Biomedical subjects

Ramón Abascal

Publications and source records attributed to Ramón Abascal.

4 recordsLinked to original sources

PubMed2005

Ultrasonic guided wave scattering in a plate overlap.

Guided wave scattering in a plate overlap is investigated by numerical calculations and experimental measurements of transmission and reflection factors from the overlap region. In the numerical study, a hybrid boundary element-finite element method is used to calculate the guided wave scattered field from the overlap region. Transmission and reflection factors are calculated for incident A0 and S0 Lamb and n0 shear horizontal waves, including higher modes generated through mode conversion phenomena. In addition, parametric studies of transmission and reflection factors in this problem are performed numerically over various incident modes, frequencies, and overlap lengths. For verification and comparison with numerical results, experiments were conducted to measure the transmission and reflection factors for incident Lamb and shear horizontal waves in steel plates with two different overlap areas. The experimental results agree well with the numerical calculations. The numerical and experimental results show that it is highly feasible to carry out efficient Lamb wave nondestructive evaluation (NDE) in overlapped plates and in multilayer structures with various lap joints by selecting various modes and tuning frequency.

Journal Article↗

PubMed2005

Lamb mode conversion at edges. A hybrid boundary element-finite-element solution.

Two general and flexible numerical techniques based on the finite-element and boundary element methods developed by the authors in a previous paper are applied to study Lamb wave propagation in multilayered plates and Lamb mode conversion at free edges for frequencies beyond the first cutoff frequency. Both techniques are supported by a meshing criterion which guarantees the accuracy of the results when a condition is fulfilled. A finite-element formulation is directly applicable to study Lamb wave propagation and reflection by simple obstacles such as a flat edge. In order to tackle Lamb wave diffraction problems by defects with more complex geometries, a hybrid boundary element-finite-element formulation is used. This technique provides a major improvement with respect to the only previous boundary element application on Lamb waves: the connecting boundary might be placed as close to the reflector as desired, reducing greatly the requirement on mesh size. Two main application problems on practical metallic plates are studied and compared with reported numerical, theoretical, and experimental results: (1) Lamb wave propagation in degraded titanium diffusion bonds, and (2) Lamb mode conversion at inclined or perpendicular free edges of steel plates for frequencies beyond the first cutoff frequency.

Journal Article↗

PubMed2005

[I125 low dose rate brachytherapy in localized prostate cancer. Preliminary results after 5 years].

OBJECTIVES: Prostatic brachytherapy by permanent implant of I125 or Pd103 is a therapeutic option in the treatment of organ confined prostate cancer We analyze preliminary results and complications after five years in the group of patients who received I125 low dose rate brachytherapy as the only intention-to-cure treatment and evaluate the differences with the standard treatment (surgery). METHODS: From a case series of more than 400 patients treated with brachytherapy as radical intention-to-cure monotherapy for organ-confined prostate cancer we excluded patients with less than 12 months of follow-up for statistical analysis; the study group includes 275 patients enrolled between april 1999 and December 2003. Mean follow-up is 31 months (12-68). Biochemical failure was defined in accordance to the ASTRO criteria. Statistical survival analysis was carried out with the SPSS statistical software using the Kaplan Meyer method. Urinary and gastrointestinal complications were evaluated in accordance to the RTOG criteria. RESULTS: Mean age was 68 years (range 49-83 years). 93% of the patients presented a clinical stage < or ='3dT2a and 7% T2b, with 60 8% of the cases having a PSA < or ='3d 10 ng/ml. Gleason score was < or ='3d 6 in 94% of the cases. 9% of the cases had a prostate volume > 50 cc. Overall 5 year survival was 96%, with a 97% disease-free survival and a 99% biochemical failure-free survival. Figure 3 and tables II-VI summarize the complications in various series including this. CONCLUSIONS: Multiple published series seem to show similar results on biochemical control of the disease when comparing surgery and low dose rate brachytherapy in organ-confined disease. In comparison to surgery, brachytherapy has the advantage of having a lower percentage of immediate postoperative complications, lower incontinence rate, and a higher number of patients preserving erectile function.

Adenocarcinoma↗

PubMed2004

Remote characterization of defects in plates with viscoelastic coatings using guided waves.

The remote inspection for defects in large metallic elements such as pipes, tubes and plates is a field where guided waves are being applied with success. There are a number of situations where a surface coating is added for corrosion protection or insulation purposes. Since the coating materials are usually viscoelastic, the guided wave inspection range may be severely reduced unless a proper mode and an adequate frequency range is selected. Previous authors found the existence of low-attenuated modes at certain frequency ranges, which were used to detect and locate defects at reasonably large distances. This paper studies the potential of guided waves for not only locating but also sizing defects in plates with viscoelastic coatings. A hybrid finite element-boundary element method which explicitly includes the attenuating characteristics of the coating is used to determine Lamb and SH mode conversion factors at corrosion defects under the coating. Through parametric studies and analysis of the numerical results, some trends and features are highlighted that could be used for sizing purposes.

Journal Article↗