The Intricacies of Mud Crack Formation

Patterns found in nature are most often astoundingly complex while also being elegant and aesthetically pleasing. Snowflakes for example consist of extremely delicate, symmetric structures of frozen ice and are always different from each other. Yet these infinite patterns are influenced by only two main controlling factors, temperature and humidity. A  more obvious example of patterns in nature are mud cracks. Although they are not as delicate and complex as snowflakes, they also exhibit some patterns that are interesting to observe. What follows are some facts I gathered from a small study about mud cracks and some  photographs taken during my training period at the Aruwakkalu limestone mine.

Mud cracks are formed quite obviously, when  mud dries up. So the main factor controlling mud crack formation is moisture content. Unlike in glass and many other materials, cracks in mud do not originate at single point and then propagate. If the rate of drying is uniform across a surface of a layer of mud, cracks will start appearing simultaneously across the surface. Mud starts to dry from the exposed surface. So when the moisture content of the surface layer starts to drop, the mud particles come close to each other as the space occupied by water is emptied. This results in the contraction of the surface layer. This causes stresses to build up on the surface layer and ultimately results in the formation of cracks. First the main cracks divide the exposed surface into a series of "islands" then, secondary cracks may occur within these islands.

primary and secondary cracks

Since drying starts from the surface, the bottom layers still contain some water and still remain expanded. Therefore the width of the crack is lesser in bottom layers, like a cut made from the surface. As the moisture content further reduces and the bottom layers also dry up, the crack propagates to the bottom layers and the gap widens. 

If the moisture content in a single layer of mud differs at the top of the layer and the bottom, the amount of contraction also differs. The top portion will contract more than the bottom portion. This will result in an upward curving of the layer like in a bimetallic strip. If the wet mud has been standing for a long period, stratification of different layers will take place. Stratified layers can be observed when a portion of the cracked mud is viewed sideways. Stratified layers can have a bigger difference in contraction rates, and if the layers are strongly adhered to each other, a more prominent curving of the layers will be seen.

stratification and upward curving of layers

If the layers are not strongly adhered, instead of curving upwards, the layers will separately contract producing a step like effect of the cracks. 

step like contraction

Although the mechanics of mud crack formation has no immediate practical application, crack formation in other substances is studied extensively. Crack formation on thin surface layers in electronic circuits can lead to peeling off of printed components and cause problems. Therefore a lot of effort is put into preventing the formation of such cracks. A very fine network of small cracks can be seen on the surface of old paintings on close inspection. This fine set of cracks is called "craquelure".  The characteristics of these cracks depend on the type of pigments, oil and also the ambient conditions at the time of painting. For this reason, these cracks are used to authenticate old paintings. 

Creating a 3D Terrain Model using Surfer

A three dimensional model of a particular land feature can be very useful for visualization. A 3D model which can be manipulated in a digital environment is even more useful, especially if volume calculations need to be performed. A good software package for this purpose is, "Surfer". It has a relatively simple user interface and is easy to learn.

Essentially what Surfer requires to create a 3D surface model is a set of spot heights along with their northing and easting coordinates. The data can be imported into Surfer by many ways, of which using a MS Excel file or an ASCII text file are simplest. The software will interpolate the data points and create a surface. The algorithm used for interpolation can be changed according to the requirement.

Obtaining spot heights of the area can be done by performing a level survey. If high accuracy is not required, a quick and easy method of obtaining spot heights is to overlay a grid with known coordinates over a topo sheet with contours. Using the contours, the heights of the vertices of the grid can be determined. Since the northing and easting of the grid are also known, it can be fed into Surfer via MS Excel Another method of creating a 3D model using Surfer is to directly import a DEM (Digital Elevation Model) into the software. DEMs can be downloaded from the USGS website.

A simple volume calculation based on spot heights obtained by the gridding method is illustrated below.

First, the grid was drawn over the contour map in the AutoCAD environment. In this example, the contour interval is 2 m, and the grid spacing has been selected as 3 m.  

The spot heights were found by using the contours closest to the vertices of the grid and the data was entered as x, y and z coordinates into an MS Excel sheet.

Using Surfer, the excel sheet was input and a grid file was created. (Grid>Data). The gridding method used for this example is "Kriging". Other methods can be used depending on the requirement.

A 3D surface was created using the grid file previously created.

This 3D surface can be used for volume calculations as well. For example, Consider that the trough indicated in the above terrain model needs to be filled with water, up to the 8m contour level and it is required to calculate the volume of water required.

