4,453 research outputs found
Searching for Scalar Dark Matter in Atoms and Astrophysical Phenomena: Variation of Fundamental Constants
We propose to search for scalar dark matter via its effects on the
electromagnetic fine-structure constant and particle masses. Scalar dark matter
that forms an oscillating classical field produces `slow' linear-in-time drifts
and oscillating variations of the fundamental constants, while scalar dark
matter that forms topological defects produces transient-in-time variations of
the constants of Nature. These variations can be sought for with atomic clock,
laser interferometer and pulsar timing measurements. Atomic spectroscopy and
Big Bang nucleosynthesis measurements already give improved bounds on the
quadratic interaction parameters of scalar dark matter with the photon,
electron, and light quarks by up to 15 orders of magnitude, while Big Bang
nucleosynthesis measurements provide the first such constraints on the
interaction parameters of scalar dark matter with the massive vector bosons.Comment: 4 pages, 1 figure, Contributed to the 11th Patras Workshop on Axions,
WIMPs and WISPs, Zaragoza, June 22 to 26, 201
Evaluating weaknesses of "perceptual-cognitive training" and "brain training" methods in sport: An ecological dynamics critique
The recent upsurge in "brain training and perceptual-cognitive training," proposing to improve isolated processes, such as brain function, visual perception, and decision-making, has created significant interest in elite sports practitioners, seeking to create an "edge" for athletes. The claims of these related "performance-enhancing industries" can be considered together as part of a process training approach proposing enhanced cognitive and perceptual skills and brain capacity to support performance in everyday life activities, including sport. For example, the "process training industry" promotes the idea that playing games not only makes you a better player but also makes you smarter, more alert, and a faster learner. In this position paper, we critically evaluate the effectiveness of both types of process training programmes in generalizing transfer to sport performance. These issues are addressed in three stages. First, we evaluate empirical evidence in support of perceptual-cognitive process training and its application to enhancing sport performance. Second, we critically review putative modularized mechanisms underpinning this kind of training, addressing limitations and subsequent problems. Specifically, we consider merits of this highly specific form of training, which focuses on training of isolated processes such as cognitive processes (attention, memory, thinking) and visual perception processes, separately from performance behaviors and actions. We conclude that these approaches may, at best, provide some "general transfer" of underlying processes to specific sport environments, but lack "specificity of transfer" to contextualize actual performance behaviors. A major weakness of process training methods is their focus on enhancing the performance in body "modules" (e.g., eye, brain, memory, anticipatory sub-systems). What is lacking is evidence on how these isolated components are modified and subsequently interact with other process "modules," which are considered to underlie sport performance. Finally, we propose how an ecological dynamics approach, aligned with an embodied framework of cognition undermines the rationale that modularized processes can enhance performance in competitive sport. An ecological dynamics perspective proposes that the body is a complex adaptive system, interacting with performance environments in a functionally integrated manner, emphasizing that the inter-relation between motor processes, cognitive and perceptual functions, and the constraints of a sport task is best understood at the performer-environment scale of analysis
Scale-dependent angle of alignment between velocity and magnetic field fluctuations in solar wind turbulence
Under certain conditions, freely decaying magnetohydrodynamic (MHD) turbulence evolves in such a way that velocity and magnetic field fluctuations delta v and delta B approach a state of alignment in which delta v proportional to delta B. This process is called dynamic alignment. Boldyrev has suggested that a similar kind of alignment process occurs as energy cascades from large to small scales through the inertial range in strong incompressible MHD turbulence. In this study, plasma and magnetic field data from the Wind spacecraft, data acquired in the ecliptic plane near 1 AU, are employed to investigate the angle theta(tau) between velocity and magnetic field fluctuations in the solar wind as a function of the time scale tau of the fluctuations and to look for the scaling relation similar to tau(1/4) predicted by Boldyrev. We find that the angle appears to scale like a power law at large inertial range scales, but then deviates from power law behavior at medium to small inertial range scales. We also find that small errors in the velocity vector measurements can lead to large errors in the angle measurements at small time scales. As a result, we cannot rule out the possibility that the observed deviations from power law behavior arise from errors in the velocity measurements. When we fit the data from 2 x 10(3) s to 2 x 10(4) s with a power law of the form proportional to tau(p), our best fit values for p are in the range 0.27-0.36
Accessing High Momentum States In Lattice QCD
Two measures are defined to evaluate the coupling strength of smeared
interpolating operators to hadronic states at a variety of momenta. Of
particular interest is the extent to which strong overlap can be obtained with
individual high-momentum states. This is vital to exploring hadronic structure
at high momentum transfers on the lattice and addressing interesting phenomena
observed experimentally. We consider a novel idea of altering the shape of the
smeared operator to match the Lorentz contraction of the probability
distribution of the high-momentum state, and show a reduction in the relative
error of the two-point function by employing this technique. Our most important
finding is that the overlap of the states becomes very sharp in the smearing
parameters at high momenta and fine tuning is required to ensure strong overlap
with these states.Comment: 10 page
Search for domain wall dark matter with atomic clocks on board global positioning system satellites
Cosmological observations indicate that 85% of all matter in the Universe is
dark matter (DM), yet its microscopic composition remains a mystery. One
hypothesis is that DM arises from ultralight quantum fields that form
macroscopic objects such as topological defects. Here we use GPS as a ~ 50,000
km aperture DM detector to search for such defects in the form of domain walls.
