The eye of the soldier beetle Chauliognathus pulchellus (Cantharidae)

1979 ◽  
Vol 203 (1153) ◽  
pp. 361-378 ◽  
Keyword(s):  
Cross Section ◽  
Focal Plane ◽  
Optical Axis ◽  
Field Size ◽  
Acceptance Angle ◽  
Corneal Surface ◽  
Physiological Properties ◽  
Cone Cells ◽  
Optical Pathway ◽  
Surface Calculation

The soldier beetle eye is unusual in having large optically isotropic corneal cones which project inwards from a thick isotropic cornea. Refraction is mainly at the corneal surface. Calculation shows that the first focal plane is near the tip of the cone, from which the optical pathway continues as a crystalline tract. At the distal end of the crystalline tract, 3 µm in diameter, the four cone cells enclose the proximal tip of the corneal cone; at the proximal end they enclose the distal tip of a long fused rhabdom rod. The eye is remarkable in that there are two classes of retinula cells; four cells contribute to the long thin axial rhabdom, 2 µm in diameter and 120 µm long, and the other four cells form two rounded rhabdoms, 10 x 4 µm in cross-section and 20 µm deep, which lie to one side of the optical axis. The physiological properties of individual retinula cells were measured by intracellular recording. The retinula cells are of three spectral types with peaks near 360, 450 and 520–530 nm. Except by the criterion of spectral sensitivity, the retinula cells sampled could not be sorted into more than one class. The measured value of the acceptance angle, near 3° in the dark-adapted state, is consistent with the hypothesis that all sampled cells were of the anatomical type that participate in the central rhabdom rod. A calculation of the theoretical field size of individual retinula cells from measurements of refractive index and lens dimensions predicts that cells which participate in the central rhabdom will have acceptance angles near 3°. The conclusion, therefore, is that only one anatomical type of cell has so far been sampled.

Der Einfluß einer streuenden Phasenplatte auf das elektronenmikroskopische Bild

1970 ◽  
Vol 25 (5) ◽  
pp. 760-765 ◽  
Author(s):  
H. G. Badde ◽  
L. Beimer
Keyword(s):  
Phase Shift ◽  
Cross Section ◽  
Focal Plane ◽  
Phase Contrast ◽  
Carbon Film ◽  
Carbon Films ◽  
Phase Shifting ◽  
Phase Plate ◽  
Different Thickness ◽  
Coherent Part

Using carbon films for phase shifting in the focal plane of the objective one has to consider the decrease of the coherent part of the electron beam. Only the unscattered part contributes to the phase contrast. After passing a 90.8 nm carbon film with a phase shift of 2 π the coherent amplitude decreases to 47%. But using a phase plate of different thickness for shifting all scattered electrons like a Zernike λ/4-plate, there will be a larger increase of contrast in images of platinum and carbon atoms than by optimal defocussing phase contrast. Calculations of phase shift and decrease of zero beam amplitude up to 1 MeV are reported. The use of Be-films with lower scattering cross section offers no large advantage.

The image trailer

1978 ◽  
Vol 48 ◽  
pp. 311-312
Author(s):  
G. D. Gatewood ◽  
R. W. Goebel ◽  
J. W. Stein
Keyword(s):  
Time Resolution ◽  
Focal Plane ◽  
Optical Axis ◽  
Steady Motion ◽  
Star Image ◽  
Better Than

To further our understanding of the limitations of ground based astrometry and to test the application of electronic centering techniques to the determination of star positions, we have assembled a device which can follow the position of a star as it is trailed across the focal plane of a telescope. A uniform above atmosphere motion is achieved by pointing the instrument slightly ahead of a star image and turning off the telescope’s drive. As the star moves into the acquisition circle of the Image Trailer (IT) the device commences a steady motion at a rate predetermined by the focal plane scale of the 76-cm Thaw photographic refractor, the star’s distance from the optical axis, and the star’s declination. Utilizing a time resolution of better than one millisecond, the IT can follow variations from the predicted rate with a precision of better than 40 milliarcseconds(mas) per second and can track stars fainter than the 16th photographic magnitude.

