Limonoids in Pummelos [Citrus grandis (L.) Osbeck]

Juice and seeds from 16 cultivars of mature pummelo fruits were analyzed for limonoid content. Pummelo juice contained an average of 18 ppm limonin and 29 ppm total limonoid glucosides. Compared to other juices, ptmnnelo contained very high concentrations of limonin and very low concentrations of limonoid glucosides. Limonin, nomilin, obacunone and trace amounts of deacetyhromilin were found in pummelo seeds. The 17–β-D-glucopyranoside derivatives (glucosides) of nomilin, nomilinic acid and obacunone were also present. Total limonoid aglycone concentration in the seeds ranged from 773 ppm to 9,900 ppm and total limonoid glucosides ranged from 130 ppm to 1,912 ppm.     

The Effective Pore Radius of Screen Wicks

The effective pore radius in screen-wick heat pipes was investigated, which is very important for the prediction of maximum heat transfer rates due to capillary limitation. An equation for the effective pore radius of the screen wicks was derived based on the model of the screen geometry. The capillary height for stainless steel and phosphor bronze screens was measured using water, ethyl alcohol, and Freon 113 as the test liquids. The effect of surface treatment (acid cleaning and oxidation) on the capillary height was also examined. From the comparison of the experimental data for water and ethyl alcohol with those for Freon 113, it was indicated that the contact angle was 24.2° for water and 16.9° for ethyl alcohol. Consequently, it was found that the effective pore radius of the screen wicks could be predicted fairly well from the expression presented in this study, and that the contact angle should be taken into consideration to evaluate the maximum capillary pressure accurately.     

A New Control Method of Suppressing the DC‐Capacitor Voltage Ripple Caused by Third‐Order Harmonic Compensation in Three‐Phase Active Power Filters

This paper proposes a new control method suitable for active power filters, which can reduce the dc capacitor voltage ripple associated with the third‐order harmonic current compensation. The proposed method superimposes a negative‐sequence fundamental current on the compensating current to cancel out the active power ripple caused by the third‐order harmonic current. As a result, the proposed method has the capability to eliminate the dc capacitor voltage ripple oscillating at double the source frequency. Experimental results obtained by a 10‐kW three‐phase diode rectifier load verify the validity of the proposed method. The proposed method exhibits a small dc capacitor voltage ripple reduced to 43% of that using the conventional method.     

Performance of Dead‐Time Compensation Methods in Three‐Phase Grid‐Connection Converters

This paper discusses the performance of compensation methods for dead‐time voltage error in voltage‐source grid‐connection pulse‐width modulation converters. The theoretical analysis in this paper reveals the relationship between the voltage error and the current ripples through the converter. The analytical results imply that the voltage error is strongly affected by the amplitude of the current ripples as well as the source power factor. This paper proposes a new compensation method which makes it possible to use two lookup tables to reduce the calculation time in the controller. The compensation characteristics are compared by using a 200‐V 5‐kW three‐phase grid‐connection converter. As a result, conventional approximation‐based compensation methods exhibit an acceptable performance in a restricted power‐factor operation range. In contrast, the turn‐off transition‐based compensation method and the proposed method have a good compensation performance all over the power factor.     

CHANGES IN CONTENT OF OCTOPINE, ACIDIC OPINES, RELATED AMINO ACIDS AND PHOSPHOARGININE IN THE ADDUCTOR MUSCLE OF THREE SPECIES OF SCALLOP DURING STORAGE

The postmortem changes of octopine (Oct), strombine (Stn), tauropine (Trn), alanopine (Aln), related amino acids and phosphoarginine (PA) in the edible adductor muscles of Chlamys nobilis, Pecten albicans and Patinopecten yessoensis during storage at 0 and 5C were examined. For this purpose, new alternative HPLC methods for the analysis of octopine and acidic opines were developed. Among opines, Oct was the major postmortem glycolytic end product of all three scallops, followed by Stn, Trn and Aln, respectively. The accumulation of Oct during storage at 0 and 5C was similar. On the contrary, almost twice as much Stn accumulated when stored at 5C compared to 0C. Trn and Aln increased to a lesser extent. Arginine and PA decreased, while glycine, taurine and alanine increased during storage.     

Microbial Biosensor System for Rapid Determination of Vitamin B6

A microbial biosensor system was based on an immobilized microorganism (Succharomyces uvarum 4288 ATCC9080) and Clark-type oxygen electrode consisting of a platinum cathode, lead anode, alkaline electrolyte, and an oxygen permeable Teflon membrane. The determination was based on the respiratory activity of the microorganism in presence of vitamin B₆. Optimum conditions were: concentration of immobilized cells on membrane: OD₆₆₀, = 0.05, temperature: 30°C. When oxygen permeable Teflon membranes (0.5 mil and 2.0 mil) were employed, relationships between vitamin B₆, (pyridoxine) and current decrease were linear in the range of 0.5 ng/mL-2.5 ng/mL and 2.5 ng/mL-12.5 ng/mL, respectively. One assay could be completed within 15 min. This system provided rapid and simple determinations of vitamin B₆ in marine products with good correlation to traditional microbial assay values.     

RAPID DETECTION OF A SMALL NUMBER OF VIABLE CELLS BY THE FLUORESCENT GLUCOSE METHOD

A fluorescent glucose, 2NBDG, was rapidly consumed by 4 different species of microorganisms: Escherichia coli, Lactobacillus acidophilus, Saccharomyces cerevisiae, and Candida tropicalis. E. coli and L. acidophilus became fluorescent enough for microscopic observation within 1 min, while S. cerevisiae and C. tropicalis became fluorescent in a longer time span. All of the 14 coliforms that were isolated from various foods consumed 2NBDG and became fluorescent within 1 min. Therefore, 2NBDG is expected to be a useful indicator of viable cells irrespective of species as long as they could assimilate glucose. This 2NBDG method is valid in counting small amount of cells, such as 10–100 cells, accurately and carefully. Also, the 2NBDG method was successfully applied to the rapid detection of a small number of E. coli in milk. The feasibility of the 2NBDG method is discussed from the viewpoint of food safety control.     

A High‐Frequency Cycloconverter Based on a Phase‐Shift Control Method

This paper proposes a new control method for a high‐frequency cycloconverter consisting of two half‐bridge inverters and a series–resonant circuit. This cycloconverter acts as an ac‐to‐ac direct power conversion circuit without any dc stage. This circuit does not require a diode bridge rectifier, and thus, can be used to reduce forward voltage drops and power losses in the diodes. A new phase‐shift control method is proposed to regulate the capacitor voltage in each half‐bridge inverter and to achieve zero‐voltage switching. The proposed phase‐shift control is theoretically discussed and is also verified by an experimental circuit consisting of superjunction power MOSFETs. As a result, the proposed high‐frequency cycloconverter exhibits a good power conversion efficiency as high as 97.7% at the rated power of 1.3 kW.     

A New PV Converter for Grid Connection Through a High‐Leg Delta Transformer Using Cooperative Control of Boost Converters and Inverters

This paper proposes a new high‐efficiency photovoltaic (PV) converter for grid connection through a high‐leg delta transformer, which is composed of a symmetrically connected boost converter and three half‐bridge inverters. One of the three half‐bridge inverters is connected to the boost converter, and the others are directly connected to the PV terminals. This circuit configuration enables to reduce the power losses in both boost converter and inverter. This paper also proposes a new cooperative control method between the symmetrically connected boost converter and inverter. The control method can reduce the average switching frequency to 75% of that in a conventional one, resulting in a great reduction in switching power loss. Experimental results show that the proposed circuit improves its European efficiency from 91.6% to 94.5%.