3,467 research outputs found
Cosmic microwave background snapshots: pre-WMAP and post-WMAP
Abbreviated: We highlight the remarkable evolution in the CMB power spectrum
over the past few years, and in the cosmological parameters for minimal
inflation models derived from it. Grand unified spectra (GUS) show pre-WMAP
optimal bandpowers are in good agreement with each other and with the one-year
WMAP results, which now dominate the L < 600 bands. GUS are used to determine
calibrations, peak/dip locations and heights, and damping parameters. These CMB
experiments significantly increased the case for accelerated expansion in the
early universe (the inflationary paradigm) and at the current epoch (dark
energy dominance) when they were combined with `prior' probabilities on the
parameters. A minimal inflation parameter set is applied in the same way to the
evolving data. Grid-based and and Monte Carlo Markov Chain methods are shown to
give similar values, highly stable over time and for different prior choices,
with the increasing precision best characterized by decreasing errors on
uncorrelated parameter eigenmodes. After marginalizing over the other cosmic
and experimental variables for a weak+LSS prior, the pre-WMAP data of Jan03 cf.
the post-WMAP data of Mar03 give Omega_{tot} =1.03^{+0.05}_{-0.04} cf.
1.02^{+0.04}_{-0.03}. Adding the flat prior, n_s =0.95^{+0.07}_{-0.04} cf.
0.97^{+0.02}_{-0.02}, with < 2\sigma evidence for a log variation of n_s. The
densities have concordance values. The dark energy pressure-to-density ratio is
not well constrained by our weak+LSS prior, but adding SN1 gives w_Q < -0.7. We
find \sigma_8 = 0.89^{+0.06}_{-0.07} cf. 0.86^{+0.04}_{-0.04}, implying a
sizable SZ effect; the high L power suggest \sigma_8 \sim 0.94^{+0.08}_{-0.16}
is needed to be SZ-compatible.Comment: 36 pages, 5 figures, 5 tables, Jan 2003 Roy Soc Discussion Meeting on
`The search for dark matter and dark energy in the Universe', published PDF
(Oct 15 2003) is http://www.cita.utoronto.ca/~bond/roysoc03/03TA2435.pd
Control theory for principled heap sizing
We propose a new, principled approach to adaptive heap sizing based on control theory. We review current state-of-the-art heap sizing mechanisms, as deployed in Jikes RVM and HotSpot. We then formulate heap sizing as a control problem, apply and tune a standard controller algorithm, and evaluate its performance on a set of well-known benchmarks. We find our controller adapts the heap size more responsively than existing mechanisms. This responsiveness allows tighter virtual machine memory footprints while preserving target application throughput, which is ideal for both embedded and utility computing domains. In short, we argue that formal, systematic approaches to memory management should be replacing ad-hoc heuristics as the discipline matures. Control-theoretic heap sizing is one such systematic approach
Widespread association between the ericoid mycorrhizal fungus Rhizoscyphus ericae and a leafy liverwort in the maritime and sub-Antarctic
A recent study identified a fungal isolate from the Antarctic leafy liverwort Cephaloziella varians as the ericoid mycorrhizal associate Rhizoscyphus ericae. However, nothing is known about the wider Antarctic distribution of R. ericae in C. varians, and inoculation experiments confirming the ability of the fungus to form coils in the liverwort are lacking.
Using direct isolation and baiting with Vaccinium macrocarpon seedlings, fungi were isolated from C. varians sampled from eight sites across a 1875-km transect through sub- and maritime Antarctica. The ability of an isolate to form coils in aseptically grown C. varians was also tested.
Fungi with 98–99% sequence identity to R. ericae internal transcribed spacer (ITS) region and partial large subunit ribosomal (r)DNA sequences were frequently isolated from C. varians at all sites sampled. The EF4/Fung5 primer set did not amplify small subunit rDNA from three of five R. ericae isolates, probably accounting for the reported absence of the fungus from C. varians in a previous study. Rhizoscyphus ericae was found to colonize aseptically-grown C. varians intracellularly, forming hyphal coils.
This study shows that the association between R. ericae and C. varians is apparently widespread in Antarctica, and confirms that R. ericae is at least in part responsible for the formation of the coils observed in rhizoids of field-collected C. varians
Stellar Kinematics in the Complicated Inner Spheroid of M31: Discovery of Substructure Along the Southeastern Minor Axis and its Relationship to the Giant Southern Stream
We present the discovery of a kinematically-cold stellar population along the
SE minor axis of the Andromeda galaxy (M31) that is likely the forward
continuation of M31's giant southern stream. This discovery was made in the
course of an on-going spectroscopic survey of red giant branch (RGB) stars in
M31 using the DEIMOS instrument on the Keck II 10-m telescope. Stellar
kinematics are investigated in eight fields located 9-30 kpc from M31's center
(in projection). A likelihood method based on photometric and spectroscopic
diagnostics is used to isolate confirmed M31 RGB stars from foreground Milky
Way dwarf stars: for the first time, this is done without using radial velocity
as a selection criterion, allowing an unbiased study of M31's stellar
kinematics. The radial velocity distribution of the 1013 M31 RGB stars shows
evidence for the presence of two components. The broad (hot) component has a
velocity dispersion of 129 km/s and presumably represents M31's virialized
spheroid. A significant fraction (19%) of the population is in a narrow (cold)
component centered near M31's systemic velocity with a velocity dispersion that
decreases with increasing radial distance, from 55.5 km/s at R_proj=12 kpc to
10.6 km/s at R_proj=18 kpc. The spatial and velocity distribution of the cold
component matches that of the "Southeast shelf" predicted by the Fardal et al.
