OpenLLM-France/wikimedia huggingface dataset:
# Practical Applications of Waves: Electromagnetic Waves

In physics, wave-particle duality holds that light and matter simultaneously exhibit properties of waves and of particles. This concept is a consequence of quantum mechanics.
In 1905, Einstein reconciled Huygens' view with that of Newton. He explained the photoelectric effect (an effect in which light did not seem to act as a wave) by postulating the existence of photons, quanta of energy with particulate qualities. Einstein postulated that the frequency of light, $f$, is related to the energy, $E$, of its photons:
* ${\begin{matrix}E=hf\end{matrix}}$
* (2.3)
where $h$ is Planck's constant ($6.626\times 10^{-34}Js$).
In 1924, De Broglie claimed that all matter has a wave-like nature. He related wavelength $\lambda$ and momentum p:
* ${\begin{matrix}\lambda ={\frac {h}{p}}\end{matrix}}$
* (2.4)
This is a generalization of Einstein's equation above, since the momentum of a photon is given by
* ${\begin{matrix}p={\frac {E}{c}},\end{matrix}}$
* (2.5)
where $c$ is the speed of light in vacuum, and $f={\frac {c}{\lambda }}$.
De Broglie's formula was confirmed three years later by guiding a beam of electrons (which have rest mass) through a crystalline grid and observing the predicted interference patterns. Similar experiments have since been conducted with neutrons and protons. Authors of similar recent experiments with atoms and molecules claim that these larger particles also act like waves. This is still a controversial subject because these experimenters have assumed arguments of wave-particle duality and have assumed the validity of de Broglie's equation in their argument.
The Planck constant h is extremely small and that explains why we don't perceive a wave-like quality of everyday objects: their wavelengths are exceedingly small. The fact that matter can have very short wavelengths is exploited in electron microscopy.
In quantum mechanics, the wave-particle duality is explained as follows: every system and particle is described by state functions which encode the probability distributions of all measurable variables. The position of the particle is one such variable. Before an observation is made the position of the particle is described in terms of probability waves which can interfere with each other.
# Two Types of Waves

We agreed that a wave was a moving set of peaks and troughs and we used water as an example. Moving peaks and troughs, with all the characteristics we described, in any medium constitute a wave. It is possible to have waves where the peaks and troughs are perpendicular to the direction of motion, like in the case of water waves. These waves are called transverse waves.
There are two additional types of waves. The first is called longitudinal waves and have the peaks and troughs in the same direction as the wave is moving. The question is how do we construct such a wave?
An example of a longitudinal wave is pressure waves moving through a gas. The peaks in this wave are places where the pressure reaches a peak and the troughs are places where the pressure is a minimum.
In the picture below we show the random placement of the gas molecules in a tube. The piston at the end moves into the tube with a repetitive motion. Before the first piston stroke the pressure is the same throughout the tube.
When the piston moves in it compresses the gas molecules together at the end of the tube. If the piston stopped moving the gas molecules would all bang into each other and the pressure would increase in the tube.
When the piston moves out again before the molecules have time to bang around then the increase in pressure moves down the tube like a pulse (single peak and trough, a single wave cycle).
As this repeats we get waves of increased and decreased pressure moving down the tubes. We can describe these pulses of increased pressure (peaks in the pressure) and decreased pressure (troughs of pressure) by a sine or cosine graph.
The second additional type of wave is the torsional wave. The peaks and troughs rotate around the direction of motion. In simpler terms, a "twisting motion" is transmitted through the medium. Of the two wave types, this is the hardest one to describe and visualize.
There are a number of examples of each type of wave. Not all can be seen with the naked eye but all can be detected.
# Important Equations and Quantities

Frequency:
* ${\begin{matrix}f={\frac {1}{T}}.\end{matrix}}$
* (2.6)
Speed:
${\begin{matrix}v&=&f\lambda \\&=&{\frac {\lambda }{T}}\end{matrix}}$
Table 2.1: Units used in Waves :
| Quantity | Symbol | S.I. Units | S.I. Units | S.I. Units | Direction |
| Amplitude | A | m | m | m | -- |
| Period | T | s | s | s | -- |
| Wavelength | $\lambda$ | m | m | m | -- |
| Frequency | f | Hz or s$^{−1}$ | Hz or s$^{−1}$ | Hz or s$^{−1}$ | -- |
| Speed | v | m.s$^{−1}$ | m.s$^{−1}$ | m.s$^{−1}$ | -- |
# HKDSE Geography/M6/Soil

