300 research outputs found
Terrain Sculptor: generalizing terrain models for relief shading
Shaded relief derived from high-resolution terrain models often contains distracting terrain details that need to be removed for medium- and small- scale mapping. When standard raster filter operations are applied to digital terrain data, important ridge tops and valley edges are blurred, altering the characteristic shape of these features in the resulting shaded relief. This paper introduces Terrain Sculptor, a software application that prepares generalized terrain models for relief shading. The application uses a generalization methodology based on a succession of raster operations. Curvature coefficients detect and accentuate important relief features. Terrain Sculptor offers a graphical user interface to adjust the algorithm to various scales and terrain resolutions
Power dynamics in software platform ecosystems
In software platform ecosystems, the technological and structural peculiarities vest the platform owner with an extremely powerful position that puts any complementor at the mercy of the platform owner's actions. Paradoxically, it is the self-determination and proactivity of the complementors that determine the ecosystem's success through their surprising outside innovations. This study addresses this power paradox by unpacking the power dynamics between platform owners and complementors. Based on an exploratory multiple-case study of six platform partnerships, we find that power in platform ecosystems unfolds as a reciprocal process of three interlocking cycles, in which both the platform owner and the complementors take an active role. The modus operandi of power in platform ecosystems is a “central power cycle” in which the complementors repeatedly evaluate whether to accept or reject the platform owner's domination power. Thriving partnerships sustain this central power cycle over time, which requires that the platform owner and the complementors dynamically adapt their wielding of power to the changing needs of the partnership (partnership adaptation cycle) or the ecosystem (ecosystem redefinition cycle). For the platform owner, this entails the occasional use of manipulation to favour a particular partnership or redefining the ecosystem's framework and sporadically wielding coercion in favour of the broader ecosystem. For the complementor, this entails over-subjectification to entice the platform owner to wield its power in favour of their partnership. Our findings have important implications for platform ecosystem and power theory, as well as managerial practice
Conversion of supraventricular arrhythmias to sinus rhythm using flecainide
We evaluated the efficacy of flecainide acetate (given intravenously to a maximal dose of2 mg kg−1 and then orally in a dose of 100 mg b.d. or 100 mg t.d.s.) in the conversion to sinus rhythm of 50 patients exhibiting supraventricular arrhythmias (39 with atrial fibrillation, 6 with atrial flutter, 4 with supraventricu tachycardia and onewith supraventricular tachycardia in association with the Wolff—Parkinson—White syndrome). Conversion was achieved in 36 patients (72%) (29 cases with atrial fibrillation, 4 cases with supraventricular tachycardia, 2 cases with atrial flutter and one case with Wolff—Parkinson-White syndrome), over a mean period of 7.4 ± 9 h. The patients in which conversion was achieved had arrhythmias which had been in existence for a shorter time (5.3 ± 9.8 days) than those in which conversion was not achieved (16.7 ± 26.2 days) (P<0.01). The mean dosage of flecainide used to achieve conversion was 2.5 ± 2.36 mg kg−1. Flecainide appears to be an effective agent for the conversion to sinus rhythm of atrial fibrillation and supraventricular tachycardias. Its efficacy in cases of atrial flutter has not yet been demonstrate
Pulmonary valve stenosis due to undifferentiated pleomorphic sarcoma
Pulmonary artery sarcomas are uncommon intracardiac tumours with poor prognosis. We report the case of a 69-year-old woman in good health presenting with rapidly progressive dyspnoea and an unfamiliar systolic murmur. Echocardiography revealed pulmonary valve stenosis due to an obstructing mobile mass. Imaging studies confirmed the presence of a contrast-enhancing lesion adherent to the valve, extending into the pulmonary trunk and right ventricular outflow tract, and suggestive of malignancy.
