1,580 research outputs found
Middlemen, Non-Profits, and Poverty
In many markets in developing countries, especially in remote areas, middlemen are thought to earn excessive profits. Non-profits come in to counter what is seen as middlemen's market power, and rich country consumers pay a "fair-trade" premium for products marketed by such non-profits. This paper provides answers to the following five questions. How exactly do middlemen and non-profits divide up the market? How do the price mark up and price pass-through differ between middleman and non-profits? What is the impact of non-profits entry on the wellbeing of the poor? Should the government subsidize the entry of non-profits, or the entry of middlemen? Should wealthy consumers in the North pay a premium for fair trade products, or should they support fair trade non-profits directly?Middlemen, Non-profits, Poverty, Market Access, Food Security and Poverty, International Development, Productivity Analysis, F15, I32, L3,
Thermal Equilibrium of String Gas in Hagedorn Universe
The thermal equilibrium of string gas is necessary to activate the
Brandenberger-Vafa mechanism, which makes our observed 4-dimensional universe
enlarge. Nevertheless, the thermal equilibrium is not realized in the original
setup, a problem that remains as a critical defect. We study thermal
equilibrium in the Hagedorn universe, and explore possibilities for avoiding
the issue aforementioned flaw. We employ a minimal modification of the original
setup, introducing a dilaton potential. Two types of potential are
investigated: exponential and double-well potentials. For the first type, the
basic evolutions of universe and dilaton are such that both the radius of the
universe and the dilaton asymptotically grow in over a short time, or that the
radius converges to a constant value while the dilaton rolls down toward the
weak coupling limit. For the second type, in addition to the above solutions,
there is another solution in which the dilaton is stabilized at a minimum of
potential and the radius grows in proportion to . Thermal equilibrium is
realized for both cases during the initial phase. These simple setups provide
possible resolutions of the difficulty.Comment: 23 pages,19 figure
Vortex Tubes in Turbulence Velocity Fields at Reynolds Numbers 300-1300
The most elementary structures of turbulence, i.e., vortex tubes, are studied
using velocity data obtained in a laboratory experiment for boundary layers
with microscale Reynolds numbers 295-1258. We conduct conditional averaging for
enhancements of a small-scale velocity increment and obtain the typical
velocity profile for vortex tubes. Their radii are of the order of the
Kolmogorov length. Their circulation velocities are of the order of the
root-mean-square velocity fluctuation. We also obtain the distribution of the
interval between successive enhancements of the velocity increment as the
measure of the spatial distribution of vortex tubes. They tend to cluster
together below about the integral length and more significantly below about the
Taylor microscale. These properties are independent of the Reynolds number and
are hence expected to be universal.Comment: 8 pages, to appear in Physical Review
Probing anisotropies of gravitational-wave backgroundswith a space-based interferometer II: Perturbative reconstruction of a low-frequency skymap
We present a perturbative reconstruction method to make a skymap of
gravitational-wave backgrounds (GWBs) observed via space-based interferometer.
In the presence of anisotropies in GWBs, the cross-correlated signals of
observed GWBs are inherently time-dependent due to the non-stationarity of the
gravitational-wave detector. Since the cross-correlated signal is obtained
through an all-sky integral of primary signals convolving with the antenna
pattern function of gravitational-wave detectors, the non-stationarity of
cross-correlated signals, together with full knowledge of antenna pattern
functions, can be used to reconstruct an intensity map of the GWBs. Here, we
give two simple methods to reconstruct a skymap of GWBs based on the
perturbative expansion in low-frequency regime. The first one is based on
harmonic-Fourier representation of data streams and the second is based on
"direct" time-series data. The latter method enables us to create a skymap in a
direct manner. The reconstruction technique is demonstrated in the case of the
Galactic gravitational wave background observed via planned space
interferometer, LISA. Although the angular resolution of low-frequency skymap
is rather restricted, the methodology presented here would be helpful in
discriminating the GWBs of galactic origins by those of the extragalactic
and/or cosmological origins.Comment: 23 pages, 12 figures, Phys.Rev.D (2005) in pres
Runaway Merging of Black Holes: Analytical Constraint on the Timescale
Following the discovery of a black hole (BH) with a mass of 10^3-10^6 M(sun)
in a starburst galaxy M82, we study formation of such a BH via successive
merging of stellar-mass BHs within a star cluster. The merging has a runaway
characteristic. This is because massive BHs sink into the cluster core and have
a high number density, and because the merging probability is higher for more
massive BHs. We use the Smoluchowski equation to study analytically the
evolution of the BH mass distribution. Under favorable conditions, which are
expected for some star clusters in starburst galaxies, the timescale of the
