Thomas Nielsen

A Reversible Nanoconfined Chemical Reaction

Hydrogen is recognized as a potential, extremely interesting energy carrier system, which can facilitate efficient utilization of unevenly distributed renewable energy. A major challenge in a future hydrogen economy is the development of a safe, compact, robust, and efficient means of hydrogen storage, in particular, for mobile applications. Here we report on a new concept for hydrogen storage using nanoconfined reversible chemical reactions. LiBH4 and MgH2 nanoparticles are embedded in a nanoporous carbon aerogel scaffold with pore size Dmax approximately 21 nm and react during release of hydrogen and form MgB2. The hydrogen desorption kinetics is significantly improved compared to bulk conditions, and the nanoconfined system has a high degree of reversibility and stability and possibly also improved thermodynamic properties. This new scheme of nanoconfined chemistry may have a wide range of interesting applications in the future, for example, within the merging area of chemical storage of renewable energy.

Confinement of MgH2 Nanoclusters within Nanoporous Aerogel Scaffold Materials

Nanoparticles of magnesium hydride were embedded in nanoporous carbon aerogel scaffold materials in order to explore the kinetic properties of hydrogen uptake and release. A new modified procedure for the synthesis of magnesium hydride nanoparticles is presented. The procedure makes use of monoliths (approximately 0.4 cm(3)) of two distinct types of nanoporous resorcinol-formaldehyde carbon aerogels loaded with dibutylmagnesium, MgBu(2). Excess MgBu(2) was removed mechanically, and the increase in mass was used as a measure of the amount of embedded MgH(2). Energy-dispersive spectrometry revealed that MgH(2) was uniformly distributed within the aerogel material. In situ synchrotron radiation powder X-ray diffraction showed that MgBu(2) transformed directly to MgH(2) at T approximately 137 degrees C and p(H(2)) = 50 bar. Two distinct aerogel samples, denoted X1 and X2, with pore volumes of 1.27 and 0.65 mL/g and average pore sizes of 22 and 7 nm, respectively, were selected. In these samples, the uptake of magnesium hydride was found to be proportional to the pore volume, and aerogels X1 and X2 incorporated 18.2 and 10.0 wt % of MgH(2), respectively. For the two samples, the volumetric MgH(2) uptake was similar, approximately 12 vol %. The hydrogen storage properties of nanoconfined MgH(2) were studied by Sieverts measurements and thermal desorption spectroscopy, which clearly demonstrated that the dehydrogenation kinetics of the confined hydride depends on the pore size distribution of the scaffold material; that is, smaller pores mediated faster desorption rates possibly due to a size reduction of the confined magnesium hydride.

Versatile in situ powder X-ray diffraction cells for solid–gas investigations

Two multipurpose sample cells of quartz (SiO2) or sapphire (Al2O3) capillaries, developed for the study of solid–gas reactions in dosing or flow mode, are presented. They allow fast change of pressure up to 100 or 300u2005bar (1u2005bar = 100u2005000u2005Pa) and can also handle solid–liquid–gas studies.

Improved Hydrogen Storage Kinetics of Nanoconfined NaAlH4 Catalyzed with TiCl3 Nanoparticles

Nanoparticles of NaAlH(4) have been infiltrated in nanoporous carbon aerogel with TiCl(3) nanoparticles in order to explore possible synergetic effects between nanoconfinement and a functionalized catalytic scaffold. Resorcinol formaldehyde carbon aerogels with an average pore size of 17 nm and total pore volume of 1.26 mL/g were infiltrated with TiCl(3) to obtain an aerogel doped with 3.0 wt % TiCl(3) nanoparticles. NaAlH(4) was melt-infiltrated into the functionalized carbon aerogel at 189 °C and p(H(2)) ∼ 186-199 bar. Energy-dispersive spectrometry (EDS) combined with focused ion beam (FIB) techniques revealed the presence of Na, Al, Ti, and Cl inside the aerogel scaffold material. The infiltrated NaAlH(4) was X-ray amorphous, whereas (27)Al magic-angle spinning (MAS) NMR spectroscopy confirmed the presence of nanoconfined NaAlH(4). Temperature-programmed desorption mass spectroscopy (TPD-MS) and Sieverts measurements demonstrated significantly improved hydrogen desorption kinetics for this new nanoconfined NaAlH(4)-TiCl(3) material as compared to nanoconfined NaAlH(4) without the catalysts TiCl(3) and to bulk ball-milled samples of NaAlH(4)-TiCl(3). We find that the onset temperature for hydrogen release was close to room temperature (T(onset) = 33 °C), and the hydrogen release rate reached a maximum value at 125 °C, which demonstrates favorable synergetic effects between nanoconfinement and catalyst addition.

