Category Archives: Stanford University

Why some 19th century immigrants went back to Europe

Moving back to Europe after emigrating to the United States was one strategy Norwegian immigrants used to lessen their poverty, research suggests.

Today’s conversation about immigration and the role of immigrants in America is not so different from the conversations that took place more than 100 years ago, when European immigrants settled in cities and on farms in the United States.

Ran Abramitzky, an economist at Stanford University, has spent the past decade analyzing data on immigrants in the United States between 1850 and 1913—the time of the country’s largest wave of migration.

“Moving permanently to the New World was one strategy that poor European immigrants used to achieve economic success.”

Norwegian immigrants who returned home in the late 19th and early 20th centuries were more likely to have held lower-skilled occupations, compared with both Norwegians who never moved and those who stayed in the United States. But upon returning to Norway, the return migrants were better off than those who had never moved and usually held higher-paying jobs.

The findings are contrary to the popular belief that return migration mostly resulted from bad shocks, such as an illness or unemployment, says Abramitzky, an associate professor of economics and coauthor of the article in the Industrial and Labor Relations Review. Instead, it appears that return migrants already hailed from poorer backgrounds before their move.

“Moving permanently to the New World was one strategy that poor European immigrants used to achieve economic success. This research suggests that temporary movement to the United States in order to accumulate savings and invest in the home country was another option available to the poor.”

The Age of Mass Migration

The new study on return migrants is the latest piece in a larger research project, which Abramitzky and colleagues began about 10 years ago, on immigration in the US between 1850 and 1913.

About 30 million Europeans immigrated during the period—the Age of Mass Migration—as America maintained open, largely unrestricted borders for European migrants until about 1914. By 1910, 22 percent of the country’s labor force was foreign-born, compared to 17 percent of today’s working population.

But, the same period also saw a high rate of return migration—one in three immigrants returned to their home country.

To learn which immigrants moved back and how they fared economically, researchers needed comprehensive data on immigrants from a single country.

“It is challenging to study these types of questions because systematic data on return migrants are not typically collected,” Abramitzky says.

Back to Norway

But Norway, which experienced a high rate of out-migration during this period, was a unique case. The country’s 1910 census asked respondents whether they spent some time in the United States, and, if so, the dates of their arrival and departure, last state of residence, and last occupation held.

Because Norway recently released digital versions of those census datasets, Abramitzky chose to focus on the Scandinavian country, conducting an unprecedented analysis of individual data on return migrants to Europe during that period.

Researchers linked the American and Norwegian census data sets to compare Norwegian migrants still living in the US in 1910 with Norwegian immigrants who returned after a couple of years—as well as to Norwegians who stayed in Norway throughout this period.

“If we want to know how today’s newcomers will fare, we can find important clues by examining what happened to those who arrived on our shores during the greatest surge of immigration in US history.”

Immigrants who held low-paid occupations or who came from rural parts of Norway were more likely to come back after moving to America. Once back home, the return migrants held higher-paid occupations than the Norwegians who never moved, despite being from poorer backgrounds.

That return migrants climbed to a higher rung on the occupational ladder may have been the result of savings accrued in the US. Many return migrants worked as farmers, often in their town of birth. When these men—who had started out as poor farm laborers—returned to Norway, they were more likely than the non-movers to purchase and work on their own farms, a more lucrative profession made possible by the increased land they were able to buy with their savings.

These temporary moves might have been necessary, because it was difficult to borrow money in Norway, which was not as advanced financially as the US.

How does identity work for immigrants in Europe?

During the Age of Mass Migration, politicians and the public raised questions about immigrants that are similar to those discussed today. Can immigrants successfully integrate into America’s society and economy? Or do they remain isolated long after they settle?

Abramitzky’s past work on immigrants from 16 sending European countries provides some clues.

