Notes, summaries, assignments, exams, and problems for University

Critical Frequency (f_c) and MUF

Critical Frequency (f_c)

The maximum frequency at which a radio wave can be transmitted vertically and still be reflected back by the ionosphere.

Formula: f_c = 9√N_max

Where N_max is the maximum electron density (electrons/m³) in the ionosphere.

Maximum Usable Frequency (MUF)

The highest frequency that can be used for skywave communication between two given points, such that the wave is still reflected by the ionosphere.

Formula: MUF = f_c / cos(θ)

Where θ is the angle of incidence.

Virtual Height

The apparent height at which a radio wave appears to be reflected from the ionosphere, assuming it traveled in a straight line at the speed of light. In reality, the wave is refracted gradually, but the virtual height helps... Continue reading "Ionospheric Radio Propagation: Key Parameters and Principles" »

1. Client Initiation and DNS Lookup

• The user enters a URL or clicks a link in the browser. The browser parses the URL and extracts the domain (e.g., www.example.com).

• A **DNS lookup** translates this domain into an IP address—acting like a digital phonebook entry.

2. Establishing the TCP Connection

The browser’s operating system (OS) creates a socket and initiates the **TCP three-way handshake** with the server:

1. SYN: Client sends a synchronization request to the server.
2. SYN-ACK: Server acknowledges the request and sends its own synchronization.
3. ACK: Client acknowledges the server's response.

Once this handshake is complete, a full-duplex TCP connection is open and ready for reliable data exchange.

3. Sending the HTTP Request Message

The client constructs... Continue reading "The Complete HTTP Request Lifecycle Explained Step-by-Step" »

JavaScript Regular Expressions: An Introduction

This concise and clear introduction to Regular Expressions (RegExp) in JavaScript covers their usage, modifiers, patterns, methods, and string integration.

Regular Expressions are powerful patterns used to match, search, and manipulate strings. In JavaScript, regular expressions are objects used with string methods to perform pattern matching.

RegExp Syntax Fundamentals

You can define a regular expression using literal notation:

const pattern = /expression/modifiers;

Or by using the RegExp constructor:

const pattern = new RegExp("expression", "modifiers");

RegExp Modifiers (Flags) Explained

Modifiers change how a Regular Expression behaves:

Understanding Political Economy

Political economy applies economic principles to the analysis of political decision-making.

Public Goods & Direct Democracy

Economists have studied several methods for choosing levels of public goods in a direct democracy.

Lindahl Pricing & Preference Revelation

Lindahl pricing results in a unanimous decision to provide an efficient quantity of public goods, but relies on honest revelation of preferences.

Majority Voting Challenges

Majority voting may lead to inconsistent decisions regarding public goods if some people's preferences are not single-peaked.

Logrolling: Trading Votes

Logrolling allows voters to express the intensity of their preferences by trading votes. However, minority gains may come at the expense... Continue reading "Political Economy: Government Decisions & Public Policy" »

Understanding Macronutrients and DRIs

Macronutrients

Macronutrients, which include protein, carbohydrates, and fat, are required by the body in relatively large amounts (hence "macro"). All three provide energy. Fiber is a type of carbohydrate.

Dietary Reference Intakes (DRIs)

The Acceptable Macronutrient Distribution Ranges (AMDRs) are part of the DRIs. They recommend a balance of macronutrients, expressed as a percentage of total dietary energy, that is associated with:

• Maintenance of a healthy weight
• The lowest risk for chronic disease
• The lowest risk for nutrient deficiencies

Consuming macronutrients below or above these ranges increases the risk of chronic disease. Notably, the age group with the highest AMDR for fat is children aged 1-3 years.... Continue reading "Macronutrient Breakdown: Carbohydrates, Sugars, and Fats" »

The Open Web Application Security Project (OWASP)

The Open Web Application Security Project (OWASP) is a non-profit foundation providing guidance on developing, purchasing, and maintaining trustworthy and secure software applications. It's an online community that produces free articles, methodologies, documentation, tools, and technologies in IoT, system software, and web application security.

Key Aspects of OWASP

• Origin: Started by Mark Curphey on September 9, 2001.
• Leadership: Jeff Williams was the volunteer Chair from late 2003 to September 2011. As of 2015, Matt Konda chaired the Board. Bill Corry was an OWASP Foundation Global Board of Directors officer in February 2023.
• Goal: To provide tools, resources, and guidelines to developers, businesses,

The aim is to create a single market in the EU where products can move as if there were no borders. This means NO:

• Customs duties between countries
• Hidden charges (CHEEs)
• National rules that make trade harder (MEEs)
• Taxes that discriminate against foreign products

Exceptions are only allowed when they are justified (e.g., health, safety, morality, etc.) and pass the proportionality test.

Prohibition of Tariffs and Charges (Art. 30 TFEU)

Prohibited between Member States:

• Customs duties (aranceles): A monetary charge for crossing a border. Always prohibited, even if small or non-protectionist.
• CHEEs (Charges Having Equivalent Effect): An impuesto disfrazado de otra cosa (tax disguised as something else). A unilateral charge on imports/exports not linked

Constructing Recombinant DNA

The following steps are involved in the construction of recombinant DNA:

1. Preparation of the Gene: Gene cloning in bacteria is achieved by cleaving DNA with enzymes called restriction endonucleases, which create small fragments. Each fragment often has a "sticky end." Since eukaryotic genes contain introns that are not processed in bacteria, the DNA for cloning is usually obtained from relevant mRNA through the process of reverse transcription. In cases where nucleotide or amino acid sequences are known, synthetic DNA may also be produced.
2. Insertion into a Vector: The vector is a vehicle, such as a plasmid or bacteriophage, used to transfer DNA into a host cell. The vector is cut with the same restriction endonuclease