Search for stop and higgsino production using diphoton Higgs boson decays

Results are presented of a search for a "natural" supersymmetry scenario with gauge mediated symmetry breaking. It is assumed that only the supersymmetric partners of the top-quark (stop) and the Higgs boson (higgsino) are accessible. Events are examined in which there are two photons forming a Higgs boson candidate, and at least two b-quark jets. In 19.7 inverse femtobarns of proton-proton collision data at sqrt(s) = 8 TeV, recorded in the CMS experiment, no evidence of a signal is found and lower limits at the 95% confidence level are set, excluding the stop mass below 360 to 410 GeV, depending on the higgsino mass

Severe early onset preeclampsia: short and long term clinical, psychosocial and biochemical aspects

Preeclampsia is a pregnancy specific disorder commonly defined as de novo hypertension and proteinuria after 20 weeks gestational age. It occurs in approximately 3-5% of pregnancies and it is still a major cause of both foetal and maternal morbidity and mortality worldwide1. As extensive research has not yet elucidated the aetiology of preeclampsia, there are no rational preventive or therapeutic interventions available. The only rational treatment is delivery, which benefits the mother but is not in the interest of the foetus, if remote from term. Early onset preeclampsia (<32 weeks’ gestational age) occurs in less than 1% of pregnancies. It is, however often associated with maternal morbidity as the risk of progression to severe maternal disease is inversely related with gestational age at onset2. Resulting prematurity is therefore the main cause of neonatal mortality and morbidity in patients with severe preeclampsia3. Although the discussion is ongoing, perinatal survival is suggested to be increased in patients with preterm preeclampsia by expectant, non-interventional management. This temporising treatment option to lengthen pregnancy includes the use of antihypertensive medication to control hypertension, magnesium sulphate to prevent eclampsia and corticosteroids to enhance foetal lung maturity4. With optimal maternal haemodynamic status and reassuring foetal condition this results on average in an extension of 2 weeks. Prolongation of these pregnancies is a great challenge for clinicians to balance between potential maternal risks on one the eve hand and possible foetal benefits on the other. Clinical controversies regarding prolongation of preterm preeclamptic pregnancies still exist – also taking into account that preeclampsia is the leading cause of maternal mortality in the Netherlands5 - a debate which is even more pronounced in very preterm pregnancies with questionable foetal viability6-9. Do maternal risks of prolongation of these very early pregnancies outweigh the chances of neonatal survival? Counselling of women with very early onset preeclampsia not only comprises of knowledge of the outcome of those particular pregnancies, but also knowledge of outcomes of future pregnancies of these women is of major clinical importance. This thesis opens with a review of the literature on identifiable risk factors of preeclampsia

Electrical leakage phenomenon in heteroepitaxial cubic silicon carbide on silicon

Heteroepitaxial 3C-SiC films on silicon substrates are of technological interest as enablers to integrate the excellent electrical, electronic, mechanical, thermal, and epitaxial properties of bulk silicon carbide into well-established silicon technologies. One critical bottleneck of this integration is the establishment of a stable and reliable electronic junction at the heteroepitaxial interface of the n-type SiC with the silicon substrate. We have thus investigated in detail the electrical and transport properties of heteroepitaxial cubic silicon carbide films grown via different methods on low-doped and high-resistivity silicon substrates by using van der Pauw Hall and transfer length measurements as test vehicles. We have found that Si and C intermixing upon or after growth, particularly by the diffusion of carbon into the silicon matrix, creates extensive interstitial carbon traps and hampers the formation of a stable rectifying or insulating junction at the SiC/Si interface. Although a reliable p-n junction may not be realistic in the SiC/Si system, we can achieve, from a point of view of the electrical isolation of in-plane SiC structures, leakage suppression through the substrate by using a high-resistivity silicon substrate coupled with deep recess etching in between the SiC structures

Efficient Solar-vapor Generation in Hollow-mesoporous Plasmonic Nanoshells

Plasmonic nanostructures have shown great promise in solar thermal applications. Here we report highly efficient solar vapor generation using hollow-mesoporous plasmonic nanoshells, where the steam production is significantly enhanced by the extended active surface and the nearly neutral buoyancy. An energy-to-vapor conversion efficiency of 69% was measured under 10x solar irradiance. We also show clear evidence of direct vapor nucleation from the plasmonic structure without bulk heating

