4,604 research outputs found
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
Lepton Phenomenology of Stueckelberg Portal to Dark Sector
We propose an extension of the Standard Model (SM) with a gauge
invariant Dark Sector connected to the SM via a new portal arising in the
framework of dark photon mass generation via Stueckelberg mechanism. This
mechanism implies the existence of a scalar field , which is
shift-transformed under this group and resembles an axion-like particle (ALP)
widely addressed in the literature in different contexts. The effective dim=5
operators constructed of the covariant derivative of the field
generate flavor non-diagonal renormalizable couplings of both and
to the SM fermions . Contrary to the conventional kinetic mixing portal,
in our scenario flavor diagonal - couplings are not proportional to
the fermion charges. These features drastically change the phenomenology of
dark photon relaxing or avoiding some previously established experimental
constraints. We focus on the phenomenology of the described scenario of the
Stueckelberg portal in the lepton sector and analyze the contribution of the
dark sector fields and to the anomalous magnetic moment of muon
, Lepton Flavor Violating decays and
conversion in nuclei. We obtain limits on the model parameters from the
existing experimental data on the corresponding observables.Comment: 15 pages, 8 figure
Multi-Zone DI Diesel Spray Combustion Model and its application for Matching the Injector Design with Piston Bowl Shape
Copyright © 2006 SAE International A multi-zone, direct-injection (DI) diesel combustion model, the so-called RK-model, has been developed and implemented in a full cycle simulation of a turbocharged engine. The combustion model takes into account: · transient evolution of fuel sprays, · interaction of sprays with swirl and walls, · evolution of near-wall flow formed after spray-wall impingement depending on impingement angle and swirl, fuel-air mixing, · interaction of near-wall flows formed by adjacent sprays, · evaporation conditions for different zones. In the model the fuel spray is divided into a number of zones with different evaporation conditions. The piston bowl is assumed to be a body of revolution of otherwise arbitrary shape. Submodels of soot and NOx formation are included. The model has been validated by experimental data obtained from high-speed and medium-speed engines over the whole operating range; a good agreement has been achieved without recalibration for different operating modes. Predictions of spray tip penetration, spray angle and ignition delay were validated by the published data obtained for diesels with multiple injection system and injection timing after the TDC. Formulas for computation of these characteristics were derived. Results obtained without recalibration of the RK-model demonstrate good agreement between the calculated and experimental heat release rate curves as well as between integral engine parameters for diesels with multiple injection being considered. To make a computational research of multiple injection strategy possible, the full cycle thermodynamic engine simulation software DIESEL-RK has been supplied with an additional tool for parametric setting of multiple injection profile by specifying a fuel fraction and delay after previous injection for each fuel portion. These parameters can be used as arguments of optimization in a future research
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
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
Measurement of Exclusive pi(0) Electroproduction Structure Functions and their Relationship to Transverse Generalized Parton Distributions
Exclusive pi(0) electroproduction at a beam energy of 5.75 GeV has been measured with the Jefferson Lab CLAS spectrometer. Differential cross sections were measured at more than 1800 kinematic values in Q(2), x(B), t, and phi(pi), in the Q(2) range from 1.0 to 4.6 GeV2, -t up to 2 GeV2, and x(B) from 0.1 to 0.58. Structure functions sigma(T) + epsilon sigma(L), sigma(TT), and sigma(LT) were extracted as functions of t for each of 17 combinations of Q(2) and x(B). The data were compared directly with two handbag-based calculations including both longitudinal and transversity generalized parton distributions (GPDs). Inclusion of only longitudinal GPDs very strongly underestimates sigma(T) + epsilon sigma(L) and fails to account for sigma(TT) and sigma(LT), while inclusion of transversity GPDs brings the calculations into substantially better agreement with the data. There is very strong sensitivity to the relative contributions of nucleon helicity-flip and helicity nonflip processes. The results confirm that exclusive pi(0) electroproduction offers direct experimental access to the transversity GPDs
Passive mode locking of a Tm,Ho:KY(WO4)(2) laser around 2 μm
We report the first demonstration, to our knowledge, of passive mode locking in a Tm3+, Ho3+-codoped KYWO42 laser operating in the 2000-2060 nm spectral region. An InGaAsSb-based quantum well semiconductor saturable absorber mirror is used for the initiation and stabilization of the ultrashort pulse generation. Pulses as short as 3.3 ps were generated at 2057 nm with average output powers up to 315 mW at a pulse repetition frequency of 132 MHz for 1.15 W of absorbed pump power at 802 nm from a Ti:sapphire laser
Partnership of State and Business in Transcaucasia: History and Current Trends
The article aims to present generally the dynamics of political and economic systems on the territory of Transcaucasia in the period from the second millennium BC to the present. This dynamics is seen as reflecting the historical experience of the Transcaucasian societies, whih is successively preserved at the present time. Institutional aspects are studied of public-private partnership projects currently being implemented by the South-Caucasian member states of the Eastern Partnership integration association
Second virial coefficients of light nuclear clusters and their chemical freeze-out in nuclear collisions
Here we develop a new strategy to analyze the chemical freeze-out of light
(anti)nuclei produced in high energy collisions of heavy atomic nuclei within
an advanced version of the hadron resonance gas model. It is based on two
different, but complementary approaches to model the hard-core repulsion
between the light nuclei and hadrons. The first approach is based on an
approximate treatment of the equivalent hard-core radius of a roomy nuclear
cluster and pions, while the second approach is rigorously derived here using a
self-consistent treatment of classical excluded volumes of light (anti)nuclei
and hadrons. By construction, in a hadronic medium dominated by pions, both
approaches should give the same results. Employing this strategy to the
analysis of hadronic and light (anti)nuclei multiplicities measured by ALICE at
TeV and by STAR at GeV, we got rid
of the existing ambiguity in the description of light (anti)nuclei data and
determined the chemical freeze-out parameters of nuclei with high accuracy and
confidence. At ALICE energy the nuclei are frozen prior to the hadrons at the
temperature MeV, while at STAR energy there is a
single freeze-out of hadrons and nuclei at the temperature
MeV. We argue that the found chemical freeze-out volumes of nuclei can be
considered as the volumes of quark-gluon bags that produce the nuclei at the
moment of hadronization.Comment: 15 pages, 4 figures, 3 table
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