Avengers at Savoy

The recently released "Avengers" movie will be screened at Savoy Wellawatte from the 11th of May 2012. This showdown of Marvel superheroes, is in my opinion one of the three most anticipated movies of 2012, the other two being "The Dark Knight Rises" and "Prometheus". It would be great if it was screened in 3D at MC superior 3D, however watching it in 2D at Savoy is better than not watching at all.. ;)  All previous Marvel superhero movies, Iron Man, Thor, Hulk and Captain America led to the events of this movie. The post credit scenes in those movies indicated it. After a long wait now that the movie will finally be shown in Sri Lanka, Marvel fans will be counting their fingers till the 11th of May.
Tickets can be booked at http://www.eapmovies.com/movie/the-avenger-english-movie/

UPDATE : Great news! Avengers will be screened in 3D at MC superior as well. Tickets can be purchased at http://www.ticketslk.com/

Optical properties of Minerals under Cross Polarized Light (CPL)

The CPL arrangement of the microscope is withe analyzer in the "In" position. The optical properties that can be observed under this arrangement are as follows,

1.  Isotropic and Anisotropic Minerals
All minerals are either Isotropic or Anisotropic. Isotropic minerals are the minerals that do not show any colour under the CPL arrangement whatsoever. These minerals appear dark. Isotropic minerals are the minerals that are very symmetric and usually belong to the cubic crystal system. Examples include Garnet and Spinel. (Garnet having pink as its optic colour turns dark when the analyzer is in. This property is used to identify garnet).
Anisotropic minerals are the minerals that show colours under the CPL arrangement. These colours are known as interference Colours. Anisotropic minerals belong to crystal systems having lower crystal symmetry. (Systems other than Cubic)

2.  Extinction Position and Angle.
Extinction position is a position reached when the microscope stage is rotated under the CPL arrangement and no colours are seen (dark positions). All Anisotropic minerals have extinction positions. All minerals show 4 extinction positions in a single rotation (90 degrees apart). At he extinction position the vibration directions of the mineral are parallel to the planes of polarization of the polarizer and the analyzer. Therefore no light reaches the eyepiece thereby giving the dark extinction position.

The extinction angle is the angle between one of the cross-hairs and the lines of cleavage of the mineral at the extinction position.

3.  Interference Colours
The colours that anisotropic minerals show under the CPL arrangement are known as Interference Colours. The maximum intensity of these colours are seen in between two extinction positions. (at 45 degree positions).

4.  Birefringence
Birefringence is the difference between the maximum and minimum Refractive index value shown by a mineral. The interference colours shown by a mineral depend on its birefringence and therefore birefringence is very useful in mineral identification.

5.  Optic Sign
Double refraction of all anisotropic minerals results in them having two refractive indices RIO and RIE. According to these values, The Optic sign is determined as follows.
RIO  >  RIE.  -  Negative (-)
RIO  <  RIE.  -  Positive (+)

6.  Interference Figures
Interference figures are important optical properties that are used in the identification of minerals, as well as to determine other properties of minerals such as,
-  Optic Sign
-  Whether a mineral is Uniaxial or Biaxial
-  2V angle of a mineral (2V angle is the angle between the two optic axes of a mineral)
Interference figures are observed under the Conoscopic Arrangement of the microscope. The thin sections have to be specifically prepared in order to observe Interference figures.

The Becke Line Method

Becke line is a band of light seen along the mineral grain boundary under the PPL arrangement when the microscope is slightly out of focus. Depending on the way the microscope is focused, the Becke line may lie within or outside the grain boundary.

The Becke line method is used to determine the relative refractive indices of two minerals. This is performed by lowering the microscope stage or increasing the focal distance (increasing the distance between the section and the objective). When this is done the Becke line will appear to move towards the material with the higher refractive index. This method is used to compare the refractive indices of two minerals or to compare the mineral with a medium with known refractive index such as Canada Balsam or Epoxy glue.

