Monday, July 20, 2009

Cesium atoms are able to take a "quantum walk"

By Casey Johnston

Inspired by I Can Haz Cheeseburger?

Computer scientists have only begun to realize the potential of quantum computing and algorithms, where computers use quantum principles to store data in qubits. One thing that could help in the development of algorithms is the "quantum walk," which involves the movement of a particle as a superposition of all possible states. Until recently, quantum walks were a theoretical construct. However, according to Science, physicists in Germany are now able to make cesium atoms arranged in an optical lattice perform a physical quantum walk.

Quantum walks were first proposed by physicist Richard Feynman and are, in terms of probability, the opposite of a random walk. A random walk might be modeled by a person flipping a coin, and for each flip he steps left for heads and right for tails. In this case, his most probable location is the center, with the probability distribution tapering off in either direction. A quantum walk involves the use of internal states and superpositions, and results in the hypothetical person "exploring" every possible position simultaneously.

When a quantum walker flips a coin, it directs him to move one way, but he maintains an "internal state" that moves the other way, making him a superposition of both directions of movement. During a quantum walk, as the quantum object takes more steps, it becomes "delocalized" over all available positions, as if its presence is blurred.

A second feature of quantum walking is matter-wave interference, as when the person flips heads and next flips tails. The second step makes the new superposition overlap the old one, and the new superposition can either amplify the old position or remove it. After all this occurs and the desired number of steps have been taken, an attempted observation will collapse the superposition and "resolve" the object to a single position.

As previously mentioned, a random walk's probability distribution has a single peak tapering off in either direction. A quantum walk's probability distribution generally has two peaks placed evenly on either side of the starting position. However, this distribution can vary depending on the initial internal state of the particle doing the walking, which can cause the final position to strongly favor one side or the other.

While it has been asserted that quantum walks might be observable in many different systems, it has long been a theoretical construct. This has changed with scientists' ability to realize a quantum walk with laser-cooled cesium atoms held in the potential wells of a one-dimensional optical lattice. Using Hadamard-type gates, which perform a sort of Fourier transform on the atoms, the cesium atoms' physical and internal states can be shifted, resulting in a distribution of locations like that seen in a theoretical quantum walk, with two peaks or one heavily-favored off-center peak.

The authors of the new paper were able to replicate the theoretical quantum behavior on walks of up to ten steps and could refocus the delocalized particle backwards through the gates to its initial site on the lattice.

The ability to conduct quantum walks has enormous implications for the field of computer science. Quantum algorithms abandon the use of transistors and bits in favor of "qubits," or quantum binary digits. While a bit can only hold one piece of data, like a 0 or 1, a qubit can hold a superposition of all possible states of data (a 0, a 1, or both). Furthermore, a qubit can be entangled with other qubits to hold all possible collective

Original here

What Apollo means to me

On July 20, 1969, at 20:17:40 GMT, human beings landed on an alien world.

That was the moment that the Eagle lander touched down on the surface of the Moon, 40 years ago today. Nearly five hours later, at 02:56:15 GMT on July 21, Neil Armstrong placed his boot in the lunar regolith, planting it firmly into history as well.

You can read all about this event and its global and historical impacts all over the web, so I won’t belabor the point here. But the Apollo missions mean something special to me, so forgive me this small indulgence. While the overall significance of the missions is interesting and fun to think about and discuss, the real stories, the ones that sink in, are the personal ones.

I was four when Armstrong, Aldrin, and Collins approached the Moon. That’s old enough to form memories of the event, but young enough that those memories are malleable; I have a hard time distinguishing what I actually saw with what I may have seen years later on TV. I seem to vaguely remember sitting on the couch with my family watching the events unfold; even at that age I was in love with science fiction and all things spacey. It’s possible my parents let me stay up late to watch that first step. It would’ve been 11:00 p.m. at our old home. But honestly, I don’t remember.

However, just a wee bit over two years later that changed. In July 1971, my parents rented a Winnebago — a monstrous recreational vehicle — and the whole family piled in so we could road trip down to Cape Canaveral. If all went according to plan, we would be there in time to watch Apollo 15 launch and make its way to the Moon.

I was six, so I remember this much better. The bathroom on the RV smelled overwhelmingly like fruit. My sister taught me that it’s OK to lie when you say something if you cross your fingers while saying it. We stopped to visit friends of my mom’s in South Carolina, and again in Georgia so my oldest brother could check out the Georgia Tech campus before applying there the next year.

