LS Scheme Research Articles

Wireless Sensor Network Coverage Optimization: Comparison of Local Search-Based Heuristics

The Maximum Lifetime Coverage Problem (MLCP) requires heuristic optimization methods due to its complexity. A real-world problem model determines how a solution is represented and the operators applied in these heuristics. Our paper describes adapting a local search scheme and its operators to MLCP optimization. The operators originate from three local search algorithms we proposed earlier: LSHMA, LSCAIA, and LSRFTA. Two steps of the LS scheme’s main loop can be executed in three different ways each. Hence, nine versions of the LS approach can be obtained. In experimental research, we verified their effectiveness. Test cases come from three benchmarks: SCP1, proposed and used in our earlier research on the three LS algorithms mentioned above, and two others found in the literature. The results obtained with SCP1 showed that the algorithm based on the hypergraph model approach (HMA) is the most effective. The remaining results of the other algorithms divide them into two groups: effective ones and weak ones. However, other benchmarks showed that the more redundant the coverage of points of interest (POIs) by sensors, the more effective the perturbation method from the approach inspired by cellular automata (CAIA). The findings expose the strengths and weaknesses of the problem-specific steps applied in the LS algorithms.

Theoretical analysis of single-ion anisotropy in d3 Mott insulators

An effective spin model for Mott insulators is determined by the symmetries involved among magnetic sites, electron fillings, and their interactions. Such a spin Hamiltonian offers insight to mechanisms of magnetic orders and magnetic anisotropy beyond the Heisenberg model. For a spin moment S bigger than 1/2, single-ion anisotropy is in principle allowed. However, for $d^3$ Mott insulators with large cubic crystal field splitting, the single-ion anisotropy is absent within the LS coupling, despite S = 3/2 local moment. On the other hand, preferred magnetic moment directions in $d^3$ materials have been reported, which calls for a further theoretical investigation. Here we derive the single-ion anisotropy interaction using the strong-coupling perturbation theory. The cubic crystal field splitting including $e_g$ orbitals, trigonal distortions, Hund's coupling, and spin-orbit coupling beyond the LS scheme are taken into account. For compressed distortion, the spin-orbit coupling at magnetic sites can favor either the easy-axis or the easy-plane while that of anions leads to easy-axis anisotropy. We apply the theory on $\rm{CrX}_3$ with X = Cl and I, and show the dependence of the single-ion anisotropy on the strength of the spin-orbit couplings of both magnetic and anion sites. Significance of the single-ion anisotropy in ideal two-dimensional magnets is also discussed.

Simulation of a Severe Sand and Dust Storm Event in March 2021 in Northern China: Dust Emission Schemes Comparison and the Role of Gusty Wind

Northern China experienced a severe sand and dust storm (SDS) on 14/15 March 2021. It was difficult to simulate this severe SDS event accurately. This study compared the performances of three dust-emission schemes on simulating PM10 concentration during this SDS event by implementing three vertical dust flux parameterizations in the Comprehensive Air-Quality Model with Extensions (CAMx) model. Additionally, a statistical gusty-wind model was implemented in the dust-emission scheme, and it was used to quantify the gusty-wind contribution to dust emissions and peak PM10 concentration. As a result, the LS scheme (Lu and Shao 1999) produced the minimum errors for peak PM10 concentrations, the MB scheme (Marticorena and Bergametti 1995) underestimated the PM10 concentrations by 70–90%, and the KOK scheme (Kok et al. 2014) overestimated PM10 concentrations by 10–50% in most areas. The gusty-wind model could reasonably reproduce the probability density function of 2-min wind speeds. There were 5–40% more dust-emission flux and 5–40% more peak PM10 concentrations generated by the gusty wind than the hourly wind in the dust-source regions. The increase of peak PM10 concentration caused by gusty wind in the non-dust-source regions was higher than in the dust-source regions, with 10–50%. Implementing the gusty-wind model could help improve the LS scheme’s performance in simulating PM10 concentrations of this severe SDS event. More work is still needed to investigate the reliability of the gusty-wind model and LS scheme on various SDS events.

Recent Advances in Least-Squares and Discontinuous Petrov–Galerkin Finite Element Methods

Abstract Least-squares (LS) and discontinuous Petrov–Galerkin (DPG) finite element methods are an emerging methodology in the computational partial differential equations with unconditional stability and built-in a posteriori error control. This special issue represents the state of the art in minimal residual methods in the L 2 L^{2} -norm for the LS schemes and in dual norm with broken test-functions in the DPG schemes.

