21,298 research outputs found
Massive production of graphene oxide from expanded graphite
In a deviation from the conventional Hummers method, a spontaneous expansion
approach was introduced with expanded graphite as the precursors. The
intercalating agent (H2SO4) was able to penetrate into the expanded graphite;
this had further expanded the graphite and as a result, a foam-like
intermediate was produced. The foam-like graphite was more easily oxidized in
reaction with the oxidant (KMnO4) to form graphene oxide (GO). Fully exfoliated
GO was obtained with expanded graphite having the median diameter ~ 15 {\mu}m
as the precursors. This procedure was much safer and productive in scalable
applications than the conventional Hummers methods
Modulated Unit-Norm Tight Frames for Compressed Sensing
In this paper, we propose a compressed sensing (CS) framework that consists
of three parts: a unit-norm tight frame (UTF), a random diagonal matrix and a
column-wise orthonormal matrix. We prove that this structure satisfies the
restricted isometry property (RIP) with high probability if the number of
measurements for -sparse signals of length
and if the column-wise orthonormal matrix is bounded. Some existing structured
sensing models can be studied under this framework, which then gives tighter
bounds on the required number of measurements to satisfy the RIP. More
importantly, we propose several structured sensing models by appealing to this
unified framework, such as a general sensing model with arbitrary/determinisic
subsamplers, a fast and efficient block compressed sensing scheme, and
structured sensing matrices with deterministic phase modulations, all of which
can lead to improvements on practical applications. In particular, one of the
constructions is applied to simplify the transceiver design of CS-based channel
estimation for orthogonal frequency division multiplexing (OFDM) systems.Comment: submitted to IEEE Transactions on Signal Processin
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Theory of the perceived motion direction of equal-spatial-frequency plaid stimuli.
At an early stage, 3 different systems independently extract visual motion information from visual inputs. At later stages, these systems combine their outputs. Here, we consider a much studied (>650 publications) class of visual stimuli, plaids, which are combinations of 2 sine waves. Currently, there is no quantitative theory that can account for the perceived motion of plaids. We consider only perceived plaid direction, not speed, and obtain a large set of data exploring the various dimensions in which same-spatial-frequency plaids differ. We find that only 2 of the 3 motion systems are active in plaid processing, and that plaids with temporal frequencies 10 Hz or greater typically stimulate only the first-order motion system, which combines the plaid components by vector summation: Each plaid component is represented by a contrast-strength vector whose length is contrast-squared times a factor representing the relative effectiveness of that component's temporal frequency. The third-order system, which becomes primary at low temporal frequencies, also represents a plaid as 2 vectors that sum according to their contrast strength: a pure plaid in which both components have equal contrast and a residual sine wave. Second-order motion is irrelevant for these plaids. These principles enable a contrast-strength-vector summation theory for the responses of the first-order and third-order motion systems. With zero parameters estimated from the data, the theory captures the essence of the full range of the plaid data and supports the counterintuitive hypothesis that motion direction is processed independently of speed at early stages of visual processing. (PsycInfo Database Record (c) 2020 APA, all rights reserved)
The Influence of Goal orientations and the other Motivational Variables on Dropouts. Case HAAGA-HELIA UAS, Bite programme.
The purpose of this study was to learn studentsâ goal orientations and find out the other influences affecting studentsâ intentions to continue their study. The data gathering methods applied in this study was paper-based questionnaire. The questionnaire were based on Niemivirta (2002) students motivational factor study. The KNIME statistical analysis platform and Excel analysis toolbak were employed to study the gathered data and identify correlational patterns.
The results indicates and demonstrates that goal orientations have impact on dropouts. The other motivational variables also have different levels of influences on goal orientations, and variables correlated with each other.
In general, the study supports that the level of goal orientations would influence studentsâ intention to drop out or not. Mastery-intrinsic orientation is the key factor causing academic withdrawal. Thus, suggesting that schools apply the Adaptive Management Platform (Dirin & Laine 2018) to track studentsâ mastery-intrinsic orientation, and stimulate studentsâ mastery-intrinsic orientation together with teachers
Simple, high-performance type II β-BaB2O4 optical parametric oscillator
A visible /near-IR optical parametric oscillator (OPO) based on type II phase matching in β-BaB2O4 (BBO) is described. Pumped at 355 nm, this OPO covers 410-2500 nm completely with a single set of standard Nd:YAG cavity optics. The output efficiency is >25 %, the linewidth of the OPO is narrower than 1 -2 cm^-1 without the use of gratings or etalons, and the signal-beam divergence is <400 ¾rad. Three type I BBO doubling crystals are used to extend the tuning range from 208 to 415 nm. Doubling efficiencies as high as 40% are easily obtained. The reasons for the high doubling and overall system efficiency are discussed
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