| 1. |
- Hugosson, Håkan Wilhelm, et al.
(författare)
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Surface energies and work functions of the transition metal carbides
- 2004
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 557:03-jan, s. 243-254
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Tidskriftsartikel (refereegranskat)abstract
- We have performed an ab initio study of the surface energies, surface electronic structures and work functions for the (10 0) surface of the, existent and hypothetical, cubic 3d (Sc-Cu), 4d (Zr-Ag) and 5d (La-Au) transition metal carbides. The calculated surface energies have been compared to predictions using a so-called bond-cutting model and a model based on the so-called bonding energies. The absolute values and rough trends of the surface energies are fairly well predicted within the simple bond-cutting model, as compared to fully self-consistent calculations, while both trends and absolute values are well reproduced within the bonding energy model. The electronic structure (densities of states) of the transition metal carbides at the surface and in the bulk have been calculated. The trends are discussed in relation to the behavior of the surface energy and the work function across the series.
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| 2. |
- Wright, Sandra, A. I., 1962, et al.
(författare)
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Barley lesion mimics, supersusceptible or highly resistant to leaf rust and net blotch
- 2013
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Ingår i: Plant Pathology. - : Wiley. - 0032-0862 .- 1365-3059. ; 62:5, s. 982-992
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Tidskriftsartikel (refereegranskat)abstract
- Lesion mimic mutants of plants have the feature of spontaneously displaying necrotic spots or bands on their leaves. Lesion mimics have often displayed enhanced resistance to biotrophic pathogens whilst showing increased susceptibility to necrotrophs. This paper identifies three novel, non-allelic mutants of barley (Hordeum vulgare), which spontaneously form necrotic leaf lesions: Necrotic leaf spot 9.3091 (nec9.3091), Mottled leaf 8.1661 (mtt8.1661) and Mottled leaf 9.2721 (mtt9.2721). The Necrotic leaf spot 8.3550 mutant (nec8.3550), formerly known as bst1, was included in the study because it is a lesion mimic mutant belonging to the same original pool. The reactions of the mutants to the biotroph Puccinia hordei and the necrotroph Pyrenophora teres f. sp. teres were investigated. Mutants nec8.3550 and mtt8.1661 were more resistant than the parental Bowman near-isogenic line with the Rph3.c gene (Bowman Rph3.c, NGB 22452) to leaf rust, caused by P.hordei. Mutants nec8.3550, mtt8.1661 and mtt9.2721 were more susceptible than Bowman Rph3.c to net blotch, caused by P.teres f. sp. teres. Autofluorescence was detected in leaf tissues of all mutants. Based on the high expression of the PR1 and Hv-HIR genes, combined with the low susceptibility to P.hordei, nec8.3550 appears to have entered a state of systemic acquired resistance, which is quite distinct from the resistance expressed in mtt8.1661. The latter mutant has low or no expression of PR1 and Hv-HIR genes, yet it is highly resistant to rust. It is also extremely susceptible to net blotch. These mutants can serve as genetic sources of novel disease resistance for barley improvement.
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| 3. |
- An, Siwen, et al.