Endovascular biopsy was attempted with no success. Surgical resection with autologous graft valve replacement and pulmonary artery reconstruction was performed. Postoperative histological examination
confirmed the diagnosis of an undifferentiated pleomorphic sarcoma. Pulmonary artery sarcoma should be considered as a rare differential diagnosis in patients presenting with dyspnoea and a crescendo-decrescendo systolic murmur increasing with inspiration. Echocardiography is a useful first diagnostic approach but multi-imaging assessment is almost always necessary for definite diagnosis. Our case provides insights into the challenges met by cardiologists, radiologists and cardiac surgeons in the management of such cases
Early results after mitral valvuloplasty for pure mitral regurgitation
In this study we present the results of 105 consecutive patients with pure mitral regurgitation who underwent surgical treatment. In all patients mitral regurgitation was associated with mitral valve prolapse: 54 patients underwent mitral valvuloplasty and 51 patients mitral valve replacement. Clinical assessment and echocardiography were used as follow-up criteria at one year after surgery. After mitral valvuloplasty, NYH A decreased from 2.7±0.8 to 1.1±0.7 (P<0.01) and workload capacity increased from 65±28% to 96±25% (P<0.001); left endsystolic atrial dimension and enddiastolic dimension decreased from 6.2±0.8 to 4.8±1.2 cm (P<0.001) and from 7.2±1.3 to 5.9±0.8 cm (P<0.01); ventricular contraction fraction did not change significantly. After mitral valve replacement, clinical and echocardiographic improvement was significant but less remarkable than after valvuloplasty; ventricular contraction fraction fell from 39±7% to 29±8% in contrast to patients undergoing mitral valvuloplasty in whom no significant change occurred. Complications were rare in both groups though only a minority of patients undergoing mitral valvuloplasty received anticoagulants. We conclude that mitral valvuloplasty in patients with pure mitral regurgitation associated with mitral valve prolapse gives excellent results, particularly regarding left ventricular function when compared with the patients after mitral valve replacemen
Long-term outcome of congenital aortic valve stenosis: predictors of reintervention.
OBJECTIVES: To evaluate long-term outcome of initial aortic valve intervention in a paediatric population with congenital aortic stenosis, and to determine risk factors associated with reintervention.
PATIENTS AND METHODS: From 1985 to 2009, 77 patients with congenital aortic stenosis and a mean age of 5.8±5.6 years at diagnosis were followed up in our institution for 14.8±9.1 years.
RESULTS: First intervention was successful with 86% of patients having a residual peak aortic gradient 1 regurgitation increased by 7%. Long-term survival after the first procedure was excellent, with 91% survival at 25 years. At a mean interval of 7.6±5.3 years, 30 patients required a reintervention (39%), mainly because of a recurrent aortic stenosis. Freedom from reintervention was 97, 89, 75, 53, and 42% at 1, 10, 15, 20, and 25 years, respectively. Predictors of reintervention were residual peak aortic gradient (p=0.0001), aortic regurgitation post-intervention >1 (p=0.02), prior balloon aortic valvuloplasty (p=0.04), and increased left ventricular posterior wall thickness (p=0.1).
