Spin-glass ordering in the diluted magnetic semiconductor Zn1-xMnxTe

Magnetic measurements on the spin-glass behavior in the bulk II-VI diluted magnetic semiconductor (DMS) ZnMnTe were made on two crystals of concentrations x = 0.43 and 0.55 taken from the same boule. Magnetization and density functional theory studies have shown paramagnetic behavior in both samples between 30 and 400 K. Below 30 K, there is a prominent peak at Tc = 15 and 23.6 K for concentrations x = 0.43 and 0.55, respectively. The splitting of the field cooled (FC) and zero field cooled (ZFC) data below this peak is indicative of a transition to a spin-glass state at low temperature for semiconductors. Therefore, through the p− and d− orbits hybridization a magnetic exchange produces the spin-glass behavior seen in the DMS ZnMnTe

Raman study of the Verwey transition in Magnetite at high-pressure and low-temperature; effect of Al doping

We report high-pressure low-temperature Raman studies of the Verwey transition in pure and Al-doped magnetite (Fe_3O_4). The low temperature phase of magnetite displays a number of additional Raman modes that serve as transition markers. These transition markers allow one to investigate the effect of hydrostatic pressure on the Verwey transition temperature. Al-doped magnetite Fe_2.8Al_0.2O_4 (TV=116.5K) displays a nearly linear decrease of the transition temperature with an increase of pressure yielding dP/dT_V = -0.096 GPa/K. In contrast pure magnetite displays a significantly steeper slope of the PT equilibrium line with dP/dT_V = -0.18 GPa/K. The slope of the PT equilibrium lines is related to the changes of the molar entropy and molar volume at the transition. We compare our spectroscopic data with that obtained from the ambient pressure specific heat measurements and find a good agreement in the optimally doped magnetite. Our data indicates that Al doping leads to a smaller entropy change and larger volume expansion at the transition. Our data displays the trends that are consistent with the mean field model of the transition that assumes charge ordering in magnetite.Comment: 17 pages, 3 figure

Utilization of a Piezoelectric Polymer to Sense Harmonics of Electromagnetic Torque

In this paper, the use of a piezoelectric polymer material to measure the harmonics of electromagnetic torque produced by a permanent magnet synchronous machine is described. The advantages of the polymer include low cost, durability, and flexibility. In addition, wide-bandwidth sensors are relatively easy to design and couple to drive system hardware for harmonic evaluation or to use in feedback-based control. To illustrate the use of the polymer, the electrical and mechanical properties of three sensors are described. The results of time-domain simulation and hardware experiments are used to validate that the voltage obtained from the sensors is linearly related to the torque ripple produced by the machine

Torque Ripple Sensor and Mitigation Mechanism

A torque ripple sensor and method for torque ripple sensing and/or mitigation. A piezoelectric sensor is positioned relative to a motor so that torque fluctuations due to torque ripple of the motor are transmitted to the sensor, resulting in strain of a piezoelectric element. A resulting signal can be amplified and conditioned for determining a magnitude of the torque ripple and/or fed into a feedback loop for applying current control or a counter-torque to the motor for torque ripple mitigation

Measurement and Control of Torque Ripple-Induced Frame Torsional Vibration in a Surface Mount Permanent Magnet Machine

A sensor to measure the stator torsional vibration due to torque ripple produced by a surface mount permanent magnet machine is first described. The sensor is relatively inexpensive and is straight forward to incorporate into a drive system. Experiments are performed to validate that the voltage produced by the sensor is linearly related to torque ripple amplitude. Closed-loop controllers are then described that adjust the stator current harmonics applied to the machine to achieve a commanded average torque while mitigating measured torsional vibration. Simulation and experimental results are used to demonstrate the effectiveness of the control techniques

Self-referencable frequency comb from a 170-fs, 1.5-μm solid-state laser oscillator

We report measurement of the first carrier-envelope offset (CEO) frequency signal from a spectrally broadened ultrafast solid-state laser oscillator operating in the 1.5μm spectral region. The f-to-2f CEO frequency beat signal is 49 dB above the noise floor (100-kHz resolution bandwidth) and the free-running linewidth of 3.6 kHz is significantly better than typically obtained by ultrafast fiber laser systems. We used a SESAM mode-locked Er:Yb:glass laser generating 170-fs pulses at a 75MHz pulse repetition rate with 110-mW average power. It is pumped by one standard telecom-grade 980-nm diode consuming less than 1.5W of electrical power. Without any further pulse compression and amplification, a coherent octave-spanning frequency comb is generated in a polarization-maintaining highly-nonlinear fiber (PM-HNLF). The fiber length was optimized to yield a strong CEO frequency beat signal between the outer Raman soliton and the spectral peak of the dispersive wave within the supercontinuum. The polarization-maintaining property of the supercontinuum fiber was crucial; comparable octave-spanning supercontinua from two non-PM fibers showed higher intensity noise and poor coherence. Astable CEO-beat was observed even with pulse durations above 200fs. Achieving a strong CEO frequency signal from relatively long pulses with moderate power levels substantially relaxes the demands on the driving laser, which is particularly important for novel gigahertz diode-pumped solid-state and semiconductor laser

No alignment of cattle along geomagnetic field lines found

This paper presents a study of the body orientation of domestic cattle on free pastures in several European states, based on Google satellite photographs. In sum, 232 herds with 3412 individuals were evaluated. Two independent groups participated in our study and came to the same conclusion that, in contradiction to the recent findings of other researchers, no alignment of the animals and of their herds along geomagnetic field lines could be found. Several possible reasons for this discrepancy should be taken into account: poor quality of Google satellite photographs, difficulties in determining the body axis, selection of herds or animals within herds, lack of blinding in the evaluation, possible subconscious bias, and, most importantly, high sensitivity of the calculated main directions of the Rayleigh vectors to some kind of bias or to some overlooked or ignored confounder. This factor could easily have led to an unsubstantiated positive conclusion about the existence of magnetoreception.Comment: Added electronic supplement with source dat

Picosecond diode-pumped 1.5 μm Er,Yb:glass lasers operating at10-100 GHz repetition rate

Stable ultrafast laser sources at multi-GHz repetition rates are important for various application areas, such as optical sampling, frequency comb metrology, or advanced high-speed return-to-zero telecom systems. We review SESAM-mode-locked Er,Yb:glass lasers operating in the 1.5μm spectral region at multi-GHz repetition rates, discussing the key improvements that have enabled increasing the repetition rate up to 100GHz. We also present further improved results with shorter pulse durations from a 100GHz Er,Yb:glass laser. With an improved SESAM design we achieved 1.1ps pulses with up to 30mW average output power. Moreover, we discuss for the first time the importance of beam quality deteriorations arising from frequency-degenerate higher order spatial modes in such laser