This means we need to calculate the volume between the modeled surface and the plane z=8. To do this, the volume calculation dialog box was opened (grid>volume..) and the upper surface was given as z=8 and for the lower surface, the grid file was selected. The calculated positive volume indicates the volume of water required to fill the trough. In this example the calculated volume is, 696.73 cubic meters. 

Optimization of production of a Mine

The main objective of a mine is to extract a mineral deposit in an economical manner and to maintain a continuous output. In order to do this, the operations performed in and out of the mine must complement each other. While intensive planing and monitoring of all unit activities is required to achieve this, the following steps will help to optimize production and reduce cost thereby increasing efficiency.

Calculate and plan production targets and compare with actual production.

In order to determine whether a mine is operating efficiently, first targets should be established. To do this, drilling and blasting cycles and hauling capabilities can be factored in initial calculations. To set more specific production targets, modelling software can be used. The important thing is to compare the actual data with these targets and to take corrective action when the production does not meet the target.

Maintain a buffer stock of material

While in normal conditions, production can be carried out without interruption, due to various reasons the rate of production can decrease or in worst cases, halt altogether. Interruptions due to bad whether in open pit mines is a good example for this. To cope up with these delays it is essential to have a stockpile of material ready to be dispatched. This stockpile will act as a buffer until production resumes and the mine will produce the expected output throughout.

Proactive maintenance of machinery

Several approaches can be taken in the case of maintenance of mine machinery. in order to minimize losses due to downtime and faulty operation it is best to employ a preventive or proactive maintenance strategy. When doing maintenance work, it is vital to get operator feedback as it will help to diagnose problems better. Another very important fact to be considered when acquiring a new fleet of machines to a mine is to obtain all the machines of one particular brand. This ensures inter machine compatibility. It also saves time and resources in ordering, acquiring and using of spare parts.

Streamline work and physical movement

A mine is a place of continuous movement. To increase efficiency, these movements must be streamlined and effective. This means that access paths and haulage ways must be as short as possible with sufficient room for maneuvering. The mine layout itself must be orderly and separate operations should not disturb each other(except in unavoidable circumstances such as blasting). These reduce cycle times of the mine and increase production.

Safety

This is a factor overlooked in most mines. However safety plays a major role in the overall efficiency of the mine. A mine with a lot of accidents suffers a lot of downtime and it will reduce production. Proper safety procedures will enable continuous operation and will also enhance working conditions, both of which will ultimately result in an increase in efficiency.

Global Tidal Variations Explained

Tides are periodic variations of the ocean surface caused by the gravitational attraction of the moon and the sun. On a fundamental level, tides can also be considered as waves. Since these tidal waves have extremely long wavelengths, they are essentially shallow water waves(Shallow water waves are waves which travel over depths lower than 1/20th their wavelength). This means that the speed of the tidal wave is proportional to the depth. The depth of the ocean basin, the time of year and month, latitude and earth's rotation affect the type and magnitude of tides. While the exact relationship between all these variables can be somewhat complex, certain scientific theories and models help simplify and explain the behavior of tides.

Depending on the occurrence of high and low tides, tidal patterns are classified into three types. These are,
1. Diurnal tides
2. Semi-diurnal tides
3. Mixed Tides.
If the tidal wave shows 1 crest and 1 trough within a period of 1 lunar day(24hrs and 50mts), then it is called a diurnal tide. If it shows two crests and two troughs or vice versa in one lunar day, it is called a semi-diurnal tide. Mixed tides are a mixture of these two, often with significantly different amplitudes.

While tidal variations can be attributed to the gravitational attraction of both the sun and moon, the effect of the moon is significantly larger. "The Equilibrium theory of tides" attempts to explain these variations with the following assumptions.
-the ocean is indefinitely deep
-no land masses are present
-no inertial forces
With these assumptions, the key tide generating forces are, gravitation and centripetal force. These two forces act differently on different locations on the earth. While the gravitational force directs to the center of the moon, the centripetal forces at different locations are parallel to each other. This is because, centripetal force is the force that keeps an object in circular orbit, and the different locations have their own circular orbits parallel to each other.

Source : Trujillo,Alan P.Essentials of oceanography / Al Trujillo, Harold Thurman. 10th ed.

The gravitational attraction provides the required centripetal force to keep the earth in orbit. However, the gravitational attraction and the required centripetal force are unequal at different locations on the earth. These two are equal only at the center of the earth. The difference between these two forces creates a resultant force which acts as shown in the diagram. It is this resultant force that is responsible for the generation of tides. This is also why, tidal bulges appear on both sides of the planet, because the resultant forces at the two sides of the earth are oppositely oriented. 

