8,582 research outputs found
Recent progress in the development of a solar neutron tracking device (SONTRAC)
We report the results of recent calibration data analysis of a prototype scintillating fiber tracking detector system designed to perform imaging, spectroscopy and particle identification on 20 to 250 MeV neutrons and protons. We present the neutron imaging concept and briefly review the detection principle and the prototype description. The prototype detector system records ionization track data on an event-by-event basis allowing event selection criteria to be used in the off-line analysis. Images of acrylic phantoms from the analysis of recent proton beam calibrations are presented as demonstrations of the particle identification, imaging and energy measurement capabilities. The measured position resolution is \u3c 500 micrometers . The measured energy resolution is 14.2 percent at 35 MeV. The detection techniques employed can be applied to measurements in a variety of disciplines including solar and atmospheric physics, radiation therapy and nuclear materials monitoring. These applications are discussed briefly as are alternative detector configurations and future development plans
Spatial Interference: From Coherent To Incoherent
It is well known that direct observation of interference and diffraction
pattern in the intensity distribution requires a spatially coherent source.
Optical waves emitted from portions beyond the coherence area possess
statistically independent phases, and will degrade the interference pattern. In
this paper we show an optical interference experiment, which seems contrary to
our common knowledge, that the formation of the interference pattern is related
to a spatially incoherent light source. Our experimental scheme is very similar
to Gabor's original proposal of holography[1], just with an incoherent source
replacing the coherent one. In the statistical ensemble of the incoherent
source, each sample field produces a sample interference pattern between object
wave and reference wave. These patterns completely differ from each other due
to the fluctuation of the source field distribution. Surprisingly, the sum of a
great number of sample patterns exhibits explicitly an interference pattern,
which contains all the information of the object and is equivalent to a
hologram in the coherent light case. In this sense our approach would be
valuable in holography and other interference techniques for the case where
coherent source is unavailable, such as x-ray and electron sources.Comment: 8 pages, 5 figure
Detection of a methanol megamaser in a major-merger galaxy
We have detected emission from both the 4_{-1}-3_{0} E (36.2~GHz) class I and
7_{-2}-8_{-1} E (37.7~GHz) class II methanol transitions towards the centre of
the closest ultra-luminous infrared galaxy Arp 220. The emission in both the
methanol transitions show narrow spectral features and have luminosities
approximately 8 orders of magnitude stronger than that observed from typical
class I methanol masers observed in Galactic star formation regions. The
emission is also orders of magnitude stronger than the expected intensity of
thermal emission from these transitions and based on these findings we suggest
that the emission from the two transitions are masers. These observations
provides the first detection of a methanol megamaser in the 36.2 and 37.7 GHz
transitions and represents only the second detection of a methanol megamaser,
following the recent report of an 84 GHz methanol megamaser in NGC1068. We find
the methanol megamasers are significantly offset from the nuclear region and
arise towards regions where there is Ha emission, suggesting that it is
associated with starburst activity. The high degree of correlation between the
spatial distribution of the 36.2 GHz methanol and X-ray plume emission suggests
that the production of strong extragalactic class I methanol masers is related
to galactic outflow driven shocks and perhaps cosmic rays. In contrast to OH
and H2O megamasers which originate close to the nucleus, methanol megamasers
provide a new probe of feedback (e.g. outflows) processes on larger-scales and
of star formation beyond the circumnuclear starburst regions of active
galaxies.Comment: Accepted for publication in ApJ
A scintillating plastic fiber tracking detector for neutron and proton imaging and spectroscopy
We report the results of recent calibration data analysis of a prototype scintillating fiber tracking detector system designed to perform imaging, spectroscopy and particle identification on 20 to 250 MeV neutrons and protons. We present the neutron imaging concept and briefly review the detection principle and the prototype description. The prototype detector system records ionization track data on an event-by-event basis allowing event selection criteria to be used in the off-line analysis. Images of acrylic phantoms from the analysis of recent proton beam calibrations (14 to 65 MeV range) are presented as demonstrations of the particle identification, imaging and energy measurement capabilities. The measured position resolution is c 500 pm. The measured energy resolution (AE/E, FWHM) is 14.2% at 35 MeV. An effective technique for track identification and data compression is presented. The detection techniques employed can be applied to measurements in a variety of disciplines including solar and atmospheric physics, radiation therapy and nuclear materials monitoring. These applications are discussed briefly as are alternative detector configurations and future development plans
