21,060 research outputs found
A dynamics-driven approach to precision machines design for micro-manufacturing and its implementation perspectives
Precision machines are essential elements in fabricating high quality micro products or micro features and directly affect the machining accuracy, repeatability and efficiency. There are a number of literatures on the design of industrial machine elements and a couple of precision machines commercially available. However, few researchers have systematically addressed the design of precision machines from the dynamics point of view. In this paper, the design issues of precision machines are presented with particular emphasis on the dynamics aspects as the major factors affecting the performance of the precision machines and machining processes. This paper begins with a brief review of the design principles of precision machines with emphasis on machining dynamics. Then design processes of precision machines are discussed, and followed by a practical modelling and simulation approaches. Two case studies are provided including the design and analysis of a fast tool servo system and a 5-axis bench-top micro-milling machine respectively. The design and analysis used in the two case studies are formulated based on the design methodology and guidelines
Critical exponents and the correlation length in the charge exchange manganite spin glass Eu_{0.5}Ba_{0.5}MnO_{3}
The critical regime of the charge exchange (CE) manganite spin glass
Eu_{0.5}Ba_{0.5}MnO_{3} is investigated using linear and non linear magnetic
susceptibility and the divergence of the third ordered susceptibility (chi{_3})
signifying the onset of a conventional freezing transition is experimentally
demonstrated. The divergence in chi{_3}, dynamical scaling of the linear
susceptibility and relevant scaling equations are used to determine the
critical exponents associated with this freezing transition, the values of
which match well with the 3D Ising universality class. Magnetic field
dependence of the spin glass response function is used to estimate the spin
correlation length which is seen to be larger than the charge/orbital
correlation length reported in this system.Comment: 4 pages, 4 Figure
Mesoscopic, Non-equilibrium Fluctuations of Inhomogeneous Electronic States in Manganites
By using the dark-field real-space imaging technique of transmission electron
microscopy (TEM), we have observed slow 200 A-scale fluctuations of
charge-ordered (CO) phase in mixed-valent manganites under a strong electron
beam irradiation. In addition to these unusual fluctuations of the CO phase, we
observed the switching-type fluctuations of electrical resistivity in the same
sample, which were found to be as large as several percents. Systematic
analysis indicates that these two different types of fluctuations with a
similar time scale of the order of seconds are interconnected through a
meta-stable insulating charge-disordered state. Current dependence of the
fluctuations suggests a non-equilibrium nature of this slow dynamics.Comment: To appear in Europhysics Letter
Spin Pseudo Gap in La2-xSrxCuO4 Studied by Neutron Scattering
Spin excitations of La2-xSrxCuO have been studied using inelastic neutron
scattering techniques in the energy range of 2 meV =< w =< 12 meV and the
temperature range of 8 K =< T =< 150 K. We observed a signature of a spin
pseudo gap in the excitation spectrum above Tc for the slightly overdoped
sample with x = 0.18. On heating, the spin pseudo gap gradually collapses
between T = 80 K and 150 K. For the x = 0.15 and 0.20, although the visibility
of gap-like structure at T ~ Tc is lower compared to the x = 0.18 sample, the
broad bump of kai"(w) appears at w ~ 5 meV,close to the spin-gap energy at base
temperature, suggests the existence of the spin pseudo gap in the normal state.Comment: revtex, 7 pages, 8 eps figures, PRB (2003) in pres
An electron paramagnetic resonance study of Pr_{0.6}Ca_{0.4}MnO_{3} across the charge ordering transition
We report the first electron paramagnetic resonance studies of single
crystals and powders of Pr_{0.6}Ca_{0.4}MnO_{3} in the 300-4.2 K range,
covering the charge ordering transition at ~ 240 K and antiferromagnetic
transition (T_N) at ~ 170 K. The asymmetry parameter for the Dysonian single
crystal spectra shows anomalous increase at T_{co}. Below T_{co} the g-value
increases continuously, suggesting a gradual strengthening of orbital ordering.
The linewidth undergoes a sudden increase at T_{co} and continues to increase
down to T_N. The intensity increases as the temperature is decreased till
T_{co} due to the renormalization of magnetic susceptibility arising from the
build up of ferromagnetic correlations. The value of the exchange constant, J,
is estimated to be 154 K.Comment: Uses Revtex3.
Magnetic Field resulting from non-linear electrical transport in single crystals of charge-ordered Pr Ca MnO}
In this letter we report that the current induced destabilization of the
charge ordered (CO) state in a rare-earth manganite gives rise to regions with
ferromagnetic correlation. We did this experiment by measurement of the I-V
curves in single crystal of the CO system
PrCaMnO and simultanously measuring the magnetization
of the current carrying conductor using a high T SQUID working at T = 77K.
We have found that the current induced destabilization of the CO state leads to
a regime of negative differential resistance which leads to a small enhancement
of the magnetization of the sample, indicating ferromagnetically aligned
moments.Comment: 4 pages LateX, 4 eps figure
Coherent Microwave Emission of a Gain-Driven Polariton
By developing a gain-embedded cavity magnonics platform, we create
gain-driven polariton (GDP) that is activated by an amplified electromagnetic
field. Distinct effects of gain-driven light-matter interaction, such as
polariton auto-oscillations, polariton phase singularity, self-selection of a
polariton bright mode, and gain-induced magnon-photon synchronization, are
theoretically studied and experimentally manifested. Utilizing the
gain-sustained photon coherence of the GDP, we demonstrate polariton-based
coherent microwave amplication (~ 40 dB) and achieve high-quality coherent
microwave emission (Q > 10^9).Comment: 6 pages, 4 figure
Determinants of second pregnancy among pregnant women: a hospital-based cross-sectional survey in China
This study aimed to explore determinants of second pregnancy and underlying reasons among pregnant Chinese women.The study was a population-based cross-sectional survey.16 hospitals in 5 provinces of Mainland China were included.A total of 2345 pregnant women aged 18 years or above were surveyed face to face by investigators between June and August 2015.The pregnancy statuses (first or second pregnancy) and reasons for entering second pregnancy.A total of 1755 (74.8%) and 590 (25.2%) women in their respective first and second pregnancies were enrolled in this study. The most common self-reported reasons for entering second pregnancy among participants included the benefits to the first child (26.1%), love of children (25.8%), adoption of the 2-child policy (11.5%), concerns about losing the first child (7.5%) and suggestions from parents (7.5%). Pregnant women with low (prevalence ratio (PR) 1.96; 95% CI 1.62 to 2.36) and moderate education level (PR 1.97; 95% CI 1.65 to 2.36) were more likely to have a second pregnancy than their higher educated counterparts. Income was inversely associated with second pregnancy. However, unemployed participants (PR 0.79; 95% CI 0.66 to 0.95) were less likely to enter a second pregnancy than those employed. Women with moderate education were 3 times more likely to have a second child following the '2-child policy' than the low education level subgroup.1 in every 4 pregnant women is undergoing a second pregnancy. The benefits of the firstborn or the love of children were the key drivers of a second pregnancy. Low socioeconomic status was positively associated with a second pregnancy as well. The new 2-child policy will have an influence on China's demographics.Xianglong Xu, Hanxiao Zuo, Zumin Shi, Yunshuang Rao, LianLian Wang, Huan Zeng, Lei Zhang, Manoj Sharma, Cesar Reis, Yong Zha
- …