A 2014 study showed that European immigrants arrived in the US with occupations comparable to native-born Americans, and his 2016 research on cultural assimilation documented that immigrants who arrived in the early 20th century chose less foreign names for their sons and daughters as they spent more time in the United States.

“If we want to know how today’s newcomers will fare, we can find important clues by examining what happened to those who arrived on our shores during the greatest surge of immigration in US history,” Abramitzky says.

“Comparing our findings with contemporary studies can illuminate the effect of modern immigration policy on migrant selection and migrant assimilation.”

Leah Boustan of Princeton University and Katherine Eriksson of the University of California, Davis, are coauthors of the study.

Source: Stanford University

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Taking DACA from immigrant moms hurts their US-born kids

A new study sheds light on the impact of rescinding the Deferred Action for Childhood Arrivals (DACA) program on immigrant mothers and their children’s health.

The Trump administration’s recent decision to end the DACA program, which granted protection from deportation to unauthorized immigrants who entered the United States as minors, affects roughly 800,000 immigrants.

Imagine “having the father leave in the morning, and always thinking, ‘will this be the last time I see him?’”

Terminating DACA may also have perilous consequences for the children of those DREAMers, however, according to a new study in Science. Researchers found that the protections offered by DACA can drastically enhance health outcomes for those children.

Researchers looked at a large sample of immigrant mothers born just before and after the cutoff date for DACA eligibility, and then followed their children’s health over time. After DACA was introduced in 2012, the group eligible for the program saw an immediate improvement in their children’s mental health: diagnoses of adjustment and anxiety disorders fell by more than 50 percent.

Here, two of the study’s authors—Jens Hainmueller, a professor of political science at Stanford University, and Fernando Mendoza, a professor of pediatrics—discuss the impact of ending DACA on the children of immigrant mothers protected by the program.

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Bug-eye design makes perovskite solar cells more durable

Packing tiny solar cells together like the micro-lenses in the compound eye of an insect could pave the way for perovskite solar panels.

For a new study, researchers used the insect-inspired design to protect the fragile photovoltaic material from deteriorating when exposed to heat, moisture, and mechanical stress.

“Perovskites are the most fragile materials ever tested in the history of our lab.”

“Perovskites are promising, low-cost materials that convert sunlight to electricity as efficiently as conventional solar cells made of silicon,” says Reinhold Dauskardt, a professor of materials science and engineering at Stanford University. “The problem is that perovskites are extremely unstable and mechanically fragile. They would barely survive the manufacturing process, let alone be durable long term in the environment.”

Most solar devices, like rooftop panels, use a flat, or planar, design. But that approach doesn’t work well with perovskite.

“Perovskites are the most fragile materials ever tested in the history of our lab,” says graduate student Nicholas Rolston, a co-lead author of the study that appears in Energy & Environmental Science. “This fragility is related to the brittle, salt-like crystal structure of perovskite, which has mechanical properties similar to table salt.”

To address the durability challenge, scientists turned to nature.

“We were inspired by the compound eye of the fly, which consists of hundreds of tiny segmented eyes,” Dauskardt says. “It has a beautiful honeycomb shape with built-in redundancy: If you lose one segment, hundreds of others will operate. Each segment is very fragile, but it’s shielded by a scaffold wall around it.”

Using the compound eye as a model, the researchers created a compound solar cell consisting of a vast honeycomb of perovskite microcells, each encapsulated in a hexagon-shaped scaffold just 0.02 inches (500 microns) wide.

“The scaffold is made of an inexpensive epoxy resin widely used in the microelectronics industry,” Rolston says “It’s resilient to mechanical stresses and thus far more resistant to fracture.”

Tests conducted during the study show that the scaffolding had little effect on how efficiently perovskite converted light into electricity.

“We got nearly the same power-conversion efficiencies out of each little perovskite cell that we would get from a planar solar cell,” Dauskardt says. “So we achieved a huge increase in fracture resistance with no penalty for efficiency.”

