Stress distribution and performance of threaded bolts in gasketed flange joints

The performance of the flange joint depends on the relaxation of load in bolts. This in turn affects the gasket stress and control of leakage. A finite element model of flange joint with threaded bolt-nut fastener having zero helix angle is developed and analyzed for stress distribution in the threaded bolt. The stress concentration factor at the thread root region is observed to be non-uniform along the circumference due to the bending behavior of the bolt in the flange joint. The maximum stress is observed in the first engaged thread. The variation in bolt load due to internal fluid, thermal and external loads are also investigated for both single and twin-gaskets (two concentric half-sized single gaskets). The gasket material and gasket configuration are observed to be potential factors causing variation in the distribution of load in the flange joint. In a flange joint subjected to external bending load, the maximum stress concentration in the bolt is observed to be in the first thread, instead of the first engaged thread. Under external bending load, the flange joint loses its structural integrity before the traces of leakage occur in the joint.     

Mechanism of Electron Trapping and Characteristics of Traps in HfO2 Gate Stacks

Electron trapping in high- gate dielectrics under constant voltage stress is investigated. It is suggested that the electron trapping occurs through a two-step process: resonant tunneling of the injected electron into the preexisting defects (fast trapping) and thermally activated migration of trapped electrons to unoccupied traps (slow trapping). Characteristics of the electron traps extracted based on the proposed model are in good agreement with the calculated properties of the negatively charged oxygen vacancies. The model successfully describes low-temperature threshold voltage instability in NMOS transistors with /TiN gate stacks.     

Trust and control: A dialectic link

The relationship between trust and control is quite relevant both for the very notion of trust and for modelling and implementing trust-control relations with autonomous systems, but it is not trivial at all. On the one side, it is true that where / when there is control there is no trust, and vice versa. However, this refers to a restricted notion of trust: i.e., "trust in y," which is just a part, a component of the global trust needed for relying on the action of another agent. It is claimed that control is antagonistic of this strict form of trust; but also that it completes and complements it for arriving to a global trust. In other words, putting control and guarantees is trust-building; it produces a sufficient trust, when trust in y's autonomous willingness and competence would not be enough. It is also argued that control requires new forms of trust: trust in the control itself or in the controller, trust in y as for being monitored and controlled; trust in possible authorities, etc. Finally, it is shown that, paradoxically, control could not be antagonistic of strict trust in y, but it can even create and increase it by making y more willing or more effective. In conclusion, depending on the circumstances, control makes y more reliable or less reliable; control can either decrease or increase trust. Two kinds of control are also analyzed, characterized by two different functions: "pushing or influencing control" aimed at preventing violations or mistakes, versus "safety, correction, or adjustment control" aimed at preventing failure or damages after a violation or a mistake. A good theory of trust cannot be complete without a theory of control.     

Eco-friendly synthesis for MCM-41 nanoporous materials using the non-reacted reagents in mother liquor

Nanoporous materials such as Mobil composite material number 41 (MCM-41) are attractive for applications such as catalysis, adsorption, supports, and carriers. Green synthesis of MCM-41 is particularly appealing because the chemical reagents are useful and valuable. We report on the eco-friendly synthesis of MCM-41 nanoporous materials via multi-cycle approach by re-using the non-reacted reagents in supernatant as mother liquor after separating the solid product. This approach was achieved via minimal requirement of chemical compensation where additional fresh reactants were added into the mother liquor followed by pH adjustment after each cycle of synthesis. The solid product of each successive batch was collected and characterized while the non-reacted reagents in supernatant can be recovered and re-used to produce subsequent cycle of MCM-41. The multi-cycle synthesis is demonstrated up to three times in this research. This approach suggests a low cost and eco-friendly synthesis of nanoporous material since less waste is discarded after the product has been collected, and in addition, product yield can be maintained at the high level.     

