Hopping Rate Research Articles

A phase transition for [formula omitted]-TASEP with a few slower particles

We consider a q-TASEP model started from step initial condition where all but finitely many particles have speed 1 and a few particles are slower. It is shown in Ferrari and Veto (2013) that the rescaled particles position of q-TASEP with identical hopping rates obeys a limit theorem à la Tracy–Widom. We adapt this work to the case of different hopping rates and show that one observes the so-called BBP transition. Our proof is a refinement of Ferrari–Vető’s and does not require any condition on the parameter q nor the macroscopic position of particles.

Satellite Frequency Hopping Communication System on the Basis of GPS Time Service and Satellite Ephemeris

A Frequency Hopping (FH) communication method for uplink and downlink of satellite and ground station on the basis of GPS time service and satellite ephemeris is proposed. By adopting the SGP4 model to predict the satellite orbit, the relative position and velocity between satellite and ground station can be calculated precisely. The ground station completes pre-correction and compensation of the propagation delay and Doppler shift that have been estimated. The result shows that our proposed system performs lower hardware complexity and higher frequency hopping rate than traditional FH system. The propagation delay estimation precision is better than 250 ns. The Doppler shift estimation precision is better than 1 Hz. When the system cost is 1%, frequency hopping rate can reach 20000 Hops/s. The proposed system has strong anti-interference ability and strong anti-interception ability.

Generic nonequilibrium steady states in an exclusion process on an inhomogeneous ring

We consider a one-dimensional totally asymmetric exclusion process on a ring with extended inhomogeneities, consisting of several segments with different hopping rates. Depending upon the underlying inhomogeneity configurations and for moderate densities, our model displays both localised (LDW) and delocalised (DDW) domain walls and delocalisation transitions of LDWs in the steady states. Our results allow us to construct the possible steady state density profiles for an arbitrary number of segments with unequal hopping rates. We explore the scaling properties of the fluctuations of LDWs and DDWs.

Tuning the reactivity of a dissociative force field: proton transfer properties of aqueous H3O(+) and their dependence on the three-body interaction.

The proton transfer properties of the dissociative water potential developed by Garofalini et al. were closely examined by carefully analyzing the pairwise screening functions of the three-body interaction. It was shown that a simultaneous adjustment of the exponential screening factor and the three-body cutoff distance enables a selective adjustment of the diffusive properties of an excess proton, while at the same time structural and other dynamical data remain unaffected to a large extend. To investigate proton transfer properties without the influence of nuclear quantum effects, deuterated systems have been investigated in addition to their hydrogen counterparts. It was shown that the suggested parameter set A leads to significantly improved diffusion coefficients and proton hopping rates. Comparison of proton transfer correlation functions to simulation data obtained from Car-Parrinello molecular dynamics simulations confirms the improved performance of the adjusted parametrization.

Two-point correlation function of an exclusion process with hole-dependent rates.

We consider an exclusion process on a ring in which a particle hops to an empty neighboring site with a rate that depends on the number of vacancies n in front of it. In the steady state, using the well-known mapping of this model to the zero-range process, we write down an exact formula for the partition function and the particle-particle correlation function in the canonical ensemble. In the thermodynamic limit, we find a simple analytical expression for the generating function of the correlation function. This result is applied to the hop rate u(n)=1+(b/n) for which a phase transition between high-density laminar phase and low-density jammed phase occurs for b>2. For these rates, we find that at the critical density, the correlation function decays algebraically with a continuously varying exponent b-2. We also calculate the two-point correlation function above the critical density and find that the correlation length diverges with a critical exponent ν=1/(b-2) for b<3 and 1 for b>3. These results are compared with those obtained using an exact series expansion for finite systems.

Anti-jamming Frequency Hopping System Using Multiple Hopping Patterns

This paper deals with the follower jamming (FJ) and partial-band jamming (PBJ) resistance for the frequency hopping (FH) communication system with low hopping rate over AWGN channel. To gain a comprehensive FJ and PBJ rejection capability, we propose a multi-pattern frequency hopping (MPFH) scheme. In MPFH, the data channel and complementary channel are hopped on separate frequency slots determined by their respective frequency patterns, which will lure the follower jammer out of aiming at the complementary channel, thus mitigating the effect of FJ. Besides, narrow-band receiver is employed to ensure its PBJ rejection capability. We further enhance the proposed scheme by employing convolutional coding and maximum-likelihood decoding. Its upper bounds on bit error rate (BER) are derived under FJ and PBJ, respectively. Effects of three FJ parameters (tracking success probability, jamming duration ratio and jamming bandwidth ratio) and one PBJ parameter (jamming bandwidth ratio) on BER performance of MPFH are investigated versus the conventional FH/BFSK and recently developed differential frequency hopping (DFH) system. Numerical and simulation results show that when under the worst-case FJ, the proposed MPFH performs as well as DFH, but outperforms the conventional FH/BFSK by more than 5 dB; on the other hand, when under worst-case PBJ, the MPFH has the similar BER performance as conventional FH/BFSK, but outperforms DFH by more than 5 dB. The proposed MPFH shows superior jamming rejection performance under both PBJ and FJ.

