Martin Jensen

Biologically Formed Mesoporous Amorphous Silica

Mesoporous crystalline silica has attracted the attention of scientists due to its extraordinary functionalities. In particular, substantial progress has been made in the synthesis of mesoporous crystalline silica using biomimetic approaches under ambient conditions. However, the biomimetic synthesis of mesoporous amorphous silica has not been well studied so far. Here we show that amorphous silica can be synthesized in aqueous solution under ambient conditions via biological catalysis. The high purity amorphous silica is obtained as spicules (average diameter: 15.6 microm) that are cemented through junctions, thereby forming the skeleton of the freshwater sponge Cauxi. We discover that such amorphous spicules themselves contain mesopores. This opens a potential avenue to develop highly durable mesoporous membranes at room temperature. We also describe the macro- and microstructural features, the mechanism of biological precipitation, and the properties of the Cauxi skeleton.

Aqueous batch rebinding and selectivity studies on sucrose imprinted polymers.

Polymers imprinted with sucrose and corresponding non-imprinted polymers are prepared photo-chemically at 3 degrees C and thermally at 65 degrees C. The pre-polymerization complex formation in dimethyl sulfoxide between sucrose and methacrylic acid via hydrogen bonding was investigated through (1)H NMR titration. The imprinting effect and the selectivity of the imprinted polymers in water are studied by batch rebinding studies with different mono and disaccharides and fitted to the Freundlich isotherm. Based on the calculated numbers of binding sites and average affinity, it is concluded that sucrose has been successfully imprinted at 3 and 65 degrees C. The polymer imprinted at 3 degrees C possesses the best recognition properties. The imprinted polymers are selective towards sucrose in water.

Stereoscopic augmented reality system for supervised training on minimal invasive surgery robots

Training in the use of robot-assisted surgery systems is necessary before a surgeon is able to perform procedures using these systems because the setup is very different from manual procedures. In addition, surgery robots are highly expensive to both acquire and maintain --- thereby entailing the need for efficient training. When training with the robot, the communication between the trainer and the trainee is limited, since the trainee often cannot see the trainer. To overcome this issue, this paper proposes an Augmented Reality (AR) system where the trainer is controlling two virtual robotic arms. These arms are virtually superimposed on the video feed to the trainee, and can therefore be used to demonstrate and perform various tasks for the trainee. Furthermore, the trainer is presented with a 3D image through a stereoscopic display. Because of the added depth perception, this enables the trainer to better guide and help the trainee. A prototype has been developed using low-cost materials and the system has been evaluated by surgeons at Aalborg University Hospital. User feedback indicated that a 3D display for the trainer is very useful as it enables the trainer to better monitor the procedure, and thereby enhances the training experience. The virtual overlay was also found to work as a good and illustrative approach for enhanced communication. However, the delay of the prototype made it difficult to use for actual training.

Configurational Entropy in Thermoset Polymers

The configurational entropy describes the atomic structure in a material and controls several material properties. Often the configurational entropy is determined through dielectric or calorimetric measurements where the difference between the entropies of the crystalline state and the amorphous state is determined. Many amorphous materials such as thermoset polymers have a high crystallization barrier, greatly limiting the applicability of the existing methods for determining the configurational entropy. In this work, a novel differential scanning calorimetry (DSC) method, based on measurement of the glass transition temperature at different heating rates, for determination of the configurational entropy is introduced. The theory behind the method has a universal character for amorphous materials, as it solely involves measurement of the glass transition temperature. The temperature dependency of the configurational entropy is determined for epoxy resins and PMMA (poly(methyl methacrylate)) to demonstrate the versatility of the method. On the basis of the findings of the introduced method, the influence of the degree of cross-linking and the chemical structure of the network is discussed.

A novel biaxial specimen for inducing residual stresses in thermoset polymers and fibre composite material

A new type of specimen configuration with the purpose of introducing a well-defined biaxial residual (axisymmetric) stress field in a neat thermoset or a fibre composite material is presented. The ability to experimentally validate residual stress predictions is an increasing need for design engineers when they challenge the material limits in present and future thermoset and composite component. In addition to the new specimen configuration, this paper presents an analytical solution for the residual stress state in the specimen. The analytical solution assumes linear elastic and isotropic material behaviour. Experimental strain release measurements and the analytical solution determine the residual stress state present in the material. A demonstration on neat epoxy is conducted and residual stress predictions of high accuracy and repeatability have been achieved. The precise determination of the biaxial stress state in the specimen after cure makes it suitable for calibrating residual stress models.

In-situ Curing Strain Monitoring of a Flat Plate Residual Stress Specimen Using a Chopped Stand Mat Glass/Epoxy Composite as Test Material

The curing stresses in a newly proposed bi-axial residual stress testing configuration are studied using a chopped strand mat glass/epoxy specimen. In-situ monitoring of the curing is conducted using dielectric and fibre Bragg grating sensors. It is confirmed that a bi-axial residual stress state can be introduced in the specimens during curing and a quantification of its magnitude is presented. An alternative decomposition method used for converting the dielectric signal into a material state variable is proposed and good agreement with models found in the literature is obtained. From the cure cycles chosen it is suggested that any stress build up in the un-vitrified state is relaxed immediately and only stress build up in the vitrified state contributes to the residual stress state in the specimen.

