星空女人频道: 2013-08-11

2013年8月17日星期六

Better batteries? Going beyond the surface of oxide films

Researchers at the Department of Energy lab learned that key surface properties of complex oxide films are unaffected by reduced levels of oxygen during fabrication -- an unanticipated finding with possible implications for the design of functional complex oxides used in a variety of consumer products, said Zheng Gai, a member of DOE's Center for Nanoscale Materials Sciences at ORNL.

The findings are detailed in a paper published in Nanoscale.

While the properties of the manganite material below the surface change as expected with the removal of oxygen, becoming an insulator rather than a metal, or conductor, researchers found that the sample showed remarkably stable electronic properties at the surface. Gai emphasized that the robustness of a surface matters because it is precisely the surface properties that determine, influence and affect the functionality of complex oxides in catalysis and batteries.

"With these materials being a promising alternative to silicon or graphene in electronic devices, the ever-decreasing size of such components makes their surface properties increasingly important to understand and control," Gai said.

While this work provides a fundamental understanding of a material used and researched for catalysts, oxide electronics and batteries, Gai and lead author Paul Snijders noted that it's difficult to speculate about possible impacts.

"I always say that in basic science we are discovering the alphabet," said Snijders, a member of ORNL's Materials Science and Technology Division. "How these letters will be designed into a useful technological book is hard to predict."

Making this discovery possible was the fact the authors did their experiment using scanning probe microscopy in a vacuum system with no exposure of the samples to the atmosphere. This contrasts with the conventional approach of growing a sample and then installing it in analysis equipment. During such a transfer, scientists expose the material to the water, nitrogen and carbon dioxide in the air.

By studying pristine samples, the ORNL team gained a surprising new understanding of the physics of the material surfaces -- an understanding that is necessary to design new functional applications, Snijders said.

Other authors of the paper, titled "Persistent metal-insulator transition at the surface of an oxygen-deficient, epitaxial manganite film," are Min Gao, Hangwen Guo, Guixin Cao, Wolter Siemons and Thomas Ward of ORNL, Hongjun Gao of the Chinese Academy of Sciences and Jian Shen of Fudan University, China. Min Gao and Snijders contributed equally to this work, which was funded by DOE's Basic Energy Sciences. A portion of the research was conducted at the Center for Nanophase Materials Sciences.

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New rechargeable flow battery could enable cheaper, more efficient energy storage

Aug. 16, 2013 — MIT researchers have engineered a new rechargeable flow battery that doesn't rely on expensive membranes to generate and store electricity. The device, they say, may one day enable cheaper, large-scale energy storage.

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The palm-sized prototype generates three times as much power per square centimeter as other membraneless systems -- a power density that is an order of magnitude higher than that of many lithium-ion batteries and other commercial and experimental energy-storage systems.

The device stores and releases energy in a device that relies on a phenomenon called laminar flow: Two liquids are pumped through a channel, undergoing electrochemical reactions between two electrodes to store or release energy. Under the right conditions, the solutions stream through in parallel, with very little mixing. The flow naturally separates the liquids, without requiring a costly membrane.

The reactants in the battery consist of a liquid bromine solution and hydrogen fuel. The group chose to work with bromine because the chemical is relatively inexpensive and available in large quantities, with more than 243,000 tons produced each year in the United States.

In addition to bromine's low cost and abundance, the chemical reaction between hydrogen and bromine holds great potential for energy storage. But fuel-cell designs based on hydrogen and bromine have largely had mixed results: Hydrobromic acid tends to eat away at a battery's membrane, effectively slowing the energy-storing reaction and reducing the battery's lifetime.

To circumvent these issues, the team landed on a simple solution: Take out the membrane.

"This technology has as much promise as anything else being explored for storage, if not more," says Cullen Buie, an assistant professor of mechanical engineering at MIT. "Contrary to previous opinions that membraneless systems are purely academic, this system could potentially have a large practical impact."

