Тип условного Условие Следствие
предложения (придаточное) (главное)
I тип – реальное условие, If he comes, I shall be glad
относится к будущему If he should come, I shall be glad
(без if) Should he come, I shall be glad
Если он придет, я буду рад
II тип – маловероятное If he came, I should be glad
условие, относится к настоя- If he should come, I should be glad
щему или будущему (форма Should he come, I should be glad
прошедшего времени с части- If he were to come, I should be glad
цей бы) Were he to come, I should be glad
Если бы он пришел, я был бы рад
(сегодня, завтра)
III тип – нереальное условие, If he had come, I should have been glad
относится к прошедшему Had he come, I should have been glad
(форма прошедшего времени Если бы он пришел, я был бы рад (вчера)
с частицей бы)
Союзы, вводящие условные предложения
If - если
In case – в случае
Provided (providing), on condition – при условии, в случае
Unless – если не …
But for – если бы не …
Exercise. Переведите следующие условные предложения
I. 1. If a solid body or a liquid is heated, it will usually expand.
2. The measurements were always correct provided the necessary instruments were used.
II. 1. Providing mercury did not expand when heated, it would not be used for taking temperatures.
2. But for electricity little could be done in a modern research laboratory.
III. 1. Provided the operator’s cabin had been equipped with electronic control, he would have been able to work faster and with greater precision.
3. The manned spaceships might not have been launched into the cosmos unless scientists had studied the information received from the space satellites.
Nanotechnology
Найдите в словаре и запишите транскрипцию следующих слов. Правильно прочитайте данные слова несколько раз вслух и постарайтесь запомнить их произношение
Successful, either, precision, approach, dimension, time-consuming, thread, issue, occur, average, flexibility, influence
Words to be learnt
to fulfill – выполнять
attempt – попытка, усилие
ultimate goal – окончательная цель
precision – точность
proof – доказательство
approach – подход, направление, способ
to strive – стараться,
simple logic gates – логичная манера поведения, образ действия
assembly – сборка, сбор
time-consuming – долговременный
three-dimensional – трёхмерный
to thread – проходить сквозь
to shrink – сжимать(ся)
feedback – обратная связь
relevant – относящийся к делу, подходящий
double-helical structure – двух-спиральная структура
strand – скрученная полоска, нить
backbone – основа, сущность; позвоночник
to occur – получаться, случаться, происходить
adjacent bases – смежные, близлежащие основы
Text
There is already one highly successful nanotechnological system: we call it life. All the goals of nanotechnology are already fulfilled in living systems, and most of our attempts at nanotechnological applications can be called biomimetic, either applying the structural principles of living systems to different compounds or using the compounds of living systems for different purposes.
Nanotechnology can be defined as the development and use of devices that have a characteristic size of only a few nanometers. The ultimate goal is to fabricate devices that have every atom in the right place. Such technology would give the opportunity to minimize the size of a device and to reduce the material, energy and time necessary to perform its task. Potential applications include electrical circuits, mechanical devices and medical instruments. Molecular biology is a source of inspiration in this field of research: Living cells can synthesize a wide variety of macromolecules with atomic precision, that all have a specific function in the cell. This can be considered as the proof that there are no physical laws that forbid the construction of structures with atomic precision.
Essentially, there are two approaches towards the fabrication of structures at or near the atomic level: The first is the 'top down' approach where the precision of existing macroscopic techniques is improved. This concept has been demonstrated in semiconductor industry, where lithographic processes are nowadays used to make integrated circuits with critical dimensions smaller than 100 nm. This precision will be improved further, but true atomic precision cannot be obtained with this approach. The second 'bottom up' approach strives to build structures using atoms or molecules as building blocks. Most striking are experiments where individual atoms are positioned on an atomically flat substrate using scanning-probe techniques. Patterns of atoms have even been demonstrated to act as simple logic gates. Such scanning-probe techniques however are not very practical: Assembly by placing a single atom at a time is a very time-consuming process.
A particularly interesting 'bottom up' approach is to assemble structures from molecular building blocks. Using synthetic chemistry, large amounts of identical building blocks can be obtained at low cost. One of the most promising ideas is to use building blocks from living systems: The advantages are that these molecules are intensively studied and that they can be synthesized with atomic precision. Moreover, DNA building blocks have been used to assemble three-dimensional structures from small synthetic building blocks.
This thesis describes experiments where we use silicon nanotechnology to address the physical properties of individual molecules. A first set of experiments probes the polymer dynamics of DNA threading through small pores. In order to fabricate holes with a diameter on the order of the diameter of DNA we have developed a new technique to controllably shrink larger silicon oxide pores with direct visual feedback. We have also addressed the question whether a single DNA molecule can carry an electrical current. This is an important issue for potential DNA-based electronics. The last topic is electrochemistry using nanometer-scale electrodes, fabricated using silicon processing. A standing goal is to develop the technology to perform electrochemical experiments on a single molecule.
Most experiments in this thesis are performed on DeoxyriboNucleic Acid (DNA). This section contains a brief review of the relevant properties of this unique molecule. The structure and function have been intensively studied and the basics can be found in many biological textbooks. It consists of two polymer chains. Each monomer consists of a sugar ring, a phosphate group, and one of the four bases Adenine (A), Guanine (G), Thymine (T) or Cytosine (C). Watson and Crick were the first to determine the double-helical structure of DNA. They found that DNA consists of two strands, running anti-parallel. On the outside are the sugar-phosphate chains, also known as the 'backbone' of the molecule. On the inside of the helix are the bases, occurring in specific pairs: Adenine (A) specifically binds to Thymine (T) and Guanine (G) to Cytosine (C). From X-ray diffraction experiments on fibers of DNA, Watson and Crick were able to deduce the double helical structure.
The structure as reported by Watson and Crick became known as the 'B-DNA' helix. The diameter is about 2 nm and the distance between two bases is 0.34 nm. Each 10.4 bases or 3.6 nm, DNA makes a full helical turn. The structure is stabilized by the base-specific hydrogen bonds between the strands and the hydrophobic interactions between adjacent bases. This B-DNA helix is the structure for DNA with a mixed sequence at physiological conditions. It should be
noted that these properties are averaged over many subunits, and that the structure can vary with temperature, buffer conditions and the local sequence of bases. An intriguing property of double-strand DNA is its moderate flexibility: It can be smoothly bent or twisted with very little influence on the helical properties. An important property for our work is the fact that DNA in solution is highly charged at neutral pH. Each phosphate group on the backbone has a negative charge, resulting in a linear charge density of 5.9 e per nanometer. The effective charge density however is considerably lower due to countering condensation.
Задание I. Расставьте вопросы в соответствии с содержанием текста
1. What are two approaches towards the fabrication of structures at or near the atomic level?
2. What is the reason of development a new technique of fabrication holes with the diameter of DNA?
3. What is important issue for potential DNA-based electronics?
4. What is the most successful nanotechnological system?
5. What is the structure of Watson and Crick stabilized by?
6. When can the structure vary?
7. What is intriguing property of double-strand DNA?
8. How can nanotechnology be defined?
9. What does DNA molecule consists of?
10. Who determined DNA as the double-helical structure?
Задание II. Задайте данные в предыдущем упражнении вопросы «по цепочке» в группе
Задание III. Будьте готовы побеседовать по теме «Nanotechnology» с преподавателем и с группой