Conoscopic arrangement of the Petrological Microscope

Observing interference figures of minerals is done under the Conoscopic view of the petrological microscope. The conoscopic arrangement is set up as follows,

1.  The medium or low power objective is selected and selected grain is brought to the centre of the cross-hairs.

2.  The light intensity is increased by using the concave mirror or the intensity controller of the electric bulb.

3.  The objective is now changed to high power and brought very close to the the thin section (almost touching it).

4.  The analyzer is put to the "IN" position.

5.  The Bertrand Lens is also put to the "IN" position. (This will make the viewing scope small)

Optic Axes of a Mineral

When double refraction is observed using a calcite crystal and when its rotated and tilted at one point the two images (the Ordinary image and the Extraordinary image) coincide and appears as one image. This direction in which no double refraction can be observed is the Optic Axis direction. While some minerals have only a single optical axis while others have two optic axes. Minerals are thus classified as follows
1.  Uniaxial Minerals - one optic axis
2.  Biaxial Minerals - two optic axes
Minerals that belong to the tetragonal and hexagonal crystal systems are uniaxial while minerals that belong to monoclinic, triclinic and orthorhombic crystal systems are biaxial.
eg.  quartz, calcite - hexagonal - uniaxial   pyroxene - orthorhombic and monoclinic - biaxial
 

Double Refraction in Minerals

Double refraction is the splitting of a single ray of light into two refracted rays when passing through an anisotropic mineral. All anisotropic minerals exhibit double refraction.
Double refraction can be practically observed by placing a transparent Calcite (Iceland spar) crystal on a sheet of paper with a black dot on it. When the dot is viewed through the crystal, two dots are seen. Also when the crystal is either rotated or tilted one of those images moves while the other remains stationary. This implies that the mineral has two refractive indices, one constant and one that varies with direction. The fixed image is called the "Ordinary image" and the moving image is called the "Extraordinary image". Similarly the rays that produce the images are also named "O-ray" and "E-ray". The Refractive indices are also identified as RIO and RIE. The relative magnitudes of RIO and RIE determine the Optic Sign of the mineral.

calcite crystal showing double refraction. image from : wikipedia

Isotropic and Anisotropic Minerals under the CPL arrangement

In the CPL arrangement of the petrological microscope, Isotropic minerals do not show any colour while anisotropic minerals show interference colours.
Isotropic minerals have high symmetry and therefore as shown in the diagram below does not alter the plane of vibartions of light that comes from the polarizer. When this light reaches the analyzer, it cannot pass through because the plane of polarization of the analyzer is perpendicular to that of the polarizer. Therefore no light moves through to the eyepiece resulting in the mineral becoming dark.

Anisotropic minerals have low symmetry and therefore alters the plane of vibration of light that passes through it. Therefore when this "altered" light reaches the analyzer, the light that has the same vibration direction as the analyzer passes through to the eyepiece. Therefore colours are seen in this case.

Birefringence

Anisotropic minerals have a range of Refractive index values at different directions. Out of these values, the Maximum RI value and the minimum RI value can be observed. The difference between the maximum and minimum values is defined as "Birefringence". The interference colours shown by a mineral depends on its birefringence. Thus based on the birefringence, all interference colours are put into a scale known as "Newton's scale of interference colours".
Anisotropic minerals are classified according to their birefringence values as,
0-0.018 - low birefringence - gives colours of high order in the scale
0.018-0.036 - moderate birefringence
0.036-0.055 - high birefringence
0.055< - very high birefringence - gives colours of high order in the scale.

birefringence chart

Note that as birefringence increases, the colours in the chart repeat but the shades become pale.

It should also be noted that when the thickness of the section of the same mineral is increased, its birefringence also increases producing the above colour scale. Therefore the above scale can also be produced with a single mineral of varying section thickness.

