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PubMed2001

Wavelength-multiplexing diffractive phase elements: design, fabrication, and performance evaluation.

We report on the wavelength-multiplexing diffractive phase element (WMDPE) capable of generating independent spot patterns for different wavelengths. The iterative method proposed by Bengtsson [Appl. Opt. 37, 1998] for designing a kinoform that produces different patterns for two wavelengths is extended to the WMDPE for multiple wavelengths (more than two wavelengths). Effectiveness of the design algorithm is verified by design and computer simulations on the WMDPE's for four and nine wavelengths. The WMDPE for three wavelengths (441.6, 543.5, and 633 nm) is designed with five phase levels and is fabricated by electron-beam lithography. We observed that the individual spot patterns are reconstructed for the design wavelengths correctly. Performance of the WMDPE is evaluated by computer simulations on the uniformity error, the light efficiency, and the contrast. On the basis of the results, the characteristics of the WMDPE's are discussed in terms of various conditions of fabrication and usage.

Journal Article↗

PubMed1997

Computational approaches for combinatorial library design and molecular diversity analysis.

New approaches for combinatorial library design and molecular diversity analysis have been developed by extending previous work from the fields of quantitative structure-activity relationship, computational chemistry, and chemical information. Recent work has begun to address design efficiency and validation of descriptors for combinatorial library design.

Chemistry, Organic↗

PubMed2005

Three-dimensional modelling and finite element analysis of the human mandible during clenching.

BACKGROUND: Until recently, very few papers have been published concerning the development, analysis and experimental verification of three-dimensional, finite element modelling of the human adult edentulous mandible. The purpose of this study was to improve the method of modelling by using computer-aided engineering (CAE) and computer-aided design (CAD) methods and to utilize the model in analyzing maxillofacial problems. METHODS: The model geometry was derived from position measurements taken from 28 diamond blade cut cross-sections of an average size human adult edentulous mandible and generated using a special sequencing method. Data on anatomical, structural, functional aspects and material properties were obtained from measurements and published data. The materials were idealized as transversely isotropic. The complete model consisted of 258 solid elements and 1635 nodes. RESULTS: The model was solved for displacements and stresses during clenching. In general, the observed displacement and stresses (tensile and compressive) were highest around the condylar region. Compressive stress was also observed around the premolar and molar bite points. CONCLUSION: This investigation has shown that the use of computer-aided modelling in conjunction with the finite element analysis could be effectively utilized in biomechanical analysis of the mandible. It could help to investigate many functional problems and could reduce the time of extensive experimentations.

Adult↗

PubMed2005

Isomeric thiazole derivatives as ligands for the neuropeptide Y5 receptor.

Sets of isomeric thiazole derivatives 1 and 2 have been synthesised in a parallel iterative solution-phase synthesis approach guided by the SAR analysis derived from biological results and computer-aided design and analysis. This synergistic and streamlined working procedure led to highly active isomeric NPY5 receptor ligands. However, a 10-fold difference at least in their respective binding affinities was consistently found for all isomeric pairs 1 and 2. The analysis of conformational differences due to heteroatom interactions in 1 and 2 revealed a favourable C=O...S interaction in 1, whereas thiazoles 2 showed a repulsive C=O...N interaction.

Computer-Aided Design↗

PubMed2005

[The study on three-dimension finite element analysis of the stress distribution in the mandible bone around dental implants].

OBJECTIVE: The aim of this study was to investigate how to model an accuracy 3-dimension Finite Element Analysis (3D-FEA) model. METHODS: Based on computed tomography (CT) scan data of a woman, a 3D finite element model of the first molar on the left was rebuilt by computer imagines process and computer aided design (CAD). Analysis of the stress distribution on a cylinder dental implant and in the bone around it was conducted. RESULTS: The stress distribution showed extremely asymmetry in bucco-lingual section: stress concentrated on the lingual side of the mandible; stress mainly was tensile in buccal side, and on the contrary compressive in lingual side. CONCLUSION: The results were more reliable because this model more really displayed the mandible.

