This paper presents important results of the European HVDC Study Group founded on an initiative by the German Commission for Electrical, Electronic and Information Technologies in September 2010. The ...main task of the Study Group has been defining "Technical Guidelines for first HVDC Grids": 1) to gain a common understanding of basic operating and design principles of HVDC grid systems, and 2) to prepare the ground for more detailed standardization work. The HVDC systems are moving from the stage of point-to-point (PTP) connectors to the stage of the transmission systems interconnecting more than two stations and utilizing multiterminal (MT), multivendor (MTMV) HVDC voltage-source converter (VSC) systems. The development will be modular, for example, in steps, starting with interconnecting PTP connectors and establishing three-pod, radial systems. Then, such simple systems may gradually be interconnected into radial and meshed HVDC-VSC systems comprising more HVDC lines and dc converter stations. This paper describes understanding, specification, and standardization of design and operation principles of the HVDC grids seen as the first needed steps toward such MTMV systems.
X-ray free-electron lasers enable the investigation of the structure and dynamics of diverse systems, including atoms, molecules, nanocrystals and single bioparticles, under extreme conditions. Many ...imaging applications that target biological systems and complex materials use hard X-ray pulses with extremely high peak intensities (exceeding 10
watts per square centimetre). However, fundamental investigations have focused mainly on the individual response of atoms and small molecules using soft X-rays with much lower intensities. Studies with intense X-ray pulses have shown that irradiated atoms reach a very high degree of ionization, owing to multiphoton absorption, which in a heteronuclear molecular system occurs predominantly locally on a heavy atom (provided that the absorption cross-section of the heavy atom is considerably larger than those of its neighbours) and is followed by efficient redistribution of the induced charge. In serial femtosecond crystallography of biological objects-an application of X-ray free-electron lasers that greatly enhances our ability to determine protein structure-the ionization of heavy atoms increases the local radiation damage that is seen in the diffraction patterns of these objects and has been suggested as a way of phasing the diffraction data. On the basis of experiments using either soft or less-intense hard X-rays, it is thought that the induced charge and associated radiation damage of atoms in polyatomic molecules can be inferred from the charge that is induced in an isolated atom under otherwise comparable irradiation conditions. Here we show that the femtosecond response of small polyatomic molecules that contain one heavy atom to ultra-intense (with intensities approaching 10
watts per square centimetre), hard (with photon energies of 8.3 kiloelectronvolts) X-ray pulses is qualitatively different: our experimental and modelling results establish that, under these conditions, the ionization of a molecule is considerably enhanced compared to that of an individual heavy atom with the same absorption cross-section. This enhancement is driven by ultrafast charge transfer within the molecule, which refills the core holes that are created in the heavy atom, providing further targets for inner-shell ionization and resulting in the emission of more than 50 electrons during the X-ray pulse. Our results demonstrate that efficient modelling of X-ray-driven processes in complex systems at ultrahigh intensities is feasible.
Sepsis is one of the most frequent causes of death among patients in intensive care units. Many therapeutic strategies have been assessed without the desired success rates. A key risk factor for ...death is hypotension due to vasodilatation with vascular hyposensitivity. However, the pathways underlying this process remain unclear. Endotoxemia induces inflammatory mediators, and this is followed by vasoplegia and decreased cardiac contractility. Although inhibition of these mediators diminishes mortality rates in animal models, this phenomenon has not been confirmed in humans. Downregulation of vasoconstrictive receptors such as angiotensin receptors, adrenergic and vasopressin receptors is seen in sepsis, which is associated with a hyporesponsiveness to vasoconstrictive mediators. Animal studies have verified that receptor downregulation is linked to the above-mentioned inflammatory mediators. Anti-inflammatory therapy with glucocorticoids reportedly improves responsiveness to catecholamines with higher survival in rats, although this has not been shown to be clinically significant in humans. Hence, there is an urgent need for in-depth studies investigating the underlying mechanisms of vasoplegia to allow for development of effective therapeutic strategies for the treatment of sepsis.
Abstract Due to the significantly improved outcome and quality of life of patients with different tumor entities after cytoreductive surgery (CRS) and HIPEC, there is an increasing number of centers ...performing CRS and HIPEC procedures. As this procedure is technically challenging with potential high morbidity and mortality, respectively, institutional experience also in the anesthetic and intensive care departments is essential for optimal treatment and prevention of adverse events. Clinical pathways have to be developed to achieve also good results in more comorbid patients with border line indications and extensive surgical procedures. The anesthesiologist has deal with relevant fluid, blood and protein losses, increased intraabdominal pressure, systemic hypo-/hyperthermia, and increased metabolic rate in patients undergoing cytoreductive surgery with HIPEC. It is of utmost importance to maintain or restore an adequate volume by aggressive substitution of intravenous fluids, which counteracts the increased fluid loss and venous capacitance during this procedure. Supplementary thoracic epidural analgesia, non-invasive ventilation, and physiotherapy are recommended to guarantee adequate pain therapy and postoperative extubation as well as fast-track concepts. Advanced hemodynamic monitoring is essential to help the anesthesiologist picking up informations about the real-time fluid status of the patient. Preoperative preconditioning is mandatory in patients scheduled for HIPEC surgery and will result in improved outcome. Postoperatively, volume status optimization, early nutritional support, sufficient anticoagulation, and point of care coagulation management is essential. This is an extensive update on all relevant topics for anesthetists and intensivists dealing with CRS and HIPEC.