Determination of the Extinction Angle of a mineral

All anisotropic minerals have what is known as an extinction position. These positions are identified as dark positions (with no colour) as the microscope stage is rotated. For each rotation there are 4 such extiction positions (90 degrees apart).
The Extinction Angle is defined as the angle between one of the cross hairs and a line of cleavage in the mineral at the extinction position.
To determine this angle, The angle reading at the extinction position is read from the microscope stage, and then the microscope stage is rotated until the cleavage lines become parallel to one of the cross hairs. The reading at his point is also taken. The difference between the two readings will give the extinction angle.

extincton position - reading1

parallel cleavage position - reading2

Extinction angle  =  reading 1 - reading 2

If the extinction position occurs when the cleavages are parallel to the cross hair, then it has an extinction angle of zero. Such minerals are said to have a  "Parallel" extinction. eg. Orthopyroxene

Beach Nourishment

Beach nourishment also called beach replenishment, is the replacement of sand lost due to erosion by sources outside the eroded beach. This helps minimize damage from storm surges, tides and tsunamis. Beach nourishment does not stop erosion.  It only mitigates its effects while eroding away the sand used in the nourishment process and eventually bringing the beach back to its original pre-nourished state. Because of this reason beach nourishment is a repetitive process. After all the "new" sand has eroded away, the beach will have to be re-nourished. While this method helps protect coastal areas it usually is very costly.

beach nourishment : image credit : wikipedia

Optical properties of Minerals under Plane Polarized Light (PPL)

The PPL arrangement of the Petrological microscope is with the Analyzer in the "out" position. The optical properties that can be seen under this arrangement are as follows,

1.  Optic Colour
This is the colour of the mineral as seen through the microscope. Often the optic colour is different to the physical colour of the mineral.
eg.  Feldspar - Colourless,  Quartz - Colourless,  Biotite - Brown,  Hornblende - Green/Yellow,  Alamandine Garnet - Pale pink

2.  Pleochroism
The change in optic colour or colour intensity when observed under the PPL arrangement while rotating the microscope stage is known as Pleochroism. This occurs when the absorption of light varies with the direction of   observation.
eg.  Feldspar, Quartz - No pleochroism  Biotite - Strongly pleocroid (yellow to dark brown)  Hypersthene - Strongly pleochroid (pink to green)  Hornblende - Moderately pleochroid (yellow to green)  Garnet - Weakly pleochroid (pale pink to pink)

3.  Relief
The effect of the mineral grain standing out with respect to the surrounding minerals or medium when viewed under the PPL arrangement is known as Relief. The relief depends on the difference between the Refractive Index of the mineral and that of the surrounding medium. If the refractive index is high with respect to the surrounding medium, so is the relief. Relief is categorized as High, Moderate and Low.

4.  Twinkling
The change in relief observed when the microscope stage is rotated is known as Twinkling. The reason for this is the variation of the refractive index of the mineral with the direction observed. Only certain minerals exhibit twinkling.
eg.  Calcite

5.  Cleavage
 The planes along which a mineral shows a tendency to split (planes of relative weakness) are known as cleavage planes. These planes can be observed as straight lines under the microscope. Cleavage angles help to identify the minerals.
eg.  Hornblende - 120degree cleavage sets.  Biotite - parallel cleavages  Pyroxene - 90 degree cleavage sets

6. Shape
The shape of the crystal also helps in the identification process.
eg.  Accicular(needle shaped) silimanite  Rounded grains of Garnet.

What causes the Tectonic Plates to move?

The currently accepted theory is that thermal convection is the main driving force. The high temperatures in the earth's interior makes the plastic rocks in the asthenosphere less dense than the rocks above and causes them to rise while the denser rocks sink below. This gives rise to convection currents just like in any other heated fluid. These slow moving currents circulate as shown in the figure below and and exerts drag on the bottom on the lithospheric plate. This frictional force is what causes the plates to move. Furthermore, as the solid and denser plate sinks below into the less dense and plastic asthenosphere it tends to sink further, pulling the rest of the plate downwards. While this is the accepted mechanism at the moment. Further research is yet to provide deeper insight regarding this process.