GPS navigation relies on precision timing signals furnished by atomic clocks
hosted on board GPS satellites. As the Earth moves through the galactic DM
halo, interactions with topological defects could cause atomic clock glitches
that propagate through the GPS satellite constellation at galactic velocities ~
300 km/s. Mining 16 years of archival GPS data, we find no evidence for DM in
the form of domain walls at our current sensitivity level. This allows us to
improve the limits on certain quadratic scalar couplings of domain wall DM to
standard model particles by several orders of magnitude.Comment: 7 pages (main text), and 12 pages for Supplementary Information. v3:
Update titl
Ratcheting synthesis
Synthetic chemistry has traditionally relied on reactions between reactants of high chemical potential and transformations that proceed energetically downhill to either a global or local minimum (thermodynamic or kinetic control). Catalysts can be used to manipulate kinetic control, lowering activation energies to influence reaction outcomes. However, such chemistry is still constrained by the shape of one-dimensional reaction coordinates. Coupling synthesis to an orthogonal energy input can allow ratcheting of chemical reaction outcomes, reminiscent of the ways that molecular machines ratchet random thermal motion to bias conformational dynamics. This fundamentally distinct approach to synthesis allows multi-dimensional potential energy surfaces to be navigated, enabling reaction outcomes that cannot be achieved under conventional kinetic or thermodynamic control. In this Review, we discuss how ratcheted synthesis is ubiquitous throughout biology and consider how chemists might harness ratchet mechanisms to accelerate catalysis, drive chemical reactions uphill and programme complex reaction sequences.<br/
Chaordic learning systems: reconceptualising pedagogy for the digital age
This article focuses on an explorative and experimental project seeking to implement Chaordic Learning Systems (CLS) as a pedagogic approach in Higher Education. We outline a project that embraced technologies of Web 2.0 to show how both physical and virtual spaces can be used to support and develop a strong and dynamic learning community in which staff and students work alongside each other to co-produce learning resources. Drawing on theories of Communities of Practice and Situated Learning a new teaching framework was introduced to a Level 5 undergraduate module (7.5 ECTS credits) that had not, until this project, used both face-to-face and online learning tools to engage students in the critical and discursive debates pertaining to sport and physical culture. We undertook this project with the belief that Higher Education should be concerned with answering the calls of an increasingly digital society for whom learning is not restricted by the physical boundaries of the university or the political landscape within which learning finds itself
Magnetic Monopole Noise
Magnetic monopoles are hypothetical elementary particles exhibiting quantized
magnetic charge and quantized magnetic flux . A classic proposal for detecting such magnetic charges is to measure the
quantized jump in magnetic flux threading the loop of a superconducting
quantum interference device (SQUID) when a monopole passes through it.
Naturally, with the theoretical discovery that a plasma of emergent magnetic
charges should exist in several lanthanide-pyrochlore magnetic insulators,
including DyTiO, this SQUID technique was proposed for their direct
detection. Experimentally, this has proven extremely challenging because of the
high number density, and the generation-recombination (GR) fluctuations, of the
monopole plasma. Recently, however, theoretical advances have allowed the
spectral density of magnetic-flux noise due to GR
fluctuations of magnetic charge pairs to be determined. These
theories present a sequence of strikingly clear predictions for the
magnetic-flux noise signature of emergent magnetic monopoles. Here we report
development of a high-sensitivity, SQUID based flux-noise spectrometer, and
consequent measurements of the frequency and temperature dependence of
for DyTiO samples. Virtually all the elements
of predicted for a magnetic monopole plasma, including the
existence of intense magnetization noise and its characteristic frequency and
temperature dependence, are detected directly. Moreover, comparisons of
simulated and measured correlation functions of the magnetic-flux
noise imply that the motion of magnetic charges is strongly
correlated because traversal of the same trajectory by two magnetic charges of
same sign is forbidden
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