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In 2016, the National Aeronautics and Space Administration (NASA) Advanced Exploration Systems (AES) project office funded testing at the NASA Glenn Research Center to evaluate the maturity of the Proton Exchange Membrane (PEM) fuel cell technology and its viability for supporting launch vehicle and space applications. This technology evaluation included vibration, reactant purity, and vacuum exposure sensitivity testing. The evaluation process did not include microgravity testing. This paper discusses the vibration sensitivity testing of two air-independent fuel cell stacks provided by different vendors to assess the ability of currently available fuel cell stack hardware to survive the projected random vibrational environment that would be encountered in an upper stage launch vehicle. Baseline performance testing was utilized to quantify stack performance and overboard leak rate at standard atmospheric conditions in order to provide a reference for posttest comparison. Both fuel cell stacks were tested at a random vibration qualification level of 10.4 grms for five minutes in each axis. Low-level sinusoidal sweeps were conducted before and after each random vibration level run to see if any significant change in resonances were detected. Following vibration facility testing, the baseline performance testing was repeated. Test results demonstrated no measurable change in fuel cell electrochemical or mechanical performance, indicating that the two evaluated PEM fuel cell stacks may be suitable for space applications pending microgravity testing.

Commercialization of lithium-oxygen batteries faces many challenges, such as electrolyte decomposition, short cycle life, low energy and power density, and high cell mass. However, the commercialization of Li O2 batteries for aeronautics is more challenging due to additional safety constraints on cyclability and performance (high specific-power and specific-energy). In this paper, we perform experiments and use the results to calibrate a 1-D finite element model to simulate discharge profiles up to 5 mA cm-2. The calibrated model is used to perform parametric studies of geometrical, microstructural, transport, and material properties for different discharge times, and discharge current densities. Next, a simulation-based optimization study shows optimal cell designs for various electrolytes for high specific-power. Results show that a high specific-power Li O2 cell needs to have a cathode with a thickness equal to oxygen diffusion length, thin separator, optimized anode, and other components with low mass. The specific-power is sensitive to discharge time, discharge current density, and microstructural and geometrical properties. Also, in some cases, electrolytes with high oxygen solubility or high external partial pressure can compensate for electrolytes with low oxygen diffusivity. However, reducing the cell mass is the most straight forward path to improving specific-power.

Proton exchange membrane (PEM) fuel cells are being developed for future NASA missions. These fuel cells use a bipolar construction, with internal manifolds to conduct product water and coolant water. The wetted surfaces of the manifolds present large voltage gradients across the product water and coolant water passages, which can induce water electrolysis in the manifolds of full-scale stacks. If not controlled, shunt currents lead to parasitic power losses and corrosion of the fuel cell metal surfaces; therefore, it is important to understand and characterize the effects of shunt currents. This analysis also applies to electrolyzers, flow-batteries and other devices where an electrolyte manifold experiences voltage gradients. In this work, electrochemical characterizations were performed to estimate these characteristics under relevant operating conditions. A numerical solution of the shunt currents is presented, and the distribution of water electrolysis and corrosion is described.

This paper presents the preliminary results of a recent National Aeronautics and Space Administration (NASA) study funded under the Advanced Exploration Systems (AES) Modular Power Systems (AMPS) project. This study evaluated multiple surface locations on both the Moon and Mars, with the goal of establishing a common approach towards technology development and system design for surface power systems that use Regenerative Fuel Cell (RFC) energy storage methods. One RFC design may not be applicable to all surface locations; however, AMPS seeks to find a unified architecture, or series of architectures, that leverages a single development approach to answer the technology need for RFC systems. Early system trades were performed to select the most effective fuel cell and electrolyzer architectures based on current state-of-the-art technology, whereas later trades will establish a detailed system design to enable a near-term ground (non-flight) demonstration. This paper focuses on the initial trade studies, presents the selected fuel cell and electrolyzer architectures for follow-on system design studies, and suggests areas for further technology investment.

NASA demonstrated the Advanced Product Water Removal (APWR) Non-Flow-Through (NFT) PEM fuel cell technology by powering the Scarab rover over three-(3) days of field operations. The latest generation APWR NFT fuel cell stackwas packaged by the Advanced Exploration Systems (AES) Modular Power Systems (AMPS) team into a nominallyrated 1-kW fuel cell power module. This power module was functionally verified in a laboratory prior to field operations on the Scarab rover, which concluded on 2 September 2015. During this demonstration, the power module satisfied all required success criteria by supporting all electrical loads as the Scarab navigated the NASA Glenn Research Center.

