Rollins K.M.,Brigham Young University |
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2010
Dynamic compaction (DC) is an economical approach for mitigating the hazard posed by collapsible soils particularly when they are deeper than 3-4 m. In this paper, case histories are provided for 15 projects at 10 locations in the United States where collapsible soils were treated with DC. For each site the soil properties, compaction procedures, and subsequent improvement are summarized. Although cohesionless and low-plasticity collapsible soils were successfully compacted, clay layers in the profile appeared to absorb energy and severely reduced compaction effectiveness. Correlations are presented for estimating the maximum depth of improvement, the degree of improvement versus depth, the depth of craters, and the level of vibration based on measurements made at the various sites. The compactive energy per volume was typically higher than for noncollapsible soils because collapsible soils are usually loose but relatively stiff. The maximum depth of improvement was similar to that for noncollapsible soils; however, significant scatter was observed about the best-fit line. Improvement was nonuniform with nearly 80% of the total improvement occurring within the top 60% of the improvement zone. The crater depth was related to a number of factors besides the drop energy including the number of drops, drop spacing, and contact pressure. The peak particle velocities were typically lower than those for noncollapsible soils at shorter distances, but the vibrations attenuated more slowly with distance. © 2010 ASCE. Source
Among bacteria, the spirochetes are characterized by their spiral shape and remarkable length—as much 50 times longer than most other bacteria. This can make cell elongation and division a laborious process. One of those spirochetes, Borrelia burgdorferi, which causes Lyme Disease, has evolved an unusual way of doing this process: Borrelia cells mark the location where their daughters will divide before dividing themselves. A Yale team led by Christine Jacobs-Wagner, director of the Microbial Sciences Institute, captured the process via single-cell microscopy. They found that spirochetes showed active synthesis of peptidoglycan—a key component of growth and division—at equally spaced regions along its length (seen here in green). These zones of growth not only defined where the mother cell would divide, but also where future daughter cells would divide as well. The research is published in the journal Proceedings of the National Academy of Sciences, along with a question-and-answer article in which Jacobs-Wagner discusses the mysteries of bacterial growth and division. More information: Brandon Lyon Jutras et al. Lyme disease and relapsing feverelongate through zones of peptidoglycan synthesis that mark division sites of daughter cells, Proceedings of the National Academy of Sciences (2016). DOI: 10.1073/pnas.1610805113
For some adults, Zika virus is a rashy, flulike nuisance. But in a handful of people, the virus may trigger a severe neurological disease. About one in 4,000 people infected by Zika in French Polynesia in 2013 and 2014 got a rare autoimmune disease called Guillain-Barré syndrome, researchers estimate in a study published online February 29 in the Lancet. Of 42 people diagnosed with Guillain-Barré in that outbreak, all had antibodies that signaled a Zika infection. Most also had recent symptoms of the infection. In a control group of hospital patients who did not have Guillain-Barré, researchers saw signs of Zika less frequently: Just 54 out of 98 patients tested showed signs of the virus. Here's what we know about Zika How Zika became the prime suspect in microcephaly mystery Efforts to control mosquitoes take on new urgency The message from this earlier Zika outbreak is that countries in the throes of Zika today “need to be prepared to have adequate intensive care beds capacity to manage patients with Guillain-Barré syndrome,” writes study coauthor Arnaud Fontanet of the Pasteur Institute in Paris and colleagues, some of whom are from French Polynesia. The study, says public health researcher Ernesto Marques of the University of Pittsburgh, “tells us what I think a lot of people already thought: that Zika can cause Guillain-Barré syndrome.” As with Zika and the birth defect microcephaly (SN: 2/20/16, p. 16), though, more work needs to be done to definitively prove the link. Several countries currently hard-hit by Zika have reported upticks in Guillain-Barré syndrome. Colombia, for instance, usually sees about 220 cases of the syndrome a year. But in just five weeks between mid-December 2015 to late January 2016, doctors diagnosed 86 cases, the World Health Organization reports. Other Zika-affected countries, including Brazil, El Salvador and Venezuela, have also reported unusually high numbers of cases. Despite the seemingly strong link between Zika and Guillain-Barré, Marques stresses that the risk of getting the syndrome after a Zika infection is quite low. “It’s important that people don’t think that if you get Zika, you are going to get Guillain-Barré.” The chance is much less than 1 percent, he