Buie, along with Martin Bazant, a professor of chemical engineering, and William Braff, a graduate student in mechanical engineering, have published their results this week in Nature Communications.

"Here, we have a system where performance is just as good as previous systems, and now we don't have to worry about issues of the membrane," Bazant says. "This is something that can be a quantum leap in energy-storage technology."

Possible boost for solar and wind energy

Low-cost energy storage has the potential to foster widespread use of renewable energy, such as solar and wind power. To date, such energy sources have been unreliable: Winds can be capricious, and cloudless days are never guaranteed. With cheap energy-storage technologies, renewable energy might be stored and then distributed via the electric grid at times of peak power demand.

"Energy storage is the key enabling technology for renewables," Buie says. "Until you can make [energy storage] reliable and affordable, it doesn't matter how cheap and efficient you can make wind and solar, because our grid can't handle the intermittency of those renewable technologies."

By designing a flow battery without a membrane, Buie says the group was able to remove two large barriers to energy storage: cost and performance. Membranes are often the most costly component of a battery, and the most unreliable, as they can corrode with repeated exposure to certain reactants.

Braff built a prototype of a flow battery with a small channel between two electrodes. Through the channel, the group pumped liquid bromine over a graphite cathode and hydrobromic acid under a porous anode. At the same time, the researchers flowed hydrogen gas across the anode. The resulting reactions between hydrogen and bromine produced energy in the form of free electrons that can be discharged or released.

The researchers were also able to reverse the chemical reaction within the channel to capture electrons and store energy -- a first for any membraneless design.

In experiments, Braff and his colleagues operated the flow battery at room temperature over a range of flow rates and reactant concentrations. They found that the battery produced a maximum power density of 0.795 watts of stored energy per square centimeter.

More storage, less cost

In addition to conducting experiments, the researchers drew up a mathematical model to describe the chemical reactions in a hydrogen-bromine system. Their predictions from the model agreed with their experimental results -- an outcome that Bazant sees as promising for the design of future iterations.

"We have a design tool now that gives us confidence that as we try to scale up this system, we can make rational decisions about what the optimal system dimensions should be," Bazant says. "We believe we can break records of power density with more engineering guided by the model."

Yury Gogotsi, a professor of materials science and engineering at Drexel University, says eliminating the membrane is the next step toward scalable, inexpensive energy storage. The group's design, he says, will help engineers better understand the physics of membraneless systems.

"You cannot have an inexpensive energy-storage system by piling up tens of thousands of individual small cells, like cellphone or computer batteries," says Gogotsi, who did not contribute to the research. "As any new technology, the laminar flow battery will need time to prove its viability. It's like a newborn baby -- we'll only know what the technology is good for after a few years."

According to preliminary projections, Braff and his colleagues estimate that the membraneless flow battery may produce energy costing as little as $100 per kilowatt-hour -- a goal that the U.S. Department of Energy has estimated would be economically attractive to utility companies.

"You can do so much to make the grid more efficient if you can get to a cost point like that," Braff says. "Most systems are easily an order of magnitude higher, and no one's ever built anything at that price."

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2013年8月16日星期五

Embedded Systems LIN slave mop-up chip meets ISO26262

2013/08/16

21aug13AS8530block AMS had introduced a LIN companion chip for MCUs that complies with the automotive ISO26262 functional safety standard, claiming it to be the first.

“ISO26262 compliance has added a new layer of complexity and difficulty to the task of designing many automotive systems,” said AMS general manager Bernd Gessner.

The 8pin AS8530 includes a LIN 2.1 transceiver, a 50mA LDO for a local MCU, a reset generator, an output voltage monitor, and a unique chip ID.

“As a differentiator, the AS8530 offers a series of system management functions through a shared pin serial interface, all within the same SOIC8 package,” said the firm. The addition of diagnosis functions provides built-in support for the requirements of ISO26262.”

