Golden Gate Bridge

Located at the northern end of San Francisco Peninsula west of the Pacific Ocean, San Francisco is the most densely populated city in the state of the California and the 12th most populous city in the US, with an estimated population of 809,000 as of 2008.

San Francisco is a popular international tourist destination renowned for its chilly summer fog, steep rolling hills, eclectic mix of Victorian and modern architecture, and its famous landmarks, including the Golden Gate Bridge, the cable cars, and Chinatown.

Tourism is the backbone of San Francisco's economy. The city attracts the fourth highest number of international tourists of any city in the US and claims Pier 39 near Fisherman's Wharf as the third most popular tourist destination in the country. With a large hotel infrastructure and a world-class convention facility in the Moscone Center, San Francisco is among the top ten destinations for conventions and conferences in North America.

what's a laser

Did you know there is something called "white light"?
Regular light from the sun or from a light bulb really contains all the colors of the rainbow. But you have to split it up to see this.
Can you split light???
YES! You can split up white light into its colors with a prism (raindrops act like tiny prisms when they make a rainbow in the sky, and a CD can break the light up into colors because it has fine grooves like a diffraction grating or a hologram).

So what's a laser?
A laser is a special source of light of only one pure color (or WAVELENGTH). You can't break up laser light into other colors.

They can FOCUS!

Lasers can be focused to a very small spot and can shine for long distances without spreading out very much (unlike a flashlight which spreads out a lot).

They generate ENERGY!

The spot contains a lot of energy - so much that some lasers can cut through thick metal (and smaller ones are used as scalpels in some kinds of surgery) .

They can carry INFORMATION!

Lower-power laser systems can be used to send and pick up information. For example, the product code scanner in a supermarket uses a laser, lenses, rotating mirrors, and a computer to "read" bar codes from products. And the tiny laser in a CD player reads EVEN tinier bumps and holes that record the music like Morse Code (bumps and holes are used something like dots and dashes).

They can be used for COMMUNICATION!

Lasers can also send information through long threads of glass called OPTICAL FIBERS. A single laser can send thousands of phone conversations through a fiber at the SAME TIME.

They make HOLOGRAMS!

Lasers are also used to make 3-D pictures called HOLOGRAMS (some engineers are working on moving holograms, so someday we may have AMAZING 3-D TV pictures - learn more about holograms at holoworld.com).

IMPORTANT SAFETY NOTE: PLEASE BE CAREFUL WITH LASERS. 
Even low-power laser pointers can cause injury if shined directly into eyes.  Children should be supervised or be old enough to understand the safety issues and handle these devices safely.

What is light

It's a kind of energy called "electromagnetic (EM) radiation" (but this kind of radiation is not harmful, except for an occasional sunburn). There are other kinds of EM radiation too (radio waves, microwaves, x-rays, etc.), but light is the part WE can see, the part that makes the rainbow.

How does light travel?
FAST and STRAIGHT.

How FAST?
About 186,000 miles per second [300,000 kilometers per second], so light from the sun takes about 8 minutes to go 93 million miles [149 million kilometers] to earth. Does this seem SLOW? Well, if you could DRIVE to the sun at 60 mph [100 kph], it would take you 177 years to get there! In one second, light can go around the earth 7 times! 

How STRAIGHT?
Perfectly straight, until something bends it. The straight paths of light are called LIGHT RAYS.

There are THREE basic ways to control light (these activities require Flash):

Block it ... with something (this makes a shadow).

 

Reflect it (change its path with a mirror)

This is called a REFLECTION. Click on the image below to see the interactive demo. Demo courtesy of Mr. David M. Harrison, Dept. of Physics, Univ. of Toronto.

Bend it

Change its direction by making it pass into another transparent material of different density, like glass or water.This is called REFRACTION, and it's how lenses work. Click on the image below to see the interactive demo. Demo courtesy of Mr. David M. Harrison, Dept. of Physics, Univ. of Toronto.

