(100) Plane ß-Ga2O3 Flake Based Field Effect Transistor and Its Hydrogen Response

2-dimensional (100) plane β phase Ga2O3 (β-Ga2O3) flake based field effect transistor (FET) was fabricated, and its electrical characteristics was analyzed. The (100) plane β-Ga2O3 flake was mechanically exfoliated from the side wall of (2 ̅01) plane β-Ga2O3 bulk substrate. The minimum thickness of 57.3 nm was obtained for the very thin (100) plane β-Ga2O3 channel layer of the FET using inductively coupled plasma etching with BCl3/N2 chemistry. The current-voltage characteristics of the FET with various β-Ga2O3 channel thickness was investigated. The dependence of the channel thickness on the drain current density, threshold voltage, transconductance, and field effect mobility was studied. The hydrogen response of the (100) plane Ga2O3 flake based FET with catalytic Pt gate surface was measured in the range of 10-500 ppm at 400˚C, and modeled with a dissociative Langmuir isotherm. The device showed a reliable responsivity to the different concentration of hydrogen exposure, and the responsivity of 25.02% was observed for the 500 ppm hydrogen at 400˚C.

Rare earth nitrides and their applications in magnetic tunnel junctions

<p>In this thesis, we investigate the rare earth nitrides, a family of materials containing many intrinsic ferromagnetic semiconductors, with a particular focus on GdN and SmN.We investigate the rare earth nitride formation reaction, explore some properties of GdN and SmN, and finally manufacture and measure magnetic tunnel junctions which incorporate rare earth nitrides. The investigations of the reaction and properties of the materials are used to improve and understand the magnetic tunnel junctions. All samples and devices are grown at room temperature, giving polycrystalline rare earth nitride films. We show that a rare earth surface can catalytically break theN2 molecule at ambient temperature and low pressures. We follow the nitrogen reacting with the rare earth to form a rare earth nitride in real time via conductance measurements. By comparing the N2 cracking, reaction, and diffusion at both a RE and a REN surface we propose a pressure range in which the nitrogen content in SmN can be manipulated and conclude that the nitrogen in the top monolayers in a SmN film is mobile. In the investigation of GdN and SmN, we find that the conductivity of SmN follows the same behaviour as GdN when changing the N2 pressure during deposition. We follow the conductance change in SmN during deposition and propose a minimum thickness for room temperature deposited SmN films for consistent conductivity measurements. We report structural and magnetic changes in GdN which has been exposed to N-ions. We also present data on materials making ohmic contact to both GdN and SmN. Finally, we report the manufacturing and investigation of magnetic tunnel junctions using GdN and SmN electrodes with a GaN tunnel barrier. A new pattern design produces 20 devices, in a single deposition, which show consistent behaviour and expands on previous work on this topic. The main focus of the investigation is the J-V characteristics of the magnetic tunnel junctions which shows clear non-linear behaviour arising from tunnelling through the GaN. A Simmons fit to the J-V characteristics yields a barrier height of 0:8 eV and barrier thicknesses close to experimentally determined thicknesses. The J-V characteristics are investigated with changing temperature and changing applied magnetic field to investigate the effect of the ferromagnetism of the GdN and SmN electrodes. The tunnel magnetoresistance (TMR) of the devices show two contributions, a low-temperature TMR contribution and a 50K TMR contribution, and the maximum TMR for all devices are between 100% to 600%. The devices can withstand current densities up to 4000A/cm² and voltages up to 5V which is promising for a wide range of future applications.</p>

