1,583 research outputs found
Harvesting vibrational energy with liquid-bridged electrodes: thermodynamics in mechanically and electrically driven RC-circuits
We theoretically study a vibrating pair of parallel electrodes bridged by a
(deformed) liquid droplet, which is a recently developed microfluidic device to
harvest vibrational energy. The device can operate with various liquids,
including liquid metals, electrolytes, as well as ionic liquids. We numerically
solve the Young-Laplace equation for all droplet shapes during a vibration
period, from which the time-dependent capacitance follows that serves as input
for an equivalent circuit model. We first investigate two existing energy
harvesters (with a constant and a vanishing bias potential), for which we
explain an open issue related to their optimal electrode separations, which is
as small as possible or as large as possible in the two cases, respectively.
Then we propose a new engine with a time-dependent bias voltage, with which the
harvested work and the power can be increased by orders of magnitude at low
vibration frequencies and by factors 2-5 at high frequencies, where frequencies
are to be compared to the inverse RC-time of the circuit.Comment: 9 pages, 6 figure
Boosting capacitive blue-energy and desalination devices with waste heat
We show that sustainably harvesting 'blue' energy from the spontaneous mixing
process of fresh and salty water can be boosted by varying the water
temperature during a capacitive mixing process. Our modified Poisson-Boltzmann
calculations predict a strong temperature dependence of the electrostatic
potential of a charged electrode in contact with an adjacent aqueous 1:1
electrolyte. We propose to exploit this dependence to boost the efficiency of
capacitive blue engines, which are based on cyclically charging and discharging
nanoporous supercapacitors immersed in salty and fresh water, respectively [D.
Brogioli, Phys. Rev. Lett. 103, 058501 (2009)]. We show that the energy output
of blue engines can be increased by a factor of order two if warm
(waste-heated) fresh water is mixed with cold sea water. Moreover, the
underlying physics can also be used to optimize the reverse process of
capacitive desalination of water
Coulometry and Calorimetry of Electric Double Layer Formation in Porous Electrodes
Coulometric measurements on salt-water-immersed nanoporous carbon electrodes
reveal, at a fixed voltage, a charge decrease with increasing temperature.
During far-out-of-equilibrium charging of these electrodes, calorimetry
indicates the production of both irreversible Joule heat and reversible heat,
the latter being associated with entropy changes during electric double layer
(EDL) formation in the nanopores. These measurements grant experimental access
--for the first time-- to the entropic contribution of the grand potential; for
our electrodes, this amounts to roughly 25% of the total grand potential energy
cost of EDL formation at large applied potentials, in contrast with
point-charge model calculations that predict 100%. The coulometric and
calorimetric experiments show a consistent picture of the role of heat and
temperature in EDL formation and provide hitherto unused information to test
against EDL models.Comment: 11 pages, 10 figure
Can Tax Rate Increases Foster Investment under Entry and Exit Flexibility? - Insights from an Economic Experiment
It is well-known that taxes affect risky investment decisions. Analytical studies
indicate that tax rate increases (decreases) can foster (hinder) investment if there is flexibility, in
particular when an exit option is available. We design an experiment based on an analytical
model with binomial random walk and entry and exit flexibility. Contrasting the underlying
model, we find accelerated investment, which is often considered as an increased willingness to
invest, on tax rate increases to be independent of the existence of an exit option. However, we
observe this investor reaction only for a tax increase, not for a tax decrease. This behavior is
driven possibly by tax salience and the mechanisms known from the theory of irreversible choice
under uncertainty. Our empirical evidence suggests that the at-first-sight unexpected tax reform
effects are more common than is predicted by the theoretical literature. Policy makers should
therefore carefully consider the behavioral aspects when anticipating taxpayer reactions. (authors' abstract)Series: WU International Taxation Research Paper Serie
Trap-Assisted Charge Generation and Recombination in State-of-the-Art Organic Photodetectors
The performance of organic photodetectors is steadily improving, and the specific detectivity, as a key figure of merit, has reached values of 1012–1013 Jones, i.e., comparable to that of silicon diodes but still considerably lower than the intrinsic limit. As with other semiconductor devices, the electrical performance of state-of-the art organic photodiodes (OPDs) is presently determined to a high degree by the presence of chemical impurities or structural defects which create carrier trapping states within the bandgap of organic active layer. This review aims to provide a comprehensive and timely account of trap-assisted charge generation and recombination in OPDs, with emphasis on the impact of these phenomena on photodetector performance parameters such as, noise and dark current density, responsivity, response speed, and ultimately, specific detectivity.</p
Fundamental measure theory for the electric double layer: implications for blue-energy harvesting and water desalination
Capacitive mixing (CAPMIX) and capacitive deionization (CDI) are promising
candidates for harvesting clean, renewable energy and for the energy efficient
production of potable water, respectively. Both CAPMIX and CDI involve
water-immersed porous carbon (supercapacitors) electrodes at voltages of the
order of hundreds of millivolts, such that counter-ionic packing is important
for the electric double layer (EDL) which forms near the surface of these
porous materials. Thus, we propose a density functional theory (DFT) to model
the EDL, where the White-Bear mark II fundamental measure theory functional is
combined with a mean-field Coulombic and a mean spherical approximation-type
correction to describe the interplay between dense packing and electrostatics,
in good agreement with molecular dynamics simulations. We discuss the
concentration-dependent potential rise due to changes in the chemical potential
in capacitors in the context of an over-ideal theoretical description and its
impact on energy harvesting and water desalination. Compared to less elaborate
mean-field models our DFT calculations reveal a higher work output for
blue-energy cycles and a higher energy demand for desalination cycles
Direct numerical simulations of the modified Poisson-Nernst-Planck equations for the charging dynamics of cylindrical electrolyte-filled pores
Understanding how electrolyte-filled porous electrodes respond to an applied
potential is important to many electrochemical technologies. Here, we consider
a model supercapacitor of two blocking cylindrical pores on either side of a
cylindrical electrolyte reservoir. A stepwise potential difference
between the pores drives ionic fluxes in the setup, which we study through the
modified Poisson-Nernst-Planck equations, solved with finite elements. We focus
our discussion on the dominant timescales with which the pores charge and how
these timescales depend on three dimensionless numbers. Next to the
dimensionless applied potential , we consider the ratio of the
pore's resistance to the bulk reservoir resistance and the ratio
of the pore radius to the Debye length . We
compare our data to theoretical predictions by Aslyamov and Janssen (),
Posey and Morozumi (), and Henrique, Zuk, and Gupta ().
