5,179 research outputs found
Prospects for Extrasolar "Earths" in Habitable Zones
We have shown that Earth-mass planets could survive in variously restricted
regions of the habitable zones (HZs) of most of a sample of nine of the 102
main-sequence exoplanetary systems confirmed by 19 November 2003. In a
preliminary extrapolation of our results to the other systems, we estimate that
roughly a half of these systems could have had an Earth-mass planet confined to
the HZ for at least the most recent 1000 Ma. The HZ migrates outwards during
the main-sequence lifetime, and so this proportion varies with stellar age.
About two thirds of the systems could have such a planet confined to the HZ for
at least 1000 Ma at sometime during the main-sequence lifetime. Clearly, these
systems should be high on the target list for exploration for terrestrial
planets. We have reached this conclusion by launching putative Earth-mass
planets in various orbits and following their fate with mixed-variable
symplectic and hybrid integrators. Whether the Earth-mass planets could form in
the HZs of the exoplanetary systems is an urgent question that needs further
study.Comment: 7 pages, 2 figure
Observing the Geometry of Warped Compactification via Cosmic Inflation
Using DBI inflation as an example, we demonstrate that the detailed geometry
of warped compactification can leave an imprint on the cosmic microwave
background (CMB). We compute CMB observables for DBI inflation in a generic
class of warped throats and find that the results (such as the sign of the tilt
of the scalar perturbations and its running) depend sensitively on the precise
shape of the warp factor. In particular, we analyze the warped deformed
conifold and find that the results can differ from those of other warped
geometries, even when these geometries approximate well the exact metric of the
warped deformed conifold.Comment: 4 pages, 3 figures. v2: References and clarifications adde
The impact of broadband in schools
The report reviews evidence for the impact of broadband in English schools, exploring; Variations in provision in level of broadband connectivity; Links between the level of broadband activity and nationally accessible performance data; Aspects of broadband connectivity and the school environment that contribute to better outcomes for pupils and teachers; Academic and motivational benefits associated with educational uses of this technology
Observations of the structure and evolution of solar flares with a soft X-ray telescope
Soft X ray flare events were observed with the S-056 X-ray telescope that was part of the ATM complement of instruments aboard SKYLAB. Analyses of these data are reported. The observations are summarized and a detailed discussion of the X-ray flare structures is presented. The data indicated that soft X-ray emitted by a flare come primarily from an intense well-defined core surrounded by a region of fainter, more diffuse emission. An analysis of flare evolution indicates evidence for preliminary heating and energy release prior to the main phase of the flare. Core features are found to be remarkably stable and retain their shape throughout a flare. Most changes in the overall configuration seem to be result of the appearance, disappearance or change in brightness of individual features, rather than the restructuring or reorientation of these features. Brief comparisons with several theories are presented
Film calibration for the Skylab/ATM S-056 X-ray telescope
The sensitometry and film calibration effort for the Skylab/ATM S-056 X-ray telescope is summarized. The apparatus and procedures used are described together with the two types of flight film used, Kodak SO-212 and SO-242. The sensitometry and processing of the flight film are discussed, and the results are presented in the form of the characteristic curves and related data. The use of copy films is also discussed
Combining evidence-based healthcare with environmental sustainability: using the toothbrush as a model
INTRODUCTION: Healthcare professionals should consider environmental sustainability when recommending medical devices to patients, although there is currently little quantitative data available. The toothbrush is a widely recommended healthcare device worldwide. The aim of this study was to compare the sustainability of different types of toothbrush.
MATERIALS AND METHODS: Four types of toothbrush were studied: a traditional plastic and electric toothbrush, as well as a plastic manual toothbrush with replaceable heads and a bamboo manual toothbrush. Life cycle assessment (LCA) methodology was applied to quantify the environmental impact of these toothbrushes over five years.
RESULTS: The electric toothbrush performed consistently poorly compared to the three manual toothbrush types and had the greatest impact in 15 out of 16 environmental categories. The bamboo and replaceable-head plastic toothbrushes had the lowest impact in all categories. The climate change potential of the electric toothbrush was 11 times greater than the bamboo toothbrush.
DISCUSSION: Switching toothbrushes from the traditional toothbrushes to bamboo or replaceable-head plastic is more environmentally sustainable. These results could be used to inform individual consumer choice, oral health recommendations, procurement of toothbrushes for public health programmes and toothbrush manufacturers. LCA methodology can be used to make healthcare more sustainable
Single-qubit unitary gates by graph scattering
We consider the effects of plane-wave states scattering off finite graphs, as
an approach to implementing single-qubit unitary operations within the
continuous-time quantum walk framework of universal quantum computation. Four
semi-infinite tails are attached at arbitrary points of a given graph,
representing the input and output registers of a single qubit. For a range of
momentum eigenstates, we enumerate all of the graphs with up to vertices
for which the scattering implements a single-qubit gate. As increases, the
number of new unitary operations increases exponentially, and for the
majority correspond to rotations about axes distributed roughly uniformly
across the Bloch sphere. Rotations by both rational and irrational multiples of
are found.Comment: 8 pages, 7 figure
The aerodynamic challenges of the design and development of the space shuttle orbiter
The major aerodynamic design challenge at the beginning of the United States Space Transportation System (STS) research and development phase was to design a vehicle that would fly as a spacecraft during early entry and as an aircraft during the final phase of entry. The design was further complicated because the envisioned vehicle was statically unstable during a portion of the aircraft mode of operation. The second challenge was the development of preflight aerodynamic predictions with an accuracy consistent with conducting a manned flight on the initial orbital flight. A brief history of the early contractual studies is presented highlighting the technical results and management decisions influencing the aerodynamic challenges. The configuration evolution and the development of preflight aerodynamic predictions will be reviewed. The results from the first four test flights shows excellent agreement with the preflight aerodynamic predictions over the majority of the flight regimes. The only regimes showing significant disagreement is confined primarily to early entry, where prediction of the basic vehicle trim and the influence of the reaction control system jets on the flow field were found to be deficient. Postflight results are analyzed to explain these prediction deficiencies
Berezinskii-Kosterlitz-Thouless transitions in an easy-plane ferromagnetic superfluid
A two-dimensional (2D) spin-1 Bose gas exhibits two
Berezenskii-Kosterlitz-Thouless (BKT) transitions in the easy-plane
ferromagnetic phase. The higher temperature transition is associated with
superfluidity of the mass current determined predominantly by a single spin
component. The lower temperature transition is associated with superfluidity of
the axial spin current, quasi-long range order of the transverse spin density
and binding of polar-core spin vortices (PCVs). Above the spin BKT temperature,
the component circulations that make up each PCV spatially separate, suggesting
possible deconfinement analogous to quark deconfinement in high energy physics.
Intercomponent interactions give rise to superfluid drag between the spin
components, which we calculate analytically at zero temperature. We present the
mass/spin superfluid phase diagram as a function of quadratic Zeeman energy
. At the system is in an isotropic spin phase with
symmetry. Here the fluid response exhibits a system size dependence, suggesting
the absence of a BKT transition. Despite this, for finite systems the decay of
spin correlations changes from exponential to algebraic as the temperature is
decreased.Comment: 4 pages + refs, 3 figures. Interpretation of Fig. 3 results has
changed since v
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