It is well established that B-Raf signaling through the MAP kinase (ERK) pathways plays a prominent role in regulating cell proliferation but how it does this is not completely understood. Here, we ...show that B-Raf serves a physiological role during mitosis in human somatic cells. Knockdown of B-Raf using short interfering RNA (siRNA) resulted in pleiotropic spindle abnormalities and misaligned chromosomes in over 80% of the mitotic cells analyzed. A second B-Raf siRNA gave similar results suggesting these effects are specific to down-regulating B-Raf protein. In agreement with these findings, a portion of B-Raf was detected at the spindle structures including the spindle poles and kinetochores. Knockdown of C-Raf (Raf-1) had no detectable effects on spindle formation or chromosome alignment. Activation of the spindle assembly checkpoint was found to be dependent on B-Raf as evident by the inability of checkpoint proteins Bub1 and Mad2 to localize to unattached kinetochores in HeLa cells treated with B-Raf siRNA. Consistent with this, live-cell imaging microscopy showed that B-Raf-depleted cells exited mitosis earlier than control non-depleted cells. Finally, we provide evidence that B-Raf signaling promotes phosphorylation and kinetochore localization of the mitotic checkpoint kinase Mps1. Blocking B-Raf expression, ERK activity, or phosphorylation at Ser-821 residue perturbed Mps1 localization at unattached kinetochores. Thus, our data implicates a mitotic role for B-Raf in regulating spindle formation and the spindle checkpoint in human somatic cells.
The 2D azimuth and rapidity structure of the two-particle correlations in relativistic A+A collisions is altered significantly by the presence of sharp inhomogeneities in superdense matter formed in ...such processes. The causality constraints enforce one to associate the long-range longitudinal correlations observed in a narrow angular interval, the so-called (soft) ridge, with peculiarities of the initial conditions of collision process. This study's objective is to analyze whether multiform initial tubular structures, undergoing the subsequent hydrodynamic evolution and gradual decoupling, can form the soft ridges. Motivated by the flux-tube scenarios, the initial energy density distribution contains the different numbers of high density tube-like boost-invariant inclusions that form a bumpy structure in the transverse plane. The influence of various structures of such initial conditions in the most central A+A events on the collective evolution of matter, resulting spectra, angular particle correlations and vn-coefficients is studied in the framework of the hydrokinetic model (HKM).
The LUXE experiment aims at studying high-field QED in electron-laser and photon-laser interactions, with the 16.5 GeV electron beam of the European XFEL and a laser beam with power of up to 350 TW. ...The experiment will measure the spectra of electrons and photons in non-linear Compton scattering where production rates in excess of \(10^9\) are expected per 1 Hz bunch crossing. At the same time positrons from pair creation in either the two-step trident process or the Breit--Wheeler process will be measured, where the expected rates range from \(10^{-3}\) to \(10^4\) per bunch crossing, depending on the laser power and focus. These measurements have to be performed in the presence of low-energy high radiation-background. To meet these challenges, for high-rate electron and photon fluxes, the experiment will use Cherenkov radiation detectors, scintillator screens, sapphire sensors as well as lead-glass monitors for back-scattering off the beam-dump. A four-layer silicon-pixel tracker and a compact sampling electromagnetic calorimeter will be used to measure the positron spectra. The layout of the experiment and the expected performance under the harsh radiation conditions will be presented.
A new design of a detector plane of sub-millimetre thickness for an electromagnetic sampling calorimeter is presented. It is intended to be used in the luminometers LumiCal and BeamCal in future ...linear e
+
e
-
collider experiments. The detector planes were produced utilising novel connectivity scheme technologies. They were installed in a compact prototype of the calorimeter and tested at DESY with an electron beam of energy 1–5 GeV. The performance of a prototype of a compact LumiCal comprising eight detector planes was studied. The effective Molière radius at 5 GeV was determined to be (8.1 ± 0.1 (stat) ± 0.3 (syst)) mm, a value well reproduced by the Monte Carlo (MC) simulation (8.4 ± 0.1) mm. The dependence of the effective Molière radius on the electron energy in the range 1–5 GeV was also studied. Good agreement was obtained between data and MC simulation.
A prototype of a luminometer, designed for a future
e
+
e
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collider detector, and consisting at present of a four-plane module, was tested in the CERN PS accelerator T9 beam. The objective of this ...beam test was to demonstrate a multi-plane tungsten/silicon operation, to study the development of the electromagnetic shower and to compare it with MC simulations. The Molière radius has been determined to be 24.0 ± 0.6 (stat.) ± 1.5 (syst.) mm using a parametrization of the shower shape. Very good agreement was found between data and a detailed Geant4 simulation.
The analysis of particle correlations as a function of relative pseudo-rapidity and azimuthal angle exhibit novel ridge-like structures that were discovered at RHIC in A + A collisions. Such an ...analysis is of great interest for forthcoming ALICE LHC experiment. This structure which is unusually wide in the longitudinal direction remains after removal of the known correlation-inducing effects such as elliptic flow and ordinary jet correlations. It could be probably explained only if one supposes that the ridge phenomenon in relativistic A + A collisions is rooted in the initial conditions of the thermal evolution of the system. The aim of this study is to check this hypothesis by an analysis of the evolution of the energy density in the system which at very initial stage of collisions has high density tube-like fluctuations with boost-invariant longitudinally homogeneous structure within some space-rapidity region. The transverse-velocity and energy density profiles, which develop in the system when it reaches the chemical freeze-out (T = 165 MeV) for different initial configurations at t 0 = 0.2 fm/c, are considered.
Micro-strip metal detector for the beam profile monitoring Pugatch, V.; Borysova, M.; Mykhailenko, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2007, Letnik:
581, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The Micro-strip Metal Detector (MMD) design and production technology, readout electronics as well as areas of applications are described. The MMD was designed for beam profile monitoring of charged ...particle and synchrotron radiation beams. Using photolithography and plasma-chemistry etching technologies we succeeded in creating detectors with a metal strip's thickness of less than
2
μ
m
and without any other materials in the working area. The principle of operation is based on the Secondary Electron Emission (SEE). The results obtained with the MMD at the monochromatic synchrotron radiation beam at HASYLAB (DESY) are also presented. The current version of the MMD allows measuring a beam profile and position with an accuracy of
20
μ
m
.
The effect of a fluctuating bumping structure of the initial conditions on spectra and the collective evolution of matter created in heavy-ion collisions in the frameworks of the Hydro-Kinetic Model ...is investigated. As moti-vated by the glasma-flux-tube scenario, the initial conditions are modeled by the set of four high energy-density tube-like fluctuations with longitudinally homogeneous structure within some space-rapidity region in a boost-invariant 2D geometry. It was found that the presence of transversally bumping tube-like fluctuations in initial conditions strongly affects the hydrodynamic evolution and leads to emergence of conspicuous structures in the calculated pion spectra. It was observed that the 4 tube initial configuration generates a four-peak structure in the final azimuthal distributions of one-particle spectra.
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