Microscopic Features of Biologically Formed Amorphous Silica

Many animals base their skeleton on calcium containing compounds and in particular calcium phosphates are prevalent as the main bone constituents. There are, however, animals that rely on different compounds for their skeleton. An example of such a class of animals is sponges, which have a skeleton constituted of silica (Muller et al, 2007). The fact that silica is used as skeleton provides the sponges with the ability to live in calcium-poor and acidic environments. Despite the characteristic composition of the skeleton, sponges have managed to spread to various living environments such as seawater (Bavestrello et al., 1995; Croce et al., 2003; W. E. G. Muller et al., 2005; Pisera, 2003; Schwab & Shore, 1971; Uriz et al., 2000) and lakes (Kaluzhnaya et al., 2005; Schroder et al., 2003). Furthermore, the prevalence of sponge across the entire planet witnesses that they can grow at different temperatures. Due to the unique features of sponges, they have been intensively studied by scientists through the last decades. Many of the studies focused on the evolutionary and biological aspect of sponges (Barthel 1986; Barthel, 1995; Calcinai et al., 2007). After clarification of the structure of the sponges, it is known that they possess unique features. As a consequence of the unique features of sponges, these creatures have attracted interest from material scientists (Wang et al., 2010) since study of sponges could lead to new materials or facilitate the production of already existing materials through biomimetic approaches. The composition and structure considerably vary from one type of sponge to another, and therefore it is not possible to address all kinds of sponges in one chapter. In this chapter, we focus on the sponge called Cauxi (Porifera, Demospongiae). From its habitat in the lower Rio Negro in the eastern Amazon basin, the natives have known and used the sponge for reinforcement of their pottery through centuries (Costa et al., 2004). Besides the fact that the sponge is known to be amorphous to X-ray diffraction (XRD), the mesoporous feature of the sponge remained unrevealed until recently (Jensen et al., 2009). In this work, we present a detailed description of the fascinating features of the Cauxi sponge and highlight differences between Cauxi and other species. This work will also shed light on the potential of biological formation of amorphous mesoporous materials at ambient conditions.

Stroke and bleeding risk scores in patients with atrial fibrillation and valvular heart disease: evaluating ‘valvular heart disease’ in a nationwide cohort study

AimsnSubstantial interest has been directed towards stroke risk stratification in patients with atrial fibrillation (AF) but prior studies have focused on AF without significant valvular heart disease (VHD), so-called non-valvular AF. A formal validation exercise addressing stroke risks in relation to the CHA2DS2-VASc risk factor(s) in AF patients with VHD is lacking. Also, the use of the HAS-BLED score in anticoagulated patients with VHD has not been previously studied. The aim of this study was to investigate stroke and bleeding rates in AF patients with VHD in relation to the CHA2DS2-VASc and HAS-BLED scores.nnnMethods and resultsnWe conducted a nationwide cohort study. VHD were categorized based on the 2017 joint European consensus document definition, i.e. Evaluated Heartvalves, Rheumatic or Artificial (EHRA) categorization, as follows: (i) EHRA Type 1 VHD, which refers to AF patients with VHD needing therapy with a Vitamin K antagonist (VKA), thus including severe native mitral stenosis and prosthetic mechanical heart valves and (ii) EHRA Type 2 VHD, which refers to AF patients with VHD needing therapy with a VKA or a non-VKA oral anticoagulant (NOAC), thus including all other forms of VHD. We identified 25xa0818 AF patients with VHD with EHRA Type 2 in 90% (nu2009=u200923xa0253). Thromboembolism and bleeding events increased with increasing CHA2DS2-VASc and HAS-BLED scores, whether with 1 or 2.5u2009years follow-up. EHRA Type 1 outcomes: The predictive value of CHA2DS2-VASc score for thromboembolism was modest, c-indexes 0.62 (0.55-0.70) at 1u2009year. The predictive value of the HAS-BLED score for bleeding was also modest being 0.59 (0.53-0.65) at 1u2009year. EHRA Type 2 outcomes: The predictive value of CHA2DS2-VASc score for thromboembolism was modest, c-indexes 0.63 (0.60-0.65) at 1u2009year. The predictive value of the HAS-BLED score for bleeding was also modest being 0.59 (0.53-0.65) at 1u2009year.nnnConclusionnThis is the first validation of CHA2DS2-VASc and HAS-BLED scores in AF patients with VHD (so-called valvular AF) using the new EHRA classification. Both scores are modestly predictive of thromboembolism and bleeding events in VHD, respectively. Event rates increased with increasing risk factors as evident by increasing CHA2DS2-VASc and HAS-BLED score points, consistent with performance of these clinical scores in non-valvular AF patients.