Skip to main content

Home/ COSEE-West/ Group items tagged it

Rss Feed Group items tagged

Gwen Noda

Galaxy Zoo Volunteers Share Pain and Glory of Research - 0 views

  •  
    Science 8 July 2011: Vol. 333 no. 6039 pp. 173-175 Galaxy Zoo Volunteers Share Pain and Glory of Research 1. Daniel Clery A project to "crowdsource" galactic classifications has paid off in ways the astronomers who started it never expected. Figure View larger version: * In this page * In a new window Space oddity. Greenish "voorwerp" spotted by a Dutch volunteer still intrigues scientists. "CREDIT: NASA, ESA, W. KEEL (UNIVERSITY OF ALABAMA), AND THE GALAXY ZOO TEAM" The automated surveys that are becoming increasingly common in astronomy are producing an embarrassment of riches for researchers. Projects such as the Sloan Digital Sky Survey (SDSS) are generating so much data that, in some cases, astronomers don't know what to do with them all. SDSS has compiled a list of more than 1 million galaxies. To glean information about galaxy evolution, however, astronomers need to know what type of galaxy each one is: spiral, barred spiral, elliptical, or something else. At present, the only reliable way to classify galaxies is to look at each one. But the SDSS list is so long that all the world's astronomers working together couldn't muster enough eyeballs for the task. Enter the "wisdom of crowds." An online effort called Galaxy Zoo, launched in 2007, set a standard for citizen-scientist participation projects. Zealous volunteers astonished the project's organizers by classifying the entire catalog years ahead of schedule. The results have brought real statistical rigor to a field used to samples too small to support firm conclusions. But that's not all. Buoyed by the curiosity and dedication of the volunteers, the Galaxy Zoo team went on to ask more-complicated classification questions that led to studies they hadn't thought possible. And in an online discussion forum on the Galaxy Zoo Web site, volunteers have pointed to anomalies that on closer inspection have turned out to be genuinely new astronomical objects. "I'm incredibly impres
Gwen Noda

Time to Adapt to a Warming World, But Where's the Science? - 0 views

  •  
    "Science 25 November 2011: Vol. 334 no. 6059 pp. 1052-1053 DOI: 10.1126/science.334.6059.1052 * News Focus Adaptation to Climate Change Adaptation to Climate Change Time to Adapt to a Warming World, But Where's the Science? 1. Richard A. Kerr With dangerous global warming seemingly inevitable, users of climate information-from water utilities to international aid workers-are turning to climate scientists for guidance. But usable knowledge is in short supply. Figure View larger version: * In this page * In a new window Adapt to that. Climate will change, but decision-makers want to know how, where, and when. "CREDIT: KOOS VAN DER LENDE/NEWSCOM" DENVER, COLORADO-The people who brought us the bad news about climate change are making an effort to help us figure out what to do about it. As climate scientists have shown, continuing to spew greenhouse gases into the atmosphere will surely bring sweeping changes to the world-changes that humans will find it difficult or impossible to adapt to. But beyond general warnings, there is another sort of vital climate research to be done, speakers told 1800 attendees at a meeting here last month. And so far, they warned, researchers have delivered precious little of the essential new science. At the meeting, subtitled "Climate Research in Service to Society,"* the new buzzword was "actionable": actionable science, actionable information, actionable knowledge. "There's an urgent need for actionable climate information based on sound science," said Ghassem Asrar, director of the World Climate Research Programme, the meeting's organizer based in Geneva, Switzerland. What's needed is not simply data but processed information that an engineer sizing a storm-water pipe to serve for the next 50 years or a farmer in Uganda considering irrigating his fields can use to make better decisions in a warming world. Researchers preparing for the next international climate assessment, due in 2013, delive
Gwen Noda

