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At least 397 records · Page 22Linked to original sources
PubMed1998

Focusing Optics for High-Energy X-ray Diffraction.

Novel focusing optical devices have been developed for synchrotron radiation in the energy range 40-100 keV. Firstly, a narrow-band-pass focusing energy-tuneable fixed-exit monochromator was constructed by combining meridionally bent Laue and Bragg crystals. Dispersion compensation was applied to retain the high momentum resolution despite the beam divergence caused by the focusing. Next, microfocusing was achieved by a bent multilayer arranged behind the crystal monochromator and alternatively by a bent Laue crystal. A 1.2 micro m-high line focus was obtained at 90 keV. The properties of the different set-ups are described and potential applications are discussed. First experiments were performed, investigating with high spatial resolution the residual strain gradients in layered polycrystalline materials. The results underline that focused high-energy synchrotron radiation can provide unique information on the mesoscopic scale to the materials scientist, complementary to existing techniques based on conventional X-ray sources, neutron scattering or electron microscopy.

Journal Article↗
PubMedDate not supplied

Augmented scene modeling and visualization by optical and acoustic sensor integration.

In this paper, underwater scene modeling from multisensor data is addressed. Acoustic and optical devices aboard an underwater vehicle are used to sense the environment in order to produce an output that is readily understandable even by an inexperienced operator. The main idea is to integrate multiple-sensor data by geometrically registering such data to a model. The geometrical structure of this model is a priori known but not ad hoc designed for this purpose. As a result, the vehicle pose is derived and model objects can be superimposed upon actual images, thus generating an augmented-reality representation. Results on a real underwater scene are reported, showing the effectiveness of the proposed approach.

Journal Article↗
PubMedDate not supplied

Contact lens status in ametropia correction: a prospective study.

BACKGROUND: Optical devices such as spectacles and contact lenses have been used to correct ametropia for many years. Recently, surgical means of correction such as photorefractive keratectomy have been introduced. All of these forms of correction are readily available in Saudi Arabia. The purpose of this study was to determine the proportion of contact lens use in ametropia correction. This survey also presents an insight into patient satisfaction with their correction and their willingness to change to another form of correction in the future. This will serve as a guide for eye care practitioners and manufacturers. METHOD: Five hundred and seventy four subjects responded to questionnaires randomly distributed among hospital patients, students and staff of King Saud University. RESULTS: Data revealed that spectacle wearers constituted 74.5 per cent of the sample population, followed by contact lens wearers (21.8 per cent) and those who had undergone photorefractive keratectomy (3.7 per cent). On the whole, 50 per cent of the population sample would change to another form of correction. Among contact lens wearers, 9.5 per cent would prefer to change to PRK and 0.4 per cent to spectacles, while 17.9 per cent of spectacle wearers would consider changing to contact lenses. CONCLUSION: Contact lenses constitute a minor proportion of ametropia corrections. Spectacles remain the most popular form of ametropia correction at the moment, but for the future, there is greater tendency towards contact lenses and PRK.

Journal Article↗
PubMed2006

Creutzfeldt-Jakob disease and vision.

This review describes a group of diseases known as the transmissible spongiform encephalopathies (TSEs), which affect animals and humans. Examination of affected brain tissue suggests that these diseases are caused by the acquisition and deposition of prion protein (PrP). Creutzfeldt-Jakob disease (CJD) is the most important form of TSE in humans with at least four different varieties of the disease. Variant CJD (vCJD), a new form of the disease found in the UK, has several features that differ from the classical forms including early age of onset, longer duration of disease, psychiatric presentation (for example, depression) and extensive florid plaque development in the brain. About 10 per cent of patients with CJD exhibit visual symptoms at disease presentation and approximately 50 per cent during the course of the disease. The most commonly reported visual symptoms include diplopia, supranuclear palsies, complex visual disturbances, homonymous visual field defects, hallucinations and cortical blindness. Saccadic and smooth pursuit movements appear to be more rarely affected. The agent causing vCJD accumulates in lymphoid tissue such as the spleen and tonsils. The cornea has lymphoid tissue in the form of corneal dendritic cells that are important in the regulation of the immune response in the anterior segment of the eye. The presence of these cells in the cornea has raised the possibility of transmission between patients via optical devices that contact the eye. Although such transmission is theoretically possible it remains highly improbable.

Animals↗
PubMed1999

Comparison of microvascular filtration in human arms with and without postmastectomy oedema.

