Asymmetric Defect Research Articles

Photochemical transformation of topological defects formed around colloidal droplets dispersed in azobenzene-containing liquid crystals

We investigated photochemical transformation of asymmetric topological defects formed around water droplets dispersed in the azobenzene-containing liquid crystals. It was found that initial structures and the photo-induced phenomena of the defects were clearly affected by chemical structures of the azobenzene compounds. In quite strong homeotropic anchoring obtained by using the azobenzene compound with a long alky chain, the hedgehog was formed around the droplets at the initial state. When the anchoring strength was decreased by changing the carbon number of the alkyl chain, a novel asymmetric defect which will be an intermediate structure between the hedgehog and the Saturn ring was observed. The ionic groups had an influence on the photochemical transformation of the defects. The azobenzene compound with a smaller ionic group induced only a change in the anchoring strength, and a disappearance of the hedgehog was observed on the irradiation with ultra-violet light. In the case of the azobenzene compound with a larger ionic group, photochemical switching of the anchoring and the transformation into the boojums was achieved. The photo-induced phenomena could be qualitative explained by an effectiveness of the cis– trans photoisomerization depending on molecular areas of the azobenzene compounds determined by the ionic groups.

P325 The morphologic changes of Amplatzer asymmetric ventricular septal defect occluder after transcatheter closure of perimembrane ventricular septal defect

P325 The morphologic changes of Amplatzer asymmetric ventricular septal defect occluder after transcatheter closure of perimembrane ventricular septal defect

Simulations of an Interface Crack Nucleation During Nanoindentaion : Molecular Dynamics and Finite Element Coupling Approach

AbstractWe carried out the nanoindentation simulations for the Ru (superlayer) / Cu (film) / SiO2 (substrate) system using the finite temperature MD-FEM coupling method. The calculations are performed for the different adhesion energies of Cu/SiO2 ranging from 0.2 to 0.6 J/m2. During loading, it was found that the interfacial crack nucleation occurs at three to four times the contact radius, driven by the tensile stress acted on the Cu/SiO2 interface. We also show that the asymmetric defect behavior have a great effect on giving birth to the crack nucleation. The observation of our simulation indicates that the mechanism of the crack nucleation strongly depends on the interfacial bonding energy.

Influence of Surface Defect Geometry on the Localization and Failure of AA6111 Sheet: Necking versus Shear

The influence of surface defect geometry on the localization and failure behaviour of AA6111 sheet has been investigated through experimentation and numerical modelling. A series of uniaxial tensile samples were produced with idealized top and bottom surface defects (i.e. grooves), located either symmetrically or asymmetrically on the opposing surfaces. The symmetric arrangement corresponds to the “groove-like” initial imperfection of the classical Marciniak- Kuczyński (M-K) model. Experimental results indicate that both the symmetry of the defects and their wavelength have a profound effect on the resulting mode of localization and failure as well as on the limit strains. Specifically, symmetric surface defects are seen to induce localization and failure through simple necking, whereas asymmetric defects tend to promote macroscopic, throughthickness shearing. Furthermore, asymmetric surface defect geometries are found to produce lower limit strains in the AA6111 sheet under study for defect wavelengths below about 1.5 mm, while the reverse is true when defect wavelengths are above 1.5 mm. Finite element method (FEM) modelling simulations are also presented, demonstrating that the experimentally-observed trends in localization and failure behaviour can be replicated using a mixed isotropic-kinematic hardening implementation of the Gurson-Tvergaard-Needleman (GTN) material model.

Transcatheter closure of perimembranous ventricular septal defects using amplatzer asymmetric ventricular septal defect occluder: Preliminary experience with 18‐month follow up

