Exploring the phase diagram of the two-impurity Kondo problem

A system of two exchange-coupled Kondo impurities in a magnetic field gives rise to a rich phase space hosting a multitude of correlated phenomena. Magnetic atoms on surfaces probed through scanning tunnelling microscopy provide an excellent platform to investigate coupled impurities, but typical high Kondo temperatures prevent field-dependent studies from being performed, rendering large parts of the phase space inaccessible. We present an integral study of pairs of Co atoms on insulating Cu2N/Cu(100), which each have a Kondo temperature of only 2.6 K. In order to cover the different regions of the phase space, the pairs are designed to have interaction strengths similar to the Kondo temperature. By applying a sufficiently strong magnetic field, we are able to access a new phase in which the two coupled impurities are simultaneously screened. Comparison of differential conductance spectra taken on the atoms to simulated curves, calculated using a third order transport model, allows us to independently determine the degree of Kondo screening in each phase.Comment: paper: 14 pages, 4 figures; supplementary: 3 pages, 1 figure, 1 tabl

Influence of cold storage time on the softening prediction in Spring Bright nectarines

With Time-resolved Reflectance Spectroscopy (TRS) the maturity of nectarines at harvest can be assessed by measuring the absorption coefficient at 670 nm (µa 670) in the fruit flesh. A kinetic model has been developed linking the optical properties as measured by TRS with the models of µa 670 and firmness decay in shelf-life at 20°C, making the prediction of the softening time for individual fruit possible. In order to study the influence of cold storage time prior to shelf life on the softening prediction, 540 (year 2003) and 870 (year 2004) ‘Spring Bright’ nectarines were measured at harvest with TRS; then fruit were put in shelf life after various periods of cold storage at 0°C (4 and 10 d, year 2003; 6, 13 and 20 days, year 2004). During the 5-day period of shelf life at 20°C, fruit were analysed for firmness by pressure test after 30, 48, 54, 72, 78, 96, 102 and 120h in 2003 and after 36, 43, 62, 87, 108 and 135h in 2004. For each year and cold storage time, the parameters of the logistic model of softening as a function of µa 670 at harvest were computed. The cold storage up to 13 days did not significantly influence the estimates of the softening rate constant (kf), of the maximum firmness at minus infinite time (Fmax) and of parameter alpha (a) in both years, whereas parameter beta (ß) in 2003 significantly decreased from -1.867 at day 4 to -2.237 at day 10. The further 7 days of cold storage in 2004 significantly affected kf, which decreased from 0.00084 at days 6 and 13 to 0.00069 at day 20, and ß which increased from -2.395 at day 6 to -2.053 at day 20. Our results indicate that the cold storage time significantly influences the softening prediction of nectarines as the longer the cold storage, the lower the softening rat

TRS-measurements as a nondestructive method assessing stage of maturity and ripening in plum (Prunus domestica L.)

n plum fruit with dark red or blue blush colour covering the whole fruit, the change in ground colour from green to yellow during maturation and ripening is masked. Hence, the maturity stage is difficult to judge. Time-resolved reflectance spectroscopy (TRS) has been used as a nondestructive method to assess changes in important internal quality factors in ‘Jubileum’ plums (Prunus domestica L.). Absorption coefficients (µa) and scattering coefficients (µs) were measured at both 670 and 758 nm during 5 days of storage. The changes in soluble solids content, titratable acidity and firmness were as expected. No change in soluble solids content was observed, while the plums became less acid and softer during storage. The TRS-measurements of plums indicated that TRS could give interesting information on internal quality factors in plums as the absorption at 670 nm was closely related to firmness, TA and TSS at the time of picking. Absorption at 758 nm was more closely related to the quality parameters after storage. The study did not indicate that scattering could be used in assessing maturity stage in plum

Assessing the Harvest Maturity of Brazilian Mangoes

No clear criterion exists to determine the optimum time to harvest mango. Some empirical relations are used to assess maturity, such as shoulder development. Moreover, as a result of the typical growing conditions in tropical climates, a huge variation in maturity and ripeness exists, seriously hampering the export of fruit in the global chain. The consequence for consumers in western countries is that sometimes mangoes are overripe at the retailer, or have to be kept for several days, even weeks, to reach the edible state, provided they do not rot in the meantime. To ensure an edible quality, the chlorophyll content in the fruit flesh, measured at harvest by Time-resolved Reflectance Spectroscopy (TRS), could be used as a maturity criterion for mango fruit. Commercially grown fruit were harvested in Brazil and transported to Italy by plane. Fruits were measured using TRS at 630 nm for absorption coefficient (µa) and skin colour. The development of µa was followed on 60 fruits during 15 days of storage at 20°C. The remainders of fruit were used to measure firmness destructively. Absorption coefficient decreased during shelf life according to a logistic pattern, as expected for colour development. Taking the variation between the individual fruit into account, 72% of the variation was accounted for. Nevertheless, µa assessed at harvest could be converted into a biological shift factor (BSF), as an expression of the maturity at harvest of each individual fruit. This biological shift factor explained about 70% of the variation in firmness development in individual fruit. These preliminary results indicate that TRS methodology coupled with BSF theory could be useful in assessing maturity at harvest and assuring acceptable eating quality of mango

Sensory profiles of various stored fruit species are affected by maturity class assessed by time-resolved reflectance spectroscopy at harvest

