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Caltech Authors (139.151 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 59.968

  1. Optimizing large parameter sets in variational quantum Monte Carlo

    Neuscamman, Eric; Umrigar, C. J.; Chan, Garnet Kin-Lic
    We present a technique for optimizing hundreds of thousands of variational parameters in variational quantum Monte Carlo. By introducing iterative Krylov subspace solvers and by multiplying by the Hamiltonian and overlap matrices as they are sampled, we remove the need to construct and store these matrices and thus bypass the most expensive steps of the stochastic reconfiguration and linear method optimization techniques. We demonstrate the effectiveness of this approach by using stochastic reconfiguration to optimize a correlator product state wave function with a Pfaffian reference for four example systems. In two examples on the two dimensional Fermionic Hubbard model, we...

  2. On the crystal structures of two inclusion compounds of tris(5-acetyl-3-thienyl)methane

    Marsh, Richard E.
    The crystal structures of the ethanol and the ethyl acetate inclusion compounds of TATM, CH(C_6-H_5OS)_3, were originally reported in space group P1, with two independent TATM molecules and one solvent molecule in the unit cell. However, the pairs of TATM molecules are closely related by centers of symmetry and the structures are better described in space group P1. Refinements in P1 led to lower e.s.d. 's and R values and to much more reasonable bond lengths, angles and U_(ij)’s for the TATM molecules; however, the solvent molecules are disordered and can be described no better in P1 than they were...

  3. Dinitrogen or dichloromethane?

    Marsh, Richard E.; Olmstead, Marilyn M.; Schaefer, William P.; Schomaker, Verner
    A recent article in this journal reports the crystal structure of (octaethylazaporphyrinato)iron(III) chloride, (OEP)Fe^(III)-Cl·CH_2Cl_3·N_2, at 130 K, in which the N_2 molecule is referred to as "unusual, but no other explanation for two equal-sized atoms separated by 1.21 (2) Å. could be found". Even more unusual is a "close contact" of 1.86 Å between two such molecules (related by a center of symmetry), forming an angle N-N≡N of 109° and thus leading to a sort of perazabuta-1,3-diene molecule. If this were a genuine new tetranitrogen molecules so gently produced, it would be a remarkable discovery, worth celebrating as a milestone in...

  4. On the Space Group of Cs_7Cd_3Br_(13)

    Marsh, Richard E.
    The crystal structure of Cs_7Cd_3Br_(13), recently described as noncentrosymmetric in space group I4̄c2, should instead be described as centrosymmetric, space group I4/mcm. Other details of the structure are effectively unchanged.

  5. Swarm Assignment and Trajectory Optimization Using Variable-Swarm, Distributed Auction Assignment and Model Predictive Control

    Morgan, Daniel; Chung, Soon-Jo; Hadaegh, Fred Y.
    This paper presents a distributed, guidance and control algorithm for reconfiguring swarms composed of hundreds to thousands of agents with limited communication and computation capabilities. This algorithm solves both the optimal assignment and collision- free trajectory generation for swarms, in an integrated manner, when given the desired shape of the swarm (without pre-assigned terminal positions). The optimal assignment problem is solved using a distributed auction assignment that can vary the number of target positions in the assignment, and the collision-free trajectories are generated using sequential convex programming. Finally, model predictive control is used to solve the assignment and trajectory generation in...

  6. A Theoretical Study of the 3d-M(smif)_2 Complexes: Structure, Magnetism, and Oxidation States

    Hachmann, Johannes; Frazier, Brenda A.; Wolczanski, Peter T.; Chan, Garnet Kin-Lic
    We carry out a theoretical investigation of the recently reported M(smif)_2 series1, 2 and find a number of interesting phenomena. These include complex potential energy surfaces with near-degenerate stationary points, low-lying states, non-trivial electron configurations, as well as non-innocent ligand behavior. The M(smif)_2 exhibit a delicate balance between geometry and electronic structure, which has implications not only for their reactivity but also for controlling their properties through ligand design. We address methodological issues and show how conceptual quantities such as oxidation states and electronic configurations can be extracted through a simple analysis of the electron and spin densities—without a complicated examination...

  7. An Evolutionary Architecture for the Automated Conceptual Design of Aerospace Systems

    Duffy, Michael; Chung, Soon-Jo; Bergman, Lawrence
    Many different approaches to total system design and optimization have been atempted. The Genetic Learning Automated Design Optimization Software (GLADOS) presented here represent a flexible evolutionary algorithm bases architecture intented to allow for the generation of conceptual or preliminary design stage aircraft designs without any human beings in the loop. The benefits of this approach being more thorough exploration of the design space, the ability to analyze and produce high commonality and modular and modular design configurations, and allowing design capabilities to directly growing computational capabilities. Both an overview of the idealized architecture as well as the results from a...

