Minimum Energy (minimum + energy)

Distribution by Scientific Domains

Terms modified by Minimum Energy

  • minimum energy conformation
  • minimum energy consumption

  • Selected Abstracts

    Innovation of visualized interactive tools for learning molecular simulation curriculum

    Wen-Tsai Sung
    Abstract The goal of molecular simulation stability is to predict the detailed structure and physical properties of molecules in bioengineer's experiment curriculum. This work succeeds in citing minimum energy and some computer graphics technologies to support this theme. Molecular structure is that given the uncountable number of possible conformations for a protein, how we can determine the lowest energy structure. In this article the authors employed the previous researches-WebDeGrator and some existing molecular graphics tools to simulate various protein folding, ligand acceptor interaction, and molecular visualization. For this reason, bioengineer experimental curriculum will be visualization and interactive among learning members. Finally, Simpson's Taxonomy and pre- and post-test examinations are applied to System Evaluation, and molecular simulation and minimum energy will be discussed. 2009 Wiley Periodicals, Inc. Comput Appl Eng Educ 18: 28,40, 2010; Published online in Wiley InterScience (; DOI 10.1002/cae.20226 [source]

    The long-term average capacity region per unit cost with application to protocols for sensor networks

    Daniela Tuninetti
    We consider a wireless sensor network where K sensors must deliver their messages within a frame of N time slots by spending a given finite energy. If the messages are not transmitted within the required delay they become useless and the residual energy is wasted. The channel is block-fading, with independent fades for each sensor and each slot. Sensors know the fading levels up to the current slot, but do not know the future fading levels. The receiver collects the signal on all the slots of the frame and performs joint decoding of all the messages. We characterize the region of long-term average achievable rates and we show that the optimal policy tends to waterfilling in time (optimal policy without delay constraints) as N increases. In this setting, we also characterize the long-term average capacity region per unit energy by showing that the optimal policy is ,one-shot', totally decentralized and extremely simple, i.e., every user spends all its available energy on the first slot of the frame, the fading gain of which is larger than a pre-computed time-varying threshold. Furthermore, the ,one-shot' policy not only makes the most efficient use of the energy, but also reduces to the minimum the interference to other users as it makes all the users transmit with the minimum energy per bit required for reliable communications. These characteristics make the ,one-shot' policy appealing for systems with severe energy limitation as wireless sensor networks. Copyright 2003 AEI [source]

    Adaptive subtraction of multiples using the L1 -norm

    A. Guitton
    ABSTRACT A strategy for multiple removal consists of estimating a model of the multiples and then adaptively subtracting this model from the data by estimating shaping filters. A possible and efficient way of computing these filters is by minimizing the difference or misfit between the input data and the filtered multiples in a least-squares sense. Therefore, the signal is assumed to have minimum energy and to be orthogonal to the noise. Some problems arise when these conditions are not met. For instance, for strong primaries with weak multiples, we might fit the multiple model to the signal (primaries) and not to the noise (multiples). Consequently, when the signal does not exhibit minimum energy, we propose using the L1 -norm, as opposed to the L2 -norm, for the filter estimation step. This choice comes from the well-known fact that the L1 -norm is robust to ,large' amplitude differences when measuring data misfit. The L1 -norm is approximated by a hybrid L1/L2 -norm minimized with an iteratively reweighted least-squares (IRLS) method. The hybrid norm is obtained by applying a simple weight to the data residual. This technique is an excellent approximation to the L1 -norm. We illustrate our method with synthetic and field data where internal multiples are attenuated. We show that the L1 -norm leads to much improved attenuation of the multiples when the minimum energy assumption is violated. In particular, the multiple model is fitted to the multiples in the data only, while preserving the primaries. [source]