Electrochemical Impedance spectroscopy (EIS) is exceptionally powerful and rapidly evolving technique for investigating electrical properties of materials and electrochemical interfacial kinetic processes in wide variety of practical systems and applications. The method offers the most powerful on-line and off-line analysis of the status of investigated media, electrodes, and probes in many different complex time– and space-resolved processes that occur in electrochemical laboratory experiments or over a lifetime of monitored samples, devices, or materials. EIS is useful as an empirical quality control procedure that can also be employed to interpret fundamental electrochemical processes [1, 2]. At NASA Glenn Research Center the EIS technique is being widely and effectively employed in characterization and performance monitoring of rechargeable energy storage devices, such as states of electrodes during charging / discharging cycles in secondary batteries and fuel cells. The technical objective for batteries is to improve the performance of rechargeable cells to meet the energy storage requirements of human missions. The approach is to develop advanced battery components to safely provide substantially higher specific energy for relatively few charge/discharge cycles. In the presented work, impedance spectroscopy and other electrochemical and surface science techniques have been widely applied to monitoring developed lithium-metal battery (LMB) cells, including investigation of the impact of novel ionic liquid electrolytes on cycle life and dendrite growth/suppression on Li anodes. Applications of EIS method allowed for efficient in situ performance monitoring of various types of electrodes and electrolytes used in experimental battery cells. The studies were focused initially on evaluating performance of separate battery components in symmetric lithium coin cells, with a purpose of future complete impedance analysis of full cells with Li anode and dedicated cathode.

Commercialization of lithium-air batteries faces many challenges, such as electrolyte decomposition, short cycle life, low energy and power density, etc. However, commercialization of Li-O2 batteries for aeronautics is much more challenging due to additional safety constraints on cyclability and performance (high specific power and specific energy). For this presentation, we will discuss inter-related aspects of physics-based modeling of a pack: cell and battery model calibration; and parameter estimation using statistical methods. In addition, we will evaluate and present optimal battery designs for high discharge current density, high discharge time, and low battery mass using simulation-based optimization. The Finite Element Model (FEM) used to simulate a Li-O2 cell is based on the work of Bevara [1]. The different aspects of the model are based on: porous electrode theory and concentrated electrolyte theory; quantum tunneling model for the resistance of conformal layer of discharge product (Li2O2) [1]; Butler-Volmer kinetics for electrochemical reaction; Fick’s diffusion for oxygen transport; and an oxygen dissolution model is applied at the air/electrolyte interface [2]. The electrolyte properties such as ion conductivity, ion diffusion, oxygen diffusion, and mass density of the electrolyte were taken from Molecular Dynamics (MD) simulations [3]; while the other model parameters, which includes mass of cell components, were calibrated to match experiments at high discharge current densities. The cell mass includes the anode, cathode, separator, electrolyte, and other components (such as current collector). This calibrated model is used to perform parametric studies on cathode thickness, porosity, tortuosity, carbon particle size, electrolyte transport and material properties, partial pressure of oxygen, discharge time, and discharge current density to study optimal designs for high specific power and energy. Traditionally, pack (several cells are connected in series and/or parallel) simulations are performed using equivalent circuit, analytical expressions, or empirical models. Here, we develop a multi-physics model to include cell level variations in pack by considering factors such as difference in pressure drop, temperature variation, and variation in manufacturing. Using “accurate” cell power and mass estimates from the multi-physics model, optimal pack design solutions will be explored and presented at the meeting. Continuum model parameters are usually taken from experiments, from first principle simulations, or are assumed. They include errors such as model error, which arise from using a simplified model, from neglecting unknown processes or interactions, or from using wrong assumptions. Bayesian inversion techniques [4] will be used to find probability distributions in parameter values such as reaction rate, reaction active area, and Li2O2 resistance and the resulting error in the predicted values of specific power will be presented. References: Bevara, V. & Andrei, P. (2014), J. Electrochem. Soc. 161 (14), A2068-A2079. Mehta, M. & Andrei, P. (2015), J. Power Sources. 286, 299-308. Liyana-Arachchi, T.; Haskins, J.; Burke, C.; Diederichsen, K.; McCloskey, B.; & Lawson, J. (2018), J. Phys. Chem. B. 122 (36), 8548 - 8559. Choi, W.; Kikumoto, H.; Choudhary, R. & Ooka, R. (2018), Applied Energy, 209, 306-321.

