This paper presents a new focusing and scanning method which focuses multiple waves on a target. The key of the method is to control excitation pulses for each element of the transducer array. The excitation pulse on ...This paper presents a new focusing and scanning method which focuses multiple waves on a target. The key of the method is to control excitation pulses for each element of the transducer array. The excitation pulse on each array element is obtained by time reversing the signal received by the same element, which is generated by an imaginary source at the target. The excitation pulses from all array elements are transmitted and arrive at the target simultaneously, and focusing is achieved. The performance of the two methods is compared in numerical examples, and it is demonstrated that the proposed method achieves a satisfactory focusing and a good signal-to-noise ratio no matter where the target location is.展开更多
In order to stabilise the operation of the blast furnace and to raise its operation efficiency,research works for the application of microwave and laser scanning technologies to the measurement have been intensively c...In order to stabilise the operation of the blast furnace and to raise its operation efficiency,research works for the application of microwave and laser scanning technologies to the measurement have been intensively carried out at China Steel Corporation(CSC).To monitor the burden profile during the operation,a microwave burden profile measuring system was developed.The system consists of a radar unit,a signal processing system, and a driving device which is capable of rotating the radar to scan the burden surface in a specified direction.A nitrogen cooling system was designed to protect the measurement system.A prototype burden profile meter was successfully tested in No.1 blast furnace in 2008,and a permanent one was installed at No.3 blast furnace.The system has provided useful information for adjusting the charging sequence in No.3 blast furnace.For another application,3 - D laser scanning technology is employed to monitor the blast furnace lining condition.To this end,a data registration method has been developed,through which two measured range images sensed at different period and locations can be fitted into the same coordinate system.In practice,the erosion of the blast furnace lining can be estimated when the current inner profile is compared with that taken before the blow-in operation. This technology is also adopted to evaluate the performance of gunning operation in the blast furnaces at CSC.展开更多
Background: The use of chest imaging in COVID-19 can be especially useful for patients with moderate to severe symptoms or comorbidities. Objective: This study aimed to demonstrate the high resolution computed tomogra...Background: The use of chest imaging in COVID-19 can be especially useful for patients with moderate to severe symptoms or comorbidities. Objective: This study aimed to demonstrate the high resolution computed tomography (CT) findings observed among the coronavirus disease 2019 (COVID-19) patients presented with pneumonia and to reveal the most frequent infiltration and distribution patterns of the disease. Methodology: This was a retrospective study. This study was performed in the Department of Radiology & Imaging at Kurmitola General Hospital, Dhaka, Bangladesh. This was the first dedicated COVID-19 hospital with a bed capacity of 500 and well-equipped ICU facilities. The recorded HRCT scan data were collected in the period from April 2020 up to May 2020 during the first wave of COVID-19 in Bangladesh. As this was a retrospective study, verbal or written consent was not obtained from all potential participants or guardians. The available demographic data as well as the medical history of all data were collected and thoroughly reviewed from the record book. These patients were RT-PCR confirmed cases of COVID-19 patients presented with pneumonia and were admitted to Kurmitola General Hospital, Dhaka, Bangladesh. All these patients underwent HRCT scans of the chest. Result: A total number of 155 COVID-19 patients with HRCT scan were evaluated. The mean age with SD of the study population was 58.03 ± 14.08 years with the range of 22 to 97 years. The male and female ratio was 2.04:1. Fibrosis of the lungs and thickening of pleura were found in 38 (24.5%) cases and 33 (21.3%) cases respectively. The involvement of both lungs was found in 32 (20.6%) cases. The presence of pneumonitis and bronchiectasis were detected in 77 (49.7%) cases and 5 (3.2%) cases respectively. Left-sided mild pleural effusion was also noted in 6 (3.9%) cases. Ground glass opacity was found in different forms. The most common form was the presence of only ground glass opacities which was 63 (40.6%) cases. Bilateral ground-glass opacities were detected in 63 (40.6%) cases. Conclusion: In conclusion, HRCT scan of the chest shows the bilateral ground-glass opacities and fibrosis of the lungs with pneumonitis in most of the COVID-19 hospital admitted patients.展开更多