    Volume of a liquid drop detaching from a sphere

    Kenji Katoh
    Abstract A theoretical and experimental study is conducted to investigate the detached volume from a pendant drop on the surface of a sphere. Observation of drop detachment by high-speed video camera reveals that the movement of the upper part of the neck of the drop is quite slow compared to that of the detaching lower part. The surface profile of the upper part was calculated approximately as a static problem using the axisymmetric Laplace equation. Using the drop profile, the system energy, including the work done by the solid,liquid wetting behavior, was calculated. Based on the condition of minimum energy, the volume of the detached part V was calculated. The volume V increases with the sphere diameter and approaches the value for the pendant drop attached to a plate. In addition, V is strongly dependent on the wettability between the sphere and the liquid and decreases with the receding contact angle. The detached volume of the water drop was measured for spheres of porous brick of various diameters. The experimental and theoretical results were found to be in good agreement. 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( DOI 10.1002/htj.20305 [source]

    Can a physics-based, all-atom potential find a protein's native structure among misfolded structures?


    Abstract Recent work has shown that physics-based, all-atom energy functions (AMBER, CHARMM, OPLS-AA) and local minimization, when used in scoring, are able to discriminate among native and decoy structures. Yet, there have been only few instances reported of the successful use of physics based potentials in the actual refinement of protein models from a starting conformation to one that ends in structures, which are closer to the native state. An energy function that has a global minimum energy in the protein's native state and a good correlation between energy and native-likeness should be able to drive model structures closer to their native structure during a conformational search. Here, the possible reasons for the discrepancy between the scoring and refinement results for the case of AMBER potential are examined. When the conformational search via molecular dynamics is driven by the AMBER potential for a large set of 150 nonhomologous proteins and their associated decoys, often the native minimum does not appear to be the lowest free energy state. Ways of correcting the potential function in order to make it more suitable for protein model refinement are proposed. 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source]

    The effect of a penalty term involving higher order derivatives on the distribution of phases in an elastic medium with a two-well elastic potential

    M. Bildhauer
    Abstract We consider the problem of minimizing 00, among functions u:,d,,,,d, u,,,=0, and measurable characteristic functions ,:,,,. Here ,+h, ,,, denote quadratic potentials defined on the space of all symmetric dd matrices, h is the minimum energy of ,+h and ,(u) denotes the symmetric gradient of the displacement field. An equilibrium state , ,,, of I [,,h, ,] is termed one-phase if ,,,0 or ,,,1, two-phase otherwise. We investigate the way in which the distribution of phases is affected by the choice of the parameters h and ,. Copyright 2002 John Wiley & Sons, Ltd. [source]

    The effect of a surface energy term on the distribution of phases in an elastic medium with a two-well elastic potential

    Michael Bildhauer
    Abstract We consider the problem of minimizing among functions u:,d,,,,d, u,,,=0, and measurable subsets E of ,. Here fh+, f, denote quadratic potentials defined on ,{symmetric dd matrices}, h is the minimum energy of fh+ and ,(u) is the symmetric gradient of the displacement field u. An equilibrium state , of J(u,E) is called one-phase if E=, or E=,, two-phase otherwise. For two-phase states, ,,,E,,, measures the effect of the separating surface, and we investigate the way in which the distribution of phases is affected by the choice of the parameters h,,, ,>0. Additional results concern the smoothness of two-phase equilibrium states and the behaviour of inf J(u,E) in the limit ,,0. Moreover, we discuss the case of additional volume force potentials, and extend the previous results to non-zero boundary values. Copyright 2002 John Wiley & Sons, Ltd. [source]

