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At least 235 records · Page 13Linked to original sources

Recent developments in the supramolecular chemistry of terpyridine-metal complexes.

This critical review describes recent developments in the field of supramolecular chemistry of terpyridine-metal complexes. The synthesis and characteristics of single as well as multiple homo- and heterometallic complexes is discussed. Furthermore, complexes containing fullerenes, biological building blocks, extended aggregates of different architectures as well as rings are presented. A special emphasis is placed upon the properties (e.g. redox properties, luminescence etc.) of functional systems. Potential applications in optical nano-devices, molecular storage units, molecular switches and solar cells are discussed.

Hydrogen Bonding↗

1,2-Bis[5-(1,3-dioxolan-2-yl)-2-ethyl-3-thienyl]-3,3,4,4,5,5-hexafluorocyclopent-1-ene, a photochromic dithienylethene.

The title compound, C23H22F6O4S2, a photochromic dithienylethene, is a promising material for optical storage and other optoelectrical devices. The molecule adopts a photoactive antiparallel conformation in the crystalline state. The distance between the two reactive C atoms which are involved in potential ring closure is 3.829 (4) A. The dihedral angles between the central cyclopentene ring and the adjacent thiophene rings are 55.38 (7) and 54.81 (9) degrees. The colourless crystals turn magenta when exposed to UV radiation and the process is reversible.

Journal Article↗

1-(2-Methyl-5-phenyl-3-thienyl)-2-(3-methyl-5-phenyl-2-thienyl)-3,3,4,4,5,5-hexafluorocyclopent-1-ene: a novel photochromic hybrid diarylethene.

The title compound, C27H18F6S2, a novel photochromic hybrid diarylethene derivative containing 2- and 3-thienyl substituents, is one of the most promising photochromic candidates with shorter wavelength for optical storage and other optoelectronic devices. In the crystal structure, the molecule adopts a photoactive antiparallel conformation. The distance between the two reactive C atoms, i.e. the ring C atoms to which the methyl groups are attached, is 3.430 (4) A. The dihedral angles between the thienyl and adjacent phenyl rings are 26.8 (2) and 33.98 (9) degrees.

Journal Article↗

Effective spherical aberration compensation by use of a nematic liquid-crystal device.

The next generation of optical data storage system beyond DVDs will use blue laser light and an objective lens with a high numerical aperture of 0.85 to increase storage capacity. Such high numerical aperture systems have an inherent higher sensitivity to aberrations. In particular, the spherical aberration caused by cover layer thickness tolerances and--more obvious--by dual-layer disks with a typical separation of approximately 20 microm between the two layers must be compensated. We propose a novel transmissive nematic liquid-crystal device, which is capable of compensating spherical aberration that occurs during the operation of optical pickup systems.

Journal Article↗

Optical neural device based on memory-type organic photoconductors.

A variable-sensitivity organic-photoconductive device has been developed by using a memory-type organic photoconductor. The device is composed of an input layer and a memory layer acting as a charge generation and a charge transport layer, respectively. A persistent high-sensitivity state, which corresponds to a modulation of synaptic weights in a neuron model, was obtained by blue light illumination. A photochemical reaction of thiomichler's ketone (TMK) in the memory layer was found to be responsible for the memory formation. As a potential application of this memory-type organic photoconductor to an optical neural device, 2-D pattern storage and calculations were performed successfully.

Animals↗

Bleaching of bacteriorhodopsin by continuous light.

A new two step photobleaching process is observed under continuous illumination of bacteriorhodopsin. This photobleaching is considerable even at physiological temperatures and becomes large at 50-60 degrees C. The photobleaching also increases with increasing pH from 7 to 10. We suggest that the bleaching at its final stage could be due to the dissociation of the retinal and a local thermal denaturation-like process. These facts may question the generally held belief that BR is a stable protein in vivo for a long period of time. Our results may have relevance also to practical applications of bacteriorhodopsin where the stability of bacteriorhodopsin is a key issue. In certain instances, the use of bacteriorhodopsin may require cooled conditions. Here, we defined the conditions under which bacteriorhodopsin is stable. The permanent photobleaching offers a new way of picture imaging and information input for bacteriorhodopsin-based optical devices.

Bacteriorhodopsins↗

Radiation dosimetry using three-dimensional optical random access memories.

Three-dimensional optical random access memories (3D ORAMs) are a new generation of high-density data storage devices. Binary information is stored and retrieved via a light induced reversible transformation of an ensemble of bistable photochromic molecules embedded in a polymer matrix. This paper describes the application of 3D ORAM materials to radiation dosimetry. It is shown both theoretically and experimentally, that ionizing radiation in the form of heavy charged particles is capable of changing the information originally stored on the ORAM material. The magnitude and spatial distribution of these changes are used as a measure of the absorbed dose, particle type and energy. The effects of exposure on 3D ORAM materials have been investigated for a variety of particle types and energies, including protons, alpha particles and 12C ions. The exposed materials are observed to fluoresce when exposed to laser light. The intensity and the depth of the fluorescence is dependent on the type and energy of the particle to which the materials were exposed. It is shown that these effects can be modeled using Monte Carlo calculations. The model provides a better understanding of the properties of these materials. which should prove useful for developing systems for charged particle and neutron dosimetry/detector applications.

