Low-temperature Breakdown Research Articles

Preharvest chilling reduces low temperature breakdown incidence of kiwifruit

To study the effects of preharvest chilling on low temperature breakdown incidence (LTB) of kiwifruit ( Actinidia deliciosa [A. Chev.] C.F. Liang and A.R. Ferguson), a mist evaporative cooling system was established in the orchard and the accumulation of temperatures below 10 °C in hours was recorded during fruit maturation. The fruit were harvested at three dates, and soluble solids content (SSC) and firmness were measured at harvest, while LTB incidence was determined following 24-week storage at −0.5 °C. Fruit harvested immature had a high LTB incidence, while late harvested fruit had low disorder incidence. Misted fruit of mid harvest and control fruit of the late harvest accumulated 180 h below 10 °C preharvest, and had significantly reduced LTB, while misted fruit of late harvest did not show any LTB incidence. The use of chilling time, rather than maturation time, as a basis of data analysis of harvest maturity indices (SSC and firmness) and LTB might allow the construction of charts for precise determination of harvest date and prediction of postharvest kiwifruit quality free of LTB.

Simulation of longitudinal instabilities in filamentary current flow during low-temperature impurity breakdown in semiconductors

Nonlinear semiconductor transport simulations based on the WIAS-TeSCA code are presented. Various regimes of low-temperature breakdown and current filamentation in n-GaAs are investigated using a drift-diffusion model with nonlinear generation-recombination kinetics. Nonlinear charge density waves are found in two-dimensional simulations of a point contact geometry with and without an additional perpendicular magnetic field. The numerical simulations of the nonlinear spatio-temporal dynamics are complemented by a linear stability analysis which reveals the possibility of undamped longitudinal fluctuations in the filamentary regime.

INFLUENCE OF STORAGE TEMPERATURE AND AT-HARVEST MATURITY ON INCIDENCE OF CHILL-RELATED DISORDERS IN ´HORT16A´ KIWIFRUIT

Chilling injury or low temperature breakdown and physiological pit occur later in storage and cause significant losses in GOLD kiwifruit (Actinidia chinensis 'Hortl6A'). This work investigated influence of maturity on both disorders and evaluated alternative storage options. Fruit of different maturities (described by flesh colour) were stored for 24 weeks at 1) 1.5 °C, or 2) 3 °C or 3) 3 °C for 12 weeks then 1.5 °C for 12 weeks. Physiological pit in fruit was greater after longer storage time, for fruit that were more mature (yellow) when harvested and fruit stored at 1.5 °C. Physiological pit was 30 times more likely to occur during storage at 1.5 C than during storage at 3 °C. Chilling injury in fruit was greater after longer storage time, for fruit that were greener when harvested and fruit that were stored at 1.5 °C. An extra week in storage increased the likelihood of chilling injury by nearly 20 %. The higher risk of pit in more mature fruit and chilling injury in less mature fruit narrows the optimal harvest window for fruit. Effectively managing maturity at harvest will be essential to ensuring fruit develop optimum storage potential and that fruit loss during storage is minimised.

Summer-pruning and preharvest calcium chloride sprays affect storability and low temperature breakdown incidence in kiwifruit

Shoots with an intermediate size of kiwifruit, cv. Hayward, were terminated to five leaves and long shoots were topped or left unpruned at 2 days after petal drop. Fruit on the vines were either untreated or given an additional treatment of 1% calcium chloride (CaCl2), four times during fruit development. Flesh firmness, soluble solids content (SSC) and calcium (Ca) content in the fruit pericarp, were measured in fruit harvested from small, medium and long shoots. Fruit were stored at 0 °C for up to 42 weeks. Low temperature breakdown (LTB) incidence was assessed after 5 days of ripening at 20 °C. Summer-pruning increased fruit SSC and Ca content by 0.5 and 30%, respectively, while CaCl2 sprays increased the fruit Ca content and firmness by 64 and 13 N, respectively. Fruit harvested from small, medium or long shoots had similar SSC and firmness at harvest and during storage, and Ca content at harvest. During storage, fruit receiving CaCl2 sprays, or both CaCl2 sprays and summer-pruning, softened more slowly, increasing storage life potential by 10–12 weeks, compared with untreated fruit. Summer-pruning did not affect fruit potential storability. Lower LTB incidence occurred in fruit from summer-pruning, preharvest CaCl2 spray treatments, or when both treatments were applied. Less LTB occurred in fruit from short shoots compared with those harvested from medium and long shoots.

