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Results for “computational design”

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At least 1,207 records · Page 67Linked to original sources
PubMed1989

Paraplegic standing controlled by functional neuromuscular stimulation: Part I--computer model and control-system design.

We have developed a planar computer model to investigate paraplegic standing induced by functional neuromuscular stimulation. The model consists of nonlinear musculotendon dynamics (pulse train activation dynamics and musculotendon actuator dynamics), nonlinear body-segmental dynamics, and a linear output-feedback control law. The model of activation dynamics is an analytic expression that characterizes the relation between the stimulus parameters (pulse width and interpulse interval) and the muscle activation. Hill's classic two-element muscle model was modified into a musculotendon actuator model in order to account for the effects of submaximal activation and tendon elasticity on development of force by the actuator. The three body-segmental, multijoint model accounts for the anterior-posterior movements of the head and trunk, the thigh, and the shank. We modeled arm movement as an external disturbance and imposed the disturbance to the body-segmental dynamics by means of a quasistatic analysis. Linearization, and at times linear approximation of the computer model, enabled us to compute a constant, linear feedback-gain matrix, whose output is the net activation needed by a dynamical joint-torque actuator. Motivated by an assumption that minimization of energy expenditure lessens muscle fatigue, we developed an algorithm that then computes how to distribute the net activation among all the muscles crossing the joint. In part II, the combined feedback control strategy is applied to the nonlinear model of musculotendon and body-segmental dynamics to study how well the body ought to maintain balance should the feedback control strategy be employed.

Biomechanical Phenomena↗
PubMedDate not supplied

Designing a test bank computer program.

This article contains all of the instructions needed to create a computerized test bank program. The program is flexible enough to allow for the sequential numbering of test items; the alteration of stems, distractors, and options to develop new test items; and the programmability to produce a hard copy objective examination, as designed by the user.

Education, Nursing↗
PubMed1995

A new three-dimensional treatment algorithm for complex surfaces: applications in surgery.

PURPOSE: Recent advances in computer technology enable automatic reconstruction of surface models using digitized contour lines and three-dimensional (3D) representation on a graphic terminal. This work was aimed at obtaining 3D reconstructions of facial bones to help guide oral surgery and complex dental implantology procedures. MATERIAL AND METHODS: The starting point was a computed tomographic examination. The limits of the cortical bone were automatically outlined and then digitized using a special computer program. The resulting data were then compiled for computer-aided design (CAD) purposes, and a virtual 3D model of the bone was mathematically computed. This model was next transferred to a computer program that piloted a CAD/computer-aided manufacture (CAM) machine that guided a laser stereolithography process. RESULTS: The early results of the use of 3D images, as well as solid models, for clinical and surgical purposes, indicate a high degree of reliability in morphologic diagnosis, determining the surgical procedure, and establishing the subsequent prognosis.

Algorithms↗
PubMed2002

[Reconstruction of the frontal bone with individual titanium implants after surgical therapy of osteomyelitis of the frontal bone].

Individually prefabricated titanium implants enable the reconstruction of the frontal bone after surgical therapy of osteomyelitis without compromising mechanical stability or aesthetic results. Primarily the infected bone tissue is removed. Helical computed tomographic systems are used for the aquisition of patient data. After being transmitted to a computer aided design system (CAD-system) this data is used for construction of the implant geometry using freeform-surfaces. The outer surface contour is derived from the contours of the bone defect. The completed computer-based implant design is finally transformed into control data to run the milling machine which produces the implant from a block of titanium. Modern industrial CAD/CAM-technology allows standardized prefabrication using data from CT-scans. The precision of all implants was predictable and duration of the reconstructive procedure could be reduced. During postoperative follow-up (5-24 months) no loss of implant or recurrence of the osteomyelitis could be observed.

Adolescent↗
PubMed2002

Thoroughly sampling sequence space: large-scale protein design of structural ensembles.

