Single Barrier Research Articles

Optimization Model for the Design of Multi-layered Permeable Reactive Barriers

Permeable reactive barriers (PRBs) are employed as in situ groundwater remediation technology. The installation of PRBs is usually a major investment, where one of the biggest cost drivers are material costs. PRBs are barriers against contaminants moving under the natural gradient, however not against groundwater contaminants. The most common construction of a PRB is a single barrier, but in the case of contaminant mixtures a multi-layered construction, i.e. a combination of different reactive materials and removal processes, is required. The most important parameters for PRB design are dimensions. The barrier must be long enough to treat the entire width of the plume (dimension perpendicular to groundwater flow) and should extend to and be keyed into an impermeable layer. The problem is to determine the optimal thickness of a PRB, which should provide a residence time appropriate for reducing the concentration of contaminants to the desired effluent concentration. In PRBs, design is accomplished using numerical methods or simulators, which are useful to predict the scenarios and evaluate the resulting groundwater flow systems to specific site conditions. On the other hand, numerical methods are complicated and may have significant errors if the discretization is too coarse or is incorrectly aligned. This paper deals with a simple, conceptual model of a one-approach optimization method for multi-layered PRB design. Based on literature and laboratory test results (residence time, density and hydraulic coefficient), a selection of layers of reactive materials was determined. Considering the lowest cost of the reactive materials, the required thicknesses of activated carbon, zeolite and zero valent iron were calculated using two different algorithms. The simple model may be used for preliminary barrier design and cost calculations. Using the optimization model in a preliminary design stage, it is possible to reject the PRB concept and avoid losing time for the complicated analysis.

Plasma-based flow control for low-pressure turbines at low-Reynolds-number

Purpose Reynolds number in small-size low-pressure turbines (LPT) can drop below 2.5 · 104 at high altitude cruise, which in turn can lead to laminar boundary layer separation on the suction surface of the blades. The purpose of this paper is to investigate the potential of an alternate current (AC)-driven Single Dielectric Barrier Discharge Plasma Actuator (AC-SDBDPA) for boundary layer control on the suction side of a LPT blade, operating at a Reynolds number of 2 · 104.Design/methodology/approach Experimental and numerical analyses were conducted. The experimental approach comprised the actuator testing over a curved plate with a shape designed to reproduce the suction surface of a LPT blade. A closed loop wind tunnel was employed. Sinusoidal voltage excitation was tested. Planar velocity measurements were performed by laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). The device electrical power dissipation was also calculated. Computational fluid dynamics (CFD) simulations using OpenFOAM© were conducted, modelling the actuator effect as a body force calculated by the dual potential algebraic model. Unsteady RANS (Reynolds Averaged Navier-Stokes equations), also known as URANS approach, with the k-ε Lam-Bremhorst Low-Reynolds turbulence model was used.Findings The AC-SDBDPA operation brought to a reduction of the separation region; in particular, the boundary layer thickness and the negative velocity values decreased substantially. Moreover, the flow angle in both the main flow and in the boundary layer was reduced by the plasma control effect. The actuation brought to a reduction of the 17 per cent in the total pressure loss coefficient. The pressure coefficient and skin friction coefficient distributions indicated that under actuation the reattacnment point was displaced upstream, meaning that the flow separation was effectively controlled by the plasma actuation. Adopting slightly higher actuation parameters could bring to a full reattachment of the flow.Practical implications The work underlines the potentialities of an AC-SDBDPA to control separation in LPTs of aeroengines.Originality/value The present work sets a methodological framework, in which the validated procedure to obtain the body force model combined with CFD simulations can be used to study a configuration with multiple actuators allocated in array without requiring further experiments.

