Agility of vortex-based nanocontact spin torque oscillators

We study the agility of current-tunable oscillators based on a magnetic vortex orbiting around a point contact in spin-valves. Theory predicts frequency-tuning by currents occurs at constant orbital radius, so an exceptional agility is anticipated. To test this, we have inserted an oscillator in a microwave interferometer to apply abrupt current variations while time resolving its emission. Using frequency shift keying, we show that the oscillator can switch between two stabilized frequencies differing by 25% in less than ten periods. With a wide frequency tunability and a good agility, such oscillators possess desirable figures of merit for modulation-based rf applications.Comment: 3 pages, 3 figure

Success and risk factors in the pre-startup phase

Why does one person actually succeed in starting a business, while a second person gives up? In order to answer this question, a sample of 517 nascent entrepreneurs (people in the process of setting up a business) was followed over a three year period. After this period, it was established that 195 efforts were successful and that 115 startup efforts were abandoned. Our research focuses on estimating the relative importance of a variety of approaches and variables in explaining pre-startup success. These influences are organized in terms of Gartner's (1985) framework of new venture creation. This framework suggests that start-up efforts differ in terms of the characteristics of the individual(s) who start the venture, the organization which they create, the environment surrounding the new venture, and the process by which the new venture is started. Logistic regression analyses are run for the sample as a whole as well as for subgroups within the sample, namely for those with high ambition vs. low ambition and for those with substantial vs. limited experience. The results point to the importance of perceived risk of the market as a predictor of getting started vs. abandoning the startup effort

Setting Up a Business in the Netherlands

Why does one person actually succeed in starting a business, while a second gives up, and a third is still trying? To answer this question, a longitudinal study was set up in which 330 nascent entrepreneurs (people setting up a business) were followed over a one-year period. After one year, 47% actually started a business, 27% was still organizing, and 26% gave up the effort. In comparison to the two other groups, starters are different in terms of gender, industry experience, start-up capital, use of third party loans, sector and current activity

Calculation of minor hysteresis loops under metastable to stable transformations in vortex matter

We present a model in which metastable supercooled phase and stable equilibrium phase of vortex matter coexist in different regions of a sample. Minor hysteresis loops are calculated with the simple assumption of the two phases of vortex matter having field-independent critical current densities. We use our earlier published ideas that the free energy barrier separating the metastable and stable phases reduces as the magnetic induction moves farther from the first order phase transition line, and that metastable to stable transformations occur in local regions of the sample when the local energy dissipation exceeds a critical value. Previously reported anomalous features in minor hysteresis loops are reproduced, and calculated field profiles are presented.Comment: 9pages, 7 figure

Spatial structure of Mn-Mn acceptor pairs in GaAs

The local density of states of Mn-Mn pairs in GaAs is mapped with cross-sectional scanning tunneling microscopy and compared with theoretical calculations based on envelope-function and tight-binding models. These measurements and calculations show that the crosslike shape of the Mn-acceptor wavefunction in GaAs persists even at very short Mn-Mn spatial separations. The resilience of the Mn-acceptor wave-function to high doping levels suggests that ferromagnetism in GaMnAs is strongly influenced by impurity-band formation. The envelope-function and tight-binding models predict similarly anisotropic overlaps of the Mn wave-functions for Mn-Mn pairs. This anisotropy implies differing Curie temperatures for Mn $\delta$-doped layers grown on differently oriented substrates.Comment: 4 pages, 4 figure

Self-Employment Across 15 European Countries:

This paper deals with differences in the rate of self-employment (business ownership) in 15 European countries for the period 1978-2000, focusing on the influence of dissatisfaction and using the framework of occupational choice. Using two different measures of dissatisfaction, in addition to the level of economic development, the unemployment rate and income differentials, we find that dissatisfaction at the level of societies is the most significant factor for explaining differences in self-employment levels. Dissatisfaction with life and with the way democracy works are both found to be positively related to self-employment. It is concluded that these are proxies for job dissatisfaction and at the same time represent other negative ‘displacements’ known to promote self-employment

The role of dissatisfaction and per capita income in explaining self-employment across 15 european countries

This paper deals with explaining the sizable differences in the rate of self-employment (business ownership) across 15 European countries in the period 1978-2000, within a framework of occupational choice, focusing on the influence of dissatisfaction and of per capita income. Using two different measures of dissatisfaction, in addition to the level of economic development and controlling for several other variables, we find that, in addition to a negative and significant impact of per capita income, dissatisfaction at the level of societies has a positive and significant influence on self-employment levels. Both dissatisfaction with life and dissatisfaction with the way democracy works are found to influence self-employment. It is concluded that these are proxies for job dissatisfaction and at the same time represent other negative "displacements" known to promote self-employment. The findings indirectly point at the potential importance of push factors within the incentive structures of modern economies

The Value of Human and Social Capital Investments for the Business Performance of Start-ups

We investigate the manifold posed question: "To what extent does investment in human and social capital, besides the effect of "talent", enhance entrepreneurial performance?". We distinguish between three different performance measures: survival, profits, and generated employment. On the basis of the empirical analysis of a rich Dutch longitudinal data set of firm founders, we conclude that specific investments indeed affect the three performance measures sub- stantially and significantly. Specific attention is paid to the unobserved talent bias. Moreover, the effect of the emergence of so called "knowledge industries" is explored

Boosting the Figure Of Merit of LSPR-based refractive index sensing by phase-sensitive measurements

Localized surface plasmon resonances possess very interesting properties for a wide variety of sensing applications. In many of the existing applications only the intensity of the reflected or transmitted signals is taken into account, while the phase information is ignored. At the center frequency of a (localized) surface plasmon resonance, the electron cloud makes the transition between in- and out-of-phase oscillation with respect to the incident wave. Here we show that this information can experimentally be extracted by performing phase-sensitive measurements, which result in linewidths that are almost one order of magnitude smaller than those for intensity based measurements. As this phase transition is an intrinsic property of a plasmon resonance, this opens up many possibilities for boosting the figure of merit (FOM) of refractive index sensing by taking into account the phase of the plasmon resonance. We experimentally investigated this for two model systems: randomly distributed gold nanodisks and gold nanorings on top of a continuous gold layer and a dielectric spacer and observed FOM values up to 8.3 and 16.5 for the respective nanoparticles