The approach combining the dynamic caustics method with high-speed photography technology is used to study the interaction between propagating cracks and three kinds of deformity inclusions（ cylinder inclusion, quadr...The approach combining the dynamic caustics method with high-speed photography technology is used to study the interaction between propagating cracks and three kinds of deformity inclusions（ cylinder inclusion, quadruple inclusion and triangular inclusion） under lowvelocity impact loading. By recording the caustic spots of crack tips at different moments during the crack propagation, the variation regulations of dynamic stress intensity factors（ DSIF） and crack growth velocity with respect to time are obtained. The experimental results showthat the resistance effects to crack growth are varied with different shapes of inclusions in specimens, and the quadruple inclusion＇s effect is more apparent. The distortion degree of caustic spots is affected by the shapes of inclusions as well, and the situation is more serious for cylinder and quadruple inclusions. The overall values of DSIFs of triangular inclusion specimen are greater than the others, and the crack growth velocities, characteristic sizes and DSIFs showprocesses of fluctuations because of the disturbance of reflection waves in specimens. The results provide an experimental basis for the analysis of strength and impact-resistance ability in structures with deformity inclusions.展开更多
The reflected optical caustics method is applied to study dynamic fracture problems in hardened cement paste. First both the unreinforced cement paste and the glass fibres reinforced cement paste specimens were fabric...The reflected optical caustics method is applied to study dynamic fracture problems in hardened cement paste. First both the unreinforced cement paste and the glass fibres reinforced cement paste specimens were fabricated and the reflective coating on the surface of the specimen was prepared. Secondly the crack path and the shadow spot patterns during the crack propagation process for the two specimens were recorded by using a multi-spark high speed camera.Thirdly some dynamic parameters of two cement paste specimens including crack onset time the dynamic stress intensity factor and crack growth velocity were determined and analyzed comparatively.This indicates that the glass fibres can improve the fracture resistance and delay fracture time.These results will play an important role in evaluating the dynamic fracture properties of cement paste.展开更多
Using digital laser dynamic caustics experimental system and conducting simulation experiment researched the influence rule of blasting excavation of a new roadway on neighboring existed different cross-section roadwa...Using digital laser dynamic caustics experimental system and conducting simulation experiment researched the influence rule of blasting excavation of a new roadway on neighboring existed different cross-section roadways. The experimental results show that the influence of blast load on adjacent roadway has a good relationship with the cross-section of roadway. The expansion distance of precrack existed in circular, arch-wall, rectangular roadway is respectively 1.76, 1.61 and 0 cm under blast load.At the same time, the direct-blast side of rectangular roadway has more obvious damage compared with circular and arch-wall roadway. It explains that plane reflects more stress wave than arc, so that it exerts more tensile failure in the direct-blast side, which leads to less stress wave diffracting to the precrack in the back-blast side. When the precrack extends, higher value dynamic stress intensity factor in circular roadway works longer than that of arch-wall roadway. Indirectly, it explains that plane's weakening function on stress wave is significantly stronger than arc. Stress wave brings about self-evident influence on the upper and bottom endpoints of the rectangular roadway, and it respectively extends 1.03, 2.06 cm along the line link direction of the center of the blasthole and the upper and bottom endpoints on the right wall.展开更多
We studied the dynamic fracture mechanical behavior of rock under different impact rates. The fracture experiment was a three-point bending beam subjected to different impact loads monitored using the reflected causti...We studied the dynamic fracture mechanical behavior of rock under different impact rates. The fracture experiment was a three-point bending beam subjected to different impact loads monitored using the reflected caustics method. The mechanical parameters for fracture of the three-poim bending beam specimen under impact load are analyzed. The mechanism of crack propagation is discussed. Experimental results show that the dynamic stress intensity factor increases before crack initiation. When the dynamic stress intensity factor reaches its maximum value the crack starts to develop. After crack initiation the dynamic stress intensity factor decreases rapidly and oscillates. As the impact rate increases the cracks initiate earlier, the maximum value of crack growth velocity becomes smaller and the values of dynamic stress intensity factor also vary less during crack propagation. The results provide a theoretical basis for the study of rock dynamic fracture.展开更多
Based on the first invariant of stress singular field in the vicinity of running tip of an interface crack, mapping equations of the caustic curve on the reference plane and the initial curve on the specimen plane are...Based on the first invariant of stress singular field in the vicinity of running tip of an interface crack, mapping equations of the caustic curve on the reference plane and the initial curve on the specimen plane are developed. The dynamic caustics are analyzed for the crack propagating along the interface between two bonded dissimilar materials. The variation of the caustic configurations is shown with the velocity change of the running crack and the ratio change of the stress intensity factors. Two characteristic dimensions are proposed that are not only practically measurable from optical caustic contours but also suitable to represent the behavior of transient caustics.展开更多
