510 research outputs found
Social and temporal dynamics mediate the distribution of ecosystem service benefits from a small-scale fishery
Small-scale fisheries are important for the livelihoods and food security of millions of people in low-income countries. Sustainably managing these dynamic social-ecological systems requires understanding links between ecosystems and human well-being: the focus of ecosystem service approaches. However, in-depth exploration of how co-production and temporal dynamics shape ecosystem benefits in small-scale fisheries remain nascent. There is thus an opportunity to better investigate pathways through which small-scale fisheries support food security. To address this gap, we ask how households allocate seafood landings across different uses, depending on supply and season. Using a daily survey, we collected panel data on landings from 15 households on Atauro Island, Timor-Leste, over six 1-week periods across three seasons, representing 630 survey days and 179 fishing trips. We found households mediate the pathways through which seafood contributes to food security. Specifically, the proportion of landings eaten, sold or shared changed with the amount landed and across seasons. As landings increased, households ate a smaller proportion and sold a greater proportion. The greatest proportion of landings were sold in the preparation season, when households save money to buy staple foods. Landings were shared with family and kin, reflecting the importance of seafood for social capital and community food security. Put broadly, households shaped a dynamic and non-linear (not directly proportional) relationship between service supply and benefits. Our findings demonstrate that seasonal context and livelihood priorities shape seafood provisioning benefits in small-scale fisheries. Careful consideration of temporal scale in ecosystem service assessments is critical for sustainable management of small-scale fisheries
Synthesis and characterization of thin film composite membranes made of PSF-TiO2/GO nanocomposite substrate for forward osmosis applications
Support layer of thin film composite (TFC) membrane plays an important role in forward osmosis (FO) performance. A new type of support layer or nanocomposite substrate was developed by incorporating titanium dioxide (TiO2)/graphene oxide (GO) into polysulfone (PSF) matrix. Prior to performance evaluation, the developed substrates were characterized with respect to surface chemistry, roughness and cross-sectional morphology. The results showed that both surface hydrophilicity and roughness of PSF-based substrates were increased upon incorporation of nanomaterials. Substrates with long finger-like voids extended from the top to the bottom could be developed upon incorporation of TiO2 (SubstrateTiO2) or TiO2/GO mixture (SubstrateTiO2/GO). The improved surface hydrophilicity and favorable structure formed are the main factors leading to higher water flux of nanocomposite substrate. Moreover, the water flux of FO using TFC membranes could be enhanced using this nanocomposite substrate. Comparing to the control TFC membrane, the TFC membranes made of SubstrateTiO2 and SubstrateTiO2/GO exhibited greater water flux with minimum increase in reverse draw solute flux. Based on the results obtained
Charge Fluctuations and Counterion Condensation
We predict a condensation phenomenon in an overall neutral system, consisting
of a single charged plate and its oppositely charged counterions. Based on the
``two-fluid'' model, in which the counterions are divided into a ``free'' and a
``condensed'' fraction, we argue that for high surface charge, fluctuations can
lead to a phase transition in which a large fraction of counterions is
condensed. Furthermore, we show that depending on the valence, the condensation
is either a first-order or a smooth transition.Comment: 16 pages, 1 figure, accepted to be published in PR
Five Dimensional Cosmological Models in General Relativity
A Five dimensional Kaluza-Klein space-time is considered in the presence of a
perfect fluid source with variable G and . An expanding universe is
found by using a relation between the metric potential and an equation of
state. The gravitational constant is found to decrease with time as whereas the variation for the cosmological constant follows as
, and
where is the equation of state parameter and is the scale factor.Comment: 13 pages, 4 figures, accepted in Int. J. Theor. Phy
(An)Isotropic models in scalar and scalar-tensor cosmologies
We study how the constants and may vary in different
theoretical models (general relativity with a perfect fluid, scalar
cosmological models (\textquotedblleft quintessence\textquotedblright) with and
without interacting scalar and matter fields and a scalar-tensor model with a
dynamical ) in order to explain some observational results. We apply
the program outlined in section II to study three different geometries which
generalize the FRW ones, which are Bianchi \textrm{V}, \textrm{VII} and
\textrm{IX}, under the self-similarity hypothesis. We put special emphasis on
calculating exact power-law solutions which allow us to compare the different
models. In all the studied cases we arrive to the conclusion that the solutions
are isotropic and noninflationary while the cosmological constant behaves as a
positive decreasing time function (in agreement with the current observations)
and the gravitational constant behaves as a growing time function
About Bianchi I with VSL
In this paper we study how to attack, through different techniques, a perfect
fluid Bianchi I model with variable G,c and Lambda, but taking into account the
effects of a -variable into the curvature tensor. We study the model under
the assumption,div(T)=0. These tactics are: Lie groups method (LM), imposing a
particular symmetry, self-similarity (SS), matter collineations (MC) and
kinematical self-similarity (KSS). We compare both tactics since they are quite
similar (symmetry principles). We arrive to the conclusion that the LM is too
restrictive and brings us to get only the flat FRW solution. The SS, MC and KSS
approaches bring us to obtain all the quantities depending on \int c(t)dt.
