The truncated moment problem via homogenization and flat extensions

This paper studies how to solve the truncated moment problem (TMP) via homogenization and flat extensions of moment matrices. We first transform TMP to a homogeneous TMP (HTMP), and then use semidefinite programming (SDP) techniques to solve HTMP. Our main results are: (1) a truncated moment sequence (tms) is the limit of a sequence of tms admitting measures on ${\mathbb{R}}^n$ if and only if its homogenized tms (htms) admits a measure supported on the unit sphere in ${\mathbb{R}}^{n+1}$; (2) an htms admits a measure if and only if the optimal values of a sequence of SDP problems are nonnegative; (3) under some conditions that are almost necessary and sufficient, by solving these SDP problems, a representing measure for an htms can be explicitly constructed if one exists.     

All-optical RZ-OOK to RZ-BPSK conversion with multicasting based on XPM in highly nonlinear fiber

We present a detailed investigation of all-optical RZ-OOK to RZ-BPSK modulation format conversion at 10 Gb/s using cross-phase modulation in a length of highly nonlinear fiber. In particular, we examine the impact of the input RZ-OOK signal characteristics, such as duty cycle, average (peak) power, optical signal to noise ratio, and degradation from residual dispersion and differential group delay on the BER performance of the converted RZ-BPSK signal. We also present results on RZ-OOK to RZ-BPSK modulation format conversion with wavelength multicasting.     

Nuclear data for space radiation

Human space flight requires protecting astronauts from the harmful effects of space radiation. The availability of measured nuclear cross-section data needed for these studies is reviewed in the present paper. The energy range of interest for radiation protection is approximately 100 MeV/n–10 GeV/n. The majority of data are for projectile fragmentation partial and total cross-sections, including both charge changing and isotopic cross-sections. The cross-section data are organized into categories which include charge changing, elemental, isotopic for total, single and double differential with respect to momentum, energy and angle. Gaps in the data relevant to space radiation protection are discussed and recommendations for future experiments are made.     

Stabilized interface methods for mechanical joints: Physics-based models and variationally consistent embedding

This paper presents the application of a new method for interfacial modeling utilizing a merger of continuous Galerkin and discontinuous Galerkin concepts to simulate the behavior of mechanical joints. The interfacial flux terms arising naturally from the discontinuous Galerkin treatment provide a mechanism to embed friction models in a variationally consistent fashion. Due to the unbiased implementation of the interface, facilitated by avoiding the master–slave concept, the deformation of the two interacting surfaces conforms to the local material and geometric attributes of the surfaces. This results in a better preservation of physics in interface mechanics. Additionally, the method is incorporated into a Variational Multiscale framework that comes equipped with a built-in error estimation module, providing numerical estimation of convergence and distinguishing discretization errors from modeling errors. A series of quasi-static numerical simulations of a lap joint under fretting conditions are conducted to compare the performance of two friction models: (i) classical Coulomb friction model and (ii) physics-based multiscale model. Hysteresis study of a three-dimensional double-bolted lap joint for the two friction models is also presented and the computed results are shown to be consistent between conforming and nonconforming meshes.     

Passive flow control by membrane wings for aerodynamic benefit

The coupling of passive structural response of flexible membranes with the flow over them can significantly alter the aerodynamic characteristic of simple flat-plate wings. The use of flexible wings is common throughout biological flying systems inspiring many engineers to incorporate them into small engineering flying systems. In many of these systems, the motion of the membrane serves to passively alter the flow over the wing potentially resulting in an aerodynamic benefit. In this study, the aerodynamic loads and the flow field for a rigid flat-plate wing are compared to free trailing-edge membrane wings with two different pre-tensions at a chord-based Reynolds number of approximately 50,000. The membrane was silicon rubber with a scalloped free trailing edge. The analysis presented includes load measurements from a sting balance along with velocity fields and membrane deflections from synchronized, time-resolved particle image velocimetry and digital image correlation. The load measurements demonstrate increased aerodynamic efficiency and lift, while the synchronized flow and membrane measurements show how the membrane motion serves to force the flow. This passive flow control introduced by the membranes motion alters the flows development over the wing and into the wake region demonstrating how, at least for lower angles of attack, the membranes motion drives the flow as opposed to the flow driving the membrane motion.     

