Location Of Aperture Research Articles

Primate head-free saccade generator implements a desired (post-VOR) eye position command by anticipating intended head motion.

Primate head-free saccade generator implements a desired (post-VOR) eye position command by anticipating intended head motion. J. Neurophysiol. 78: 2811-2816, 1997. When we glance between objects, the brain ultimately controls gaze direction in space. However, it is currently unclear how this is allocated into separate commands for eye and head movement. To determine the role of desired final eye position commands, and their coordination with intended head movement, we trained three monkeys to make large gaze shifts while wearing opaque goggles with a monocular 8 degrees aperture. Animals eventually developed a new set of context-dependent eye-head coordination strategies, in particular expanding the head range and compressing the eye-in-head range toward the aperture (while wearing the goggles). However, when we shifted the location of the aperture to a different subsection of the normal head-free oculomotor range (by covering the original aperture and creating a new one), eye-head saccades failed to acquire visual targets, because they continued to drive the eye ultimately toward the now occluded original aperture. Even when a head-stationary saccade acquired the new aperture, subsequent head-free saccades drove the eye eccentrically toward a point that anticipated the intended head movement, such that the subsequent vestibuloocular reflex slow phase brought the eye onto the location of the original aperture. Animals could only acquire the new aperture consistently after several days of retraining. These results suggest that 1) eye-head coordination is achieved by a plastic, context-dependent neural operator that uses information about initial eye/head position and intended movement to compute desired combinations of final eye/head position and 2) acquisition of these positions involves sophisticated anticipatory compensations for subsequent movement components, akin to those observed previously in complex oral and manual behaviors.

Microgametogenesis in Plumbago zeylanica (Plumbaginaceae). 1. Descriptive cytology and three‐dimensional organization

The generative cell is initiated as a small, lenticular, unpolarized cell with a cell wall traceable to two origins: the external segment originates as intine, while an inner callose positive cell wall forms de novo. As the lenticular generative cell begins its migration into the pollen cytoplasm, the generative cell becomes polarized both externally and internally, displaying a characteristic shape and patterns of organelle distribution oriented with respect to the vegetative nucleus and independent of pollen aperture location. Separation of the generative cell from the pollen wall begins at the end opposite the vegetative nucleus and results in an elongating protuberance at the opposite end of the generative cell; this becomes associated with a preformed groove located on the surface of the vegetative nucleus. The generative cell subsequently separates from the intine near the vegetative nucleus and moves progressively toward the opposite end of the cell; during this separation, the edge of the wall facing the intine becomes callose‐positive and remains so until separating from the intine. The generative cell becomes a free cell within the pollen, which is in physical association with the vegetative nucleus. Generative cell organization and organelle content become increasingly polarized during maturation, with microtubules evident both in the elongating protuberance of the generative cell and in association with organelles. The generative nucleus migrates away from the vegetative nucleus and toward the plastid‐rich end of the generative cell, whereas mitochondria are more generally distributed within the cell. Generative cell polarization is made permanent during mitotic division and cytokinesis, i.e., two sperm cells differing in morphology are formed: the larger cell associated with the vegetative nucleus (Svn) contains a majority of the mitochondria, and the smaller, unassociated sperm cell (Sua) receives the plastids.

Improved electronic gate technique, for particle counting and sizing in liquids

Particle counting and measurements of particle size distributions in liquids can be based on pulse height analysis of signals obtained from a changing gate impedance, upon particle transition. Signal-to-noise ratio is markedly improved, making use of a four-electrode detector. An instrumentation amplifier with a high-pass filter is used as a preamplifier. Cylindrical electrodes and a coaxial aperture location result in a decreased detector capacitance, lowering the signal detection level and contributing to improved pulse shape. Volume sampling is flexible and accurate, making use of a stepping motor actuated digital sampling system. A newly developed baseline restorer, combined with a log-antilog amplifier circuit, allows for linearisation of the pulse height/particle size relationship.

Analysis of a series-fed aperture-coupled patch array antenna

A full-wave spectral domain model of a series-fed, traveling-wave aperture-coupled patch array antenna is presented. This configuration allows for performance optimization by adjustment of the aperture size, aperture location, and patch size. The theory successfully predicts the input impedance and far-field patterns of various C-band configurations.

Design for a New Low Energy and Photo-Emission Electron Microscope for Surface Science Studies

A new LEEM/PEEM apparatus has been designed for the study of surfaces and surface processes in Ultra High Vacuum (UHV). The design follows the general layout of the microscope operated succesfully by Prof. Bauer and coworkers, but differs significantly in a number of details. We designed a magnetic/electrostatic cathode lens with a resolution limit close to that of the uniform electrostatic accelerating field between sample and lens. The projection system consists of transfer lens, intermediate lens and projector lens. Total magnification is between 1,000x and 10,000x, with a field of view between 4 and 40 micrometer. The illuminating system features a continuously adjustable range of illumination, such that the loss of image intensity at high magnification can be balanced by a reduction of the illumiated area, without significant loss of electron beam intensity. Both bright field and dark field imaging are possible. The location of the diffraction aperture in the projection column allows for more flexible operation of the microscope in dark field mode. Care has been taken in the design of the microscope to integrate the stringent vacuum requirements with the geometric constraints of the electron optical components. A sample stage, featuring two orthogonal translations and two (eucentric) tilts, sample heating, as well as in situ sample exchange capability has been constructed. All motions are driven by remote control, UHV compatible piezoelectric actuators, eliminating the need for mechanical feedthroughs, and ensuring a short mechanical path between sample and cathode lens. In situ deposition, using e-beam evaporators and/or Knudsen cells will be possible. A sample preparation chamber contains standard surface cleaning and analytical equipment. We will report on the progress in the construction of this machine.

