Offset Variation Research Articles

Minimally Invasive HEROS (Higher External ROtator Sparing) Posterior-lateral Approach for Total Hip Arthroplasty: Surgical Technique and Preliminary Results.

Minimally invasive approaches for Total Hip Arthroplasty (THA) are extremely popular among both patients and surgeons. Even though many surgical techniques have been described with overall satisfactory results, one of the most feared complications that still burdens THA is early dislocation, particularly for the most popular, posterior-lateral, approach. The purpose of this report is to describe an original, minimally invasive, posterior-lateral technique, which spares the proximal external rotator muscle tendons of the hip (Higher External ROtator-Sparing; HEROS), while presenting its preliminary clinical and radiographic results. From 2018 to 2020, 100 patients underwent THA, performed by the same surgeon using the HEROS technique. In all cases, the same cementless prosthesis was implanted. The Modified Harris Hip Score (MHHS) was obtained before surgery and at the last follow-up visit. The osteointegration and orientation of the prosthetic components were radiographically evaluated, and the restoration of the femoral offset was analyzed. Seventy-seven patients were assessed at a mean follow-up of 28 months. At the time of surgery, the average age of the patients was 72 years. There were 36 females and 41 males with a mean BMI of 27. The diagnoses were primary arthritis, avascular necrosis of the femoral head and fracture of the femoral neck. The mean surgical time was 76 minutes. The average MHHS score at follow-up was excellent. The mean offset variation was approximately 1 mm. There was an intra-operative fracture and an early infection of the wound. There were no dislocations. All patients returned to activities of daily living and were satisfied with the cosmetic appearance of the wound. The present study confirmed that this simple, minimally invasive approach is effective for restoring pain-free joint function and preventing implant dislocation with a low incidence of complications.

A LoC Ion Imaging Platform for Spatio-Temporal Characterisation of Ion-Selective Membranes.

In this paper, a complete Lab-on-Chip (LoC) ion imaging platform for analysing Ion-Selective Membranes (ISM) using CMOS ISFET arrays is presented. An array of 128 × 128 ISFET pixels is employed with each pixel featuring 4 transistors to bias the ISFET to a common drain amplifier. Column-level 2-step readout circuits are designed to compensate for array offset variations in a range of up to ±1 V. The chemical signal associated with a change in ionic concentration is stored and fed back to a programmable gain instrumentation amplifier for compensation and signal amplification through a global system feedback loop. This column-parallel signal pipeline also integrates an 8-bit single slope ADC and an 8-bit R-2R DAC to quantise the processed pixel output. Designed and fabricated in the TSMC 180 nm BCD process, the System-on-Chip (SoC) operates in real time with a maximum frame rate of 1000 fps, whilst occupying a silicon area of 2.3 mm × 4.5 mm. The readout platform features a high-speed digital system to perform system-level feedback compensation with a USB 3.0 interface for data streaming. With this platform we show the first reported analysis and characterisation of ISMs using an ISFETs array through capturing real-time high-speed spatio-temporal information at a resolution of 16 μm in 1000 fps, extracting time-response and sensitivity. This work paves the way of understanding the electrochemical response of ISMs, which are widely used in various biomedical applications.

Application of deep raman spectroscopy to detect ammonium nitrate concealed in color fabrics

Detection of concealed Improvised Explosive Devices (IEDs) is a prerequisite for forensic and homeland security investigations. In this case, fabrics are common barriers for hidden explosives to be seen or detected. Deep Raman spectroscopy is a well-known detection method that provides detailed vibrational information about the depth profiling of Raman-active materials. In this research, a combination of space-resolved and time-resolved Raman techniques was successfully used to acquire high-quality ammonium nitrate Raman spectra concealed in white and brown synthetic fabric as a highly fluorescing barrier. The signal-to-background noise ratio was calculated in all the experiments. Concerning the result for white synthetic fabric, the optimum value was at 180 ns gate delay and 2 mm offset. These values were at 100 ns gate delay and 3 mm offset for brown synthetic fabrics. The role of retarded Raman photons in offset and gate delay variations was discussed too. As the results showed, implementing TR-SORS to identify the IEDs concealed in color fabrics caused the accelerated rejection of high fluorescence from the container surface and led to improved Raman signal.

