19,345 research outputs found
Tuning electronic structure of graphene via tailoring structure: theoretical study
Electronic structures of graphene sheet with different defective patterns are
investigated, based on the first principles calculations. We find that
defective patterns can tune the electronic structures of the graphene
significantly. Triangle patterns give rise to strongly localized states near
the Fermi level, and hexagonal patterns open up band gaps in the systems. In
addition, rectangular patterns, which feature networks of graphene nanoribbons
with either zigzag or armchair edges, exhibit semiconducting behaviors, where
the band gap has an evident dependence on the width of the nanoribbons. For the
networks of the graphene nanoribbons, some special channels for electronic
transport are predicted.Comment: 5 figures, 6 page
An exact solution of spherical mean-field plus orbit-dependent non-separable pairing model with two non-degenerate j-orbits
An exact solution of nuclear spherical mean-field plus orbit-dependent
non-separable pairing model with two non-degenerate j-orbits is presented. The
extended one-variable Heine-Stieltjes polynomials associated to the Bethe
ansatz equations of the solution are determined, of which the sets of the zeros
give the solution of the model, and can be determined relatively easily. A
comparison of the solution to that of the standard pairing interaction with
constant interaction strength among pairs in any orbit is made. It is shown
that the overlaps of eigenstates of the model with those of the standard
pairing model are always large, especially for the ground and the first excited
state. However, the quantum phase crossover in the non-separable pairing model
cannot be accounted for by the standard pairing interaction.Comment: 5 pages, 1 figure, LaTe
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Highly Stable Luminous "snakes" from CsPbX3 Perovskite Nanocrystals Anchored on Amine-Coated Silica Nanowires
CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs) are known for their exceptional optoelectronic properties, yet the material's instability toward polar solvents, heat, or UV irradiation greatly limits its further applications. Herein, an efficient in situ growing strategy has been developed to give highly stable perovskite NC composites (abbreviated CsPbX3@CA-SiO2) by anchoring CsPbX3 NCs onto silica nanowires (NWs), which effectively depresses the optical degradation of their photoluminescence (PL) and enhances stability. The preparation of surface-functionalized serpentine silica NWs is realized by a sol-gel process involving hydrolysis of a mixture of tetraethyl orthosilicate (TEOS), 3-aminopropyltriethoxysilane (APTES), and trimethoxy(octadecyl)silane (TMODS) in a water/oil emulsion. The serpentine NWs are formed via an anisotropic growth with lengths up to 8 μm. The free amino groups are employed as surface ligands for growing perovskite NCs, yielding distributed monodisperse NCs (∼8 nm) around the NW matrix. The emission wavelength is tunable by simple variation of the halide compositions (CsPbX3, X = Cl, Br, or I), and the composites demonstrate a high photoluminescence quantum yield (PLQY 32-69%). Additionally, we have demonstrated the composites CsPbX3@CA-SiO2 can be self-woven to form a porous 3D hierarchical NWs membrane, giving rise to a superhydrophobic surface with hierarchical micro/nano structural features. The resulting composites exhibit high stability toward water, heat, and UV irradiation. This work elucidates an effective strategy to incorporate perovskite nanocrystals onto functional matrices as multifunctional stable light sources
Distributionally Robust Circuit Design Optimization under Variation Shifts
Due to the significant process variations, designers have to optimize the
statistical performance distribution of nano-scale IC design in most cases.
