High Rotational Frequencies Research Articles

Microbial community structure in pasture and hayfield soils of the Helderberg region of New York State: a comparison of management strategies

ABSTRACTMicrobial communities in pasture and hayfield soils in upstate New York were studied to ascertain how land and livestock management practices influence microbial community structure. Three management approaches were compared: conventional pasture management (CM; low livestock density, low rotation frequency), multi-paddock management (MP; high livestock density, high rotation frequency) and mowing for hay (no livestock). Microbial functional groups were quantified by PLFA analysis. Soil attributes were measured, and management details were obtained by interviewing landowners. Microbial biomass in MP soils was higher, more diverse and contained proportionately more fungal (F) than bacterial (B) biomass than did CM and hayfield soils. Microbial biomass, diversity and F:B ratios in CM and hayfield soils were not different. Multivariate analyses suggest that different variables control microbial community structure in MP and CM soils.

Backbending, seniority, and Pauli blocking of pairing correlations at high rotational frequencies in rapidly rotating nuclei

Backbending, seniority, and Pauli blocking of pairing correlations at high rotational frequencies in rapidly rotating nuclei

Superconducting AC Homopolar Machines for High-Speed Applications

This paper presents a novel high-speed alternating current (AC) homopolar motor/generator design using stationary ReBCO excitation windings. Compact, lightweight, high-efficiency motors and generators are sought for a multitude of applications. AC homopolar synchronous machines are an ideal choice for such applications as these machines enable very high rotational frequencies. These machines include both AC armature winding and direct current (DC) excitation winding within the stationary part of the machine. The stationary excitation winding magnetizes a solid steel rotor, enabling operating speeds limited only by the mechanical stress limit of the rotor steel. The operating speeds are many multiples of conventional power 50/60 Hz machines. Significant cooling requirements limit machines of this type utilizing copper excitation windings to only a few kilowatts. However, megawatt ratings become possible when superconductor coils are used. This paper describes the design and analysis of an AC homopolar machine in the context of developing a 500 kW flywheel system to be used for energy recovery and storage in commuter rail subway systems. Different approaches are discussed for an AC armature employing conventional copper coils. Challenges of building and cooling both armature and field coils are discussed and preferred approaches are suggested. Calculations of the machine performance are then made.

Nonlinear analysis of the friction-induced vibrations of a rotor-stator system

In this paper, the vibratory dynamics of a system consists of a rotor and a stator with friction at the interface is studied. The main goal is to study how taking into account the deviation of the relative velocities associated with each point of the interface (rotor/stator) influences the model. The inclusion of this deviation, not usually modeled for this type of system, allows taking the friction plane into account. However, introducing this mechanism in a model with a friction interface leads to damping that in turn has an impact on the values and the convergence of the amplitudes of vibration. In addition, the deviation has a significant impact only when the rotation frequency of the rotating part is low. Thus this paper also focuses on the separation occurring at the interface. The method used to take this separation into account is presented. The addition of this separation in the model makes it possible to obtain more physically realistic limit cycles in the case of high rotation frequency. These two phenomena are combined in order to obtain physical amplitudes.

Vibration Reduction of Large Unbalanced Rotor Supported by Externally Pressurized Gas Journal Bearings With Asymmetrically Arranged Gas Supply Holes (Verification of the Effectiveness of a Supply Gas Pressure Control System)