Oedema is caused by impaired lymphatic drainage and/or increased microvascular filtration. To assess a postulated role for the latter in postmastectomy oedema, filtration was studied in the forearms of 14 healthy subjects and 22 patients with chronic, unilateral arm oedema caused by surgical and radiological treatment for breast cancer. A new non-contact optical device (the Perometer) and a conventional mercury strain gauge were used simultaneously to record forearm swelling rates caused by microvascular filtration during applied venous congestion. Filtration rate (FR) per 100 ml tissue was measured over 10-15 min at a venous pressure of 30 cmH2O, a pressure reached in the dependent forearm (FR30), and then at 60 cmH2O (FR60). Apparent filtration capacity of 100 ml soft tissue (CFCa) was calculated from FR60 - FR30/30, after adjustment for bone volume. The Perometer and strain gauge gave similar results in normal and oedematous arms. Mean CFCa in healthy subjects was (3.8+/-0.4) x 10(-3) ml (100 ml)-1 cmH2O-1 min-1, close to literature values. In the patients, FR30 was 47 % lower in the oedematous forearm than in the opposite, unaffected forearm (P = 0.04). FR60 showed a similar trend but did not reach significance (P = 0.15). The values of CFCa of (2.2+/-0.5) x 10(-3) ml (100 ml)-1 cmH2O-1 min-1 in the oedematous arm and (2.8+/-0.5) x 10(-3) ml (100 ml)-1 cmH2O-1 min-1 in the unaffected arm were not significantly different (P = 0.47). When differences in arm volume on the two sides were taken into account, the total fluid load on the lymphatic system of the oedematous forearm was (411.0+/-82.2) x 10(-3) ml min-1 at 30 cmH2O and (1168+/-235.6) x 10(-3) ml min-1 at 60 cmH2O, similar to the normal side, namely (503.7+/-109.3) 10(-3) ml min-1 and (1063+/-152.0) x 10(-3) ml min-1, respectively (P >/= 0.50). The filtration capacity of the entire oedematous forearm (CFCa scaled up by total soft tissue volume), (25.4+/-6.2) x 10(-3) ml cmH2O-1 min-1, was not significantly greater than that of the normal forearm, (18.3+/-2.6) x 10(-3) ml cmH2O-1 min-1 (P = 0.40). The results indicate that no major change occurs in the microvascular hydraulic permeability-area product of the forearm, or in the total filtration load on the lymph drainage system during dependency, in the arm with postmastectomy oedema compared with the normal arm. This argues against a significant haemodynamic contribution to postmastectomy oedema.

Aged↗
PubMed1991

Postoperative elevation of eyeglasses from the nasal bridge.

After surgery on the proximal nose, wearing eyeglasses can be difficult and uncomfortable. In addition, pressure on the skin underneath the eyeglass nose pads may modify wound healing. We describe simple techniques using readily available materials and optical devices that either reduce or remove pressure on the nose from eyeglasses.

Eyeglasses↗
PubMed1991

Primary success with low vision aids in age-related macular degeneration.

The benefit obtained from various low vision aids (LVAs) was studied in 65 consecutive patients with atrophic (70.3%) or disciform (29.7%) age-related macular degeneration (ARMD). 13.8% were able to read newsprint with age-related reading correction under proper lighting conditions. The primary success achieved with LVAs was good, 91.4% of patients being able to read newsprint. In most cases a simple magnifier (52.3%), high-powered reading glasses (10.8%) or Fonda's glasses (12.8%) were sufficient. The magnification preferred was 5x or less in 25.6% and greater than 5x to 9x in 48.8%. Patients with disciform degeneration required higher magnification than those with atrophic degeneration. It is concluded that most patients with ARMD found low vision aids useful for reading purposes and that a simple optical device was sufficient to achieve reading vision.

Age Factors↗
PubMedDate not supplied

Daily use of the physio dialysis system: long-term experience.