本文提出了一种低剖面锥形波束漏波天线,该天线实现了宽仰角扫描范围和较低的方位面不圆度水平。通过在平行板波导表面刻蚀一系列同心圆环漏波结构,实现了导波模式向锥形辐射波束的转换。为有效拓宽俯仰面内的扫描范围,对单元格的色散...本文提出了一种低剖面锥形波束漏波天线,该天线实现了宽仰角扫描范围和较低的方位面不圆度水平。通过在平行板波导表面刻蚀一系列同心圆环漏波结构,实现了导波模式向锥形辐射波束的转换。为有效拓宽俯仰面内的扫描范围,对单元格的色散特性进行了理论分析。利用漏波结构的等效电路模型,提取了对应的集总电路元件参数。同时,评估了不同探针配置对不圆度水平的影响,并最终设计了一种基于接地共面波导的八路等功分馈电网络。实测结果表明,该天线能够工作于30.0 GHz~37.0 GHz的频率范围,相对带宽达21%,仰角扫描范围为45°。该天线具有稳定的全向辐射特性,方位面不圆度低于1.6 d B,交叉极化水平优于-22 d B。所设计的天线可满足毫米波卫星通信和引信探测等领域的应用需求。展开更多
In close-aperture Z-scan experiments, a small aperture is conventionally located in the far-field thereby enabling the detection of slight changes in the laser beam profile due to the Kerr-lensing effect. In this work...In close-aperture Z-scan experiments, a small aperture is conventionally located in the far-field thereby enabling the detection of slight changes in the laser beam profile due to the Kerr-lensing effect. In this work, by numerically solving the Fresnel-Kirchhoff diffraction integrals, the amount of transmitted power through apertures has been evaluated and a parametric study on the role of the various parameters that can influence this transmitted power has been done. In order to perform a comprehensive analysis, we have used a nonlinear phase shift optimized for nonlocal nonlinear media in our calculations. Our results show that apertures will result in the formation of symmetrical fluctuations on the wings of Z-scan transmittance curves. It is further shown that the appearance of these fluctuations can be ascribed to the natural diffraction of the Gaussian beam as it propagates up to the aperture plane. Our calculations reveal that the nonlocal parameter variations can shift the position of fluctuations along the optical axis, whereas their magnitude depends on the largeness of the induced nonlinear phase shift. It is concluded that since the mentioned fluctuations are produced by the natural diffraction of the Gaussian beam itself, one must take care not to mistakenly interpret them as noise and should not expect to eliminate them from experimental Z-scan transmittance curves by using apertures with different sizes.展开更多
In this article, two terahertz transmission imaging systems are built with a 2.52 THz continuous wave laser and two types of sensors. One is array scanning system using a 124×124 pyro-electric array camera as the...In this article, two terahertz transmission imaging systems are built with a 2.52 THz continuous wave laser and two types of sensors. One is array scanning system using a 124×124 pyro-electric array camera as the detector; the other is a point-wise scanning system utilizing a Golay cell as the detector. The imaging speed and quality is briefly analyzed. Terahertz （THz） imaging results demonstrate that the array scanning system has higher imaging speed with lower resolution. The point-wise scanning system has higher imaging quality with lower speed.展开更多
Our recent scanning tunneling microscopy （STM） studies of the NaFelxCoxAs phase diagram over a wide range of dopings and temperatures are reviewed. Similar to the high-Tc cuprates, the iron-based superconductors lie...Our recent scanning tunneling microscopy （STM） studies of the NaFelxCoxAs phase diagram over a wide range of dopings and temperatures are reviewed. Similar to the high-Tc cuprates, the iron-based superconductors lie in close proximity to a magnetically ordered phase. Therefore, it is widely believed that magnetic interactions or fluctuations play an important role in triggering their Cooper pairings. Among the key issues regarding the electronic phase diagram are the properties of the parent spin density wave （SDW） phase and the superconducting （SC） phase, as well as the interplay between them. The NaFe l-xCoxAs is an ideal system for resolving these issues due to its rich electronic phases and the charge-neutral cleaved surface. In our recent work, we directly observed the SDW gap in the parent state, and it exhibits unconventional features that are incompatible with the simple Fermi surface nesting picture. The optimally doped sample has a single SC gap, but in the underdoped regime we directly viewed the microscopic coexistence of the SDW and SC orders, which compete with each other. In the overdoped regime we observed a novel pseudogap-like feature that coexists with supercon- ductivity in the ground state, persists well into the normal state, and shows great spatial variations. The rich electronic structures across the phase diagram of NaFel_xCoxAs revealed here shed important new light for defining microscopic models of the iron-based superconductors. In particular, we argue that both the itinerant electrons and local moments should be considered on an equal footing in a realistic model.展开更多
