CMOS magnetic field to frequency converter

In this paper, a CMOS magnetic field to frequency converter with high resolution is presented. It is composed of two voltage-controlled ring oscillators whose output frequency differences linearly vary with the magnetic field perpendicular to the chip surface. The prototype circuit has been fabricated in a 0.5-/spl mu/m CMOS process and operated at a 5-V supply voltage. The measured sensitivity is 24 kHz/mT and the power consumption is 5.1 mW. The small equivalent resolution of at least 20 /spl mu/T can be achieved. The frequency offset is 42 kHz when no magnetic field applied. Its nonlinearity within /spl plusmn/120 mT is smaller than 0.56%.     

3600m~3/h空分设备氮水预冷系统存在的三个问题

分析 36 0 0m3 /h空分设备氮水预冷系统存在的三个问题及原因 ,指出氮水预冷系统在操作中需注意的四个方面。     

Improvement of the /spl mu/-Hall magnetic sensor sensitivity at low frequency

We have developed a configuration for precision magnetic measurements associating a /spl mu/-Hall sensor, a modulated ferromagnetic antenna, and an analog electronic circuitry. This association is not only able to remove the 1/f noise of the Hall sensor, but also to achieve an ultimate noise level even lower than thermal white noise of the Hall sensor. The system main characteristics are the following: bandwidth 645 Hz, noise level white and lower than 10 nT//spl radic/Hz above 0.1 Hz, slew rate 10/sup -1/ T/s and system dynamic 84 dB in a 1-Hz bandwidth. The performances of the modulated sensor are compared to those of a dc operated sensor.     

High frequency magnetic mechanism of Ni-substituted Co2Z hexagonal ferrite

The magnetic properties, especially the high frequency magnetic mechanism, of Ni-substituted Co₂Z hexagonal ferrite were studied. The polycrystalline Z-type hexagonal ferrite of Ba₃Ni_xCo_2−xFe₂₄O₄₁ (0 ≤ x ≤ 2) were prepared by solid-state reaction. The results indicate that Ni-substituted Co₂Z samples all exhibit typical soft magnetic character. Substitution of Ni for Co will turn the planar magnetocrystalline anisotropy of Co₂Z to uniaxial anisotropy when x ≥ 1, so that the permeability drops dramatically and domain wall resonance appears in the frequency spectra. With the rise of Ni amount or sintering temperature, domain wall resonance strengthens gradually.     

铌、钒微合金化生产HRB400钢筋的分析

主要分析了Nb、V微合金化的机理、特点，比较了在钢中的存在形态以及各自的析出特性以及铌、钒微合金化生产HRB400钢筋工艺流程的区别。     

High frequency magnetic eigen excitations in a spin valve submitted to CPP DC current

We study the magnetization dynamics induced at low field by spin-transfer in a pillar-shaped spin valve. The spin valve is a square of 150 nm× 150 nm patterned from a film of IrMn 7 nm/CoFe, 2.4 nm/Ru, 0.8 nm/CoFe, 4.4 nm/Cu, 2.6 nm/CoFe, and 3.6 nm. The spin valve is studied in its anti-parallel state at 50 K. The high frequency voltage noise generated by the DC current flowing through the magneto-resistive device is used to identify the excitations induced by spin-transfer. Between an instability current of 1.72 mA and the switching current of 1.89 mA, we demonstrate the existence of pre-switch steady-state excitations, i.e. low amplitude precession. We study the frequency (10 GHz, red shift −1.46 GHz/mA) of this excitation, its line width (78–246 MHz), the power it carries (113 nW), and the current dependance thereof. We discuss those experimental findings using the formalism of Sun et al. and Valet et al., and show that the experimental behavior can be described by a macrospin approximation only at the very onset of the pre-switch excitations. The early saturation of the excitation power and the non-monotonic switching probability with the current are experimental indications that the pre-switch excitations are strongly non-uniform when approaching the switching current.     

Synthesis,characterization and low frequency a.c. conduction of polyaniline/fly ash composites

In situ polymerization of aniline was carried out in the presence of fly ash (FA) to synthesize polyaniline/ fly ash (PANI/FA) composites. The PANI/FA composites have been synthesized with various compositions (15, 20, 30 and 40 wt%) of FA in PANI. The composites, thus synthesized have been characterized by infrared spectroscopy and X-ray diffraction. The morphology of these samples was studied by scanning electron microscopy. Further the a.c. conductivity of these composites have been investigated in the frequency range 10²–10⁶ Hz. The presence of polarons and bipolarons are made responsible for frequency dependence of a.c. conductivity in these composites. The Cole-Cole plots indicate clear shift in the distribution of relaxation times as the wt% of FA in PANI changes. These composites show almost symmetric semicircles of Cole-Cole plots indicating the Debye-type relaxation in their polarization response.     

