43,180 research outputs found
Time- and frequency-domain polariton interference
We present experimental observations of interference between an atomic spin
coherence and an optical field in a {\Lambda}-type gradient echo memory. The
interference is mediated by a strong classical field that couples a weak probe
field to the atomic coherence through a resonant Raman transition. Interference
can be observed between a prepared spin coherence and another propagating
optical field, or between multiple {\Lambda} transitions driving a single spin
coherence. In principle, the interference in each scheme can yield a near unity
visibility.Comment: 11 pages, 5 figure
Kinetics of viral self-assembly: the role of ss RNA antenna
A big class of viruses self-assemble from a large number of identical capsid
proteins with long flexible N-terminal tails and ss RNA. We study the role of
the strong Coulomb interaction of positive N-terminal tails with ss RNA in the
kinetics of the in vitro virus self-assembly. Capsid proteins stick to
unassembled chain of ss RNA (which we call "antenna") and slide on it towards
the assembly site. We show that at excess of capsid proteins such
one-dimensional diffusion accelerates self-assembly more than ten times. On the
other hand at excess of ss RNA, antenna slows self-assembly down. Several
experiments are proposed to verify the role of ss RNA antenna.Comment: 4 pages, 3 figures, several experiments are proposed, a new idea of
experiment is adde
British economic growth : 1270 - 1870
We provide annual estimates of GDP for England between 1270 and 1700 and
for Great Britain between 1700 and 1870, constructed from the output side. The GDP
data are combined with population estimates to calculate GDP per capita. We find
English per capita income growth of 0.20 per cent per annum between 1270 and 1700,
although growth was episodic, with the strongest growth during the Black Death crisis of
the fourteenth century and in the second half of the seventeenth century. For the period
1700-1870, we find British per capita income growth of 0.48 per cent, broadly in line
with the widely accepted Crafts/Harley estimates. This modest trend growth in per capita
income since 1270 suggests that, working back from the present, living standards in the
late medieval period were well above âbare bones subsistenceâ. This can be reconciled
with modest levels of kilocalorie consumption per head because of the very large share of
pastoral production in agriculture
An extended model of the quantum free-electron laser
Previous models of the quantum regime of operation of the Free Electron Laser
(QFEL) have performed an averaging and the application of periodic boundary
conditions to the coupled Maxwell - Schrodinger equations over short, resonant
wavelength intervals of the interaction. Here, an extended, one-dimensional
model of the QFEL interaction is presented in the absence of any such averaging
or application of periodic boundary conditions, the absence of the latter
allowing electron diffusion processes to be modeled throughout the pulse. The
model is used to investigate how both the steady-state (CW) and pulsed regimes
of QFEL operation are affected. In the steady-state regime it is found that the
electrons are confined to evolve as a 2-level system, similar to the previous
QFEL models. In the pulsed regime Coherent Spontaneous Emission (CSE) due to
the shape of the electron pulse current distribution is shown to be present in
the QFEL regime for the first time. However, unlike the classical case, CSE in
the QFEL is damped by the effects of quantum diffusion of the electron
wavefunction. Electron recoil from the QFEL interaction can also cause a
diffusive drift between the recoiled and non-recoiled parts of the electron
pulse wavefunction, effectively removing the recoiled part from the primary
electron-radiation interaction.Comment: Submitted to Optics Expres
Legumes in soil fertility management: The case of pigeonpea in smallholder farming systems of Zimbabwe
We investigated the current use of legumes in soil fertility management and the feasibility of promoting use of pigeonpea in smallholder farming systems of a Communal Area in Northeast of Zimbabwe. Participatory rural appraisal methods were used to establish farmer management strategies and perceptions on major constraints to crop productivity. Soil fertility parameters were evaluated through farmer participatory experiments. The study revealed limited cultivation of legumes for both human nutrition and soil fertility management. Legumes were generally regarded as women's crops, and therefore minor, because of men's domination over women in the household decision-making process. Balancing gender interests in terms of allocation of inputs and distribution of benefits at household level was identified as a major challenge to the implementation of legume technologies. Poor extension thrusts with respect to legume production, and poor agronomic practices were identified as major production constraints. Over-emphasis on maize in the current extension packages led to the relegation of legumes to the status of 'minor crops'. Participatory experiments suggested that pigeonpea can be successfully grown by farmers under poor soil fertility conditions. The crop yielded about 3 to 9 t ha-1 of shoot biomass in a single cropping season, and up to 23 t ha-1 after two seasons of growth. High amounts leaf litter released by the crop in one season (up to 3 t ha-1) are considered a potentially viable source of nutrients for subsequent crops, as confirmed by a 22% maize yield increase obtained from a field that was previous cultivated with pigeonpea.
