Photoluminescence rings in Corbino disk at quantizing magnetic fields

Spatially resolved photoluminescence of modulation doped AlGaAs/GaAs heterojunction was investigated in a sample of Corbino disk geometry subject to strong perpendicular magnetic fields. Significant spatial modulation of the photoluminescence was observed in form of one or more concentric rings which travelled across the sample when the magnetic field strength was varied. A topology of the observed structure excludes the possibility of being a trace of an external current. The effect is attributed to formation of compressible and incompressible stripes in a 2DEG density gradient across the sample.Comment: 5 two-column pages, 4 figures (one of them in color

Interplay between mesoscopic phase separation and bulk magnetism in the layered NaxCoO2

Specific heat of the layered NaxCoO2 (x=0.65, 0.70 and 0.75) oxides has been measured in the temperature range of 3-360 K and magnetic field of 0 and 9 T. The analysis of data, assuming the combined effect of inter-layer superexchange and the phase separation into mesoscopic magnetic domains with localized spins embedded in a matrix with itinerant electronic character, suggests that the dominant contribution to the specific heat in the region of short-range ordering is mediated by quasi-2D antiferromagnetic clusters, perpendicular to the CoO2 layers

Ammonia Thermometry of Star Forming Galaxies

With a goal toward deriving the physical conditions in external galaxies, we present a study of the ammonia (NH$_3$) emission and absorption in a sample of star forming systems. Using the unique sensitivities to kinetic temperature afforded by the excitation characteristics of several inversion transitions of NH$_3$, we have continued our characterization of the dense gas in star forming galaxies by measuring the kinetic temperature in a sample of 23 galaxies and one galaxy offset position selected for their high infrared luminosity. We derive kinetic temperatures toward 13 galaxies, 9 of which possess multiple kinetic temperature and/or velocity components. Eight of these galaxies exhibit kinetic temperatures $>100$ K, which are in many cases at least a factor of two larger than kinetic temperatures derived previously. Furthermore, the derived kinetic temperatures in our galaxy sample, which are in many cases at least a factor of two larger than derived dust temperatures, point to a problem with the common assumption that dust and gas kinetic temperatures are equivalent. As previously suggested, the use of dust emission at wavelengths greater than 160 $\mu$m to derive dust temperatures, or dust heating from older stellar populations, may be skewing derived dust temperatures in these galaxies to lower values. We confirm the detection of high-excitation OH $^2\Pi_{3/2}$ J=9/2 absorption toward Arp220 (Ott et. al. 2011). We also report the first detections of non-metastable NH$_3$ inversion transitions toward external galaxies in the (2,1) (NGC253, NGC660, IC342, and IC860), (3,1), (3,2), (4,3), (5,4) (all in NGC660) and (10,9) (Arp220) transitions.Comment: 29 pages, 22 figures, final version following proof corrections accepted for publication in Ap

Coloured mulch as a weed control technology and yield booster for summer savory

An investigation into the effect of coloured mulch technology as a technique to control weeds when growing the essential oil plant, summer savory (Satureja hortensis) was made. As well as weed control, the effects on the production of crop biomass and essential oil content and quality were also considered. The mulch treatments produced significantly more biomass than either of the control treatments (which used no mulch either with or without herbicide). The white mulch treatment produced the greatest biomass, closely followed by the red mulch treatment. The blue mulch treatment was third in ranking, although not significantly greater than the black mulch. Estimates of the quantity of essential oil produced by each treatment followed a similar trend to that shown by biomass production

The number of glutamate receptors opened by synaptic stimulation in single hippocampal spines

The number of receptors opening after glutamate release is critical for understanding the sources of noise and the dynamic range of synaptic transmission. We imaged [Ca2+] transients mediated by synaptically activated NMDA receptors (NMDA-Rs) in individual spines in rat brain slices. We show that Ca2+ influx through single NMDA-Rs can be reliably detected, allowing us to estimate the number of receptors opening after synaptic transmission. This number is small: at the peak of the synaptic response, less than one NMDA-R is open, on average. Therefore, stochastic interactions between transmitter and receptor contribute substantially to synaptic noise, and glutamate occupies a small fraction of receptors. The number of receptors opening did not scale with spine volume, and smaller spines experience larger [Ca2+] transients during synaptic transmission. Our measurements further demonstrate that optical recordings can be used to study single receptors in intact systems

Revised physical elements of the astrophysically important O9.5+O9.5V eclipsing binary system Y Cyg

Thanks to its long and rich observational history and rapid apsidal motion, the massive eclipsing binary Y Cyg represents one of the cornestones to critical tests of stellar evolution theory for massive stars. Yet, the determination of the basic physical properties is less accurate than it could be given the existing number of spectral and photometric observations. Our goal is to analyze all these data simultaneously with the new dedicated series of our own spectral and photometric observations from observatories widely separated in longitude. We obtained new series of UBV observations at three observatories separated in local time to obtain complete light curves of Y Cyg for its orbital period close to 3 days. This new photometry was reduced and carefully transformed to the standard UBV system using the HEC22 program. We also obtained new series of red spectra secured at two observatories and re-analyzed earlier obtained blue electronic spectra. Our analyses provide the most accurate so far published value of the apsidal period of 47.805 +/- 0.030 yrs and the following physical elements: M1=17.72+/-0.35$ Msun, M2=17.73+/-0.30 Msun, R1=5.785+/-0.091 Rsun, and R2=5.816+/-0.063 Rsun. The disentangling thus resulted in the masses, which are somewhat higher than all previous determinations and virtually the same for both stars, while the light curve implies a slighly higher radius and luminosity for star 2. The above empirical values imply the logarithm of the internal structure constant log k2 = -1.937. A comparison with Claret's stellar interior models implies an age close to 2 millions yrs for both stars. The claimed accuracy of modern element determination of 1-2 per cent seems still a bit too optimistic and obtaining new high-dispersion and high-resolution spectra is desirable.Comment: 13 pages; accepted for publication in Astronomy and Astrophysic