Time comparison via OTS-2

The time comparisons carried out via OTS-2 between the Technical University Graz (Austria) and the Van Swinden Laboratory Delft (Netherlands) are discussed. The method is based on the use of the synchronization pulse in the TV-frame of the daily evening broadcasting of a French TV-program to Northern Africa. Corrections, as a consequence of changes in the position of the satellite coordinates are applied weekly after reception of satellite coordinates. A description of the method is given as well as some of the particular techniques used in both the participating laboratories. Preliminary results are presented

Sensor performance analysis

The theory is described and the equations required to design are developed and the performance of electro-optical sensor systems that operate from the visible through the thermal infrared spectral regions are analyzed. Methods to compute essential optical and detector parameters, signal-to-noise ratio, MTF, and figures of merit such as NE delta rho and NE delta T are developed. A set of atmospheric tables are provided to determine scene radiance in the visible spectral region. The Planck function is used to determine radiance in the infrared. The equations developed were incorporated in a spreadsheet so that a wide variety of sensor studies can be rapidly and efficiently conducted

The Effect of Music Tempo on Muscular Endurance During the Bench Press

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Synthesis, Characterization and Application of intermetallic Pd-X (Ga, Zn) Nanoparticles derived from ternary Hydrotalcite-like precursors

A novel, feasible synthesis approach for supported intermetallic Pd2Ga and PdZn nanoparticles derived from Hydrotalcite-like compounds (HTlc) is introduced. Ternary HTlc with the nominal composition (Pd2+,M2+)0.70(M3+)0.30(OH)2(CO3)0.15 ∙ m H2O are synthesized by pH-controlled co-precipitation. Mg2+/Ga3+ and Zn2+/Al3+ are chosen as M2+/M3+ combinations to permit formation of the nanocrystalline Pd2Ga and PdZn intermetallic compounds on a porous MgO/MgGa2O4 and ZnO/ZnAl2O4 support, respectively. In addition, a PdMgAl HTlc is prepared as monometallic Pd reference compound on a MgO/MgAl2O4 support. Incorporation of Pd2+ into the HT structure requires octahedral coordination, while Pd2+ ions prefer square planar coordination in aqueous solution. At the same substitution degree of M2+ by Pd2+, complete insertion is achieved for PdZnAl HT. In case of PdMgGa and PdMgAl HT a minor fraction is present as segregated Pd2+ on the external surface of the platelet-like particles with a local environment similar to PdO, i.e. in a square planar coordination. A limit of incorporation into the HT lattice exists at < 1 mol% for the Pd2+ containing precursors. Upon thermal decomposition in reductive atmosphere, intermetallic and metallic nanoparticles ranging from below 2 nm to 6 nm in size and exhibiting monomodal particle size distributions are formed. Alloying of Pd with Ga and Zn changes the crystal structure as well as the electronic structure and leads to the increased formation of isolated adsorption sites at the surface. Furthermore, dynamic surface changes of intermetallic Pd2Ga nanoparticles were noticed at longer exposure time to CO and higher CO coverage. This is attributed to the decomposition into metallic Pd and Ga2O3. The nanostructured Pd2Ga catalyst shows excellent performance in the selective semi-hydrogenation of acetylene similar to a bulk Pd2Ga model catalyst. In comparison to the elemental Pd catalyst the selectivity to ethylene is drastically improved by formation of Pd2Ga. Interestingly, the nanostructered catalyst slowly activates in the feed gas. The activation is triggered faster by a treatment in oxidative atmosphere. These dynamics of the Pd2Ga nanoparticles can be explained by the interplay of surface decomposition into Pd0 and Ga2O3 in oxygen and reversal of the strong-metal support interaction state leading to an increased activity. Furthermore, increased activities and selectivities in methanol steam reforming and methanol synthesis from CO2 are observed for the Pd2Ga and PdZn nanoparticles in contrast to the unmodified Pd particles. These structurally modified Pd catalysts exhibit a considerably lower selectivity to CO and enhanced formation of methanol compared to the monometallic Pd catalyst.Abstract i Zusammenfassung iii Danksagung v List of Figures x List of Tables xiv List of Abbreviations xv Chapter 1: Introduction and Overview 1 1.1. Intermetallic compounds 1 1.2. Motivation 2 1.3. Synthesis strategy for binary Pd-X intermetallic nanoparticles 3 1.4. Pd-Ga system 6 1.5. The Pd-Ga intermetallic compound Pd2Ga 7 1.6. Pd-Zn phase system 9 1.7. Pd-Ga IMCs as selective acetylene hydrogenation catalysts 10 1.8. Pd based IMCs in methanol synthesis and methanol steam reforming 13 1.9. Aims of this work and thesis structure 15 1.10. References 17 Chapter 2: Intermetallic Compound Pd2Ga as a Selective Catalyst for the Semi-Hydrogenation of Acetylene: From Model to High performance Catalyst 21 2.1 Introduction 22 2.2 Experimental Section 24 2.2.1 Synthesis Procedures 24 2.2.2 Characterization Techniques 24 2.2.3 Catalytic Measurements 25 2.3 Results and Discussion 27 2.4 Conclusion 34 2.5 References 36 Chapter 3: Dynamic Surface Processes of nanostructured Pd2Ga catalysts derived from ternary Hydrotalcite-like Precursors 38 3.1 Introduction 39 3.2 Experimental 40 3.2.1 Synthesis conditions 40 3.2.2 Characterization 41 3.2.3 Catalytic performance in the selective hydrogenation of acetylene 43 3.3 Results and Discussion 44 3.3.1 Structural and textural properties of the precursor material 44 3.3.2 Reduction and intermetallic phase formation 49 3.3.3 Structural properties of Pd2Ga nanoparticles 54 3.3.4 IR characterization of supported Pd2Ga nanoparticles during exposure to CO 58 3.3.5 Catalytic performance 62 3.4 Conclusions 69 3.5 References 71 Supplementary Information 73 Chapter 4: Methanol Synthesis and Methanol Steam Reforming of Supported Pd2Ga and PdZn Intermetallic Nanoparticles 79 4.1. Introduction 80 4.2 Experimental 81 4.2.1 Synthesis conditions 81 4.2.2 Characterization 82 4.2.3 Catalytic performance 84 4.2.3.1 Methanol synthesis from CO2 84 4.2.3.2 Methanol steam reforming 85 4.3 Results and discussion 86 4.3.1 Properties of the HTlc precursors 86 4.3.2 Reducibility of the HTlc precursors and IMC formation 88 4.3.2.1 TPR and MS measurements 88 4.3.2.2 XANES measurements 91 4.3.3 Properties of the ex-HTlc samples after reduction 93 4.4 Catalytic properties of the IMCs 97 4.4.1 Methanol synthesis from CO2 97 4.4.2 Steam reforming of methanol 100 4.5 Conclusion 102 4.6 References 103 Supplementary Information 105 Chapter 5: Final summary and conclusion 108 Appendix xvii Curriculum vitae xvii Publications xvii Oral presentations xviii Patent application xviii Poster presentations xi

