共查询到20条相似文献,搜索用时 125 毫秒
1.
A. Grabowski 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(4):605-611
We present and study data concerning human behavior in four online social systems: (i) an Internet community of friends of
over 107 people, (ii) a music community website with over 106 users, (iii) a gamers’ community server with over 5 × 106 users and (iv) a booklovers’ website with over 2.5 × 105 users. The purpose of those systems is different; however, their properties are very similar. We have found that the distribution
of human activity (e.g., the sum of books read or songs played) has the form of a power law. Moreover, the relationship between
human activity and time has a power-law form, too. We present a simple interest-driven model of the evolution of such systems
which explains the emergence of two scaling regimes. 相似文献
2.
Andrzej Grabowski 《Physica A》2007,385(1):363-369
We study a large social network consisting of over 106 individuals, who form an Internet community and organize themselves in groups of different sizes. On the basis of the users’ list of friends and other data registered in the database we investigate the structure and time development of the network. The structure of this friendship network is very similar to the structure of different social networks. However, here a degree distribution exhibiting two scaling regimes, power-law for low connectivity and exponential for large connectivity, was found. The groups size distribution and distribution of number of groups of an individual have power-law form. We found very interesting scaling laws concerning human dynamics. Our research has shown how long people are interested in a single task. 相似文献
3.
Sangman Han 《Physica A》2008,387(23):5946-5951
We empirically study various network properties of an online community. The numbers of articles written by each user to the bulletin boards of each of the others are used to construct the directed and weighted network B, and gifting behaviors among users are also kept track of, to build the network G which is again directed and weighted. Detailed analysis reveals that B and G have very different network properties. In particular, whereas B contains many more bidirectional links than directed arcs, G shows the opposite characteristic. The number of writings on bulletin boards is found to decay with the distance from the hub vertex, which reflects the structural assortativeness in B. We also observe that the activities in writings and purchases are negatively correlated with each other for highly active users in B. 相似文献
4.
Yong-Hong Zhang Masao Nomura Yasuhiko Fujii Takao Oi 《Isotopes in environmental and health studies》2013,49(3):279-288
Isotope effects of cerium were observed in malate and lactate complex formations during the long-distance displacement chromatographic processes at 313 K. Heavier isotopes were found fractionated in the frontal edges of the Ce adsorption bands in both the systems, registering a preference of the heavier isotopes for the Ce(III) complexes in the solution phase over the simply hydrated Ce(III) ions in the resin phase. The fractionation coefficients ? for the 136Ce/140Ce, 138Ce/140Ce and 142Ce/140Ce isotopic pairs were 7.1 × 10?6, 5.2 × 10?6 and ?2.1 × 10?6 for the malate system, and 4.8 × 10?6, 4.5 × 10?6 and?2.6×10?6 for the lactate system, respectively. They all show the mass-dependent law if the deviation of ? for the 138Ce/140Ce pair was considered merely due to the isobaric interference in Ce isotopic ratio measurements, suggesting the molecular vibration, rather than the nuclear field shift, mainly contributes to the Ce isotope effects in the complex formation systems. The absolute values of ? between the two systems are comparable, suggesting no instinct difference in structural properties between Ce malate and lactate complexes involved. 相似文献
5.
A total of 49 students, about half of them male, from various countries and 4 student helpers attended the 2008 China Complex Systems Summer School organized by the Santa Fe Institute and the Chinese Academy of Sciences held in Beijing. We studied the development of the social network among these participants during the school, which lasted for 4 weeks, by carrying out surveys at different times of the school. The students got to know each other through various activities, including being roommates, eating together everyday, attending lectures, doing group projects, sight-seeing visits, etc. The topological structures and various properties of the network are discussed. The results indicate how the participants became friends as time went by. By considering the correlations between reciprocal evaluations via the Pearson’s correlation coefficient, it is found that the ethnicity and gender are important factors in establishing personal relationships and in getting mutually consistent perceptions on the relationships. We also study the clique components and community structures in the networks. 相似文献
6.