(Invited) Material Considerations for the Development of III-Nitride Power Devices

AlGaN is of high interest for high-power electronics based on vertical structures due to its high breakdown field and electron mobility. Recent studies in GaN based p-n junctions indicate a dielectric strength in the range of 3.3–3.75 MVcm-1, resulting in a Baliga’s figure of merit several times larger than that of SiC. However, high breakdown voltages (>4kV) are currently confined to GaN p-n junctions indicating GaN and AlGaN surface instabilities. Consequently, defect-free metal-nitride interface and passivation of Al/GaN are necessary for breakthroughs in high power vertical Al/GaN Schottky diodes. Accordingly, we report defect-free behavior in Ni/GaN Schottky diodes with unity ideality factor and fabricated by photolithography. They also exhibit high temperature stability (>600 oC) and low leakage with forward and reverse I-V-T characteristics successfully modeled by a single homogeneous barrier (0.7 eV) by ATLAS simulations. It is significant that the forward and reverse characteristics could be modeled by a common set of parameters without a defect based second diode to model the reverse leakage. XPS chemical and electronic analysis was employed to determine the surface treatment necessary to obtain such a Schottky interface. Consequently, we demonstrate the suitability of GaN surface and interface with metals for high power electronics. Although a near-ideal diode may be obtained on GaN, the relatively low barrier height limits the GaN Schottky diode to operating voltages <1000V. Increasing the barrier by controlling the Fermi level pinning and producing a camel junction by surface Mg doping is possible. Passivation is the next challenge to implementing Al/GaN based high power electronics. Silicon nitride has emerged as the standard passivation material for GaN and low Al composition AlxGa1-xN (x<0.3). However, the bandgap of silicon nitride is lower than AlGaN for x>0.75 and the feasibility of silicon nitride functioning as an insulating dielectric (by providing appropriate electron/hole barriers) in Al rich AlGaN and AlN is uncertain. Similarly, reduction of surface states by silicon nitride passivation has not been reported for Al rich AlGaN (x>0.3). In this work, we have employed X-ray photoelectron spectroscopy to determine the band offsets and interface Fermi level at the hetero-junction formed by stoichiometric silicon nitride deposited on metal polar AlxGa1-xN (of varying Al composition ‘x’) via high temperature low pressure chemical vapor deposition. Silicon nitride is found to form a type II staggered band alignment with AlGaN for all Al compositions (0<x<1) and presents an electron barrier into AlGaN even at higher Al compositions where Eg(AlGaN)>Eg(Si3N4). No band bending is observed in AlGaN for x<0.6 and indicating excellent passivation beyond x=0.3. Further a reduced band bending (by 1 eV relative to free surface) is observed for x>0.6. The Fermi level in silicon nitride is found to be at 3 eV with respect to its valence band and is likely due to silicon (≡Si0/-1) dangling bonds. The presence of band bending for x>0.6 is seen as a likely consequence of Fermi level alignment at Si3N4/AlGaN hetero-structure and not due to interface states indicating likely passivation on AlGaN beyond x=0.6. Photoelectron spectroscopy is corroborated by capacitance-voltage measurements. A shift in the interface Fermi level from the conduction band in Si3N4/n-GaN to the valence band in Si3N4/p-GaN is observed which strongly indicates no or greatly reduced mid-gap interface states. Further, required compensation of spontaneous polarization charge is typically performed by oppositely charged surface states/defects on free surface is hypothesized to be replaced by oppositely charged silicon dangling bonds (≡Si0/-1) after passivation. This hypothesis is supported by characterization of silicon nitride on N-polar GaN. In conclusion, HT LPCVD silicon nitride is found to be a suitable passivation for Al rich AlGaN.

Mechanistic Investigation of Thermal and Photoreactions between Boron and Silane.

