Single-phase Technique Research Articles

Load Frequency Control Design for Complex Power Systems Implementing Integral Single-Phase Sliding Mode Control

This paper proposes a Decentralized Integral Single-phase Sliding Mode Control (DISSMC) for Load Frequency Control (LFC) in Complex Power Systems with Multi-Source generation (CPSMS), integrating reheat, hydro, gas, and wind turbines. A generalized structure is employed to model Multi-Area Linked Power Systems (MALPS), providing a realistic representation of diverse power plants. The proposed method formulates an integral Sliding Surface (SS) to mitigate the chattering phenomena and ensures finite-time stability through a continuous control law. Additionally, a single-phase technique eliminates the reaching phase, ensuring immediate trajectory control. The MATLAB/Simulink simulations validate the DISSMC's effectiveness in stabilizing frequency fluctuations and managing load variations across three interconnected regions, each hosting different power plant types. The results highlight the proposed controller's robustness and adaptability to dynamic load and renewable energy source fluctuations.

Advanced Sliding Mode Design for Optimal Automatic Generation Control in Multi-Area Multi-Source Power System Considering HVDC Link

The multi-area multi-source power system (MAMSPS), which uses a variety of power sources including gas, hydro, thermal, and renewable energy, has recently been implemented to balance the growing demand for electricity and the overall capacity for power generation. In this paper, an integral sliding mode control with a single-phase technique (ISMCSP) is applied to two areas, with each area including gas–wind–thermal power systems with HVDC system. Firstly, a two-area gas–wind–thermal power system with HVDC (TAGWTPSH) is the first model in this scheme to consider the parameter uncertainties of a MAMSPS. Secondly, sliding mode design law with a single-phase technique is introduced to alleviate chattering and oscillation problems. Then, power system stability is ensured by the Lyapunov control theory based on the new LMIs technique. Thirdly, the ISMCSP’s effectiveness in a MAMSPS is also assessed under random load patterns and parameter variations regarding settling time and over-/undershoot. The ISMCSP was created to alter the fundamental sliding mode control, and therefore the suggested approach performs better than recently published approaches. This is demonstrated by the frequency overshoot deviation value in frequency deviations: 0.7 × 10−3 to 2.8 × 10−3 for the TAGWTPSH with the suggested ISMCSP. In the last case, for random changes in load from −0.4 to +0.5 p. u, the proposed ISMCSP method still stabilizes the frequency of the areas meeting the standard requirements for AGC.

Thermal energy development in magnetohydrodynamic flow utilizing titanium dioxide, copper oxide and aluminum oxide nanoparticles: Thermal dispersion and heat generating formularization

Background: The main aim of this article heat transfer in thermal engineering deals with the production, use, transformation, and transfer of thermal energy. Engineering and industrial fields including food packaging, the production of food additives, electronic cooling, microturbines, etc. Heavily rely on heat transmission. Due to its intriguing potential in industries like the production of polymers, paper, crystal glass, etc., scientists from all over the world have endeavored to investigate the effect of heat transmission on fluid flows past an expandable surface.Purpose: The use of a single-phase technique to assess Newtonian nanofluid flow along stretched surfaces with heat transfer convective models is emphasized in this research. A mathematical formulation is used to do the numerical computations for copper oxide (CuO), aluminum oxide (Al2O3), and titanium dioxide (TiO2) nanoparticles using water (H2O) as the base fluid.Formulation: The fifth-order Runge-Kutta shooting method procedure with shelling performance are used to solve non-linear ordinary differential equations with boundary conditions numerically. Researched and analyzed for changes in several parameters, plots illustrating the effects of motivated and non-motivated MHD are given to explain the physical values.Finding: Dispersion of solid items in the working fluid is reported to significantly improve thermal performance. The Biot number determines how convective the border is. With an increase in the Biot number, the fluid’s temperature drops significantly. It has been demonstrated that Copper oxide (CuO), nanoparticles are more efficient than Titanium Dioxide (TiO2) and Aluminum Oxide for thermal enhancement (Al2O3).Novelty: As far as the authors are aware, no studies have been done on the steady MHD flow and convective heat transfer of nanofluids over a nonuniform stretched surface under the influence of a heat source and viscous dissipation.