Rare earth nitrides and their applications in magnetic tunnel junctions

<p>In this thesis, we investigate the rare earth nitrides, a family of materials containing many intrinsic ferromagnetic semiconductors, with a particular focus on GdN and SmN.We investigate the rare earth nitride formation reaction, explore some properties of GdN and SmN, and finally manufacture and measure magnetic tunnel junctions which incorporate rare earth nitrides. The investigations of the reaction and properties of the materials are used to improve and understand the magnetic tunnel junctions. All samples and devices are grown at room temperature, giving polycrystalline rare earth nitride films. We show that a rare earth surface can catalytically break theN2 molecule at ambient temperature and low pressures. We follow the nitrogen reacting with the rare earth to form a rare earth nitride in real time via conductance measurements. By comparing the N2 cracking, reaction, and diffusion at both a RE and a REN surface we propose a pressure range in which the nitrogen content in SmN can be manipulated and conclude that the nitrogen in the top monolayers in a SmN film is mobile. In the investigation of GdN and SmN, we find that the conductivity of SmN follows the same behaviour as GdN when changing the N2 pressure during deposition. We follow the conductance change in SmN during deposition and propose a minimum thickness for room temperature deposited SmN films for consistent conductivity measurements. We report structural and magnetic changes in GdN which has been exposed to N-ions. We also present data on materials making ohmic contact to both GdN and SmN. Finally, we report the manufacturing and investigation of magnetic tunnel junctions using GdN and SmN electrodes with a GaN tunnel barrier. A new pattern design produces 20 devices, in a single deposition, which show consistent behaviour and expands on previous work on this topic. The main focus of the investigation is the J-V characteristics of the magnetic tunnel junctions which shows clear non-linear behaviour arising from tunnelling through the GaN. A Simmons fit to the J-V characteristics yields a barrier height of 0:8 eV and barrier thicknesses close to experimentally determined thicknesses. The J-V characteristics are investigated with changing temperature and changing applied magnetic field to investigate the effect of the ferromagnetism of the GdN and SmN electrodes. The tunnel magnetoresistance (TMR) of the devices show two contributions, a low-temperature TMR contribution and a 50K TMR contribution, and the maximum TMR for all devices are between 100% to 600%. The devices can withstand current densities up to 4000A/cm² and voltages up to 5V which is promising for a wide range of future applications.</p>

Recommendations for deck primary supporting members design as applied to pillarless construction of ro-ro ships

Статья посвящена вопросам определения размеров набора грузовых стационарных палуб морских стальных судов типа Ro-Ro на ранних стадиях проектирования. В силу большого расстояния между поперечными переборками в случае отсутствия пиллерсов карлингсы палуб не являются опорами для рамных бимсов. Однако, как показывает практика, они всегда включаются в конструктивную схему палубы, так как позволяют разнести локальную нагрузку между соседними рамными бимсами, обеспечивают устойчивость их стенок, а также вовлекаются в работу в составе перекрытия при некоторых сценариях нагружения. В литературе отсутствуют рекомендации по выбору расчётной ширины их присоединенного пояска, расчётных значений изгибающих моментов и перерезывающих сил при восприятии нагрузки от разного типа груза. Исследование выполнялось на примере перекрытия грузовой палубы длиной 64,4 м на основе МКЭ. Были разработаны КЭ-модели палубы в балочной и оболочечно-балочной идеализациях. Вторая модель использовалась для оценки адекватности результата, получаемого на более простой модели. Рассмотрены 8 сценариев нагрузки. При определении ширины присоединенного пояска за величину условного пролёта принималось расстояние между точками, в которых величина изгибающего момента принимает нулевое значение. Показано, что карлингсы активно вовлекаются в работу при частичной загрузке трюма контейнерами в несколько ярусов, а также при работе погрузчика. Расчётная ширина их присоединенного пояска составила 0,60…0,75 расстояния между карлингсами при действии нагрузки от колёсной техники и оказалась близка к этому расстоянию при восприятии нагрузки от контейнеров при их поперечной укладке. Авторами предложено в качестве первого приближения значение расчётного изгибающего момента для карлингсов определять в долях от соответствующего значения для рамных бимсов. The paper deals with a design of deck primary structures of Ro-Ro vessels at early design stages. Due to the large distance between transverse bulkheads, in the case of no pillar construction, deck girders cannot be considered as supports for deck transverses. The common practice however, is to provide deck structures with deck girders anyway. It helps to distribute the local loads between transverses and to ensure the stability of deck transverses web plates. In addition, for a localized loads on deck structures girders to some extent contribute to local strength of the deck. Practically, deck girder scantlings are usually larger than those based on the minimum thickness, web depth and slenderness requirements of classification society rules. There are no publications proposing recommendations for deck girders design in pillarless structures of ro-ro ships at the early stages. Prescriptive recommendations should primarily include design bending moment value and effective breadth of the attached plate in different loading scenarios. The results presented in this paper are based on the linear finite element (FE) analysis of Ro-Ro deck having a length of 64.4 meters. Since the goal of the study was to develop recommendations for structural design aligned with prescriptive requirements of RS rules the research is provided with beam analysis carried out for 8 different loading scenarios. All of the reference calculations were made in FESTA-2020 software developed in SMTU as a part of CAD/СAE software ALMAZ-K. Verification is made with more sophisticated shell model analysis carried out in ANSYS with similar assumptions. The effective breadth of deck girders attached plate is calculated considering a distance between zero bending moment points as a nominal span. It is shown that the deck girders are highly stressed in loading cases with stacked containers and working fork lift. The calculated width of their attached plate which is in range from 0.60 to 0.75 of the distance between girders S under the load from the wheeled vehicles turns out to be close to Sin case of loading of transversely stacked containers. The authors propose to determine value of the design bending moment for deck girders at the early stages depending on span and loading of deck transverses.

