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Electron trapping by neutral pristine ferroelectric domain walls in BiFeO3

Electron trapping by neutral pristine ferroelectric domain walls in BiFeO3

The effect of the DW and of the charge accumulation on the electronic structure is analyzed next in Fig. 6, where we show the layer-resolved density of states (DOS) for the different charging situations investigated here. For both the neutral and the positively charged systems the DOS appears little perturbed by the presence of the DW, and it is essentially identical regardless of the layer on which it is projected. In contrast, when excess electrons are introduced, one can clearly observe the formation of two narrow peaks in the DOS localized at the layers adjacent to the DW. The gap level close to the valence band originates from occupied Fe d orbitals oriented along Fe-O bonds being pushed energetically upward, while the one at higher energy is from the Fe d orbitals that are directed away from Fe-O bonds and are occupied by the excess electron. The same electron trapping (small electron polaron) has been discussed in the case of charged domain walls in ErMnO 3 [18] and PbTiO 3 [19]. In

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Electron trapping in metal-insulator-semiconductor structures on n-GaN with SiO2 and Si3N4 dielectrics

Electron trapping in metal-insulator-semiconductor structures on n-GaN with SiO2 and Si3N4 dielectrics

To explain electron trapping in SiO 2 samples we invoke the concept of border trap presented by Fleetwood et al. 17 In essence, these are traps spatially close to but not at the dielectric/semiconductor interface. Physical separation dis- connects the border traps from electrical activity at the inter- face up to the point that energetic carriers are capable of traversing the region of separation. Given our experimental results and considerations made so far, we attribute to border traps the electron trapping in SiO 2 samples. Further, we sug-

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On the correct implementation of Fermi-Dirac statistics and electron trapping in nonlinear electrostatic plane wave propagation in collisionless plasmas

On the correct implementation of Fermi-Dirac statistics and electron trapping in nonlinear electrostatic plane wave propagation in collisionless plasmas

In conclusion, we have presented a general framework of weak coherent structures in partially Fermi-Dirac degen- erate plasmas. These coherent structures are necessarily determined by the electron trapping nonlinearity and hence are beyond any realm of linear Vlasov theory. This implies that even in the infinitesimal amplitude limit, linear Landau and/or van Kampen theory fail as possible descriptive approaches to these structures. 29,33 The spatial profiles of the potential /ðxÞ in the small amplitude limit are of cnoidal hole character, similar is in the classical case, and are given by the already known expressions (see Ref. 33 and referen- ces therein). The NDR on the other hand is for given b; w again of thumb shape type but appears to be rather sensitive to the electron degeneracy characterized by the normalized chemical potential l. An important aspect of the nonlinear theory in the small but finite amplitude limit is that the elec- tron density is described by half-power expansions of the electrostatic potential. Different results 34 not giving rise to

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Electron trapping and acceleration on a downward density ramp: a two-stage approach

Electron trapping and acceleration on a downward density ramp: a two-stage approach

Increasing the power of the ‘injection’ pulse does not help at all, surprisingly. The injection of an electron bunch with a low absolute energy spread and emittance on a density downramp turns out to be a rather delicate process. Too many electrons will be injected when the ‘injection’ pulse is too powerful, and the entire effect will be spoiled. We performed a simulation using a 40 TW laser pulse focused onto a 15 µ m wide spot, in an attempt to trap more electrons. However, in such a configuration the laser pulse is too powerful: rather than seeing some gentle electron injection at the bottom of the ramp only, wave breaking and electron trapping happen over the entire length of the ramp. Large quantities of electrons are injected into the wakefield, obscuring the coveted low-energy, low-spread, low-emittance bunch. The simulation results for this case are displayed in figure 3. We also conducted simulations with 20 and 40 TW pulses focused on a 7.5 µ m wide spot (not shown), with similar results. These results show that the true strength of the downramp scheme lies in the production of low-spread, low-emittance electron bunches by a laser pulse of moderate power (10 TW), and not in the production of high-charge, high-energy pulses by high-power laser pulses.

