Testing the Hubble Law with the IRAS 1.2 Jy Redshift Survey

We test and reject the claim of Segal et al. (1993) that the correlation of redshifts and flux densities in a complete sample of IRAS galaxies favors a quadratic redshift-distance relation over the linear Hubble law. This is done, in effect, by treating the entire galaxy luminosity function as derived from the 60 micron 1.2 Jy IRAS redshift survey of Fisher et al. (1995) as a distance indicator; equivalently, we compare the flux density distribution of galaxies as a function of redshift with predictions under different redshift-distance cosmologies, under the assumption of a universal luminosity function. This method does not assume a uniform distribution of galaxies in space. We find that this test has rather weak discriminatory power, as argued by Petrosian (1993), and the differences between models are not as stark as one might expect a priori. Even so, we find that the Hubble law is indeed more strongly supported by the analysis than is the quadratic redshift-distance relation. We identify a bias in the the Segal et al. determination of the luminosity function, which could lead one to mistakenly favor the quadratic redshift-distance law. We also present several complementary analyses of the density field of the sample; the galaxy density field is found to be close to homogeneous on large scales if the Hubble law is assumed, while this is not the case with the quadratic redshift-distance relation.Comment: 27 pages Latex (w/figures), ApJ, in press. Uses AAS macros, postscript also available at http://www.astro.princeton.edu/~library/preprints/pop682.ps.g

Geomorphic evolution of pleistocene Lake Bonneville: temporal implications for surface processes on Mars

Journal ArticlePleistocene Lake Bonneville of the Great Basin offers unparalleled insight into temporal constraints for understanding the development of similar analog environments and processes on Mars. The extensive and well preserved lake system exhibits many intact features that include: prominent shorelines, spits, bay mouth barriers, deltas, gullies, outburst channels, and playa lake features, including patterned grounds and downwind aeolian systems. Although water is recognized as a geomorphic agent on Mars, remotely sensed datasets by themselves have limited utility for inferring how long it took for the formation of specific features. With the Lake Bonneville analog, we can address how long standing water might be geomorphically effective, and infer the rate of development for specific landforms (e.g., coastlines, wavecut terraces, outflow channels, rills)

The CaMKII/NMDA receptor complex controls hippocampal synaptic transmission by kinase-dependent and independent mechanisms.

CaMKII is one of the most studied synaptic proteins, but many critical issues regarding its role in synaptic function remain unresolved. Using a CRISPR-based system to delete CaMKII and replace it with mutated forms in single neurons, we have rigorously addressed its various synaptic roles. In brief, basal AMPAR and NMDAR synaptic transmission both require CaMKIIα, but not CaMKIIβ, indicating that, even in the adult, synaptic transmission is determined by the ongoing action of CaMKIIα. While AMPAR transmission requires kinase activity, NMDAR transmission does not, implying a scaffolding role for the CaMKII protein instead. LTP is abolished in the absence of CaMKIIα and/or CaMKIIβ and with an autophosphorylation impaired CaMKIIα (T286A). With the exception of NMDAR synaptic currents, all aspects of CaMKIIα signaling examined require binding to the NMDAR, emphasizing the essential role of this receptor as a master synaptic signaling hub

Author Correction: The CaMKII/NMDA receptor complex controls hippocampal synaptic transmission by kinase-dependent and independent mechanisms.

The originally published version of this Article contained errors in Figure 5, for which we apologise. In panel c, the scatter graph was inadvertently replaced with a scatter graph comprising a subset of data points from panel d. Furthermore, the legends to Figures 5c and 5d were inverted. These errors have now been corrected in both the PDF and HTML versions of the Article, and the incorrect version of Fig. 5c is presented in the Author Correction associated with this Article

Impact of ancestral sequence reconstruction on mechanistic and structural enzymology

Ancestral sequence reconstruction (ASR) provides insight into the changes within a protein sequence across evolution. More specifically, it can illustrate how specific amino acid changes give rise to different phenotypes within a protein family. Over the last few decades it has established itself as a powerful technique for revealing molecular common denominators that govern enzyme function. Here, we describe the strength of ASR in unveiling catalytic mechanisms and emerging phenotypes for a range of different proteins, also highlighting biotechnological applications the methodology can provide.</p

Ancestral reconstruction of mammalian FMO1 enables structural determination, revealing unique features that explain its catalytic properties

