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Search Results: 1 - 10 of 250873 matches for " Thomas R Loveland "
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Simulated responses of soil organic carbon stock to tillage management scenarios in the Northwest Great Plains
Zhengxi Tan, Shuguang Liu, Zhengpeng Li, Thomas R Loveland
Carbon Balance and Management , 2007, DOI: 10.1186/1750-0680-2-7
Abstract: Model simulations show that the average amount of C (kg C ha-1yr-1) released from croplands between 1972 and 2000 was 246 with ATM, 261 with CT, and 210 with NT. The reduction in the rate of C emissions with conversion of CT to NT at the ecoregion scale is much smaller than those reported at plot scale and simulated for other regions. Results indicate that the response of SOC to tillage practices depends significantly on baseline SOC levels: the conversion of CT to NT had less influence on SOC stocks in soils having lower baseline SOC levels but would lead to higher potentials to mitigate C release from soils having higher baseline SOC levels.For assessing the potential of agricultural soils to mitigate C emissions with conservation tillage practices, it is critical to consider both the crop rotations being used at a local scale and the composition of all cropping systems at a regional scale.Many studies have identified the potential of soils cultivated with conservation practices (e.g., no-till) to sequester large amounts of carbon (C) [1,2]. It is estimated that conservation tillage practices across the United States may drive large-scale sequestration on the order of 24–40 Tg C yr-1 (Tg: teragram; 1 Tg = 1012 g), and that additional C sequestration of 25–63 Tg C yr-1 can be achieved through other modifications to traditional agricultural practices [3]. In regard to the C credit scenario established by the Kyoto Protocol, it is widely suggested that conversion of conventional tillage (CT) to no-till (NT) can help to support the profitability of C credits for farmers. The uncertainties of these sequestration scenarios, however, depend on soil organic carbon (SOC) monitoring and/or models [2].Recently, eddy-covariance measurements have been used to evaluate the contribution of NT practice to C dynamics in corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) rotation ecosystems at regional and national scales [1,2]. However, the relationships between net ecosystem
Predicting the production of neutron rich heavy nuclei in multi-nucleon transfer reactions using GRAZING-F
R. Yanez,W. Loveland
Physics , 2015,
Abstract: Background: Multi-nucleon transfer reactions have recently attracted attention as a possible path to the synthesis of new neutron-rich heavy nuclei. Purpose: We study transfer reactions involving massive nuclei with the intention of understanding if the semi-classical model GRAZING coupled to an evaporation and fission competition model can satisfactory reproduce experimental data on transfer reactions in which fission plays a role. Methods: We have taken the computer code GRAZING and have added fission competition to it (GRAZING-F) using our current understanding of $\Gamma_n/\Gamma_f$, fission barriers and level densities. Results: The code GRAZING-F seems to satisfactory reproduce experimental data for $+1p$, $+2p$ and $+3p$ transfers, but has limitations in reproducing measurements of larger above-target and below-target transfers. Nonetheless, we use GRAZING-F to estimate production rates of neutron-rich $N=126$ nuclei, actinides and transactinides. Conclusions: The GRAZING code, with appropriate modifications to account for fission decay as well as neutron emission by excited primary fragments, does not predict large cross sections for multi-nucleon transfer reactions leading to neutron-rich transactinide nuclei, but predicts opportunities to produce new neutron-rich actinide isotopes.
Overcoming the learning curve in hand-assisted laparoscopic live donor nephrectomy – a study in the animal model
J Loveland, C Joseph, D Liakos, R Botha, R Botha
South African Journal of Surgery , 2011,
Abstract: The demand for kidneys in South Africa is staggering. Only 38% of the kidney transplants done in 2008 were from related living donors. Laparoscopic living donor nephrectomy has been shown to have the advantages of decreased postoperative pain, better cosmesis and a quicker return to work when compared with the open technique. With limited surgical expertise, a realistic model was needed to overcome the learning curve. Methods. A total of 21 nephrectomies were performed on 12 pigs. The transperitoneal hand-assisted laparoscopic technique was used. Results. The median operative time was 75 minutes and the median warm ischaemic time 88 seconds. Three cases were aborted owing to major vascular injuries. Discussion. The advent of laparoscopic techniques has been associated with an increase in morbidity and complications in donor and recipient during the initial learning curve. We found that with our porcine model, 21 nephrectomies were adequate in overcoming the learning curve. After 15 nephrectomies no complications were noted.