A refined cellular automaton model to rectify impractical vehicular movement behavior

When implementing cellular automata (CA) into a traffic simulation, one common defect yet to be rectified is the abrupt deceleration when vehicles encounter stationary obstacles or traffic jams. To be more in line with real world vehicular movement, this paper proposes a piecewise-linear movement to replace the conventional particle-hopping movement adopted in most previous CA models. Upon this adjustment and coupled with refined cell system, a new CA model is developed using the rationale of Forbes’ et al. car-following concept. The proposed CA model is validated on a two-lane freeway mainline context. It shows that this model can fix the unrealistic deceleration behaviors, and thus can reflect genuine driver behavior in the real world. The model is also capable of revealing Kerner’s three-phase traffic patterns and phase transitions among them. Furthermore, the proposed CA model is applied to simulate a highway work zone wherein traffic efficiency (maximum flow rates) and safety (speed deviations) impacted by various control schemes are tested.     

Structure, bonding, and aggregation of selenium-containing organolithium species

1,3-Dioxo compounds can be prepared from selenium-mediated carbonylation of lithium enolates in the presence of carbon monoxide. Intermediates in this reaction include several organic species that contain both selenium and lithium. The first step in understanding the detailed reaction mechanism is to understand the structure of these intermediates. Like most organolithium compounds, these species can exist as aggregates in solution. The B3LYP density functional theory (DFT) method was used to examine the gas phase and THF solvated structures of these compounds. The calculations showed that each of the compounds forms dimers or higher aggregates in the gas phase. Aggregates are also formed in THF solution, although solvation favors lower aggregates as compared to the gas phase.     

Olefin‐Dependent Discrimination between Two Nonheme HO?FeVO Tautomeric Species in Catalytic H2O2 Epoxidations

Wet oxygenase models : Unprecedented high levels of water incorporation into products (up to 75 %) is observed in epoxidation reactions with H₂O₂ by a bioinspired nonheme iron catalyst. A surprising substrate‐dependent incorporation of water is observed, and is proposed to arise from fast equilibrium between two high‐valent HO? Fe^V?O isomeric species exhibiting different reactivity.

     

Copper(II) complexes of a biphenyl-based ligand: Tuning the needs of the metal with those of the ligand

The novel pyrazole-containing tetradentate ligand 2,2′-bis[[(3,5-dimethylpyrazol-1-yl)methyl]amino]-1,1′-biphenyl (N₄-mpz), 1, was synthesized and three Cu(II) complexes, 2–4, were prepared from this compound. These complexes were characterized by a combination of elemental analysis, FAB-MS and electrochemistry and were shown to have the structure of [Cu(N₄-mpz)(Pz)]X₂ where X = BF₄ or ClO₄ or [Cu(N₄-mpz)(Cl)]Cl. The X-ray structure of [Cu(N₄-mpz)(Pz)] (ClO₄)₂ · CH₃OH, 2, was determined and it showed the Cu(II) coordinated by the four nitrogen donors from the ligand along with an exogenous pyrazole donor that had been extracted from another molecule of the ligand. Cyclic voltammetry studies indicated that the complexes undergo quasi-reversible one-electron reductions in acetonitrile at potentials between 396 and 422 mV versus Ag/AgCl.     

Localized excitation in the hybridization gap in YbAl3

The intermediate valence compound YbAl3 exhibits a broad magnetic excitation in the inelastic neutron scattering spectrum with characteristic energy E1 approximately 50 meV, equal to the Kondo energy (T(K) approximately 600-700 K). In the low temperature (T < T(coh) approximately 40 K) Fermi liquid state, however, a new peak in the scattering occurs at E2 approximately 33 meV, which lies in the hybridization gap that exists in this compound. We report inelastic neutron scattering results for a single-crystal sample. The scattering at energies near E1 qualitatively has the momentum (Q) dependence expected for interband scattering across the indirect gap. The scattering near E2 has a very different Q dependence: it is a weak function of Q over a large fraction of the Brillouin zone and is smallest near (1/2,1/2, 1/2). A possibility is that the peak at E2 arises from a spatially localized excitation in the hybridization gap.