A rotor supported by gas bearings vibrates within the clearance. If the static imbalance of the rotor is large, even if the rotation speed is low, large amplitude vibration is generated by the centrifugal force. This is a serious problem because the risk of bearing damage increases. In order to solve this problem, an externally pressurized gas journal bearing with asymmetrically arranged gas supply holes has been developed. This type of bearing has a large load capacity as compared with the conventional symmetric gas supply bearing because pressurized gases are supplied to the loaded and counter-loaded side bearing surfaces via asymmetrically arranged gas supply holes. The bearing has a new gas supply mechanism in which gas is supplied from the rotor through inherent orifices. The characteristics of the developed bearing are beneficial from the viewpoint of using the bearing in rotational-type vibration exciters. In other words, this rotor has a large static imbalance. Numerical calculations of the characteristics of this bearing were performed, and the resulting characteristics were compared with those of a conventional symmetric gas supply journal bearing. The bearing load capacity of the developed bearing is considerably larger than that of conventional symmetric type bearings. The load capacity increases owing to the asymmetry of the gas supply holes. In the controlled gas supply pressure condition, rotor radial vibration during rotation can theoretically be zero. A test rig and gas control system to realize vibration reduction was constructed. A rotational test under the gas pressure control condition was conducted using a large unbalanced rotor taking advantage of this property. The control program was constructed using matlab and simulink. The devices were driven by a digital signal processor. The magnitude of the unbalance of the rotor is 13.5 × 10−3 kg m. The bearing diameter and length were 60 and 120 mm, respectively. The rotational vibration amplitude decreased at a high rotational frequency under the proposed bearing configuration, although the amplitude increases monotonically with the frequency in the conventional bearing. When the gas supply pressure was controlled synchronously with the rotation frequency modulation of the large unbalanced rotor, the amplitude of the vibration amplitude was greatly reduced. The rotor of the test rig was safely supported by this bearing, and effective data for practical operation were obtained.

Three-dimensional analysis of the vestibulo-ocular reflex and the ability to distinguish the direction of centripetal acceleration in humans during eccentric rotation with the right ear facing downwards

This study was conducted to evaluate the linear vestibulo-ocular reflex (lVOR) mediated by the saccule, and to investigate the relationship between the lVOR and the ability to distinguish the direction of centripetal acceleration during centric and eccentric rotation. Participants sat on a chair in darkness, with the right ear facing downwards, either directly above the center of rotation, or with their nose out, nose in, right shoulder out, or left shoulder out against the center of rotation (eccentric rotation). Participants were given no information about the chair position, and were rotated sinusoidally at 0.1–0.7 Hz. Three-dimensional eye movements during rotation were analyzed. Participants were asked to describe the position of the chair after rotation. Correctly reporting the five possible chair positions requires recognition of the direction of centripetal acceleration. We analyzed the rate of correct answers to assess participants’ ability to identify the direction of centripetal acceleration. lVOR mediated by the saccule was observed only at high rotational frequencies. The rate of correct answers was higher at high rotational frequencies than that at low rotational frequencies. These results indicate that high rotational frequency is important for both lVOR mediated by the saccule and distinguishing the direction of centripetal acceleration.

Lightweight fast rotating Fermi-chopper, proof of principle for a scalable array chopper

The concept of the Fermi chopper array based on small Fermi rotors is explored. The advantages of such an array would be very low stored kinetic energy even for very fast running large area choppers and emerging possibilities for new and very flexible focussing schemes. The work comprises the investigation of a drive concept with a small motor and the design of a precise phase control. Further the rotor mechanics (stress and deformation) at high rotation frequencies has been optimised by FE-calculations. A chopper concept is studied with a small high speed motor connected to the rotor by means of an elastic shaft. This concept is comparable to the model of the “de Laval” or “Jeffcott” rotor.The development from a first layout of the Fermi rotor to a prototype aiming at high running speeds up to 1000Hz is described and results for transmission, blocking and pulse shapes obtained at the ESS test beamline are reported.

Structures and dynamics in a two-dimensional dipolar dust particle system

The effects of electric dipole moment, the number of dipolar particles, and system temperature on the structures and dynamics of a dipolar dust particle system are studied by molecular dynamics simulations. The results show that the larger electric dipole moment is favorable for the formation of a long-chain structure, the larger number of dipolar dust particles promotes the formation of the multi-chain structure, and the higher system temperature can cause higher rotation frequency. The trajectories, mean square displacement (MSD), and the corresponding spectrum functions of the MSDs are also calculated to illustrate the dynamics of the dipolar dust particle system, which is also closely related to the growth of dust particles. Some simulations are qualitatively in agreement with our experiments and can provide a guide for the study on dust growth, especially on the large-sized particles.

