Exploring magnetism in graphene by electronic charge and spin transport

De rol van ferromagnetische materialen is in de afgelopen eeuw enorm gegroeid, met name in de technologie voor dataopslag. Hun magnetische eigenschappen komen voort uit geordende rangschikking van de spins van elektronen. Deze spin ordening kan echter worden verstoord door thermische fluctuaties en in feite zijn er slechts drie elementen ferromagnetisch boven kamertemperatuur: kobalt, nikkel en ijzer. Na tientallen jaren onderzoek werd begrepen dat ferromagnetisme op kamertemperatuur alleen mogelijk is voor materialen met hoge concentraties magnetische atomen. Maar recentelijk werd er ook ferromagnetisme geclaimd in materialen zonder magnetische elementen, grafiet in het bijzonder, waardoor het gevestigde paradigma in twijfel werd getrokken. Dit nieuwe type ferromagnetisme kan worden verklaard door de aanwezigheid van niet-magnetische defecten, zoals roostervacatures of chemisch geadsorbeerde atomen, maar de oorzaak staat nog altijd ter discussie. De isolatie van grafeen, een goed geleidende tweedimensionale laag grafiet, leverde een nieuwe koolstof allotroop als testobject voor mogelijk defect geïnduceerd magnetisme. Om een dergelijk magnetisme te verifiëren kozen we voor de spin transport techniek in nanoschaal spin-valve devices. Hierin kunnen processen met invloed op spin coherentie worden gediagnosticeerd, wat inzicht biedt in de interacties tussen spins en magnetische momenten. Dit proefschrift presenteert een vergelijkende studie tussen spin transport in ongerept en defect (gehydrogeneerd) grafeen, maar ook in grafeen met een verhoogde concentratie van nucleaire spin. Ondanks dat de vraag over defect geïnduceerd magnetisme in grafeen open blijft voor verdere experimentele opheldering, wordt een veelzijdige werkset geleverd om spin transport in aanwezigheid van interne magnetische velden van gevarieerde oorsprong te interpreteren

Endovascular treatment of nutcracker syndrome : a case report

Background: The "nutcracker" syndrome is most commonly caused by arterial compression of the left renal vein between the superior mesenteric artery and the aorta. As a consequence venous blood pressure increases within the renal pelvis, ureter and gonadal veins. This compression syndrome may be treated by endovascular stent implantation into the left renal vein. Case report: A 20 year old female patient was referred to us, suffering from pain in her left side, gross proteinuria and the suspicion of "nutcracker" syndrome. Symptoms were present for the last 3 years. Angio MRI was performed and confirmed compression of the left renal vein between the aorta and the superior mesenteric artery. The patient was qualified for endovascular treatment. A self expandable metallic stent, diameter 16 x 40 mm was implanted into the left renal vein. Control venography confirmed good placement of the stent and a good immediate hemodynamic effect of the procedure. The patient remains symptom free in a 14 month follow up period. Conclusions: At present, endovascular stenting seems to be the method of choice for the treatment of the nutcracker syndrome

Atomically thin mica flakes and their application as ultrathin insulating substrates for graphene

We show that it is possible to deposit, by mechanical exfoliation on SiO2/Si wafers, atomically thin mica flakes down to a single monolayer thickness. The optical contrast of these mica flakes on top of a SiO2/Si substrate, which depends on their thickness, the illumination wavelength and the SiO2 substrate thickness, can be quantitatively accounted for by a Fresnel law based model. The preparation of atomically thin insulating crystalline sheets will enable the fabrication of ultrathin defect-free insulating substrates, dielectric barriers or planar electron tunneling junctions. Additionally, we show that few-layer graphene flakes can be deposited on top of a previously transferred mica flake. Our transfer method relies on viscoelastic stamps, as those used for soft lithography. A Raman spectroscopy study shows that such an all-dry deposition technique yields cleaner and higher quality flakes than conventional wet-transfer procedures based on lithographic resists.Comment: 11 pages, 5 figures, 1 graphical abstrac

Synthesis and Catalytic Study of NiAg Bimetallic Core–Shell Nanoparticles

This publication presents the synthesis of core–shell nanoparticles, where the core was Ni, and the shell was a Ag–Ni nano alloy. The synthesis was based on the reduction of Ni and Ag ions with sodium borohydride in the presence of trisodium citrate as a stabilizer. In order to determine the phase composition of the obtained nanoparticles, an XRD study was performed, and in order to identify the oxidation states of the nanoparticle components, an XPS spectroscopic study was performed. The composition and shape of the particles were determined using the HR-TEM EDS test. The obtained nanoparticles had a size of 11 nm. The research on catalytic properties was carried out in the model methylene blue reduction system. The investigation of the catalytic activity of colloids was carried out with the use of UV–Vis spectrophotometry. The Ag–Ni alloy was about ten times more active than were pure silver nanoparticles of a similar size

