Micro-perforated panel (MPP) absorber is increasingly gaining popularity as an alternative sound absorber in buildings compared to the well-known synthetic porous materials. A single MPP has a typical feature of a Helmholtz resonator with a high amplitude of absorption but a narrow absorption frequency bandwidth. To improve the bandwidth, a single MPP can be cascaded with another single MPP to form a double-layer MPP. This paper proposes the introduction of inhomogeneous perforation in the double-layer MPP system (DL-iMPP) to enhance the absorption bandwidth of a double-layer MPP. Mathematical models are proposed using the equivalent electrical circuit model and are validated with experiments with good agreement. It is revealed that the DL-iMPP produces a wider half-absorption bandwidth compared to the conventional homogeneous double-layer MPP. The absorption bandwidth to higher frequencies can be effectively controlled by reducing the air cavity between the iMPPs and to the lower frequencies by increasing the back cavity depth at the second layer.
Objectives: This study aimed to evaluate and compare the effect of plasma treatment versus conventional treatment on the micro shear bond strength (μSBS), surface roughness, and wettability of three different CAD/CAM materials. Materials and methods: Sixty cylindrical specimens (5 mm diameter ×3 mm height) were prepared from three different CAD/CAM materials: Group A: Zirconia, Group B: Lithium disilicate, and Group C: Resin nano-ceramic. Each group was subdivided into two subgroups according to surface treatment used: Subgroup I: Conventional treatment, zirconia was sandblasted with Al2O3, while lithium disilicate and resin nano-ceramic were etched with hydrofluoric acid. Subgroup II: Plasma treatment, the surface of each material was tr
... Show MoreThis study examines the analysis of the contents of the international public relations campaign in confronting the Covid-19 virus, which was taken from the (Your Health is a Trust) campaign for the World Health Organization, Iraq office.The research problem revolves around a main question that is, what are the axes of the campaign (Your Health is a Trust) established by the World Health Organization (Iraq office) in the prevention of Covid 19 virus?From this main question, several sub-questions emerged that this study answered on their Facebook page, and the communication activities of the Covid-19 awareness campaign. In the content analysis form, as this form included a number of main themes and main categoriesthat were adopted in analyzin
... Show MoreThis study is an attempt to investigate the semantic and syntactic features of English and Arabic verbs of eating. After surveying the literature on the meaning of verbs in both languages, three chapters address the major issues in this subject. The problem to be investigated in this study can be summarized in the following points: 1. The overlapping of semantic and syntactic features within the category of verbs of eating in English and Arabic. 2. Which semantic classification is more accurate and through which method? 3. Which classification, the semantic or the syntactic, is more important? This study hypothesized the following: 1. The semantic features are more influential in analyzing the category of verbs of eating than the syntactic
... Show MoreThe present paper is very important for study of biodiversity of Iraq , to know how the
changes going and how the laughing dove S. senegalensis was a rare species in Iraq and now
is common and also the (baz) gosh hawk A. gentilis is common and the most famous 6rd of
pray in Iraq, till now missing from ornithologist and bird watcher to record it
An experimental investigation of natural convection heat transfer from an isothermal horizontal,vertical and inclined heated square flat plates with and without circular hole, were carried out in two cases, perforated plates without an impermeable adiabatic hole "open core" and perforated plates with an impermeable adiabatic hole "closed core" by adiabatic plug. The experiments covered the laminar region with a range of Rayleih number of (1.11x106 ≤RaLo≤4.39x106 ), at Prandtle number (Pr=0.7). Practical experiments have been done with variable inclination angles from horizon (Ф=0o ,45o,90o,135oand 180o),facing upward (0o≤Ф<90o), and downward (90o
≤Ф<180o). The results showed that the temperature gradient increases whi
Background: To evaluate the bony supports of the teeth adjacent to the area of cleft in patient with unilateral cleft lip and palate and to compare these measurements with the measurements of the same teeth in non-cleft side by using CBCT. Materials and methods: The CBCT scans of 30 patients having cleft lip( unilateral) and palate(unilateral), were analyzed and the measurements of the alveolar bony support for teeth that are adjacent to the cleft area were measured with those teeth located on opposite side (non- clef) side. For each tooth, the measurements will taken for the distance between the( cementoenamel junction) (CEJ) and the bony crest (AC) at the( buccal area) was measured and the thickness of the buccal plate At zero, one, tw
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