Permanent waving is very popular in Japan. Polypeptide chains (main chains) form the principal components of hair, and they are lined up longitudinally. Hair relaxation is also called straight permanent waving, and th...Permanent waving is very popular in Japan. Polypeptide chains (main chains) form the principal components of hair, and they are lined up longitudinally. Hair relaxation is also called straight permanent waving, and there are methods that change curly or wavy hair into straight hair. Hair damage as a result of winding, combing, and using high-temperature hairdressing irons is also often seen. By using scanning electron micrographs (SEM) we showed broken hairs and hair damage caused by permanent wave solutions. The hair damage is obvious when comparisons are made with the condition of the hair surface, condition of the cuticle, etc. Hair swelling by permanent wave solutions, manipulations such as winding, etc., inadequate rinsing with water, procedures on injured hair at the outset, etc., are considered possible reasons for any of these types of injury.展开更多
针对可重复使用飞行器热防护结构在复杂多场耦合环境下易产生层间脱粘损伤的关键问题,提出基于超声导波与域自适应迁移学习的无损检测方法。通过设计4类典型粘接缺陷的隔热瓦试件,结合双向正交扫描策略与超声激励–接收机制,实现粘接区...针对可重复使用飞行器热防护结构在复杂多场耦合环境下易产生层间脱粘损伤的关键问题,提出基于超声导波与域自适应迁移学习的无损检测方法。通过设计4类典型粘接缺陷的隔热瓦试件,结合双向正交扫描策略与超声激励–接收机制,实现粘接区域的高效覆盖检测。针对试件个体差异引起的信号漂移问题,采用基于峰值比例阈值的相位对齐方法,通过优化窗口长度同步保留损伤敏感特征并抑制噪声干扰。进一步构建域自适应迁移学习网络(Domain-adaptive transfer learning,DATL),实现跨试件损伤特征的分布对齐。试验表明,在跨试件测试场景下,DATL模型准确率仅下降3.9%,域间分布差异指数从0.31降至0.10;在目标域数据量不足40%时,其准确率仍达85%,较卷积神经网络(Convolutional neural network,CNN)提升19.4%。该方法缓解了对损伤类型和试件一致性的依赖,可降低在役热防护结构脱粘检测的误报率与漏检率,为可重复使用飞行器的快速无损检测与健康评估提供了一种可行的解决参考方案。展开更多
In this paper a millimeter-wave （MMW） squint indirect holographic method is presented, which is suitable for imaging with a large field-of-view. The proposed system employs the squint operation mode to remove the ba...In this paper a millimeter-wave （MMW） squint indirect holographic method is presented, which is suitable for imaging with a large field-of-view. The proposed system employs the squint operation mode to remove the background and twin- image interferences, which achieves a similar effect to off-axis holography but leaves out the large-aperture quasi-optical component. The translational scanning manner enables a large field of view and ensures the image uniformity, which is difficult to realize in off-axis holography. In addition, a corresponding imaging algorithm for the presented scheme is developed to reconstruct the image from the recorded hologram. Some imaging results on typical objects, obtained with electromagnetic simulation, demonstrate good performance of the imaging scheme and validate the effectiveness of the image reconstruction algorithm.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11174322 and 11074273)the Research Council of Norway (GrantNo. 186923/I30)
文摘This paper presents a new focusing and scanning method which focuses multiple waves on a target. The key of the method is to control excitation pulses for each element of the transducer array. The excitation pulse on each array element is obtained by time reversing the signal received by the same element, which is generated by an imaginary source at the target. The excitation pulses from all array elements are transmitted and arrive at the target simultaneously, and focusing is achieved. The performance of the two methods is compared in numerical examples, and it is demonstrated that the proposed method achieves a satisfactory focusing and a good signal-to-noise ratio no matter where the target location is.
文摘In order to stabilise the operation of the blast furnace and to raise its operation efficiency,research works for the application of microwave and laser scanning technologies to the measurement have been intensively carried out at China Steel Corporation(CSC).To monitor the burden profile during the operation,a microwave burden profile measuring system was developed.The system consists of a radar unit,a signal processing system, and a driving device which is capable of rotating the radar to scan the burden surface in a specified direction.A nitrogen cooling system was designed to protect the measurement system.A prototype burden profile meter was successfully tested in No.1 blast furnace in 2008,and a permanent one was installed at No.3 blast furnace.The system has provided useful information for adjusting the charging sequence in No.3 blast furnace.For another application,3 - D laser scanning technology is employed to monitor the blast furnace lining condition.To this end,a data registration method has been developed,through which two measured range images sensed at different period and locations can be fitted into the same coordinate system.In practice,the erosion of the blast furnace lining can be estimated when the current inner profile is compared with that taken before the blow-in operation. This technology is also adopted to evaluate the performance of gunning operation in the blast furnaces at CSC.
