130,767 research outputs found
Resonance frequency shift in a cavity with a thin conducting film near a conducting wall
No full textWe show that a very thin conducting film (whose thickness can be much smaller than the skin depth), placed nearby a wall of an electromagnetic cavity, can produce the same shift of the resonance frequency as a bulk conducting slab, provided the displacement of the film from the wall is much bigger than the skin depth. We derive a simple analytical formula for the frequency shift and compare it with exact numerical calculations and experimental dat
CLINICAL EFFICACY OF PULSATILE PERFUSION IN ELDERLY PATIENTS UNDERGOING CARDIAC SURGERY: hemodynamic energy, vascular reactivity, endothelial integrity and renal function
No full textObiettivi: La superiorità della perfusione pulsata rispetto a quella non-pulsata per la circolazione extracorporea (CEC) a breve termine rimane controversa. Pazienti anziani sono più sensibili alla qualità della perfusione in CEC e quindi possono meglio beneficiare dei teorici benefici di una perfusione pulsata. Obiettivo del presente studio è stato quello di valutare, in pazienti anziani sottoposti alla sostituzione valvolare aortica (SVA), gli effetti emodinamici, vascolari, endoteliali e renali della perfusione pulsata (PP) o non-pulsata (PN) durante la CEC.
Metodi: Quaranta pazienti (età media 80±3 anni, EuroScore 5.9±1.5) con la stenosi valvolare aortica isolata sono stati prospetticamente randomizzatri e soddivisi in due gruppi secondo la tecnica di perfusione (PP o PN) durante l’intervento cardiaco. La perfusione pulsata è stata valutata in termini di l’energy equivalent pressure (EEP) e di surplus hemodynamic energy (SHE). Le curve della pressione e del flusso sono state rilevate e registrate durante la CEC mediante l’utilizzo di flussimetri e trasduttori di pressione esterni. Una valutazione emodinamica con calcolo della portata, delle resistenze vascolari sistemiche (SVRi) e delle resistenze polmonare (PVRi) è stata eseguita durante l’intervento e nelle successive 18 ore. Markers plasmatici della integrità endoteliale (inter-cellular adhesive molecule–1 (ICAM-I), endothelina–1 (ET-1), von Willebrand factor (vWF)), e-NOS eritrocitaria, e markers del danno renale acuto (N-acetyl-β-D-glucosaminidase (NAG), molecola del danno renale–1 (KIM-1) and neutrophil-gelatinase associated lipocalin (NGAL)) sono stati rilevati nel periodo perioperatorio e nelle successive 18 ore.
Resulti: Nel gruppo di pazienti con flusso pulsato, EEP valutato in arteria radiale del paziente è stata 7.3% piu alta rispetto alla pressione media (MAP), corrispondente a 5150±2291 ergs/cm3 della SHE. Nel gruppo non-pulsato EEP e MAP sono stati uguali. Non è stata rilevata alcuna differenza nella pressione di perfusione media (55±9 mmHg in gruppo PP vs 60±13 mm Hg in gruppo PN) ed nel flusso medio (4.4±0.5 vs 4.3±0.4). Le resistenze vascolari sistemiche, nel gruppo pulsato, sono state significativamente più basse durante clampaggio aortico fino l’inizio della fase di riscaldamento (ANOVA interazione gruppo-tempo p=0.06). Anche le resistenze vascolari polmonari, nel gruppo pulsato, sono state significativamente più basse dopo la somministrazione di protamina e a 2 ore dopo l’arrivo in terapia intensiva (ANOVA interazione gruppo-tempo p=0.02). Nei pazienti con PP, la marcata riduzione delle resistenze vascolari sistemiche ha richiesto un più alto uso di farmaci vasopressori (p=0.01) nel periodo postoperatorio. I dosaggi di ICAM, vWF, ET-I ed eNOS hanno mostrato marcate differenze prima e dopo la CEC ma alcuna differenza significativa tra i due gruppi. Nessun differenza significativa è stata trovata tra i valori pre- e postoperatori del clearance creatinina nel gruppo pulsato (71 ± 26 vs 61 ± 35 mL/min p=0.95) mentre si è osservata una riduzione significativa nel gruppo non-pulsato (70 ± 28 vs 47 ± 16 mL/min p=0.001). Inoltre il gruppo pulsato ha dimostrato valori più bassi di NGAL alla chiusura dello sterno (p=0.01) e a 2 ore in TIPO (p=0.02) e di NAG urinario postoperatorio a 18 ore in TIPO (p=0.003). I due gruppi sono stati comparabili in termini di livelli dei lattati perioperatori, sanguinamento dai tubi di grenaggio, trasfusioni dei componenti del sangue, tempi di ricovero in terapia intensiva e reparto di degenza e complicanze precoci.
Conclusioni: Nei pazienti anziani sottoposti a sostituzione valvolare aortica, il flusso pulsato in CEC ha mostrato una buona perfusione d’organo con migliore preservazione della funzione renale. Tuttavia la vasodilatazione indotta dalla perfusione pulsata ha richiesto un più alto uso di farmaci vasopressori nel periodo postoperatorio.Objective(s): the superiority of pulsatile perfusion over non-pulsatile during short-term cardiopulmonary bypass (CPB) is still controversial. Elderly patients are the most sensible to the perfusion quality and could benefit from pulsatile CPB. The objective of the study was to analyze hemodynamic effects, vascular reactivity, endothelial integrity and renal function in elderly patients undergoing aortic valve replacement (AVR) with either pulsatile (PP) or non-pulsatile (NP) CPB.