Megalocytiviruses have been associated with epizootics resulting in significant economic losses in public aquaria and food-fish and ornamental fish industries, as well as threatening wild fish stocks. The present report describes characteristics of the first megalocytivirus from a wild temperate North American fish, the threespine stickleback Gasterosteus aculeatus. Moribund and dead fish sampled after transfer to quarantine for an aquarium exhibit had amphophilic to basophilic intracytoplasmic inclusions (histopathology) and icosahedral virions (transmission electron microscopy) consistent with an iridovirus infection. Phylogenetic analyses of the major capsid, ATPase, and DNA polymerase genes confirmed the virus as the first known member of the genus Megalocytivirus (family Iridoviridae) from a gasterosteid fish. The unique biologic and genetic properties of this virus are sufficient to establish a new Megalocytivirus species to be formally known as the threespine stickleback iridovirus (TSIV). The threespine stickleback is widely distributed throughout the northern hemisphere in both freshwater and estuarine environments. The presence of megalocytiviruses with broad host specificity and detrimental economic and ecologic impacts among such a widely dispersed fish species indicates the need for sampling of other stickleback populations as well as other North American sympatric marine and freshwater ichthyofauna.

Solvent free polymer electrolytes were made consisting of Li(+) and pyrrolidinium salts of trifluoromethanesulfonimide added to a series of hyperbranched poly(ethylene oxide)s (PEO). The polymers were connected by triazine linkages and crosslinked by a sol-gel process to provide mechanical strength. The connecting PEO groups were varied to help understand the effects of polymer structure on electrolyte conductivity in the presence of ionic liquids. Polymers were also made that contain poly(dimethylsiloxane) groups, which provide increased flexibility without interacting with lithium ions. When large amounts of ionic liquid are added, there is little dependence of conductivity on the polymer structure. However, when smaller amounts of ionic liquid are added, the inherent conductivity of the polymer becomes a factor. These electrolytes are more conductive than those made with high molecular weight PEO imbibed with ionic liquids at ambient temperatures, due to the amorphous nature of the polymer.

The coding region of c- myc mRNA encompassing the coding region determinant (CRD) nucleotides (nts) 1705–1792 is critical in regulating c- myc mRNA stability. This is in part due to the susceptibility of c- myc CRD RNA to attack by an endoribonuclease. We have previously purified and characterized a mammalian endoribonuclease that cleaves c- myc CRD RNA in vitro . This enzyme is tentatively identified as a 35 kDa RNase1-like endonuclease. In an effort to understand the sequence and secondary structure requirements for RNA cleavage by this enzyme, we have determined the secondary structure of the c- myc CRD RNA nts 1705–1792 using RNase probing technique. The secondary structure of c- myc CRD RNA possesses five stems; two of which contain 4 base pairs (stems I and V) and three consisting of 3 base pairs (stems II, III, and IV). Endonucleolytic assays using the c- myc CRD and several c- myc CRD mutants as substrates led to the following conclusions: (i) the enzyme prefers to cleave in between the dinucleotides UA, CA, and UG in single-stranded regions; (ii) the enzyme is more specific towards UA dinucleotides. These properties further distinguish the enzyme from previously described mammalian endonuclease that cleaves c- myc mRNA in vitro .

Commercial lithium/polycarbon monofluoride batteries [Li–(CF)n] are typically current-limited and are therefore not implemented in high-rate or low-temperature applications. Recent results suggest, however, that CF-based cathodes that use sub-fluorinated CFx (SFCFx) active materials in a thin electrode form factor are able to support very high currents (up to 5 C) while still providing a significant fraction of their specific capacity. In this work, the low temperature efficacy of these materials is examined in a −40 °C environment. CF0.54 and CF0.65 powders were characterized using X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopy. These materials were then implemented in a spray-deposited electrode using a 1-mil (∼25 μm) aluminum foil current collector and PVDF as a binder. Electrochemical tests showed that these materials were able to deliver specific capacity values up to five times greater than commercial CF1.08 powder inserted into identically fabricated test cells tested at −40 °C. Testing also indicated that a room-temperature pre-discharge step was necessary to condition the electrode materials before exposure to the low-temperature test environment.

