共查询到20条相似文献,搜索用时 31 毫秒
1.
M. Kociak K. Hirahara K. Suenaga S. Iijima 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(4):457-469
We present a general and systematic method for determining the chiral indices of carbon nanotubes. This method relies on the
semi-quantitative analysis of experimental selected area diffraction pattern intensities, together with extensive comparison
with kinematic theory. We show how to retrieve the chiral indices of single walled or multiwalled carbon nanotubes, even when
their radii are large (up to approximately 40 ?). All theoretical and experimental sources of errors are discussed. By discussing
the experimental case of a double-walled carbon nanotube, we show how it is possible to determine the chiral indices of each
of its constituant tubes independently, by analyzing parts of the diffraction pattern where the contributions of these tubes
do not interfere. Using the parts where all the contributions do interfere, we successfully crosschecked independently the
preceding determination.
Received 23 December 2003 Published online 7 May 2003 相似文献
2.
D. Blaschke M.K. Volkov V.L. Yudichev 《The European Physical Journal A - Hadrons and Nuclei》2003,17(1):103-110
The phase diagram for quark matter is investigated within a simple Nambu-Jona-Lasinio model without vector correlations. It
is found that the phase structure in the temperature-density plane depends sensitively on the parametrization of the model.
We present two schemes of parametrization of the model where, within the first one, a first-order phase transition from a
phase with broken chiral symmetry to a color superconducting phase for temperatures below the triple point at T
t = 55 MeV occurs, whereas for the second one a second-order phase transition for temperatures below T
t = 7 MeV is found. In the latter case, there is also a coexistence phase of broken chiral symmetry with color superconductivity,
which is a new finding within this class of models. Possible consequences for the phenomenology of the QCD phase transition
at high baryon densities are discussed.
Received: 3 January 2003 / Accepted: 21 February 2003 / Published online: 24 April 2003 相似文献
3.
G. Bonanno D. Valenti B. Spagnolo 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(3):405-409
We study a generalization of the Heston model, which consists of
two coupled stochastic differential equations, one for the stock
price and the other one for the volatility. We consider a cubic
nonlinearity in the first equation and a correlation between the
two Wiener processes, which model the two white noise sources.
This model can be useful to describe the market dynamics
characterized by different regimes corresponding to normal and
extreme days. We analyze the effect of the noise on the
statistical properties of the escape time with reference to the
noise enhanced stability (NES) phenomenon, that is the noise
induced enhancement of the lifetime of a metastable state. We
observe NES effect in our model with stochastic volatility. We
investigate the role of the correlation between the two noise
sources on the NES effect. 相似文献
4.
V. Beato H. Engel L. Schimansky-Geier 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(3):323-329
We study the propagation of periodic pulse trains in excitable media exposed to external spatio-temporal noise using the
light-sensitive Belousov-Zhabotinsky reaction with the underlying Oregonator model as representative example. In the weak
noise
approximation we find noise-induced transitions in the dispersion relation of pulse trains. We discuss noise-enhanced propagation
of
pulse trains within a certain wave-length range caused by external noise of moderate strength. 相似文献
5.
Alexey E. Rastegin 《Frontiers of Physics》2018,13(5):130318
We address the case in which querying the oracle in Grover’s algorithm is exposed to noise including phase distortions. The oracle-box wires can be altered by an opposing party that tries to prevent reception of correct data from the oracle. This situation reflects an experienced truth that any access to prophetic knowledge cannot be common and direct. To study this problem, we introduce a simple model of collective phase distortions on the basis of a phase-damping channel. In the model, the probability of success is not altered via the oracle-box wires per se. Phase distortions of the considered type can hardly be detected via any one-time query to the oracle. However, the probability of success is significantly changed when such errors are introduced as an intermediate step in the Grover iteration. We investigate the probability of success with respect to variations of the parameter that characterizes the amount of phase errors. It turns out that the probability of success decreases significantly even if the error is not very high. Moreover, this probability quickly reduces to the value of one half, which corresponds to the completely mixed state. We also study trade-off relations between quantum coherence and the probability of success in the presence of noise of the considered type. 相似文献
6.
