2,654 research outputs found
The fear of bad smell: Health risk awareness related to using waste in agricultural production in Vietnam
Waste watersWater reuseAgricultural productionFish farmingIrrigation waterPublic healthRisksSkin diseasesOrganic fertilizersWomen
Experimental investigation of the Landau-Pomeranchuk-Migdal effect in low-Z targets
In the CERN NA63 collaboration we have addressed the question of the
potential inadequacy of the commonly used Migdal formulation of the
Landau-Pomeranchuk-Migdal (LPM) effect by measuring the photon emission by 20
and 178 GeV electrons in the range 100 MeV - 4 GeV, in targets of
LowDensityPolyEthylene (LDPE), C, Al, Ti, Fe, Cu, Mo and, as a reference
target, Ta. For each target and energy, a comparison between simulated values
based on the LPM suppression of incoherent bremsstrahlung is shown, taking
multi-photon effects into account. For these targets and energies, we find that
Migdal's theoretical formulation is adequate to a precision of better than
about 5%, irrespective of the target substance.Comment: 8 pages, 13 figure
Experimental investigations of synchrotron radiation at the onset of the quantum regime
The classical description of synchrotron radiation fails at large Lorentz
factors, , for relativistic electrons crossing strong transverse
magnetic fields . In the rest frame of the electron this field is comparable
to the so-called critical field T. For quantum corrections are essential for the description of
synchrotron radiation to conserve energy. With electrons of energies 10-150 GeV
penetrating a germanium single crystal along the axis, we have
experimentally investigated the transition from the regime where classical
synchrotron radiation is an adequate description, to the regime where the
emission drastically changes character; not only in magnitude, but also in
spectral shape. The spectrum can only be described by quantum synchrotron
radiation formulas. Apart from being a test of strong-field quantum
electrodynamics, the experimental results are also relevant for the design of
future linear colliders where beamstrahlung - a closely related process - may
limit the achievable luminosity.Comment: 11 pages, 18 figures, submitted to PR
Parity Violation in Neutron Resonances in 107,109Ag
Parity nonconservation (PNC) was studied in p-wave resonances in Ag by measuring the helicity dependence of the neutron total cross section. Transmission measurements on natural Ag were performed in the energy range 32 to 422 eV with the time-of-flight method at the Manuel Lujan Neutron Scattering Center at Los Alamos National Laboratory. A total of 15 p-wave neutron resonances were studied in 107Ag and ninep-wave resonances in 109Ag. Statistically significant asymmetries were observed for eight resonances in 107Ag and for four resonances in109Ag. An analysis treating the PNC matrix elements as random variables yields a weak spreading width of Îw=(2.67-1.21+2.65)Ă10-7âeV for107Ag and Îw=(1.30-0.74+2.49)Ă10-7âeV for 109Ag
Ionization of hydrogen and hydrogenic ions by antiprotons
Presented here is a description of the ionization of hydrogen and hydrogenic
ions by antiproton-impact, based on very large scale numerical solutions of the
time-dependent Schr\"odinger equation in three spatial dimensions and on
analysis of the topology of the electronic eigenenergy surfaces in the plane of
complex internuclear distance. Comparison is made with other theories and very
recent measurements.Comment: RevTex document, 11 pages, 4 Postscript figures are available from
the authors, in press Phys. Rev. Let
Neutron Resonance Spectroscopy of 106Pd, and 108Pd from 20â2000 eV
Parity nonconserving asymmetries have been measured in p-wave resonances of 106Pd and 108Pd. The data analysis requires knowledge of the neutron resonance parameters. Transmission and capture Îł-ray yields were measured for En=20â2000 eV with the time-of-flight method at the Los Alamos Neutron Science Center (LANSCE). A total of 28 resonances in 106Pd and 32 resonances in 108Pd were studied. The resonance parameters for 106Pd are new for all except one resonance. In 108Pd six new resonances were observed and the precision improved for many of the resonance parameters. A Bayesian analysis was used to assign orbital angular momentum for the resonances studied
Parity Nonconservation in 106Pd and 108Pd Neutron Resonances
Parity nonconservation (PNC) has been studied in the neutron p-wave resonances of 106Pd and 108Pd in the energy range of 20 to 2000 eV. Longitudinal asymmetries in p-wave capture cross sections are measured using longitudinally polarized neutrons incident on âŒ20-g metal-powder targets at LANSCE. A CsI Îł-ray detector array measures capture cross section asymmetries as a function of neutron energy which is determined by the neutron time-of-flight method. A total of 21 p-wave resonances in 106Pd and 21 p-wave resonances in 108Pd were studied. One statistically significant PNC effect was observed in106Pd, and no effects were observed in 108Pd. For 106Pd a weak spreading width of Îw=34-28+47Ă10-7âeV was obtained. For 108Pd an upper limit on the weak spreading width of Îw\u3c12Ă10-7âeV was determined at the 68% confidence level
Mid-Infrared Spectroscopy of Lensed Galaxies at 1<z<3: The Nature of Sources Near the MIPS Confusion Limit
We present Spitzer/IRS mid-infrared spectra for 15 gravitationally lensed, 24
micron--selected galaxies, and combine the results with 4 additional very faint
galaxies with IRS spectra in the literature. The median intrinsic 24 micron
flux density of the sample is 130 microJy, enabling a systematic survey of the
spectral properties of the very faint 24 micron sources that dominate the
number counts of Spitzer cosmological surveys. Six of the 19 galaxy spectra
(32%) show the strong mid-IR continuua expected of AGN; X-ray detections
confirm the presence of AGN in three of these cases, and reveal AGNs in two
other galaxies. These results suggest that nuclear accretion may contribute
more flux to faint 24 micron--selected samples than previously assumed. Almost
all the spectra show some aromatic (PAH) emission features; the measured
aromatic flux ratios do not show evolution from z=0. In particular, the high
S/N mid-IR spectrum of SMM J163554.2+661225 agrees remarkably well with
low--redshift, lower--luminosity templates. We compare the rest-frame 8 micron
and total infrared luminosities of star--forming galaxies, and find that the
behavior of this ratio with total IR luminosity has evolved modestly from z=2
to z=0. Since the high aromatic--to--continuum flux ratios in these galaxies
rule out a dominant contribution by AGN, this finding implies systematic
evolution in the structure and/or metallicity of infrared sources with
redshift. It also has implications for the estimates of star forming rates
inferred from 24 micron measurements, in the sense that at z ~2, a given
observed frame 24 micron luminosity corresponds to a lower bolometric
luminosity than would be inferred from low-redshift templates of similar
luminosity at the corresponding rest wavelength.Comment: Accepted to the Astrophysical Journal. Full-res version at
ftp://ftp.ociw.edu/pub/jrigby/jrigby-irs.pd
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