33,913 research outputs found
Towards a Base UML Profile for Architecture Description
This paper discusses a base UML profile for architecture description as supported by existing Architecture Description Languages (ADLs). The profile may be extended so as to enable architecture modeling both as expressed in conventional ADLs and according to existing runtime infrastructures (e.g., system based on middleware architectures).
Origin of conductivity cross over in entangled multi-walled carbon nanotube network filled by iron
A realistic transport model showing the interplay of the hopping transport
between the outer shells of iron filled entangled multi-walled carbon nanotubes
(MWNT) and the diffusive transport through the inner part of the tubes, as a
function of the filling percentage, is developed. This model is based on
low-temperature electrical resistivity and magneto-resistance (MR)
measurements. The conductivity at low temperatures showed a crossover from
Efros-Shklovski (E-S) variable range hopping (VRH) to Mott VRH in 3 dimensions
(3D) between the neighboring tubes as the iron weight percentage is increased
from 11% to 19% in the MWNTs. The MR in the hopping regime is strongly
dependent on temperature as well as magnetic field and shows both positive and
negative signs, which are discussed in terms of wave function shrinkage and
quantum interference effects, respectively. A further increase of the iron
percentage from 19% to 31% gives a conductivity crossover from Mott VRH to 3D
weak localization (WL). This change is ascribed to the formation of long iron
nanowires at the core of the nanotubes, which yields a long dephasing length
(e.g. 30 nm) at the lowest measured temperature. Although the overall transport
in this network is described by a 3D WL model, the weak temperature dependence
of inelastic scattering length expressed as L_phi ~T^-0.3 suggests the
possibility for the presence of one-dimensional channels in the network due to
the formation of long Fe nanowires inside the tubes, which might introduce an
alignment in the random structure.Comment: 29 pages,10 figures, 2 tables, submitted to Phys. Rev.
Dynamics of horizontal-like maps in higher dimension
We study the regularity of the Green currents and of the equilibrium measure
associated to a horizontal-like map in C^k, under a natural assumption on the
dynamical degrees. We estimate the speed of convergence towards the Green
currents, the decay of correlations for the equilibrium measure and the
Lyapounov exponents. We show in particular that the equilibrium measure is
hyperbolic. We also show that the Green currents are the unique invariant
vertical and horizontal positive closed currents. The results apply, in
particular, to Henon-like maps, to regular polynomial automorphisms of C^k and
to their small pertubations.Comment: Dedicated to Professor Gennadi Henkin on the occasion of his 65th
birthday, 37 pages, to appear in Advances in Mat
Inhibition of DNA ejection from bacteriophage by Mg+2 counterions
The problem of inhibiting viral DNA ejection from bacteriophages by
multivalent counterions, specifically Mg counterions, is studied.
