Two-center interference and ellipticity in high-order harmonic generation from H2+_2^+

We present a theoretical investigation into the two-center interference in aligned H$_2^+$. The influence of the laser field on the recombination step is investigated by comparing laser-induced harmonic generation with harmonic generation from field-free collisions of Gaussian wave packets with the core. We find that for different Gaussian wave packets colliding with the molecule, the interference minimum occurs at the same alignment angle. The same result is obtained for the laser-induced spectrum when only a single electronic trajectory per harmonic contributes. When multiple electronic trajectories contribute, we find an effect on the minimum position because the interference between short and long trajectories is alignment-dependent. The two-center interference and the influence of the Coulombic potential are clearly seen not only in the harmonic intensity and phase but also in the polarization direction and ellipticity. We observe significant ellipticity of the emitted radiation around the two-center interference minimum.Comment: 10 pages, 15 figures; v2: clearer figures and other small changes; v3: small correction

The digital age project: strategies that enable older social housing residents to use the internet

Provides insights into the factors affecting technology adoption for older and disadvantaged people, and provides training and interface guidelines and a potential model for other public housing communities to become more digitally aware. Research Aims The experience of social housing communities in countries like the United Kingdom suggests that while access to digital infrastructure and equipment is important, access alone does not equate to digital inclusion. The aim of this research was two-fold, namely to: Understand the impact of access to and use of the internet, within a community of potentially vulnerable consumers; and, Determine the strategies that may assist people living in public housing communities to become more digitally aware and enable them to take advantage of online services such as health, government, news, shopping and methods of online communication. The research also sought to determine what benefits may flow from information technology skills to perceptions of social connectedness, self-efficacy, resilience, health and well-being. Given that people with low levels of computer literacy typically face greater risk of cognitive overload in attempting to learn new technologies, the principles and guidelines from Cognitive Load Theory were applied to training materials and activities to minimise cognitive load and thereby facilitate learning. The research was designed with a view to providing important insights into the factors affecting technology adoption for older and disadvantaged people, as well as providing training and interface guidelines and a potential model for other public housing communities to become more digitally aware

Entrepreneurial exit in real and imagined markets

Entrepreneurs exit their business due to selection pressures experienced in the market place, i.e. business failure. Next to this well known ex-post decision to exit, entrepreneurs select exantewhether they are willing to pursue an entrepreneurial career at all, or to give up theseentrepreneurial intentions. Hardly anything is known about the latter selection process in imagined markets that precedes the variety creation and selection process in real markets. This paper explores and explains the prevalence of these two selection processes using survey data on 20,000 individuals in 27 European countries and the US in 2007. We distinguish business failures from exit by sell-off. Results indicate that individuals in the US are less likely to exit imagined markets, and are more likely to have exited the real market (especially by selling their business) than Europeans. Individuals in a Corporatist welfare state regime have relatively high chances to exit imagined markets. Business owners in urban environments are more likely to fail, while individuals with a high risk tolerance, a high education and self-employed parents are less likely to exit in imagined as well as in real markets (via business failure). This study shows that exit in real and in imagined markets is differently affected by competition and institutions. These selection environments have differential effects on entrepreneurial aspirations and actions of individuals, and provide evidence for the dissimilar nature of exit in real and exit in imagined markets.

Entrepreneurial exit and entrepreneurial engagement

Arguing that entrepreneurial exit is an indicator of accumulated entrepreneurial human capital (like ability and experience) we investigate whether such an exit in the recent past positively relates to posterior engagement in various stages of the entrepreneurial process (i.e. potential, intentional, nascent, young, and established entrepreneurship). We use individual-level data for 24 countries that participated in the Global Entrepreneurship Monitor during the years 2004, 2005 and 2006 (some 350,000 observations). Our findings indeed show that recent exit experience decreases the probability of undertaking no entrepreneurial activity, and that it increases the probabilities of being a potential or an intentional entrepreneur. We also investigate under what conditions recent exit increases engagement in entrepreneurial activities. Most important factors that influence entrepreneurial (re-)engagement are gender, fear of failure and knowing an entrepreneur, while educational attainment does not seem to be relevant. Also, some interesting country differences are found. �

Business Takeover or New Venture? Individual and Environmental Determinants from a Cross-Country Study

Whereas the determinants of entrepreneurial choice have been thoroughly analyzed in the literature, little is known about the preferred mode of entry into entrepreneurship, such as taking over an existing business or starting a new venture. Using a large international dataset, this study reports considerable differences in takeover preferences across 33 countries. Hierarchical (multi-level) regressions are performed to explore individual-level and country-level determinants of the preferred mode of entry. At the individual level, a person’s human capital, risk attitude, and inventiveness influence the preference for starting a new venture versus taking over an existing business. At the country level, the culture-inherent level of risk tolerance, the country’s level of innovation output, and the administrative difficulty of starting a new business are found to explain the between-country variation in the preferred mode of entry. Implications of our findings for research and practice are also discussed.entrepreneurship;occupational choice;business takeover;entry mode;new venture start;multi-level analysis

Control of recollision wave packets for molecular orbital tomography using short laser pulses

The tomographic imaging of arbitrary molecular orbitals via high-order harmonic generation requires that electrons recollide from one direction only. Within a semi-classical model, we show that extremely short phase-stabilized laser pulses offer control over the momentum distribution of the returning electrons. By adjusting the carrier-envelope phase, recollisions can be forced to occur from mainly one side, while retaining a broad energy spectrum. The signatures of the semi-classical distributions are observed in harmonic spectra obtained by numerical solution of the time-dependent Schr\"{o}dinger equation.Comment: 8 pages, 4 figures; v2: Added some extra clarifications; v3: minor grammatical change

Entrepreneurial exit, ability and engagement across countries in different stages of development

Entrepreneurial ability has been suggested to be an important predictor of entrepreneurial engagement. In this paper we investigate the extent to which different types of recent entrepreneurial exit experiences foster entrepreneurial ability and subsequent entrepreneurial engagement. We discriminate between several exit modes and distinguish the following engagement levels: potential, intentional, nascent, young and established entrepreneurship. We use individual-level data for 67 countries that participated in the Global Entrepreneurship Monitor during 2007, 2008 and 2009. Our findings indeed show that entrepreneurial exit directly fosters entrepreneurial engagement as well as indirectly through enhanced entrepreneurial ability. We also find dat positive as well as negative exit experiences foster subsequent entrepreneurial engagement. In addition, the impacts of exit on ability and exit on engagement increase with the stage of development of a country.

Climbing the Entrepreneurial Ladder: The Role of Gender

We investigate whether women and men differ with respect to the steps they take in the entrepreneurial process, distinguishing between five successive steps described by the following positions: (1) "never thought about it"; (2) "thinking about starting up a business"; (3) "taking steps to start a business"; (4) "running a business for less than three years"; (5) "running a business for more than three years". This paper provides insights into the manner in which women and men climb the entrepreneurial ladder and the factors that influence their position on the ladder. We use data from the 2006 "Flash Eurobarometer survey on Entrepreneurship" consisting of more than 10,000 observations for 25 member states of the European Union, Norway, Iceland and the United States. Findings suggest that for men it is easier to climb the ladder and that this may be attributed partly to their higher tolerance of risk.entrepreneurship;determinants;gender;ordered multinomial logit;nascent entrepreneurship