Surface materials of the Viking landing sites

Martian surface materials viewed by the two Viking landers (VL-1 and VL-2) range from fine-grained nearly cohesionless soils to rocks. Footpad 2 of VL-1, which landed at 2.30 m/s, penetrated 16.5 cm into very fine grained dunelike drift material; footpad 3 rests on a rocky soil which it penetrated ≈3.6 cm. Further penetration by footpad 2 may have been arrested by a hard substrate. Penetration by footpad 3 is less than would be expected for a typical lunar regolith. During landing, retroengine exhausts eroded the surface and propelled grains and rocks which produced craters on impact with the surface. Trenches excavated in drift material by the sampler have steep walls with up to 6 cm of relief. Incipient failure of the walls and failures at the end of the trenches are compatible with a cohesion near 10–10^2 N/m^2. Trenching in rocky soil excavated clods and possibly rocks. In two of five samples, commanded sampler extensions were not achieved, a situation indicating that buried rocks or local areas with large cohesions (≥10 kN/m^2) or both are present. Footpad 2 of VL-2, which landed at a velocity between 1.95 and 2.34 m/s, is partly on a rock, and footpad 3 appears to have struck one; penetration and leg strokes are small. Retroengine exhausts produced more erosion than occurred for VL-1 owing to increased thrust levels just before touchdown. Deformations of the soil by sampler extensions range from doming of the surface without visible fracturing to doming accompanied by fracturing and the production of angular clods. Although rocks larger than 3.0 cm are abundant at VL-1 and VL-2, repeated attempts to collect rocks 0.2–1.2 cm across imbedded in soil indicate that rocks in this size range are scarce. There is no evidence that the surface sampler of VL-2, while it was pushing and nudging rocks ≈25 cm across, spalled, chipped, or fractured the rocks. Preliminary analyses of surface sampler motor currents (≈25 N force resolution) during normal sampling are consistent with cohesionless frictional soils (ϕ ≈ 36°) or weakly cohesive frictionless soils (C < 2 kN/m^2). The soil of Mars has both cohesion and friction

ERK/MAPK Signaling Is Required for Pathway-Specific Striatal Motor Functions

The ERK/MAPK intracellular signaling pathway is hypothesized to be a key regulator of striatal activity via modulation of synaptic plasticity and gene transcription. However, prior investigations into striatal ERK/MAPK functions have yielded conflicting results. Further, these studies have not delineated the cell-type-specific roles of ERK/MAPK signaling due to the reliance on globally administered pharmacological ERK/MAPK inhibitors and the use of genetic models that only partially reduce total ERK/MAPK activity. Here, we generated mouse models in which ERK/MAPK signaling was completely abolished in each of the two distinct classes of medium spiny neurons (MSNs). ERK/MAPK deletion in D1R-MSNs (direct pathway) resulted in decreased locomotor behavior, reduced weight gain, and early postnatal lethality. In contrast, loss of ERK/MAPK signaling in D2R-MSNs (indirect pathway) resulted in a profound hyperlocomotor phenotype. ERK/MAPK-deficient D2R-MSNs exhibited a significant reduction in dendritic spine density, markedly suppressed electrical excitability, and suppression of activity-associated gene expression even after pharmacological stimulation. Our results demonstrate the importance of ERK/MAPK signaling in governing the motor functions of the striatal direct and indirect pathways. Our data further show a critical role for ERK in maintaining the excitability and plasticity of D2R-MSNs

A Polymorphism in the α4 Nicotinic Receptor Gene (Chrna4) Modulates Enhancement of Nicotinic Receptor Function by Ethanol