RĂSUMĂ
Les investigations sur l' utilisation des lĂ©gumineuses dans la gestion de fertilitĂ© du sol ainsi que les possibilitĂ©s d' incorporer le pois cajan dans le systĂšme agricole de petits fermiers ont Ă©tĂ© fait dans un milieu rural au Nord-Est du Zimbabwe. La mĂ©thode "Participatory rural appraisal" a Ă©tĂ© utilisĂ©e pour dĂ©terminer les stratĂ©gies de gestion du sol et les perceptions qui contribuent Ă la rĂ©duction de la productivitĂ© de la rĂ©colte. Les paramĂštres de fertilitĂ© du sol ont Ă©tĂ© analysĂ©s en collaboration avec des agriculteurs. Cette Ă©tude a rĂ©velĂ© qu' il y a une utilisation limitĂ©e de lĂ©gumineuses dans l' alimentation des gens ainsi que dans la gestion de fertilitĂ© du sol. Les lĂ©gumineuses sont gĂ©neralement considĂ©rĂ©es commes la rĂ©colte pour les femmes, sur ce, de peu d' importance, et Ă cause de la domination des hommes dans la prise de dĂ©cision dans le foyer. L'exĂ©cution des tĂ©chnologies d' incorporer les lĂ©gumineuses dans le systĂšme de production agricole s' est heurtĂ©e Ă un problĂšme majeur de domination de l'homme, ses prĂ©fĂ©rences dans la rĂ©partition et la distributions des intrants et les bĂ©nĂ©fices. Un autre problĂšme identifiĂ©, c'est une vulgarisation trĂšs limitĂ©e de la production de lĂ©gumineuses et une difficile adaptation agronomique de variĂ©tĂ©s de lĂ©gumineuses qui sont dĂ©jĂ dans le systĂšme. Le systĂšme de vulgarisation existant s'est concentrĂ© plus sur la production du maĂŻs, ce qui a menĂ© Ă considĂ©rer les lĂšgumineuses commes les plantes de moins d' importance. Les expĂ©riences participatives ont suggerĂ© que le pois cajan peut ĂȘtre produit par les fermiers dans des sols moins fertiles. La production a Ă©tĂ© estimĂ©e de 3 Ă 9 t ha-1 de biomasse dans une seule saison de production, et de 23 t ha-1 aprĂšs deux saisons. Une quantitĂ© considĂ©rable de litiĂšre de feuilles venant de plantes dans une seule saison (jusqu'a 3 t ha-1) est considĂ©ree comme une source importante de nutriments pour les plantes consĂ©cutives, comme l' augmention de 22% de production de maĂŻs l'a confirmĂ© aprĂšs une culture de pois cajan.
(Af Crop Science and Production: 2001 9(4): 629-644
Fire behaviour in a semi-arid Baikiaea plurijuga savanna woodland on Kalahari sands in western Zimbabwe
Human-induced fires are a major disturbance in Baikiaea plurijuga woodland savannas that are economically important for timber production. Most fires occur during the late dry season, when they may severely damage woody plants. Prescribed burning during the early dry season is a management strategy to reduce fuel loads and thus the incidence of intense fires during the late dry season. There is, however, little information on fire behaviour characteristics of early dry season fires.We studied the relationship between experimental fuel conditions and fire behaviour by lighting 15 fires during the early dry season in a Baikiaea woodland. Fire intensity ranged from 25 to 1341 kW m[superscript (-1)], while rate of spread of fire varied between 0.01 and 0.35ms[superscript (-1)]. Fire intensity and rate of spread were positively related to flame height, leaf-scorch height and proportion of the area burnt. The relationships suggest that fire characteristics can be retrospectively determined using a variable such as scorch height. The grass fuel load, wind speed, relative humidity and to a lesser extent fuel moisture were important predictors of rate of spread, flame height, leaf-scorch height and proportion of the area burnt, with no impact due to the litter fuel load. The grass fuel load and wind speed had a positive effect on rate of spread, whereas relative humidity and fuel moisture had a negative effect. These findings indicate that managers can predict the likely damage to woody plants during an early dry season burn by assessing the grass fuel load and weather conditions at the time of burning
- âŠ