Recovery of peripheral refractive errors and ocular shape in rhesus monkeys (Macaca mulatta) with experimentally induced myopia
AbstractThis study aimed to investigate the changes in ocular shape and relative peripheral refraction during the recovery from myopia produced by form deprivation (FD) and hyperopic defocus. FD was imposed in six monkeys by securing a diffuser lens over one eye; hyperopic defocus was produced in another six monkeys by fitting one eye with −3D spectacle. When unrestricted vision was re-established, the treated eyes recovered from the vision-induced central and peripheral refractive errors. The recovery of peripheral refractive errors was associated with corresponding changes in the shape of the posterior globe. The results suggest that vision can actively regulate ocular shape and the development of central and peripheral refractions in infant primates
Zero permeability and zero permittivity band gaps in 1D metamaterial photonic crystals
We consider layered heterostructures combining ordinary positive index
materials and dispersive metamaterials. We show that these structures can
exhibit a new type of photonic gap around frequencies where either the magnetic
permeability \mu or the electric permittivity \epsilon of the metamaterial is
zero. Although the interface of a semi-infinite medium with zero refractive
index (a condition attained either when \mu= 0 or when \epsilon= 0) is known to
give full reflectivity for all incident polarizations, here we show that a gap
corresponding to \mu = 0 occurs only for TE polarized waves, whereas a gap
corresponding to \epsilon = 0 occurs only for TM polarized waves. These band
gaps are scale-length invariant and very robust against disorder, although they
may disappear for the particular case of propagation along the stratification
direction.Comment: 7 pages, 5 figure
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Revealing nascent proteomics in signaling pathways and cell differentiation.
Regulation of gene expression at the level of protein synthesis is a crucial element in driving how the genetic landscape is expressed. However, we are still limited in technologies that can quantitatively capture the immediate proteomic changes that allow cells to respond to specific stimuli. Here, we present a method to capture and identify nascent proteomes in situ across different cell types without disturbing normal growth conditions, using O-propargyl-puromycin (OPP). Cell-permeable OPP rapidly labels nascent elongating polypeptides, which are subsequently conjugated to biotin-azide, using click chemistry, and captured with streptavidin beads, followed by digestion and analysis, using liquid chromatography-tandem mass spectrometry. Our technique of OPP-mediated identification (OPP-ID) allows detection of widespread proteomic changes within a short 2-hour pulse of OPP. We illustrate our technique by recapitulating alterations of proteomic networks induced by a potent mammalian target of rapamycin inhibitor, MLN128. In addition, by employing OPP-ID, we identify more than 2,100 proteins and uncover distinct protein networks underlying early erythroid progenitor and differentiation states not amenable to alternative approaches such as amino acid analog labeling. We present OPP-ID as a method to quantitatively identify nascent proteomes across an array of biological contexts while preserving the subtleties directing signaling in the native cellular environment
Higgs algebraic symmetry of screened system in a spherical geometry
The orbits and the dynamical symmetries for the screened Coulomb potentials
and isotropic harmonic oscillators have been studied by Wu and Zeng [Z. B. Wu
and J. Y. Zeng, Phys. Rev. A 62,032509 (2000)]. We find the similar properties
in the responding systems in a spherical space, whose dynamical symmetries are
described by Higgs Algebra. There exists a conserved aphelion and perihelion
vector, which, together with angular momentum, constitute the generators of the
geometrical symmetry group at the aphelia and perihelia points .Comment: 8 pages, 1 fi
The complete mitochondrial genome of the lowland paca (Cuniculus paca) and its phylogenetic relationship with other New World hystricognath rodents
The lowland paca (Cuniculus paca) is a nocturnal, widespread, and solitary large-sized rodent in the family Cuniculidae, and one of the most frequently hunted mammals in the Neotropical forests of Latin America. We assembled the first complete mitochondrial genome of lowland paca using three closely related hystricognath species as reference sequences. The mitochondrial genome is 16,770 basepairs (bp) in length, with similar characteristics of vertebrate mitochondrial genomes. We performed phylogenetic analyses using 26 mitochondrial genome of hystricognath species based on thirteen protein-coding genes. The result confirms the taxonomical placement among the New World hystricognath rodents with high support. The placement is consistent with previous phylogenetic studies based on individual mitochondrial and nuclear genes. The current study improves the phylogenic resolution of hystricognath rodents
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