Ultrashort intense-field optical vortices produced with laser-etched mirrors

We introduce a simple and practical method to create ultrashort intense optical vortices for applications involving high-intensity lasers. Our method utilizes femtosecond laser pulses to laser-etch grating lines into laser-quality gold mirrors. These grating lines holographically encode an optical vortex. We derive mathematical equations for each individual grating line to be etched, for any desired (integer) topological charge. We investigate the smoothness of the etched grooves. We show that they are smooth enough to produce optical vortices with an intensity that is only a few percent lower than in the ideal case. We demonstrate that the etched gratings can be used in a folded version of our 2f-2f setup [Mariyenko et al., Opt. Express 19, 7599 (2005)] to compensate angular dispersion. Lastly, we show that the etched gratings withstand intensities of up to 10^12 W/cm2.Comment: 14 pages, 12 figures, submitted to Optics Expres

Board composition, process, and activism: evidence within American firms

This study provided an empirical test of the effects of compositional and process variables on board activism. The attributes examined were functional area knowledge, independence, duality, and effort norms. The findings from this study provided support for the positive relationships between both functional area knowledge and effort norms and board activism. The strong relationship between effort norms and activism indicates the importance of process variables in board research and the need for additional research using process variables in a board context giving further insight into board activism and governance. Additionally, the relationship between functional area knowledge and board activism highlights how boards ability to meet cognitive demands is critical in board performance. These results as well as future research directions are examined in the discussion.board activism, board governance, board attributes, strategic management.

Knowledge tree: Putting discourse into computer‐based learning

Most CBL materials currently in use model only the declarative aspects of the learning process. If such courseware is used without careful planning, this can be dangerous because one of the most fundamental aspects of education is the dialogue that occurs between teachers and the students. Traditionally, this has taken place in informal discussions as well as in formal small‐group learning sessions such as the conventional tutorial. However, as the student‐staff ratio increases, so does the opportunity for this type of personal dialogue decrease. Modern networking technology offers a huge potential to add discourse to CBL, but there are many pedagogical problems involved with the intrinsically ephemeral and anarchic nature both of the Internet and of most conferencing or bulletin‐board systems. In this paper we describe a software system called Knowledge Tree (KT) which we have developed to address some of these issues. KT combines a hierarchical concept‐oriented database functionality with that of a Usenet‐style bulletin board Using this, a knowledge garden may be developed for any subject area. These each contain a hypermedia database of frequently asked questions, together with answers provided by subject experts. There is provision for inter‐student discussions of problems and issues. When students ask new questions these are automatically emailed to a relevant subject expert (determined by a subject‐specific concept thesaurus). The answer is then placed in the database which eventually grows to become a valuable teaching resource. KT is discipline‐independent as the concept thesaurus can be changed to encapsulate any domain of knowledge. We have used it in support of conventional lecture courses, as an important component of a multimedia course, and for general IT support. These examples illustrate the role that this system can play both in basic information provision, and in facilitating the discussion of deep issues

Increased Frequency of Moderate Intensity Walking Increases Consumption of Low Energy Density Foods

Panek-Scarborough, L., Temple, J., University at Buffalo, Buffalo, NY Figure 1: Mean + SEM change in laboratory energy consumed from pre to post exercise intervention from HED foods (top) and LED foods (bottom). The 5 day/week group consumed significantly more energy from LED food from pre- to post-exercise treatment (p = 0.002) compared to the other groups. Background: There is evidence that exercise has an effect on the type and amount of food consumed. One factor that regulates eating is the reinforcing value of food. While previous studies have demonstrated interactions between exercise and eating, to date, no one has investigated the influence of exercise frequency on the reinforcing value of food. Purpose: The purpose of this study was to test the hypothesis that varying frequencies of a short-term exercise regimen alters the reinforcing value of low energy density (LED) and high energy density (HED) foods in sedentary male and female adults. In addition, we predicted that increased frequency of physical activity would be associated with greater intake of LED foods and reduced intake of HED foods. Methods: Eighteen to 50 year old sedentary adults were randomized to 0, 1, 3, or 5 days/week of exercise. We measured the reinforcing value and intake of LED and HED foods at baseline and again after two weeks of exercise. Results: We found no effect of exercise frequency on the reinforcing value of HED or LED food over time (all p \u3e 0.05). However, exercise frequency effected the amount of energy consumed from LED food (p = 0.002) with the 5 days/week group consuming significantly more LED food after two weeks of exercise compared to the other groups. There was no significant effect of exercise frequency on energy intake from HED foods. Conclusion: This study suggests that increasing exercise frequency in sedentary adults may increase consumption of healthier food options, such as fruits and vegetables. Future studies will examine the impact of a longer exercise intervention and/or a higher intensity or interval type training on the reinforcing value of food and on LED and HED food intake

Solubility studies of ultra pure transition elements in ultra pure alkali metals

Solubility of pure iron, molybdenum, niobium, and tantalum in liquid potassiu

Intense-Field Ionization of Monoaromatic Hydrocarbons using Radiation Pulses of Ultrashort Duration: Monohalobenzenes and Azabenzenes

Using 50-fs, 800-nm pulses, we study the intense-field ionization and fragmentation of the monohalobenzenes C_(6)H_(5)-X (X=F, Cl, Br, I) and of the heterocyclics azabenzene C5H5N (pyridine) and the three diazabenzenes C_(4)H_(4)N_(2) (pyridazine, pyrimidine, and pyrazine). Avoiding focal intensity averaging we find indications of resonance-enhanced MPI. In the monohalobenzenes the propensity for fragmentation increases for increasing Z: fluorobenzene yields predominantly C6H5Fn+, while iodobenzene yields atomic ions with charges up to I^(8+). We ascribe this to the heavy-atom effect: the large charge of the heavy halogens' nuclei induces ultrafast intersystem crossing to dissociative triplet states