310 research outputs found
Optimisation of the Read-out Electronics of Muon Drift-Tube Chambers for Very High Background Rates at HL-LHC and Future Colliders
In the ATLAS Muon Spectrometer, Monitored Drift Tube (MDT) chambers and sMDT
chambers with half of the tube diameter of the MDTs are used for precision muon
track reconstruction. The sMDT chambers are designed for operation at high
counting rates due to neutron and gamma background irradiation expected for the
HL-LHC and future hadron colliders. The existing MDT read-out electronics uses
bipolar signal shaping which causes an undershoot of opposite polarity and same
charge after a signal pulse. At high counting rates and short electronics dead
time used for the sMDTs, signal pulses pile up on the undershoot of preceding
background pulses leading to a reduction of the signal amplitude and a jitter
in the drift time measurement and, therefore, to a degradation of drift tube
efficiency and spatial resolution. In order to further increase the rate
capability of sMDT tubes, baseline restoration can be used in the read-out
electronics to suppress the pile-up effects. A discrete bipolar shaping circuit
with baseline restoration has been developed and used for reading out sMDT
tubes under irradiation with a 24 MBq 90Sr source. The measurements results
show a substantial improvement of the performance of the sMDT tubes at high
counting rates
A High-Resolution Combined Scanning Laser- and Widefield Polarizing Microscope for Imaging at Temperatures from 4 K to 300 K
Polarized light microscopy, as a contrast-enhancing technique for optically
anisotropic materials, is a method well suited for the investigation of a wide
variety of effects in solid-state physics, as for example birefringence in
crystals or the magneto-optical Kerr effect (MOKE). We present a microscopy
setup that combines a widefield microscope and a confocal scanning laser
microscope with polarization-sensitive detectors. By using a high numerical
aperture objective, a spatial resolution of about 240 nm at a wavelength of 405
nm is achieved. The sample is mounted on a He continuous flow cryostat
providing a temperature range between 4 K and 300 K, and electromagnets are
used to apply magnetic fields of up to 800 mT with variable in-plane
orientation and 20 mT with out-of-plane orientation. Typical applications of
the polarizing microscope are the imaging of the in-plane and out-of-plane
magnetization via the longitudinal and polar MOKE, imaging of magnetic flux
structures in superconductors covered with a magneto-optical indicator film via
Faraday effect or imaging of structural features, such as twin-walls in
tetragonal SrTiO. The scanning laser microscope furthermore offers the
possibility to gain local information on electric transport properties of a
sample by detecting the beam-induced voltage change across a current-biased
sample. This combination of magnetic, structural and electric imaging
capabilities makes the microscope a viable tool for research in the fields of
oxide electronics, spintronics, magnetism and superconductivity.Comment: 14 pages, 11 figures. The following article has been accepted by
Review of Scientific Instruments. After it is published, it will be found at
http://aip.scitation.org/journal/rs
Approximate exploitability: Learning a best response in large games
A standard metric used to measure the approximate optimality of policies in
imperfect information games is exploitability, i.e. the performance of a policy
against its worst-case opponent. However, exploitability is intractable to
compute in large games as it requires a full traversal of the game tree to
calculate a best response to the given policy. We introduce a new metric,
approximate exploitability, that calculates an analogous metric using an
approximate best response; the approximation is done by using search and
reinforcement learning. This is a generalization of local best response, a
domain specific evaluation metric used in poker. We provide empirical results
for a specific instance of the method, demonstrating that our method converges
to exploitability in the tabular and function approximation settings for small
games. In large games, our method learns to exploit both strong and weak
agents, learning to exploit an AlphaZero agent
New Solutions to the Firing Squad Synchronization Problems for Neural and Hyperdag P Systems
We propose two uniform solutions to an open question: the Firing Squad
Synchronization Problem (FSSP), for hyperdag and symmetric neural P systems,
with anonymous cells. Our solutions take e_c+5 and 6e_c+7 steps, respectively,
where e_c is the eccentricity of the commander cell of the dag or digraph
underlying these P systems. The first and fast solution is based on a novel
proposal, which dynamically extends P systems with mobile channels. The second
solution is substantially longer, but is solely based on classical rules and
static channels. In contrast to the previous solutions, which work for
tree-based P systems, our solutions synchronize to any subset of the underlying
digraph; and do not require membrane polarizations or conditional rules, but
require states, as typically used in hyperdag and neural P systems
Model study for the nonequlibrium magnetic domain structure during the growth of nanostructured ultrathin films
The nonequilibrium magnetic domain structure of growing ultrathin
ferromagnetic films with a realistic atomic structure is studied as a function
of coverage and temperature. We apply a kinetic Monte Carlo method to a
micromagnetic model describing the transition from superparamagnetic islands at
low coverages to a closed ferromagnetic film. The magnetic relaxation and the
island growth happen simultaneously. Near the percolation threshold a
metastable magnetic domain structure is obtained with an average domain area
ranging between the area of individual magnetic islands and the area of the
large domains observed for thicker ferromagnetic films. We conclude that this
micro-domain structure is controlled and stabilized by the nonuniform atomic
nanostructure of the ultrathin film, causing a random interaction between
magnetic islands with varying sizes and shapes. The average domain area and
domain roughness are determined. A maximum of the domain area and a minimum of
the domain roughness are obtained as a function of the temperature.Comment: 19 pages, 4 Postscript figures; to be published in J. Magn. Magn.
