In our previous article where we discussed the mind-boggling complexity of our eyes’ retinas. We learned about the ten separate layers of cells, but we did not elaborate on the intricacies of their creation. We also learned how the substance in the cone cells, called rhodopsin, is destroyed on exposure to light and then regenerated in the dark. We thus touched on the wisdom behind the existence of both night and day.

The destruction of rhodopsin is caused by the generation of electricity after its contact with light. This electric impulse is transmitted from cones and rods to either horizontal or bipolar (having two poles) cells. The section between these two different layers of cells is called the outer plexiform layer, where horizontal cells receive electric impulses from rods and cones, and carry them to neighboring bipolar cells. The horizontal cells are also charged with transmitting electricity horizontally between rod and cone cells. The signals make it possible for shapes to be carried to the central nervous system in an appropriate contrast. Other signals are blocked so that the borders of the place of contact with light can be clarified in the brain, which does not receive an excessive load of signals. If it were not for these cells, it would be harder to perceive borders because the line of difference between two different colors would not become clear.

Bipolar cells have two opposite poles. They are created as one of two types, in accordance with their functions: one amplifies generated electric impulses, while the other inhibits the transmission of excessive impulses from around the perceived object to the brain. Bipolar cells provide the contrast necessary for making borders clear. They make clear vision possible, and yet most people have never heard of this wondrous gift inside their retinas!

How is contrast enabled?

Thanks to an innate ability, our brain does not occupy itself with regions that have the same color or the same light. It will not be stimulated much if, for example, a wall is completely white or a car is bright red all over. If, however, there are other colors on the wall, say, a white moon or star on a red background, then there will be more stimulation in the brain. Suppose we place the shape of a crescent on the wall. The stimulated parts of the brain will lie along the sharp ends of the crescent, not in the inside or outside of it. The stimulation in the brain is less associated with non-contrasting regions than contrasts in view. The higher the contrast, i.e. the greater the difference between light and dark areas, the greater the degree of stimulation.

Amacrine cells in the inner plexiform layer of the retina enable horizontal transmission. There are up to 30 different types of these cells, and they carry out at least five to six functions. For instance, one type of Amacrine cell transmits electric impulses from cones and rods to bipolar cells, then to other Amacrine cells, then to ganglion cells, and finally to the brain.

Another type of Amacrine cell responds strongly to the onset of the visual signal, while another to its completion. One other type reveals the difference in light intensity regardless of direction, while still others respond to the movement of a light point in a certain direction in the retina, causing a perception in the brain as to the direction of the light.

Further research may reveal yet more functions. Amacrine cells might have such functions as regulating the intensity of electric impulses specific to each wavelength and generating different levels of impulses for moving or stationary objects.

The function of the ganglion cells in the innermost layer of the retina is to help ensure that the electric impulse generated and corrected in the retina is eventually transmitted to the brain. Three distinct ganglion cells are identified in the retina. These cells are represented with the letters W, X, and Y. W cells are assigned the task of transmitting signals from rod cells, which produce black and white visual signals in the dark. Making up about 40 percent of all ganglion cells, they have diameters of less than 10 micrometers and transmit signals at a speed of 8 m/sec. It is evident that these cells are assigned the task of perceiving objects in the dark as rough, vague shapes.

X cells, on the other hand, transmit electric impulses to the brain, creating precise color pictures of objects. Making up 55 percent of ganglion cells, they have midsize diameters (10-15 micrometers) and transmit signals at a speed of 14 m/sec.

The largest of ganglion cells (with diameters as long as 35 micrometers), Y cells are assigned the task of transmitting instant changes in sight. Making up only 5 percent of ganglion cells, they send signals at speeds of 50 m/sec.

Sending intense signals in split seconds, Y cells inform the central nervous system immediately in case of a threat or an unusual encounter. When our body or eyes face a threat, these cells help protect us by warning the brain to move away from the threat or close our eyelids rapidly. If it were not for these cells, we would not be able to reflexively close our eyes and thus protect them. It’s incredible to ponder how complex these systems are – and how perfectly they’ve been created.

