Aspects of vegetation resilience and change in relation to major environmental disturbances in the semi-arid parts of Kordofan region-Sudan

The aim of this study has been to investigate the different responses of vegetation to the major environmental disturbances and discontinuities in Kordofan region of the Sudan. Data used have been obtained from fieldwork survey, aerial photographs and a landsat image in combination with existing maps and statistics on vegetation, climate, agriculture and population. Results obtained have shown that most plant species are neither randomly distributed nor indications of the postulated regularity of distribution were detected. Such a distributional pattern was explained through the pattern of surface properties. These have included rainfall, soil characteristics, micro-topography and the type of vegetation itself. The different types of vegetation identified were shown to reflect various succession stages following either excessive cultivation, grazing or both. Climatically conditioned natural vegetation is virtually absent as the effect is almost entirely masked by man's activities. Evidence presented showed that various types of woodland were formerly more extensive and that they have been replaced by secondary shrubland, bushland and grassland. Most plant communities have been explained by their history of cultivation and grazing pressure. These two were found to interpret the process of successional changes, to radically alter its dynamics and to set plant species on a wide variety of paths which is largely controlled by the pressure exerted. Achieved result indicated that vegetation in the area has persisted to exist and to re-establish itself after virtual elimination. This is shown to reflect a high degree of resilience in the system. Evidence were shown that if the vegetation is protected and the climatic and edaphic conditions were favourable, it will eventually be succeeded by a richer type of vegetation. It has not been possible to prove neither to reject the claim often found in literature that the vegetation zones in this region are constantly shifting southward as a result of overgrazing, overcultivation and accelerated soil erosion. However, it has been possible to recognise a process of successional changes which varies from one place to another in terms of nature and intensity depending largely on site characteristics

Dipole-dipole interaction between a quantum dot and graphene nanodisk

We study theoretically the dipole-dipole interaction and energy transfer in a hybrid system consisting of a quantum dot and graphene nanodisk embedded in a nonlinear photonic crystal. In our model a probe laser field is applied to measure the energy transfer between the quantum dot and graphene nanodisk while a control field manipulates the energy transfer process. These fields create excitons in the quantum dot and surface plasmon polaritons in the graphene nanodisk which interact via the dipole-dipole interaction. Here the nonlinear photonic crystal acts as a tunable photonic reservoir for the quantum dot, and is used to control the energy transfer. We have found that the spectrum of power absorption in the quantum dot has two peaks due to the creation of two dressed excitons in the presence of the dipole-dipole interaction. The energy transfer rate spectrum of the graphene nanodisk also has two peaks due to the absorption of these two dressed excitons. Additionally, energy transfer between the quantum dot and the graphene nanodisk can be switched on and off by applying a pump laser to the photonic crystal or by adjusting the strength of the dipole-dipole interaction. We show that the intensity and frequencies of the peaks in the energy transfer rate spectra can be modified by changing the number of graphene monolayers in the nanodisk or the separation between the quantum dot and graphene. Our results agree with existing experiments on a qualitative basis. The principle of our system can be employed to fabricate nano-biosensors, optical nano-switches, and energy transfer devices

Étude de l'adsorption de l'atrazine sur le charbon actif en poudre en présence de tensioactifs