Brimicombe PD Roberts NW Jaradat S Southern C Wang ST Huang CC Dimasi E Pindak R Gleeson HF 《The European physical journal. E, Soft matter》2007,23(3):281-287
A binary mixture of an antiferroelectric liquid-crystal material containing a selenium atom and a highly chiral dopant is
investigated using resonant X-ray scattering. This mixture exhibits a remarkably wide four-layer intermediate smectic phase,
the structure of which is investigated over a temperature range of 16K. Analysis of the resonant X-ray scattering data allows
accurate measurement of both the helicoidal pitch and the distortion angle as a function of temperature. The former decreases
rapidly as the SmC
* phase is approached, whilst the latter remains constant over the temperature range studied at 8°±3° . We also observe that the senses of the helicoidal pitch and the unit cell of the repeating four-layer structure are opposite
in this mixture and that there is no pitch inversion over the temperature range studied. 相似文献
7.
B. Borasoy E. Epelbaum H. Krebs D. Lee U. -G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2008,35(3):357-367
We discuss lattice simulations of the ground state of dilute neutron matter at next-to-leading order in chiral effective field
theory. In a previous paper the coefficients of the next-to-leading-order lattice action were determined by matching nucleon-nucleon
scattering data for momenta up to the pion mass. Here the same lattice action is used to simulate the ground state of up to
12 neutrons in a periodic cube using Monte Carlo simulations. We explore the density range from 2% to 8% of normal nuclear
density and analyze the ground-state energy as an expansion about the unitarity limit with corrections due to finite scattering
length, effective range, and P -wave interactions. 相似文献
8.
S. Spezia L. Curcio A. Fiasconaro N. Pizzolato D. Valenti B. Spagnolo P. Lo Bue E. Peri S. Colazza 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(3):453-458
We investigate the role of the noise in the mating behavior between individuals of Nezara viridula (L.), by analyzing the temporal and spectral features of the non-pulsed type female calling song emitted by single individuals.We
have measured the threshold level for the signal detection, by performing experiments with the calling signal at different
intensities and analyzing the insect response by directionality tests performed on a group of male individuals. By using a
sub-threshold signal and an acoustic Gaussian noise source, we have investigated the insect response for different levels
of noise, finding behavioral activation for suitable noise intensities. In particular, the percentage of insects which react
to the sub-threshold signal, shows a non-monotonic behavior, characterized by the presence of a maximum, for increasing levels
of the noise intensity. This constructive interplay between external noise and calling signal is the signature of the non-dynamical
stochastic resonance phenomenon. Finally, we describe the behavioral activation statistics by a soft threshold model which
shows stochastic resonance. We find that the maximum of the ensemble average of the input-output cross-correlation occurs
at a value of the noise intensity very close to that for which the behavioral response has a maximum. 相似文献
9.
N. Olivi-Tran N. Fraysse P. Girard M. Ramonda D. Chatain 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):217-222
We have performed noise measurements on suspended ropes of single wall carbon nanotubes (SWNT) between 1 and 300 K for different
values of dc current through the ropes. We find that the shot noise is suppressed by more than a factor 100 compared to the
full shot noise 2eI. We have also measured an individual SWNT and found a level of noise which is smaller than the minimum expected. Another
finding is the very low level of 1/f noise, which is significantly lower than previous observations. We propose two possible interpretations for the strong shot
noise reduction: i) Transport within a rope takes place through few nearly ballistic tubes within a rope and possibly involves
non integer effective charges with e
*∼ 0.3e. ii) A substantial fraction of the tubes conduct with a strong reduction of effective charge (by more than a factor 50).
Received 25 January 2002 Published online 19 July 2002 相似文献
10.
B. Spagnolo A. Dubkov 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):299-303
The one-dimensional overdamped Brownian motion in a symmetric
periodic potential modulated by external time-reversible noise is
analyzed. The calculation of the effective diffusion coefficient
is reduced to the mean first passage time problem. We derive
general equations to calculate the effective diffusion coefficient
of Brownian particles moving in arbitrary supersymmetric potential
modulated by: (i) an external white Gaussian noise and (ii) a
Markovian dichotomous noise. For both cases the exact expressions
for the effective diffusion coefficient are derived. We obtain
acceleration of diffusion in comparison with the free diffusion
case for fast fluctuating potentials with arbitrary profile and
for sawtooth potential in case (ii). In this case the parameter
region where this effect can be observed is given. We obtain also
a finite net diffusion in the absence of thermal noise. For
rectangular potential the diffusion slows down, for all parameters
of noise and of potential, in comparison with the case when
particles diffuse freely. 相似文献
11.
