Outdoor Studies Research Articles

Polarized skylight-based heading measurements: a bio-inspired approach.

Many insects such as desert ants, crickets, locusts, dung beetles, bees and monarch butterflies have been found to extract their navigation cues from the regular pattern of the linearly polarized skylight. These species are equipped with ommatidia in the dorsal rim area of their compound eyes, which are sensitive to the angle of polarization of the skylight. In the polarization-based robotic vision, most of the sensors used so far comprise high-definition CCD or CMOS cameras topped with linear polarizers. Here, we present a 2-pixel polarization-sensitive visual sensor, which was strongly inspired by the dorsal rim area of desert ants' compound eyes, designed to determine the direction of polarization of the skylight. The spectral sensitivity of this minimalistic sensor, which requires no lenses, is in the ultraviolet range. Five different methods of computing the direction of polarization were implemented and tested here. Our own methods, the extended and AntBot method, outperformed the other three, giving a mean angular error of only 0.62° ± 0.40° (median: 0.24°) and 0.69° ± 0.52° (median: 0.39°), respectively (mean ± standard deviation). The results obtained in outdoor field studies show that our celestial compass gives excellent results at a very low computational cost, which makes it highly suitable for autonomous outdoor navigation purposes.

Performance analysis of PV panels based on different technologies after two years of outdoor exposure in Fukushima, Japan

Nominal values reported for PV Systems are measured at carefully-controlled test conditions. While being strictly standardized to achieve a good benchmarking capability for different, newly manufactured panels; these conditions hardly exist in real-life implementation sites. To add to the problem, highly varying climate, precipitation, scorching sun and freezing snow wear out these systems in the long run. Therefore, actual performance of any PV system is, inevitably, different than those reported under standard test conditions. In order to have a more accurate expectation of power generation over the lifetime of a system, it is important to know the impact of local conditions and the resilience of PV panels to them. To this end, several outdoor performance studies have been reported around the world and the literature is growing. This work reports the impact of Fukushima's weather, which is known to be windy in autumn and have heavy snowfall in the winter, on the installed PV systems. Also, numerous panels belonging to different PV technologies and manufacturers are installed side-by-side to compare the variation in their performances and, thus, benchmark their quality and resilience. To investigate possible impact of micro-climate, or local geographical conditions, two test sites in Fukushima Prefecture are utilized. Finally, a sample PV system calculation is presented to showcase the impacts of these findings on a PV system in planning and operation stages.

Prediction of ground reaction forces in level and incline/decline walking from a multistage analysis of plantar pressure data

Knowing the ground reaction forces (GRFs) during walking has various biomechanical applications in injury prevention, gait analysis, as well as prosthetic and footwear design. The current study presents a method for predicting the GRFs in level and incline/decline walking that may be used in various outdoor biomechanics studies geared towards the above applications. The method was developed to predict the complete set of GRFs at walking inclinations of 0°, ±5°, ±10°, ±15°, and ±20°. Plantar pressure insoles were used to obtain inclination-specific, linear regression models based on three periods of gait stance phase, and the model-determined GRFs were compared with those measured from a forceplate. The three periods were determined based on the observed shifting of load-bearing insole sensors from heel to forefoot during walking, i.e., heel-strike, midstance, and toe-off. Six subjects wearing minimalist shoes fitted with plantar pressure insoles containing 99 pressure sensors performed ten walking trials at each of the aforementioned inclinations on an adjustable ramp with an embedded forceplate. Data from contact of the instrumented shoes with the forceplate were used to create linear regressions to transform insole pressure data into a complete set of GRFs. The root mean square error (RMSE) over peak recorded values were on average 10%, 3%, 21% for level walking and 11%, 4%, 23% for ramp walking in the respective anteroposterior, vertical, and mediolateral directions. The multistage linear regression model developed in the current study may be an acceptable option for estimating GRFs during walking in various environments without the restraint of a forceplate.

Embodied life-long learning in nature, narratives and older bodies -‘quit or crash’

ABSTRACTThis paper considers the significance of exploring the experiences and perspectives of older people who choose to participate in nature-based physical activities in evocative and imaginative ways. It highlights the need for research in outdoor studies to take seriously the turn to the body and the senses that is occurring in much social science and physical culture research, together with recognising the changing demographics in Western cultures which show a significant increase in the proportion of older people. The body has been separated from mind, emotions and feelings in much research in outdoor studies, and ageing studies and physical activity. For the most part, ageing studies have tended toward physiological perspectives with the dominance of medical research promoting biological empirical approaches to investigations. This paper considers theoretical perspectives which are embodied and emplaced and how such frameworks might contribute to the advancement of research on ageing and the outdoors. Sensory lived experiences are considered.

