739 research outputs found
Influence of head models on neuromagnetic fields and inverse source localizations
BACKGROUND: The magnetoencephalograms (MEGs) are mainly due to the source currents. However, there is a significant contribution to MEGs from the volume currents. The structure of the anatomical surfaces, e.g., gray and white matter, could severely influence the flow of volume currents in a head model. This, in turn, will also influence the MEGs and the inverse source localizations. This was examined in detail with three different human head models. METHODS: Three finite element head models constructed from segmented MR images of an adult male subject were used for this study. These models were: (1) Model 1: full model with eleven tissues that included detailed structure of the scalp, hard and soft skull bone, CSF, gray and white matter and other prominent tissues, (2) the Model 2 was derived from the Model 1 in which the conductivity of gray matter was set equal to the white matter, i.e., a ten tissuetype model, (3) the Model 3 consisted of scalp, hard skull bone, CSF, gray and white matter, i.e., a five tissue-type model. The lead fields and MEGs due to dipolar sources in the motor cortex were computed for all three models. The dipolar sources were oriented normal to the cortical surface and had a dipole moment of 100 ÎŒA meter. The inverse source localizations were performed with an exhaustive search pattern in the motor cortex area. A set of 100 trial inverse runs was made covering the 3 cm cube motor cortex area in a random fashion. The Model 1 was used as a reference model. RESULTS: The reference model (Model 1), as expected, performed best in localizing the sources in the motor cortex area. The Model 3 performed the worst. The mean source localization errors (MLEs) of the Model 3 were larger than the Model 1 or 2. The contour plots of the magnetic fields on top of the head were also different for all three models. The magnetic fields due to source currents were larger in magnitude as compared to the magnetic fields of volume currents. DISCUSSION: These results indicate that the complexity of head models strongly influences the MEGs and the inverse source localizations. A more complex head model performs better in inverse source localizations as compared to a model with lesser tissue surfaces
Did Cryptic Invasion of North America by Common Reed Change Exposure to Pollen Allergens?
Common reed, Phragmites australis (reed), is a very tall grass that spread greatly to
occupy large areas near many eastern North American cities over the past century. Its
aerially dispersed pollen is known to incite allergic reactions, and possibly asthma, in
some persons, but is not distinguished from that of any other grass in routine pollen
monitoring. We hypothesize that this regional expansion by reed has increased late-season
exposure to grass-pollen allergens in parts of these metropolitan areas. The
information available indicates that reed's geographic location, high abundance, small
pollen size, release of pollen relatively far above ground, substantial pollen
productivity, pollen allergen composition, and late season of pollen release all point to
its potential importance for a large number of persons whose health may be degraded
by grass pollen. If the other common late-flowering grasses in the same area have
larger pollen grains, it may be possible to visually distinguish reed pollen captured by
monitoring devices. If not, ratios of stable isotopes of carbon in the pollen may permit
differentiation. Otherwise, analytical techniques based on molecular differences need
further development in order to estimate local population exposure to allergens from
reed. Some 90 million North Americans may live close enough to large tracts of reed to
be exposed to substantial concentrations of its pollen, so much more attention to this
situation seems warranted. If reed pollen were found to be a health hazard for a
particular metropolitan area, removal of the pollen sources may be more feasible than is
the case for many other species
Zwischen Freiheitszugewinn, zugemuteter Emanzipation und Schaffung neuer AbhÀngigkeit: Kursbindung in der Alphabetisierung/Grundbildung
Der Beitrag stellt erste Ergebnisse einer Studie vor, die sich mit dem Verbleib ehemaliger Teilnehmender an Alphabetisierungskursen beschĂ€ftigt. In der Annahme, dass Kurse der Erwachsenenbildung in der Regel einen Anfang und ein Ende haben, gehen die Autorinnen dem PhĂ€nomen nach, dass sich Teilnehmende im Bereich der Alphabetisierung eher durch ein dauerhaftes Verweilen im Kurs auszeichnen. Anhand des Datenmaterials rekonstruieren sie mögliche Motive des Verweilens, die schlieĂlich in die Forderung nach einer "Ausgangsberatung" -analog der Eingangs- und Lernberatung im Kurs- mĂŒnden, die zur Professionalisierung von in der Alphabetisierung TĂ€tigen beitragen könnte
In silico investigation of a KCNQ1 mutation associated with short QT syndrome
Short QT syndrome (SQTS) is a rare condition characterized by abnormally âshortâ QT intervals on the ECG and increased susceptibility to cardiac arrhythmias and sudden death. This simulation study investigated arrhythmia dynamics in multi-scale human ventricle models associated with the SQT2-related V307L KCNQ1 âgain-of-functionâ mutation, which increases slow-delayed rectifier potassium current (IKs). A Markov chain (MC) model recapitulating wild type (WT) and V307L mutant IKs kinetics was incorporated into a model of the human ventricular action potential (AP) for investigation of QT interval changes and arrhythmia substrates. In addition, the degree of simulated IKs inhibition necessary to normalize the QT interval and terminate re-entry in SQT2 conditions was quantified. The developed MC model accurately reproduced AP shortening and reduced effective refractory period associated with altered IKs kinetics in homozygous (V307L) and heterozygous (WT-V307L) mutation conditions, which increased the lifespan and dominant frequency of re-entry in 3D human ventricle models. IKs reductions of 58% and 65% were sufficient to terminate re-entry in WT-V307L and V307L conditions, respectively. This study further substantiates a causal link between the V307L KCNQ1 mutation and pro-arrhythmia in human ventricles, and establishes partial inhibition of IKs as a potential anti-arrhythmic strategy in SQT2
Exploiting Term Hiding to Reduce Run-time Checking Overhead
One of the most attractive features of untyped languages is the flexibility
in term creation and manipulation. However, with such power comes the
responsibility of ensuring the correctness of these operations. A solution is
adding run-time checks to the program via assertions, but this can introduce
overheads that are in many cases impractical. While static analysis can greatly
reduce such overheads, the gains depend strongly on the quality of the
information inferred. Reusable libraries, i.e., library modules that are
pre-compiled independently of the client, pose special challenges in this
context. We propose a technique which takes advantage of module systems which
can hide a selected set of functor symbols to significantly enrich the shape
information that can be inferred for reusable libraries, as well as an improved
run-time checking approach that leverages the proposed mechanisms to achieve
large reductions in overhead, closer to those of static languages, even in the
reusable-library context. While the approach is general and system-independent,
we present it for concreteness in the context of the Ciao assertion language
and combined static/dynamic checking framework. Our method maintains the full
expressiveness of the assertion language in this context. In contrast to other
approaches it does not introduce the need to switch the language to a (static)
type system, which is known to change the semantics in languages like Prolog.