image credit : Invitation to Oceanography, 5th edition, Paul R. Pinet

Focus, Hypocenter and Epicenter of an Earthquake

The terms Epicenter, Hypocenter and Focus are used a lot to describe earthquakes and earthquake related events and can sometimes lead to confusion. The two terms Focus and Epicenter actually carry two different meanings.
The focus of an earthquake is the point where the fault begins to rupture. It is where the strain energy stored in the rock is released and is often located underground. Earthquakes are classified according to their focal depths as, shallow-focus earthquakes, mid-focus earthquakes and deep-focus earthquakes.
The term hypocenter means the same as focus, although hypocenter is also used to refer to a nuclear explosion site (ground zero)
The epicenter is the the point on the earth's surface directly above the focus. Thus the epicenter represents a geographic location on the earth's surface. This means that the focus lies at a focal depth below the epicenter.

source : http://earthquakesandplates.files.wordpress.com/2008/05/epicenter.gif

source : http://en.wikipedia.org/wiki/File:Epicenter.png

More info : earthquakes and plates  ,  wikipedia

Great ideas seldom disappear.

Tetris, a puzzle game invented in 1984 by Alexey Pajitnov is arguably one of the best video games ever created. It is based on a remarkably simple idea but provides a pleasant yet challenging gameplay experience. Despite having so many modern high-end games with realistic graphics and sounds at the present, Tetris is still widely played and enjoyed around the world. According to wikipedia, research has shown that playing tetris contributes to efficient cognitive functioning. 

Here is a sample of the famous game. It is a true classic.

Preparing a Thin Section of a Rock

Thin sections of rocks are prepared in order to observe them in Petrological Microscopes. Thin sections are prepared by grinding rocks to a thickness of micrometers  (0.03mm) so that its features such as mineral grains, cleavages, twinning and optical properties of those minerals can be observed.

thin section of Gabbro - image from wikipedia

The procedure adopted in preparing thin sections is explained below.

1.  The sample to be sectioned and is determined and the direction of the cut is selected such that it is cut across structures such as layering, foliation, cleavages etc.

2.  A rectangular slice having a size of about 3x2x0.5 cm is cut using a diamond wheel.

3.  One surface of the slice is polished using Carborundum powder from coarse to fine varieties.

4.  The polished specimen is mounted onto a glass slide, polished side down using epoxy glue. (Care should be taken to avoid air bubbles)

5.  The other side of the rock specimen is ground and polished using carborundum powder to bring the thickness of the section to 0.03mm.

6.  The cover slip is fixed onto the polished section using Canada Balsam. (The cover slip protects the thin section)

The following diagram depicts the prepared thin section (thicknesses are exaggerated for clarity)

thin section 

This method is used for preparing thin sections of hard rocks. In order to prepare a thin section from a soft rock, first the rock must be strengthened using a glue, and the same procedure must be followed.

Sand grains can be directly mounted on Canada Balsam and polished if necessary before covering with a cover slide. This method is used to observe the interior of individual grains of sand.

Parts of a Petrological Microscope

A Petrological Microscope also called a Polarizing Microscope is an essential instrument in optical mineralogy and Petrology. It is used to observe thin sections of rocks under polarized light and to identify their physical and optical properties. The microscope is widely used to identify and classify rocks and minerals. Given below is a schematic diagram of a petrological microscope and its parts.

parts of  a petrological microscope

The function of each part are as follows,

Light Source - Provides light into the microscope for viewing. Usually an electric bulb or a two sided(plane and concave) mirror.

Polarizing unit 1 - This converts normal light into plane polarized light and is situated below the microscope stage.

Condenser System - This removes the effects of interference of light by changing the phase of light.

Diaphragm Lever - This lever is used to control the intensity of light.

Microscope Stage - This is a graduated, rotatable disk on which the thin sections are mounted for viewing purposes.

Objective - This contains several objective lenses of different magnifying power that can be selected. These lenses are of usually of three types. Low power objectives(3.5x) that provide a large coverage of the thin section where the micro-structures and grain percentages can be observed, Medium power objectives(10x) that shows several grains in considerable detail and can be used for identification purposes, and High power objectives(40x-50x) that show a single grain in very fine detail and used for advanced analysis.

