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排序方式: 共有68条查询结果,搜索用时 15 毫秒
1.
Eun Jin Lee Yohannes H. Rezenom David H. RussellBhimanagouda S. Patil Kil Sun Yoo 《Food chemistry》2012,131(3):852-861
The chemical structures of pink-red pigments responsible for ‘pinking’ in macerated onion were tentatively elucidated using HPLC with a diode array detector and tandem mass spectrometry. All pigments were produced in conditions that approximated the natural process as closely as possible, using mixtures of onion thiosulphinates, the enzyme alliinase, and free amino acids. The isotopic distribution of protonated molecules of pink-red pigments produced from individual amino acids indicated the absence of sulphur, with the exception of pigment produced from cystine. The pigments had a basic polymethine framework containing two pyrrole rings (3,4-dimethyl-1H-pyrrole and 3,4-dimethyl-2,5-dihydro-1H-pyrrole) bridged by methines. The side chains attached to the nitrogen of the pyrrole rings were derived from the reacting amino acid. The simplest pink-red pigment, produced from glycine, was identified as 2-(2-(3-(1-(carboxymethyl)-3,4-dimethyl-1H-pyrrol-2(5H)-ylidene)prop-1-en-1-yl)-3,4-dimethyl-1H-pyrrol-1-yl)acetic acid. The pigment from alanine was identified as 2-(2-(3-(1-(carboxymethyl)-3,4-dimethyl-1H-pyrrol-2-yl)allylidene)-3,4-dimethyl-2,5-dihydro-1H-pyrrol-1-yl)propanoic acid. The chemical structures of pink-red pigments from leucine, asparagine, glutamine, tyrosine, and cystine also were determined. 相似文献
2.
Francesca Tinti Siraye E. Debebe Wendimagegn Mammo Teketel Yohannes Nadia Camaioni 《Synthetic Metals》2011,161(9-10):794-798
Transport of holes in thin films of a low-bandgap alternating polyfluorene copolymer, APFO-Green5, was investigated by means of admittance spectroscopy as a function of field and temperature. The values of hole mobility were evaluated from the position of the maxima in the plots of the negative differential susceptance as a function of frequency. Hole mobility was found to be strongly field- and temperature-dependent. The charge transport parameters were extracted by analyzing the mobility data by the uncorrelated and the correlated Gaussian Disorder Models. 相似文献
3.
Yohannes Yihdego Bediaku G. Kafui Zarko Veljkovic 《Energy Sources, Part A: Recovery, Utilization, and Environmental Effects》2018,40(17):2079-2096
Oil shale is an organic-rich, fine-grained sedimentary rock, containing kerogen, from which liquid hydrocarbons (called shale oil) can be produced. The oil shale deposits in the Tigray region are found in the northern parts of Ethiopia, Eastern Africa. They are of Upper Paleozoic in age, existing as remnants of the Cretaceous erosion period, underlain by tillites and overlain by sandstones. They were formed during the glacial retreat followed by marine deposition of shales in a basin created by the enormous load of the glaciers. The Ethiopian-Tigray oil shale deposits cover an area extending over approximately 30 km2, with an average mineable bed-thickness of 55 m, showing on the upper part inter-beds and laminations of shaley limestones. The oil shale resources in this region are estimated to be approximately 4 billion tonnes. The exploitation of the Ethiopian-Tigray oil shale deposits is an excellent alternative to fulfill the fuel and other petroleum products’ demand of Ethiopia. This study sheds light on the oil shale resources in the Ethiopian region of Tigray, as they are fairly investigated, regarding their geological characterization, and future strategies for their exploration and exploitation potential. In addition, the oil shale deposits in Jordan are also moderately investigated, as Jordan is considered a promising country for shale oil, taking into account that Jordan has no other hydrocarbon resources (such as crude oil and natural gas), unlike many other countries in the MENA (Middle East and North Africa) region, as MENA sets on “seas” of oil and natural gas. Furthermore, oil shale in the USA is also briefly investigated, as the USA is being the world’s largest country of oil shale resources and reserves. Also, some other issues related to the oil shale industry are investigated, such as economics, extraction technologies of shale oil, and the environmental impacts. 相似文献
4.
Frank van Steenbergen Abraham Mehari Haile Taye Alemehayu Tena Alamirew Yohannes Geleta 《Water Resources Management》2011,25(7):1899-1913
This article discusses spate irrigation in Ethiopia and aims to take stock of the current status of spate irrigation development.
It summarizes experiences so far and formulates a number of recommendations on the development of this upcoming resource management
system. It argues that raised weirs are useful mainly in areas where a large head for spate flow diversion is required, but
that traditional earthen structures with conical stone/gabion reinforcements are cost-effective and technically adequate for
floodwater distribution and management. It contends that the practical successes of sediment settling ponds (gravel traps)
are at best mixed. Even where a small basin is justified, it can only ever trap a small proportion of the incoming sediment
load. It is better to allow large floods with excessive sediment load (>100,000 ppm) to by-pass upstream intakes to be diverted
lower down the system, and provide additional livelihood opportunities in downstream areas in the form of rangeland and agro-forestry
development. This is particularly useful in the lowlands of Ethiopia with large pastoral community where spate irrigation
is yet to make in-roads. The article further explains that water rights in spate are different from the sharing and allocation
of perennial flows—they are dynamic and respond to a situation that differs from year to year as well as within a year and
that a certain degree of inequity among users is inevitable. Keeping the command area compact can ensure two or more irrigation
turns and this can highly increase productivity as crops are no longer in the ‘stress zone’. To transform spate irrigation
in Ethiopia from subsistence to a business-oriented production system, the article proposes the promotion of cash crops including
pulses and oil seeds as well as encouraging investors to go for bio-fuel development and agro-forestry in the lowland areas
where huge potential exist. To avoid vehement conflicts that may arise among the settled agricultural and pastoral communities
due to the implementation of the business-oriented production system, the traditional rights of the pastoral communities must
be respected and their rangeland and water resources be safeguarded. For maximum yield, soil moisture conservation measures
such as pre-irrigation land preparation, deep ploughing and mulching are essential as is the conjunctive use of spate flow
and groundwater. Last, but most important, the article emphasizes that farmers need to be placed at the heart of any spate
irrigation development programme as primary beneficiaries, managers and operators as well as part of the decision making institution. 相似文献
5.
