Assessment of alternative herbicides for residential sewer root treatment and their effects on downstream treatment plant nitrification.

The conveyance of wastewater in sewer pipes can be severely limited by the growth of plant roots, which can be controlled with herbicides. However, adding herbicides in sewer lines may affect downstream biological wastewater treatment processes. The effects of three herbicides (Dithiopyr, Penoxsulam, and Triclopyr) on the mortality of cottonwood tree roots and on downstream biological nitrification were determined. The results showed that Triclopyr achieved the highest root mortality (96%) followed by Penoxsulam (77%) and Dithiopyr (75%). At concentrations used at the point of application in sewer pipes, all herbicides caused nitrification inhibition and reduction in organic carbon removal in activated sludge. However, no inhibition was observed at the more diluted concentrations approximately equal to levels that may reach the wastewater treatment facility. Overall, Triclopyr appears to be the best performing herbicide with the highest root kill.

Publisher's Note: Enhanced Tunneling Electroresistance in Ferroelectric Tunnel Junctions due to the Reversible Metallization of the Barrier [Phys. Rev. Lett. 116, 197602 (2016)].

This corrects the article DOI: 10.1103/PhysRevLett.116.197602.

Enhanced Tunneling Electroresistance in Ferroelectric Tunnel Junctions due to the Reversible Metallization of the Barrier.

Realizing a large tunneling electroresistance (TER) effect is crucial for device application of ferroelectric tunnel junctions (FTJs). FTJs are typically composed of a thin ferroelectric layer sandwiched by two metallic electrodes, where TER generally results from the dependence of the effective tunneling barrier height on the ferroelectric polarization. Since the resistance depends exponentially not only on barrier height but also on barrier width, TER is expected to be greatly enhanced when one of the electrodes is a semiconductor where the depletion region near the interface can be controlled via ferroelectric polarization. To explore this possibility, we perform studies of SrRuO_{3}/BaTiO_{3}/n-SrTiO_{3} FTJs, where n-SrTiO_{3} is an electron doped SrTiO_{3} electrode, using first-principles density functional theory. Our studies reveal that, in addition to modulation of the depletion region in n-SrTiO_{3}, the BaTiO_{3} barrier layer becomes conducting near the interface for polarization pointing into n-SrTiO_{3}, leading to dramatic enhancement of TER. The effect is controlled by the band alignment between the semiconductor and the ferroelectric insulator and opens the way for experimental realization of enhanced TER in FTJs through the choice of a semiconducting electrode and interface engineering.

Giant Enhancement of Magnetic Anisotropy in Ultrathin Manganite Films via Nanoscale 1D Periodic Depth Modulation.

The relatively low magnetocrystalline anisotropy (MCA) in strongly correlated manganites (La,Sr)MnO_{3} has been a major hurdle for implementing them in spintronic applications. Here we report an unusual, giant enhancement of in-plane MCA in 6 nm La_{0.67}Sr_{0.33}MnO_{3} (LSMO) films grown on (001) SrTiO_{3} substrates when the top 2 nm is patterned into periodic stripes of 100 or 200 nm width. Planar Hall effect measurements reveal an emergent uniaxial anisotropy superimposed on one of the original biaxial easy axes for unpatterned LSMO along ⟨110⟩ directions, with a 50-fold enhanced anisotropy energy density of 5.6×10^{6} erg/cm^{3} within the nanostripes, comparable to the value for cobalt. The magnitude and direction of the uniaxial anisotropy exclude shape anisotropy and the step edge effect as its origin. High resolution transmission electron microscopy studies reveal a nonequilibrium strain distribution and drastic suppression in the c-axis lattice constant within the nanostructures, which is the driving mechanism for the enhanced uniaxial MCA, as suggested by first-principles density functional calculations.

Mechanical Tuning of LaAlO3/SrTiO3 Interface Conductivity.