APM 08279+5255: Keck Near- and Mid-IR High-Resolution Imaging

We present Keck high-resolution near-IR (2.2 microns; FWHM~0.15") and mid-IR (12.5 microns; FWHM~0.4") images of APM08279+5255, a z=3.91 IR-luminous BALQSO with a prodigious apparent bolometric luminosity of 5x10^{15} Lsun, the largest known in the universe. The K-band image shows that this system consists of three components, all of which are likely to be the gravitationally lensed images of the same background object, and the 12.5 micron image shows a morphology consistent with such an image configuration. Our lens model suggests that the magnification factor is ~100 from the restframe UV to mid-IR, where most of the luminosity is released. The intrinsic bolometric luminosity and IR luminosity of APM08279+5255 are estimated to be 5x10^{13} Lsun and 1x10^{13} Lsun, respectively. This indicates that APM 08279+5255 is intriniscally luminous, but it is not the most luminous object known. As for its dust contents, little can be determined with the currently available data due to the uncertainties associated with the dust emissivity and the possible effects of differential magnification. We also suggest that the lensing galaxy is likely to be a massive galaxy at z~3.Comment: 32 pages, 4 tables, 11 figures; Accepted for publication in Ap

The Mid-Infrared Instrument for the James Webb Space Telescope, VII: The MIRI Detectors

The MIRI Si:As IBC detector arrays extend the heritage technology from the Spitzer IRAC arrays to a 1024 x 1024 pixel format. We provide a short discussion of the principles of operation, design, and performance of the individual MIRI detectors, in support of a description of their operation in arrays provided in an accompanying paper (Ressler et al. (2015)). We then describe modeling of their response. We find that electron diffusion is an important component of their performance, although it was omitted in previous models. Our new model will let us optimize the bias voltage while avoiding avalanche gain. It also predicts the fraction of the IR-active layer that is depleted (and thus contributes to the quantum efficiency) as signal is accumulated on the array amplifier. Another set of models accurately predicts the nonlinearity of the detector-amplifier unit and has guided determination of the corrections for nonlinearity. Finally, we discuss how diffraction at the interpixel gaps and total internal reflection can produce the extended cross-like artifacts around images with these arrays at short wavelengths, ~ 5 microns. The modeling of the behavior of these devices is helping optimize how we operate them and also providing inputs to the development of the data pipeline