A new series of polymer electrolytes for use as membranes for lithium batteries are described. Electrolytes were made by polymerization between cyanuric chloride and diamino-terminated poly(ethylene oxide)s, followed by cross-linking via a sol-gel process. Thermal analysis and lithium conductivity of freestanding polymer films were studied. The effects of several variables on conductivity were investigated, such as length of backbone PEO chain, length of branching PEO chain, extent of branching, extent of cross-linking, salt content, and salt counterion. Polymer films with the highest percentage of PEO were found to be the most conductive, with a maximum lithium conductivity of 3.9 x 10(exp -5) S/cm at 25 C. Addition of plasticizer to the dry polymers increased conductivity by an order of magnitude.

This paper describes a series of rod-coil block co-polymers that produce easy to fabricate, dimensionally stable films with good ionic conductivity down to room temperature for use as electrolytes for lithium polymer batteries. The polymers consist of short, rigid rod polyimide segments, alternating with flexible, polyalkylene oxide coil segments. The highly incompatible rods and coils should phase separate, especially in the presence of lithium ions. The coil phase would allow for conduction of lithium ions, while the rigid rod phase would provide a high degree of dimensional stability. An optimization study was carried out to study the effect of four variables (degree of branching, formulated molecular weight, polymerization solvent and lithium salt concentration) on ionic conductivity, glass transition temperature and dimensional stability in this system.

We employ molecular dynamics (MD) simulation and experiment to investigate the structure, thermodynamics, and transport of N-methyl-N-butylpyrrolidinium bis(trifluoromethylsufonyl)imide ([pyr14][TFSI]), N-methyl-N-propylpyrrolidinium bis(fluorosufonyl)imide ([pyr13][FSI]), and 1-ethyl-3-methylimidazolium boron tetrafluoride ([EMIM][BF4]), as a function of Li-salt mole fraction (0.05 ≤ xLi(+) ≤ 0.33) and temperature (298 K ≤ T ≤ 393 K). Structurally, Li(+) is shown to be solvated by three anion neighbors in [pyr14][TFSI] and four anion neighbors in both [pyr13][FSI] and [EMIM][BF4], and at all levels of xLi(+) we find the presence of lithium aggregates. Pulsed field gradient spin-echo NMR measurements of diffusion and electrochemical impedance spectroscopy measurements of ionic conductivity are made for the neat ionic liquids as well as 0.5 molal solutions of Li-salt in the ionic liquids. Bulk ionic liquid properties (density, diffusion, viscosity, and ionic conductivity) are obtained with MD simulations and show excellent agreement with experiment. While the diffusion exhibits a systematic decrease with increasing xLi(+), the contribution of Li(+) to ionic conductivity increases until reaching a saturation doping level of xLi(+) = 0.10. Comparatively, the Li(+) conductivity of [pyr14][TFSI] is an order of magnitude lower than that of the other liquids, which range between 0.1 and 0.3 mS/cm. Our transport results also demonstrate the necessity of long MD simulation runs (∼200 ns) to converge transport properties at room temperature. The differences in Li(+) transport are reflected in the residence times of Li(+) with the anions (τ(Li/-)), which are revealed to be much larger for [pyr14][TFSI] (up to 100 ns at the highest doping levels) than in either [EMIM][BF4] or [pyr13][FSI]. Finally, to comment on the relative kinetics of Li(+) transport in each liquid, we find that while the net motion of Li(+) with its solvation shell (vehicular) significantly contributes to net diffusion in all liquids, the importance of transport through anion exchange increases at high xLi(+) and in liquids with large anions.

Proton exchange membrane (PEM) fuel cells are being developed for future NASA missions. These fuel cells use metallic bipolar plates, with internal manifolds to direct product water and coolant water. The wetted surfaces of the manifolds present large voltage gradients across the product water and coolant water passages, which can induce water electrolysis in the manifolds of full-scale stacks. As such, shunt currents lead to parasitic power losses and corrosion of the fuel cell metal surfaces; therefore, it is important to understand and characterize the effects of shunt currents. This analysis also applies to electrolyzers, flowbatteries and other devices where an electrolyte manifold experiences voltage gradients. In this work, electrochemical characterizations were performed to estimate these characteristics under relevant operating conditions. A numerical solution of the shunt currents is presented, and regions prone to water electrolysis and corrosion are identified.

