Multiple Trapping Research Articles

Hybrid immersed interface-immersed boundary methods for AC dielectrophoresis

Dielectrophoresis, a nonlinear electrokinetic transport mechanism, has become popular in many engineering applications including manipulation, characterization and actuation of biomaterials, particles and biological cells. In this paper, we present a hybrid immersed interface–immersed boundary method to study AC dielectrophoresis where an algorithm is developed to solve the complex Poisson equation using a real variable formulation. An immersed interface method is employed to obtain the AC electric field in a fluid media with suspended particles and an immersed boundary method is used for the fluid equations and particle transport. The convergence of the proposed algorithm as well as validation of the hybrid scheme with experimental results is presented. In this paper, the Maxwell stress tensor is used to calculate the dielectrophoretic force acting on particles by considering the physical effect of particles in the computational domain. Thus, this study eliminates the approximations used in point dipole methods for calculating dielectrophoretic force. A comparative study between Maxwell stress tensor and point dipole methods for computing dielectrophoretic forces are presented. The hybrid method is used to investigate the physics of dielectrophoresis in microfluidic devices using an AC electric field. The numerical results show that with proper design and appropriate selection of applied potential and frequency, global electric field minima can be obtained to facilitate multiple particle trapping by exploiting the mechanism of negative dielectrophoresis. Our numerical results also show that electrically neutral particles form a chain parallel to the applied electric field irrespective of their initial orientation when an AC electric field is applied. This proposed hybrid numerical scheme will help to better understand dielectrophoresis and to design and optimize microfluidic devices.

Investigation of e-h Trapping Efficiency in Eu3+ Doped YPO4 Using VUV Spectroscopy

Absorption of Vacuum Ultraviolet (VUV) radiation creates excited e – h pairs in rare – earth doped phosphors that can either be trapped by a defect state (killer) or Ln3+ activator. The e – h trapping efficiency by Ln3+ is proportional to the rate of transfer to the activators. Recent work on YBO3:Eu3+ nano-sized particles indicate that with decreasing particle size, there is an increase in loss of energy to surface states [1]. Micron-sized Ln3+ doped YBO3 particles seem to have no surface loss effects. Our ultimate goal is to study particle size effects on surface loss and trapping efficiency in Ln3+ doped phosphor compounds. To develop a point of reference for surface loss and trapping efficiency for other nano-sized Ln3+ doped phosphor compounds, the corresponding micron-sized phosphors must be analyzed first. Thus, the e - h trapping efficiencies under VUV excitation have been determined from absorbance and excitation spectra for micron-sized Ln3+ doped YBO3, YPO4, and LaPO4. Several of these phosphor compounds contain multiple d(Ln3+) and or a Ln2+ - charge transfer (CT) state in the band gap for e - h trapping to occur. For a single CT strap state, a unique method for estimating the transfer efficiency under VUV excitation has been developed [2], and we have recently proposed a method to determine transfer efficiencies under VUV excitation for each of the individual trap states for Ln3+ doped phosphor compounds that contain multiple trap states [3]. Treating these data using accepted kinetic models allows us to calculate relative trapping efficiencies as well as the degree of surface loss. To understand the trapping mechanism, the Ln3+ energy levels relative to host states must be taken into consideration. We have developed an energy level scheme of Ln2+ and Ln3+ ground states relative to the valence band maximum (VBM) of Ln3+ doped compounds using techniques proposed by Dorenbos and Thiel [4,5,6]. Results indicate that if the Ln3+ ground state is higher in energy than the VBM, and d – orbitals are in the band gap, e - h trapping by the activator will form a 5d(Ln3+) state. The e - h trapping efficiency shows a positive linear correlation with the energy difference of the Ln3+ ground state and VBM. That is, the observed trapping efficiency appears to be dictated by hole trapping efficiency of the Ln3+ ground state for the corresponding activators. For the activators with the Ln3+ ground state approximately equivalent to or lower in energy relative to the VBM, and a Ln2+ ground state CT that is in the band gap, a linear correlation is observed between the trapping efficiency and the difference in energy between the CT state and conduction band edge (CBE). In this case, a CT state is formed and the trapping efficiency must be dictated by the electron trapping efficiency for the corresponding activator. Having completed a preliminary study of the micron – sized materials, data will be presented on our studies of surface loss effects in the nano – sized materials.

