4,788 research outputs found
Stimulation of B-lymphocyte colony formation in vitro by sera from patients with leukaemia or lymphoma.
Studies were made on the effects of 665 sera, from normal donors or patients with various diseases, on B-lymphocyte colony formation in agar by mouse spleen cells. Undiluted serum from most normal donors inhibited colony formation, but 43-53% of sera from patients with histiocytic lymphoma, lymphocytic lymphoma or Hodgkin's disease stimulated colony formation, serum activity correlating with the stage of the disease. Moderate colony-stimulating activity was observed with serum taken from patients with acute lymphoid or myeloid leukaemia following, but not prior to, chemotherapy. Colony stimulating activity was not correlated with the blood group of serum donors and could not be ascribed to the presence of endotoxin, red cells or mouse red cell haemagglutinins in the active sera. Elevated colony stimulating activity was not observed in sera from patients with non-neoplastic disorders ot haemopoiesis or with diseases of other organ systems
Imaging the Cosmic Matter Distribution using Gravitational Lensing of Pregalactic HI
21-cm emission from neutral hydrogen during and before the epoch of cosmic
reionisation is gravitationally lensed by material at all lower redshifts.
Low-frequency radio observations of this emission can be used to reconstruct
the projected mass distribution of foreground material, both light and dark. We
compare the potential imaging capabilities of such 21-cm lensing with those of
future galaxy lensing surveys. We use the Millennium Simulation to simulate
large-area maps of the lensing convergence with the noise, resolution and
redshift-weighting achievable with a variety of idealised observation
programmes. We find that the signal-to-noise of 21-cm lens maps can far exceed
that of any map made using galaxy lensing. If the irreducible noise limit can
be reached with a sufficiently large radio telescope, the projected convergence
map provides a high-fidelity image of the true matter distribution, allowing
the dark matter halos of individual galaxies to be viewed directly, and giving
a wealth of statistical and morphological information about the relative
distributions of mass and light. For instrumental designs like that planned for
the Square Kilometer Array (SKA), high-fidelity mass imaging may be possible
near the resolution limit of the core array of the telescope.Comment: version accepted for publication in MNRAS (reduced-resolution
figures
Cosmological Information in the Gravitational Lensing of Pregalactic HI
We study the constraints which the next generation of radio telescopes could
place on the nature of dark energy, dark matter and inflation by studying the
gravitational lensing of high redshift 21 cm emission, and we compare with the
constraints obtainable from wide-angle surveys of galaxy lensing. If the
reionization epoch is effectively at z ~ 8 or later, very large amounts of
cosmological information will be accessible to telescopes like SKA and LOFAR.
We use simple characterizations of reionization history and of proposed
telescope designs to investigate how well the two-dimensional convergence power
spectrum, the three-dimensional matter power spectrum, the evolution of the
linear growth function, and the standard cosmological parameters can be
measured from radio data. The power spectra can be measured accurately over a
wide range of wavenumbers at z ~ 2, and the evolution in the cosmic energy
density can be probed from z ~ 0.5 to z ~ 7. This results in a characterization
of the shape of the power spectra (i.e. of the nature of dark matter and of
inflationary structure generation) which is potentially more precise than that
obtained from galaxy lensing surveys. On the other hand, the dark energy
parameters in their conventional parametrization (Omega_Lambda, w_o, w_a) are
somewhat less well constrained by feasible 21 cm lensing surveys than by an
all-sky galaxy lensing survey although a 21 cm surveys might be more powerful
than galaxy surveys for constraining models with "early" dark energy. Overall,
the best constraints come from combining surveys of the two types. This results
in extremely tight constraints on dark matter and inflation, and improves
constraints on dark energy, as judged by the standard figure of merit, by more
than an order of magnitude over either survey alone.Comment: submitted to MNRAS, 12 pages, error in computer code corrected which
changed constraints on some cosmological parameters, change to lensing
estimator to improve performanc
Peering into the black hole - the quality of black mortality data in Por~ Elizabeth and the rest of South Africa
