A Multi-User Carrier Structure for Deploying Pegasus-Launched Micro-Satellites

Now that the viability of the Pegasus air launched booster has been demonstrated, it is possible, and indeed appropriate, to devise methods for exploiting the launcher so that it can launch multiple micro-satellites. Such spacecraft may be launched for a single user, or the capacity of a single launcher may be divided among multiple users. In fact, not all of the satellites on a single launch need to be placed into the same orbit. This paper describes a concept, developed by OSC, to place multiple micro-satellites into various orbits using a single Pegasus launch vehicle. The concept makes use of separable \u27\u27pallets which may be stacked, one on top of the other within the Pegasus fairing. Each pallet can have an integral propulsion system and may transport from one to six micro-satellites into an orbit modified from the reference orbit provided by the launch vehicle. Examples are given as to how the system may be used to implement a variety of mission options. If a constellation of communications satellites are deployed by this approach, global coverage can be provided at what is believed to be the lowest cast available today. The mechanical and propulsion system designs of the pallet are discussed and user constraints are reviewed. The performance capability of the Pegasus vehicle is reviewed as it impacts the individual micro-satellite payload mass

Insulin resistance induced by antiretroviral drugs: Current understanding of molecular mechanisms

The increase in incidence of HIV infection continues to be a major public health problem across the world, but more especially in sub-Saharan Africa. Treatment with highly active antiretroviral therapy (HAART) has improved the prognosis of patients with AIDS, but it has also increased the incidence of various metabolic disorders, in particular insulin resistance accompanied by dyslipidaemia, hyperglycaemia and lipodystrophy. This is often accompanied by frank type 2 diabetes and increased mortality from cardiovascular disease. It is important to understand the mechanistic basis for these side-effects as the incidence of these is likely to increase as the rollout of antiretroviral drugscontinues.Keywords: HIV protease inhibitors; insulin resistance; insulin signalling pathwa

The In-Orbit Performance of Four Microsat Spacecraft

On January 22, 1990, Ariane V-35 placed four Microsat spacecraft into orbit. The orbit achieved is nearly perfectly sun synchronous at 800 km altitude. The satellites, cubic structures measuring only 23 cm per side, were developed by the Radio Amateur Satellite Corporation of North America (AMSAT-NA). The time required to complete the project, from conception to delivery of the four satellites to Kourou, was exactly two years. Each satellite in orbit has a different mission and is performing in accordance with its intended design, although additional software is still being written to enhance the operating characteristics for each mission. This paper reviews the design objectives of the four spacecraft and summarizes their in-orbit performance against these prelaunch technical objectives. The level of technology employed by the Microsat spacecraft is briefly discussed and the software approach taken in implementing a real-time, multitasking operating system is summarized. The paper reviews the AMSAT experience as the first payload user group of the Ariane ASAP structure. Some of the findings regarding the current technology and how it may be expanded to fulfill other mission needs has been touched upon

Fusion to snowdrop lectin magnifies the oral activity of insecticidal omega-Hexatoxin-Hv1a peptide by enabling its delivery to the central nervous system

