20 | New Scientist | 13 February 2021Invasive speciesMoving pack makes
power as you walkA BACKPACK fitted with shock
absorbers that generate electricity
is easier to carry and can power
LEDs and other devices.
The bag is suspended on sliding
rails that allow it to move up and
down, with a pair of rubber ropes
on a pulley system acting like a
car’s suspension to reduce the
impact of the pack as you walk.
This reduces the force generated
by the contents of the pack jigglingWe may have solved
one Martian mysteryFOR years, researchers have argued
about whether strange streaks on
the surface of Mars are caused by
flowing water or sliding dust. It
seems both sides may be right.
Recurring slope lineae (RSLs)
are dark stripes that appear to
flow down the sides of craters on
Mars during the warmest parts
of the year. Janice Bishop at the
SETI Institute in California and
her colleagues were studying
the strange behaviour of salty
sediments in Antarctica when they
realised that similar processes
could cause RSLs on Mars.
They used soils similar to those
found on Mars to test their idea.
When they added a small amount
of water, it percolated through
the soil and brought salts to the
surface. These created a crust
with pockets of air beneath it that
formed as the salts expanded with
water and then contracted again.Solar system^ TechnologyAUSTRALIA is looking at using a
type of herpes virus as a biological
agent to cut the number of carp in
the country’s waterways.
Since its introduction there
in the late 1960s, the common
carp (Cyprinus carpio) has led to
a decline in native fish and plants.
Ivor Stuart at the Arthur
Rylah Institute for Environmental
Research, which is the biodiversity
research organisation for the state
government of Victoria, and his
colleagues have now estimated the
size of the problem. They calculated
that, in a year with average rainfall,
there are roughly 199 million
carp in Australia – equivalent
to 215,450 tonnes of fish.
“Carp tend to impact the amenity
and biodiversity of an aquatic
system when they reach 80 to 100
kilograms per hectare,” says Stuart.The researchers found that carp
pass this threshold for biodiversity
impact in 54 per cent of wetlands,
70 per cent of rivers in general and
97 per cent of large, lowland rivers.
The estimate was calculated
using a database the team created,
based on 574,145 carp caught at
4831 sites between 1994 and
2018, plus the results of 153
research studies (Biological
Conservation, doi.org/ghtmsm).
While trapping helps control the
carp, the Fisheries Research and
Development Corporation (FRDC),
on behalf of Australia’s government,
is assessing possible use of cyprinid
herpesvirus 3 as a broader control
strategy. This is a highly contagious
virus that kills common and koi carp.
“Australia would be a world
first in this regard,” says Jennifer
Marshall at the FRDC. Donna LuVirus could be unleashed to
control carp in world first
about by around 21 per cent.
“When we are walking, the mass
centre of the body moves up and
down,” says Jia Cheng at Tsinghua
University, China, who developed
the prototype with his colleagues.
An ordinary backpack moves with
this mass centre, but the pulley
system cancels that motion out,
then uses the relative movement
between bag and body to power
a triboelectric nanogenerator
(TENG) that converts mechanical
energy into electricity.
When worn by someone who
is walking, the backpack’s TENG
converts 14 per cent of the bag’s
movement into 118 microjoules
of electrical energy. The team
used this to power LEDs, a
fluorescent light or a watch
(ACS Nano, doi.org/ftvb).
The current version is around
3 kilograms – too heavy to be
widely used, but Cheng thinks this
can be reduced to make it more
feasible. He hopes to bring the
next version down to 1 kilogram.
Chris Stokel-Walker“It’s like a seasoning mix with
salt in it: just a little bit of water
and it sticks to everything and
gets all crusty and stuck in the
shaker,” says Bishop.
Recent observations of the
Martian surface have shown that
RSLs are more likely to occur after
dust storms. Dumping dust on
thin, salty crusts could cause them
to collapse into the air pockets
beneath. That could then trigger
more dust to slide downhill,
causing what we see as RSLs
(Science Advances, doi.org/ftkn).
“The whole RSL story is
complicated because we are not
there and we can’t test it,” says
Bishop. The rovers that have
been on Mars can only dig a few
centimetres down, so can’t tell us
anything about the possibilities
of processes like the one Bishop
and her colleagues suggest could
cause RSLs. However, the Rosalind
Franklin rover, planned to launch
in 2022, will have the capability
to dig deeper, so it may be able to
solve the mystery. Leah CraneVO
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NANO 2021News In brief