Theory of intrinsic propagation losses in topological edge states of planar photonic crystals

Using a semi-analytic guided-mode expansion technique, we present theory and analysis of intrinsic propagation losses for topological photonic crystal slab waveguide structures with modified honeycomb lattices of circular or triangular holes. Although conventional photonic crystal waveguide structures, such as the W1 waveguide, have been designed to have lossless propagation modes, they are prone to disorder-induced losses and backscattering. Topological structures have been proposed to help mitigate this effect as their photonic edge states may allow for topological protection. However, the intrinsic propagation losses of these structures are not well understood and the concept of the light line can become blurred. For four example topological edge state structures, photonic band diagrams, loss parameters, and electromagnetic fields of the guided modes are computed. Two of these structures, based on armchair edge states, are found to have significant intrinsic losses for modes inside the photonic band gap, more than 100 dB/cm, which is comparable to or larger than typical disorder-induced losses using slow-light modes in conventional photonic crystal waveguides, while the other two structures, using the valley Hall effect and inversion symmetry, are found to have a good bandwidth for exploiting lossless propagation modes below the light line.Comment: 10 pages, 9 figure

Preparing Our Kids for Education, Work and Life: A Report of the Task Force on Youth Aging Out

Summarizes a study of Massachusetts youth transitioning out of foster care, and offers recommendations for policies, practices, and resource conditions, including "Five Core Resources" to prepare them for higher education, work, and adulthood

Developing biomaterials through enhancing organic/inorganic interfaces

The socioeconomic demand for biomaterials has never been greater. Formulation at the organic/inorganic interface of materials has enabled the conception of several biomaterial systems for bone healing. In Chapter 2, a poly( ether ether ketone) (PEEK) and calcium sulphate (CS) composite is formulated. Inclusion of the polymer slowed CS degradation and augmented the mechanical properties significantly. Chapters 3 and 4 explore the formation mechanism of tubular calcium phosphate structures from a gel/solution interface. Both the composition and microstructure of tubules were analogous to features of bone. To demonstrate the bone graft application of these structures, a model bone defect was augmented with particles that could generate tubular calcium phosphate in the presence of tissue. 3D computed tomography reconstructions revealed bone-like mineral deposition throughout the cavity. Chapter 5 explores the chemical coupling of hydroxyapatite particles within a PEEK matrix, a composite that may be used to fabricate spinal fusion devices. Physical properties of composites were improved by a reduction in HA debonding, the presence of fewer micro cracks, and more effective load transfer between phases. Together, the research puts forward a novel collection ofbiomaterials that may be applied to the treatment of bone fractures and fusion of the spine

X-ray Observations of the Compact Source in CTA 1

The point source RX J0007.0+7302, at the center of supernova remnant CTA 1, was studied using the X-Ray Multi-mirror Mission. The X-ray spectrum of the source is consistent with a neutron star interpretation, and is well described by a power law with the addition of a soft thermal component that may correspond to emission from hot polar cap regions or to cooling emission from a light element atmosphere over the entire star. There is evidence of extended emission on small spatial scales which may correspond to structure in the underlying synchrotron nebula. No pulsations are observed. Extrapolation of the nonthermal spectrum of RX J0007.0+7302 to gamma-ray energies yields a flux consistent with that of EGRET source 3EG J0010+7309, supporting the proposition that there is a gamma-ray emitting pulsar at the center of CTA 1. Observations of the outer regions of CTA 1 with the Advanced Satellite for Cosmology and Astrophysics confirm earlier detections of thermal emission from the remnant and show that the synchrotron nebula extends to the outermost reaches of the SNR.Comment: 5 pages, including 4 postscript figs.LaTex. Accepted for publication by Ap

Imaging the Thermal and Kinematic Sunyaev-Zel'dovich Effect Signals in a Sample of Ten Massive Galaxy Clusters: Constraints on Internal Velocity Structures and Bulk Velocities

We have imaged the Sunyaev-Zel'dovich (SZ) effect signals at 140 and 270 GHz towards ten galaxy clusters with Bolocam and AzTEC/ASTE. We also used Planck data to constrain the signal at large angular scales, Herschel-SPIRE images to subtract the brightest galaxies that comprise the cosmic infrared background (CIB), Chandra imaging to map the electron temperature $T_e$ of the intra-cluster medium (ICM), and HST imaging to derive models of each galaxy cluster's mass density. The galaxy clusters gravitationally lens the background CIB, which produced an on-average reduction in brightness towards the galaxy clusters' centers after the brightest galaxies were subtracted. We corrected for this deficit, which was between 5-25% of the 270 GHz SZ effect signal within $R_{2500}$. Using the SZ effect measurements, along with the X-ray constraint on $T_e$, we measured each galaxy cluster's average line of sight (LOS) velocity $v_z$ within $R_{2500}$, with a median per-cluster uncertainty of +-700 km/s. We found an ensemble-mean of 430+-210 km/s, and an intrinsic cluster-to-cluster scatter $\sigma_{int}$ of 470+-340 km/s. We also obtained maps of $v_z$ over each galaxy cluster's face with an angular resolution of 70". All four galaxy clusters previously identified as having a merger oriented along the LOS showed an excess variance in these maps at a significance of 2-4$\sigma$, indicating an internal $v_z$ rms of $\gtrsim$1000 km/s. None of the six galaxy clusters previously identified as relaxed or plane of sky mergers showed any such excess variance.Comment: Accepted for publication in Ap