(författare)
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Signal-to-Noise Ratio Optimization in X-ray Fluorescence Spectrometry for Chromium Contamination Analysis
- 2021
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Ingår i: Talanta. - : Elsevier BV. - 0039-9140 .- 1873-3573. ; 230
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Tidskriftsartikel (refereegranskat)abstract
- In most cases, direct X-ray fluorescence (XRF) analysis of solutions entails technical difficulties due to a high X-ray scattering background resulting in a spectrum with a poor signal-to-noise ratio (SNR). Key factors that determine the sensitivity of the method are the energy resolution of the detector and the amount of scattered radiation in the energy range of interest. Limiting the width of the primary spectrum by the use of secondary targets, or filters, can greatly improve the sensitivity for specific portions of the spectrum. This paper demonstrates a potential method for SNR optimization in direct XRF analysis of chromium (Cr) contamination. The suggested method requires minimal sample preparation and achieves higher sensitivity compared to existing direct XRF analysis. Two states of samples, fly ash and leachate from municipal solid waste incineration, were investigated. The effects of filter material, its absorption edge and filter thickness were analyzed using the combination of Monte Carlo N-Particle (MCNP) code and energy-dispersive XRF spectrometry. The applied filter removes primary photons with energies interfering with fluorescence photons from the element of interest, thus results in lower background scattering in the spectrum. The SNR of Cr peak increases with filter thickness and reaches a saturation value when further increased thickness only increases the measurement time. Measurements and simulations show that a Cu filter with a thickness between 100 μm and 140 μm is optimal for detecting Cr by taking into account both the SNR and the exposure time. With direct XRF analysis for solutions, the limit of quantitation (LOQ) of the achieved system was 0.32 mg/L for Cr, which is well below the allowed standard limitation for landfills in Sweden. This work shows that XRF can gain enough sensitivity for direct monitoring to certify that the Cr content in leachate is below environmental limits.
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| 4. |
- Smith, Anderson D., et al.
(författare)
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Resistive graphene humidity sensors with rapid and direct electrical readout
- 2015
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 7:45, s. 19099-19109
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate humidity sensing using a change of the electrical resistance of single-layer chemical vapor deposited (CVD) graphene that is placed on top of a SiO2 layer on a Si wafer. To investigate the selectivity of the sensor towards the most common constituents in air, its signal response was characterized individually for water vapor (H2O), nitrogen (N-2), oxygen (O-2), and argon (Ar). In order to assess the humidity sensing effect for a range from 1% relative humidity (RH) to 96% RH, the devices were characterized both in a vacuum chamber and in a humidity chamber at atmospheric pressure. The measured response and recovery times of the graphene humidity sensors are on the order of several hundred milliseconds. Density functional theory simulations are employed to further investigate the sensitivity of the graphene devices towards water vapor. The interaction between the electrostatic dipole moment of the water and the impurity bands in the SiO(2)d substrate leads to electrostatic doping of the graphene layer. The proposed graphene sensor provides rapid response direct electrical readout and is compatible with back end of the line (BEOL) integration on top of CMOS-based integrated circuits.
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| 5. |
- Rahmani, Rizan, et al.
(författare)
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Identification and synthesis of putative pheromone components of the threatened salt marsh bagworm moth, Whittleia retiella (Lepidoptera: Psychidae)
- 2020
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Ingår i: Journal of Chemical Ecology. - : Springer Science and Business Media LLC. - 0098-0331 .- 1573-1561. ; 46, s. 115-127
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Tidskriftsartikel (refereegranskat)abstract
- Whittleia retiella (Newman, 1847) is a threatened salt marsh species of the bagworm moth family Psychidae. For its preservation it is necessary to develop efficient tools to survey its distribution and habitat requirements in order to use appropriate conservation methods. Such tools may be pheromone-based monitoring systems, which have documented efficacy in establishing the occurrence of cryptic insect species in nature. By using gas chromatography combined with electroantennographic detection (GC-EAD), we found two compounds in female W. retiella headspace samples and whole-body extracts that elicited electrophysiological activity in male antennae. Gas chromatograpy coupled with mass spectrometry (GC-MS) operating in electron impact (EI) mode and comparison of the analytical data with those of synthetic reference compounds showed the chemical structures of these putative pheromone components to be (1S)-1-methylpropyl (5Z)-dec-5-enoate and 1-methylethyl (5Z)-dec-5-enoate. Field assays using baits loaded with synthetic compounds revealed that conspecific males were attracted to (1S)-1-methylpropyl (5Z)-dec-5-enoate alone or in combination with 1-methylethyl (5Z)-dec-5-enoate, whereas 1-methylethyl (5Z)-dec-5-enoate neither attracted nor repelled males in the field assays when tested alone. This study shows the potential of using (1S)-1-methylpropyl (5Z)-dec-5-enoate for monitoring W. retiella to gather more detailed information about the geographic distribution and habitat needs of this rare moth.
