258 research outputs found
Low cost manufacturing of light trapping features on multi-crystalline silicon solar cells : jet etching method and cost analysis
No full textThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 127-128).An experimental study was conducted in order to determine low cost methods to improve the light trapping ability of multi-crystalline solar cells. We focused our work on improving current wet etching methods to achieve the desired light trapping features which consists in micro-scale trenches with parabolic cross-sectional profiles with a target aspect ratio of 1.0. The jet etching with a hard mask method, which consists in impinging a liquid mixture of hydrofluoric, nitric and acetic acids through the opening of hard mask, was developed. First, a computational fluid dynamics simulation was conducted to determine the desired jet velocity and angle to be used in our experiments. We find that using a jet velocity of 3 m/s and a jetting angle of 45° yields the necessary flow characteristics for etching high aspect ratio features. Second, we performed experiments to determine the effect of jet etching using a photo-resist mask and thermally grown silicon oxide mask on multiple silicon substrates : , , and multi-crystalline silicon. Compared to a baseline of etching with no jet, we find that the jet etching process can improve the light trapping ability of the baseline features by improving their aspect ratio up to 65.2% and their light trapping ability up to 38.1%. The highest aspect ratio achieved using the jet etching process was 0.62. However, it must be noted that the repeatability of the results was not consistent: significant variations in the results of the same experiment occurred, making the jet etching process promising but difficult to control. Finally, we performed a cost analysis in order to determine the minimum efficiency that a jet etching process would have to achieve to be cost competitive and its corresponding features aspect ratio. We find that a minimum cell efficiency of 16.63% and feature aspect ratios of 0.57 are necessary for cost competitiveness with current solar cell manufacturing technology.by Amine Berrada Sounni.S.M.in Technology and PolicyS.M
A Review of the Mycotoxin Enniatin B
No full textMycotoxin enniatin B (ENN B) is a secondary metabolism product by Fusarium fungi. It is a well-known antibacterial, antihelmintic, antifungal, herbicidal, and insecticidal compound. It has been found as a contaminant in several food commodities, particularly in cereal grains, co-occurring also with other mycotoxins. The primary mechanism of action of ENN B is mainly due to its ionophoric characteristics, but the exact mechanism is still unclear. In the last two decades, it has been a topic of great interest since its potent mammalian cytotoxic activity was demonstrated in several mammalian cell lines. Moreover, the co-exposure in vitro with other mycotoxins enhances its toxic potential through synergic effects, depending on the concentrations tested. Despite its clear cytotoxic effect, European Food Safety Authority stated that acute exposure to ENNs, such as ENN B, does not indicate concern for human health, but a concern might be the chronic exposure. However, given the lack of relevant toxicity data, no firm conclusion could be drawn and a risk assessment was not possible. In fact, very few studies have been carried out in vivo and, in these studies, no adverse effects were observed. So, research on toxicological effects induced by ENN B is still on-going. Recently, some studies are dealing with new advances regarding ENN B. This review summarizes the information on biochemical and biological activity of ENN B, focusing on toxicological aspects and on the latest advances in research on ENN B
Migrant Necropolitics at the Table: Civilized Cannibalism in Mahi Binebine\u27s \u3cem\u3eCannibales\u3c/em\u3e
No full textIn Cannibales, the Maghrebi Francophone author Mahi Binebine revisits the encounter between the so-called “cannibals” and the European colonizer in the context of illegal immigration where bodies become commodities exchangeable for social improvements creating a different form of cannibalism. It is no longer the usual dichotomy between the civilized and the savage that is at work but rather a “civilized” European imperialist who feeds himself on a migrant’s flesh. This article argues that this representation works as a “colonial fragment” from the past but contextualized in today’s globalization. Binebine’s morbid depiction of an ambivalent postcolonial cannibalistic encounter translates as a representation of migrants in terms of cannibalistic necropolitics. The illegal migrant has no choice but to be swallowed by a narcissistic exocannibalism which seeks to incorporate what it feeds on to a total unity suggesting a bleak future not only for illegal migrants but for globalization as possibly devouring itself
Ligophorus hamzati Hafidi & Diamanka & Rkhami & Pariselle 2013, n. sp.
