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Results for “Inverse design”

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At least 55 records · Page 3Linked to original sources
PubMed2000

Discussing the capabilities of Laplacian Minimization.

This paper discusses the properties and capabilities of linear inverse solutions to the neuroelectromagnetic inverse problem obtained under the assumption of smoothness (Laplacian Minimization). Simple simulated counterexamples using smooth current distributions as well as single or multiple active dipoles are presented to refute some properties attributed to a particular implementation of the Laplacian Minimization coined LORETA. The problem of the selection of the test sources to be used in the evaluation is addressed and it is demonstrated that single dipoles are far from being the worst test case for a smooth solution as generally believed. The simulations confirm that the dipole localization error cannot constitute the tool to evaluate distributed inverse solutions designed to deal with multiple sources and that the necessary condition for the correct performance of an inverse is the adequate characterization of the source space, i.e., the characterization of the properties of the actual generators.

Brain Mapping↗
PubMed2001

The efficacy of adjusting the ankle in the treatment of subacute and chronic grade I and grade II ankle inversion sprains.

OBJECTIVE: The purpose of this study was to determine the efficacy of adjusting the ankle in the treatment of subacute and chronic grade I and grade II ankle inversion sprains. DESIGN: A single-blind, comparative, controlled pilot study. SETTING: Technikon Natal Chiropractic Day Clinic. PARTICIPANTS: Thirty patients with subacute and chronic grade I and grade II ankle inversion sprains. Patients were recruited from the public; they responded to advertisements placed in newspapers and on notice boards around the campus and local sports clubs. INTERVENTION: Each of the 15 patients in the treatment group received the ankle mortise separation adjustment. Each of the 15 patients in the placebo group received 5 minutes of detuned ultrasound treatment. Each participant received a maximum of 8 treatment sessions spread over a period of 4 weeks. MAIN OUTCOME MEASURE: Patients were evaluated at the first treatment, at the final treatment, and at a 1-month follow-up consultation. Subjective scores were obtained by means of the short-form McGill Pain Questionnaire and the Numerical Pain Rating Scale 101. Objective measurements were obtained from goniometer readings measuring ankle dorsiflexion range of motion and algometer readings measuring pain threshold over the ankle lateral ligaments. A functional evaluation of ankle function was also used. RESULTS: Although both groups showed improvement, statistically significant differences in favor of the adjustment group were noted with respect to reduction in pain, increased ankle range of motion, and ankle function. CONCLUSIONS: This study appears to indicate that the mortise separation adjustment may be superior to detuned ultrasound therapy in the management of subacute and chronic grade I and grade II inversion ankle sprains.

Adolescent↗
PubMedDate not supplied

Stochastic error whitening algorithm for linear filter estimation with noisy data.

Mean squared error (MSE) has been the most widely used tool to solve the linear filter estimation or system identification problem. However, MSE gives biased results when the input signals are noisy. This paper presents a novel stochastic gradient algorithm based on the recently proposed error whitening criterion (EWC) to tackle the problem of linear filter estimation in the presence of additive white disturbances. We will briefly motivate the theory behind the new criterion and derive an online stochastic gradient algorithm. Convergence proof of the stochastic gradient algorithm is derived making mild assumptions. Further, we will propose some extensions to the stochastic gradient algorithm to ensure faster, step-size independent convergence. We will perform extensive simulations and compare the results with MSE as well as total-least squares in a parameter estimation problem. The stochastic EWC algorithm has many potential applications. We will use this in designing robust inverse controllers with noisy data.

Algorithms↗
PubMed2006

Sampling design for the World Health Survey in Brazil.

This paper describes the sample design used in the Brazilian application of the World Health Survey. The sample was selected in three stages. First, the census tracts were allocated in six strata defined by their urban/rural situation and population groups of the municipalities (counties). The tracts were selected using probabilities proportional to the respective number of households. In the second stage, households were selected with equiprobability using an inverse sample design to ensure 20 households interviewed per tract. In the last stage, one adult (18 years or older) per household was selected with equiprobability to answer the majority of the questionnaire. Sample weights were based on the inverse of the inclusion probabilities in the sample. To reduce bias in regional estimates, a household weighting calibration procedure was used to reduce sample bias in relation to income, sex, and age group.

