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See detailDésertification au Sahel : Crise climatique ou anthropique ?
Ozer, André ULg; Ozer, Pierre ULg

in Bulletin des Séances de l’Académie Royale des Sciences d’Outre-Mer = Mededelingen der Zittingen van de Koninklijke Academie voor Overzeese Wetenschappen (2005), 51(4), 395-423

Over the last decades, the Sahel suffered two dramatic contiguous droughts. At present, and since the early 1990s, rainfalls have recorded an amelioration that tends towards the average of precipitation ... [more ▼]

Over the last decades, the Sahel suffered two dramatic contiguous droughts. At present, and since the early 1990s, rainfalls have recorded an amelioration that tends towards the average of precipitation previous to the 1970s. However, this improvement may be due to increasing rainfall intensity and it seems that the length of the rainy season did not show any extension when compared to the 1970s and 1980s. Moreover, the Sahelian population has been multiplied by 3 since 1950 and is foreseen to be multiplied by 10 by the second half of the 21st century. Increasing urban population levels are much more impressive and bring about important environmental disruptions every day. Such increasing human pressure leads to uncontrolled deforestation in order to meet the needs in fuel wood, wood for construction and shifting cultivation. In addition, the ever-increasing number of herds for contracting range conditions leads to overgrazing. All these processes cause the degradation of the vegetation cover, a constant diminution of crop yields, as well as a strong reduction of biodiversity. One of the consequences is the reactivation of previously fixed dunes that were formed during the last interpluvial phase (18,000 BP). This article provides a state-of-the-art of the present controversy about desertification processes and concludes that if the droughts of the 1970s and 1980s have had dramatic consequences for the population of the Sahel, current and coming increasing human pressure will intensify the desertification of the southern fringe of the Sahara. [less ▲]

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See detailDésertification au Sahel: Historique et perspectives
Ozer, Pierre ULg; Hountondji, Yvon ULg; Niang, Abdoul Jelil et al

in Bulletin de la Société Géographique de Liège (2010), 54

Over the last decades, the Sahel of West Africa has suffered two dramatic contiguous droughts. Currently, and since the late 1980s, rainfall amounts tend to catch up with the pre-1970 levels. However ... [more ▼]

Over the last decades, the Sahel of West Africa has suffered two dramatic contiguous droughts. Currently, and since the late 1980s, rainfall amounts tend to catch up with the pre-1970 levels. However, this improvement seems to occur through increased rainfall intensities but the duration of the rainy season did not significantly change since the 1970s and the 1980s. On the other hand, the Sahelian population has tripled since 1950 and it is foreseen to be multiplied by 10 by the second half of the 21st century. Increasing urban population levels are still much more impressive and cause profound environmental degradation. Such an increasing human pressure leads to uncontrolled deforestation in order to satisfy the needs in fuel and construction wood and to make place for shifting cultivation. In addition, larger and larger herds occupying contracting pasture areas leads to overgrazing and trampling. All these processes provoke the degradation of the vegetation cover, a constant diminution of crop yields, and a strong reduction of the biodiversity. This article provides a state of the art of recent findings and controversy that surround the desertification processes. We conclude that, if the droughts of the 1970s and 1980s have had dramatic consequences for the population of the Sahel, the future very high human pressure on the environment will most likely enhance the desertification of the southern fringe of the Sahara, especially in the case of the alarming climate change scenarios forecasting rainfall decrease all over the Sahel. [less ▲]

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See detailDésertification dans le Sud nigérien, interprétation d’une image SPOT
Karimoune, Salifou; Donnay, Jean-Paul ULg; Ozer, André ULg

in Actes des journées scientifiques du réseau de télédétection de l’UREF : Outil micro-informatiques et télédétection de l’évolution des milieux (1993)

Detailed reference viewed: 35 (1 ULg)
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See detailDésertification des parcours arides au Maroc
Mahyou, Hamid ULg; Tychon, Bernard ULg; Balaghi, Riad et al

in Tropicultura (2010), 28(2), 107-114

Rangeland or natural arid pastures of Morocco are ecosystems where there is a natural or seminatural vegetation composed of steppes, shrubs and grassland. They cover about 82% of the Moroccan arid lands ... [more ▼]

