An asymptotic maximum likelihood for estimating the nominal angle of a spatially distributed source

This paper proposes a large-sample approximation of the maximum-likelihood estimator for direction finding in the presence of a spatially spread source. The key idea is to replace the parametric estimate of the four-dimensional nuisance parameter vector with the approximate one that depends on just one parameter of interest, called the nominal angle, thus permitting the use of one-dimensional optimization techniques. The proposed estimator is shown to be strongly consistent and asymptotically efficient, and the Cramér–Rao bound on its standard deviation is derived. Simulations show the estimator to outperform previously proposed estimators, such as the subspace-based estimator and others based on one-dimensional search.     

Large-scale synthesis of WO3 nanoplates by a microwave-hydrothermal method

Tungsten oxide (WO₃) nanoplates were synthesized by a 270 W microwave-hydrothermal reaction of Na₂WO₄·2H₂O and citric acid (C₆H₈O₇·H₂O) in deionized water. X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) were used to reveal the synthesis of WO₃ complete rectangular nanoplates in the solution of 0.2 g citric acid for 180 min, with O-W-O FTIR stretching modes at 819 and 741 cm⁻¹, and two prominent O-W-O Raman stretching modes at 804 and 713 cm⁻¹. The 2.71 eV indirect energy gap, and 430-460 nm blue emission wavelength range of WO₃ complete rectangular nanoplates were determined using UV-visible and photoluminescence (PL) spectrometers. The formation mechanism was also proposed according to the experimental results.     

Biomolecule and surfactant-assisted hydrothermal synthesis of PbS crystals

PbS crystals were hydrothermally synthesized using Pb(NO₃)₂, l-cysteine, and N-cetyl pyridinium chloride in solutions with different pH values at 140 °C. Flower-like, granular and truncated cubic PbS crystals composing of Pb and S were detected using an X-ray diffractometer (XRD), a scanning electron microscope (SEM), a transmission electron microscope (TEM), a selected area electron diffraction (SAED) technique and an energy dispersive X-ray (EDX) analyzer. In addition, a Raman spectrometer revealed the presence of the first and second overtone modes at 436 and 602 cm⁻¹, respectively. Emission spectra of the products were detected at 412 nm using a photoluminescence (PL) spectrometer.     

Validation of void fraction models and correlations using a flow pattern transition mechanism model in relation to the identification of annular vertical downflow in-tube condensation of R134a

This paper reports the experimental investigation of a model for predicting flow pattern transitions and for the validation of void fraction models and correlations proposed in the authors' previous publications and for the identification of flow regimes in data corresponding to annular flow downward condensation of R134a in a vertical smooth copper tube having an inner diameter of 8.1 mm and a length of 500 mm. R134a and water are used as working fluids on the tube side and annular side, respectively, of a double tube heat exchanger. Condensation experiments are done at mass fluxes of 260 and 515 kg m^− 2 s^− 1 in the high mass flux region of R134a. The condensing temperatures are between 40 and 50 °C; heat fluxes are between 10.16 and 66.61 kW m^− 2. A mathematical model proposed by Soliman based on the models of Kosky and Lockhart–Martinelli is used to determine the condensation film thickness of R134a. Comparative void fraction values are determined indirectly using the measured data under laminar and turbulent flow conditions together with various void fraction models and correlations reported in the literature. There is good agreement between the void fraction results obtained from the theoretical model and those obtained from the void fraction models of Soliman, Chisholm and Armand, Turner and Wallis, Smith, Spedding and Spence previously proposed in the authors' publications and tested against their experimental database. Various well-known flow regime correlations from the literature are investigated to identify the flow regime occurring in the test tube, the correlations of Taitel and Dukler, Dobson, Akbar et al., Breber et al., Cavallini et al., and Sardesai et al. can provide accurate estimates of the annular flow conditions in spite of their different working conditions.     

A performance comparison of vapour-compression refrigeration system using various alternative refrigerants

A theoretical performance study on a traditional vapour-compression refrigeration system with refrigerant mixtures based on HFC134a, HFC152a, HFC32, HC290, HC1270, HC600, and HC600a was done for various ratios and their results are compared with CFC12, CFC22, and HFC134a as possible alternative replacements. In spite of the HC refrigerants' highly flammable characteristics, they are used in many applications, with attention being paid to the safety of the leakage from the system, as other refrigerants in recent years are not related with any effect on the depletion of the ozone layer and increase in global warming. Theoretical results showed that all of the alternative refrigerants investigated in the analysis have a slightly lower performance coefficient (COP) than CFC12, CFC22, and HFC134a for the condensation temperature of 50 °C and evaporating temperatures ranging between − 30 °C and 10 °C. Refrigerant blends of HC290/HC600a (40/60 by wt.%) instead of CFC12 and HC290/HC1270 (20/80 by wt.%) instead of CFC22 are found to be replacement refrigerants among other alternatives in this paper as a result of the analysis. The effects of the main parameters of performance analysis such as refrigerant type, degree of subcooling, and superheating on the refrigerating effect, coefficient of performance and volumetric refrigeration capacity are also investigated for various evaporating temperatures.     