Modeling the inherent flexibility of the protein backbone as part of computational protein design is necessary to capture the behavior of real proteins and is a prerequisite for the accurate exploration of protein sequence space. We present the results of a broad exploration of sequence space, with backbone flexibility, through a novel approach: large-scale protein design to structural ensembles. A distributed computing architecture has allowed us to generate hundreds of thousands of diverse sequences for a set of 253 naturally occurring proteins, allowing exciting insights into the nature of protein sequence space. Designing to a structural ensemble produces a much greater diversity of sequences than previous studies have reported, and homology searches using profiles derived from the designed sequences against the Protein Data Bank show that the relevance and quality of the sequences is not diminished. The designed sequences have greater overall diversity than corresponding natural sequence alignments, and no direct correlations are seen between the diversity of natural sequence alignments and the diversity of the corresponding designed sequences. For structures in the same fold, the sequence entropies of the designed sequences cluster together tightly. This tight clustering of sequence entropies within a fold and the separation of sequence entropy distributions for different folds suggest that the diversity of designed sequences is primarily determined by a structure's overall fold, and that the designability principle postulated from studies of simple models holds in real proteins. This has important implications for experimental protein design and engineering, as well as providing insight into protein evolution.

Amino Acid Sequence↗
PubMed1987

Computer-aided dosage form design. II. Methods for defining a zero-order sustained-release delivery system of maximum formulating flexibility.

Classical methods employing pharmacokinetic data to calculate zero-order release rates for sustained release products require that a constant-rate drug delivery system must have a duration which is exactly equal to the desired dosage interval. This traditional approach fails to establish the minimum acceptable duration and also fails to provide any flexibility in the formulation goal. While it does calculate one pair of duration and dose values, there are infinite pairs of values capable of maintaining the desired plasma concentrations using the selected dosing interval. In the current method, computer simulations are used to establish the boundary conditions within which any pair of duration and dose values will maintain the desired levels when administered on the chosen dosing interval. By comparing the boundary conditions for every subject in a group, a single set of conditions which would work for the entire group can be selected. These final limits represent the broadest specifications for zero-order drug delivery system design for that particular drug combined with the plasma concentration goals and the desired dosing interval. The method is illustrated using theophylline pharmacokinetics.

Adult↗
PubMed2005

The mini-screen: an innovative device for computer assisted surgery systems.

In this paper we focus on the design of Computer Assisted Surgery (CAS) systems and more generally Augmented Reality (AR) systems that assist a user in performing a task on a physical object. Digital information or new actions are defined by the AR system to facilitate or to enrich the natural way the user would interact with the real environment. We focus on the outputs of such systems, so that additional digital information is smoothly integrated with the real environment of the user, by considering an innovative device for displaying guidance information: the mini-screen. We first motivate the choice of the mini-screen based on the ergonomic property of perceptual continuity and then present a design space useful to create interaction techniques based on a mini-screen. Two versions of a Computer ASsisted PERicardial (CASPER) puncture application, as well as a computer assisted renal puncture application, developed in our teams, are used to illustrate the discussion.

Computer Terminals↗
PubMed1991

Computational method for the design of enzymes with altered substrate specificity.

A combination of enzyme kinetics and X-ray crystallographic analysis of site-specific mutants has been used to probe the determinants of substrate specificity for the enzyme alpha-lytic protease. We now present a generalized model for understanding the effects of mutagenesis on enzyme substrate specificity. This algorithm uses a library of side-chain rotamers to sample conformation space within the binding site for the enzyme-substrate complex. The free energy of each conformation is evaluated with a standard molecular mechanics force field, modified to include a solvation energy term. This rapid energy calculation based on coarse conformation sampling quite accurately predicts the relative catalytic efficiency of over 40 different alpha-lytic protease-substrate combinations. Unlike other computational approaches, with this method it is feasible to evaluate all possible mutations within the binding site. Using this algorithm, we have successfully designed a protease that is both highly active and selective for a non-natural substrate. These encouraging results indicate that it is possible to design altered enzymes solely on the basis of empirical energy calculations.

Algorithms↗
PubMed2003

Design of a novel globular protein fold with atomic-level accuracy.

