Efficient Solvability of the Weighted Vertex Coloring Problem for Some Two Hereditary Graph Classes

Journal of Applied and Industrial Mathematics - The weighted vertex coloring problem for a given weighted graph is to minimize the number of colors so that for each vertex the number of the colors...     

Modeling of Dielectric Relaxation in Clays at Negative and Positive Temperatures

Russian Physics Journal - Experimental data are presented on measuring the complex dielectric permittivity (CDP) of clays completely moistened with distilled water in the frequency range from 1 kHz...     

Experimental Study of the Self-Compression of a Wave Packet upon Total Internal Reflection in a Transparent Insulator

JETP Letters - The formation and self-recovery of a single-cycle light bullet after total internal reflection of a femtosecond pulse in a transparent insulator in the region of anomalous dispersion...     

Spectral-Luminescent Properties and Photolysis of Some Phenol Derivatives

Russian Physics Journal - The spectral-luminescent properties and photolysis of phenol and some of its derivatives have been considered experimentally and by methods of quantum chemistry. It has...     

Assessment of Noise Exposure of Sawmill Workers in Southwest,Nigeria

Economic wood processing employs the use of industrial machines for cutting, shaping, milling, and sawing timber, thereby leading to the generation of high levels of noise. Published data from empirical studies have categorized noise as an environmental hazard of global significance. Furthermore, noise exposure limits for different industries and all the industrial machines available has not been formally established as it presently exists in developed nations around the world. Therefore, this study assessed the daily exposure of sawmills workers to noise in Southwestern Nigeria. Reconnaissance surveys were first carried out in Osun, Oyo, Ondo, Ekiti, Lagos, and Ogun States to select sawmills that were fully operational and fit for the study. Two fully functional sawmills in two cities of each State were eventually selected for data collection, making a total of 24 sawmills, while the Circular Machines (CM), Planer Machines (PM), and Band-saw Machines (BM) were the machines in each sawmill considered. Two machines each of CM, PM, and BM were considered in each sawmill, making a total of forty-eight (48) machines each of CM, PM, and BM. Sound data were collected between 7 am and 7 pm each day for six days (between Monday and Saturday) using Extech 407732 sound level meter and all stabilized measurements were taken three times at different intervals. The data collected were in three different periods: Machine No-work Period (NP_m), Machine Idle Period (IP_m), and Machine Working Period (WP_m). A two–way Analysis of Variance (ANOVA) was carried out at P < 0.05 to determine whether there is a significant difference in the sound level average before and after the break, for both the idle and working periods of the three machines considered. This was also done to determine whether there is a significant difference between the sound level average of the results collected during idle and working periods of the three machines. Noise Pollution Levels (L_np) ranged from 83.20 dB (PM) to 107.65 (BM) and 93.42 (CM and PM) – 116.00 (BM) respectively, while IP_m also gave the least noise pollution level of 95.79 dB and WP_m gave the highest level of 102.88 dB. The results revealed that all the machines’ L_np values in the working period are more than the 90 dB acceptable limit the recommendation value of 90 dB while 89.6% of CMs, 75% of PMs, and 89.6% of BM had their L_np above 90 dB in the idle period respectively. The minimum and the maximum noise dose levels for IP_m, WP_m and overall are 0.09 (BM) and 2.37 (CM), 0.50 (CM), and 4.77 (PM) and 0.69 (BM) and 6.64 (PM) respectively. The study found out that the fundamental contributing factors to the high noise levels in sawmills are poor machine maintenance, use of old and obsolete machines, poor housekeeping strategy, limited space, workers’ negligence, lack of PPE, and lack of occupational safety training. The study recommends that proper workplace practices such as use of personal protective equipment, new and modern machines, training, and occupational safety programmes be implemented in the considered sawmills.     

State Observer for a Four-Dimensional System with Vector Output

Differential Equations - The problem of synthesizing an observer with linear error dynamics for a four-dimensional system with vector output is considered. Necessary and sufficient conditions for...     

Electrical Properties of the Polycrystalline BiFe0.95Co0.05O3 Films

Physics of the Solid State - Semiconductor BiFe0.95Co0.05O3 thin-film compounds have been synthesized by a burst technique. The film surface morphology and the effect of electronic doping via...     

Determination of the Yarkovsky Effect Parameter for Asteroids with Small Perihelion Distances

Russian Physics Journal - Results of determining the Yarkovsky effect parameter for all asteroids with small perihelion distances known by January, 2021 are presented. A comparison is performed...     

Combustion characteristics and kinetics of DPR Korea’s anthracite in O2/N2 and O2/CO2 atmosphere

Journal of Thermal Analysis and Calorimetry - In O2/N2 and O2/CO2 atmospheres with oxygen concentrations of 21%, 30%, and 50%, combustion characteristics index, apparent activation energy, and...     

First representative of phosphorylated formic acid hydrazides with three P—C bonds: synthesis and addition to the phosphorylated 4-methylenequinones

Russian Chemical Bulletin - Diethylphosphinylmethanehydrazide, the first representative of the phosphorylated formic acid hydrazides with three P—C bonds was obtained, which can exhibit...