1,377 research outputs found
Focus and setting in mobile learning research: a review of the literature
Mobile learning (mLearning) is an ubiquitous learning activity supported by the appropriate mobile technology and pedagogical approach. Mobile learning research has experienced a significant growth in the last half a decade, following the increase in innovative applications and the expansion of the contexts in which mLearning is deployed. Based on a review of publications found in international conference proceedings and journals, this study classifies mLearning research according to its focus, and proposes a classification framework. Patterns in shifting research focus are identified and some defining characteristics of the approaches undertaken are elicited. The results of the analysis show that while mobile learning research continues to be motivated by the innovative mobile technology it is also increasingly concerned with the development of a theoretical foundation in order to underpin the new paradigm and inform contemporary mobile learning design and practice
Comparing Geometrical and Delay Radio Emission Heights in Pulsars
We use a set of carefully selected published average multifrequency
polarimetric observations for six bright cone dominated pulsars and devise a
method to combine the multifrequency polarization position angle (PPA) sweep
traverses. We demonstrate that the PPA traverse is in excellent agreement with
the rotating vector model over this broad frequency range confirming that radio
emission emanates from perfectly dipolar field lines.
For pulsars with central core emission in our sample, we find the peak of
central core component to lag the steepest gradient of the PPA traverse at
several frequencies. Also significant frequency evolution of the core width is
observed over this frequency range. The above facts strongly suggest: (a) the
peak core emission does not lie on the fiducial plane containing the dipole
magnetic axis and the rotation axis, and (b) the core emission does not
originate from the polar cap surface.Comment: Accepted for publication in Astronomy and Astrophysic
Axisymmetric force-free magnetosphere of a pulsar. I. The structure close to the magnetic axis
The stationary axisymmetric force-free magnetosphere of a pulsar is studied
analytically. The pulsar equation is solved in the region close to the magnetic
axis. Proceeding from linearization of the current function in the axial
region, we find the axial magnetic flux function valid at any altitude above
the neutron star. This function is used as a starting approximation to develop
series for the non-linear pulsar equation in the polar region. Taking into
account the quasi-monopolar character of the pulsar magnetic flux at infinity,
we obtain unique asymptotic series for the flux and current functions. At
infinity, both functions are close but not equivalent to those known for the
case of a force-free monopole. The flux function at the top of the polar gap is
found to differ from the dipolar one at the neutron star surface. With our
results, the transverse current sheet closing the pulsar circuit at the neutron
star surface is consistently incorporated into the global magnetospheric
structure, the backward particle flow at small polar angles can be excluded and
the stationary cascade scenario looks admissible. The present paper is the
first step toward complete analytic description of the pulsar force-free
magnetosphere allowing for the plasma-producing gaps and pulsar current circuit
closure.Comment: 8 pages, 2 figures; accepted for publication in MNRA
BdlA, DipA and Induced Dispersion Contribute to Acute Virulence and Chronic Persistence of Pseudomonas aeruginosa
The human pathogen Pseudomonas aeruginosa is capable of causing both acute and chronic infections. Differences in virulence are attributable to the mode of growth: bacteria growing planktonically cause acute infections, while bacteria growing in matrix-enclosed aggregates known as biofilms are associated with chronic, persistent infections. While the contribution of the planktonic and biofilm modes of growth to virulence is now widely accepted, little is known about the role of dispersion in virulence, the active process by which biofilm bacteria switch back to the planktonic mode of growth. Here, we demonstrate that P. aeruginosa dispersed cells display a virulence phenotype distinct from those of planktonic and biofilm cells. While the highest activity of cytotoxic and degradative enzymes capable of breaking down polymeric matrix components was detected in supernatants of planktonic cells, the enzymatic activity of dispersed cell supernatants was similar to that of biofilm supernatants. Supernatants of non-dispersing Delta bdlA biofilms were characterized by a lack of many of the degradative activities. Expression of genes contributing to the virulence of P. aeruginosa was nearly 30-fold reduced in biofilm cells relative to planktonic cells. Gene expression analysis indicated dispersed cells, while dispersing from a biofilm and returning to the single cell lifestyle, to be distinct from both biofilm and planktonic cells, with virulence transcript levels being reduced up to 150-fold compared to planktonic cells. In contrast, virulence gene transcript levels were significantly increased in non-dispersing Delta bdlA and Delta dipA biofilms compared to wild-type planktonic cells. Despite this, bdlA and dipA inactivation, resulting in an inability to disperse in vitro, correlated with reduced pathogenicity and competitiveness in cross-phylum acute virulence models. In contrast, bdlA inactivation rendered P. aeruginosa more persistent upon chronic colonization of the murine lung, overall indicating that dispersion may contribute to both acute and chronic infections