Mosissa Adi Teketel Yohannes Theodros Solomon 《Solar Energy Materials & Solar Cells》2004,83(2-3):301
The photoelectrochemical properties of a solid-state photoelectrochemical cell (PEC) based on poly(3-hexylthiophene), P3HT, and an ion-conducting polymer electrolyte, amorphous poly(ethylene oxide), POMOE, complexed with I3−/I− redox couple has been constructed and studied. The current–voltage characteristics in the dark and under white light illumination, transient photocurrent and photovoltage studies, photocurrent action spectra for front and back side illuminations and an open-circuit voltage and short-circuit current dependence on light intensity have been studied. An open-circuit voltage of 130 mV and a short-circuit current of 0.47 μA cm−2 were obtained at light intensity of 100 mW/cm2. IPCE% of 0.024% for front side illumination (ITO/PEDOT) and IPCE% of 0.003% for backside illumination (ITO/P3HT) were obtained. 相似文献
6.
A solid-state photoelectrochemical solar energy conversion device based on blend of poly(3-hexylthiophene) (P3HT) and fullerene (C60) has been constructed and characterized. The photoelectrochemical performance parameters of the device were compared with pure P3HT solid-state photoelectrochemical cell. The current–voltage characteristics in the dark and under white light illumination and photocurrent spectra for front- and backside illuminations have been studied. The following device parameters were obtained: an open-circuit voltage of 97.8 mV and a short-circuit current of 7.28 μA/cm2 at light intensity of 100 mW/cm2; IPCE% of 0.43% for front side illumination (ITO/PEDOT) and IPCE% of 0.01% for backside illumination (ITO/P3HT:C60). The dependence of the short-circuit current and an open-circuit voltage on the light intensity and time have also been studied. 相似文献
7.
The study of flame development characteristics is crucial in the study of flame propagation, extinction, and for the investigation of combustion cyclic variability in SI engine. The aim of this study is to investigate the characteristics of flame development in a lean-stratified combustion of Natural Gas Engine (CNG) in a single cylinder direct injection (DI) engine at a specific motor speed, and fixed injection timing and air-fuel ratio by varying only the swirl level at the intake. The engine was set to run at 1800 rpm with half-load throttled. The ignition advance was set at 21.5 BTDC, and to create an overall lean and stratified mixture, injection timing was set at 61 BTDC with an air-fuel-ratio of 40.5 (λ=2.35). Variable turbulent flow conditions near spark-plug were created by positioning the swirl control valves (SCV) at the intake port just before the two intake valves. This was done by setting one of the valves at full open position and the other one at 0% closed, 50% closed and 100% closed positions in order to achieve medium tumble (no swirl), medium swirl and high swirl flows in the cylinder, respectively. An endoscope and CCD camera assembly was utilized to capture the flame images from the tumble plane at the intake side of the engine ever), 2 CA degrees after ignition timing (AIT) for 40 CAs. It was observed that flame growth rate and flame convection velocity are increasing with increasing the swirl level. The total combustion duration is, thus, shorter in swirl induced combustion than without. However, COV in IMEP is greater in swirl induced flow cases than the medium tumble. 相似文献
8.
P. L. Cavallotti G. Zangari V. Sirtori A. Manara 《Journal of Electronic Materials》1995,24(4):371-378
The introduction of no-clean pastes and fluxes for the surface mount technology process needs testing methods of high sensitivity
and reliability to evaluate the activity of the residues after the reflow process. An electrochemical method is proposed,
suitable to ascertain the reactivity and the corrosion risk of these residues. Products of normal use are tested, and their
behavior described and compared. Surface morphologies and compositions are examined after reflow and after testing. Local
surface oxides are investigated with x-ray photoelectron spectroscopy. Surface analytical results are interpreted and related
to the electrochemical behavior of solder joints. Tin is shown to have the most important role toward the onset of possible
localized corrosion. 相似文献
9.
Yohannes Eneyew Ayalew 《Information & Communications Technology Law》2019,28(2):208-224
Freedom of expression is a foundational stone for democracy and embraces a number of other rights, including – freedom to seek, receive, and impart information using any medium. Around 16 million Ethiopians, comprising 15.4% of the total population, use the Internet. The Ethiopian Internet shutdown saga has been marked by competing narratives. On one hand, the government has been using two governing narratives, i.e. national security narrative and ‘economic growth’ narrative to justify shutdowns of the Internet. But, the individuals’ self-expressions on social media find itself as competing narrative. Since 2016, the Internet has been closed more than six times under the cloak of national security, quelling rising protests, controlling strikes, and exam cheating. As such, freedom of expression of millions has been muzzled. The article argues blanket Internet shutdowns do not meet the caveats of human rights law. 相似文献
10.