Simulation study of random sequential adsorption of mixtures on a triangular lattice

Random sequential adsorption of binary mixtures of extended objects on a two-dimensional triangular lattice is studied numerically by means of Monte Carlo simulations. The depositing objects are formed by self-avoiding random walks on the lattice. We concentrate here on the influence of the symmetry properties of the shapes on the kinetics of the deposition processes in two-component mixtures. Approach to the jamming limit in the case of mixtures is found to be exponential, of the form: $\theta(t) \sim \theta_{jam}-\Delta\theta \exp (-t/\sigma),$ and the values of the parameter $\sigma$ are determined by the order of symmetry of the less symmetric object in the mixture. Depending on the local geometry of the objects making the mixture, jamming coverage of a mixture can be either greater than both single-component jamming coverages or it can be in between these values. Results of the simulations for various fractional concentrations of the objects in the mixture are also presented.Comment: 11 figures, 2 table

BER Performance of IM/DD FSO System with OOK using APD Receiver

In this paper, the performance of intensity-modulated with direct detection (IM/DD) free space optical (FSO) system using the on-off keying (OOK) and avalanche photodiode (APD) receiver is observed. The gamma-gamma model is used to describe the effect of atmospheric turbulence since it provides good agreement in the wide range of atmospheric conditions. In addition, the same FSO system with equal gain combining applied at the reception is analyzed. After theoretical derivation of the expression for the bit error rate (BER), the numerical integration with previously specified relative calculation error is performed. Numerical results are presented and confirmed by Monte Carlo simulations. The effects of the FSO link and receiver parameters on the BER performance are discussed. The results illustrate that the optimal APD gain in the minimum BER sense depends considerably on the link distance, atmospheric turbulence strength and receiver temperature. In addition, the value of this optimal gain is slightly different in the case of spatial diversity application compared with single channel reception

Ferromagnetic resonance with a magnetic Josephson junction

We show experimentally and theoretically that there is a coupling via the Aharonov-Bohm phase between the order parameter of a ferromagnet and a singlet, s-wave, Josephson supercurrent. We have investigated the possibility of measuring the dispersion of such spin waves by varying the magnetic field applied in the plane of the junction and demonstrated the electromagnetic nature of the coupling by the observation of magnetic resonance side-bands to microwave induced Shapiro steps.Comment: 6 pages, 5 figure

Transport properties of clean and disordered Josephson junction arrays

We investigate the influence of quantum fluctuations and weak disorder on the vortex dynamics in a two-dimensional superconducting Berezinskii-Kosterlitz-Thouless system. The temperature below which quantum fluctuations dominate the vortex creep is determined, and the transport in this quantum regime is described. The crossover from quantum to classical regime is discussed and the quantum correction to the classical current-voltage relation is determined. It is found that weak disorder can effectively reduce the critical current as compared to that in the clean system.Comment: 4 pages, 2 figure

The Effect of Randomness on the Mott State

We reinvestigate the competition between the Mott and the Anderson insulator state in a one-dimensional disordered fermionic system by a combination of instanton and renormalization group methods. Tracing back both the compressibility and the ac-conductivity to a vanishing kink energy of the electronic displacement field we do not find any indication for the existence of an intermediate (Mott glass) phase.Comment: 4 page

Analiza i načini poboljšanja performansi bežičnih optičkih telekomunikacionih sistema u uslovima atmosferske turbulencije

