First Commercial-Grade Aircraft Flies On Hydrogen Fuel Cells

"It uses solar energy to drive electrolytic converters to produce
gaseous hydrogen for use in the cold fuel cells"

Hey, I've heard that approach to electric motive power someplace
before. :-)

Like Jim said in another message thread, hydrogen research was done
extensively decades ago. But the efficiency of electrolysis, fuel
cells and photovoltaics have vastly improved to the point today where
hydrogen power is now evidentially feasible, at least experimentally.
But this is only the beginning of gaseous hydrogen (H2) powered
aircraft technology.

The future is Liquid H2 (LH2) that contains three-times the energy
density of gasoline, and is three times lighter in weight. Together
with today's efficient cryocooler technology
https://link.springer.com/chapter/10...306-47112-4_10 and
high-efficiency solar panels, the production of liquid hydrogen from
water will soon revolutionize electric motive power throughout the
world all without producing any environmentally harmful byproducts.

Storage of LH2 is not a limiting issue, as today you can purchase a
cheap dewar on Amazon that claims a 175days holding time:
https://www.amazon.com/BestEquip-Nit.../dp/B07MJQDB43
That technology stores hydrogen at ambient atmospheric pressure, and
is eminently adaptable to aircraft fuel tanks.

LH2 availability is easily produced locally on-site anywhere there is
water and sunlight. It's about time ...

While the efficiency of photovoltaics may be only around 20% to 30%
efficient, they operate for decades without any moving parts, so once
generating stations are built, their maintenance is orders of
magnitude less than petrochemical production, refining, and transport.
It doesn't take a degree in engineering to comprehend the significance
of zero-emission ~95% efficient electric motors compared to ~20% to
30% efficient smog producing internal combustion engines. The stored
energy of hundreds of millions of years of solar power locked away in
carboniferous strata enabled our species to drag itself out of the
stone-age into the industrial-age; with the environment on the brink
of collapse, the time is upon us to progress to the next technological
age before it's too late. (The oceans are rising as a result of
melting polar ice. 60% of animal species have gone extinct in within
the past fifty years. Forests are disappearing at an alarming rate.
There are no longer any sea stars on the Pacific coast of North
America. ...)

Today, fuel-cell development has progressed to ~60% efficiency with
only byproducts of heat and water. It is immediately evident, that
systems of hydrogen fuel-cells powering electric motors can
theoretically double motive power production easily, and without
further polluting our once-magnificent Edenesque Terrestrial Paradise.

Forward thinking billionaires, like Elon Musk, use their wealth for
good to bring a sustainable future into reality, while evil, greedy
billionaires, like the oil baron Koch brothers and unscrupulous hedge
fund manager Mercers, use their money and power to put a criminal
fraud in the Whit House to open sacred protected old-growth forests to
rapacious logging
https://www.pbs.org/newshour/show/tr...talists-dismay
and supporting the dying coal industry.

This is a time in the evolution of humankind to cast off the archaic
technologies that have brought Earth's closed-cycle environment to the
brink of disaster, and develop sustainable technologies that will
serve us in reversing the industrial destruction of our once
miraculous habitat, and enable closed-cycle extraterrestrial
exploration and habitation in mankind's march toward our future
destiny.

Let's hope those with the power to effect positive change are able to
vanquish the those pathetically misguided avaricious wealthy who cling
to their backward looking vision, and lead us to the sunlight uplands
of a splendid future...

---------------------------------------------------------------------------
https://www.avweb.com/aviation-news/...gen-fuel-cells

First Commercial-Grade Aircraft Flies On Hydrogen Fuel Cells

Paul Bertorelli
September 26, 20203

With pure battery powered aircraft still short on endurance, hydrogen
fuel cell technology is gaining traction. And in the U.K. this week,
ZeroAvia flew the first commercially viable aircraft—a Piper M-class
airframe—on a combination of batteries and fuel cells. The flight took
place at the company’s R&D headquarters at Cranfield, northwest of
London.

The flight was part of the U.K.’s HyFlyer R&D project that’s aimed at
creating reduced-carbon aviation powerplants. ZeroAvia has previously
flown the same M-class on pure battery power, but this week’s
demonstration marked the first time hydrogen fuel cells have been
added to the power mix. The flight was a short one, but ZeroAvia CEO
Val Miftakhov said that by the end of the year, the company will
demonstrate a 300-mile flight at about 200 knots.