In tropical rainforests, because of the high temperature and rainfall, infiltration is rapid, and thus chemical weathering of the bedrock occurs rapidly. For example, carbon dioxide, sulphur dioxide and humic acid are dissolved in rainwater to form solutions which wear the rock. Organic acids (from living plants) and humic acids (from dead plants) also wear the rock. As the bedrock is weathered, they turn into regolith and then soil. This process is covered in E1.
The soil characteristics of tropical rainforests are summed up in this table:
| Aspect | Characteristic | Reason |
| With reference to organisms and nutrients... |||
| Level of organic matter (thickness of litter) | Small | Fast decomposition rate |
| Decomposition rate | Rapid, creates a thin layer of humus | Rapid nutrient uptake |
| Nutrient uptake rate | Rapid | Luxuriant vegetation |
| Soil fertility (soil nutrient content) | Low, soil nutrient concentrated on topsoil | Rapid nutrient uptake |
| Leaching | Rapid, washes away potassium, sodium, magnesium and calcium, as well as silicon | Heavy rainfall |
| With reference to weathering... |||
| Chemical weathering rate | Rapid | High temperature and rainfall |
| Soil type | Reddish, yellowish and brownish oxisol | Oxidation occurs as the soil is wet and exposed to the air. Iron and aluminium oxides are thus formed by oxidation. |
| Soil particle size | Fine and clayey | Rapid chemical weathering |
| Soil permeability and soil porosity | Low and low | Fine and clayey soils |
| Water retention capability | High | Fine and clayey soils |
| Soil profile | Thick, up to 30 m, supports vegetation | Rapid chemical weathering |
| Soil horizons | Mature, merging boundaries | Rapid chemical weathering |
| Soil pH | Slightly acidic, around 6 | Presence of iron oxides |
| Notes on Soil Terminology |||
| Soil terminology not yet introduced in previous chapters are explained here: ↑ Litter refers to dead organic matter on the forest floor, mainly dead leaves and branches. ↑ The process by which rainfall washes away mineral nutrients in soil. ↑ The image on the right is a soil profile. ↑ The soil 'layers' on the right are soil horizons. |||
# HKDSE Geography/M6/Agriculture
## Shifting Cultivation

It is a type subsistence farming. It has the following characteristics:
* Polyculture: A wide variety of crops is grown to ensure good nutrition, maintain stable food supply and preserve soil nutrients
* Non-sedentary: They shift from place to place.
* Low-technology: They rely on simple tools.
* Low productivity.
To open up a new piece of rainforest, indigenous people first use the method of slash-and-burn. The trees' ashes serve as fertilisers to improve soil fertility. After growing crops for a while, the land will become infertile and unsuitable for agriculture. They will then abandon the piece of land so that vegetation can regenerate during the fallowing period. Later, they will return to the original piece of land for farming after 50-100 years.
Shifting cultivation used to be sustainable when the fallowing period was sufficiently long and allowed time for the soil to regenerate. Yet with the rise in population and decrease in forest size, the fallowing period has been greatly shortened, rendering it unsustainable:
# HKDSE Geography/M6/Natural Resource Extraction

Various forms of natural resource extraction are performed in the tropical rainforests.

## Hunting and Gathering

Hunting and gathering refers to the collection of food resources, such as wild animals, fish, and plant parts (such as shoots and roots), mainly for consumption.
* Is it agriculture?
* Hunting and gathering is not a form of agriculture as there is no growing or grazing involved.

### Impacts

* Hunting and gathering is originally a sustainable practice as the indigenous tribes of the tropical rainforests are scarce in number.
* However, growing tribe populations have raised the level of destruction dealt by hunting and gathering, so their food sources are starting to thin out.
* Some tribesmen and outsiders have begun to hunt endangered species such as the rhinoceros for commercial gain, threatening the biodiversity of the tropical rainforest in so doing.

## Hydro-Electric Power

Hydro-electric power can be extracted from rivers in tropical rainforests.

