Unfavorable Ambient Conditions Research Articles

Evaluation of Fire Hazard in Electrical Installations Due to Unfavorable Ambient Thermal Conditions

Evaluation of fire hazard caused by electrical installations is a difficult and important topic, and it limits the possibility of loss of life or health of people, as well as the occurrence of significant property damage. In particular, this hazard was caused by power cables and especially photovoltaic (PV) installations. The authors proved that power cables directly exposed to strong solar radiation are likely to exceed maximum permissible temperature in unfavorable ambient conditions. Overheated and damaged cable insulation can be a source of electric shock and a strong leakage current causing fire. In the case of typical PV connectors (MC4 connectors), the main problem is poor contact at the connections of the PV cables. A poor connection can even cause the connector to melt, as shown in this study. In the paper, the authors present a computer simulation regarding critical thermal points of electrical installations, in particular, of the PV type. It may be an indication of what should be paid attention to when designing and implementing such installations. This is important for the safety of people and buildings.

Dynamics of Air Humidity in a Concentrator Photovoltaic Module with a Drying Device

We have studied the dynamics of air humidity in the interior of a concentrator photovoltaic (CPV) module equipped with air-drying device filled with moisture-absorbing material based on silica gel. A new design of the air-drying device was developed for preventing the deposition of condensate onto the surfaces of a Fresnel lens, solar cell, and CPV module. Under unfavorable ambient conditions (relative humidity up to 95%), this device allowed to reduce the inner humidity to 25–55% at cyclic temperature variation within 15–45°C and to increase the dew point deficit up to 10–25°C.

Role of Graphitic Nitrogen and π-Conjugated Functional Groups in Selective Oxidation of Alcohols: A DFT based Mechanistic Elucidation.

Selective oxidation of alcohols to aldehydes is challenging reaction due to its accessibility to overoxidation. In this study, we have made an attempt to unravel the mechanistic aspects of selective oxidation of allyl alcohols that contain multiple functional groups catalyzed by N-doped graphene. The role of graphitic nitrogen and the presence of π-conjugated functional groups are demonstrated using the state-of-the-art density functional theory calculations. The detailed reaction mechanism for aerobic oxidation of allyl alcohol (AA) and cinnamyl alcohol (CA) are investigated. The formation of activated oxygen species (AOS) over N-doped graphene (NG) has been adopted from our previous report. The results revealed that ketonic AOS oxidizes allyl alcohols into aldehydes selectively with a relatively lower activation barrier of 20.1 kcal mol-1 . The oxidation of alcohols with the AOS formed at the edge results in high activation barriers owing to its high thermodynamic stability. Similarly, AOS formed at the center leads to the formation of H2 O2 along with high activation barriers. As a consequence, AOS formed at the center is less active when compared to ketonic AOS. The overoxidation of aldehyde is only possible due to the formation of H2 O2 . However, it is unlikely to happen due to unfavorable ambient conditions. The presence of multiple π-conjugated functional groups is responsible for the significant reduction in the activation barriers of the second hydrogen transfer step due to the stabilization of intermediate by increasing the acidic nature of the intermediates. On the basis of the results, a generalized reaction mechanism has been proposed. These results would definitely shed light on the effective fabrication of catalysts for oxidation of alcohol and sustainable energy.

In Situ Intermediates Determination and Cytotoxicological Assessment in Catalytic Oxidation of Formaldehyde: Implications for Catalyst Design and Selectivity Enhancement under Ambient Conditions.

Formation and decay of formaldehyde oxides (CH2OO) affect the complete oxidation of formaldehyde. However, the speciation and reactivity of CH2OO are poorly understood because of its extremely fast kinetics and indirect measurements. Herein, three isomers of CH2OO (i.e., main formic acid, small dioxirane, and minor CH2OO Criegee) were in situ determined and confirmed as primary intermediates of the room-temperature catalytic oxidation of formaldehyde with two reference catalysts, that is, TiO2/MnO x-CeO2 and Pt/MnO x-CeO2. CH2OO Criegee is quite reactive, whereas formic acid and dioxirane have longer lifetimes. The production, stabilization, and removal of the three intermediates are preferentially performed at high humidity, matching well with the decay rate of CH2OO at approximately 6.6 × 103 s-1 in humid feed gas faster than 4.0 × 103 s-1 in dry feed. By contrast, given that a thinner water/TiO2 interface was well-defined in TiO2/MnO x-CeO2, fewer reductions in the active sites and catalytic activity were found when humidity was decreased. Furthermore, lethal intermediates mostly captured at the TiO2/MnO x-CeO2 surface suppressed the toxic off-gas emissions. This study provides practical insights into the rational design and selectivity enhancement of a reliable catalytic process for indoor air purification under unfavorable ambient conditions.

Controlling the thermal environment of underground power cables adjacent to heating pipeline using the pavement surface radiation properties

This paper shows how the pavement surface radiation properties can be used to control the thermal environment of 110 kV underground cables in order to increase their ampacity. It is assumed that the ampacity is additionally affected by the cable bedding size and an underground heating pipeline. Thanks to an experimental apparatus, some useful data were collected for the validation of two different finite element method based models that predict the effect of the pavement surface radiation properties on the cable ampacity. The first model corresponds to the experimental apparatus and actual indoor conditions, while the second one corresponds to the theoretical case and assumed outdoor conditions (taking into account the thermal effects of solar radiation, cable bedding size, and heating pipeline). This paper examines two possible cases of outdoor conditions, one corresponding to summer period (the most unfavorable ambient conditions) and another one corresponding to winter period (the most common winter conditions in Serbia). This proposed new method is based on the experimental data and generalized using the finite element method in COMSOL. It is found that the ampacity of the considered 110 kV cable line can be increased up to 25.4 % for the most unfavorable ambient conditions and up to 8 % for the most common winter conditions.

