and assuring the quality of medical information on the internet. JAMA 1997;277:1244-5. 4 Wyatt JC. Measuring quality and impact of the world wide web [commentary]. BMJ 1997;314:1879-81. 5 Shon J, Marshall J, Musen MA. The impact of displayed awards on the credibility and retention of web site information. AbstractObjectives To describe techniques for retrieval and appraisal used by consumers when they search for health information on the internet. Design Qualitative study using focus groups, naturalistic observation of consumers searching the world wide web in a usability laboratory, and in-depth interviews. Participants A total of 21 users of the internet participated in three focus group sessions. 17 participants were given a series of health questions and observed in a usability laboratory setting while retrieving health information from the web; this was followed by in-depth interviews. Setting Heidelberg, Germany. Results Although their search technique was often suboptimal, internet users successfully found health information to answer questions in an average of 5 minutes 42 seconds (median 4 minutes 18 seconds) per question. Participants in focus groups said that when assessing the credibility of a website they primarily looked for the source, a professional design, a scientific or official touch, language, and ease of use. However, in the observational study, no participants checked any "about us" sections of websites, disclaimers, or disclosure statements. In the post-search interviews, it emerged that very few participants had noticed and remembered which websites they had retrieved information from. Conclusions Further observational studies are needed to design and evaluate educational and technological innovations for guiding consumers to high quality health information on the web. IntroductionLittle is known about how consumers retrieve and assess health information on the world wide web. Some surveys have elicited data by using semistructured questionnaires or focus groups, 1-3 but little (if any) unobtrusive observational research has been done to explore how consumers are actually surfing the web. Although several criteria for quality of health websites have been proposed-including disclosure of site owners, authors, and update cycle 4 5 -little or nothing is known about whether and to what degree such markers are recognised or even looked at by consumers or what other credibility markers consumers are looking for. We aimed to obtain qualitative and semiquantitative data to generate some hypotheses on how consumers might search for and appraise health information. MethodsWe used multiple methods of data collection that are commonly used in studies of human-computer interactions, 6 combining focus groups, 7 naturalistic observation of consumers searching the internet, and post-search in-depth interviews. Two researchers independently analysed transcripts by using N5 (NUD*IST 5.0; QSR International, Melbourne) with the grounded theory approach. 8 Participants in the focus groups and the observatio...

We present a combined theoretical and experimental study of spatiotemporal propagation effects in terahertz (THz) generation in gases using two-color ionizing laser pulses. The observed strong broadening of the THz spectra with increasing gas pressure reveals the prominent role of spatiotemporal reshaping and of a plasma-induced blueshift of the pump pulses in the generation process. Results obtained from (3+1)-dimensional simulations are in good agreement with experimental findings and clarify the mechanisms responsible for THz emission.

The shift towards more open and interconnected innovation activities has been a major topic in recent academic and practitioner discussions. Firms must connect their in-house R&D activities with external partners, such as leading customers or universities, to increase the effectiveness of their innovation activities. Hence, management needs to define where to search for valuable knowledge in its environment. In this paper we argue that knowledge search has to reflect the heterogeneity of various knowledge sources with regard to the knowledge they can provide and how these sources can be activated. We hypothesize that search strategies driven by science, suppliers and the product market will contribute differently to innovation success with new-to-market versus imitated products. Moreover, we explore the effect of these types of knowledge search within different sectoral patterns of innovation. Our empirical analysis rests on a sample of almost 5,000 firms from five Western European countries. The results support our hypotheses and highlight the potentials and shortcomings of different types of knowledge search.

Applications ranging from nonlinear terahertz spectroscopy to remote sensing require broadband and intense THz radiation which can be generated by focusing two-color laser pulses into a gas. In this setup, THz radiation originates from the buildup of the electron density in sharp steps of attosecond duration due to tunnel ionization, and subsequent acceleration of free electrons in the laser field. We show that the spectral shape of the THz pulses generated by this mechanism is determined by superposition of contributions from individual ionization events. This provides a straightforward analogy with linear diffraction theory, where the ionization events play the role of slits in a grating. This analogy offers simple explanations for recent experimental observations and opens new avenues for THz pulse shaping based on temporal control of the ionization events. We illustrate this novel technique by tailoring the spectral width and position of the resulting radiation using multi-color pump pulses.

Terahertz (THz) radiation produced by the filamentation of two-color pulses over long distances in argon is numerically investigated using a comprehensive model in full space-time-resolved geometry. We show that the dominant physical mechanism for THz generation in the filamentation regime at clamping intensity is based on quasi-dc plasma currents. The calculated THz spectra for different pump pulse energies and pulse durations are in agreement with previously reported experimental observations. For the same pulse parameters, near-infrared pump pulses at 2  μm are shown to generate a more than 1 order of magnitude greater THz yield than pumps centered at 800 nm.