651 research outputs found
Renormalized transport of inertial particles in surface flows
Surface transport of inertial particles is investigated by means of the
perturbative approach, introduced by Maxey (J. Fluid Mech. 174, 441 (1987)),
which is valid in the case the deflections induced on the particle trajectories
by the fluid flow can be considered small. We consider a class of compressible
random velocity fields, in which the effect of recirculations is modelled by an
oscillatory component in the Eulerian time correlation profile. The main issue
we address here is whether fluid velocity fluctuations, in particular the
effect of recirculation, may produce nontrivial corrections to the streaming
particle velocity. Our result is that a small (large) degree of recirculation
is associated with a decrease (increase) of streaming with respect to a
quiescent fluid. The presence of this effect is confirmed numerically, away
from the perturbative limit. Our approach also allows us to calculate the
explicit expression for the eddy diffusivity, and to compare the efficiency of
diffusive and ballistic transport.Comment: 18 pages, 13 figures, submitted to JF
Eddy diffusivities of inertial particles under gravity
The large-scale/long-time transport of inertial particles of arbitrary mass
density under gravity is investigated by means of a formal multiple-scale
perturbative expansion in the scale-separation parametre between the carrier
flow and the particle concentration field. The resulting large-scale equation
for the particle concentration is determined, and is found to be diffusive with
a positive-definite eddy diffusivity. The calculation of the latter tensor is
reduced to the resolution of an auxiliary differential problem, consisting of a
coupled set of two differential equations in a (6+1)-dimensional coordinate
system (3 space coordinates plus 3 velocity coordinates plus time). Although
expensive, numerical methods can be exploited to obtain the eddy diffusivity,
for any desirable non-perturbative limit (e.g. arbitrary Stokes and Froude
numbers). The aforementioned large-scale equation is then specialized to deal
with two different relevant perturbative limits: i) vanishing of both Stokes
time and sedimenting particle velocity; ii) vanishing Stokes time and finite
sedimenting particle velocity. Both asymptotics lead to a greatly simplified
auxiliary differential problem, now involving only space coordinates and thus
easy to be tackled by standard numerical techniques. Explicit, exact
expressions for the eddy diffusivities have been calculated, for both
asymptotics, for the class of parallel flows, both static and time-dependent.
This allows us to investigate analytically the role of gravity and inertia on
the diffusion process by varying relevant features of the carrier flow, as e.g.
the form of its temporal correlation function. Our results exclude a universal
role played by gravity and inertia on the diffusive behaviour: regimes of both
enhanced and reduced diffusion may exist, depending on the detailed structure
of the carrier flow.Comment: 8 figures (12 plots), submitted to JF
Towards an Integrative Approach for Automated Literature Reviews Using Machine Learning
Due to a huge amount of scientific publications which are mostly stored as unstructured data, complexity and workload of the fundamental process of literature reviews increase constantly. Based on previous literature, we develop an artifact that partially automates the literature review process from collecting articles up to their evaluation. This artifact uses a custom crawler, the word2vec algorithm, LDA topic modeling, rapid automatic keyword extraction, and agglomerative hierarchical clustering to enable the automatic acquisition, processing, and clustering of relevant literature and subsequent graphical presentation of the results using illustrations such as dendrograms. Moreover, the artifact provides information on which topics each cluster addresses and which keywords they contain. We evaluate our artifact based on an exemplary set of 308 publications. Our findings indicate that the developed artifact delivers better results than known previous approaches and can be a helpful tool to support researchers in conducting literature reviews
Duality in Perturbation Theory and the Quantum Adiabatic Approximation
Duality is considered for the perturbation theory by deriving, given a series
solution in a small parameter, its dual series with the development parameter
being the inverse of the other. A dual symmetry in perturbation theory is
identified. It is then shown that the dual to the Dyson series in quantum
mechanics is given by a recent devised series having the adiabatic
approximation as leading order. A simple application of this result is given by
rederiving a theorem for strongly perturbed quantum systems.Comment: 9 pages, revtex. Improved english and presentation. Final version
accepted for publication by Physical Review
A modern review of the two-level approximation
The paradigm of the two-level atom is revisited and its perturbative analysis
is discussed in view of the principle of duality in perturbation theory. The
models we consider are a two-level atom and an ensemble of two-level atoms both
interacting with a single radiation mode. The aim is to see how the latter can
be actually used as an amplifier of quantum fluctuations to the classical level
through the thermodynamic limit of a very large ensemble of two-level atoms [M.
