5,327 research outputs found
Spectra of ultrabroadband squeezed pulses and the finite-time Unruh-Davies effect
We study spectral properties of quantum radiation of ultimately short
duration. In particular, we introduce a continuous multimode squeezing operator
for the description of subcycle pulses of entangled photons generated by a
coherent-field driving in a thin nonlinear crystal with second order
susceptibility. We find the ultrabroadband spectra of the emitted quantum
radiation perturbatively in the strength of the driving field. These spectra
can be related to the spectra expected in an Unruh-Davies experiment with a
finite time of acceleration. In the time domain, we describe the corresponding
behavior of the normally ordered electric field variance.Comment: 11 pages, 5 figure
Development and test of resistive superconducting fault current limiter; acting time and its recovery conditions
Resistive-type of superconducting fault current limiters (RSFCL) have been developed for medium voltage class aiming to operate at 1 MVA power capacity and short time recovery (< 2 s). A RSFCL in form of superconducting modular device was designed and constructed using 50 m-length of YBCO coated conductor tapes for operation under 1 kV / 1 kA and acting time of 0.1 s. In order to increase the acting time the RSFCL was combined with an air-core reactor in parallel to increase the fault limiting time up to 1 s. The tests determined the electrical and thermal characteristics of the combined resistive/ inductive protection unit. The combined fault current limiter reached a limiting current of 583 A, corresponding to a limiting factor of 3.3 times within an acting time of up to 1 s
Hybrid GMR Sensor Detecting 950 pT/sqrt(Hz) at 1 Hz and Room Temperature.
Advances in the magnetic sensing technology have been driven by the increasing demand for the capability of measuring ultrasensitive magnetic fields. Among other emerging applications, the detection of magnetic fields in the picotesla range is crucial for biomedical applications. In this work Picosense reports a millimeter-scale, low-power hybrid magnetoresistive-piezoelectric magnetometer with subnanotesla sensitivity at low frequency. Through an innovative noise-cancelation mechanism, the 1/f noise in the MR sensors is surpassed by the mechanical modulation of the external magnetic fields in the high frequency regime. A modulation efficiency of 13% was obtained enabling a final device's sensitivity of ~950 pT/Hz1/2 at 1 Hz. This hybrid device proved to be capable of measuring biomagnetic signals generated in the heart in an unshielded environment. This result paves the way for the development of a portable, contactless, low-cost and low-power magnetocardiography device
Active Metal Brazing of Machinable Aluminum Nitride-Based Ceramic to Stainless Steel
Shapal!-M machinable AlN-based ceramic and AISI 304 stainless steel were joined by active metal
brazing, at 750, 800, and 850 !C, with a dwell stage of 10 min at the processing temperature, using a 59Ag-
27.25Cu-12.5In-1.25Ti (wt.%) filler foil. The influences of temperature on the microstructural features of
brazed interfaces and on the shear strength of joints were assessed. The interfacial microstructures were
analyzed by scanning electron microscopy (SEM), and the composition of the phases detected at the
interfaces was evaluated by energy dispersive X-ray spectroscopy (EDS). The fracture surfaces of joints
were analyzed by SEM, EDS, and GIXRD (Grazing Incidence X-Ray Diffraction). Reaction between the
liquid braze and both base materials led to the formation of a Ti-rich layer, adjacent to each base material.
Between the Ti-rich layers, the interfaces consist of a (Ag) solid-solution matrix, where coarse (Cu) particles
and either Cu-In or Cu-In-Ti and Cu-Ti intermetallics phases are dispersed. The stronger joints, with shear
strength of 220±32 MPa, were produced after brazing at 800 !C. Fracture of joints occurred preferentially
not only through the ceramic sample but also across the adjoining TiN layer, independent of the
brazing temperature
Population structure of Pentaclethra macroloba (Willd.) Kuntze in high and low floodplains of the Amazonian estuary.
The flood cycle of floodplain forests and topographic variations are important factors of diversification and morphological and ecophysiological adaptations of the plant community. Pentaclethra macroloba is a hyperdominant species adapted to flood variations. The objective of this study was to characterize the P. macroloba population structure between environments with high topography, flooded only during the rainy season and peak flood of the river, (high várzea-HV) and low topography with daily flood (low várzea-LV). The study was carried in the MazagĂŁo Experimental Field, Brazil. Four plots of 1 ha were installed in each environment. All individuals with DBH ≥ 5 cm were measured and georeferenced. ANOVA test, 0.05% probability, was applied to verify the structural differences between two environments. The HV had higher population density (51.2 individuals.ha-1) compared to the LV (36.7 individuals.ha-1), although without significance. Basal area was higher in the HV (10.42 m²) in comparison with LV (5.90 m²), with significant difference (F = 7.13, p = 0.00795). The maximum DAP of HV was 67 cm with mean of 24 cm. The LV presented maximum DBH of 42 cm with mean of 21 cm, showing structural difference between the two environments (F = 6.22, p = 0.0131). The aggregation index showed high aggregation in the LV (R = 0.89) than in the HV (R = 0.79), differing significantly between the two environments (F = 11.31, p = 0.0008). Frequency and time of flooding are ecological drives that structure the population of pracaxizeiro causing morphological and ecophysiological adaptations to the individual
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