Hydrogen-methane fuel control systems for turbojet engines

Design, development, and test of a fuel conditioning and control system utilizing liquid methane (natural gas) and liquid hydrogen fuels for operation of a J85 jet engine were performed. The experimental program evaluated the stability and response of an engine fuel control employing liquid pumping of cryogenic fuels, gasification of the fuels at supercritical pressure, and gaseous metering and control. Acceptably stable and responsive control of the engine was demonstrated throughout the sea level power range for liquid gas fuel and up to 88 percent engine speed using liquid hydrogen fuel

Compound Multiple Access Channels with Partial Cooperation

A two-user discrete memoryless compound multiple access channel with a common message and conferencing decoders is considered. The capacity region is characterized in the special cases of physically degraded channels and unidirectional cooperation, and achievable rate regions are provided for the general case. The results are then extended to the corresponding Gaussian model. In the Gaussian setup, the provided achievable rates are shown to lie within some constant number of bits from the boundary of the capacity region in several special cases. An alternative model, in which the encoders are connected by conferencing links rather than having a common message, is studied as well, and the capacity region for this model is also determined for the cases of physically degraded channels and unidirectional cooperation. Numerical results are also provided to obtain insights about the potential gains of conferencing at the decoders and encoders.Comment: Submitted to IEEE Transactions on Information Theor

Constructive Multiuser Interference in Symbol Level Precoding for the MISO Downlink Channel

This paper investigates the problem of interference among the simultaneous multiuser transmissions in the downlink of multiple antennas systems. Using symbol level precoding, a new approach towards the multiuser interference is discussed along this paper. The concept of exploiting the interference between the spatial multiuser transmissions by jointly utilizing the data information (DI) and channel state information (CSI), in order to design symbol-level precoders, is proposed. In this direction, the interference among the data streams is transformed under certain conditions to useful signal that can improve the signal to interference noise ratio (SINR) of the downlink transmissions. We propose a maximum ratio transmission (MRT) based algorithm that jointly exploits DI and CSI to glean the benefits from constructive multiuser interference. Subsequently, a relation between the constructive interference downlink transmission and physical layer multicasting is established. In this context, novel constructive interference precoding techniques that tackle the transmit power minimization (min power) with individual SINR constraints at each user's receivers is proposed. Furthermore, fairness through maximizing the weighted minimum SINR (max min SINR) of the users is addressed by finding the link between the min power and max min SINR problems. Moreover, heuristic precoding techniques are proposed to tackle the weighted sum rate problem. Finally, extensive numerical results show that the proposed schemes outperform other state of the art techniques.Comment: Submitted to IEEE Transactions on Signal Processin

Relaying Simultaneous Multicast Messages

The problem of multicasting multiple messages with the help of a relay, which may also have an independent message of its own to multicast, is considered. As a first step to address this general model, referred to as the compound multiple access channel with a relay (cMACr), the capacity region of the multiple access channel with a "cognitive" relay is characterized, including the cases of partial and rate-limited cognition. Achievable rate regions for the cMACr model are then presented based on decode-and-forward (DF) and compress-and-forward (CF) relaying strategies. Moreover, an outer bound is derived for the special case in which each transmitter has a direct link to one of the receivers while the connection to the other receiver is enabled only through the relay terminal. Numerical results for the Gaussian channel are also provided.Comment: This paper was presented at the IEEE Information Theory Workshop, Volos, Greece, June 200

Symbol Based Precoding in The Downlink of Cognitive MISO Channels

This paper proposes symbol level precoding in the downlink of a MISO cognitive system. The new scheme tries to jointly utilize the data and channel information to design a precoding that minimizes the transmit power at a cognitive base station (CBS); without violating the interference temperature constraint imposed by the primary system. In this framework, the data information is handled at symbol level which enables the characterization the intra-user interference among the cognitive users as an additional source of useful energy that should be exploited. A relation between the constructive multiuser transmissions and physical-layer multicast system is established. Extensive simulations are performed to validate the proposed technique and compare it with conventional techniques.Comment: CROWNCOM 201

The effects of radiation damage and annealing on the diffusion of helium from zircon

The relationship between radiogenic ⁴He in zircon, and its associated radiation damage to the crystal lattice, have been of scientific interest since the earliest attempts at geochronology, and remain an active topic of research today in the pursuit of understanding the timing of low-temperature geological processes. Recently, the complex interrelationships between ⁴He diffusion kinetics, time, temperature, and radiation damage were quantified into a complete model for the zircon (U-Th)/He (ZHe) thermochronometric system: the Zircon Radiation Damage Accumulation and Annealing Model (ZRDAAM). Many researchers have taken issue with the predictions of this model, however, particularly at moderate to high radiation doses (~3 × 10¹⁷ – 2 × 10¹⁹ α/g). In this submission, the relationship between radiation damage and ⁴He diffusion kinetics are examined in greater detail to identify sources of discrepancy between observations and model predictions. Using zircons from three geologically distinct localities, this work represents the largest study on the diffusion kinetics of ⁴He from zircon to date, including 26 cycled step-heating analyses. A new behavior is observed in diffusion kinetics behavior, termed ‘rollover’: a thermally activated decrease in diffusivities, interpreted as low-temeprature annealing. Comparing the results of modeled and observed ZHe dating and step-heating analyses, we find significant discrepancies with model predictions in agreement with previous research. The source of these discrepancies is identified as low-temperature annealing, a process distinct from epitaxial recrystallization, resulting in significant effects on diffusional behavior, and not accounted for in the ZRDAAM. Results reveal that the damage threshold beyond which model diffusivities increase is too high, likely as a result of extensive prior geological annealing of the high-damage Sri Lankan zircons used to calibrate the ZRDAAM. Furthermore, the use of a single alpha dose appears inappropriate for capturing the full complexity of the ZHe system. Lastly, these results strongly suggest that the diffusion of ⁴He from zircon proceeds in a manner similar to a homogeneous gas, in spite of the fact that natural ⁴He concentrations are often strongly heterogeneous. This work is a significant step forward in the improvement of ZHe thermochronology, and will yield to the recovery of more accurate and robust thermal histories.Geological Science

Heath Lake SSSI, Berkshire: report on sediment analysis 2016

Heath Lake is located in the county of Berkshire (Figure 1) and was designated as a Site of Special Scientific Interest (SSSI) in 1989 for its “specialist communities of native plants and animals...[and] populations of some uncommon and rare aquatic plant species” (Natural England, 2016). Described as a lowland acid lake with nutrient poor waters, it has historically been habitat to both aquatic and marginal plant communities which are more characteristic of upland lakes in Wales, northern England and Scotland