Is the Helmholtz equation really sign-indefinite?

The usual variational (or weak) formulations of the Helmholtz equation are sign-indefinite in the sense that the bilinear forms cannot be bounded below by a positive multiple of the appropriate norm squared. This is often for a good reason, since in bounded domains under certain boundary conditions the solution of the Helmholtz equation is not unique at wavenumbers that correspond to eigenvalues of the Laplacian, and thus the variational problem cannot be sign-definite. However, even in cases where the solution is unique for all wavenumbers, the standard variational formulations of the Helmholtz equation are still indefinite when the wavenumber is large. This indefiniteness has implications for both the analysis and the practical implementation of finite element methods. In this paper we introduce new sign-definite (also called coercive or elliptic) formulations of the Helmholtz equation posed in either the interior of a star-shaped domain with impedance boundary conditions, or the exterior of a star-shaped domain with Dirichlet boundary conditions. Like the standard variational formulations, these new formulations arise just by multiplying the Helmholtz equation by particular test functions and integrating by parts

Early transformation of the Chinese power sector to avoid additional coal lock-in

Emission reduction from the coal-dominated power sector is vital for achieving China's carbon mitigation targets. Although the coal expansion has been slowed down due to the cancellation of and delay in new construction, coal-based power was responsible for over one third of China's energy-related CO2 emissions by 2018. Moreover, with a technical lifetime of over 30 years, current investment in coal-based power could hinder CO2 mitigation until 2050. Therefore, it is important to examine whether the current coal-based power planning aligns with the long-term climate targets. This paper introduces China's Nationally Determined Contribution (NDC) goals and an ambitious carbon budget along with global pathways well-below 2 degrees that are divided into five integrated assessment models, which are two national and three global models. We compare the models' results with bottom-up data on current capacity additions and expansion plans to examine if the NDC targets are in line with 2-degree pathways. The key findings are: 1. NDC goals alone are unlikely to lead to significant reductions in coal-based power generation. On the contrary, more plants may be built before 2030; 2. this would require an average of 187–261 TWh of annual coal-based power capacity reduction between 2030 and 2050 to achieve a 2 °C compatible trajectory, which would lead to the stranding of large-scale coal-based power plants; 3. if the reduction in coal power can be brought forward to 2020, the average annual coal-based power reduction required would be 104–155 TWh from 2020 to 2050 and the emissions could peak earlier; 4. early regulations in coal-based power would require accelerated promotion of alternatives between 2020 and 2030, with nuclear, wind and solar power expected to be the most promising alternatives. By presenting the stranding risk and viability of alternatives, we suggest that both the government and enterprises should remain cautious about making new investment in coal-based power sector

Revealing the true partitioning character of zirconium in additively manufactured polycrystalline superalloys

International audienc

System integration of wind and solar power in Integrated Assessment Models: A cross-model evaluation of new approaches

Mitigation-Process Integrated Assessment Models (MP-IAMs) are used to analyze long-term transformation pathways of the energy system required to achieve stringent climate change mitigation targets. Due to their substantial temporal and spatial aggregation, IAMs cannot explicitly represent all detailed challenges of integrating the variable renewable energies (VRE) wind and solar in power systems, but rather rely on parameterized modeling approaches. In the ADVANCE project, six international modeling teams have developed new approaches to improve the representation of power sector dynamics and VRE integration in IAMs. In this study, we qualitatively and quantitatively evaluate the last years' modeling progress and study the impact of VRE integration modeling on VRE deployment in IAM scenarios. For a comprehensive and transparent qualitative evaluation, we first develop a framework of 18 features of power sector dynamics and VRE integration. We then apply this framework to the newly-developed modeling approaches to derive a detailed map of strengths and limitations of the different approaches. For the quantitative evaluation, we compare the IAMs to the detailed hourly-resolution power sector model REMIX. We find that the new modeling approaches manage to represent a large number of features of the power sector, and the numerical results are in reasonable agreement with those derived from the detailed power sector model. Updating the power sector representation and the cost and resources of wind and solar substantially increased wind and solar shares across models: Under a carbon price of 30$/tCO2 in 2020 (increasing by 5% per year), the model-average cost-minimizing VRE share over the period 2050–2100 is 62% of electricity generation, 24%-points higher than with the old model version

Impact of plasma Lp-PLA2 activity on the progression of aortic stenosis : the PROGRESSA study.