Therefore, in order to study their behavior we impose some physical
restrictions like for example the condition q<0 (accelerating universe). In
this way we find that is a growing time function and Lambda is a decreasing
time function whose sing depends on the equation of state, w, while the
exponents of the scale factor must satisfy the conditions
and
, i.e. for all equation of state relaxing in this way the
Kasner conditions. The behavior of depends on two parameters, the equation
of state and a parameter that controls the behavior of
therefore may be growing or decreasing.We also show that through
the Lie method, there is no difference between to study the field equations
under the assumption of a var affecting to the curvature tensor which the
other one where it is not considered such effects.Nevertheless, it is essential
to consider such effects in the cases studied under the SS, MC, and KSS
hypotheses.Comment: 29 pages, Revtex4, Accepted for publication in Astrophysics & Space
Scienc
The Persistence Length of a Strongly Charged, Rod-like, Polyelectrolyte in the Presence of Salt
The persistence length of a single, intrinsically rigid polyelectrolyte
chain, above the Manning condensation threshold is investigated theoretically
in presence of added salt. Using a loop expansion method, the partition
function is consistently calculated, taking into account corrections to
mean-field theory. Within a mean-field approximation, the well-known results of
Odijk, Skolnick and Fixman are reproduced. Beyond mean-field, it is found that
density correlations between counterions and thermal fluctuations reduce the
stiffness of the chain, indicating an effective attraction between monomers for
highly charged chains and multivalent counterions. This attraction results in a
possible mechanical instability (collapse), alluding to the phenomenon of DNA
condensation. In addition, we find that more counterions condense on slightly
bent conformations of the chain than predicted by the Manning model for the
case of an infinite cylinder. Finally, our results are compared with previous
models and experiments.Comment: 13 pages, 2 ps figure
Quantum Griffiths effects and smeared phase transitions in metals: theory and experiment
In this paper, we review theoretical and experimental research on rare region
effects at quantum phase transitions in disordered itinerant electron systems.
After summarizing a few basic concepts about phase transitions in the presence
of quenched randomness, we introduce the idea of rare regions and discuss their
importance. We then analyze in detail the different phenomena that can arise at
magnetic quantum phase transitions in disordered metals, including quantum
Griffiths singularities, smeared phase transitions, and cluster-glass
formation. For each scenario, we discuss the resulting phase diagram and
summarize the behavior of various observables. We then review several recent
experiments that provide examples of these rare region phenomena. We conclude
by discussing limitations of current approaches and open questions.Comment: 31 pages, 7 eps figures included, v2: discussion of the dissipative
Ising chain fixed, references added, v3: final version as publishe
Large enhancement of deuteron polarization with frequency modulated microwaves
We report a large enhancement of 1.7 in deuteron polarization up to values of
0.6 due to frequency modulation of the polarizing microwaves in a two liters
polarized target using the method of dynamic nuclear polarization. This target
was used during a deep inelastic polarized muon-deuteron scattering experiment
at CERN. Measurements of the electron paramagnetic resonance absorption spectra
show that frequency modulation gives rise to additional microwave absorption in
the spectral wings. Although these results are not understood theoretically,
they may provide a useful testing ground for the deeper understanding of
dynamic nuclear polarization.Comment: 10 pages, including the figures coming in uuencoded compressed tar
files in poltar.uu, which also brings cernart.sty and crna12.sty files neede
Bianchi II with time varying constants. Self-similar approach
We study a perfect fluid Bianchi II models with time varying constants under
the self-similarity approach. In the first of the studied model, we consider
that only vary and The obtained solution is more general that
the obtained one for the classical solution since it is valid for an equation
of state while in the classical solution
Taking into account the current observations, we conclude
that must be a growing time function while is a positive
decreasing function. In the second of the studied models we consider a variable
speed of light (VSL). We obtain a similar solution as in the first model
arriving to the conclusions that must be a growing time function if
is a positive decreasing function.Comment: 10 pages. RevTeX
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