  8. A highly solvated zinc(II) tetrakis(pentafluorophenyl)-β-octabromoporphyrin

    Marsh, Richard E.; Schaefer, William P.; Hodge, Julia A.; Hughes, Maureen E.; Gray, Harry B.; Lyons, James E.; Ellis, Paul E., Jr.
    The title compound, {4,5,9,10,14,15,19,20-octabromo-2,7,12,17-tetrakis(pentafluorophenyl)-21,22,23,- 24-tetraazapentacyclo[16.2.1.1^(3,6).1^(8,11).1^(13,16)]tetracosa-1,3(21),4,6,8(22),9,11,13(23),14,16,18(24),19-dodecaene }zinc(II) (carbon tetrachloride, o-dichlorobenzene, acetone, methanol, water solvate) has a large tetrahedral distortion, with the Br atoms as much as 1.83 Å from the plane of the N atoms. The distortion affects primarily bond angles and bond torsion angles; bond distances in the molecule are normal. Several different solvents are incorporated into the crystal, providing a close (2.16 Å) O atom as an axial neighbor to Zn and a more distant (3.16 Å) Cl atom, in the opposite axial site.

  9. On the crystal structure of bis(dipicolinato)ferrate(III) dihydrate

    Marsh, Richard E.
    The structure of [H_5O_2]+[Fe(C_7H_3NO_4)_2]^- was recently described and refined [Cousson, Nectoux & Rizkalla (1992). Acta Cryst. C48, 1354-1357] in space group Pnn2 [orthorhombic, a= 8.860 (8), b = 11.007 (2), c = 16.316 (4) Å, Z = 4]; it is better described in Pnna. Revised coordinates are given.

  10. Structure of a syn-aldol addition product of benzaldehyde and a prolinol-derived O-silacyclopentyl ketene N,O-acetal

    Marsh, Richard E.; Schaefer, William P.; Kephart, Susan E.; Myers, Andrew G.
    The compound (5S,6S,11aS)-hexahydro-6-methyl-5- phenylspiro[l H,7 H-pyrrolo[2,l-e][l,3,6,2]dioxazasilonine- 3,1'-silacyclopentan]-7-one (1) results from the silicon-directed condensation of the prolinol-derived O-silacyclopentyl ketene N,O-acetal (2) with benzaldehyde. The five-membered pyrrolidine ring has an envelope conformation and the silacyclopentyl ring has an en-type conformation with C17 and C18 on opposite sides of the C16-Si-C19 plane. Both of these rings appear to be disordered.

  11. On the structure of 9-amino-2,7-di-tert-butylacridine

    Marsh, Richard E.
    The crystal structure of 9-amino-2,7-di-tert-butylacridine hydrochloride monohydrate, C_(21)H_(27)N_2^+.Cl^-.H_2O, has been described in space group P3_1 [trigonal, a = 11.086 (2), c = 14.367 (4) Å, Z = 3; McKenna, Agbandje & Neidle (1992). Acta Cryst. C48, 188-190]. It is properly described in space group P3_121. Further refinement in P3_121, based on the original F values, leads to an improved R (0.049 vs 0.067) and to a revised position for the Cl^- ion.

  12. On predicting scan profiles: the nature of the 'aberration function'

    Destro, Riccardo; Marsh, Richard E.
    In an earlier treatment [Destro & Marsh (1987). Acta Cryst. A43, 711-718], an attempt was made to predict the shapes of high-angle θ-2θ scan profiles by convoluting a low-angle profile with the presumedly known spectral distribution function for the incident (crystal-monochromated Mo Kα) radiation but it was found necessary to introduce a third component, an 'aberration function', that varied with the Bragg angle θ. It is shown here that the primary purpose of the aberration function is to correct for defects in the spectral-distribution function. In particular, the effective intensity ratio between the K_(α2) and K_(α1) spectral lines can apparently...

  13. The Space Group of AgTaS_3

    Marsh, Richard E.
    The crystal structure of AgTaS_3, recently described in space group Cmc2_1, is properly described in Cmcm. The revised space group evidences the centrosymmetric nature of the structure.

