407 research outputs found
Kinematics signature of a giant planet in the disk of AS 209
[abridged] ALMA observations of dust in protoplanetary disks are revealing
the existence of sub-structures such as rings, gaps and cavities. Such
morphology are expected to be the outcome of dynamical interaction between the
disk and planets. However, other mechanisms are able to produce similar dust
sub-structures. A solution is to look at the perturbation induced by the planet
to the gas surface density and/or to the kinematics. In the case of the disk
around AS 209, a prominent gap has been reported in the surface density of CO
at au. Recently, Bae et al. (2022) detected a localized velocity
perturbation in the CO emission along with a clump in CO
at nearly 200 au, interpreted as a gaseous circumplanetary disk. We
report a new analysis of ALMA archival observations of CO and CO
J=2-1. A clear kinematics perturbation (kink) is detected in multiple channels
and over a wide azimuth range in both dataset. We compared the observed
perturbation with a semi-analytic model of velocity perturbations due to
planet-disk interaction. The observed kink is not consistent with a planet at
200\,au as this would require a low gas disk scale height () in
contradiction with previous estimate ( at au). When
we fix the disk scale height to 0.118 (at au) we find instead that a
planet of 3-5 M at 100 au induces a kinematics perturbation similar
to the observed one. Thus, we conclude that a giant protoplanet orbiting at au is responsible of the large scale kink as well as of the
perturbed dust and gas surface density previously detected. The position angle
of the planet is constrained to be between 60-100. Future
observations with high contrast imaging technique in the near- and mid-
infrared are needed to confirm the presence and position of such a planet.Comment: Accepted by A&
Mathematical model for acid water neutralization with anomalous and fast diffusion
In this paper we model the neutralization of an acid solution in which the hydrogen ions are transported according to Cattaneo’s diffusion. The latter is a modification of classical Fickian diffusion in which the flux adjusts to the gradient with a positive relaxation time. Accordingly the evolution of the ions concentration is governed by the hyperbolic telegraph equation instead of the classical heat equation. We focus on the specific case of a marble slab reacting with a sulphuric acid solution and we consider a one-dimensional geometry. We show that the problem is multi-scale in time, with a reaction time scale that is larger than the diffusive time scale, so that the governing equation is reduced to the one-dimensional wave equation. The mathematical problem turns out to be a hyperbolic free boundary problem where the consumption of the slab is described by a nonlinear differential equation. Global well posedness is proved and some numerical simulations are provided.Fil: Ceretani, Andrea Noemí. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina. Universidad Austral. Facultad de Ciencias Empresariales; ArgentinaFil: Bollati, Julieta. Universidad Austral. Facultad de Ciencias Empresariales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas Ingeniería y Agrimensura. Escuela de Ciencias Exactas y Naturales. Departamento de Matemática; ArgentinaFil: Fusi, L.. Università degli Studi di Firenze; ItaliaFil: Rosso, F.. Università degli Studi di Firenze; Itali
Papia civitas gloriosa: urban geomorphology for a thematic itinerary on geocultural heritage in Pavia (Central Po Plain, N Italy)
The interaction between geomorphological processes and anthropogenic activities produces an impressive association of geomorphological and archaeological heritage in urban contexts. We analyzed the urban geomorphology and the geo- and cultural heritage in the town of Pavia (N Italy). The city is located in a strategic position, on a series of fluvial terraces where the Romans founded a colony, probably in the place of an Iron Age Gaul settlement. In Medieval Times and the Modern Era, Pavia sprawled outside the Roman walls, creating new urban areas and modifying the landscape. Geomorphological and GIS-spatial analyses integrated with anthropic landform surveying, archaeological data and historical cartography were performed. This multi-disciplinary approach allowed an investigation into how urban development was firstly adapted and then superimposed onto fluvial landforms. As a result, a flexible geocultural itinerary is proposed for linking geoheritage with cultural heritage, and for disseminating urban geomorphology key-concepts
Preparación de morteros y hormigones no tradicionales a base de cemento portland, metacaolín y yeso (15,05%)
In a thorough previous research (1), it appeared that creation, evolution and development of the values of compressive mechanical strength (CS) and flexural strength (FS), measured in specimens 1x1x6cm of mortar type ASTM C 452-68 (2), manufactured by ordinary Portland cement P-1 (14.11% C3A) or PY-6 (0.00% C3A), metakaolin and gypsum (CaSO4∙2H2O) -or ternary cements, CT-, were similar to the ones commonly developed in mortars and concretes of OPC. This paper sets up the experimental results obtained from non-traditional mortars and concretes prepared with such ternary cements -TC-, being the portland cement/metakaolin mass ratio, as follows: 80/20, 70/30 and 60/40. Finally, the behaviour of these cements against gypsum attack, has been also determined, using the following parameters: increase in length (ΔL%), compressive, CS, and flexural, FS, strengths, and ultrasound energy, UE.
