3,214 research outputs found
Effect of mixed convection on laminar vortex breakdown in a cylindrical enclosure with a rotating bottom plate
© 2020 Elsevier Masson SAS Vortex breakdown plays a central role in the performance of countless rotating machinery applications, many of which contain thermal gradients either inadvertently or by design. The effect of thermal gradients on vortex breakdown and further flow development in a cylindrical domain with a rotating bottom plate is examined using the Generalized Integral Transformation Technique (GITT) with a streamfunction-only formulation. A thermal gradient is imposed in the axial direction, such that the buoyancy forces oppose the base flow driven by the rotation of the lower plate, i.e. the temperature difference acts to stabilize the flow. The hybrid numerical-analytical approach is shown to accurately capture vortex breakdown phenomena for a variety of conditions involving single, double and triple recirculation bubbles. The buoyancy forces – expressed in terms of the Richardson number (Ri) – act to suppress vortex breakdown in all cases examined and led to a series of flow transitions with increasing Ri, characterized by the appearance of a stratified structure with multiple fluid layers. These flow transitions have a significant impact on the overall performance of the system. The torque coefficient decreases with Ri, compared to the base (isothermal) case following an empirical power law relationship, which is independent of Reynolds number, aspect ratio or number of fluid layers present. Flow stratification suppresses the transport of angular momentum; azimuthal velocity is shown to decline exponentially in the regions where layering occurs, accompanied by a sharp reduction in the Nusselt number, as fluid layers act to insulate the upper plate
Left Atrial Volume: an Old Echocardiographic Measure with Renewed Prognostic Significance: a Study in Patients with Dilated Cardiomyopathy
Recentemente, surgiram alguns trabalhos que
ressaltaram a importância do cálculo do
volume da aurícula esquerda (VAE) como um
marcador de eventos cardíacos adversos. Foi
objectivo deste estudo avaliar a importância
prognóstica deste parâmetro em doentes (dts)
com deficiente função ventricular esquerda e
correlacioná-lo com outros parâmetros
clássicos de prognóstico – consumo de O2
(VO2 max) e pro-BNP (pBNP).
Métodos: Analisou-se o volume da aurícula
esquerda (VAE) por método de Simpson, numa população de 35 dts com cardiopatia dilatada (idiopática e isquémica) com fracção de ejecção (FE) 31±9,6% doentes (dts) eram de sexo masculino e a média de idades foi de
50,5±10,5 anos. Toda a população efectuou
estudos de ecocardiografia convencional
(incluindo avaliação por M-mode, bidimensional e Doppler), prova cardiorespiratória (VO2max) e doseamento de
pro-BNP. O tempo médio de seguimento foi de
24 ± 4 meses, tendo-se considerado como
eventos cardíacos (EC): internamento por
insuficiência cardíaca, transplante e morte.
Resultados: Dos parâmetros da ecocardiografia
- o diâmetro da AE foi de 46,6±5,7mm, as dimensões do VE em diástole – 73,5±10mm e
em sístole -58,9±11mm, a média da fracção
de ejecção foi de 31±9,6%, o VAE foi de
78,6±33 ml, os volumes do VE foram de
214±82ml em diástole e de 153±75ml em
sístole, 15 dts tinham padrão restritivo de
enchimento ventricular (E/A>2), a média da
área (Doppler cor) da insuficiência mitral foi de 4±3,3cm2, 14 dts tinham E/E’>15. O VO2
max médio foi de 20±5,8ml/kg/min e o pro-BNP de 3146±4629pg/mL. Para além da correlação de outros parâmetros clássicos ecocardiográficos com o prognóstico (volumes
VE, FE e E/E’), o VAE e o volume indexado
da AE (VAE/SC) mostraram uma correlação
com o prognóstico (EC) com r=0,4 (p=0,02)
que não se verificou para o diâmetro da AE
(p=ns). Em relação à tolerância ao esforço,
houve uma correlação inversa entre o diâmetro, o volume e o volume indexado da
AE e o VO2max, com maior significado
estatístico para o VAE e VAE/SC com
r=-0,48, p=0,008. Quanto ao pro-BNP, quer o
diâmetro, quer o VAE (ou volume indexado)
tiverem o mesmo nível de significado
estatístico (r=0,43; p=0,02). O valor predictivo de eventos (curvas ROC) para o VAE foi de 70ml e de 37ml/m2 para o VAE/m2.
Conclusão: O volume da aurícula esquerda/volume indexado é um parâmetro
ecocardiográfico com significado prognóstico
em dts com deficiente função ventricular
esquerda, correlacionando-se com a tolerância
ao esforço e pro-BNP
Correlation Between NT-proBNP Values and Changes in Functional Capacity in Patients with Chronic Heart Failure
OBJECTIVE: We set out to evaluate whether changes in N-terminal pro-brain natriuretic peptide (proBNP) can predict changes in functional capacity, as determined by cardiopulmonary exercise testing (CPET), in patients with chronic heart failure (CHF) due to dilated cardiomyopathy (DCM).