Apparent Diffusion Coefficient (ADC) as a quantitative parameter in diffusion weighted MR imaging in gynecologic cancer: Dependence on b-values used.

Abstract Background. Diffusion weighted imaging (DWI) has gained interest as an imaging modality for assessment of tumor extension and response to cancer treatment. The purpose of this study is to assess the impact of the choice of b-values on the calculation of the Apparent Diffusion Coefficient (ADC) for locally advanced gynecological cancer and to estimate a stable interval of diffusion gradients that allows for best comparison of the ADC between patients and institutions. Material and methods. Six patients underwent a high resolution single shot EPI based DWI scan with 16 different diffusion gradients on a 3 Tesla Philips Achieva MR-scanner. Data analysis was performed by applying a monoexponential and a biexponential model to the acquired data. The biexponential function models the effect of both perfusion and diffusion. Results and conclusion. ADC changes of up to 40% were seen with the use of different b-values. Using a lower b-value ≥ 150 s/mm2 and an upper b-value ≥ 700 s/mm2 limited the variation to less that 10% from the reference ADC value. By eliminating the contribution of perfusion the uncertainty of quantitative ADC values were significantly reduced.

Hydrogen storage and phase transformations in Mg–Pd nanoparticles

Microstructure refinement and synergic coupling among different phases are currently explored strategies to improve the hydrogen storage properties of traditional materials. In this work, we apply a combination of these methods and synthesize Mg–Pd composite nanoparticles by inert gas condensation of Mg vapors followed by vacuum evaporation of Pd clusters. Irreversible formation of the Mg6Pd intermetallic phase takes place upon vacuum annealing, resulting in Mg/Mg6Pd composite nanoparticles. Their hydrogen storage properties are investigated and connected to the undergoing phase transformations by gas-volumetric techniques and in situ synchrotron radiation powder x-ray diffraction. Mg6Pd transforms reversibly into different Mg–Pd intermetallic compounds upon hydrogen absorption, depending on temperature and pressure. In particular, at 573 K and 1 MPa hydrogen pressure, the metal-hydride transition leads to the formation of Mg3Pd and Mg5Pd2 phases. By increasing the pressure to 5 MPa, the Pd-richer MgPd in...

False confessions and the relationship with offending behaviour and personality among Danish adolescents

Purpose. The main aim of the study was to examine false confessions to police, parents and teachers and their relationship to personality and self-reported offending. n n n nMethod. The participants were 715 students in further education in Denmark. Each was asked about false admissions made to teachers and parents in the past, as well as about confessions or denials (true and false) made to the police during questioning. The participants completed questionnaires relating to offending and personality. n n n nResults. Seventy-three (10%) of the participants said they had been interrogated by the police, of whom thirty-seven (51%) said they had committed the offence. Five (7%) said they had given a false confession to police, whereas one hundred and seven (15%) of the total sample said they had given a false confession to parents or teachers. False confessions to teachers and parents were best predicted by the rate of self-reported offending and high compliance. The single most commonly reported reason for making a false confession was to protect a friend. n n n nConclusions. The findings in the present study corroborate many of those found in similar Icelandic studies, although there were some differences, including fewer people being interrogated in Denmark and a higher base-rate of innocence of those interrogated. The study indicates that false confessions to police do happen on occasions which needs to be recognized by the authorities.