This study reports our experience in the nonsurgical closure of perimembranous ventricular septal defects in children and adolescents with the Amplatzer asymmetric ventricular septal defect occluder and the outcome of an 18-month follow up. Twenty patients (median age:10 years; median weight:32 kg) with perimembranous ventricular septal defect were selected for transcatheter closure with the Amplatzer device. The prosthesis diameter chosen was 1-2 mm larger than the largest measured diameter of the defect on transesophageal echo (TEE). All patients were put on oral aspirin (5 mg/kg/day in children and 150 mg/day in adults) five days prior to and for six months after closure. Follow-up evaluation at 48 hr and 1, 6, 12 and 18 months included clinical examination, electrocardiogram, and a transthoracic echocardiogram. The mean defect diameter on color flow mapping on TEE was 7.1 +/- 2.3 mm. The device diameter ranged from 6-14 mm (median = 8 mm). One patient developed an anaphylactic reaction to contrast. The procedure was successful in 17 out of 19 patients where it was attempted (89.4%). In two patients with associated significant aortic valve prolapse and mild aortic regurgitation the device could not be successfully deployed. A trivial residual shunt observed during postdeployment left ventricular angiogram in 7 of 17 patients (41.2%) completely disappeared at one month follow-up. Three patients had right bundle branch block (2 complete and 1 incomplete) whereas one developed junctional escape rhythm with a right bundle branch block morphology. One patient had clinically silent thromboembolism to the left vertebral artery and another patient had hemolysis which resolved spontaneously within 48 hr. Follow-up at 13.5 +/- 5.3 months (range 1-18 months) revealed no residual shunt. The left ventricular internal dimension in diastole decreased significantly from 45 +/- 6 mm to 40 +/- 6 mm (P < 0.01) at the time of the last follow up. The baseline tricuspid regurgitation (n = 4) and aortic regurgitation (n = 3) remained unchanged during the follow up period. None of the patients developed left ventricular outflow tract obstruction or new aortic or tricuspid regurgitation. There were no other device related complications such as device migration, systemic thromboembolism, infective endocarditis, pericardial effusion or delayed conduction disturbances. In carefully selected children and young adults, the Amplatzer asymmetric ventricular septal defect occluder is a promising device for transcatheter closure of perimembranous ventricular septal defect with encouraging results on short term follow up.

Correlation of Asymmetric Glaucomatous Visual Field Damage and Water-Drinking Test Response

To determine whether there is a correlation between asymmetric glaucomatous visual field (VF) damage and water-drinking test (WDT) response. A retrospective analysis was conducted of VF and WDT data from 101 patients with glaucoma in clinical therapy, who were receiving treatment with the same topical medication in both eyes, and asymmetric VF defect. Eyes were classified according to mean deviation (MD) into "better" and contralateral "worse" eyes. Maximum mean difference in basal IOP was 2 mm Hg between both eyes. The peak IOP and fluctuation obtained with the WDT were compared between both groups. For the statistical analysis, the Tukey post hoc multiple comparison test and paired t-test were used. Better and contralateral worse eyes presented mean MDs of -4.6 +/- 5.3 and -9.0 +/- 7.4 dB, respectively (P < 0.001). Mean basal IOPs were 13.9 +/- 3.3 and 13.9 +/- 3.1 mm Hg, respectively (P = 0.67). Mean maximum IOPs after water ingestion were 16.5 +/- 3.8 mm Hg in the group with less severe VF defect and 17.2 +/- 4.1 mm Hg in the contralateral group with worse visual fields (P < 0.001). Mean fluctuation (maximum IOP - minimum IOP after water ingestion) was 3.6 +/- 1.8 and 4.4 +/- 2.2 mm Hg (P < 0.001), respectively. Eyes with worse MDs presented higher IOP peaks and fluctuation after water ingestion. This study demonstrates a lower capacity of eyes with worse glaucomatous lesion to respond to a stimulus that leads to a transitory elevation of IOP.

Direct observation of Gouy phase shift in a propagating optical vortex

Direct observation of Gouy phase shift on an optical vortex was presented through investigating the intensity profiles of a modified LG_p;m beam with an asymmetric defect, around at the focal point. It was quantitatively found that the rotation profile of a modified LG_p;m beam manifests the Gouy phase effect where the rotation direction depends on only the sign of topological charge m. This profile measurement method by introducing an asymmetric defect is a simple and useful technique for obtaining the information of the Gouy phase shift, without need of a conventional interference method. In addition, the 3-dimernsional trajectory of the defect was found to describe a uniform straight line.