Bounds and Vision - 0 views

  •  
    Information Science Bounds and Vision Atlas of Science Visualizing What We Know by Katy Börner MIT Press, Cambridge, MA, 2010. 266 pp. $$29.95, £22.95. ISBN 9780262014458. 1. Mason A. Porter + Author Affiliations 1. The reviewer is at the Oxford Centre for Industrial and Applied Mathematics, Mathematical Institute, University of Oxford, Oxford OX1 3LB, UK, and at the CABDyN Complexity Centre and Somerville College, University of Oxford. 1. E-mail: porterm@maths.ox.ac.uk Visualization is a crucial but underappreciated part of science. As venues like the American Physical Society's Gallery of Fluid Motion and Gallery of Nonlinear Images illustrate every year, good visuals can make science more beautiful, more artistic, more tangible, and often more discernible. Katy Börner's continuing exhibition Places & Spaces: Mapping Science (1) and her book Atlas of Science: Visualizing What We Know arise from a similar spirit but are much more ambitious. Visualization is one of the most compelling aspects of science. Breathtaking visuals from sources like fractals and Disneyland's long-dead "Adventure Thru Inner Space" ride are what originally inspired me toward my personal scientific path, so I welcome any resource that promises to bring the visual joys of discovery to a wide audience. Importantly, Börner's exhibition and book are not mere artistic manifestations, although they would be impressive accomplishments even if that were her only goal. Some scientists have occasionally had great success in the visual arts; for example, physicist Eric Heller has long exhibited the gorgeous fruits of his research on quantum chaos and other topics (2). To fully appreciate Börner's efforts, however, one must be conscious that she is deeply concerned not just with visualization itself but with the science of visualization. Accordingly, her book discusses the history of the science of visualization, where it is now, and where she thinks it can go. Atlas of Scie
Gwen Noda

The Ten Best Ocean Stories of 2012 | Surprising Science - 0 views

  •  
    December 18, 2012 The Ten Best Ocean Stories of 2012 | | | Share on redditReddit | Share on diggDigg | Share on stumbleuponStumble | Share on emailEmail | More Sharing ServicesMore Two market squids mating 2012 was a big year for squid science. Photo Credit: © Brian Skerry, www.brianskerry.com Despite covering 70 percent of the earth's surface, the ocean doesn't often make it into the news. But when it does, it makes quite a splash (so to speak). Here are the top ten ocean stories we couldn't stop talking about this year, in no particular order. Add your own in the comments! 2012: The Year of the Squid From the giant squid's giant eyes (the better to see predatory sperm whales, my dear), to the vampire squid's eerie diet of remains and feces, the strange adaptations and behavior of these cephalopods amazed us all year. Scientists found a deep-sea squid that dismembers its own glowing arm to distract predators and make a daring escape. But fascinating findings weren't relegated to the deep: at the surface, some squids will rocket themselves above the waves to fly long distances at top speeds. James Cameron Explores the Deep Sea Filmmaker James Cameron has never shied away from marine movie plots (See: Titanic, The Abyss), but this year he showed he was truly fearless, becoming the first person to hit the deepest point on the seafloor (35,804 feet) in a solo submarine. While he only managed to bring up a single mud sample from the deepest region, he found thriving biodiversity in the other deep-sea areas his expedition explored, including giant versions of organisms found in shallow water. Schooling sardines form a "bait ball." Small fish, such as these schooling sardines, received well-deserved attention for being an important part of the food chain in 2012. Photo Credit: © Erwin Poliakoff, Flickr Small Fish Make a Big Impact Forage fish-small, schooling fish that are gulped down by predators-should be left in the ocean for larger fish, marin
Gwen Noda

Gulf Drilling Disaster Triggers Scrutiny of Mediterranean Oil Rush - 0 views

  •  
    "Oil Exploration Oil Exploration Gulf Drilling Disaster Triggers Scrutiny of Mediterranean Oil Rush 1. Laura Margottini* A rush to find and extract oil in the Mediterranean Sea is threatening one of the planet's marine biodiversity hot spots, scientists warn. PANTELLERIA, ITALY-This tiny speck in the Mediterranean, home to a few thousand people, seems like one of the most tranquil places in the world. But looks are deceptive. Pantelleria, in the Strait of Sicily halfway between Palermo and Tunis, is close to one of the world's busiest shipping lanes, and of late, its waters have also become the center of a new oil rush. Attracted by Italy's easygoing drilling regulations and low tax on oil extraction, dozens of companies have new plans for exploration and drilling in this part of the Mediterranean Sea. At a recent meeting here,* however, scientists, conservationists, and environmental activists warned that such efforts put several important biodiversity hot spots in danger. An oil disaster like the Deepwater Horizon explosion, which sent oil gushing into the Gulf of Mexico for months, could easily ruin the Mediterranean ecology for a century or longer, some said. The Italian government has recently issued 66 permissions for drilling around its coasts and 25 concessions for exploration. Another 67 applications for exploration are under review. "Italy now represents the region that holds the most exciting and significant long-term opportunities," one company, Northern Petroleum, says on its Web site. The Strait of Sicily is the center of attention, but other biodiversity hot spots, such as the Tremiti Islands in the Adriatic Sea, could soon be explored as well. Italy isn't alone. Tunisia, for example, has granted concessions for oil exploration for most of its Mediterranean waters, without much political opposition. But the areas coveted by oil companies are ecological treasures, researchers and groups such as Greenpeace Italy stress. Last year, the Uni
Gwen Noda