Between layers of cells there also lie layers of network that house neurons and their connections (synapses). These cells too have subgroups trained to carry out specific tasks. All of these cells are built according to certain specifications so that they can transmit stimuli to the brain when they receive light. Extremely severe visual problems develop when even a single layer of these types of cells is missing. Every one of the layers in our eyes is immensely special, and it is hard to imagine them to have been randomly placed there. It should be born in mind that this article simply skipped numerous elements of the retina and their chemical functions. Taking the precise measurements and mechanisms into account, we can only feel greater awe and love in the face of the incredible art devoted to the creation.

The first article can be found at https://fountainmagazine.com/2018/issue-126-november-december-2018/retina-the-mind-boggler

Will there be wars over elements like there have been over petroleum and water? What element have we been using in color televisions? What substance is used to make energy saving, environmental light bulbs?

Each of the elements found in the periodic table have their own characteristics. After they have been cooked in the pot of the universe, these substances that are offered to our service can be radioactive (like uranium), metallic (like magnesium) and even gaseous (like helium). Seventeen of the elements not easily found among the layers underground have unique properties. These elements are called rare-earth elements, because it is hard to discover and mine them.

Rare-earth elements are in many of our everyday devices. The data projected on a computer screen is transmitted via optic cables containing erbium. The light of a tablet device is generated by the phosphorescent element europium. We actually touch indium covered surfaces when we scroll our fingers on touch screen monitors. When listening through headphones, we are using neodymium magnets that are ten times stronger than iron magnets.

From space technologies to defense industries, from cell phones to LED lighting, many such rare-earth elements are used in every stage of our lives. These elements – many of which we cannot live without, even though we’ve never heard of them – were recorded into the Critical Materials Strategy Document published by the U.S. Department of Energy in 2010. In a public announcement, the department declared fourteen of the elements as specially significant regarding clean energy, listed six of them as critical, and the other four as near critical. Fifteen elements, beginning with lanthanum and ending with lutetium, numbered between 57 and 71, comprise lanthanides. Combined with scandium and yttrium, these make up the seventeen rare-earth elements.

The elements that we touch on screens

Indium (atomic number 49) gains the properties of electrical conductivity and optic transparency when combined with tin, which, at number 50, is indiums’s neighbor on the periodic table. Optical transparency is a desired property for plasma screen and television technologies. Indium is also an important material for mobile phone touchscreens. Interestingly, when indium combines with cadmium, also as a neighbor at number 48, it loses the optical transparency. Instead, it is able to absorb light. Light harvesting is a very critical feature in the production of solar cells.

The relationship of indium with its two neighbors opens new horizons for scientists. In the near future, it is hoped that many unknown and interesting features will be unearthed by investigating the known elements of the periodic table. It is amazing that these elements have been around for thousands of years in the universe only to be discovered by technological advancements.

The need for rare-elements in the world is around fifty thousand tons. The current recorded reserve for rare-earth elements is 110 Million tons. Currently, 95% of the demand for rare-earth elements is supplied by China, yet the country only has 35% of the world’s reserves. Therefore scientists are constantly searching for rare-earth element mines to eliminate the Chinese monopoly and to boost the production of these rare materials. In recent years, China has gotten into political debates with Japan and the United States by curbing rare-earth element exports. Economic journals covering these debates wondered if “element wars” were near. In 2010, a massive reserve of elements, enough to sustain worldwide demand, was discovered in the Pacific Ocean. Developed countries are now planning to recycle rare-earth elements from used devices due to low reserves.

Yttrium, europium, and terbium (atomic numbers 39, 63 and 65) have been known for a long time. Terbium and yttrium are named after the Swedish town of Ytterby. Yttrium is the first rare-earth element discovered, at the end of 18th century. Plastics containing europium are used to make laser products; it’s also used as an element to provide the red color on television screens. Yttrium has a supplementary role that enhances europium’s red color production. And terbium oxide activates the green phosphorescence of television tubes with its yellow-green phosphorescent property.

Terbium also enables an 80% reduction of energy consumption in light bulbs. This makes it one of the most wanted elements in the $2 billion rare-earth element market. Today, when we purchase class A type light bulbs, we are actually buying rare elements like terbium.