Updated evaluation of sonic boom noise metrics

There is no internationally agreed-upon standard noise metric that can be used to quantify sonic boom levels from overflight of supersonic aircraft. Several laboratory studies have investigated perception of sonic booms in outdoor environments, as well as in indoor environments, where transmission loss alters the spectral content and level of the sonic boom and additional factors such as secondary rattle noise and vibration affect perception. Each study has previously been evaluated separately for performance of noise metrics, and the results do not clearly indicate a preferred metric. Meta-analyses have also been performed to evaluate the performance of metrics across five of these studies. An additional sixth study of human response that incorporates rattle noise resulting from sonic booms at representative levels was recently conducted and has been added to the meta-analysis. The analysis considered thirteen metrics with three meta-analysis methodologies: individual subject ratings for indoor studies, mean ratings for indoor studies, and mean ratings for both indoor and outdoor studies. Considering both indoor and outdoor studies, this latest analysis confirmed previous results on the five metrics with highest correlation (r2) across studies: PL, BSEL, DSEL, ESEL, and ISBAP (Indoor Sonic Boom Annoyance Predictor).

Current Status of Outdoor Lifetime Testing of Organic Photovoltaics.

Performance degradation is one of the key obstacles limiting the commercial application of organic photovoltaic (OPV) devices. The assessment of OPV stability and lifetime are usually based on simulated degradation experiments conducted under indoor conditions, whereas photovoltaic devices experience different environmental conditions under outdoor operation. Besides the intrinsic degradation of OPV devices due to the evolution of optoelectronic and morphological structure during long‐term operation, outdoor environmental changes can impose extra stresses and accelerate the degradation of OPV modules. Although outdoor studies on long‐term OPV stability are restricted by the long data collection times, they provide direct information on OPV stability under mixed degradation stresses and are therefore invaluable from the point of view of both research and practical application. Here, an overview of the current status of outdoor lifetime studies of OPVs is provided. After a summary of device lifetime extrapolated from indoor studies, outdoor lifetime testing platforms are introduced and the operational lifetime of various OPV devices are reviewed. The influence of climate and weather parameters on device performance and burn‐in phenomena observed during the degradation of OPVs is then discussed. Finally, an outlook and directions for future research in this field are suggested.

A Review of Airborne Particulate Matter Effects on Young Children’s Respiratory Symptoms and Diseases

Exposure to airborne fine particulate matter (PM2.5) carries substantial health risks, particularly for younger children (0–10 years). Epidemiological evidence indicates that children are more susceptible to PM health effects than adults. We conducted a literature review to obtain an overview of existing knowledge regarding the correlation of exposure to short- and long-term PM concentrations with respiratory symptoms and disease in children. A collection of scientific papers and topical reviews were selected in cooperation with two experienced paediatricians. The literature review was performed using the keywords “air pollution”, “particulate matter”, “children’s health” and “respiratory” from 1950 to 2016, searching the databases of Scopus, Google Scholar, Web of Science, and PubMed. The search provided 45,191 studies for consideration. Following the application of eligibility criteria and experts’ best judgment to titles and abstracts, 28 independent studies were deemed relevant for further detailed review and knowledge extraction. The results showed that most studies focused mainly on the effect of short-term exposure in children, and the reported associations were relatively homogeneous amongst the studies. Most of the respiratory diseases observed in outdoor studies were related to changes in lung function and exacerbation of asthma symptoms. Allergic reactions were frequently reported in indoor studies. Asthma exacerbation, severe respiratory symptoms and moderate airway obstruction on spirometry were also observed in children due to various sources of indoor pollution in households and schools. Mixed indoor and outdoor studies indicate frequent occurrence of wheezing and deterioration of lung function. There is good evidence of the adverse effect of short-term exposure to PM on children’s respiratory health. In terms of long-term exposure, fine particles (PM0.1–PM2.5) represent a higher risk factor than coarse particles (PM2.5–PM10). Additional research is required to better understand the heterogeneous sources and the association of PM and adverse children’s health outcomes. We recommend long-term cooperation between air quality specialists, paediatricians, epidemiologists, and parents in order to improve the knowledge of PM effects on young children’s respiratory health.

