable in our simulations. Notably, the most frequent noncanonical conformer α/γ = t/t was unstable in both tested force fields. Possible reasons for this instability are discussed. Our work reveals a potentially important artifact in RNA force fields and highlights a need for further force field refinement.
Jiang, Fan; Han, Wei; Wu, Yun-Dong
2013-03-14
The local conformational (φ, ψ, χ) preferences of amino acid residues remain an active research area, which are important for the development of protein force fields. In this perspective article, we first summarize spectroscopic studies of alanine-based short peptides in aqueous solution. While most studies indicate a preference for the P(II) conformation in the unfolded state over α and β conformations, significant variations are also observed. A statistical analysis from various coil libraries of high-resolution protein structures is then summarized, which gives a more coherent view of the local conformational features. The φ, ψ, χ distributions of the 20 amino acids have been obtained from a protein coil library, considering both backbone and side-chain conformational preferences. The intrinsic side-chain χ(1) rotamer preference and χ(1)-dependent Ramachandran plot can be generally understood by combining the interaction of the side-chain Cγ/Oγ atom with two neighboring backbone peptide groups. Current all-atom force fields such as AMBER ff99sb-ILDN, ff03 and OPLS-AA/L do not reproduce these distributions well. A method has been developed by combining the φ, ψ plot of alanine with the influence of side-chain χ(1) rotamers to derive the local conformational features of various amino acids. It has been further applied to improve the OPLS-AA force field. The modified force field (OPLS-AA/C) reproduces experimental (3)J coupling constants for various short peptides quite well. It also better reproduces the temperature-dependence of the helix-coil transition for alanine-based peptides. The new force field can fold a series of peptides and proteins with various secondary structures to their experimental structures. MD simulations of several globular proteins using the improved force field give significantly less deviation (RMSD) to experimental structures. The results indicate that the local conformational features from coil libraries are valuable for
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.
NASA Astrophysics Data System (ADS)
Morgan, J. P.; de Monserrat, A.; Hall, R.; Taramon, J. M.; Perez-Gussinye, M.
2015-12-01
This work focuses on improving current 2D numerical approaches to modeling the boundary conditions associated with computing accurate deformation and melting associated with continental rifting. Recent models primarily use far-field boundary conditions that have been used for decades with little assessment of their effects on asthenospheric flow beneath the rifting region. All are clearly extremely oversimplified — Huismans and Buiter assume there is no vertical flow into the rifting region, with the asthenosphere flowing uniformly into the rifting region from the sides beneath lithosphere moving in the opposing direction, Armitage et al. and van Wijk use divergent velocities on the upper boundary to impose break-up within a Cartesian box, while other studies generally assume there is uniform horizontal flow away from the center of rifting, with uniform vertical flow replenishing the material pulled out of the sides of the computational region. All are likely to significantly shape the pattern of asthenospheric flow beneath the stretching lithosphere that is associated with pressure-release melting and rift volcanism. Thus while ALL may lead to similar predictions of the effects of crustal stretching and thinning, NONE may lead to accurate determination of the the asthenospheric flow and melting associated with lithospheric stretching and breakup. Here we discuss a suite of numerical experiments that compare these choices to likely more realistic boundary condition choices like the analytical solution for flow associated with two diverging plates stretching over a finite-width region, and a high-resolution 2-D region embedded within a cylindrical annulus 'whole mantle cross-section' at 5% extra numerical problem size. Our initial results imply that the choice of far-field boundary conditions does indeed significantly influence predicted melting distributions and melt volumes associated with continental breakup. For calculations including asthenospheric melting
Conformally-invariant scalar field with trace-free energy-momentum tensor in Robertson-Walker models
NASA Astrophysics Data System (ADS)
Singh, N. I.; Singh, N. B.
1992-02-01
Exact solutions of Einstein's field equations for a conformally-invariant scalar field with trace-free energy-momentum tensor is presented for the Robertson-Walker models with K = + 1, - 1. The physical properties of the solution are also studied
Wave functions of symmetry-protected topological phases from conformal field theories
NASA Astrophysics Data System (ADS)
Scaffidi, Thomas; Ringel, Zohar
2016-03-01
We propose a method for analyzing two-dimensional symmetry-protected topological (SPT) wave functions using a correspondence with conformal field theories (CFTs) and integrable lattice models. This method generalizes the CFT approach for the fractional quantum Hall effect wherein the wave-function amplitude is written as a many-operator correlator in the CFT. Adopting a bottom-up approach, we start from various known microscopic wave functions of SPTs with discrete symmetries and show how the CFT description emerges at large scale, thereby revealing a deep connection between group cocycles and critical, sometimes integrable, models. We show that the CFT describing the bulk wave function is often also the one describing the entanglement spectrum, but not always. Using a plasma analogy, we also prove the existence of hidden quasi-long-range order for a large class of SPTs. Finally, we show how response to symmetry fluxes is easily described in terms of the CFT.
Spherically-Symmetric Gravitational Fields in Conformal Gravity and Their Sources
NASA Astrophysics Data System (ADS)
Verbin, Yosef; Brihaye, Yves
Conformal Gravity1 (CG) was proposed as a possible alternative to Einstein gravity ("GR"), which may supply the proper framework for a solution to some of the most annoying problems of theoretical physics like those of the cosmological constant, the dark matter and the dark energy. It is based on the Weyl tensor Cκλμν such that the gravitational Lagrangian and the field equations are {L}_g = - 1/2αC_{κ λ μ ν } C^{κ λ μ ν }quad ; quad W_{μ ν } = {α}/{2}T_{μ ν } (1) where α is a dimensionless positive parameter, Tμν is the energy-momentum tensor and Bach tensor Wμν replaces the Einstein tensor of GR…
Out-of-time-ordered correlators and purity in rational conformal field theories
NASA Astrophysics Data System (ADS)
Caputa, Paweł; Numasawa, Tokiro; Veliz-Osorio, Alvaro
2016-11-01
In this paper we investigate measures of chaos and entanglement in rational conformal field theories in 1 + 1 dimensions. First, we derive a formula for the late time value of the out-of-time-ordered correlators for this class of theories. Our universal result can be expressed as a particular combination of the modular S-matrix elements known as anyon monodromy scalar. Next, in the explicit setup of an SUN Wess-Zumino-Witten model, we compare the late time behavior of the out-of-time-ordered correlators and the purity. Interestingly, in the large-c limit, the purity grows logarithmically as in holographic theories; in contrast, the out-of-time-ordered correlators remain, in general, nonvanishing.
Numerical tests of conjectures of conformal field theory for three-dimensional systems
NASA Astrophysics Data System (ADS)
Weigel, Martin; Janke, Wolfhard
1998-11-01
The concept of conformal field theory provides a general classification of statistical systems on two-dimensional geometries at the point of a continuous phase transition. Considering the finite-size scaling of certain special observables, one thus obtains not only the critical exponents but even the corresponding amplitudes of the divergences analytically. A first numerical analysis brought up the question whether analogous results can be obtained for those systems on three-dimensional manifolds. Using Monte Carlo simulations based on the Wolff single-cluster update algorithm we investigate the scaling properties of O(n) symmetric classical spin models on a three-dimensional, hyper-cylindrical geometry with a toroidal cross-section considering both periodic and antiperiodic boundary conditions. Studying the correlation lengths of the Ising, the XY, and the Heisenberg model, we find strong evidence for a scaling relation analogous to the two-dimensional case, but in contrast here for the systems with antiperiodic boundary conditions.
Bisht, Gobind; Nesterenko, Sergiy; Kulinsky, Lawrence; Madou, Marc
2012-08-01
Electrospinning is a versatile technique for production of nanofibers. However, it lacks the precision and control necessary for fabrication of nanofiber-based devices. The positional control of the nanofiber placement can be dramatically improved using low-voltage near-field electrospinning (LV-NFES). LV-NFES allows nanofibers to be patterned on 2D and 3D substrates. However, use of NFES requires low working distance between the electrospinning nozzle and substrate, manual jet initiation, and precise substrate movement to control fiber deposition. Environmental factors such as humidity also need to be controlled. We developed a computer-controlled automation strategy for LV-NFES to improve performance and reliability. With this setup, the user is able to control the relevant sensor and actuator parameters through a custom graphic user interface application programmed on the C#.NET platform. The stage movement can be programmed as to achieve any desired nanofiber pattern and thickness. The nanofiber generation step is initiated through a software-controlled linear actuator. Parameter setting files can be saved into an Excel sheet and can be used subsequently in running multiple experiments. Each experiment is automatically video recorded and stamped with the pertinent real-time parameters. Humidity is controlled with ±3% accuracy through a feedback loop. Further improvements, such as real-time droplet size control for feed rate regulation are in progress.
Yang, Xiaoxia; Zhai, Feng; Hu, Hai; Hu, Debo; Liu, Ruina; Zhang, Shunping; Sun, Mengtao; Sun, Zhipei; Chen, Jianing; Dai, Qing
2016-04-20
A new hybridized plasmon-phonon polariton mode in graphene/h-BN van der Waals heterostructures is presented, featuring the ultrahigh field confinement characteristic of the graphene plasmon and the long lifetime property of the h-BN transverse optical phonon. This enables an ultralong hybrid plasmon lifetime of up to 1.6 ps (with ultrahigh mode confinement up to >l0(2)/7000 and ultrasmall group velocity down to 0.001c, where c is the speed of light in vacuum), superior to any localized plasmon ever demonstrated.
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.
Spin pair geometry revealed by high-field DEER in the presence of conformational distributions
NASA Astrophysics Data System (ADS)
Polyhach, Ye.; Godt, A.; Bauer, C.; Jeschke, G.
2007-03-01
Orientation selection on two nitroxide-labelled shape-persistent molecules is demonstrated by high-field pulsed electron-electron double resonance experiments at a frequency of 95 GHz with a commercial spectrometer. The experiments are performed with fixed observer and pump frequencies by variation of the magnetic field, so that the variation of both the dipolar frequencies and the modulation depths can be analyzed. By applying the deadtime-free four-pulse double electron-electron resonance (DEER) sequence, the lineshapes of the dipolar spectra are obtained. In the investigated linear biradical and equilateral triradical the nitroxide labels undergo restricted dynamics, so that their relative orientations are not fixed, but are correlated to some extent. In this situation, the general dependence of the dipolar spectra on the observer field can be satisfyingly modelled by simple geometrical models that involve only one rotational degree of freedom for the biradical and two rotational degrees of freedom for the triradical. A somewhat better agreement of the dipolar lineshapes for the biradical is obtained by simulations based on a molecular dynamics trajectory. For the triradical, small but significant deviations of the lineshape are observed with both models, indicating that the technique can reveal deficiencies in modelling of the conformational ensemble of a macromolecule.
Conformational Entropy Mechanism for Periodic Motion of DNA under Constant-Field Gel Electrophoresis
NASA Astrophysics Data System (ADS)
Azuma, Ryuzo; Takayama, Hajime
2006-06-01
Entropic elasticity of a single charged polymer undergoing gel electrophoresis is a fundamental theme of polymer statistical physics since the discovery of “periodic” behavior in constant field gel electrophoresis (CFGE). In the present work we address the problem numerically by two steps. In the first step, we carry out Brownian dynamics (BD) simulations on CFGE by solving semi-microscopic Langevin equations of a polymer consisting of beads separated by a mean distance much smaller than the Kuhn length. Results are analyzed based on coarse-graining over the Kuhn length scale. We show the averaged elongation-contraction motion involves asymmetric V-shaped configurations whose shorter arm length depends on the field and the temperature consistently with what is expected when the BD chain is described by the freely-jointed chain (FJC) model with a suitable Kuhn length. To our knowledge, this is the first numerical confirmation of the FJC model itself from a submicroscopic description of polymer motion. The saturation of chain mobility in high fields agrees well with the nonlinear dependence of this shorter arm length on the field. In the second step, we discuss the periodic elongation-contraction motion of the coarse-grained chain by such a simplified model as a one-dimensional chain consisting of beads, elastic strings, and obstacles. The results from these two chain models indicate that the periodic elongation-contraction motion of DNA under CFGE is self-organized by a balance between the field force and the conformational entropic force.
A field-space conformal-solution method: Binary vapor-liquid phase behavior
NASA Astrophysics Data System (ADS)
Storvick, T. S.; Fox, J. R.
1990-01-01
The field-space conformal solution method provides an entirely new thermodynamic framework for the description of fluid mixtures in terms of the properties of a pure reference fluid. The utility and performance of the method are examined in the special case of vapor-liquid equilibrium correlation for simple mixtures. This is one of several cases in which field-space methods have numerical or theoretical advantages over methods presently used in mixture property correlation; only properties along the vapor pressure curve of the purefluid reference system are required for a complete description of the mixture phase behavior. Vapor-liquid equilibrium data for three binary hydrocarbon mixtures, n-butane + n-pentane, n-butane + n-hexane, and n-butane + n-octane, are correlated with a simple implementation of the method having two independent mixture parameters. Two pure-fluid equations of state, a Peng-Robinson equation and a 32-constant modified Benedict-Webb-Rubin equation, are tested as reference systems. The effects of differences in the quality of the reference system and of a range of mixture component size ratios are examined.
Tian, Mei-ling; Fang, Ting; Du, Mu-ying; Zhang, Fu-sheng
2016-04-01
To explore an efficient, safe, and speedy application of pulsed electric field (PEF) technology for enzymatic modification, effects of PEF treatment on the enzymatic activity, property and kinetic parameters of α-amylase were investigated. Conformational transitions were also studied with the aid of circular dichroism (CD) and fluorescence spectra. The maximum enzymatic activity of α-amylase was obtained under 15 kV/cm electric field intensity and 100 mL/min flow velocity PEF treatment, in which the enzymatic activity increased by 22.13 ± 1.14% compared with control. The activation effect could last for 18 h at 4 °C. PEF treatment could widen the range of optimum temperature for α-amylase, however, it barely exerted any effect on the optimum pH. On the other hand, α-amylase treated by PEF showed an increase of Vmax, t1/2 and ΔG, whereas a decrease of Km and k were observed. Furthermore, it can be observed from fluorescence and CD spectra that PEF treatment had increased the number of amino acid residues, especially that of tryptophan, on α-amylase surface with enhanced α-helices by 34.76% and decreased random coil by 12.04% on α-amylase when compared with that of untreated. These changes in structure had positive effect on enhancing α-amylase activity and property.
NASA Astrophysics Data System (ADS)
Wang, Dong; Zhang, Qiaosheng; Li, Yue; Wang, Yiwen; Zhu, Junming; Zhang, Shaomin; Zheng, Xiaoxiang
2014-06-01
Objective. Many serious concerns exist in the long-term stability of brain-machine interfaces (BMIs) based on spike signals (single unit activity, SUA; multi unit activity, MUA). Some studies showed local field potentials (LFPs) could offer a stable decoding performance. However, the decoding stability of LFPs was examined only when high quality spike signals were recorded. Here we aim to examine the long-term decoding stability of LFPs over a larger time scale when the quality of spike signals was from good to poor or even no spike was recorded. Approach. Neural signals were collected from motor cortex of three monkeys via silicon arrays over 230, 290 and 690 days post-implantation when they performed 2D center out task. To compare long-term stability between LFPs and spike signals, we examined them in neural signals characteristics, directional tuning properties and offline decoding performance, respectively. Main results. We observed slow decreasing trends in the number of LFP channels recorded and mean LFP power in different frequency bands when spike signals quality decayed over time. The number of significantly directional tuning LFP channels decreased more slowly than that of tuning SUA and MUA. The variable preferred directions for the same signal features across sessions indicated non-stationarity of neural activity. We also found that LFPs achieved better decoding performance than SUA and MUA in retrained decoder when the quality of spike signals seriously decayed. Especially, when no spike was recorded in one monkey after 671 days post-implantation, LFPs still provided some kinematic information. In addition, LFPs outperformed MUA in long-term decoding stability in a static decoder. Significance. Our results suggested that LFPs were more durable and could provide better decoding performance when spike signals quality seriously decayed. It might be due to their resistance to recording degradation and their high redundancy among channels.
Santangelo, Andrea; Provensi, Gustavo; Costa, Alessia; Blandina, Patrizio; Ricca, Valdo; Crescimanno, Giuseppe; Casarrubea, Maurizio; Passani, M Beatrice
2017-02-01
Markers of histaminergic dysregulation were found in several neuropsychiatric disorders characterized by repetitive behaviours, thoughts and stereotypies. We analysed the effect of acute histamine depletion by means of i. c.v. injections of alpha-fluoromethylhistidine, a blocker of histidine decarboxylase, on the temporal organization of motor sequences of CD1 mice behaviour in the open-field test. An ethogram encompassing 9 behavioural components was employed. Durations and frequencies were only slightly affected by treatments. However, as revealed by multivariate t-pattern analysis, histamine depletion was associated with a striking increase in the number of behavioural patterns. We found 42 patterns of different composition occurring, on average, 520.90 ± 50.23 times per mouse in the histamine depleted (HD) group, whereas controls showed 12 different patterns occurring on average 223.30 ± 20.64 times. Exploratory and grooming behaviours clustered separately, and the increased pattern complexity involved exclusively exploratory patterns. To test the hypothesis of a histamine-dopamine interplay on behavioural pattern phenotype, non-sedative doses of the D2/D3 antagonist sulpiride (12.5-25-50 mg/kg) were additionally administered to different groups of HD mice. Sulpiride counterbalanced the enhancement of exploratory patterns of different composition, but it did not affect the mean number of patterns at none of the doses used. Our results provide new insights on the role of histamine on repetitive behavioural sequences of freely moving mice. Histamine deficiency is correlated with a general enhancement of pattern complexity. This study supports a putative involvement of histamine in the pathophysiology of tics and related disorders.
Conklin, Chris J.; Middleton, Devon M.; Alizadeh, Mahdi; Finsterbusch, Jürgen; Raunig, David L.; Faro, Scott H.; Shah, Pallav; Krisa, Laura; Sinko, Rebecca; Delalic, Joan Z.; Mulcahey, M.J.; Mohamed, Feroze B.
2016-01-01
Magnetic resonance based diffusion imaging has been gaining more utility and clinical relevance over the past decade. Using conventional echo planar techniques, it is possible to acquire and characterize water diffusion within the central nervous system (CNS); namely in the form of Diffusion Weighted Imaging (DWI) and Diffusion Tensor Imaging (DTI). While each modality provides valuable clinical information in terms of the presence of diffusion and its directionality, both techniques are limited to assuming an ideal Gaussian distribution for water displacement with no intermolecular interactions. This assumption neglects pathological processes that are not Gaussian therefore reducing the amount of potentially clinically relevant information. Additions to the Gaussian distribution measured by the excess kurtosis, or peakedness, of the probabilistic model provide a better understanding of the underlying cellular structure. The objective of this work is to provide mathematical and experimental evidence that Diffusion Kurtosis Imaging (DKI) can offer additional information about the micromolecular environment of the pediatric spinal cord. This is accomplished by a more thorough characterization of the nature of random water displacement within the cord. A novel DKI imaging sequence based on a tilted 2D spatially selective radio frequency pulse providing reduced field of view (FOV) imaging was developed, implemented, and optimized on a 3 Tesla MRI scanner, and tested on pediatric subjects (healthy subjects: 15; patients with spinal cord injury (SCI):5). Software was developed and validated for post processing of the DKI images and estimation of the tensor parameters. The results show statistically significant differences in mean kurtosis (p < 0.01) and radial kurtosis (p < 0.01) between healthy subjects and subjects with SCI. DKI provides incremental and novel information over conventional diffusion acquisitions when coupled with higher order estimation algorithms
NASA Astrophysics Data System (ADS)
Savoini, P.; Lembege, B.
2013-12-01
The ion foreshock located upstream of the Earth's bow shock is populated with ions reflected back by the shock front with an high energy gain. In-situ spacecraft measurements have clearly established the existence of two distinct populations in the foreshock upstream of quasi-perpendicular shock region (i.e. for 45° ≤ ΘBn≤ 90°, where ΘBn is the angle between the shock normal and the upstream magnetostatic field): (i) field-aligned (';FAB') ion beams characterized by a gyrotropic distribution, and (ii) gyro-phase bunched (';GPB') ions characterized by a NON gyrotropic distribution, which exhibits a non-vanishing perpendicular bulk velocity. The purpose of the present work is to identify the possible sources of the different backstreaming ions and is based on the use of 2D PIC simulations of a curved shock, where full curvature effects, time of flight effects and both electrons and ions dynamics are fully described by a self consistent approach. Our analysis evidences that the two populations mentionned above may have different origins identified both in terms of interaction time and distance of penetration within the shock front. In particular, ours simulations evidence that "GPB" and ';FAB' populations are characterized by a short (Δinter= 1 to 2 tci) and much larger (Δinter= 1 to 10 tci) interaction time respectively, where τci is the ion upstream gyroperiod. In addition, a deeper statistical analysis of ion trajectories evidences that: (i) both populations can be discriminated in terms of injection angle into the shock front (i.e. defined between the local normal to the shock front and the gyration velocity vector at the time ions reach the front). Such a behavior explains how reflected ions can be splitted in the observed two populations "FAB" and "GPB". (ii) ion trajectories strongly differ between the "FAB" and "GPB" populations at the shock front. In particular, ';FAB' ions suffer multi-bounces whereas ';GPB '; ions make only one bounce. Such
NASA Technical Reports Server (NTRS)
Laskowski, B. C.; Jaffe, R. L.; Komornicki, A.
