共查询到20条相似文献,搜索用时 31 毫秒
1.
Daning Hu Hsinchun Chen Zan Huang Mihail C. Roco 《Journal of nanoparticle research》2007,9(4):529-542
Academic nanoscale science and engineering (NSE) research provides a foundation for nanotechnology innovation reflected in
patents. About 60% or about 50,000 of the NSE-related patents identified by “full-text” keyword searching between 1976 and
2004 at the United States Patent and Trademark Office (USPTO) have an average of approximately 18 academic citations. The
most cited academic journals, individual researchers, and research articles have been evaluated as sources of technology innovation
in the NSE area over the 28-year period. Each of the most influential articles was cited about 90 times on the average, while
the most influential author was cited more than 700 times by the NSE-related patents. Thirteen mainstream journals accounted
for about 20% of all citations. Science, Nature and Proceedings of the National Academy of Sciences (PNAS) have consistently
been the top three most cited journals, with each article being cited three times on average. There is another kind of influential
journals, represented by Biosystems and Origin of Life, which have very few articles cited but with exceptionally high frequencies. The number of academic citations per year from
ten most cited journals has increased by over 17 times in the interval (1990–1999) as compared to (1976–1989), and again over
3 times in the interval (2000–2004) as compared to (1990–1999). This is an indication of increased used of academic knowledge
creation in the NSE-related patents. 相似文献
2.
L. Gauvin J. Vannimenus J.-P. Nadal 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(2):293-304
The collective behavior in a variant of Schelling’s segregation model is characterized with methods borrowed from statistical
physics, in a context where their relevance was not conspicuous. A measure of segregation based on cluster geometry is defined
and several quantities analogous to those used to describe physical lattice models at equilibrium are introduced. This physical
approach allows to distinguish quantitatively several regimes and to characterize the transitions between them, leading to
the building of a phase diagram. Some of the transitions evoke empirical sudden ethnic turnovers. We also establish links
with ‘spin-1’ models in physics. Our approach provides generic tools to analyze the dynamics of other socio-economic systems. 相似文献
3.
N. J. Moura M. B. Ribeiro 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(1):101-120
This work presents an empirical study of the evolution of the personal income distribution in Brazil. Yearly samples available
from 1978 to 2005 were studied and evidence was found that the complementary cumulative distribution of personal income for
99% of the economically less favorable population is well represented by a Gompertz curve of the form G(x) = exp [exp (A-Bx)],
where x is the normalized individual income. The complementary cumulative distribution of the remaining 1% richest part of
the population is well represented by a Pareto power law distribution P(x) = βx-α. This result means that similarly to other countries, Brazil’s income distribution is characterized by a well defined two
class system. The parameters A, B, α, β were determined by a mixture of boundary conditions, normalization and fitting methods
for every year in the time span of this study. Since the Gompertz curve is characteristic of growth models, its presence here
suggests that these patterns in income distribution could be a consequence of the growth dynamics of the underlying economic
system. In addition, we found out that the percentage share of both the Gompertzian and Paretian components relative to the
total income shows an approximate cycling pattern with periods of about 4 years and whose maximum and minimum peaks in each
component alternate at about every 2 years. This finding suggests that the growth dynamics of Brazil’s economic system might
possibly follow a Goodwin-type class model dynamics based on the application of the Lotka-Volterra equation to economic growth
and cycle. 相似文献
4.
5.
Molin Liu Jianbo Lu Yuanxing Gui 《The European Physical Journal C - Particles and Fields》2009,59(1):107-116
On the basis of the 4D momentum, the influence of quintessence on the gravitational frequency shift and the deflection of
light are examined in modified Schwarzschild space. We find that the frequency of a photon depends on the state parameter
of the quintessence w
q: the frequency increases for −1<w
q<−1/3 and decreases for −1/3<w
q<0. Meanwhile, we adopt an integral power number a (a=3ω
q+2) to solve the orbital equation of photon. The photon’s potentials become higher with the decrease of ω
q. The behavior of the bending light sensitively depends on the state parameter ω
q. In particular, for the case of ω
q=−1, there is no influence on the deflection of light by quintessence. Furthermore, according to the H-masers of the GP-A
redshift experiment and long-baseline interferometry, the constraints on the quintessence field in the solar system are presented
here. 相似文献
6.