Ultrahigh-Field DCE-MRI of Angiogenesis in a Novel Angiogenesis Mouse Model

To be able to screen and identify potential candidate agents for noninvasive imaging of diseases involving angiogenesis, a standardized in vivo angiogenesis model is needed. Angiogenesis is a common feature of many pathological conditions and has become an important target for diagnosis and treatment, with many noninvasive imaging agents emerging.

Tracer kinetic model selection for dynamic contrast-enhanced magnetic resonance imaging of locally advanced cervical cancer

Abstract Background. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) offers a unique capability to probe tumour microvasculature. Different analysis of the acquired data will possibly lead to different conclusions. Therefore, the objective of this study was to investigate under which conditions the Tofts (TM), extended Tofts (ETM), compartmental tissue uptake model (C-TU) and 2-compartment exchange model (2CXM) were the optimal tracer kinetic models (TKMs) for the analysis of DCE-MRI in patients with cervical cancer. Material and methods. Ten patients with locally advanced cervical cancer (FIGO: IIA/IIB/IIIB/IVA – 1/5/3/1) underwent DCE-MRI prior to radiotherapy. From the two-parameter TM it was possible to extract the forward volume transfer constant (Ktrans) and the extracellular-extravascular volume fraction (ve). From the three-parameter ETM, additionally the plasma volume fraction (vp) could be extracted. From the three-parameter C-TU it was possible to extract information about the blood flow (Fp), permeability-surface area product (PS) and vp. Finally, the four-parameter 2CXM extended the C-TU to include ve. For each voxel, corrected Akaike information criterion (AICc) values were calculated, taking into account both the goodness-of-fit and the number of model parameters. The optimal model was defined as the model with the lowest AICc. Results. All four TKMs were the optimal model in different contiguous regions of the cervical tumours. For the 24 999 analysed voxels, the TM was optimal in 17.0%, the ETM was optimal in 2.2%, the C-TU in 23.4% and the 2CXM was optimal in 57.3%. Throughout the tumour, a high correlation was found between Ktrans(TM) and Fp(2CXM), ρ = 0.91. Conclusion. The 2CXM was most often optimal in describing the contrast agent enhancement of pre-treatment cervical cancers, although this model broke down in a subset of the tumour voxels where overfitting resulted in non-physiological parameter estimates. Due to the possible overfitting of the 2CXM, the C-TU was found more robust and when 2CXM was excluded from comparison the C-TU was the preferred model.

Theranostic tumor targeted nanoparticles combining drug delivery with dual near infrared and 19F magnetic resonance imaging modalities

Combining imaging and drug delivery of theranostic nanoparticles has enabled concurrent diagnosis and therapy of diseases. Here, we describe a novel theranostic system that combines two imaging tracers, perfluorooctyl bromide (PFOB) for 19F magnetic resonance imaging (MRI) and indocyanine green (ICG) for near infrared (NIR) imaging, with the chemotherapeutic agent doxorubicin (Dox) into poly (lactic-co-glycolic acid)- poly (ethylene-glycol)-folate (PLGA-PEG-folate) nanoparticles. Cell culture studies using flow cytometry, confocal laser scanning microscope imaging, and 19F MRI showed enhanced uptake of nanoparticles via folate receptors expressed on human nasopharyngeal epidermal carcinoma (KB) cells. In vivo, higher MRI and fluorescence signals were obtained from tumors with 19F MRI and NIR, respectively, using folate-receptor-targeted nanoparticles compared with non-targeted equivalents. An in vitro cytotoxicity assay showed that folate-targeted nanoparticles were able to kill cancer cells more efficiently than non-folate conjugated particles. Our results suggest a potential use of PLGA-PEG-folate PFOB/ICG/Dox nanoparticles as a targeted chemotherapy agent traceable by either 19F MRI or NIR imaging.