236 research outputs found
Low-Afterglow, High-Refractive-Index Liquid Scintillators for Fast-Neutron Spectrometry and Imaging Applications
For ion and neutron spectrometry and imaging applications at a high intensity
pulsed laser facility, fast liquid scintillators with very low afterglow are
required. Furthermore, neutron imaging with fiber (or liquid-core) capillary
arrays calls for scintillation materials with high refractive index. To this
end, we have examined various combinations of established mixtures of fluors
and solvents, that were enriched alternatively with nitrogen or oxygen.
Dissolved molecular oxygen is known to be a highly effective quenching agent,
that efficiently suppresses the population of the triplet states in the fluor,
which are primarily responsible for the afterglow. For measuring the glow
curves of scintillators, we have employed the time-correlated single photon
counting (TCSPC) technique, characterized by high dynamic range of several
orders of magnitude in light intensity. In this paper we outline the
application for the fast scintillators, briefly present the scintillation
mechanism in liquids, describe our specific TCSPC method and discuss the
results.Comment: 5 pages, Contribution to SORMA WEST 2008. To be published in IEEE
TNS, 200
StarobylĂŠ vĂ˝mladkovĂŠ lesy v krajinÄ ÄeskĂŠ republiky
Ancient coppice woodlands are forest stands of coppice origin with a long-term continual development and preserved typical natural and historic elements of old coppices. Significant natural elements in ancient coppices include polycormons of coppice shoots, pollard trees, trees with holes, dendrotelms, reserved trees, ecotones, glades and significant plant and animal species. Significant historic elements of localities with ancient coppices include archaeological monuments, boundary ditches and walls, boundary stones, boundary trees, myths and legends, sacral objects, old roads and paths, technical objects and plough land remainders. The paper presents differentiation of assumptions for the occurrence of ancient coppices in the territory of the Czech Republic using the COPF coefficient and examples of results from basic regional inventory (KuĹim region) and detailed local survey (locality LebeÄĂĄk) of coppice-originated forests. The extinction of the phenomenon of ancient coppice woodlands would mean irreparable impoverishment of the natural and cultural heritage.Za starobylĂŠ vĂ˝mladkovĂŠ lesy oznaÄujeme lesnĂ porosty vĂ˝mladkovĂŠho pĹŻvodu s dlouhodobĂ˝m kontinuĂĄlnĂm vĂ˝vojem a zachovanĂ˝mi typickĂ˝mi pĹĂrodnĂmi a historickĂ˝mi prvky starĂ˝ch paĹezin. K vĂ˝znamnĂ˝m pĹĂrodnĂm prvkĹŻm ve starobylĂ˝ch paĹezinĂĄch patĹĂ vĂ˝mladkovĂŠ polykormony, hlavatĂŠ stromy, doupnĂŠ stromy, dendrotelmy, vĂ˝stavky, ekotony, svÄtliny a vĂ˝znamnĂŠ druhy rostlin a ĹživoÄichĹŻ. Mezi vĂ˝znamnĂŠ historickĂŠ prvky lokalit starobylĂ˝ch vĂ˝mladkovĂ˝ch lesĹŻ ĹadĂme archeologickĂŠ pamĂĄtky, hraniÄnĂ pĹĂkopy a valy, hraniÄnĂ kameny, hraniÄnĂ stromy, povÄsti a legendy, sakrĂĄlnĂ objekty, starĂŠ cesty a stezky, technickĂŠ objekty a zbytky pluĹžiny. V ÄlĂĄnku je prezentovĂĄna diferenciace pĹedpokladĹŻ vĂ˝skytu starobylĂ˝ch paĹezin na ĂşzemĂ ÄeskĂŠ republiky s vyuĹžitĂm koeficientu COPF a pĹĂklady vĂ˝sledkĹŻ zĂĄkladnĂho regionĂĄlnĂho (KuĹimsko) a podrobnĂŠho lokĂĄlnĂho (LebeÄĂĄk) prĹŻzkumu lokalit lesĹŻ vĂ˝mladkovĂŠho pĹŻvodu. ZĂĄnik fenomĂŠnu starobylĂ˝ch paĹezin by znamenal nenapravitelnĂŠ ochuzenĂ pĹĂrodnĂho a kulturnĂho dÄdictvĂ.O
A real-time active routing approach via a database for airport surface movement
Airports face challenges due to the increasing volume of air traffic and tighter environmental restrictions which result in a need to actively integrate speed profiles into conventional routing and scheduling procedure. However, only until very recently, the research on airport ground movement has started to take into account such a speed profile optimisation problem actively so that not only time efficiency but also fuel saving and decrease in airport emissions can be achieved at the same time. It is envisioned that the realism of planning could also be improved through speed profiles. However, due to the multi-objective nature of the problem and complexity of the investigated models (objective functions), the existing speed profile optimisation approach features high computational demand and is not suitable for an on-line application. In order to make this approach more competitive for real-world application and to meet limits imposed by International Civil Aviation Organization for on-line decision time,
