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Benefits Of Biophotonics

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Autor:  anton  01 November 2010
Tags:  Benefits,  Biophotonics
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History

Alexander Gurwitsch around 1930

Around 1923 Alexander Gurwitsch discovers an "ultraweak" photon emission from living systems (onions, yeast,...), since he suggested connections between photon emission and cell division rate. He calls this photonemission "mitogenetic radiation". His experiments indicate that the wavelength is in the range around 260 nm (Bibliography under Gurwisch and also Ruth (1977, 1979)).

Around 1950: Russian scientists rediscover "ultraweak photon emission" from living organisms. Most results are published in "Biophysics" (engl.) and originally in "Biofizika").( Bibliography under Ruth, 1979).

Italian nuclear physicists discover by chance "bioluminescence" of seedlings. They do not think that this finding is significant, but they publish the results. (Colli et al. 1954, 1955, Ruth 1979).

The Russian biophysicist and the American chemist enunciate the first theory of ultraweak photonemission (UWPE) from biological systems, the so called "imperfection" theory. UWPE shall be an expression of the deviation from equilibrium, some kind of distortion of metabolic processes (Zhuravlev 1972, Seliger 1975, Ruth 1979).

Independently from each other and by different motivations scientific groups in Australia (Quickenden), Germany (Fritz-Albert Popp), Japan (Inaba), and Poland (Slawinski) show evidence of ultraweak photon emission from biological systems by use of modern single-photon counting systems.

Need and Relevance

The field of optics is one of the oldest and most important branches of the sciences. Long before the theory of electromagnetism was developed, optical phenomena were studied, characterized, and used as probes of nature. Since the invention of the laser a half-century ago, this tool has become the preeminent source for all studies involving light. It too has revolutionized countless areas of high technology including telecommunications, data storage, semiconductor manufacturing, healthcare technology, metrology, imaging, and more.

The field of applied biosciences is an emerging discipline at the intersection of molecular and cellular biology, the physical sciences, and materials engineering. Equipped with the tools of modern molecular biology, powerful characterizations, theory, and computation, scientists in this area seek to develop a physical understanding of the exquisite and complex behaviors of biological systems.

The particular focus of the applied biosciences uncovers the biological principles of self-organization, recognition, regulation, replication, communication, and cooperation that characterize living systems, allowing scientists to extend these principles in the synthesis of modern materials. This field has advanced to become a promising area of applied science, blurring the border between traditional scientific disciplines and offering new routes for the design of materials where organization precedes function. The technological promise of applied bioscience includes the health applications of biomedical and biotechnology, but also encompasses a host of novel nanotechnologies.

Currently, data convergence is driving the development of communication systems and services. Therefore, the merging of telecommunications, computing and audiovisual systems, and growth of wide-band services demands explosive increase in the capacity of communication systems. Optical technologies have great potential for the implementation of high-speed systems due to their potential for a decrease in size, weight and power consumption and an increase in speed, capacity, bandwidth, and fan-out and integration degree. Actually, the recent wide-scale deployment of dense wavelength division multiplexing (DWDM) systems is already a clear demonstration of the advantages of optical systems and rapid progress of device technologies. However, in order to be able to fulfill the bandwidth requirements, new mass producible and heavily integrated photonic components and modules (passive and active) have to be developed.

The communication market is really strong in Europe, and expert research teams exist for developing novel devices in close collaboration with global contributors. The high population density, for example in Asia, potentially represents a really wide economical open space for these new communication products. This integrated project completely fulfils the priorities of the European Commission, particularly the priority 1.1.2.iii, IST / components and microsystems.

The aim is to associate advanced materials technologies (sol-gel and polymers), processing technologies (laser writing, electron beam lithography, ion implantation, silicon on insulator, pulsed laser deposition and microelectronic technologies) and modern integration and packaging technologies (silicon on insulator, micro-electromechanical systems and low temperature co-fired ceramics) to fabricate passive and active hybrid integrated modules and systems for optical communication applications. Full exploitation of these technologies requires deep theoretical understanding of the physical phenomena as well as strong modeling and simulation capabilities of processes and modules. In the short term, this hybrid integration approach is the aim; however, in the future, we will also concentrate on full photonic integration allowing for the full integration of active and passive structures and devices into single substrates. The thermal stability, sensitivity to ageing and reliability of components are relevant evaluation criteria. In particular, main effort is focused on passive and active amplitude and phase filtering of guided waves as well as processing signals in the wavelength domain. These systems are required to fully exploit 40-Gbit/s and 100 G-bit/s networks in the future. The final goal to fabricate new mass-producible, highly integrated components will be reached by technological developments and innovations with new emerging technologies and combination of matured technologies.

