5,608 research outputs found
The Zeta Function Method and the Harmonic Oscillator Propagator
We show how the pre-exponential factor of the Feynman propagator for the
harmonic oscillator can be computed by the generalized -function method.
Besides, we establish a direct equivalence between this method and Schwinger's
propertime method.Comment: 12 latex pages, no figure
One-dimensional symmetry and Liouville type results for the fourth order Allen-Cahn equation in R
In this paper, we prove an analogue of Gibbons' conjecture for the extended
fourth order Allen-Cahn equation in R N , as well as Liouville type results for
some solutions converging to the same value at infinity in a given direction.
We also prove a priori bounds and further one-dimensional symmetry and rigidity
results for semilinear fourth order elliptic equations with more general
nonlinearities
Advances in surface EMG signal simulation with analytical and numerical descriptions of the volume conductor
Surface electromyographic (EMG) signal modeling is important for signal interpretation, testing of processing algorithms, detection system design, and didactic purposes. Various surface EMG signal models have been proposed in the literature. In this study we focus on 1) the proposal of a method for modeling surface EMG signals by either analytical or numerical descriptions of the volume conductor for space-invariant systems, and 2) the development of advanced models of the volume conductor by numerical approaches, accurately describing not only the volume conductor geometry, as mainly done in the past, but also the conductivity tensor of the muscle tissue. For volume conductors that are space-invariant in the direction of source propagation, the surface potentials generated by any source can be computed by one-dimensional convolutions, once the volume conductor transfer function is derived (analytically or numerically). Conversely, more complex volume conductors require a complete numerical approach. In a numerical approach, the conductivity tensor of the muscle tissue should be matched with the fiber orientation. In some cases (e.g., multi-pinnate muscles) accurate description of the conductivity tensor may be very complex. A method for relating the conductivity tensor of the muscle tissue, to be used in a numerical approach, to the curve describing the muscle fibers is presented and applied to representatively investigate a bi-pinnate muscle with rectilinear and curvilinear fibers. The study thus propose an approach for surface EMG signal simulation in space invariant systems as well as new models of the volume conductor using numerical methods
Beta inputs to motor neurons do not directly contribute to volitional force modulation
Neural oscillatory activity in the beta band (13–30 Hz) is prominent in the brain and it is transmitted partly linearly to the spinal cord and muscles. Multiple views on the functional relevance of beta activity in the motor system have been proposed. Previous simulation work suggested that pools of spinal motoneurons (MNs) receiving a common beta input could demodulate this activity, transforming it into low-frequency neural drive that could alter force production in muscles. This may suggest that common beta inputs to muscles have a direct role in force modulation. Here we report the experimental average levels and ranges of common beta activity in spinal MNs projecting to single muscles and use a computational model of a MN pool to test if the experimentally observed beta levels in MNs can influence force. When beta was modelled as a continuous activity, the amplitude needed to produce non-negligible changes in force corresponded to beta representation in the MN pool that was far above the experimental observations. On the other hand, when beta activity was modelled as short-lived events (i.e. bursts of beta activity separated by intervals without beta oscillations), this activity approximated levels that could cause small changes in force with estimated average common beta inputs to the MNs compatible with the experimental observations. Nonetheless, bursting beta is unlikely to be used for force control due to the temporal sparsity of this activity. It is therefore concluded that beta oscillations are unlikely to contribute to the voluntary modulation of force
Anaesthesia training for interns at a metropolitan training complex: does it make the grade?
Background: Most anaesthesia-related mortality that occurs in level 1 hospitals in South Africa is avoidable. Improving training during internship, and consequently the skills of community service officers, could lead to safer anaesthesia practices.Objectives: The objectives of the study were to determine whether or not the timing of the anaesthesia rotation during internship and other factors affected the outcome of the assessment at the end of the anaesthesia rotation, and to compare the perceptions of first- and second-year interns regarding their confidence levels at the end of their rotation.Method: We conducted a retrospective study that compared 298 intern assessments over a three-year period. It included the assessment of interns by senior doctors in respect of three cases, an overall assessment of the interns’ performance, and the number of cases carried out by them. In addition, a questionnaire was used to assess the interns’ confidence levels at the end of the rotation.Results: Little variation in the results was evident across comparisons of the year of internship, gender and age. Comparison according to university showed a slight variation. A wide variation in the number of obstetric cases (range 5–58) and endotracheal intubations (range 6–54) was observed. Over 80% of interns, regardless of the year, were confident enough to administer general anaesthesia and perform an endotracheal intubation. However, this perception of confidence by interns did not relate to the assessment of their competence.Conclusion: The variance in the ability of interns to perform anaesthesia could not be accounted for by the training year, institution of undergraduate study, age or gender. It is likely that the assessment technique used did not provide a true reflection of the acquired skills or longevity of knowledge by interns. Further research in this area is recommended.Keywords: anaesthesia, interns, training, standard
Bioactivity of the Andean aromatic plants Aloysia citriodora and Bursera graveolens essential oils against the blowfly Calliphora vomitoria
Tropical Andes is a biodiversity hot spot rich in aromatic plant species, whose potential as a source
of active compounds for insect pests’ control is still largely underexploited. Here, the Essential Oils
(EOs) extracted from two Ecuadorian plants, the shrub Aloysia citriodora (Verbenaceae) and the
tree Bursera graveolens (Burseraceae), were chemically analysed and tested for their bioactivity
against the blue blowfly Calliphora vomitoria (Linnaeus, 1758) (Diptera: Calliphoridae). This fly is a
vector of pathogenic microorganisms, dangerous in factories and stores where fresh meat is
processed, stored, and sold. The main components of the A. citriodora EO are geranial and
limonene, while in the B. graveolens EO they are limonene and α-terpineol. The effects of the two
EOs were evaluated against C. vomitoria by a behavioural assay in a two-choice olfactometer
(concentrations range 0.07-2.8 ÎĽL L-1 air). Besides, the insecticidal properties of the two EOs were
tested by fumigation (EOs concentrations from 6.06 to 36.36 ÎĽL L-1 air), by contact with topical
applications using a Burkard micro dispenser (EOs dose from 0.10 to 0.60 ÎĽl EO/fly), and by
ingestion of a mucilage containing EOs (from 15 to 75 ÎĽl EO mL-1 mucilage), sucrose, and agarose.
Furthermore, the ovicidal activity was assessed (concentrations from 0.006 to 0.075 ÎĽL EO cm-2 of
filter paper). The results of the behavioural assay showed a stronger repellent effect exerted by
the A. citriodora EO, while all the toxicity tests revealed dose-dependent mortality of the blowflies
and eggs
Effective action in DSR1 quantum field theory
We present the one-loop effective action of a quantum scalar field with DSR1
space-time symmetry as a sum over field modes. The effective action has real
and imaginary parts and manifest charge conjugation asymmetry, which provides
an alternative theoretical setting to the study of the particle-antiparticle
asymmetry in nature.Comment: 8 page
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