says. And it’s too early to say whether the rate of Guillain-Barré estimated in the paper will be the same in ongoing Zika outbreaks, says Anna Durbin, a vaccine researcher at Johns Hopkins University. “We have a number now, but it’s not perfect,” she says. Ongoing studies in Brazil and other countries affected by Zika will help refine the rate. As suspected and confirmed Zika infections climbed in Colombia (black lines), cases of Guillain-Barré syndrome rose, too (blue bars). New cases of Guillain-Barré may be added retrospectively as they are confirmed. The syndrome begins as the body’s immune system attacks peripheral nerves, causing weakness or tingling sensations in the lower extremities. In severe cases, total paralysis can result, leaving people dependent on ventilators in intensive care units while they recover. Three to 5 percent of people with Guillain-Barré die from complications, scientists estimate. Other viruses, including HIV, influenza and dengue (like Zika, a flavivirus), are known to spark Guillain-Barré, possibly through their interactions with the body’s immune system, though the details remain mysterious. The timing of Guillain-Barré’s onset may make it easier for scientists to pin the disorder on Zika. Because the syndrome shows up days or weeks after an infection subsides, Guillain-Barré may offer a quicker readout of Zika’s effects than waiting months to see if microcephaly in babies are born to infected mothers, the WHO’s Bruce Aylward said in a news briefing February 19. Scientists conducting a multinational Guillain-Barré study may soon expand their study, called the International Guillain-Barre Syndrome Outcome Study, into Brazil and Colombia to look for signs of Zika infection in people with the syndrome. “We are developing a new version of the IGOS protocol that is more focused on Zika and other flaviviruses, to support the research in those countries,” says Bart Jacobs, an immunologist at Erasmus University Medical Center in Rotterdam, the Netherlands, who’s helping supervise the study. Further studies could also help explain why some people are susceptible to Guillain-Barré. Genetics, previous viral infections or toxins may all play a role.
News Article | May 4, 2016
Researchers in California made use of the mouth and teeth of sea urchins as inspiration in developing a new claw-like device that can collect sediment samples during expeditions to other planets. Sea urchins have long been known for their intricate mouthpiece, consisting of powerful muscles and sharp curved teeth capable of cutting and boring holes even into the hardest of rocks. A sizeable colony of these marine creatures can even decimate whole kelp forests simply by uprooting the existing seaweed and chipping away through the rocks. Marine biologists and engineers at the University of California, San Diego took a cue from the sea urchin's impressive mouthpiece to develop new equipment for future Mars rovers. They used how the teeth and muscles in the creature's mouth were arranged to create a robotic claw that can gather sediments samples better than the shovels that space vehicles have been using in the past. "Our goal was a bioinspired device that's more precise and efficient at grabbing ground samples from different areas, and won't disturb the surrounding area like a shovel would," Michael Frank, a PhD candidate at the Jacobs School of Engineering at UC San Diego, said. Frank and his colleagues focused their efforts in analyzing the importance of the keel, a T-shaped structure found running down the middle part of each of the sea urchin's teeth. Based on the team's simulations, the creature's teeth that had keels received 16 percent less stress compared to those that did not have keels when they were exposed to a 10-pound load. Those that had the T-shaped structure also had a 4 percent higher mass than those that did not have it. The researchers made use of engineering to replicate the structure of the sea urchin's mouth. Their first design closely resembled the natural framework of the mouthpiece but failed to collect sand samples. The second one had flattened teeth so that it would be able to scoop sediment samples better, but the mouthpiece had trouble opening properly. The third version of the mechanical mouthpiece featured teeth that were connected to other parts of the device differently, which allowed it to operate its opening without difficulties. The researchers were able to make adjustments to the mouthpiece's design quickly through the use of the university's 3D printers. The team tested the claw-like device by attaching it to a small remote-operated rover. They used it to collect sand from a beach at first and then proceeded to use the device to collect sediments that resembled the density and humidity of those found on Mars. The mechanical mouthpiece was able to gather sediments efficiently on both occasions. The researchers hope that their new claw-like device could be added to rovers that will be deployed to other parts of space in the future. The findings of the UC San Diego study are featured in the Journal of Visualized Experiments. © 2016 Tech Times, All rights reserved. Do not reproduce without permission.
