[Preliminary study on three-dimensional morphological reconstruction method for external nose defect based on three-dimensional face template]

Objective: To provide a new solution for the digital design of nasal prostheses, this study explores the three-dimensional (3D) facial morphology completion method for external nasal defects based on the non-rigid registration process of 3D face template. Methods: A total of 20 male patients with tooth defect and dentition defect who visited the Department of Prosthodontics, Peking University School and Hospital of Stomatology from June to December 2022 were selected, age 18-45 years old. The original 3D facial data of patients were collected, and the 3D facial data of the external nose defect was constructed in Geomagic Wrap 2021 software. Using the structured 3D face template data constructed in the previous research of the research group, the 3D face template was deformed and registered to the 3D facial data of external nose defect (based on the morphology of non-defective area) by non-rigid registration algorithm (MeshMonk program), and the personalized deformed data of the 3D face template was obtained, as the complemented facial 3D data. Based on the defect boundary of the 3D facial data of the external nose defect, the complemented external nose 3D data can be cut out from the complemented facial 3D data. Then the nasofacial angle and nasolabial angle of the complemented facial 3D data and the original 3D facial data was compared and analyzed, the ratio between the nose length and mid-face height, nose width and medial canthal distance of the complemented facial 3D data was measured, the edge fit between the edge curve of the complemented external nose 3D data and the defect edge curve of the 3D facial data of external nose defect was evaluated, and the morphological difference of the nose between the complemented external nose 3D data and the original 3D facial data was analyzed. Results: There was no significant statistically difference (t=-0.23, P=0.823; Z=-1.72, P=0.086) in the nasofacial angle (28.2°±2.9°, 28.4°±3.5° respectively) and nasolabial angle [95.4°(19.2°), 99.9°(9.5°) respectively] between the 20 original 3D facial data and the complemented facial 3D data. The value of the ratio of nose length to mid-face height in the complemented facial 3D data was 0.63±0.03, and the value of the ratio of nose width to medial canthal distance was 1.07±0.08. The curve deviation (root mean square value) between the edge curve of the complemented external nose 3D data and the defect edge curve of the 3D facial data of external nose defect was (0.37±0.09) mm, the maximum deviation was (1.14±0.32) mm, and the proportion of the curve deviation value within±1 mm was (97±3)%. The distance of corresponding nose landmarks between the complemented facial 3D data and the original 3D facial data were respectively, Nasion: [1.52(1.92)] mm; Pronasale: (3.27±1.21) mm; Subnasale: (1.99±1.09) mm; Right Alare: (2.64±1.34) mm; Left Alare: (2.42± 1.38) mm. Conclusions: The method of 3D facial morphology completion of external nose defect proposed in this study has good feasibility. The constructed complemented external nose 3D data has good facial coordination and edge fit, and the morphology is close to the nose morphology of the original 3D facial data.

[Construction and application of virtual patients in prosthodontics]

In recent years, with the rapid development of digital technology, the application of oral virtual patients in prosthodontics, orthodontics, oral and maxillofacial surgery, and other disciplines has gradually increased. Although the focus on oral virtual patients varies in different disciplines, the application of oral virtual patients in assisting the prediction of treatment effects and the formulation of treatment plans will have good prospects. The construction accuracy and presentation effects of oral virtual patients can be influenced by the source of three-dimensional (3D) image, and methods of registration. Based on the studies and clinical experiences of our team, researches of other teams, the source of 3D images, the construction methods, and the clinical applications of virtual patients in prosthodontics will be presented, so as to provide a reference for normalized application and development of oral virtual patients and to offer a future development direction of oral virtual patients.

[Application and research progress of digital virtual simulated design in dental esthetic rehabilitation]

In dental esthetic rehabilitation, patients pay great attention to the rehabilitative esthetic effect before teeth preparation, and this is also an important content of doctor-patient communication. Along with the development and combined application of intraoral scan, three-dimensional (3D) face scan, digital design, numerical control machining and 3D printing technology, digital technology is gradually applied to the virtual simulated design before irreversible operation in dental esthetic rehabilitation. Digital technology can be used in dentistry to simulate the esthetic outcome in advance, to assist communication among the dentists, patients and dental technicians, and to realize satisfactory outcome in the final restorations precisely, which, as a result, increases the clinical satisfaction. This review focuses on the application of digital virtual simulated design technology in dental esthetic rehabilitation, analyzes the current research development, deficiency and future prospects, so as to provide guidance for clinical diagnosis and treatment.