Frasca, Phys. Lett. A {\bf 283}, 271 (2001)] and how can remove Schr\"odinger
cat states. The thermodynamic limit can be very effective for producing both
classical states and decoherence on a quantum system that evolves without
dissipation. Decoherence without dissipation is indeed an effect of a single
two-level atom interacting with an ensemble of two-level atoms, a situation
that proves to be useful to understand recent experiments on nanoscale devices
showing unexpected disappearance of quantum coherence at very low temperatures.Comment: 20 pages, no figures. Revised version accepted for publication in
Annals of Physic
The Universality of the Fundamental Plane of E and S0 Galaxies. Spectroscopic data
We present here central velocity dispersion measurements for 325 early-type
galaxies in eight clusters and groups of galaxies, including new observations
for 212 galaxies. The clusters and groups are the A262, A1367, Coma (A1656),
A2634, Cancer and Pegasus clusters, and the NGC 383 and NGC 507 groups. The new
measurements were derived from medium dispersion spectra, that cover 600 A
centered on the Mg Ib triplet at lambda ~ 5175. Velocity dispersions were
measured using the Tonry & Davis cross-correlation method, with a typical
accuracy of 6%. A detailed comparison with other data sources is made.Comment: 12 pages, 5 tables, 3 figures, to appear in AJ. Note that tables 2
and 3 are in separate files, as they should be printed in landscape forma
ZD7288 enhances long-term depression at early postnatal medial perforant path-granule cell synapses
Hyperpolarization-activated, cyclic nucleotide-gated nonselective (HCN) channels modulate both membrane potential and resistance and play a significant role in synaptic plasticity. We compared the influence of HCN channels on long-term depression
(LTD) at the medial perforant path-granule cell synapse in early postnatal (P9–15) and adult (P30–60) rats. LTD was elicited
in P9–15 slices using low-frequency stimulation (LFS, 900 pulses, 1Hz; 80 ± 4% of baseline). Application of the specific HCN
channel blocker ZD7288 (10 μM) before LFS significantly enhanced LTD (62 ± 4%; P < 0.01), showing HCN channels restrain LTD induction. However, when ZD7288 was applied after LFS, LTD was similar to control values and significantly different from
the values obtained with ZD7288 application before LFS (81 ± 5%; P < 0.01), indicating that HCN channels do not modulate
LTD expression. LTD in slices from adult rats were only marginally lower compared to those in P9–15 slices (85 ± 6%), but bath
application of ZD7288 prior to LFS resulted in the same amount of LTD (85 ± 5%). HCN channels in adult tissue hence lose their modulatory effect. In conclusion, we found that HCN channels at the medial perforant path-granule cell synapse compromise
LFS-associated induction, but not expression of LTD in early postnatal, but not in adult, rats
Insights on physical behavior while working from home:An ecological momentary assessment study
Ever since the COVID-19 pandemic, working from home (WFH) has emerged as a common alternative work environment, but the possible influence on daily physical behavior (PB) (i.e., physical activity (PA), sedentary behavior (SB)) remains unclear. This study aimed to examine daily associations between PB and the work environment (i.e., WFH, working at the office (WAO)), as well as to explore and identify patterns of PB within each work environment. An observational study using a dual-accelerometer system to continuously assess PB for at least 5 days was conducted. The sample consisted of 55 participants providing 276 days of assessment. Additional demographic, contextual, and psychological variables were measured via baseline questionnaire and several smartphone prompts per day. To analyze the effects of the work environment on PB, multilevel analyses were conducted. For the identification of patterns within each work environment, latent class trajectory modelling was applied. Associations between the work environment and various PA parameters were found, indicating that WFH has a negative effect on MVPA time, steps, and physical activity intensity (MET), but a positive effect on short PA bouts (≤5 min). No associations between the work environment and any SB parameter (i.e., SB time, SB breaks, SB bouts) were found. Latent class trajectory modelling revealed three MVPA patterns for days WFH, and two patterns for days WAO. Given the growing prevalence of WFH and the positive health effects associated with MVPA, daily-tailored solutions to enhance MPVA while WFH are urgently needed.</p
Insights on physical behavior while working from home: An ecological momentary assessment study
Ever since the COVID-19 pandemic, working from home (WFH) has emerged as a common alternative work environment, but the possible influence on daily physical behavior (PB) (i.e., physical activity (PA), sedentary behavior (SB)) remains unclear. This study aimed to examine daily associations between PB and the work environment (i.e., WFH, working at the office (WAO)), as well as to explore and identify patterns of PB within each work environment.
An observational study using a dual-accelerometer system to continuously assess PB for at least 5 days was conducted. The sample consisted of 55 participants providing 276 days of assessment. Additional demographic, contextual, and psychological variables were measured via baseline questionnaire and several smartphone prompts per day. To analyze the effects of the work environment on PB, multilevel analyses were conducted. For the identification of patterns within each work environment, latent class trajectory modelling was applied.
Associations between the work environment and various PA parameters were found, indicating that WFH has a negative effect on MVPA time, steps, and physical activity intensity (MET), but a positive effect on short PA bouts (≤5 min). No associations between the work environment and any SB parameter (i.e., SB time, SB breaks, SB bouts) were found. Latent class trajectory modelling revealed three MVPA patterns for days WFH, and two patterns for days WAO.
Given the growing prevalence of WFH and the positive health effects associated with MVPA, daily-tailored solutions to enhance MPVA while WFH are urgently needed
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