1,760 research outputs found
Non-adiabatic pumping in an oscillating-piston model
We consider the prototypical "piston pump" operating on a ring, where a
circulating current is induced by means of an AC driving. This can be regarded
as a generalized Fermi-Ulam model, incorporating a finite-height moving wall
(piston) and non trivial topology (ring). The amount of particles transported
per cycle is determined by a layered structure of phase-space. Each layer is
characterized by a different drift velocity. We discuss the differences
compared with the adiabatic and Boltzmann pictures, and highlight the
significance of the "diabatic" contribution that might lead to a
counter-stirring effect.Comment: 6 pages, 4 figures, improved versio
A systematic literature review on the development and use of mobile learning (web) apps by early adopters
Surveys in mobile learning developed so far have analysed in a global way the
effects on the usage of mobile devices by means of general apps or apps already
developed. However, more and more teachers are developing their own apps to
address issues not covered by existing m-learning apps. In this article, by
means of a systematic literature review that covers 62 publications placed in
the hype of teacher-created m-learning apps (between 2012 and 2017, the early
adopters) and the usage of 71 apps, we have analysed the use of specific
m-learning apps. Our results show that apps have been used both out of the
classroom to develop autonomous learning or field trips, and in the classroom,
mainly, for collaborative activities. The experiences analysed only develop low
level outcomes and the results obtained are positive improving learning,
learning performance, and attitude. As a conclusion of this study is that the
results obtained with specific developed apps are quite similar to previous
general surveys and that the development of long-term experiences are required
to determine the real effect of instructional designs based on mobile devices.
These designs should also be oriented to evaluate high level skills and take
advantage of mobile features of mobile devices to develop learning activities
that be made anytime at anyplace and taking into account context and realistic
situations. Furthermore, it is considered relevant the study of the role of
educational mobile development frameworks in facilitating teachers the
development of m-learning apps
Glacial-interglacial vegetation dynamics in South Eastern Africa coupled to sea surface temperature variations in the Western Indian Ocean
Glacial-interglacial fluctuations in the vegetation of South Africa might elucidate the climate system at the edge of the tropics between the Indian and Atlantic Oceans. However, vegetation records covering a full glacial cycle have only been published from the eastern South Atlantic. We present a pollen record of the marine core MD96-2048 retrieved by the Marion Dufresne from the Indian Ocean similar to 120 km south of the Limpopo River mouth. The sedimentation at the site is slow and continuous. The upper 6 m (spanning the past 342 Ka) have been analysed for pollen and spores at millennial resolution. The terrestrial pollen assemblages indicate that during interglacials, the vegetation of eastern South Africa and southern Mozambique largely consisted of evergreen and deciduous forests. During glacials open mountainous scrubland dominated. Montane forest with Podocarpus extended during humid periods was favoured by strong local insolation. Correlation with the sea surface temperature record of the same core indicates that the extension of mountainous scrubland primarily depends on sea surface temperatures of the Agulhas Current. Our record corroborates terrestrial evidence of the extension of open mountainous scrubland (including fynbos-like species of the high-altitude Grassland biome) for the last glacial as well as for other glacial periods of the past 300 Ka
Early feeding to modify digestive enzyme activity in broiler chickens
Objective. To evaluate the effect on digestive enzyme activity in broiler chickens by providing food in the first 48 hrs. after birth. Materials and methods. After incubating 300 fertile eggs from Hubbard breeding and immediately after hatching, the chicks were randomly assigned to treatments: fasting (from hatching to 48 hrs.); Hydrated Balanced Food (HBF) from birth to 48 hrs.; commercial hydrating supplement (CHS) from birth to 48 hrs. The diets were provided ad libitum. After 48 hrs. a commercial diet was fed. At birth and at 48 and 72 hrs. of age 30 chicks/treatment were sacrificed to determine the enzyme activity of maltase, sucrase, alkaline phosphatase, phytase, a-amylase, trypsin and lipase in samples of duodenal or pancreatic homogenate. Results. The supply of HBF or CHS during the first 48 hrs. of life increased the activity of maltase, sucrase and phytase in the first 3 days of life, with values between 1.2 and up to 4-fold compared to the control (p<0.05). Chickens that fasted for the first 48 hrs. had higher activity of the pancreatic enzymes a-amylase, trypsin, and lipase at 72 hrs. of life (p<0.05). Conclusions. The food supply in the first 48 hrs. after hatching increases the duodenal enzyme activity in the intestinal brush border during the first 3 days of age in broiler chickens
Recommended from our members
Association Between High Perceived Stress Over Time and Incident Hypertension in Black Adults: Findings From the Jackson Heart Study.