CONCLUSIONS: Aortic valve intervention is a safe and effective procedure for congenital aortic stenosis with excellent survival results. However, rate of reintervention is high and influenced by increased left ventricular posterior wall thickness pre-intervention, prior balloon valvuloplasty, higher residual peak systolic valve gradient, and more than mild regurgitation post-intervention. The study highlights that long-term follow-up is recommended for these patients
Estimating network related risks: A methodology and an application in the transport sector
Networks such as
transportation, water, and power are critical lifelines for society. Managers
plan and execute interventions to guarantee the operational state of their
networks under various circumstances, including after the occurrence of
(natural) hazard events. Creating an intervention program demands knowing the
probable direct and indirect consequences (i.e., risk) of the various hazard
events that could occur in order to be able to mitigate their effects. This paper
introduces a methodology to support network managers in the quantification of
the risk related to their networks. The methodology is centered on the
integration of the spatial and temporal attributes of the events that need to
be modeled to estimate the risk. Furthermore, the methodology supports the
inclusion of the uncertainty of these events and the propagation of these
uncertainties throughout the risk modeling. The methodology is implemented
through a modular simulation engine that supports the updating and swapping
of models according to the needs of network managers. This work demonstrates
the usefulness of the methodology and simulation engine through an
application to estimate the potential impact of floods and mudflows on a road
network located in Switzerland. The application includes the modeling of
(i) multiple time-varying hazard events; (ii) their physical and functional
effects on network objects (i.e., bridges and road sections); (iii) the
functional interrelationships of the affected objects; (iv) the resulting
probable consequences in terms of expected costs of restoration, cost of
traffic changes, and duration of network disruption; and (v) the restoration
of the network.</p
Maxwell Fields and Shear-Free Null Geodesic Congruences
We study and report on the class of vacuum Maxwell fields in Minkowski space
that possess a non-degenerate, diverging, principle null vector field (null
eigenvector field of the Maxwell tensor) that is tangent to a shear-free null
geodesics congruence. These congruences can be either surface forming (the
tangent vectors proportional to gradients) or not, i.e., the twisting
congruences. In the non-twisting case, the associated Maxwell fields are
precisely the Lienard-Wiechert fields, i.e., those Maxwell fields arising from
an electric monopole moving on an arbitrary worldline. The null geodesic
congruence is given by the generators of the light-cones with apex on the
world-line. The twisting case is much richer, more interesting and far more
complicated. In a twisting subcase, where our main interests lie, it can be
given the following strange interpretation. If we allow the real Minkowski
space to be complexified so that the real Minkowski coordinates x^a take
complex values, i.e., x^a => z^a=x^a+iy^a with complex metric g=eta_abdz^adz^b,
the real vacuum Maxwell equations can be extended into the complex and
rewritten as curlW =iWdot, divW with W =E+iB. This subcase of Maxwell fields
can then be extended into the complex so as to have as source, a complex
analytic world-line, i.e., to now become complex Lienard-Wiechart fields. When
viewed as real fields on the real Minkowski space, z^a=x^a, they possess a real
principle null vector that is shear-free but twisting and diverging. The twist
is a measure of how far the complex world-line is from the real 'slice'. Most
Maxwell fields in this subcase are asymptotically flat with a time-varying set
of electric and magnetic moments, all depending on the complex displacements
and the complex velocities.Comment: 3
Acute ascending aortic dissection complicating open heart surgery: cerebral perfusion defines the outcome
OBJECTIVE: This retrospective study was designed to assess the risks of acute ascending aorta dissection (AAD) as a rare but potentially fatal complication of open heart surgery. METHOD: Among 8624 cardiac surgical procedures under cardiopulmonary bypass (CPB) and cardioplegic myocardial protection from 1978 to 1997, 10 patients (0.12%) presented with a secondary or so called 'iatrogenic' AAD. There were seven men and three women, mean age 64 +/- 9 years, ranging from 47 to 79. The original procedures involved five coronary artery bypass grafts (CABG), one repeat CABG, one aortic valve replacement (AVR), one AVR and CABG, one mitral valvuloplasty (MVP) and CABG and one ascending aorta replacement. We retrospectively analyzed their hospital records. RESULTS: Group I consisted of seven patients with AAD intraoperatively and group II consisted of three patients who developed acute AAD 8-32 days after cardiac surgery. In group I, treatment consisted of the original procedure, plus grafting of the ascending aorta in six patients and closed plication and aortic wrapping in one. In group II, two patients received a dacron graft and one patient developed lethal tamponnade due to aortic rupture before surgery. Postoperatively, six patients responded well and three died (33%), two patients from group I on the 2nd postoperative day with severe post-anoxic encephalopathy, and one from group II with severe peroperative cardiogenic shock. CONCLUSION: Preventing AAD with the appropriate means remains standard practice in cardiac surgery. If AAD occurs, it requires prompt diagnosis and interposition graft to allow a better prognosis. Intraoperative AAD happens at the beginning of CPB jeopardizing perfusion of the supra-aortic arteries
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