Negative frequency tuning of a carbon nanotube nano-electromechanical resonator

A suspended, doubly clamped single wall carbon nanotube is characterized as driven nano-electromechanical resonator at cryogenic temperatures. Electronically, the carbon nanotube displays small bandgap behaviour with Coulomb blockade oscillations in electron conduction and transparent contacts in hole conduction. We observe the driven mechanical resonance in dc-transport, including multiple higher harmonic responses. The data shows a distinct negative frequency tuning at finite applied gate voltage, enabling us to electrostatically decrease the resonance frequency to 75% of its maximum value. This is consistently explained via electrostatic softening of the mechanical mode.Comment: 4 pages, 4 figures; submitted for the IWEPNM 2013 conference proceeding

Analyses of the reasons for the decreased service time of CrN-coated die for aluminy hot extrusion – a case study

Presented study shows that considerable reserves still exist for increasing the service times (lifetimes) of CrN – coated dies for Al hot extrusion. The main reasons for the decreased service times are revealed and explained regarding the selected CrN - coated die for hot extrusion, i.e. why the service time of the coated-die is not in accordance with the wear resistance of the CrN - coating. The shaping of the bearing surface and presence of the scratches, size and amount of nonmetalic inclusions in the die steel, nodular defects in the CrN - coating, as well as thicknesses uniformity of CrN - coatings along the bearing surface, are relevant influential parameters

An Exploration of Co-Workers’ Group Identification as Moderator of the Leadership-Health Link

This study explores the leadership-health link from a social identity perspective. It focuses on leadership behaviors that seek to form a strong shared social identity (i.e., identity leadership) and the contextual influence of co-workers’ group identification. In a sample of 319 members in 77 workgroups, data supports the indirect link of identity leadership and reduced symptoms of burnout via perceived social support. However, contrary to our expectation, high levels of co-workers’ group identification weakened the relationship of identity leadership and perceived social support. The implications of this finding for the understanding of leadership as a group process are discussed

Subsidizing vocational training for disadvantaged youth in developing countries: evidence from a randomized trial

This paper evaluates the impact of a randomized training program for disadvantaged youth introduced in Colombia in 2005. This randomized trial offers a unique opportunity to examine the impact of training in developing countries. We use originally collected data on individuals randomly offered and not offered training. The program raises earnings and employment, especially for women. Women offered training earn 18% more and have a 0.05 higher probability of employment than those not offered training, mainly in formal sector jobs. Cost-benefit analysis of these results suggests that the program generates much larger net gains than those found in developed countries

Band structure of helimagnons in MnSi resolved by inelastic neutron scattering

A magnetic helix realizes a one-dimensional magnetic crystal with a period given by the pitch length $\lambda_h$. Its spin-wave excitations -- the helimagnons -- experience Bragg scattering off this periodicity leading to gaps in the spectrum that inhibit their propagation along the pitch direction. Using high-resolution inelastic neutron scattering the resulting band structure of helimagnons was resolved by preparing a single crystal of MnSi in a single magnetic-helix domain. At least five helimagnon bands could be identified that cover the crossover from flat bands at low energies with helimagnons basically localized along the pitch direction to dispersing bands at higher energies. In the low-energy limit, we find the helimagnon spectrum to be determined by a universal, parameter-free theory. Taking into account corrections to this low-energy theory, quantitative agreement is obtained in the entire energy range studied with the help of a single fitting parameter.Comment: 5 pages, 3 figures; (v2) slight modifications, published versio

Nanometer Scale Mapping of the Density of States in an Inhomogeneous Superconductor

Using high speed scanning tunneling spectroscopy, we perform a full mapping of the quasiparticle density of states (DOS) in single crystals of BiPbSrCaCuO(2212). The measurements carried out at 5 K showed a complex spatial pattern of important variations of the local DOS on the nanometer scale. Superconducting areas are co-existing with regions of a smooth and larger gap-like DOS structure. The superconducting regions are found to have a minimum size of about 3 nm. The role of Pb-introduced substitutional disorder in the observed spatial variations of the local DOS is discussed.Comment: 4 page Letter with 3 figures (2 color figures