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Introduction
This is the post print version of the chapter - Copyright @ 2003 The editorsThis book is about surrogacy and, more specifically, surrogate motherhood. It is a collection of essays that aims to provide a contemporary and international picture of a practice, traceable to ancient times, devised to solve the problem of childlessness. The collection, which explores surrogacy from a variety of perspectives including law, policy, medicine and psychology, is timely. For although there is nothing new in the notion that a woman might bear a child for someone else, there is some evidence that the incidence of surrogacy is increasing and technology has developed to make ever more complex arrangements possible
Alternative determinism principle for topological analysis of chaos
The topological analysis of chaos based on a knot-theoretic characterization
of unstable periodic orbits has proved a powerful method, however knot theory
can only be applied to three-dimensional systems. Still, the core principles
upon which this approach is built, determinism and continuity, apply in any
dimension. We propose an alternative framework in which these principles are
enforced on triangulated surfaces rather than curves and show that in dimension
three our approach numerically predicts the correct topological entropies for
periodic orbits of the horseshoe map.Comment: Accepted for publication as Rapid Communication in Physical Review
Environmental variables, pesticide pollution and meiofaunal community structure in two contrasting temporarily open/closed false bay estuaries
Environmental variables (including natural and anthropogenic stressors) and meiobenthic communities were sampled in a ânaturalâ (Rooiels) and a âdisturbedâ (Lourens) estuary in the Western Cape, South Africa, bimonthly for 20 months. A primary aim of the study was to assess if the meiobenthic community structure is driven by different variables when comparing ânaturalâ versus âdisturbedâ system. Due to the much smaller catchment of the Rooiels Estuary, many environmental variables were significantly different (p<0.001) from the variables in the Lourens Estuary, e.g. salinity, temperature, pH, total suspended solids, nitrate and depth. No pesticide concentrations were expected in the Rooiels Estuary due to the absence of agricultural development in the catchment. However, chlorpyrifos (8.9 ”g/kg), prothiofos (22.0 ”g/kg) and cypermethrin concentrations (0.42 ”g/kg) were detected frequently, with the highest concentrations recorded during the summer months. Principal response curve analysis showed that temporal variability between sampling dates explained 42% of the variance in environmental variables and pesticide concentrations and spatial variability between the 2 estuaries explained 58%. Variables contributing most to the differences were higher concentrations of endosulfan, p,p-DDE and nitrate concentrations in the Lourens Estuary and larger grain size and higher salinity at the bottom in the Rooiels Estuary. In general the meiofaunal community in the Rooiels Estuary showed a significantly higher number of taxa (p<0.001), a significantly higher Shannon Wiener Diversity Index (
Asymptotic Exit Location Distributions in the Stochastic Exit Problem
Consider a two-dimensional continuous-time dynamical system, with an
attracting fixed point . If the deterministic dynamics are perturbed by
white noise (random perturbations) of strength , the system state
will eventually leave the domain of attraction of . We analyse the
case when, as , the exit location on the boundary
is increasingly concentrated near a saddle point of the
deterministic dynamics. We show that the asymptotic form of the exit location
distribution on is generically non-Gaussian and asymmetric,
and classify the possible limiting distributions. A key role is played by a
parameter , equal to the ratio of the stable
and unstable eigenvalues of the linearized deterministic flow at . If
then the exit location distribution is generically asymptotic as
to a Weibull distribution with shape parameter , on the
length scale near . If it is generically
asymptotic to a distribution on the length scale, whose
moments we compute. The asymmetry of the asymptotic exit location distribution
is attributable to the generic presence of a `classically forbidden' region: a
wedge-shaped subset of with as vertex, which is reached from ,
in the limit, only via `bent' (non-smooth) fluctuational paths
that first pass through the vicinity of . We deduce from the presence of
this forbidden region that the classical Eyring formula for the
small- exponential asymptotics of the mean first exit time is
generically inapplicable.Comment: This is a 72-page Postscript file, about 600K in length. Hardcopy
requests to [email protected] or [email protected]
AAA gunnermodel based on observer theory
The Luenberger observer theory is used to develop a predictive model of a gunner's tracking response in antiaircraft artillery systems. This model is composed of an observer, a feedback controller and a remnant element. An important feature of the model is that the structure is simple, hence a computer simulation requires only a short execution time. A parameter identification program based on the least squares curve fitting method and the Gauss Newton gradient algorithm is developed to determine the parameter values of the gunner model. Thus, a systematic procedure exists for identifying model parameters for a given antiaircraft tracking task. Model predictions of tracking errors are compared with human tracking data obtained from manned simulation experiments. Model predictions are in excellent agreement with the empirical data for several flyby and maneuvering target trajectories
One hundred ten consecutive primary orthotopic liver transplants under FK 506 in adults.
An account is given of the 6- to 12-month survival, and causes of failure in 110 consecutive patients who underwent primary liver transplantation under treatment from the outset with FK 506 and steroids. The patient survival is 92.7%, and the first graft survival is 87.3%. At a very high frequency, the patients achieved good graft function, and they had a relatively low morbidity that was partially ascribable to minimal use and early discontinuance (in 60% of cases) of steroids. Renal dysfunction and other adverse findings were largely confined to patients with poor initial graft function and consequent apparent alteration of the kinetics of FK 506 elimination, causing functional overdosage. Results compare very favorably with our past record using conventional immunosuppression, and support the belief that FK 506 is a superior immunosuppressive agent which is suitable for chronic administration
High Density Mesoscopic Atom Clouds in a Holographic Atom Trap
We demonstrate the production of micron-sized high density atom clouds of
interest for meso- scopic quantum information processing. We evaporate atoms
from 60 microK, 3x10^14 atoms/cm^3 samples contained in a highly anisotropic
optical lattice formed by interfering di racted beams from a holographic phase
plate. After evaporating to 1 microK by lowering the con ning potential, in
less than a second the atom density reduces to 8x10^13 cm^- 3 at a phase space
density approaching unity. Adiabatic recompression of the atoms then increases
the density to levels in excess of 1x10^15 cm^-3. The resulting clouds are
typically 8 microns in the longest dimension. Such samples are small enough to
enable mesoscopic quantum manipulation using Rydberg blockade and have the high
densities required to investigate new collision phenomena.Comment: 4 pages, 4 figures, submitted to PR
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