How do plants survive in the desert?

C4 cycle.
WINDOW PLANT

HONEY MESQUITE


YELLOW DAISY FOUND IN THE DESERT


These 'Desert plants' have lots of special features to help them survive in the desert. One example is that:
-They have very long roots to reach far below in the ground to obtain as much water as possible.-> Mesquite has roots as long as 50m. Mesquite belongs to the Legume family- restores nitrogen to the soil. There are 3 common species of mesquite: Honey Mesquite, Screwbean Mesquite and Velvet Mesquite.
-Tough outer coats and painful thorns to prevent animals of the desert from trying to eat the plant for its water supply.
-Pebble plants grow partially underground to avoid the heat-> they are neat little plants that are mistaken for pebbles and are usually white or yellow.
-Window plants grow entirely underground-> window plant have a long cigar shape poking into the ground with only a small green part "leaf" to absorb sunlight.
-Mosses and lichens soak up dew.
-Trees with shrivelled, brown and dead looking most of the time then suddenly turns green when there is rain are called RESSURECTION TREES -> flower of a Jericho is a dry ball that can live for years and opens when damp.
-Daisies are found in most deserts-> Yellow desert daisies are cushion plants that grow to 5-20cm. They flower from May to June. These daisies maximize the energy gained from the process of photosynthesis. (C4 cycle) The C4 cycle, another, efficient pathway used by plants living in areas with low levels of carbon dioxide, to convert carbon dioxide into a form usable by the plants during photosynthesis.
-Cacti and Ice plants store water. -> Ice plants are now considered as invasive species. They are strong and reproduce quickly, easily growing into a thick ground cover that wipes out other plant life and depletes soil nutrients. The only way to control ice plant is to uproot it physically. These Ice plants are pinkish-purple in colour and have long and thin petals.
-Saguaro Cactus: These cacti are large in size and have an expandable stem that helps them to store water. During rainy season, water is absorbed by a large network of roots which is then stored in the expandable stems. This cacti has a long lifespan and grows very fast.
-Old Man Cactus: It has fine, white hair on its stems. The silvery, white hair on the stems of the cacti reflect the sun, thus preventing excess loss of water.
-Tumbleweed: Young plants are bright green in color and grow close to the soil surface. As the plant grows it develops ridged branches with thin needle like spikes. After maturity the tumbleweed becomes a dull green with transparent flowers and tiny leaves.
- Barrel Cactus: These cacti are shaped like a barrel and grow up to a height of about 1 meter. The cacti has many long, yellowish spines that store water during the rains. When the climate is hot and dry, these spines shrink in size as an adaptive technique.
www.buzzle.com
www.wikipedia.org
www.australiandesert.com
Reference book: 1000 plants

THE LEVER PRINCIPLE!

The lever is a simple machine consisting of a bar supported at some stationary point along its length and used to overcome resistance at a second point by application of force at a third point. The stationary point of a lever is known as its fulcrum.

The Lever Principle has been found by experiment where two equal forces were acting in opposite directions, i.e., clockwise and counterclockwise, and applied to a uniform lever at equal distances from the fulcrum counteract each other and established a state of equilibrium, or balance, in the lever. Experiment has also shown that two unequal forces when acting in opposite directions will bring about an equilibrium when the product of the magnitude of one force and its effort arm, or lever arm (the distance of its point of application from the fulcrum), is equal to the product of the magnitude of the other force and its effort arm. In physics the product of a force by its effort arm is called moment of the force. The general conclusion known as the principle of moments states that equilibrium is established when the sum of the moments of the forces acting in a clockwise direction is equal to the sum of the moments of the forces acting in a counterclockwise direction. It is possible, as a result, to overcome a very large force at a short distance from the fulcrum with a very small force at a great distance from the fulcrum. Archimedes is supposed to have boasted, having the lever in mind, that given a place to stand he could move the Earth.

Summary

This term i have learnt many things. 1. SI units of mass, density, volume eg.
2.Formula for calculating the voulme of a sphere, cone, pyramid eg. 3. Formula for calculating pressure, density, work done, weight/force eg. 4. How to calculate moments 5. How to calculate force exerted on a lever 6. Instruments to measure- mass: spring balance eg. This is just a short summary of what we have learnt and most interestingly, we learnt many out of the textbook facts.

Can we trap sound?( Eg. like when i say "ahhh" and then i stop, can it be heard still without a recording machine)

Architecture of a ship

SHIPS!!!

HOW DOES A STRESS BALL HELP TO RELIEVE STRESS?

MEDICINE BALLS!

Medicine balls are generally constructed of a leather or vinyl covered nylon cloth, and filled with impact absorbing materials to give them weight. Vinyl covered medicine balls typically are sand filled and are not used for exercises requiring bouncing. Sand or steel shot filled neoprene bags are also used for medicine ball exercises not requiring bouncing.[1]
Some medicine balls have an inner half sphere of dense material in varying thicknesses and seamed together with an outer rubber shell. Other medicine balls have a thin rubber bladder covered by a thick rubber outer surface. Medicine balls that are constructed with an inner rubber bladder and rubber outer surface incorporate an air valve to pump up the ball and increase the bounce. The outer rubber surface has indented designs for easy handling. Over time the rubber surface may wear down if the medicine ball has been used on rough surfaces.
Other types of medicine ball include balls made of gel-filled polyvinyl chloride shells, balls made of solid polyurethane, and neoprene bags filled with sand or steel shot. The materials can vary depending on the desired weight and density.
A basketball can be filled with sand, stitched shut, and used as an effective low-price medicine ball where resources are scarce, and is popular in, for example, home "garage" gymnasia.
www.wikipedia.org

Does our blood expand on a hot day?

SUPER GLUE!!!!

