Optical Artefact Research Articles

Insights into the structure and morphogenesis of the giant basal spicule of the glass sponge Monorhaphis chuni

BackgroundA basal spicule of the hexactinellid sponge Monorhaphis chuni may reach up to 3 m in length and 10 mm in diameter, an extreme case of large spicule size. Generally, sponge spicules are of scales from micrometers to centimeters. Due to its large size many researchers have described its structure and properties and have proposed it as a model of hexactinellid spicule development. Thorough examination of new material of this basal spicule has revealed numerous inconsistencies between our observations and earlier descriptions. In this work, we present the results of detailed examinations with transmitted light and epifluorescence microscopy, SEM, solid state NMR analysis, FTIR and X-ray analysis and staining of Monorhaphis chuni basal spicules of different sizes, collected from a number of deep sea locations, to better understand its structure and function.ResultsThree morphologically/structurally different silica layers i.e. plain glassy layer (PG), tuberculate layer (TL) and annular layer (AL), and an axial cylinder (AC) characterize adult spicules. Young, immature spicules display only plain glassy silica layers which dominate the spicule volume. All three layers i.e. PG, TL and AL can substitute for each other along the surface of the spicule, but equally they are superimposed in older parts of the spicules, with AL being the most external and occurring only in the lower part of the spicules and TL being intermediate between AL and PG. The TL, which is composed of several thinner layers, is formed by a progressive folding of its surface but its microstructure is the same as in the PG layer (glassy silica). The AL differs significantly from the PG and TL in being granular and porous in structure. The TL was found to display positive structures (tubercles), not depressions, as earlier suggested. The apparent perforated and non-perforated bands of the AL are an optical artefact. The new layer type that we called the Ripple Mark Layer (RML) was noted, as well as narrow spikes on the AL ridges, both structures not reported earlier. The interface of the TL and AL, where tubercles fit into depressions of the lower surface of the AL, represent tenon and mortise or dovetail joints, making the spicules more stiff/strong and thus less prone to breaking in the lower part. Early stages of the spicule growth are bidirectional, later growth is unidirectional toward the spicule apex. Growth in thickness proceeds by adding new layers. The spicules are composed of well condensed silica, but the outermost AL is characterized by slightly more condensed silica with less water than the rest. Organics permeating the silica are homogeneous and proteinaceous. The external organic net (most probably collagen) enveloping the basal spicule is a structural element that bounds the sponge body together with the spicule, rather than controlling tubercle formation. Growth of various layers may proceed simultaneously in different locations along the spicule and it is sclerosyncytium that controls formation of silica layers. The growth in spicule length is controlled by extension of the top of the axial filament that is not enclosed by silica and is not involved in further silica deposition. No structures that can be related to sclerocytes (as known in Demospongiae) in Monorhaphis were discovered during this study.ConclusionsOur studies resulted in a new insight into the structure and growth of the basal Monorhaphis spicules that contradicts earlier results, and permitted us to propose a new model of this spicule’s formation. Due to its unique structure, associated with its function, the basal spicule of Monorhaphis chuni cannot serve as a general model of growth for all hexactinellid spicules.

Ionization quenching correction for a 3D scintillator detector exposed to scanning proton beams

The ionization quenching phenomenon in scintillators must be corrected to obtain accurate dosimetry in particle therapy. The purpose of this study was to develop a methodology for correcting camera projection measurements of a 3D scintillator detector exposed to proton pencil beams. Birks’ ionization quenching model and the energy deposition by secondary electrons (EDSE) model were used to correct the light captured by a prototype 3D scintillator detector. The detector was made of a 20 cm × 20 cm × 20 cm tank filled with liquid scintillator, and three cameras. The detector was exposed to four proton-beam energies (84.6, 100.9, 144.9, and 161.6 MeV) at The University of Texas MD Anderson Cancer Center’s Proton Therapy Center. The dose and track averaged linear energy transfer (LET) were obtained using validated Monte Carlo (MC) simulations. The corrected light output was compared to the dose calculated by the MC simulation. Optical artefact corrections were used to correct for refraction at the air–scintillator interface, and image perspective. These corrections did not account for the non-orthogonal integration of data off the central axis of the image. Therefore, we compared the light output to an integrated MC dose and LET along the non-orthogonal path. After accounting for the non-orthogonal integration of the data, the corrected light output reduced the dose error at the Bragg peak region from 15% to 3% for low proton-beam energies. Overall, the doses at the Bragg peak region using the Birks’ model and EDSE model were less than ±3% and ±7% of the MC dose, respectively. We have improved the application of Birks’ model quenching corrections in 3D scintillators by numerically projecting the dose and LET 3D grid to camera projections. This study shows that scintillator projections can be corrected using average LET values at the central axes.

