3,044 research outputs found
The potential of performance targets (imihigo) as drivers of energy planning and extending access to offâgrid energy in rural Rwanda
Rwanda has one of the lowest electrification rates in SubâSaharan Africa and ambitious targets of boosting energy access, with an encouraged private sector involvement. However, barriers such as endâuser awareness and participation in policy and business model design prohibit the pace of rural electrification. A case of Rwanda is analyzed, pointing to the potential of the imihigo (performance contracts) framework. Given the adoption of householdâlevel performance contracts, which can include energy access, it is proposed they could drive local participation among offâgrid communities. Results of a survey with 218 users of Solar Home Systems in NorthâWestern Rwanda and from five focus groups show that villageâlevel energy targets impact on the prioritization of energy target setting among households. Including offâgrid energy options in the imihigo booklets distributed to households could influence awareness raising and allow private sector providers to act in a more targeted way, prioritizing areas with most prevalent energy targets. Additionally, community meetings (umuganda) tied to imihigo offer participatory spaces for information and feedback sharing. These will assist in the design of energy planning and business models, which best fit local needs and respond to the challenges faced by the energy poor
De Sitter Holography with a Finite Number of States
We investigate the possibility that, in a combined theory of quantum
mechanics and gravity, de Sitter space is described by finitely many states.
The notion of observer complementarity, which states that each observer has
complete but complementary information, implies that, for a single observer,
the complete Hilbert space describes one side of the horizon. Observer
complementarity is implemented by identifying antipodal states with outgoing
states. The de Sitter group acts on S-matrix elements. Despite the fact that
the de Sitter group has no nontrivial finite-dimensional unitary
representations, we show that it is possible to construct an S-matrix that is
finite-dimensional, unitary, and de Sitter-invariant. We present a class of
examples that realize this idea holographically in terms of spinor fields on
the boundary sphere. The finite dimensionality is due to Fermi statistics and
an `exclusion principle' that truncates the orthonormal basis in which the
spinor fields can be expanded.Comment: 23 pages, 1 eps figure, LaTe
Scattering and Diffraction in Magnetospheres of Fast Pulsars
We apply a theory of wave propagation through a turbulent medium to the
scattering of radio waves in pulsar magnetospheres. We find that under
conditions of strong density modulation the effects of magnetospheric
scintillations in diffractive and refractive regimes may be observable. The
most distinctive feature of the magnetospheric scintillations is their
independence on frequency.
Results based on diffractive scattering due to small scale inhomogeneities
give a scattering angle that may be as large as 0.1 radians, and a typical
decorrelation time of seconds.
Refractive scattering due to large scale inhomogeneities is also possible,
with a typical angle of radians and a correlation time of the order
of seconds. Temporal variation in the plasma density may also result
in a delay time of the order of seconds. The different scaling of the
above quantities with frequency may allow one to distinguish the effects of
propagation through a pulsar magnetosphere from the interstellar medium. In
particular, we expect that the magnetospheric scintillations are relatively
more important for nearby pulsars when observed at high frequencies.Comment: 19 pages, 1 Figur
Time series analysis of malaria in Afghanistan: using ARIMA models to predict future trends in incidence
Additional file 6: Annex 1. Right side: Autocorrelation (ACF) and partial autocorrelation (PACF) functions of the residuals from ARIMA model (1, 0, 1) ÄÂ (1, 0, 1)12 on log-transformed, differenced data. Left side: ACF and PACF of the residuals from ARIMA model (4, 0, 1) ÄÂ (1, 0, 1)12 on log-transformed, differenced data
Triple-horizon spherically symmetric spacetime and holographic principle
We present a family of spherically symmetric spacetimes, specified by the
density profile of a vacuum dark energy, which have the same global structure
as the de Sitter spacetime but the reduced symmetry which leads to a
time-evolving and spatially inhomogeneous cosmological term. It connects
smoothly two de Sitter vacua with different values of cosmological constant and
corresponds to anisotropic vacuum dark fluid defined by symmetry of its
stress-energy tensor which is invariant under the radial boosts. This family
contains a special class distinguished by dynamics of evaporation of a
cosmological horizon which evolves to the triple horizon with the finite
entropy, zero temperature, zero curvature, infinite positive specific heat, and
infinite scrambling time. Non-zero value of the cosmological constant in the
triple-horizon spacetime is tightly fixed by quantum dynamics of evaporation of
the cosmological horizon.Comment: Honorable Mentioned Essay - Gravity Research Foundation 2012;
submitted to Int. J. Mod. Phys.
"Charged" Particle's Tunneling from Rotating Black Holes
The behavior of a scalar field theory near the event horizon in a rotating
black hole background can be effectively described by a two dimensional field
theory in a gauge field background. Based on this fact, we proposal that the
quantum tunneling from rotating black hole can be treated as "charged"
particle' s tunneling process in its effectively two dimensional metric. Using
this viewpoint and considering the corresponding "gauge charge" conservation,
we calculate the non-thermal tunneling rate of Kerr black hole and Myers-Perry
black hole, and results are consistent with Parikh-Wilczek's original result
for spherically symmetric black holes. Especially for Myers-Perry black hole
which has multi-rotation parameters, our calculation fills in the gap existing
in the literature applying Parikh-Wilczek's tunneling method to various types
black holes. Our derivation further illuminates the essential role of effective
gauge symmetry in Hawking radiation from rotating black holes.Comment: 15 pages, no figure; any comments are welcome
Scattering of positrons and electrons by alkali atoms
Absolute total scattering cross sections (Q sub T's) were measured for positrons and electrons colliding with sodium, potassium, and rubidium in the 1 to 102 eV range, using the same apparatus and experimental approach (a beam transmission technique) for both projectiles. The present results for positron-sodium and -rubidium collisions represent the first Q sub T measurements reported for these collision systems. Features which distinguish the present comparisons between positron- and electron-alkali atom Q sub T's from those for other atoms and molecules (room-temperature gases) which have been used as targets for positrons and electrons are the proximity of the corresponding positron- and electron-alkali atom Q sub T's over the entire energy range of overlap, with an indication of a merging or near-merging of the corresponding positron and electron Q sub T's near (and above) the relatively low energy of about 40 eV, and a general tendency for the positron-alkali atom Q sub T's to be higher than the corresponding electron values as the projectile energy is decreased below about 40 eV
GaN evaporation and enhanced diffusion of Ar during high-temperature ion implantation
GaN films were implanted with 150 keV Ar+ at temperatures up to 1100 °C to a dose of 3Ă1015 cm-2. Concentration profiles of Ar were measured by secondary ion mass spectroscopy and depth distributions of ion-induced damage were estimated from Rutherford backscattering/channeling spectra. No redistribution of Ar atoms was detected up to 700 °C. At 1000 °C a deep penetrating diffusion tail and a shift of the Ar peak to the surface were observed. At temperatures higher than 800 °C shift of the damage peak to the surface was also observed. We attributed the shift of the Ar peak and the damage peaks to evaporation of thin layer of GaN during high-temperature implantation and estimated its temperature dependence
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