Adult↗
PubMed2000

Inverse planning incorporating organ motion.

Accurate targeting is important in intensity-modulated radiation therapy (IMRT). The positional uncertainties of structures with respect to the external beams arise in part from random organ motion and patient setup errors. While it is important to improve immobilization and reduce the influence of organ motion, the residual effects should be included in the IMRT plan design. Current inverse planning algorithms follow the conventional approach and include uncertainties by assuming population-based margins to the target and sensitive structures. Margin around a structure represents a "hard boundary" and the fact that a structure has a spatial probability distribution has been completely ignored. With increasing understanding of spatial uncertainties of structures and the technical capability of fine-tuning the dose distribution on an individual beamlet level in IMRT, it seems timely and important to fully utilize the information in the planning process. This will reduce the "effective" margins of the structures and facilitate dose escalation. Instead of specifying a "hard margin," we describe an inverse planning algorithm which takes into consideration positional uncertainty in terms of spatial probability distribution. The algorithm was demonstrated by assuming that the random organ motion can be represented by a three-dimensional Gaussian distribution function. Other probability distributions can be dealt with similarly. In particular, the commonly used "hard margin" is a special case of the current approach with a uniform probability distribution within a specified range. The algorithm was applied to plan treatment for a prostate case and a pancreatic case. The results were compared with those obtained by adding a margin to the clinical target volume. Better sparing of the sensitive structures were obtained in both cases using the proposed method for approximately the same target coverage.

Algorithms↗
PubMed2005

An inverse methodology for high-frequency RF coil design for MRI with de-emphasized B1 fields.

An inverse methodology for the design of biologically loaded radio-frequency (RF) coils for magnetic resonance imaging applications is described. Free space time-harmonic electromagnetic Green's functions and de-emphasized B1 target fields are used to calculate the current density on the coil cylinder. In theory, with the B1 field de-emphasized in the middle of the RF transverse plane, the calculated current distribution can generate an internal magnetic field that can reduce the central overemphasis effect caused by field/tissue interactions at high frequencies. The current distribution of a head coil operating at 4 T (170 MHz) is calculated using an inverse methodology with de-emphasized B1 target fields. An in-house finite-difference time-domain routine is employed to evaluate B1 field and signal intensity inside a homogenous cylindrical phantom and then a complete human head model. A comparison with a conventional RF birdcage coil is carried out and demonstrates that this method can help in decreasing the normal bright region caused by field/tissue interactions in head images at 170 MHz and higher field strengths.

Brain↗
PubMed2005

[Cloning and analysis of the complete genome of a Goose circovirus from Yongkang Zhejiang].

To investigate the mechanism of avian influenza outbreak wildly in water fowls, the co-pathogens, especially that caused immuno-depression were studied. A pair of degenerated primers, which amplified a fragment of 552bp in length, was designed and synthesized based on the published goose and other Circovirus sequences. The specific PCR product was amplified from the goose sample of Yongkang avian influenza case of Zhejiang Province. The fragment was then sequenced and the result showed the existence of the GoCV. The opposite part of the genome was further amplified using inverse primers designed based on the 552bp sequence obtained and the 1821bp full length genomic sequence of GoCV-yk01 was compiled using Seqman program of DNAStar. Sequence analysis showed that the GoCV-yk01 possessed common features of circovirus included potential replication associated stem-loop structure and the Rep protein motifs. Homology analysis showed that the sequence of GoCV-yk01 had 91% approximately 93% similarity to that of Taiwan and Germany strains. Phylogenetic analysis with ClustalW, however, showed that the GoCV-yk01 was on a different branch away from Taiwan and Germany strains. Circovirus usually causes immuno-depression and results in secondary infection, as it infects rapid growing cells as lymphocyte. It is speculated that the infection of GoCV may be a part of the reason of the avian influenza outbreak of the Yongkang case. The GoCV-yk01 is the first GoCV strain reported in mainland of China.

Animals↗
PubMed2006

Searching for alloy configurations with target physical properties: impurity design via a genetic algorithm inverse band structure approach.

