PN Regenerative Ranging and Its Compatibility With Telecommand and Telemetry Signals

This paper investigates the performance of a satellite communication system which the onboard receiver regenerates the uplink pseudonoise (PN) ranging sequence. Using phase modulation, the PN ranging signal is transmitted together with the telecommand signal in the uplink and the telemetry signal in the downlink. Various ranging sequences are taken into consideration and tested prior to final international adoption. The reciprocal interference among telemetry, telecommand, and ranging signals is evaluated in terms of bit error rate and ranging phase acquisition time.     

Hydrogen desorption from a hydride container under different heat exchange conditions

The desorption behavior of a hydrogen storage prototype loaded with AB₅H₆ hydride, whose equilibrium pressure makes it suitable for both feeding a PEM fuel cell and being charged directly from a low pressure water electrolyzer without need of additional compression, was studied. The nominal 70 L hydrogen storage capacity of the container (T = 20 °C, P = 101.3 kPa) suffices for ca. 2.5 h operation of a 50 W hydrogen/oxygen fuel cell stack. The hydride container is provided with aluminum extended surfaces to enhance heat exchange with the surrounding medium. These surfaces consist of internal disk-shaped metal foils and external axial fins. The characterization of the storage prototype at different hydrogen discharge flow rates was made by monitoring the internal pressure and the temperatures of the external wall and at the center inside the container.     

Development of a novel metal hydride–air secondary battery

A laboratory metal hydride/air cell was evaluated. Charging was via a bifunctional air gas-diffusion electrode. Mixed nickel and cobalt oxides, supported on carbon black and activated carbon, were used as catalysts in this electrode. At 30mAcm–2 in 6m KOH, the air electrode potentials were –0.2V (oxygen reduction) and +0.65V (oxygen evolution) vs Hg/HgO. The laboratory cell was cycled for 50 cycles at the C/2 rate (10mAcm–2). The average discharge/charge voltages of the cell were 0.65 and 1.6V, respectively. The initial capacity of the metal hydride electrode decreased by about 15% after 50 cycles.     

The role of lymphocyte subsets in accelerated diabetes in nonobese diabetic-rat insulin promoter-B7-1 (NOD-RIP-B7-1) mice

B7-1 transgene expression on the pancreatic islets in nonobese diabetic (NOD) mice leads to accelerated diabetes, with >50% of animals developing diabetes before 12 wk of age. The expression of B7-1 directly on the pancreatic beta cells, which do not normally express costimulator molecules, converts the cells into effective antigen-presenting cells leading to an intensified autoimmune attack. The pancreatic islet infiltrate in diabetic mice consists of CD8 T cells, CD4 T cells, and B cells, similar to diabetic nontransgenic NOD mice. To elucidate the relative importance of each of the subsets of cells, the NOD-rat insulin promoter (RIP)-B7-1 animals were crossed with NOD.beta2microglobulin -/- mice which lack major histocompatibility complex class I molecules and are deficient in peripheral CD8 T cells, NOD.CD4 -/- mice which lack T cells expressing CD4, and NOD.muMT -/- mice which lack B220-positive B cells. These experiments showed that both CD4 and CD8 T cells were necessary for the accelerated onset of diabetes, but that B cells, which are needed for diabetes to occur in normal NOD mice, are not required. It is possible that B lymphocytes play an important role in the provision of costimulation in NOD mice which is unnecessary in the NOD-RIP-B7-1 transgenic mice.     