Several studies indicate that ethanol enhances the activity of α4β2 nicotinic acetylcholine receptors (nAChR). Our laboratory has identified a polymorphism in the α4 gene that results in the substitution of an alanine (A) for threonine (T) at amino acid position 529 in the second intracellular loop of the α4 protein. Mouse strains expressing the A variant have, in general, greater nAChR-mediated 86 Rb + efflux in response to nicotine than strains with the T variant. However, the possibility of the polymorphism modulating the effects of ethanol on the 86 Rb + efflux response has not been investigated. Methods : We have used the 86 Rb + efflux method to study the acute effects of ethanol on the function of the α4β2 nAChR in the thalamus in six different mouse strains. Experiments were also performed on tissue samples taken from F2 intercross animals. The F2 animals were derived from A/J mice crossed with a substrain of C57BL/6J mice that carried a null mutation for the gene encoding the β2 nAChR subunit. Results : In strains carrying the A polymorphism (A/J, AKR/J, C3H/Ibg), coapplication of ethanol (10–100 mM) with nicotine (0.03–300 μM) increased maximal ion flux when compared with nicotine alone with no effect on agonist potency. In contrast, ethanol had little effect on the nicotine concentration-response curve in tissue prepared from strains carrying the T polymorphism (Balb/Ibg, C57BL/6J, C58/J). Experiments with the F2 hybrids demonstrated that one copy of the A polymorphism was sufficient to produce a significant enhancement of nAChR function by ethanol (50 mM) in animals that were also β2 +/+. Ethanol had no effect on nicotine concentration-response curves in T/T β2 +/+ animals. Conclusions : The results suggest that the A/T polymorphism influences the initial sensitivity of the α4β2 nAChR to ethanol.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65432/1/01.ALC.0000067973.41153.BC.pd

Comparison of Motion Correction Methods Incorporating Motion Modelling for PET/CT Using a Single Breath Hold Attenuation Map

Introducing motion models into respiratory motion correction methods can lead to a reduction in blurring and artefacts. However, the pool of research where motion modelling methods are applied to combined positron emission tomography and computed tomography is relatively shallow. Previous work used non-attenuation corrected time-of-flight data to fit motion models, not only to motion correct the volumes themselves, but also to warp a single attenuation map to the positions of the initial gated data. This work seeks to extend previous work to offer a comparison of respiratory motion correction methods, not only with and without motion models, but also to compare pair-wise and group-wise registration techniques, on simulation data, in a low count scenario, where the attenuation map is from a pseudo-breath hold acquisition. To test the methods, 4-Dimensional Extended Cardiac Torso images are constructed, simulated and reconstructed without attenuation correction, then motion corrected using one of pair-wise, pair-wise with motion model, group-wise and group-wise with motion model registration. Next these motion corrected volumes are registered to the breath hold attenuation map. The positron emission tomography data are then reconstructed using deformed attenuation maps and motion corrected. Evaluation compares the results of these methods against non-motion corrected and motion free examples. Results indicate that the incorporation of motion models and group-wise registration, improves contrast and quantification

Hobson’s choice? Constraints on accessing spaces of creative production

Successful creative production is often documented to occur in urban areas that are more likely to be diverse, a source of human capital and the site of dense interactions. These accounts chart how, historically, creative industries have clustered in areas where space was once cheap in the city centre fringe and inner city areas, often leading to the development of a creative milieu, and thereby stimulating further creative production. Historical accounts of the development of creative areas demonstrate the crucial role of accessible low-cost business premises. This article reports on the findings of a case study that investigated the location decisions of firms in selected creative industry sectors in Greater Manchester. The study found that, while creative activity remains highly concentrated in the city centre, creative space there is being squeezed and some creative production is decentralizing in order to access cheaper premises. The article argues that the location choices of creative industry firms are being constrained by the extensive city centre regeneration, with the most vulnerable firms, notably the smallest and youngest, facing a Hobson’s choice of being able to access low-cost premises only in the periphery. This disrupts the delicate balance needed to sustain production and begs the broader question as to how the creative economy fits into the existing urban fabric, alongside the competing demands placed on space within a transforming industrial conurbation