Through our numerical approach, we delineate the validity of these theories and
the assumptions on which they were based.Comment: 14 pages, 13 figure
A validated expert-based habitat suitability assessment for eagle owls in Limburg, the Netherlands
Motivated by the high turnover rate of the Eurasian eagle owl (Bubo bubo) population in the south of the province of Limburg, the Netherlands, which is linked to extremely high concentrations of PCBs (polychlorinated biphenyls) and DDE (dichlorodiphenyldichloroethylene) found in owl carcasses, a habitat suitability (HS) assessment for this region was conducted to identify possible sources of PCBs in the environment. Twelve environmental characteristics (ECs) that are known to influence the presence of the species were selected. With each EC, a suitability index (SI) was associated and a uninorm was used to aggregate these individual SIs into one overall HS index value. The HS assessment was validated using GPS tracking data of six adult eagle owls. Further, Ivlev’s electivity index and Manly’s habitat selection index were used to compare the area used with what is available in the landscape. To describe the former, we considered both the probability of occurrence and the home range of the tracked individuals. The resulting HS map shows that quarries and vegetation structures, such as hedgerows or solitary trees, are the main attractors for the species, though also forest edges, orchards, and tree and fruit nurseries attract the species in the study area. Hence, further field sampling campaigns to identify possible sources of poisoning should focus on parcels with these land covers. Such a prioritization of parcels becomes possible using our approach
Productivity of Chlorella sorokiniana in a short light-path (SLP) panel photobioreactor under high irradiance
Maximal productivity of a 14 mm light-path panel photobioreactor under high irradiance was
determined. Under continuous illumination of 2100 ÎĽmol photons m-2 s-1 with red LEDs (light
emitting diodes) the effect of dilution rate on photobioreactor productivity was studied. The
light intensity used in this work is similar to the maximal irradiance on a horizontal surface at
latitudes lower than 37Âş.
Chlorella sorokiniana, a fast-growing green microalga, was used as a reference strain in this
study. The dilution rate was varied from 0.06 h-1 to 0.26 h-1. The maximal productivity was
reached at a dilution rate of 0.24 h-1, with a value of 7.7 g of dry weight m-2 h-1 (m2 of
illuminated photobioreactor surface) and a volumetric productivity of 0.5 g of dry weight L-1 h-
1. At this dilution rate the biomass concentration inside the reactor was 2.1 g L-1 and the
photosynthetic efficiency was 1.0 g dry weight per mol photons. This biomass yield on light
energy is high but still lower than the theoretical maximal yield of 1.8 g mol photons-1 which
must be related to photosaturation and thermal dissipation of absorbed light energy
Impact of Alkyl Chain Length on the Formation of Regular- and Reverse-Graded Quasi-2D Perovskite Thin Films
Crystallization of low-dimensional perovskites is a complex process that leads to multidimensional films comprising two-dimensional (2D), quasi-2D, and three-dimensional (3D) phases. Most quasi-2D perovskite films possess a regular gradient with 2D phases located at the bottom of the film and 3D phases at the top. Recently, multiple studies have reported reverse-graded perovskite films, where the location of the 2D and 3D structures is inverted. The underlying reasons for such a peculiar phase distribution are unclear. While crystallization of regular-graded quasi-2D perovskites has been described as starting with 3D phases from the liquid-air interface, the film formation of reverse-graded films has not been investigated yet. Here, we examine the impact of the alkyl chain length on the formation of regular- and reverse-graded perovskites using n-alkylammonium ions. We find that long alkyl chains reverse the phase distribution gradient. By combining photoluminescence spectroscopy with in situ optical absorption measurements, we demonstrate that crystallization starts at the liquid-N2 interface, though as 3D phases for short-chain n-alkylammonium ions and as quasi-2D phases for long chains. We link this behavior to enhanced van der Waals interactions between long-chain n-alkylammonium ions in polar solvents and their tendency to accumulate at the liquid-N2 interface, creating a concentration gradient along the film thickness.</p
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