[Advances in computer aided design and computer aided manufacturing of removable partial denture]

Computer aided design, numerically controlled milling, additive manufacturing and other digital technologies have been widely used in clinical practice of prosthodontics. The application of these technologies not only changed the design and manufacturing workflow of removable partial denture (RPD), but also improved the production efficiency of dentures, and changed the design and manufacturing concept of dentures. A large number of researches on computer aided design and computer aided manufacturing (CAD/CAM) of RPD have emerged in recent years, including researches on the properties of selective laser melting metal powder and other new dental materials, the innovative design of retainers, connectors, artificial teeth and other denture components, high precision manufacturing of the RPD framework, denture base and artificial teeth, quantitative laboratory evaluations of the accuracy, adaption and mechanical properties of RPD with new structures and made of new materials, clinical evaluations of RPD and others. This paper introduces these recent developments in CAD/CAM of RPD.

A decagonal quasicrystal with rhombic and hexagonal tiles decorated with icosahedral structural units

The structure of a decagonal quasicrystal in the Zn58Mg40Y2 (at.%) alloy was studied using electron diffraction and atomic resolution Z-contrast imaging techniques. This stable Frank-Kasper Zn-Mg-Y decagonal quasicrystal has an atomic structure which can be modeled with a rhombic/hexagonal tiling decorated with icosahedral units at each vertex. No perfect decagonal clusters were observed in the Zn-Mg-Y decagonal quasicrystal, which differs from the Zn-Mg-Dy decagonal crystal with the same space group P10/mmm. Y atoms occupy the center of 'dented decagon' motifs consisting of three fat rhombic and two flattened hexagonal tiles. About 75% of fat rhombic tiles are arranged in groups of five forming star motifs, while the others connect with each other in a 'zigzag' configuration. This decagonal quasicrystal has a composition of Zn68.3Mg29.1Y2.6 (at.%) with a valence electron concentration (e/a) of about 2.03, which is in accord with the Hume-Rothery criterion for the formation of the Zn-based quasicrystal phase (e/a = 2.0-2.15).

Ab initio determination of atomic structure of Zn-Zr precipitates in a Mg-Nd-Zn-Zr alloy

The atomic structure of nanometre-sized Zn-Zr precipitates in a Mg alloy is determined by combining tilt series of micro-beam electron diffraction with atomic resolution Z-contrast imaging. The stoichiometry of the Zn-Zr precipitates is Zn₂Zr₃ with a primitive tetragonal structure (space group P4₂/mnm, a = b = 0.761 nm, c = 0.682 nm). There are 20 atoms in the unit cell of tetragonal Zn₂Zr₃, comprising 12 Zr atoms at the 4d, 4f, 4g positions and eight Zn atoms at the 8j positions.

[Preliminary clinical application of complete digital workflow of design and manufacturing occlusal splint for sleep bruxism]

OBJECTIVE

To establish a complete workflow of digital design and manufacturing occlusal splint for sleep bruxism, which can be preliminarily applied in clinical use, thus observe the clinical efficacy.

METHODS

Twenty-four patients with sleep bruxism were recruited in the study and randomly divided into two groups by using random number tables. Digital-occlusal-splint (experimental group) treatment plan and traditional-occlusal-splint (control-group) treatment plan were carried out for each group, respectively. For experimental group, digital models of patients' both dental arches and the occlusion relationship after elevation were captured using an intraoral scanner. The occlusal splint was carried out by computer aided design/computer aided manufacturing (CAD/CAM), including splint designing and milling. For control group, the traditional soft occlusal splint was fabricated by vacuum laminator. The two kinds of occlusal splints were tried in the patients from each group, and the occlusal contacts were tested respectively by T-scan analysis system, which recorded the changes of occlusal indicators in the two groups. The retention, appearance and occlusal comfort degree were evaluated by the two groups of patients. Mann-Whitney test was performed with IBM SPSS 20.0 software, and bilateral test was performed. P<0.05 was considered to be statistically significant.