BACKGROUND: Hypovolaemia has been implicated as a major causal factor of morbidity during haemodialysis (HD). In order to avoid the appearance of destabilising hypovolaemia a biofeedback control system for intra-HD blood volume (BV) change modelling has been developed (Hemocontrol, Hospal Italy). It is based on an adaptive controller incorporated into a HD machine (Integra, Hospal Italy). The Hemocontrol biofeedback system (HBS) monitors BV contraction during HD with an optical device; furthermore, HBS modulates BV contraction rates (by adjusting the ultrafiltration rate--UFR) and the refilling rate (by adjusting dialysate conductivity--DC) in order to obtain the desired pre-determined BV trajectories. METHODS: Nineteen patients prone to hypotension (7 males, 12 females, mean age 64.5 +/- 3.0 SEM years, on maintenance HD for 80.5 +/- 13.2 months) volunteered for the prospective study which aimed to compare the efficacy and safety of bicarbonate HD treatmentequipped with HBS, as a whole (HBS),with the gold standard, bicarbonate treatment, equipped with a constant UFR and DC (BD). The study included one period of 6 months of BD always preceding a follow-up period of HBS treatment ranging from 14 to 30 months (mean 24.0 +/- 1.6). RESULTS: The overall occurrence of symptomatic hypotension and muscle cramps was significantly less in HBS treatment. Self-evaluation of intra- and inter-HD symptoms (the worst score was o and the best one 10) did reveal a statistically significant difference, as far as post-HD fatigue is concerned (6.2 +/- 0.2 in HBS vs. 4.3 +/- 0.1 in BD treatment, p < 0.0001). No difference between the two treatments was observed when comparing pre- and post-HD lying blood pressure, heart rate, body weights and body weight changes. CONCLUSIONS: HBS is an effective treatment. Hypovolaemia-associated morbidity occurs less in BD treatment than HBS. Furthermore, HBS is a safe treatment in the medium-term because these results are achieved without potentially harmful changes in blood pressure, body weight and serum sodium concentration.

Bicarbonates↗
PubMed2003

Nonlinear characteristics of single-reed instruments: quasistatic volume flow and reed opening measurements.

A wind instrument can be described as a closed feedback loop made up of a linear passive element-the resonator-and a lumped nonlinear element-the mouthpiece. A method for measuring the nonlinear characteristics of the mouthpiece-nonlinear flow relationship-in static condition is given. An artificial mouth is used in which the volume flow is deduced from the pressure difference between both sides of a constriction (orifice) which takes place in the resonator. The orifice also plays the role of a nonlinear absorber, thwarting possible reed oscillations. This allows the measurement of the complete characteristics. In addition, the reed opening is measured using an optical device. Results are compared to a model in which the reed is reduced to its stiffness and the flow is governed by the Bernoulli equation. It is shown that the reed stiffness and the ratio of the effective surface of the jet and the reed opening are constant in a large range of openings. Standard range values of embouchure parameters are given.

Air Pressure↗
PubMed2003

Surface-driven switching of liquid crystals using redox-active groups on electrodes.

Electrochemical control of the oxidation state of ferrocene-decorated electrodes leads to surface-driven changes in the orientations of thermotropic liquid crystals. When the electrodes possess nanometer-scale topography, voltages of 0.0 to 0.3 volts (versus a counter electrode in a two-electrode cell) can drive changes in the orientation of the liquid crystals in the plane and/or out of the plane of the electrodes. Electrodes not supporting ferrocene do not lead to surface-driven orientational transitions. The in-plane transitions are driven by the reorganization of the monolayer of ferrocene upon oxidation of ferrocene to ferrocenium. The out-of-plane transition reflects a dielectric coupling between the liquid crystal and the diffuse part of an electrical double layer that evolves upon oxidation of ferrocene to ferrocenium. These results suggest new ways to couple the orientations of liquid crystals to chemical and electrical stimuli in electro-optical devices and chemical sensors.

Journal Article↗
PubMed2003

Compensation of the birefringence of a polymer by a birefringent crystal.

We report a method for compensating the birefringence of optical polymers by doping them with inorganic birefringent crystals. In this method, an inorganic birefringent material is chosen that has the opposite birefringence to that of the polymer and has rod-shaped crystals that are oriented when the polymer chains are oriented. The birefringence of the polymer is thus compensated by the opposing birefringence of the crystal. Birefringence is minimized in various polymer optical devices by adjusting process conditions, because it degrades the performance of devices. This method minimizes it, independent of process conditions, which potentially improves the productivity of devices.

Journal Article↗
PubMed2004

Enhancement of ferroelectricity in strained BaTiO3 thin films.

Biaxial compressive strain has been used to markedly enhance the ferroelectric properties of BaTiO3 thin films. This strain, imposed by coherent epitaxy, can result in a ferroelectric transition temperature nearly 500 degrees C higher and a remanent polarization at least 250% higher than bulk BaTiO3 single crystals. This work demonstrates a route to a lead-free ferroelectric for nonvolatile memories and electro-optic devices.

