Bài thực hành nghe Tiếng Anh nâng cao - Bài 21 - Thẩm Tâm Vy - Năm 2018 (Có âm thanh)

 Thẩm Tâm Vy, December 23rd, 2018 PRACTISE LISTENING 21 ~ FOR ADVANCED LEARNERS 
PRACTISE LISTENING FOR ADVANCED LEANERS 21 
Tropical Diseases 
Learning The Lines 
Scanning mosquitoes with infrared light could help control malaria 
 Malaria killed 435,000 people last year, most of them in Africa. The parasite that 
causes the illness is carried by females of some, but not all, species of mosquitoes of the 
genus Anopheles. An insect becomes infected by biting an infected human being. Over 
the course of ten to 12 days, the parasites then multiply inside her. Once this has 
happened she transmits them with her bite. 
 The threat posed by an individual mosquito thus depends on its species, sex and age. 
Knowing these for lots of local insects gives a better idea of where, when and how to 
intervene in a particular place. If the locals are, for example, of a species that prefers to 
bite people inside houses, or to rest indoors after feeding, fumigating household 
interiors is the best approach. If not, it may be better to locate and disrupt breeding sites, 
using aerial spraying. 
 Sex is easy to determine. Males have bushy mouths—in essence, beards. Females do 
not. Determining species and age, though, is slow and laborious. DNA must be 
sequenced. Bodies must be dissected under microscopes. Chemical analyses must be 
performed. Laboratories in Britain and Tanzania are therefore testing an alternative—
infrared spectroscopy. Mario González-Jiménez, a chemist at the University of 
Glasgow, uses a diamond and a piece of steel that act as a hammer and anvil, crushing 
the mosquito to be analysed. The infrared light is then provided by a laser. With the 
insect duly splattered across one facet of the diamond, this laser is shone through the 
crystal onto it. The light reflected back out of the crystal by the insect’s remains is run 
through a spectroscope for analysis. 
 Part of the incident light will have been absorbed by various chemicals in the 
mosquito—particularly chitin (a structural carbohydrate), proteins and lipids in the 
animal’s cuticle. This absorption shows up in the reflected light’s spectrum as an 
absence of certain frequencies. These absences are called Fraunhofer lines, after the 
German physicist who discovered them two centuries ago. Particular molecules create 
particular patterns of Fraunhofer lines, as the missing light energy has been absorbed to 
drive the vibrations of atomic bonds within those molecules. Properly analysed, 
Fraunhofer lines provide information about the exact chemical make-up of whatever is 
reflecting the light. Their patterns in spectra therefore correspond to the different 
chemistries of species, sexes and ages. That permits the construction of a library, with 
which unknown insects can be compared. 
 Diamond geezers 
 That, at least, is the theory. Dr GonzálezJiménez is trying to put it into practice. His 
methods are now 83% accurate at recognising species, and close to 100% accurate at 
recognising age. He and his colleagues are also using the process to try to determine 
how resistant the now-dead insect being examined would have been to insecticides. 
 What works in a laboratory in a Scottish city might not, though, work in the African 
countryside. The person in charge of testing that out is Fredros Okumu, science director 
of the Ifakara Health Institute, a Tanzanian organisation. Ifakara runs Mosquito City, a 
research facility in the Kilombero River valley. Mosquito City’s buzzing, whining 
“biospheres” mimic local field conditions, even down to banana plants and goats. 
Besides testing the equipment, Dr Okumu and his team are also trying to extend the 
range of data that mosquito spectra can provide, including into the way the insects 
behave. Some mosquitoes, for example, feed only on people. Others dine as well on 
chickens, cows and goats. This is all valuable information. But it will be much more 
valuable if it can be gathered easily in the field. Engineers at Glasgow are therefore 
working on a laser optimised to emit light at the frequencies best suited for analysing 
mosquitoes. 
 Meanwhile, those at Ifakara are experimenting with shoebox-sized versions of the 
apparatus that can be taken into the countryside. Their aim is eventually to shrink this to 
something the size of a mobile phone. That could shine a whole new light on the 
problem of malaria.  [Source: The Economist, UK version, December 23rd, 2018] 
 Notes. 
 - fumigating: phun xịt khí độc để diệt côn trùng, sâu bọ 
 - spectroscopy bản sao chụp quang phổ || spectroscope: máy chiếu quang phổ 
 - cuticle: [sinh học] lớp biểu bì 
 - spectra [<= spectrum]: quang phổ 
 - Fraunhofer lines: In 1802, the English chemist William Hyde Wollaston was the first 
person to note the appearance of a number of dark features in the solar spectrum. In 
1814, Fraunhofer independently rediscovered the lines and began a systematic study 
and careful measurement of the wavelength of these features. In all, he mapped over 
570 lines, and designated the principal features with the letters A through K, and 
weaker lines with other letters. Modern observations of sunlight can detect many 
thousands of lines. [Wikipedia]