In the year ending 30 June 1989, 26,8% of 5345 deaths in the Port Elizabeth area were classified as ill-defined. A study was undertaken in an attempt to identify the reasons for the high proportion of such deaths. Copies of all death notifications and death register forms of black people in the area served by the Port Elizabeth City Health Department were collected for a 6-week period. Of the 316 deaths, 154 (48,7%) were certified by medical practitioners at a hospital, 158 (50%) by the police and 4 (1,3%) by private medical practitioners. Of the police-certified deaths 116 (73,4%) were recorded as due to 'natural causes', with the remainder being submitted to autopsy. Of the hospital deaths, 26% were not adequately described in the section for the cause of death on the death certificate. Review of national mortality data for 1985 showed that only 29,9% of ill-defined deaths (in all population groups) were certified by a medical practitioner. The prime source of deaths classifed as ill-defined, both in Port Elizabeth and nationally, were those not certified by a medical practitioner. Strategies aimed' at minimising the number of deaths certified by the police need to be developed
Australian Eclecticism and Theorizing in Information Systems Research
explains a variety of IS research approaches found in Australia, and relates them the the history of IS research and teaching in Australia, and to Australian culture in genera
Generating continuous variable quantum codewords in the near-field atomic lithography
Recently, D. Gottesman et al. [Phys. Rev. A 64, 012310 (2001)] showed how to
encode a qubit into a continuous variable quantum system. This encoding was
realized by using non-normalizable quantum codewords, which therefore can only
be approximated in any real physical setup. Here we show how a neutral atom,
falling through an optical cavity and interacting with a single mode of the
intracavity electromagnetic field, can be used to safely encode a qubit into
its external degrees of freedom. In fact, the localization induced by a
homodyne detection of the cavity field is able to project the near-field atomic
motional state into an approximate quantum codeword. The performance of this
encoding process is then analyzed by evaluating the intrinsic errors induced in
the recovery process by the approximated form of the generated codeword.Comment: 9 pages, 5 figure
Filling of the Mott-Hubbard gap in the high temperature photoemission spectrum of (V_0.972Cr_0.028)_2O_3
Photoemission spectra of the paramagnetic insulating (PI) phase of
(V_0.972Cr_0.028)_2O_3, taken in ultra high vacuum up to the unusually high
temperature (T) of 800 K, reveal a property unique to the Mott-Hubbard (MH)
insulator and not observed previously. With increasing T the MH gap is filled
by spectral weight transfer, in qualitative agreement with high-T theoretical
calculations combining dynamical mean field theory and band theory in the local
density approximation.Comment: 4 pages, 4 figure
Resonant enhancement of ultracold photoassociation rate by electric field induced anisotropic interaction
We study the effects of a static electric field on the photoassociation of a
heteronuclear atom-pair into a polar molecule. The interaction of permanent
dipole moment with a static electric field largely affects the ground state
continuum wave function of the atom-pair at short separations where
photoassociation transitions occur according to Franck-Condon principle.
Electric field induced anisotropic interaction between two heteronuclear ground
state atoms leads to scattering resonances at some specific electric fields.
Near such resonances the amplitude of scattering wave function at short
separation increases by several orders of magnitude. As a result,
photoaasociation rate is enhanced by several orders of magnitude near the
resonances. We discuss in detail electric field modified atom-atom scattering
properties and resonances. We calculate photoassociation rate that shows giant
enhancement due to electric field tunable anisotropic resonances. We present
selected results among which particularly important are the excitations of
higher rotational levels in ultracold photoassociation due to electric field
tunable resonances.Comment: 14 pages,9 figure
Cavity Assisted Nondestructive Laser Cooling of Atomic Qubits
We analyze two configurations for laser cooling of neutral atoms whose
internal states store qubits. The atoms are trapped in an optical lattice which
is placed inside a cavity. We show that the coupling of the atoms to the damped
cavity mode can provide a mechanism which leads to cooling of the motion
without destroying the quantum information.Comment: 12 page
Optical properties of V2O3 in its whole phase diagram
Vanadium sesquioxide V2O3 is considered a textbook example of Mott-Hubbard
physics. In this paper we present an extended optical study of its whole
temperature/doping phase diagram as obtained by doping the pure material with
M=Cr or Ti atoms (V1-xMx)2O3. We reveal that its thermodynamically stable
metallic and insulating phases, although macroscopically equivalent, show very
different low-energy electrodynamics. The Cr and Ti doping drastically change
both the antiferromagnetic gap and the paramagnetic metallic properties. A
slight chromium content induces a mesoscopic electronic phase separation, while
the pure compound is characterized by short-lived quasiparticles at high
temperature. This study thus provides a new comprehensive scenario of the
Mott-Hubbard physics in the prototype compound V2O3
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