### Impacts

* Aside from maintaining a steady supply of power, HEP has several other advantages: It facilitates navigation, prevents floods downstream, and so on.
* However, damming destroys the river's local ecosystem and the habitats of the aquatic life which originally inhabited it.
* The Itaipu Dam
* The Itaipu Dam is a joint venture between Brazil and Paraguay. Its power generated exceeds even the Sanxia dam. It serves 75% of Paraguay's energy, as well as 17% of Brazil's. (Source)

## Commercial Logging/Lumbering

Logging has always occurred in tropical rainforests as small amounts of wood are used as firewood for heating and fuelwood for power generation. They may also be burnt into charcoal and sold in local markets. However, in recent years, corporations have massively increased the scale of logging to produce expensive exotic woods in the tropical rainforests. The wood is made into various products, including paper, furniture and construction materials. Teak, rosewood and mahogany are examples of precious rainforest woods.

### Impacts

The impacts of commercial logging will be discussed in the next chapter.

## Mining

Two types of mining are commonly practised in tropical rainforests:
* Alluvial mining refers to the extraction of minerals from alluvial deposits in rivers.
* Opencast mining refers to the extraction of minerals in a pit.

### Impacts

* Alluvial mining pollutes rivers by disposing slag.
* Opencast mining destroys a large area of the tropical rainforest as all the vegetation and the topsoil of the mining site is removed.
* On-site refining of minerals releases poisons such as mercury and cyanide into the rainforest soil, posing a public health risk.
* Mining disturbs the lives of tribespeople. Clashes between indigenous tribes and miners are frequent.
* Impacts of mining on Brazil
* 90% of the catch at Tapajós River have been found to be poisoned by mercury.
* The Brazilian military had to forcefully eject gold miners from the forest as they were disturbing the local tribes.
* 6100 sq. km of forest land is cleared every year in Carajas Mineral Province.
* (Source)
# HKDSE Geography/M6

HKDSE Geography
* Objectives
* Living with our physical environment
** M1: Opportunities and Risks
** M2a: Rivers
** M2b: Coasts
* Facing changes in the human environment
** M3: Industry
** M4: Sustainable City
development mutually exclusive?
* Confronting global challenges
** M5: Famines and Agriculture
** M6: Tropical Rainforests
** M7: Global Warming
* Elective modules
** E1: Dynamic Earth
** E2: Climate
** E3: Transport
** E4: Zhujiang Delta

## Guiding Questions

* What is happening to tropical rainforests?
* What would a tropical rainforest look like before large-scale deforestation? Why does it look like that?
* What is the evidence for saying that tropical rainforest is a complex but fragile ecosystem?
* Why are tropical rainforests all over the world disappearing at a faster rate in recent times?
* What is the impact of large-scale deforestation in tropical rainforest regions?
* How will it affect the local and global environments?
* How will it affect the indigenous people?
* How will it affect our lives in Hong Kong?
* How can tropical rainforests be prevented from disappearing?
* Will the protection of tropical rainforests hinder the development of the local economy?
* Can we strike a balance?
* What price has to be paid to protect tropical rainforests, and who should pay?
* Evaluate the effectiveness of the measures
# HKDSE Geography/M5/The Sahel

Characteristics:
* Commercial farming
* Irrigation farming
* Arable farming
* High-technology farming
* Capital-intensive farming
* Extensive farming
* Monoculture
* Low labour input
# HKDSE Geography/M5/Types of Agriculture

There are several ways to classify agriculture:
| Output type | Arable farming | Crop cultivation only |
| Output type | Pastoral farming | Livestock rearing only |
| Output type | Mixed farming | Both crop cultivation and livestock rearing |
| Output use | Subsistence farming | Farm outputs are for own consumption |
| Output use | Commercial farming | Farm outputs are for sale in the market |
| Input-land ratio | Intensive farming | High input-land ratio |
| Input-land ratio | Extensive farming | Low input-land ratio |
| Input proportion | Labour-intensive farming | Labour is the most important input |
| Input proportion | Capital-intensive farming | Capital and technology are the most important inputs |
| Permanance of site | Sedentary farming | The farmland or pastureland is permanent |
| Permanance of site | Non-sedentary farming | The farmland or pastureland is temporary and constantly moves |
| Technology level | High-technology farming | High technology and a lot of energy is used |
| Technology level | Low-technology farming | Low technology and little energy is used |
| Output variety | Monoculture | Only one type of crop is grown on the land |
| Output variety | Polyculture | Multiple crop types are grown on the land |
| Output variety | Specialised farming | A farm specialises in certain types of crops |
| Water use | Irrigation farming | Farming that requires irrigation of crops |
| Water use | Rain-fed farming | Farming that relies mainly on rainfall as a water source |

## Important Examples

* Wheat-sheep farming in Australia is an example of extensive mixed farming.
* Greenhouse cultivation is an example of intensive commercial farming.
* Nomadic herding and shifting cultivation (more about that in M7) are examples of non-sedentary farming.

