Given a weighted undirected graph G = (V, E), a tree (respectively tour) cover of an edge-weighted graph is a set of edges which forms a tree (resp. closed walk) and covers every other edge in the graph. The tree (resp. tour) cover... more
Given a weighted undirected graph G = (V, E), a tree (respectively tour) cover of an edge-weighted graph is a set of edges which forms a tree (resp. closed walk) and covers every other edge in the graph. The tree (resp. tour) cover problem is of finding a minimum weight tree (resp. tour) cover of G. Arkin, Halldorsson and Hassin
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With the growth in data traffic, modern MAN networks are moving away from traditional circuit-switched networking technologies towards high-speed packet-switched networking technologies, which support best data traffic, offering high... more
With the growth in data traffic, modern MAN networks are moving away from traditional circuit-switched networking technologies towards high-speed packet-switched networking technologies, which support best data traffic, offering high flexibility, cost-effective and easy-installation solution. Circuit emulation service (CES) is introduced in packet-switched networks in order for them to support traditional TDM (circuit-switched) traffic. Modified packet bursting (MPB) is introduced in
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Circuit Emulation Service is a new technology which allows the transport of TDM service such as PDH (E1/T1/E3/T3) as well as SONET/SDH circuit over a packet switched network. This paper presents the simulation based performance evaluation... more
Circuit Emulation Service is a new technology which allows the transport of TDM service such as PDH (E1/T1/E3/T3) as well as SONET/SDH circuit over a packet switched network. This paper presents the simulation based performance evaluation and QoS guarantee of circuit emulation service over a peculiar metropolitan optical ring network.
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The solubility properties of a series of nitroaromatic compounds have been determined and utilized with known linear solvation energy relationships to calculate their sorption properties in a series of chemoselective polymers. These... more
The solubility properties of a series of nitroaromatic compounds have been determined and utilized with known linear solvation energy relationships to calculate their sorption properties in a series of chemoselective polymers. These measurements and results were used to design a series of novel chemoselective polymers to target polynitroaromatic compounds. The polymers have been evaluated as thin sorbent coatings on surface
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ABSTRACT We propose a Klein tunneling transistor based on the geometrical optics of DFs. We consider the case of a prismatic active region generated by a triangular gate. In this region, total internal reflection may occur, which leads to... more
ABSTRACT We propose a Klein tunneling transistor based on the geometrical optics of DFs. We consider the case of a prismatic active region generated by a triangular gate. In this region, total internal reflection may occur, which leads to the controllable suppression of transistor transmission. We study the transmission and the current in this device by means of non-equilibrium Green's function (NEGF) simulation.
High-performance strained Silicon-On-Insulator (sSOI) nanowires (NW) with gate width (WNW) and length (LG) scaled down to 10nm are presented. For the first time, effectiveness of sSOI substrates is demonstrated for ultra-scaled N-FET NW... more
High-performance strained Silicon-On-Insulator (sSOI) nanowires (NW) with gate width (WNW) and length (LG) scaled down to 10nm are presented. For the first time, effectiveness of sSOI substrates is demonstrated for ultra-scaled N-FET NW (LG=10nm) with an outstanding ION current (ION=1420μA/μm at IOFF=300nA/μm) and an excellent electrostatic immunity (DIBL=82mV/V). P-FET NW performance enhancement is achieved using in-situ HCl+GeH4 etching and selective epitaxial growth of boron-doped Si0.7Ge0.3 for the formation of recessed Sources/Drains (S/D). We show an ION improvement up to +100% induced by recessed SiGe S/D for LG=13nm P-FET NW. Finally, size- and orientation-dependent strain impact on short channel performances is discussed. Si NWs provide the best opportunities for strain engineering.
