检索结果-南通市图书馆

Has global deforestation accelerated due to the COVID-19 pandemic?

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

journal of Forestry Research 2023年第4期34卷 1153-1165页

作者： jonnathan Céspedes janelle M.Sylvester Lisset Pérez-Marulanda Paula Paz-Garcia Louis Reymondin Mehran Khodadadi jhon j.Tello Augusto Castro-nunez The Alliance of Bioversity International and International Center for Tropical Agriculture(CIAT) Km 17 Recta Cali-PalmiraCaliColombia Department of Geosciences and Natural Resource Management University of CopenhagenCopenhagenDenmark Leibniz Centre for Agricultural Landscape Research(ZALF) MünchebergGermany

As the COVID-19 pandemic unfolded,questions arose as to whether the pandemic would amplify or pacify tropical deforestation.Early reports warned of increased deforestation rates;however,these studies were limited to a few months in 2020 or to selected regions.To better understand how the pandemic infl uenced tropical deforestation globally,this study used historical deforestation data(2004–2019)from the Terra-i pantropical land cover change monitoring system to project expected deforestation trends for 2020,which were used to determine whether observed deforestation deviated from expected trajectories after the fi rst COVID-19 cases were reported.Time series analyses were conducted at the regional level for the Americas,Africa and Asia and at the country level for Brazil,Colombia,Peru,the Democratic Republic of Congo and Indonesia.Our results suggest that the pandemic did not alter the course of deforestation trends in some countries(e.g.,Brazil,Indonesia),while it did in others(e.g.,Peru).We posit the importance of monitoring the long-term eff ects of the pandemic on deforestation trends as countries prioritize economic recovery in the aftermath of the pandemic.

关键词： Deforestation COVID-19 Time series Terra-i Drivers of deforestation monitoring

Description of a Propulsion Unit Used in Guiding a Walking Machine by Recognizing a Three-point Bordered Path

在线全文

学校读者我要写书评

暂无评论

Chinese journal of Mechanical Engineering 2016年第6期29卷 1157-1166页

作者： nunez-ALTAMIRANO Diego A jUAREZ-CAMPOS Ignacio MARQUEZ-PEREZ Lucia FLORES-DIAZ Ociel School of Mechanical Engineering Universidad Michoacana de San Nicolas de Hidalgo Morelia Michoacan Mexico

A reconfigurable propulsion unit based on the Peaucellier-Lipkin mechanism has the ability to describe exact straight or curved paths depending on the selected ratio between the lengths of two of its links. The Peaucellier-Lipkin mechanism with one degree of freedom is transformed into a more sophisticated parallel kinematic chain by including four more degrees of freedom. The resulting propulsion unit is able to adapt its kinematic structure and reach instant centers of rotation, in accordance with the presence of three points that border a geometric path. A laser sensor mounted on the body of the machine detects each point. Once the machine has detected the exact location of the border of the road, it walks along a curve parallel to that border. Although the proposed research describes only one propulsion unit or leg, the methodology can be applied to all the legs of the walking machine. The novel 5-DOF leg is able to reach different centers of rotation, providing either the concave or convex arcs that satisfy the basic principle of displacement of walking machines.

关键词： Propulsion unit Peaucellier-Lipkin walking machine straight line mechanism.

Learning the Mapping x→Σi=1^d xi^(2):the Cost of Finding the Needle in a Haystack

在线全文

学校读者我要写书评

暂无评论

Communications on Applied Mathematics and Computation 2021年第2期3卷 313-335页

作者： jiefu Zhang Leonardo Zepeda-nunez Yuan Yao Lin Lin Department of Mathematics University of CaliforniaBerkeleyBerkeleyCA 94720USA Department of Mathematics University of Wisconsin-MadisonMadisonWI 53706USA Department of Mathematics Hong Kong University of Science and TechnologyClear Water BayKowloonHong KongChina Computational Research Division Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA

