Structure and electronic properties of molybdenum monoatomic wires encapsulated in carbon nanotubes

Monoatomic chains of molybdenum encapsulated in single walled carbon nanotubes of different chiralities are investigated using density functional theory. We determine the optimal size of the carbon nanotube for encapsulating a single atomic wire, as well as the most stable atomic arrangement adopted by the wire. We also study the transport properties in the ballistic regime by computing the transmission coefficients and tracing them back to electronic conduction channels of the wire and the host. We predict that carbon nanotubes of appropriate radii encapsulating a Mo wire have metallic behavior, even if both the nanotube and the wire are insulators. Therefore, encapsulating Mo wires in CNT is a way to create conductive quasi one-dimensional hybrid nanostructures.Comment: 8 pages, 10 figure

Impact of dimerization and stretching on the transport properties of molybdenum atomic wires

We study the electrical and transport properties of monoatomic Mo wires with different structural characteristics. We consider first periodic wires with inter-atomic distances ranging between the dimerized wire to that formed by equidistant atoms. We find that the dimerized case has a gap in the electronic structure which makes it insulating, as opposed to the equidistant or near-equidistant cases which are metallic. We also simulate two conducting one-dimensional Mo electrodes separated by a scattering region which contains a number of dimers between 1 and 6. The $I-V$ characteristics strongly depend on the number of dimers and vary from ohmic to tunneling, with the presence of different gaps. We also find that stretched chains are ferromagnetic.Comment: 8 pages, 7 figure

Derivation of the physical parameters of the jet in S5 0836+710 from stability analysis

A number of extragalactic jets show periodic structures at different scales that can be associated with growing instabilities. The wavelengths of the developing instability modes and their ratios depend on the flow parameters, so the study of those structures can shed light on jet physics at the scales involved. In this work, we use the fits to the jet ridgeline obtained from different observations of S5 B0836$+$710 and apply stability analysis of relativistic, sheared flows to derive an estimate of the physical parameters of the jet. Based on the assumption that the observed structures are generated by growing Kelvin-Helmholtz (KH) instability modes, we have run numerical calculations of stability of a relativistic, sheared jet over a range of different jet parameters. We have spanned several orders of magnitude in jet-to-ambient medium density ratio, and jet internal energy, and checked different values of the Lorentz factor and shear layer width. This represents an independent method to obtain estimates of the physical parameters of a jet. By comparing the fastest growing wavelengths of each relevant mode given by the calculations with the observed wavelengths reported in the literature, we have derived independent estimates of the jet Lorentz factor, specific internal energy, jet-to-ambient medium density ratio and Mach number. We obtain a jet Lorentz factor $\gamma \simeq 12$, specific internal energy of $\varepsilon \simeq 10^{-2}\,c^2$, jet-to-ambient medium density ratio of $\eta\approx 10^{-3}$, and an internal (classical) jet Mach number of $M_\mathrm{j}\approx 12$. We also find that the wavelength ratios are better recovered by a transversal structure with a width of $\simeq 10\,\%$ of the jet radius. This method represents a powerful tool to derive the jet parameters in all jets showing helical patterns with different wavelengths.Comment: Accepted for publication in A&A, 15 pages, 12 figure

Star polymers rupture induced by constant forces

In this work, we study the breakage process of an unknotted three-arm star-shaped polymer when it is pulled from its free ends by a constant force. The star polymer configuration is described through an array of monomers coupled by anharmonic bonds, while the rupture process is tracked in three-dimensional space by means of Langevin Molecular Dynamics simulations. The interaction between monomers is described by a Morse potential, while a Weeks-Chandler-Anderson energetic contribution accounts for the excluded volume interaction. We explore the effect of the molecular architecture on the distributions of rupture times over a broad interval of pulling forces and star configurations. It was found that the rupture time distribution of the individual star arms is strongly affected by the star configuration imposed by the pulling forces and the length of the arms. We also observed that for large pulling forces the rupture time distributions resemble the dominant features observed for linear polymer chains. The model introduced here provides the basic ingredients to describe the effects of tensile forces on stress-induced degradation of branched macromolecules and polymer networks.Fil: García, Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Febbo, Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Vega, Daniel Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Milchev, A.. Bulgarian Academy of Sciences; Bulgari

Instruction: Core Competencies

The ISU Library’s Instruction Competencies Task Force reviewed and adapted the national ALA/ACRL Proficiencies for Instruction Librarians Standards to guide instruction-related professional development and teaching practices of ISU librarians who teach

Are You Out There? Challenges of Connecting with Distance Learners

Many colleges and universities have increased the number and breadth of distance learning (DL) courses and online degree programs. In a growing DL environment, more rigorous and sustained attention to DL needs is necessary to encourage recognition of the campus academic library as a viable resource, and to facilitate its access and use by students who may never visit campus. With low staffing and stripped budgets, what can libraries do to ensure that online and physical collections and services are easily available to DL students, many of whom live at a great distance from campus? An initial environmental scan done by librarians and campus staff on a DL library taskforce identified areas of concern. To begin working on these issues, a library DL committee was formed. That committee initiated a series of surveys to both DL instructors and students to hear from them directly concerning what was working well and what challenges might exist in using our library’s collections and services at a distance. The student survey has been especially helpful and has been repeated three times over five years, most recently in 2016. The DL committee has used survey results from over 900 student survey respondents to guide improvements to the library website, off-campus login, communication issues, the provision of interlibrary loan services, and online instruction. The committee has collaborated with various campus units and staff, including the Registrar’s Office, campus DL administrators and staff, the campus Teaching Improvement center, instructional technology staff who create DL courses, and IT staff, among others. This presentation will address some of the major issues students identified as problems, and the changes we have implemented, including our library’s efforts to reach out and regularly connect with our growing number of DL students. </p

Reading Race: Using Book Discussions to Start Dialogues on White Fragility and Other Racisms

The following presentation should be cited as Vega Garcia, Susan A. and Inefuku, Harrison W. Reading Race: Using Book Discussions to Start Dialogues on White Fragility and Other Racisms. IDEAL 2019 Conference, Columbus, Ohio, Aug. 6, 2019.</p

Spin-dependent electronic conduction along zigzag graphene nanoribbons bearing adsorbed Ni and Fe nanostructures

Using SMEAGOL, an ab initio computational method that combines the non-equilibrium Green's function formalism with density-functional theory, we calculated spin-specific electronic conduction in systems consisting of single Fen and Nin nanostructures (n = 1−4) adsorbed on a hydrogen-passivated zigzag graphene nanoribbon. For each cluster we considered both ferromagnetically and antiferromagnetically coupled ribbon edges (Ferro-F and Ferro-A systems, respectively). Adstructures located laterally on Ferro-A ribbons caused significant transmittance loss at energies 0.6–0.25 eV below the Fermi level for one spin and 0.2–0.4 eV above the Fermi level for the other, allowing the potential use of these systems in transistors to create a moderately spin-polarized current of one or the other sign depending on the gate voltage. Ni₃ and Ni₄ clusters located at the centre of Ferro-F ribbons exhibited a strong spin-filtering effect in a narrow energy window around the Fermi level