Identifying Single or Multiple Poverty Trap: An Application to Indian Household Panel Data

The paper examines the household asset dynamics in India as well as Indian rural States. The paper contributes to the empirical analysis of poverty trap by investigating the presence of one potential poverty trap to simultaneous poverty trap. The paper uses the India Human Development Survey for the year 1993 and 2005. We use the local polynomial regression with Epanechnikov kernel weights to test the existence of multiple or single equilibrium in asset poverty dynamics. Moreover, we use the partial linear mixed model to test the impact of illiteracy trap and under-nutrition trap on asset dynamics process. Across all the States we find only single dynamic asset equilibrium for rural households. However the nature of the asset dynamics varies from one state to another. We find that, in most of the States, asset accumulation does not take place and welfare dynamics is very poor in rural areas. Further, we find under-nutrition trap uniformly affect the asset accumulation in most of the States. However an illiteracy trap affects the asset level heterogeneously over the income and regional distribution. We find the most deprived States (Bihar, Uttar Pradesh, Orissa and Madhya Pradesh) have the multiple poverty trap compared to richer States. Our result implies that asset dynamics of the household varies in the long term according to the types of traps. Government and policy makers should take pointed policy and programme based on whether the poor are trapped and in what ways.

Time-of-Flight Current Shapes in Molecularly Doped Polymers: Effects of Sample Thickness and Irradiation Side and Carrier Generation Width

The time-of-flight (TOF) current transients from solution-cast, free-standing films of p-diethylaminobenzaldehyde diphenyhydrazone in bisphenol A polycarbonate (DEH:PC) have been studied using electron gun induced charge generation. Changes in the shape of the current transient, cusp formation in particular, with film thickness, electron-beam penetration depth, and the side of the sample irradiated, have been analyzed with a two-layer multiple trapping model, and indicate that the time-of-flight transients of solution-cast films can be problematic in that plateau formation does not necessarily imply nondispersive charge transport. The results are consistent with the existence of thin surface layers which are depleted of the hole transport material. The depleted layer on the surface of the film that was exposed to air during coating/drying is always thicker than it is for the surface contacting the substrate. Depletion could occur through transport material sublimation, surface physical characteristics suc...

Persistent luminescence, TL and OSL characterization of beta irradiated SrAl2O4:Eu2+, Dy3+ combustion synthesized phosphor

The persistent luminescence (PLUM), thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of strontium aluminates co-doped with Eu+2 and Dy+3 exposed to beta radiation is reported. The phosphor was synthesized by the combustion synthesis method employing a highly exothermic redox reaction between the metal nitrates [Al(NO3)3, Sr(NO3)2, Eu(NO3)3 and Dy(NO3)3] and organic fuel carbohydrazide (CH6N4O). The long decay PLUM emission, TL and OSL were measured as a function of beta radiation dose. A wide emission band centered at 510nm (green) related to Eu2+ ions and lattice defects were observed for the synthesized samples. The presence of a variety of defects and aggregates were responsible for the observed broad 100°C peaked TL glow curve of the irradiated sample which is composed of several overlapped TL peaks. The existence of multiple trapping levels, with different trapping/detrapping probabilities, is behind the particular features for the PLUM, TL and OSL emissions. We conclude that in the SrAl2O4:Eu2+, Dy3+ phosphors, the low temperature TL peaked around 30–75°C is responsible for the PLUM emission and those around 100°C were related to very stable trapping states which provide suitable radiation storage properties to be used as a PLUM/TL/OSL radiation phosphor.