It also has a two-wire serial port (sharing the Enable and TX pins) that allows status registers and diagnosis information to be read by the local microcontroller.

And there is a window watchdog, and back-up registers to store data when the microcontroller shuts down.

“These features are crucial in the design of ISO26262-compliant systems, which must be able to cease operation safely when in a fault condition, before the vehicle is at risk of endangering passengers or other road users,” said AMS. “The AS8530 is suitable for any LIN-networked sensor and actuator slaves, including those found in door modules, sunroofs and headlight positioning units. It is suited to safety-critical systems that require an ASIL grading under the provisions of ISO26262.”

The LDO is factory set to 3.3V or 5V.

Normal, power-saving, stand-by and sleep modes can be triggered through the Enable pin.

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DSPs, General 640GFLOPS card for image sensor processing

2013/08/16

07aug13agility

CommAgility’s AMC-4C6678 Advanced Mezzanine Card (AMC) DSP board has four TMS320C6678 fixed- and floating-point octal core DSPs from Texas Instruments running at 1.25GHz.

The total aggregated performance is 640GFLOPS and 1,280GMACS.

Intended for image sensor processing and stepper control, the AMC-4C6678 has I/O to support the 32 DSP cores. PCI Express and Gigabit Ethernet interfaces use on-board switches for maximum flexibility and access to all DSPs on the card.

A serial rapidIO (SRIO) link is directly connected to one DSP, shared using Hyperlink and then extends to the second DSP pair. 8Gbyte of DDR3 SDRAM is provided as standard, with 2Gbyte allocated to each DSP. 256Mbyte of flash memory is also provided, which can be used to store DSP boot code.

Available software includes full board support libraries and an IP stack with Telnet/TFTP for Ethernet-based board control and upgrade.

The new module is a compact full-size, single width PICMG AMC.0 R2.0 AMC, and is suitable for use in both ATCA carriers and MicroTCA chassis.

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Business Maxim buys power chip firm Volterra

2013/08/16

24jul13CEO Tunc Doluca_2 Fabless Californian power chip maker Volterra is to be acquired by Maxim.

“Volterra is an industry leader in high-current, high-performance, and high-density power management solutions,” said Maxim. “The company develops highly integrated solutions primarily for the enterprise, cloud computing, communications, and networking markets.”

“With Volterra, we will strengthen our position in the enterprise and communications markets,” said Maxim CEO Tunç Doluca. “We add a talented team and leading-edge proprietary technology in high-current power management solutions, which further diversifies our business model.”

The firm will be acquired for $23 per share in a transaction valued at $605m equity value; $450m enterprise value, said Maxim.

Pending regulatory approvals, Maxim’s acquisition of Volterra is expected to close “early in the December quarter”, said Maxim.

Related news
Altium ups Maxim part count on Designer
Maxim at 30: CEO interview

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Analogue / Linear / Mixed Signal ICs Intersil designs voltage chip for space systems

2013/08/16

Intersil has designed its latest radiation hardened (rad-hard) voltage references to have low output noise.

The ISL71090SEH12 and ISL71090SEH25 voltage references are fabbed on an SOI-based PR40 process specified to provide Single Event Latch-up (SEL) immunity to ensure robust performance in heavy ion environments.

The ISL71090SEHx voltage references when used in analogue-to-digital conversion provide initial voltage accuracy of ±0.05%, and ±0.15% over the entire military temperature and radiation exposure ranges.

The temperature coefficient is 10ppm/deg C and output noise is specified at 2µVp-p at 2.5Vout, and 1µVp-p at 1.25Vout.

Input voltage range is 4V to 30V and supports multiple system power rails.

SET mitigation designed to use single output capacitor for LET threshold of 86MeV.cm2/mg.

The ISL71090SEHx voltage references (1.25V and 2.5V) are available now in 8-lead flatpack. The ISL71090SEH12EV1Z and ISL71090SEH25EV1Z evaluation boards offer two voltage options, 1.25V and 2.5V respectively, and measure the performance of the ISL71090SEHx voltage references.

