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Search Results: 1 - 10 of 226769 matches for " Donald R.;Hopmans "
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Software to model soil water retention curves (SWRC, version 2.00)
Dourado-Neto, Durval;Nielsen, Donald R.;Hopmans, Jan W.;Reichardt, Klaus;Bacchi, Osny Oliveira Santos;
Scientia Agricola , 2000, DOI: 10.1590/S0103-90162000000100031
Abstract: a software for the adjustment of soil water retention curves (swrc) is presented, using twelve models found in the literature.
Software to model soil water retention curves (SWRC, version 2.00)
Dourado-Neto Durval,Nielsen Donald R.,Hopmans Jan W.,Reichardt Klaus
Scientia Agricola , 2000,
Abstract: A software for the adjustment of soil water retention curves (SWRC) is presented, using twelve models found in the literature.
Carbon isotopic composition of branched tetraether membrane lipids in soils suggest a rapid turnover and a heterotrophic life style of their source organism(s)
J. W. H. Weijers, G. L. B. Wiesenberg, R. Bol, E. C. Hopmans,R. D. Pancost
Biogeosciences (BG) & Discussions (BGD) , 2010,
Abstract: Branched Glycerol Dialkyl Glycerol Tetraethers (GDGTs) are membrane spanning lipids synthesised by as yet unknown bacteria that thrive in soils and peat. In order to obtain more information on their ecological niche, the stable carbon isotopic composition of branched GDGT-derived alkanes, obtained upon ether bond cleavage, has been determined in a peat and various soils, i.e. forest, grassland and cropland, covered by various vegetation types, i.e., C3- vs. C4-plant type. These δ13C values are compared with those of bulk organic matter and higher plant derived n-alkanes from the same soils. With average δ13C values of 28‰, branched GDGTs in C3 soils are only slightly depleted (ca. 1‰) relative to bulk organic carbon and on average 8.5‰ enriched relative to plant wax-derived long-chain n-alkanes ( nC29–nC33). In an Australian soil dominantly covered with C4 type vegetation, the branched GDGTs have a δ13C value of 18‰, clearly higher than observed in soils with C3 type vegetation. As with C3 vegetated soils, branched GDGT δ13C values are slightly depleted (1‰) relative to bulk organic carbon and enriched (ca. 5‰) relative to n-alkanes in this soil. The δ13C values of branched GDGT lipids being similar to bulk organic carbon and their co-variation with those of bulk organic carbon and plant waxes, suggest a heterotrophic life style and assimilation of relatively heavy and likely labile substrates for the as yet unknown soil bacteria that synthesise the branched GDGT lipids. However, a chemoautotrophic lifestyle, i.e. consuming respired CO2, could not be fully excluded based on these data alone. Based on a natural labelling experiment of a C3/C4 crop change introduced on one of the soils 23 years before sampling and based on a free-air CO2 enrichment experiment with labelled CO2 on another soil, a turnover time of ca. 18 years has been estimated for branched GDGTs in these arable soils.
A brief review of soil water, solute transport and regionalized variable analysis
Nielsen, D.R.;Hopmans, J.W.;Kutílek, M.;Wendroth, O.;
Scientia Agricola , 1997, DOI: 10.1590/S0103-90161997000300012
Abstract: we initially review basic concepts of the forces acting on soil water, soil water potential and soil water retention, and equations to describe soil water movement under water-saturated and unsaturated conditions. processes of infiltration, evaporation and redistribution of water will be presented for simple initial and boundary conditions occurring within homogeneous soil columns. next we consider the physical, chemical and biological processes within a soil profile that distribute, dilute or concentrate solute species within the liquid phase of a soil the relative concentration of solutes in the liquid phase governs not only the retention and transport of water within soils but also contributes to our understanding of managing the quality of water within soils and that moving below the recall of plant roots deeper into the vadose zone. a complete set of references about this subject is available in kutílek & nielsen (1994). in the last section we recall the differences between classical statistical concepts and those that utilize the coordinates of space and time at which state variables across the landscape are observed. our presentation win cover the basic ideas about autocorrelation, crosscorrelation, applied time series analyses, state space analyses and similar techniques currently being used to enhance field research and investigations of land and water management.