The influence of pre-storage delayed cooling on quality and disorder incidence in ‘Honeycrisp’ apple fruit

Abstract The influence of a pre-storage, 7-day, 20 °C warming period on post-harvest apple ( Malus xdomestica Borkh.) fruit quality and disorder expression—soft scald and low temperature breakdown in particular, were investigated in ‘Honeycrisp’ fruit grown in the Annapolis Valley of Nova Scotia. The apples from 7-year old trees were harvested from three commercial sites on Sept 30, 2002 (early) and Oct 10, 2002 (late), after which, half of the fruit was immediately cooled to 5 °C (control), while the other half was held for 7 days at 20 °C (delayed cooling treatment). Both the control and delay cooled apples were then stored at either 3 or 5 °C in controlled atmosphere (CA) (2.5 kPa O 2 ; 1–1.5 kPa CO 2 ) or refrigerated air (RA) storage for 4 and 6 months. Fruit quality measurements and disorder incidence were recorded following storage removal and a 7-day shelf-life at 20 °C. Delayed cooling had no effect on fruit firmness, soluble solids (%), titratable acidity, epidermal greasiness, senescent breakdown, and bitter pit (the incidence of these latter disorders was low), while moisture loss from the delay cooled fruit ranged from 1.2 to 1.3% following the 7-day treatment. Delayed cooling strongly suppressed the development of the storage disorders soft scald and low temperature breakdown, which in the control fruit reached upwards to 30% of the sample. No CA- or RA-related differences in these disorders were observed in the fruit receiving the pre-storage delayed cooling treatment. Storage rot was not influenced by delayed cooling and was present in upwards to 32% of the fruit from the late-harvested apples after 6 months of storage. In regions where soft scald and low temperature breakdown are serious postharvest problems, it appears that a delayed cooling period prior to storage will help minimize economic loss.

Electron mobility measurement inn−GaAsat low-temperature impurity breakdown

Electron mobility measurement in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>n</mml:mi><mml:mo>−</mml:mo><mml:mi mathvariant="normal">GaAs</mml:mi></mml:math>at low-temperature impurity breakdown

Magnetoresistance effect of a current density filament in n-GaAs

Magnetoresistance of a current density filament formed by the low-temperature impurity breakdown has been measured in high-purity n-GaAs samples at 4.2 K, under magnetic fields of less than 260 mT. The resistivity of the bendable filament was measured as a function of the magnetic field intensity; it shows a good agreement with the calculated results based on ionized impurity scattering theory. For a relatively low applied electric bias, the magnetic field induces an instability of the filament, whose mechanism is discussed in detail.

The effects of storage conditions on the keeping quality of ‘Gala’ apples

SummaryExperiments were conducted over three years to determine the optimum storage conditions for ‘Gala’ apples. Fruit was stored in a range of carbon dioxide and oxygen concentrations at 1.5 and 3.58°C and in air at 0 and 1.58°C. Firmness during storage was retained most effectively at high carbon dioxide concentrations and low oxygen concentrations. During a subsequent 7 d simulated marketing period in air at 20°C, softening was greater in samples which had been stored in oxygen concentrations above 1% than in samples from 1% oxygen. The content of flavour volatiles declined rapidly after storage for ten weeks, but the scores for acceptability given by a sensory panel declined only slowly during storage and were positively correlated with firmness. Storage in air at 08C was limited to ten weeks, after which fruit was unacceptably soft. Firmness was maintained adequately at 1.58C in <1% CO2 + 1% O2 and 5% CO2 + 1% O2 , but the development of scald and low-temperature breakdown limited the storage life of the variety to 21 and 27 weeks, respectively. The incidence of disorders was not related to the starch-iodine staining pattern at harvest.

Discontinuities and Hysteresis in the I–V Characteristics of n-GaAs at Low Temperatures

We present experimental investigations of current filamentation in n-GaAs films in the regime of low-temperature impurity breakdown. Using a laser-scanning microscope, we were able to reconstruct current filaments in biasing regions of multistability. It is shown that discontinuities and hysteresis frequently observed in current-voltage characteristics are due to the interaction of filaments with material imperfections. In particular filaments remain in energetically unfavourable configurations when squeezed or pinned by defects.

Cell wall properties of kiwifruit affected by low temperature breakdown

Low temperature breakdown (LTB) is a physiological disorder that can affect kiwifruit (Actinidia deliciosa cv Hayward) and some selections of Actinidia chinensis fruit after several months of cold storage. One of its symptoms manifests as the ‘grainy’ appearance of the outer pericarp, followed by water-soaking associated with extreme softening of the fruit. Observation by light microscopy and SEM suggested that the ‘grainy’ appearance of LTB-affected kiwifruit was associated with the presence of gas bubbles, occurring in some cells. Bulk porosity of the cell wall, determined using polyethylene glycol (PEG) of different molecular mass, decreased with increasing severity of the symptoms. Cell wall analysis revealed that the amount of cell wall material (CWM) was 30% higher in ‘grainy’ tissue than in unaffected tissue, and that galactosyl content in the CWM of outer pericarp tissue was 70% higher in affected compared to unaffected tissue. The same trends in LTB-affected tissue were observed in two selections of Actinidia chinensis. Since tissues were excised from fruit of the same firmness, differences reported here are related to the development of LTB.

