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91.
E. Da Ponte M. Fleckenstein P. Leinenkugel A. Parker N. Oppelt C. Kuenzer 《International journal of remote sensing》2013,34(12):3196-3242
The tropical forest cover has varied greatly over the last few decades. The rapid advance of agricultural crops and illegal clearings in natural areas has resulted in the conversion of the majority of the world’s forest into desolated patches. Although rates of deforestation have decreased compared to previous years, forest loss still remains a crucial concern. Latest studies conducted on a global scale identified the Latin American continent as one of the regions exhibiting the highest rates of deforestation in the world. The dynamics of forests over the past 40 years has attracted numerous remote-sensing-based studies to monitor forest loss, analyse patterns, and understand the drivers of land conversion. This review article provides a comprehensive overview of the remote-sensing-based studies of tropical forest dynamics in Latin America. Following an introduction with respect to global forest mapping products, a general outline of tropical forest ecoregions and drivers of deforestation in Latin America is provided. Subsequently, a review and categorization of the existing studies is presented, where focus is laid on selected sensors and data analysis methodologies apply. Furthermore, a case study for the whole of Paraguay is presented; Paraguay is a region which contains highly diverse ecosystems that have been ravaged as a result of deforestation over the past 40 years. The main results, challenges, and future needs are discussed. 相似文献
92.
Summary Concentrates of natural linoleic acid (linoleic acid content, 85–95%) have been prepared in 50–72% yields from corn oil fatty
acids by preferential precipitation of the saturated and monounsaturated fatty acids at room temperature as their urea complexes.
By a similar procedure, concentrates of natural linolenic acid (linolenic acid content, 87–89%) have been prepared in 55–61%
yields from perilla oil fatty acids by preferential precipitation of the saturated, monounsaturated, and diunsaturated fatty
acids. Although concentrates of natural linolenic acid containing only 66–70% linolenic acid were obtained from linseed oil
fatty acids, yields were 87–90%.
A levelling-off effect has been observed in the use of the preferential precipitation technique in raising the purity of concentrates
of linoleic and linolenic acid. This parallels the experience in the purification of these acids by low-temperature crystallization.
The preceding papers in this series are references 12 and 13.
Presented at the Fall Meeting of the American Oil Chemists' Society, Cincinnati, O., Oct. 20–22, 1952.
One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S.
Department of Agriculture. 相似文献
93.
94.
Edmund F. Jordan Steven Smith Ronald E. Koos Winfred E. Parker Bohdan Artymyshyn A. N. Wrigley 《应用聚合物科学杂志》1978,22(6):1509-1528
Compositionally and structurally varied copolymers all containing n-octadecyl acrylate were prepared and evaluated as viscosity index improvers in a common base oil under conditions of low shear. Systems evaluated over a range of copolymer and blend composition were: copolymers of n-octadecyl acrylate with, respectively, methyl methacrylate, 2-ethylhexyl acrylate, and n-dodecyl acrylate; and homopolymers of poly(n-octadecyl acrylate), prepared with a wide range of molecular weights. Properties were compared with those of blends of commercial methacrylate copolymers (acryloids) which had been freed of their entraining liquid. Mixtures of base oil with copolymers of n-octadecyl acrylate and methyl methacrylate, compared at fixed SAE viscosities, were the most efficient of all blends studied. They had the smallest rate of change of viscosity with temperature (as measured by their ASTM slopes), particularly in the composition region of incipient polymer precipitation at room temperature. Efficiency of certain of these composition was somewhat greater than that of the acryloids. A parameter that related concentration and weight-average molecular weight was used to correlate all of the data for ASTM slope and viscosity. Empirical relations developed by using this parameter enabled rheological data to be estimated that agree within 6% of experimental values for the case of thermodynamically good base oil solvents. These data demonstrated the relatively small contributions of copolymer structure to viscosity index improvement. 相似文献
95.
