US measles cases reach 20-year high

US measles cases reach 20-year high

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Repurposed fridge creates water out of thin air – Telegraph

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Think fast, robot: Algorithm that harnesses data from new sensor could make autonomous robots more nimble

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Is the Universe entirely mathematical?

Is the Universe Entirely Mathematical? NEW VIDEO with MIT Professor Max Tegmark

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Unexpected water explains surface chemistry of nanocrystals.

Danylo Zherebetskyy and his colleagues at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) found unexpected traces of water in semiconducting nanocrystals.

The water as a source of small ions for the of colloidal sulfide (PbS) nanoparticles allowed the team to explain just how the surface of these important particles are passivated, meaning how they achieve an overall balance of positive and negative ions. This has been a big question for some fifteen years, and the answer washes up in hydroxyl groups from water that had been thought not to be there.

“Passivation is required mostly in colloidal solutions, which is the cheap way to produce nanoparticles. Imagine the surface of the nanostructure: there are ligands, also called surfactants, binding to the surface,” explains Zherebetskyy. “The surfactants define a lot of the chemical and physical properties of the nanoparticles.”

“We can synthesize a very beautiful nanostructure, and know how to control even the shape. But how to control the shape is related to how you passivate a surface during the growth process, and exactly how ligands passivate the surface [and how electronic structures happen] has never been well understood,” adds Lin-Wang Wang, senior staff scientist at Berkeley Lab and leader of Berkeley Lab’s Computational Material Science and Nano Science Group.

The first step in making a PbS nanocrystal is to dissolve lead oxide in hot oleic acid. This forms one of the , which is lead plus long oleate ligands, and a byproduct of water. “You heat the precursors [to dry them], so people thought that all the water had been evaporated,” explains Wang.

“People were really puzzled about how the surface can be passivated,” he continues. The nanocrystals have an excess of lead ions relative to sulfate, which means that a surfactant of 2- charge is needed to passivate each extra 2+ lead ion. Each oleic acid molecule (oleate) has charge 1-, but experiments show that the number of extra lead atoms is roughly equal to the number of oleates. Thus it does not make sense that the precursor behaves as though it is passivated.

But doing calculations and following the synthesis processes suggested to Zherebetskyy and Wang that there might still be water in the precursor molecules: indeed, a series of spectroscopic experiments showed that the water binds strongly to the precursors and serves as a source of hydroxyl groups, charge 1-, that can also allow passivation.

“Oleates are big. Imagine them like a tube,” explains Zherebetskyy. “The radius of this tube is too large to form such a dense packing that completely passivates the lead atoms.” That is, they are too big to cram around the lead without interfering with each other. His research was an effort to find what ‘something else’ was needed to fully passivate the nanocrystal.

When the team found that water binds strongly to the precursor lead oleate, to the point that less than half of it is removed during the synthesis and dehydration process, they had uncovered the source of small hydroxyl groups that bind to the lead between oleates.

These findings have been reported in a Science paper titled “Hydroxylation of the Surface of PbS Nanocrystals Passivated with Oleic Acid.” Wang is the corresponding author and Zherebetskyy is the lead. Other authors are Marcus Scheele, Yingjie Zhang, Noah Bronstein, Christopher Thompson, David Britt, Miquel Salmeron and Paul Alivisatos.

“It is very difficult to detect hydroxyl because water is everywhere; hydroxyl spectroscopic peaks can be confused with those from water, and your sample might not be pure,” says Wang. “We used all the spectroscopy techniques.”

Noah Bronstein saw a very interesting feature during routine transmission electron microscope (TEM) observations during particle synthesis: only the lead-rich facets of the PbS molecule were covered by oleates. This was the first observation to suggest that Zherebetskyy and Wang’s theory was right: “They had predicted the binding energy of the ligand onto the lead-rich facet should be much higher,” says Bronstein.

The other facet of the nanocrystal, with both lead and sulfur exposed, was bare of ligands. “Once we saw that, we tried other things to look for water in the lead precursor; or hydroxyl on the nanoparticle surface,” adds Bronstein. He used infrared spectroscopy to verify the presence of water on precursor lead-oleates, and nuclear magnetic resonance to show that the lead oleate acted as a drying agent, grabbing water out of the solvent. During synthesis, hydroxyl groups from the water stayed tightly bound to the lead oleate.

“But X-ray photoemission spectroscopy (XPS) was really the golden bullet that showed the presence of hydroxyl,” says Bronstein.

Yingjie Zhang ran XPS experiments to provide direct proof that hydroxyl groups remain bonded to the surface. “You need several control samples – a PbS nanocrystal with lead oxide precursor and another precursor that does not involve water during synthesis,” he says. To achieve this, he used a nanocrystal sample produced from lead chloride instead of lead oxide, such that there was no way for to be generated in the reaction with oleic acid. In the end, he observed an oxygen emission peak from one nanocrystal and a chlorine peak from the other, proving that there is indeed hydroxyl on the PbS surface synthesized from lead oxide precursors.

“Since nanoparticles started to be implemented in the first prototype devices, people have asked what’s going on at the surface and how we can adjust properties by changing the organic molecules on the surface,” says Zherebetskyy.

And it’s not just PbS – many other nanoparticles are synthesized similarly using or other big ligands. Knowing how nanoparticles are passivated provides the opportunity to consider ways of engineering surface structures in order to fine-tune their electrical properties for a range of applications.

What Are You So Afraid Of?

From the desk of Zedie.

Obesity rates climbing worldwide, most comprehensive global study to date shows .