The task of using the machine learning to approximate the mapping x→Σi=1^d xi^(2)with Xi∈[-1,1]seems to be a trivial one.Given the knowledge of the separable structure of the function,one can design a sparse network to represent the function very accurately,or even exactly.When such structural information is not available,and we may only use a dense neural network,the optimization procedure to find the sparse network embedded in the dense network is similar to finding the needle in a haystack,using a given number of samples of the function.We demonstrate that the cost(measured by sample complexity)of finding the needle is directly related to the Barron norm of the function.While only a small number of samples are needed to train a sparse network,the dense network trained with the same number of samples exhibits large test loss and a large generalization gap.To control the size of the generalization gap,we find that the use of the explicit regularization becomes increasingly more important as d increases.The numerically observed sample complexity with explicit regularization scales as G(d^(2.5)),which is in fact better than the theoretically predicted sample complexity that scales as 0(d^(4)).Without the explicit regularization(also called the implicit regularization),the numerically observed sample complexity is significantly higher and is close to 0(d^(4.5)).

关键词： Machine learning Sample complexity Generalization error

Developmental and Feedforward Control of the Expression of Folate Biosynthesis Genes in Tomato Fruit

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Molecular Plant 2010年第1期3卷 66-77页

作者： jeffrey C. Wallera Tariq A. Akhtar Aurora Lara-nunez jesse F. Gregory lli Ryan R McQuinn james j. Giovannoni Andrew D. Hanson Horticultural Sciences Department University of Florida Gainesville FL 32611 USA Food Science and Human Nutrition Department University of Florida Gainesville FL 32611 USA United States Department of Agriculture-Agricultural Research Service and Boyce Thompson Institute for Plant Research Ithaca NY 14853 USA

Little is known about how plants regulate their folate content, including whether the expression of folate biosynthesis genes is orchestrated during development or modulated by folate levels. Nor is much known about how folate levels impact the expression of other genes. These points were addressed using wild-type tomato fruit and fruit engineered for high folate content. In wild-type fruit, the expression of genes specifying early steps in folate biosynthesis declined during development but that of other genes did not. In engineered fruit overexpressing foreign GTP cyclohy- drolase I and aminodeoxychorismate synthase genes, the expression of the respective endogenous genes did not change, but that of three downstream pathway genes--aminodeoxychorismate lyase, dihydroneopterin aldolase, and mitochondrial folylpolyglutamate synthase--respectively increased by up to 7.8-, 2.8-, and 1.7-fold, apparently in response to the build-up of specific folate pathway metabolites. These results indicate that, in fruit, certain folate pathway genes are developmentally regulated and that certain others are subject to feedforward control by pathway intermediates. Micro- array analysis showed that only 14 other transcripts （of 11 000 surveyed） increased in abundance by two-fold or more in high-folate fruit, demonstrating that the induction of folate pathway genes is relatively specific.

关键词： Folate biosynthesis fruit development metabolic engineering transcript profiling.

Gradient analysis of saline groundwater dynamics along spatial transects in the Chaco

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Gradient analysis of saline groundwater dynamics along spati...

Wind Energy Generation Potential in Union Hidalgo, Mexico： A Preliminary Study

ⅩⅪ International Grassland Congress and the Ⅷ International Rangeland Congress

作者： A.Glatzle L.Reimer G.Roth j.Cobo nunez Iniciativa para la Investigacion y Trans ferencia de Tecnologia Agraria Sostenible（INTTAS） Loma Plata 1045 C.d.c.883 AsuncionParaguay

＜正＞Introduction The transitional zone between the dry and the semi-humid Chaco is characterized by a high table of saline groundwater.Dryland salinity is commonly observed at the edges of seasonally inundated grasslands in landscape depressions without external runoff（so called water camps） surrounded by native drought deciduous thorn bush.So far,little information had been available on groundwater characteristics（depth and conductivity） as related to soil salinity.