this paper introduces a pre-computed database acting as a middleware to effectively separate the planning (routing and scheduling) module and the speed profile generation module. Employing a database not only circumvents duplicative optimisation for the same taxiway segments, but also completely avoids the computation of speed profiles during the on-line decision support owing a great deal to newly proposed database initialization procedures. Moreover, the added layer of database facilitates, in the future, more complex and realistic models to be considered in the speed profile generation module, without sacrificing on-line decision time. The experimental results carried out using data from a major European hub show that the proposed approach is promising in speeding up the search process
Neutralino Dark Matter in Minimal Supergravity: Direct Detection vs. Collider Searches
We calculate expected event rates for direct detection of relic neutralinos
as a function of parameter space of the minimal supergravity model. Numerical
results are presented for the specific case of a Ge detector. We find
significant detection rates ( events/kg/day) in regions of parameter
space most favored by constraints from and the cosmological
relic density of neutralinos. The detection rates are especially large in
regions of large , where many conventional signals for supersymmetry
at collider experiments are difficult to detect. If the parameter
is large, then there is a significant probability that the first direct
evidence for supersymmetry could come from direct detection experiments, rather
than from collider searches for sparticles.Comment: 25 page REVTEX file including 9 PS figure
Anomaly-Free Gauged R-Symmetry
We review the gauging of an R-symmetry in local and global susy. We then
construct the first anomaly-free models. We break the R-symmetry and susy at
the Planck scale and discuss the low-energy effects. We include a solution to
the mu-problem, and the prediction of observable effects at HERA. The models
also nicely allow for GUT-scale baryogenesis and R-parity violation without the
sphaleron interactions erasing the baryon-asymmetry.Comment: 6 pages, latex, no figures. Talk presented at SUSY-95. Work done in
collaboration with A. Chamseddin
Myelin-associated glycoprotein gene mutation causes Pelizaeus-Merzbacher disease-like disorder
Pelizaeus-Merzbacher disease is an X-linked hypomyelinating leukodystrophy. Lossos et al. describe a family with an early-onset Pelizaeus-Merzbacher disease-like phenotype that slowly evolves into complicated hereditary spastic paraplegia, affecting both the CNS and PNS. Exome sequencing reveals a causative homozygous missense mutation in MAG, which encodes myelin associated glycoprotei
Computational personality recognition in social media
A variety of approaches have been recently proposed to automatically infer users' personality from their user generated content in social media. Approaches differ in terms of the machine learning algorithms and the feature sets used, type of utilized footprint, and the social media environment used to collect the data. In this paper, we perform a comparative analysis of state-of-the-art computational personality recognition methods on a varied set of social media ground truth data from Facebook, Twitter and YouTube. We answer three questions: (1) Should personality prediction be treated as a multi-label prediction task (i.e., all personality traits of a given user are predicted at once), or should each trait be identified separately? (2) Which predictive features work well across different on-line environments? (3) What is the decay in accuracy when porting models trained in one social media environment to another
Cellularly-Driven Differences in Network Synchronization Propensity Are Differentially Modulated by Firing Frequency
