Shelf life extension of fresh fruit and vegetables by chitosan treatment

Among alternatives that are currently under investigation to replace the use of synthetic fungicides to control postharvest diseases in fresh produce and to extend their shelf life, chitosan application has shown promising disease control, at both preharvest and postharvest stages. Chitosan shows a dual mode of action, on the pathogen and on the plant, as it reduces the growth of decay-causing fungi and foodborne pathogens and induces resistance responses in the host tissues. Chitosan coating forms a semipermeable film on the surface of fruit and vegetables, thereby delaying the rate of respiration, decreasing weight loss, maintaining the overall quality, and prolonging the shelf life. Moreover, the coating can provide a substrate for incorporation of other functional food additives, such as minerals, vitamins, or other drugs or nutraceutical compounds that can be used to enhance the beneficial properties of fresh commodities, or in some cases the antimicrobial activity of chitosan. Chitosan coating has been approved as GRAS substance by USFDA, and its application is safe for the consumer and the environment. This review summarizes the most relevant and recent knowledge in the application of chitosan in postharvest disease control and maintenance of overall fruit and vegetable quality during postharvest storage.     

Time-domain solution of field-excited multiconductor transmissionline equations

Analytical solution of lossless field-excited multiconductor transmission lines is presented. The equivalent circuit of a multiconductor transmission line with distributed sources is reduced to a simple lumped parameter circuit with independent voltage sources at both the ends of the transmission line. The transient source waveforms are analytically estimated for exponential time dependence of the external field, as EMP, ESD, and lightning. The method is suitable for a direct implementation in computer-aided circuit analysis codes and enables a very fast analysis for any load condition. Some numerical results are presented for single conductor and multiconductor lines excited by all EMP plane-wave field     

A molecular dynamics study of lead-bismuth-silicate glasses

We present the results of molecular dynamics (MD) simulations of the structure of ternary lead-bismuth-silicate glasses of compositions xPbO(0.3-x)Bi_1.50.7SiO₂, x=0.06, 0.15, 0.24, and their totally reduced forms, i.e. xPb(0.3-x)Bi0.7SiO₂, x=0.06, 0.15, 0.24 systems. The simulations have been performed in the microcanonical (NVE) ensemble, using two-body interaction potentials. The results can be summarized as follows. With increasing PbO content in unreduced xPbO(0.3-x)Bi_1.50.7SiO₂ glasses, the Pb-O and Bi-O first pair distribution function (PDF) peaks become sharper, and the fraction of strained 2 and 3 member Si-O-Si-O- rings decreases significantly. In the case of reduced xPb(0.3-x)Bi0.7SiO₂ glasses, similarly as in reduced binary lead-silicate and bismuth-silicate glasses, a strong tendency to agglomeration of neutral atoms occurs. The metallic phase is composed of Pb-Bi alloy. The agglomeration tendency increases with increasing Pb content     

Electromagnetic interference from digital signal transmission onpower line carrier channels

A procedure is presented to evaluate the electromagnetic field generated by a digital transmission system on multiconductor power-line carrier channels. The vertical component of the electric field and the horizontal component of the magnetic field are defined by approximate formulaes of varying accuracy, depending on the frequency and the distance from phase conductors. Field sources are the currents traveling along the line, which are evaluated by means of an accurate simulation model of the transmission system and a rigorous wave propagation algorithm. Frequency spectra and lateral profiles of the field components are computed for single-phase and two-phase couplings on a horizontal power line. Digital channel capacity is shown to increase as the pulse repetition interval T decreases. However, if T increases, the harmonic content of the input signal code increases and, consequently, electromagnetic pollution rises for a given carrier channel. It is concluded that the EMI (electromagnetic interference) level is an important constraint which must be taken into account when choosing T and, more generally, in the design of the digital transmission system     