1985-01-01
The structure, torsional potentials, vibrational spectra, and harmonic force fields for s-cis and s-trans isomers of methacryloyl fluoride are examined to understand the conformational properties of the molecules and their relationship to macroscopic polymer properties. The structure is found to be in good agreement with experiment. It is shown by calculations that the energy difference between the cis and the transisomers is less than 1 kcal/mol at both the split valence and the split valence polarized levels, with the trans form favored. Analysis of the torsional potentials indicates that a rigid rotor model provides a reasonable description of the motion of the COF group in the molecule. The torsional barrier to interconvert the s-trans to the s-cis form is found to be 7.0 kcal/mol. A fit of the data to a three-term Fourier series shows that it is possible to reproduce the experimentally derived barrier, even though a direct determination indicates that the barrier is higher.
Parent Hamiltonians for lattice Halperin states from free-boson conformal field theories
NASA Astrophysics Data System (ADS)
Hackenbroich, Anna; Tu, Hong-Hao
2017-03-01
We introduce a family of many-body quantum states that describe interacting spin one-half hard-core particles with bosonic or fermionic statistics on arbitrary one- and two-dimensional lattices. The wave functions at lattice filling fraction ν = 2 / (2 m + 1) are derived from deformations of the Wess-Zumino-Witten model su (3)1 and are related to the (m + 1 , m + 1 , m) Halperin fractional quantum Hall states. We derive long-range SU(2) invariant parent Hamiltonians for these states which in two dimensions are chiral t-J-V models with additional three-body interaction terms. In one dimension we obtain a generalisation to open chains of a periodic inverse-square t-J-V model proposed in [25]. We observe that the gapless low-energy spectrum of this model and its open-boundary generalisation can be described by rapidity sets with the same generalised Pauli exclusion principle. A two-component compactified free boson conformal field theory is identified as the low-energy effective theory for the periodic inverse-square t-J-V model.
Constraining conformal field theories with a higher spin symmetry in d > 3 dimensions
NASA Astrophysics Data System (ADS)
Alba, Vasyl; Diab, Kenan
2016-03-01
We study unitary conformal field theories with a unique stress tensor and at least one higher-spin conserved current in d > 3 dimensions. We prove that every such theory contains an infinite number of higher-spin conserved currents of arbitrarily high spin, and that Ward identities generated by the conserved charges of these currents imply that the correlators of the stress tensor and the conserved currents of the theory must coincide with one of the following three possibilities: a) a theory of n free bosons (for some integer n), b) a theory of n free fermions, or c) a theory of nd-2/2 -forms. For d even, all three structures exist, but for d odd, it may be the case that the third structure (c) does not; if it does exist, it is unclear what theory, if any, realizes it. This is a generalization of the result proved in three dimensions by Maldacena and Zhiboedov [1]. This paper supersedes the previous paper by the authors [2].
Thermalization and revivals after a quantum quench in conformal field theory.
Cardy, John
2014-06-06
We consider a quantum quench in a finite system of length L described by a 1+1-dimensional conformal field theory (CFT), of central charge c, from a state with finite energy density corresponding to an inverse temperature β≪L. For times t such that ℓ/2
NASA Astrophysics Data System (ADS)
Dubail, J.; Santachiara, R.; Emig, T.
2017-03-01
Systems as diverse as binary mixtures and inclusions in biological membranes, and many more, can be described effectively by interacting spins. When the critical fluctuations in these systems are constrained by boundary conditions, critical Casimir forces (CCF) emerge. Here we analyze CCF between boundaries with alternating boundary conditions in two dimensions, employing conformal field theory (CFT). After presenting the concept of boundary changing operators, we specifically consider two different boundary configurations for a strip of critical Ising spins: (I) alternating equi-sized domains of up and down spins on both sides of the strip, with a possible lateral shift, and (II) alternating domains of up and down spins of different size on one side and homogeneously fixed spins on the other side of the strip. Asymptotic results for the CCF at small and large distances are derived. We introduce a novel modified Szegö formula for determinants of real antisymmetric block Toeplitz matrices to obtain the exact CCF and the corresponding scaling functions at all distances. We demonstrate the existence of a surface renormalization group flow between universal force amplitudes of different magnitude and sign. The Casimir force can vanish at a stable equilibrium position that can be controlled by parameters of the boundary conditions. Lateral Casimir forces assume a universal simple cosine form at large separations.
Marginal fluctuations as instantons on M2/D2-branes
NASA Astrophysics Data System (ADS)
Naghdi, M.
2014-03-01
We introduce some (anti-) M/D-branes through turning on the corresponding field strengths of the 11- and 10-dimensional supergravity theories over spaces, where we use and for the internal spaces. Indeed, when we add M2/D2-branes on the same directions with the near horizon branes of the Aharony-Bergman-Jafferis-Maldacena model, all symmetries and supersymmetries are preserved trivially. In this case, we obtain a localized object just in the horizon. This normalizable bulk massless scalar mode is a singlet of and , and it agrees with a marginal boundary operator of the conformal dimension of . However, after performing a special conformal transformation, we see that the solution is localized in the Euclideanized space and is attributable to the included anti-M2/D2-branes, which are also necessary to ensure that there is no back-reaction. The resultant theory now breaks all supersymmetries to , while the other symmetries are so preserved. The dual boundary operator is then set up from the skew-whiffing of the representations and for the supercharges and scalars, respectively, while the fermions remain fixed in of the original theory. Besides, we also address another alternate bulk to boundary matching procedure through turning on one of the gauge fields of the full gauge group along the same lines with a similar situation to the one faced in the AdS/CFT correspondence. The latter approach covers the difficulty already faced with in the bulk-boundary matching procedure for as well.
NASA Astrophysics Data System (ADS)
Frauendiener, Jörg
2004-12-01
The notion of conformal infinity has a long history within the research in Einstein's theory of gravity. Today, "conformal infinity" is related to almost all other branches of research in general relativity, from quantisation procedures to abstract mathematical issues to numerical applications. This review article attempts to show how this concept gradually and inevitably evolved from physical issues, namely the need to understand gravitational radiation and isolated systems within the theory of gravitation, and how it lends itself very naturally to the solution of radiation problems in numerical relativity. The fundamental concept of null-infinity is introduced. Friedrich's regular conformal field equations are presented and various initial value problems for them are discussed. Finally, it is shown that the conformal field equations provide a very powerful method within numerical relativity to study global problems such as gravitational wave propagation and detection.
Series of (2+1)-dimensional stable self-dual interacting conformal field theories
NASA Astrophysics Data System (ADS)
Cheng, Meng; Xu, Cenke
2016-12-01
Using the duality between seemingly different (2+1)-dimensional [(2 +1 )d ] conformal field theories (CFT) proposed recently [D. T. Son, Phys. Rev. X 5, 031027 (2015), 10.1103/PhysRevX.5.031027; M. A. Metlitski and A. Vishwanath, Phys. Rev. B 93, 245151 (2016), 10.1103/PhysRevB.93.245151; C. Wang and T. Senthil, Phys. Rev. X 6, 011034 (2015), 10.1103/PhysRevX.6.011034; C. Wang and T. Senthil, Phys. Rev. X 5, 041031 (2015), 10.1103/PhysRevX.5.041031; C. Wang and T. Senthil, Phys. Rev. B 93, 085110 (2016), 10.1103/PhysRevB.93.085110; C. Xu and Y.-Z. You, Phys. Rev. B 92, 220416 (2015), 10.1103/PhysRevB.92.220416; D. F. Mross et al., Phys. Rev. Lett. 117, 016802 (2016), 10.1103/PhysRevLett.117.016802; A. Karch and D. Tong, arXiv:1606.01893; N. Seiberg et al., arXiv:1606.01989; P.-S. Hsin and N. Seiberg, arXiv:1607.07457], we study a series of (2 +1 )d stable self-dual interacting CFTs. These CFTs can be realized (for instance) on the boundary of the 3 d bosonic topological insulator protected by U(1) and time-reversal symmetry (T ), and they remain stable as long as these symmetries are preserved. When realized as a boundary system, these CFTs can be driven into anomalous fractional quantum Hall states once T is broken. We demonstrate that the newly proposed dualities allow us to study these CFTs quantitatively through a controlled calculation, without relying on a large flavor number of matter fields. We also propose a numerical test for our results, which would provide strong evidence for the originally proposed duality between Dirac fermion and QED.
Three-Dimensional Dose Optimization for Noncoplanar Treatment Planning with Conformal Fields.
NASA Astrophysics Data System (ADS)
Ma, Ying-Chang L.
1990-01-01
Recent advances in imaging techniques, especially three dimensional reconstruction of CT images, have made precision tumor localization feasible. These imaging techniques along with developments in computer controlled radiation treatment machines have provided an important thrust in developing better techniques for cancer treatment. This often requires a complex noncoplanar beam arrangements and elaborate treatment planning, which, unfortunately, are time consuming, costly and dependent on operator expertise and experience. A reliable operator-independent dose optimization tool is therefore desirable, especially for 3D treatment planning. In this dissertation, several approaches (linear programming, quadratic programming, and direct search methods) of computer optimization using various criteria including least sire fitting on the 90% isodose to target periphery, dose uniformity, and integral dose are presented. All of these methods are subject to restrictions on the upper limit of the dose to critical organs. In the quadratic programming approach, Kuhn-Tucker theory was employed to convert the quadratic problem into one which permits application of the very powerful, revised simplex method. Several examples are used to analyze the effectiveness of these dose optimization approaches. The studies show that the quadratic programming approach with the criteria of least square fitting and critical organ constraints is superior in efficiency for dose optimization in 3D treatment planning, particularly for cases with a large number of beams. Use of least square fitting allows one to deduce optimized plans for irregularly shaped targets by employing a multi-isocentric technique. Our studies also illustrate the advantages of using irregular conformal fields, optimized beam energy, and noncoplanar beam arrangements in contrast to the conventional treatment which uses a symmetrical rectangular collimator, fixed beam energy, and coplanar beam arrangements. Optimized plans can
NASA Astrophysics Data System (ADS)
Shah, Jainil; Mann, Steve D.; Tornai, Martin P.; Richmond, Michelle; Zentai, George
2014-03-01
The 2D and 3D modulation transfer functions (MTFs) of a custom made, large 40x30cm2 area, 600- micron CsI-TFT based flat panel imager having 127-micron pixellation, along with the micro-fiber scintillator structure, were characterized in detail using various techniques. The larger area detector yields a reconstructed FOV of 25cm diameter with an 80cm SID in CT mode. The MTFs were determined with 1x1 (intrinsic) binning. The 2D MTFs were determined using a 50.8 micron tungsten wire and a solid lead edge, and the 3D MTF was measured using a custom made phantom consisting of three nearly orthogonal 50.8 micron tungsten wires suspended in an acrylic cubic frame. The 2D projection data was reconstructed using an iterative OSC algorithm using 16 subsets and 5 iterations. As additional verification of the resolution, along with scatter, the Catphan® phantom was also imaged and reconstructed with identical parameters. The measured 2D MTF was ~4% using the wire technique and ~1% using the edge technique at the 3.94 lp/mm Nyquist cut-off frequency. The average 3D MTF measured along the wires was ~8% at the Nyquist. At 50% MTF, the resolutions were 1.2 and 2.1 lp/mm in 2D and 3D, respectively. In the Catphan® phantom, the 1.7 lp/mm bars were easily observed. Lastly, the 3D MTF measured on the three wires has an observed 5.9% RMSD, indicating that the resolution of the imaging system is uniform and spatially independent. This high performance detector is integrated into a dedicated breast SPECT-CT imaging system.
Friedan, D.H.; Martinec, E.J.; Shenker, S.H.
1988-12-01
The present contract supported work by Daniel H. Frieden, Emil J, Martinec and Stephen H. Shenker (principal investigators), Research Associates, and graduate students in theoretical physics at the University of Chicago. Research has been conducted in areas of string theory and two dimensional conformal and superconformal field theory. The ultimate objectives have been: to expose the fundamental structure of string theory so as to eventually make possible effective nonperturbative calculations and thus a comparison of sting theory with experiment, the complete classification of all two dimensional conformal and superconformal field theories thus giving a complete description of all classical ground states of string and of all possible two (and 1 + 1) dimensional critical phenomena, and the development of methods to describe, construct and solve two dimensional field theories. Work has also been done on skyrmion and strong interaction physics.
NASA Astrophysics Data System (ADS)
Friedan, Daniel
2010-03-01
An abstract argument is offered that the ideal physical systems for asymptotically large-scale quantum computers are near-critical quantum circuits, critical in the bulk, whose bulk universality classes are described by 1+1d conformal field theories. One in particular -- the Monster conformal field theory -- is especially ideal, because all of its bulk couplings are irrelevant.
𝜖-expansion in critical ϕ3-theory on real projective space from conformal field theory
NASA Astrophysics Data System (ADS)
Hasegawa, Chika; Nakayama, Yu
2017-03-01
We use a compatibility between the conformal symmetry and the equations of motion to solve the one-point function in the critical ϕ3-theory (a.k.a. the critical Lee-Yang model) on the d = 6 ‑ 𝜖 dimensional real projective space to the first nontrivial order in the 𝜖-expansion. It reproduces the conventional perturbation theory and agrees with the numerical conformal bootstrap result.
Ansarihadipour, Hadi; Bayatiani, Mohamadreza
2016-01-01
Background Electromagnetic fields (EMF) are associated with oxidative stress, which is in turn associated with reactive oxygen species (ROS), anemia, and hypoxia. Objectives This study focused on the synergistic effects of lead ions and EMF on oxidative modifications in hemoglobin (Hb) and plasma proteins. Patients and Methods In this experimental study, the blood samples were obtained from age- and sex-matched healthy subjects at Arak University of Medical Sciences, Arak, Iran. The collected bloods were prepared as 55 samples and then divided into different groups for incubating with 0 to 100 uM of lead ions in 2 mT and 50 Hz of EMF for 120 minutes. The carbonyl group was determined to be an oxidative biomarker in plasma proteins. The ferric reducing ability of plasma (FRAP) was considered to be an antioxidant power of human plasma. The conformational changes in hemoglobin, met-Hb, and hemichrome were considered to be oxidative markers in red blood cells. To predict the factors affecting the oxyHb, the artificial neural network (MLP: 11,2,2,1) in SPSS software was applied. Results The test subjects showed increased concentrations of metHb (1.8 ± 0.19 vs. 1.36 ± 0.25) and hemichrome (6.01 ± 0.57) in relation to the control subjects. The decreased absorbance at 340 nm (0.88 ± 0.09 vs. 1.07 ± 0.08) demonstrated the reduced interaction between the globin chain and the heme ring. The decreased absorbance at 420 nm (Soret band) (2.96 ± 0.13) and the increased absorbance at 630 nm (0.07 ± 0.002 vs. 0.064 ± 0.005) indicated the conversion of oxyHb to metHb, which confirmed the oxidative damage to the erythrocytes. The linear regression analysis showed significant positive correlations between lead concentration and the percentage of plasma carbonyl content (R2 = 0.96), the relation of plasma carbonyl content to Hb absorbance at 630 nm (R2 = 0.97), and the relation of plasma carbonyl content to metHb concentration (R2 = 0.95) after 120 minutes incubation with lead
Not Available
1990-01-01
A very theoretical description is given of research in two- dimensional critical phenomena and conformal field theory. Major progress is reported in the field of fluctuating two-dimensional surfaces. A discretized representation of fluctuating geometry is used where surfaces are represented by triangulations; continuum surfaces are recovered by taking the size of the triangles to zero. One of the central goals of the theory of critical phenomena is to find all possible universality classes of n-dimensional critical phenomena; this goal has been translated into the problem of clasifying all possible scale-invariant euclidean quantum field theories. (RWR)
NASA Technical Reports Server (NTRS)
Thompson David S.; Soni, Bharat K.
2001-01-01
An integrated geometry/grid/simulation software package, ICEG2D, is being developed to automate computational fluid dynamics (CFD) simulations for single- and multi-element airfoils with ice accretions. The current version, ICEG213 (v2.0), was designed to automatically perform four primary functions: (1) generate a grid-ready surface definition based on the geometrical characteristics of the iced airfoil surface, (2) generate high-quality structured and generalized grids starting from a defined surface definition, (3) generate the input and restart files needed to run the structured grid CFD solver NPARC or the generalized grid CFD solver HYBFL2D, and (4) using the flow solutions, generate solution-adaptive grids. ICEG2D (v2.0) can be operated in either a batch mode using a script file or in an interactive mode by entering directives from a command line within a Unix shell. This report summarizes activities completed in the first two years of a three-year research and development program to address automation issues related to CFD simulations for airfoils with ice accretions. As well as describing the technology employed in the software, this document serves as a users manual providing installation and operating instructions. An evaluation of the software is also presented.
NASA Astrophysics Data System (ADS)
Du, Xinyu; Zhao, Chunlin; Zhang, Jinxi; Ren, Kailiang
2016-10-01
In this investigation, the chain conformation transformation of the piezoelectric polymer of a poly(L-Lactic Acid) (PLLA) film was analyzed under an electric field for the first time using infrared spectroscopy. It is revealed that the piezoelectric shear mode coefficient d14 (˜10 pC/N) of a stretched α form PLLA film mainly comes from the rotation of C O dipoles inside the polymer main chain. The reorientation of the dipoles causes the deformation of the crystal structure, which corresponds to a shear mode strain macroscopically in the PLLA film along a 45° direction to the polymer length. The back-bone of the molecular chain keeps its own conformation of a 103 helix under an external field up to 100 MV/m.
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.
2005-08-01
that compared to customized electron bolu s radiotherapy for post-mastectomy irradiation, ECT with multi-energy, multi-segmente d treatment fields has...PTV dos e homogeneity was quite good . Use of the treatment plan modification techniques improved dose sparin g for the non-target portion of the...phantom . For the patient treatment plans, the algorithm provided acceptable results for PTV conformality and dose homogeneity, in comparison to the bolus
NASA Astrophysics Data System (ADS)
Luna Acosta, German Aurelio
The masses of observed hadrons are fitted according to the kinematic predictions of Conformal Relativity. The hypothesis gives a remarkably good fit. The isospin SU(2) gauge invariant Lagrangian L(,(pi)NN)(x,(lamda)) is used in the calculation of d(sigma)/d(OMEGA) to 2nd-order Feynman graphs for simplified models of (pi)N(--->)(pi)N. The resulting infinite mass sums over the nucleon (Conformal) families are done via the Generalized-Sommerfeld-Watson Transform Theorem. Even though the models are too simple to be realistic, they indicate that if (DELTA)-internal lines were to be included, 2nd-order Feynman graphs may reproduce the experimental data qualitatively. The energy -dependence of the propagator and couplings in Conformal QFT is different from that of ordinary QFT. Suggestions for further work are made in the areas of ultra-violet divergences and OPEC calculations.
Bdzil, John Bohdan
2016-09-21
The full level-set function code, DSD3D, is fully described in LA-14336 (2007) [1]. This ASCI-supported, DSD code project was the last such LANL DSD code project that I was involved with before my retirement in 2007. My part in the project was to design and build the core DSD3D solver, which was to include a robust DSD boundary condition treatment. A robust boundary condition treatment was required, since for an important local “customer,” the only description of the explosives’ boundary was through volume fraction data. Given this requirement, the accuracy issues I had encountered with our “fast-tube,” narrowband, DSD2D solver, and the difficulty we had building an efficient MPI-parallel version of the narrowband DSD2D, I decided DSD3D should be built as a full level-set function code, using a totally local DSD boundary condition algorithm for the level-set function, phi, which did not rely on the gradient of the level-set function being one, |grad(phi)| = 1. The narrowband DSD2D solver was built on the assumption that |grad(phi)| could be driven to one, and near the boundaries of the explosive this condition was not being satisfied. Since the narrowband is typically no more than10*dx wide, narrowband methods are discrete methods with a fixed, non-resolvable error, where the error is related to the thickness of the band: the narrower the band the larger the errors. Such a solution represents a discrete approximation to the true solution and does not limit to the solution of the underlying PDEs under grid resolution.The full level-set function code, DSD3D, is fully described in LA-14336 (2007) [1]. This ASCI-supported, DSD code project was the last such LANL DSD code project that I was involved with before my retirement in 2007. My part in the project was to design and build the core DSD3D solver, which was to include a robust DSD boundary condition treatment. A robust boundary condition treatment was required, since for an important local
On the field description of conformal Galilean particle with intrinsic rotations
Kireev, A.N.; Takahashi, Y. . Theoretical Physics Inst.)
1992-05-30
This paper reports that a fiber-preserving realization of conformal extension of the Galilei algebra is found in the presence of intrinsic rotations. The Lagrangian density and the conservation laws of a non-relativistic spinning particles are constructed explicitly.
NASA Astrophysics Data System (ADS)
Rajabpour, M. A.
2016-12-01
We calculate formation probabilities of the ground state of the finite size quantum critical chains using conformal field theory (CFT) techniques. In particular, we calculate the formation probability of one interval in the finite open chain and also formation probability of two disjoint intervals in a finite periodic system. The presented formulas can be also interpreted as the Casimir energy of needles in particular geometries. We numerically check the validity of the exact CFT results in the case of the transverse field Ising chain.
