The Effect of Symmetry Lowering on the Dielectric Response of BaZrO3BaZrO_3

We use first-principles density functional theory calculations to investigate the dielectric response of BaZrO$_3$ perovskite. A previous study [Arkbarzadeh {\em et al.} Phys. Rev. B {\bf 72}, 205104 (2005)] reported a disagreement between experimental and theoretical low temperature dielectric constant $\epsilon$ for the high symmetry BaZrO$_3$ structure. We show that a fully relaxed 40-atom BaZrO$_3$ structure exhibits O$_6$ octahedral tilting, and $\epsilon$ that agrees with experiment. The change in $\epsilon$ from high-symmetry to low-symmetry structure is due to increased phonon frequencies as well as decreased mode effective charges.Comment: 4 pages, 2 figure

Optical-to-optical interface device

An investigation was conducted to develop an optical-to-optical interface device capable of performing real-time incoherent-to-incoherent optical image conversion. The photoactivated liquid crystal light valve developed earlier represented a prototype liquid crystal light valve device capable of performing these functions. A device was developed which had high performance and extended lifetime

Reflective liquid crystal light valve with hybrid field effect mode

There is disclosed a high performance reflective mode liquid crystal light valve suitable for general image processing and projection and particularly suited for application to real-time coherent optical data processing. A preferred example of the device uses a CdS photoconductor, a CdTe light absorbing layer, a dielectric mirror, and a liquid crystal layer sandwiched between indium-tin-oxide transparent electrodes deposited on optical quality glass flats. The non-coherent light image is directed onto the photoconductor; this reduces the impedance of the photoconductor, thereby switching the AC voltage that is impressed across the electrodes onto the liquid crystal to activate the device. The liquid crystal is operated in a hybrid field effect mode. It utilizes the twisted nematic effect to create a dark off-state (voltage off the liquid crystal) and the optical birefringence effect to create the bright on-state. The liquid crystal thus modulates the polarization of the coherent read-out or projection light responsively to the non-coherent image. An analyzer is used to create an intensity modulated output beam

Photovoltage in curved 1D systems

Curvature of quantum wire results in intrasubband absorption of IR radiation that induces stationary photovoltage in presence of circular polarization. This effect is studied in ballistic (collisionless) and kinetic regimes. The consideration is concentrated on quantum wires with curved central part. It is shown, that if mean free path is shorter than length of the curved part the photovoltage does not depend on the wire shape, but on the total angle of rotation of wire tangent. It is not the case when mean free path is finite or large. This situation was studied for three specific shapes of wires: "hard angle", "open book" and "$\Omega$-like".Comment: 12 pages, 1 figur

Structure and dielectric response in the high TcT_c ferroelectric Bi(Zn,Ti)O3_3-PbTiO3_3 solid solutions

Theoretical {\em ab initio} and experimental methods were used to investigate the $x$Bi(Zn,Ti)O$_3$-(1-$x$)PbTiO$_3$ (BZT-PT) solid solution. We find that hybridization between Zn 4$p$ and O 2$p$ orbitals allows the formation of short, covalent Zn-O bonds, enabling favorable coupling between A-site and B-site displacements. This leads to large polarization, strong tetragonality and an elevated ferroelectric to paraelectric phase transition temperature. nhomogeneities in local structure near the 90$^\circ$ domain boundaries can be deduced from the asymetric peak broadening in the neutron and x-ray diffraction spectra. These extrinsic effects make the ferroelectric to paraelectric phase transition diffuse in BZT-PT solid solutions

Degradation and reuse of radiative thermal protection system materials for the space shuttle

Three silicide coated columbium alloys and two cobalt alloys were subjected to identical simulated reentry profiling exposures in both static (controlled vacuum leak) and dynamic (hypersonic plasma shear) environments. Primary emphasis in the columbium alloy evaluation was on the Cb752 and C129Y alloys with a lesser amount on FS85. Commercial silicide coatings of the R512E and VH109 formulations were used. The coated specimens were intentionally defected to provide the types of coating flaws that are expected in service. Temperatures were profiled up to peak temperatures of either 2350 F or 2500 F for 15 minutes in each cycle

Long term variability of Cygnus X-1: VII. Orbital variability of the focussed wind in Cyg X-1 / HDE 226868 system