RESULTS

The complete workflow of digital design and manufacturing occlusal splint was successfully established. During the clinical use, there was no statistical difference in the retention evaluation of two kinds of occlusal splints between the two groups of patients (Z=-0.538, P=0.590). The appearance score (Z=2.038, P=0.042) and the occlusal comfort score (Z=-2.579, P=0.010) of the experimental group were higher than those of the control group, with statistically significant differences. The T-scan analysis results showed that only the second molar on both sides of the traditional occlusal splint had occlusal contact in intercupsal position, while the digital occlusal splint had stable and bilaterally balanced contact between the maxillary and mandibular teeth. Furthermore, the occlusal force was uniformly distributed in the experimental group.

CONCLUSION

The complete workflow of digital occlusal splint improves the occlusal design, greatly simplifies and optimizes the traditional process of making occlusal splint. This new method is resource-saving and environmental-friendly, and it is able to serve patients more conveniently and efficiently.

High sensitization efficiency and energy transfer routes for population inversion at low pump intensity in Er organic complexes for IR amplification

Organic erbium complexes have long been of interest due to their potential for using the strong absorption into the organic to sensitise the erbium emission. Despite this interest there is remarkably little quantitative information on how effective the approach is and the discussion of the energy transfer mechanism is generally vague. Here we accurately quantify the sensitisation as a function of excitation pump density and model it using a rate equation approach. As a result, we can calculate the degree of population inversion for the erbium ions as a function of the pump intensity. We demonstrate that even when we increase the erbium concentration in the films from ~10 to ~80% we find a relatively small decrease in the sensitisation which we attribute to the large (>20 Å) Förster radius for the sensitisation process. We show that we can obtain population inversion in our films at very low pump powers ~600 mW/cm2. The calculated Förster radius for the organic erbium complexes suggests design rules for energy transfer between antennas and erbium ions in molecular systems and hybrid organic-inorganic nanoparticles.

[Application of digital design of orthodontic-prosthodontic multidisciplinary treatment plan in esthetic rehabilitation of anterior teeth]

OBJECTIVE

To develop a digital workflow of orthodontic-prosthodontic multidisciplinary treatment plan which can be applied in complicated anterior teeth esthetic rehabilitation, in order to enhance the efficiency of communication between dentists and patients, and improve the predictability of treatment outcome.

METHODS

Twenty patients with the potential needs of orthodontic-prosthodontic multidisciplinary treatment to solve their complicated esthetic problems in anterior teeth were recruited in this study. Digital models of patients' both dental arches and soft tissues were captured using intra oral scanner. Direct prosthodontic (DP) treatment plan and orthodontic-prosthodontic (OP) treatment plan were carried out for each patient. For DP treatment plans, digital wax-up models were directly designed on original digital models using prosthodontic design system. For OP treatment plans, virtual-setups were performed using orthodontic analyze system according to orthodontic and esthetic criteria and imported to prosthodontic design system to finalize the digital wax-up models. These two treatment plans were shown to the patients and demonstrated elaborately. Each patient rated two treatment plans using visual analogue scales and the medians of scores of two treatment plans were analyzed using signed Wilcoxon test. Having taken into consideration various related factors, including time, costs of treatment, each patient chose a specific treatment plan. For the patients chose DP treatment plans, digital wax-up models were exported and printed into resin diagnostic models which would be utilized in the prosthodontic treatment process. For the patients chose OP treatment plans, virtual-setups were used to fabricate aligners or indirect bonding templates and digital wax-up models were also exported and printed into resin diagnostic models for prosthodontic treatment after orthodontic treatment completed.

RESULTS

The medians of scores of DP treatment plan and OP treatment plan were calculated and analyzed by IBM SPSS 20. The median of scores of DP treatment plan was 8.4, the minimum value was 6.9 and the maximum value was 9.3. The median of scores of OP treatment plan was 9.0, the minimum value was 7.9 and the maximum value was 9.6. The median of scores of OP was significantly higher than that of DP (Z=-3.23, P<0.01). Finally, 12 patients chose OP treatment plans and 8 patients chose DP treatment plans.

CONCLUSION

For cases with complex esthetic problems in anterior teeth, a digital workflow can demonstrate final treatment outcome and help patients make suitable treatment decisions. In our study, the orthodontic-prosthodontic multidisciplinary treatment plan is feasible which can provide predictions of treatment outcome and improve esthetic outcome with patients' satisfaction.

