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61.
A novel Ka-band folded waveguide (FW) amplifier for traveling wave tubes (TWT) is investigated. The dispersion curve and interaction impedance are obtained and compared to the normal FW circuit by numerical simulation. The interaction impedance is higher than a normal circuit through the whole band. We also study the beamwave interaction in this novel circuit, and the nonlinear large-signal performance is analyzed by a 3-D particlein-cell code MAGIC3D. A much higher continuous-wave (CW) output power with a considerably shorter circuit compared to a normal circuit is predicted by our simulation. Moreover, the novel FW even has a broader 3-dB bandwidth. It therefore will be useful in designing a miniature but high-power and broadband millimeter-wave TWT. 相似文献
62.
We considered a Bak-Sneppen model on a Sierpinski gasket fractal. We calculated the avalanche size distribution and the distribution of distances between subsequent minimal sites. To observe the temporal correlations of the avalanche, we estimated the return time distribution, the first-return time, and the all-return time distribution. The avalanche size distribution follows the power law, P(s)∼s−τ, with the exponent τ=1.004(7). The distribution of jumping sites also follows the power law, P(r)∼r−π, with the critical exponent π=4.12(4). We observe the periodic oscillation of the distribution of the jumping distances which originated from the jumps of the level when the minimal site crosses the stage of the fractal. The first-return time distribution shows the power law, Pf(t)∼t−τf, with the critical exponent τf=1.418(7). The all-return time distribution is also characterized by the power law, Pa(t)∼t−τa, with the exponent τa=0.522(4). The exponents of the return time satisfy the scaling relation τf+τa=2 for τf?2. 相似文献
63.
Andrzej Grabowski 《Physica A》2009,388(6):961-966
The model of opinion formation in human population based on social impact theory is investigated numerically. On the basis of a database received from the on-line game server, we examine the structure of social network and human dynamics. We calculate the activity of individuals, i.e. the relative time devoted daily to interactions with others in the artificial society. We study the influence of correlation between the activity of an individual and its connectivity on the process of opinion formation. We find that such correlations have a significant influence on the temperature of the phase transition and the effect of the mass media, modeled as an external stimulation acting on the social network. 相似文献
64.
Tomohiro Hasumi 《Physica A》2009,388(4):477-482
We study statistical properties of spatial distances between successive earthquakes, the so-called hypocenter intervals, produced by a two-dimensional (2D) Burridge-Knopoff model involving stick-slip behavior. It is found that cumulative distributions of hypocenter intervals can be described by the q-exponential distributions with q<1, which is also observed in nature. The statistics depend on a friction and stiffness parameters characterizing the model and a threshold of magnitude. The conjecture which states that qt+qr∼2, where qt and qr are an entropy index of time intervals and spatial intervals, respectively, can be reproduced semi-quantitatively. It is concluded that we provide a new perspective on the Burridge-Knopoff model which addresses that the model can be recognized as a realistic one in view of the reproduction of the spatio-temporal interval statistics of earthquakes on the basis of nonextensive statistical mechanics. 相似文献
65.
Alexander S. Balankin Daniel Morales Matamoros Antonio Horta Rangel Didier Samayoa Ochoa 《Physica A》2009,388(9):1780-1790
We study the scaling properties of forced folding of thin materials of different geometry. The scaling relations implying the topological crossovers from the folding of three-dimensional plates to the folding of two-dimensional sheets, and further to the packing of one-dimensional strings, are derived for elastic and plastic manifolds. These topological crossovers in the folding of plastic manifolds were observed in experiments with predominantly plastic aluminum strips of different geometry. Elasto-plastic materials, such as paper sheets during the (fast) folding under increasing confinement force, are expected to obey the scaling force-diameter relation derived for elastic manifolds. However, in experiments with paper strips of different geometry, we observed the crossover from packing of one-dimensional strings to folding two dimensional sheets only, because the fractal dimension of the set of folded elasto-plastic sheets is the thickness dependent due to the strain relaxation after a confinement force is withdrawn. 相似文献
66.
