After suspension of medical examinations to immigrant and diversity visa applicants in Liberia for several months, the United States Embassy near Monrovia has announced the resumption of the process, beginning today, February 16. Visa activities were suspended in Liberia and transferred to Ghana because of the exacerbating Ebola epidemic that affected the country since last year.A medical examination completed by an approved panel of physicians is a requirement for all immigrant and diversity visa applications., a U.S. Embassy release states. The U.S Embassy urges visa applicants in Liberia previously scheduled for an immigrant or a diversity visa interview to follow the updated instructions concerning medical examinations on its website. It further advises all visa applicants, both immigrant and diversity, to review the revised instructions for obtaining a medical examination, indicating that future applicants should review the website and contact the panel physician directly to schedule a medical exam before their interview date. The Consular Section, urges all immigrant and diversity visa applicants to expect extended wait times as its panel of physicians work to schedule applicants whose cases have been pending. It clarifies that applicants may still travel to another country for medical exams if approved by the panel of physicians associated with the Embassy or Consulate in that country. Since Ebola worsened in Liberia last year, travelers from Liberia to the USA have been undergoing most of their processes in other West African countries, including Ghana. The Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, cautioned American Embassy staffs families last year to avoid making nonessential travels to the Ebola affected countries of Guinea, Liberia and Sierra Leone. With favorable reports of reduction in new cases in Liberia, the U.S. Government recently lifted the ban, thus paving the way for travelers to travel to and from Liberia. The reported positive development also led President Barack Obama to announce the withdrawal of most of the U.S. troops from Liberia at the end of April. What remains, according to travelers, is building full confidence in Liberians wishing to travel to the United States and the resumption of Delta Airlines flights to Liberia.Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window)
(Phys.org)—A team of researchers working at Sandia National Laboratories in New Mexico has found an explanation for the variety of sounds people hear when witnessing a falling meteor—sounds that should not be heard until minutes later due to the long distances involved. In their paper published in Scientific Reports, the team describes experiments they conducted with transducer materials and what they learned by doing so. Citation: Sandia researchers offer explanation for hissing and popping noises heard from meteors (2017, February 8) retrieved 18 August 2019 from https://phys.org/news/2017-02-sandia-explanation-hissing-noises-heard.html Journal information: Scientific Reports Explore further © 2017 Phys.org This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Meteor seen from the site of the Atacama Large Millimeter Array (ALMA). Credit: ESO/C. Malin Over the years, witnesses of falling meteors have reported hearing a wide variety of noises that appear to come from the rapidly descending fireball. While it is not surprising that meteors would emit noise as they streak through the Earth’s atmosphere, it is surprising that they would be heard during the meteor’s descent because of the distance. Meteors are generally first noticed as they begin burning many miles high in the atmosphere—and most land equally far away from witnesses. So, how could people hear emitted sounds as they are being made? That was what the team at Sandia Labs sought to answer.The team began with a theory that the noise was not actually generated by the meteor itself, but by nearby objects. They believed the bright light generated by the fireball comes in pulses and that those pulses cause a rapid rise in the temperature of the air through which they travel. The nearly instant air pressure change would result in pressure waves, which would be converted into acoustic waves when they crashed into what the team described as dielectric transducers—heat absorbing objects such as leaves, hair or even a shirt someone was wearing.To test their theory, the researchers studied photographs and video of meteors and plotted the intensity of the light generated. Then they calculated the likely acoustic waves that would result if they struck various objects. Next, they fired similar light pulses at materials to see if noises similar to those reported by meteor witnesses could be heard. They report that such sounds were, indeed, generated, suggesting that their theory was correct—the first to attempt to explain meteor noise due to light. They have called it a “photoacoustic hypothesis.” Geminids meteor shower peaks Tuesday amid full moon More information: Richard Spalding et al. Photoacoustic Sounds from Meteors, Scientific Reports (2017). DOI: 10.1038/srep41251AbstractConcurrent sound associated with very bright meteors manifests as popping, hissing, and faint rustling sounds occurring simultaneously with the arrival of light from meteors. Numerous instances have been documented with −11 to −13 brightness. These sounds cannot be attributed to direct acoustic propagation from the upper atmosphere for which travel time would be several minutes. Concurrent sounds must be associated with some form of electromagnetic energy generated by the meteor, propagated to the vicinity of the observer, and transduced into acoustic waves. Previously, energy propagated from meteors was assumed to be RF emissions. This has not been well validated experimentally. Herein we describe experimental results and numerical models in support of photoacoustic coupling as the mechanism. Recent photometric measurements of fireballs reveal strong millisecond flares and significant brightness oscillations at frequencies ≥40 Hz. Strongly modulated light at these frequencies with sufficient intensity can create concurrent sounds through radiative heating of common dielectric materials like hair, clothing, and leaves. This heating produces small pressure oscillations in the air contacting the absorbers. Calculations show that −12 brightness meteors can generate audible sound at ~25 dB SPL. The photoacoustic hypothesis provides an alternative explanation for this longstanding mystery about generation of concurrent sounds by fireballs.