Lunar surface mechanical properties

The surface material at the Surveyor 5 site is granular and slightly cohesive. Spacecraft footpads plowed trenches in this material as the spacecraft slid during landing. For a compressible soil model, a static bearing capacity of 2.7 newtons/cm^2 gave best agreement with the observations. Static firing of the vernier engines against the surface moved surface particles; a crater 20 cm in diameter and about 1 cm deep was produced, apparently at engine shutdown. The permeability of the soil to gases, to a depth of about 25 cm, is 1 × 10^(−8) cm^2, corresponding to soil particles mostly 2 to 60 μ in diameter

Photochemistry of Furyl- and Thienyldiazomethanes: Spectroscopic Characterization of Triplet 3-Thienylcarbene

Photolysis (λ \u3e 543 nm) of 3-thienyldiazomethane (1), matrix isolated in Ar or N2 at 10 K, yields triplet 3-thienylcarbene (13) and α-thial-methylenecyclopropene (9). Carbene 13 was characterized by IR, UV/vis, and EPR spectroscopy. The conformational isomers of 3-thienylcarbene (s-E and s-Z) exhibit an unusually large difference in zero-field splitting parameters in the triplet EPR spectrum (|D/hc| = 0.508 cm–1, |E/hc| = 0.0554 cm–1; |D/hc| = 0.579 cm–1, |E/hc| = 0.0315 cm–1). Natural Bond Orbital (NBO) calculations reveal substantially differing spin densities in the 3-thienyl ring at the positions adjacent to the carbene center, which is one factor contributing to the large difference in D values. NBO calculations also reveal a stabilizing interaction between the sp orbital of the carbene carbon in the s-Z rotamer of 13 and the antibonding σ orbital between sulfur and the neighboring carbon—an interaction that is not observed in the s-E rotamer of 13. In contrast to the EPR spectra, the electronic absorption spectra of the rotamers of triplet 3-thienylcarbene (13) are indistinguishable under our experimental conditions. The carbene exhibits a weak electronic absorption in the visible spectrum (λmax = 467 nm) that is characteristic of triplet arylcarbenes. Although studies of 2-thienyldiazomethane (2), 3-furyldiazomethane (3), or 2-furyldiazomethane (4) provided further insight into the photochemical interconversions among C5H4S or C5H4O isomers, these studies did not lead to the spectroscopic detection of the corresponding triplet carbenes (2-thienylcarbene (11), 3-furylcarbene (23), or 2-furylcarbene (22), respectively)

REC, Drosophila MCM8, Drives Formation of Meiotic Crossovers

Crossovers ensure the accurate segregation of homologous chromosomes from one another during meiosis. Here, we describe the identity and function of the Drosophila melanogaster gene recombination defective (rec), which is required for most meiotic crossing over. We show that rec encodes a member of the mini-chromosome maintenance (MCM) protein family. Six MCM proteins (MCM2–7) are essential for DNA replication and are found in all eukaryotes. REC is the Drosophila ortholog of the recently identified seventh member of this family, MCM8. Our phylogenetic analysis reveals the existence of yet another family member, MCM9, and shows that MCM8 and MCM9 arose early in eukaryotic evolution, though one or both have been lost in multiple eukaryotic lineages. Drosophila has lost MCM9 but retained MCM8, represented by REC. We used genetic and molecular methods to study the function of REC in meiotic recombination. Epistasis experiments suggest that REC acts after the Rad51 ortholog SPN-A but before the endonuclease MEI-9. Although crossovers are reduced by 95% in rec mutants, the frequency of noncrossover gene conversion is significantly increased. Interestingly, gene conversion tracts in rec mutants are about half the length of tracts in wild-type flies. To account for these phenotypes, we propose that REC facilitates repair synthesis during meiotic recombination. In the absence of REC, synthesis does not proceed far enough to allow formation of an intermediate that can give rise to crossovers, and recombination proceeds via synthesis-dependent strand annealing to generate only noncrossover products