The effect of size and distribution of titanium carbide on the microstructure and mechanical properties of non-burning β titanium alloy Ti-25V-15Cr-2Al-0.2C-0.2Si (mass fraction, %) was investigated. The microstructu...The effect of size and distribution of titanium carbide on the microstructure and mechanical properties of non-burning β titanium alloy Ti-25V-15Cr-2Al-0.2C-0.2Si (mass fraction, %) was investigated. The microstructure of the heat-treated and exposed alloy was studied using optical microscopy(OM), scanning electron microscopy(SEM) and transmission electron microscopy(TEM). It is found that carbides with finer size and more uniform distribution can suppress the formation of α precipitates more effectively, and can especially decrease the amount of grain boundary α precipitates after long-term exposure at 540℃ (the expected application temperature). Thus, significant improvement in thermal stability can be achieved by refining carbide particles in the matrix of the alloy.展开更多
The effect of heat treatment and thermal exposure on the microstructure and mechanical properties of non burning β titanium alloy Ti 25V 15Cr 2Al 0.2C (mass fraction, %) was investigated. It is found that the amount ...The effect of heat treatment and thermal exposure on the microstructure and mechanical properties of non burning β titanium alloy Ti 25V 15Cr 2Al 0.2C (mass fraction, %) was investigated. It is found that the amount of α precipitation in samples after solution treatment followed by air cooling increases with increasing solution temperature. After solution treatment, the alloy was subjected to two different heat treatments to stabilize the material. The results show that the single ageing treatment(700 ℃, 4 h, AC) leads to a large amount of α precipitation, while the triplex treatment(850 ℃, 2 h, FC+700 ℃, 6 h, FC+540 ℃, 6 h, AC) significantly suppresses the formation of α precipitates. It is more important that after long term exposure at 540 ℃(the expected application temperature) samples heat treated by the triplex treatment have markedly higher ductility than those given the single aging treatment. The intermetallic compound TiCr 2 is observed in samples after long term exposure, which further degrades the ductility of the alloy.展开更多
Background Patients with epilepsy are at risk of sudden unexpected death. Neu rogenic cardiac arrhythmias have been postulated as a cause. Electrocardiograms (ECG) can be monitored by use of an implantable loop record...Background Patients with epilepsy are at risk of sudden unexpected death. Neu rogenic cardiac arrhythmias have been postulated as a cause. Electrocardiograms (ECG) can be monitored by use of an implantable loop recorder for up to 18 month s. We aimed to determine the frequency of cardiac arrhythmias in patients with r efractory focal seizures over an extended period. Methods 20 patients received a n implantable loop recorder at one hospital in the UK. Devices were programmed t o record automatically if bradycardia ( < 40 beats per min) or tachycardia ( > 1 40 beats per min) were detected. Additionally, in the event of a seizure, patien ts and relatives could initiate ECG recording with an external activator device. Data were analysed at regular intervals and correlated with seizure diaries. Fi ndings More than 220 000 patient hours were monitored over 24 months, during w hich ECGs were captured on implantable loop recorders in 377 seizures. One patie nt withdrew from the study. In 16 patients, median heart rate during habitual se izures exceeded 100 beats per min. Ictal bradycardia ( < 40 beats per min) was r are, occurring in eight (2 1% ) recorded events, in seven patients. Four pati ents (21% ) had bradycardia or periods of asystole with subsequent permanent pa cemaker insertion. Three of these four (16% of total) had potentially fatal as ystole. Interpretation Clinical characteristics of patients with peri ictal ca rdiac abnormalities are closely similar to those at greatest risk of sudden unex pected death in epilepsy. Asystole might underlie many of these deaths, which wo uld have important implications for the investigation of similar patients and af fect present cardiac pacing policies.展开更多
Objectives: To examine the cerebral structure of 14 patients with partial seizures and acquired lesions, 20 patients with malformations of cortical development (MCDs), and 45 patients with partial seizures and normal ...Objectives: To examine the cerebral structure of 14 patients with partial seizures and acquired lesions, 20 patients with malformations of cortical development (MCDs), and 45 patients with partial seizures and normal conventional MRI using whole- brain T2 mapping and statistical parametric mapping (SPM). Methods: T2 maps were calculated, and individual patients were compared with a group of 30 control subjects using SPM. Results: T2 mapping and objective voxel- by- voxel statistical comparison identified regions of increased T2 signal in all 14 patients with acquired nonprogressive cerebral lesions and partial seizures. In all of these, the areas of increased T2 signal concurred with abnormalities identified on visual inspection of conventional MRI. In 18 of 20 patients with MCDs, SPM detected regions of increased T2 signal, all of which corresponded to abnormalities identified on visual inspection of conventional MRI. In addition, in both groups, there were areas that were normal on conventional imaging, which demonstrated abnormal T2 signal. Voxel- by- voxel statistical analysis identified increased T2 signal in 23 of the 45 patients with cryptogenic focal epilepsy. In 20 of these, the areas of increased T2 signal concurred with epileptiform EEG abnormality and clinical seizure semiology. Group analysis of MRI- negative patients with electroclinical seizure onset localizing to the left and right temporal and left and right frontal regions revealed increased T2 signal within the white matter of each respective lobe. Conclusions: T2 mapping analyzed using statistical parametric mapping was sensitive in patients with malformations of cortical development and acquired cerebral damage. Increased T2 signal in individual and grouped MRInegative patients suggests that minor structural abnormalities exist in occult epileptogenic cerebral lesions.展开更多
基金Project(2000 2005) supported by Beijing Institute of Aeronautical Materials in China and Rolls-Royce Plc in UK
文摘The effect of size and distribution of titanium carbide on the microstructure and mechanical properties of non-burning β titanium alloy Ti-25V-15Cr-2Al-0.2C-0.2Si (mass fraction, %) was investigated. The microstructure of the heat-treated and exposed alloy was studied using optical microscopy(OM), scanning electron microscopy(SEM) and transmission electron microscopy(TEM). It is found that carbides with finer size and more uniform distribution can suppress the formation of α precipitates more effectively, and can especially decrease the amount of grain boundary α precipitates after long-term exposure at 540℃ (the expected application temperature). Thus, significant improvement in thermal stability can be achieved by refining carbide particles in the matrix of the alloy.