Spatially hybrid computations for streamer discharges: II. Fully 3D simulations
We recently have presented first physical predictions of a spatially hybrid
model that follows the evolution of a negative streamer discharge in full three
spatial dimensions; our spatially hybrid model couples a particle model in the
high field region ahead of the streamer with a fluid model in the streamer
interior where electron densities are high and fields are low. Therefore the
model is computationally efficient, while it also follows the dynamics of
single electrons including their possible run-away. Here we describe the
technical details of our computations, and present the next step in a
systematic development of the simulation code. First, new sets of transport
coefficients and reaction rates are obtained from particle swarm simulations in
air, nitrogen, oxygen and argon. These coefficients are implemented in an
extended fluid model to make the fluid approximation as consistent as possible
with the particle model, and to avoid discontinuities at the interface between
fluid and particle regions. Then two splitting methods are introduced and
compared for the location and motion of the fluid-particle-interface in three
spatial dimensions. Finally, we present first results of the 3D spatially
hybrid model for a negative streamer in air
On Hilberg's Law and Its Links with Guiraud's Law
Hilberg (1990) supposed that finite-order excess entropy of a random human
text is proportional to the square root of the text length. Assuming that
Hilberg's hypothesis is true, we derive Guiraud's law, which states that the
number of word types in a text is greater than proportional to the square root
of the text length. Our derivation is based on some mathematical conjecture in
coding theory and on several experiments suggesting that words can be defined
approximately as the nonterminals of the shortest context-free grammar for the
text. Such operational definition of words can be applied even to texts
deprived of spaces, which do not allow for Mandelbrot's ``intermittent
silence'' explanation of Zipf's and Guiraud's laws. In contrast to
Mandelbrot's, our model assumes some probabilistic long-memory effects in human
narration and might be capable of explaining Menzerath's law.Comment: To appear in Journal of Quantitative Linguistic
Uncoupling DISC1 × D2R Protein-Protein Interactions Facilitates Latent Inhibition in Disc1-L100P Animal Model of Schizophrenia and Enhances Synaptic Plasticity via D2 Receptors
Both Disrupted-In-Schizophrenia-1 (DISC1) and dopamine receptors D2R have significant contributions to the pathogenesis of schizophrenia. Our previous study demonstrated that DISC1 binds to D2R and such protein-protein interaction is enhanced in patients with schizophrenia and Disc1-L100P mouse model of schizophrenia (Su et al., 2014). By uncoupling DISC1 × D2R interaction (trans-activator of transcription (TAT)-D2pep), the synthesized TAT-peptide elicited antipsychotic-like effects in pharmacological and genetic animal models, without motor side effects as tardive dyskinesia commonly seen with typical antipsychotic drugs (APDs), indicating that the potential of TAT-D2pep of becoming a new APD. Therefore, in the current study, we further explored the APD-associated capacities of TAT-D2pep. We found that TAT-D2pep corrected the disrupted latent inhibition (LI), as a hallmark of schizophrenia associated endophenotype, in Disc1-L100P mutant mice—a genetic model of schizophrenia, supporting further APD’ capacity of TAT-D2pep. Moreover, we found that TAT-D2pep elicited nootropic effects in C57BL/6NCrl inbred mice, suggesting that TAT-D2pep acts as a cognitive enhancer, a desirable feature of APDs of the new generation. Namely, TAT-D2pep improved working memory in T-maze, and cognitive flexibility assessed by the LI paradigm, in C57BL/6N mice. Next, we assessed the impact of TAT-D2pep on hippocampal long-term plasticity (LTP) under basal conditions and upon stimulation of D2 receptors using quinpirole. We found comparable effects of TAT-D2pep and its control TAT-D2pep-scrambled peptide (TAT-D2pep-sc) under basal conditions. However, under stimulation of D2R by quinpirole, LTP was enhanced in hippocampal slices incubated with TAT-D2pep, supporting the notion that TAT-D2pep acts in a dopamine-dependent manner and acts as synaptic enhancer. Overall, our experiments demonstrated implication of DISC1 × D2R protein-protein interactions into mechanisms of cognitive and synaptic plasticity, which help to further understand molecular-cellular mechanisms of APD of the next generation
Alterations to nuclear architecture and genome behavior in senescent cells.
The organization of the genome within interphase nuclei, and how it interacts with nuclear structures is important for the regulation of nuclear functions. Many of the studies researching the importance of genome organization and nuclear structure are performed in young, proliferating, and often transformed cells. These studies do not reveal anything about the nucleus or genome in nonproliferating cells, which may be relevant for the regulation of both proliferation and replicative senescence. Here, we provide an overview of what is known about the genome and nuclear structure in senescent cells. We review the evidence that nuclear structures, such as the nuclear lamina, nucleoli, the nuclear matrix, nuclear bodies (such as promyelocytic leukemia bodies), and nuclear morphology all become altered within growth-arrested or senescent cells. Specific alterations to the genome in senescent cells, as compared to young proliferating cells, are described, including aneuploidy, chromatin modifications, chromosome positioning, relocation of heterochromatin, and changes to telomeres
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