Non‐geostationary satellite orbit communications satellite constellations history

This special issue of the journal on ‘constellations’ comes at a critical time in their development as a second wave of such non‐geostationary satellite orbit (NGSO) systems is being planned and deployed. These mega‐constellations as they have become known are, with a few exceptions, very much larger than those in the first wave and are focused on broadband and 5G applications rather than speech and narrow band data as those deployed in the first wave during the 1990s. However, as we explain in this editorial, there are many similarities in the design and business plans to the first wave and, perhaps, many similar lessons to be learned.     

Design of Trehalose-Based Amide/Sulfonamide C-type Lectin Receptor Signaling Compounds

Mincle agonists have been shown to induce inflammatory cytokine production, such as tumor necrosis factor-alpha (TNF) and promote the development of a Th1/Th17 immune response that might be crucial to development of effective vaccination against pathogens such as Mycobacterium tuberculosis. As an expansion of our previous work, a library of 6,6′-amide and sulfonamide α,α-d -trehalose compounds with various substituents on the aromatic ring was synthesized efficiently in good to excellent yields. These compounds were evaluated for their ability to activate the human C-type lectin receptor Mincle by the induction of cytokines from human peripheral blood mononuclear cells. A preliminary structure–activity relationship (SAR) of these novel trehalose diamides and sulfonamides revealed that aryl amide-linked trehalose compounds demonstrated improved activity and relatively high potency cytokine production compared to the Mincle ligand trehalose dibehenate adjuvant (TDB) and the natural ligand trehalose dimycolate (TDM) inducing dose-dependent and human-Mincle-specific stimulation in a HEK reporter cell line.     

Diffuse color patterning using blended electrochromic polymers for proof‐of‐concept adaptive camouflage plaques

A study using three different pairs of electrochromic polymers (ECPs) synthesized onto plaques by means of a modified vapor phase polymerization (VPP) technique is presented. Restriction of the respective polymerization times, allowed both faster and slower polymerizing monomers to be controlled, and produced blended plaques with visually diffuse interfaces. The ECPs within the blended plaques retain their individual electrochromic behavior and when encapsulated into an electrochromic device, show outstanding optical switching performance with little degradation evident over 10,000 cycles, coupled with a switching time of the order of 1 second. Blends also allow multiple diffuse color changes within an electrochromic device, due to the difference in oxidation potentials of the individual ECPs, making them candidates for adaptive camouflage use. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42158.     

Phase equilibria studies in the CaO–SiO2–Al2O3–MgO system with CaO/SiO2 ratio of 0.9

Phase equilibria and liquidus temperatures in the CaO–SiO₂–Al₂O₃–MgO system at a CaO/SiO₂ weight ratio of 0.9 in the liquid phase have been experimentally determined employing high-temperature equilibration and quenching technique followed by electron probe X-ray microanalysis. Isotherms at 1573, 1623, 1673, and 1773 K were determined and the primary phase fields of wollastonite, melilite, olivine, periclase, spinel, and corundum have been located. Compositions of the olivine and melilite solid solutions were analyzed and discussed. Comparisons between the newly constructed diagram, existing data, and FactSage predicted phase diagrams were performed and differences were discussed. The present study will be useful for guidance of industrial practices and further development of thermodynamic modeling.     

Examining housing discrimination across race,gender and felony history

Those who have been convicted of crimes are subjected to a stigma that affects many aspects of their social lives. The “felon” label brings collateral consequences that make it difficult to obtain basic human needs, including housing. This study uses the audit method to examine the effects of race, gender, and criminal history on housing outcomes. Testers, exhibiting characteristics suggestive of race and gender and disclosing one of three offenses, placed phone calls to rental property owners across the Midwest to inquire about renting a property. We found powerful negative effects for those with a criminal record seeking apartments, regardless of whether the offense was sexual or drug-related. However, we found no differences between minority and non-minority testers. We explain these findings in the context of housing as an essential resource for formerly incarcerated individuals.     

Physico-chemical controls on phosphorus cycling in two lowland streams. Part 2--the sediment phase

This article investigates the temporal and spatial controls on sediment-phosphorus (P) dynamics in two contrasting sub-catchments of the River Kennet, England. Suspended sediment (collected under representative flow conditions) and size-fractionated bedload (collected weekly for one year) from the Rivers Lambourn and Enborne was analysed for a range of physico-chemical determinands. Total P concentrations were highest in the most mobile fractions of sediment: suspended sediment, fine silt and clay and organic matter (mean concentrations of 1758, 1548 and 1440 microg P g(-1) dry sediment, respectively). Correlation analysis showed significant relationships between total P and total iron (n= 110), total manganese (n= 110), organic matter (n= 110) and specific surface area (n= 28) in the Lambourn (r2 0.71, 0.68, 0.62 and 0.52, respectively) and between total P and total iron (n= 110), total manganese (n= 110) and organic matter (n= 110) in the Enborne (r2 0.74, 0.85 and 0.68, respectively). These data highlight the importance of metal oxyhydroxide adsorption of P on fine particulates and organic matter. However, high total P concentrations in the granule gravel and coarse sand size fraction during the summer period (mean concentration 228 microg P g(-1) dry sediment) also highlight the role of calcite co-precipitation on P dynamics in the Lambourn. P to cation ratios in Lambourn sediment indicated that fine silt and clay and granule gravel and coarse sand size fractions were potential sources of P release to the water column during specific periods of the summer and autumn. In the Enborne, however, only the granule gravel and coarse sand size fraction had high ratios and a slow, constant release of P was observed. In addition, scanning electron microscopy work confirmed the association of P with calcite in the Lambourn and P with iron on clay particles in the Enborne. The study highlighted the importance of the chemical and physical properties of the sediment in influencing the mechanisms controlling P storage and release within river channels.     

