Click for Philadelphia, Pennsylvania Forecast


Print This Issue
Front Page
All About Teaching
Subscribe to E-Alamanc!

Research Roundup

Designing Accessible Passenger Trains
As the deadline for compliance with the Americans with Disabilities Act draws closer, the commuter and passenger trains used in large swaths of the United States remain inaccessible to passengers in wheelchairs. Meanwhile, the elevated platforms many regional rail systems have erected to address this problem have created another, forcing bulky freight shipments off the rails and onto some of the busiest roadways in the nation.

Dr. Edward K. Morlok, professor of transportation and systems engineering, has designed a new train car that's fully accessible to disabled passengers, compatible with freight trains and spacious enough to carry nearly 40 percent more passengers. Penn has filed for patent protection.

Problems arise when two different levels of platforms are found alongside the same set of tracks, a situation common in the northeastern U.S. Older low-level platforms deny access to disabled passengers, who cannot mount stairs to enter cars. Newer high-level platforms block the passage of freight trains, funneling truck traffic onto congested highways.

Dr. Morlok's answer to this dilemma is a split-level car divided into three sections, with the two ends at the level of a high platform (four feet above the rails) and the longer middle portion accessible from lower platforms (eight inches above the rails). Doors are situated at both levels, opening only at the appropriate stations, and a small lift within the car permits disabled passengers to move between levels.

Because the central portion of the car is lower, a second level can be added above it. To fit within railroad height restrictions in the Northeast, the double-deck levels are nested together to yield full headroom over aisles. The tri-level configuration carries some 130 passengers, compared to about 94 in current-generation cars with similarly wide seats.

Dr. Morlok estimates that by more rapidly loading and unloading passengers, his design could shave six percent off the time it takes a commuter train to run its route and boost ridership two to four percent. Because fewer staffers would be required to assist passengers as they board and alight, the new design could slash train staffing costs by up to a third.

Dr. Morlok has also developed a second car design whose vestibule features a stairwell that can rotate for access to either high or low platforms. Such a design would save considerable time for trains stopping at both types of platform; currently most such trains have to be reconfigured manually by conductors.

back to top

Giant Self-assembled Liquid Crystal Lattice
A new liquid crystal lattice created by scientists at Penn and the University of Sheffield may be invisible to the naked eye, but it's a giant in its own way.

Uniting hundreds of thousands of atoms, this supramolecular structure is one of the most complex ever made via self-assembly, where molecules organize themselves into larger structures. It's the first organic compound to assume an intricate structure previously seen only in metals such as uranium and various metal alloys.The work is described in a paper published on the web site of the journal Science.

Among self-assembled structures, bigger is better. Dr. Virgil Percec, professor of chemistry, says if this lattice can attain dimensions equaling the wavelength of light the material could represent a new class of photonic crystals and a new approach to telecommunications. Such work could also yield molecular-scale electronics.

To create these large nanostructures, Dr. Percec and his colleagues started with a supersized building block: a carefully designed, well-defined and highly branched molecule referred to as a dendron. When thousands of these tree-like molecules come together, they organize themselves, unaided, into discrete microscopic spheres.

In the liquid crystal phase, each sphere consists of 12 tapered dendrons linked at their narrow end. Dr. Percec and his colleagues observed 30 of these globular structures arrange themselves into a tetragonal lattice whose repeat unit is a rectangular prism containing 255,240 atoms and measuring 169 by 169 by 88 angstroms. This repeat unit size is comparable to the crystal form of some spherical virus particles isolated from plants.

Using increasingly sophisticated techniques, scientists engineer self-assembling molecules to arrange themselves into much larger, functioning objects. The field draws inspiration from nature, where proteins and cells are genetically encoded to arrange themselves into functional entities.

Self-assembly may prove useful in a wide range of fields, many involving encapsulation of materials: drug delivery, adhesives, pesticides, composites, coatings and paints, photographic and imaging media, catalysis, microfabrication and microelectronics. Dr. Percec's group is now tweaking the structure of their dendron molecules so they might assemble into hollow spheres.