In recent years, complex-oxide heterostructures and their interfaces have become the focus of significant research activity, primarily driven by the discovery of emerging states and functionalities that open up opportunities for the development of new oxide-based nanoelectronic devices. The highly conductive state at the interface between insulators LaAlO3 and SrTiO3 is a prime example of such emergent functionality, with potential application in high electron density transistors. In this report, we demonstrate a new paradigm for voltage-free tuning of LaAlO3/SrTiO3 (LAO/STO) interface conductivity, which involves the mechanical gating of interface conductance through stress exerted by the tip of a scanning probe microscope. The mechanical control of channel conductivity and the long retention time of the induced resistance states enable transistor functionality with zero gate voltage.

Electric control of spin injection into a ferroelectric semiconductor.

Electric-field control of spin-dependent properties has become one of the most attractive phenomena in modern materials research due to the promise of new device functionalities. One of the paradigms in this approach is to electrically toggle the spin polarization of carriers injected into a semiconductor using ferroelectric polarization as a control parameter. Using first-principles density-functional calculations, we explore the effect of ferroelectric polarization of electron-doped BaTiO3 (n-BaTiO3) on the spin-polarized transmission across the SrRuO3/n-BaTiO3(001) interface. Our study reveals that, in this system, the interface transmission is negatively spin polarized and that ferroelectric polarization reversal leads to a change in the transport spin polarization from -65% to -98%. Analytical model calculations demonstrate that this is a general effect for ferromagnetic-metal-ferroelectric-semiconductor systems and, furthermore, that ferroelectric modulation can even reverse the sign of spin polarization. The predicted effect provides a nonvolatile mechanism to electrically control spin injection in semiconductor-based spintronics devices.

Enhanced tunnelling electroresistance effect due to a ferroelectrically induced phase transition at a magnetic complex oxide interface.

The range of recently discovered phenomena in complex oxide heterostructures, made possible owing to advances in fabrication techniques, promise new functionalities and device concepts. One issue that has received attention is the bistable electrical modulation of conductivity in ferroelectric tunnel junctions (FTJs) in response to a ferroelectric polarization of the tunnelling barrier, a phenomenon known as the tunnelling electroresistance (TER) effect. Ferroelectric tunnel junctions with ferromagnetic electrodes allow ferroelectric control of the tunnelling spin polarization through the magnetoelectric coupling at the ferromagnet/ferroelectric interface. Here we demonstrate a significant enhancement of TER due to a ferroelectrically induced phase transition at a magnetic complex oxide interface. Ferroelectric tunnel junctions consisting of BaTiO3 tunnelling barriers and La(0.7)Sr(0.3)MnO3 electrodes exhibit a TER enhanced by up to ~10,000% by a nanometre-thick La(0.5)Ca(0.5)MnO3 interlayer inserted at one of the interfaces. The observed phenomenon originates from the metal-to-insulator phase transition in La(0.5)Ca(0.5)MnO3, driven by the modulation of carrier density through ferroelectric polarization switching. Electrical, ferroelectric and magnetoresistive measurements combined with first-principles calculations provide evidence for a magnetoelectric origin of the enhanced TER, and indicate the presence of defect-mediated conduction in the FTJs. The effect is robust and may serve as a viable route for electronic and spintronic applications.

Multiferroic materials based on organic transition-metal molecular nanowires.

We report on the density functional theory aided design of a variety of organic ferroelectric and multiferroic materials by functionalizing crystallized transition-metal molecular sandwich nanowires with chemical groups such as -F, -Cl, -CN, -NO(2), ═O, and -OH. Such functionalized polar wires exhibit molecular reorientation in response to an electric field. Ferroelectric polarizations as large as 23.0 µC/cm(2) are predicted in crystals based on fully hydroxylized sandwich nanowires. Furthermore, we find that organic nanowires formed by sandwiching transition-metal atoms in croconic and rhodizonic acids, dihydroxybenzoquinone, dichloro-dihydroxy-p-benzoquinone, or benzene decorated by -COOH groups exhibit ordered magnetic moments, leading to a multiferroic organometallic crystal. When crystallized through hydrogen bonds, the microscopic molecular reorientation translates into a switchable polarization through proton transfer. A giant interface magnetoelectric response that is orders of magnitude greater than previously reported for conventional oxide heterostructure interfaces is predicted.