Perovskites with flipped crystals boost solar cells

But could the new device withstand the kind of heat and humidity that conventional rooftop solar panels endure?

To find out, researchers exposed encapsulated perovskite cells to temperatures of 185 F (85 C) and 85 percent relative humidity for six weeks. Despite these extreme conditions, the cells continued to generate electricity at relatively high rates of efficiency.

Can this hybrid material double solar cell efficiency?

Dauskardt and colleagues have filed a provisional patent for the new technology. To improve efficiency, they are studying new ways to scatter light from the scaffold into the perovskite core of each cell.

“We are very excited about these results,” he says. “It’s a new way of thinking about designing solar cells. These scaffold cells also look really cool, so there are some interesting aesthetic possibilities for real-world applications.”

Postdoctoral scholars Brian Watson and Adam Printz and also co-lead authors of the work. The National Science Foundation and a grant from the Stanford Precourt Institute for Energy provided funding.

Source: Stanford University

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College freshmen pick certain friends for stressful times

College freshmen turn to empathic people during stressful times, research shows.

“The transition to college can be tumultuous,” says Jamil Zaki, an assistant professor of psychology at Stanford University and coauthor of the study. “Whom you end up making friendships with can play a significant role in how you’ll deal with the stress and hardship of freshman year.”

A 2008 poll conducted by the Associated Press and mtvU found that 40 percent of college students said they felt stress regularly—and almost 1 in 5 seriously considered dropping out of school.

With those high stress levels in mind, the researchers, including Stanford economics professor Matthew Jackson and former Stanford doctoral candidate Desmond Ong, put nearly 200 Stanford freshmen—who had recently moved into first-year dorms—through a battery of personality tests and questionnaires. Students also answered questions related to social networks within their dorms, for example, “Who usually makes you feel positive?” or “Who do you turn to when something bad happens?”

Their goal was to determine which students occupied central roles in these different networks—notably groups based on trust and fun/excitement. The researchers found that individuals were more particular about whom they included in their trust networks compared to groups related to fun and excitement. In those selective trust networks, freshmen were more likely to include highly empathic students.

“Empathic people are the ears and shoulders of these communities.”

In contrast, when students wanted to feel positive and have fun, they were more likely to seek out dorm mates high in happiness. This suggests that students’ personalities are related to the different roles that they play in supporting their communities.

“What we find here is not only that people’s networks of fun-based friendships are denser than their more trust- and stress-based networks,” Jackson says, “but also that more central people in a network have personalities that match the purpose of that network in intuitive ways. ”

Just as you need the right outfit for a particular occasion, college freshmen need certain friends for certain situations.

When you need a dose of fun, engaging with a positive and happy friend can lift your mood. But that friend may not be the best person to go to when you need someone to confide in. An empathic friend, on the other hand, may be just the right person for helping you through difficult and challenging times.

“Empathic individuals were more likely to help their dorm mates and provide support during difficult times,” says Sylvia Morelli, an assistant professor of psychology at the University of Illinois at Chicago and lead author of the study. “These freshmen became magnets for close relationships in their new dorms.”

“Empathic people are the ears and shoulders of these communities,” Zaki says.

This research shows that people know the difference between these two types of individuals. They spend time with individuals high in positive emotion, but target empathic individuals when they are stressed.

These oxytocin genes may influence number of friends

“The study offers an opportunity for college students to examine their own relationships,” says Morelli, a former postdoctoral fellow in Stanford’s Social Neuroscience Lab, “especially against the landscape of social media where they can have seemingly countless ‘friends’ across the country and the world. Our work suggests that people will turn to only a small handful of these friends when things get stressful, and that they will trust their friends who show empathy and concern.”

An additional coauthor of the study is Rucha Makati of the University of Illinois at Chicago. The National Institute of Mental Health, the National Science Foundation, and an A*STAR National Science Scholarship supported the work.

The study appears in the Proceedings of the National Academy of Sciences.