Direct experimental observation of the Hall angle in the low-temperature breakdown regime ofn−GaAs

Using the technique of photoluminescence imaging during electrical transport in crossed electric and magnetic fields, the rotation of the current flow direction has been observed. The rotation angle is identically the Hall angle. As a model system, a thin n-type GaAs layer in the regime of low-temperature impurity breakdown has been used, generating filamentary current patterns. The measurement of the Hall angle allows one to determine the mobility inside current filaments.

Computer-simulation investigation of nonlinear transport dynamics in a compensated semiconductor during low-temperature electric breakdown

The possibility of chaotic behavior of the current in a partially compensated semiconductor during low-temperature electrical breakdown is explored by computer simulation. The influence of random fluctuations in the parameters or the variables of the mathematical model, as well as the effect of some weak periodic disturbances of the current density in the semiconductor, are discussed. As a result, various pictures of chaotic oscillations of the current are obtained, including a transition to a chaotic regime through period doubling, which is characteristic of the Feigenbaum scenario.

Visualization of lateral movement of current-filaments in n-GaAs

In the regime of low-temperature impurity breakdown the influence of a magnetic field on current filaments yields complex voltage oscillations. With a new optical technique the spatio-temporal dynamics of filaments involving nucleation, lateral movements and extinction have been visualized corresponding to a certain type of electrical oscillation.

Disorders in `Cortland' Apple Fruit Are Induced by Storage at 0 °C in Controlled Atmosphere

The effects of low temperature in controlled-atmosphere storage on five strains of `Cortland' apples (Malus ×domestica Borkh.) grown in Nova Scotia were investigated. The apples were held in either standard controlled-atmosphere (2.5 kPa O2 and 4.5 kPa CO2) or low-oxygen (1.5 kPa O2 and 1.5 kPa CO2) storage at 0 or 3 °C for 4 and 8 months. The results indicated that `Cortland' apples are sensitive to low temperature, but not to low oxygen or high CO2. Low temperature (0 vs. 3 °C) caused an increase in low-temperature breakdown, core browning, and vascular breakdown, while having no significant effect on fruit firmness, soluble solids concentration (SSC), titratable acidity, loss of mass, or superficial scald development. Low oxygen (1.5 vs. 2.5 kPa) or high CO2 (4.5 vs. 1.5 kPa) in the storage atmosphere had no significant effect on fruit firmness, SSC, titratable acidity, loss of mass, or the incidence of storage disorders.

Prediction of storage quality of ‘Cox’s Orange Pippin’ apples from nutritional and meteorological data using multiple regression models selected by cross validation

SummaryAn experiment was carried out over a six year period to relate the storage quality of ‘Cox’s Orange Pippin’ apples to the mineral composition of leaves, fruitlets and fruits and to the climatic conditions during development. The apples were sampled from 24 orchards over a wide geographic area. The extent to which physiological disorders, bitter pit and low temperature breakdown (LTB), and quality attributes, greenness and firmness, of stored fruit could be predicted either before or at harvest was determined. For each response variable, a short-list of up to 12 potential explanatory variables was selected from an initial set of up to 54 possible explanatory variables, using stepwise regression techniques. Predictive models were generated by selecting variables from the initial short-list using a cross validation technique. The average incidence of bitter pit in controlled atmosphere (CA) storage at 1.2% O2 (<1% CO2) was 4% compared with 12% for similar samples stored in air. Predictive models accounted for up to 67% of the variance in bitter pit in air-stored fruit but the percentage was lower (39%) for fruit stored in CA. The concentrations of calcium and potassium in fruit were particularly important for predicting bitter pit in air-stored fruit but less so for fruit stored in CA where more explanatory variables were required for prediction. Fifty one per cent of the variance of LTB in fruit stored in CA was accounted for by a nine-variable model incorporating three climatic variables. A simple three-variable model (leaf nitrogen concentration, harvest firmness and fruit dry weight) accounted for 67% of the variance in ex-store firmness and the addition of other nutritional and climatic variables increased the percentage variance accounted for to 76%. Seventy-one per cent of the variance in the greenness of fruit after CA storage was accounted for by a six-variable model. The possible physiological significance of the explanatory variables in each model is discussed.

