A new book plays on the mystery of physics machines

December 9, 2011 | 10:53 am

Underground and closed off from visitors, experiments in particle physics often hide, rather than flaunt, the exotic and intricate machines that seem more at home in a science fiction blockbuster. No space shuttles, rockets or rovers wow visitors at today’s physics laboratories. The tried and true conduit from the underground to the outside world remains in most part the camera.

Polarized electron source, Bates Linear Accelerator Center, MIT, Massachusetts, 2007. Photo: Stanley Greenberg

In his new book, “Time Machines,” New York-based photographer Stanley Greenberg immersed himself within physics machinery to capture the cannon-like CMS detector before installation at the LHC, the frigid lifelessness surrounding the ICECUBE Neutrino Observatory in Antarctica and the Frankenstein mystique of Fermilab’s Cockroft-Walton accelerator. Greenberg’s book assembles 80 rich, black-and-white photos that distill from the complex machines a space-age style and individual personalities – preserving a romanticism free of scientific overload.

“Their massive cement blocks, multi-story electronics, and miles of circumference dwarf their human makers as intestines of tubes and wires converge Leviathan-like into the ultimate probe of the tiniest and the most hidden secrets of the vast universe,” writes David Cassidy in his imaginative, yet informative, introduction to “Time Machines.”

In his previous works, Greenberg, who is no stranger to towering structures, delved into sub-city tunnels, toured waterfront shipyards and scaled the skeletons of burgeoning buildings. He then left his home in New York City on a five-year quest to photograph the infrastructure and equipment of the most advanced high-energy and nuclear physics laboratories.

“It’s an almost completely hidden kind of world,” Greenberg said. “That’s always been an attraction to me – the places people can’t go.”

Assuming access to laboratories to be a challenge, Greenberg instead discovered open doors and smiling scientists, who often invited him before he asked.

Drawn by sweeping patterns that slice across his lens and massive structures that hemorrhage off the pages of his book, Greenberg has, for the most part, let the reader’s mind simply admire the machinery and wander what roles these strange instruments would fill.

“There are parts you see that will hopefully become metaphors for the whole,” Greenberg said.

While the book does briefly explain the experiments in the introduction and appendix, this is not a science book – it is a celebration of science.

What’s left out of the book are hundreds of old negatives from an era when bubble chambers were ubiquitous in the field. Greenberg collected and borrowed these abstract portraits of particles in the hope of one day displaying them in a gallery.

The collection in this book is simply one selection of weird and complex experiments from across physics history. Yet each otherworldly machine by being framed within a photograph is frozen in its own unique and immutable time.

All travel for the book was funded by the Alfred P. Sloan Foundation, and the NSF Artists and Writers Program funded Greenberg’s trip to the South Pole.

Brad Hooker

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Freeing positronium from their dangling bonds

December 7, 2011 | 10:10 am

Last summer David Cassidy, a scientist at the University of California, Riverside, was busy using silicon to study positronium formation when his team noticed that the positronium, sitting on the silicon surface, didn’t behave as it should have.

Setup for positronium formation with silicon at the University of California, Riverside. Image: David Cassidy

As the silicon was heated, the amount of positronium leaving the surface increased, as expected. What was surprising, however, was the fact that, even as the silicon’s temperature was hiked up, the energy of the positronium atoms being ejected from the surface didn’t increase along with it.

The positronium emission energy had nothing to do with the material’s temperature.

“The positronium energy wasn’t changing, which doesn’t make any sense if you think it’s coming from a thermal distribution, because it should obviously get hotter if you heat the target up,” Cassidy says. “That’s how we found out that something different was going on.”

Positronium is an electron-positron pair. It survives for tens of nanoseconds before the two particles annihilate each other.

In the typical recipe, positrons stuck on the surface of some material grab hold of an electron, forming positronium. If the material is heated, the positronium gets a thermal kick and leaves the surface, with an energy that depends on the temperature.  The temperature dependence of thermal positronium can be easily measured.

But the positronium in the UC Riverside silicon setup was falling off the material spontaneously.

“It’s metastable, sitting there on the edge of a cliff,” says Allen Mills, head of Cassidy’s group.

