16,099 research outputs found
The detection of gear noise computed by integrating the Fourier and Wavelet methods
This paper presents a new gearbox noise detection algorithm based on analyzing specific points
of vibration signals using the Wavelet Transform. The proposed algorithm is compared with a previouslydeveloped
algorithm associated with the Fourier decomposition using Hanning windowing. Simulation
carried on real data demonstrate that the WT algorithm achieves a comparable accuracy while having a lower
computational cost. This makes the WT algorithm an appropriate candidate for fast processing of noise gear box
Server resource dimensioning and routing of service function chain in NFV network architectures
The Network Function Virtualization (NFV) technology aims at virtualizing the network service with the execution of the single service components in Virtual Machines activated on Commercial-off-the-shelf (COTS) servers. Any service is represented by the Service Function Chain (SFC) that is a set of VNFs to be executed according to a given order. The running of VNFs needs the instantiation of VNF instances (VNFI) that in general are software components executed on Virtual Machines. In this paper we cope with the routing and resource dimensioning problem in NFV architectures. We formulate the optimization problem and due to its NP-hard complexity, heuristics are proposed for both cases of offline and online traffic demand. We show how the heuristics works correctly by guaranteeing a uniform occupancy of the server processing capacity and the network link bandwidth. A consolidation algorithm for the power consumption minimization is also proposed. The application of the consolidation algorithm allows for a high power consumption saving that however is to be paid with an increase in SFC blocking probability
Uninsurable Investment Risks
The authors study a general-equilibrium economy in which agents have the ability to invest in a risky technology. The investment risk cannot be fully insured with optimal contracts, because shocks are private information. The authors show that the presence of these risks may lead to an underaccumulation of capital relative to an economy where idiosyncratic shocks can be fully insured. They also show that, although the availability of state-contingent (optimal) contracts cannot provide full insurance, it brings the aggregate stock of capital close to the complete markets level. Institutional reforms that make the use of these contracts possible have important welfare consequences.Economic models; Financial institutions; Financial markets
Evaluating Pension Portability Reforms: The Tax Reform Act of 1986 as a Natural Experiment
This paper uses the Tax Reform Act of 1986 as a natural experiment to evaluate the job mobility response of prime-aged US employees participating in employer sponsored defined benefit pension plans to a reduction in the vesting period for pension rights accrual. We apply difference-in-differences methods using data from the Survey of Income and Program Participation to estimate the treatment impact of this policy change. We find that on average the reform had no significant effects on voluntary job mobility of the treated group. Our findings are robust to the use of different control groups and difference-in-differences estimators.Labour mobility, employer-provided pension plans, vesting, program evaluation, propensity score matching
The effects of retardation on the topological plasmonic chain: plasmonic edge states beyond the quasistatic limit
We study a one-dimensional plasmonic system with non-trivial topology: a
chain of metallic nanoparticles with alternating spacing, which is the
plasmonic analogue to the Su-Schreiffer-Heeger model. We extend previous
efforts by including long range hopping with retardation and radiative damping,
which leads to a non-Hermitian Hamiltonian with frequency dependence. We
calculate band structures numerically and show that topological features such
as quantised Zak phase persist due to chiral symmetry. This predicts parameters
leading to topologically protected edge modes, which allows for positioning of
disorder-robust hotspots at topological interfaces, opening up novel
nanophotonics applications
Extracting convergent surface energies from slab calculations
The formation energy of a solid surface can be extracted from slab
calculations if the bulk energy per atom is known. It has been pointed out
previously that the resulting surface energy will diverge with slab thickness
if the bulk energy is in error, in the context of calculations which used
different methods to study the bulk and slab systems. We show here that this
result is equally relevant for state-of-the-art computational methods which
carefully treat bulk and slab systems in the same way. Here we compare
different approaches, and present a solution to the problem that eliminates the
divergence and leads to rapidly convergent and accurate surface energies.Comment: 3 revtex pages, 1 figure, in print on J. Phys. Cond. Mat
Asymptotics of surface-plasmon redshift saturation at sub-nanometric separations
Many promising nanophotonics endeavours hinge upon the unique plasmonic
properties of nanometallic structures with narrow non-metallic gaps, which
support super-concentrated bonding modes that singularly redshift with
decreasing separations. In this letter, we present a descriptive physical
picture, complemented by elementary asymptotic formulae, of a nonlocal
mechanism for plasmon-redshift saturation at subnanometric gap widths. Thus, by
considering the electron-charge and field distributions in the close vicinity
of the metal-vacuum interface, we show that nonlocality is asymptotically
manifested as an effective potential discontinuity. For bonding modes in the
near-contact limit, the latter discontinuity is shown to be effectively
equivalent to a widening of the gap. As a consequence, the resonance-frequency
near-contact asymptotics are a renormalisation of the corresponding local ones.
Specifically, the renormalisation furnishes an asymptotic plasmon-frequency
lower bound that scales with the -power of the Fermi wavelength. We
demonstrate these remarkable features in the prototypical cases of nanowire and
nanosphere dimers, showing agreement between our elementary expressions and
previously reported numerical computations
Surface-plasmon resonances of arbitrarily shaped nanometallic structures in the small-screening-length limit
According to the hydrodynamic Drude model, surface-plasmon resonances of
metallic nanostructures blueshift owing to the nonlocal response of the metal's
electron gas. The screening length characterising the nonlocal effect is often
small relative to the overall dimensions of the metallic structure, which
enables us to derive a coarse-grained nonlocal description using matched
asymptotic expansions; a perturbation theory for the blueshifts of arbitrary
shaped nanometallic structures is then developed. The effect of nonlocality is
not always a perturbation and we present a detailed analysis of the "bonding"
modes of a dimer of nearly touching nanowires where the leading-order
eigenfrequencies and eigenmode distributions are shown to be a renormalisation
of those predicted assuming a local metal permittivity
Factorization in exclusive semileptonic radiative B decays
We derive a new factorization relation for the semileptonic radiative decay B
-> \pi \ell \nu \gamma in the kinematical region of a slow pion p_\pi ~ \Lambda
and an energetic photon E_\gamma >> \Lambda, working at leading order in
\Lambda/m_b. In the limit of a soft pion, the nonperturbative matrix element
appearing in this relation can be computed using chiral perturbation theory. We
present a phenomenological study of this decay, which may be important for a
precise determination of the exclusive nonradiative decay.Comment: 10 pages, 3 figures; minor corrections, one reference adde
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