A major challenge of computational protein design is the creation of novel proteins with arbitrarily chosen three-dimensional structures. Here, we used a general computational strategy that iterates between sequence design and structure prediction to design a 93-residue alpha/beta protein called Top7 with a novel sequence and topology. Top7 was found experimentally to be folded and extremely stable, and the x-ray crystal structure of Top7 is similar (root mean square deviation equals 1.2 angstroms) to the design model. The ability to design a new protein fold makes possible the exploration of the large regions of the protein universe not yet observed in nature.

Algorithms↗
PubMed1985

Computerized imaging for soft tissue and osseous reconstruction in the head and neck.

Recent developments in computer-aided medical imaging coupled with the related emergence of computer-aided design and manufacturing technology have had a significant effect on our management of patients with congenital and acquired head and neck deformities. In our institution, plain film skull radiography, cephalometry, and pluridirectional tomography have been largely replaced by high-resolution CT scanning augmented by planar reformations and three-dimensional surface reconstructions. A sophisticated computer-assisted radiologic imaging unit has been established to assist the surgeon and researcher. This marriage of advanced radiographic techniques, industrial computer-aided design technology, and clinical surgery have allowed us to better define aberrant anatomy, design new operative solutions for familiar as well as unusual problems, and quantitate changes of surgery and growth over time.

Adolescent↗
PubMed1986

Simulation in vitro of pulsatile vascular hemodynamics using a CAD/CAM-designed cam disc and roller follower.

An in vitro perfusion circuit is described that is capable of stimulating pulsatile peripheral vascular hemodynamics. A novel feature of its design is the incorporation of a computer-aided design and manufacture disc cam and roller follower for delivery of pulsatile hemodynamics. To date approximately 75 canine carotids have been perfused for periods of 2-24 h. The delivery of quantifiable hemodynamics in vitro via the rotation of a cam and roller follower has been found to be highly reliable on a cycle-to-cycle basis.

Animals↗
PubMed2006

Structural and computational characterization of the SHV-1 beta-lactamase-beta-lactamase inhibitor protein interface.

Beta-lactamase inhibitor protein (BLIP) binds a variety of class A beta-lactamases with affinities ranging from micromolar to picomolar. Whereas the TEM-1 and SHV-1 beta-lactamases are almost structurally identical, BLIP binds TEM-1 approximately 1000-fold tighter than SHV-1. Determining the underlying source of this affinity difference is important for understanding the molecular basis of beta-lactamase inhibition and mechanisms of protein-protein interface specificity and affinity. Here we present the 1.6A resolution crystal structure of SHV-1.BLIP. In addition, a point mutation was identified, SHV D104E, that increases SHV.BLIP binding affinity from micromolar to nanomolar. Comparison of the SHV-1.BLIP structure with the published TEM-1.BLIP structure suggests that the increased volume of Glu-104 stabilizes a key binding loop in the interface. Solution of the 1.8A SHV D104K.BLIP crystal structure identifies a novel conformation in which this binding loop is removed from the interface. Using these structural data, we evaluated the ability of EGAD, a program developed for computational protein design, to calculate changes in the stability of mutant beta-lactamase.BLIP complexes. Changes in binding affinity were calculated within an error of 1.6 kcal/mol of the experimental values for 112 mutations at the TEM-1.BLIP interface and within an error of 2.2 kcal/mol for 24 mutations at the SHV-1.BLIP interface. The reasonable success of EGAD in predicting changes in interface stability is a promising step toward understanding the stability of the beta-lactamase.BLIP complexes and computationally assisted design of tight binding BLIP variants.

Amino Acid Sequence↗
PubMed2002

[The computer aided-therapy system of tumor thermal-treatment instrument using HIFU technology].

Tumor thermal-treatment instrument is a newly developed medical instrument using HIFU technology. On the basis of a brief introduction of the system structure, this paper emphasizes the computer aided-therapy system applying a lot of computer technologies such as digital signal processing, digital signal communication computer aided design, artificial intelligence and database management system. Finally a concise therapy process using computer aided-therapy system is also introduced.

Artificial Intelligence↗