An experimental investigation into the constant velocity water entry of wedge-shaped sections

Constant velocity water entry is important in understanding planing and slamming of marine vessels. A test rig has been developed that drives a wedge section with end plates down guides to enter the water vertically at near constant velocity. Entry force and velocity are measured. Analysis of the test data shows that the wetting factor is about 1.6 at low deadrise angles and reduces nearly linearly to 1.3 at 451 deadrise angle. The added mass increases quadratically with immersed depth until the chines become wetted. It then continues to increase at a reducing rate, reaching a maximum value between 20% and 80% greater than at chine immersion. The flow momentum drag coefficient is estimated from the results to be 0.78 at 51 deadrise angle reducing to 0.41 at 451 deadrise angles. Constant velocity exit tests show that the momentum of the added mass is expended in driving the water above the surface level and that exit forces are low and equivalent to a drag coefficient of about 1.0-1.3. Considerable dynamic noise limits the accuracy of the results, particularly after chine immersion

High-Technology Entrepreneurship in Silicon Valley

The economic expansion of the late 1990s created many opportunities for business creation in Silicon Valley, but the opportunity cost of starting a business was also high during this period because of the exceptionally tight labor market. A new measure of entrepreneurship derived from matching files from the Current Population Survey (CPS) is used to provide the first test of the hypothesis that business creation rates were high in Silicon Valley during the "Roaring 90s." Unlike previous measures of firm births based on large, nationally representative datasets, the new measure captures business creation at the individual-owner level, includes both employer and non-employer business starts, and focuses on only hi-tech industries. Estimates indicate that hi-tech entrepreneurship rates were lower in Silicon Valley than the rest of the United States during the period from January 1996 to February 2000. Examining the post-boom period, we find that entrepreneurship rates in Silicon Valley increased from the late 1990s to the early 2000s. Although Silicon Valley may be an entrepreneurial location overall, we provide the first evidence that the extremely tight labor market of the late 1990s, especially in hi-tech industries, may have suppressed business creation during this period.entrepreneurship, high-technology, Silicon Valley, economic geography, regional clusters

A Compact Formula for Rotations as Spin Matrix Polynomials

Group elements of SU(2) are expressed in closed form as finite polynomials of the Lie algebra generators, for all definite spin representations of the rotation group. The simple explicit result exhibits connections between group theory, combinatorics, and Fourier analysis, especially in the large spin limit. Salient intuitive features of the formula are illustrated and discussed

Ternary Virasoro - Witt Algebra

A 3-bracket variant of the Virasoro-Witt algebra is constructed through the use of su(1,1) enveloping algebra techniques. The Leibniz rules for 3-brackets acting on other 3-brackets in the algebra are discussed and verified in various situations.Comment: 6 pages, Late

Are Computers Good for Children? The Effects of Home Computers on Educational Outcomes

Although computers are universal in the classroom, nearly twenty million children in the United States do not have computers in their homes. Surprisingly, only a few previous studies explore the role of home computers in the educational process. Home computers might be very useful for completing school assignments, but they might also represent a distraction for teenagers. We use several identification strategies and panel data from the two main U.S. datasets that include recent information on computer ownership among children -- the 2000-2003 CPS Computer and Internet Use Supplements (CIUS) matched to the CPS Basic Monthly Files and the National Longitudinal Survey of Youth 1997 -- to explore the causal relationship between computer ownership and high school graduation and other educational outcomes. Teenagers who have access to home computers are 6 to 8 percentage points more likely to graduate from high school than teenagers who do not have home computers after controlling for individual, parental, and family characteristics. We generally find evidence of positive relationships between home computers and educational outcomes using several identification strategies, including controlling for typically unobservable home environment and extracurricular activities in the NLSY97, fixed effects models, instrumental variables, and including future computer ownership and falsification tests. Home computers may increase high school graduation by reducing non-productive activities, such as truancy and crime, among children in addition to making it easier to complete school assignments.technology, computers, education

An atavistic Lie algebra

An infinite-dimensional Lie Algebra is proposed which includes, in its subalgebra and limits, most Lie Algebras routinely utilised in physics. It relies on the finite oscillator Lie group and appears applicable to twisted noncommutative QFT and CFT

Wigner Trajectory Characteristics in Phase Space and Field Theory

Exact characteristic trajectories are specified for the time-propagating Wigner phase-space distribution function. They are especially simple---indeed, classical---for the quantized simple harmonic oscillator, which serves as the underpinning of the field theoretic Wigner functional formulation introduced. Scalar field theory is thus reformulated in terms of distributions in field phase space. Applications to duality transformations in field theory are discussed.Comment: 9 pages, LaTex2

Self-dual Yang-Mills fields in pseudoeuclidean spaces

The self-duality Yang-Mills equations in pseudoeuclidean spaces of dimensions $d\leq 8$ are investigated. New classes of solutions of the equations are found. Extended solutions to the D=10, N=1 supergravity and super Yang-Mills equations are constructed from these solutions.Comment: 9 pages, LaTeX, no figure

Matrix Membranes and Integrability

This is a pedagogical digest of results reported in Phys Lett B405 (1997) 37, and an explicit implementation of Euler's construction for the solution of the Poisson Bracket dual Nahm equation. But it does not cover 9 and 10-dimensional systems, and subsequent progress on them [hep-th/9707190]. Cubic interactions are considered in 3 and 7 space dimensions, respectively, for bosonic membranes in Poisson Bracket form. Their symmetries and vacuum configurations are explored. Their associated first order equations are transformed to Nahm's equations, and are hence seen to be integrable, for the 3-dimensional case, by virtue of the explicit Lax pair provided. Most constructions introduced also apply to matrix commutator or Moyal Bracket analogs