519 research outputs found
Cohomology of groups of diffeomorphims related to the modules of differential operators on a smooth manifold
Let be a manifold and be the cotangent bundle. We introduce a
1-cocycle on the group of diffeomorphisms of with values in the space of
linear differential operators acting on When is the
-dimensional sphere, , we use this 1-cocycle to compute the
first-cohomology group of the group of diffeomorphisms of , with
coefficients in the space of linear differential operators acting on
contravariant tensor fields.Comment: arxiv version is already officia
Improvement in HSS grade for early stands of hot strip mills - Metallurgical features and mechanical properties assessment
peer reviewedAurora and Kosmos grades are HSS alloys belonging to the complex Fe-Cr-C-X
system, where X is a strong carbide former element of the V, Mo or W type.
Both alloys were metallurgically characterised prior to their comparison.
Metallurgical analyses involved phases identification and carbides quantification by
using Scanning Electron Microscopy and Energy Dispersive X rays. Differential
Thermal Analysis was performed to allow a better understanding of the solidification
sequence of studied alloys while mechanical tests performed were compressive at
room temperature and bulk hardness at usual service temperatures. An attempt was
made in order to connect experimental results to the good behaviour in operation of
Aurora grade.
In fact Aurora grade appeared to exhibit strong metallurgical differences when
compared to Kosmos grade, especially as concern in nature and amount of carbides
A rewriting of the relation between the acolinearity of annihilation photons and their energy in the context of positron emission tomography
Acolinearity of the annihilation photons observed in Positron Emission
Tomography (PET) is described as following a Gaussian distribution. However, it
is never explicitly said if it refers to the amplitude of the acolinearity
angle or its 2D distribution relative to the case without acolinearity (herein
defined as the acolinearity deviation). Since the former is obtained by
integrating the latter, a wrong interpretation would lead to very different
results. The paper of Shibuya et al. (2007), differs from the previous studies
since it is based on the precise measurement of the energy of the annihilation
photons. They also show that acolinearity follows a Gaussian distribution in
the context of PET. However, their notation, which relies on being on the plane
where the two annihilation photons travel, could mean that their observation
refers to the amplitude of the acolinearity angle. If that understanding is
correct, it would mean that acolinearity deviation follows a 2D Gaussian
distribution divided by the norm of its argument. Thus, we revisited the proof
presented in Shibuya et al. (2007) by using an explicit description of the
acolinearity in the 3D unit sphere
Metformin reduces left ventricular eccentric remodeling in experimental volume overload in the rat
Left ventricular hypertrophy (LVH) is often associated with a change in myocardial energy substrate preference
from fatty acids to glucose. A possible anti hypertrophic treatment strategy could aim at stimulating or restoring
normal myocardial energy metabolism. Metformin, an adenosine monophosphate-activated protein kinase (AMPK)
activator used in the management of glucose metabolism in diabetes, is also a fatty acid oxidation stimulator. The
effect of metformin on the development of eccentric LVH and ventricular function in chronic left ventricular (LV)
volume overload (VO) is unknown. This study was designed to study this question in a VO rat model caused by
severe aortic valve regurgitation (AR). Male Wistar rats were divided in four groups (13-15 animals / group): Shams
(S) treated or not (C) with metformin (M; 100 mg/kg/d PO) and severe ARreceiving or not metformin. Treatment was
started one week before surgery and the animals were sacrificed 9 weeks later. As expected AR rats developed
severe eccentric LVH during the course of the protocol. Metformin treatment did not influence the total heart weight.
However, LV remodeling associated with the severe VO was severe in ARM than in ARC. Fractional shortening, a
marker of systolic function, was significantly higher in ARM compared to ARC group. Metformin also increased the
activity of enzymes associated with fatty acid oxidation while inhibiting phosphofructokinase, a glycolytic enzyme. A
2 month treatment with metformin reduced LV eccentric remodeling associated with severe VO and helped maintain
a better systolic function
Endurance training or beta-blockade can partially block the energy metabolism remodeling taking place in experimental chronic left ventricle volume overload.
BACKGROUND:
Patients with chronic aortic valve regurgitation (AR) causing left ventricular (LV) volume overload can remain asymptomatic for many years despite having a severely dilated heart. The sudden development of heart failure is not well understood but alterations of myocardial energy metabolism may be contributive. We studied the evolution of LV energy metabolism in experimental AR.
METHODS:
LV glucose utilization was evaluated in vivo by positron emission tomography (microPET) scanning of 6-month AR rats. Sham-operated or AR rats (n = 10-30 animals/group) were evaluated 3, 6 or 9 months post-surgery. We also tested treatment intervention in order to evaluate their impact on metabolism. AR rats (20 animals) were trained on a treadmill 5 times a week for 9 months and another group of rats received a beta-blockade treatment (carvedilol) for 6 months.
RESULTS:
MicroPET revealed an abnormal increase in glucose consumption in the LV free wall of AR rats at 6 months. On the other hand, fatty acid beta-oxidation was significantly reduced compared to sham control rats 6 months post AR induction. A significant decrease in citrate synthase and complex 1 activity suggested that mitochondrial oxidative phosphorylation was also affected maybe as soon as 3 months post-AR.Moderate intensity endurance training starting 2 weeks post-AR was able to partially normalize the activity of various myocardial enzymes implicated in energy metabolism. The same was true for the AR rats treated with carvedilol (30 mg/kg/d). Responses to these interventions were different at the level of gene expression. We measured mRNA levels of a number of genes implicated in the transport of energy substrates and we observed that training did not reverse the general down-regulation of these genes in AR rats whereas carvedilol normalized the expression of most of them.
CONCLUSION:
This study shows that myocardial energy metabolism remodeling taking place in the dilated left ventricle submitted to severe volume overload from AR can be partially avoided by exercise or beta-blockade in rats
Angiotensin II converting enzyme inhibition improves survival, ventricular remodeling and myocardial energetics in experimental aortic regurgitation.
Background— Aortic valve regurgitation (AR) is a volume-overload disease causing severe eccentric left ventricular (LV) hypertrophy and eventually heart failure. There is currently no approved drug to treat patients with AR. Many vasodilators including angiotensin-converting enzyme inhibitors have been evaluated in clinical trials, but although some results were promising, others were inconclusive. Overall, no drug has yet been able to improve clinical outcome in AR and the controversy remains. We have previously shown in an animal model that captopril (Cpt) reduced LV hypertrophy and protected LV systolic function, but we had not evaluated the clinical outcome. This protocol was designed to evaluate the effects of a long-term Cpt treatment on survival in the same animal model of severe aortic valve regurgitation.
Methods and Results—Forty Wistar rats with AR were treated or untreated with Cpt (1 g/L in drinking water) for a period of 7 months to evaluate survival, myocardial remodeling, and function by echocardiography as well as myocardial metabolism by µ positron emission tomography scan. Survival was significantly improved in Cpt-treated animals with a survival benefit visible as soon as after 4 months of treatment. Cpt reduced LV dilatation and LV hypertrophy. It also significantly improved the myocardial metabolic profile by restoring the level of fatty acids metabolic enzymes and use.
Conclusions—In a controlled animal model of pure severe aortic valve regurgitation, Cpt treatment reduced LV remodeling and LV hypertrophy and improved myocardial metabolic profile and survival. These results support the need to reevaluate the role of angiotensin-converting enzyme inhibitors in humans with AR in a large, carefully designed prospective clinical trial
Image-derived input function in dynamic human PET/CT: methodology and validation with 11C-acetate and 18F-fluorothioheptadecanoic acid in muscle and 18F-fluorodeoxyglucose in brain
International audienc
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