METHODS: We studied 37 patients with CHF due to DCM, 81% non-ischemic, 28 male, who performed symptom-limited treadmill CPET, with the modified Bruce protocol, in two consecutive evaluations, with determination of proBNP after 10 minutes rest prior to CPET. The time between evaluations was 9.6+/-5.5 months, and age at first evaluation was 41.1+/-13.9 years (21 to 67). RESULTS IN THE FIRST AND SECOND EVALUATIONS RESPECTIVELY WERE: NYHA functional class >II 51% and 16% (p<0.001), sinus rhythm 89% and 86.5% (NS), left ventricular ejection fraction 24.9+/-8.9% and 26.6+/-8.6% (NS), creatinine 1.03+/-0.25 and 1.09+/-0.42 mg/dl (NS), taking ACE inhibitors or ARBs 94.5% and 100% (NS), beta-blockers 73% and 97.3% (p<0.001), and spironolactone 89% and 89% (NS). We analyzed the absolute and percentage variation (AV and PV) in peak oxygen uptake (pVO2--ml/kg/min) and proBNP (pg/ml) between the two evaluations.
RESULTS: (1) pVO2 AV: -17.4 to 15.2 (1.9+/-5.7); pVO2 PV: -56.1 to 84% (11.0+/-25.2); proBNP AV: -12850 to 5983 (-778.4+/-3332.5); proBNP PV: -99.0 to 379.5% (-8.8+/-86.3); (2) The correlations obtained--r value and p value [r (p)]--are shown in the table below; (3) We considered that a coefficient of variation of pVO2 PV of >10% represented a significant change in functional capacity. On ROC curve analysis, a proBNP PV value of 28% showed 80% sensitivity and 79% specificity for pVO2 PV of >10% (AUC=0.876, p=0.01, 95% CI 0.75 to 0.99).
CONCLUSIONS: In patients with CHF due to DCM, changes in proBNP values correlate with variations in pVO2, as assessed by CPET. However, our results suggest that only a proBNP PV of >28% predicts a significant change in functional capacity
Enzymatic hydrolysis of esters from 2-carboxy-6- methoxy-2,3-dihydrobenzofuran acid
In this work we describe the results of the enzymatic hydrolysis of esters from 2-carboxy-6-methoxy-2,3-dihydrobenzofuran acid using Candida antarctica lipase supported on acrylic resin, with enantiomeric excesses ranging between 80 to 99%
Prognostic Implications of Tissue Doppler in Patients with Dilated Cardiomyopathy
Previous studies have shown that a ratio of early transmitral flow velocity to early diastolic velocity of the mitral annulus (E/E') of > 15, obtained by tissue Doppler imaging (TDI), correlates with left ventricular filling pressure.
OBJECTIVE: The aim of our study was to assess whether E/E' provides prognostic information in patients with dilated cardiomyopathy.
METHODS: We studied 33 patients with dilated cardiomyopathy and mean ejection fraction of 31%. All the patients underwent routine two-dimensional and Doppler echocardiographic examination and TDI to determine early peak velocity of the mitral annulus. Pro-B-type natriuretic peptide (pro-BNP) and peak oxygen consumption (VO2max) were also measured. Patients were divided into two groups according to the value of E/E': Group I (n = 15 patients) with E/E' > or = 15 and Group II (n = 18 patients) with E/E' < 15. Patients were followed for 12+/-4 months; new hospital admission due to heart failure, heart transplantation and death were considered as cardiac events.
RESULTS: There were significant differences between the two groups in conventional two-dimensional echocardiographic measurements (dimensions and ejection fraction) and Doppler parameters (mitral inflow). With regard to mitral annular velocities obtained by TDI at two different points (septum and lateral wall), the E', A' and S' velocities differed significantly between the two groups, with lower velocities in Group I. Systolic velocity measured in the lateral portion of the mitral annulus showed the most significant difference: Group I - 4.46 cm/sec versus Group II - 7.19 cm/sec, p < 0.00001. Pro-BNP was 5622 pg/ml in Group I, and 1254 pg/ml in Group II, p = 0.004. VO2 max was significantly different between the two groups: Group I - 17.6 ml/kg/min versus Group II - 22.8 ml/kg/min, p = 0.004. During follow-up, events were more common in Group I, with 9 patients (60%) having events, while in Group II, the event rate was 11.1% (2 patients), p = 0.004.
CONCLUSION: The ratio of early transmitral flow velocity to early diastolic velocity of the mitral annulus is a powerful predictor of clinical outcome. Lower velocities of mitral annulus on TDI are expected in patients with E/E' > or = 15. Systolic velocities of under 5 cm/sec measured in the lateral portion of the mitral annulus appeared to be strongly related to prognosis
Dynamic Role-Based Access Control for Decentralized Applications
Access control management is an integral part of maintaining the security of
an application. Although there has been significant work in the field of cloud
access control mechanisms, however, with the advent of Distributed Ledger
Technology (DLT), on-chain access control management frameworks hardly exist.