The fine print: There are actually other ways to bend or deflect light, including diffraction gratings and holographic lenses.  These depend on the wave nature of light, and are a little more difficult to explain.   Scientists have also found that gravity can bend light, but it takes a very large object with strong gravity such as a star to bend light very much, so it's not an effect you see every day!

Light is produced, controlled, and detected in so many ways around you!

 And many more things such as

• contact lenses,
• lenses for TV, movie, and photographic cameras,
• fax machines, telescopes,
• microscopes and magnifiers,
• medical systems
• other projectors (overhead, movie, slide, TV),
• weather and spy satellites, and
• solar energy systems
• (not to mention a little thing like PLANTS which use light to grow and to make the oxygen we breathe - but engineers don't make plants).

Teachers awards

Do you know an inspirational teacher?
If you know a teacher who deserves recognition, please nominate them for an award. We are looking for teachers who inspire in their pupils and colleagues a love of physics or science in the primary context. It is not a competition, but rather a wish to spotlight and celebrate the work of teachers in the classroom.

There are awards available for teachers of physics and teachers of primary science. Nominations can come from a variety of sources, including head teachers, colleagues, governors, advisers, Institute Branch representatives, parents and even students.

The winners will be chosen by a panel of current and former teachers and there are no restrictions on the number of awards in each category. The panel is looking for teachers who:

• are outstanding teachers of physics or primary science
• have inspired pupils beyond the classroom
• have inspired and supported colleagues
• have worked with the wider education community

Award-winners typically have a minimum of 7 years’ teaching experience.

Good nominations use anecdote and example to bring classroom experiences to life and explain why the teacher makes a difference. Evidence from pupils or former pupils is very helpful in illustrating a teacher’s exceptional qualities.

Nominations for 2012 awards
Nomination forms and additional advisory notes for the 2012 awards are given below. There is also a form that referees may wish to use for their supporting statement. These forms can be completed electronically and emailed to the Institute or downloaded and printed out for completion by hand .

carbon nanotubes

Carbon nanotubes

Introduction :

Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, which is significantly larger than any other material. These cylindrical carbon molecules have novel properties that make them potentially useful in many applications in nanotechnology, electronics, optics and other fields of materials science, as well as potential uses in architectural fields. They exhibit extraordinary strength and unique electrical properties, and are efficient thermal conductors. Their final usage, however, may be limited by their potential toxicity and controlling their property changes IN RESPONSE TO CHEMICAL TREATMENT.

Nanotubes are members of the fullerene structural family, which also includes the spherical buckyballs. The ends of a nanotube might be capped with a hemisphere of the buckyball structure. Their name is derived from their size, since the diameter of a nanotube is on the order of a few nanometers (approximately 1/50,000th of the width of a human hair), while they can be up to several millimeters in length (as of 2008). Nanotubes are categorized as single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs).

The nature of the bonding of a nanotube is described by applied quantum chemistry, specifically, orbital hybridization. The chemical bonding of nanotubes is composed entirely of sp2 bonds, similar to those of graphite. This bonding structure, which is stronger than the sp3 bonds found in diamonds, provides the molecules with their unique strength. Nanotubes naturally align themselves into "ropes" held together by Van der Waals forces.







Types of carbon nanotubes and related structures :

     

single-walled nanotubes

Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometer, with a tube length that can be many millions of times longer. The structure of a SWNT can be conceptualized by wrapping a one-atom-thick layer of graphite called graphene into a seamless cylinder. The way the graphene sheet is wrapped is represented by a pair of indices (n,m) called the chiral vector. The integers n and m denote the number of unit vectors along two directions in the honeycomb crystal lattice of graphene. If m = 0, the nanotubes are called "zigzag". If n = m, the nanotubes are called "armchair". Otherwise, they are called "chiral".
Single-walled nanotubes are an important variety of carbon nanotube because they exhibit electric properties that are not shared by the multi-walled carbon nanotube (MWNT) variants. In particular, their band gap can vary from zero to about 2 eV and their electrical conductivity can show metallic or semi conducting behavior, whereas MWNTs are zero-gap metals. Single-walled nanotubes are the most likely candidate for miniaturizing electronics beyond the micro electromechanical scale currently used in electronics. The most basic building block of these systems is the electric wire, and SWNTs can be excellent conductors. One useful application of SWNTs is in the development of the first intramolecular field effect transistors (FET). Production of the first intramolecular logic gate using SWNT FETs has recently become possible as well. To create a logic gate you must have both a p-FET and an n-FET. Because SWNTs are p-FETs when exposed to oxygen and n-FETs otherwise, it is possible to protect half of an SWNT from oxygen exposure, while exposing the other half to oxygen. This results in a single SWNT that acts as a NOT logic gate with both p and n-type FETs within the same molecule.
Single-walled nanotubes are dropping precipitously in price, from around $1500 per gram as of 2000 to retail prices of around $50 per gram of as-produced 40-60% by weight SWNTs as of March 2010