Hand-assisted laparoscopic live donor nephrectomy – initial experience
J Loveland, D Liakos, C Joseph, JR Botha, R Britz
South African Journal of Surgery , 2011,
Abstract: Introduction. The advantages of minimally invasive live donor nephrectomy have been well documented, with no adverse effect on graft function. Minimal access nephrectomy has now become the standard of care in many units. We have adopted the hand-assisted laparoscopic live donor (HALLDN) technique, and present our initial experience with the first 24 cases. Material and methods. HALLDNs were performed transperitoneally. Primary outcomes included total operative time, warm ischaemic time, time to discharge, and postoperative complications. Warm ischaemic time was measured from the time of clamping the renal artery to the time of perfusing the kidney on the back table. Results. Mean total operative time was 143 minutes and mean warm ischaemic time 188 seconds. A downward trend was displayed for operative times. Mean time to discharge was 60 hours. A right nephrectomy was performed in 2 cases. No surgical morbidity is reported. We describe one donor mortality. Discussion. Our results compare favourably with those documented in the literature. Aberrant renal vascular anatomy had no adverse effect on operative or warm ischaemic times. HALLDN proved beneficial in patients with a high BMI. Conclusion. Surgical experience is vital when performing HALLDN. Overcoming the learning curve with an animal model is beneficial.
Fusion of 9,11Li with 208Pb
Loveland W.
EPJ Web of Conferences , 2011, DOI: 10.1051/epjconf/20111702003
Abstract: The fusion excitation functions for the reaction of 9Li with 70Zn and 208Pb were measured. In the reaction with 70Zn, the evaporation residues (EVRs) were detected by a radiochemical separation of the As and Ge EVRs followed by β-counting. In the reaction with 208Pb, the At EVRs were detected by α-counting. In both systems, one observes substantial sub-barrier fusion enhancement that cannot be explained by coupled channels calculations. The implication of these studies for the study of the 11Li + 208Pb reaction are discussed.
Synthesis of new neutron-rich heavy nuclei: An experimentalist's view
W. Loveland
Physics , 2013,
Abstract: I attempt to experimentally evaluate the prospects of synthesizing new neutron- rich superheavy nuclei. I consider three possible synthetic paths to neutron- rich superheavy nuclei: (a) the use of neutron-rich radioactive beams. (b) the use of damped collisions and (c) the use of multi-nucleon transfer reactions. I consider the prospects of synthesizing new n-rich isotopes of Rf-Bh using light n-rich radioactive beams and targeted beams from ReA3, FRIB and SPIRAL2. For the damped collision path, I present the results of a study of a surrogate reaction, 160Gd + 186W. These data indicate the formation of Au (trans-target) fragments and the depletion of yields of target-like fragments by fission and fragment emission. The data are compared to predictions of Zagrebaev and Greiner. For the multi-nucleon transfer reactions, the results of a study of the 136Xe + 208Pb reaction are discussed. I consider the possibility of multi-nucleon transfer reactions with radioactive beams.
An experimentalist's view of the uncertainties in understanding heavy element synthesis
W. Loveland
Physics , 2014, DOI: 10.1140/epja/i2015-15120-2
Abstract: The overall uncertainties in predicting heavy element synthesis cross sections are examined in terms of the uncertainties associated with the calculations of capture cross sections, fusion probabilities and survival probabilities. Attention is focussed on hot fusion reactions. The predicted heavy element formation cross sections are uncertain to at least one order of magnitude.