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ABSTRACT By means of atomistic tight-binding calculations, we investigate the effects of uniaxial strain on the electronic bandstructure of twisted graphene bilayer. We find that the bandstructure is dramatically deformed and the... more
ABSTRACT By means of atomistic tight-binding calculations, we investigate the effects of uniaxial strain on the electronic bandstructure of twisted graphene bilayer. We find that the bandstructure is dramatically deformed and the degeneracy of the bands is broken by strain. As a conseqence, the number of Dirac cones can double and the van Hove singularity points are separated in energy. The dependence of these effects on the strength of strain, its applied direction and the twist angle is carefully clarified. As an important result, we demonstrate that the position of van Hove singularities can be modulated by strain, suggesting the possibility of observing this phenomenon at low energy in a large range of twist angle (i.e., larger than $10^\circ$). Unfortunately, these interesting/important phenomena have not been clarified in the previous works based on the continuum approximation. While they are in good agreement with available experiments, our results provide a detailed understanding of the strain effects on the electronic properties and may motivate other investigations of electronic transport in this type of graphene lattice.
We investigate the effects of uniaxial strain on the transport properties of vertical devices made of two misoriented (or twisted) graphene layers, which partially overlap each other. We find that because of the different orientations of... more
We investigate the effects of uniaxial strain on the transport properties of vertical devices made of two misoriented (or twisted) graphene layers, which partially overlap each other. We find that because of the different orientations of the two graphene lattices, their Dirac points can be displaced and separated in the k-space by the effects of strain. Hence, a finite conduction gap as large as a few hundred meV can be obtained in the device with a small strain of only a few percent. The dependence of this conduction gap on the strain magnitude, strain direction, channel orientation and twist angle are clarified and presented. On this basis, the strong modulation of conductance and significant improvement of Seebeck coefficient are shown. The suggested devices therefore may be very promising for improving applications of graphene, e.g., as transistors or strain and thermal sensors.
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ABSTRACT This article presents a Density-Gradient (DG) calibration for 2D quantum confinement on Tri-Gate Silicon on insulator cross section for which the top gate interface is -oriented and the lateral gate interfaces are -oriented. To... more
ABSTRACT This article presents a Density-Gradient (DG) calibration for 2D quantum confinement on Tri-Gate Silicon on insulator cross section for which the top gate interface is -oriented and the lateral gate interfaces are -oriented. To calibrate the DG model, we use self-consistent Poisson-Schrödinger calculations and fit the capacitance vs gate voltage (C-V) curves. We first calibrate DG model for one-dimensional quantum confinement (1D) on planar devices cross section for both crystal orientations. Then, we check the validity of the parameters obtained for the two-dimensional (2D) quantum confinement on tri-gate architecture cross-section. The DG model allows a good description of the C-V curves in the case of 2D quantum confinement and the parameters are still valid when we reduce the Tri-Gate cross section up to 4 nm by side.
ABSTRACT We compute the electron and hole mobilities in ultrathin body and buried oxide, fully depleted silicon on insulator devices with various high-k metal gate-stacks using nonequilibrium Green's functions (NEGF). We compare... more
ABSTRACT We compute the electron and hole mobilities in ultrathin body and buried oxide, fully depleted silicon on insulator devices with various high-k metal gate-stacks using nonequilibrium Green's functions (NEGF). We compare our results with experimental data at different back gate biases and temperatures. That way, we are able to deembed the different contributions to the carrier mobility in the films (phonons, front and back interface roughness, and remote Coulomb scattering). We discuss the role played by each mechanism in the front and back interface inversion regimes. We draw attention, in particular, to the clear enhancement of electron- and hole--phonons interactions in the films. These results show that FDSOI devices are a foremost tool to sort out the different scattering mechanisms in Si devices, and that NEGF can provide valuable inputs to technology computer aided design.