Multi-walled nanotubes
Multi-walled nanotubes (MWNT) consist of multiple rolled layers (concentric tubes) of graphite. There are two models which can be used to describe the structures of multi-walled nanotubes.
 In the Russian Doll model, sheets of graphite are arranged in concentric cylinders, e.g. a (0,8) single-walled nanotube (SWNT) within a larger (0,10) single-walled nanotube.
 In the Parchment model, a single sheet of graphite is rolled in around itself, resembling a scroll of parchment or a rolled newspaper.
The interlayer distance in multi-walled nanotubes is close to the distance between graphene layers in graphite, approximately 3.4 Å.



The special place of double-walled carbon nanotubes (DWNT) must be emphasized here because their morphology and properties are similar to SWNT but their resistance to chemicals is significantly improved.
This is especially important when functionalization is required (this means grafting of chemical functions at the surface of the nanotubes) to add new properties to the CNT. In the case of SWNT, covalent functionalization will break some C=C double bonds, leaving "holes" in the structure on the nanotube and thus modifying both its mechanical and electrical properties. In the case of DWNT, only the outer wall is modified.
DWNT synthesis on the gram-scale was first proposed in 2003 by the CCVD technique, from the selective reduction of oxide solutions in methane and hydrogen .



Torus


A stable nanobud structure
A nanotorus is theoretically described as carbon nanotube bent into a torus (doughnut shape). Nanotori are predicted to have many unique properties, such as magnetic moments 1000 times larger than previously expected for certain specific radii. Properties such as magnetic moment, thermal stability, etc. vary widely depending on radius of the torus and radius of the tube.

Nanobud
Carbon nanobuds are a newly created material combining two previously discovered allotropes of carbon: carbon nanotubes and fullerenes. In this new material, fullerene-like "buds" are covalently bonded to the outer sidewalls of the underlying carbon nanotube. This hybrid material has useful properties of both fullerenes and carbon nanotubes. In particular, they have been found to be exceptionally good field emitters. In composite materials, the attached fullerene molecules may function as molecular anchors preventing slipping of the nanotubes, thus improving the composite’s mechanical properties.








Properties :

Strength
Carbon nanotubes are the strongest and stiffest materials yet discovered in terms of tensile strength and elastic modulus respectively. This strength results from the covalent sp² bonds formed between the individual carbon atoms. In 2000, a multi-walled carbon nanotube was tested to have a tensile strength of 63 gigapascals (GPa). (This, for illustration, translates into the ability to endure tension of a weight equivalent to 6300 kg on a cable with cross-section of 1 mm2.) Since carbon nanotubes have a low density for a solid of 1.3 to 1.4 g•cm−3, its specific strength of up to 48,000 kN•m•kg−1 is the best of known materials, compared to high-carbon steel's 154 kN•m•kg−1.
Under excessive tensile strain, the tubes will undergo plastic deformation, which means the deformation is permanent. This deformation begins at strains of approximately 5% and can increase the maximum strain the tubes undergo before fracture by releasing strain energy.
CNTs are not nearly as strong under compression. Because of their hollow structure and high aspect ratio, they tend to undergo buckling when placed under compressive, torsional or bending stress.
Hardness
Diamond is considered to be the hardest material, and it is well known that graphite transforms into diamond under conditions of high temperature and high pressure. One study succeeded in the synthesis of a super-hard material by compressing SWNTs to above 24 GPa at room temperature. The hardness of this material was measured with a nanoindenter as 62–152 GPa. The hardness of reference diamond and boron nitride samples was 150 and 62 GPa, respectively. The bulk modulus of compressed SWNTs was 462–546 GPa, surpassing the value of 420 GPa for diamond.
Kinetic
Multi-walled nanotubes, multiple concentric nanotubes precisely nested within one another, exhibit a striking telescoping property whereby an inner nanotube core may slide, almost without friction, within its outer nanotube shell thus creating an atomically perfect linear or rotational bearing. This is one of the first true examples of molecular nanotechnology, the precise positioning of atoms to create useful machines. Already this property has been utilized to create the world's smallest rotational motor. Future applications such as a gigahertz mechanical oscillator are also envisaged Electrical.

