ABSTRACT
BACKGROUND: Ileoanal pouch is a demanding procedure with many potential technical complications including bladder or ureteral injury, while inflammation or stricture of the anastomosis or anal transition zone may lead to the formation of strictures and fistulae, including to the adjacent urethra. Pouch urinary tract fistulae are rare. We aimed to describe the presentation, diagnostic workup, and management of patients with pouch urinary at our center. METHODS: Our prospectively maintained pouch registry was queried using diagnostic codes and natural language processing free-text searches to identify ileoanal pouch patients diagnosed with any pouch-urinary tract fistula from 1997 to 2022. Descriptive statistics and pouch survival using Kaplan-Meier curves are presented. Numbers represent frequency (proportion) or median (range). RESULTS: Over 25 years, urinary fistulae were observed 27 pouch patients; of these, 16 of the index pouches were performed at our institution [rate 0.3% (16/5236)]. Overall median age was 42 (27-62) years, and 92.3% of the patients were male. Fistula locations included pouch-urethra in 13 patients (48.1%), pouch-bladder in 12 patients (44.4%), and anal-urethra in 2 (7.4%). The median time from pouch to fistula was 7.0 (0.3-38) years. Pouch excision and end ileostomy were performed in 12 patients (bladder fistula, n = 3; urethral fistula, n = 9), while redo ileal pouch-anal anastomosis (IPAA) was performed in 5 patients (bladder fistula, n = 3; urethral fistula, n = 2). The 5-year overall pouch survival after fistula to the bladder was 58.3% vs. 33.3% with urethral fistulae (p = 0.25). CONCLUSION: Pouch-urinary tract fistulae are a rare, morbid, and difficult to treat complication of ileoanal pouch that requires a multidisciplinary, often staged, surgical approach. In the long term, pouches with bladder fistulae were more likely to be salvaged than pouches with urethral fistulae.
Subject(s)
Colonic Pouches , Postoperative Complications , Urinary Fistula , Humans , Male , Adult , Female , Middle Aged , Colonic Pouches/adverse effects , Urinary Fistula/etiology , Urinary Fistula/surgery , Postoperative Complications/etiology , Time Factors , Registries , Prospective Studies , Proctocolectomy, Restorative/adverse effects , Urinary Bladder Fistula/etiology , Urinary Bladder Fistula/surgery , Kaplan-Meier EstimateABSTRACT
A granulation method using a planetary centrifugal mixer, called planetary centrifugal granulation, has been developed for small-scale production, such as extemporaneous preparation in pharmacies. Although the impact of its operational parameters on granulation is described, the scale effect has not been investigated. Therefore, we aimed to reveal the effects of vessel size and vessel filling rate on granule properties. In this study, ibuprofen 20% granules consisting of lactose, cornstarch, sodium carmellose, and talc were used as model granules. Granulation was performed using geometrically similar containers, 6-58 mL, with a filling rate of 20-70%. After granulation, we monitored the granule properties, for example, median diameter (d50), span of particle size distribution, and sphericity. At filling rates of 40% and 50% in the 58-mL vessel, the granules grew larger in diameter, and at a rate of 30%, the granules showed a higher sphericity. When the filling rate was 30%, d50 became larger and the span decreased as the vessel size increased. The yields of the granules were higher than 95% when using the 12-58 mL vessel. Lastly, the drug content uniformity and drug dissolution behavior of the granules produced in different vessel size were examined. The granules showed similar drug consistencies and drug dissolution profiles. In conclusion, the quality of the products was not affected by changes in vessel size. Thus, pharmacists could prepare and compound the granule formulations with high yield and appropriate quality using an adequate vessel in the same manner.