The Principle of Adaptive Excitation for Photoluminescence Imaging of Silicon: Theory

An approach that determines the charge carrier lifetime from photoluminescence (PL) imaging that is virtually not affected by lateral charge carrier drift and diffusion and image smearing due to photon scattering is proposed. The approach attempts to create a laterally uniform charge carrier density within a sample with non‐homogeneous recombination properties via illumination with spatially varying intensity. Lateral excess charge carrier drift and diffusion is inherently absent in this situation. Furthermore, as a homogeneous PL intensity is monitored, any optical artefact induced by photon scattering in the investigated wafer or the detection charge‐coupled device is strongly suppressed compared to conventional PL imaging. Using numeric simulations of different lifetime distribution scenarios, including one based on measured micro‐photoluminescence (μ‐PL) lifetime data, we demonstrate the feasibility of this proposed “Adaptive Excitation Photoluminescence Imaging” (Ax‐PLI) method.

A multi-topographical-instrument analysis: the breast implant texture measurement

Capsular contracture is a major complication after implant-based breast augmentation. To address this tissue reaction, most manufacturers texture the outer breast implant surfaces with calibrated salt grains. However, the analysis of these surfaces on sub-micron scales has been under-studied. This scale range is of interest to understand the future of silicone particles potentially released from the implant surface and the aetiology of newly reported complications, such as Anaplastic Large Cell Lymphoma.The surface measurements were accomplished by tomography and by two optical devices based on interferometry and on focus variation. The robustness of the measurements was investigated from the tissue scale to the cellular scale.The macroscopic pore-based structure of the textured implant surfaces is consistently measured by the three instruments. However, the multi-scale analyses start to be discrepant in a scale range between 50 µm and 500 µm characteristic of a finer secondary roughness regardless of the pore shape. The focus variation and the micro-tomography would fail to capture this roughness regime because of a focus-related optical artefact and of step-shaped artefact respectively.

Optical edge effects create conjunctival indentation thickness artefacts.

Conjunctival compression observed in ultrahigh resolution optical coherence tomography (UHR-OCT) images of contact lens edges could be actual tissue alteration, may be an optical artefact arising from the difference between the refractive indexes of the lens material and the conjunctival tissue, or could be a combination of the two. The purpose of this study is to image the artefact with contact lenses on a non-biological (non-indentable) medium and to determine the origins of the observed conjunctival compression. Two-dimensional cross-sectional images of the edges of a selection of marketed silicone hydrogel and hydrogel lenses (refractive index ranging from 1.40 to 1.43) were acquired with a research grade UHR-OCT system. The lenses were placed on three continuous surfaces, a glass sphere (refractive index n = 1.52), a rigid contact lens (n = 1.376) and the cornea of a healthy human subject (average n = 1.376). The displacement observed was analysed using ImageJ. The observed optical displacement ranged between 5.39(0.06) μm with Acuvue Advance and 11.99(0.18) μm with Air Optix Night & Day when the lens was imaged on the glass reference sphere. Similarly, on a rigid contact lens displacement ranged between 5.51(0.03) and 9.72(0.12) μm. Displacement was also observed when the lenses were imaged on the human conjunctiva and ranged from 6.49(0.80) μm for the 1-day Acuvue Moist to 17.4(0.22) μm for the Pure Vision contact lens. An optical displacement artefact was observed when imaging a contact lens on two rigid continuous surfaces with UHR-OCT where compression or indentation of the surface could not have been a factor. Contact lenses imaged in situ also exhibited displacement at the intersection of the contact lens edge and the conjunctiva, likely a manifestation of both the artefact and compression of the conjunctiva.