runaway merging is at most of order 10^7 yr. This is short enough to account
for the presence of a BH heavier than 10^3 M(sun) in an ongoing starburst
region.Comment: 10 pages, no figures, to appear in The Astrophysical Journal
(Letters
Thermodynamics of four-dimensional black objects in the warped compactification
We reinvestigate the thermodynamics of black objects (holes and strings) in
four-dimensional braneworld models that are originally constructed by Emparan,
Horowitz and Myers based on the anti-de Sitter (AdS) C-metric. After proving
the uniqueness of slicing the AdS C-metric, we derive thermodynamic quantities
of the black objects by means of the Euclidean formulation and find that we
have no necessity of requiring any regularization to calculate their classical
action. We show that there exist the Bekenstein-Hawking law and the
thermodynamic first law. The thermodynamic mass of the localized black hole on
a flat brane is negative, and it differs from the one previously derived. We
discuss the thermodynamic stabilities and show that the BTZ black string is
more stable than the localized black holes in a canonical ensemble, except for
an extreme case. We also find a braneworld analogue of the Hawking-Page
transition between the BTZ black string and thermal AdS branes. The localized
black holes on a de Sitter brane is discussed by considering Nariai instanton,
comparing the study of "black cigar" in the five-dimensional braneworld model.Comment: 15 pages, 4 figures, RevTex4, typos fixed, minor correction
Valence and Na content dependences of superconductivity in NaxCoO2.yH2O
Various samples of sodium cobalt oxyhydrate with relatively large amounts of
Na ions were synthesized by a modified soft-chemical process in which a
NaOH aqueous solution was added in the final step of the procedure. From these
samples, a superconducting phase diagram was determined for a section of a
cobalt valence of +3.48, which was compared with a previously obtained
one of +3.40. The superconductivity was significantly affected by the
isovalent exchanger of Na and HO, rather than by variation of
Co valence, suggesting the presence of multiple kinds of Fermi surface.
Furthermore, the high-field magnetic susceptibility measurements for one sample
up to 30 T indicated an upper critical field much higher than the Pauli limit
supporting the validity of the spin-triplet pairing mechanism.Comment: 4 figures and 1 tabl
Pulse-density-modulated power control of a 4 kW, 450 kHz voltage-source inverter for induction melting applications
This paper presents a 4 kW, 450 kHz voltage-source inverter with a series resonant circuit for induction melting applications, which is characterized by the power control based on pulse density modulation (PDM). The pulse-density-modulated inverter makes an induction melting system simple and compact, thus leading to higher efficiency. A modulation strategy is proposed to realize the induction melting system capable of operation at the frequency and power level of interest. Some interesting experimental results are shown to verify the validity of the concept </p
Gluon-propagator functional form in the Landau gauge in SU(3) lattice QCD: Yukawa-type gluon propagator and anomalous gluon spectral function
We study the gluon propagator in the Landau gauge in
SU(3) lattice QCD at = 5.7, 5.8, and 6.0 at the quenched level. The
effective gluon mass is estimated as MeV for fm. Through the functional-form analysis of
obtained in lattice QCD, we find that the Landau-gauge
gluon propagator is well described by the Yukawa-type
function with MeV for fm in the
four-dimensional Euclidean space-time. In the momentum space, the gluon
propagator with GeV is
found to be well approximated with a new-type propagator of ,
which corresponds to the four-dimensional Yukawa-type propagator. Associated
with the Yukawa-type gluon propagator, we derive analytical expressions for the
zero-spatial-momentum propagator , the effective mass ,
and the spectral function of the gluon field. The mass parameter
turns out to be the effective gluon mass in the infrared region of
1fm. As a remarkable fact, the obtained gluon spectral function
is almost negative-definite for , except for a positive
-functional peak at .Comment: 20 pages, 15 figure
Confirmation of a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor and antiferromagnetic second-nearest-neighbor interactions in RbCuMoO
We have investigated magnetic properties of RbCuMoO
powder. Temperature dependence of magnetic susceptibility and magnetic-field
dependence of magnetization have shown that this cuprate is a model compound of
a one-dimensional spin-1/2 Heisenberg system with ferromagnetic
first-nearest-neighbor (1NN) and antiferromagnetic second-nearest-neighbor
(2NN) competing interactions (competing system). Values of the 1NN and 2NN
interactions are estimated as K and K (). This value of suggests that the ground state is a
spin-singlet incommensurate state. In spite of relatively large and
, no magnetic phase transition appears down to 2 K, while an
antiferromagnetic transition occurs in other model compounds of the competing
system with ferromagnetic 1NN interaction. For that reason,
RbCuMoO is an ideal model compound to study properties of
the incommensurate ground state that are unconfirmed experimentally.Comment: 6 pages, 4 figure
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