Comparison of three Under-Frequency Load Shedding Schemes referring to the Power System of Sri Lanka

To cater the consumers with high quality electricity, a reliable Power System (PS) is a must. Recently several major changes have been taken place in the PS of Sri Lanka. Today the PS of Sri Lanka, that operates under Ceylon Electricity Board (CEB) is comprised with 3 numbers of coal Power Plants (PPs), each having a generation capacity of 300 MW, a combined cycle PP (Yugadanavi) and considerably extended transmission network [1], [2]. To maintain the stability of a PS, the balance between power generation and consumption (demand) is a must. In any event, the first few seconds of frequency degradation and recovery after a major generator trip is essentially be accomplished by governor control. When the PS‟s self-regulation is insufficient to establish a stable state, the system frequency (SF) will continue to drop until it is arrested by automatic under-frequency load shedding (UFLS) to re-establish the load-generation balance within the time constraints necessary to avoid system collapse [3], [4]. Therefore it has become necessary to review the performance of the present CEB LS Scheme (LSS) and suggest amendments where necessary. This paper proposes two LSSs which can address the recent changes taken place in the Sri Lanka PS while maintaining stability. Having simulated the PS of Sri Lanka, performance comparison of the CEB LSS which is being implemented in Sri Lanka and the proposed LSSs (PLSSs) are presented. Results show that the LSS should exclusively be specific for a particular PS. It depends on factors such as electrical PS practice, regulations, largest generator capacity, electricity consumption pattern etc.

겨울철 황사 모의시 황사배출량 산정식과 입력자료의 평가: 2007년 12월 29일 황사사례 연구

A case study was conducted for a severe wintertime dust event that occurred on December 29, 2007 in Korea. Three different dust emission schemes, namely, those of Marticorena and Bergametti (1995), Lu and Shao (1999), and Shao (2004) (hereinafter, referred to MB, LS, and S04 schemes, respectively) were implemented in Weather Research Forecast with Chemistry (WRF/Chem) to assess their performance in simulating wintertime Asian dust events. WRF/Chem simulation reproduces dust emission over Mongolia on December 27 and 28, 2007 and the onset timing of the dust event in Korea well. There is, however, a huge difference among the estimated dust emission amounts for the three schemes; the dust concentration derived by MB scheme is 6 times larger than that from LS scheme. The three schemes overestimate dust concentrations when comparing to observed surface-level mass concentrations in Ganghwa, Seoul, and Yeongwol. This discrepancy is thought to be mainly due to the overestimated model winds and the surface condition such as snow cover fraction, which did not adequately represent the real conditions. Considering frozen soil effect on dust emission, the model results are comparable with observation data: it is important to consider frozen soil in simulating wintertime dust events.

Comparison of vertical dust flux by implementing three dust emission schemes in WRF/Chem

[1] Vertical dust flux parameterizations were assessed by implementing three different dust emission schemes, namely, those of Marticorena and Bergametti (1995), Lu and Shao (1999), and Shao (2004) (hereinafter referred to as MB, LS, and S04 schemes, respectively) in Weather Research and Forecasting with Chemistry (WRF/Chem). Through sensitivity tests, the scattering of vertical dust fluxes resulting from different parameterizations was shown even under the condition of same horizontal sand flux. The difference between the estimated vertical dust fluxes of three emission schemes ranges from the order of 101 for sand to the order of 102 for clay. The MB scheme generally produces higher dust emissions than the LS and S04 schemes, and the difference is the greatest for clay because the MB scheme considers vertical dust flux to be related to clay content, while the LS and S04 schemes consider it to be inversely proportional to surface hardness. To investigate the performance of each dust emission scheme in the simulation of Asian dust events, a case study was carried out for a severe Asian dust event that took place between 30 March and 1 April 2007. Simulation results reproduced the outbreak and transport pattern of dust plumes satisfactorily. However, the estimated dust emission amounts in each scheme differed greatly, particularly in loamy soil. The total dust emission amounts averaged for the main dust source region in this Asian dust event for five consecutive days are 84 Tg, 149 Tg, and 532 Tg for the LS, S04, and MB schemes, respectively.