On the electrode configurations in a large single phase liquid xenon detector for dark matter searches

In the near future there will be the request for very large liquid Xenon (LXe) detectors for Dark Matter (DM) searches in the 50-ton range. To avoid an impractically long, single drift space of a dual-phase detector, it seems beneficial to use the single-phase technique. Since electrons then can drift in any direction, we can segment the homogeneous medium and thus avoid an excessive maximum drift path of order 4 m. The shorter detector length has several benefits, e.g. requiring a lower cathode voltage for the same drift field. We can easily split the TPC into two regions with the cathode in the center and two anodes at the top and bottom. One also can use multiple TPCs stacked on top of each other in the same liquid volume to reduce the maximum drift length even further.A further division of the drift space by installing an additional anode in the center would require S2 photons to traverse the liquid for several times the Rayleigh scattering length in LXe, which is only 30–40 cm. This seems to be excessive for good x-y localization. We therefore suggest a geometry of two independent TPCs with two drift spaces each.Despite earlier publications concerns persisted about the effect of shadowing. A detailed FEM model of the anode regions shows that with an aligned wire arrangement the drifting electrons impinge sideways on the anode in a narrow angular range of width 15°–20°. Most S2 photons are emitted in full view of the close-by PMT array. About 37% of the S2 photons are shadowed by the anode wire out of which 30% will be reflected back again on the gold plating of the wires. Thus we can observe 74% of the total S2 light. Compared to a dual-phase detector, however, we do not suffer from the extraction efficiency, sometimes reported as low as 50%.

Production data analysis in gas condensate reservoirs using type curves and the equivalent single phase approach

Most modern production data type curve (PDTC) techniques, which are used in the estimation of reservoir and well productivity parameters such as permeability, drainage radius and skin, were originally developed with the assumption of Darcy flow (i.e. laminar flow, with pressure gradient proportional to the fluid superficial velocity, in accordance with Darcy's law) of a single-phase fluid. Two-phase conditions, e.g. in a gas condensate reservoir (GCR) operating below dewpoint pressure, introduce nonlinearities into the diffusivity equation, making the use of single-phase techniques questionable, and potentially producing erroneous parameter estimates. A common approach to linearizing the system is by the use of pseudovariables which account for the two-phase effects in addition to the pressure-dependence of fluid properties.In this study, GCR production data generated using homogeneous fine-grid compositional simulation models, were first analysed using a well-known conventional (single-phase) modern PDTC technique, namely the Blasingame type curves for radial flow around a vertical well in a circular drainage area. The conventional techniques were then modified using an equivalent single phase concept, which was employed in the computation of two-phase pseudovariables for use with the single-phase PDTC. To compute these two-phase pseudovariables, pressure-saturation/kr relationships are required. These were determined using a technique, which employs fluid component weight fractions and gas fractional flow of a fluid with constant fixed total composition. Sensitivities were conducted on reservoir fluid richness (maximum liquid dropout from 1% to 42%), relative permeability curves, degree of reservoir undersaturation and well operating pressures, to examine their impact on production decline response and subsequent conventional PDTC analysis, as well as their impact on the effectiveness of the equivalent single-phase based approach used in this study.The paper first highlights the impact of two-phase flow conditions in GCRs on conventional PDTC analysis, in terms of the quality of the type curve match (TCM) and estimates of permeability, drainage radius and skin. Then it is shown that, in GCR analysis where the impact of two-phase effects are important, significant improvements can be obtained, both in the quality of the TCM and subsequent parameter estimates, through the use of pseudovariables computed using equivalent single phase concepts. The results also identify conditions under which, depending on the fluid richness and/or the degree of undersaturation, two-phase effects, although present, may not significantly impact the quality of interpretation of long-term production data from GCRs, using conventional single-phase PDTC techniques.