Because of the symmetry and unique electronic structure of graphene, the structure of a nanotube strongly affects its electrical properties. For a given (n,m) nanotube, if n = m, the nanotube is metallic; if n − m is a multiple of 3, then the nanotube is semiconducting with a very small band gap, otherwise the nanotube is a moderate semiconductor. Thus all armchair (n = m) nanotubes are metallic, and nanotubes (6,4), (9,1), etc. are semiconducting.
However, this rule has exceptions, because curvature effects in small diameter carbon nanotubes can influence strongly electrical properties. Thus, (5,0) SWCNT that should be semiconducting is in fact metallic according to the calculations. And vice versa, zigzag and chiral SWCNTs with small diameters that should be metallic have finite gap (armchair nanotubes remain metallic). In theory, metallic nanotubes can carry an electrical current density of 4 × 109 A/cm2 which is more than 1,000 times greater than metals such as copper.
Multiwalled carbon nanotubes with interconnected inner shells show superconductivity with a relatively high transition temperature Tc = 12 K. In contrast, the Tc value is an order of magnitude lower for ropes of single-walled carbon nanotubes or for MWNTs with usual, non-interconnected shells.

Defects
As with any material, the existence of a crystallographic defect affects the material properties. Defects can occur in the form of atomic vacancies. High levels of such defects can lower the tensile strength by up to 85%. Another form of carbon nanotube defect is the Stone Wales defect, which creates a pentagon and heptagon pair by rearrangement of the bonds. Because of the very small structure of CNTs, the tensile strength of the tube is dependent on its weakest segment in a similar manner to a chain, where the strength of the weakest link becomes the maximum strength of the chain.
Crystallographic defects also affect the tube's electrical properties. A common result is lowered conductivity through the defective region of the tube. A defect in armchair-type tubes (which can conduct electricity) can cause the surrounding region to become semi conducting, and single monatomic vacancies induce magnetic properties.
Crystallographic defects strongly affect the tube's thermal properties. Such defects lead to phonon scattering, which in turn increases the relaxation rate of the phonons. This reduces the mean free path and reduces the thermal conductivity of nanotube structures. Phonon transport simulations indicate that substitutional defects such as nitrogen or boron will primarily lead to scattering of high-frequency optical phonons. However, larger-scale defects such as Stone Wales defects cause phonon scattering over a wide range of frequencies, leading to a greater reduction in thermal conductivity.

Synthesis :