Objectives : The purpose of this prospective study was to examine the relationship between plasma lipoprotein–associated phospholipase A2 (Lp-PLA2) activity and the progression rate of aortic stenosis (AS). Background : We recently reported that Lp-PLA2 is highly expressed in stenotic aortic valves where it may contribute to the mineralization of valvular interstitial cells. Methods : Patients with AS were prospectively recruited in the PROGRESSA (Metabolic Determinants of the Progression of Aortic Stenosis) study. AS progression rate was assessed by annualized increase in peak aortic jet velocity (Vpeak), mean gradient (MG), and aortic valve area index (AVAi). Circulating Lp-PLA2 activity was measured and dichotomized based on the median value. Results : Of 183 patients included in this subanalysis of the PROGRESSA study, 70% were men and the mean age was 66 ± 13 years. Over the 2.5 ± 1.4 years of follow up, the AS progression rate tended to be higher in patients with high versus low Lp-PLA2 activity (annualized Vpeak = 0.17 ± 0.23 m/s vs. 0.12 ± 0.18 m/s; p = 0.14). There was a significant interaction (p < 0.05) between baseline AS severity and Lp-PLA2 activity with respect to impact on AS progression rate. In patients with mild AS (i.e., Vpeak <3 m/s; n = 123), increased Lp-PLA2 activity was associated with a significantly faster AS progression rate (Vpeak 0.16 ± 0.18 m/s vs. 0.09 ± 0.14 m/s; p = 0.01) but not in patients with moderate or severe AS (p = 0.99). After adjustment for other risk factors, increased Lp-PLA2 activity remained independently associated with faster AS progression rate (p = 0.005) in the former subset. Conclusions : There was no significant association between plasma Lp-PLA2 activity or mass and stenosis progression in the whole cohort. However, increased Lp-PLA2 activity was associated with a faster stenosis progression rate in the subset of patients with mild AS. These findings provide an impetus for the elaboration of a randomized trial targeting Lp-PLA2 activity in patients with early stages of calcific aortic valve disease

Visceral adiposity and left ventricular mass and function in patients with aortic stenosis : the PROGRESSA study

