57,838 research outputs found
Frequency Modulation of Spin-Transfer Oscillators
Spin-polarized dc electric current flowing into a magnetic layer can induce
precession of the magnetization at a frequency that depends on current. We show
that addition of an ac current to this dc bias current results in a frequency
modulated (FM) spectral output, generating sidebands spaced at the modulation
frequency. The sideband amplitudes and shift of the center frequency with drive
amplitude are in good agreement with a nonlinear FM model that takes into
account the nonlinear frequency-current relation generally induced by spin
transfer. Single-domain simulations show that ac current modulates the cone
angle of the magnetization precession, in turn modulating the frequency via the
demagnetizing field. These results are promising for communications and signal
processing applications of spin-transfer oscillators.Comment: 13 pages, 3 Figure
Impact of water saving irrigation systems on water use, growth and yield of irrigated lowland rice
To meet the growing demand for food and other needs from an increasing population, the rice production in Sri Lanka, which was 3.87 million tonnes in 2008, has to be increased to 4.2 million tonnes by the year 2020. This requirement could be achieved by increasing productivity and/or by increasing the cultivated extent. In 2008, about 77 % and 68 % of the total paddy land extent was cultivated with either partial or full irrigation during the maha and yala seasons, respectively. A considerable extent of paddy land was either not cultivated or cultivated for other crops due to the scarcity of water in the dry and intermediate zones. Furthermore, with increased competition for water for domestic and industrial needs and climate change, there will be further reductions in the availability of water for rice cultivation. Conserving irrigation water would increase the cultivated extent of land while reducing the probability of ate season water-stress in the cultivated rice crop. We studied the impact of different soil water regimes on water use, nutrient uptake, growth and grain yield of 3 – 3� age lowland rice at the Rice Research and Development Institute, Batalagoda, Ibbagamuwa. There was no significant difference in the grain yield in rice when grown under either saturated or flooded conditions, but the yield decreased significantly with alternate wetting and drying. However, under saturated conditions, the irrigation water requirement was significantly lower than the flooded condition. The lowest irrigation water requirement was recorded with saturated to dry conditions. The irrigation water requirement under flooded conditions, when compared with the saturated condition, increased by 39 % during the yala season. During the maha season, even though the total irrigation requirement was lower, when compared to saturated conditions, four times more irrigation water was required under flooded conditions. There was a significant increase in plant dry matter production and leaf N (nitrogen) under saturated conditions, when compared with conventional flooded conditions. These findings suggest that when soil water is maintained at a saturated level in lowland rice, a considerable amount of irrigation water could be saved without sacrificing grain yield.Length: pp.57-64RiceIrrigated farmingWater conservationIrrigation systems
Probing ferroelectricity in highly conducting materials through their elastic response: persistence of ferroelectricity in metallic BaTiO3-d
The question whether ferroelectricity (FE) may coexist with a metallic or
highly conducting state, or rather it must be suppressed by the screening from
the free charges, is the focus of a rapidly increasing number of theoretical
studies and is finally receiving positive experimental responses. The issue is
closely related to the thermoelectric and multiferroic (also magnetic)
applications of FE materials, where the electrical conductivity is required or
spurious. In these circumstances, the traditional methods for probing
ferroelectricity are hampered or made totally ineffective by the free charges,
which screen the polar response to an external electric field. This fact may
explain why more than 40 years passed between the first proposals of FE metals
and the present experimental and theoretical activity. The measurement of the
elastic moduli, Young's modulus in the present case, versus temperature is an
effective method for studying the influence of doping on a FE transition
because the elastic properties are unaffected by electrical conductivity. In
this manner, it is shown that the FE transitions of BaTiO3-d are not suppressed
by electron doping through O vacancies; only the onset temperatures are
depressed, but the magnitudes of the softenings, and hence of the piezoelectric
activity, are initially even increased
Type A GABA-receptor-dependent synaptic transmission sculpts dendritic arbor structure in Xenopus tadpoles in vivo.