Theoretical exploration of the optoelectronic properties of InAsNBi/InAs heterostructures for infrared applications: A multi-band k·p approach

We have investigated numerous electronic and optical aspects of the InAsNBi material, considering a multi-band k·p Hamiltonian. We have scrutinised electronic band dispersion, changes in spin–orbit splitting energy (so), charge carrier effective mass, band offset, and optical gain variations of InAsNBi and Quantum Well (QW) structures lattice-matched to InAs. The band gap of InAs0.9209N0.0291Bi0.05 is observed to be 131 meV under lattice-matched conditions, and the operating wavelength equivalent to this bandgap is 9.46 μm, which corresponds to the atmospheric Long Wavelength Infrared (LWIR) communication window of 8–12 μm. In order to tune the bandgap of a quantum confined heterostructure over a wide range, strain analysis plays a pivotal role. While compressive strain of 0.7% offers a band gap of 96 meV, tensile strain of 1.16% generates a band gap to 178 meV, which is almost equivalent to the room temperature bandgap of InSb. Under the influence of strain, spin-orbit splitting energy (Δso) spans the range from 0.31 eV to 0.45 eV. In addition to this, the inclusion of N and Bi into InAs reduces the effective mass of electrons to 0.01343 m0, which is ∼0.5 times of InAs. We have also computed the band structure of the InAsNBi/InAs QW heterostructure and found that under the influence of tensile strain with N = 2.5% and Bi = 1%, there is a changeover from Type-I to Type-II heterostructure. Indeed, InAsNBi can be a potential material for realizing various optoelectronic applications such as atmospheric LWIR communication, intermediate band solar cells, and night vision cameras.

Garmin GPSMAP 66sr: Assessment of Its GNSS Observations and Centimeter-Accurate Positioning.

In 2020, Garmin released one of the first consumer devices with a dual-frequency GNSS chip and a quadrifilar helix antenna: GPSMAP 66sr. The device is intended to serve as a positioning and navigation device for outdoor recreation purposes with positioning accuracies on the few meter level. However, due to its highly accurate GNSS dual-frequency carrier-phase observations, the equipment can also be used for centimeter-accurate positioning. We performed extensive test measurements and analyzed the quality of its code and carrier-phase observations. We calibrated the Garmin GPSMAP 66sr antenna with respect to its phase-center offset and phase-center variations. We also performed dual-frequency GPS/Galileo precise point positioning (PPP) and precise relative positioning in baselines to virtual reference stations (VRS). We demonstrate and explain how centimeter-accurate positioning can be achieved with this novel kind of equipment.

Characterization of organic matter in marine sediments to estimate age offset of bulk radiocarbon dating

Radiocarbon dating of Arctic marine sediment is often challenging due to the low availability of calcareous fossils. Consequently, bulk organic matter dating has at times been used to establish sediment core chronologies. Yet, radiocarbon dates based on bulk organic matter often appear to deviate vastly from dates based on fossils, mainly caused by input of allochthounous carbon, including terrigenous organic matter. In this study, we aim to examine the link between the composition of the bulk organic matter and the age offsets between the bulk radiocarbon dates and those obtained from calcareous foraminiferal tests. All samples are taken from the marine sediment core AMD14-204C from offshore Upernavik (eastern Baffin Bay). The radiocarbon dates for bulk organic matter are on average ∼3000 years older than the radiocarbon dates based on foraminifera, but with changing age offsets throughout the record. To investigate the cause of this age offset and its variations over time, we applied core scanning, X-ray Fluorescence analysis, stable isotopes, organic pyrolysis and microscopic organic petrology to examine the distribution and characterization of the organic matter. The results show that the older organic matter includes clastic input of reworked sedimentary rocks potentially originating from West Greenland and/or the Canadian Arctic Archipelago. Changes in the input of contemporary marine algal produced organic matter versus both terrigenous input and reworked ancient organic matter appear to control the age offsets between the bulk and foraminifera dates. A low Hydrogen Index and low δ13Corg values together with a high Oxygen Index, indicative of high influence of terrigenous organic matter, seem to correspond to samples with the largest age offsets; 1000–2000 years greater than in other samples. To examine the cause of the variations in the age offsets, a new quantification of the autochthonous organic matter as a fraction of the TOC was calculated. This shows that samples with the largest age offsets contained the lowest fraction (as low as ∼12%) of autochthonous organic matter in the TOC.

