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I Ardelean

Publications and source records attributed to I Ardelean.

15 recordsLinked to original sources
PubMed2001

Diffusion measurements with the aid of nutation spin echoes appearing after two inhomogeneous radiofrequency pulses in inhomogeneous magnetic fields.

Nutation echoes are generated by radiofrequency (RF) pulses with an inhomogeneous amplitude, B(1) = B(1)(r), in inhomogeneous magnetic fields, B(0) = B(0)(r). The two gradients of strengths G(1) and G(0), respectively, must be aligned in parallel for a maximum echo signal. After two RF pulses, two echoes appear at times tau(a) = 2 tau(1) + tau(2) + (G(1)/G(0))tau(1) and tau(b) = 2 tau(1) + tau(2) + 2(G(1)/G(0))tau(1), where tau(1) is the RF pulse duration and tau(2) the interpulse interval. It is shown that these echoes can favorably be employed for the determination of self-diffusion coefficients even in the poor experimental situation one often faces in low-resolution or low-field NMR. The signal intensity is comparable to that of ordinary Hahn echoes. Diffusion coefficients and spin-lattice relaxation times can be evaluated from the same experimental data set if both nutation echoes are recorded. Test experiments are in good agreement with literature data. Applications of the technique to "inside out" NMR, well logging NMR, surface coil NMR, toroid cavity NMR, etc., are suggested.

Journal Article↗
PubMed2000

Diffusion measurements using the nonlinear stimulated echo.

The nonlinear stimulated echo that is generated by a sequence of three radiofrequency pulses, 90 degrees-tau(1)-90 degrees-tau(2)-45 degrees, in high magnetic fields (or at low temperatures) in the presence of pulsed or steady field gradients can be applied for measurements of the diffusion coefficient. Corresponding test experiments are reported. Steady gradients can be used without knowledge of the relaxation times. Remarkably the attenuation of the nonlinear stimulated echo by diffusion is substantially stronger than in the case of the ordinary stimulated echo.

Diffusion↗
PubMed2000

Two-pulse nutation echoes generated by gradients of the radiofrequency amplitude and of the main magnetic field.

A two-pulse NMR nutation spectroscopy scheme is suggested that leads to a new type of spin echoes. The amplitude of the radiofrequency (RF) pulses as well as the external magnetic field are assumed to be subject to gradients G(1) and G(0), respectively, in the same but otherwise arbitrary direction. Multiple echoes are predicted and observed at times k(G(1)/G(0))tau(1) and tau -/+ k(G(1)/G(0))tau(1) (k = 1, 2, 3, ...) after the second RF pulse, where tau(1) represents the radiofrequency pulse duration, and tau is the spacing of the RF pulses. Based on these echoes, a method for diffusion measurements is proposed that simultaneously provides the spin-lattice relaxation time and the self-diffusion coefficient.

Diffusion↗
PubMed2000

The nutation spin echo and its use for localized NMR

A suitably matched combination of unidirectional gradient pulses of the radio frequency amplitude B(1) and of the main magnetic field B(0) produces an unconventional type of spin echo, the nutation echo. The echo signal becomes volume selective if the gradients to be matched are inhomogeneously distributed in space. An example is a combination of a constant B(0) gradient and the inhomogeneous B(1) gradient of a surface coil. We suggest a method for localized NMR on this basis. Nutation echoes can also be used to map the spatial distribution of B(1) gradients of an arbitrary radio frequency coil geometry with the aid of a small probe sample. Copyright 2000 Academic Press.

Journal Article↗
PubMed1997

Multiple nonlinear stimulated echoes.

Three-pulse sequences in the presence of magnetic field gradients at high magnetic fields produce multiple nonlinear stimulated echoes (NOSE) at times ntau1 after the third pulse, where n is an integer and tau1 the interval between the first two pulses. These phenomena are due to the demagnetizing field produced by the spatial modulation of the nuclear magnetization arising in the sample after the first two pulses. The theory is presented and compared with experiments. The dependence of the NOSE amplitudes on the flip angles and on the pulse intervals is described. Implications for multidimensional NMR experiments based on sequences of three or more pulses in the presence of field gradients are discussed.

Dimethylpolysiloxanes↗
PubMedDate not supplied

Biomechanical interpretations of some bony structures in the skull.

For the causal understanding of some evolutive morphological particularities at the level of the lateral wall of orbits (in mammals and in man), the authors have resorted to biomechanical interpretations of bony structures at the cranium level. To this effect some stress factors as well as the modeling effect on the local bone morphogenesis have been analysed.

Animals↗
PubMedDate not supplied

Bioelectrical conversion in sensors with living cells.

Bacterial metabolism can drive various processes with biotechnological significance, like in the case of biosensors for probing organic compounds, or in biofuel cells. Here we present some of our results connected with the construction of a bacterial electrode with Pseudomonas sp. for probing glucose in body fluids, and those related to biofuel cells with anaerobic bacteria (Clostridium sp.). The output of the bioselective electrode linearly indicates glucose concentrations in the 2.5 x 10(-5)-1.25 x 10(-4) M domain, with a sensitivity limit of 10(-5) M. The time constant is 10 min, and it works for more than ten days. The amperometric response of biofuel cells with Clostridium sp. offers the electrical image of the state of the bacterial culture itself, thus being a promising tool for the automated control of the bacterial suspensions used in fermentative reactors.

Biosensing Techniques↗