Binary systems with an accreting compact object are a unique chance to investigate the strong, clumpy, line-driven winds of early type supergiants by using the compact object's X-rays to probe the wind structure. We analyze the two-component wind of HDE 226868, the O9.7Iab giant companion of the black hole Cyg X-1 using 4.77 Ms of RXTE observations of the system taken over the course of 16 years. Absorption changes strongly over the 5.6 d binary orbit, but also shows a large scatter at a given orbital phase, especially at superior conjunction. The orbital variability is most prominent when the black hole is in the hard X-ray state. Our data are poorer for the intermediate and soft state, but show signs for orbital variability of the absorption column in the intermediate state. We quantitatively compare the data in the hard state to a toy model of a focussed Castor-Abbott-Klein-wind: as it does not incorporate clumping, the model does not describe the observations well. A qualitative comparison to a simplified simulation of clumpy winds with spherical clumps shows good agreement in the distribution of the equivalent hydrogen column density for models with a porosity length on the order of the stellar radius at inferior conjunction; we conjecture that the deviations between data and model at superior conjunction could be either due to lack of a focussed wind component in the model or a more complicated clump structure.Comment: proposed for acceptance in A&A, 11 pages, 11 figures (two in appendix

The SMC SNR 1E0102.2-7219 as a Calibration Standard for X-ray Astronomy in the 0.3-2.5 keV Bandpass

The flight calibration of the spectral response of CCD instruments below 1.5 keV is difficult in general because of the lack of strong lines in the on-board calibration sources typically available. We have been using 1E 0102.2-7219, the brightest supernova remnant in the Small Magellanic Cloud, to evaluate the response models of the ACIS CCDs on the Chandra X-ray Observatory (CXO), the EPIC CCDs on the XMM-Newton Observatory, the XIS CCDs on the Suzaku Observatory, and the XRT CCD on the Swift Observatory. E0102 has strong lines of O, Ne, and Mg below 1.5 keV and little or no Fe emission to complicate the spectrum. The spectrum of E0102 has been well characterized using high-resolution grating instruments, namely the XMM-Newton RGS and the CXO HETG, through which a consistent spectral model has been developed that can then be used to fit the lower-resolution CCD spectra. We have also used the measured intensities of the lines to investigate the consistency of the effective area models for the various instruments around the bright O (~570 eV and 654 eV) and Ne (~910 eV and 1022 eV) lines. We find that the measured fluxes of the O VII triplet, the O VIII Ly-alpha line, the Ne IX triplet, and the Ne X Ly-alpha line generally agree to within +/-10 % for all instruments, with 28 of our 32 fitted normalizations within +/-10% of the RGS-determined value. The maximum discrepancies, computed as the percentage difference between the lowest and highest normalization for any instrument pair, are 23% for the O VII triplet, 24% for the O VIII Ly-alpha line, 13% for the Ne IX triplet, and 19% for the Ne X Ly-alpha line. If only the CXO and XMM are compared, the maximum discrepancies are 22% for the O VII triplet, 16% for the O VIII Ly-alpha line, 4% for the Ne IX triplet, and 12% for the Ne X Ly-alpha line.Comment: 16 pages, 11 figures, to be published in Proceedings of the SPIE 7011: Space Telescopes and Instrumentation II: Ultraviolet to Gamma Ray 200

IMPACT: The Journal of the Center for Interdisciplinary Teaching and Learning. Volume 8, Issue 2, Summer 2019

Many of us look for ways to help students forge concrete connections between their academic studies and the real world. Universities encourage professors to develop community-based learning, allowing students to contribute to the community beyond their campus in a way that enhances their academic studies and enables them to create these connections. Scholars have theorized the many benefits of community-based learning, but professors have many questions about how to implement community-based learning in practice. What does a successful community-based learning assignment look like? What are the different ways to assess students’ learning experiences in community-based learning assignments? How can one build effective partnerships with community organizations? In these pages, you will find practical advice, theoretical framework, and firsthand accounts of community-engaged teaching across disciplines. Learn from professors who have designed assignments allowing students to complete community projects with refugees, prisoners, veterans, elementary school children, science museums, nursing homes, public libraries, and ESL populations. Students in an Anthropology course, for instance, conduct oral history interviews with refugees, and provide written transcriptions of the interviews that the refugees can then use as a learning tool in ESL classes. In a Science Methods class, students collaborate with an aquarium to produce meaningful exhibits that educate the public. First-year writing students work with veterans to create autobiographical films and write papers related to the project