Adverse effects of pore-pressure drainage on stress measurements performed in deep tunnels: an example from the Lower Kihansi hydroelectric power project, Tanzania

We describe a campaign to measure stress within a gneissic ridge near the edge of the Tanzanian craton. The measurements were conducted to determine whether the level of minimum principal stress along the trajectory of a hydropower pressure tunnel attained the level of 10 MPa, as required to leave the tunnel unlined. Extrapolation of early hydrofracture and overcoring measurements conducted mostly in boreholes drilled behind face suggested that the requisite level was not quite met. However, the minimum principal stress estimates from the instantaneous shut-in pressures (ISIPs) of the hydrofracture tests generally showed large scatter and were sometimes less than the estimated pre-disturbance pore pressure. It was suspected that the stress tests were affected by stress alteration around the tunnel due to pore pressure drainage. To test this, hydrofracture and hydro-jacking tests were conducted in two long, horizontal holes drilled ahead of the excavation face into relatively undrained rock, and a third vertical hole drilled behind the face. All were near the critical location where the pressure tunnel enters the powerhouse. The minimum principal stress estimates in the ahead-of-face holes were found to be much higher than those from the behind-face hole, consistent with the hypothesis. Estimates of the drawdown in pore pressure about the tunnel and test holes suggested a coupling factor between drawdown and minimum principal stress magnitude of approximately unity. This is slightly higher than predicted from an hydromechanical model that explains the coupling between the pore-pressure and stress fields in terms of fracture compliance and poro-elasticity of intact blocks. Nonetheless, both results demonstrate the importance of accounting for drawdown when conducting stress measurements in boreholes drilled from tunnels. We also note some instances where hydrofracture and hydro-jacking tests yielded different estimates for the minimum principal stress magnitude.     

Methods to calculate the response time of heat and smoke detectors installed below large unobstructed ceilings

Recently developed methods to calculate the time required for ceiling mounted heat and smoke detectors to respond to growing fires are reviewed. A computer program that calculates activation times for both fixed temperature and rate of rise heat detectors in response to fires that increase in heat release rate proportionally with the square of time from ignition is given. This program produces nearly equivalent results to the tables published in Appendix C, Guide for Automatic Fire Detector Spacing (NFPA 72E, 1984). A separate method and corresponding program are provided to calculate response time for fires having arbitrary heat release rate histories. This method is based on quasi-steady ceiling layer gas flow assumptions. Assuming a constant proportionality between smoke and heat released from burning materials, a method is described to calculate smoke detector response time, modeling the smoke detector as a low temperature heat detector in either of the two response time models.Nomenclature A g/(c _p T ) - c _p specific heat capacity of ambient air - C _s smoke mass concentration - D effective binary diffusion coefficient - g acceleration of gravity - H vertical distance from fuel to ceiling - I light intensity - I_o initial light intensity - L light beam length - _s smoke gas mass production rate per unit volume - OD optical density per unit length (see Equation 8) - fire energy release rate - energy release rate per unit volume - r radial distance from fire axis to the detector - RTI response time index, the product of the detector thermal time constant and the square root of the gas speed used in the test to measure the time constant.⁹ - t time - t ₂ ^* dimensionless time t/[A^{–1/5 –1/5} H^4/5) - (t ₂ ^* ) _f dimensionless time for time delay for gas front travel - T ambient temperature - T gas temperature at detector location - T _s temperature of detector sensing elements - T T — T - T ₂ ^* dimensionless temperature differences T/[A^2/5(T _f /g) ^2/5 H^–3/5] - U gas speed at the detector location - U ₂ ^* dimensionless gas speed U/[A H]^1/5 - Y _s local ratio of smoke mass to total mass in flow - proportionality constant for t²-fire growth = Q/t² - ambient air density Reference: David D. Evans and David W. Stroup, Methods to Calculate the Response Time of Heat and Smoke Detectors Installed Below Large Unobstructed Ceilings,Fire Technology, Vol. 22, No. 1, February 1985, p. 54. Note: This paper is a contribution of the National Bureau of Standards and is not subject to copyright.     

Biodegradation of urea in river waters under controlled laboratory conditions

The biodegradation of urea in river waters has been evaluated under laboratory conditions. Urea will degrade to ammonia at a rate depending on the bacterial state of the river water and on the water temperature. Under normal conditions no breakdown may be expected to occur at temperatures below 8°C for 14 days contact. In river waters with a high suspended solids content, simulating extreme winter river conditions, a maximum breakdown of 3–6 per cent daily of the original urea levels was found for temperatures not exceeding 8°C during the first 7 days contact.     

The collapse of welded aluminium plate girders—an experimental study

Twenty-two tests conducted to study the collapse behaviour of welded aluminium girders are described. The girders are of varying proportions, have transverse or longitudinal web stiffeners and are subjected to different combinations of shear and bending loads. It is observed that, although shear sway mechanisms similar to those for steel girders do develop, the webs of aluminium girders may fracture in the heat affected zones adjacent to the perimeter welds. These fractures develop at some stage during the formation of the collapse mechanism and are the consequence, rather than the cause, of failure. It is shown that the tension field theory, originally developed for steel girders, may overestimate the shear-carrying capacity of aluminium girders and it is concluded that the theory requires some modification before it can be applied with confidence to aluminium girders.