Fröb, Markus B.; Verdaguer, Enric E-mail: enric.verdaguer@ub.edu
2016-03-01
We derive the leading quantum corrections to the gravitational potentials in a de Sitter background, due to the vacuum polarization from loops of conformal fields. Our results are valid for arbitrary conformal theories, even strongly interacting ones, and are expressed using the coefficients b and b' appearing in the trace anomaly. Apart from the de Sitter generalization of the known flat-space results, we find two additional contributions: one which depends on the finite coefficients of terms quadratic in the curvature appearing in the renormalized effective action, and one which grows logarithmically with physical distance. While the first contribution corresponds to a rescaling of the effective mass, the second contribution leads to a faster fall-off of the Newton potential at large distances, and is potentially measurable.
NASA Astrophysics Data System (ADS)
Dowker, J. S.
2016-04-01
I compute the conformal weights of the twist operators of free scalar fields for charged Rényi entropy in both odd and even dimensions. Explicit expressions can be found, in odd dimensions as a function of the chemical potential in the absence of a conical singularity and thence by images for all integer coverings. This method, developed some time ago, is equivalent, in results, to the replica technique. A review is given. The same method applies for even dimensions but a general form is more immediately available. For no chemical potential, the closed form in the covering order is written in an alternative way related to old trigonometric sums. Some derivatives are obtained. An analytical proof is given of a conjecture made by Bueno, Myers and Witczak-Krempa regarding the relation between the conformal weights and a corner coefficient (a universal quantity) in the Rényi entropy.
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.
ERIC Educational Resources Information Center
STILWELL, ROBERT
PARTICIPANTS IN THE 1966 NDEA LANGUAGE INSTITUTE HELD AT WEST VIRGINIA UNIVERSITY WERE THOSE SECONDARY SCHOOL TEACHERS WHO HAD PREVIOUSLY ATTENDED AN NDEA INSTITUTE FOR ADVANCED TRAINING IN THEIR PRINCIPAL LANGUAGE TEACHING FIELD, BUT WHO FROM CHOICE OR NECESSITY HAD BEEN ASSIGNED FRENCH OR SPANISH AS A SECOND TEACHING FIELD. THE REPORT OF THIS…
Magnetic field driven 2D-3D crossover in the S =1/2 frustrated chain magnet LiCuVO4
NASA Astrophysics Data System (ADS)
Prozorova, L. A.; Sosin, S. S.; Svistov, L. E.; Büttgen, N.; Kemper, J. B.; Reyes, A. P.; Riggs, S.; Prokofiev, A.; Petrenko, O. A.
2015-05-01
We report on a heat-capacity study of high-quality single-crystal samples of LiCuVO4—a frustrated spin S =1/2 chain system—in a magnetic field amounting to 3/4 of the saturation field. A detailed examination of magnetic phase transitions observed in this field range shows that although the low-field helical state clearly has three-dimensional properties, the field-induced spin-modulated phase turns out to be quasi-two-dimensional. The model proposed in this paper allows one to qualitatively understand this crossover, thus eliminating the presently existing contradictions in the interpretations of NMR and neutron-scattering measurements.
James R. Wood; T.J. Bornhorst; William B. Harrison; W. Quinlan
2002-04-01
The fault study continues to find more faults and develop new techniques to visualize them. Data from the Dundee Formation has been used to document 11 major faults in the Michigan Basin which have now been verified using data from other horizons. These faults control the locations of many of the large anticlinal structures in the Michigan Basin and likely controlled fluid movements as well. The surface geochemistry program is also moving along well with emphasis on measuring samples collected last sampling season. The new GC laboratory is now functional and has been fully staffed as of December. The annual project review was held March 7-9 in Tampa, Florida. Contracts are being prepared for drilling the Bower's prospects in Isabella County, Michigan, this spring or summer. A request was made to extend the scope of the project to include the Willison Basin. A demonstration well has been suggested in Burke County, N. Dakota, following a review of 2D seismic and surface geochem. A 3D seismic survey is scheduled for the prospect.
James R. Wood; A. Wylie; W. Quinlan
2004-10-01
One of the principal objectives of this demonstration project is to test surface geochemical techniques for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. During this reporting period, microbial samples were collected from the Trusty Steed prospect area in Grand Traverse County, Michigan. The samples were analyzed using the Microbial Oil Surveying Technique (MOST) technique and revealed only a local (1-point) anomaly. A decision to resample over that point is pending, but drilling has been postponed for the time being. The main news this reporting period is that in the Bear Lake area, northwest Michigan, Federated Oil & Gas Properties' Charlich-Fauble 2-9HD horizontal lateral, has cumulative production of more than 72,000 barrels of oil and is still producing 50 to 75 bopd from a Silurian Niagaran reef reservoir eighteen months after the well was completed. Surface geochemical surveys conducted in the demonstration area were consistent with production results although the ultimate decision to drill was based on interpretation of conventional subsurface and 2D seismic data. The surface geochemical techniques employed were Solid Phase MicroExtraction (SPME) and MOST. The geochemical results have been submitted to World Oil for publication. New geochemical surveys are planned for November in the Springdale quadrangle in Manistee County, Michigan. These surveys will concentrate on sampling over the trace of the proposed horizontal wells rather than a broad grid survey.
Kahn, K; Bruice, T C
2000-08-01
The molecular structures and barriers for the internal rotation around the OC-CO single bond in four alpha-ketoamides and eight alpha-ketocarbonyls have been determined from the MP3/aug-cc-pVDZ and MP2/aug-cc-pVDZ calculations. Alpha-ketocarbonyls with non-bulky substituents adopt planar conformations with two carbonyl oxygens in s-trans arrangement. The s-cis conformation is significantly less stable due to the electrostatic repulsion between the two carbonyl groups. Primary and secondary alpha-ketoamides are planar when the substituent at the carbonyl carbon is hydrogen or methyl group but tertiary alpha-ketoamides adopt a conformation where the OC-CO unit is significantly bent. Based on current ab initio structural data, a set of OPLS-AA force field parameters has been derived. These parameters can be used for the modeling of a variety of alpha-ketoamide or alpha-ketocarbonyl containing drugs such as novel protease inhibitors or neuroregenerative polyketides.
James R. Wood; W. Quinlan
2003-01-01
Presented in this quarterly report is the Case History and Well Summary for the Vernon Field demonstration project in Isabella County, Michigan. This new case history and well summary format organizes and presents the technical and historical details of the Vernon Field demonstration, as well as the field demonstration results and the applicability of these results to other demonstration projects. This format could be duplicated for other demonstration projects and will be used on all subsequent field demonstrations as they near completion. Planning for the annual project meeting in Tampa, Florida has begun. This meeting will be held March 7-9, 2003 at the same site as the last three meetings. The goals of this project were to: (1) test the use of multi-lateral wells to recover bypassed hydrocarbons and (2) to access the potential of using surface geochemistry to reduce drilling risk. Two new demonstration wells, the State-Smock and the Bowers 4-25, were drilled to test the Dundee Formation at Vernon Field for bypassed oil. Neither well was commercial, although both produced hydrocarbon shows. An extensive geochemical survey in the vicinity of Vernon Field, covering much of Isabella County, has produced a base map for interpretation of anomalies in Michigan. Several potential new anomalies were discovered that could be further investigated.
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.
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.
Magnetic-field-induced stripe order and a 2D vortex glass phase in La1.905 Ba 0.095 CuO 4
NASA Astrophysics Data System (ADS)
Tranquada, John; Wen, Jinsheng; Jie, Qing; Han, Su Jung; Li, Qiang; Huecker, Markus; Xu, Zhijun; Zhang, Liyuan; Gu, Genda; Zimmermann, M. V.; Singh, D. K.
2011-03-01
We have measured the resistivity parallel and perpendicular to the Cu O2 planes in La 1.905 Ba 0.095 Cu O4 (Tc = 32 K) as a function of perpendicular magnetic field. We have discovered a significant regime of field and temperature where the perpendicular resistivity is finite (and large) but the parallel resistivity is zero. This regime appears to correspond to a quasi-two-dimensional vortex glass phase, a state that theory predicts cannot exist at finite temperature. It seems to be stabilized by field-induced charge and spin stripe order, which we have detected with x-ray and neutron diffraction, respectively. Supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC02-98CH10886.
NASA Astrophysics Data System (ADS)
Xu, Shuang; Zhao, Dong-xia; Gong, Li-dong; Liu, Cui; Yang, Zhong-Zhi
2015-01-01
ABEEMσπ polarizable force field (PFF) with fluctuating charges works well for searching stable conformations of Val-dipeptide and Val-tripeptide, showing importance of the polarization. The results demonstrate that ABEEMσπ PFF is able to search out all the 6 types of stable conformations of Val-dipeptide and 34 types of stable conformations of Val-tripeptide that are just all exactly found by the calculations of ab initio B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) methods. In contrast, the force fields with the fixed-charges (FC), such as ABEEMσπ-FC, AMBER-FC 99sb and OPLS/AA-FC force fields can only search out less or much less numbers of stable conformations for them.
NASA Astrophysics Data System (ADS)
Kumagai, I.; Yanagisawa, T.; Kurita, K.
2002-12-01
Both numerical and experimental models of thermal plumes suggest that mantle plumes entrain surrounding mantle and their morphology (temperature and compositional fields in the plume head) evolves as they rise. Recent geochemical and isotopic studies of mantle plume products have revealed mixing of the ambient mantle with the primitive plume source. In order to make a quantitative comparison of the geophysical modeling with geological evidences, it is desired to show a precise image of spatial and temporal evolution of temperature and compositional fields in the plumes. Here, we present preliminary results of our laboratory experiments on thermal starting plumes using a quantitative technique of digital image processing. By coupling Particle Image Velocimetry (PIV) with Laser Induced Fluorescence (LIF) we can measure simultaneous 2-dimensional transient velocity and temperature fields in a thermal plume. Our experiments were conducted in a transparent rectangular tank containing a viscous fluid. Buoyancy in the form of heat was injected into the fluid by operating a heater at the base of the tank. The flow was marked with tracer particles for velocity and with the fluorescence dye, Rhodamine B, for temperature measurements. The particles and the fluorescence dye were illuminated and exited by a thin vertical sheet of laser light that was oriented to contain the axis of symmetry. We succeeded in simultaneous measurements of ascent velocity of the plume head, precise velocity field within the plume head, and evolution of the temperature field. This makes clear their relation and is useful for considering the entrainment process of plumes. Our aim of this study is to clarify the physics of entrainment and mixing phenomena of starting plumes, and to make quantitative geophysical models of mantle plumes connecting with geological and seismic evidences. In this presentation, we will show that this quantitative technique is a powerful tool for approaching these issues.
James R. Wood; T.J. Bornhorst; S.D. Chittichk; William B. Harrison; W. Quinlan
2001-01-01
The geochemical sampling team collected additional 148 samples at Vernon Field along 5 new traverses. Most of the locations were sampled for three types of analyses: microbial, iodine and enzyme leach; no results from the second batch of samples were available in time for this report. In addition to the sampling, a study was begun on the feasibility of collecting and analyzing hydrocarbon gases (C1-C8) directly. Although several companies offer these services, the cost ($200-300/sample w/o sampling fee) is high, on par with the cost of a 3D seismic survey, and may not include the raw data. However direct sampling of reservoir gases collecting in the soil appear to offer the best approach and should be included in this study. It would probably work well at Vernon Field. It may be possible to lower costs considerably; initial estimates of $20/sample for GCMS (Gas Chromatography--mass spectrometry) analysis are attractive and might induce to Michigan producers to include soil surveys in their routine field work-ups. A complete set of digital data was assembled for Vernon Field and nearby locations. The set consists of well locations, formation top picks, lithologies and scanned images of driller's reports and scout tickets. Well logs are still being located. The annual meeting for the Class Revisit work group is tentatively scheduled for the week of March 1-7 in Tampa, Fl. By that time all of the geochemical data will be available and final decisions regarding drilling can be made.
James R. Wood; W. Quinlan
2003-07-01
The principal objective of this demonstration project is to test surface geochemical techniques for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. As part of the project, a field demonstration was undertaken to assess the validity and usefulness of the microbial surface geochemical technique. The surface geochemistry data showed a strong anomaly in the Myrtle Beach area that would justify drilling by itself and even more so in conjunction with the structural interpretation from the 3D seismic data. The Myrtle Beach geochemical survey indicated a good to excellent prospect which was confirmed by drilling. Presented in this quarterly report is the Case History and Well Summary for the Myrtle Beach area in Burke County, North Dakota. This case history presents the important technical details regarding the geochemistry and the two vertical wells that are part of this field demonstration, and the applicability of these results to other demonstration projects. This format could be duplicated for other demonstration projects and is being used on all subsequent field demonstrations as they near completion.
James R. Wood; W. Quinlan
2003-04-01
The principal objective of the study was to test a new analytical technique, Solid-Phase Microextraction (SPME), for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. This involved measuring the effectiveness of SPME to extract hydrocarbons under controlled conditions in the laboratory. As part of the study, a field demonstration was undertaken to assess the validity and usefulness of the laboratory results. Presented in this quarterly report is the condensed version of the Case History and Well Summary for the Bear Lake area in Manistee County, Michigan. The full version will be in the annual report. The condensed case history presents the important technical details regarding the geochemistry and horizontal lateral for Bear Lake, as well as the field demonstration results and the applicability of these results to other demonstration projects. This format could be duplicated for other demonstration projects and will be used on all subsequent field demonstrations as they near completion.
NASA Astrophysics Data System (ADS)
De Wilde, Juray; Lorant, Christophe; Descamps, Pierre
2017-04-01
In atmospheric-pressure plasma reactors, the flow dynamics can be complex, determine the reactor performance and complicate scale-up. Coupling computational fluid dynamics to the calculation of the electric field and plasma chemistry is challenging because of the numerical stiffness introduced by the difference in time scale of the different phenomena involved. Focusing on low-temperature, atmospheric-pressure pure nitrogen plasma, a model and model reduction based solution strategy to deal with the numerical stiffness are presented and evaluated. The influence of the electric field on the flow dynamics and species concentration fields is first qualitatively studied by means of 2D simulations of a sharp-end plate-to-plane configuration. Next, a specific reactor prototype for low-temperature, atmospheric-pressure plasma-enhanced chemical vapor deposition for in-line surface treatments is simulated to illustrate the importance of accounting for the detailed flow dynamics.
Jiang, Nan; Ma, Jing
2008-10-09
The solution conformation of alpha-conotoxin GI and its two single disulfide analogues are simulated using a polarizable force field in combination with the molecular fragmentation quantum chemical calculation. The polarizability is explicitly described by allowing the partial charges and fragment dipole moments to be variables, with values coming from the linear-scaling energy-based molecular fragmentation calculations at the B3LYP/6-31G(d) level. In comparison with the full quantum chemical calculations, the fragmentation approaches can yield precise ground-state energies, dipole moments, and static polarizabilities for peptides. The B3LYP/6-31G(d) charges and fragment-centered dipole moments are introduced in calculations of electrostatic terms in both AmberFF03 and OPLS force fields. Our test calculations on the gas-phase glucagon (PDB code: 1gcn) and solvated alpha-conotoxin GI (PDB code: 1not) demonstrate that the present polarization model is capable of describing the structural properties (such as the relative conformational energies, intramolecular hydrogen bonds, and disulfide bonds) with accuracy comparable to some other polarizable force fields (ABEEM/MM and OPLS-PFF) and the quantum mechanics/molecular mechanics (QM/MM) hybrid model. The employment of fragment-centered dipole moments in calculations of dipole-dipole interactions can save computational time in comparison with those polarization models using atom-centered dipole moments without much loss of accuracy. The molecular dynamics simulations using the polarizable force field demonstrate that two single disulfide GI analogues are more flexible and less structured than the native alpha-conotoxin GI, in agreement with NMR experiments. The polarization effect is important in simulations of the folding/unfolding process of solvated proteins.
Fattal, D R; Ben-Shaul, A
1994-01-01
A molecular, mean-field theory of chain packing statistics in aggregates of amphiphilic molecules is applied to calculate the conformational properties of the lipid chains comprising the hydrophobic cores of dipalmitoyl-phosphatidylcholine (DPPC), dioleoyl-phosphatidylcholine (DOPC), and palmitoyl-oleoyl-phosphatidylcholine (POPC) bilayers in their fluid state. The central quantity in this theory, the probability distribution of chain conformations, is evaluated by minimizing the free energy of the bilayer assuming only that the segment density within the hydrophobic region is uniform (liquidlike). Using this distribution we calculate chain conformational properties such as bond orientational order parameters and spatial distributions of the various chain segments. The lipid chains, both the saturated palmitoyl (-(CH2)14-CH3) and the unsaturated oleoyl (-(CH2)7-CH = CH-(CH2)7-CH3) chains are modeled using rotational isomeric state schemes. All possible chain conformations are enumerated and their statistical weights are determined by the self-consistency equations expressing the condition of uniform density. The hydrophobic core of the DPPC bilayer is treated as composed of single (palmitoyl) chain amphiphiles, i.e., the interactions between chains originating from the same lipid headgroup are assumed to be the same as those between chains belonging to different molecules. Similarly, the DOPC system is treated as a bilayer of oleoyl chains. The POPC bilayer is modeled as an equimolar mixture of palmitoyl and oleoyl chains. Bond orientational order parameter profiles, and segment spatial distributions are calculated for the three systems above, for several values of the bilayer thickness (or, equivalently, average area/headgroup) chosen, where possible, so as to allow for comparisons with available experimental data and/or molecular dynamics simulations. In most cases the agreement between the mean-field calculations, which are relatively easy to perform, and the
2006-06-16
benchmark them against improper fielding? Determine if the process asks the tactical commander to accept risks . 47 The acquisition framework establishes...capability within the strategic framework . Tactical risk becomes an issue for discussion at this point because of the nature of the overall strategy...package fielding and placement of the Multiple Launch Rocket System case study within the acquisition framework . Literary review briefly details rapid
Stopper, U.; Aigner, M.; Ax, H.; Meier, W.; Sadanandan, R.; Stoehr, M.; Bonaldo, A.
2010-04-15
Several laser diagnostic measurement techniques have been applied to study the lean premixed natural gas/air flames of an industrial swirl burner. This was made possible by equipping the burner with an optical combustion chamber that was installed in the high-pressure test rig facility at the DLR Institute of Combustion Technology in Stuttgart. The burner was operated with preheated air at various operating conditions with pressures up to p = 6 bar and a maximum thermal power of P = 1 MW. The instantaneous planar flow field inside the combustor was studied with particle image velocimetry (PIV). Planar laser induced fluorescence (PLIF) of OH radicals on a single-shot basis was used to determine the shape and the location of the flame front as well as the spatial distribution of reaction products. 1D laser Raman spectroscopy was successfully applied for the measurement of the temperature and the concentration of major species under realistic gas turbine conditions. Results of the flow field analysis show the shape and the size of the main flow regimes: the inflow region, the inner and the outer recirculation zone. The highly turbulent flow field of the inner shear layer is found to be dominated by small and medium sized vortices. High RMS fluctuations of the flow velocity in the exhaust gas indicate the existence of a rotating exhaust gas swirl. From the PLIF images it is seen that the primary reactions happened in the shear layers between inflow and the recirculation zones and that the appearance of the reaction zones changed with flame parameters. The results of the multiscalar Raman measurements show a strong variation of the local mixture fraction allowing conclusions to be drawn about the premix quality. Furthermore, mixing effects of unburnt fuel and air with fully reacted combustion products are studied giving insights into the processes of the turbulence-chemistry interaction. (author)
Mu, Zhiping; Dobrucki, Lawrence W; Liu, Yi-Hwa
The imaging of distributed sources with near-field coded aperture (CA) remains extremely challenging and is broadly considered unsuitable for single-photon emission computerized tomography (SPECT). This study proposes a novel CA SPECT reconstruction approach and evaluates the feasibilities of imaging and reconstructing distributed hot sources and cold lesions using near-field CA collimation and iterative image reconstruction. Computer simulations were designed to compare CA and pinhole collimations in two-dimensional radionuclide imaging. Digital phantoms were created and CA images of the phantoms were reconstructed using maximum likelihood expectation maximization (MLEM). Errors and the contrast-to-noise ratio (CNR) were calculated and image resolution was evaluated. An ex vivo rat heart with myocardial infarction was imaged using a micro-SPECT system equipped with a custom-made CA module and a commercial 5-pinhole collimator. Rat CA images were reconstructed via the three-dimensional (3-D) MLEM algorithm developed for CA SPECT with and without correction for a large projection angle, and 5-pinhole images were reconstructed using the commercial software provided by the SPECT system. Phantom images of CA were markedly improved in terms of image quality, quantitative root-mean-squared error, and CNR, as compared to pinhole images. CA and pinhole images yielded similar image resolution, while CA collimation resulted in fewer noise artifacts. CA and pinhole images of the rat heart were well reconstructed and the myocardial perfusion defects could be clearly discerned from 3-D CA and 5-pinhole SPECT images, whereas 5-pinhole SPECT images suffered from severe noise artifacts. Image contrast of CA SPECT was further improved after correction for the large projection angle used in the rat heart imaging. The computer simulations and small-animal imaging study presented herein indicate that the proposed 3-D CA SPECT imaging and reconstruction approaches worked reasonably
James R. Wood; A. Wylie; W. Quinlan
2005-04-01
In this reporting period two main accomplishments stand out. The Springdale task is in play in the northern Michigan Basin and the geochemical survey work over the Springdale prospect continued to progress. We still need to characterize the play in terms of the type of trap (basal reef diagenetic (?)) and its relation to the well documented pinnacle reef play. Also, we have become aware that Capac Field in the southern reef trend (Figure 1) is a possible analog to Springdale and so will be looking more closely at the literature on that field, particularly the work by Bowers (1987). Future work is directed toward further defining the Springdale project via more wells and examination and characterization of well cuttings. One to two more geochemical surveys are planned, one this spring and a final one in early fall. Based on current oil prices and Springdale production as of January 2005, an ROI, (defined as Total liquids revenue, $5.45m/DOE support, $1.45m) better than 3.75. This does not include gas revenues, which have not yet been calculated.
