Nonlinear optics with full three-dimensional illumination

We investigate the nonlinear optical process of third-harmonic generation in the thus far unexplored regime of focusing the pump light from a full solid angle, where the nonlinear process is dominantly driven by a standing dipole-wave. We elucidate the influence of the focal volume and the pump intensity on the number of frequency-tripled photons by varying the solid angle from which the pump light is focused, finding good agreement between the experiments and numerical calculations. As a consequence of focusing the pump light to volumes much smaller than a wavelength cubed the Gouy phase does not limit the yield of frequency-converted photons. This is in stark contrast to the paraxial regime. We believe that our findings are generic to many other nonlinear optical processes when the pump light is focused from a full solid angle.Comment: 6 pages main text + 4 pages appendix, modified abstract and introduction + some other minor change

Combining Quote-Driven and Order-Driven Trading Systems in Next-Generation Stock Markets: An Experimental Investigation

We use computer-based simulations of a stock market as a background environment for experimental tests of the integration of an order-driven trading system into a dealer/quote-driven market. Experimental subjects traded using a traditional dealer quote screen (such as Nasdaq in the U.S. or the London Stock Exchange's SEAQ), to which was added a public limit order facility. Data captured on subjects' trading decisions under different market structures revealed that: (1) When available, the limit order facility was used by the subjects, attracting some orders that would have otherwise gone to dealers, and reducing investor trading costs. (2) The relative use of market orders and limit orders was related to the bid-ask spread; wider spreads (higher cost of immediate trading) led subjects to enter fewer market orders. (3) Limit order use was reduced when the dealers were provided with an "informational advantage. " (4) While the introduction of a limit order facility did not have a substantial effect on dealer profit margins, dealers' activities as a percentage of total market volume declined. Overall, we find the simulation environment is a workable device for analyzing the effect of market design changes on trader behavior and market quality. It can provide solid guidance on market structure issues, such as how best to incorporate a limit order facility in a competing dealer market.Information Systems Working Papers Serie

Optical devices using an external cavity semiconductor laser

A dual-mode optical device selectively operative in signal generation and amplification modes is disclosed herein. The dual-mode device includes a body of semiconductor material having opposed from and rear facets. During operation in the amplification mode, light is input through the front facet and is amplified within the body of the optical gain material. An at least partially optically reflective surface is positioned a first predetermined distance from one of the facets during operation of the device in the amplification mode. In the signal generation mode, the at least partially optically reflective surface is positioned a second predetermined distance from the one facet so as to induce optical oscillation within the body of semiconductor material. In a preferred implementation, a semiconductor diode laser having opposed first and second facets is utilized as an optical source. An at least partially optically reflective surface is positioned a predetermined distance from one of the first and second facets in order that a resonant cavity is formed therebetween. The predetermined distance between the at least partially optically reflective surface and the one facet may be modulated, thereby allowing modulation of optical output produced by the semiconductor diode laser

Magnetic pulse generation for high-speed magneto-optic switching

In this article, the magnetic pulse characteristics needed to achieve high-speed magneto-optic (MO) switching are investigated. A fiber-based, MO, low-voltage optical switch capable of 200 ns switching is presented, along with the special circuit characteristics for magnetic field generation for high-speed switching. The switch consists of the optical system, the MO material (bismuth substituted iron garnet [(Bi1.1Tb1.9)(Fe4.25Ga0.75)O12]), and a high-speed magnetic field driving circuit. A Faraday rotator is placed within the interferometric loop of a fiber-optic Sagnac interferometer, and interference at the output ports is controlled by the applied field. The fast switching speed is accomplished via the special design of the magnetic pulse generation circuitry. The applied magnetic field overshoots the field necessary to achieve the desired Faraday rotation and then settles to a steady state field. If the duration of the overshoot is less than the time it takes the material to saturate, a fast optical switching time can be achieved without saturating the material. The effects of the overshoot amplitude and duration and steady-state amplitude on optical rise time (determined by domain wall velocity) are studied and experimental results are presented

Plug flow and the breakdown of Bagnold scaling in cohesive granular flows

Cohesive granular media flowing down an inclined plane are studied by discrete element simulations. Previous work on cohesionless granular media demonstrated that within the steady flow regime where gravitational energy is balanced by dissipation arising from intergrain forces, the velocity profile in the flow direction scales with depth in a manner consistent with the predictions of Bagnold. Here we demonstrate that this Bagnold scaling does not hold for the analogous steady-flows in cohesive granular media. We develop a generalization of the Bagnold constitutive relation to account for our observation and speculate as to the underlying physical mechanisms responsible for the different constitutive laws for cohesive and noncohesive granular media.Comment: 8 pages, 10 figure