J. Zhang H. Huang 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(2):247-251
In order to describe the entangled network structure in polymer melts visually, we propose an evolving network model with
community structure. This network model grows according to the inner-community and inter-community preferential mechanisms
of both community sizes and node degrees. Numerical simulation results indicate that the cumulative distribution of community
size and node degree distribution follow power-law distributions P(S≥s)∼s-υ and P(k)∼k-γ respectively, with the exponents of υ≥1 and . 相似文献
7.
Z. W. Liu X. F. Yang A. M. Zhu G. L. Zhao Y. Xu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(3):365-373
The hydroxyl radical (OH) plays an important role in combustion systems,
atmospheric chemistry and the removal of air pollutants by non-thermal
plasmas. The present work reports the determination of the hydroxyl radicals
in atmospheric dielectric barrier discharge plasmas via near infrared
continuous wave cavity ring-down spectroscopy. The P-branches of OH
X2Πi (ν' = 2 ←ν′′ = 0) bands were used for its number density measurements. The minimum measurable absorption coefficient is about
3 × 10-8 cm-1 in DBD plasmas. At certain experimental
conditions (a.c. frequency of 70 kHz, 6700 ppm H2O in He, 1 atm), when
the peak-to-peak discharge voltage varied from 6 kV to 10.4 kV, the
determined OH radical concentration increased from (2.1 ± 0.1) ×
1013 molecules cm-3 to (3.7 ± 0.1) × 1013 molecules cm-3. The plasma gas temperature, derived from the Boltzmann plots of OH rotational population distributions, ranged from 312
± 10 K to 363 ± 10 K when the discharge voltage was raised in the above range.
The influences of O2 and N2 addition on the production of OH
radicals have been also investigated. 相似文献
8.
In this Letter, we propose a growing network model that can generate scale-free networks with a tunable community strength. The community strength, C, is directly measured by the ratio of the number of external edges to that of the internal ones; a smaller C corresponds to a stronger community structure. By using the Kuramoto model, we investigated the phase synchronization on this network and found an abnormal region (C?0.002), in which the network has even worse synchronizability than the unconnected case (C=0). On the other hand, the community effect will vanish when C exceeds 0.1. Between these two extreme regions, a stronger community structure will hinder global synchronization. 相似文献
9.
Jing Tang Fung Suong Ou Huei Pei Kuo Min Hu William F. Stickle Zhiyong Li R. Stanley Williams 《Applied Physics A: Materials Science & Processing》2009,96(4):793-797
We created novel surface-enhanced Raman spectroscopy (SERS) substrates by metalization (Ag) of Si nanograss prepared by a
Bosch process which involves deep reactive ion etching of single crystalline silicon. No template or lithography was needed
for making the Si nanograss, thus providing a simple and inexpensive method to achieve highly sensitive large-area SERS substrates.
The dependence of the SERS effect on the thickness of the metal deposition and on the surface morphology and topology of the
substrate prior to metal deposition was studied in order to optimize the SERS signals. We observed that the Ag-coated Si nanograss
can achieve uniform SERS enhancement over large area (∼1 cm ×1 cm) with an average EF (enhancement factor) of 4.2×108 for 4-mercaptophenol probe molecules.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
10.
We introduce a new simple pseudo tree-like network model, deterministic complex network (DCN). The proposed DCN model may simulate the hierarchical structure nature of real networks appropriately and have the unique property of ‘skipping the levels’, which is ubiquitous in social networks. Our results indicate that the DCN model has a rather small average path length and large clustering coefficient, leading to the small-world effect. Strikingly, our DCN model obeys a discrete power-law degree distribution P(k)∝k−γ, with exponent γ approaching 1.0. We also discover that the relationship between the clustering coefficient and degree follows the scaling law C(k)∼k−1, which quantitatively determines the DCN's hierarchical structure. 相似文献
11.