No full textLigophorus hamzati n. sp. (Fig. 5) TYPE MATERIAL. — Holotype MNHN HEL315; paratypes MNHN (9) HEL316, BMNH (10) 2012.12.17.4. MATERIAL EXAMINED. — 30 specimens mounted in ammonium picrate-glycerol. TYPE HOST. — Liza grandisquamis (Mugilidae). SITE OF INFECTION. — Gills, between secondary gill lamellae. TYPE LOCALITY. — Grand Lahou Lagoon, Ivory Coast (5°08’11”N, 5°01’33”E). ETYMOLOGY. — Hamzati is given for Hamzat, name of the son of the first author of this article. FIG. 5. – Ligophorus hamzati n. sp.: morphological structures as in Fig. 1. Abbreviations: see Material & Methods. Scale bar: 30 µm. DESCRIPTION Flattened adult, 580 ± 33 (410-537) [30] long and 80 ± 10 (65-116) [30] wide at gonad level, pharynx: 26 (20-33) [28] larger diameter. Haptor well demarcated with 14 marginal hooks: 13 ± 0.9 (8-17) [360] long. Dorsal anchor with guard two time longer than shaft: a = 43 ± 4 (34-50) [60]; b = 34 ± 3 (28-39) [60]; c = 6 ± 0.7 (4-7) [60]; d = 13 ± 1.5 (9-16) [60]; e = 7 ± 0.8 (6-9) [60]. Dorsal bar V-shaped: 20 ± 2 (17-24) [30] long, 4 ± 0.7 (3-6) [30] wide and 7 ± 1.1 (5-10) [30] high. Ventral anchor: a = 42 ± 2 (36-45) [60]; b = 34 ± 2 (31-37) [60]; c = 7 ± 0.8 (5-10) [60]; d = 11 ± 1.3 (8-14) [60]; e = 7 ± 0.6 (6-9) [60]. Ventral bar, 39 ± 3 (32-47) [30] long and 9 ± 2 (6-13) [30] wide, with small antero-median protuberance and two lateral and symmetrical expansions: 10 ± 3 (4-18) [30] apart. MCO as copulatory tube: 92 ± 6 (81-100) [30] long, passes through a tubular accessory piece, 48 ± 7 (38-59) [30] long, with bifurcated distal extremity, each branches bifurcated also. Vagina: 51 ± 10 (21-67) [30] long. REMARKS This species is distinguished from all Ligophorus species by the shape of the accessory piece of the copulatory organ, which is bifurcated two times at its distal extremities. DISCUSSION The co-existence of fish hosts with a great difference in Ligophorus species richness is not exceptional. Euzet & Suriano (1977) observed only one species (Lig. angustus Euzet & Suriano, 1977) from Chelon labrosus (Risso, 1827) in the Mediterranean Sea, whereas the other mullet species may be parasitized by at least two species. Six species were reported from Liza carinata by Dmitrieva et al. (2012) and from Liza subviridis by Soo and Lim (2012), and at least 14 species were reported from M. cephalus by Dmitrieva et al. (2012). Similar differences in monogenean species richness were reported from cichlid hosts in West Africa by Pariselle et al. (2003). These authors drew a parallel between parasite species richness and host genetic diversity, which were both shaped by fluctuations of host populations through bottleneck or vicariant events. Therefore, in the case of Ligophorus from studied African mugilids, only the population of Liza bandialensis, which is endemic to a very limited area in Senegal, may have suffered numerous bottleneck events, leading to reductions in its size, and in turn to the loss of all its monogenean parasites. Among the three other widely distributed Liza species in Africa, Liza falcipinnis, which was infected by only one Ligophorus species, may have had a more stable history (and thus, a lower genetic and parasitic diversity) when compared to Liza grandisquamis, which was infected by three Ligophorus species and Liza dumerili, which according to Berrada Rkhami et al. (1993) was infected by over ten Ligophorus species.Published as part of Hafidi, Fouzia El, Diamanka, Arfang, Rkhami, Ouafae Berrada & Pariselle, Antoine, 2013, New species of Ligophorus (Monogenea, Ancyrocephalidae), parasite of Liza spp. (Teleostei, Mugilidae) off the Northwestern African coast, pp. 215-225 in Zoosystema 35 (2) on pages 222-224, DOI: 10.5252/z2013n2a6, http://zenodo.org/record/516044
Finite Frequency H-infinity Filtering for Discrete-Time Uncertain Systems
