29,915 research outputs found
Outcomes of Valve-Sparing Aortic Root Replacement (David I Procedure) at a Single Center in Kazakhstan.
No full textValve-sparing aortic root replacement, commonly known as the David procedure, stands as a pioneering surgical technique aimed at addressing aortic root aneurysms while retaining the patient's native aortic valve. This procedure signifies a significant advancement in cardiac surgery, offering patients the potential for improved outcomes both in the short and long term.
Aims. The aim of the study was to analyze short- and long-term outcomes after valve sparing aortic root replacement operation using David I technique.
Methods. From January 2013 to November 2020 a total 124 David I procedures were performed. We analyzed survival and freedom from reoperation. Follow-up was performed 8 years postoperatively.
Results. Early mortality was 0.8% (n = 1). Mean age was 48.25 ± 17.42. The left ventricular ejection fraction (%) before discharge was significantly increased (p = 0.038) after surgery. The 1, 3, 6, 8 –year survival and freedom from reoperation rates were 99%, 99%, 98%, 87% and 99%, 98%, 95%, 91% retrospectively.
Conclusion. David procedure is a valuable option for treating aortic root aneurysms offering the potential for excellent long-term outcomes, especially when the native aortic valve can be preserved. The decision should be made on a case-by-case basis, considering the patient's individual factors and the expertise of the surgical team
Differential representation of drug-seeking within ventral pallidal subregions
No full textVentral pallidum (VP) neurons exhibit changes in firing rate (FR) immediately prior to and/or following cocaine-reinforced responses. We first aimed to determine whether the changes in FR surrounding cocaine-seeking responses were coincident with behaviors such as approaching the manipulandum, responding on the manipulandum, and retreating away from the manipulandum. Second, we aimed to determine whether changes in FR during cocaine-seeking behaviors differed between VP subregions. Prior to recordings, animals exhibited both task and skill learning, replicating previous results using this operant. 171 single-units in the ventromedial VP (VPvm) and 48 in the dorsolateral VP (VPdl) were recorded in welltrained animals during cocaine self-administration. Baseline FR and waveform characteristics did not differ between subregions. VPdl neurons exhibited a greater absolute change in FR over VPvm neurons during approaches as well as approaches divided into cued and uncued conditions. VPdl neurons exhibited a greater absolute change in FR over the VPvm during responses as well as responses divided into those cued/reinforced and uncued/unreinforced conditions. VPdl neurons were more likely to exhibit a similar change in FR during approach and response than VPvm neurons. VPvm neurons were heterogeneous, changing FRs during approach or response alone, or both. No differences were found between subregions during retreat behavior. VPdl neurons exhibited a greater absolute change in FR over the VPvm for retreats in which the pump was activated prior to or during a retreat, but not for retreats when the pump was not activated. Given that VPdl neurons exhibited a greater change in FR than VPvm neurons during approach and response, VPdl may be involved in the expression of drug-seeking behaviors through projections to "motoric" regions such as subthalamic nucleus and substantia nigra. Furthermore, because VPdl neurons were more likely to continue their change of FR from approach through response while VPvm were more selective (e.g., approach alone, response alone), it is suggested that cocaine-seeking behaviors are differentially represented within VP subregions. The VPvm projects primarily to the mediodorsal thalamus and ventral tegmental area. Heterogeneous firing patterns within the VPvm may be involved in maintaining a representation of behavioral characteristics or sequences of self-administration behaviors.Ph. D.Includes bibliographical referencesby David Hamilton Roo
Range Unit Root (RUR) Tests: Robust against Nonlinearities, Error Distributions, Structural Breaks and Outliers
