Hysteretic magnetotransport in p-type AlGaAs heterostructures with In/Zn/Au ohmic contacts

The two-terminal magneto-conductance of a hole gas in C-doped AlGaAs/GaAs heterostructures with ohmic contacts consisting of alloyed In/Zn/Au displays a pronounced hysteresis of the conductance around zero magnetic field. The hysteresis disappears above magnetic fields of around 0.5 T and temperatures above 300 mK. For magnetic fields below 10 mT we observe a pronounced dip in the magneto-conductance. We tentatively discuss these experimental observations in the light of superconductivity of the ohmic contacts.Comment: 4+ pages, 3 figures

Comparison of anti-Aspergillus activity of Origanum vulgare L. essential oil and commercial biocide based on silver ions and hydrogen peroxide

The antifungal activities of Origanum vulgare essential oil (EO) and of a biocide based on silver and hydrogen peroxide (Sanosil S003) against seven Aspergillus species isolated from different substrata (stone, brick, silk and paper) of cultural heritage objects in Serbia were evaluated. Microdilution, agar dilution and microatmosphere methods were used to determine minimal fungistatic and minimal fungicidal concentrations (MIC and MFC), and light microscopy to determine structural abnormalities. MIC and MFC values for O. vulgare EO ranged from 0.2 to 5 mg mL−1 and for Sanosil S003 from 5 to 250 mg mL−1. Aspergillus sp. sect. fumigati was the most susceptible isolate, where MIC and MFC values were achieved at 0.5 mg mL−1 for O. vulgare EO, while MIC and MFC values for Sanosil S003 were achieved at 5 and 10 mg mL−1, respectively. Morpho-physiological changes were documented in all isolates, including lack of sporulation, depigmentation of conidiogenous apparatus and conidia, and presence of aberrant fungal structures. O. vulgare EO exhibited stronger anti-Aspergillus activity than Sanosil S003, as demonstrated by the higher MIC and MFC values and fewer morpho-physiological changes observed in the tested Sanosil S003 concentrations. O. vulgare EO could be an excellent alternative to commercial biocides, with high potential in the field of cultural heritage conservation

Quantum-critical spin dynamics in quasi-one-dimensional antiferromagnets

By means of nuclear spin-lattice relaxation rate 1/T1, we follow the spin dynamics as a function of the applied magnetic field in two gapped one-dimensional quantum antiferromagnets: the anisotropic spin-chain system NiCl2-4SC(NH2)2 and the spin-ladder system (C5H12N)2CuBr4. In both systems, spin excitations are confirmed to evolve from magnons in the gapped state to spinons in the gapples Tomonaga-Luttinger-liquid state. In between, 1/T1 exhibits a pronounced, continuous variation, which is shown to scale in accordance with quantum criticality. We extract the critical exponent for 1/T1, compare it to the theory, and show that this behavior is identical in both studied systems, thus demonstrating the universality of quantum critical behavior

Mold attack on frescoes and stone walls of Gradac monastery

Microfungi can colonize stone surfaces and form sub-aerial biofilms which can lead to biodeterioration of historic monuments. In this investigation samples for mycological analyses were collected from stone material with visible alteration on stone walls of Gradac monastery exterior. The prevailing fungi found on stone walls were dematiaceous hyphomycetes with melanized hyphae and reproductive structures (Alternaria, Aureobasidium, Cladosporium and Epicoccum species). The frescoes inside the monastery building were also analyzed for the presence of mycobiota. The predominant fungi found on frescoes were osmophilic species from genera Aspergillus and Penicillium. The significant result is identification of human pathogen species Aspergillus fumigatus on frescoes

Microwave response of thin niobium films under perpendicular static magnetic fields

The microwave response of high quality niobium films in a perpendicular static magnetic field has been investigated. The complex frequency shift was measured up to the upper critical fields. The data have been analyzed by the effective conductivity model for the type-II superconductors in the mixed state. This model is found to yield consistent results for the coherence lengths in high-kappa superconducting samples, and can be used with HTSC even at temperatures much below T_c. It is shown that for samples with high values of depinning frequency, one should measure both components of the complex frequency shift in order to determine the flow resistivity. The thick Nb film (160 nm) has low resistivity at 10 K, comparable to the best single crystals, and low kappa value. In contrast, the thinnest (10 nm) film has kappa ~ 9.5 and exhibits a high depinning frequency (~20 GHz). The upper critical field determined from microwave measurements is related to the radius of nonoverlaping vortices, and appears to be larger than the one determined by the transition to the normal state.Comment: 8 pages, 7 figures; submitted to PRB; measured rho_n; changes due to the referees' comments (abstract, conclusions, extended introduction

The effect of Nepeta rtanjensis essential oil on test micromycetes mycelia growth

