Self tolerance in a minimal model of the idiotypic network

We consider the problem of self tolerance in the frame of a minimalistic model of the idiotypic network. A node of this network represents a population of B lymphocytes of the same idiotype which is encoded by a bit string. The links of the network connect nodes with (nearly) complementary strings. The population of a node survives if the number of occupied neighbours is not too small and not too large. There is an influx of lymphocytes with random idiotype from the bone marrow. Previous investigations have shown that this system evolves toward highly organized architectures, where the nodes can be classified into groups according to their statistical properties. The building principles of these architectures can be analytically described and the statistical results of simulations agree very well with results of a modular mean field theory. In this paper we present simulation results for the case that one or several nodes, playing the role of self, are permanently occupied. We observe that the group structure of the architecture is very similar to the case without self antigen, but organized such that the neighbours of the self are only weakly occupied, thus providing self tolerance. We also treat this situation in mean field theory which give results in good agreement with data from simulation.Comment: 7 pages, 6 figures, 1 tabl

Motivating and Steering With Comparative Data

Several managerial strategies — particularly goal setting combined with performance feedback — can be very effective in improving an organization’s performance at outputfocused tasks. But can such strategies be adapted to achieve societal outcomes that are less operational and definable, more ambiguous and ambitious, perhaps more political? Can they be adapted to help steer social integration by, for example, enhancing social justice and strengthening citizenship? Recognizing how different kinds of targets, different kinds of feedback, and different kinds of reward structures affect team and individual motivation can help public officials design not only better strategies for directly producing output results, but also better strategies for indirectly fostering broader outcome purposes of, for example, social integration

Cutbacks vs. PerformanceStat: What's the Conflict? Financial Deficits and Attention

Reductions in any organization’s financial budget can cause reductions in the organization’s performance (its outputs and outcomes). It is not obvious, however, that the primary cause will be direct: Less money to spend means less can be done. Instead, the bigger impact may come through the opportunity costs created by the financial cuts on the time budget of the members of the leadership team. For the attention that they must pay to any budget reductions automatically reduces the attention that they can devote performance improvements — and to everything else. It isn’t the financial cuts themselves. Rather, it is that the deficit in the financial budget creates a deficit in the leadership team’s time budget. The funding deficit in the financial budget imposes an attention deficit in the time budget

The transition from subsonic to supersonic cracks

We present the full analytical solution for steady-state in-plane crack motion in a brittle triangular lattice. This allows quick numerical evaluation of solutions for very large systems, facilitating comparisons with continuum fracture theory. Cracks that propagate faster than the Rayleigh wave speed have been thought to be forbidden in the continuum theory, but clearly exist in lattice systems. Using our analytical methods, we examine in detail the motion of atoms around a crack tip as crack speed changes from subsonic to supersonic. Subsonic cracks feature displacement fields consistent with a stress intensity factor. For supersonic cracks, the stress intensity factor disappears. Subsonic cracks are characterized by small-amplitude, high-frequency oscillations in the vertical displacement of an atom along the crack line, while supersonic cracks have large-amplitude, low-frequency oscillations. Thus, while supersonic cracks are no less physical than subsonic cracks, the connection between microscopic and macroscopic behavior must be made in a different way. This is one reason supersonic cracks in tension had been thought not to exist. In continuum fracture theory, the energy flowing into the crack tip becomes negative or imaginary for crack speeds faster than the Rayleigh wave speed. This would suggest that supersonic cracks are not physically allowed. In response to this, we study the energy flow in our supersonic solutions in the lattice. First, we construct an energy flux vector in the lattice analogous to the Poynting vector in electromagnetism. This allows us to calculate the energy flow at each atom in the lattice. We find that there is positive energy flux into the crack tip for both subsonic and supersonic solutions in the lattice.Physic

Comparison of techniques for the estimation of flow parameters of fan inflow turbulence from noisy hot-wire data

Turbulence parameters, in particular integral length scale (ILS) and turbulence intensity (Tu), are key input parameters for various applications in aerodynamics and aeroacoustics. The estimation of these parameters is typically performed using data obtained via hot-wire measurements. On the one hand, hot-wire measurements are affected by external disturbances resulting in increased measurement noise. On the other hand, commonly applied turbulence parameter estimators lack in robustness. If not addressed correctly, both issues may impede the accuracy of the turbulence parameter estimation. In this article, a procedure consisting of several signal processing steps is presented to filter non-turbulence related disturbances from the unsteady velocity data. The signal processing techniques comprise time- and frequency-domain approaches. For the turbulence parameter estimation, two different models of the turbulence spectra—the von Kármán model and the Bullen model—are fitted to match the spectrum of the measured data. The results of several parameter estimation techniques are compared. Computational Fluid Dynamics (CFD) data are used to validate the estimation techniques and also to assess the influence of the variation in window size on the estimated parameters. Additionally, hot-wire data from a high-speed fan rig are analyzed. ILS and Tu are assessed at several radial positions for two fan speeds. It is found that most techniques yield similar values for ILS and Tu. The comparison of the fitted spectra with the spectra of the measured data shows a good agreement in most cases provided that a sufficiently fine frequency resolution is applied. The ratio of ILS and Tu of the velocity components in longitudinal and transverse direction allows the assessment of flow-isotropy. Results indicate that the turbulence is anisotropic for the investigated flow fields

Comparison of Techniques for the Estimation of Flow Parameters of Fan Inflow Turbulence from Noisy Hot-Wire Data