Synthesis and Catalytic Study of NiAg Bimetallic Core–Shell Nanoparticles

This publication presents the synthesis of core–shell nanoparticles, where the core was Ni, and the shell was a Ag–Ni nano alloy. The synthesis was based on the reduction of Ni and Ag ions with sodium borohydride in the presence of trisodium citrate as a stabilizer. In order to determine the phase composition of the obtained nanoparticles, an XRD study was performed, and in order to identify the oxidation states of the nanoparticle components, an XPS spectroscopic study was performed. The composition and shape of the particles were determined using the HR-TEM EDS test. The obtained nanoparticles had a size of 11 nm. The research on catalytic properties was carried out in the model methylene blue reduction system. The investigation of the catalytic activity of colloids was carried out with the use of UV–Vis spectrophotometry. The Ag–Ni alloy was about ten times more active than were pure silver nanoparticles of a similar size

Milk-Derived Carbon Quantum Dots: Study of Biological and Chemical Properties Provides Evidence of Toxicity

Carbon dots (CDs) are carbon-based zero-dimensional nanomaterials that can be prepared from a number of organic precursors. In this research, they are prepared using fat-free UHT cow milk through the hydrothermal method. FTIR analysis shows C=O and C-H bond presence, as well as nitrogen-based bond like C-N, C=N and –NH2 presence in CDs, while the absorption spectra show the absorption band at 280 ± 3 nm. Next, the Biuret test was performed, with the results showing no presence of unreacted proteins in CDs. It can be said that all proteins are converted in CDs. Photo luminance spectra shows the emission of CDs is 420 nm and a toxicity study of CDs was performed. The Presto Blue method was used to test the toxicity of CDs for murine hippocampal cells. CDs at a concentration of 4 mg/mL were hazardous independent of synthesis time, while the toxicity was higher for lower synthesis times of 1 and 2 h. When the concentration is reduced in 1 and 2 h synthesized CDs, the cytotoxic effect also decreases significantly, ensuring a survival rate of 60–80%. However, when the synthesis time of CDs is increased, the cytotoxic effect decreases to a lesser extent. The CDs with the highest synthesis time of 8 h do not show a cytotoxic effect above 60%. The cytotoxicity study shows that CDs may have a concentration and time–dependent cytotoxic effect, reducing the number of viable cells by 40%

Role of DTI-MRI parameters in diagnosis of ALS: useful biomarkers for daily practice? Tertiary centre experience and literature review

Introduction. Despite the rapid development of neuroimaging techniques, the diagnosis of amyotrophic lateral sclerosis (ALS) remains a significant challenge. Magnetic resonance imaging (MRI) is important for ruling out ALS mimickers, while Diffusion Tensor Imaging (DTI) is a useful tool for the identification of cortical tract damage. The aim of this study was to identify the optimal set of DTI parameters to support the diagnosis of ALS that could be applied to everyday MRI and be used as a disease biomarker in daily practice. Material and methods. Forty-seven ALS patients and 55 age- and gender-matched healthy individuals underwent MRI using a 1.5-Tesla scanner including a DTI sequence with 30 spatial directions and a b-value 0/1,000 s/mm2. Two independent researchers measured the DTI parameters: fractional anisotropy (FA), TRACE and apparent diffusion coefficient (ADC) using freehand regions of interest (ROIs) placed along both corticospinal tracts (CSTs), starting at the level of the internal capsule and ending at the medulla. Results. Statistical significance was only achieved for fractional anisotropy (FA) (ALS vs controls, p < 0.001). The highest sensitivity was found in the brainstem (cerebral peduncles, pons and pyramids) where it ranged from 72.3% to 80.9%, whereas the highest specificity was observed at the level of the internal capsule (94.6%). The combined highest sensitivity and specificity was obtained in the pons (72.3% and 72.7%, respectively). Classifier based positive predictive values for Youden index cut-off scores varied between 60.7% and 69.4%. Conclusions. Fractional anisotropy (FA) measured at the level of the brainstem was shown to be the single most relevant parameter in differentiating patients with ALS from healthy subjects. This has the potential to become an ALS-specific biomarker for patient identification in daily practice

Principles of management of patients with autosomal dominant polycystic kidney disease (ADPKD), candidates for kidney and/or liver transplantation — recommendations of the PTT Working Group, part II

These guidelines address management of patients with autosomal dominant polycystic kidney disease who are candidates for kidney and/or liver transplantation. The guidelines include such issues as qualifying for transplantation, indications for nephrectomy, indications for simultaneous kidney and liver transplantation, qualification of a living donor, and qualification for renal replacement therapy in patients with a failing transplanted kidney