Consistency Analysis of the GNSS Antenna Phase Center Correction Models

For the same antenna type, numerical differences among the phase center correction (PCC) models released by different institutes can reach several millimeters, which is far beyond the nominal calibration accuracy. This contribution introduces a new method to evaluate the consistency of these PCC models. We first investigated the coupling of phase center offset (PCO) and phase center variation (PCV) through simulation experiments, and the results show that the calibrated PCO values under different strategies may result in large differences, and so do PCV values due to strong coupling with PCO. This is further confirmed by field calibration experiments. Moreover, a new datum parameter is introduced to equivalently transform the PCC models to assess the consistency of PCC models of the same antenna type calibrated under different strategies or by different facilities. It is also essential to perform consistency analysis of PCC models in the coordinate domain. We further investigated these PCC models through a simulated positioning experiment. The results show that millimeter-level consistency of PCC models will lead to the same level of positioning precision in the coordinate domain. Moreover, as a comparison, both baseline positioning and PPP were performed with an antenna-type JAV_RINGANT_G3T NONE based on real observations. Multiday results showed that the average RMS of the positioning differences between PCC models from robot and anechoic chamber calibration is less than 1 mm for the baseline solution and 4 mm for the PPP solution, although the PCC model differences can reach 6 mm in L1 and 4 mm in L2, respectively. Finally, we also investigated the distribution of position biases without PCC or with inaccurate PCC. Considering the actual GPS constellation, we found that position biases have a strong correlation with latitude, if PCV values fluctuate greatly with the users’ elevation angle.

An offset calibration technique for CIS column-parallel SAR ADCs using memory

A column-parallel 10-bit SAR ADC for high-speed image sensors has been implemented. A fast offset calibration technique using memory is proposed to compensate for the offset mismatch, accompanied by an ADC designed for a narrow space the size of a single column pitch. The memory accumulates the variation of the offset to track the offset within two cycles. After applying the offset calibration technique, the offset variation of the ADC measured in each column is improved from 4.27LSB to 0.39LSB. The fixed-pattern noise (FPN) is also improved from 4.14LSB to 0.34LSB. This calibration method covers an offset range of ±32LSB. The implemented ADC achieves a maximum speed of 500kS/s. The maximum frame rate of the sensor is 3000fps. The power consumption of the sensor, excluding the LVDS interface, is 71mW. This sensor is designed in a TowerJazz CIS 180nm process with one poly four metal. The supply voltage of the analog and digital domains is 3.3V and 1.8V, respectively.

Feasibility of Non-invasive Measurement of Tumour NAD(H) by In Vivo Phosphorus-31 Magnetic Resonance Spectroscopy.