[Diagnossis and treatment of complicated anterior teeth esthetic defects by combination of whole-process digital esthetic rehabilitation with periodontic surgery]

OBJECTIVE

To explore a new method of whole-process digital esthetic prosthodontic rehabilitation combined with periodontic surgery for complicated anterior teeth esthetic defects accompanied by soft tissue morphology, to provide an alternative choice for solving this problem under the guidance of three-dimensional (3D) printing digital dental model and surgical guide, thus completing periodontic surgery and digital esthetic rehabilitation of anterior teeth.

METHODS

In this study, 12 patients with complicated esthetic problems accompanied by soft tissue morphology in their anterior teeth were included. The dentition and facial images were obtained by intra-oral scanning and three-dimensional (3D) facial scanning and then calibrated. Two esthetic designs and prosthodontic outcome predictions were created by computer aided design /computer aided manufacturing (CAD/CAM) software combined with digital photography, including consideration of white esthetics and comprehensive consideration of pink-white esthetics. The predictive design of prostheses and the facial appearances of the two designs were evaluated by the patients. If the patients chose the design of comprehensive consideration of pink-white esthetics, they would choose whether they would receive periodontic surgery before esthetic rehabilitation. The dentition design cast of those who chose periodontic surgery would be 3D printed for the guide of periodontic surgery accordingly.

RESULTS

In light of the two digital designs based on intra-oral scanning, facing scanning and digital photography, the satisfaction rate of the patients was significantly higher for the comprehensive consideration of pink-white esthetic design (P<0.05) and more patients tended to choose priodontic surgery before esthetic rehabilitation. The 3D printed digital dental model and surgical guide provided significant instructions for periodontic surgery, and achieved success transfer from digital design to clinical application. The prostheses were fabricated by CAD/CAM, thus realizing the whole-process digital esthetic rehabilitation.

CONCLUSION

The new method for esthetic rehabilitation of complicated anterior teeth esthetic defects accompanied by soft tissue morphology, including patient-involved digital esthetic analysis, design, esthetic outcome prediction, 3D printing surgical guide for periodontic surgery and digital fabrication is a practical technology. This method is useful for improvement of clinical communication efficiency between doctor-patient, doctor-technician and doctors from different departments, and is conducive to multidisciplinary treatment of this complicated anterior teeth esthetic problem.

Functionalisation of ligands through click chemistry: long-lived NIR emission from organic Er(iii) complexes with a perfluorinated core and a hydrogen-containing shell

Erbium complexes with a fluorinated organic core shell linked to a hydrogen-containing shell, have been synthesized using the click reaction between erbium(iii) bis(perfluoro-4-azidophenyl)phosphinate and a series of alkynes.

[Progress in research and application of the edentulous custom trays]

Well designed and fabricated custom tray is the precondition to acquire qualified edentulous impression and key to successful complete denture. It has shown that primary impression without custom trays is hard to meet clinical requirements for successful restoration of complete denture. According to the fabrication techniques, edentulous custom tray can be classified into several types such as: compound trimming technique, handcrafted technique with polymerizing acrylic resin based on the study cast, and computer aided design and three dimensional printing(CAD & 3DP) technique based on the primary impression or study cast, etc. With regard to some special edentulous jaws, the custom tray and impression techniques such as open-window, frame cut, closed-mouth custom trays, and so on can be applied to acquire accurate impressions. All above technologies have their own characteristics and emphases. In clinic, appropriate custom trays should be selected according to residual ridge condition, oral status, and other clinical requirements of each edentulous patient.

Direct measurement of precipitate induced strain in an Al-Zn-Mg-Cu alloy with aberration corrected transmission electron microscopy

Precipitates and their associated strain fields significantly influence mechanical properties and, consequently, the industrial performance of aluminum alloys. In this work, we present a direct measurement of strains induced by η' and η precipitates in an Al-Zn-Mg-Cu alloy using aberration-corrected high-resolution transmission electron microscopy and quantitative strain analysis. The results demonstrate that the strain induced by precipitates in the Al-Zn-Mg-Cu alloy shows significant tensile strains perpendicular to the longitudinal direction of the precipitate discs on the side of the discs and along the longitudinal direction at both ends of the η' and η precipitates. This strain field can be described by an equivalent dislocation model, in which the lattice mismatch between the precipitate and the matrix is equivalent to a series of dislocation pairs along the precipitate/matrix interfaces.