Capacitance matrix calculation of a wire conductor line: a new FEMapproach

An original finite-element approach is presented to calculate the capacitance matrix of a uniform multiconductor wire line. The examined two-dimensional (2-D) domain is discretized by nodal-based triangular elements where the Laplace equation is solved. A new procedure is developed to take into account the presence of the wires, which are assumed to be located in the vertex nodes of the FEM mesh. Through the proposed procedure, the physical dimensions of the wire cross sections are considered modifying the terms of the local stiffness matrix in the finite elements surrounding the wires. A further modification of the local FEM matrices allows one to consider the logarithmic variation of the electrical potential around the wires. The procedure is efficient from a numerical point of view since it avoids the fine discretization of the nonconductive region surrounding the wire while achieving a good numerical accuracy. Numerical examples are given and compared with the analytical solutions for canonical configurations, including wires with a dielectric cover     

Detection and localization of defects in shielded cables by time-domain measurements with UWB pulse injection and clean algorithm postprocessing

An experimental procedure to detect and localize defects in shielded cables is presented. First, time-domain measurements are carried out by injecting a short rise time pulse in the input section of the shielded cable. Then, the clean algorithm is applied to the measurement results to identify possible damages in the cable line. The localization of the cable section with defects is finally obtained in a very simple way due to the adopted method of measurement in time domain using a ultrawide-band pulser with a very fast rise time. The proposed method is validated by detecting and localizing known defects purposely introduced in test cables.     

Prediction of Temperature Increase in Human Eyes Due to RF Sources

A numerical study is proposed to investigate the effects of different RF sources on the specific absorption rate (SAR) and maximum temperature increase in the human eye at different frequencies. In particular, a new model of the human head is presented and compared with an anatomical model of the visible human. The high resolution (0.5 mm) of the proposed model allows to consider more eye tissues than previous studies distinguishing the sclera from the retina and choroid. New values of blood perfusion and metabolic rate of these tissues are derived. A plane-wave field is considered as far-field exposure, while realistic models of mobile phone and dipole antennas are used as primary sources for near-field exposure. The obtained results show that the distributions of the SAR and temperature increase depend on the frequency, position, and kind of sources. Finally, attention is paid to the maximum temperature increase in the lens for the SAR values prescribed by the Commission on Non-Ionizing Radiation Protection. To this aim, a scaling approach is proposed, and significant values of temperature increase are found (about C for general public exposure and about 1.5 degC for occupational exposure) for the most critical cases of near-field exposures.     

Field analysis of penetrable conductive shields by thefinite-difference time-domain method with impedance network boundaryconditions (INBCs)

Impedance network boundary conditions (INBCs) are implemented in the finite-difference time-domain (FDTD) method to analyze the electromagnetic field around penetrable shield structures. The shield region is eliminated from the computational domain and the INBCs are applied on the new boundary surfaces, i.e., shield surfaces, to take into account the field discontinuity produced by the shield. The INBCs represent an important extension of the well-known surface impedance boundary conditions (SIBCs) since the INBCs model accurately the coupling of the electromagnetic fields through penetrable shields and lead to a significant reduction of the number of the FDTD unknowns. The INBC expressions are given analytically in both frequency and time domains, and the INBC implementation in a FDTD code is discussed. The proposed INBC-FDTD method is numerically efficient because the resulting convolution integrals are recursively solved. Furthermore, approximate time-constant INBCs are proposed which are valid for many practical applications. The analysis of transient electromagnetic fields around penetrable conductive shields in simple test configurations are presented and compared with the analytical solutions     

Current-field and conductivity-field characteristics of thinlayers: the predictions of the Bottger-Bryksin model

Phonon-assisted hopping of electrons between spatially distinct locations is one of the basic transport mechanisms in solids. In the present contribution compare the current-field, and differential conductivity-field characteristics, calculated within the Bottger-Bryksin model applied to thin layers with spatially nonuniform distributions S(x) of hopping centers. In particular, we consider exponential and bi-exponential spatial distributions of centers, i.e. S(x) ∝ exp(-x/D), and S(x) -∝[exp(-x/D) + exp(-(L x)/D)], where L is the layer thickness, and D the distribution parameter. Although the model allows the calculations for both on-diagonal (energetic) and off-diagonal (positional) disorder, here we discuss only the case of discrete energy level of hopping centers. We show that the Bottger-Bryksin model predicts a strong 'tapping' effect in the case, where the surface densities of hopping centers at both contacts differ significantly. In such cases wide field intervals of negative differential conductivity are expected