• Journal of Radiation Protection and Research
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• v.45 no.4
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• pp.171-177
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• 2020

Background: This study aims to determine the effective atomic number (Zeff) from dual-energy image sets obtained using a conventional computed tomography (CT) simulator. The estimated Zeff can be used for deriving the stopping power and material decomposition of CT images, thereby improving dose calculations in radiation therapy. Materials and Methods: An electron-density phantom was scanned using Philips Brilliance CT Big Bore at 80 and 140 kVp. The estimated Zeff values were compared with those obtained using the calibration phantom by applying the Rutherford, Schneider, and Joshi methods. The fitting parameters were optimized using the nonlinear least squares regression algorithm. The fitting curve and mass attenuation data were obtained from the National Institute of Standards and Technology. The fitting parameters obtained from stopping power and material decomposition of CT images, were validated by estimating the residual errors between the reference and calculated Zeff values. Next, the calculation accuracy of Zeff was evaluated by comparing the calculated values with the reference Zeff values of insert plugs. The exposure levels of patients under additional CT scanning at 80, 120, and 140 kVp were evaluated by measuring the weighted CT dose index (CTDIw). Results and Discussion: The residual errors of the fitting parameters were lower than 2%. The best and worst Zeff values were obtained using the Schneider and Joshi methods, respectively. The maximum differences between the reference and calculated values were 11.3% (for lung during inhalation), 4.7% (for adipose tissue), and 9.8% (for lung during inhalation) when applying the Rutherford, Schneider, and Joshi methods, respectively. Under dual-energy scanning (80 and 140 kVp), the patient exposure level was approximately twice that in general single-energy scanning (120 kVp). Conclusion: Zeff was calculated from two image sets scanned by conventional single-energy CT simulator. The results obtained using three different methods were compared. The Zeff calculation based on single-energy exhibited appropriate feasibility.

• Journal of Satellite, Information and Communications
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• v.12 no.2
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• pp.51-55
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• 2017

This paper aims to maximize the energy harvesting rate and channel capacity in RF-energy harvesting networks (RF-EHNs) under the constraints of maximum transmit power and minimum quality of service (QoS) in terms of rate capacity for each user. We study a multi-user RF-EHN with frequency division multiple access (FDMA) in a Rayleigh channel. An access point (AP) simultaneously transmitting wireless information and power in the RF-EHN serves a subset of active users which have a power-splitting antenna. To gauge the network performance, we define energy efficiency (EE) and propose an optimization solution for maximizing EE with Lagrangian dual decomposition theory. In simulation results, we confirm that the EE is effectively maximized by the proposed solution with satisfying the given constraints.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.1
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• pp.97-115
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• 2022

Smart power grid is a user friendly system that transforms the traditional electric grid to the one that operates in a co-operative and reliable manner. Demand Response (DR) is one of the important components of the smart grid. The DR programs enable the end user participation by which they can communicate with the electricity service provider and shape their daily energy consumption patterns and reduce their consumption costs. The increasing demands of electricity owing to growing population stresses the need for optimal usage of electricity and also to look out alternative and cheap renewable sources of electricity. The solar and wind energy are the promising sources of alternative energy at present because of renewable nature and low cost implementation. The proposed work models a smart home with renewable energy units. The random nature of the renewable sources like wind and solar energy brings an uncertainty to the model developed. A stochastic dual descent optimization method is used to bring optimality to the developed model. The proposed work is validated using the simulation results. From the results it is concluded that proposed work brings a balanced usage of the grid power and the renewable energy units. The work also optimizes the daily consumption pattern thereby reducing the consumption cost for the end users of electricity.

• Proceedings of the Korean Nuclear Society Conference
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• 2005.10a
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• pp.266-267
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• 2005

• Journal of the Korean Society of Radiology
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• v.17 no.2
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• pp.207-213
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• 2023

Computed tomography (CT) images are used as the basis for proton Bragg peak position estimation and treatment plan simulation. During the Hounsfield Unit (HU) based proton stopping power ratio (SPR) estimation, small differences in the patient's density and elemental composition lead to uncertainty in the Bragg peak positions along the path of the proton beam. In this study, we investigated the potential of dual-energy computed tomography image-based proton SPRs prediction accuracy to reduce the uncertainty of Bragg peak position prediction. Single- and dual-energy images of an electron density phantom (CIRS Model 062M electron density phantom, CIRS Inc., Norfolk, VA, USA) were acquired using a computed tomography system (Somatom Definition AS, Siemens Health Care, Forchheim, Germany) to estimate the SPRs of the proton beam. To validate the method, it was compared to the SPRs estimated from standard data provided by the National Institute of Standards and Technology (NIST). The results show that the dual-energy image-based method has the potential to improve accuracy in predicting the SPRs of proton beams, and it is expected that further improvements in predicting the position of the proton's Bragg peak will be possible if a wider variety of substitutes with different densities and elemental compositions of the human body are used to predict the SPRs.