What appeared to be pushing it off the cliff was not the heat itself, but a consequence of the rise in temperature: the movement of the electrons in the surface material. As the temperature goes up, the electrons, with positrons clinging to them, move differently. When the arrangement of the positronium is just right, it flies off.

“Our idea was that it has a transient existence that can be thermally activated by moving some electrons from somewhere to somewhere else,” Mills says.

Or, in other words, posits Cassidy, “It’s really the electronic activation that you’re looking at, not the positronium emission.”

That the positronium flies off with a fixed energy means that it’s in a fixed energy state when it’s sitting on the surface. If you can control the state it’s in, you can control the energy with which it’s emitted.

“It’s only held at the surface because it’s not in the right arrangement to leave,” Mills says. “It has to make arrangements, call a babysitter and stuff, to fall off spontaneously.”

The team decided to heat silicon with a laser, bringing electrons to the surface in a controlled way, readying them for take-off. With a laser, they could control the electron population and manipulate their energy states.

Using a laser also enables researchers to activate the electrons in the material without having to heat it up, meaning that positronium production doesn’t have to be restricted to materials at hotter temperatures, which is typically the case. Being able to efficiently generate positronium at low temperatures opens up new experimental arenas. Cryogenic traps, for example, are not well suited to positronium experiments that require a metal at 1000 kelvins.

Mills and Cassidy are no strangers to positronium. They were the first to observe di-positronium, a two-positronium molecule, and had made plenty of it, not in silicon, but in porous films where the positronium molecules would hang out in the little voids dotting the film.

The move from porous films to the silicon made sense. Silicon, a semiconductor, is widely used in the tech industry. But beyond its use in broader applications, it turned out it was useful as part of a kind of positronium factory. For one, it’s resilient and easy to maintain. Metals, by contrast, require constant cleaning. And where the porous films, which are insulators, can not only become damaged at low temperatures but also, by nature, build up charge and discourage electron movement, silicon doesn’t. Its conducting electrons are easy for any off-the-shelf laser to bring to the surface.

“It might be a really handy way around those problems,” Cassidy said. “You don’t need any fancy lasers to create the positronium.”

Both Mills and Cassidy emphasize that their guesses as to exactly what’s happening at the silicon surface are just that – hypotheses. As the discovery happened by chance, they hadn’t planned on following the thread of this strange non-correlation between positronium energy and temperature, but they’d love to hear what others might have to say about it.

“I’d really like some theorists to weigh in on this and tell us precisely what’s going on,” Cassidy says. “There are a lot of details related to how the electrons are getting into these particular phases, what those states are and how they interact with each other – all that stuff that somebody more theoretically minded could help with.”

Leah Hesla

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Digital artist wins first CERN, Ars Electronica joint-residency competition

December 6, 2011 | 9:49 am

Artist Julius von Bismarck with an early version of his invention, the Fulgerator. Image courtesy of Julius von Bismarck

CERN and international cyberarts organization Ars Electronica declared Julius von Bismarck the winner of their first digital arts joint-residency program today. The 28-year-old German artist will spend two months at CERN near Geneva, Switzerland, and a third month at Ars Electronica in Austria, collaborating with scientists and digital experts to create a physics-inspired artwork as part of the Collide@CERN program.

Von Bismarck wasn’t sure as a student whether he wanted to pursue physics or art. Now he is excited for the opportunity to combine them. “The root reason as to why I am an artist is the same as it would be for being a scientist: finding out what there is out in the world and how I can contribute to our understanding of it,” he said in the CERN press release.

The bearded Berliner is most famous for his invention of the Fulgurator, an apparatus that looks like a camera but actually projects a secret image that shows up only in other peoples’ photos. He used the device when President Barack Obama spoke in Berlin, projecting a cross onto his podium that appeared in press photos, as well as at Tiananmen Square in Beijing, where tourists found their photos contained the image of a white dove over Mao Zedong’s face in a prominently hanging portrait.

Von Bismarck is cautious about the device’s potential for misuse. He’s turned down numerous offers from advertisement agencies looking to exploit its function. As he says in a video for the arts and media initiative the Creators Project:

“I believe that all technology that’s invented should also be questioned. I believe that an invention is also a political statement. If I build a machine that can change the world, then I have to back it up as the creator. That’s why every technician and every engineer also acts as a politician and as someone who is responsible for our future.”

