33,854 research outputs found
Suppression of stimulated Brillouin scattering in optical fibers using a linearly chirped diode laser
The output of high power fiber amplifiers is typically limited by stimulated Brillouin scattering (SBS). An analysis of SBS with a chirped pump laser indicates that a chirp of 2.5 × 10^(15) Hz/s could raise, by an order
of magnitude, the SBS threshold of a 20-m fiber. A diode laser with a constant output power and a linear chirp of 5 × 10^(15) Hz/s has been previously demonstrated. In a low-power proof-of-concept experiment, the threshold for SBS in a 6-km fiber is increased by a factor of 100 with a
chirp of 5 × 10^(14) Hz/s. A linear chirp will enable straightforward coherent combination of multiple fiber amplifiers, with electronic compensation of path length differences on the order of 0.2 m
Developing Nations and Developing Surveys: Measuring Inner Wellbeing in Zambia and India, 2010-2013
In the present chapter, we summarize the results of a programme of research that we have undertaken concerning domains of inner wellbeing (i.e., individuals’ feelings and thoughts about what they can do and be) as experienced by individuals in villages within two nations in the global South (i.e., Zambia and India). Results of confirmatory factor analyses for Zambia at Time 1 (in 2010, n = 361) and for India at Time 1 (in 2011, n = 287) indicated that, although we had expected seven to eight intercorrelated domains to emerge, inner wellbeing was best regarded as a unidimensional construct. However, after we engaged in intensive reflection and extensive reconceptualization and measurement of inner wellbeing, results for Zambia Time 2 (in 2012, n = 344) and for India Time 2 (in 2013, n = 335) indicated that inner wellbeing was best regarded as a multidimensional construct with seven intercorrelated domains (i.e., economic confidence, agency/participation, social connections, close relationships, physical/mental health, competence/selfworth, and values/meaning). Implications for the conceptualization and measurement of inner wellbeing within the global South, and for theoretical and methodological issues concerning wellbeing in general, are discussed
X-ray and Radio Interactions in the Cores of Cooling Flow Clusters
We present high resolution ROSAT x-ray and radio observations of three
cooling flow clusters containing steep spectrum radio sources at their cores.
All three systems exhibit strong signs of interaction between the radio plasma
and the hot intracluster medium. Two clusters, A133 and A2626, show enhanced
x-ray emission spatially coincident with the radio source whereas the third
cluster, A2052, exhibits a large region of x-ray excess surrounding much of the
radio source. Using 3-D numerical simulations, we show that a perturbed jet
propagating through a cooling flow atmosphere can give rise to amorphous radio
morphologies, particularly in the case where the jet was ``turned off'' and
allowed to age passively. In addition, the simulated x-ray surface brightness
produced both excesses and deficits as seen observationally.Comment: 25 pages, 10 figures, accepted for publication in A
Spin Gap in a Doped Kondo Chain
We show that the Kondo chain away from half-filling has a spin gap upon the
introduction of an additional direct Heisenberg coupling between localized
spins. This is understood in the weak-Kondo-coupling limit of the
Heisenberg-Kondo lattice model by bosonization and in the strong-coupling limit
by a mapping to a modified t-J model. Only for certain ranges of filling and
Heisenberg coupling does the spin gap phase extend from weak to strong
coupling.Comment: 4 pages RevTeX including 4 eps figures; minor corrections and
clarification
A Theoretical Model for the Relation for Supermassive Black Holes in Galaxies
We construct a model for the formation of black holes within galactic bulges.
The initial state is a slowly rotating isothermal sphere, characterized by
effective transport speed \aeff and rotation rate . The black hole
mass is determined when the centrifugal radius of the collapse flow exceeds the
capture radius of the central black hole. This model reproduces the observed
correlation between black hole masses and galactic velocity dispersions, \mbh
\approx 10^8 M_\odot (\sigma/200 \kms)^4, where \sigma = \sqrt{2} \aeff.
This model also predicts the ratio \mrat of black hole mass to host mass:
\mrat 0.004 (\sigma/200 \kms).Comment: 9 pages, 2 figures, submitted to Astrophysical Journal Letter
Heisenberg exchange in magnetic monoxides
The superexchange intertacion in transition-metal oxides, proposed initially
by Anderson in 1950, is treated using contemporary tight-binding theory and
existing parameters. We find also a direct exchange for nearest-neighbor metal
ions, larger by a factor of order five than the superexchange. This direct
exchange arises from Vddm coupling, rather than overlap of atomic charge
densities, a small overlap exchange contribution which we also estimate. For
FeO and CoO there is also an important negative contribution, related to Stoner
ferromagnetism, from the partially filled minority-spin band which broadens
when ionic spins are aligned. The corresponding J1 and J2 parameters are
calculated for MnO, FeO, CoO, and NiO. They give good accounts of the Neel and
the Curie-Weiss temperatures, show appropriate trends, and give a reasonable
account of their volume dependences. For MnO the predicted value for the
magnetic susceptibility at the Neel temperature and the crystal distortion
arising from the antiferromagnetic transition were reasonably well given.
Application to CuO2 planes in the cuprates gives J=1220oK, compared to an
experimental 1500oK, and for LiCrO2 gives J1=4 50oK compared to an experimental
230oK.Comment: 21 pages, 1 figure, submitted to Phys. Rev. B 1/19/07. Realized
J=4V^2/U applies generally, as opposed to J=2V^2/U from one-electron theory
(1/28 revision
Evolution of the Spin Gap Upon Doping a 2-Leg Ladder
The evolution of the spin gap of a 2-leg ladder upon doping depends upon the
nature of the lowest triplet excitations in a ladder with two holes. Here we
study this evolution using various numerical techniques for a t-t'-J ladder as
the next-near-neighbor hopping t' is varied. We find that depending on the
value of t', the spin gap can evolve continuously or discontinuously and the
lowest triplet state can correspond to a magnon, a bound magnon-hole-pair, or
two separate quasi-particles. Previous experimental results on the
superconducting two-leg ladder Sr12Ca2Cu24O41 are discussed.Comment: 4 pages, latex, submitted to PR
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