203 research outputs found
Changes in the concentration and size-distribution of the sub-micron particles associated with the sea- and land-breezes at a coastal station
Surface measurements of the size-distribution of submicron aerosol particles in the range of 0.003 to 1 μm diameter have been made on 6-8 January 1998, at Thiruvananthapuram during an inter-comparison campaign of the Indian Ocean experiment (INDOEX). The results are studied with respect to the setting-in of the sea- and land-breezes at the station. Observations show an increase of up to an order of magnitude in aerosol concentrations of all size categories with the setting-in of the land breeze at 1800-1900 IST. High concentrations of aerosol particles prevail throughout the period of the land breeze at night-time. Aerosol concentrations remarkably decrease at about 1000 IST with the arrival of much cleaner air with the sea breeze. During the land breeze at night-time, the size-distributions of aerosol particles is bimodal with the maximum at 0.075 and 0.024 μm diameters. During the sea breeze, especially in the afternoon, the maximum in the accumulation mode shifts to a slightly higher size (0.133 μm) and the maximum in the nucleation mode seems to shift to a smaller size (0.013 μm or smaller). The size-distribution curves during the daytime are mostly open-ended at the small particle-size end. The enhanced coagulation of aerosol particles and the gas-to-particle conversion processes have been proposed to explain the shift of maxima in the accumulation mode and the enhanced generation of small particles in the nucleation mode in the afternoon, respectively
Background aerosol concentration derived from the atmospheric electric conductivity measurements made over the Indian Ocean during INDOEX
Measurements of the atmospheric electric conductivity on board ORV Sagarkanya during her three cruises over the Indian Ocean (17° N to 20° S, 57° E to 79° E) during the periods of December to March 1996-1997, 1998, and 1999 are reported. The results show that the values of atmospheric conductivity over the southern hemisphere are 2 to 3 times of that over the northern Indian Ocean and the north-to-south gradients extend up to the Intertropical Convergence Zone (ITCZ) and have large interseasonal and intraseasonal variations. The values of electric conductivity have been used to calculate the aerosol concentrations. The latitudinal variations of the aerosol concentration have been observed to have positive gradients from the Indian coastline to the ITCZ, and the gradients are different during the three cruises. The aerosol concentrations attain their pristine level only at 15°-20° S in this season. Because of the large interseasonal variability of the aerosol concentration observed over the northern Indian Ocean, it is concluded that estimating any secular change in the background aerosol pollution may be a futile exercise in this area
Airborne measurements of submicron aerosols across the coastline at Bhubaneswar during ICARB
Airborne measurements of the number concentration and size distribution of aerosols from 13 to 700 nm diameter have been made at four vertical levels across a coastline at Bhubaneswar (20◦25N, 85◦83E) during the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB)
programme conducted in March–April 2006. The measurements made during the constant-level flights at 0.5, 1, 2 and 3 km altitude levels extend ∼100 km over land and ∼150km over ocean. Aerosol number concentrations vary from 2200 to 4500 cm−3 at 0.5 km level but are almost constant at ∼ 6000 cm−3 and ∼ 800 cm−3 at 2 and 3 km levels, respectively. At 1km level, aerosol number concentration shows a peak of 18,070 cm−3 around the coastline. Most of the aerosol size distribution curves at 0.5 km and 1 km levels are monomodal with a maxima at 110nm diameter which shifts to 70 nm diameter at 2 and 3 km levels. However, at the peak at 1 km level, number concentration has a bimodal distribution with an additional maximum appearing in nucleation mode. It is proposed that this maxima in nucleation mode at 1 km level may be due to the formation and transport of new particles from coastal region
Size-distribution of submicron aerosol particles over the Indian Ocean during IFP-99 of INDOEX
