3,174 research outputs found
Retrieval Properties of Hopfield and Correlated Attractors in an Associative Memory Model
We examine a previouly introduced attractor neural network model that
explains the persistent activities of neurons in the anterior ventral temporal
cortex of the brain. In this model, the coexistence of several attractors
including correlated attractors was reported in the cases of finite and
infinite loading. In this paper, by means of a statistical mechanical method,
we study the statics and dynamics of the model in both finite and extensive
loading, mainly focusing on the retrieval properties of the Hopfield and
correlated attractors. In the extensive loading case, we derive the evolution
equations by the dynamical replica theory. We found several characteristic
temporal behaviours, both in the finite and extensive loading cases. The
theoretical results were confirmed by numerical simulations.Comment: 12 pages, 7 figure
Magnetic strong coupling in a spin-photon system and transition to classical regime
We study the energy level structure of the Tavis-Cumming model applied to an
ensemble of independent magnetic spins coupled to a variable number of
photons. Rabi splittings are calculated and their distribution is analyzed as a
functin of photon number and spin system size . A sharp
transition in the distribution of the Rabi frequency is found at . The width of the Rabi frequency spectrum diverges as
at this point. For increased number of photons , the Rabi
frequencies converge to a value proportional to . This
behavior is interpreted as analogous to the classical spin resonance mechanism
where the photon is treated as a classical field and one resonance peak is
expected. We also present experimental data demonstrating cooperative, magnetic
strong coupling between a spin system and photons, measured at room
temperature. This points towards quantum computing implementation with magnetic
spins, using cavity quantum-electrodynamics techniques.Comment: Received 8 April 2010; revised manuscript received 17 June 2010;
published 14 July 201
Quantum Monte Carlo Study on Magnetization Processes
A quantum Monte Carlo method combining update of the loop algorithm with the
global flip of the world line is proposed as an efficient method to study the
magnetization process in an external field, which has been difficult because of
inefficiency of the update of the total magnetization. The method is
demonstrated in the one dimensional antiferromagnetic Heisenberg model and the
trimer model. We attempted various other Monte Carlo algorithms to study
systems in the external field and compared their efficiency.Comment: 5 pages, 9 figures; added references for section 1, corrected typo
Nonexponential Relaxation of Magnetization at the Resonant Tunneling Point under a Fluctuating Random Noise
Nonexponential relaxation of magnetization at resonant tunneling points of
nanoscale molecular magnets is interpreted to be an effect of fluctuating
random field around the applied field. We demonstrate such relaxation in
Langevin equation analysis and clarify how the initial relaxation (square-root
time) changes to the exponential decay. The scaling properties of the
relaxation are also discussed.Comment: 4 pages, 4 fgiure
Ordered phase and phase transitions in the three-dimensional generalized six-state clock model
We study the three-dimensional generalized six-state clock model at values of
the energy parameters, at which the system is considered to have the same
behavior as the stacked triangular antiferromagnetic Ising model and the
three-state antiferromagnetic Potts model. First, we investigate ordered phases
by using the Monte Carlo twist method (MCTM). We confirmed the existence of an
incompletely ordered phase (IOP1) at intermediate temperature, besides the
completely ordered phase (COP) at low-temperature. In this intermediate phase,
two neighboring states of the six-state model mix, while one of them is
selected in the low temperature phase. We examine the fluctuation the mixing
rate of the two states in IOP1 and clarify that the mixing rate is very stable
around 1:1.
The high temperature phase transition is investigated by using
non-equilibrium relaxation method (NERM). We estimate the critical exponents
beta=0.34(1) and nu=0.66(4). These values are consistent with the 3D-XY
universality class. The low temperature phase transition is found to be of
first-order by using MCTM and the finite-size-scaling analysis
The Mu2e crystal calorimeter
The Mu2e Experiment at Fermilab will search for coherent, neutrino-less conversion of negative muons into electrons in the field of an Aluminum nucleus, μ− + Al → e− +Al. Data collection start is planned for the end of 2021. The dynamics of such charged lepton flavour violating (CLFV) process is well modelled by a two-body decay, resulting in a mono-energetic electron with an energy slightly below the muon rest mass. If no events are observed in three years of running, Mu2e will set an upper limit on the ratio between the conversion and the capture rates R_μe = μ− + A(Z,N) → e− + A(Z,N)/μ− + A(Z,N) → ν_μ− + A(Z−1,N) of ≤ 6 × 10^(−17) (@ 90% C.L.). This will improve the current limit of four order of magnitudes with respect to the previous best experiment. Mu2e complements and extends the current search for μ → e γ decay at MEG as well as the direct searches for new physics at the LHC. The observation of such CLFV process could be clear evidence for New Physics beyond the Standard Model. Given its sensitivity, Mu2e will be able to probe New Physics at a scale inaccessible to direct searches at either present or planned high energy colliders. To search for the muon conversion process, a very intense pulsed beam of negative muons (~ 10^(10) μ/sec) is stopped on an Aluminum target inside a very long solenoid where the detector is also located. The Mu2e detector is composed of a straw tube tracker and a CsI crystals electromagnetic calorimeter. An external veto for cosmic rays surrounds the detector solenoid. In 2016, Mu2e has passed the final approval stage from DOE and has started its construction phase. An overview of the physics motivations for Mu2e, the current status of the experiment and the required performances and design details of the calorimeter are presented
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