Computer Simulation↗

PubMed2003

Three-dimensional relationship between the critical contact angle and the torque angle.

The purpose of this study was to analyze the relationship between the critical contact angle and the torque angle in an orthodontic bracket and archwire assembly in 3 dimensions. Three-dimensional mathematical models were created with geometric bracket-archwire parameters that included 2 slot sizes, 3 bracket widths, and 3 to 4 wire sizes. From this, 3-dimensional mathematical equations (3DMEs) for the critical contact angle and the maximum torque that result in critical contact angles of 0 were derived and calculated. To evaluate the effects of archwire-bracket parameters on critical contact angles, analysis of variance (ANOVA) was performed at the significance level of P < or = .05. For all bracket-archwire combinations, the critical contact angle decreased as bracket width, torque angle, and wire size increased. Therefore, all bracket-archwire parameters except slot height had an effect on the critical contact angle. Results of the critical contact angle produced from our 3DMEs were the same as those produced by 3D computer-aided design (SolidWorks Corp, Concord, Mass), thus confirming the validity of our derived equations. In addition, the effect of a beveled edge was investigated in some archwires. Furthermore, torsional play angles were calculated and found to be similar to those in previous reports. The results of this study provide theoretic and experimental bases for clinical orthodontic practice and indicate that torque angles should be included in the evaluation of the critical contact angle.

Analysis of Variance↗

PubMed2006

A computational approach to botanical drug design by modeling quantitative composition-activity relationship.

Herbal medicine has been successfully applied in clinical therapeutics throughout the world. Following the concept of quantitative composition-activity relationship, the presented study proposes a computational strategy to predict bioactivity of herbal medicine and design new botanical drug. As a case, the quantitative relationship between chemical composition and decreasing cholesterol effect of Qi-Xue-Bing-Zhi-Fang, a widely used herbal medicine in China, was investigated. Quantitative composition-activity relationship models generated by multiple linear regression, artificial neural networks, and support vector regression exhibited different capabilities of predictive accuracy. Moreover, the proportion of two active components of Qi-Xue-Bing-Zhi-Fang was optimized based on the quantitative composition-activity relationship model to obtain new formulation. Validation experiments showed that the optimized herbal medicine has greater activity. The results indicate that the presented method is an efficient approach to botanical drug design.

Algorithms↗

PubMed2002

Computer-integrated finite element modeling of human middle ear.

The objective of this study was to produce an improved finite element (FE) model of the human middle ear and to compare the model with human data. We began with a systematic and accurate geometric modeling technique for reconstructing the middle ear from serial sections of a freshly frozen temporal bone. A geometric model of a human middle ear was constructed in a computer-aided design (CAD) environment with particular attention to geometry and microanatomy. Using the geometric model, a working FE model of the human middle ear was created using previously published material properties of middle ear components. This working FE model was finalized by a cross-calibration technique, comparing its predicted stapes footplate displacements with laser Doppler interferometry measurements from fresh temporal bones. The final FE model was shown to be reasonable in predicting the ossicular mechanics of the human middle ear.

Acoustic Stimulation↗

PubMed2005

Changes in the mechanical environment of stenotic arteries during interaction with stents: computational assessment of parametric stent designs.

