Side Of Aperture Research Articles

Useful relations for the analysis of stellar scintillation at the entrance pupil of a telescope.

The development of new techniques for characterizing atmospheric optical turbulence (OT) has become an active topic of research again in recent years. In order to facilitate these studies, we reconsidered known theoretical results and obtained some new practically useful conclusions. We introduce a dimensionless Fresnel filter, which allows us to approximate a polychromatic weighting function (WF) by a monochromatic one with a typical precision of several percent. A so-called dimensionless WF can be easily scaled for a receiving aperture of any size. For the case of a circular aperture and monochromatic radiation, an analytical expression for the WF was found. The WFs for a square aperture and for a circular aperture match with relative difference less than 0.01 if the circular aperture diameter is 1.15 times larger than the square aperture side. A linear digital filter can be applied to the scintillation signal from an image detector. As an example of digital filtering, we considered the power law filter ∝f5/3 with the WF being constant in a wide range of altitudes. We discuss the main limitations of this approach for measuring OT integral: finite pixel size, aliasing, and finite image detector size.

A Channel Model for Bi-viscous Fluid Flow in Fractures

In the last decade, the interest towards fluids characterized by a complex rheology has increased in the scientific community. Physicochemical, rheological and fluid mechanical approaches are adopted to characterize the peculiarities of non-Newtonian fluids. These fluids show remarkable properties that can be exploited to improve remediation techniques or optimize industrial operations. While the existence of actual yield stress is still debated, the presence of a plug or pseudo-plug zone is frequent in emulsions, soft glassy materials, jammed non-colloidal suspensions or colloidal gels. Even if simple yield stress models are often faulted because of their acknowledged deficiencies, they allow to study important phenomena without introducing excessive complexity. In this study, the randomness describing the aperture field of a natural rock fracture is coupled with a bi-viscous fluid rheology of parameter $$\epsilon$$ , representing the viscosity ratio; the cases $$\epsilon =0$$ and $$\epsilon \rightarrow {1}$$ represent the Bingham and Newtonian behaviour, respectively. The conceptual model proposed describes the flow of such fluids through a fracture with aperture variable along a single direction, the aperture being constant along the other. The aperture variation is modelled via a generic probability distribution function of assigned mean and variance. Two limit flow cases are considered: (1) parallel arrangement (PA), representing the case of maximum conductance, with the fluid flowing in the direction of channels of constant aperture; and (2) series arrangement (SA), the case of minimum conductance, with flow directed orthogonally to the constant aperture side of the fracture. Results are illustrated for log normal and gamma aperture distributions. The influence of aperture variability and applied pressure gradient on flow rate is investigated for both arrangements. The pressure gradient affects in a nonlinear fashion the flow rate, with a marked increase around a threshold value for both PA and SA. The channel flow rate exhibits a direct dependency upon aperture variability for PA, an inverse one for SA. The shape of the distribution has an impact on model responses: for the PA, the influence is significant but limited to an intermediate threshold range of pressure gradients, while results for the SA are affected in the whole range of pressure gradient. An example application in dimensional form is included.

Analysis of flat-topped Gaussian vortex beam scintillation properties in atmospheric turbulence

We analyze the scintillation properties of a flat-topped Gaussian vortex beam propagating in a weakly turbulent atmosphere. We utilize a random phase screen model to perform this analysis. We evaluate the scintillation against the changes of topological charge, beam order, operating wavelength, receiver aperture side length, and source size parameters. The results show that using a flat-topped Gaussian vortex beam with a high topological charge causes a reduction in scintillation. Increasing the receiver aperture side length reduces scintillation level. As the source size increases, scintillation decreases. Our results also indicate that a flat-topped Gaussian vortex beam with high topological charges has less scintillation than the fundamental Gaussian beam. We believe that our findings will be useful in improving the performance of next-generation optical communication links and networks.