High fusion performance at high Ti/Te in JET-ILW baseline plasmas with high NBI heating power and low gas puffing

This paper presents the transport analysis of high density baseline discharges in the 2016 experimental campaign of the Joint European Torus with the ITER-Like Wall (JET-ILW), where a significant increase in the deuterium–deuterium (D–D) fusion neutron rate (~2.8 × 1016 s−1) was achieved with stable high neutral beam injection (NBI) powers of up to 28 MW and low gas puffing. Increase in Ti exceeding Te were produced for the first time in baseline discharges despite the high electron density; this enabled a significant increase in the thermal fusion reaction rate. As a result, the new achieved record in fusion performance was much higher than the previous record in the same heating power baseline discharges, where Ti = Te. In addition to the decreases in collisionality and the increases in ion heating fraction in the discharges with high NBI power, Ti > Te can also be attributed to positive feedback between the high Ti/Te ratio and stabilisation of the turbulent heat flux resulting from the ion temperature gradient driven mode. The high Ti/Te ratio was correlated with high rotation frequency. Among the discharges with identical beam heating power, higher rotation frequencies were observed when particle fuelling was provided by low gas puffing and pellet injection. This reveals that particle fuelling played a key role for achieving high Ti/Te, and the improved fusion performance.

Investigation of cutting force oscillations when high productivity milling

The article analyzes cutting force oscillations of high-productivity milling. Based on end-milling experiments using a milling machine tool, characteristics of spatial oscillations of cutting forces were identified. The data analysis using software and oscillation theory methods showed that at high spindle rotation frequencies under certain milling conditions, interaction of the cutting edges and the workpiece is not uniform which deteriorates the machined surface. As the spindle rotation frequency increases due to resonances in the tool and spindle and mutual oscillations of the workpiece and the tool, the cutting force spectrum varies. Some extra harmonic components appear. They index the failure of interaction of the cutting edges and the workpiece.

Conditions for escape of a rotor in a rotary nanobearing from short triple-wall nanotubes

In a short nanobearing system made from carbon nanotubes, the rotor with high rotational frequency may escape from the stator, which may cause a stability problem to the system of a nanodevice with such a nanobearing. In the present work, nanobearings with tri-walled nanotubes are investigated to reveal the conditions for the moving away of the free inner tube from the high-speed rotating middle tube. Experimental results show that the escape happens when the radii difference between the two rotors is larger than 0.34 nm and the rotational frequency of the middle tube is higher than a critical value. And before the escape occurs, the rotational frequency of the inner tube is lower than this critical value. Due to the radii difference being larger than 0.34 nm, the two rotors are non-coaxial, and the centrifugal force of the inner tube results in strong radial and axial interactions between the edges of the two rotors. When the relative sliding speed is relatively high, an edge of the inner rotor will pass through the potential barrier at the adjacent edge of the middle rotor, and further escape from the middle rotor occurs. The selection of a longer middle rotor with smaller radius can increase the critical rotational frequency of the middle rotor.

Rotor Temperature Estimation in Doubly-Fed Induction Machines Using Rotating High-Frequency Signal Injection

Thermal monitoring is a common feature in most electric machine drives since thermal overloading is one of the most common causes of motor failures. Contact-type sensors are normally used to measure the stator temperature in electric machines. However, use of this type of sensor is not advisable in the rotor as it requires cabling to a rotating part or the use of a wireless transmission system. Consequently, measurement of the rotor temperature is not easy in practice and is not normally implemented in standard machines. An alternative to rotor temperature measurement is rotor temperature estimation. To date, only thermal models have been used for rotor temperature estimation in doubly-fed induction machines (DFIMs). This paper proposes rotor temperature estimation in DFIMs using high-frequency signal injection. The proposed method estimates the rotor temperature from the rotor high frequency resistance, which is a function of the rotor windings temperature. The method does not interfere with the normal operation of the drive and can be implemented in existing DFIM drives without requiring additional hardware.

