Pinning control of fractional-order weighted complex networks

In this paper, we consider the pinning control problem of fractional-order weighted complex dynamical networks. The well-studied integer-order complex networks are the special cases of the fractional-order ones. The network model considered can represent both directed and undirected weighted networks. First, based on the eigenvalue analysis and fractional-order stability theory, some local stability properties of such pinned fractional-order networks are derived and the valid stability regions are estimated. A surprising finding is that the fractional-order complex networks can stabilize itself by reducing the fractional-order q without pinning any node. Second, numerical algorithms for fractional-order complex networks are introduced in detail. Finally, numerical simulations in scale-free complex networks are provided to show that the smaller fractional-order q, the larger control gain matrix D, the larger tunable weight parameter , the larger overall coupling strength c, the more capacity that the pinning scheme may possess to enhance the control performance of fractional-order complex networks

The role of electron-electron interactions in two-dimensional Dirac fermions

The role of electron-electron interactions on two-dimensional Dirac fermions remains enigmatic. Using a combination of nonperturbative numerical and analytical techniques that incorporate both the contact and long-range parts of the Coulomb interaction, we identify the two previously discussed regimes: a Gross-Neveu transition to a strongly correlated Mott insulator, and a semi-metallic state with a logarithmically diverging Fermi velocity accurately described by the random phase approximation. Most interestingly, experimental realizations of Dirac fermions span the crossover between these two regimes providing the physical mechanism that masks this velocity divergence. We explain several long-standing mysteries including why the observed Fermi velocity in graphene is consistently about 20 percent larger than the best values calculated using ab initio and why graphene on different substrates show different behavior.Comment: 11 pages, 4 figure

Ephemeral active regions and coronal bright points: A solar maximum Mission 2 guest investigator study

A dominate association of coronal bright points (as seen in He wavelength 10830) was confirmed with the approach and subsequent disappearance of opposite polarity magnetic network. While coronal bright points do occur with ephemeral regions, this association is a factor of 2 to 4 less than with sites of disappearing magnetic flux. The intensity variations seen in He I wavelength 10830 are intermittent and often rapid, varying over the 3 minute time resolution of the data; their bright point counterparts in the C IV wavelength 1548 and 20 cm wavelength show similar, though not always coincident time variations. Ejecta are associated with about 1/3 of the dark points and are evident in the C IV and H alpha data. These results support the idea that the anti-correlation of X-ray bright points with the solar cycle can be explained by the correlation of these coronal emission structures with sites of cancelling flux, indicating that, in some cases, the process of magnetic flux removal results in the release of energy. That the intensity variations are rapid and variable suggests that this process works intermittently

Structural Polymorphism of the Cytoskeleton: A Model of Linker-Assisted Filament Aggregation

The phase behavior of charged rods in the presence of inter-rod linkers is studied theoretically as a model for the equilibrium behavior underlying the organization of actin filaments by linker proteins in the cytoskeleton. The presence of linkers in the solution modifies the effective inter-rod interaction and can lead to inter-filament attraction. Depending on the system's composition and physical properties such as linker binding energies, filaments will either orient perpendicular or parallel to each other, leading to network-like or bundled structures. We show that such a system can have one of three generic phase diagrams, one dominated by bundles, another by networks, and the third containing both bundle and network-like phases. The first two diagrams can be found over a wide range of interaction energies, while the third occurs only for a narrow range. These results provide theoretical understanding of the classification of linker proteins as bundling proteins or crosslinking proteins. In addition, they suggest possible mechanisms by which the cell may control cytoskeletal morphology.Comment: 17 pages, 3 figure

Dislocation filters in GaAs on Si

Cross section transmission electron microscopy has been used to analyse dislocation filter layers (DFLs) in five similar structures of GaAs on Si that had different amounts of strain in the DFLs or different annealing regimes. By counting threading dislocation (TD) numbers through the structure we are able to measure relative changes, even though the absolute density is not known. The DFLs remove more than 90% of TDs in all samples. We find that the TD density in material without DFLs decays as the inverse of the square root of the layer thickness, and that DFLs at the top of the structure are considerably more efficient than those at the bottom. This indicates that the interaction radius, the distance that TDs must approach to meet and annihilate, is dependent upon the TD density

Quantum oscillations of the magnetic torque in the nodal-line Dirac semimetal ZrSiS

