356 research outputs found
Beam optics and lattice design for particle accelerators
The goal of this manuscript is to give an introduction into the design of the
magnet lattice and as a consequence into the transverse dynamics of the
particles in a synchrotron or storage ring. Starting from the basic principles
of how to design the geometry of the ring we will briefly review the transverse
motion of the particles and apply this knowledge to study the layout and
optimization of the principal elements, namely the lattice cells. The detailed
arrangement of the accelerator magnets within the cells is explained and will
be used to calculate well defined and predictable beam parameters. The more
specific treatment of low beta insertions is included as well as the concept of
dispersion suppressors that are an indispensable part of modern collider rings.Comment: 36 pages, contribution to the CAS - CERN Accelerator School: Course
on High Power Hadron Machines; 24 May - 2 Jun 2011, Bilbao, Spai
Introduction to Particle Accelerators and their Limitations
The paper gives a short overview of the principles of particle accelerators,
their historical development and the typical performance limitations. After an
introduction to the basic concepts, the main emphasis is to sketch the layout
of modern storage rings and their limitations in energy and machine
performance. Examples of existing machines - among them clearly the LHC at CERN
- demonstrate the basic principles and the technical and physical limits that
we face today in the design and operation of these particle colliders. Pushing
for ever higher beam energies motivates the design of the future collider
studies and beyond that, the development of more efficient acceleration
techniques.Comment: 26 pages, contribution to the CAS - CERN Accelerator School: High
Gradient Wakefield Accelerators, 11-22 March 2019, Sesimbra, Portugal. arXiv
admin note: substantial text overlap with arXiv:1705.0960
Estimating the Effective Elasticity Properties of a Diamond/-SiC Composite Thin Film by 3D Reconstruction and Numerical Homogenization
The main aim of the present work is to estimate the effective elastic
stiffnesses of a two-phase diamond/-SiC composite thin film that is
fabricated by chemical vapor deposition. The parameters of linear elasticity
are determined by numerical homogenization. The database is sparse since for
the 3D volume of interest only two micrographs displaying the phase
distributions in perpendicular planes are available; micrographs each of a
cross-section and the surface of the thin film. A representative volume element
(RVE) is reconstructed by an optimization software and by means of identified
material symmetries in 2D of the specimen. The elastic homogenization results
indicate that the two-phase diamond/-SiC composite exhibits the behavior
of transverse isotropy, for which the set of six independent material
parameters is identified
Low-Emittance Tuning for Circular Colliders
The 100 km FCC-ee e⁺/e⁻ circular collider requires luminosities in the order of 10³⁵ cm⁻² s⁻¹ and very low emittances of 0.27 nm·prad for the horizontal plane and 1 pm·prad in the vertical. In order to reach these requirements, extreme focusing of the beam is needed in the interaction regions, leading to a vertical beta function of 0.8 mm at the IP. These challenges make the FCC-ee design particularly susceptible to misalignment and field errors. This paper describes the tolerance of the machine to magnet alignment errors and the effectiveness of optics and orbit correction methods that were implemented in order to bring the vertical dispersion to acceptable values, which in turn limits the vertical emittance. Thousands of misalignment and error seeds were introduced in MADX simulations and a comprehensive correction strategy, which includes macros based upon Dispersion Free Steering (DFS), linear coupling correction based on Resonant Driving Terms (RDTs) and response matrices, was implemented. The results are summarized in this paper
Prognostic value of the ABCD2 score beyond short-term follow-up after transient ischemic attack (TIA) - a cohort study