Obstacles and solutions.

It's easy to see the benefits of employing optical technologies in telecom networks, but right now there are plenty of obstacles in the way of turning dreams into reality.

One of the big obstacles is cost. Carrier budgets are tightening, and a lot of optical gear is still very expensive. Analysts agree that operators cannot continue to absorb reductions in bandwidth prices unless system vendors and components manufacturers reduce costs drastically.

Another is space. The deployment of DWDM in networks has led to a huge increase in the number of boxes in carrier sites – so much so that the footprint of equipment has become a crucial issue.

Another obstacle is time to market. New developments are happening so fast that life cycles of equipment are shrinking dramatically. Vendors can't afford to dilly-dally, developing from the ground up. They need to buy off-the-shelf subsystems to get their products to market much more quickly.

Guess what? These and many other obstacles could be swept to one side by developments in integrated optics. A whole bunch of vendors, many of them startups, are working hard to put multiple optical functions on a single optical "chip." An optical chip in this context means a wafer-based component that can be processed using the same automated manufacturing techniques that are used in the electronic chip industry.

Many vendors are targeting passive devices in the first instance – circuits that switch, attenuate, or filter light, but don't amplify it. They plan to incorporate active devices, like lasers and amplifiers, at a later date. In parallel developments, vendors are putting the electronic control circuits on the same chip as the optical functions. After all, optics cannot exist without electronics: You need the electrons in order to create photons in the first place. Bringing all three together – passives, actives, and electronics – will be the next obvious step. Eventually the hope is to develop the optical equivalent of the electronic integrated circuit. In other words, a chip that does its thinking in optics. The bottom line here is processing speed. Optics has the theoretical potential to carry more information per second.

If they succeed the impact on telecom equipment and networks could be just as massive as the impact of electronic chips on pretty much everything. The systems business could become a lot more streamlined and rapid. Telecom equipment that currently occupies whole racks could be shrunk into a single component. Telecom services could end up following Moore's law – doubling in performance and halving in price every 18 months. All the same, photonic integrated circuits promise to have such a profound impact on telecom networks that it's important to understand what's going on for at least erudition purpose. Couple examples may illustrate that the proposed technology is not as futuristic as some may think.

1.The use of light rather than electrons to carry information is of increasing importance in high-speed communication. A major challenge in "photonics" is to combine components that can manipulate light with traditional chips. Now, Kerry Vahala and co-workers at the California Institute of Technology have fabricated microresonators-on-a-chip that have "Q" values ten thousand times larger than existing devices. Resonators are widely used in electronics, microwaves and optics. There has been much interest in on-chip resonators in the last decade but the Q factor - the figure of merit for a resonant system - has been limited to about ten thousand. However, many applications require Q factors that are several orders of magnitude higher.

Silicon dioxide microresonator

Vahala and co-workers have made toroid-shaped microcavities on silicon wafers that have Q factors of over a hundred million. The cavity confines light in a "whispering gallery" mode in which it orbits around the edge of the cavity at precise resonant frequencies as a result of total internal reflection.

The devices were fabricated on silicon wafers that had been coated with a layer of silicon dioxide. The researchers use photolithography, standard etching techniques and laser treatment to produce the structure shown in the figure above. The technique leaves the edges of the device smooth, which is important for the efficient confinement of light, and does not affect the underlying silicon dioxide support layer.

These devices could be used in a wide range of applications, such as optical sensors and microchip lasers. As standard processing techniques have been used to make the microresonators, they can be produced in large quantities. "Furthermore, they can be integrated with other functions such as electronic circuits," Vahala told PhysicsWeb. The team now hopes to improve the Q factor of their device. "We hope to get it above one billion," said Vahala.