Rangeland or natural arid pastures of Morocco are ecosystems where there is a natural or seminatural vegetation composed of steppes, shrubs and grassland. They cover about 82% of the Moroccan arid lands. These areas represent livelihoods for thousands of people and protect the country from desertification. Despite the importance of the rangelands and the threat of desertification, it is surprising that up to date there is no comprehensive assessment of their condition and their evolution, hindering any plan for desertification alleviation. However, the available information on selected pilot areas shows that these rangelands are threatened by desertification. It’s associated with biodiversity loss and contributes to climate change. The leading causes of land degradation are the human actions combined with climate. The establishment of a comprehensive surveillance system based on remote sensing, biophysics and socio-economic data must be envisaged to provide policymakers with an operational tool adapted to the spatio-temporal monitoring of desertification. [less ▲]

Detailed reference viewed: 342 (26 ULg)
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See detailLa désertification est-elle en recul au Sahel ?
Ozer, Pierre ULg; Gassani, Jean; Hountondji, Yvon ULg et al

in Bois et Forêts des Tropiques (2007), 293

Land degradation trends in arid, semi-arid and subhumid areas are such that the General Assembly of the United Nations has declared 2006 the International Year of Deserts and Desertification. Surprisingly ... [more ▼]

Land degradation trends in arid, semi-arid and subhumid areas are such that the General Assembly of the United Nations has declared 2006 the International Year of Deserts and Desertification. Surprisingly, a global review carried out for the Millennium Ecosystem Assessment concluded that existing data do not support the claim that the African Sahel is a desertification hotspot. Here, we try to understand the reasons why such conclusions were drawn. [less ▲]

Detailed reference viewed: 248 (42 ULg)
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See detailDesertification in the Sahel: climatic or human driven causes?
Ozer, Pierre ULg; Ozer, André ULg

Conference (2009, July 07)

Over the last decades, the Sahel of West Africa has suffered two dramatic contiguous droughts. Currently, and since the early 1990, rainfalls record an amelioration that tends towards the average of ... [more ▼]

Over the last decades, the Sahel of West Africa has suffered two dramatic contiguous droughts. Currently, and since the early 1990, rainfalls record an amelioration that tends towards the average of precipitation previous to the 1970s. However, this improvement may be due to increasing rainfall intensity and it seems that the length of the rainy season did not show any extension when compared to the 1970s and 1980s. On the other hand, the Sahelian population has been multiplied by 3 since 1950 and is foreseen to be multiplied by 10 by the second half of the 21st century. Increasing urban population levels are much more impressive and conduct important environmental distresses every day. Such increasing human pressure leads to uncontrolled deforestation in order to satisfy the needs in fuel wood, wood for construction and shifting cultivation. In addition, always larger herds for contracting range conditions lead to overgrazing and trampling. All these processes provoke the degradation of the vegetation cover, a constant diminution of crop yields, as well as a strong reduction of the biodiversity. One of the numerous consequences is the reactivation of previously fixed dunes that were formed during the last interpluvial phase (18000 BP). Our research provides a state of the art of recent findings and controversy that surround the desertification processes and concludes that if the droughts of the 1970s and 1980s have had dramatic consequences for the population of the Sahel, current and coming increasing human pressure will very likely enhance desertification processes of the southern fringe of the Sahara. [less ▲]

Detailed reference viewed: 313 (45 ULg)
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See detailDesertification of arid Rangelands in Morocco
Mahyou, Hamid ULg; Tychon, Bernard ULg; Paul, Roger ULg et al

Conference (2011, February 24)

Rangeland or natural arid pastures of Morocco are ecosystems where there is a natural or seminatural vegetation composed of steppes, shrubs and grassland. They cover about 82% of the Moroccan arid lands ... [more ▼]

Rangeland or natural arid pastures of Morocco are ecosystems where there is a natural or seminatural vegetation composed of steppes, shrubs and grassland. They cover about 82% of the Moroccan arid lands. These areas represent livelihoods for thousands of people and protect the country from desertification. Despite the importance of the rangelands and the threat of desertification, it is surprising that up to date there is no comprehensive assessment of their condition and their evolution, hindering any plan for desertification alleviation. However, the available information on selected pilot areas shows that these rangelands are threatened by desertification. It’s associated with biodiversity loss and contributes to climate change. The leading causes of land degradation are the human actions combined with climate. The establishment of a comprehensive surveillance system based on remote sensing, biophysics and socio-economic data must be envisaged to provide policymakers with an operational tool adapted to the spatio-temporal monitoring of desertification. [less ▲]

