The Economist - USA (2019-07-13)

The EconomistJuly 13th 2019 Science & technology 73

2

1

constantcurrent,voltagecanbereduced.

Allthisfreesupspaceelsewhereinthe

vehicle,allowinganelectriccartobede-

signedfromscratchtobemoreefficient

andthereforecheapertorun.Otherbene-

fitsalsocomefromlightness.A smaller

batterycanbetoppedupmoreeffectively

bytheregenerativebrakingbuiltintothe

module,aswellasbeingfastertorecharge

whenpluggedintothemains.Indigohas

triedthet1 outonprototypecars rede-

signedtobemoreaerodynamic.Itreckons

theseprototypesneedonlya tenthofthe

powerrequiredbya combustion-engined

vehicle,evenathighwayspeeds.

Acombinationofa lightervehicleand

lightercomponentsinthet1 modulesalso

reducestheamountofunsprungweight.

Asforrideandcomfort,theactivesuspen-

sionandtheabilitytocontrolseparately

thepowerappliedto eachwheelpermit

bettergripandincreasedstabilityduring

brakingandcornering.

Indigoistalkingtocarmakersandcom-

ponentsfirmsandhopes,bytheendofthe

year,tolanditsfirstproductioncontract.

Dr Hemond expects particular interest

fromfirms developing ride-sharing and

autonomousvehicles.Thesortof small,

sleekvehicles orpersonal-mobility pods

whichsuchin-wheeldrivesystemsmight

inspirewouldbeaworldawayfromthe

perambulatory Lohner-Porsche. Butthey

wouldhavemadePorschehimselfwonder

whatmighthavebeenhadhestuckwith

theelectricmotor. 7

H

umans are creatures with sophisti-

cated colour vision, so the market for

pigments is big—about $30bn a year. In

this marketplace, however, not all colours

are equal. In particular, bright reds, much

desired for their attention-grabbing quali-

ties, are tricky to make, and each of the ex-

isting options has flaws.

The especially vivid reds made from

cadmium, lead and mercury are toxic and

so their use is now restricted. Cochineal,

created by crushing up Dactylopius coccus, a

species of scale insect, is safe to handle and

consume, but its safety is trumped in the

minds of some by its animal origin. A cam-

paign by vegans in 2012, for example,

forced Starbucks to remove cochineal from

its Strawberry Frappuccinos. Other red pig-

ments, meanwhile, either start off dull (ox-

ides of iron) or fade to dullness unless giv-

enspecialprotectionfrom ultraviolet light

(Pigment Red 254, the source of Ferraris’

characteristic scarlet livery). The hunt is

therefore on for a non-toxic, non-contro-

versial, chemically stable red.

One of those searching is Mas Subrama-

nian, a materials scientist at Oregon State

University. Dr Subramanian already has

one new pigment to his name. In 2009,

when trying to find a material known as a

multiferroic, which has distinctive elec-

tronic and magnetic properties, one of his

research students mixed oxides of yttrium,

indium and manganese and heated them

to 1,200°C. The result was a powder as bril-

liant as a bluebird’s wing. YInMn (pic-

tured), as it is now known, was the first

new blue discovered for two centuries.

The perfect red has so far eluded Dr Sub-

ramanian—in part because it is hard to

predict the colour of a material before you

make it. Small alterations to a crystal’s

structure can dramatically alter which

parts of the spectrum that crystal absorbs

and which it reflects. The green of emeralds

and the red of rubies, for instance, are both

caused by chromium atoms, but the atoms

in question are bonded into their respec-

tive lattices in different ways.

As it happens, rubies are one of Dr Sub-

ramanian’s inspirations. His hope is that

by piggybacking on the structure of their

crystals—already known to yield an appro-

priately, well, ruby, colour—he might be

able to reproduce the effect. A weakness of

this approach is that rubies themselves

make an unsatisfactory pigment. When

crushed, they become pale pink.

A second avenue may be more promis-

ing. Many inorganic reds, including those

based on cadmium, lead and mercury, are

semiconductors. Dr Subramanian and his

team hope to use tin—a metal in the same

group of the periodic table as lead—to pro-

duce a similarly vibrant, though non-toxic,

semiconductor pigment.

Inevitably, the semiconductor ap-

proach does bring problems of its own. A

semiconductor’s colour depends on a phe-

nomenon called its band gap. This is the

ease with which its atoms can shed elec-

trons. The process of shedding requires en-

ergy, often in the form of light, so a sub-

stance’s band gap helps determine which

frequencies of light it absorbs and which it

reflects. Unfortunately, band gaps can,

themselves, be altered by exposure to ener-

gy in the form of heat or light. That changes

the pigment’s colour.

For example, mercury sulphide, known

to painters as vermilion, has a small band

gap. This means it absorbs much of the vis-

ible spectrum, reflecting only red because

red light is insufficiently energetic to shift

the relevant electrons. If the gap is dimin-

ished still more, as sometimes happens

when vermilion is exposed to light, the pig-

ment absorbs all visible light and turns

black. Making a semiconducting red is not

enough, then. It also needs to stay red

when in use. And that essential property

remains elusive.

Dr Subramanian and his team have got

close. The tin approach has resulted in

some promising flame-bright supercon-

ducting oranges. But shrinking the band

gaps of such materials just that little bit

further, to the point where a brilliant red is

reflected instead, has so far proved beyond

their chemical skills. 7

A team of chemists are searching for a

new red pigment

Pigments

Studying scarlet

Not yet available in red

E

arly human fossils are so rare that

each new discovery may rewrite the

textbooks. A chance find two years ago in

Morocco, for example, pushed the origin of

Homo sapiensback to at least 315,000 years

ago, from a previous minimum of 260,000

years based on remains found in South Af-

rica. Now, as they report in this week’s Na-

ture, a group of palaeontologists have ex-

tended the known geographical range of

early Homo sapiensfrom Africa to Europe.

Katerina Harvati of the University of

Tübingen, in Germany, and her colleagues

found the relevant skull fragment not in

the ground, but in a museum in Athens. It

was one of a pair of specimens dug up in

the 1970s from Apidima, a cave in southern

Greece. Both were recognised as being hu-

man fossils of some sort, but had not been

dated or properly analysed. Dr Harvati and

A newly reinterpreted fossil muddies

the waters of human history

Palaeoanthropology

The ancientest

Greek