Precautionary savings and wealth accumulation with parameter uncertainty and learning

This paper considers the intertemporal consumption/savings decision when income follows a random walk with drift and the drift coefficient is unknown. Instead agents are Bayesian learners, combining prior and sample information to form a posterior for the drift coefficient and future income. This parameter uncertainty increases by an order of magnitude the uncertainty of future income over that generated by unknown future shocks to income and can lead agents to have much more precautionary savings and hence to accumulate more wealth than otherwise. In a calibration exercise it is shown that for a plausible specification of the level of prior information and real interest rate, that the level of aggregate wealth due to this parameter uncertainty could be larger than that generated by unknown future shocks to income, the latter of which has been estimated elsewhere to potentially account for 60 percent of US aggregate wealth. --Permanent Income Hypothesis, Precautionary Savings, Parameter Uncertainty, Bayesian learning, Wealth Accumulation.

Developing a NASA Lead-Free Policy for Electronics - Lessons Learned

The National Aeronautics and Space Administration (NASA) is not required by United States or international law to use lead-free (Pb-free) electronic systems but international pressure in the world market is making it increasingly important that NASA have a Pb-free policy. In fact, given the international nature of the electronics market, all organizations need a Pb-free policy. This paper describes the factors which must be taken into account in formulating the policy, the tools to aid in structuring the policy and the unanticipated and difficult challenges encountered. NASA is participating in a number of forums and teams trying to develop effective approaches to controlling Pb-free adoption in high reliability systems. The activities and status of the work being done by these teams will be described. NASA also continues to gather information on metal whiskers, particularly tin based, and some recent examples will be shared. The current lack of a policy is resulting in "surprises" and the need to disposition undesirable conditions on a case-by-case basis. This is inefficient, costly and can result in sub-optimum outcomes

Packaging Concerns/Techniques for Large Devices

This slide presentation reviews packaging challenges and options for electronic parts. The presentation includes information about non-hermetic packages, space challenges for packaging and complex package variations

Lead-Free Electronics: Impact for Space Electronics

Pb is used as a constituent in solder alloys used to connect and attach electronic parts to printed wiring boards (PWBs). Similar Pbbearing alloys are electroplated or hot dipped onto the terminations of electronic parts to protect the terminations and make them solderable. Changing to Pb-free solders and termination finishes has introduced significant technical challenges into the supply chain. Tin/lead (Sn/Pb) alloys have been the solders of choice for electronics for more than 50 years. Pb-free solder alloys are available but there is not a plug-in replacement for 60/40 or 63/37 (Sn/Pb) alloys, which have been the industry workhorses

NASA Feedback to DLA Land & Maritime Moratorium on Wafer Fab Audits

On September 29, 2017 the Defense Logistics Agency (DLA), Land and Maritime, announced that on September 1, 2017 they had begun a moratorium on the auditing of wafer fabrication facilities (fabs) used in the production of semiconductor die for military (MIL) qualified integrated circuits and discrete semiconductors (transistors and diodes). The announcement said the moratorium would last for six months initially and would apply to all wafer fabs qualified to MIL-PRF-19500 (discretes) and MIL-PRF-38535 (ICs) located, onshore or offshore. The stated rationale behind this action was to give DLA time to evaluate the risk of modifying current surveillance practices across 70+ Federal Stock Classes (FSC) under the jurisdiction of the DLA Qualifying Activity (VQ). The objective was to free up the resources used in these audits so they could be redirected towards audits of other commodities which were under resourced, notably connectors. In the announcement letter, DLA-VQ requested data from the community to assist with decisions on wafer fab re-audit cycle modifications. NASA used available information on current and historical audit schedules to gather such data and analyzed it to provide an in-depth understanding of the impact of locations, part types, in-house or out-of-house fabs on those schedules over time. This presentation provides the results of NASA's data analysis and suggest some changes to auditing practices that could increase efficient use of resources without significant increases in risk

Electrical, Electronic and Electromechanical (EEE) Parts for Spaceflight Applications: A NASA Electronic Parts and Packaging Historical Perspective

This presentation provides a brief NASA-perspective of the major historical milestones in the development of space quality electrical, electronic, and electromechanical (EEE) components in the USA from the dawn of the space age through present

Physical and Electrical Characterization of Aluminum Polymer Capacitors

Polymer aluminum capacitors from several manufacturers with various combinations of capacitance, rated voltage, and ESR values were physically examined and electrically characterized. The physical construction analysis of the capacitors revealed three different capacitor structures, i.e., traditional wound, stacked, and laminated. Electrical characterization results of polymer aluminum capacitors are reported for frequency-domain dielectric response at various temperatures, surge breakdown voltage, and other dielectric properties. The structure-property relations in polymer aluminum capacitors are discussed