2.Nanovation Technologies Inc. has entered the testing phase of its development of a fully integrated optical circuit, a technology that promises to deliver faster, higher-capacity communications to the marketplace by the end of the year, in packages significantly smaller than today's electronic circuits.

________________________________________

Nanovation's integrated optical circuit comprises a photonics ring laser, photonics switch and a strongly confined waveguide.

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"We have the building blocks to create all-photonic circuits, and these circuits can be 100 times smaller and operate 100 times faster with greater efficiencies," said Bob Tatum, president and CEO of Nanovation. The integrated optical circuits combine Nanovation's patented photonic ring lasers, photonic switches and strongly confined waveguides. The technology came out of Northwestern University's Transfer Technology Program, and the devices are being developed and tested at Nanovation's nanofabrication facilities on the university's campus in Evanston, Ill. Similar to today's semiconductor integrated circuits (ICs), the photonic devices are planar, allowing them to be fabricated onto GaAs or InP semiconductor wafers, according to Roydn Jones, senior vice president for engineering. Jones compares the situation with integrated optical circuits to the early days of semiconductor chips because of the ability to achieve a high level of integration. "Because of the size of devices and the ability to route photons [in waveguideswithlessthan5µmradii], we could have thousands of devices on a single optical IC, "he said. The first patented device that enables this technology is the photonic ring laser, a circular waveguide etched on the substrate. When this ring is electrically or optically pumped, it emits laser light. Placing another planar waveguide close to the ring allows light to be coupled from the photonic ring. The output photonics can be routed to other optical devices just as electrons are routed with metal lines on conventional integrated circuits. "The optical IC is really very similar to die-on chips, but it uses photons instead of electrons, "Jones said. The second patented device is an optical resonator, which can switch light from one waveguide to another. Initial applications are in add/drop filters, multiplexers and demultiplexers, and high-speed optical switches for telecommunications applications such as wavelength division multiplexing (WDM) and dense WDM. The technology will revolutionize several industries in the same way the transistor did years ago, Tatum said. "The transistor was a big deal, but this is even bigger. Photons run faster than electrons, and the circuits are smaller. They do not generate heat, and that eliminates any kind of electromechanical radiations here is no interference, in other words, with photons as there is with electrons.

Exploring discoveries

There are different directions for scientists to find out how photonic IC should be constructed. One special way to employ properties of light is to use soft X rays. Neville Smith in his article “Science with Soft X Rays” describes possible outcomes of research being conducted on X rays:

“Synchrotron radiation with photon energies at or below 1 keV is giving new insights into such areas as wet cell biology, condensed matter physics and extreme ultraviolet optics technology. Researchers using synchrotron radiation fall into two fairly distinct camps: users of the soft x-ray and vacuum ultraviolet (VUV) region of the spectrum and users of the hard x-ray region. The distinction can be expressed quantitatively by comparing the energies of a photon and an electron whose wavelengths are 1 Е.

The scientific question posed by the users of hard x rays tends to be, Where are the atoms? The emphasis is on the determination of crystal structures and molecular structures using techniques such as x-ray diffraction. Therefore, the photon used as the probe should have a wavelength comparable to interatomic distances. With photon wavelength ph 1 Е, we have

E (photon) hc /ph 12.4 keV.

In the soft x-ray/VUV region, on the other hand, the question tends to be, What are the electrons doing as they migrate between the atoms? The emphasis is on studies of chemical bonding and valence band structures using techniques such as photoelectron emission spectroscopy. For users of this region, the probing photo electron should have a wavelength comparable to interatomic distances. With electron wavelength el 1 Е (and electron mass m ), we have

E (electron) h 2 /(2 m el 2 ) 150 eV.

This natural division of researchers in terms of two energy regions of interest is reflected in the Argonne National Laboratory, optimized for delivery of hard x rays, and the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory (LBNL), optimized for soft x-ray/VUV science (see Physics Today, January 1994, page 18).