文摘Background: The use of chest imaging in COVID-19 can be especially useful for patients with moderate to severe symptoms or comorbidities. Objective: This study aimed to demonstrate the high resolution computed tomography (CT) findings observed among the coronavirus disease 2019 (COVID-19) patients presented with pneumonia and to reveal the most frequent infiltration and distribution patterns of the disease. Methodology: This was a retrospective study. This study was performed in the Department of Radiology & Imaging at Kurmitola General Hospital, Dhaka, Bangladesh. This was the first dedicated COVID-19 hospital with a bed capacity of 500 and well-equipped ICU facilities. The recorded HRCT scan data were collected in the period from April 2020 up to May 2020 during the first wave of COVID-19 in Bangladesh. As this was a retrospective study, verbal or written consent was not obtained from all potential participants or guardians. The available demographic data as well as the medical history of all data were collected and thoroughly reviewed from the record book. These patients were RT-PCR confirmed cases of COVID-19 patients presented with pneumonia and were admitted to Kurmitola General Hospital, Dhaka, Bangladesh. All these patients underwent HRCT scans of the chest. Result: A total number of 155 COVID-19 patients with HRCT scan were evaluated. The mean age with SD of the study population was 58.03 ± 14.08 years with the range of 22 to 97 years. The male and female ratio was 2.04:1. Fibrosis of the lungs and thickening of pleura were found in 38 (24.5%) cases and 33 (21.3%) cases respectively. The involvement of both lungs was found in 32 (20.6%) cases. The presence of pneumonitis and bronchiectasis were detected in 77 (49.7%) cases and 5 (3.2%) cases respectively. Left-sided mild pleural effusion was also noted in 6 (3.9%) cases. Ground glass opacity was found in different forms. The most common form was the presence of only ground glass opacities which was 63 (40.6%) cases. Bilateral ground-glass opacities were detected in 63 (40.6%) cases. Conclusion: In conclusion, HRCT scan of the chest shows the bilateral ground-glass opacities and fibrosis of the lungs with pneumonitis in most of the COVID-19 hospital admitted patients.
文摘本文提出了一种低剖面锥形波束漏波天线,该天线实现了宽仰角扫描范围和较低的方位面不圆度水平。通过在平行板波导表面刻蚀一系列同心圆环漏波结构,实现了导波模式向锥形辐射波束的转换。为有效拓宽俯仰面内的扫描范围,对单元格的色散特性进行了理论分析。利用漏波结构的等效电路模型,提取了对应的集总电路元件参数。同时,评估了不同探针配置对不圆度水平的影响,并最终设计了一种基于接地共面波导的八路等功分馈电网络。实测结果表明,该天线能够工作于30.0 GHz~37.0 GHz的频率范围,相对带宽达21%,仰角扫描范围为45°。该天线具有稳定的全向辐射特性,方位面不圆度低于1.6 d B,交叉极化水平优于-22 d B。所设计的天线可满足毫米波卫星通信和引信探测等领域的应用需求。
文摘In close-aperture Z-scan experiments, a small aperture is conventionally located in the far-field thereby enabling the detection of slight changes in the laser beam profile due to the Kerr-lensing effect. In this work, by numerically solving the Fresnel-Kirchhoff diffraction integrals, the amount of transmitted power through apertures has been evaluated and a parametric study on the role of the various parameters that can influence this transmitted power has been done. In order to perform a comprehensive analysis, we have used a nonlinear phase shift optimized for nonlocal nonlinear media in our calculations. Our results show that apertures will result in the formation of symmetrical fluctuations on the wings of Z-scan transmittance curves. It is further shown that the appearance of these fluctuations can be ascribed to the natural diffraction of the Gaussian beam as it propagates up to the aperture plane. Our calculations reveal that the nonlocal parameter variations can shift the position of fluctuations along the optical axis, whereas their magnitude depends on the largeness of the induced nonlinear phase shift. It is concluded that since the mentioned fluctuations are produced by the natural diffraction of the Gaussian beam itself, one must take care not to mistakenly interpret them as noise and should not expect to eliminate them from experimental Z-scan transmittance curves by using apertures with different sizes.