With support from the U.K. government—about $3.5 million (£2.75
million)—ZeroAvia’s short-term goal is to prove the technology is
suitable for short revenue flights in aircraft like the M-class, but
it will eventually be suitable for a 20-seat regional airliner such as
the Twin Otter, Dornier 228 or the Cessna Sky Courier, now undergoing
certification in Wichita. Such fuel cell powerplants would be in the
range of 800 horsepower and would be comparable to Pratt & Whitney’s
ubiquitous PT6 turbine.

Aware that the hydrogen infrastructure is critical to the concept,
ZeroAvia is addressing that at Cranfield with its own hydrogen
production station. It uses solar energy to drive electrolytic
converters to produce gaseous hydrogen for use in the cold fuel cells
ZeroAvia is using. This week’s demonstration flight used some battery
power, but not as a power buffer. Miftakhov said at a press conference
on Friday that it is possible to fly solely on hydrogen.

Zero Avia’s goal is develop reliable and scalable hydrogen powerplants
that airframers can use in place of fossil fuel engines. “We believe
that there are a lot of aircraft manufacturers that know what they’re
doing. What’s needed in the industry is to build powerplants that can
use clean fuel. And that’s what we’re focusing on,” he said.

ZeroAvia started as a U.S. company but moved to the U.K. this year
because of a more favorable investment climate and serious government
interest in low-carbon energy sources.
-------------------------------------------------------------------

https://www.zeroavia.com
Our Mission

ZeroAvia enables zero emission air travel at scale, starting with 500
mile short-haul trips, at half of today’s cost.

Novel approach removes many limitations of the current zero emission
programs.

ZeroAvia’s achievement is the first step to realising the
transformational possibilities of moving from fossil fuels to
zero-emission hydrogen as the primary energy source for commercial
aviation. Eventually, and without any new fundamental science
required, hydrogen-powered aircraft will match the flight distances
and payload of the current fossil fuel aircraft.

ZeroAvia will now turn its attention to the next and final stage of
its six-seat development program - a 250-mile zero emission flight out
of an airfield in Orkney before the end of the year. The demonstration
of this range is roughly equivalent to busy major routes such as Los
Angeles to San Francisco or London to Edinburgh.

Intelligent Energy will optimise its high power fuel cell technology
for application in aviation whilst EMEC, producers of green hydrogen
from renewable energy, will supply the hydrogen required for flight
tests and develop a mobile refuelling platform compatible with the
plane.

In addition to all the aircraft work, ZeroAvia and EMEC have developed
the Hydrogen Airport Refuelling Ecosystem (HARE) at Cranfield Airport
- a microcosm of what the hydrogen airport ecosystem will look like in
terms of green hydrogen production, storage, refuelling and fuel cell
powered-flight. This also marks another world’s first - a fully
operational hydrogen production and refueling airport facility for
primary commercial aircraft propulsion.

ZeroAvia’s hydrogen-electric powertrain is projected to have lower
operating costs than its jet-fuelled competition due to lower fuel and
maintenance costs. The company plans to control hydrogen fuel
production and supply for its powertrains, and other commercial
customers, substantially reducing the fuel availability and pricing
risks for the entire market.

Larry Dighera wrote:

"It uses solar energy to drive electrolytic converters to produce
gaseous hydrogen for use in the cold fuel cells"

Hey, I've heard that approach to electric motive power someplace
before. :-)

Like Jim said in another message thread, hydrogen research was done
extensively decades ago. But the efficiency of electrolysis, fuel
cells and photovoltaics have vastly improved to the point today where
hydrogen power is now evidentially feasible, at least experimentally.
But this is only the beginning of gaseous hydrogen (H2) powered
aircraft technology.

The future is Liquid H2 (LH2) that contains three-times the energy
density of gasoline, and is three times lighter in weight. Together
with today's efficient cryocooler technology
https://link.springer.com/chapter/10...306-47112-4_10 and
high-efficiency solar panels, the production of liquid hydrogen from
water will soon revolutionize electric motive power throughout the
world all without producing any environmentally harmful byproducts.

Don't hold your breath.

High efficiency solar cells means about 25% efficient, up from the
previous 15% of twenty years ago.

