Perforated Screens Research Articles

A Method of Determining the Impulse Response Function for an Elastic Scattering Lidar-Nephelometer with Coaxial Sounding Scheme. Part I

A coaxial sounding scheme in a pulsed lidar and nephelometer regime used for measurements of the intensity of propagation of a beam within a layer and a given extinction coefficient is considered. Measurement of the impulse response function by means of perforated screens is evaluated in the nephelometer regime.

Art Concept

The work rendered on the cover of JMEWS 11:3 is part of an ongoing series in which I want to link the concept of physical borders and divisions created geographically with corporeal divisions in the form of anatomical dissections. While doing research on anatomy, I came across a field called cross-sectional anatomical dissection. The visual inspiration was taken from Wilhelm Braune, who performed horizontal dissections on frozen cadavers and in 1877 published The Atlas of Topographical Anatomy. I found the cross sections in this book intriguing, as they created an uncommon perspective of the human body. I decided to create a work based on cross sections of my own body, which involved a rather performative act of 3-D scanning and processing of my upright body with an accuracy and detail of 0.3 mm. The three-dimensional rendering of my body was then cross-sectioned into horizontal quarter-inch-thick slices, 542 slices from head to toe. I chose a few slices from each section of the body and nested them into two pentagonal panels, creating a decagram. At the time I was also researching shanasheel (Iraqi) or mashrabiya. These wooden perforated screens are used in homes as an architectural element to conceal the private from the public.The JMEWS 11:3 cover image by Hayv Kahraman (Detail Decagram 2) evokes a refusal to be objectified but also the layers that block possibilities for fully seeing, whether one looks from the inside out or from the outside in. It offers the illusion of wholeness, which is often mapped onto women’s bodies. This volume wraps up a three-issue initiative in which authors affiliated with autonomous “feminist formations” throughout the region discussed their priorities and challenges at a particularly tumultuous historical moment. They wrote in English, French, Farsi, and Arabic. Reading them together one can discern threads of continuity and difference. The conflicts and challenges are stark, but so is the beauty and creativity, as in Kahraman’s constellation of corporeality, dissection, and architecture. The “feminist formation” essays communicate energy, commitment, and layers of complexity that exceed the hegemonic available frames for seeing and understanding.

Magnetic hybridization enhanced transmission through ultra-long subwavelength hole

A perforated metallic screen is intentionally engineered by inserting a chain of metallic bars (MBs) inside a square hole. The transmission through this subwavelength hole is significantly enhanced and the values of its peaks still maintain a high level with an increase in screen thickness. By examining the induced surface currents and charge distributions, we show that the high transmission is attributed to the hybridization of the magnetic dipoles that are excited between the MBs and the antithetic metallic surfaces. The proposed structures may have applications in long-distance energy transport and frequency combs, and may open up new perspectives in the engineering of enhanced transmission phenomena.

Digital canopy photography: Exposed and in the raw

Estimates of the canopy gap fraction, on which calculations of leaf area index (LAI) are based, are sensitive to photographic exposure in upward-facing images. In this article we describe a simple, automated method of image acquisition and processing that eliminates both subjectivity and the need for the operator to consider photographic exposure in the field. A key strength of our methodology was the use of a test apparatus (perforated aluminum screen) with a precisely known gap fraction; this allowed us to separate the confounding effects of gap size and gap fraction on the optimal photographic exposure for a canopy. We took photographs of the test apparatus at different photographic exposures; we varied the gap fraction by covering a proportion of the holes in the screen, and also varied gap size by varying the distance of the camera from the screen. We acquired both raw images and JPEG images. We found that the optimal exposure of JPEG images varied with both gap size and gap fraction, not just gap fraction as previously assumed. Underexposing by one stop yielded raw data that were never clipped resulting in data loss, but that used most of the 14-bit range of the raw file. We also found that it was easily possible to standardize photographic exposure during image processing by acquiring raw images in the field; thus eliminating the variation in estimated gap fraction and LAI associated with exposure variations. This result was replicated in both fisheye images and cover images that we acquired in real canopies. We recommend the following protocol for acquiring canopy images in future studies:1.Shoot raw using one stop of underexposure.2.Convert propriety-format raw files to DNG format using the free software Adobe DNG Converter.3.Contrast stretch the blue channel of the image and save as JPG for further analysis. The authors can supply MATLAB script to perform this step.

