Experimental evaluation on noise reduction performance of a motorcycle helmet

Motorcycle helmets are generally thought to be only protection of motorcycle drivers against head injuries as well as loud noise in traffic. While there have been several papers on noise elimination capabilities of motorcycle helmets, no controlled study has been reported to compare different types of test conditions in literature. The purpose of this study is to assess noise reduction capacities of a motorcycle helmet under different types of acoustical loadings as well as environments and to identify better test condition. Firstly, a Head & Torso simulator with and without the motorcycle helmet in a built acoustical cabinet was exposed to digitally generated sound to investigate insertion loss values. Besides, the Head & Torso simulator was fixed onto a motorcycle to simulate actual driving conditions. Sound pressure levels were captured at the ear level to obtain insertion loss values in case of motorcycle noise for different engine speeds. By comparing calculated insertion losses, it was revealed that considerable differences existed between tests for different conditions. Beneficial interpretations were deduced and thus, a practical solution was presented for accurate measurements acoustic performance of the motorcycle helmets in laboratory conditions

Microtensile bond strength of two different adhesive systems to dentin (an in vivo and in vitro study)

Abstract no. 496published_or_final_versio

A Prevention and a Traction System for Ransomware Attacks

Over the past three years, especially following WannaCry malware, ransomware has become one of the biggest concerns for private businesses, state, and local government agencies. According to Homeland Security statistics, 1.5 million ransomware attacks have occurred per year since 2016. Cybercriminals often use creative methods to inject their malware into the target machines and use sophisticated cryptographic techniques to hold hostage victims' files and programs unless a certain amount of equivalent Bitcoin is paid. The return to the cybercriminals is so high (estimated \$1 billion in 2019) without any cost because of the advanced anonymity provided by cryptocurrencies, especially Bitcoin \cite{Paquet-Clouston2019}. Given this context, this study first discusses the current state of ransomware, detection, and prevention systems. Second, we propose a global ransomware center to better manage our concerted efforts against cybercriminals. The policy implications of the proposed study are discussed in the conclusion section

On noise reduction of motorcycle helmets

Motorcycle helmets are mandatory on the safe driving, in spite of that the helmet usage rate decreases by the reason of discomfort. One of the most common complaints of the drivers is noise in the helmet. The noise may be structural bourne or air bourne. In this paper, measurements were performed to determine the external noise reduction of the motorcycle helmets, which is a preliminary study to improve the sound quality. The measurements were carried out on a specially designed field to provide a controlled acoustic environment. A Head & Torso simulator was used to measure noise in the built cabinet that produced by an omnidirectional sound source. The in-cab calibration was provided by in-house microphones. The excitation sounds were generated by using special software on the computer and the output was transmitted to the speaker cabinet via a sound card connected to an amplifier. Two types of motorcycle helmets were tested and the sound reduction results were compared

A study of noise source localization in motorcycles

In civilized and developing countries, the number of the motorcycles in transportation systems is increasing day by day. With the growing demand of the motorcycles, the noise caused by these vehicles has constituted an important role in the noise pollution. On the other hand, the drivers are suffering from the permanent damages that are generated by the motorcycle noise. For overcoming these drawbacks, the first necessary is to determine the noise sources in motorcycles. The purposes of this study are the determination of the noise sources in motorcycles by sound intensity method and investigation of the effects of the motorcycle noises on the drivers. Firstly, sound levels were measured at idle mode and at three different engine speeds for investigated motorcycle by using the sound intensity probe. Besides these measurements, the sound levels were also captured at the ear level with and without a helmet. Then the results were analyzed by taking into the consideration of the helmet usage and the driving speed

Higher spin fields and the problem of cosmological constant

The cosmological evolution of free massless vector or tensor (but not gauge) fields minimally coupled to gravity is analyzed. It is shown that there are some unstable solutions for these fields in De Sitter background. The back reaction of the energy-momentum tensor of such solutions to the original cosmological constant exactly cancels the latter and the expansion regime changes from the exponential to the power law one. In contrast to the adjustment mechanism realized by a scalar field the gravitational coupling constant in this model is time-independent and the resulting cosmology may resemble the realistic one.Comment: 15 pages, Latex twic