A preferential attachment model for a growing network incorporating the deletion of edges is studied and the expected asymptotic degree distribution is analyzed. At each time step t=1,2,…, with probability π1>0 a new vertex with one edge attached to it is added to the network and the edge is connected to an existing vertex chosen proportionally to its degree, with probability π2 a vertex is chosen proportionally to its degree and an edge is added between this vertex and a randomly chosen other vertex, and with probability π3=1−π1−π2<1/2 a vertex is chosen proportionally to its degree and a random edge of this vertex is deleted. The model is intended to capture a situation where high-degree vertices are more dynamic than low-degree vertices in the sense that their connections tend to be changing. A recursion formula is derived for the expected asymptotic fraction pk of vertices with degree k, and solving this recursion reveals that, for π3<1/3, we have pk∼k−(3−7π3)/(1−3π3), while, for π3>1/3, the fraction pk decays exponentially at rate (π1+π2)/2π3. There is hence a non-trivial upper bound for how much deletion the network can incorporate without losing the power-law behavior of the degree distribution. The analytical results are supported by simulations. 相似文献
67.
Gain versus tuning issues to Q-switch with Yb<Superscript>3+</Superscript>:LSO and amplify broad-bandwidth pulses 总被引:1,自引:0,他引:1
We report on the development of Incoherent Broadband Cavity Enhanced Absorption Spectroscopy (IBBCEAS) using a blue light
emitting diode (LED) for the detection of NO2 in laboratory ambient air. Absorption of the oxygen collisional pair in the atmosphere was also detected in the same spectral
range. The mirror reflectivity was determined using a standard gas sample mixture of NO2, and calibrated with the help of the absorption spectrum of the oxygen collisional pair in pure oxygen at atmospheric pressure.
Optimization of the experimental parameters was investigated and is discussed in detail. For the first time in IBBCEAS involving
broadband absorption spectra, averaging time for signal-to-noise ratio enhancement has been optimized using Allan variance
plot. 18.1 ppbv NO2 in laboratory ambient air has been retrieved from the absorption spectra using differential fitting method over a 40 nm spectral
region centered at 470 nm. A minimum detection sensitivity of about 2.2 ppbv (1σ) for NO2 at atmospheric pressure has been achieved using the optimal averaging time of 100 s by means of a high finesse optical cavity
formed with two moderate reflectivity (∼99.55%) mirrors. No purging of the cavity mirrors by high purity He or N2 gas streams was necessary to prevent contamination of the mirror faces for the in situ measurements. 相似文献
68.
Y. C. Chou E. Cho T. -h. Chou T. M. Hong 《The European physical journal. E, Soft matter》2009,29(2):157-161
By measuring the distribution function of the end-to-end distance, we find that strongly shaken bead chains exhibit many properties,
such as the rigid-rod-to-Gaussian chain transition, scaling, fast drop of loop formation probability in the short-chain regime,
and enhancement of loop formation probability for kinked chains, of long-chain polymers. Though there is difference in local
details between our chains and the worm-like chains, our results are consistent with recent calculations based on the worm-like
chain model in many respects. 相似文献
69.
Y. Huang L. Wu S. Q. Zhu 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):431-438
The interaction between the evolution of the game and the underlying network structure with evolving snowdrift game model
is investigated. The constructed network follows a power-law degree distribution typically showing scale-free feature. The
topological features of average path length, clustering coefficient, degree-degree correlations and the dynamical feature
of synchronizability are studied. The synchronizability of the constructed networks changes by the interaction. It will converge
to a certain value when sufficient new nodes are added. It is found
that initial payoffs of nodes greatly affect the synchronizability. When initial payoffs for players are equal, low common
initial payoffs may lead to more heterogeneity of the network and good
synchronizability. When initial payoffs follow certain distributions, better synchronizability is obtained compared to equal
initial payoff. The result is also true for phase synchronization of nonidentical oscillators. 相似文献
70.
Optical Switching in Silicon Nanowaveguide Ring Resonators Based on Kerr Effect and TPA Effect 下载免费PDF全文
We analyze theoretically the 1 × 2 low-power all-optical switching in silicon nanowaveguide ring resonators (RR) based on the Kerr effect and two-photon absorption (TPA), and give a comparison between both the all-optical switches. The calculation shows that the switching power of the TPA-RR switch is 3 orders smaller than that of the Kerr-RR switch. The switching time for both the switches is about 100ps. 相似文献