Neodymium (number 60), which emits a green light via laser pointers, is also used in the magnets of electric motors. When neodymium combines with boron and iron, it makes a magnet twelve times stronger than simple iron magnets. Because it is significantly less dense than iron, it makes electric motors and laptop computers much lighter. Another interesting feature of neodymium is that it enhances the data storage capacity of hard drives. Furthermore, neodymium is wanted for electrical devices and wind turbines.

The union of elements

Dysprosium was discovered in 1886 and can never be found in a free form in nature. This is because it exists in a compound form with other minerals, like gadolinite. Dysprosium is also known for its magnetic property, and when mixed with terbium and iron, it forms a substance called Terfenol-D. In a magnetic field, Terfenol-D has unique transformational abilities. Dysprosium is utilized in laser production together with vanadium, and it emits infrared radiation when used with cadmium.

The magnetic alloys of iron, boron, and neodymium lose their magnetic features beyond 300 degrees Celsius. However when this alloy is combined with dysprosium at a 5% ratio, that problem disappears. Therefore, these magnets are used for electric turbines and hard disc motors. Dysprosium also makes magnets in electric motors 95% lighter. And dysprosium and nickel mixed fillings are used as cooling rods in nuclear reactors.

The human mind becomes fascinated after seeing all the wisdom and properties involved in these lifeless elements. Either we conclude that these elements have doctorate degrees in physics and chemistry from Harvard University, or we may express our weakness and fascination in front of The Grand Creator who created and presented these elements for our benefit.

Is the yellow color in glasses from the planet Ceres?

Since Dell recalled four million laptop computers in 2006, because of a possible explosion caused by overheating battery, scientists’ eyes have been focused on lanthanum and cerium. These two elements are considered to be safer than other alternatives. Lanthanum and cerium are used in electrical equipment and energy saving light bulbs, and are classified as critical elements in these processes, along with tellurium. Cerium, named after the planet Ceres, is responsible for the yellow coloration in glasses. Cerium is also used in polishes, ceramics, and petrol refineries. Tellurium is produced indirectly, unlike most other elements. The production of cadmium takes place during zinc production, and tellurium during copper refining. Tellurium is a cheaper element that has been used in combination with cadmium on solar cells since 2009; before then, most solar cells used expensive silicon panels.

Elements in our lives, from space rockets to ultrasound imaging

Hafnium, tantalum, erbium, and technetium are important elements, even though they are not listed critical. Even though hafnium and technetium are not rare-earth elements, they were still added to the critical material strategy document produced by the US Department of Energy. Hafnium is employed in space rockets for its resistance against extreme temperatures and wearing. Hafnium oxide is a valuable material for electronic transistors since it is a very effective electric insulator. It is 20% faster than the silicon oxide that is commonly used in transistors. A transistors length is around 65 nanometers when silicon oxide is used, but it is only 32 nanometers with transistors made of hafnium oxide. This 50% decrease enables smaller devices.

Touchscreens containing indium, laptop computers powered by lithium ion batteries, and cell phones with hafnium transistors are some of today’s technological wonders. Would these inventions still be possible without these elements? Could we reach the high capacities in hard discs without the tantalum? Would we be able to protect ourselves from electric leakage in computers without high quality electric insulators such as tantalum oxide?

Radioactive technetium, which was discovered in 1937, is the first artificially produced element. The technetium 99 isotope is used in nuclear medicine. Technetium produced from uranium has a half life of 211,000 years, as opposed to the 6 hour half life of the technetium 99 isotope. The number of technetium based nuclear medicinal tests, like ultrasounds and x-ray imaging, is estimated to be above thirty million annually.

We take advantage of these elements in every stage of our lives, from medicine to technology. Could we become dependent upon elements the way we are upon petroleum? Only time will tell. Either these elements will be replaced by other materials, or other technologies will outdate the current technologies. It is also possible new elements will be discovered.

A majority of our modern technologies would not exist without these elements that were dispersed among the earth billions of years ago. These elements were placed here for our benefit, and so we could utilize them, and produce institutes of scientific research and education to study them.