Measurements of the size-distribution of submicron aerosol particles of diameter from 0.003 to 1 μm are made over the Indian Ocean during the IFP-99 of the Indian Ocean Experiment (INDOEX). Measurements are made during the onward journey from Goa to Port Louis, Mauritius from 20 January to 11 February 1999 onboard ORV Sagar Kanya and during the return journey from Port Louis to Male from 22 February to 1 March 1999 onboard Ronald H. Brown. Observations show large concentrations in the range of 2-6 × 103 particles/cm3 over the Indian Ocean in the northern hemisphere and these drop down to about 500 particles/cm3 in the southern hemisphere. However, the aerosol concentrations show a peak of about 3 × 103 particles/cm3 at 13°S. In the northern hemisphere, the concentration of particles of diameter < 0.0749 μm increases from 14°N to 1°N and then steeply falls. On the other hand, the concentration of particles of diameter > 0.0749 μm keeps decreasing up to 6°S. Size distributions of particles at open sea in the northern hemisphere show a maximum at 0.133 μm and minimum at 0.0422 μm and are generally openended at the smaller size end. The size-distributions of particles are sometimes relatively flat from 0.0133 to 0.237 μm when the particle concentrations are low in the southern hemisphere. The transport and accumulation of aerosol particles in the Inter-Tropical Convergence Zone is discussed. The relative abundance of large versus small particles is examined with respect to the variation of surface atmospheric pressure along the route
Airborne measurements of submicron aerosols across the coastline at Bhubaneswar during ICARB
Airborne measurements of the number concentration and size distribution of aerosols from 13 to 700 nm diameter have been made at four vertical levels across a coastline at Bhubaneswar (20°25'N, 85°83'E) during the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) programme conducted in March-April 2006. The measurements made during the constant-level flights at 0.5, 1, 2 and 3 km altitude levels extend ~100 km over land and ~150km over ocean. Aerosol number concentrations vary from 2200 to 4500 cm-3 at 0.5 km level but are almost constant at ~6000 cm-3 and ~800 cm-3 at 2 and 3 km levels, respectively. At 1km level, aerosol number concentration shows a peak of 18,070 cm-3 around the coastline. Most of the aerosol size distribution curves at 0.5 km and 1 km levels are monomodal with a maxima at 110 nm diameter which shifts to 70 nm diameter at 2 and 3 km levels. However, at the peak at 1 km level, number concentration has a bimodal distribution with an additional maximum appearing in nucleation mode. It is proposed that this maxima in nucleation mode at 1 km level may be due to the formation and transport of new particles from coastal regions
Master equation approach to magnon relaxation and dephasing
There has been a recent upsurge of interest in the quantum properties of
magnons for quantum information processing. An important issue is to examine
the stability of quantum states of magnons against various relaxation and
dephasing channels. Since the interaction of magnons in magnetic systems may
fall in the ultra-strong and even deep-strong coupling regimes, the relaxation
process of magnon states is quite different from the more common quantum
optical systems. Here we study the relaxation and dephasing of magnons based on
the Lindblad formalism and derive a generalized master equation that describes
the quantum dynamics of magnons. Employing this master equation, we identify
two distinct dissipation channels for squeezed magnons, i.e., the local
dissipation and collective dissipation, which play a role for both ferromagnets
and antiferromagnets. The local dissipation is caused by the independent
exchange of angular momentum between the magnonic system and the environment,
while the collective dissipation is dressed by the parametric interactions of
magnons and it enhances the quantumness and thermal stability of squeezed
magnons. Further, we show how this formalism can be applied to study the pure
dephasing of magnons caused by four-magnon scattering and magnon-phonon
interactions. Our results provide the theoretical tools to study the
decoherence of magnons within a full quantum-mechanical framework and further
benefit the use of quantum states of magnons for information processing.Comment: 13 pages, 3 figure
Pure dephasing of magnonic quantum states
For a wide range of nonclassical magnonic states that have been proposed and demonstrated recently, a new time scale besides the magnon lifetime - the magnon dephasing time - becomes important, but this time scale is rarely studied. Considering exchange interaction and spin-phonon coupling, we evaluate the pure magnon dephasing time and find it to be smaller than the magnon lifetime at temperatures of a few kelvins. By examining a magnonic cat state as an example, we show how pure dephasing of magnons destroys and limits the survival of quantum superpositions. Thus it will be critical to perform quantum operations within the pure dephasing time. We further derive the master equation for the density matrix describing such magnonic quantum states taking into account the role of pure dephasing. This methodology can be generalized to include additional dephasing channels that experiments are likely to encounter in the future. Our findings enable one to design and manipulate robust quantum states of magnons for information processing