Importance of the redox status of nicotinamide adenine dinucleotide (NAD), including its oxidized (NAD+) and reduced (NADH) forms, has been shown in many biological processes. However, NAD(H) redox status assessment is traditionally limited to biochemical assays in vitro or optical redox imaging (ORI) for superficial tissues in vivo and for deep tissues ex vivo. In recent years, phosphorous-31 magnetic resonance spectroscopy (31P-MRS) was utilized to quantify NAD+, NADH, and the redox ratio NAD+/NADH in normal tissues in vivo. The quantification is based on the spectral fitting of the upfield shoulder of the αATP peak that contains signals of NAD+ (a quartet) and NADH (a singlet), assuming pH-independence of peak positions. To evaluate the feasibility of measuring tumour NAD(H) redox status in vivo, we fitted single voxel 31P-MR spectra of subcutaneous mouse xenografts of human breast cancer cell lines acquired on a 9.4-T horizontal bore preclinical MR scanner. We found larger variations in the chemical shift offsets of NAD+ and NADH from αATP in these tumours than the literature values of normal tissues. Furthermore, our 31P-MR spectra of αATP, NAD+, and NADH solution phantoms indicated that the chemical shift of αATP and thus the offsets between NAD(H) and αATP were pH dependent. Therefore, whether tumour pH should be incorporated into the spectral fitting model should be further evaluated. Additionally, spectral resolution and signal-to-noise ratio should be improved by optimising 31P-MRS protocols, increasing data acquisition time, and using a more sensitive coil for signal detection.

THE MINIMIZATION METHOD OF THE THERMAL DRIFT INFLUENCE ON ANALOG INTEGRATED CIRCUITS

The existing offset cancellation methods are based on digital-to-converters (DAC) and the calibration paths. During thermal drift the parameters of transistors in calibration pa¬t¬h change, which increase the offset of the system. The proposed offset cancellation meth¬od includes current DAC which is directly connected to the output of the system. The absence of the calibration path makes the circuit more stable during temperature drifts without voltage-current-voltage conversion. The offset variation of the circuit during thermal drift is reduced 19 times (1.42 mV). The circuit occupies 43.2 % less area as in the current DAC, only transistors have been used instead of the resistor-transistor structure of voltage DAC. Power consumption increases 7 % as the branch of the current DAC is always on.

On Satellite-Borne GPS Data Quality and Reduced-Dynamic Precise Orbit Determination of HY-2C: A Case of Orbit Validation with Onboard DORIS Data

Haiyang-2C (HY-2C) is a dynamic, marine-monitoring satellite that was launched by China and is equipped with an onboard dual-frequency GPS receiver named HY2_Receiver, which was independently developed in China. HY-2C was successfully launched on 21 September 2020. Its precise orbit is an important factor for scientific research applications, especially for marine altimetry missions. The performance of the HY2_Receiver is assessed based on indicators such as the multipath effect, ionospheric delay, cycle slip and data utilization, and assessments have suggested that the receiver can be used in precise orbit determination (POD) missions involving low-Earth-orbit (LEO) satellites. In this study, satellite-borne GPS data are used for POD with a reduced-dynamic (RD) method. Phase centre offset (PCO) and phase centre variation (PCV) models of the GPS antenna are established during POD, and their influence on the accuracy of orbit determination is analysed. After using the PCO and PCV models in POD, the root mean square (RMS) of the carrier-phase residuals is around 0.008 m and the orbit overlap validation accuracy in each direction reaches approximately 0.01 m. Compared with the precise science orbit (PSO) provided by the Centre National d’Etudes Spatiales (CNES), the RD orbit accuracy of HY-2C in the radial (R) direction reaches 0.01 m. The accuracy of satellite laser ranging (SLR) range validation is better than 0.03 m. Additionally, a new method is proposed to verify the accuracy of the RD orbit of HY-2C by using space-borne Doppler orbitography and radiopositioning integrated by satellite (DORIS) data directly. DORIS data are directly compared to the result calculated using the accurate coordinates of beacons and the RD orbit, and the results indicate that the external validation of HY-2C RD orbit has a range rate accuracy of within 0.0063 m/s.

