6,637 research outputs found
ATHENA: Mathematical Reasoning with Thought Expansion
Solving math word problems depends on how to articulate the problems, the
lens through which models view human linguistic expressions. Real-world
settings count on such a method even more due to the diverse practices of the
same mathematical operations. Earlier works constrain available thinking
processes by limited prediction strategies without considering their
significance in acquiring mathematical knowledge. We introduce Attention-based
THought Expansion Network Architecture (ATHENA) to tackle the challenges of
real-world practices by mimicking human thought expansion mechanisms in the
form of neural network propagation. A thought expansion recurrently generates
the candidates carrying the thoughts of possible math expressions driven from
the previous step and yields reasonable thoughts by selecting the valid
pathways to the goal. Our experiments show that ATHENA achieves a new
state-of-the-art stage toward the ideal model that is compelling in variant
questions even when the informativeness in training examples is restricted.Comment: EMNLP 2023 (main); 13 pages, 5 figures, 8 table
Biocidal activity in soils by biochar from pyrolysis biorefinery process
Useful soil applications of biochar, the biocarbon solid coproduct of biomass pyrolysis, will likely improve the economics of pyrolysis biorefineries. Adding biochar to soils to achieve any number of goals should also consider unintended effects upon soil biology. Herein, we explored two biocidal activities of fluidized-bed fast pyrolysis biochars (FPBC) created over a temperature range of 450-700 oC on the survival of pathogenic E. coli O157:H7 and beneficial arbuscular mycorrhizas (AM) symbioses in soils. For pathogen decontamination, FPBC created at \u3c 500°C proved microbiologically inert, while that created at 600°C proved biocidal over 7 weeks of sampling (P \u3c 0.05) with populations significantly reduced at 3% and 3.5% concentration (5.34 and 5.84 log CFU/g, respectively) compared with concentrations of 0.0-2.0%. Ageing of FPBC created under similar conditions for 2 years resulted in loss of efficacy. FPBC greatly reduced colonization of roots by the AM fungus when we examined the interaction of biochar addition and arbuscular mycorrhizal (AM) fungus inoculation upon growth and phosphorus (P) uptake by Allium porrum L. These responses could be related to physicochemical properties of the biochars as higher surface areas were accompanied by higher AM fungus colonization. The findings are pertinent to selecting pyrolysis biorefinery biochars for application to agricultural soils for purposes such as inactivation of pathogenic bacteria while being mindful of potential impacts upon the AM symbiosis if applied.
Biochar II: Production, Characterization and Applications. Cetraro (Calabrial) Italy, September 15-20, 2019
Electronic Spin Transport in Dual-Gated Bilayer Graphene
The elimination of extrinsic sources of spin relaxation is key in realizing
the exceptional intrinsic spin transport performance of graphene. Towards this,
we study charge and spin transport in bilayer graphene-based spin valve devices
fabricated in a new device architecture which allows us to make a comparative
study by separately investigating the roles of substrate and polymer residues
on spin relaxation. First, the comparison between spin valves fabricated on
SiO2 and BN substrates suggests that substrate-related charged impurities,
phonons and roughness do not limit the spin transport in current devices. Next,
the observation of a 5-fold enhancement in spin relaxation time in the
encapsulated device highlights the significance of polymer residues on spin
relaxation. We observe a spin relaxation length of ~ 10 um in the encapsulated
bilayer with a charge mobility of 24000 cm2/Vs. The carrier density dependence
of spin relaxation time has two distinct regimes; n<4 x 1012 cm-2, where spin
relaxation time decreases monotonically as carrier concentration increases, and
n>4 x 1012 cm-2, where spin relaxation time exhibits a sudden increase. The
sudden increase in the spin relaxation time with no corresponding signature in
the charge transport suggests the presence of a magnetic resonance close to the
charge neutrality point. We also demonstrate, for the first time, spin
transport across bipolar p-n junctions in our dual-gated device architecture
that fully integrates a sequence of encapsulated regions in its design. At low
temperatures, strong suppression of the spin signal was observed while a
transport gap was induced, which is interpreted as a novel manifestation of
impedance mismatch within the spin channel
Single to Double Hump Transition in the Equilibrium Distribution Function of Relativistic Particles
We unveil a transition from single peaked to bimodal velocity distribution in
a relativistic fluid under increasing temperature, in contrast with a
non-relativistic gas, where only a monotonic broadening of the bell-shaped
distribution is observed. Such transition results from the interplay between
the raise in thermal energy and the constraint of maximum velocity imposed by
the speed of light. We study the Bose-Einstein, the Fermi-Dirac, and the
Maxwell-J\"uttner distributions, all exhibiting the same qualitative behavior.
We characterize the nature of the transition in the framework of critical
phenomena and show that it is either continuous or discontinuous, depending on
the group velocity. We analyze the transition in one, two, and three
dimensions, with special emphasis on two-dimensions, for which a possible
experiment in graphene, based on the measurement of the Johnson-Nyquist noise,
is proposed.Comment: 5 pages, 5 figure
Interface Coupling in Twisted Multilayer Graphene by Resonant Raman Spectroscopy of Layer Breathing Modes.
Raman spectroscopy is the prime nondestructive characterization tool for graphene and related layered materials. The shear (C) and layer breathing modes (LBMs) are due to relative motions of the planes, either perpendicular or parallel to their normal. This allows one to directly probe the interlayer interactions in multilayer samples. Graphene and other two-dimensional (2d) crystals can be combined to form various hybrids and heterostructures, creating materials on demand with properties determined by the interlayer interaction. This is the case even for a single material, where multilayer stacks with different relative orientations have different optical and electronic properties. In twisted multilayer graphene there is a significant enhancement of the C modes due to resonance with new optically allowed electronic transitions, determined by the relative orientation of the layers. Here we show that this applies also to the LBMs, which can be now directly measured at room temperature. We find that twisting has a small effect on LBMs, quite different from the case of the C modes. This implies that the periodicity mismatch between two twisted layers mostly affects shear interactions. Our work shows that ultralow-frequency Raman spectroscopy is an ideal tool to uncover the interface coupling of 2d hybrids and heterostructures
The sign problem across the QCD phase transition
The average phase factor of the QCD fermion determinant signals the strength
of the QCD sign problem. We compute the average phase factor as a function of
temperature and baryon chemical potential using a two-flavor NJL model. This
allows us to study the strength of the sign problem at and above the chiral
transition. It is discussed how the anomaly affects the sign problem.
Finally, we study the interplay between the sign problem and the endpoint of
the chiral transition.Comment: 9 pages and 9 fig
A Numerical Study on Metallic Powder Flow in Coaxial Laser Cladding
In coaxial laser cladding, the quality and property of deposition products are greatly influenced by the powder flow, which is responsible to transport additive materials to the deposition point on a substrate precisely. The metallic powder flow in coaxial laser cladding is simulated by a numerical model based on the gas-solid flow theory. The characteristics of powder concentration distribution between coaxial nozzle and deposition point for a kind of nickel based alloy powder are studied by the proposed model. The relationship between the process parameters and powder flow characteristics, such as focus distance from the nozzle exit and maximum powder concentration, is analyzed to optimize the powder feeding process. In addition, the influence of substrate with different surface shapes on the powder flow is investigated. The results can be used as a guideline for the location of the substrate and the selection of proper processing parameters for coaxial laser cladding
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