The energy landscape of glassy dynamics on the amorphous hafnium diboride surface.

Direct visualization of the dynamics of structural glasses and amorphous solids on the sub-nanometer scale provides rich information unavailable from bulk or conventional single molecule techniques. We study the surface of hafnium diboride, a conductive ultrahigh temperature ceramic material that can be grown in amorphous films. Our scanning tunneling movies have a second-to-hour dynamic range and single-point current measurements extend that to the millisecond-to-minute time scale. On the a-HfB2 glass surface, two-state hopping of 1-2 nm diameter cooperatively rearranging regions or "clusters" occurs from sub-milliseconds to hours. We characterize individual clusters in detail through high-resolution (<0.5 nm) imaging, scanning tunneling spectroscopy and voltage modulation, ruling out individual atoms, diffusing adsorbates, or pinned charges as the origin of the observed two-state hopping. Smaller clusters are more likely to hop, larger ones are more likely to be immobile. HfB2 has a very high bulk glass transition temperature Tg, and we observe no three-state hopping or sequential two-state hopping previously seen on lower Tg glass surfaces. The electronic density of states of clusters does not change when they hop up or down, allowing us to calibrate an accurate relative z-axis scale. By directly measuring and histogramming single cluster vertical displacements, we can reconstruct the local free energy landscape of individual clusters, complete with activation barrier height, a reaction coordinate in nanometers, and the shape of the free energy landscape basins between which hopping occurs. The experimental images are consistent with the compact shape of α-relaxors predicted by random first order transition theory, whereas the rapid hopping rate, even taking less confined motion at the surface into account, is consistent with β-relaxations. We make a proposal of how "mixed" features can show up in surface dynamics of glasses.

Stochastic resonance of charge carrier diffusion in a nonhomogeneous medium in the presence of an harmonic external potential

The dynamics of charge carriers (electrons) hopping through a nonhomogeneous medium in semiconductor layer is investigated by changing a thermal noise of strength D and an external harmonic potential V(x). The nonhomogeneous medium exhibits denser trap distribution around the center, which biases the electrons to therein concentrate. Applying also a monostable potential at the center further enhances the accumulation of electrons. However, by applying a nonhomogeneous hot temperature in the vicinity of the potential minimum forced the electrons to diffuse away from the center and redistribute around two points. Thermally activated rate of hopping and diffusion of electrons in a nonhomogeneous medium, as a function of model parameters, is also considered in the high barrier limit. Using two states approximation, I have also studied the stochastic resonance (SR) of the electrons dynamics in the presence of a time-varying signal. I found a strong spectral amplification η and lower temperature occurrence of its peak as compared to previous works [M. Asfaw, B. Aragie and M. Bekele, Eur. Phys. J. B 79, 371 (2011); B. Aragie, Y. B. Tateka and M. Bekele, Eur. Phys. J. B 87, 101 (2014)].

Maintenance of order in a moving strong condensate

We investigate the conditions under which a moving condensate may exist in a driven mass transport system. Our paradigm is a minimal mass transport model in which n − 1 particles move simultaneously from a site containing n > 1 particles to the neighbouring site in a preferred direction. In the spirit of a zero-range process the rate u(n) of this move depends only on the occupation of the departure site. We study a hopping rate u(n) = 1 + b/nα numerically and find a moving strong condensate phase for b > bc(α) for all α > 0. This phase is characterised by a condensate that moves through the system and comprises a fraction of the system's mass that tends to unity. The mass lost by the condensate as it moves is constantly replenished from the trailing tail of low occupancy sites that collectively comprise a vanishing fraction of the mass. We formulate an approximate analytical treatment of the model that allows a reasonable estimate of bc(α) to be obtained. We show numerically (for α = 1) that the transition is of mixed order, exhibiting a discontinuity in the order parameter as well as a diverging length scale as .