Assessing Compatibility of Isaria fumosorosea and Buprofezin for Mitigation of Aleurodicus rugioperculatus (Hemiptera: Aleyrodidae): An Invasive Pest in the Florida Landscape.

Rugose spiraling whitefly (RSW), Aleurodicus rugioperculatus Martin (Hemiptera: Aleyrodidae) is a new invasive whitefly pest in the Florida landscape, known to feed on a wide range of plants including palms, woody ornamentals, shrubs, and fruits. With the objective to find an alternative to neonicotinoid insecticides, and develop an ecofriendly management program for RSW, in the current study we evaluated the efficacy of a biopesticide containing the entomopathogenic fungi, Isaria fumosorosea Wize (Hypocreales: Clavicipitaceae), and an insect growth regulator buprofezin applied alone and in combination under laboratory and field conditions. Before assessing the two products, their compatibility was studied at six different concentrations of buprofezin. No significant inhibitive effect of buprofezin was observed on I. fumosorosea spore germination, and the average linear growth of the colony measured 14 d postinoculation. Under laboratory conditions, I. fumosorosea treatments (alone or mixed with buprofezin) provided higher RSW mortality than buprofezin alone. However, in both outdoor cage studies, the efficacy of buprofezin treatments (alone or mixed with I. fumosorosea) was higher than I. fumosorosea alone. A significant reduction in RSW population was reported for more than 5 wk in buprofezin alone and more than 7 wk in the combination treatments. In fall of 2014 and summer of 2015, the mean whitefly mortality observed during the 10-wk assessment period was 52.4 and 42.1% for I. fumosorosea, 79.6 and 79.0% for buprofezin, and 87.6 and 84.3% in mixed treatments, respectively. Results suggest that buprofezin can offer an effective alternate in the battle against invasive whiteflies such as RSW in Florida ecosystems, either as a stand-alone strategy or in an integrated approach.

Shelf life and outdoor degradation studies of organic bulk heterojunction solar cells

We studied the degradation of different types of bulk heterojunction devices, in which the materials comprising the active layer and/or the materials used for the back electrode are varied. The devices are deposited on ITO covered glass and have the structure PEDOT:PSS/BHJ/Me, where PEDOT:PSS is the hole transport layer, BHJ (bulk heterojunction) is the active layer comprising a polymer donor (e.g. PTB7, PCDTBT) and a fullerene derivative acceptor (e.g. PC60BM, PC70BM) deposited by spin coating, Me is the metal back contact, which is either Ag or Al deposited by magnetron sputtering or thermal evaporation. The device performance was monitored after storage in the dark at ambient conditions by following the evolution of the J-V curve over time. Results of real conditions outdoor degradation studies are also presented. The stability of the different solar cell structures studied is compared.

The Impact of Transculturality on Student Experience of Higher Education

Background: Higher education outdoor studies programs retain a critical interest in student experiences as they seek to prepare citizens in a globalized, yet simultaneously neo-nationalist, world. Purpose: This research explored the impact of transculturality on the student experience of outdoor studies in the Transcultural European Outdoor Studies (TEOS) Masters, a course hosted by three universities in three countries. Methodology/Approach: A longitudinal study of the student experience, using a conceptual framework of self, place, transculturality, and outdoor learning theory underpins the research. Semistructured online interviews and one face-to-face retrospective interview were conducted with four participants throughout the course (Semesters 1, 2, 3), plus an additional five participants prior to the end of Semester 3. Findings/Conclusions: The findings elucidate students’ transcultural self-growth and transcultural capabilities, including resilience, intelligence, and fatigue. Implications: Although challenges exist for course design, considerations of transcultural pedagogy and curricula, reflective practices, support for students and teaching staff, cultural learning experiences (including language acquisition), and a willingness to move beyond traditional models of curricula at the university level are recommended.