Net-value of the relativistic crystal field effect

The relativistic crystal field theory in case of the rare earth ion doped materials is presented. In order to calculate the values of crystal field splittings the effectively relativistic crystal field operators are applied. The matrix elements of these operators are evaluated in the non-relativistic LS scheme, whereas the radial integrals include one electron Dirac–Fock wavefunctions. The numerical results of the relativistic crystal field effects are presented for Ce3+ or Yb3+ ions in LuPO4, and they are compared with those obtained from the non-relativistic approach.

Excitation Energies, Oscillator Strengths and Radiative Rates in Triply Ionised Phosphorous

We have calculated the excitation energies for the lowest 23 LS and 43 fine-structure levels as well as oscillator strengths and radiative decay rates for the transitions among (1s22s22p6) 3s2 (1S), 3s3p (1,3Po), 3p2 (1S, 3P, 1D), 3s3d (1,3D), 3s4s (1,3S), 3p3d (1,3Po, 1,3Do, 1,3Fo), 3s4p (1,3Po), 3s4d (1,3D), 3s4f (1,3Fo) and 3p4s (1,3Po) states in P IV. These states are represented by extensive configuration-interaction (CI) wavefunctions obtained with the CIV3 computer code of Hibbert. The calculations have been carried out in both LS and intermediate-coupling schemes. Relativistic effects are included through the Breit-Pauli approximation via spin-orbit, spin-other-orbit, spin-spin, Darwin and mass correction terms. We have also calculated the radiative lifetimes from our radiative decay rates. Our results are compared with other theoretical calculations and the available experimental data.

Wannier theory for double photoionization of noble gases

The Wannier theory not only gives the threshold laws for processes such as near-threshold double photoionization, but also predicts an angular correlation between the two escaping electrons. Within the frame of this theory and using an LS scheme the authors derive the triple, double differential and integral cross sections, for noble gases ions left in the ground or first excited states. The approach should allow a direct comparison with forthcoming experiments, as it uses the individual angles of the two electrons. In the case of unfavoured final states, which have a node when the angle between these electrons is 180', the triple differential cross sections depend critically on the angular correlation. The authors give their detailed structure in space for double ionization by both polarized and unpolarized photons. They also show that a particular choice of Euler angles allows a straightforward integration which leads to the double differential cross sections.

Energy levels in the jj coupling scheme

These authors show how to determine Energy levels in the jj coupling so they can be compared with the energy levels from the LS scheme to find out which ones give a better match with exper...

Lifetime trends for the n=3 singlet states in the Mg sequence

Theoretical lifetime trends are reported for all bound singlet states in the n=3 complex of the Mg sequence for Z⩽26. Calculations are based on MCHF wavefunctions and include only dipole allowed transitions in the LS scheme. For states that are entering the bound spectrum, the reported lifetime is an upper bound. At sufficiently high Z, all these states can decay only through Δn=0 transitions and several lifetime trends become similar. Implications for the cascade problem in beam-foil spectroscopy are discussed.

Separation of spurious c.m. effects within the shell nucleon configuration framework in α-transfer structure studies

An exact method for the separation of the residual c.m. spurious contamination within the shell nucleon configuration framework has been derived from cluster model formulations. Expressions for the spurious weight α-spectroscopic amplitude and other factors relevant to α-transfer reactions have been obtained. Available methods to calculate α spectroscopic amplitude are extended to include excited shell nucleon configurations. Within the bounds of practically (i.e. within a few ħω above the lowest configurations), the number of configurations in the extended treatment is relatively small, and therefore easily manageable. The calculations proposed are applicable to wave functions decomposed in terms of shell configuration states in the jj as well as the LS scheme.

Time-differential-free hyperfine field measurement at low recoil velocities

A time-differential plunger technique has been used to observe the temporal attenuation of a $gamma$-ray angular distribution. Nuclei of $sup 152$Sm were Coulomb excited by 3 and 4 MeV $alpha$ particles. A dominant static hyperfine interaction was observed from which a magnetic field at the nucleus of 2.6 less than or equal to H (0) less than or equal to 2.9 MOe was deduced. This value is in agreement with the field calculated in the LS scheme. The static interaction may originate in a number of one- and two-electron processes that occur at the target surface. (AIP)

Odd Configurations of Neutral Titanium (Ti i)

The structure of the configurations (3d + 4s)34p in Ti i has been interpreted in the electrostatic approximation by treating radial parameters as free variables and obtaining a least-squares fit of theoretical to experimental term energies. Full provision was made for interactions between the configurations. All observed terms are accounted for and the mean error of the final fit is 355 cm−1. Major eigenvector components in an LS scheme are tabulated for each term.