In this paper, it is of key for us to find that the lengths of positive and negative semi-cycles of nontrivial solutions of (1.1) occur periodically with prime period 15 with the rule,,,,,,, and in a period.
Mainly, the lengths of positive and negative semicycles of its nontrivial solutions are found to occur periodically with prime period 15.
Assuming that, as neutralizing antibodies, IgG antibodies persist several years after infection, this result (and the WNV history in the studied area since 1962) suggest that the Camargue is an epidemic area, with outbreaks that occur periodically and are separated by long silent periods.
Outbreaks of encephalitis occur periodically.
Droughts occur periodically, and hurricanes may strike the islands on rare occasions.
Ebola outbreaks occur periodically in Africa, where the pathogen was first discovered in 1976.
Destructive cyclones may strike the area early in the year, and earthquakes occur periodically.
Thefts of stained-glass windows occur periodically in the New York region, with thieves sometimes selling them to antiques dealers.
In the African meningitis belt, epidemics of meningococcal disease occur periodically, although unpredictably, every few years.
Large meningococcal group A epidemics occur periodically in the Sudan, a country within the "meningitis belt" of Sub-Saharan Africa. Sub-Saharan Africa
Yet for millions of Americans, nausea and its frequent aftermath, vomiting, are facts of life that occur periodically over many months.