Super glue also known as Cyanoacrylate which is the generic name for cyanoacrylate based fast-acting adhesives such as methyl 2-cyanoacrylate, ethyl-2-cyanoacrylate (commonly sold under trade names like SuperGlue and Krazy Glue), n-butyl cyanoacrylate (used in the veterinary glues Vetbond and LiquiVet and skin glues like Indermil and Histoacryl). 2-octyl cyanoacrylate is a medical grade glue encountered under various trade names; e.g., LiquiBand, SurgiSeal, FloraSeal, Dermabond, and Nexaband. Cyanoacrylate adhesives are sometimes known as "instant glues". The abbreviation "CA" is commonly used for industrial grades.

http://www.wikipedia.org/

What i have learnt this term

Something interesting i learnt from Mr lyndon lim, is that not all parts of the school has equal stability. He said that the toilet has the least stability and if too many girls are in one cubicle, for all we know the floor might crack and just fall causing serious damage. During lessons, we have watched many airplane videos and i have gained much knowledge from them. Some of them teached me about how the planes work. One example is that there are small turbines that generate electricity when the plane has run out of fuel. Another example is how the fuel engines work- X-feed and so on. In all, iwould like to continue in ESP and learn more interesting stuff/ facts.

On a hot day will we get more water since it expands when it gains heat?

10 airplane and helikopter crashes.

How to Survive an Airplane Crash

!!!!!!!!!!!!

How to make bath salt

Materials:
Bottle or Jar
Epsom Salts
Food Coloring
Perfume or Essential Oil
Instructions:Combine the desired amount of Epsom salts (enough to fit in your bottle or jar) with food coloring. Mix well so color is even. Add your perfume or essential oil and mix again. Spread the mixture out on a sheet of wax paper to dry for a couple of hours and then put it in the bottle or jar.
While the salts can be used right away, the perfume or essential oil will blend better with the salt if it is allowed to set in the jar for a few weeks.

Are lefties better at sports?

LEFTIES!!!
­Bring up left-handedness in a conversation and the lefties in your midst will inevitably steer the discussion into all-too-familiar territory. Unless you happen to live in a culture where southpaws are still persecuted as witches, you'll quickly find them talking up just how freaking awesome they think they are.
Perhaps this brash pride stems from childhoods full of right-handed scissors and writing desks. Maybe it's all that elbow bumping with righties at the dining table. Whatever their reasons, give them enough time and they'll inevitably bring up some of the notable celebrities and historical figures who share their bizarre physical condition, everyone from Phil Collins to Charlemagne.
If you have to endure a rant from a left-handed sports fan, they'll probably rattle off such superstars as Arnold Palmer, Bobby Orr, John McEnroe and Oscar De La Hoya and Babe Ruth (although the Babe supposedly wrote right-handed). All told, the list of southpaw sports stars is actually pretty impressive, especially when you consider that lefties only account for roughly 10 percent of the human population -- a number that has remained steady for more than 10,000 years [source: Faurie and Raymond].
While the same can't be said for lefties, numbers don't lie. A disproportionately high percentage of left-handed athletes have long dominated the world of sports. So what gives? Do they really have something special going for them, or are cabals of devious lefties merely trying to spin a right-handed world in their favor?
In this article, we'll explore the impact that left-handedness has on the world of sports, as well as brutal hand-to-hand combat. We'll also look at the way in which similar examples of polymorphism, or genetic variation, are expressed in other organisms and how it affects the biggest game of all: survival of the fittest.
www.howstuffworks.com

THE PREVIOUS POST WAS ON OVERLOADED AIRPLANE.

The principles of weight and balance should have been understood by all pilots during their initial training. It is clear that, afterwards, some forget, don't bother or are caught in 'traps' There have been several fatal accidents to general aviation aircraft in which overloading, or out-of-limits centre of gravity (cg), were contributory factors.An overloaded aircraft may fail to become airborne, while out-of-limits centre of gravity seriously affects the stability and controllability. Pilots must appreciate the effects of weight and balance on the performance and handling of aircraft, particularly in combination with performance reducing factors, such as long or wet grass, a 'tired' engine(s), severe or un-coordinated manoeuvres, turbulence, high ambient temperatures and emergency situations.

The effects of overloading include:
• reduced acceleration and increased take- off speed, requiring a longer take-off run and distance to clear a 50 ft obstacle;• decreased angle of climb reducing obstacle clearance capability after take-off;• higher take-off speeds imposing excessive loads on the landing gear, especially if the runway is rough;• reduced ceiling and rate of climb;• reduced range;• impaired manoeuvrability;• impaired controllability;• increased stall speeds;• increased landing speeds, requiring a longer runway;• reduced braking effectiveness;• reduced structural strength margins;• on twin-engined aircraft, failure to climb or maintain height on one engine.
It must be realised, that with many four and six seat aircraft, it is not possible to fill all the seats, use the maximum baggage allowance, fill all the fuel tanks and remain within the approved weight and centre of gravity limits. You may have to reduce the number of passengers, baggage, or fuel load or possibly a combination of all three. Better that a passenger travels by bus or by train than in an ambulance!
The aircraft weight used in the example calculation in the Flight Manual/Pilot's Operating Handbook is for a new aircraft usually with little or no equipment. The weight and/ or other data used in the example MUST NOT be used as the basis for operational weight and balance calculations. Whenever significant equipment is added a new empty weight and cg position must be provided for the Weight and Balance Schedule. This is the only valid source of data. You must use this actual equipped weight and be sure whether this includes such items as engine oil, fire extinguisher, first aid kit, life jackets, etc. The actual weight of a well equipped single engined aircraft can be as much as 170 lb (77 kg) greater than a basic aircraft – the invisible passenger! Periodic re-weighing of an aircraft is sensible – many owners have been surprised by the increase.
Estimating the weight of baggage can result in variations from half to double the correct weight. If there is a remote possibility of being close to the maximum take-off weight, you must weigh the baggage. (Pocket-sized spring balances can be obtained from fishing/hardware shops and are a handy standby if 'scales' are not available.) Note that, on some aircraft, if the maximum baggage allowance is used, restrictions are placed on rear seat occupancy. When carrying freight, check for any gross errors in the declared weight. There may also be a weight per unit area limitation on the baggage compartment floor. Make sure the baggage/ freight is properly stowed and secured so that it cannot move and does not obstruct exits or emergency equipment. Beware of items such as flammable substances, acids, mercury, magnetic materials, etc which are classified as Dangerous Goods with special controls that apply even in general aviation aircraft. Again, if the aircraft is anywhere near maximum weight, the passengers must be weighed or asked for their weight (even if it means embarrassing your spouse or friends). The risk of embarrassment is a better option than the effect of the aircraft being overweight. Remember, passengers’ weight when flying is NOT their stripped weight. Allow for clothes, shoes, wallets and handbags! Check your own weight as equipped for flying and compare it with the weight you admit to. Fuel gauges are often inaccurate and estimates of the weight of part filled fuel tanks should err on the high side for weight (but NOT endurance) purposes. Be careful of mixed units such as litres/lbs/kgs/Imp gallons/US gallons.h) If a long range or extra tank(s) have been fitted, the extra fuel could add a lot to the weight. Check that the contents marked at the filler cap(s) are the same as in the Pilot's Handbook/Flight Manual or Supplement and are the ones you used for your calculations.
Note:
1 kg =2.205 lb 1 lb = 0.454kg 1 inch =2.54 cm 1 cm = 0.394 inches 1 ft = 0.305 metre 1 m = 3.28 ft 1 Imp gall =4.546 litres 1 litre = 0.22 Imp gall 1 US gall = 3.785 litres 1 litre = 0.264 USG 1 Imp gall =1.205 US gall 1 USG = 0.83 Imp gall
balance (centre of gravity)Balance refers to the location of the centre of gravity (cg) along the longitudinal axis of the aircraft. The cg is the point about which an aircraft would balance if it were possible to suspend it from that point. There are forward and aft limits established during certification flight testing; they are the extreme cg positions at which the longitudinal stability requirements can be met. Operation outside these limits means you would be flying in an area where the aircraft's handling has not been investigated, or is unsatisfactory. The limits for each aircraft are contained in the Pilot's Operating Handbook/Flight Manual. The aircraft must not be flown outside these limits.The cg is measured from a datum reference, which varies from one aircraft type to another, check the Handbook/ Flight Manual.

