Harmonic Energy Research Articles

Systematic review of cystic duct closure techniques in relation to prevention of bile duct leakage after laparoscopic cholecystectomy.

AIMTo study the effect of different techniques of cystic duct closure on bile leakage after laparoscopic cholecystectomy (LC) for biliary disease.METHODSA systematic search of MEDLINE, Cochrane and EMBASE was performed. Rate of cystic duct leakage (CDL) was the primary outcome. Risk of bias was evaluated. Odds ratios were analyzed for comparison of techniques and pooled event rates for non-comparative analyses. Pooled event rates were compared for each of included techniques.RESULTSOut of 1491 articles, 38 studies were included. A total of 47491 patients were included, of which 38683 (81.5%) underwent cystic duct closure with non-locking (metal) clips. All studies were of low-moderate methodological quality. Only two studies reported separate data on uncomplicated and complicated gallbladder disease. For overall CDL, an odds ratio of 0.4 (95%CI: 0.06-2.48) was found for harmonic energy vs clip closure and an odds ratio of 0.17 (95%CI: 0.03-0.93) for locking vs non-locking clips. Pooled CDL rate was around 1% for harmonic energy and metal clips, and 0% for locking clips and ligatures.CONCLUSIONBased on available evidence it is not possible to either recommend or discourage any of the techniques for cystic duct closure during LC with respects to CDL, although data point out a slight preference for locking clips and ligatures vs other techniques. No separate recommendation can be made for complicated gallbladder disease.

Extension of water-window harmonic cutoff by laser defocusing-assisted phase matching.

We extend a recently demonstrated scheme [Optica4, 976 (2017)OPTIC82334-253610.1364/OPTICA.4.000976] to overcome the limit of conventional harmonic cutoff for different pulse durations, laser wavelengths, and gas targets. By tuning the truncation of long wavelength lasers, we show that the defocusing-assisted phase matching (DAPM) can be achieved in a tightly focused beam and highly ionized short gas cell, and can be used to effectively extend the harmonic cutoff energy and optimize its yield. An analysis of phase matching reveals that at longer wavelengths, greater cutoff extension to the water window region is achieved because of the larger harmonic intrinsic phase (proportional to the cube of laser wavelength), and because DAPM works at relatively higher laser intensities using a Ne target. This scheme provides a promising method for efficiently generating intense attosecond light sources in the extreme ultraviolet to x-rays.

Advancement of flow velocity measurements in excised canine larynx model

In the classic source-filter model of speech production, flow modulation is the source of sound. Modulation of the flow refers to the fact that the volume flow, Q, is changing as the glottis opens and closes. Furthermore, studies have shown that the maximum flow declination rate (MFDR), which occurs during the latter part of the closing phase, is highly correlated with acoustic intensity (loudness) and acoustic energy in the higher harmonics. Therefore, measurements of the glottal airflow can provide important insights into voice mechanisms, dysfunction and efficiency. In recent years, particle image velocimetry (PIV) have become the method of choice for measuring Q because the technique can quantify, non-intrusively, the spatial and temporal information of the flow. The discussion includes progress of PIV measurements, from 2D to tomographic measurements, in the excised canine larynx model. Key findings related to intraglottal flow and glottal geometry, and their extension to modeling of voice mechanisms, are described.

Power Quality Enhancement Using Current Injection Technique in a Zigzag Configured Autotransformer-Based 12-Pulse Rectifier

This paper proposes a DC-side circuit configuration that improves the harmonic suppression ability of a 12-pulse diode bridge rectifier (DBR) using a zigzag configured autotransformer. The DC-side circuit uses a single-phase DBR along with interphase transformer which generates the required circulating current thereby modifies the DC currents at the DBR output, in turn shapes the input line current near to a sine wave. The proposed single-phase DBR is connected in parallel with the load which enables to reuse the harmonic energy thus improving the energy conversion efficiency. The zigzag configured autotransformer used for 12-pulse DBR possesses the inbuilt ability to hinder the zero-sequence components, which expel the need of zero sequence blocking transformer. The proposed configuration is analyzed, simulated in MATLAB Simulink and the simulation results are presented, which confirm the reduction of total harmonic distortion (THD) in the input line current thereby improving the power quality under large load variations. Furthermore, the viability of the proposed configuration is verified by experimental results, which confirm the suitability of the proposed configuration in industrial applications.

