3,382 research outputs found
Collective Modes of Massive Dirac Fermions in Armchair Graphene Nanoribbons
We report the plasmon dispersion characteristics of intrinsic and extrinsic
armchair graphene nanoribbons of atomic width N = 5 using a p_z-orbital tight
binding model with third-nearest-neighbor (3nn) coupling. The coupling
parameters are obtained by fitting the 3nn dispersions to that of an extended
Huckel theory. The resultant massive Dirac Fermion system has a band gap E_g
\approx 64 meV. The extrinsic plasmon dispersion relation is found to approach
a common dispersion curve as the chemical potential increases, whereas
the intrinsic plasmon dispersion relation is found to have both energy and
momentum thresholds. We also report an analytical model for the extrinsic
plasmon group velocity in the q \rightarrow 0 limit
An Extended Huckel Theory based Atomistic Model for Graphene Nanoelectronics
An atomistic model based on the spin-restricted extended Huckel theory (EHT)
is presented for simulating electronic structure and I-V characteristics of
graphene devices. The model is applied to zigzag and armchair graphene
nano-ribbons (GNR) with and without hydrogen passivation, as well as for
bilayer graphene. Further calculations are presented for electric fields in the
nano-ribbon width direction and in the bilayer direction to show electronic
structure modification. Finally, the EHT Hamiltonian and NEGF (Nonequilibrium
Green's function) formalism are used for a paramagnetic zigzag GNR to show
2e2/h quantum conductance.Comment: 5 pages, 8 figure
A theoretical model for single molecule incoherent scanning tunneling spectroscopy
Single molecule scanning tunneling spectroscopy (STS), with dephasing due to
elastic and inelastic scattering, is of some current interest. Motivated by
this, we report an extended Huckel theory (EHT) based mean-field
Non-equilibrium Green's function (NEGF) transport model with electron-phonon
scattering treated within the self-consistent Born approximation (SCBA).
Furthermore, a procedure based on EHT basis set modification is described. We
use this model to study the effect of the temperature dependent dephasing, due
to low lying modes in far-infrared range for which hw<<kT, on the resonant
conduction through highest occupied molecular orbital (HOMO) level of a phenyl
dithiol molecule sandwiched between two fcc-Au(111) contacts. Furthermore, we
propose to include dephasing in room temperature molecular resonant conduction
calculations.Comment: 12 pages, 5 figure
Exploring the effects of capital mobility on the saving–investment nexus: evidence from Icelandic historical data
We explore the effects of capital mobility on the relationship between
saving and investment using historical data for Iceland. First, we analyse
the saving–investment (S-I) correlation for the period of restricted capital
mobility using data from 1960 and 1994. We then add a period of free
capital mobility between 1994 and 2008 and estimate the correlation for
the period 1960–2008. Finally, we extend our analysis to the 2008 to
2016 period, when capital controls were imposed in response to the
crisis. Institutions matter: We find institutional changes, in particular,
Iceland’s entry into the European Single Market in 1994, coincided with
a fall in the long-run correlation between saving and investment.
However, the correlation weakens further when we include the postcrisis regime of capital controls, suggesting a weaker relationship
between savings and investment in this regime. We discuss the possible
reasons for this pattern and also the implications of our findings for
post-crisis policy in small open economies
Poverty and Its Determinants in Pakistan: Evidence from Pslm 2010-11
This study estimates the poverty in terms of head count ratio, poverty gap and squared poverty gap by using the fresh available PSLM data for the year 2010-11 in Pakistan. This study also finds its economic determinants by estimating multiple OLS regression.The results show that the headcount ratio, poverty gap and squared poverty gap are statistically significant 15.06 %, 2.29 % and 0.55 %, respectively in Pakistan. All of the poverty estimates arestatistically significant almost double in rural areas as compared to urban areas. The comparisons of the poverty estimates of this year with the previous ones of2007-08 at urban, rural and nationallevel show that poverty decreased statistically significantly. Among the provinces it is the highest in Baluchistan and the lowest in Sindh. The comparison of provincial poverty estimates of this year with the same ones of previous year (2007-08) depict that poverty decreased in all of the provinces, but it is statistically significant only in case of Baluchistan.Further the resultsshow that Poverty has statistically significantinverse relationship with education. Households having animals for transportation, owning residential buildings, shops and commercial buildings and living in urban areas have less poverty than those who do not. But it hasstatistically significant positive association with the household size and dependency ratio. The household size is greater in poor families than the rich ones. As far as household head’s employment status, occupation and industry is concerned, it is highest in sharecroppers,elementary occupations, and community, social services. At a policy level, it is suggested that Govt. should focus more on education and generationof employment opportunities. Further it should provide loansto lower income groups on reduced rates for housing facilities andto start their own businesses like shops.Family planning should be encouraged especially in poor families.All such policies should focus more on rural areas of especially Baluchistan and KPK in Pakistan. Keywords: Poverty; Education; Animal for transportation; Household size; Dependency ratio; Family planning; Residential building;Shops; Pakistan
A new record of Pycnodactylopsis tomentosa (Fåhraeus 1842) (Coleoptera: Curculionidae) from Sindh, Pakistan.
An atomistic quantum transport solver with dephasing for field-effect transistors
Extended Huckel theory (EHT) along with NEGF (Non-equilibrium Green's
function formalism) has been used for modeling coherent transport through
molecules. Incorporating dephasing has been proposed to theoretically reproduce
experimental characteristics for such devices. These elastic and inelastic
dephasing effects are expected to be important in quantum devices with the
feature size around 10nm, and hence an efficient and versatile solver is
needed. This model should have flexibility to be applied to a wide range of
nano-scale devices, along with 3D electrostatics, for arbitrary shaped contacts
and surface roughness. We report one such EHT-NEGF solver with dephasing by
self-consistent Born approximation (SCBA). 3D electrostatics is included using
a finite-element scheme. The model is applied to a single wall carbon nanotube
(CNT) cross-bar structure with a C60 molecule as the active channel. Without
dephasing, a negative differential resistance (NDR) peak appears when the C60
lowest unoccupied molecular orbital level crosses a van Hove singularity in the
1D density of states of the metallic CNTs acting as contacts. This NDR
diminishes with increasing dephasing in the channel as expected.Comment: to appear in Journal of Computational Electronic
Indirect Estimation of Link Delays by Directly Observing a Triplet of Network Metrics
AbstractThis paper presents an improved indirect estimation link delays from a triplet of network metrics; path delays, packet loss rate (PLR), and jitter by using indirect inverse modeling techniques. conventionally a network metric is estimated by directly observing another network parameter. Based on the evidence in the literature that path delays, PLR, and jitter are interdependent, this work exploits this mutual interdependent of this triplet of metrics based on the notion that a better observation leads to better estimation. We applied NTF1 model, a variation of non negative tensor factorization (NTF) for this purpose and estimated link delay from a triplet of metrics. Evaluation process used data from an experimental test bed that consists of standard networking devices. The estimated link delays were correlated to actual link delays to benchmark the accuracy of estimation. Results showed a better correlation between the estimated and measured link delays when a triplet of metrics is used
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