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ABSTRACT We investigate remote surface roughness (RSR) scattering by the SiO2/HfO2 interface in Fully Depleted Silicon-on-Insulator devices using Non-Equilibrium Green's Functions. We show that the RSR mobility is controlled by... more
ABSTRACT We investigate remote surface roughness (RSR) scattering by the SiO2/HfO2 interface in Fully Depleted Silicon-on-Insulator devices using Non-Equilibrium Green's Functions. We show that the RSR mobility is controlled by cross-correlations between the surface roughness profiles at the Si/SiO2 and SiO2/HfO2 interfaces. Therefore, surface roughness and remote surface roughness cannot be modeled as two independent mechanisms. RSR tends to enhance the total mobility when the Si/SiO2 interface and SiO2 thickness profiles are correlated, and to decrease the total mobility when they are anti-correlated. We discuss the implications for the high-κ/Metal gate technologies.
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ABSTRACT As the characteristic size of the devices is now reaching the sub-15 nm range, it has become essential to assess the effects of quantum corrections on the electrical performances. The Non-Equilibrium Green's Functions... more
ABSTRACT As the characteristic size of the devices is now reaching the sub-15 nm range, it has become essential to assess the effects of quantum corrections on the electrical performances. The Non-Equilibrium Green's Functions (NEGF) method is one of the most versatile frameworks for that purpose. It can deal with quantum confinement, elastic and inelastic scattering in a seamless way. Although numerically intensive, NEGF has benefited from recent advances in computational methodologies and from the increasing availability of high-performance computers. It has now reached a level of maturity where it can be applied to industrial technologies and complement semi-classical modeling.
A series of chemoselective polymers have been designed and synthesized in order to enhance the nitroaromatic sorption properties of coated acoustic wave devices. Acoustic wave devices coated with a thin layer of chemiselective polymer can... more
A series of chemoselective polymers have been designed and synthesized in order to enhance the nitroaromatic sorption properties of coated acoustic wave devices. Acoustic wave devices coated with a thin layer of chemiselective polymer can provide highly sensitive ...
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The performance of 2 μm thick damascene Cu lines embedded in low K material are evaluated. The process is well control over a 200 mm wafer, provided that tiling is used. A minimum linewidth of 560 nm is achieved. The RF performance of... more
The performance of 2 μm thick damascene Cu lines embedded in low K material are evaluated. The process is well control over a 200 mm wafer, provided that tiling is used. A minimum linewidth of 560 nm is achieved. The RF performance of substrate and metal lines in the 1 - 100 GHz frequency range is investigated with coplanar waveguides.
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Strongly enhanced thermoelectric properties are predicted for graphene nanoribbons (GNRs) with optimized pattern. By means of nonequilibrium Green's function atomistic simulation of electron and phonon transport, we analyze the... more
Strongly enhanced thermoelectric properties are predicted for graphene nanoribbons (GNRs) with optimized pattern. By means of nonequilibrium Green's function atomistic simulation of electron and phonon transport, we analyze the thermal and electrical properties of perfect GNRs as a function of their width and their edge orientation to identify a strategy likely to degrade the thermal conductance while retaining high electronic
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ABSTRACT We discuss the effect of strains on the electron and hole mobilities in silicon nanowires with diameters near 10 nm. We show that silicon nanowires are very sensitive to strains, so that strain engineering shall be a highly... more
ABSTRACT We discuss the effect of strains on the electron and hole mobilities in silicon nanowires with diameters near 10 nm. We show that silicon nanowires are very sensitive to strains, so that strain engineering shall be a highly efficient booster for nanowire technologies.
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ABSTRACT The thermoelectric properties of defected graphene nanoribbons (GNRs) and multi-junction (MJ) GNRs coupling periodic armchair sections of different width are analyzed by means of Green’s function techniques to simulate electron... more
ABSTRACT The thermoelectric properties of defected graphene nanoribbons (GNRs) and multi-junction (MJ) GNRs coupling periodic armchair sections of different width are analyzed by means of Green’s function techniques to simulate electron and phonon transport. Among the different strategies likely to enhance the thermoelectric performance, the effects of edge disorder and random vacancies are shown to be small since they lead to the concomitant degradation of the phonon thermal conductance and of the electronic conductance, which finally reduces the thermoelectric factor ZT. However, the periodic distribution of vacancies and the structuring of GNRs in MJ-GNRs both lead to the enhancement of the figure of merit ZT. In the latter case, in addition to the strong reduction of the phonon thermal conductance, an effect of resonant tunneling of electrons allows retaining high electronic conductance and enhancing significantly the thermopower. Finally, by introducing a periodic distribution of vacancies in the MJ-GNR, the maximum value ZT=0.4 is reached at room temperature.