However, the absolute maximum efficency for silicon cells, limited
by the laws of physics, is 29.43%.

Using concentrators, i.e. lenses and mirrors, GaAs cells in labratories
have achieved about 35%.

Commercially available solar cells max out at about 20%.

snip

While the efficiency of photovoltaics may be only around 20% to 30%
efficient, they operate for decades without any moving parts,

At continuously declining efficiencies and require constant cleaning.

Don't forget the cost of land which will get you about 1 kW of raw
solar energy per square meter at Noon on a clear day in the South
West, or about 200 W after conversion.

Just like fusion, solar energy and hydrogen will be here any day
now...


--
Jim Pennino

On Mon, 28 Sep 2020 15:57:55 -0000, wrote:


High efficiency solar cells means about 25% efficient, up from the
previous 15% of twenty years ago.

However, the absolute maximum efficency for silicon cells, limited
by the laws of physics, is 29.43%.

Using concentrators, i.e. lenses and mirrors, GaAs cells in labratories
have achieved about 35%.



It would seem that photovoltaic technology marches inexorably forward.

Don't miss the article at the bottom of this page: Six-junction III–V
solar cell with 47.1% efficiency [under 143 Suns concentration]

-----------------------------------------------------------------
https://newatlas.com/energy/tandem-s...rd-efficiency/
New silicon/perovskite solar cell world record nears 30% efficiency
By Michael Irving
December 10, 2020

A small lab sample of the new tandem silicon/perovskite solar cell
designEike Köhnen/HZB
VIEW 1 IMAGES

Silicon has long been the gold standard for solar cells, but it’s
beginning to reach its limit. Perovskite is emerging as a promising
partner, and now engineers have achieved a new efficiency record
closing in on 30 percent for this kind of tandem solar cell.

Ever since perovskite burst onto the solar cell scene around a decade
ago, it’s broken efficiency records at a blistering pace – especially
when it’s paired with silicon. Just five years ago, tandem solar cells
had a maximum efficiency of 13.7 percent, two years ago it was up to
25.2 percent, and earlier this year the tech hit 27.7 percent.

Now, a team led by scientists at Helmholtz-Zentrum Berlin (HZB) have
managed to squeeze an impressive 29.15 percent efficiency out of their
tandem silicon-perovskite solar cell. That’s approaching the milestone
30 percent mark, and not too far off the theoretical limit of 35
percent.

For reference, the efficiency of either silicon or perovskite alone
usually maxes out at around 20 percent. They play well together
because they absorb different wavelengths of light – silicon focuses
mostly on the red and infrared part of the spectrum, while perovskite
excels at green and blue light.

To make the new device, the team started with a perovskite composition
with a 1.68-eV band gap. Then they developed a new substrate made of
carbazole-based molecules with methyl group substitution, which helped
electrons flow through to the electrode more efficiently.

In its current form, the solar cell was tested in a 1 cm2 (0.2 in2)
sample, but the researchers say that it should be relatively simple to
scale up to more practical sizes.

Earlier this year this efficiency record was certified at Fraunhofer
ISE and listed in the NREL chart, which has kept track of solar cell
technology progress since 1976. Now, a study describing the new work
has been published in the journal Science.

Source: Helmholtz-Zentrum Berlin via Eurekalert
-------------------------------

https://science.sciencemag.org/content/370/6522/1300

Monolithic perovskite/silicon tandem solar cell with 29% efficiency
by enhanced hole extraction

View ORCID ProfileAmran Al-Ashouri1,*, View ORCID ProfileEike
Köhnen1,*, View ORCID ProfileBor Li1, View ORCID ProfileArtiom
Magomedov2, View ORCID ProfileHannes Hempel3, View ORCID ProfilePietro
Caprioglio1,4, View ORCID ProfileJosé A. Márquez3, View ORCID
ProfileAnna Belen Morales Vilches5, Ernestas Kasparavicius2, View
ORCID ProfileJoel A. Smith6,7, View ORCID ProfileNga Phung6, View
ORCID ProfileDorothee Menzel1, View ORCID ProfileMax Grischek1,4, View
ORCID ProfileLukas Kegelmann1, View ORCID ProfileDieter Skroblin8,
View ORCID ProfileChristian Gollwitzer8, View ORCID ProfileTadas
Malinauskas2, View ORCID ProfileMarko Jošt1,9, View ORCID
ProfileGašper Matic9, View ORCID ProfileBernd Rech10,11, View ORCID
ProfileRutger Schlatmann5,12, View ORCID ProfileMarko Topic9, View
ORCID ProfileLars Korte1, View ORCID ProfileAntonio Abate6, View ORCID
ProfileBernd Stannowski5,13, View ORCID ProfileDieter Neher4, View
ORCID ProfileMartin Stolterfoht4, View ORCID ProfileThomas Unold3,
View ORCID ProfileVytautas Getautis2, View ORCID ProfileSteve
Albrecht1,11,†
See all authors and affiliations