Existing access control management mechanisms are tightly coupled with the
business logic, resulting in governance issues, non-coherent with existing
Identity Management Solutions, low security, and compromised usability. We
propose a novel framework to implement dynamic role-based access control for
decentralized applications (dApps). The framework allows for managing access
control on a dApp, which is completely decoupled from the business application
and integrates seamlessly with any dApps. The smart contract architecture
allows for the independent management of business logic and execution of access
control policies. It also facilitates secure, low cost, and a high degree of
flexibility of access control management. The proposed framework promotes
decentralized governance of access control policies and efficient smart
contract upgrades. We also provide quantitative and qualitative metrics for the
efficacy and efficiency of the framework. Any Turing complete smart contract
programming language is an excellent fit to implement the framework. We expect
this framework to benefit enterprise and non-enterprise dApps and provide
greater access control flexibility and effective integration with traditional
and state of the art identity management solutions.Comment: 6 pages, 3 figures, 1 tabl
Usefulness of Low-Dose Dobutamine Echocardiography in Idiopathic Dilated Cardiomyopathy
INTRODUCTION: Low-dose dobutamine stress echocardiography is a common and useful technique to assess myocardial viability in patients with ischemic cardiomyopathy.
OBJECTIVE: To evaluate the use of low-dose dobutamine stress echocardiography in determining the functional status of patients with idiopathic dilated cardiomyopathy (IDCM).
METHODS: Prospective study of 28 patients with IDCM by transthoracic echocardiography (2D), low-dose dobutamine stress echocardiography, cardiopulmonary exercise testing (CPET) and measurement of pro-BNP.
RESULTS: The mean age of the population was 50.3 +/- 11.5 years, 9 female and 19 male. Mean ejection fraction was 32.1 +/- 9.8%. All were in sinus rhythm. The following parameters were analyzed in 2D echocardiography and after dobutamine: dimensions of left atrium (LA) and of left ventricle in diastole and systole, shortening fraction (%), left ventricular end-diastolic (EDV) and end-systolic volumes (ESV), ejection fraction (EF), and mitral inflow (E, A, E/A ratio and deceleration time). In CPET, we considered the following parameters: peak VO2 and % maximal peak VO2 attained. We compared echo results with CPET. There was a correlation between age and peak VO2 (r = -0.38 with p = 0.049). In 2D echo, there was a correlation between baseline EF and LA dimensions and peak VO2 (r = 0.45 / p = 0.004 and r = -0.49 / p = 0.014, respectively). After dobutamine echo, there was a correlation between some echo parameters and peak VO2: EF - r = 0.59 / p = 0.001, LA dimensions - r = 0.56 / p = 0.007, and ESV - r = -0.45 / p = 0.026. Percentage maximal peak VO2 attained correlated with LA dimensions measured in 2D echo and after dobutamine (r = -0.398 / p = 0.036 and r = -0.674 / p = 0.02 respectively) and EF after dobutamine (r = -0.389 / p = 0.04). The value of pro-BNP correlated with LA dimensions and baseline EF (r = 0.44 / p = 0.02 and r = -0.57 / p = 0.002, respectively), and the correlation was maintained after inotropic stimulation with dobutamine (r = 0.57 / p = 0.001 and r = -0.55 / p = 0.0039).
CONCLUSION: Low-dose dobutamine stress echocardiography showed stronger correlations with cardiopulmonary exercise testing than the parameters evaluated by conventional echocardiography and could be used to determine the functional status of patients with dilated cardiomyopathy; patients with greater ejection fraction after inotropic stimulation had better cardiopulmonary tests
Sign-reversal of the in-plane resistivity anisotropy in hole-doped iron pnictides
The in-plane anisotropy of the electrical resistivity across the coupled
orthorhombic and magnetic transitions of the iron pnictides has been
extensively studied in the parent and electron-doped compounds. All these
studies universally show that the resistivity across the long
orthorhombic axis - along which the spins couple antiferromagnetically
below the magnetic transition temperature - is smaller than the resistivity
of the short orthorhombic axis , i. e. .
Here we report that in the hole-doped compounds
BaKFeAs, as the doping level increases, the
resistivity anisotropy initially becomes vanishingly small, and eventually
changes sign for sufficiently large doping, i. e. . This
observation is in agreement with a recent theoretical prediction that considers
the anisotropic scattering of electrons by spin-fluctuations in the
orthorhombic/nematic state.Comment: This paper has been replaced by the new version offering new
explanation of the experimental results first reported her
Efficient Certified Resolution Proof Checking
We present a novel propositional proof tracing format that eliminates complex
processing, thus enabling efficient (formal) proof checking. The benefits of
this format are demonstrated by implementing a proof checker in C, which
outperforms a state-of-the-art checker by two orders of magnitude. We then
formalize the theory underlying propositional proof checking in Coq, and
extract a correct-by-construction proof checker for our format from the
formalization. An empirical evaluation using 280 unsatisfiable instances from
the 2015 and 2016 SAT competitions shows that this certified checker usually
performs comparably to a state-of-the-art non-certified proof checker. Using
this format, we formally verify the recent 200 TB proof of the Boolean
Pythagorean Triples conjecture
- …