Dynamical Model for the Process of Withdrawal Formation at Deep Drilling of Small Diameter Holes w ith the Increased Relative Length

Рассматривается процесс обработки глубоких отверстий малых диаметров (менее 23,0мм) с отношением длины к диаметру (относительной длиной) более 100. Основной проблемой при изготовлении таких отверстий является предотвращение брака дорогостоящих деталей по уводу и непрямолинейности оси. Ключевой операцией технологического процесса, обеспечивающей заданные величины указанных параметров глубоких отверстий, является операция глубокого сверления. Данная операция осуществляется с применением специального инструмента и оснастки с наружным подводом смазочно-охлаждающей жидкости (СОЖ) при вращении заготовки и поступательном движении инструмента. Применяемый инструмент, обладая малой продольно-поперечной и крутильной жесткостью, работает при высоких частотах вращения заготовки и давлениях СОЖ и испытывает вследствие влияния на процесс глубокого сверления различных факторов кинематическое возмущение с частотой вращения заготовки, что является основной причиной дальнейшего изменения увода по длине обработки. Процесс образования увода является динамическим, длины инструмента могут проходить резонансные значения, что приводит к нестабильности образования и изменения увода. Анализ результатов известных исследований показал, что они не учитывают особенностей образования увода при глубоком сверлении отверстий малых диаметров повышенной относительной длины. Представлены результаты теоретических исследований по разработке динамической модели процесса образования увода с учетом особенностей процесса глубокого сверления отверстий малых диаметров повышенной относительной длины, предложены рекомендации по уменьшению увода и непрямолинейности оси, включая управление уводом.

The Slowest Spinning X-Ray Pulsar in an Extragalactic Globular Cluster

Abstract Neutron stars are thought to be born rapidly rotating and then exhibit a phase of rotation-powered pulsations as they slow down to 1–10 s periods. The significant population of millisecond pulsars observed in our Galaxy is explained by the recycling concept: during an epoch of accretion from a donor star in a binary system, the neutron star is spun up to millisecond periods. However, only a few pulsars are observed during this recycling process, with relatively high rotational frequencies. Here we report the detection of an X-ray pulsar with in the globular cluster B091D in the Andromeda galaxy, the slowest pulsar ever found in a globular cluster. This bright (up to 30% of the Eddington luminosity) spinning-up pulsar, persistent over the 12 years of observations, must have started accreting less than 1 Myr ago and has not yet had time to accelerate to hundreds of Hertz. The neutron star in this unique wide binary with an orbital period in a 12 Gyr old, metal-rich star cluster accretes from a low-mass, slightly evolved post-main-sequence companion. We argue that we are witnessing a binary formed at a relatively recent epoch by getting a ∼0.8 star in a dynamical interaction—a viable scenario in a massive, dense globular cluster like B091D with high global and specific stellar encounter rates. This intensively accreting non-recycled X-ray pulsar therefore provides a long-sought missing piece in the standard pulsar recycling picture.

Network simulation-based optimization of centrifugo-pneumatic blood plasma separation.

Automated and robust separation of 14 μl of plasma from 40 μl of whole blood at a purity of 99.81% ± 0.11% within 43 s is demonstrated for the hematocrit range of 20%-60% in a centrifugal microfluidic polymer disk. At high rotational frequency, red blood cells (RBCs) within whole blood are concentrated in a radial outer RBC collection chamber. Simultaneously, plasma is concentrated in a radial inner pneumatic chamber, where a defined air volume is enclosed and compressed. Subsequent reduction of the rotational frequency to not lower than 25 Hz enables rapid transfer of supernatant plasma into a plasma collection chamber, with highly suppressed resuspension of red blood cells. Disk design and the rotational protocol are optimized to make the process fast, robust, and insusceptible for undesired cell resuspension. Numerical network simulation with lumped model elements is used to predict and optimize the fluidic characteristics. Lysis of the remaining red blood cells in the purified plasma, followed by measurement of the hemoglobin concentration, was used to determine plasma purity. Due to the pneumatic actuation, no surface treatment of the fluidic cartridge or any additional external means are required, offering the possibility for low-cost mass fabrication technologies, such as injection molding or thermoforming.