We investigate the statistical properties of the empirical data taken from the Chinese stock market during the time period from January, 2006 to July, 2007. By using the methods of detrended fluctuation analysis (DFA) and calculating correlation coefficients, we acquire the evidence of strong correlations among different stock types, stock index, stock volume turnover, A share (B share) seat number, and GDP per capita. In addition, we study the behavior of “volatility”, which is now defined as the difference between the new account numbers for two consecutive days. It is shown that the empirical power-law of the number of aftershock events exceeding the selected threshold is analogous to the Omori law originally observed in geophysics. Furthermore, we find that the cumulative distributions of stock return, trade volume and trade number are all exponential-like, which does not belong to the universality class of such distributions found by Xavier Gabaix et al. [Xavier Gabaix, Parameswaran Gopikrishnan, Vasiliki Plerou, H. Eugene Stanley, Nature, 423 (2003)] for major western markets. Through the comparison, we draw a conclusion that regardless of developed stock markets or emerging ones, “cubic law of returns” is valid only in the long-term absolute return, and in the short-term one, the distributions are exponential-like. Specifically, the distributions of both trade volume and trade number display distinct decaying behaviors in two separate regimes. Lastly, the scaling behavior of the relation is analyzed between dispersion and the mean monthly trade value for each administrative area in China. 相似文献
7.
Emanuele Pugliese Claudio Castellano Matteo Marsili Luciano Pietronero 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(3):319-327
We introduce and study a model of an interacting population of agents who collaborate in groups which compete for limited
resources. Groups are formed by random matching agents and their worth is determined by the sum of the efforts deployed by
agents in group formation. Agents, on their side, have to share their effort between contributing to their group’s chances
to outcompete other groups and resource sharing among partners, when the group is successful. A simple implementation of this
strategic interaction gives rise to static and evolutionary properties with a very rich phenomenology. A robust emerging feature
is the separation of the population between agents who invest mainly in the success of their group and agents who concentrate
in getting the largest share of their group’s profits. 相似文献
8.
J. K. Baria 《Czechoslovak Journal of Physics》2004,54(4):469-485
A model pseudopotential depending on an effective core radius but otherwise parameter free is used to study the interatomic
interactions, phonon dispersion curves (inq and r-space analysis), phonon density of states, mode Grüneisen parameters, dynamical elastic constants (C
11,C
12 andC
44), bulk modulus (B), shear modulus (C′), deviation from Cauchy relation (C
12–C
44), Poisson’s ratio (σ), Young’s modulus (Y), behavior of phonon frequencies in the elastic limit independent of the direction (Y
1), limiting value in the [110] direction (Y
2), degree of elastic anisotropy (A), maximum frequencyω
max, mean frequency 〈ω〉, 〈ω
2〉1/2=(〈ω〉/〈ω
−1〉)1/2, fundamental frequency 〈ω
2〉, and propagation velocities of the elastic constants in Cu, Ag, Au, Ni, Pd, and Pt. The contribution of s-like electrons
is calculated in the second-order perturbation theory for the model potential while that of d-like electrons is taken into
account by introducing repulsive short-range Born-Mayer like term. Very recently proposed screening function due to Sarkar
et al. has been used to obtain the screened form factor. The theoretical results are compared with experimental findings wherever
possible. A good agreement between theoretical investigations and experimental findings has proved the ability of our model
potential for predicting a large number of physical properties of transition metals. 相似文献
9.
We found an exact expression for the Flory radius R
F of Gaussian polymers placed in an external periodic field. This solution is expressed in terms of the two parameters η and
a that describe the reduced strength of an external field and the period of the field to the polymer gyration radius ratio,
respectively. R
F is found to be a decaying function of η for any values of a . Provided that the gyration radius is of the order of the period of an external field or less, the ground-state (GS) approximation
of the exact result for R
F is shown to give qualitatively incorrect results. In addition to the “ground-state” contribution, the exact solution for
R
F contains an additional term that is overlooked by the GS approximation. This term gives rise to the fact that R
F as a function of η exhibits power law behavior (rather than exponential decay obtained from the GS result) once η exceeds
the threshold value ηcon . 相似文献
10.
Dipanjali Behera Sunil K. Tripathy Tushar R. Routray 《International Journal of Theoretical Physics》2010,49(10):2569-2581
Bulk Viscous anisotropic Bianchi-III cosmological models are investigated with time dependent gravitational and cosmological
constants in the framework of Einstein’s general relativity. In order to get some useful information about the time varying
nature of G and Λ, we have assumed an exponentially decaying rest energy density of the universe. The extracted Newtonian gravitational
constant G varies with time but its time varying nature depends on bulk viscosity and the anisotropic nature of the model. The cosmological
constant Λ is found to decrease with time to a small but positive value for the models. 相似文献
11.