Alpha Particles↗

Clinical application of a magneto-optical disk image filing system/image save and carry (ISAC) system.

We propose the utilization of portable magneto optical disks for image filing. The main problems in PACS are the need for a high-speed local area network (LAN) and a large mass storage device. An image filing system--image save and carry (ISAC)--is one solution for these problems in present PACS and requires minimal additional hardware and cost for the installation. Whenever a patient is examined, the clerk carries the medical record and the ISAC magneto-optical disk for recording image data, and after inspection records the image data into the magneto-optical disk. We investigated the number of image retrievals done for inpatients and outpatients in 1988 at our radiation therapy department. The data storage requirements were on the average 18.5 MB for outpatients and 173.9 MB for inpatients. An ISAC display console needs also an easy-to-use man/machine interface for specifying images and image display characteristics in order to realize the ISAC system.

Computer Systems↗

Information partnerships--shared data, shared scale.

How can one company gain access to another's resources or customers without merging ownership, management, or plotting a takeover? The answer is found in new information partnerships, enabling diverse companies to develop strategic coalitions through the sharing of data. The key to cooperation is a quantum improvement in the hardware and software supporting relational databases: new computer speeds, cheaper mass-storage devices, the proliferation of fiber-optic networks, and networking architectures. Information partnerships mean that companies can distribute the technological and financial exposure that comes with huge investments. For the customer's part, partnerships inevitably lead to greater simplification on the desktop and more common standards around which vendors have to compete. The most common types of partnership are: joint marketing partnerships, such as American Airline's award of frequent flyer miles to customers who use Citibank's credit card; intraindustry partnerships, such as the insurance value-added network service (which links insurance and casualty companies to independent agents); customer-supplier partnerships, such as Baxter Healthcare's electronic channel to hospitals for medical and other equipment; and IT vendor-driven partnerships, exemplified by ESAB (a European welding supplies and equipment company), whose expansion strategy was premised on a technology platform offered by an IT vendor. Partnerships that succeed have shared vision at the top, reciprocal skills in information technology, concrete plans for an early success, persistence in the development of usable information for all partners, coordination on business policy, and a new and imaginative business architecture.

Economic Competition↗

Optical emission from a charge-tunable quantum ring

Quantum dots or rings are artificial nanometre-sized clusters that confine electrons in all three directions. They can be fabricated in a semiconductor system by embedding an island of low-bandgap material in a sea of material with a higher bandgap. Quantum dots are often referred to as artificial atoms because, when filled sequentially with electrons, the charging energies are pronounced for particular electron numbers; this is analogous to Hund's rules in atomic physics. But semiconductors also have a valence band with strong optical transitions to the conduction band. These transitions are the basis for the application of quantum dots as laser emitters, storage devices and fluorescence markers. Here we report how the optical emission (photoluminescence) of a single quantum ring changes as electrons are added one-by-one. We find that the emission energy changes abruptly whenever an electron is added to the artificial atom, and that the sizes of the jumps reveal a shell structure.

Journal Article↗

A ten channel fibre-optic device for distributed sensing of underground hydrocarbon leakage.

With millions of fuel storage tanks and oil pipelines installed around the world, there is inevitably frequent leakage of potentially hazardous hydrocarbons. As many of these installations are below ground, it can often be many years before the extent of the leak is discovered. We have previously reported the development of a sensor for the detection of such subterranean leaks, using infrared reflectometry to interrogate a hydrocarbon sensitive membrane. However, a single sensor cannot provide any information about the flow rate or direction of the leak. This paper describes the extension of the technology to a multi-channel distributed sensing system, using optical fibres capable of distributing the sensors over large subterranean areas. Results are reported from the evaluation of the device, which consisted of monitoring the movement of different hydrocarbons (gasoline, diesel and insulating oil) through a vertical sand-filled vessel.

Environmental Monitoring↗

Basics of videodisc and optical disk technology.

This article outlines basic videodisc and optical disk technology. Both optical and capacitance videodisc technology are described. Optical disk technology as a mass digital image and data storage device is defined and briefly compared with other established information storage media including magnetic tape and microforms. The article includes a look into the future of videodisc and optical disk.

Information Systems↗

Direct-bandgap properties and evidence for ultraviolet lasing of hexagonal boron nitride single crystal.

The demand for compact ultraviolet laser devices is increasing, as they are essential in applications such as optical storage, photocatalysis, sterilization, ophthalmic surgery and nanosurgery. Many researchers are devoting considerable effort to finding materials with larger bandgaps than that of GaN. Here we show that hexagonal boron nitride (hBN) is a promising material for such laser devices because it has a direct bandgap in the ultraviolet region. We obtained a pure hBN single crystal under high-pressure and high-temperature conditions, which shows a dominant luminescence peak and a series of s-like exciton absorption bands around 215 nm, proving it to be a direct-bandgap material. Evidence for room-temperature ultraviolet lasing at 215 nm by accelerated electron excitation is provided by the enhancement and narrowing of the longitudinal mode, threshold behaviour of the excitation current dependence of the emission intensity, and a far-field pattern of the transverse mode.