Differential rotation of plasma in the GOL-3 multiple-mirror trap during injection of a relativistic electron beam

Results of spectral and magnetic diagnostics of plasma differential rotation in the GOL-3 multiplemirror trap are presented. It is shown that the maximum frequency of plasma rotation about the longitudinal axis reaches 0.5 MHz during the injection of a relativistic electron beam into the plasma. The data of two diagnostics agree if there is a region with a higher rotation frequency near the boundary of the electron beam. Plasma differential rotation can be an additional factor stabilizing interchange modes in the GOL-3 facility.

A Model for the Braking Indices of Pulsars

Stars known as pulsars are generally modeled as magnetized spheres made of neutrons with high rotation frequency. It is known that such stars are spinning down and this braking is measured by a parameter, n, known as braking index. For the canonical model such parameter should have a single value for all pulsars: n = 3. However, from observations it is known that n diverges from 3. In this work, differently from the canonical model, we have hypothesized the existence of a variation of the moment of inertia of the star through a time-varying radius. Using energy conservation we find the values for the variation of the radius of our pulsar sample. Our results indicate that it may be reasonable to consider that the radius of pulsars can be changing with time.

Lumbar and seat cushions reduce whole-body vibration exposures in car driving

Whole-body vibration (WBV) has been associated with risk factors of low back pain among exposed drivers. The present study examined the efficacy of the use of lumbar cushion and seat cushion in reducing exposure to WBV. A total of 24 male participants completed 24 experimental sessions, a combination of two levels of rotational amplitude, three levels of rotational frequency and four levels of seating conditions. In each session, they were exposed to a five-minute vibration stimulus. The main and interaction effects of rotational amplitude, rotational frequency, and seating condition were significant (p < 0.01). The use of lumbar cushion and seat cushion reduced WBV exposure up to 12%, and the decline was more substantial at higher rotational frequency (i.e., higher speed) and higher rotational amplitude (i.e., rougher road condition). Lumbar and seat cushions can be used to improve driving health aspect in occupational setting.

Проектирование высокооборотных генераторов большой мощности с постоянными магнитами на роторе

To meet the constantly growing level of energy consumption, significant attention is paid to development and construction of generators fitted with high-coercive permanent magnets made using alloys of rare-earth metals. The article describes an approach to designing large-capacity generators with permanent magnets, high unit power capacities of which are achieved owing to a high rotation frequency. The article presents an algorithm and gives a designing examples in which the generator’s basic parameters, namely, the bore diameter and the gap length, are determined not only proceeding from the electromagnetic loads (the linear load and induction in the gap), but also taking into account the rotor’s mechanical strength, which is estimated from the maximum admissible linear rotor speed at its peripheral surface, and the strength of the clamping sheath made of nonferromagnetic material that embraces the magnets over the external cylindrical surface. The article presents a calculation method for checking the stability of magnets used in the designed generator to demagnetization and points out the specific features pertinent to calculating the angular and external characteristics of a permanent-magnet generator in carrying out check calculations using a mesh model and phasor diagram.

Modern ssNMR for heterogeneous catalysis

This review is devoted to modern applications of solid state NMR (ssNMR) to the structural studies of heterogeneous catalysts. Recent developments of ssNMR combining high magnetic fields up to 23.5T, high rotation frequencies up to 120kHz, and the new software of spectra acquisition and processing coupled with quantum chemistry calculations allow unravel the 3D structure of active sites of the sophisticated structures, such as heterogeneous catalysts. Moreover, this opens a possibility of investigation of low sensibility nuclei that are generally assigned as inappropriate for NMR. Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy (DNP-SENS) is another powerful technique extending NMR application for surface feature investigation. Combination of modern ssNMR (including DNP) and DFT calculations synthesize the most powerful approach (so called NMR crystallography) of structural research of catalysts which is demonstrated on several remarkable application examples on challenging nuclei.