Worldwide, there has been a startling increase in rates of obesity and overweight in both adults (28% increase) and children (up by 47%) in the past 33 years, with the number of overweight and obese people rising from 857 million in 1980 to 2.1 billion in 2013, according to a major new analysis. However, the rates vary widely throughout the world with more than half of the world’s 671 million obese individuals living in just ten countries—the USA, China and India, Russia, Brazil, Mexico, Egypt, Germany , Pakistan, and Indonesia,

Credit: © nito / Fotolia

Worldwide, there has been a startling increase in rates of obesity and overweight in both adults (28% increase) and children (up by 47%) in the past 33 years, with the number of overweight and obese people rising from 857 million in 1980 to 2.1 billion in 2013, according to a major new analysis from the Global Burden of Disease Study 2013, published in The Lancet.

However, the rates vary widely throughout the world with more than half of the world’s 671 million obese individuals living in just ten countries — the USA (more than 13%), China and India (15% combined), Russia, Brazil, Mexico, Egypt, Germany , Pakistan, and Indonesia.

Over the past three decades, the highest rises in obesity levels among women have been in Egypt, Saudi Arabia, Oman, Honduras and Bahrain, and among men in New Zealand, Bahrain, Kuwait, Saudi Arabia, and the USA.

In high-income countries, some of the highest increases in adult obesity prevalence have been in the USA (where roughly a third of the adult population are obese), Australia (where 28% of men and 30% of women are obese), and the UK (where around a quarter of the adult population are obese).

The findings come from a comprehensive new analysis of the global, regional, and national prevalence of overweight and obesity in adults aged 20 years and older and children and adolescents aged 2-19 years between 1980 and 2013.

The authors warn that the study presents a worrying picture of substantial rises in obesity rates across the world and say that concerted action is urgently needed to reverse this trend.

Led by Professor Emmanuela Gakidou from the Institute for Health Metrics and Evaluation at the University of Washington in the USA, a team of international researchers performed a comprehensive search of the available data from surveys, reports, and the scientific literature to track trends in the prevalence of overweight (body mass index of 25kg/m² or higher) and obesity (BMI of 30kg/m² or higher) in 188 countries in all 21 regions of the world from 1980 to 2013.

Key findings include:

  • In the developed world, men have higher rates of obesity than women, while the opposite is true in developing countries. Currently, 62% of the world’s obese people live in developing countries.
  • The greatest gain in overweight and obesity occurred globally between 1992 and 2002, mainly among people aged between 20 and 40.
  • Especially high rates of overweight and obesity have already been reached in Tonga where levels of obesity in men and women exceed 50%, and in Kuwait, Libya, Qatar, and the Pacific Islands of Kiribati, Federated States of Micronesia, and Samoa where most (more than 50%) of women are obese.
  • The prevalence of overweight and obesity in childhood has increased remarkably in developed countries, from 17% in 1980 to 24% in 2013 in boys and from 16% to 23% in girls. Similarly, in developing countries, rates have risen from roughly 8% to 13% in both boys and girls over the three decades.
  • In 2013, the proportion of obesity in girls reached 23% in Kuwait, and 30% or more in Samoa, Micronesia and Kiribati, the highest levels calculated. Similar trends in obesity were found in boys, with the Pacific Islands of Samoa and Kiribati showing the greatest obesity prevalence.
  • Within Western Europe, levels of obesity in boys ranged from 14% in Israel and 13% in Malta, to 4% in The Netherlands and Sweden. Levels of obesity in girls were highest in Luxembourg (13%) and Israel (11%), and lowest in the Netherlands Norway, and Sweden (4%).
  • In developed countries, the rate of increase in adult obesity has started to slow down in the past 8 years, and there is some evidence that more recent birth cohorts are gaining weight more slowly than previous ones.

According to Professor Gakidou, “Unlike other major global health risks, such as tobacco and childhood nutrition, obesity is not decreasing worldwide. Our findings show that increases in the prevalence of obesity have been substantial, widespread, and have arisen over a short time. However, there is some evidence of a plateau in adult obesity rates that provides some hope that the epidemic might have peaked in some developed countries and that populations in other countries might not reach the very high rates of more than 40% reported in some developing countries.”

“Our analysis suggests that the UN’s target to stop the rise in obesity by 2025 is very ambitious and is unlikely to be achieved without concerted action and further research to assess the effect of population-wide interventions, and how to effectively translate that knowledge into national obesity control programmes. In particular, urgent global leadership is needed to help low-and middle-income countries intervene to reduce excessive calorie intake, physical inactivity, and active promotion of food consumption by industry.”

Commenting on the implications of the study, Professor Klim McPherson from Oxford University in the UK writes, “An appropriate rebalancing of the primal needs of humans with food availability is essential, which would entail curtailing many aspects of production and marketing for food industries. To prevent unsustainable health consequences, BMI needs to return to what it was 30 years ago. Lobstein calculated that to reduce BMI to 1980 levels in the UK would require an 8% reduction in consumption across the country, costing the food industry roughly £8·7 billion per year.”

He adds, “The solution has to be mainly political and the questions remain, as with climate change, where is the international will to act decisively in a way that might restrict economic growth in a competitive world, for the public’s health? Nowhere yet, but voluntary salt reduction might be setting a more achievable trend. Politicians can no longer hide behind ignorance or confusion.”

Story Source:

The above story is based on materials provided by The Lancet. Note: Materials may be edited for content and length.

Journal Reference:

  1. Marie Ng, Emmanuela Gakidou et al. Global, regional, and national prevalence of overweight and obesity in children and adults during 1980–2013: a systematic analysis for the Global Burden of Disease Study 2013. The Lancet, 2014; DOI: 10.1016/S0140-6736(14)60460-8