Quality Fade in Medical Device Manufacturing: Thinness of Airway Breathing Circuit Plastic

Mechanical respirators typically use a plastic circuit apparatus to pass gases from the ventilator to the patient. Structural integrity of these circuits is crucial for maintaining oxygenation. Anesthesiologists, respiratory therapists, and other critical care professionals rely on the circuit to be free of defects. The American Society for Testing and Materials maintains standards of medical devices and had a standard (titled Standard Specification for Anesthesia Breathing Tubes) that included circuits. This standard, which was last updated in 2008, has since been withdrawn. Lack of a defined standard can invite quality fade—the phenomenon whereby manufacturers deliberately but surreptitiously reduce material quality to widen profit margins. With plastics, this is often in the form of thinner material. A minimum thickness delineated in the breathing circuit standard would help ensure product quality, maintain tolerance to mechanical insults, and avert leaks. Our impression is that over the recent years, the plastic in many of the commercially available breathing circuits has gotten thinner. We experienced a circuit leak in the middle of a laminectomy due to compromised plastic tubing in a location that evaded the safety circuit leak check that is performed prior to surgery. This compromised ventilation and oxygenation in the middle of a surgery in which the patient is positioned prone and hence with a minimally accessible airway; it could have resulted in anoxic brain injury or death. The incident led us to reflect on the degree of thinness of the circuit's plastic.

Limitations on ACI Code Minimum Thickness Requirements for Flat Slab

Reinforced concrete two-way flat slabs are considered one of the most used systems in the construction of commercial buildings due to the ease of construction and suitability for electrical and mechanical paths. Long-term deflection is an essential parameter in controlling the behavior of this slab system, especially with long spans. Therefore, this study is devoted to investigating the validation of the ACI 318-19 Code long-term deflection limitations of a wide range of span lengths of two-way flat slabs with and without drop panels. The first part of the study includes nonlinear finite element analysis of 63 flat slabs without drops and 63 flat slabs with drops using the SAFE commercial software. The investigated parameters consist of the span length (4, 5, 6, 7, 8, 9, and 10m), compressive strength of concrete (21, 35, and 49 MPa), the magnitude of live load (1.5, 3, and 4.5 kN/m2), and the drop thickness (0.25tslab, 0.5tslab, and 0.75tslab). In addition, the maximum crack width at the top and bottom are determined and compared with the limitations of the ACI 224R-08. The second part of this research proposes modifications to the minimum slab thickness that satisfy the permissible deflection. It was found, for flat slabs without drops, the increase in concrete compressive strength from 21MPa to 49MPa decreases the average long-term deflection by (56, 53, 50, 44, 39, 33 and 31%) for spans (4, 5, 6, 7, 8, 9, and 10 m) respectively. In flat slab with drop panel, it was found that varying drop panel thickness t2 from 0.25 to 0.75 decreases the average long-term deflection by (45, 41, 39, 35, 31, 28 and 25%) for span lengths (4, 5, 6, 7, 8, 9 and 10 m) respectively. Limitations of the minimum thickness of flat slab were proposed to vary from Ln/30 to Ln/19.9 for a flat slab without a drop panel and from Ln/33 to Ln/21.2 for a flat slab with drop panel. These limitations demonstrated high consistency with the results of Scanlon and Lee's unified equation for determining the minimum thickness of slab with and without drop panels. Doi: 10.28991/cej-2021-03091769 Full Text: PDF

Drop impact on superheated surfaces: short-time dynamics and transition to contact

