Performance of optical flow techniques for motion analysis of fluorescent point signals in confocal microscopy

Optical flow approaches calculate vector fields which determine the apparent velocities of objects in time-varying image sequences. They have been analyzed extensively in computer science using both natural and synthetic video sequences. In life sciences, there is an increasing need to extract kinetic information from temporal image sequences which reveals the interplay between form and function of microscopic biological structures. In this work, we test different variational optical flow techniques to quantify the displacements of biological objects in 2D fluorescent image sequences. The accuracy of the vector fields is tested for defined displacements of fluorescent point sources in synthetic image series which mimic protein traffic in neuronal dendrites, and for GABA_BR1 receptor subunits in dendrites of hippocampal neurons. Our results reveal that optical flow fields predict the movement of fluorescent point sources within an error of 3% for a maximum displacement of 160?nm. Displacement of agglomerated GABA_BR1 receptor subunits can be predicted correctly for maximum displacements of 640?nm. Based on these results, we introduce a criteria to derive the optimum parameter combinations for the calculation of the optical flow fields in experimental images. From these results, temporal sampling frequencies for image acquisition can be derived to guarantee correct motion estimation for biological objects.     

Rheology of Okenia hypogaea Starch Dispersions in Aqueous Solution of DMSO

The aim of this work was to study the rheological behavior of Okenia hypogea starch dispersions (OSD) in aqueous solution (90/10, v/v) of dimethyl sulfoxide (DMSO). Okenia starch dispersions with 3 and 7 % (w/v) total solids were prepared at 20 °C and rheological tests were undertaken at 20, 40 and 60 °C, using a shear rate controlled rotational viscometer. The data fitted better the power law than the Casson model. Flow curves and flow behavior index indicated shear‐thinning behavior. All rheological parameters were affected by the solids concentration and the measurement temperature. As regards amylose and amylopectin content okenia starch is grouped among “ordinary” (non‐waxy) starches. Overall, OSD behaved similarly to potato starch dispersions and corn starch dispersions used as controls.     

Thermal analysis and measurement of a solar pond prototype to study the non-convective zone salt gradient stability

Solar ponds combine solar energy collection with long-term storage and can provide reliable thermal energy at temperature ranges from 50 to 90 °C. A solar pond consists of three distinct zones. The first zone, which is located at the top of the pond and contains the less dense saltwater mixture, is the absorption and transmission region, also known as the upper convective zone (UCZ). The second zone, which contains a variation of saltwater densities increasing with depth, is the gradient zone or non-convective zone (NCZ). The last zone is the storage zone or lower convective zone (LCZ). In this region, the density is uniform and near saturation. The stability of a solar pond prototype was experimentally performed. The setup is composed of an acrylic tube with a hot plate emulating the solar thermal energy input. A study of various salinity gradients was performed based on the Stability Margin Number (SMN) criterion, which is used to satisfy the dynamic stability criterion. It was observed that erosion of the NCZ was accelerated due to mass diffusion and convection in the LCZ. It can be determined that for this prototype the density of the NCZ is greatly affected as the SMN reaches 1.5.     

Order Selection and Inference with Long Memory Dependent Data

In empirical studies selection of the order of a model is routinely invoked. A common example is the order selection of an autoregressive model via Akaike's AIC, Schwarz's BIC or Hannan and Quinn's HIC. The criteria are based on the conditional sum of squares (CSS). However, the computation of the CSS might be difficult for some models such as Bloomfield's exponential model and/or when we allow for long memory dependence. The main aim of the article is thus to propose an alternative way to compute the criterion by using the decomposition of the variance of the innovation errors in terms of its frequency components. We show its validity to obtain the correct order the model. In addition, as a by‐product, we describe a simple (two‐step) estimator of the parameters of the model.     

Monovinyl Sulfone β‐Cyclodextrin. A Flexible Drug Carrier System

Cyclodextrins have been conjugated to target various receptors and have also been functionalized with carbohydrates for targeting specific organs. However, this approach is based on a rigid design that implies the ad hoc synthesis of each cyclodextrin‐targeting agent conjugate. We hypothesized that: 1) a modular design that decouples the carrier function from the targeting function leads to a flexible system, 2) combining the reactivity of the vinyl sulfone group toward biomolecules that act as targeting agents with the ability of cyclodextrin to form complexes with a wide range of drugs may yield a versatile system that allows the targeting of different organs with different drugs, and 3) the higher reactivity of histidine residues toward the vinyl sulfone group can be exploited to couple the cyclodextrin to the targeting system with a degree of regioselectivity. As a proof of concept, we synthesized a monovinyl sulfone β‐cyclodextrin (module responsible for the payload), which, after coupling to recombinant antibody fragments raised against Trypanosoma brucei (module responsible for targeting) and loading with nitrofurazone (module responsible for therapeutic action) resulted in an effective delivery system that targets the surface of the parasites and shows trypanocidal activity.     

Thermal stability of transition alumina nanocrystals with different microstructures

The preparation of well-crystallized boehmite nanoparticles with different morphologies, encompassing from aciculae or rods of 320, 150 and 70?nm of length to platelets of 50?nm in diameter, allowed a comparative study of their respective thermal evolutions as alumina precursors. Static thermal treatments of boehmite nanocrystals at 600, 1000 and 1200?°C and a dynamic, in situ synchrotron study between 100 and 1000?°C revealed that original boehmite microstructures, i.e. size and shape of the nanoparticles, were kept not only in γ-Al₂O₃ but also in transitional aluminas up to 1000?°C. Specifically, at that temperature, acicular samples presented θ-Al₂O₃ structure, while in platelet-like nanoparticles δ-Al₂O₃ was identified. Each precursor morphology favored the respective transition phase, extending the thermal stability range over the limits previously reported in the literature.The described methodology was successfully applied to tailor-make transitional Al₂O₃ nanocrystals with microstructures ranging from fibers and rods to platelets, enhancing their thermal stability and thus their potential applications. Different transition sequences were also reported for the different shapes of nano-boehmite precursors.     

Optimization of a batch reactor to produce the elastomeric copolyester prepolymer copoly(ethylene‐polyoxyethylene terephthalate)(CEPT)

A mathematical algorithm that optimizes the reactor to produce the elastomeric copolyester copoly(ethylene‐polyoxyethylene terephthalate), CEPT, is shown in this work. The optimization was carried out this way: First, an initial isothermal guess of temperature profile is made and the differential equtions system, which describes the CEPT production process, is solved, Second, the reaction time is fixed and the objective function is calculated. Third, the adjoint variable equations system is solved and the Hamiltonian's function is calculated. Fourth, a new temperature profile is found by using the control vector iteraction procedure. Finally, steps one to three are repeated until the objective function reaches a minimum value. The results of the optimization establish that the copolytransesterification reactor should be operated initially to high temperature (about 285°C), which should be reduced quickly to near 250°C to purposely diminish the production of by‐products.