Multifractality in stock indexes: Fact or Fiction?

Multifractal analysis and extensive statistical tests are performed upon intraday minutely data within individual trading days for four stock market indexes (including HSI, SZSC, S&P 500, and NASDAQ) to check whether the indexes (instead of the returns) possess multifractality. We find that the mass exponent τ(q) is linear and the singularity α(q) is close to 1 for all trading days and all indexes. Furthermore, we find strong evidence showing that the scaling behaviors of the original data sets cannot be distinguished from those of shuffled time series. Hence, the so-called multifractality in the intraday stock market indexes is merely an illusion.     

Ultrafast magneto-optics in nickel: magnetism or optics?

Several magnetic and optical processes contribute to the magneto-optical response of nickel thin films after excitation by a femtosecond laser pulse. We achieved a first complete identification by explicitly measuring the time-resolved Kerr ellipticity and rotation, as well as its temperature and magnetic field dependence in epitaxially grown (111) and (001) oriented Cu/Ni/Cu wedges. The first hundreds of femtoseconds the response is dominated by state filling effects. The true demagnetization takes approximately 0.5-1 ps. At the longer (sub-ns) time scales the spins are found to precess in their anisotropy field. Simple and transparent models are introduced to substantiate our interpretation.     

Superconductivity in MgB2: clean or dirty?

A large number of experimental facts and theoretical arguments favor a two-gap model for superconductivity in MgB2. However, this model predicts strong suppression of the critical temperature by interband impurity scattering and, presumably, a strong correlation between the critical temperature and the residual resistivity. No such correlation has been observed. We argue that this fact can be understood if the band disparity of the electronic structure is taken into account, not only in the superconducting state, but also in normal transport.     

Hall effect noise: Fluctuations in number or mobility?

The purpose of this paper is to show that the 1/f noise in the Hall voltage as reported by Brophy and Rostoker can be interpreted in terms of fluctuations in the mobility of free-charge carriers. Brophy and Rostoker have claimed that 1/f noise in the Hall voltage is a direct proof of 1/f fluctuations in the free-carrier density. Their conclusion is shown to be wrong.     

Causality in Reversed Time Series: Reversed or Conserved?

The inference of causal relations between observable phenomena is paramount across scientific disciplines; however, the means for such enterprise without experimental manipulation are limited. A commonly applied principle is that of the cause preceding and predicting the effect, taking into account other circumstances. Intuitively, when the temporal order of events is reverted, one would expect the cause and effect to apparently switch roles. This was previously demonstrated in bivariate linear systems and used in design of improved causal inference scores, while such behaviour in linear systems has been put in contrast with nonlinear chaotic systems where the inferred causal direction appears unchanged under time reversal. The presented work explores the conditions under which the causal reversal happens—either perfectly, approximately, or not at all—using theoretical analysis, low-dimensional examples, and network simulations, focusing on the simplified yet illustrative linear vector autoregressive process of order one. We start with a theoretical analysis that demonstrates that a perfect coupling reversal under time reversal occurs only under very specific conditions, followed up by constructing low-dimensional examples where indeed the dominant causal direction is even conserved rather than reversed. Finally, simulations of random as well as realistically motivated network coupling patterns from brain and climate show that level of coupling reversal and conservation can be well predicted by asymmetry and anormality indices introduced based on the theoretical analysis of the problem. The consequences for causal inference are discussed.     

Iron-mineral-based magnetoreceptor in birds: polarity or inclination compass?

In the present paper we demonstrate that the iron-mineral-based magnetoreceptor model developed in [1] can provide birds with a magnetic compass in addition to the generally believed “magnetic map". We show that the iron-mineral-based magnetoreceptor system possesses all properties of a polarity compass, which is extremely important for avian navigation. We study how parameters of the magnetoreceptor system influence on the properties of the compass and show that at certain conditions it acquires features of an inclination compass. In the present paper we address the question of avian magnetoreception theoretically and suggest several experiments which should be performed for better understanding of the iron-mineral-based compass in birds.     

Micro-transitions or breathers in L-alanine?

Within mean field approximation, a procedure is elaborated to consider noise induced phase transitions with arbitrary relations between the noises of different degrees of freedom. The proposed approach is applied to investigate effects of cross correlation between noises in the generalized synergetic model of Lorenz type. This cross correlation is shown to induce phase transitions of the dynamical system under consideration. Additionally, we find the correlation between noises transforms a synergetic behavior to a thermodynamic one. Received 13 November 2002 Published online 11 April 2003 RID="a" ID="a"e-mail: dikh@sumdu.edu.ua     

Reentrant layering in rare gas adsorption: preroughening or premelting?