Spatiotemporal pattern formation in neuronal networks depends on the interplay between cellular and network synchronization properties. The neuronal phase response curve (PRC) is an experimentally obtainable measure that characterizes the cellular response to small perturbations, and can serve as an indicator of cellular propensity for synchronization. Two broad classes of PRCs have been identified for neurons: Type I, in which small excitatory perturbations induce only advances in firing, and Type II, in which small excitatory perturbations can induce both advances and delays in firing. Interestingly, neuronal PRCs are usually attenuated with increased spiking frequency, and Type II PRCs typically exhibit a greater attenuation of the phase delay region than of the phase advance region. We found that this phenomenon arises from an interplay between the time constants of active ionic currents and the interspike interval. As a result, excitatory networks consisting of neurons with Type I PRCs responded very differently to frequency modulation compared to excitatory networks composed of neurons with Type II PRCs. Specifically, increased frequency induced a sharp decrease in synchrony of networks of Type II neurons, while frequency increases only minimally affected synchrony in networks of Type I neurons. These results are demonstrated in networks in which both types of neurons were modeled generically with the Morris-Lecar model, as well as in networks consisting of Hodgkin-Huxley-based model cortical pyramidal cells in which simulated effects of acetylcholine changed PRC type. These results are robust to different network structures, synaptic strengths and modes of driving neuronal activity, and they indicate that Type I and Type II excitatory networks may display two distinct modes of processing information
Identification of factors required for meristem function in Arabidopsis using a novel next generation sequencing fast forward genetics approach
<p>Abstract</p> <p>Background</p> <p>Phenotype-driven forward genetic experiments are powerful approaches for linking phenotypes to genomic elements but they still involve a laborious positional cloning process. Although sequencing of complete genomes now becomes available, discriminating causal mutations from the enormous amounts of background variation remains a major challenge.</p> <p>Method</p> <p>To improve this, we developed a universal two-step approach, named 'fast forward genetics', which combines traditional bulk segregant techniques with targeted genomic enrichment and next-generation sequencing technology</p> <p>Results</p> <p>As a proof of principle we successfully applied this approach to two Arabidopsis mutants and identified a novel factor required for stem cell activity.</p> <p>Conclusion</p> <p>We demonstrated that the 'fast forward genetics' procedure efficiently identifies a small number of testable candidate mutations. As the approach is independent of genome size, it can be applied to any model system of interest. Furthermore, we show that experiments can be multiplexed and easily scaled for the identification of multiple individual mutants in a single sequencing run.</p
Hippocampal Desynchronization of Functional Connectivity Prior to the Onset of Status Epilepticus in Pilocarpine-Treated Rats
Status epilepticus (SE), a pro-epileptogenic brain insult in rodent models of temporal lobe epilepsy, is successfully induced by pilocarpine in some, but not all, rats. This study aimed to identify characteristic alterations within the hippocampal neural network prior to the onset of SE. Sixteen microwire electrodes were implanted into the left hippocampus of male Sprague-Dawley rats. After a 7-day recovery period, animal behavior, hippocampal neuronal ensemble activities, and local field potentials (LFP) were recorded before and after an intra-peritoneal injection of pilocarpine (350 mg/kg). The single-neuron firing, population neuronal correlation, and coincident firing between neurons were compared between SE (nâ=â9) and nonSE rats (nâ=â12). A significant decrease in the strength of functional connectivity prior to the onset of SE, as measured by changes in coincident spike timing between pairs of hippocampal neurons, was exclusively found in SE rats. However, single-neuron firing and LFP profiles did not show a significant difference between SE and nonSE rats. These results suggest that desynchronization in the functional circuitry of the hippocampus, likely associated with a change in synaptic strength, may serve as an electrophysiological marker prior to SE in pilocarpine-treated rats
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