Know Your Ocean | Science and Technology | Ocean Today - 0 views

  •  
    NARRATOR: Even though the ocean covers seventy percent of the Earth's surface, people tend to know more information about land than the sea. As a result, our understanding of the ocean is often incomplete or full of misconceptions. How well do you know the ocean? You may think Earth has five separate oceans. They're clearly labeled on our maps. But, in actuality, these are all connected, and part of one global ocean system. Ever wonder why the ocean is blue? You may have heard its because the water reflects the color of the sky. Not quite. Sunlight contains all the colors of the rainbow. When it hits the ocean, it gets scattered by the water molecules. Blue light is scattered the most, which is why the ocean appears blue. Even more interesting is that floating plants and sediments in the water can cause light to bounce in such a way for the ocean to appear green, yellow, and even red! Another idea some people have is that the sea floor is flat. Actually, just like land, the sea floor has canyons, plains, and mountain ranges. And many of these features are even bigger than those found on land. You may also think that our ocean's saltwater is just a mix of water and table salt. Not so. Seawater's "salt" is actually made of dissolved minerals from surface runoff. That is, excess water from rain and melting snow flowing over land and into the sea. This is why the ocean doesn't have the same level of salinity everywhere. Salinity varies by location and season. Finally, you may have heard that melting sea ice will cause sea levels to rise. In reality, sea ice is just frozen seawater, and because it routinely freezes and melts, its volume is already accounted for in the ocean. Sea levels can rise, however, from ice that melts off land and into the ocean. Understanding basic facts about the ocean is important since it affects everything from our atmosphere to our ecosystems. By knowing your ocean, you are better prepared to help protect it.
Gwen Noda

USC researcher experiments with changing ocean chemistry | 89.3 KPCC - 0 views

  •  
    "USC researcher experiments with changing ocean chemistry Jan. 19, 2011 | Molly Peterson | KPCC In his lab, USC's Dave Hutchins is simulating possible future atmospheres and temperatures for the Earth. He says he's trying to figure out how tiny organisms that form the base of the food web will react to a more carbon-intense ocean. Burning fossil fuels doesn't just put more carbon into the atmosphere and help warm the climate. It's also changing the chemistry of sea water. KPCC's Molly Peterson visits a University of Southern California researcher who studies the consequences of a more corrosive ocean. Tailpipes and refineries and smokestacks as far as the eye can see in Los Angeles symbolize the way people change the planet's climate. They remind Dave Hutchins that the ocean's changing too. Hutchins teaches marine biology at USC. He says about a third of all the carbon, or CO2, that people have pushed into earth's atmosphere ends up in sea water - "which is a good thing for us because if the ocean hadn't taken up that CO2 the greenhouse effect would be far more advanced than it is." He smiles. Hutchins says that carbon is probably not so good for the ocean. "The more carbon dioxide that enters the ocean the more acidic the ocean gets." On the pH scale, smaller numbers represent more acidity. The Monterey Bay Aquarium Research Institute estimates we've pumped 500 million tons of carbon into the world's oceans. Dave Hutchins at USC says that carbon has already lowered the pH value for sea water. "By the end of this century we are going to have increased the amount of acid in the ocean by maybe 200 percent over natural pre-industrial levels," he says. "So we are driving the chemistry of the ocean into new territory - into areas that it has never seen." Hutchins is one of dozens of scientists who study the ripples of that new chemistry into the marine ecosystem. Now for an aside. I make bubbly water at home with a soda machine, and to do that, I pump ca
Gwen Noda

UnderwaterTimes.com | Ocean Probes To Help Refine Climate Change Forecastin - 0 views