The arm is the horizontal distance (defined by the manufacturer) from the reference datum to the item of weight. The moment is the product of the weight of an item multiplied by its arm. Remember the see- saw, where a small weight at a large distance can be balanced by a large weight at a small distance.

Exceeding the forward cg limit usually results in:• difficulty in rotating to take-off attitude;• increased stall or minimum flying speed against full up elevator;• extra tail downforce requires more lift from wing resulting in greater induced drag. This means higher fuel consumption and reduced range;• inadequate nose up trim in the landing configuration necessitating a pull force throughout the approach making it more difficult to fly a stable approach;• difficulty in flaring and holding the nose wheel off after touch down. Many modern aircraft have deliberately restricted elevator travel (for stall behaviour reasons). Inability to hold the nose up during a bounce on landing can result in damaged nose landing gear and propeller; increased loads on the nose landing gear.d) Exceeding the aft cg usually results in:• pitch up at low speed and high power, leading to premature rotation on take-off or to inadvertent stall in the climb or during a go-around;• on a tail wheel type, difficulty in raising the tail and in maintaining directional control on the ground;• difficulty in trimming especially at high power;• longitudinal instability, particularly in turbulence, with the possibility of a reversal of control forces;• degraded stall qualities to an unknown degree;• more difficult spin recovery, unexplored spin behaviour, delayed or even inability to recover.
Relatively small, but very heavy objects can make a big difference, e.g. a tool box or spare parts. Be careful where you stow them and make sure they cannot move.On many aircraft the cg moves as fuel is used; on some aircraft types it could move the cg forward to beyond the forward limit when flying solo. On other types the cg moves rearward with fuel use, thus, on a loaded aircraft the cg could move to beyond the aft limit. Aft mounted long range tanks have a large effect. Careful cg calculation prior to flight will reveal any likely problems.The following cg terms may be used (mainly on aircraft certificated to US regulations):Normal category – normal flying, no spinning or aerobatic manoeuvres, bank angle may be restricted to 60°.Utility category – manoeuvres in which bank angles exceed 60°, spinning (if permitted). No aerobatics.There may be cg or weight restrictions on certain manoeuvres e.g. steep turns, spinning, aerobatics etc, imposed by the Pilot's Operating Handbook, Flight Manual or UK Supplement (e.g.: on the Socata Rallye, the rear seats must be removed to remain within the permitted cg range for spinning or aerobatics).Very light (or heavy) pilots flying solo may need ballast or other measures, particularly in some homebuilt and tandem two seat aircraft.Any ballast (permanent or temporary) must be securely fixed.
When parachute dropping remember the effect of the movement of parachutists prior to and immediately after dropping.
calculationThe Pilot's Operating Handbook or Flight Manual contains a Weight and Balance section, with a worked example. The Limitations Section contains the permitted weight and cg limits. (Check to see if there are any supplements which further restrict weight or cg range.) The presentation varies from aircraft to aircraft and may be diagrammatic, graphical or tabular. You must be familiar with the method for your aircraft. Examples follow:

MAGLEV TRAIN

Maglev trains work in one of two ways; both methods are based on the same concept but involve different approaches. German engineers have developed Electromagnetic Suspension (EMS) while the Japanese engineers have developed Electrodynamic Suspension (EDS), the newest EDS technology being the inductrack.