The ability to artificially grow different configurations of semiconductor alloys--random structures, spontaneously ordered and layered superlattices--raises the issue of how different alloy configurations may lead to new and different alloy physical properties. We address this question in the context of nitrogen impurities in GaP, which form deep levels in the gap whose energy and optical absorption sensitively depend on configuration. We use the "inverse band structure" approach in which we first specify a desired target physical property (such as the deepest nitrogen level, or lowest strain configuration), and then we search, via genetic algorithm, for the alloy atomic configurations that have this property. We discover the essential structural motifs leading to such target properties. This strategy opens the way to efficient alloy design.

Journal Article↗
PubMed2004

Effects of perfluorooctane sulfonate and perfluorooctanoic acid on the zooplanktonic community.

This comparative survey summarizes six individual studies on the ecological effects of two common perfluorinated surfactants, PFOS and PFOA, on zooplankton. We compare the test designs and quantify the relative sensitivity and statistical power (1-beta > or = 0.8). The survey compares 30-L indoor microcosm to 12,000-L outdoor microcosm experiments, with 225-mL single species laboratory tests as reference. By this we elucidate the extrapolation of ecological effects in space and complexity. Generally, zooplankton had lower tolerance toward PFOS than toward PFOA. With increasing concentrations the zooplankton community became simplified toward more robust rotifer species, which, as an indirect effect, increased their abundance due to a shift in competition and predation. The statistical power of the designs exhibits inverse proportionality between complexity and realism, indoor microcosm>outdoor microcosm. Surprisingly, the 30-L study had a lower LOEC value for Daphnia magna than the laboratory chronic test, indicating that D. magna and D. pulicaria were not the most sensitive species and that laboratory tests are not always conservative relative to microcosm experiments. Food scarcity due to phytotoxicity was not the reason for the difference.

Alkanesulfonic Acids↗
PubMed2001

Broadband proton decoupling for in vivo brain spectroscopy in humans.

A new decoupling sequence, PBAR, is described for broadband heteronuclear decoupling in vivo in humans at 1.5T. The sequence uses non-adiabatic, frequency- and amplitude-modulated inversion pulses designed to minimize decoupling sidebands at low applied gammaB(2) RF field levels and to cover only the narrow range of resonance offsets encountered in practice. The offset dependence of the decoupling efficiency of PBAR is demonstrated and compared to the conventional WALTZ-4 sequence. At the same average power levels, PBAR had slightly reduced bandwidth but significantly less intense decoupling sidebands. Applications of PBAR are shown in vivo in the human brain both for (31)P and natural abundance (13)C spectroscopy using volume decoupling coils. The PBAR sequence allows whole brain [(1)H]-[13]C decoupling to be performed at 1.5T with a standard head coil within FDA guidelines for RF power deposition. Magn Reson Med 45:226-232, 2001.

Brain Chemistry↗
PubMed1986

Respiration-related neurons in the medial nuclear complex of the solitary tract of the cat.

Respiration-related (RR) neuronal activity was systematically searched for in the nuclear complex of the solitary tract (nTS) with special interest focused on regions located medially to the ventrolateral subnucleus (vlnTS) which is widely considered to be the anatomical location of the dorsal respiratory group (DRG). The experiments were carried out on cats under pentobarbitone anaesthesia, paralyzed and artificially ventilated. RR activity was recorded consistently not only in the vlnTS, but also in more medial regions. R alpha-type neurons were often encountered in ventral and medial aspects of the nTS. R beta-type neurons and expiration-related neurons were found also in ventral regions of the nTS. A small number of 'late onset' and 'early burst' inspiration-related neurons was found respectively in ventral and ventromedial regions of the nTS. The activity of neurons presenting a rhythmic pattern completely determined by lung volume changes due to the respirator was consistently recorded both in ventral and medial areas of the nTS. Most of these neurons were excited by lung inflation and displayed a discharge pattern characteristic of P-neurons. A few neurons, designated as 'inverse' P-neurons displayed an opposite behaviour, being inhibited by lung inflation. The results are consistent with both histological and neurophysiological studies showing that pulmonary stretch receptor afferents terminate also on the medial side of the solitary tract. It is suggested that the DRG is not restricted to the vlnTS, but comprises also neurons located in more medial regions of the nTS.

