University of Texas at Dallas

About: University of Texas at Dallas is a education organization based out in Richardson, Texas, United States. It is known for research contribution in the topics: Population & Computer science. The organization has 14986 authors who have published 35589 publications receiving 1293714 citations. The organization is also known as: UT-Dallas & UT Dallas.

How does it STAC up? Revisiting the scaffolding theory of aging and cognition.

Abstract: “The Scaffolding Theory of Aging and Cognition (STAC)”, proposed in 2009, is a conceptual model of cognitive aging that integrated evidence from structural and functional neuroimaging to explain how the combined effects of adverse and compensatory neural processes produce varying levels of cognitive function. The model made clear and testable predictions about how different brain variables, both structural and functional, were related to cognitive function, focusing on the core construct of compensatory scaffolding. The present paper provides a revised model that integrates new evidence about the aging brain that has emerged since STAC was published 5 years ago. Unlike the original STAC model, STAC-r incorporates life-course factors that serve to enhance or deplete neural resources, thereby influencing the developmental course of brain structure and function, as well as cognition, over time. Life-course factors also influence compensatory processes that are engaged to meet cognitive challenge, and to ameliorate the adverse effects of structural and functional decline. The revised model is discussed in relation to recent lifespan and longitudinal data as well as emerging evidence about the effects of training interventions. STAC-r goes beyond the previous model by combining a life-span approach with a life-course approach to understand and predict cognitive status and rate of cognitive change over time.

2D MoS 2 as an efficient protective layer for lithium metal anodes in high-performance Li–S batteries

Abstract: Among the candidates to replace Li-ion batteries, Li–S cells are an attractive option as their energy density is about five times higher (~2,600 Wh kg−1). The success of Li–S cells depends in large part on the utilization of metallic Li as anode material. Metallic lithium, however, is prone to grow parasitic dendrites and is highly reactive to several electrolytes; moreover, Li–S cells with metallic Li are also susceptible to polysulfides dissolution. Here, we show that ~10-nm-thick two-dimensional (2D) MoS2 can act as a protective layer for Li-metal anodes, greatly improving the performances of Li–S batteries. In particular, we observe stable Li electrodeposition and the suppression of dendrite nucleation sites. The deposition and dissolution process of a symmetric MoS2-coated Li-metal cell operates at a current density of 10 mA cm−2 with low voltage hysteresis and a threefold improvement in cycle life compared with using bare Li-metal. In a Li–S full-cell configuration, using the MoS2-coated Li as anode and a 3D carbon nanotube–sulfur cathode, we obtain a specific energy density of ~589 Wh kg−1 and a Coulombic efficiency of ~98% for over 1,200 cycles at 0.5 C. Our approach could lead to the realization of high energy density and safe Li-metal-based batteries. An ~10-nm-thick MoS2 layer stabilizes lithium metal anodes and the composite can be used in full-cell Li–S batteries with enhanced performances.

Band alignment of two-dimensional transition metal dichalcogenides: application in tunnel field effect transistors

Abstract: Tunnel field effect transistors (TFETs) based on vertical stacking of two dimensional materials are of interest for low-power logic devices. The monolayer transition metal dichalcogenides (TMDs) with sizable band gaps show promise in building p-n junctions (couples) for TFET applications. Band alignment information is essential for realizing broken gap junctions with excellent electron tunneling efficiencies. Promising couples composed of monolayer TMDs are suggested to be VIB-MeX2 (Me= W, Mo; X= Te, Se) as the n-type source and IVB-MeX2 (Me = Zr, Hf; X= S, Se) as the p-type drain by density functional theory calculations.

Dielectric properties of hexagonal boron nitride and transition metal dichalcogenides: from monolayer to bulk

Abstract: Hexagonal boron nitride (h-BN) and semiconducting transition metal dichalcogenides (TMDs) promise greatly improved electrostatic control in future scaled electronic devices. To quantify the prospects of these materials in devices, we calculate the out-of-plane and in-plane dielectric constant from first principles for TMDs in trigonal prismatic and octahedral coordination, as well as for h-BN, with a thickness ranging from monolayer and bilayer to bulk. Both the ionic and electronic contribution to the dielectric response are computed. Our calculations show that the out-of-plane dielectric response for the transition-metal dichalcogenides is dominated by its electronic component and that the dielectric constant increases with increasing chalcogen atomic number. Overall, the out-of-plane dielectric constant of the TMDs and h-BN increases by less than 15% as the number of layers is increased from monolayer to bulk, while the in-plane component remains unchanged. Our computations also reveal that for octahedrally coordinated TMDs the ionic (static) contribution to the dielectric response is very high (4.5 times the electronic contribution) in the in-plane direction. This indicates that semiconducting TMDs in the tetragonal phase will suffer from excessive polar-optical scattering thereby deteriorating their electronic transport properties. The out-of-plane dielectric constant of transition metal dichalcogenides and h-BN is thickness-dependent, unlike their in-plane counterpart. A team led by William Vandenberghe at the University of Texas at Dallas performed calculations of the optical and static relative permittivity of free-standing monolayer, bilayer, and bulk transition metal dichalcogenides, in the in-plane and out-of-plane directions. In h-BN, the in-plane contribution was found to be larger than its out-of-plane counterpart, and independent on the number of h-BN layers. Conversely, the out-of-plane h-BN dielectric constant showed an increase when going from monolayer to bulk. In transition metal dichalcogenides, the dielectric constant components displayed similar trends to those observed in h-BN with regards to their thickness evolution. The calculations also indicated that the electronic component dominates the overall dielectric response for most of the analyzed 2D materials.