http://www.monorails.org/webpix%202/TPmagEMS.jpg; http://www.monorails.org/webpix%202/TPmagEDS.jpg; http://www.monorails.org/webpix%202/TPmagINDU.jpg
Maglev trains need strong magnetic fields, faster changing fields, thicker material with lower resistivity such as copper, silver, aluminum etc… in order to go fast.
(EMS) "Transrapid International"
http://www.hk-phy.org/energy/transport/trans_phy/images/ems_maglev.gif
Method: Electromagnetic Suspension is based on magnetic attraction; it is very complex and somewhat unstable.
How Does It Work?: Electromagnets line the undercarriage of the train, while the "track" (seen in this diagram as the guideway) is lined with coils. Because the current is constantly changing, the polarity of the coils also changes, permitting the system of magnetic fields to pull and push the train along the guideway. A power source is constantly supplying power to the electromagnets allowing the interaction between the coils and electromagnets to levitate the train. The train levitates about 1cm and remains like this even when it's not moving. The distance is continuously monitored and corrected by computers to avoid accidents. The guidance magnets on the left of the undercarriage are use to stabilize the train, helping it avoid hitting the sides while it's moving.
How Fast? These trains can reach speeds up to 438km/h with passengers on board.
On-board Emergency Equipment: EMS trains are equipped with battery power supplies in case of power failures (trains can suddenly stop levitating and potentially crash), this allows the train to come to a smooth stop.
Potential Health Risks: *Passengers with pacemakers must be careful! The strength of the magnetic fields that are being produced is believed to interfere and disrupt pacemakers.
EDS
http://www.magnet.fsu.edu/education/tutorials/magnetacademy/superconductivity101/images/superconductivity-maglevcut.jpg
Method: Electrodynamic Suspension is based on the repulsion of magnets. The magnetic levitation force balances the weight of the car at a stable position. It is for this reason that the EDS system is believed to be safer than the EMS system.
How Does It Work?: Super-cooled superconducting magnets are placed on the train cars while electromagnetic coils are placed along the track. Superconductors are used because they can conduct electricity even after the power supply has been shut off (unlike the EMS system). When the trains get close to the coils a current is induced which allows the train to levitate about 10 cm and center itself in the middle of the guideway. To get the train moving a second set of coils are placed along the guidance coils and after the train reaches approximately 100km/h the propulsion coils are activated. The electric current that is constantly changing allows for a change in polarity of the electromagnets which in turn pushes and pulls the superconducting magnets of the passing train to allocate movement.
Environmentally Friendly?: By chilling the coils using cryogenics engineers are able to save energy, however the process is very expensive.
How Fast?: These trains can reach speeds up to 522km/h, which is considerably faster than the EMS trains.
Disadvantage/Advantage: EDS train must roll on rubber wheels until they reach a lift-off speed of about 100km/h which causes resistance. However having these wheels is an advantage during a power outage, it allows the train can come to a smooth/safe.
Inductrack
http://www.spacecable.org.uk/Images/Inductrack.jpgA power supply is used to accelerate the train until it levitates and if the power fails is can safely slow down on its auxiliary wheels. The magnets are made from a neodymium-iron-boron alloy (creates a bigger magnetic field) and are arranged in a Halbach array, concentrating the magnetic field above it. The track is an array of short-circuited wires which create a magnetic field and repels the magnets allowing the train to levitate. These types of trains levitate higher, (about 2.54 cm) and are much more stable. There are two designs, Inductrack I which is designed for high speeds and Inductrack II which is designed for slower speeds.

Free-fall maneuvers
In freefall most skydivers start by learning to maintain a stable belly to earth "arch" position[2]. In this position the average fall rate is around 190 km/h (120 mph). Learning a stable arch position is a basic skill essential for a reliable parachute deployment. Next, jumpers learn to move or turn in any direction while remaining belly to earth. Using these skills a group of jumpers can create sequences of formations on a single jump, a discipline formerly known as relative work (RW) and now as formation skydiving (FS). In the late 1980s more experienced jumpers started experimenting with freeflying, falling in any orientation other than belly to earth. Today many jumpers start freeflying soon after they earn their license, bypassing the traditional flat-flying stepping stone.
[edit]
Parachute operation and landing

White sand circular target at a drop zone
The decision of when to deploy the parachute is a matter of safety. A parachute should be deployed sufficiently high to give the parachutist time to handle a malfunction. 600 metres (1,970 ft) is the practical minimum for advanced skydivers.[3] Skydivers monitor their altimeters during freefall to decide when to open their parachutes. Many skydivers open higher to practice their parachute flying skills. During a "hop-and-pop," a jump in which the parachute is deployed immediately upon exiting the aircraft, it is not uncommon to be under canopy as high as 1200 to 1500 meters (4000 to 5000 ft).
Parachute flying involves two challenges. Firstly to avoid injury and secondly to land where planned, often on a designated target. Some experienced skydivers enjoy performing aerobatic maneuvers with parachutes, the most notable being the "Swoop". This is a thrilling, but dangerous maneuver entailing a steep, high speed landing approach, before leveling off a couple of feet above the ground to maintain a fast glide parallel to the surface. Swoops as far as 180 metres (590 ft) have been achieved.
A modern parachute or canopy "wing" can glide substantial distances. Elliptical canopies go faster and farther, and some small, highly loaded canopies glide faster than it is possible to run, which can make them very challenging to land. A highly experienced skydiver using a very small canopy can achieve over 100 km/h (60 mph) horizontal speeds in landing.
Today, the majority of skydiving related injuries and deaths happen under a fully opened and functioning parachute; the most common cause being poorly-executed, radical maneuvers near to the ground, such as hook turns, or landing flares performed either too high or too low.[4]
www.wikipedia.org

Scuba diving

Hazards and dangers

According to a 1970 North American study, diving was (on a man-hours based criteria) 96 times more dangerous than driving an automobile.

[11] According to a 2000 Japanese study, every hour of recreational diving is 36 to 62 times riskier than automobile driving.[12]

Injuries due to changes in air pressure
For a full list, see Diving hazards and precautions.
Divers must avoid injuries caused by changes in air pressure. The weight of the water column above the diver causes an increase in air pressure in any compressible material (wetsuit, lungs, sinus) in proportion to depth, in the same way that atmospheric air causes a pressure of 101.3 kPa (14.7 pounds-force per square inch) at sea level. Pressure injuries are called barotrauma[3] and can be quite painful, in severe cases causing a ruptured eardrum or damage to the sinuses. To avoid them, the diver equalizes the pressure in all air spaces with the surrounding water pressure when changing depth. The middle ear and sinus are equalized using one or more of several techniques, which is referred to as clearing the ears.
The mask is equalized by periodically exhaling through the nose.
If a drysuit is worn, it too must be equalized by inflation and deflation, similar to a buoyancy compensator.
If properly equalized, the sinus passages can stand the increased pressure of the water with no problems. However, congestion due to cold, flu or allergies may impair the ability to equalize the pressure. This may result in permanent damage to the eardrum. Although there are many dangers involved in scuba diving, divers can decrease the dangers through proper training and education. Open-water certification programs highlight diving physiology, safe diving practices, and diving hazards.