  •  
    Ocean Probes To Help Refine Climate Change Forecasting; 'Oceanography Is Risky; You Lose Things' by Underwatertimes.com News Service - August 5, 2011 17:43 EST LOS ANGELES, California -- A USC researcher has opened a new window to understanding how the ocean impacts climate change. Lisa Collins, environmental studies lecturer with the USC Dornsife College, spent four years collecting samples from floating sediment traps in the San Pedro Basin off the Los Angeles coast, giving scientists a peek at how much carbon is locked up in the ocean and where it comes from. Collins' research suggests that the majority of particulate organic carbon (POC) falling to the basin floor is marine-derived, not the result of runoff from rainfall. This means that the ocean off the coast of Southern California is acting as a carbon "sink" - taking carbon out of the atmosphere via phytoplankton and locking it up in sediment. Though estimates regarding the effect of carbon in the ocean already exist, her hard data can help climatologists create more accurate predictions of how carbon will impact global warming. What is unique about Collins' study is that it is not just a snapshot of POC falling, but rather a finely detailed record of four years of POC production, showing how much fell and when. "It's all tied to climate change," said Collins, who started the research as a graduate student working for USC Earth Sciences Professor Will Berelson. "This lets us see patterns. "Our data can help climate modelers better predict the interactions between the oceans and atmosphere with respect to carbon which can help them better predict how much carbon dioxide will end up sequestered over the long term as sediments in the ocean," she said. Collins' study is among the longest of its kind in the region. A similar study was conducted in Santa Monica Basin from 1985-1991, and another is currently underway in Hawaii. Her findings appear in the August issue of Deep-Sea Research I. Between Janua
Gwen Noda

Governments refusal to address ocean acidification. - Sacramento Political Buzz | Exami... - 0 views

  •  
    Global warming…the Earth is steadily getting warmer. The why is it getting warmer question will solicit so many theories that it would drive one mad to sort through them all. Global warming itself is sort of a misnomer; it is a symptom of the problem, not the cause. The cause for all the debate is whether or not the atmospheric increase of CO2 gas over the last two-hundred years has affected the Earth's climate. Recently scientists have discovered another reason to be concerned about the increasing level of atmospheric CO2. It is startling that the media and science has hardly touched upon ocean acidification. It would not be surprising if you have never heard this term. A LexisNexis search of the news wire services found in the past week there were 348 articles that mentioned global warming. Three articles contained ocean acidification. In the last 2 years, a LexisNexis search of all sources found a mere 216 articles that mentioned ocean acidification. That is a worldwide search of newspapers, magazines and wire services. The New York Times did not mention it a single time, but they ran so many Global Warming articles that there were too many matches for the page to display.
Gwen Noda

NSF Touts Family-Friendly Policies as Boon to Women - 0 views

  •  
    "Scientific Workforce NSF Touts Family-Friendly Policies as Boon to Women 1. Jeffrey Mervis Young women are forever asking Meg Urry, an astrophysicist at Yale University, if it's possible "to have a successful scientific career and a family." A tenured professor with both, Urry tells them "yes." Perhaps more telling, however, is that the issue doesn't seem to interest half of her students. "I've never been asked that question by a man," she says. This week, the National Science Foundation (NSF) rolled out a set of family-friendly policies that it hopes will reduce the number of young women who jettison scientific careers because of responsibilities outside the lab. "Too many women give up because of conflicts between their desire to start a family and their desire to ramp up their careers," says John Holdren, the president's science adviser and head of the Office of Science and Technology Policy. It was a rare moment in the spotlight for the low-profile basic research agency: First Lady Michelle Obama announced the policies at a White House ceremony touting the importance of women to the nation's economic recovery and, in particular, the need to improve the proportion of women in the so-called STEM (science, technology, engineering, and mathematics) workforce. Figure View larger version: * In this page * In a new window Lending a hand. First Lady Michelle Obama applauds the work of young women in science at a White House event. "CREDIT: NATIONAL SCIENCE FOUNDATION" The new policies will allow both male and female grant recipients to defer an award for up to 1 year or receive a no-cost extension of an existing grant. NSF also hopes to increase its use of "virtual reviews" of grant proposals so that scientists don't need to travel as often to the agency's Arlington, Virginia, headquarters. The only change with any price tag attached is a new program of supplemental awards to investigators going on family leave, allowing them to hi
Gwen Noda