James R. Wood; A. Wylie; W. Quinlan
2004-04-01
One of the main objectives of this demonstration project is to test surface geochemical techniques for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. As part of the project, several field demonstrations were undertaken to assess the validity and usefulness of the microbial surface geochemical technique. The important observations from each of these field demonstrations are briefly reviewed in this annual report. These demonstrations have been successful in identifying the presence or lack of hydrocarbons in the subsurface and can be summarized as follows: (1) The surface geochemistry data showed a fair-to-good microbial anomaly that may indicate the presence of a fault or stratigraphic facies change across the drilling path of the State Springdale & O'Driscoll No.16-16 horizontal demonstration well in Manistee County, Michigan. The well was put on production in December 2003. To date, the well is flowing nearly 100 barrels of liquid hydrocarbons per day plus gas, which is a good well in Michigan. Reserves have not been established yet. Two successful follow-up horizontal wells have also been drilled in the Springdale area. Additional geochemistry data will be collected in the Springdale area in 2004. (2) The surface geochemistry sampling in the Bear Lake demonstration site in Manistee County, Michigan was updated after the prospect was confirmed and production begun; the original subsurface and seismic interpretation used to guide the location of the geochemical survey for the Charlich Fauble re-entry was different than the interpretation used by the operator who ultimately drilled the well. As expected, the anomaly appears to be diminishing as the positive (apical) microbial anomaly is replaced by a negative (edge) anomaly, probably due to the pressure draw-down in the reservoir. (3) The geochemical sampling program over the Vernon Field, Isabella County, Michigan is now
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
Meshfree natural vibration analysis of 2D structures
NASA Astrophysics Data System (ADS)
Kosta, Tomislav; Tsukanov, Igor
2014-02-01
Determination of resonance frequencies and vibration modes of mechanical structures is one of the most important tasks in the product design procedure. The main goal of this paper is to describe a pioneering application of the solution structure method (SSM) to 2D structural natural vibration analysis problems and investigate the numerical properties of the method. SSM is a meshfree method which enables construction of the solutions to the engineering problems that satisfy exactly all prescribed boundary conditions. This method is capable of using spatial meshes that do not conform to the shape of a geometric model. Instead of using the grid nodes to enforce boundary conditions, it employs distance fields to the geometric boundaries and combines them with the basis functions and prescribed boundary conditions at run time. This defines unprecedented geometric flexibility of the SSM as well as the complete automation of the solution procedure. In the paper we will explain the key points of the SSM as well as investigate the accuracy and convergence of the proposed approach by comparing our results with the ones obtained using analytical methods or traditional finite element analysis. Despite in this paper we are dealing with 2D in-plane vibrations, the proposed approach has a straightforward generalization to model vibrations of 3D structures.
James R. Wood; W. Quinlan
2003-10-01
The principal objective of this demonstration project is to test surface geochemical techniques for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. During this reporting period, a new field demonstration, Springdale Prospect in Manistee County, Michigan was begun to assess the validity and usefulness of the microbial surface geochemical technique. The surface geochemistry data showed a fair-to-good microbial anomaly that may indicate the presence of a fault or stratigraphic facies change across the drilling path. The surface geochemistry sampling at the original Bear Lake demonstration site was updated several months after the prospect was confirmed and production begun. As expected, the anomaly appears to be diminishing as the positive (apical) anomaly is replaced by a negative (edge) anomaly, probably due to the pressure draw-down in the reservoir.
James R. Wood; T.J. Bornhorst; S.D. Chittick; William B. Harrison; W. Quinlan
2001-10-31
Two major accomplishments resulted from Phase I. One is the success of the surface geochemistry program, which collected over 800 samples from the site of the 1st demonstration well in Vernon Field and has pretty well provided us with the tools to delineate favorable ground from unfavorable. The second is the recent detailed mapping of the Central Michigan Basin that for the first time revealed the presence of at least two major faults that control the location of many of the reservoirs in the Michigan Basin. These faults were located from structure maps obtained by contouring the surface of the Dundee Formation using top picks from 9861 wells in 14 counties. Faults were inferred where the contour lines were most dense (''stacked'').
NASA Technical Reports Server (NTRS)
Monta, William J.
1992-01-01
A pitot-rake survey of the simulated exhaust of a half-span scramjet nozzle model was conducted in the Langley 20-Inch Mach 6 Tunnel to provide an additional data set for computational fluid dynamics (CFD) code comparisons. A wind-tunnel model was tested with a 26-tube pitot rake that could be manually positioned along the mid-semispan plane of the model. The model configuration had an external expansion surface of 20 degrees and an internal cowl expansion of 12 degrees; tests were also performed with a flow fence. Tests were conducted at a free-stream Reynolds number of approximately 6.5 x 10(exp 6) per foot and a model angle of attack of -0.75 degrees. The two exhaust gas mediums that were tested were air and a Freon 12-argon mixture. Each medium was tested at two jet total pressures at approximately 28 and 14 psia. This document presents the flow-field survey results in graphical as well as tabular form, and several observations concerning the results are discussed. The surveys reveal the major expected flow-field characteristics for each test configuration. For a 50-percent freon 12 and 50-percent argon mixture by volume (Fr-Ar), the exhaust jet pressures were slightly higher than those for air. The addition of a flow fence slightly raised the pitot pressure for the Fr-Ar mixture, but it produced little change for air. For the Fr-Ar exhaust, the plume was larger and the region between the shock wave and plume was smaller.
Schulz-Wendtland, R; Bani, M; Lux, M P; Schwab, S; Loehberg, C R; Jud, S M; Rauh, C; Bayer, C M; Beckmann, M W; Uder, M; Fasching, P A; Adamietz, B; Meier-Meitinger, M
2012-05-01
Purpose: Experimental study of a new system for digital 2D and 3D full-field mammography (FFDM) using a high resolution detector based on two shifts of a-Se. Material and Methods: Images were acquired using the new FFDM system Amulet® (FujiFilm, Tokio, Japan), an a-Se detector (receptor 24 × 30 cm(2), pixel size 50 µm, memory depth 12 bit, spatial resolution 10 lp/mm, DQE > 0.50). Integrated in the detector is a new method for data transfer, based on optical switch technology. The object of investigation was the Wisconsin Mammographic Random Phantom, Model 152A (Radiation Measurement Inc., Middleton, WI, USA) and the same parameters and exposure data (Tungsten, 100 mAs, 30 kV) were consistently used. We acquired 3 different pairs of images in the c-c and ml planes (2D) and in the c-c and c-c planes with an angle of 4 degrees (3D). Five radiologists experienced in mammography (experience ranging from 3 months to more than 5 years) analyzed the images (monitoring) which had been randomly encoded (random generator) with regard to the recognition of details such as specks of aluminum oxide (200-740 µm), nylon fibers (0.4-1.6 mm) and round lesions/masses (diameters 5-14 mm), using special linear glasses for 3D visualization, and compared the results. Results: A total of 225 correct positive decisions could be detected: we found 222 (98.7 %) correct positive results for 2D and 3D visualization in each case. Conclusion: The results of this phantom study showed the same detection rates for both 2D and 3D imaging using full field digital mammography. Our results must be confirmed in further clinical trials.
NASA Astrophysics Data System (ADS)
Aggarwal, Priyanka; Sharma, Shivalika; Singh, Sunny; Kaur, Harsimran; Hazra, Ram Kuntal
2017-04-01
Inclusion of coulomb interaction emerges with the complexity of either convergence of integrals or separation of variables of Schrödinger equations. For an N-electron system, interaction terms grow by N(N-1)/2 factors. Therefore, 2-e system stands as fundamental basic unit for generalized N-e systems. For the first time, we have evaluated e-e correlations in very simple and absolutely terminating finite summed hypergeometric series for 2-D double carrier parabolic quantum dot in both zero and arbitrary non-zero magnetic field (symmetric gauge) and have appraised these integrals in variational methods. The competitive role among confinement strength, magnetic field, mass of the carrier and dielectric constant of the medium on energy level diagram, level-spacing statistics, heat capacities (Cv at 1 K) and magnetization (T ∼ (0-1)K) is studied on systems spanning over wide range of materials (GaAs,Ge,CdS,SiO2 and He, etc). We have also constructed an exact theory for generalized correlated N-e 2-D quantum dots via multi-pole expansion but for the sake of compactness of the article we refrain from data.
James R. Wood; A. Wylie; W. Quinlan
2004-01-01
The principal objective of this demonstration project is to test surface geochemical techniques for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. During this reporting period, a new field demonstration, Springdale Prospect in Manistee County, Michigan was begun to assess the validity and usefulness of the microbial surface geochemical technique. The surface geochemistry data showed a fair-to-good microbial anomaly that may indicate the presence of a fault or stratigraphic facies change across the drilling path. The main news this reporting period is the confirmed discovery of producing hydrocarbons at the State Springdale & O'Driscoll No.16-16 demonstration well in Manistee County. This well was spudded in late November, tested and put on production in December 2003. To date it is flowing nearly 100 barrels of liquid hydrocarbons per day, which is a good well in Michigan. Reserves have not been established yet. The surface geochemistry sampling at the Springdale demonstration site will be repeated this spring after the well has been on production for several months to see if the anomaly pattern changes. We expect that the anomaly will diminish as the original positive (apical) anomaly is replaced by a negative (edge) anomaly, probably due to the pressure draw-down in the reservoir. This is the behavior that we observed at the Bear lake demonstration well reported last quarter.
Mégardon, Geoffrey; Tandonnet, Christophe; Sumner, Petroc; Guillaume, Alain
2015-01-01
Dynamic Neural Field models (DNF) often use a kernel of connection with short range excitation and long range inhibition. This organization has been suggested as a model for brain structures or for artificial systems involved in winner-take-all processes such as saliency localization, perceptual decision or target/action selection. A good example of such a DNF is the superior colliculus (SC), a key structure for eye movements. Recent results suggest that the superficial layers of the SC (SCs) exhibit relatively short range inhibition with a longer time constant than excitation. The aim of the present study was to further examine the properties of a DNF with such an inhibition pattern in the context of target selection. First we tested the effects of stimulus size and shape on when and where self-maintained clusters of firing neurons appeared, using three variants of the model. In each model variant, small stimuli led to rapid formation of a spiking cluster, a range of medium sizes led to the suppression of any activity on the network and hence to no target selection, while larger sizes led to delayed selection of multiple loci. Second, we tested the model with two stimuli separated by a varying distance. Again single, none, or multiple spiking clusters could occur, depending on distance and relative stimulus strength. For short distances, activity attracted toward the strongest stimulus, reminiscent of well-known behavioral data for saccadic eye movements, while for larger distances repulsion away from the second stimulus occurred. All these properties predicted by the model suggest that the SCs, or any other neural structure thought to implement a short range MH, is an imperfect winner-take-all system. Although, those properties call for systematic testing, the discussion gathers neurophysiological and behavioral data suggesting that such properties are indeed present in target selection for saccadic eye movements. PMID:26539103
Test of the Anti-de Sitter-Space/Conformal-Field-Theory Correspondence Using High-Spin Operators
Benna, M. K.; Benvenuti, S.; Klebanov, I. R.; Scardicchio, A.
2007-03-30
In two remarkable recent papers the planar perturbative expansion was proposed for the universal function of the coupling appearing in the dimensions of high-spin operators of the N=4 super Yang-Mills theory. We study numerically the integral equation derived by Beisert, Eden, and Staudacher, which resums the perturbative series. In a confirmation of the anti-de Sitter-space/conformal-field-theory (AdS/CFT) correspondence, we find a smooth function whose two leading terms at strong coupling match the results obtained for the semiclassical folded string spinning in AdS{sub 5}. We also make a numerical prediction for the third term in the strong coupling series.
Jabbari, Keyvan; Azarmahd, Nazli; Babazade, Shadi; Amouheidari, Alireza
2013-04-01
Radiotherapy plays an essential role in the management of breast cancer. Three-dimensional conformal radiation therapy (3D-CRT) is applied based on 3D image information of anatomy of patients. In 3D-CRT for breast cancer one of the common techniques is tangential technique. In this project, various parameters of tangential and supraclavicular fields are optimized. This project has been done on computed tomography images of 100 patients in Isfahan Milad Hospital. All patients have been simulated and all the important organs have been contoured by radiation oncologist. Two techniques in supraclavicular region are evaluated including: 1-A single field (Anterior Posterior [AP]) with a dose of 200 cGy per fraction with 6 MV energy. This is a common technique. 2-Two parallel opposed fields (AP-Posterior Anterior [PA]). The dose of AP was 150 cGy with 6 MV energy and PA 50 cGy with 18 MV. In the second part of the project, the tangential fields has been optimized with change of normalization point in five points: (1) Isocenter (Confluence of rotation gantry axis and collimator axis) (2) Middle of thickest part of breast or middle of inter field distance (IFD) (3) Border between the lung and chest wall (4) Physician's choice (5) Between IFD and isocenter. Dose distributions have been compared for all patients in different methods of supraclavicular and tangential field. In parallel opposed fields average lung dose was 4% more than a single field and the maximum received heart dose was 21.5% less than a single field. The average dose of planning tumor volume (PTV) in method 2 is 2% more than method 1. In general AP-PA method because of a better coverage of PTV is suggested. In optimization of the tangential field all methods have similar coverage of PTV. Each method has spatial advantages and disadvantages. If it is important for the physician to reduce the dose received by the lung and heart, fifth method is suggested since in this method average and maximum received dose
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
Kanade, Santosh R; Paul, Beena; Rao, A G Appu; Gowda, Lalitha R
2006-05-01
Field bean (Dolichos lablab) contains a single isoform of PPO (polyphenol oxidase)--a type III copper protein that catalyses the o-hydroxylation of monophenols and oxidation of o-diphenols using molecular oxygen--and is a homotetramer with a molecular mass of 120 kDa. The enzyme is activated manyfold either in the presence of the anionic detergent SDS below its critical micellar concentration or on exposure to acid-pH. The enhancement of kcat upon activation is accompanied by a marked shift in the pH optimum for the oxidation of t-butyl catechol from 4.5 to 6.0, an increased sensitivity to tropolone, altered susceptibility to proteolytic degradation and decreased thermostability. The Stokes radius of the native enzyme is found to increase from 49.1+/-2 to 75.9+/-0.6 A (1 A=0.1 nm). The activation by SDS and acid-pH results in a localized conformational change that is anchored around the catalytic site of PPO that alters the microenvironment of an essential glutamic residue. Chemical modification of field bean and sweet potato PPO with 1-ethyl-3-(3-dimethylaminopropyl)carbodi-imide followed by kinetic analysis leads to the conclusion that both the enzymes possess a core carboxylate essential to activity. This enhanced catalytic efficiency of PPO, considered as an inducible defence oxidative enzyme, is vital to the physiological defence strategy adapted by plants to insect herbivory and pathogen attack.
On the conformal field theories for bosonic strings in PP-waves
NASA Astrophysics Data System (ADS)
Mukhopadhyay, Partha
2008-11-01
Recently Kazama and Yokoi (arXiv:0801.1561 [hep-th]) have used a phase-space method to study the Virasoro algebra of type IIB superstring theory in the maximally supersymmetric R-R plane wave background in a semi-light-cone gauge. Two types of normal ordering have been considered, namely ``phase space normal ordering" (PNO) and ``massless normal ordering" (MNO). The second one, which is the right one to choose in flat background, has been discarded with the argument that the Virasoro algebra closes only in the first case. To understand this issue better with a completely covariant treatment we consider the easiest case of bosonic strings propagating in an arbitrary pp-wave of the simplest kind. Using the phase-space method we show that MNO is the right one to choose, at least in this case, because of the following reason. For both types of normal ordering the energy-momentum tensor satisfies the desired Virasoro algebra up to anomalous terms proportional to the space-time equation of motion of the background. However, it is MNO which gives rise to the correct spectrum - we compute the quadratic space-time action by restricting the string field inside a transverse Hilbert space. This turns out to be non-diagonal. Diagonalizing this action reproduces the spectrum directly obtained in light-cone quantization. The same method with PNO gives rise to a spectrum with negative dimensions.
Imaging of conformational changes
Michl, Josef
2016-03-13
Control of intramolecular conformational change in a small number of molecules or even a single one by an application of an outside electric field defined by potentials on nearby metal or dielectric surfaces has potential applications in both 3-D and 2-D nanotechnology. Specifically, the synthesis, characterization, and understanding of designed solids with controlled built-in internal rotational motion of a dipole promises a new class of materials with intrinsic dielectric, ferroelectric, optical and optoelectronic properties not found in nature. Controlled rotational motion is of great interest due to its expected utility in phenomena as diverse as transport, current flow in molecular junctions, diffusion in microfluidic channels, and rotary motion in molecular machines. A direct time-resolved observation of the dynamics of motion on ps or ns time scale in a single molecule would be highly interesting but is also very difficult and has yet to be accomplished. Much can be learned from an easier but still challenging comparison of directly observed initial and final orientational states of a single molecule, which is the basis of this project. The project also impacts the understanding of surface-enhanced Raman spectroscopy (SERS) and single-molecule spectroscopic detection, as well as the synthesis of solid-state materials with tailored properties from designed precursors.
Stemkens, B; Tijssen, RHN; Denis de Senneville, B Denis; Lagendijk, JJW; Berg, CAT van den
2015-06-15
Purpose: To estimate full field-of-view abdominal respiratory motion from fast 2D image navigators using a 4D-MRI based motion model. This will allow for radiation dose accumulation mapping during MR-Linac treatment. Methods: Experiments were conducted on a Philips Ingenia 1.5T MRI. First, a retrospectively ordered 4D-MRI was constructed using 3D transient-bSSFP with radial in-plane sampling. Motion fields were calculated through 3D non-rigid registration. From these motion fields a PCA-based abdominal motion model was constructed and used to warp a 3D reference volume to fast 2D cine-MR image navigators that can be used for real-time tracking. To test this procedure, a time-series consisting of two interleaved orthogonal slices (sagittal and coronal), positioned on the pancreas or kidneys, were acquired for 1m38s (dynamic scan-time=0.196ms), during normal, shallow, or deep breathing. The coronal slices were used to update the optimal weights for the first two PCA components, in order to warp the 3D reference image and construct a dynamic 4D-MRI time-series. The interleaved sagittal slices served as an independent measure to test the model’s accuracy and fit. Spatial maps of the root-mean-squared error (RMSE) and histograms of the motion differences within the pancreas and kidneys were used to evaluate the method. Results: Cranio-caudal motion was accurately calculated within the pancreas using the model for normal and shallow breathing with an RMSE of 1.6mm and 1.5mm and a histogram median and standard deviation below 0.2 and 1.7mm, respectively. For deep-breathing an underestimation of the inhale amplitude was observed (RMSE=4.1mm). Respiratory-induced antero-posterior and lateral motion were correctly mapped (RMSE=0.6/0.5mm). Kidney motion demonstrated good motion estimation with RMSE-values of 0.95 and 2.4mm for the right and left kidney, respectively. Conclusion: We have demonstrated a method that can calculate dynamic 3D abdominal motion in a large volume
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.
Conformal differential invariants
NASA Astrophysics Data System (ADS)
Kruglikov, Boris
2017-03-01
We compute the Hilbert polynomial and the Poincaré function counting the number of fixed jet-order differential invariants of conformal metric structures modulo local diffeomorphisms, and we describe the field of rational differential invariants separating generic orbits of the diffeomorphism pseudogroup action. This resolves the local recognition problem for conformal structures.
