78,731 research outputs found
Efficacy of laser preionization with a semiconductor source and propene addition
It is established that propene is an effective additive instabilising uv preionised CO2 TEA laser discharges: its effect being particularly pronounced with semiconductor-edge preionised lasers where the preionisation levels are shown to be low
Continuation of development of nitrides for space nuclear reactors
Alloy nitrides (U,Zr), (U,Ce), and (U,Y) were prepared and exposed to vacuum at temperatures to 1700 C (1973 K) and compared with pure UN. Weight loss data and physical observations showed that the alloy samples were more stable than UN. In weight loss, (U,Zr)N was 3 times as stable as UN at 1600 C (1873 K) for 100 hr at 0.000002 torr (0.000266n/sq.m.)
Quantum signatures of breather-breather interactions
The spectrum of the Quantum Discrete Nonlinear Schr\"odinger equation on a
periodic 1D lattice shows some interesting detailed band structure which may be
interpreted as the quantum signature of a two-breather interaction in the
classical case. We show that this fine structure can be interpreted using
degenerate perturbation theory.Comment: 4 pages, 4 fig
Scale-Free topologies and Activatory-Inhibitory interactions
A simple model of activatory-inhibitory interactions controlling the activity
of agents (substrates) through a "saturated response" dynamical rule in a
scale-free network is thoroughly studied. After discussing the most remarkable
dynamical features of the model, namely fragmentation and multistability, we
present a characterization of the temporal (periodic and chaotic) fluctuations
of the quasi-stasis asymptotic states of network activity. The double (both
structural and dynamical) source of entangled complexity of the system temporal
fluctuations, as an important partial aspect of the Correlation
Structure-Function problem, is further discussed to the light of the numerical
results, with a view on potential applications of these general results.Comment: Revtex style, 12 pages and 12 figures. Enlarged manuscript with major
revision and new results incorporated. To appear in Chaos (2006
Pneumococcal conjugate vaccine given shortly after birth stimulates effective antibody concentrations and primes immunological memory for sustained infant protection.
BACKGROUND: In developing countries, newborn immunization with pneumococcal conjugate vaccines (PCVs) could protect young infants who are at high risk of invasive pneumococcal disease (IPD) but might lead to immune tolerance. METHODS: In a randomized trial, young infants received 7-valent PCV at 6, 10, and 14 weeks (Expanded Programme on Immunization [EPI] group) or 0, 10, and 14 weeks (newborn group). Safety was monitored actively at 2-7 days and then passively. Serum samples obtained at birth and 6, 10, 14, 18, 36, and 37 weeks were assayed by enzyme-linked immunosorbent assay for anticapsular immunoglobulin G concentration and avidity. Infants were boosted with either 7-valent PCV or one-fifth dose of pneumococcal polysaccharide vaccine at 36 weeks. Nasopharyngeal swab samples were obtained at 18 and 36 weeks. RESULTS: Three-hundred neonates and young infants were enrolled. Newborn vaccination was well tolerated. Adverse events occurred equally in each group; none was related to immunization. One infant, immunized at birth, died of unrelated neonatal sepsis. At 18 weeks, protective concentrations (≥0.35 μg/mL) were achieved against each serotype by ≥87% of infants with no significant differences between groups. Geometric mean concentrations were higher in the EPI group for serotypes 4, 9V, 18C, and 19F at 18 weeks and for serotype 4 at 36 weeks. Avidity was greater in the newborn group for serotypes 4, 6B, and 19F at 18 weeks and for serotype 19F at 36 weeks. Booster responses and vaccine-type/nonvaccine-type carriage prevalence did not differ between groups. CONCLUSIONS: PCV was safe, immunogenic, and primed for memory when given at birth. There was no evidence of immune tolerance. Vaccination beginning at birth offers an alternative to control IPD in vulnerable young infants
Localizing coalescing massive black hole binaries with gravitational waves
Massive black hole binary coalescences are prime targets for space-based
gravitational wave (GW) observatories such as {\it LISA}. GW measurements can
localize the position of a coalescing binary on the sky to an ellipse with a
major axis of a few tens of arcminutes to a few degrees, depending on source