MnZn铁氧体/FeSiAl粉末复合体磁芯的制备及其高频EMI抑制性能

介绍了MnZn铁氧体/FeSiAl粉末复合体磁芯的设计思路和制备过程,并研究了复合体磁芯的高频EMI抑制性能。首先分析了两种材料的高频EMI的抑制机理并完成了复合体磁芯制备工艺的设计,然后介绍了MnZn铁氧体/FeSiAl复合体磁芯的制备过程,详细分析了复合体磁芯的Fe-SiAl粉末氧化膜包覆和内部相间反应的关键工艺,并对不同工艺制备的磁芯磁损耗性能进行对比测试和分析。试验结果表明:FeSiAl粉末通过氧化膜包覆工艺后烧结成型制备磁芯高频EMI抑制性能较好,在频率范围为1~1.8GHz磁导率虚部都保持了较高的数值(平均值9.98),最高值达13.33;另外通过氧化膜包覆工艺处理后FeSiAl粉末和MnZn铁氧体混合,通过粘接压制方法制备的复合体磁芯,综合了两种材料的优点,高频EMI抑制性能较好(平均值8.64),而通过烧结制备的复合体磁芯,由于内部相间反应不易控制,造成EMI抑制性能下降。     

Ceo2/Cus Nanoplates Electroreduce Co2 to Ethanol with Stabilized Cu+ Species

Copper-based electrocatalysts effectively produce multicarbon (C₂₊) compounds during the electrochemical CO₂ reduction (CO₂RR). However, big challenges still remain because of the chemically unstable active sites. Here, cerium is used as a self-sacrificing agent to stabilize the Cu⁺ of CuS, due to the facile Ce³⁺/Ce⁴⁺ redox. CeO₂-modified CuS nanoplates achieve high ethanol selectivity, with FE up to 54% and FE_C2+ ≈ 75% in a flow cell. Moreover, in situ Raman spectroscopy and in situ Fourier-transform infrared spectroscopy indicate that the stable Cu⁺ species promote C C coupling step under CO₂RR. Density functional theory calculations further reveal that the stronger ^*CO adsorption and lower C C coupling energy, which is conducive to the selective generation of ethanol products. This work provides a facile strategy to convert CO₂ into ethanol by retaining Cu⁺ species.     

Spin-flip contribution to the “in-plane” conductivity of magnetic multilayers

The “in-plane” conductivity of magnetic multilayers is calculated within the semiclassical approximation. The band structure is obtained with a tight-binding Hubbard Hamiltonian solved in the Hartree-Fock approximation. Once self-consistency is reached, the spin-orbit coupling term is added and a further diagonalization is performed. As it is well-known, quantum well states appear in the band structure of superlattices. By calculating the conductivity as a function of the Fermi energy we find that there is a considerable influence of these quantum well states if their energy is close to the Fermi level when the spin-orbit coupling is taken into account.     

The low frequency internal friction and electric magnetic properties in La0.7Pb0.3MnO3 bulk materials

The polycrystalline samples of La_0.7Pb_0.3MnO₃ synthesized by the sol–gel method were studied by the low frequency internal friction measurements and the resistance and ac susceptibility measurements. There are two internal friction peaks at 258 and 198 K, respectively, the peak positions of which do not shift with frequency but the peak heights of which decrease with increasing frequencies. The modulus softening is evident at the corresponding temperatures. Corresponding to the two internal friction peaks, there are two resistance peaks, and a sharp rise and a following continuous decrease of ac susceptibility. It is suggested that the high temperature peaks correspond to the paramagnetic (PM) to ferromagnetic (FM) transition, while the low temperature peaks originate from the process of an anti-ferromagnetic phase (AFM) separating from the ferromagnetic matrix (phase separation) in polycrystalline materials. The peak positions of internal friction and resistance will move towards higher temperature when the sample was annealed in flowing oxygen, and the low temperature peaks become smaller.     

Ultra-high velocity impacts: cratering studies of microscopic impacts from 3 km/s to 30 km/s

Cratering experiments performed under carefully controlled conditions at impact velocities ranging from 3 km/s to 30 km/s into a wide variety of target materials are presented. These impact experiments use the 6 MV vertical Van de Graaff accelerator of the Ion Beam Facility at the Los Alamos National Laboratory to electrostatically accelerate highly charged iron micro-spheres. The sub-micron spheres, from a random size distribution, are shocklessly accelerated along an 8 m flight path. Ultra-sensitive charge detectors monitor the passage of the projectiles at a rate of up to 100 projectiles/second. An online computer records and displays in real time the charge, velocity and mass of the projectiles and provides cross correlation between the events observed by the several in-flight charge detectors and impact detectors. Real-time logic controls an electrostatic kicker which deflects projectiles of selected charge and velocity onto the target. Thus each experiment consists of an ensemble of 10 to 40 impacts onto a single target within a narrow window of the projectile parameter space, providing excellent statistical resolution of each data point.