Humans Are Driving Extreme Weather; Time to Prepare - 0 views

  •  
    "Science 25 November 2011: Vol. 334 no. 6059 p. 1040 DOI: 10.1126/science.334.6059.1040 * News & Analysis Climate Change Humans Are Driving Extreme Weather; Time to Prepare 1. Richard A. Kerr Figure View larger version: * In this page * In a new window Thai floods 2011 Hurricane Katrina 2005 Texas drought 2011 "CREDITS (LEFT TO RIGHT): PAULA BRONSTEIN/GETTY IMAGES; JEFF SCHMALTZ, MODIS RAPID RESPONSE TEAM, NASA/GSFC; NOAA" An international scientific assessment finds for the first time that human activity has indeed driven not just global warming but also increases in some extreme weather and climate events around the world in recent decades. And those and likely other weather extremes will worsen in coming decades as greenhouse gases mount, the report finds. But uncertainties are rife in the still-emerging field of extreme events. Scientists cannot attribute a particular drought or flood to global warming, and they can say little about past or future trends in the risk of high-profile hazards such as tropical cyclones. Damage from weather disasters has been climbing, but the report can attribute that trend only to the increasing exposure of life and property to weather risks. Climate change may be involved, but a case cannot yet be made. Despite the uncertainties, the special report from the Intergovernmental Panel on Climate Change (IPCC) released 18 November stresses that there is still reason for taking action now. The panel recommends "low-regrets measures," such as improvements in everything from drainage systems to early warning systems. Such measures would benefit society in dealing with the current climate as well as with almost any range of possible future climates. The report takes a cautious, consensus-based approach that draws on the published literature. Headlines and even some scientists may point to the current Texas drought or the 2003 European heat wave as the result of the strengthening greenhouse. But the report fin
Gwen Noda

http://www.oceanacidification.org.uk - 0 views

  •  
    The term ocean acidification is used to describe the ongoing decrease in ocean pH caused by human CO2 emissions, such as the burning of fossil fuels. It is the little known consequence of living in a high CO2 world, dubbed at the 2009 United Nations Climate Change Conference (COP15) as the "evil twin of climate change". The oceans currently absorb approximately half of the CO2 produced by burning fossil fuel; put simply, climate change would be far worse if it were not for the oceans. However, there is a cost to the oceans - when CO2 dissolves in seawater it forms carbonic acid and as more CO2 is taken up by the oceans surface, the pH decreases, moving towards a less alkaline and therefore more acidic state. Already ocean pH has decreased by about 30% and if we continue emitting CO2 at the same rate by 2100 ocean acidity will increase by about 150%, a rate that has not been experienced for at least 400,000 years. Such a monumental alteration in basic ocean chemistry is likely to have wide implications for ocean life, especially for those organisms that require calcium carbonate to build shells or skeletons. Ocean acidification is a relatively new field of research, with most of the studies having been conducted over the last decade. While it is gaining some attention among policy makers, international leaders and the media, scientists find there is still a lack of understanding.
Gwen Noda

A Cartography of the Anthropocene - 0 views

  •  
    So, might you ask, what is the Anthropocene? First, the etymology. The Ancient Greek [anthropos] means "human being" while [kainos] means "new, current." The Anthropocene would thus be best defined as the new human-dominated period of the Earth's history. The term was proposed in 2000 by Paul J. Crutzen, Nobel Prize in 1995 for his work on atmospheric chemistry and his research on stratospheric ozone depletion (the so-called "hole"), and by Eugene F. Stoermer in a publication (p. 17) of the International Geosphere-Biosphere Programme. But the concept itself, the idea that human activity affects the Earth to the point where it can cross a new age, is not new and dates back to the late nineteenth century. Different terms were proposed over the decades, such as Anthropozoic (Stoppani, 1873), Noosphere (de Chardin, 1922; Vernadsky, 1936), Eremozoic (Wilson, 1992), and Anthrocene (Revkin, 1992). It seems that the success of the term chosen by Crutzen and Stoermer is due to the luck of having been made at the appropriate time, when humankind became more than ever aware of the extent of its impact on global environment. It should be noted that Edward O. Wilson (who suggested Eremozoic, "the age of loneliness") popularized the terms "biodiversity" and "biophilia." Technically, the Anthropocene is the most recent period of the Quaternary, succeding to the Holocene. The Quaternary is a period of the Earth's history characterized by numerous and cyclical glaciations, starting 2,588,000 years ago (2.588 Ma). The Quaternary is divided into three epochs: the Pleistocene, the Holocene, and now the Anthropocene.
Gwen Noda