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Business Industrial IC market flat

2013/08/16

Inustrial IC revenue grewb1% y-y in Qi to $7.7 billion , says IHS. Q4 had seen a 3 % decline y-o-y.

“The industrial semiconductor market’s performance was encouraging, especially in light of continuing global economic uncertainty and the seasonal nature of the market, which typically sees slower movement in the first quarter of every year,” says Robbie Galoso, at IHS, “Some large segments of the industry, particularly avionics and oil and gas process-automation equipment, saw muscular double-digit gains, helping to drive up overall revenue.”

In another positive development, several large industrial semiconductor suppliers also reported very lean inventories because of strong orders from customers.

Infineon, ADI and TI saw sequential declines in industrial chip stockpiles as their days of inventory (DOI) measure fell well below average.

“The individual sectors for lighting, security, climate control and medical imaging were deleteriously impacted in the first quarter,” says Galoso.

The military and civil aerospace market had the most robust performance among all industrial semiconductor segments in the first quarter. Avionics was especially vigorous, driven by commercial aircraft sales from pan-European entity EADS Airbus and U.S. maker Boeing, up 9 percent and 14 percent, respectively, on the quarter.

The oil and gas exploration market also saw solid revenue growth, with strong subsea systems and drilling equipment driving sales for ABB, Honeywell and GE.

In contrast to those high-performing segments, lackluster sales were reported in the markets for building and home control, for energy generation and distribution, and for test and measurement. One other market, manufacturing and process automation, reported stable growth, even though its sector for motor drives remained in negative territory.

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Spaceflight alters bacterial social networks

Aug. 15, 2013 — When astronauts launch into space, a microbial entourage follows. And the sheer number of these followers would give celebrities on Twitter a run for their money. The estimate is that normal, healthy adults have ten times as many microbial cells as human cells within their bodies; countless more populate the environment around us. Although invisible to the naked eye, microorganisms -- some friend, some foe -- are found practically everywhere.

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Microorganisms like bacteria often are found attached to surfaces living in communities known as biofilms. Bacteria within biofilms are protected by a slimy matrix that they secrete. Skip brushing your teeth tomorrow morning and you may personally experience what a biofilm feels like.

One of NASA's goals is to minimize the health risks associated with extended spaceflight, so it is critical that methods for preventing and treating spaceflight-induced illnesses be developed before astronauts embark upon long-duration space missions. It is important for NASA to learn how bacterial communities that play roles in human health and disease are affected by spaceflight.

In two NASA-funded studies -- Micro-2 and Micro-2A -- biofilms made by the bacteria Pseudomonas aeruginosa were cultured on Earth and aboard space shuttle Atlantis in 2010 and 2011 to determine the impact of microgravity on their behavior. P. aeruginosa is an opportunistic human pathogen that is commonly used for biofilm studies. The research team compared the biofilms grown aboard the International Space Station bound space shuttle with those grown on the ground. The study results show for the first time that spaceflight changes the behavior of bacterial communities.

Although most bacterial biofilms are harmless, some threaten human health and safety. Biofilms can exhibit increased resistance to the immune system's defenses or treatment with antibiotics. They also can damage vital equipment aboard spacecraft by corroding surfaces or clogging air and water purification systems that provide life support for astronauts. Biofilms cause similar problems on Earth.

"Biofilms were rampant on the Mir space station and continue to be a challenge on the International Space Station, but we still don't really know what role gravity plays in their growth and development," said Cynthia Collins, Ph.D., principal investigator for the study and assistant professor in the Department of Chemical and Biological Engineering at the Center for Biotechnology and Interdisciplinary Studies at the Rensselaer Polytechnic Institute in Troy, N.Y. "Before we start sending astronauts to Mars or embarking on other long-term spaceflight missions, we need to be as certain as possible that we have eliminated or significantly reduced the risk that biofilms pose to the human crew and their equipment."