The dynamic fracture behavior of TA 15ELI alloy with lath-like microstructure was studied by caustics method. Specimens with double-side pre-notch were tested under the plane-stress condition at mode-II loading with a...The dynamic fracture behavior of TA 15ELI alloy with lath-like microstructure was studied by caustics method. Specimens with double-side pre-notch were tested under the plane-stress condition at mode-II loading with a drop hammer system. Caustics information recorded in films illustrated the histories of both crack length and stress intensity factor. The dynamic fracture toughness and crack growth velocity of TA15ELI with lath-like microstructure were determined to be 279 MPa.m1/2 and 32.6 m/s, respectively. SEM fractograph analysis showed a mixed feature of mainly plastic mode for TA 15ELI alloy in dynamic mode-II fracture. Shear localization was observed in the vicinity of the crack initiation area.展开更多
An experimental technique for determining the anti plane stress intensity factor K Ⅲ of a three dimensional crack, which is very difficult to obtain by other experimental methods, has been presented by using...An experimental technique for determining the anti plane stress intensity factor K Ⅲ of a three dimensional crack, which is very difficult to obtain by other experimental methods, has been presented by using reflected caustics in combination with the stress freezing and stress releasing technique. The results of this experimental method coincided favorably with the theoretical analysis results of Tweed and Rooke.展开更多
Using a plexiglass sample and by means of real-time holographic interferometry and shadow optical method of caustics, the different features of dynamic variation in stress (strain) field, plastic area and nucleation z...Using a plexiglass sample and by means of real-time holographic interferometry and shadow optical method of caustics, the different features of dynamic variation in stress (strain) field, plastic area and nucleation zone (shadow area) when the sample fractures during loading (loading-fracture) and unloading (unloading-fracture) are studied visually. The results show that the strain nuclei (zones with dense fringes) appear first at the tips of prefabricated cracks at low stress, and then the shadow areas of caustics form with the increase of load. These nuclei and shadow areas can become larger, or smaller, when the process of loading, or unloading, goes on. When the stress is kept within a certain range, the shadow areas of caustics can become larger and smaller alternatively with repeated loading and unloading (cyclic loading). However, when loading and unloading at high stress, in particular when the macrofracture is about to appear, the variations of the shadow areas of caustics are irreversible and quite different. The shadow areas of caustics expand rapidly at an increasing speed when loading-fracture appears. In contrast, the shadow areas of caustics expand at a lower speed when unloading-fracture appears; besides, there is a circular shadow in front of the sharp-angle shaped area.展开更多
In this paper, a vector ray-tracing model (VRT) is used to simulate the optical caustic structures associated with the secondary rainbow for an ellipsoidal droplet illuminated by a Gaussian beam. The optical caustics ...In this paper, a vector ray-tracing model (VRT) is used to simulate the optical caustic structures associated with the secondary rainbow for an ellipsoidal droplet illuminated by a Gaussian beam. The optical caustics of drops with an equatorial radius a = 50 μm, 100 μm, 200 μm, and 500 μm are studied at the same drop/beam ratios (i.e. γ the ratio between the droplet equatorial radius and the Gaussian beam waist) using concentric illumination with a Gaussian beam, and the effect of droplet size on the optical caustics is analyzed. The curvature of the rainbow fringe and the evolution of the cusp caustics position, in this case, are obtained;the diameter range of droplet shape (ellipsoid) measured by Gaussian beam illumination is broadened. Based on this model, the effects of the relative positions d = 0, 0.5y<sub>R</sub>, and y<sub>R</sub> on the optical caustics of the droplet when the center of the Gaussian beam deviates from the droplet center (the center of the Gaussian beam waist is on the same y-axis as the droplet center) are discussed. The optical caustics of the droplet when the center of the Gaussian beam is off the droplet center (the center of the Gaussian beam waist is on the z-axis with the droplet center) are also discussed. The effects of the relative positions of the center of the beam waist and the droplet center d = 0, 0.5y<sub>R</sub>, and y<sub>R</sub> on the optical caustics are also discussed. A method of measuring droplet shape with Gaussian beam illumination is proposed when the beam waist center is coaxial with the droplet center.展开更多
Ingestion of caustics by children is serious because of the increase in their frequency and the difficulties due to their management. Objective: To improve the management of caustic lesions in Pediatric Department at ...Ingestion of caustics by children is serious because of the increase in their frequency and the difficulties due to their management. Objective: To improve the management of caustic lesions in Pediatric Department at the University Hospital of Brazzaville. Patients and Methods: Prospective study was conducted from January 2014 to December 2015 in the Pediatric Departments of the UHB and centers of digestive endoscopy in Brazzaville. All children who ingested a caustic product and hospitalized were included after obtaining parental’s consent. The studied parameters were: Age, sex, nature and quantity of the caustic, the family’s attitude, clinical signs, endoscopic results according to Zagar’s classification, therapeutic modalities and evolution. Results: 8292 children were hospitalized and 68 because of the ingestion of caustic, a frequency of 0.8%. The average age was 23.6 months [2 months - 16 years]. The male sex was predominant (57.4%). Ingestion was accidental in 88.2% and voluntary in 11.8%. Factors favoring ingestion were storage methods (81.5%) and parental’s inattention or negligence (10.8%). Bleach was the most incriminated caustic (54.4%) followed by caustic soda (29.4%). The estimated quantity ingested was assumed to be minimal in 61.7%. Unsuitable acts were practiced by the family before the medical consultation in 66.1%. The dominant symptoms were digestive (47%) and neurological (25%). The average time to perform endoscopy was 48 hours in 88.2%. Endoscopy revealed lesions in 51.7%, the different stages were I (12 cases), II (16 cases) and III (3 cases). The mains factors of gravity were inappropriate gestures (85%) and the non-respect of the fasting (9%). Proton pump inhibitors were used in 50%. The evolution was favorable for in 73.5%. Conclusion: Ingestion of caustics by children is most often accidental favored by the inadequate packaging and storage. Prevention is about educating people in order to reduce their frequency.展开更多