Effects of transcatheter closure of perimembranous ventricular septal defects: intermediate and long-term follow-up of 68 cases

To evaluate the curative effects of transcatheter closure on perimembranous ventricular septal defects (PMVSDs) using unbalanced Amplatzer asymmetric ventricular septal defect occluder (AAVSDO). The data of 68 patients of PMVSDs with a diameter of 6.7 mm (3 to 12 mm) and the diameter of ventricular septal rim below the aortic valve of 2.7 +/- 1.1 mm (1-5 mm), 27 males and 41 females, aged 15.6 +/- 11.5 (1.5-44), weighing 42.8 +/- 15.2 kg (10-72 kg), treated with AAVSDO, the diameter of which was 1-2 mm larger than the largest diameter of the defects determined by angled left ventriculography, from September 2002 to January 2005 were prospectively analyzed. The patients were followed up for 221 +/- 130 days (90 to 750 days). Seventy-one procedures were performed. The device was implanted successfully in 65 of the 68 patients (95.6%). The selected device diameter was 8.4 mm (4 to 14 mm). Device was lost in one patient during the procedure, which was successfully managed by recapturing the device with a snare device and redeploying it. During the procedure, transient complete left bundle branch block and right bundle branch block occurred in 6 and 5 patients respectively. On follow-up evaluation, transient junctional rhythm occurred in one patient, and accelerated ventricular rhythm in 1. After deployment of the device, the immediate complete closure rate was 43% (28/68), increased to 81.5% (53/68) on the day next to the procedure, and reached 100% 6 months after. One patient adopted surgical reparation because hemolysis occurred after the device implanted. The hospitalization time was 4.5 +/- 3.6 days (2-8 days). The X-ray exposure time was 14.8 +/- 10.7 min (6-48 min). The procedure time 72.6 +/- 38.7 min (35-186 min). One patient was diagnosed as with deep vein thrombosis because of right leg swelling at the seventh day after the procedure. The symptoms disappeared after anticoagulation treatment with low molecule weight heparin. During the scheduled long-term follow-up all patients were doing well. No episode of endocarditis, procedure-related death, or wire disruption was recorded. The initial and long-term follow-up results of transcatheter closure of PMVSDs are promising with high success and occlusion rates. Transcatheter closure of PMVSDs using AAVSDO appears to be the first line choice for suitable patients with such defects.

Bistability and gap soliton in one-dimensional photonic crystal containing single-negative materials

We study the nonlinear responses of the defect structure made up of the one-dimensional photonic crystal containing alternate single-negative layers with a nonlinear defect layer centered in the structure. The output intensity curves and transmission spectra with different nonlinear coefficients α and different incident angles are observed. To one's interest, it is found that the position of the transmission peak is almost invariant with the incident angle changing from 0° to 30°. The spatial distribution and the relative phase shift of the electric field in the defect structure are also studied. Solitons are founded in the electric field distribution. With different incident angles, the locations of the peaks and the maxima and minima of the solitons do not move. The only difference introduced from different incident angles is the amplitudes of the electric field at the same position. Similarly, we find the curves of the phase shift of the electric fields with different incident angles have the same shape, only the values at the same position are different from each other. At last, we also investigate the asymmetric nonlinear defect structure formed by changing the position of the defect layer. The similar insensitive characteristic to the incident angle in the transmission property, electric field distribution and relative phase shift are found.

Coupling-reducingk-points for supercell models of defects in three-dimensional photonic crystals

The optimum choice of k-point for supercell calculations of defect states in a three-dimensional photonic crystal is investigated for the case of a supercell with a simple cubic (SC) structure. By using the k-point (1/4,1/4,1/4) it is possible to eliminate the symmetric part of the repeated-image couplings for the first three neighbour shells in the SC lattice. This result is shown to hold also for the case of non-equivalent axes (e.g.?a distorted lattice, or an asymmetric defect structure). A specific example of a donor defect in a woodpile structure demonstrates that use of this k-point can lead to order-of-magnitude gains in computational efficiency.

