Speed Of Shrinkage Research Articles

The Evolution of Microwave-Induced Thermoacoustic Signals Generated During Pulsed Microwave Ablation in Bovine Liver

The temperature dependence of microwave-induced thermoacoustic signals generated in tissue may be exploited to monitor microwave ablation in real-time. We present an experimental study investigating the evolution of microwave-induced thermoacoustic signals that are generated within an ablation zone during microwave ablation in bovine liver tissue. An X-band interstitial coaxial ablation antenna is used to simultaneously heat liver tissue to temperatures up to 90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C and excite thermoacoustic signals via the absorption of pulsed microwave energy. Thermoacoustic signals are detected using a single-element ultrasound transducer located at the surface of the tissue. Both fresh and boiled liver tissue samples are used in experiments to decouple the influence of temperature and tissue coagulation on thermoacoustic signal characteristics. We identify two thermoacoustic signal characteristics of interest: arrival time of the pulse at the ultrasound receiver and the energy in the pulse. We find that the time difference of arrival over the course of microwave ablation grows in magnitude due to temperature-dependent speed of sound and tissue shrinkage. Thermoacoustic signal energy generally increases throughout microwave ablation, implying an increasing temperature-dependent thermal expansion coefficient of liver tissue. Of the two characteristics, time difference of arrival shows the most promise as a trackable feature for monitoring microwave ablation in real time.

Extension of the fib MC 2010 for basic and drying shrinkage of alkali‐activated slag concretes

AbstractAlkali‐activated slag is an alternative to ordinary Portland cement that has been studied for the past 20 years. One of the main challenges for its practical use is understanding and controlling its shrinkage behavior. In this study, new experimental results for two alkali‐activated slag concrete mixes are presented under both sealed and unsealed conditions. The results show that basic shrinkage increases with increased sodium silicate ratio. Under unsealed conditions, the age to exposure to drying has a most significant impact on the final drying shrinkage. Finally, the mechanisms explaining shrinkage of such materials are discussed and thefib Model Code 2010 is extended for alkali‐activated slag concrete using the new experimental results. The extended model consists of four parameters influencing the final values and the speed of both basic shrinkage and drying shrinkage. It is extensively compared with experimental datasets from the literature and improves significantly predictions compared with the original models for both basic and drying shrinkage. This demonstrates clearly the feasibility to extend it for predicting shrinkage of alkali‐activated slag concrete.

Fast Setting, Low Carbon Infrastructure Rehabilitation Using Belitic Calcium Sulfoaluminate (BCSA) Concrete

Rapid-setting binders such as Belitic Calcium Sulfoaluminate (BCSA) are increasingly important as the demand for rehabilitation and fast return to service of roads and bridges grows. Speed of construction, low shrinkage, and low carbon footprint are the key features of BCSA concrete. The binder was first developed in the United States in the mid-seventies. It allows pavement, bridge decks or other concrete infrastructure to be replaced and returned to service in a matter of hours. BCSA concrete slabs placed at the Seattle International Airport (SEA) in the 1990s are still in service 20 years later. The binder also allows innovation in pavement design. Taking advantage of the low shrinkage of BCSA concrete, a single 40 ft x 40 ft airport slab without joints was placed at this airport, as an alternative to the placement of four contiguous conventional-size portland slabs. BCSA was also to be the basis for the design of various rapid-setting performance-engineered concretes, such as low-permeability or UHPC concrete. This paper will review recent concrete applications based on BCSA cement, and the opportunities they offer in building a more resilient, lower carbon concrete infrastructure.

Dredging: A conservative surgical approach for treatment of large cystic lesions of the jaws.

Treatment modalities of odontogenic cystic lesions of the jaws range from conservative to radical. "Dredging" may be considered the "middle path" between conservative and radical treatment options. It comprises three entities-decompression, followed by repeated scraping of the lesion, and finally, peripheral ostectomy providing margin clearance but without significant morbidity. To evaluate the outcome of "dredging" in the management of large cystic lesions of the jaws, without major resections and maintaining normal functions. This prospective study was conducted on 30 patients. Inclusion criteria were odontogenic cystic lesions at least 2 cm in size either in the proximity of vital structures or in children with developing tooth germs or so large that upon enucleation, can result in pathological fracture. All underwent decompression followed by dredging performed at every 2 to 3 months intervals. Drastic decrease in size of the lesion as measured on Cone Beam Computed Tomography (CBCT) and new bone formation was evident in all patients. The total Reduction Rate (RR) of the cystic lesions was 88.79% in 9.2 months. RR was highest in Calcifying epithelial odontogenic cyst (CEOC) followed by Unicystic Ameloblastoma (UA), Odontogenic Keratocysts (OKC), Dentigerous cyst (DC), and Radicular Cyst (RC) in CBCT. The mean speed of shrinkage was fastest in CEOC, followed by OKC, UA, RC, and DC after dredging. Shrinkage was higher in patients below 20 years of age (P 0.012) and patients with large cystic lesions (P 0.00447). The results suggest that dredging with regular, long-term follow-up can be a successful treatment method for large cystic lesions in young adults. This method includes the benefits of both conservative and radical treatment methods but lacks the disadvantages of either.

