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排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Zachary Freudenburg Khaterah Kohneshin Erik Aarnoutse Mariska Vansteensel Mariana Branco Sacha Leinders Max van den Boom Elmar G. M. Pels Nick Ramsey 《控制理论与应用(英文版)》2021,19(4):444-454
While brain computer interfaces (BCIs) offer the potential of allowing those suffering from loss of muscle control to once
again fully engage with their environment by bypassing the affected motor system and decoding user intentions directly from
brain activity, they are prone to errors. One possible avenue for BCI performance improvement is to detect when the BCI user
perceives the BCI to have made an unintended action and thus take corrective actions. Error-related potentials (ErrPs) are
neural correlates of error awareness and as such can provide an indication of when a BCI system is not performing according
to the user’s intentions. Here, we investigate the brain signals of an implanted BCI user suffering from locked-in syndrome
(LIS) due to late-stage ALS that prevents her from being able to speak or move but not from using her BCI at home on a
daily basis to communicate, for the presence of error-related signals. We first establish the presence of an ErrP originating
from the dorsolateral pre-frontal cortex (dLPFC) in response to errors made during a discrete feedback task that mimics the
click-based spelling software she uses to communicate. Then, we show that this ErrP can also be elicited by cursor movement
errors in a continuous BCI cursor control task. This work represents a first step toward detecting ErrPs during the daily
home use of a communications BCI. 相似文献
2.
Liliana Martelo Alfonso Jiménez Artur JM Valente Hugh D Burrows Ana T Marques Michael Forster Ullrich Scherf Mercedes Peltzer Sofia M Fonseca 《Polymer International》2012,61(6):1023-1030
Films of neat and plasticized biodegradable poly(lactic acid) (PLA) matrices containing anionic conjugated polyelectrolytes, poly[9,9‐bis(4‐phenoxybutylsulfonate)]fluorene‐2,7‐diyl‐alt‐arylenes, with 1,4‐phenylene and 4,4″‐p‐terphenylene, respectively, as arylene groups or a neutral poly(9,9‐dialkylfluorene) for comparison were prepared by solution casting. These films were characterized using differential scanning calorimetry, thermogravimetry, scanning electron microscopy and fluorescence spectroscopy. In addition, the effects of plasticizer on the thermal properties and the oxygen permeability of the PLA films were measured through the oxygen transmission rate. Results show that it is possible to obtain thin, optically transparent and luminescent films with potential in oxygen sensing, exhibiting good thermal and photochemical stability. At high polyelectrolyte content, evidence is found for phase separation and aggregate formation and it is no longer possible to obtain completely homogeneous films. The possibility of incorporating the cationic metal complex tris(2,2′‐bipyridyl)ruthenium(II) into plasticized PLA films containing conjugated polyelectrolytes for dual‐wavelength ratiometric luminescence sensing is also discussed. Copyright © 2012 Society of Chemical Industry 相似文献
3.
Ali H. Ammouri Ramsey F. Hamade 《The International Journal of Advanced Manufacturing Technology》2012,58(9-12):991-1001
This paper presents a novel actuator design for vibration-induced micromachining. The bi-directional ultrasonic elliptical vibration actuator (BUEVA) possesses a combination of features that renders it suitable for the machining a wide range of materials over a variety of cutting parameters. The cutting motion is an elliptical tool motion that resembles “spoon feeding”. This cutting action is in contrast to in-plane, horizontal motion utilized by most existing setups. The motion is arrived at through a combination of motions along the tool's axial and transverse directions and by vibrating out of phase and is generated by two stacked ceramic multilayer actuator ring piezo elements. Another distinguishing feature of BUEVA is the use of piezo stacks which ensure high blocking force compared to low force of piezo benders as used in many existing actuators. Furthermore, the amplitude and frequency of vibration of the tool are controlled on-line in order to vary the cutting depth and cutting speed according to the desired cutting parameters. This is a desirable characteristic which allows one to “dial-in” a desirable cutting speed for different workpiece materials. Another attractive BUEVA feature is that the design is very compact and can fit easily into the working space of most milling machining centers without the need for custom motion setups. An off the shelf TiALN-coated carbide turning tool is utilized as the cutting tool. Furthermore, refined versions of previously reported models by other workers in the micromachining field have been developed. Experimental force and surface roughness measurements are compared versus these ideal calculations from the improved models. Compared with these reference models, our refined calculations show improvements in describing chip geometry based on corrected tool motion and which, consequently, resulted in improved estimates of both surface roughness and cutting forces. Verification cutting tests in two different materials (Al2024 and Plexiglas) show good surface integrity and dimensional definition with roughness measurements in reasonable correlation to the refined model calculations. 相似文献
4.