Vadose zone measurement and modeling
Hopmans, J. W.;Clausnitzer, V.;Kosugi, K.I.;Nielsen, D.R.;Somma, F.;
Scientia Agricola , 1997, DOI: 10.1590/S0103-90161997000300004
Abstract: the following treatise is a summary of some of the ongoing research activities in the soil physics program at the university of california in davis. each of the four listed areas win be presented at the workshop on special topics on soil physics and crop modeling in piracicaba at the university of sao paulo. we limited ourselves to a general overview of each area, but will present a more thorough discussion with examples at the workshop.
Selected research opportunities in soil physics
Nielsen, D.R.;Kutilek, M.;Wendroth, O.;Hopmans, J.W.;
Scientia Agricola , 1997, DOI: 10.1590/S0103-90161997000300010
Abstract: selected research opportunities are discussed in order to guide soil science research, with emphasis on soil physics, with the aim of improving agricultural productivity and environmental quality.
Carbon isotopic composition of branched tetraether membrane lipids in soils suggest a rapid turnover and a heterotrophic life style of their source organism(s)
J. W. H. Weijers,G. L. B. Wiesenberg,R. Bol,E. C. Hopmans
Biogeosciences Discussions , 2010, DOI: 10.5194/bgd-7-3691-2010
Abstract: Branched Glycerol Dialkyl Glycerol Tetraethers (GDGTs) are membrane spanning lipids synthesised by as yet unknown bacteria that thrive in soils and peat. In order to obtain more information on their ecological niche, the stable carbon isotopic composition of branched GDGT-derived alkanes, obtained upon ether bond cleavage, has been determined in various soils, i.e. peat, forest, grassland and cropland, covered by various vegetation types, i.e., C3- vs. C4-plant type. These δ13C values are compared with those of bulk organic matter and higher plant derived n-alkanes from the same soils. With average δ13C values of 28‰, branched GDGTs in C3 soils are only slightly depleted (ca. 1‰) relative to bulk organic carbon and on average 8.5‰ enriched relative to plant wax-derived long-chain n-alkanes (nC29–nC33). In an Australian soil covered with C4 type vegetation, the branched GDGTs have a δ13C value of 18‰, clearly higher than observed in soils with C3 type vegetation. As with C3 vegetated soils, branched GDGT δ13C values are slightly depleted (1‰) relative to bulk organic carbon and enriched (ca. 5‰) relative to n-alkanes in this soil. The δ13C values of branched GDGT lipids being similar to bulk organic carbon and their co-variation with those of bulk organic carbon and plant waxes, suggest a heterotrophic life style and assimilation of relatively heavy and likely labile substrates for the as yet unknown soil bacteria that synthesise the branched GDGT lipids. However, a chemoautotrophic lifestyle, i.e. consuming respired CO2, could not be fully excluded based on these data alone. Based on a natural labelling experiment of a C3/C4 crop change introduced on one of the soils 23 years before sampling and based on a free air CO2 enrichment experiment with labelled CO2 on another soil, a turnover time of ca. 17 years has been estimated for branched GDGTs in these arable soils.
