MA Mechanic Reading Comprehension

PASSAGE 1:

Ever since the establishment of the California Air Resources Board (CARB) and Environmental Protection Agency (EPA), significant strides have been made in diesel engine emission control technology. The diesel emission control is being achieved using strategies involving in-situ and after-treatment techniques and even with their effective combinations. Among these techniques, recirculation of the exhaust gases back to the engine inlet is an in-situ approach for Nitrogen Oxide (NOx) control.

Moreover, exhaust gas recirculation (EGR) has been used for controlling the onset of combustion process. Over the last five decades, the vehicle population across the globe has grown significantly. The concern over vehicular pollution increased steadily after the 1960s Los Angeles episode. It is well known that vehicular emissions vary with engine type, operating conditions, and fuel utilized, and all these aspects need to be addressed simultaneously for their abatement. The severity of engine pollutants depends on their concentration and exposure time and severely affects human health. Owing to inherent fuel economy advantage, diesel engines have made inroads into automotive applications beside their usual stationary domain. However, diesel fuel-operated vehicles are the major source of NOx and particulate emissions and are responsible for the deterioration of ambient air quality. Many countries like Brazil, China, Sri Lanka, Denmark, and France are in the process of eliminating diesel vehicles and enforcing heavy taxes and levies on such vehicles. Recently, the Indian government banned the registration of diesel-run private cars with a capacity of 2000cc and above in certain cities. It is imperative that the sustenance of diesel-operated engines is possible with ultra-low emissions and lower fuel consumption. The NOx-PM trade-off in diesel engines is a classical challenge for developing emission control technology and hence stands at the forefront of diesel engine development. The NOx/PM emission could be restricted through in-cylinder control measures well ahead of their formation, or through after-treatment control devices which involve the conversion of NOx/PM emission to relatively benign compounds

1.The word “strides” in line 2 is similar in meaning to ——.

1) advances

2) borders

3) motivations

4) changes

2.This passage is mainly about ——-.

1) the best technique for managing the exhaust gases

2) the strategies used by Environmental Agency Protection

3) the ways of controlling the emissions from diesel engines

4) effective methods involving in-situ and after-treatment procedures

3.The vehicular emissions, according to the passage, rely on all of the following EXCEPT ——-.

1) type of engine

2) regional conditions

3) operating status

4) kinds of fuel used

4.Diesel engines, as stated in this passage, ——-.

1) are the main causes of air pollution

2) have more inherent fuel economy advantage

3) are increasingly being used despite restricted rules

4) are more common in countries like Brazil, China, Sri Lanka, Denmark, and France

5.The NOx emissions could be controlled best by ——–.

1) supervising the engine manufacturing processes

2) banning the registration of diesel cars completely

3) enforcing heavy taxes and levies on using private cars

4) conversion of harmful NOx to environmentally friendly gases

PASSAGE 2:

Magnetic bearings have been used to achieve noncontact suspension of a flywheel rotor, thus eliminating issues of friction and wear associated with high-speed applications using mechanical bearings. The suspension is achieved through an opposing set of electromagnets between which the rotor is positioned. The position of the rotor can be controlled via the magnetic forces, and the forces can be regulated by adjusting the magnet coil voltage or current. The magnetic forces exert attractive forces on the rotor shaft, and for this reason magnetic bearings are inherently unstable and require closed-loop control. A self-sensing magnetic bearing is a special type of magnetic bearing in that the rotor position information is deduced from the electromagnetic interaction between the stator and rotor. The feedback is based solely on the measured current in the electromagnets, making it possible to design the bearing system without position sensors. This results in a significant advantage because of a considerable reduction in manufacturing costs and the complexity of the system, as well as the elimination of the failure modes associated with the sensors. A self-sensing magnetic bearing with linear control was first proposed. A linearized model of the self-sensing magnetic bearing was also developed in, but the results suggested that the proposed configuration resulted in poor robustness and disturbance rejection. Subsequent experiments have confirmed this view. In particular, disturbance to the system caused by rotor imbalance is commonly encountered, since imperfections in rotor design and manufacture cannot be avoided.

6.Magnetic bearings, according to the passage, are capable of ——.

1) reducing friction between rotating objects

2) supporting rotors in the absence of mechanical contacts

3) constraining relative motion to only desired motion

4) restricting wear associated with high-speed application

7.If the coil current is regulated, ——.

1) the position of the rotor is adjusted

2) the supply voltage can be altered

3) the suspension system is achieved

4) the magnetic forces can be controlled

8.The instability of the magnetic bearing is due to ——-.

1) the closed loop having control of the rotor

2) the deduction of the rotor position information

3) the electromagnetic interactions between the rotor and stator

4) the permanent effect of magnetic forces on the rotor shaft

9.Which sentence, as stated in the passage, is NOT true?

1) The existence of sensors leads to failures in bearing systems.

2) Manufacturing a perfect rotor design is currently impossible.

3) A self-sensing magnetic bearing is a complex and costly system.

4) The formation of a linearized model of the self-sensing magnetic model was rejected.

10.The writer of this passage wants to ——-.

1) illuminate

2) criticize

3) compare

4) innovate

PASSAGE 3:

One of the major themes that runs through physical science is the Conservation Laws.

These laws tell us that an isolated system in equilibrium will have identifiable properties that cannot change. These are often referred to as constants. These constants of an object/system are said to be conserved, and the resulting conservation laws can be considered the most fundamental principle of the system. In mechanics, examples of conserved quantities include energy and momentum. Studying motion from the basis of the law of conservation provides a unique advantage when compared to other methods, the ability to relate that motion to energy. The connection between motion and the conservation laws is possible because all mechanical motion is the result of some form of energy transformation. An understanding that energy is a conserved quantity allows one to follow that energy in all its various forms. Thus, a key question is to ask when studying a particular phenomenon is: Where does the energy of a system come from and where does it go?

11.This passage is mainly about ——.

1) equilibrium and conservation

2) identifiable properties of an isolated system

3) laws of physical science

4) motion as a unique advantage

12.In mechanics, energy and momentum, according to the passage, ——–.

1) are repeatedly created and destroyed

2) are considered as the constants of an isolated object in equilibrium

3) are in inverse relationship with each other

4) are considered the most fundamental qualities of a system

13.Motion and energy, as stated in the passage, ——-.

1)are related to the abstract qualities of an object

2) determine the origin of the energy

3) can be related to each other through the conservation laws

4) are the resulting forms of an isolated system

14.The word “key” in line 11 can be substituted by ——-.

1) relevant

2) common

3) difficult

4) critical

15.Studying a particular phenomenon, as mentioned in the passage, —–.

1) reveals the direction of an object's motion

2) allows one to follow that object in all its various forms

3) leads to questions about the source and destination of energy

4) depends on our understanding of all constant laws in physics

MA Mechanic Reading Comprehension

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