Journal Article↗

Molecular reorientation by photoinduced modulation of rotational mobility.

To explain the large photoinduced molecular reorientation phenomena observed in dye-doped liquids and liquid crystals, the hypothesis was formed that the rotational mobility of dye molecules is strongly altered during their electronic excitation. Here, we report the direct measurement of a 30%-50% mobility decrease of photoexcited anthraquinone dye molecules dissolved in a cyanophenyl liquid host. This mobility reduction is ascribed to an excited-state reinforcement of intermolecular hydrogen bonding. These results provide fully independent evidence for the validity of current models of the photoinduced reorientation and a working demonstration of the design concepts of "fluctuating-friction" molecular motors. We propose that a light-induced modulation of molecular mobility associated with electronic photoexcitation is of general relevance to the behavior of photosensitive organic materials, currently investigated for applications in optical data storage, liquid-crystal displays, and organic optoelectronic devices.

Anthraquinones↗

Multifunctional double-layered diffractive optical element.

We propose a novel multifunctional double-layered diffractive optical element (DOE) based on the fractional Talbot effect. This DOE consists of two layers: one is the encoding layer, in which multiple sub-DOEs, i.e., multiple optical functions, are encoded; the other is the decoding layer, which is a properly designed Talbot illuminator. This DOE can perform each of the multiple optical functions one by one by shifting the encoding layer. Experimental results demonstrate that this method is efficient. This device should be highly interesting for integrated optics, optical interconnection, secure optical storage, and dynamic optical fiber communications.

Journal Article↗

Radiation dosimetry using three-dimensional optical random access memories.

The ability to determine particle type and energy plays an important role in the dosimetry of heavy charged particles (HCP) and neutrons. A new approach to radiation dosimetry is presented, which is shown to be capable of particle type and energy discrimination. This method is based on utilising radiation induced changes in the digital information stored on three-dimensional optical random access memories (3D ORAM). 3D ORAM is a small cube (a few mm3) composed of poly(methyl methacrylate) doped with a photochromic dye. and it was originally proposed as a memory device in high speed parallel computers. A Nd:YAG laser system is used to write and read binary information (bits) on the ORAM, which functions as a charged particle detector. Both the read and the write processes use two laser beams that simultaneously strike the material to cause a colour change at their intersection (similar to the darkening of light-sensitive sunglasses when exposed to sunlight.) The laser produces colour changes in the ORAM, which then reverts to the original colour ('bit-flips') at sites where energy is deposited from interaction with incident HCP or neutron-recoil protons. The feasibility of this approach was demonstrated both theoretically and experimentally. Calculations based on track structure theory (TST) predict that when HCP interact with the ORAM material, the local energy deposition is capable of inducing measurable 'bit-flips'. These predictions were recently confirmed experimentally using two types of ORAM systems, one based on spirobenzopyran and the other on anthracene, as the photochromic dyes.

Computer Storage Devices↗

infoRAD: computers for clinical practice and education in radiology. Teleradiology, information transfer, and PACS: implications for diagnostic imaging in the 1990s.

Picture archiving and communication systems (PACS) provide image viewing at diagnostic, reporting, consultation, and remote workstations; archival on magnetic or optical media by means of short- or long-term storage devices; communications by means of local or wide area networks or public communication services; and integrated systems with modality interfaces and gateways to health care facilities and departmental information systems. Research indicates three basic needs for image and report management: (a) improved communication and turnaround time between radiologists and other imaging specialists and referring physicians, (b) fast reliable access to both current and previously obtained images and reports, and (c) space-efficient archival support. Although PACS considerations are much more complex than those associated with single modalities, the same basic purchase criteria apply. These criteria include technical leadership, image quality, throughput, life cost (eg, initial cost, maintenance, upgrades, and depreciation), and total service. Because a PACS takes much longer to implement than a single modality, the customer and manufacturer must develop a closer working relationship than has been necessary in the past.

Computer Systems↗

Amphiphilic azo polymer spheres, colloidal monolayers, and photoinduced chromophore orientation.

In this work, azobenzene-containing colloidal spheres have been fabricated and used to construct photoresponsive monolayers. The colloidal spheres were prepared from an amphiphilic azobenzene-containing random copolymer through hydrophobic aggregation of the polymer chains, which was induced by adding the selective solvent (H2O) into a THF solution of the polymer. The size and size distribution of the spheres depended on the initial concentration of the azo polymer in THF and the H2O/THF ratio. Adjusting those factors and optimizing other preparation conditions, uniform colloidal spheres could be obtained. Monolayers composed of hexagonally close-packed colloidal spheres were prepared by the capillary-force-driven method. The colloidal monolayers showed obvious dichroism after laser irradiation due to the photoinduced azo-chromophore orientation occurred in the spheres. The orientation order parameter was related to the irradiation time and estimated to be 0.09 at the photostationary state. The colloidal spheres and their monolayers can potentially be used as building blocks or media for reversible optical data storage, photo-switching, sensors, and other photo-driven devices.

Journal Article↗