While considering a mirror and light rays coming either from a point source or from infinity,the reflected light rays may have an envelope,called a caustic curve.In this paper,we study developable surfaces as mirrors....While considering a mirror and light rays coming either from a point source or from infinity,the reflected light rays may have an envelope,called a caustic curve.In this paper,we study developable surfaces as mirrors.These caustic surfaces,described in a closed form,are also developable surfaces of the same type as the original mirror surface.We provide efficient,algorithmic computation to find the caustic surface of each of the three types of developable surfaces(cone,cylinder,and tangent surface of a spatial curve).We also provide a potential application of the results in contemporary free-form architecture design.展开更多
Caustic ingestion is a relatively rare but potentially catastrophic gastroentero-logical emergency.Upper gastrointestinal(GI)endoscopy is currently regarded as the gold standard modality not only to assess the depth a...Caustic ingestion is a relatively rare but potentially catastrophic gastroentero-logical emergency.Upper gastrointestinal(GI)endoscopy is currently regarded as the gold standard modality not only to assess the depth and the extension of GI caustic injury,but also to guide the appropriate treatment.Intriguingly,contrast-enhanced computed tomography(CECT)has recently emerged as a promising non-invasive and more accurate alternative to endoscopy in this setting.However,to date,evidence concerning the role of CECT as an alternative or complementary diagnostic tool to endoscopy in caustic ingestion is still limited.The aim of our review was to summarize and discuss the current evidence concerning the role of CECT in the emergency diagnosis of caustic ingestion and its value in assessing injury severity among non-pediatric patients.展开更多
BACKGROUND Corrosive ingestion remains an important global pathology with high morbidity and mortality.Data on the acute management of adult corrosive injuries from sub-Saharan Africa is scarce,with international inve...BACKGROUND Corrosive ingestion remains an important global pathology with high morbidity and mortality.Data on the acute management of adult corrosive injuries from sub-Saharan Africa is scarce,with international investigative algorithms,relying heavily on computed tomography(CT),having limited availability in this setting.AIM To investigate the corrosive injury spectrum in a low-resource setting and the applicability of parameters for predicting full-thickness(FT)necrosis and mortality.METHODS A retrospective analysis of a prospective corrosive injury registry(March 1,2017–October 31,2023)was performed to include all adult patients with acute corrosive ingestion managed at a single,academic referral centre in Cape Town,South Africa.Patient demographics,corrosive ingestion details,initial investigations,management,and short-term outcomes were described using descriptive statistics while multivariate analysis with receiver operator characteristic area under the curve graphs(ROC AUC)were used to identify factors predictive of FT necrosis and 30-day mortality.RESULTS One-hundred patients were included,with a mean age of 32 years(SD:11.2 years)and a male predominance(65.0%).The majority(73.0%)were intentional suicide attempts.Endoscopy on admission was the most frequent initial investigation performed(95 patients),while only 17 were assessed with CT.Seventeen patients had full thickness necrosis at surgery,of which eleven underwent emergency resection and six were palliated.Thirty-day morbidity and mortality were 27.0%and 14.0%,respectively.Patients with full thickness necrosis and those with an established perforation had a 30-day mortality of 58.8%and 91.0%,respectively.Full thickness necrosis was associated with a cumulative 2-year survival of only 17.6%.Multivariate analyses with ROC AUC showed admission endoscopy findings,CT findings,and blood gas findings(pH,base excess,lactate),to all have significant predictive value for full thickness necrosis,with endoscopy proving to have the best predictive value(AUC 0.850).CT and endoscopy findings were the only factors predictive of early mortality,with CT performing better than endoscopy(AUC 0.798 vs 0.759).CONCLUSION Intentional corrosive injuries result in devastating morbidity and mortality.Locally,early endoscopy remains the mainstay of severity assessment,but referral for CT imaging should be considered especially when blood gas findings are abnormal.展开更多
Rationale:Acute caustic ingestion from suicidal intent is not usual in emergency departments in developed countries.One of the substances commonly ingested by suicidal patients,phosphoric acid,tends to cause multi-sys...Rationale:Acute caustic ingestion from suicidal intent is not usual in emergency departments in developed countries.One of the substances commonly ingested by suicidal patients,phosphoric acid,tends to cause multi-system derangements.Patient’s Concern:A 41-year-old male patient presented with complaints of throat discomfort,severe generalized abdominal pain,and multiple episodes of hematemesis after ingesting a restroom cleaning solution.Diagnosis:Poisoning by acute caustic ingestion(containing<30%phosphoric acid and<4%ethylene glycol).Interventions:The patient was administered 50 mL of 8.4%sodium bicarbonate solution followed by an isotonic sodium bicarbonate solution running at 500 mL/h,a hyperkalemia kit,ceftriaxone,metronidazole,omeprazole,and atropine.The patient then underwent urgent hemodialysis.Outcomes:The patient suffered gastrointestinal bleeding as a result of local caustic injury.In addition,his course of illness was complicated by severe acidemia from high anion gap metabolic acidosis and deranged electrolytes(hyperphosphatemia,hyperkalemia,and hypocalcemia).He developed multi-organ failure and eventually demised.Lessons:The clinician needs to be mindful of the multi-system complications arising from such a caustic ingestion.These patients need to be monitored closely for deterioration,and have prompt management of the various arising complications,to reduce the high morbidity and mortality associated with this condition.展开更多