关键词： dryland salinity groundwater grassland bushland electrical conductivity soil humidity Chaco

来源： cnki会议评论

在线全文

cnki会议

学校读者我要写书评

暂无评论

journal of Energy and Power Engineering 2011年第2期5卷 149-154页

作者： j.R. Dorrego O. Lastres A. nunez G. Hernfindez U. Miranda R. Saldana Instituto de Estudio de la Energia de la Universidad del ISTMO Tehuantepec Oaxaca Alkxico Centro de Investigacion en Energia UNAM Temixeo Morelos Mexico Gerencia de Energias No Conveneionales Instituto de Investigaciones Electricas Reforma 113 Col. Palmira Cuernavaca Morelos C. P. 62490

Union Hidalgo municipality in Oaxaca State, Mexico, is located in an area with attractive wind potential. For this reason, this paper presents a preliminary study of the technical feasibility of wind power generation in Union Hidalgo, by a micro-study with a higher resolution than that used in Wind Resource Atlas of Oaxaca, published in April 2004. In this work, the wind map of Union Hidalgo was generated using the micro-scale model WAsP 9.1, with a resolution of 50 meters. Wind speed and direction data recorded at 15 m and 32 m agl (above ground level) over four years and seven months in a surface anemometer station were used. With Class 7 wind patterns, the results show values that justify the installation of wind turbines to produce electricity in the area. Estimated capacity factors (55% on average) are comparable with those obtained in wind power plants already operating in areas near Union Hidalgo and sites with high wind potential in other parts of the world. The topography of the study area is predominantly flat, and together with the directional behavior of the wind, which comes from the NNW 44% of the time, this favors the introduction of wind power plants in the area.

关键词：风力发电厂墨西哥联盟风能资源风力涡轮机微观尺度联合集团数据记录

美籍非裔男性与女性左心室肥厚预后价值的比较

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

世界核心医学期刊文摘（心脏病学分册） 2005年第4期1卷 29-30页

作者： nunez E. Arnett D. K. Benjamin E. j. 郭宁

Echocardiographically determined left ventricular(LV) hypertrophy may be a str onger risk factor of cardiovascular disease(CVD) for women than for men, althoug h it is unclear whether reported gender differences are real or attributable to confounding. We evaluated echocardiographic LV hypertrophy(defined as LV mass/he ight 2.7justing for age, body mass index, hyper tension, diabetes mellitus, ratio of total cholesterol to high-density lipoprot ein cholesterol, current smoking, and education level. LV hypertrophy was signif icantly predictive of incident CVD, and the association shown by analyses of mat ched propensity scores was similar in men and women(incidence rate ratio 1.88 vs 1.92, p=0.97 for men, population-attributable risk 0.22 vs 0.26, p< 0.07 for w omen). In the multivariate analysis, we found comparable effect estimates for LV hypertrophy (incidence rate ratio 1.66 vs 2.09, p=0.55 for men; population-att ributable risk 0.24 vs 0.32, p< 0.07 for women). Thus, LV hypertrophy is a stron g predictor of CVD in African-Americans, and the effect of LV hypertrophy on CV D is similar in men and women.

关键词：预后价值心室肥厚冠状动脉血心源性死亡致命性心肌梗死心血管疾病左心室管成形术超声心动图高密度脂蛋白

Randomized Control Trial of Video-Feedback Intervention to Promote Positive Parenting in Lima, Peru： A Pilot Study

在线全文

学校读者我要写书评

暂无评论

Psychology Research 2018年第5期8卷 214-223页

作者： Magaly Nóblega Katherine Fourment j.an nunez del Prado Patricia Bárrig-jó Gabriela Conde Francesco Marinelli Pontifical Catholic University of Peru Lima Peru

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

酶法处理对大豆和葵花籽油脂浸出率的影响

黑龙江粮食 1996年第3期 48-54页

作者： H.Dominguez M.j.nunez j.M.Lema 石永峰甘肃省粮食科学研究所 735000

本文对油籽进行酶法处理能够提高油脂的浸出率问题,经过对大豆和葵花籽这两种油籽用不同配方的酶进行处理时的有关参数,如油籽的粒度、水分、水解时间以及所用酶/油籽的比率等,对浸出率的影响进行了分析,提出了操作参数,供油脂科技工作... 详细信息

本文对油籽进行酶法处理能够提高油脂的浸出率问题,经过对大豆和葵花籽这两种油籽用不同配方的酶进行处理时的有关参数,如油籽的粒度、水分、水解时间以及所用酶/油籽的比率等,对浸出率的影响进行了分析,提出了操作参数,供油脂科技工作者参考。

关键词：酶大豆葵花籽浸出率粒度水分水解时间比率