Noise, transient dynamics, and the generation of realistic interspike interval variation in square-wave burster neurons

First return maps of interspike intervals for biological neurons that generate repetitive bursts of impulses can display stereotyped structures (neuronal signatures). Such structures have been linked to the possibility of multicoding and multifunctionality in neural networks that produce and control rhythmical motor patterns. In some cases, isolating the neurons from their synaptic network revealsirregular, complex signatures that have been regarded as evidence of intrinsic, chaotic behavior. We show that incorporation of dynamical noise into minimal neuron models of square-wave bursting (either conductance-based or abstract) produces signatures akin to those observed in biological examples, without the need for fine-tuning of parameters or ad hoc constructions for inducing chaotic activity. The form of the stochastic term is not strongly constrained, and can approximate several possible sources of noise, e.g. random channel gating or synaptic bombardment. The cornerstone of this signature generation mechanism is the rich, transient, but deterministic dynamics inherent in the square-wave (saddle-node/homoclinic) mode of neuronal bursting. We show that noise causes the dynamics to populate a complex transient scaffolding or skeleton in state space, even for models that (without added noise) generate only periodic activity (whether in bursting or tonic spiking mode).Comment: REVTeX4-1, 18 pages, 9 figure

Photometric and Obscurational Completeness

We report a method that uses "completeness" to estimate the number of exrasolar planets discovered by an observing program with a direct-imaging instrument. We develop a completeness function for Earth-like planets on "habitable" orbits for an instrument with a central field obscuration, uniform sensitivity in an annular detection zone, and limiting sensitivity that is expressed as a "delta magnitude" with respect to the star, determined by systematic effects (given adequate exposure time). We demonstrate our method of estimation by applying it to our understanding of the coronagraphic version of the Terrestrial Planet Finder (TPF-C) mission as of October 2004. We establish an initial relationship between the size, quality, and stability of the instrument's optics and its ability to meet mission science requirements. We provide options for increasing the fidelity and versatility of the models on which our method is based, and we discuss how the method could be extended to model the TPF-C mission as a whole, to verify that its design can meet the science requirements.Comment: 15 pages, 9 figures, 3 tables. High resolution version of figures may be viewed at http://sco.stsci.edu/astroph/march05/. ApJ, in pres

Introduction to the Symposium Convergence on Delaware: Corporate Bankruptcy and Corporate Governance

Bankruptcy is back. The use of Chapter 11 by large, publicly held firms was a subject of much debate in the academic and popular press in the late 1980s and the early 1990s. Firms such as Texaco, Revco, LTV, Federated Department Stores, Maxwell Communications, TWA, and Eastern Airlines all filed for bankruptcy during that time. The economic boom of the mid- and late 1990s, however, resulted in a relative dearth of high-profile bankruptcy cases. The recent economic downturn has moved corporate reorganizations back into the spotlight. The Chapter 11 filings by firms such as Enron, Global Crossing, the Loewen Group, US Airways, United Airlines, and WorldCom have focused attention once again on Chapter 11. Yet today\u27s bankruptcy practice has changed notably since our last wave of major bankruptcies. The most visible change in the reorganization of large, publicly held companies in the past fifteen years has been the rise of the Delaware bankruptcy court. As of 1990, a firm looking to reorganize under Chapter 11 would most likely file its bankruptcy petition in the Southern District of New York. Today, such firms look first and foremost to Delaware, Indeed, other courts are changing their practices to mirror those of Delaware. This switch in the lead venue of reorganization practice raises two sets of questions. The first set of questions focuses directly on this trend. Delaware\u27s prominence in corporate law has spawned a decades-old debate over why firms choose Delaware and whether the forces that drive firms to Delaware create a body of corporate law that advances or impedes societal interests. The rise of the Delaware bankruptcy court raises similar inquiries. In short, we need to explore why firms now choose to file for reorganization in Delaware, and whether the switch to Delaware is one that should be applauded or condemned

Disunity, distance, disregard: The political failure of islamism in late colonial indonesia

<p>This article examines the failure of Islamism to make a greater political impact in Indonesia through these years. That failure would have decisive ramifications for the future shape of the Indonesian state, in that it left Islamism politically and intellectually impoverished and politically marginalized in the face of the dominant claims of pseudo-secular nationalists. In part, its failure flowed from organizational and administrative weakness, but it was centrally rooted in the strategic, political and intellectual shortcomings of Islamist politicians'. That opportunity was never taken up effectively. For the most part, the list decade or so of the colonial period witnessed Islamism's intellectually unsophisticated, internally divided and counter-productive efforts to progress its agenda</p><p>Copyright (c) 2014 by SDI. All right reserved.</p><p><strong>DOI: <span><a href="http://dx.doi.org/10.15408/sdi.v16i1.488">10.15408/sdi.v16i1.488</a></span></strong></p