Abstract GS3-02: PALLET: A neoadjuvant study to compare the clinical and antiproliferative effects of letrozole with and without palbociclib

Abstract Background: CDK4/6 inhibitors, such as palbociclib, are used to treat ER+ metastatic breast cancer in combination with endocrine therapy with trials ongoing in patients with primary disease. No biomarkers exist to identify those who do/do not benefit from added CDK4/6 inhibition. PALLET is an investigator-initiated/led phase II randomized trial collaboration between UK and NSABP investigators evaluating the biological and clinical effects of palbociclib with letrozole combination as neoadjuvant therapy. Methods: Postmenopausal women with ER+ primary breast cancer and tumors &amp;gt;2.0cm (ultrasound) were randomized to one of 4 treatment groups (3:2:2:2 ratio): Group A: letrozole (2.5mg/d) for 14 weeks; Group B: letrozole for 2 weeks followed by letrozole + palbociclib to 14 weeks; Group C: palbociclib for 2 weeks followed by letrozole + palbociclib to 14 weeks; Group D: letrozole + palbociclib for 14 weeks. Palbociclib was given 125mg/d PO on a 21 days on, 7 days off schedule. Post-14 week treatment was at the discretion of the treating clinician including letrozole until surgery. Core-cut biopsies were taken at baseline, 2 weeks and 14 weeks. Co-primary endpoints for letrozole alone vs palbociclib groups (Group A vs Groups B+C+D) were: (i) change in Ki67 (IHC) between baseline and 14 weeks (log-fold change, Mann-Whitney test); (ii) clinical response (ultrasound) after 14 weeks (4 group, ordinal, Mann-Whitney test). Complete cell-cycle arrest (CCCA) (Ki67≤2.7%) was analyzed using a logistic regression model adjusting for recruitment region. Pre-specified exploratory biomarkers included c-PARP (apoptosis). Results: 307 patients were recruited between 27 Feb 2015 and 08 Mar 2018; 103 were randomized to letrozole alone and 204 to letrozole + palbociclib. 279 (90.9%) patients were evaluable for 14 week clinical response. Clinical response was not significantly different between letrozole vs letrozole + palbociclib groups [(p=0.20; CR+PR 49.5% (46/93) vs 54.3% (101/186) and PD 5.4% (5/93) vs 3.2% (6/186)] nor was the small proportion of patients with pathological CR (1/87, 1.1% vs 6/180, 3.3%; p=0.43). 190 (61.9%) patients were evaluable for 14 week change in Ki67. The median log-fold change in Ki67 was greater with letrozole + palbociclib vs letrozole alone (-4.1 vs -2.2; p&amp;lt;0.001) corresponding to a geometric mean change of -97.4% vs -88.5%. Similarly, a greater proportion of patients who received letrozole + palbociclib achieved CCCA (90% vs 59%, p&amp;lt;0.001). 146 (47.6%) patients were evaluable for c-PARP and the log-fold change (suppression) was greater with letrozole + palbociclib vs letrozole alone (-0.80 vs -0.42; p=0.003) corresponding to a geometric mean change of -56.8% vs -31.4%. Other biomarkers of response / resistance are being evaluated. A higher proportion of patients had a grade ≥3 toxicity on letrozole + palbociclib than letrozole alone (49.8% vs 17.0%; p&amp;lt;0.001) mainly due to asymptomatic neutropenia. Conclusion: Adding palbociclib to letrozole markedly enhanced the suppression of malignant cell proliferation as assessed by Ki67 but did not substantially increase the clinical response of primary ER+ breast cancer over a 14-week period. Concurrent reductions in cell death may have reduced the speed of tumor shrinkage. Citation Format: Dowsett M, Jacobs S, Johnston S, Bliss J, Wheatley D, Holcombe C, Stein R, McIntosh S, Barry P, Dolling D, Snowdon C, Perry S, Batten L, Dodson A, Martins V, Modi A, Cornman C, Puhalla S, Wolmark N, Julian T, Pogue-Geile K, Robidoux A, Provencher L, Boileau JF, Shalaby I, Thirlwell M, Fisher K, Huang Bartlett C, Koehler M, Osborne K, Rimawi M. PALLET: A neoadjuvant study to compare the clinical and antiproliferative effects of letrozole with and without palbociclib [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr GS3-02.