Journal Article↗
PubMed1996

Photoinduced Magnetization of a Cobalt-Iron Cyanide

Photoinduced magnetization was observed in a Prussian blue analog, K0.2Co1.4- [Fe(CN)6]&middot;6.9H2O. An increase in the critical temperature from 16 to 19 kelvin was observed as a result of red light illumination. Moreover, the magnetization in the ferrimagnetic region below 16 kelvin was substantially increased after illumination and could be restored almost to its original level by thermal treatment. These effects are thought to be caused by an internal photochemical redox reaction. Furthermore, blue light illumination could be used to partly remove the enhancement of the magnetization. Such control over magnetic properties by optical stimuli may have application in magneto-optical devices.

Journal Article↗
PubMed1981

Plasticity in the vestibulo-ocular reflex: a new hypothesis.

The vestibulo-ocular reflex functions to prevent head movements from disturbing retinal images by generating compensatory eye movements to offset the head movements. In the monkey--the species mainly under consideration here--this reflex is machine-like and very effective. In the short-term, the VOR operates as an open-loop control system without the benefit of feedback and its performance is fixed and immutable: No matter what pattern of eye-head coordination the animal uses to view external objects, there is a continuing need for the VOR and it continues to operate; however, should the VOR consistently fail to stabilize the retinal images during head turns, it will gradually undergo long-term adaptive gain changes that restore, that stability. This adaptive capability is ultimately dependent upon vision, and a variety of optical devices that disturb the visual input normally associated with lead turns have been used to induce large changes in the reflex. Insofar as the monkey is concerned, all of the available evidence suggests to us that the modifiable elements underlying these long-term adjustments are located in the brainstem vestibular pathways and not, as previously suggested by others, in the floccular lobes of the cerebellum. However, the flocculus does appear to have an important, inductive role in the adaptive process providing at least part of the error signal guiding the long-term adjustments in the brainstem. In our view, the VOR is a particularly well-defined example of a plastic system and promises to be a most useful model for studying the cellular mechanisms underlying memory and learning the central nervous system.

Animals↗
PubMed1984

Signals used to compute errors in monkey vestibuloocular reflex: possible role of flocculus.

Adaptive changes were induced in the vestibuloocular reflex (VOR) of monkeys by oscillating them while they viewed the visual scene through optical devices ("spectacles") that required changes in the amplitude of eye movement during head turns. The "gain" of the VOR (eye velocity divided by head velocity) during sinusoidal oscillation in darkness underwent gradual changes that were appropriate to reduce the motion of images on the retina during the adapting procedures. Bilateral ablation of the flocculus and ventral paraflocculus caused a complete and enduring loss of the ability to undergo adaptive changes in the VOR. Partial lesions caused a substantial but incomplete loss of the adaptive capability. We conclude that the flocculus is necessary for adaptive changes in the monkey's VOR. Further experiments in normal animals determined the types of stimuli that were necessary and/or sufficient to cause changes in VOR gain. Full-field visual stimulation was not necessary to induce adaptive changes in the VOR. Monkeys tracked a small spot in conditions that elicited the same combination of eye and head movements seen during passive oscillation with spectacles. The gain of the VOR showed changes 50-70% as large as those produced by the same duration of oscillation with spectacles. Since the effective tracking conditions cause a consistent correlation of floccular output with vestibular inputs, these data are compatible with our previous suggestion that the flocculus may provide signals used by the central nervous system to compute errors in the gain of the VOR. Prolonged sinusoidal optokinetic stimulation with the head stationary caused only a slight increase in VOR gain. Left-right reversal of vision and eye movement during sinusoidal vestibular oscillation caused decreases in VOR gain. In rabbits, both of these stimulus conditions produced large increases in the gain of the VOR, which implied that eye velocity signals were used instead of vestibular inputs to compute errors in the VOR. Our different results argue that vestibular signals are necessary for computing errors in VOR gain in the monkey. The species difference may reflect the additional role that smooth pursuit eye movements play in stabilizing gaze during head turns in monkeys.

Animals↗
PubMed1998

Systemic vascular resistance in intradialytic hypotension determined by means of impedance cardiography.

