High energy proton micro-bunches from a laser plasma accelerator

Recent advances on laser-driven ion accelerators have sparked an increased interest in such energetic particle sources, particularly towards the viability of their usage in a breadth of applications, such as high energy physics and medical applications. Here, we identify a new ion acceleration mechanism and we demonstrate, via particle-in-cell simulations, for the first time the generation of high energy, monochromatic proton micro-bunches while witnessing the acceleration and self-modulation of the accelerated proton beam in a dual-gas target, consisting of mixed ion species. In the proposed ion acceleration mechanism due to the interaction of an ultra-short, ultra-intense (2 PW, 20 fs) laser pulses with near-critical-density partially ionized plasmas (C & H species), we numerically observed high energy monochromatic proton microbunches of high quality (peak proton energy 350 MeV, laser to proton conversion efficiency ~10 −4 and angular divergence <10 degree), which can be of high relevance for medical applications. We envisage that through this scheme, the range of attained energies and the monochromaticity of the accelerated protons can be increased with existing laser facilities or allow for laser-driven ion acceleration investigations to be pursued at moderate energies in smaller scale laser laboratories, hence reducing the size of the accelerators. The use of mixed-gas targets will enable high repetition rate operation of these accelerators, free of plasma debris and electromagnetic pulse disruptions

Design and modeling of a novel damage-free steel column base

Column bases are fundamental components of a steel frame. However their design has not yet received appropriate attention. Conventional steel column bases cannot be easily repaired if damaged and exhibit difficult-to-predict and simulate stiffness, strength and hysteretic behaviour. This paper proposes a novel demountable and fully repairable column base for resilient steel buildings. The new column base isolates damage in easy-to-replace structural elements with the goal of minimizing repair time and disruption of the building service in the aftermath of a strong earthquake. Moreover, it can be easily constructed and deconstructed to enable sustainable steel frame designs. It provides significant flexibility in the design, with rotational stiffness and moment resistance that can be independently tuned. It has self-centering capability for reducing residual drifts. The paper presents design rules, an analytical hysteretic model and a 3D finite element model for the new column base

NUTRIENT EFFECTS IN INFLAMMATORY BOWEL DISEASE

PhDAbstract Background: Not only does IBD lead to nutritional deficiencies, but also nutrients influence its pathophysiology: exclusive enteral nutrition (EEN) is an effective primary treatment in Crohn’s disease; and vitamin D (VitD) is involved in its pathogenesis and course. Aims: We hypothesised that nutrients impact on the course of IBD. We therefore studied the effect of EEN i) on long term clinical course in children; ii) on CD58, a costimulatory molecule at the intestinal epithelial cell (IEC) lines, iii) adults with Crohn’s disease. We examined the possible effect of serum vitamin D levels on the course of IBD and also the possible role of ethnicity in our paediatric and adult populations that were treated with EEN but also in our general adult population. Results Chapter II: 56 paediatric patients with Crohn’s disesase were followed up for 5 years. 57% of patients achieved remission after 6 weeks of EEN. Achievement of clinical remission within 6 weeks of EEN was significantly associated with a longer time to relapse and to treatment escalation. VitD deficiency was common; and those patients who were deficient were significantly more likely to require corticosteroids and also needed thiopurines sooner. Chapter III: CD58 was expressed in the IEC isolated from IBD patients and healthy controls. EN down-regulated the expression of CD58 on IEC lines. Chapter IV: 22 adult patients with Crohn’s disease with a mean age of 30.8 years were given EEN and followed up for a mean time of 1.9 years. 22.7% of patients went into clinical remission and 77.3% experienced a clinical response. By the end of follow up 63.6% (14/22) of patients had clinically relapsed and 36.4% required surgery during their follow up. There was no difference between South Asian and Caucasian patients in the disease outcomes after administration of EEN. Chapter V: Bangladeshis were more often vitamin D deficient than white Caucasian patients; however vitamin D status was not associated with the course of IBD. Bangladeshis developed perianal disease and required thiopurines earlier in their disease course. Bangladeshi patients with UC had more extensive disease. Conclusions: EEN, when successful, improves the long term outcome of Crohn’s disease in children, possibly in part, by down-regulating CD58 on the IEC. VitD deficiency may influence the clinical course of IBD; however our results were contradictory between children and adults and significantly limited by the assessment of the vitamin D level at a single time point