Detailed reference viewed: 61 (3 ULg)
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See detailDesertification process in the sahelian belt of West Africa: What's the state of play?
Hountondji, Yvon ULg; Sokpon, Nestor; Nicolas, Jacques ULg et al

in Ozer, André; Swinne, Danielle (Eds.) Desertification: Migration, Health, Remediation and Local Governance (2008)

Detailed reference viewed: 46 (5 ULg)
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See detailLa désertification, cancer environnemental du Sud
Ozer, Pierre ULg

Article for general public (2005)

La désertification, problématique environnementale majeure pour le XXIe siècle, menace constamment près du tiers de la planète. Pourtant l'opinion publique se désintéresse de cette cause et les médias n ... [more ▼]

La désertification, problématique environnementale majeure pour le XXIe siècle, menace constamment près du tiers de la planète. Pourtant l'opinion publique se désintéresse de cette cause et les médias n'accordent que difficilement une petite place à ce sujet alors qu'ils font un large écho aux changements climatiques, à la perte de biodiversité, ou encore aux catastrophes naturelles. [...] [less ▲]

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See detailDesertification: migration, health, remediation and local governance
Marchal, Jean ULg

(2008)

Le terme de désertification est souvent associé dans les esprits à l'avancée du désert dont les dunes de sable envahissent lentement et inexorablement les régions fertiles proches. Cette vision populaire ... [more ▼]

Le terme de désertification est souvent associé dans les esprits à l'avancée du désert dont les dunes de sable envahissent lentement et inexorablement les régions fertiles proches. Cette vision populaire de la désertification a perdu tout fondement dans la plupart des milieux scientifiques : les déserts africains ne poursuivent pas leur inlassable marche vers le Sud, détruisant tout sur leur passage. On définit aujourd'hui la désertification comme un phénomène surtout socio-économique où les ressources naturelles se dégradent par les pressions démographiques et des pratiques d'occupation du sol présentant un caractère non durable. Les processus de formation de nouvelles régions désertiques où la diversité se trouve détruite sont fortement corrélés à la dégradation des sols, c'est-à-dire à l'appauvrissement progressif de leurs potentiels physiques, biologiques et économiques. Cette dégradation des sols menace sérieusement la productivité globale et, par conséquent, la subsistance de la population. Elle réduit la diversité de la vie végétale et animale, comme elle force les populations à se déplacer et à changer leur mode de vie, ce qui a aussi des conséquences sur la diversité, de culture, de langue et de savoir, des communautés habitant la zone dégradée. [less ▲]

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See detailDesertificazione in Africa
Ozer, Pierre ULg

Scientific conference (2010, November 10)

Detailed reference viewed: 46 (5 ULg)
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See detailDéserts, poussières et migrations
Ozer, Pierre ULg

Article for general public (2006)

Chaque année, le Sahara injecte près d'un milliard de tonnes de poussières dans l'atmosphère. Plus de 100 millions de tonnes de ces poussières prennent la direction de l'Europe. Beaucoup d'entre elles se ... [more ▼]

Chaque année, le Sahara injecte près d'un milliard de tonnes de poussières dans l'atmosphère. Plus de 100 millions de tonnes de ces poussières prennent la direction de l'Europe. Beaucoup d'entre elles se perdent dans la Méditerranée avant d'atteindre le Vieux Continent. D'autres retombent au gré des pluies et recouvrent périodiquement nos véhicules. Elles constituent un véritable problème de santé publique dans le sud de l'Europe, comme en Espagne, car l'importante concentration de ces fines particules dégrade la qualité de l'air que nous respirons. Certes, ce phénomène a toujours existé. Mais il a très fortement augmenté depuis les années 1980, depuis que les zones péridésertiques sont sujettes aux processus de plus en plus pressants de désertification. La végétation ayant disparu sur des centaines de millions d'hectares, de nouveaux sols ont été emportés par le vent. [...] [less ▲]