Background : Recent studies have reported that obesity, metabolic syndrome, and diabetes are associated with left ventricular (LV) hypertrophy (LVH) and dysfunction in patients with aortic stenosis (AS). The purpose of this study was to examine the association between amount and distribution of body fat and LVH and systolic dysfunction in AS patients. Methods : One hundred twenty-four patients with AS were prospectively recruited in the PROGRESSA (Metabolic Determinants of the Progression of Aortic Stenosis) study and underwent Doppler echocardiography and computed tomography scan. Presence and severity of LVH was assessed according to LV mass indexed for height2.7 and LV dysfunction according to global longitudinal strain (GLS). Computed tomography was used to quantify abdominal visceral (VAT) and subcutaneous (SAT) adipose tissue, and total adipose tissue (TAT). Results : Body mass index (BMI) correlated strongly with TAT (r = 0.85), moderately with VAT (r = 0.70), and SAT (r = 0.69), and weakly with the proportion of VAT (VAT/TAT ratio: r = 0.19). In univariate analysis, greater BMI, TAT, VAT, SAT, and VAT/TAT were associated with increased LV mass index and greater VAT and VAT/TAT ratio were associated with reduced GLS. Multivariate analysis revealed that larger BMI (P < 0.0001) and greater VAT/TAT ratio (P = 0.01) were independently associated with higher prevalence of LVH, and only the VAT/TAT ratio (P = 0.03) was independently associated with reduced GLS. Conclusions : The results of this study suggest that total and visceral adiposity are independently associated with LVH in patients with AS. Furthermore, impairment of LV systolic function does not appear to be influenced by total obesity but is rather related to excess visceral adiposity. These findings provide impetus for elaboration of interventional studies aiming at visceral adiposity in the AS population.De récentes études ont rapporté que l’obésité, le syndrome métabolique et le diabète étaient associés à l’hypertrophie (HVG) et à la dysfonction ventriculaire gauche des patients souffrant d’une sténose aortique (SA). Le but de cette étude était d’examiner le lien entre la quantité et la répartition de la graisse corporelle, l’HVG et la dysfonction systolique chez les patients souffrant d’une SA. Méthodes : Cent vingt-quatre patients souffrant d’une SA ont été recrutés de manière prospective dans l’étude PROGRESSA (Metabolic Determinants of the Progression of Aortic Stenosis), et ont subi une échocardiographie Doppler et une tomodensitométrie. La présence et la sévérité de l’HVG ont été évaluées au moyen de la masse VG indexée par la taille2.7 et la dysfonction systolique du VG par la déformation longitudinale globale du VG (DLG). La tomodensitométrie a été utilisée pour quantifier le tissu adipeux abdominal viscéral (TAV) et sous-cutané (TAS), et le tissu adipeux total (TAT). Résultats : L’indice de masse corporelle (IMC) corrélait fortement avec le TAT (r = 0,85), modérément avec le TAV (r = 0,70) et le TAS (r = 0,69), et faiblement avec la proportion de TAV (rapport TAV/TAT : r = 0,19). En analyse multivariée, des IMC, TAT, TAV, TAS et VAT/TAT plus élevés étaient associés à une augmentation de la masse VG indexée et un TAV et un rapport TAV/TAT plus élevés étaient associés à la réduction de la DLG. L’analyse multivariée a révélé qu’un IMC plus élevé (P < 0,0001) et un rapport TAV/TAT plus élevé (P = 0,01) étaient indépendamment associés à une HVG plus importante, et seul un rapport TAV/TAT était indépendamment associé à une réduction de la DLG. Conclusions : Les résultats de cette étude montrent que l’adiposité totale et l'adiposité viscérale sont indépendamment associées à une HVG chez les patients souffrant d’une SA. De plus, la détérioration de la fonction systolique VG ne semble pas être influencée par l’obésité totale, mais est plutôt liée à une adiposité viscérale excessive. Ces résultats incitent à l’élaboration d’études interventionnelles visant l’adiposité viscérale dans la population souffrant de SA

Drugs Associated with More Suicidal Ideations Are also Associated with More Suicide Attempts

In randomized controlled trials (RCTs), some drugs, including CB1 antagonists for obesity treatment, have been shown to cause increased suicidal ideation. A key question is whether drugs that increase or are associated with increased suicidal ideations are also associated with suicidal behavior, or whether drug-induced suicidal ideations are unlinked epiphenomena that do not presage the more troubling and potentially irrevocable outcome of suicidal behavior. This is difficult to determine in RCTs because of the rarity of suicidal attempts and completions.To determine whether drugs associated with more suicidal ideations are also associated with more suicide attempts in large spontaneous adverse event (AE) report databases.Generalized linear models with negative binomial distribution were fitted to Food and Drug Administration (FDA) Adverse Event (AE) Reporting System (AERS) data from 2004 to 2008. A total of 1,404,470 AEs from 832 drugs were analyzed as a function of reports of suicidal ideations; other non-suicidal adverse reactions; drug class; proportion of reports from males; and average age of subject for which AE was filed. Drug was treated as the unit of analysis, thus the statistical models effectively had 832 observations.Reported suicide attempts and completed suicides per drug.832 drugs, ranging from abacavir to zopiclone, were evaluated. The 832 drugs, as primary suspect drugs in a given adverse event, accounted for over 99.9% of recorded AERS. Suicidal ideations had a significant positive association with suicide attempts (p<.0001) and had an approximately 131-fold stronger magnitude of association than non-suicidal AERs, after adjusting for drug class, gender, and age.In AE reports, drugs that are associated with increased suicidal ideations are also associated with increased suicidal attempts or completions. This association suggests that drug-induced suicidal ideations observed in RCTs plausibly represent harbingers that presage the more serious suicide attempts and completions and should be a cause for concern

Advantages of the single delay model for the assessment of insulin sensitivity from the intravenous glucose tolerance test

The Minimal Model, (MM), used to assess insulin sensitivity (IS) from Intra-Venous Glucose-Tolerance Test (IVGTT) data, suffers from frequent lack of identifiability (parameter estimates with Coefficients of Variation (CV) less than 52%). The recently proposed Single Delay Model (SDM) is evaluated as a practical alternative