4,930 research outputs found
BASIC PRINCIPLE OF RIDING ON A SNAKEBOARD
This paper describes the mathematical model of a derivative of a skateboard known as the snakeboard. Equations of motion of the model are derived and their analytical and numerical investigations are fulfilled assuming harmonic excitation for the angles of rotation by feet and a torso of the rider. The possibility of the forward motion for the snakeboard is analyzed
Mirror symmetry for Del Pezzo surfaces: Vanishing cycles and coherent sheaves
We study homological mirror symmetry for Del Pezzo surfaces and their mirror
Landau-Ginzburg models. In particular, we show that the derived category of
coherent sheaves on a Del Pezzo surface X_k obtained by blowing up CP^2 at k
points is equivalent to the derived category of vanishing cycles of a certain
elliptic fibration W_k:M_k\to\C with k+3 singular fibers, equipped with a
suitable symplectic form. Moreover, we also show that this mirror
correspondence between derived categories can be extended to noncommutative
deformations of X_k, and give an explicit correspondence between the
deformation parameters for X_k and the cohomology class [B+i\omega]\in
H^2(M_k,C).Comment: 40 pages, 9 figure
Long-term operation of a multi-channel cosmic muon system based on scintillation counters with MRS APD light readout
A Cosmic Ray Test Facility (CRTF) is the first large-scale implementation of
a scintillation triggering system based on a new scintillation technique known
as START. In START, the scintillation light is collected and transported by WLS
optical fibers, while light detection is performed by pairs of avalanche
photodiodes with the Metal-Resistor-Semiconductor structure operated in the
Geiger mode (MRS APD). START delivers 100% efficiency of cosmic muon detection,
while its intrinsic noise level is less than 10^{-2} Hz. CRTF, consisting of
160 START channels, has been continuously operated by the ALICE TOF
collaboration for more than 25 000 hours, and has demonstrated a high level of
stability. Fewer than 10% of MRS APDs had to be replaced during this period.Comment: Proceedings of NDIP-2008. 8 pages, 8 figures, 6 reference
Radiation Damage Studies of Silicon Photomultipliers
We report on the measurement of the radiation hardness of silicon
photomultipliers (SiPMs) manufactured by
Fondazione Bruno Kessler in Italy (1 mm and 6.2 mm), Center of
Perspective Technology and Apparatus in Russia (1 mm and 4.4 mm), and
Hamamatsu Corporation in Japan (1 mm). The SiPMs were irradiated using a
beam of 212 MeV protons at Massachusetts General Hospital, receiving fluences
of up to protons per cm with the SiPMs at operating
voltage. Leakage currents were read continuously during the irradiation. The
delivery of the protons was paused periodically to record scope traces in
response to calibrated light pulses to monitor the gains, photon detection
efficiencies, and dark counts of the SiPMs. The leakage current and dark noise
are found to increase with fluence. Te leakage current is found to be
proportional to the mean square deviation of the noise distribution, indicating
the dark counts are due to increased random individual pixel activation, while
SiPMs remain fully functional as photon detectors. The SiPMs are found to
anneal at room temperature with a reduction in the leakage current by a factor
of 2 in about 100 days.Comment: 35 pages, 25 figure
Регенеративный усилитель чирпированных импульсов на кристалле Yb3+:LuAlO3 с усилением отдельных спектральных компонент для применений в терагерцовой области спектра
Compact diode-pumped chirped pulse regenerative amplifier systems with pulse repetition rate of hundreds kilohertz based on Yb3+-doped crystals are of practical importance for wide range of applications such as materials processing, medicine, scientific research, etc. The aim of this work was to study the Yb3+:LuAlO3 crystal based dual wavelength chirped pulse regenerative amplifier. Perovskite-like aluminate crystals have unique spectroscopic properties that allowed to use amplifier active element gain spectrum as an amplitude filter for amplified pulse spectrum and even obtained dual wavelength amplification without any additional components. In our work a simple way to obtain dual-wavelength operation of chirped pulse regenerative amplifier by using the active medium gain spectrum as an amplitude filter for the formation of the amplified pulses spectrum demonstrated for the first time to our knowledge. Maximum output power of 5.4 W of chirped pulses (3.8 W after compression) and optical-to-optical efficiency of 22.5 % have been obtained for Yb:LuAP E//b-polarization at 200 kHz repetition rate. Compressed amplified pulse duration was about 708 fs while separate spectral components durations were 643 fs and 536 fs at 1018.3 nm and 1041.1 nm central wavelengths, respectively. Performed investigations show high potential of Yb3+:LuAP crystals as active elements of compact diode pumped chirped pulse regenerative amplifiers
Высокомощный лазер на кристалле Yb3+:YAlO3, работающий в режиме синхронизации мод на основе полупроводниковых зеркал с насыщающимся поглотителем
Yttrium aluminium perovskite YAlO3 (YAP) crystal, doped with rare-earth ions, has been extensively studied as a diode-pumped laser host material. The wide interest to rare-earth ions doped YAP crystals is explained by its good thermal and mechanical properties, high natural birefringence, widely used Czochralski growth method. The aim of this work was to study the Yb3+:YAlO3 crystal as an active medium for high power mode-locked laser. Yb3+-doped perovskite-like aluminate crystals have unique spectroscopic and thermooptical properties that allowed using these crystals as an active medium of high power continuous wave (CW) and modelocked (ML) bulk lasers with diode pumping. In our work spectroscopic properties of Yb:YAP crystal and laser characteristics in CW and ML regimes are investigated. Maximum output power of 4 W with optical-to-optical efficiency of 16.3 % and 140 fs pulse duration have been obtained for Yb:YAP E //c-polarization with 10 % output coupler transmittance. Tunability range as wide as 67 nm confirms high promise of using Yb:YAP crystal for lasers working in wide spectral range
- …