A 3D face registration algorithm based on conformal mapping

SummaryRecently, 3D facial datasets are more easily available, and at the same time, the research of 3D face becomes more and more important. One of the most important research fields is 3D face registration, which plays an important role in face recognition, face shape analysis, and face animation. However, one of the most challenging issues in 3D face registration is to obtain a unique mapping for faces with different expression and landmark constraints. In this paper, we propose a novel conformal mapping algorithm to deal with the 3D face registration. Besides, the calculation is about harmonic energy, which makes our method applicable to low‐quality meshes. We begin with a harmonic mapping, then minimize the harmonic energy by a specific boundary condition on surfaces, and to obtain the conformal mapping, finally, we use a landmark‐constrained surface registration algorithm to register faces. Numerical experiments on various surfaces demonstrate the efficiency and robustness of our method.

Study of Low and High Harmonic Energy Amplification Due to Outer Surf-zone Wave Breaking

Study of Low and High Harmonic Energy Amplification Due to Outer Surf-zone Wave Breaking

A Hybrid ac/dc Low Voltage Distribution Network for Improved Harmonics Management and Energy Conservation

The increasing use of numerous power electronics equipment in low voltage distribution network demand new and innovative solutions to mitigate harmonics and improve efficiency. In this paper a novel hybrid ac/dc distribution system which accommodates both ac and dc loads is proposed in which the dc loads are powered by dc supply itself with a view to reduce harmonics and neutral loading of distribution transformers. Furthermore, a harmonic power recovery scheme is also incorporated into the network which promotes conservation of energy by fruitfully utilizing the harmonic power which is otherwise wasted in the primary delta winding of transformer. The simulation and experimental results of a prototype distribution system demonstrate the effectiveness of the system.

Horizontal curves of hyperbolic metrics

We analyse the fine convergence properties of one parameter families of hyperbolic metrics that move always in a horizontal direction, i.e. orthogonal to the action of diffeomorphisms. Such families arise naturally in the study of general curves of metrics on surfaces, and in one of the gradients flows for the harmonic map energy.

Negative effect of driving power on far-field sound energy density in cavitating liquids

The distributions of total sound energy density in cavitating liquids in a long container were reported. The total far-field energy density abnormally decreased with increasing the driving power, demonstrating the negative effect of the driving power on the far-field sound energy density. This effect could not be attributed to the classical damping and scattering of cavitation bubbles. Spectral analysis revealed that when the sound pressure was a little above the cavitation threshold, the sound energy transferred to harmonics did not constitute a large fraction of the total sound energy. However, by continuously improving the pressure, the proportion of harmonic energy evidently increased, owing to the strong nonlinear effect of cavitation bubbles. For a propagating sound wave, the harmonics attenuated faster than the fundamental ones, which resulted in an unexpectedly less sound energy reaching far field under high driving, compared with low driving. As a result, the negative effect appeared. Further experiments revealed that the size of the region in which the negative effect appeared depended not only on the driving power but also on the cavitation threshold of the host liquid, and the negative effect disappeared when the driving power was decreased or when using liquids with a high cavitation threshold.