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| 6. |
- Hugosson, Håkan Wilhelm, et al.
(författare)
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Sulfur- and Oxygen-Induced Alterations of the Iron (001) Surface Magnetism and Work Function : A Theoretical Study
- 2013
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:12, s. 6161-6171
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and magnetic properties of atomic sulfur and oxygen adsorbed on the iron (001) surface are examined using density functional theory (DFT). The sulfur/oxygen coverage is considered from a quarter of one monolayer (ML) to a full monolayer. The work function change, magnetic properties, and density of states are determined and compared. We find that the work function increases with sulfur coverage in agreement with experiment. We also find that sulfur interacts strongly with the surface layer and that the magnetic moment of the Fe surface decreases as the sulfur coverage increases. In the case of oxygen adsorption, we find that the magnetic moment of the surface Fe atoms instead increases. We show that the difference in surface magnetic moment between sulfur adsorption and oxygen adsorption can be simply explained combining the Slater-Pauling rigid band model linking d-occupation and magnetic moment with an electronegativity argument. Moreover, the work function of the Fe surface as a function of oxygen coverage is found to be very sensitive to overlayer arrangement, here seen in the cases of 0.5 ML c(2 x 2) and 0.5 ML p(2 x 1). This is shown to result from large differences in the surface dipole moment change induced by the oxygen adsorption in the two different overlayer arrangements.
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| 7. |
- Chilo, José, 1960-, et al.
(författare)
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A flexible electronic nose for odor discrimination using different methods of classification
- 2009
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Ingår i: 2009 16th IEEE-NPSS Real Time Conference - Conference Record. - New York : IEEE. - 9781424444557 ; , s. 317-320, s. 317-320
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Konferensbidrag (refereegranskat)abstract
- Ovarian cancer is one of the leading causes of death from cancer in women. The lifetime risk is around 1.5%, which makes it the second most common gynecologic malignancy (the first one being breast cancer). To have a definitive diagnose, a surgical procedure is generally required and suspicious areas (samples) will be removed and sent for microscopic and other analysis. This paper describes the result of a pilot study in which an electronic nose is used to "smell" the aforementioned samples, analyze the multi-sensor signals and have a close to real-time answer on the detection of cancer. Besides being fast, the detection method is inexpensive and simple. Experimental analysis using real ovarian carcinoma samples shows that the use of proper algorithms for analysis of the multi-sensor data from the electronic nose yielded surprisingly good results with more than 77% classification rate. The electronic nose used in this pilot study was originally developed to be used as a "bomb dog" and can distinguish between e.g. TNT, Dynamex, Prillit. However, it was constructed to be a flexible multi-sensor device and the individual (16) sensors can easily be replaced/exchanged. This is suggestive for further investigations to obtain even better results with new, specific sensors. In another pilot experiment, headspace of an ovarian carcinoma sample and a control sample were analyzed using gas chromatography-mass spectrometry. Significant differences in chemical composition and compound levels were recorded, which would explain the different response obtained with the electronic nose.
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| 8. |
- Elgammal, Karim, et al.
(författare)
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Density functional calculations of graphene-based humidity and carbon dioxide sensors : effect of silica and sapphire substrates
- 2017
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Ingår i: Surface Science. - : Elsevier. - 0039-6028 .- 1879-2758. ; 663, s. 23-30
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Tidskriftsartikel (refereegranskat)abstract
- We present dispersion-corrected density functional calculations of water and carbon dioxide molecules adsorption on graphene residing on silica and sapphire substrates. The equilibrium positions and bonding distances for the molecules are determined. Water is found to prefer the hollow site in the center of the graphene hexagon, whereas carbon dioxide prefers sites bridging carbon-carbon bonds as well as sites directly on top of carbon atoms. The energy differences between different sites are however minute - typically just a few tenths of a millielectronvolt. Overall, the molecule-graphene bonding distances are found to be in the range 3.1-3.3 (A) over circle. The carbon dioxide binding energy to graphene is found to be almost twice that of the water binding energy (around 0.17 eV compared to around 0.09 eV). The present results compare well with previous calculations, where available. Using charge density differences, we also qualitatively illustrate the effect of the different substrates and molecules on the electronic structure of the graphene sheet.