Effects of breathing high pressure gas

Decompression sickness
Main article: Decompression sickness
The diver must avoid the formation of gas bubbles in the body, called decompression sickness[3] or 'the bends', by releasing the water pressure on the body slowly while ascending and allowing gases trapped in the bloodstream to gradually break solution and leave the body, called "off-gassing." This is done by making safety stops or decompression stops and ascending slowly using dive computers or decompression tables for guidance. Decompression sickness must be treated promptly, typically in a recompression chamber. Administering enriched-oxygen breathing gas or pure oxygen to a decompression sickness stricken diver on the surface is a good form of first aid for decompression sickness, although fatality or permanent disability may still occur.[13]

Nitrogen narcosis
Main article: Nitrogen narcosis
Nitrogen narcosis or inert gas narcosis is a reversible alteration in consciousness producing a state similar to alcohol intoxication in divers who breathe high pressure gas at depth.[3] The mechanism is similar to that of nitrous oxide, or "laughing gas," administered as anesthesia. Being "narced" can impair judgment and make diving very dangerous. Narcosis starts to affect some divers at 66 feet (20 meters). At 66 feet (20 m), Narcosis manifests itself as slight giddiness. The effects increase drastically with the increase in depth. Almost all divers are able to notice the effects by 132 feet (40 meters). At these depths divers may feel euphoria, anxiety, loss of coordination and lack of concentration. At extreme depths, hallucinogenic reaction and tunnel vision can occur. Jacques Cousteau famously described it as the "rapture of the deep". Nitrogen narcosis occurs quickly and the symptoms typically disappear during the ascent, so that divers often fail to realize they were ever affected. It affects individual divers at varying depths and conditions, and can even vary from dive to dive under identical conditions. However, diving with trimix or heliox dramatically reduces the effects of inert gas narcosis.

Oxygen toxicity
Main article: Oxygen toxicity
Oxygen toxicity occurs when oxygen in the body exceeds a safe "partial pressure" (PPO2).[3] In extreme cases it affects the central nervous system and causes a seizure, which can result in the diver spitting out his regulator and drowning. Oxygen toxicity is preventable provided one never exceeds the established maximum depth of a given breathing gas. For deep dives (generally past 180 feet / 55 meters), divers use "hypoxic blends" containing a lower percentage of oxygen than atmospheric air. For more information, see Oxygen toxicity.

Refraction and underwater vision
Main article: Underwater vision

A diver wearing an Ocean Reef full face mask
Water has a higher refractive index than air; it's similar to that of the cornea of the eye. Light entering the cornea from water is hardly refracted at all, leaving only the eye's crystalline lens to focus light. This leads to very severe hypermetropia. People with severe myopia, therefore, can see better underwater without a mask than normal-sighted people.
Diving masks and diving helmets and fullface masks solve this problem by creating an air space in front of the diver's eyes.[2] The refraction error created by the water is mostly corrected as the light travels from water to air through a flat lens, except that objects appear approximately 34% bigger and 25% closer in salt water than they actually are. Therefore total field-of-view is significantly reduced and eye-hand coordination must be adjusted.
(This affects underwater photography: a camera seeing through a flat window in its casing is affected the same as its user's eye seeing through a flat mask window, and so its user must focus for the apparent distance to target, not for the real distance.)
Divers who need corrective lenses to see clearly outside the water would normally need the same prescription while wearing a mask. Generic and custom corrective lenses are available for some two-window masks. Custom lenses can be bonded onto masks that have a single front window.
A "double-dome mask" has curved windows in an attempt to cure these faults, but this causes a refraction problem of its own.
Commando frogmen concerned about revealing their position when light reflects from the glass surface of their diving masks may instead use special contact lenses to see underwater.
As a diver descends, he must periodically exhale through his nose to equalize the internal pressure of the mask with that of the surrounding water. Swimming goggles are not suitable for diving because they only cover the eyes and thus do not allow for equalization. Failure to equalise the pressure inside the mask may lead to a form of barotrauma known as mask squeeze.[2][14]

Controlling buoyancy underwater

Diver under the Salt Pier in Bonaire.
To dive safely, divers must control their rate of descent and ascent in the water.[3] Ignoring other forces such as water currents and swimming, the diver's overall buoyancy determines whether he ascends or descends. Equipment such as the diving weighting systems, diving suits (Wet, Dry & Semi-dry suits are used depending on the water temperature) and buoyancy compensators can be used to adjust the overall buoyancy.[2] When divers want to remain at constant depth, they try to achieve neutral buoyancy. This minimizes gas consumption caused by swimming to maintain depth.
The downward force on the diver is the weight of the diver and his equipment minus the weight of the same volume of the liquid that he is displacing; if the result is negative, that force is upwards. Diving weighting systems can be used to reduce the diver's weight and cause an ascent in an emergency. Diving suits, mostly being made of compressible materials, shrink as the diver descends, and expand as the diver ascends, creating buoyancy changes. The diver can inject air into some diving suits to counteract the compression effect and squeeze. Buoyancy compensators allow easy and fine adjustments in the diver's overall volume and therefore buoyancy. For open circuit divers, changes in the diver's lung volume can be used to adjust buoyancy.