What kind of outdoor educator do you want to become? Trying something different in outdoor studies in higher education

This paper seeks to explore a way of responding to tensions present in formal education and outdoor education in UK higher education. Separation of the doing from the knowing could perhaps be limiting students’ ability to become reflective practitioners and respond creatively to an ever-changing modern world. A different way of organising the curriculum through the concept of ‘occupations’ was the innovation and basis for an action research approach, with data gathered through the authors’ observations, logs and diaries. Findings suggested that not only is the connection between education and experience important, the relationship with the landscape that it takes place in is central, in conjunction with the social context. Implications are that agency and autonomy within the learning experience leads to increased motivation and understanding that the process can be open and emergent and about change.

The laboratory environmental algae pond simulator (LEAPS) photobioreactor: Validation using outdoor pond cultures of Chlorella sorokiniana and Nannochloropsis salina

A bench-scale photobioreactor system, the Laboratory Environmental Algae Pond Simulator (LEAPS), was designed and constructed to simulate outdoor pond cultivation for a wide range of geographical locations and seasons. The LEAPS consists of six well-mixed glass column photobioreactors submerged in a temperature controlled waterbath (−2°C to >60°C) and illuminated from above by a programmable multicolor LED lighting system (0 to 2500μmol/m2-s). Measured incident light intensities and water temperatures deviated from the respective light and temperature setpoints on average only 2.3% and 0.9%, demonstrating accurate simulation of light and temperature conditions measured in outdoor ponds. In order to determine whether microalgae strains cultured in the LEAPS exhibit the same linear phase biomass productivity as in outdoor ponds, Chlorella sorokiniana and Nannochloropsis salina were cultured in the LEAPS bioreactors using light and temperature scripts measured previously in the respective outdoor pond studies. For Chlorella sorokiniana, the summer season biomass productivity in the LEAPS was 6.6% and 11.3% lower than in the respective outdoor ponds in Rimrock, Arizona, and Delhi, California; however, these differences were not statistically significant. For Nannochloropsis salina, the winter season biomass productivity in the LEAPS was 9.2% higher than in the respective outdoor ponds in Tucson, Arizona, a difference shown to be not statistically significant. Potential reasons for the positive or negative divergence in LEAPS performance, relative to outdoor ponds, are discussed. To demonstrate the utility of the LEAPS in predicting productivity, two other strains – Scenedesmus obliquus and Stichococcus minor – were evaluated using the summer season script for Rimrock, Arizona. For both strains, the productivity was around 11.6g/m2-day at 25cm culture depth. In conclusion, the LEAPS is an accurate pond simulator and thus offers a reliable, fast, and cost-effective way to screen microalgae strains and operating conditions for high biomass productivity and co-product yields.

The journey as a transcultural experience for international students

An international two-year Erasmus Mundus MA, Transcultural European Outdoor Studies (TEOS), uses the journey as a central metaphorical concept, the “peregrinatio academica”, and experiential pedagogy. Students study human nature interactions through the lens of outdoor education and recreation while travelling for a semester at a time in three European countries: England, Norway and Germany. We argue that the transcultural concept is facilitated by the diverse nationalities of the student cohort and the concept and experience of the journey. Empirical evidence from student feedback, course discussions, and staff reflections is used to explore the ways in which the programme elucidates ideas of expert and Eurocentric knowledge of landscape and learning by valuing individual knowledge constructions and new research. Simultaneously, we argue that the typical European “gaze” on the “other” somehow is reversed as “others” gaze at European cultures, and, to some degree, contribute to destabilizing culturally taken-for-granted knowledge. This offers new opportunities for a more nuanced transcultural exploration of human nature interactions in diverse landscapes and cultures. We conclude that the knowledge and skills developed by this programme supports the development of “transculturalized” students with the enhanced capacity to shift between and discuss diverse positions and ways of viewing and knowing.

Construction of Bacillus thuringiensis Simulant Strains Suitable for Environmental Release

