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At least 1,711 records · Page 95Linked to original sources
PubMed2003

Are lichens active under snow in continental Antarctica?

Photosynthetic activity, detected as chlorophyll a fluorescence, was measured for lichens under undisturbed snow in continental Antarctica using fibre optics. The fibre optics had been buried by winter snowfall after being put in place the previous year under snow-free conditions. The fibre optics were fixed in place using specially designed holding devices so that the fibre ends were in close proximity to selected lichens. Several temperature and PPFD (photosynthetic photon flux density) sensors were also installed in or close to the lichens. By attaching a chlorophyll a fluorometer to the previously placed fibre optics it proved possible to measure in vivo potential photosynthetic activity of continental Antarctic lichens under undisturbed snow. The snow cover proved to be a very good insulator for the mosses and lichens but, in contrast to the situation reported for the maritime Antarctic, it retained the severe cold of the winter and prevented early warming. Therefore, the lichens and mosses under snow were kept inactive at subzero temperatures for a prolonged time, even though the external ambient air temperatures would have allowed metabolic activity. The results suggest that the major activity period of the lichens was at the time of final disappearance of the snow and lasted about 10-14 days. The activation of lichens under snow by high air humidity appeared to be very variable and species specific. Xanthoria mawsonii was activated at temperatures below -10 degrees C through absorption of water from high air humidity. Physcia dubia showed some activation at temperatures around -5 degrees C but only became fully activated at thallus temperatures of 0 degrees C through liquid water. Candelariella flava stayed inactive until thallus temperatures close to zero indicated that liquid water had become available. Although the snow cover represented the major water supply for the lichens, lichens only became active for a brief time at or close to the time the snow disappeared. The snow did not provide a protected environment, as reported for alpine habitats, but appeared to limit lichen activity. This provides at least one explanation for the observed negative effect of extended snow cover on lichen growth.

Adaptation, Physiological↗
PubMed2001

Optical implementation of continuous-variable quantum cloning machines.

We propose an optical implementation of the Gaussian continuous-variable quantum cloning machines. We construct a symmetric N-->M cloner which optimally clones coherent states, and we also provide an explicit design of a class of asymmetric 1-->2 cloning machines. All proposed cloning devices can be built from just a single nondegenerate optical parametric amplifier and several beam splitters.

Journal Article↗
PubMed2004

On the suitability of near-infrared (NIR) systems for next-generation brain-computer interfaces.

A brain-computer interface (BCI) gives those suffering from neuromuscular impairments a means to interact and communicate with their surrounding environment. A BCI translates physiological signals, typically electrical, detected from the brain to control an output device. A significant problem with current BCIs is the lengthy training periods involved for proficient usage, which can often lead to frustration and anxiety on the part of the user. Ultimately this can lead to abandonment of the device. The primary reason for this is that relatively indirect measures of cognitive function, as can be gleaned from the electroencephalogram (EEG), are harnessed. A more suitable and usable interface would need to measure cognitive function more directly. In order to do this, new measurement modalities, signal acquisition and processing, and translation algorithms need to be addressed. In this paper, we propose a novel approach, using non-invasive near-infrared imaging technology to develop a user-friendly optical BCI. As an alternative to the traditional EEG-based devices, we have used practical non-invasive optical techniques to detect characteristic haemodynamic responses due to motor imagery and consequently created an accessible BCI that is simple to attach and requires little user training.

Algorithms↗
PubMed2004

Devic's neuromyelitis optica treated with intravenous gamma globulin (IVIG).

BACKGROUND: Devic's syndrome is a demyelinating disease of the spinal cord and optic nerves. It tends to have a poor prognosis, probably due to the occurrence of necrosis within lesions. There is no proven effective treatment although relapses are commonly treated with corticosteroids and people with recurrent attacks may be managed with chronic immune suppressing treatments. Intravenous gamma globulin (IVIG) and plasma exchange are reasonable treatment options because Devic's syndrome is believed to be antibody mediated. We report two patients of Devic's syndrome that stabilized following initiation of monthly IVIG. PATIENT 1: A 42-year-old woman with a 23 year history of Devic's syndrome continued to have frequent attacks of optic neuritis unresponsive to daily corticosteroids and azathioprine. Since initiation of monthly IVIG 5 1/2 years ago she has had no further definite attacks. She has also noted minimal improvement in color perception. PATIENT 2: A 58-year-old woman with a three year history of Devic's syndrome experienced five attacks during the first 16 months of disease. Monthly IVIG was associated with complete cessation of relapses and significantly improved neurological status over one year of treatment. CONCLUSIONS: Because active Devic's disease often results in severe, permanent neurological impairment, preventive intervention should be considered. These cases suggest that IVIG may be effective in preventing attacks and possibly in enhancing neurological recovery. Randomized controlled trials will be needed to confirm this and to determine optimal dosing and treatment duration.