Science 11 Dec 2020:
Vol. 370, Issue 6522, pp. 1300-1309
DOI: 10.1126/science.abd4016
Article
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Efficiency from hole-selective contacts
Perovskite/silicon tandem solar cells must stabilize a perovskite
material with a wide bandgap and also maintain efficient charge
carrier transport. Al-Ashouri et al. stabilized a perovskite with a
1.68–electron volt bandgap with a self-assembled monolayer that acted
as an efficient hole-selective contact that minimizes nonradiative
carrier recombination. In air without encapsulation, a tandem silicon
cell retained 95% of its initial power conversion efficiency of 29%
after 300 hours of operation.

Science, this issue p. 1300

Abstract
Tandem solar cells that pair silicon with a metal halide perovskite
are a promising option for surpassing the single-cell efficiency
limit. We report a monolithic perovskite/silicon tandem with a
certified power conversion efficiency of 29.15%. The perovskite
absorber, with a bandgap of 1.68 electron volts, remained phase-stable
under illumination through a combination of fast hole extraction and
minimized nonradiative recombination at the hole-selective interface.
These features were made possible by a self-assembled,
methyl-substituted carbazole monolayer as the hole-selective layer in
the perovskite cell. The accelerated hole extraction was linked to a
low ideality factor of 1.26 and single-junction fill factors of up to
84%, while enabling a tandem open-circuit voltage of as high as 1.92
volts. In air, without encapsulation, a tandem retained 95% of its
initial efficiency after 300 hours of operation.

https://www.sciencemag.org/about/sci...-article-reuse
-------------------------------------------------------

https://www.helmholtz-berlin.de/pubb...seitenid=74699

29.01.2020
World Record: Efficiency of perovskite silicon tandem solar cell jumps
to 29.15 per cent

The tandem solar cell was realized on a typical laboratory scale of
one square centimeter. However, scaling up is possible. © Eike
Köhnen/HZB

The illustration shows the structure of the tandem solar cell: between
the thin perovskite layer (black) and the silicon layer (blue) are
functional intermediate layers.
The illustration shows the structure of the tandem solar cell: between
the thin perovskite layer (black) and the silicon layer (blue) are
functional intermediate layers. © Eike Köhnen/HZB

Video Player

How does a perovskite silicon cell work? 02:14
In the race for ever higher efficiency levels, an HZB development team
has once again pulled ahead. The groups of Steve Albrecht and Bernd
Stannowski have developed a tandem solar cell made of the
semiconductors perovskite and silicon, that converts 29.15 per cent of
the incident light into electrical energy. This value has been
officially certified by the CalLab of the Fraunhofer Institute for
Solar Energy Systems (ISE) and means that surpassing the 30 per cent
efficiency mark is now within reach.

While silicon converts mostly the red portions of sunlight into
electricity, perovskite compounds primarily utilise the blue portions
of the spectrum. A tandem solar cell made of stacked silicon and
perovskite thus achieves significantly higher efficiency than each
individual cell on its own.

Prof. Bernd Stannowski from the HZB Institute PVcomB and Prof. Steve
Albrecht, who heads a team funded by the German Federal Ministry of
Education and Research (BMBF) at HZB, have already jointly set new
records for monolithic tandem solar cells on several occasions. At the
end of 2018, the team presented a tandem solar cell made of silicon
with a metal-halide perovskite that achieved an efficiency of 25.5 per
cent. Then Oxford Photovoltaics Ltd. announced a value of 28 per cent.