    Magnetic jets from swirling discs

    D. Lynden-Bell
    ABSTRACT A broad swathe of astrophysical phenomena, ranging from tubular planetary nebulae through Herbig,Haro objects, radio galaxy and quasar emissions to gamma-ray bursts and perhaps high-energy cosmic rays, may be driven by magnetically dominated jets emanating from accretion discs. We give a self-contained account of the analytic theory of non-relativistic magnetically dominated jets wound up by a swirling disc and making a magnetic cavity in a background medium of any prescribed pressure, p(z). We solve the time-dependent problem for any specified distribution of magnetic flux P(R, 0) emerging from the disc at z= 0, with any specified disc angular velocity ,d(R). The physics required to do this involves only the freezing of the lines of force to the conducting medium and the principle of minimum energy. In a constant pressure environment, the magnetically dominated cavity is highly collimated and advances along the axis at a constant speed closely related to the maximum circular velocity of the accretion disc. Even within the cavity the field is strongly concentrated towards the axis. The twist in the jet field ,B,,/,|Bz|, is close to and the width of the jet decreases upwards. By contrast, when the background pressure falls off with height with powers approaching z,4, the head of the jet accelerates strongly and the twist of the jet is much smaller. The width increases to give an almost conical magnetic cavity with apex at the source. Such a regime may be responsible for some of the longest strongly collimated jets. When the background pressure falls off faster than z,4, there are no quasi-static configurations of well-twisted fields and the pressure confinement is replaced by a dynamic effective pressure or a relativistic expansion. In the regimes with rapid acceleration, the outgoing and incoming fields linking the twist back to the source are almost anti-parallel so there is a possibility that magnetic reconnections may break up the jet into a series of magnetic ,smoke-rings' travelling out along the axis. [source]

    The environments of FRII radio sources

    M. J. Hardcastle
    Using ROSAT observations, we estimate gas pressures in the X-ray-emitting medium surrounding 63 FRII radio galaxies and quasars. We compare these pressures with the internal pressures of the radio-emitting plasma estimated by assuming minimum energy or equipartition. In the majority of cases (including 12/13 sources with modelled, spatially resolved X-ray emission) radio sources appear to be underpressured with respect to the external medium, suggesting that simple minimum-energy arguments underestimate the internal energy density of the sources. We discuss possible departures from the minimum-energy condition and the consequences of our result for models of the dynamics of radio galaxies, in particular self-similar models. [source]

    Low Energy Biphasic Waveform Cardioversion of Atrial Arrhythmias in Pediatric Patients and Young Adults

    Background: Low-dose biphasic waveform cardioversion has been used for the termination of atrial arrhythmias in adult patients. The energy required for termination of atrial arrhythmias in pediatric patients is not known. The objective of this study is to determine the minimum energy required for successful external cardioversion of atrial arrhythmias in pediatric patients using biphasic waveform current. Methods: Prospective study of all patients less than 24 years of age with and without congenital heart disease undergoing synchronized cardioversion for atrial arrhythmias. Patients were assigned to receive an initial biphasic energy shock of 0.2,0.5 J/kg and if unsuccessful in terminating the arrhythmia, subsequent sequential shocks of 1 and 2 J/kg would be administered until cardioversion was achieved. The end point of the cardioversion protocol was successful cardioversion or delivery of three shocks. Results: Between June 2005 and June 2006, 16 patients underwent biphasic cardioversion for atrial flutter or fibrillation. The mean age was 14.7 6.4 years (range: 2 weeks to 24 years). The mean weight was 51 21 kg (range: 3.8,82 kg). Seven patients had normal cardiac anatomy, three had a single ventricle (Fontan), two had a Senning operation; the remaining four patients had varied forms of congenital heart disease. The median length of time that the patients were in tachycardia was 12 hours (range: 5 minutes to 2 months). Using either transthoracic echocardiography (TTE) or transesophageal echocardiography (TEE), no thrombi were identified in any patient. All patients were successfully cardioverted with biphasic waveform energy. The successful energy shock was 0.35 0.19 J/kg (range: 0.2,0.9 J/kg). All but one patient were successfully cardioverted with less than 0.5 J/kg. The transthoracic impedance range was between 41 and 144 ,; one patient had an impedance of 506 , (2-week-old infant with a weight of 3.8 kg). The mean current delivered was 5.4 2.2 A (range: 1,11 A). Conclusion: Low-dose energy using biphasic waveform shocks can be used for successful termination of atrial arrhythmias in pediatric patients with and without congenital heart disease. [source]

    The Impact of Catecholamines on Defibrillation Threshold in Patients with Implanted Cardioverter Defibrillators