Transition of dislocation nucleation induced by local stress concentration in nanotwinned copper

Metals with a high density of nanometre-scale twins have demonstrated simultaneous high strength and good ductility, attributed to the interaction between lattice dislocations and twin boundaries. Maximum strength was observed at a critical twin lamella spacing (∼15 nm) by mechanical testing; hence, an explanation of how twin lamella spacing influences dislocation behaviours is desired. Here, we report a transition of dislocation nucleation from steps on the twin boundaries to twin boundary/grain boundary junctions at a critical twin lamella spacing (12–37 nm), observed with in situ transmission electron microscopy. The local stress concentrations vary significantly with twin lamella spacing, thus resulting in a critical twin lamella spacing (∼18 nm) for the transition of dislocation nucleation. This agrees quantitatively with the mechanical test. These results demonstrate that by quantitatively analysing local stress concentrations, a direct relationship can be resolved between the microscopic dislocation activities and macroscopic mechanical properties of nanotwinned metals.

Metallic materials with a nanometre-scaled lamella structure can have properties that are very different from their coarser-grained counterparts. Here, the authors demonstrate how dislocations in such a material—nanotwinned copper—can nucleate in two distinctly different mechanisms depending on local stress

Organo-erbium systems for optical amplification at telecommunications wavelengths

Modern telecommunications rely on the transmission and manipulation of optical signals. Optical amplification plays a vital part in this technology, as all components in a real telecommunications system produce some loss. The two main issues with present amplifiers, which rely on erbium ions in a glass matrix, are the difficulty in integration onto a single substrate and the need of high pump power densities to produce gain. Here we show a potential organic optical amplifier material that demonstrates population inversion when pumped from above using low-power visible light. This system is integrated into an organic light-emitting diode demonstrating that electrical pumping can be achieved. This opens the possibility of direct electrically driven optical amplifiers and optical circuits. Our results provide an alternative approach to producing low-cost integrated optics that is compatible with existing silicon photonics and a different route to an effective integrated optics technology.

Direct subangstrom measurement of surfaces of oxide particles

Using aberration-corrected transmission electron microscopy combined with first-principles calculations, we show that the surface structure of Co3O4, a typical complex oxide, can be directly imaged and quantitatively analyzed at the subangstrom scale. The atomic positions of both light oxygen and heavier cobalt within the surface layers have been measured to an accuracy of several picometers. The surface electronic structure analysis suggests a polarity compensation model based on the electronic polarizability of surface ions.

Layer resolved structural relaxation at the surface of magnetic FePt icosahedral nanoparticles

The periodic shell structure and surface reconstruction of metallic FePt nanoparticles with icosahedral structure has been quantitatively studied by high-resolution transmission electron microscopy with focal series reconstruction with sub-angstrom resolution. The icosahedral FePt nanoparticles fabricated by the gas phase condensation technique in vacuum have been found to be surprisingly oxidation resistant and stable under electron beam irradiation. We find the lattice spacing of (111) planes in the surface region to be size dependent and to expand by as much as 9% with respect to the bulk value of Fe52Pt48. Controlled removal of the (111) surface layers in situ results in a similar outward relaxation of the new surface layer. This unusually large layerwise outward relaxation is discussed in terms of preferential Pt segregation to the surface forming a Pt enriched shell around a Fe-rich Fe/Pt core.

Identifying an O2 Supply Pathway in CO Oxidation on Au/TiO2(110): A Density Functional Theory Study on the Intrinsic Role of Water

Au catalysis has been one of the hottest topics in chemistry in the last 10 years or so. How O2 is supplied and what role water plays in CO oxidation are the two challenging issues in the field at the moment. In this study, using density functional theory we show that these two issues are in fact related to each other. The following observations are revealed: (i) water that can dissociate readily into OH groups can facilitate O2 adsorption on TiO2; (ii) the effect of OH group on the O2 adsorption is surprisingly long-ranged; and (iii) O2 can also diffuse along the channel of Ti (5c) atoms on TiO2(110), and this may well be the rate-limiting step for the CO oxidation. We provide direct evidence that O2 is supplied by O2 adsorption on TiO2 in the presence of OH and can diffuse to the interface of Au/TiO2 to participate in CO oxidation. Furthermore, the physical origin of the water effects on Au catalysis has been identified by electronic structure analyses: There is a charge transfer from TiO2 in the presence of OH to O2, and the O2 adsorption energy depends linearly on the O2 charge. These results are of importance to understand water effects in general in heterogeneous catalysis.