In 2010 and 2011, during the STS-132 and STS-135 missions aboard space shuttle Atlantis, astronauts in space and scientists on Earth performed nearly simultaneous parallel experiments; both teams cultured samples of P. aeruginosa bacteria using conditions that encouraged biofilm formation.

Identical hardware designed for growing cells during spaceflight were used for both the flight and ground studies. According to Collins, "artificial urine was chosen as a growth medium because it is a physiologically relevant environment for the study of biofilms formed both inside and outside the human body."

Biofilms were cultured inside specialized fluid processing apparatus composed of glass tubes divided into chambers. The researchers loaded each tube with a membrane that provided a surface on which the bacteria could grow; the artificial urine was used for the bacteria's nourishment. Samples of P. aeruginosa were loaded into separate chambers within each tube.

The prepared tubes were placed in groups of eight inside another specialized device called a group activation pack (GAP) -- designed to activate all of the bacterial cultures at once. The research team prepared identical sets of GAPs for the concurrent spaceflight and ground experiments.

Astronauts aboard the shuttle initiated the flight experiments by operating the GAPs and introducing the bacteria to the artificial urine medium. Scientists on Earth performed the same operations with the control group of GAPs at NASA's Kennedy Space Center in Florida. After activation, the GAPs were housed in incubators on Earth and aboard the shuttle to maintain temperatures appropriate for bacterial growth.

After the microgravity samples returned to Earth, the researchers determined the thickness of the biofilms, the number of living cells and the volume of biofilm per area on the membranes. Additionally, they used a microscopy technique that allowed them to capture high-resolution images at different depths within the biofilms, revealing details of their three-dimensional structures.

What the scientists found was that the P. aeruginosa biofilms grown in space contained more cells, more mass and were thicker than the control biofilms grown on Earth. When they viewed the microscopy images of the space-grown biofilms, the researchers saw a unique, previously unobserved structure consisting of a dense mat-like "canopy" structure supported above the membrane by "columns." The Earth grown biofilms were uniformly dense, flat structures. These results provide the first evidence that spaceflight affects community-level behavior of bacteria.

Microbes experience "low shear" conditions in microgravity that resemble conditions inside the human body, but are difficult to study. According to Collins, "Beyond its importance for astronauts and future space explorers, this research also could lead to novel methods for preventing and treating human disease on Earth. Examining the effects of spaceflight on biofilm formation can provide new insights into how different factors, such as gravity, fluid dynamics and nutrient availability affect biofilm formation on Earth. Additionally, the research findings one day could help inform new, innovative approaches for curbing the spread of infections in hospitals."

NASA's Space Biology Program funded the Micro-2 and Micro-2A investigations. Related space biology research continues aboard the space station, including recently selected studies that are planned for future launch to the orbiting laboratory.

Wherever we go, microbial communities will faithfully follow, making this evidence of the effects of spaceflight on bacterial physiology relevant to human health. That bacterial biofilms exhibit different behavior in space versus on Earth is critical information as NASA strives to keep astronauts healthy and safe during future long-duration space missions.

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New species of carnivore looks like a cross between a house cat and a teddy bear

The team's discovery is published in the Aug. 15 issue of the journal ZooKeys.

The olinguito (oh-lin-GHEE-toe) looks like a cross between a house cat and a teddy bear. It is actually the latest scientifically documented member of the family Procyonidae, which it shares with raccoons, coatis, kinkajous and olingos. The 2-pound olinguito, with its large eyes and woolly orange-brown fur, is native to the cloud forests of Colombia and Ecuador, as its scientific name, "neblina" (Spanish for "fog"), hints. In addition to being the latest described member of its family, another distinction the olinguito holds is that it is the newest species in the order Carnivora -- an incredibly rare discovery in the 21st century.

