15,645 research outputs found
Quasiconformality and mass
We identify universal quasiconformal (walking) behaviour in non-Abelian gauge
field theories based on the mass-dependent all-order beta-function introduced
in arXiv:0908.1364. We find different types of walking behaviour in the
presence of (partially) massive species. We employ our findings to the
construction of candidate theories for dynamical electroweak symmetry breaking
by walking technicolour.Comment: 16 pages, 8 figures
Endohedral Impurities in Carbon Nanotubes
A generalization of the Anderson model that includes pseudo-Jahn-Teller
impurity coupling is proposed to describe distortions of an endohedral impurity
in a carbon nanotube. Treating the distortion within mean-field theory,
spontaneous axial symmetry breaking is found when the vibronic coupling
strength g exceeds a critical value g. The effective potential in the
symmetry-broken state is found to have O(2) symmetry, in agreement with
numerical calculations. For metallic zigzag nanotubes endohedrally-doped with
transition metals in the dilute limit, the low-energy properties of the system
may display two-channel Kondo behavior; however, strong vibronic coupling is
seen to exponentially suppress the Kondo energy scale.Comment: 4 pages, 2 figure
Optimal solutions for complex design problems: Using isoperformance software for human factors trade offs
A major application of isoperformance is as a trade-off methodology of the three major drivers of system design; equipment, training variables, and user characteristics. The flexibility of isoperformance allows each of these three components to be nearly any rational variation. For example, aptitude may be military Armed Forces Qualification Testing (AFQT) categories, cutoff scores within a selection procedure, or simply dichotomizing high and low scorers (pass/fail). Equipment may be new versus old, 'smart' versus dumb, high versus low resolution, etc. Training may be short versus long or varieties of media types (lecture versus CAI/CBI versus self-paced workbooks). In its final computerized form isoperformance lets the user set an operational level of performance (e.g., a jet pilot in a simulated emergency must take prescribed corrective action and clear the plane in several seconds, pilot astronauts will check out all shuttle flight systems within 30 minutes, or Mission Specialists must handle sucdessfully a required number of job elements). At this point the computer program guides the user through any requested trade-offs of the three components while maintaining the specified operational level of performance through isoperformance curves. A demonstration of the computer program is currently available
Investigating the Presence of Regional Economic Growth Convergence in the Philippines using Kalman Filter
This paper investigates the presence of stochastic and dynamic convergence of the 14 regional economies in the Philippines in terms of per capita Gross Regional Domestic Product (GRDP) using regional panel data from 1988 to 2007. Stochastic convergence, which indicates convergence of regions in the long-run, is tested using Levin, Lin & Chu (LLC) and Im, Pesaran & Shin (IPS) panel unit root tests. The presence of convergence, on one hand, indicates that the economically laggard regions are gaining on the economically better-performing regions with respect to per capita GRDP. On the other hand, the lack of convergence indicates a need to reevaluate existing regional and national economic policies on development. Dynamic convergence reveals several convergence characteristics of individual regions over time. Dynamic convergence is determined by the time-varying parameter (TVP) model derived using the Kalman Filter. The paper proceeds to examine the individual convergence behavior of each region based on the value of the estimate of the parameter of the TVP. The results show that out of the 14 regions studied, seven regions are found to converge towards the average of the national per capita GDP growth rate over 1988 to 2007 while six regions lag behind the average of the national per capita GDP growth rate over the same period. No region converges towards the economic growth rate of National Capital Region, the lead region used in the study.Panel Unit Root Test, Time-varying Parameter (TVP) Model, Kalman Filter, Stochastic Convergence, Dynamic Convergence
Anharmonicity and self-energy effects of the E2g phonon in MgB2
We present a Raman scattering study of the E2g phonon anharmonicity and of
superconductivity induced self-energy effects in MgB2 single crystals. We show
that anharmonic two phonon decay is mainly responsible for the unusually large
linewidth of the E2g mode. We observe ~ 2.5 % hardening of the E2g phonon
frequency upon cooling into the superconducting state and estimate the
electron-phonon coupling strength associated with this renormalization.Comment: 4 pages, 3 figures, accepted to PR
Space station integrated propulsion and fluid systems study
The program study was performed in two tasks: Task 1 addressed propulsion systems and Task 2 addressed all fluid systems associated with the Space Station elements, which also included propulsion and pressurant systems. Program results indicated a substantial reduction in life cycle costs through integrating the oxygen/hydrogen propulsion system with the environmental control and life support system, and through supplying nitrogen in a cryogenic gaseous supercritical or subcritical liquid state. A water sensitivity analysis showed that increasing the food water content would substantially increase the amount of water available for propulsion use and in all cases, the implementation of the BOSCH CO2 reduction process would reduce overall life cycle costs to the station and minimize risk. An investigation of fluid systems and associated requirements revealed a delicate balance between the individual propulsion and fluid systems across work packages and a strong interdependence between all other fluid systems
Inhomogeneous CuO_{6} Tilt Distribution and Charge/Spin Correlations in La_{2-x-y}Nd_{y}Sr_{x}CuO$_{4} around commensurate hole concentration
Phononic and magnetic Raman scattering are studied in
LaNdSrCuO with three doping concentrations: x ~
1/8, y = 0; x ~ 1/8, y = 0.4; and x = 0.01, y = 0. We observe strong disorder
in the tilt pattern of the CuO_{6} octahedra in both the orthorhombic and
tetragonal phases which persist down to 10 K and are coupled to bond disorder
in the cation layers around 1/8 doping independent of Nd concentration. The
weak magnitude of existing charge/spin modulations in the Nd doped structure
does not allow us to detect the specific Raman signatures on lattice dynamics
or two-magnon scattering around 2200 cm-1.Comment: to be published in Phys. Rev.
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