Ventilation and thermal conditions in secondary schools in the Netherlands: Effects of COVID-19 pandemic control and prevention measures.

During the COVID-19 pandemic, the importance of ventilation was widely stressed and new protocols of ventilation were implemented in school buildings worldwide. In the Netherlands, schools were recommended to keep the windows and doors open, and after a national lockdown more stringent measures such as reduction of occupancy were introduced. In this study, the actual effects of such measures on ventilation and thermal conditions were investigated in 31 classrooms of 11 Dutch secondary schools, by monitoring the indoor and outdoor CO2 concentration and air temperature, both before and after the lockdown. Ventilation rates were calculated using the steady-state method. Pre-lockdown, with an average occupancy of 17 students, in 42% of the classrooms the CO2 concentration exceeded the upper limit of the Dutch national guidelines (800 ppm above outdoors), while 13% had a ventilation rate per person (VRp) lower than the minimum requirement (6 l/s/p). Post-lockdown, the indoor CO2 concentration decreased significantly while for ventilation rates significant increase was only found in VRp, mainly caused by the decrease in occupancy (average 10 students). The total ventilation rate per classrooms, mainly induced by opening windows and doors, did not change significantly. Meanwhile, according to the Dutch national guidelines, thermal conditions in the classrooms were not satisfying, both pre- and post-lockdown. While opening windows and doors cannot achieve the required indoor environmental quality at all times, reducing occupancy might not be feasible for immediate implementation. Hence, more controllable and flexible ways for improving indoor air quality and thermal comfort in classrooms are needed.

Drought-induced lacuna formation in the stem causes hydraulic conductance to decline before xylem embolism in Selaginella.

Lycophytes are the earliest diverging extant lineage of vascular plants, sister to all other vascular plants. Given that most species are adapted to ever-wet environments, it has been hypothesized that lycophytes, and by extension the common ancestor of all vascular plants, have few adaptations to drought. We investigated the responses to drought of key fitness-related traits such as stomatal regulation, shoot hydraulic conductance (Kshoot ) and stem xylem embolism resistance in Selaginella haematodes and S. pulcherrima, both native to tropical understory. During drought stomata in both species were found to close before declines in Kshoot , with a 50% loss of Kshoot occurring at -1.7 and -2.5 MPa in S. haematodes and S. pulcherrima, respectively. Direct observational methods revealed that the xylem of both species was resistant to embolism formation, with 50% of embolized xylem area occurring at -3.0 and -4.6 MPa in S. haematodes and S. pulcherrima, respectively. X-ray microcomputed tomography images of stems revealed that the decline in Kshoot occurred with the formation of an air-filled lacuna, disconnecting the central vascular cylinder from the cortex. We propose that embolism-resistant xylem and large capacitance, provided by collapsing inner cortical cells, is essential for Selaginella survival during water deficit.

Evaluating hypoxia alleviation through induced downwelling.

Hypoxia, a condition of low dissolved oxygen concentration, is a widespread problem in marine and freshwater ecosystems. To date, prevention and mitigation of hypoxia has centered on nutrient reduction to prevent eutrophication. However, nutrient reduction is often slow and sometimes insufficient to remedy hypoxia. We investigate the utility of a complementary strategy of pumping oxygenated surface water to depth, termed induced downwelling, as a technique to remedy hypoxia in the bottom water of marine and freshwater ecosystems. We introduce simple energy-based models and apply them to depth profiles in hypoxic estuaries, lakes, and freshwater reservoirs. Our models indicate that induced downwelling may be ~3 to 102 times more efficient than bubbling air, and 104 to 106 times more efficient than fountain aerators, at oxygenating hypoxic bottom waters. A proof-of-concept downwelling field experiment highlighted potential advantages and shortcomings. We estimate that regional-scale downwelling for continual hypoxia avoidance would require 0.4 to 4 megawatts per cubic kilometer of water (depending on local conditions), or 50 to 500 US dollars per hour per cubic kilometer of water (assuming 125 USD MWh-1 of electricity). Many potential side effects of downwelling are discussed, each of which would need to be explored and assessed before implementation. Downwelling does not replace nutrient management strategies, but under some circumstances may provide an efficient means to augment these strategies.

Efficacy and safety evaluation of systemic extremely low frequency magnetic fields used in the healing of diabetic foot ulcers--phase II data.

BACKGROUND AND AIMS: Cellular and animal models investigating extremely low frequency magnetic fields (ELF-MF) have reported promotion of leukocyte-endothelial interactions, angiogenesis, myofibroblast and keratinocyte proliferation, improvement of peripheral neuropathy and diabetic wound healing. In humans, it has also been reported that systemic exposure to ELF-MF stimulates peripheral blood mononuclear cells, promoting angiogenesis and healing of chronic leg ulcers. The aim of the study was to investigate the effect of exposing different blood volumes to specific ELF-MFs (120 Hz sinusoidal waves of 0.4-0.9 mT RMS) to induce healing of diabetic foot ulcers (DFUs). METHODS: Twenty six diabetic patients with non-responsive DFUs were divided into two exposure groups to receive treatment and record healing time. The forearm group, exposed to ELF-MF 2 h/day, twice weekly (3.6 l of blood/session); and the thorax group, exposed 25 min/day, 2 times/week (162.5 l of blood/session). Treatment period was 100 days or upon complete healing. Ulcer recurrences and adverse effects were investigated during short-term (<1 year) and long-term (3.4-7.8 years) follow-up. RESULTS: Mean healing time was 61.48 ± 33.08 days in the forearm group and 62.56 ± 29.33 days for the thorax group. No adverse effects or ulcer recurrences in the original ulcer site were reported during treatment, the short-term follow-up period or the long-term follow-up period in both groups. CONCLUSIONS: Healing time was independent of the amount of blood exposed to ELF-MF used in this trial. ELF-MFs are effective and safe and could be applied to non-healing DFUs in conjunction with other preventive interventions to reduce DFUs complications.