10,974 research outputs found
Observation of Muon Neutrino Disappearance with the MINOS Detectors in the NuMI Neutrino Beam
This Letter reports results from the MINOS experiment based on its initial exposure to neutrinos from the Fermilab NuMI beam. The rates and energy spectra of charged current ν_μ interactions are compared in two detectors located along the beam axis at distances of 1 and 735 km. With 1.27×10^(20) 120 GeV protons incident on the NuMI target, 215 events with energies below 30 GeV are observed at the Far Detector, compared to an expectation of 336±14 events. The data are consistent with ν_μ disappearance via oscillations with Δm_(32)^2|=2.74_(-0.26)^(+0.44)×10^(-3)  eV^2 and sin^2(2θ_(23))>0.87 (68% C.L.)
First observations of separated atmospheric ν_μ and ν̅ _μ events in the MINOS detector
The complete 5.4 kton MINOS far detector has been taking data since the beginning of August 2003 at a
depth of 2070 meters water-equivalent in the Soudan mine, Minnesota. This paper presents the first
MINOS observations of ν_μ and ν̅ _μ charged-current atmospheric neutrino interactions based on an
exposure of 418 days. The ratio of upward- to downward-going events in the data is compared to the
Monte Carlo expectation in the absence of neutrino oscillations, giving R^(data)_(up/down/R^(MC)_(up/down) =
0:62^(+0.19)_(0:14)(stat.) ± 0.02(sys.). An extended maximum likelihood analysis of the observed L/E distributions
excludes the null hypothesis of no neutrino oscillations at the 98% confidence level. Using the curvature of
the observed muons in the 1.3 T MINOS magnetic field ν_μ and ν̅ _μ interactions are separated. The ratio of
ν̅ _μ to ν_μ events in the data is compared to the Monte Carlo expectation assuming neutrinos and
antineutrinos oscillate in the same manner, giving R^(data)_(ν_μ/ν̅ _μ) / R^(MC)_(ν_μ/ν̅ _μ) = 0.96^(+0:38)_(0.27)(stat.) ± 0.15(sys.), where
the errors are the statistical and systematic uncertainties. Although the statistics are limited, this is the first
direct observation of atmospheric neutrino interactions separately for ν_μ and ν̅ _μ
The spatial distribution of O-B5 stars in the solar neighborhood as measured by Hipparcos
We have developed a method to calculate the fundamental parameters of the
vertical structure of the Galaxy in the solar neighborhood from trigonometric
parallaxes alone. The method takes into account Lutz-Kelker-type biases in a
self-consistent way and has been applied to a sample of O-B5 stars obtained
from the Hipparcos catalog. We find that the Sun is located 24.2 +/- 1.7
(random) +/- 0.4 (systematic) pc above the galactic plane and that the disk
O-B5 stellar population is distributed with a scale height of 34.2 +/- 0.8
(random) +/- 2.5 (systematic) pc and an integrated surface density of (1.62 +/-
0.04 (random) +/- 0.14 (systematic)) 10^{-3} stars pc^{-2}. A halo component is
also detected in the distribution and constitutes at least ~5% of the total
O-B5 population. The O-B5 stellar population within ~100 pc of the Sun has an
anomalous spatial distribution, with a less-than-average number density. This
local disturbance is probably associated with the expansion of Gould's belt.Comment: 14 pages, 3 figures, to appear in the May 2001 issue of the
Astronomical Journa
Controlling the quantum dynamics of a mesoscopic spin bath in diamond
Understanding and mitigating decoherence is a key challenge for quantum
science and technology. The main source of decoherence for solid-state spin
systems is the uncontrolled spin bath environment. Here, we demonstrate quantum
control of a mesoscopic spin bath in diamond at room temperature that is
composed of electron spins of substitutional nitrogen impurities. The resulting
spin bath dynamics are probed using a single nitrogen-vacancy (NV) centre
electron spin as a magnetic field sensor. We exploit the spin bath control to
dynamically suppress dephasing of the NV spin by the spin bath. Furthermore, by
combining spin bath control with dynamical decoupling, we directly measure the
