Observations on the regulation of uricase activity during development of Drosophila melanogaster

To elucidate the mechanisms involved in the regulation of uricase activity in Drosophila melanogaster , a comparative analysis of the patterns of uricase activity during development was undertaken for the wild type, Ore-R , and the mutants ry 2 and ma-1 . Uricase activity in ry 2 and ma-l , unlike that in Ore-R , increased rapidly following emergence of the adult. This study indicates that uricase in Drosophila , in contrast to that in several microorganisms, is not induced by uric acid, since ry 2 and ma-l with no detectable uric acid have higher activity than the wild type.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44180/1/10528_2004_Article_BF00485555.pd

On wormholes with arbitrarily small quantities of exotic matter

Recently several models of traversable wormholes have been proposed which require only arbitrarily small amounts of negative energy to hold them open against self-collapse. If the exotic matter is assumed to be provided by quantum fields, then quantum inequalities can be used to place constraints on the negative energy densities required. In this paper, we introduce an alternative method for obtaining constraints on wormhole geometries, using a recently derived quantum inequality bound on the null-contracted stress-energy averaged over a timelike worldline. The bound allows us to perform a simplified analysis of general wormhole models, not just those with small quantities of exotic matter. We then use it to study, in particular, the models of Visser, Kar, and Dadhich (VKD) and the models of Kuhfittig. The VKD models are constrained to be either submicroscopic or to have a large discrepancy between throat size and curvature radius. A recent model of Kuhfittig is shown to be non-traversable. This is due to the fact that the throat of his wormhole flares outward so slowly that light rays and particles, starting from outside the throat, require an infinite lapse of affine parameter to reach the throat.Comment: 30 pages, 2 figure

Divide & Concur: Separate Opinions & Legal Change

To the extent concurring opinions elicit commentary at all, it is largely contempt. They are condemned for muddying the clarity of the law, fracturing the court, and diminishing the authoritative voice of the majority. But what if this neglect, or even disdain, of concurring opinions is off the mark? In this article, we argue for the importance of concurring opinions, demonstrating how they serve as the pulse and compass of legal change. Concurring opinions let us know what is happening below the surface of the law, thereby encouraging litigants to push the law in particular directions. This is particularly true of a type of concurrence we identify here for the frst time: the pivotal concurrence. Pivotal concurrences occur when one or more members of a court majority also choose to write separately, undercutting the majority\u27s rule in the case. Under the Supreme Court\u27s rule of fve, lower courts ought to disregard pivotal concurrences and adhere to the majority opinion. But as we show here, that is hardly the case. Utilizing a dataset created for this purpose, we demonstrate that pivotal concurrences are more common than one might think, are becoming yet more so, and-despite the Supreme Court\u27s admonition to the contrary-are taken quite seriously by lower courts. Especially in constitutional, salient cases, lower courts appear to disregard a binding majority opinion in favor of the path offered by the concurrence. Rather than condemning this, we rely on the historical development of concurrences to show the vitalfunction they play in motivating and smoothing the way for legal change. Contrary to conventional wisdom, we argue, there is beauty in a fractured court. Precisely in those cases that are most high-stakes and most contentious, it is inportant that the Justices reveal their individual views. Those views send essential signals to litigants and lawyers about where legal change is possible and where it is not, helping both to temper expectations and to move the law itself

Divide & Concur: Separate Opinions & Legal Change

To the extent concurring opinions elicit commentary at all, it is largely contempt. They are condemned for muddying the clarity of the law, fracturing the court, and diminishing the authoritative voice of the majority. But what if this neglect, or even disdain, of concurring opinions is off the mark? In this article, we argue for the importance of concurring opinions, demonstrating how they serve as the pulse and compass of legal change. Concurring opinions let us know what is happening below the surface of the law, thereby encouraging litigants to push the law in particular directions. This is particularly true of a type of concurrence we identify here for the frst time: the pivotal concurrence. Pivotal concurrences occur when one or more members of a court majority also choose to write separately, undercutting the majority\u27s rule in the case. Under the Supreme Court\u27s rule of fve, lower courts ought to disregard pivotal concurrences and adhere to the majority opinion. But as we show here, that is hardly the case. Utilizing a dataset created for this purpose, we demonstrate that pivotal concurrences are more common than one might think, are becoming yet more so, and-despite the Supreme Court\u27s admonition to the contrary-are taken quite seriously by lower courts. Especially in constitutional, salient cases, lower courts appear to disregard a binding majority opinion in favor of the path offered by the concurrence. Rather than condemning this, we rely on the historical development of concurrences to show the vitalfunction they play in motivating and smoothing the way for legal change. Contrary to conventional wisdom, we argue, there is beauty in a fractured court. Precisely in those cases that are most high-stakes and most contentious, it is inportant that the Justices reveal their individual views. Those views send essential signals to litigants and lawyers about where legal change is possible and where it is not, helping both to temper expectations and to move the law itself

Magnetic Field Effects on the Far-Infrared Absorption in Mn_12-acetate

We report the far-infrared spectra of the molecular nanomagnet Mn_12-acetate (Mn_12) as a function of temperature (5-300 K) and magnetic field (0-17 T). The large number of observed vibrational modes is related to the low symmetry of the molecule, and they are grouped together in clusters. Analysis of the mode character based on molecular dynamics simulations and model compound studies shows that all vibrations are complex; motion from a majority of atoms in the molecule contribute to most modes. Three features involving intramolecular vibrations of the Mn_12 molecule centered at 284, 306 and 409 cm-1 show changes with applied magnetic field. The structure near 284 cm$^{-1}$ displays the largest deviation with field and is mainly intensity related. A comparison between the temperature dependent absorption difference spectra, the gradual low-temperature cluster framework distortion as assessed by neutron diffraction data, and field dependent absorption difference spectra suggests that this mode may involve Mn motion in the crown.Comment: 5 pages, 4 figures, PRB accepte