Sengupta, Neelanjana; Maekawa, Hiroaki; Zhuang, Wei; Toniolo, Claudio; Mukamel, Shaul; Tobias, Douglas J.; Ge, Nien-Hui
2010-01-01
We have investigated the sensitivity of two-dimensional infrared (2D IR) spectroscopy to peptide helicity with an experimental and theoretical study of Z-[L-(αMe)Val]8-OtBu in CDCl3. 2D IR experiments were carried out in the amide-I region under the parallel and the double-crossed polarization configurations. In the latter polarization configuration, the 2D spectra taken with the rephasing and nonrephasing pulse sequences exhibit a doublet feature and a single peak, respectively. These cross-peak patterns are highly sensitive to the underlying peptide structure. Spectral calculations were performed on the basis of a vibrational exciton model, with the local mode frequencies and couplings calculated from snapshots of molecular dynamics (MD) simulation trajectories using six different models for the Hamiltonian. Conformationally variant segments of the MD trajectory, while reproducing the main features of the experimental spectra, are characterized by extraneous features, suggesting that the structural ensembles sampled by the simulation are too broad. By imposing periodic restraints on the peptide dihedral angles with the crystal structure as a reference, much better agreement between the measured and the calculated spectra was achieved. The result indicates that the structure of Z-[L-(αMe)Val]8-OtBu in CDCl3 is a fully developed 310-helix with only a small fraction of α-helical or nonhelical conformations in the middle of the peptide. Of the four different combinations of pulse sequences and polarization configurations, the nonrephasing double-crossed polarization 2D IR spectrum exhibits the highest sensitivity in detecting conformational variation. Of the six local mode frequency models tested, the electrostatic maps of Mukamel and Cho perform the best. Our results show that the high sensitivity of 2D IR spectroscopy can provide a useful basis for developing methods to improve the sampling accuracy of force fields and for characterizing the relative merits of
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.
NASA Astrophysics Data System (ADS)
Ji, Youn-Sang; Dong, Kyung-Rae; Kim, Chang-Bok; Chung, Woon-Kwan; Cho, Jae-Hwan; Lee, Hae-Kag
2012-10-01
This study evaluated the gating-based 4-D conformal radiation therapy (4D-CT) treatment planning by a comparison with the common 3-D conformal radiation therapy (3D-CT) treatment planning and examined the change in treatment field size and dose to the tumors and adjacent normal tissues because an unnecessary dose is also included in the 3-D treatment planning for the radiation treatment of tumors in the chest and abdomen. The 3D-CT and gating-based 4D-CT images were obtained from patients who had undergone radiation treatment for chest and abdomen tumors in the oncology department. After establishing a treatment plan, the CT treatment and planning system were used to measure the change in field size for analysis. A dose volume histogram (DVH) was used to calculate the appropriate dose to planning target volume (PTV) tumors and adjacent normal tissue. The difference in the treatment volume of the chest was 0.6 and 0.83 cm on the X- and Y-axis, respectively, for the gross tumor volume (GTV). Accordingly, the values in the 4D-CT treatment planning were smaller and the dose was more concentrated by 2.7% and 0.9% on the GTV and clinical target volume (CTV), respectively. The normal tissues in the surrounding normal tissues were reduced by 3.0%, 7.2%, 0.4%, 1.7%, 2.6% and 0.2% in the bronchus, chest wall, esophagus, heart, lung and spinal cord, respectively. The difference in the treatment volume of the abdomen was 0.72 cm on the X-axis and 0.51 cm on the Y-axis for the GTV; and 1.06 cm on the X-axis and 1.85 cm on the Y-axis for the PTV. Therefore, the values in the 4D-CT treatment planning were smaller. The dose was concentrated by 6.8% and 4.3% on the GTV and PTV, respectively, whereas the adjacent normal tissues in the cord, Lt. kidney, Rt. kidney, small bowels and whole liver were reduced by 3.2%, 4.2%, 1.5%, 6.2% and 12.7%, respectively. The treatment field size was smaller in volume in the case of the 4D-CT treatment planning. In the DVH, the 4D-CT treatment
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.
Conformal Janus on Euclidean sphere
NASA Astrophysics Data System (ADS)
Bak, Dongsu; Gustavsson, Andreas; Rey, Soo-Jong
2016-12-01
We interpret Janus as an interface in a conformal field theory and study its properties. The Janus is created by an exactly marginal operator and we study its effect on the interface conformal field theory on the Janus. We do this by utilizing the AdS/CFT correspondence. We compute the interface free energy both from leading correction to the Euclidean action in the dual gravity description and from conformal perturbation theory in the conformal field theory. We find that the two results agree each other and that the interface free energy scales precisely as expected from the conformal invariance of the Janus interface.
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.
Agrawal, Yogyata; Kedawat, Garima; Kumar, Pawan; Dwivedi, Jaya; Singh, V. N.; Gupta, R. K.; Gupta, Bipin Kumar
2015-01-01
A facile method to produce conformal coated reduced graphene oxide (rGO) on vertically aligned titanium oxide (TiO2) nanotubes three dimensional (3D) arrays (NTAs) is demonstrated for enhanced field emission display applications. These engineered nano arrays exhibit efficient electron field emission properties such as high field emission current density (80 mA/cm2), low turn-on field (1.0 V/μm) and field enhancement factor (6000) with high emission current stability. Moreover, these enhancements observed in nano arrays attribute to the contribution of low work function with non-rectifying barriers, which allow an easy injection of electrons from the conduction band of TiO2 into the Fermi level of reduced graphene oxide under external electric field. The obtained results are extremely advantageous for its potential application in field emission devices. PMID:26152895
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
NASA Astrophysics Data System (ADS)
Christodoulides, Kyriakos
2014-07-01
We study single and coupled first-order differential equations (ODEs) that admit symmetries with tangent vector fields, which satisfy the N-dimensional Cauchy-Riemann equations. In the two-dimensional case, classes of first-order ODEs which are invariant under Möbius transformations are explored. In the N dimensional case we outline a symmetry analysis method for constructing exact solutions for conformal autonomous systems. A very important aspect of this work is that we propose to extend the traditional technical usage of Lie groups to one that could provide testable predictions and guidelines for model-building and model-validation. The Lie symmetries in this paper are constrained and classified by field theoretical considerations and their phenomenological implications. Our results indicate that conformal transformations are appropriate for elucidating a variety of linear and nonlinear systems which could be used for, or inspire, future applications. The presentation is pragmatic and it is addressed to a wide audience.
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.
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.
NASA Astrophysics Data System (ADS)
Haldane, F. D. M.; Ha, Z. N. C.; Talstra, J. C.; Bernard, D.; Pasquier, V.
1992-10-01
The SU(n) quantum chains with inverse-square exchange exhibit a novel form of Yangian symmetry compatible with periodic boundary conditions, allowing states to be countable. We characterize the ``supermultiplets'' of the spectrum in terms of generalized ``occupation numbers.'' We embed the model in the k=1 SU(n) Kac-Moody algebra and obtain a new classification of the states of conformal field theory, adapted to particlelike elementary excitations obeying fractional statistics.
Song, Haipeng; Ritz, Sandra; Knoll, Wolfgang; Sinner, Eva-Kathrin
2009-10-01
Progressive depositions of cerebral amyloid are primary neuropathologic features of Alzheimer's disease (AD). The amyloid is composed of a 39-42 amino acid peptide called the amyloid beta-protein (Abeta). Repeated investigation suggests that the conformational transition of Abeta from alpha-helix or random coil to beta-sheet structure plays a key role in the inappropriate accumulation of cerebral amyloid plaques. In this manuscript, we describe a fluorescence-based immunoassay technology to investigate the conformation and topology of Abeta peptides interacting with peptide-tethered planar lipid bilayers. Dual monoclonal antibodies (mAbs) labelled with fluorophores were employed to recognise a linear N- and a beta-sheet C-terminus of Abeta peptides on the model membrane, respectively. Kinetics of antibody-Abeta binding were determined by surface plasmon field-enhanced fluorescence spectroscopy (SPFS). The conformational transition of Abeta by melatonin, a defined beta-sheet breaker, was probed using paired monoclonal antibodies. The Abeta interaction with the membrane was evaluated by carefully analyzing the change in kinetic/affinity parameters in the presence or absence of melatonin. These results show that SPFS can be used to examine conformational transition of Abeta on an artificial membrane, providing a novel and versatile platform for conveniently monitoring protein-membrane interaction and screening for new beta-sheet breakers.
Kamiya, Yukiko; Yanagi, Kotaro; Kitajima, Toshihiko; Yamaguchi, Takumi; Chiba, Yasunori; Kato, Koichi
2013-01-01
High mannose-type oligosaccharides are enzymatically trimmed in the endoplasmic reticulum, resulting in various processing intermediates with exposed glycotopes that are recognized by a series of lectins involved in glycoprotein fate determination in cells. Although recent crystallographic data have provided the structural basis for the carbohydrate recognition of intracellular lectins, atomic information of dynamic oligosaccharide conformations is essential for a quantitative understanding of the energetics of carbohydrate–lectin interactions. Carbohydrate NMR spectroscopy is useful for characterizing such conformational dynamics, but often hampered by poor spectral resolution and lack of recombinant techniques required to produce homogeneous glycoforms. To overcome these difficulties, we have recently developed a methodology for the preparation of a homogeneous high mannose-type oligosaccharide with 13C labeling using a genetically engineered yeast strain. We herein successfully extended this method to result in the overexpression of 13C-labeled Man9GlcNAc2 (M9) with a newly engineered yeast strain with the deletion of four genes involved in N-glycan processing. This enabled high-field NMR analyses of 13C-labeled M9 in comparison with its processing product lacking the terminal mannose residue ManD2. Long-range NOE data indicated that the outer branches interact with the core in both glycoforms, and such foldback conformations are enhanced upon the removal of ManD2. The observed conformational variabilities might be significantly associated with lectins and glycan-trimming enzymes. PMID:24970159
This section provides information on: current laws, regulations and guidance, policy and technical guidance, project-level conformity, general information, contacts and training, adequacy review of SIP submissions
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.
2D quasiperiodic plasmonic crystals
Bauer, Christina; Kobiela, Georg; Giessen, Harald
2012-01-01
Nanophotonic structures with irregular symmetry, such as quasiperiodic plasmonic crystals, have gained an increasing amount of attention, in particular as potential candidates to enhance the absorption of solar cells in an angular insensitive fashion. To examine the photonic bandstructure of such systems that determines their optical properties, it is necessary to measure and model normal and oblique light interaction with plasmonic crystals. We determine the different propagation vectors and consider the interaction of all possible waveguide modes and particle plasmons in a 2D metallic photonic quasicrystal, in conjunction with the dispersion relations of a slab waveguide. Using a Fano model, we calculate the optical properties for normal and inclined light incidence. Comparing measurements of a quasiperiodic lattice to the modelled spectra for angle of incidence variation in both azimuthal and polar direction of the sample gives excellent agreement and confirms the predictive power of our model. PMID:23209871
NASA Astrophysics Data System (ADS)
Schaibley, John R.; Yu, Hongyi; Clark, Genevieve; Rivera, Pasqual; Ross, Jason S.; Seyler, Kyle L.; Yao, Wang; Xu, Xiaodong
2016-11-01
Semiconductor technology is currently based on the manipulation of electronic charge; however, electrons have additional degrees of freedom, such as spin and valley, that can be used to encode and process information. Over the past several decades, there has been significant progress in manipulating electron spin for semiconductor spintronic devices, motivated by potential spin-based information processing and storage applications. However, experimental progress towards manipulating the valley degree of freedom for potential valleytronic devices has been limited until very recently. We review the latest advances in valleytronics, which have largely been enabled by the isolation of 2D materials (such as graphene and semiconducting transition metal dichalcogenides) that host an easily accessible electronic valley degree of freedom, allowing for dynamic control.
Verbaro, Daniel; Ghosh, Indrajit; Nau, Werner M; Schweitzer-Stenner, Reinhard
2010-12-30
Structural preferences in the unfolded state of peptides determined by molecular dynamics still contradict experimental data. A remedy in this regard has been suggested by MD simulations with an optimized Amber force field ff03* ( Best, R. Hummer, G. J. Phys. Chem. B 2009 , 113 , 9004 - 9015 ). The simulations yielded a statistical coil distribution for alanine which is at variance with recent experimental results. To check the validity of this distribution, we investigated the peptide H-A(5)W-OH, which with the exception of the additional terminal tryptophan is analogous to the peptide used to optimize the force fields ff03*. Electronic circular dichroism, vibrational circular dichroism, and infrared spectroscopy as well as J-coupling constants obtained from NMR experiments were used to derive the peptide's conformational ensemble. Additionally, Förster resonance energy transfer between the terminal chromophores of the fluorescently labeled peptide analogue H-Dbo-A(5)W-OH was used to determine its average length, from which the end-to-end distance of the unlabeled peptide was estimated. Qualitatively, the experimental (3)J(H(N),C(α)), VCD, and ECD indicated a preference of alanine for polyproline II-like conformations. The experimental (3)J(H(N),C(α)) for A(5)W closely resembles the constants obtained for A(5). In order to quantitatively relate the conformational distribution of A(5) obtained with the optimized AMBER ff03* force field to experimental data, the former was used to derive a distribution function which expressed the conformational ensemble as a mixture of polyproline II, β-strand, helical, and turn conformations. This model was found to satisfactorily reproduce all experimental J-coupling constants. We employed the model to calculate the amide I' profiles of the IR and vibrational circular dichroism spectrum of A(5)W, as well as the distance between the two terminal peptide carbonyls. This led to an underestimated negative VCD couplet and an
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.
Jomehzadeh, Ali; Shokrani, Parvaneh; Mohammadi, Mohammad; Amouheidari, Alireza
2016-01-01
Background: The use of electronic portal imaging devices (EPIDs) is a method for the dosimetric verification of radiotherapy plans, both pretreatment and in vivo. The aim of this study is to test a 2D EPID-based dosimetry algorithm for dose verification of some plans inside a homogenous and anthropomorphic phantom and in vivo as well. Materials and Methods: Dose distributions were reconstructed from EPID images using a 2D EPID dosimetry algorithm inside a homogenous slab phantom for a simple 10 × 10 cm2 box technique, 3D conformal (prostate, head-and-neck, and lung), and intensity-modulated radiation therapy (IMRT) prostate plans inside an anthropomorphic (Alderson) phantom and in the patients (one fraction in vivo) for 3D conformal plans (prostate, head-and-neck and lung). Results: The planned and EPID dose difference at the isocenter, on an average, was 1.7% for pretreatment verification and less than 3% for all in vivo plans, except for head-and-neck, which was 3.6%. The mean γ values for a seven-field prostate IMRT plan delivered to the Alderson phantom varied from 0.28 to 0.65. For 3D conformal plans applied for the Alderson phantom, all γ1% values were within the tolerance level for all plans and in both anteroposterior and posteroanterior (AP-PA) beams. Conclusion: The 2D EPID-based dosimetry algorithm provides an accurate method to verify the dose of a simple 10 × 10 cm2 field, in two dimensions, inside a homogenous slab phantom and an IMRT prostate plan, as well as in 3D conformal plans (prostate, head-and-neck, and lung plans) applied using an anthropomorphic phantom and in vivo. However, further investigation to improve the 2D EPID dosimetry algorithm for a head-and-neck case, is necessary. PMID:28028511
Conformal vectors and stellar models
NASA Astrophysics Data System (ADS)
Manjonjo, A. M.; Maharaj, S. D.; Moopanar, S.
2017-02-01
The relationship between conformal symmetries and relativistic spheres in astrophysics is studied. We use the nonvanishing components of the Weyl tensor to classify the conformal symmetries in static spherical spacetimes. It is possible to find an explicit connection between the two gravitational potentials for both conformally flat and nonconformally flat cases. We show that the conformal Killing vector admits time dependence in terms of quadratic, trigonometric and hyperbolic functions. The Einstein and Einstein-Maxwell field equations can be written in terms of a single potential, any choice of which leads to an exact solution. Previous results of conformally invariant static spheres are contained in our treatment.
NASA Astrophysics Data System (ADS)
Mo, Jie-Xiong; Li, Gu-Qiang; Xu, Xiao-Bao
2016-10-01
In this paper, we investigate the thermodynamics of higher-dimensional f( R) black holes in the extended phase space. Both the analytic expressions and the numerical results for the possible critical physical quantities are obtained. It is proved that meaningful critical specific volume only exists when p is odd. This unique phenomenon may be attributed to the combined effect of f( R) gravity and conformally invariant Maxwell field. It is also shown that the ratio P_cv_c/T_c differs from that of higher-dimensional charged AdS black holes in Einstein gravity. However, the ratio for four-dimensional f( R) black holes is the same as that of four-dimensional RN-AdS black holes, implying that f( R) gravity does not influence the ratio. So the ratio may be related to conformally invariant Maxwell field. To probe the phase transition, we derive the explicit expression of the Gibbs free energy with its graph plotted. A phase transition analogous to the van der Waals liquid-gas system takes place between the small black hole and the large black hole. Classical swallow tail behavior, characteristic of first-order phase transitions, can also be observed in the Gibbs free energy graph. Critical exponents are also calculated. It is shown that these exponents are exactly the same as those of other AdS black holes, implying that neither f( R) gravity nor conformally invariant Maxwell field influence the critical exponents. Since the investigated black hole solution depends on the form of the function f( R), we discuss in detail how our results put constraint on the form of the function f( R) and we also present a simple example.
The General Conformity requirements ensure that the actions taken by federal agencies in nonattainment and maintenance areas do not interfere with a state’s plans to meet national standards for air quality.
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.
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.
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
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.
Laurence, J A; French, P W; Lindner, R A; Mckenzie, D R
2000-09-21
Microwave exposure under "athermal" conditions occurs when no temperature rise can be measured by conventional thermometry. The existence of biological effects arising from the athermal exposure is still controversial, partly because of a lack of the linear dose response relation. We propose a model in which pulsed microwave radiation causes a triggering of the heat shock or stress response by altering the conformation of proteins through a transient heating of the protein and its close environment. We support this by modelling using the heat diffusion equation and show that pulsed exposure even when athermal can lead to transient temperature excursions outside the normal range. We propose that the power window phenomenon in which biological effects are observed at low power levels may be caused by an incomplete triggering of the heat shock response.
Molecular mechanics conformational analysis of tylosin
NASA Astrophysics Data System (ADS)
Ivanov, Petko M.
1998-01-01
The conformations of the 16-membered macrolide antibiotic tylosin were studied with molecular mechanics (AMBER∗ force field) including modelling of the effect of the solvent on the conformational preferences (GB/SA). A Monte Carlo conformational search procedure was used for finding the most probable low-energy conformations. The present study provides complementary data to recently reported analysis of the conformations of tylosin based on NMR techniques. A search for the low-energy conformations of protynolide, a 16-membered lactone containing the same aglycone as tylosin, was also carried out, and the results were compared with the observed conformation in the crystal as well as with the most probable conformations of the macrocyclic ring of tylosin. The dependence of the results on force field was also studied by utilizing the MM3 force field. Some particular conformations were computed with the semiempirical molecular orbital methods AM1 and PM3.
Killing Initial Data on spacelike conformal boundaries
NASA Astrophysics Data System (ADS)
Paetz, Tim-Torben
2016-08-01
We analyze Killing Initial Data on Cauchy surfaces in conformally rescaled vacuum space-times satisfying Friedrich's conformal field equations. As an application, we derive the KID equations on a spacelike ℐ-.
Available information in 2D motional Stark effect imaging.
Creese, Mathew; Howard, John
2010-10-01
Recent advances in imaging techniques have allowed the extension of the standard polarimetric 1D motional Stark effect (MSE) diagnostic to 2D imaging of the internal magnetic field of fusion devices [J. Howard, Plasma Phys. Controlled Fusion 50, 125003 (2008)]. This development is met with the challenge of identifying and extracting the new information, which can then be used to increase the accuracy of plasma equilibrium and current density profile determinations. This paper develops a 2D analysis of the projected MSE polarization orientation and Doppler phase shift. It is found that, for a standard viewing position, the 2D MSE imaging system captures sufficient information to allow imaging of the internal vertical magnetic field component B(Z)(r,z) in a tokamak.
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.
Charged conformal Killing spinors
Lischewski, Andree
2015-01-15
We study the twistor equation on pseudo-Riemannian Spin{sup c}-manifolds whose solutions we call charged conformal Killing spinors (CCKSs). We derive several integrability conditions for the existence of CCKS and study their relations to spinor bilinears. A construction principle for Lorentzian manifolds admitting CCKS with nontrivial charge starting from CR-geometry is presented. We obtain a partial classification result in the Lorentzian case under the additional assumption that the associated Dirac current is normal conformal and complete the classification of manifolds admitting CCKS in all dimensions and signatures ≤5 which has recently been initiated in the study of supersymmetric field theories on curved space.
2-D Finite Element Cable and Box IEMP Analysis
Scivner, G.J.; Turner, C.D.
1998-12-17
A 2-D finite element code has been developed for the solution of arbitrary geometry cable SGEMP and box IEMP problems. The quasi- static electric field equations with radiation- induced charge deposition and radiation-induced conductivity y are numerically solved on a triangular mesh. Multiple regions of different dielectric materials and multiple conductors are permitted.
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.
Millar, J.M.
1986-02-01
High field solid-state NMR lineshapes suffer from inhomogeneous broadening since resonance frequencies are a function of molecular orientation. Time domain zero field NMR is a two-dimensional field-cycling technique which removes this broadening by probing the evolution of the spin system under zero applied field. The simplest version, the sudden transition experiment, induces zero field evolution by the sudden removal of the applied magnetic field. Theory and experimental results of this experiment and several variations using pulsed dc magnetic fuelds to initiate zero field evolution are presented. In particular, the pulsed indirect detection method allows detection of the zero field spectrum of one nuclear spin species via another (usually protons) by utilizing the level crossings which occur upon adiabatic demagnetization to zero field. Experimental examples of proton/deuteron systems are presented which demonstrate the method results in enhanced sensitivity relative to that obtained in sudden transition experiments performed directly on deuterium. High resolution /sup 2/H NQR spectra of a series of benzoic acid derivatives are obtained using the sudden transition and indirect detection methods. Librational oscillations in the water molecules of barium chlorate monohydrate are studied using proton and deuterium ZF experiments. 177 refs., 88 figs., 2 tabs.