Animals↗
PubMed2004

A structural basis for constitutive activity in the human CAR/RXRalpha heterodimer.

The X-ray crystal structure of the human constitutive androstane receptor (CAR, NR1I3)/retinoid X receptor alpha (RXRalpha, NR2B1) heterodimer sheds light on the mechanism of ligand-independent activation of transcription by nuclear receptors. CAR contains a single-turn Helix X that restricts the conformational freedom of the C-terminal AF2 helix, favoring the active state of the receptor. Helix X and AF2 sit atop four amino acids that shield the CAR ligand binding pocket. A fatty acid ligand was identified in the RXRalpha binding pocket. The endogenous RXRalpha ligand, combined with stabilizing interactions from the heterodimer interface, served to hold RXRalpha in an active conformation. The structure suggests that upon translocation, CAR/RXRalpha heterodimers are preorganized in an active conformation in cells such that they can regulate transcription of target genes. Insights into the molecular basis of CAR constitutive activity can be exploited in the design of inverse agonists as drugs for treatment of obesity.

Binding Sites↗
PubMed1997

Planning, delivery, and quality assurance of intensity-modulated radiotherapy using dynamic multileaf collimator: a strategy for large-scale implementation for the treatment of carcinoma of the prostate.

PURPOSE: To improve the local control of patients with adenocarcinoma of the prostate we have implemented intensity modulated radiation therapy (IMRT) to deliver a prescribed dose of 81 Gy. This method is based on inverse planning and the use of dynamic multileaf collimators (DMLC). Because IMRT is a new modality, a major emphasis was on the quality assurance of each component of the process and on patient safety. In this article we describe in detail our procedures and quality assurance program. METHODS AND MATERIALS: Using an inverse algorithm, we have developed a treatment plan consisting five intensity-modulated (IM) photon fields that are delivered with DMLC. In the planning stage, the planner specifies the number of beams and their directions, and the desired doses for the target, the normal organs and the "overlap" regions. Then, the inverse algorithm designs intensity profiles that best meet the specified criteria. A second algorithm determines the leaf motion that would produce the designed intensity pattern and produces a DMLC file as input to the MLC control computer. Our quality assurance program for the planning and treatment delivery process includes the following components: 1) verification of the DMLC field boundary on localization port film, 2) verification that the leaf motion of the DMLC file produces the planned dose distribution (with an independent calculation), 3) comparison of dose distribution produced by DMLC in a flat phantom with that calculated by the treatment planning computer for the same experimental condition, 4) comparison of the planned leaf motions with that implemented for the treatment (as recorded on the MLC log files), 5) confirmation of the initial and final positions of the MLC for each field by a record-and-verify system, and 6) in vivo dose measurements. RESULTS: Using a five-field IMRT plan we have customized dose distribution to conform to and deliver 81 Gy to the PTV. In addition, in the overlap regions between the PTV and the rectum, and between the PTV and the bladder, the dose is kept within the tolerance of the respective organs. Our QA checks show acceptable agreement between the planned and the implemented leaf motions. Correspondingly, film and TLD dosimetry indicates that doses delivered agrees with the planned dose to within 2%. As of September 15, 1996, we have treated eight patients to 81 Gy with IMRT. CONCLUSION: For complex planning problems where the surrounding normal tissues place severe constraints on the prescription dose, IMRT provides a powerful and efficient solution. Given a comprehensive and rigorous quality-assurance program, the intensity-modulated fields can be efficaciously and accurately delivered using DMLC. IMRT treatment is now ready for routine implementation on a large scale in our clinic.

Adenocarcinoma↗
PubMed1998

Modeling human eye aberrations and their compensation for high-resolution retinal imaging.

