3,188 research outputs found
Non-universal coarsening and universal distributions in far-from equilibrium systems
Anomalous coarsening in far-from equilibrium one-dimensional systems is
investigated by simulation and analytic techniques. The minimal hard core
particle (exclusion) models contain mechanisms of aggregated particle
diffusion, with rates epsilon<<1, particle deposition into cluster gaps, but
suppressed for the smallest gaps, and breakup of clusters which are adjacent to
large gaps. Cluster breakup rates vary with the cluster length x as kx^alpha.
The domain growth law x ~ (epsilon t)^z, with z=1/(2+alpha) for alpha>0, is
explained by a scaling picture, as well as the scaling of the density of double
vacancies (at which deposition and cluster breakup are allowed) as 1/[t(epsilon
t)^z]. Numerical simulations for several values of alpha and epsilon confirm
these results. An approximate factorization of the cluster configuration
probability is performed within the master equation resulting from the mapping
to a column picture. The equation for a one-variable scaling function explains
the above results. The probability distributions of cluster lengths scale as
P(x)= 1/(epsilon t)^z g(y), with y=x/(epsilon t)^z. However, those
distributions show a universal tail with the form g(y) ~ exp(-y^{3/2}), which
disagrees with the prediction of the independent cluster approximation. This
result is explained by the connection of the vacancy dynamics with the problem
of particle trapping in an infinite sea of traps and is confirmed by
simulation.Comment: 30 pages (10 figures included), to appear in Phys. Rev.
Extension of the Morris-Shore transformation to multilevel ladders
We describe situations in which chains of N degenerate quantum energy levels,
coupled by time-dependent external fields, can be replaced by independent sets
of chains of length N, N-1,...,2 and sets of uncoupled single states. The
transformation is a generalization of the two-level Morris-Shore transformation
[J.R. Morris and B.W. Shore, Phys. Rev. A 27, 906 (1983)]. We illustrate the
procedure with examples of three-level chains
Pre-Mix and on-site mixing of fumigants
Pre-Mix or On-Site mixing, a common practice with liquid insecticides, has benefits of increased synergy with fumigants. Both Pre-Mix and On-Site mixing have some issues with compatibility (e.g., active ingredient chemical stability; material compatibility; reaction with other ingredients). In addition to its fumigant properties, carbon dioxide (CO2), has a synergistic effect on other fumigants and reduces flammability. The general consensus on the amount of CO2 to improve efficacy is in the range 5%-20%. The early recognition of the benefits of CO2 to overcome the flammability of potential fumigants by Jones (1933), initiated safe and more effective fumigant mixtures: examples are ethylene oxide (12.2 vol%), ethyl formate (14.4 vol%) and propylene oxide (8.3 vol%). The main advantage of gaseous phosphine (PH3) use is reduced generation time and uniform PH3 distribution in hours not days. Other advantages of gaseous PH3 include accurate metering of PH3 fumigation levels and reduction of Occupational Health and Safety exposure to PH3. Gaseous PH3 in a Pre-Mix with liquid CO2 or mixed On-Site with gaseous CO2 or N2+Air to reduce the PH3 level below Lower Explosive Level of 16,000 ppm. A critical impurity of CO2 when mixing with PH3 is oxygen which must be less than 0.01% to avoid the formation of the polymer, (P2H4CO2)n. Large quantities of PH3 are used to treat grain storage up to 280,000 tonne [CBH, WA] and multiple 30,000 tonne silos at Dalian, China (1.4 Mt facility). Reports indicate synergy with a mixture of propylene oxide (C3H6O), sulfuryl fluoride (SO2F2) and CO2. This mixture is an attractive candidate for a Pre-Mix or On-Site mixing of a non-flammable synergized mixture with reported 100% efficacy for all insect life stages. Keywords: Fumigant mixtures, Synergised, Non-flammable, On-site mixing
Reflector antennas with low sidelobes, low cross polarization, and high aperture efficiency
Techniques are presented for computing the horn near field patterns on the subreflectors and for correcting the phase center errors of the horn pattern by shaping the subreflector surface. The diffraction pattern computations for scanned beams are described. The effects of dish aperture diffraction on pattern bandwidth are investigated. A model antenna consisting of a reflector, shaped subreflector, and corrugated feed horn is described
Dark-State Polaritons for multi-component and stationary light fields
We present a general scheme to determine the loss-free adiabatic
eigensolutions (dark-state polaritons) of the interaction of multiple probe
laser beams with a coherently driven atomic ensemble under conditions of
electromagnetically induced transparency. To this end we generalize the
Morris-Shore transformation to linearized Heisenberg-Langevin equations
describing the coupled light-matter system in the weak excitation limit. For
the simple lambda-type coupling scheme the generalized Morris-Shore
transformation reproduces the dark-state polariton solutions of slow light.