I have lots of other memories that are trivial to others but which I cherish. But still and all, we finally reached Kennedy Space Center. I remember touring the area, and I also remember being on the tour bus and getting up pretty close to the Saturn V. I wonder now if that’s a distorted memory; it’s hard to imagine they let tourists get as close as my semi-fuzzy recollection indicates.

And then the day arrived. We parked on the banks of the Banana River and waited for the moment. I wandered off a bit to play on my own (times were different then), and I distinctly remember finding a blue plastic kiddie pool upside down on the river bank. I flipped it over, and a billion mosquitoes exploded out of it! Not too surprisingly, that’s one of the stronger memories I have from that day.

And then the moment finally arrived. I remember nothing of the countdown, but boy oh boy do I remember the launch. A man next to me had a camera that he was frantically snapping away with; I remember the noise of the shutter and him winding it, trying to keep up with the rocket lifting off into the sky miles away.

I can still picture the mighty Saturn V as it punched upward. It was magnificent, and even at the age of six I had some idea of what this all meant. I stood there, clutching the little scale model rocket my parents bought me on the KSC tour in one hand, and the blue plastic figurine of an Apollo astronaut standing on the Moon I had in the other. I still remember bringing that plastic model to school for show-and-tell when we got back home.

That memory of the launch is a powerful one for me even today, all these years later. I asked my dad years later what motivated him and mom to pack the whole family up into that RV and take us down there. He replied that it was something he thought we should all see. It was history being made in front of us, and not something you get a chance to see very often.

I asked him that for another reason. My father was a quality control engineer, and did a lot of government contract work. In fact — and this makes me proud, let me tell ya — he worked on the quality control for the astronauts’ food program. I don’t know what precisely he did for the program, to be honest, but he was involved for some time. I know he did some work on the packaging, including the freeze-dried food and the spaghetti the astronauts took with them. That’s why I asked him why we went to see the launch; I wondered if it was because the trip was work-related for him. But it wasn’t. He and mom wanted to share with us the sheer joy and wonder of humanity’s first tentative journey away from Earth.

We should all strive to be such people.

Years later, when my father died, my mom asked all us kids if we wanted any of his books or other items. I stood in front of his bookshelf, admiring the many texts on codebreaking, mathematics, the history of cryptography. He was fascinated by these topics, and was something of a dabbler in math; a formula he invented is published in the CRC handbook used by grad students across the planet.

My eyes fell on a magazine I hadn’t seen before; it was a 25th anniversary retrospective of Apollo. I opened it up, and to my surprise, found this picture:

That’s Apollo 12 astronaut Pete Conrad, the third man to walk on the Moon. Clearly, dad must’ve met him and talked about the food program. Conrad had a great sense of humor, and signed the picture appropriately.

My dad was a major reason I’m a scientist now, and helped instill in me and all my siblings a love of science and space. My memories of Apollo are inextricably entangled with memories of my father from back then too. So to me, Apollo is personal.

I can take a mental step back and look at the whole picture: what that one small step meant, how it inspired a planet, what NASA did that day, and even how its faltered in many ways since then. But sometimes the real story, the human story, is the first-person account of events.

That’s how it plays in my head when I picture that hot July day in 1971, and that mental film is always running when I write about Apollo. It may not be at the forefront of my mind, but it’s there. Even without it I might still be inspired to write what I do. And though I strongly doubt it, I suppose it’s remotely possible that I’d still be where I am today without having had my parents expose me directly to space travel.

But they did. And I’m a better man for having it as a part of me.

Massive Black Holes Roaming Edge of Milky Way -A Galaxy Insight

Hundreds of rogue black holes should be traveling the Milky Way's outskirts, each containing the mass of 1,000 to 100,000 suns.

Avi Loeb -Harvard-Smithsonian Center for Astrophysics

New calculations by Ryan O'Leary and Avi Loeb of the Harvard-Smithsonian Center for Astrophysics suggest that hundreds of massive rogue black holes, left over from the galaxy-building days of the early universe, may wander the Milky Way.

The Earth appears safe, however, with the closest rogue black hole thousands of light-years away.

"These black holes are relics of the Milky Way's past," said Loeb. "You could say that we are archaeologists studying those relics to learn about our galaxy's history and the formation history of black holes in the early universe."

According to theory, rogue black holes originally lurked at the centers of tiny, low-mass galaxies. Over billions of years, those dwarf galaxies smashed together to form full-sized galaxies like the Milky Way.