This study explores the extraction of rare earth elements(REEs)from high-ash run-of-mine and discard coal sourced from the Waterberg Coalfield.Three distinct methods were employed:(1)ultrasonic-assisted caustic digest...This study explores the extraction of rare earth elements(REEs)from high-ash run-of-mine and discard coal sourced from the Waterberg Coalfield.Three distinct methods were employed:(1)ultrasonic-assisted caustic digestion;(2)direct acid leaching;and(3)ultrasonic-assisted caustic-acid leaching.Inductively coupled plasma mass spectrometry was utilized to quantify REEs in both the coals and resultant leachates.Leaching the coals with 40%NaOH at 80℃,along with 40 kHz sonication,yielded a total rare earth element(TREE)recovery of less than 2%.Notable enrichment of REEs was observed in the run-of-mine and discard coal by 17%and 19%,respectively.Upon employing 7.5%HCl,a recovery of less than 11.0%for TREE was achieved in both coal samples.However,leaching the caustic digested coal samples with 7.5%HCl significantly enhanced the TREE recovery to 88.8%and 80.0%for run-of-mine and discard coal,respectively.X-ray diffraction analysis identified kaolinite and quartz as the predominant minerals.Scanning electron microscopyenergy dispersive microanalysis revealed monazite and xenotime as the REE-bearing minerals within the coal samples.These minerals were found either liberated,attached to,or encapsulated by the clay-quartz matrices.Further mineralogical assessments highlighted the increased REE concentrations in coals post-caustic digestion and subsequent recovery during acid leaching.This increase was attributed to the partial dissolution of kaolinite encapsulating the RE-phosphates and the digestion of REE-bearing minerals.Notably,undissolved REE-bearing elements in the caustic-acid-leached coal indicated the necessity of harsh leaching conditions to augment REE recovery from these coal samples.展开更多
The dynamic fracture behavior of the three-point bending beam with double deformity inclusions under impact loading is studied by using digital high-speed photography in combination with the transmission-type dynamic ...The dynamic fracture behavior of the three-point bending beam with double deformity inclusions under impact loading is studied by using digital high-speed photography in combination with the transmission-type dynamic caustic method. The experimental results indicate that the fluctuation of crack propagation velocity v first increases and then decreases in the crack propagation process. During the process of crack propagating into the inclusion area, the fracture resistance effect of the circular inclusion is the most significant and the effects of triangular and square inclusions are less obvious. The stress intensity factor near the crack tip increases during the propagation process and reaches its maximum value when the crack tip is close to the inclusions. The crack tip’s dynamic stress intensity factor （ DSIF） decreases when the crack exceeds the middle area of the double inclusions. These results provide an experimental basis and scientific foundation to strengthen the evaluation and fracture analysis of the structure containing deformity inclusions.展开更多
Introduction: Though common in society, caustic accidental ingestion is rare in the agricultural industry. This study describes a case of ingestion of nitric acid used as an agricultural fertilizer by an ordinary work...Introduction: Though common in society, caustic accidental ingestion is rare in the agricultural industry. This study describes a case of ingestion of nitric acid used as an agricultural fertilizer by an ordinary worker at the Société de Cultures Légumières. Clinical Case: This is a 33-year-old unschooled woman who ingested a sip of nitric acid from an abandoned labelled acid canister near a farming plot of land. She showed a burn of the oral cavity with a bleeding tablecloth and an intense retrosternal pain. The duodenal oesophagus fibroscopy screening that was carried out 18 hours after the accident, revealed an esophagitis class 2b. The tests revealed no anomalies. Fifteen (15) days after the accident, the FOGD was normal. Following an 8-month-follow up, no signs of stenosis or degeneration were noted. Conclusion: The accidental ingestion of nitric acid is rare in adult. Its treatment is mainly symptomatic and aims at preserving vital functions without directly fighting the ingested substance off. The right actions must be integrated into the 15-minute Health and Safety awarenesssessions for optimum pre-hospital management. The hospital evaluation is mandatory and is carried out thanks to the digestive endoscopy, which is still relevant in this indication, but is completed by the thoraco-abdominal CT. The latter is very sensitive the transmural necrosis diagnosis.展开更多
Since the first report of use of endoscopy in children in the 1970 s, there has seen an exponential growthin published experience and innovation in the field. In this review article we focus on modern age therapeutic ...Since the first report of use of endoscopy in children in the 1970 s, there has seen an exponential growthin published experience and innovation in the field. In this review article we focus on modern age therapeutic endoscopy practice, explaining use of traditional as well as new and innovative techniques, for diagnosis and treatment of diseases in the paediatric upper gastrointestinal tract.展开更多