文摘In this article, two terahertz transmission imaging systems are built with a 2.52 THz continuous wave laser and two types of sensors. One is array scanning system using a 124×124 pyro-electric array camera as the detector; the other is a point-wise scanning system utilizing a Golay cell as the detector. The imaging speed and quality is briefly analyzed. Terahertz （THz） imaging results demonstrate that the array scanning system has higher imaging speed with lower resolution. The point-wise scanning system has higher imaging quality with lower speed.
基金supported by the National Basic Research Program of China(Grant Nos.2009CB929400 and 2010CB923003)
文摘Our recent scanning tunneling microscopy （STM） studies of the NaFelxCoxAs phase diagram over a wide range of dopings and temperatures are reviewed. Similar to the high-Tc cuprates, the iron-based superconductors lie in close proximity to a magnetically ordered phase. Therefore, it is widely believed that magnetic interactions or fluctuations play an important role in triggering their Cooper pairings. Among the key issues regarding the electronic phase diagram are the properties of the parent spin density wave （SDW） phase and the superconducting （SC） phase, as well as the interplay between them. The NaFe l-xCoxAs is an ideal system for resolving these issues due to its rich electronic phases and the charge-neutral cleaved surface. In our recent work, we directly observed the SDW gap in the parent state, and it exhibits unconventional features that are incompatible with the simple Fermi surface nesting picture. The optimally doped sample has a single SC gap, but in the underdoped regime we directly viewed the microscopic coexistence of the SDW and SC orders, which compete with each other. In the overdoped regime we observed a novel pseudogap-like feature that coexists with supercon- ductivity in the ground state, persists well into the normal state, and shows great spatial variations. The rich electronic structures across the phase diagram of NaFel_xCoxAs revealed here shed important new light for defining microscopic models of the iron-based superconductors. In particular, we argue that both the itinerant electrons and local moments should be considered on an equal footing in a realistic model.
文摘Permanent waving is very popular in Japan. Polypeptide chains (main chains) form the principal components of hair, and they are lined up longitudinally. Hair relaxation is also called straight permanent waving, and there are methods that change curly or wavy hair into straight hair. Hair damage as a result of winding, combing, and using high-temperature hairdressing irons is also often seen. By using scanning electron micrographs (SEM) we showed broken hairs and hair damage caused by permanent wave solutions. The hair damage is obvious when comparisons are made with the condition of the hair surface, condition of the cuticle, etc. Hair swelling by permanent wave solutions, manipulations such as winding, etc., inadequate rinsing with water, procedures on injured hair at the outset, etc., are considered possible reasons for any of these types of injury.
文摘针对可重复使用飞行器热防护结构在复杂多场耦合环境下易产生层间脱粘损伤的关键问题,提出基于超声导波与域自适应迁移学习的无损检测方法。通过设计4类典型粘接缺陷的隔热瓦试件,结合双向正交扫描策略与超声激励–接收机制,实现粘接区域的高效覆盖检测。针对试件个体差异引起的信号漂移问题,采用基于峰值比例阈值的相位对齐方法,通过优化窗口长度同步保留损伤敏感特征并抑制噪声干扰。进一步构建域自适应迁移学习网络(Domain-adaptive transfer learning,DATL),实现跨试件损伤特征的分布对齐。试验表明,在跨试件测试场景下,DATL模型准确率仅下降3.9%,域间分布差异指数从0.31降至0.10;在目标域数据量不足40%时,其准确率仍达85%,较卷积神经网络(Convolutional neural network,CNN)提升19.4%。该方法缓解了对损伤类型和试件一致性的依赖,可降低在役热防护结构脱粘检测的误报率与漏检率,为可重复使用飞行器的快速无损检测与健康评估提供了一种可行的解决参考方案。
基金Project supported by the National Natural Science Foundation of China (Grant Nos.11174280,60990323,and 60990320)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No.YYYJ-1123)
文摘In this paper a millimeter-wave （MMW） squint indirect holographic method is presented, which is suitable for imaging with a large field-of-view. The proposed system employs the squint operation mode to remove the background and twin- image interferences, which achieves a similar effect to off-axis holography but leaves out the large-aperture quasi-optical component. The translational scanning manner enables a large field of view and ensures the image uniformity, which is difficult to realize in off-axis holography. In addition, a corresponding imaging algorithm for the presented scheme is developed to reconstruct the image from the recorded hologram. Some imaging results on typical objects, obtained with electromagnetic simulation, demonstrate good performance of the imaging scheme and validate the effectiveness of the image reconstruction algorithm.