Subject(s)
Ibuprofen , Lactose , Drug Compounding/methods , Particle Size , Powders , StarchABSTRACT
BACKGROUND: The aim of this study was to investigate whether the lamellar and lateral structure of intercellular lipid of stratum corneum (SC) can be evaluated from millimeter-sized SC (MSC) by X-ray diffraction. MATERIALS AND METHODS: A 12 mm × 12 mm SC sheet from hairless mouse was divided into 16 pieces measuring 3 mm × 3 mm square. From another sheet, 4 pieces of ultramillimeter-sized SC (USC:1.5 mm × 1.5 mm square) were prepared. Small and wide-angle X-ray diffraction (SAXD and WAXD) measurements were performed on each piece. For MSC and USC, changes in the lamellar and lateral structure after the application of d-limonene were measured. RESULTS: The intensity of SAXD peaks due to the lamellar phase of long periodicity phase (LPP) and WAXD peaks due to the lateral hydrocarbon chain-packing structures varied in MSC and USC pieces, although over the 12 mm × 12 mm SC sheet. These results indicated that the intercellular lipid components and their proportion appeared nearly uniform. Application of d-limonene on MSC and USC piece with strong peaks in SAXD and the WAXD resulted in the disappearance of peaks due to the lamellar phase of LPP and decrease in peak intensity for the lateral hydrocarbon chain-packing structures. These changes are consistent with normal-sized sample results. CONCLUSION: We found that the selection of a sample piece with strong diffraction peaks due to the lamellar and lateral structure enabled evaluation of the SC structure in small-sized samples by X-ray diffraction.
Subject(s)
Epidermis/chemistry , Lipids/analysis , X-Ray Diffraction , Animals , Epidermis/ultrastructure , Mice , Mice, Hairless , SynchrotronsABSTRACT
We examined the stability and release profiles of dexamethasone dipropionate (DDP) from admixtures by using an innovator ointment (Methaderm [IM]), two generic ointments (Promethasone [GP] and Mainvate [GM]), and a heparinoid ointment. The admixtures were prepared using a spatula and an ointment slab and were stored at room temperature. Microscopic and Fourier transform-Raman spectrometric analyses showed that crystallization of DDP in admixtures of IM after 1 week of storage occured. And DDP crystals in all admixtures of GP and GM were observed. DDP was not decomposed in the admixtures after storage. Cumulative DDP permeation across a silicone membrane in a 1-week storage sample of the IM system decreased with DDP crystallization and reached a plateau after 2 weeks. In the GP and GM systems, DDP permeation decreased after 1 week of storage and increased again after 2 and 4 weeks. Each admixture was separated into 3 phases (liquid, lower, and upper solid phases) by ultracentrifugation to determine the apparent solubility of DDP. The DDP contents in the upper solid phase of the IM admixtures at 1, 2, and 4 weeks were lower than that in the 0-week sample. No significant differences were observed in the DDP content between the liquid phases throughout the storage period. Therefore, the amount of DDP dissolved in the upper solid phase may influence DDP release from the IM admixtures. The GP and GM systems showed no significant differences in the apparent DDP solubility. These results indicate that the dispersion state of DDP in the tested admixtures may be altered with storage.
Subject(s)
Anti-Inflammatory Agents/chemistry , Dexamethasone/analogs & derivatives , Heparinoids/administration & dosage , Steroids/administration & dosage , Anti-Inflammatory Agents/administration & dosage , Chemistry, Pharmaceutical , Chromatography, High Pressure Liquid , Crystallization , Dexamethasone/administration & dosage , Dexamethasone/chemistry , Drug Stability , Drug Storage , Emulsions , Heparinoids/chemistry , Hydrogen-Ion Concentration , Indicators and Reagents , Membranes, Artificial , Ointments , Permeability , Spectrum Analysis, Raman , Steroids/chemistry , UltracentrifugationABSTRACT
The ultrasound software package Enhanced Needle Visualization (ENV) has been reported to provide improved ultrasound imaging of needles even at steep insertion angles. ENV has three settings: shallow, medium and steep. However, the angles are unknown. We examined the advantages and indications of ENV in an in vitro study. A 22-gauge needle was inserted into pork meat using the in-plane technique. The needle was positioned at zero, 30, 45 and 60 degree angles, and 1, 2, 3 and 4 cm in-depth from the probe. The ultrasound visibility in each ENV setting was objectively evaluated and graded as 'not visible', 'poor', 'visible', 'good' and 'excellent' in ascending order. At zero degrees we found no advantage of ENV. At 30 degrees, the needle exhibited better visibility with 'good' or above grade in the shallow setting at all depths and in the medium setting at depths of 1, 2 and 3 cm than in the off position. At 45 degrees, needle visibility significantly increased from 'not visible' in the off position to 'visible' or above in the steep settings at depths of 1, 2 and 3 cm. At 60 degrees the objective visibility was 'not visible' in the off position and significantly increased to 'poor' in the steep setting. We recommend selecting the shallow setting for needles with an insertion angle of 30 degrees and the steep setting for 45 degrees within the advantageous area. This technique may allow safer ultrasound procedures for various unprecedented approaches.