Density functional theory and high-level ab initio calculations were performed to elucidate the detailed reaction mechanism from B and SiH4 to a structure with two bridging H atoms (Si(μ-H2)BH2, silicon tetrahydroborate). On the basis of the calculated results, this reaction mechanism includes both thermal and photochemical reactions. Especially, thermal conversion of silylene dihydroborate (H2B═SiH2) to Si(μ-H2)BH2 is not feasible because two high energetic barriers must be overcome. In contrast, the reverse reaction is feasible because it is effectively only necessary to overcome a single barrier. The characteristics of the excited states of H2B═SiH2 and Si(μ-H2)BH2 have been identified. Two successive conical intersections (CIs) are involved in the photochemical reaction. The BSiH4 bending coordinate is almost parallel to the reaction coordinate near the regions from the second CI to Si(μ-H2)BH2. The activated BSiH4 bending mode lift the degeneracy of the second CI, thereby the reaction readily proceeds to Si(μ-H2)BH2. All calculated results in this work reasonably well describe the recent experimental observations.

Incoherent scattering can favorably influence energy filtering in nanostructured thermoelectrics

Investigating in detail the physics of energy filtering through a single planar energy barrier in nanostructured thermoelectric generators, we reinforce the non-trivial result that the anticipated enhancement in generated power at a given efficiency via energy filtering is a characteristic of systems dominated by incoherent scattering and is absent in ballistic devices. In such cases, assuming an energy dependent relaxation time τ(E) = kEr, we show that there exists a minimum value rmin beyond which generation can be enhanced by embedding nanobarriers. For bulk generators with embedded nanobarriers, we delve into the details of inter sub-band scattering and show that it has finite contribution to the enhancement in generation. We subsequently discuss the realistic aspects, such as the effect of smooth transmission cut-off and show that for r > rmin, the optimized energy barrier is just sufficiently wide enough to scatter off low energy electrons, a very wide barrier being detrimental to the performance. Analysis of the obtained results should provide general design guidelines for enhancement in thermoelectric generation via energy filtering. Our non-equilibrium approach is typically valid in the absence of local quasi-equilibrium and hence sets the stage for future advancements in thermoelectric device analysis, for example, Peltier cooling near a barrier interface.

Insight into hydraulic conductivity testing of geosynthetic clay liners (GCLs) exhumed after 5 and 7 years in a cover

Four geosynthetic clay liners (GCLs) serving as single liners were exhumed from below 0.7 m of silty sand on a 3:1 (horizontal:vertical) north-facing slope at the QUELTS site in Godfrey, Ontario, after 5 and 7 years. The 300 mm GCL overlaps with 0.4 kg/m supplemental bentonite were all physically intact. The exchangeable bound sodium was completely replaced with divalent cations. The GCL with the smallest needle-punched bundle size (average of 0.7 mm) and percentage area covered by bundles (4%) maintained low hydraulic conductivity (k) when tested under 0.07–1.2 m head with 10 mmol/L CaCl2solution as the permeant. For GCLs with larger bundles (1.1–1.6 mm) and higher percentage area covered by bundles (9%–14%), k was low when the head was low (0.07 m). Once the applied head increased, k increased by 1–4 orders of magnitude depending on the (i) hydraulic gradient, (ii) size and number of the needle-punched bundles, and (iii) structure and mass of the bentonite per unit area. The results suggest that the GCLs can perform effectively as a single hydraulic barrier in covers providing that the head above the GCL is kept low (e.g., by a suitable drainage layer above the GCL).

