18,166 research outputs found
A stability index for detonation waves in Majda's model for reacting flow
Using Evans function techniques, we develop a stability index for weak and
strong detonation waves analogous to that developed for shock waves in
[GZ,BSZ], yielding useful necessary conditions for stability. Here, we carry
out the analysis in the context of the Majda model, a simplified model for
reacting flow; the method is extended to the full Navier-Stokes equations of
reacting flow in [Ly,LyZ]. The resulting stability condition is satisfied for
all nondegenerate, i.e., spatially exponentially decaying, weak and strong
detonations of the Majda model in agreement with numerical experiments of [CMR]
and analytical results of [Sz,LY] for a related model of Majda and Rosales. We
discuss also the role in the ZND limit of degenerate, subalgebraically decaying
weak detonation and (for a modified, ``bump-type'' ignition function)
deflagration profiles, as discussed in [GS.1-2] for the full equations.Comment: 36 pages, 3 figure
Direct CP Violation in Untagged B-Meson Decays
Direct CP violation can exist in untagged, neutral B-meson decays to certain
self-conjugate, hadronic final states. It can occur if the resonances which
appear therein permit the identification of distinct, CP-conjugate states -- in
analogy to stereochemistry, we term such states ``CP-enantiomers.'' These
states permit the construction of a CP-odd amplitude combination in the
untagged decay rate, which is non-zero if direct CP violation is present. The
decay B\to \pi^+\pi^-\pi^0, containing the distinct CP-conjugate states \rho^+
\pi^- and \rho^- \pi^+, provides one such example of a CP-enantiomeric pair. We
illustrate the possibilities in various multi-particle final states.Comment: 8 pages, ReVTeX 4.
A Complete Theory of Everything (will be subjective)
Increasingly encompassing models have been suggested for our world. Theories
range from generally accepted to increasingly speculative to apparently bogus.
The progression of theories from ego- to geo- to helio-centric models to
universe and multiverse theories and beyond was accompanied by a dramatic
increase in the sizes of the postulated worlds, with humans being expelled from
their center to ever more remote and random locations. Rather than leading to a
true theory of everything, this trend faces a turning point after which the
predictive power of such theories decreases (actually to zero). Incorporating
the location and other capacities of the observer into such theories avoids
this problem and allows to distinguish meaningful from predictively meaningless
theories. This also leads to a truly complete theory of everything consisting
of a (conventional objective) theory of everything plus a (novel subjective)
observer process. The observer localization is neither based on the
controversial anthropic principle, nor has it anything to do with the
quantum-mechanical observation process. The suggested principle is extended to
more practical (partial, approximate, probabilistic, parametric) world models
(rather than theories of everything). Finally, I provide a justification of
Ockham's razor, and criticize the anthropic principle, the doomsday argument,
the no free lunch theorem, and the falsifiability dogma.Comment: 26 LaTeX page
Novel observables for exploring QCD collective evolution and quantum entanglement within individual jets
We postulate that non-perturbative QCD effects occurring during parton
fragmentation can result in collective effects of a multi-parton system,
reminiscent of those observed in high-energy hadronic or nuclear interactions
with large final-state particle multiplicity. Proton-proton collisions at the
Large Hadron Collider showed surprising signatures of a strongly interacting,
thermalized quark-gluon plasma, which was thought only to form in collisions of
large nuclear systems. Another puzzle observed earlier in
collisions is that production yields of various hadron species appear to follow
a thermal-like distribution with a common temperature. We propose searches for
thermal and collective properties resulting from parton fragmentation processes
using high multiplicity jets in high-energy elementary collisions. Several
novel observables are studied using the PYTHIA 8 Monte Carlo event generator.
Experimental observation of such collectivity will offer a new view of
non-perturbative QCD dynamics of multi-parton systems at the smallest scales.
Absence of any collective effects may offer new insights into the role of
quantum entanglement in the observed thermal behavior of particle production in
high energy collisions.Comment: 14 pages, 12 figures. Updated to mirror version accepted by journa
Semiclassical and relaxation limits of bipolar quantum hydrodynamic model
The global in-time semiclassical and relaxation limits of the bipolar quantum
hydrodynamic model for semiconductors are investigated in . We prove that
the unique strong solution converges globally in time to the strong solution of
classical bipolar hydrodynamical equation in the process of semiclassical limit
and to that of the classical Drift-Diffusion system under the combined
relaxation and semiclassical limits.Comment: 21 page
mGluR5 antagonism inhibits cocaine reinforcement and relapse by elevation of extracellular glutamate in the nucleus accumbens via a CB1 receptor mechanism.