The reentrant layering transition found in rare gas adsorption on solid substrates has conflictually been explained in terms either of preroughening (PR) or of top layer melting-solidification phenomena. We obtain adsorption isotherms of Lennard-Jones particles on an attractive substrate by off lattice grand canonical Monte Carlo simulation, and reproduce reentrant layering. Microscopic analysis confirms a transformation of the top surface layer from solid to quasiliquid across the transition. At the same time, however, the surface coverage is found to switch from close to one to close to half, the latter indicating a disordered flat surface and establishing PR as the underlying mechanism. We conclude that top layer melting can trigger PR. In turn, PR appears to act as the threshold transition for surface melting in rare gas solids.     

Surface anisotropy in nanomagnets: transverse or Néel?

Through the hysteresis loop and magnetization spatial distribution we study and compare two models for surface anisotropy in nanomagnets: a model with transverse anisotropy axes and Néel's model. While surface anisotropy in the transverse model induces several jumps in the hysteresis loop because of the cluster-wise switching of spins, in the Néel model the jumps correspond to successive coherent partial rotations of the whole bunch of spins. These calculations together with some hints from available experimental results, suggest that Néel's model for surface anisotropy is more appropriate.     

Melody lead in piano performance: expressive device or artifact?

As reported in the recent literature on piano performance, an emphasized voice (the melody) tends to be played not only louder than the other voices, but also about 30 ms earlier (melody lead). It remains unclear whether pianists deliberately apply melody lead to separate different voices, or whether it occurs because the melody is played louder (velocity artifact). The velocity artifact explanation implies that pianists initially strike the keys simultaneously; it is only different velocities that make the hammers arrive at different points in time. The measured note onsets in these studies, mostly derived from computer-monitored pianos, represent the hammer-string impact times. In the present study, the finger-key contact times are calculated and analyzed as well. If the velocity artifact hypothesis is correct, the melody lead phenomenon should disappear at the finger-key level. Chopin's Ballade op. 38 (45 measures) and Etude op. 10/3 (21 measures) were performed on a B?sendorfer computer-monitored grand piano by 22 skilled pianists. The hammer-string asynchronies among voices closely resemble the results reported in the literature. However, the melody lead decreases almost to zero at the finger-key level, which supports the velocity artifact hypothesis. In addition to this, expected onset asynchronies are predicted from differences in hammer velocity, if finger-key asynchronies are assumed to be zero. They correlate highly with the observed melody lead.     

Production or conservation in CHP networks?

In Sweden, Combined generation of Heat and Power (CHP) is in common practice. Different fuels are burnt in a boiler and the steam is used for generating electricity. The heat that has to be transferred from the condenser in the plant is used in the district heating grid. This grid is thus used as a cooling facility necessary for electricity production. However, energy conservation the Swedish building stock is also encouraged, and if this is utilized in district heated buildings it results in fewer possibilities for electricity production. This might be a major drawback when nuclear power is abolished, as is the result from a consensus some years ago. This paper deals with the question of whether it is better to conserve both heat and electricity, to save only one of the energy forms or if it is cheaper to produce more energy, instead of saving. A case study is presented dealing with Malmö, in the South of Sweden, and it is shown that energy conservation in district heated buildings cannot yield profitability: neither can conservation in the electricity grid, even if it gets closer to profitable savings. It is assumed that the total cost of heating, insulation and electricity is paid by the society and the minimum point for this cost will characterize the best solution.     

Nanosciences: Evolution or revolution?

In miniaturized objects fabricated by modern technology the smallest linear size may be of a few nanometers. In the field of microelectronics, the advantages of such a miniaturization are huge (increased complexity and reliability, reduced costs). The technology is now approaching the limits where further size reduction will be impossible, except for very novel techniques such as molecular electronics. Miniaturization research has also led to the discovery of nanometric objects such as carbon nanotubes, which turn out to be particularly appropriate for inventing new materials. Miniaturization techniques have been progressively applied in other fields, with the hope of obtaining improvements similar to those encountered in microelectronics. Examples are biochips, which concentrate on a few cm² the recognition of ADN sequences, or ‘lab-on-a-chip’ devices, each of which constitutes a whole laboratory of chemical analysis, or MEMs (Micro Electro Mechanical Systems). New therapies will use miniaturized objects with multiple functions: For instance a nanoparticle can both recognize the target organ thanks to an appropriate protein, and deliver the therapeutic molecule to this target. These results have only been possible through new observation instruments, able to observe and manipulate nano objects. Is the observed evolution really a revolution of science and techniques? This is a point discussed in the conclusion, which also deals with risks associated to nanotechnologies, while the need for a social regulation is stressed.     

Highly conductive polymers: superconductivity in nanochannels or an experimental artifact?

There is a significant body of literature concerning the potential formation of electrically conductive moieties in polymeric materials. The conductive path is not associated with conjugation (such as in the case of ‘conductive polymers’) but rather associated with a new conductivity route. The objective of the experiments reported herein was to provide insight into the phenomenon of unusually high electrical conductivity in polymers that have been reported by several research groups. In some experiments, the test apparatus did indeed indicate high levels of conductance. Arguments pro and con for high conductivity based on known physical phenomena and the collected data were examined.