The orbital plane of the moon is inclined by approximately 28.5 degrees to the earth's axis of rotation. This causes the tidal bulges also to orient as shown below. The earth rotates through these tidal bulges. This explains the occurrence of diurnal and semi-diurnal tidal patterns explained above. By inspecting the diagram below it can be seen that high latitude locations receive diurnal tides, equatorial regions receive semi-diurnal tides and mid latitude locations receive mixed tides. 

Source : Trujillo,Alan P.Essentials of oceanography / Al Trujillo, Harold Thurman. 10th ed.

This shows how the equilibrium theory explains the occurrence of the diurnal and semi-diurnal tides. This means that, tidal patterns on earth should be related to latitude. According to the above diagram it is also seen that tidal heights should also vary with latitude, with the highest tidal heights in mid latitude regions. However, the following tide map of the world shows that no such connection between tidal characteristics and latitude can be observed. This is where the equilibrium theory of tides fails.

-world tidal patterns- Source : Invitation to oceanography / Paul R. Pinet. — 5th ed.

The equilibrium theory of tides does not take into account the depth variations of the ocean basins. It also neglects the effect of the earth's rotation. To overcome these issues, another theory, "The Dynamic Theory of Tides" was proposed. Proposed in the 18th century by Pierre Simon Laplace, it attempts to explain tidal variations with the Coriolis Force.

To illustrate this theory, consider a large rectangular ocean basin in the northern hemisphere. when the water level rises in the upper portion of the basin due to the tidal action, the Coriolis force deflects the mass of travelling water towards the right. this causes the water to build up in the upper right corner of the basin. The resulting pressure gradient causes the water to flow downwards, but is again deflected to the right by the Coriolis force. This cycle continues, and it results in a counterclockwise oscillation of the water mass. The nodal point where the water does not oscillate is known as an "Amphidromic Point."

Source : Invitation to oceanography / Paul R. Pinet. — 5th ed

If the ocean basin is situated in the southern hemisphere, the Coriolis force will deflect the water towards the left side, and the resulting oscillation would be clockwise. While ocean basins found on earth are not ideal basins like the above explained, several Amphidromic Points can be identified in the earth's oceans through tidal action. This amphidromic system of tides better explains the tidal variations depicted in the above tidal map. Since the amphidromic system is an oscillatory system, tides can undergo resonance. If the natural period of the ocean basin equals the period of the tides, tidal resonance will occur creating a massive tidal wave. An example of this is the Bay of Fundy where tidal ranges of over 17metres have been observed.

Global Amphidromic Points - Source : Invitation to oceanography / Paul R. Pinet. — 5th ed

The depth of ocean basins also affect tidal heights. As explained above, tides being shallow water waves, have speeds that are proportional to depth. This means that a lower depth would cause the tidal wave to slow down, and due to the conservation of energy, the amplitude of the wave would increase, thus creating a higher tide. Taking all these factors into consideration, tides can be accurately modeled and predicted.

This understanding of tidal action opens up means of using it as an energy source. In places where a high tide variation is present, tidal energy can be tapped into by building dams to trap the incoming tidal flood current, and then channeling them through turbines like in a hydro-power plant. Power plants of this type are already in operation around the world, an exmaple is the La Rance tidal power plant at St. Malo, France. Tidal power plants do not pose a significant threat to the environment and are therefore are a good alternate source of renewable energy.

eZ Cash - Behind the Veil

An interesting point came up in our last Marketing Management lecture-the true motive of Dialog eZ Cash. Whether it is merely a convenient mobile payment method or a tool to acquire information about customer behavior was discussed. In this information age, information about the spending patterns of customers is potentially worth millions to organizations. This type of information can be used for targeted advertising. It can bring massive profits to an organization by helping them to better understand  their customers and to cater specifically according to their requirements.

Although Dialog eZ cash is not extremely popular, it's certainly catching on. Despite some concerns about delays and problems in withdrawing cash from merchants, it is undoubtedly a convenient mobile payment method. While the newer payment methods via NFC are quicker and more straightforward, at present only a handful of smartphones used in Sri Lanka are equipped with NFC. In this regard eZ cash scores by being accessible to the masses. This also broadens their source of customer information. Such information is valuable only if it's extensive. Whenever a customer uses eZ cash, information about the transaction amount, place and type gets recorded at the company servers. Users of eZ cash agree to their information being used, stored, analyzed or transferred by Dialog without the consent of the user, when subscribing for the service.

users agree to their information being stored,analyzed and transferred. source: http://www.dialog.lk/content/uploads/pdfs/tc/ez-cash-tc-eng.pdf

Collecting customer information is not necessarily a bad thing. Most of us are familiar with the personalized search results and news feeds in Google and Facebook which  utilize search history, browsing patterns and location to serve personalized information. While some people argue that this is an invasion of privacy, it is often helpful to most of us. Personalized search results bring relevant information quickly. The data collected by eZ cash also could be put into good use like this, to serve customers better and to personalize the telecommunication giant's service.

