It is necessary for concrete structure with mass section to have a rational crack control plan based on analysis of thermal stress from hydration heat. Because mass concrete can cause crack to deteriorate durability of structure. So, this study reports two examples: one is a process to calculate an adiabatic temperature rise and a reaction rate for evaluate thermal stress.
The long-time protection function protects cables (phases and neutral)
against overloads. This function is based on true rms measurements.
The thermal memory continuously accounts for the amount of heat in the cables,
both before and after tripping, whatever the value of the current (presence of
an overload or not). The thermal memory optimises the long-time protection
function of the circuit breaker by taking into account the temperature rise in the
cables. The thermal memory assumes a cable cooling time of approximately
Glaciers are melting, sea levels are rising, cloud forests are drying, and wildlife is scrambling to keep pace. It's becoming clear that humans have caused most of the past century's warming by releasing heat-trapping gases as we power our modern lives. Called greenhouse gases, their levels are higher now than in the last 650,000 years.
MECHANICAL AND ELECTRICAL BRAKES
Brake Selection for a Known Load 24.1 Mechanical Brake Surface Area and Cooling Time 24.3 Band Brake Heat Generation, Temperature Rise, and Required Area 24.6 Designing a Brake and Its Associated Mechanisms 24.8 Internal Shoe Brake Forces and Torque Capacity 24.15 Analyzing Failsafe Brakes for Machinery
Source: HANDBOOK OF MECHANICAL ENGINEERING CALCULATIONS
MECHANICAL AND ELECTRICAL BRAKES
Brake Selection for a Known Load 24.1 Mechanical Brake Surface Area and Cooling Time 24.3 Band Brake Heat Generation, Temperature Rise, and Required Area 24.6 Designing a Brake and Its Associated Mechanisms 24.8 Internal Shoe Brake Forces and Torque Capacity 24.15 Analyzing Failsafe Brakes for Machinery 24.17
BRAKE SELECTION FOR A KNOWN LOAD
Choose a suitable brake to stop a 50-hp (37.3-kW) motor automatically when power is cut off.
Since the dawn of history, human activities have always been closely related to friction,
the resistance to sliding. It is thanks to friction that one can stand and walk on
the ground, one can wear clothes, one can make fire by rubbing two sticks together,
or one can even start and stop a car. In these cases friction is very useful for human
beings. In many other cases, however, human activities have been very much hampered
by friction since ancient times. How to diminish friction is one of the most
basic technological problems.
For example, when a heavy...
With global populations on the rise and the increasing threat associated with climate change, the need for the development of low emission energy resources is clear. Geothermal energy, which originates from the underground heat of the earth (Sankaran, 2002), has the advantage of being a low-emission, baseload energy resource. Unlike other alternative energy resources, geothermal energy production does not fluctuate with time of day or season.
It may have already occurred to you that this "toughest job you'll ever love seems almost
impossible. Look at some of the obstacles you may be facing. Your students are numerous;
many may be older than you. Textbooks are scarce, and again, many may be older than you.
The physical conditions are austere, with a tin roof that creaks as the temperature rises and
obliterates all other sound when the rains come. Pictures and posters disappear from the
classroom walls. Desks are too few. The blackboard has been worn to a light grey and chalk
These power ratings and currents are given for an ambient temperature of 50°C (122°F) at the factory-set switching frequency,
used in continuous operation (factory-set switching frequency of 4 kHz for ATV71H 037M3 to D15M3X and 2.5 kHz for ATV71H D18M3X
Above this factory setting, the drive will reduce the switching frequency automatically in the event of excessive temperature rise.
For continuous operation above the factory setting, derating must be applied to the nominal drive current in accordance with the curves
on page 14.
While such investigations yield differing effects dependent on the situation, the common observation of a temperature change has been associated with the presence of mechanical energy, which is required to overcome frictional resistance as sliding at the contact interface occurs. The energy, dissipated through conversion into thermal energy, is manifested as a temperature rise. At the microlevel, this increase can be substantial. A localized change in material properties, an enhancement in chemical reactivity, and ultimately, failure of the mechanical system can result.
The Review uses the results from one particular model, PAGE2002, to illustrate how
the estimates derived from these integrated assessment models change in response
to updated scientific evidence on the probabilities attached to degrees of temperature
rise. The choice of model was guided by our desire to analyse risks explicitly - this is
one of the very few models that would allow that exercise. Further, its underlying
assumptions span the range of previous studies.
As output decreased the unemployment rate increased, rising from 4.6% in 2007 to a peak of
10.1% in October 2009, and remaining only slightly below that high into 2011. The U.S.
unemployment rate has not been at this level since 1982, when in the aftermath of the 1981
recession it reached 10.8%, the highest rate of the post-war period. (During the Great Depression
the unemployment rate reached 25%.) This rise in the unemployment rate translates to about
7 million persons put out of work during the recession. Another 8.
While there is much to learn about these risks, the temperatures that may result from
unabated climate change will take the world outside the range of human experience.
This points to the possibility of very damaging consequences.
The impacts of climate change are not evenly distributed - the poorest
countries and people will suffer earliest and most. And if and when the
damages appear it will be too late to reverse the process. Thus we are forced
to look a long way ahead.
A first critical step in developing a comprehensive safety and
health program is to identify physical and health hazards in the
workplace. This process is known as a "hazard assessment."
Potential hazards may be physical or health-related and a compre-
hensive hazard assessment should identify hazards in both
categories. Examples of physical hazards include moving objects,
fluctuating temperatures, high intensity lighting, rolling or pinching
objects, electrical connections and sharp edges. Examples of health
hazards include overexposure to harmful dusts, chemicals or
Viet Nam is considered as one of the most vulnerable countries due to CC and sea level rise. If sea level rise of 1 m, Viet Nam will loose about 12% of land, 23% of population will be affected. Typhoons occur more frequently with higher intensity. Temperature increases and change in rainfall pattern will affect agriculture and water resources.
Global warming is the rising average temperature of Earth's atmosphere and oceans since the late 19th century and its projected continuation. Since the early 20th century, Earth's average surface temperature has increased by about 0.8 °C, with about two thirds of the increase occurring since 1980. Warming of the climate system is unequivocal, and scientists are more than 90% certain that most of it is caused by increasing concentrations of greenhouse gases produced by human activities such as deforestation and the burning of fossil fuels.
Explores public and government involvement in combating global warming, and reviews conservation programs that have been developed by countries, international institutions, private organizations, and individuals.Global warming is the rising average temperature of Earth's atmosphere and oceans since the late 19th century and its projected continuation.
An Introduction to Microelectromechanical Systems Engineering
The Sandbox: Materials for M E M S
devices are made of n-type and p-type bismuth telluride elements, and are used to cool high-performance microprocessors, laser diodes, and infrared sensors. Peltier devices have proven difficult to implement as micromachined thin film structures.
The world’s climate is changing, and it will continue to change throughout the 21st century and beyond. Rising temperatures, new precipitation patterns, and other changes are already affecting many aspects of human society and the natural world. Climate change is transforming ecosystems at extraordinary rates and scales.
The scientific evidence is clear: before 2020 global greenhouse gas emissions (GHG) must peak and by 2050 they must be reduced by 50-85% below 2000 levels, in order to avoid a rise in global temperature of 2°C or more above the preindustrial level.2 Without ambitious international action, new scientific research3 predicts close to, or even more than, a metre of sea level rise by the end of this century, due to melting glaciers and expansion of the oceans. Tthese and other changes will have serious economic and human consequences....