Microcalorimetric study of the self-discharge of the NiOOH/Ni(OH)2 electrode in a hydrogen environment

A microcalorimetric method has been used to investigate the self-discharge behaviour of nickel oxyhydroxide electrodes in a pressurized gaseous hydrogen environment. It was found that the heat generation rate is proportional to hydrogen pressure, and is significantly dependent on the immersion state of the electrode in the electrolyte. Hence, diffusion of dissolved hydrogen gas towards or within the electrode controls, at least partially, the self-discharge rate. However, the heat generation decreases exponentially with time, indicating that self-discharge is also proportional to the amount of the charged active material available for the reaction. The presence of Mg, Co and Cd oxides or hydroxides appears to inhibit self-discharge. It was found that direct chemical reaction between dissolved hydrogen and the active material dominates, while in addition, electrochemical oxidation of hydrogen coupled with electrochemical reduction of the active material might also occur at a much smaller rate than the direct reaction.     

Applying discrete event simulation to the design of a service delivery system in the aerospace industry: a case study

This paper presents the results of a simulation study concerned with the design of a service delivery system. In particular, it shows how discrete event simulation can be used at the point of signing a long-term service contract to assess whether a service delivery system will be able to comply with the contractual terms over time. This study also proposes a methodology based on the Monte Carlo simulation to estimate the service demand in a context where the installed base evolves dynamically over time. Such a methodology has been used to verify the discrete event simulation model. This research is based on real data from a leading global supplier of human to machine electronic controls operating in the aerospace industry. This supplier has recently signed a major contract for the provision of several devices and related services. These devices will be installed on aircrafts progressively entering service over the next seven years.     

Long-Haul Optically Uncompensated IMDD Transmission With MLSE Using the M-Method

Recent experimental evidence with off-line processing has shown that intensity-modulation direct-dectection receivers using maximum-likelihood sequence estimation (MLSE) can successfully operate over a very long distance without any optical dispersion compensation. One hurdle towards the actual exploitation of the technology is the required complexity of the processor, which grows exponentially with distance. In this letter, we investigate the use of a complexity-reduction algorithm originally proposed for nonoptical communications, called the M-method. We show by simulation that over 400 and 700 km of G.652 fiber, at 10.7 Gb/s, the M-method allows us to operate with virtually no excess penalty with respect to conventional MLSE, while keeping track of only 32 and 128 trellis states, respectively, out of optimum full-fledged trellises requiring 512 and 8192 states, respectively. We investigate the robustness of the algorithm versus limited analog-digital resolution and confirm its effectiveness by testing it over experimental data at 10 Gb/s over 1040 km.     

Morphological changes in mouse embryos cryopreserved by different techniques

Cryopreservation of mammalian embryos is an important tool for the application of reproductive biotechnologies. Subjective evaluation to determine embryo viability is often used. The determination of the best cryopreservation protocol depends on morphological and molecular analysis of cellular injuries. The main objective of this study was to compare two methods of cryopreservation by assessing morphological alterations of frozen embryos using light, fluorescence, and transmission electron microscope. Fresh (control), slow frozen, and vitrified mouse embryos were composed. To evaluate the viability of the embryos, the cell membrane integrity was assessed using Hoechst33342 and propidium iodide (H/PI) staining. Morphological analyses using hematoxylin and eosin (HE) staining were performed to test different techniques (in situ, paraffin, and historesin) by both light and fluorescence microscopy. Transmission electron microscope was used to detect ultrastructural alterations in Spurr- and Araldite-embedded samples. H/PI staining detected more membrane permeability in the vitrification (69.8%) than in the slow freezing (48.4%) or control (13.8%) groups (P < 0.001). Historesin-embedded samples showed to be more suitable for morphological analyses because cellular structures were better identified. Nuclear evaluation in historesin sections showed the induction of pycnosis in slow freezing and vitrification groups. Cytoplasm evaluation revealed a condensation and an increase in eosinophilic intensity (indicating apoptosis) in the slow freezing group, and weakly eosinophilic structures and degenerated cells (indicating oncosis) in the vitrification group (P < 0.05). Ultrastructural analyses confirmed HE morphological findings. It was concluded that both cryopreservation techniques resulted in oncosis and apoptosis injuries. However, vitrification caused more severe cellular alterations and reduced embryonic viability compared to slow freezing.