A new view of orb webs: multiple trap designs in a single structure

Spider orb webs are impressive for their apparently uniform geometric patterns. There are, however, consistent, substantial and taxonomically widespread periphery-to-hub differences in the distances between both adjacent radii and between sticky spiral lines. Radii in typical orbs were on average about 4–5 times farther apart at the outer edge than the inner edge of the area covered by sticky lines. Distances between sticky spiral loops were on average about two times larger near the outer edge than in more inner portions. This pattern in sticky spiral spacing was absent in the modified orbs of Nephila clavipes, in which distances between radii varied less. Thus, patterns in sticky spiral spacing may be related to inter-radial spacing; there is, however, probably no single explanation for all of the different patterns of sticky spiral spacing. The patterned differences in radius and sticky spiral spacing have important consequences for understanding orb function, because the lines in a prey's immediate vicinity largely determine whether it will be stopped and then retained, and elementary physics dictates that contact with more lines will tend to increase prey being stopped and retained. Rather than being a unit trap with a single set of prey capture properties, an orb has locally different trapping properties in different sectors. Abandoning the previous typological style of discussion of ‘the’ ability of a given design to stop and retain prey promises to lead to improved understanding of orb web designs. Published 2014. This article is a U.S. Government work and is in the public domain in the USA, Biological Journal of the Linnean Society, 2014, 111, 437–449.

Multiple band light trapping in ultraviolet, visible and near infrared regions with TiO2 based photonic materials.

TiO2 based photonic materials (TiO2 PMs) with hierarchical top-nanonet/bottom-nanotube structures were fabricated by a facile two-step electrochemical anodization method. The TiO2 PMs demonstrated multiple band light trapping activity not only in the ultraviolet and visible regions, but also in the near infrared region.

Dehydrogenation of hydrocarbons with metal-carbon multiple bonds and trapping of a titanium(II) intermediate.

Reacting (PNP)Ti[double bond, length as m-dash]CH(t)Bu(CH2(t)Bu) with 2,2'-bipyridine (bipy) in cyclohexane or heptane results in dehydrogenation, cleanly producing cyclohexene and 1-heptene, respectively, and a Ti(II) intermediate that is trapped by bipy to produce [(PNP)Ti(III)(CH2(t)Bu)(bipy˙(-))] (1). This titanium(ii) intermediate reduces the bipy ligand upon coordination to form a Ti(III) center, where the unpaired electron is antiferromagnetically coupled to the electron of the reduced [bipy˙(-)] π-radical moiety, giving an overall diamagnetic species. Complex 1 has been characterized by NMR and UV-vis spectroscopies as well as single crystal X-ray diffraction studies.

Effect of energetic disorder on the open-circuit voltage in organic bulk heterojunction composites

Under open-circuit condition, the current is not extracted and the photogenerated carriers in principle disappear only by recombination. We study the open-circuit voltage and transient photovoltage under the effect of bulk recombination in a medium with energetic disorder by using the multiple trapping (MT) model. The key parameter in the MT model is the dispersion parameter given by the ratio of thermal energy to the characteristic energy of trap states. We show that depends linearly on the logarithm of the light intensity and the slope depends on the of the MT model. Under the continuous irradiation of light, the photovoltage response to the weak perturbation by a pulsed light obeys pseudo-first-order decay. The rate as a function of is independent of the dispersion parameter. However, it obeys the power law as a function of light intensity, and the exponent is given by , which reduces to 1/2 in the absence of energetic disorder.

Hierarchical spatial capture–recapture models: modelling population density in stratified populations

Summary Capture–recapture studies are often conducted on populations that are stratified by space, time or other factors. In this paper, we develop a Bayesian spatial capture–recapture (SCR) modelling framework for stratified populations – when sampling occurs within multiple distinct spatial and temporal strata. We describe a hierarchical model that integrates distinct models for both the spatial encounter history data from capture–recapture sampling, and also for modelling variation in density among strata. We use an implementation of data augmentation to parameterize the model in terms of a latent categorical stratum or group membership variable, which provides a convenient implementation in popular BUGS software packages. We provide an example application to an experimental study involving small‐mammal sampling on multiple trapping grids over multiple years, where the main interest is in modelling a treatment effect on population density among the trapping grids. Many capture–recapture studies involve some aspect of spatial or temporal replication that requires some attention to modelling variation among groups or strata. We propose a hierarchical model that allows explicit modelling of group or strata effects. Because the model is formulated for individual encounter histories and is easily implemented in the BUGS language and other free software, it also provides a general framework for modelling individual effects, such as are present in SCR models.