Les tensioactifs, adjuvants participant à la formulation des pesticides peuvent se trouver en compétition avec ces derniers lors de l'adsorption sur charbon actif en poudre (CAP) utilisé au cours du traitement de potabilisation des eaux. L'adsorption de l'atrazine, qui reste l'un des produits phytosanitaires le plus souvent détecté dans les eaux de surface malgré les réglementations sur son utilisation, a été étudiée en présence de trois tensioactifs afin de déterminer l'influence de ces derniers; il a été choisi un tensioactif anionique (DSS), cationique (BHTA), et un non ionique (DE6). Les résultats ont montré que quelle que soit la nature du tensioactif, celui-ci diminue toujours l'adsorption de l'atrazine pour des pH variant de 3,5 à 10 ce qui a pour conséquence une diminution à la fois de la constante de vitesse (Adams et Bohart) et de la capacité d'adsorption (Langmuir). L'étude de l'influence de l'ordre d'introduction des différents éléments participant à l'adsorption (CAP, atrazine, tensioactif) a montré que la fixation préalable de DSS anionique, favorisée en milieu acide, inhibe davantage l'élimination de l'atrazine. L'application des modèles d'adsorption compétitive et non compétitive de Langmuir n'a pas permis de définir avec certitude la nature des interactions entre l'herbicide et les différents tensioactifs.Atrazine, in spite of the restrictions concerning its use, remains one of the most prevalent pesticides in natural surface waters. If a sudden pollution incident occurs, powdered activated carbon (PAC) is used during the flocculation step of water treatment; under such circumstances, atrazine might be in adsorption competition with surfactants included in commercial formulations. The aim of this study was thus to determine the influence of three surfactants [anionic (sodium dodecylsulphate, SDS), cationic (hexadecyl-trimethylammonium bromide, HTAB) and nonionic (2-dodecyloxy-pentaethanoxy)-ethanol, DE6)] on atrazine adsorption onto PAC. At pH 5.5, adsorption onto PAC of atrazine alone was estimated to be 230 mg. g-¹; it was inhibited whatever the nature of the surfactant (cationic anionic or nonionic: figs. 2, 3 and 4). The adsorption capacities (Langmuir) and the kinetic constants (Adams & Bohart) decreased in the presence of the surfactants (table 4) and this diminution was most important for HTAB (fig. 5), perhaps the consequence of a steric effect.The adsorption onto PAC of the molecular form of atrazine (pK=1.68) was not affected by the pH variations. However, when the pH was increased (3.5 to 10) in the presence of SDS, adsorption onto PAC of the anionic surfactant decreased and atrazine adsorption increased (fig. 9). In contrast, for the same experimental conditions but with the cationic surfactant HTAB, adsorption of the surfactant increased over the pH range 3.5 to 10 and the relative adsorption of atrazine diminished (fig. 9). The nonionic surfactant DE6 had no influence.A study of the introduction order of the different components (atrazine, SDS surfactant and PAC) showed the same final equilibrium distribution of atrazine was obtained (fig. 10), regardless of the order of introduction. A similar result was obtained for the adsorption of SDS (fig. 11).For all these cases, the Langmuir equation yielded the adsorption capacity for atrazine and the equilibrium constant. However, competitive and noncompetitive adsorption models (table 1) were unsuccessful in predicting the nature of the interactions between atrazine and the surfactants (table 5)

Influence du dodécylsulfate de sodium sur l'adsorption des acides humiques sur charbon actif en poudre

L'objectif de ce travail est d'étudier l'influence d'un tensioactif anionique, le dodécylsulfate de sodium (DSS) sur l'adsorption d'acides humiques (AH), sur le charbon actif en poudre (CAP).L'adsorption sur CAP, en fonction du temps, des AH seuls, puis du DSS seul, a été effectuée en réacteur discontinu, à différents pH (7,0 et 10,5). Les mêmes expériences ont été réalisées avec le mélange des deux composés et l'on a pu constater une inhibition réciproque de leur adsorption, moins importante à pH basique (10,5).L'influence de l'ordre d'introduction des coadsorbats, sur l'adsorption de chacun d'eux, a permis de montrer que l'inhibition de l'adsorption des AH sur CAP par le DSS est encore plus importante lorsque les AH sont ajoutés sur une suspension DSS-CAP déjà en équilibre. Aucune désorption du DSS n'a pu être mise en évidence après 24 heures. Ces résultats pourraient permettre de conclure à une adsorption « compétitive » des AH et du DSS sur les mêmes sites superficiels du charbon actif.Ce travail permet de préciser les phénomènes d'adsorption pouvant intervenir entre divers micropolluants susceptibles de s'adsorber simultanément soit sur des sédiments naturels, soit sur charbon actif lors du traitement des eaux naturelles.The removal of humic acids (HA) from natural waters is a very old yet modern problem : humic substances are at the origin of the coloration of water but also, they give off nocive trihalomethanes during chlorination.Humic acids are also known to be a metal micropollutant vector and their behavior is not well defined when there is coadsorption.The purpose of this work was to study the effect of an anionic surfactant, sodium dodecyl sulphate (SDS), on the adsorption on powdered activated carbon (PAC) of humic substances from a commercial source, as a function of the pH (7.0 or 10.5), as well as the effect of the order of introduction of the coadsorbate.Results (fig. 1 to 3 and fig. 6) showed an inhibition of the adsorption for both HA and SDS in the presence of the coadsorbate. The inhibition was more significant for a pH = 7.0.Results of the influence of the order of introduction of the coadsorbate on the adsorption (fig. 4 and 5) showed a more significant inhibition of HA adsorption when HA were introduced into the equilibrium suspension SDS-PAC (the contact lime was 24 hours).Table 1 gives parameter values of the Langmuir equation for the adsorption on PAC of HA atone or with SDS.All these results suggest that a competition on the same sites occurs during the adsorption on PAC of HA and SDS

