The Design, Development and Testing of a Propulsion System for the SNAP-1 Nanosatellite

It has frequently been proposed to use very small nanosatellites for missions requiring orbital agility. Whether it be swarms of satellites for scientific or remote-sensing measurements, constellations for communications or single satellites for remote inspection, all require some way of modifying their respective orbits. Novel, high-technology solutions to this requirement have been proposed from MEMS to solar sails. Notwithstanding the eventual availability of such advanced nanosatellite propulsion technologies, the Surrey Space Centre has developed a miniature propulsion subsystem using technology readily available today. On 28th June 2000 Surrey launched SNAP-1, the first in a series of Surrey Nanosatellite Application Platform missions. Amongst other features of this new 6.5 kg nanosatellite is a butane liquefied gas propulsion subsystem to meet the spacecraft\u27s mission requirement of 1 m/s delta V. With a total mass budget of 450 grams, including propellant, dry mass, structural support and drive electronics, this propulsion system will be one of the smallest ever to have flown on a spacecraft. This paper describes some of the interesting challenges in producing such a small system, especially in a seven month concept to launch site program. The flight propulsion system will be described, including novel techniques such as using a coiled tube in the place of a conventional propellant tank. The choice of butane as a propellant will be discussed

Triply Threaded [4]Rotaxanes

[4]Rotaxanes featuring three axles threaded through a single ring have been prepared through active metal template synthesis. Nickel-catalyzed sp3-sp3 homocouplings of alkyl bromide ‘half threads’ through 37- and 38-membered 2,2':6',2"-terpyridyl macrocycles generates triply-threaded [4]rotaxanes in up to 11 % yield. An analogous 39-membered macrocycle produced no rotaxane products under similar conditions. The constitutions of the [4]rotaxanes were determined by NMR spectroscopy and mass spectrometry. Doubly-threaded [3]rotaxanes were also obtained from the reactions but no [2]rotaxanes were isolated, suggesting that upon demetallation the axle of a singly-threaded rotaxane can slip through a macrocycle that is sufficiently large to accommodate three threads

Soliton solutions in an effective action for SU(2) Yang-Mills theory: including effects of higher-derivative term

The Skyrme-Faddeev-Niemi (SFN) model which is an O(3) $\sigma$ model in three dimensional space upto fourth-order in the first derivative is regarded as a low-energy effective theory of SU(2) Yang-Mills theory. One can show from the Wilsonian renormalization group argument that the effective action of Yang-Mills theory recovers the SFN in the infrared region. However, the thoery contains an additional fourth-order term which destabilizes the soliton solution. In this paper, we derive the second derivative term perturbatively and show that the SFN model with the second derivative term possesses soliton solutions.Comment: 7 pages, 3 figure

Detailed analysis of paternal knockout <i>Grb10 </i>mice suggests effects on stability of social behavior, rather than social dominance

Imprinted genes are highly expressed in monoaminergic regions of the midbrain and their functions in this area are thought to have an impact on mammalian social behaviors. One such imprinted gene is Grb10, of which the paternal allele is generally recognized as mediating social dominance behavior. However, there has been no detailed study of social dominance in Grb10 +/p mice. Moreover, the original study examined tube‐test behavior in isolated mice 10 months of age. Isolation testing favors more territorial and aggressive behaviors, and does not address social dominance strategies employed in group housing contexts. Furthermore, isolation stress impacts midbrain function and dominance related behavior, often through alterations in monoaminergic signaling. Thus, we undertook a systematic study of Grb10 +/p social rank and dominance behavior within the cage group, using a number of convergent behavioral tests. We examined both male and female mice to account for sex differences and tested cohorts aged 2, 6 and 10 months to examine any developments related to age. We found group‐housed Grb10 +/p mice do not show evidence of enhanced social dominance, but cages containing Grb10 +/p and wild‐type mice lacked the normal correlation between three different measures of social rank. Moreover, a separate study indicated isolation stress induced inconsistent changes in tube test behavior. Taken together, these data suggest future research on Grb10 +/p mice should focus on the stability of social behaviors, rather than dominance per se