Transverse pattern modifications in a stable apertured laser resonator

The effects of hard apertures on the transversal mode distribution and the output near and far field distributions are investigated both theoretically and experimentally. Wavefronts propagating in different directions inside a CO(2) laser cavity were measured at the same plane and found to have different transversal amplitude profiles. The influence of intracavity aperture's location and diameter on the near field distribution and far field beam quality were measured and calculated. Quantitative figures of merit are introduced to evaluate the departure of the transversal mode patterns from ideal Gaussians.

Influence of aperture location on free convection in partially divided enclosures

Influence of aperture location on free convection in partially divided enclosures

Attempts by human speakers to reproduce Fant's nomograms

Fant's nomograms, which constitute a simulation of the acoustic resonances which result from different vocal tract shapes, were checked against natural vowels by two phoneticians carefully producing a full range of vowel articulation in which (a) the location of the minimum aperture in the vocal tract and (b) the lip aperture were separately varied. Spectrographic measurements of formant frequencies were made, some with synchronised lip photographs. Ultrasonic and radiographic methods were used to verify vocal tract constriction size. In many major respects our data agreed with Fant's predictions, but three main kinds of discrepancies were noted: firstly, we could not produce as great a range of variations as occurs in the nomograms; secondly, when an [i]-like constriction is moved as far forward as possible, the frequency of F2 does not decrease; and thirdly, variations in lip rounding affect high front vowels and high back vowels differently with no gradual change from one class to the other as in Fant's data.

Menière's disease - roentgenologic diagnosis.

Radiologic diagnosis in Menière's disease should not be based on the vestibular aqueducts tomographic reproducibility. Instead, valuable preoperative information should be given about the size and location of the aqueducts external aperture in relation to the posterior and lateral semicircular canals. In saccotomy the semicircular canals are landmarks for identification of the endolymphatic sac. The periaqueductal pneumatization is demonstrated to be partly decisive for the vestibular aqueducts gross morphology. In Menière's disease either a sparse or a total lack of periaqueductal pneumatization is observed in most of all cases. The development of peri- and infralabyrinthine pneumatization is also decisive for the position of the foveate impression, which houses the extraosseous part of the endolymphatic sac. Its location and size can be evaluated by tomographic characterization of the vestibular aqueducts external aperture.

Theory of Cavity-Mode-Mixing Effects in Internally Scanned Lasers

An analysis of cavity-mode-mixing effects is given for a variety of cavity geometries and coupling parameters in the presence of a continuous transverse aperture velocity. The paper represents an extension of the previous work by Fox and Li, and Boyd and Gordon to include the effects of time-dependent changes in the transverse aperture location. The average beam profile in the scanning reference frame is calculated through a continuous reexpansion of the optical field in terms of the set of self-reproducing modes characteristic of the same cavity under static transverse boundary conditions. Results are specifically given for square aperture, plane-parallel, concentric, and confocal geometry for light, plane polarized orthogonally to the scan velocity. The effects of a random variation in the mirror-transmission coefficient are calculated, and it is shown that these effects are largely averaged out in the scanning process. Cavities of the type considered earlier by Pole and Myer and by Beiser are specifically considered. A method of evaluating different real systems with the present calculations is discussed; it is shown that a "push-pull"-type scanning laser should have an inherent scan velocity roughly twice that for the single-ended scanning laser geometry previously considered for the same degree of beam degradation and other cavity parameters. A method is developed for the derivation of self-reproducing confocal modes which arise with stationary, continuously varying aperture transmission functions. The method is specifically applied to a confocal Gaussian gain aperture and to a nonsymmetric confocal gain aperture. It is shown that the odd-symmetry mode of the Gaussian gain aperture dominates over the even-symmetry mode at low-gain coefficients, in opposition to the normal diffraction-limited rectangular-transmission-aperture case. An extension of the scanning problem is given to include the transverse displacement of a continuous gain aperture; it is shown formally that the solution of the continuous-aperture problem goes continuously over to the rectangular-aperture results at low values of the gain. The method is specifically applied to a hypothetical scanning laser employing swept Gaussian and nonsymmetric gain apertures.

Acute obstruction of the afferent loop after gastrectomy

Acute obstruction of the afferent loop is an unusual and disastrous complication after gastrectomy. It is most commonly caused by a rare form of internal herniation. Comprehension of the anatomic defects in retroanastomotic herniation involves a detailed knowledge of the boundaries of the apertures created after gastroenteric anastomoses. The pathophysiology is related to the continued secretion of bile, pancreatic juice, and succus entericus into the obstructed loop. The x-ray and clinical evidence of a mass in the left upper quadrant after gastrectomy, when coupled with the absence of afferent loop filling in a patient whose vomitus or gastric aspirate does not contain bile, should be considered diagnostic of acute obstruction of the afferent loop. The roentgenogram presented is believed to be the first appearing in the literature. The modes of prophylaxis and surgical therapy are related to the type of herniation, location of the hernial aperture, the inciting causes, and viability of the incarcerated bowel.