Current filaments in the impact ionization breakdown of p-Germanium forced by geometric boundary conditions

Samples of weakly doped p-Germanium with well defined tip-shaped contact geometries were electrically driven into the regime of low-temperature impact ionization breakdown. The contact geometry enables a controlled growth of high conducting current filaments. Contact distances between 30 and 109 μm were used. A minimal filament diameter of about 13 μm is estimated from the measurements by a simple growth model based on the assumption of geometrically forced boundary conditions. Furthermore, numerical values were extracted for the conductivity inside a filament region. These results are slightly below the values estimated under the assumption of total ionization.

Mineralogy of the sulphide deposits at Sulitjelma, northern Norway

The pyritic VMS deposits at Sulitjelma, northern Norway have been regionally metamorphosed at amphibolite facies during the Caledonide Orogen. The deposits contain a wide diversity of sulphide, sulphosalt and related minerals, which are systematically discussed with reference to their occurrence, paragenesis and mineral chemistry. Most of these minerals are, however, rare to absent within the massive deposits, which are dominantly composed of pyrite with subordinate chalcopyrite, sphalerite and pyrrhotite. Galena, arsenopyrite, cubanite, molybdenite, stannite and tetrahedrite occur in minor amounts. Syn-metamorphic mobilisation has, however, resulted in the redistribution of a range of elements, including Cu, Pb, Sb, As, Ni and Au. These elements have been reconcentrated into mobilised segregations, where they have crystallised, under retrograde conditions, into a range of discrete phases. Ore mobilisation, which took place along tectonically-controlled pathways is, however, of a highly localised nature, with a considerable range in mineral textures and parageneses observed in different samples. Typical associations within these mobilisates include a range of CuPbSb and CuPbAs sulphosalts, including bournonite, meneghinite, seligmannite and jordanite, breithauptite, nisbite, costibite, arsenopyrite and gudmundite. Co-existing galena is characterised by elevated concentrations of Ag, Bi and Se. Argentian tetrahedrite (9–17 wt% Ag), the chief Ag-carrier in the deposits, as well as other Ag-bearing phases, including pyrargyrite, hessite and empressite, are strongly enriched in the mobilisates. Gold, as electrum (50–75 wt% Au), and more rarely as aurostibite, is also relatively enriched in the mobilisate samples over those from more massive parts of the deposits. A further range of minerals, including native antimony, native arsenic, allargentum, dyscrasite, argentite, mckinstryite (?), jalpaite (?) and native silver occur as low temperature breakdown products of earlier-formed minerals. Preserved textures do not contradict a model involving more than a one phase of mobilisation during the metamorphic evolution.

Dynamics of nascent current filaments in low-temperature impurity breakdown.

We present two-dimensional simulations showing the spatiotemporal dynamics of the formation of current filaments in n-type GaAs films in the regime of impurity impact ionization breakdown. From the spatial distribution of carrier densities, electron temperature, current density, and electric field for nascent and for fully developed filaments, we find a three-stage scenario for breakdown: (i) front creation and propagation from the cathode, (ii) stagnation in the phase of a rudimentary filament, (iii) filament growth. Our model combines semiclassical rate equations with microscopic transport parameters, which are obtained from Monte Carlo simulations. \textcopyright{} 1996 The American Physical Society.

Low temperature breakdown and current filamentation in n-type GaAs with homogeneous and partially ordered Si doping

We present an experimental and theoretical study of the breakdown caused by impurity impact ionization in n-GaAs. The observed difference in the electric field strengths for the breakdown threshold and the bistability regime between homogeneous and partially ordered doping with Si donors is explained and confirmed by numerical simulations, applying a weighted ensemble Monte Carlo method in the case of the inhomogeneous problem. Furthermore, conditions for the appearance of hysteresis loops are experimentally investigated as a function of load resistance and sample width. The transitions between different branches of the current-voltage characteristics can be understood as switching between homogeneous states and current filaments in good agreement with theoretical predictions on the basis of a simple generation-recombination model.

Type-I intermittency in semiconductor breakdown: An experimental confirmation.

Spontaneous oscillations developing during low-temperature impact ionization breakdown in extrinsic germanium are looked at with respect to characteristic features of the type-I intermittent route to chaos. We have examined the scaling behavior of the mean laminar phase length upon varying the transverse magnetic field applied. Taking into account the distribution of the phase lengths, the return map of the oscillation maxima, and the prevailing reinjection probability, we present experimental evidence that type-I intermittency takes place in a spatially extended macroscopic system with self-generated dynamics.