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A micro-electro-mechanical-system-based thermal shear-stress sensor with self-frequency compensation
By applying the micro-electro-mechanical-system (MEMS) fabrication technology, we developed a micro-thermal sensor to measure surface shear stress. The heat transfer from a polysilicon heater depends on the normal velocity gradient and thus provides the surface shear stress. However, the sensitivity of the shear-stress measurements in air is less than desirable due to the low heat capacity of air. A unique feature of this micro-sensor is that the heating element, a film 1 µm thick, is separated from the substrate by a vacuum cavity 2 µm thick. The vacuum cavity prevents the conduction of heat to the substrate and therefore improves the sensitivity by an order of magnitude. Owing to the low thermal inertia of the miniature sensing element, this shear-stress micro-sensor can provide instantaneous measurements of small-scale turbulence. Furthermore, MEMS technology allows us make multiple sensors on a single chip so that we can perform distributed measurements. In this study, we use multiple polysilicon sensor elements to improve the dynamic performance of the sensor itself. It is demonstrated that the frequency-response range of a constant-current sensor can be extended from the order of 100 Hz to 100 kHz
Macro aerodynamic devices controlled by micro systems
Micro-ElectroMechanical-Systems (MEMS) have emerged as a major enabling technology across the engineering disciplines. In this study, the possibility of applying MEMS to the aerodynamic field was explored. We have demonstrated that microtransducers can be used to control the motion of a delta wing in a wind tunnel and can even maneuver a scaled aircraft in flight tests. The main advantage of using micro actuators to replace the traditional control surface is the significant reduction of radar cross-sections. At a high angle of attack, a large portion of the suction loading on a delta wing is contributed by the leading edge separation vortices which originate from thin boundary layers at the leading edge. We used microactuators with a thickness comparable to that of the boundary layer in order to alter the separation process and thus achieved control of the global motion by minute perturbations
PT-Symmetric Quantum Theory Defined in a Krein Space
We provide a mathematical framework for PT-symmetric quantum theory, which is
applicable irrespective of whether a system is defined on R or a complex
contour, whether PT symmetry is unbroken, and so on. The linear space in which
PT-symmetric quantum theory is naturally defined is a Krein space constructed
by introducing an indefinite metric into a Hilbert space composed of square
integrable complex functions in a complex contour. We show that in this Krein
space every PT-symmetric operator is P-Hermitian if and only if it has
transposition symmetry as well, from which the characteristic properties of the
PT-symmetric Hamiltonians found in the literature follow. Some possible ways to
construct physical theories are discussed within the restriction to the class
K(H).Comment: 8 pages, no figures; Refs. added, minor revisio
Normalization Perturbation: A Simple Domain Generalization Method for Real-World Domain Shifts
Improving model's generalizability against domain shifts is crucial,especially for safety-critical applications such as autonomous driving.Real-world domain styles can vary substantially due to environment changes andsensor noises, but deep models only know the training domain style. Such domainstyle gap impedes model generalization on diverse real-world domains. Ourproposed Normalization Perturbation (NP) can effectively overcome this domainstyle overfitting problem. We observe that this problem is mainly caused by thebiased distribution of low-level features learned in shallow CNN layers. Thus,we propose to perturb the channel statistics of source domain features tosynthesize various latent styles, so that the trained deep model can perceivediverse potential domains and generalizes well even without observations oftarget domain data in training. We further explore the style-sensitive channelsfor effective style synthesis. Normalization Perturbation only relies on asingle source domain and is surprisingly effective and extremely easy toimplement. Extensive experiments verify the effectiveness of our method forgeneralizing models under real-world domain shifts.<br