A. R. Bulsara V. In A. Kho G. Anderson C. Obra P. Longhini J. Neff S. Baglio B. Ando A. Palacios 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(1):109-118
We consider the performance of a nonlinear dynamic device, operated as a threshold detector, in the time domain. The device
is characterized by a figure-of-merit that involves the mean residence times in its two stable steady states, as well as the
dispersion in this quantity stemming from a noise floor. As a particular example, we consider a coupled (overdamped) oscillator
system, the underpinnings of a coupled core magnetometer (CCM). We provide a detailed discussion of how the device is used,
in practice, to detect a weak dc target magnetic field, and explain the importance of characteristic time-scales in the problem
specifically the device time-constant, the noise correlation time and the observation time (to obtain an averaged reading
in the presence of noise). A device “Resolution” is introduced as a performance measure and is, analytically, computed under
specific (but realistic for practical applications) conditions. This measure is shown to be independent of the target signal;
in fact it depends only on the noise and device parameters, in the weak signal limit (that is of interest in most applications).
The resolution is seen to be analogous to the inverse of a response signal-to-noise ratio. 相似文献
12.
V. Lensky V. Baru E. Epelbaum C. Hanhart J. Haidenbauer A. Kudryavtsev U. -G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2007,33(4):339-348
We discuss the possibility to extract the neutron-neutron scattering length ann from experimental spectra on the reaction γd → π+
nn . The transition operator is calculated to high accuracy from chiral perturbation theory. We argue that for properly chosen
kinematics, the theoretical uncertainty of the method can be as low as 0.1 fm. 相似文献
13.
K. Mallick P. Marcq 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):553-561
We study analytically and numerically the problem of a nonlinear mechanical oscillator with additive noise in the absence
of damping. We show that the amplitude, the velocity and the energy of the oscillator grow algebraically with time. For Gaussian
white noise, an analytical expression for the probability distribution function of the energy is obtained in the long-time
limit. In the case of colored, Ornstein-Uhlenbeck noise, a self-consistent calculation leads to (different) anomalous diffusion
exponents. Dimensional analysis yields the qualitative behavior of the prefactors (generalized diffusion constants) as a function
of the correlation time.
Received 10 October 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: mallick@spht.saclay.cea.fr 相似文献
14.
15.
We explore the NJL model with Polyakov loops for a system of three colors and two flavors within the mean-field approximation, where both chiral symmetry and confinement are taken into account. We focus on the phase structure of the model and study the chiral and Polyakov loop susceptibilities. 相似文献
16.
17.
Hui-Juan Cao 《Physics letters. A》2008,372(17):2971-2975
We propose a scheme to detect the chirality for a system consisting of three coupled quantum dots. The chirality is found to be determined by the frequency of the transition between chiral states under the chiral symmetry broken perturbation. The results are important to construct quantum gates and to demonstrate chiral entangle states in the triangle spin dots. 相似文献
18.
Verhulst model with Lévy white noise excitation 总被引:1,自引:0,他引:1
A. A. Dubkov B. Spagnolo 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(3):361-367
The transient dynamics of the Verhulst model perturbed by arbitrary non-Gaussian white noise is investigated. Based on the
infinitely divisible distribution of the Lévy process we study the nonlinear relaxation of the population density for three
cases of white non-Gaussian noise: (i) shot noise; (ii) noise with a probability density of increments expressed in terms
of Gamma function; and (iii) Cauchy stable noise. We obtain exact results for the probability distribution of the population
density in all cases, and for Cauchy stable noise the exact expression of the nonlinear relaxation time is derived. Moreover
starting from an initial delta function distribution, we find a transition induced by the multiplicative Lévy noise, from
a trimodal probability distribution to a bimodal probability distribution in asymptotics. Finally we find a nonmonotonic behavior
of the nonlinear relaxation time as a function of the Cauchy stable noise intensity. 相似文献
19.
S. E. Mangioni H. S. Wio 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(1):67-73
We analyze the effect of a colored non Gaussian noise on a model of
a random walker moving along a ratchet potential. Such a model was
motivated by the transport properties of motor proteins, like
kinesin and myosin. Previous studies have been realized assuming
white noises. However, for real situations, in general we could
expect that those noises be correlated and non Gaussian. Among other
aspects, in addition to a maximum in the current as the noise
intensity is varied, we have also found another optimal value of the
current when departing from Gaussian behavior. We show the relevant
effects that arise when departing from Gaussian behavior,
particularly related to current's enhancement, and discuss its
relevance for both biological and technological situations. 相似文献