Avoiding losing body heat

Dry suit for reducing exposure
Main article: Diving suit
Water conducts heat from the diver 25 times[15] better than air, which can lead to hypothermia even in mild water temperatures.[3] Symptoms of hypothermia include impaired judgment and dexterity[16], which can quickly become deadly in an aquatic environment. In all but the warmest waters, divers need the thermal insulation provided by wetsuits or drysuits.[2]
In the case of a wetsuit, the suit is designed to minimize heat loss. Wetsuits are generally made of neoprene that has small gas cells, generally nitrogen, trapped in it during the manufacturing process. The poor thermal conductivity of this expanded cell neoprene means that wetsuits reduce loss of body heat by conduction to the surrounding water. The neoprene in this case acts as an insulator.
The second way in which wetsuits reduce heat loss is to trap a thin layer of water between the diver's skin and the insulating suit itself. Body heat then heats the trapped water. Provided the wetsuit is reasonably well-sealed at all openings (neck, wrists, legs), this reduces water flow over the surface of the skin, reducing loss of body heat by convection, and therefore keeps the diver warm (this is the principle employed in the use of a "Semi-Dry")

Spring suit and steamer
In the case of a drysuit, it does exactly that: keeps a diver dry. The suit is sealed so that frigid water cannot penetrate the suit. Drysuit undergarments are often worn under a drysuit as well, and help to keep layers of air inside the suit for better thermal insulation. Some divers carry an extra gas bottle dedicated to filling the dry suit. Usually this bottle contains argon gas, because of its better insulation as compared with air.[17]
Drysuits fall into two main categories neoprene and membrane; both systems have their good and bad points but generally their thermal properties can be reduced to:
Membrane: usually a trilaminate construction; owing to the thinness of the material (around 1 mm), these require an undersuit, usually of high insulation value if diving in cooler water.
Neoprene: a similar construction to wetsuits; these are often considerably thicker (7–8 mm) and have sufficient insulation to allow a lighter-weight undersuit (or none at all); however on deeper dives the neoprene can compress to as little as 2 mm thus losing a proportion of their insulation. Compressed or crushed neoprene may also be used (where the neoprene is pre-compressed to 2–3 mm) which avoids the variation of insulating properties with depth.

Avoiding skin cuts and grazes
Diving suits also help prevent the diver's skin being damaged by rough or sharp underwater objects, marine animals or coral.

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Scuba diving

BREATHING UNDERWATER:D
Water normally contains dissolved oxygen from which fish and other aquatic animals extract all their required oxygen as the water flows past their gills. Humans lack gills and do not otherwise have the capacity to breathe underwater unaided by external devices.[3] Although the feasibility of filling and artificially ventilating the lungs with a dedicated liquid (Liquid breathing) has been established for some time,[6] the size and complexity of the equipment allows only for medical applications with current technology.[7]
Early diving experimenters quickly discovered it is not enough simply to supply air in order to breathe comfortably underwater. As one descends, in addition to the normal atmospheric pressure, water exerts increasing pressure on the chest and lungs—approximately 1 bar or 14.7 psi for every 33 feet or 10 meters of depth—so the pressure of the inhaled breath must almost exactly counter the surrounding or ambient pressure to inflate the lungs. It generally becomes difficult to breathe through a tube past three feet under the water.[3]
By always providing the breathing gas at ambient pressure, modern demand valve regulators ensure the diver can inhale and exhale naturally and virtually effortlessly, regardless of depth.
Because the diver's nose and eyes are covered by a diving mask; the diver cannot breathe in through the nose, except when wearing a full face diving mask. However, inhaling from a regulator's mouthpiece becomes second nature very quickly.

Open-circuit
The most commonly used scuba set today is the "single-hose" open circuit 2-stage diving regulator, coupled to a single pressurized gas cylinder, with the first stage on the cylinder and the second stage at the mouthpiece.[2] This arrangement differs from Emile Gagnan's and Jacques Cousteau's original 1942 "twin-hose" design, known as the Aqua-lung, in which the cylinder's pressure was reduced to ambient pressure in one or two or three stages which were all on the cylinder. The "single-hose" system has significant advantages over the original system.
In the "single-hose" two-stage design, the first stage regulator reduces the cylinder pressure of about 200 bar (3000 psi) to an intermediate level of about 10 bar (145 psi) The second stage demand valve regulator, connected via a low pressure hose to the first stage, delivers the breathing gas at the correct ambient pressure to the diver's mouth and lungs. The diver's exhaled gases are exhausted directly to the environment as waste. The first stage typically has at least one outlet delivering breathing gas at unreduced tank pressure. This is connected to the diver's pressure gauge or computer, in order to show how much breathing gas remains.

Rebreather

An Inspiration electronic fully closed circuit rebreather
Main article: Rebreathers
Less common are closed and semi-closed rebreathers,[8] which unlike open-circuit sets that vent off all exhaled gases, reprocess each exhaled breath for re-use by removing the carbon dioxide buildup and replacing the oxygen used by the diver.
Rebreathers release few or no gas bubbles into the water, and use much less oxygen per hour because exhaled oxygen is recovered; this has advantages for research, military[2], photography, and other applications. The first modern rebreather was the MK-19 that was developed at S-Tron by Ralph Osterhout that was the first electronic system.[citation needed] Rebreathers are more complex and more expensive than sport open-circuit scuba, and need special training and maintenance to be safely used.[8]
Because the nitrogen in the system is kept to a minimum, decompressing is much less complicated than traditional open-circuit scuba systems and, as a result, divers can stay down longer. Because rebreathers produce very few bubbles, they do not disturb marine life or make a diver’s presence known; this is useful for underwater photography, and for covert work.

Gas mixtures



Nitrox cylinder marked up for use
Main article: Breathing gas
For some diving, gas mixtures other than normal atmospheric air (21% oxygen, 78% nitrogen, 1% trace gases) can be used,[2][3] so long as the diver is properly trained in their use. The most commonly used mixture is Enriched Air Nitrox, which is air with extra oxygen, often with 32% or 36% oxygen, and thus less nitrogen, reducing the likelihood of decompression sickness. The reduced nitrogen may also allow for no or less decompression stop times and a shorter surface interval between dives. A common misconception is that nitrox can reduce narcosis, but research has shown that oxygen is also narcotic.[9][10]
Several other common gas mixtures are in use, and all need specialized training. The increased oxygen levels in nitrox help fend off decompression sickness; however, below the maximum operating depth of the mixture, the increased partial pressure of oxygen can lead to oxygen toxicity. To displace nitrogen without the increased oxygen concentration, other diluents can be used, often helium, when the resultant mixture is called trimix.
For technical dives, some of the cylinders may contain different gas mixture for each phase of the dive, typically designated as Travel, Bottom, and Decompression. These different gas mixtures may be used to extend bottom time, reduce inert gas narcotic effects, and reduce decompression times.

