606 research outputs found
Models and experimental results from the wide aperture Nb-Ti magnets for the LHC upgrade
MQXC is a Nb-Ti quadrupole designed to meet the accelerator quality
requirements needed for the phase-1 LHC upgrade, now superseded by the high
luminosity upgrade foreseen in 2021. The 2-m-long model magnet was tested at
room temperature and 1.9 K. The technology developed for this magnet is
relevant for other magnets currently under development for the high-luminosity
upgrade, namely D1 (at KEK) and the large aperture twin quadrupole Q4 (at CEA).
In this paper we present MQXC test results, some of the specialized heat
extraction features, spot heaters, temperature sensor mounting and voltage tap
development for the special open cable insulation. We look at some problem
solving with noisy signals, give an overview of electrical testing, look at how
we calculate the coil resistance during at quench and show that the heaters are
not working We describe the quench signals and its timing, the development of
the quench heaters and give an explanation of an Excel quench calculation and
its comparison including the good agreement with the MQXC test results. We
propose an improvement to the magnet circuit design to reduce voltage to ground
values by factor 2. The program is then used to predict quench Hot-Spot and
Voltages values for the D1 dipole and the Q4 quadrupole.Comment: 8 pages, Contribution to WAMSDO 2013: Workshop on Accelerator Magnet,
Superconductor, Design and Optimization; 15 - 16 Jan 2013, CERN, Geneva,
Switzerlan
The synaptic vesicle protein CSP alpha prevents presynaptic degeneration
Cysteine string protein α (CSPα)âan abundant synaptic vesicle protein that contains a DNA-J domain characteristic of Hsp40 chaperonesâis thought to regulate Ca2+ channels and/or synaptic vesicle exocytosis. We now show that, in young mice, deletion of CSPα does not impair survival and causes no significant changes in presynaptic Ca2+ currents or synaptic vesicle exocytosis as measured in the Calyx of Held synapse. At 2â4 weeks of age, however, CSPα-deficient mice develop a progressive, fatal sensorimotor disorder. The neuromuscular junctions and Calyx synapses of CSPα-deficient mice exhibit increasing neurodegenerative changes, synaptic transmission becomes severely impaired, and the mutant mice die at âŒ2 months of age. Our data suggest that CSPα is not essential for the normal operation of Ca2+ channels or exocytosis but acts as a presynaptic chaperone that maintains continued synaptic function, raising the possibility that enhanced CSPα function could attenuate neurodegenerative diseases
Electric-field-induced spin-flop in BiFeO3 single crystals at room-temperature
Bismuth ferrite, BiFeO3, is the only known room-temperature 'multiferroic'
material. We demonstrate here, using neutron scattering measurements in high
quality single crystals, that the antiferromagnetic and ferroelectric orders
are intimately coupled. Initially in a single ferroelectric state, our crystals
have a canted antiferromagnetic structure describing a unique cycloid. Under
electrical poling, polarisation re-orientation induces a spin flop. We argue
here that the coupling between the two orders may be stronger in the bulk than
that observed in thin films where the cycloid is absent
CD28 between tolerance and autoimmunity: The side effects of animal models [version 1; referees: 2 approved]
Regulation of immune responses is critical for ensuring pathogen clearance and for preventing reaction against self-antigens. Failure or breakdown of immunological tolerance results in autoimmunity. CD28 is an important co-stimulatory receptor expressed on T cells that, upon specific ligand binding, delivers signals essential for full T-cell activation and for the development and homeostasis of suppressive regulatory T cells. Many in vivo mouse models have been used for understanding the role of CD28 in the maintenance of immune homeostasis, thus leading to the development of CD28 signaling modulators that have been approved for the treatment of some autoimmune diseases. Despite all of this progress, a deeper understanding of the differences between the mouse and human receptor is required to allow a safe translation of pre-clinical studies in efficient therapies. In this review, we discuss the role of CD28 in tolerance and autoimmunity and the clinical efficacy of drugs that block or enhance CD28 signaling, by highlighting the success and failure of pre-clinical studies, when translated to humans
Room temperature coexistence of large electric polarization and magnetic order in BiFeO3 single crystals
From an experimental point of view, room temperature ferroelectricity in
BiFeO3 is raising many questions. Electric measurements made a long time ago on
solid-solutions of BiFeO3 with Pb(Ti,Zr)O3 indicate that a spontaneous electric
polarization exists in BiFeO3 below the Curie temperature TC=1143K. Yet in most
reported works, the synthesised samples are too conductive at room temperature
to get a clear polarization loop in the bulk without any effects of extrinsic
physical or chemical parameters. Surprisingly, up to now there has been no
report of a P(E) (polarization versus electric field) loop at room temperature
on single crystals of BiFeO3. We describe here our procedure to synthesize
ceramics and to grow good quality sizeable single crystals by a flux method. We
demonstrate that BiFeO3 is indeed ferroelectric at room-temperature through
evidence by Piezoresponse Force Microscopy and P(E) loops. The polarization is
found to be large, around 60 microC/cm2, a value that has only been reached in
thin films. Magnetic measurements using a SQUID magnetometer and Mossbauer
spectroscopy are also presented. The latter confirms the results of NMR
measurements concerning the anisotropy of the hyperfine field attributed to the
magnetic cycloidal structure.Comment: 27 pages, 12 figure
Towards the effective potential of the Littlest Higgs model
We compute the relevant parameters of the combined Higgs and \phi scalar
effective potential in the Littlest Higgs (LH) model. These parameters are
obtained as the sum of two kind of contributions. The first one is the one-loop
radiative corrections coming from fermions and gauge bosons. The second one is
obtained at the tree level from the higher order effective operators needed for
the ultraviolet completion of the model. Finally we analyze the restrictions
that the requirement of reproducing the standard electroweak symmetry breaking
of the SM set on the LH model parameters.Comment: 23 pages, 3 figures. Version accepted in EPJ
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