"The discovery of the olinguito shows us that the world is not yet completely explored, its most basic secrets not yet revealed," said Kristofer Helgen, curator of mammals at the Smithsonian's National Museum of Natural History and leader of the team reporting the new discovery. "If new carnivores can still be found, what other surprises await us? So many of the world's species are not yet known to science. Documenting them is the first step toward understanding the full richness and diversity of life on Earth."

Discovering a new species of carnivore, however, does not happen overnight. This one took a decade, and was not the project's original goal -- completing the first comprehensive study of olingos, several species of tree-living carnivores in the genus Bassaricyon, was. Helgen's team wanted to understand how many olingo species should be recognized and how these species are distributed -- issues that had long been unclear to scientists. Unexpectedly, the team's close examination of more than 95 percent of the world's olingo specimens in museums, along with DNA testing and the review of historic field data, revealed existence of the olinguito, a previously undescribed species.

The first clue came to Helgen from the olinguito's teeth and skull, which were smaller and differently shaped than those of olingos. Examining museum skins revealed that this new species was also smaller overall with a longer and denser coat; field records showed that it occurred in a unique area of the northern Andes Mountains at 5,000 to 9,000 feet above sea level -- elevations much higher than the known species of olingo. This information, however, was coming from overlooked olinguito specimens collected in the early 20th century. The question Helgen and his team wanted to answer next was: Does the olinguito still exist in the wild?

To answer that question, Helgen called on Roland Kays, director of the Biodiversity and Earth Observation Lab at the North Carolina Museum of Natural Sciences, to help organize a field expedition.

"The data from the old specimens gave us an idea of where to look, but it still seemed like a shot in the dark," Kays said. "But these Andean forests are so amazing that even if we didn't find the animal we were looking for, I knew our team would discover something cool along the way."

The team had a lucky break that started with a camcorder video. With confirmation of the olinguito's existence via a few seconds of grainy video shot by their colleague Miguel Pinto, a zoologist in Ecuador, Helgen and Kays set off on a three-week expedition to find the animal themselves. Working with Pinto, they found olinguitos in a forest on the western slopes of the Andes, and spent their days documenting what they could about the animal -- its characteristics and its forest home. Because the olinguito was new to science, it was imperative for the scientists to record every aspect of the animal. They learned that the olinguito is mostly active at night, is mainly a fruit eater, rarely comes out of the trees and has one baby at a time.

In addition to body features and behavior, the team made special note of the olinguito's cloud forest Andean habitat, which is under heavy pressure of human development. The team estimated that 42 percent of historic olinguito habitat has already been converted to agriculture or urban areas.

"The cloud forests of the Andes are a world unto themselves, filled with many species found nowhere else, many of them threatened or endangered," Helgen said. "We hope that the olinguito can serve as an ambassador species for the cloud forests of Ecuador and Colombia, to bring the world's attention to these critical habitats."

While the olinguito is new to science, it is not a stranger to people. People have been living in or near the olinguito's cloud forest world for thousands of years. And while misidentified, specimens have been in museums for more than 100 years, and at least one olinguito from Colombia was exhibited in several zoos in the United States during the 1960s and 1970s. There were even several occasions during the past century when the olinguito came close to being discovered but was not. In 1920, a zoologist in New York thought an olinguito museum specimen was so unusual that it might be a new species, but he never followed through in publishing the discovery.

Giving the olinguito its scientific name is just the beginning. "This is the first step," Helgen said. "Proving that a species exists and giving it a name is where everything starts. This is a beautiful animal, but we know so little about it. How many countries does it live in? What else can we learn about its behavior? What do we need to do to ensure its conservation?" Helgen is already planning his next mission into the clouds.

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More than 28 cups of coffee a week may endanger health in under 55s

Aug. 15, 2013 — Nearly 400 million cups of coffee are consumed every day in America. Drinking large amounts of coffee may be bad for under-55s, according to a new study published in Mayo Clinic Proceedings. A study of more than 40,000 individuals found a statistically significant 21% increased mortality in those drinking more than 28 cups of coffee a week and death from all causes, with a greater than 50% increased mortality risk in both men and women younger than 55 years of age. Investigators warn that younger people in particular may need to avoid heavy coffee consumption. No adverse effects were found in heavy coffee drinkers aged over 55.