Properties of 3-manifolds for relativists

In canonical quantum gravity certain topological properties of 3-manifolds are of interest. This article gives an account of those properties which have so far received sufficient attention, especially those concerning the diffeomorphism groups of 3-manifolds. We give a summary of these properties and list some old and new results concerning them. The appendix contains a discussion of the group of large diffeomorphisms of the $l$-handle 3-manifold.Comment: 20 pages. Plain-TeX, no figures, 1 Table (A4 format

Non-monotonic field-dependence of the ZFC magnetization peak in some systems of magnetic nanoparticles

We have performed magnetic measurements on a diluted system of gamma-Fe2O3 nanoparticles (~7nm), and on a ferritin sample. In both cases, the ZFC-peak presents a non-monotonic field dependence, as has already been reported in some experiments,and discussed as a possible evidence of resonant tunneling. Within simple assumptions, we derive expressions for the magnetization obtained in the usual ZFC, FC, TRM procedures. We point out that the ZFC-peak position is extremely sensitive to the width of the particle size distribution, and give some numerical estimates of this effect. We propose to combine the FC magnetization with a modified TRM measurement, a procedure which allows a more direct access to the barrier distribution in a field. The typical barrier values which are obtained with this method show a monotonic decrease for increasing fields, as expected from the simple effect of anisotropy barrier lowering, in contrast with the ZFC results. From our measurements on gamma-Fe2O3 particles, we show that the width of the effective barrier distribution is slightly increasing with the field, an effect which is sufficient for causing the observed initial increase of the ZFC-peak temperatures.Comment: LaTeX file 19 pages, 9 postscript figures. To appear in Phys. Rev. B (tentative schedule: Dec.97

Approaching human 3D shape perception with neurally mappable models

Humans effortlessly infer the 3D shape of objects. What computations underlie this ability? Although various computational models have been proposed, none of them capture the human ability to match object shape across viewpoints. Here, we ask whether and how this gap might be closed. We begin with a relatively novel class of computational models, 3D neural fields, which encapsulate the basic principles of classic analysis-by-synthesis in a deep neural network (DNN). First, we find that a 3D Light Field Network (3D-LFN) supports 3D matching judgments well aligned to humans for within-category comparisons, adversarially-defined comparisons that accentuate the 3D failure cases of standard DNN models, and adversarially-defined comparisons for algorithmically generated shapes with no category structure. We then investigate the source of the 3D-LFN's ability to achieve human-aligned performance through a series of computational experiments. Exposure to multiple viewpoints of objects during training and a multi-view learning objective are the primary factors behind model-human alignment; even conventional DNN architectures come much closer to human behavior when trained with multi-view objectives. Finally, we find that while the models trained with multi-view learning objectives are able to partially generalize to new object categories, they fall short of human alignment. This work provides a foundation for understanding human shape inferences within neurally mappable computational architectures and highlights important questions for future work

Moduli Dependent mu-Terms in a Heterotic Standard Model

In this paper, we present a formalism for computing the non-vanishing Higgs mu-terms in a heterotic standard model. This is accomplished by calculating the cubic product of the cohomology groups associated with the vector bundle moduli (phi), Higgs (H) and Higgs conjugate (Hbar) superfields. This leads to terms proportional to phi H Hbar in the low energy superpotential which, for non-zero moduli expectation values, generate moduli dependent mu-terms of the form H Hbar. It is found that these interactions are subject to two very restrictive selection rules, each arising from a Leray spectral sequence, which greatly reduce the number of moduli that can couple to Higgs-Higgs conjugate fields. We apply our formalism to a specific heterotic standard model vacuum. The non-vanishing cubic interactions phi H Hbar are explicitly computed in this context and shown to contain only four of the nineteen vector bundle moduli.Comment: 23 pages, LaTe

Dynamic Perturbations of the T-Cell Receptor Repertoire in Chronic HIV Infection and following Antiretroviral Therapy

HIV infection profoundly affects many parameters of the immune system and ultimately leads to AIDS, yet which factors are most important for determining resistance, pathology, and response to antiretroviral treatment - and how best to monitor them - remain unclear. We develop a quantitative high-throughput sequencing pipeline to characterize the TCR repertoires of HIV-infected individuals before and after antiretroviral therapy, working from small, unfractionated samples of peripheral blood. This reveals the TCR repertoires of HIV(+) individuals to be highly perturbed, with considerably reduced diversity as a small proportion of sequences are highly overrepresented. HIV also causes specific qualitative changes to the repertoire including an altered distribution of V gene usage, depletion of public TCR sequences, and disruption of TCR networks. Short-term antiretroviral therapy has little impact on most of the global damage to repertoire structure, but is accompanied by rapid changes in the abundance of many individual TCR sequences, decreases in abundance of the most common sequences, and decreases in the majority of HIV-associated CDR3 sequences. Thus, high-throughput repertoire sequencing of small blood samples that are easy to take, store, and process can shed light on various aspects of the T-cell immune compartment and stands to offer insights into patient stratification and immune reconstitution