Clinical studies have identified factors such as the stent design and the deployment technique that are one cause for the success or failure of angioplasty treatments. In addition, the success rate may also depend on the stenosis type. Hence, for a particular stenotic artery, the optimal intervention can only be identified by studying the influence of factors such as stent type, strut thickness, geometry of the stent cell, and stent-artery radial mismatch with the wall. We propose a methodology that allows a set of stent parameters to be varied, with the aim of evaluating the difference in the mechanical environment within the wall before and after angioplasty with stenting. Novel scalar quantities attempt to characterize the wall changes inform of the contact pressure caused by the stent struts, and the stresses within the individual components of the wall caused by the stent. These quantities are derived numerically and serve as indicators, which allow the determination of the correct size and type of the stent for each individual stenosis. In addition, the luminal change due to angioplasty may be computed as well. The methodology is demonstrated by using a full three-dimensional geometrical model of a postmortem specimen of a human iliac artery with a stenosis using imaging data. To describe the material behavior of the artery, we considered mechanical data of eight different vascular tissues, which formed the stenosis. The constitutive models for the tissue components capture the typical anisotropic, nonlinear and dissipative characteristics under supra-physiological loading conditions. Three-dimensional stent models were parametrized in such a way as to enable new designs to be generated simply with regard to variations in their geometric structure. For the three-dimensional stent-artery interaction we use a contact algorithm based on smooth contact surfaces of at least C-continuity, which prevents numerical problems known from standard facet-based contact algorithm. The proposed methodology has the potential to provide a scientific basis for optimizing treatment procedures and stent geometries and materials, to help stent designers examine new stent designs "virtually," and to assist clinicians in choosing the most suitable stent for a particular stenosis.

Adult↗

PubMed1993

Parametric modelling of a knee joint prosthesis.

This paper presents an approach for the establishment of a parametric model of knee joint prosthesis. Four different sizes of a commercial prosthesis are used as an example in the study. A reverse engineering technique was employed to reconstruct the prosthesis on CATIA, a CAD (computer aided design) system. Parametric models were established as a result of the analysis. Using the parametric model established and the knee data obtained from a clinical study on 21 pairs of cadaveric Asian knees, the development of a prototype prosthesis that suits a patient with a very small knee joint is presented. However, it was found that modification to certain parameters may be inevitable due to the uniqueness of the Asian knee. An avenue for rapid modelling and eventually economical production of a customized knee joint prosthesis for patients is proposed and discussed.

Asian People↗

PubMedDate not supplied

A tool for designing digital test objects for module performance evaluation in medical digital imaging.

Currently, medical digital imaging systems are characterized by the introduction of additional modules such as digital display, image compression and image processing, as well as film printing and digitization. These additional modules require performance evaluation to ensure high image quality. A tool for designing computer-generated test objects applicable to performance evaluation of these modules is presented. The test objects can be directly used as digital images in the case of film printing, display, compression and image processing, or indirectly as images on film in the case of digitization. The performance evaluation approach is quality control protocol based. Digital test object design is user-driven according to specifications related to the requirements of the modules being tested. The available quality control parameters include input/output response curve, high contrast resolution, low contrast discrimination, noise, geometric distortion and field uniformity. The tool has been designed and implemented according to an object oriented approach in Visual C++ 5.0, and its user interface is based on the Microsoft Foundation Class Library version 4.2, which provides interface items such as windows, dialog boxes, lists, buttons, etc. The compatibility with DICOM 3.0 part 10 image formats specifications allows the integration of the tool in the existing software framework for medical digital imaging systems. The capability of the tool is demonstrated by direct use of the test objects in case of image processing, and indirect use of the test objects in case of film digitization.

Algorithms↗

PubMed2004

Design of new cognition enhancers: from computer prediction to synthesis and biological evaluation.

To discover new cognition enhancers, a set of virtually designed synthesizable compounds from different chemical series was investigated using two computer-aided approaches. One of the approaches is prediction of biological activity spectra for substances (PASS) and the second is prediction of toxicity, mutagenicity, and carcinogenicity (DEREK). To increase the probability of finding new chemical entities, we investigated a heterogeneous set of highly diverse chemicals including different types of heterocycles: five-membered (thiophenes, thiazoles, imidazoles, oxazoles, pyrroles), six-membered (pyridines, pyrimidines), seven-membered (diazepines, triazepines), fused five+six-membered heterocycles (indoles, benzothiazoles, purines, indolizines, neutral, mesoionic, and cationic azolopyridines). A database including 5494 structures of compounds was created. On the basis of the PASS and DEREK prediction results, eight compounds with the highest probability of cognition-enhancing effect were selected. The cognition-enhancing activity testing showed that all of the selected compounds had a pronounced antiamnesic effect and were found to reduce significantly scopolamine-induced amnesia of passive avoidance reflex (PAR). The action of compounds at doses of 1 and 10 mg/kg caused a statistically significant increase in latent time of reflex and in the number of animals, which did not enter the dark chamber when testing the PAR. Therefore, on the basis of computer prediction, new cognition-enhancing agents were discovered within the chemical series, in which this activity was not known previously.

