4,278 research outputs found
The Construction of Verification Models for Embedded Systems
The usefulness of verification hinges on the quality of the verification model. Verification is useful if it increases our confidence that an artefact bahaves as expected. As modelling inherently contains non-formal elements, the qualityof models cannot be captured by purely formal means. Still, we argue that modelling is not an act of irrationalism and unpredictable geniality, but follows rational arguments, that often remain implicit. In this paper we try to identify the tacit rationalism in the model construction as performed by most people doing modelling for verification. By explicating the different phases, arguments, and design decisions in the model construction, we try to develop guidelines that help to improve the process of model construction and the quality of models
Lumbar puncture for the generalist
The safe and successful performance of a lumbar puncture demands a working and yet specific knowledge as well as competency in performance. This review aims to aid understanding of the knowledge framework, the pitfalls and complications of lumbar puncture. It includes special reference to three dimensional relationships, functional anatomy, imaging anatomy, normal variation and living anatomy. A lumbar puncture is a commonly performed procedure for diagnostic and therapeutic purposes. Epidural and spinal anaesthesia, for example, are common in obstetric practice and involve the same technique as a lumbar puncture except for the endpoint of the needle being in the epidural space and subarachnoid space respectively. The procedure is by no means innocuous and some anatomical pitfalls include inability to find the correct entry site for placement of the lumbar puncture needle and lack of awareness of structures in relation to the advancing needle. Headache is the most common complication and it is important to avoid traumatic and dry taps, herniation syndromes and injury to the terminal end of the spinal cord. With a thorough knowledge of the contraindications, the regional anatomy and rationale of the technique and adequate prior skills practice, a lumbar puncture can be performed safely and successfully
The effect of different frequencies of ultrasound on the activity of horseradish peroxidase
Ultrasound technology has been studied by food researchers as an alternative method for thermal processing. The use of ultrasound as a way to inactivate and/or activate enzymes has been widely studied at low frequencies (20–40 kHz), however, little research on the effect of high frequencies has been reported. Thus, the effect of high and low frequency ultrasound on commercial horseradish peroxidase with a concentration of 0.005 mg mL−1 is described. Experiments were performed for 60 min using 20, 378, 583, 862, 995, 1144 and 1175 kHz ultrasound at power levels (acoustic energy) between 2.1 and 64 W. Residual activity was monitored using a spectrophotometric method and data analysis was performed using ANOVA. A significant enhancement of enzyme inactivation (p < 0.05) was observed at each frequency with an increase of sonication time and power. Inactivation of peroxidase by ultrasound followed first order kinetics and an increase of the rate constant with the power applied was observed for all the frequencies studied. Overall, low frequency (20 kHz) and low power are not effective on the enzyme inactivation and the level of residual activity remained high. The use of 378 and 583 kHz (48 W) is particularly effective for complete enzyme inactivation
Time-resolved fluorescence observation of di-tyrosine formation in horseradish peroxidase upon ultrasound treatment leading to enzyme inactivation
The application of ultrasound to a solution can induce cavitional phenomena and generate high localised temperatures and pressures. These are dependent of the frequency used and have enabled ultrasound application in areas such as synthetic, green and food chemistry. High frequency (100 kHz to 1 MHz) in particular is promising in food chemistry as a means to inactivate enzymes, replacing the need to use periods of high temperature. A plant enzyme, horseradish peroxidase, was studied using time-resolved fluorescence techniques as a means to assess the effect of high frequency (378 kHz and 583 kHz) ultrasound treatment at equivalent acoustic powers. This uncovered the fluorescence emission from a newly formed species, attributed to the formation of di-tyrosine within the horseradish peroxidase structure caused by auto-oxidation, and linked to enzyme inactivation
Macroscopic evidence of microscopic dynamics in the Fermi-Pasta-Ulam oscillator chain from nonlinear time series analysis
The problem of detecting specific features of microscopic dynamics in the
macroscopic behavior of a many-degrees-of-freedom system is investigated by
analyzing the position and momentum time series of a heavy impurity embedded in
a chain of nearest-neighbor anharmonic Fermi-Pasta-Ulam oscillators. Results
obtained in a previous work [M. Romero-Bastida, Phys. Rev. E {\bf69}, 056204
(2004)] suggest that the impurity does not contribute significantly to the
dynamics of the chain and can be considered as a probe for the dynamics of the
system to which the impurity is coupled. The () entropy, which measures
the amount of information generated by unit time at different scales of
time and of the observable, is numerically computed by methods of nonlinear
time-series analysis using the position and momentum signals of the heavy
impurity for various values of the energy density (energy per degree
of freedom) of the system and some values of the impurity mass . Results
obtained from these two time series are compared and discussed.Comment: 7 pages, 5 figures, RevTeX4 PRE format; to be published in Phys. Rev.
