The frequency is defined as the number of vibrations per second, and its unit is (times/second). We usually use f to represent. Vibrating once per second is called 1Hz (Hertz). We often hear examples such as 50Hz and 60Hz in our lives.

At the beginning of the COVID-19 outbreak, Australia, located in the Asia-Pacific region, achieved good results during the period due to the strict response measures adopted by its government. It successfully controlled the local epidemic. Many people believe that the key to control lies in the early forced closure of the city, and the relevant supporting measures are properly matched. Under the condition that the public can maintain a basic quality of life, everything seems to be under control.

All type of liquid has an expanding volume due to the heat including water. In a closed-loop, water volume increased due to the heat transfer. The extra volume also increases the water pressure. In our house, in every tank-type water heater, cold water is heated as it enters the water heater tank. This increases the overall water volume and pressure inside the tank, which must be relieved to avoid the potentially negative effects of thermal expansion.

Pressure switches are designed to automatically sense when the pressure has changed. They are used widely in the Water Well Industry as they are mainly used in systems that have pressurized liquids. Most pressure switches have the capability of making field adjustments, but some do not. You need to know your water pump setting and have the correct pressure range before you select your pressure switch.

The COVAX program is expected to deliver at least 2 billion doses of vaccine worldwide by the end of 2021. 1.3 billion will be sent to 92 low-income countries participating in the program, bringing the vaccine rate of these countries to 20% of the population. Its vaccination can be roughly divided into three stages. In the first stage, medical staff and social care workers who need to take care of patients give priority to the vaccination rate of 3%. In the second stage, age over 65 and those whose disease has high risk are in danger of COVID-19 need to achieve a 20% vaccination rate. In the third stage, other priority groups will be gradually opened to further increase the vaccination rate.