coherence and temporal correlations of different groups of bath spins. These
results uncover a new arena for fundamental studies on decoherence and enable
novel avenues for spin-based magnetometry and quantum information processing
A Hidden Population of Massive Stars with Circumstellar Shells Discovered with the Spitzer Space Telescope
We have discovered a large number of circular and elliptical shells at 24
microns around luminous central sources with the MIPS instrument on-board the
Spitzer Space Telescope. Our archival follow-up effort has revealed 90% of
these circumstellar shells to be previously unknown. The majority of the shells
is only visible at 24 microns, but many of the central stars are detected at
multiple wavelengths from the mid- to the near-IR regime. The general lack of
optical counterparts, however, indicates that these sources represent a
population of highly obscured objects. We obtained optical and near-IR
spectroscopic observations of the central stars and find most of these objects
to be massive stars. In particular, we identify a large population of sources
that we argue represents a narrow evolutionary phase, closely related or
identical to the LBV stage of massive stellar evolution.Comment: 23 pages, 9 figures, accepted for publication in A
The shape of the CMB lensing bispectrum
Lensing of the CMB generates a significant bispectrum, which should be
detected by the Planck satellite at the 5-sigma level and is potentially a
non-negligible source of bias for f_NL estimators of local non-Gaussianity. We
extend current understanding of the lensing bispectrum in several directions:
(1) we perform a non-perturbative calculation of the lensing bispectrum which
is ~10% more accurate than previous, first-order calculations; (2) we
demonstrate how to incorporate the signal variance of the lensing bispectrum
into estimates of its amplitude, providing a good analytical explanation for
previous Monte-Carlo results; and (3) we discover the existence of a
significant lensing bispectrum in polarization, due to a previously-unnoticed
correlation between the lensing potential and E-polarization as large as 30% at
low multipoles. We use this improved understanding of the lensing bispectra to
re-evaluate Fisher-matrix predictions, both for Planck and cosmic variance
limited data. We confirm that the non-negligible lensing-induced bias for
estimation of local non-Gaussianity should be robustly treatable, and will only
inflate f_NL error bars by a few percent over predictions where lensing effects
are completely ignored (but note that lensing must still be accounted for to
obtain unbiased constraints). We also show that the detection significance for
the lensing bispectrum itself is ultimately limited to 9 sigma by cosmic
variance. The tools that we develop for non-perturbative calculation of the
lensing bispectrum are directly relevant to other calculations, and we give an
explicit construction of a simple non-perturbative quadratic estimator for the
lensing potential and relate its cross-correlation power spectrum to the
bispectrum. Our numerical codes are publicly available as part of CAMB and
LensPix.Comment: 32 pages, 10 figures; minor changes to match JCAP-accepted version.
CMB lensing and primordial local bispectrum codes available as part of CAMB
(http://camb.info/
Light nuclei in galactic globular clusters : constraints on the self-enrichment scenario from nucleosynthesis
Hydrogen-burning is the root cause of the star-to-star abundance variations
of light nuclei in Galactic globular clusters (GC). In the present work we
constrain the physical conditions that gave rise to the observed abundance
patterns of Li, C, N, O, Na, Mg, Al, as well as Mg isotopes in the typical case
of NGC6752. We perform nucleosynthesis calculations at constant temperature,
adopting realistic initial abundances for the proto-cluster gas. We use a
detailed nuclear reaction network and state-of-the-art nuclear reaction rates.