Transcatheter closure of perimembranous ventricular septal defects with the amplatzer asymmetric ventricular septal defect occluder: Preliminary experience in children

Transcatheter closure of perimembranous ventricular septal defects with the amplatzer asymmetric ventricular septal defect occluder: Preliminary experience in children

High Frequency Electron Spin Resonance Study of Hydrogenated Microcrystalline Silicon

AbstractDangling bond defects (DB) in hydrogenated microcrystalline silicon (μc-Si:H) have been studied by X-band (9 GHz) Q-band (33 GHz) and W-band (90 GHz) electron spin resonance (ESR) spectroscopy. In X-band ESR spectra, all the samples showed asymmetric dangling bond defect signal at g = 2.005 – 2.006. The DB signal shape shows little dependence on substrate temperature in the X-band electron spin resonance (ESR) spectra. In the Q-band and W-band ESR spectra, existence of two centers in DB signals is clearly indicated by the shape of the spectra. The Q-band ESR spectra shape reviles that the peak of one center is at g = 2.0055andthe other is around at g = 2.0060. In addition, the DB signal showed dependence on substrate temperature. The dependence of the DB signals can be explained by difference of intensity ratio of the peaks by these two centers. The signal at g = 2.0060 is consistent with the asymmetric ESR signal observed in the microcrystalline silicon embedded in SiO2. W-band ESR measurement indicates that the signal observed at g = 2.0060 is due to single inhomogeneous species and does not consist of plural species.

Self-forces on electric and magnetic linear sources in the presence of a torsional defect

In this work we calculate the magnetic and electric self-forces on a long straight wire, induced by an axially asymmetric topological line defect carrying singular torsion, the edge dislocation. We consider both the case of a constant current along the wire and the case of a static, uniformly charged, wire. We also show how these self-forces are related by a Lorentz transformation.

Vacancy formation in (Pb,La)(Zr,Ti)O3 capacitors with oxygen deficiency and the effect on voltage offset

Vacancy-related defect profiles have been measured for La0.5Sr0.5CoO3/(Pb0.9La0.1)(Zr0.2Ti0.8)O3/La0.5Sr0.5CoO3 ferroelectric capacitors using a variable-energy positron beam. By varying the layer thickness and the postgrowth processing in a reducing ambient, a capacitor showing oxygen deficiency dominantly in the top electrode and one with deficiency in both electrodes were produced. The capacitor with an asymmetric defect profile showed a voltage offset polarization–voltage hysteresis loop, that with a symmetric distribution of vacancy-related defects showed no offset. These results are discussed in the context of current models for imprint.

Permeative flow and the compatability of smectic C zig-zag defects with compressive and dilative regions

Mukai and Nakagawa have predicted that hairpin and lightning defects correspond to compressive and dilative regions in the smetic C layer structure. Walton et al. have previously used the Helfrich-Hurault effect and an induced SmA-SmC phase transition to reconfirm the existence of such dilated and compressed regions under situations of permeative flow. In the present work, flow-induced compression and dilation is used to confirm the first prediction. Situations of asymmetric zig-zag defect generation are observed and some possible explanations offered. Situations in which flow is induced by mechanical cell deformation, and where electric field-induced director switching leads to material pumping are also discussed.

Stability of the mobility-lifetime product of holes in undoped a-Si:H under illumination

Stability of the mobility-lifetime product of holes has been studied by measuring the ambipolar diffusion length ( L amb) in undoped a-Si:H films. After 80 hours of AM1 light soaking L amb decreases from 217 to 152 nm, whereas photoconductivity excited by a HeNe laser with an intensity of 1.7 mW/cm 2 decreases from 7.12 × 10 −6 to 2 × 10 −7 Ω −1 cm −1. Furthermore, L amb does not decrease in the first 10 minutes. These results are attributed to the asymmetric defect density ( N d) dependence of the mobility-lifetime products of electrons and holes due to the inherent asymmetry between the density-of-states distributions of the conduction and valence band tail states. Numerical simulation shows that the recombination path via the band tail states dominates over that via the defects when N d < 3 × 10 16 cm −3.

Scattering of electrons in copper by a Frenkel pair defect

The Korringa-Kohn-Rostoker (KKR) Green function extended-defect formalism. used to describe the scattering of Bloch electrons in a dilute alloy, is generalised to include an asymmetric defect centered on a lattice site. The revised theory is then used to investigate conduction electron scattering from Frenkel pairs in Cu. Such defects consist of two self-interstitial atoms centered on a vacant lattice site forming a dumb-bell oriented along the (100) axis. The generalized formalism allows one to calculate the cluster t matrix T for the Frenkel pair cluster including the surrounding displaced nearest neighbors. It was found that the interstitials at the vacant lattice site could still be treated within the muffin-tin potential as a central scatterer characterised by a t matrix which is nondiagonal in the angular momentum. Electron scattering rates and Dingle temperatures are calculated and discussed in view of preliminary experimental results.