scholarly journals A Giant Meridian Circle - Reflector

1995 ◽  
Vol 166 ◽  
pp. 360-360
Author(s):  
V.N. Yershov
Keyword(s):  
Focal Plane ◽  
Optical Axis ◽  
Focal Length ◽  
Vertical Plane ◽  
Optical Scheme ◽  
Infrared Observations ◽  
Secondary Mirror ◽  
Axis Position ◽  
Reference Grid ◽  
Reading System

A 1.5 m reflector is proposed for infrared and optical meridian observations in order to extend the fundamental coordinate system to faintest objects and to the K-infrared waveband. Classical meridian circles are unfit for the infrared observations because their lens objectives do not give good images in the infrared. But reflectors are almost never used as meridian circles due to uncertainties in their optical axis position. The main problem is that the secondary mirror is not connected with the micrometer and the circle reading system. In order to overcome this difficulty the author proposes to use an intermediary focal plane between the primary and the secondary mirrors where a luminous reference grid of wires might be placed. The Gregory optical scheme has such a focal plane, and its secondary mirror forms images of a star and the grid at the micrometer's detecting area. At the same time a special champher around the primary's central hole forms anautocollimated image of the grid near the grid itself. The micrometer measures the star image coordinates relative to two images of the reference grid. So, observations will not be affected by displacements of the secondary mirror and by those of the micrometer. The telescope's equivalent focal length has been chosen as 3 m, and the optical system has been transformed into an aplanatic Mersenne combined with an aplanatic focal reducer corrector (Popov, 1988). A new autocollimated circle reading system is chosen for the instrument (Yershov and Nemiro, 1994). The observations will be linked to the fixed optical axis of two long-focus collimators placed at the prime vertical plane.

scholarly journals Assessment of scattered dose contribution to healthy tissue in radiation therapy using water phantom

2010 ◽  
Vol 25 (3) ◽  
pp. 212-216 ◽  
Author(s):  
Waheed Arshed ◽  
Ikramullah Qazi ◽  
Asad Ullah ◽  
Khalid Mahmood ◽  
Iftikhar Hussain ◽  
...  
Keyword(s):  
Radiation Therapy ◽  
Cancer Therapy ◽  
Cross Section ◽  
Incident Beam ◽  
Incident Radiation ◽  
Field Size ◽  
Limiting Factors ◽  
Dose Fractionation ◽  
Dose Delivery ◽  
Water Phantom

In cancer therapy using gamma radiation one of the limiting factors in dose delivery is the safety of the healthy tissues and organs around the cancerous mass. Better collimation and dose fractionation are employed to achieve this. In the present paper results of scattered dose to healthy tissues around the incident beam cross-section or beam boundaries have been estimated using IAEA standard water phantom and Co-60 incident radiation. It has been observed that scattered dose to healthy tissues increases linearly from 4% to 7% of the incident dose of 185 cGy to 200 cGy at the centre of the beam, at 5 cm depth in water, as we increase the incident beam field size from 5 cm x 5 cm to 10 cm x 10 cm. Also the maximum unwanted scattered dose for any field size remains closer to the incident beam boundaries.

scholarly journals Effect of Corneal Tilt on the Determination of Asphericity

Sensors ◽  
2021 ◽  
Vol 21 (22) ◽  
pp. 7636
Author(s):  
Alejandra Consejo ◽  
Arwa Fathy ◽  
Bernardo T. Lopes ◽  
Renato Ambrósio ◽  
Jr. Abass
Keyword(s):  
Contact Lenses ◽  
Optical Axis ◽  
Optimization Procedure ◽  
Nonlinear Least Squares ◽  
Cross Sectional Study ◽  
Implant Design ◽  
Corneal Surface ◽  
Cross Sectional ◽  
Significant Difference ◽  
Corneal Asphericity