Radiotherapy of high-grade gliomas: current standards and new concepts, innovations in imaging and radiotherapy, and new therapeutic approaches

The current standards in radiotherapy of high-grade gliomas (HGG) are based on anatomic imaging techniques, usually computed tomography (CT) scanning and magnetic resonance imaging (MRI). The guidelines vary depending on whether the HGG is a histological grade 3 anaplastic glioma (AG) or a grade 4 glioblastoma multiforme (GBM). For AG, T2-weighted MRI sequences plus the region of contrast enhancement in T1 are considered for the delineation of the gross tumor volume (GTV), and an isotropic expansion of 15 to 20 mm is recommended for the clinical target volume (CTV). For GBM, the Radiation Therapy Oncology Group favors a two-step technique, with an initial phase (CTV1) including any T2 hyperintensity area (edema) plus a 20 mm margin treated with up to 46 Gy in 23 fractions, followed by a reduction in CTV2 to the contrast enhancement region in T1 with an additional 25 mm margin. The European Organisation of Research and Treatment of Cancer recommends a single-phase technique with a unique GTV, which comprises the T1 contrast enhancement region plus a margin of 20 to 30 mm. A total dose of 60 Gy in 30 fractions is usually delivered for GBM, and a dose of 59.4 Gy in 33 fractions is typically given for AG. As more than 85% of HGGs recur in field, dose-escalation studies have shown that 70 to 75 Gy can be delivered in 6 weeks with relevant toxicities developing in < 10% of the patients. However, the only randomized dose-escalation trial, in which the boost dose was guided by conventional MRI, did not show any survival advantage of this treatment over the reference arm. HGGs are amongst the most infiltrative and heterogeneous tumors, and it was hypothesized that the most highly aggressive areas were missed; thus, better visualization of these high-risk regions for radiation boost could decrease the recurrence rate. Innovations in imaging and linear accelerators (LINAC) could help deliver the right doses of radiation to the right subvolumes according to the dose-painting concept. Advanced imaging techniques provide functional information on cellular density (diffusion MRI), angiogenesis (perfusion MRI), metabolic activity and cellular proliferation [positron emission tomography (PET) and magnetic resonance spectroscopy (MRS)]. All of these non-invasive techniques demonstrated good association between the images and histology, with up to 40% of HGGs functionally presenting a high activity within the non-contrast-enhanced areas in T1. New LINAC technologies, such as intensity-modulated and stereotactic radiotherapy, help to deliver a simultaneous integrated boost (SIB) > 60 Gy. Trials delivering a SIB into a biological GTV showed the feasibility of this treatment, but the final results, in terms of clinical benefits for HGG patients, are still pending. Many issues have been identified: the variety of MRI and PET machines (and amino-acid tracers), the heterogeneity of the protocols used for image acquisition and post-treatment, the geometric distortion and the unreliable algorithms for co-registration of brain anatomy with functional maps, and the semi-quiescent but highly invasive HGG cells. These issues could be solved by the homogenization of the protocols and software applications, the simultaneous acquisition of anatomic and functional images (PET-MRI machines), the combination of complementary imaging tools (perfusion and diffusion MRI), and the concomitant addition of some ad hoc targeted drugs against angiogenesis and invasiveness to chemoradiotherapy. The integration of these hybrid data will construct new synthetic metrics for fully individualized treatments.

Accuracy of stone casts obtained by different impression materials

Several impression materials are available in the Brazilian marketplace to be used in oral rehabilitation. The aim of this study was to compare the accuracy of different impression materials used for fixed partial dentures following the manufacturers' instructions. A master model representing a partially edentulous mandibular right hemi-arch segment whose teeth were prepared to receive full crowns was used. Custom trays were prepared with auto-polymerizing acrylic resin and impressions were performed with a dental surveyor, standardizing the path of insertion and removal of the tray. Alginate and elastomeric materials were used and stone casts were obtained after the impressions. For the silicones, impression techniques were also compared. To determine the impression materials' accuracy, digital photographs of the master model and of the stone casts were taken and the discrepancies between them were measured. The data were subjected to analysis of variance and Duncan's complementary test. Polyether and addition silicone following the single-phase technique were statistically different from alginate, condensation silicone and addition silicone following the double-mix technique (p < or = .05), presenting smaller discrepancies. However, condensation silicone was similar (p > or = .05) to alginate and addition silicone following the double-mix technique, but different from polysulfide. The results led to the conclusion that different impression materials and techniques influenced the stone casts' accuracy in a way that polyether, polysulfide and addition silicone following the single-phase technique were more accurate than the other materials.

