29,114 research outputs found
Beyond capitalism and liberal democracy: on the relevance of GDH Coleâs sociological critique and alternative
This article argues for a return to the social thought of the often ignored early 20th-century English thinker GDH Cole. The authors contend that Cole combined a sociological critique of capitalism and liberal democracy with a well-developed alternative in his work on guild socialism bearing particular relevance to advanced capitalist societies. Both of these, with their focus on the limitations on âfree communal serviceâ in associations and the inability of capitalism to yield emancipation in either production or consumption, are relevant to social theorists looking to understand, critique and contribute to the subversion of neoliberalism. Therefore, the authors suggest that Coleâs associational sociology, and the invitation it provides to think of formations beyond capitalism and liberal democracy, is a timely and valuable resource which should be returned to
Radial Redshift Space Distortions
The radial component of the peculiar velocities of galaxies cause
displacements in their positions in redshift space. We study the effect of the
peculiar velocities on the linear redshift space two point correlation
function. Our analysis takes into account the radial nature of the redshift
space distortions and it highlights the limitations of the plane parallel
approximation. We consider the problem of determining the value of \beta and
the real space two point correlation function from the linear redshift space
two point correlation function. The inversion method proposed here takes into
account the radial nature of the redshift space distortions and can be applied
to magnitude limited redshift surveys that have only partial sky coverage.Comment: 26 pages including 11 figures, to appear in Ap
The Bispectrum as a Signature of Gravitational Instability in Redshift-Space
The bispectrum provides a characteristic signature of gravitational
instability that can be used to probe the Gaussianity of the initial conditions
and the bias of the galaxy distribution. We study how this signature is
affected by redshift distortions using perturbation theory and high-resolution
numerical simulations. We obtain perturbative results for the multipole
expansion of the redshift-space bispectrum which provide a natural way to break
the degeneracy between bias and present in measurements of the
redshift-space power spectrum. We propose a phenomenological model that
incorporates the perturbative results and also describes the bispectrum in the
transition to the non-linear regime. We stress the importance of non-linear
effects and show that inaccurate treatment of these can lead to significant
discrepancies in the determination of bias from galaxy redshift surveys. At
small scales we find that the bispectrum monopole exhibits a strong
configuration dependence that reflects the velocity dispersion of clusters.
Therefore, the hierarchical model for the three-point function does not hold in
redshift-space.Comment: 19 pages, 4 figures. Revised version accepted for publication in Ap
An Analytical Approach to Inhomogeneous Structure Formation
We develop an analytical formalism that is suitable for studying
inhomogeneous structure formation, by studying the joint statistics of dark
matter halos forming at two points. Extending the Bond et al. (1991) derivation
of the mass function of virialized halos, based on excursion sets, we derive an
approximate analytical expression for the ``bivariate'' mass function of halos
forming at two redshifts and separated by a fixed comoving Lagrangian distance.
Our approach also leads to a self-consistent expression for the nonlinear
biasing and correlation function of halos, generalizing a number of previous
results including those by Kaiser (1984) and Mo & White (1996). We compare our
approximate solutions to exact numerical results within the excursion-set
framework and find them to be consistent to within 2% over a wide range of
parameters. Our formalism can be used to study various feedback effects during
galaxy formation analytically, as well as to simply construct observable
quantities dependent on the spatial distribution of objects. A code that
implements our method is publicly available at
http://www.arcetri.astro.it/~evan/GeminiComment: 41 Pages, 11 figures, published in ApJ, 571, 585. Reference added,
Figure 2 axis relabele
Lyman Break Galaxies at z>4 and the Evolution of the UV Luminosity Density at High Redshift
We present initial results of a survey for star-forming galaxies in the
redshift range 3.8 < z < 4.5. This sample consists of a photometric catalog of
244 galaxies culled from a total solid angle of 0.23 square degrees to an
apparent magnitude of I_{AB}=25.0. Spectroscopic redshifts in the range 3.61 <
z < 4.81 have been obtained for 48 of these galaxies; their median redshift is
=4.13. Selecting these galaxies in a manner entirely analogous to our large
survey for Lyman break galaxies at smaller redshift (2.7 < z < 3.4) allows a
relatively clean differential comparison between the populations and integrated
luminosity density at these two cosmic epochs. Over the same range of UV
luminosity, the spectroscopic properties of the galaxy samples at z~4 and z~3
are indistinguishable, as are the luminosity function shapes and the total
integrated UV luminosity densities (rho_{UV}(z=3)/rho_{UV}(z=4) = 1.1 +/-0.3).
