Microelectronic systems that are intended for use in high shock and vibration environments are encapsulated to achieve stable and reliable operation. The physical design of the electronic assembly, the material properties of the encapsulant, and the magnitude and frequency of the inertial loading must all be factored into the system design. Overall robustness to shock and vibration are improved by minimizing the physical size and mass of the system, which increases its stiffness and reduces the magnitude of the inertial forces that must be supported. This work describes the development of an encapsulation process and facilities that are optimized for building high-reliability microelectronic systems that range between one and five cubic centimeters in volume. Finite Element Analysis (FEA) is used to ensure that sensitive components are not overstressed by the encapsulant as a result of residual curing stresses and inertial loading effects. Computational Fluid Dynamics (CFD) software is used to model the filling process, with the objective of identifying locations prone to void formation. The CFD models are validated via cross sectioning mechanical replicas of the system and by encapsulating enclosures fitted with viewing windows to allow sequential photographs of the progression of the fill frontier. During fabrication, the encapsulant is dispensed under vacuum while being observed with a stereoscopic microscope. An essential component of the process is characterization of the encapsulant materials. Coefficient of thermal expansion and cure shrinkage of the encapsulant are determined by casting a sample onto a thin metal strip and extracting stress parameters with equations of a bimetallic strip. The surface energies of the encapsulant on materials in the system are measured by a modified sessile drop technique in which the material is dispensed on a coupon, cured and then measured with a profilometer. These tests are performed on each lot of material when received and periodically afterwards to monitor the condition of inventory. This paper provides a detailed description of the design process and facilities using examples from representative products.
In low income countries, existing drip irrigation systems are cost prohibitive to many smallholder farmers. Companies are working to develop efficient, low-cost irrigation systems by using technologies such as positive displacement (PD) pumps and pressure compensating (PC) emitters. However, these two technologies have not been paired in an efficient and cost-effective manner. Here we describe a proof-of-concept pump control algorithm that demonstrates the feasibility of exploiting the physical relationship between the input electrical power to a PD pump and the hydraulic behavior of a system of PC emitters in order to determine the optimal pump operating point. The development and validation of this control algorithm was conducted in partnership with the Kenya-based irrigation company SunCulture. This control method is expected to reduce cost, improve system efficiency, and increase accessibility of irrigation systems to smallholder farmers.
Measuring and understanding the mechanical properties of blood clots can provide insights into disease progression and the effectiveness of potential treatments. However, several limitations hinder the use of standard mechanical testing methods to measure the response of soft biological tissues, like blood clots. These tissues can be difficult to mount, and are inhomogeneous, irregular in shape, scarce, and valuable. To remedy this, we employ in this work Volume Controlled Cavity Expansion (VCCE), a technique that was recently developed, to measure local mechanical properties of soft materials in their natural environment. Through a highly controlled volume expansion of a water bubble at the tip of an injection needle, paired with simultaneous measurement of the resisting pressure, we obtain a local signature of whole blood clot mechanical response. Comparing this data with predictive theoretical models, we find that a 1-term Ogden model is sufficient to capture the nonlinear elastic response observed in our experiments and produces shear modulus values that are comparable to values reported in the literature. Moreover, we find that bovine whole blood stored at 4°C for greater than 2 days exhibits a statistically significant shift in the shear modulus from 2.53 ± 0.44 kPa on day 2 (N = 13) to 1.23 ± 0.18 kPa on day 3 (N = 14). In contrast to previously reported results, our samples did not exhibit viscoelastic rate sensitivity within strain rates ranging from 0.22 - 21.1 s-1. By surveying existing data on whole blood clots for comparison, we show that this technique provides highly repeatable and reliable results, hence we propose the more widespread adoption of VCCE as a path forward to building a better understanding of the mechanics of soft biological materials.
Estrogen's role in cell growth and proliferation has long been appreciated both in the normal development of secondary sexual characteristics and in diseased states in cancers of the breast, ovaries and uterus. We are beginning to appreciate estrogen's expanded role in maintaining such diverse functions as the skin's elasticity, the health of the central nervous system, bone density and cardiac health. Estrogen plays out its roles in varied tissues by binding to two major ligand activated nuclear receptors, estrogen receptor alpha (ER-a) and estrogen receptor beta (ER-b). The interrelationship of the two receptors plays a role in the responsiveness of certain breast cancers to drug treatment. Though the ligand binding sites of the two receptors differ by only two amino acids, the overall degree of homology between ER-a and ER-b is low. The body uses the receptor selectivity to its advantage by dispersing the receptors in varying ratios to different tissues. Of these actions ER-a is thought to be responsible for the majority with ER-b playing a minor role in all and having more significance in the cardiovascular and skeletal systems. Small molecules have been identified which bind to one or the other receptors with differing binding affinities. These selective estrogen receptor modulators (SERMs) hold the potential to be pharmacologically effective in treating diseases specific to one type of estrogen receptor while not affecting the other. For example, ER-a and ER-b are both present in breast tissue, and the ratio of beta to alpha is being examined as one indicator in determining the likelihood of successful treatment of breast cancer by certain drugs. Here we use changes in the fluorescence polarization to calculate binding affinities for each of several small molecules to ER-a and ER-b.
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