B.M. Roehner 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):175-187
It is a common belief nowadays that the world economy is fairly well “integrated”. Yet, this belief often turns out to be
in contradiction with empirical evidence. As a matter of fact the way distant markets interact is a question that has largely
been ignored by economists. In this series of two papers we examine the role that space, that is to say geographical distance,
plays in the economics of commodity markets. The first of these papers presents the empirical evidence while the second develops
a theoretical framework. The empirical enquiry discloses several noteworthy features, e.g. (i) with respect to spatial interaction there is a sharp contrast between stock markets and commodity markets. While there
is almost perfect spatial arbitrage in the first case, this is not true for commodity markets. (ii) In spite of their chaotic
behavior in the course of time commodity prices display well defined spatial patterns, (iii) as in statistical physics and
fluid dynamics interactions can be described in terms of correlation length. The correlation length of a set of markets is
seen to increase along with the number of transactions; it also increases when transport costs decline as was the case during
the “transportation revolution” of the mid-nineteenth century. Using the notion of correlation length one is able to give
a quantitative meaning to the otherwise ill-defined concept of market integration.
Received 17 May 1999 and Received in final form 31 May 1999 相似文献
12.
D. Helbing A. F. Johansson 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(4):549-562
Daganzo’s criticisms of second-order fluid approximations of traffic flow [C. Daganzo, Transpn. Res. B. 29, 277 (1995)] and Aw and Rascle’s proposal how to overcome them [A. Aw, M. Rascle, SIAM J. Appl. Math. 60, 916 (2000)] have stimulated an intensive scientific activity in the field of traffic modeling. Here, we will revisit their
arguments and the interpretations behind them. We will start by analyzing the linear stability of traffic models, which is
a widely established approach to study the ability of traffic models to describe emergent traffic jams. Besides deriving a
collection of useful formulas for stability analyses, the main attention is put on the characteristic speeds, which are related
to the group velocities of the linearized model equations. Most macroscopic traffic models with a dynamic velocity equation
appear to predict two characteristic speeds, one of which is faster than the average velocity. This has been claimed to constitute a theoretical inconsistency. We will carefully discuss arguments
for and against this view. In particular, we will shed some new light on the problem by comparing Payne’s macroscopic traffic
model with the Aw-Rascle model and macroscopic with microscopic traffic models. 相似文献
13.
É. Falcon S. Fauve C. Laroche 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):183-186
We report experimental results on the behavior of an ensemble of inelastically colliding particles, excited by a vibrated
piston in a vertical cylinder. When the particle number is increased, we observe a transition from a regime where the particles
have erratic motions (“granular gas”) to a collective behavior where all the particles bounce like a nearly solid body. In
the gas-like regime, we measure the density of particles as a function of the altitude and the pressure as a function of the
number N of particles. The atmosphere is found to be exponential far enough from the piston, and the “granular temperature”, T, dependence on the piston velocity, V, is of the form , where is a decreasing function of N. This may explain previous conflicting numerical results.
Received 1 February 1999 相似文献
14.
In this paper we have obtained some new exact solutions of Einstein’s field equations in a spatially homogeneous and anisotropic
Bianchi type-V space-time with perfect fluid distribution along with heat-conduction and decaying vacuum energy density Λ
by applying the variation law for generalized Hubble’s parameter that yields a constant value of deceleration parameter. We
find that the constant value of deceleration parameter is reasonable for the present day universe. The variation law for Hubble’s
parameter generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential
form. Using these two forms, Einstein’s field equations are solved separately that correspond to expanding singular and non-singular
models of the universe respectively. The cosmological constant Λ is found to be a decreasing function of time and positive
which is corroborated by results from recent supernovae Ia observations. Expressions for look-back time-redshift, neoclassical
tests (proper distance d(z)), luminosity distance red-shift and event horizon are derived and their significance are described in detail. The physical
and geometric properties of spatially homogeneous and anisotropic cosmological models are discussed. 相似文献
15.
The paper reports the pulsed laser-based time-resolved time-dependent Photo-acoustic (PA) spectroscopy of NO2 gas in a specially designed multi mode-Resonant PA Cell which is made of Stainless Steel and has a “Q” value of the order of 79. Furthermore the designed cell allows us to excite some of the longitudinal, radial and azimuthal
resonance modes of the photo-acoustic signals simultaneously in a very efficient manner. The presence of many newly excited
modes occur at 7050 Hz, 10350 Hz and 14650 Hz frequencies is observed for the first time in NO2 at room temperature. These results are obtained by employing second harmonics i.e. λ=532 nm pulses from Q-switched Nd:YAG laser having 7 ns pulse duration. Some of the new acoustic spectrum lines at higher frequencies are recorded
between 0.5–10 ms data acquisition time, which also extends the frequency monitoring range of our system. The study also highlights
some of the important aspects such as the decaying behavior of some of these resonant acoustic spectrum lines occur on the
expense of others as well as the saturation behavior of some other modes in the NO2 gas sample. The estimated low level detection limit of NO2 buffered in air is of the order of 17.9 ppbV. 相似文献
16.