A description of the problems encountered in creating the first continuously oscillating laser (the helium-neon "optical maser") is given, together with some previously unpublished data taken by the author on the excitation transfer process between helium metastables and the upper laser levels in neon. Research on the helium-neon excitation transfer problem is traced back to a little-known paper by Headrick and Duffendack published in 1931. An interesting historical coincidence is noted in that most of the people who did pioneering work in the laser field had some connection with the Physics Department at Columbia University. That probability arose because Columbia was the birthplace of induced resonance experiments in physics during the 1930s.

The acute toxicity of the antisapstain wood preservative Bardac 2280 (principal active ingredient 80% didecyldimethylammonium chloride, DDAC) was tested with four fish and four aquatic invertebrate species. White sturgeon fry (Acipenser transmontanus) were the most sensitive fish species tested with a 24-h 50% lethal concentration (LC50) value between 1 and 10 ppb Bardac 2280. The 96-h LC50 values for the three other fish species ranged from 0.39 ppm for fathead minnows (Pimephales promelas) to 2.0 ppm for juvenile starry flounder (Platichthys stellatus). Developmental stage altered the sensitivity of coho salmon to Bardac 2280, with alevins being approximately twice as sensitive as smolts. Altering salinity up to 30‰ seawater had no significant effect on the toxicity of Bardac 2280 to coho smolts. The 48-h LC50 values for Daphnia magna, Mysidopsis bahia, Hyalella azteca, and Neomysis mercedis were 0.037 ppm, 0.039 ppm, 0.106 ppm, and 0.947 ppm, respectively. Bardac 2280 characteristically produced steep concentration–response curves for fish, i.e., a concentration range considerably less than 10-fold for a complete range of mortality, and caused no major symptoms of sublethal stress in juvenile starry flounder following a 24-h exposure.

The primary goal of this study was to investigate the possibility of using early life stages of white sturgeon (Acipenser transmontanus) (eggs, larvae and fry) as a species relevant to the Fraser River, B.C., for the acute and sublethal toxico-logical testing of forest industry effluents. Here we report the first successful acute toxicity tests for 8-day-old larvae and 42-day-old fry exposed to several chemicals known to be released into the Fraser River (i.e., 6 monochlorovanillin [6 MVAN], 4,5 dichloroguaiacol [4,5 DCG], 4,5 dichlorocatechol [4,5 DCAT], pentachlorophenol [PCP], and didecyldimethylammonium chloride [DDAC]). In most cases, white sturgeon fry were at the lower end of the range for acute toxicity values for chlorinated phenolic compounds, when compared with other juvenile fish species, and they were extremely sensitive to DDAC. The larval stage was usually more sensitive than the fry stage. Acute toxicity tests with fertilized eggs were unsuccessful. A postexposure growth study was inconclusive because neither control nor toxicant-exposed larvae and fry withstood the additional handling used for measuring body mass. At 62-days-old, fry were more tolerant of handling. This allowed measurement of their swimming performance. Although we have concerns about the reliability of using larvae for acute toxicity testing at this time, 60-day-old white sturgeon fry would appear to be both a sensitive and relevant species for assessing environmental impacts relevant to the Fraser River.

This study compared gender trends for self-reported work values of 384 nontraditional college students in 1982 and 335 different nontraditional college students in 1992. Results measured by D. Nevill and D. E. Super's (1989) Values Scale indicated that female values preferences moved toward Altruism and Variety and away from Autonomy and Advancement. Male values preferences remained relatively constant, except for a significant drop in Aesthetics. The most important finding was that there were many more similarities than differences in men's and women's values preferences for both 1982 and 1992. The top 3 rankings for both years were identical: Economic Security, Achievement, and Ability Utilization.

Advanced electrode materials with increased specific capacity and voltage performance are critical to the development of Li-ion batteries with increased specific energy and energy density. Although performance metrics for individual electrodes are critically important, a fundamental understanding of the interactions of electrodes in a full cell is essential to achieving the desired performance, and for establishing meaningful goals for electrode performance. This paper presents practical design considerations for matching positive and negative electrodes in a viable design. Methods for predicting cell-level discharge voltage, based on laboratory data for individual electrodes, are presented and discussed.