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Electron trapping in noncrystalline remote plasma deposited Hf- aluminate alloys for gate dielectric applications

Electron trapping in noncrystalline remote plasma deposited Hf- aluminate alloys for gate dielectric applications

AlO terminal 1 ⫺ groups. However, the AlO terminal 1 ⫺ group does not occur naturally in any crystalline material and, therefore, is assumed to be less stable than the SiO terminal 1 ⫺ group, which is a constituent of all silicate glasses in the low alloy. 19 In ad- dition, empirical calculations based on electronegativity models also indicate that it is significantly less stable than the SiO terminal 1 ⫺ group due to a higher ratio of electrons to nuclear charge. This suggests that the bonding and antibond- ing states of the AlO terminal 1 ⫺ may be in or near the band gap of silicon and, therefore, be active as trapping/defect states. For the Ta aluminates the localized Ta d state is low in energy, and may overlap with this network disruption defect state, thereby making it difficult, if not impossible to distinguish between the disruption defect state and the localized Ta d state based on an analysis of J vs T data alone. 6,18 This point is supported by the quantitative differences between low temperature trapping of the Ta and Hf aluminate alloys. The trapping in the Ta aluminate devices is larger, consistent with the trapping state being an intrinsic energy level of the alloy,

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Overview on recent progress in magnetron injection gun theory and design for high power gyrotrons

Overview on recent progress in magnetron injection gun theory and design for high power gyrotrons

Three important issues related to MIG theory and design were presented: (i) Two electron trapping mechanisms were discussed while design criteria were proposed for the suppression of the electron trapping mechanisms. (ii) The influence of a possible emitter ring radial displacement in relation to its neighboring parts on the beam quality was numerically investigated. The results show that such a ra- dial displacement significantly influences the gyrotron op- eration. A new type of emitter ring with coated edge rims could suppress that sensitivity. (iii) The influence of the specified emitter ring temperature inhomogeneity on the beam quality was also shortly discussed.

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Development of CZT strip detector modules for 0.05- to 1-MeV gamma-ray imaging and spectroscopy

Development of CZT strip detector modules for 0.05- to 1-MeV gamma-ray imaging and spectroscopy

the imaging volume (8 ¥ 8 ¥ thickness mm 3 ). Table 2 summarizes the results. At 122 keV we find good agreement between measurement and theory for the 5 mm detector. We attribute the lower than expected response of the 10 mm detector to two factors both of which reduce the number of triggered events: 1) electron trapping reducing the signal amplitude for events near the cathode causing some of these to fall below the trigger threshold and 2) a significant fraction of the electrons are collected on the strips for events occurring under the corners of the unit cell (pixel) with this detector. At 662 keV we suspect that the higher than expected number of detections is due to Compton scattering from passive material surrounding the detector. Further study is planned to better assess the efficiency of our detectors.

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Readout and performance of thick CZT strip detectors with orthogonal coplanar anodes

Readout and performance of thick CZT strip detectors with orthogonal coplanar anodes

Fig. 7 shows the energy resolution distribution for all pixels of four prototype detector modules as determined from a Gaussian fit to the 122 keV peak. Detector UNH-Y-2 (bottom panel) is 10 mm thick; the others are 5 mm thick. Note that only 56 pixels are included in the histogram for detector UNH-Y-2 as one pixel row channel (8 pixels) was too noisy to measure. No correction for electron trapping has been made here.

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Does Polaronic Self-Trapping Occur at Anatase TiO2 Surfaces?

Does Polaronic Self-Trapping Occur at Anatase TiO2 Surfaces?

that energy supplied to the anatase surface to overcome the trap will allow electrons to move favourable back into the bulk. The deep defect levels from the electron trap around 1 eV below the conduction band indicates the energy required to excite the electron back into the conduction band. The calculated strain energy, which is the energy to distort the lattice site in order to trap charge, indicates that the energy to form the trap is higher than the electron trapping energy, where the largest localization shown by the spin is associated with the strongest trap on the 107 surface. These results show that electron trapping of excess electrons in anatase crystals will occur when surface structural defects such as steps, and kinks are present.

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OSL-thermochronometry of feldspar from the KTB borehole, Germany

