Background: The most common bariatric surgery, Roux-en-Y gastric bypass, leads to glycemia normal... more Background: The most common bariatric surgery, Roux-en-Y gastric bypass, leads to glycemia normalization in most patients long before there is any appreciable weight loss. This effect is too large to be attributed purely to caloric restriction, so a number of other mechanisms have been proposed. The most popular hypothesis is enhanced production of an incretin, active glucagon-like peptide-1 (GLP-1), in the lower intestine. We therefore set out to test this hypothesis with a model which is simple enough to be robust and credible. Method: Our method involves (1) setting up a set of time-dependent equations for the concentrations of the most relevant species, (2) considering an "adiabatic" (or quasi-equilibrium) state in which the concentrations are slowly varying compared to reaction rates (and which in the present case is a postprandial state), and (3) solving for the dependent concentrations (of e.g. insulin and glucose) as an independent concentration (of e.g. GLP-1) is varied. Results: Even in the most favorable scenario, with maximal values for (i) the increase in active GLP-1 concentration and (ii) the effect of GLP-1 on insulin production, enhancement of GLP-1 alone cannot account for the observations. I.e., the largest possible decrease in glucose predicted by the model is smaller than reported decreases, and the model predicts no decrease whatsoever in glucose×insulin, in contrast to large observed decreases in homeostatic model assessment insulin resistance (HOMA-IR). On the other hand, both effects can be accounted for if the surgery leads to a substantial increase in some substance that opens an alternative insulin-independent pathway for glucose transport into muscle cells, which perhaps uses the same intracellular pool of GLUT-4 that is employed in an established insulin-independent pathway stimulated by muscle contraction during exercise. Conclusions: Glycemia normalization following Roux-en-Y gastric bypass is undoubtedly caused by a variety of mechanisms, which may include caloric restriction, enhanced GLP-1, and perhaps others proposed in earlier papers on this subject. However, the present results suggest that another possible mechanism should be added to the list of candidates: enhanced production in the lower intestine of a substance which opens an alternative insulin-independent pathway for glucose transport.
phase separation due to differentiated cell-cell adhesion. Various nontrivial emerging patterns r... more phase separation due to differentiated cell-cell adhesion. Various nontrivial emerging patterns resembling observed tumor morphology were identified over the parameter space of our model. However, the previous development and analysis of our model have been implicitly based on the assumption of a homogeneous microenvironmental background and unrestricted boundaries. Most clinically relevant tumors are constrained by particular organ tissue structures that may co-evolve with the progressing tumors and have profound impact on tumor-microenvironment interactions. Here we adopt a recently developed diffuse-domain approach, utilizing the Cahn-Hilliard equation framework we have previously established, to adapt partial-differential-equation models of tumor growth to a co-evolving tissue geometry. We will demonstrate this approach by modeling the growth of lymphoma within a lymph node and ductal carcinoma in situ within mammary ducts.
In December 2011 the Qatar National Historic Environment Record (QNHER), Qatar Museum Authority a... more In December 2011 the Qatar National Historic Environment Record (QNHER), Qatar Museum Authority and University of Birmingham, collaborated with Texas A & M University – Qatar (TAMUQ) to visualize sea level change and its effects on patterns of human occupation on a site specific level. This data was derived from extensive coring and subsurface modeling in Wādī debayān, north western Qatar. During prehistory the wadi would have been subject to dynamic periods of environmental change. This has been related to two periods of dramatic sea-level rise during the Holocene geological epoch (12000BP to the present era). Evidence from other sites in Qatar indicate that these two episodes may have reached ‘highstands’ of between 1 and 3m above modern sea level.
Vizualising the prehistoric environment of the wadi presents an important opportunity to test several of our assumptions about these past environments in the wadi and contribute to ongoing research aims. Immersive visualization allows the examination the dramatic effects dynamic environmental change would have had upon past populations and prehistoric environments in the Arabian Gulf. This tool not only has applications for academic based research but also for providing uncomplicated public access. There are important benefits for schools, universities and museums, where visual representation can convey concepts more readily than descriptive narrative.
