11,641 research outputs found
The optical and near-infrared properties of nearby groups of galaxies
We present a study of the optical (BRI) and near-infrared (JHK) luminosity
fuctions (LFs) of the GEMS sample of 60 nearby groups of galaxies between
0<z<0.04, with our optical CCD photometry and near-IR photometry from the 2MASS
survey. The LFs in all filters show a depletion of galaxies of intermediate
luminosity, two magnitudes fainter than L*, within 0.3 R{500} from the centres
of X-ray faint groups. This feature is not as pronounced in X-ray bright
gropus, and vanishes when LFs are found out to R{500}, even in the X-ray dim
groups. We argue that this feature arises due to the enhanced merging of
intermediate-mass galaxies in the dynamically sluggish environment of low
velocity-dispersion groups, indicating that merging is important in galaxy
evolution even at z~0.Comment: to appear in the proceedings of the ESO workshop "Groups of Galaxies
in the Nearby Universe", Santiago, Dec 5-9, 2005. Eds. I. Saviane, V. Ivanov,
& J. Borissova (Springer Verlag); 5 page
Structure of CdTe/ZnTe superlattices
The structure of CdTe/ZnTe superlattices has been analyzed through Ξ/2Ξ xâray diffraction, photoluminescence, and in situ reflection highâenergy electron diffraction (RHEED) measurements. Samples are found to break away from Cd_(x)Zn_(1âx)Te buffer layers as a consequence of the 6% lattice mismatch in this system. However, defect densities in these superlattices are seen to drop dramatically away from the buffer layer interface, accounting for the intense photoluminescence and highâaverage strain fields seen in each of our samples. Observed variations in residual strains suggest that growth conditions play a role in forming misfit defects. This could explain discrepancies with calculated values of critical thickness based on models which neglect growth conditions. Photoluminescence spectra reveal that layerâtoâlayer growth proceeded with single monolayer uniformity, suggesting highly reproducible growth. Our results give hope for relatively defectâfree Cd_(x)Zn_(1âx)Te/Cd_(y)Zn_(1ây)Te superlattices with the potential for applications to optoelectronics offered by intense visible light emitters
Dynamical systems arising from elliptic curves
We exhibit a family of dynamical systems arising from rational points on elliptic curves in an attempt to mimic the familiar toral automorphisms. At the non-archimedean primes, a continuous map is constructed on the local elliptic curve whose topological entropy is given by the local canonical height. Also, a precise formula for the periodic points is given. There follows a discussion of how these local results may be glued together to give a map on the adelic curve. We are able to give a map whose entropy is the global canonical height and whose periodic points are counted asymptotically by the real division polynomial (although the archimedean component of the map is artificial). Finally, we set out a precise conjecture about the existence of elliptic dynamical systems and discuss a possible connection with mathematical physics
Experimental Study of Parametric Autoresonance in Faraday Waves
The excitation of large amplitude nonlinear waves is achieved via parametric
autoresonance of Faraday waves. We experimentally demonstrate that phase
locking to low amplitude driving can generate persistent high-amplitude growth
of nonlinear waves in a dissipative system. The experiments presented are in
excellent agreement with theory.Comment: 4 pages, 4 eps figures, to appear in Phys. Rev. Let
Testing the existence of optical linear polarization in young brown dwarfs
Linear polarization can be used as a probe of the existence of atmospheric
condensates in ultracool dwarfs. Models predict that the observed linear
polarization increases withthe degree of oblateness, which is inversely
proportional to the surface gravity. We aimed to test the existence of optical
linear polarization in a sample of bright young brown dwarfs, with spectral
types between M6 and L2, observable from the Calar Alto Observatory, and
cataloged previously as low gravity objects using spectroscopy. Linear
polarimetric images were collected in I and R-band using CAFOS at the 2.2 m
telescope in Calar Alto Observatory (Spain). The flux ratio method was employed
to determine the linear polarization degrees. With a confidence of 3,
our data indicate that all targets have a linear polarimetry degree in average
below 0.69% in the I-band, and below 1.0% in the R-band, at the time they were
observed. We detected significant (i.e. P/ 3) linear polarization
for the young M6 dwarf 2MASS J04221413+1530525 in the R-band, with a degree of
= 0.81 0.17 %.Comment: Accepted for publication in MNRA
Accommodation of lattice mismatch in Ge_(x)Si_(1âx)/Si superlattices
We present evidence that the critical thickness for the appearance of misfit defects in a given material and heteroepitaxial structure is not simply a function of lattice mismatch. We report substantial differences in the relaxation of mismatch stress in Ge_(0.5)Si_(0.5)/Si superlattices grown at different temperatures on (100) Si substrates. Samples have been analyzed by xâray diffraction, channeled Rutherford backscattering, and transmission electron microscopy. While a superlattice grown at 365â°C demonstrates a high degree of elastic strain, with a dislocation density <10^5 cm^(â2) , structures grown at higher temperatures show increasing numbers of structural defects, with densities reaching 2Ă10^(10) cm^(â2) at a growth temperature of 530â°C. Our results suggest that it is possible to freeze a latticeâmismatched structure in a highly strained metastable state. Thus it is not surprising that experimentally observed critical thicknesses are rarely in agreement with those predicted by equilibrium theories
Crop Production for Pacific Islands: Instructor Manual
An entry level university course with specific reference to Pacific Island conditions. Instructor's can either use the materials directly from the manual or adapt them to suit their needs. Chapters include: agroecology; climate; world food crops; and crop production. Each chapter contains objectives, vocabulary, lecture outlines, suggested activities, and transparency masters.Funded through the US Department of Agriculture Cooperative State Research Service
Understanding and predicting the temporal variability of sediment grain size characteristics on high-energy beaches
Amplitude equations and pattern selection in Faraday waves
We present a systematic nonlinear theory of pattern selection for parametric
surface waves (Faraday waves), not restricted to fluids of low viscosity. A
standing wave amplitude equation is derived from the Navier-Stokes equations
that is of gradient form. The associated Lyapunov function is calculated for
different regular patterns to determine the selected pattern near threshold.
For fluids of large viscosity, the selected wave pattern consists of parallel
stripes. At lower viscosity, patterns of square symmetry are obtained in the
capillary regime (large frequencies). At lower frequencies (the mixed
gravity-capillary regime), a sequence of six-fold (hexagonal), eight-fold, ...
patterns are predicted. The regions of stability of the various patterns are in
quantitative agreement with recent experiments conducted in large aspect ratio
systems.Comment: 12 pages, 1 figure, Revte
The Trilinear Hamiltonian: A Zero Dimensional Model of Hawking Radiation from a Quantized Source
We investigate a quantum parametric amplifier with dynamical pump mode,
viewed as a zero-dimensional model of Hawking radiation from an evaporating
black hole. The conditions are derived under which the spectrum of particles
generated from vacuum fluctuations deviates from the thermal spectrum predicted
for the conventional parametric amplifier. We find that significant deviations
arise when the pump mode (black hole) has emitted nearly half of its initial
energy into the signal (Hawking radiation) and idler (in-falling particle)
modes. As a model of black hole dynamics, this finding lends support to the
view that late-time Hawking radiation contains information about the quantum
state of the black hole and is entangled with the black hole's quantum
gravitational degrees of freedom.Comment: 18 pages, 6 figures, Submitted to New Journal of Physics focus issue:
"Classical and Quantum Analogues for Gravitational Phenomena and Related
Effects
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