Dc electric field effect on the anomalous exponent of the hopping conduction in the one-dimensional disorder model

The dc electric field effect on the anomalous exponent of the hopping conduction in the disorder model is investigated. First, we explain the model and derive an analytical expression of the effective waiting time for the general case. We show that the exponent depends on the external field. Then we focus on a one-dimensional system in order to illustrate the features of the anomalous exponent. We derive approximate expressions of the anomalous exponent of the system analytically. For the case of a weak field, the anomalous exponent is consistent with that of diffusive systems. This is consistent with the treatments of Barkai et al. [Phys. Rev. E 63, 046118 (2001)] and our result supports their theory. On the other hand, for the case of a strong field and a strong disorder, the time evolution of the exponent clearly differs from that in the weak field. The exponent is consistent with the well-known expression of the anomalous exponent in the multiple trapping model at mesoscopic time scales. In the long-time limit, a transition of the anomalous exponent to the same value of the weak field occurs. These findings are verified by the Monte Carlo simulation.

Double quantum dot in a quantum dash: Optical properties

We study the optical properties of highly elongated, highly flattened quantum dot structures, also referred to as quantum dashes, characterized by the presence of two trapping centers located along the structure. Such a system can exhibit some of the properties characteristic for double quantum dots. We show that sub- and super-radiant states can form for certain quantum dash geometries, which is manifested by a pronounced transfer of intensity between spectral lines, accompanied by the appearance of strong electron-hole correlations. We also compare exciton absorption spectra and polarization properties of a system with a single and double trapping center and show how the geometry of multiple trapping centers influences the optical properties of the system. We show that for a broad range of trapping geometries the relative absorption intensity of the ground state is larger than that of the lowest excited states, contrary to the quantum dash systems characterized by a single trapping center. Thus, optical properties of these structures are determined by fine details of their morphology.

Optical manipulation of aerosol droplets using a holographic dual and single beam trap

We present optical trapping and manipulation of pure water and salt water airborne droplets of various sizes ranging from sub-micrometers up to several tens of micrometers in a holographic dual and single beam trap. In the dual beam trap, successful fusion of droplets as well as precise delivery of many droplets and manipulation of multiple droplets are demonstrated. Furthermore, employing the transfer of the orbital angular momentum of light from Laguerre-Gaussian beams, we show that the water droplets orbit around the beam propagation axis and their tangential speed can be controlled by beam waist magnitude. We also demonstrate that sub-micrometer sized pure water droplets can be trapped and manipulated by a single beam trap with a relatively low numerical aperture. In this case, multiple stable trapping positions were observed, both theoretically and experimentally, which were due to the optical intensity oscillations in the focal region of the laser beam.

Charge‐transfer‐induced doping at an electron donor (α‐sexithiophene)/acceptor (C60) interface and mobility improvement

AbstractWe studied various aspects relating to surface charge‐transfer‐induced doping at an organic/organic interface using in situ electrical measurements with a field‐effect transistor (FET) during the formation of the electron donor/acceptor interface. Adsorption of the electron‐accepting molecules (C60) on top of the electron donating molecules (α‐6T) led to an increase in the FET hole mobility in an α‐6T film. Under illumination, the FET hole mobility in the α‐6T film with C60 deposition was significantly increased in comparison with that in the dark due to exciton dissociation at the C60/α‐6T interface, resulting in a large threshold voltage shift. The origin of the mobility increase is explained by the multiple trapping and release (MTR) model in which the mobility is determined by the carrier density. Various phenomena relevant to charge transfer and charge transport at the organic/organic interface are reported and their origins are discussed. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Role of Connexin 43 in Helicobacter pylori VacA-Induced Cell Death