Trajectory Mapping and Applications to Data from the Upper Atmosphere Research Satellite

The problem of creating synoptic maps from asynoptically gathered trace gas data has prompted the development of a number of schemes. Most notable among these schemes are the Kalman filter, the Salby-Fourier technique, and constituent reconstruction. This paper explores a new technique called trajectory mapping. Trajectory mapping creates synoptic maps from asynoptically gathered data by advecting measurements backward or forward in time using analyzed wind fields. A significant portion of this work is devoted to an analysis of errors in synoptic trajectory maps associated with the calculation of individual parcel trajectories. In particular, we have considered (1) calculational errors; (2) uncertainties in the values and locations of constituent measurements, (3) errors incurred by neglecting diabatic effects, and (4) sensitivity to differences in wind field analyses. These studies reveal that the global fields derived from the advection of large numbers of measurements are relatively insensitive to the errors in the individual trajectories. The trajectory mapping technique has been successfully applied to a variety of problems. In this paper, the following two applications demonstrate the usefulness of the technique: an analysis of dynamical wave-breaking events and an examination of Upper Atmosphere Research Satellite data accuracy

CD4+ T Cells Reactive to Enteric Bacterial Antigens in Spontaneously Colitic C3H/HeJBir Mice: Increased T Helper Cell Type 1 Response and Ability to Transfer Disease

C3H/HeJBir mice are a new substrain that spontaneously develop colitis early in life. This study was done to determine the T cell reactivity of C3H/HeJBir mice to candidate antigens that might be involved in their disease. C3H/HeJBir CD4+ T cells were strongly reactive to antigens of the enteric bacterial flora, but not to epithelial or food antigens. The stimulatory material in the enteric bacteria was trypsin sensitive and restricted by class II major histocompatibility complex molecules, but did not have the properties of a superantigen. The precursor frequency of interleuken (IL)-2–producing, bacterial-reactive CD4+ T cells in colitic mice was 1 out of 2,000 compared to 1 out of 20,000–25,000 in noncolitic control mice. These T cells produced predominately IL-2 and interferon γ, consistent with a T helper type 1 cell response and were present at 3–4 wk, the age of onset of the colitis. Adoptive transfer of bacterial-antigen–activated CD4+ T cells from colitic C3H/HeJBir but not from control C3H/HeJ mice into C3H/HeSnJ scid/scid recipients induced colitis. These data represent a direct demonstration that T cells reactive with conventional antigens of the enteric bacterial flora can mediate chronic inflammatory bowel disease

Structural analysis of mitochondrial rRNA gene variants identified in patients with deafness

The last few years have witnessed dramatic advances in our understanding of the structure and function of the mammalian mito-ribosome. At the same time, the first attempts to elucidate the effects of mito-ribosomal fidelity (decoding accuracy) in disease have been made. Hence, the time is right to push an important frontier in our understanding of mitochondrial genetics, that is, the elucidation of the phenotypic effects of mtDNA variants affecting the functioning of the mito-ribosome. Here, we have assessed the structural and functional role of 93 mitochondrial (mt-) rRNA variants thought to be associated with deafness, including those located at non-conserved positions. Our analysis has used the structural description of the human mito-ribosome of the highest quality currently available, together with a new understanding of the phenotypic manifestation of mito-ribosomal-associated variants. Basically, any base change capable of inducing a fidelity phenotype may be considered non-silent. Under this light, out of 92 previously reported mt-rRNA variants thought to be associated with deafness, we found that 49 were potentially non-silent. We also dismissed a large number of reportedly pathogenic mtDNA variants, 41, as polymorphisms. These results drastically update our view on the implication of the primary sequence of mt-rRNA in the etiology of deafness and mitochondrial disease in general. Our data sheds much-needed light on the question of how mt-rRNA variants located at non-conserved positions may lead to mitochondrial disease and, most notably, provide evidence of the effect of haplotype context in the manifestation of some mt-rRNA variants

Deletion of the dominant autoantigen in NZB mice with autoimmune hemolytic anemia : Effects on autoantibody and T-helper responses

Peer reviewedPublisher PD