Subject(s)
Anesthesia, Conduction , Ultrasonography, Interventional/methods , Humans , Needles , SoftwareABSTRACT
We demonstrate high-finesse plasmonic metamaterial with strong resonant response in the near-IR spectral range fabricated using a thin low-loss film of gold monocrystal. The monocrystal was grown using specially formulated simplified crystal growth procedure based on epitaxial deposition, which makes it readily accessible to both plasmonics and metamaterials communities.
Subject(s)
Gold/chemistry , Membranes, Artificial , Nanostructures/chemistry , Nanostructures/ultrastructure , Surface Plasmon Resonance/methods , Crystallization/methods , Infrared Rays , Manufactured Materials , Materials TestingABSTRACT
This work examines the recent developments in non-traditional catalyst-assisted chemical vapour deposition of carbon nanotubes (CNTs) with a view to determining the essential role of the catalyst in nanotube growth. A brief overview of the techniques reliant on the structural reorganization of carbon to form CNTs is provided. Additionally, CNT synthesis methods based upon ceramic, noble metal, and semiconducting nanoparticle catalysts are presented. Experimental evidence is provided for CNT growth using noble metal and semiconducting nanoparticle catalysts. A model for CNT growth consistent with the experimental results is proposed, in which the structural reorganization of carbon to form CNTs is paramount.
ABSTRACT
We report that hybridizing semiconductor quantum dots with plasmonic metamaterial leads to a multifold intensity increase and narrowing of their photoluminescence spectrum. The luminescence enhancement is a clear manifestation of the cavity quantum electrodynamics Purcell effect and can be controlled by the metamaterial's design. This observation is an essential step towards understanding loss compensation in plasmonic metamaterials with gain media and for developing metamaterial-enhanced gain media.
ABSTRACT
We previously we attempted to make a three-dimensional human skin model consisting of three different cells, dendritic cells, keratinocytes and fibroblasts (KDF-Skin) to evaluate immunoreactions in human skin; however, this model had various problems; for example (1) the incubation period for the construction of this model is long (about three weeks); (2) to construct the collagen gel, high amounts of fibroblasts are needed; and (3) the horny layer of keratinocytes in this skin model is thinner than that of keratinocytes in real human skin. In order to overcome these problems, a new three-dimensional human skin model utilizing a handy scaffold of collagen vitrigel membrane (VG-KDF-Skin) was constructed. As a result, after 14 days incubation, the epidermis layer of normal human keratinocytes was thicker than the keratinocyte layer of KDF-Skin. The incubation period for VG-KDF-Skin construction was 7 days shorter than that of KDF-Skin, and the number of fibroblasts needed to seed VG-KDF-Skin was four times fewer than that of KDF-Skin. After the application of sensitizers such as DNCB, VG-KDF-Skin induced the expression of CD86 and cytokine release. These results suggest that the new three-dimensional human skin model consisting of dendritic cells, keratinocytes, fibroblasts and collagen vitrigel membrane was more useful for alternative animal testing than the KDF-Skin model.