Voltage Multiplier Cells Applied to Non-Isolated DC–DC Converters

This paper introduces the use of the voltage multiplier technique applied to the classical non-isolated dc-dc converters in order to obtain high step-up static gain, reduction of the maximum switch voltage, zero current switching turn-on. The diodes reverse recovery current problem is minimized and the voltage multiplier also operates as a regenerative clamping circuit, reducing the problems with layout and the EMI generation. These characteristics allows the operation with high static again and high efficiency, making possible to design a compact circuit for applications where the isolation is not required. The operation principle, the design procedure and practical results obtained from the implemented prototypes are presented for the single-phase and multiphase dc-dc converters. A boost converter was tested with the single-phase technique, for an application requiring an output power of 100 W, operating with 12 V input voltage and 100 V output voltage, obtaining efficiency equal to 93%. The multiphase technique was tested with a boost interleaved converter operating with an output power equal to 400 W, 24 V input voltage and 400 V output voltage, obtaining efficiency equal to 95%.

Multislice CT with single–phase technique in patients with suspected pancreatic cancer

The purpose of this study was to evaluate the role of multislice computed tomography (MSCT) with a single-phase technique in patients with suspected pancreatic cancer (PC). Seventy-eight patients underwent MSCT with the following technical parameters: collimation: 4x1 mm; pitch 1; 120 kVp; 260 mAs. The pre-contrast scan was followed by a single acquisition phase in the caudocranial direction from the inferior hepatic margin to the diaphragm with a 60-s delay after IV administration of 150 ml of iodinated contrast material at a rate of 3 ml/s. Two radiologists assessed the single images independently. Receiver operating characteristics (ROC) curves were obtained for each of the two observers. The final diagnosis was pancreatic cancer in 46 cases and chronic pancreatitis in 32 cases. Areas under the curve (AZ) for diagnosis and evaluation of disease resectability were 0.97 and 0.93 for the first observer (p=ns), and 0.97 and 0.90 for the second observer (p=ns). The mean difference in tissue attenuation values between the cancer and normal pancreas was 72 +/- 3 Hounsfield units (HU). No statistically significant differences were observed in the degree of opacification between the peripancreatic arteries and veins. MSCT with a single-phase technique is an accurate and reproducible method for diagnosis and evaluation of disease resectability in patients with suspected PC, ensuring optimal tumour-to-pancreas contrast and maximal opacification of the main peripancreatic arterial and venous structures.

Value of the Single-Phase Technique in MDCT Assessment of Pancreatic Tumors

Value of the Single-Phase Technique in MDCT Assessment of Pancreatic Tumors

Value of the Single-Phase Technique in MDCT Assessment of Pancreatic Tumors

Value of the Single-Phase Technique in MDCT Assessment of Pancreatic Tumors

The impact of introducing intensity modulated radiotherapy into routine clinical practice

Background and purpose Intensity modulated radiotherapy (IMRT) at the Royal Marsden Hospital London was introduced in July 2001. Treatment delivery was dynamic using a single-phase technique. Concerns were raised regarding increased clinical workload due to introduction of new technology. The potential increased use of resources was assessed. Patients and methods IMRT patient selection was within guidelines of clinical trials and included patients undergoing prostate plus pelvic lymph node (PPN) irradiation and head and neck cancer (HNC) treatment. Patient planning, quality assurance and treatment times were collected for an initial IMRT patient group. A comparative group of patients with advanced HNC undergoing two- or three-phase conventional radiotherapy, requiring matched photon and electron fields, were also timed. Results The median overall total planning time for IMRT was greater for HNC patients compared to the PPN cohort. For HNC the overall IMRT planning time was significantly longer than for conventional. The median treatment time for conventional two- or three-phase HNC treatments, encompassing similar volumes to those treated with IMRT, was greater than that for the IMRT HNC patient cohort. A reduction in radiographer man hours per patient of 4.8 h was recorded whereas physics time was increased by 4.9 h per patient. Conclusions IMRT currently increases overall planning time. Additional clinician input is required for target volume localisation. Physics time is increased, a significant component of this being patient specific QA. Radiographer time is decreased. For HNC a single phase IMRT treatment has proven to be more efficient than a multiple phase conventional treatment. IMRT has been integrated smoothly and efficiently into the existing treatment working day. This preliminary study suggests that IMRT could be a routine treatment with efficient use of current radiotherapy resources.