OSL-thermochronometry of feldspar from the KTB borehole, Germany

The slow accumulation and emptying of electron traps in a mineral in nature can be studied under laboratory-accelerated conditions using artificial sources of radioactivity and heat, relying on the fundamental geochronometric assumption that the system behaviour is governed by the same physical laws across many or- ders of magnitude of kinetic rates (e.g. Reiners and Ehlers, 2005; Chen and Pagonis, 2011). To determine the growth of feldspar IRSL50as a function of cumulative irradiation, we used a com-mon modification of the Wallinga et al.’s (2000) Single Aliquot Regenerative-dose (SAR) protocol for feldspar IRSL50(Table2, left column). In the scope of this study, the minor systematic effect of irradiation temperature on the ionisation cross section of feldspar IRSL50(<10% effect in the 0 – 80 °C range; Wallinga et al., 2002) was not considered significan t due to the logarithmic relation-ship between dose rate and apparent palaeotemperature (Hoyt et al., 1971; Guralnik et al., 2013). Thus, all samples were irradiated at room temperature as in standard feldspar IRSL dating, leaving the assessment of minor effects due to elevated-temperature ir-radiation for more technical studies in the future. To determine the decrease of luminescence as a function of cumulative isothermal storage, we replaced the SAR fading protocol of Murray et al. (2009)with the short-shine isothermal decay experiment of Auclair et al.(2003), favouring the latter time-saving procedure (Table2, right column) in light of indistinguishable data obtained by both methods during preliminary testing. Aiming to constrain the mirroring effects of electron trapping and detrapping across the widest experimentally-feasible time domain, both protocols in Table2were adjusted to sample the luminescence response evenly across 3 – 4 orders of magnitude of time. Standard quality criteria included rejection of a few self-inconsistent measurements, in which dose recycling and/or dose recovery deviated from unity by more than 10% (e.g. Buylaert et al., 2011, and references therein).

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Rearrangement and trapping of organozinc carbenoids.

Rearrangement and trapping of organozinc carbenoids.

ppm) as the internal standard. Infrared spectra were recorded on a Perkin Elmer 811, 983G or FT-IR 1600 spectrometer. Mass spectra and accurate mass measurements were recorded under electron impact conditions using VG 305, VG 7070, VG 707OB, VG 12-253, VG ZAB-E and VG ZAB-SE instruments, under chemical ionisation conditions using a VG-ZAB-SE or an AutospecQ instrument with the stated gas, and under fast atom bombardment conditions using a VG 7070, VG-ZAB-SE or AutospecQ instrument in the stated matrix. Gas chromatography coupled mass spectrometry was recorded on a VG 16F machine coupled to a Perkin Elmer series 204 chromatograph using helium as the carrier gas, and a BPl 25 m x 0.20 mm column (polydimethylsiloxane, 0.25 pm film). Gas chromatography was performed on a Hewlett-Packard 5780 machine (flame ionisation detector) with a 2.5 m APL column, or on a Hewlett-Packard 5890A machine (flame ionisation detector) with a 25 m x 0.32 mm BPX5 column (crosslinked 95% polydimethylsiloxane/5% polydiphenylsiloxane, 0.5 pm film) or with a 25 m x 0.10 mm BP5 column (95% poly dimethy lsiloxane/5 % polydiphenylsiloxane, 0.1 pm film) using helium or hydrogen as the carrier gas. Melting points were determined on a Reichert hot- stage apparatus and are uncorrected. Boiling points for bulb to bulb or 'kugelrohr' distillations refer to uncorrected air temperatures. Optical rotations were recorded on an Optical Activity Polaar 2000 instrument. Microanalyses were performed in the Imperial College Chemistry Department or University College Chem istry Departm ent microanalytical laboratories.

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Enhanced Trapping of HIV 1 by Human Cervicovaginal Mucus Is Associated with Lactobacillus crispatus Dominant Microbiota

Enhanced Trapping of HIV 1 by Human Cervicovaginal Mucus Is Associated with Lactobacillus crispatus Dominant Microbiota

CVM can exhibit markedly different macroscopic characteris- tics (e.g., color and consistency) over time as well as between women. Nevertheless, it is important to note that the physical properties of the local environment (i.e., at the length scale of HIV virions) that enable or block HIV diffusional mobility in CVM are distinct from the macroscopic physical properties of the mucus gel (36, 37). For example, in our previous study (11), as well as the current work, the bulk viscoelasticities of CVM did not appear to differ between the CVM specimens that trapped HIV and those that failed to trap HIV, including those with substantial quantities of G. vaginalis. Likewise, variations in the macroscopic properties of CVM do not necessarily compromise its ability to serve as an effective and consistent diffusional barrier against HIV and other STIs. Consequently, the key to harnessing CVM as a protective barrier is to better understand the complex molecular and bio- physical interactions that occur within CVM, and our current effort to link vaginal microbial communities to HIV mobility in CVM provides important first clues as to how the innate diffu- sional barrier properties of CVM may be reinforced against STIs. Trapping or even slowing viruses in mucus is likely an effective mechanism of mucosal protection that operates not only by re- ducing the viral load arriving at target cells and purging trapped viruses by natural mucus clearance mechanisms but also by in- creasing the likelihood of inactivation via other innate protective mechanisms (e.g., defensins, thermal inactivation, etc. [38, 39]) while virus penetration of mucus is delayed. The potential effec- tiveness of trapping in mucus is perhaps best exemplified by stud-

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Innovative Approach for Maximizing CO2 Storage and Enhancing Oil Recovery by Co-Optimization and Latestage Optimization

Innovative Approach for Maximizing CO2 Storage and Enhancing Oil Recovery by Co-Optimization and Latestage Optimization

The solubility trapping of IW500-3-12, IW500-12-12 and IW1000-12-12 are shown in Figure 9. From the graph it can be seen that as the water injection rate increases, the solubility trapping increases. Also, as the water injection interval increases, the solubility trapping increases. This agrees with the findings in the solubility trapping in the previous subsection.

