Attenuation of low-frequency electromagnetic waves in the Earth's lower ionosphere under the influence of strong local disturbances in the atmosphere.

The value and duration of attenuation of low frequency waves (1...10 kHz) in the presence of a strong local disturbance of the atmosphere have been estimated. Sources of significant local disturbances of the atmosphere are, for example, precipitation of energetic particles of radiation belts; electromagnetic pulses of lightning discharges; radiation of powerful low-frequency ground-based transmitters; invasion of large meteors. Strong local disturbances lead to an increase of ionization (concentration of free electrons) of the environment by several orders of magnitude in the region of space whose characteristic dimensions are comparable to the length of the wave (tens and hundreds of kilometers). As such a disturbance, we use the previously developed macroscopic model of an instantaneous, point release of a relatively large amount of energy in the atmosphere below the ionosphere. This model makes it possible to estimate the features of the propagation of low-frequency waves through the disturbed layer of the lower ionosphere by changing only two initial parameters: the disturbance energy and its initial height. It is shown that the attenuation value is almost independent of frequency and geo- and heliophysical conditions. For initial heights up to 50 km, the fading duration does not exceed ~ 2 min. With an increase of the initial altitude, the attenuation in the lower ionosphere becomes extremely large. However, for heights of 50 ... 70 km (depending on the value of energy), the horizontal size of the disturbance decreases significantly, which leads to a decrease in the fading time to tens of seconds for initial heights of more than 80 km.

Amendment of Herbicide Spray Solutions with Adjuvants to Modify Droplet Spreading and Fading Characteristics on Weeds

Improving the coverage area and fading time of herbicidal droplets on weeds has the potential to enhance the biological control effectiveness. Droplet spreading and fading behaviors on five different weeds were characterized for spray solutions containing a 1.25% glyphosphate Rodeo herbicide amended with each of three different adjuvants (nonionic surfactant Kinetic, nonionic organosilicone surfactant DyneAmic, and nonionic surfactant and antifoaming agent Preference). The five weeds were ragweed, crabgrass, yellow nutsedge, common purslane, and spurge. Tests were conducted by depositing single 300 and 600 µm herbicidal droplets with different adjuvant concentrations on weed leaves inside an environment control chamber. A droplet at a higher adjuvant concentration had greater coverage area on weed surfaces. Preference-amended herbicidal droplets had the largest coverage area increase for all five weeds, and generally followed by droplets with Kinetic and DyneAmic except for 300 µm droplet on purslane and 600 µm droplet on spurge. In comparison with the herbicidal solution containing Rodeo and water only, with addition of adjuvants the 600 µm droplets increased the coverage area by 2.13 to 5.47, 1.76 to 2.56, 1.84 to 2.07, and 2.40 to 4.49-fold on crabgrass, yellow nutsedge, common purslane, and spurge, respectively, while the 300 µm droplets increased the coverage area on ragweed by 3.88 to 5.86-fold. In contrast, fading times of all 300 µm droplets decreased with the adjuvant addition except for DyneAmic applied on purslane. However, fading times of 600 µm droplets did not have increase or decrease trends with adjuvants, which depended on types of the adjuvant and weed. The overall comparison by integrated index (coverage area × fading time) indicated that a spray droplet at higher adjuvant concentration was likely to have a higher integrated index. In addition, Preference amended droplets had significantly more integrated index increase for crabgrass and nutsedge, while DyneAmic had more increase for purslane. Therefore, appropriate selections of spray adjuvants during herbicide applications could significantly increase droplet deposition effectiveness for controlling specific weeds. Keywords: Spray droplet, Spray additive, Herbicide application, Surfactant, Weed control.

Dimming strategies for open office lighting: User experience and acceptance

Sensor-triggered control strategies can limit the energy consumption of lighting by considering the presence of users in the office and dimming lighting down when it is not needed. In multi-user offices, the application of occupancy-based dimming at room level limits the energy saving potential. However, zone- or desk-based dimming may affect the comfort of co-workers due to its dynamics. This paper reports the assessment by 17 participants (30–50 years of age) of occupancy-based dimming in a mock-up office, using different dimming speeds. Participants consisted of co-workers experiencing changes triggered by others, and actors triggering these light changes. While the participants performed an office-based task, the luminaire above the actors’ desk was dimmed from approximately 550 lx to 350 lx (average horizontal illuminance), and vice versa. The participants evaluated the dimming conditions regarding their noticeability and acceptability. The study showed that the noticeability of light changes due to dimming, increases when fading times become shorter. Dimming with a fading time of at least two seconds was experienced as acceptable by more than 70% of the participants. The results of this experiment provide insights to system behaviour that does not compromise user experience while addressing energy efficient use of electric lighting.

Fading Activities of Herbicidal Droplets Amended with Emulsifiable Spray Adjuvants on Cucurbitaceous Leaves

Understanding reactions of surfactant-amended droplets on difficult-to-wet weed surfaces could help develop application strategies to increase herbicide efficacy. Behaviors of herbicidal droplets containing different emulsifiable anti-evaporation spray adjuvants were investigated by characterizing 250 and 450 µm herbicidal droplet dispersion and fading time on cucurbitaceous leaves placed inside a 20°C chamber at 30% and 60% relative humidity (RH). Droplet maximum coverage area increased with droplet size but not with RH, while droplet fading time increased with both droplet size and RH. Despite 450 µm droplets having greater maximum coverage area than 250 µm droplets, the larger droplets had higher fading rates and lower ratios of maximum coverage area to droplet volume. Droplet maximum coverage area and fading time on leaves were affected by adding spray adjuvants to the herbicide-only solution. The Uptake surfactant was more effective than the other two surfactants (AntiEvap+BS1000 and Enhance) in increasing droplet maximum coverage area and fading time. Compared to the herbicide-only solution, addition of Uptake surfactant to the herbicide solution could increase maximum coverage area by 68% and 52% for 250 and 450 µm droplets, respectively, but addition of AntiEvap+BS1000 or Enhance surfactants did not show significant increase. Similarly, addition of Uptake surfactant to the herbicide-only solution increased droplet fading times by 11.1% and 13.2% at 30% and 60% RH, respectively, for 250 µm droplets and by 34.7% and 2.8% at 30% and 60% RH, respectively, for 450 µm droplets. In contrast, addition of AntiEvap+BS1000 surfactant reduced fading time, and addition of Enhance surfactant did not significantly affect fading time. Therefore, appropriate selection of spray adjuvants for herbicide applications could significantly influence droplet deposit behaviors on cucurbitaceous leaves, leading to improved effectiveness of weed control. Keywords: Herbicide application, Spray deposition, Spray droplet, Surfactant, Weed control.