Subject(s)
Dendritic Cells/metabolism , Fibroblasts/metabolism , Keratinocytes/metabolism , Membranes, Artificial , Skin, Artificial , Tissue Scaffolds , Animal Testing Alternatives , B7-2 Antigen/metabolism , Cell Culture Techniques/methods , Cells, Cultured , Coculture Techniques/methods , Collagen Type I/chemistry , Cytokines/metabolism , Dendritic Cells/cytology , Dendritic Cells/drug effects , Fibroblasts/cytology , Fibroblasts/drug effects , Gels , Humans , Irritants/toxicity , Keratinocytes/cytology , Keratinocytes/drug effects , Models, Biological , Time FactorsABSTRACT
We report room-temperature broadband laser emission in the near-ultraviolet to the blue-green spectral range using color centers in MgO microcrystals. The lasing MgO microcrystals are obtained through a solid phase reaction between SiO and Mg at 450 degrees C in an argon atmosphere and are mostly composed of an accumulation of microcubes enclosed by [100] facets. The laser action was observed in the wavelength region from 350 to 600 nm without using cavity mirrors. In the present MgO microcrystals, some of the color centers will be stabilized at the interfaces and/or boundaries of the microcrystalline domains, probably explaining the stable laser action even at room temperature.
ABSTRACT
Solid dispersions of spironolactone (SPI) with porous silica (Sylysia 730 and Sylysia 350) were prepared by the solvent method. The physicochemical properties of the prepared solid dispersions were evaluated by powder X-ray diffractometry (PXRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and atomic force microscopy (AFM). In the SEM study, no differences in the surface condition between Sylysia 350 and the solid dispersion of a Sylysia 350:SPI system in a weight ratio of 1:1 were observed. However, AFM phase images showed that the surface of the solid dispersion of the Sylysia 350:SPI system (weight ratio of 1:1) was rather smooth due to the adsorption of SPI as compared with that of a Sylysia 350 intact. The results of PXRD and DSC data in the solid dispersion of the Sylysia 350:SPI system (weight ratio of 1:1) indicated that the molecular state of the adsorbed SPI changed from crystalline to amorphous. Although the decrease in the SPI concentration increased with the amorphous fraction in the solid dispersion, the diffraction peaks due to SPI crystals still remained in the solid dispersion of a Sylysia 730:SPI system (weight ratio of 1:1), indicating that the mean pore diameter and specific surface area of an additive are some of the important factors for the amorphization of SPI crystals. The dissolution property of the SPI from the solid dispersions was remarkably improved in comparison with that of SPI crystals. The dissolution rate of the SPI from the solid dispersions with Sylysia 350 was faster than that of the SPI from the solid dispersions with Sylysia 730. The difference in the dissolution properties of SPI from both the solid dispersions was attributed to the difference in the molecular state of the SPI in both the solid dispersions. In the stability test, the amorphous state of the SPI in the solid dispersion of the Sylysia 350:SPI system (weight ratio of 1:1) was maintained for 2 weeks at 25 degrees C and 0% RH, while the amorphous SPI without Sylysia 350 crystallized under the same conditions.