Experimental results obtained from these non-traditional mortars and concretes, show an increase in length (ΔL), in CS and FS, and in UE values, when there is addition of metakaolin.En una exhaustiva investigación anterior (1), se pudo comprobar que la creación, evolución y desarrollo de los valores de resistencias mecánicas a compresión, RMC, y flexotracción, RMF, proporcionados por probetas de 1x1x6 cm, de mortero 1:2,75, selenitoso tipo ASTM C 452-68 (2) -que habían sido preparadas con arena de Ottawa, cemento portland, P-1 (14,11% C3A) o PY- 6 (0,00% C3A), metacaolín y yeso (CaSO4∙2H2O)-, fue semejante a la que, comúnmente, desarrollan los morteros y hormigones tradicionales de cemento portland. En el presente trabajo se exponen los resultados experimentales obtenidos de morteros y hormigones no tradicionales, preparados con dichos cementos ternarios, CT, siendo las proporciones porcentuales en masa ensayadas, cemento portland/metacaolín, las siguientes: 80/20, 70/30 y 60/40. Finalmente, el comportamiento de estos cementos frente el ataque del yeso, se ha determinado mediante los siguientes parámetros: incremento de longitud (ΔL%), resistencias mecánicas a compresión, RMC, y flexotracción, RMF, y energía de ultrasonido, EU.
Los resultados experimentales obtenidos con tales morteros y hormigones no tradicionales, han dado un aumento de los valores de ΔL, RM y EU, con la cantidad de metacaolín añadida
Preparación de la dosificación de un hormigón con humo de sílice, cuya RMC sea > 40 kp/cm2, a edades iniciales (5-10 horas)
Silica fume (SF) or microsilica is related mainly with preparation of High Resistance Concrete. This has justified its use -together with portland cement (I-42'5/SR,MR) and an superfiuidifying additive- in the preparation of a concrete whose value for compressive mechanical resistance at early ages (only 5 to 10 hours) is higher than 40 kp/cm2, instead of preparing it with the portland cement plus a setting accelerator or "model" dosage.
The experimental techniques used to reach that objective have been: ultrasound energy and a press for breaking 30 x 15 mm specimens, and a maximum load of 2001. With the first technique, in only 25 days, 13 different dossages were prepared, which were compared to the "model" dosage, and two more that did not contain neither setting accelerator nor SF, this means that they had been prepared with the same portland cement, same fine and coarse aggregates and the same consistency, and that they would act as "reference" for all previous ones.
In such a way the dosage was found: E, in this case, that was the same as the "model" as for the amount of fine and coarse aggregates, but not as for the amount of the portland cement used which this time was 360 kg/m3 instead of 400kg/m3 SF content 40 kg/m3 and water 144 l/m3Al humo de sílice(HSE) o microsílice, se le relaciona, principalmente, con la preparación de hormigones de alta resistencia. Esta peculiar característica, ha justificado su utilización -junto a cemento portland (un I-42,5/SR,MR) y un aditivo superfluidificante- en la preparación de un hormigón cuyo valor de resistencia mecánica a compresión a edades iniciales (5 a 10 horas, solamente) fuera superior a 40 kp/cm2, en lugar de prepararlo con dicho cemento portland y un acelerador de fraguado o dosificación "patrón”.
Las técnicas experimentales utilizadas para alcanzar dicho objetivo han sido: la energía de ultrasonido y una prensa para la rotura de probetas de 30x15 cm, de 200 t de carga máxima. Mediante la primera de las técnicas, el sistema de tanteo y en tan sólo 25 días, se logró preparar hasta un total de 13 dosificaciones diferentes, las cuales fueron comparadas con dicha dosificación "patrón" y otras dos que no poseían ni acelerador de fraguado, ni HSE; es decir, que habían sido preparadas con el mismo cemento portland, los mismos áridos gruesos y finos y la misma consistencia plástica, las cuales actuarían como "referencia " de todas las anteriores.
