1,141 research outputs found
Expression patterns of chondrocyte genes cloned by differential display in tibial dyschondroplasia
AbstractTibial dyschondroplasia (TD) appears to involve a failure of the growth plate chondrocytes within growing long bones to differentiate fully to the hypertrophic stage, resulting in a mass of prehypertrophic chondrocytes which form the avascular TD lesion. Many biochemical and molecular markers of chondrocyte hypertrophy are absent from the lesion, or show reduced expression, but the cause of the disorder remains to be identified. As differentiation to the hypertrophic state is impaired in TD, we hypothesised that chondrocyte genes that are differentially expressed in the growth plate should show altered expression in TD. Using differential display, four genes, B-cadherin, EF2, HT7 and Ex-FABP were cloned from chondrocytes stimulated to differentiate to the hypertrophic stage in vitro, and their differential expression confirmed in vivo. Using semi-quantitative RT-PCR, the expression patterns of these genes were compared in chondrocytes from normal and TD growth plates. Surprisingly, none of these genes showed the pattern of expression that might be expected in TD lesion chondrocytes, and two of them, B-cadherin and Ex-FABP, were upregulated in the lesion. This indicates that the TD phenotype does not merely reflect the absence of hypertrophic marker genes, but may be influenced by more complex developmental mechanisms/defects than previously thought
Genetic and genomic tools to improve drought tolerance in wheat
Tolerance to drought is a quantitative trait, with a complex phenotype, often confounded by plant phenology. Breeding for drought tolerance is further complicated since several types of abiotic stress, such as high temperatures, high irradiance, and nutrient toxicities or deficiencies can challenge crop plants simultaneously. Although marker-assisted selection is now widely deployed in wheat, it has not contributed significantly to cultivar improvement for adaptation to low-yielding environments and breeding has relied largely on direct phenotypic selection for improved performance in these difficult environments. The limited success of the physiological and molecular breeding approaches now suggests that a careful rethink is needed of our strategies in order to understand better and breed for drought tolerance. A research programme for increasing drought tolerance of wheat should tackle the problem in a multi-disciplinary approach, considering interaction between multiple stresses and plant phenology, and integrating the physiological dissection of drought-tolerance traits and the genetic and genomics tools, such as quantitative trait loci (QTL), microarrays, and transgenic crops. In this paper, recent advances in the genetics and genomics of drought tolerance in wheat and barley are reviewed and used as a base for revisiting approaches to analyse drought tolerance in wheat. A strategy is then described where a specific environment is targeted and appropriate germplasm adapted to the chosen environment is selected, based on extensive definition of the morpho-physiological and molecular mechanisms of tolerance of the parents. This information was used to create structured populations and develop models for QTL analysis and positional cloning.Delphine Fleury, Stephen Jefferies, Haydn Kuchel and Peter Langridg
Predictability of large future changes in a competitive evolving population
The dynamical evolution of many economic, sociological, biological and
physical systems tends to be dominated by a relatively small number of
unexpected, large changes (`extreme events'). We study the large, internal
changes produced in a generic multi-agent population competing for a limited
resource, and find that the level of predictability actually increases prior to
a large change. These large changes hence arise as a predictable consequence of
information encoded in the system's global state.Comment: 10 pages, 3 figure
Theory of Networked Minority Games based on Strategy Pattern Dynamics
We formulate a theory of agent-based models in which agents compete to be in
a winning group. The agents may be part of a network or not, and the winning
group may be a minority group or not. The novel feature of the present
formalism is its focus on the dynamical pattern of strategy rankings, and its
careful treatment of the strategy ties which arise during the system's temporal
evolution. We apply it to the Minority Game (MG) with connected populations.