<p>Abstract</p> <p>Background</p> <p>Transient ischemic attack (TIA) patients are at a high vascular risk. Recently the ABCD<sup>2 </sup>score was validated for evaluating short-term stroke risk after TIA. We assessed the value of this score to predict the vascular outcome after TIA during medium- to long-term follow-up.</p> <p>Methods</p> <p>The ABCD<sup>2 </sup>score of 176 TIA patients consecutively admitted to the Stroke Unit was retrospectively calculated and stratified into three categories. TIA was defined as an acute transient focal neurological deficit caused by vascular disease and being completely reversible within 24 hours. All patients had to undergo cerebral MRI within 5 days after onset of symptoms as well as extracranial and transcranial Doppler and duplex ultrasonography. At a median follow-up of 27 months, new vascular events were recorded. Multivariate Cox regression adjusted for EDC findings and heart failure was performed for the combined endpoint of cerebral ischemic events, cardiac ischemic events and death of vascular or unknown cause.</p> <p>Results</p> <p>Fifty-five patients (32.0%) had an ABCD<sup>2 </sup>score ≤ 3, 80 patients (46.5%) had an ABCD2 score of 4-5 points and 37 patients (21.5%) had an ABCD<sup>2 </sup>score of 6-7 points. Follow-up data were available in 173 (98.3%) patients. Twenty-two patients (13.8%) experienced an ischemic stroke or TIA; 5 (3.0%) a myocardial infarction or acute coronary syndrome; 10 (5.7%) died of vascular or unknown cause; and 5 (3.0%) patients underwent arterial revascularization. An ABCD<sup>2 </sup>score > 3 was significantly associated with the combined endpoint of cerebral or cardiovascular ischemic events, and death of vascular or unknown cause (hazard ratio (HR) 4.01, 95% confidence interval (CI) 1.21 to 13.27). After adjustment for extracranial ultrasonographic findings and heart failure, there was still a strong trend (HR 3.13, 95% CI 0.94 to 10.49). Whereas new cardiovascular ischemic events occurred in 9 (8.3%) patients with an ABCD<sup>2 </sup>score > 3, this happened in none of the 53 patients with a score ≤ 3.</p> <p>Conclusions</p> <p>An ABCD<sup>2 </sup>score > 3 is associated with an increased general risk for vascular events in the medium- to long-term follow-up after TIA.</p
A novel OSA-related model of intermittent hypoxia in endothelial cells under flow reveals pronounced inflammatory pathway activation
Obstructive sleep apnea (OSA) is a common sleep-related breathing disorder characterized by recurrent episodes of upper airway obstruction and subsequent hypoxia. In patients with OSA, severity and number of these hypoxic events positively correlate with the extent of associated cardiovascular pathology. The molecular mechanisms underlying intermittent hypoxia (IH)-driven cardiovascular disease in OSA, however, remain poorly understood—partly due to the lack of adequate experimental models. Here, we present a novel experimental approach that utilizes primary human endothelial cells cultivated under shear stress. Oxygen partial pressure dynamics were adopted in our in vitro model according to the desaturation-reoxygenation patterns identified in polysomnographic data of severe OSA patients (n = 10, with 892 severe desaturations, SpO2<80%). Using western blot analysis, we detected a robust activation of the two major inflammatory pathways ERK and NF-κB in endothelial cells, whereas no HIF1α and HIF2α protein stabilization was observed. In line with these findings, mRNA and protein expression of the pro-inflammatory adhesion and signaling molecule ICAM-1 and the chemokine CCL2 were significantly increased. Hence, we established a novel in vitro model for deciphering OSA-elicited effects on the vascular endothelium. First data obtained in this model point to the endothelial activation of pro-inflammatory rather than hypoxia-associated pathways in OSA. Future studies in this model might contribute to the development of targeted strategies against OSA-induced, secondary cardiovascular disease
Transcranial Doppler ultrasonography predicts cardiovascular events after TIA
<p>Abstract</p> <p>Background</p> <p>Transient ischemic attack (TIA) patients are at high vascular risk. We assessed the value of extracranial (ECD) and transcranial (TCD) Doppler and duplex ultrasonography to predict clinical outcome after TIA.</p> <p>Methods</p> <p>176 consecutive TIA patients admitted to the Stroke Unit were recruited in the study. All patients received diffusion-weighted imaging, standardized ECD and TCD. At a median follow-up of 27 months, new vascular events were recorded.</p> <p>Results</p> <p>22 (13.8%) patients experienced an ischemic stroke or TIA, 5 (3.1%) a myocardial infarction or acute coronary syndrome, and 5 (3.1%) underwent arterial revascularization. ECD revealed extracranial ≥ 50% stenosis or occlusions in 34 (19.3%) patients, TCD showed intracranial stenosis in 15 (9.2%) and collateral flow patterns due to extracranial stenosis in 5 (3.1%) cases. Multivariate analysis identified these abnormal ECD and TCD findings as predictors of new cerebral ischemic events (ECD: hazard ratio (HR) 4.30, 95% confidence interval (CI) 1.75 to 10.57, P = 0.01; TCD: HR 4.73, 95% CI 1.86 to 12.04, P = 0.01). Abnormal TCD findings were also predictive of cardiovascular ischemic events (HR 18.51, 95% CI 3.49 to 98.24, P = 0.001).</p> <p>Conclusion</p> <p>TIA patients with abnormal TCD findings are at high risk to develop further cerebral and cardiovascular ischemic events.</p
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