Kadir Can and Mehmet Ramazanoglu are science teachers in Ankara, Turkey.

In May 2003, Roderick Mackinnon’s research group at Rockefeller University has published the three-dimensional atomic structure of a voltage-gated potassium channel. MacKinnon also received the Nobel Prize in 2003 for the first potassium channel structure

How electrical signals are conducted through nerve cells has been understood with some detail in the last fifty years, after the seminal work of Hodgkin and Huxley, which earned them a Nobel Prize in 1963. After 40 years, another study is appreciated in the scientific community as the end of one era and the beginning of another one.

Cells, body’s building blocks, are bound by membranes that are impermeable to ions, atoms that carry positive or negative charge. Nerve cells are specialized for having very long arms that can carry electric potentials on their membranes for very long distances. The electric potential (voltage difference) is the result of unequal number of charges across the inside and outside of the cell membrane. Hodgkin and Huxley explained the movement of the electric potential on the membranes by the selective opening of ion channels, proteins embedded in membranes to allow the passage of certain ions. As channels are opened in one part of the nerve cell to allow an electrical potential change, the neighboring stretches somehow sense the change in voltage and open their channels as well. The propagation of the electric potential depends on the fast sensing, opening and closing of these channels. The molecular details of these voltage-gated channels have been somewhat obscure; however important properties have been determined using methods pioneered by Hodgkin and Huxley, generally dubbed electrophysiology, the study of biological material using electrical methods. Scientists

have imagined channel proteins as many helices running through the membrane, some of which could be pulled to the inside or outside of the cell depending on the voltage across the

membrane. Movement of these helices across the membrane could open channels for potassium or sodium. Finally in May 2003, Roderick Mackinnon’s research group at Rockefeller University has published the three-dimensional atomic structure of a voltage-gated potassium channel. MacKinnon also received the Nobel Prize in 2003 for the first potassium channel structure, which explained the selectivity of a potassium channel for allowing only potassium ions to pass, but nothing else.

MacKinnon is a mixed structural biologist and electrophysiologist. His group has isolated potassium channel molecules from membranes, and tested them for strict functionality as it has been observed that protein molecules isolated out of their natural environments may lose their activities and chemical properties. The next step of their study was to crystallize the channel molecules-much like forming salt crystals-and diffract x-rays through the aligned molecules in the lattice of their crystals. These diffraction patterns are mathematically solved to give atomic positions of electrons, hence atoms, in the protein crystal. Several research groups failed at this step, since purified potassium channels never formed crystals, as flexible protein molecules are unlikely to form crystals. Here, MacKinnon cleverly used antibodies they developed specifically against the channel. These antibodies, used radically differently than they are in nature, overcame the flexibility of the voltage-sensing regions of the channel, by binding to the channel and fixing it to a specific conformation. The ordered channel crystallized and gave the structure of the potassium channel and the antibody bound to it.

The structure of the channel consists mostly of helices, which in the center surround a potassium-conduction pore, and “voltage-sensing paddles” in the periphery. When the gate is closed, the helical paddles lay parallel at the cellular side of the membrane. Gate opening only happens when the paddles are pulled through the membrane to the outer side as voltage pulls the positive charge of the paddles to the outside (see figure). Now, it looks like 50 years of data collected by electrophysiologists and biochemists can be explained coherently (such as the observed 14 positive charges residing on the paddles moving through the membrane). As is usual with such discoveries, many new questions are asked, such as how the charged paddles can go through the oily, highly uncharged membranes. There are also valid scientific objections, such as the antibody distorting the potassium channel structure. However, this is one of those bright moments in any field of research, when researchers go over the threshold of collection of enough observations to discovery and understanding.

References

• Jiang, Y., Lee, A., Chen, J., Ruta, V., Cadene, M., Chait, B.T., MacKinnon, R., Nature 423, 33-41 (2003).
• Jiang, Y., Ruta, V., Chen, J., Lee, A., MacKinnon, R., Nature 423, 42-48 (2003).
• Sigworth, F.J., Nature 423, 21-22 (2003).