The effect of loading rate on the dynamic fracture properties and the failure mechanisms of glass fiber-reinforced composite materials under mode I fracture is studied. Dynamic reflective caustic experiments are carr...The effect of loading rate on the dynamic fracture properties and the failure mechanisms of glass fiber-reinforced composite materials under mode I fracture is studied. Dynamic reflective caustic experiments are carried out for two loading rates. By measuring the characteristic dimensions of the shadow spots during the caustic experiments, the dynamic SIFs are calculated for different loading rates. The experimental results indicate that the dynamic fracture toughness Kid increases remarkably with increasing loading rate, and the crack grows faster under the high-velocity impact. Moreover, by examining the crack growth routes and the fracture surfaces, it is shown that the loading rate also greatly affects the failure mechanisms at micro-scale.展开更多
Dynamic fracture behaviour of crack curving in bent beams has been investigated. In order to understand the propagation mechanism of such cracks under impact, an experimental method is used that combines dynamic photo...Dynamic fracture behaviour of crack curving in bent beams has been investigated. In order to understand the propagation mechanism of such cracks under impact, an experimental method is used that combines dynamic photoelasticity with dynamic caustics to study the interaction of the flexural waves and the crack. From the state change of the transient stresses in polymer specimen, the curving fracture in the impulsively loaded beams is analyzed. The dynamic responses of crack tips are evaluated by the stress intensity factors for the cracks running in varying curvature paths under bending stress wave.展开更多
基金The National Natural Science Foundation of China(No.51374210,51134025)the 111 Project(No.B14006)
文摘The approach combining the dynamic caustics method with high-speed photography technology is used to study the interaction between propagating cracks and three kinds of deformity inclusions（ cylinder inclusion, quadruple inclusion and triangular inclusion） under lowvelocity impact loading. By recording the caustic spots of crack tips at different moments during the crack propagation, the variation regulations of dynamic stress intensity factors（ DSIF） and crack growth velocity with respect to time are obtained. The experimental results showthat the resistance effects to crack growth are varied with different shapes of inclusions in specimens, and the quadruple inclusion＇s effect is more apparent. The distortion degree of caustic spots is affected by the shapes of inclusions as well, and the situation is more serious for cylinder and quadruple inclusions. The overall values of DSIFs of triangular inclusion specimen are greater than the others, and the crack growth velocities, characteristic sizes and DSIFs showprocesses of fluctuations because of the disturbance of reflection waves in specimens. The results provide an experimental basis for the analysis of strength and impact-resistance ability in structures with deformity inclusions.
基金The Ph.D.Programs Foundation of Ministry of Education of China(No.20120023120020)the National Natural Science Foundation of China(No.51404273)
文摘The reflected optical caustics method is applied to study dynamic fracture problems in hardened cement paste. First both the unreinforced cement paste and the glass fibres reinforced cement paste specimens were fabricated and the reflective coating on the surface of the specimen was prepared. Secondly the crack path and the shadow spot patterns during the crack propagation process for the two specimens were recorded by using a multi-spark high speed camera.Thirdly some dynamic parameters of two cement paste specimens including crack onset time the dynamic stress intensity factor and crack growth velocity were determined and analyzed comparatively.This indicates that the glass fibres can improve the fracture resistance and delay fracture time.These results will play an important role in evaluating the dynamic fracture properties of cement paste.
基金provided by the National Natural Science Foundation of China (Nos. 51274204 and 51134025)National Key Basic Research Program (No. 2010CB732002)The Ministry of Education Program for New Century Excellent Talents to Support Project of China (No. NCET-12-0965)
文摘Using digital laser dynamic caustics experimental system and conducting simulation experiment researched the influence rule of blasting excavation of a new roadway on neighboring existed different cross-section roadways. The experimental results show that the influence of blast load on adjacent roadway has a good relationship with the cross-section of roadway. The expansion distance of precrack existed in circular, arch-wall, rectangular roadway is respectively 1.76, 1.61 and 0 cm under blast load.At the same time, the direct-blast side of rectangular roadway has more obvious damage compared with circular and arch-wall roadway. It explains that plane reflects more stress wave than arc, so that it exerts more tensile failure in the direct-blast side, which leads to less stress wave diffracting to the precrack in the back-blast side. When the precrack extends, higher value dynamic stress intensity factor in circular roadway works longer than that of arch-wall roadway. Indirectly, it explains that plane's weakening function on stress wave is significantly stronger than arc. Stress wave brings about self-evident influence on the upper and bottom endpoints of the rectangular roadway, and it respectively extends 1.03, 2.06 cm along the line link direction of the center of the blasthole and the upper and bottom endpoints on the right wall.
基金the support of the National Natural Science Foundation of China (Grant No.50774086 and 50874109)
文摘We studied the dynamic fracture mechanical behavior of rock under different impact rates. The fracture experiment was a three-point bending beam subjected to different impact loads monitored using the reflected caustics method. The mechanical parameters for fracture of the three-poim bending beam specimen under impact load are analyzed. The mechanism of crack propagation is discussed. Experimental results show that the dynamic stress intensity factor increases before crack initiation. When the dynamic stress intensity factor reaches its maximum value the crack starts to develop. After crack initiation the dynamic stress intensity factor decreases rapidly and oscillates. As the impact rate increases the cracks initiate earlier, the maximum value of crack growth velocity becomes smaller and the values of dynamic stress intensity factor also vary less during crack propagation. The results provide a theoretical basis for the study of rock dynamic fracture.