Background: The most common bariatric surgery, Roux-en-Y gastric bypass, leads to glycemia normal... more Background: The most common bariatric surgery, Roux-en-Y gastric bypass, leads to glycemia normalization in most patients long before there is any appreciable weight loss. This effect is too large to be attributed purely to caloric restriction, so a number of other mechanisms have been proposed. The most popular hypothesis is enhanced production of an incretin, active glucagon-like peptide-1 (GLP-1), in the lower intestine. We therefore set out to test this hypothesis with a model which is simple enough to be robust and credible. Method: Our method involves (1) setting up a set of time-dependent equations for the concentrations of the most relevant species, (2) considering an "adiabatic" (or quasi-equilibrium) state in which the concentrations are slowly varying compared to reaction rates (and which in the present case is a postprandial state), and (3) solving for the dependent concentrations (of e.g. insulin and glucose) as an independent concentration (of e.g. GLP-1) is varied. Results: Even in the most favorable scenario, with maximal values for (i) the increase in active GLP-1 concentration and (ii) the effect of GLP-1 on insulin production, enhancement of GLP-1 alone cannot account for the observations. I.e., the largest possible decrease in glucose predicted by the model is smaller than reported decreases, and the model predicts no decrease whatsoever in glucose×insulin, in contrast to large observed decreases in homeostatic model assessment insulin resistance (HOMA-IR). On the other hand, both effects can be accounted for if the surgery leads to a substantial increase in some substance that opens an alternative insulin-independent pathway for glucose transport into muscle cells, which perhaps uses the same intracellular pool of GLUT-4 that is employed in an established insulin-independent pathway stimulated by muscle contraction during exercise. Conclusions: Glycemia normalization following Roux-en-Y gastric bypass is undoubtedly caused by a variety of mechanisms, which may include caloric restriction, enhanced GLP-1, and perhaps others proposed in earlier papers on this subject. However, the present results suggest that another possible mechanism should be added to the list of candidates: enhanced production in the lower intestine of a substance which opens an alternative insulin-independent pathway for glucose transport.
phase separation due to differentiated cell-cell adhesion. Various nontrivial emerging patterns r... more phase separation due to differentiated cell-cell adhesion. Various nontrivial emerging patterns resembling observed tumor morphology were identified over the parameter space of our model. However, the previous development and analysis of our model have been implicitly based on the assumption of a homogeneous microenvironmental background and unrestricted boundaries. Most clinically relevant tumors are constrained by particular organ tissue structures that may co-evolve with the progressing tumors and have profound impact on tumor-microenvironment interactions. Here we adopt a recently developed diffuse-domain approach, utilizing the Cahn-Hilliard equation framework we have previously established, to adapt partial-differential-equation models of tumor growth to a co-evolving tissue geometry. We will demonstrate this approach by modeling the growth of lymphoma within a lymph node and ductal carcinoma in situ within mammary ducts.
In December 2011 the Qatar National Historic Environment Record (QNHER), Qatar Museum Authority a... more In December 2011 the Qatar National Historic Environment Record (QNHER), Qatar Museum Authority and University of Birmingham, collaborated with Texas A & M University – Qatar (TAMUQ) to visualize sea level change and its effects on patterns of human occupation on a site specific level. This data was derived from extensive coring and subsurface modeling in Wādī debayān, north western Qatar. During prehistory the wadi would have been subject to dynamic periods of environmental change. This has been related to two periods of dramatic sea-level rise during the Holocene geological epoch (12000BP to the present era). Evidence from other sites in Qatar indicate that these two episodes may have reached ‘highstands’ of between 1 and 3m above modern sea level.
Vizualising the prehistoric environment of the wadi presents an important opportunity to test several of our assumptions about these past environments in the wadi and contribute to ongoing research aims. Immersive visualization allows the examination the dramatic effects dynamic environmental change would have had upon past populations and prehistoric environments in the Arabian Gulf. This tool not only has applications for academic based research but also for providing uncomplicated public access. There are important benefits for schools, universities and museums, where visual representation can convey concepts more readily than descriptive narrative.
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Papers by O. Bouhali
Vizualising the prehistoric environment of the wadi presents an important opportunity to test several of our assumptions about these past environments in the wadi and contribute to ongoing research aims. Immersive visualization allows the examination the dramatic effects dynamic environmental change would have had upon past populations and prehistoric environments in the Arabian Gulf. This tool not only has applications for academic based research but also for providing uncomplicated public access. There are important benefits for schools, universities and museums, where visual representation can convey concepts more readily than descriptive narrative.
Vizualising the prehistoric environment of the wadi presents an important opportunity to test several of our assumptions about these past environments in the wadi and contribute to ongoing research aims. Immersive visualization allows the examination the dramatic effects dynamic environmental change would have had upon past populations and prehistoric environments in the Arabian Gulf. This tool not only has applications for academic based research but also for providing uncomplicated public access. There are important benefits for schools, universities and museums, where visual representation can convey concepts more readily than descriptive narrative.