Metabotropic glutamate receptor 5 (mGluR5) antagonism inhibits cocaine self-administration and reinstatement of drug-seeking behavior. However, the cellular and molecular mechanisms underlying this action are poorly understood. Here we report a presynaptic glutamate/cannabinoid mechanism that may underlie this action. Systemic or intra-nucleus accumbens (NAc) administration of the mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) dose-dependently reduced cocaine (and sucrose) self-administration and cocaine-induced reinstatement of drug-seeking behavior. The reduction in cocaine-taking and cocaine-seeking was associated with a reduction in cocaine-enhanced extracellular glutamate, but not cocaine-enhanced extracellular dopamine (DA) in the NAc. MPEP alone, when administered systemically or locally into the NAc, elevated extracellular glutamate, but not DA. Similarly, the cannabinoid CB1 receptor antagonist, rimonabant, elevated NAc glutamate, not DA. mGluR5s were found mainly in striatal medium-spiny neurons, not in astrocytes, and MPEP-enhanced extracellular glutamate was blocked by a NAc CB1 receptor antagonist or N-type Ca++ channel blocker, suggesting that a retrograde endocannabinoid-signaling mechanism underlies MPEP-induced glutamate release. This interpretation was further supported by our findings that genetic deletion of CB1 receptors in CB1-knockout mice blocked both MPEP-enhanced extracellular glutamate and MPEP-induced reductions in cocaine self-administration. Together, these results indicate that the therapeutic anti-cocaine effects of mGluR5 antagonists are mediated by elevation of extracellular glutamate in the NAc via an endocannabinoid-CB1 receptor disinhibition mechanism
Experiences with flipped learning in subjects in consecutive stages of a Civil Engineering programme
CONTEXT Flipped learning is an instructional approach which allows instructors the opportunity to use a blending of online and face to face learning activities. The main affordance of flipped learning is the opportunity to free up class time to allow students and instructors to engage in collaborative learning activities designed to consolidate and deepen conceptual understanding of the subject material. Research has shown that participating in flipped instruction can change the way students approach their studies and improve motivation. PURPOSE OR GOAL We are interested in students’ experience of the flipped environment, particularly their expectations of a learning environment, and the level of responsibility they take for their own learning. The purpose of this analysis is to create a baseline against which future instances of flipped learning can be compared. APPROACH Student perceptions of flipped instruction were investigated through survey responses and observations of students in a first year subject (Engineering Mechanics) a second year subject (Engineering Computations) and a third year subject (Construction Materials) in a Civil Engineering degree programme. In particular, students were asked to explain the impact of the flipped activities on their learning experience including any changes in how they approach their studies or managed their time. OUTCOMES Most students in each of the three subjects agreed that they ‘liked’ flipped instruction compared to the traditional lecture format. The majority of students in each subject also agreed that it is reasonable to expect students to prepare before attending a face to face session. However, some students made strong negative comments demonstrating how the flipped environment did not meet their expectations of how learning should be organised. This study suggests that students in the second and third year subjects were not necessarily showing signs of better self-regulation and time management skills or being more comfortable with taking more responsibility for their own learning. CONCLUSIONS Flipped learning challenges students to develop metacognitive skills such as time management, self-regulation and self-evaluation, while providing opportunities to deepen conceptual understanding of the subject material. Given the different experience of students, both within a particular subject and between subjects at different stages of their degree, we need to provide scaffolding to assist students to understand how to make the most of these learning opportunities, including how to approach them, evaluate their learning, develop their judgement and the required learning skills
CP Asymmetries in B to f_0 K_S Decays
We consider the branching ratio and the CP asymmetries in B to f_0(980)K_S
decay to the end of determining the deviation of the time-dependent CP
asymmetry from sin(2 beta) arising from Standard Model physics. We obtain Delta
S_{f_0 K_S} within the context of the QCD factorization framework for the B to
f_0(980)K_S decay amplitudes assuming the f_0(980) is a q\bar{q} state and
employing a random scan over the theoretical parameter space to assess the
possible range in Delta S_{f_0 K_S}. Imposing the value of the experimental
branching ratio within 1 sigma and 3 sigma, respectively, of its central value
as a constraint, we find the range of Delta S_{f_0 K_S} to be [0.018, 0.033]
for a scan in which the parameters are allowed to vary within 1 sigma of their
central values and the range [-0.019, 0.064] for a scan in which the parameters
vary within 3 sigma of their central values.Comment: 27 pages, 10 figures, references adde
The Histone Acetyltransferase MOF Is a Key Regulator of the Embryonic Stem Cell Core Transcriptional Network
SummaryPluripotent embryonic stem cells (ESCs) maintain self-renewal and the potential for rapid response to differentiation cues. Both ESC features are subject to epigenetic regulation. Here we show that the histone acetyltransferase Mof plays an essential role in the maintenance of ESC self-renewal and pluripotency. ESCs with Mof deletion lose characteristic morphology, alkaline phosphatase (AP) staining, and differentiation potential. They also have aberrant expression of the core transcription factors Nanog, Oct4, and Sox2. Importantly, the phenotypes of Mof null ESCs can be partially suppressed by Nanog overexpression, supporting the idea that Mof functions as an upstream regulator of Nanog in ESCs. Genome-wide ChIP-sequencing and transcriptome analyses further demonstrate that Mof is an integral component of the ESC core transcriptional network and that Mof primes genes for diverse developmental programs. Mof is also required for Wdr5 recruitment and H3K4 methylation at key regulatory loci, highlighting the complexity and interconnectivity of various chromatin regulators in ESCs
Information Evolution in Complex Networks
Many biological phenomena or social events critically depend on how
information evolves in complex networks. A seeming paradox of the information
evolution is the coexistence of local randomness, manifested as the stochastic
distortion of information content during individual-individual diffusion, and
global regularity, illustrated by specific non-random patterns of information
content on the network scale. The current research pursues to understand the
underlying mechanisms of such coexistence. Applying network dynamics and
information theory, we discover that a certain amount of information,
determined by the selectivity of networks to the input information, frequently
survives from random distortion. Other information will inevitably experience
distortion or dissipation, whose speeds are shaped by the diversity of
information selectivity in networks. The discovered laws exist irrespective of
noise, but the noise accounts for their intensification. We further demonstrate
the ubiquity of our discovered laws by applying them to analyze the emergence
of neural tuning properties in the primary visual and medial temporal cortices
of animal brains and the emergence of extreme opinions in social networks
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