We also study the approach experimentally and evaluate the overhead reduction
achieved in the run-time checks.Comment: 26 pages, 10 figures, 2 tables; an extension of the paper version
accepted to PADL'18 (includes proofs, extra figures and examples omitted due
to space reasons
Neutron diffraction analysis of stress and strain partitioning in a two-phase microstructure with parallel-aligned phases
By time-of-flight (TOF) neutron diffraction experiments, the influence of segregation-induced microstructure bands of austenite (γ) and martensite (α′ ) phases on the partitioning of stress and strain between these phases was investigated. Initially, tensile specimens of a Co-added stainless steel were heat treated by quenching and partitioning (Q&P) processing. Tensile specimens were subsequently loaded at 350 °C parallel to the length of the bands within the apparent elastic limit of the phase mixture. Lattice parameters in both axial and transverse directions were simultaneously measured for both phases. The observation of a lattice expansion for the γ phase in the transverse direction indicated a constraint on the free transverse straining of γ arising from the banded microstructure. The lateral contraction of α′ imposed an interphase tensile microstress in the transverse direction of the γ phase. The multiaxial stress state developed in the γ phase resulted in a large deviation from the level of plastic strain expected for uniaxial loading of single phase γ. Since segregation-induced banded microstructures commonly occur in many engineering alloys, the analysis of stress and strain partitioning with the present Q&P steel can be used to interpret the observations made for further engineering alloys with two-phase microstructures
Persistent Effects of Herbaceous Species on the Infectious Lethality of Soil for Conifer Seedlings
Seeds of the coniferous trees Abies balsamea, Picea mariana, and Pinus strobus were sown in the laboratory in two soils taken from groundâlayer patches differing in species composition, one of which was dominated by Aegopodium podagraria (goutweed). This permitted inference whether herbaceous species may affect the favorableness of the soil for establishment of these trees. Weibull distributions were fitted to the time course of aggregate seedling emergence and post-emergence mortality, enabling seedling lifespan to be inferred without monitoring of each individual. A higher percentage of Abies seeds developed into emerged seedlings in the goutweed soil, likely because of less preemergence mortality incited by pathogens. Picea and Pinus emergence percentages were similar in both soils. Most emerged seedlings died within weeks, with symptoms of diseases incited by soilâ or seedâborne fungi. Although the timing of seedling emergence did not differ between soils, seedlings died more quickly on the goutweed soil, largely because of a faster development of postâemergence dampingâoff. Total post-emergence mortality of Picea and Pinus was greater on the goutweed soil. The relative frequencies of the several symptoms exhibited by dying seedlings varied between the two soils, suggesting that the groundâlayer species differentially affected the microbial communityâs composition or interactions with the seedlings. Symptom frequencies differed among tree species. Local spatial variation in herbaceous species composition appeared to produce patchy infectious lethality of soil for tree seedlings, an indirect effect that was observed after the herbaceous plants had been removed
Degradation Kinetics of Lignocellulolytic Enzymes in a Biogas Reactor Using Quantitative Mass Spectrometry
The supplementation of lignocellulose-degrading enzymes can be used to enhance the performance of biogas production in industrial biogas plants. Since the structural stability of these enzyme preparations is essential for efficient application, reliable methods for the assessment of enzyme stability are crucial. Here, a mass-spectrometric-based assay was established to monitor the structural stability of enzymes, i.e., the structural integrity of these proteins, in anaerobic digestion (AD). The analysis of extracts of Lentinula edodes revealed the rapid degradation of lignocellulose-degrading enzymes, with an approximate half-life of 1.5 h. The observed low structural stability of lignocellulose-degrading enzymes in AD corresponded with previous results obtained for biogas content. The established workflow can be easily adapted for the monitoring of other enzyme formulations and provides a platform for evaluating the effects of enzyme additions in AD, together with a characterization of the biochemical methane potential used in order to determine the biodegradability of organic substrates
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