  14. Structure of an anti-aldol addition product of benzaldehyde and a pseudoephedrine-derived O-silyl ketene N,O-acetal

    Marsh, Richard E.; Schaefer, William P.; Widdowson, Katherine L.; Myers, Andrew G.
    [4S-(4R*,5R*,8R*,9S*)]-2,2,5,6,8-Pentamethyl-4,9-diphenyl-1,3-dioxa-6-aza-2-silacyclononan-7-one, C_(22)H_(29)NO_3Si, M_r = 383.56, monoclinic, P2_1, a = 6.550 (3), b = 17.318 (6), c = 20.129 (6) Å, β = 98.83 (3)°, V = 2256.2 (14) Å^3, Z = 4, D_x = 1.13 g cm^(-3), λ(Mo Kα) = 0.71073 Å, µ = 1.18 cm^(-1), F(000) = 824, room temperature, R on F = 0.039 for 4305 reflections with F_o^2 > 3σ(F_o^2). The two independent molecules in this structure have nearly the same configuration and geometry, with average Si-C bond distances of 1.842 (3) Å and average Si-O bond distances of 1.636 (7) Å; angles at Si differ from...

  15. Simultaneous Water Vapor and Dry Air Optical Path Length Measurements and Compensation with the Large Binocular Telescope Interferometer

    Defrère, D.; Hinz, P.; Downey, E.; Böhm, M.; Danchi, W. C.; Durney, O.; Ertel, S.; Hill, J. M.; Hoffmann, W. F.; Mennesson, B.; Millan-Gabet, R.; Montoya, M.; Pott, J.-U.; Skemer, A.; Spalding, E.; Stone, J.; Vaz, A.
    The Large Binocular Telescope Interferometer uses a near-infrared camera to measure the optical path length variations between the two AO-corrected apertures and provide high-angular resolution observations for all its science channels (1.5-13 microns). There is however a wavelength dependent component to the atmospheric turbulence, which can introduce optical path length errors when observing at a wavelength different from that of the fringe sensing camera. Water vapor in particular is highly dispersive and its effect must be taken into account for high-precision infrared interferometric observations as described previously for VLTI/MIDI or the Keck Interferometer Nuller. In this paper, we describe the...

  16. The cone of Betti tables over three non-collinear points in the plane

    Gheorghita, Iulia; Sam, Steven V.
    We describe the cone of Betti tables of all finitely generated graded modules over the homogeneous coordinate ring of three non-collinear points in the projective plane. We also describe the cone of Betti tables of all finite length modules.

  17. Quantifying resource competition and its effects in the TX-TL system

    Gyorgy, Andras; Murray, Richard M.
    Without accounting for the limited availability of shared cellular resources, the standard model of gene expression fails to reliably predict experimental data obtained in vitro. To overcome this limitation, we develop a dynamical model of gene expression explicitly modeling competition for scarce resources. In addition to accurately describing the experimental data, this model only depends on a handful of easily identifiable parameters with clear physical interpretation. Based on this model, we then characterize the combinations of protein concentrations that are simultaneously realizable with shared resources. As application examples, we demonstrate how the results can be used to explain similarities/differences among...

  18. Toward Long-Distance Subdiffraction Imaging Using Coherent Camera Arrays

    Holloway, Jason; Asif, M. Salman; Sharma, Manoj Kumar; Matsuda, Nathan; Horstmeyer, Roarke; Cossairt, Oliver; Veeraraghavan, Ashok
    In this work, we propose using camera arrays coupled with coherent illumination as an effective method of improving spatial resolution in long distance images by a factor often and beyond. Recent advances in ptychography have demonstrated that one can image beyond the diffraction limit of the objective lens in a microscope. We demonstrate a similar imaging system to image beyond the diffraction limit in long range imaging. We emulate a camera array with a single camera attached to an XY translation stage. We show that an appropriate phase retrieval based reconstruction algorithm can be used to effectively recover the lost...

  19. Analysis of distributed ADMM algorithm for consensus optimization in presence of error

    Majzoobi, Layla; Lahouti, Farshad
    ADMM is a popular algorithm for solving convex optimization problems. Applying this algorithm to distributed consensus optimization problem results in a fully distributed iterative solution which relies on processing at the nodes and communication between neighbors. Local computations usually suffer from different types of errors, due to e.g., observation or quantization noise, which can degrade the performance of the algorithm. In this work, we focus on analyzing the convergence behavior of distributed ADMM for consensus optimization in presence of additive node error. We specifically show that (a noisy) ADMM converges linearly under certain conditions and also examine the associated convergence...

  20. Resilient decentralized consensus-based state estimation for smart grid in presence of false data

    Etemad, Reza Hassani; Lahouti, Farshad
    State estimation is an essential part of energy management system in smart grid as it is a basis for many of the associated management and control processes. In this paper, we present a decentralized state estimation approach, based on consensus optimization and the alternating direction method of multipliers, that is robust against certain harsh class of false data injection schemes. The proposed scheme provides a reliable estimate of the global system state in a distributed manner even if the system is regionally unobservable to some regional controllers, but globally observable across regions. The scheme also accommodates different communication network topologies...

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