Mater., accepted (2001); completely revised manuscrip
Distribution of chromosome 18 and X centric heterochromatin in the interphase nucleus of cultured human cells
In situ hybridization of human chromosome 18 and X-specific alphoid DNA-probes was performed in combination with three dimensional (3D) and two dimensional (2D) image analysis to study the interphase distribution of the centric heterochromatin (18c and Xc) of these chromosomes in cultured human cells. 3D analyses of 18c targets using confocal laser scanning microscopy indicated a nonrandom disposition in 73 amniotic fluid cell nuclei. The shape of these nuclei resembled rather flat cylinders or ellipsoids targets were preferentially arranged in a domain around the nuclear center, but close to or associated with the nuclear envelope. Within this domain, however, positionings of the two targets occurred independently from each other, i.e., the two targets were observed with similar frequencies at the same (upper or lower) side of the nuclear envelope as those on opposite sides. This result strongly argues against any permanent homologous association of 18c. A 2D analytical approach was used for the rapid evaluation of 18c positions in over 4000 interphase nuclei from normal male and female individuals, as well as individuals with trisomy 18 and Bloom's syndrome. In addition to epithelially derived amniotic fluid cells, investigated cell types included in vitro cultivated fibroblastoid cells established from fetal lung tissue and skin-derived fibroblasts. In agreement with the above 3D observations 18c targets were found significantly closer (P < 0.01) to the center of the 2D nuclear image (CNI) and to each other in all these cultures compared to a random distribution derived from corresponding ellipsoid or cylinder model nuclei. For comparison, a chromosome X-specific alphoid DNA probe was used to investigate the 2D distribution of chromosome X centric heterochromatin in the same cell types. Two dimensional Xc-Xc and Xc-CNI distances fit a random distribution in diploid normal and Bloom's syndrome nuclei, as well as in nuclei with trisomy X. The different distributions of 18c and Xc targets were confirmed by the simultaneous staining of these targets in different colors within individual nuclei using a double in situ hybridization approach
Myoglobin regulates fatty acid trafficking and lipid metabolism in mammary epithelial cells
Myoglobin (MB) is known to bind and deliver oxygen in striated muscles at high expression levels. MB is also expressed at much reduced levels in mammary epithelial cells, where the protein´s function is unclear. In this study, we aim to determine whether MB impacts fatty acid trafficking and facilitates aerobic fatty acid ß-oxidation in mammary epithelial cells. We utilized MB-wildtype versus MB-knockout mice and human breast cancer cells to examine the impact of MB and its oxygenation status on fatty acid metabolism in mouse milk and mammary epithelia. MB deficient cells were generated through CRISPR/Cas9 and TALEN approaches and exposed to various oxygen tensions. Fatty acid profiling of milk and cell extracts were performed along with cell labelling and immunocytochemistry. Our findings show that MB expression in mammary epithelial cells promoted fatty acid oxidation while reducing stearyl-CoA desaturase activity for lipogenesis. In cells and milk product, presence of oxygenated MB significantly elevated indices of limited fatty acid ß-oxidation, i.e., the organelle-bound removal of a C2 moiety from long-chain saturated or monounsaturated fatty acids, thus shifting the composition toward more saturated and shorter fatty acid species. Presence of the globin also increased cytoplasmic fatty acid solubility under normoxia and fatty acid deposition to lipid droplets under severe hypoxia. We conclude that MB can function in mammary epithelia as intracellular O-dependent shuttle of oxidizable fatty acid substrates. MB’s impact on limited oxidation of fatty acids could generate inflammatory mediator lipokines, such as 7-hexadecenoate. Thus, the novel functions of MB in breast epithelia described herein range from controlling fatty acid turnover and homeostasis to influencing inflammatory signalling cascade. Future work is needed to analyse to what extent these novel roles of MB also apply to myocytic cell physiology and malignant cell behaviour, respectively