Solar and Lighting Transmission through Complex Fenestration Systems of Office Buildings in a Warm and Dry Climate of Chile

Overheating, glare, and high-energy demand are recurrent problems in office buildings in Santiago, Chile (33°27'S; 70°42'W) during cooling periods. Santiago climate is warm and dry, with high solar radiation and temperature during most of the year. The objective of this paper is to evaluate the thermal and daylighting performance of office buildings transparent façades composed of three different complex fenestration systems (CFS). Each CFS contains a different external shading device (ESD): (1) external roller, (2) vertical undulated and perforated screens, and (3) tilted undulated and perforated screens. The study was carried out by in situ monitoring in three office buildings in Santiago, Chile. Buildings were selected from a database of 103 buildings, representing those constructed between 2005 and 2011 in the city. The monitoring consisted of measuring the short wave solar and daylighting transmission through fenestration systemsby means of pyranometers and luxometers, respectively. This paper shows measurements that were carried out during summer period. A good performance is observed in a building with the external roller system. This system—applied to a northwest façade—shows a regular and high solar and daylighting control of incoming solar radiation. The other two ESD systems evidence a general good performance. However, some deficiencies at certain times of the day were detected, suggesting a non-appropriated design.

Energy Efficient Shading Strategies for Windows of Hospital ICUs in the Desert

Hospitals, everywhere, are considered heavy energy consumers. Hospital Intensive Care Unit spaces pose a special challenge, where design guidelines requires the provision of external windows for daylighting and external view. Window protection strategies could be employed to reduce energy loads without detriment effect on comfort or health care. This paper addresses the effectiveness of using various window strategies on the annual cooling, heating and lighting energy use of a typical Hospital Intensive Unit space. Series of experiments were performed using the EnergyPlus simulation software for a typical Intensive Care Unit (ICU) space in Cairo, located in the Egyptian desert. This study concluded that the use of shading systems is more effective in conserving energy in comparison with glazing of different types, in the Cairo ICUs. The highest energy savings in the West and South orientations were accomplished by external perforated solar screens, followed by overhangs positioned at a protection angle of 45°.

Enhanced plasmonic Brewster transmission through metascreens by tapered slits

The recently introduced plasmonic Brewster transmission through free-standing perforated metallic screens (metascreens), which offers ultrabroadband total light transmission has been demonstrated both theoretically and experimentally. This anomalous phenomenon is attributed to impedance matching between the guided modes supported by ultranarrow straight slits and transverse-magnetic impinging waves at a specific oblique incidence. However, this impedance matching mechanism is significantly influenced by the presence of realistic substrates leading to reduce the plasmonic Brewster transmission. To circumvent this substrate influence, the author proposes to carve periodically tapered slits on metascreens to enable the impedance matching at the input and output surface and thus enhance transmission at the Brewster angle. This finding is applied to realize ultrathin perfect absorbers with a broad bandwidth of operation.

Experimental and numerical study of the sloshing motion in a rectangular tank with a perforated screen

Rectangular tanks partially filled with water and fitted with vertical perforated screens have been proposed as Tuned Liquid Dampers to mitigate the vibratory response of land buildings, under wind or earthquake excitation. Similar devices are used as anti-rolling tanks aboard ships. Experiments are performed on a rectangular tank with one screen at mid length. The tank is subjected to forced horizontal and rolling motions, harmonic and irregular. The open-area ratio of the screen is kept constant while the motion amplitudes and frequencies are varied. The frequency range covers the first three natural sloshing modes of the clean tank (without screen). Force measurements are converted into matrices of added mass/inertia and damping coefficients. A simple numerical model is proposed, based on linearized potential flow theory and quadratic discharge equation at the screen, following earlier works by the first author. Good agreement is reported between experimental and numerical hydrodynamic coefficients.

Broadband Brewster transmission through 2D metallic gratings

Recently, we have introduced a mechanism to achieve ultrabroadband light funnelling and total transmission through 1D narrow metallic gratings at a specific incidence angle, the so-called plasmonic Brewster angle. This phenomenon is based on impedance matching between the guided modes supported by ultranarrow linear slits and transverse-magnetic waves at oblique incidence. In this paper, we demonstrate that such phenomenon, representing the equivalent of Brewster transmission for plasmonic screens, can also occur in 2D metallic gratings of various structural forms and shapes, and that it may be made insensitive to the azimuthal, or polarization, angle φ. This finding may have relevant implications to realize large funneling, absorption and squeezing of light in perforated metallic screens.