Cystic brain metastases had slower speed of tumor shrinkage but similar prognosis compared with solid tumors that underwent radiosurgery treatment.

PurposeTraditionally, radiosurgery was considered less effective for patients with cystic brain metastases. However, comparisons of prognosis between cystic and solid brain metastases in cancer patients have been seldom reported. We aimed to compare the survival between cystic and solid brain metastases and assess risk factors for overall survival after brain metastases (BMOS) in patients who underwent radiosurgery treatment.Patients and methodsThe Kaplan–Meier method and multivariate Cox regression analysis were used to compare survival time and evaluate risk factors for BMOS.ResultsA total of 356 patients (including 498 brain metastases) were analyzed in our study, including 67 patients (67/356, 18.8%) with 75 cystic brain metastases. There is no statistical significance in BMOS between patients with cystic (17 months, range: 3–64 months) and solid (17.5 months, range: 1–65 months) brain metastases (P=0.148). However, the volume of cystic brain metastases decreased more slowly than solid brain metastases (P<0.05). The results indicated that high recursive partitioning analysis classification (P=0.006), large volume of brain metastases (P=0.006), and different primary lesion (especially gastrointestinal tract tumor) (P=0.001) were associated with poor prognosis in patients with brain metastases.ConclusionThere is no difference in prognosis and local control between patients with cystic and solid brain metastases who underwent radiosurgery. However, the rate and speed of tumor shrinkage were lower in cystic brain metastases after radiotherapy. Patients with larger brain metastases had shorter survival time, regardless of cystic or solid brain metastases.

Marsupialization of mandibular cystic ameloblastoma: Retrospective study of 7 years.

This retrospective study investigated the reduction rate and speed of shrinkage after marsupialization in mandibular cystic ameloblastoma and clarified whether marsupialization is appropriate for unicystic ameloblastoma and multicystic ameloblastoma. Sixty-three patients with mandibular cystic ameloblastoma were initially treated with marsupialization. Premarsupialization and postmarsupialization panoramic radiographs were reviewed for reduction rate and speed of shrinkage, and then were evaluated with age, sex, tumor location, and tumor type. The overall recurrence rate was 4.5% (2/44). The average reduction rate after marsupialization was 65.6%. No significant difference was found between unicystic ameloblastoma and multicystic ameloblastoma in reduction rate. The speed of shrinkage of unicystic ameloblastoma was significantly faster than that of multicystic ameloblastoma (P < .05). Similarly, patients with multicystic ameloblastoma had longer marsupialization periods than those with unicystic ameloblastoma (P < .05). Marsupialization is effective in reducing tumor size for both unicystic ameloblastoma and multicystic ameloblastoma. Marsupialization plus second-stage curettage is recommended as the primary treatment for mandibular cystic ameloblastoma.

Introduction to the Special Issue on Solid-State Sensors

It is my great pleasure to introduce the Seventh Special Issue of the IEEE TRANSACTIONS ON ELECTRON DEVICES on Solid-State Image Sensors. Previous special issues were published in February 1976, August 1985, May 1991, October 1997, January 2003, and November 2009. During the six-year interval since the last special issue, significant changes have occurred in the field of solid-state image sensors. This is due, in particular, to the drive for low-power, high integration, compact imaging systems. Now that the speed of pixel shrinkage is slowing down, various new technologies are being developed to increase the functionality of the sensors, to make them more compact, to make them faster, to increase their dynamic range, etc. Papers reflecting these trends in the image sensor technology are well represented in this special issue.