Be stars and binaries in the field of the SMC open cluster NGC330 with VLT-FLAMES
Observations of hot stars belonging to the young cluster SMC-NGC330 and its
surrounding region were obtained with the VLT-GIRAFFE facilities in MEDUSA
mode. We investigated the B and Be star properties and proportions in this
environment of low metallicity. We also searched for rapid variability in Be
stars using photometric databases. With spectroscopic measurements we
characterized the emission and properties of Be stars. By cross-correlation
with photometric databases such as MACHO and OGLE, we searched for binaries in
our sample of hot stars, as well as for short-term variability in Be stars. We
report on the global characteristics of the Be star sample (131 objects). We
find that the proportion of early Be stars with a large equivalent width of the
Halpha emission line is higher in the SMC than in the LMC and MW. We find a
slight increase in the proportion of Be stars compared to B-type stars with
decreasing metallicity. We also discovered spectroscopic and photometric
binaries, and for the latter we give their orbital period. We identify 13 Be
stars with short-term variability. We determine their period(s) and find that 9
Be stars are multiperiodic.Comment: english not yet corrected, 23 pages, 4th article about the study in
the LMC NGC2004 and SMC NGC33
Exchange-induced frustration in Fe/NiO multilayers
Using spin-polarized low-energy electron microscopy to study magnetization in
epitaxial layered systems, we found that the area vs perimeter relationship of
magnetic domains in the top Fe layers of Fe/NiO/Fe(100) structures follows a
power-law distribution, with very small magnetic domain cutoff radius (about 40
nm) and domain wall thickness. This unusual magnetic microstructure can be
understood as resulting from the competition between antiferromagnetic and
ferromagnetic exchange interactions at the Fe/NiO interfaces, rather than from
mechanisms involving the anisotropy and dipolar forces that govern length
scales in conventional magnetic domain structures. Statistical analysis of our
measurements validates a micromagnetic model that accounts for this interfacial
exchange coupling.Comment: 15 pages, 2 figure
Molecular Detection of Anaerobic Ammonium-Oxidizing (Anammox) Bacteria in High-Temperature Petroleum Reservoirs
Anaerobic ammonium-oxidizing (anammox) process plays an important role in the nitrogen cycle of the worldwide anoxic and mesophilic habitats. Recently, the existence and activity of anammox bacteria have been detected in some thermophilic environments, but their existence in the geothermal subterranean oil reservoirs is still not reported. This study investigated the abundance, distribution and functional diversity of anammox bacteria in nine out of 17 high-temperature oil reservoirs by molecular ecology analysis. High concentration (5.31–39.2 mg l−1) of ammonium was detected in the production water from these oilfields with temperatures between 55°C and 75°C. Both 16S rRNA and hzo molecular biomarkers indicated the occurrence of anammox bacteria in nine out of 17 samples. Most of 16S rRNA gene phylotypes are closely related to the known anammox bacterial genera Candidatus Brocadia, Candidatus Kuenenia, Candidatus Scalindua, and Candidatus Jettenia, while hzo gene phylotypes are closely related to the genera Candidatus Anammoxoglobus, Candidatus Kuenenia, Candidatus Scalindua, and Candidatus Jettenia. The total bacterial and anammox bacterial densities were 6.4 ± 0.5 × 103 to 2.0 ± 0.18 × 106 cells ml−1 and 6.6 ± 0.51 × 102 to 4.9 ± 0.36 × 104 cell ml−1, respectively. The cluster I of 16S rRNA gene sequences showed distant identity (<92%) to the known Candidatus Scalindua species, inferring this cluster of anammox bacteria to be a new species, and a tentative name Candidatus “Scalindua sinooilfield” was proposed. The results extended the existence of anammox bacteria to the high-temperature oil reservoirs
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