2,235 research outputs found
Incorporation of the statistical uncertainty in the background estimate into the upper limit on the signal
We present a procedure for calculating an upper limit on the number of signal
events which incorporates the Poisson uncertainty in the background, estimated
from control regions of one or two dimensions. For small number of signal
events, the upper limit obtained is more stringent than that extracted without
including the Poisson uncertainty. This trend continues until the number of
background events is comparable with the signal. When the number of background
events is comparable or larger than the signal, the upper limit obtained is
less stringent than that extracted without including the Poisson uncertainty.
It is therefore important to incorporate the Poisson uncertainty into the upper
limit; otherwise the upper limit obtained could be too stringent.Comment: 14 pages, 4 figure
Holographic optical elements: Fabrication and testing
The basic properties and use of holographic optical elements were investigated to design and construct wide-angle, Fourier-transform holographic optical systems for use in a Bragg-effect optical memory. The performance characteristics are described along with the construction of the holographic system
On the stratigraphic integrity of leaf-wax biomarkers in loess paleosols
Paleoenvironmental and paleoclimate reconstructions based on molecular
proxies, such as those derived from leaf-wax biomarkers, in loess-paleosol
sequences represent a promising line of investigation in Quaternary research.
The main premise of such reconstructions is the synsedimentary deposition of
biomarkers and dust, which has become a debated subject in recent years. This
study uses two independent approaches to test the stratigraphic integrity of
leaf-wax biomarkers: (i) long-chain n-alkanes and fatty acids are
quantified in two sediment-depth profiles in glacial till on the Swiss
Plateau, consisting of a Holocene topsoil and the underlying B and C
horizons. Since glacial sediments are initially very poor in organic matter,
significant amounts of leaf-wax biomarkers in the B and C horizons of those
profiles would reflect postsedimentary root-derived or microbial
contributions. (ii) Compound-specific radiocarbon measurements are conducted
on n-alkanes and n-alkanoic (fatty) acids from several depth intervals in
the loess section "Crvenka", Serbia, and the results are compared to
independent estimates of sediment age.
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We find extremely low concentrations
of plant-wax n-alkanes and fatty acids in the B and C horizons below the
topsoils in the sediment profiles. Moreover, compound-specific radiocarbon
analysis yields plant-wax <sup>14</sup>C ages that agree well with published
luminescence ages and stratigraphy of the Serbian loess deposit. Both
approaches confirm that postsedimentary, root-derived or microbial
contributions are negligible in the two investigated systems. The good
agreement between the ages of odd and even homologues also indicates that
reworking and incorporation of fossil leaf waxes is not particularly relevant
either
Early last glacial maximum in the southern Central Andes reveals northward shift of the westerlies at ~39 ka
The latitudinal position of the southern westerlies has been suggested to be a key parameter for the climate on Earth. According to the general notion, the southern westerlies were shifted equatorward during the global Last Glacial Maximum (LGM: ~24â18 ka), resulting in reduced deep ocean ventilation, accumulation of old dissolved carbon, and low atmospheric CO<sub>2</sub> concentrations. In order to test this notion, we applied surface exposure dating on moraines in the southern Central Andes, where glacial mass balances are particularly sensitive to changes in precipitation, i.e. to the latitudinal position of the westerlies. Our results provide robust evidence that the maximum glaciation occurred already at ~39 ka, significantly predating the global LGM. This questions the role of the westerlies for atmospheric CO<sub>2</sub>, and it highlights our limited understanding of the forcings of atmospheric circulation
The spatial distribution of sedimentary compounds and their environmental implications in surface sediments of Lake Khar Nuur (Mongolian Altai)
Lake sediments are valuable natural archives to reconstruct paleoclimate and paleoenvironmental changes which consist of inorganic and organic sediment compounds of allochthonous origin from the catchment and of autochthonous production in the lake. However, for robust paleo-reconstructions it is important to develop a better understanding about sedimentation processes, the origin of inorganic and organic sediment compounds and their distribution within the lake. In this context, modern process studies provide important insights, although environmental and anthropological changes can affect the spatial distribution of sediment compounds through time. Therefore, in this study the spatial distribution of grain size and geochemical proxies in 52 surface sediment samples from Lake Khar Nuur, a small high-altitude lake in the Mongolian Altai with a small and anthropogenically used hydrological catchment, is investigated. The results show a distinct sediment focussing in the two deep basins of the lake, which therefore act as accumulation zones. In those accumulation zones, total organic carbon (TOC), total nitrogen (N) and their isotopic composition (ÎŽ13CTOC, ÎŽ15N) as well as n-alkanes indicate that organic sediment compounds are a mixture of both allochthonous and autochthonous origin. While the recent catchment vegetation consists of grasses/herbs and the shrub Betula nana (L.) with distinct differences in their n-alkane homologue patterns, those differences are not reflected in the sediment surface samples which rather indicates that grass-derived n-alkanes become preferentially incorporated in the lake. Extensive anthropogenic activity such as grazing and housing in the southern part of the catchment causes soil erosion which is well reflected by high TOC, N and sulphur (S) contents and 15N depleted ÎŽ15N values at the central southern shore, i.e. increased allochthonous sediment input by anthropogenicallyinduced soil erosion. Overall, the surface sediments of Lake Khar Nuur origin from allochthonous and autochthonous sources and are focussed in the accumulation zones of the lake, while their distribution is both environmentally and anthropogenically driven