Turbulence parameters, in particular integral length scale (ILS) and turbulence intensity (Tu), are key input parameters for various applications in aerodynamics and aeroacoustics. The estimation of these parameters is typically performed using data obtained via hot-wire measurements. On the one hand, hot-wire measurements are affected by external disturbances resulting in increased measurement noise. On the other hand, commonly applied turbulence parameter estimators lack in robustness. If not addressed correctly, both issues may impede the accuracy of the turbulence parameter estimation. In this article, a procedure consisting of several signal processing steps is presented to filter non-turbulence related disturbances from the unsteady velocity data. The signal processing techniques comprise time- and frequency-domain approaches. For the turbulence parameter estimation, two different models of the turbulence spectra—the von Kármán model and the Bullen model—are fitted to match the spectrum of the measured data. The results of several parameter estimation techniques are compared. Computational Fluid Dynamics (CFD) data are used to validate the estimation techniques and also to assess the influence of the variation in window size on the estimated parameters. Additionally, hot-wire data from a high-speed fan rig are analyzed. ILS and Tu are assessed at several radial positions for two fan speeds. It is found that most techniques yield similar values for ILS and Tu. The comparison of the fitted spectra with the spectra of the measured data shows a good agreement in most cases provided that a sufficiently fine frequency resolution is applied. The ratio of ILS and Tu of the velocity components in longitudinal and transverse direction allows the assessment of flow-isotropy. Results indicate that the turbulence is anisotropic for the investigated flow fields

CRAFT test rig for assessing the aeroacoustic impact of fans of electrically powered urban/regional aircraft

A comprehensive assessment of the noise generation and the acoustic impact of electric propulsion fans is an essential part of urban/regional aircraft development and can provide important guidance on design changes for increased acceptance. Experimental investigations at the CRAFT (Co/Counter Rotating Acoustic Fan Test rig) test facility provide important contributions, e.g. to reveal unexplored correlations between the often disturbed inflow and the acoustics of the fan, to provide realistic input for the assessment of auditory perception and to validate modelling approaches. The presentation gives an overview of current fan designs and the wide range of applications of the CRAFT test rig

Morphology and segmentation of the western Galápagos Spreading Center, 90.5°–98°W : plume-ridge interaction at an intermediate spreading ridge

Author Posting. © American Geophysical Union 2003. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 4 (2003): 8515, doi:10.1029/2003GC000609.Complete multibeam bathymetric coverage of the western Galápagos Spreading Center (GSC) between 90.5°W and 98°W reveals the fine-scale morphology, segmentation and influence of the Galápagos hot spot on this intermediate spreading ridge. The western GSC comprises three morphologically defined provinces: A Western Province, located farthest from the Galápagos hot spot west of 95°30′W, is characterized by an axial deep, rift valley morphology with individual, overlapping, E-W striking segments separated by non-transform offsets; A Middle Province, between the propagating rift tips at 93°15′W and 95°30′W, with transitional axial morphology strikes ∼276°; An Eastern Province, closest to the Galápagos hot spot between the ∼90°50′W Galápagos Transform and 93°15′W, with an axial high morphology generally less than 1800 m deep, strikes ∼280°. At a finer scale, the axial region consists of 32 individual segments defined on the basis of smaller, mainly <2 km, offsets. These offsets mainly step left in the Western and Middle Provinces, and right in the Eastern Province. Glass compositions indicate that the GSC is segmented magmatically into 8 broad regions, with Mg # generally decreasing to the west within each region. Striking differences in bathymetric and lava fractionation patterns between the propagating rifts with tips at 93°15′W and 95°30′W reflect lower overall magma supply and larger offset distance at the latter. The structure of the Eastern Province is complicated by the intersection of a series of volcanic lineaments that appear to radiate away from a point located on the northern edge of the Galápagos platform, close to the southern limit of the Galápagos Fracture Zone. Where these lineaments intersect the GSC, the ridge axis is displaced to the south through a series of overlapping spreading centers (OSCs); abandoned OSC limbs lie even farther south. We propose that southward displacement of the axis is promoted during intermittent times of increased plume activity, when lithospheric zones of weakness become volcanically active. Following cessation of the increased plume activity, the axis straightens by decapitating southernmost OSC limbs during short-lived propagation events. This process contributes to the number of right stepping offsets in the Eastern Province.This work was supported by NSF grants OCE98- 18632 to the University of Hawai’i and OCE98-19117 to the Woods Hole Oceanographic Institution; support was provided to M. B. by a CIW/DTM Postdoctoral Fellowshi

s-RT-MELT for rapid mutation scanning using enzymatic selection and real time DNA-melting: new potential for multiplex genetic analysis

The rapidly growing understanding of human genetic pathways, including those that mediate cancer biology and drug response, leads to an increasing need for extensive and reliable mutation screening on a population or on a single patient basis. Here we describe s-RT-MELT, a novel technology that enables highly expanded enzymatic mutation scanning in human samples for germline or low-level somatic mutations, or for SNP discovery. GC-clamp-containing PCR products from interrogated and wild-type samples are hybridized to generate mismatches at the positions of mutations over one or multiple sequences in-parallel. Mismatches are converted to double-strand breaks using a DNA endonuclease (Surveyor™) and oligonucleotide tails are enzymatically attached at the position of mutations. A novel application of PCR enables selective amplification of mutation-containing DNA fragments. Subsequently, melting curve analysis, on conventional or nano-technology real-time PCR platforms, detects the samples that contain mutations in a high-throughput and closed-tube manner. We apply s-RT-MELT in the screening of p53 and EGFR mutations in cell lines and clinical samples and demonstrate its advantages for rapid, multiplexed mutation scanning in cancer and for genetic variation screening in biology and medicine