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ABSTRACT We show that the maximum degree of a graph GG is equal to the minimum number of ocm sets covering GG, where an ocm set is the vertex-disjoint union of elementary odd cycles and one matching, and a collection of ocm sets covers GG... more
ABSTRACT We show that the maximum degree of a graph GG is equal to the minimum number of ocm sets covering GG, where an ocm set is the vertex-disjoint union of elementary odd cycles and one matching, and a collection of ocm sets covers GG if every edge is in the matching of an ocm set or in some odd cycle of at least two ocm sets.
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Abstract - In a typical slotted bus-based optical metropolitan network, the position of access node on the network's bus have a large impact on the network performance. We refer to this problem in data transmission as the unfairness... more
Abstract - In a typical slotted bus-based optical metropolitan network, the position of access node on the network's bus have a large impact on the network performance. We refer to this problem in data transmission as the unfairness property. In fact, the first nodes on the bus have ...
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Abstract This paper presents a comparison of reservation protocols used in optical burst switches (OBS) with quality of service (QoS). In terms of performance criteria, byte loss rate, end-to-end delay and access delay are considered. A... more
Abstract This paper presents a comparison of reservation protocols used in optical burst switches (OBS) with quality of service (QoS). In terms of performance criteria, byte loss rate, end-to-end delay and access delay are considered. A 2-state MMPP (Markov modulated ...
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ABSTRACT It has been shown in a recent study that unstrained/strained graphene junctions could be promising candidates to improve the poor performance resulting from the gapless nature of the material in graphene devices. Although the... more
ABSTRACT It has been shown in a recent study that unstrained/strained graphene junctions could be promising candidates to improve the poor performance resulting from the gapless nature of the material in graphene devices. Although the energy bandgap of strained graphene still remains zero, the shift of Dirac points in the $k$-space due to strain-induced deformation of graphene lattice can lead to the appearance of a finite conduction gap of several hundreds meV even with a strain of only a few percent. However, since essentially depending on the magnitude of Dirac point shift, such a conduction gap strongly depends on the direction of applied strain and the transport direction. In this work a systematic study of conduction gap properties with respect to these quantities is hence presented and the obtained results are carefully analyzed. Our study thus provides useful information for further investigations to exploit graphene strain junctions in electronic applications.
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ABSTRACT In this work, we investigate thermoelectric properties of junctions consisting of two partially overlapped graphene sheets coupled to each other in the cross-plane direction. It is shown that because of the weak van-der Waals... more
ABSTRACT In this work, we investigate thermoelectric properties of junctions consisting of two partially overlapped graphene sheets coupled to each other in the cross-plane direction. It is shown that because of the weak van-der Waals interactions between graphene layers, the phonon conductance in these junctions is strongly reduced, compared to that of single graphene layer structures, while their electrical performance is weakly affected. By exploiting this effect, we demonstrate that the thermoelectric figure of merit can reach values higher than 1 at room temperature in junctions made of gapped graphene materials, for instance, graphene nanoribbons and graphene nanomeshes. The dependence of thermoelectric properties on the junction length is also discussed. This theoretical study hence suggests an efficient way to enhance thermoelectric efficiency of graphene devices.
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Given a directed graph G with non-negative cost on the arcs, a directed tour cover T of G is a cycle (not necessary simple) in G such that either head or tail (or both of them) of every arc in G is touched by T. The minimum directed tour... more
Given a directed graph G with non-negative cost on the arcs, a directed tour cover T of G is a cycle (not necessary simple) in G such that either head or tail (or both of them) of every arc in G is touched by T. The minimum directed tour cover problem (DToCP) which is to find a ...