Synthetic Paths to the Heaviest Elements
W. Loveland
Physics , 2012, DOI: 10.1088/1742-6596/420/1/012004
Abstract: The cross section for producing a heavy reaction product, $\sigma$$_{EVR}$, can be represented by the equation \sigma_{EVR} = \sum_{J=0}^{J_\max} \sigma_{capture} (E_{c.m.},J) P_{CN} (E^*,J) W_{sur}(E^*,J), where $\sigma_{capture}(E_{c.m.},J)$ is the capture cross section at center of mass energy E$_{c.m.}$ and spin J. P$_{CN}$ is the probability that the projectile-target system will evolve from the contact configuration inside the fission saddle point to form a completely fused system rather than re-separating (quasifission, fast fission). W$_{sur}$ is the probability that the completely fused system will de-excite by neutron emission rather than fission. I discuss results of experiments that characterize these quantities in heavy element synthesis reactions. I also discuss the possibilities of synthesizing heavy nuclei using damped collisions and reactions using radioactive beams.
Divergent Pathways in COS-7 Cells Mediate Defective Internalization and Intracellular Routing of Truncated G-CSFR Forms in SCN/AML
Melissa G. Hunter, Morgan McLemore, Daniel C. Link, Megan Loveland, Alexander Copelan, Belinda R. Avalos
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0002452
Abstract: Background Expression of truncated G-CSFR forms in patients with SCN/AML induces hyperproliferation and prolonged cell survival. Previously, we showed that ligand internalization is delayed and degradation of truncated G-CSFR forms is defective in patients with SCN/AML. Methodology/Principal Findings In this study, we investigated the potential roles of dileucine and tyrosine-based motifs within the cytoplasmic domain of the G-CSFR in modulating ligand/receptor internalization. Using standard binding assays with radiolabeled ligand and COS-7 cells, substitutions in the dileucine motif or deletion of tyrosine residues in the G-CSFR did not alter internalization. Attachment of the transferrin receptor YTRF internalization motif to a truncated G-CSFR form from a patient with SCN/AML corrected defective internalization, but not receptor degradation suggesting that receptor internalization and degradation occur independently via distinct domains and/or processes. Conclusions Our data suggest that distinct domains within the G-CSFR mediate separate processes for receptor internalization and degradation. Our findings using standard binding assays differ from recently published data utilizing flow cytometry.
G-CSFR Ubiquitination Critically Regulates Myeloid Cell Survival and Proliferation
Jing Ai, Lawrence J. Druhan, Megan J. Loveland, Belinda R. Avalos
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003422
Abstract: The granulocyte colony-stimulating factor receptor (G-CSFR) is a critical regulator of granulopoiesis. Mutations in the G-CSFR in patients with severe congenital neutropenia (SCN) transforming to acute myelogenous leukemia (AML) have been shown to induce hypersensitivity and enhanced growth responses to G-CSF. Recent studies have demonstrated the importance of the ubiquitin/proteasome system in the initiation of negative signaling by the G-CSFR. To further investigate the role of ubiquitination in regulating G-CSFR signaling, we generated a mutant form of the G-CSFR (K762R/G-CSFR) which abrogates the attachment of ubiquitin to the lysine residue at position 762 of the G-CSFR that is deleted in the Δ716 G-CSFR form isolated from patients with SCN/AML. In response to G-CSF, mono-/polyubiquitination of the G-CSFR was impaired in cells expressing the mutant K762R/G-CSFR compared to cells transfected with the WT G-CSFR. Cells stably transfected with the K762R/G-CSFR displayed a higher proliferation rate, increased sensitivity to G-CSF, and enhanced survival following cytokine depletion, similar to previously published data with the Δ716 G-CSFR mutant. Activation of the signaling molecules Stat5 and Akt were also increased in K762R/G-CSFR transfected cells in response to G-CSF, and their activation remained prolonged after G-CSF withdrawal. These results indicate that ubiquitination is required for regulation of G-CSFR-mediated proliferation and cell survival. Mutations that disrupt G-CSFR ubiquitination at lysine 762 induce aberrant receptor signaling and hyperproliferative responses to G-CSF, which may contribute to leukemic transformation.
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