276 research outputs found
Molecular Dynamics Simulation Study of a Polymer Droplet Transport Over an Array of Spherical Nanoparticles
This study uses molecular dynamics simulations to evaluate the dynamic behavior of a partially wetting polymer droplet driven over a nanostructured interface. We consider the bead-spring model to represent a polymeric liquid that partially wets a rough surface composed of a periodic array of spherical particles. Results show that at sufficiently small values of external force, the droplet remains pinned at the particle\u27s surface, whereas above the threshold its motion consists of alternating periods of pinning and rapid displacements between neighboring particles. The latter process involves large periodic variation of the advancing and receding contact angles due to the attachment and detachment of the contact line. Finally, upon increasing the external force, the droplet\u27s center of mass is steadily displaced, while at the same time the oscillation amplitude of the receding contact angle as well as the maximum contact angle hysteresis remain relatively unchanged
A Strategy for Dynamic Programs: Start over and Muddle through
In the setting of DynFO, dynamic programs update the stored result of a query
whenever the underlying data changes. This update is expressed in terms of
first-order logic. We introduce a strategy for constructing dynamic programs
that utilises periodic computation of auxiliary data from scratch and the
ability to maintain a query for a limited number of change steps. We show that
if some program can maintain a query for log n change steps after an
AC-computable initialisation, it can be maintained by a first-order dynamic
program as well, i.e., in DynFO. As an application, it is shown that decision
and optimisation problems defined by monadic second-order (MSO) formulas are in
DynFO, if only change sequences that produce graphs of bounded treewidth are
allowed. To establish this result, a Feferman-Vaught-type composition theorem
for MSO is established that might be useful in its own right
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Three method-combination protocol for improving purity of extracellular vesicles
Extracellular vesicles (EVs) are nanosized structures able to carry proteins, lipids and genetic material from one cell to another with critical implications in intercellular communication mechanisms. Even though the rapidly growing EVs research field has sparked great interest in the last 20 years, many biological and technical aspects still remain challenging. One of the main issues that the field is facing is the absence of consensus regarding methods for EVs concentration from biofluids and tissue culture medium. Yet, not only can classic methods be time consuming, commercialized kits are also often quite expensive, especially when research requires analyzing numerous samples or concentrating EVs from large sample volumes. In addition, EV concentration often results in either low final yield or significant contamination of the vesicle sample with proteins and protein complexes of similar densities and sizes. Eventually, low vesicle yields highly limit any further application and data reproducibility while contamination greatly impacts extensive functional studies. Hence, there is a need for accessible and sustainable methods for improved vesicle concentration as this is a critical step in any EVs-related research study. In this brief report, we describe a novel combination of three well-known methods in order to obtain moderate-to-high yields of EVs with reduced protein contamination. We believe that such methods could be of high benefits for in vitro and in vivo functional studies
A Strategy for Dynamic Programs: Start over and Muddle Through
A strategy for constructing dynamic programs is introduced that utilises periodic computation of auxiliary data from scratch and the ability to maintain a query for a limited number of change steps. It is established that if some program can maintain a query for log n change steps after an AC^1-computable initialisation, it can be maintained by a first-order dynamic program as well, i.e., in DynFO. As an application, it is shown that decision and optimisation problems defined by monadic second-order (MSO) and guarded second-order logic (GSO) formulas are in DynFO, if only change sequences that produce graphs of bounded treewidth are allowed. To establish this result, Feferman-Vaught-type composition theorems for MSO and GSO are established that might be useful in their own right
Reachability and Distances under Multiple Changes
Recently it was shown that the transitive closure of a directed graph can be updated using first-order formulas after insertions and deletions of single edges in the dynamic descriptive complexity framework by Dong, Su, and Topor, and Patnaik and Immerman. In other words, Reachability is in DynFO.
In this article we extend the framework to changes of multiple edges at a time, and study the Reachability and Distance queries under these changes. We show that the former problem can be maintained in DynFO(+, x) under changes affecting O({log n}/{log log n}) nodes, for graphs with n nodes. If the update formulas may use a majority quantifier then both Reachability and Distance can be maintained under changes that affect O(log^c n) nodes, for fixed c in N. Some preliminary results towards showing that distances are in DynFO are discussed
Feasibility of using ammonia-water mixture in high temperature concentrated solar power plants with direct vapour generation
AbstractConcentrated solar power plants have attracted an increasing interest in the past few years – both with respect to the design of various plant components, and extending the operation hours by employing different types of storage systems. One approach to improve the overall plant performance is to use direct vapour generation with water/steam as both the heat transfer fluid in the solar receivers and the cycle working fluid. This enables to operate the plant with higher turbine inlet temperatures. Available literature suggests that it is feasible to use ammonia-water mixture at high temperatures without corroding the equipment by using suitable additives with the mixture. This paper assesses the thermodynamic feasibility of using ammonia-water mixture in high temperature (450 ̊C) and high pressure (over 100 bar) concentrated solar power plants with direct vapour generation. The following two cases are compared for the analysis: a simple Rankine cycle and an ammonia-water cycle with a separator for varying the ammonia mass fraction within the cycle. Thermodynamic simulations are performed using Aspen Plus and MATLAB, and performances in terms of overall plant efficiency are evaluated. The comparison between the two cycles when operating from a two-tank molten-salt storage system is also presented. The results suggest that the ammonia-water mixtures show a clear advantage while operating from storage but the simple Rankine cycle outperforms the ammonia-water cycle when the heat input is from solar receiver only
Energy and exergy analysis of the Kalina cycle for use in concentrated solar power plants with direct steam generation
AbstractIn concentrated solar power plants using direct steam generation, the usage of a thermal storage unit based only on sensible heat may lead to large exergetic losses during charging and discharging, due to a poor matching of the temperature profiles. By the use of the Kalina cycle, in which evaporation and condensation takes place over a temperature range, the efficiency of the heat exchange processes can be improved, possibly resulting also in improved overall performance of the system. This paper is aimed at evaluating the prospect of using the Kalina cycle for concentrated solar power plants with direct steam generation. The following two scenarios were addressed using energy and exergy analysis: generating power using heat from only the receiver and using only stored heat. For each of these scenarios comparisons were made for mixture concentrations ranging from 0.1 mole fraction of ammonia to 0.9, and compared to the conventional Rankine cycle. This comparison was then also carried out for various turbine inlet pressures (100bar to critical pressures). The results suggest that there would be no benefit from using a Kalina cycle instead of a Rankine cycle when generating power from heat taken directly from the solar receiver. Compared to a baseline Rankine cycle, the efficiency of the Kalina cycle was about around 5% lower for this scenario. When using heat from the storage unit, however, the Kalina cycle achieved efficiencies up to 20% higher than what was achieved using the Rankine cycle. Overall, when based on an average assumed 18hours cycle, consisting of 12hours using heat from the receiver and 6hours using heat from the storage, the Kalina cycle and Rankine cycle achieved almost equal efficiencies. A Kalina cycle operating with an ammonia mole fraction of about 0.7 returned an averaged efficiency of about 30.7% compared to 30.3% for the Rankine cycle
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