We see no evidence at these bright magnitudes for the steep decline in the star
formation density inferred from fainter photometric Lyman-break galaxies in the
Hubble Deep Field (HDF). If the true luminosity density at z~4 is somewhat
higher than implied by the HDF, as our ground-based sample suggests, then the
emissivity of star formation as a function of redshift is essentially constant
for all z>1 once internally consistent corrections for dust are made. This
suggests that there is no obvious peak in star formation activity, and that the
onset of substantial star formation in galaxies occurs at z > 4.5. [abridged
abstract]Comment: To appear in the ApJ, minor revisions to match accepted versio
Hierarchy of Conservation Laws of Diffusion--Convection Equations
We introduce notions of equivalence of conservation laws with respect to Lie
symmetry groups for fixed systems of differential equations and with respect to
equivalence groups or sets of admissible transformations for classes of such
systems. We also revise the notion of linear dependence of conservation laws
and define the notion of local dependence of potentials. To construct
conservation laws, we develop and apply the most direct method which is
effective to use in the case of two independent variables. Admitting
possibility of dependence of conserved vectors on a number of potentials, we
generalize the iteration procedure proposed by Bluman and Doran-Wu for finding
nonlocal (potential) conservation laws. As an example, we completely classify
potential conservation laws (including arbitrary order local ones) of
diffusion--convection equations with respect to the equivalence group and
construct an exhaustive list of locally inequivalent potential systems
corresponding to these equations.Comment: 24 page
Scanning Quantum Decoherence Microscopy
The use of qubits as sensitive magnetometers has been studied theoretically
and recent demonstrated experimentally. In this paper we propose a
generalisation of this concept, where a scanning two-state quantum system is
used to probe the subtle effects of decoherence (as well as its surrounding
electromagnetic environment). Mapping both the Hamiltonian and decoherence
properties of a qubit simultaneously, provides a unique image of the magnetic
(or electric) field properties at the nanoscale. The resulting images are
sensitive to the temporal as well as spatial variation in the fields created by
the sample. As an example we theoretically study two applications of this
technology; one from condensed matter physics, the other biophysics. The
individual components required to realise the simplest version of this device
(characterisation and measurement of qubits, nanoscale positioning) have
already been demonstrated experimentally.Comment: 11 pages, 5 low quality (but arXiv friendly) image
The Evolution of the Galaxy Sizes in the NTT Deep Field: a Comparison with CDM Models
The sizes of the field galaxies with I<25 have been measured in the NTT Deep
Field. Intrinsic sizes have been obtained after deconvolution of the PSF with a
multigaussian method. The reliability of the method has been tested using both
simulated data and HST observations of the same field. The distribution of the
half light radii is peaked at r_{hl} 0.3 arcsec, in good agreement with that
derived from HST images at the same magnitude. An approximate morphological
classification has been obtained using the asymmetry and concentration
parameters. The intrinsic sizes of the galaxies are shown as a function of
their redshifts and absolute magnitudes using photometric redshifts derived
from the multicolor catalog. While the brighter galaxies with morphological
parameters typical of the normal spirals show a flat distribution in the range
r_{d}=1-6 kpc, the fainter population at 0.4<z<0.8 dominates at small sizes. To
explore the significance of this behaviour, an analytical rendition of the
standard CDM model for the disc size evolution has been computed. The model
showing the best fit to the local luminosity function and the Tully-Fisher
relation is able to reproduce at intermediate redshifts a size distribution in
general agreement with the observations, although it tends to underestimate the
number of galaxies fainter than M_B~ -19 with disk sizes r_d~ 1-2 kpc.Comment: 16 pages, 11 figures, ApJ in press, Dec 199
Energy focusing inside a dynamical cavity
We study the exact classical solutions for a real scalar field inside a
cavity with a wall whose motion is self-consistently determined by the pressure
of the field itself. We find that, regardless of the system parameters, the
long-time solution always becomes nonadiabatic and the field's energy
concentrates into narrow peaks, which we explain by means of a simple
mechanical system. We point out implications for the quantized theory.Comment: 5 pages, 6 figures, double column, submitted to P.R.
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