World record certified
Now the HZB team can report the next record. The value of 29.15 per
cent has been certified by the Fraunhofer Institute for Solar Energy
Systems (ISE) and now appears in the charts of the National Renewable
Energy Lab (NREL), USA. The NREL chart has been tracking the rising
efficiency levels for nearly all types of solar cell since 1976.
Perovskite compounds have only been included since 2013 – and the
efficiency of this class of material has increased more than in any
other material since then.

“We developed a special electrode contact layer for this cell in
collaboration with the group of Prof. Vytautas Getautis (Kaunas
University of Technology), and also improved intermediate layers“,
explain Eike Köhnen and Amran Al-Ashouri, doctoral students in
Albrecht's group. The new electrode contact layer also permitted
improvement of the perovskite compound‘s composition in the HZB
HySPRINT laboratory. This compound is now more stable when illuminated
in the tandem solar cell and improves the balance of electrical
currents contributed by the top and bottom cells. The silicon bottom
cell comes from Stannowski's group and features a special
silicon-oxide top layer for optically coupling the top and bottom
cells.

Upscaling is feasible
All processes used to realise this one-square-centimeter cell are also
suitable in principle for large surface areas. Scaling up with the
help of vacuum deposition processes is very promising, as initial
tests have already shown.

The realistic practical efficiency limit for tandem cells made of
silicon and perovskite is about 35 per cent. Next, the HZB team wants
to break the 30 per cent efficiency barrier. Albrecht explains that
initial ideas for this are already under discussion.

More Information:

Steve Albrecht heads the junior research group Perovskite Tandem Solar
Cells and is a junior professor at the TU Berlin. He is researching
the organic-inorganic material perovskite, which is one of the biggest
surprises in solar cell research: In just six years, the efficiency of
perovskite solar cells has quintupled. In addition, perovskite layers
can be produced from solution and in future can be printed
cost-effectively on large areas.

Albrecht's team, in cooperation with other groups from HZB, has
already set several world records for tandem solar cells made of
perovskite in combination with inorganic semiconductors. In September
2019, they presented a tandem solar cell made of CIGS and perovskite
that achieves a certified efficiency of 23.26 percent, which is still
the current world record for this material combination. They also
developed an industry relevant perovskit/PERC solar cell in 2019 with
a PV industry partner.
-------------------------------------------------------------

https://www.eurekalert.org/pub_relea...-pts120720.php

NEWS RELEASE 10-DEC-2020
Perovskite/silicon tandem solar cells on the magic threshold of 30%
efficiency

The current world record tandem solar cell provided stable performance
for 300 hours - even without encapsulation

HELMHOLTZ-ZENTRUM BERLIN FÜR MATERIALIEN UND ENERGIE

Research News

IMAGE
IMAGE: THE SCHEMATIC STRUCTURE OF THE TANDEM SOLAR CELL STACK IN 3D.
view more

CREDIT: EIKE KOEHNEN/HZB

Solar cells consisting of two semiconductors with differing band gaps
can achieve considerably higher efficiencies when used in tandem
compared to the individual cells on their own. This is because tandem
cells use the solar spectrum more efficiently. In particular,
conventional silicon solar cells primarily convert the infrared
components of light efficiently into electrical energy, while certain
perovskite compounds can effectively utilise the visible components of
sunlight, making this a powerful combination.

In the beginning of 2020, a team headed by Prof. Steve Albrecht at the
HZB broke the previous world record for tandem solar cells made of
perovskite and silicon (28.0%, Oxford PV), setting a new world record
of 29.15%. Compared to the highest certified and scientifically
published efficiency (26.2% in DOI: 10,1126/science.aba3433), this is
a giant step forward. The new value has been certified at Fraunhofer
ISE and listed in the NREL chart (press release here). Now, the
results have been published in the journal Science with a detailed
explanation of the fabrication process and underlying physics.

"29.15% efficiency is not only the record for this technology but is
at the very top of the entire Emerging PV category in the NREL chart",
says Eike Köhnen, PhD student on Albrecht's team and shared first
author of the study. In addition, the new perovskite/silicon tandem
cell is characterised by consistent performance during more than 300
hours under continuous exposure to air and simulated sunlight without
being protected by encapsulation. The team utilised a complex
perovskite composition with a 1.68 eV band gap and focussed on
optimising the substrate interface.