Gaseous fission products removal from an interior cavity of a fuel element in a multielement EGC

The results of optimization calculations of a gas-removal apparatus in the form of a tube with a capillary tip are presented. Specifically, a criterion for choosing the length of a gas-removal tube for securing serviceability during a period of formation of an isothermal cavity in a uranium dioxide kernel is developed, the requirements for the geometric characteristics of a perforated protective screen are presented, and a mechanism for restoring the serviceability of the gas-removal system during a malfunction owing to mass transfer in irregular operating regimes of the EGC is described and substantiated. It is shown that uranium dioxide with sub-stoichiometric composition and single-crystal tungsten must be used for the gas-removal tube in order for the tube to be chemically stable and stable under thermal cycling. The results of reactor tests of an EGC are presented, and qualitatively confirm the computational results.

External perforated window Solar Screens: The effect of screen depth and perforation ratio on energy performance in extreme desert environments

In hot arid desert environments, the solar radiation passing through windows increases the cooling loads and the energy consumption of buildings. Shading of windows can reduce these loads. Unlike the woven solar screens, wooden solar screens have a thickness that provides selective shading properties. Perforated wooden solar screens were traditionally used for windows shading. Developing modern types of these shading systems can lead to significant energy savings.The paper addresses the influence of changing the perforation percentage and depth of these screens on the annual energy loads, hence defining the optimum depth/perforation configurations for various window orientations. Series of experiments were performed using the EnergyPlus simulation software for a typical residential building in the Kharga Oasis, located in the Egyptian desert. A range of perforation percentages and depths were tested.Conclusions prove that external fixed deep perforated solar screens could effectively achieve energy savings up to 30% of the total energy consumption in the West and South orientations. Optimum range of depths and perforation percentages were recommended. These are: 80–90% perforation rate and 1:1 depth/opening width ratio. These lighter and deeper solar screen configurations were found to be more efficient in energy consumption in comparison with the traditional ones.

External perforated Solar Screens for daylighting in residential desert buildings: Identification of minimum perforation percentages

The desert climate is endowed by clear sky conditions, providing an excellent opportunity for optimum utilization of natural light in daylighting building indoor spaces. However, the sunny conditions of the desert skies, in countries like Egypt and Saudi Arabia, result in the admittance of direct solar radiation, which leads to thermal discomfort and the incidence of undesired glare. One type of shading systems that is used to permit daylight while controlling solar penetration is “Solar Screens”. Very little research work addressed different design aspects of external Solar Screens and their influence on daylighting performance, especially in desert conditions, although these screens proved their effectiveness in controlling solar radiation in traditional buildings throughout history.This paper reports on the outcomes of an investigation that studied the influence of perforation percentage of Solar Screens on daylighting performance in a typical residential living room of a building in a desert location. The objective was to identify minimum perforation percentage of screen openings that provides adequate illuminance levels in design-specific cases and all-year-round.Research work was divided into three stages. Stage one focused on the analysis of daylighting illuminance levels in specific dates and times, while the second stage was built on the results of the first stage, and addressed year round performance using Dynamic Daylight Performance Metrics (DDPMs). The third stage addressed the possibility of incidence of glare in specific cases where illuminance levels where found very high in some specific points during the analysis of first stage. The research examined the daylighting performance in an indoor space with a number of assumed fixed experimentation parameters that were chosen to represent the principal features of a typical residential living room located in a desert environment setting.Stage one experiments demonstrated that the screens fulfilled the requirements of the majority of tested cases. Illuminance levels in the examined residential space were satisfactory in 83% of the near zone cases and 53% in the mid-length zone, while the far zone suites 40% of the cases. Screen influence on daylighting was found to be very much dependent on the orientation of the window and time of the day.In stage two, the percentage of annual “Daylight Availability” was very much related to screen perforation percentage. As perforation percentage decreased, the percentage of Daylit and Over lit spaces decreased. At the same time, Partially Daylit areas of the space increased with similar percentages irrespective of the orientation. As a result of the twofold research stages, it is recommended to utilize a minimum of 80% perforation percentages for spaces similar to the tested case in the South orientation.In stage three, an initial investigation suggests that the use of screens can significantly reduce the occurrence of glare phenomena. Also, it is suggested to study the efficiency of designing Solar Screens that have non-uniform perforation ratios. These could prove useful in improving the illuminance levels in the mid-length and far zones of the unsatisfactory cases.In conclusion, minimum perforation percentages for Solar Screens were presented for specific design cases that encompassed different orientations, seasons and time of the day. In addition, a tool that could be used by architects for based on required annual “Daylit” areas for the design of Solar Screens that effectively achieve functional needs was provided.