Heat transfer enhancement and pressure drop characteristics of TiO2–water nanofluid in a double-tube counter flow heat exchanger

This article reports an experimental study on the forced convective heat transfer and flow characteristics of a nanofluid consisting of water and 0.2 vol.% TiO₂ nanoparticles. The heat transfer coefficient and friction factor of the TiO₂–water nanofluid flowing in a horizontal double-tube counter flow heat exchanger under turbulent flow conditions are investigated. The Degussa P25 TiO₂ nanoparticles of about 21 nm diameter are used in the present study. The results show that the convective heat transfer coefficient of nanofluid is slightly higher than that of the base liquid by about 6–11%. The heat transfer coefficient of the nanofluid increases with an increase in the mass flow rate of the hot water and nanofluid, and increases with a decrease in the nanofluid temperature, and the temperature of the heating fluid has no significant effect on the heat transfer coefficient of the nanofluid. It is also seen that the Gnielinski equation failed to predict the heat transfer coefficient of the nanofluid. Finally, the use of the nanofluid has a little penalty in pressure drop.     

Solid-state synthesis of cubic ZnTe nanocrystals using a microwave plasma

Cubic ZnTe nanocrystals were produced from 1:1 and 1.8:1 molar ratios of Zn:Te by a 900 W microwave plasma. The phase was detected using X-ray diffraction (XRD), which are in accordance with those of the simulations, and selected area electron diffraction (SAED). Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the products were nanocrystals with different orientations, including three longitudinal optical (LO) vibrations at 205, 410 and 620 cm^? 1 and a transverse optical (TO) vibration at 166 cm^? 1. Their green emissions were detected at 562 nm (2.21 eV) using luminescence spectrophotometry.     

Transient solid-state production of nanostructured CuS flowers

CuS (hcp) with different morphologies was produced using a transient solid-state reaction by the direct flow of electricity through solids, containing 1:1 molar ratio of Cu:S powders, in a high vacuum system for different lengths of time. X-ray diffraction (XRD), selected area electron diffraction (SAED), and scanning and transmission electron microscopies (SEM and TEM) specified that the products were nanostructured CuS flowers, and nanostructured CuS composing of nanoparticles with different orientations, controlled by the length of time. Raman vibrations were detected at 474.5 cm^− 1, and photoluminescent (PL) emissions at 347.5 nm. Both the XRD and SAED patterns are in accordance with those obtained by the corresponding simulations.     

A model of energy management analysis,case study of a sugar factory in Turkey

This study presents a case study of energy management in a sugar factory in Turkey. The main idea of the study is to analyse energy consumption, the quantity of material production, and figure out a suitable energy efficiency for the case study of a sugar factory subsequently. Firstly, a material production and energy consumption audit were performed for the sugar factory. Secondly, energy efficiency was calculated from the energy data. The SPSS (Statistical Package for the Social Sciences) statistical software was used to ensure the accuracy of the data. The factory’s energy consumption was calculated as 43,590.25 toe (tons of oil equivalent) over the last year. These results were used for CUSUM (Cumulative Sum Deviation Method) graphics. This research poses the consumption of energy, cost of energy and the relationship between energy usage and material production of sugar. The unit of energy cost was 688.22 [$/toe] for the last year. This result showed that the factory decreased the unit of energy by optimisation. The results indicated that the investigated sugar factory should pay attention to the energy management issue in order to comply with the Energy Efficiency of Turkish Law and Directives.     

Transformation of cubic AgBiS2 from nanoparticles to nanostructured flowers by a microwave-refluxing method

Cubic AgBiS₂ nanoparticles and flower-like clusters were successfully synthesized by microwave refluxing of CH₃COOAg, Bi(NO₃)₃·5H₂O and thiosemicarbazide (NH₂NHCSNH₂) in ethylene glycol. The phase was detected by X-ray diffraction (XRD) and selected area electron diffraction (SAED). The SAED pattern was also in accordance with that of the simulation. Scanning and transmission electron microscopy (SEM and TEM) revealed the gradual transformation of nanoparticles into flower-like clusters by increasing microwave power. Their UV–visible absorption and photoluminescence (PL) emission were detected by spectrometry. Possible formation mechanism of nanoparticles and nanostructured flowers was also proposed according to the experimental results.