Slot - the slot is used to insert accessory plates for different viewing purposes.

Analyzer (polarizing unit 2) - This is also a light polarizing unit. However the plane of polarization is perpendicular to that of the polarizing unit that is situated below the microscope stage. This can be set in either "in" or "out" positions.

Bertrand lens - This is a special lens system that is used to observe interference figures. This too can be ste in either "in or "out" positions. When the Bertrand lens is in the "in" position, the view seen from the eyepiece is smaller.

Eye piece - This is the lens through which the observer views the thin section. It has a circular view with centre cross-hairs to help viewing.

The petrological microscope can be set up in two arrangements depending on viewing purposes and optical properties of the minerals. They are,
1.  PPL arrangement (Plane Polarized Light) - analyzer is out, Bertrand lens is out
2.  CPL arrangement (Cross Polarized Light) - analyzer is in Bertrand lens is out.

Tsunami - to hit or not to hit..

I must admit that I did not notice the tremors that hit Colombo in the afternoon although most people had. I was at McDonalds having my lunch at the time, and when I stepped out I saw so many people gathered on the Galle road with their cellphones held to their ears. I was wondering about this strange behaviour when my mother called and told me about the earthquake and a possibility of a tsunami and asked me to come to her office at once. At this moment I just had a hunch that a tsunami was not going to hit although I had no information at that time whatsoever to come to such a conclusion.
The main shock had a Richter scale magnitude of 8.6 and caused widespread panic and also brought about the release of tsunami warnings in several countries including Sri Lanka. Having had an  extremely bad experience with the 2004 indian ocean tsunami these actions were appropriate. However even after the estimated arrival times had been issued, no tsunami arrived.
Earthquakes are not rare. Hundreds of earthquakes occur throughout the globe at any given time. Most of them are too small to even notice. The rare ones with the large magnitudes are the ones that cause trouble. The following diagram shows the data from USGS of some recorded earthquakes. In order to minimize the number of earthquakes displayed, only the details of earthquakes that are greater than 5.4 in magnitude in the region depicted in the map are given. (click on image to enlarge)

source - USGS -  http://earthquake.usgs.gov/earthquakes/map/

Note that in total 6985 earthquakes have been recorded in the past 30 days. The one that is highlighted is the 8.6 main shock that raised concerns of a tsunami. The rest are aftershocks. Clearly this earthquake took place very close to the epicenter of the 2004 one and therefore was expected to replicate the same effects, but it did not.

While Tsunamis can be generated by various methods such as earthquakes, landslides and even meteor strikes earthquake generated tsunamis are the most common, although the largest recorded tsunami was caused by a landslide at Lituya bay, Alaska (source : http://geology.com/records/biggest-tsunami.shtml). It must be noted however that not all earthquakes can cause a tsunami. Several conditions need to be fulfilled for the generation of a tsunami wave. They are as follows
1.  The earthquake should have a large magnitude ( greater than 7.0)
2.  The earthquake should be a shallow focus earthquake (focal depth less than 70km)
3.  The epicenter of the earthquake must be at an active plate margin near or in the ocean.
4.  There should be a vertical displacement of the plate (a thrust fault).
5.  The displacement should occur over a considerable area to displace a large volume of water.
Although not a hard and fast rule, these conditions need to be satisfied for a tsunami. The earthquake that hit today(11.04.2012) did not fulfill all these conditions.
Given below are the details of today's earthquake.

source - USGS -  http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/usc000905e.php 

While the earthquake had a large enough magnitude and a shallow focus, the earthquake occurred as a result of strike slip faulting and not thrust faulting (source : http://earthquake.usgs.gov/earthquakes/eventpage/usc000905e#summary) . Therefore there has not been a considerable vertical motion of the plates in order to displace a large volume of water. This was the reason why a devastating tsunami was not generated.
While we were lucky today and the warnings and preparation were seemingly unnecessary, we can now be assured that proper warnings will be given and that we are prepared to take necessary measures in the case of an actual threat.

