257 research outputs found
Enhanced Position Verification for VANETs using Subjective Logic
The integrity of messages in vehicular ad-hoc networks has been extensively
studied by the research community, resulting in the IEEE~1609.2 standard, which
provides typical integrity guarantees. However, the correctness of message
contents is still one of the main challenges of applying dependable and secure
vehicular ad-hoc networks. One important use case is the validity of position
information contained in messages: position verification mechanisms have been
proposed in the literature to provide this functionality. A more general
approach to validate such information is by applying misbehavior detection
mechanisms. In this paper, we consider misbehavior detection by enhancing two
position verification mechanisms and fusing their results in a generalized
framework using subjective logic. We conduct extensive simulations using VEINS
to study the impact of traffic density, as well as several types of attackers
and fractions of attackers on our mechanisms. The obtained results show the
proposed framework can validate position information as effectively as existing
approaches in the literature, without tailoring the framework specifically for
this use case.Comment: 7 pages, 18 figures, corrected version of a paper submitted to 2016
IEEE 84th Vehicular Technology Conference (VTC2016-Fall): revised the way an
opinion is created with eART, and re-did the experiments (uploaded here as
correction in agreement with TPC Chairs
High quality ultrafast transmission electron microscopy using resonant microwave cavities
Ultrashort, low-emittance electron pulses can be created at a high repetition
rate by using a TM deflection cavity to sweep a continuous beam across
an aperture. These pulses can be used for time-resolved electron microscopy
with atomic spatial and temporal resolution at relatively large average
currents. In order to demonstrate this, a cavity has been inserted in a
transmission electron microscope, and picosecond pulses have been created. No
significant increase of either emittance or energy spread has been measured for
these pulses.
At a peak current of pA, the root-mean-square transverse normalized
emittance of the electron pulses is m rad in the direction parallel to the streak of the cavity, and
m rad in the perpendicular
direction for pulses with a pulse length of 1.1-1.3 ps. Under the same
conditions, the emittance of the continuous beam is
m rad.
Furthermore, for both the pulsed and the continuous beam a full width at half
maximum energy spread of eV has been measured
Mechanical cell-matrix feedback explains pairwise and collective endothelial cell behavior in vitro
In vitro cultures of endothelial cells are a widely used model system of the
collective behavior of endothelial cells during vasculogenesis and
angiogenesis. When seeded in an extracellular matrix, endothelial cells can
form blood vessel-like structures, including vascular networks and sprouts.
Endothelial morphogenesis depends on a large number of chemical and mechanical
factors, including the compliancy of the extracellular matrix, the available
growth factors, the adhesion of cells to the extracellular matrix, cell-cell
signaling, etc. Although various computational models have been proposed to
explain the role of each of these biochemical and biomechanical effects, the
understanding of the mechanisms underlying in vitro angiogenesis is still
incomplete. Most explanations focus on predicting the whole vascular network or
sprout from the underlying cell behavior, and do not check if the same model
also correctly captures the intermediate scale: the pairwise cell-cell
interactions or single cell responses to ECM mechanics. Here we show, using a
hybrid cellular Potts and finite element computational model, that a single set
of biologically plausible rules describing (a) the contractile forces that
endothelial cells exert on the ECM, (b) the resulting strains in the
extracellular matrix, and (c) the cellular response to the strains, suffices
for reproducing the behavior of individual endothelial cells and the
interactions of endothelial cell pairs in compliant matrices. With the same set
of rules, the model also reproduces network formation from scattered cells, and
sprouting from endothelial spheroids. Combining the present mechanical model
with aspects of previously proposed mechanical and chemical models may lead to
a more complete understanding of in vitro angiogenesis.Comment: 25 pages, 6 figures, accepted for publication in PLoS Computational
Biolog
Changing Behaviour towards Aerobic and Strength Exercise (BASE): Design of a randomised, phase I study determining the safety, feasibility and consumer-evaluation of a remotely-delivered exercise programme in persons with multiple sclerosis
Background
Multiple sclerosis is a chronic progressive neurological disease. Evidence attests to the benefits of exercise, guidelines for exercise in multiple sclerosis are available. Remote-delivery of exercise adherence programmes based on the exercise guidelines require urgent testing.
Aims
The design, and outcomes of Behaviour towards Aerobic and Strength Exercise in MS (BASE-MS), a remotely-delivered exercise training study based principles of behaviour change, will further evaluate the remote-delivery of the current exercise guidelines.
Methods
BASE is a 4-month clinically relevant randomised controlled trial to explore the delivery of a remotely supervised, guidelines-based exercise programme for persons with multiple sclerosis, underpinned by principles of health behaviour change. Initially, 72 persons with mild to moderate multiple sclerosis will be randomised in a 1:1:1 allocation to receive the BASE programme, or act as controls continuing usual care. On programme completion, exercise participants will be further randomised to an optimised adherence treatment or usual adherence. Our online survey assesses the primary outcome of exercise participation, and secondary outcomes of symptoms, and correlates of behaviour change at baseline, month four, month five and month eleven. Online surveys will capture coach and participant feedback to identify the contexts, mechanisms and outcomes of BASE implementation.
Conclusions
The research and clinical landscape for MS management must remain in-step with public health and health communication. BASE tests the remote-delivery of the current exercise guidelines for exercise in persons with MS. Safety, feasibility and evaluative outcomes will provide rich data for future remote-delivery of exercise in neurological conditions
Theory and particle tracking simulations of a resonant radiofrequency deflection cavity in TM mode for ultrafast electron microscopy
We present a theoretical description of resonant radiofrequency (RF)
deflecting cavities in TM mode as dynamic optical elements for
ultrafast electron microscopy. We first derive the optical transfer matrix of
an ideal pillbox cavity and use a Courant-Snyder formalism to calculate the 6D
phase space propagation of a Gaussian electron distribution through the cavity.
