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Design, characterization, and fabrication of solar-retroreflective cool-wall materials
Raising urban albedo increases the fraction of incident sunlight returned to outer space, cooling cities and their buildings. We evaluated the angular distribution of solar radiation incident on exterior walls in 17 U S. climates to develop performance parameters for solar-retroreflective walls, then applied first-principle physics and ray-tracing simulations to explore designs. Our analysis indicates that retroreflective walls must function at large incidence angles to reflect a substantial portion of summer sunlight, and that this will be difficult to attain with materials that rely on total internal reflection. Gonio-spectrophotometer measurements of the solar spectral bi-directional reflectivity of a bicycle reflector showed little to no retroreflection at large incidence angles. Visual comparisons of retroreflection to specular first-surface reflection for four different retroreflective safety films using violet and green lasers suggest their retroreflection to be no greater than 0.09 at incidence angles up to 45°, and no greater than 0.30 at incidence angles of up to 70°. Attempts to produce a two-surface retroreflector with orthogonal mirror grooves by cutting and polishing an aluminum block indicate that residual surface roughness impedes retroreflection. Ongoing efforts focus on forming orthogonal surfaces with aluminized Mylar film, a material with very high specular reflectance across the solar spectrum. We investigated (1) folding or stamping a free film; (2) adhering the film to a pre-shaped substrate; or (3) attaching the film to a flat ductile substrate, then shaping. The latter two methods were more successful but yielded imperfect right angles
Glass-Like Heat Conduction in High-Mobility Crystalline Semiconductors
The thermal conductivity of polycrystalline semiconductors with type-I
clathrate hydrate crystal structure is reported. Ge clathrates (doped with Sr
and/or Eu) exhibit lattice thermal conductivities typical of amorphous
materials. Remarkably, this behavior occurs in spite of the well-defined
crystalline structure and relatively high electron mobility (). The dynamics of dopant ions and their interaction with the
polyhedral cages of the structure are a likely source of the strong phonon
scattering.Comment: 4 pages, 3 postscript figures, to be published, Phys. Rev. Let
Paedophiles in the community: inter-agency conflict, news leaks and the local press
This article explores the leaking of confidential information about secret Home Office plans to house convicted paedophiles within a local community (albeit inside a prison). It argues that a politics of paedophilia has emerged in which inter-agency consensus on the issue of âwhat to doâ with high-profile sex offenders has broken down. Accordingly, the article situates newspaper âoutingâ of paedophiles in the community in relation to vigilante journalism and leaked information from official agencies. The article then presents research findings from a case study of news events set in train following a whistle-blowing reaction by Prison Officersâ Association officials to Home Office plans. Drawing from a corpus of 10 interviews with journalists and key protagonists in the story, the article discusses both the dynamics of whistle blowing about paedophiles and also what happens after the whistle has blown
Reporting underage consensual sex after the Teddy Bear case: A different perspective
Doctors and researchers face a complex dilemma regarding the mandatory reporting of consensual underage sex, because of contradictions between the Childrenâs Act and the Sexual Offences Act. When providing underage children with sexual and reproductive health services, they have had to decide whether to provide these confidentially, in terms of the Childrenâs Act, or thereafter report the consensual but illegal sexual behaviour to the police, in terms of the Sexual Offences Act. The recent Teddy Bear Clinic for Abused Children, and Resources Aimed at the Prevention of Child Abuse and Neglect (RAPCAN) v. Minister of Justice and Constitutional Development case addressed whether consensual underage sex ought to be a criminal offence and thus reported. The court held that aspects of sections 15 and 16 of the Sexual Offences Act infringed on the constitutional rights of adolescents (aged 12 - 15 years) by proscribing many consensual sexual activities. McQuoid-Mason has described this case in detail. He submits that following the judgement, doctors are no longer under a reporting obligation in relation to consensual underage sex. We respectfully disagree. This article critiques McQuoid-Masonâs approach, sets out our views on the mandatory reporting obligations after the Teddy Bear case and concludes with some comments on the judgementâs implications for researchers and medical practitioners
Glasslike vs. crystalline thermal conductivity in carrier-tuned Ba8Ga16X30 clathrates (X = Ge, Sn)
The present controversy over the origin of glasslike thermal conductivity
observed in certain crystalline materials is addressed by studies on
single-crystal x-ray diffraction, thermal conductivity k(T) and specific heat
Cp(T) of carrier-tuned Ba8Ga16X30 (X = Ge, Sn) clathrates. These crystals show
radically different low-temperature k(T) behaviors depending on whether their
charge carriers are electrons or holes, displaying the usual crystalline peak
in the former case and an anomalous glasslike plateau in the latter. In
contrast, Cp(T) above 4 K and the general structural properties are essentially
insensitive to carrier tuning. We analyze these combined results within the
framework of a Tunneling/Resonant/Rayleigh scatterings model, and conclude that
the evolution from crystalline to glasslike k(T) is accompanied by an increase
both in the effective density of tunnelling states and in the resonant
scattering level, while neither one of these contributions can solely account
for the observed changes in the full temperature range. This suggests that the
most relevant factor which determines crystalline or glasslike behavior is the
coupling strength between the guest vibrational modes and the frameworks with
different charge carriers.Comment: 8 pages, 4 figures, 4 tables, submitted to Phys. Rev.
Cage-size control of guest vibration and thermal conductivity in Sr8Ga16Si30-xGex
We present a systematic study of thermal conductivity, specific heat,
electrical resistivity, thermopower and x-ray diffraction measurements
performed on single-crystalline samples of the pseudoquaternary type-I
clathrate system Sr8Ga16Si30-xGex, in the full range of 0 < x < 30. All the
samples show metallic behavior with n-type majority carriers. However, the
thermal conductivity and specific heat strongly depend on x. Upon increasing x
from 0 to 30, the lattice parameter increases by 3%, from 10.446 to 10.726 A,
and the localized vibrational energies of the Sr guest ions in the
tetrakaidekahedron (dodecahedron) cages decrease from 59 (120) K to 35 (90) K.
Furthermore, the lattice thermal conductivity at low temperatures is largely
suppressed. In fact, a crystalline peak found at 15 K for x = 0 gradually
decreases and disappears for x > 20, evolving into the anomalous glass-like
behavior observed for x = 30. It is found that the increase of the free space
for the Sr guest motion directly correlates with a continuous transition from
on-center harmonic vibration to off-center anharmonic vibration, with
consequent increase in the coupling strength between the guest's low-energy
modes and the cage's acoustic phonon modes.Comment: 7 pages, 7 figures, submitted to PR
Assessment and Control of an Invasive Aquaculture Species: An Update on Nile Tilapia (\u3cem\u3eOreochromis niloticus\u3c/em\u3e) in Coastal Mississippi after Hurricane Katrina
Stuart Hall and the theory and practice of articulation
In this article, I argue that the idea of articulation links three different dimensions of Stuart Hallâs work: it is central to the work of cultural politics, to the work of hegemony, and to his practice of embodied pedagogy. I claim that his approach to pedagogy entails the art of listening combined with the practice of theorising in the service of expanding who belongs to the public. This involves the work of translation, finding ways of addressing different audiences. I treat each of these aspects in turn, drawing out the salience of articulation for each and suggest that these three dimensions are themselves articulated by Hallâs commitment to the theory and practice of articulation
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