To quantify the effect of levelling the corneal surface around the optical axis on the calculated values of corneal asphericity when conic and biconic models are used to fit the anterior corneal surface. This cross-sectional study starts with a mathematical simulation proving the concept of the effect that the eye’s tilt has on the corneal asphericity calculation. Spherical, conic and biconic models are considered and compared. Further, corneal asphericity is analysed in the eyes of 177 healthy participants aged 35.4 ± 15.2. The optical axis was determined using an optimization procedure via the Levenberg–Marquardt nonlinear least-squares algorithm, before fitting the corneal surface to spherical, conic and biconic models. The influence of pupil size (aperture radii of 1.5, 3.0, 4.0 and 5.0 mm) on corneal radius and asphericity was also analysed. In computer simulations, eye tilt caused an increase in the apical radii of the surface with the increase of the tilt angle in both positive and negative directions and aperture radii in all models. Fitting the cornea to spherical models did not show a significant difference between the raw-measured corneal surfaces and the levelled surfaces for right and left eyes. When the conic models were fitted to the cornea, changes in the radii of the cornea among the raw-measured corneal surfaces’ data and levelled data were not significant; however, significant differences were recorded in the asphericity of the anterior surfaces at radii of aperture 1.5 mm (p < 0.01). With the biconic model, the posterior surfaces recorded significant asphericity differences at aperture radii of 1.5 mm, 3 mm, 4 mm and 5 mm (p = 0.01, p < 0.01, p < 0.01 & p < 0.01, respectively) in the nasal temporal direction of right eyes and left eyes (p < 0.01, p < 0.01, p < 0.01 & p < 0.01, respectively). In the superior–inferior direction, significant changes were only noticed at aperture radii of 1.5 mm for both right and left eyes (p = 0.05, p < 0.01). Estimation of human corneal asphericity from topography or tomography data using conic and biconic models of corneas are affected by eyes’ natural tilt. In contrast, the apical radii of the cornea are less affected. Using corneal asphericity in certain applications such as fitting contact lenses, corneal implant design, planning for refractive surgery and mathematical modelling when a geometrical centre of the eye is needed should be implemented with caution.

scholarly journals A 24-Hour Cycle in Single Locust and Mantis Photoreceptors

1981 ◽  
Vol 91 (1) ◽  
pp. 307-322 ◽  
Author(s):  
G. A. HORRIDGE ◽  
J. DUNIEC ◽  
L. MARČELJA
Keyword(s):  
Point Source ◽  
Diurnal Rhythm ◽  
Capture Efficiency ◽  
The Other ◽  
Field Size ◽  
Acceptance Angle ◽  
Response Curves ◽  
Spontaneous Breakdown ◽  
Intensity Response ◽  
Quantal Responses

1. When fixed during the night the rhabdom of the locust and mantis is much broader than when fixed during the day. 2. Dark-adapted ommatidia of the locust and mantis by day and night have a zone of vacuoles around the rhabdom tip, but when light-adapted this zone is replaced by cytoplasm rich in mitochondria. 3. Illumination of the rhabdom in the night state causes the microvilli to swell and the rhabdom to break down over the course of about 1 h. 4. A diurnal rhythm is apparent in the spontaneous breakdown of the rhabdom in the morning even though the eye has seen no light for 12 h. 5. Intensity/response curves (peak of the response in mV plotted against log intensity of stimulus) show an increase in sensitivity during the night even though the stimulus is a point source on axis. 6. On the other hand, counts of bumps (quantal responses to individual photons) show no change in photon capture efficiency at night when the stimulus is a point source. 7. Strong illumination of the eye in the night state causes a desensitization which continues for 1 h. 8. Measurements of the acceptance angle in the dark-adapted day and night states show that field size is an indicator of the diameter of the rhabdom tip, but actual fields are larger than those calculated from the anatomical dimensions.