Powder of carbon nanotubes
Techniques have been developed to produce nanotubes in sizeable quantities, including arc discharge, laser ablation, high pressure carbon monoxide (HiPCO), and chemical vapor deposition (CVD). Most of these processes take place in vacuum or with process gases. CVD growth of CNTs can occur in vacuum or at atmospheric pressure. Large quantities of nanotubes can be synthesized by these methods; advances in catalysis and continuous growth processes are making CNTs more commercially viable.
Arc discharge
Nanotubes were observed in 1991 in the carbon soot of graphite electrodes during an arc discharge, by using a current of 100 amps, that was intended to produce fullerenes. However the first macroscopic production of carbon nanotubes was made in 1992 by two researchers at NEC's Fundamental Research Laboratory. The method used was the same as in 1991. During this process, the carbon contained in the negative electrode sublimates because of the high discharge temperatures. Because nanotubes were initially discovered using this technique, it has been the most widely-used method of nanotube synthesis.
The yield for this method is up to 30 percent by weight and it produces both single- and multi-walled nanotubes with lengths of up to 50 micrometers with few structural defects.
Laser ablation
In the laser ablation process, a pulsed laser vaporizes a graphite target in a high-temperature reactor while an inert gas is bled into the chamber. Nanotubes develop on the cooler surfaces of the reactor as the vaporized carbon condenses. A water-cooled surface may be included in the system to collect the nanotubes.
This process was developed by Dr. Richard Smalley and co-workers at Rice University, who at the time of the discovery of carbon nanotubes, were blasting metals with a laser to produce various metal molecules. When they heard of the existence of nanotubes they replaced the metals with graphite to create multi-walled carbon nanotubes.
Later that year the team used a composite of graphite and metal catalyst particles (the best yield was from a cobalt and nickel mixture) to synthesize single-walled carbon nanotubes.
The laser ablation method yields around 70% and produces primarily single-walled carbon nanotubes with a controllable diameter determined by the reaction temperature. However, it is more expensive than either arc discharge or chemical vapor deposition.

Chemical vapor deposition (CVD)


Nanotubes being grown by plasma enhanced chemical vapor deposition
The catalytic vapor phase deposition of carbon was first reported in 1959, but it was not until 1993 that carbon nanotubes were formed by this process. In 2007, researchers at the University of Cincinnati (UC) developed a process to grow aligned carbon nanotube arrays of 18 mm length on a FirstNano ET3000 carbon nanotube growth system.
During CVD, a substrate is prepared with a layer of metal catalyst particles, most commonly nickel, cobalt, iron, or a combination. The metal nanoparticles can also be produced by other ways, including reduction of oxides or oxides solid solutions. The diameters of the nanotubes that are to be grown are related to the size of the metal particles. This can be controlled by patterned (or masked) deposition of the metal, annealing, or by plasma etching of a metal layer. The substrate is heated to approximately 700°C. To initiate the growth of nanotubes, two gases are bled into the reactor: a process gas (such as ammonia, nitrogen or hydrogen) and a carbon-containing gas (such as acetylene, ethylene, ethanol or methane). Nanotubes grow at the sites of the metal catalyst; the carbon-containing gas is broken apart at the surface of the catalyst particle, and the carbon is transported to the edges of the particle, where it forms the nanotubes. This mechanism is still being studied. The catalyst particles can stay at the tips of the growing nanotube during the growth process, or remain at the nanotube base, depending on the adhesion between the catalyst particle and the substrate.
CVD is a common method for the commercial production of carbon nanotubes. For this purpose, the metal nanoparticles are mixed with a catalyst support such as MgO or Al2O3 to increase the surface area for higher yield of the catalytic reaction of the carbon feedstock with the metal particles. One issue in this synthesis route is the removal of the catalyst support via an acid treatment, which sometimes could destroy the original structure of the carbon nanotubes. However, alternative catalyst supports that are soluble in water have proven effective for nanotube growth.
If a plasma is generated by the application of a strong electric field during the growth process (plasma enhanced chemical vapor deposition*), then the nanotube growth will follow the direction of the electric field. By adjusting the geometry of the reactor it is possible to synthesize vertically aligned carbon nanotubes (i.e., perpendicular to the substrate), a morphology that has been of interest to researchers interested in the electron emission from nanotubes. Without the plasma, the resulting nanotubes are often randomly oriented. Under certain reaction conditions, even in the absence of a plasma, closely spaced nanotubes will maintain a vertical growth direction resulting in a dense array of tubes resembling a carpet or forest.