Amnesia↗

PubMed2026

Application of Three-Dimensionally Printed Surgical Guides in Precise Sacral Tumor Excision and Defect Reconstruction.

OBJECTIVE: Precise resection of sacral tumors remains technically demanding due to their deep anatomical location and close proximity to critical neurovascular structures. Conventional freehand techniques often result in suboptimal resection margins, excessive blood loss, and compromised lumbopelvic stability. This study evaluated whether patient-specific three-dimensional (3D)-printed guiding templates improve surgical accuracy and perioperative outcomes in sacral tumor resection and reconstruction. METHODS: Nineteen patients undergoing en bloc sacral tumor resection (S1-S3 involvement) with spinopelvic reconstruction (2006-2020) were retrospectively analyzed. Patients were divided into a 3D-printing group (n = 10) and a conventional freehand group (n = 9). In the 3D-printing group, computer-aided design and 3D-printed templates were used for osteotomy, screw placement, and defect reconstruction. Perioperative metrics, surgical accuracy, and complications were compared between groups using Welch's t-test and the Hodges-Lehmann method; oncologic events during follow-up were recorded descriptively. RESULTS: The 3D-printing group demonstrated significantly shorter operative time (456.5 ± 62.36 vs. 574.44 ± 114.58 min, p = 0.012), reduced blood loss (4081.40 ± 838.99 vs. 5090.0 ± 1059.67 mL, p = 0.034), and fewer fluoroscopic exposures (4.2 ± 0.79 vs. 10.0 ± 1.58, p < 0.001) compared with the conventional group. Osteotomy accuracy was also superior in the 3D-printing group, with significantly lower angular deviation (3.33° ± 0.45° vs. 6.79° ± 2.16°, p = 0.0012). Postoperative complication rates were comparable (30% vs. 44.4%, p = 0.649), but hospital stay was significantly shorter in the 3D-printing group (10.7 ± 2.71 vs. 18.11 ± 4.01 days, p < 0.001). CONCLUSION: Patient-specific 3D-printed guiding templates enhance precision in sacral tumor excision and reconstruction, improving surgical efficiency and perioperative safety. This computer-assisted, template-guided approach represents a valuable advancement for complex sacral oncologic surgery.

Humans↗

PubMed2002

Substrate mimetics in protease catalysis: characteristics, kinetics, and synthetic utility.

This article reviews the latest developments in protease-catalyzed peptide synthesis focusing on the use of substrate mimetics. The substrate mimetics approach takes advantage of the characteristic of this novel type of substrates to direct the enzyme to recognize an alternative site on the acyl donor, i.e. the site-specific ester leaving group, mediating the acceptance of originally poorly reactive acyl moieties. At first the kinetics and catalytic mechanism of substrate mimetics-mediated reactions are discussed on the basis of hydrolysis, peptide synthesis, protein-ligand docking, and molecular dynamics studies. By the example of the Glu-specific V8 protease and the aromatic amino acid-specific chymotrypsin both the empirical and computer-aided design of specific substrate mimetics is described. The influence of the leaving group specifically recognized by the enzyme is also considered. The benefits of these artificial substrates over common acyl donor components are illustrated by selected synthesis reactions of small peptides, peptide isosteres, non-peptidic carboxylic acid amides, and the coupling of peptide fragments at non-specific ligation sites resulting in biologically active peptide products. Finally, this review focuses on critical syntheses that uses specific-amino acid-containing peptides as the reactants of ligation. Based on these, the restrictions of the substrate mimetics approach is critically discussed and techniques to their overcoming are presented.

Acylation↗

PubMed2002

An advanced computer-aided geometric modeling and fabrication method for human middle ear.