Source: Stanford University

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Nuclear war would be ‘catastrophic’ for Earth’s climate

Daily headlines warn of the dangers to nations and citizens in the event of a nuclear war, but little attention goes to what such an event would do to the environment.

Paul N. Edwards, a science and technology historian at Stanford University, discusses what the effects of a nuclear war would be on Earth itself—and how that in turn would affect us.


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This redesign would cut bias on Airbnb

In a study involving nearly 9,000 Airbnb users, researchers propose that implementing features that emphasize a user’s reputation can offset harmful social bias.

The “share economy,” in which people rent goods and services, including their homes and automobiles, has numerous benefits for people trying to make extra money. One downside, however, is the prospect of people’s biases about race, gender, or other factors affecting their decisions about whom to do business with.

The new study that analyzes Airbnb users and data suggests measures that enhance a user’s reputation, like stars or reviews, can counteract these harmful prejudices. The results, the Stanford University researchers say, indicate sites that use reputational tools create a fairer and more diverse online marketplace.

The share economy, also referred to as “collaborative consumption” and “peer-to-peer lending,” has allowed everyday citizens to turn into entrepreneurs, taking advantage of an industry that’s projected to grow to $335 billion by 2025, according to the Brookings Institution.

Share economy transactions are distinctive because, unlike most other e-commerce dealings, they have an intimate feeling to them. Think about when you purchase a pair of shoes online either directly from a retailer or from a third-party site: there’s rarely, if ever, a human element to the transaction.

But when you reserve an apartment on Airbnb, there’s a personal feel—you’re staying at someone’s home. Because of that element, you become attentive to the personal characteristics (ex. gender, age, etc.) of the home’s owner or the guest, says Bruno Abrahao, a visiting assistant professor at Stanford’s Institute for Research in the Social Sciences and the study’s lead author. That attentiveness to details peripheral to the transaction can lead to bias.

People like us

The researchers in this study focused on a certain type of bias called homophily, a natural tendency to develop trustful relationships with people similar to themselves, and how best to counteract it. The study is part of a broader research project analyzing trust and technology at Stanford.

The researchers recruited nearly 9,000 Airbnb users for their experiment, conducted on an online platform external to Airbnb’s. The participants were shown mock profiles of other Airbnb users with varying demographic and reputation information.

Algorithms don’t yet spare us from bias

The researchers created two experimental groups. Group 1 included profiles with some demographic similarities to the study participant (ex. a single male in his 20s viewing a profile of a user with comparable age, gender, and marital status). Group 2 included profiles with completely different personal traits from the participant, but with better reputations—conveyed by impressive star ratings and number of reviews – than those in Group 1. (Profiles from Group 1 were included in Group 2 for comparison).

To test for evidence of bias, participants played a behavioral game where they were asked to invest credits in the various profiles. The amount of credits a person invested in each profile served as a measure of trust.

In the first group, participants invested greatly in the similar profiles. The more similar the profiles were, the more the participant trusted them, succumbing to bias.

In the second group, however, the researchers noticed a shift. Participants invested significantly more in users whose characteristics were completely different than their own, but who had better reputations. Those profiles’ reputation mechanisms counteracted people’s penchant for favoring users similar to themselves.

Maximize trust

Knowing the robust effects reputation features had in the experiment, the researchers then analyzed 1 million actual interactions between hosts and guests on the Airbnb platform. They found that hosts with better reputations were attracting more demographically diverse guests, as their data predicted should happen.

Ride-share drivers discriminate against black riders

This finding offers evidence that reputation systems used by Airbnb and other sites on the sharing economy platform may allow users, like the study’s participants, “to extend trust to those who exhibited a high degree of dissimilarity in the social space,” the authors write.

Not only can offsetting these social biases be beneficial for users seeking services, but also for marginalized hosts offering them, Abrahao says.

“The fundamental question we wanted to answer is whether technology can be used to influence people’s perception of trust,” Abrahao says. “These platforms can engineer tools that have great influence in how people perceive each other and can make markets fairer, especially to users from underrepresented minorities.”