Each time two proto-galaxies with central black holes collided, their black holes merged to form a single, "relic" black hole. During the merger, directional emission of gravitational radiation would cause the black hole to recoil. A typical kick would send the black hole speeding outward fast enough to escape its host dwarf galaxy, but not fast enough to leave the galactic neighborhood completely. As a result, such black holes would still be around today in the outer reaches of the Milky Way halo.

One telltale sign could mark a rogue black hole: a surrounding cluster of stars yanked from the dwarf galaxy when the black hole escaped. Only the stars closest to the black hole would be tugged along, so the cluster would be very compact.

Due to the cluster's small size on the sky, appearing to be a single star, astronomers would have to look for more subtle clues to its existence and origin. For example, its spectrum would show that multiple stars were present, together producing broad spectral lines. The stars in the cluster would be moving rapidly, their paths influenced by the gravity of the black hole.

"The surrounding star cluster acts much like a lighthouse that pinpoints a dangerous reef," explained O'Leary. "Without the shining stars to guide our way, the black holes would be all but impossible to find."

The number of rogue black holes in our galaxy depends on how many of the proto-galactic building blocks contained black holes at their cores, and how those proto-galaxies merged to form the Milky Way. Finding and studying them will provide new clues about the history of our galaxy

"Until now, astronomers were not searching for such a population of highly compact star clusters in the Milky Way's halo," said Loeb. "Now that we know what to expect, we can examine existing sky surveys for this new class of objects."

Loeb and O'Leary's journal paper will be published in the Monthly Notices of the Royal Astronomical Society and is available online at http://arxiv.org/abs/0809.4262.

Posted by Casey Kazan.

"You Want Me to Walk On the Freakin' Moon Wearing What?!"

By Jack Loftus

These shots of gear from the first Apollo moon mission show just how far we have—and haven't—come in the 40 years since man first walked on the moon.

The suits shown here are part of a collection of Apollo-era artifacts on display right now at the National Air and Space Museum.

The exhibit is part of a 40th anniversary celebration for the event that attention-seeking idiots say never happened so that they can get a few extra clicks and adSense dollars on their crock conspiracy theory web site. Tons more pics over at io9. Can we go back now, please? [io9]

Original here

* Earth Sciences * Astronomy * Environment * Space Exploration Astronauts deal with flooded toilet in orbit

By MARCIA DUNN , AP Aerospace Writer

This image provided by NASA shows the underside of the crew cabin near the nose cap of the Space Shuttle Endeavour taken by an Expedition 20 crewmember during a survey of the approaching vehicle prior to docking with the International Space Station Friday July 17, 2009. Endeavour crew performed a back-flip for the rendezvous pitch maneuver. Mission Control said Saturday Endeavour looks to be in fine shape for re-entry at the end of the month. Areas where the heat tiles were dinged during Wednesday's launch can be seen in this image. (AP Photo/NASA)

(AP) -- The bathroom lines at the already crowded space shuttle and space station complex got a lot longer Sunday because of a flooded toilet. One of two commodes aboard the international space station malfunctioned, right in the middle of complicated robotic work being conducted by the two crews. The pump separator apparently flooded.

Mission Control advised the astronauts to hang an "out of service" sign on the until it could be fixed. In the meantime, the six space station residents had to get in line to use their one good toilet. And Endeavour's seven astronauts were restricted to the shuttle bathroom.

There have never been so many people - 13 - together in space. The toilet repair work fell to Belgian Frank De Winne, who had to don goggles, gloves and a mask.

Flight director Brian Smith declined to speculate whether overuse caused the toilet trouble.

"We don't yet know the extent of the problem," Smith told reporters. "It may turn out to be of no consequence at all. It could turn out to be significant. It's too early to tell right now."

Teams of specialists in Houston and Moscow hurriedly convened to discuss the problem. The Russian-built, multimillion-dollar toilet flew up on a shuttle last November.

Smith said there is no urgency to the bathroom situation, at least for now. But he said if the toilet remains out of action for several days, "then we'll readdress the situation and see what we have to do."

Going into this mission, NASA wanted at least four of Endeavour's crew to use the space station's bathrooms, so the shuttle tank would not fill up.

As long as Endeavour is docked to the space station, it cannot eject any waste water. The nozzle is located near the newly installed porch on the Japanese lab; the attach mechanisms for experiments could corrode if sprayed by water.

Two bathrooms ultimately are needed for a full station crew of six. Smith said he did not know how long six occupants could rely on a single toilet.

Both the shuttle and station are equipped with other ways for the astronauts to relieve themselves, Smith said, including Apollo-era urine collection bags.