He will visit CERN for a week in January to choose his science-inspiration partner, a physics mentor who will co-blog and present work with von Bismarck throughout the program. His residency in Geneva will likely start in March.

For more on the artist residency program, see this symmetry story.

Amy Dusto

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DOE’s Intensity Frontier Workshop packed with ideas and people

December 5, 2011 | 9:29 am

As a postdoc, Giovanni Tassielli has the whole particle physics landscape to survey for the most stimulating future job prospects.

The researcher from INFN in Italy feels a pull toward the most challenging experiments at the Intensity Frontier: those that seek out the rarest of all particle interactions, the smallest of effects and provide a glimpse of physics beyond what experiments at particle colliders can reach.

More than 500 scientists attended last week's Intensity Frontier Workshop.

“I love the precision,” said Tassielli while attending a Department of Energy-organized workshop in Washington, D.C., last week to explore scientific opportunities at the Intensity Frontier. This research area uses densely packed particle beams and complex detectors to allow physicists to see particle interactions occurring as rarely as once in a million million times.

Tassielli says it’s a research area that the world should invest in exploring to expand our understanding of nature, just as other scientists explore the depths of the ocean or craters of the moon.

The Fundamental Physics at the Intensity Frontier Workshop was set up to survey existing research and future scientific possibilities in this area, and to gauge the level of interest from the physics community. Organizers had to start turning people away after the 515 participant cap was reached more than a week before the workshop. Participant enthusiasm and energy exceeded expectations, said Glen Crawford, head of the research and technology division of DOE’s Office of High Energy Physics.

“There were a lot of lively discussions,” he said. “There were lots of young people asking good questions, people saying, ‘I learned something,’ people stopping you in the hall and saying, ‘This is great. I’m exploring opportunities for what I want to do next.’”

Yuhsain Tsi, a theory postdoc from Cornell University, said he’s interested in neutrino physics because Intensity Frontier science has as much discovery opportunity as other areas of particle physics.

Physicists spent three days in six working groups listening to more than 100 presentations identifying promising research areas that use neutrinos, nucleons, nuclei, heavy quarks, charged leptons and exotic particles such as axions. The consensus was that a host of experiments have the potential to answer the biggest questions: How did the universe begin? What is it made of? How does it work? How did we come to exist? Answers from this research could aid studies in cosmology, nuclear physics and other areas of particle physics.

“What came out was that there is a broad program that has interconnections inside the Intensity Frontier and outside the Intensity Frontier that addresses fundamental symmetries of physics,” said workshop co-convenor Harry Weerts from Argonne National Laboratory.

Experiments probing the Intensity Frontier are currently running in Europe, Asia and the United States, with more proposed for the future. Flip Tanedo, a theory postdoc from Cornell University, said the ability to work face-to-face with experimental colleagues on an experiment in the United States is a key draw of the Intensity Frontier and opens the door to more productive research.

The results of the workshop will be summarized in a report that will be presented to the DOE and the High Energy Physics Advisory Panel before its March meeting. This report will provide a survey of the physics community’s thoughts about the Intensity Frontier and its scientific potential.

“The Intensity Frontier is rich. That is what we have discovered during the last three days,” said JoAnne Hewett, co-convener and SLAC physicist, said in a closing speech at the workshop. “And I think we have demonstrated a strong desire to do this physics.”

Tona Kunz

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On neutrinos and nanoseconds: Physicists partner with professional timekeeper

December 1, 2011 | 2:11 pm

Professional timekeeper Demetrios Matsakis does not wear a watch. Image: Amy Dusto

When Demetrios Matsakis, the head of the U.S. Naval Observatory department that deals with measuring time, received an email from a Fermilab physicist in late September, he had immediate suspicions. The physicist asked if a two-way satellite transfer, one of the Naval Observatory’s specialties, would work in a particular timing measurement.

“This is about neutrinos, isn’t it?” Matsakis wrote back. Yes, it was.

