A clip-on electroosmotic pump for oscillating flow in microfluidic cell culture devices

Recent advances in microfluidic devices put a high demand on small, robust and reliable pumps suitable for high-throughput applications. Here we demonstrate a compact, low-cost, directly attachable (clip-on) electroosmotic pump that couples with standard Luer connectors on a microfluidic device. The pump is easy to make and consists of a porous polycarbonate membrane and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) electrodes. The soft electrode and membrane materials make it possible to incorporate the pump into a standard syringe filter holder, which in turn can be attached to commercial chips. The pump is less than half the size of the microscope slide used for many commercial lab-on-a-chip devices, meaning that these pumps can be used to control fluid flow in individual reactors in highly parallelized chemistry and biology experiments. Flow rates at various electric current and device dimensions are reported. We demonstrate the feasibility and safety of the pump for biological experiments by exposing endothelial cells to oscillating shear stress (up to 5 dyn/cm²) and by controlling the movement of both micro- and macroparticles, generating steady or oscillatory flow rates up to ± 400 μL/min.     

Dynamic response of NDVI to soil moisture variations during different hydrological regimes in the Sahel region

Over the last few decades, the African Sahel has become the focus of many studies regarding vegetation dynamics and their relationships with climate and people. This is because rainfall limits the production of biomass in the region, a resource on which people are directly dependent for their livelihoods. In this study, we utilized a remote-sensing approach to answering the following two questions: (1) how does the dynamic relationship between soil moisture and plant growth vary across hydrological regimes, and (2) are vegetation-type-dependent responses to soil moisture availability detectable from satellite imagery? In order to answer these questions, we studied the relationship between monthly modelled soil moisture as an indicator for water availability and the remotely sensed normalized difference vegetation index (NDVI) as a proxy for vegetation growth between a “recovery rainfall period” (1982 to 1997) and a “stable rainfall period” (1998 to 2013), at different time lags across the Sahel region. Using windowed cross-correlation, we find a strong significant positive relationship between NDVI and soil moisture at a concurrent time and at NDVI lagging behind soil moisture by 1 month for grassland, cropland, and deciduous shrubland vegetation – the dominant vegetation classes in the Sahel. South of the Sahel (the Sudanian and Guinean areas), we find longer optimal lags (soil moisture lagged by 1–3 months) in association with mixed forest and deciduous shrubland. We find no major significant change in optimal lag between the recovery and stable periods in the Sahelian region; however, in the Sudanian and Guinean areas, we observe a trend towards shorter time lags. This change in optimal lag suggests a vegetation change, which may be a response to a climatic shift or land-use change. This approach of identifying spatiotemporal trends in optimal lag correlations between modelled soil moisture and NDVI could prove to be a useful tool for mapping vegetation change and ecosystem behaviour, in turn helping inform climate change mitigation approaches and agricultural planning.     

Nested Tracking Graphs

Tracking graphs are a well established tool in topological analysis to visualize the evolution of components and their properties over time, i.e., when components appear, disappear, merge, and split. However, tracking graphs are limited to a single level threshold and the graphs may vary substantially even under small changes to the threshold. To examine the evolution of features for varying levels, users have to compare multiple tracking graphs without a direct visual link between them. We propose a novel, interactive, nested graph visualization based on the fact that the tracked superlevel set components for different levels are related to each other through their nesting hierarchy. This approach allows us to set multiple tracking graphs in context to each other and enables users to effectively follow the evolution of components for different levels simultaneously. We demonstrate the effectiveness of our approach on datasets from finite pointset methods, computational fluid dynamics, and cosmology simulations.     