Much of Sunday - the eve of the 40th anniversary of man's first moon landing - was spent using a pair of robot arms to move a large cargo carrier, loaded with batteries and spare parts, from the shuttle to the station. It was a relatively quiet day sandwiched between spacewalks.

The 13-by-8-foot platform holds an antenna, pump and engine for the station's rail car, all of which will be removed and secured to the space station during a spacewalk Monday. NASA wants to store as many big spare parts as possible at the space station, before shuttles stop flying at the end of next year.

Also on the carrier are six batteries that will be plugged into the station by spacewalking later in the week, replacing old batteries.

In all, five spacewalks are planned during Endeavour's 1 1/2-week space station visit.

As for the Apollo 11 anniversary, Smith noted that the Mercury, Gemini and Apollo programs contributed to today's . He observed that he wasn't born when Neil Armstrong and Buzz Aldrin walked on the moon July 20, 1969; neither were two of the 13 spacefarers.

Cooking With Sound: Bio-Mass Burning Stove Also Converts Heat Into Sound Then Electricity

Researchers are developing a bio-mass burning cooking stove which also converts heat into acoustic energy and then into electricity, all in one unit. (Credit: Image courtesy of University of Nottingham)

A low-cost generator with the potential to transform lives in the world’s poorest communities is now being tested across the UK and in Nepal. The Score project, led by The University of Nottingham, is developing a bio-mass burning cooking stove which also converts heat into acoustic energy and then into electricity, all in one unit.

The £2 million Score project (Stove for Cooking, Refrigeration and Electricity) brings together experts from across the world to develop the biomass-powered generator. By developing an affordable, versatile domestic appliance Score aims to address the energy needs of rural communities in Africa and Asia, where access to power is extremely limited.

Researchers in the Department of Electrical and Electronic Engineering at The University of Nottingham are working on the generator’s Linear Alternator — the part which turns the sound energy into electricity. The system uses special configurations of magnets which generate electrical energy from sound. Computer simulations of the linear alternator have proved successful, and test models are currently being constructed in the department’s workshops.

Nottingham researchers are working with Dai-ichi, one of Malaysia’s largest loudspeaker manufacturers, to bring down production costs through good design practice. Though the Score unit does not physically resemble the average loudspeaker, it is compatible with the Dai-ichi manufacturing process.

Score has been invited by Dai-ichi to exhibit at the “Better City Better Life” EXPO 2010 in Shanghai China from May to October 2010 to showcase its new advanced technology to 70 million expected visitors.

The aim of the Score project is to make a low-cost, high efficiency generator that can be used in the world’s poorest countries. The generator has a cost target of £20 per household, based on the production of a million units. The generator will weigh between 10 and 20kg. The target is to generate an hour’s use per kilogram of fuel — which could be wood, dung or any other locally-available biomass material.

Dr Chitta Saha, Research Assistant at Nottingham said: “The current Linear Alternator design is very exciting for me as it solves many of the problems we had with using loudspeakers as alternators, but can still be made cheaply. My mum lives in Bangladesh — she is so proud that I am working on such a worthwhile project that she can see will help her community.”

The University of Manchester, City University London and Queen Mary, University of London and the Charity Practical Action are partners in the project — from researching engine design to the manufacture and distribution of the stove in the developing world. The project will work with governments, universities and civil organisation across Africa and Asia, many of whom have already offered support. This collaboration will ensure the device is affordable, socially acceptable and that there is scope for communities to develop businesses to manufacture and repair locally.

Mark Johnson, Professor of Advanced Power Conversion at Nottingham, said: "I am particularly pleased with the way that the Score consortium, with partners from very different technical backgrounds, has developed into a cohesive research team. We now have solutions to the fundamental technical problems and the first demonstrators delivering significant electrical power, have been realised"

The Score team is now looking for sponsorship to fund testing in the countries in which the generator will eventually be deployed. Indeed Germany’s Department of International Development (GTZ South Africa) has already signed a Memorandum of Understanding to provide funding to test the stove in southern Africa.

Paul H Riley, Score Project Director says “We have had tremendous interest in the Score project from around the world and the Score community —launched a few months ago — is working extremely well. This includes entrepreneurs and volunteers that adapt the stove for local use among its members.”

Practical Action, a charity which promotes the development of sustainable technology to tackle poverty in developing countries, is already leading field trials in Nepal and Kenya. The charity will expand the test sites when more units are made available.

