4,254 research outputs found
Manufacturing and fabrication, part 3
The accessibility of material and energy off the Earth and the leverage that these nonterrestrial resources can exert on the space transportation system are important influences on the long-term goal of exploring the solar system. Research on separation of lunar materials and manufacturing of useful products from them is in its infancy. A few possible processes and products are described in this report. Specific attention is given to oxygen, metal, and silicate products
Time scale of entropic segregation of flexible polymers in confinement: Implications for chromosome segregation in filamentous bacteria
We report molecular dynamics simulations of the segregation of two
overlapping chains in cylindrical confinement. We find that the entropic
repulsion between the chains can be sufficiently strong to cause segregation on
a time scale that is short compared to the one for diffusion. This result
implies that entropic driving forces are sufficiently strong to cause rapid
bacterial chromosome segregation.Comment: Minor changes. Added some references, corrected the labels in figure
6 and reformatted in two columns. Also added reference to published version
in PR
Object orientation without extending Z
The good news of this paper is that without extending Z,
we can elegantly specify object-oriented systems, including encapsulation,
inheritance and subtype polymorphism (dynamic dispatch). The
bad news is that this specification style is rather different to normal
Z specifications, more abstract and axiomatic, which means that it is
not so well supported by current Z tools such as animators. It also enforces
behavioural subtyping, unlike most object-oriented programming
languages. This paper explains the proposed style, with examples, and
discusses its advantages and disadvantages
Impurity-induced tuning of quantum well states in spin-dependent resonant tunneling
We report exact model calculations of the spin-dependent tunneling in double
magnetic tunnel junctions in the presence of impurities in the well. We show
that the impurity can tune selectively the spin channels giving rise to a wide
variety of interesting and novel transport phenomena. The tunneling
magnetoresistance, the spin polarization and the local current can be
dramatically enhanced or suppressed by impurities. The underlying mechanism is
the impurity-induced shift of the quantum well states (QWS) which depends on
the impurity potential, impurity position and the symmetry of the QWS.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
The Alcohol Health Alliance: the emergence of an advocacy coalition to stimulate policy change
This paper provides an account of the emergence and early development of the Alcohol Health Alliance (AHA), a coalition of organizations including medical bodies, charities and alcohol health campaigners. Launched in 2007, the AHA aimed to re-frame awareness of alcohol consumption and related harms, to gain greater policy saliency for health compared to criminal justice priorities, and to shift policy towards adopting a population approach as compared to a targeted approach to intervention. The strategies used by the AHA to mobilize support and re-frame understanding of the alcohol problem, were successful in the short term. The alliance benefited from their links with established powerful institutions that helped them secure a strong presence within the policy arena and in the media, not least by forging relationships with political allies. However, in the longer term, it may be difficult to maintain a position of strength and to combat pre-existing entrenched relationships that favour competing alternative perceptions of the alcohol problem and the appropriate policy response
Surface nano-patterning through styrene adsorption on Si(100)
We present an ab initio study of the structural and electronic properties of
styrene molecules adsorbed on the dimerized Si(100) surface at different
coverages, ranging from the single-molecule to the full monolayer. The
adsorption mechanism primarily involves the vinyl group via a [2+2]
cycloaddition process that leads to the formation of covalent Si-C bonds and a
local surface derelaxation, while it leaves the phenyl group almost
unperturbed. The investigation of the functionalized surface as a function of
the coverage (e.g. 0.5 -- 1 ML) and of the substrate reconstruction reveals two
major effects. The first results from Si dimer-vinyl interaction and concerns
the controlled variation of the energy bandgap of the interface. The second is
associated to phenyl-phenyl interactions, which gives rise to a regular pattern
of electronic wires at surface, stemming from the pi-pi coupling. These
findings suggest a rationale for tailoring the surface nano-patterning of the
surface, in a controlled way.Comment: 19 pages (preprint), 4 figures, supplementary materia
High-frequency spin valve effect in ferromagnet-semiconductor-ferromagnet structure based on precession of injected spins
New mechanism of magnetoresistance, based on tunneling-emission of spin
polarized electrons from ferromagnets (FM) into semiconductors (S) and
precession of electron spin in the semiconductor layer under external magnetic
field, is described. The FM-S-FM structure is considered, which includes very
thin heavily doped (delta-doped) layers at FM-S interfaces. At certain
parameters the structure is highly sensitive at room-temperature to variations
of the field with frequencies up to 100 GHz. The current oscillates with the
field, and its relative amplitude is determined only by the spin polarizations
of FM-S junctions at relatively large bias voltage.Comment: 5 pages, 2 figures, (v2) new plot with a dependence of current J on
magnetic field H added in Fig.2 (top panel), minor amendments in the text;
(v3) minor typos corrected. To appear in Phys. Rev. Letter
Magnetic Diode Effect in Double Barrier Tunnel Junctions
A quantum statistical theory of spin-dependent tunneling through asymmetric
magnetic double barrier junctions is presented which describes ballistic
and diffuse tunneling by a single analytical expression. It is evidenced that
the key parameter for the transition between these two tunneling regimes is the
electron scattering. For these junctions a strong asymmetric behaviour in the
I-V characteristics and the tunnel magnetoresistance (TMR) is predicted which
can be controlled by an applied magnetic field. This phenomenon relates to the
quantum well states in the middle metallic layer. The corresponding resonances
in the current and the TMR are drastically phase shifted under positive and
negative voltage.Comment: 10 pages, 4 Postscript figures, submitted to Europhys. Let
Report of the Terrestrial Bodies Science Working Group. Volume 4: The moon
A rationale for furture exploration of the moon is given. Topics discussed include the objectives of the lunar polar orbiter mission, the mission profile, and general characteristics of the spacraft to be used
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