Measurement of crystal thickness and orientation from selected-area Fourier transformation of a high-resolution electron hologram

Precise knowledge of crystal thickness and orientation is critical for reliable interpretation of high-resolution transmission electron micrographs. In this paper, we propose a criterion of S(2)(T, u, v), which measures the crystal thickness by intensity matching of the selected-area Fourier transform of experimental holograms with the calculated electron diffraction pattern at a series of trial thicknesses (T) and crystal tilts (u, v). This criterion has been demonstrated successfully for local thickness determination from a simulated high-resolution image of a wedge-shaped YBa(2)Cu(3)O(7-delta) and from an experimental hologram of a Si crystal.

HRTEM analysis of nanocrystallization during uniaxial compression of a bulk metallic glass at room temperature

Nanocrystallization during deformation of metallic glass at room temperature has significant implications to understand its deformation mechanism. We present here direct high-resolution transmission electron microscopy (HRTEM) observations of nanocrystallization in a Zr(55)AI(10)Ni(5)Cu(30) bulk metallic glass (BMG) fractured by uniaxial compression at room temperature. The formed nanocrystallites are Zr(2)Cu, with the average diameter of less than 10nm, and are distributed within the round-like regions of localized plastic deformation. We also show direct evidence of atomic neighbor distance increases associated with the shrinkage and broadening of diffused ring pattern from local deformed areas, which may enhance atomic mobility so that nanocrystallization occurred. Our results demonstrate that the origin of the room-temperature deformation of BMG can be attributed to the local atomic spacing increases induced by localization of plastic flow under uniaxial compression test.

Differential expression of MT1-MMP (MMP-14) and collagenase III (MMP-13) genes in normal and wounded rat corneas

PURPOSE

Several members of the matrix metalloproteinase (MMP) group have been identified in the rat cornea during corneal wound healing. The aim of the present study was to identify additional members of the MMP gene family in the rat cornea and localize the expression of membrane type-1 matrix metalloproteinase (MT1-MMP; MMP-14) and collagenase III (MMP-13) in normal and wounded corneas.

METHODS

Adult rats underwent laser keratectomy on the right eye. Unwounded left eyes were normal controls. Corneas were collected and processed at different times post-wounding. Reverse transcription-polymerase chain reaction (RT-PCR) and DNA sequencing were used to discover the MMP genes expressed in the corneas. In situ hybridization was performed to localize the mRNA expression of MMP-14 and MMP-13.

RESULTS

MMP-13 mRNA was detected in epithelial cells of wounded corneas, but not in normal controls; MMP-14 was found in both normal and wounded corneas. MMP-14 mRNA was expressed predominantly in the stromal keratocytes and rarely in the basal epithelial cells in normal and wounded corneas. MMP-13 mRNA was localized exclusively to basal cells of the epithelium at the wounded area from 6 hours to 3 days after wounding.

CONCLUSIONS

MMP-14 and MMP-13 expression in rat corneas parallels that of gelatinases A and B, respectively. MMP-13 may play an important role in the gelatinase B-associated proteolytic cascade that allows rapid turnover of the extracellular matrix (ECM) components during corneal wound healing. MMP-14 may contribute to removing abnormal ECM components through activation of gelatinase A in rat corneas.

Plan-view imaging of oxygen-induced reconstruction on Ag(110) surface. II. Effect of high-energy electron thinning

The feasibility and the limitation of the 'high-energy electron thinning' method for the production of surface-science-grade samples in situ in the electron microscope are studied. Exploiting the electron beam supplied by high-voltage electron gun in electron microscope, this method can be readily realized. An obvious advantage of this method is that we can monitor the sample surface concurrently. However, this sample preparation method depends strongly on the sample material and the local environment within the electron microscope. Factors relating to the electron thinning speed are briefly discussed.