BACKGROUND: Recurrent intradialytic hypotension still is a major source of discomfort in hemodialysis patients today, its origin being subject to extensive research. Different hypotheses have been raised to unravel this problem, without forming one coherent point of view. The aim of this study was to gain more insight into the mechanisms causing intradialytic hypotension by determining cardiovascular performance noninvasively during hemodialysis in a large group of patients. METHODS: In the present study the variations in blood volume, stroke volume, cardiac output and systemic vascular resistance were investigated in 68 patients on chronic intermittent hemodialysis utilizing bioelectrical impedance cardiography. In addition, blood volume was monitored continuously with an on-line optical device. RESULTS: Twenty-four patients experienced symptomatic hypotension during dialysis treatment. Compared to the hemodynamically stable patients, the hypotensive patients manifested a slightly greater decline in blood volume (mean +/- SEM; -9.4 +/- 1.2 vs. -6.5 +/- 0.8%, p = 0.04) and cardiac output (-11.8 +/- 4.2 vs. -7.3 +/-2.7%, p = NS). The main difference, however, was a highly significant decrease in systemic vascular resistance (-17.9 +/- 4.4%) in the hypotensive group compared to a rise in the stable group (+6.2 +/- 3.5%, p < 0.001). CONCLUSION: Intradialytic hypotension seems the consequence of an inadequate compensatory response to ultrafiltration-induced blood volume reduction, resulting in a fall in systemic vascular resistance. The degree of hypovolemia itself appears to be less important in the origin of acute, intradialytic hypotensive episodes. Noninvasive monitoring during hemodialysis provides an opportunity to gain more insight into the pathophysiology of intradialytic hypotension and offers the possibility for controlled intervention and possible prevention of this complication.

Blood Volume↗
PubMed2004

New diagnostic approaches for early detection of gastric cancer.

Detection of gastric cancer in early stages is vitally important for ascertaining better prognosis and quality of life for the patients. Therefore, every endoscopist should be trained to master enough diagnostic skills to identify early gastric cancer that often shows minimal alteration from the surrounding mucosa, easily evading detection. For the first step, it is essential that endoscopists understand the normal gastric mucosa as well as the mucosal changes caused by chronic H. pylori infection, a high-risk condition for the development of gastric cancer. Once a suspicious lesion is identified, use of a dye-spraying method may be useful to clarify structural alteration caused by neoplastic changes and facilitate the biopsy sampling. Development of zoom (magnifying) endoscopy enabling 80x magnification with a one-touch switch from conventional endoscopic observation helps to identify the detailed surface structure as well as the vascular architecture of the mucosa without tissue biopsy. Combined with chromoendoscopy, this powerful endoscopic method can be used to identify small cancer foci or delineate the margin of early gastric cancer that can be treatable by mucosal dissection. Other new modalities using a variety of optical devices have been developed but the real value of their utility still remains to be proven in the actual clinical settings.

Diagnosis, Differential↗
PubMed1997

Aetiology of herniation of the hindbrain in craniosynostosis. An investigation incorporating intracranial pressure monitoring and magnetic resonance imaging.

The occurrence and extent of herniation of the hindbrain has been evaluated in a population of children with craniosynostosis by means of magnetic resonance imaging of the craniocervical junction. The role of intracranial pressure (ICP), posterior fossa size and hydrocephalus in the development of this deformity has also been assessed. Magnetic resonance imaging (Siemens Magnetom 1.5T) was reviewed in 27 cases of craniosynostosis in whom there had been no previous cranial vault surgery. The position of the cerebellar tonsils in relation to the plane of the foramen magnum was measured and an index of the size of the posterior fossa relative to the rest of the cranial vault was also calculated for each case. The presence of hydrocephalus (requiring a cerebrospinal fluid diversion procedure) was documented. In 22 of these cases overnight, subdural ICP monitoring using the Camino fibre optic device had also been performed. Herniation of the hindbrain below the plane of the foramen magnum occurred in 10 of 27 cases (37%). The level of ICP showed a significant correlation with the extent of hindbrain herniation (p < 0.001) as did small posterior fossa size (p = 0.0035). Hydrocephalus was present in 4 patients, all of whom had hindbrain herniation. The extent of hindbrain herniation did not correlate with age (p = 0.48). We propose that herniation of the hindbrain in craniosynostosis is a consequence of brain deformation occurring in response to the physical forces imposed by a combination of the anatomical deformity at the skull base and intracranial hypertension rather than a primary malformation of brain development as commonly supposed.

Arnold-Chiari Malformation↗