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Thermoluminescence Properties of Gamma and C5+ Ion Beam Irradiated Sr2(1-X)(Dy,Na)Xznwo6 Phosphors

Thermoluminescence Properties of Gamma and C5+ Ion Beam Irradiated Sr2(1-X)(Dy,Na)Xznwo6 Phosphors

ion beam irradiate phosphors show similar nature. The glow curve has three distinguishable overlapping components of glow peaks. The relative intensities of component glow peaks are different for both type of irradiation. Glow curves were analyzed by deconvolution and calculation of trapping parameters using Chen’s peak shape method for understanding the nature of trapping centers which results different glow peaks.

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Comprehensive mammalian genetics: history and future prospects of gene trapping in the mouse

Comprehensive mammalian genetics: history and future prospects of gene trapping in the mouse

Gene trapping combined with methods to monitor induction of expression of the trapped gene have now been used in a variety of cell types. Gogos et al. (1996) trapped genes using a retrovirus containing SA β geo in C2C12 myoblasts that can be induced to differentiate into myotubes. They looked for genes in which the β gal expression was up-regulated during this differentiation proc- ess. One of the genes they identified was cathepsin B. Kerr et al. (1991) used transfection of a gene trap vector containing SA β geo followed by FACs sorting to identify gene trap events that were responsive to LPS treatment in a B-lineage cell line. LPS can induce the differentiation of some B-cell lineages. They made replica plates of the gene trap clones, treated them with LPS and looked for gene traps in which β gal expression was modulated. They identified 3 repressed and 2 induced gene trap lines and the 5’ RACE products of all 5 genes were novel. Others have devel- oped sorting and selection schemes to identify induced or sup- pressed gene trap events. Gogos et al. (1997) used gene trap vectors containing SAhygtk (a hygromycin/thymidine kinase fusion gene, Fig. 2C) or SA β geo. They trapped genes in NIH 3T3 cells and either FACs sorted (for SA β geo gene traps) or gancyclovir treated (for SAhygtk gene traps) to remove constitutively expressed gene traps. They then induced myoD expression to examine genes regulated by myoD using either FACs sorting (for SA β geo traps) or hygromycin selection (for SAhygtk traps) to identify up-regulated genes. These protocols proved useful for identifying gene traps induced by myoD expression and eliminated the steps of clone picking and replica plating thus reducing the effort required to identify regulated genes. Similarly, others have trapped and iden- tified genes induced during differentiation of myeloid precursor cells into appropriate lineages or P19 cells into neurons (Imai et al., 1995; Jonsson et al., 1996). Russ et al. (1996) developed a cre-lox based switch to allow selection for genes up-regulated during programmed cell death in a hematopoietic precursor cell line (Fig. 2D). The switch allowed them to select for genes that are induced by factor deprivation in a cell line that responds to such deprivation by undergoing apoptosis. Once again the need for clone picking and replica plating was eliminated. In addition, the use of cre- recombinase promoter trap vectors in combination with a separate

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Optical micromanipulation using dispersion compensated and phase shaped ultrashort pulsed lasers

Optical micromanipulation using dispersion compensated and phase shaped ultrashort pulsed lasers

The work described in this chapter indicates that trapping of Lorentz-Mie-sized particles is independent of pulse duration. A recent theoretical paper discussed the possibility of a material-independent pulse duration eect on optical trap- ping in the Rayleigh regime[71]. Our own theory and modelling indicate no pulse duration dependence in any size regime, but there have been no experi- ments addressing this question so far. Although we attempted to perform these measurements for Rayleigh-sized particles as well, the limited available trap- ping power (47mW at maximum) prevented us from trapping single 50nm or 100nm silica particles for long enough to make measurements. Gold, silver, and polymer have higher polarisability and therefore stronger trapping at the same average power, but nonlinear eects such as ablation and cavitation prevented us from trapping these materials with ultrashort pulses. Large polymer particles could be trapped without damage at low average powers, as described earlier in this thesis, but the average powers required for trapping Rayleigh-sized particles were far above this damage threshold.