Automatic differentiation of rigid body dynamics for optimal control and estimation

Abstract

Many algorithms for control, optimization and estimation in robotics depend on derivatives of the underlying system dynamics, e.g. to compute linearizations, sensitivities or gradient directions. However, we show that when dealing with rigid body dynamics, these derivatives are difficult to derive analytically and to implement efficiently. To overcome this issue, we extend the modelling tool ‘RobCoGen’ to be compatible with Automatic Differentiation. Additionally, we propose how to automatically obtain the derivatives and generate highly efficient source code. We highlight the flexibility and performance of the approach in two application examples. First, we show a trajectory optimization example for the quadrupedal robot HyQ, which employs auto-differentiation on the dynamics including a contact model. Second, we present a hardware experiment in which a six-DoF robotic arm avoids a randomly moving obstacle in a go-to task by fast, dynamic replanning.     

Seasonal variation of coherence in SAR interferograms in Kiruna,Northern Sweden

This article presents the results of a study conducted to quantify the seasonal variation of coherence in synthetic aperture radar (SAR) interferograms in Kiruna, Northern Sweden. In SAR interferometry (InSAR), coherence is an important concept that provides a good indication of the phase stability of the scatterers. Therefore, in this study, the degree of coherence is used as a parameter to identify the seasonal variation interferograms. For this study, 34 Radarsat-2 ultra-fine beam mode (U6D) images of the Kiruna area (67°51?N, 20°14?E) and the improved digital elevation model (DEM) created by merging the Radarsat-2 DEM and ASTER DEM were used to produce 561 differential interferograms. The interferograms were arranged in three different ways for the analysis, with the first including common master interferograms (with the summer master image), the second including the sequential interferograms that have the shortest temporal baseline, and the third accounting for all possible combinations of the interferograms (full network of interferograms). Following this step, the variation of coherence for forest areas, urban areas, and flat waste rock areas was studied. This study shows that interferograms generated for the Kiruna region exhibit seasonal variations in coherence due to the ground snow layer in winter. Furthermore, when there is water on the ground due to the melting of the snow layer (in the spring) or due to rains in autumn, the coherence is reduced considerably. Another significant feature is that there is a significant change in summer-to-summer coherence for some regions even over the course of a few years. Based on this study, it is clear that the winter Radarsat-2 U6D beam mode images are not suitable for differential interferometric SAR (DInSAR) deformation measurements in flat waste rock regions in Kiruna. It is expected that even with winter images, PSInSAR or CTM techniques will be able to provide better deformation measurements, but, in this study, those techniques were not assessed. The next step will be to study the seasonal variations in coherence in natural or man-made targets/persistent scatterers using persistent scatter InSAR (PSInSAR) or coherence target monitoring (CTM) techniques.     

Treatment of clinical stage I testicular cancer and a possible role for new biological prognostic parameters

Three different treatment strategies for patients with stage I non-seminomatous testicular cancer are available that will all result in long-term survival in more than 98% of the patients: a "wait and see" strategy with follow-up and chemotherapy in cases of tumour progression, retroperitoneal lymphadenectomy, with or without application of systemic chemotherapy, in cases of retroperitoneal metastases (pathological stage II disease) or primary adjuvant chemotherapy following inguinal orchiectomy. Each treatment strategy is associated with specific side-effects. In several studies histological characteristics of the primary tumour, particularly the presence of vascular invasion and of embryonal carcinoma cells, have been demonstrated to be significant prognostic factors for the risk of occult retroperitoneal metastases in patients with stage I disease. In addition, new biological prognostic factors determined by flow cytometry, cytogenetic analysis or molecular-biological DNA or RNA analysis have been investigated, among which alterations of the p53 tumour-suppressor gene may represent a promising new prognostic factor. Although alterations of p53 gene expression seem to be associated with advanced tumour stage and may predict retroperitoneal metastatic disease, the independent role of these molecular genetic alterations needs to be prospectively studied. Currently a risk-adapted treatment strategy based on the histological criteria of vascular invasion and the presence of embryonal carcinoma can be used to stratify patients into a "high-" and "low-risk" group with respect to tumour progression. While primary-nerve-sparing retroperitoneal lymphadenectomy or adjuvant chemotherapy with two cycles of platinum, etoposide and bleomycin may be appropriate for patients with a high risk (above 40%) for tumour progression, a "wait-and-see" strategy can be used for "low-risk" (less than 15% risk of progression) patients. Molecular investigations of prognostic factors may be able to improve further the stratification of patients into these different risk categories.     