Score community member Mark Loweth works in Tajikistan, one of the poorer countries in Central Asia. He has adapted a variation of a Score Stove to ensure it is suitable for the communities it is aimed at.

“We are very excited with the Score technology as it has the capability of bringing small scale electrical generation to households in the developing world,” he said.

“We plan to field test 20 units in Tajikistan when funding is available through a jointly owned, locally registered company utilising the experience and extensive local knowledge of expatriates and nationals with strong links to rural communities.”

Other members of the international Score Community are investigating how a Score Stove could best be adapted for their local environments.

South African Score community member Rynier Ferreira said: “We are adapting a Score Stove to work with paraffin (kerosene) as many rural communities in South Africa are still highly dependant on it as a major fuel source for cooking. Adapting a Score Stove for paraffin will increase not only the safety aspect for stoves using this type of fuel, but will give the people in these rural communities the additional advantage of electricity and refrigeration.”

Gorge Crowson is also testing the stove in southern Africa after joining the Score community: He said: “We have identified a number of waste materials that can be burnt in a Score Stove and are actively seeking financial support to set up assembly plants in Southern Africa and a distribution network, once the test phase is completed.”

It’s thought that more units will be available for testing in field trials at the start of next year, with full production of the Score generator taking place after 2012.

The Score consortium is funded by grants from the Engineering and Physical Sciences Research Council as part of its initiative on energy and international development.

Kees deBlok of Aster Thermoakoestische Systemen in the Netherlands and Scott Backhaus of Los Alamos International Laboratories are acting as consultants to the Score project.

City bees are all the buzz

Veteran beekeeper Jim Fischer consults with a newcomer.

(Mary Knox Merrill/Staff/The Christian Science Monitor)

By Bridget Huber

Mary Knox Merrill/Staff/The Christian Science Monitor

A new beekeeper inspects a hive at her Manhattan home. Beekeeping is illegal in the city and can carry a \$2,000 fine. But urban gardeners are pushing for passage of a bill, introduced by a city councilor, that would lift the ban – and boost pollination and honey production. Some other cities allow the practice.

New York

Honeybees may not be the first thing that come to mind when you think of Brooklyn. Yet here’s Yeshwant Chitalkar, high on a rooftop in the Red Hook section of the New York borough, opening a bright blue hive to check on its queen. The vista is a mix of parks, light industrial areas, and housing projects. Dr. Chitalkar works methodically, barehanded, carefully lifting out the hive’s frames, which are covered in a velvety, undulating layer of bees.

He is one of a growing number of urbanites who keep bees in cities across the country. Their motivations vary: Some are worried about the environmental impact of fewer bees to pollinate food crops. And some are urban gardeners who want to make their gardens more productive. Others say beekeeping is a way to connect with nature even in the heart of the concrete jungle.

Oh, and there’s the honey, too. Counterintuitive as it might seem, urban hives are generally as productive and healthy as rural ones. In a good year, one hive can produce up to 200 pounds of honey.

Urban beekeeping isn’t all sweet, though. It can be hard, dirty work and the challenges are many: jittery neighbors; vandals; city ordinances banning the activity; and problems, such as mites and parasites, that vex beekeepers everywhere.

But that doesn’t daunt those who want to keep bees. This year there are at least 30 new hives in community gardens, on rooftops, and in backyards across New York. Most are the result of a series of beekeeping classes taught last winter by Jim Fischer, a veteran beekeeper who lives in Manhattan.

Mr. Fischer and some of his students formed the Gotham City Honey Co-op to buy beekeeping equipment in bulk, and hope eventually to set up a site where members can extract and bottle their honey. The co-op also plans to brand its honey and sell it to specialty stores.

The only hitch: Beekeeping is illegal in New York City.

Mr. Fischer and other Big Apple beekeepers are confident that the honeybee ban will be lifted soon. A city councilor has introduced a bill to legalize it, and urban gardening groups are pushing for it to be passed.

The situation is quite different in Chicago, where City Hall’s green roof boasts a beehive. Michael Thompson, who helped install the city-owned hive, has been keeping bees within the city limits since the 1970s.

Today he is the farm manager at the Chicago Honey Co-op, which has about a hundred hives on the city’s West Side. Many belong to people who give half their honey to the co-op in exchange for keeping their hives at the site.

The city is an ideal spot for bees, Mr. Thompson learned when he moved there from a rural area where he kept bees.

“It’s much better to keep bees in a city,” he says. In rural and suburban areas, pesticides sprayed for agriculture and mosquito control can also harm bees. But in the city, the use of these kinds of pesticides is less widespread.