Experimentally, it is known that MgSO salt has a strong and non-monotonic
effect on the amount of DNA ejected. There exists an optimal concentration at
which the minimum amount of DNA is ejected from the virus. At lower or higher
concentrations, more DNA is ejected from the capsid. We propose that this
phenomenon is the result of DNA overcharging by Mg multivalent
counterions. As Mg concentration increases from zero, the net charge of
DNA changes from negative to positive. The optimal inhibition corresponds to
the Mg concentration where DNA is neutral. At lower/higher
concentrations, DNA genome is charged. It prefers to be in solution to lower
its electrostatic self-energy, which consequently leads to an increase in DNA
ejection. By fitting our theory to available experimental data, the strength of
DNADNA short range attraction energies, mediated by Mg, is found to
be 0.004 per nucleotide base. This and other fitted parameters agree
well with known values from other experiments and computer simulations. The
parameters are also in aggreement qualitatively with values for tri- and
tetra-valent counterions.Comment: 17 pages, 4 figures, improved manuscript. Submitted to J. Chem. Phys
(2010
Nanomechanical displacement detection using coherent transport in ordered and disordered graphene nanoribbon resonators
Graphene nanoribbons provide an opportunity to integrate phase-coherent
transport phenomena with nanoelectromechanical systems (NEMS). Due to the
strain induced by a deflection in a graphene nanoribbon resonator, coherent
electron transport and mechanical deformations couple. As the electrons in
graphene have a Fermi wavelength \lambda ~ a_0 = 1.4 {\AA}, this coupling can
be used for sensitive displacement detection in both armchair and zigzag
graphene nanoribbon NEMS. Here it is shown that for ordered as well as
disordered ribbon systems of length L, a strain \epsilon ~ (w/L)^2 due to a
deflection w leads to a relative change in conductance \delta G/G ~ (w^2/a_0L).Comment: 4 Pages, 4 figure
User's manual for rocket combustor interactive design (ROCCID) and analysis computer program. Volume 2: Appendixes A-K
The appendices A-K to the user's manual for the rocket combustor interactive design (ROCCID) computer program are presented. This includes installation instructions, flow charts, subroutine model documentation, and sample output files. The ROCCID program, written in Fortran 77, provides a standardized methodology using state of the art codes and procedures for the analysis of a liquid rocket engine combustor's steady state combustion performance and combustion stability. The ROCCID is currently capable of analyzing mixed element injector patterns containing impinging like doublet or unlike triplet, showerhead, shear coaxial and swirl coaxial elements as long as only one element type exists in each injector core, baffle, or barrier zone. Real propellant properties of oxygen, hydrogen, methane, propane, and RP-1 are included in ROCCID. The properties of other propellants can be easily added. The analysis models in ROCCID can account for the influences of acoustic cavities, helmholtz resonators, and radial thrust chamber baffles on combustion stability. ROCCID also contains the logic to interactively create a combustor design which meets input performance and stability goals. A preliminary design results from the application of historical correlations to the input design requirements. The steady state performance and combustion stability of this design is evaluated using the analysis models, and ROCCID guides the user as to the design changes required to satisfy the user's performance and stability goals, including the design of stability aids. Output from ROCCID includes a formatted input file for the standardized JANNAF engine performance prediction procedure
Political uncertainty and housing markets
This paper examines the causal effects of political uncertainty on housing markets. We used US gubernatorial elections from 1982 to 2018 as a source of exogenous variation in political uncertainty and exploited the regional variations in residential housing markets. We used neighboring states without elections and counties at the state borders without elections as control groups. We found that higher political uncertainty causes (a) a decrease in house price growth; (b) a decrease in the number of housing transactions; and (c) an increase in the number of building permits. These effects are stronger during election years when election outcomes present higher uncertainty. We further examined the impact of political uncertainty on mortgage markets and found that mortgage demand and supply decrease in election years
Third type of domain wall in soft magnetic nanostrips
Magnetic domain walls (DWs) in nanostructures are low-dimensional objects
that separate regions with uniform magnetisation. Since they can have different
shapes and widths, DWs are an exciting playground for fundamental research, and
became in the past years the subject of intense works, mainly focused on
controlling, manipulating, and moving their internal magnetic configuration. In
nanostrips with in-plane magnetisation, two DWs have been identified: in thin
and narrow strips, transverse walls are energetically favored, while in thicker
and wider strips vortex walls have lower energy. The associated phase diagram
is now well established and often used to predict the low-energy magnetic
configuration in a given magnetic nanostructure. However, besides the
transverse and vortex walls, we find numerically that another type of wall
exists in permalloy nanostrips. This third type of DW is characterised by a
three-dimensional, flux closure micromagnetic structure with an unusual length
and three internal degrees of freedom. Magnetic imaging on
lithographically-patterned permalloy nanostrips confirms these predictions and
shows that these DWs can be moved with an external magnetic field of about 1mT.
An extended phase diagram describing the regions of stability of all known
types of DWs in permalloy nanostrips is provided.Comment: 19 pages, 7 figure
- …