33 research outputs found
3C 220.3: a radio galaxy lensing a submillimeter galaxy
Herschel Space Observatory photometry and extensive multiwavelength followup
have revealed that the powerful radio galaxy 3C 220.3 at z=0.685 acts as a
gravitational lens for a background submillimeter galaxy (SMG) at z=2.221. At
an observed wavelength of 1mm, the SMG is lensed into three distinct images. In
the observed near infrared, these images are connected by an arc of 1.8" radius
forming an Einstein half-ring centered near the radio galaxy. In visible light,
only the arc is apparent. 3C 220.3 is the only known instance of strong
galaxy-scale lensing by a powerful radio galaxy not located in a galaxy cluster
and therefore it offers the potential to probe the dark matter content of the
radio galaxy host. Lens modeling rejects a single lens, but two lenses centered
on the radio galaxy host A and a companion B, separated by 1.5", provide a fit
consistent with all data and reveal faint candidates for the predicted fourth
and fifth images. The model does not require an extended common dark matter
halo, consistent with the absence of extended bright X-ray emission on our
Chandra image. The projected dark matter fractions within the Einstein radii of
A (1.02") and B (0.61") are about 0.4 +/- 0.3 and 0.55 +/- 0.3. The mass to
i-band light ratios of A and B, M/L ~ 8 +/- 4 Msun/Lsun, appear comparable to
those of radio-quiet lensing galaxies at the same redshift in the CASTLES, LSD,
and SL2S samples. The lensed SMG is extremely bright with observed f(250um) =
440mJy owing to a magnification factor mu~10. The SMG spectrum shows luminous,
narrow CIV 154.9nm emission, revealing that the SMG houses a hidden quasar in
addition to a violent starburst. Multicolor image reconstruction of the SMG
indicates a bipolar morphology of the emitted ultraviolet (UV) light suggestive
of cones through which UV light escapes a dust-enshrouded nucleus.Comment: 17 pages, 14 Figures, accepted for publication in Ap
Thermoelectric properties of tetrathiotetracene iodide crystals: modeling and experiment
A more complete physical model for nanostructured crystals of tetrathiotetracene-iodide that takes into account the interaction of carriers with the neighboring one-dimensional (1D) conductive chains and also the scattering on impurities and defects is presented. For simplicity, the 2D approximation is applied. It is shown that this model describes very well the temperature dependencies of electrical conductivity in the temperature interval between 180 and 300 K, and of the Seebeck coefficient between 50 and 300 K, the highest temperature for which the measurements were reported. For lower temperatures, it is necessary to also consider the fluctuations of dielectric phase that appear before the metalâdielectric transition. It is found that the predictions made in the 1D approximation are valid only if the crystal purity is not very high, and the electrical conductivity is limited up to âŒ3.5Ă106Ωâ1mâ1 and the thermoelectric figure of merit up to ZTâŒ4
Police performance measurement: an annotated bibliography
This study provides information to assist those involved in performance measurement in police organisations. The strategies used to identify the literature are described. Thematic sections cover; general overviews; methodological issues; performance management in other industries; national, international and cross-national studies; frameworks (e.g. Compstat; the Balanced Scorecard); criticisms (particularly unintended consequences); crime-specific measures; practitioner guides; performance evaluation of individual staff; police department plans and evaluations; annotated bibliographies in related areas, and; other literature. Our discussion offers two conclusions: the measures best aligned with performance are typically more expensive, while most operational data should only provide contextual information; the philosophy of open governance should be pursued to promote transparency, accountability and communication to improve police performance
Problematizing fit and survival: transforming the law of requisite variety through complexity misalignment
The law of requisite variety is widely employed in management theorizing and is linked with core strategy themes such as contingency and fit. We reflect upon requisite variety as an archetypal borrowed concept. We contrast its premises with insights from the institutional literature and commitment literature, draw propositions that set boundaries to its applicability, and review the ramifications of what we call âcomplexity misalignment.â In this way we contradict foundational assumptions of the law, problematize adaptation- and survival-centric views of strategizing, and theorize the role of human agency in variously complex regimes
Thermal evaporation and x-ray photostability of dodecyl-passivated silicon nanoparticles
Abstract
X-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy have been used to study the makeup of thin films of 6.5 nm diameter dodecyl-capped silicon nanoparticles (SiNPs) formed in a one-pot synthesis method of micelle reduction. Thermostability measurements show the SiNPs undergo thermal desorption at âŒ240 °C, a higher temperature than for SiNPs capped by shorter hydrocarbon layers owing to the greater size of the nanoparticle system in this case. Suspensions of SiNPs are found to evaporate in a UHV environment intact with the hydrocarbon passivating layer preserved and form thin films which are visualized with microimaging FTIR spectroscopy. The stability of the capping layer within thick SiNP films under extended exposure (up to 2160 s) to 140 eV photons has been examined where XPS spectra show the breakdown of the passivating layer allowing the underlying silicon core to undergo subsequent oxidation.</jats:p
Ligand doping on the hybrid thermoelectric materials based on terthiophene-capped silicon nanoparticles
Synthesis of low-oxide blue luminescent alkyl-functionalized silicon nanoparticles with no nitrogen containing surfactant
Bridging silicon nanoparticles and thermoelectrics: phenylacetylene functionalization
Silicon is a promising alternative to current thermoelectric materials (Bi2Te3). Silicon nanoparticle based materials show especially low thermal conductivities due to their high number of interfaces, which increases the observed phonon scattering. The major obstacle with these materials is maintaining high electrical conductivity. Surface functionalization with phenylacetylene shows an electrical conductivity of 18.1 S mâ1 and Seebeck coefficient of 3228.8 ÎŒV Kâ1 as well as maintaining a thermal conductivity of 0.1 W Kâ1 mâ1. This gives a ZT of 0.6 at 300 K which is significant for a bulk silicon based material and is similar to that of other thermoelectric materials such as Mg2Si, PbTe and SiGe alloys