Mammals rely on the oxidative flavin-containing monooxygenases (FMOs) to detoxify numerous and potentially deleterious xenobiotics; this activity extends to many drugs, giving FMOs high pharmacological relevance. However, our knowledge regarding these membrane-bound enzymes has been greatly impeded by the lack of structural information. We anticipated that ancestral-sequence reconstruction could help us identify protein sequences that are more amenable to structural analysis. As such, we hereby reconstructed the mammalian ancestral protein sequences of both FMO1 and FMO4, denoted as ancestral flavin-containing monooxygenase (AncFMO)1 and AncFMO4, respectively. AncFMO1, sharing 89.5% sequence identity with human FMO1, was successfully expressed as a functional enzyme. It displayed typical FMO activities as demonstrated by oxygenating benzydamine, tamoxifen, and thioanisole, drug-related compounds known to be also accepted by human FMO1, and both NADH and NADPH cofactors could act as electron donors, a feature only described for the FMO1 paralogs. AncFMO1 crystallized as a dimer and was structurally resolved at 3.0 Å resolution. The structure harbors typical FMO aspects with the flavin adenine dinucleotide and NAD(P)H binding domains and a C-terminal transmembrane helix. Intriguingly, AncFMO1 also contains some unique features, including a significantly porous and exposed active site, and NADPH adopting a new conformation with the 2'-phosphate being pushed inside the NADP+ binding domain instead of being stretched out in the solvent. Overall, the ancestrally reconstructed mammalian AncFMO1 serves as the first structural model to corroborate and rationalize the catalytic properties of FMO1

Effect of root spacing on interpretation of blade penetration tests-full-scale physical modelling

The spatial distribution of plant roots is an important parameter when the stability of vegetated slopes is to be assessed. Previous studies in both laboratory and field conditions have shown that a penetrometer adapted with a blade-shaped tip can be used to detect roots from sudden drops in penetrometer resistance. Such drops can be related to root properties including diameter, stiffness and strength using simpleWinkler foundation models, thereby providing a field instrument for rapid quantification of root properties and distribution. While this approach has proved useful for measuring single widely-spaced roots, it has not previously been determined how the penetrometer response changes as a result of roots being in close proximity. Therefore in this study 1-g physical modelling (at 1:1 scale) was conducted to study the effect of vertical root spacing using horizontal, straight 3D-printed root analogues. Results showthatwhen roots are closely spaced, there is significant interaction between them, resulting in higher apparent root displacements to failure and an increased amount of energy being dissipated. This preliminary work shows that the interpretive models used to analyse the penetrometer trace require further development to account for root-soil-root interactions in densely rooted soil.</p

Comparison of new <i>in situ </i>root-reinforcement measuring devices to existing techniques

Mechanical root-reinforcement is difficult to quantify. Existing in-situ methods are cumbersome, while modelling requires parameters which are difficult to acquire. In this paper, two new in-situ measurement devices are introduced ('cork screw' and 'pin vane') and their performance is compared to field vane and laboratory direct shear strength measurements in fallow and rooted soil. Both new methods show a close correlation with field vane readings in fallow soil. Tests in reinforced soil show that both new methods can be installed without significant root disturbance. The simplicity of both new methods allows for practical in-situ use and both can be used to study soil stress-strain behaviour, thus addressing some major limitations in existing methodologies for characterising rooted soil.</p

Long-Term Potentiation: One Kind or Many?

Do neurobiologists aim to discover natural kinds? I address this question in this chapter via a critical analysis of classification practices operative across the 43-year history of research on long-term potentiation (LTP). I argue that this 43-year history supports the idea that the structure of scientific practice surrounding LTP research has remained an obstacle to the discovery of natural kinds

Nonmonotonical crossover of the effective susceptibility exponent

We have numerically determined the behavior of the magnetic susceptibility upon approach of the critical point in two-dimensional spin systems with an interaction range that was varied over nearly two orders of magnitude. The full crossover from classical to Ising-like critical behavior, spanning several decades in the reduced temperature, could be observed. Our results convincingly show that the effective susceptibility exponent gamma_eff changes nonmonotonically from its classical to its Ising value when approaching the critical point in the ordered phase. In the disordered phase the behavior is monotonic. Furthermore the hypothesis that the crossover function is universal is supported.Comment: 4 pages RevTeX 3.0/3.1, 5 Encapsulated PostScript figures. Uses epsf.sty. Accepted for publication in Physical Review Letters. Also available as PostScript and PDF file at http://www.tn.tudelft.nl/tn/erikpubs.htm