Theoretical study of stability and charge-transport properties of coronene molecule and some of its halogenated derivatives: a path to ambipolar organic-based materials?

We have carefully investigated the structural and electronic properties of coronene and some of its fluorinated and chlorinated derivatives, including full periphery substitution, as well as the preferred orientation of the non-covalent dimer structures subsequently formed. We have paid particular attention to a set of methodological details, to first obtain single-molecule magnitudes as accurately as possible, including next the use of modern dispersion-corrected methods to tackle the corresponding non-covalently bound dimers. Generally speaking, this class of compounds is expected to self-assembly in neighboring π-stacks with dimer stabilization energies ranging from -20 to -30 kcalmol(-1) at close distances around 3.0-3.3 Å. Then, in a further step, we have also calculated hole and electron transfer rates of some suitable candidates for ambipolar materials, and corresponding charge mobility values, which are known to critically depend on the supramolecular organization of the samples. For coronene and per-fluorinated coronene, we have found high values for their hopping rates, although slightly smaller for the latter due to an increase (decrease) of the reorganization energies (electronic couplings).

Structural and Dielectric Properties of (Bi1-xBax)(Fe1-xTix)O3 Multiferroic Ceramics

Phase transitions, dielectric permittivity, and conductivity of (Bi1-xBax)(Fe1-xTix)O3 (x = 0.05 and 0.1) [BFO-(Ba,Ti)] multiferroic ceramics have been studied as functions of temperature and frequency. In situ synchrotron x-ray diffraction revealed rhombohedral–cubic transitions in the temperature ranges 760–780°C in BFO-5%(Ba,Ti), and 720–750°C in BFO-10%(Ba,Ti). A one-dimensional barrier model with intrinsic barriers B every lattice constant a and extrinsic barriers B + Δ is introduced to describe the dielectric response and conductivity. This work revealed that (Ba,Ti) substitutions can enhance the intrinsic barriers and reduce the hopping rate of charge carriers, thereby giving the desired effect of decreasing the conductivity.

Zoned Inhomogeneity in Asymmetric Exclusion Processes with Random Update and Off-Ramp

In this letter, we investigate asymmetric simple exclusion processes (ASEPs) with zoned inhomogeneity and off-ramp by the means of theoretical analysis and simulations. According to the theoretical analysis, we can find that the phase diagrams existing in this one-lane system varies with different hopping rate p and off-ramp rate q and the condition for p&lt;0.5 and p&gt;0.5 is distinctly different . It should be noticed that LD/LD, LD/HD and MC/HD can exist in this system no matter how hopping rate p and off-ramp rate q change.

Packet Error Rate Performance of IEEE802.11g under Bluetooth Interface

This study approaches the issues concerning the coexistence of the IEEE 802.11g wireless networks and the ad-hoc Bluetooth networks that operate within the same 2.4 GHz band. The performance of 802.11g is evaluated by simulating the PER (Packet Error Rate) parameter and coverage area. The simulation experiments are based on the worst case scenario presumption, which entails the transmission of HV1 packet which HV1 link requires transmission on 100% of the Bluetooth (BT) time slots using the maximum hop rate of 1600 hops/sec. The paper suggests a practical approach to mitigate the interference using symbol erasures technique through the assessment of the PER parameter at various Eb/No values. The results show that the symbol erasures can effectively mitigate the interference and enhance the performance of the 802.11g.

Structural, electrical and electrochemical properties of novel Li4+2x+yZnxMySi1-x-yO4 (where x = 0.04, y = 0.03;M = Al, Cr) ceramic electrolytes