Dual-profiled corrugated hybrid horn antenna

ABSTRACTA novel compact dual-profiled corrugated hybrid horn antenna (DPCHHA) feed for a shaped reflector antenna is presented in this abstract. Presently employed at Ku-band (10.95–11.7 GHz), the DPCHHA consists of four sections, viz. stepped section at throat, axial corrugated section followed by radial corrugated dual-profiled sections at aperture side. The horn is optimised using software TICRA CHAMP and fabricated using aluminium alloy 6061T6. The measured results agree well with predicted one. The DPCHHA has demonstrated measured return loss>20 dB, cross-polarisation (<−40 dB) and adequate edge taper (16–17 dB) at ±28° along with compact size (approximately 4.9λ aperture diameter and 5λ length at the highest frequency). Thus, this approach provides additional degree of flexibility to design a variety of horn antennas with tailored radio frequency performances for specific size of reflector antenna.

Thermodynamic analysis of an organic rankine cycle using a tubular solar cavity receiver

In this study, a non-regenerative Organic Rankine Cycle (ORC) has been thermodynamically analyzed under superheated conditions, constant evaporator pressure of 2.5MPa, and condenser temperature of 300K. R113, R601, R11, R141b, Ethanol and Methanol were employed as the working fluid. A parabolic dish concentrator with a square prismatic tubular cavity receiver was used as the heat source of the ORC system. The effects of the tube diameter, the cavity depth, and the solar irradiation on the thermodynamic performance of the selected working fluid were investigated. Some thermodynamic parameters were analyzed in this study. These thermodynamic parameters included the thermal efficiency, second law efficiency, total irreversibility, availability ratio, mass flow rate, and net power output. The results showed that, among the selected working fluids, methanol had the highest thermal efficiency, net power output, second law efficiency, and availability ratio in the range of turbine inlet temperature (TIT) considered. On the other hand, methanol had the smallest total irreversibility in the same range of TIT. The results showed also that mass flow rate and consequently the net power output increased for higher solar irradiation, smaller tube diameter, and for the case of cubical cavity receiver (i.e. cavity depth h equal to the receiver aperture side length a).

A Design of Dual-band Microstrip Antennas using Stacked Inverted-L-shaped Parasitic Elements for GPS Applications

In this paper, newly proposed dual-band microstrip antennas using stacked inverted-L-shaped parasitic elements are presented for GPS and bands. For making dual band which has large interval, ( band) inverted-L-shaped parasitic elements were stacked at both side of radiation apertures on the half-wavelength( band) patch antennas. The resonance in the parasitic elements occurs through coupling to the patch. Next, due to using circular polarization at GPS, ( band) inverted-L-shaped parasitic elements was stacked using sequential rotation technique on the patch and both side of the diagonal corners of the antenna were eliminated to make dual-band circular polarization. The designed circular polarized antenna`s dimensions are ( is the free-space wavelength at 1.227 GHz). Measured -10 dB bandwidths was 120 MHz(7.6%) and 82.5 MHz(6.7%) at GPS and bands. and 3 dB axial ration bandwidths are 172 MHz(10.9%) and 25 MHz(2.03%), respectively. All of these cover the respective required system bandwidths. Within each of the designed bands, broadside radiation patterns were observed.

Predation on Greek Albinaria (Pulmonata: Clausiliidae) by Poiretia (Pulmonata: Oleacinidae) and by an unknown organism making circular holes: possible drivers of shell evolution

Albinaria is an extremely species-rich genus of land snails, with about a hundred species occurring in limestone habitats in Greece. Among their predators are other terrestrial snails, namely Poiretia dilatata peloponnesica on the Peloponnese and P. compressa on the Ionian Islands. The elongated holes Poiretia make in shells were investigated in samples of empty Albinaria shells, in order to compare predation rates in different Albinaria populations. Another type of predation mark, frequently found on Albinaria shells, is a small, circular or nearly circular hole, made by an unknown organism. Poiretia predation rates reached up to 21% in the Albinaria populations studied and they were significantly higher in species with high rib prominence vs low rib prominence, as well as in sinistral species vs dextral species. Circular-hole predation reached up to 36%, but did not seem to be consistently connected with conchological traits. Marks made by P. compressa occurred most frequently on the abapertural side of Albinaria shells, whereas marks made by P. dilatata peloponnesica occurred most frequently on the apertural side. Circular-hole predation marks were located most often on the apertural side of Albinaria shells. Hybrids between Albinaria species generally seemed to suffer the same level of predation as one or both of their parent species. Predation pressure is substantial in the investigated populations and shows significant differences, but assessing its contribution to shell evolution requires more study.