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| 9. |
- Ahonen-Jonnarth, Ulla, et al.
(författare)
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Organic acids produced by mycorrhizal Pinus sylvestris exposed to elevated aluminium and heavy metals concentrations
- 2000
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 146:3, s. 557-567
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Tidskriftsartikel (refereegranskat)abstract
- A cultivation method was developed to enable exposure of ectomycorrhizal plants with intact extramatrical mycelium to solutions containing different concentrations of aluminium or heavy metals. Pinus sylvestris seedlings colonized by Suillus variegatus (two isolates), Rhizopogon roseolus or Paxillus involutus (two isolates) were used. Seedlings were transferred to Petri dishes containing glass beads and exposed to elevated concentrations of Al, Cd, Cu, or Ni in two ways: immediately following transfer; and after allowing mycorrhizal seedlings to develop an extraradical mycelium that colonized the interface between the upper surface of the beads and the metal-containing solution. Production of organic acids in mycorrhizal and non-mycorrhizal systems was measured by withdrawing samples from the solution and analyzing by HPLC. In most experiments, levels of oxalic acid were significantly higher in mycorrhizal treatments than in non-mycorrhizal controls. The measured levels of organic acids were variable, but the results obtained suggest that production of oxalic acid is stimulated by exposure to elevated Al in mycorrhizal seedlings colonized by S. variegatus and R. roseolus. Elevated Al concentrations also increased oxalic acid production by non-mycorrhizal seedlings significantly in two of four Al experiments performed, but the measured concentrations were significantly lower than in corresponding mycorrhizal treatments in both cases. Malonic acid was found in the culture solution of non-mycorrhizal had P. involutus-colonized seedlings, but only trace amounts were found in S. variegatus or R. roseolus-infected seedlings. Citric, shikimic, lactic, acetic, propionic, fumaric, formic, iso-butyric and butyric acid were found in variable concentrations. Production of oxalic acid by seedlings ColoniZed by S. variegatus BL or P. involutus was not stimulated by exposure to 0.44 μM Cd or 17 μM Ni. Exposure to 0.157 mM CU in two separate experiments using P. involutus 87.017 and two strains of S. variegatus (BL and 159) appeared to stimulate production of oxalic acid irrespective of mycorrhizal status or species.
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| 10. |
- Björling, Mikael
(författare)
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Interaction between Surfaces with Attached Poly(ethylene oxide) Chains
- 1992
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 25:15, s. 3956-3970
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents a self-consistent mean-field lattice theory of the Scheutjens-Fleer type where segments may adapt to temperature and the local environment by changing their distribution among internal states. Some new features are introduced in the theoretical treatment of incompressible systems, and it is demonstrated how the chemical potential may be calculated without reference to a bulk system. The theory is applied to make a qualitative prediction for the interaction between surfaces with grafted poly-(ethylene oxide), or PEO, chains. A simple two-state model for the PEO segments is used. The attractive force between the PEO-covered surfaces in water is predicted to be related to the temperature-dependent solubility of PEO in water. The contributions to the force are illustrated by simple examples. The attractive force does not change monotonically upon changing the graft density. At low coverages a strong bridging attraction is predicted if the surfaces are hydrophobic. As the surfaces become more polar, repulsion sets in at a larger separation and the overall attraction becomes less strong. A calculated, closed, solubility gap for a crude model of micelles of nonionic surfactants is presented.
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