GRACE-FO Antenna Phase Center Modeling and Precise Orbit Determination with Single Receiver Ambiguity Resolution

Precise knowledge of the phase center location of the global navigation satellite system (GNSS) antenna is a prerequisite for precise orbit determination (POD) of the low Earth orbit (LEO) satellite. The phase center offset (PCO) and phase center variation (PCV) values for the LEO antenna obtained from ground calibration cannot reflect the error sources encountered in the actual spacecraft environment. PCV corrections are estimated by ionosphere free (IF) carrier phase post-fit residuals of reduced dynamic orbit determination. Ambiguity resolution (AR) plays a crucial role in achieving the best orbit accuracy. The single receiver AR concept is realized using wide-lane (WL) and narrow-lane (NL) bias products. Single difference (SD) observations between satellites are applied to remove the receiver dependent phase bias. SD AR and traditional double difference (DD) AR methods are applied to fix the ambiguities. The recovered SD and DD IF ambiguities are taken as pseudo-observations to constrain the undifferenced IF ambiguity parameters in the POD process. The LEO orbits based on float ambiguity (FA), SD, AR, and DD AR are investigated. One year’s data collected by the Gravity Recovery And Climate Experiment Follow-On (GRACE-FO) mission and GPS precise products provided by the Center for Orbit Determination in Europe (CODE) were analyzed. Precise orbit generated by the Jet Propulsion Laboratory (JPL), independent satellite laser ranging (SLR), and K-band ranging (KBR) measurements were utilized to assess the orbit accuracy. More than 98% of SD WL and 95% of SD NL ambiguities are fixed, which confirms the good quality of the bias products and correctness of the SD AR method. With PCV corrections, the average phase residuals of DD and SD AR solutions are 0.13 and 0.41 mm, which indicates improved consistency between applied models and observations. Compared with JPL’s orbit, the SD AR orbits achieve the accuracy of 6.0, 6.2, and 5.1 mm in along-track, cross-track, and radial directions. The SD AR solutions show an average improvement of 18.3% related to the FA orbits while 6.3% is gained by the DD AR approach. The root mean squares (RMSs) of SLR residuals for FA, DD AR, and SD AR solutions are 11.5, 10.2, and 9.6 mm, which validate the positive effect of AR on POD. Standard deviation (STD) of KBR residuals for SD AR orbits is 1.8 mm while 0.9 mm is achieved by the DD AR method. The explanation is that the phase bias products used for SD AR are not free of errors and the errors may degrade the KBR validation. In-flight PCV calibration and ambiguity resolution improve the LEO orbit accuracy effectively.

Electric Field-Modulated Charge Transfer in Geometrically Tailored MoX2/WX2 (X = S, Se) Heterostructures

Light-induced interlayer charge transfer in staggered-type heterostructures (HSs) in transition-metal dichalcogenides provides the opportunity to improve the performance of optoelectronic applications. Herein, we employ density functional theory to investigate the vertical electric-field-controlled interlayer charge transfer in stacked MoX2/WX2 (X=S, Se) HSs. Upon application of electric field from −3 to 3 V/nm, we observe the band-alignment transition, band inversion, and offset variations in these HSs. Furthermore, these electric fields are found to modulate charge localization/delocalization across the layers, which provides insight into charge transfer. The positive electric field is supposed to localize the charges in WS2, whereas the charges are localized in MoS2 at negative electric field. Based on charge localization/delocalization, our study suggests that the interlayer hole transfer upon MoS2 photoexcitation can be suppressed at higher positive electric fields, whereas electron transfer can be blocked by excitation of WS2. In contrast, negative electric fields (of −3 V/nm) can induce interlayer hole and electron transfer. Owing to the tunability of interlayer charge transfer by means of a vertical electric field, our findings bear paramount importance in modulating electron–hole recombination and charge-transfer time, which is beneficial for future optoelectronic devices.

The impact of image acquisition time on registration, delineation and image quality for magnetic resonance guided radiotherapy of prostate cancer patients.