2D depiction of nonbonding interactions for protein complexes.
Zhou, Peng; Tian, Feifei; Shang, Zhicai
2009-04-30
A program called the 2D-GraLab is described for automatically generating schematic representation of nonbonding interactions across the protein binding interfaces. The input file of this program takes the standard PDB format, and the outputs are two-dimensional PostScript diagrams giving intuitive and informative description of the protein-protein interactions and their energetics properties, including hydrogen bond, salt bridge, van der Waals interaction, hydrophobic contact, pi-pi stacking, disulfide bond, desolvation effect, and loss of conformational entropy. To ensure these interaction information are determined accurately and reliably, methods and standalone programs employed in the 2D-GraLab are all widely used in the chemistry and biology community. The generated diagrams allow intuitive visualization of the interaction mode and binding specificity between two subunits in protein complexes, and by providing information on nonbonding energetics and geometric characteristics, the program offers the possibility of comparing different protein binding profiles in a detailed, objective, and quantitative manner. We expect that this 2D molecular graphics tool could be useful for the experimentalists and theoreticians interested in protein structure and protein engineering.
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
Radiative heat transfer in 2D Dirac materials.
Rodriguez-López, Pablo; Tse, Wang-Kong; Dalvit, Diego A R
2015-06-03
We compute the radiative heat transfer between two sheets of 2D Dirac materials, including topological Chern insulators and graphene, within the framework of the local approximation for the optical response of these materials. In this approximation, which neglects spatial dispersion, we derive both numerically and analytically the short-distance asymptotic of the near-field heat transfer in these systems, and show that it scales as the inverse of the distance between the two sheets. Finally, we discuss the limitations to the validity of this scaling law imposed by spatial dispersion in 2D Dirac materials.
Radiative heat transfer in 2D Dirac materials
Rodriguez-López, Pablo; Tse, Wang -Kong; Dalvit, Diego A. R.
2015-05-12
We compute the radiative heat transfer between two sheets of 2D Dirac materials, including topological Chern insulators and graphene, within the framework of the local approximation for the optical response of these materials. In this approximation, which neglects spatial dispersion, we derive both numerically and analytically the short-distance asymptotic of the near-field heat transfer in these systems, and show that it scales as the inverse of the distance between the two sheets. In conclusion, we discuss the limitations to the validity of this scaling law imposed by spatial dispersion in 2D Dirac materials.
Sieradzan, Adam K.; Krupa, Paweł; Scheraga, Harold A.; Liwo, Adam; Czaplewski, Cezary
2015-01-01
The UNited RESidue (UNRES) model of polypeptide chains is a coarse-grained model in which each amino-acid residue is reduced to two interaction sites, namely a united peptide group (p) located halfway between the two neighboring α-carbon atoms (Cαs), which serve only as geometrical points, and a united side chain (SC) attached to the respective Cα. Owing to this simplification, millisecond Molecular Dynamics simulations of large systems can be performed. While UNRES predicts overall folds well, it reproduces the details of local chain conformation with lower accuracy. Recently, we implemented new knowledge-based torsional potentials (Krupa et. al. J. Chem. Theory Comput., 2013, 9, 4620–4632) that depend on the virtual-bond dihedral angles involving side chains: Cα ⋯ Cα ⋯ Cα ⋯ SC (τ(1)), SC ⋯ Cα ⋯ Cα ⋯ Cα (τ(2)), and SC ⋯ Cα ⋯ Cα ⋯ SC (τ(3)) in the UNRES force field. These potentials resulted in significant improvement of the simulated structures, especially in the loop regions. In this work, we introduce the physics-based counterparts of these potentials, which we derived from the all-atom energy surfaces of terminally-blocked amino-acid residues by Boltzmann integration over the angles λ(1) and λ(2) for rotation about the Cα ⋯ Cα virtual-bond angles and over the side-chain angles χ. The energy surfaces were, in turn, calculated by using the semiempirical AM1 method of molecular quantum mechanics. Entropy contribution was evaluated with use of the harmonic approximation from Hessian matrices. One-dimensional Fourier series in the respective virtual-bond-dihedral angles were fitted to the calculated potentials, and these expressions have been implemented in the UNRES force field. Basic calibration of the UNRES force field with the new potentials was carried out with eight training proteins, by selecting the optimal weight of the new energy terms and reducing the weight of the regular torsional terms. The force field was
2D materials for photon conversion and nanophotonics
NASA Astrophysics Data System (ADS)
Tahersima, Mohammad H.; Sorger, Volker J.
2015-09-01
The field of two-dimensional (2D) materials has the potential to enable unique applications across a wide range of the electromagnetic spectrum. While 2D-layered materials hold promise for next-generation photon-conversion intrinsic limitations and challenges exist that shall be overcome. Here we discuss the intrinsic limitations as well as application opportunities of this new class of materials, and is sponsored by the NSF program Designing Materials to Revolutionize and Engineer our Future (DMREF) program, which links to the President's Materials Genome Initiative. We present general material-related details for photon conversion, and show that taking advantage of the mechanical flexibility of 2D materials by rolling MoS2/graphene/hexagonal boron nitride stack to a spiral solar cell allows for solar absorption up to 90%.
2d-retrieval For Mipas-envisat
NASA Astrophysics Data System (ADS)
Steck, T.; von Clarmann, T.; Grabowski, U.; Höpfner, M.
Limb sounding of the Earth's atmosphere provides vertically high resolved profiles of geophysical parameters. The long ray path through the atmosphere makes limb sounders sensitive to even little abundant species. On the other hand, horizontal in- homogeneities, if not taken into account properly, can cause systematic errors within the retrieval process. Especially for limb emission measurements in the mid IR, at- mopheric temperature gradients result in considerable vmr retrieval errors if they are neglected. We present a dedicated method of taking full 2D fields of state parameters (indepen- dent of tangent points) into account in the forward model and in the retrieval. The basic idea is that the 2D state vector is updated sequentially for each limb scan. This method is applied to the 2D retrieval of temperature and vmr for simulated radiances as expected from MIPAS-ENVISAT.
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)
Breev, A. I.; Kozlov, A. V.
2016-01-01
Within the framework of the method of orbits, expressions have been obtained for the vacuum averages of the energy-momentum tensor of a scalar field with an arbitrary coupling constant in a spacetime with a nonstationary metric of Robertson-Walker type, where space is a homogeneous Riemannian manifold. It is shown that the vacuum averages of the energy-momentum tensor are determined by the complete set of solutions of the reduced equation with a smaller number of independent variables and with algebraic characteristics of homogeneous space.
NASA Astrophysics Data System (ADS)
Azreg-Aïnou, Mustapha
2014-05-01
We derive a shortcut stationary metric formula for generating imperfect fluid rotating solutions, in Boyer-Lindquist coordinates, from spherically symmetric static ones. We explore the properties of the curvature scalar and stress-energy tensor for all types of rotating regular solutions we can generate without restricting ourselves to specific examples of regular solutions (regular black holes or wormholes). We show through examples how it is generally possible to generate an imperfect fluid regular rotating solution via radial coordinate transformations. We derive rotating wormholes that are modeled as imperfect fluids and discuss their physical properties. These are independent on the way the stress-energy tensor is interpreted. A solution modeling an imperfect fluid rotating loop black hole is briefly discussed. We then specialize to the recently discussed stable exotic dust Ellis wormhole as emerged in a source-free radial electric or magnetic field, and we generate its, conjecturally stable, rotating counterpart. This turns out to be an exotic imperfect fluid wormhole, and we determine the stress-energy tensor of both the imperfect fluid and the electric or magnetic field.
2D nanostructures for water purification: graphene and beyond.
Dervin, Saoirse; Dionysiou, Dionysios D; Pillai, Suresh C
2016-08-18
Owing to their atomically thin structure, large surface area and mechanical strength, 2D nanoporous materials are considered to be suitable alternatives for existing desalination and water purification membrane materials. Recent progress in the development of nanoporous graphene based materials has generated enormous potential for water purification technologies. Progress in the development of nanoporous graphene and graphene oxide (GO) membranes, the mechanism of graphene molecular sieve action, structural design, hydrophilic nature, mechanical strength and antifouling properties and the principal challenges associated with nanopore generation are discussed in detail. Subsequently, the recent applications and performance of newly developed 2D materials such as 2D boron nitride (BN) nanosheets, graphyne, molybdenum disulfide (MoS2), tungsten chalcogenides (WS2) and titanium carbide (Ti3C2Tx) are highlighted. In addition, the challenges affecting 2D nanostructures for water purification are highlighted and their applications in the water purification industry are discussed. Though only a few 2D materials have been explored so far for water treatment applications, this emerging field of research is set to attract a great deal of attention in the near future.
Sparse radar imaging using 2D compressed sensing
NASA Astrophysics Data System (ADS)
Hou, Qingkai; Liu, Yang; Chen, Zengping; Su, Shaoying
2014-10-01
Radar imaging is an ill-posed linear inverse problem and compressed sensing (CS) has been proved to have tremendous potential in this field. This paper surveys the theory of radar imaging and a conclusion is drawn that the processing of ISAR imaging can be denoted mathematically as a problem of 2D sparse decomposition. Based on CS, we propose a novel measuring strategy for ISAR imaging radar and utilize random sub-sampling in both range and azimuth dimensions, which will reduce the amount of sampling data tremendously. In order to handle 2D reconstructing problem, the ordinary solution is converting the 2D problem into 1D by Kronecker product, which will increase the size of dictionary and computational cost sharply. In this paper, we introduce the 2D-SL0 algorithm into the reconstruction of imaging. It is proved that 2D-SL0 can achieve equivalent result as other 1D reconstructing methods, but the computational complexity and memory usage is reduced significantly. Moreover, we will state the results of simulating experiments and prove the effectiveness and feasibility of our method.
Mean flow and anisotropic cascades in decaying 2D turbulence
NASA Astrophysics Data System (ADS)
Liu, Chien-Chia; Cerbus, Rory; Gioia, Gustavo; Chakraborty, Pinaki
2015-11-01
Many large-scale atmospheric and oceanic flows are decaying 2D turbulent flows embedded in a non-uniform mean flow. Despite its importance for large-scale weather systems, the affect of non-uniform mean flows on decaying 2D turbulence remains unknown. In the absence of mean flow it is well known that decaying 2D turbulent flows exhibit the enstrophy cascade. More generally, for any 2D turbulent flow, all computational, experimental and field data amassed to date indicate that the spectrum of longitudinal and transverse velocity fluctuations correspond to the same cascade, signifying isotropy of cascades. Here we report experiments on decaying 2D turbulence in soap films with a non-uniform mean flow. We find that the flow transitions from the usual isotropic enstrophy cascade to a series of unusual and, to our knowledge, never before observed or predicted, anisotropic cascades where the longitudinal and transverse spectra are mutually independent. We discuss implications of our results for decaying geophysical turbulence.
NASA Astrophysics Data System (ADS)
Alim, Karen; Armon, Shahaf; Shraiman, Boris I.; Boudaoud, Arezki
2016-10-01
Growth pattern dynamics lie at the heart of morphogenesis. Here, we investigate the growth of plant leaves. We compute the conformal transformation that maps the contour of a leaf at a given stage onto the contour of the same leaf at a later stage. Based on the mapping we predict the local displacement field in the leaf blade and find it to agree with the experimentally measured displacement field to 92%. This approach is applicable to any two-dimensional system with locally isotropic growth, enabling the deduction of the whole growth field just from observation of the tissue contour.
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.
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.
Belyaev, Igor Y; Hillert, Lena; Protopopova, Marina; Tamm, Christoffer; Malmgren, Lars O G; Persson, Bertil R R; Selivanova, Galina; Harms-Ringdahl, Mats
2005-04-01
We used exposure to microwaves from a global system for mobile communication (GSM) mobile phone (915 MHz, specific absorption rate (SAR) 37 mW/kg) and power frequency magnetic field (50 Hz, 15 muT peak value) to investigate the response of lymphocytes from healthy subjects and from persons reporting hypersensitivity to electromagnetic field (EMF). The hypersensitive and healthy donors were matched by gender and age and the data were analyzed blind to treatment condition. The changes in chromatin conformation were measured with the method of anomalous viscosity time dependencies (AVTD). 53BP1 protein, which has been shown to colocalize in foci with DNA double strand breaks (DSBs), was analyzed by immunostaining in situ. Exposure at room temperature to either 915 MHz or 50 Hz resulted in significant condensation of chromatin, shown as AVTD changes, which was similar to the effect of heat shock at 41 degrees C. No significant differences in responses between normal and hypersensitive subjects were detected. Neither 915 MHz nor 50 Hz exposure induced 53BP1 foci. On the contrary, a distinct decrease in background level of 53BP1 signaling was observed upon these exposures as well as after heat shock treatments. This decrease correlated with the AVTD data and may indicate decrease in accessibility of 53BP1 to antibodies because of stress-induced chromatin condensation. Apoptosis was determined by morphological changes and by apoptotic fragmentation of DNA as analyzed by pulsed-field gel electrophoresis (PFGE). No apoptosis was induced by exposure to 50 Hz and 915 MHz microwaves. In conclusion, 50 Hz magnetic field and 915 MHz microwaves under specified conditions of exposure induced comparable responses in lymphocytes from healthy and hypersensitive donors that were similar but not identical to stress response induced by heat shock.
McDaniel, Jesse G; Choi, Eunsong; Son, Chang-Yun; Schmidt, J R; Yethiraj, Arun
2016-01-14
The conformational properties of polymers in ionic liquids are of fundamental interest but not well understood. Atomistic and coarse-grained molecular models predict qualitatively different results for the scaling of chain size with molecular weight, and experiments on dilute solutions are not available. In this work, we develop a first-principles force field for poly(ethylene oxide) (PEO) in the ionic liquid 1-butyl 3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) using symmetry adapted perturbation theory (SAPT). At temperatures above 400 K, simulations employing both the SAPT and OPLS-AA force fields predict that PEO displays ideal chain behavior, in contrast to previous simulations at lower temperature. We therefore argue that the system shows a transition from extended to more compact configurations as the temperature is increased from room temperature to the experimental lower critical solution temperature. Although polarization is shown to be important, its implicit inclusion in the OPLS-AA force is sufficient to describe the structure and energetics of the mixture. The simulations emphasize the difference between ionic liquids from typical solvents for polymers.
Jafar-Zanjani, Samad; Cheng, Jierong; Mosallaei, Hossein
2016-04-10
An efficient auxiliary differential equation method for incorporating 2D inhomogeneous dispersive impedance sheets in the finite-difference time-domain solver is presented. This unique proposed method can successfully solve optical problems of current interest involving 2D sheets. It eliminates the need for ultrafine meshing in the thickness direction, resulting in a significant reduction of computation time and memory requirements. We apply the method to characterize a novel broad-beam leaky-wave antenna created by cascading three sinusoidally modulated reactance surfaces and also to study the effect of curvature on the radiation characteristic of a conformal impedance sheet holographic antenna. Considerable improvement in the simulation time based on our technique in comparison with the traditional volumetric model is reported. Both applications are of great interest in the field of antennas and 2D sheets.
Chuang, Hsun-Jen; Chamlagain, Bhim; Koehler, Michael; Perera, Meeghage Madusanka; Yan, Jiaqiang; Mandrus, David; Tománek, David; Zhou, Zhixian
2016-03-09
We report a new strategy for fabricating 2D/2D low-resistance ohmic contacts for a variety of transition metal dichalcogenides (TMDs) using van der Waals assembly of substitutionally doped TMDs as drain/source contacts and TMDs with no intentional doping as channel materials. We demonstrate that few-layer WSe2 field-effect transistors (FETs) with 2D/2D contacts exhibit low contact resistances of ∼0.3 kΩ μm, high on/off ratios up to >10(9), and high drive currents exceeding 320 μA μm(-1). These favorable characteristics are combined with a two-terminal field-effect hole mobility μFE ≈ 2 × 10(2) cm(2) V(-1) s(-1) at room temperature, which increases to >2 × 10(3) cm(2) V(-1) s(-1) at cryogenic temperatures. We observe a similar performance also in MoS2 and MoSe2 FETs with 2D/2D drain and source contacts. The 2D/2D low-resistance ohmic contacts presented here represent a new device paradigm that overcomes a significant bottleneck in the performance of TMDs and a wide variety of other 2D materials as the channel materials in postsilicon electronics.
Chuang, Hsun -Jen; Chamlagain, Bhim; Koehler, Michael; ...
2016-02-04
Here, we report a new strategy for fabricating 2D/2D low-resistance ohmic contacts for a variety of transition metal dichalcogenides (TMDs) using van der Waals assembly of substitutionally doped TMDs as drain/source contacts and TMDs with no intentional doping as channel materials. We demonstrate that few-layer WSe2 field-effect transistors (FETs) with 2D/2D contacts exhibit low contact resistances of ~0.3 kΩ μm, high on/off ratios up to >109, and high drive currents exceeding 320 μA μm–1. These favorable characteristics are combined with a two-terminal field-effect hole mobility μFE ≈ 2 × 102 cm2 V–1 s–1 at room temperature, which increases to >2more » × 103 cm2 V–1 s–1 at cryogenic temperatures. We observe a similar performance also in MoS2 and MoSe2 FETs with 2D/2D drain and source contacts. The 2D/2D low-resistance ohmic contacts presented here represent a new device paradigm that overcomes a significant bottleneck in the performance of TMDs and a wide variety of other 2D materials as the channel materials in postsilicon electronics.« less
Low Cost 2-D Heatshield Materials
1982-03-05
fabric or tapes (i.e., the warp and fill yarns cross at right angles) do not provide the stretch and conformability characteristics necessary to...manufacture a tapewrapped heatshield which contains a shingle angle greater than a few degrees. This is a result of the continuous yarns in the...needed conformability since neither the warp or fill yarns are continuous. In addition, the material has the ability for limited stretch since movement
In situ hybridization study of CYP2D mRNA in the common marmoset brain
Shimamoto, Yoshinori; Niimi, Kimie; Kitamura, Hiroshi; Tsubakishita, Sae; Takahashi, Eiki
2016-01-01
The common marmoset is a non-human primate that has increasingly employed in the biomedical research including the fields of neuroscience and behavioral studies. Cytochrome P450 (CYP) 2D has been speculated to be involved in psycho-neurologic actions in the human brain. In the present study, to clarify the role of CYP2D in the marmoset brain, we investigated the expression patterns of CYP2D mRNA in the brain using in situ hybridization (ISH). In addition, to identify the gene location of CYP2D19, a well-studied CYP2D isoform in the common marmoset, a fluorescence in situ hybridization (FISH) study was performed. Consistent with findings for the human brain, CYP2D mRNA was localized in the neuronal cells of different brain regions; e.g., the cerebral cortex, hippocampus, substantia nigra, and cerebellum. FISH analysis showed that the CYP2D19 gene was located on chromosome 1q, which is homologous to human chromosome 22 on which the CYP2D6 gene exists. These results suggest that CYP2D in the marmoset brain may play the same role as human CYP2D6 in terms of brain actions, and that the CYP2D19 gene is conserved in a syntenic manner. Taken together, these findings suggest that the common marmoset is a useful model for studying psychiatric disorders related to CYP2D dysfunction in the brain. PMID:27356856
Laboratory Experiments On Continually Forced 2d Turbulence
NASA Astrophysics Data System (ADS)
Wells, M. G.; Clercx, H. J. H.; Van Heijst, G. J. F.
There has been much recent interest in the advection of tracers by 2D turbulence in geophysical flows. While there is a large body of literature on decaying 2D turbulence or forced 2D turbulence in unbounded domains, there have been very few studies of forced turbulence in bounded domains. In this study we present new experimental results from a continuously forced quasi 2D turbulent field. The experiments are performed in a square Perspex tank filled with water. The flow is made quasi 2D by a steady background rotation. The rotation rate of the tank has a small (<8 %) sinusoidal perturbation which leads to the periodic formation of eddies in the corners of the tank. When the oscillation period of the perturbation is greater than an eddy roll-up time-scale, dipole structures are observed to form. The dipoles can migrate away from the walls, and the interior of the tank is continually filled with vortexs. From experimental visualizations the length scale of the vortexs appears to be largely controlled by the initial formation mechanism and large scale structures are not observed to form at large times. Thus the experiments provide a simple way of cre- ating a continuously forced 2D turbulent field. The resulting structures are in contrast with most previous laboratory experiments on 2D turbulence which have investigated decaying turbulence and have observed the formations of large scale structure. In these experiments, decaying turbulence had been produced by a variety of methods such as the decaying turbulence in the wake of a comb of rods (Massen et al 1999), organiza- tion of vortices in thin conducting liquids (Cardoso et al 1994) or in rotating systems where there are sudden changes in angular rotation rate (Konijnenberg et al 1998). Results of dye visualizations, particle tracking experiments and a direct numerical simulation will be presented and discussed in terms of their oceanographic application. Bibliography Cardoso,O. Marteau, D. &Tabeling, P
ERIC Educational Resources Information Center
Hills, Laura A.
