2,651 research outputs found
Spatial Interference: From Coherent To Incoherent
It is well known that direct observation of interference and diffraction
pattern in the intensity distribution requires a spatially coherent source.
Optical waves emitted from portions beyond the coherence area possess
statistically independent phases, and will degrade the interference pattern. In
this paper we show an optical interference experiment, which seems contrary to
our common knowledge, that the formation of the interference pattern is related
to a spatially incoherent light source. Our experimental scheme is very similar
to Gabor's original proposal of holography[1], just with an incoherent source
replacing the coherent one. In the statistical ensemble of the incoherent
source, each sample field produces a sample interference pattern between object
wave and reference wave. These patterns completely differ from each other due
to the fluctuation of the source field distribution. Surprisingly, the sum of a
great number of sample patterns exhibits explicitly an interference pattern,
which contains all the information of the object and is equivalent to a
hologram in the coherent light case. In this sense our approach would be
valuable in holography and other interference techniques for the case where
coherent source is unavailable, such as x-ray and electron sources.Comment: 8 pages, 5 figure
Characterization of Hardness and Elastic Modulus of a Pharmaceutical Material for Multiple Crystal Orientations
Nanoindentation has made it possible to test material properties of extremely brittle molecular crystals, which include many pharmaceuticals. An antifungal, griseofulvin, is tested to determine differences in hardness and elastic modulus for different crystal orientations. Hardness and elastic modulus are determined by nanoindentation on single crystals that are rotated in 15° intervals. There are differences in hardness at rotation degrees of 45°, 60°, and 75° from the 0° orientation and differences in elastic modulus at rotation degrees of 15°, 60°, and 75° from the 0° orientation. It is also found that the elastic modulus and hardness values of the 75° rotation are only similar to the 60° rotation. Griseofulvin displays anisotropy in hardness and elastic modulus, which implies that different crystal rotations activate different slip systems. Further work is needed to correlate rotation angle with the crystal structure as well as confirm these findings on another crystal
Non-linear and quantum optics of a type II OPO containing a birefringent element Part 1: Classical operation
We describe theoretically the main characteristics of the steady state regime
of a type II Optical Parametric Oscillator (OPO) containing a birefringent
plate. In such a device the signal and idler waves are at the same time
linearly coupled by the plate and nonlinearly coupled by the
crystal. This mixed coupling allows, in some well-defined range of the control
parameters, a frequency degenerate operation as well as phase locking between
the signal and idler modes. We describe here a complete model taking into
account all possible effects in the system, \emph{i.e.} arbitrary rotation of
the waveplate, non perfect phase matching, ring and linear cavities. This model
is able to explain the detailed features of the experiments performed with this
system.Comment: To be published in EPJ
Planar spin exchange in LiNiO_2
We study the planar spin exchange couplings in LiNiO2 using a perturbative
approach. We show that the inclusion of the trigonal crystal field splitting at
the Oxygen sites leads to the appearance of antiferromagnetic exchange
integrals in deviation from the Goodenough-Kanamori-Anderson rules for this 90
degree bond. That gives a microscopic foundation for the recently observed
coexistence of ferromagnetic and antiferromagnetic couplings in the
orbitally-frustrated state of LiNiO2. (F. Reynaud et al, Phys. Rev. Lett. 86,
3638 (2001))Comment: latex, revtex4, 6 pages, 3 figure
Mortensen Observer for a class of variational inequalities -Lost equivalence with stochastic filtering approaches
We address the problem of deterministic sequential estimation for a nonsmooth
dynamics in R governed by a variational inequality, as illustrated by the
Skorokhod problem with a reflective boundary condition at 0. For smooth
dynamics, Mortensen introduced an energy for the likelihood that the state
variable produces-up to perturbations disturbances-a given observation in a
finite time interval, while reaching a given target state at the final time.
