1,601 research outputs found
Recent developments in the Dutch CAPTECH programme
AbstractThis paper describes the reach done in the Dutch CAPTECH programme. The research aims to reduce the CO2 capture cost with 50%. In order to achieve this, a wide portfolio of future technologies is being investigated
Nonlinear semi-analytical model for simulation of few-mode fiber transmission
In this letter, a nonlinear semi-analytical model (NSAM) for simulation of few-mode fiber transmission is proposed. The NSAM considers the mode mixing arising from the Kerr effect and waveguide imperfections. An analytical explanation of the model is presented, as well as simulation results for the transmission over a two mode fiber (TMF) of 112 Gb/s using coherently detected polarization multiplexed quadrature phase-shift-keying modulation. The simulations show that by transmitting over only one of the two modes on TMFs, long-haul transmission can be realized without increase of receiver complexity. For a 6000-km transmission link, a small modal dispersion penalty is observed in the linear domain, while a significant increase of the nonlinear threshold is observed due to the large core of TMF
Signal processing in the TGF-beta superfamily ligand-receptor network
The TGF-beta pathway plays a central role in tissue homeostasis and
morphogenesis. It transduces a variety of extracellular signals into
intracellular transcriptional responses that control a plethora of cellular
processes, including cell growth, apoptosis, and differentiation. We use
computational modeling to show that coupling of signaling with receptor
trafficking results in a highly versatile signal-processing unit, able to sense
by itself absolute levels of ligand, temporal changes in ligand concentration,
and ratios of multiple ligands. This coupling controls whether the response of
the receptor module is transient or permanent and whether or not different
signaling channels behave independently of each other. Our computational
approach unifies seemingly disparate experimental observations and suggests
specific changes in receptor trafficking patterns that can lead to phenotypes
that favor tumor progression.Comment: 33 pages, 7 figure
Robust improvement of the asymmetric post-buckling behavior of a composite panel by perturbing ïŹber paths
The buckling behavior of structures is highly sensitive to imperfections, i.e., deviations from the geometry and material properties of the ideal structure. In this paper, an approach is presented in which the effects of spatially varying ïŹber misalignments in composite structures are assessed through random ïŹeld analysis and are subsequently used to improve the structure while simultaneously making it more robust to ïŹber misalignments. Effects of misalignments are quantiïŹed by applying random ïŹelds on the structure, which represent ïŹber misalignments. Using analyses of the effect of the random local stiffness changes due to ïŹber misalign- ments, a pattern of the relative inïŹuence these local changes have on the buckling load is created. By applying a small change to local ïŹber orientation corresponding to this pattern to the original structure, the performance of the design is improved. Additional stochastic analyses are performed using the improved design, reanalyzing the effects local ïŹber misalignments have on the structural performance and the subsequent changes in robustness. Stochastic results show an overall increase in the mean buckling load and a reduction in the coefïŹcient of variation in the analysis of the perturbed structure. The approach is applied to a composite panel exhibiting asymmetric postâbuckling behavior, i.e., having an unstable postâbuckling branch and an (initially) stable branch. Results show that perturbations in the ïŹber path can nudge a structure into a more stable postâ buckling path by promoting a postâbuckling path using local changes in structural stiffness. The robustness of improved designs can also increase, making structures less susceptible to local ïŹber misalignments
Stabilization of self-coherent OFDM with injection locked laser
With the rebirth of coherent detection, various algorithms have come forth to alleviate phase noise, one of the main impairments for coherent receivers. These algorithms provide stable compensation, however they limit the DSP. With this key issue in mind, Fabry Perot filter based self coherent optical OFDM was analyzed which does not require phase noise compensation reducing the complexity in DSP at low OSNR. However, the performance of such a receiver is limited due to ASE noise at the carrier wavelength, especially since an optical amplifier is typically employed with the filter to ensure sufficient carrier power. Subsequently, the use of an injection-locked laser (ILL) to retrieve the frequency and phase information from the extracted carrier without the use of an amplifier was recently proposed. In ILL based system, an optical carrier is sent along with the OFDM signal in the transmitter. At the receiver, the carrier is extracted from the OFDM signal using a Fabry-Perot tunable filter and an ILL is used to significantly amplify the carrier and reduce intensity and phase noise. In contrast to CO-OFDM, such a system supports low-cost broad linewidth lasers and benefits with lower complexity in the DSP as no carrier frequency estimation and correction along with phase noise compensation is required
OrganicâInorganic Surface Modifications for Titanium Implant Surfaces
