Mode space approach for tight-binding transport simulations in graphene nanoribbon field-effect transistors including phonon scattering

In this paper, we present a mode space method for atomistic non-equilibrium Green's function simulations of armchair graphene nanoribbon FETs that includes electron-phonon scattering. With reference to both conventional and tunnel FET structures, we show that, in the ideal case of a smooth electrostatic potential, the modes can be decoupled in different groups without any loss of accuracy. Thus, inter-subband scattering due to electron-phonon interactions is properly accounted for, while the overall simulation time considerably improves with respect to real-space, with a speed-up factor of 40 for a 1.5-nm-wide device. Such factor increases with the square of the device width. We also discuss the accuracy of two commonly used approximations of the scattering self-energies: the neglect of the off-diagonal entries in the mode-space expressions and the neglect of the Hermitian part of the retarded self-energy. While the latter is an acceptable approximation in most bias conditions, the former is somewhat inaccurate when the device is in the off-state and optical phonon scattering is essential in determining the current via band-to-band tunneling. Finally, we show that, in the presence of a disordered potential, a coupled mode space approach is necessary, but the results are still accurate compared to the real-space solution.Comment: 10 pages, 12 figures. Copyright (2013) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physic

Boosting the voltage gain of graphene FETs through a differential amplifier scheme with positive feedback

We study a possible circuit solution to overcome the problem of low voltage gain of short-channel graphene FETs. The circuit consists of a fully differential amplifier with a load made of a cross-coupled transistor pair. Starting from the device characteristics obtained from self-consistent ballistic quantum transport simulations, we explore the circuit parameter space and evaluate the amplifier performance in terms of dc voltage gain and voltage gain bandwidth. We show that the dc gain can be effectively improved by the negative differential resistance provided by the cross-coupled pair. Contact resistance is the main obstacle to achieving gain bandwidth products in the terahertz range. Limitations of the proposed amplifier are identified with its poor linearity and relatively large Miller capacitance.Comment: 19 pages, 10 figure

Ruolo prognostico di marcatori molecolari nella gestione del paziente affetto da sindrome mielodisplastica ad alto rischio.

Le sindromi mielodisplastiche sono disordini clonali della cellula staminale ematopoietica, con conseguente diseritropoiesi midollare e citopenie periferiche, nonchè possibile evoluzione in leucemia acuta. La classificazione di tali patologie è piuttosto complessa e negli ultimi anni si sono ricercati marcatori molecolari per una buona diagnosi e successiva prognosi. In particolare RPS14 è stato riscontrato essere down regolato nelle sindromi 5q-, ma anche in altri sottotipi di mielodisplasie. L'analisi della sua espressione sembra essere utile nell'indirizzare i pazienti al trattamento

Semianalytical quantum model for graphene field-effect transistors

We develop a semianalytical model for monolayer graphene field-effect transistors in the ballistic limit. Two types of devices are considered: in the first device, the source and drain regions are doped by charge transfer with Schottky contacts, while, in the second device, the source and drain regions are doped electrostatically by a back gate. The model captures two important effects that influence the operation of both devices: (i) the finite density of states in the source and drain regions, which limits the number of states available for transport and can be responsible for negative output differential resistance effects, and (ii) quantum tunneling across the potential steps at the source-channel and drain-channel interfaces. By comparison with a self-consistent non-equilibrium Green's function solver, we show that our model provides very accurate results for both types of devices, in the bias region of quasi-saturation as well as in that of negative differential resistance.Comment: 10 pages, 14 figure

Sit-to-Walk predicts Freezing of Gait status over than cognitive load: an experimental study with Linear Discriminant Analysis.

Freezing of Gait (FoG) is one of the most debilitating symptom of patients with Parkinson Disease (PwP) as it could leads to fall and loss of independence. We evaluated the motor behavior in simple and complex gait movements with three groups of participants: PwP with and without FoG in ON state condition, and participants without neurologic and gait disorders. All participants were required to walk, to begin to walk (Step Initiation), and raise from a chair for walking (Sit-to-Walk). Analysis of variance helped to identify task-specific kinematic and kinetic variables which differentiate among the three groups. Classification accuracy of such variables was obtained by training a Linear Discriminant Analysis \u2013 LDA algorithm on reduced sub-samples, and by testing it on the left out subjects

Management of Congenital Diaphragmatic Hernia (CDH): role of molecular genetics

Congenital diaphragmatic hernia (CDH) is a relatively common major life-threatening birth defect that results in significant mortality and morbidity depending primarily on lung hypoplasia, persistent pulmonary hypertension, and cardiac dysfunction. Despite its clinical relevance, CDH multifactorial etiology is still not completely understood. We reviewed current knowledge on normal diaphragm development and summarized genetic mutations and related pathways as well as cellular mechanisms involved in CDH. Our literature analysis showed that the discovery of harmful de novo variants in the fetus could constitute an important tool for the medical team during pregnancy, counselling, and childbirth. A better insight into the mechanisms regulating diaphragm development and genetic causes leading to CDH appeared essential to the development of new therapeutic strategies and evidence-based genetic counselling to parents. Integrated sequencing, development, and bioinformatics strategies could direct future functional studies on CDH; could be applied to cohorts and consortia for CDH and other birth defects; and could pave the way for potential therapies by providing molecular targets for drug discovery

Graphene Base Transistors: A Simulation Study of DC and Small-Signal Operation

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Simultaneous presentation of Waldenström macroglobulinemia and multiple myeloma: multidisciplinary diagnosis, treatment and 30-month follow-up.

Waldenström macroglobulinemia and multiple myeloma are mature B-cell neoplasms deriving from post-germinal cells at different stages of differentiation. The simultaneous presentation of Waldenström macroglobulinemia and multiple myeloma in the same patient is a very rare phenomenon and, so far, only two cases have been described. We report the case of a 75-year Caucasian female patient, with a silent clinical history, who presented with anemia and two different monoclonal proteins (IgMκ and IgGκ). The trephine biopsy showed the presence of a dual population, represented by small lymphoplasmacytoid cells and by plasma cells, which infiltrated the bone marrow with a clearly different pattern. Both immunohistochemistry and flow cytometry demonstrated the biclonal origin such neoplastic cells, since lymphoplasmacytoid cells resulted IgMκ while plasma cells were IgGκ. This biclonal pattern was further confirmed by the demonstration of a different IgH gene rearrangement of the two neoplasms. The patient was treated with bortezomib, dexamethasone and rituximab, achieving partial remission of both Waldenström macroglobulinemia and multiple myeloma. After a 30-month follow-up, she is in stable disease. Multiple myeloma has been described in association with other indolent B-cell neoplasms, mostly chronic lymphocytic leukemia, while Waldenström macroglobulinemia can be followed by diffuse large B-cell lymphoma in some instances, after chemotherapy. The association of Waldenström macroglobulinemia and multiple myeloma seems to be very rare. Our study shows that an integrated diagnostic work-up is very useful in such cases, with an interesting role for flow cytometry. [J Clin Exp Hematop 53(1): 29-36, 2013]

Donor-transmitted Triple-Hit Lymphoma in a Renal Allograft Recipient

simultaneous appearance of DLBCL in the donor and recipient after renal transplantatio