9,194 research outputs found
Strong mobility degradation in ideal graphene nanoribbons due to phonon scattering
We investigate the low-field phonon-limited mobility in armchair graphene
nanoribbons (GNRs) using full-band electron and phonon dispersion relations. We
show that lateral confinement suppresses the intrinsic mobility of GNRs to
values typical of common bulk semiconductors, and very far from the impressive
experiments on 2D graphene. Suspended GNRs with a width of 1 nm exhibit a
mobility close to 500 cm^2/Vs at room temperature, whereas if the same GNRs are
deposited on HfO2 mobility is further reduced to about 60 cm^2/Vs due to
surface phonons. We also show the occurrence of polaron formation, leading to
band gap renormalization of ~118 meV for 1 nm-wide armchair GNRs.Comment: 11 pages, 4 figure
Atomistic quantum transport modeling of metal-graphene nanoribbon heterojunctions
We calculate quantum transport for metal-graphene nanoribbon heterojunctions
within the atomistic self-consistent Schr\"odinger/Poisson scheme. Attention is
paid on both the chemical aspects of the interface bonding as well the
one-dimensional electrostatics along the ribbon length. Band-bending and doping
effects strongly influence the transport properties, giving rise to conductance
asymmetries and a selective suppression of the subband formation. Junction
electrostatics and p-type characteristics drive the conduction mechanism in the
case of high work function Au, Pd and Pt electrodes, while contact resistance
becomes dominant in the case of Al.Comment: 4 pages, 5 figure
Simulation of hydrogenated graphene Field-Effect Transistors through a multiscale approach
In this work, we present a performance analysis of Field Effect Transistors
based on recently fabricated 100% hydrogenated graphene (the so-called
graphane) and theoretically predicted semi-hydrogenated graphene (i.e.
graphone). The approach is based on accurate calculations of the energy bands
by means of GW approximation, subsequently fitted with a three-nearest neighbor
(3NN) sp3 tight-binding Hamiltonian, and finally used to compute ballistic
transport in transistors based on functionalized graphene. Due to the large
energy gap, the proposed devices have many of the advantages provided by
one-dimensional graphene nanoribbon FETs, such as large Ion and Ion/Ioff
ratios, reduced band-to-band tunneling, without the corresponding disadvantages
in terms of prohibitive lithography and patterning requirements for circuit
integration
Lithuanian pension system’s reforms transformations and forecasts
The aim of this article is to describe the Lithuanian pension system, its reform process and its long-term financial sustainability. We define therefore the current reforms in the public pension system, influenced by the last economic crisis and social challenges. Also, we forecast the financial dynamics of the public pension system, in the light of raising social expenses (due to second pillar pension reforms) and of demographic trends (like ageing society and low fertility). Results reveal the long-term sustainability of the system, albeit at a cost of initial negative balances to be covered with public budget. Policy solutions could improve sustainability by encouraging and extending employment (especially for the disadvantaged) and by building trust in both public and private pension systems
Study of sequential semileptonic decays of b hadrons produced at the Tevatron
We present a study of rates and kinematical properties of lepton pairs
contained in central jets with transverse energy E_T > 15 GeV that are produced
at the Fermilab Tevatron collider. We compare the data to a QCD prediction
based on the HERWIG and QQ Monte Carlo generator programs.We find that the data
are poorly described by the simulation, in which sequential semileptonic decays
of single b quarks (b --> l c X with c --> l s X) are the major source of such
lepton pairs.Comment: 25 pages, 8 figures. Some typos were fixed in the text and
bibliography. Submitted to Phys. Rev.
To reorient is easier than to orient: An on-line algorithm for reorientation of graphs
We define an on-line (incremental) algorithm that, given a (possibly infinite) pseudo-transitive oriented graph, produces a transitive reorientation. This implies that a theorem of Ghouila-Houri is provable in RCA_0 and hence is computably true
A study of boiling water flow regimes at low pressures
"A comprehensive experimental program to examine flow regimes at pressures below 100 psia for boiling of water in tubes was carried out. An electrical probe, which measures the resistance of the fluid between the centerline of the flow and the tube wall, was used to identify the various flow regimes. This probe proved to be an ideal detection device, because of its simplicity, reproducibility, and accurate representation of the flow pattern within the heated test section. The major flow regimes observed were bubbly, slug and annular flow. Under certain conditions at high flow rates, a wispy-annular flow patern was observed. The effects of mass velocity (0.2 x 10 - 2.4 x 100 lbm/hr-ft2), inlet temperature (100, 150, 2000F), exit pressure (30, 100 psia), quality (x = -10 - +7 percent), purity (9, 40 PPM NaCl; 1-3 megohm-cm), length (L/D-30, 6Q, 90), diameter 0.094, 0.242 in.), and orientation (vertical and horizontal on the flow regimes were studied. Flow regime maps on coordinates of mass velocity and quality are presented for these conditions. Bubbly and slug flow occurred primarily in the subcooled region, while fully developed annular flow was reached at equilibrium qualities between 2 and 4 percent. The transitions between the different flows were shifted to regions of increased subcooling when velocity, pressure, and heat flux increased, and when inlet temperature decreased. Purity and geometry had little affect on the flow regime boundaries.(cont.) The shifting of the transitions is related to the agglomeration point, which is that point at which the bubbles so coalesce that slug flow is first observed. The agglomeration point depends on the point of incipient boiling, the number of bubbles in the flow, and the number of collisions per bubble. These latter quantities in turn depend on velocity, temperature, pressure, and heat flux. The flow regime information obtained in this study s~hould be of value in correlating and interpreting low pressure heattransfer data. The flow regime data were found to be useful in explaining the effect of inlet temperature on burnout heat flux.Sponsored by the Solid State Sciences Division, Air Force Office of Scientific Research D.S.R
- …