Silicon is a promising and attractive anode material to replace graphite for high capacity lithium ion cells since its theoretical capacity is ∼10 times of graphite and it is an abundant element on earth. However, there are challenges associated with using silicon as Li-ion anode due to the significant first cycle irreversible capacity loss and subsequent rapid capacity fade during cycling. In this paper, cyclic voltammetry and electrochemical impedance spectroscopy are used to build a fundamental understanding of silicon anodes. The results show that it is difficult to form the SEI film on the surface of Si anode during the first cycle, the lithium ion insertion and de-insertion kinetics for Si are sluggish, and the cell internal resistance changes with the state of lithiation after electrochemical cycling. These results are compared with those for extensively studied graphite anodes. The understanding gained from this study will help to design better Si anodes.

Epidemiologists in Denver, Los Angeles and Sweden are asking us to believe that magnetic fields of 2 milligauss from power distribution lines are a serious cause of childhood leukemia. What started as a series of sensational articles in The New Yorker magazine by Paul Brodeur (later collected into a book), bringing the earliest of these studies to the attention of the general public, has turned into a new growth industry. Several government agencies, not to mention the private electric power industry, have already sponsored multimillion‐dollar studies of the problem; a number of small companies selling 60‐Hz gaussmeters have sprung into existence and are doing a land‐office business; and the public concern over this issue has become a bonanza to groups of people doing epidemiological and biological research on the effects of electromagnetic fields. Hastily contrived legislation in a number of states has legalized the status quo for fields from power lines, and the threat of still more ill‐thought‐out legi...

The reproductive risks of electromagnetic fields (EMF) were evaluated based on an extensive review of the scientific literature pertaining to human epidemiologic studies, secular trend data, in vivo animal studies and in vitro studies, and biologic plausibility. The epidemiologic studies involving the reproductive effects of EMF exposures to human populations have included populations exposed to: (1) video display terminals (VDTs), and (2) power lines and household appliances. The clinical use of diagnostic MRI (magnetic resonance imaging) has been increasing, but there are few reports or studies of pregnant women or individuals of reproductive age who have been exposed to MRI, and whose reproductive performance has been evaluated. The population that has been studied most frequently are women exposed to VDTs, but their EMF exposures are extremely low and frequently are at the level of the ambient EMF in a house or office. The results of epidemiologic studies involving VDTs are generally negataive for the reproductive effects that have been studied. Based on the number of studies, the exposure levels, and the fairly consistent results, it can be argued that VDT epidemiologic studies should no longer be given priority. There have been fewer studies concerned with the reproductive risks of power lines, electric substations, and home appliances. In some publications, positive findings for reproductive risks were reported, but the more consistent findings indicate that EMF, even at these higher exposures, do not generate a measurable increase in reproductive failures in the human population. When compared to other fields of human epidemiology, it is obvious that these studies have many difficulties. Exposures are rarely determined. Studies frequently involve small sample sizes and the investigators rarely have a combined expertise in EMF physics, engineering, and reproductive biology. Because of the allegation that there may be particular windows of frequency, wave shape, and intensity that may be deleterious, it is impossible to disregard low frequency EMF exposures as having no deleterious reproductive effects. Yet the epidemiologic data that are available would point in that direction. Secular trend data analysis of birth defect incidence data indicate that increasing generation of electric power during this century is not associated with a concomitant rise in the incidence of birth defects. There are over 70 EMF research projects dealing with animal and in vitro studies that are concerned with some aspect of reproduction and growth. Unfortunately, a large proportion of the embryology studies utilized the chick embryo and evaluated the presence or absence of teratogenesis after 48 to 52 hours of development. The chick embryo studies were of little assistance to the epidemiologist or clinician in determining whether EMF exposure represents a hazard to the human embryo, and the results were, in any case, inconsistent. Embryo culture or cell culture studies are also of little assistance in determining the human risk of EMF. In vitro or in vivo studies in nonhuman species can be used to study mechanisms and the effects that have been suggested by human investigations. Only well designed whole-animal teratology studies are appropriate when the epidemiologists and clinical teratologists are uncertain about the environmental risks. Other aspects of reproductive failure such as abortion, infertility, stillbirth, and prematurity cannot be addressed by in vitro or culture experiments. In fact, it is very difficult to design and interpret nonprimate in vivo studies. Biologic plausability for teratogenesis can be supported if an agent such as EMF can be demonstrated to be cytotoxic or mutagenic. The studies dealing with mutagenesis, cell death, and cell proliferation using in vitro systems do not indicate that EMF have the potential for deleteriously affecting proliferating and differentiating embryonic cells at the exposures to which populations are usually exposed. Of course, there is no environmental agent that has no effect, deleterious or not, at very high exposures. While there does not appear to be measurable risk of reproductive failure and birth defects from EMF exposures in humans, a modest program of investigation is warranted epidemiologically and in the laboratory to answer some of the issues that have been raised that need clarification. It does not appear that the risk of EMF exposure is significant and, therefore, although preparing conducted research in the area of EMF risks is appropriate, it does not necessitate a massive expenditure of resources.