Since contemporary radio-frequency (RF) communication systems are characterized by overcrowded and licensed spectrum, limited bandwidth and relatively low transmission data rates, the use of these technologies does not provide a series of new demands that future generations of telecommunications systems have to realize. Although optical fiber systems allow more bandwidth and higher transmission rates, they are characterized by complicated and expensive implementation. As one possible solution for the "last mile" problem, Free Space Optics (FSO) technology has gained importance since it provides simultaneously the optical fibre systems data rates and the flexibility of wireless communications. The optical signal at the reception is converted into an electrical one by photodiode after transmission via the atmospheric channel. Commercial FSO systems generally use intensity modulation (IM) with OOK scheme at the transmitting part of the system, while direct detection (DD) is performed at the reception. The FSO system employing IM/DD with OOK scheme and PIN photodiode at the receiver is analyzed in the thesis. The outage probability and error rate expressions are presented, which are used to examine the effect of atmospheric turbulence and pointing errors. The FSO systems with subcarrier intensity modulation (SIM) employing various modulations in electrical domain (phase shift keying (PSK), differential phase shift keying (DPSK) and quadrature amplitude modulation (QAM)) are analyzed in the continuation of the thesis. The error rate expressions are derived. The SIM-PSK and SIM- DPSK FSO system analysis is performed considering more general case when the hardware imperfections of the receiver electrical part are taken into account. The ergodic and outage capacity analysis is also presented, taking into consideration the probability of the optical signal blockage due to random obstacles. Based on the derived results, the FSO link optimization is done in order to achieve better system performance. Furthermore, the analysis of FSO systems with avalanche (APD) photodiode at the reception is presented. The bit error rate expressions for the FSO systems employing IM/DD with OOK scheme, SIM-PSK and SIM-BDPSK are derived. Based on the presented results, the APD gain optimization is performed in order to achieve minimal values of the error rate. The use of relaying technology is investigated as a method to improve system performance. The mixed RF/FSO systems with fixed and variable AF (Amplify and Forward) relays are analyzed. Beside the noise-limited scenario, the more general case, when the relay is affected by noise and interference, is also considered. The outage probability and error rate expressions are presented, which are utilized to determine the effects of the RF and FSO link conditions on system performance. The determination of a variable gain is performed based on instantaneous channel state information (CSI), which is happened to be outdated in practical scenario. Therefore, the analytical expressions for the outage probability and error rate are derived, considering the RF/FSO system with variable AF relay based on outdated CSI. Further improvement of the system performance is achieved by using diversity combining techniques in the RF domain by multiple parallel relaying. The analytical expressions for the system performance are derived for the RF/FSO system with partial relay selection based on outdated CSI. The RF/FSO system with fixed AF relays is considered, as well as the RF/FSO system with variable AF relays when the amplification gain is determined by the same outdated CSI used for relay selection. The effect of RF channel state is examined, as well as the influence of atmospheric conditions, pointing errors and FSO aperture design on the system performance. A developed simulation model is utilized to confirm the numerical results obtained by the analytical expressions presented in the dissertation thesis

Carrier drift velocity and edge magnetoplasmons in graphene

We investigate electron dynamics at the graphene edge by studying the propagation of collective edge magnetoplasmon (EMP) excitations. By timing the travel of narrow wave-packets on picosecond time scales around exfoliated samples, we find chiral propagation with low attenuation at a velocity which is quantized on Hall plateaus. We extract the carrier drift contribution from the EMP propagation and find it to be slightly less than the Fermi velocity, as expected for an abrupt edge. We also extract the characteristic length for Coulomb interaction at the edge and find it to be smaller than for soft, depletion edge systems.Comment: 5 pages, 3 figures of main text and 6 pages, 6 figures of supplemental materia

Optimization of Collateral Value Distribution

Loan Loss Provisioning (LLP) is an amount of reserve that banks "put aside" to cover loss in case that loan goes in default, meaning that clients do not repay it. It is a safety buffer for preserving banks liquidity and capital adequacy. On the other hand, the Loan Loss Provisioning is a cost. In the Profit and Lost statement of banks, LLP decreases profit. It is a good tool/mechanism for risk management, but also expensive one, and that is why it is important for banks to optimize it in every possible way. The aim of optimization is to distribute collateral value to the connected loans, in a way to minimize amount of LLP. It can be done easily on a one loan level, but creating a universal algorithm that is applicable to all loans and all collaterals on the Bank portfolio level, is the goal to be achieved

Distribution of velocities and acceleration for a particle in Brownian correlated disorder: inertial case

We study the motion of an elastic object driven in a disordered environment in presence of both dissipation and inertia. We consider random forces with the statistics of random walks and reduce the problem to a single degree of freedom. It is the extension of the mean field ABBM model in presence of an inertial mass m. While the ABBM model can be solved exactly, its extension to inertia exhibits complicated history dependence due to oscillations and backward motion. The characteristic scales for avalanche motion are studied from numerics and qualitative arguments. To make analytical progress we consider two variants which coincide with the original model whenever the particle moves only forward. Using a combination of analytical and numerical methods together with simulations, we characterize the distributions of instantaneous acceleration and velocity, and compare them in these three models. We show that for large driving velocity, all three models share the same large-deviation function for positive velocities, which is obtained analytically for small and large m, as well as for m =6/25. The effect of small additional thermal and quantum fluctuations can be treated within an approximate method.Comment: 42 page

Phase dynamics of ferromagnetic Josephson junctions

We have investigated the classical phase dynamics of underdamped ferromagnetic Josephson junctions by measuring the switching probability in both the stationary and nonstationary regimes down to 350 mK. We found the escape temperature to be the bath temperature, with no evidence of additional spin noise. In the nonstationary regime, we have performed a pump-probe experiment on the Josephson phase by increasing the frequency of the junction current bias. We show that an incomplete energy relaxation leads to dynamical phase bifurcation. Bifurcation manifests itself as premature switching, resulting in a bimodal switching distribution. We directly measure the phase relaxation time by following the evolution of the bimodal switching distribution when varying the bias frequency. Numerical simulations account for the experimental values of the phase relaxation time.Comment: 4 pages, 3 figure