“People have the perception that a hive in the city can’t make any honey at all,” Fischer says. “That’s just not true.”

Honeybees can find abundant nectar in parks and along tree-lined boulevards. Also, urban areas often have extensive ornamental gardens in bloom throughout the growing season.

But Nick Calderone, associate professor of entomology at Cornell University in Ithaca, N.Y., injects a note of caution. He says that hives can thrive in cities only if they’re near green spaces or gardens.

Many of the beekeepers Fischer knows are urban gardeners who began keeping bees because they wanted to increase their crops’ productivity. “If you want local food, you need local bees,” he says.

That’s why Roger Repohl of the Bronx became a beekeeper 10 years ago. Although his plants had plenty of flowers, they produced few vegetables. When he asked for advice from someone in the city’s Parks Department, he was told: “ ‘Oh, we don’t have pollinators in the South Bronx,’ ” he relates.

Although “some pollination is done by wind and rain, the majority is done by insects – including beetles, flies, butterflies, and, most significantly, by bees,” says Dr. Calderone. Many native species of bees are important pollinators, but their numbers have declined as their habitat has disappeared to development and large-scale agriculture.

Honeybees, which aren’t native to the United States, are used as pollinators on large farms as well as in personal gardens. But they are struggling, too.

The number of managed honeybee colonies in the US has dropped from 5 million to 2.5 million since the 1940s, according to the US Department of Agriculture.

And two mites that appeared in the US in the 1980s have been wreaking havoc on honeybee colonies since, says Calderone. Before their advent, home beekeepers might have lost 5 percent of their colonies per year and a migratory beekeeper 10 to 15 percent. Now, during bad years, beekeepers may lose five times that many colonies.

Then there’s the little-understood but much-publicized disease known as colony collapse disorder (CCD), which causes the mysterious disappearance of adult bees from colonies. While CCD’s cause is still not understood, “it’s certainly real and it’s certainly killing lots of bees, but exactly what it is, is hard to say,” says Calderone.

In urban areas, these problems haven’t discouraged gardeners from becoming beekeepers, And that’s good for all residents of the city, says Calderone. “Unless you want a totally sterile environment that’s devoid of all life other than people, you’re going to need plants. And to keep them functioning, you’re going to need pollinators.”

Toni Burnham, who blogs about urban beekeeping (City Bees), was inspired to start hives after hearing about London beekeepers. She has established several hives and was a consultant on the successful effort to put beehives on the White House lawn.

She sees beekeeping as a key part of maintaining a healthy city. “If those plants that are the bottom line for ecological health in my town can produce adequate fruit and leaves, there’s a whole range of bugs, snakes, and birds that can survive,” she says.

One of the biggest challenges for urban beekeepers is neighbors who are unhappy about living near beehives. Many people are afraid of bees, and much of that fear is rooted in misunderstanding, says Fischer.

Since bee populations have declined, people understand them less, says Fischer, who as a child spent the summers playing baseball barefoot. Back then, grass-seed mixes included red clover, a bee favorite. Inevitably, children stepped on bees. There were tears, but parents took it in stride – “the response was a hug and a cookie,” he says.

Today, many people mistake one bodily response to a bee sting – some swelling and itching – for an allergic reaction and take their children to the emergency room, Fischer says.

If their nests are threatened, bees will sting. But, Calderone says, they don’t generally do so when away from their nests.

Still, bee swarms, which occur when part or all of a colony leaves its home en masse to find a new one, make headlines. Fischer, who is frequently called to remove them in New York, once was called to a site where a swarm had landed on a newspaper box. When he got there, police had closed the intersection and cordoned off the area with yellow crime scene tape. Several television crews were filming. “Swarms scare the civilians,” he says.

But swarms aren’t particularly dangerous, he says. The bees may number in the thousands, but lack a hive to defend and are focused on finding a new home, although they will sting if provoked. Fischer calls them “the most docile configuration of bees.”

Still, “it’s important to cultivate respect for [honeybees]. They’re not chickens, cats, or dogs,” says Mr. Repohl, whose community garden regularly hosts school groups.

Keeping bees may have another benefit for busy city dwellers – encouraging them to slow down. Ms. Burnham, who says she’s the type of person who drinks too much coffee and waves her hands around when she’s talking, likens beekeeping to yoga: “I plan my movements, and I do them deliberately. I’m thinking about the effect of my motions on these creatures. I have to be in a different way,” she says.