Subject(s)
Mineralocorticoid Receptor Antagonists/chemistry , Spironolactone/chemistry , Calorimetry, Differential Scanning , Crystallization , Drug Compounding , Excipients , Microscopy, Atomic Force , Microscopy, Electron, Scanning , Mineralocorticoid Receptor Antagonists/administration & dosage , Silicon Dioxide , Solvents , Spironolactone/administration & dosage , X-Ray DiffractionABSTRACT
BACKGROUND: Heat shock protein 70 (HSP70) is induced by a wide variety of stresses in addition to hyperthermia. Recent studies have clarified that mechanical stretching and pressure overload can induce HSP70 in some tissues and cells. However, it remains unclear whether HSP70 is induced in stretch-subjected lungs, such as those under mechanical ventilation. This study was designed to investigate the effects of high peak airway pressure (PAP) ventilation on HSP70 expression in intact rat lungs. METHODS: Male Sprague-Dawley rats were randomly allocated to one of three groups: non-ventilated (anesthesia alone) control group; PAP 15 cm H(2)O group (P15); and PAP 30 cm H(2)O group (P30). The rats in the PAP groups were subjected to pressure-controlled assisted ventilation at the appropriate PAP for 30 min. Rats were killed at 12, 24 and 48 h after ventilation or anesthesia alone, and the lungs were removed. The lung tissues were processed for immunohistochemical and Western blotting analyses of HSP70. RESULTS: Following 30 min of pressure-controlled assisted ventilation, HSP70 expression in the P30 group was significantly up-regulated in bronchiolar cells and subepithelial tissues at 12 h, and this up-regulation continued throughout the observation period. In contrast, there were no significant differences between the control and P15 groups, although the expression of HSP70 was higher in the P15 group than in the control group at all time points. CONCLUSIONS: HSP70 was induced by high PAP ventilation, but its specific role and induction mechanism remain unclear. Therefore, further investigations should be encouraged.
Subject(s)
HSP70 Heat-Shock Proteins/metabolism , Lung/metabolism , Respiration, Artificial , Airway Resistance , Animals , Blotting, Western , Immunohistochemistry , Male , Rats , Rats, Sprague-DawleyABSTRACT
To evaluate the main intake source of arsenic by the villagers from arsenic-affected families in Jalangi and Domkol blocks in Mushidabad district, West Bengal-India, we determined the concentrations of arsenic in tube-well water and in food composites, mainly including vegetables and cereals collected from the surveyed families which were cultivated in that region. The daily dietary intakes of arsenic by the villagers were estimated and the excretions of arsenic through urine and hair were determined. The arsenic concentrations in hair and urine of the studied population living in mild (2.78 microg/L), moderate (30.7 microg/L) and high (118 microg/L) arsenic-affected families were 133, 1,391 and 4,713 microg/kg and 43.1, 244 and 336 microg/L, respectively. The linear regressions show good correlations between arsenic concentrations in water vs hair (r(2)=0.928, p<0.001) and water vs urine (r(2)=0.464, p<0.01). Approximately 29.4%, 58.1% and 62.1% of adult population from mild, moderate and high arsenic-affected families were suffering from arsenical skin manifestations. The mean arsenic concentrations of food composites (vegetables and cereals) in high arsenic-affected families are not significantly different from mild arsenic-affected families. The daily dietary intakes of arsenic from water and food composites of the studied population, living in high, moderate and mild arsenic-affected families were 568, 228 and 137 microg, respectively. The linear regressions show good correlations between arsenic concentrations in hair vs daily dietary intake (r(2)=0.452, p<0.001) and urine vs daily dietary intake (r(2)=0.134, p<0.001). The water for drinking contributed 6.07%, 26.7% and 58.1% of total arsenic in our study from mild, moderate and high arsenic-affected families. The result suggested that the contaminated water from high arsenic-affected families should be the main source for intake of arsenic. On contrary, the contribution of arsenic-contaminated food composites from mild and moderate arsenic-affected families might be the main source for intake of arsenic. The Food and Agriculture Organization/World Health Organization (FAO/WHO) provisional tolerable weekly intake (PTWI) values of arsenic in our study were 3.32, 5.75 and 12.9 microg/kg body weight/day from mild, moderate and high arsenic-affected families, respectively, which is higher than the recommended PTWI value of arsenic (2.1 microg/kg body weight/day).
