Fast magnetization reversal of a magnetic nanoparticle induced by cosine chirp microwave field pulse

We investigate the magnetization reversal of single-domain magnetic nanoparticle driven by the circularly polarized cosine chirp microwave pulse (CCMP). The numerical findings, based on the Landau-Lifshitz-Gilbert equation, reveal that the CCMP is by itself capable of driving fast and energy-efficient magnetization reversal. The microwave field amplitude and initial frequency required by a CCMP are much smaller than that of the linear down-chirp microwave pulse. This is achieved as the frequency change of the CCMP closely matches the frequency change of the magnetization precession which leads to an efficient stimulated microwave energy absorption (emission) by (from) the magnetic particle before (after) it crosses over the energy barrier. We further find that the enhancement of easy-plane shape anisotropy significantly reduces the required microwave amplitude and the initial frequency of CCMP. We also find that there is an optimal Gilbert damping for fast magnetization reversal. These findings may provide a pathway to realize the fast and low-cost memory device.

ROLE OF RESPIRATORY RATE IN THE TOLERABILITY OF PERSONAL RESPIRATORY PROTECTION EQUIPMENT

The factor limiting the tolerance of personal respiratory protection equipment should be considered the frequency of respiratory movements, which reflexively changes when additional respiratory resistance occurs. Unfortunately, there is almost no information in the available literature about changes in the tolerability of personal respiratory protection equipment at different rates of respiratory movements. The purpose of this work was to study the tolerability of personal respiratory protection equipment when changing the frequency of respiratory movements.The study was conducted on practically healthy persons of both sexes (78 people), aged from 20 to 36 years. To simulate the conditions for the use of personal respiratory protection equipment, inspiratory resistive respiratory loads of 20% of the maximum intraoral pressure during the Mueller test were used. The tolerance of personal respiratory protection equipment was assessed using the Borg visual analogue of dyspnea scale, which reflected the level of subjective discomfort that occurs when additional respiratory resistance is turned on. During the action of additional respiratory resistance, the persons were asked to hold the frequency of respiratory movements, which was set using a special setting.An increase in the rate of respiratory movements against the background of additional respiratory resistance leads to a significant deterioration in the objective and subjective indicators of the functional state of the persons; replacing the inhaled air with an oxygen-rich respiratory mixture with carbon dioxide absorption did not lead to a significant improvement in the functional state. A moderate decrease (up to 70% of the initial frequency of respiratory movements) in the rate of respiration leads to an improvement in the indicators of adaptive activity in conditions of additional respiratory resistance. A significant decrease (up to 35% of the initial frequency of respiratory movements) in the rate of respiration under conditions of additional respiratory resistance leads to a deterioration of objective and subjective indicators of the functional state of the subjects.An increase in peak respiratory flow rates caused by an increase in the rate of respiration, in accordance with the well – known Rohrer equation, significantly increases inelastic resistance and, as a result, respiratory needs. These needs can be met at some time due to a significant increase in the work of the respiratory muscles, but due to fatigue of the latter, psychoemotional tension increases quite quickly and the use of personal respiratory protection equipment is abandoned.

Mathematical Representations in Magazine Advertisements: Have the Messages Changed in a Decade?

Although people's ideas about mathematics and mathematicians often develop from their school and home experiences, such ideas also are influenced by interactions with popular media. In this article, I report on findings from a study in which I analyzed magazine advertisements for representations of mathematics and mathematicians. Data collection took place in two phases, approximately a decade apart. In each phase, I reviewed a year’s worth of issues in each of six diverse, popular magazines for mathematical representations in advertisements. The frequency of mathematical advertisements decreased from Phase 1 to Phase 2, but the initial frequency was already extremely low, indicating mathematics’ invisibility in popular media. This lack of representation may be due to mathematics not being seen as a “cool” way to sell a product or service since mathematics is linked to many negative stereotypes. The representations were similar in the two phases, with mathematics often depicted in stereotypical ways, such as being difficult or stressful. People rarely featured in the mathematical advertisements, which serves to further dehumanize mathematics. Generally, the findings were consistent with those from studies of other popular media, such as movies and books.

ДИНАМИЧЕСКИЕ ХАРАКТЕРИСТИКИ СОВРЕМЕННЫХ ВЫСОКОСКОРОСТНЫХ СИСТЕМ СИНХРОНИЗАЦИИ

Представлены результаты исследований динамических характеристик современных высокоскоростных систем синхронизации: инновационной глобально линеаризованной системы синхронизации (ГЛСС) и системы ФАПЧ с импульсным частотно-фазовым детектором с накачкой заряда. Показано, что при значительных начальных частотных расстройках выигрыш в быстродействии системы ГЛСС может достигать порядка и выше. The paper highlights the results of research of modern high-speed synchronization systems dynamic characteristics, namely: the Globally Linearized Synchronization System (GLSS) and the PLL system with a pulsed frequency-phase detector with charge pumping. It has been shown that with significant initial frequency detuning, the acquisition speed gain of the GLSS system can reach an order of magnitude and higher.

THE INVESTIGATION OF END MILL FEEDS ON CNC ROUTER MACHINE USING VIBRATION METHOD

Vibration on End Mill Feeds will occur due to friction between the workpiece and end mill. The friction which occurs will cause tool wear in the insert blade. At this point, the tool wear experienced by the end mill can be seen from the imperfect feed of the workpiece that is resulted. Therefore, it is necessary to find out a method that can quickly and accurately detect tool wear at the end mill. The one that was experimented in this study was the vibration method. The vibration response was measured at their x, y, and z axes with rotation speeds of 2500 rpm, 3500 rpm, and 4500 rpm. At the broken end mill, it was shown that frequencies resulted did not affect the rotation while in the standard end mill. The initial frequency was highly influenced by spindle rotations treated on it.

Design and characterization of tunable three-dimensional acoustic composite metamaterials

Purpose The purpose of this paper is to developing a kind of acoustic metamaterial with wide frequency band especially in low frequency region. At the same time, its the tunability of sound insulation frequency is achieved. Design/methodology/approach A three-dimensional (3D) acoustic metamaterial consisting of rigid frame, spherical attachment and thin film is proposed. The material parameters and the effect of the attachment hole on the forbidden band are investigated by finite element simulation. The sound insulation effect of the structure is validated by the combination of simulation and experiment. Findings The results show that the elastic modulus of the structural material determines the initial frequency of the forbidden band of the proposed 3D acoustic metamaterials. The lower the elastic modulus of the structural material, the lower the initial frequency of the forbidden band. The material parameters of the frame mainly affect the initial frequency of the first forbidden band, and the material parameters of the attachment will affect both the initial and termination frequency of the first forbidden band. Holes in the attachments reduce the band gap width. The characteristic curve moves down with the increase of subtracted mass. Research limitations/implications The findings may greatly benefit the application of the acoustic metamaterials in the fields of sound insulation and noise reduction. Originality/value This acoustic metamaterial structure has excellent sound insulation performance. At the same time, the single cell structure can be assembled into any shape. The structure can achieve sound selective filtering and combination control.

Selection on mutators is not frequency-dependent

The evolutionary fate of mutator mutations – i.e., genetic variants that raise the genome-wide mutation rate – in asexual populations is often described as being frequency (or number) dependent. This common intuition suggests that mutators can invade a population by hitchhiking with a sweeping beneficial mutation, but only when sufficiently frequent to produce such a mutation before non-mutators do. Here, we use stochastic, agent-based simulations to show that neither the strength nor the sign of selection on mutators depend on their initial frequency, and while the overall probability of hitchhiking increases predictably with frequency, the per-capita probability of fixation remains unchanged.