Background: The spider-venom peptide v-hexatoxin-Hv1a (Hv1a) targets insect voltage-gated calcium channels, acting directly at sites within the central nervous system. It is potently insecticidal when injected into a wide variety of insect pests, but it has limited oral toxicity. We examined the ability of snowdrop lectin (GNA), which is capable of traversing the insect gut epithelium, to act as a ‘‘carrier’’ in order to enhance the oral activity of Hv1a. Methodology/Principal Findings: A synthetic Hv1a/GNA fusion protein was produced by recombinant expression in the yeast Pichia pastoris. When injected into Mamestra brassicae larvae, the insecticidal activity of the Hv1a/GNA fusion protein was similar to that of recombinant Hv1a. However, when proteins were delivered orally via droplet feeding assays, Hv1a/ GNA, but not Hv1a alone, caused a significant reduction in growth and survival of fifth stadium Mamestra brassicae (cabbage moth) larvae. Feeding second stadium larvae on leaf discs coated with Hv1a/GNA (0.1–0.2% w/v) caused $80% larval mortality within 10 days, whereas leaf discs coated with GNA (0.2% w/v) showed no acute effects. Intact Hv1a/GNA fusion protein was delivered to insect haemolymph following ingestion, as shown by Western blotting. Immunoblotting of nerve chords dissected from larvae following injection of GNA or Hv1a/GNA showed high levels of bound proteins. When insects were injected with, or fed on, fluorescently labelled GNA or HV1a/GNA, fluorescence was detected specifically associated with the central nerve chord. Conclusions/Significance: In addition to mediating transport of Hv1a across the gut epithelium in lepidopteran larvae, GNA is also capable of delivering Hv1a to sites of action within the insect central nervous system. We propose that fusion to GNA provides a general mechanism for dramatically enhancing the oral activity of insecticidal peptides and proteins

Turning the tide: rhythmic aggregation behaviour in Anurida maritima (Collembola) is entrained by inundation

Numerous foreshore species evolved the ability to predict tidal change and adjust behaviour and metabolism accordingly. The intertidal collembolan Anurida maritima (Guérin-Méneville, 1836) shows endogenously controlled rhythmic changes in behaviour that anticipate the tides. Animals forage during low tide and hide in large aggregations in the substrate during high tide. Here, artificial tidal environments and time-lapse photography were used to investigate if this behaviour is responsive to key environmental cues. It is shown that the precise rhythmicity of aggregation behaviour is dependent on periodic inundations. In the absence of such inundations, rhythmic aggregation patterns dissipate and are no longer accurate after 14 days. Slowly shifting the artificial tides, showed that rhythmic aggregation behaviour in A. maritima is responsive and adjusts to a newly-imposed tidal regimen. This suggests that the species has the ability to synchronise to newly encountered tidal conditions under natural conditions. The findings provide a robust foundation for advancing detailed chronobiological research on A. maritima as a model organism to gain a deeper understanding of biological time-keeping

Time variation of fundamental couplings and dynamical dark energy

Scalar field dynamics may give rise to a nonzero cosmological variation of fundamental constants. Within different scenarios based on the unification of gauge couplings, the various claimed observations and bounds may be combined in order to trace or restrict the time history of the couplings and masses. If the scalar field is responsible for a dynamical dark energy or quintessence, cosmological information becomes available for its time evolution. Combining this information with the time variation of couplings, one can determine the interaction strength between the scalar and atoms, which may be observed by tests of the Weak Equivalence Principle. We compute bounds on the present rate of coupling variation from experiments testing the differential accelerations for bodies with equal mass and different composition and compare the sensitivity of various methods. In particular, we discuss two specific models of scalar evolution: crossover quintessence and growing neutrino models.Comment: 26 pages, 2 figures; minor typos & added references, to be published in JCA

Influence of synoptic atmospheric conditions on movement of individual sea-ice floes in Fram Strait, late summer 2010

In this paper we investigate the effect on sea-ice movement of changes in the synoptic atmospheric conditions in late boreal summer 2010. Our study area is the western Fram Strait, a crucial passage for the transport of ice out of the Arctic basin. Ice dynamics here affect the movement of ice in the East Greenland Current, the transpolar drift and ice extent in the Arctic Ocean. In contrast to other times of the year, when the Fram Strait wind field is characterized by strong, persistent northerlies, we show that the weaker, more variable winds typical during late summer for the Fram Strait can slow movement of ice floes out of the area, thus slowing the export of ice from the Arctic Ocean at the end of summer, a time crucial for ice export. The Arctic Ocean could lose even more of the ice that survives the summer if this was not the case. This would leave the Arctic Ocean in an even more vulnerable position with regard to the amount of multi-year ice remaining the following summer