Ferroelectric instability under screened Coulomb interactions.

We explore the effect of charge carrier doping on ferroelectricity using density functional calculations and phenomenological modeling. By considering a prototypical ferroelectric material, BaTiO(3), we demonstrate that ferroelectric displacements are sustained up to the critical concentration of 0.11 electron per unit cell volume. This result is consistent with experimental observations and reveals that the ferroelectric phase and conductivity can coexist. Our investigations show that the ferroelectric instability requires only a short-range portion of the Coulomb force with an interaction range of the order of the lattice constant. These results provide a new insight into the origin of ferroelectricity in displacive ferroelectrics and open opportunities for using doped ferroelectrics in novel electronic devices.

Organic multiferroic tunnel junctions with ferroelectric poly(vinylidene fluoride) barriers.

Organic materials are promising for applications in spintronics due to their long spin-relaxation times in addition to their chemical flexibility and relatively low production costs. Most studies of organic materials for spintronics focus on nonpolar dielectrics or semiconductors, serving as passive elements in spin transport devices. Here, we demonstrate that employing organic ferroelectrics, such as poly(vinylidene fluoride) (PVDF), as barriers in magnetic tunnel junctions (MTJs) allows new functionality in controlling the tunneling spin polarization via the ferroelectric polarization of the barrier. Using first-principles methods based on density functional theory we investigate the spin-resolved conductance of Co/PVDF/Co and Co/PVDF/Fe/Co MTJs as model systems. We show that these tunnel junctions exhibit multiple resistance states associated with different magnetization configurations of the electrodes and ferroelectric polarization orientations of the barrier. Our results indicate that organic ferroelectrics may open a new and promising route in organic spintronics with implications for low-power electronics and nonvolatile data storage.

Highly spin-polarized conducting state at the interface between nonmagnetic band insulators: LaAlO3/FeS2 (001).

First-principles density functional calculations demonstrate that a spin-polarized two-dimensional conducting state can be realized at the interface between two nonmagnetic band insulators. The (001) surface of the diamagnetic insulator FeS(2) (pyrite) supports a localized surface state deriving from Fe d orbitals near the conduction band minimum. The deposition of a few unit cells of the polar perovskite oxide LaAlO(3) leads to electron transfer into these surface bands, thereby creating a conducting interface. The occupation of these narrow bands leads to an exchange splitting between the spin subbands, yielding a highly spin-polarized conducting state distinct from the rest of the nonmagnetic, insulating bulk. Such an interface presents intriguing possibilities for spintronics applications.

Giant tunneling electroresistance effect driven by an electrically controlled spin valve at a complex oxide interface.

A giant tunneling electroresistance effect may be achieved in a ferroelectric tunnel junction by exploiting the magnetoelectric effect at the interface between the ferroelectric barrier and a magnetic La(1-x)Sr(x)MnO3 electrode. Using first-principles density-functional theory we demonstrate that a few magnetic monolayers of La(1-x)Sr(x)MnO3 near the interface act, in response to ferroelectric polarization reversal, as an atomic-scale spin valve by filtering spin-dependent current. This produces more than an order of magnitude change in conductance, and thus constitutes a giant resistive switching effect.

Suppression of octahedral tilts and associated changes in electronic properties at epitaxial oxide heterostructure interfaces.

Epitaxial oxide interfaces with broken translational symmetry have emerged as a central paradigm behind the novel behaviors of oxide superlattices. Here, we use scanning transmission electron microscopy to demonstrate a direct, quantitative unit-cell-by-unit-cell mapping of lattice parameters and oxygen octahedral rotations across the BiFeO3-La0.7 Sr0.3 MnO3 interface to elucidate how the change of crystal symmetry is accommodated. Combined with low-loss electron energy loss spectroscopy imaging, we demonstrate a mesoscopic antiferrodistortive phase transition near the interface in BiFeO3 and elucidate associated changes in electronic properties in a thin layer directly adjacent to the interface.