Lisicon-type ceramic electrolytes, Li4.11Zn0.04Al0.03Si0.93O4 and Li4.11Zn0.04Cr0.03Si0.93O4, were synthesized by sol gel method. X-ray diffraction was applied to investigate the phase, structure and unit cell parameters of both solid electrolytes. The information of particles size distribution was obtained by laser particle sizer. Meanwhile, energy dispersive X-ray was used for elemental composition analysis. The complex impedance spectroscopy was carried out in the frequency range 10Hz–10MHz and temperature range 273K to 773K to study the electrical properties of the electrolytes. Both compounds were indexed to the monoclinic unit cell in the space group P21/m. The particle size in Cr substituted sample was smaller compared to that in the Al substituted sample. The EDX results showed that the chemical compositions for both compounds were very close to the designed compositions. The Li4.11Zn0.04Cr0.03Si0.93O4 compound gave slightly higher total conductivity values of 3.16×10−5 S cm−1 at ambient temperature and 1.78×10−3 S cm−1 at 773K compared to Li4.11Zn0.04Al0.03Si0.93O4 which showed total conductivity values of 1.16×10−5 S cm−1 at ambient temperature and 1.12×10−3 S cm−1 at 773K. The conductivity-frequency spectra were used to estimate the ionic hopping rate in the structure. The dielectric constant and dielectric loss were found to decrease with the increase of frequency but increased with the increase of temperature. Ionic transference number corresponding to Li+ ion transport determined by means of Bruce and Vincent technique is 0.93 and 0.94 for Li4.11Zn0.04Al0.03Si0.93O4 and Li4.11Zn0.04Cr0.03Si0.93O4 respectively. Linear sweep voltammetry results demonstrated that the Li4.11Zn0.04Cr0.03Si0.93O4 and Li4.11Zn0.04Al0.03Si0.93O4 ceramic electrolytes was electrochemically stable up to 4.10V and 3.5V versus a Li/Li+ reference electrode respectively.

Erratum to: Stochastic resonance of charge carriers diffusing in a nonhomogeneous medium with nonhomogeneous temperature

We investigate the dynamics of charge carriers hopping from one trap to the other trap along an n-type semiconductor layer consisting of a spatially nonhomogeneous trap distribution of depth Φ assisted by thermal noise. The trap profile is denser at the center and decays as one moves outward. In presence of a uniform background temperature, the charge carriers tend to accumulate around the center. Moreover, applying a nonhomogeneous temperature which is hot at the location of the maximum of trap density, results in a new redistribution of charge carriers which pile up around two points symmetrically positioned with respect to the center of the semiconductor layer making the system to behave like a bistable potential. The thermally activated rate of hopping of charge carriers as a function of the model parameters is studied in the high barrier limit. Using the two-state approximation, the stochastic resonance (SR) of the charge carriers dynamics in the presence of time varying external signal is also investigated.

Frequency dependent electrical properties of Na2Pb2R2W2Ti4Nb4O30 (R = Nd, Sm) ceramics

In the present research work, frequency dependent electrical properties of tungsten bronze structured compounds Na2Pb2R2W2Ti4Nb4O30 (R = Nd, Sm) are reported. X-ray diffraction (XRD) study of polycrystalline ceramic samples confirms the formation of compounds with orthorhombic structure. Analysis of frequency dependent electrical data in the framework of modulus and conductivity formalism suggests the presence of thermally activated relaxation process in the compounds, which show Arrhenius behavior. The magnitudes of activation energies give the nature of the relaxing species. The real and imaginary parts of complex modulus trace the depressed semicircle in complex plane, suggesting non-Debye type relaxation process in the materials. The power law behavior of admittance data is successfully modeled by introducing constant phase element (CPE) to the equivalent circuit. A large value of power law parameter (n) of CPE below ferroelectric transition temperature (Tc) is attributed to the cooperative response of the dipoles which is reduced above Tc. This behavior is correlated with the frequency dependence of CPE, suggesting a physical meaning to it. The frequency dependent AC conductivity at different temperatures follows Jonscher’s universal power law. Almond and West formalism is used to estimate the hopping rate, activation enthalpy and charge carrier concentration in the materials.

Crossover properties of a one-dimensional reaction-diffusion process with a transport current

1D non-equilibrium models of particles subjected to a coagulation-diffusion process are important in understanding non-equilibrium dynamics, and fluctuation-dissipation relations. We consider in this paper transport properties in finite and semi-infinite one-dimensional chains. A set of particles freely hop between nearest-neighbor sites, with the additional condition that, when two particles meet, they merge instantaneously into one particle. A localized source of particle-current is imposed at the origin as well as a non-symmetric hopping rate between the left and right directions (particle drift). This model was previously studied with exact results for the particle density by Hinrichsen et al [] in the long-time limit. We are interested here in the crossover process between a scaling regime and long-time behavior, starting with a chain filled with particles. As in the previous reference [], we employ the empty-interval-particle method, where the probability of finding an empty interval between two given sites is considered. However a different method is developed here to treat the boundary conditions by imposing the continuity and differentiability of the interval probability, which allows for a closed and unique solution, especially for any given initial particle configuration. In the finite size case, we find a crossover between the scaling regime and two different exponential decays for the particle density as a function of the input current. Precise asymptotic expressions for the particle density and coagulation rate are given.