When a volatile drop impacts on a superheated solid, air drainage and vapour generation conspire to create an intermediate gas layer that delays or even prevents contact between the liquid and the solid. In this article, we use high-speed synchronized reflection interference and total internal reflection imaging to measure the short-time dynamics of the intermediate gas film and to probe the transition between levitation and contact. We observe that the substrate temperature strongly affects the vertical position of the liquid–gas interface and that the dynamic Leidenfrost transition is influenced by both air and vapour drainage (i.e. gas drainage), and evaporation, the latter giving rise to hitherto unreported vertical oscillations of the gas film that can trigger liquid–solid contact. We first derive scaling relations for the height of the gas film trapped under the drop's centreline, called the dimple height, and the minimum film thickness at short times. The former is set by a competition between gas drainage and liquid inertia, similarly as for isothermal impacts, while the latter strongly depends on the vapour production. The gas pressure, at the location where the minimum thickness is reached, is determined by liquid inertia and vapour production and ultimately balanced by the increasing interfacial curvature, determining the minimum thickness. We show that, in the low impact velocity limit, the transient stability of the draining gas film remarkably makes dynamic levitation less demanding than static levitation. We characterize the vertical gas film oscillations by measuring their frequency and monitoring their occurrence in the parameter space spanned by surface temperature and impact velocity. Finally, we model the occurrence of these oscillations and account for their frequency through a hydrodynamic mechanism.

A Flexible Single Loop Setup for Water-Borne Transient Electromagnetic Sounding Applications

Water-borne transient electromagnetic (TEM) soundings provide the means necessary to investigate the geometry and electrical properties of rocks and sediments below continental water bodies, such as rivers and lakes. Most water-borne TEM systems deploy separated magnetic transmitter and receiver loop antennas—typically in a central or offset configuration. These systems mostly require separated floating devices with rigid structures for both loop antennas. Here, we present a flexible single-loop TEM system, the light-weight design of which simplifies field procedures. Our system also facilitates the use of different geometries of the loop antenna permitting to adjust the depth of investigation (DOI) and the minimum sounding depth in the field. We measure the turn-off ramp with an oscilloscope and use the DOI to assess the minimum and maximum exploration depth of our single-loop TEM system, respectively. A reduction of the loop-antenna size improves early-time TEM data due to a reduced length of the turn-off ramp, whereas an increase of the loop-antenna size enhances the signal strength at late times, which allows to investigate deeper structures below the lake bed. We illustrate the capabilities of our system with a case study carried out at Lake Langau in Austria. Our results show that our system is capable of reaching a DOI of up to 50m (with a maximum radius of the circular loop of 11.9m), while it also resolves the water layer down to a minimum thickness of 6.8m (when the radius is reduced to 6.2m).

A New Standard Design of Lightning Protection System for Offshore and Nearshore Oil and Gas at Tropic Area

Based on NFPA-780, offshore platforms, which made from metal framework of a structure are thought of as "grounded" to the ocean and therefore are not needed to be installed external Lightning Protection System (LPS). PHE ONWJ which located at offshore tropic area has implemented NFPA 80 but still experience lightning hit. It generated fire at vent stack andcause operations interference. So that, the objective of this study is to redesign LPS for tropic area. Firstly, the methodology for this study was conducting literature review from previous researches for lightning protection system at tropic area and researches which underlyingNFPA-780. The literature reviews were focusing on lightning characteristic for tropic area andthe lightning density data from local lighting strike monitors surrounding PHE ONWJ. The result of literature reviews would be the basis of lightning strike event reviews in PHE ONWJ facilities. Subsequently, the authors conducted the equipment layout review using rolling sphere method based on previous lightning strike location. Lastly, Authors proposed the recommendationsfor typical LPS for oil and gas at tropic area. Based on literature reviews,lightning characteristic at tropic area has peak strike current twice the sub-tropic and longer "tail" so that the charge current is larger. Larger the charge current of lightning cause greaterimpact into metal structure that is metal melting. Based on NFPA 780/2011, the offshore platform, which is made by metal, and vessel with minimum thickness 4.8 mm are self-protected. However, based on calculation, with the characteristic of lightning at tropic area, the recommendedminimum vessel thickness is 10 mm. This calculation reinforces the fact that standard of Lightning Protection System in NFPA 780/2011 is not sufficient to be applied in tropic area like Indonesia. After calculating the tropic lightning strike range using rolling sphere method, it isrecommended to redesign lightning protection system for some locations at offshore platform and near shore facilities of PHE ONWJ.The lightning protections system locations and quantities are depending on the area and the needed protected equipment in it.The installation isincluding extended mast terminal, free standing mast, low inductive Double Shielded Down Conductor(DSDC), Lightning Event Counter (LEC), and good grounding system at the platform.