We report a study of quantum oscillations (QO) in the magnetic torque of the nodal-line Dirac semimetal ZrSiS in the magnetic fields up to 35 T and the temperature range from 40 K down to 2 K, enabling high resolution mapping of the Fermi surface (FS) topology in the $k_z=\pi$ (Z-R-A) plane of the first Brillouin zone (FBZ). It is found that the oscillatory part of the measured magnetic torque signal consists of low frequency (LF) contributions (frequencies up to 1000 T) and high frequency (HF) contributions (several clusters of frequencies from 7-22 kT). Increased resolution and angle-resolved measurements allow us to show that the high oscillation frequencies originate from magnetic breakdown (MB) orbits involving clusters of individual $\alpha$ hole and $\beta$ electron pockets from the diamond shaped FS in the Z-R-A plane. Analyzing the HF oscillations we have unequivocally shown that the QO frequency from the dog-bone shaped Fermi pocket ($\beta$ pocket) amounts $\beta=591(15)$ T. Our findings suggest that most of the frequencies in the LF part of QO can also be explained by MB orbits when intraband tunneling in the dog-bone shaped $\beta$ electron pocket is taken into account. Our results give a new understanding of the novel properties of the FS of the nodal-line Dirac semimetal ZrSiS and sister compounds

Potential of mean force and the charge reversal of rodlike polyions

A simple model is presented to calculate the potential of mean force between a polyion and a multivalent counterion inside a polyelectrolite solution. We find that under certain conditions the electrostatic interactions can lead to a strong attraction between the polyions and the multivalent counterions, favoring formation of overcharged polyion-counterion complexes. It is found that small concentrations of salt enhance the overcharging, while an excessive amount of salt hinders the charge reversal. The kinetic limitations to overcharging are also examined.Comment: To be published in the special issue of Molecular Physics in honor of Prof. Ben Wido

Beat-wave generation of plasmons in semiconductor plasmas

It is shown that in semiconductor plasmas, it is possible to generate large amplitude plasma waves by the beating of two laser beams with frequency difference close to the plasma frequency. For narrow gap semiconductors (for example n-type InSb), the system can simulate the physics underlying beat wave generation in relativistic gaseous plasmas.Comment: 11 pages, LaTex, no figures, no macro

Electron-electron interaction in carbon nanostructures

The electron-electron interaction in carbon nanostructures was studied. A new method which allows to determine the electron-electron interaction constant $\lambda_c$ from the analysis of quantum correction to the magnetic susceptibility and the magnetoresistance was developed. Three types of carbon materials: arc-produced multiwalled carbon nanotubes (arc-MWNTs), CVD-produced catalytic multiwalled carbon nanotubes (c-MWNTs) and pyrolytic carbon were used for investigation. We found that $\lambda_c$=0.2 for arc-MWNTs (before and after bromination treatment); $\lambda_c$ = 0.1 for pyrolytic graphite; $\lambda_c >$ 0 for c-MWNTs. We conclude that the curvature of graphene layers in carbon nanostructures leads to the increase of the electron-electron interaction constant $\lambda_c$.Comment: 12 pages, 18 figures, to be published in the Proceedings of the NATO Advanced Research Workshop on Electron Correlation in New Materials and Nanosystems, NATO Science Series II, Springer, 200

Fusion-Fission of 16O+197Au at Sub-Barrier Energies

The recent discovery of heavy-ion fusion hindrance at far sub-barrier energies has focused much attention on both experimental and theoretical studies of this phenomenon. Most of the experimental evidence comes from medium-heavy systems such as Ni+Ni to Zr+Zr, for which the compound system decays primarily by charged-particle evaporation. In order to study heavier systems, it is, however, necessary to measure also the fraction of the decay that goes into fission fragments. In the present work we have, therefore, measured the fission cross section of 16O+197Au down to unprecedented far sub-barrier energies using a large position sensitive PPAC placed at backward angles. The preliminary cross sections will be discussed and compared to earlier studies at near-barrier energies. No conclusive evidence for sub-barrier hindrance was found, probably because the measurements were not extended to sufficiently low energies.Comment: Fusion06 - Intl. Conf. on Reaction Mechanisms and Nuclear Structure at the Coulomb Barrier, San Servolo, Venezia, Italy, March 19-223, 2006 5 pages, 4 figure