Additional coauthors are from Stanford and Airbnb. The National Science Foundation supported the work, which appears in the Proceedings of the National Academy of Sciences.

Source: Stanford University

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Why Americans resist higher taxes for the wealthy

Americans may resist raising taxes on the wealthy as a way to address inequality due to our beliefs in “equal treatment,” say political scientists.

“If many US voters don’t support higher tax rates, it’s not because they are uninformed, distracted, or confused,” explains David Stasavage of New York University, coauthor of the paper with Stanford University’s Kenneth Scheve. “It’s for a more simple reason: they don’t think this would be fair.”

Many have wondered, in an era of increasing inequality, why there hasn’t there been more support for raising taxes. Many progressives have concluded that voters are uninformed or distracted by other issues—or that money in politics allows the rich to buy the policies they want.

An alternative, and long-standing view, stretching from Renaissance Florence to today, argues against progressive taxation, positing that just as everyone in a democracy should have the same vote, everyone should also pay the same tax rate.

To address the validity of this latter view—that many people may not want to raise taxes on the rich because they think it would violate a norm of equal treatment in a democracy—the researchers examined US survey data from 2014 and 2016.

They also conducted a survey in 2017 that had a unique experimental component. In it, some respondents were randomly assigned to receive a question about the importance of equal voting rights (e.g., “How important is it that the government guarantees equal voting rights?”) while others were asked a “control” question (e.g., “How important is it that the United States government celebrates Thanksgiving?”).

The 2017 results showed that those who received the equal voting rights question were substantially less likely than those in the control group to say that the wealthy should pay higher tax rates than everyone else. In other words, the equality prompt was associated with opposition to progressive taxation—regardless of how respondents answered the equality and control questions.

The authors note that in spite of the link between equal treatment and opposition to progressive taxation, there is support for changing the tax code in ways that would, in effect, raise taxes on the wealthy.

WWI and WWII led to higher taxes for the rich

Specifically, many respondents who opposed progressive taxation still said that they care about inequality. Moreover, they indicated that they would also support tax reform that reduces loopholes that currently allow the wealthy to pay lower effective tax rates than everyone else.

“There are competing standards of fairness when it comes to tax policy, and voters who oppose higher taxes on wealthy subscribe to a norm of equal treatment,” observes Stasavage, professor in NYU’s political department. “However, those who believe in equal treatment don’t want to see the wealthy pay lower rates than everyone else, as is now often the case.

“For this reason, there would be very substantial support today for tax reform that cuts loopholes used by the wealthy. More generally, those who support doing something about inequality need to consider how policies that address this problem can be framed so as to bring proponents of ‘equal treatment’ on board.”

In their book Taxing the Rich: A History of Fiscal Fairness in the United States and Europe (Princeton 2016), Scheve and Stasavage explored related tax matters. In it, they considered evidence from 20 countries covering the past 200 years in offering an in-depth account of progressive taxation.

They found that governments don’t tax the rich just because inequality is high or rising—rather, they do it when people believe that such taxes compensate for the state unfairly privileging the wealthy.

The new research was presented at September’s Annual Meeting of the American Political Science Association.

Source: New York University

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This mistake makes us buy junky stuff online

When online shopping, most people pick inferior products that have many reviews from consumers over higher quality products that have fewer reviews.

A recent study by Derek Powell, a postdoctoral research fellow at Stanford University, finds that most people fail to do a simple statistical task when viewing online ratings and reviews, leading them to purchase inferior products.

Follow the leaders

When shopping online, consumers engage in a type of social learning by which they become informed from the decisions of others. For example, you’re probably more likely to purchase a book at the top of the New York Times‘ best-sellers list or buy an app that’s been downloaded millions of times.

“People seem to have this belief that popularity is good and are willing to use that as an important cue when making decisions.”