Correction for Self-Heating When Using Thermometers as Heaters in Precision Control Applications

In precision control applications, thermometers have temperature-dependent electrical resistance with germanium or other semiconductor material thermistors, diodes, metal film and wire, or carbon film resistors. Because resistance readout requires excitation current flowing through the sensor, there is always ohmic heating that leads to a temperature difference between the sensing element and the monitored object. In this work, a thermistor can be operated as a thermometer and a heater, simultaneously, by continuously measuring the excitation current and the corresponding voltage. This work involves a method of temperature readout where the temperature offset due to self-heating is subtracted exactly

The Mid-Infrared Instrument for the James Webb Space Telescope, VIII: The MIRI Focal Plane System

We describe the layout and unique features of the focal plane system for MIRI. We begin with the detector array and its readout integrated circuit (combining the amplifier unit cells and the multiplexer), the electronics, and the steps by which the data collection is controlled and the output signals are digitized and delivered to the JWST spacecraft electronics system. We then discuss the operation of this MIRI data system, including detector readout patterns, operation of subarrays, and data formats. Finally, we summarize the performance of the system, including remaining anomalies that need to be corrected in the data pipeline

High Resolution Infrared Imaging of the Compact Nuclear Source in NGC4258

We present high resolution imaging of the nucleus of NGC4258 from 1 micron to 18 microns. Our observations reveal that the previously discovered compact source of emission is unresolved even at the near-infrared resolution of about 0.2 arcsec FWHM which corresponds to about 7 pc at the distance of the galaxy. This is consistent with the source of emission being the region in the neighborhood of the purported 3.5*10^7 M_sun black hole. After correcting for about 18 mags of visual extinction, the infrared data are consistent with a F_nu \propto nu^(-1.4+/-0.1) spectrum from 1.1 micron to 18 micron, implying a non-thermal origin. Based on this spectrum, the total extinction corrected infrared luminosity (1-20 micron) of the central source is 2*10^8 L_sun. We argue that the infrared spectrum and luminosity of the central source obviates the need for a substantial contribution from a standard, thin accretion disk at these wavelengths and calculate the accretion rate through an advection dominated accretion flow to be Mdot \sim 10^(-3) M_sun/yr. The agreement between these observations and the theoretical spectral energy distribution for advection dominated flows provides evidence for the existence of an advection dominated flow in this low luminosity AGN.Comment: 21 pages, 5 figures, Appearing in Mar 2000 ApJ vol. 53

The Compact Nucleus of the Deep Silicate Absorption Galaxy NGC 4418

High resolution, Hubble Space Telescope (HST) near-infrared and Keck mid-infrared images of the heavily extinguished, infrared luminous galaxy NGC 4418 are presented. These data make it possible to observe the imbedded near-infrared structure on scales of 10-20 pc, and to constrain the size of the mid-infrared emitting region. The 1.1-2.2 um data of NGC 4418 show no clear evidence of nuclear star clusters or of a reddened active galactic nucleus. Instead, the nucleus of the galaxy consists of a ~100-200 pc linear structure with fainter structures extending radially outward. The near-infrared colors of the linear feature are consistent with a 10-300 Myr starburst suffering moderate levels (few magnitudes) of visual extinction. At 7.9-24.5 um, NGC 4418 has estimated size upper limits in the range of 30-80 pc. These dimensions are consistent with the highest resolution radio observations obtained to date of NGC 4418, as well as the size of 50-70 pc expected for a blackbody with a temperature derived from the 25 um, 60 um, and 100 um flux densities of the galaxy. Further, a spectral energy distribution constructed from the multi-wavelength mid-infrared observations show the strong silicate absorption feature at 10 um, consistent with previous mid-infrared observations of NGC 4418. An infrared surface brightness of 2.1x10^13 L_sun kpc^-2 is derived for NGC 4418. Such a value, though consistent with the surface brightness of warm ultraluminous infrared galaxies (ULIGs: L_IR [8-1000 um] >~ 10^12 L_sun) such as IRAS 05189-2524 and IRAS 08572+3915, is not large enough to distinguish NGC 4418 as a galaxy powered by an Active Galactic Nucleus (AGN), as opposed to a lower surface brightness starburst.Comment: LaTex, 7 pages, including 2 jpg figures and 3 postscript figures, AJ, in press (May, 2003