Abnormal cytokine expression in Sézary and adult T-cell leukemia cells correlates with the functional diversity between these T-cell malignancies.

The Sézary syndrome (SzS) and adult T-cell leukemia (ATL) are malignant proliferations of mature T-lymphocytes that possess distinct functions. Sézary cells function as helper cells, whereas ATL cells are usually suppressor effectors. Although phenotypically similar (CD4+/CD7-/CD8-), these functional differences between the T-cell lymphoproliferative disorders suggest different patterns of cytokine expression. We wished to delineate the cytokine mechanisms potentially underlying the diverse functional characteristics of SzS and ATL. Therefore, we analyzed the expression of interleukins (IL) 2, 4, and 5, gamma-interferon, and transforming growth factor beta 1 in the highly purified leukemic T-cells from 5 SzS and 5 ATL patients. Decreased mRNA and protein levels of IL-2, gamma-interferon, and IL-5 were detected in mitogen-stimulated ATL and SzS cells when compared to similarly cultured normal CD4+ cells. In contrast, IL-4 production was markedly up-regulated in the leukemic cells of 4/5 SzS patients as compared to ATL and normal controls. Finally, fresh ATL cells secreted higher levels of transforming growth factor beta 1 into the culture medium than the malignant T-cells from SzS patients. Collectively these results suggest that, similar to the murine CD4-expressing T-cell subsets Th1 and Th2, different cytokine profiles exist in a human population of CD4+ T-cells. Moreover, the distinct patterns of IL-4 and transforming growth factor beta 1 expression by SzS and ATL cells, respectively, are most consistent with the functional differences (i.e., helper versus suppressor activity) between these T-cell malignancies and thus may play important roles in the pathogenesis of the paraneoplastic features associated with these two leukemias.

Magnetic gating of a 2D topological insulator.

Deterministic control of transport properties through manipulation of spin states is one of the paradigms of spintronics. Topological insulators offer a new playground for exploring interesting spin-dependent phenomena. Here, we consider a ferromagnetic 'gate' representing a magnetic adatom coupled to the topologically protected edge state of a two-dimensional (2D) topological insulator to modulate the electron transmission of the edge state. Due to the locked spin and wave vector of the transport electrons the transmission across the magnetic gate depends on the mutual orientation of the adatom magnetic moment and the current. If the Fermi energy matches an exchange-split bound state of the adatom, the electron transmission can be blocked due to the full back scattering of the incident wave. This antiresonance behavior is controlled by the adatom magnetic moment orientation so that the transmission of the edge state can be changed from 1 to 0. Expanding this consideration to a ferromagnetic gate representing a 1D chain of atoms shows a possibility to control the spin-dependent current of a strip of a 2D topological insulator by magnetization orientation of the ferromagnetic gate.

Complex band structure of topological insulator Bi2Se3.

Topological insulators are very interesting from a fundamental point of view, and their unique properties may be useful for electronic and spintronic device applications. From the point of view of applications it is important to understand the decay behavior of carriers injected in the band gap of the topological insulator, which is determined by its complex band structure (CBS). Using first-principles calculations, we investigate the dispersion and symmetry of the complex bands of Bi2Se3 family of three-dimensional topological insulators. We compare the CBS of a band insulator and a topological insulator and follow the CBS evolution in both when the spin-orbit interaction is turned on. We find significant differences in the CBS linked to the topological band structure. In particular, our results demonstrate that the evanescent states in Bi2Se3 are non-trivially complex, i.e. contain both the real and imaginary contributions. This explains quantitatively the oscillatory behavior of the band gap obtained from Bi2Se3 (0 0 0 1) slab calculations.

Gas chromatographic method for the analysis of allelopathic natural products in rye (Secale cereale L.).