Of the various means for nanotube synthesis, CVD shows the most promise for industrial-scale deposition, because of its price/unit ratio, and because CVD is capable of growing nanotubes directly on a desired substrate, whereas the nanotubes must be collected in the other growth techniques. The growth sites are controllable by careful deposition of the catalyst. In 2007, a team from Meijo University demonstrated a high-efficiency CVD technique for growing carbon nanotubes from camphor. Researchers at Rice University, until recently led by the late Dr. Richard Smalley, have concentrated upon finding methods to produce large, pure amounts of particular types of nanotubes. Their approach grows long fibers from many small seeds cut from a single nanotube; all of the resulting fibers were found to be of the same diameter as the original nanotube and are expected to be of the same type as the original nanotube. Further characterization of the resulting nanotubes and improvements in yield and length of grown tubes are needed.
CVD growth of multi-walled nanotubes is used by several companies to produce materials on the ton scale, including NanoLab, Bayer, Arkema, Nanocyl, Nanothinx, Hyperion Catalysis, Mitsui, and Showa Denko.

Ohm's Law

Ω Ohm's Law describes the relationship between both the (V) voltage, which reflects the strength of the flow of electric charges .. And (R) resistance that are resistant to the flow .. And the result is true that the current flow (I)
Relationship is very easy and simple .. The more effort or less the resistance the greater the current flowing .. And increase the resistance limit the flow of current as is evident in the law of Ohm
Voltage = current * resistance
Current = voltage / resistance

New technology turned the human body heat into electrical energy

Santorini is cut off communication during an important call via mobile phone due to power outages of the battery, and the need to be recharged, for example, or going to discover too late that has missed an important appointment, because the hour hand has suddenly stopped working. But is it possible to imagine doing connections through a mobile phone without the need for a battery, only depending on the temperature of the body? This idea may seem closer to science fiction, but it may turn into reality, after that, a group of scientists from the German Fraunhofer Institute to reach a new method to convert body heat into electric current.

Is a scientific principle and applications of new





This technique depends on the principle of scientific known since 1821, discovered the world of nature the German Thomas Sepik, also confirmed Peter Hbas, one of the researchers involved the project, said in an interview for our website, saying: "The principle has been known for a time, a so-called born Alkahrouhrrari, who works at the the impact of the so-called Sepik, or influence Alkahrouhrrari. by this generator can convert between degrees temperature difference between the two objects to different electrical energy, or to the difference voltage. We have developed new circuits can be turned this small difference in voltage potential difference to a large , that is, to a large electric current, can be relied upon to run electronic devices known. "





The body's energy instead of batteries





Bildunterschrift: Großansicht des Bildes mit der Bildunterschrift: Is it possible to dispense with batteries in the future? There is already a demo of this technology at the Fraunhofer Institute, where one can put his hand on the device that generates a quantity of energy sufficient to power sensors temperature and to send information wirelessly, and there are some practical applications that have been in the industrial field, but so far limited, and in this framework, Hbas says: "It's about, of course, the efficiency of circuits used. At the moment, still the energy that can be gained from the heat of the body is limited, for example, enough to run a watch, or a device to measure the pulse, or things like that."





Technique can serve the patients lying on their beds in intensive care, and Mahatin wire from each side, as these devices powered by electricity to measure blood pressure or heart rate or body temperature, can be replaced devices are plugged in electric generator of the human body itself, as can send the information on these devices wirelessly to the control unit of the medical doctor or therapist.





The recipient's phone - Does it work without a battery?





Bildunterschrift: Großansicht des Bildes mit der Bildunterschrift: in the distant future, may be running a mobile phone without the need for batteries ... And applications of this technology, although still limited so far because of the small amount of energy that can be generated, but taking into account the developments that occur on the circuit, which makes them more efficient, you can imagine that using this technique in a larger number of systems. Which is confirmed by Hbas saying that in the near future can be dispensed with completely imagine the batteries in some of the hardware or the need for shipped at a lower rate.





Among the devices that can be in the future to rely on that technology, mobile device, though this is in the opinion of Hbas still a distant dream, where he says: "It's difficult with mobile phones, because they need so far to a large amount of energy to run, but Thanks to technological development in manufacturing, which serves to reduce the amount of energy required to run them significantly, it can be to imagine that this is achieved in the distant future. "