• Structural Engineering and Mechanics
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• v.92 no.1
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• pp.99-110
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• 2024

The crack propagation path can be considered as a boundary problem in which the crack advances towards the interior of the domain. Consequently, this poses an optimization problem wherein the local crack-growth direction angle can be treated as a design variable. The advantage of this approach is that the continuous minimization of strain energy naturally leads to the mode I propagation path. Furthermore, this procedure does not rely on the precise characterization of the stress field at the crack tip and is independent of stress intensity factors. This paper proposes an algorithm based on internal point exploration as well as shape sensitivity optimization and strain energy minimization to determine the crack propagation direction. To implement this methodology, the algorithm utilizes a modeling GUI associated with an academic analysis program based on the Dual Boundary Elements Method and determines the propagation path by exploiting the elastic strain energy at points in the domain that are candidates to be included in the boundary. The sensitivity of the optimal solution is also assessed in the vicinity of the optimum point, ensuring the stability and robustness of the solution. The results obtained demonstrate that the proposed methodology accurately predicts the crack propagation direction in Mode I opening for a single crack (lateral and central). Furthermore, robust optimal solutions were achieved in all cases, indicating that the optimal solution was not highly sensitive to changes in the design variable in the vicinity of the optimal point.

• ETRI Journal
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• v.38 no.4
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• pp.746-756
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• 2016

Owing to the intermittent power generation of renewable energy sources (RESs), future wireless cellular networks are required to reliably aggregate power from retailers. In this paper, we propose a distributed power allocation (DPA) scheme for base stations (BSs) powered by retailers with heterogeneous RESs in order to deal with the unreliable power supply (UPS) problem. The goal of the proposed DPA scheme is to maximize our well-defined utility, which consists of power satisfaction and unit power costs including added costs as a non-subscriber, based on linear and quadratic cost models. To determine the optimal amount of DPA, we apply dual decomposition, which separates the master problem into sub-problems. Optimal power allocation from each retailer can be obtained by iteratively coordinating between the BSs and retailers. Finally, through a mathematical analysis, we show that the proposed DPA can overcome the UPS for BSs powered from heterogeneous RESs.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1007-1014
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• 2018

A novel dual DC-DC flyback converter with leakage-energy recycling is presented in this paper. Only an active switch is used for this converter. A pulse-width-modulation strategy is adopeted to control this switch. Two transformers are employed for the proposed converter. During the switch ON-period, the primary windings of the two transformers store energies. At the switch OFF-period, the energies stored in the primary windings of the two transformers are released to the output via the secondary windings of the two transformers. Meanwhile, the leakage energies of the two transformers can be recycled. The operating principles and steady-state analyses of the proposed converter are described in detail. A prototype circuit of the proposed converter is implemented for verifying the performances.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.7
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• pp.81-90
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• 2009

Due to environmental issues, the development of low energy consumption products has become one of the main topics in the home appliance industry. The energy consumption of a refrigerator depends on the efficiency of its compressor as well as on the refrigerator cycle design, such as the capacity modulation. In this study, a dual capacity, i.e., two-step capacity modulation (TCM), reciprocating compressor is developed. In a TCM compressor, capacity modulation is achieved by changing the dead volume in the cylinder. Instead of a concentric sleeve, an eccentric sleeve, a key, and a spring are used to change the dead volume for the clockwise and counterclockwise rotation of a motor. When the compressor changes its operating mode from full capacity to partial capacity or in opposite direction, the key may collide with the eccentric sleeve. The structural reliability and mode change reliability were confirmed by analysis and experiment.

• Journal of Korea Multimedia Society
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• v.10 no.6
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• pp.760-769
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• 2007

In this paper, we consider a group mobility model to formulate a clustering mechanism called Dual Coalescent Energy-Efficient Algorithm (DCEE) which is scalable, distributed and energy-efficient for wireless mesh network. The differences of the network nodes will be distinguished to exploit heterogeneity of the network. Furthermore, a topology control, that is, adjusting the transmission range to further reduce power consumption will be integrated with the cluster formation to improve network lifetime and connectivity. Along with network lifetime and power consumption, clusterhead changes will be measured as a performance metric to evaluate the. effectiveness and robustness of the algorithm.