With partners from Lithuania (the group of Prof. Vytautas Getautis)
they developed an intermediate layer of organic molecules that arrange
themselves autonomously into a self-assembled monolayer (SAM). It
consisted of a novel carbazole-based molecule with methyl group
substitution (Me-4PACz). This SAM was applied to the electrode and
facilitated the flow of the electrical charge carriers. "We first
prepared the perfect bed, so to speak, on which the perovskite lays
on", says Amran Al-Ashouri, who is also a member of Albrecht's team
and shared first author of the study.

The researchers then used a range of complementary investigation
methods to analyse the different processes at the interfaces between
perovskite, SAM, and the electrode: "In particular, we optimised what
is called the fill factor, which is influenced by how many charge
carriers are lost on their way out of the perovskite top cell",
explains Al-Ashouri. While the electrons flow off in the direction of
sunlight through the C60 layer, the "holes" move in the opposite
direction through the SAM layer into the electrode. "However, we
observed that the extraction of holes is much slower than electron
extraction, which limited the fill factor", says Al-Ashouri. However,
the new SAM layer considerably accelerated the hole transport and thus
simultaneously contributes to improved stability of the perovskite
layer.

Through a combination of photoluminescence spectroscopy, modelling,
electrical characterisation, and terahertz conductivity measurements,
it was possible to distinguish the various processes at the interface
of the perovskite material and to determine the origin of significant
losses.

Many partners were involved in the project, including Kaunas
University of Technology/Lithuania, University of Potsdam, University
of Ljubljana/Slovenia, University of Sheffield/UK, as well as the
Physikalisch-Technische Bundesanstalt (PTB), HTW Berlin, and the
Technische Universität Berlin, where Albrecht holds a junior
professorship. The work on the individual perovskite and silicon cells
took place in the HZB labs HySPRINT and PVcomB, respectively. "Each
partner brought their own special expertise to the project, so we were
able to achieve this breakthrough together", says Albrecht. The
maximum possible efficiency is already within reach: the researchers
analysed the two cells individually and calculated a maximum possible
efficiency of 32.4% for this design. "We can certainly achieve over
30%", says Albrecht.

###

Published in Science 2020, 11. December: Over 29%- efficient
Monolithic Perovskite/Silicon Tandem Solar Cell Enabled by Enhanced
Hole Extraction
-----------------------------------------------

https://www.pv-magazine.com/2020/04/...47-1-effiency/


Six-junction III–V solar cell with 47.1% efficiency
A U.S. research group has developed a new solar cell, based on six
active photoactive layers, to capture light from a specific part of
the solar spectrum. The scientists claim that they could potentially
reach a 50% efficiency rate with the new cell.

APRIL 14, 2020 EMILIANO BELLINI

HIGHLIGHTS
MODULES & UPSTREAM MANUFACTURING
TECHNOLOGY AND R&D
UNITED STATES

NREL scientists John Geisz (left) and Ryan France.

Image: Dennis Schroeder, NREL

Researchers from the U.S. Department of Energy’s National Renewable
Energy Laboratory (NREL) have developed a six-junction III–V solar
cell with a 47.1% conversion efficiency rate under 143?Suns
concentration.

They said that they have achieved an efficiency rate of 39.2% under
one-sun illumination. The cell is based on six different photoactive
layers fabricated with alloys of III–V semiconductors, which can each
capture light from a specific part of the solar spectrum.

“The device contains about 140 total layers of various III-V materials
to support the performance of these junctions, and yet is three times
narrower than a human hair,” the scientists said.

The cell could be used in concentrator photovoltaics and has the
potential to reach a 50% efficiency rate, they added. However,
resistive barriers inside the cell impede the flow of current, which
is the main obstacle to achieving the 50% target, they acknowledged in
Six-junction III-V solar cells with 47.1% conversion efficiency under
143 suns concentration, which was published in Nature Energy this
week.

Popular content
In June, other NREL researchers – in partnership with scientists from
the Korea Advanced Institute of Science and Technology – demonstrated
a way to produce gallium arsenide (GaAs) solar cells with a reusable
germanium substrate. NREL has also worked with Chicago-based Microlink
Devices in the past to produce a three-junction cell with a
record-setting 37.75% conversion efficiency rate.

The cost of producing solar cells based on compounds of III-V element
materials – named according to the groups of the periodic table they
belong to – has thus far limited such technologies to niche
applications, including drones and satellites, where low weight and
high efficiency are more pressing concerns than cost.
-----------------------------------------------------