We derive closed, analytic expressions for the increase in transverse emittance
and energy spread of the electron distribution. We demonstrate that for the
special case of a beam focused in the center of the cavity, the low emittance
and low energy spread of a high quality beam can be maintained, which allows
high-repetition rate, ultrafast electron microscopy with 100 fs temporal
resolution combined with the atomic resolution of a high-end TEM. This is
confirmed by charged particle tracking simulations using a realistic cavity
geometry, including fringe fields at the cavity entrance and exit apertures
Direct magneto-optical compression of an effusive atomic beam for high-resolution focused ion beam application
An atomic rubidium beam formed in a 70 mm long two-dimensional
magneto-optical trap (2D MOT), directly loaded from a collimated Knudsen
source, is analyzed using laser-induced fluorescence. The longitudinal velocity
distribution, the transverse temperature and the flux of the atomic beam are
reported. The equivalent transverse reduced brightness of an ion beam with
similar properties as the atomic beam is calculated because the beam is
developed to be photoionized and applied in a focused ion beam. In a single
two-dimensional magneto-optical trapping step an equivalent transverse reduced
brightness of A/(m sr eV) was
achieved with a beam flux equivalent to nA. The
temperature of the beam is further reduced with an optical molasses after the
2D MOT. This increased the equivalent brightness to A/(m sr eV). For currents below 10 pA, for which disorder-induced
heating can be suppressed, this number is also a good estimate of the ion beam
brightness that can be expected. Such an ion beam brightness would be a six
times improvement over the liquid metal ion source and could improve the
resolution in focused ion beam nanofabrication.Comment: 10 pages, 8 figures, 1 tabl
Dual mode microwave deflection cavities for ultrafast electron microscopy
This paper presents the experimental realization of an ultrafast electron
microscope operating at a repetition rate of 75 MHz based on a single compact
resonant microwave cavity operating in dual mode. This elliptical cavity
supports two orthogonal TM modes with different resonance frequencies
that are driven independently. The microwave signals used to drive the two
cavity modes are generated from higher harmonics of the same Ti:Sapphire laser
oscillator. Therefore the modes are accurately phase-locked, resulting in
periodic transverse deflection of electrons described by a Lissajous pattern.
By sending the periodically deflected beam through an aperture, ultrashort
electron pulses are created at a repetition rate of 75 MHz. Electron pulses
with fs pulse duration are created with only W
of microwave input power; with normalized rms emittances of
pm rad and pm rad for
a peak current of nA. This corresponds to an rms normalized
peak brightness of A/m sr V, equal
to previous measurements for the continuous beam. In addition, the FWHM energy
spread of eV is also unaffected by the dual mode
cavity. This allows for ultrafast pump-probe experiments at the same spatial
resolution of the original TEM in which a 75 MHz Ti:Sapphire oscillator can be
used for exciting the sample. Moreover, the dual mode cavity can be used as a
streak camera or time-of-flight EELS detector with a dynamic range
Design and characterization of dielectric filled TM microwave cavities for ultrafast electron microscopy
Microwave cavities oscillating in the TM mode can be used as dynamic
electron-optical elements inside an electron microscope. By filling the cavity
with a dielectric material it becomes more compact and power efficient,
facilitating the implementation in an electron microscope. However, the
incorporation of the dielectric material makes the manufacturing process more
difficult. Presented here are the steps taken to characterize the dielectric
material, and to reproducibly fabricate dielectric filled cavities. Also
presented are two versions with improved capabilities. The first, called a
dual-mode cavity, is designed to support two modes simultaneously. The second
has been optimized for low power consumption. With this optimized cavity a
magnetic field strength of 2.84 0.07 mT was generated at an input power
of 14.2 0.2 W. Due to the low input powers and small dimensions, these
dielectric cavities are ideal as electron-optical elements for electron
microscopy setups
Effective and Efficient Stand Magnifier Use in Visually Impaired Children
Contains fulltext :
167758.pdf (publisher's version ) (Open Access)PURPOSE: The main objective of this study was to analyze the effectiveness and efficiency of magnifier use in children with visual impairment who did not use a low vision aid earlier, in an ecologically valid goal-directed perceptuomotor task. METHODS: Participants were twenty-nine 4- to 8-year-old children with visual impairment and 47 age-matched children with normal vision. After seeing a first symbol (an Lea Hyvarinen [LH] symbol), children were instructed to (1) move the stand magnifier as quickly as possible toward a small target symbol (another LH symbol that could only be seen by using the magnifier), (2) compare the two symbols, and (3) move the magnifier to one of two response areas to indicate whether the two symbols were identical. Performance was measured in terms of accuracy, response time, identification time, and movement time. Viewing distance, as well as hand and eye dominance while using the magnifier was assessed. RESULTS: There were no significant differences between the two groups in accuracy, reaction time, and movement time. Contrary to the prediction, children with visual impairment required less time to identify small symbols than children with normal vision. Both within-subject and between-subject variability in viewing distance were smaller in the visually impaired group than in the normally sighted group. In the visually impaired group, a larger viewing distance was associated with shorter identification time, which in turn was associated with higher accuracy. In the normally sighted group, a faster movement with the magnifier and a faster identification were associated with increasing age. CONCLUSION: The findings indicate that children with visual impairment can use the stand magnifier adequately and efficiently. The normally sighted children show an age-related development in movement time and identification time and show more variability in viewing distance, which is not found in visually impaired children. Visually impaired children seem to choose a standard but less adaptive strategy in which they primarily used their preferred hand to manipulate the magnifier and their preferred eye to identify the symbol. TRIAL REGISTRATION: Registered at http://www.trialregister.nl; NTR2380.11 p
- …