22,183 research outputs found
Measuring and analysing vibration motors in insoles via accelerometers
Purpose: Falling is a major public health concern among elderly people, and they often cause serious injuries1,2. They most frequently occur during walking and are associated with the chronic deterioration in the neuromuscular and sensory systems, as well as with ankle muscle weakness and lower endurance of these muscles to fatigue1,3. Vibrating insoles, providing a subsensory mechanical noise signal to the plantar side of the feet, may improve balance in healthy young and older people and in patients with stroke or diabetic neuropathy4. The object of this study is to find the most suitable vibrator to put into the insole which can effectively improve the balance control of the elderlies. Method: We choose three different vibration actuators (micro vibration motor, brushless motor and eccentric motor) with two different weights on the insole. First, we put three same motors and two accelerometers on the insole, as shown in Figure1, then attach another layer on both side of the insole. Second, connect the motors to the power supply and the accelerometer to NI PXI-1033 spectrum analyzer which is used to collect the accelerometers' data. At last, using Fast Fourier Transform (FFT) to analyze and compare the results to see which motor is the most stable and suitable to put into the insole. Results & Discussion: The results showed that the most stable one is the brushless motor. The reason why the frequency is stable is that the relationship between voltage and frequency is linear, and the error is small through continuous measurements. On the other hand, when a person weight 55 kg stands on the insole, the frequency isn't affected by the weight. These two results appear very similar to each other, as shown in Figure 2. According to the result, we use the brushless motor to be our vibrator in the insole, and hope this will help the elderlies improve their balance control ability more efficiency
Multi-wavelength variability properties of Fermi blazar S5 0716+714
S5 0716+714 is a typical BL Lacertae object. In this paper we present the
analysis and results of long term simultaneous observations in the radio,
near-infrared, optical, X-ray and -ray bands, together with our own
photometric observations for this source. The light curves show that the
variability amplitudes in -ray and optical bands are larger than those
in the hard X-ray and radio bands and that the spectral energy distribution
(SED) peaks move to shorter wavelengths when the source becomes brighter, which
are similar to other blazars, i.e., more variable at wavelengths shorter than
the SED peak frequencies. Analysis shows that the characteristic variability
timescales in the 14.5 GHz, the optical, the X-ray, and the -ray bands
are comparable to each other. The variations of the hard X-ray and 14.5 GHz
emissions are correlated with zero-lag, so are the V band and -ray
variations, which are consistent with the leptonic models. Coincidences of
-ray and optical flares with a dramatic change of the optical
polarization are detected. Hadronic models do not have the same nature
explanation for these observations as the leptonic models. A strong optical
flare correlating a -ray flare whose peak flux is lower than the
average flux is detected. Leptonic model can explain this variability
phenomenon through simultaneous SED modeling. Different leptonic models are
distinguished by average SED modeling. The synchrotron plus synchrotron
self-Compton (SSC) model is ruled out due to the extreme input parameters.
Scattering of external seed photons, such as the hot dust or broad line region
emission, and the SSC process are probably both needed to explain the
-ray emission of S5 0716+714.Comment: 43 pages, 13 figures, 3 tables, to be appeared in Ap
Microwave performance of high-density bulk MgB2
We have performed microwave measurements on superconducting
hot-isostatically- pressed (HIPed) bulk MgB2 using a parallel-plate resonator
technique. The high density and strength of the HIPed material allowed
preparation of samples with mirror-like surfaces for microwave measurements.
The microwave surface resistance decreased by about 40% at 20 K when the
root-mean-square surface roughness was reduced from 220 nm to 110 nm through
surface-polishing and ion-milling. The surface resistance was independent of
surface microwave magnetic field at least up to 4 Oe and below 30 K. We
attribute this behavior, and the overall low surface resistance (~0.8 mOhms at
10 GHz and 20 K), to the high density of our samples and the absence of weak
links between grains
The influence of structural defects on intra-granular critical currents of bulk MgB2
Bulk MgB2 samples were prepared under different synthesis conditions and
analyzed by scanning and transmission electron microscopy. The critical current
densities were determined from the magnetization versus magnetic field curves
of bulk and powder-dispersed-in-epoxy samples. Results show that through a slow
cooling process, the oxygen dissolved in bulk MgB2 at high synthesis
temperatures can segregate and form nanometer-sized coherent precipitates of
Mg(B,O)2 in the MgB2 matrix. Magnetization measurements indicate that these
precipitates act as effective flux pinning centers and therefore significantly
improve the intra-grain critical current density and its field dependence.Comment: 4 pages, 4 figures, to be published in IEE Transactions in Applied
Superconductivit
Assessing the integrity of steel structural components with stress raisers using the Theory of Critical Distances
This paper assesses and evaluates the detrimental effect of standard and complex geometrical features on the static strength of samples made of Q460 steel. The experimental results generated by testing four types of notched specimens were analyzed using the Theory of Critical Distances (TCD). The considered configurations included uniaxial tension tests on standard notched round bars and double-side U-notched flat plate specimens. In particular, our attention was focused on the fracture behavior of two specimens containing complex geometrical features subjected to pure-shear and tensile-shear local stress states. The common feature of these two notched specimens was that cracks were seen to initiate, within the material, away from the stress raisers, even though obvious stress concentrations existed at notch tip. The performed validation exercise confirms the accuracy and reliability of the linear-elastic TCD in estimating the fracture initiation position and static strength of standard notched round bars and double-side U-notched flat plate specimens. In the meantime, the linear-elastic method proposed in this paper can also be used as an effective approach to assess the fracture behavior of metallic components having complex geometry
Renormalization Group and Universality
It is argued that universality is severely limited for models with multiple
fixed points. As a demonstration the renormalization group equations are
presented for the potential and the wave function renormalization constants in
the scalar field theory. Our equations are superior compared with the
usual approach which retains only the contributions that are non-vanishing in
the ultraviolet regime. We find an indication for the existence of relevant
operators at the infrared fixed point, contrary to common expectations. This
result makes the sufficiency of using only renormalizable coupling constants in
parametrizing the long distance phenomena questionable.Comment: 32pp in plain tex; revised version to appear in PR
On the Connection Between Momentum Cutoff and Operator Cutoff Regularizations
Operator cutoff regularization based on the original Schwinger's proper-time
formalism is examined. By constructing a regulating smearing function for the
proper-time integration, we show how this regularization scheme simulates the
usual momentum cutoff prescription yet preserves gauge symmetry even in the
presence of the cutoff scales. Similarity between the operator cutoff
regularization and the method of higher (covariant) derivatives is also
observed. The invariant nature of the operator cutoff regularization makes it a
promising tool for exploring the renormalization group flow of gauge theories
in the spirit of Wilson-Kadanoff blocking transformation.Comment: 28 pages in plain TeX, no figures. revised and expande
Flow Equations for U_k and Z_k
By considering the gradient expansion for the wilsonian effective action S_k
of a single component scalar field theory truncated to the first two terms, the
potential U_k and the kinetic term Z_k, I show that the recent claim that
different expansion of the fluctuation determinant give rise to different
renormalization group equations for Z_k is incorrect. The correct procedure to
derive this equation is presented and the set of coupled differential equations
for U_k and Z_k is definitely established.Comment: 5 page
- …