Isotope Effect in the Magneto-Optoelectronic Response of Organic Light-Emitting Diodes Based on Donor–Acceptor Exciplexes

The isotope effect is studied in the magneto-electroluminescence (MEL) and pulsed electrically detected magnetic resonance of organic light-emitting diodes based on thermally activated delayed fluorescence (TADF) from donor–acceptor exciplexes that are either protonated (H) or deuterated (D). It is found that at ambient temperature, the exchange of H to D has no effect on the spin-dependent current and MEL responses in the devices. However, at cryogenic temperatures, where the reverse intersystem crossing (RISC) from triplet to singlet exciplex diminishes, a pronounced isotope effect is observed. These results show that the RISC process is not governed by the hyperfine interaction as thought previously, but proceeds through spin-mixing in the triplet exciplex. The observations are corroborated by electrically detected transient spin nutation experiments that show relatively long dephasing time at ambient temperature, and interpreted in the context of a model that involves exchange and hyperfine interactions in the spin triplet exciplex. These findings deepen the understanding of the RISC process in TADF materials.     

Mathematical modelling of lignin pyrolysis

Seven lignins from different sources were pyrolysed (i) isothermally in vacuum over the temperature range 300–1300 °C and (ii) at a constant heating rate of 30 °C min^?1 and a pressure of 0.1 MPa over the temperature range 150–900 °C. The mass fraction of each product—char, tar and gas species—and the elemental composition of the char and the tar were determined for the flash pyrolysis experiments. The evolution rates of the gas species and the tar versus the dynamic temperature of pyrolysis were determined for the constant heating rate pyrolysis experiments. Although the amount of each product species varied from lignin to lignin, the evolution rates were insensitive to the lignin source and the extraction process. To model the data, modifications were made to a recently developed model of coal pyrolysis. The model proved to be successful in simulating both the data from vacuum flash pyrolysis and constant heating rate pyrolysis of Iotech lignin.     

Silver-halide optical fiber for infrared absorption spectroscopy: optically pumped intersubband transitions in quantum-well structures

A silver-halide infrared optical fiber is used in a double-beam spectrometer, demonstrating the ability to guide small infrared signals efficiently. We show that a fractional transmission change of less than 1% is easily measured. Use of the fiber may obviate the necessity for the unfriendly optics currently used in spectrometry systems to probe remote sample zones. As a specific example, we were able to guide with high efficiency an infrared signal to and from a sample that was mounted in a cryostat. Using this setup, we measured the photoinduced absorption due to the e1 ? e2 intersubband transition in a GaAs-GaAlAs multiple quantum-well structure.     

The evolution of transport protocols: An evolutionary game perspective

Today’s Internet is well adapted to the evolution of protocols at various network layers. Much of the intelligence of congestion control is delegated to the end users and they have a large amount of freedom in the choice of the protocols they use. In the absence of a centralized policy for a global deployment of a unique protocol to perform a given task, the Internet experiences a competitive evolution between various versions of protocols. The evolution manifests itself through the upgrading of existing protocols, abandonment of some protocols and appearance of new ones. We highlight in this paper the modeling capabilities of the evolutionary game paradigm for explaining past evolution and predicting the future one. In particular, using this paradigm we derive conditions under which (i) a successful protocol would dominate and wipe away other protocols, or (ii) various competing protocols could coexist. In the latter case we also predict the share of users that would use each of the protocols. We further use evolutionary games to propose guidelines for upgrading protocols in order to achieve desirable stability behavior of the system.     

Elastic and dissipative moduli of pressure-supported cellular substances

A unified approach is presented for modeling the elastic and dissipative moduli of substances composed of pressurized cells. The substances examined include liquid foams, physiological tissues such as lung and udder, and plant tissues such as vegetables and leaves. All are characterized by macroscopic elastic moduli linearly proportional to the inflating pressure. An isotropic dodecahedron is chosen to represent the basic microunit of such a structure. Variational statements of nonlinear structural mechanics, applied to the dodecahedron, bring out the specific macromechanical properties of the cellular material under static and dynamic loading, in terms of the mechanical attributes of its microunits.     

Impact of macrodiversity on capacity and coverage of cellular network

This paper proposes an analytical study of downlink macrodiversity. Considering a mobile in macrodiversity with two base stations, we first characterize and compute explicitely the load induced in a cell by downlink macrodiversity. We show that in most cases this load is positive, increasing the total cell load. We moreover show that the contribution of the macrodiversity to the cell load can be negative in the sense that the macrodiversity can increase the cell’s capacity. Afterward, we propose a new framework for the study of cellular networks called the fluid model which allows to calculate analytically that load. The key idea of the fluid model is to approximate the discrete base stations (BS) entities by a continuum of transmitters which are spatially distributed in the network. This allows us to obtain simple analytical expressions of the main characteristics of the network. In this paper, we focus on the downlink other-cell interference factor f, which we define here as the ratio of outer cell received power (i.e. the power received from other cells) to the inner cell received power. This fluid model allows calculating the influence of interference on any mobile in a cell, whatever its position. The fluid analysis we develop enables to calculate the load of a cell analytically, and to quantify the macrodiversity impact. We generalize our analysis, considering a macrodiversity with a great number of base stations of the network.     