Effect of H− ion extraction on a plasma sheath under an external weak magnetic field

The extraction of negative ions inevitably leads to the destruction of the original plasma state. To understand the effect of extraction on a plasma sheath under a weak magnetic filter field, the time-dependent behavior of H− ion extraction from a negative ion source has been studied by particle-in-cell simulation in the collisionless limit. The simulation results have shown that the plasma sheath would undergo a transient process, in which there exists an edge electrostatic wave that propagates counterclockwise along the wall with a velocity of 4 mm/ns until it reaches the other side of extraction aperture. The thickness of the plasma sheath and the plasma potential both increase greatly at the final quasi-steady-state. For comparison, the results of extracting positive ions are also given.

Study of the Shielding Properties of Enclosures With Apertures at Higher Frequencies Using the Transmission-Line Modeling Method

The transmission-line modeling method and an analytical formulation are employed in this paper to investigate the electromagnetic shielding performance of enclosures with apertures. The effects of some related parameters, which are neglected in the formulation, are analyzed over a broad-band (0-3 GHz) to make the formulation optimal, and the shielding performance at some frequency points is studied in detail. Finally, approaches to improve shielding effectiveness are proposed. For the enclosures we studied, the theoretical analysis and simulation results illustrate that the analytical formulation can predict shielding effectiveness accurately when the frequency of the incident wave is less than 1 GHz, while when the frequency is more than 1 GHz, its applicability declines remarkably. Fortunately, the simulation results indicated that the shielding effectiveness can be improved to a certain extent by adjusting the spacing between apertures, selecting appropriate shapes of apertures, ensuring the longer side of apertures is not perpendicular to the polarization direction of the incident wave, and installing sensitive equipment according to the propagation direction in the case of that these properties of the incident wave are known.

Higher mode sound transmission from a point source through a rectangular aperture

This paper considers the higher-order scattered and transmitted wave fields that result when an acoustic wave from a point source impinges at an arbitrary angle on a rectangular aperture in a rigid, thick wall. In this analysis, it is assumed that free field conditions exist on both sides of the aperture. Although the full scattered and transmitted pressure fields contain both modal sum and modal coupling effects, the modal coupling effects of the higher-order modes are ignored such that an approximate analytical solution to the uncoupled analysis can be utilized. Experiments have been undertaken to measure the sound pressure levels in the transmitted field that result when sound from a point source impinges on the opposite side of a rectangular aperture. Measurements were made with the source located at the required position to drive a particular in-aperture higher-order mode. The source was also located at positions that did not directly excite any in-aperture higher-order mode at a cut-on frequency. These results indicate that the approximate analysis developed here gives accurate solutions whether or not any mode of the aperture is driven at cut-on. Thus, the method can be used for any relative location of a source from a rectangular aperture of any dimensions.

Resonant infrared transmission and effective medium response of subwavelength H-fractal apertures

The transmission through periodic arrays of subwavelength H-fractal apertures in a gold film at infrared wavelengths is investigated numerically. H-fractal apertures support subwavelength cut-off resonances that are hybridized with surface plasmons along the sidewalls of the aperture. Enhanced transmission occurs at wavelengths that are about ten times the aperture side length. The highly subwavelength size scale of the H-fractal enables an effective medium parameter description for the aperture array, which reveals a lossy plasma permittivity and a diamagnetic permeability.

Soft‐tissue imprints in fossil and Recent cephalopod septa and septum formation

Several soft-tissue imprints and attachment sites have been discovered on the inside of the shell wall and on the apertural side of the septum of various fossil and Recent ectocochleate cephalopods. In addition to the scars of the cephalic retractors, steinkerns of the body chambers of bactritoids and some ammonoids from the Moroccan and the German Emsian (Early Devonian) display various kinds of striations; some of these striations are restricted to the mural part of the septum, some start at the suture and terminate at the anterior limit of the annular elevation. Several of these features were also discovered in specimens of Mesozoic and Recent nautilids. These structures are here interpreted as imprints of muscle fibre bundles of the posterior and especially the septal mantle, blood vessels as well as the septal furrow. Most of these structures were not found in ammonoids younger than Middle Devonian. We suggest that newly formed, not yet mineralized (or only slightly), septa were more tightly stayed between the more numerous lobes and saddles in more strongly folded septa of more derived ammonoids and that the higher tension in these septa did not permit soft-parts to leave imprints on the organic preseptum. It is conceivable that this permitted more derived ammonoids to replace the chamber liquid faster by gas and consequently, new chambers could be used earlier than in other ectocochleate cephalopods, perhaps this process began even prior to mineralization. This would have allowed faster growth rates in derived ammonoids.