F. Wang P. Weber K. Yamasaki S. Havlin H. E. Stanley 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(2):123-133
We discuss recent results concerning statistical regularities in the
return intervals of volatility in financial markets. In particular, we
show how the analysis of volatility return intervals, defined as the
time between two volatilities larger than a given threshold, can help
to get a better understanding of the behavior of financial time
series. We find scaling in the distribution of return intervals for
thresholds ranging over a factor of 25, from 0.6 to 15 standard
deviations, and also for various time windows from one minute up to
390 min (an entire trading day). Moreover, these results are
universal for different stocks, commodities, interest rates as well as
currencies. We also analyze the memory in the return intervals which
relates to the memory in the volatility and find two scaling regimes,
ℓ<ℓ* with α1=0.64±0.02 and ℓ> ℓ*
with α2=0.92±0.04; these exponent values are similar to
results of Liu et al. for the volatility. As an application, we use
the scaling and memory properties of the return intervals to suggest a
possibly useful method for estimating risk. 相似文献
12.
J. Lecointre D. S. Belic J. J. Jureta R. Janev P. Defrance 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,50(3):265-278
Absolute cross sections for electron-impact dissociative excitation and
ionization of CD+
4 leading to formation of ionic products (CD2+
4, CD+
3, CD+
2, CD+, C+, D+
3, D+
2, and D+) have been measured. The animated crossed-beams
method is applied in the energy range from the reaction threshold up to 2.5 keV. Around 100 eV, the maximum cross sections
are found to be (3.8±0.2) ×10-19 cm2,
cm2,
(7.1±0.8) ×10-17 cm2, (9.0±0.8) ×
10-17 cm2 and (3.7±0.4) ×10-17 cm2 for the
heavy carbonaceous ions CD2+
4, CD+
3, CD+
2, CD+ and C+ respectively. For the light fragments, D+
3, D+
2, and D+, the cross sections around the maximum are
found to be (5.0±0.6) ×10-19 cm2, (1.7±
0.2) ×10-17 cm2 and (10.6±1.0) ×10-17 cm2, respectively. The cross sections are presented in closed analytic
forms convenient for implementation in plasma simulation codes. The analysis
of ionic product velocity distributions allows determination of the kinetic
energy release distributions which are seen to extend from 0 to 9 eV for
heavy fragments, and up to 14 eV for light ones. The comparison of present
energy thresholds and kinetic energy release with available published data
gives information about states contributing to the observed processes.
Individual contributions for dissociative excitation and dissociative
ionization are determined for each detected product. A complete database
including cross sections and energies is compiled for use in fusion
application. 相似文献
13.
Abstract Three new bands of the B 2Σ+–X 2Σ+ system of 12C17O+ have been investigated using conventional spectroscopic techniques. The spectra were observed in a graphite hollow‐cathode lamp by discharging molecular oxygen (enriched in about 45% of the 17O2 isotope) under 1.0 Torr pressure. The rotational analysis of the 2–4, 2–5, and 2–6 bands was performed with the effective Hamiltonian of Brown (Brown et al., J. Mol. Spectrosc. 1979; 74: 294–318). Molecular constants were derived from a merge calculation, including both the current wavenumbers and the spectroscopic data published by the authors previously. The principal equilibrium constants for the ground state of 12C17O+ are ωe=2185.9658(84), ωe x e = 14.7674(11), B e=1.927001(38), αe=1.8236(22)×10?2, γe=?0.331(28)×10?4, D e=6.041(12)×10?6, βe=0.100(31)×10?7 cm?1, and the equilibrium constants for the excited state are σe=45876.499(15), ωe=1712.201(12), ωe x e=27.3528(39), B e=1.754109(35), αe=2.8706(57)×10?2, γe = ?1.15(19)×10?4, D e=7.491(20)×10?6, βe=2.13(12)×10?7, γe = 2.0953(97)×10?2, and αγe=?9.46(59)×10?4 cm?1, respectively. Rydberg–Klein–Rees potential energy curves were constructed for the B 2Σ+ and X 2Σ+ states of this molecule, and Franck–Condon factors were calculated for the vibrational bands of the B–X system. 相似文献
14.
