252 research outputs found
Phase Transitions and Conductivties of Floquet Fluids
We investigate the phase structure and conductivity of a relativistic fluid
in a circulating electric field with a transverse magnetic field. This system
exhibits behavior similar to other driven systems such as strongly coupled
driven CFTs [Rangamani2015] or a simple anharmonic oscillator. We identify
distinct regions of fluid behavior as a function of driving frequency, and
argue that a "phase" transition will occur. Such a transition could be
measurable in graphene, and may be characterized by sudden discontinuous
increase in the Hall conductivity. The presence of the discontinuity depends on
how the boundary is approached as the frequency or amplitude is dialed. In the
region where two solution exists the measured conductivity will depend on how
the system is prepared.Comment: v2: corrected typos and updated reference
Thermal Corrections to R\'enyi entropies for Free Fermions
We calculate thermal corrections to R\'{e}nyi entropies for free massless
fermions on a sphere. More specifically, we take a free fermion on
and calculate the leading thermal correction
to the R\'{e}nyi entropies for a cap like region with opening angle .
By expanding the density matrix in a Boltzmann sum, the problem of finding the
R\'{e}nyi entropies can be mapped to the problem of calculating a two point
function on an sheeted cover of the sphere. We follow previous work for
conformal field theories to map the problem on the sphere to a conical region
in Euclidean space. By using the method of images, we calculate the two point
function and recover the R\'{e}nyi entropies.Comment: 15 pages, 5 figure
Tracing Through Scalar Entanglement
As a toy model of a gapped system, we investigate the entanglement entropy of
a massive scalar field in 1+1 dimensions at nonzero temperature. In a small
mass m and temperature T limit, we put upper and lower bounds on the two
largest eigenvalues of the covariance matrix used to compute the entanglement
entropy. We argue that the entanglement entropy has exp(-m/T) scaling in the
limit m >> T. We comment on the relation between our work and the
Ryu-Takayanagi proposal for computing the entanglement entropy holographically.Comment: 17 pages, 11 figures; v2 ref added, typos fixed; v3 refs added, minor
clarifications, version to appear in PR
Three-color Sagnac source of polarization-entangled photon pairs
We demonstrate a compact and stable source of polarization-entangled pairs of
photons, one at 810 nm wavelength for high detection efficiency and the other
at 1550 nm for long-distance fiber communication networks. Due to a novel
Sagnac-based design of the interferometer no active stabilization is needed.
Using only one 30 mm ppKTP bulk crystal the source produces photons with a
spectral brightness of 1.13x10^6 pairs/s/mW/THz with an entanglement fidelity
of 98.2%. Both photons are single-mode fiber coupled and ready to be used in
quantum key distribution (QKD) or transmission of photonic quantum states over
large distances.Comment: 7 pages, 4 figure
Don't Thrash: How to Cache Your Hash on Flash
This paper presents new alternatives to the well-known Bloom filter data
structure. The Bloom filter, a compact data structure supporting set insertion
and membership queries, has found wide application in databases, storage
systems, and networks. Because the Bloom filter performs frequent random reads
and writes, it is used almost exclusively in RAM, limiting the size of the sets
it can represent. This paper first describes the quotient filter, which
supports the basic operations of the Bloom filter, achieving roughly comparable
performance in terms of space and time, but with better data locality.
Operations on the quotient filter require only a small number of contiguous
accesses. The quotient filter has other advantages over the Bloom filter: it
supports deletions, it can be dynamically resized, and two quotient filters can
be efficiently merged. The paper then gives two data structures, the buffered
quotient filter and the cascade filter, which exploit the quotient filter
advantages and thus serve as SSD-optimized alternatives to the Bloom filter.
The cascade filter has better asymptotic I/O performance than the buffered
quotient filter, but the buffered quotient filter outperforms the cascade
filter on small to medium data sets. Both data structures significantly
outperform recently-proposed SSD-optimized Bloom filter variants, such as the
elevator Bloom filter, buffered Bloom filter, and forest-structured Bloom
filter. In experiments, the cascade filter and buffered quotient filter
performed insertions 8.6-11 times faster than the fastest Bloom filter variant
and performed lookups 0.94-2.56 times faster.Comment: VLDB201
Data for life cycle assessment of legume biorefining for alcohol
Benchmarking the environmental sustainability of alcohol produced from legume starch against alcohol produced from cereal grains requires considering of crop production, nutrient cycling and use of protein-rich co-products via life cycle assessment. This article describes the mass balance flows behind the life cycle inventories for gin produced from wheat and peas (Pisum sativum L.) in an associated article summarising the environmental footprints of wheat- and pea-gin [1], and also presents detailed supplementary results. Activity data were collected from interviews with actors along the entire gin value chain including a distillery manager and ingredient and packaging suppliers. Important fertiliserand animal-feed substitution effects of co-product use were derived using detailed information and models on nutrient flows and animal feed composition, along with linear optimisation modelling. Secondary data on environmental burdens of specific materials and processes were obtained from the Ecoinvent v3.4 life cycle assessment database. This article provides a basis for further quantitative evaluation of the environmental sustainability of legume-alcohol value chains
Just the tonic! Legume biorefining for alcohol has the potential to reduce Europe’s protein deficit and mitigate climate change
Industrialised agriculture is heavily reliant upon synthetic nitrogen fertilisers and imported protein feeds, posing environmental and food security challenges. Increasing the cultivation of leguminous crops that biologically fix nitrogen and provide high protein feed and food could help to address these challenges. We report on the innovative use of an important leguminous crop, pea (Pisum sativum L.), as a source of starch for alcohol (gin) production, yielding protein-rich animal feed as a co-product. We undertook life cycle assessment (LCA) to compare the environmental footprint of 1 L of packaged gin produced from either 1.43 kg of wheat grain or 2.42 kg of peas via fermentation and distillation into neutral spirit. Allocated environmental footprints for pea-gin were smaller than for wheat-gin across 12 of 14 environmental impact categories considered. Global warming, resource depletion, human toxicity, acidification and terrestrial eutrophication footprints were, respectively, 12%, 15%, 15%, 48% and 68% smaller, but direct land occupation was 112% greater, for pea-gin versus wheat-gin. Expansion of LCA boundaries indicated that co-products arising from the production of 1 L of wheat- or pea-gin could substitute up to 0.33 or 0.66 kg soybean animal feed, respectively, mitigating considerable greenhouse gas emissions associated with land clearing, cultivation, processing and transport of such feed. For pea-gin, this mitigation effect exceeds emissions from gin production and packaging, so that each L of bottled pea gin avoids 2.2 kg CO2 eq. There is great potential to scale the use of legume starches in production of alcoholic beverages and biofuels, reducing dependence on Latin American soybean associated with deforestation and offering considerable global mitigation potential in terms of climate change and nutrient leakage — estimated at circa 439 Tg CO2 eq. and 8.45 Tg N eq. annually
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