351 research outputs found
Adiabatic quantum pumping of a desired ratio of spin current to charge current
We present a prescription for generating pure spin current or spin selective
current, based on adiabatic quantum pumping in a tight-binding model of a one
dimensional conductor. A formula for the instantaneous pumped current is
derived without introducing the scattering matrix. Our calculations indicate
that some pumping cycles produce the maximum value 2 of pumped spin while
others reverse the direction of current as a result of small alterations of the
pumping cycle. We find pumping cycles which produce essentially any ratio of
spin current to charge current.Comment: 8 pages, 7 figures, to be published in PR
An IPMC-Enabled Bio-Inspired bending/twisting Fin for Underwater Applications
This paper discusses the design, fabrication, and characterization of an ionic polymer–metal composite (IPMC) actuator-based bio-inspired active fin capable of bending and twisting motion. It is pointed out that IPMC strip actuators are used in the simple cantilever configuration to create simple bending (flapping-like) motion for propulsion in underwater autonomous systems. However, the resulting motion is a simple 1D bending and performance is rather limited. To enable more complex deformation, such as the flapping (pitch and heaving) motion of real pectoral and caudal fish fins, a new approach which involves molding or integrating IPMC actuators into a soft boot material to create an active control surface (called a \u27fin\u27) is presented. The fin can be used to realize complex deformation depending on the orientation and placement of the actuators. In contrast to previously created IPMCs with patterned electrodes for the same purpose, the proposed design avoids (1) the more expensive process of electroless plating platinum all throughout the surface of the actuator and (2) the need for specially patterning the electrodes. Therefore, standard shaped IPMC actuators such as those with rectangular dimensions with varying thicknesses can be used. One unique advantage of the proposed structural design is that custom shaped fins and control surfaces can be easily created without special materials processing. The molding process is cost effective and does not require functionalizing or \u27activating\u27 the boot material similar to creating IPMCs. For a prototype fin (90 mm wide × 60 mm long× 1.5 mm thick), the measured maximum tip displacement was approximately 44 mm and the twist angle of the fin exceeded 10°. Lift and drag measurements in water where the prototype fin with an airfoil profile was dragged through water at a velocity of 21 cm s−1 showed that the lift and drag forces can be affected by controlling the IPMCs embedded into the fin structure. These results suggest that such IPMC-enabled fin designs can be used for developing active propeller blades or control surfaces on underwater vehicles
Adiabatic quantum pumping in an Aharonov-Bohm loop and in a Si-like nanowire: Role of interference in real space and in momentum space
We study the consequences of interference effects on the current generated by
adiabatic quantum pumping in two distinct one-dimensional (1D) lattice model.
The first model contains an Aharonov-Bohm (AB) loop within a tight-binding
chain of lattice sites. The static AB phase is shown to strongly affect
interference between the two arms of the loop, serving as an on-off switch and
regulator for the pumped current. The second model simulates pumping in
semiconductors with indirect band-gaps, by utilizing a tight-binding chain with
next-nearest-neighbor coupling. The model exhibits signatures of interference
between degenerate conduction band states with different Fermi wavevectors.Comment: 7 pages, 7 figure
Effect of NaBH4 on properties of nanoscale zero-valent iron and its catalytic activity for reduction of p-nitrophenol
International audienceThe reduction of p-nitrophenol (p-NP) to p-aminophenol (p-AP) by nanoscale zero-valent iron (NZVI)/NaBH4 system in an oxygen environment was studied by means of liquid chromatography, spectroscopy (vibration and X-ray photoelectron), solid analyses (transmission electron microscopy and X-ray diffraction) and density functional theory (DFT) calculations. Addition of NaBH4 into NZVI suspension showed the disintegration of NZVI (60-100 nm), resulting in the formation of much smaller particles (15-40 nm) due to the chemical etching of outermost surfaces (i.e., magnetite). Interestingly, complete reduction of p-NP and high conversion efficiency of p-AP (> 98%) were observed in NZVI/NaBH4 system even after four recycling which is quite comparable with widely used noble metallic catalysts. Surface analysis confirmed that NaBH4 can prevent the oxidation of NZVI surface, leading to the continuous reduction of p-NP in oxygen environments. Experimental results and DFT calculations suggested that not only the formation of smaller NZVI but also thermodynamic preferences for reduction of p-NP on outermost surfaces of NZVI (i.e. magnetite) may significantly affect the reduction process of p-NP in NZVI/NaBH4 system. These novel findings can promote the development of new NZVI technologies which can be used for wastewater reductive treatment in oxygen environment
Estimation of Detection Performance for Vehicle FMCW Radars Using EM Simulations
This paper proposes a systematic method for estimating detection performances of a frequency-modulated continuous wave radar using electromagnetic simulations. The proposed systematic method includes a radar system simulator that can obtain range-Doppler images using the electromagnetic (EM) simulations in conjunction with a test setup employed for performance evaluation of multiple targets at different velocities in a traffic environment. This method is then applied for optimizing the half-power beamwidths of the antenna array using an evaluation metric defined to improve the detection strengths for the multiple targets. The optimized antenna has vertical and horizontal half-power beam widths of 10??? and 60???, respectively. The results confirm that that the proposed systematic method is suitable to improve the radar detection performance with the enhanced radar-Doppler images