基金The project supported by the National Natural Science Foundation of Chinathe Scientific Commission of Yunnan Province of China
文摘Based on the first invariant of stress singular field in the vicinity of running tip of an interface crack, mapping equations of the caustic curve on the reference plane and the initial curve on the specimen plane are developed. The dynamic caustics are analyzed for the crack propagating along the interface between two bonded dissimilar materials. The variation of the caustic configurations is shown with the velocity change of the running crack and the ratio change of the stress intensity factors. Two characteristic dimensions are proposed that are not only practically measurable from optical caustic contours but also suitable to represent the behavior of transient caustics.
文摘The dynamic fracture behavior of TA 15ELI alloy with lath-like microstructure was studied by caustics method. Specimens with double-side pre-notch were tested under the plane-stress condition at mode-II loading with a drop hammer system. Caustics information recorded in films illustrated the histories of both crack length and stress intensity factor. The dynamic fracture toughness and crack growth velocity of TA15ELI with lath-like microstructure were determined to be 279 MPa.m1/2 and 32.6 m/s, respectively. SEM fractograph analysis showed a mixed feature of mainly plastic mode for TA 15ELI alloy in dynamic mode-II fracture. Shear localization was observed in the vicinity of the crack initiation area.
文摘An experimental technique for determining the anti plane stress intensity factor K Ⅲ of a three dimensional crack, which is very difficult to obtain by other experimental methods, has been presented by using reflected caustics in combination with the stress freezing and stress releasing technique. The results of this experimental method coincided favorably with the theoretical analysis results of Tweed and Rooke.
基金Key project from China Seismological Bureau (9691309020301)and State Natural Sciences Foundation of China (19732060 and 46764010
文摘Using a plexiglass sample and by means of real-time holographic interferometry and shadow optical method of caustics, the different features of dynamic variation in stress (strain) field, plastic area and nucleation zone (shadow area) when the sample fractures during loading (loading-fracture) and unloading (unloading-fracture) are studied visually. The results show that the strain nuclei (zones with dense fringes) appear first at the tips of prefabricated cracks at low stress, and then the shadow areas of caustics form with the increase of load. These nuclei and shadow areas can become larger, or smaller, when the process of loading, or unloading, goes on. When the stress is kept within a certain range, the shadow areas of caustics can become larger and smaller alternatively with repeated loading and unloading (cyclic loading). However, when loading and unloading at high stress, in particular when the macrofracture is about to appear, the variations of the shadow areas of caustics are irreversible and quite different. The shadow areas of caustics expand rapidly at an increasing speed when loading-fracture appears. In contrast, the shadow areas of caustics expand at a lower speed when unloading-fracture appears; besides, there is a circular shadow in front of the sharp-angle shaped area.
文摘In this paper, a vector ray-tracing model (VRT) is used to simulate the optical caustic structures associated with the secondary rainbow for an ellipsoidal droplet illuminated by a Gaussian beam. The optical caustics of drops with an equatorial radius a = 50 μm, 100 μm, 200 μm, and 500 μm are studied at the same drop/beam ratios (i.e. γ the ratio between the droplet equatorial radius and the Gaussian beam waist) using concentric illumination with a Gaussian beam, and the effect of droplet size on the optical caustics is analyzed. The curvature of the rainbow fringe and the evolution of the cusp caustics position, in this case, are obtained;the diameter range of droplet shape (ellipsoid) measured by Gaussian beam illumination is broadened. Based on this model, the effects of the relative positions d = 0, 0.5y<sub>R</sub>, and y<sub>R</sub> on the optical caustics of the droplet when the center of the Gaussian beam deviates from the droplet center (the center of the Gaussian beam waist is on the same y-axis as the droplet center) are discussed. The optical caustics of the droplet when the center of the Gaussian beam is off the droplet center (the center of the Gaussian beam waist is on the z-axis with the droplet center) are also discussed. The effects of the relative positions of the center of the beam waist and the droplet center d = 0, 0.5y<sub>R</sub>, and y<sub>R</sub> on the optical caustics are also discussed. A method of measuring droplet shape with Gaussian beam illumination is proposed when the beam waist center is coaxial with the droplet center.
文摘Ingestion of caustics by children is serious because of the increase in their frequency and the difficulties due to their management. Objective: To improve the management of caustic lesions in Pediatric Department at the University Hospital of Brazzaville. Patients and Methods: Prospective study was conducted from January 2014 to December 2015 in the Pediatric Departments of the UHB and centers of digestive endoscopy in Brazzaville. All children who ingested a caustic product and hospitalized were included after obtaining parental’s consent. The studied parameters were: Age, sex, nature and quantity of the caustic, the family’s attitude, clinical signs, endoscopic results according to Zagar’s classification, therapeutic modalities and evolution. Results: 8292 children were hospitalized and 68 because of the ingestion of caustic, a frequency of 0.8%. The average age was 23.6 months [2 months - 16 years]. The male sex was predominant (57.4%). Ingestion was accidental in 88.2% and voluntary in 11.8%. Factors favoring ingestion were storage methods (81.5%) and parental’s inattention or negligence (10.8%). Bleach was the most incriminated caustic (54.4%) followed by caustic soda (29.4%). The estimated quantity ingested was assumed to be minimal in 61.7%. Unsuitable acts were practiced by the family before the medical consultation in 66.1%. The dominant symptoms were digestive (47%) and neurological (25%). The average time to perform endoscopy was 48 hours in 88.2%. Endoscopy revealed lesions in 51.7%, the different stages were I (12 cases), II (16 cases) and III (3 cases). The mains factors of gravity were inappropriate gestures (85%) and the non-respect of the fasting (9%). Proton pump inhibitors were used in 50%. The evolution was favorable for in 73.5%. Conclusion: Ingestion of caustics by children is most often accidental favored by the inadequate packaging and storage. Prevention is about educating people in order to reduce their frequency.
