592 research outputs found
Composite particles with minimum uncertainty in spacetime
Composite particles---atoms, molecules, or microspheres---are unique tools
for testing joint quantum and general relativistic effects, macroscopic limits
of quantum mechanics, and searching for new physics. However, all studies of
the free propagation of these particles find that they delocalise into separate
internal energy components, destroying their spatial coherence. This renders
them unsuitable for experimental applications, as well as theoretical studies
where they are used as idealised test masses or clocks. Here we solve this
problem by introducing a new class of states with minimal uncertainty in
space-time that fully overcome the delocalisation. The relevant physics comes
from minimising the uncertainty between position and velocity, rather than
position and momentum, while directly accounting for mass as an operator. Our
results clarify the nature of composite particles, providing a currently
missing theoretical tool with direct relevance for studies of joint foundations
of quantum and relativistic phenomena, which removes a roadblock that could
limit near-future quantum tests using composite particles.Comment: 5 figures, version 4 updated text, reordering of sections, new
appendix on contractive state
Neutron-induced 2.2 MeV background in gamma ray telescopes
Neutron-induced gamma ray production is an important source of background in Compton scatter gamma ray telescopes where organic scintillator material is used. Most important is deuteron formation when atmospheric albedo and locally produced neutrons are thermalized and subsequently absorbed in the hydrogenous material. The resulting 2.2 MeV gamma ray line radiation essentially represents a continuous isotropic source within the scintillator itself. Interestingly, using a scintillator material with a high hydrogen-to-carbon ratio to minimize the scintillator material with a high hydrogen-to-carbon ratio to minimize the neutron-induced 4.4 MeV carbon line favors the np reaction. The full problem of neutron-induced background in Compton scatter telescopes has been previously discussed. Results are presented of observations with the University of California balloon-borne Compton scatter telescope where the 2.2 MeV induced line emission is prominently seen
The late Roman harbor temple of Berenike. Results of the 2010 season of excavations
Excavations in 2010 in the southwestern harbor at Berenike documented two distinct
structures. One built of white gypsum/anhydrite ashlars was the earlier of the two. The later one,
with walls composed mainly of extinct coral heads, but incorporating portions of the earlier ashlar
structure, lay immediately southeast of the former. The later edifice, and the focus of this article,
dated to the 4th and 5th centuries AD and clearly had a religious function. Excavations documented
two major phases of this shrine and suggested that multiple creeds were venerated here, including
one perhaps of South Arabian origin. Along with numerous cult objects made of metal, stone,
terracotta, ostrich eggs and cowry shells there was ample floral and faunal evidence for offerings made or consumed by devotees.Iwona Zyc
Respuesta ecofisiológica de poblaciones de <i>Sorghum halepense</i> ante dosis reducidas de nicosulfurón
Las malezas constituyen una de las principales limitaciones en los sistemas de producción a escala mundial. Prueba de ello es la gran cantidad de herbicidas utilizados actualmente para mantener a las malezas en niveles que permitan la productividad de los cultivos. Los esfuerzos en reducir el uso de herbicidas, tanto por razones económicas como ambientales (Buhler, 1999), han introducido a la práctica el manejo integrado de malezas, como es el uso de dosis reducidas de herbicidas (Buhler et al., 1993; Prostko y Meade, 1993). Además las malezas presentan la capacidad de adaptarse rápidamente a los cambios ambientales y producir diferentes fenotipos. Dicha capacidad se denomina plasticidad fenotípica (Schmalhausen, 1949). Entre las malezas consideradas más perjudiciales del mundo para la agricultura se encuentra Sorghum halepense (sorgo de Alepo) (Holm et al., 1977 McWhorter, 1989), tiene importancia en 30 cultivos diferentes y en 53 países (Holm et al., 1977). La interferencia de Sorghum halepense con los cultivos se presenta tanto por la competencia por recursos limitantes (agua, luz y nutrientes), como por la incidencia alelopática hacia los cultivos. Son pocas las investigaciones realizadas sobre el uso de dosis reducidas de herbicidas para el control de Sorghum halepense, además, pocos trabajos han puesto su interés sobre la respuesta ecofisiológica (tasa fotosintética, conductancia estomática al vapor de agua, tasa transpiratoria y biomasa total) y el comportamiento del rebrote (biomasa aérea) de poblaciones de Sorghum halepense, cuando son tratadas con dosis reducidas de herbicidas. Teniendo en cuenta lo establecido, el objetivo primario de este estudio es evaluar la respuesta ecofisiológica de siete poblaciones de Sorghum halepense, de diferentes localidades argentinas, frente a dosis reducidas de nicosulfurón tratando de determinar si se modifica el rebrote de las mismas luego del tratamiento con nicosulfurón. Las poblaciones de regiones subhúmedas presentarían una mayor capacidad de rebrotar.Facultad de Ciencias Agrarias y Forestale
Inhomogeneity of donor doping in SrTiO3 substrates studied by fluorescence-lifetime imaging microscopy
Fluorescence-lifetime imaging microscopy (FLIM) was applied to investigate
the donor distribution in SrTiO3 single crystals. On the surfaces of Nb- and
La-doped SrTiO3, structures with different fluorescence intensities and
lifetimes were found that could be related to different concentrations of Ti3+.