Effect of decompression on cystic lesions of the mandible: 3-dimensional volumetric analysis

Decompression is effective in reducing both the size of cystic lesions on jaws and the associated morbidity of resection. However, quantitative measurement of reduced volume after decompression among different cystic diseases has not been fully investigated. We have retrospectively investigated the difference in reduction in volume among keratocystic odontogenic tumours (n=17), unicystic ameloblastomas (n=10), and dentigerous cysts (n=10) of the posterior mandible using 3-dimensional computed tomography (CT). Various other influential factors such as age, sex, the presence of impacted teeth, and the number of drains were also recorded. There was no significant difference in the speed of shrinkage among the 3 groups, but there was a significant correlation (p<0.01) between the initial detected volume of the lesion and the absolute speed of shrinkage in each type of cyst. Initial volume was also significantly associated (p<0.01) with reduction of total volume in each type of cyst. Age may correlate negatively with the rate of reduction in dentigerous cysts, which means that the older the patient is, the less the reduction. Treatment seemed to last longer as the speed of shrinkage lessened in the keratocystic tumours and dentigerous cysts (p<0.05) as multiple regression has shown. The relative speed of shrinkage of unicystic ameloblastomas seemed to be slower when an impacted tooth was involved in the lesion (p=0.019). However, the sample size was too small to make any definite statistical statement. These results suggest that the rate of reduction of volume was related to the original size of the lesion. Despite the need for a second operation and longer duration of treatment compared with excision alone, decompression is a valuable way of reducing the size of large cystic lesions, with low morbidity and recurrence rate. There was no difference in the rate of reduction according to the underlying histopathological picture.

Dewetting of a droplet induced by the adsorption of surfactants on a glass substrate.

The dewetting of a surfactant droplet, induced by the adsorption of surfactants on a hydrophilic glass substrate, was observed experimentally. After being dropped onto the substrate, the droplet began shrinking and the speed of shrinkage increases with the surfactant concentration. We explained this dynamics, which is known as reactive dewetting, semi-quantitatively by expanding a simple theoretical model originally proposed and discussed qualitatively by M. E. R. Shanahan and P.-G. de Gennes [Start-up of a reactive droplet, C. R. Acad. Sci. Paris, 1997, 324, 261-268]. In addition, for the surfactant droplet with a concentration near or higher than the critical micelle concentration (CMC), we found that it maintains a large final contact area compared with that in the case of the low surfactant concentration. We discussed this phenomenon by taking the decrease in the vapor-liquid and solid-liquid interfacial tensions into consideration.

Decompression as a Treatment for Odontogenic Cystic Lesions of the Jaw

To evaluate the effectiveness of decompression as the primary treatment of odontogenic cystic lesions of the jaw involving factors that affect relative shrinking speed and bone regeneration. A total of 32 patients with odontogenic cystic lesions of the jaw underwent decompression with customized thermoplastic resin stents. Clinical examinations and pre- and postdecompression panoramic radiographs were analyzed. The mean relative speed of shrinkage of radicular cysts (RCs; 3.37 cm(2)/month) was faster than those of keratocystic odontogenic tumors (KCOTs; 2.87 cm(2)/month) and unicystic ameloblastomas (UABs; 2.71 cm(2)/month). The relative shrinking size increased linearly in a time-dependent manner for KCOTs (r = 0.849, P < .001), RCs (r = 0.681, P = .319), and UABs (r = 0.146, P = .730); a similar relation was detected between the primary radiolucent area of cystic lesions before decompression and relative shrinking speed after decompression in KCOTs (r = 0.481, P = .032), RCs (r = 0.260, P = .673), and UABs (r = 0.370, P = .366), but patient age did not affect the relative speed of shrinkage (P > .05). Furthermore, the increase in bone density was more significant in RCs than in KCOTs (P = .026) and UABs (P = .012) after decompression. Decompression was effective in reducing odontogenic cystic lesions of the jaw and increasing bone density. For aggressive lesions, secondary definitive surgery was necessary.

Volumetric change of flowable composite resins due to polymerization as measured with an electronic mercury dilatometer

Introduction During polymerization the distance between groups of atoms/molecules decreases with a resultant volume change that is known as shrinkage [1-3]. Polymerization shrinkage as low as 2% in composites may generate enough tension to destroy the marginal integrity between the restoration and the tooth structure which could result in micro-leakage, post-operative

Effects of the patient's age and the size of the primary lesion on the speed of shrinkage after marsupialisation of keratocystic odontogenic tumours, dentigerous cysts, and radicular cysts