Sexual dimorphism in shells of the southwestern Atlantic gastropod Olivella plata (Ihering, 1908) (Gastropoda: Olividae)

Sexual dimorphism in shells of the southwestern Atlantic gastropod Olivella plata (Ihering, 1908) (Gastropoda: Olividae)

Field Enhancement of Nano-Sized Metal Aperture with and without Surrounding Corrugations through Resonant Surface Plasmons

The different behaviors of the surface plasmons along the in-plane surface of silver sheet and along the side wall of bare aperture inside the same sheet are analyzed, and their respect roles to the final field enhancement are discussed as well. The short pitch surface plasmons resonance along the side wall of the aperture is regarded as the origin of the thickness dependence of the field enhancement at the exit side of the aperture. Several solutions such as corrugation incident plane, protrusion design at the exit side to realize maximized field enhancement at the exit side of aperture are proposed. Furthermore, the step and non-step nano-sized silver apertures surrounded with circular surface corrugation structures were compared in detail. It was proved that if the 40 nm sized step aperture with circular grating the near-field intensity can reach up to around 1000 times enhancement factor at the immediate exit and around 400 times enhancement even if at the plane of 10 nm away from exit of aperture.

顎裂部自家腸骨海綿骨細片移植術術後の骨吸収について―梨状孔下縁形態における評価―

Grafting of autogenous particulate cancellous bone and marrow to residual alveolar clefts in patients with cleft lip and palate is a well-established procedure for non-prosthetic rehabilitation with canine eruption into the grafted bone or for maintenance treatment after achieving arch alignment. Various analyses of the effect of grafting have been reported, but nearly all previous studies focused on non-prosthetic rehabilitation. The reconstruction of alveolar bone has been evaluated on only intraoral radiographs.We consider the purposes of bone grafting to the alveolar cleft to be not only non-prosthetic rehabilitation, but also correction of anomalies around the nasal cavity. We evaluated the status of bone bridge formation and bone resorption in 146 unilateral clefts of the prepalate and palate, which underwent bone grafting between 1996 and 2000. We also examined factors related to bone anomalies around both the alveolar ridge and the piriform aperture.Our results showed that age at bone grafting had a signifcant influence on resorption. Thus, we consider the time of bone grafting to be very important. Grafting should be done before 11 years of age and eruption of the canines. In addition, orthodontic space closure, which includes tooth root guidance to the grafted bone after alveolar bone grafting, is necessary for bone bridge formation on the piriform aperture side.

A Middle Devonian symbiotic relationship involving a gastropod, a trepostomatous bryozoan, and an inferred secondary occupant

Morris, P. J., Linsley, R. M. & Cottrell. J. F. 1991 01 15: A Middle Devonian symbiotic relationship involving a gastropod, a trepostomatous bryozoan. and an inferred sceondary occupant. Lethaia, Vol. 24. pp. 55–67. Oslo. ISSN 0024–1164. The high-spired gastropod Palaeozygopleuru (Loxonematacea) of the Hamilton Group (Middle Devonian) in New York State is often entrusted by the trepostomatous bryozoan Leptotrypella (Hetero-trypidae). The form of this enerustation leads us to infer a secondary occupant that dwelled in empty shells of Palaeozygopleura while the bryozoan grew upon them. Encrusted specimens usually have an open aperture, thin or no enerustation on the apertural side of the gastropod shell. and thick encrustation on the abapertural side. While the aperture is invariably open. the columellar and parictal lips of the aperture, and the apertural face of the first whorl are usually encrusted. While the gastropod is alive, this area rests upon the dorsal surface of the foot and the remainder of the shell rests upon the substratc. These encrustation patterns suggest that an occupant of the shell. other than the gastropexl. prevented overgrowth of the aperture and oriented the shell aperture-down. This allowed ahapertural growth of the bryozoan. The presence of thin encrustation on the apertural side of the shell is problematical. It requires either the presence of a secondary occupant capable of holding a thinly encrusted shell off the substrate, or the ability of the juvenile bryozoan colony to extend onto portions of the shell that were in contact with the substrate. The presence of a secondary occupant. such as a sipunculan worm. capable of lifting the shell, but usually resting it aperture-down on the substrate seems the most suitable explanation for the nature of the encrustation. Gastropoda. bryozoa. symbiosis. Devoniun. hermit crab, Sipuncula