The estimation of the spectral density of a spatial random process by diffraction requires that the parameters of the diffraction system be compatible with the statistical properties of the process. Otherwise, the estimate of the spectrum can be unstable or unduly biased. The relation between the second-order statistics of the process and the parameters of a basic diffraction system that are required for reasonable spectral estimates is investigated. Such parameters include aperture dimensions, wavelength, focal length of the lens, and scanning slit size. With the typical diffraction system, it is difficult to estimate the power spectrum because of the presence of the zero-order aperture-diffracted light. A technique is furnished in this paper for spectral estimation at dc. Experimental results are furnished for film grain and total film noise. It is shown that the residual phase noise of film at dc even under so-called matched conditions is large enough to prevent the accurate estimation of the dc value of grain noise.

In conventional real-time electrooptical signal processors, the variation of the output intensity with time is directly detected with a photodetector. As a result of this, any information carried in the phase of the light is lost. However, if the light is detected coherently, i.e., it is heterodyned with another coherent local oscillator light source on the detector surface, the phase associated with the amplitude of the light may be preserved. This paper presents the results of a theoretical and experimental study of the properties of real-time electrooptical spectrum analyzers with coherent detection. Basic equations of operation are presented and discussed, and confirmed by experiment, and it is concluded that the construction of such devices is feasible.

The ventricle of the salmonid heart consists of an outer compact layer of circumferentially arranged cardiomyocytes encasing a spongy myocardium that spans the lumen of the ventricle with a fine arrangement of muscular trabeculae. While many studies have detailed the anatomical structure of fish hearts, few have considered how these two cardiac muscle architectures are attached to form a functional working unit. The present study considers how the spindle-like cardiomyocytes, unlike the more rectangular structure of adult mammalian cardiomyocytes, form perpendicular connections between the two muscle layers that withstand the mechanical forces generated during cardiac systole and permit a simultaneous, coordinated contraction of both ventricular components. Therefore, hearts of rainbow trout (Oncorhynchus mykiss) and sockeye salmon (Oncorhynchus nerka) were investigated in detail using scanning electron microscopy (SEM) and various light microscopic techniques. In contrast to earlier suggestions, we found no evidence for a distinct connective tissue layer between the two muscle architectures that might ‘glue’ together the compact and the spongy myocardium. Instead, the contact layer between the compact and the spongy myocardium was characterized by a significantly higher amount of desmosome-like (D) and fascia adhaerens-like (FA) adhering junctions compared with either region alone. In addition, we observed that the trabeculae form muscular sheets of fairly uniform thickness and variable width rather than thick cylinders of variable diameter. This sheet-like trabecular anatomy would minimize diffusion distance while maximizing the area of contact between the trabecular muscle and the venous blood as well as the muscle tension generated by a single trabecular sheet.

This chapter contains sections titled: Structure of an AM Wave Amplitude Modulators Amplitude Detectors Systems Derived from AM Analysis of Modulating and Demodulating Circuits Effect of Distortion in Transmitting Medium Multiplexing of AM Channels

An introductory, graduate-level look at modern communications in general and radio communications in particular. This seminal presentation of the applications of communication theory to signal and receiver design brings you valuable insights into the fundamental concepts underlying today's communications systems, especially wireless communications. Coverage includes: AM, FM Phase Modulation, PCM, fading, and diversity receivers. This is a classic reissue of a book published by McGraw Hill in 1966.