Between the two energy values just derived lies the soft x-ray region, with photon energies of 100¬1000 eV. Such soft x rays are used in spectroscopy of inner shell (core) electrons, particularly for elements in the first row of the periodic table. These important elements have only one core level (the K-shell), and the core electron binding energy is in the soft x-ray region--for example, the binding energies of 1s electrons in carbon, nitrogen, and oxygen are 290, 400, and 530 eV, respectively. Core-level spectroscopy is a powerful technique both because of its elemental specificity and because it can reveal details of an atom's chemical bonding state, which has a significant effect on some spectral features just above the absorption edge. Also falling within the soft x-ray region are the L-edges of the transition metals, which come from the dipole-permitted transition from the 2 p core level to the 3d valence level. Of particular interest are the elemental ferromagnets iron (with L-edge energy 710 eV), cobalt (780 eV), and nickel (850 eV). Fairly recently, the discoveries of cuprate high-temperature superconductors and manganate colossal magnetoresistance materials have propelled the L-edges of copper (930 eV) and manganese (640 eV) into prominence. The L-edge is attractive to researchers studying the new materials because of its ability to probe the 3 d valence electrons that are responsible for their remarkable properties.

Coherence and interferometry

Following Moore's Law, the density of circuit elements on microchips has doubled roughly every 18 months, resulting in smaller, faster, and cheaper computers. However, optical lithography, the present technology of microchip manufacture, cannot continue indefinitely on this course. The materials from which one could conceivably make optical lenses, CaF2, MgF2, and LiF, will not transmit light at wavelengths less than 100 nm, which limits the size of features that could be fabricated in this way. One alternative being considered is to switch from refractive optics to reflective optics--that is, mirrors. The availability of molybdenum¬silicon mirror coatings that have reflectances as high as 70% provides special impetus for reflective technology. The optimum wavelength, determined as a compromise between the conflicting requirements of fine lateral spatial resolution and large depth of focus into the chip structure, is about 13 nm. This wavelength is popularly referred to as extreme ultraviolet (EUV); the corresponding photon energy is 100 eV, which qualifies it as a soft x ray.

Figure

A consortium of microelectronics companies (Intel, Motorola, and Advanced Micro Devices) has joined forces with a consortium of national laboratories (Lawrence Livermore, Sandia, and LBNL) to build a prototype EUV stepper, an optical camera of the sort that will produce small computer chips. A schematic of such a stepper is shown in figure to the right. It comprises a four-mirror optic that produces a reduced image of the design mask on the wafer. To attain the required high reflectivity at 13 nm wavelength, the mirrors in the device must be curved and coated with interfering multilayers. In actual chip manufacture, the light source will not be synchrotron radiation but rather an EUV-emitting plasma. The role of synchrotron radiation for this technology is to measure the optics.

An old adage says, "If you can't measure it, you can't make it." At LBNL, Jeff Bokor is leading a team that has been entrusted with the task of interferometric characterization of the high-precision mirrors required for the stepper. As part of this effort, the team has developed an at-wavelength phase-shifting point-diffraction interferometer (PS/PDI). The PS/PDI first passes the beam from an ALS undulator through a pinhole to generate a high-amplitude, perfectly spherical wave.

A diffraction grating then splits the light into two parts: a test beam, which passes through the optic being measured, generating an aberrated wavefront characteristic of the imperfections in the test optic; and a reference beam, which passes unobstructed through the test optic and then is forced through a second pinhole to generate a perfectly spherical reference wavefront that interferes with the test beam. The resulting interferogram reveals the departures from figure accuracy. The design goal was for a test accuracy of 0.10 nm over the surface of the mirror, and the accuracy actually achieved was 0.05 nm. This length is the Bohr radius of a hydrogen atom! A four-mirror optic manufactured at Sandia has already been tested with very satisfactory results.

This work demonstrates that coated optics can be produced to the desired tolerance, thereby enhancing the prospects of EUV lithography as the next technology of choice for the manufacture of ever denser microchips.

Great promise for the future

The preceding is an attempt to convey some of the richness of the science that can be done with synchrotron radiation in the soft x-ray and VUV regions of the spectrum and to show some of the promise of the newer high-brightness facilities. However, there is much more activity in the field than could be covered in this article.

