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Understanding phenomena such as evaporation and imbibition of picoliter droplets into porous substrates is crucial in printing industry to achieve a higher printing quality and print speed. After printing, the residual pigment must remain fixed at the desired location on a substrate and be of a desired volume to yield a high resolution and vibrantly printed page that has become the expectation of modern printing technology. Current research entails not only chemical composition of the ink but also how this links to the dynamics and interactions that occur between the ink and the substrate at every stage of the printed spot formation, including evaporation, wetting, and imbibition. In this paper, we present an instrument that can print on-demand picoliter volume droplets of ink onto substrates and then immediately record on evolution of the resulting dynamics when these two materials interact. This high-speed laser speckle imaging (HS-LSI) technique has been developed to monitor nanometer displacement of the drying and imbibing ink droplet at a high frame rate, up to 20000 Hz, given the short timescales of these interactions. We present the design of the instrument, discuss the related challenges and the theory underlying the LSI technique, specifically how photons non-evasively probe opaque objects in a multiple scattering regime, and show how this technique can unravel the dynamics of drying and imbibition. We will finish giving a validation on the instrument and an example of its usage.

We present the development of a multi-position indentation setup capable of spatially mapping mechanically heterogeneous materials. A detailed description of the indentation instrumentation is first provided, emphasizing force sensitivity, noise reduction, and signal fidelity. We first present indentation experiments on soft hydrogels that are submerged in water and show how the large contributions to the measured force due to the air-water surface tension can be avoided. The displacement field of the indented hydrogel is visualized using fluorescently coated microspheres embedded in the hydrogel, allowing simultaneous mapping of the stress and strain fields for a soft polymer network. We then fabricate a polymer network with patterned elasticity using halftone UV lithography and map the elastic modulus with the multi-position indentation instrument. The applied UV pattern is found back in the measured elastic modulus map, showing the capability of the multi-position indentation setup to map mechanically heterogeneous polymer networks.

Contains fulltext : 183916.pdf (publisher's version ) (Open Access)

Contains fulltext : 168712.pdf (preprint version ) (Open Access)

In this thesis a problem of determining the optimal pacing strategy to minimize travel time is considered. The problem is restricted to a straight race track with constant slope and rolling resistance, and no headwind. It is expressed as an optimal control problem that can be solved using Pontryagin's Maximum Principle. The control variable is the cyclist's power, which is modelled according to a hyperbolic power-time relationship, where a maximum power level is assumed. The Hamiltonian is linear with respect to this control variable. The minimum time problem is redefined as a maximum excursion problem, which is related to Goddard’s problem of a rocket's ascent through the atmosphere. It turns out that the optimal pacing problem is a singular control problem. Such problems are difficult to solve, both numerically and analytically, and they only occur sporadically in control theory. It is proven that the singular control only accurs during a single interval; optimal pacing starts with maximum power and decays through a singular control to minimum power. The singular arc may be degenerate; a bang-bang control might be optimal, depending on the length of the race track and the amount of available energy. The solution of the pacing problem has been obtained partly numerical and partly analytical. It applies to a straight course without bends, but it can be extended to an arbitrary course by dividing it into straight segments between bends and optimize over all distributions of energy over the segments.

Herein, we present a facile strategy to controllably build up dendrimicelles by self-assembly of anionic PAMAM dendrimers with cationic–neutral diblock copolymers. We present a systematic study incorporating a full decade (0–9) of dendrimer generations, tracing the gradual variation from aggregates (G0 and G1) to self-assembled micelles (G2–G8), and an unidendrimer micelle structure (G9) by different scattering techniques (light and X-ray). The formed micelles (G2–G9) are spherical in shape with a hydrodynamic radius of about 25 nm. Interestingly, the micellar size, structure and number of incorporated block copolymers are independent of the dendrimer generation (for G2 to G9), while the aggregation number of the dendrimers decreases from 108 to 1, and the stability of the micelles increases upon an increase in the dendrimer generation. Moreover, the micelles with lower generation dendrimers transform from spherical into worm-like structures upon an increase in the positive charge fraction (excess polymers) or ionic strength, while micelles with higher generation dendrimers do not show such a transition. This differential behavior is in-line with a change from a flexible configuration into rigid globular nanoparticles with increasing dendrimer generation. The reported systematic investigation of dendrimicelles comprising a full decade of dendrimer generations provides the basis for versatile strategies focused on building up new (multi)functional materials, e.g. by packing multiple types of dendrimers with different functional groups or encapsulated cargos controllably within one micelle.