The absorption coefficient measured at harvest at 670 nm (μa670) by timeresolved reflectance spectroscopy (TRS) is a non-destructive maturity index used to evaluate the biological age of fruit, i.e., the fruit maturity stage. The μa670 was successfully used to classify nectarine, apple and mango fruit into maturity classes each one having distinctive ripening behaviors. Aiming at studying the influence of TRS maturity class assessed at harvest on the sensory profiles of various fruit species after storage, 'Jonagored' apples, 'Abbé Fétel' pears, 'Morsiani 90' nectarines and 'Spring Belle' peaches were measured at harvest by TRS at 670 nm, ranked on the basis of decreasing μa670 (increasing maturity) and classified as less (LeM), medium and more (MoM) mature. Then fruit were randomized into batches of 30 fruits, each one corresponding to a storage atmosphere (apples: CA, NA; pears: CA, NA, DCA) or to a storage temperature (peaches, nectarines: 0, 4°C). After storage, fruit were put in shelf life at 20°C to reach the ripening degree for consumption. Sensory analyses (QDA profiles) were carried out on LeM and MoM fruit using a panel of 10 assessors. Our results indicate that, for all the species, besides the influence of storage conditions, there was also a great influence of TRS maturity classification at harvest. MoM apples and pears developed physiological disorders such as mealiness and graininess when stored in NA, whereas showed well balanced sensory characteristics when stored in CA and DCA, becoming after storage soft, juicy, sweet, but sour enough. MoM nectarines stored both at 0 and 4°C became woolly, while the LeM ones stored at 0°C developed the best sensory characteristics. MoM peaches stored at 0°C showed the best sensory profile and the LeM ones stored at 4°C the worst. So TRS maturity classification at harvest can give indications on the best storage conditions in order to obtain fruit with sensory characteristics than can satisfy the consumer

Modeling mango ripening during shelf life based on pulp color nondestructively measured by time-resolved reflectance spectroscopy

Non-destructive techniques could help mango growers to pick fruit at the proper maturity degree and to monitor fruit quality during storage and marketing to satisfy the consumer expectations. The absorption coefficient non-destructively measured at 540 nm (μa540) by time-resolved reflectance spectroscopy (TRS) was shown to be a maturity index for mango fruit and was highly correlated with pulp color parameters and carotenoids content. The aim of this work was to model μa540 using the biological shift factor theory to verify if μa540 is able to assess the maturity degree of individual mango fruit and then to use μa540 to model pulp color in order to relate μa540 to an important index of mango ripening. Mango fruit (Mangifera indica L. cv Tommy Atkins) at commercial maturity for ship and air transport maturities, were measured by TRS, ranked according to decreasing μa540 (decreasing maturity), randomized into six batches per transport maturity and analyzed for μa540 and pulp color parameters after 0, 1, 2, 5, 6 and 7 days of shelf life at 20 °C. The μa540 as a function of biological shift factor increased during ripening following a logistic/exponential model (R2adj=99%) with a faster rate in less mature fruit than in more mature ones. The changes in pulp color during mango ripening depended on fruit maturity (i.e., μa540) and on time of shelf life at 20 °C. By converting the μa540 into the biological shift factor it was possible to model the increasing trend of a*, b*, C*, and IY and the decreasing trend of L* and h° during the shelf life period explaining 91.2–99.8% of the variation and to differentiate mango fruit according to their biological age. Similarly to μa540, color changes occurred earlier in more mature fruit and later in less mature ones with the same pattern in time. There is a synchronization between changes of μa540 and changes of a*, b*, C* and yellowness during ripening in mango fruit which allows to use μa540 to sort fruit according to their maturity degree and then to optimize fruit management along the supply chain

Optical Absorption and Scattering Phenomena in 'Jubileum' Plums in Relation to Their Colour Properties

Absorption and scattering of laser light pulse passing through the fruit determine among others, the optical properties of the product. Efforts have been made in the recent past to utilize innovative techniques such as time-resolved reflectance spectroscopy (TRS) to study the quality aspects of different fruit such as nectarines. These optical properties have been well related to firmness, sugars, acids and other quality attributes. TRS measurements were performed on ‘Jubileum’ plums at two different wavelengths: 670 nm and 758 nm. The fruit were harvested in Norway and brought to Italy under protected conditions. After sorting the fruit by size, TRS measurements were made and the fruit were randomized for different examinations of quality aspects. It was observed that the absorption coefficient (µa) increased for both wavelengths as ripening progressed towards the melting stage of the fruit. The µa values at 670 nm were higher than those at 758 nm. The higher rate in the µa was distinguishable from the third day onwards as the fruit ripened. Similarly, it was interesting to note that the internal colour measured after destructing the fruit related well with the TRS absorption coefficient (µa), i.e., a decrease in the CIE L* (towards darker region) and b* (towards blue) value along with an increase in a* (towards red) from third day of storag

A Hybrid Screen-Printed Strip for Enhanced Electroanalysis towards Lead and Cadmium in Multi-Matrices

Although heavy metals represent a major treat for ecosystem and human health, reference methods for their monitoring are characterized by time-consuming procedures, skilled personel and sophisticated equipment (e.g. ICP-MS, AAS). The development of portable solutions is required, particularly improving interventions and reducing complexity. To this regards, an electrochemical strip for the determination of lead and cadmium in clinical, environmental and food matrices have been developed. The Bismuth film-based flexible device has been optimized and it has been able to detect cadmium and lead, respectively, down to the detection limit of 1.3 and 2 ppb. The use of Whatman No.1 chromatographic paper has allowed to improve the sensitivity towards the detection of heavy metals, because of the porosity that allowed to pre-concentrate species. This led to an improvement in the sensitivity, with a detection limit of 0.3 and 0.5 ppb, respectively, to cadmium and lead, and offers the possibility to tune the sensitivity according to needs, e.g., improving the number of pre-concentration steps. Subsequently, the application of the electrochemical sensor in drinking water, mussel and blood serum was evaluated, demonstrating how these hybrid polyester-paper electrochemical strips can significantly lower the time and costs for on-site measurements, through analytical methods of simple use. The accuracy has been evaluated by comparison with ICP-MS measurements, giving satisfactory results