Risk Assessment of Fluid Migration Into Freshwater Aquifers in Colorado Basins

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 181680, “A Continued Assessment of the Risk of Migration of Hydrocarbons or Fracturing Fluids Into Freshwater Aquifers in the Piceance, Raton, and San Juan Basins of Colorado,” by C.H. Stone, SPE, A.W. Eustes, SPE, and W.W. Fleckenstein, SPE, Colorado School of Mines, prepared for the 2016 SPE Annual Technical Conference and Exhibition, Dubai, 26–28 September. The paper has not been peer reviewed. Wellbore-construction methods, especially casing-and-cementing practices for the protection of freshwater aquifers, have been reviewed in the Piceance, Raton, and San Juan Basins in Colorado. The assessment confirms that natural-gas migration occurs infrequently but can happen from poorly constructed wellbores. Analysis confirmed no occurrence of hydraulic-fracturing-fluid contamination. The significance of these results is to help quantify the risks associated with natural-gas development as related to the contamination of surface aquifers. Introduction The prevention of contamination of freshwater aquifers has been a prime concern in drilling operations since the inception of drilling. Surface casing has long been the primary barrier to prevent contamination of freshwater aquifers through wellbores. The probability of leakage into aquifers from wellbores during shale development has a wide range of estimates, complicated by the presence of hydrocarbons at shallow depths in many parts of the world. An earlier paper reviewed the process and outcomes of a study for the Wattenberg Field in the Denver-Julesberg Basin. This study continues the examination of the contamination of aquifers in the subsurface during the completion and the production phases of the well and quantifies the risk of contamination of aquifers through failure of the wellbore for three other major basins in Colorado, the Piceance, Raton, and San Juan Basins. This synopsis focuses on the assessment of the Piceance Basin. Barrier Definition. Common vertical, deviated, and horizontal subsurface wellbore-barrier designs were grouped and ranked on the basis of the risk of multiple barrier failures (Fig. 1). For the sake of clarity, pressure monitoring of the casing annulus [surface annulus pressure (SAP)] was not assumed to be an additional barrier during the production phase even though it is frequent and often required by state regulations. Well-barrier designs can vary from field to field depending on geology, trajectory, depths, anticipated pressures, expected hydraulic-treatment rates, and estimated production rates. Whether a well is horizontal, vertical, or deviated has no significance with respect to the ultimate protection of freshwater aquifers because the wells are designed to protect the shallow vertical section of each oil and gas well. Multiple barriers must be in place near the depth of the freshwater aquifer to prevent breaching of a single barrier potentially leading to contamination.

Modeling and Performance Assessment of Alternative Cover Systems on a Waste Rock Storage Area

The selection and design of an appropriate mine waste cover system for the local climatic conditions, unsaturated and saturated material properties, and available cover materials is important to mine waste management. We investigated the performance of various cover configurations for minimizing the ingress of water and oxygen into the northern waste rock storage area of the Kisladag gold mine, in Usak, Western Turkey. SEEP/W and VADOSE/W software were used to model the flow in unsaturated and saturated zones and to assess the performance of various cover systems. The accuracy of input data was checked during calibration for steady-state conditions with SEEP/W. Subsequently, bedrock, waste rock, and three different cover alternatives were modeled under transient conditions for 20 years using daily climatic data. All three alternatives (enhanced store-and-release, and double and single capillary barriers) were effective in limiting infiltration. However, capillary barrier covers were more effective in limiting oxygen ingress than enhanced store-and-release covers.

Li7 -induced reaction on Monat : A study of complete versus incomplete fusion

Several investigations on the complete-incomplete fusion (CF-ICF) dynamics of $\alpha$-cluster well-bound nuclei has been contemplated above the Coulomb barrier ($\sim$ 4-7 MeV/nucleon) in recent years. It is therefore expected to observe significant ICF over CF in the reactions induced by a weakly bound $\alpha$-cluster nucleus at slightly above the barrier. In order to investigate CF-ICF in the loosely bound system, $^{\text{7}}$Li beam was bombarded on the $^{\text{nat}}$Mo foils, separated by the aluminium (Al) catcher foils alternatively, within $\sim$ 3-6.5 MeV/nucleon. Evaporation residues produced in each foil were identified by the $\gamma$-ray spectrometry. Measured cross section data of the residues were compared with the theoretical model calculations based on the equilibrium (EQ) and preequilibrium (PEQ) reaction mechanisms. The experimental cross section of $^{\text{101m,100,99m,97}}$Rh, $^{\text{97,95}}$Ru, $^{\text{99m,96,95,94,93m+g}}$Tc and $^{\text{93m}}$Mo residues measured at various projectile energies were satisfactorily reproduced by the simplified coupled channel approach in comparison to single barrier penetration model calculation. Significant cross section enhancement in the $\alpha$-emitting channels was observed compared to EQ and PEQ model calculations throughout observed energy region. The ICF process over CF was analyzed by comparing with EMPIRE. The increment of the incomplete fusion fraction was observed with increasing projectile energies. Theoretical model calculations reveal that compound reaction mechanism is the major contributor to the production of residues. Theoretical evaluations substantiate the contribution of ICF over the CF in $\alpha$-emitting channels.

