From a single-band metal to a high-temperature superconductor via two thermal phase transitions

The nature of the pseudogap phase of cuprate high-temperature superconductors is a major unsolved problem in condensed matter physics. We studied the commencement of the pseudogap state at temperature T* using three different techniques (angle-resolved photoemission spectroscopy, polar Kerr effect, and time-resolved reflectivity) on the same optimally doped Bi2201 crystals. We observed the coincident, abrupt onset at T* of a particle-hole asymmetric antinodal gap in the electronic spectrum, a Kerr rotation in the reflected light polarization, and a change in the ultrafast relaxational dynamics, consistent with a phase transition. Upon further cooling, spectroscopic signatures of superconductivity begin to grow close to the superconducting transition temperature (T(c)), entangled in an energy-momentum-dependent manner with the preexisting pseudogap features, ushering in a ground state with coexisting orders.     

Steam treatment to prevent carrot decay during storage

Organically grown carrots (Daucus carota L.) have a relatively short storage and shelf life, mainly because chemical measures cannot be implemented to control plant pathogens. Laboratory experiments demonstrated that steam treatments substantially reduced decay of stored organically grown carrots. Prior to being packaged, winter carrots were exposed to 3 s of steam. After 60 days of storage at 0.5°C plus an additional week at shelf conditions (20°C), 2% of the carrots were decayed, as opposed to 23% in the nontreated control. When carrot was inoculated with the fungi Alternaria alternata, [(Fr. : Fr.) Keissler] A. radicina (Meier) and Sclerotinia sclerotiorum [(Lib.) De Bary], percentages of decay, after similar periods of storage and shelf life, were 5% for steam-treated carrot and 65% for the nontreated control. In semi-commercial experiments carrots were treated with steam during the sorting process, and similar results were obtained. Higher decay was found in spring-grown carrots because of the presence of the bacterium Erwinia carotovora.sub. sp. carotovora     

Tracking Cooper pairs in a cuprate superconductor by ultrafast angle-resolved photoemission

In high-temperature superconductivity, the process that leads to the formation of Cooper pairs, the fundamental charge carriers in any superconductor, remains mysterious. We used a femtosecond laser pump pulse to perturb superconducting Bi(2)Sr(2)CaCu(2)O(8+δ) and studied subsequent dynamics using time- and angle-resolved photoemission and infrared reflectivity probes. Gap and quasiparticle population dynamics revealed marked dependencies on both excitation density and crystal momentum. Close to the d-wave nodes, the superconducting gap was sensitive to the pump intensity, and Cooper pairs recombined slowly. Far from the nodes, pumping affected the gap only weakly, and recombination processes were faster. These results demonstrate a new window into the dynamical processes that govern quasiparticle recombination and gap formation in cuprates.     

Inhibition of Tomato Root Growth in Culture by aVerticillium Dahliae Phytotoxin

To assess the relationship betweenVerticilliun dahliae toxin and the stunting effect in V.dahliae-infected plants, an assay was developed based on the inhibition of elongation of cultured tomato roots. The toxin inhibited growth of roots and development of secondary roots in disease-susceptible plants, tomato cv. ’Hosen-Eilon’(veve) and eggplant, whereas root growth was enhanced in tomato cv. ’VF-134’, which carries theVe gene for resistance, and in a non-host plant, onion. The toxin also inhibited the incorporation of [¹⁴C]-glutamic acid and [¹⁴C]-uridine into TCA-precipitable material in susceptible but not in resistant tomato roots. Cells from toxin-treated susceptible roots were smaller than those from resistant roots, suggesting that the toxin impeded cell growth rather than cell division. Since toxin-induced stunting cannot be detected using leaf bioassays, we suggest that the root inhibition assay can be used as a reliable tool for Verticillium disease tolerance screening studies with theV. dahliae toxin as probe.     

Using the Tabor Atomizer System to maintain weight and firmness in stored potato tubers

A new fogger — the Tabor Atomizer System — features unique atomizers, based on compressed air and water. The droplets produced have a very small mass (less than 10m,) and behave like a dry cloud, producing 96%–98% relative humidity (RH) without depositing free water on the tubers. After 6 months of storage at 10 C, with 96%–98% RH applied with the Tabor Atomizer System (room A), 92%–94% applied with a spin-disk humidifier (room B), and 82%–86% with no added humidity (room C), the weight losses for stored potatoes were 2%, 7%, and 12%, respectively. The firmness of the tubers expressed as newtons (N) required to penetrate the tubers before storage and after 6 months in room A, B, or C was 76, 74, 68, or 63 N, respectively.     