Plant population and fungicide economically reduce winter wheat yield gap in Kansas
Master of ScienceDepartment of AgronomyRomulo P. LollatoWinter wheat (Triticum aestivum L.) water limited yield potential in Kansas averages 5.2 Mg ha⁻¹; however, state-level yields rarely surpassed 3.4 Mg ha⁻¹. Our objective was to quantify the contribution of individual management practices to reduce wheat yield gaps (YG) economically. An incomplete factorial treatment structure established in a randomized complete block design with six replications was used to evaluate 14 treatments during two years in Manhattan, Belleville, and Hutchinson Kansas. Sites were combined based on tillage practice, growing region in Kansas, and disease pressure. Thus, Manhattan had low disease pressure, was no-tilled, and in eastern Kansas for 2015-16 and 2016-17 (two site years). Meanwhile, Belleville and Hutchinson had high disease pressure, were conventionally tilled, and in central Kansas for 2015-16 and 2016-17 (four site years). We individually added six treatments to a farmer’s practice control (FP) or removed from a water-limited yield control (Y[subscript]w), which received all treatments. Practices were additional split-nitrogen (N), sulfur (S), chloride (Cl), increased plant population, foliar fungicide, and plant growth regulator (PGR). Percent YG was calculated by block and site-year using the Y[subscript]w as reference for potential yield. Orthogonal contrasts indicated yield under no-till which had low disease pressure increased from the FP by the full Y[subscript]w (+0.37 Mg ha⁻¹), but also by the individual practices split-N (+0.28 Mg ha⁻¹), S (+0.26 Mg ha⁻¹), increased plant population (+0.36 Mg ha⁻¹), and fungicide (+0.18 Mg ha⁻¹). In the conventional till which had high disease pressure, wheat yield was increased by 1.18 Mg ha⁻¹ from the Y[subscript]w and by 1.44 Mg ha⁻¹ from the fungicide. The Y[subscript]w and split-N increased grain protein concentration in no-till and conventional-till on average by 9 g kg-1 and 12 g kg-1, respectively. Across all inputs, orthogonal contrasts indicated that the FP yield gap was 8% in no-till which had low disease pressure. Likewise, the orthogonal contrasts indicated that across individual treatments the YG was reduced by split-N (6%), S (5%), Cl (3%), increased plant population (8%), and fungicide (4%). Meanwhile, orthogonal contrasts indicated that the FP yield gap was 20% across all inputs and across individual inputs reduced to 5% from fungicide under conventional-till which had high disease pressure. Fungicide increased net return (+36.65 ha⁻¹). While a high-cost input (i.e. fungicide) only economically reduced YG greater than 20%; however, a low-cost input (i.e. increased plant population) economically reduced YG less than 20%
New insights into electron spin dynamics in the presence of correlated noise
The changes of the spin depolarization length in zinc-blende semiconductors
when an external component of correlated noise is added to a static driving
electric field are analyzed for different values of field strength, noise
amplitude and correlation time. Electron dynamics is simulated by a Monte Carlo
procedure which keeps into account all the possible scattering phenomena of the
hot electrons in the medium and includes the evolution of spin polarization.
Spin depolarization is studied by examinating the decay of the initial spin
polarization of the conduction electrons through the D'yakonov-Perel process,
the only relevant relaxation mechanism in III-V crystals. Our results show
that, for electric field amplitude lower than the Gunn field, the dephasing
length shortens with the increasing of the noise intensity. Moreover, a
nonmonotonic behavior of spin depolarization length with the noise correlation
time is found, characterized by a maximum variation for values of noise
correlation time comparable with the dephasing time. Instead, in high field
conditions, we find that, critically depending on the noise correlation time,
external fluctuations can positively affect the relaxation length. The
influence of the inclusion of the electron-electron scattering mechanism is
also shown and discussed.Comment: Published on "Journal of Physics: Condensed Matter" as "Fast Track
Communications", 11 pages, 9 figure
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