An hourly based performance comparison of an integrated micro-structural perforated shading screen with standard shading systems

This article evaluates the performance of an integrated micro structural perforated shading screen (MSPSS). Such a system maintains a visual connection with the outdoors while imitating the shading functionality of a venetian blind. Building energy consumption is strongly influenced by the solar gains and heat transfer through the transparent parts of the fenestration systems. MSPSS is angular-dependent shading device that provides an effective strategy in the control of daylight, solar gains and overheating through windows. The study focuses on using direct experimental methods to determine bi-directional transmittance properties of shading systems that are not included as standard shading options in readily available building performance simulation tools. The impact on the indoor environment, particularly temperature and daylight were investigated and compared to three other static complex fenestration systems. The bi-directional description of the systems was used throughout the article. The simulations were validated against outdoor measurements of solar and light transmittance.

Modeling the damping properties of perforated screens traversed by a bias flow and backed by a cavity at low Strouhal number

Acoustic absorption properties of perforated screens traversed by a bias flow and backed by a resonant cavity are examined at a new absorption regime. The reflection coefficient of these dampers can be canceled at specific frequencies for low Strouhal numbers St ⪡ 1 and Helmholtz numbers of order unity He ∼ 1 . This regime differs from the classical one where resonance is sought at low Helmholtz numbers He ⪡ 1 and large Strouhal numbers St ⪢ 1 . A theoretical analysis is carried out and analytical expressions are derived to determine conditions for optimal absorption in this regime. It is shown that the optimal bias flow velocity and back cavity length can be fixed separately. The former is determined by the plate porosity and the latter controls the peak absorption frequency. This operating regime at low Strouhal numbers enables to increase sound absorption at low frequencies over a larger frequency bandwidth around the peak absorption frequency than the one obtained with a damping system working at high Strouhal numbers. This is confirmed by experiments carried out on a set of dampers in the frequency range 100–1000 Hz. Predictions of the reflection coefficient, including effects of bias flow velocity and cavity depth, show good agreement with experimental data for small pressure perturbation levels. These elements can contribute to the development of robust dampers to control low frequency thermoacoustic instabilities in gas turbines and jet engines.

É possível validar estatisticamente um dispositivo experimental com 10 ratos, de baixo custo, para pesquisa em tabagismo passivo?

INTRODUCAO: Pessoas nao tabagistas que convivem com a fumaca produzida por fumantes podem sofrer os danos causados por esta exposicao. Diversos estudos experimentais demonstraram os efeitos negativos do tabagismo, tanto ativo quanto passivo. A fim de simular a exposicao passiva a fumaca do cigarro em ratos, foi desenvolvido e validado um aparato (Braga-Gazzalle) simples, barato e de facil manutencao no Laboratorio de Habilidades Medicas e Pesquisa Cirurgica - PUCRS. METODO: O sistema de inalacao consiste em uma caixa de polipropileno de 40x33x17 cm, dividida em dois compartimentos por uma tela de metal: o maior para ratos e o menor para cigarros. Um ventilador gera um fluxo interno continuo de ar para que a fumaca produzida pela ponta acesa alcance os animais. Apos aprovacao no Comite de Etica, 5 ratos (Grupo A) foram expostos durante 2 horas diarias a fumaca, comparado ao grupo controle de 5 ratos (Grupo B). Apos exposicao de 4 semanas, dosou-se a carboxihemoglobina (CoHb) serica. Os animais foram entao sacrificados. A analise estatistica utilizada foi o teste t-Student, com 5% de significância. RESULTADOS: No Grupo A, a media dos percentuais de CoHb serica foi de 11,52 ± 4,40%, enquanto no Grupo B a media encontrada foi de 0,3 ± 0,2%. Os niveis de carboxihemoglobina observados no Grupo A foram muito maiores do que no Grupo B (p < 0,001). CONCLUSOES: O modelo experimental desenvolvido pelos autores provou que expoe adequadamente os animais a fumaca passiva. O aparato se mostrou confiavel, de facil manutencao e, sobretudo, de baixo custo operacional.

On the acoustic performance of hybrid mufflers.

The acoustic attenuation of hybrid mufflers including perforated screens and sound‐absorbent materials is investigated in the current study. An analytical method based on a 2‐D mode matching technique is used to model an axisymmetrical hybrid muffler. In the theoretical analysis, the hybrid muffler is divided into a number of sections in different homogeneous media with different acoustical characteristics. The acoustic properties of sound absorbent materials and perforated screens are taken into account to obtain eigenfunctions for wave propagation through the air and sound absorbent materials. A system of equations can be solved by matching the acoustic pressure and axial velocity across different sections, which leads to the solution for the determination of the muffler’s transmission loss (TL). The numerical predictions of TL show good agreements with published experimental data. The developed analytical approach is then used to examine the effect of the inner structure of the hybrid mufflers on their...