Value of the Single-Phase Technique in MDCT Assessment of Pancreatic Tumors

The purpose of our study was to determine the diagnostic value of single-phase MDCT in patients with suspected pancreatic carcinoma. Seventy-one patients (41 men, 30 women; mean age, 63 years; range, 29-80 years) with suspected pancreatic tumor underwent MDCT. Scanning was performed on an MDCT scanner with 0.5-sec gantry rotation and acquisition of 4 slices per rotation. Unenhanced scanning was followed by one set of scanning in the caudocranial direction from the inferior hepatic margin to the diaphragm with a scanning delay of 60 sec after the IV injection of 150 mL of contrast material delivered at 3 mL/sec. Two reviewers independently scored images in a blinded fashion for the presence of tumor and assessment of resectability. Receiver operating characteristic analysis was performed. A final histopathologic diagnosis derived from surgical findings was obtained in 42 patients; in the remaining 29 patients, percutaneous fine-needle aspiration biopsy coupled with a 1-year clinical follow-up to determine development of local, regional or distant neoplasm served as gold standard proof of diagnosis. Final diagnosis was pancreatic cancer in 40 patients (27 ductal adenocarcinoma, nine mucinous cystoadenocarcinoma, two neuroendocrine tumors, one lymphoma, and one papillary cystoadenocarcinoma) and chronic pancreatitis in 31. The mean tumor size was 2.4 cm (range, 4-1 cm). Values for the area under the curve (A(z)) for the assessment of tumor detection were 0.97 for reviewer 1 and 0.96 for reviewer 2 (p = not significant). A(z) values for tumor resectability were 0.90 for reviewer 1 and 0.90 for reviewer 2 (p = not significant). No statistically significant differences were observed between superior mesenteric artery and vein opacification with the hepatic parenchyma enhanced at a time closer to the peak hepatic enhancement, optimizing the detection of hepatic lesions. Thin-section single-phase MDCT is an accurate technique for the diagnosis and assessment of resectability in patients with a suspected pancreatic neoplasm. This technique provides optimal tumor-to-pancreas contrast and maximal pancreatic parenchymal and peripancreatic vascular enhancement. It allows visualization of the entire liver and the whole upper abdomen during the portal phase for accurate identification of liver metastases and peritoneal seeding.

IX. 1Mono- and biphasic asymmetric hydroformylation with rhodium catalysts of the diphosphine ligand NAPHOS and its sulfonated derivatives

Both enantiomers of the diphosphine 2,2′-bis(diphenylphosphinomethyl)-1, 1′-binaphthyl NAPHOS were prepared by resolution of the racemic P,P′-dioxide and subsequently applied in the rhodium-catalyzed, asymmetric hydroformylation of styrene. Optically active, highly water-soluble derivatives BINAS were prepared by direct sulfonation of the enantiopure diphosphine NAPHOS and applied in aqueous/organic, two-phase hydroformylation of styrene. The catalytically active rhodium complexes HRh(CO) 2(PP) of both NAPHOS and BINAS were prepared and characterized by infrared and NMR spectroscopy. Optical yields are lower in two-phase hydroformylation compared with the conventional single-phase (organic solvent) technique.

FREE SURFACE FLOW AND HEAT TRANSFER IN CAVITIES: THE SEA ALGORITHM

This study concerns the mathematical modeling of heat transfer and free surface motion under gravity, in cavities partially filled with a liquid. This two-phase flow problem is solved using a single-phase technique that assumes the air and liquid occupying the volume of the cavity can be treated as a single fluid with a sharp property discontinuity at the interface. A two-valued scalar advection equation is solved to mark the extent of each fluid. This idea is simple in concept, but requires careful application for two reasons: (1) The interface must remain sharp throughout the simulation; and (2) the equations of motion have to be expressed in a way that prevents the numerical “smothering” of the lighter fluid by the heavy one during the iteration process. To satisfy (1), the Van Leer TVD differencing scheme is adopted for the scalar advection equation, with appropriate flux corrections in the momentum and enthalpy equations. To satisfy (2), the continuity equation is expressed in volumetric form. The technique is incorporated in the scalar equation algorithm (SEA), It is applied to two problems, the first being the collapse of a liquid column in a sealed cavity with wall heat transfer, and the second the filling and simultaneous cooling of a mold with liquid aluminum.

