The great wheel of the seasons will continue to turn. Try to watch as the sun rises due east and sets due west on the day of the equinox. Day and night sides of Earth at the instant of the September equinox September 23 at Universal Time. The shadow line at left going through North America depicts sunset September 22 and the shadow line to the right of Africa represents sunrise September The lunar calendars are almost here!
Which African Countries Are Located on the Equator?
View the moon phases throughout the year. Read more: Everything you need to know about the September equinox He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York. Amazing June for noctilucent clouds. Eduardo J. Author information Article notes Copyright and License information Disclaimer.
Corresponding author. Conflict of interest statement: The authors declare that the paper has been submitted without conflict of interest, and without funding. Received Mar 16; Accepted Apr This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This article has been cited by other articles in PMC.
Abstract Background It is necessary to know the in vitro behavior of different attachment systems to be used clinically. Material and Methods The study used an implant replica compatible with the abutments of both systems. Conclusions Both systems presented acceptable retention capacities after 14, cycles. Open in a separate window. Figure 1.
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Figure 2. Results Table 1 shows descriptive statistics for changing retention strength in the two study groups over the cycle sequence described above. Figure 3. Box plot shows the distribution of retention values obtained by the two groups. Table 2 Mann Whitney Test Results. Conclusions Within the limitations of this in vitro laboratory study, the following conclusions may be drawn.
Testing the retention of attachments for implant overdentures - validation of an original force measurement system. J Oral Rehabil. Lehmann KM. Studies on the retention forces of snap-on attachments. Quintessence Dent Technol. Int J Prosthodont. Besimo CE, Guarneri A. In vitro retention force changes of prefabricated attachments for overdentures. Retention of ERA direct overdenture attachments before and after fatigue loading.
Attachment systems for mandibular two-implant overdentures: a review of in vitro investigations on retention and wear features.
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Scherer M, McGlumphy E. Int J Oral Maxillofac Implant. Effects of in vitro cyclic dislodging on retentive force and removal torque of three overdenture attachment systems. Clin Oral Implants Res. Wear simulation effects on overdenture stud attachments. Dent Mater J. Retention characteristics of attachment systems for implant overdentures. J Prosthodont. Effect of implant angulation on attachment retention in mandibular two-implant overdentures: A clinical study. Clin Implant Dent Relat Res. Influence of attachment wear on retention of mandibular overdenture.
Attachment systems for implant retained overdentures: a literature review. Implant Dent. Evaluation of stable retentive properties of overdenture attachments.
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The service life of implant-retained overdenture attachment systems. J Prosthet Dent. Retention of prefabricated attachments for implant stabilized overdentures in the edentulous mandible: An in vitro study. The in vitro effect of different implant angulations and cyclic dislodgement on the retentive properties of an overdenture attachment system.
Attachment systems for implant overdenture: influence of implant inclination on retentive and lateral forces. Analysis of retention and wear of ball attachments. Quintessence Int. Complications associated with the ball, bar and Locator attachments for implant-supported overdentures.
Stress analysis of mandibular two-implant overdenture with different attachment systems. The water in the equatorial air cools it slightly. Many cultures thrive in warm equatorial regions.
The Fang people of Gabon, for instance, are successful farmers who take advantage of the warm temperature and long rainy season to cultivate crop s such as corn, yams, and plantains. The Fang also raise livestock that have adapted to the climate, such as goats and chickens. Not all equatorial regions are hot and humid, however. Mount Kilimanjaro, Tanzania, is only kilometers miles from the Equator, but its elevation creates a climate with cool, dry weather and even alpine glacier s.
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The Andes are another equatorial region lacking the hot, humid climate often associated with the Equator. The mountain range includes a desert with almost no rain the Atacama , as well as some of the tallest peaks on Earth. Here, too, cultures have thrived for thousands of years. The Aymara people of the Altiplano of Bolivia, Peru, and Chile, are primarily an urban people who identify strongly with the innovative navigation al successes of their ancestors. In the 20th century, the Aymara helped build railroads through the high, equatorial Andes.
Many plant and animal species thrive in equatorial climates. The Amazon and Congo rain forest ecosystem s, for example, are amazingly rich in biodiversity. A single hectare 2. The equatorial savanna of Kenya includes mammals such as lions, cheetahs, and elephants. The chilly equatorial Andes are famous for its camelid species: llamas, alpacas, vicunas, and guanacos.
Earth's equatorial bulge pushes Mount Chimborazo, near the Equator in the Ecuadorian Andes, further from the center of the Earth.
However, elevation is measured from sea level, not the center of the Earth. Mount Everest is 8, meters 29, feet above sea level, while Mount Chimborazo is just 6, meters 20, feet above sea level. Crossing the Line Sailors have elaborate rituals and celebrations when they cross the Equator, which they call crossing the line. Sailors who have never crossed the line are called pollywogs. Pollywogs are usually the target of embarrassing practical jokes. Short Sunsets The time it takes for the sun to set and rise at the Equator is the fastest on Earth.
The transition from day to night takes only a few minutes. Regions are the basic units of geography. Satellites can be natural, like moons, or made by people. Sea level is determined by measurements taken over a year cycle. Jeannie Evers, Emdash Editing. Caryl-Sue, National Geographic Society. For information on user permissions, please read our Terms of Service.
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