Diagnosis and management of left valvular heart disease with advanced echocardiography and cardiac computed tomography

This thesis explored the diagnosis, management and prognosis of the most common valvular heart diseases: aortic stenosis (AS) and mitral regurgitation (MR) and enlightened their challenging types: the discordant low-gradient severe AS and the secondary MR in non-ischemic cardiomyopathy. This thesis provides new insights into the use of fusion aortic valve area index, by  incorporating the measurement of left ventricular outflow tract area on cardiac computed tomography in the continuity equation, for the diagnosis of low-gradient AS. For the treatment of low-gradient AS, TAVR is shown to result in reverse LV remodeling and functional recovery. In comparison to other minimal invasive surgical methods it results in less prosthesis-patient-mismatch although paravalvular aortic regurgitation is a caveat. Regarding the diagnostic assessment of secondary MR due to LV dysfunction this thesis concluded that LV GLS reflects the real LV dysfunction while LVEF overestimates LV function without accounting for the forward LV flow. Mitral valve repair offers LV reverse remodeling and increase in forward flow when used for the treatment of this challenging condition. Regarding the prognostication of low-gradient AS and secondary MR this thesis advocates for the evaluation of the valvular calcium on cardiac computed tomography and the evaluation of LV GLS and forward flow that are associated with survival.LUMC / Geneeskund

Self-centering steel column base with metallic energy dissipation devices

Column bases of seismic-resistant steel frames are typically designed as full-strength to ensure that plastic hinges develop in the bottom end of the first-storey columns. Alternatively, column bases may be designed as partial-strength and dissipate energy through inelastic deformations in their main components (i.e., base plate, steel anchor rods). Both design philosophies result in difficult-to-repair damage and residual drifts. Moreover, the second design philosophy results in complex hysteretic behaviour with strength and stiffness deterioration. This paper proposes a partial-strength low-damage self-centering steel column base. The column base provides flexibility in the design as its rotational stiffness and moment resistance can be independently tuned. The paper presents an analytical model that predicts the stiffness, strength, and hysteretic behaviour of the column base. In addition, a design procedure and detailed finite element models are presented. The paper evaluates the effectiveness of the column base by carrying out nonlinear dynamic analyses on a prototype steel building designed as post-tensioned self-centering moment-resisting frame. The results demonstrate the potential of the column base to reduce the residual first-storey drifts and protect the first-storey columns from yielding.</p

Highly efficient few-cycle laser wakefield electron accelerator

A significant part of the laser wakefield acceleration (LWFA) research effort focuses on studying high-energy, quasi-monoenergetic electron beams. For other applications, such as the production and application of intense betatron x-ray radiation, Bremsstrahlung gamma-rays and positron beams, the beam's spectral quality is secondary to the number of electrons produced. This work discusses 3D particle-in-cell simulations of a highly efficient LWFA acceleration process, generating a broad spectrum of electrons, driven by a 12 TW few-cycle laser on high-density gas targets. In some cases, laser absorption in plasma exceeds 80%, and up to 27% of the driving laser energy is transferred to electrons over 20 MeV leaving the plasma. We also observe a deceleration of the accelerated beam at the plasma downramp and plasma exit, which arises from transitioning from laser-driven to beam-dominated wake, and also from the induced axial electric field. This effect is similar to magnetic vortex acceleration, where the induced axial electric field, instead of accelerating plasma ions, would slow down the opposite-charged electron beam and also a strong return current and backward electron beam

Self-guided wakefield experiments driven by petawatt class ultra-short laser pulses

We investigate the extension of self-injecting laser wakefield experiments to the regime that will be accessible with the next generation of petawatt class ultra-short pulse laser systems. Using linear scalings, current experimental trends and numerical simulations we determine the optimal laser and target parameters, i.e. focusing geometry, plasma density and target length, that are required to increase the electron beam energy (to > 1 GeV) without the use of external guiding structures.Comment: 15 pages, 8 figure