皮皮学，免费搜题
登录
搜题
【简答题】
什么是螺纹联接的防松？按防松原理分，螺纹联接常用的防松方法有哪些？
拍照语音搜题，微信中搜索"皮皮学"使用
参考答案：
参考解析：
知识点：
皮皮学刷刷变学霸
举一反三
【单选题】按照《证券监督管理条例》的要求,以下关于证券公司独立董事的规定说法正确的是()。
A.
独立董事连任时间最多不超过7年
B.
任何人员最多可以在3家证券公司担任独立董事
C.
独立董事应当在股东(大)会上提交工作报告
D.
出于公司业务保密需要,某些情況下,独立董事享有的知情权可以少于其他董事
【单选题】Microbubbles: A new technique to treat disease involves the careful injection of tiny, drug-coated bubbles in the bloodstream. A Thilo Hoelscher, a neurologist at the University of Califomia, San Dieg...
B.
What makes this approach particularly interesting is that Dr Hoelscher wants to start treating stroke patients as soon as they are heaved into an ambulance, rather than waiting until they arrive in the emergency room. He plans to start a feasibility study before the end of the year in which some of San Diego's ambulances will be equipped with portable ultrasonic transducers. Andrei Alexandrov, a pioneer in theutic-ultrasound research who now directs the stroke centre at the University of Alabama, is pursuing a similar approach. He is designing an easy-to-use ultrasound helmet that an emergency-room nurse can attach before administering a vial of microbubbles. Both schemes are examples of a new idea in medicine, Which is to use tiny bubbles of gas not merely to highlight organs during ultrasonic scanning, as has been done for several years, but also as a form. of treatment. With clinical trials now getting under way, experts think it will take around five years for these new therapies to reach patients.
C.
Microbubbles are not just any old bubbles. They contain a chemically stable gas, such as perfluoropropane, instead of air. This gas is encapsulated in a fatty shell rather like a very small balloon. Even the largest microbubbles being tested for medical use are only five microns across, less than the diameter of a red blood cell. More advanced bubbles are only a few hundred nanometres across and can move easily through the lining of a blood vessel. They may also, crucially, be able to cross the blood-brain barrier, a tightly sealed layer of cells that protects the brain from erous chemicals including many drugs. If you put such a drug in the suce layer of a microbubble, you might be able to smuggle it into the brain.
D.
Having got into the brain (or anywhere else), a well-designed microbubble should also be able find a particular target. That is because the fatty layer can include molecules such as antibodies, which link up with proteins found on the suces of only one type of cell. A bubble with such an antibody in it would thus stick only to that type of cell. This sort of approach is being tested by Mark Borden and Paul Dayton, who work at another of the University of California's campuses, in Davis. They have demonstrated in rats that bubbles with an appropriate outer layer can be equipped with molecules that stick specifically to diseased cells. These molecules are initially hidden under a polymer layer to pr the immune system from destroying the bubbles. When the bubble arrives at its target, however, it is blasted with ultrasound in a way that exposes the molecule and makes the bubble stick.
E.
The two researchers can also use sound waves to steer bubbles towards a target, as if those bubbles were surfing a wave in the sea. Moreover, they can slow the bubbles down when they arrive where they are wanted. Once the bubbles have stuck good and fast to their targets, turning up the ultrasound still further will burst them, so that they release their payloads precisely where they can do most good. The result is smaller, better-aimed doses of drugs, which should mean fewer side-effects. In principle, such paytoads could be small-molecule drugs such as those used for cancer chemotherapy. They could be theutic prot
相关题目：