Adult↗
PubMed1995

Imaging the dorsal hippocampus: light reflectance relationships to electroencephalographic patterns during sleep.

We assessed the correspondence of 660 nm light reflectance changes from the dorsal hippocampus with slow wave electroencephalographic (EEG) activity during quiet sleep (QS) and rapid eye movement (REM) sleep in four cats. An optic probe, attached to a charge-coupled-device (CCD) video camera, was placed on the dorsal hippocampal surface to collect reflectance images simultaneously with EEG, which was measured by macroelectrodes placed around the probe circumference. Spectral estimates of EEG and light reflectance amplitude indicated that reflectance changes occurred in a similar frequency range as EEG changes. Dividing the image into 10 subregions revealed that reflectance changes at the rhythmical slow wave activity band (RSA, 4-6 Hz) persisted in localized regions during QS and REM sleep, but regional changes showed considerable wave-by-wave independence between areas and from slow wave electrical activity. Peak frequencies for reflectance changes corresponded to fast RSA frequencies observed in the EEG. Optical changes most likely derive from fast-acting physical phenomena, rather than from alterations in blood perfusion, and provide increased spatial resolution over that offered by electrical measurements.

Animals↗
PubMed2004

Very large electro-optic responses in H-bonded heteroaromatic films grown by physical vapour deposition.

A crucial goal for modern telecommunications systems is development of very high-speed components for broadband (>100 GHz), all-optical signal/information processing. The core component of such technologies is the electro-optic modulator, which encodes electrical signals onto fibre-optic transmissions. A significant challenge therefore is obtaining materials that have large electro-optic responses and that can be readily fabricated into devices at low cost. We report here on the realization of high-response heteroaromatic organic chromophores that can be straightforwardly self-organized from the vapour phase into intrinsically acentric, high-quality, micrometre-scale films. These pi-conjugated electro-optically active films (with second-order susceptibilities up to approximately 100 pm V(-1)) are thermally stable and conveniently grown by a simple physical vapour deposition process in a few hours. Supramolecular acentricity is achieved without electric field poling, enforced by biomimetic heterocycle-hydroxycarbonyl head-to-tail hydrogen-bonding.

Crystallization↗
PubMed2003

Optical heterodyne surface-plasmon resonance biosensor.

A novel optical heterodyne surface-plasmon resonance (SPR) biosensor with a Zeeman laser is proposed. Two surface plasma waves are excited by two correlated p-polarized waves in a SPR device of the Kretschmann configuration. Two reflected p waves are optically heterodyned such that the magnitude of the heterodyned signal is proportional to the multiplication of two attenuated reflected p waves. Then the detection sensitivity and the dynamic range based on this amplitude-sensitive method are enhanced. In the experiment, the kinetics between mouse immunoglobulin G (IgG) and rabbit antimouse IgG is obtained from sensograms of various concentrations of antimouse IgG. A detection sensitivity of 0.2 nM was achieved. In addition, a concentration of 5 ng/ml of protein G interacting with mouse IgG was measured successfully.

Animals↗
PubMed2002

Measurement of adhesive forces between S. epidermidis and fibronectin-coated surfaces using optical tweezers.

BACKGROUND AND OBJECTIVES: Biomaterial-mediated infection, a common cause of medical device failure, is initiated by bacterial adhesion to an adsorbed protein layer on the implant surface. This adhesion is thought to be mediated by specific molecules present on the bacterial cell surface. Optical tweezers can be used to measure the adhesive force between a single bacterium and a protein-coated surface. STUDY DESIGN/MATERIALS AND METHODS: Using optical tweezers, a bacterium was trapped and brought in contact with a 10-microm diameter polystyrene microsphere coated with fibronectin. The minimum force required to detach the cell from the bead was determined over a range of fibronectin concentrations and contact times. RESULTS: The detachment forces were integer multiples of an 18-pN base value that was independent of contact time and coating concentration; we propose that the variation in force is related to the number of bonds formed. CONCLUSIONS: These experiments demonstrate that optical tweezers can be used to investigate the adhesion of individual bacteria to surfaces. The results suggest that S. epidermidis has surface proteins capable of binding fibronectin.