The Mortensen observer is the minimiser of this energy. For dynamics given by a
variational inequality and therefore not reversible in time, we study the
definition of a Mortensen estimator. On the one hand, we address this problem
by relaxing the boundary constraint of the synthetic variable and then
proposing an approximated variant of the Mortensen estimator that uses the
resulting nonlinear smooth dynamics. On the other hand, inspired by the smooth
dynamics approach, we study the vanishing viscosity limit of the
Hamilton-Jacobi equation satisfied by the Hopf-Cole transform of the solution
of the robust Zakai equation. We prove a stability result that allows us to
interpret the limiting solution as the value function associated with a control
problem rather than an estimation problem. In contrast to the case of smooth
dynamics, here the zero-noise limit of the robust form of the Zakai equation
cannot be understood from the Bellman equation of the value function arising in
Mortensen's deterministic estimation. This may unveil a violation of
equivalence for non-reversible dynamics between the Mortensen approach and the
low noise stochastic approach for nonsmooth dynamics
A Blueprint for Equitable AI
We convened two diverse groups of experts in late 2022 to discuss how they might advise building and distributing artificial intelligence for equitable outcomes. In advance of these virtual roundtables, we provided some suggested readings, which are listed at the end of this report, along with a few definitions to start the conversation. This report represents a summary of the discussions.Many of the ideas explored are not new, nor do the participants offer silver bullets to ongoing challenges. But there is value in exploring them together to build the muscle and future institutions required for civil discourse on the role technology plays in our lives. We hope this report inspires greater curiosity among technologists and the communities they serve, and spurs and shapes the development of markets, norms, and policies toward achieving greater equity
Mathematical formulation of a dynamical system with dry friction subjected to external forces
We consider the response of a one-dimensional system with friction. S.W. Shaw
(Journal of Sound and Vibration, 1986) introduced the set up of different
coefficients for the static and dynamic phases (also called stick and slip
phases). He constructs a step by step solution, corresponding to an harmonic
forcing. In this paper, we show that the theory of variational inequalities
provides an elegant and synthetic approach to obtain the existence and
uniqueness of the solution, avoiding the step by step construction. We then
apply the theory to a real structure with real data and show that the model is
quite accurate. In our case, the forcing motion comes from dilatation, due to
temperature
Secular Trend and Risk Factors for Antimicrobial Resistance in Escherichia coli Isolates in Switzerland 1997-2007
Abstract : Background: : Antibacterial resistance in Escherichia coli isolates of urinary infections, mainly to fluoroquinolones, is emerging. The aim of our study was to identify the secular trend of resistant E. coli isolates and to characterize the population at risk for colonization or infections with these organisms. Patients and Methods: : Retrospective analysis of 3,430 E.coli first isolates of urine specimens from patients admitted to the University Hospital Basel in 1997, 2000, 2003, and 2007. Results: : Resistance to ciprofloxacin, trimethoprim/sulfamethoxazole, and amoxicillin/clavulanate has increased over the 10-year study period (from 1.8% to 15.9%, 17.4% to 21.3%, and 9.5% to 14.5%, respectively). A detailed analysis of the 2007 data revealed that independent risk factors for ciprofloxacin resistance were age (5.3% 75 years; odds ratio [OR] 1.29 per 10 years, 95% confidence interval [CI] 1.15-1.45, p < 0.001) and male gender (OR 1.59, 95% CI 1.05-2.41, p = 0.04). In contrast, nosocomial E. coli isolates were associated with lower odds of ciprofloxacin resistance (OR 0.51, 95% CI 0.28-0.67, p < 0.001). The frequency of resistant isolate rates was not influenced by the clinical significance (i.e., colonization vs urinary tract infection, UTI) or by whether the urine was taken from a urinary catheter. Importantly, the increase in ciprofloxacin resistance paralleled the increase in ciprofloxacin consumption in Switzerland (Pearson's correlation test R2= 0.998, p = 0.002). Of note, resistance was less frequent in isolates sent in by general practitioners. However, after adjustment for age and gender, only resistance against amoxicillin/clavulanate was found to be less frequent (OR 0.34, 95% CI 0.16-0.92, p = 0.03). Conclusion: : Our study reveals that resistance rates have been increasing during the last decade. Published resistance rates may lack information due to important differences regarding age, gender, and probable origin of the isolates. Empirical therapy for UTI should be guided more on individual risk profile and local resistance data than on resistance data bank
The Bragdon Committee
The original format of this document was an active HTML page(s) located under https://www.fhwa.dot.gov/infrastructure/history.cfm. The Federal Highway Administration converted the HTML page(s) into an Adobe\uae Acrobat\uae PDF file to preserve and support reuse of the information it contained. The intellectual content of this PDF is an authentic capture of the original HTML file. Hyperlinks and other functions of the HTML webpage may have been lost, and this version of the content may not fully work with screen reading software.This resource describes the Bragdon Committee and their role in the interstate highway program during the late 1950\u2019s and early 1960\u2019s. Details of the committee\u2019s role, recommendations for the program, and economic considerations they determined based on their assessment of the program itself
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