2006-01-01
This paper draws on data from a year-long ethnographic study of a group of 12- to 13-year-old girls that explored the processes through which they negotiated gendered physicality within the context of physical education. Bourdieu's concepts of habitus and social fields and McNay's extension of his work underpin a discussion of three contexts where…
Active exterior cloaking for the 2D Laplace and Helmholtz equations.
Vasquez, Fernando Guevara; Milton, Graeme W; Onofrei, Daniel
2009-08-14
A new cloaking method is presented for 2D quasistatics and the 2D Helmholtz equation that we speculate extends to other linear wave equations. For 2D quasistatics it is proven how a single active exterior cloaking device can be used to shield an object from surrounding fields, yet produce very small scattered fields. The problem is reduced to finding a polynomial which is close to 1 in a disk and close to 0 in another disk, and such a polynomial is constructed. For the 2D Helmholtz equation it is numerically shown that three exterior cloaking devices placed around the object suffice to hide it.
Scale invariance vs conformal invariance
NASA Astrophysics Data System (ADS)
Nakayama, Yu
2015-03-01
In this review article, we discuss the distinction and possible equivalence between scale invariance and conformal invariance in relativistic quantum field theories. Under some technical assumptions, we can prove that scale invariant quantum field theories in d = 2 space-time dimensions necessarily possess the enhanced conformal symmetry. The use of the conformal symmetry is well appreciated in the literature, but the fact that all the scale invariant phenomena in d = 2 space-time dimensions enjoy the conformal property relies on the deep structure of the renormalization group. The outstanding question is whether this feature is specific to d = 2 space-time dimensions or it holds in higher dimensions, too. As of January 2014, our consensus is that there is no known example of scale invariant but non-conformal field theories in d = 4 space-time dimensions under the assumptions of (1) unitarity, (2) Poincaré invariance (causality), (3) discrete spectrum in scaling dimensions, (4) existence of scale current and (5) unbroken scale invariance in the vacuum. We have a perturbative proof of the enhancement of conformal invariance from scale invariance based on the higher dimensional analogue of Zamolodchikov's c-theorem, but the non-perturbative proof is yet to come. As a reference we have tried to collect as many interesting examples of scale invariance in relativistic quantum field theories as possible in this article. We give a complementary holographic argument based on the energy-condition of the gravitational system and the space-time diffeomorphism in order to support the claim of the symmetry enhancement. We believe that the possible enhancement of conformal invariance from scale invariance reveals the sublime nature of the renormalization group and space-time with holography. This review is based on a lecture note on scale invariance vs conformal invariance, on which the author gave lectures at Taiwan Central University for the 5th Taiwan School on Strings and
Interplay between Anderson and Stark Localization in 2D Lattices
Kolovsky, A. R.
2008-11-07
This Letter studies the dynamics of a quantum particle in 2D lattices with on-site disorder in the presence of a static field. It is shown that the particle is localized along the field direction, while in the orthogonal direction to the field it shows diffusive dynamics for algebraically large times. For weak disorder an analytical expression for the diffusion coefficient is obtained by mapping the problem to a band random matrix. This expression is confirmed by numerical simulations of the particle's dynamics, which also indicate the existence of a universal equation for the diffusion coefficient, valid for an arbitrary disorder strength.
Orthotropic Piezoelectricity in 2D Nanocellulose
NASA Astrophysics Data System (ADS)
García, Y.; Ruiz-Blanco, Yasser B.; Marrero-Ponce, Yovani; Sotomayor-Torres, C. M.
2016-10-01
The control of electromechanical responses within bonding regions is essential to face frontier challenges in nanotechnologies, such as molecular electronics and biotechnology. Here, we present Iβ-nanocellulose as a potentially new orthotropic 2D piezoelectric crystal. The predicted in-layer piezoelectricity is originated on a sui-generis hydrogen bonds pattern. Upon this fact and by using a combination of ab-initio and ad-hoc models, we introduce a description of electrical profiles along chemical bonds. Such developments lead to obtain a rationale for modelling the extended piezoelectric effect originated within bond scales. The order of magnitude estimated for the 2D Iβ-nanocellulose piezoelectric response, ~pm V‑1, ranks this material at the level of currently used piezoelectric energy generators and new artificial 2D designs. Such finding would be crucial for developing alternative materials to drive emerging nanotechnologies.
Orthotropic Piezoelectricity in 2D Nanocellulose
García, Y.; Ruiz-Blanco, Yasser B.; Marrero-Ponce, Yovani; Sotomayor-Torres, C. M.
2016-01-01
The control of electromechanical responses within bonding regions is essential to face frontier challenges in nanotechnologies, such as molecular electronics and biotechnology. Here, we present Iβ-nanocellulose as a potentially new orthotropic 2D piezoelectric crystal. The predicted in-layer piezoelectricity is originated on a sui-generis hydrogen bonds pattern. Upon this fact and by using a combination of ab-initio and ad-hoc models, we introduce a description of electrical profiles along chemical bonds. Such developments lead to obtain a rationale for modelling the extended piezoelectric effect originated within bond scales. The order of magnitude estimated for the 2D Iβ-nanocellulose piezoelectric response, ~pm V−1, ranks this material at the level of currently used piezoelectric energy generators and new artificial 2D designs. Such finding would be crucial for developing alternative materials to drive emerging nanotechnologies. PMID:27708364
Orthotropic Piezoelectricity in 2D Nanocellulose.
García, Y; Ruiz-Blanco, Yasser B; Marrero-Ponce, Yovani; Sotomayor-Torres, C M
2016-10-06
The control of electromechanical responses within bonding regions is essential to face frontier challenges in nanotechnologies, such as molecular electronics and biotechnology. Here, we present Iβ-nanocellulose as a potentially new orthotropic 2D piezoelectric crystal. The predicted in-layer piezoelectricity is originated on a sui-generis hydrogen bonds pattern. Upon this fact and by using a combination of ab-initio and ad-hoc models, we introduce a description of electrical profiles along chemical bonds. Such developments lead to obtain a rationale for modelling the extended piezoelectric effect originated within bond scales. The order of magnitude estimated for the 2D Iβ-nanocellulose piezoelectric response, ~pm V(-1), ranks this material at the level of currently used piezoelectric energy generators and new artificial 2D designs. Such finding would be crucial for developing alternative materials to drive emerging nanotechnologies.
2D microwave imaging reflectometer electronics
Spear, A. G.; Domier, C. W. Hu, X.; Muscatello, C. M.; Ren, X.; Luhmann, N. C.; Tobias, B. J.
2014-11-15
A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.
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 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.
Vertical heterostructures based on graphene and other 2D materials
Antonova, I. V.
2016-01-15
Recent advances in the fabrication of vertical heterostructures based on graphene and other dielectric and semiconductor single-layer materials, including hexagonal boron nitride and transition-metal dichalcogenides, are reviewed. Significant progress in this field is discussed together with the great prospects for the development of vertical heterostructures for various applications, which are associated, first of all, with reconsideration of the physical principles of the design and operation of device structures based on graphene combined with other 2D materials.
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.
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.
Andolino, David L.; Hoene, Ted; Xiao, Lu; Buchsbaum, Jeffrey; Chang, Andrew L.
2011-11-15
Purpose: To assess the potential reduction in breast dose for young girls with Hodgkin's lymphoma (HL) treated with breast-sparing proton therapy (BS-PT) as compared with three-dimensional conformal involved-field photon radiotherapy (3D-CRT). Methods and Materials: The Clarian Health Cancer Registry was queried for female pediatric patients with the diagnosis of HL who received radiotherapy at the Indiana University Simon Cancer Center during 2006-2009. The original CT simulation images were obtained, and 3D-CRT and BS-PT plans delivering 21 Gy or cobalt gray equivalent (CGE) in 14 fractions were created for each patient. Dose-volume histogram data were collected for both 3D-CRT and BS-PT plans and compared by paired t test for correlated samples. Results: The cancer registry provided 10 female patients with Ann Arbor Stage II HL, aged 10-18 years at the time of treatment. Both mean and maximum breast dose were significantly less with BS-PT compared with 3D-CRT: 0.95 CGE vs. 4.70 Gy (p < 0.001) and 21.07 CGE vs. 23.11 Gy (p < 0.001), respectively. The volume of breast receiving 1.0 Gy/CGE and 5.0 Gy/CGE was also significantly less with BS-PT, 194 cm{sup 3} and 93 cm{sup 3}, respectively, compared with 790 cm{sup 3} and 360 cm{sup 3} with 3D-CRT (p = 0.009, 0.013). Conclusion: Breast-sparing proton therapy has the potential to reduce unnecessary breast dose in young girls with HL by as much as 80% relative to involved-field 3D-CRT.
Validation and testing of the VAM2D computer code
Kool, J.B.; Wu, Y.S. )
1991-10-01
This document describes two modeling studies conducted by HydroGeoLogic, Inc. for the US NRC under contract no. NRC-04089-090, entitled, Validation and Testing of the VAM2D Computer Code.'' VAM2D is a two-dimensional, variably saturated flow and transport code, with applications for performance assessment of nuclear waste disposal. The computer code itself is documented in a separate NUREG document (NUREG/CR-5352, 1989). The studies presented in this report involve application of the VAM2D code to two diverse subsurface modeling problems. The first one involves modeling of infiltration and redistribution of water and solutes in an initially dry, heterogeneous field soil. This application involves detailed modeling over a relatively short, 9-month time period. The second problem pertains to the application of VAM2D to the modeling of a waste disposal facility in a fractured clay, over much larger space and time scales and with particular emphasis on the applicability and reliability of using equivalent porous medium approach for simulating flow and transport in fractured geologic media. Reflecting the separate and distinct nature of the two problems studied, this report is organized in two separate parts. 61 refs., 31 figs., 9 tabs.
Jang, Si Young; Liu, H. Helen; Mohan, Radhe; Siebers, Jeffrey V.
2007-04-15
Because of complex dose distributions and dose gradients that are created in three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiation therapy (IMRT), photon- and electron-energy spectra might change significantly with spatial locations and doses. This study examined variations in photon- and electron-energy spectra in 3D-CRT and IMRT photon fields. The effects of spectral variations on water-to-material stopping-power ratios used in Monte Carlo treatment planning systems and the responses of energy-dependent dosimeters, such as thermoluminescent dosimeters (TLDs) and radiographic films were further studied. The EGSnrc Monte Carlo code was used to simulate megavoltage 3D-CRT and IMRT photon fields. The photon- and electron-energy spectra were calculated in 3D water phantoms and anthropomorphic phantoms based on the fluence scored in voxel grids. We then obtained the water-to-material stopping-power ratios in the local voxels using the Spencer-Attix cavity theory. Changes in the responses of films and TLDs were estimated based on the calculated local energy spectra and published data on the dosimeter energy dependency. Results showed that the photon-energy spectra strongly depended on spatial positions and doses in both the 3D-CRT and IMRT fields. The relative fraction of low-energy photons (<100 keV) increased inversely with the photon dose in low-dose regions of the fields. A similar but smaller effect was observed for electrons in the phantoms. The maximum variation of the water-to-material stopping-power ratio over the range of calculated dose for both 3D-CRT and IMRT was negligible (<1.0%) for ICRU tissue, cortical bone, and soft bone and less than 3.6% for dry air and lung. Because of spectral softening at low doses, radiographic films in the phantoms could over-respond to dose by more than 30%, whereas the over-response of TLDs was less than 10%. Thus, spatial variations of the photon- and electron-energy spectra should be considered
Bajpai, Anubha; Agarwal, Neeraj; Gupta, Satya P
2014-06-01
A quantitative structure-activity relationship (QSAR) study was performed on a series of indole amide analogues reported by Dai et al. [Bioorg Med Chem Lett (2003), 13, 1897-1901] to act as histone deacetylase (HDAC) inhibitors. The multiple regression analysis (MRA) revealed a model showing the significant dependence of the activity on molar refractivity (MR) and global topological charge index (GTCI) of the compounds, suggesting that inhibition of the HDAC by this series of compounds might involve the dispersion interaction with the receptor, where charge transfer between pairs of atoms might greatly help to polarize the molecule. The MRA results were then compared with those obtained by Guo et al. [Bioorg Med Chem (2005), 13, 5424-5434] by comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA). It was found that MRA gave as good results and had as good predictive ability as CoMFA and CoMSIA. Besides, MRA was also able to throw the light on the physicochemical properties of the molecules that were involved in drug-receptor interactions, while CoMFA and CoMSIA could not. The dispersion interaction between the molecule and the active site of the receptor is suggested to be the main interaction.
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.
NASA Astrophysics Data System (ADS)
Wei, Xiao-Kun; Shao, Wei; Shi, Sheng-Bing; Zhang, Yong; Wang, Bing-Zhong
2015-07-01
An efficient conformal locally one-dimensional finite-difference time-domain (LOD-CFDTD) method is presented for solving two-dimensional (2D) electromagnetic (EM) scattering problems. The formulation for the 2D transverse-electric (TE) case is presented and its stability property and numerical dispersion relationship are theoretically investigated. It is shown that the introduction of irregular grids will not damage the numerical stability. Instead of the staircasing approximation, the conformal scheme is only employed to model the curve boundaries, whereas the standard Yee grids are used for the remaining regions. As the irregular grids account for a very small percentage of the total space grids, the conformal scheme has little effect on the numerical dispersion. Moreover, the proposed method, which requires fewer arithmetic operations than the alternating-direction-implicit (ADI) CFDTD method, leads to a further reduction of the CPU time. With the total-field/scattered-field (TF/SF) boundary and the perfectly matched layer (PML), the radar cross section (RCS) of two 2D structures is calculated. The numerical examples verify the accuracy and efficiency of the proposed method. Project supported by the National Natural Science Foundation of China (Grant Nos. 61331007 and 61471105).
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.
Bootstrapping 2D CFTs in the semiclassical limit
NASA Astrophysics Data System (ADS)
Chang, Chi-Ming; Lin, Ying-Hsuan
2016-08-01
We study two-dimensional conformal field theories in the semiclassical limit. In this limit, the four-point function is dominated by intermediate primaries of particular weights along with their descendants, and the crossing equations simplify drastically. For a four-point function receiving sufficiently small contributions from the light primaries, the structure constants involving heavy primaries follow a universal formula. Applying our results to the four-point function of the {Z}_2 twist field in the symmetric product orbifold, we produce the Hellerman bound and the logarithmically corrected Cardy formula that is valid for h ≥ c/12.
Conformations of organophosphine oxides
De Silva, Nuwan; Zahariev, Federico; Hay, Benjamin P.; Gordon, Mark S.; Windus, Theresa L.
2015-07-17
The conformations of a series of organophosphine oxides, OP(CH_{3})_{2}R, where R = methyl, ethyl, isopropyl, tert-butyl, vinyl, and phenyl, are predicted using the MP2/cc-pVTZ level of theory. Comparison of potential energy surfaces for rotation about P–C bonds with crystal structure data reveals a strong correlation between predicted location and energetics of minima and histograms of dihedral angle distributions observed in the solid state. In addition, the most stable conformers are those that minimize the extent of steric repulsion between adjacent rotor substituents, and the torsional barriers tend to increase with the steric bulk of the rotating alkyl group. MM3 force field parameters were adjusted to fit the MP2 results, providing a fast and accurate model for predicting organophosphine oxides shapes—an essential part of understanding the chemistry of these compounds. As a result, the predictive power of the modified MM3 model was tested against MP2/cc-pVTZ conformations for triethylphosphine oxide, OP(CH_{2}CH_{3})_{3}, and triphenylphosphine oxide, OP(Ph)_{3}.
Conformations of organophosphine oxides
De Silva, Nuwan; Zahariev, Federico; Hay, Benjamin P.; ...
2015-07-17
The conformations of a series of organophosphine oxides, OP(CH3)2R, where R = methyl, ethyl, isopropyl, tert-butyl, vinyl, and phenyl, are predicted using the MP2/cc-pVTZ level of theory. Comparison of potential energy surfaces for rotation about P–C bonds with crystal structure data reveals a strong correlation between predicted location and energetics of minima and histograms of dihedral angle distributions observed in the solid state. In addition, the most stable conformers are those that minimize the extent of steric repulsion between adjacent rotor substituents, and the torsional barriers tend to increase with the steric bulk of the rotating alkyl group. MM3 forcemore » field parameters were adjusted to fit the MP2 results, providing a fast and accurate model for predicting organophosphine oxides shapes—an essential part of understanding the chemistry of these compounds. As a result, the predictive power of the modified MM3 model was tested against MP2/cc-pVTZ conformations for triethylphosphine oxide, OP(CH2CH3)3, and triphenylphosphine oxide, OP(Ph)3.« less
Controlling avalanche criticality in 2D nano arrays
Zohar, Y. C.; Yochelis, S.; Dahmen, K. A.; Jung, G.; Paltiel, Y.
2013-01-01
Many physical systems respond to slowly changing external force through avalanches spanning broad range of sizes. Some systems crackle even without apparent external force, such as bursts of neuronal activity or charge transfer avalanches in 2D molecular layers. Advanced development of theoretical models describing disorder-induced critical phenomena calls for experiments probing the dynamics upon tuneable disorder. Here we show that isomeric structural transitions in 2D organic self-assembled monolayer (SAM) exhibit critical dynamics with experimentally tuneable disorder. The system consists of field effect transistor coupled through SAM to illuminated semiconducting nanocrystals (NCs). Charges photoinduced in NCs are transferred through SAM to the transistor surface and modulate its conductivity. Avalanches of isomeric structural transitions are revealed by measuring the current noise I(t) of the transistor. Accumulated surface traps charges reduce dipole moments of the molecules, decrease their coupling, and thus decrease the critical disorder of the SAM enabling its tuning during experiments. PMID:23677142
Controlling avalanche criticality in 2D nano arrays.
Zohar, Y C; Yochelis, S; Dahmen, K A; Jung, G; Paltiel, Y
2013-01-01
Many physical systems respond to slowly changing external force through avalanches spanning broad range of sizes. Some systems crackle even without apparent external force, such as bursts of neuronal activity or charge transfer avalanches in 2D molecular layers. Advanced development of theoretical models describing disorder-induced critical phenomena calls for experiments probing the dynamics upon tuneable disorder. Here we show that isomeric structural transitions in 2D organic self-assembled monolayer (SAM) exhibit critical dynamics with experimentally tuneable disorder. The system consists of field effect transistor coupled through SAM to illuminated semiconducting nanocrystals (NCs). Charges photoinduced in NCs are transferred through SAM to the transistor surface and modulate its conductivity. Avalanches of isomeric structural transitions are revealed by measuring the current noise I(t) of the transistor. Accumulated surface traps charges reduce dipole moments of the molecules, decrease their coupling, and thus decrease the critical disorder of the SAM enabling its tuning during experiments.
Solution NMR conformation of glycosaminoglycans.
Pomin, Vitor H
2014-04-01
Nuclear magnetic resonance (NMR) spectroscopy has been giving a pivotal contribution to the progress of glycomics, mostly by elucidating the structural, dynamical, conformational and intermolecular binding aspects of carbohydrates. Particularly in the field of conformation, NOE resonances, scalar couplings, residual dipolar couplings, and chemical shift anisotropy offsets have been the principal NMR parameters utilized. Molecular dynamics calculations restrained by NMR-data input are usually employed in conjunction to generate glycosidic bond dihedral angles. Glycosaminoglycans (GAGs) are a special class of sulfated polysaccharides extensively studied worldwide. Besides regulating innumerous physiological processes, these glycans are also widely explored in the global market as either clinical or nutraceutical agents. The conformational aspects of GAGs are key regulators to the quality of interactions with the functional proteins involved in biological events. This report discusses the solution conformation of each GAG type analyzed by one or more of the above-mentioned methods.
Patient tolerance of rectal balloons in conformal radiation treatment of prostate cancer
Ronson, Brian B.; Yonemoto, Les T.; Rossi, Carl J.; Slater, James M.; Slater, Jerry D. . E-mail: jdslater@dominion.llumc.edu
2006-04-01
Purpose: To evaluate patient tolerance of intrarectal balloons used during conformal prostate irradiation. Methods and Materials: A retrospective analysis was performed on 3,561 patients who underwent conformal radiation for prostate cancer. Therapy consisted of proton irradiation of the prostate and seminal vesicles and X-ray treatment of the pelvis when warranted. The number of treatments in which the balloon was tolerated was recorded. Results were stratified according to method of irradiation (protons alone vs. combined proton/X-ray) and method of planning (2D vs. 3D planning of X-ray fields in patients undergoing combination treatment). Results: Of all the patients evaluated, 3,474 (97.6%) tolerated the balloon throughout treatment; 87 (2.4%) declined the balloon for 1 or more treatments and tolerated the balloon for 85.5% of their treatments. Chi-square analysis revealed a significant tolerance advantage in those who received protons alone compared with combination treatment (99.5% vs. 95.7%; p < 0.001). In patients undergoing combination treatment, chi-square analysis did not reveal significant tolerance differences in patients undergoing 3D vs. 2D planning for pelvic X-ray fields (95.74% vs. 95.72%; p = 0.990). Conclusions: Intrarectal balloons are well tolerated over a course of conformal prostate irradiation.