Adhesiveness↗
PubMed2003

Corneal replacement using a synthetic hydrogel cornea, AlphaCor: device, preliminary outcomes and complications.

PURPOSE: Clinical assessment of outcome of corneal replacement with a synthetic cornea, AlphaCor, in patients considered at too high risk for conventional penetrating keratoplasty with donor tissue to be successful, but excluding indications such as end-stage dry eye that might be suited to traditional prosthokeratoplasty. METHODS: All patients in the multicentre clinical trial were managed according to an approved protocol, with Ethics Committee approval in each centre. Preoperative visual acuity ranged from perception of light (PL) to 6/60 (20/200). Implantation was by means of an intralamellar technique, with a conjunctival flap in most cases. Tissues anterior to the optic were removed as a secondary procedure. RESULTS: Up to 30 November 2001, 40 AlphaCor devices had been implanted in 38 patients, of mean age 60 years. Follow-up ranged from 0.5 months to 3 years. There had been one extrusion (2.5%) and four cases (10%) where a device had been removed due to melt-related complications. All five of these cases received a donor corneal graft after the device was removed, with these grafts remaining anatomically satisfactory and epithelialised to date. Corneal melts in AlphaCor recipients were found to be strongly associated with a history of ocular herpes simplex infection. Two further devices (5%) were removed owing to reduced optic clarity after presumed drug-related deposition, and have been successfully replaced with second devices. Mean preoperative best-corrected visual acuity was hand movements. Visual acuities after surgery ranged from PL to 6/6(-2) (20/20(-2)). CONCLUSIONS: Early results suggest that the AlphaCor, previously known as the Chirila keratoprosthesis (Chirila KPro), has a low incidence of the complications traditionally associated with keratoprostheses and can be effective in restoring vision in patients considered untreatable by conventional corneal transplantation. Importantly, the device can be replaced with a donor graft in the event of development of a significant complication. A history of ocular herpes simplex is a contraindication to AlphaCor implantation. Ongoing monitoring of clinical outcomes in all patients will allow the indications for AlphaCor, as opposed to donor grafts, to be determined.

Adult↗
PubMed2002

Conductive carbon filled polymeric electrodes: novel ion optical elements for time-of-flight mass spectrometers.

A new technique employing conductive polymeric electrodes for the generation of linear electric fields is proposed and validated. A hollow cylinder comprised of DuPont's Vespel SP-22, a polymer loaded with conductive carbon particles, is used to enhance the performance of a hybrid reflectron compared to a conventional dual stage gridless reflectron composed of discrete metal ring electrodes. Both devices have comparable physical dimensions and nearly identical ion optical properties. Instrumental resolution measurements are used to validate this novel design.

Journal Article↗
PubMed2000

n-type colloidal semiconductor nanocrystals.

Colloidal semiconductor nanocrystals combine the physical and chemical properties of molecules with the optoelectronic properties of semiconductors. Their colour is highly controllable, a direct consequence of quantum confinement on the electronic states. Such nanocrystals are a form of 'artificial atoms' (ref. 4) that may find applications in optoelectronic systems such as light-emitting diodes and photovoltaic cells, or as components of future nanoelectronic devices. The ability to control the electron occupation (especially in n-type or p-type nanocrystals) is important for tailoring the electrical and optical properties, and should lead to a wider range of practical devices. But conventional doping by introducing impurity atoms has been unsuccessful so far: impurities tend to be expelled from the small crystalline cores (as observed for magnetic impurities), and thermal ionization of the impurities (which provides free carriers) is hindered by strong confinement. Here we report the fabrication of n-type nanocrystals using an electron transfer approach commonly employed in the field of conducting organic polymers. We find that semiconductor nanocrystals prepared as colloids can be made n-type, with electrons in quantum confined states.

Journal Article↗
PubMed1997

Light scattering changes follow evoked potentials from hippocampal Schaeffer collateral stimulation.