通过区熔定向凝固法,生长出[001]易磁化方向与晶体轴向之间存在不同取向差的Fe81Ga19合金单晶体和Fe81Ga19合金多晶体.极图测试结果显示,Fe81Ga19合金单晶体的[001]方向与轴向取向差分别为12°,5°和3°.采用电阻应变片法测定相应磁致伸缩应变,与外加磁场方向平行的轴向磁致伸缩应变分别为254×10-6,271×10-6<
关键词:
磁致伸缩
81Ga19合金')" href="#">Fe81Ga19合金
晶体取向 相似文献
15.
Zhiming Rao Qiaomei Lu Liangzhou Fang Lishuang She Haigang Yan Wenting Chen 《光谱学快报》2013,46(3):249-264
Abstract The effects of three systems on the chemiluminescence (CL) intensity have been studied in this paper, such as leucogen–potassium permanganate–rhodamine B, leucogen–cerium (IV)–rhodamine B, and leucogen–luminol–hydrogen peroxide (called system 1, system 2, and system 3, respectively). The mechanism of these reactions is also discussed. Surfactant (CTMAB) has a remarkably sensitive effect on these systems mentioned above. Therefore, three new flow injection chemiluminescence methods for the determination of leucogen have been established. For system 1, the linear range is 8.0×10?8 to 4.0×10?5 g mL?1, with limits of detection 2×10?8 g mL?1; the relative standard deviation is 2.5% (n=11, Cs=4.0×10?6 g mL?1). For system 2, the linear range is 1.0×10?8 to 5.0×10?6 g mL?1, with limits of detection 3×10?9 g mL?1; the relative standard deviation is 5.1% (n=11, Cs=1.0×10?6 g mL?1). For system 3, the linear range is 4.0×10?8 to 2.0×10?6 g mL?1, with limits of detection 1×10?8 g mL?1; the relative standard deviation is 1.3% (n=11, Cs=1.0×10?7 g mL?1). Compared with the three methods above, system 3 is confirmed as the best method. This method has been applied to the determination of leucogen with satisfactory results. 相似文献
16.
D. Q. Wei X. S. Luo Y. L. Zou 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(2):279-282
We investigate how firing activity of complex neural
networks depends on the random long-range connections and coupling
strength. Network elements are described by excitable
space-clamped FitzHugh-Nagumo (SCFHN) neurons with the values of
parameters at which no firing activity occurs. It is found that
for a given appropriate coupling strength C, there exists a
critical fraction of random connections (or randomness) p*,
such that if p > p* the firing neurons, which are absent in the
nearest-neighbor network, occur. The firing activity becomes
more frequent as randomness p is
further increased. On the other hand, when the p is smaller,
there are no active neurons in network, no matter what the value
of C is. For a given larger p, there exist optimal coupling
strength levels, where firing activity reaches its maximum. To the
best of our knowledge, this is a novel mechanism for the emergence
of firing activity in neurons. 相似文献
17.
Nonlinear optical response of Ge nanocrystals in silica matrix with excitation of femtosecond pulses
H.P. Li C.H. Kam Y.L. Lam Y.X. Jie W. Ji A.T.S. Wee C.H.A. Huan 《Applied physics. B, Lasers and optics》2001,72(5):611-615
We report an investigation of third-order optical nonlinearities in Ge nanocrystals (∼6 nm radius) embedded in silica matrix
using the Z-scan and pump-probe techniques with femtosecond laser pulses at 780-nm wavelength. The nanocrystallite Ge samples
were prepared using magnetron co-sputtering and post-thermal annealing at 800 °C. The nonlinear absorption coefficient and
refractive index of the Ge nanocrystals were determined to be in the range from 1.8×10-7 to 6.8×10-7 cm/W and 1.5×10-12 to 8.0×10-12 cm2/W, respectively, which are proportional to the Ge atomic fraction in the matrix. Relaxation of the nonlinear response was
found to have two characteristic time constants, 1.8 ps and 65 ps. The mechanisms responsible for the observed nonlinear response
are discussed.
