Improving Tracer Particle Surface Properties for Wind Tunnel Research

The surface properties of micron size polystyrene latex microspheres (PSLs) modified with quaternary alkylammonium (QA) surfactants were investigated, with a focus on the relationship between surface chemistry and adhesion. These investigations were motivated by the need to develop non-fouling tracer particles for wind tunnel studies. The goals were to relate the work of adhesion between particles and substrates to the type and amount of QA modifier in order to optimize the performance of PSL tracers. Surfactant-free emulsion polymerization (SFEP) can produce PSLs for wind tunnel tracers. Covalentlybound charged groups (derived from the initiator) stabilize PSL surfaces in water. This work used PSLs with anionic surface groups. Previous studies indicated that surface-bound charged groups on PSLs have a significant impact on their interfacial energy. Modifying charged surface groups therefore offers a method to modulate PSL interfacial properties. In this work, PSLs and films were modified by adsorption of QA surfactants

A role for the extracellular calcium-sensing receptor in cell-cell communication in pancreatic islets of Langerhans

Background: The extracellular calcium-sensing receptor (CaR) is expressed in many tissues that are not associated with Ca2+ homeostasis, including the endocrine cells in pancreatic islets of Langerhans. We have demonstrated previously that pharmacological activation of the CaR stimulates insulin secretion from islet -cells and insulin-secreting MIN6 cells. Methods: In the present study we have investigated the effects of CaR activation on MIN6 cell proliferation and have used shRNA-mediated CaR knockdown to determine whether the CaR is involved in the regulation of insulin secretion via cell-cell communication. Results: CaR activation caused the phosphorylation and activation of the p42/44 MAPK signalling cascade, and this activation was prevented by the shRNA-induced down-regulation of CaR mRNA expression. CaR activation also resulted in increased proliferation of MIN6 cells, consistent with the known role of the p42/44 MAPK system in the regulation of -cell proliferation. Down-regulation of CaR expression had no detectable effects on glucose-induced insulin secretion from MIN6 cells maintained as monolayers, but blocked the increases in insulin secretion that were observed when the cells were configured as three-dimensional islet-like structures (pseudoislets), consistent with a role for the CaR in cell-cell communication in pseudoislets. Conclusion: It is well established that islet function is dependent on communication between islet cells and the results of this study suggest that the CaR is required for -cell to -cell interactions within islet-like structures

What\u27s a Name Worth?: Experimental Tests of the Value of Attribution in Intellectual Property

Despite considerable research suggesting that creators value attribution – i.e., being named as the creator of a work – U.S. intellectual property (IP) law does not provide a right to attribution to the vast majority of creators. On the other side of the Atlantic, however, many European countries give creators, at least in their copyright laws, much stronger rights to attribution. At first blush it may seem that the U.S. has gotten it wrong, and the Europeans have made a better policy choice in providing to creators a right that they value. But for reasons we will explain in this Article, matters are a lot more complicated than that. This Article reports a series of experiments that are the first to attempt to quantitatively measure the value of attribution to creators. In previous research, we have shown that creators of IP are subject to a “creativity effect” that results in them assigning substantially higher value to their works than neoclassical economic theory predicts. The first two experiments reported in this Article suggest a way that the creativity effect may be reduced – creators are willing to sacrifice significant economic payments in favor of receiving attribution for their work. The value to creators of attribution raises the question whether U.S. IP law should be re-structured to provide attribution as a creator’s default right. The third and most important experiment reported here casts doubt on the value of giving creators such a default right, because creators value attribution differently depending on whether the legal rule gives it to them as an initial entitlement or not. When creators are given a right to attribution as a default they value credit four times higher than when attribution is not the default option. Our findings make clear that creators value attribution, and that the prospect of obtaining it can lead to a more efficient level of transacting. At the same time, and paradoxically, our findings also suggest that before we restructure American law, which provides no right to attribution for the vast majority of creators, we need to take care, because it is possible, under conditions that we will describe, that providing creators with a default right to attribution will result in less efficient transacting. Finally, our findings have important implications for property theory which are broader than IP law or attribution rights. Our third experiment suggests that a party who enjoys a default legal right as part of her initial complement of rights will tend to treat that legal right in a fashion similar to any other form of initial entitlement, and overvalue it relative to what neoclassical theory would predict. This suggests a principle regarding how to efficiently structure default rules in any setting. All other factors being equal, an efficiently-structured default rule will locate the initial legal entitlement in the party who is either less likely to overvalue the entitlement, or, if overvaluation seems inevitable regardless of where the initial entitlement is placed, is likely to overvalue it less

International Foot and Ankle Biomechanics Community (i-FAB): past, present and beyond

The International Foot and Ankle Biomechanics Community (i-FAB) is an international collaborative activity which will have an important impact on the foot and ankle biomechanics community. It was launched on July 2nd 2007 at the foot and ankle session of the International Society of Biomechanics (ISB) meeting in Taipei, Taiwan. i-FAB is driven by the desire to improve our understanding of foot and ankle biomechanics as it applies to health, disease, and the design,development and evaluation of foot and ankle surgery, and interventions such as footwear, insoles and surfaces

Proportional-Integral Extremum Seeking for Optimizing Power of Vapor Compression Systems