Michaela Hayes, who has a new hive in Brooklyn, agrees. “I love the bees; they’re so peaceful,” she says. Ms. Hayes dreams of the day when she’ll make ginger beer from her honey, but for now she’s content to watch the bees as they go about their business. “They’re fascinating to me. It’s kind of like a big science experiment for adults.”

Top 10 DIY Projects that Harness the Power of the Sun

By Kevin Purdy

Cheap, powerful, and available almost everywhere—solar energy is a truly great thing. With these 10 sun-powered projects, you can turn a sunny day off into some brag-worthy, possibly money-saving backyard tech.

Photo by david.nikonvscanon.

10. Engrave wood with a "sun laser"

Leave them alone long enough, and nearly every kid will investigate, or at least hear about, the devastating effects of magnifying glasses and clear, sunny weather on insects. Route that fascination with concentrated sunlight into some wood engraving. Aluminum foil (or, preferably, foil tape), sunglasses, a razor blade, and a magnifying glass are all you need to get creative with an old piece of wood or other dark objects. You'll need to provide supervision, lest bad aim turn into a kindling incident, but it's a great project for kids, as well as a unique way to leave your mark with style. (Original post)

9. Heat water in your backyard

It's not an efficient way to keep your hot tub filled, but the kind of solar-powered water heater detailed at the Instructables link above can get a big batch of water up to 170F without requiring any work from your water heater, and the kit costs around \$5 with the right parts suppliers. Even if you pay a bit more, think about how often the backyard grill, deck, or pool could use a little cleaning with some hot, soapy water. This project gets you a free source of ever-ready cleaning water, and at a pretty neat price. (Original post)

8. Start a fire with a soda can and chocolate

This little project is the most reliant on a strong bit of sunlight, but totally worth the effort when you pull it off. The chocolate polishes the bottom of a soda can, which better focuses and intensifies sunlight reflections, creating a cone of fire-starting power that leaves your fellow campers impressed—or the other attendees at the park picnic grateful you were there when they forgot the matches. (Original post)

7. Convert a lawnmower to solar power

If you've got a small-ish lawn, a battery-powered mower is much easier on your and your neighbors' ears, and it saves you the hassle and cost of gas refills. Take those eco-benefits to the next level by converting a gas-guzzling push mower to use a solar-charged battery. Appropedia's version is a definite weekend project for an older model, but if you've got a newer battery mower, it's not too hard to simply start charging it with a solar panel instead of your wall socket, and this guide will help get you there. (Original post)

6. Estimate your home's solar potential

A solar-powered house sounds like a neat idea in abstract, but how would you know if your house's roof could really sustain worthwhile energy? Luckily, a big search company has overhead images of just about every house out there, and mashup tool RoofRay can use that image, plus your location's average sunlight and some roof details, to get a starting estimate on whether you can use the sun to push back on your power meter a bit. (Original post)

5. Extend Wi-Fi to your backyard

Probably the least practical and most expensive of the projects listed here, the solar-powered Wi-Fi extender is definitely the most rewarding from a geek cred and green power perspective. Popular Science explains in great detail how to solder and network together a semi-standard Linksys Wi-Fi router, range extender, solar panel, battery, and higher-powered antenna, and then set it up to grab Wi-Fi from your household's main network and expand it to the great outdoors—or, at least, the outdoors behind your house. That leaves you with regular web access anywhere around your property, without having to worry about running cables across the lawn. (Original post)

4. Cook with a cardboard box

There's an entire realm of recipes and cookbooks that purport to help you get cooking done in the summer without turning on your oven. Skip the gazpacho and the house-warming heat with an oven built from aluminum foil, construction paper, plastic, and a few other household items, including a firm cardboard box. It's great for saving energy, saving time, and feeling like you really made the most of a warm, sunny day. Want to get a bit more efficient and physics-y with your outdoor oven? Try a parabolic solar cooker. Photo by thescarletmanuka. (Original post)

3. Build a greenhouse for \$50

If you're lucky enough to live where plants and food grow all year, you already know the power of photosynthesis. For those who could use a little more prep time for their seedlings, a longer growing season, or just a buffer against the occasional plant-punching dry spell, The Door Garden explains how to take some light construction materials—\$50 if you happen to have most of it lying around, about \$150 purchased new—and build a greenhouse that will withstand most winters and thrive in every other season. Just got a few plants you want to get started with condensed solar power? Try the mini-greenhouse made from a window. (Original post)

