3,034 research outputs found
Microspore embryogenesis in barley: anther pre-treatment stimulates plant defence gene expression
Microspore embryogenesis (ME) is a process in which the gametophytic pollen programme of the microspore is reorientated towards a new embryo sporophytic programme. This process requires a stress treatment, usually performed in the anther or isolated microspores for several days. Despite the universal use of stress to induce ME, very few studies have addressed the physiological processes that occur in the anther during this step. To further understand the processes triggered by stress treatment, we followed the response of anthers by measuring the expression of stress-related genes in two barley (Hordeum vulgare L.) cultivars differing in their ME response. Genes encoding enzymes involved in oxidative stress (glutathione-S-transferase, GST; oxalate oxidase, OxO), in the synthesis of jasmonic acid (13-lipoxygenase, Lox; allene oxide cyclase, AOC; allene oxide synthase, AOS) and in the phenylpropanoid pathway (phenylalanine ammonia lyase, PAL), as well as those encoding PR proteins (Barwin, chitinase 2b, Chit 2b; glucanase, Gluc; basic pathogenesis-related protein 1, PR1; pathogenesis-related protein 10, PR10) were up-regulated in whole anthers upon stress treatment, indicating that anther perceives stress and reacts by triggering general plant defence mechanisms. In particular, both OxO and Chit 2b genes are good markers of anther reactivity owing to their high level of induction during the stress treatment. The effect of copper sulphate appeared to limit the expression of defence-related genes, which may be correlated with its positive effect on the yield of microspor
Can Andean Potato be agronomically biofortified with iron and zinc fertilizers?
This field research shows that application of Zn fertilizers or Zn-enriched NPK fertilizers offers a prompt solution to increasing the Zn concentration in Andean potato tubers, and represents a useful complementary approach to on-going breeding programs. The diploid Chaucha cultivars that showed high tuber Zn concentrations in the absence of Zn fertilization also showed correspondingly higher Zn concentration in tubers following foliar and soil applied Zn. High levels of Zn in potato tubers may significantly improve the diets of Zn-deficient populations with high intake of potato and contribute to better nutritio
Molecular semiconductors and the Ioffe–Regel criterion: A terahertz study on band transport in DBTTT
Terahertz electromodulation spectroscopy provides insight into the physics of charge carrier transport in molecular semiconductors. The work focuses on thin-film devices of dibenzothiopheno[6,5-b:6′,5′-f]thieno[3,2-b]thiophene. Frequency-resolved data show a Drude-like response of the hole gas in the accumulation region. The temperature dependence of the mobilities follows a T1/2 power law. This indicates that the thermal mean free path of the charge carriers is restricted by disorder. Only a fraction of approximately 5% of the injected carriers fulfills the Ioffe–Regel criterion and participates in band transport.info:eu-repo/semantics/publishe
Conductivity in organic semiconductors hybridized with the vacuum field
Organic semiconductors have generated considerable interest for their
potential for creating inexpensive and flexible devices easily processed on a
large scale [1-11]. However technological applications are currently limited by
the low mobility of the charge carriers associated with the disorder in these
materials [5-8]. Much effort over the past decades has therefore been focused
on optimizing the organisation of the material or the devices to improve
carrier mobility. Here we take a radically different path to solving this
problem, namely by injecting carriers into states that are hybridized to the
vacuum electromagnetic field. These are coherent states that can extend over as
many as 10^5 molecules and should thereby favour conductivity in such
materials. To test this idea, organic semiconductors were strongly coupled to
the vacuum electromagnetic field on plasmonic structures to form polaritonic
states with large Rabi splittings ca. 0.7 eV. Conductivity experiments show
that indeed the current does increase by an order of magnitude at resonance in
the coupled state, reflecting mostly a change in field-effect mobility as
revealed when the structure is gated in a transistor configuration. A
theoretical quantum model is presented that confirms the delocalization of the
wave-functions of the hybridized states and the consequences on the
conductivity. While this is a proof-of-principle study, in practice
conductivity mediated by light-matter hybridized states is easy to implement
and we therefore expect that it will be used to improve organic devices. More
broadly our findings illustrate the potential of engineering the vacuum
electromagnetic environment to modify and to improve properties of materials.Comment: 16 pages, 13 figure
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Direct iminization of PEEK
Semi-crystalline poly(ether ketone)s are important high-temperature engineering thermoplastics, but are difficult to characterize at the molecular level because of their insolubility in conventional organic solvents. Here we report that polymers of this type, including PEEK, react cleanly at high temperatures with low-volatility aralkyl amines to afford stable, noncrystalline poly(ether-imine)s, which are readily soluble in solvents such as chloroform, THF and DMF and so characterizable by conventional size-exclusion chromatography
Detection of sub-shot-noise spatial correlation in high-gain parametric down-conversion
Using a 1GW-1ps pump laser pulse in high gain parametric down-conversion
allows us to detect sub-shot-noise spatial quantum correlation with up to one
hundred photoelectrons per mode, by means of a high efficiency CCD. The
statistics is performed in single-shot over independent spatial replica of the
system. The paper highlights the evidence of quantum correlation between
symmetrical signal and idler spatial areas in the far field, in the high gain
regime. In accordance with the predictions of numerical calculations the
observed transition from the quantum to the classical regime is interpreted as
a consequence of the narrowing of the down-converted beams in the very high
gain regime.Comment: 4,2 pages, 4 figure
Efficient unidirectional nanoslit couplers for surface plasmons
Plasmonics is based on surface plasmon polariton (SPP) modes which can be
laterally confined below the diffraction limit, thereby enabling ultracompact
optical components. In order to exploit this potential, the fundamental
bottleneck of poor light-SPP coupling must be overcome. In established SPP
sources (using prism, grating} or nanodefect coupling) incident light is a
source of noise for the SPP, unless the illumination occurs away from the
region of interest, increasing the system size and weakening the SPP intensity.
Back-side illumination of subwavelength apertures in optically thick metal
films eliminates this problem but does not ensure a unique propagation
direction for the SPP. We propose a novel back-side slit-illumination method
based on drilling a periodic array of indentations at one side of the slit. We
demonstrate that the SPP running in the array direction can be suppressed, and
the one propagating in the opposite direction enhanced, providing localized
unidirectional SPP launching.Comment: 13 pages, 4 figure
Discovering Crystal Forms of the Novel Molecular Semiconductor OEG-BTBT
This work is focused on a polymorphic and crystallographic study of a novel p-type organic semiconductor 2,7-bis(2-(2-methoxyethoxy)ethoxy)benzo[b]benzo[4,5]thieno[2,3-d]thiophene (OEG-BTBT). The well-known BTBT core is functionalized by eight-atom-long oligoethylene glycol side chains. Our results demonstrate the discovery of three crystal forms of the OEG-BTBT molecule, namely, Form I, Form II, and Form III, in different experimental conditions. Crystal structures of Form I and Form III are reported, while only unit cell indexing of Form II could be determined. Form I and Form II are enantiotropically related, and Form II is stable at temperatures higher than 127 °C. The kinetics of transformation to Form II was studied by the Avrami equation. Form III is a solvate crystal form which is rarely observed in the field of organic electronics, and upon release of dichloromethane, it converts to Form I. Furthermore, we studied the mechanical properties of the Form I crystals, which exhibit plastic bending upon applying mechanical stress in the [100] direction. This distinct mechanical behavior is rationalized by the slip layer topology, the intermolecular interactions energies from energy frameworks, and the Hirshfeld surface analysis
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