Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Computational methods”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,063 records · Page 59Linked to original sources
PubMed2004

Method for computing the three-dimensional capacity dimension from two-dimensional projections of fractal aggregates.

The current theory of projections of fractals is considered in this paper with application to fractal aggregates. In particular, this theory does not accurately enable the computation of the capacity dimension of three-dimensional aggregates from the capacity dimension of their two-dimensional projections. Herein we propose to compute the three-dimensional capacity dimension from the perimeter-based fractal dimension, using a semiempirical equation, an approach not applied earlier.

Journal Article↗
PubMedDate not supplied

A new method of computing spin-lattice relaxation maps in magnetic resonance imaging using fast scanning protocols.

A new algorithm to compute spin-lattice relaxation (T1) maps in magnetic resonance imaging (MRI) by using fast imaging protocols and monitoring the magnetization evolution towards a steady state is proposed. This algorithm uses a general least-squares fit to multiple point experimental data and is thus much more precise than the standard two-point fit. Since this imaging protocol is designed to consume time comparable to that of standard clinical protocols, it has an advantage in comparison to traditional multiple point protocols, which require considerably longer scanning times. In addition to T1 maps the protocol can generate final images suitable for clinical diagnosis. Thus it is possible to generate relaxation data without considerably lengthening the total required MRI study time. The results of phantom testing of this protocol are reported.

Algorithms↗
PubMed2002

Approximating the head-related transfer function using simple geometric models of the head and torso.

The head-related transfer function (HRTF) for distant sources is a complicated function of azimuth, elevation and frequency. This paper presents simple geometric models of the head and torso that provide insight into its low-frequency behavior, especially at low elevations. The head-and-torso models are obtained by adding both spherical and ellipsoidal models of the torso to a classical spherical-head model. Two different numerical techniques--multipole reexpansion and boundary element methods--are used to compute the HRTF of the models in both the frequency domain and the time domain. These computed HRTFs quantify the characteristics of elevation-dependent torso reflections for sources above the torso-shadow cone, and reveal the qualitatively different effects of torso shadow for sources within the torso-shadow cone. These effects include a torso bright spot that is prominent for the spherical torso, and significant attenuation of frequencies above 1 kHz in a range of elevations. Both torso reflections and torso shadow provide potentially significant elevation cues. Comparisons of the model HRTF with acoustic measurements in the horizontal, median, and frontal planes confirm the basic validity of the computational methods and establish that the geometric models provide good approximations of the HRTF for the KEMAR mannequin with its pinnae removed.

Acoustics↗
PubMed1978

Method for computing motion in a two-dimensional cochlear model.

We describe an effective technique for computing the steady-state motion in a two-dimensional cochlear model. With the cochlear fluid assumed incompressible and inviscid, the problem reduces to solving Laplace's equation for a region with a yielding boundary (corresponding to the basilar membrane). From an integral equation representation of this solution, a pair of second-order differential equations is derived. The solution of these differential equations gives the velocity of the basilar membrane and hence other related quantities, e.g., displacement, pressure, driving-point impedance at the stapes. Higher-order approximations, as well as extensions to nonlinear membranes are discussed.

Acoustic Stimulation↗