13,946 research outputs found

    On the structure of the scalar mesons f0(975)f_0(975) and a0(980)a_0(980)

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    We investigate the structure of the scalar mesons f0(975)f_0(975) and a0(980)a_0(980) within realistic meson-exchange models of the ππ\pi\pi and πη\pi\eta interactions. Starting from a modified version of the J\"ulich model for ππ\pi\pi scattering we perform an analysis of the pole structure of the resulting scattering amplitude and find, in contrast to existing models, a somewhat large mass for the f0(975)f_0(975) (mf0=1015m_{f_0}=1015 MeV, Γf0=30\Gamma_{f_0}=30 MeV). It is shown that our model provides a description of J/ψϕππ/ϕKKJ/\psi\rightarrow\phi\pi\pi/\phi KK data comparable in quality with those of alternative models. Furthermore, the formalism developed for the ππ\pi\pi system is consistently extended to the πη\pi\eta interaction leading to a description of the a0(980)a_0(980) as a dynamically generated threshold effect (which is therefore neither a conventional qqq\overline{q} state nor a KKK\overline{K} bound state). Exploring the corresponding pole position the a0(980)a_0(980) is found to be rather broad (ma0=991m_{a_0}=991 MeV, Γa0=202\Gamma_{a_0}=202 MeV). The experimentally observed smaller width results from the influence of the nearby KKK\overline{K} threshold on this pole.Comment: 25 pages, 15 Postscript figure

    Reinstatement of long-term memory following erasure of its behavioral and synaptic expression in Aplysia.

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    Long-term memory (LTM) is believed to be stored in the brain as changes in synaptic connections. Here, we show that LTM storage and synaptic change can be dissociated. Cocultures of Aplysia sensory and motor neurons were trained with spaced pulses of serotonin, which induces long-term facilitation. Serotonin (5HT) triggered growth of new presynaptic varicosities, a synaptic mechanism of long-term sensitization. Following 5HT training, two antimnemonic treatments-reconsolidation blockade and inhibition of PKM--caused the number of presynaptic varicosities to revert to the original, pretraining value. Surprisingly, the final synaptic structure was not achieved by targeted retraction of the 5HT-induced varicosities but, rather, by an apparently arbitrary retraction of both 5HT-induced and original synapses. In addition, we find evidence that the LTM for sensitization persists covertly after its apparent elimination by the same antimnemonic treatments that erase learning-related synaptic growth. These results challenge the idea that stable synapses store long-term memories

    Heating of the Intracluster Gas in the Triangulum Australis Cluster

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    ASCA and ROSAT X-ray data are used to obtain two-dimensional maps of the gas temperature, pressure and specific entropy in the Triangulum Australis cluster of galaxies. We find that this hot (T_e=10.3+-0.8 keV) system probably has a temperature peak (T_e>12 keV) at the cluster core, which approximately corresponds to the adiabatic relation. An underdense gas sector, found in the ROSAT cluster image eastward of the core, has a higher temperature than average at that radius. At this higher temperature, the gas pressure in this region is equal to that of the rest of the cluster at the same radius, but the specific entropy of this gas is significantly higher (although the temperature difference itself is only marginally significant). We speculate that the existence of this region of underdense high-entropy gas, as well as the adiabatic central temperature peak, indicate recent or ongoing heating of the intergalactic medium in this cluster. The most probable source of such heating is a subcluster merger, for which the hydrodynamic simulations predict a qualitatively similar temperature structure. We point out that entropy maps can provide a physically meaningful way of diagnosing merging clusters and comparing the predictions of merger simulations to the data.Comment: Text revised to give more technical details and clarify discussion. Accepted for ApJ Letters. Latex, 5 pages incl. figures, macros include

    Direct measurements of the polarization of terrestrial kilometric radiation from Voyagers 1 and 2

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    Terrestrial radiation measurements obtained with planetary radio astronomy experiments on Voyager-1 and 2 during the early portions of each flight show the signals to be predominantly left-hand circularly polarized. Since these emissions were most probably generated above the Northern Hemisphere auroral zone, it is concluded that the radiation is emitted primarily in the extraordinary mode

    Root Growth and Development of Float Tobacco Transplants Before and After Transplanting

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    In the production of float tobacco transplants, the seedling produces at least two different kinds of roots. The “media” roots are those that grow in the soilless medium within the float tray cell. They have a normal branched appearance similar to roots produced on soil-bed grown transplants. The “water” roots grow through the soilless medium in tray cells and into the nutrient solution below the float tray. They tend to be very fragile and less branched than roots growing in the soilless medium. In removal of seedlings from tray cells during transplanting, “water” roots are usually badly damaged or destroyed, which could affect establishment of transplants in the field since the most critical period in the development of tobacco plants occurs immediately after transplanting. When these young plants are removed from the protective environment of the float bed system and are subjected to radically different and sometimes adverse field conditions, stress on the juvenile plants is created. Field establishment of these young plants is dependent upon growth or new formation of the “media” and “water” roots. To maximize establishment of transplants, it is important to know how the \u27\u27water roots and the media roots develop in the float system and their contribution to transplant establishment during the first few weeks after transplanting. The objectives of this study were: 1) to characterize the growth of media and \u27\u27water roots on tobacco seedlings in the float system, and 2) to assess tobacco transplant growth with or without \u27\u27water\u27\u27 roots, at two and four weeks after transplanting
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