Sand Mining and Storm Damage

Beach sand mining has increased during the past few decades as river sand has gradually depleted causing several environmental problems. Beach/sea sand is not suitable for construction purpose as a replacement for river sand due to its salinity. The salinity in the sea sand can corrode steel reinforcements and cause structural failures if used in concrete. However the sea sand can be thoroughly washed to remove its salinity before using it for construction purposes. Due to this reason beach sand is mined increasingly in order to avert the environmental damage caused by mining river sand.
This is not a good solution because beach sand mining has its own harmful side effects. While most will agree that offshore mining is not very environmental friendly few realize that beach sand mining is as catastrophic. The sand on the beach and in the sea belong to one dynamic system. Removing sand from the beach therefore will disturb this balance.

image from http://www.seafriends.org.nz/oceano/beach.htm

This is what a typical healthy beach looks like. Even the sand far away from the water are part of the beach. The dunes on a beach serve a purpose.

image from http://www.seafriends.org.nz/oceano/beach.htm

The above picture depicts the behaviour of the sand during a storm. Note how sand is borrowed from the fore dunes to create a bank below the sea level. This bank helps to break the waves and dissipate energy thus minimizing the damage caused by the storm.
So what would happen if the sand is carelessly removed from the beach? There wouldn't be a way for the beach to adapt during a storm. This will lead to severe inundation and damage.
The sand in a healthy beach undergoes a cycle known as the "beach cycle". The beach continuously adapts by moving sand and sediments and rebuilds itself after storm damage by itself. Removing sand from the beach could disturb this cycle and cause long term effects such as severe coastal erosion. This makes it necessary to explore alternative methods to mine sand. Deep sea sand mining, carried out far away from the coast could be a possible solution although its effects and impacts should be thoroughly assessed first.

Ballooning in Sri Lanka

Recently I got an opportunity to fly in a hot air balloon over Dambulla. Having traveled only in mechanized aircraft such as aeroplanes and helicopters before, this was a different and an interesting experience for me. Hot air balloons are one of the simplest modes of flight and it is because of this simplicity that it is such  a unique and wonderful experience.
The method it works cannot be simpler, The air in the balloon is heated using a gas burner, Hot air is less denser than the surrounding air, so it creates lift. You can only control the force of lift in a hot air balloon, that is by varying the heat given to the air. Where you go is out of your control. It depends on the direction the wind blows. This is why hot air ballooning is considered a sport rather than a mode of transport.
Balloon flights are usually scheduled early in the morning because the air is still and calm at that time. During later hours of the day the increasing temperatures give rise to thermals-columns of rising air that can interfere with the balloon and make maneuvering difficult. (Interestingly, thermals that hinder a balloon flight are the essential ingredient in gliding(which I'm awaiting to try out) where the force required to stay airborne is provided by thermals.) Therefore the morning is the best time for ballooning, besides  the sunrise seen from a balloon is a sight to behold..
Once airborne the balloon drifts away until you decide to land. Landing is done by allowing the heated air to escape by opening a vent at the top of the balloon by means of ropes and cables. Just like any other air sport, a smooth landing demands skill and practice.

heating the air to inflate

straightening the balloon

just before takeoff

sunrise

the gas burner

shadow of the balloon

opening the vent to land

Fruits? No thanks..

Most people stare at me in  disbelief when I tell them that I don't eat fruits. Although I cannot give a reason as to why I hate fruits, and knowing that fruits are one of the main source of vitamins and minerals, I'm not that worried by it because I eat my vegetables.. Well most of it. There was a time when used to take small servings of apples and pineapples. These were the only fruits of which the smell did not make me want to vomit. But now I don't eat even these fruits. However I do enjoy fresh mandarin and orange juice, and an occasional packeted mango juice of a particular brand. That's it. That's the closest I ever come to eating fruits. I know that not eating fruits but drinking some fruit juices sounds weird and illogical. But it is an aspect of myself that even though I don't fully understand, defines me in a unique way.

looks pretty but no thanks..