A two-temperature chemically non-equilibrium model describing in a self-consistent manner the heat transfer, the plasma chemistry, the electric and magnetic field in a high-current free-burning arc in argon has been developed. The model is aimed at unifying the description of a thermionic tungsten cathode, a flat copper anode, and the arc plasma including the electrode sheath regions. The heat transfer in the electrodes is coupled to the plasma heat transfer considering the energy fluxes onto the electrode boundaries with the plasma. The results of the non-equilibrium model for an arc current of 200 A and an argon flow rate of 12 slpm are presented along with results obtained from a model based on the assumption of local thermodynamic equilibrium (LTE) and from optical emission spectroscopy. The plasma shows a near-LTE behaviour along the arc axis and in a region surrounding the axis which becomes wider towards the anode. In the near-electrode regions, a large deviation from LTE is observed. The results are in good agreement with experimental findings from optical emission spectroscopy.
Life in 24-h society relies on the use of artificial light at night that might disrupt synchronization of the endogenous circadian timing system to the solar day. This could have a negative impact on sleep–wake patterns and psychiatric symptoms. The aim of the study was to investigate the influence of evening light emitted by domestic and work place lamps in a naturalistic setting on melatonin levels and alertness in humans. Healthy subjects (6 male, 3 female, 22–33 years) were exposed to constant dim light (<10 lx) for six evenings from 7:00 p.m. to midnight. On evenings 2 through 6, 1 h before habitual bedtime, they were also exposed to light emitted by 5 different conventional lamps for 30 min. Exposure to yellow light did not alter the increase of melatonin in saliva compared to dim light baseline during (38 ± 27 pg/mL vs. 39 ± 23 pg/mL) and after light exposure (39 ± 22 pg/mL vs. 44 ± 26 pg/mL). In contrast, lighting conditions including blue components reduced melatonin increase significantly both during (office daylight white: 25 ± 16 pg/mL, bathroom daylight white: 24 ± 10 pg/mL, Planon warm white: 26 ± 14 pg/mL, hall daylight white: 22 ± 14 pg/mL) and after light exposure (office daylight white: 25 ± 15 pg/mL, bathroom daylight white: 23 ± 9 pg/mL, Planon warm white: 24 ± 13 pg/mL, hall daylight white: 22 ± 26 pg/mL). Subjective alertness was significantly increased after exposure to three of the lighting conditions which included blue spectral components in their spectra. Evening exposure to conventional lamps in an everyday setting influences melatonin excretion and alertness perception within 30 min.
Abstract. While metal vapours have an important impact on the efficiency of the pulsed gas metal arc welding process, only a few papers are focused on this effect. In this paper, methods based on emission spectroscopy are performed to improve the understanding of the physical phenomena occurring during the high-current pulse. Boltzmann plots applied to iron lines, the Stark broadening of the 696.5 nm argon line and composition calculations assuming local thermodynamic equilibrium are used to determine characteristic parameters of the plasma. It is observed that the central part of the arc is mainly composed of iron. The percentage of iron increases quickly at the beginning of the high-current pulse, and slowly decreases, when the central part broadens. During the high-current phase the temperature profile has a minimum value of around 8000 K at the axis of the arc while the argon envelope of the central part reaches temperatures of approximately 13.000 K. High percentage of iron and high radiation of the plasma at the centre can explain the measured shape of the temperature profile.PACS number: 52.70.Kz 52.80Mg 81.20.Vj Keywords: Pulsed gas metal arc welding, GMAW, emission spectroscopy, Stark broadening Boltzmann plot IntroductionGas metal arc welding (GMAW) processes are widely used in industry to produce robust and high quality welded seams connecting metallic workpieces. GMAW processes use an electric arc in order to melt the welding wire so that metal droplets falling from the wire to the workpiece form the join. During the process the arc is enclosed in a shielding gas (typically argon) in order to control the current conduction path and protect the molten metal from oxidation by the atmospheric air. By using a pulsed current, it is possible to obtain a One Drop Per Pulse (ODPP) mode, which is characterized by a stable, periodical and controllable metal transfer to the workpiece [1]. The pulsed GMAW (GMAW-P) process is an effective way of achieving a controlled metal transfer to the workpiece over a wide range of heat and mass transfer rates [1]. Because of their good properties, ODPP GMAW-P processes are widely used in industry. They are intensively studied, in order to control, optimize and predict the quality of the welding seams.The conditions needed to obtain an ODPP are well studied in literature [1][2][3][4]. Parameters
Our results indicate some new relevance for the application of melanopic lux as an additional metric to predict non-visual light effects of electrical light sources for nursing homes, work places, and homes.
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