Physical and Electrical Characterization of Polymer Aluminum Capacitors

Polymer aluminum capacitors from several manufacturers with various combinations of capacitance, rated voltage, and ESR values were physically examined and electrically characterized. The physical construction analysis of the capacitors revealed three different capacitor structures, i.e., traditional wound, stacked, and laminated. Electrical characterization results of polymer aluminum capacitors are reported for frequency-domain dielectric response at various temperatures, surge breakdown voltage, and other dielectric properties. The structure-property relations in polymer aluminum capacitors are discussed

Real-Time Analysis of Drosophila Post-Embryonic Haemocyte Behaviour

BACKGROUND: The larval stage of the model organism Drosophila is frequently used to study host-pathogen interactions. During embryogenesis the cellular arm of the immune response, consisting of macrophage-like cells known as plasmatocytes, is extremely motile and functions to phagocytise pathogens and apoptotic bodies, as well as produce extracellular matrix. The cellular branch of the larval (post-embryonic) innate immune system consists of three cell types-plasmatocytes, crystal cells and lamellocytes-which are involved in the phagocytosis, encapsulation and melanisation of invading pathogens. Post-embryonic haemocyte motility is poorly understood thus further characterisation is required, for the purpose of standardisation. METHODOLOGY: In order to examine post-embryonic haemocyte cytoskeletal dynamics or migration, the most commonly used system is in vitro cell lines. The current study employs an ex vivo system (an adaptation of in vitro cell incubation using primary cells), in which primary larval or pre-pupal haemocytes are isolated for short term analysis, in order to discover various aspects of their behaviour during events requiring cytoskeleton dynamics. SIGNIFICANCE: The ex vivo method allows for real-time analysis and manipulation of primary post-embryonic haemocytes. This technique was used to characterise, and potentially standardised, larval and pre-pupal haemocyte cytoskeleton dynamics, assayed on different extracellular matrices. Using this method it was determined that, while larval haemocytes are unable to migrate, haemocytes recovered from pre-pupae are capable of migration

Reliability Evaluation of Base-Metal-Electrode Multilayer Ceramic Capacitors for Potential Space Applications

Base-metal-electrode (BME) ceramic capacitors are being investigated for possible use in high-reliability spacelevel applications. This paper focuses on how BME capacitors construction and microstructure affects their lifetime and reliability. Examination of the construction and microstructure of commercial off-the-shelf (COTS) BME capacitors reveals great variance in dielectric layer thickness, even among BME capacitors with the same rated voltage. Compared to PME (precious-metal-electrode) capacitors, BME capacitors exhibit a denser and more uniform microstructure, with an average grain size between 0.3 and 0.5 m, which is much less than that of most PME capacitors. BME capacitors can be fabricated with more internal electrode layers and thinner dielectric layers than PME capacitors because they have a fine-grained microstructure and do not shrink much during ceramic sintering. This makes it possible for BME capacitors to achieve a very high capacitance volumetric efficiency. The reliability of BME and PME capacitors was investigated using highly accelerated life testing (HALT). Most BME capacitors were found to fail with an early avalanche breakdown, followed by a regular dielectric wearout failure during the HALT test. When most of the early failures, characterized with avalanche breakdown, were removed, BME capacitors exhibited a minimum mean time-to-failure (MTTF) of more than 105 years at room temperature and rated voltage. Dielectric thickness was found to be a critical parameter for the reliability of BME capacitors. The number of stacked grains in a dielectric layer appears to play a significant role in determining BME capacitor reliability. Although dielectric layer thickness varies for a given rated voltage in BME capacitors, the number of stacked grains is relatively consistent, typically around 12 for a number of BME capacitors with a rated voltage of 25V. This may suggest that the number of grains per dielectric layer is more critical than the thickness itself for determining the rated voltage and the life expectancy of the BME capacitor. The leakage current characterization and the failure analysis results suggest that most of these early avalanche failures are due to the extrinsic minor construction defects introduced during fabrication of BME capacitors. The concentration of the extrinsic defects must be reduced if the BME capacitors are considered for high reliability applications. There are two approaches that can reduce or prevent the occurrence of early failure in BME capacitors: (1) to reduce the defect concentration with improved processing control; (2) to prevent the use of BME capacitors under harsh external stress levels so that the extrinsic defects will never be triggered for a failure. In order to do so appropriate dielectric layer thickness must be determined for a given rated voltage