Scholarship & Creativity

Scientist: Winds could pose challenges for Mars landing

Martian winds probably won't cause serious problems for NASA's current Phoenix Mars Lander mission but could complicate efforts to collect soil and ice at the landing site, according to U-M atmospheric scientist Nilton Renno.

The Phoenix lander begins to shut down operations as winter sets in. The far northern latitudes on Mars experience no sunlight during winter. This marks the end of the mission because the solar panels can no longer charge the batteries on the lander and the frost covering the region as the atmosphere cools will bury the lander in ice. (Image by Corby Waste, Jet Propulsion Laboratory)

New results from U-M wind tunnel tests suggest that winds could blow away some of the laboriously collected soil and ice, but probably not enough to affect onboard laboratory experiments, says Renno, a member of the Phoenix science team.

"Basically, my conclusion is that if you do the delivery properly and plan it well, you can guarantee that a large fraction of the sample is going to fall inside the instrument intake," says Renno, an associate professor in the College of Engineering's Department of Atmospheric, Oceanic and Space Sciences.

The Phoenix spacecraft, which was sent into orbit Aug. 4, will land on the planet's northern arctic plains next spring, analyzing soil and ice to see if it could support microbial life. An 8-foot robotic arm will scoop up the soil and dump it into onboard science instruments.

With funding from NASA, Renno and his graduate students have been studying the possibility that Martian winds could blow away bits of falling soil and ice as the samples are dropped.

Winds of up to 11 mph are expected much of the time at the Phoenix landing site during the three-month main mission, which begins with arrival on May 25, 2008. Renno calculated that if the soil samples were dropped from a height of 4 inches—as called for in the original mission plan—the vast majority of the particles wouldn't make it into the instrument intakes under windy conditions.

Based in part on Renno's work, the Phoenix team decided to move the Phoenix scoop closer to the science-instrument intakes before dropping the soil, he said.

Additional U-M tests concerning the dust cloud likely to be kicked up by the Phoenix landing engines have been delayed until September.
—Jim Erickson, News Service

Online reviews affect sales, for better or worse

When it comes to online product reviews, more is not necessarily better, says a University business professor.

With the increasing popularity of user-generated online reviews of retail products and services, this form of word-of-mouth advertising can help a growing number of consumers in their purchasing decisions. But it can also help—or hurt—retailers.

A new study by Hila Etzion, assistant professor of business information technology at Stephen M. Ross School of Business, and colleague Naveen Awad of Wayne State University examined the relationship between the number of online reviews and sales.

Using data collected from a large online retailer of electronic products over a six-year period, the researchers found that the number of reviews has a significant positive effect on sales of products that are perceived favorably by consumers, while volume has a significant negative impact on sales of products with poor consumer ratings.

In other words, more reviews are good for sales of highly rated products, but bad for those with negative ratings. Retailers should consider this tradeoff when they decide whether to facilitate the growth of online reviews systems, the researchers say.

In addition, their analysis shows that the relationship between volume of reviews and sales changes over time as volume increases.

"We find that reviews have a major impact on sales—either positive or negative—only when the number of reviews posted reaches a certain threshold value," Etzion says. "Until the volume reaches this threshold, consumers deem the ratings information as unreliable, and thus changes in volume do not have a significant effect on consumer product choice."

However, once a significant number of poor reviews accumulate for a product, more bad reviews do not have an additional negative impact on sales, the researchers say. But this is not the case for products perceived more favorably, where an increase in good reviews continues to have a positive effect on sales.

The study also found that when there is enough dissimilarity among the ratings of competing products, the number of reviews does not affect sales.
—Bernie DeGroat, News Service

Patterns of welfare, work linked to children's behavior problems

Older children whose mothers left welfare for work score lower on math and reading tests than their peers, a new study from the University indicates.

However, the study shows that older children whose mothers remain on welfare also have lower math and reading scores than their peers.

These findings may have been caused by factors other than welfare, says the study's author Nicole Gardner Neblett, who was a post-doctoral fellow in the Gerald R. Ford School of Public Policy when she conducted the study.

It examined single mothers' employment and welfare experiences and how they might affect children. The findings indicate that the pattern of mothers' welfare and work experiences does make a difference.

Data were collected from the Panel Study of Income Dynamics—a national survey that gathers information on topics such as income, family, employment—and the Child Development Supplement, which tracks the well-being of children and their families. The U-M study analyzed 820 children ages 3 to 12 and their single mothers.

Children whose mothers left welfare for work also were more likely to experience behavior problems than other children. Girls whose mothers left welfare for work also scored lower on math and reading tests than boys.

Other research indicates children whose mothers transitioned to work from welfare may assume additional household responsibilities as well as experience more unsupervised time.

For children whose mothers left welfare for work, younger children scored similarly on their reading and math tests to other children their age. Older children whose mothers left welfare, however, were vulnerable when it comes to their test scores, which may place them at risk for lower academic achievement, Neblett says.

Other studies show that when single mothers experience economic stress they are more likely to respond to adolescents with harsh punishment, which contributes to problematic behaviors.

"Given that single mothers have the responsibility to be both parent and breadwinner, they may need additional support and resources to face the stress of meeting both roles," she says.

The study appears in the August issue of the Journal of Family Issues.
—Jared Wadley, News Service

New predictors found for patients with aorta tear

Each year, 10,000 Americans suffer a sudden tear in the lining of their body's largest blood vessel, the aorta. It's often misdiagnosed, and it can kill if not treated immediately. Actor John Ritter died of such a tear in 2003.

A study published in the July 26 New England Journal of Medicine by an international team of researchers may offer hope for aortic dissection survivors, and give guidance for their physicians. The researchers, led by U-M Cardiovascular Center experts, propose a new way to predict post-hospital death risk for aortic dissection patients, and a new model for the mechanism behind that risk.

Their model focuses on a phenomenon that easily can be seen on modern medical-imaging scans: the presence of blood clots in the channel created when the layers of the aorta separate like two layers of an onion.

"It appears that this may be a new predictor of which patients are most at risk—knowledge that might help guide decisions about when it's wise to proceed with more aggressive treatment and when we can hold off," says lead author Dr. Thomas Tsai, a fellow in cardiovascular medicine.

The study involves data from 201 patients with aortic dissections in their descending aortas, who survived to hospital discharge and were followed for up to three years or until their deaths as part of International Registry of Acute Aortic Dissection (IRAD), which is headquartered at the CVC and supported in part by the Medical School, the Mardigian Foundation and the Varbedian Fund for Aortic Research.

Senior author Dr. Kim Eagle, primary IRAD investigator, says, "I believe that we are beginning a new era of scientific discovery in aortic diseases at U-M and in IRAD." Eagle is the Albion Walter Hewlett Professor of Cardiovascular Medicine and a director of the Cardiovascular Center.
—Kara Gavin, UMHS