We present a stochastic game that models ambush/search in a finite region Q which has area but no other structure. The searcher can search a unit area of Q in unit time or adopt an "ambush" mode for a certain period. The searcher "captures" the hider when the searched region contains the hider's location or if the hider moves while the searcher is in ambush mode. The payoff in this zero sum game is the capture time. Our game is motivated by the (still unsolved) princess and monster game on a star graph with a large number of leaves., Delft Institute of Applied Mathematics, Electrical Engineering, Mathematics and Computer Science

Item does not contain fulltext, The presence, dissolution, agglomeration state, and release of materials in the nano-size range from food containing engineered nanoparticles during human digestion is a key question for the safety assessment of these materials. We used an in vitro model to mimic the human digestion. Food products subjected to in vitro digestion included (i) hot water, (ii) coffee with powdered creamer, (iii) instant soup, and (iv) pancake which either contained silica as the food additive E551, or to which a form of synthetic amorphous silica or 32 nm SiO(2) particles were added. The results showed that, in the mouth stage of the digestion, nano-sized silica particles with a size range of 5-50 and 50-500 nm were present in food products containing E551 or added synthetic amorphous silica. However, during the successive gastric digestion stage, this nano-sized silica was no longer present for the food matrices coffee and instant soup, while low amounts were found for pancakes. Additional experiments showed that the absence of nano-sized silica in the gastric stage can be contributed to an effect of low pH combined with high electrolyte concentrations in the gastric digestion stage. Large silica agglomerates are formed under these conditions as determined by DLS and SEM experiments and explained theoretically by the extended DLVO theory. Importantly, in the subsequent intestinal digestion stage, the nano-sized silica particles reappeared again, even in amounts higher than in the saliva (mouth) digestion stage. These findings suggest that, upon consumption of foods containing E551, the gut epithelium is most likely exposed to nano-sized silica.

Suppose that a hider possesses a continuously divisible resource that he may distribute around a circle. The resources on a random arc in the circle are lost. The hider has a priori information on the length of the arc and he wants to maximize the probability that the retrieved portion exceeds a critical quantity, which is enough to survive on. We show that there exists an optimal resource distribution, which uses a finite number of point caches of equal size, establishing a conjecture of Kikuta and Ruckle. Our result is related to a conjecture of Samuels’ on-tail probabilities., Delft Institute of Applied Mathematics, Electrical Engineering, Mathematics and Computer Science

Item does not contain fulltext, Targeted delivery of nanoparticles (NPs) carrying vaccine components to dendritic cells (DCs) is a promising strategy to initiate antigen-specific immune responses. Improving the interactions between nanoparticle-carried ligands and receptors on DCs is a major challenge. These NPs are generally coated with poly(ethylene glycol) (PEG), to shield non-specific interactions, and antibodies, to facilitate specific delivery to DC surface receptors. We have devised a strategy to covalently link PEG molecules of various chain length (Mw 2000-20000 g/moL) to poly(lactic-co-)glycolic acid (PLGA) NP vaccines. We coated these NPs with various antibodies recognizing the DC-specific receptor DC-SIGN to study the effects of shielding and antibody type on antibody--receptor interactions. Chemical attachment of PEG to the particle surface was followed by detailed zeta potential, DLS and NMR studies, and analyzed by analytical chemistry. Increasing the PEG chain length increased particle size and polydispersity index and reduced the intracellular degradation rate of encapsulated antigens. Binding and uptake of NPs by human DCs was affected by both PEG chain length and antibody type. NPs coated with PEG-3000 had the optimal chain length for antibody--receptor interactions and induction of antigen-specific T-cell responses. Interestingly, clear differences were observed upon targeting distinct epitopes of the same receptor. Binding and uptake of NPs carrying antibodies recognizing the carbohydrate recognition domain of DC-SIGN was enhanced when compared to those carrying antibodies recognizing the receptor's neck region. In conclusion, our data show that PEG chains cannot be extended beyond a certain length for shielding purposes without compromising the efficacy of targeted delivery. Thereby, the implications of our findings are not limited to the future design of nanovaccines specifically targeted to DC-SIGN, but apply to the general design of targeted nanocarriers.

Contains fulltext : 89065.pdf (publisher's version ) (Closed access), Vaccine efficacy is strongly enhanced by antibody-mediated targeting of vaccine components to dendritic cells (DCs), which are professional antigen presenting cells. However, the options to link antigens or immune modulators to a single antibody are limited. Here, we engineered versatile nano- and micrometer-sized slow-release vaccine delivery vehicles that specifically target human DCs to overcome this limitation. The nano- (NPs) and microparticles (MPs), with diameters of approximately 200nm and 2microm, consist of a PLGA core coated with a polyethylene glycol-lipid layer carrying the humanized targeting antibody hD1, which does not interact with complement or Fc receptors and recognizes the human C-type lectin receptor DC-SIGN on DCs. We studied how these particles interact with human DCs and blood cells, as well as the kinetics of PLGA-encapsulated antigen degradation within DCs. Encapsulation of antigen resulted in almost 38% degradation for both NPs and MPs 6days after particle ingestion by DCs, compared to 94% when nonencapsulated, soluble antigen was used. In contrast to the MPs, which were taken up rather nonspecifically, the NPs effectively targeted human DCs. Consequently, targeted delivery only improved antigen presentation of NPs and induced antigen-dependent T cell responses at 10-100 fold lower concentrations than nontargeted NPs.