1,370 research outputs found
Working with the homeless: The case of a non-profit organisation in Shanghai
This article addresses a two-pronged objective, namely to bring to the fore a much neglected social issue of homelessness, and to explore the dynamics of state-society relations in contemporary China, through a case study of a non-profit organisation (NPO) working with the homeless in Shanghai. It shows that the largely invisible homelessness in Chinese cities was substantially due to exclusionary institutions, such as the combined household registration and 'detention and deportation' systems. Official policy has become much more supportive since 2003 when the latter was replaced with government-run shelters, but we argue that the NPO case demonstrates the potential for enhanced longer-term support and enabling active citizenship for homeless people. By analysing the ways in which the NPO offers services through collaboration and partnership with the public (and private) actors, we also argue that the transformations in postreform China and the changes within the state and civil society have significantly blurred their boundaries, rendering state-society relations much more complex, dynamic, fluid and mutually embedded
XMM-Newton observations expose AGN in apparently normal galaxies
We have performed a detailed analysis of 3 optically normal galaxies
extracted from the XMM Bright Serendipitous Source Sample. Thanks to the good
statistics of the XMM-Newton data, we have unveiled the presence of an AGN in
all of them. In particular, we detect both X-ray obscured (N_H>10^{22} cm^{-2})
and unobscured (N_H<10^{22} cm^{-2}) AGN with intrinsic 2--10 keV luminosities
in the range between 10^{42} -- 10^{43} erg s^{-1}. We find that the X-ray and
optical properties of the sources discussed here could be explained assuming a
standard AGN hosted by galaxies with magnitudes M_R<M^*, taking properly into
account the absorption associated with the AGN, the optical faintness of the
nuclear emission with respect to the host galaxy, and the inadequate set--up
and atmospheric conditions during the optical spectroscopic observations. Our
new spectroscopic observations have revealed the expected AGN features also in
the optical band. These results clearly show that optical spectroscopy
sometimes can be inefficient in revealing the presence of an AGN, which instead
is clearly found from an X-ray spectroscopic investigation. This remarks the
importance of being careful in proposing the identification of X-ray sources
(especially at faint fluxes) when only low quality optical spectra are in hand.
This is particularly important for faint surveys (such as those with XMM-Newton
and Chandra), in which optically dull but X-ray active objects are being found
in sizeable numbers.Comment: Accepted for publication on A&A; 11 pages, 8 figure
Measurement of the Cosmic Ray Energy Spectrum and Composition from 10^{17} to 10^{18.3} eV Using a Hybrid Fluorescence Technique
We study the spectrum and average mass composition of cosmic rays with
primary energies between 10^{17} eV and 10^{18} eV using a hybrid detector
consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon
array. Measurements have been made of the change in the depth of shower maximum
as a function of energy. A complete Monte Carlo simulation of the detector
response and comparisons with shower simulations leads to the conclusion that
the cosmic ray intensity is changing f rom a heavier to a lighter composition
in this energy range. The spectrum is consistent with earlier Fly's Eye
measurements and supports the previously found steepening near 4 \times 10^{17}
eV .Comment: 39 pages, 15 figures, in revtex4 epsf style, submited to AP
Measurement of Scintillation and Ionization Yield and Scintillation Pulse Shape from Nuclear Recoils in Liquid Argon
We have measured the scintillation and ionization yield of recoiling nuclei
in liquid argon as a function of applied electric field by exposing a
dual-phase liquid argon time projection chamber (LAr-TPC) to a low energy
pulsed narrow band neutron beam produced at the Notre Dame Institute for
Structure and Nuclear Astrophysics. Liquid scintillation counters were arranged
to detect and identify neutrons scattered in the TPC and to select the energy
of the recoiling nuclei. We report measurements of the scintillation yields for
nuclear recoils with energies from 10.3 to 57.3 keV and for median applied
electric fields from 0 to 970 V/cm. For the ionization yields, we report
measurements from 16.9 to 57.3 keV and for electric fields from 96.4 to 486
V/cm. We also report the observation of an anticorrelation between
scintillation and ionization from nuclear recoils, which is similar to the
anticorrelation between scintillation and ionization from electron recoils.
Assuming that the energy loss partitions into excitons and ion pairs from
Kr internal conversion electrons is comparable to that from Bi
conversion electrons, we obtained the numbers of excitons () and ion
pairs () and their ratio () produced by nuclear recoils from
16.9 to 57.3 keV. Motivated by arguments suggesting direction sensitivity in
LAr-TPC signals due to columnar recombination, a comparison of the light and
charge yield of recoils parallel and perpendicular to the applied electric
field is presented for the first time.Comment: v2 to reflect published versio
Cumulant expansion for studying damped quantum solitons
The quantum statistics of damped optical solitons is studied using
cumulant-expansion techniques. The effect of absorption is described in terms
of ordinary Markovian relaxation theory, by coupling the optical field to a
continuum of reservoir modes. After introduction of local bosonic field
operators and spatial discretization pseudo-Fokker-Planck equations for
multidimensional s-parameterized phase-space functions are derived. These
partial differential equations are equivalent to an infinite set of ordinary
differential equations for the cumulants of the phase-space functions.
