Monthly Archives: May 2013

The Petri Dish!

Google is commemorating today the achievements of the scientist Julius Richard Petri with a Google Doodle that shows his invention – the Petri dish – in action.

Today would have been the German bacteriologist’s 160th birthday. In the animation on the Google homepage, the word “Google” is replaced with a series of the dishes in the Google colours. A hand appears, swabbing each of them, then you can watch as the bacteria grow.
Julius Richard Petri (May 31, 1852 – December 20, 1921) was a German microbiologist who is generally credited with inventing the Petri dish while working as assistant to pioneering bacteriologist Robert Koch.

Petri dishes are often used to make plates that are used for microbiology studies. The dish is partially filled with warm liquid containing agar, and a mixture of specific ingredients that may include nutrients, blood, salts, carbohydrates, dyes, indicators, amino acids and antibiotics. After the agar cools and solidifies, the dish is ready to receive a microbe-laden sample in a process known as inoculation or “plating.” For virus or phage cultures, a two-step inoculation is needed: bacteria are grown first to provide hosts for the viral inoculum.

Often, the bacterial sample is diluted on the plate by a process called “streaking”: a sterile plastic stick, or a wire loop which has been sterilized by heating is used to take the first sample, and make a streak on the agar dish. Then a fresh stick, or a newly-sterilized loop, passes through that initial streak, and spreads the plated bacteria onto the dish. This is repeated a third, and sometimes a fourth time, resulting in individual bacterial cells that are isolated on the plate, which then divide and grow into single “clonal” bacterial colonies.
Petri plates are sometimes incubated upside down (agar on top) to lessen the risk of contamination from settling airborne particles and to prevent water condensation from accumulating and disturbing the cultured microbes.

P&R Labpak supply a wide range of petri dishes – glass and disposable plastic in various diameters.  If you need any, why not contact us?

We also supply various agars and media from all leading brands.

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New GPS solution provides three-minute tsunami alerts

The invention of GPS Systems has benefitted many people but it is being put to new uses.

Researchers have shown that, by using global positioning systems (GPS) to measure ground deformation caused by a large underwater earthquake, they can provide accurate warning of the resulting tsunami in just a few minutes after the earthquake onset. For the devastating Japan 2011 event, the team reveals that the analysis of the GPS data and issue of a detailed tsunami alert would have taken no more than three minutes.

Most tsunamis, including those in offshore Sumatra, Indonesia in 2004 and Japan in 2011, occur following underwater ground motion in subduction zones, locations where a tectonic plate slips under another causing a large earthquake. To a lesser extent, the resulting uplift of the sea floor also affects coastal regions. There, researchers can measure the small ground deformation along the coast with GPS and use this to determine tsunami information.
“High-precision real-time processing and inversion of these data enable reconstruction of the earthquake source, described as slip at the subduction interface. This can be used to calculate the uplift of the sea floor, which in turn is used as initial condition for a tsunami model to predict arrival times and maximum wave heights at the coast,” says lead-author Andreas Hoechner from the German Research Centre for Geosciences (GFZ).
In the new Natural Hazards and Earth System Sciences paper, the researchers use the Japan 2011 tsunami, which hit the country’s northeast coast in less than half an hour and caused significant damage, as a case study. They show that their method could have provided detailed tsunami alert as soon as three minutes after the beginning of the earthquake that generated it.
“Japan has a very dense network of GPS stations, but these were not being used for tsunami early warning as of 2011. Certainly this is going to change soon,” states Hoechner.

The scientists used raw data from the Japanese GPS Earth Observation Network (GEONET) recorded a day before to a day after the 2011 earthquake. To shorten the time needed to provide a tsunami alert, they only used data from 50 GPS stations on the northeast coast of Japan, out of about 1200 GEONET stations available in the country.

At present, tsunami warning is based on seismological methods. However, within the time limit of 5 to 10 minutes, these traditional techniques tend to underestimate the earthquake magnitude of large events. Furthermore, they provide only limited information on the geometry of the tsunami source (see note). Both factors can lead to underprediction of wave heights and tsunami coastal impact. Hoechner and his team say their method does not suffer from the same problems and can provide fast, detailed and accurate tsunami alerts.
The next step is to see how the GPS solution works in practice in Japan or other areas prone to devastating tsunamis. As part of the GFZ-lead German Indonesian Tsunami Early Warning System project, several GPS stations were installed in Indonesia after the 2004 earthquake and tsunami near Sumatra, and are already providing valuable information for the warning system.

“The station density is not yet high enough for an independent tsunami early warning in Indonesia, since it is a requirement for this method that the stations be placed densely close to the area of possible earthquake sources, but more stations are being added,” says Hoechner.