Electrical circuit analogies are often used to design microfluidic systems because they simplify device design, providing simple relationships between fluid flow rate, driving forces, and channel dimensions. However, such approximations often significantly overestimate flow rates in situations where start-up energy losses from establishing kinetic head are similar in magnitude to the energy required to overcome viscous shear stresses, as is often the case within complex microfluidic networks. These reduced flows can be more accurately predicted within an electrical analogy framework that accounts for the nonlinear flow resistance generated on the transient regime of start-up flow. In this work, standard flow resistance expressions are modified to account for such effects, and the onset of nonlinear resistance is predicted by a dimensionless parameter, $\xi = Re\frac{D}{L},$ which is dependent on the Reynolds number and the channel length. As a demonstration, variable fluid resistance is shown to dramatically affect the flow performance of common microfluidic units such as T-junctions and serpentine channels, and the change in performance is accurately predicted. Experimental and theoretical analysis of T-junctions further shows that variable flow resistance causes the ratio of flows through the junction to converge toward unity with respect to an increasing total flow rate. In addition, serpentine channels are shown to exaggerate these start-up effects, owing to compounded energetic demand associated with changing a flow’s direction. As a result, serpentine channels cause the ratio of flow rates exiting a T-junction to diverge from unity with respect to an increasing flow rate. 相似文献
5.
7.
Norman F. Ramsey 《Journal of Modern Optics》2013,60(12):1647-1651
Two different topics are discussed: (1) early (1950) stimulated emission amplification observed with a pure LiF crystal having an inverted population of the nuclear spin system and (2) the atomic H-maser. 相似文献
8.
Claire D. Stevenson Andrew D. Ramsey Owen T. Nevin William Sinclair 《Landscape Research》2013,38(4):553-559
Abstract The grey squirrel Sciurus carolinensis is thought to have contributed to the decline of red squirrel S. vulgaris populations in the UK through resource competition and disease spread. This study used mtDNA sequencing to assess patterns of grey squirrel dispersal in the UK. Patterns of genetic variation within the dloop sequence were characterised for seven grey squirrel populations. Infiltration directions and potential barriers to dispersal are identified and discussed, with a focus on Cumbria, a county at the forefront of grey squirrel expansion. Understanding the dynamics of grey squirrel dispersal will aid their management at a landscape scale and enhance the conservation of red squirrels. 相似文献
9.
10.
Although polymer blend nanocomposites are widely studied, the balance between stiffness and toughness has not yet been investigated in detail. Some materials producers as well as some sectors in the automotive industry try to improve the toughness of materials without an important loss in stiffness. With this in mind, the aim of the study reported here was to obtain a good balance between toughness and stiffness of polymer blends with different amounts of clay and compatibilizer. In this context, the microstructure of polyamide 6/ethylene–propylene–diene metallocene terpolymer/(ethylene–propylene–diene copolymer)‐graft‐(maleic anhydride) blends with various amounts of clay (2, 3, 4 and 5 wt%) and compatibilizer (10 and 20 wt%) was studied to analyse the achieved morphology to understand the macroscopic properties. The morphology of the rubber phase and the dispersion of the montmorillonite (MMT) are the main factors that influence the mechanical properties. In this sense, the highest Young's modulus is achieved for nanoblends with 5 wt% of MMT, although this nanoblend has the lowest value of notched Izod impact strength. The results obtained suggest that there is a clear trade‐off between stiffness, toughness and temperature behaviour when the ratio of (ethylene–propylene–diene copolymer)‐graft‐(maleic anhydride) to MMT is 5:1. Copyright © 2009 Society of Chemical Industry 相似文献