Here we treat a closed-loop dual-V scheme wherein two counter-propagating
control fields generate a quasi stationary pattern of two counter-propagating
probe fields -- so-called stationary light. We show that contrary to previous
predictions,there exists a single unique dark-state polariton; it obeys a
simple propagation equation.Comment: 6 pages, 2 figure
The role of quantum fluctuations in the optomechanical properties of a Bose-Einstein condensate in a ring cavity
We analyze a detailed model of a Bose-Einstein condensate trapped in a ring
optical resonator and contrast its classical and quantum properties to those of
a Fabry-P{\'e}rot geometry. The inclusion of two counter-propagating light
fields and three matter field modes leads to important differences between the
two situations. Specifically, we identify an experimentally realizable region
where the system's behavior differs strongly from that of a BEC in a
Fabry-P\'{e}rot cavity, and also where quantum corrections become significant.
The classical dynamics are rich, and near bifurcation points in the mean-field
classical system, the quantum fluctuations have a major impact on the system's
dynamics.Comment: 11 pages, 11 figures, submitted to PR
Time Averaged Quantum Dynamics and the Validity of the Effective Hamiltonian Model
We develop a technique for finding the dynamical evolution in time of an
averaged density matrix. The result is an equation of evolution that includes
an Effective Hamiltonian, as well as decoherence terms in Lindblad form.
Applying the general equation to harmonic Hamiltonians, we confirm a previous
formula for the Effective Hamiltonian together with a new decoherence term
which should in general be included, and whose vanishing provides the criteria
for validity of the Effective Hamiltonian approach. Finally, we apply the
theory to examples of the AC Stark Shift and Three- Level Raman Transitions,
recovering a new decoherence effect in the latter.Comment: 7 pages, 2 figure
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A review of the population and conservation status of British mammals
This report presents the first comprehensive review of the status of British mammal populations for over 20 years. The population size, range size, temporal trends and future prospects of Britain’s 58 terrestrial mammals are assessed.
The review presents the most up-to-date assessment of population size and status for the 58 terrestrial mammals in Britain. The report highlights an urgent requirement for more research to assess population densities in key habitats, and to assess the percentage of potentially suitable habitat where a given species actually occurs: at present, uncertainty levels are unacceptably high
Phosphine generator trial using external air dilution
A commercial phosphine (PH3) generator manufactured by Beijing Liangmao Technology Development Company Limited, China was used in a fumigation trial on 5000 tonne bunker storage. The generator’s production of PH3 is controlled by the rate of dosing conventional aluminum phosphide (AlP) tablets into 100 kg water in the reaction chamber.Because PH3 is flammable and explosive if certain a concentration is reached in air, it is usually mixed with carbon dioxide (CO2) in the weight ratio of 50:1. This trial’s objective was to minimise the amount of CO2 and dilute the generated PH3 with air. The PH3 generated is purged from the reaction chamber by a continuous low flow of regulated CO2 gas. The PH3-rich CO2 purge stream was fed into the suction inlet of an external venturi. A high pressure fan was used to produce the air flow through the venturi to create the vacuum to suck in and dilute the PH3 rich stream from the generator. The PH3 was diluted in the air-flow to ensure a non-flammable concentration of less than 1% (10.000 ppm) and thence fed directly into the bunker storage. The trial successfully demonstrated the viability of generating phosphine in this manner, and excellent results in PH3 concentration and distribution was achieved in very short time periods. The capacity of the generator was limited to 8 kg of AlP tablets, equivalent to 2.667 kg of PH3, or sufficient to fumigate 2667 m3 of grain at a dosage rate of 1 g/m3. A much larger version of the machine would be required to fumigate medium size bunker storages in the 10.000 to 15.000 tonne range. Notwithstanding, the generator offers an attractive package combining the speed and convenience associated with the use of gaseous PH3 with the low cost of AlP formulations. Keywords: Phosphine fumigant, On-site generator, Metallic phosphide, Non-flammabl
Discovery of Raman-scattered lines in the massive luminous emission-line star LHA 115-S 18
LHA 115-S 18 is a very peculiar emission-line star exhibiting the B[e]
phenomenon. Located in the Small Magellanic Cloud, its spectrum shows features
of an extremely wide range of excitation and ionization stages, extending from
highly ionized atomic lines (Si IV, C IV, He II) in the UV and optical regions
to molecular emission bands of CO and TiO in the optical and IR regions. The
most distinguishing spectral characteristic of LHA 115-S 18 is the high
variability detected in the He II {\lambda}4686 emission line, which can be a
very conspicuous or completely invisible feature.
In this work, we report on another peculiarity of LHA 115-S 18. From
high-resolution optical spectra taken between 2000 and 2008, we discovered the
appearance and strengthening of two emission features at {\lambda}6825 \AA, and
{\lambda}7082 \AA,, which we identified as Raman-scattered lines. This is the
first time these lines have been detected in the spectrum of a massive luminous
B[e] star. As the classification of LHA 115-S 18 is highly controversial, we
discuss how the discovery of the appearance of Raman-scattered lines in this
peculiar star might help us to solve this puzzle.Comment: Letter accepted for publication in MNRAS. 5 pages, 3 figure
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