Traditional tsunami early warning methods use hypocentre (the point directly beneath the epicentre where the seismic fault begins to rupture) and magnitude only, meaning the source of the earthquake and tsunami is regarded as a point source. However, especially in the case of subduction earthquakes, it can have a large extension: in Japan in 2011 the connection between the tectonic plates broke on a length of about 400km and the Sumatra event in 2004 had a length of some 1500km. To get a good tsunami prediction, it is important to consider this extension and the spatial slip distribution.

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The amazing properties of Borosilicate Glass

Borosilicate glass is a type of glass with the main glass-forming constituents silica and boron oxide. Borosilicate glasses are known for having very low coefficients of thermal expansion (~3 × 10−6 /°C at 20°C), making them resistant to thermal shock, more so than any other common glass. Such glass is less subject to thermal stress and is commonly used for the construction of reagent bottles, flasks, beakers and many other laboratory glassware items. Borosilicate glass is sold under such trade names as Pyrex, Schott & Simax.


Borosilicate glass was first developed by German glassmaker Otto Schott in the late 19th century and sold under the brand name “Duran” in 1893. After Corning Glass Works introduced Pyrex in 1915, the name became a synonym for borosilicate glass in the English-speaking world.

Chemical Properties
Borosilicate glass has a very high resistance to attack from water, acids, salt solutions, halogens and organic solvents. Only hydrofluoric acid, hot concentrated phosphoric acid and strong alkaline solutions cause appreciable corrosion of the glass.

Hydrolytic resistance For many applications, it is important that laboratory glassware has excellent hydrolytic resistance; e.g. during steam sterilisation procedures, where repeated exposure to water vapour at high temperature can leach out alkali (Na+) ions. Pyrex borosilicate glass for example has a relatively low alkali metal oxide content and consequently a high resistance to attack from water. Pyrex fits into Class 1 of glasses for hydrolytic resistance according to ISO 719 (98°C) and ISO 720 (121°C).

Acid resistance
Glasses with a high percentage weight of silica (SiO2) are less likely to be attacked by acids. Pyrex borosilicate glass is over 80% silica and therefore remarkably resistant to acids (with the exception of hot concentrated phosphoric acid and hydrofluoric acid). Glass is separated into 4 acid resistance classes and Pyrex corresponds to Class 1 in accordance with DIN 12116 and meets the requirements of ISO 1776.

Alkali resistance
Alkaline solutions attack all glasses and Pyrex can be classified as moderately resistant. The alkali resistance of Pyrex borosilicate glass meets Class 2 requirements as defined by ISO 695 and DIN 52322.

High usage temperature


The maximum permissible operating temperature for DURAN® borosilicate glass is 500 °C. Above a temperature of 525 °C the glass begins to soften and above a temperature of 860 °C it changes to the liquid state.

DURAN® can be cooled down to the maximum possible negative temperature and is therefore suitable for use with liquid nitrogen (approx. – 196 °C). During such use/ freezing. In general DURAN® products are recommended for use down to – 70 °C. During thawing ensure that the temperature difference does not exceed 100 K.


The link below shows how Duran glass is made

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Just a pinch of salt….

Salt, also known as table salt or rock salt (halite), is a crystalline mineral that is composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of ionic salts. It is absolutely essential for animal life, but can be harmful to animals and plants in excess. Salt is one of the oldest, most ubiquitous food seasonings and salting is an important method of food preservation. The taste of salt (saltiness) is one of the basic human tastes.
Salt for human consumption is produced in different forms: unrefined salt (such as sea salt), refined salt (table salt), and iodized salt. It is a crystalline solid, white, pale pink or light grey in colour, normally obtained from sea water or rock deposits. Edible rock salts may be slightly greyish in colour because of mineral content.
Because of its importance to survival, salt has often been considered a valuable commodity during human history. However, as salt consumption has increased during modern times, scientists have become aware of the health risks associated with high salt intake, including high blood pressure in sensitive individuals. Therefore, some health authorities have recommended limitations of dietary sodium, although others state the risk is minimal for typical western diets.

Additives in table salt

Most table salt sold for consumption contain additives which address a variety of health concerns, especially in the developing world. The identities and amounts of additives vary widely from country to country.