Four logic states of tunneling magnetoelectroresistance in ferromagnetic shape memory alloy based multiferroic tunnel junctions

This study illustrates the approach to obtain four logic states of ferromagnetic shape memory alloy based multiferroic tunnel junction (MFTJ). In order to achieve giant tunneling electroresistance (TER) and tunneling magnetoresistance (TMR), Ni-Mn-In and Ni-Mn-Sb layers were chosen as electrodes, as well as the concept of the composite barrier was adopted using the STO/PZT [SrTiO3, Strontium Titanate/PbZr0.52Ti0.48O3 (Lead Zirconate Titanate)] (dielectric/ferroelectric) barrier layer. Equated to MFTJ with a single PZT barrier, the introduction of a STO paraelectric (dielectric) barrier is shown to be effective in improving both the TER and TMR of the MFTJs. Particularly, the TER ratio is greatly enhanced by 168% relative TER change: ΔTERTER=TER2−TER1TER1×100. This is described in terms of the increased asymmetry in the electrostatic modulation on the barrier potential profile with respect to the Ferroelectric (FE) polarization direction. We show that due to the coupling between FE polarization and magnetization at the junction between the barrier and the electrode of a MFTJ, the spin polarization of the tunneling electrons can be reversibly and remanently flipped by switching the FE polarization of the barrier. In addition to the analysis of memory function, the exchange bias phenomena are also studied. A negative exchange bias field of “HEB” ∼−98 Oe occurred at 300 K in these bilayers.

Robust barrier option pricing by frame projection under exponential Lévy dynamics

ABSTRACTWe present an efficient method for robustly pricing discretely monitored barrier and occupation time derivatives under exponential Lévy models. This includes ordinary barrier options, as well as (resetting) Parisian options, delayed barrier options (also known as cumulative Parisian or Parasian options), fader options and step options (soft-barriers), all with single and double barriers, which have yet to be priced with more general Lévy processes, including KoBoL (CGMY), Merton’s jump diffusion and NIG. The method’s efficiency is derived in part from the use of frame-projected transition densities, which transform the problem into the Fourier domain and accelerate the convergence of intermediate expectations. Moreover, these expectations are approximated by Toeplitz matrix-vector multiplications, resulting in a fast implementation. We devise an augmentation approach that contributes to the method’s robustness, adding protection against mis-specifying a proper truncation support of the transition density. Theoretical convergence is verified by a series of numerical experiments which demonstrate the method’s efficiency and accuracy.

Comparison of Electron Transmittance and Tunneling Current through a Trapezoidal Potential Barrier with Spin Polarization Consideration by using Analytical and Numerical Approaches

In this study, we report an analytical calculation of electron transmittance and polarized tunneling current in a single barrier heterostructure of a metal-GaSb-metal by considering the Dresselhaus spin orbit effect. Exponential function, WKB method and Airy function were used in calculating the electron transmittance and tunneling current. A Transfer Matrix Method, as a numerical method, was utilized as the benchmark to evaluate the analytical calculation. It was found that the transmittances calculated under exponential function and Airy function is the same as that calculated under TMM method at low electron energy. However, at high electron energy only the transmittance calculated under Airy function approach is the same as that calculated under TMM method. It was also shown that the transmittances both of spin-up and spin-down conditions increase as the electron energy increases for low energies. Furthermore, the tunneling current decreases with increasing the barrier width.