No full textSince the seminal paper by Dickey and Fuller in 1979, unit-root tests have conditioned the standard approaches to analysing time series with strong serial dependence in mean behaviour, the focus being placed on the detection of eventual unit roots in an autoregressive model fitted to the series. In this paper, we propose a completely different method to test for the type of long-wave patterns observed not only in unit-root time series but also in series following more complex data-generating mechanisms. To this end, our testing device analyses the unit-root persistence exhibited by the data while imposing very few constraints on the generating mechanism. We call our device the range unit-root (RUR) test since it is constructed from the running ranges of the series from which we derive its limit distribution. These nonparametric statistics endow the test with a number of desirable properties, the invariance to monotonic transformations of the series and the robustness to the presence of important parameter shifts. Moreover, the RUR test outperforms the power of standard unit-root tests on near-unit-root stationary time series; it is invariant with respect to the innovations distribution and asymptotically immune to noise. An extension of the RUR test, called the forward?backward range unit-root (FB-RUR) improves the check in the presence of additive outliers. Finally, we illustrate the performances of both range tests and their discrepancies with the Dickey?Fuller unit-root test on exchange rate series.Publicad
The Great Wars, The Great Crash, and the Unit Root Hypothesis: Some New Evidence About an Old Stylized Fact
No full textFor decades, the prevailing sentiment among economists was that growth rates remain constant over the long run. Kaldor considered this to be one of the six important 'stylized facts' that theory should address, and until the emergence of endogenous growth models, this was a fundamental feature of growth theory. This paper uses an endogenous trend break model to investigate the unit root hypothesis for 16 countries, using annual GDP data spanning up to 130 years. Rejection of the unit root, which is facilitated by the inclusion of a trend break, introduces the possibility of examining the long run behavior of growth rates. We find that most countries exhibited fairly steady growth for a period lasting several decades. The termination of this period was usually characterized by a significant, and sudden, drop in GDP levels. But rather than simply returning to their previous steady state path, as predicted by the standard neoclassical growth model, most countries continued to grow at roughly double their prebreak rates for many decades, even after their original growth path had been surpassed.
The effectiveness of David procedure for aneurysm of the root and ascending part of the aorta
No full textThe aim – comparison of the results of David and Bentall operations in patients with aneurysms of the root and ascending aorta.
Materials and methods. The one-centre study included 85 patients who underwent planned and urgent surgical treatment from 2019 to 2022. The patients were divided into two groups depending on the type of surgical intervention: the Bentall procedure was performed in the I group, while the David procedure was performed in the II group.
Results. The study did not determine statistically significant differences in such indicators as the duration of artificial blood circulation and the time of aortic clamping. No significant differences were found in the duration of artificial lung ventilation and stay in the intensive care unit. However, the total length of hospital stay in the group of patients with David procedure was statistically lower and was 17.3 (8–35) days, while in the group with Bentall operation it was 23.7 (10–40) days (p = 0.01). The results of our analysis show that the early postoperative clinical results of the David and Bentall procedures are good and there are no significant differences. During David procedure, a statistically significant positive result of surgical treatment was revealed by such an indicator as the degree of insufficiency on the aortic valve (before and after the operation, 2.7 ± 1.3 and 0.8 ± 0.6, respectively, p < 0.05). In addition to the above indicator, significant results were found in the indicators: left ventricular end-diastolic size and left ventricular end-diastolic volume.