Hollow Mesoporous Plasmonic Nanoshells for Enhanced Solar Vapor Generation

In the past decade, nanomaterials have made their way into a variety of technologies in solar energy, enhancing the performance by taking advantage of the phenomena inherent to the nanoscale. Recent examples exploit plasmonic core/shell nanoparticles to achieve efficient direct steam generation, showing great promise of such nanoparticles as a useful material for solar applications. In this paper, we demonstrate a novel technique for fabricating bimetallic hollow mesoporous plasmonic nanoshells that yield a higher solar vapor generation rate compared with their solid-core counterparts. On the basis of a combination of nanomasking and incomplete galvanic replacement, the hollow plasmonic nanoshells can be fabricated with tunable absorption and minimized scattering. When exposed to sun light, each hollow nanoshell generates vapor bubbles simultaneously from the interior and exterior. The vapor nucleating from the interior expands and diffuses through the pores and combines with the bubbles formed on the outer wall. The lack of a solid core significantly accelerates the initial vapor nucleation and the overall steam generation dynamics. More importantly, because the density of the hollow porous nanoshells is essentially equal to the surrounding host medium these particles are much less prone to sedimentation, a problem that greatly limits the performance and implementation of standard nanoparticle dispersions

Dislocations in AlGaN: Core Structure, Atom Segregation and Optical Properties

We conducted a comprehensive investigation of dislocations in Al0.46Ga0.54N. Using aberration-corrected scanning transmission electron microscopy and energy dispersive X-ray spectroscopy, the atomic structure and atom distribution at the dislocation core have been examined. We report that the core configuration of dislocations in AlGaN is consistent with that of other materials in the III-Nitride system. However, we observed that the dissociation of mixed-type dislocations is impeded by alloying GaN with AlN, which is confirmed by our experimental observation of Ga and Al atom segregation in the tensile and compressive parts of the dislocations, respectively. Investigation of the optical properties of the dislocations shows that the atom segregation at dislocations has no significant effect on the intensity recorded by cathodoluminescence in the vicinity of the dislocations. These results are in contrast with the case of dislocations in In0.09Ga0.91N where segregation of In and Ga atoms also occurs but results in carrier localization limiting non-radiative recombination at the dislocation. This study therefore sheds light on why InGaN-based devices are generally more resilient to dislocations than their AlGaN-based counterparts

Atomic resolution imaging of dislocations in algan and the efficiency of UV LEDs

[Abstract not available

Research data supporting "Optical and structural properties of dislocations in InGaN"

The figures in this dataset are taken from the associated publication in the Journal of Applied Physics. Data to support figures 2–6 are provided. The following are captions for the figures in the Journal of Applied Physics. Figure 1 – (a) AFM, (b) SEM, and (c) room temperature panchromatic CL taken on the same area of sample B. Figure 2 – (a) AFM, continuous wave (CW) mode CL (b) integrated intensity and (c) peak wavelength, and pulsed mode CL (d) integrated intensity and (e) peak wavelength of the same region of sample D at 300 K (corresponding to the area highlighted in (a)). (f) Streak map taken in the surrounding material, and (g) extracted time decay curve at the spectral position indicated by a square in (g). (The black regions in (e) correspond to pixels where the CL signal was too low to extract accurate value of peak wavelength.) Figure 3 – Room temperature panchromatic CL image of samples (a) A, (b) B, (c) C, and (d) D. In inset of (d), panchromatic CL with brightness and contrast adjusted to reveal CL intensity variation at dislocations. Plots of the (e) intensity ratio and (f) energy shift on the center and on the facet of the V-pit as a function of indium content and dislocation type. Figure 4 – Molecular dynamics results of distribution and length of In-N-In chains in supercells of overall composition 5.5% (a) and 20% (b). (c) Probability of indium atom to be part of multiple atom chain. Figure 5 – Wavelength dependence of (a) decay time τdecay and (b) rise time τrise recorded at 15 K on the bright spot of an edge-type dislocation in samples B and D. In background, corresponding time integrated emission spectra (B in violet, and D in blue), and in dotted line, the time response of the system. Figure 6 – Wavelength dependence of the decay time τdecay recorded at 300 K on (a) the surrounding material and (b) bright spot of an edge-type dislocation in sample D, with corresponding time integrated emission spectra and streak map. For direct comparison, the surrounding emission spectrum (the same as in (a)) is added as the dotted line in (b). Figure 7 – ADF-STEM (a,e), dark field TEM images taken under g=11 ̅00 (b,f) and g=0002 (c,g) condition, and EDX mapping of In fraction (d,h) of a V-pit in sample B (a-d) and sample D (e-h).ERC (FP7/2007-2013)/No. 279361 (MACONS) ERC Starting Grant 307636 “SCOPE" Lindemann Trust Fellowship EPSRC grant EP/M010627/