This appendix contains sections titled: Matrix Definitions Reduction to Diagonal Hermitian Form in Independent Variates Characteristic Function and P.D.F. of Hermitian Quadratic Form

This chapter contains sections titled: Carrier Telegraphy Relation of Character or Code Performance to Binary Error Rate Representations of Bandpass Signals, Noise, and Filtering On-off Keying Frequency-shift Keying (FSK) Phase-shift Keying (PSK) Suboptimum versus Matched Filters

This appendix contains sections titled: Basic Definitions and Elementary Properties Transform Representations Symmetry and Antisymmetry Relations Series Representations Probability That One Rice Variate Exceeds Another The Joint Distribution of Two Correlated Rayleigh Variates Additional Integrals

This chapter contains sections titled: Statistical Decision Theory Decision Theory in the Case of Binary-signal Repetition Neyman-Pearson Theory of Testing Hypotheses with Application to Radar Signal Shape and Matched Filters Transmission of Two Known Messages of Arbitrary Shape Sampling of Band-limited Signals Decision-theory Approach to M -ary Signal Transmission

This chapter contains sections titled: Phase Modulation Frequency Modulation Spectral Resolution for Sinusoidal Angle Modulation Transmission through Linear Networks The FM Interference Problem Compound CW Modulation Systems

This chapter contains sections titled: Summary of Statistical Properties of Noise Orthogonal Series Representations of Noise A Simple Application to Binary Transmission Narrowband Noise and Envelope Detection Application to Binary Transmission Hilbert-transform Representation of Signals Preenvelope and Envelope of Signals; Application to Noise Low-pass Equivalents of Bandpass Signals ]]>

This chapter contains sections titled: S/N Ratios in AM Spectral Analysis of Envelope Detectors Correlation-function Method of Determining Power Spectrum Frequency-modulation Noise Analysis FM Noise Output, Carrier Absent Second Threshold in FM: Decrease in Output Signal Zero-crossing Analysis A Heuristic Approach to FM Threshold Analysis��-��Rice's ?>Clicks ?> Analysis Threshold Extension in FM: FMFB Demodulators and Phase-locked Loops FM Spectrum Analysis, Noiselike Modulating Signal

This chapter contains sections titled: Role of Fading Channels within the Radio Spectrum Phenomenological Descriptions of Multipath and Fading High-frequency Ionospheric-skywave Propagation Tropospheric-scatter Propagation Single Binary Channels in Slow, Nonselective Rayleigh Fading Signal Behavior in Channels with Arbitrary Selectivity and Rapidity

This chapter contains sections titled: Optimum Combining for Digital Signaling in Slow, Nonselective Fading Performance of Quadratic Combiner Systems in Slow, Multiplicative Fading Performance of Suboptimal Systems Diversity Operation Involving Energy Sharing and Energy Detection Wideband Antimultipath Systems (Rake)

Recently, NASA formally completed the Polymer Energy Rechargeable System (PERS) Program, which was established in 2000 in collaboration with the Air Force Research Laboratory (AFRL) to support the development of polymer-based, lithium-based cell chemistries and battery technologies to address the next generation of aerospace applications and mission needs. The goal of this program was to ultimately develop an advanced, space-qualified battery technology, which embodied a solid polymer electrolyte (SPE) and complementary components, with improved performance characteristics that would address future aerospace battery requirements. Programmatically, the PERS initiative exploited both interagency collaborations to address common technology and engineering issues and the active participation of academia and private industry. The initial program phases focused on R&D activities to address the critical technical issues and challenges at the cell level. A variety of cell and polymeric electrolyte concepts were pursued as part of the development efforts undertaken at numerous governmental, industrial and academic laboratories. Numerous candidate electrolyte materials were developed, synthesized and optimized for evaluation. Utilizing the component screening facility and the "standardized" test procedures developed at the NASA Glenn Research Center, electrochemical screening and performance evaluations of promising candidate materials were completed. This overview summarizes test results for a variety of candidate electrolyte materials that were developed under the PERS Program. Electrolyte properties are contrasted and compared to the original project goals, and the strengths and weaknesses of the electrolyte chemistries are discussed. Limited cycling data for full-cells using lithium metal and vanadium oxide electrodes are also presented. Based on measured electrolyte properties, the projected performance characteristics and temperature limitations of batteries utilizing the advanced electrolytes and components have been estimated. Limitations for the achievement of practical performance levels are also discussed, as well as needs for future research and development.

We examined the consequence of remarkably fast growth rates in transgenic fish, using swimming performance as a physiological fitness variable. Substantially faster growth rates were achieved by the insertion of an "all-salmon" growth hormone gene construct in transgenic coho salmon (Oncorhynchus kisutch). On an absolute speed basis, transgenic fish swam no faster at their critical swimming speed than smaller non-transgenic controls, and much slower than older non-transgenic controls of the same size. Thus, we find a marked trade-off between growth rate and swimming performance, and these results suggest that transgenic fish may be an excellent model to evaluate existing ideas regarding physiological design.