Although simplistic, our analysis provides original results and new constraints
on the self-enrichment scenario for GCs. Our parametrized calculations allow us
to determine a narrow range of temperature where the observed extreme
abundances of all light elements and isotopes in NGC6752 are nicely reproduced
simultaneously. This agreement is obtained after mixing of the H-processed
material with 30 % of unprocessed gas. The observed C-N, O-Na, Mg-Al, Li-Na and
F-Na anticorrelations, as well as the behaviour of the Mg isotopes can be
recovered by assuming mixing with even larger dilution factors. Li production
by the stars that build up the other abundance anomalies is not mandatory in
the case of NGC 6752. Observations of O, Na, Mg and Al constrain the
temperature range for H-burning; such temperatures are encountered in the two
main candidate ``polluters'' proposed for GCs, namely massive AGBs and the most
massive main-sequence stars. (Abridged).Comment: 15 pages, 8 figures, accepted in Astronomy and Astrophysic
Ehrlichia chaffeensis Co-Opts Phagocytic Hemocytes for Systemic Dissemination in the Lone Star Tick, Amblyomma americanum
Introduction: Hematophagous arthropods can acquire and transmit several pathogens of medical importance. In ticks, the innate immune system is crucial in the outcome between vector-pathogen interaction and overall vector competence. However, the specific immune response(s) elicited by the immune cells known as hemocytes remains largely undefined in Ehrlichia chaffeensis and its competent tick vector, Amblyomma americanum. Methods: We utilized injection of clodronate liposome to deplete tick granulocytes combined with infection with E. chaffeensis to demonstrate their essential role in microbial infection. Results: Here, we show that granulocytes, professional phagocytic cells, are integral in eliciting immune responses against commensal and pathogen infection. The chemical depletion of granulocytes led to decreased phagocytic efficiency of tissue-associated hemocytes. We demonstrate that E. chaffeensis can infect circulating hemocytes, and both cell-free plasma and hemocytes from E. chaffeensis-infected ticks can establish Ehrlichia infection in recipient ticks. Lastly, we provide evidence to show that granulocytes play a dual role in E. chaffeensis infection. Depleting granulocytic hemocytes increased Ehrlichia load in the salivary gland and midgut tissues. In contrast, granulocyte depletion led to a reduced systemic load of Ehrlichia. Conclusion: This study has identified multiple roles for granulocytic hemocytes in the control and systemic dissemination of E. chaffeensis infection
Assessing the value of BMI and aerobic capacity as surrogate markers for the severity of left ventricular diastolic dysfunction in patients with type 2 diabetes who are obese
Left ventricular diastolic dysfunction (LVDD) is one of the earliest signs for abnormal cardiac function in patients with type 2 diabetes (T2DM). It is important to explore the risk factors that will assist in identifying the severity of the LVDD in this population. We examined the influences of fitness and fatness on the level of left ventricular (LV) impairment in patients with T2DM. Twenty-five patients (age: 64.0 ± 2.5 years, body mass index [BMI] = 36.0 ± 1.5 kg/m2, mean ± standard error of measurement) with T2DM and preserved systolic function, but impaired diastolic function, mitral valve (MV) E/e\u27, participated in the study. LV function was assessed using a stress echocardiograph, aerobic power was assessed with a sign- and symptom-limited graded exercise test, and the fatness level was assessed using Dual-energy X-ray absorptiometry and BMI. Patients in the higher 50% of BMI had higher lateral and septal MV E/e\u27 (∼34% and ∼25%, respectively, both P < 0.001), compared to those in the lower 50% of BMI, with no difference in LV ejection fraction (LVEF) (P > 0.05). In addition, a higher BMI correlated with a higher lateral (r = 0.62, P < 0.001) and septal (r = 0.56, P < 0.01) E/e\u27. There was no such relationship for VO2peak. BMI and VO2peak were not correlated with LV systolic function (ejection fraction). In individuals with T2DM and diastolic dysfunction, a higher BMI was associated with worsening diastolic function independent of their aerobic capacity. The data provide a simple and practical approach for clinicians to assist in the early identification and diagnostics of functional changes in the heart diastolic function in this population
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