Marsupialisation, by which a surgical window is created in the cavity of a cystic lesion, has been recommended to avoid the formation of a bony defect in the jaw and a reduction in a patient's quality of life. However, information about the factors that affect the reduction in the size of a cyst after marsupialisation is limited. We have studied the effects of the patient's age and the size of the primary lesion on the speed of shrinkage after marsupialisation of keratocystic odontogenic tumours (KCOTs), dentigerous cysts, and radicular cysts. The speed of shrinkage (mm2/month) was evaluated by measuring the radiolucent area on panoramic radiographs taken before and after marsupialisation for KCOT (n=28), dentigerous cysts (n=26), and radicular cysts (n=18) in the mandibular molar regions. The mean duration of marsupialisation for each type of cyst was 11 (5), 8 (5), and 5 (2) months, respectively. The radiolucent area decreased linearly in the 3 types depending on the time after marsupialisation: r=−0.86 (p<0.01), r=−0.73 (p<0.01), and r=−0.72 (p<0.01), respectively. The relative speed of shrinkage did not correlate with the age of the patients, though it did correlate with the size of the radiolucent area before marsupialisation in KCOT (r=0.69, p<0.01) and radicular cysts (r=0.73, p<0.01). These results suggest that the size of a cyst before marsupialisation may affect the speed of shrinkage in KCOT and radicular cysts, while the age of the patient does not.

Rearrangement and elimination of ordered surface layers of crystalline bubble structures due to gas diffusion

We describe a hitherto unknown self-organising effect in wet crystalline bubble structures exposed to air. Due to the escape of gas from the bubbles in the top surface layer, bubbles shrink and create space for the bubbles of the lower layers to interpose themselves at the top. This occurs irregularly, but finally a newly ordered bidisperse top layer is formed. This process can be followed for several episodes of elimination of surface layers. The crystalline orientation influences the speed of shrinkage and formation of the bidisperse top layer. Compared with diffusion of a single bubble or monodisperse monolayer on top of a liquid pool, the diffusion is much faster. This may be accounted for by the extra buoyancy force leading to a larger exposure of the bubbles at the surface.

The Linear Shrinkage and Microhardness of Packable Composites Polymerized by QTH or PAC Unit

This study evaluated the effectiveness of a plasma arc curing (PAC) unit for packable resin composite curing. The amount and speed of polymerization shrinkage and the microhardness of packable composites were evaluated in order to compare the PAC unit's effectiveness with a quartz tungsten halogen (QTH) unit. Sure Fil (Dentsply Caulk), Pyramid (BISCO Inc) and Synergy Compact (Colténe/Whaledent) were used as the packable composites. In the case of curing with the PAC unit, the composites were light cured with Apollo 95E (DMD System Inc) for 1 second (Group 1), 2 seconds (Group 2), 3 seconds (Group 3), 6 seconds (Group 4) and 12 seconds (Group 5). For light curing with the QTH unit, the composites were light cured for 60 seconds using XL3000 (Group 6). The linear polymerization shrinkage of each composite was measured using a custom made linometer, and the data was stored in a computer every 0.5 to 0.55 seconds for a total of 60 seconds. For each composite, the amount of polymerization was compared using one-way ANOVA with Tukey at the 95% confidence level. In order to compare the speed of polymerization, the peak time (PT), showing the highest speed of polymerization and maximum speed of polymerization (Smax), were determined from the data and compared using one-way ANOVA with Tukey at the 95% confidence level for each material. Based on the statistical analysis among the PAC-cure groups (Groups 1 through 5), the group that was not statistically different from the QTH-cure group (Group 6) in the amount of linear polymerization shrinkage was determined for each material, and the corresponding curing time of the group was defined as the tentative minimum PAC-curing time (TMPT). For microhardness measurements, the samples were placed in a 2-mm thick Teflon plate. Twenty specimens, randomly divided into the PAC-cure group (Group 1) or the QTH-cure group (Group 2), were prepared for each material. In Group 1, each composite was light cured for TMPT with the PAC unit. In Group 2, each composite was light cured for 60 seconds with the QTH unit. Microhardness was measured on the upper and lower surface. For each material, the microhardness of the upper and lower surface of Groups 1 and 2 was analyzed using two-way ANOVA with Tukey at the 95% confidence level. The amount of polymerization was Group 1<Group 2<Group 3<Group 4<Groups 5, 6 in the Sure Fil composite (p<0.05); Groups 1, 2<Group 3<Groups 4, 6<Group 5 in the Synergy Compact composite (p<0.05) and Group 1 <Group 2 <Group 3 <Groups 4, 6 <Group 5 in the Pyramid composite (p<0.05) Regarding the speed of polymerization, the order of PT was G1, G2, G3<G4, G5<G6 (p<0.05). The order of Rmax was G6<G1, G2, G3, G4, G5 in Sure Fil; G6<G1<G2, G3, G4<G5 in Synergy Compact (p<0.05) and G6<G1<G2, G3<G4, G5 in Pyramid (p<0.05) On the upper surface, there was no statistical difference in microhardness between Groups 1 and 2 in all materials. On the lower surface, the microhardness of Group 2 was significantly higher than Group 1 in all materials. In all materials in Group 1 and the Synergy Compact of Group 2, microhardness of the upper surface was significantly higher than the lower surface (p<0.05). In Sure Fil and Pyramid of Group 2, there was no difference in microhardness between the upper and lower surfaces.