Effect of Molecular Fluctuations on Hole Diffusion within Dye Monolayers

Measured hole diffusion coefficients in dye monolayers are larger than can be explained by a charge hopping model with a static distribution of parameters describing intermolecular hole transfer. We show that large amplitude fluctuations of the tethered dye configurations on the surface could explain the observed diffusion rates by enabling charges trapped in particular configurations to escape as the dye orientation changes. We present a multiscale model of hole transport that includes the effect of dynamic rearrangement of the monolayer of anchored dyes. Conformations of pairs of indolene dye molecules (both D102 and D149) were generated by a rigid molecular packing algorithm and Car–Parrinello molecular dynamics to mimic the conformational and configurational disorder of a dye monolayer adsorbed to an anatase (101) titanium dioxide surface. The electronic coupling (Jij) for each pair of neighboring dyes was calculated to build distributions representing the disorder in a real system. These values were used as inputs to Marcus’ non-adiabatic equation for charge transfer to calculate the rate of hole hopping for each pair. Hole diffusion was simulated with a continuous time random walk, accounting for different time scales of molecular rearrangement (changes in the dye geometry). The dynamic nature of configurational disorder was captured by reassigning the values of Jij, drawn from the aforementioned distributions, after a fixed renewal time. We found hole diffusion coefficients of 3.3 × 10–8 and 9.2 × 10–8 cm2 s–1 for D102 and D149, respectively, for a renewal time of 10–7 s. This is in good agreement with the corresponding measured coefficients for D102 and D149 of 9.6 × 10–8 and 2.5 × 10–7 cm2 s–1, whereas the diffusion coefficients are underestimated by at least a factor of 15 if the dynamics are ignored. Fast rearrangement of dye monolayer configuration may explain the high lateral hole diffusion coefficients determined experimentally. Our results indicate that both chemical structure and the availability of different packing configurations must be considered when designing conductive molecular monolayers.

Realization of the Open-Boundary Totally Asymmetric Simple Exclusion Process on a Ring

We propose a misanthrope process, defined on a ring, which realizes the totally asymmetric simple exclusion process with open boundaries. In the misanthrope process, particles have no exclusion interaction in contrast to those in the simple exclusion process, while the hop rates depend on both numbers of particles at departure and arrival sites. Arranging the hop rates, we can recover the simple exclusion property and moreover have condensation if the number of particles exceeds that of sites. One condensate grows at an arbitrary single site and then behaves as an external reservoir providing and absorbing particles. It is known that, under some condition, the misanthrope process has an exact solution for the steady-state probability distribution. We exploit this to investigate the present model in an analytical manner.

Random Walk Numerical Simulation of Disordered Semiconductor Heterojunctions

Many recent advances in novel solar cell technologies are based on charge separation in disordered semiconductor heterojunctions. In this work we use the Random Walk Numerical Simulation (RWNS) method to model the dynamics of electrons and holes in two disordered semiconductors in contact. Calculations are performed by simultaneously moving electrons and holes in two semiconductors in contact, according to Miller-Abrahams hopping rates, also we have implemented the Marcus hopping model. Recombination is taken into account by implementing a tunnelling distance-dependent recombination mechanism across the interface. This way, charge separation for specific heterostructures with energy distributions of surface traps in the two semiconductors involved can be adequately simulated.We show that several fundamental features of bulk heterojunction (BHJ) and quantum dot (QD) sensitised solar cells can be accounted for by this model. The dependence of the open-circuit voltage on the HOMO energy of the donor material in BHJ solar cells is accurately predicted assuming short recombination distances and a diffusion mechanism of transport. In addition, the variation of the voltage with temperature is adequately reproduced. The linearity and recombination order in electron density for both types of solar cell can be extracted in two ways: (1) the behaviour of the open-circuit voltage as a function of the illumination intensity, and (2) from the variation of the recombination current with respect to the open-circuit photovoltage. The RWNS model in combination with exponential disorder and an activated tunnelling mechanism for transport and recombination is shown to reproduce correctly experimental charge separation. This provides a theoretical basis to study relevant features of novel solar cell technologies. This allows for the interpretation of impedance spectroscopy measurements [1]. References. 1. Mandujano-Ramírez, H. J.; González-Vázquez, J. P.; Oskam, G.; Dittrich, T.; Garcia-Belmonte, G.; Mora-Seró, I.; Bisquert, J.; Anta, J. A. Charge separation at disordered semiconductor heterojunctions from random walk numerical simulations. Phys. Chem. Chem. Phys., 2014, doi. 10.1039/C3CP54237H, in press.