Entropy and Correlations in Lattice Gas Automata without Detailed Balance
We consider lattice gas automata where the lack of semi-detailed balance
results from node occupation redistribution ruled by distant configurations;
such models with nonlocal interactions are interesting because they exhibit
non-ideal gas properties and can undergo phase transitions. For this class of
automata, mean-field theory provides a correct evaluation of properties such as
compressibility and viscosity (away from the phase transition), despite the
fact that no H-theorem strictly holds. We introduce the notion of locality -
necessary to define quantities accessible to measurements - by treating the
coupling between nonlocal bits as a perturbation. Then if we define
operationally ``local'' states of the automaton - whether the system is in a
homogeneous or in an inhomogeneous state - we can compute an estimator of the
entropy and measure the local channel occupation correlations. These
considerations are applied to a simple model with nonlocal interactions.Comment: 13 pages, LaTeX, 5 PostScript figures, uses psfig. Submitted to Int.
J. Mod. Phys.
A simple measure of memory for dynamical processes described by the generalized Langevin equation
Memory effects are a key feature in the description of the dynamical systems
governed by the generalized Langevin equation, which presents an exact
reformulation of the equation of motion. A simple measure for the estimation of
memory effects is introduced within the framework of this description.
Numerical calculations of the suggested measure and the analysis of memory
effects are also applied for various model physical systems as well as for the
phenomena of ``long time tails'' and anomalous diffusion
Design of Field Experiments for Adaptive Sampling of the Ocean with Autonomous Vehicles
Due to the highly non-linear and dynamical nature of oceanic phenomena, the predictive capability
of various ocean models depends on the availability of operational data. A practical method to improve the
accuracy of the ocean forecast is to use a data assimilation methodology to combine in-situ measured and
remotely acquired data with numerical forecast models of the physical environment. Autonomous surface and
underwater vehicles with various sensors are economic and efficient tools for exploring and sampling the
ocean for data assimilation; however there is an energy limitation to such vehicles, and thus effective resource
allocation for adaptive sampling is required to optimize the efficiency of exploration. In this paper, we use
physical oceanography forecasts of the coastal zone of Singapore for the design of a set of field experiments
to acquire useful data for model calibration and data assimilation. The design process of our experiments
relied on the oceanography forecast including the current speed, its gradient, and vorticity in a given region of
interest for which permits for field experiments could be obtained and for time intervals that correspond to
strong tidal currents. Based on these maps, resources available to our experimental team, including
Autonomous Surface Craft (ASC) are allocated so as to capture the oceanic features that result from jets and
vortices behind bluff bodies (e.g., islands) in the tidal current. Results are summarized from this resource
allocation process and field experiments conducted in January 2009.Singapore. National Research Foundatio
Predictions of Radial Gas Holdup Profiles in Bubble Column Reactors
Gas Holdup and its Profile Are Important Parameters to Be Characterized in Bubble Column Reactors. Proper Prediction of the Radial Gas Holdup Profiles is Necessary for Determining Liquid Mixing, Flow Regime Transition, Heat and Mass Transfer. in This Study, the Following Gas Holdup Profile Form, Which Can Be Fitted to the Observed Holdup Profiles, is Proposed: EG = EG (N + 2/n + 2 - 2c) [1 - C(R/R)n]. the Parameters N and C Needed to Describe the Gas Holdup Profile Are Correlated with Appropriate Dimensionless Groups. N = 2.188 X 103 ReG-0.598 Frg0.146 MoL-0.004, C = 4.32 X 10-2 ReG0.2492. However, the Cross-Sectional Average Gas Holdup, EG, Can Be Estimated using the Available Correlations for overall Gas Holdup. the Agreement between the Correlation Predictions and Experimental Data is Reasonable over Wide Range of Operating Conditions. © 2001 Elsevier Science Ltd. All Rights Reserved
-Scale Decoupling of the Mechanical Relaxation and Diverging Shear Wave Propagation Lengthscale in Triphenylphosphite
We have performed depolarized Impulsive Stimulated Scattering experiments to
observe shear acoustic phonons in supercooled triphenylphosphite (TPP) from
10 - 500 MHz. These measurements, in tandem with previously performed
longitudinal and shear measurements, permit further analyses of the relaxation
dynamics of TPP within the framework of the mode coupling theory (MCT). Our
results provide evidence of coupling between the shear and
longitudinal degrees of freedom up to a decoupling temperature = 231 K. A
lower bound length scale of shear wave propagation in liquids verified the
exponent predicted by theory in the vicinity of the decoupling temperature
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