A green illusion

An analysis reveals that satellite-observed increases in canopy greenness during dry seasons, which were previously interpreted as positive responses of Amazon forests to more sunlight, are in fact an optical artefact. See Letter p.221 Recent remote-sensing data from the Amazon suggested that there is a 'green up' of vegetation during dry seasons, implying that light rather than water is the major limiting factor for forest productivity. Douglas Morton and colleagues have now reanalysed the evidence and show that the green up is in fact an optical artefact of the observation method, the result of changes in the relative azimuth angle of satellite observations between the June solstice and September equinox. Correcting for this removes the green-up phenomenon, adding support to other studies that indicate that water availability, rather than light, is the main driver of plant productivity in Amazon forests.

Emancipating the Image: The Beijing Olympics, Regeneration, and the Power of Performance

“In China, what makes an image true is that it is good for people to see it.” - Susan Sontag, On Photography, 1971 In The Practice of Everyday Life, Michel de Certeau gazes down upon New York City from the 110th floor of the World Trade Centre and sees the island of Manhattan as an image. In particular, he witnesses the famous Manhattan skyline as a powerful ‘image-text’ containing a multiplicity of meanings, interpretations, and symbols. Considering the possibilities of the city as visual simulacrum he asks: “[i]s the immense texturology spread out before one’s eyes anything more than a representation; an optical artefact?” Twenty or so years after De Certeau wandered the streets of New York and pondered its pictorial power, such a perspective can be applied to Olympic and Post Olympic Beijing. The Olympic Games gave the world an opportunity to read Beijing’s powerful image-text following thirty years of rapid transformation. David Harvey argues that this transformation has turned Beijing from “a closed backwater, to an open centre of capitalist dynamism.” However, in the creation of this image-text, another subtler and altogether very different image-text has been deliberately erased from the public gaze. This more concealed image-text offers a significant counter narrative on the city’s public image and criticises the simulacrum constructed for the 2008 Olympics, both implicitly and explicitly. It is the ‘everyday’ image-text of a disappearing city still in the process of being bulldozed to make way for the neoliberal world’s next megalopolis. It exists most prominently as a filmic image text; in film documentaries about a ‘real’ hidden Beijing just below the surface of the government sponsored ‘optical artefact.’ Film has thus become a key medium through which to understand and preserve a physical city on the verge of erasure.

Dynamic force microscopy with quartz tuning forks at high oscillation amplitudes

Dynamic force microscopy (DFM) with the self-oscillator (SO)method allows reasonably high scanning rates even with highQ-factors of the resonant force sensor, typical of cantilevers in ultra-high vacuum and ofquartz tuning forks. However, due to simpler interpretation of force spectroscopymeasurements, small oscillation amplitudes (sub-nm level) are generally preferred. Inapplications like ‘apertureless’ scanning near-field optical microscopy (SNOM), oscillationamplitudes of the order of 5–10 nm are needed to increase optical sensitivity and toapply standard optical artefact suppression methods. This motivates the studyof the behaviour of tuning forks driven at such high amplitudes, as comparedto usual air-operated cantilevers. Both constant-excitation-amplitude (CE) andconstant-oscillation-amplitude (CA) modes of SO-DFM are analysed, since the CA mode ismore convenient for SNOM applications, denoting remarkable differences. In particular,possible instability effects, previously found in CE mode, are not anticipated for CAmode. It is shown how resonance and approach (‘isophase’) curves in both modescan be conveniently described in terms of the usual ‘normalized frequency shift’γ and of a‘normalized gain’ η, defined as a measurement of surface dissipation.