基金Project supported by the European Union and the European Social Fund(No.EFOP-3.6.3-VEKOP-16-2017-00002).Open Access funding provided by European Union and the European Social Fund。
文摘While considering a mirror and light rays coming either from a point source or from infinity,the reflected light rays may have an envelope,called a caustic curve.In this paper,we study developable surfaces as mirrors.These caustic surfaces,described in a closed form,are also developable surfaces of the same type as the original mirror surface.We provide efficient,algorithmic computation to find the caustic surface of each of the three types of developable surfaces(cone,cylinder,and tangent surface of a spatial curve).We also provide a potential application of the results in contemporary free-form architecture design.
文摘Caustic ingestion is a relatively rare but potentially catastrophic gastroentero-logical emergency.Upper gastrointestinal(GI)endoscopy is currently regarded as the gold standard modality not only to assess the depth and the extension of GI caustic injury,but also to guide the appropriate treatment.Intriguingly,contrast-enhanced computed tomography(CECT)has recently emerged as a promising non-invasive and more accurate alternative to endoscopy in this setting.However,to date,evidence concerning the role of CECT as an alternative or complementary diagnostic tool to endoscopy in caustic ingestion is still limited.The aim of our review was to summarize and discuss the current evidence concerning the role of CECT in the emergency diagnosis of caustic ingestion and its value in assessing injury severity among non-pediatric patients.
文摘BACKGROUND Corrosive ingestion remains an important global pathology with high morbidity and mortality.Data on the acute management of adult corrosive injuries from sub-Saharan Africa is scarce,with international investigative algorithms,relying heavily on computed tomography(CT),having limited availability in this setting.AIM To investigate the corrosive injury spectrum in a low-resource setting and the applicability of parameters for predicting full-thickness(FT)necrosis and mortality.METHODS A retrospective analysis of a prospective corrosive injury registry(March 1,2017–October 31,2023)was performed to include all adult patients with acute corrosive ingestion managed at a single,academic referral centre in Cape Town,South Africa.Patient demographics,corrosive ingestion details,initial investigations,management,and short-term outcomes were described using descriptive statistics while multivariate analysis with receiver operator characteristic area under the curve graphs(ROC AUC)were used to identify factors predictive of FT necrosis and 30-day mortality.RESULTS One-hundred patients were included,with a mean age of 32 years(SD:11.2 years)and a male predominance(65.0%).The majority(73.0%)were intentional suicide attempts.Endoscopy on admission was the most frequent initial investigation performed(95 patients),while only 17 were assessed with CT.Seventeen patients had full thickness necrosis at surgery,of which eleven underwent emergency resection and six were palliated.Thirty-day morbidity and mortality were 27.0%and 14.0%,respectively.Patients with full thickness necrosis and those with an established perforation had a 30-day mortality of 58.8%and 91.0%,respectively.Full thickness necrosis was associated with a cumulative 2-year survival of only 17.6%.Multivariate analyses with ROC AUC showed admission endoscopy findings,CT findings,and blood gas findings(pH,base excess,lactate),to all have significant predictive value for full thickness necrosis,with endoscopy proving to have the best predictive value(AUC 0.850).CT and endoscopy findings were the only factors predictive of early mortality,with CT performing better than endoscopy(AUC 0.798 vs 0.759).CONCLUSION Intentional corrosive injuries result in devastating morbidity and mortality.Locally,early endoscopy remains the mainstay of severity assessment,but referral for CT imaging should be considered especially when blood gas findings are abnormal.
文摘Rationale:Acute caustic ingestion from suicidal intent is not usual in emergency departments in developed countries.One of the substances commonly ingested by suicidal patients,phosphoric acid,tends to cause multi-system derangements.Patient’s Concern:A 41-year-old male patient presented with complaints of throat discomfort,severe generalized abdominal pain,and multiple episodes of hematemesis after ingesting a restroom cleaning solution.Diagnosis:Poisoning by acute caustic ingestion(containing<30%phosphoric acid and<4%ethylene glycol).Interventions:The patient was administered 50 mL of 8.4%sodium bicarbonate solution followed by an isotonic sodium bicarbonate solution running at 500 mL/h,a hyperkalemia kit,ceftriaxone,metronidazole,omeprazole,and atropine.The patient then underwent urgent hemodialysis.Outcomes:The patient suffered gastrointestinal bleeding as a result of local caustic injury.In addition,his course of illness was complicated by severe acidemia from high anion gap metabolic acidosis and deranged electrolytes(hyperphosphatemia,hyperkalemia,and hypocalcemia).He developed multi-organ failure and eventually demised.Lessons:The clinician needs to be mindful of the multi-system complications arising from such a caustic ingestion.These patients need to be monitored closely for deterioration,and have prompt management of the various arising complications,to reduce the high morbidity and mortality associated with this condition.