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Charge transport in organic solar cells

Charge transport in organic solar cells

Dispersive transport in organic semiconductors is usually thought to be caused by the energetic relaxation of hot charge carriers within their density of states [76]. Spectroscopic measurements and Monte Carlo simulations have revealed energetic re- laxation extending even to the microsecond timescales, where it could be relevant to bulk charge transport [228, 229]. Even if the bulk of the energetic relaxation were to occur on very fast timescales, there is still the question of whether residual thermal- ization might continue to long, microsecond timescales. This energetic relaxation is often understood to cause a time-dependent mobility and therefore explain dispersive current transients [217, 230], yet we will show in this chapter that this commonly-used model is inconsistent with our observations in high efficiency organic solar cell ma- terials. Instead, there is an alternative mechanism for the creation of a distribution of carrier velocities, namely, via trapping. This observation has a very direct im- pact on the numerous models, theories and experimental results describing dispersive charge transport in disordered organic semiconductors. Furthermore, it points to a new strategy for improving charge transport “management” in devices such as organic solar cells.

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Invading and expanding : range dynamics and ecological consequences of the Greater White Toothed Shrew (Crocidura russula) invasion in Ireland

Invading and expanding : range dynamics and ecological consequences of the Greater White Toothed Shrew (Crocidura russula) invasion in Ireland

All available sighting and live-trap data on C. russula (with associated dates) were collated for 2006–2013 (Figs 1A and S2; Table S1) based on records from the National Biodiversity Data Centre in Ireland (www.biodiversity.ie) and small mammal trapping studies in the region [18,24,30,31]. In addition, data on prey identification from barn owl and kestrel pellets and identification of prey remains from nest inspections were also included [35–37]. Both predators are known to feed on the range of small mammal species present in Ireland (including C. russula [18]). They are central-place foragers which after a period of post- fledging dispersal are largely sedentary within a relatively small home range and show a high level of fidelity to specific nest and roost sites within that range [38–40]. Available data on C. russula from the scats of pine martens (Martes martes) were not included because the exact sampling dates were not known [41]. We used all available data to provide an initial estimate of the expansion rate for C. russula (km/yr). We partitioned the data by date, making sure that data from one survey were not split between subsets (date bins were 2008, 2009, Jan-Sept 2010, Oct 2010–Feb 2011, Mar 2011–Mar 2012, Apr 2012–Dec 2012, 2013). For each subset we calculated the area, A, of the minimum convex polygon (MCP) for C. russula and fitted a linear regression of the radial range of the species distribution (km) against the median date (yr) of the data points in each subset. Our resulting estimate of the radial expansion rate is the slope of this regression line.

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Air Trapping: A Cause of Heterogeneous Attenuation

Air Trapping: A Cause of Heterogeneous Attenuation

To assess the features of presentation of air trapping, all variables (age, sex, indices of pulmonary function test results, air trapping score, HU value, and rate of change in lung volume) were compared in differed cohorts. One was divided by diagnosis, and the other was divided by air trapping findings. Differences in diagnoses were ac- cepted to ascertain the feature of diagnosis that may overlap the results for affecting factors of air trapping. In the diagnosis cohort, diagnoses with less than five pa- tients were excluded because they were not suitable for statistical analysis. The air trapping cohort was divided according to air trapping score, wherein “absence” in- cluded the score 0 and “presence” included scores 1 to 3.

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Influence of forest fragmentation on the distribution of small terrestrial mammals in fir beech commercial forest

Influence of forest fragmentation on the distribution of small terrestrial mammals in fir beech commercial forest

On the contrary, Lešo and Bútora (2010) found out different distribution of AF and CG in fragmented fir-beech forests of different age. AF significantly preferred open young forest stands occurring within the clearing after wind-break. Increasing density of mature trees negatively in- fluenced its abundance. CG significantly pre- ferred microhabitats with mature trees and it was a dominant species in mature stand. The low seed supply in mature fir-beech forest during periods between seed years of beech may be a reason for different microhabitat preferences of two domi- nant rodent species. AF might have preferred the clearing due to the higher food supply provided by various gramineous plants, and as a stronger com- petitor, push out CG to the temporarily subopti- mal habitats. Suchomel et al. (2012) considered beech plantations with high abundance of AF as a Table 3. Mann-Whitney U test of the mean trapping ef-

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