The dc power control for a liquid-fed resistojet

A simple breadboard power controller was designed and demonstrated for a new liquid-fed water resistojet. The 1-piece laboratory model thruster has an integrated vaporizer/superheater using a single heating element. Heater temperature was maintained at or near a preset reference value with the closed loop controller providing pulse width modulated (PWM) dc power into the thruster heater. A combined thruster, temperature readout, PWM transfer function was experimentally determined. This transfer function was used to design a proportional plus integral controller that demonstrated zero steady state error, conservative stability margins and adequate transient response to step changes in propellant flow rate, input voltage and temperature reference. Initial turn-on temperature overshoot from room temperature to a 650 C setpoint was 80 C. In addition, EMI was alleviated by reducing heater dI/dt and dV/dt using a simple diode-inductor-capacitor network. Based on limited initial tests, thruster preheat with no propellant flow was necessary to achieve stable system operation during startup. Breadboard power efficiency was 99 percent at 1 kW, and component mass was 0.4 kg excluding the power loss and mass of an input filter required for spacecraft integration

Resistojet control and power for high frequency ac buses

Resistojets are operational on many geosynchronous communication satellites which all use dc power buses. Multipropellant resistojets were selected for the Initial Operating Capability (IOC) Space Station which will supply 208 V, 20 kHz power. This paper discusses resistojet heater temperature controllers and passive power regulation methods for ac power systems. A simple passive power regulation method suitable for use with regulated sinusoidal or square wave power was designed and tested using the Space Station multipropellant resistojet. The breadboard delivered 20 kHz power to the resistojet heater. Cold start surge current limiting, a power efficiency of 95 percent, and power regulation of better than 2 percent were demonstrated with a two component, 500 W breadboard power controller having a mass of 0.6 kg

Low power arcjet thruster pulse ignition

An investigation of the pulse ignition characteristics of a 1 kW class arcjet using an inductive energy storage pulse generator with a pulse width modulated power converter identified several thruster and pulse generator parameters that influence breakdown voltage including pulse generator rate of voltage rise. This work was conducted with an arcjet tested on hydrogen-nitrogen gas mixtures to simulate fully decomposed hydrazine. Over all ranges of thruster and pulser parameters investigated, the mean breakdown voltages varied from 1.4 to 2.7 kV. Ignition tests at elevated thruster temperatures under certain conditions revealed occasional breakdowns to thruster voltages higher than the power converter output voltage. These post breakdown discharges sometimes failed to transition to the lower voltage arc discharge mode and the thruster would not ignite. Under the same conditions, a transition to the arc mode would occur for a subsequent pulse and the thruster would ignite. An automated 11 600 cycle starting and transition to steady state test demonstrated ignition on the first pulse and required application of a second pulse only two times to initiate breakdown

Does Housing Wealth Make Us Less Equal? The Role of Durable Goods in the Distribution of Wealth

We study the role an illiquid durable consumption good plays in determining the level of precautionary savings and the distribution of wealth in a standard Aiyagari model (i.e. a model with heterogeneous agents, idiosyncratic uncertainty, and borrowing constraints). Transactions costs induce an inaction region over which the durable stock and the associated user cost are not adjusted in response to changes in income, increasing, on average, the volatility of non-durable consumption. The volatility of total consumption is then a function of the share of the durable good in the utility function and the width of the inaction region. We are particularly interested in parameterizations which increase the precautionary motive for saving through an increase in "committed expenditure risk". We find, for an empirically relevant share of durable consumption and for all transaction costs below an upper threshold, that the level of precautionary savings is increasing in the transaction costs. Transaction costs have only a modest impact on the degree of wealth dispersion, as measured by the Gini index, as the associated increase in savings is close to linear in wealth. While we are unable to match the dispersion of wealth in the data, we increase the dispersion over a single asset model (Gini index of .71 for financial assets and .37 for total wealth) and we are able to match the relative dispersion of financial to durable assets, i.e. we find financial assets much more unequal than durable assets. We also match the ratio of housing wealth to total wealth for the median agent. We calibrate the model to data from the PSID, the CES, and the SCFPrecautionary Savings, Wealth Distribution, Durable Goods

Demand and Reimbursement Effects of Healthcare Reform: Health Care Utilization and Infant Mortality in Thailand

The Thai 30 Baht program was one of the largest health system reforms ever undertaken by a low-middle income country. In addition to lowering the cost of care for the previously uninsured in public facilities, it also entailed a fourfold increase in funding provided to hospitals to care for the poorest 30% of the population (who were already publicly insured). For the previously uninsured, we find that the 30 Baht program led to increased health care utilization, as well as a shift from private to public sources of care. But, we find a larger increase for the poor who were previously publicly insured, especially amongst infants and women of childbearing age. Using vital statistics records, we find that the increased access to healthcare by the publicly insured poor led to a reduction in their infant mortality of at least 6.5 per 1,000 births. This suggests significant improvements in infant mortality rates can be achieved through increased access to healthcare services for the poor and marginalized groups.

Commercial Drones and Privacy: Can We Trust States with ‘Drone Federalism’?

Judge Andrew Napolitano said recently of unmanned aircraft systems (“UAS”), or “drones,” that “[t]he first American patriot that shoots down one of these drones that comes too close to his children in his backyard will be an American hero.

The Faithless Employee: A Case Involving the Legal and Accounting Issues Associated with Employee Theft of Company Funds

This case explores the areas of public accounting/auditing and business law as they relate to the conduct of an employee who intentionally and unlawfully obtains, and, negotiates for his own benefit, his employer’s negotiable instruments (checks). In particular, this case involves an accountant who unlawfully acquired negotiable instruments, purportedly drawn by the employer and made payable to the accountant as a result of the accountant’s improper use of his employer’s computerized accounting system. Because of his position, his knowledge of the system, and the lack of proper accounting controls, he was able to write company checks to himself and to manipulate the deductions to his paycheck

Modulation of the host Th1 immune response in pigeon protozoal encephalitis caused by Sarcocystis calchasi

Pigeon protozoal encephalitis (PPE) is an emerging central-nervous disease of domestic pigeons (Columba livia f. domestica) reported in Germany and the United States. It is caused by the apicomplexan parasite Sarcocystis calchasi which is transmitted by Accipter hawks. In contrast to other members of the Apicomplexa such as Toxoplasma and Plasmodium, the knowledge about the pathophysiology and host manipulation of Sarcocystis is scarce and almost nothing is known about PPE. Here we show by mRNA expression profiling a significant down-modulation of the interleukin (IL)-12/IL-18/interferon (IFN)-γ axis in the brains of experimentally infected pigeons during the schizogonic phase of disease. Concomitantly, no cellular immune response was observed in histopathology while immunohistochemistry and nested PCR detected S. calchasi. In contrast, in the late central-nervous phase, IFN-γ and tumor necrosis factor (TNF) α-related cytokines were significantly up-modulated, which correlated with a prominent MHC-II protein expression in areas of mononuclear cell infiltration and necrosis. The mononuclear cell fraction was mainly composed of T-lymphocytes, fewer macrophages and B-lymphocytes. Surprisingly, the severity and composition of the immune cell response appears unrelated to the infectious dose, although the severity and onset of the central nervous signs clearly was dose-dependent. We identified no or only very few tissue cysts by immunohistochemistry in pigeons with severe encephalitis of which one pigeon repeatedly remained negative by PCR despite severe lesions. Taken together, these observations may suggest an immune evasion strategy of S. calchasi during the early phase and a delayed-type hypersensitivity reaction as cause of the extensive cerebral lesions during the late neurological phase of disease