This paper presents a practical and systematic method for reconstructing accurate computer and physical models of the entire human middle ear. The proposed method starts with the histological section preparation of human temporal bone. Through tracing outlines of the middle ear components on the sections, a set of discrete points is obtained and employed to construct B-spline curves that represent the exterior contours of the components using a curve-fitting technique. The surface-skinning technique is then employed to quilt the B-spline curves for smooth boundary surfaces of the middle ear components using B-spline surfaces. The solid models of the middle ear components are constructed using these surfaces and then assembled to create the entire middle ear in a computer-aided design environment. This method not only provides an effective way to visualize and measure the three-dimensional structure of the middle ear, but also provides a detailed knowledge of middle ear geometry that is required for finite element analysis or multibody dynamic analysis of the human middle ear. In addition, the geometric model constructed using the proposed method is smooth and can be fabricated in various scales using solid freeform fabrication technology. The physical model of the human middle ear is extremely effective in realizing the middle ear anatomy and enhancing discussion and collaboration among researchers and physicians.

Anatomy, Cross-Sectional↗

PubMed2005

The effect of a tightly bound water molecule on scaffold diversity in the computer-aided de novo ligand design of CDK2 inhibitors.

We have determined the effects that tightly bound water molecules have on the de novo design of cyclin-dependent kinase-2 (CDK2) ligands. In particular, we have analyzed the impact of a specific structural water molecule on the chemical diversity and binding mode of ligands generated through a de novo structure-based ligand generation method in the binding site of CDK2. The tightly bound water molecule modifies the size and shape of the binding site and we have found that it also imposed constraints on the observed binding modes of the generated ligands. This in turn had the indirect effect of reducing the chemical diversity of the underlying molecular scaffolds that were able to bind to the enzyme satisfactorily. [Figure: see text].

Binding Sites↗

PubMed2003

Absolute interferometric test of aspheres by use of twin computer-generated holograms.

A complete absolute interferometric test of axially symmetric aspheres is presented. The method is based on a specially designed computer-generated hologram (CGH) that reconstructs an aspherical wave as well as a spherical auxiliary wave. Since both phase functions have the same symmetry and their pattern is simultaneously encoded, we call this type of multiplex hologram a Twin-CGH. The spherical wave is used for calibration. The aberrations of the spherical auxiliary wave are measured absolutely with either a spherical mirror or an absolute test for Fresnel zone plates. Thus the two types of aberration inherent in the CGH can be identified and separated from each other. The errors of the spherical wave can be transferred to those of the aspherical wave. Two different methods thatuse Twin-CGHs for absolute testing of aspheric surfaces are described. Test procedures are explained, equations are derived, and experimental results are presented. A mutual comparison of the two results and a comparison with the established N-position rotation test are given.

Journal Article↗

PubMed1995

A tricyclic ring system replaces the variable regions of peptides presented by three alleles of human MHC class I molecules.

BACKGROUND: Cytotoxic T-lymphocytes (CTLs) recognize complexes of short peptides with major histocompatibility complex (MHC) class I molecules. MHC molecules are polymorphic, and the products of different MHC alleles bind to different subsets of peptides. This is due to differences in the shape of the peptide-binding groove on the surface of the MHC protein, especially the 'pockets' into which anchor residues at each end of the peptide fit. Non-peptidic ligands for class I molecules may be useful clinically. RESULTS: By applying computer-aided design methods guided by X-ray structures, we designed and synthesized several MHC class I ligands, based on known peptide ligands, in which the tricyclic, aromatic compound phenanthridine replaced the central amino acids of the peptides. These semi-peptidic fluorescent ligands bound with high affinity and with allelic specificity to the peptide-binding groove of different MHC class I molecules, forming crystallizable complexes. CONCLUSIONS: Specificity for binding to different MHC class I molecules can be imparted to the common phenanthridine element by judicious choice of terminal peptidic elements from either nonamer or decamer peptides. The phenanthridine-based ligands have a long bound half-life, as do antigenic peptides.

Alleles↗