Effect of β-sitosterol on the curcumin-loaded liposomes: Vesicle characteristics, physicochemical stability, in vitro release and bioavailability
In this work, the effect of β-sitosterol (Sito) on vesicle characteristics, physicochemical stability as well as the in vitro release and bioavailability of curcumin-loaded liposomes (Cur-LP) was studied. When 20–33 mol% of Sito was incorporated, encapsulation efficiency of curcumin was improved due to the high amount of liquid-ordered domains in membranes. At 50 mol% Sito a lower encapsulation efficiency was observed possibly due to membrane defects. The physical, thermal and photo stability of curcumin in liposomes were markedly improved with increasing the amount of Sito. First-order kinetics fitted best the curcumin release dynamics of Sito containing liposomes, clearly showing that sustained release improved with increasing amounts of Sito in liposomes. Simulated digestion studies suggested that Sito concentration of about 20–33 mol% improved the bioavailability of curcumin in liposomes. These study shows that Sito is an applicable and potential route in forming healthier cholesterol-free curcumin-loaded liposomes for functional supplements
Efficient magneto-optical trapping of Yb atoms with a violet laser diode
We report the first efficient trapping of rare-earth Yb atoms with a
high-power violet laser diode (LD). An injection-locked violet LD with a 25 mW
frequency-stabilized output was used for the magneto-optical trapping (MOT) of
fermionic as well as bosonic Yb isotopes. A typical number of
atoms for Yb with a trap density of cm was
obtained. A 10 mW violet external-cavity LD (ECLD) was used for the
one-dimensional (1D) slowing of an effusive Yb atomic beam without a Zeeman
slower resulting in a 35-fold increase in the number of trapped atoms. The
overall characteristics of our compact violet MOT, e.g., the loss time of 1 s,
the loading time of 400 ms, and the cloud temperature of 0.7 mK, are comparable
to those in previously reported violet Yb MOTs, yet with a greatly reduced cost
and complexity of the experiment.Comment: 5 pages, 3 figures, 1 table, Phys. Rev. A (to be published
Hierarchically heterostructured metal hydr(oxy)oxides for efficient overall water splitting
The design of highly efficient electrocatalysts containing non-precious metals is crucial for promoting overall water splitting in alkaline media. In particular, Janus catalysts simultaneously facilitating the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are desirable. Herein, we fabricated a unique hierarchical heterostructure via growing Ni4W6O21(OH)2·4H2O (denoted as Ni-W-O) nanosheets on NiMoO4 rods, which was indispensable for regulating the morphology of the Ni-W-O structure. This heterostructure of Ni-W-O/NiMoO4 could be utilized as an electrocatalyst to realize superior activity for overall water splitting in 1.0 M KOH. It substantially promoted overall water splitting with 1.6 V at 30 mA cm-2, outperforming numerous bifunctional electrocatalysts under the same conditions. Notably, the remarkable stability for continuously splitting water endowed this hierarchical heterostructure with potential applications on a large scale. This work emphasizes the effectively controlled growth of heterostructured non-noble-metal catalysts for energy-conversion reaction
Angular Dependence of X-ray Absorption Spectrum for Field-aligned Fe-based Superconductors
Anisotropic Fe K-edge and As K-edge X-ray absorption near edge spectrum
(XANES) measurements on superconducting (T_c = 52 K)
(Sm_{0.95}La_{0.05})FeAs(O_{0.85}F_{0.15}) field-aligned microcrystalline
powder are presented. The angular dependence of Fe pre-edge peak (dipole
transition of Fe-1s electrons to Fe-3d/As-4p hybrid bands) relative to the
tetragonal ab-plane of aligned powder indicates larger density of state (DOS)
along the c-axis, and is consistent with the LDA band structure calculation.
The anisotropic Fe K-edge spectra exhibit a chemical shift to lower energy
compared to FeO which are closely related to the itinerant character of
Fe^{2+}-3d^6 orbitals. The anisotropic As K-edge spectra are more or less the
mirror images of Fe K-edge due to the symmetrical Fe-As hybridiztion in the
FeAs layer. Angular dependence of As main peak (dipole transition of As-1s
electrons to higher energy hybrid bands) was observed suggesting character of
As-4d e_g orbitals.Comment: 4 pages, 6 figures, accepted 9/11/2009 Physical Review B (B15
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