This problem has been investigated for decades under the formulation of
stochastic optimization, which minimizes the expected value of a performance
metric while assuming that the distribution of process variation is exactly
given. This paper rethinks the variation-aware circuit design optimization from
a new perspective. First, we discuss the variation shift problem, which means
that the actual density function of process variations almost always differs
from the given model and is often unknown. Consequently, we propose to
formulate the variation-aware circuit design optimization as a distributionally
robust optimization problem, which does not require the exact distribution of
process variations. By selecting an appropriate uncertainty set for the
probability density function of process variations, we solve the shift-aware
circuit optimization problem using distributionally robust Bayesian
optimization. This method is validated with both a photonic IC and an
electronics IC. Our optimized circuits show excellent robustness against
variation shifts: the optimized circuit has excellent performance under many
possible distributions of process variations that differ from the given
statistical model. This work has the potential to enable a new research
direction and inspire subsequent research at different levels of the EDA flow
under the setting of variation shift.Comment: accepted by ICCAD 2023, 8 page
Projective Ranking-based GNN Evasion Attacks
Graph neural networks (GNNs) offer promising learning methods for
graph-related tasks. However, GNNs are at risk of adversarial attacks. Two
primary limitations of the current evasion attack methods are highlighted: (1)
The current GradArgmax ignores the "long-term" benefit of the perturbation. It
is faced with zero-gradient and invalid benefit estimates in certain
situations. (2) In the reinforcement learning-based attack methods, the learned
attack strategies might not be transferable when the attack budget changes. To
this end, we first formulate the perturbation space and propose an evaluation
framework and the projective ranking method. We aim to learn a powerful attack
strategy then adapt it as little as possible to generate adversarial samples
under dynamic budget settings. In our method, based on mutual information, we
rank and assess the attack benefits of each perturbation for an effective
attack strategy. By projecting the strategy, our method dramatically minimizes
the cost of learning a new attack strategy when the attack budget changes. In
the comparative assessment with GradArgmax and RL-S2V, the results show our
method owns high attack performance and effective transferability. The
visualization of our method also reveals various attack patterns in the
generation of adversarial samples.Comment: Accepted by IEEE Transactions on Knowledge and Data Engineerin
Agriculture intensifies soil moisture decline in Northern China
Northern China is one of the most densely populated regions in the world. Agricultural activities have intensified since the 1980s to provide food security to the country. However, this intensification has likely contributed to an increasing scarcity in water resources, which may in turn be endangering food security. Based on in-situ measurements of soil moisture collected in agricultural plots during 1983–2012, we find that topsoil (0–50cm) volumetric water content during the growing season has declined significantly (p < 0.01), with a trend of −0.011 to −0.015 m3 m−3 per decade. Observed discharge declines for the three large river basins are consistent with the effects of agricultural intensification, although other factors (e.g. dam constructions) likely have contributed to these trends. Practices like fertilizer application have favoured biomass growth and increased transpiration rates, thus reducing available soil water. In addition, the rapid proliferation of water-expensive crops (e.g., maize) and the expansion of the area dedicated to food production have also contributed to soil drying. Adoption of alternative agricultural practices that can meet the immediate food demand without compromising future water resources seem critical for the sustainability of the food production system
Boosting the eco-friendly sharing economy: The effect of gasoline prices on bikeshare ridership in three U.S. metropolises
Transportation has become the largest CO2 emitter in the United States in recent years with low gasoline prices standing out from many contributors. As demand side changes are called for reducing car use, the fast-growing sharing economy shows great potential to shift travel demand away from single-occupancy vehicles. Although previous inter-disciplinary research on shared mobility has explored its multitudes of benefits, it is yet to be investigated how the uptake of this eco-friendly sharing scheme is affected by gasoline prices. In this study, we examine the impact of gasoline prices on the use of bikeshare programs in three U.S. metropolises: New York City, Boston, and Chicago. Using bikeshare trip data, we estimate the impact of citywide gasoline prices on both bikeshare trip duration and trip frequency in a generalized linear regression setting. The results suggest that gasoline prices significantly affect bikeshare trip frequency and duration, with a noticeable surge in short trips. Doubling gasoline prices could help save an average of 1933 gallons of gasoline per day in the three cities, approximately 0.04% of the U.S. daily per capita gasoline consumption. Our findings indicate that fuel pricing could be an effective policy tool to support technology driven eco-friendly sharing mobility and boost sustainable transportation
A Novel Deep Learning based Automatic Auscultatory Method to Measure Blood Pressure
Background:
It is clinically important to develop innovative techniques that can accurately measure blood pressures (BP) automatically.
Objectives:
This study aimed to present and evaluate a novel automatic BP measurement method based on deep learning method, and to confirm the effects on measured BPs of the position and contact pressure of stethoscope.
Methods:
30 healthy subjects were recruited. 9 BP measurements (from three different stethoscope contact pressures and three repeats) were performed on each subject. The convolutional neural network (CNN) was designed and trained to identify the Korotkoff sounds at a beat-by-beat level. Next, a mapping algorithm was developed to relate the identified Korotkoff beats to the corresponding cuff pressures for systolic and diastolic BP (SBP and DBP) determinations. Its performance was evaluated by investigating the effects of the position and contact pressure of stethoscope on measured BPs in comparison with reference manual auscultatory method.
Results:
The overall measurement errors of the proposed method were 1.4 ± 2.4 mmHg for SBP and 3.3 ± 2.9 mmHg for DBP from all the measurements. In addition, the method demonstrated that there were small SBP differences between the 2 stethoscope positions, respectively at the 3 stethoscope contact pressures, and that DBP from the stethoscope under the cuff was significantly lower than that from outside the cuff by 2.0 mmHg (P < 0.01).
Conclusion:
Our findings suggested that the deep learning based method was an effective technique to measure BP, and could be developed further to replace the current oscillometric based automatic blood pressure measurement method
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