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Stiletto heel

DISADVANTAGES OF WEARING STILETTO HEELS!!

All high heels counter the natural functionality of the foot, which can create skeleton/muscular problems if they are worn excessively. Stiletto heels are no exception, but some people assume that because they are thinner they must be worse for you. In fact, they are safer to wear than the other extreme of high heel fashion, the platform shoe.[citation needed] Despite their impracticality, their popularity remains undiminished - as Terry DeHavilland (UK shoe designer) has said, "people say they're bad for the feet but they're good for the mind. What's more important?"
Stiletto heels undoubtedly concentrate a large amount of force into a small area. The great pressure transmitted through such a heel (allegedly greater than that exerted by an elephant standing on one foot[4]) can cause damage to carpets and floors. The stiletto heel will also sink into soft ground, making it impractical for outdoor wear on grass.

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Density

What substance, other than water, is less dense as a solid than as a liquid?
Only bismuth and water share this characteristic. Density (the mass per unit volume or mass/volume) refers to how compact or crowded a substance is. For instance, the density of water is 1 g/cm3 (gram per cubic centimeter) or 1 kg/l (kilogram per liter); the density of a rock is 3.3 g/cm3; pure iron is 7.9 g/cm3; and the Earth (as a whole) is 5.5 g/cm3 (average). Water as a solid (i.e., ice) floats, which is a good thing; otherwise, ice would sink to the bottom of every lake or stream.
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Density

Why is liquid water more dense than ice?
Pure liquid water is most dense at 39.2°F (3.98°C) and decreases in density as it freezes. The water molecules in ice are held in a relatively rigid geometric pattern by their hydrogen bonds, producing an open, porous structure. Liquid water has fewer bonds; therefore, more molecules can occupy the same space, making liquid water more dense than ice.
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A History of Fish Glue as an Artist's Material: Applications in Paper and Parchment Artifacts

FISH GLUE!!!!

Glue can be extracted from fish by heating the skin or bones in water. The purest form of fish glue, made from the membrane of the air bladder (swim bladder) of certain species of fish such as the sturgeon, is also called isinglass (fig. 1). Isinglass can be produced from various species of fish using diverse manufacturing processes. Depending on the manufacture, the purity of isinglass can vary. Historic sources do not always specify which part of the fish was used to make the glue.
There is no record telling us exactly when and where the first animal or fish glue adhesives were used. However, it is known that at least 3500 years ago these adhesives were used in Egypt. Even though Egyptian records do not describe in detail the adhesive preparation process, they do tell us that it was made by being melted over fire and then applied with a brush (Darrow 1930, 9).
From the first-century Roman scholar Plinius we learn that two kinds of glue were used in antiquity: animal glue (taurokolla in Greek, gluten taurinum in Latin), made from the skins of bulls, and fish glue (ichtyokolla) made from some parts of fishes. In references to the glue used by ancient craftsmen, both terms xylokolla (in Greek) and gluten fabrile (in Latin) are cited; however, it is not clear to which kind of glue these terms applied (Gug 1975, 37).
In an eighth-century European manuscript from the Cathedral of Lucca, fish glue is recorded as a material for painting. A. P. Laurie translated this manuscript into English in 1926; it tells that the pigments in fresco paintings were applied to wet plaster without mixing them with a binding medium, using only water. For panel paintings wax was mixed with the pigments, and for illuminating parchment manuscripts fish skin glue was used (Laurie 1926, 107).
In the Middle Ages in a twelfth-century treatise on methods and recipes for painting and illuminating by the German Benedictine monk Theophilus, fish glue appears once again. In his Schedula Diversarum Artium (Ch. XXX) he gives directions for grinding gold and then mixing it with fish glue for use in gilding of illuminated manuscripts. He continues, (Ch. XXXIII):
... on every sort of glue for pictures of gold, if you have not a bladder cut up thick parchment or vellum. ... Prepare also the skin of an eel. ... Prepare thus also the bones of the head of the wolf-fish, washed and dried, carefully washed in warm water three times. To which ever of these you have prepared, add a third part of very transparent gum, simmer it a little, and you can keep it as long as you wish. (Laurie 1926, 167)
In discussing ink preparation, Theophilus also mentions fish glue among such other materials as yolk of egg, white of egg, parchment, cherry gum, plum-tree gum, and linseed oil (Laurie 1926, 170).
In around 1390 Cennino Cennini (an Italian artist trained by Agnolo Gaddi), the author of the Craftsman's Handbook (Il Libro dell'Arte), mentions earlier applications of fish glue in restoration: "This glue is made from various kinds of fish . . . it is good and excellent for mending lutes and other fine paper, wooden or bone objects" (Cennini [ca. 1390] 1960, 66-67).
Historical Uses of Fish Glue
As we can see from ancient and medieval records, fish glue was both a common and important adhesive for many special applications; adapted by artists, it was used from the time of ancient Egypt to twentieth-century France, in painting media, coatings and grounds, in the gilding of illuminated manuscripts, and in pastel fixatives.
Illuminated Parchment Manuscripts: Sizing, Gilding, and Repair
In medieval Europe, parchment was the main material for writing. It was usually made from sheep or calf skin, but occasionally from the skins of such other animals as goat, antelope, and gazelle. Preparation of the parchment was a time-consuming procedure requiring special skills. One of the many steps in the process was sizing of the parchment, which enhanced its strength and prevented the writing medium from penetrating too deeply, allowing the parchment to be reused. When the parchment was to be used over again, the old ink or gouache-like medium was removed from the surface by rubbing pumice over it; the area was then softened so it could absorb new writing.
Two types of size application, coating and impregnation, were employed. The sizing solution was generally produced from scraps of parchment or trimmings of the whole skin of an animal. Small pieces were then soaked and boiled in fresh water. Fish glue was also used to size parchment. According to D. V. Thompson, this size was prepared from the sounds (air bladders) of stockfish and sturgeon in a manner similar to that used for parchment preparation (Thompson [1936] 1956, 59).