Parameterization of variations for wave energy over bottom slopes

Wave energy transfer through a shallow water region, produced by nonlinearity, was investigated using random wave simulations based on JONSWAP spectra in a physical experiment. To confirm the role of topography, slopes of β = 1/15, 1/30, and 1/45 were installed in a flume. The shoaling effect was first examined by comparing the experimental data with the theoretically predicted values. A wavelet-based bispectrum was then used to investigate the role of the bottom slope in energy transfer. Next, the evolution of energy transfer in the total, primary, and higher harmonic frequency bands was investigated using the wavelet-based energy spectrum. Based on the data from each slope, empirical formulas expressing the dimensionless energy parameters as a function of the local water depth were derived. The bottom slope was confirmed to have an influence on the variation in the total energy and primary harmonic energy, but its effect was shown to be negligible for the higher harmonic energy. Novel formulas were derived to represent the combined slope effect.

The computation of conformal map by harmonic diffeomorphisms between surfaces

Harmonic map is the critical point of the corresponding integral with respect to the square norm of the gradient or energy density. The harmonic energy defined on Riemann surfaces will decrease along its gradient line direction and reduce to the limit conformal map. Harmonic map between surfaces is a diffeomorphism which is associated to a unique Beltrami differential. So a harmonic diffeomorphism sequence corresponds to an Beltrami differential sequence. When boundary map is restricted on a unit circle, the Beltrami differential sequence changes with constant conformal modulus. In this paper, we consider the conformal map between surfaces by the Beltrami differential sequence with constant conformal modulus, which is equivalent to a decreasing harmonic energy sequence with fixed boundary correspondence, and provide the corresponding algorithms for numerical computation. Furthermore, we will discuss the convergence of proposed algorithms, which provides theoretical foundation for numerical experiments.

Efficient frequency conversion for cubic harmonic generation at 266 nm in centrosymmetric α-BBO crystal.

Direct third-harmonic generation (THG) is a third-order nonlinear process without the restriction to the symmetric characteristic of crystals. It is of great interest for setting up a χ(3) optical parametric oscillator which can be used in multiphoton quantum correlation. To obtain pure and strong THG, we proposed to elect the centrosymmetric crystal with delocalized π bond as the nonlinear media during the frequency conversion process. An unprecedented cubic harmonic energy 37.6μJ (average power ∼37.6 mW, conversion efficiency ∼2.5%) at 266nm was generated in α-BBO crystal (not the β-BBO), indicating direct THG in practical application. These results also demonstrated a succinct and efficient way to generate deep-UV laser and another development direction of nonlinear crystals in UV region.

Radial Symmetry of p-Harmonic Minimizers

"It is still not known if the radial cavitating minimizers obtained by Ball [J.M. Ball, Discontinuous equilibrium solutions and cavitation in nonlinear elasticity, Phil. Trans. R. Soc. Lond. A 306 (1982) 557--611] (and subsequently by many others) are global minimizers of any physically reasonable nonlinearly elastic energy". The quotation is from [J. Sivaloganathan and S. J. Spector, Necessary conditions for a minimum at a radial cavitating singularity in nonlinear elasticity, Ann. Inst. H. Poincare Anal. Non Lineaire 25 (2008), no. 1, 201--213] and seems to be still accurate. The model case of the $p$-harmonic energy is considered here. We prove that the planar radial minimizers are indeed the global minimizers provided we prescribe the admissible deformations on the boundary. In the traction free setting, however, even the identity map need not be a global minimizer.

Nanoengineering of strong field processes in solids

We present a theoretical investigation of the effect of quantum confinement on high harmonic generation in semiconductor materials by systematically varying the confinement width along one or two directions transverse to the laser polarization. Our analysis shows a growth in high harmonic efficiency concurrent with a reduction of ionization. This decrease in ionization comes as a consequence of an increased band gap resulting from the confinement. The increase in harmonic efficiency results from a restriction of wave packet spreading, leading to greater recollision probability. Consequently, nanoengineering of one and two-dimensional nanosystems may prove to be a viable means to increase harmonic yield and photon energy in semiconductor materials driven by intense laser fields.