2. Charge an iPhone/iPod with the sun

We're big fans of the MintyBoost DIY USB charger kit, a great project for electronic beginners and pros alike. It was only a matter of time, then, until someone switched the power source from AA batteries in an Altoids case to a lithium-ion battery with solar charging capabilities. Completing the modified kit isn't a great leap more difficult than the original, and once you do, you'll be glad to get a lot more use out of your windowsills, and hand over a lot less money at the grocery store every few weeks. It's not necessarily the most effective method of charging, but it's undeniably cool. (Original post)

1. Sun jar garden light

The solar-powered outdoor lights they sell at your local garden/home improvement store can be subtle or original-looking—if you want to pay a premium. Otherwise, you're stuck with painted plastic and models that hold a pretty weak charge. The sun jars constructed by our own Jason, on the other hand, cost only about \$11 each—less if you have jars or batteries on hand—and give off a pretty neat glow, powered entirely by solar energy from earlier that day.

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Severn tidal power scheme should not go ahead, warns Environment Agency

John Vidal

The Weston barrage, running 10 miles across the Severn estuary between Weston-super-Mare and Cardiff, is the largest of four tidal power schemes being considered by government Photograph: Matt Cardy/Getty Images

A giant tidal energy scheme which the government is counting on to meet ambitious new green energy targets set this week should not be built because it would be so ecologically destructive, the chair of the Environment Agency has warned ministers.

The government's roadmap to a low-carbon UK called for a 34% cut in emissions by 2020, with the power sector contributing the bulk of that saving. The Weston barrage, running 10 miles across the Severn estuary between Weston-super-Mare and Cardiff, is by far the largest of four tidal power schemes being considered by government and would be the centrepiece of the nation's renewable energy plan.

It could generate 8.6 gigawatts of zero-carbon electricity from the Severn – the equivalent of eight large coal-fired power stations – and would be the single largest renewable energy project in Europe.

But the £5bn flagship scheme would permanently flood nearly 35,000 hectares (86,000 acres) of internationally protected wetlands. It would also destroy some of Britain's most important fisheries in the Severn, Wye and Usk catchment areas, said Lord Smith in an interview with the Guardian.

"The great wall across the Severn channel poses the classic environmental dilemma. It would generate 5% of all the UK's electricity needs but at a huge cost in terms of fishing and habitats. These immense environmental impacts outweigh the carbon reduction benefits which you would get. We are advising the government on this pretty strongly," said the government's chief environmental adviser.

"There must be ways of harnessing tidal power from the estuary without the gross impacts that the Weston scheme would have. I regret that we are not putting as much effort as we could into tidal reefs and defences. We should be addressing the possibility of tidal power around the country. Tidal energy should be one of the key ways of generating electricity", he said.

Smith's comments will not be welcomed by the government which this week committed itself to generating 20% of the UK's energy from renewable sources within only 11 years, but it is meeting technical and planning delays with wind power.

A decision on the barrage will be given next year but ministers are keen to see it started because it would contribute more to emission cuts than any other scheme. The energy minister, Lord Hunt, said this week: "The Cardiff-Weston barrage has the potential to save the equivalent of the yearly CO2 emissions from all homes in Wales."

The barrage, which would be a huge engineering feat on the scale of some of the world's biggest construction projects, is shaping up to be one the most contentious environmental issues of the decade. The National Trust, the RSPB and WWF, together representing more than 5 million people, have said that a barrage would be "economically dubious" and "ecologically disastrous".

They have also argued that 5m tonnes of CO2 would be emitted during construction and another 5m tonnes during transport of the materials, undermining claims that the barrage would help reduce emissions.

Smith also warned the nuclear industry, another part of the energy and climate change secretary, Ed Miliband's "trinity" of low-carbon electricity plans, that climate change could seriously affect their costs. He said the agency would demand that nuclear power companies build major sea defences to protect nuclear power against the sea level rises expected over the next 100 years.

"Virtually all the new [nuclear] stations are by the sea. We will look at them on a case-by-case basis but all sites must be fully defensible. The power companies know that they will have to defend them on a very large scale. Protection against flood risk must be absolute."

Smith also questioned Miliband's intention to preserve low-cost mass air travel, revealed in the Guardian this week. Calling for a debate on the future of aviation, he argued that climate change made it doubtful people could fly so much in 40 years' time. "By 2050 we should have reduced greenhouse gases by 80%, which means we will have 20% left. How much of that 20% should be taken by aviation?

"Aeroplanes will get more efficient but they will not be able to completely remove their carbon emissions. By 2050 we will need to have decided how much flying we can do. "

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