The flip side to this story is the consequences if this data falls into the wrong hands. It can be used for spamming or in the worst case, for fraud and theft. A security breach or something similar could turn out to be a threat to customers. Dialog would surely be aware of this and have taken necessary measures to avoid such a situation. Still, some people don't feel comfortable about their information being used in this way. But complete anonymity in today's world is impossible to achieve. The best is to be aware and mindful of how your information is used and shared by the services that you use.

Man of Steel Flies to Sri Lanka

The highly anticipated Superman reboot will hopefully be screened at Savoy 3D from the 26th of June 2013. The movie is listed under the upcoming movies section with the above release date, and a countdown is on display on the home page of the EAP movies website. being only 14 days after the world release date fans won't have to wait too long. However there have been occasions in the past where movies that were shown on countdown never actually made it to the theater. Hopefully it does not happen this time.

Building upon the success of the Dark Knight trilogy, this reboot differs from the previous Superman movies while having some similarities with the Batman movies. It has a more realistic take on the superhero and from its trailer it is evident that the "S" on his chest does not even mean "Super"! :) Fans of the DC universe who want to see a Justice League movie-a superhero ensemble movie like the Avengers or even just a Superman Batman team up movie will be delighted to see that Man of Steel is set in the same universe and timeline as Batman. According to the director of the movie, There is a scene in the movie where the villain destroys a satellite with the Wayne enterprises logo on it. Wayne enterprises is owned by Bruce Wayne a.k.a Batman and therefore a ensemble movie cannot be written off. So keep your eyes open :)

image from : http://manofsteel.warnerbros.com

3D experience at MC Platinum Ruined!

There have been several complaints about the active shutter glasses issued at MC Platinum 3D. The most common issues are, one lens being completely blacked out, or simply that the glasses don't produce the expected "3D effect". These problems arise because the glasses are of the active shutter type, and are required to be powered by batteries. I mentioned about this problem in a previous post of mine, but I didn't think it will occur so soon until I saw it for myself. If you find out that your pair of glasses is not working once the movie starts, you will probably miss the first half of the movie completely. But luckily, there is a way to find out whether your pair is in working condition before the movie starts.

The Cause

Like I mentioned before, this problem arises because the glasses are powered by batteries and are synchronized via an Infra Red signal emitter. So if the batteries go down, there can be synchronization errors leading to flickering or a distorted 3D effect. If the batteries run down completely, the glasses will stop working altogether and either one or both the lenses will go completely black, or the glass will look clear and normal but will not produce the 3D effect. This is the worst scenario, because if you don't identify it before the movie starts, then you are in trouble. So here is how to check it beforehand.

How to Check

Soon as you get the glass, go into the theater (It won't work outside the theater) and while holding the glasses about a foot away from your face, look through both lenses at a well lit area. (the theater will be well lit before the movie starts) Looking at the white screen also would do. If you see a slight flickering in both lenses you are good to go. If you don't see any flickering, if only one lens flickers, or else if one lens appears to be a shade darker than the other lens, then the glasses are faulty and you will have to get it changed.

Movie fans should not go through this hassle in a properly maintained theater. It is the responsibility of the theater personnel to replace the batteries regularly and to check the glasses from time to time. From the experience I had today, it is evident that about half of the glasses are faulty. and watching a movie with faulty glasses like that can lead to severe headaches and nausea. Unfortunately, the personnel at MC platinum just don't care about this issue. When complaining about this issue all they did was nod in approval as if to say, "yes we know about the problem, but we just don't care!"

If this happened in another country, people would sue the theater. But this is Sri Lanka and sometimes we suffer in silence. I'm just hoping that this problem will be sorted out soon. If not, and if its a movie that you really can't miss(like Iron Man 3), make sure that you check your glasses before the movie starts. Hope this guide was useful :)


UPDATE (19/2/2014)

These problems due to the battery powered active glasses will not arise again because MC Platinum has switched from active shutter to a polarized filter projection system. The passive glasses used in this method will not cause any of the above problems. 

the new lightweight polarized glasses