Quantitative elemental analysis by transmission electron spectroscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 528-529
Author(s):  
David Joy ◽  
Dennis Maher ◽  
Peggy Mochel
Keyword(s):  
Cross Section ◽  
Electron Spectroscopy ◽  
Acceptance Angle ◽  
Ionization Cross ◽  
X Ray ◽  
Transmission Electron ◽  
Efficiency Factors ◽  
Image Position ◽  
Integrated Intensities ◽  
Fundamental Formula

In transmission electron spectroscopy the fundamental formula for elemental quantitation using inner-shell excitations gives the number n of atoms per cm2 contributing to the K-edge aswhere Ik and Io are the integrated intensities in the K-edge and zero-loss peak, respectively. Both of these integrals are measured for a spectrometer acceptance angle 2α and an energy interval ΔE. The parameter αk(α,ΔE) is the ionization cross-section for the same angular and energy parameters. The variation of αk with α and ΔE is a function of the generalized oscillator strength and little detailed information on this quantity is available. Therefore it is necessary to proceed empirically and the simplest assumption is thatwhere σk is a saturation (x-ray) cross-section and ηα,ηΔEcan be identified with efficiency factors.The accuracy of Equation (1) for K-edges from light elements (Li ≤ Z ≤ Al) is being tested by computer curve fitting and background stripping (see Fig. 1).

Dislocation lines in the hyperbolic umbilic diffraction catastrophe

2006 ◽  
Vol 462 (2072) ◽  
pp. 2299-2313 ◽  
Author(s):  
J.F Nye
Keyword(s):  
Diffraction Pattern ◽  
Cross Section ◽  
Focal Plane ◽  
Dislocation Line ◽  
Three Dimensional ◽  
Circular Cross Section ◽  
Optical Vortices ◽  
Nodal Lines ◽  
Wave Interference ◽  
A Chain

The three-dimensional pattern of the hyperbolic umbilic diffraction catastrophe is computed from an integral representation. A detailed description is given of the geometrical arrangement of the wave dislocation lines (optical vortices) on which the diffraction pattern is based. From a crossed grid of nodal lines in the focal plane, two bundles of dislocation lines spring out symmetrically into the regions of 4-wave interference. Each dislocation line then follows a chain of curved segments which approximate successive steps along lattice vectors in the space group Fmmm . The result is a bundle of helices of non-circular cross-section that gradually straighten out until, far from the focal plane, they become the dislocations of the Pearcey diffraction pattern for the cusp catastrophe. A new phenomenon is the multiple puncturing of the caustic surface by a series of helical dislocations.

scholarly journals PbS and CCD Array Autocollimation Micrometers for the Infrared Meridian Circle

1995 ◽  
Vol 167 ◽  
pp. 337-338
Author(s):  
V. N. Yershov
Keyword(s):  
Focal Plane ◽  
Optical Axis ◽  
Meridian Circle ◽  
Pulkovo Observatory ◽  
Primary Mirror ◽  
Small Constant ◽  
Ccd Array ◽  
Secondary Mirror ◽  
Axis Position ◽  
Optical Unit

A new infrared meridian instrument is being developed at Pulkovo Observatory. The main purpose of the instrument is to extend the fundamental coordinate system to the K-infrared waveband and to faint stars at visual and I-wavebands. The instrument has a 30-cm primary mirror made from astrositall. An intermediate focal plane is used to introduce luminous reference marks. One can obtain autocollimated images of the marks at the intermediate focal plane with the use of a polished chamber located around the central hole of the primary mirror. The secondary mirror of the telescope forms images of the marks and of their autocollimated counterparts and passes them to the plane of a photodetector (Fig. 1.). The luminous marks give a reference frame for the measurements. These measurements are not affected by displacements of any optical unit placed after the intermediate focal plane or by displacements of the detector. The measurements are done relative to the coordinates of the average between positions of the luminous mark and its autocollimated image. Any small constant difference between the center of curvature and the optical axis position can be determined in the laboratory.

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