Detailed reference viewed: 517 (54 ULg)
See detailLe désherbage mécanique, une technique d'avenir
Dardenne, J.; Dewez, G.; Vandersmissen, P. et al

in Revue de l’Agriculture = Landbouwtijdschrift (1992), 45(6), 1193-1200

Detailed reference viewed: 26 (1 ULg)
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See detailDesiccation cracks formation in clay-barrier for nuclear waste disposal
Hubert, Julien ULg; Prime, Noémie; Plougonven, Erwan ULg et al

Conference (2016, February 16)

In geotechnical engineering, the desiccation cracking of soil is commonly observed. This phenomenon is detrimental to the behavior of earth material and earth structure. Desiccation cracks can lead to the ... [more ▼]

In geotechnical engineering, the desiccation cracking of soil is commonly observed. This phenomenon is detrimental to the behavior of earth material and earth structure. Desiccation cracks can lead to the overall failure of many geotechnical structures: • They can affect the slope stability of earth dams or embankments; • They can initiate internal erosion of embankments due to water flow through the cracks; • They can compromise the efficiency of soil barriers such as landfill liners and top covers. Nowadays, the storage of nuclear waste in deep impermeable geological layers is considered. These storages are based on the multi-barrier principle, the last of which being the host rock, typically a clayey material. In this context, maintaining the very low hydraulic conductivity of the host rock is crucial. Unfortunately, the ventilation of excavated galleries causes convective drying of the host material and can lead to crack formation. This work aims to understand in which conditions exactly, during convective drying, does cracking occur in clayey materials. An experimental campaign has been carried out to characterize the drying behavior of Boom clay which is the host rock at the underground research facility in Mol (Belgium). X-Ray micro-tomography has been used to analyze crack development as well as shrinkage. The experiments are used to calibrate the transfer parameters of a convective drying law based on the limit layer model. This calibration is based on agreement of the drying kinetics. A numerical study is then performed and aims at reproducing the behavior observed during the experiments. A thermo-hydro-mechanical coupled model is used to determine the stress distribution during the drying and a tensile failure criterion is suggested to predict crack genesis. Simulations are performed using the in-house built FEM code LAGAMINE. [less ▲]

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See detailDesiccation-tolerance : an advantage for the biotechnological applications of bacteria
Weekers, F.; Jacques, Ph.; Springael, D. et al

Poster (1999, July)

Detailed reference viewed: 26 (1 ULg)
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See detailDesign aids for the design of steel moment connections
Jaspart, Jean-Pierre ULg

in Proceedings of the 5th International Colloquium on Stability of Metal Structures (1996)

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See detailDesign and analysis of an SOI MEMS voltage step-up converter
Gleeson, R.; Kraft, Michaël ULg; White, N. M.

in Journal of Micromechanics and Microengineering (2013), 23(11), 114017

Detailed reference viewed: 16 (1 ULg)
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See detailDesign and analysis of MEMS step up voltage converters
Gleeson, R.; Kraft, Michaël ULg; White, Neil

in IEEE Sensors 2012 (2012, November)

This paper presents a comprehensive analysis of voltage step-up converters for energy harvesting and other low-power applications. The step-up operation is based on isolating the charge of a mechanically ... [more ▼]

This paper presents a comprehensive analysis of voltage step-up converters for energy harvesting and other low-power applications. The step-up operation is based on isolating the charge of a mechanically variable capacitor and varying the gap between the electrodes by an appropriate method of providing an actuation force i.e. electrostatic or physical. Two devices are presented; a bi-stable device and a resonant device, specifically designed for solar and vibration energy harvesting respectively. The bi-stable device introduces a separate electrostatic actuator element to manipulate the variable capacitor electrodes, whereas, in the case of the resonant device, ambient vibrations provide the necessary actuation force. System-level Multisim models have been developed and verified using 3D FEM Coventorware and MEMS+ simulations. The devices were then fabricated using a dicing-free Silicon-on-Insulator (SOI) process developed at the Southampton Nanofabrication Centre. [less ▲]

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See detailDesign and analysis of SOI MEMS voltage step up converters
Gleeson, R.; Kraft, Michaël ULg; White, N. M.

in Proceedings PowerMEMS 2012 (2012, December)

Detailed reference viewed: 13 (2 ULg)
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See detailDesign and analysis of two types of MEMS DC-DC step up voltage converters
Gleeson, R.; White, N. M.; Kraft, Michaël ULg

in MME 2011: Proceedings (2011)

Detailed reference viewed: 18 (0 ULg)