Biomedical subjects

M H van Putten

Publications and source records attributed to M H van Putten.

5 recordsLinked to original sources

PubMed2001

Proposed source of gravitational radiation from a torus around a black hole.

Long gamma-ray bursts (GRBs) could be emitted from rapidly spinning black-hole-torus systems, resulting from either hypernovae or black-hole-neutron-star coalescence. We show that a nonaxisymmetric torus may also radiate gravitational radiation, powered by the spin energy of the black hole. The coupling to the spin energy of the black hole operates by equivalence in poloidal topology to pulsar magnetospheres. Results calculated in the suspended-accretion state indicate that GRBs are potentially the most powerful LIGO/VIRGO burst sources in the Universe, with an expected duration of 10-15 s on a horizontal branch of 1-2 kHz in the f(f) diagram.

Journal Article↗

PubMed2000

Electron-positron outflow from black holes.

Cosmological gamma-ray bursts (GRBs) appear as the brightest transient phenomena in the Universe. The nature of their central engine is a missing link in the theory of fireballs to stellar mass progenitors, and may be associated with low mass black holes. In contact with an external magnetic field B, black hole spin produces a gravitational potential on the wave function of charged particles. We show that a rapidly rotating black hole of mass M produces outflow from initially electrostatic equilibrium with normalized isotropic emission approximately 10(48)(B/B(c))(2)(M/7M)(2)sin (2) theta erg/s, where B(c) = 4.4x10(13) G. The half-opening angle satisfies theta >or = square root[B(c)/3B]. The outflow proposed as input to GRB fireball models.

Astronomical Phenomena↗

PubMed1997

A silicon bidirectional flow sensor for measuring respiratory flow.

We describe a solid-state, silicon integrated, bidirectional flow sensor for respiratory applications. The sensor is a thermal vector sensor. The electronic circuitry for obtaining bidirectional sensitivity is presented together with actual application to a healthy volunteer put on mechanical ventilation. The sensor's input flow range is from -60 to +60 L/min, and its rise-time is < or = 40 ms and fall-time is < or = 60 ms. The effect of changes in gas composition as used in mechanically ventilated patients on the sensor output signal are estimated to be less than 2%. The temperature sensitivity is about -1.5% per degree Celsius.

Equipment Design↗

PubMed1989

A quasi-static model for the ring capacitor applicator.

The electromagnetic heat dissipation in a radially layered biological tissue inside a ring capacitor (RC) applicator has been investigated. A quasi-static model is introduced to compute the relevant electromagnetic field quantities. The method of computation employs the spatial Fourier transform of all field quantities with respect to the axial coordinate. After an iterative solution of a dual boundary value problem for the electric potential and the current density at the electrodes, an inverse Fourier transform is carried out to compute the quantities that are of interest to the deep-body system at hand. Comparison of numerical results with phantom measurements shows excellent agreement.

Electric Conductivity↗

PubMedDate not supplied

A three-dimensional model for the 'coaxial TEM' deep-body hyperthermia applicator.

A rigorous three-dimensional electromagnetic model predicting the complete field distribution in the space interior to the 'coaxial TEM' applicator is presented. The applicator consists of a radiating ring aperture, with a given electric-field distribution in the wall of a hollow circular cylinder. The method of calculation employs the spatial Fourier transform of all field quantities with respect to the axial co-ordinate, after which the field equations are solved in the spectral domain. Subsequently, an inverse Fourier transform is carried out to compute the quantities that are of interest to the optimum clinical deep-body hyperthermia system. Numerical results for a number of representative applicator configurations are given. The present results are compared with the ones that are obtained by a model based on the far-field approximation of a distribution of dipole sources located in the ring aperture.

Humans↗