327 research outputs found
Real-time Optimal Resource Allocation for Embedded UAV Communication Systems
We consider device-to-device (D2D) wireless information and power transfer
systems using an unmanned aerial vehicle (UAV) as a relay-assisted node. As the
energy capacity and flight time of UAVs is limited, a significant issue in
deploying UAV is to manage energy consumption in real-time application, which
is proportional to the UAV transmit power. To tackle this important issue, we
develop a real-time resource allocation algorithm for maximizing the energy
efficiency by jointly optimizing the energy-harvesting time and power control
for the considered (D2D) communication embedded with UAV. We demonstrate the
effectiveness of the proposed algorithms as running time for solving them can
be conducted in milliseconds.Comment: 11 pages, 5 figures, 1 table. This paper is accepted for publication
on IEEE Wireless Communications Letter
Adjustment of Vietnamese labour market in time of economic fluctuations and structural changes
Dans cet article, nous examinons les ajustements du marchĂ© du travail aux fluctuations Ă©conomiques, compte tenu des transformations structurelles en cours ainsi que des changements Ă court terme. Nous utilisons pour cela des donnĂ©es des recensements de la population ou publiĂ©es dans les annuaires statistiques de l’Office GĂ©nĂ©ral de la Statistique pour les sĂ©ries Ă long terme, et les enquĂŞtes emploi conduites entre 2007 Ă 2012 pour les donnĂ©es Ă court terme. Cet article souligne la profonde transformation du marchĂ© du travail au cours des dernières dĂ©cennies. La population active a doublĂ© en 25 ans et la part de l'agriculture est passĂ©e en dessous du seuil de 50 %. L’absorption de l'offre de travail a donc Ă©tĂ© l'un des principaux dĂ©fis pour l'Ă©conomie vietnamienne sur cette pĂ©riode. Le secteur des entreprises familiales agricoles et non-agricoles a Ă©tĂ© le principal pourvoyeur d'emplois au cours de ces annĂ©es. Le marchĂ© du travail s'est adaptĂ© au rĂ©cent ralentissement Ă©conomique Ă travers diffĂ©rents canaux. Le chĂ´mage est restĂ© stable mais le nombre de personnes inactives a augmentĂ©. La quantitĂ© de travail a Ă©galement Ă©tĂ© affectĂ©e par une rĂ©duction significative du nombre d'heures travaillĂ©es. Alors que le secteur non agricole a gĂ©nĂ©rĂ© plus d'emplois pour les travailleurs qualifiĂ©s, un flux de travailleurs non-qualifiĂ©s vers l’agriculture a Ă©tĂ© observĂ©. En raison de facteurs dĂ©mographiques, l'absorption de l'offre de travail et la crĂ©ation de nouveaux emplois ne sont plus le principal problème. En revanche, l’Ă©volution rĂ©cente du marchĂ© du travail appelle Ă la mise en oeuvre de politiques structurelles en vue d’amĂ©liorer les conditions de travail, la pĂ©riode Ă©tant particulièrement favorable pour mener ces politiques puisque le Vietnam profite actuellement du dividende dĂ©mographique
Retrieval of material properties of monolayer transition-metal dichalcogenides from magnetoexciton energy spectra
Reduced exciton mass, polarizability, and dielectric constant of the
surrounding medium are essential properties for semiconduction materials, and
they can be extracted recently from the magnetoexciton energies. However, the
acceptable accuracy of the previously suggested method requires very high
magnetic intensity. Therefore, in the present paper, we propose an alternative
method of extracting these material properties from recently available
experimental magnetoexciton s-state energies in monolayer transition-metal
dichalcogenides (TMDCs). The method is based on the high sensitivity of exciton
energies to the material parameters in the Rytova-Keldysh model. It allows us
to vary the considered material parameters to get the best fit of the
theoretical calculation to the experimental exciton energies for the ,
, and states. This procedure gives values of the exciton reduced mass
and 2D polarizability. Then, the experimental magnetoexciton spectra compared
to the theoretical calculation gives also the average dielectric constant.
Concrete applications are presented only for monolayers WSe and WS from
the recently available experimental data. However, the presented approach is
universal and can be applied to other monolayer TMDCs. The mentioned fitting
procedure requires a fast and effective method of solving the Schr\"{o}dinger
of an exciton in monolayer TMDCs with a magnetic field. Therefore, we also
develop such a method in this study for highly accurate magnetoexciton
energies.Comment: 8 pages, 4 figures, 4 table
Ultrasound-assisted extraction of GAC peel : an optimization of extraction conditions for recovering carotenoids and antioxidant capacity
The peel of Gac fruit (Momordica cochinchinensis Spreng.), which is considered as waste of Gac processing, has been found to possess high levels of carotenoids and other antioxidants. This study aimed at determining the optimal conditions of an ultrasound-assisted extraction for recovering carotenoids and antioxidant capacity from Gac peel. A response surface methodology using the Box–Behnken design was employed to investigate the impact of extraction time, temperature and ultrasonic power on the recovery of total carotenoid and antioxidant capacity. The results showed that an extraction time of 76 min, temperature of 50 °C and ultrasonic power of 250 W were the optimal conditions for the extraction. The experimental carotenoid yield and antioxidant capacity obtained under the optimal extraction conditions were validated as 269 mg/100 g DW (dry weight) and 822 µM TE (Trolox equivalent)/100 g DW, respectively. These values were not significantly different from the values predicted by the models. The HPLC analysis for carotenoid composition showed that β-carotene, lycopene and lutein were the principal carotenoids of the extract, which constitute 86% of the total carotenoid content. Based on the obtained results, the ultrasound-assisted extraction using ethyl acetate under the above optimal conditions is suggested for the simultaneous recovery of carotenoids and antioxidant capacity from Gac peel
Contribution of forest to rural households’ livelihood: evidences from Da river basin in the northwest mountainous region of Vietnam
This paper examined how forest has contributed to rural households’ livelihood in Da river basin, the northwest mountainous region of Vietnam. The results revealed that forest predominantly contributes to the total income of rural residents in the region. Specifically, forestry land area, access to non-timber forest products, and payment for forest environmental services significantly affected household’s income in the region. However, rural people in the region have still faced several difficulties that constrain household’s livelihood. Of these difficulties, lack of financial capital, epidemic diseases in animal husbandry, limited access to market information and natural disaster are popular barriers to livelihood of people in the region. This paper also recommended several policies to improve rural livelihood in Da river basin. These includes: (i) integrating issues regarding payment for forest environmental services and REDD+ into socioeconomic development plan; (ii) improving awareness of local people on sustainable natural capital use through ecosystem conservation policy; (iii) providing preferential credit and training on agricultural production techniques; and (iv) encouraging market-oriented agriculture.Â
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