Background and PurposeMagnetic resonance (MR) guided radiotherapy utilizes MR images for (online) plan adaptation and image guidance. The aim of this study was to investigate the impact of variation in MR acquisition time and scan resolution on image quality, interobserver variation in contouring and interobserver variation in registration.Materials and MethodsNine patients with prostate cancer were included. Four T2-weighted 3D turbo spin echo (T2w 3D TSE) sequences were acquired with different acquisition times and resolutions. Two radiologists assessed image quality, conspicuity of the capsule, peripheral zone and central gland architecture and motion artefacts on a 5 point scale. Images were delineated by two radiation oncologists and interobserver variation was assessed by the 95% Hausdorff distance. Seven observers registered the MR images on the planning CT. Registrations were compared on systematic offset and interobserver variation.ResultsAcquisition times ranged between 1.3 and 6.3 min. Overall image quality and capsule definition were significantly worse for the MR sequence with an acquisition time of 1.3 min compared to the other sequences. Median 95% Hausdorff distance showed no significant differences in interobserver variation of contouring. Systematic offset and interobserver variation in registration were small (<1 mm) and of no clinical significance.ConclusionsOur results can be used to effectively shorten overall fraction time for online adaptive MR guided radiotherapy by optimising the imaging sequence used for registration. From the sequences studied, a sequence of 3.1 min with anisotropic voxels of 1.2 × 1.2 × 2.4 mm3 provided the shortest acquisition time without compromising image quality.

Patterning of transition metal dichalcogenides catalyzed by surface plasmons with atomic precision

Summary Plasmon-induced charge transfer has drawn considerable interests and spurred rapid developments of photovoltaics and photocatalysis. Various plasmonic metal/transition metal dichalcogenide (TMD) heterostructures have been developed to promote charge separation. For plasmon-induced catalysis, the transformation of TMDs is rare, and the erosion of TMDs has not yet been reported. Here, we report the etching of two-dimensional TMDs by planar surface plasmon polaritons (SPPs). We found that SPPs can etch various TMDs into desired layers and lateral size through controlling the light power and incident direction. In aqueous media, the strong plasmonic coupling at Au/MoS2 interface generates holes in the valence band of MoS2 that can weaken its interlayer interaction. As a synergistic effect, the plasmonic hot electrons produce oxidizing H2O2 to dissolve MoS2 from the top layers. Our results provide a new perspective for understanding the plasmonic coupling at metal-TMD interfaces and a reliable route toward fabricating well-defined TMDs.

Design and development of GMR based low range pressure sensor for medical ventilator application

In this report, we present a thermally compensated low range magnetic pressure sensor. The fabricated sensor consists of a corrugated stainless steel (SS) diaphragm, a permanent magnet, a giant magnetoresistance (GMR) sensor, and a signal conditioning unit. The diaphragm with a permanent magnet produces a magnetic field which changes under the exposure of external pressure. The GMR sensor is placed asymmetrically with reference to the cylindrical axis of a magnet, which results in an output voltage proportional to external pressure. Simulations were performed to optimize the design having a linear output with higher sensitivity of the order of 14.97 μV/V/mbar, which is close to the experimentally measured value of 13 μV/V/mbar at room temperature. The sensor prototypes were fabricated in pressure ranges: ± 30 and ± 70 mbar. The fabricated pressure sensor prototypes were tested in different temperature ranges and calibrated for offset, linearity, and thermal variations using a commercial sensor signal conditioner. The performance of the calibrated sensors was evaluated at different temperatures and over an extended period. Furthermore, the performance of the sensor was experimentally evaluated in an indigenously developed medical ventilator, and compared with an existing commercial MEMS pressure sensor for a longer duration. The performance of the prototype sensor was found to be equivalent with an accuracy of ±0.1 mbar for an operation in the range of ± 30 mbar.

Understanding the Selective Deposition of Li Metal on Nonuniform Electrode Surfaces Using Atomic Force Microscopy

The use of lithium metal in secondary batteries has been impeded by its tendency to form dendrites: branching conductive structures of metal that can lead to capacity loss and, ultimately, internal shorts in the battery. Patterned electrodes, in addition to artificially increasing the current density of cells by increasing the surface area available for reaction, also generate a nonuniform electric field in the vicinity of the electrode surface. This nonuniform electric field, though rapidly screened by the electrolyte, can promote inhomogeneous deposition and Solid Electrolyte Interphase formation. As the consequence of these effects is not theoretically apparent since Solid Electrolyte Interphase volume and conductivity changes can, in principle, offset variations in local current density, we have performed experiments to examine the deposition of Li on nonuniform electrode surfaces using Atomic Force Microscopy. We measure the local variations in topography, SEI thickness, and composition, and discuss their implications for the formation of dendrites in Li metal.