Helicobacter pylori colonizes the human stomach and confers an increased risk for the development of peptic ulceration, noncardia gastric adenocarcinoma, and gastric lymphoma. A secreted H. pylori toxin, VacA, can cause multiple alterations in gastric epithelial cells, including cell death. In this study, we sought to identify host cell factors that are required for VacA-induced cell death. To do this, we analyzed gene trap and short hairpin RNA (shRNA) libraries in AZ-521 human gastric epithelial cells and selected for VacA-resistant clones. Among the VacA-resistant clones, we identified multiple gene trap library clones and an shRNA library clone with disrupted expression of connexin 43 (Cx43) (also known as gap junction protein alpha 1 [GJA1]). Further experiments with Cx43-specific shRNAs confirmed that a reduction in Cx43 expression results in resistance to VacA-induced cell death. Immunofluorescence microscopy experiments indicated that VacA did not colocalize with Cx43. We detected production of the Cx43 protein in AZ-521 cells but not in AGS, HeLa, or RK-13 cells, and correspondingly, AZ-521 cells were the most susceptible to VacA-induced cell death. When Cx43 was expressed in HeLa cells, the cells became more susceptible to VacA. These results indicate that Cx43 is a host cell constituent that contributes to VacA-induced cell death and that variation among cell types in susceptibility to VacA-induced cell death is attributable at least in part to cell type-specific differences in Cx43 production.

Photocarrier localization and recombination dynamics in Cu2ZnSnS4 single crystals

We have studied the photocarrier localization and recombination dynamics in Cu2ZnSnS4 single crystals at room temperature. The band-gap energy and tail states below the band edge were evaluated by a combination of photoluminescence (PL), PL excitation, photocurrent, and femtosecond transient reflectivity spectroscopy. The photocarriers are rapidly localized to shallow tail states within a typical time constant of several picoseconds to a few tens of picoseconds. The sub-nanosecond PL decay dynamics indicate the importance of multiple carrier trapping processes in the shallow tail states. Therefore, it is concluded that the tail states dominate the optical responses of Cu2ZnSnS4 single crystals.

Adult-Specific Systemic Over-Expression Reveals Novel In Vivo Effects of the Soluble Forms of ActRIIA, ActRIIB and BMPRII

Bone morphogenetic proteins (BMPs)/growth differentiation factors (GDFs), which belong to the TGF-beta superfamily, are pleiotropic factors that play a role in regulating the embryonic development and postnatal homeostasis of various organs and tissues by controlling cellular differentiation, proliferation and apoptosis. Conventional transgenic and knockout (KO) mouse approaches have provided only limited information regarding the in vivo functions of BMP signaling in adult animals due to the effects on prenatal development and the difficulty in manipulating multiligand signals simultaneously. We recently produced transgenic chimeric mice(Tg chimeras) in which the soluble IgG1-Fc fusion protein of three BMP type II receptors (ActRIIA, ActRIIB, BMPRII) was highly circulated (281-709 μg/ml), specifically in adult mouse blood. Since each BMP receptor can bind to multiple BMP ligands, these Tg chimeras should be useful to investigate the effects of trapping multiple BMP ligands. Remarkably, some phenotypes were unexpected based on previous studies, such as KO mouse analyses, presumably representing the effects of the multiple ligand trapping. These phenotypes included increased red blood cells (RBCs) and decreased viability in adults. In a further study, we focused on the phenotype of increased RBCs and found that extramedullary hematopoiesis in the spleen, not in the bone marrow, was increased using histological and flow cytometric analyses. Although it remains to be elucidated whether the transgene products affect the tissues directly or indirectly, our data provide novel and important insight into the biological functions of the soluble IgG1-Fc fusion protein of three BMP type II receptors in adults, and our approach should have broad applications to research on other ligand receptor families and studies involving mouse models.

