3,218 research outputs found
Heat fluctuations for harmonic oscillators
Heat fluctuations of a harmonic oscillator in contact with a thermostat and
driven out of equilibrium by an external deterministic force are studied
experimentally and theoretically within the context of Fluctuation Theorems. We
consider the case of a periodic forcing of the oscillator, and we calculate the
analytic probability density function of heat fluctuations. The limit of large
time is discussed and we show that heat fluctuations satisfy the conventional
fluctuation theorem, even if a different fluctuation relation exists for this
quantity. Experimental results are also given for a transient state.Comment: Submitted to Europhysics Letter
ANALYSING THE LOW ADOPTION OF WATER CONSERVATION TECHNOLOGIES BY SMALLHOLDER FARMERS IN SOUTHERN AFRICA
Natural resource degradation and water scarcity are a global concern, which typically threatens the sustainability of smallholder farmers' livelihoods in semi-arid developing areas. As part of research efforts, a number of water-conservation technologies (WCT) have been developed, yet with low adoption rates in smallholder farming environments. This paper discusses the concepts of adoption and innovation, comparing the perspectives of research operators to the ones of smallholder farmers. Discrepancies are highlighted and ultimately explain low uptake of technologies by farmer. Then it addresses socio-economic factors affecting such adoption. It is argued that WCT show specific traits: (1) diversity and applicability to different time and spatial scales; (2) hence, the dependency upon a context. These traits influence dissemination and adoption of WCT, and should not be ignored, from the early stage of technology development. It is shown that adoption does not only depend on individual farmers willingness, but also upon the role of property rights on resources, and collective action at community level. Other specific issues and factors like the demand for WCT, the role of public sector and research, and related biases are also discusses. It finally draws some recommendations towards rural livelihoods that are more sustainable. Farmers' participation in technology development, taking account of local indigenous knowledge and sound institutional arrangements are among other the pathways that are suggested towards a better integration of technology development and innovation processes.adoption, innovation, water conservation, technologies, collective action, property rights, sustainability, livelihoods, Resource /Energy Economics and Policy,
Temporal recompression through a scattering medium via a broadband transmission matrix
The transmission matrix is a unique tool to control light through a
scattering medium. A monochromatic transmission matrix does not allow temporal
control of broadband light. Conversely, measuring multiple transmission
matrices with spectral resolution allows fine temporal control when a pulse is
temporally broadened upon multiple scattering, but requires very long
measurement time. Here, we show that a single linear operator, measured for a
broadband pulse with a co-propagating reference, naturally allows for spatial
focusing, and interestingly generates a two-fold temporal recompression at the
focus, compared with the natural temporal broadening. This is particularly
relevant for non-linear imaging techniques in biological tissues.Comment: 4 pages, 3 figure
Outflows in Infrared-Luminous Starbursts at z < 0.5. II. Analysis and Discussion
We have performed an absorption-line survey of outflowing gas in 78
starburst-dominated, infrared-luminous galaxies. This is the largest study of
superwinds at z < 3. Superwinds are found in almost all infrared-luminous
galaxies, and changes in detection rate with SFR--winds are found twice as
often in ultraluminous infrared galaxies (ULIRGs) as in less-luminous
galaxies--reflect different wind geometries. The maximum velocities we measure
are 600 km/s, though most of the outflowing gas has lower velocities (100-200
km/s). (One galaxy has velocities exceeding 1000 km/s.) Velocities in LINERs
are higher than in HII galaxies, and outflowing ionized gas often has higher
velocities than the neutral gas. Wind properties (velocity, mass, momentum, and
energy) scale with galaxy properties (SFR, luminosity, and galaxy mass),
consistent with ram-pressure driving of the wind. Wind properties increase
strongly with increasing galactic mass, contrary to expectation. These
correlations flatten at high SFR (> 10-100 M_sun/yr), luminosities, and masses.
This saturation is due to a lack of gas remaining in the wind's path, a common
neutral gas terminal velocity, and/or a decrease in the efficiency of
thermalization of the supernovae energy. It means that mass entrainment
efficiency, rather than remaining constant, declines in galaxies with SFR > 10
M_sun/yr and M_K < -24. Half of our sample consists of ULIRGs, which host as
much as half of the star formation in the universe at z > 1. The powerful,
ubiquitous winds we observe in these galaxies imply that superwinds in massive
galaxies at redshifts above unity play an important role in the evolution of
galaxies and the intergalactic medium.Comment: 68 pages, 20 figures in AASTeX preprint style; to appear in September
issue of ApJS; Figure 17 replaced with correct versio
Enhanced nonlinear imaging through scattering media using transmission matrix based wavefront shaping
Despite the tremendous progresses in wavefront control through or inside
complex scattering media, several limitations prevent reaching practical
feasibility for nonlinear imaging in biological tissues. While the optimization
of nonlinear signals might suffer from low signal to noise conditions and from
possible artifacts at large penetration depths, it has nevertheless been
largely used in the multiple scattering regime since it provides a guide star
mechanism as well as an intrinsic compensation for spatiotemporal distortions.
Here, we demonstrate the benefit of Transmission Matrix (TM) based approaches
under broadband illumination conditions, to perform nonlinear imaging. Using
ultrashort pulse illumination with spectral bandwidth comparable but still
lower than the spectral width of the scattering medium, we show strong
nonlinear enhancements of several orders of magnitude, through thicknesses of a
few transport mean free paths, which corresponds to millimeters in biological
tissues. Linear TM refocusing is moreover compatible with fast scanning
nonlinear imaging and potentially with acoustic based methods, which paves the
way for nonlinear microscopy deep inside scattering media
Spin-Orbit Qubits of Rare-Earth-Metal Ions in Axially Symmetric Crystal Fields
Contrary to the well known spin qubits, rare-earth qubits are characterized
by a strong influence of crystal field due to large spin-orbit coupling. At low
temperature and in the presence of resonance microwaves, it is the magnetic
moment of the crystal-field ground-state which nutates (for several s) and
the Rabi frequency is anisotropic. Here, we present a study of the
variations of with the magnitude and direction of the
static magnetic field for the odd Er isotope in a single
crystal CaWO:Er. The hyperfine interactions split the
curve into eight different curves which are fitted
numerically and described analytically. These "spin-orbit qubits" should allow
detailed studies of decoherence mechanisms which become relevant at high
temperature and open new ways for qubit addressing using properly oriented
magnetic fields
Unboundedness of adjacency matrices of locally finite graphs
Given a locally finite simple graph so that its degree is not bounded, every
self-adjoint realization of the adjacency matrix is unbounded from above. In
this note we give an optimal condition to ensure it is also unbounded from
below. We also consider the case of weighted graphs. We discuss the question of
self-adjoint extensions and prove an optimal criterium.Comment: Typos corrected. Examples added. Cute drawings. Simplification of the
main condition. Case of the weight tending to zero more discussed
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