Matsakis, head of the Time Service Department, soon found himself advising physicist Carl Rosenfeld and his partners on MINOS, a Fermilab neutrino experiment. This year another neutrino experiment, called OPERA, found the subatomic particles seemed to beat the speed of light while traveling between CERN in Switzerland and Gran Sasso National Laboratory in Italy. This is considered impossible under special relativity. The MINOS collaboration plans to double-check the OPERA experiment’s result.

While on a personal trip to Europe this week, Matsakis stopped by CERN and met with OPERA researcher Dario Autiero, who first presented the perplexing neutrino results on Sept. 23.

Matsakis did not wear a watch on his trip to CERN, nor has he ever. He’s like many people in that he doesn’t want “to be ruled by time,” he said. Instead, Matsakis does the ruling.

In his job, Matsakis keeps the official time for the United States and the U.S. Department of Defense and, together with the National Institute of Standards and Technology, keeps the official time for the United States. This involves maintaining more than 100 atomic clocks and GPS systems calibrated to within one nanosecond of each other – not a simple task.

“A good cesium clock on a bad day can be off by five nanoseconds,” he said. In terms of GPS, one nanosecond can translate to being off in position on the ground by one meter. About 30 people work under him to take care of the time.

Together Matsakis and Autiero reviewed electronic timing systems and discussed all sorts of little details that could affect the measurements of the times neutrinos left CERN and arrived at Gran Sasso.

“There’s a lot I don’t know,” Matsakis said. One thing he learned about at CERN was the idea of a blind measurement in calibrations: Neither of two groups measuring separate clocks knows in advance what time they should see, so they don’t make any corrections until after comparing results and noticing a discrepancy. Matsakis isn’t sure whether this is a better method than just correcting a clock as soon as one realizes it doesn’t give the right time, but he’s open to trying it.

When he gets home, he and his counterparts at NIST will advise MINOS on their next steps in developing a better timing system. “I’m giving them a detailed shopping list, down to what model, what part and what company,” he said in a car ride between experimental sites he was touring with Autiero.

“Just in time for Christmas,” Autiero joked.

Amy Dusto

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D.C. workshop envisions the Intensity Frontier

November 29, 2011 | 12:00 pm

Fermilab Today published this story on Nov. 29, 2011. For more information about the workshop follow the hashtag #intensityfrontier. 

At the Intensity Frontier, scientists use high energy beams and sensitive particle detectors to explore rare subatomic processes in search of answers to profound questions. More than 500 scientists are gathering this week to discuss the future role of the U.S. in these experiments. They will discuss the most exciting opportunities, the potential for new discoveries and the equipment and technology required for these new experiments.

The workshop, named “Fundamental Physics at the Intensity Frontier” and held from Nov. 30 to Dec. 2 near Washington, D.C., is split into six working groups. Speakers from each group will provide an overview of their study area and its future goals to an audience spanning the breadth of the physics community. Then medium-sized groups will break away for debates and discussions designed to stimulate open conversations.

“This will be a good opportunity for people in more specialized areas to interact and learn from each other and hopefully reinforce each other’s case for this physics,” said Jack Ritchie, a co-convener for the Heavy Quarks group and professor in the physics department at the University of Texas, Austin.

In recent years, the Intensity Frontier has become a top priority for fields like nuclear physics, according to Michael Ramsey-Musolf, a physics professor at the University of Wisconsin at Madison and a co-convener for the Nucleons, Nuclei and Atoms group.

“There’s a lot of synergy between high-energy physics, nuclear physics and cosmology and they all meet at the Intensity Frontier field,” he said.

The workshop also brings together scientists from similar research areas, such as muon physicists from experiments like Muon g-2, Mu2e and the proposed Long-Baseline Neutrino Experiment, according to David Hertzog, a University of Washington physics professor and member of the Charged Leptons group.

“This community is scattered all over the planet,” he said. “In any one snapshot you don’t have everybody in the same room like this.”

While the DOE’s Office of Science will use the event to evaluate the science opportunities for the U.S. particle physics community in this field, the workshop will also be a learning experience for those new to the Intensity Frontier.

“It will be very good for me to learn more about what the physics goals are,” said Gerben Stavenga, a postdoctoral fellow researching theoretical physics and a speaker for the Proton Decay group. “We’re looking forward to what the Intensity Frontier will bring us.”