## Important Relationships

Also note these relationships:
* Arable farming is preferred in areas with favourable physical inputs like high rainfall and temperature. Irrigation farming and pastoral farming are practiced in areas with more severe conditions.
* Areas with large and low-cost labour supply generally practice intensive farming.
* Areas with favourable cultural factors are more likely to practice commercial farming. Areas far away from markets with limited technology and capital tend to practice subsistence farming.
# HKDSE Geography/M6/Climate

Most tropical rainforests have tropical maritime climate or equatorial climate. The properties are discussed below.
In this page, we discuss only the general climate of rainforests. Rainforests have a set of distinct microclimates within them, and we will discuss this later.

## Insolation and Temperature

Tropical rainforests have the following climatic characteristics:
* Intense insolation, at least 10 hours a day
** Because they are located in equatorial regions / large angle of the sun due to low latitude
* High annual mean temperature: 26°C
** Because they are located in equatorial regions / large angle of the sun due to low latitude
* Small diurnal range of temperature - 7-8°C
** Because the dense cloud cover produces a blanket effect
* Small annual range of temperature - 2-4°C
** Because of the small annual range of insolation in equatorial areas
*** Result: Lack of seasonality - no distinct winter / cold season
As a result of high insolation, evapotranspiration rate is also high.
Detailed explanations for the above patterns can be found in M7 and E2.

## Rainfall

Tropical rainforests have the following rainfall patterns:
* High annual rainfall, above 2000 mm, and exceeds potential evapo-transpiration
* Lack of seasonal patterns in rainfall / no obvious dry season, rainfall is evenly distributed throughout the year
** Result: Lack of seasonality - no dry season
** Exception: In tropical monsoon regions, there is more rainfall in summer.
Rain usually occurs as showers or thunderstorms. They are in the form of convection rain, and usually rain in afternoon (where the land receives the most intense sunlight).

## Relative Humidity

Tropical rainforests have high relative humidity. We will look at exact numbers in the microclimate section.

## Winds

Wind is generally weak in tropical rainforests because the friction of the air is large, due to the dense vegetation cover.
* Exception: In monsoon areas, onshore and offshore monsoon winds are frequent.
# HKDSE Geography/M6/Settlement

Many rainforest countries establish settlements in rainforests to ease population pressure in more densely-populated urban areas. An example is Indonesian transmigration. The tree canopy disappears to make way for urban expansion.
Many countries build transport networks in rainforests to improve accessibility. This encourages economic growth and investment in the area. This is dangerous to the rainforest because by dividing the rainforest into fragmented portions, the ecological integrity of it is destroyed. Roads also give access to corporations and locals who may exploit rainforest resources thanks to the increase in accessibility.
# HKDSE Geography/M6/Tropical Rainforests
## The Tropical Rainforest Biome

Tropical rainforests are a biome. A biome is an area that has similar climatic characteristics and thus gives rise to similar vegetation.
However, a place located in the tropical rainforest biome does not necessarily have tropical rainforests. This is because the area may not have been matured enough, or may have been damaged by natural disasters or human activities.
Biomes are as follows:
In this section, we will study the tropical rainforest as a biome, and look at the general characteristics of tropical rainforest. In the next section we shall study it as an ecosystem.

## Distrubution

Tropical rainforests are distributed in three major areas:
* East Africa. Most of the tropical rainforests are found at the Congo Basin.
* South America. Most of the tropical rainforests are found at the Amazon Basin.
* Southeast Asia.
The rest are scattered around the globe.
This diagram shows tropical rainforests in dark green (areas in light green are temperate forests):
Note how the regions here are smaller than the tropical rainforest biome regions we saw above.
# High School Probability and Statistics/Normal Distribution

* Standard Normal Probability Distribution
* Density Curve of the Normal Distribution
* Applications of the Normal Distribution
← Geometric Probability Distribution · Standard Normal Probability Distribution →
# High School Probability and Statistics/Planning and Conducting an Experiment or Study

