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

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

Plane-symmetric inhomogeneous magnetized viscous fluid universe with a variable Λ\Lambda

The behavior of magnetic field in plane symmetric inhomogeneous cosmological models for bulk viscous distribution is investigated. The coefficient of bulk viscosity is assumed to be a power function of mass density $(\xi =\xi_{0}\rho^{n})$. The values of cosmological constant for these models are found to be small and positive which are supported by the results from recent supernovae Ia observations. Some physical and geometric aspects of the models are also discussed.Comment: 18 pages, LaTex, no figur

Constraining the dark energy with galaxy clusters X-ray data

The equation of state characterizing the dark energy component is constrained by combining Chandra observations of the X-ray luminosity of galaxy clusters with independent measurements of the baryonic matter density and the latest measurements of the Hubble parameter as given by the HST key project. By assuming a spatially flat scenario driven by a "quintessence" component with an equation of state $p_x = \omega \rho_x$ we place the following limits on the cosmological parameters $\omega$ and $\Omega_{\rm{m}}$: (i) $-1 \leq \omega \leq -0.55$ and $\Omega_{\rm m} = 0.32^{+0.027}_{-0.014}$ (1$\sigma$) if the equation of state of the dark energy is restricted to the interval $-1 \leq \omega < 0$ (\emph{usual} quintessence) and (ii) $\omega = -1.29^{+0.686}_{-0.792}$ and $\Omega_{\rm{m}} = 0.31^{+0.037}_{-0.034}$ ($1\sigma$) if $\omega$ violates the null energy condition and assume values $< -1$ (\emph{extended} quintessence or ``phantom'' energy). These results are in good agreement with independent studies based on supernovae observations, large-scale structure and the anisotropies of the cosmic background radiation.Comment: 6 pages, 4 figures, LaTe

Discrete symmetries, invisible axion and lepton number symmetry in an economic 3-3-1 model

We show that Peccei-Quinn and lepton number symmetries can be a natural outcome in a 3-3-1 model with right-handed neutrinos after imposing a Z_11 x Z_2 symmetry. This symmetry is suitably accommodated in this model when we augmented its spectrum by including merely one singlet scalar field. We work out the breaking of the Peccei-Quinn symmetry, yielding the axion, and study the phenomenological consequences. The main result of this work is that the solution to the strong CP problem can be implemented in a natural way, implying an invisible axion phenomenologically unconstrained, free of domain wall formation and constituting a good candidate for the cold dark matter.Comment: 17 pages, Revtex

Cosmological consequences of a Chaplygin gas dark energy

A combination of recent observational results has given rise to what is currently known as the dark energy problem. Although several possible candidates have been extensively discussed in the literature to date the nature of this dark energy component is not well understood at present. In this paper we investigate some cosmological implications of another dark energy candidate: an exotic fluid known as the Chaplygin gas, which is characterized by an equation of state $p = -A/\rho$, where $A$ is a positive constant. By assuming a flat scenario driven by non-relativistic matter plus a Chaplygin gas dark energy we study the influence of such a component on the statistical properties of gravitational lenses. A comparison between the predicted age of the universe and the latest age estimates of globular clusters is also included and the results briefly discussed. In general, we find that the behavior of this class of models may be interpreted as an intermediary case between the standard and $\Lambda$CDM scenarios.Comment: 7 pages, 5 figures, to appear in Phys. Rev.

Holographic \Lambda(t)CDM model in a non-flat universe

The holographic $\Lambda(t)$CDM model in a non-flat universe is studied in this paper. In this model, to keep the form of the stress-energy of the vacuum required by general covariance, the holographic vacuum is enforced to exchange energy with dark matter. It is demonstrated that for the holographic model the best choice for the IR cutoff of the effective quantum field theory is the event horizon size of the universe. We derive the evolution equations of the holographic $\Lambda(t)$CDM model in a non-flat universe. We constrain the model by using the current observational data, including the 557 Union2 type Ia supernovae data, the cosmic microwave background anisotropy data from the 7-yr WMAP, and the baryon acoustic oscillation data from the SDSS. Our fit results show that the holographic $\Lambda(t)$CDM model tends to favor a spatially closed universe (the best-fit value of $\Omega_{k0}$ is -0.042), and the 95% confidence level range for the spatial curvature is $-0.101<\Omega_{k0}<0.040$. We show that the interaction between the holographic vacuum and dark matter induces an energy flow of which the direction is first from vacuum to dark matter and then from dark matter to vacuum. Thus, the holographic $\Lambda(t)$CDM model is just a time-varying vacuum energy scenario in which the interaction between vacuum and dark matter changes sign during the expansion of the universe.Comment: 8 pages, 4 figures. version for publication in EPJC. arXiv admin note: text overlap with arXiv:1112.235

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

The effects of various ratios of sunflower oil and surfactant on household type cake quality

The aim of this study was to determine the effects of sunflower oil (0, 5, 10, 15%) and surfactant (acetic and lactic acid esters of mono and diglycerides; 0, 0.25, 0.5, 0.75, 1%) on the quality of the wheat flour based household type cake. The variable ingredients were used as alone or in combinations in cake manufacture; therefore 20 different batter formulations were formed. Quality characteristics of cake samples (volume, symmetry, uniformity, shrinkage, weight loss, crumb–grain structure, crumb firmness) were investigated. Both components had a significant (P < 0.05) impact on cake quality. In trial conditions, it was determined that the effect of surfactant on cake quality was greater than the oil. In cake batter, using up to a certain level (0.5%) surfactant was improved the cake volume and porosity. When the surfactant was used at 0.75 and 1% levels, these cake properties were deteriorated. The softness of the cakes have been measured as maximum when surfactant was used alone in increasing order from 0 to 1%. Sunflower oil improved the cake quality up to a limited extent. This improvement generally occurred at 5% level. Usage of oil with higher levels declined cake properties significantly. In combination formula, it was determined that using surfactant made using more oil in the batter formula possible. Careful attention should be paid to the appropriate level of use of oil and surfactant in cake production. Otherwise, significant declines occurred in cake quality. It was concluded that high-quality household-type cakes can be made if both ingredients were combined the use of 5–10% oil and 0.75–1% surfactant. © 2017, Springer Science+Business Media, LLC