Reflections On: Our Planet and Its Life, Origins, and Futures - 0 views

  •  
    "The theme of the 175th Annual Meeting of the American Association for the Advancement of Science (AAAS), "Our Planet and Its Life, Origins, and Futures," celebrated an enormous breadth of scientific accomplishments that transcends many subdisciplines of the natural and social sciences. It was intended to be both a reflection on what has been learned and a look forward to what must yet be better known if we are to make wise choices as stewards of our planet. The program committee saw this as an opportunity to examine how we have come to know and understand the coevolution of life with its interacting biological, biogeochemical, and physical environments. Further advances in this area are essential to develop scenarios that can be useful in guiding decisions to address some of society's most pressing problems. We must work toward a future that embraces the wise application of science to improve human health and well-being and to sustain the great diversity of life on our planet. "
Gwen Noda

ScienceDirect.com - Earth-Science Reviews - Recognising ocean acidification in deep tim... - 0 views

  •  
    "Recognising ocean acidification in deep time: An evaluation of the evidence for acidification across the Triassic-Jurassic boundary Sarah E. GreeneCorresponding author contact information, 1, E-mail the corresponding author, Rowan C. Martindale1, E-mail the corresponding author, Kathleen A. Ritterbush E-mail the corresponding author, David J. Bottjer E-mail the corresponding author, Frank A. Corsetti E-mail the corresponding author, William M. Berelson E-mail the corresponding author Department of Earth Sciences, University of Southern California, Los Angeles, California, USA 90089 Received 22 July 2011. Accepted 17 March 2012. Available online 5 April 2012. While demonstrating ocean acidification in the modern is relatively straightforward (measure increase in atmospheric CO2 and corresponding ocean chemistry change), identifying palaeo-ocean acidification is problematic. The crux of this problem is that the rock record is a constructive archive while ocean acidification is essentially a destructive (and/or inhibitory) phenomenon. This is exacerbated in deep time without the benefit of a deep ocean record. Here, we discuss the feasibility of, and potential criteria for, identifying an acidification event in deep time. Furthermore, we investigate the evidence for ocean acidification during the Triassic-Jurassic (T-J) boundary interval, an excellent test case because 1) it occurs in deep time, beyond the reach of deep sea drilling coverage; 2) a potential trigger for acidification is known; and 3) it is associated with one of the 'Big Five' mass extinctions which disproportionately affected modern-style invertebrates. Three main criteria suggest that acidification may have occurred across the T-J transition. 1) The eruption of the Central Atlantic Magmatic Province (CAMP) and the associated massive and rapid release of CO2 coincident with the end-Triassic mass extinction provide a suitable trigger for an acidification event (
Gwen Noda

Dogs Take Lead in Sniffing Out Arctic Oil - The Pew Charitable Trusts - 0 views

  •  
    Publication: The Guardian Author: Suzanne Goldenberg 03/12/2012 - When it comes to drilling for oil in the harsh and unpredictable Arctic, Shell has gone to the dogs, it seems. A dachshund and two border collies to be specific. The dogs' ability to sniff out oil spills beneath snow and ice has been tested and paid for by Shell - and other oil companies and government research organisations - in preparation for the industry's entry into the forbidding Arctic terrain. The company hopes to begin drilling for oil off the north-west coast of Alaska in June. ... Others said the study should be an embarrassment to the industry. "This is another example of how we do not have adequate science and technology yet to drill in the Arctic Ocean - particularly in ice," Marilyn Heiman, the director of the US Arctic Programme for the Pew Environment Group said in an email. "It is embarrassing that using dogs to sniff out oil is the best technology we have to track oil under ice. Industry needs to invest in research to determine how to track oil under ice, as well as significantly improve spill response capability in ice, before [being] allowed to drill in ice conditions."
Gwen Noda

Imagine it!²: The Power of Imagination (movie) - 0 views

  •  
    Imagine It!2: The Power of Imagination The second movie by Imagine It! Project.
1 - 20 of 102 Next › Last »
Showing 20 items per page