* Surveys and Sampling
* Experimental Design
← Applications of the Normal Distribution · Surveys and Sampling →
# High School Probability and Statistics/The Basics

* Independent Events
* Conditional Probability
* Discrete Random Variables
* Standard Distributions
* Shape, Center, and Spread of a Normal Distribution
* Measures of Central Tendency
# High School Probability and Statistics/Visualizations of Data

* Histograms and Frequency Distributions
* Common Graphs and Data Plots
* Box-and-Whisker Plots
← Measures of Spread · Histograms and Frequency Distributions →
# High School Probability and Statistics/Probability

* Events, Sample Spaces, and Probability
* Compound Events
* The Complement of an Event
* Conditional Probability
* Additive and Multiplicative Rules
* Basic Counting Rules
← Box-and-Whisker Plots · Events, Sample Spaces, and Probability →
# High School Probability and Statistics/Regression and Correlation

* Scatterplots and Linear Correlation
* Least-Squares Regression
* Inferences about Regression
* Multiple Regression
← Testing a Hypothesis for Samples · Scatterplots and Linear Correlation →
# High School Probability and Statistics/Sampling Distributions and Estimations

* Sampling Distributions
* The z-Score and the Central Limit Theorem
* Binomial Distribution and Binomial Expressions
* Confidence Intervals
* Sums and Differences of Independent Random Variables
* Student's t-Distribution
← Experimental Design · Sampling Distributions →
# High School Trigonometry
## Table of Contents

    Authors
* Trigonometry and Right Angles
* Circular Functions
* Trigonometric Identities
* Inverse Functions and Trigonometric Equations
* Triangles and Vectors
* Polar Equations
* Complex Numbers

## Resources

* PDF Version (info)
* Common Errors (info)
* Teacher's Guide (info)
This material was adapted from the original CK-12 book that can be found here. This work is licensed under the Creative Commons Attribution-Share Alike 3.0 United States License
# High School Probability and Statistics/Non-Parametric Statistics

* Introduction to Non-Parametric Statistics
* Rank Sum Test and Rank Correlation
* Kruskal-Wallis Test and the Runs Test
← Two-Way ANOVA Test · Introduction to Non-Parametric Statistics →
# Handbook of Management Scales/Gender equality
## Gender equality (CR = 0.75)
### Description

Hofstede's five cultural factors are reconceptualized as ten personal cultural orientations: independence, interdependence, power, social inequality, masculinity, gender equality, risk aversion, ambiguity intolerance, tradition, and prudence. A new 40-item scale is developed to measure these personal cultural orientations. Much effort has been invested in ensuring validity, reliability, and cross-cultural measurement equivalence of the new scale.

### Definition

Gender equality is the extent to which people perceive men and women as equal in terms of social roles, capabilities, rights, and responsibilities.

### Items

* It is ok for men to be emotional sometimes. (0.78)
* Men do not have to be the sole bread winner in a family. (0.75)
* Men can be as caring as women. (0.73)
* Women can be as ambitious as men. (0.72)

### Source

* Sharma (2010): Measuring Personal Cultural Orientations: Scale Development and Validation. Journal of the Academy of Marketing Science, Vol. 38, No. 6, pp. 787–806
# Handbook of Management Scales/General outsourcing
## General outsourcing (alpha = 0.85)
### Items

* My company engages frequently in outsourcing activities.
* My company easily outsources different activities.
* Top management has a positive attitude towards the outsourcing of activities.

### Source

* Verwaal et al. (2009): Value Creation and Value Claiming in Strategic Outsourcing Decisions: A Resource Contingency Perspective. Journal of Management, Vol. 35, No. 2, pp. 420-444.

### Related Scales

* Outsourcing intent
# Handbook of Management Scales/Group esteem
## Group esteem
### Description

Group esteem was measured with four items taken from Ellemers, Kortekaas & Ouwerkerk (1999).

### Items

* I think my group has little to be proud of (reverse-coded).
* I feel good about my group.
* I have little respect for my group.
* I would rather not tell that I belong to this group.

### Source

* Zhang et al. (2014): Relational Versus Collective Identification Within Workgroups: Conceptualization, Measurement Development, and Nomological Network Building. Journal of Management, Vol. 40, No. 6, pp. 1700–1731

### Comments

It seems that the third and fourth items are reverse-coded, too.