De esta manera se logró la dosificación buscada, la E, en este caso, que fue la misma que la "patrón" en cuanto a la cantidad de áridos-gruesos y finos(arena), que no, en cambio, en cuanto a la cantidad de cemento portland utilizado, la cual pasaría a ser de 360 kg/m3 en lugar de 400 kg/m3 de HSE, que fue de 40 kg/m3 y de agua de amasado, que fue de 144 l/m3
Use and misuse of multivariable approaches in interventional cardiology studies on drug-eluting stents: a systematic review.
Aims: Randomized clinical trials (RCTs) are the most reliable evidence, even if they require important resource and logistic efforts. Large, cost-free and real-world datasets may be easily accessed yielding to observational studies, but such analyses often lead to problematic results in the absence of careful methods, especially from a statistic point of view. We aimed to appraise the performance of current multivariable approaches in the estimation of causal treatment and effects in studies focusing on drug-eluting stents (DES). Methods and Results: Pertinent studies published in the literature were searched, selected, abstracted, and appraised for quality and validity features. Six studies with a logistic regression were included, all of them reporting more than 10 events for covariates and different length of follow-up, with an overall low risk of bias. Most of the 15 studies with a Cox proportional hazard analysis had a different follow-up, with less than 10 events for covariates, yielding an overall low or moderate risk of bias. Sixteen studies with propensity score were included: the most frequent method for variable selection was logistic regression, with underlying differences in follow-up and less than 10 events for covariate in most of them. Most frequently, calibration appraisal was not reported in the studies, on the contrary of discrimination appraisal, which was more frequently performed. In seventeen studies with propensity and matching, the latter was most commonly performed with a nearest neighbor-matching algorithm yet without appraisal in most of the studies of calibration or discrimination. Balance was evaluated in 46% of the studies, being obtained for all variables in 48% of them. Conclusions: Better exploitation and methodological appraisal of multivariable analysis is needed to improve the clinical and research impact and reliability of nonrandomized studies. (J Interven Cardiol 2012;**:1-1
TIMI, GRACE and alternative risk scores in Acute Coronary Syndromes: A meta-analysis of 40 derivation studies on 216,552 patients and of 42 validation studies on 31,625 patients.
BACKGROUND: Acute coronary syndromes (ACS) represent a difficult challenge for physicians. Risk scores have become the cornerstone in clinical and interventional decision making.
METHODS AND RESULTS: PubMed was systematically searched for ACS risk score studies. They were divided into ACS studies (evaluating Unstable Angina; UA, Non ST Segment Elevation Myocardial Infarction; NSTEMI, and ST Segment Elevation Myocardial Infarction; STEMI), UA/NSTEMI studies or STEMI studies. The c-statistics of validation studies were pooled when appropriate with random-effect methods. 7 derivation studies with 25,525 ACS patients and 15 validation studies including 257,654 people were formally appraised. Pooled analysis of GRACE scores, both at short (0.82; 0.80-0.89 I.C 95%) and long term follow up (0.84; 0.82-0.87; I.C 95%) showed the best performance, with similar results to Simple Risk Index (SRI) derivation cohorts at short term. For NSTEMI/UA, 18 derivation studies with 56,560 patients and 18 validation cohorts with 56,673 patients were included. Pooled analysis of validations studies showed c-statistics of 0.54 (95% CI = 0.52-0.57) and 0.67 (95% CI = 0.62-0.71) for short and long term TIMI validation studies, and 0.83 (95% CI = 0.79-9.87) and 0.80 (95% CI = 0.74-0.89) for short and long term GRACE studies. For STEMI, 15 studies with 134,557 patients with derivation scores, and 17 validation studies with 187,619 patients showed a pooled c-statistic of 0.77 (95% CI = 0.71-0.83) and 0.77 (95% CI = 0.72-0.85) for TIMI at short and long term, and a pooled c-statistic of 0.82 (95% CI = 0.81-0.83) and 0.81 (95% CI = 0.80-0.82) for GRACE at short and long terms respectively.
CONCLUSIONS: TIMI and GRACE are the risk scores that up until now have been most extensively investigated, with GRACE performing better. There are other potentially useful ACS risk scores available however these have not undergone rigorous validation. This study suggests that these other scores may be potentially useful and should be further researched
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