redshift, and a minor axis which is times smaller. Neglecting weak
gravitational lensing, the GWs would also determine the source's luminosity
distance to better than percent accuracy for close sources, degrading to
several percent for more distant sources. Weak lensing cannot, in fact, be
neglected and is expected to limit the accuracy with which distances can be
fixed to errors no less than a few percent. Assuming a well-measured cosmology,
the source's redshift could be inferred with similar accuracy. GWs alone can
thus pinpoint a binary to a three-dimensional ``pixel'' which can help guide
searches for the hosts of these events. We examine the time evolution of this
pixel, studying it at merger and at several intervals before merger. One day
before merger, the major axis of the error ellipse is typically larger than its
final value by a factor of . The minor axis is larger by a factor
of , and, neglecting lensing, the error in the luminosity distance is
larger by a factor of . This large change over a short period of
time is due to spin-induced precession, which is strongest in the final days
before merger. The evolution is slower as we go back further in time. For , we find that GWs will localize a coalescing binary to within $\sim 10\
\mathrm{deg}^2$ as early as a month prior to merger and determine distance (and
hence redshift) to several percent.Comment: 30 pages, 10 figures, 5 tables. Version published in Ap
Searches for Long-lived Particles at the Tevatron Collider
Several searches for long-lived particles have been performed using data from
p-pbar collisions from Run II at the Tevatron. In most cases, new analysis
techniques have been developed to carry out each search and/or estimate the
backgrounds. These searches expand the discovery potential of the CDF and D0
experiments to new physics that may have been missed by traditional search
techniques. This review discusses searches for (1) neutral, long-lived
particles decaying to muons, (2) massive, neutral, long-lived particles
decaying to a photon and missing energy, (3) stopped gluinos, and (4) charged
massive stable particles. It summarizes some of the theoretical and
experimental motivations for such searches.Comment: submitted to Mod. Phys. Lett.
Correlated radial velocity and X-ray variations in HD 154791/4U 1700+24
We present evidence for approximately 400-d variations in the radial velocity
of HD 154791 (V934 Her), the suggested optical counterpart of 4U 1700+24. The
variations are correlated with the previously reported approximately 400 d
variations in the X-ray flux of 4U 1700+24, which supports the association of
these two objects, as well as the identification of this system as the second
known X-ray binary in which a neutron star accretes from the wind of a red
giant. The HD 154791 radial velocity variations can be fit with an eccentric
orbit with period 404 +/- 3 d, amplitude K=0.75 +/- 0.12 km/s and eccentricity
e=0.26 +/- 0.15. There are also indications of variations on longer time scales
>~ 2000 d. We have re-examined all available ASM data following an unusually
large X-ray outburst in 1997-98, and confirm that the 1-d averaged 2-10 keV
X-ray flux from 4U 1700+24 is modulated with a period of 400 +/- 20 d. The mean
profile of the persistent X-ray variations was approximately sinusoidal, with
an amplitude of 0.108 +/- 0.012 ASM count/s (corresponding to 31% rms). The
epoch of X-ray maximum was approximately 40 d after the time of periastron
according to the eccentric orbital fit. If the 400 d oscillations from HD
154791/4U 1700+24 are due to orbital motion, then the system parameters are
probably close to those of the only other neutron-star symbiotic-like binary,
GX 1+4. We discuss the similarities and differences between these two systems.Comment: 6 pages, 2 figures; accepted by Ap
LISA Science Results in the Presence of Data Disturbances
Each spacecraft in the Laser Interferometer Space Antenna houses a proof mass
which follows a geodesic through spacetime. Disturbances which change the proof
mass position, momentum, and/or acceleration will appear in the LISA data
stream as additive quadratic functions. These data disturbances inhibit signal
extraction and must be removed. In this paper we discuss the identification and
fitting of monochromatic signals in the data set in the presence of data
disturbances. We also present a preliminary analysis of the extent of science
result limitations with respect to the frequency of data disturbances
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