Impact of geomagnetic excursions on atmospheric chemistry and dynamics
Geomagnetic excursions, i.e. short periods in time with much weaker
geomagnetic fields and substantial changes in the position of the geomagnetic
pole, occurred repeatedly in the Earth's history, e.g. the Laschamp event
about 41 kyr ago. Although the next such excursion is certain to come,
little is known about the timing and possible consequences for the state of
the atmosphere and the ecosystems. Here we use the global chemistry climate
model SOCOL-MPIOM to simulate the effects of geomagnetic excursions on
atmospheric ionization, chemistry and dynamics. Our simulations show
significantly increased concentrations of nitrogen oxides (NO<sub>x</sub>)
in the entire stratosphere, especially over Antarctica (+15%), due to
enhanced ionization by galactic cosmic rays. Hydrogen oxides
(HO<sub>x</sub>) are also produced in greater amounts (up to +40%) in
the tropical and subtropical lower stratosphere, while their destruction by
reactions with enhanced NO<sub>x</sub> prevails over the poles and in high
altitudes (by â5%). Stratospheric ozone concentrations decrease globally
above 20 km by 1â2% and at the northern hemispheric tropopause by up to
5% owing to the accelerated NO<sub>x</sub>-induced destruction. A 5%
increase is found in the southern lower stratosphere and troposphere. In
response to these changes in ozone and the concomitant changes in atmospheric
heating rates, the Arctic vortex intensifies in boreal winter, while the
Antarctic vortex weakens in austral winter and spring. Surface wind anomalies
show significant intensification of the southern westerlies at their poleward
edge during austral winter and a pronounced northward shift in spring. Major
impacts on the global climate seem unlikely
Preservation Methods Differ in Fecal Microbiome Stability, Affecting Suitability for Field Studies.
Immediate freezing at -20°C or below has been considered the gold standard for microbiome preservation, yet this approach is not feasible for many field studies, ranging from anthropology to wildlife conservation. Here we tested five methods for preserving human and dog fecal specimens for periods of up to 8 weeks, including such types of variation as freeze-thaw cycles and the high temperature fluctuations often encountered under field conditions. We found that three of the methods-95% ethanol, FTA cards, and the OMNIgene Gut kit-can preserve samples sufficiently well at ambient temperatures such that differences at 8 weeks are comparable to differences among technical replicates. However, even the worst methods, including those with no fixative, were able to reveal microbiome differences between species at 8 weeks and between individuals after a week, allowing meta-analyses of samples collected using various methods when the effect of interest is expected to be larger than interindividual variation (although use of a single method within a study is strongly recommended to reduce batch effects). Encouragingly for FTA cards, the differences caused by this method are systematic and can be detrended. As in other studies, we strongly caution against the use of 70% ethanol. The results, spanning 15 individuals and over 1,200 samples, provide our most comprehensive view to date of storage effects on stool and provide a paradigm for the future studies of other sample types that will be required to provide a global view of microbial diversity and its interaction among humans, animals, and the environment. IMPORTANCE Our study, spanning 15 individuals and over 1,200 samples, provides our most comprehensive view to date of storage and stabilization effects on stool. We tested five methods for preserving human and dog fecal specimens for periods of up to 8 weeks, including the types of variation often encountered under field conditions, such as freeze-thaw cycles and high temperature fluctuations. We show that several cost-effective methods provide excellent microbiome stability out to 8 weeks, opening up a range of field studies with humans and wildlife that would otherwise be cost-prohibitive
Josephson junction between anisotropic superconductors
The sin-Gordon equation for Josephson junctions with arbitrary misaligned
anisotropic banks is derived. As an application, the problem of Josephson
vortices at twin planes of a YBCO-like material is considered. It is shown that
for an arbitrary orientation of these vortices relative to the crystal axes of
the banks, the junctions should experience a mechanical torque which is
evaluated. This torque and its angular dependence may, in principle, be
measured in small fields, since the flux penetration into twinned crystals
begins with nucleation of Josephson vortices at twin planes.Comment: 6 page
Digital optical recorder-reproducer system
A mass archival optical recording and reproduction system includes a recording light source such as a laser beam focussed and directed upon an acousto-optic linear modulator array (or page composer) that receives parallel blocks of data converted from a serial stream of digital data to be stored. The page composer imparts to the laser beam modulation representative of a plurality of parallel channels of data and through focussing optics downstream of the page composer parallel arrays of optical spots are recorded upon a suitable recording medium such as a photographic film floppy disc. The recording medium may be substantially frictionlessly and stably positioned for recording at a record/read station by an air-bearing platen arrangement which is preferably thermodynamically non-throttling so that the recording film may be positioned in the path of the information-carrying light beam in a static or dynamic mode. During readout, the page composer is bypassed and a readout light beam is focussed directly upon the recording medium containing an array of previously recorded digital spots, a sync bit, data positioning bits, and a tracking band. The readout beam which has been directed through the recording medium is then imaged upon a photodetector array, the output of which may be coupled to suitable electronic processing circuitry, such as a digital multiplexer, whereby the parallel spot array is converted back into the original serial data stream
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