An analytical approximation for single barrier options under stochastic volatility models

The aim of this paper is to derive an approximation formula for a single barrier option under local volatility models, stochastic volatility models, and their hybrids, which are widely used in practice. The basic idea of our approximation is to mimic a target underlying asset process by a polynomial of the Wiener process. We then translate the problem of solving first hit probability of the asset process into that of a Wiener process whose distribution of passage time is known. Finally, utilizing the Girsanov’s theorem and the reflection principle, we show that single barrier option prices can be approximated in a closed-form. Furthermore, ample numerical examples will show the accuracy of our approximation is high enough for practical applications.

“Wind energy is not an issue for government”: Barriers to wind energy development in Newfoundland and Labrador, Canada

Despite having amongst the strongest potential for wind energy development (WED) of any jurisdiction in North America, the Canadian province of Newfoundland and Labrador (NL) remains dependent on fossil fuels for economic activity, government revenue, as well as electricity generation. The study is a comprehensive assessment of barriers to renewable energy development in NL, with a focus on wind energy. While NL is chosen as the primary case study, the study's theoretical breadth provides insights for other renewable energy (RE) development and policy contexts as well. Seventeen semi-structured expert interviews were conducted with respondents from academia, community groups, government, and the private sector. An analytical framework was employed and directed content analysis was utilized. A large majority of expert respondents (65%) classified the current state of WED in the province as ‘unfavourable’. In total, 19 unique barriers were identified; the most significant barriers to WED were found to be political (71% of respondents), economic (65%), as well as related to lack of knowledge and agreement (53 and 41%, respectively). The study demonstrates that there is no single barrier to the development of RE sources; as such, comprehensive policy solutions comprised of financial, educational, legislative, and consultative components are required.

Anisotropic transport of normal metal-barrier-normal metal junctions in monolayer phosphorene

We study transport properties of a phosphorene monolayer in the presence of single and multiple potential barriers of height U0 and width d, using both continuum and microscopic lattice models, and show that the nature of electron transport along its armchair edge (x direction) is qualitatively different from its counterpart in both conventional two-dimensional electron gas with Schrödinger-like quasiparticles and graphene or surfaces of topological insulators hosting massless Dirac quasiparticles. We show that the transport, mediated by massive Dirac electrons, allows one to achieve collimated quasiparticle motion along x and thus makes monolayer phosphorene an ideal experimental platform for studying Klein paradox in the context of gapped Dirac materials. We study the dependence of the tunneling conductance as a function of d and U0, and demonstrate that for a given applied voltage V its behavior changes from oscillatory to decaying function of d for a range of U0 with finite non-zero upper and lower bounds, and provide analytical expression for these bounds within which G decays with d. We contrast such behavior of G with that of massless Dirac electrons in graphene and also with that along the zigzag edge (y direction) in phosphorene where the quasiparticles obey an effective Schrödinger equation at low energy. We also study transport through multiple barriers along x and demonstrate that these properties hold for transport through multiple barriers as well. Finally, we suggest concrete experiments which may verify our theoretical predictions.

Enhanced current transport in GaN/AlN based single and double barrier heterostructures

Current transport through a unique structure design employing high quality GaN based heterostructure with sharp interfaces has been investigated. A novel approach of structure design has been adopted to enhance the current transport in GaN heterostructures with a specific number of barrier layers of AlN which includes Single Barrier Heterostructure (SBH) and Double Barrier Heterostructure (DBH) devices. The high band gap AlN can act as a barrier for current conduction between GaN layers and help in effectively enhancing the current transport in the device through tunneling phenomena. A highly enhanced current transport in comparison with No Barrier Heterostructure (NBH) has been observed in SBH and a further improvement is perceived in DBH. Moreover, the phenomenon of current conduction is explained through drift-diffusion model, in which current enhancement upon subsequent addition of high bandgap barrier layer has resulted in localized high electric field and thus charge carrier velocity overshoots. Further, this has also been explained via quantum model, by interference of transmitted and reflected electron wave at interfaces. UV photodetectors using such heterostructure designs with and without AlN barrier layers in metal-semiconductor-metal geometry have been fabricated. The UV photodetection device developed using DBH yields photoresponsivity 80 times higher as compared to NBH device under UV illumination (325nm). Employment of such structures will enable scaling up the production of highly efficient optoelectronic devices.