For a surrogate bacterium to be used in outdoor studies, it is important to consider environmental and human safety and ease of detection. Recently, Bacillus thuringiensis, a popular bioinsecticide bacterium, has been gaining attention as a surrogate bacterium for use in biodefense. In this study, we constructed simulant strains of B. thuringiensis with enhanced characteristics for environmental studies. Through transposon mutagenesis, pigment genes were inserted into the chromosome, producing yellow-colored colonies for easy detection. To prevent persistence of spores in the environment, a genetic circuit was designed to produce a spore without sporulation capability. Two loxP sites were inserted, one on each side of the spo0A gene, which encodes a sporulation master regulator, and a sporulation-dependent Cre expression cassette was inserted into the chromosome. This genetic circuit successfully deleted spo0A during sporulation, producing spores that lacked the spo0A gene. In addition, two major α/β-type small acid-soluble spore protein (SASP) genes, predicted by synteny analysis, were deleted. The spores of the mutant strain showed increased UV-C sensitivity and quickly lost viability when tested in a solar simulator. When the spores of the mutant strain were administered to the lungs of BALB/c mice, cells were quickly removed from the body, suggesting enhanced in vivo safety. All strains constructed in this study contain no antibiotic resistance markers and all heterologous genes were inserted into the chromosome, which are useful features for simulants to be released into the environment.IMPORTANCEB. thuringiensis has recently been receiving increasing attention as a good spore simulant in biodefense research. However, few studies were done to properly address many important features of B. thuringiensis as a simulant in environmental studies. Since spores can persist in the environment for years after release, environmental contamination is a big problem, especially when genetically engineered strains are used. To solve these problems, we report here the development of B. thuringiensis simulant strains that are capable of forming yellow colonies for easy detection, incapable of forming spores more than once due to a genetic circuit, and lacking in two major SASP genes. The genetic circuit to produce a spore without sporulation capability, together with the deletion of SASP genes, ensures the environmental and human safety of the simulant strains developed in this study. All of these features will allow wider use of B. thuringiensis as a simulant for Bacillus anthracis in environmental release studies.

Laboratory bioassays and field-cage trials of Metarhizium spp. isolates with field-collected Mormon crickets (Anabrus simplex)

The Mormon cricket (MC) is an important pest in the western United States. This study evaluated the virulence in the laboratory of 32 isolates of Metarhizium spp. towards field-collected MCs. Additionally, four isolates were tested in outdoor field-cage studies. All 32 Metarhizium isolates were pathogenic towards the MC (could induce some mortality in the laboratory), including four isolates of the grasshopper-specialist species M. acridum. Virulence varied considerably among the isolates. Field studies, conducted in 2008–2009, showed a statistically significant effect of fungal treatments in both years. Pairwise comparison of the survival curves, however, revealed that, in 2008, three of the isolates did not differ statistically from the non-fungus control treatment. In 2009, all three of the isolates tested had significantly lower survival rates than the control treatment: MCs exposed to M. robertsii isolate DWR 346 had the lowest survival with a LT50 of 16 days. We hypothesize that the poor field performance resulted from a combination of negative environmental effects and isolate selection, and propose that further field studies with additional isolates are needed to identify an efficacious fungal agent for MC biocontrol.

Outdoor Orientation Programs: A Critical Review of Program Impacts on Retention and Graduation

Outdoor orientation programs have a growing literature demonstrating positive impacts with students transitioning to college (Bell, Gass, Nafizer, & Starbuck, 2014). One of the most valued outcomes for colleges and universities is retention of students until successful graduation. This is an outcome few outdoor orientation researchers have studied, but one that many programs claim to influence. This paper provides an overview of the literature of outdoor orientation programs retention studies, with specific attention placed on selection bias. This study used a control group (randomized selection), a convenience group (nonparticipants), and a comparison group (matched by covariates) to assess the differences in retention outcomes. Findings indicate (a) similarities between sampling through random selection and covariate matching, but not by convenience sampling and (b) generally positive retention results for participation in outdoor orientation programs, including small effect sizes for retention (OR = 1.91–2.38) and graduation (OR = 1.07–1.81), but few statistically significant results (p < .05).

Root architecture of sorghum genotypes differing in root angles under different water regimes

ABSTRACTPlant root architecture offers the potential for increasing soil water accessibility, particularly under water-limited conditions. The objectives of this study were to evaluate the root architecture in two genotypes of sorghum (Sorghum bicolor (L.) Moench) differing in root angles and to assess the influence of different deficit irrigation regimes on root architecture. The response of two sorghum genotypes, ‘Early Hegari-Sart’ (EH; steep root angle) and ‘Bk7’ (shallow root angle) to four irrigation treatments was investigated in two replicated outdoor studies using large pots. The results indicated that EH possessed steeper brace and crown root angles, fewer brace roots, greater root biomass, and root length density than Bk7 at deeper soil depths (i.e., 15–30 and 30–45 cm) compared with a shallower depth (i.e., 0–15 cm). Across the soil profile, EH had greater root length density and length of roots of small diameter (<1 mm) than Bk7. Accordingly, EH showed more rapid soil-water capture than Bk7. Different levels of irrigation input greatly affected root architecture. Severe deficit irrigation (25% of full crop transpiration throughout the season) increased the angle and number of crown roots, root biomass, and root length density compared with 75 and 100% of full crop transpiration treatments. Consequently, root system architecture can be effectively manipulated through both genotypic selection and irrigation management to ensure optimal performance under different levels of soil available water.