Using HPP (hydrogen peroxide plus) to inhibit potato sprouting during storage

Potatoes (Solanum tuberosum L.) samples, cv. Desiree, were treated for sprout control and stored at 10 ± 1 C for 6 months. Those treated four times with HPP (hydrogen peroxide plus), applied with the “Tabor Atomizing System”, had a 0% rate of sprouting. Those treated with CIPC (chloro-isopropyl N-phenyl carbamate) also had no sprouting, while the nontreated control had 84%. A single treatment with HPP or CIPC resulted, after 6 months of storage at 10 ± 1, in sprouting rates of 61 and 58%, respectively, vs. 87% in the untreated control.     

Type C virus from cell cultures of chemically induced rat hepatomas

Type C RNA viruses are present in cell cultures from transplantable and primary hepatomas induced by aromatic amine carcinogens. Virus yield was markedly enhanced by treating the cells with bromodeoxyuridine. Preparations of rat hepatoma-associated virus obtained from cultures treated with this compound were deficient in DNA polymerase activity.     

All-optical nonlinearities in organics

Recognition that organic solids possess some of the largest all-optical nonlinearities of all known materials has resulted in an interdisciplinary effort directed at both the basic understanding and exploitation of these effects. Parallel efforts on ionrganic semiconductors have already reached a mature stage whereby the origin of the effects, together with the prospects for device applications, are well known and appreciated. In this article, a unified picture of nonlinear optical phenomena in both classes of materials is presented. The specific implications for organic-based optical devices are discussed.     

Combining physical, chemical and biological methods for synergistic control of postharvest diseases: A case study of Black Root Rot of carrot

Combining different control methods can improve control efficacy, increase the spectrum of controlled pathogens and reduce the possibility of resistance development. To be successful, however, the different methods need to be compatible: the first treatment should not have any deleterious effect on the succeeding one; preferably, it should contribute to its efficacy. In the last few years, carrot growers in Israel have begun to brush carrots before storage to remove the outer peel of the root. In the present study we show that this practice enhances the appearance of Black Root Rot during storage, a postharvest disease caused by the fungus Thielaviopsis basicola. The chemical fungicide iprodione is usually applied before storage to reduce the development of postharvest diseases. We evaluated the efficacy of combining physical, low-residue chemical and biological control agents as an alternative to the conventional chemical control approach. A technology for the precise application of steam and combined application with stabilized hydrogen peroxide (Tsunami^® 100) or a yeast commercial product (Shemer™) were tested. Used alone, both the steam and Tsunami were highly effective at reducing disease decay but were phytotoxic to the roots. Application of combined treatments of sublethal steam followed by a sublethal dosage of Tsunami or Shemer improved efficacy and disease control by 80 and 86%, respectively. These combinations showed a synergistic effect as compared to each of the treatments alone. The same pattern, effecting up to 54% disease control, was observed with the non-compatible combination of applying Tsunami first, washing it off with water and then applying Shemer. Thus disease-control agents can potentially be used for a short period, then washed off, if needed, and efficiently followed by application of a biological control agent. The biological pathway and mode of action are still under investigation but to the best of our knowledge, this is the first study to mathematically demonstrate synergistic effects of sublethal treatments applied sequentially to control postharvest disease as a potential method to reduce the use of chemicals in fruit and vegetables.     

Diffusion of nonequilibrium quasi-particles in a cuprate superconductor

We report a transport study of nonequilibrium quasi-particles in a high-transition-temperature cuprate superconductor using the transient grating technique. Low-intensity laser excitation (at a photon energy of 1.5 electron volts) was used to introduce a spatially periodic density of quasi-particles into a high-quality untwinned single crystal of YBa2Cu3O6.5. Probing the evolution of the initial density through space and time yielded the quasi-particle diffusion coefficient and the inelastic and elastic scattering rates. The technique reported here is potentially applicable to precision measurements of quasi-particle dynamics not only in cuprate superconductors but in other electronic systems as well.