Spitzer observations of extragalactic H II regions - III. NGC 6822 and the hot star, H II region connection

Using the short-high module of the Infrared Spectrograph on the Spitzer Space Telescope, we have measured the [S IV] 10.51, [Ne II] 12.81, [Ne III] 15.56, and [S III] 18.71-micron emission lines in nine H II regions in the dwarf irregular galaxy NGC 6822. These lines arise from the dominant ionization states of the elements neon (Ne$^{++}$, Ne$^+$) and sulphur (S$^{3+}$, S$^{++}$), thereby allowing an analysis of the neon to sulphur abundance ratio as well as the ionic abundance ratios Ne$^+$/Ne$^{++}$ and S$^{3+}$/S$^{++}$. By extending our studies of H II regions in M83 and M33 to the lower metallicity NGC 6822, we increase the reliability of the estimated Ne/S ratio. We find that the Ne/S ratio appears to be fairly universal, with not much variation about the ratio found for NGC 6822: the median (average) Ne/S ratio equals 11.6 (12.2$\pm$0.8). This value is in contrast to Asplund et al.'s currently best estimated value for the Sun: Ne/S = 6.5. In addition, we continue to test the predicted ionizing spectral energy distributions (SEDs) from various stellar atmosphere models by comparing model nebulae computed with these SEDs as inputs to our observational data, changing just the stellar atmosphere model abundances. Here we employ a new grid of SEDs computed with different metallicities: Solar, 0.4 Solar, and 0.1 Solar. As expected, these changes to the SED show similar trends to those seen upon changing just the nebular gas metallicities in our plasma simulations: lower metallicity results in higher ionization. This trend agrees with the observations.Comment: 22 pages, 13 figures. To be published in MNRAS. reference added and typos fixed. arXiv admin note: text overlap with arXiv:0804.0828, which is paper II by Rubin et al. (2008

Liquidity, Markets and Trading in Action

This open access book addresses four standard business school subjects: microeconomics, macroeconomics, finance and information systems as they relate to trading, liquidity, and market structure. It provides a detailed examination of the impact of trading costs and other impediments of trading that the authors call “frictions”. It also presents an interactive simulation model of equity market trading, TraderEx, that enables students to implement trading decisions in different market scenarios and structures. Addressing these topics shines a bright light on how a real-world financial market operates, and the simulation provides students with an experiential learning opportunity that is informative and fun. Each of the chapters is designed so that it can be used as a stand-alone module in an existing economics, finance, or information science course. Instructor resources such as discussion questions, Powerpoint slides and TraderEx exercises are available online

Community Recommendations for Improving Sustainable Scientific Software Practices

Multiple focus groups were conducted to elicit perspectives from members of the Earth science informatics community on the sustainability of scientific software. Recommendations that the participants offered for near-term community actions and activities are described

Combining Quote-Driven and Order-Driven Trading Systems in Next-Generation Stock Markets: An Experimental Investigation

We use computer-based simulations of a stock market as a background environment for experimental tests of the integration of an order-driven trading system into a dealer/quote-driven market. Experimental subjects traded using a traditional dealer quote screen (such as Nasdaq in the U.S. or the London Stock Exchange's SEAQ), to which was added a public limit order facility. Data captured on subjects' trading decisions under different market structures revealed that: (1) When available, the limit order facility was used by the subjects, attracting some orders that would have otherwise gone to dealers, and reducing investor trading costs. (2) The relative use of market orders and limit orders was related to the bid-ask spread; wider spreads (higher cost of immediate trading) led subjects to enter fewer market orders. (3) Limit order use was reduced when the dealers were provided with an "informational advantage. " (4) While the introduction of a limit order facility did not have a substantial effect on dealer profit margins, dealers' activities as a percentage of total market volume declined. Overall, we find the simulation environment is a workable device for analyzing the effect of market design changes on trader behavior and market quality. It can provide solid guidance on market structure issues, such as how best to incorporate a limit order facility in a competing dealer market.Information Systems Working Papers Serie

Summer 1973

What Happens to Herbicides in the Environmen? (page 3) Agricultural Chelates--What They Are, What They Do (6) Turfgrass Cultivars (9) Vandalism on the Golf Course (13) Massachusetts Seed laws (20