Objectives
To compare quantitative image quality parameters in abdominal dual-energy computed tomography angiography (DE-CTA) using an advanced image-based (Mono+) reconstruction algorithm for ...virtual monoenergetic imaging and standard DE-CTA.
Methods
Fifty-five patients (36 men; mean age, 64.2 ± 12.7 years) who underwent abdominal DE-CTA were retrospectively included. Mono + images were reconstructed at 40, 50, 60, 70, 80, 90 and 100 keV levels and as standard linearly blended M_0.6 images (60 % 100 kV, 40 % 140 kV). The contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) of the common hepatic (CHA), splenic (SA), superior mesenteric (SMA) and left renal arteries (LRA) were objectively measured.
Results
Mono+ DE-CTA series showed a statistically superior CNR for 40, 50, 60, 70 and 80 keV (
P
< 0.031) compared to M_0.6 images for all investigated arteries except SMA at 80 keV (
P
= 0.08). CNR at 40 keV revealed a mean relative increase of 287.7 % compared to linearly blended images among all assessed arteries (
P
< 0.001). SNR of Mono+ images was consistently significantly higher at 40, 50, 60 and 70 keV compared to M_0.6 for CHA and SA (
P
< 0.009).
Conclusions
Compared to linearly blended images, Mono+ reconstructions at low keV levels of abdominal DE-CTA datasets significantly improve quantitative image quality.
Key Points
•
Mono+ combines increased attenuation with reduced image noise compared to standard DE-CTA.
•
Mono+ shows superior contrast-to-noise ratios at low keV compared to linearly-blended images.
•
Contrast-to-noise ratio in monoenergetic DE-CTA peaks at 40 keV.
•
Mono+ reconstructions significantly improve quantitative image quality at low keV levels.
Objectives
To define optimal keV settings for advanced monoenergetic (Mono+) dual-energy computed tomography (DECT) in patients with head and neck squamous cell carcinoma (SCC).
Methods
DECT data of ...44 patients (34 men, mean age 55.5 ± 16.0 years) with histopathologically confirmed SCC were reconstructed as 40, 55, 70 keV Mono + and M_0.3 (30 % 80 kV) linearly blended series. Attenuation of tumour, sternocleidomastoid muscle, internal jugular vein, submandibular gland, and noise were measured. Three radiologists with >3 years of experience subjectively assessed image quality, lesion delineation, image sharpness, and noise.
Results
The highest lesion attenuation was shown for 40 keV series (248.1 ± 94.1 HU), followed by 55 keV (150.2 ± 55.5 HU;
P
= 0.001). Contrast-to-noise ratio (CNR) at 40 keV (19.09 ± 13.84) was significantly superior to all other reconstructions (55 keV, 10.25 ± 9.11; 70 keV, 7.68 ± 6.31; M_0.3, 5.49 ± 3.28; all
P
< 0.005). Subjective image quality was highest for 55 keV images (4.53; κ = 0.38,
P
= 0.003), followed by 40 keV (4.14; κ = 0.43,
P
< 0.001) and 70 keV reconstructions (4.06; κ = 0.32,
P
= 0.005), all superior (
P
< 0.004) to linear blending M_0.3 (3.81; κ = 0.280,
P
= 0.056).
Conclusions
Mono + DECT at low keV levels significantly improves CNR and subjective image quality in patients with head and neck SCC, as tumour CNR peaks at 40 keV, and 55 keV images are preferred by observers.
Key Points
•
Mono + DECT combines increased contrast with reduced image noise, unlike linearly blended images.
•
Mono + DECT imaging allows for superior CNR and subjective image quality.
•
Head and neck tumour contrast-to-noise ratio peaks at 40 keV.
•
55 keV images are preferred over all other series by observers.
New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced ...phenomena. Particularly, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. Here we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ions during the fragmentation of XeF2 molecules following X-ray absorption at the Xe site.
Abstract
The free expansion of a planar plasma surface is a fundamental non-equilibrium process relevant for various fields but as-yet experimentally still difficult to capture. The significance of ...the associated spatiotemporal plasma motion ranges from astrophysics and controlled fusion to laser machining, surface high-harmonic generation, plasma mirrors, and laser-driven particle acceleration. Here, we show that x-ray coherent diffractive imaging can surpass existing approaches and enables the quantitative real-time analysis of the sudden free expansion of laser-heated nanoplasmas. For laser-ionized SiO
2
nanospheres, we resolve the formation of the emerging nearly self-similar plasma profile evolution and expose the so far inaccessible shell-wise expansion dynamics including the associated startup delay and rarefaction front velocity. Our results establish time-resolved diffractive imaging as an accurate quantitative diagnostic platform for tracing and characterizing plasma expansion and indicate the possibility to resolve various laser-driven processes including shock formation and wave-breaking phenomena with unprecedented resolution.
Using ultrafast ≃2.5 fs and ≃25 fs self-amplified spontaneous emission pulses of increasing intensity and a novel experimental scheme, we report the concurrent increase of stimulated emission in ...the forward direction and loss of out-of-beam diffraction contrast for a Co/Pd multilayer sample. The experimental results are quantitatively accounted for by a statistical description of the pulses in conjunction with the optical Bloch equations. The dependence of the stimulated sample response on the incident intensity, coherence time, and energy jitter of the employed pulses reveals the importance of increased control of x-ray free electron laser radiation.
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