Charge Trapping Dynamics in PbS Colloidal Quantum Dot Photovoltaic Devices

The efficiency of solution-processed colloidal quantum dot (QD) based solar cells is limited by poor charge transport in the active layer of the device, which originates from multiple trapping sites provided by QD surface defects. We apply a recently developed ultrafast electro-optical technique, pump-push photocurrent spectroscopy, to elucidate the charge trapping dynamics in PbS colloidal-QD photovoltaic devices at working conditions. We show that IR photoinduced absorption of QD in the 0.2-0.5 eV region is partly associated with immobile charges, which can be optically detrapped in our experiment. Using this absorption as a probe, we observe that the early trapping dynamics strongly depend on the nature of the ligands used for QD passivation, while it depends only slightly on the nature of the electron-accepting layer. We find that weakly bound states, with a photon-activation energy of 0.2 eV, are populated instantaneously upon photoexcitation. This indicates that the photogenerated states show an intrinsically bound-state character, arguably similar to charge-transfer states formation in organic photovoltaic materials. Sequential population of deeper traps (activation energy 0.3-0.5 eV) is observed on the ~0.1-10 ns time scales, indicating that most of carrier trapping occurs only after substantial charge relaxation/transport. The reported study disentangles fundamentally different contributions to charge trapping dynamics in the nanocrystal-based optoelectronic devices and can serve as a useful tool for QD solar cell development.

Long-term stabilization of sprayed zinc oxide thin film transistors by hexafluoropropylene oxide self assembled monolayers

Surface functionalization of solution processed zinc oxide layers was studied in transistors with bottom-gate bottom-contact configuration aiming at suppression of trapping processes to increase device stability. Saturation of electrically active surface sites and formation of a moisture barrier to decrease the impact of humid atmosphere was successfully shown by binding hexafluoropropylene oxide (HFPO) on the metal oxide semiconductor. Deep trap level related electrical parameters, i.e., stability, hysteresis, and on-set voltage, improved rapidly within 60 s of exposure which was attributed to occupation of sites characterized by low adsorption energies, e.g., at edges. In contrast, shallow trap level related parameters, i.e., mobility, showed a much slower process of improvement. Identical behavior was determined for the contact angle. A physical model is presented by applying first order reaction kinetics equation to Young's law and multiple trapping and release model which relates the dependence of the contact angle and the mobility to the hexafluoropropylene oxide deposition time. Consistent time constants of τ = ≪1 min, 2 min, and 250 min were extracted for mobility and contact angle which implies a direct dependence on the surface coverage. Mobility decreased at short deposition times, recovered at medium deposition times and improved strongly by 2.4 cm2 V−1 s−1 for long deposition times of 1400 min. A microscopic model of these phenomena is given with interpretation of the different time constants found in the experiment.

Charge Transfer in E. coli DNA Photolyase: Understanding Polarization and Stabilization Effects via QM/MM Simulations

We study fast hole transfer events in E. coli DNA photolyase, a key step in the photoactivation process, using a multiscale computational method that combines nonadiabatic propagation schemes and linear-scaling quantum chemical methods with molecular mechanics force fields. This scheme allows us to follow the time-dependent evolution of the electron hole in an unbiased fashion; that is, no assumptions about hole wave function localization, time scale separation, or adiabaticity of the process have to be made beforehand. DNA photolyase facilitates an efficient long-range charge transport between its flavin adenine dinucleotide (FAD) cofactor and the protein surface via a chain of evolutionary conserved Trp residues on the sub-nanosecond time scale despite the existence of multiple potential trap states. By including a large number of aromatic residues along the charge transfer pathway into the quantum description, we are able to identify the main pathway among alternative possible routes. The simulations show that charge transfer, which is extremely fast in this protein, occurs on the same time scale as the protein response to the electrostatic changes; that is, time-scale separation as often presupposed in charge transfer studies seems to be inappropriate for this system. Therefore, coupled equations of motion, which propagate electrons and nuclei simultaneously, appear to be necessary. The applied computational model is shown to capture the essentials of the reaction kinetics and thermodynamics while allowing direct simulations of charge transfer events on their natural time scale.