Expressions for the mean success rate among the agents and for the mean success
rate for agents with neighbors are derived. We also use the theory to
estimate the value of connectivity above which the Binary-Agent-Resource
system with high resource level goes into the high-connectivity state.Comment: 24 pages, 3 figures, submitted to PR
Dynamical Solution of the On-Line Minority Game
We solve the dynamics of the on-line minority game, with general types of
decision noise, using generating functional techniques a la De Dominicis and
the temporal regularization procedure of Bedeaux et al. The result is a
macroscopic dynamical theory in the form of closed equations for correlation-
and response functions defined via an effective continuous-time single-trader
process, which are exact in both the ergodic and in the non-ergodic regime of
the minority game. Our solution also explains why, although one cannot formally
truncate the Kramers-Moyal expansion of the process after the Fokker-Planck
term, upon doing so one still finds the correct solution, that the previously
proposed diffusion matrices for the Fokker-Planck term are incomplete, and how
previously proposed approximations of the market volatility can be traced back
to ergodicity assumptions.Comment: 25 pages LaTeX, no figure
Network oscillations at the boundary of an equatorial coronal hole
We investigate intensity oscillations observed simultaneously in the quiet
chromosphere and in the corona, above an enhanced network area at the boundary
of an equatorial coronal hole. A Fourier analysis is applied to a sequence of
images observed in the 171 A and 1600 A passbands of TRACE. Four interesting
features above the magnetic network are further investigated by using a wavelet
analysis. Our results reveal that, in both the 171 A and 1600 A passbands,
oscillations above the magnetic network show a lack of power at high
frequencies (5.0-8.3 mHz), and a significant power at low (1.3-2.0 mHz) and
intermediate frequencies (2.6-4.0 mHz). The global 5-min oscillation is clearly
present in the 4 analyzed features when seen in the 1600 A passband, and is
also found with enhanced power in feature 1 (leg of a large coronal loop) and
feature 2 (legs of a coronal bright point loop) when seen in the 171 A
passband. Two features above an enhanced network element (feature 3 and feature
4) show repeated propagating behaviors with a dominant period of 10 min and 5
min, respectively. We suggest these oscillations are likely to be slow
magneto-acoustic waves propagating along inclined magnetic field lines, from
the lower solar atmosphere into the corona. The energy flux carried by these
waves is estimated of the order of 40 erg cm\^{-2} s\^{-1} for the 171 A
passband and is far lower than the energy required to heat the quiet corona.
For the 1600 A passband, the energy flux is about 1.4*10^6 erg cm\^{-2}
s\^{-1}, which is about one third of the required energy budget for the
chromosphere.Comment: 7 pages, 8 figure
Spectral line shape of resonant four-wave mixing induced by broad-bandwidth lasers
We present a theoretical and experimental study of the line shape of resonant four-wave mixing induced by broad-bandwidth laser radiation that revises the theory of Meacher, Smith, Ewart, and Cooper (MSEC) [Phys. Rev. A 46, 2718 (1992)]. We adopt the same method as MSEC but correct for an invalid integral used to average over the distribution of atomic velocities. The revised theory predicts a Voigt line shape composed of a homogeneous, Lorentzian component, defined by the collisional rate Ī, and an inhomogeneous, Doppler component, which is a squared Gaussian. The width of the inhomogeneous component is reduced by a factor of ā2 compared to the simple Doppler width predicted by MSEC. In the limit of dominant Doppler broadening, the width of the homogeneous component is predicted to be 4Ī, whereas in the limit of dominant homogeneous broadening, the predicted width is 2Ī. An experimental measurement is reported of the line shape of the four-wave-mixing signal using a broad-bandwidth, "modeless", laser resonant with the Q1 (6) line of the A2 Ī£ - X2 Ī (0,0) system of the hydroxyl radical. The measured widths of the Voigt components were found to be consistent with the predictions of the revised theory
VFISV: Very Fast Inversion of the Stokes Vector for the Helioseismic and Magnetic Imager
In this paper we describe in detail the implementation and main properties of
a new inversion code for the polarized radiative transfer equation (VFISV: Very
Fast inversion of the Stokes vector). VFISV will routinely analyze pipeline
data from the Helioseismic and Magnetic Imager (HMI) on-board of the Solar
Dynamics Observatory (SDO). It will provide full-disk maps (40964096
pixels) of the magnetic field vector on the Solar Photosphere every 10 minutes.
For this reason VFISV is optimized to achieve an inversion speed that will
allow it to invert 16 million pixels every 10 minutes with a modest number
(approx. 50) of CPUs. Here we focus on describing a number of important
details, simplifications and tweaks that have allowed us to significantly speed
up the inversion process. We also give details on tests performed with data
from the spectropolarimeter on-board of the Hinode spacecraft.Comment: 23 pages, 9 figures (2 color). Submitted for publication to Solar
Physic
"Oh! What a tangled web we weave": Englishness, communicative leisure, identity work and the cultural web of the English folk morris dance scene
In this paper, we consider the relationship between Englishness and the English folk morris dance scene, considering how the latter draws from and reinforces the former. Englishness is considered within the context of the cultural web; a tool more often applied to business management but linked to a sociological viewpoint here. By doing so, we draw the connections between this structured business model and the cultural identity of Englishness. Then, we use the framework of the cultural web and theories of leisure, culture and identity to understand how morris dancers see their role as dancers and ācommunicative leisureā agents in consciously defending Englishness, English traditions and inventions, the practices and traditions of folk and morris, and the various symbolic communities they inhabit. We argue that most morris dancers in our research become and maintain their leisured identities as dancers because they are attracted to the idea of tradition ā even if that tradition is invented and open to change
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