Radiology for the people

The general population of developing nations has not received sufficient radiological diagnostic services. Surveys will pinpoint the areas of greatest need. The best course seems to be to provide many basic diagnostic units of simple design rather than only a few sophisticated centers. The role of the radiologist is to oversee physician-technician training, equipment design, and system development. Only with a well-planned, comprehensive approach can the benefits of modern radiology reach the greatest number of people.     

Volvulus of the sigmoid colon

The clinical presentation and treatment of 31 consecutive patients with sigmoid volvulus are reviewed. Nearly half of these patients had a history of mental illness and one-third of all patients were chronically constipated. The main clinical features of abdominal pain and gross abdominal distension had been present for an average of 8 days before presentation of the patient to hospital. The clinical diagnosis of sigmoid volvulus was not difficult but the presence of non-viable bowel was more difficult to establish. A silent abdomen was the most valuable indication of the presence of gangrenous bowel. Conservative measures, including sigmoidoscopy and therapeutic barium enema, successfully reduced the volvulus in half of the cases so treated. In those patients undergoing surgery the procedure associated with the lowest mortality was sigmoid resection with end-to-end anastomosis. The overall mortality was 35%.     

酒石酸铵络合沉淀法制备CeO2纳米晶与表征

以硝酸铈、酒石酸铵为原料,采用络合沉淀法制备了CeO2纳米晶.考察研究了煅烧温度、形成沉淀的操作方式等影响因素.样品用XRD、TEM和SEM等测试方法进行了表征.由SEM照片,观察到样品形貌为蓬松泡沫状多孔性立体结构,从小区HRTEM照片,可以看到很清楚的晶格条纹,表明小颗粒均为CeO2纳米晶.     

粘土-SA01吸附和分离洛神葵红色素的研究

研究了吸附和分离洛神葵色素的方法和条件,粘土-SA01对洛神葵色素具有较好的吸附能力,温度、酸度等因素对吸附能力有一定影响。温度升高吸附较快,但温度升高到30℃以上时随着时间的延长色素的稳定性受影响。粘土-SA01对洛神葵色素的吸附能力在pH=1左右时比其它酸度条件下更强。乙醇浓度对粘土-SA01上色素的解脱效果有影响,乙醇浓度为40%时解吸效果最佳。     

Fabrication and characterization of micromachined rectangularwaveguide components for use at millimeter-wave and terahertzfrequencies

The fabrication and characterization of micromachined reduced-height air-filled rectangular waveguide components suitable for integration is reported in this paper. The lithographic technique used permits structures with heights of up to 100 μm to be successfully constructed in a repeatable manner. Waveguide S-parameter measurements at frequencies between 75-110 GHz using a vector network analyzer demonstrate low loss propagation in the TE₁₀ mode reaching 0.2 dB per wavelength. Scanning electron microscope photographs of conventional and micromachined waveguides show that the fabrication technique can provide a superior surface finish than possible with commercially available components. In order to circumvent problems in efficiently coupling free-space propagating beams to the reduced-height G-band waveguides, as well as to characterize them using quasi-optical techniques, a novel integrated micromachined slotted horn antenna has been designed and fabricated, E-, H-, and D-plane far-field antenna pattern measurements at different frequencies using a quasi-optical setup show that the fabricated structures are optimized for 180-GHz operation with an E-plane half-power beamwidth of 32° elevated 35° above the substrate, a symmetrical H-plane pattern with a half-power beamwidth of 23° and a maximum D-plane cross-polar level of -33 dB. Far-field pattern simulations using HFSS show good agreement with experimental results     

Investigation of Supercurrent in the Quantum Hall Regime in Graphene Josephson Junctions

In this study, we examine multiple encapsulated graphene Josephson junctions to determine which mechanisms may be responsible for the supercurrent observed in the quantum Hall (QH) regime. Rectangular junctions with various widths and lengths were studied to identify which parameters affect the occurrence of QH supercurrent. We also studied additional samples where the graphene region is extended beyond the contacts on one side, making that edge of the mesa significantly longer than the opposite edge. This is done in order to distinguish two potential mechanisms: (a) supercurrents independently flowing along both non-contacted edges of graphene mesa, and (b) opposite sides of the mesa being coupled by hybrid electron–hole modes flowing along the superconductor/graphene boundary. The supercurrent appears suppressed in extended junctions, suggesting the latter mechanism.     

Self-assembly of a sulphur-terminated graphene nanoribbon within a single-walled carbon nanotube

The ability to tune the properties of graphene nanoribbons (GNRs) through modification of the nanoribbon's width and edge structure widens the potential applications of graphene in electronic devices. Although assembly of GNRs has been recently possible, current methods suffer from limited control of their atomic structure, or require the careful organization of precursors on atomically flat surfaces under ultra-high vacuum conditions. Here we demonstrate that a GNR can self-assemble from a random mixture of molecular precursors within a single-walled carbon nanotube, which ensures propagation of the nanoribbon in one dimension and determines its width. The sulphur-terminated dangling bonds of the GNR make these otherwise unstable nanoribbons thermodynamically viable over other forms of carbon. Electron microscopy reveals elliptical distortion of the nanotube, as well as helical twist and screw-like motion of the nanoribbon. These effects suggest novel ways of controlling the properties of these nanomaterials, such as the electronic band gap and the concentration of charge carriers.     

绿色建筑中风环境模拟流程的标准化研究

采用计算机辅助设计对建筑室外风环境进行分析是绿色建筑区域规划的重要内容.然而,风环境的模拟流程工作千差万别,有必要对风环境的模拟工作建立一套标准化的模拟流程.从绿色建筑规划设计优化角度对风环境模拟的模型简化、计算区域选择、边界条件设置、数学模型选取、迭代次数设置、网络无关性检验等方面建立了一个完整的风环境模拟流程,用于...