The antifungal activity of Nepeta rtanjensis Diklić et Milojević essential oil on mycelia growth has been performed by macrodilution method. The most efficient impact of N. rtanjensis essential oil on mycelia growth in vitro was found in Alternaria species with the same value of minimal inhibitory quantity (MIQ) of 0.6 μl/ml. Bipolaris spicifera and Cladosporium cladosporoioides had MIQ values of 1.0 μl/ml whereas Trichoderma viride with MIQ value of 1.6 μl/ml showed the most efficient defense against the essential oil examined. The values of minimal fungicidal quantity (MFQ) in Alternaria sp. 2, B. spicifera and C. cladosporioides match the MIQ values whereas MFQ values in Alternaria sp. 1 is 0.8 μl/ml, and in T. viride 1.8 μl/ml.Makrodilucionom metodom testiran je uticaj etarskog ulja endemične biljke Nepeta rtanjensis (Lamiaceae) na micelijalni rast mikromiceta: Alternaria sp. 1, Alternaria sp. 2, Bipolaris spicifera, Cladosporium cladosporioides i Trichoderma viride. Hemijska analiza etarskog ulja N. rtanjensis pokazala je apsolutnu dominaciju 4aα, 7α, 7aβ nepetalaktona (79.89%). Najefikasniji uticaj na rast micelije in vitro zabeležen je kod vrsta roda Alternaria sa istom vrednošću minimalne inhibitorne količine (MIK) od 0.6 μl/ml. Bipolaris spicifera i Cladosporium cladosporioides su imali MIK 1.0 μl/ml, dok je Trichoderma viride, sa vrednošću MIK od 1.6 μl/ml, pokazala najveću otpornost na dejstvo ispitivanog ulja. Vrednosti minimalne fungicidne količine (MFK) se kod Alternaria sp. 2 (0.6 μl/ml), B. spicifera (1.0 μl/ml) i C. cladosporioides (1.0 μl/ml) poklapaju sa vrednostima MIK, dok je kod Alternaria sp. 1 MFK 0.8 μl/ml, a kod T. viride 1.8 μl/ml. Etarsko ulje N. rtanjensis pokazalo je jako antifungalno dejstvo na rast micelije testiranih mikromiceta.nul

Morpho-physiological characteristics and interactions of isolates of Mycogone perniciosa (Magnus) Delacr

Mycogone perniciosa (Magnus) Delacr., which causes wet bubble disease of Agaricus bisporus Lange (Imb), results in a considerable crop loss on mushroom farms in Serbia. The isolation and identification of five isolates of M. perniciosa from diseased fruit bodies of white button mushroom from mushroom units in Serbia, Bosnia and Herzegovina and Holland were made. Morpho-physiological characteristics and inter-relationships of the obtained isolates were studied. Macroscopic and microscopic investigations of different zones between colonies of the isolates of M. perniciosa revealed the phenomenon of the hyphal interference between different isolates. The obtained results suggest that hyphal interference could serve as an additional parameter for a more reliable determination of fungal specifity.Mycogone perniciosa (Magnus) Delacr., izazivač oboljenja mokre truleži najčešći je uzročnik gubitaka u gajilištima Agaricus bisporus Lange (Imb) u Srbiji. Izvršena je izolacija i identifikacija 5 izolata M. perniciosa sa obolelih plodonosnih tela šampinjona iz gajilišta u Srbiji, Bosni i Hercegovini i Holandiji. Ispitivane su morfo-fiziološke karakteristike kao i stepen srodnosti proučavanih izolata na osnovu analize međusobnog delovanja kolonija, odnosno korišćenjem fenomena hifalne interferencije. Makroskopska i mikroskopska istraživanja odnosa izolata i dobijeni rezultati ukazuju da hifalna interferencija može predstavljati dodatni parametar u razlikovanju izolata M. perniciosa. Izolati dobijeni iz gajilišta u Srbiji slični su međusobno, kao i izolati iz Holandije koji su pokazali međusobnu sličnost ali se razlikuju od prethodnih. Izolati iz Bosne i Hercegovine razlikovali su se i od srpskih i od holandskih.Projekat ministarstva br. 14304

Graph products of spheres, associative graded algebras and Hilbert series

Given a finite, simple, vertex-weighted graph, we construct a graded associative (non-commutative) algebra, whose generators correspond to vertices and whose ideal of relations has generators that are graded commutators corresponding to edges. We show that the Hilbert series of this algebra is the inverse of the clique polynomial of the graph. Using this result it easy to recognize if the ideal is inert, from which strong results on the algebra follow. Non-commutative Grobner bases play an important role in our proof. There is an interesting application to toric topology. This algebra arises naturally from a partial product of spheres, which is a special case of a generalized moment-angle complex. We apply our result to the loop-space homology of this space.Comment: 19 pages, v3: elaborated on connections to related work, added more citations, to appear in Mathematische Zeitschrif

Upper critical field, penetration depth, and depinning frequency of the novel high-temperature superconductor LaFeAsO0.9_{0.9}F0.1_{0.1} studied by microwave surface impedance

Temperature and magnetic field dependent measurements of the microwave surface impedance of superconducting LaFeAsO$_{0.9}$F$_{0.1}$ (\Tc $\approx$ 26K) reveal a very large upper critical field ($B_{\rm c2} \approx 56$T) and a large value of the depinning frequency ($f_{0}\approx 6$GHz); together with an upper limit for the effective London penetration depth, $\lambda_{\rm eff} \le 200 \rm nm$, our results indicate a strong similarity between this system and the high-$T_{\rm c}$ superconducting cuprates.Comment: 4 pages, 6 figures, minor corrections and rephrasin