Observing other people’s choices is only a part of social learning, though. The other is noting the resulting outcomes through mechanisms like online star ratings. How people interpret—or fail to interpret—this data is affecting their decision-making in a negative way.

The researchers presented 138 adults with a series of cellphone cases (in pairs) to purchase. Each case was accompanied by its average star rating and number of reviews. The star ratings varied minimally, but one of the cases always had 125 more reviews than the other.

Across two experiments, the researchers found that participants preferred the case that had more reviews, despite the fact that the way they set up the experiment, that case was likely to be inferior. (The researchers assessed the product’s quality not by stars or reviews alone, but by analyzing millions of reviews on

Decisions, decisions

Think about it this way. Twenty-five people review a product and award an average 2.9 rating (out of five stars). While the rating is below average, there’s a possibility that with such few reviews the product may not be as poor as indicated, Powell says.

Now imagine 150 consumers give that same product a 2.9 rating. That’s six times as many people rating the product below average. That should be a stronger signal of the product’s poor quality.

Participants took the high number of reviews as a signal of quality, says Powell, rather than as an indicator of how accurately the review score should reflect the true quality of the product. Instead of conducting a rather simple statistical analysis to arrive at that conclusion, consumers are taking the number of reviews at face value.

Liking different brands could hurt your relationship

“What they’re doing is simply weighing cues,” Powell says. “People seem to have this belief that popularity is good and are willing to use that as an important cue when making decisions.”

Powell and his fellow researchers found evidence of this trend beyond their experiments. They examined 15 million reviews of more than 350,000 actual products on and found that there was no relationship between the number of reviews and its rating.

“It doesn’t necessarily mean that better things don’t become more popular,” says Powell, “but as a consumer, when you’re looking at this data point (number of reviews), it’s not telling you anything.”

Crowd consuming

Overcoming this bias is difficult, Powell says, because consumers find comfort in popularity.

“There are lots of contexts where following the herd is the rational thing to do,” he says. “If there isn’t enough information available, that can be a smart thing to do.

“But what we’re arguing is that you have more information than just what people did; you also have what happened—did they like it, were they happy or unhappy with their purchase.”

To dominate others, we pick products with wider ‘faces’

Powell suggests consumers should focus on whether the product’s score is above or below average—product averages usually range from 3.7 to 4, depending on the product’s category, he says—then apply that rating to the number of reviews. Examining those figures in concert should supply consumers with confidence that the product’s rating reflects its true quality.

The study appears in the journal Psychological Science.

The study’s coauthors are from Indiana University and the University of California, Los Angeles.

Source: Stanford University

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Panels keep things cool by sending heat into space

A system of panels on a building’s roof can cool water enough to be used in air conditioning and refrigeration by sending heat into space—all without electricity.

Since 2013, Shanhui Fan, professor of electrical engineering at Stanford University, and his students and research associates have employed a roof as a testbed for a high-tech mirror-like optical surface that could be the future of lower-energy cooling systems.

Research published in 2014 first showed the cooling capabilities of the optical surface on its own. Now, Fan and former research associates Aaswath Raman and Eli Goldstein have shown that the system involving these surfaces can cool flowing water to a temperature below that of the surrounding air.

cooling system roof panels
A fluid-cooling panel being tested on the roof of the Packard Electrical Engineering Building. This is an updated version of the panels used in earlier research. (Credit: Aaswath Raman)

“This research builds on our previous work with radiative sky cooling but takes it to the next level. It provides for the first time a high-fidelity technology demonstration of how you can use radiative sky cooling to passively cool a fluid and, in doing so, connect it with cooling systems to save electricity,” says Raman, co-lead author of the paper in Nature Energy.

Together, Fan, Goldstein, and Raman have founded the company SkyCool Systems, which is working on further testing and commercializing this technology.

