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Abstract

Heating, ventilation and air conditional (HVAC) system provides a cold ventilation for the comfort of the driver and passengers in a vehicle. However, the vibration induced by the HVAC contributes to a reasonable level of noise emission, and hissing is one of the critical noises. So far, the characterization of hissing noise from the vehicle is least to be reported compared to other type of noises. Hence, this paper investigates the occurrence of hissing noise from several HVAC components. A lab-scale HVAC system was developed to imitate the real-time operations of the vehicle HVAC system. Two engine conditions, namely as ambient and operating conditions, were tested at speed of 850 rpm and 850–1400 rpm, with the blower speed maintained constantly at one level. The result shows that the hissing noise from the labscale HVAC was produced at frequency range of 4000–6000 Hz. The finding also highlights that the main component contributors of noise emission are an evaporator and a thermal expansion valve. The validation with a real vehicle system showed a good consensus whereby the hissing noise was produced at the similar operating frequency ranges. Also, the hissing noise was found to be louder when in an operating condition which could be taken into consideration by the vehicle manufacturers to improve the HVAC design.
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Authors and Affiliations

Mohd Hafiz Abdul Satar
1
Ahmad Zhafran Ahmad Mazlan
1
Muhd Hidayat Hamdan
1
Mohd Syazwan Md Isa
1
Muhd Abdul Rahman Paiman
2
Mohd Zukhairi Abd Ghapar
2

  1. The Vibration Lab, School of Mechanical Engineering, Universiti Sains Malaysia 14300 Nibong Tebal, Penang, Malaysia
  2. Testing & Development, Vehicle Development & Engineering, Proton Holdings Berhad, 40000 Shah Alam, Selangor, Malaysia
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Abstract

Periodontitis is a highly prevalent, chronic immune-inflammatory disease of the periodontium that results in the periodontium and alveolar bone loss’s progressive destruction. In this study, the induction of periodontal disease via retentive ligature, lipopolysaccharide, and their combination at three different times were compared in a rat model. Seventy-two Sprague Dawley rats were distributed into four treatment groups: 1) control group with no treatment; 2) application of 4/0 nylon ligature around second maxillary molars; 3) combination of ligature and LPS injection (ligature-LPS); 4) intragingival injection of Porphyromonas gingivalis lipopolysaccharide ( Pg-LPS) to the palatal mucosa of the second maxillary molars. Six rats were sacrificed from each group after 7, 14, and 30 days of periodontal disease induction. Alveolar bone loss, attachment loss, number of inflammatory cells, and blood vessels were evaluated histologically. A micro-CT scan was used as a parameter to know the rate of alveolar bone loss. Parametric data were analyzed using two-way ANOVA followed by Bonferroni correction with a significance set at 5%. Non-parametric data were analyzed using Kruskal-Wallis, followed by multiple comparisons with Bonferroni correction. The histological results revealed significant destructive changes in the periodontal tissues and alveolar bone following the ligature and ligature-LPS induction techniques. These changes were evident as early as seven days, maintained until 14 days post-treatment, and declined with time. The ligature technique was effective in inducing acute periodontal disease. The LPS injection technique did not induce alveolar bone loss, and its combination to ligature added insignificant effects.
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Bibliography


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Authors and Affiliations

H. Mustafa
1 2
C.H. Cheng
1
R. Radzi
1
L.S. Fong
1
N.M. Mustapha
1
H.O. Dyary
2

  1. Faculty of Veterinary Medicine, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
  2. College of Veterinary Medicine, University of Sulaimani, Sulaymaniyah, Kurdistan Region, Iraq
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Abstract

This paper presents an analysis of non-metallic inclusions occurring in high-silicon steels containing about 3% Si of terms of their type, volume fraction and morphology. The inclusions were divided into 3 main groups: oxides, sulfides, nitrides which together can also form complex. The work was based on numerous metallographic observations in two sections (longitudinal and transverse to the rolling direction). The study was performed on three casts differing in chemical composition. The analyzed casts were characterized by a different content of non-metallic inclusions, which can be associated with slight differences in chemical composition. The analyzed results showed that the most common inclusions were oxides and nitrides. Sulfides occurred sporadically.
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Authors and Affiliations

K. Ścibisz
1
ORCID: ORCID
J. Krawczyk
2
ORCID: ORCID

  1. ArcelorMittal Poland S.A. Unit in Krakow, Tadeusza Sendzimira 1 Str., 31-752 Krakow, Poland; AGH University of Krakow, Faculty of Metals Engineering and Computer Science, AGH Do ctoral School, al. Mickiewicza 30, 30-059 Krakow, Poland
  2. AGH University of Krakow, Faculty of Metals Engineering and Computer Science, Al. Mickiewicza 30, 30-059 Krakow, Poland

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