The target materials used include single crystal copper and single crystal aluminum, gold, and quartz as well as pyrolytic graphic and anoxy used in composite materials of interest to space applications. We also conducted impact experiments onto thin Mylar and nickel foils. This paper presents these experiments and summarizes the cratering characterization performed to date. Emphasis is placed on cratering results in several materials over a range of impact velocities.     

Low frequency magnetic shielding of YBa2Cu3O7-δ: Agx high temperature superconductors

Two measurement systems were used to investigate the low frequency magnetic shielding behavior of pure YBa₂Cu₃O_7−δ, silver doped YBa₂Cu₃O_7−δ, a packed powder, a laser ablated thin film and copper. It was found that factors which influence low frequency magnetic shielding include material composition, microstructure and properties, external a.c. and d.c. fields and sample dimensions. Among the experimental materials, only bulk ceramics showed good shielding factors which were constant with frequency in the range 10–3000 Hz. A macroscopic shielding current was necessary for a good shield. The thickness of the ceramic played a crucial role in shielding. Flux breakthrough occurred when the external field exceeded a certain value. The breakthrough field increased with sample thickness. The influence of d.c. fields on the shielding behaviour depended on the history and magnitudes of the fields. Magnetic shielding hysteresis was observed and its potential application is discussed.     

Liquid helium centrifugal pump characteristics from 80 g/s to 1200 g/s

The large amount of data collected from three different centrifugal liquid helium pumps tested, namely with 80, 600 and 1200 g/s nominal mass flow are reviewed. The data include the analysis of the characteristic curves, their total efficiencies, their Net Positive Suction Head (NPSH) and the slip factor. The 1200 g/s pumps tested are of the full emission type, with curved blades, whilst the other pumps have straight blades. The pumps were also tested at different rotary speeds. The pumps were manufactured by Barber & Nichols (Denver, USA).     

Temperature of laser-cooled /sup 171/Yb/sup +/ ions and application to a microwave frequency standard

Microwave frequency standards based on buffer gas-cooled /sup 171/Yb/sup +/ ions have demonstrated high stability but are limited in accuracy by the second-order Doppler shift caused by thermal motion. We have previously obtained near shot noise-limited Ramsey fringes with a laser-cooled ion cloud. Here, we present measurements confirming that the ion temperature remains <1 K throughout the microwave interrogation period for a Ramsey pulse separation of up to 10 s and longer. The potential stability of the ions as a frequency standard is better than /spl sigma//sub y/ (/spl tau/)=5/spl times/10/sup -14/ /spl tau//sup -1/2/, and estimates of the systematic offsets to the clock frequency and their uncertainties indicate that a total uncertainty of four parts in 10/sup 15/ or better is achievable.     

An impact technique to accelerate flier plates to velocities over 12 km/s

Very high pressure and acceleration is necessary to launch flier plates to hypervelocities. In addition, the high pressure loading must be uniform, structured, and shockless, i.e., time-dependent to prevent the flier plate from either fracturing or melting. In this paper, a novel technique is described which allows the use of 100 GPa megabar loading pressures and 10⁹-g acceleration to launch intact flier plates to velocities of 12.2 km/s. The technique has been used to launch nominally 1-mm thick aluminum, magnesium, and titanium alloy plates to velocities over 10 km/s, and 0.5-mm thick aluminum and titanium alloy plates to velocities of 12.2 km/s.     

Thermal Release of Hidden Magnetic Moments in High T c Bi:2223/Ag Superconducting Tape During Warming to T c

We report on measurements of the evolution of the magnetization ??M??, upon warming from T ₀ (77?K) to T _c , for Bi:2223/Ag tape prepared by the continuous filling and forming (CTFF) with the locus of ??M?? initially situated along bridges between the envelopes of the major hysteresis curves. Concentric, oppositely directed magnetic moments coexist in the specimens when ??M?? lies along the bridges. We focused on the cases where ??M??=0, hence before warming, the constituent moments cancel each other exactly. Since they diminish in magnitude at different rates as T is increased to T _c , their sequential ??release?? leads to a rich variety of phenomena. A comparison of experimental and theoretical results shows that our simple model semiquantitatively reproduces the major features of the observations on the specimen of Bi:2223/Ag tape.     

用Co部分置换Fe对Fe73.5Cu1Nb3Si13.5B9合金高频磁性的影响

研究了(Fe100-xCox)73 5Cu1Nb3Si13.5B9(x=0、50)纳米晶软磁合金的高频磁特性.结果表明,用Co部分置换Fe后,仍可形成纳米晶结构,并且可以显著提高合金的高频特性.与典型的Fe73.5Cu1Nb3Si13.5B9纳米晶软磁合金相比,其复数磁导率实部μ略有下降,但表征损耗的复数磁导率虚部μ"却大幅度降低,从而可显著提高软磁材料的截止使用频率fr及品质因数Q,本文初步探讨了在Fe73 5Cu1Nb3Si13.5B9合金基础上,用Co置换Fe而使高频特性得到改善的机理.