Dissipating heat into space

Radiative sky cooling is a natural process that everyone and everything does, resulting from the moments of molecules releasing heat. You can witness it for yourself in the heat that comes off a road as it cools after sunset. This phenomenon is particularly noticeable on a cloudless night because, without clouds, the heat we and everything around us radiates can more easily make it through Earth’s atmosphere, all the way to the vast, cold reaches of space.

“…we’re no longer limited by what the air temperature is, we’re limited by something much colder: the sky and space.”

“If you have something that is very cold—like space—and you can dissipate heat into it, then you can do cooling without any electricity or work. The heat just flows,” explains Fan, who is senior author of the paper. “For this reason, the amount of heat flow off the Earth that goes to the universe is enormous.”

Although our own bodies release heat through radiative cooling to both the sky and our surroundings, we all know that on a hot, sunny day, radiative sky cooling isn’t going to live up to its name. This is because the sunlight will warm you more than radiative sky cooling will cool you.

To overcome this problem, the team’s surface uses a multilayer optical film that reflects about 97 percent of the sunlight while simultaneously being able to emit the surface’s thermal energy through the atmosphere. Without heat from sunlight, the radiative sky cooling effect can enable cooling below the air temperature even on a sunny day.

“With this technology, we’re no longer limited by what the air temperature is, we’re limited by something much colder: the sky and space,” says Goldstein, co-lead author of the paper.

The experiments published in 2014 were performed using small wafers of a multilayer optical surface, about 8 inches in diameter, and only showed how the surface itself cooled. Naturally, the next step was to scale up the technology and see how it works as part of a larger cooling system.

Potential and predictions

For their latest paper, the researchers created a system where panels covered in the specialized optical surfaces sat atop pipes of running water and tested it on the roof of the Packard Building on the Stanford University campus in September 2015. These panels were slightly more than 2 feet in length on each side and the researchers ran as many as four at a time.

With the water moving at a relatively fast rate, they found the panels could consistently reduce the temperature of the water 3 to 5 degrees Celsius below ambient air temperature over a period of three days.

Windows go clear to dark and back in 1 minute

The researchers also applied data from this experiment to a simulation where their panels covered the roof of a two-story commercial office building in Las Vegas—a hot, dry location where their panels would work best—and contributed to its cooling system. They calculated how much electricity they could save if, in place of a conventional air-cooled chiller, they used vapor-compression system with a condenser cooled by their panels.

They found that, in the summer months, the panel-cooled system would save 14.3 megawatt-hours of electricity, a 21 percent reduction in the electricity used to cool the building. Over the entire period, the daily electricity savings fluctuated from 18 percent to 50 percent.

Energy savings

Right now, SkyCool Systems is measuring the energy saved when panels are integrated with traditional air conditioning and refrigeration systems at a test facility, and Fan, Goldstein, and Raman are optimistic that this technology will find broad applicability in the years to come.

The researchers are focused on making their panels integrate easily with standard air conditioning and refrigeration systems and they are particularly excited at the prospect of applying their technology to the serious task of cooling data centers.

Fan has also carried out research on various other aspects of radiative cooling technology. He and Raman have applied the concept of radiative sky cooling to the creation of an efficiency-boosting coating for solar cells. With Yi Cui, a professor of materials science and engineering at the university and of photon science at SLAC National Accelerator Laboratory, Fan developed a cooling fabric.

Here’s what happens when you overheat

“It’s very intriguing to think about the universe as such an immense resource for cooling and all the many interesting, creative ideas that one could come up with to take advantage of this,” he says.

The Advanced Research Projects Agency-Energy (ARPA-E) of the US Department of Energy funded this work.

Source: Stanford University

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New dads are older than ever

Dads in the United States are getting older, a four-decade study of 168,867,480 live births shows.

In that time frame, the average age of fathers of newborns rose by 3.5 years. Men over the age of 40 now account for about 9 percent of all US births and men over the age of 50 account for nearly 1 percent.