Cross-coupling effects in circuit-QED stimulated Raman adiabatic passage

Stimulated Raman adiabatic passage is a quantum protocol that can be used for robust state preparation in a three-level system. It has been commonly employed in quantum optics, but recently this technique has drawn attention also in circuit quantum electrodynamics. The protocol relies on two slowly varying drive pulses that couple the initial and the target state via an intermediate state, which remains unpopulated. Here we study the detrimental effect of the parasitic couplings of the drives into transitions other than those required by the protocol. The effect is most prominent in systems with almost harmonic energy level structure, such as the transmon. We show that under these conditions in the presence of decoherence there exists an optimal STIRAP amplitude for population transfer.

Effect of multiple rescattering processes on harmonic emission in spatially inhomogeneous field**Project supported by the National Natural Science Foundation of China (Grant Nos. 11404204, 11274215, and 11504221), the Natural Science Foundation for Young Scientists of Shanxi Province, China (Grant No. 2015021023), Program for the Top Young Academic Leaders of Higher Learning Institutions of Shanxi Province, China, and Innovation Project for

The effect of multiple rescattering processes on the harmonic emission from He atom in a spatially inhomogeneous field is discussed by solving the one-dimensional time-dependent Schrödinger equation and the classical equation of motion. By establishing the physical model of the harmonic emission in the inhomogeneous field, we discuss the related characters of the multiple rescatterings process in the harmonic generation process. It shows that the second rescattering rather than the first rescattering tends to determine the harmonic cutoff energy when the inhomogeneous parameter is larger than 0.0055. Additionally, with the classical simulation, the underlying physical mechanism of the continuum–continuum harmonics is also revealed. Moreover, this work may provide new physical insight into the harmonic generation in an inhomogeneous field, and is beneficial to further extract the harmonic emission from molecular systems.

An automated, quantitative, and case-specific evaluation of deformable image registration in computed tomography images

A prerequisite for adaptive dose-tracking in radiotherapy is the assessment of the deformable image registration (DIR) quality. In this work, various metrics that quantify DIR uncertainties are investigated using realistic deformation fields of 26 head and neck and 12 lung cancer patients. Metrics related to the physiologically feasibility (the Jacobian determinant, harmonic energy (HE), and octahedral shear strain (OSS)) and numerically robustness of the deformation (the inverse consistency error (ICE), transitivity error (TE), and distance discordance metric (DDM)) were investigated. The deformable registrations were performed using a B-spline transformation model. The DIR error metrics were log-transformed and correlated (Pearson) against the log-transformed ground-truth error on a voxel level. Correlations of r ⩾ 0.5 were found for the DDM and HE. Given a DIR tolerance threshold of 2.0 mm and a negative predictive value of 0.90, the DDM and HE thresholds were 0.49 mm and 0.014, respectively. In conclusion, the log-transformed DDM and HE can be used to identify voxels at risk for large DIR errors with a large negative predictive value. The HE and/or DDM can therefore be used to perform automated quality assurance of each CT-based DIR for head and neck and lung cancer patients.

An Adaptive Carrier Frequency Optimization Method for Harmonic Energy Unbalance Minimization in a Cascaded H-Bridge-Based Active Power Filter

Cascaded H-bridge (CHB) based active power filters (APF) can compensate high-order harmonics in medium and high-voltage systems with relatively low switching frequency. This paper reveals that a severe dc capacitor energy unbalance can be induced by harmonic energy exchange if the frequency of APF output current coincides with the switching harmonic frequency of CHB cells. The mechanism of harmonic energy exchange is analyzed, and it is found that the dc capacitor energy unbalance is essentially affected by the carrier frequency of CHB. A noninteger ratio carrier frequency can be adopted to avoid the divergence of dc voltage, but there is still a significant low-frequency ripple on the dc voltage. This paper proposes an adaptive carrier frequency optimization method. By predicting the dc voltage ripple amplitude under different carrier frequencies, this method can adaptively select the optimal carrier frequency to minimize the dc voltage ripple. The proposed method is also proved to be robust against system parameter variations, and it can be implemented by a practical and simple linear computation method. Results obtained from simulation, experimental prototype, and field test are finally presented to verify the proposed adaptive carrier frequency optimization method.

