Motion synchronization in unmanned aircrafts formation control with communication delays

This paper proposes a formation control strategy for unmanned aircrafts using a virtual structure. Cross coupled sliding mode controllers are introduced to cope with uncertainties in the attitude measurement systems of the unmanned aircrafts and unmeasurable bounded external disturbances such as wind effects, and also to provide motion synchronization in the multi-agent system. This motion synchronization strategy improves the agents convergence to their desired positions, and this is useful for a multi-agent system with faulty agents.Moreover, the proposed motion synchronization strategy is not restricted to specific communication topologies, and sufficient conditions are provided to guarantee the multi-agent system stability in the presence of communication delays. Numerical simulations are presented for a team of five unmanned aircrafts to make a pentagon formation and confirm the accepted performance of the proposed control strategy.     

Magnetoelastic properties of ErMn6Sn6 intermetallic compound

The thermal expansion and magnetostriction of polycrystalline sample of the ErMn₆Sn₆ intermetallic compound with hexagonal HfFe₆Ge₆-type structure are investigated in the temperature range of 77 K to above 400 K. The thermal expansion measurement of the sample shows anomalous behavior around its T_N=340 K. The isofield curves of volume magnetostriction also reveal anomalies at paramagnetic-antiferromagnetic and antiferromagnetic-ferrimagnetic phase transitions. In the antiferromagnetic state, the transition to ferrimagnetism can be induced by an applied magnetic field. The threshold field for the metamagnetic transition H_th increases from 0.18 T at 84 K to about 1 T around 220 K, and then decreases monotonously to T_N. This behavior is well consistent with that observed earlier on magnetization curves attributed to exchange-related metamagnetic transition rather than the anisotropy-related one. Furthermore, the low H_th values suggest that the Mn-Mn coupling in ErMn₆Sn₆ is not so strong. The experimental results obtained are discussed in the framework of two-magnetic sublattice by bearing in mind the lattice parameter dependence of the interlayer Mn-Mn exchange interaction in this layered compound. From the temperature dependence of magnetostriction values and considering the magnetostriction relation of a hexagonal structure, we attempt to determine the signs of some of the magnetostriction constants for this compound.     

Determination of organic compounds in water using dispersive liquid-liquid microextraction

A new microextraction technique termed dispersive liquid-liquid microextraction (DLLME) was developed. DLLME is a very simple and rapid method for extraction and preconcentration of organic compounds from water samples. In this method, the appropriate mixture of extraction solvent (8.0 microL C2Cl4) and disperser solvent (1.00 mL acetone) are injected into the aqueous sample (5.00 mL) by syringe, rapidly. Therefore, cloudy solution is formed. In fact, it is consisted of fine particles of extraction solvent which is dispersed entirely into aqueous phase. After centrifuging, the fine particles of extraction solvent are sedimented in the bottom of the conical test tube (5.0 +/- 0.2 microL). The performance of DLLME is illustrated with the determination of polycyclic aromatic hydrocarbons (PAHs) in water samples by using gas chromatography-flame ionization detection (GC-FID). Some important parameters, such as kind of extraction and disperser solvent and volume of them, and extraction time were investigated. Under the optimum conditions the enrichment factor ranged from 603 to 1113 and the recovery ranged from 60.3 to 111.3%. The linear range was 0.02-200 microg/L (four orders of magnitude) and limit of detection was 0.007-0.030 microg/L for most of analytes. The relative standard deviations (RSDs) for 2 microg/L of PAHs in water by using internal standard were in the range 1.4-10.2% (n = 5). The recoveries of PAHs from surface water at spiking level of 5.0 microg/L were 82.0-111.0%. The ability of DLLME technique in the extraction of other organic compounds such as organochlorine pesticides, organophosphorus pesticides and substituted benzene compounds (benzene, toluene, ethyl benzene, and xylenes) from water samples were studied. The advantages of DLLME method are simplicity of operation, rapidity, low cost, high recovery, and enrichment factor.     

Determination of organophosphorus pesticides in water samples by single drop microextraction and gas chromatography-flame photometric detector

In this paper we have developed single drop microextraction (SDME) with modified 1.00 microl microsyringe, followed by gas chromatography with flame photometric detector (GC-FPD) for determination of 13 organophosphorus pesticides (OPPs) in water samples. By using a 1.00 microl microsyringe the repeatability of drop volume and injection were improved, because of using maximum volume of microsyringe and no dead volume. On the other hand, the modification of needle tip caused increasing cross section of needle tip and increasing adhesion force between needle tip and drop, thereby increasing drop stability and achieving a higher stirrer speed (up to 1700 rpm). The method used 0.9 microl of carbon tetrachloride as extractant solvent, 40 min extraction time, stirring at 1300 rpm and no salt addition. The enrichment factor of this method ranged from 540 to 830. The linear ranges were 0.01-100 microg/l (four orders of magnitude) and limits of detection were 0.001-0.005 microg/l for most of analyte. The relative standard deviation (RSD%) for 2 microg/l of OPPs in water by using internal standard was in the range 1.1-8.6% (n = 5). The recoveries of OPPs from farm water at spiking level of 1.0 microg/l were 91-104%.     