The types of circulating fatty acids influence vascular reactivity

The objective of this study was to investigate the relationship between the composition of FA in serum lipids, a marker of dietary fat intake, and vascular reactivity using a combination of cross-sectional and intervention approaches. Fifty-six middle-aged subjects were evaluated in a cross-sectional protocol regarding the relationship between the proportion of FA in serum cholesterol esters and vascular reactivity using measurements of forearm blood flow (FBF) with venous occlusion plethysmography during hyperemia. Another 19 middle-aged subjects were given a rapeseed oil-based diet rich in mono-and polyunsaturated FA or a control diet rich in saturated FA during two consecutive 4-wk periods separated by a 4-wk washout period. In the cross-sectional protocol, the FA 18:0 and 20:3 were positively related to resting FBF, whereas an inverse relationship was seen for the FA 20:5 and 22:6 (P<0.05−0.01). Opposite relationships were seen between these four FA and the relative increase in maximal FBF during hyperemia (P<0.05−0.01). In the intervention protocol, the saturated diet increased resting FBF, as well as the relative increase in maximal FBF during reactive hyperemia, compared to the diet rich in unsaturated FA (P<0.05). Both the cross-sectional and intervention data support the view that the composition of serum FA, which at least partly reflects the quality of dietary fat, plays a role in determinations of vascular reactivity.     

Measurement of Indentation Residual Stresses in Materials Susceptible to Slow Crack Growth

Knowledge of the size and distribution of the indentation residual stress field is important when interpreting slow crack growth data for indented ceramic materials. A technique based on compressively loading indentation cracks has been used to measure the wedging residual stresses at radial indentation cracks. The method also gives information on the fatigue limit and can be applied on any ceramic material susceptible to slow crack growth. Soda–lime glass specimens were indented and the resulting residual stresses, wedging the radial cracks, were measured as a function of indentation load. Calculations of K ₀, the fatigue limit, were made for both virgin indentation cracks and cracks aged until saturation. The magnitude of closing stress needed to prevent slow crack growth was found to depend linearly on the indentation load. For example, for indentation loads of 20 and 60 N, the corresponding closing stresses were 14 and 26 MPa, respectively.     

A Split‐Intein‐Based Method for the Efficient Production of Circularized Nanodiscs for Structural Studies of Membrane Proteins

Phospholipid nanodiscs are a native‐like membrane mimetic that is suitable for structural studies of membrane proteins. Although nanodiscs of different sizes exist for various structural applications, their thermal and long‐term stability can vary considerably. Covalently circularized nanodiscs are a perfect tool to overcome these limitations. Existing methods for the production of circularized nanodiscs can be time‐consuming and technically demanding. Therefore, an easy in vivo approach, in which circularized membrane scaffold proteins (MSPs) can be directly obtained from Escherichia coli culture, is reported herein. Nostoc punctiforme DnaE split‐intein fusions with MSPs of various lengths are used and consistently provide circularized nanodiscs in high yields. With this approach, a large variety of circularized nanodiscs, ranging from 7 to 26 nm in diameter, that are suitable for NMR spectroscopy and electron microscopy (EM) applications can be prepared. These nanodiscs are superior to those of the corresponding linear versions in terms of stability and size homogeneity, which affects the quality of NMR spectroscopy data and EM experiments. Due to their long‐term stability and homogeneity, the presented small circular nanodiscs are suited for high‐resolution NMR spectroscopy studies, as demonstrated with two membrane proteins of 17 or 32 kDa in size. The presented method will provide easy access to circularized nanodiscs for structural studies of membrane proteins and for applications in which a defined and stable nanodisc size is required.