601 research outputs found
Scaling study of Si and strained Si n-MOSFETs with different high-k gate stacks
Using ensemble Monte Carlo device simulations, this paper studies the impact of interface roughness and soft-optical phonon scattering on the performance of sub-100nm Si and strained Si MOSFETs with different high-k gate stacks. Devices with gate lengths down to 25nm have been investigated
Interaction Between Hot Carrier Aging and PBTI Degradation in nMOSFETs: Characterization, Modelling and Lifetime Prediction
Modelling of the interaction between Hot Carrier Aging (HCA) and Positive Bias Temperature Instability (PBTI) has been considered as one of the main challenges in nanoscale CMOS circuit design. Previous works were mainly based on separate HCA and PBTI instead of Interacted HCA-PBTI Degradation (IHPD). The key advance of this work is to develop a methodology that enables accurate modelling of IHPD through understanding the charging/discharging and generation kinetics of different types of defects during the interaction between HCA and PBTI. It is found that degradation during alternating HCA and PBTI stress cannot be modelled by independent HCI/PBTI. Different stress sequence, i.e. HCA-PBTI-HCA and PBTI-HCA-PBTI, lead to completely different degradation kinetics. Based on the Cyclic Anti-neutralization Model (CAM), for the first time, IHPD has been accurately modelled for both short and long channel devices. Complex degradation mechanisms and kinetics can be well explained by our model. Our results show that device lifetime can be underestimated by one decade without considering interaction
Charge dynamics in the Mott insulating phase of the ionic Hubbard model
We extend to charge and bond operators the transformation that maps the ionic
Hubbard model at half filling onto an effective spin Hamiltonian. Using these
operators we calculate the amplitude of the charge density wave in different
dimensions. In one dimension, the charge-charge correlations at large distance
d decay as 1/(d^3 ln^{3/2}d), in spite of the presence of a charge gap, as a
consequence of remaining charge-spin coupling. Bond-bond correlations decay as
(-1)^d 1/(d ln^{3/2}d) as in the usual Hubbard model.Comment: 4 pages, no figures, submitted to Phys. Rev. B printing errors
corrected and some clarifications adde
ε-Aminocaproic acid does not increase adverse effects in cardiac surgery: an analysis of 2,852 cases
The dimerized phase of ionic Hubbard models
We derive an effective Hamiltonian for the ionic Hubbard model at half
filling, extended to include nearest-neighbor repulsion. Using a spin-particle
transformation, the effective model is mapped onto simple spin-1 models in two
particular cases. Using another spin-particle transformation, a slightly
modified model is mapped into an SU(3) antiferromagnetic Heisenberg model whose
exact ground state is known to be spontaneously dimerized. From the effective
models several properties of the dimerized phase are discussed, like
ferroelectricity and fractional charge excitations. Using bosonization and
recent developments in the theory of macroscopic polarization, we show that the
polarization is proportional to the charge of the elementary excitations
Charge and spin excitations of insulating lamellar copper oxides
A consistent description of low-energy charge and spin responses of the
insulating Sr_2CuO_2Cl_2 lamellar system is found in the framework of a
one-band Hubbard model which besides includes hoppings up to 3^{rd}
nearest-neighbors. By combining mean-field calculations, exact diagonalization
(ED) results, and Quantum Monte Carlo simulations (QMC), we analyze both charge
and spin degrees of freedom responses as observed by optical conductivity,
ARPES, Raman and inelastic neutron scattering experiments. Within this
effective model, long-range hopping processes flatten the quasiparticle band
around . We calculate also the non-resonant A_{1g} and B_{1g} Raman
profiles and show that the latter is composed by two main features, which are
attributed to 2- and 4-magnon scattering.Comment: 6 pages, 3 figures, To be published in PRB (july
Toward reliable population estimates of wolves by combining spatial capture-recapture models and non-invasive DNA monitoring
Decision-makers in wildlife policy require reliable population size estimates to justify interventions, to build acceptance and support in their decisions and, ultimately, to build trust in managing authorities. Traditional capture-recapture approaches present two main shortcomings, namely, the uncertainty in defining the effective sampling area, and the spatially-induced heterogeneity in encounter probabilities. These limitations are overcome using spatially explicit capture-recapture approaches (SCR). Using wolves as case study, and non-invasive DNA monitoring (faeces), we implemented a SCR with a Poisson observation model in a single survey to estimate wolf density and population size, and identify the locations of individual activity centres, in NW Iberia over 4,378 km. During the breeding period, posterior mean wolf density was 2.55 wolves/100 km (95%BCI = 1.87-3.51), and the posterior mean population size was 111.6 ± 18.8 wolves (95%BCI = 81.8-153.6). From simulation studies, addressing different scenarios of non-independence and spatial aggregation of individuals, we only found a slight underestimation in population size estimates, supporting the reliability of SCR for social species. The strategy used here (DNA monitoring combined with SCR) may be a cost-effective way to generate reliable population estimates for large carnivores at regional scales, especially for endangered species or populations under game management.J.V.L.B. was supported by a Ramon & Cajal research contract (RYC-2015-18932) from the Spanish Ministry of Economy, Industry and Competitiveness. R.G. was supported by research contract (IF/00564/2012) from the Portuguese Foundation for Science and Technology (FCT). Tis work was partially supported by the project PTDC/BIA-EVF/2460/2014 (FCT).Peer Reviewe
Self-Similarity and Localization
The localized eigenstates of the Harper equation exhibit universal
self-similar fluctuations once the exponentially decaying part of a wave
function is factorized out. For a fixed quantum state, we show that the whole
localized phase is characterized by a single strong coupling fixed point of the
renormalization equations. This fixed point also describes the generalized
Harper model with next nearest neighbor interaction below a certain threshold.
Above the threshold, the fluctuations in the generalized Harper model are
described by a strange invariant set of the renormalization equations.Comment: 4 pages, RevTeX, 2 figures include
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