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Evidence for complete and partial surface renewal at an air-water interface
A wind-wave flume is used to determine the extent to which the thermal boundary layer (TBL) at a wind-forced air-water interface is completely renewed from below. We measure skin temperature, Tskin, radiometrically, temperature immediately below the TBL, Tsubskin, using a temperature profiler, and net heat flux using the gradient flux technique. The Tskin probability density function, p(Tskin), and surface renewal time scale, Ï„, were measured using passive and active infrared imaging techniques, respectively. We find that the mean percentile rank of Tsubskin in p(Tskin) is 99.90, implying that complete surface renewal occurs. This result suggests an alternative to radiometric measurement of Tskin through the simple combination of an infrared camera and an in situ temperature sensor. Comparison of the temperature difference across the TBL to the expected cooling implies that a significant portion of events only partially renew the TBL. This result should impact efforts to improve air-sea transfer models
Concentration fields near air-water interfaces during interfacial mass transport: oxygen transport and random square wave analysis
A new approach to estimation of global air-sea gas transfer velocity fields using dual-frequency altimeter backscatter
Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): C11003, doi:10.1029/2006JC003819.A new approach to estimating air-sea gas transfer velocities based on normalized backscatter from the dual-frequency TOPEX and Jason-1 altimeters is described. The differential scattering of Ku-band (13.6 GHz) and C-band (5.3 GHz) microwave pulses is used to isolate the contribution of small-scale waves to mean square slope and gas transfer. Mean square slope is derived for the nominal wave number range 40–100 rad m−1 by differencing mean square slope estimates computed from the normalized backscatter in each band, using a simple geometric optics model. Model parameters for calculating the differenced mean square slope over this wave number range are optimized using in situ optical slope measurements. An empirical relation between gas transfer velocity and mean square slope, also based on field measurements, is then used to derive gas transfer velocities. Initial results demonstrate that the calculated transfer velocities exhibit magnitudes and a dynamic range which are generally consistent with existing field measurements. The new algorithm is used to construct monthly global maps of gas transfer velocity and to illustrate seasonal transfer velocity variations over a 1-year period. The measurement precision estimated from >106 duplicate observations of the sea surface by TOPEX and Jason-1 altimeters orbiting in tandem is better than 10%. The estimated overall uncertainty of the method is ±30%. The long-term global, area-weighted, Schmidt number corrected, mean gas transfer velocity is 13.7 ± 4.1 cm h−1. The new approach, based on surface roughness, represents a potential alternative to commonly used parameterizations based on wind speed.Financial support for this research from the
National Aeronautics and Space Administration through Jet Propulsion
Laboratory contract 961425 and the NOAA Global Carbon Cycle Program
under grant NA16GP2918, Office of Global Programs is gratefully acknowledged
On the use of finite strip method for buckling analysis of moderately thick plate by refined plate theory and using new types of functions
Study on stability and free vibration behavior of porous FGM beams
International audienceIn this paper, buckling and free vibration of imperfect, functionally graded beams, including porosities, are investigated, using a higher order shear strain theory. Due to defects during the manufacturing process, micro porosities may appear in the material, hence the appearance of this imperfection in the structure. The material properties of the beams are assumed to vary regularly, with power and sigmoid law, in the direction of thickness. A novel porosity distribution affecting the functionally graded volume fraction is presented. For the compact formulation used for cementite-based materials and already used in P-FGM, we have adapted it for the distribution of S-FGM. The equations of motion in the FG beam are derived using Hamilton's principle. The boundary conditions for beam FG are assumed to be simply supported. Navier's solution is used to obtain the closed form solutions of the FG beam. The numerical results of this work are compared with those of other published research to verify accuracy and reliability. The comparisons of different shear shape functions, the influence of porosity, thickness and inhomogeneity parameters on buckling and free vibration of the FG beam are all discussed. It is established that the present work is more precise than certain theories developed previously. Copyright © 2022 Techno-Press, Ltd
Induced heat transfer from human skin: its relationship to blood perfusion in the tissue
Induced heat transfer from human skin: its relationship to blood perfusion in the tissue
Adjustment to College in the United States: Perceptions of Qatari Students
Given the rapid growth of Qatar's economy over recent decades, workforce demand for highly-skilled Qatari nationals has increased (Berrebi, Martorell, & Tanner, 2009; Qatar General Secretariat for Development Planning, 2008). There is therefore a great deal of interest in supporting Qatari student success at high-quality post-secondary educational institutions, both in Qatar and abroad. An increasing number of Qatari post-secondary students, particularly males, are specifically choosing to attend college in the United States, with 1,191 Qatari college students studying abroad in the US (Institute of International Education, 2014). Because these Qatari students are earning degrees abroad for the purpose of fulfilling critical jobs when they return, it is important to understand factors contributing to the academic persistence and performance of Qatari students in the US. This qualitative study is part of a collaborative research effort undertaken by investigators based in the United States and Qatar to better understand Qatari student perspectives on their post-secondary adjustment and success. Here, we report findings from structured interviews with Qatari nationals studying abroad in the US, all of whom were males who were, or had recently been, undergraduates at state universities and/or community colleges in Oregon (n = 21). Approximately two-thirds were in business or economics programs and about a third in STEM programs (science, technology, engineering, or mathematics). Most of the interviews were conducted in Arabic and translated into English for transcription, coding, and thematic analysis (Braun & Clarke, 2006). The goal of the study described here was to augment the existing literature about international college student persistence and academic performance with a qualitative, open-ended exploration of Qatari students' perceptions of the barriers to, and facilitators or potential facilitators of, their adjustment to college in the United States. In general, study findings resonate with much of what is known about the adjustment experiences of international students in unfamiliar settings-specifically regarding