60,262 research outputs found
Large angle magnetization dynamics measured by time-resolved ferromagnetic resonance
A time-resolved ferromagnetic resonance technique was used to investigate the
magnetization dynamics of a 10 nm thin Permalloy film. The experiment consisted
of a sequence of magnetic field pulses at a repetition rate equal to the
magnetic systems resonance frequency. We compared data obtained by this
technique with conventional pulsed inductive microwave magnetometry. The
results for damping and frequency response obtained by these two different
methods coincide in the limit of a small angle excitation. However, when
applying large amplitude field pulses, the magnetization had a non-linear
response. We speculate that one possible cause of the nonlinearity is related
to self-amplification of incoherence, known as the Suhl instabilities.Comment: 23 pages, 8 figures, submitted to PR
Non-white frequency noise in spin torque oscillators and its effect on spectral linewidth
We measure the power spectral density of frequency fluctuations in
nanocontact spin torque oscillators over time scales up to 50 ms. We use a
mixer to convert oscillator signals ranging from 10 GHz to 40 GHz into a band
near 70 MHz before digitizing the time domain waveform. We analyze the waveform
using both zero crossing time stamps and a sliding Fourier transform, discuss
the different limitations and advantages of these two methods, and combine them
to obtain a frequency noise spectrum spanning more than five decades of Fourier
frequency . For devices having a free layer consisting of either a single
NiFe layer or a Co/Ni multilayer we find a
frequency noise spectrum that is white at large and varies as \emph{}
at small . The crossover frequency ranges from \approx\unit[10^{4}]{Hz} to
\approx\unit[10^{6}]{Hz} and the component is stronger in the
multilayer devices. Through actual and simulated spectrum analyzer
measurements, we show that frequency noise causes both broadening and a
change in shape of the oscillator's spectral line as measurement time
increases. Our results indicate that the long term stability of spin torque
oscillators cannot be accurately predicted from models based on thermal (white)
noise sources
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
Tuned liquid dampers simulation for earthquake response control of buildings
This paper is focused on the study of an earthquake protection system, the Tuned Liquid Damper (TLD), which
can, if adequately designed, reduce earthquake demands on buildings. This positive effect is accomplished taking
into account the oscillation of the free surface of a fluid inside a tank (sloshing). The behaviour of an isolated
Tuned Liquid Damper, subjected to a sinusoidal excitation at its base, with different displacement amplitudes,
was studied by finite element analysis. The efficiency of the TLD in improving the seismic response of an existing building, representative of modern architecture buildings in southern European countries was also evaluated based on linear dynamic analyses
Electric properties of the baryon anti-decuplet in the SU(3) chiral quark-soliton model
We investigate the electric form factors and charge radii of the pentaquark
baryons within the framework of the chiral quark-soliton model. We consider the
rotational and linear corrections, assuming isospin symmetry and
employing the symmetry-conserving quantization. The flavor-decomposed charge
densities of the are presented. The electric form factors and charge
radii of the charged pentaquark baryons turn out to be very similar to those of
the corresponding octet baryons. The charge radii of the neutral pentaquark
baryons are obtained to be very tiny and positive. The strange electric form
factor of the pentaquark proton is shown to be larger than the corresponding
one of the proton by around 20%. We also present the charge radii of the baryon
decuplet for comparison.Comment: 11 pages, 7 figure
Graded-index optical fiber emulator of an interacting three-atom system: illumination control of particle statistics and classical non-separability
We show that a system of three trapped ultracold and strongly interacting
atoms in one-dimension can be emulated using an optical fiber with a
graded-index profile and thin metallic slabs. While the wave-nature of single
quantum particles leads to direct and well known analogies with classical
optics, for interacting many-particle systems with unrestricted statistics such
analoga are not straightforward. Here we study the symmetries present in the
fiber eigenstates by using discrete group theory and show that, by spatially
modulating the incident field, one can select the atomic statistics, i.e.,
emulate a system of three bosons, fermions or two bosons or fermions plus an
additional distinguishable particle. We also show that the optical system is
able to produce classical non-separability resembling that found in the
analogous atomic system.Comment: 14 pages, 5 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
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