From graduate students to Fermilab physicists and DOE staff, the community in attendance will comprise a large spectrum of physics professionals. The working groups have spent months preparing for the workshop.

“It’s going to be a big crowd of people and a wide range of physics to cover,” said Rouven Essig, an assistant professor from Stony Brook University and co-convener for the Hidden Sector Photons, Axions, and WISPs group. “Many eyes are on the workshop and it will have an important impact on the future direction of this field.”

Brad Hooker

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Physicists talk turkey

November 23, 2011 | 11:46 am

Looking for some help with cooking your Thanksgiving feast this holiday? Here are a couple of ways that particle physics can lend a hand.

The plastic industry uses particle accelerators to treat the sturdy shrink wrap that keep Butterball turkeys and many other food products fresh.

Not sure how long to cook your turkey? Take some advice from SLAC Director Emeritus Pief Panofsky and use the equation he derived for the holiday: t = W^(2/3)/1.5, where t is the cooking time in hours and W is the weight of the stuffed turkey, in pounds. The constant 1.5 was determined empirically.

If a Butterball turkey will take the spotlight on your table, you have particle accelerators to thank for its freshness. The food industry uses particle accelerators to produce the sturdy, heat-shrinkable film that Butterballs come wrapped in. When a beam of electrons from a particle accelerator hits the plastic wrapping, it causes a chemical reaction that makes the film super strong and heat resistant. The food industry purchases the treated shrink wrap from plastic manufacturers in the form of bags or rolls. A turkey gets placed inside, and voila, a fresh meal will soon grace your Thanksgiving table.

From all of us at symmetry magazine, have a wonderful Thanksgiving!

Elizabeth Clements

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Muppet scientists at the LHC

November 23, 2011 | 10:32 am

If a big family trip to the movies is one of your Thanksgiving traditions, you might soon find yourself sitting with a fat tub of buttery popcorn at a screening of The Muppets, released today.

In the film, characters from original Muppets television show, which ran from 1976 to 1981, reunite after years apart to save their old theater from being razed by an oil tycoon. Physics fans will cheer to see that bespectacled scientist Dr. Bunsen Honeydew and his harried assistant, Beaker, seem to have moved on from their careers at Muppet Labs to work on the ATLAS experiment at the Large Hadron Collider. (Perhaps Beaker finally finished his post-doc.)

In the preview below, Kermit and the gang find the two in the ATLAS detector hall, where the frazzled red-head is sucked into a pneumatic tube system and shrunk small enough to fit in Dr. Honeydew’s pocket. LHC scientists are still puzzled as to how the Muppet could possibly enter the striped tubes, which are actually filled with cryogenics and superconducting magnets.

ATLAS physicist Steve Goldfarb said he hopes the Muppets will actually stop by the laboratory now that they’ve finished filming. “I have a lot of empathy for Beaker,” he said, “especially since I’ve worked on hardware.”

Read about more intersections of particle physics machines and cinema here and here.

Kathryn Grim

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Tabletop ATLAS assembly, no hardhat required

November 22, 2011 | 4:00 pm

Physicist Sascha Mehlhase may have missed the actual construction of the ATLAS detector at CERN, but he found another way to experience the joy of building it – a way reminiscent of his childhood and the contents of a particularly good toy box he once had. He made the detector out of Legos.

Two colleagues at Mehlhase’s office at the Niels Bohr Institute in Copenhagen put forward the idea of building the detector out of Legos for a public event last year, but they never got around to doing it themselves. Last month as a similar event approached, Mehlhase decided to go for it. To the displeasure of his wife, he spent an entire weekend using the free digital designer software on Lego.com to translate photos and 3D renderings from the ATLAS website into a plan for plastic.

He scaled the model to a Lego man, a few centimeters in height, corresponding to a two-meter tall human, which made the finished masterpiece nearly a half-meter in height. The fixed selection of blocks, however, meant that everything didn’t scale with exactly 100 percent accuracy.

“Sometimes in LEGO you get these pieces in lengths of two, four, six or eight when a seven would be perfect,” Mehlhase said.

