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- Boström, Anders E, 1951, et al.
(författare)
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Scattering of elastic waves by a rectangular crack in an anisotropic half-space
- 2003
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Ingår i: Wave Motion. - 0165-2125. ; 38, s. 91-107
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Tidskriftsartikel (refereegranskat)abstract
- The scattering of elastic waves by a rectangular crack in a half-space of arbitrary anisotropy is considered. The application in mind is ultrasonic testing of thick-walled anisotropic components where the crack is close to a planar back surface. The orientation of the crack and the back surface may be arbitrary relative the anisotropy. The scattering problem is formulated as hypersingular integral equation for the crack-opening-displacement (COD) by means of a half-spce Green's tensor. The integral equation is solved by expanding the COD in a double series of Chebyshev functions with the correct behavior along the crack's edges. Insertion inte the integral equation and projection onto the same set of functions result in a linear system of equations for the expansion coefficients appearing in the representation of the COD. The transmitting transducer is modeled by the traction beneath it on the scanning surface and the incident field may then be calculated. An electromechanical reciprocity relation is used to model the receiving transducer. Numerical examples are included which show the influence of the anisotropy and espcially the prexence of a nearby planar back surface.
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| 3. |
- Diligent, O, et al.
(författare)
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The low-frequency reflection and scattering of the S0 Lamb mode from a circular through-thickness hole in a plate: Finite Element, analytical and experimental studies
- 2002
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 1520-8524 .- 0001-4966. ; 112:6, s. 2589-2601
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Tidskriftsartikel (refereegranskat)abstract
- A study of the interaction of the S0 Lamb wave with a circular through-thickness hole in a plate is presented. The study is limited to the nondispersive frequency range of this wave, in which the distributions of stress and displacement are simple. This allows a Finite Element analysis to be undertaken using a two-dimensional membrane discretization. Predictions of the direct reflection of the S0 mode and the lateral scattering of the SH0 mode are made for a range of diameters of the hole. At the same time, an analytical solution based on modal superposition is developed, and this is also used to predict the reflection and scattering coefficients. Both sets of predictions are validated by experimental measurements. It is found that the trends of the reflection coefficients for different hole diameters, frequencies and distances from the hole satisfy a simple normalization. On a detailed scale, the functions exhibit undulations which are shown to result from the interference of the direct reflection with secondary reflections which arrive slightly later.
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| 4. |
- Franzén, Thomas, 1955-, et al.
(författare)
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Prospective evaluation of laparoscopic and open 360o fundoplication in mild and severe gastro-oesophageal reflux disease
- 2002
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Ingår i: European Journal of Surgery. - 1102-4151 .- 1741-9271. ; 168:10, s. 539-545
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE:To investigate the relationship between five-year control of reflux and early postoperative oesophageal function after total fundoplication done either laparoscopically or through a laparotomy in severe and mild reflux disease.DESIGN:Prospective open study.SETTING:University hospital, Sweden.PATIENTS:In the group with severe disease 9 patients had a laparotomy and 7 laparoscopy. The corresponding figures for the group with mild disease were 21 and 34 respectively.RESULTS:The increase in lower oesophageal sphincter pressure 6 months after operation in patients with recurrent disease was significantly less than that for patients with good reflux control (p < 0.01). In patients who had laparotomy, including 30% (9/30) with severe reflux disease, good long-term reflux control was found in 93% (27/29). In patients operated on laparoscopically including 17% (7/41) with severe reflux disease good long-term reflux control was found in 90% (35/39).CONCLUSION:The mechanism of recurrence differed between patients with severe disease who had a laparotomy and patients with mild disease operated on laparoscopically. Early postoperative manometry was prognostic for recurrence. Long-term reflux control seems to be similar after laparotomy and laparoscopy. Further randomised studies are needed.
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| 5. |
- Franzén, Thomas, 1955-, et al.
(författare)
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Reliability of 24-hour oesophageal pH monitoring under standardized conditions
- 2002
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Ingår i: Scandinavian Journal of Gastroenterology. - : Informa UK Limited. - 0036-5521 .- 1502-7708. ; 37:1, s. 6-8
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND:Twenty-four-hour pH monitoring is an investigation technique that can give both false-positive and false-negative results, depending on patient factors such as diet and different activities. The aim was to study the reproducibility of 24-h oesophageal pH monitoring under as standardized conditions as possible in patients with symptoms of gastro-oesophageal reflux disease.METHODS:Antimony pH electrodes were used in 22 adult patients who were investigated twice, 6 weeks apart, under identical conditions. They were hospitalized and were served a standardized diet which had been tested to contain no lower than pH 5.0. Neither coffee nor smoking was allowed. The patients had to refrain from proton-pump inhibitors for 10 days and H2 blockers for 2 days prior to the investigation. The paired t test was used.RESULTS:There was no significant difference in total reflux time, upright or supine reflux time, or longest reflux periods between the two test occasions. However, there were discordant results in six patients who had normal total reflux time on one test occasion but pathological results on the other.CONCLUSION:Since the biological variability of gastro-oesophageal reflux is not negligible from time to time, a normal 24-h oesophageal pH test should be assessed with caution.
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| 6. |
- Tibbling Grahn, Lita, et al.
(författare)
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Gastric bile monitoring : An in vivo and in vitro study of bilitec reliability
- 2002
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Ingår i: Scandinavian Journal of Gastroenterology. - : Informa UK Limited. - 0036-5521 .- 1502-7708. ; 37:11, s. 1334-1337
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Tidskriftsartikel (refereegranskat)abstract
- Background: It has been claimed that the combination of bile and hydrochloride acid (HCl) has a noxious effect on intestinal mucosa. The aim was to study the reliability of the Bilitec 2001 method in monitoring the presence of bile in repeated tests and at different pH and water dilutions. Methods: 24-h esophageal pH and gastric Bilitec monitoring were performed twice with an interval of 6 weeks in 23 patients with symptomatic gastroesophageal reflux (GER). In vitro tests of pH and Bilitec recordings were performed with different mixtures of bile, HCl and water. Results: Gastric bile was present in 37% of the recording time, 28% during day time and 47% during nights. No significant difference was found between the two test occasions. The maximum bile concentration in the stomach was significantly lower in patients with severe pathological GER than in those with normal GER. When concentrated bile was diluted with the same volume of HCl, the pH level fell below 4. The maximum absorption limit with Bilitec in concentrated bile was gradually reduced with decreasing pH. The Bilitec technique recorded the presence of bile even at a pH of 1.4, but not if the bile was diluted with water at a ratio of 1:100 or more. Conclusions: Bilitec gastric recordings show the same clinical result when repeated under standardized conditions. The Bilitec technique is not reliable for monitoring the amount and concentration of bile in the stomach. Bile reflux cannot be monitored with the pH recording technique.
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