We assessed relationships of evoked electrical and light scattering changes from cat dorsal hippocampus following Schaeffer collateral stimulation. Under anesthesia, eight stimulating electrodes were placed in the left hippocampal CA field and an optic probe, coupled to a photodiode or a charge-coupled device camera to detect scattered light changes, was lowered to the contralateral dorsal hippocampal surface. Light at 660 +/- 10 (SE) nm illuminated the tissue through optic fibers surrounding the optic probe. An attached bipolar electrode recorded evoked right hippocampal commissural potentials. Electrode recordings and photodiode output were simultaneously acquired at 2.4 kHz during single biphasic pulse stimuli 0.5 ms in duration with 0.1-Hz intervals. Camera images were digitized at 100 Hz. An average of 150 responses was calculated for each of six stimulating current levels. Stimuli elicited a complex population synaptic potential that lasted 100-200 ms depending on stimulus intensity and electrode position. Light scattering changes peaked 20 ms after stimuli and occurred simultaneously with population spikes. A long-lasting light scattering component peaked 100-500 ms after the stimulus, concurrently with larger population postsynaptic potentials. Optical signals occurred over a time course similar to that for electrical signals and increased with larger stimulation amplitude to a maximum, then decreased with further increases in stimulation current. Camera images revealed a topographic response pattern that paralleled the photodiode measurements and depended on stimulation electrode position. Light scattering changes accompanied fast electrical responses, occurred too rapidly for perfusion, and showed a stimulus intensity relationship not consistent with glial changes.

Animals↗
PubMed2002

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↗
PubMed2005

Polarization properties of a nematic liquid-crystal spatial light modulator for phase modulation.

The polarization properties of a nematic zero-twist liquid-crystal (NLC) spatial light modulator (SLM) were studied. A large ratio between the liquid-crystal (LC) layer thickness and the pixel pitch combined with spatial variations in the applied electric field causes fringing fields between pixels. Depending on the LC alignment, the electric field components within the LC layer can result in a twist deformation. The produced inhomogeneous optical anisotropy affects the polarization of light propagating through the device. We experimentally examined polarization effects in different diffraction orders for both binary and blazed phase gratings. Simulations of the LC deformation together with finite-difference time-domain simulations for the optical propagation were used to calculate the corresponding far-field intensities. It was demonstrated how rigorous simulations of the NLC SLM properties can be used to understand the polarization features of different diffraction orders.

Journal Article↗
PubMed2004

Fluoroscope-aided retrograde placement of guide wire for tracheal intubation in patients with limited mouth opening.

Passing a retrograde catheter/wire into the pharynx through a cricothyroid puncture can facilitate tracheal intubation in difficult situations where either a flexible fibre-optic bronchoscope or an expert user of such a device is not available. Some mouth opening is essential for the oral and/or nasal retrieval of the catheter/wire from the pharynx. Two patients with temporo-mandibular joint (TMJ) ankylosis and extremely limited mouth opening required gap arthroplasty of the TMJ under general anaesthesia. Because we did not have a flexible fibre-optic bronchoscope, we performed fluoroscopy-assisted nasal retrieval of the guide wire passed up through a cricothyroid puncture and subsequently accomplished wire-guided naso-tracheal intubation. In the absence of a flexible fibre-optic bronchoscope, this technique is a very useful aid to intubation in patients with limited mouth opening.

Adult↗
PubMed2006

[I have tested for you. Pachymetry devices].

Different techniques are currently available to measure central corneal thickness: optical pachymetry, ultrasound pachymetry, optical coherence pachymetry, slit-scanning pachymetry, specular microscopy, and confocal microscopy. Ultrasound pachymetry is the gold standard. It is a noncontact and rapid technique with high precision, approximately 1%. The correlation between optical coherence pachymetry and ultrasound pachymetry is high, with a 0.99 correlation coefficient. Nevertheless, optical coherence pachymetry measurements seem underestimated compared to ultrasound pachymetry measurements. Correlation of ultrasound pachymetry with the other techniques is less satisfying. If the ultrasound probe can be decontaminated for each patient, ultrasound pachymetry seems to be the best technique for measuring central corneal thickness. Otherwise, optical coherence pachymetry seems to be the most advantageous technique.

Cornea↗
PubMed1978

Use of optical distance sensing to track tongue motion.

We have designed a device that uses a reflected-light-sensing technique to monitor tongue movement in the frontal oral cavity. The sensing unit is composed of a LED light source and a phototransistor, mounted together onto an artificial palate, and attached to the had palate. The basic sensing function of this unit is governed by the formula r/(r2 + xo2)3/2 rather than by the inverse square distance law. In this equation, r is the distance between the sensor and the reflector, namely, the tongue surface. The xo is the separation between the source and the photosensor. Two potential problems, the beam dispersion effect of the light source and the nonparallel movement of the tongue, were anticipated. They can be theoretically represented or technically prevented. The softness of the tongue and the protuberances of its surface are also favorable aspects of this method, creating special light reflection from the tongue surface. The available output function was from 0 to 40 or 50 mm. This gives the device the capability of detecting both vowel and consonantal articulation. The method can be useful to further speech research and the development of a language teaching aid system.

Evaluation Studies as Topic↗