Received: 21 August 2000 / Revised version: 17 January 2001 / Published online: 30 March 2001 相似文献
18.
M. Batty R. Carvalho A. Hudson-Smith R. Milton D. Smith P. Steadman 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(3):303-314
Many aggregate distributions of urban activities such as city
sizes reveal scaling but hardly any work exists on the properties of spatial
distributions within individual cities, notwithstanding considerable
knowledge about their fractal structure. We redress this here by examining
scaling relationships in a world city using data on the geometric properties
of individual buildings. We first summarise how power laws can be used to
approximate the size distributions of buildings, in analogy to city-size
distributions which have been widely studied as rank-size and lognormal
distributions following Zipf [Human Behavior and the Principle of Least Effort (Addison-Wesley, Cambridge, 1949)] and Gibrat [Les Inégalités économiques (Librarie du Recueil Sirey, Paris, 1931)]. We then extend this
analysis to allometric relationships between buildings in terms of their
different geometric size properties. We present some preliminary analysis of
building heights from the Emporis database which suggests very
strong scaling in world cities. The data base for Greater London is then
introduced from which we extract 3.6 million buildings whose scaling
properties we explore. We examine key allometric relationships between these
different properties illustrating how building shape changes according to
size, and we extend this analysis to the classification of buildings
according to land use types. We conclude with an analysis of two-point
correlation functions of building geometries which supports our non-spatial
analysis of scaling. 相似文献
19.
Wavelength-modulation spectroscopy using a frequency-doubled current-modulated diode laser 总被引:1,自引:0,他引:1
We have studied atomic absorption in an argon discharge by wavelength-modulation spectroscopy with a frequency-doubled diode
laser. The tunable wavelength-modulated radiation at 430 nm was generated by frequency doubling a current-modulated 860-nm
diode laser in a KNbO3 crystal. 2f-, 4f- and 6f-harmonic spectra as a function of diode laser modulation depth were measured on a Doppler-broadened
sample of excited argon atoms produced in a capacitively coupled plasma chamber. Characterisation of the harmonic signals
was accomplished. Minimum detectable absorbances of 7.7×10-5 and 1.9×10-4 based on a 3σ criterion (σ being the standard deviation of the noise) were estimated for 2f- and 4f-harmonic detection of
the frequency-doubled radiation with a time constant of 0.1 s. The concentrations of argon in the 1s4 state were found to be in the range of 3×108 to 1.2×1011 cm-3 for the experimental conditions studied.
Received: 25 February 2002 / Revised version: 4 April 2002 / Published online: 14 May 2002 相似文献
20.
A new quantitative method for micro amounts of nucleic acids in aqueous solution is proposed using Eu3+-benzoylacetone (BA) complex as fluorescent probe in the presence of cetyltrimethyl-ammonium bromide (CTMAB). Under the optimum
condition, the ratio of the fluorescence intensities with and without nucleic acids is proportional to the concentration of
nucleic acid in the range of 1.0 × 10−9 to 5.0 × 10−6 g/mL for herring sperm DNA (hsDNA), 3.0 × 10−9 to 1.0 × 10−6 g/mL for calf thymus DNA(ctDNA) and 8.0 × 10−9 to 1.0 × 10−6 g/mL for yeast RNA (yRNA), and their detection limits are 0.33, 0.21 and 0.99 ng/mL, respectively. Actual sample (DNA of
Arabidopsis thaliana) was determined satisfactorily. In addition, the interaction mechanism is also investigated. 相似文献