Home > Press > Record-breaking steel could be used for body armor, shields for satellites Abstract: A team of engineers has developed and tested a type of steel with a record-breaking ability to withstand an impact without deforming permanently. The new steel alloy could be used in a wide range of applications, from drill bits, to body armor for soldiers, to meteor-resistant casings for satellites. Credit: USC The material is an amorphous steel alloy, a promising subclass of steel alloys made of arrangements of atoms that deviate from steel's classical crystal-like structure, where iron atoms occupy specific locations. Researchers are increasingly looking to amorphous steel as a source of new materials that are affordable to manufacture, incredibly hard, but at the same time, not brittle. The researchers believe their work on the steel alloy, named SAM2X5-630, is the first to investigate how amorphous steels respond to shock. SAM2X5-630 has the highest recorded elastic limit for any steel alloy, according to the researchers--essentially the highest threshold at which the material can withstand an impact without deforming permanently. The alloy can withstand pressure and stress of up to 12.5 giga-Pascals or about 125,000 atmospheres without undergoing permanent deformations. The researchers, from the University of California, San Diego, the University of Southern California and the California Institute of Technology, describe the material's fabrication and testing in a recent issue of Nature Scientific Reports. "Because these materials are designed to withstand extreme conditions, you can process them under extreme conditions successfully," said Olivia Graeve, a professor of mechanical engineering at the Jacobs School of Engineering at UC San Diego, who led the design and fabrication effort. Veronica Eliasson, an assistant professor at USC, led the testing efforts. To make the solid materials that comprise the alloy, Graeve and her team mixed metal powders in a graphite mold. The powders were then pressurized at 100 mega-Pascals, or 1000 atmospheres, and exposed to a powerful current of 10,000 Ampers at 1165°F (630°C) during a process called spark plasma sintering. The spark plasma sintering technique allows for enormous time and energy savings, Graeve said. "You can produce materials that normally take hours in an industrial setting in just a few minutes," she said. The process created small crystalline regions that are only a few nanometers in size, with hints of structure, which researchers believe are key to the material's ability to withstand stress. This finding is promising because it shows that the properties of these types of metallic glasses can be fine-tuned to overcome shortcomings such as brittleness, which have prevented them from becoming commercially applicable on a large scale, Eliasson said. Researchers at USC tested how the alloy responds to shock without undergoing permanent deformations by hitting samples of the material with copper plates fired from a gas gun at 500 to 1300 meters per second. The material did deform on impact, but not permanently. The Hugoniot Elastic Limit (the maximum shock a material can take without irreversibly deforming) of a 1.5-1.8 mm-thick piece of SAM2X5-630 was measured at 11.76 ± 1.26 giga-Pascals. By comparison, stainless steel has an elastic limit of 0.2 giga-Pascals, while that of tungsten carbide (a high-strength ceramic used in military armor) is 4.5 giga-Pascals. This isn't to say that SAM2X5-630 has the highest elastic limit of any material known; diamonds top out at a whopping 60 giga-Pascals-- they're just not practical for many real-world applications. "The fact that the new materials performed so well under shock loading was very encouraging and should lead to plenty of future research opportunities," said Eliasson. The primary focus of future research efforts on these alloys is increasing the weight of the materials to make them more resistant to impacts. ### In addition to Graeve and Eliasson, co-authors include: Gauri R. Khanolkar and Andrea M. Hodge at USC, Michael B. Rauls at Caltech and James Kelly from the Department of Mechanical and Aerospace Engineering at UC San Diego. This research was supported by the Defense Threat Reduction Agency, grant HDTRA1-11-1-0067. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.