Milky Way Tomography with the SkyMapper Southern Survey. II. Photometric Recalibration of SMSS DR2

Abstract We apply the spectroscopy-based stellar-color regression (SCR) method to perform an accurate photometric recalibration of the second data release from the SkyMapper Southern Survey (SMSS DR2). From comparison with a sample of over 200,000 dwarf stars with stellar atmospheric parameters taken from GALAH+ DR3 and with accurate, homogeneous photometry from Gaia DR2, zero-point offsets are detected in the original photometric catalog of SMSS DR2, in particular for the gravity- and metallicity-sensitive uv bands. For the uv bands, the zero-point offsets are close to zero at very low extinction, and then steadily increase with E(B − V), reaching as large as 0.174 and 0.134 mag respectively, at E(B − V) ∼ 0.5 mag. These offsets largely arise from the adopted dust term in the transformations used by SMSS DR2 to construct photometric calibrators from the ATLAS reference catalog. For the gr bands, the zero-point offsets exhibit negligible variations with the E(B − V) of Schlegel et al. due to their tiny coefficients on the dust term in the transformation. Our study also reveals small but significant spatial variations of the zero-point offsets in all uvgr bands. External checks using Strömgren photometry, WD loci, and the SDSS Stripe 82 standard-star catalog independently confirm the zero-points found by our revised SCR method.

Study of Experimental Vibration Due to Misalignment of Pulley-Belt in Rotary Machine

This study aims to investigate the vibration of rotary machine due to misalignment of its pulley-belt, experimentally. Here, the rotary machine is driven by an AC motor with pulley-belt transmission that positioned on the outer portion of shaft-rotor. To generate vibration of rotary machine, pulley-belt is conditioned to have a combination of offset and angular misalignments. Offset misalignment variations are 0, 2, 4, and 6 mm and angular misalignment variations are 0ᵒ, 2ᵒ, 4ᵒ, and 6ᵒ. Vibration of rotary machine is measured on the bearing housing by use MEMS-based accelerometers. The measured signal of vibration acceleration is acquired with a data acquisition device to obtain vibration spectrum. From the investigation to vibration spectrum has been done, it can be concluded that vibration of rotary machine has characteristic with dominant frequencies at 1xRPM of shaft and at 1xRPM of motor. The vibration amplitude at 1xRPM of shaft is higher than the vibration amplitude at 1xRPM of motor. From this investigation, it is not possible to find differences in the characteristics of vibrations significantly that occur between vibrations due to offset misalignment, angular misalignment or their combination.

Ab initio analytic calculation of point defects in AlGaN/GaN heterointerfaces

One of the major challenges for the GaN-based high-electron-mobility transistors (HEMTs) used as high power devices is to understand the effect of defects, especially on the band alignment. Using ab initio calculation, herein we investigate the variations of band offsets with interfacial structure, defect position, interface states and Al content in Al x Ga1-x N/GaN heterostructures (x = 0.06, 0.13, 0.19, 0.25). It was found that N vacancy (VN) and Ga anti-site (GaN) introduce nonlocal interface states and the change of valence band offset (VBO) depends on the defect location. While the interface states induced by Ga vacancy (VGa) and N anti-site (NGa) show strong localization behavior, and their impact on VBO is independent on the defect position. The low symmetry of wurtzite nitride and the lattice mismatch between AlGaN and GaN will generate polarization charge (spontaneous polarization and piezoelectric polarization) at the interface. Along the direction of polarization field, VN and GaN lying in the AlGaN side change the VBO most pronouncedly. These theoretical results provide useful guidance for control of point defects in AlGaN/GaN HEMTs, which have profound impact on the performance and reliability of GaN-based devices.