Confocal microscopic observations of the human cornea following overnight contact lens wear

Background: Striae and folds are observed with a slidamp biomicroscope in the cornea following overnight contact lens wear. These phenomena are poorly understood. The aim of this study is to employ confocal microscopy to observe and document these and other morphological changes in die human cornea following overnight contact lens wear. Methods: Slitlamp biomicroscopy, slit‐scanning confocal microscopy and ultrasonic pachometry were performed on both eyes of 13 subjects (3M, 10F, age 24 ± 3 years) before and after eight hours overnight wear of a ‐3.00 D Bausch & Lomb one day disposable soft contact lens (Dk/t = 15.1 times 10‐9 (cm/sec) x {ml O2/ml x mmHg)) in one eye; the other non‐lens‐wearing eye acted as a control. Results: Following sleep, both corneas were swollen (lens‐wearing eye 11.8 ± 3.8 per cent; control eye 2.1 ± 1.9 per cent) and the stroma of both corneas displayed an apparent reduction in keratocyte density (lens‐wearing eye 21 per cent; control eye 10 per cent). Folds were observed with the slidamp biomicroscope and long, straight, dark, orthogonal lines were observed widi die confocal microscope, in the posterior stroma of the oedematous lens‐wearing eyes. Such features were not observed in die control eyes. The keratocytes appeared less distinct with greater levels of corneal oedema. Conclusion: The apparent loss of keratocytes following overnight lens wear is an optical artefact that can be explained in terms of corneal oedema causing volumetric tissue expansion and a loss of optical clarity, which hampers keratocyte detection. These findings place the onus on researchers postulating a loss of stromal keratocytes following clinical interventions, such as contact lens wear, to account for the effects of oedema.

A Combined Optical and Mechanical Reference Artefact for Coordinate Measuring Machines

The calibration of CMMs using calibrated ball plates or hole plates is a well established technique. In the case of CMMs equipped with optical sensors based upon CCD cameras a series of artefacts based upon chromium-on-glass structures have been proposed. Calibration of these artefacts can not be performed using the reversal method which can be used for ball or hole plates. A new two-dimensional artefact based upon mechanical elements has been developed allowing both optical and mechanical probing and calibration. This artefact combines in one piece the possibilities of performance verification of both optical and mechanical CMMs. The mechanical elements have been manufactured with form errors less than 3 urn and using a special surface preparation that makes optical CNC-measurements non-problematic. Reproducibilities better than 0.5 μm have been obtained in optical probing. Calibration of the artefact can be carried out using reversal methods using both optical and mechanical probing.

The microscope in the history of pathology. With a note on the pathology of fat cells.

Between the birth of the microscope and the birth of microscopic pathology there is a puzzling gap of almost 250 years. Six reasons have been given to explain it: secrecy of the art, high cost of the apparatus, technical difficulty, the notion that the microscope was a toy, lack of new ideas, neglect by Universities. Suspecting that poor optics must have been another major factor in discouraging microscopy, we placed ourselves in the conditions of an experimenter trying to understand acute inflammation in a transparent tissue shortly before 1830 (i.e. before the invention of Lister's achromatic objective and of the condenser). We used a Culpeper-type microscope, and a piece of inflamed omentum, fresh, unfixed and unstained. The resolution proved inadequate to recognize the tissue changes of acute inflammation; and the interpretation of these changes was further complicated by the optical artefact known as “reticular image”.

An optical artefact in the microscopic study of fluorescent materials.

In all microscopical studies based on fluorescence an artefact occurs which is due to reflection or diffraction of the primary light. Available filters do not completely eliminate visible light from the primary beam and this light can produce pseudo-fluorescence of the same order of magnitude as that of the true fluorescence. A method for estimating the contribution of pseudo-fluorescence to the total apparent fluorescence is described.

An Optical Artefact with Phase Contrast

OETTLE1 notes that under certain conditions of oblique illumination objects with refractive index only slightly greater than that of the surrounding medium show an appearance “bright on one side but dark on the other”. He does not consider the possibility of unintentional oblique illumination with phase contrast; it is this which has been studied in the present experiments.