文摘The effect of heat treatment and thermal exposure on the microstructure and mechanical properties of non burning β titanium alloy Ti 25V 15Cr 2Al 0.2C (mass fraction, %) was investigated. It is found that the amount of α precipitation in samples after solution treatment followed by air cooling increases with increasing solution temperature. After solution treatment, the alloy was subjected to two different heat treatments to stabilize the material. The results show that the single ageing treatment(700 ℃, 4 h, AC) leads to a large amount of α precipitation, while the triplex treatment(850 ℃, 2 h, FC+700 ℃, 6 h, FC+540 ℃, 6 h, AC) significantly suppresses the formation of α precipitates. It is more important that after long term exposure at 540 ℃(the expected application temperature) samples heat treated by the triplex treatment have markedly higher ductility than those given the single aging treatment. The intermetallic compound TiCr 2 is observed in samples after long term exposure, which further degrades the ductility of the alloy.
文摘Background Patients with epilepsy are at risk of sudden unexpected death. Neu rogenic cardiac arrhythmias have been postulated as a cause. Electrocardiograms (ECG) can be monitored by use of an implantable loop recorder for up to 18 month s. We aimed to determine the frequency of cardiac arrhythmias in patients with r efractory focal seizures over an extended period. Methods 20 patients received a n implantable loop recorder at one hospital in the UK. Devices were programmed t o record automatically if bradycardia ( < 40 beats per min) or tachycardia ( > 1 40 beats per min) were detected. Additionally, in the event of a seizure, patien ts and relatives could initiate ECG recording with an external activator device. Data were analysed at regular intervals and correlated with seizure diaries. Fi ndings More than 220 000 patient hours were monitored over 24 months, during w hich ECGs were captured on implantable loop recorders in 377 seizures. One patie nt withdrew from the study. In 16 patients, median heart rate during habitual se izures exceeded 100 beats per min. Ictal bradycardia ( < 40 beats per min) was r are, occurring in eight (2 1% ) recorded events, in seven patients. Four pati ents (21% ) had bradycardia or periods of asystole with subsequent permanent pa cemaker insertion. Three of these four (16% of total) had potentially fatal as ystole. Interpretation Clinical characteristics of patients with peri ictal ca rdiac abnormalities are closely similar to those at greatest risk of sudden unex pected death in epilepsy. Asystole might underlie many of these deaths, which wo uld have important implications for the investigation of similar patients and af fect present cardiac pacing policies.
文摘Objectives: To examine the cerebral structure of 14 patients with partial seizures and acquired lesions, 20 patients with malformations of cortical development (MCDs), and 45 patients with partial seizures and normal conventional MRI using whole- brain T2 mapping and statistical parametric mapping (SPM). Methods: T2 maps were calculated, and individual patients were compared with a group of 30 control subjects using SPM. Results: T2 mapping and objective voxel- by- voxel statistical comparison identified regions of increased T2 signal in all 14 patients with acquired nonprogressive cerebral lesions and partial seizures. In all of these, the areas of increased T2 signal concurred with abnormalities identified on visual inspection of conventional MRI. In 18 of 20 patients with MCDs, SPM detected regions of increased T2 signal, all of which corresponded to abnormalities identified on visual inspection of conventional MRI. In addition, in both groups, there were areas that were normal on conventional imaging, which demonstrated abnormal T2 signal. Voxel- by- voxel statistical analysis identified increased T2 signal in 23 of the 45 patients with cryptogenic focal epilepsy. In 20 of these, the areas of increased T2 signal concurred with epileptiform EEG abnormality and clinical seizure semiology. Group analysis of MRI- negative patients with electroclinical seizure onset localizing to the left and right temporal and left and right frontal regions revealed increased T2 signal within the white matter of each respective lobe. Conclusions: T2 mapping analyzed using statistical parametric mapping was sensitive in patients with malformations of cortical development and acquired cerebral damage. Increased T2 signal in individual and grouped MRInegative patients suggests that minor structural abnormalities exist in occult epileptogenic cerebral lesions.
