Defect Engineering: Graphene Gets Designer Defects

An extended one-dimensional defect that has the potential to act as a conducting wire has been embedded in another perfect graphene sheet.Comment: 2 pages, 1 figur

Mechanical properties of connected carbon nanorings via molecular dynamics simulation

Stable, carbon nanotori can be constructed from nanotubes. In theory, such rings could be used to fabricate networks that are extremely flexible and offer a high strength-to-density ratio. As a first step towards realizing such nanochains and nanomaile, the mechanical properties of connected carbon nanorings were investigated via molecular dynamics simulation. The Young's modulus, extensibility and tensile stength of nanorings were estimated under conditions that idealize the constraints of nanochains and nanomaile. The results indicate nanorings are stable under large tensile deformation. The calculated Young's modulus of nanorings was found increase with deformation from 19.43 GPa to 121.94 GPa (without any side constraints) and from 124.98 GPa to 1.56 TPa (with side constraints). The tensile strength of unconstrained and constrained nanorings is estimated to be 5.72 and 8.522 GPa, respectively. The maximum strain is approximately 39% (nanochains) and 25.2% (nanomaile), and these deformations are completely reversible

A theoretical review of the operation of vibratory stress relief with particular reference to the stabilization of large-scale fabrications

Vibratory stress relief (VSR) is widely used on large welded fabrications to stabilize the structures so that they do not distort during further machining or during operational duty. The level of applied stress achieved during VSR on such structures is only 5–10 per cent of the yield stress. It is, therefore, not obvious how these applied loads come to modify the level of residual stress. It is suggested here that the reason for the success of VSR applied to large fabrications lies (a) in the origin of the residual stresses and (b) in the partial relief of these residual stresses by the initiation of the transformation of retained austenite particles (in the size range from 1 to 25 µm) by the movement of dislocations into positions that are favourable for the nucleation of martensite embryos. The shear deformation associated with the transformation of retained austenite into martensite will reduce the residual stress field to the point where the stability of the structure may be assured

Quantized Optical Vortex-array Eigenstates in a Rotating Frame

Linear combinations of Bessel beams can be used to effectively trap light within cylindrical domains. Such hard traps can be used to produce states that exhibit stationary arrays of optical vortices from the perspective of a steadily rotating frame. These patterned singularities can be engineered to have singularities of the same or mixed charges and the requisite rotation rates are quantized even though the setting is purely linear. A hydrodynamic interpretation is that the vortices are at rest within a compressible, two-dimensional fluid of light

Trapped Vortex Dynamics Implemented in Composite Bessel Beams

The divergence-free nature of Bessel beams can be harnessed to effectively trap optical vortices in free space laser propagation. We show how to generate arbitrary vortex configurations in Bessel traps to investigate few-body vortex interactions within a dynamically-evolving fluid of light, which is a formal analog to a non-interacting Bose gas. We implement--theoretically and experimentally--initial conditions of vortex configurations first predicted in harmonically-trapped quantum fluids, in the limit of weak atomic interactions, and model and measure the resultant dynamics. These hard trap dynamics are distinct from the harmonic trap predictions due to the non-local interactions that occur among the hard wall boundary and steep phase gradients that nucleate other vortices. By simultaneously presenting experimental demonstrations with the theoretical proposal, we validate the potential application of using Bessel hard wall traps as testing grounds for engineering few-body vortex interactions within trapped, two-dimensional compressible fluids

The Anatomy of Geometric Phase for an Optical Vortex Transiting a Lens

We present an analytical means of quantifying the fractional accumulation of geometric phase for an optical vortex transiting a cylindrical lens. The standard fiber bundle of a Sphere of Modes is endowed with a Supplementary Product Space at each point so that the beam waists and their positions can be explicitly tracked as functions of lens transit fraction. The method is applied to quantify the accumulation of geometric phase across a single lens as a function of initial state and lens position within the beam. It can be readily applied to a series of lenses as well.Comment: 10 pages, 13 figure

Initial Optical Vortex Amplitude Structure Determines Pair Annihilation

We show that annihilation dynamics between oppositely charged optical vortex pairs can be manipulated by modifying only the initial size of the vortex cores. When sufficiently close together, vortices with strongly overlapped cores annihilate more quickly than vortices with smaller cores that must wait for diffraction to cause meaningful core overlap. We present numerical simulations and experimental measurements for vortices with hyperbolic tangent cores of various initial sizes. We also show that decreasing the core size of an annihilating pair can prevent the annihilation event

Pump-tailored Alternative Bell State Generation in the First-Order Hermite-Gaussian basis

We demonstrate entangled-state swapping, within the Hermite-Gaussian basis of first-order modes, directly from the process of spontaneous parametric down-conversion within a nonlinear crystal. The method works by explicitly tailoring the spatial structure of the pump photon such that it resembles the product of the desired entangled spatial modes exiting the crystal. Importantly, the result is an entangled state of balanced HG modes, which may be beneficial in applications that depend on symmetric accumulations of geometric phase through optics or in applications of quantum sensing and imaging with azimuthal sensitivity. Furthermore, the methods are readily adaptable to other spatial mode bases

Database computing in HEP

The major SSC experiments are expected to produce up to 1 Petabyte of data per year each. Once the primary reconstruction is completed by farms of inexpensive processors, I/O becomes a major factor in further analysis of the data. We believe that the application of database techniques can significantly reduce the I/O performed in these analyses. We present examples of such I/O reductions in prototypes based on relational and object-oriented databases of CDF data samples