676 research outputs found
Scaling behavior of online human activity
The rapid development of Internet technology enables human explore the web
and record the traces of online activities. From the analysis of these
large-scale data sets (i.e. traces), we can get insights about dynamic behavior
of human activity. In this letter, the scaling behavior and complexity of human
activity in the e-commerce, such as music, book, and movie rating, are
comprehensively investigated by using detrended fluctuation analysis technique
and multiscale entropy method. Firstly, the interevent time series of rating
behaviors of these three type medias show the similar scaling property with
exponents ranging from 0.53 to 0.58, which implies that the collective
behaviors of rating media follow a process embodying self-similarity and
long-range correlation. Meanwhile, by dividing the users into three groups
based their activities (i.e., rating per unit time), we find that the scaling
exponents of interevent time series in three groups are different. Hence, these
results suggest the stronger long-range correlations exist in these collective
behaviors. Furthermore, their information complexities vary from three groups.
To explain the differences of the collective behaviors restricted to three
groups, we study the dynamic behavior of human activity at individual level,
and find that the dynamic behaviors of a few users have extremely small scaling
exponents associating with long-range anticorrelations. By comparing with the
interevent time distributions of four representative users, we can find that
the bimodal distributions may bring the extraordinary scaling behaviors. These
results of analyzing the online human activity in the e-commerce may not only
provide insights to understand its dynamic behaviors but also be applied to
acquire the potential economic interest
Revisiting the Pion Leading-Twist Distribution Amplitude within the QCD Background Field Theory
We study the pion leading-twist distribution amplitude (DA) within the
framework of SVZ sum rules under the background field theory. To improve the
accuracy of the sum rules, we expand both the quark propagator and the vertex
(z\cdot \tensor{D})^n of the correlator up to dimension-six operators in the
background field theory. The sum rules for the pion DA moments are obtained, in
which all condensates up to dimension-six have been taken into consideration.
Using the sum rules, we obtain \left|_{\rm 1\;GeV} = 0.338 \pm
0.032, \left|_{\rm 1\;GeV} = 0.211 \pm 0.030 and
\left|_{\rm 1\;GeV} = 0.163 \pm 0.030. It is shown that the
dimension-six condensates shall provide sizable contributions to the pion DA
moments. We show that the first Gegenbauer moment of the pion leading-twist DA
is , which is consistent with those
obtained in the literature within errors but prefers a larger central value as
indicated by lattice QCD predictions.Comment: 13 pages, 7 figure
Constraint of -moments calculated with QCD sum rules on the pion distribution amplitude models
So far, the behavior of the pionic leading-twist distribution amplitude (DA)
which is universal physical quantity and enters the
high-energy processes involving pion based on the factorization theorem has
not been completely consistent. The form of is usually
described by phenomenological models and constrained by the experimental data
of the exclusive processes containing pion or the moments calculated with the
QCD sum rules and lattice QCD theory. Obviously, an appropriate model is very
important for us to determine the exact behavior of . In
this paper, by adopting the least squares method to fit the -moments
calculated with QCD sum rules based on the background field theory, we perform
an analysis for several commonly used models of the pionic leading-twist DA in
the literature, such as the truncation form of the Gegenbauer polynomial
series, the light-cone harmonic oscillator model, the form from the
Dyson-Schwinger equations, the model from the light-front holographic AdS/QCD
and a simple power-law parametrization form.Comment: 10 pages, 2 figure
Realization of Zero-Refractive-Index Lens with Ultralow Spherical Aberration
Optical complex materials offer unprecedented opportunity to engineer
fundamental band dispersion which enables novel optoelectronic functionality
and devices. Exploration of photonic Dirac cone at the center of momentum space
has inspired an exceptional characteristic of zero-index, which is similar to
zero effective mass in fermionic Dirac systems. Such all-dielectric zero-index
photonic crystals provide an in-plane mechanism such that the energy of the
propagating waves can be well confined along the chip direction. A
straightforward example is to achieve the anomalous focusing effect without
longitudinal spherical aberration, when the size of zero-index lens is large
enough. Here, we designed and fabricated a prototype of zero-refractive-index
lens by comprising large-area silicon nanopillar array with plane-concave
profile. Near-zero refractive index was quantitatively measured near 1.55 um
through anomalous focusing effect, predictable by effective medium theory. The
zero-index lens was also demonstrated to perform ultralow longitudinal
spherical aberration. Such IC compatible device provides a new route to
integrate all-silicon zero-index materials into optical communication, sensing,
and modulation, and to study fundamental physics on the emergent fields of
topological photonics and valley photonics.Comment: 14 pages, 4 figure
Analysis of an age-structured dengue model with multiple strains and cross immunity
Dengue fever is a typical mosquito-borne infectious disease, and four strains of it are currently found. Clinical medical research has shown that the infected person can provide life-long immunity against the strain after recovering from infection with one strain, but only provide partial and temporary immunity against other strains. On the basis of the complexity of transmission and the diversity of pathogens, in this paper, a multi-strain dengue transmission model with latency age and cross immunity age is proposed. We discuss the well-posedness of this model and give the terms of the basic reproduction number R0 = max{R1, R2} , where Ri is the basic reproduction number of strain i (i = 1, 2). Particularly, we obtain that the model always has a unique diseasefree equilibrium P0 which is locally stable for R0 1, the strain-i dominant equilibrium Pi is locally stable for Rj < R∗ i (i, j = 1, 2, i 6= j). Additionally, the threshold criteria on the uniformly persistence, the existence and global asymptotically stability of coexistence equilibrium are also obtained. Finally, these theoretical results and interesting conclusions are illustrated with some numerical simulations
Synthesis and nuclear magnetic resonance shielding effect of three triazine-linked porphyrin compounds
Three porphyrin compounds, monomer Por I, dimer Por II and trimer Por III have been synthesized from the reaction of cyanuric chloride, 5-(4-hydroxyphenyl)-10,15,20-triphenyl porphyrin and 1-phenylpiperazine. The properties of these novel porphyrins in nuclear magnetic shielding, the shift, coupling and splitting of beta hydrogens, were studied by ¹H NMR spectroscopy. The results shown that beta hydrogens in dimer and trimer were shielded by porphyrin ring greatly and displayed the complicated signal peaks
Insecticidal effect of volatile compounds from plant materials of Murraya exotica against Red Imported Fire Ant Workers
The effect of volatile compounds from the mashed fresh, fallen, and dried leaves of Murraya exotica on the behavior of red imported fire ant (Solenopsis invicta, RIFA) workers was investigated by fumigation toxicity bioassay. The volatile compounds from different mashed leaves (fresh, fallen, and dried leaves) of M. exotica were collected by solid-phase microextraction and identified by gas chromatography–mass spectrometry. β-Caryophyllene, α-cedrene, α-copaene, β-cubebene, and germacrene D were identified as major components of the volatile compounds. In exposure time from 1 d to 9 d, the mortality of RIFA increased from 5.00% to 100.00% (fresh leaves), 11.67% to 93.33% (fallen leaves), and 15.00% to 83.33% (dried leaves) in minor workers, whereas in major workers, the increases were from 13.33% to 93.33% (fresh leaves), 6.67% to 83.33% (fallen leaves), and 10.00% to 60.00% (dried leaves). The volatile compounds reduced the walking and grasping abilities and aggregation rate of RIFA workers. Results indicate that mashed leaves of M. exotica have potential for controlling RIFA
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