2,703 research outputs found
High resolution powder blast micromachining
Powder blasting, or Abrasive Jet Machining (AJM), is a technique in which a particle jet is directed towards a target for mechanical material removal. It is a fast, cheap and accurate directional etch technique for brittle materials like glass, silicon and ceramics. By introducing electroplated copper as a new mask material, the feature size of this process was decreased. It was found that blasting with 9 ”m particles (compared with 30 ”m particles) result in a higher slope of the channel sidewall. The aspect ratio of powder blasted channels was increased by using the high resistance of the copper mask in combination with the use of 9 ”m particles. Furthermore, our measurements show how the blast lag (small channels etch slower compared to wider channels) is decreased by using smaller particles
Michaelis-Menten dynamics in protein subnetworks
To understand the behaviour of complex systems it is often necessary to use
models that describe the dynamics of subnetworks. It has previously been
established using projection methods that such subnetwork dynamics generically
involves memory of the past, and that the memory functions can be calculated
explicitly for biochemical reaction networks made up of unary and binary
reactions. However, many established network models involve also
Michaelis-Menten kinetics, to describe e.g. enzymatic reactions. We show that
the projection approach to subnetwork dynamics can be extended to such
networks, thus significantly broadening its range of applicability. To derive
the extension we construct a larger network that represents enzymes and enzyme
complexes explicitly, obtain the projected equations, and finally take the
limit of fast enzyme reactions that gives back Michaelis-Menten kinetics. The
crucial point is that this limit can be taken in closed form. The outcome is a
simple procedure that allows one to obtain a description of subnetwork
dynamics, including memory functions, starting directly from any given network
of unary, binary and Michaelis-Menten reactions. Numerical tests show that this
closed form enzyme elimination gives a much more accurate description of the
subnetwork dynamics than the simpler method that represents enzymes explicitly,
and is also more efficient computationally
Electron - nuclear recoil discrimination by pulse shape analysis
In the framework of the ``ULTIMA'' project, we use ultra cold superfluid 3He
bolometers for the direct detection of single particle events, aimed for a
future use as a dark matter detector. One parameter of the pulse shape observed
after such an event is the thermalization time constant. Until now it was
believed that this parameter only depends on geometrical factors and superfluid
3He properties, and that it is independent of the nature of the incident
particles. In this report we show new results which demonstrate that a
difference for muon- and neutron events, as well as events simulated by heater
pulses exist. The possibility to use this difference for event discrimination
in a future dark matter detector will be discussed.Comment: Proseedings of QFS 2007, Kazan, Russia; 8 pages, 4 figures. Submited
to J. Low Temp. Phy
Self-gravitating Brownian systems and bacterial populations with two or more types of particles
We study the thermodynamical properties of a self-gravitating gas with two or
more types of particles. Using the method of linear series of equilibria, we
determine the structure and stability of statistical equilibrium states in both
microcanonical and canonical ensembles. We show how the critical temperature
(Jeans instability) and the critical energy (Antonov instability) depend on the
relative mass of the particles and on the dimension of space. We then study the
dynamical evolution of a multi-components gas of self-gravitating Brownian
particles in the canonical ensemble. Self-similar solutions describing the
collapse below the critical temperature are obtained analytically. We find
particle segregation, with the scaling profile of the slowest collapsing
particles decaying with a non universal exponent that we compute perturbatively
in different limits. These results are compared with numerical simulations of
the two-species Smoluchowski-Poisson system. Our model of self-attracting
Brownian particles also describes the chemotactic aggregation of a
multi-species system of bacteria in biology
AXES at TRECVid 2011
The AXES project participated in the interactive known-item search task (KIS) and the interactive instance search task (INS) for TRECVid 2011. We used the same system architecture and a nearly identical user interface for both the KIS and INS tasks. Both systems made use of text search on ASR, visual concept detectors, and visual similarity search. The user experiments were carried out with media professionals and media students at the Netherlands Institute for Sound and Vision, with media professionals performing the KIS task and media students participating in the INS task. This paper describes the results and findings of our experiments
Post-collapse dynamics of self-gravitating Brownian particles in D dimensions
We address the post-collapse dynamics of a self-gravitating gas of Brownian
particles in D dimensions, in both canonical and microcanonical ensembles. In
the canonical ensemble, the post-collapse evolution is marked by the formation
of a Dirac peak with increasing mass. The density profile outside the peak
evolves self-similarly with decreasing central density and increasing core
radius. In the microcanonical ensemble, the post-collapse regime is marked by
the formation of a ``binary''-like structure surrounded by an almost uniform
halo with high temperature. These results are consistent with thermodynamical
predictions
Exact analytical solution of the collapse of self-gravitating Brownian particles and bacterial populations at zero temperature
We provide an exact analytical solution of the collapse dynamics of
self-gravitating Brownian particles and bacterial populations at zero
temperature. These systems are described by the Smoluchowski-Poisson system or
Keller-Segel model in which the diffusion term is neglected. As a result, the
dynamics is purely deterministic. A cold system undergoes a gravitational
collapse leading to a finite time singularity: the central density increases
and becomes infinite in a finite time t_coll. The evolution continues in the
post collapse regime. A Dirac peak emerges, grows and finally captures all the
mass in a finite time t_end, while the central density excluding the Dirac peak
progressively decreases. Close to the collapse time, the pre and post collapse
evolution is self-similar. Interestingly, if one starts from a parabolic
density profile, one obtains an exact analytical solution that describes the
whole collapse dynamics, from the initial time to the end, and accounts for non
self-similar corrections that were neglected in previous works. Our results
have possible application in different areas including astrophysics,
chemotaxis, colloids and nanoscience
Thermodynamics of self-gravitating systems
Self-gravitating systems are expected to reach a statistical equilibrium
state either through collisional relaxation or violent collisionless
relaxation. However, a maximum entropy state does not always exist and the
system may undergo a ``gravothermal catastrophe'': it can achieve ever
increasing values of entropy by developing a dense and hot ``core'' surrounded
by a low density ``halo''. In this paper, we study the phase transition between
``equilibrium'' states and ``collapsed'' states with the aid of a simple
relaxation equation [Chavanis, Sommeria and Robert, Astrophys. J. 471, 385
(1996)] constructed so as to increase entropy with an optimal rate while
conserving mass and energy. With this numerical algorithm, we can cover the
whole bifurcation diagram in parameter space and check, by an independent
method, the stability limits of Katz [Mon. Not. R. astr. Soc. 183, 765 (1978)]
and Padmanabhan [Astrophys. J. Supp. 71, 651 (1989)]. When no equilibrium state
exists, our relaxation equation develops a self-similar collapse leading to a
finite time singularity.Comment: 54 pages. 25 figures. Submitted to Phys. Rev.
- âŠ