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ABSTRACT Given a directed graph G with non negative cost on the arcs, a directed tree cover of G is a rooted directed tree such that either head or tail (or both of them) of every arc in G is touched by T. The minimum directed tree cover... more
ABSTRACT Given a directed graph G with non negative cost on the arcs, a directed tree cover of G is a rooted directed tree such that either head or tail (or both of them) of every arc in G is touched by T. The minimum directed tree cover problem (DTCP) is to find a directed tree cover of minimum cost. The problem is known to be NP-hard. In this paper, we show that the weighted Set Cover Problem (SCP) is a special case of DTCP. Hence, one can expect at best to approximate DTCP with the same ratio as for SCP. We show that this expectation can be satisfied in some way by designing a purely combinatorial approximation algorithm for the DTCP and proving that the approximation ratio of the algorithm is max {2, ln (D + )} with D + is the maximum outgoing degree of the nodes in G.
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ABSTRACT Though the energy bandgap of strained graphene remains zero, the shift of Dirac points in the k-space due to strain-induced deformation of graphene lattice can lead to the appearance of a finite conduction gap of several hundreds... more
ABSTRACT Though the energy bandgap of strained graphene remains zero, the shift of Dirac points in the k-space due to strain-induced deformation of graphene lattice can lead to the appearance of a finite conduction gap of several hundreds meV in strained/unstrained junctions with a strain of only a few percent. This conduction gap strongly depends on the direction of applied strain and the transport direction. Here, we study its properties with respect to these quantities. This work provides useful information for further exploiting graphene strained junctions in electronic applications.
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Prototype surface acoustic wave chemical sensor systems are described, which can detect and identify toxic vapors in real-time at trace concentrations. To operate autonomously for long periods, without failure, requires a thorough... more
Prototype surface acoustic wave chemical sensor systems are described, which can detect and identify toxic vapors in real-time at trace concentrations. To operate autonomously for long periods, without failure, requires a thorough understanding of the hardware and software requirements of the sensor system. The SAWCAD and SAWRHINO prototypes, which implement several improvements to the hardware, over previously developed systems, are described. Software for vapor detection and neural network identification are also discussed. Preliminary results from two new software enhancements are described. Improved chemical discrimination occurs when the response slopes are incorporated into the analysis of the SAW ambient data. The generalized rank annihilation method is shown to be a powerful tool for extracting pure component analyte signatures from trap and purge gas solid chromatographic SAW data.
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ABSTRACT The transport characteristics and the possibility of controlling the negative differential conductance (NDC) in graphene tunnel field-effect transistors are investigated by means of numerical simulation. We find that an NDC... more
ABSTRACT The transport characteristics and the possibility of controlling the negative differential conductance (NDC) in graphene tunnel field-effect transistors are investigated by means of numerical simulation. We find that an NDC effect can be achieved while the peak current and the peak-to-valley ratio (PVR) are controllable by tuning the gate voltage. Moreover, compared to the case of P-N junctions (Esaki diodes), the controllability of the potential profile in the gated region is shown to make the peak current higher and the PVR much less sensitive to the transition length between the two highly doped zones of the source and drain contacts. This work can stimulate further applications of this device in the field of high-frequency circuits, besides its potential for low-power digital operation.
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The phonon-assisted resonant tunneling is studied for the double barrier structures in a longitudinal magnetic field. Using the scattering matrix approach with an appropriate one-particle Green's function we are able to calculate the... more
The phonon-assisted resonant tunneling is studied for the double barrier structures in a longitudinal magnetic field. Using the scattering matrix approach with an appropriate one-particle Green's function we are able to calculate the current and the zero frequency shot noise power spectrum in a large range of the magnetic field and to any order of the electron phonon interaction. Obtained results describe well the relevant experimental data and provide new suggestions for further examinations.