    Objectives: To determine the effect of physiologic catecholamine concentrations on the defibrillation threshold (DFT) in patients with implanted cardioverter defibrillators. Background: DFT is the minimum energy delivered by an implanted cardioverter defibrillator that successfully converts ventricular fibrillation. DFT testing is performed under conscious sedation. Since activities of daily living enhance sympathetic tone substantially over these nadir levels, it is important to explore the impact of catecholamines on DFT. Methods: In this double-blind study, we determined DFT by the step-down method. Patients (n = 50) were stratified by beta-blocker use and then randomized to a 7-minute infusion of epinephrine, norepinephrine, or placebo. After study infusion, DFT testing was repeated. Changes in DFT with different study medications were compared. Subgroup analyses of the effects of catecholamines on DFT, based on beta-blocker use, were also performed. Results: Norepinephrine reduced DFT from baseline measurements by 22.6% (P = 0.008). Neither epinephrine nor placebo impacted DFT (P = 0.999, P = 0.317, respectively). In the subgroup analyses, DFT was reduced with norepinephrine regardless of beta-blocker use, while epinephrine reduced DFT among those receiving beta-blockers. No change in DFT was observed in either of the placebo subgroups. Conclusions: Elevation of plasma norepinephrine concentrations reduces the DFT, while elevations in epinephrine had no effect. Norepinephrine seems to reduce DFT regardless of beta-blocker therapy but epinephrine's effects are beta-blocker dependent. [source]

    The mean-field approximation in quantum electrodynamics: The no-photon case

    Christian Hainzl
    We study the mean-field approximation of quantum electrodynamics (QED) by means of a thermodynamic limit. The QED Hamiltonian is written in Coulomb gauge and does not contain any normal ordering or choice of bare electron/positron subspaces. Neglecting photons, we properly define this Hamiltonian in a finite box [,L/2; L/2)3, with periodic boundary conditions and an ultraviolet cutoff ,. We then study the limit of the ground state (i.e., the vacuum) energy and of the minimizers as L goes to infinity, in the Hartree-Fock approximation. In the case with no external field, we prove that the energy per volume converges and obtain in the limit a translation-invariant projector describing the free Hartree-Fock vacuum. We also define the energy per unit volume of translation-invariant states and prove that the free vacuum is the unique minimizer of this energy. In the presence of an external field, we prove that the difference between the minimum energy and the energy of the free vacuum converges as L goes to infinity. We obtain in the limit the so-called Bogoliubov-Dirac-Fock functional. The Hartree-Fock (polarized) vacuum is a Hilbert-Schmidt perturbation of the free vacuum and it minimizes the Bogoliubov-Dirac-Fock energy. 2006 Wiley Periodicals, Inc. [source]

    Gauged harmonic maps, Born-Infeld electromagnetism, and magnetic vortices

    Fanghua Lin
    We study maps from a 2-surface into the standard 2-sphere coupled with Born-Infeld geometric electromagnetism through an Abelian gauge field. Such a formalism extends the classical harmonic map model, known as the ,-model, governing the spin vector orientation in a ferromagnet allows us to obtain the coexistence of vortices and antivortices characterized by opposite, self-excited, magnetic flux lines. We show that the Born-Infeld free parameter may be used to achieve arbitrarily high local concentration of magnetic flux lines that the total minimum energy is an additive function of these quantized flux lines realized as the numbers of vortices antivortices. In the case where the underlying surface, or the domain, is compact, we obtain a necessary sufficient condition for the existence of a unique solution representing a prescribed distribution of vortices antivortices. In the case where the domain is the full plane, we prove the existence of a unique solution representing an arbitrary distribution of vortices and antivortices. Furthermore, we also consider the Einstein gravitation induced by these vortices, known as cosmic strings, establish the existence of a solution representing a prescribed distribution of cosmic strings cosmic antistrings under a necessary sufficient condition that makes the underlying surface a complete surface with respect to the induced gravitational metric. 2003 Wiley Periodicals, Inc. [source]