The EconomistOctober 17th 2020 Science & technology 692
1polymer sandwiched between them. This
structure has many interacting resonance
modes. It is this that gives it its frequency
range. The trick that turns it into a power
source is that the ceramics are piezoelec-
tric—meaning they can convert the vibra-
tions of acoustic energy into electrical en-
ergy and vice versa. And, the ocean being a
noisy place, there is a lot of acoustic energy
around to convert. A device powered by a
piezoelectric broadband resonator can
thus constantly replenish its batteries
without them having to be changed.
The resonator also, though, has a sec-
ond use. It acts as an acoustic modem that
receives instructions to and broadcasts
data from the instrument it is part of. To
prove this works, Dr Adib and his col-
leagues used a resonator-based acoustic
modem to communicate 60 metres across
the Charles river, which separates mit’s
home town of Cambridge from Boston—
and, indeed, flows directly past the front of
the institute. The Charles is nowhere near
as noisy as the open ocean, so they had to
supply the sound to power the resonator
artificially, using an underwater loud-
speaker. Thus supplied, however, the de-
vice was able to transmit data at a rate of 20
kilobits a second. This is about the same as
a conventional acoustic modem.
Dr Adib has also, by attaching the reso-
nator to an appropriate sensor, used it to
transmit information about water tem-
perature, acidity and salinity. Indeed, he
sees sensors as an important market for the
new devices. One application would be
monitoring conditions in fish farms. An-
other would be in tracking tags for sea crea-
tures—though the current minimum size
of a resonator means this would, for the
moment, be practical only for large ani-
mals such as whales.Ring my chimes
Resonators could be employed, as well, as
nodes in underwater communications
networks—extending the range over which
a message can be sent. And they might be
used in underwater navigation beacons
that would provide precise location data to
submersibles unable (because signals
from satellites are radio waves) to employ
the global positioning system or one of its
equivalents for the purpose.
More specifically, America’s navy,
which is sponsoring the project, has plans
to use resonator-powered devices as sen-
tries. An array of such devices could calcu-
late the range and direction of a source of
sound such as a ship or submarine and
send it back to base.
Dr Adib and his team are now working
on extending the devices’ capabilities.
Their immediate goals include communi-
cating between pairs of them over a dis-
tance of a kilometre, and building net-
works that have hundreds of nodes. 7C
hildbirth is messy. When a baby
comes out, a lot else comes out with it.
Some of this material is inevitable, such as
the amniotic fluid that presages birth and
the placenta which follows it. But a fair bit
of faeces is discharged, too.
From an evolutionary perspective, that
seems surprising. Exposing newborns to
such bacteria-laden excrement looks risky.
Yet no mechanism has arisen to stop it hap-
pening. Evidence is mounting, moreover,
that far from being harmful, this exposure
is actually important for the development
of the child’s immune system. Interaction
with the multitude of microscopic organ-
isms a baby picks up when it is born helps
that system to learn friend from foe. With-
out it, immune disorders like allergies and
type-1 diabetes may follow. Components of
the gut flora are also involved in digesting
certain foodstuffs containing complex car-
bohydrates, and an unbalance in the rele-
vant microbial mix is implicated in obesity.
Babies born via Caesarean section (ie,
surgical removal directly from the womb)
do not get such a biological baptism, and
their guts are left bacterially bereft as a con-
sequence. That has left doctors wondering
how best to give them what they are miss-
ing. In the past, researchers have skirted
around the central point by swabbing the
faces of newborns with bacteria collected
from their mothers’ vaginas. To no avail.
Willem de Vos and Sture Andersson of the
University of Helsinki, have therefore tak-
en the bull by the horns. In a paper just
published in Cell they demonstrate that
feeding newborns a dose of their mothers’
gut bacteria, in the form of faeces inoculat-
ed into breast milk, seems more fruitful.
Dr de Vos and Dr Andersson selected
seven mothers-to-be who had elected, for
medical reasons, to have their children de-
livered by Caesarean. They were screened
to make sure they had no pathogenic bacte-
ria in their faeces. And none had recently
taken antibiotics.
Collectively, these seven women gave
birth to five girls and two boys, all healthy.
Each of the newborns was syringe-fed a
dose of breast milk immediately after
birth—a dose that had been inoculated
with a few grams of faeces collected three
weeks earlier from its mother. None of the
babies showed any adverse reactions to
this procedure. All then had their faeces
analysed regularly during the following
weeks. For comparison, the researcherscollected faecal samples from 47 other in-
fants, 29 of which had been born normally
and 18 by Caesarean section.
Dr de Vos and Dr Andersson found that,
though the bacterial populations in the
faeces of the seven treated infants initially
resembled those found in the faeces of the
untreated Caesarean-born infants, this
quickly changed. Within three weeks their
gut floras had come to resemble the bacte-
rial mix seen in the vaginally born infants.
Whether this shift to normality will reduce
the chances of children treated in this way
developing immune-related maladies later
in life remains to be determined by longer
and larger studies—which Dr de Vos and Dr
Andersson are now planning. 7How to arm Caesarean babies with the
bacteria they needGut microbesGerm lines
T
rees loomlarge in both environmental
science and the wider social and politi-
cal movement of environmentalism. Not
for nothing are greens sometimes called
“tree-huggers”. Generally, the arboreal
news is gloomy, as large areas of forest are
cleared and either burned or taken on a
one-way trip to the saw mill. But a paper
published in this week’s Nature, by Martin
Brandt of the University of Copenhagen
and Compton Tucker of nasa, America’s
space agency, brings some welcome good
news. A part of the world previously seen as
lacking in trees has actually been shown to
harbour almost 2bn of them.
The area in question embraces the west-
ern end of the Sahara desert and the semi-
desert Sahel region to its south. Few trees
have shown up here in past surveys be-Arid areas have more trees than
previously thoughtEcologyNot so deserted