Slip-resistant silver-feet: shell form and mode of life in lower Pleistocene Argyropeza from Fiji

Asymmetric sculpture in the form of tubercles or ridges on the shells of large (mean shell length ~60 mm) turritelliform gastropods has previously been shown to enhance efficiency of the shell as a penetration anchor in burrowing through coarse sediment. The small (&lt;8 mm) turritelliform shells of all species of Argyropeza (Family Cerithiidae) have both of these ratchetlike sculptural features. Four lines of evidence from Lower Pleistocene A. divina and A. schepmaniana from Fiji support the interpretation that they help resist back-slippage: cross-orientation, frictional asymmetry, allometric shallowing, and allometric densing of sculptural elements. In addition, excellent state of preservation including protoconch sculpture, near coplanarity of aperture and ventral side of shell, and susceptibility to drilling predation by naticids support the conclusion that these gastropods burrowed in the sediment that formed the siltstone in which they are now preserved. A direct relationship is proposed between height of ratchet sculpture on turritelliform gastropod shells of approximate length range 5–100 mm and the grain size of sediments they inhabit ranging from silts to coarse sands.

Single-ring magnetic cusp ion source

The single-ring cusp ion source discussed in this paper was developed to provide a dc ion beam in a nonpumped D–T neutron generator. The source operates at 0.25 Pa and produces a uniform-density beam through an aperture of 1.3-cm diameter. At the standard operating voltage of 150 V and arc current of 10 A, the atomic ion content of the 200-mA deuterium ion beam is about 60%, and the ion impurity level is less than 0.5%. The ion output of the source was examined at arc currents of up to 40 A and found to be a linear function; in addition, very high D+ yields were realized. With the aid of a shielded Langmuir probe, we have determined such plasma properties as electron energy, plasma potential, floating potential, and current density throughout the volume of the source. It was observed that the plasma is effectively confined by the magnetic field and there is evidence of an electron energy filtering mechanism similar to that found in multicusp ion sources. Electron energy on the filament side of the cusp has been determined to be about 75 eV and on the aperture side about 12 eV. Since the electron impact cross section for ionizing diatomic deuterium is maximum at 75 eV and the cross section for dissociating D+2 to D+ is greatest near 12 eV, we believe that a very effective two-step ionization process accounts for the high D+ yield of the single-ring magnetic cusp source. Plasma potentials measured have values close to the voltage of the anode, and the floating potentials are seen to be directly related to electron energy values. The floating potential is near cathode voltage where electron energies are high, and close to anode voltage where electron energies are low.

A study on the improvement of the picture of side looking sonar—Part 1

A preliminary study for the realization of the synthetic aperture side looking sonar was done. The quantization effect of the picture was estimated by using usual side looking sonar's record and digital image processing techniques. The optimum sampling rate of the sonar data in order not to lose the information included but to save the memory was given. Ratio of length and breadth of the record was corrected by assuming the vehicle's speed. The effect of random phase error on the synthetic array was computed. The maximum allowable motion fluctuation of the vehicle in order to conserve the quality of the synthetic image would be given.

Functional interpretation of lyre-shaped Bryozoa

Colonies of Late Paleozoic lyre-shaped fenestrate bryozoans began growth on rigid substrates which were on the sea floor. After production of a basal disc, a fenestrate network developed in the shape of an erect bowed fan. The fenestrate fan was initially concave on the apertural side, but the curvature reversed a few millimeters above the base. Colonies were then separated along or just above the basal disc, and rested directly on the sea floor. The zooecial apertures were directed upward. The lateral margin of the fan grew to form the supporting struts of the soon-to-be lyre-shaped colony. An open vault formed below the upwardly bowed fan.Lyre-shaped colonies are interpreted to have lain on the sea floor so that each had the proximal end on the upcurrent side. Feeding zooids were on the upper surface and pulled water through their expanded tentacles. The filtered water passed through the fenestrules, into the vault, and out the open end of the vault, which was on the downcurrent side.