Which Are the Main Parental Barriers to Active Commuting to School in Ecuador?

Background Cardiovascular diseases are the leading cause of death in most countries of Latin America and physical inactivity is an important risk factor. Daily behaviors such as active commuting to school can provide a significant source of physical activity for children to improve the cardiovascular health. Parental perceptions of the environment such as distance to school or neighborhood safety are important to determine active commuting to school. The aim of this study was two-fold: to determine parental barriers to active commuting to school in Ecuadorian children and adolescents and to examine the association between the parental barriers and mode of commuting to school. Methods Parents of children (n=172, aged 9-12) and parents of adolescents (n=209, aged 13-18) completed a self-reported questionnaire about perceived parental barriers to active commuting to school. Differences of the parental perceived barriers between parents of children and parents of adolescents were analyzed using Chi-square test for every single barrier and Student T-test for independent samples to analyze the number of parental perceived barriers. The association between children's mode of commuting and parental barriers for each group of parents was examined using logistic regression analysis. Results The most common barriers reported by Ecuadorian parents of children were traffic volume (51.7%), traffic speed (50.0%) and crime (50.0%), whereas the most common barriers reported by Ecuadorian parents of adolescents were traffic speed (44.5%), distance to school (44.0%) and crime (44.0%). Parents of children reported absence of adults to walk with as the most important barrier compared to parents of adolescents (36.6% and 21.5% respectively, p=0.001). Parents of children who perceived as barriers distance to school (OR: 11.022; p Conclusions The most frequent perceived barriers for Ecuadorian parents were traffic volume, traffic speed, crime and distance, whereas barriers for parents of children were higher than parents of adolescents. Parents of children were more concern about presence of adults to walk with than parents of adolescents. It is important to improve the parental perceptions of distance and safety in dangerous intersections to promote active commuting to school in Ecuador.

Dark spot growth and its acceleration factor in organic light-emitting diodes with single barrier structure

Using organic light-emitting diodes (OLEDs) without encapsulation, dark spot growth and its acceleration factor at high temperature and high humidity were measured and compared with those of edge shrink at the cathode edge. The water permeation model explained the time evolution of dark spots and edge shrink, and the acceleration factor was the same between dark spots and edge shrink. The acceleration factor of edge shrink was proportional to the relative humidity at a constant temperature and showed Arrhenius temperature dependence.

Robust Replication of Barrier-Style Claims on Price and Volatility

We show how to price and replicate a variety of barrier-style claims written on the $\log$ price $X$ and quadratic variation $\langle X \rangle$ of a risky asset. Our framework assumes no arbitrage, frictionless markets and zero interest rates. We model the risky asset as a strictly positive continuous semimartingale with an independent volatility process. The volatility process may exhibit jumps and may be non-Markovian. As hedging instruments, we use only the underlying risky asset, zero-coupon bonds, and European calls and puts with the same maturity as the barrier-style claim. We consider knock-in, knock-out and rebate claims in single and double barrier varieties.

Nucleation and growth of a core-shell composite nucleus by diffusion.

The critical radius of a core-shell-type nucleus grown by diffusion in a phase-separated solution is studied. A kinetic critical radius rather than the thermodynamic critical radius of standard classical nucleation theory can be defined from the diffusional growth equations. It is shown that there exist two kinetic critical radii for the core-shell-type nucleus, for which both the inner-core radius and the outer-shell radius will be stationary. Therefore, these two critical radii correspond to a single critical point of the nucleation path with a single energy barrier even though the nucleation looks like a two-step process. The two radii are given by formulas similar to that of classical nucleation theory if the Ostwald-Freundlich boundary condition is imposed at the surface of the inner nucleus and that of the outer shell. The subsequent growth of a core-shell-type postcritical nucleus follows the classical picture of Ostwald's step rule. Our result is consistent with some of the experimental and numerical results which suggest the core-shell-type critical nucleus.