525 research outputs found
Nonlocal ultrafast demagnetization dynamics of Co/Pt multilayers by optical field enhancement
The influence on ultrafast demagnetization dynamics of metallic nano-structured gratings deposited on thin films of magnetic Co/Pt multilayers is investigated by the time-resolved optical Kerr effect. Depending on the polarization of the pump pulse, a pronounced enhancement of the demagnetization amplitude is found. Calculation of the inhomogeneous optical field distribution due to plasmon interaction and time-dependent solutions of the coupled electron, lattice, and spin temperatures in two dimensions show good agreement with the experimental data, as well as giving evidence of non-local demagnetization dynamics due to electron diffusion.BMBF, 05K10KTB, Verbundprojekt: FSP 301 - FLASH: Nanoskopische Systeme. Teilprojekt 1.1: Universelle Experimentierkammer für Streuexperimente mit kohärenten Femtosekunden-Röntgenpulsen Multi Purpose Coherent Scattering Chamber for FLASH and XFEL 'MPscatt
Pre-Production and Quality Assurance of the Mu2e Calorimeter Silicon Photomultipliers
The Mu2e electromagnetic calorimeter has to provide precise information on
energy, time and position for 100 MeV electrons. It is composed of 1348
un-doped CsI crystals, each coupled to two large area Silicon Photomultipliers
(SiPMs). A modular and custom SiPM layout consisting of a 32 array of
66 mm UV-extended monolithic SiPMs has been developed to fulfill
the Mu2e calorimeter requirements and a pre-production of 150 prototypes has
been procured by three international firms (Hamamatsu, SensL and Advansid). A
detailed quality assurance process has been carried out on this first batch of
photosensors: the breakdown voltage, the gain, the quenching time, the dark
current and the Photon Detection Efficiency (PDE) have been determined for each
monolithic cell of each SiPMs array. One sample for each vendor has been
exposed to a neutron fluency up to 8.5~~10 1 MeV (Si) eq.
n/cm and a linear increase of the dark current up to tens of mA has been
observed. Others 5 samples for each vendor have undergone an accelerated aging
in order to verify a Mean Time To Failure (MTTF) higher than 10
hours.Comment: NDIP 2017 - New Developments In Photodetection, 3-7 July 2017, Tours
(France
Ordering in a spin glass under applied magnetic field
Torque, torque relaxation, and magnetization measurements on a AuFe spin
glass sample are reported. The experiments carried out up to 7 T show a
transverse irreversibility line in the (H,T) plane up to high applied fields,
and a distinct strong longitudinal irreversibility line at lower fields. The
data demonstrate for that this type of sample, a Heisenberg spin glass with
moderately strong anisotropy, the spin glass ordered state survives under high
applied fields in contrast to predictions of certain "droplet" type scaling
models. The overall phase diagram closely ressembles those of mean field or
chiral models, which both have replica symmetry breaking transitions.Comment: 4 pages, 3 figures, accepted for PR
Energy and time resolution for a LYSO matrix prototype of the Mu2e experiment
We have measured the performances of a LYSO crystal matrix prototype tested
with electron and photon beams in the energy range 60450 MeV. This study has
been carried out to determine the achievable energy and time resolutions for
the calorimeter of the Mu2e experiment.Comment: 2 pages, 3 figures, 13th Pisa Meeting on Advanced Detector
Autonomous stochastic resonance in fully frustrated Josephson-junction ladders
We investigate autonomous stochastic resonance in fully frustrated
Josephson-junction ladders, which are driven by uniform constant currents. At
zero temperature large currents induce oscillations between the two ground
states, while for small currents the lattice potential forces the system to
remain in one of the two states. At finite temperatures, on the other hand,
oscillations between the two states develop even below the critical current;
the signal-to-noise ratio is found to display array-enhanced stochastic
resonance. It is suggested that such behavior may be observed experimentally
through the measurement of the staggered voltage.Comment: 6 pages, 11 figures, to be published in Phys. Rev.
Cerebral oxygenation and blood flow in term infants during postnatal transition : BabyLux project
Objectives: A new device that combines, for the first time, two photonic technologies (time-resolved near-infrared spectroscopy and diffuse correlation spectroscopy) was provided and tested within the BabyLux project. Aim was to validate the expected changes in cerebral oxygenation and blood flow. Methods: A pulse oximeter and the BabyLux device were held in place (right hand/wrist and frontoparietal region, respectively) for 10 min after birth in healthy term infants delivered by elective caesarean section. Pulse oximeter saturation (SpO 2 ), cerebral tissue oxygen saturation (StO 2 ) and blood flow index (BFI) were measured over time. Tissue oxygen extraction (TOE) and cerebral metabolic rate of oxygen index (CMRO 2 I) were calculated. Results: Thirty infants were enrolled in two centres. After validity check of data, 23% of infants were excluded from TOE and CMRO 2 I calculation due to missing data. As expected, SpO 2 (estimate 3.05 %/min; 95% CI 2.78 to 3.31 %/min) and StO 2 (estimate 3.95 %/min; 95% CI 3.63 to 4.27 %/min) increased in the first 10 min after birth, whereas BFI (estimate -2.84
710 -9 cm 2 /s/min; 95% CI -2.50
710 -9 to -3.24
710 -9 cm 2 /s/min) and TOE (estimate -0.78 %/min; 95% CI -1.12 to -0.45 %/min) decreased. Surprisingly, CMRO 2 I decreased (estimate -7.94
710 -8 /min; 95% CI -6.26
710 -8 to -9.62
710 -8 /min). Conclusions: Brain oxygenation and BFI during transition were successfully and simultaneously obtained by the BabyLux device; no adverse effects were recorded, and the BabyLux device did not limit the standard care. The preliminary results from clinical application of the BabyLux device are encouraging in terms of safety and feasibility; they are consistent with previous reports on brain oxygenation during transition, although the interpretation of the decreasing CMRO 2 I remains open. Trial registration number: NCT02815618
Design, status and perspective of the Mu2e crystal calorimeter
The Mu2e experiment at Fermilab will search for the charged lepton flavor
violating process of neutrino-less coherent conversion in the field
of an aluminum nucleus. Mu2e will reach a single event sensitivity of about
that corresponds to four orders of magnitude improvements
with respect to the current best limit. The detector system consists of a straw
tube tracker and a crystal calorimeter made of undoped CsI coupled with Silicon
Photomultipliers. The calorimeter was designed to be operable in a harsh
environment where about 10 krad/year will be delivered in the hottest region
and work in presence of 1 T magnetic field. The calorimeter role is to perform
/e separation to suppress cosmic muons mimiking the signal, while
providing a high level trigger and a seeding the track search in the tracker.
In this paper we present the calorimeter design and the latest RD results.Comment: 4 pages, conference proceeding for a presentation held at TIPP'2017.
To be published on Springer Proceedings in Physic
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