Diacritical study of light, electrons and sound scattering by particles and holes

We discuss the differences and similarities in the interaction of scalar and vector wave fields with particles and holes. Analytical results are provided for the transmission of isolated and arrayed small holes as well as surface modes in hole arrays for light, electrons and sound. In contrast to the optical case, small-hole arrays in perforated perfect screens cannot produce acoustic or electronic surface-bound states. However, unlike electrons and light, sound is transmitted through individual holes approximately in proportion to their area, regardless of their size. We discuss these issues with a systematic analysis that allows one to explore both common properties and unique behavior in wave phenomena for different material realizations.

Submillimeter Wave Frequency Selective Surface With Polarization Independent Spectral Responses

This paper reports the design, construction and electromagnetic performance of a new freestanding frequency selective surface (FSS) structure which generates coincident spectral responses for dual polarization excitation at oblique angles of incidence. The FSS is required to allow transmission of 316.5-325.5 GHz radiation with a loss les 0.6 dB and to achieve ges 30 dB rejection from 349.5-358.5 GHz. It should also exhibit crosspolarization levels below -25 dB, all criteria being satisfied simultaneously for TE and TM polarizations at 45 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deg</sup> incidence. The filter consists of two identical, 30 mm diameter, 12.5 mum thick, optically flat, perforated metal screens separated by 450 mu m. Each of the ap 5000 unit cells contains two nested, short circuited, rectangular loop slots and a rectangular dipole slot. The nested elements provide a passband spectral response centered at 320 GHz in the TE and TM planes; the dipole slot increases the filter roll-off above resonance. The FSS was fabricated from silicon-on-insulator wafers using precision micromachining and plating processes including the use of deep reactive ion etching (DRIE) to pattern the individual slots and remove the substrate under the periodic arrays. Quasi-optical transmission measurements in the 250-360 GHz range yielded virtually identical copolarized spectral responses, with the performance meeting or exceeding the above specifications. Experimental results are in excellent agreement with numerical predictions.

Efeito do arejamento no processo de compostagem da fracção sólida do chorume de pecuária leiteira

Manure surpluses in dairy farms can be reduced by separation of the solid fraction from slurry whereas composting allows the stabilization of the organic matter of the solid fraction. The solid fraction can be exported to other farms with a high demand for organic amendments after composting because this turns cattle slurry solids into a uniform, easily handled, organically stable, without pathogens or viable weed seeds that can be land applied and marketed as a soil amendment. However, when 60% moisture content of solids is exceeded, and this is the situation for most separated slurry solids, oxygen movement is somewhat restricted. Therefore, the effect of turning the compost pile must be researched since it provides oxygen for the decomposition process. Dairy cattle slurry solids from two different farms located at the NW Portugal (Vila do Conde), with 70% and 78% moisture contents, were removed from the tank using an auger encased in a perforated stainless steel screen, allowing removal of excess water. Twelve pile treatments of 15 m3 of freshly separated solids were placed in bare soil. The effects of using straw as a framework and of turning with a tractor-mounted front-end loader were evaluated through chemical analysis on pile samples collected over a 15 week period. Thermophilic temperatures were achieved soon after separation for 70% moisture solids, but these temperatures were attained for 78% moisture solids only once mixed with straw, indicating that differences in bedding material affects the temperature and oxygen concentration during composting. Moreover, solids with initial 70% moisture had a faster rate of composting and took shorter time to reach maturity than solids with 78% moisture. Although chemical evolution based on parameters such as pH, electrical conductivity and C/N ratio provided substantial evidence that agronomical suitable compost can be obtained, future challenges include optimizing the process to minimize the loss of nitrogen in the form of ammonia gas, given that pH ranged from 8 to 9 throughout the compost process.

Analytic mode matching for a circular dissipative silencer containing mean flow and a perforated pipe

An analytic mode matching scheme that includes higher order modes is developed for a straight-through circular dissipative silencer. Uniform mean flow is added to the central airway and a concentric perforated screen separates the mean flow from a bulk reacting porous material. Transmission loss predictions are compared with experimental measurements and good agreement is demonstrated for three different silencers. Furthermore, it is demonstrated that, when mean flow is present, the axial kinematic matching condition should equate to that chosen for the radial kinematic boundary condition over the interface between the airway and the material. Accordingly, if the radial matching conditions are continuity of pressure and displacement, then the axial matching conditions should also be continuity of pressure and displacement, rather than pressure and velocity as previously thought. When a perforated screen is present the radial pressure condition changes, but the radial kinematic condition should always remain equivalent to that chosen for the axial kinematic matching condition; here, results indicate that continuity of displacement should be retained when a perforated screen is present.