Methods: forty elderly patients (age 80±3 years old, EuroScore 5.9±1.5) with aortic valve stenosis were prospectively randomized for surgery with either PP or NP perfusion performed by centrifugal pump. Pulsatility was evaluated in terms of energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE). Flow and pressure curves were recorded at 6 time-points during CPB with external flow-meters and collected in computer-based system. Systemic (SVRi), pulmonary (PVRi) vascular resistance, plasma markers of endothelial integrity (inter-cellular adhesive molecule–1 (ICAM-I), endothelin–1 (ET-1), von Willebrand factor (vWF)), erythrocyte e-NOS and urinary acute kidney injury makers (N-acetyl-β-D-glucosaminidase (NAG), kidney injury molecule–1 (KIM-1) and neutrophil gelatinase associated lipocalin (NGAL)) were collected during 24 hours of perioperative period together with pre- and postoperative creatinine clearance assessment.
Results: In PP group, EEP calculated in patient’s radial artery was at average 7.3% higher than mean arterial pressure (MAP), which corresponded to an increase of 5150±2291 ergs/cm3 of SHE. In NP group EEP and MAP were equal. Mean perfusion pressure (55±9 mmHg in PP group vs 60±13 mm Hg in NP group) and flow (4.4±0.5 vs 4.3±0.4) showed no difference between the groups. SVRi was significantly lower during cross-clamp period in PP group until rewarming phase and just after removing of cross-clamp (ANOVA Group-time interaction p=0.06). PVRi was significantly lower in PP group after protamine administration and up to 2 hours in ICU (ANOVA Group-time interaction p=0.02). Lower vascular resistance induced by PP required higher perioperative dosages of vasopressor drugs infusion (p=0.01). ICAM, vWF, ET-I and eNOS showed marked variations at early post-CPB period without important difference between the groups. No significant difference between pre- and post-operative creatinine clearance was found in PP group (71 ± 26 vs 61 ± 35 mL/min p=0.951) while statistically significant decrement was observed in NP group (70 ± 28 vs 47 ± 16 mL/min p=0.001). PP group showed lowed mean urinary NAG level at 18 hours postoperatively (p=0.003) and lower NGAL levels at sternum closure (p=0.01) and 2 hours postoperatively (p=0.02). PP and NP patients were comparable in perioperative lactate levels, drainage blood loss, transfusion rates, ICU and hospital stay periods and early complications.
Conclusions: In elderly patients undergoing aortic valve surgery, pulsatile flow provided a good organ perfusion with better preserved renal function. However, pulsatile perfusion induced lower systemic and pulmonary vascular resistance results in augmented postoperative vasopressor requirements
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Modified Open Circuit and Vacuum-assisted Venous Return Reduces Blood Usage During Cardiopulmonary Bypass
No full textObjectives: To determine whether vacuum-assisted venous return has clinical advantages over conventional gravity drainage apart from allowing the use of smaller cannulas, shorter tubing and reduced priming.
Methods: A total of 80 CABG operations were performed at our institution
between July 1999 to December 2010, using vacuum-assisted venous return
with small venous cannulas connected to short tubing. These were randomized
with 80 CABG operations using conventional gravity drainage. Priming volume,
hematocrit value, red blood cell usage, and total blood product usage were
compared by means of multivariate analysis.
Results: The priming volume was 780+/-140mL for small-cannula vacuumassisted
venous return, 1300+/-88mL for gravity drainage (P <.0001). Smaller
priming resulted in higher hematocrit values both at the beginning of cardiopulmonary
bypass (26%+/-5% compared with 21%+/-4%, respectively, P <.0001)
and at the end (28%+/-4% compared with 24%+/-4%, respectively, P <.0001).
Red cell transfusions were used in 12% of the patients having small-cannula
vacuum-assisted venous return and 41% of the patients having gravity drainage
(P =.001); total blood product usage was 15% and 61%, respectively (P =.001).
Despite a postoperative blood loss, length of stay in intensive care unit was
similar in both groups; the association of vacuum-assisted venous return with
lowered blood product usage was confirmed also in the postoperative period.
Conclusions: Modified open circuit and vacuum-assisted venous return result in 1) higher hematocrit values during cardiopulmonary bypass and 2) decreased red cell and total blood product usage
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Scholarly Communication and Publishing Lunch and Learn Talk #11: The ULS Open Access Author Fee Fund
No full textAt the May 2014 talk, you will learn about the ULS Open Access Author Fee Fund--what it is, why we do it, how it works, and how the program is going so far
The R&D Tax Incentives
No full textThis article sets out some background information and reflections of the author on the R&D tax incentive schemes included in the Common Corporate Tax Base (CCTB) Proposal. In particular the author analyzes the stimulus to private R&D through ad hoc tax incentives included in the CCTB Proposal and dives into the actual provisions included in the Proposal highlighting the most relevant issues connected with their design and interpretation. Moreover, the author explores the interaction between the CCTB Proposal and the granting by Member States of domestic R&D tax incentives
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