Furthermore, the inhomogeneous distribution of donors caused a non-uniform
conductivity of the surface, which complicates the production of potential
electronic devices by the deposition of oxide thin films on top of doped single
crystals. Hence, we propose FLIM as a convenient technique (length scale: 1
m) for characterizing the quality of doped oxide surfaces, which could
help to identify appropriate substrate materials
The “Square Feature” in the harbor: Excavations in Berenike 2010–2011
The Berenike Project team explored, as one of a number of objectives, a square
feature situated on an island or promontory in the southwestern harbor bay of the Berenike
port, directly to the northwest of the “Lotus Temple”. The report is a preliminary assessment
of the results of excavations carried out in 2010 and 2011, which uncovered the inside of the
structure as well as a continuous surface of melted gypsum anhydrite around it that was
proved to be at least in part a tumble of large wall ashlars. A provisional dating of the
remains suggests an early Roman origin for the structure, which may have been a sanctuary.
The findings indicate that it was already abandoned in the 4th–5th centuries when the
neighboring “Lotus Temple”, uncovered concurrently by the Polish–American team, was at
its peak. Finds included an inscribed altar dedicated to Domitian(?), discovered among the
tumble of a stone basin and unidentified installation, and some remains of bronze statuary,
oil lamps, glass beads and other finds.Iwona Zyc
Testing the Universality of the Stellar IMF with Chandra and HST
The stellar initial mass function (IMF), which is often assumed to be
universal across unresolved stellar populations, has recently been suggested to
be "bottom-heavy" for massive ellipticals. In these galaxies, the prevalence of
gravity-sensitive absorption lines (e.g. Na I and Ca II) in their near-IR
spectra implies an excess of low-mass ( ) stars over that
expected from a canonical IMF observed in low-mass ellipticals. A direct
extrapolation of such a bottom-heavy IMF to high stellar masses (
) would lead to a corresponding deficit of neutron stars and black
holes, and therefore of low-mass X-ray binaries (LMXBs), per unit near-IR
luminosity in these galaxies. Peacock et al. (2014) searched for evidence of
this trend and found that the observed number of LMXBs per unit -band
luminosity () was nearly constant. We extend this work using new and
archival Chandra X-ray Observatory (Chandra) and Hubble Space Telescope (HST)
observations of seven low-mass ellipticals where is expected to be the
largest and compare these data with a variety of IMF models to test which are
consistent with the observed . We reproduce the result of Peacock et al.
(2014), strengthening the constraint that the slope of the IMF at
must be consistent with a Kroupa-like IMF. We construct an IMF model
that is a linear combination of a Milky Way-like IMF and a broken power-law
IMF, with a steep slope ( ) for stars < 0.5 (as
suggested by near-IR indices), and that flattens out ( ) for
stars > 0.5 , and discuss its wider ramifications and limitations.Comment: Accepted for publication in ApJ; 7 pages, 2 figures, 1 tabl
Evidence for Elevated X-ray Emission in Local Lyman Break Galaxy Analogs
In this paper, we study the relationship between the 2-10 keV X-ray
luminosity (L_X), assumed to originate from X-ray binaries (XRBs), and star
formation rate (SFR) in UV-selected z<0.1 Lyman break analogs (LBAs). We
present Chandra observations for four new GALEX-selected LBAs. Including
previously studied LBAs, Haro 11 and VV 114, we find that LBAs demonstrate
L_X/SFR ratios that are elevated by ~1.5sigma compared to local galaxies,
similar to the ratios found for stacked LBGs in the early Universe (z>2). We
show that these LBAs are unlikely to harbor AGN, based on their optical and
X-ray spectra and the spatial distribution of the X-rays in three spatially
extended cases. We expect that high-mass X-ray binaries (HMXBs) dominate the
X-ray emission in these galaxies, based on their high specific SFRs
(sSFRs=SFR/M* > 10^{-9}/yr), which suggest the prevalence of young stellar
populations. Since both LBAs and LBGs have lower dust attenuations and
metallicities compared to similar samples of more typical local galaxies, we
investigate the effects of dust extinction and metallicity on the L_X/SFR for
the broader population of galaxies with high sSFRs (>10^{-10}/yr). The
estimated dust extinctions (corresponding to column densities of
N_H<10^{22}/cm^2) are expected to have insignificant effects on observed
L_X/SFR ratio for the majority of galaxy samples. We find that the observed
relationship between L_X/SFR and metallicity appears consistent with
theoretical expectations from X-ray binary population synthesis models.
Therefore, we conclude that lower metallicities, related to more luminous HMXBs
such as ultraluminous X-ray sources (ULXs), drive the elevated L_X/SFR observed
in our sample of z<0.1 LBAs. The relatively metal-poor, active mode of star
formation in LBAs and distant z>2 LBGs may yield higher total HMXB luminosity
than found in typical galaxies in the local Universe.Comment: 11 pages, 7 figures, Submitted to ApJ (references updated in v2
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