Edmund F. Jordan George R. Riser Bohdan Artymyshyn Winfred E. Parker John W. Pensabene A. N. Wrigley 《应用聚合物科学杂志》1969,13(8):1777-1794
Mechanical and solution properties, melting transitions, torsional stiffness temperatures, Tf, and selected modulus-temperature curves are presented for copolymers of the N-n-alkylacrylamides with vinylidene chloride. Copolymers were prepared at 60°C across the range of compositions, using as comonomers N-n-butyl-, octyl-, dodecyl- and oleyl-acrylamide, which have amorphous side-chains, and N-n-octadecyl acrylamide and n-octadecyl acrylate whose side-chains are crystalline. The mechanical properties reflected the effect of the decline in backbone crystallinity and the simultaneous development of strong intermolecular interactions in the amorphous stage. Copolymers were stiff or showed brittle failure across the compositional range except when intermolecular forces were reduced (with n-octadrcyl acrylate) and side-chain crystallization eliminated (with N-oleylacrylamide). These systems and the n-dodecylacrylamide copolymers had yield strengths less than brittle strengths and substantial elongations. Backbone crystallinity was eliminated at about 15 mole % amide and side-chain crystallinity vanished at less than 10 mole % of the amide in the N-n-octadecylacrylamide series. No depression in side-chain melting point occurred with dilution by segments of vinylidene chloride. Over-all decline in the flex-temperature was the normal monotonic function of composition except that values increased in magnitude at high vinylidene chloride contents, the effect presumably being caused by the presence of crystallinity. An empirical equation was developed which permitted the calculation of Tf for any N-n-alkylacrylamide composition with any number of carbon atoms in the side-chain, above 3. 相似文献
96.
An undergraduate computer engineering laboratory that supports a one-quarter computer arithmetic course is described. This course is required for the computer engineering degree and is taken as a technical option by many students in electrical engineering and computer science. The features of this state-of-the-art laboratory include a local area network of computers, remote access via the campus network, electronic mail, online documentation, and automatic program submittal, grading, and plagiarism detection 相似文献
97.
We describe how transform techniques may be applied to the design of arrayed-waveguide gratings (AWG's). A hybrid Fourier-Fresnel transform model indicates that a flat AWG router passband over 30% of the device free-spectral range (FSR) is feasible. Minimized passband ripple is achieved by applying a subparabolic phase-profile (phase-exponent P=1.82) to the Fourier plane of the AWG. Simulations of a complex-apodized AWG with passband 3 dB width increased from 1 to 12 nm, with a near-trapezoidal amplitude response, and band-edge group delay of 70 ps reduced to 10 ps are presented for a device with a FSR of 40 nm 相似文献
98.
Julian Parker 《Computer Fraud & Security》2003,2003(10):4-5
The Woolf Reforms, recently instituted to make civil litigation more user friendly, targeted, amongst other things, the investigator’s best friend, the Anton Piller Order (AP). The Order was targeted directly, by having its name changed to the Search Order, and indirectly, in that Woolf aimed to make claimants expend more effort in finding solutions before resorting to the “nuclear option” of the AP. 相似文献
99.
Erik Mannens Davy Van Deursen Rapha?l Troncy Silvia Pfeiffer Conrad Parker Yves Lafon Jack Jansen Michael Hausenblas Rik Van de Walle 《Multimedia Tools and Applications》2012,59(2):691-715
To make media resources a prime citizen on the Web, we have to go beyond simply replicating digital media files. The Web is based on hyperlinks between Web resources, and that includes hyperlinking out of resources (e.g., from a word or an image within a Web page) as well as hyperlinking into resources (e.g., fragment URIs into Web pages). To turn video and audio into hypervideo and hyperaudio, we need to enable hyperlinking into and out of them. The W3C Media Fragments Working Group is taking on the challenge to further embrace W3C??s mission to lead the World Wide Web to its full potential by developing a Media Fragment protocol and guidelines that ensure the long-term growth of the Web. The major contribution of this paper is the introduction of Media Fragments as a media-format independent, standard means of addressing media resources using URIs. Moreover, we explain how the HTTP protocol can be used and extended to serve Media Fragments and what the impact is for current Web-enabled media formats. 相似文献
100.
The α-phase of the Al−Mn−Si ternary system has been precipitated from four liquid solutions (2.8 wt% Mn−3.7 wt% Si, 4.5 wt%
Mn−7 wt% Si, 7.7 wt% Mn−10 wt% Si and 8.7 wt% Mn−12.6 wt% Si) and equilibrated slightly over the melting point of the (secondary)
solid solution. Quenching into water enabled the precipitates to be separated from the solid solution and the co-nodal tie-lines
for the α-phase and liquid to be determined. The silicon content varied from 9.8 to 11.8 wt%, while the manganese content,
29.6±0.6 wt%, did not vary significantly. The lattice parameter of the cubic unit cell decreased from 1.267 6(2) nm to 1.265
10(4) nm with increasing silicon. Neutron powder diffraction showed silicon to constitute approximately 50% of atoms on the
icosahedral aluminium sublattices and 70% of a six-fold aluminium site in the interstices between the almost spherical, 54-atom
clusters. This decrease in unit cell volume is interpreted as evidence for substitution of the silicon atoms on the six-fold
sublattice. 相似文献