Fig. 2. Using prepared isinglass to consolidate flaking media on parchment.
Thompson also mentions fish glue in the context of stabilization (mending) of damaged sheets of parchment, ground preparation for laying gold or pigments, and as a binding medium (fig. 2). The purpose of the binder was to hold particles of pigments together allowing for the paint to be firmly attached to the surface of the parchment. The area on which the gold leaf would be laid was coated first with a solution of fish glue. The property of fish glue to adhere well to the porous parchment support made it a useful material for illumination of manuscripts with gold leaf and painting.
Oriental Painting and Calligraphy on Paper: Binding Medium
In China various kinds of animal glues were implemented as binders in paint media during the T'ang dynasty (618-906 a.d.). According to records of this period, for example, one of the essential components of lampblack ink was proteinaceous glue (Sze 1956, 67-68). One of the high quality inks used at that time was made from donkey hides and then mixed with carbon pigment. It is the glossy characteristics of that particular ink that make it easily distinguishable by specialists today. The particular kinds of animal glue that were used during the manufacturing process have, over thousands of years, preserved the distinct features of this finest quality ink.
The Chinese of the T'ang Dynasty manufactured many grades of animal glue. Glues were produced from horns and hides of deer, hides of cow, and skins of fish. Chinese documents of the ninth century record the employment of hide and fish glue in paint media (Winter [1936] 1956, 117). Fish glue from Wu (Kiangsu province) was mentioned, among other paint binders, such as ox glue from Santung and a stag-horn glue from Yun (Yannan province) by the T'ang critic, Chang Yen-yuan (Siren 1936, 232). These glues bind particles of pigments together, forming a film over the ink surface as the ink dries. This coating functions as an organic barrier, which protects ink from the hazardous effects of the environment. The glue also provides an adhesion between particles of pigments and the support. Chinese traditional supports on which ink was applied were, and still are, made from porous materials such as paper and silk. These supports allow the binding medium mixed with pigment to penetrate into the fibers and create a strong bond with it that is beneficial for the stability of an ink medium.
Gouache on Paper and Board: Glazing and Coating
In the nineteenth century some artists experimented with non-traditional techniques. Some of these innovations were taken seriously by other artists of the time, but they often failed. The gouache paintings by M. Pierran, for example, which were coated heavily with glue in order to obtain a special effect, were exhibited in the 1834 Salon. These gouaches with their glossy surfaces resembled oil paintings. The technique involves application of the mixture of gouache with a large amount of gum and fish glue. These paintings over time have developed delamination and cracking (Bazzi 1960, 109).
Another method of painting with watercolor on specially prepared Bristol board was developed by C. J. Robertson, for which he received the Medal of Isis from the Society for Encouragement of the Arts, London. The process, from the backing of a Bristol board to the coating, was elaborate. When the picture was completed it was "varnished" with a solution of fish glue and then with a good quality picture varnish. "The advantages of the method are that the color, which stays very brilliant and transparent, may be worked over in a way impossible by any ordinary method. A similar method is described by Vibert" (Bazzi 1960, 108).
Artists' experiments with coating and glazing of paintings and drawings with fish glue were recorded as early as the seventeenth century. Fish glue produced by boiling of the swim bladders of sturgeons was experimentally used by Van Dyck in his tempera paintings. When fish glue was applied in many layers and in glazed coats, the film formed was easily chipped off (Doerner 1984, 224-225).
These earlier attempts demonstrate that fish glue used alone forms a brittle film. As with any other adhesive, when and where it is appropriate to apply should be considered carefully. Perhaps the brittleness of the film formed by this glue motivated artists to introduce various plasticizers that are also used in conjunction with fish glue in restoration. Molasses in England and honey in Russia have often been used as natural plasticizers. For example, isinglass glue mixed with honey had been used for the consolidation of delaminated paint in Russian icons as early as the seventeenth century (Petukhova 1993).
Drawings: Pastel Binder and Fixative
The makeup of soft pastels has not been changed much since the fifteenth century when this medium came into existence. Pulverized color pigments combined usually with white chalk were rolled together into cylinders or other shapes with a small amount of binder. Gum tragacanth and methyl cellulose are probably the most favorable binders in modern manufacturing of soft pastels, although in early recipes, milk, beer, ale, or fish glue had been employed (Maheux 1988, 41).
Methods for fixing pastels have been a great concern for artists working in this medium. Various techniques, from powdering the surface of pastel with gum arabic and then fixing it with hot steam and spraying it with a mixture of water, glue and spirit, to spraying the verso of the pastel with skimmed milk, have been implemented by artists in order to protect this fragile medium from unavoidable deterioration. Milk, water, thin tempera, resin, spirit, and also glue solutions have been the main components of many recipes for pastel fixatives.
Among the artists seriously searching for a method to stabilize the pastel medium and experimenting with isinglass glue, as a component of fixatives are Latour and Degas. The following recipe described by Loriot, and perhaps also used by Latour, includes isinglass glue:
Melt about 150 grains of isinglass in about 3/4 pt. of pure water in a double saucepan over a low fire. Strain through fine linen and pour on to a plate while hot. Add 2 parts of wine spirit to 1 part of glue. (Bazzi 1960, 98)
The method of fixing pastel with this solution, as Maria Bazzi recommends, is by spraying the verso of artwork.
Besides its applications in graphic arts, fish glue material can be found in priming, binding paint medium, glazing, and coating of easel and encaustic paintings and icons. It proved to be an excellent adhesive for wooden objects since the time of ancient Egyptians, who knew the unique qualities of this material.
Conclusion
It is my belief that conservators have a responsibility to preserve not only the physical structure of an object but also the knowledge left to us by our fellow artists and restorers of an earlier age. Those materials that well served artists and restorers for centuries should not be forgotten. We might find them very useful even today if we have a fresh look at their properties and methods of application. In this article I hope to reawaken the historic knowledge of the use of fish glue, one of the earliest artist's materials, and to encourage its scientific research and its use in conservation of historic and artistic works.

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