No full text14th International Multi-Conference on Systems, Signals & Devices (SSD), Marrakech, MOROCCO, MAR 28-31, 2017International audienceThis paper is concerned with the problem of finite frequency (FF) H-infinity filter design for linear time-invariant discrete-time systems with polytopic uncertainties. Our aim is to design a new filter guaranteeing an H-infinity performance bound in a FF ranges. The H-infinity filter in designed to deal with noises in Low Frequency (LF) domain. By utilizing the Generalized Kalman-Yakubovich-Popov (GKYP) lemma, projection lemma, and we introduce many slack matrices, the conditions on the existence of H-infinity filters for LF range is unified in terms of solving a set of linear matrix inequalities (LMIs). Finally, an illustrative example is provided to show the effectiveness of the proposed method in comparison with the existing methods
SPARK : an educator\u27s look at connection in 21st century American schools
No full textConnection, creativity in the classroom and miracles are possible, even in today\u27s standardized climate. The author gives examples that prove damaged systems can be overcome and difficult situations surmounted. Her hope is that this integrative master\u27s project will show a true exploration of what it means to have an inner voice, to find and free it, and eventually express it
NK and T cells constitute two major, functionally distinct intestinal epithelial lymphocyte subsets in the chicken
No full textNon-mammalian NK cells have not been characterized in detail; however, their analysis is essential for the understanding of the NK cell receptor phylogeny. As a first step towards defining chicken NK cells, several tissues were screened for the presence of NK cells, phenotypically defined as CD8(+) cells lacking T- or B-lineage specific markers. By this criteria, approximately 30% of CD8(+) intestinal intraepithelial lymphocytes (IEL), but <1% of splenocytes or peripheral blood lymphocytes were defined as NK cells. These CD8(+)CD3(-) IEL were used for the generation of the 28-4 mAb, immunoprecipitating a 35-kDa glycoprotein with a 28-kDa protein core. The CD3 and 28-4 mAb were used to separate IEL into CD3(+) IEL T cells and 28-4(+) cells, both co-expressing the CD8 antigen. During ontogeny, 28-4(+) cells were abundant in the IEL and in the embryonic spleen, where two subsets could be distinguished according to their CD8 and c-kit expression. Most importantly, 28-4(+) IEL lysed NK-sensitive targets, whereas intestinal T cells did not have any spontaneous cytolytic activity. These results define two major, phenotypically and functionally distinct IEL subpopulations, and imply an important role of NK cells in the mucosal immune system
On the Relationship between Holding Time and Exit Returns of Venture Capital Firms – A Case Study of a Venture Capital Firm in China
No full textDespite more than two decades of development at a meaningful scale, China’s venture capital (VC) industry has not accumulated sufficient historical experience, and no clear pattern of investment styles regarding preferences for investment stages has emerged. Many firms prefer pre-IPO (initial public offering) projects, while the government tries to shift funds to earlier stages to support the development of technological innovation and small and medium- sized enterprises. From fund managers’ perspective, are there significant differences in the returns when VC investments are made at different stages of projects? This issue is of critical relevance to both the development of the VC industry and policymaking.
Due to the complexity and inaccuracy of industry data, it is difficult to quantify this issue. Based on existing literature and using the historical data of a company in China, this research attempts to ascertain the relationship between VC firms’ project holding time and the returns on the investment. The author formerly worked with S company, which was established in 1999; the firm has by far the largest number of investment projects and most prominent performance among all native Chinese VC firms. As of March 2021, S company had invested in 1,244 projects, including 183 projects that had been publicly listed via IPOs or listed through M&A. These investments are spread across the entire country, cover various industries, and involve all stages of project development. As such, S company offers the best Chinese case for this study.