Plan-view imaging of oxygen-induced reconstruction on Ag(110) surface. I. The possibility of imaging surface oxygen

Surface reconstruction on Ag(110) induced by oxygen adsorption was studied by the plan-view imaging technique of high-resolution electron microscopy (HREM). Systematic multislice simulations were carried out to find the optimal experimental conditions for imaging the surface oxygen. It was found theoretically that there exist a series of characteristic values of objective lens defoci and sample thicknesses under which the surface and the bulk can be imaged clearly and simultaneously. These optimal imaging conditions were used to interpret the experimental micrographs. While the basic features of the surface reconstruction of O/Ag(110) in the HREM images are consistent with those revealed by scanning tunnelling microscopy (STM), there are some new features that have not been reported with STM. These phenomena give some evidence to the existence of subsurface oxygen.

The coherent electron microdiffraction of a single translation domain boundary in β-Ni3Nb phase

The microdiffraction from a single translation domain boundary (TDB) in β-Ni3Nb has been recorded by using a Hitachi HF-2000 field emission gun transmission electron microscope, while high-resolution transmission electron microscopy images were used to assist the analysis. The diffraction splitting effect of a TDB is well explained by the kinematics and dynamic calculations, and complex diffraction characteristics have been studied by using dynamics simulation.

The bile acid-inducible baiF gene from Eubacterium sp. strain VPI 12708 encodes a bile acid-coenzyme A hydrolase

The human intestinal Eubacterium sp. strain VPI 12708 has been shown to have a multistep biochemical pathway for bile acid 7alpha-dehydroxylation. A bile acid-inducible operon encoding 9 open reading frames has been cloned and sequenced from this organism. Several of the genes in this operon have been shown to catalyze specific reactions in the 7alpha-dehydroxylation pathway. The baiF gene from this operon was cloned, expressed in Escherichia coli, and found to encode a novel bile acid-coenzyme A (CoA) hydrolase. The subunit molecular mass of the purified bile acid-CoA hydrolase was calculated to be 47,466 daltons and the native enzyme had a relative molecular weight of 72,000. The K m and Vmax for cholyl-coenzyme A (CoA) hydrolysis was approximately 175 microm and 374 micromol/min per mg protein, respectively. The enzyme used cholyl-CoA, 3-dehydrocholyl-CoA, and chenodeoxycholyl-CoA as substrates. No hydrolytic activity was detected using acetyl-CoA, isovaleryl-CoA, palmitoyl-CoA, or phenylacetyl-CoA as substrates. Amino acid sequence database searches showed no significant similarity of bile acid-CoA hydrolase to other thioesterases, but significant amino acid sequence identity was found with Escherichia coli carnitine dehydratase. The characteristic thioesterase active site Gly-X-Ser-X-Gly motif was not found in the amino acid sequence of this enzyme. Bile acid-CoA hydrolase from Eubacterium sp. strain VPI 12708 may represent a new family of thioesterases.

Expression of gelatinases A and B, and TIMPs 1 and 2 during corneal wound healing

PURPOSE

To determine the expression of gelatinases A and B and the localization of tissue inhibitors of metalloproteinase (TIMP)-1 and TIMP-2 during the early stages of corneal wound healing in rats. METHODS. One eye each of 30 adult Sprague-Dawley rats was treated with excimer laser keratectomy; the other eye was untreated. Frozen sections of corneas obtained 6, 18, and 24 hours and 3 and 7 days after wounding were used to perform immunoconfocal microscopy and in situ hybridization.

RESULTS

Gelatinase B was immunolocalized to the basement membrane zone and superficial stroma, and its mRNA was exclusively localized to basal epithelial cells migrating across the wound at 18 and 24 hours and 3 days after wounding. Tissue inhibitor of metalloproteinase-1 was also immunolocalized to the basement membrane zone and superficial stroma at the same time points. Gelatinase A was immunolocalized to the epithelium and stroma of normal corneas and was predominant in the basal epithelium and superficial stroma at 3 and 7 days after wounding. In situ hybridization confirmed gelatinase A expression by the epithelial cells and the stromal keratocytes. Tissue inhibitor of metalloproteinase-2 was immunolocalized to the epithelium in normal and wounded corneas. Intense TIMP-2 labeling of the basement membrane zone was noted 3 days after wounding.