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Drinking coffee has become a normal daily routine for large numbers of people worldwide. According to the latest National Coffee Drinking Study from the National Coffee Association, more than 60% of American adults drink coffee every day, consuming on average just over three cups a day.

Coffee has long been suspected to contribute to a variety of chronic health conditions, although earlier studies on coffee consumption in relation to deaths from all causes and deaths from coronary heart disease are limited, and the results are often controversial.

A multicenter research team investigated the effect of coffee consumption on death from all causes and deaths from cardiovascular disease in the Aerobics Center Longitudinal Study (ACLS) cohort, with an average follow-up period of 16 years and a relatively large sample size of over 40,000 men and women.

Between 1979 and 1998, nearly 45,000 individuals aged between 20 and 87 years old participated and returned a medical history questionnaire assessing lifestyle habits (including coffee consumption) and personal and family medical history. The investigators examined a total of 43,727 participants (33,900 men and 9,827 women) in their final analysis.

During the 17-year median follow-up period there were 2,512 deaths (men: 87.5%; women: 12.5%), 32% of these caused by cardiovascular disease. Those who consumed higher amounts of coffee (both men and women) were more likely to smoke and had lower levels of cardiorespiratory fitness.

All participants were followed from the baseline examination to date of death or until December 31, 2003. Deaths from all causes and deaths from cardiovascular disease were identified through the National Death Index or by accessing death certificates.

Younger men had a trend towards higher mortality even at lower consumption, but this became significant at about 28 cups per week where there was a 56% increase in mortality from all causes. Younger women who consumed more than 28 cups of coffee per week also had a greater than 2-fold higher risk of all-cause mortality than those who did not drink coffee.

Senior investigator Steven H. Blair, PED, of the Department of Biostatistics and Epidemiology, Arnold School of Public Health, University of South Carolina, emphasizes that "Significantly, the results did not demonstrate any association between coffee consumption and all-cause mortality among older men and women. It is also important to note that none of the doses of coffee in either men or women whether younger or older had any significant effects on cardiovascular mortality."

Coffee is a complex mixture of chemicals consisting of thousands of components. Recent research has found that coffee is one of the major sources of antioxidants in the diet and has potential beneficial effects on inflammation and cognitive function. However, it is also well-known that coffee has potential adverse effects because of caffeine's potential to stimulate the release of epinephrine, inhibit insulin activity, and increase blood pressure and levels of homocysteine.

"Thus, all of these mechanisms could counterbalance one another. Research also suggests that heavy coffee drinkers may experience additional risk through potential genetic mechanisms or because of confounding through the deleterious effects of other risk factors with which coffee drinking is associated," say lead authors, Junxiu Liu, MD, Department of Biostatistics and Epidemiology, and Xuemei Sui, MD, MPH, PhD, Department of Exercise Science, both at the Arnold School of Public Health, University of South Carolina, "Therefore, we hypothesize that the positive association between coffee and mortality may be due to the interaction of age and coffee consumption, combined with a component of genetic coffee addiction."

The investigators suggest that younger people in particular should avoid heavy coffee consumption of more than 28 cups a week or four cups in a typical day. However, they emphasize that further studies are needed in different populations to assess details regarding the effects of long-term coffee consumption and changes in coffee consumption over time on all-cause and cardiovascular disease mortality.

Leading expert Carl J. Lavie, MD, of the Department of Cardiovascular Diseases, Ochsner Medical Center, New Orleans, and a co-author of this study, explains that "There continues to be considerable debate about the health effects of caffeine, and coffee specifically, with some reports suggesting toxicity and some even suggesting beneficial effects."

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