second language proficiency, other academic factors, social support, and daily living experiences-with additional lessons learned for specifically supporting Qatari students in English-speaking post-secondary institutions. For example, second language proficiency consistently appears in the literature as the most important factor influencing international student adjustment, particularly since a lack of proficiency in the host language can interact with other potential stressors in both academic and sociocultural domains. In the present study, Qatari students almost universally reported challenges related to mastering English to an extent that would make it possible for them to undertake college-level coursework successfully. In particular, students noted that they lacked the specialized vocabulary needed for college-level work, and many lacked confidence in their ability to communicate with other students and professors. These experiences contributed to a sense of isolation and caused problems in daily situations in the community, such as shopping or social settings with English-speaking students. Students also described how their college adjustment was hampered by problems with English despite having participated in classes and programs-both in Qatar and abroad-that were intended to improve their English language proficiency. Students also reported factors that facilitated adjustment by helping them overcome perceived English deficiencies, and many said their English improved as a result of being in English-only environments, for example, through a home stay program, by seeking out English-speaking friends, or through taking classes with non-Arabic speaking students or professors. Beyond language difficulties, many other academic factors can pose challenges to international students' adjustment. Studies have documented several types of stressors resulting from a mismatch between students' previous academic experiences and what is required for success in the host institution, and many of these are reflected in the Qatari student experiences in Oregon. For example, students may be under prepared in terms of mastery of prerequisite material, may be accustomed to teaching and learning styles that differ from those typical of Western higher education, and may experience additional academic stress if they feel that they are failing to live up to family expectations and/or the expectations of a sponsoring organization in their home country (Smith & Khawaja, 2011). In this study, it was common for students to describe themselves as academically unprepared for college in the US, noting differences in expectations between secondary school in Qatar and college in the US, both in terms of the level of effort required, and the expectation for the student to be responsible for his own education. Students also reported academic stress and confusion related to unfamiliar requirements and policies, insufficient or ill-informed advising, or professors that did not understand how to teach international and/or Arab students. Overall, the main facilitators of successful academic adjustment cited by the Qatari students were interactions with helpful students, faculty and staff. Many emphasized that other Arab students were their first line of academic support, some received helpful support from American tutors and advisors, and smaller classes were seen as beneficial. Social support is another key theme that appears frequently in the literature on international students' adjustment (Araujo, 2011; Smith & Khawaja, 2011; Zhang & Goodson, 2011). A lack of social support can contribute to feelings of loneliness, homesickness and/or isolation, and it can also mean that students have fewer resources to draw on in their coping efforts. The literature consistently reflects that international students tend to rely on support from "co-nationals" or "co-culturals,"- i.e., other students from similar backgrounds-though relationships with students from the host country are also important contributors to international students' adjustment and well-being (Al-sharideh, Goe, & Al-sharideh, 2014; Du & Wei, 2015; Hirai, Frazier, & Syed, 2015; Zhang & Goodson, 2011). In this study, the Qatari students consistently described how they relied on social support to combat loneliness and isolation, but also for practical information and advice. Almost universally, other Qatari students, as well as students from other Gulf or Arab countries, were seen as the key source of social support. However, these students typically reported having no American friends, though this tended not to be viewed as a problem. Indeed, students described spending most of their discretionary time with co-culturals, and while this was primarily viewed very positively, it could also be a distraction from academic responsibilities. Lastly, research on international student adjustment frequently includes a focus on daily living challenges that arise in an environment that is structured by unfamiliar rules, laws, mores and expectations. However, these difficulties were only somewhat reflected in this study. While the students reported some challenges related to housing and generally feeling "shy" when interacting in the community, the most stressful situations appeared to stem from interactions with formal authority Figs. (immigration officials and the police). More frequently, however, students commented that they felt comfortable and welcomed by Americans and by the Oregon towns and communities in which they were studying. Students in the university towns found them "safe," "calm," "quiet," and "comfortable," while students in Portland noted that they had chosen to attend school there because the city had a reputation for having little crime, and because the residents were seen as helpful and welcoming. Although this study is limited by the small sample size and the fact that all of the students were attending college in Oregon, findings suggest avenues for further exploration. A key area for future investigation would be the development and testing of programs, policies and interventions consistent with study findings and existing research, and also, in most cases, consistent with what the participants themselves suggested as ways of improving Qatari students' adjustment experiences. For example, students offered several recommendations to reduce adjustment stress through efforts undertaken in Qatar to improve students' preparation prior to their departure for the US. Many comments focused on the need for improved instruction in English, with suggestions regarding how college preparatory programs could be improved to focus on academic writing and reasoning in English. Further, students and researchers alike recommend secondary school information sessions and intensive pre-departure orientation programs focused on what to expect academically, socially, legally, and culturally when studying and living in the US, with experienced study abroad students playing an important role in these efforts. Additionally, some students reported very positive experiences from homestay programs in the US, specifically for accelerated language practice and practical support adjusting to the new country, and such experiences could be better developed and marketed to pre-departure Qatari students.qscienc
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