The influence of urban planning-related pledge budget on local election votes: A city case in Korea
Most election pledges require a significant budget for their implementation. In the case of a candidate for the head of a local government who presented his pledges related to urban planning by subdividing them into voting districts, we tested how the size of the budget committed to the voters affected the votes. Based on the urban planning-related pledged budget, the economic utility value of one vote was estimated to be about 2050 USD. In elections for local government heads, as the pledged budget related to urban planning increased, the vote percentage and the degree of competition for votes increased positively. Moreover, when the pledged budget related to urban planning exceeded a certain level, the slope of the vote percentage curve tended to be gentle. The slope of the curve is steep in the section up to the pledged budget of 50 million USD, and the slope becomes gentle in the next section. This study was based on a specific case that was limited in terms of space and time, and it was limited to analyzing only the election pledge and election result data without considering the socioeconomic background factors of the voters.Y
Controlled Flow of Spin-Entangled Electrons via Adiabatic Quantum Pumping
We propose a method to dynamically generate and control the flow of
spin-entangled electrons, each belonging to a spin-singlet, by means of
adiabatic quantum pumping. The pumping cycle functions by periodic time
variation of localized two-body interactions. We develop a generalized approach
to adiabatic quantum pumping as traditional methods based on scattering matrix
in one dimension cannot be applied here. We specifically compute the flow of
spin-entangled electrons within a Hubbard-like model of quantum dots, and
discuss possible implementations and identify parameters that can be used to
control the singlet flow.Comment: 4 pages, 3 figure
Transformers meet Stochastic Block Models: Attention with Data-Adaptive Sparsity and Cost
To overcome the quadratic cost of self-attention, recent works have proposed
various sparse attention modules, most of which fall under one of two groups:
1) sparse attention under a hand-crafted patterns and 2) full attention
followed by a sparse variant of softmax such as -entmax. Unfortunately,
the first group lacks adaptability to data while the second still requires
quadratic cost in training. In this work, we propose SBM-Transformer, a model
that resolves both problems by endowing each attention head with a
mixed-membership Stochastic Block Model (SBM). Then, each attention head
data-adaptively samples a bipartite graph, the adjacency of which is used as an
attention mask for each input. During backpropagation, a straight-through
estimator is used to flow gradients beyond the discrete sampling step and
adjust the probabilities of sampled edges based on the predictive loss. The
forward and backward cost are thus linear to the number of edges, which each
attention head can also choose flexibly based on the input. By assessing the
distribution of graphs, we theoretically show that SBM-Transformer is a
universal approximator for arbitrary sequence-to-sequence functions in
expectation. Empirical evaluations under the LRA and GLUE benchmarks
demonstrate that our model outperforms previous efficient variants as well as
the original Transformer with full attention. Our implementation can be found
in https://github.com/sc782/SBM-Transformer .Comment: 19 pages, 8 figure
Reconciling Repeatable Timing with Pipelining and Memory Hierarchy
This paper argues that repeatable timing is more important and more achievable than predictable timing. It describes microarchitecture approaches to pipelining and memory hierarchy that deliver repeatable timing and promise comparable or better performance compared to established techniques. Specifically, threads are interleaved in a pipeline to eliminate pipeline hazards, and a hierarchical memory architecture is outlined that hides memory latencies
Replenishment of microRNA-188-5p restores the synaptic and cognitive deficits in 5XFAD Mouse Model of Alzheimer’s Disease
MicroRNAs have emerged as key factors in development, neurogenesis and synaptic functions in the central nervous system. In the present study, we investigated a pathophysiological significance of microRNA-188-5p (miR-188-5p) in Alzheimer’s disease (AD). We found that oligomeric Aβ(1-42) treatment diminished miR-188-5p expression in primary hippocampal neuron cultures and that miR-188-5p rescued the Aβ(1-42)-mediated synapse elimination and synaptic dysfunctions. Moreover, the impairments in cognitive function and synaptic transmission observed in 7-month-old five familial AD (5XFAD) transgenic mice, were ameliorated via viral-mediated expression of miR-188-5p. miR-188-5p expression was down-regulated in the brain tissues from AD patients and 5XFAD mice. The addition of miR-188-5p rescued the reduction in dendritic spine density in the primary hippocampal neurons treated with oligomeric Aβ(1-42) and cultured from 5XFAD mice. The reduction in the frequency of mEPSCs was also restored by addition of miR-188-5p. The impairments in basal fEPSPs and cognition observed in 7-month-old 5XFAD mice were ameliorated via the viral-mediated expression of miR-188-5p in the hippocampus. Furthermore, we found that miR-188 expression is CREB-dependent. Taken together, our results suggest that dysregulation of miR-188-5p expression contributes to the pathogenesis of AD by inducing synaptic dysfunction and cognitive deficits associated with Aβ-mediated pathophysiology in the disease
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