CONCLUSIONS

Unlike gelatinase A, gelatinase B is expressed exclusively by migrating basal epithelial cells after wounding. The matrix metalloproteinase-tissue inhibitor of metalloproteinase (MMP)/TIMP systems may play an important role in the early stages of corneal wound healing after excimer laser keratectomy.

Applications of microdiffraction related to HREM

This paper deals with the coherent and the incoherent microdiffraction, as well as their applications, for example, determination of the nature of defects and boundaries, measurement of the strain field and identification of the symmetry, etc. The localized structure information obtained from microdiffraction has been compared with and complements that provided by HREM.

Microstructure investigations of ball milled materials

HREM and FEG TEM were emphasized and extensively used to follow the most subtle changes in the structure and composition of ball-milled Cu, Fe-Cu, and thermally decomposed Fe60Cu40. Some significant results are obtained and summarized as follows: HREM shows that the deformation of ball-milled copper proceeds mainly by twinning and shear bands (SBs) formation. The nano-grains formed during ball milling (BM) contain a high density of dislocations. The grain boundaries (GBs) of nanocrystalline (NC) Cu prepared by BM are ordered, curved, and strained, but disordering, lattice distortion, and nanovoids in local regions were frequently observed. Nanoscale composition analysis on mechanically alloyed Fe16Cu84 shows that the average Fe content in both the interior of grains and the GBs is close to the designed composition, which proves that a supersaturated solid solution has really formed. However, the Fe content is rather inhomogeneous between the larger and smaller grains, which infers the inhomogeneous mixing of Fe and Cu during mechanical alloying (MA). NC structure and the mechanical force-enhanced fast diffusion are the reasons of the formation of supersaturated solid solutions in immiscible systems with positive enthalpy of mixing. HREM observations carried out with the thermally decomposed Fe60Cu40 solid solution show that the Nishiyama (N-W) or Kurdyumov-Sachs (K-S) orientation relationships exist between alpha-Fe and Cu. Energy dispersive X-ray spectra (EDXS) results show that the Cu content in these alpha-Fe grains reaches as high as 9.5 at.% even after heating to 1,400 degrees C, which is even higher than the maximum solubility of Cu in gamma-Fe at 1,094 degrees C.

Image segmentation and bright contrast spot localization of the high resolution atomic image

Some basic quantitative analysis techniques of digitized high resolution atomic image are developed in this paper. We describe how to divide the atomic image into small independent areas with special structure information by the valley mesh segmentation method. The procedure is with regard to the bright contrast spot segmentation of atomic images. We suggest several ways for bright contrast spot localization in images. Calculation routines for peak detection and weighted local position average methods for this purpose are given.

The defects and intergrowth of lead oxides revealed by HRTEM

High-resolution transmission electron microscopy (HRTEM) and electron diffraction were used to investigate the microstructure of natural lead oxides found in Panzhihua Mountain, China. The electron diffraction patterns showed crossing of diffraction spots along 〈110〉 directions in litharge and along 〈100〉 directions in massicot and the structural images showed the domain-like texture, probably constructed by arrays of planar defects in the fundamental structures. Based upon the structure of these oxides the possible structural models of planar defects are discussed and the orientation relationship of litharge and massicot is determined.

A HREM study of nonbasal twinning and superlattices in ilmenite

The microstructures of natural ilmenite found in Panzhihua district, China, were examined by high-resolution electron microscopy (HREM). The [{\bar 1}2{\bar 1}0] structural images showed clearly the (10{\bar 1}1) nonbasal twinning which seems to be coincident with the [{\bar 1}012] rotation twinning. The superlattices with periodicities of 16.8 and 12.6 Å, respectively, as well as the unit-cell twinning related to the ordering of (10{\bar 1}1) multiple twinnings were observed. The superlattice resulting from the ordering arrangement of (10{\bar 1}1) stacking faults related to the slip systems suggested by Heuer [Philos, Mag. (1966), 13, 379–893] were also detected. Possible genetic aspects are considered.

High-resolution electron microscopic investigation of supported platinum particles reduced at high temperatures

High-resolution electron microscopy has been used to characterize the platinum particles supported on TiO2 or ZnO. After reduction at elevated temperatures, the metallic particles display a regular, faceted shape, and several superstructures, Pt3 Ti(C), Pt3 Ti(H), PtTi, and PtZn, have been found. These results, which may involve strong metal-support interaction, have been confirmed by optical diffraction and image simulation.