The findings come from the first comprehensive analysis of all live births reported to a federal data depository in the United States from 1972-2015.

The National Vital Statistics System records births and deaths reported by all 50 states, as well as self-reported maternal and, where available, paternal ages, levels of education, and race and parent ethnicity. While the CDC periodically produces reports on maternal statistics, little information about newborns’ dads has been available until now.

Between 1972 and 2015 the average paternal age at the time of an American child’s birth rose from 27.4 years to 30.9 years. Asian-American dads—and in particular, Japanese- and Vietnamese-American dads—are the oldest, at 36 years of age on average. Paternal age rose with more years of education; the typical newborn’s father with a college degree is 33.3 years old.

Over the same time period, the share of newborns’ fathers who were older than 40 doubled from 4.1 percent to 8.9 percent, while the share who were over 50 rose from 0.5 percent to 0.9 percent. Similar trends of increasing age have been reported in other industrialized countries.

Older moms, too

The steadily advancing age of newborns’ fathers is likely to carry public health implications, says Michael Eisenberg, an assistant professor of urology at Stanford University and senior author of the study in Human Reproduction.

A rising paternal age can affect the total number of children a man will have, which can affect the demographics of the population. In addition, “every potential dad acquires an average of two new mutations in his sperm each year. And there are associations between older fatherhood and higher rates of autism, schizophrenia, chromosomal abnormalities, some pediatric cancers, and certain rare genetic conditions.”

“Fewer people being born means fewer productive workers a generation down the road.”

On the flip side, older fathers are more likely to have better jobs and more resources, more likely to have reasonably stable lifestyles, and more likely to live with their children and, thus, be more involved in child-rearing.

“Maternal ages at birth have been increasing, too,” Eisenberg says. “In fact, they’ve advanced even more than paternal ages have in the same time frame. This may be a consequence of women waiting longer to get married or putting off childbearing as the years they spend in higher education increase and as careers become more central to their lives.

“The result is that the average age difference between moms and dads has been shrinking, from 2.7 years in 1972 to 2.3 years in 2015.”

‘Boomerang’ dads boost daughters, not sons

This convergent pattern appears to apply to all racial, regional, age, and education categories, Eisenberg says. “We’ve seen a lot of changes in the last several decades. Contraception is more reliable and widespread. Women have become more integrated into the workforce. This seems to be reflected in an increasing parity in parental ages over the last four decades.”

Advancing parental age leaves fewer years for childbearing and is likely to exert a follow-on effect of reducing the average family size over the long haul, with potentially huge economic and public health ramifications.

“Fewer people being born means fewer productive workers a generation down the road,” Eisenberg says. “This can obviously have profound tax and economic implications.”

Birth records

While parental-data reporting to the National Vital Statistics System by some states was spotty in the early years of the period under study, it’s been running at virtually 100 percent since 1985, at least for mothers.

In 2015, the latest year available, information about newborns’ fathers was missing in one of every nine births. That could be because the father was unknown or because the mother didn’t wish to report his name or any details about him.

Evidence indicates that, on the whole, young children whose paternal data appears in their birth records have better health outcomes.

Dads say these words more if they have little girls

Paternal-data reporting rates vary according to mothers’ race, ethnicity, age, education, and regional location, the analysis showed, with the reporting rate for African-American newborns consistently the lowest for all races.

Over the past decade, African-American mothers under the age of 20 reported paternal data only half the time. However, the rate of paternal reporting for children born to African-American mothers has grown from its low of 63 percent in 1985 to a current rate of 70.9 percent.

Overall paternal reporting for US births has risen to its current 88.4 percent since reaching a nadir of 85.5 percent in 1991.

The youngest dad recorded during the 44-year period covered in the study was 11 years old; the oldest was 88. But the world-record holder, is a man from India who early in this decade fathered two children at the age of 94 and 96 with a wife who was in her late 50s, Eisenberg says.

“Unfortunately, they wound up separating.”

Source: Stanford University

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