Conclusions. The good immediate results of Bentall and David operations suggest that surgical repair of ascending and aortic root aneurysms using these operations can be equally safe when performed according to absolute anatomical indications and by an experienced surgical team. If both operations might be used in a particular patient, the valve-sparing operation should be preferred, given the lower risk of postoperative complications associated with the presence of a mechanical or biological prosthesis (such as thromboembolism, bleeding associated with anticoagulants, and structural deterioration of the bioprosthesis)
Dr. David Root
No full textDr. David Root examines an unidentified, pediatric patient at North Carolina Baptist Hospital in what appears to be the Out Patient Department.Info from Katherine Davis Oral History #59:2
Testing for a unit root in the presence of a possible break in trend
No full textIn this paper we consider the issue of testing a time series for a unit root in the possible presence of a break in a linear deterministic trend at some unknown point in the series. We propose a break fraction estimator which, in the presence of a break in trend, is consistent for the true break fraction at rate Op(T^-1) when there is either a unit root or near-unit root in the stochastic component of the series. In contrast to other estimators available in the literature, when there is no break in trend, our proposed break fraction estimator converges to zero at rate Op(T^-1/2). Used in conjunction with a quasi difference (QD) detrended unit root test that incorporates a trend break regressor in the deterministic component, we show that these rates of convergence ensure that known break fraction null critical values are applicable asymptotically. Unlike available procedures in the literature this holds even if there is no break in trend (the true break fraction is zero), in which case the trend break regressor is dropped from the deterministic component and standard QD detrended unit root test critical values then apply. We also propose a second testing procedure which makes use of a formal pre-test for a trend break in the series, including a trend break regressor only where the pre-test rejects the null of no break. Both procedures ensure that the correctly sized (near-) efficient unit root test that allows (does not allow) for a break in trend is applied in the limit when a trend break does (does not) occur.Unit root test; quasi difference de-trending; trend break; pre-test; asymptotic power
Estimation in threshold autoregressive models with a stationary and a unit root regime
No full textThis paper treats estimation in a class of new nonlinear threshold autoregressive models with both a stationary and a unit root regime. Existing literature on nonstationary threshold models have basically focused on models where the nonstationarity can be removed by differencing and/or where the threshold variable is stationary. This is not the case for the process we consider, and nonstandard estimation problems are the result. This paper proposes a parameter estimation method for such nonlinear threshold autoregressive models using the theory of null recurrent Markov chains. Under certain assumptions, we show that the ordinary least squares (OLS) estimators of the parameters involved are asymptotically consistent. Furthermore, it can be shown that the OLS estimator of the coefficient parameter involved in the stationary regime can still be asymptotically normal while the OLS estimator of the coefficient parameter involved in the nonstationary regime has a nonstandard asymptotic distribution. In the limit, the rate of convergence in the stationary regime is asymptotically proportional to n-1/4, whereas it is n-1 in the nonstationary regime. The proposed theory and estimation method are illustrated by both simulated data and a real data example.Autoregressive process; null-recurrent process; semiparametric model; threshold time series; unit root structure.
Stephanie Mathson interviews essayist and memoirist Robert Root
No full textEssayist and memoirist Robert Root, professor of English at Central Michigan University, talks about his book "Recovering Ruth" and the genealogical research research in his work and his role as both a university professor and an author. He also shares his views on creative nonfiction, Michigan as a source of inspiration, and works in progress. Root is interviewed by Stephanie Mathson of the Michigan State University Libraries for the MSU Libraries' Michigan Writers Series
Data Files for Beachgrass Invasion and Root-Associated Fungi Studies
No full textFull descriptions of the files and their variables are included in the readme.txt documentation file.Datasets for beachgrass experiments conducted in the field and growth chamber. The overall goals of the experiments to understand the ecological factors underlying community assembly of fungal endophytes found in beachgrass roots, and to understand the drivers behind beachgrass invasion. Files include plant measurements, fungal colonization, and fungi identified using culture-based and next-generation Illumina sequencing.NSF Integrative Graduate Education and Research Traineeship Introduced Species and Genotypes program (DGE-0653827)NSF Graduate Research Fellowship program (NSF 00039202)Puget Sound Mycological Society Ben Woo FellowshipUniv. of Minnesota Rothman FellowshipNSF Dimensions of Biodiversity (DEB 1045608)Environmental Protection Agency (EPA/NCER R833836)David, Aaron S; Seabloom, Eric W; May, Georgiana. (2016). Data Files for Beachgrass Invasion and Root-Associated Fungi Studies. Retrieved from the University Digital Conservancy, http://doi.org/10.13020/D6S88B
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