51,903 research outputs found
Low-frequency microwave radiometer for N-ROSS
The all weather, global determination of sea surface temperature (SST) has been identified as a requirement needed to support naval operations. The target SST accuracy is + or - 1.0 K with a surface resolution of 10 km. Investigations of the phenomenology and technology of remote passive microwave sensing of the ocean environment over the past decade have demonstrated that this objective is presently attainable. Preliminary specification and trade off studies were conducted to define the frequency, polarization, scan geometry, antenna size, and other esstential parameters of the low frequency microwave radiometer (LFMR). It will be a dual polarized, dual frequency system at 5.2 and 10.4 GHz using a 4.9 meter deployable mesh surface antenna. It is to be flown on the Navy-Remote Ocean Sensing System (N-ROSS) satellite scheduled to be launched in late 1988
Frontiers of finance: Evolution and efficient markets
In this review article we explore several recent advances in the quantitative
modeling of financial markets. We begin with the Efficient Markets Hypothesis
and describe how this controversial idea has stimulated a number of new
directions of research, some focusing on more elaborate mathematical models
that are captable of rationalizing the empirical facrts, others taking a
completely different different tack in rejecting rationality altogether. One of
the most promising directions is to view financial markets from a biological
perspective and, specifically, with an evolutionary framework in which markets,
instruments, institutions, and investors interact and evolve dynamically
according to the "law" of economic selection. Under this view, financial agents
compete and adapt, but they do not necessarily do so in an optimal fashion.
Evolutionary and ecological models of financial markets is truly a new frontier
whose exploration has just begun.Comment: 2 page
MASH1 activates expression of the paired homeodomain transcription factor Phox2a, and couples pan-neuronal and subtype-specific components of autonomic neuronal identity
We have investigated the genetic circuitry underlying the determination of neuronal identity, using mammalian peripheral autonomic neurons as a model system. Previously, we showed that treatment of neural crest stem cells (NCSCs) with bone morphogenetic protein-2 (BMP-2) leads to an induction of MASH1 expression and consequent autonomic neuronal differentiation. We now show that BMP2 also induces expression of the paired homeodomain transcription factor Phox2a, and the GDNF/NTN signalling receptor tyrosine kinase c-RET. Constitutive expression of MASH1 in NCSCs from a retroviral vector, in the absence of exogenous BMP2, induces expression of both Phox2a and c-RET in a large fraction of infected colonies, and also promotes morphological neuronal differentiation and expression of pan-neuronal markers. In vivo, expression of Phox2a in autonomic ganglia is strongly reduced in Mash1 -/- embryos. These loss- and gain-of-function data suggest that MASH1 positively regulates expression of Phox2a, either directly or indirectly. Constitutive expression of Phox2a, by contrast to MASH1, fails to induce expression of neuronal markers or a neuronal morphology, but does induce expression of c-RET. These data suggest that MASH1 couples expression of pan-neuronal and subtype-specific components of autonomic neuronal identity, and support the general idea that identity is established by combining subprograms involving cascades of transcription factors, which specify distinct components of neuronal phenotype
Algon: a framework for supporting comparison of distributed algorithm performance
Programmers often need to use distributed algorithms to add non-functional behaviour such as mutual exclusion, deadlock detection and termination, to a distributed application. They find the selection and implementation of these algorithms daunting. Consequently, they have no idea which algorithm will be best for their particular application. To address this difficulty the Algon framework provides a set of pre-coded distributed algorithms for programmers to choose from, and provides a special performance display tool to support choice between algorithms. The performance tool is discussed. The developer of a distributed application will be able to observe the performance of each of the available algorithms according to a set of of widely accepted and easily-understandable performance metrics and compare and contrast the behaviour of the algorithms to support an informed choice. The strength of the Algon framework is that it does not require a working knowledge of algorithmic theory or functionality in order for the developer to use the algorithms
Reconstruction of coded aperture images
Balanced correlation method and the Maximum Entropy Method (MEM) were implemented to reconstruct a laboratory X-ray source as imaged by a Uniformly Redundant Array (URA) system. Although the MEM method has advantages over the balanced correlation method, it is computationally time consuming because of the iterative nature of its solution. Massively Parallel Processing, with its parallel array structure is ideally suited for such computations. These preliminary results indicate that it is possible to use the MEM method in future coded-aperture experiments with the help of the MPP
Dissociation and ionization of molecular gas in the spiral arms of M51
Researchers derive the star formation rate and efficiency in the arm and interarm regions of M51 from observations of the molecular (Lo et al. 1987) and ionized (van der Hulst et al. 1988) phases of the interstellar medium, and show that the HI observations of Tilanus and Allen (1989) are consistent with dissociation of molecular gas by these young, massive stars if n sub H greater than or equal to 200 cm (-2). However, these stars are not able to dissociate or ionize all the gas, and at least 60 percent must remain molecular in the interarm regions. The efficiency of star formation in M51 seems to be similar to that in the Galaxy, and does not appear to be enhanced in the spiral arms. Therefore, the effect of the strong density wave may be only to concentrate the gas, and hence the young stars, to the arm regions
Exact spectral function of a Tonks-Girardeau gas in a lattice
The single-particle spectral function of a strongly correlated system is an
essential ingredient to describe its dynamics and transport properties. We
develop a general method to calculate the exact spectral function of a strongly
interacting one-dimensional Bose gas in the Tonks-Girardeau regime, valid for
any type of confining potential, and apply it to bosons on a lattice to obtain
the full spectral function, at all energy and momentum scales. We find that it
displays three main singularity lines. The first two can be identified as the
analogs of Lieb-I and Lieb-II modes of a uniform fluid; the third one, instead,
is specifically due to the presence of the lattice. We show that the spectral
function displays a power-law behaviour close to the Lieb-I and Lieb-II
singularities, as predicted by the non-linear Luttinger liquid description, and
obtain the exact exponents. In particular, the Lieb-II mode shows a divergence
in the spectral function, differently from what happens in the dynamical
structure factor, thus providing a route to probe it in experiments with
ultracold atoms.Comment: 10 pages, 3 figure
- …