A particularly promising area of current research is soft x-ray emission spectroscopy, a photon-in/photon-out technique in which the incident beam photon energy is chosen to knock out core electrons of, say, carbon atoms. Valence electrons can then decay into the resulting hole by releasing soft x-ray photons, whose spectrum replicates the local valence density of states.

The technique has the power of photoelectron emission as well as atomic specificity. Since the detected particle is a photon rather than an electron, the measurements do not have to be done in ultrahigh vacuum, as photoelectron emission measurements do. Because a high vacuum is not needed, soft x-ray emission spectroscopy can be used to study buried interfaces and the wet samples that are of intense interest in catalysis, biology, and environmental science. The absorption cross sections are very small, however, and a high-brightness source is required to achieve the full potential of this technique.

Another promising area is high-resolution spectroscopy in the gas phase. A synchrotron-based experiment is being done in atomic and molecular physics and in chemical dynamics that are not possible with laser sources.

The potential of high coherence, one of the three brightness advantages, remains relatively unexploited. Fledgling attempts at speckle and dynamic scattering have only just begun in the soft x-ray range.

The length scales that can be probed in this way are, of course, greater than those accessible using hard x rays, but the larger soft x-ray cross section (which scales as the square of the wavelength) is a real advantage.

Thus, we can confidently expect a surge of effort in dynamic scattering studies of systems with the appropriate length scale in magnetism, soft matter, and biology. It is obvious that we have only scratched the surface of "Science with Soft X Rays". (www.physicstoday.org)

Latest breakthrough

WEST BETHLEHEM, Pa., May 27 US researchers have developed a laser beam that is about one million times brighter than conventional lasers. Physicists at Lehigh University said the laser produces a rainbow of visible and invisible colors by focusing the beam in a specially designed optical fiber that confines light in a glass core with a diameter 40 times smaller than a human hair. The tiny solid glass core is surrounded by a cladding, or casing, that contains air holes along the length of the fiber. Visible light waves emerge from the fiber as white light, which contains all the colors of the spectrum. The colors are dispersed by the precisely spaced grooves of a diffraction grating, in the same way that water drop lets create a rainbow.

Potential uses for the super laser range from medical applications including noninvasive imaging of live tissues to all-optical networks, in which light waves, not electronics, perform switching, routing, amplifying and other functions, the physicists said. Jean Toulouse, professor of physics, and Iavor Veltchev, research associate in the Center for Optical Technologies (COT), are the first scientists at Lehigh and among the few in the world to achieve and study the phenomenon, which is called "supercontinuum generation in nonlinear fibers ." The phenomenon can be observed in a new class of optical fibers, called photonic crystal fibers. These fibers consist of a tiny solid glass core surrounded by a cladding, or casing, which contains air holes along the length of the fiber. When Toulouse and Veltchev run a demonstration in their lab, incoming infrared (IR) light waves, which are invisible to the human eye, are converted to visible light waves. As the IR light propagates, or spreads , through a one – meter – long fiber , the light appears first orange , then yellow and finally green . IR and UV light of varying wavelengths are also generated at both ends of the visible spectrum . The visible light waves emerge from the fiber as white light, which contains all the colors of the spectrum. The colors are dispersed by the precisely spaced grooves of a diffraction grating, in the same way that water droplets create a rainbow. Potential uses for supercontinuum generation in nonlinear fiber optics range from medical applications, including noninvasive imaging of live tissues, to all-optical networks, in which light waves, not electronics, perform switching, routing, amplifying and other functions. Nonlinear optical effects are the main focus of the COT’s all-optical network research thrust, which Toulouse directs. Toulouse receives funding from the National Science Foundation. Supercontinuum generation is not observed in conventional optical fibers, Toulouse says, because their optical intensity (the optical power per unit area) is too low. In the new fibers, the light is confined in a much smaller core and the optical intensity is much greater. This modifies the optical properties of the medium (the fiber), creating new, nonlinear optical effects. Linear optical effects occur when the optical intensity of light is not great enough to alter the properties of the medium (especially the speed at which the light propagates) through which the light is passing. Nonlinear effects occur when the light’s optical intensity alters the properties of the medium, which, in turn, affects the manner in which the light itself propagates. The increased intensity, says Veltchev, also causes a corresponding increase in the refraction, or bending, of the light wave by the medium . Nonlinear effects cause different parts of a wave to move at different velocities and distort the light’s periodic sinusoidal pattern. These effects generate new wavelengths and result in what Toulouse calls an "avalanche effect” as more wavelengths are generated, more distortion results, leading to yet more wavelengths.