Apical placement of needle tip with an injection‐thermoplasticized gutta‐percha technique for root canal obturation

It is recommended that when injection-thermoplasticized gutta-percha is used as the obturation technique, the root canal space should be prepared in such a way that the 23-gauge injection needle tip can be placed at a distance 3 to 5 mm short of the working length. In this study the apical seal and extent of gutta-percha were evaluated when the 23-gauge tip was placed at a distance 4 mm, 6 mm, and 8 mm short of the working length. Ninety-nine human single-rooted mandibular incisors and premolars divided into 3 equal groups were used. Their crowns were separated at the cementoenamel junction and their roots were stored in sodium hypochlorite for 1 week. The roots were then instrumented from size 20 at the working length to size 70:4 mm short of the working length in group A, 6 mm in group B, and 8 mm in group C. Following instrumentation, 3 randomly selected roots of each group were used as control. The remaining 30 roots of each group were covered with aluminium foil and embedded in acrylic blocks. The root canals were then dried, coated with sealer (Roth 811) and obturated by injection of thermoplasticized gutta-percha using the single-phase technique. Vertical condensation followed. The roots were immersed in dye for 3 days and then demineralized, dehydrated and cleared in xylene. Measurements of linear dye penetration for the apical seal and for underextension were done by 2 independent examiners under a stereomicroscope. The results of this study showed no statistically significant difference in leakage between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Sealing ability of thermoplasticized gutta-percha in root canal obturation using a sectional vs. a single-phase technique.

Properly prepared straight root canals of freshly extracted maxillary canines and central incisors were used to evaluate the sealing ability of the sectional thermoplasticized gutta-percha obturation technique, with or without sealer and the single-phase thermoplasticized gutta-percha filling technique. The teeth were divided into 3 groups (A, B, C) of 20 teeth and were obturated using the 3 thermoplasticized gutta-percha techniques. Group A: single phase with sealer; group B: sectional technique without sealer; and group C: sectional technique with sealer. The obturated teeth were immersed in India ink for 3 days followed by clearing procedures. The teeth were then examined under a stereo microscope and the linear leakage was recorded. Statistical unpaired Student's t-tests showed significantly less dye penetration in teeth obturated using the sectional technique with sealer (group C) than in teeth obturated with the single-phase technique with sealer (group A) or the sectional technique without sealer (group B).

Comparison of the single-phase and two-phase numerical model formulation for saturated-unsaturated groundwater flow

Two numerical methods are developed for transient saturated-unsaturated two-dimensional ground-water flow. One formulation uses the usual single-phase formulation with a passive air phase at constant pressure. The second model uses a full two-phase air-water formulation. The numerical results for both formulations are compared on some test problems. In some cases, the single-phase formulation and the two-phase formulations give greatly different results. This can be explained in terms of the fractional flow curve for the air-water system. The single-phase technique generally requires less computational work than the two-phase formulation, although there are some situations where the numerical performance of the single-phase formulation is very poor.

Modified single-phase LPE technique for In 1− x Ga x As 1− y P y laser structures

A modified single-phase technique for growth of epitaxial layers of the quaternary compound, In1−xGaxAs1−yPy has been used to fabricate high-quality laser structures in the 1.3 and 1.55 μm-wavelength range. This method permits the concentration of small amounts of phosphorus in the InGa:As melt to be maintained accurately and independent of the history of the graphite boat. Growth of planar structures having small variations in wavelength and uniformity in layer thickness of the order of hundreds of ångströms was easily repeatable. Laser structures, in addition, had low values for threshold current density and gave high yields for both the 1.3 and 1.55 μm wavelength ranges.