Subject(s)
Arsenic/toxicity , Food Contamination/statistics & numerical data , Hair/chemistry , Water Pollutants, Chemical/toxicity , Adult , Arsenic/urine , Child , Environmental Exposure , Environmental Monitoring , Epidemiological Monitoring , Female , Food Analysis , Humans , India/epidemiology , Male , Water Pollutants, Chemical/urine , Water SupplyABSTRACT
Ishigami et al. (Ishigami et al., 1998) reported that squalene monohydroperoxide (SQOOH) induced skin damage in hairless mice. Kohno and Takahashi (Kohno and Takahashi, 1993) reported that SQOOH induced cytotoxicity against Chinese hamster lung fibroblasts. We have already evaluated the efficacy of extracts obtained from Brazilian herbal medicines in protecting the normal human epidermis keratinocytes [NHEK(B)] against the cytotoxicity caused by SQOOH. The EtOAc extract was separated by silica-gel column chromatography into eight fractions. Fractions (Fr) 1,3 and 5 significantly protected rat basophilic leukemia (RBL-2H3) cells from the release of beta-hexosaminidase due to SQOOH. Additionally, Fr5-1 was most effective in a Gunze three-dimensional cultured human skin model (Vitrolife-skin) against the cytotoxicity due to SQOOH and the release of interleukin (IL)-2 and IL-4. The mixture of cinchonains Ia and Ib and the mixture of cinchonains IIa and IIb were isolated from Fr3 and Fr5-1, respectively. The results suggest that the addition of SQOOH caused the reduction in cell viability and the release of beta-hexosaminidase and cytokines as chemical mediators. The extract of Catuaba (Anemopaegma mirandum) prevented these toxic effects with the main active agents suggested to be cinchonains IIa and IIb.
Subject(s)
Antioxidants/pharmacology , Cinchona Alkaloids/pharmacology , Plants, Medicinal , Squalene/analogs & derivatives , Squalene/toxicity , beta-N-Acetylhexosaminidases/antagonists & inhibitors , Animals , Antioxidants/isolation & purification , Cell Line, Tumor , Cell Survival/drug effects , Cinchona Alkaloids/isolation & purification , Humans , Hydro-Lyases , Interleukin-2/biosynthesis , Interleukin-4/biosynthesis , Plant Extracts/chemistry , Rats , Tetrazolium Salts , Thiazoles , Tissue Culture Techniques , beta-N-Acetylhexosaminidases/biosynthesisABSTRACT
Titanium dioxide (TiO(2)) has been reported to produce OH radical under ultraviolet-A (UVA) irradiation and to induce cytotoxicity. Various crystal forms and sizes of TiO(2) with UVA irradiation from OH radical generation was analysed spin trapping-X band (electron-spin resonance (ESR) spectroscopy. The amount of OH radical was determined with ESR signal intensity of the adducts in which OH radical was trapped with the spin-trapping reagent dimethyl pyrroline-N-oxide (DMPO). The formation of OH radicals varied in both crystal size and form of TiO(2). Irradiation of the anatase form of TiO(2) produced large numbers of OH radical in TiO(2) and UVA in a dose-dependent manner, but rutil form (90 nm in size) showed less OH radical generation. The crystal size had large influence on OH radical generation, but the optimum size for the OH radical generation was different between both forms. The UVA absorption spectrum of TiO(2) differed in regard to crystal size and form of TiO(2), but no relation was observed between UVA absorbency and OH radical formation. The cytotoxicity of TiO(2)-UVA irradiation was determined against Chinese hamster ovary (CHO) cells and a significant relationship was obtained between the cytotoxicity and the OH generation. Measurement of the amount of OH radical production by UVA irradiation with ESR is needed to clarify the effect of crystal form or sizes of TiO(2) on OH radical production and cytotoxicity.