基金The research was also supported by the National Research Foundation(NRF)of South Africa's SARChI Clean Coal Technology Grant(86421)。
文摘This study explores the extraction of rare earth elements(REEs)from high-ash run-of-mine and discard coal sourced from the Waterberg Coalfield.Three distinct methods were employed:(1)ultrasonic-assisted caustic digestion;(2)direct acid leaching;and(3)ultrasonic-assisted caustic-acid leaching.Inductively coupled plasma mass spectrometry was utilized to quantify REEs in both the coals and resultant leachates.Leaching the coals with 40%NaOH at 80℃,along with 40 kHz sonication,yielded a total rare earth element(TREE)recovery of less than 2%.Notable enrichment of REEs was observed in the run-of-mine and discard coal by 17%and 19%,respectively.Upon employing 7.5%HCl,a recovery of less than 11.0%for TREE was achieved in both coal samples.However,leaching the caustic digested coal samples with 7.5%HCl significantly enhanced the TREE recovery to 88.8%and 80.0%for run-of-mine and discard coal,respectively.X-ray diffraction analysis identified kaolinite and quartz as the predominant minerals.Scanning electron microscopyenergy dispersive microanalysis revealed monazite and xenotime as the REE-bearing minerals within the coal samples.These minerals were found either liberated,attached to,or encapsulated by the clay-quartz matrices.Further mineralogical assessments highlighted the increased REE concentrations in coals post-caustic digestion and subsequent recovery during acid leaching.This increase was attributed to the partial dissolution of kaolinite encapsulating the RE-phosphates and the digestion of REE-bearing minerals.Notably,undissolved REE-bearing elements in the caustic-acid-leached coal indicated the necessity of harsh leaching conditions to augment REE recovery from these coal samples.
基金The National Basic Research Program of China(973 Program)(No.2011CB606105)the National Natural Science Foundation of China(No.51374210,51134025)
文摘The dynamic fracture behavior of the three-point bending beam with double deformity inclusions under impact loading is studied by using digital high-speed photography in combination with the transmission-type dynamic caustic method. The experimental results indicate that the fluctuation of crack propagation velocity v first increases and then decreases in the crack propagation process. During the process of crack propagating into the inclusion area, the fracture resistance effect of the circular inclusion is the most significant and the effects of triangular and square inclusions are less obvious. The stress intensity factor near the crack tip increases during the propagation process and reaches its maximum value when the crack tip is close to the inclusions. The crack tip’s dynamic stress intensity factor （ DSIF） decreases when the crack exceeds the middle area of the double inclusions. These results provide an experimental basis and scientific foundation to strengthen the evaluation and fracture analysis of the structure containing deformity inclusions.
文摘Introduction: Though common in society, caustic accidental ingestion is rare in the agricultural industry. This study describes a case of ingestion of nitric acid used as an agricultural fertilizer by an ordinary worker at the Société de Cultures Légumières. Clinical Case: This is a 33-year-old unschooled woman who ingested a sip of nitric acid from an abandoned labelled acid canister near a farming plot of land. She showed a burn of the oral cavity with a bleeding tablecloth and an intense retrosternal pain. The duodenal oesophagus fibroscopy screening that was carried out 18 hours after the accident, revealed an esophagitis class 2b. The tests revealed no anomalies. Fifteen (15) days after the accident, the FOGD was normal. Following an 8-month-follow up, no signs of stenosis or degeneration were noted. Conclusion: The accidental ingestion of nitric acid is rare in adult. Its treatment is mainly symptomatic and aims at preserving vital functions without directly fighting the ingested substance off. The right actions must be integrated into the 15-minute Health and Safety awarenesssessions for optimum pre-hospital management. The hospital evaluation is mandatory and is carried out thanks to the digestive endoscopy, which is still relevant in this indication, but is completed by the thoraco-abdominal CT. The latter is very sensitive the transmural necrosis diagnosis.
文摘Since the first report of use of endoscopy in children in the 1970 s, there has seen an exponential growthin published experience and innovation in the field. In this review article we focus on modern age therapeutic endoscopy practice, explaining use of traditional as well as new and innovative techniques, for diagnosis and treatment of diseases in the paediatric upper gastrointestinal tract.
基金supported by the National Natural Science Foundation of China (No.10672002).
文摘The effect of loading rate on the dynamic fracture properties and the failure mechanisms of glass fiber-reinforced composite materials under mode I fracture is studied. Dynamic reflective caustic experiments are carried out for two loading rates. By measuring the characteristic dimensions of the shadow spots during the caustic experiments, the dynamic SIFs are calculated for different loading rates. The experimental results indicate that the dynamic fracture toughness Kid increases remarkably with increasing loading rate, and the crack grows faster under the high-velocity impact. Moreover, by examining the crack growth routes and the fracture surfaces, it is shown that the loading rate also greatly affects the failure mechanisms at micro-scale.
基金The project supported by the National Natural Science Foundation of Chinathe Scientific Commussion of Yunnan Province of China
文摘Dynamic fracture behaviour of crack curving in bent beams has been investigated. In order to understand the propagation mechanism of such cracks under impact, an experimental method is used that combines dynamic photoelasticity with dynamic caustics to study the interaction of the flexural waves and the crack. From the state change of the transient stresses in polymer specimen, the curving fracture in the impulsively loaded beams is analyzed. The dynamic responses of crack tips are evaluated by the stress intensity factors for the cracks running in varying curvature paths under bending stress wave.