Daylighting is becoming more popular in commercial buildings and manufacturing facilities in the United States. After Thomas Edison invented the electric light, most architects changed their building plans and designed for more and more artificial lighting. As a result, only a very small percentage of the light used in major buildings and facilities came directly from the sun. Recently, the Europeans have realized the importance of daylighting and begun to use a reasonable percentage of sunlight in their buildings. The Rocky Mountain Institute, Snow-mass, Colorado, has investigated the benefits of daylighting and reported that daylighting increased productivity and reduced absenteeism by 15 percent. Also, sunlight reduces the heating and cooling bill.

In 1993, Wal-Mart Stores Inc. opened a prototype store in Lawrence, Kansas, with nine special skylights designed by Andersen Corp., Bayport, Minnesota. The architectural firm of Leo A. Daly, Omaha, Nebraska, opened an office building in 1983 with l5ft high window walls and a glazed roof. About 50% of its electricity bill for lighting was saved as a result (Reno Gazette-Journal, November 27, 1995). Daylighting is an inexpensive way of lighting interiors since the sun is a ‘free’ light source which can be further exploited by installing skylights on the roof. On an overcast day, the light entering through a 2 sq. ft skylight area is equivalent to three 100-watt light bulbs.

There are two additional reasons for installing skylights. First, the cooling load of a building can be reduced by using daylight. The reason for this is that whereas about 80% of the power of an electric light is converted to heat, sunlight has a far lower heat content and therefore requires far less air-conditioning. Second, just at the time when there is the heaviest demand for electricity (and other utilities) from manufacturing facilities, namely during the summer, sunlight is at its most plentiful and available: in short, skylights can significantly reduce peak load stresses and costs.

An illumination level of 50 footcandles (540 Lux) at the work site is the design standard in industrial facilities. A large portion of this illumination level comes from electric lights of fluorescent and incandescent lamps. Almost 5% of electricity consumption in the US is used up to provide adequate illumination in commercial and industrial buildings.

In production facilities generally, there is a lack of awareness about the energy conservation potential of skylights. Some manufacturers are so unaware about the cost savings that can be achieved by daylighting that they do not have skylights in their production areas, and leave lamps on in work areas throughout daylight hours. In other places which do have them, skylights have been neglected to the extent that they are so dirty they block the incoming sunlight.

Since heating and cooling load are increased with increased skylight surface area, there is a limitation associated with this measure. Some authorities have suggested that the optimum skylight surface area should be reckoned at between 2 and 4% of roof surface area. However, since the measure depends upon local climate conditions, the range should be allowed to vary between 2 and 10%. In many potential sites, heating only (and not cooling) is the principal consideration. Generally, therefore, building designers with heating costs in mind tend to prefer 2% for cold climates and 10% for warm climates.

Heating load and costs will increase when skylights are installed. However, the increase in heating cost is considerably smaller than the saving from reduced lighting cost. The average unit cost of electricity is three times greater than that of natural gas (typically preferred for heating). In any case, heat loss from the skylights can be minimized by double glazing them. In view of the favourable financial balance and the productivity improvements to be expected from daylight working, the benefits from installing skylights generally offset any negative consequences of doing so.

The amount of savings in electric lighting consumption and costs depends on climate and operating periods. The payback period for installing skylights ranges from one to five years. They can be an expensive roof aperture, but it is relevant to note that the lifetime of a skylight is more than twenty years. The skylights need to be cleaned at least once annually, which means that service and maintenance costs are negligible. Skylights are most cost- effective in uninsulated ceilings in climates, like that of southern California, which have no heating season. In such climates, the workplace roof is typically covered with corrugated metal sheets making skylights both easy and cheap to install: corrugated fibreglass sheets can be cut and fitted in place of the metal sheets wherever the skylights are required.

References 

• MURDOCH, B. J. (1985) Illumination Engineering: From Edison’s Lamp to the Laser, Macmillan Publishing Company, New York.
• NUTFER, D. W., BRITTON A. J. and HEFFINGTON W. M. (1993) ‘Conserve Energy to Cut Operating Costs’, Chemical Engineering, September, pp.126-37.
• PIERSON, J. (1995) ‘Natural light gets warm welcome’, Reno Gazette-Journal, November 27, pp.2ff.