Subject(s)
CHO Cells/drug effects , Hydroxyl Radical , Photosensitizing Agents/toxicity , Titanium/toxicity , Animals , CHO Cells/metabolism , CHO Cells/radiation effects , Cell Survival/drug effects , Cell Survival/radiation effects , Cricetinae , Crystallization , Dose-Response Relationship, Drug , Dose-Response Relationship, Radiation , Electron Spin Resonance Spectroscopy , Hydroxyl Radical/metabolism , Photosensitizing Agents/radiation effects , Spin Trapping , Titanium/radiation effects , Ultraviolet RaysABSTRACT
An investigation of total arsenic in food composites, collected from the villagers, was carried out in arsenic-affected areas of the Murshidabad district, West Bengal where the agricultural system is mostly groundwater dependent. The shallow, large-diameter tubewells installed for agricultural irrigation contain an appreciable amount of arsenic (mean 0.085 mg/l, n=6). Even the soil is arsenic-contaminated (mean 11.35 mg/kg, n=36), so some arsenic can be expected in the food chain from crops cultivated in this area. The results revealed that the individual food composite and food groups containing the highest mean arsenic concentrations (microg/kg) are potato skin (292.62 and 104), leaf of vegetables (212.34 and 294.67), arum leaf (331 and 341), papaya (196.50 and 373), rice (226.18 and 245.39), wheat (7 and 362), cumin (47.86 and 209.75), turmeric powder (297.33 and 280.9), cereals and bakery goods (156.37 and 294.47), vegetables (91.73 and 123.22), spices (92.22 and 207.60) and miscellaneous items (138.37 and 137.80) for the Jalangi and Domkal blocks, respectively. Arsenic is absorbed by the skin of most of the vegetables. The arsenic concentration in fleshy vegetable material is low (mean 2.72 microg/kg, n=45). Higher levels of arsenic were observed in cooked items compared with raw. Daily dietary intakes of arsenic (microg) from the foodstuffs for adults are 171.20 and 189.13 and for children are 91.89 and 101.63 in the Jalangi and Domkal blocks, respectively.
Subject(s)
Arsenic/analysis , Food Analysis , Food Contamination , Adult , Agriculture , Arsenic/administration & dosage , Arsenic/toxicity , Child , Diet , Edible Grain/chemistry , Feeding Behavior , Female , Food Chain , Humans , India , Male , Oryza/chemistry , Plant Leaves/chemistry , Soil Pollutants/analysis , Solanum tuberosum/chemistry , Spices/analysis , Vegetables/chemistry , Water Pollutants/analysisABSTRACT
We present theoretical evidence that the paramagnetic E' defect centers in amorphous silicon dioxide (a-SiO(2)) do not have the same microscopic structures as those well-defined in the corresponding crystalline counterparts such as alpha-quartz. We then present alternative models of some paramagnetic defects that account for the underlying experimental features of the E'-center variants in a-SiO(2). We suggest that our new model should take the place of the conventional defect model of a-SiO(2).
ABSTRACT
We provide a new model of the peroxy-radical defect in amorphous silica on the basis of quantum-chemical calculations applied to clusters of atoms to model the defect. In this model, the 29Si hyperfine splittings of the peroxy radical arise from a single silicon, in agreement with the previous experimental findings. Furthermore, we show that the present model of the peroxy radical is consistent with the diffusion-limited anneal mechanism of the E'gamma center, although our model of the E'gamma center is different from the conventional charged oxygen vacancy model.
ABSTRACT
We here present a series of ab initio quantum-chemical calculations on clusters of atoms modeling several oxygen-deficiency-related defects in amorphous silica and illustrate how these defect centers will change their atomic configurations upon photoionization. We first give theoretical evidence that structural conversion from a neutral oxygen monovacancy to a divalent Si defect is possible, explaining the observed photoluminescence properties associated with these defects.
ABSTRACT
We propose a mechanism of photostructural changes in amorphous As2S3 ( a-As2S3) on the basis of ab initio molecular orbital calculations on clusters of atoms modeling the local structure of the amorphous system. We have found that trigonal AsS3 pyramidal units can be transformed into a fivefold coordinated As site having four As-S bonds and one As-As bond via a photoionization process. This photoinduced coordination defect center exhibits a lower photoabsorption energy as compared with the usual pyramidal structure, explaining the observed photodarkening effect of a-As2S3.