Focused Practice

I. Answer the following questions:

1. Why have magnetoresistive recording heads heralded a new interest in the basic properties of magnetic materials?

2. Why has there been a keen interest in pushing materials to larger magnetoresistance?

3. How are new multilayer films being developed?

4. What other novel sensors have been proposed?

5. What is a sense current used for?

6. What controls the resolution of the sensor along the track?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: Magnetoresistive recording heads.

Unit 13 Grammar: The Gerund Word List:

1. membrane	мембрана, пленка
2. desalination	опреснение
3. reverse osmosis	обратный осмос (обратная диффузия)
4. quantum leap	количественный скачок
5. trend	направление, тенденция
6. osmotic pressure	осмотическое давление
7. rather than	а не; скорее...чем
8. porous sublayer	пористый подслой
9. in situ	на месте
10. as compared to	по сравнению с
11. tolerance	стойкость, выносливость

Progress in Membrane Science and Technology for Seawater Desalination

Membrane technologies have been incessantly progressing during the past forty years. No limit in the future progress is currently in sight. Contributions to membrane science and technology, upon reaching a critical mass, will result in another quantum leap that is equivalent to the historic announcement of the Loeb-Sourirajan membrane in nineteen sixty. There are some new trends observable in the following four areas: membrane development, membrane characterization, membrane transport and membrane system design. Membrane development deals with recent progresses in the development of reverse osmosis membranes used for desalination.

To increase the pure water recovery by a membrane module from the conventional 40 % to 60 % is a trend observable in seawater desalination technology. Since the osmotic pressure of the retentate will increase from 4.5 to 7.0 MPa when the water recovery increases from 40 to 60 %, the development of a high pressure vessel as well as the development of a membrane that will show little compaction under a high pressure is necessary. Kawada reported recently on the development of a reverse osmosis membrane that was suitable for operation at 9 MPa. He found that membrane compaction took place at the porous sublayer rather than at the skin layer. An attempt was therefore made to reduce the compaction by making a large number of uniform pores of small sizes at the surface of the porous sublayer on which an aromatic polyamide skin layer was coated by in-situ polycondensation.

The stability of the membrane module productivity increased significantly as compared to the conventional seawater desalination membrane.

One of the drawbacks of composite membranes based on aromatic polyamide is poor chlorine tolerance. Many attempts have been made to improve the chlorine resistance of composite membranes by changing the molecular structure of the monomers used for the polymerization. A patent was recently issued on a composite membrane that is chlorine resistant.