1,754 research outputs found
Digital carrier demodulator employing components working beyond normal limits
In a digital device, having an input comprised of a digital sample stream at a frequency F, a method is disclosed for employing a component designed to work at a frequency less than F. The method, in general, is comprised of the following steps: dividing the digital sample stream into odd and even digital samples streams each at a frequency of F/2; passing one of the digital sample streams through the component designed to work at a frequency less than F where the component responds only to the odd or even digital samples in one of the digital sample streams; delaying the other digital sample streams for the time it takes the digital sample stream to pass through the component; and adding the one digital sample stream after passing through the component with the other delayed digital sample streams. In the specific example, the component is a finite impulse response filter of the order ((N + 1)/2) and the delaying step comprised passing the other digital sample streams through a shift register for a time (in sampling periods) of ((N + 1)/2) + r, where r is a pipline delay through the finite impulse response filter
Mechanical Response of a Small Swimmer Driven by Conformational Transitions
A conformation space kinetic model is constructed to drive the deformation
cycle of a three-sphere swimmer to achieve propulsion at low Reynolds number.
We analyze the effect of an external load on the performance of this kinetic
swimmer, and show that it depends sensitively on where the force is exerted, so
that there is no general force--velocity relation. We discuss how the
conformational cycle of such swimmers should be designed to increase their
performance in resisting forces applied at specific points.Comment: 4 pages, 3 figures; accepted for publication in Phys. Rev. Let
Synthetic Mechanochemical Molecular Swimmer
A minimal design for a molecular swimmer is proposed that is a based on a
mechanochemical propulsion mechanism. Conformational changes are induced by
electrostatic actuation when specific parts of the molecule temporarily acquire
net charges through catalyzed chemical reactions involving ionic components.
The mechanochemical cycle is designed such that the resulting conformational
changes would be sufficient for achieving low Reynolds number propulsion. The
system is analyzed within the recently developed framework of stochastic
swimmers to take account of the noisy environment at the molecular scale. The
swimming velocity of the device is found to depend on the concentration of the
fuel molecule according to the Michaelis-Menten rule in enzymatic reactions.Comment: 4 pages, 3 figure
A molecular dynamics simulation of DNA damage induction by ionizing radiation
We present a multi-scale simulation of early stage of DNA damages by the
indirect action of hydroxyl (OH) free radicals generated by electrons
and protons. The computational method comprises of interfacing the Geant4-DNA
Monte Carlo with the ReaxFF molecular dynamics software. A clustering method
was employed to map the coordinates of OH-radicals extracted from the
ionization track-structures onto nano-meter simulation voxels filled with DNA
and water molecules. The molecular dynamics simulation provides the time
evolution and chemical reactions in individual simulation voxels as well as the
energy-landscape accounted for the DNA-OH chemical reaction that is
essential for the first principle enumeration of hydrogen abstractions,
chemical bond breaks, and DNA-lesions induced by collection of ions in clusters
less than the critical dimension which is approximately 2-3 \AA. We show that
the formation of broken bonds leads to DNA base and backbone damages that
collectively propagate to DNA single and double strand breaks. For illustration
of the methodology, we focused on particles with initial energy of 1 MeV. Our
studies reveal a qualitative difference in DNA damage induced by low energy
electrons and protons. Electrons mainly generate small pockets of
OH-radicals, randomly dispersed in the cell volume. In contrast,
protons generate larger clusters along a straight-line parallel to the
direction of the particle. The ratio of the total DNA double strand breaks
induced by a single proton and electron track is determined to be 4
in the linear scaling limit. The tool developed in this work can be used in the
future to investigate the relative biological effectiveness of light and heavy
ions that are used in radiotherapy.Comment: 7 pages, 7 figures, accepted for publication in Physics in Medicine
and Biolog
Application of basic and composite thrombelastography parameters in monitoring of the antithrombotic effect of the low molecular weight heparin dalteparin: an in vivo study
<p>Abstract</p> <p>Background</p> <p>Low molecular weight heparin (LMWH) is in vast usage for treatment of thromboembolic diseases such as deep venous thrombosis and acute coronary syndromes. There are certain clinical situations where a quick point of care testing of the effect of LMWH would be useful. At this point there are no point of care devices available in the market for monitoring the effect of LMWH. Thrombelastography (TEG) evaluates the viscoelastic properties of blood during coagulation. The clinical application of TEG in monitoring LMWH treatment is not yet well defined. The purpose of this in vivo study was to systematically evaluate the most suitable TEG parameters for evaluation of the antithrombotic effect of LMWH. We furthermore evaluated for the first time the usefulness of the composite TEG parameter the Thrombodynamic Ratio (TDR) in monitoring LMWH treatment.</p> <p>Methods</p> <p>Healthy male volunteers (n = 7) were injected subcutaneously with the LMWH dalteparin 120 IU/kg. TEG parameters and antifactor Xa levels were measures at baseline, 2, 4, 5 and 24 hours after the injection. Correlation between TEG parameters and antiXa were calculated. The sensitivity and specificity of the TEG parameters for plasma levels of antiXa in the therapeutic range of 0.5 - 1.0 U/ml were calculated.</p> <p>Results</p> <p>All basic TEG parameters correlated significantly with antiXa levels. Among the basic parameters, the TEG reaction time R had the best correlation with antiXa levels with the most favorable combination of sensitivity and specificity for the therapeutic range of antiXa levels (r = 0.82, p < 0.0001, sensitivity 68%, specificity 100%). The composite TEG parameter TDR demonstrated the best correlation with antiXa levels, and an even more favorable combination of sensitivity and specificity compared to any of the basic parameters (r = - 0.87, p < 0.0001, sensitivity 95%, specificity 79%).</p> <p>Conclusion</p> <p>The TEG reaction time R and TDR are the most suitable TEG parameters for evaluation of the antithrombotic effect of dalteparin with a highly significant correlation with antiXa levels in healthy male volunteers. Measures for uniform clinical use of these parameters are proposed. Larger clinical trials are needed to correlate R and TDR with clinical outcomes.</p
Lifshitz Interaction between Dielectric Bodies of Arbitrary Geometry
A formulation is developed for the calculation of the
electromagnetic--fluctuation forces for dielectric objects of arbitrary
geometry at small separations, as a perturbative expansion in the dielectric
contrast. The resulting Lifshitz energy automatically takes on the form of a
series expansion of the different many-body contributions. The formulation has
the advantage that the divergent contributions can be readily determined and
subtracted off, and thus makes a convenient scheme for realistic numerical
calculations, which could be useful in designing nano-scale mechanical devices
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