Evaluasi Kesesuaian Lahan Kualitatif dan Kuantitatif Pertanaman Nanas (Ananas Comosus [L] Merr) Kelompok Tani Makmur di Desa Astomulyo Kecamatan Punggur Kabupaten Lampung Tengah

Nanas (Ananas comosus (L) Merr) merupakan tanaman hortikultura yang banyak dibudidayakan di Kabupaten Lampung Tengah. Budidaya tanaman nanas (Ananas comosus (L) Merr) dinilai akan sangat menguntungkan, mengingat dengan biayaproduksi yang tidak terlalu mahal serta kebutuhan masyarakat akan buah nanas semakin meningkat. Untuk mengoptimalkan hasil produksi, daya dukung, potensi dan hambatan yang ada untuk suatu penggunaan lahan tertentu dalam budidaya harus kita ketahui, untuk itu dilakukan evaluasi lahan. Penelitian ini bertujuan untuk mengevaluasi kesesuaian lahan kualitatif dan kuantitatif pada pertanaman nanas (Ananas comosus (L) Merr) Kelompok Tani Makmur Desa Astomulyo KecamatanPunggur Kabupaten Lampung Tengah. Evaluasi kesesuaian lahan kualitatif dilakukan menggunakan kriteria biofisik menurut Djaenuddin dkk. (2011), sedangkan penilaian secara kuantitatif adalah dengan menganalisa kelayakan finansial budidaya tanaman nanas dengan menghitung nilai NPV, Net B/C Ratio, IRR dan BEP. Hasil penelitian menunjukkan bahwa lahan pertanaman nanas (Ananas comosus (L) Merr) Kelompok Tani Makmur Desa Astomulyo termasuk ke dalam kelas kesesuaian lahan sesuai marginal dengan faktor pembatas ketersediaan air (S3wa), dan secara finansial menunjukkan bahwa nilai NPV sebesar Rp113.896.094,- , Net B/C sebesar 5,48, IRRsebesar 219%tahun -1 dan BEP (titik impas) akan dicapai dalam waktu 1 tahun 11 bulan 1 hari.Hal ini menunjukkan bahwa USAha budidaya tanaman nanas ini menguntungkan dan layak untuk dikembangkan

Pelatihan Pemanfaatan Gulma Eceng Gondok sebagai Pupuk Alternatif

Eceng Gondok sebagai masalah bagi jaringan drainase, di Kota Makassar, juga dirasakan oleh berbagai negara di dunia. Di Amerika tanaman eceng gondok dengan nama latin Eichornia crassipes, sejak 1960 oleh pemerintah telah berdiri Water Hyacinth Society yang merupakan asosiasi para ilmuwan, praktisi dan pengusaha untuk mengontrol atau menanggulangi masalah penyebaran eceng gondok. Asosiasi ini kemudian berganti nama menjadi Aquatic Plant management Society (APMS) yang meliputi pengkajian aspek-aspek biologis, ekologis dan pengontrolan pertumbuhan tumbuh-tumbuhan air pada umumnya dan tidak hanya terbatas pada eceng godok. Penelitian mengenai aspek-aspek ekologi eceng gondok di Indonesia sampai saat ini masih belum banyak dilakukan orang, padahal sebagai tanaman yang mengepung di permukaan air ini, memiliki nilai penting yang tinggi, terutama untuk pipik alternatif. Penyebarannya yang cukup luas, penyesuaiannya yang baik terhadap lingkungan, gangguan dan kerugian yang sangat berarti yang dapat ditimbulkannya, cara pengendaliannya yang sulit dan cara pemanfaatannya yang belum diketahui dengan baik sebenarnya merupakan alasan-alasan yang menarik untuk memanfaatkan tanaman ini secara menyeluruh. Salah satunya dengan melatih masyarakat, menjadikannya sebagai pupuk alternatif