This paper reviews current physicochemical and biochemical coating techniques that are investigated to enhance bone regeneration at the interface of titanium implant materials. By applying coatings onto titanium surfaces that mimic the organic and inorganic components of living bone tissue, a physiological transition between the non-physiological titanium surface and surrounding bone tissue can be established. In this way, the coated titanium implants stimulate bone formation from the implant surface, thereby enhancing early and strong fixation of bone-substituting implants. As such, a continuous transition from bone tissue to implant surface is induced. This review presents an overview of various techniques that can be used to this end, and that are inspired by either inorganic (calcium phosphate) or organic (extracellular matrix components, growth factors, enzymes, etc.) components of natural bone tissue. The combination, however, of both organic and inorganic constituents is expected to result into truly bone-resembling coatings, and as such to a new generation of surface-modified titanium implants with improved functionality and biological efficacy
Activation of Rac-1 and RhoA contributes to podocyte injury in chronic kidney disease
Rho-family GTPases like RhoA and Rac-1 are potent regulators of cellular signaling that control gene expression, migration and inflammation. Activation of Rho-GTPases has been linked to podocyte dysfunction, a feature of chronic kidney diseases (CKD). We investigated the effect of Rac-1 and Rho kinase (ROCK) inhibition on progressive renal failure in mice and studied the underlying mechanisms in podocytes. SV129 mice were subjected to 5/6-nephrectomy which resulted in arterial hypertension and albuminuria. Subgroups of animals were treated with the Rac-1 inhibitor EHT1846, the ROCK inhibitor SAR407899 and the ACE inhibitor Ramipril. Only Ramipril reduced hypertension. In contrast, all inhibitors markedly attenuated albumin excretion as well as glomerular and tubulo-interstitial damage. The combination of SAR407899 and Ramipril was more effective in preventing albuminuria than Ramipril alone. To study the involved mechanisms, podocytes were cultured from SV129 mice and exposed to static stretch in the Flexcell device. This activated RhoA and Rac-1 and led via TGFÎČ to apoptosis and a switch of the cells into a more mesenchymal phenotype, as evident from loss of WT-1 and nephrin and induction of α-SMA and fibronectin expression. Rac-1 and ROCK inhibition as well as blockade of TGFÎČ dramatically attenuated all these responses. This suggests that Rac-1 and RhoA are mediators of podocyte dysfunction in CKD. Inhibition of Rho-GTPases may be a novel approach for the treatment of CKD
Critical assessment of human metabolic pathway databases: a stepping stone for future integration
<p>Abstract</p> <p>Background</p> <p>Multiple pathway databases are available that describe the human metabolic network and have proven their usefulness in many applications, ranging from the analysis and interpretation of high-throughput data to their use as a reference repository. However, so far the various human metabolic networks described by these databases have not been systematically compared and contrasted, nor has the extent to which they differ been quantified. For a researcher using these databases for particular analyses of human metabolism, it is crucial to know the extent of the differences in content and their underlying causes. Moreover, the outcomes of such a comparison are important for ongoing integration efforts.</p> <p>Results</p> <p>We compared the genes, EC numbers and reactions of five frequently used human metabolic pathway databases. The overlap is surprisingly low, especially on reaction level, where the databases agree on 3% of the 6968 reactions they have combined. Even for the well-established tricarboxylic acid cycle the databases agree on only 5 out of the 30 reactions in total. We identified the main causes for the lack of overlap. Importantly, the databases are partly complementary. Other explanations include the number of steps a conversion is described in and the number of possible alternative substrates listed. Missing metabolite identifiers and ambiguous names for metabolites also affect the comparison.</p> <p>Conclusions</p> <p>Our results show that each of the five networks compared provides us with a valuable piece of the puzzle of the complete reconstruction of the human metabolic network. To enable integration of the networks, next to a need for standardizing the metabolite names and identifiers, the conceptual differences between the databases should be resolved. Considerable manual intervention is required to reach the ultimate goal of a unified and biologically accurate model for studying the systems biology of human metabolism. Our comparison provides a stepping stone for such an endeavor.</p
Effect of spatially varying material properties on the post-buckling behaviour of composite panels utilising geodesic stochastic fields
The post-buckling behaviour of panels can be very sensitive to imperfections
or variations in materials or geometry. This paper presents an
ecient numerical model to calculate the eects of material stiffness
variations on the non-linear response of a structure. This is done by
first defining a geodesic mesh on which a unit variance random field is
generated. This field uses the true geodesic distance on the structure to
calculate how points in the field should be correlated. The fields generated
are projected onto a 3D structural mesh which is used for assembly and
post-processing of the structural model. The structural model, based on
the Unified Formulation is capable of accurate non-linear calculations of
both straight and curved elements. Baseline results generated using the
implementation are compared to those in literature, and verified using
Abaqus. Random material variations are then applied to the structure
in a Monte Carlo analysis. The analyses show that the local variation
of stiffness can have a variety of effects on the non-linear response of
structures. Aside from the change of mean stiffness causing a change in
bifurcation or limit point load, the different stiffness distributions can
affect and trigger competing buckling modes and post-buckling modes
and affect their corresponding post-buckling load-deflection paths
- âŠ