Collision Risk Mitigating System for Light Rail Vehicles(LRV)

Abstract This piece is dedicated tothedescription of the development of collision risk mitigating system. The proposed concept of control system is designed to enhance safety ofpassengers, a driver and other people in vicinityof light rail vehicles (tramways).The requirements were fulfilled thanks to the application of lidar sensor and feature of vehicle positioning on the track map created basingon precise measurements with the use of satellite navigation systemReal Time Kinematic. The map allows to eliminate errors of system operation and to enhance resistance to unfavorable ambient conditions, i.e.temperature or fog. The system calculates work braking distance for particular vehicle speed. In case of obstacle detection which is closer to vehicle than the calculated braking distance, the driver is informed about a collision risk with a buzzer and optical signalization. The system has already been implemented and tested.

Fasting-induced daily torpor in desert hamsters (Phodopus roborovskii)

Daily torpor is frequently expressed in small rodents when facing energetically unfavorable ambient conditions. Desert hamsters (Phodopus roborovskii, ~20g) appear to be an exception as they have been described as homeothermic. However, we hypothesized that they can use torpor because we observed reversible decreases of body temperature (Tb) in fasted hamsters. To test this hypothesis we (i) randomly exposed fasted summer-acclimated hamsters to ambient temperatures (Tas) ranging from 5 to 30°C or (ii) supplied them with different rations of food at Ta 23°C. All desert hamsters showed heterothermy with the lowest mean Tb of 31.4±1.9°C (minimum, 29.0°C) and 31.8±2.0°C (minimum, 29.0°C) when fasted at Ta of 23°C and 19°C, respectively. Below Ta 19°C, the lowest Tb and metabolic rate increased and the proportion of hamsters using heterothermy declined. At Ta 5°C, nearly all hamsters remained normothermic by increasing heat production, suggesting that the heterothermy only occurs in moderately cold conditions, perhaps to avoid freezing at extremely low Tas. During heterothermy, Tbs below 31°C with metabolic rates below 25% of those during normothermia were detected in four individuals at Ta of 19°C and 23°C. Consequently, by definition, our observations confirm that fasted desert hamsters are capable of shallow daily torpor. The negative correlation between the lowest Tbs and amount of food supply shows that heterothermy was mainly triggered by food shortage. Our data indicate that summer-acclimated desert hamsters can express fasting-induced shallow daily torpor, which may be of significance for energy conservation and survival in the wild.

Major solar eruptions and high-energy particle events during solar cycle 24

We report on a study of all major solar eruptions that occurred on the front-side of the Sun during the rise to peak phase of cycle 24 (first 62 months) in order to understand the key factors affecting the occurrence of large solar energetic particle events (SEPs) and the ground levels enhancement (GLE) events. The eruptions involve major flares with soft X-ray peak flux >/= 5.0 x10-5 Wm-2 (i.e., flare size >/= M5.0) and accompanying coronal mass ejections (CMEs). The selection criterion was based on the fact that the only front-side GLE in cycle 24 (GLE 71) had a flare size of M5.1. Only ~37% of the major eruptions from the western hemisphere resulted in large SEP events. Almost the same number of large SEP events was produced in weaker eruptions (flare size <M5.0), suggesting that the soft X-ray flare is not a good indicator of SEP or GLE events. On the other hand, the CME speed is a better indicator of SEP and GLE events because it is consistently high supporting the shock acceleration mechanism for SEPs and GLEs. We found the CME speed, magnetic connectivity to Earth, and ambient conditions as the main factors that contribute to the lack of high energy particle events during cycle 24. Several eruptions poorly connected to Earth (eastern-hemisphere or behind-the-west-limb events) resulted in very large SEP events detected by the STEREO spacecraft. Some very fast CMEs, likely to have accelerated particles to GeV energies, did not result in a GLE event because of poor latitudinal connectivity. The stringent latitudinal requirement suggests that the highest energy particles are likely accelerated in the nose part of shocks. There were also well-connected fast CMEs, which did not seem to have accelerated high energy particles due to possible unfavorable ambient conditions (high Alfven speed, overall reduction in acceleration efficiency in cycle 24).

Changes in Foraging Activity of the Southern Harvester Ant Pogonomyrmex badius (Latreille) in Response to Fire

-The southern harvester ant Pogonomyrmex badius (Latreille) is common in the sandhill habitat of Florida, a habitat strongly influenced by fire. We documented changes in foraging activity of the ant in response to a planned burn in an area of sandhill. Measurements related to foraging activity were made several times before and after burning: number of foraging trunks and direction and length of each trunk, to estimate foraging area; number of individuals emerging from colony entrances; number of individuals outside colony entrances; number of individuals engaged in foraging; and number of items returned to colonies. Only number of individuals emerging from colony entrances and foraging area changed in response to the burn: both increased. We suggest that ecological conditions in the plots, namely the unfavorable ambient conditions often present and the low densities of colonies, in large part dictated the way in which foraging activity could change after the burn. The changes observed may be a general response of the southern harvester ant to changes in resource availability; however, other causes, such as alteration of physical structure in the vicinity of colonies, may underlie changes in foraging activity and these need to be examined.