Anovel experimental technology for testing efficacy of air purifiers on pollen reduction.

BackgroundAllergenic pollen exposure is mostly seen as an outdoor phenomenon but studies have shown an indoor exposure: different pollen species including birch and grass pollen in houses, schools, and shops are leading to long-lasting symptoms even after the pollen season because pollen settle on surfaces and re-enter the indoor air depending on ventilation. To reduce indoor pollen load, windows need to be closed and devices should be used: as pure wiping and cleaning of surfaces is mostly not sufficient, air cleaners may be helpful in reducing pollen counts in indoor environment.ObjectiveThe efficacy of an air cleaner is usually described by the filtration rate of standard dust particle sizes which is not necessarily related to clinical efficacy.MethodsA novel study design was developed using the technical equipment of a new mobile exposure chamber to investigate participants with allergic rhinitis (individual observational, controlled, prospective, single arm study).ResultsThe tested air cleaner reduced the grass pollen-induced (4000 grass pollen/m3 over 90 min) nasal symptoms (total nasal symptom score) significantly from 6 and 4 points (1st and 2nd exposure in sham run) to less than 1 point when air cleaner was activated.ConclusionsThe novel study protocol is suitable for testing efficacy of air cleaners and the tested air cleaner is effective in reducing clinical symptoms due to grass pollen in an indoor environment.

Corrosion Behavior of Al 6063 in Qatar's Desert and Marine Environments

Aluminum and its alloys have been widely used outdoors, especially in construction, electrical engineering and other applications, due to their high corrosion resistance, thermal and electrical conductivity and relatively low cost. The corrosion behavior of aluminum alloys indoor was significantly investigated compared to the outdoor studies. In addition, there is no investigation so far regarding atmospheric corrosion either in marine or desert areas in Qatar.The aim of this article is to investigate the atmospheric corrosion behavior for different exposure times (six and twelve months) of welded and non-welded Al 6063 alloy with and without crevices at seven different sites in Qatar State that represent desert, industrial, coastal and marine environments. Avergae pit densities, pit depths, pit mouth areas and aspect ratios, pitting factor and corrosion rates for the alloy at each location were measured. In addition, electrochemical characterization techniques were used in non aggressive for the collected coupons to examine the effect of exposure on the naturally formed oxide layer. Furthermore, scanning electron microscope (SEM) coupled with energy dispersive X-ray (EDX) was used to study the susceptibility of studied alloys to intergranular corrosion (IGC) and the effect of sulfur compounds and chloride ions concentration on the suceptibility for this type of corrosion. The results showed that the number, the size and the depth of pits depend on the aggressiveness of the site environment. In addition, Al 6063 alloy has the tendency for IGC at the different environments. Chloride ions were responsible for the pitting initiation while, sulfur compounds were responsible for IGC propagation. The rate of corrosion for Al 6063 alloy specimens from different sites follows the following order: North field (marine) > Ras Laffan (on shore) > Seaside Mesaieed (on shore) > Halul Island (on Shore) > Industrial Mesaieed > Dukhan (on shore) > Desert. Figure 1

Aiming for Progress in Understanding Underwater Noise Impact on Fish: Complementary Need for Indoor and Outdoor Studies.

Anthropogenic noise can be detrimental to aquatic life through physical harm and behavioral impact. Physical harm to fish only occurs very close to typically brief but high-power sources. Behavioral impact occurs at more moderate levels and is spatially and temporally much more widespread. More studies are needed to get a better understanding of the behavioral impact on fish. Indoor and outdoor studies vary in their acoustic and behavioral validity and in the amount of experimental control. Although each approach has its limitations, scientific progress and applied insights will depend on the exploitation of their complementary potential.