Influence of Si/Al ratio on the properties of faujasites enriched in silicon

Zeolite Y with different Si/Al ratios prepared by secondary synthesis with (NH 4 ) 2 SiF 6 have been studied by XRD, d.t.a., i.r., and t.p.d. methods. In comparison with zeolite Y dealuminated by EDTA extraction and hydrothermal treatment, these zeolites have higher crystallinity and thermal stability. The relationships among crystal collapse temperature, unit cell size, i.r. asymmetric stretch frequency, defect factor, and Al/(Al + Si) ratio of these zeolites have been described. T.p.d. measurements showed that the number of acid sites on the zeolites equals approximately the number of tetrahedral aluminum sites in the framework and their acid strength is stronger than that of conventional zeolite Y. I.r. pyridine adsorption studies indicated that the acid sites are mainly Brönsted-type acid sites.

The potential role of redox cycling as a mechanism for chemical teratogenesis.

A survey of the literature indicates that several chemicals whose reduced metabolites are capable of undergoing redox cycling in biological systems also possess significant teratogenic properties when tested in vivo. We have initiated investigations to determine whether the embryotoxic effects of such chemicals could result from their redox cycling properties and whether redox cycling could be an important mechanism in chemical teratogenesis. In order to obviate the potentially confounding influences of maternal factors, our initial studies have been performed with a whole embryo culture system with redox cycling agents added directly to the culture medium. Several representative redox cycling agents including doxorubicin, paraquat, a series of nitroheterocycles, nitrosofluorene, and diethylstilbestrol (converted metabolically to redox cycling quinone/semiquinone radicals) have been investigated thus far. The nitroheterocycles which bear nitro groups with comparatively high redox potentials produced a striking, asymmetric defect involving primarily the right half of the prosencephalic and mesencephalic regions. The effect was exacerbated under conditions of low O2 tension. Accumulated data to date strongly suggest that reduction of the nitro group is an essential feature in the embryotoxic mechanism. Quinones (doxorubicin, paraquat) and compounds metabolically converted to quinones (diethylstilbestrol) appeared to produce embryotoxic effects via mechanisms not associated with redox cycling. Nitrosofluorene embryotoxicity was markedly exacerbated by changes in both intra- and extracellular glutathione levels, but definitive dependence on a radical-mediated effect or redox cycling was not demonstrated.

The Potential Role of Redox Cycling as a Mechanism for Chemical Teratogenesis

A survey of the literature indicates that several chemicals whose reduced metabolites are capable of undergoing redox cycling in biological systems also possess significant teratogenic properties when tested in vivo. We have initiated investigations to determine whether the embryotoxic effects of such chemicals could result from their redox cycling properties and whether redox cycling could be an important mechanism in chemical teratogenesis. In order to obviate the potentially confounding influences of maternal factors, our initial studies have been performed with a whole embryo culture system with redox cycling agents added directly to the culture medium. Several representative redox cycling agents including doxorubicin, paraquat, a series of nitroheterocycles, nitrosofluorene, and diethylstilbestrol (converted metabolically to redox cycling quinone/semiquinone radicals) have been investigated thus far. The nitroheterocycles which bear nitro groups with comparatively high redox potentials produced a striking, asymmetric defect involving primarily the right half of the prosencephalic and mesencephalic regions. The effect was exacerbated under conditions of low O2 tension. Accumulated data to date strongly suggest that reduction of the nitro group is an essential feature in the embryotoxic mechanism. Quinones (doxorubicin, paraquat) and compounds metabolically converted to quinones (diethylstilbestrol) appeared to produce embryotoxic effects via mechanisms not associated with redox cycling. Nitrosofluorene embryotoxicity was markedly exacerbated by changes in both intra- and extracellular glutathione levels, but definitive dependence on a radical-mediated effect or redox cycling was not demonstrated.