HVEM MAINTENANCE, OPERATION & UPGRADES

高压电子显微镜(Hvem)就是其中之一。 美国致力于生物研究的仪器。尽管有些人 它的能力可以被更现代的工具取代， HVEM仍然具有用于超厚切片、层析成像的独特能力 在高倾斜度和结晶学。这是至关重要的，必须是 维护和改进，使其能够继续为 生物圈。去年开始的这项雄心勃勃的计划已经 被削减，主要是因为我们的一名员工不再 在这里工作。我们将我们的努力集中在以下方面： 对用户影响最大的开发。HVEM 继续运行良好，常规生产优于1纳米 决议。TRD的目标是确保长期的 HVEM的可靠性，改进用户功能，扩展能力 成像厚(几微米)的切片和支架 结晶学发展。去年有几个项目是 承担了。Diffstak泵，是从威斯康星州获得的 HVEM，安装在摄像机上，并将摄象盒抽水 连接已修改。这些变化增加了相机的泵送 容量增加了大约十倍。由此带来的改进 按压时间允许用户更快地恢复拍照 在更换了一大堆胶卷之后。这通常允许两个 层析成像系列将在一天内获得；而以前仅 通常可以得到一个完整的系列。此外， 更好的极限真空度，可在“开窗”状态下运行 而不会降低柱真空度。这会缩短相机的拍摄时间 周期时间缩短约30%。这些因素加快了断层扫描数据的速度 收藏意义重大，它们还提供了一个吸尘器在 该塔，将提高运行和可靠性 乐器。制造了100个用于相机的新盒式磁带， 经过测试并投入使用，我们的两台摄像机--最初的那台 与我们的仪器一起提供的和从威斯康星州获得的-是 调整后，任何一盒磁带都能很好地与 摄影机。新的盒式磁带足以提供一套供使用 高分辨率胶片(柯达4489)和高感光胶片(杜蒙 LoDose)。样本对辐射敏感的用户现在可以 在低剂量条件下更容易操作。中的断层扫描项目 尤其将受益于拥有新的盒式磁带，因为在 除了能够更快、更大地拍摄低剂量图像之外 可以将成组的盒式磁带装入相机中，从而减少 转换是必需的。铀衬里，最初随附 在透镜柱的两个位置处形成真空密封。这些 衬里是由烧结铀制成的，不提供可靠的 海豹突击队。这家商店已经用荧光粉制造了替换零件。 青铜，这些部件将使柱真空提高至少一个 安装时的系数为2。安装将是 在下一次拆卸透镜柱以进行清洁时完成。 对高压电路的修改是在协商后进行的 与Haefely公司的一名工程师一起， 高压发电机和高压电子加速器。在.期间 在会诊时，发现一条电路出现了故障 连接在一起。这一点得到了纠正，几个可变电阻器 用固定电阻代替，提高了电路的稳定性。 至少具有同等重要性的电路的适当测试点 确定了模块并收集了基准性能数据。这 已经收到了回报，当一次高压故障发生时 发生了，对测试点电压的检查很快发现 问题的根源。来年计划的项目包括 其驱动因素是可靠性和用户便利性的提高。 开发网站(见TRD“hvem/IVEM网站以获取远程 在线图像查看“)将完成。一个新的计算机化 将设计和制造用于舞台倾斜的控制器。这将是 提高了倾斜的可靠性、准确性和易用性。一个 用于工作台位置控制和读出类似装置也将 设计和制造。它将允许用户重新定位 更快速和准确的样本，并将允许轻松返回 先前标记的位置。一种电路，用于确定适当的 曝光将被设计并集成到相机控制中，以便 正确的曝光时间将自动实现。这个 摄像机将通过安装快门来保护，该快门 除非用户实际正在查看样本，否则会自动关闭。 这将防止可能发生的意外损坏，例如在 使用切分胶片相机。

The high-voltage electron microscope (HVEM) is one of two such instruments in the US devoted to biological research. Although some of its capabilities can be taken over by more modern instruments, the HVEM still has unique capability for very thick sections, tomography at high tilt and crystallography. It is essential that the HVEM be maintained and improved so that it can continue to serve the biological community. The ambitious program begun last year has had to be curtailed, primarily because one of our staff is no longer employed here. We have concentrated our efforts on those aspects of development which have the greatest impact on the user. The HVEM continues to operate very well and routinely produces better than 1 nm resolution. The goals of this TRD are to ensure the long-term reliability of the HVEM, improve user functions, extend capability for imaging thick (several micrometer) sections, and support crystallography development. Last year several projects were undertaken. The Diffstak pump, which was obtained from the Wisconsin HVEM, was installed on the camera, and the camera box pumping connection was modified. These changes increased the camera pumping capacity by about a factor of ten. The resulting improvement in pump-down time allows the user to resume taking pictures more rapidly after a load of film has been replaced. This often allows two tomographic series to be obtained in one day; whereas, previously only one complete series could usually be obtained. In addition, the better ultimate vacuum allows operation in "window open" condition without degradation of the column vacuum. This shortens the camera cycle time by about 30%. These factors speed up tomographic data collection significantly, and they also provide a cleaner vacuum in the column, which will improve the operation and reliability of the instrument. One hundred new cassettes for the camera were fabricated, tested and put into service, and both our cameras--the one originally supplied with our instrument and that obtained from Wisconsin--were adjusted so that any of the cassettes would work well with either camera. The new cassettes are sufficient to provide sets for use with high-resolution film (Kodak 4489) and high-sensitivity film (Dumont LoDose). Users whose specimens are radiation-sensitive can now operate more easily in low-dose conditions. Tomographic projects in particular will benefit from having the new cassettes since, in addition to being able to take low-dose images more rapidly, larger groups of cassettes can be loaded into the camera reducing the number of change-over's required. Uranium liners, originally supplied with the HVEM, form vacuum seals at two places in the lens column. These liners are made from sintered uranium, and do not provide reliable seals. The shop has fabricated replacement parts from phosphor bronze, and these parts will improve the column vacuum by at least a factor of two when they are installed. Installation will be accomplished when the lens column is next disassembled for cleaning. Modifications to the high-voltage circuitry were made in consultation with an engineer from the Haefely company, the manufacturers of the high-voltage generator and electron accelerator for the HVEM. During the consultation, a circuit was discovered not to have been properly connected. This was corrected and several variable resistors were replaced by fixed resistors to improve the stability of the circuitry. Of at least equal importance, appropriate test points for the circuit modules were determined and baseline performance data collected. This has already paid off when an incident of high-voltage failure occurred, and examination of test-point voltages quickly uncovered the sources of the problem. Projects planned for this coming year are driven by improvements in reliability and user convenience. Development of the web site (see TRD "HVEM/IVEM websites for remote on-line image viewing") will be completed. A new computerized controller for stage tilt will be designed and fabricated. This will increase the reliability, accuracy and ease of use of tilting. A similar device for stage position control and readout will also be designed and fabricated. It will allow the user to reposition the specimen more quickly and accurately and will allow easy return to previously marked positions. A circuit to determine the proper exposure will be designed and integrated into the camera control so that the correct exposure time will automatically be achieved. The video camera will be protected by installing a shutter which automatically closes unless the user is actually viewing the specimen. This will prevent inadvertent damage which could occur, e.g., during use of the cut film camera.