(2007) orbital model of the progenitor of the giant southern stream. The
metallicity distribution of the cold component matches that of the giant
southern stream, but is about 0.2 dex more metal rich on average than that of
the hot spheroidal component. We discuss the implications of our discovery on
the interpretation of the intermediate-age spheroid population found in this
region in recent ultra-deep HST imaging studies.Comment: 23 pages, 16 figures, 2 tables, accepted for publication in the
Astrophysical Journal. Changes from previous version: expanded discussion in
sections 4.2 and 7.2, removal of section 7.1.4 and associated figure
(discussion moved to section 7.1.2
The helminth parasite heligmosomoides polygyrus attenuates EAE in an IL-4Rα-dependent manner
Helminth parasites are effective in biasing Th2 immunity and inducing regulatory pathways that minimize excessive inflammation within their hosts, thus allowing chronic infection to occur whilst also suppressing bystander atopic or autoimmune diseases. Multiple sclerosis (MS) is a severe autoimmune disease characterized by inflammatory lesions within the central nervous system; there are very limited therapeutic options for the progressive forms of the disease and none are curative. Here, we used the experimental autoimmune encephalomyelitis (EAE) model to examine if the intestinal helminth Heligmosomoides polygyrus and its excretory/secretory products (HES) are able to suppress inflammatory disease. Mice infected with H. polygyrus at the time of immunization with the peptide used to induce EAE (myelin-oligodendrocyte glycoprotein, pMOG), showed a delay in the onset and peak severity of EAE disease, however, treatment with HES only showed a marginal delay in disease onset. Mice that received H. polygyrus 4 weeks prior to EAE induction were also not significantly protected. H. polygyrus secretes a known TGF-β mimic (Hp-TGM) and simultaneous H. polygyrus infection with pMOG immunization led to a significant expansion of Tregs; however, administering the recombinant Hp-TGM to EAE mice failed to replicate the EAE protection seen during infection, indicating that this may not be central to the disease protecting mechanism. Mice infected with H. polygyrus also showed a systemic Th2 biasing, and restimulating splenocytes with pMOG showed release of pMOG-specific IL-4 as well as suppression of inflammatory IL-17A. Notably, a Th2-skewed response was found only in mice infected with H. polygyrus at the time of EAE induction and not those with a chronic infection. Furthermore, H. polygyrus failed to protect against disease in IL-4Rα−/− mice. Together these results indicate that the EAE disease protective mechanism of H. polygyrus is likely to be predominantly Th2 deviation, and further highlights Th2-biasing as a future therapeutic strategy for MS
Quantum Monte Carlo Study of Hole Binding and Pairing Correlations in the Three-Band Hubbard Model
We simulated the 3-band Hubbard model using the Constrained Path Monte Carlo
(CPMC) method in search for a possible superconducting ground state. The CPMC
is a ground state method which is free of the exponential scaling of computing
time with system size. We calculated the binding energy of a pair of holes for
systems up to unit cells. We also studied the pairing correlation
functions versus distance for both the d-wave and extended s-wave channels in
systems up to . We found that holes bind for a wide range of
parameters and that the binding increased as the system size is increased.
However, the pairing correlation functions decay quickly with distance.
For the extended s channel, we found that as the Coulomb interaction on
the Cu sites is increased, the long-range part of the correlation functions is
suppressed and fluctuates around zero. For the channel, we
found that the correlations decay rapidly with distance towards a small
positive value. However, this value becomes smaller as the interaction or
the system size is increased.Comment: 21 pages, 13 Postscript figures, Submitted to Phys. Rev.
From Tetraquark to Hexaquark: A Systematic Study of Heavy Exotics in the Large Limit
A systematic study of multiquark exotics with one or heavy quarks in
the large limit is presented. By binding a chiral soliton to a heavy
meson, either a normal -quark baryon or an exotic -quark baryon
is obtained. By replacing the heavy quark with heavy antiquarks, exotic
-quark and -quark mesons are obtained. When , they are
just the normal triquark baryon , the exotic pentaquark baryon , tetraquark di-meson and the hexaquark
di-baryon respectively. Their
stabilities and decays are also discussed. In particular, it is shown that the
``heavy to heavy'' semileptonic decays are described by the Isgur--Wise form
factors of the normal baryons.Comment: 14 pages in REVTeX, no Figure
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