Dr. Percec is joined in the Science paper by co-authors Wook-Dong Cho at Penn and Goran Unger, Yongsong Liu and Xiangbing Zeng at the University of Sheffield. The research was funded by the UK Engineering and Physical Sciences Research Council and the NSF.

back to top

Insect Antibiotics: A Model for Therapeutic Agents
For antibiotics, the best way to beat bacterial defenses may be to avoid them altogether. Researchers at the School of Medicine have discovered that Cecropin A, a member of a family of antibiotic proteins produced by insects, may kill bacteria and avoid resistance by entering bacterial cells and taking control of their genetic machinery.

While most antibiotics kill bacteria by attacking critical enzyme systems, Cecropin A somehow slips inside the bacteria and turns specific genes on and off. The findings challenge conventional thinking on how these antibiotics function, and may aid in turning antimicrobial peptides like Cecropin A into therapeutic agents.

"For decades, researchers have studied Cecropin A and focused on its obvious effects against bacterial cell walls and membranes. These antibiotics certainly do disrupt outer structures of the bacterial cell, but there's much more to the story," said Dr. Paul H. Axelsen, associate professor of pharmacology and infectious diseases. "Before the bacterial cell dies, Cecropin A enters the cell and alters the way its genes are regulated. It's like sneaking over the castle wall and opening the gates from the inside. We need to understand this mechanism of action because it may explain why bacteria are unable to develop resistance to this family of antibiotics."

Dr. Axelsen's findings were described in the January issue of the Antimicrobial Agents and Chemotherapy, a publication of the American Society for Microbiology. In their study, Dr. Axelsen and his colleagues treated E. coli with small doses of Cecropin A--not enough to kill the bacteria, but enough to see what genes are affected when bacteria are exposed to the antibiotic. They found that transcript levels for 26 genes are affected, 11 of which code for proteins whose functions are unknown. Even more surprising for the researchers, the genes are not the same as the ones affected when bacteria experience nutritional, thermal, osmotic, or oxidative stress.

Despite years of research, there remains much to know about the antibiotics produced by insects. Cecropin A was discovered in the Cecropia moth, also known as the silkworm moth, the largest moth in North America. Since insects do not have an immune system as humans do, they rely on polypeptide antibiotics like Cecropin A to fight off infections. These proteins are highly selective--they readily kill bacteria, but are harmless to human and other animal cells. Moreover, bacteria that are susceptible initially stay susceptible--researchers have not seen bacteria develop resistance to their action. For this reason, these antibiotics offer a potentially invaluable model for new therapeutic agents.

This research was supported by grants from NIH, American Heart Association, and from Affymetrix's donation of E. coli GeneChip Microarrays. 

back to top

Women in Region: Facing Significant Inequality
The women's movement has shattered some glass ceilings, but full-time working women in Philadelphia still earn 25 percent less than men, with the wage disparity for women in "pink collar jobs" even greater.

Researchers from Penn and Solutions for Progress joined leaders from Women's Way in releasing the Women's Way report, A Change of Pace: Accelerating Women's Progress.

According to the report, women working full-time in 2001 in the Philadelphia region of Bucks, Chester, Delaware, Montgomery and Philadelphia counties earned a median income of $31,375 while men working full-time earned a median income of $42,050, or $10,675 more than women.

Further, women were overrepresented in "pink collar jobs" such as personal care, health-care support and administrative support. These occupations represent the lowest paying jobs in the workforce with median hourly wages ranging from $7.40 to $10.18.

Dr. Dana L. Barron, associate director of the Alice Paul Center for Research on Women and Gender, in collaboration with Laryssa Mykyta, senior policy analyst with Solutions for Progress, collected and analyzed data from federal agencies including the Census Bureau and the U.S. Department of Labor, and from published reports.

Their report covers income and occupations, poverty and economic security, housing, responsibility for care giving, work/family balance, assets and wealth, influence, aging and retirement and reproductive rights. It offers policy recommendations designed to accelerate the pace of women's progress in achieving fair and equitable compensation for their work.

Between September 2001 and August 2002, researchers conducted a telephone survey of residents in the Philadelphia metropolitan area to determine public attitudes and priorities. The research team also interviewed leaders of women's non-profit groups, directors of community organizations and academic experts on gender and wage issues.

Dr. Barron said that the report definitively demonstrates that area residents are aware of gender inequalities and adamant that their public officials take action to remedy them. Copies of the report are available at

See more Research Roundup from other Almanac issues.

  Almanac, Vol. 49, No. 25, March 18, 2003