12,426 research outputs found
Perturbations of Single-field Inflation in Modified Gravity Theory
In this paper, we study the case of single field inflation within the
framework of modified gravity theory where the gravity part has an arbitrary
form . Via a conformal transformation, this case can be transformed into
its Einstein frame where it looks like a two-field inflation model. However,
due to the existence of the isocurvature modes in such a
multi-degree-of-freedom (m.d.o.f.) system, the (curvature) perturbations are
not equivalent in two frames, so in despite of its convenience, it is illegal
to treat the perturbations in its Einstein frame as the "real" ones as we
always do for pure theory or single field with nonminimal coupling. Here
by pulling the results of curvature perturbations back into its original Jordan
frame, we show explicitly the power spectrum and spectral index of the
perturbations in the Jordan frame, as well as how it differs from the Einstein
frame. We also fit our results with the newest Planck data. Since there are
large parameter space in these models, we show that it is easy to fit the data
very well.Comment: 9 pages, 1 figure, substantially improved, matching with the
published versio
Disentangle plume-induced anisotropy in the velocity field in buoyancy-driven turbulence
We present a method of disentangling the anisotropies produced by the cliff
structures in turbulent velocity field and test it in the system of turbulent
Rayleigh-B\'{e}nard (RB) convection. It is found that in the RB system the
cliff structures in the velocity field are generated by thermal plumes. These
cliff structures induce asymmetry in the velocity increments, which leads us to
consider the plus and minus velocity structure functions (VSF). The plus
velocity increments exclude cliff structures, while the minus ones include
them. Our results show that the scaling exponents of the plus VSFs are in
excellent agreement with those predicted for homogeneous and isotropic
turbulence (HIT), whereas those of the minus VSFs exhibit significant
deviations from HIT expectations in places where thermal plumes abound. These
results demonstrate that plus and minus VSFs can be used to quantitatively
study the effect of cliff structures in the velocity field and to effectively
disentangle the associated anisotropies caused by these structures.Comment: 10 pages, 5 figure
A Search Strategy of Level-Based Flooding for the Internet of Things
This paper deals with the query problem in the Internet of Things (IoT).
Flooding is an important query strategy. However, original flooding is prone to
cause heavy network loads. To address this problem, we propose a variant of
flooding, called Level-Based Flooding (LBF). With LBF, the whole network is
divided into several levels according to the distances (i.e., hops) between the
sensor nodes and the sink node. The sink node knows the level information of
each node. Query packets are broadcast in the network according to the levels
of nodes. Upon receiving a query packet, sensor nodes decide how to process it
according to the percentage of neighbors that have processed it. When the
target node receives the query packet, it sends its data back to the sink node
via random walk. We show by extensive simulations that the performance of LBF
in terms of cost and latency is much better than that of original flooding, and
LBF can be used in IoT of different scales
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