A. Bohm 《Letters in Mathematical Physics》1979,3(6):455-461
Exponentially decaying ‘Gamow state’ vectors are obtained from S-matrix poles in the lower half of the second sheet and are defined as functionals over a subspace of the nuclear space Φ.
Exponentially growing ‘Gamow state’ vectors are obtained from S-matrix poles in the upper half of the second sheet and are defined as functionals over another subspace of Φ. On functionals
over these two subspaces the dynamical group of time development splits into two semigroups. 相似文献
17.
William J. Thistleton John A. Marsh Kenric P. Nelson Constantino Tsallis 《Central European Journal of Physics》2009,7(3):387-394
We study a strictly scale-invariant probabilistic N-body model with symmetric, uniform, identically distributed random variables.
Correlations are induced through a transformation of a multivariate Gaussian distribution with covariance matrix decaying
out from the unit diagonal, as ρ/r
α for r =1, 2, ..., N-1, where r indicates displacement from the diagonal and where 0 ⩽ ρ ⩽ 1 and α ⩾ 0. We show numerically that the sum of the N dependent random variables is well modeled by a compact support q-Gaussian distribution. In the particular case of α = 0 we obtain q = (1-5/3 ρ) / (1- ρ), a result validated analytically in a recent paper by Hilhorst and Schehr. Our present results with
these q-Gaussian approximants precisely mimic the behavior expected in the frame of non-extensive statistical mechanics. The
fact that the N → ∞ limiting distributions are not exactly, but only approximately, q-Gaussians suggests that the present system is not exactly, but only approximately, q-independent in the sense of the q-generalized central limit theorem of Umarov, Steinberg and Tsallis. Short range interaction (α > 1) and long range interactions
(α < 1) are discussed. Fitted parameters are obtained via a Method of Moments approach. Simple mechanisms which lead to the
production of q-Gaussians, such as mixing, are discussed.
相似文献
18.
The magnetic behavior of a solid solution, Ca3 x Yx CO2 O6, based on the ‘exotic’ spin-chain compound, Ca3Co2O6, crystallizing in K4CdCl6-derived rhombohedral structure is investigated. Among the compositions investigated(x = 0.0, 0.3, 0.5, 0.75 and 1.0), single-phase formation persists up tox = 0.75, with the elongation of the c-axis. The present investigations reveal that the temperature at which the ‘so-called’
‘partially disordered antiferromagnetic structure’ sets in (which occurs at 24 K for the parent compound,x = 0.0) undergoes gradual reduction with the substitution of Y for Ca, attaining the value of about 2.2 K for the nominalx = 1.0. The trend observed in this characteristic temperature is opposite to that reported under external pressure, thereby
establishing that Y substitution exerts negative chemical pressure. Anomalous steps observed in the isothermal magnetization
at very low temperatures (around 2 K) forx = 0.0, which have been proposed to arise from ‘quantum tunneling effects’ are found to vanish by a small substitution (x = 0.3) of Y for Ca. Systematics in AC and DC magnetic susceptibility behavior with Y substitution for Ca have also been probed.
We believe that the present results involving the expansion of chain length without disrupting the magnetic chain may be useful
to the overall understanding of the novel magnetism of the parent compound. 相似文献
19.
In this paper we examine the possibility of having an exception to the recent observation by L. Randall amd M. Wise, which
states that “a significant branching ratios to both e
+
e
− and γ
γ is possible only if new physics beyond that in the SM couples directly to electrons”. We consider resonances decaying into
diphotons and dielectrons final states predicted in U(1)
B−L
extensions of the SM. We find that these new resonances can’t decay into e
+
e
− and γ
γ final states with comparably measurable branching ratios although such resonances are directly coupled to electrons. 相似文献
20.
P. Rosenbusch 《Applied physics. B, Lasers and optics》2009,95(2):227-235
We investigate the hyperfine transition of magnetically trapped non-condensed atoms. The two principal frequency shifts, the
second order Zeeman effect and the mean field interaction are considered. Analytic models of the mean frequency and its trap
induced spread are developed. Comparisons with existing experiments evaluate the role of the atoms’ oscillatory motion. The
analytic model proves to be equivalent to existing Monte Carlo simulations. The formulae provide a simple tool for optimising
the design of a new experiment. Applied to the two-photon transition |F=1,m
F
=−1〉→|F=2,m
F
=1〉 in 87Rb and the conditions of a typical atom chip experiment, a line spread as small as 11 mHz is predicted giving a quality factor
of 1012. The system is promising for application in precision instruments such as compact atomic clocks. 相似文献