Pole-assignment problem for discrete-time linear periodic systems

This paper considers the pole-assignment problem for discrete-time linear periodic systems through the use of linear periodic state-variable feedback control. It is shown that if the N-periodic system with m inputs and n states is completely reachable then the problem can be reduced to the pole-assignment problem for a discrete-time linear invariant system with Nm inputs and n states.     

ACOUSTIC IMPULSE RESPONSE FOR MEASURING THE FIRMNESS OF MANDARIN DURING STORAGE

The objective of this research was to evaluate the ability of acoustic impulse response for monitoring the mandarin firmness change during storage. The dominant resonant frequency, stiffness coefficient (SC) and elasticity coefficient (EC) decrease with storage time. A good correlation was established between the acoustic parameters (SC and EC) and fruit compression force, and the correlation coefficients were 0.88 and 0.92, respectively. Acoustic impulse response gives a good indication of firmness change for mandarin during storage. The change of EC was more prominent (greatest), and hence it can be a better index of mandarin firmness. The nondestructive acoustic test might replace conventional destructive test for mandarin to determine fruit firmness and expected shelf life.     

Field and Poynting vectors of homogeneous waves in uniaxial and absorbing dielectric media

The propagation of a homogeneous plane wave in uniaxial and absorbing dielectric media is described in detail. Complete expressions for electric displacement field, electric field, magnetic field and Poynting vector are derived using a new formalism that simplifies the interpretation of polarization. These expressions are analysed and verified in some particular situations. Whilst absorption is directly determined by the absorption coeffcient k, the field geometry depends exclusively on the absorption index X for given ordinary and extraordinary refractive indices. When ordinary and extraordinary absorption indices are equal, the field geometry coincides with the field geometry in a transparent medium with the same refractive index as the absorbing medium.     

Micropropagation of <i>Prosopis chilensis</i> (Mol.) Stuntz from young and mature plants

Prosopis chilensis (Mol.) Stuntz (Algarrobo de Chile) is an important native tree species that can be grown in arid and semiarid regions for wood and forage production and environmental protection. Developing a simple and reliable in vitro protocol for cloning it would enable to improve it genetically. Explants of P.chilensis were taken from 4 months-old plants grown in the greenhouse or from adult trees grown in a natural environment. Nodal segments 1 – 2 cm long containing an axillary bud were selected from elongating shoots. These cuttings were aseptically cultured on two agar-solid basal media, MS or BTMm, and treated with 0.05 mg L^-1 BA and 3 mg L^-1 of either IAA, IBA or NAA. Sucrose (3% w/v) was used as carbon source. The percentage of sprouted cuttings and whole plant regeneration as well as its shoot and root length were recorded. Number, length and dry weight of shoots and roots were also measured. Rooting was successful with cuttings taken from young or adult plants, but explants from young plants showed a better response. Culturing in BTMm resulted in significantly greater shoot and root biomass than culturing in MS. Moreover, this response was higher in young explants when IBA was used as growth regulator. This paper reports a simple and effective method to micropropagate P. chilensis from young and adult plants.     

Viability of microencapsulated Bifidobacterium animalis ssp. lactis BB12 in kefir during refrigerated storage

The viability of free and immobilized cells of Bifidobacterium animalis ssp. lactis BB12 incorporated into kefir was studied for 28 days during refrigerated storage. The immobilized bifidobacteria were added directly to previously prepared kefir. Titratable acidity, pH, ethanol, fat, protein and lactose were evaluated in the kefir with bifidobacteria after the storage. The survival of the free and microencapsulated bifidobacteria was evaluated during the storage period and in simulated gastric juice. The pH of kefirs ranged from 4.3 to 4.6. Encapsulation improved significantly the survival of bifidobacteria during exposure to nisin, during the storage period and in simulated gastric juice.     

IMAGE SEGMENTATION USING A MODIFIED SPLIT AND MERGE TECHNIQUE

In this paper, a reformulation of the processes that composed the split and merge technique is proposed. A recursive split process is done first; then, after the merge process, a segmentation of the image is obtained. This is possible because the merging is implemented like a growth process, so the grouping has been eliminated. The use of a complete quadtree helps to achieve the reformulation. The determination of the region uniformity in each process is carried out with a different predicate, because of the different nature of the two processes. Experiments on a blocks world image and an industrial parts image are included to show the result of applying the algorithm.