Conventionally, online methods for minimizing power consumption of vapor compression systems rely on the use of physical models. These model-based approaches attempt to describe the influence of commanded inputs, disturbances and setpoints on the thermodynamic behavior of the system and the resultant consumed electrical power. These models are then used online to predict the combination of inputs for a measured set of thermodynamic conditions that both meets the heat load and minimizes power consumption. However, these models of vapor compression systems must contain nonlinear terms of sufficient complexity in order to accurately describe the region near the optimum operating point(s), but also must rely on simplifying assumptions in order to produce a mathematically tractable representation. For these reasons, model-based online optimization of vapor compression machines have not gained traction in application, and have created an opportunity for model-free techniques such as extremum seeking control, which is gradient descent optimization implemented as a feedback controller. While traditional perturbation-based extremum seeking controllers for vapor compression systems have proven effective at minimizing power without requiring a process model, the algorithm\u27s requirement for multiple distinct timescales has limited the applicability of this method to laboratory tests where boundary conditions can be carefully controlled, or simulation studies with unrealistic convergence times. Perturbation-based extremum seeking requires that the control input be manipulated with a time constant approximately two orders of magnitude slower than the slowest vapor compression system dynamics, otherwise instabilities in the closed loop system occur. As a result, convergence to the optimum for slow processes such as thermal systems is restrictive due to inefficient estimation of the gradient, and slow (integral-action dominated) adaptation in the extremum seeking control law. In order to address this timescale separation issue, we have previously developed an algorithm called ``time-varying extremum seeking that more efficiently estimates the gradient of the performance metric and applied this algorithm to the problem of setpoint optimization for compressor temperatures. That algorithm improved the convergence rate to one timescale slower than the vapor compression machine dynamics. In this paper, we optimize power consumption through the application of a newly-developed proportional--integral extremum seeking controller (PI-ESC) that converges at the same timescale as the process. This method uses the improved gradient estimation routines of time-varying extremum seeking but also modifies the control law to include terms proportional to the estimated gradient. This modification of the control law, in turn, requires a revision to the gradient estimator in order to avoid bias. PI-ESC is applied to the problem of compressor discharge temperature selection for a vapor compression system so that power consumption is minimized. Because of the improved convergence properties of PI-ESC, we show that optimum values of discharge temperature can be tracked in the presence of realistic disturbances such as variation in the outdoor air temperature---enabling application of extremum seeking control to vapor compression systems in environments where previous methods have failed. The method is demonstrated experimentally on a 2.8 kW split ductless room air conditioner and in simulation using a custom-developed Modelica model

Dynamic Charge Management for Vapor Compression Cycles

Because vapor compression air-conditioners and heat pumps consume significant amounts of electrical power in today\u27s residential and commercial buildings, energy optimization of these systems is becoming increasingly important from the perspectives of both environmental conservation and economic value. Corresponding efforts to improve the energy efficiency of these machines require attention to all stages of system design, installation, and operation, due to the myriad factors influencing power consumption. Among the many variables that must be optimized, one particularly salient variable is the mass of refrigerant contained within the cycle, or the refrigerant charge; this variable is strongly coupled to many other variables in the system, including the electrical power consumption, the system pressures, and the degree of subcooling and superheat in the heat exchangers. As such, the mass of refrigerant in the system must be carefully tuned for a given set of operational conditions to maximize the system\u27s energy efficiency. In practice, field-installed vapor compression systems are often not charged with the mass of refrigerant that optimizes energy efficiency for the conditions in which systems actually operate. In accordance with the conventional view of the refrigerant charge as a static system parameter, the mass of refrigerant is often specified to maximize the average energy efficiency over a set of multiple conditions. This approach results in suboptimal energy efficiency at any one of the conditions within the rating set, and furthermore often results in lower energy efficiency at non-rated conditions. Such an impact is especially evident in reversible heat pump cycles because the optimal refrigerant mass for a cycle over a range of conditions in cooling mode is often very different than the optimal refrigerant mass in heating mode. As today\u27s system manufacturers sell equipment across large geographic ranges with a wide range of ambient conditions and operational requirements, the cumulative impact of operating these systems with suboptimal refrigerant charge is generally a much higher rate of energy consumption than would be observed with cycles that incorporate an optimally specified refrigerant charge. In this paper, we describe a system architecture for a vapor compression system that enables the circulating refrigerant charge to be modulated as a function of time, effectively allowing the refrigerant charge to be optimized for a predicted or observed set of operational conditions. This is accomplished by dynamically controlling the amount of refrigerant sequestered in a storage vessel (referred to as a dynamic receiver) that is continuously coupled to the other components of the system. We first explore alternate system architectures that have been previously proposed for similar purposes, and elaborate on the opportunities that are afforded by this particular candidate architecture. A set of first-principles physics-based dynamic models are then developed using the Modelica language, and a candidate controller architecture is discussed that directly optimizes the electrical power consumption by using this new dynamic receiver. Finally, we will compare energy performance of this proposed system with that of conventional system architectures to evaluate its benefits over a range of operational conditions

Model Predictive Control of Variable Refrigerant Flow Systems

Model Predictive Control (MPC) of vapor compression systems (VCSs) offers several advantages over conventional control methods (such as multivariable process control with selector logic) in terms of 1) the resulting closed-loop performance and 2) the control engineering design process. VCSs are multivariable systems and feature constraints on system variables and actuators that must be enforced during steady-state and transient operation. We present the design and validation of an MPC for a split ductless VCS. The design regulates room temperature with zero steady state error for unknown changes in the thermal load and enforces constraints on system variables such as compressor discharge temperature and actuator ranges and rates. We show how the MPC design can evolve during the engineering process by adding and modifying constraints and process variables. The design methodology provides guarantees in terms of closed loop stability and convergence. Importantly, in contrast to other published results on MPC for VCSs, our design makes use of only available temperature measurements and does not require pressure or mass flow measurements which are typically not available in production VCSs