Introducing an appropriate truncation condition, the resulting finite set of
cumulant evolution equations can be solved numerically. Solutions are presented
in Gaussian approximation and the quantum noise is calculated, with special
emphasis on squeezing and the recently measured spectral photon-number
correlations [Spaelter et al., Phys. Rev. Lett. 81, 786 (1998)].Comment: 17 pages, 13 figures, revtex, psfig, multicols, published in
Phys.Rev.
Observational constraints on the co-evolution of supermassive black holes and galaxies
The star formation rate (SFR) and black hole accretion rate (BHAR) functions
are measured to be proportional to each other at z < ~3. This close
correspondence between SF and BHA would naturally yield a BH mass-galaxy mass
correlation, whereas a BH mass-bulge mass correlation is observed. To explore
this apparent contradiction we study the SF in spheroid-dominated galaxies
between z=1 and the present day. We use 903 galaxies from the COMBO-17 survey
with M* >2x10^10M_sun, ultraviolet and infrared-derived SFRs from Spitzer and
GALEX, and morphologies from GEMS HST/ACS imaging. Using stacking techniques,
we find that <25% of all SF occurs in spheroid-dominated galaxies (Sersic index
n>2.5), while the BHAR that we would expect if the global scalings held is
three times higher. This rules out the simplest picture of co-evolution, in
which SF and BHA trace each other at all times. These results could be
explained if SF and BHA occur in the same events, but offset in time, for
example at different stages of a merger event. However, one would then expect
to see the corresponding star formation activity in early-stage mergers, in
conflict with observations. We conclude that the major episodes of SF and BHA
occur in different events, with the bulk of SF happening in isolated disks and
most BHA occurring in major mergers. The apparent global co-evolution results
from the regulation of the BH growth by the potential well of the galactic
spheroid, which includes a major contribution from disrupted disk stars.Comment: 14 pages, 5 figures, accepted for publication in Ap
The XMM-Newton Optical/UV Monitor Telescope
The XMM-OM instrument extends the spectral coverage of the XMM-Newton
observatory into the ultraviolet and optical range. It provides imaging and
time-resolved data on targets simultaneously with observations in the EPIC and
RGS. It also has the ability to track stars in its field of view, thus
providing an improved post-facto aspect solution for the spacecraft. An
overview of the XMM-OM and its operation is given, together with current
information on the performance of the instrument.Comment: Accepted by A&A for publication in the Special Issue on 1st science
with XMM Newton, 9 page
Surface molecular tailoring using pH-switchable supramolecular dendron-ligand assemblies
[Image: see text] The rational design of materials with tailored properties is of paramount importance for a wide variety of biological, medical, electronic and optical applications. Here we report molecular level control over the spatial distribution of functional groups on surfaces utilizing self-assembled monolayers (SAMs) of pH-switchable surface-appended pseudorotaxanes. The supramolecular systems were constructed from a poly(aryl ether) dendron-containing a dibenzo[24]crown-8 (DB24C8) macrocycle and a thiol ligand-containing a dibenzylammonium recognition site and a fluorine end group. The dendron establishes the space (dendritic effect) that each pseudorotaxane occupies on the SAM. Following SAM formation, the dendron is released from the surface by switching off the noncovalent interactions upon pH stimulation, generating surface materials with tailored physical and chemical properties
Three-dimensional quantization of the electromagnetic field in dispersive and absorbing inhomogeneous dielectrics
A quantization scheme for the phenomenological Maxwell theory of the full
electromagnetic field in an inhomogeneous three-dimensional, dispersive and
absorbing dielectric medium is developed. The classical Maxwell equations with
spatially varying and Kramers-Kronig consistent permittivity are regarded as
operator-valued field equations, introducing additional current- and
charge-density operator fields in order to take into account the noise
associated with the dissipation in the medium. It is shown that the equal-time
commutation relations between the fundamental electromagnetic fields
and and the potentials and in the Coulomb gauge
can be expressed in terms of the Green tensor of the classical problem. From
the Green tensors for bulk material and an inhomogeneous medium consisting of
two bulk dielectrics with a common planar interface it is explicitly proven
that the well-known equal-time commutation relations of QED are preserved
Exact expression for the diffusion propagator in a family of time-dependent anharmonic potentials
We have obtained the exact expression of the diffusion propagator in the
time-dependent anharmonic potential . The
underlying Euclidean metric of the problem allows us to obtain analytical
solutions for a whole family of the elastic parameter a(t), exploiting the
relation between the path integral representation of the short time propagator
and the modified Bessel functions. We have also analyzed the conditions for the
appearance of a non-zero flow of particles through the infinite barrier located
at the origin (b<0).Comment: RevTex, 19 pgs. Accepted in Physical Review
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