Background Chronic psychological stress has been associated with hypertension, but few studies have examined this relationship in blacks. We examined the association between perceived stress levels assessed annually for up to 13 years and incident hypertension in the Jackson Heart Study, a community-based cohort of blacks. Methods and Results Analyses included 1829 participants without hypertension at baseline (Exam 1, 2000-2004). Incident hypertension was defined as blood pressureâ„140/90 mm Hg or antihypertensive medication use at Exam 2 (2005-2008) or Exam 3 (2009-2012). Each follow-up interval at risk of hypertension was categorized as low, moderate, or high perceived stress based on the number of annual assessments between exams in which participants reported "a lot" or "extreme" stress over the previous year (low, 0 high stress ratings; moderate, 1 high stress rating; high, â„2 high stress ratings). During follow-up (median, 7.0 years), hypertension incidence was 48.5%. Hypertension developed in 30.6% of intervals with low perceived stress, 34.6% of intervals with moderate perceived stress, and 38.2% of intervals with high perceived stress. Age-, sex-, and time-adjusted risk ratios (95% CI) associated with moderate and high perceived stress versus low perceived stress were 1.19 (1.04-1.37) and 1.37 (1.20-1.57), respectively (P trend<0.001). The association was present after adjustment for demographic, clinical, and behavioral factors and baseline stress (P trend=0.001). Conclusions In a community-based cohort of blacks, higher perceived stress over time was associated with an increased risk of developing hypertension. Evaluating stress levels over time and intervening when high perceived stress is persistent may reduce hypertension risk
Boundary conditions: The path integral approach
The path integral approach to quantum mechanics requires a substantial
generalisation to describe the dynamics of systems confined to bounded domains.
Non-local boundary conditions can be introduced in Feynman's approach by means
of boundary amplitude distributions and complex phases to describe the quantum
dynamics in terms of the classical trajectories. The different prescriptions
involve only trajectories reaching the boundary and correspond to different
choices of boundary conditions of selfadjoint extensions of the Hamiltonian.
One dimensional particle dynamics is analysed in detail.Comment: 8 page
Nonadiabatic pumping in classical and quantum chaotic scatterers
We study directed transport in periodically forced scattering systems in the
regime of fast and strong driving where the dynamics is mixed to chaotic and
adiabatic approximations do not apply. The model employed is a square potential
well undergoing lateral oscillations, alternatively as two- or single-parameter
driving. Mechanisms of directed transport are analyzed in terms of asymmetric
irregular scattering processes. Quantizing the system in the framework of
Floquet scattering theory, we calculate directed currents on basis of
transmission and reflection probabilities obtained by numerical wavepacket
scattering. We observe classical as well as quantum transport beyond linear
response, manifest in particular in a non-zero current for single-parameter
driving where according to adiabatic theory, it should vanish identically.Comment: 13 pages, 8 figure
Electrophysiological and morphological heterogeneity of slow firing neurons in medial septal/diagonal band complex as revealed by cluster analysis
Slow firing septal neurons modulate hippocampal and neocortical functions. Electrophysiologically, it is unclear whether slow firing neurons belong to a homogeneous neuronal population. To address this issue, whole-cell patch recordings and neuronal reconstructions were performed on rat brain slices containing the medial septum/diagonal band complex (MS/DB). Slow firing neurons were identified by their low firing rate at threshold (\u3c 5Hz) and lack of time-dependent inward rectification (Ih). Unsupervised cluster analysis was used to investigate whether slow firing neurons could be further classified into different subtypes. The parameters used for the cluster analysis included latency for first spike, slow afterhyperpolarizing potential, maximal frequency and action potential (AP) decay slope. Neurons were grouped into three major subtypes. The majority of neurons (55%) were grouped as cluster I. Cluster II (17% of neurons) exhibited longer latency for generation of the first action potential (246.5±20.1 ms). Cluster III (28% of neurons) exhibited higher maximal firing frequency (25.3±1.7 Hz) when compared to cluster I (12.3±0.9 Hz) and cluster II (11.8±1.1 Hz) neurons. Additionally, cluster III neurons exhibited faster action potentials at suprathreshold. Interestingly, cluster II neurons were frequently located in the medial septum whereas neurons in cluster I and III appeared scattered throughout all MS/DB regions. Shollâs analysis revealed a more complex dendritic arborization in cluster III neurons. Cluster I and II neurons exhibited characteristics of âtrueâ slow firing neurons whereas cluster III neurons exhibited higher frequency firing patterns. Several neurons were labeled with a cholinergic marker, Cy3-conjugated 192 IgG (p75NTR), and cholinergic neurons were found to be distributed among the three clusters. Our findings indicate that slow firing medial septal neurons are heterogeneous and that soma location is an important determinant of their electrophysiological properties. Thus, slow firing neurons from different septal regions have distinct functional properties, most likely related to their diverse connectivity
Vacuum Energy and Renormalization on the Edge
The vacuum dependence on boundary conditions in quantum field theories is
analysed from a very general viewpoint. From this perspective the
renormalization prescriptions not only imply the renormalization of the
couplings of the theory in the bulk but also the appearance of a flow in the
space of boundary conditions. For regular boundaries this flow has a large
variety of fixed points and no cyclic orbit. The family of fixed points
includes Neumann and Dirichlet boundary conditions. In one-dimensional field
theories pseudoperiodic and quasiperiodic boundary conditions are also RG fixed
points. Under these conditions massless bosonic free field theories are
conformally invariant. Among all fixed points only Neumann boundary conditions
are infrared stable fixed points. All other conformal invariant boundary
conditions become unstable under some relevant perturbations. In finite volumes
we analyse the dependence of the vacuum energy along the trajectories of the
renormalization group flow providing an interesting framework for dark energy
evolution. On the contrary, the renormalization group flow on the boundary does
not affect the leading behaviour of the entanglement entropy of the vacuum in
one-dimensional conformally invariant bosonic theories.Comment: 10 pages, 1 eps figur
- âŠ