  • Iodine and Iodide
  • Fluoride
  • Anti-caking agents
  • Iron
  • Other additives

Too much or too little salt in the diet can lead to muscle cramps, dizziness, or electrolyte disturbance, which can cause neurological problems, or death.  Drinking too much water, with insufficient salt intake, puts a person at risk of water intoxication (hyponatremia)

Lowering salt in diet

It is a misconception that sea salt has a lower sodium content than table salt, — they are both basically sodium chloride.  A low sodium diet reduces the intake of sodium by the careful selection of food. This aim can also be achieved by the use of a salt substitute, and Potassium chloride is widely used for this purpose. Although recommended limits for potassium are higher than for sodium, potassium has its own health disadvantages, and it is advised that such a salt substitute not be used by those taking certain prescription drugs.  Another possibility being researched is the use of seaweed granules in the manufacture of processed foods as an alternative to salt.

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How Boomerangs Work

Classic boomerangs have two arms or wings normally of equal length. They are joined at the elbow, at an angle of between 105° and 110°. The reason for this angle lies in the origins of boomerang manufacture; most boomerangs were made from the junction of a tree with its lateral (sideways) root. Each arm usually has a tapered tip, which is a carry-over from the ancestor of the boomerang – the killer stick.

All boomerangs are either right or left-handed – one is an exact mirror image of the other. This is to allow right and left-handed throwers to launch their boomerangs with relative ease because it’s far more comfortable to throw away from, rather than across, the body. Having said this, it is possible to throw an opposite handed boomerang, with a few adjustments to your throwing action.
During the flight of the boomerang, the effect of many different aerodynamic principles can be seen. Bernoulli’s theorem, Newton’s laws of motion, gyroscopic stability, gyroscopic precession and many others all have a bearing on the action of the boomerang.
When the boomerang leaves the thrower’s hand, it will be spinning very fast. As each arm of the boomerang has an aerofoil shape, similar in cross-section to that of an aircraft wing, air moving over the top of each wing has to travel further, and therefore faster, than air passing beneath the wings. Bernoulli’s theorem states that ‘air travelling at a higher speed creates less pressure than slower moving air’. As a result, the boomerang experiences a ‘lift’1 force.
Newton’s second law of motion states that ‘the rate of change of momentum of an object is equal to the force applied to that object’. For an object with constant mass, this reduces to the well-known formula Force applied = Mass x Acceleration. The force here is a combination of friction and other resistive forces. To reduce the acceleration (or deceleration, since the force is negative), the mass needs to be large, but not so large that the boomerang falls quickly to the ground.
The length of the boomerang’s arms, and the angle at which they are joined, allow the boomerang to spin in a stable plane as a result of the spin imparted on launching. This is known as gyroscopic stability. If this were not the case, the motion of the boomerang would at best be unpredictable. At worst, the boomerang would lose its spin rapidly, and be unable to sustain flight.
We now have a stable, rapidly spinning boomerang, moving forward from the force of the throw. We now need to take a slightly closer look at the effect of Bernoulli’s theorem. As each wing rotates forward, into the direction of travel, it creates more lift than the other wing because the relative air speed is higher. If you imagine the spinning boomerang as a clock face, sideways on, this leads to the maximum force being created near the 12 o’clock position.
Due to the gyroscopic stability of the spinning boomerang, the effect of this force manifests itself at 90° further round the cycle of spin – at the 9 o’clock position of our clock face. The action of this force is to change the direction of flight – to the left for a right-handed boomerang and vice versa. Compare this with a ‘no hands’ bicycle turn – the only difference being the magnitude of the force. A small force over most of the duration of the flight produces a large, smooth turn for the boomerang, while a sudden strong force produces an abrupt bicycle turn.

As the boomerang travels, it loses velocity2. Eventually, gyroscopic precession becomes the dominant force. Coupled with the initial ‘off-vertical’ tilt, the effect is to push the boomerang over on its side, so that it spins in a horizontal plane.
The effect of each of these principles varies with the way in which the boomerang is thrown. The basic flight path of a boomerang is circular, although advanced throwers can produce a virtually triangular flight path.
1This is slightly misleading – the boomerang is thrown in a near vertical position, so the resulting ‘lift’ actually acts sideways.
2As it is rare to get absolutely dead-calm conditions, the wind starts to have an effect. This means that it is necessary to launch the boomerang 50° off the wind – the flight path should curl across the wind, and end with the boomerang being almost ‘blown back’ to the thrower.
The origin of the term is uncertain, and many researchers have different theories on how the word entered the English vocabulary. One source asserts that the term entered the language in 1827, adapted from an extinct Aboriginal language of New South Wales, Australia, but mentions a variant, wo-mur-rang, which it dates from 1798. The boomerang was first encountered by western people at Farm Cove (Port Jackson), Australia, in December 1804 where its use as a weapon was witnessed during a tribal skirmish.

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