Low-frequency approximation for high-order harmonic generation by a bicircular laser field

We present low-frequency approximation (LFA) for high-order harmonic generation (HHG) process. LFA represents the lowest-order term of an expansion of the final-state interaction matrix element in powers of the laser-field frequency $\ensuremath{\omega}$. In this approximation the plane-wave recombination matrix element which appears in the strong-field approximation is replaced by the exact laser-free recombination matrix element calculated for the laser-field dressed electron momenta. First, we have shown that the HHG spectra obtained using the LFA agree with those obtained solving the time-dependent Schr\odinger equation. Next, we have applied this LFA to calculate the HHG rate for inert gases exposed to a bicircular field. The bicircular field, which consists of two coplanar counter-rotating fields having different frequencies (usually $\ensuremath{\omega}$ and $2\ensuremath{\omega}$), is presently an important subject of scientific research since it enables efficient generation of circularly polarized high-order harmonics (coherent soft x rays). Analyzing the photorecombination matrix element we have found that the HHG rate can efficiently be calculated using the angular momentum basis with the states oriented in the direction of the bicircular field components. Our numerical results show that the HHG rate for atoms having $p$ ground state, for higher high-order harmonic energies, is larger for circularly polarized harmonics having the helicity $\ensuremath{-}1$. For lower energies the harmonics having helicity $+1$ prevails. The transition between these two harmonic energy regions can appear near the Cooper minimum, which, in the case of Ar atoms, makes the selection of high-order harmonics having the same helicity much easier. This is important for applications (for example, for generation of attosecond pulse trains of circularly polarized harmonics).

Strong anharmonicity in the phonon spectra of PbTe and SnTe from first principles

At room temperature, PbTe and SnTe are efficient thermoelectrics with a cubic structure. At low temperature, SnTe undergoes a ferroelectric transition with a critical temperature strongly dependent on the hole concentration, while PbTe is an incipient ferroelectric. By using the stochastic self-consistent harmonic approximation, we investigate the anharmonic phonon spectra and the occurrence of a ferroelectric transition in both systems. We find that vibrational spectra strongly depend on the approximation used for the exchange-correlation kernel in density-functional theory. If gradient corrections and the theoretical volume are employed, then the calculation of the phonon frequencies as obtained from the diagonalization of the free-energy Hessian leads to phonon spectra in good agreement with experimental data for both systems. In PbTe we evaluate the linear thermal expansion coefficient $\ensuremath{\gamma}=2.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{4.pt}{0ex}}{\text{K}}^{\ensuremath{-}1}$, finding it to be in good agreement with experimental value of $\ensuremath{\gamma}=2.04\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{4.pt}{0ex}}{\text{K}}^{\ensuremath{-}1}$. Furthermore, we study the phonon spectrum and we do reproduce the transverse optical mode phonon satellite detected in inelastic neutron scattering and the crossing between the transverse optical and the longitudinal acoustic modes along the $\mathrm{\ensuremath{\Gamma}}\mathrm{X}$ direction. The phonon satellite becomes broader at high temperatures but its energy is essentially temperature independent, in agreement with experiments. We decompose the self-consistent harmonic free energy in second-, third-, and fourth-order anharmonic terms. We find that the third- and fourth-order terms are small. However, treating the third-order term perturbatively on top of the second-order self-consistent harmonic free energy overestimates the energy of the satellite associated with the transverse optical mode. On the contrary, a perturbative treatment on top of the harmonic Hamiltonian breaks down and leads to imaginary phonon frequencies already at 300 K. In the case of SnTe, we describe the occurrence of a ferroelectric transition from the high-temperature $Fm\overline{3}m$ structure to the low-temperature $R3m$ one. The transition temperature is, however, underestimated with respect to the experimental one. No satellites are present in the SnTe phonon spectra despite a not negligible anharmonic broadening of the zone-center TO mode.