High fidelity information processing in folic acid chemotaxis of Dictyostelium amoebae

Living cells depend upon the detection of chemical signals for their existence. Eukaryotic cells can sense a concentration difference as low as a few per cent across their bodies. This process was previously suggested to be limited by the receptor–ligand binding fluctuations. Here, we first determine the chemotaxis response of Dictyostelium cells to static folic acid gradients and show that they can significantly exceed this sensitivity, responding to gradients as shallow as 0.2% across the cell body. Second, using a previously developed information theory framework, we compare the total information gained about the gradient (based on the cell response) to its upper limit: the information gained at the receptor–ligand binding step. We find that the model originally applied to cAMP sensing fails as demonstrated by the violation of the data processing inequality, i.e. the total information exceeds the information at the receptor–ligand binding step. We propose an extended model with multiple known receptor types and with cells allowed to perform several independent measurements of receptor occupancy. This does not violate the data processing inequality and implies the receptor–ligand binding noise dominates both for low- and high-chemoattractant concentrations. We also speculate that the interplay between exploration and exploitation is used as a strategy for accurate sensing of otherwise unmeasurable levels of a chemoattractant.     

Discrete bending forces and their Jacobians

Computation of bending forces on triangle meshes is required for numerous simulation and geometry processing applications. In particular it is a key component in cloth simulation. A common quantity in many bending models is the hinge angle between two adjacent triangles. This angle is straightforward to compute, and its gradient with respect to vertex positions (required for the forces) is easily found in the literature. However, the Hessian of the bend angle, which is required to compute the associated force Jacobians is not documented in the literature. Force Jacobians are required for efficient numerics (e.g., implicit time stepping, Newton-based energy minimization) and are thus highly desirable. Readily available computations of the force Jacobian, such as those produced by symbolic algebra systems, or by autodifferentiation codes, are expensive to compute and therefore less useful. We present compact, easily reproducible, closed form expressions for the Hessian of the bend angle. Compared to automatic differentiation, we measure up to 7× speedup for the evaluation of the bending forces and their Jacobians.     

Spin dependent reactions of polaron pairs in PPV-based organic diodes

We characterize spin dependent kinetics of polaron pairs (PP) reactions in polymer organic light emitting diodes (OLED) based on a derivative of poly(phenylene-vinylene) [PPV], namely MEH-PPV as the active layer, using the dynamic response of the magnetic resonance effect on electroluminescence, injected current, and photocurrent. We found that at 10 K and under forward bias, the in-phase component of both electroluminescence detected magnetic resonance (ELDMR) and current detected magnetic resonance (CDMR) responses are positive at low microwave modulation frequency, f; but both reverse sign at a frequency f₀ that depends on the microwave power, current density, and device architecture. The similarity between ELDMR and CDMR response dynamics show that the two phenomena share a common origin. We identify the underlying ELDMR mechanism as due to current density increase under resonance conditions. From a model fit to the data that involves both spin singlet and triplet PP dynamics, we obtained their effective recombination and spin-lattice relaxation rates. We found that the spin-lattice relaxation rate in the active layer increases with the current density in the device, showing the importance of spin–spin interaction in spin dependent reactions in OLED. Unlike ELDMR and CDMR the reverse bias photocurrent detected magnetic resonance (PCDMR) is negative at low f. The negative sign is the result of the dynamic equilibrium between the resonantly reduced PP density and the photogenerated mobile charge carrier density.     

Spatial analysis of air pollution and cancer incidence rates in Haifa Bay, Israel

The Israel National Cancer Registry reported in 2001 that cancer incidence rates in the Haifa area are roughly 20% above the national average. Since Haifa has been the major industrial center in Israel since 1930, concern has been raised that the elevated cancer rates may be associated with historically high air pollution levels. This work tests whether persistent spatial patterns of metrics of chronic exposure to air pollutants are associated with the observed patterns of cancer incidence rates. Risk metrics of chronic exposure to PM₁₀, emitted both by industry and traffic, and to SO₂, a marker of industrial emissions, was developed. Ward-based maps of standardized incidence rates of three prevalent cancers: Non-Hodgkin's lymphoma, lung cancer and bladder cancer were also produced. Global clustering tests were employed to filter out those cancers that show sufficiently random spatial distribution to have a nil probability of being related to the spatial non-random risk maps. A Bayesian method was employed to assess possible associations between the morbidity and risk patterns, accounting for the ward-based socioeconomic status ranking. Lung cancer in males and bladder cancer in both genders showed non-random spatial patterns. No significant associations between the SO₂-based risk maps and any of the cancers were found. Lung cancer in males was found to be associated with PM₁₀, with the relative risk associated with an increase of 1 μg/m³ of PM₁₀ being 12%. Special consideration of wards with expected rates < 1 improved the results by decreasing the variance of the spatially correlated residual log-relative risk.