Carbon isotopic composition of branched tetraether membrane lipids in soils suggest a rapid turnover and a heterotrophic life style of their source organism(s)
J. W. H. Weijers,G. L. B. Wiesenberg,R. Bol,E. C. Hopmans
Biogeosciences (BG) & Discussions (BGD) , 2010, DOI: 10.5194/bg-7-2959-2010
Abstract: Branched Glycerol Dialkyl Glycerol Tetraethers (GDGTs) are membrane spanning lipids synthesised by as yet unknown bacteria that thrive in soils and peat. In order to obtain more information on their ecological niche, the stable carbon isotopic composition of branched GDGT-derived alkanes, obtained upon ether bond cleavage, has been determined in a peat and various soils, i.e. forest, grassland and cropland, covered by various vegetation types, i.e., C3- vs. C4-plant type. These δ13C values are compared with those of bulk organic matter and higher plant derived n-alkanes from the same soils. With average δ13C values of 28‰, branched GDGTs in C3 soils are only slightly depleted (ca. 1‰) relative to bulk organic carbon and on average 8.5‰ enriched relative to plant wax-derived long-chain n-alkanes ( nC29–nC33). In an Australian soil dominantly covered with C4 type vegetation, the branched GDGTs have a δ13C value of 18‰, clearly higher than observed in soils with C3 type vegetation. As with C3 vegetated soils, branched GDGT δ13C values are slightly depleted (1‰) relative to bulk organic carbon and enriched (ca. 5‰) relative to n-alkanes in this soil. The δ13C values of branched GDGT lipids being similar to bulk organic carbon and their co-variation with those of bulk organic carbon and plant waxes, suggest a heterotrophic life style and assimilation of relatively heavy and likely labile substrates for the as yet unknown soil bacteria that synthesise the branched GDGT lipids. However, a chemoautotrophic lifestyle, i.e. consuming respired CO2, could not be fully excluded based on these data alone. Based on a natural labelling experiment of a C3/C4 crop change introduced on one of the soils 23 years before sampling and based on a free-air CO2 enrichment experiment with labelled CO2 on another soil, a turnover time of ca. 18 years has been estimated for branched GDGTs in these arable soils.
Postulated Vasoactive Neuropeptide Autoimmunity in Fatigue-Related Conditions: A Brief Review and Hypothesis
Donald R. Staines
Clinical and Developmental Immunology , 2006, DOI: 10.1080/17402520600568252
Abstract: Disorders such as chronic fatigue syndrome (CFS) and gulf war syndrome (GWS) are characterised by prolonged fatigue and a range of debilitating symptoms of pain, intellectual and emotional impairment, chemical sensitivities and immunological dysfunction. Sudden infant death syndrome (SIDS) surprisingly may have certain features in common with these conditions. Post-infection sequelae may be possible contributing factors although ongoing infection is unproven. Immunological aberration may prove to be associated with certain vasoactive neuropeptides (VN) in the context of molecular mimicry, inappropriate immunological memory and autoimmunity.
Current understanding of the relationship between cervical manipulation and stroke: what does it mean for the chiropractic profession?
Donald R Murphy
Chiropractic & Manual Therapies , 2010, DOI: 10.1186/1746-1340-18-22
Abstract: This new understanding has shifted the focus for the chiropractic physician from one of attempting to "screen" for "risk of complication to manipulation" to one of recognizing the patient who may be having VADS so that early diagnosis and intervention can be pursued. In addition, this new understanding presents the chiropractic profession with an opportunity to change the conversation about CMT and VADS by taking a proactive, public health approach to this uncommon but potentially devastating disorder.Cervical manipulative therapy (CMT) and vertebral artery dissection and stroke (VADS) have been linked in controversy for at least 75 years [1]. At the center of the controversy have been neurologists and other medical practitioners who have often perceived VADS to be a relatively frequent complication to CMT [2,3] and chiropractors, who have generally perceived VADS after manipulation to be exceedingly rare [4-6]. Others have been involved as well [7,8]. Starting with isolated case reports and culminating in four case-control studies, our understanding of the relationship between CMT and VADS has evolved considerably. The purpose of this commentary is to present an overview of the history of this relationship and to discuss how the chiropractic profession and other professionals who use manual therapy can move forward and focus on the wellbeing of patients and the public while avoiding defensiveness.There are several pathophysiologic processes that can lead to stroke, such as atherosclerosis, hemorrhage secondary to aneurism or arteriovenous malformation, and arterial dissection. Arterial dissection is a specific process in which a tear occurs in the wall of the involved artery [9]. Cervical artery dissection is a general term for dissection that involves either the carotid artery (carotid artery dissection) or vertebral artery (vertebral artery dissection). As vertebral artery dissection has been found to have an association with visits to chiropractic physicians, th
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