The amounts and speed of polymerization shrinkage and microhardness in LED cured composites

# This study evaluated the effectiveness of the light emitting diode(LED) units for composite curing. To compare its effectiveness with conventional quartz tungsten halogen (QTH) light curing unit, the micro- hardness of 2mm composite, Z250, which had been light cured by the LEDs (Ultralume LED2, FreeLight, Developing product D1) or QTH (XL 3000) were compared on the upper and lower surface. One way ANO- VA with Tukey and Paired t-test was used at 95% levels of confidence. In addition, the amount of linear polymerization shrinkage was compared between composites which were light cured by QTH or LEDs using a custom-made linometer in 10s and 60s of light curing, and the amount of linear polymerization shrinkage was compared by one way ANOVA with Tukey . The amount of polymerization shrinkage at 10s was XL3000 > Ultralume 2, 40, 60> FreeLight, D1 (P Ultralume 2, 60> Ultralume 2,40> FreeLight, D1 (P<0.05) The microhardness on the upper and lower surface was as follows; XL 3000 ABSTRACT

Structure of large-scale vortices and unsteady reverse flow in the reattaching zone of a turbulent separation bubble

This paper describes experiments concerning the structure of large-scale vortices and the unsteady reverse-flow properties in the reattaching zone of a nominally two-dimensional separation bubble formed at the leading edge of a blunt flat plate with right-angled corners. The experiment was performed in a wind tunnel with a constant Reynolds number 2.6 × 104 (based on the main-flow velocity and the thickness of the plate). Split-film probes, being sensitive to instantaneous reversals of flow direction, were extensively employed. An important feature of this study is a judicious use of surface-pressure fluctuations as a conditioning signal to educe the structure of the large-scale vortices.Distributions of fluctuating-velocity vectors and contour lines of high-frequency turbulent energy in a few space–time domains are presented and discussed. The most economical interpretation of these space-time distributions is that the large-scale vortices in the reattaching zone are hairpin vortices whose configuration is sketched in the text. The unsteady flow in the reattaching zone is mainly governed by two agents; the motion of the large-scale vortices and the low-frequency unsteadiness. The unsteady flow is clarified in terms of the motion (in a space–time domain) of zeros of the longitudinal velocity close to the surface of the plate; the effects of the two agents on this motion are presented separately. On the basis of these results, a mathematical model of the unsteady flow in the reattaching zone is suggested and found to yield good comparison with measured reverse-flow intermittency and frequency of local-flow reversals. It appears that the separation bubble experiences shrinkage and enlargement in connection with the low-frequency unsteadiness and that the speed of shrinkage is much greater than that of enlargement. The strength of the large-scale vortices in the reattaching zone seems to be dependent on the phase of the low-frequency unsteadiness.

Weld Cracking Behavior under Restraint (Part 2)

Generally speaking, intensity of restraint in a weld joint increases according to the decrease of temperature. In many cases, however, the intensity of restraint is defined by the final value of it.In the present paper, considering the change of restraint during welding, relations between shrinkage speed and cracking during and after welding were investigated.In the previous report, experiments were conducted under the condition such that the speed of shrinkage is kept almost constant and it was reported that cracking is occurred in narrow range of temperature for both weldments of a mild steel and a high strength steel. However, in this report, the effects of shrinkage speed were investigated for both weldments of a mild steel and a high strength steel of 60 kg/mm2 strength level.The results obtained are as follows ;(1) Shrinkage speed and magnitude of reaction stress were widely changed by changing the gauge length of restraint, and weld cracking was occurred in wider range of temperature.(2) In mild steel weldments, weld crack is occurred only during cooling and crack intiation is not observed after cooled to room temperature.(3) However, in high strength steel weldments, crack initiation is observed during cooling and also after cooled to room temperature.(4) Especially the cracking after cooled to room temperature occures at a lower reaction stress range and the incubation period for these crack initiations (abont 20 hours after welded) was measured.The incubation time is insensitive to the applied reaction stress. Such cracking would be “Delayed failure” by hydrogen embrittlement.