He convinced the head of his group to buy the 10,000 pieces his design called for, which arrived in a huge package with about two-thirds of its contents in need of sorting. Mehlhase and a few students started doing this by color and then by type – a task he estimates took about a quarter of the total time.

Soon Mehlhase discovered that the project was more formidable than he’d foreseen. An instruction manual created by the Lego software yielded “4,500 pages of almost useless material,” Mehlhase said. Because the detector is a symmetrical machine, inside-out assembly makes more sense than bottom-to-top, which the computer didn’t realize.

So he abandoned the manual. Instead, over the course of a few weeks, he spent 33 hours comparing the digital Lego design he’d made with his bins of sorted pieces, figuring out by sight where things should go.

“So far I’ve managed everything without glue,” he said.

The public event passed, but Mehlhase was on a mission. Brick by primary-colored brick he toiled. A few challenges scientists faced in creating the real ATLAS detector proved challenging in the LEGO model as well. For example, the outer magnets in both structures are much heavier than some internal pieces, yet they need to support themselves without breaking.

Mehlhase finished the mini-detector, complete with tiny technicians and red block “ATLAS” sign, in early November. His group at Copenhagen plans to use it for outreach. A few other institutions have emailed him about the designs, and he said he’d gladly share. He says he’d like to see his Lego ATLAS design at CERN one day.

For now Mehlhase plans to display the model in a glass case in the hallway outside his office. The real ATLAS detector may belong to the thousands of physicists who built and run it, but this one is all Copenhagen’s.

All images courtesy of Sascha Mehlhase.

Amy Dusto

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Favored Higgs hiding spot remains after most complete search yet

November 18, 2011 | 5:30 am

The Standard Model Higgs boson is excluded at a 95 percent confidence level everywhere the thick black line drops below the red line. Image: ATLAS and CMS experiments

The CMS and ATLAS experiments at the Large Hadron Collider have backed the Standard Model Higgs boson, if it exists, into a corner with their first combined Higgs search result.

The study, made public today, eliminates several hints the individual experiments saw in previous analyses but leaves in play the favored mass range for the Higgs boson, between 114 and 141 GeV. ATLAS and CMS ruled out at a 95 percent confidence level a Higgs boson with a mass between 141 and 476 GeV.

The new result combines eight studies of predicted decays of the Higgs boson using data the experiments collected up to July. Physicists expected to be able to rule out an even wider mass range, between 125 and 500 GeV, based on the amount of data used and the sensitivities of the different search modes. But small excesses that could be the result of statistical fluctuations or could indicate the presence of a hidden particle reduced the range of masses that could be excluded.

“I think it could be an interesting message the data is telling us,” said physicist Eilam Gross of the Weizmann Institute of Science, who shares leadership of the ATLAS experiment’s Higgs group. “Any discovery starts with the inability to exclude.”

Several related measurements indirectly suggest a Standard Model Higgs boson exists at the lower end of the mass range.

Almost a year of work, more than 50 meetings and plenty of diplomacy went into calculating the LHC experiments’ first combination of Higgs search results. Experts from both collaborations worked together for more than seven months to devise the combination procedure and for about one month to come up with the combined result. Then the two collaborations, each a few thousand members strong, took about a month to review and approve it.

“This is really a landmark achievement,” said CMS physicist Vivek Sharma of the University of California, San Diego, co-leader of the Higgs combination group. “Combining LHC Higgs search results is not a straightforward process. There’s a lot going on under the hood.”

Since July, the two experiments have accumulated two to four times as much data. By the end of 2012, they hope to at least double that.

The end of the Standard Model Higgs search is in sight, said ATLAS physicist Bill Murray of the U.K. Science and Technology Facilities Council, co-leader of the Higgs combination group. “This year’s data will probably give us the answer, but next year we will be able to announce it firmly,” he said.

So far, the ATLAS and CMS experiments have not yet decided to produce a second Higgs combination based on results from the full 2011 dataset. The two experiments are still in competition; they might wait to see what they can accomplish on their own before working together again.

“This was a chance to go through the process when the results were uncontroversial,” Sharma said. “Now we’re in discovery mode. The next time won’t be so calm.”

Kathryn Grim

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