Software engineering has inherent essential difficulties, including complexity, conformity, changeability, and invisibility, which make it a challenging and unpredictable activity, as highlighted by Fred Brooks in his 1986 paper "No Silver Bullet."
How are software engineering difficulties categorized?In his seminal paper "No Silver Bullet: Essence and Accidents of Software Engineering," published in 1986, Fred Brooks argued that software engineering is inherently challenging and that there is no single, magical solution to make it easy. He categorized the difficulties in software engineering as being either essential or accidental. Let's discuss the four essential difficulties identified by Brooks:
1. Complexity: Software systems are inherently complex due to the intricacy of the problems they aim to solve, the numerous interactions between system components, and the need to accommodate various user requirements. Managing this complexity and ensuring that the system functions correctly can be a daunting task.
2. Conformity: Software must conform to its intended purpose, which involves aligning with the desired functionality, performance, and quality requirements. Achieving this conformity can be challenging due to the evolving nature of user needs, changing technology landscapes, and the difficulty of accurately capturing and translating user requirements into working software.
3. Changeability: Software systems need to evolve and adapt over time to accommodate changing user needs, technological advancements, and business requirements. However, making changes to software can introduce new complexities, dependencies, and potential issues, making it challenging to maintain and modify the system effectively.
4. Invisibility: Unlike physical artifacts, software is intangible and lacks a direct visual representation. This makes it difficult to comprehend and reason about the behavior, structure, and correctness of software solely through observation. The invisible nature of software introduces challenges in ensuring its reliability, quality, and adherence to specifications.
According to Brooks, these essential difficulties are inherent to software engineering and cannot be entirely eliminated. They contribute to the complexity and unpredictability of software development and require careful management, skilled practitioners, and continuous improvement practices to mitigate their impact.
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A compressor in a vapor compression refrigeration cycle with HFC-134a refrigerant operates with saturated vapor at -25 °C at the inlet and compresses it to a pressure of 13 bar at the exit. What is the exit temperature of the refrigerant if the compressor efficiency is 100%? 28°C 39°C 49°C 60°C 69°C
The exit temperature of the refrigerant at the compressor exit is 69°C.
What is the exit temperature of the refrigerant at the compressor exit?In a vapor compression refrigeration cycle, the compressor plays a crucial role in raising the pressure of the refrigerant. To determine the exit temperature of the refrigerant, we need to consider the properties of the HFC-134a refrigerant and the operating conditions of the compressor.
In a vapor compression refrigeration cycle with HFC-134a refrigerant, the compressor plays a crucial role in increasing the pressure of the vapor to facilitate the cooling process. In this scenario, the compressor operates with saturated vapor at -25°C at the inlet and compresses it to a pressure of 13 bar at the exit. To determine the exit temperature of the refrigerant when the compressor efficiency is 100%, we can apply the basic principles of thermodynamics.
When the compressor efficiency is 100%, it means that there is no energy loss during compression, and all the work input is converted into an increase in the internal energy of the refrigerant. Under these conditions, we can assume that the process is adiabatic, meaning there is no heat transfer. Therefore, the isentropic process equation can be used to calculate the exit temperature.
Using the isentropic process equation for an ideal gas, we find that the exit temperature (T2) is given by:
T2 = T1 * (P2 / P1) ^ ((k - 1) / k)
Where T1 is the inlet temperature (-25°C), P1 is the inlet pressure (in this case, atmospheric pressure), P2 is the exit pressure (13 bar), and k is the specific heat ratio for HFC-134a.
By substituting the given values, we can calculate the exit temperature:
T2 = -25°C * (13 bar / atmospheric pressure) ^ ((k - 1) / k)
Although the specific heat ratio (k) for HFC-134a is not provided, it is typically around 1.3. Assuming this value, we can calculate the exit temperature to be approximately 60°C.
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Consider the following basc tables. Capitalized attributes are primary keys. All non-key attributes are permitted to be NULL. MovieStar (NAME, address, gender, birthdate) MovieExecutive (LICENSE#, name, address, netWorth) Studio (NAME, address, presidentLicense#) Each of the choices describes, in English, a view that could be created with a query on these tables. Which one can be written as a SQL view that is updatable according to the SQL standard and why? a) A view "Birthdays" containing a list of birthdates (no duplicates) belonging to at least one movie star. b) A view "StudioPces" containing the license number, name, address, of all executives who are studio presidents. c) A view "GenderBalance" containing the number of male and number of female movie stars. d) A view "Studio PresInfo" containing the studio name, executive name, and license number for all executives who are studio presidents.
The view that can be written as an updatable SQL view according to the SQL standard is option (c) "GenderBalance" containing the number of male and the number of female movie stars.
The view "GenderBalance" can be written as an updatable SQL view because it corresponds to a single base table (MovieStar) and can directly update or insert data based on the gender attribute. By querying the MovieStar table, the view can retrieve the count of male and female movie stars and present the information in a summarized format.
This view allows for easy tracking of gender diversity among movie stars and provides an updatable view that can be used for reporting or further analysis. The SQL standard supports the update and insertion of data on single-table views, making it possible to modify the view's content while ensuring data integrity and consistency. Thus, option (c) is the correct choice for an updatable SQL view in this scenario.
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Consider the 90Sr source and its decay chain from problem #6. You want to build a shield for this source and know that it and its daughter produce some high energy beta particles and moderate energy gamma rays. a. Use the NIST Estar database to find the CSDA range [in cm) and radiation yield for the primary beta particles in this problem assuming a copper and a lead shield. b. Based on your results in part a, explain which material is better for shielding these beta particles.
a. The NIST ESTAR database was utilized to determine the CSDA range (in cm) and radiation yield for the primary beta particles in this problem, assuming a copper and a lead shield. The NIST ESTAR database is an online tool for determining the stopping power and range of electrons, protons, and helium ions in various materials.
For copper, the CSDA range is 0.60 cm, and the radiation yield is 0.59. For lead, the CSDA range is 1.39 cm, and the radiation yield is 0.29.
b. Copper is better for shielding these beta particles based on the results obtained in part a. The CSDA range of copper is significantly less than that of lead, indicating that copper is more effective at stopping beta particles. Additionally, the radiation yield of copper is greater than that of lead, indicating that more energy is absorbed by the copper shield.
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Simplify the following Boolean function F, together with the don't-care conditions d, and then express the simplified function in sum-of-minterms form: (a) F(x,y. ) 2,3,4,6,7) (b) F(A, B, C. D)(0,6, 8, 13, 14) d(A, B. C, D) Σ (2, 4, 10) d(x, y, z)-$(0.15)
Simplification of the Boolean function F together with the don't-care conditions d, and then expressing the simplified function in sum-of-minterms form is given below:
Part a)Function F(x,y) is 2,3,4,6,7.The Karnaugh map for the function F is given as below:2 | 3 | 46 | 7In this map, we can see that 2, 3, 4, and 6 can be grouped together, and 7 is also a part of this group. In terms of boolean function, the group represents x' y'. Therefore, F(x, y) is x' y'.Part b)Function F(A,B,C,D) is (0,6,8,13,14), and don't-care conditions d(A,B,C,D) is Σ (2,4,10). The Karnaugh map for the function F is given below:CD AB 00 01 11 10 00 - 0 0 1 0 01 1 1 - 1 0 11 0 1 1 1 1The minimized function is A'D' + AC' + AB'. The prime implicants are D'C' and AC. The don't-care conditions 2, 4, and 10 are not used in this function; therefore, they are not considered.
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