The emergence of dendritic arbor structure in vivo depends on synaptic inputs. We tested whether inhibitory GABAergic synaptic transmission regulates Xenopus optic tectal cell dendritic arbor development in vivo by expressing a peptide corresponding to an intracellular loop (ICL) of the γ2 subunit of GABAAR which is required to anchor GABAA receptors to the postsynaptic scaffold. GFP-tagged ICL (EGFP-ICL) was distributed in a punctate pattern at putative inhibitory synapses, identified by VGAT-immunoreactive puncta. ICL expression completely blocked GABAAR - mediated transmission in 36% of transfected neurons and significantly reduced GABAAR - mediated synaptic currents relative to AMPAR-mediated synaptic currents in the remaining transfected neurons without altering release probability or neuronal excitability. Further analysis of ICL-expressing neurons with residual GABAAR- mediated inputs showed that the capacity of benzodiazepine to enhance GABAergic synaptic responses was reduced in ICL-expressing neurons, indicating that they were likely depleted of γ2 subunit-containing GABAAR. Neurons expressing a mutant form of ICL were comparable to controls. In vivo time-lapse images showed that ICL-expressing neurons have more sparsely branched dendritic arbors which expand over larger neuropil areas than EGFP-expressing control neurons. Analysis of branch dynamics indicated that ICL expression affected arbor growth by reducing rates of branch addition. Furthermore, we found that decreasing GABAergic synaptic transmission with ICL expression blocked visual experience dependent dendritic arbor structural plasticity. Our findings establish an essential role for inhibitory GABAergic synaptic transmission in the regulation of dendritic structural plasticity in Xenopus in vivo
The M2/M5 BPS Partition Functions from Supergravity
In the framework of the AdS/CFT duality, we calculate the supersymmetric
partition function of the superconformal field theories living in the world
volume of either -branes or -branes. We used the dual
supergravity partition function in a saddle point approximation over
supersymmetric Black Holes. Since our BHs are written in asymptotically global
co-ordinates, the dual SCFTs are in for . The
resulting partition function shows phase transitions, constraints on the phase
space and allowed us to identify unstable BPS Black hole in the phase.
These configurations should correspond to unstable configurations in the dual
theory. We also report an intriguing relation between the most general Witten
Index, computed in the above theories, and our BPS partition functions.Comment: 9 pages, 2 columns, 4 figures, revtex, typos corrected, reference
adde
Numerical simulation of the initial stage of unipolar arcing in fusion-relevant conditions
A model for the initial phase of unipolar arcing has been developed with account of an
external energy source which triggers the arcing, the vaporization of the atoms from the heated
surface, the ions and electrons produced by ionization of the vapor, the electron emission from
the metal surface, and melt motion and surface deformation. Current transfer outside the arc
attachment is taken into account and the potential difference between the plasma and the metal
surface (the plate) is evaluated from the condition that the net current transferred to the plate is
zero at each moment. The model is used for simulation of the interaction of an external energy
load (laser beam) with a tungsten plate immersed in a helium background plasma. The results
revealed the formation of a crater, but no jet formation or droplet detachment. If the plate is large
(R = 100 mm), the peak temperature attained is 5200 K, and the plate potential remains below
the plasma potential. If the plate is small (R = 10 mm), a peak temperature of 7500 K is reached,
the potential of the plate surpasses the plasma potential, circulation of the melt at the pool
periphery occurs, and the erosion (which is mainly due to the vaporization of the metal atoms in
the spot) reaches the value of 37 μg.info:eu-repo/semantics/publishedVersio
Performance of a Low Noise Front-end ASIC for Si/CdTe Detectors in Compton Gamma-ray Telescope
Compton telescopes based on semiconductor technologies are being developed to
explore the gamma-ray universe in an energy band 0.1--20 MeV, which is not well
covered by the present or near-future gamma-ray telescopes. The key feature of
such Compton telescopes is the high energy resolution that is crucial for high
angular resolution and high background rejection capability. The energy
resolution around 1 keV is required to approach physical limit of the angular
resolution due to Doppler broadening. We have developed a low noise front-end
ASIC (Application-Specific Integrated Circuit), VA32TA, to realize this goal
for the readout of Double-sided Silicon Strip Detector (DSSD) and Cadmium
Telluride (CdTe) pixel detector which are essential elements of the
semiconductor Compton telescope. We report on the design and test results of
the VA32TA. We have reached an energy resolution of 1.3 keV (FWHM) for 60 keV
and 122 keV at 0 degree C with a DSSD and 1.7 keV (FWHM) with a CdTe detector.Comment: 6 pages, 7 figures, IEEE style file, to appear in IEEE Trans. Nucl.
Sc
Adverse Events among HIV/MDR-TB Co-Infected Patients Receiving Antiretroviral and Second Line Anti-TB Treatment in Mumbai, India.
Significant adverse events (AE) have been reported in patients receiving medications for multidrug- and extensively-drug-resistant tuberculosis (MDR-TB & XDR-TB). However, there is little prospective data on AE in MDR- or XDR-TB/HIV co-infected patients on antituberculosis and antiretroviral therapy (ART) in programmatic settings
Far Infrared Slab Lensing and Subwavelength Imaging in Crystal Quartz
We examine the possibility of using negative refraction stemming from the
phonon response in an anisotropic crystal to create a simple slab lens with
plane parallel sides, and show that imaging from such a lens should be possible
at room temperature despite the effects of absorption that are inevitably
present due to phonon damping. In particular, we consider the case of crystal
quartz, a system for which experimental measurements consistent with all-angle
negative refraction have already been demonstrated. Furthermore, we investigate
the possibility of subwavelength imaging from such materials, and show that it
should be possible for certain configurations.Comment: 12 pages, 10 figure
- …