H3PW12O40催化水相介质中苯并恶嗪和喹唑啉合成（英文）简

A heteropolyacid efficiently catalyzed the cyclocondensation reaction of 2-aminobenzamide and salicylamide with aldehydes and ketones to afford good yields of benzoxazine and quinazoline ring systems in an aqueous medium. The method gives clean reactions, has simple workup procedure, and uses environment friendly conditions.     

Development of a Sensitive Methodology for the Analysis of Chlorobenzenes in Water Samples by Combination of Homogeneous Liquid‐liquid Microextraction via Flotation Assistance and Gas Chromatography‐flame Ionization Detection

In this study, a simple, rapid and efficient method, homogeneous liquid‐liquid microextraction via flotation assistance (HLLME‐FA) combined with gas chromatography – flame ionization detection (GC‐FID), for the determination of chlorobenzenes (CBs) in water samples, has been described. In this research, a special extraction cell was designed to facilitate collection of the low‐density solvent extraction. No centrifugation was required in this procedure. The water sample solution was added into the extraction cell which contained an appropriate mixture of extraction and homogeneous solvents. By using air flotation, the organic solvent was collected at the conical part of the designed cell. Parameters affecting extraction efficiency were investigated and optimized. Under the optimum conditions, the detection limits, the precisions and the linearity of the method were found in the range of 0.2 to 1.5 µg L^‐1, 5.7–9.3% (RSD, n =5) and 0.5–200 µg L^‐1, respectively.     

Synthesis of phthalazine compounds using heterogeneous base catalyst based on silica nanoparticles obtained from rice husk

Research on Chemical Intermediates - In this study, the nanoparticles of amorphous silica were easily extracted from low-cost rice husk ash. They were functionalized with 3-(chloropropyl)...     

A NEW APPROACH TO FREE VIBRATION ANALYSIS OF A BEAM WITH A BREATHING CRACK BASED ON MECHANICAL ENERGY BALANCE METHOD

In this paper, a new approach to free vibration analysis of a cracked cantilever beam is proposed. By considering the effect of opening and closing the crack during the beam vibration, it is modeled as a fatigue crack. Also, local stiffness changes at the crack location are considered to be a nonlinear amplitude-dependent function and it is assumed that during one half a cycle, the frequencies and mode shapes of the beam vary continuously with time. In addition, by using the experimental tests, it is shown that the local stiffness at the crack location varies continuously between the two extreme values corresponding to the fully closed and the fully open cases of the crack. Then, by using the mechanical energy balance the dynamic response of the cracked beam is obtained at every time instant. The results show that for a specific crack depth, by approaching the crack location to the fixed end of the beam, more reduction in the fundamental frequency occurs. Furthermore, for a specific crack location, the fundamental frequency diminishes and the nonlinearity of the system increases by increasing the crack depth. In order to validate the results, the variations of the fundamental frequency ratio against the crack location are compared with experimental results.     

Distribution of trace elements in the marine sediments along the South China Sea,Malaysia

In order to complete having data base of elemental assessment of the east coast of Peninsular Malaysia marine sediments along the South China Sea coasts, trace elements are analyzed and their distribution in marine sediments is undertaken. The present study is done parallel with pervious study on elemental assessment of heavy metals, rare earth elements and actinides in the marine sediments of the east coast of Peninsular Malaysia. Thirty surface sediment samples were collected in this area, including regions of Kelantan, Terengganu, Pahang, Rompin and Johor Baharu. Multielemental analysis was carried out by instrumental neutron activation analysis and inductively coupled plasma atomic emission spectroscopy. In both cases methodology validation was performed by certified reference material analyses. For the surface elemental distributions the enrichment factor values, average I _geo and mC _d values indicate that the trace elements of the surface sediments are uncontaminated in all sampling stations that are consistent with previous studies results of heavy metals, rare earth elements and actinides.     

Magnetoelastic properties of GdMn6Sn6 intermetallic compound

We studied the thermal expansion and magnetostriction of polycrystalline samples of GdMn₆Sn₆ intermetallic compound with hexagonal HfGe₆Fe₆-type structure in the temperature range of 77-520 K. The thermal expansion measurement of the sample shows anomalous behavior around its T_C=434 K and T_M=309 K, possibly the point of collapse-like reduction of Mn moments. In addition, the isofield curves of anisotropic and volume magnetostriction reveal anomalies around paramagnetic to ferrimagnetic phase transition. The obtained experimental results are discussed in the framework of two-magnetic sublattices by bearing in mind the lattice parameter dependence of interlayer Mn-Mn exchange interaction in this layered compound. From the temperature dependence of magnetostriction values and considering the magnetostriction relation of a hexagonal structure, we attempt to determine the signs of some of the magnetostriction constants as well as a comparison of their orders of magnitude for this compound.