Accurate and reproducible methods for the analysis of plant allelochemicals are a requirement for the study of chemical interactions between plants. This paper describes a method for sample preparation and quantitative analysis of the allelopathic chemical content of rye (Secale cereale L.) using gas chromatography (GC). Sample preparation consists of extraction of freeze-dried rye vegetative tissue with aqueous ethanol followed by partitioning of the allelochemicals into ethyl acetate, evaporation, and derivatization using the trimethylsilylating reagent N-methyl-N-trimethylsilyltrifluoroacetamide. GC analysis of the silylated mixture was performed using flame ionization detection. This method permits analysis of all known rye allelopathic agents including 2,4-dihydroxy-1,4-benzoxazin-3-one, its corresponding glucoside, 2-benzoxazolinone, beta-hydroxybutyric acid, and beta-phenyllactic acid. Identities of all compounds were confirmed by GC/MS analysis.

Local currents in a 2D topological insulator.

Symmetry protected edge states in 2D topological insulators are interesting both from the fundamental point of view as well as from the point of view of potential applications in nanoelectronics as perfectly conducting 1D channels and functional elements of circuits. Here using a simple tight-binding model and the Landauer-Büttiker formalism we explore local current distributions in a 2D topological insulator focusing on effects of non-magnetic impurities and vacancies as well as finite size effects. For an isolated edge state, we show that the local conductance decays into the bulk in an oscillatory fashion as explained by the complex band structure of the bulk topological insulator. We demonstrate that although the net conductance of the edge state is topologically protected, impurity scattering leads to intricate local current patterns. In the case of vacancies we observe vortex currents of certain chirality, originating from the scattering of current-carrying electrons into states localized at the edges of hollow regions. For finite size strips of a topological insulator we predict the formation of an oscillatory band gap in the spectrum of the edge states, the emergence of Friedel oscillations caused by an open channel for backscattering from an impurity and antiresonances in conductance when the Fermi energy matches the energy of the localized state created by an impurity.

Interferon-gamma upregulates MUC1 expression in haematopoietic and epithelial cancer cell lines, an effect associated with MUC1 mRNA induction.

Epithelial mucin-1 (MUC1) is an important target antigen that it is overexpressed in both epithelial and haematological cancers including multiple myeloma (MM) and some lymphomas and leukaemias. MUC1 has adhesive and immunosuppressive properties, which may promote cancer progression. These studies evaluated the effect of IFNs on MUC1 expression, since these agents are widely used in clinical cancer therapy. MUC1 and interferon (IFN) receptor expression were measured by radioligand binding. Changes in MUC1 mRNA levels in response to IFN-gamma were assessed by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). IFN-gamma was found to be a more potent inducer of MUC1 expression than IFN-alpha. 125I-IFN binding studies indicated that both IFN receptors were expressed in most of the cell lines. With IFN-gamma treatment, there was upregulation of MUC1 mRNA. IFN-gamma has a more consistent and more potent effect upon MUC1 induction than IFN-alpha. The ability to upregulate MUC1 across a broad range of cancer types by a clinically available cytokine, IFN-gamma, has important implications for enhancing immunotherapeutic approaches targeting MUC1.

Human B lymphocytes express the p75 component of the interleukin 2 receptor.

The nature of the interleukin 2 (IL-2) receptor on purified human B lymphocytes was examined. Both normal and malignant cells showed evidence of a 70-75,000 mol. wt (p75) IL-2 binding molecule as assessed by 125I-labeled IL-2 binding and receptor cross-linking. On normal, Tac-negative B lymphocytes the estimated number of p75 binding sites was 1100 per cell and the dissociation constant (Kd) was 1.7 nM. Consistent with this, cross-linking experiments demonstrated the presence of an IL-2 binding molecule of 70-75,000 mol. wt. Purified B cells from patients with hairy cell leukemia and chronic lymphocytic leukemia (CLL) also expressed the p75 IL-2 binding molecule. In the HCL samples, a small number of high-affinity IL-2 binding sites were detected (27-90) while the majority of binding sites (2100-10,800) were typical of low-affinity p55 Tac binding. IL-2 added to the purified normal and CLL B lymphocytes led to the induction of p55 Tac expression and the generation of high-affinity IL-2 receptors. This response to IL-2 was equivalent to the response observed when normal B lymphocytes were stimulated by Staphylococcus aureus Cowan I.