Effects of Film Stress Modulation Using TiN Metal Gate on Stress Engineering and Its Impact on Device Characteristics in Metal Gate/High- $k$ Dielectric SOI FinFETs

In this letter, the effects of TiN-induced strain engineering on device characteristics for a metal gate/high-k silicon-on-insulator fin-shaped field-effect transistors were studied. From a convergent-beam electron-diffraction analysis and simulation study, a 3-nm TiN electrode was found to lead to significantly higher tensile stress on the Si substrate than a 20-nm TiN electrode. This high stress-induced fast bulk carrier generation results in the transient current-time characteristics. Therefore, 3- and 20-nm TiN electrodes are the excellent choice for nMOSFETs and pMOSFETs, respectively, which is from the standpoint of strain engineering, threshold voltage (V_th), and performance. Due to the metal-induced strain, I_dsat improvements of 15% and 12% for nMOSFETs and pMOSFETs, respectively, were achieved.     

Charge trapping and detrapping characteristics in hafnium silicate gate stack under static and dynamic stress

The V/sub th/ instability of nMOSFET with HfSiON gate dielectric under various stress conditions has been evaluated. It is shown that after constant voltage stress, the threshold voltage (V/sub th/) relaxes to its initial prestress value. The relaxation rate is strongly affected by the stress duration and magnitude rather than injected charge flux or magnitude of the V/sub th/ shift. It is proposed that spatial distribution of trapped charges, which is strongly affected by the stress conditions, determines the relaxation rate. The implications of the electron trapping/detrapping processes on electrical evaluation of the high-/spl kappa/ gate dielectrics are discussed.     

The Effect of Nanoscale Nonuniformity of Oxygen Vacancy on Electrical and Reliability Characteristics of HfO2 MOSFET Devices

To understand the influence of oxygen vacancies in on the electrical and reliability characteristics, we have investigated area-dependent leakage-current characteristics of HfO₂ with large-area device and conducting atomic force microscopy (C-AFM). Unlike with the large-area analysis with typical capacitor and transistor, a clear evidence of oxygen vacancy was observed in nanoscale-area measurement using the C-AFM. Similar observations were made in various postdeposition annealing ambients to investigate the generation and reduction of oxygen vacancy in HfO₂ . With optimized postdeposition annealing for oxygen vacancy, significantly reduced charge trapping was observed in HfO₂ nMOSFET.     

Atomistic Modeling of the Structural and Thermal Conductivity of the InSb

A new parametrization for the previous empirical interatomic potential for indium antimonite is presented. This alternative parametrization is designed to correct the energetic sequence of structures. The effective empirical interatomic potential proposed consists of two and three body interactions which has the same functional form of the interatomic potential proposed by Vashishta et. al. to study other semiconductors (Branicio et al., 2003; Ebbsjo et al., 2000; Shimojo et al., 2000; Vashishta et al., 2008). Molecular dynamics simulations (MD) are performed to study high pressure phases of InSb up to 70 GPa and its thermal conductivity as a function of temperature. The rock-salt to cesium chloride, expected to occur at high pressures, is observed with the proposed interatomic potential.     

Forward propagation in a half-space with an irregular boundary

The parabolic wave equation (PWE) has been used extensively for modeling the propagation of narrow beams in weakly inhomogeneous random media. Corrections have been developed to accommodate wider scattering angles and boundaries have been introduced. Nonetheless, the formalism remains approximate and irregular surfaces with general boundary conditions present difficulties that have yet to be overcome. This paper presents an alternative approach to the entire class of propagation problems that strictly involve forward propagation. Forward-backward iteration has been shown to be a powerful procedure for computing the source functions that support propagation over irregular boundaries at low grazing angles. We show that the source functions for any unidirectional sweep can be computed by using a marching solution. This is not only more efficient than the single-sweep computation, but it facilitates accommodation of inhomogeneities in the propagation media. An exact equation for forward propagation in unbounded inhomogeneous media is used to derive a correction term that is applied at each forward-marching step. Results that combine ducting atmospheres and rough-surface scattering effects are presented for both the Dirichlet and Neumann boundary conditions     

Ionospheric scintillation theory--A mini-review

In this paper we briefly review the theories that are used to interpret ionospheric scintillation data. We have emphasized the full structure of the complex signal, because it is now being directly measured with a number of satellites that carry multifrequency phase-coherent beacons. The data that have been analyzed to date clearly show that large phase variations (greater than one radian) are an omnipresent feature of transionospheric signals.