5,095 research outputs found
10 THz Ultrafast Function Generator - generation of rectangular and triangular pulse trains-
We report the synthesis of arbitrary optical waveforms by manipulating the
spectral phases of Raman sidebands with a wide frequency spacing line-by-line.
Trains of rectangular and triangular pulses are stably produced at an ultrahigh
repetition rate of 10.6229 THz, reminiscent of an ultrafast function generator.Comment: 7 Pages, 5 Figure
Systematic characterization of thermodynamic and dynamical phase behavior in systems with short-ranged attraction
In this paper we demonstrate the feasibility and utility of an augmented
version of the Gibbs ensemble Monte Carlo method for computing the phase
behavior of systems with strong, extremely short-ranged attractions. For
generic potential shapes, this approach allows for the investigation of
narrower attractive widths than those previously reported. Direct comparison to
previous self-consistent Ornstein-Zernike approximation calculations are made.
A preliminary investigation of out-of-equilibrium behavior is also performed.
Our results suggest that the recent observations of stable cluster phases in
systems without long-ranged repulsions are intimately related to gas-crystal
and metastable gas-liquid phase separation.Comment: 10 pages, 8 figure
ELAN as flexible annotation framework for sound and image processing detectors
Annotation of digital recordings in humanities research still is, to a largeextend, a process that is performed manually. This paper describes the firstpattern recognition based software components developed in the AVATecH projectand their integration in the annotation tool ELAN. AVATecH (AdvancingVideo/Audio Technology in Humanities Research) is a project that involves twoMax Planck Institutes (Max Planck Institute for Psycholinguistics, Nijmegen,Max Planck Institute for Social Anthropology, Halle) and two FraunhoferInstitutes (Fraunhofer-Institut für Intelligente Analyse- undInformationssysteme IAIS, Sankt Augustin, Fraunhofer Heinrich-Hertz-Institute,Berlin) and that aims to develop and implement audio and video technology forsemi-automatic annotation of heterogeneous media collections as they occur inmultimedia based research. The highly diverse nature of the digital recordingsstored in the archives of both Max Planck Institutes, poses a huge challenge tomost of the existing pattern recognition solutions and is a motivation to makesuch technology available to researchers in the humanities
Nonlinearities and Effects of Transverse Beam Size in Beam Position Monitors (revised)
The fields produced by a long beam with a given transverse charge
distribution in a homogeneous vacuum chamber are studied. Signals induced by a
displaced finite-size beam on electrodes of a beam position monitor (BPM) are
calculated and compared to those produced by a pencil beam. The non-linearities
and corrections to BPM signals due to a finite transverse beam size are
calculated for an arbitrary chamber cross section. Simple analytical
expressions are given for a few particular transverse distributions of the beam
current in a circular or rectangular chamber. Of particular interest is a
general proof that in an arbitrary homogeneous chamber the beam-size
corrections vanish for any axisymmetric beam current distribution.Comment: REVTeX, 8 pages, 9 figures. Corrected Eqs. (7),(22),(25) and Figs.
2-9. Expande
Reverse-selective diffusion in nanocomposite membranes
The permeability of certain polymer membranes with impenetrable
nanoinclusions increases with the particle volume fraction (Merkel et al.,
Science, 296, 2002). This intriguing observation contradicts even qualitative
expectations based on Maxwell's classical theory of conduction/diffusion in
composites with homogeneous phases. This letter presents a simple theoretical
interpretation based on classical models of diffusion and polymer physics. An
essential feature of the theory is a polymer-segment depletion layer at the
inclusion-polymer interface. The accompanying increase in free volume leads to
a significant increase in the local penetrant diffusivity, which, in turn,
increases the bulk permeability while exhibiting reverse selectivity. This
model captures the observed dependence of the bulk permeability on the
inclusion size and volume fraction, providing a straightforward connection
between membrane microstructure and performance
Surface-mediated attraction between colloids
We investigate the equilibrium properties of a colloidal solution in contact
with a soft interface. As a result of symmetry breaking, surface effects are
generally prevailing in confined colloidal systems. In this Letter, particular
emphasis is given to surface fluctuations and their consequences on the local
(re)organization of the suspension. It is shown that particles experience a
significant effective interaction in the vicinity of the interface. This
potential of mean force is always attractive, with range controlled by the
surface correlation length. We suggest that, under some circumstances,
surface-induced attraction may have a strong influence on the local particle
distribution
A Simulation Method to Resolve Hydrodynamic Interactions in Colloidal Dispersions
A new computational method is presented to resolve hydrodynamic interactions
acting on solid particles immersed in incompressible host fluids. In this
method, boundaries between solid particles and host fluids are replaced with a
continuous interface by assuming a smoothed profile. This enabled us to
calculate hydrodynamic interactions both efficiently and accurately, without
neglecting many-body interactions. The validity of the method was tested by
calculating the drag force acting on a single cylindrical rod moving in an
incompressible Newtonian fluid. This method was then applied in order to
simulate sedimentation process of colloidal dispersions.Comment: 7pages, 7 figure
International Entrepreneurship Education
Entrepreneurship for engineering students must be taught within the global context. Lacking that, graduates will be ill prepared to be internationally competitive. Any engineering graduate who does not scour the earth for new ideas, developments and designs is not competitive. And any engineer who does not look at the total world marketplace for sale of products is limiting potential success. This paper will outline what every entrepreneurially minded student should have in the way of competencies, attitudes, communication strategies, cultural understandings, business mores, multinational corporate logistics, and macroeconomics understandings. It will outline cultural soft skills needed, as well as hard-nosed business skills. Many US universities may be prepared to work effectively with internationally minded students, but engineering students typically do not get involved ñ only 2 to 3 percent of engineering students get a meaningful international exposure prior to graduation. Among other constraints, engineering faculty members are less than aggressive in encouraging them to get such experience. To meet the needs of engineering students, institutional and individual partnerships must be created to promote international collaborations, including design projects, international internships, exposure to successful entrepreneurs from other parts of the world including developing countries, etc
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