We introduced a mathematical eye model using Gullstrand's six-surface eye model modified by clinically measured aspherical data to study human eye aberrations and their compensation for high-resolution retinal imaging. Ray tracing was used to characterize aberrations and point spread functions (PSFs) of the eye model. By using the Zernike polynomial decomposition of the calculated pupil function, we quantified the wavefront aberrations. Based on calculated PSFs, we designed optical inverse filters to reduce the aberrations for a large pupil size and improve the resolution. Spherical aberration and oblique astigmatism were found to be in good agreement with published experimental measurements. Spherical aberration and defocus were the most significant aberrations for on-axis imaging, whereas oblique astigmatism and coma combined with spherical aberration and defocus were most significant for off-axis imaging. The best retinal image resolution occurred at 2- to 3-mm pupil diameter. After aberration correction for an 8-mm diameter pupil, the resolutions for on-axis or 9 degrees off-axis imaging points were very close to diffraction-limited resolutions. Over a limited field of view (FOV), retinal image resolution of the eye model can be greatly improved by aberration correction using aspheric and astigmatic lenses. For imaging large FOVs, space-variant compensation techniques will be required for aberration correction.

Astigmatism↗
PubMed2006

Waveform design for ultrasonic pulse-inversion fundamental imaging.

Pulse-inversion (PI) fundamental imaging exhibits significantly better contrast detection than linear and second-harmonic imaging. PI fundamental imaging involves two firings with inverted waveforms. When the returning echoes from the two firings are summed, the residual signal related to tissue is limited to even-order harmonics, whereas for microbubbles, the fundamental signal is not completely canceled due to the echo under compression differing from that under rarefaction. The efficacy of PI fundamental imaging has been reported previously. In this study, we investigated the performance of PI fundamental imaging using both simulations and in vitro experiments with various transmit waveforms, including coded excitation and asymmetrical waveforms (i.e., asymmetrical between compression and rarefaction). For coded excitation, a longer waveform was found to increase the similarity in the responses to positive and negative pulses, thus lowering the contrast between microbubbles and tissue. In addition, imperfect pulse compression also decreases the contrast because it increases the residue fundamental signal emanating from tissue. Using asymmetrical waveforms noticeably increased the residual microbubble signal in the fundamental band but the nonzero DC component that is inherent in such waveforms also increases the tissue fundamental signal. The combination of these two effects decreases the contrast. From these results, it is concluded that the use of coded excitation is undesirable in PI fundamental imaging and that the waveforms should contain no DC component. Furthermore, the transmit waveform needs to be appropriately windowed in order to reduce spectral leakage. Therefore, a Gaussian pulse with the pulse length determined by the signal-to-noise ratio of the imaging system is generally optimal for PI fundamental imaging.

Artifacts↗
PubMed2000

Efficient inverse scattering algorithm for the design of grating-assisted codirectional mode couplers

An efficient method for the design of optical devices based on codirectional grating-assisted mode coupling is presented. A low-complexity algorithm is developed to calculate the coupling function of a grating that accurately matches an arbitrarily given target spectral response. The method relies on the synthesis of the grating impulse response by means of an exact differential layer-peeling algorithm.

Journal Article↗
PubMed1992

[Lefort 1 osteotomy. The proposal of an outline modification].

A modified outline of Lefort 1 osteotomy using an "inverse step" design is proposed which ensures simple and effective down-fracture and pterygo-maxillary separation. Osteosynthesis of the mobilized fragment is facilitated due to the improved contact of bone surfaces, particularly laterally. Combined rigid and supple osteosyntheses allow some degree of post-operative adjustment.

Bone Transplantation↗
PubMed1994

A pattern-analysis methodology for esophageal motility records.

The features of the esophageal contractile activity recorded during swallowing have been investigated using a signal-processing approach. Data of a 10 min recording taken from 10 normal subjects have been examined. The final features of each peristaltic wave are a set of parameters comprising the locations and magnitudes of the local wavelets contributing to the peristaltic. The approach is based on an inverse filtering technique. The inverse filter, designed with a knowledge of an average peristaltic profile formed by coherent averaging of many peristaltic examples aligned to their maxima, is used to refine the process of locating the local wavelets. It is shown that the inferred wavelet structure offers a good basis for modelling the different peristaltics, and that it suggests new parameters for esophageal characterization and classification procedures.

Deglutition↗