Assessing climate effects on railway earthworks Using MASW

Many parts of the UK’s rail network were constructed in the mid‐19th century long before the advent of modern construction standards. Historic levels of low investment, poor maintenance strategies and the deleterious effects of climate change have resulted in critical elements of the rail network being at significant risk of failure. The majority of failures which have occurred over recent years have been triggered by extreme weather events. Advance assessment and remediation of earthworks is, however, significantly less costly than dealing with failures reactively. It is therefore crucial that appropriate approaches for assessment of the stability of earthworks are developed, so that repair work can be better targeted and failures avoided wherever possible. This extended abstract briefly discusses some preliminary results from an ongoing geophysical research project being carried out in order to study the impact of climate or seasonal weather variations on the stability of a century old railway embankment on the Gloucestershire Warwickshire steam railway line in Southern England

Construction of the Pauli-Villars-regulated Dirac vacuum in electromagnetic fields

Using the Pauli-Villars regularization and arguments from convex analysis, we construct solutions to the classical time-independent Maxwell equations in Dirac's vacuum, in the presence of small external electromagnetic sources. The vacuum is not an empty space, but rather a quantum fluctuating medium which behaves as a nonlinear polarizable material. Its behavior is described by a Dirac equation involving infinitely many particles. The quantum corrections to the usual Maxwell equations are nonlinear and nonlocal. Even if photons are described by a purely classical electromagnetic field, the resulting vacuum polarization coincides to first order with that of full Quantum Electrodynamics.Comment: Final version to appear in Arch. Rat. Mech. Analysi

Draft Genome Sequence of Magnetovibrio blakemorei Strain MV-1, a Marine Vibrioid Magnetotactic Bacterium.

We report here the genome sequence of Magnetovibrio blakemorei MV-1, a marine vibrioid magnetotactic bacterium with a single polar flagellum. The current assembly consists of 91 contigs with a combined size of 3,638,804 bp (54.3% G+C content). This genome allows for further investigations of the molecular biomineralization mechanisms of magnetosome formation

D-Brane Dynamics and NS5 Rings

We consider the classical motion of a probe D-brane moving in the background geometry of a ring of NS5 branes, assuming that the latter are non-dynamical. We analyse the solutions to the Dirac-Born-Infield (DBI) action governing the approximate dynamics of the system. In the near horizon (throat) approximation we find several exact solutions for the probe brane motion. These are compared to numerical solutions obtained in more general cases. One solution of particular interest is when the probe undergoes oscillatory motion through the centre of the ring (and perpendicular to it). By taking the ring radius sufficiently large, this solution should remain stable to any stringy corrections coming from open-strings stretching between the probe and the NS5-branes along the ring.Comment: 17 pages, Latex, 8 figures; References adde

Maternal Cortisol Concentrations During Pregnancy and Sex-Specific Associations With Neonatal Amygdala Connectivity and Emerging Internalizing Behaviors

Background: Maternal cortisol during pregnancy has the potential to influence rapidly developing fetal brain systems that are commonly altered in neurodevelopmental and psychiatric disorders. Research examining maternal cortisol concentrations across pregnancy and offspring neurodevelopment proximal to birth is needed to advance understanding in this area and lead to insight into the etiology of these disorders. Methods: Participants were 70 adult women recruited during early pregnancy and their infants born after 34 weeks gestation. Maternal cortisol concentrations were assessed serially over 4 days in early, mid, and late gestation. Resting state functional connectivity magnetic resonance imaging of the neonatal amygdala was examined. Mothers reported on children's internalizing behavior problems at 24 months of age. Results: Maternal cortisol concentrations during pregnancy were significantly associated with neonatal amygdala connectivity in a sex-specific manner. Elevated maternal cortisol was associated with stronger amygdala connectivity to brain regions involved in sensory processing and integration, as well as the default mode network in girls, and with weaker connectivity to these brain regions in boys. Elevated maternal cortisol was associated with higher internalizing symptoms in girls only, and this association was mediated by stronger neonatal amygdala connectivity. Conclusions: Normative variation in maternal cortisol during pregnancy is associated with the coordinated functioning of the amygdala soon after birth in a sex-specific manner. The identified pathway from maternal cortisol to higher internalizing symptoms in girls via alterations in neonatal amygdala connectivity may be relevant for the etiology of sex differences in internalizing psychiatric disorders, which are more prevalent in women

D-brane dynamics near compactified NS5-branes

We examine the dynamics of a $Dp$-brane in the background of $k$ coincident, parallel $NS$5-branes which have had one of their common transverse directions compactified. We find that for small energy, bound orbits can exist at sufficiently large distances where there will be no stringy effects. The orbits are dependent upon the energy density, angular momentum and electric field. The analysis breaks down at radial distances comparable with the compactification radius and we must resort to using a modified form of the harmonic function in this region.Comment: Latex, 20 pages, 6 figs, references adde