"What we see in the nonlinear regime," said Toulouse, "is that if we send light in at one wavelength, we generate many other wavelengths" -- thus achieving supercontinuum generation in nonlinear fiber optics. The high optical intensity necessary for supercontinuum generation is achieved by the tight confinement of the incoming light wave in the extremely small core of the fiber, Toulouse said. Toulouse and Veltchev begin their demonstration by using lenses to steer and focus the incident, or incoming, light waves with a wavelength (the distance between two adjacent crests of the wave) of approximately 800 nanometers (1 nm is one one-billionth of a meter). At 800 nm, the light waves fall within the infrared range and are not visible. The incident light wave, being powerful enough, creates nonlinear effects inside the glass fiber, generating new light waves with longer and shorter wavelengths (visible and multicolored). This is caused by two factors. First, the light waves are confined to a solid glass core inside the optical fiber that measures only 2.5 microns in diameter. (A micron is one one-millionth of a meter; 2.5 microns is roughly one-fourtieth the thickness of a typical human hair.) By contrast, the core of a typical optical fiber measures 10 microns in diameter. And a typical laser beam has a diameter of about two millimeters, almost 1000 times greater than the diameter of the Lehigh researchers’ new optical fiber core.

The optical intensity (power transmitted per unit area) in the core of these new fibers, said Toulouse, is thus almost a million times greater than the intensity in the core of a typical laser, given that the area of a circle equals pi times the radius squared. The creation of nonlinear effects is also triggered by air holes in the cladding around the fiber core. The holes force the light to remain confined inside the narrow glass core, Toulouse says, because "light hates to be in air when it can be in a medium where it travels more slowly." The tight confinement of light inside the new PCFs forces the waves to propagate coherently (with a well-defined initial-phase relationship), thus producing the full spectrum of visible colors.

The optical fiber used by Toulouse and Veltchev costs up to several thousand dollars per meter, and it is manufactured by only five companies in the world, several of which have ties to the COT. Toulouse has contacts with other researchers who have achieved supercontinuum generation in nonlinear fibers. In 2002, he spent six months studying the nonlinear effects of new types of optical fibers at the University of Bath in England, with the very people who invented PCFs in 1992 . Veltchev has a PhD in physics from the Free University of Amsterdam (The Netherlands) and will soon join the Fox Chase Cancer Research Center near Philadelphia on a project using laser radiation in cancer treatment.

Conclusion

Photonics is the technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and information processing."

Electricity and electronics uses electrons, photonics uses photons - the fundamental particles of light. In the same way that electronics was critical for technological development in the 20th century, photonics will be critical in the 21st century.

The global communications network is probably one of the largest endeavors ever taken on by humans. We have seen that there is not one technology but several technologies coming together to build this network. As our demand for communications increases, more and more technologies become obsolete or inadequate. The breakthrough created by the manufacture of optical fibers and of semiconductor lasers has given birth to a new discipline: photonics, or the science of mastering light.

A single optical fibre is able to carry the equivalent of 300,000,000 simultaneous telephone calls. This new photonics technology enables, for the first time, sufficient capacity to meet the forecast demand for fully interactive, multimedia, internet services.

By replacing copper cables with glass, new photonic networks can span the globe with light highways linking cities, countries and continents and capable of transmitting information via multiple channels of different wavelengths - just as broadcasting uses multiple TV and radio channels to transmit audio and visual information.

Optical fiber and photonic technologies can also be used in other industrial applications. Theoretically, almost any physical or environmental parameter can be measured using light, including temperature, strain, electric current, vibration, chemical and biological pollution, or sound.

A growing area is biophotonics, where photonics technology is used to develop new procedures and techniques in biotechnology, microbiology, medicine, surgery and other life sciences, including veterinary medicine. Photonics has a growing reputation in solving clinical and research problems through advanced spectroscopy, lasers, microscopy and fiber optic imaging.



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