Instantons in 2D U(1) Higgs model and 2D CP(N-1) sigma models
NASA Astrophysics Data System (ADS)
Lian, Yaogang
2007-12-01
In this thesis I present the results of a study of the topological structures of 2D U(1) Higgs model and 2D CP N-1 sigma models. Both models have been studied using the overlap Dirac operator construction of topological charge density. The overlap operator provides a more incisive probe into the local topological structure of gauge field configurations than the traditional plaquette-based operator. In the 2D U(1) Higgs model, we show that classical instantons with finite sizes violate the negativity of topological charge correlator by giving a positive contribution to the correlator at non-zero separation. We argue that instantons in 2D U(1) Higgs model must be accompanied by large quantum fluctuations in order to solve this contradiction. In 2D CPN-1 sigma models, we observe the anomalous scaling behavior of the topological susceptibility chi t for N ≤ 3. The divergence of chi t in these models is traced to the presence of small instantons with a radius of order a (= lattice spacing), which are directly observed on the lattice. The observation of these small instantons provides detailed confirmation of Luscher's argument that such short-distance excitations, with quantized topological charge, should be the dominant topological fluctuations in CP1 and CP 2, leading to a divergent topological susceptibility in the continuum limit. For the CPN-1 models with N > 3 the topological susceptibility is observed to scale properly with the mass gap. Another topic presented in this thesis is an implementation of the Zolotarev optimal rational approximation for the overlap Dirac operator. This new implementation has reduced the time complexity of the overlap routine from O(N3 ) to O(N), where N is the total number of sites on the lattice. This opens up a door to more accurate lattice measurements in the future.
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.
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.
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.
Campuzano, S; Pedrero, M; Nikoleli, G-P; Pingarrón, J M; Nikolelis, D P
2017-03-15
Owing to the outstanding conductivity and biocompatibility as well as numerous other fascinating properties of two-dimensional (2D)-nanomaterials, 2D-based nanohybrids have shown unparalleled superiorities in the field of electrochemical biosensors. This review highlights latest advances in electrochemical immunosensors for clinical biomarkers based on different hybrid 2D-nanomaterials. Particular attention will be given to hybrid nanostructures involving graphene and other graphene-like 2D-layered nanomaterials (GLNs). Several recent strategies for using such 2D-nanomaterial heterostructures in the development of modern immunosensors, both for tagging or modifying electrode transducers, are summarized and discussed. These hybrid nanocomposites, quite superior than their rival materials, will undoubtedly have an important impact within the near future and not only in clinical areas. Current challenges and future perspectives in this rapidly growing field are also outlined.
NASA Astrophysics Data System (ADS)
Mikhalev, A. V.; Pinchuk, I. A.
2005-06-01
The structure of Steinberg conformal algebras is studied; these are analogues of Steinberg groups (algebras, superalgebras).A Steinberg conformal algebra is defined as an abstract algebra by a system of generators and relations between the generators. It is proved that a Steinberg conformal algebra is the universal central extension of the corresponding conformal Lie algebra; the kernel of this extension is calculated.
NASA Astrophysics Data System (ADS)
McGarry, Conor K.; Butterworth, Karl T.; Trainor, Colman; McMahon, Stephen J.; O'Sullivan, Joe M.; Prise, Kevin M.; Hounsell, Alan R.
2012-10-01
The aim of this work is to determine the out-of-field survival of cells irradiated with either the primary field or scattered radiation in the presence and absence of intercellular communication following delivery of conformal, IMRT and VMAT treatment plans. Single beam, conformal, IMRT and VMAT plans were created to deliver 3 Gy to half the area of a T80 flask containing either DU-145 or AGO-1522 cells allowing intercellular communication between the in- and out-of-field cell populations. The same plans were delivered to a similar custom made phantom used to hold two T25 culture flasks, one flask in-field and one out-of-field to allow comparison of cell survival responses when intercellular communication is physically inhibited. Plans were created for the delivery of 8 Gy to the more radio-resistant DU-145 cells only in the presence and absence of intercellular communication. Cell survival was determined by clonogenic assay. In both cell lines, the out-of-field survival was not statistically different between delivery techniques for either cell line or dose. There was however, a statistically significant difference between survival out-of-field when intercellular communication was intact (single T80 culture flask) or inhibited (multiple T25 culture flasks) to in-field for all plans. No statistically significant difference was observed in-field with or without cellular communication to out-of-field for all plans. These data demonstrate out-of-field effects as important determinants of cell survival following exposure to modulated irradiation fields when cellular communication between differentially irradiated cell populations is present. This data is further evidence that refinement of existing radiobiological models to include indirect cell killing effects is required.
Hybrid 3D-2D printing for bone scaffolds fabrication
NASA Astrophysics Data System (ADS)
Seleznev, V. A.; Prinz, V. Ya
2017-02-01
It is a well-known fact that bone scaffold topography on micro- and nanometer scale influences the cellular behavior. Nano-scale surface modification of scaffolds allows the modulation of biological activity for enhanced cell differentiation. To date, there has been only a limited success in printing scaffolds with micro- and nano-scale features exposed on the surface. To improve on the currently available imperfect technologies, in our paper we introduce new hybrid technologies based on a combination of 2D (nano imprint) and 3D printing methods. The first method is based on using light projection 3D printing and simultaneous 2D nanostructuring of each of the layers during the formation of the 3D structure. The second method is based on the sequential integration of preliminarily created 2D nanostructured films into a 3D printed structure. The capabilities of the developed hybrid technologies are demonstrated with the example of forming 3D bone scaffolds. The proposed technologies can be used to fabricate complex 3D micro- and nanostructured products for various fields.
Volumetric elasticity imaging with a 2-D CMUT array.
Fisher, Ted G; Hall, Timothy J; Panda, Satchi; Richards, Michael S; Barbone, Paul E; Jiang, Jingfeng; Resnick, Jeff; Barnes, Steve
2010-06-01
This article reports the use of a two-dimensional (2-D) capacitive micro-machined ultrasound transducer (CMUT) to acquire radio-frequency (RF) echo data from relatively large volumes of a simple ultrasound phantom to compare three-dimensional (3-D) elasticity imaging methods. Typical 2-D motion tracking for elasticity image formation was compared with three different methods of 3-D motion tracking, with sum-squared difference (SSD) used as the similarity measure. Differences among the algorithms were the degree to which they tracked elevational motion: not at all (2-D search), planar search, combination of multiple planes and plane independent guided search. The cross-correlation between the predeformation and motion-compensated postdeformation RF echo fields was used to quantify motion tracking accuracy. The lesion contrast-to-noise ratio was used to quantify image quality. Tracking accuracy and strain image quality generally improved with increased tracking sophistication. When used as input for a 3-D modulus reconstruction, high quality 3-D displacement estimates yielded accurate and low noise modulus reconstruction.
Building 3D scenes from 2D image sequences
NASA Astrophysics Data System (ADS)
Cristea, Paul D.
2006-05-01
Sequences of 2D images, taken by a single moving video receptor, can be fused to generate a 3D representation. This dynamic stereopsis exists in birds and reptiles, whereas the static binocular stereopsis is common in mammals, including humans. Most multimedia computer vision systems for stereo image capture, transmission, processing, storage and retrieval are based on the concept of binocularity. As a consequence, their main goal is to acquire, conserve and enhance pairs of 2D images able to generate a 3D visual perception in a human observer. Stereo vision in birds is based on the fusion of images captured by each eye, with previously acquired and memorized images from the same eye. The process goes on simultaneously and conjointly for both eyes and generates an almost complete all-around visual field. As a consequence, the baseline distance is no longer fixed, as in the case of binocular 3D view, but adjustable in accordance with the distance to the object of main interest, allowing a controllable depth effect. Moreover, the synthesized 3D scene can have a better resolution than each individual 2D image in the sequence. Compression of 3D scenes can be achieved, and stereo transmissions with lower bandwidth requirements can be developed.
Volumetric Elasticity Imaging with a 2D CMUT Array
Fisher, Ted G.; Hall, Timothy J.; Panda, Satchi; Richards, Michael S.; Barbone, Paul E.; Jiang, Jingfeng; Resnick, Jeff; Barnes, Steve
2010-01-01
This paper reports the use of a two-dimensional (2D) capacitive micro-machined ultrasound transducer (CMUT) to acquire radio frequency (RF) echo data from relatively large volumes of a simple ultrasound phantom to compare 3D elasticity imaging methods. Typical 2D motion tracking for elasticity image formation was compared to three different methods of 3D motion tracking, with sum-squared difference (SSD) used as the similarity measure. Differences among the algorithms were the degree to which they tracked elevational motion: not at all (2D search), planar search, combination of multiple planes, and plane independent guided search. The cross correlation between the pre-deformation and motion-compensated post-deformation RF echo fields was used to quantify motion tracking accuracy. The lesion contrast-to-noise ratio was used to quantify image quality. Tracking accuracy and strain image quality generally improved with increased tracking sophistication. When used as input for a 3D modulus reconstruction, high quality 3D displacement estimates yielded accurate and low noise modulus reconstruction. PMID:20510188
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
Eikonalization of conformal blocks
Fitzpatrick, A. Liam; Kaplan, Jared; Walters, Matthew T.; Wang, Junpu
2015-09-03
Classical field configurations such as the Coulomb potential and Schwarzschild solution are built from the t-channel exchange of many light degrees of freedom. We study the CFT analog of this phenomenon, which we term the 'eikonalization' of conformal blocks. We show that when an operator T appears in the OPE Ο(x)Ο(0), then the large spin Fock space states [TT···T]_{ℓ} also appear in this OPE with a computable coefficient. The sum over the exchange of these Fock space states in an
Eikonalization of conformal blocks
Fitzpatrick, A. Liam; Kaplan, Jared; Walters, Matthew T.; ...
2015-09-03
Classical field configurations such as the Coulomb potential and Schwarzschild solution are built from the t-channel exchange of many light degrees of freedom. We study the CFT analog of this phenomenon, which we term the 'eikonalization' of conformal blocks. We show that when an operator T appears in the OPE Ο(x)Ο(0), then the large spin Fock space states [TT···T]ℓ also appear in this OPE with a computable coefficient. The sum over the exchange of these Fock space states in an correlator build the classical 'T field' in the dual AdS description. In some limits the sum of all Fock spacemore » exchanges can be represented as the exponential of a single T exchange in the 4-pt correlator of O. Our results should be useful for systematizing 1/ℓ perturbation theory in general CFTs and simplifying the computation of large spin OPE coefficients. As examples we obtain the leading log ℓ dependence of Fock space conformal block coefficients, and we directly compute the OPE coefficients of the simplest ‘triple-trace’ operators.« less
Scattering Via Conformal Higher Spin Exchanges
NASA Astrophysics Data System (ADS)
Tseytlin, A. A.
We consider a model of massless scalars interacting (via bilinear conserved currents) with conformal higher spin fields in flat space. We compute the tree-level four-scalar scattering amplitude using a natural prescription for summation over an infinite set of conformal higher spin exchanges and find that it vanishes. Independently, we show that the vanishing of the scalar scattering amplitude is, in fact, implied by the global conformal higher spin symmetry of this model.
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
Differential patterns of 2D location versus depth decoding along the visual hierarchy.
Finlayson, Nonie J; Zhang, Xiaoli; Golomb, Julie D
2017-02-15
Visual information is initially represented as 2D images on the retina, but our brains are able to transform this input to perceive our rich 3D environment. While many studies have explored 2D spatial representations or depth perception in isolation, it remains unknown if or how these processes interact in human visual cortex. Here we used functional MRI and multi-voxel pattern analysis to investigate the relationship between 2D location and position-in-depth information. We stimulated different 3D locations in a blocked design: each location was defined by horizontal, vertical, and depth position. Participants remained fixated at the center of the screen while passively viewing the peripheral stimuli with red/green anaglyph glasses. Our results revealed a widespread, systematic transition throughout visual cortex. As expected, 2D location information (horizontal and vertical) could be strongly decoded in early visual areas, with reduced decoding higher along the visual hierarchy, consistent with known changes in receptive field sizes. Critically, we found that the decoding of position-in-depth information tracked inversely with the 2D location pattern, with the magnitude of depth decoding gradually increasing from intermediate to higher visual and category regions. Representations of 2D location information became increasingly location-tolerant in later areas, where depth information was also tolerant to changes in 2D location. We propose that spatial representations gradually transition from 2D-dominant to balanced 3D (2D and depth) along the visual hierarchy.
Prinz, V Ya; Seleznev, Vladimir
2016-12-13
It is a well-known fact that bone scaffold topography on micro- and nanometer scale influences the cellular behavior. Nano-scale surface modification of scaffolds allows the modulation of biological activity for enhanced cell differentiation. To date, there has been only a limited success in printing scaffolds with micro- and nano-scale features exposed on the surface. To improve on the currently available imperfect technologies, in our paper we introduce new hybrid technologies based on a combination of 2D (nano imprint) and 3D printing methods. The first method is based on using light projection 3D printing and simultaneous 2D nanostructuring of each of the layers during the formation of the 3D structure. The second method is based on the sequential integration of preliminarily created 2D nanostructured films into a 3D printed structure. The capabilities of the developed hybrid technologies are demonstrated with the example of forming 3D bone scaffolds. The proposed technologies can be used to fabricate complex 3D micro- and nanostructured products for various fields.
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.
Scientometric analysis and bibliography of digit ratio (2D:4D) research, 1998-2008.
Voracek, Martin; Loibl, Lisa Mariella
2009-06-01
A scientometric analysis of modern research on the second-to-fourth digit ratio (2D:4D), a widely studied putative marker for prenatal androgen action, is presented. In early 2009, this literature totalled more than 300 publications and, since its initiation in 1998, has grown at a rate slightly faster than linear. Key findings included evidence of publication bias and citation bias, incomplete coverage and outdatedness of existing reviews, and a dearth of meta-analyses in this field. 2D:4D research clusters noticeably in terms of researchers, institutions, countries, and journals involved. Although 2D:4D is an anthropometric trait, most of the research has been conducted at psychology departments, not anthropology departments. However, 2D:4D research has not been predominantly published in core and specialized journals of psychology, but rather in more broadly scoped journals of the behavioral sciences, biomedical social sciences, and neurosciences. Total citation numbers of 2D:4D papers for the most part were not larger than their citation counts within 2D:4D research, indicating that until now, only a few 2D:4D studies have attained broader interest outside this specific field. Comparative citation analyses show that 2D:4D research presently is commensurate in size and importance to evolutionary psychological jealousy research, but has grown faster than the latter field. In contrast, it is much smaller and has spread more slowly than research about the Implicit Association Test Fifteen conjectures about anticipated trends in 2D:4D research are outlined, appendixed by a first-time bibliography of the entirety of the published 2D:4D literature.
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
Line-source excitation of realistic conformal metasurface cloaks
NASA Astrophysics Data System (ADS)
Padooru, Yashwanth R.; Yakovlev, Alexander B.; Chen, Pai-Yen; Alù, Andrea
2012-11-01
Following our recently introduced analytical tools to model and design conformal mantle cloaks based on metasurfaces [Padooru et al., J. Appl. Phys. 112, 034907 (2012)], we investigate their performance and physical properties when excited by an electric line source placed in their close proximity. We consider metasurfaces formed by 2-D arrays of slotted (meshes and Jerusalem cross slots) and printed (patches and Jerusalem crosses) sub-wavelength elements. The electromagnetic scattering analysis is carried out using a rigorous analytical model, which utilizes the two-sided impedance boundary conditions at the interface of the sub-wavelength elements. It is shown that the homogenized grid-impedance expressions, originally derived for planar arrays of sub-wavelength elements and plane-wave excitation, may be successfully used to model and tailor the surface reactance of cylindrical conformal mantle cloaks illuminated by near-field sources. Our closed-form analytical results are in good agreement with full-wave numerical simulations, up to sub-wavelength distances from the metasurface, confirming that mantle cloaks may be very effective to suppress the scattering of moderately sized objects, independent of the type of excitation and point of observation. We also discuss the dual functionality of these metasurfaces to boost radiation efficiency and directivity from confined near-field sources.
Conformal and projective symmetries in Newtonian cosmology
NASA Astrophysics Data System (ADS)
Duval, C.; Gibbons, G. W.; Horváthy, P. A.
2017-02-01
Definitions of non-relativistic conformal transformations are considered both in the Newton-Cartan and in the Kaluza-Klein-type Eisenhart/Bargmann geometrical frameworks. The symmetry groups that come into play are exemplified by the cosmological, and also the Newton-Hooke solutions of Newton's gravitational field equations. It is shown, in particular, that the maximal symmetry group of the standard cosmological model is isomorphic to the 13-dimensional conformal-Newton-Cartan group whose conformal-Bargmann extension is explicitly worked out. Attention is drawn to the appearance of independent space and time dilations, in contrast with the Schrödinger group or the Conformal Galilei Algebra.
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.
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
Unprecedented folding in linker based flexible tripodal molecule and their conformational analysis
NASA Astrophysics Data System (ADS)
Gaurav, Archana; Kumar, Ranjeet; Gupta, Hariom; Ravikumar, K.; Sridhar, B.; Tewari, Ashish Kumar
2017-04-01
Here, we first time report the flexible tripodal molecules, contained propylene as a linker, thiocyanuric acid as central core and, p-nitro phenol 1 and pyridazinone 2 as terminal for conformational studies. The conformational studies of these tripodal molecules have been carried by X-ray crystallography, 2D-NOESY spectra and computational studies. Both the molecules have shown folded conformations in solid and solution state however solid state conformation is not stable in gaseous state.
Completeness of the classical 2D Ising model and universal quantum computation.
Van den Nest, M; Dür, W; Briegel, H J
2008-03-21
We prove that the 2D Ising model is complete in the sense that the partition function of any classical q-state spin model (on an arbitrary graph) can be expressed as a special instance of the partition function of a 2D Ising model with complex inhomogeneous couplings and external fields. In the case where the original model is an Ising or Potts-type model, we find that the corresponding 2D square lattice requires only polynomially more spins with respect to the original one, and we give a constructive method to map such models to the 2D Ising model. For more general models the overhead in system size may be exponential. The results are established by connecting classical spin models with measurement-based quantum computation and invoking the universality of the 2D cluster states.
Spectroscopic properties of multilayered gold nanoparticle 2D sheets.
Yoshida, Akihito; Imazu, Keisuke; Li, Xinheng; Okamoto, Koichi; Tamada, Kaoru
2012-12-11
We report the fabrication technique and optical properties of multilayered two-dimensional (2D) gold nanoparticle sheets ("Au nanosheet"). The 2D crystalline monolayer sheet composed of Au nanoparticles shows an absorption peak originating from a localized surface plasmon resonance (LSPR). It was found that the absorption spectra dramatically change when the monolayers are assembled into the multilayers on different substrates (quartz or Au). In the case of the multilayers on Au thin film (d = 200 nm), the LSPR peak is shifted to longer wavelength at the near-IR region by increasing the number of layers. The absorbance also depends on the layer number and shows the nonlinear behavior. On the other hand, the multilayers on quartz substrate show neither such LSPR peak shift nor nonlinear response of absorbance. The layer number dependence on metal surfaces can be interpreted as the combined effects between the near-field coupling of the LSPR and the far-field optics of the stratified metamaterial films, as proposed in our previous study. We also report the spectroscopic properties of hybrid multilayers composed of two kinds of monolayers, i.e., Au nanosheet and Ag nanosheet. The combination of the different metal nanoparticle sheets realizes more flexible plasmonic color tuning.
2D Numerical MHD Models of Solar Explosive Events
NASA Astrophysics Data System (ADS)
Roussev, I.
2001-10-01
Observations of the Sun reveal a great variety of dynamic phenomena interpretable as a manifestation of magnetic reconnection. These range from small-scale 'Explosive events' seen in the 'quiet' Sun, through violent flares observed in active regions. The high degree of complexity of the magnetic field inferred from observations may locally produce a fruitful environment for the process of magnetic reconnection to take place. Explosive events are associated with regions undergoing magnetic flux cancellation. This thesis presents a 2-dimensional (2D) numerical study devoted to explore the idea that the salient spectral signatures seen in explosive events are most probably caused by bi-directional outflow jets as a results of an ongoing magnetic reconnection. In order to provide qualitative results needed for the better physical interpretation of solar explosive events, several models intended to represent a 'quiet' Sun transition of solar explosive events, several models intended to represent a 'quiet' Sun transition region undergoing magnetic reconnection are examined, in both unstratified and gravitationally stratified atmospheres. The magnetic reconnection is initiated in an ad hoc manner, and the dynamic evolution is followed by numerically solving the equations of 2D dissipative magnetohydrodynamics (MHD), including the effects of field-aligned thermal conduction, radiative losses, volumetric heating, and anomalous resistivity.
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
Transmission of acoustic waves through mixing layers and 2D isotropic turbulence
NASA Astrophysics Data System (ADS)
Juve, D.; Blanc-Benon, P.; Comte-Bellot, G.
Ray tracing and parabolic equation methods have been used to study the properties of acoustic waves transmitted through turbulent velocity fields. A numerical simulation permits individual realizations of the turbulent field, which then allow, if desired, an ensemble averaging of the fields. Two flows have been considered, 2D isotropic turbulence and a 2D mixing layer. The following complementary aspects are developed: the occurrence of caustics, the reinforced or weakened zones of the acoustic field, the eigenrays between a source and a receiver, and the associated travel times, variances, and scintillation index.