In this study, multiple regression analyses are performed using the following parameters: absolute return (multiple) and relative return (annualized average return) are the dependent variables; project holding time (from investment to IPO) is the independent variable; and a variety of variables, i.e., IPO board, exit method, project characteristics, and stock issuance intensity (the number of issuances in the year the VC investment was made and went public via an IPO), are used as control variables. The analyses lead to the following conclusions. Absolute return is positively correlated with holding time, and relative return is negatively correlated with holding time; given the projects’ relatively high rates of return, in a time of low interest rates, it would be a sound choice for fund investors to entrust experienced fund managers to invest in early stages of projects and hold the investments for a reasonable amount of time; additionally, IPO board has a significant impact on return, and project size, geographic area in which the project is located, and capital market environment do not have a significant impact on exit return, indicating that the VC industry is insensitive to short-term macro factors and that, to some extent, its operations can transcend investment periods. In addition to the regression analyses, this study reviews other indicators of S company, for example, the historical exit rate and the current value of projects that have not gone public, to examine the relationship between a fund’s overall rate of return and holding time. This study also performs a supplemental analysis using data on peer VC firms, and the results support the above findings. 中国风险投资行业规模化发展 20 多年，还没有形成足够的历史经验、针对 项目投资阶段未形成清晰的风格划分。很多公司倾向于 PREIPO 项目，而政府极 力推动资金向早期转移，扶持科技创新和中小企业的发展。从资金管理人的角度， 投资不同的项目阶段持有不同周期，是否存在收益的明显差异?这个问题对行 业发展和政策导向都有重要的参考意义。
该议题由于行业数据繁杂且不准确而难以量化，本文在参考国内外文献的 基础上，以一个案例公司的历史数据为研究基础，寻找项目持有时间和收益的相 关关系。作者曾就职于 S 公司，该公司成立于 1999 年，是最早从事风险投资、 投资项目数量最多、也是业绩最为突出的中国本土风险投资机构，截止 2021 年 3 月共投资项目 1244 个、直接上市及并购上市项目 183 个，投资项目覆盖全国、 涵盖各阶段各行业、且历史以来投资风格未发生重大变化，是中国本土案例的最 好代表。
本文将上市退出绝对收益(收益倍数)和相对收益(年化平均收益率)分别 作为被解释变量，将项目持有时间(投资到上市)作为解释变量，并使用上市板 块、退出方式、项目特征、发行速度和资本市场热度等多个指标作为控制变量进 行多元回归，得出结论:绝对收益和持有时间正相关，相对收益和持有时间负相 关，鉴于较高的上市项目收益率水平，在低利率时代，基金出资人托付于经验丰 富的管理人，投资较为早期阶段项目并持有适当时间，是一个良好选择。同时， 项目退出板块对收益有明显影响，项目规模和所处区域、资本市场环境等对退出 收益没有明显影响，说明风险投资行业对短期的宏观因素敏感性不强、一定程度 上可以跨越周期。本文进一步参考 S 公司的历史退出率、未上市项目现值等指 标，对基金总体收益和持有时间的关系进行探讨，并对同行业数据进行补充分析， 支持了上述结论。 </p
THE EVOLUTION OF SOCIAL MEDIA INDUSTRY, FROM THE START UP UNTIL NOW, THE VIRTUAL PLANET
No full textTrabajo Fin de Grado leído en la Universidad Rey Juan Carlos en el curso académico 2023/2024. Directores/as: Cristina Pérez PérezSocial media has become this whole virtual planet that we live in.
It completely altered our brains and the way we communicate. We, as civilians, are more reliant on the use of social media platforms for more than just communication. We use them on our day-to-day tasks, and on things that we need or simply because it's an easy access to information. This study analyzes the social and financial effects that social media platforms and social media has nowadays. Studying the development of the industry, the main competitors and the way businesses use social media to their advantage. The author wants to prove that social media platforms are the future. Their constant growth shows up for it and their fast-growing platforms would be considered the best way to communicate what we want the world to see. Whether as a business and using it as a marketing weapon or as a buyer and using it as a search engine
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