POP-IN AND CRACK ARREST IN AN HY80 WELD

It is generally thought that, when a material is in its brittle to ductile transition, it is more difficult to design for crack arrest than to prevent crack initiation (cleavage). This report shows that this is not always true for weldments. Comparison is made between compact crack arrest (CCA), K_a, and crack tip opening displacement (CTOD), K_Jc, toughness for the same HY80 weld. The value of K_a is shown to be much higher than the minimum K_Jc for pop-in fracture initiation. It is considered that the results support the conclusion of Japanese research workers (Arimochi and Isaka) that small pop-ins (in the CTOD test) propagate and arrest without load drop. It follows that prediction of structural failure for weldments need not be based on minimum pop-in toughness from CTOD tests.     

89-GHz fT room-temperature silicon MOSFETs

The authors report the implementation of deep-submicrometer Si MOSFETs that at room temperature have a unity-current-gain cutoff frequency (f_T) of 89 GHz, for a drain-to-source bias of 1.5 V, a gate-to-source bias of 1 V, a gate oxide thickness of 40 Å, and a channel length of 0.15 μm. The fabrication procedure is mostly conventional, except for the e-beam defined gates. The speed performance is achieved through an intrinsic transit time of only 1.8 ps across the active device region     

The effects of case libraries on problem solving

Abstract The purpose of the study was to investigate the effects of providing access to a case library of related stories while undergraduates solved ill-structured problems. While solving complex food product development problems, the experimental group accessed experts' stories of similar, previously solved problems; the comparable group accessed fact sheets (expository representation of stories' content); and the control group accessed text selected at random from a textbook dealing with issues unrelated to the stories. On multiple-choice questions assessing processes related to problem solving (prediction, inferences, explanations, etc.), experimental students out-performed the comparable and control groups. Performance on short-answer questions also assessing problem-related skills was not significantly different, in part because of test fatigue. Analysis of interviews identified a number of factors that students used in deciding how to apply their study strategies, including causal factors, grounding phenomenon, grounding in context, and outcomes.     

Swords to plowshares: Shock wave applications to advanced lithography

xtreme ltra iolet ithography (EUVL) seeks to apply radiation in a wavelength region centered near 13 nm to produce microcircuits having feature sizes 0.1 micron or less. A critical requirement for the commercial application of this technology is the development of an economical, compact source of this radiation which is suitable for lithographic applications. A good candidate is a laser-plasma source, which is generated by the interaction of an intermediate intensity laser pulse (up to 10¹² W/cm²) with a metallic target. While such a source has radiative characteristics which satisfy the needs of an EUVL source, the debris generated during the laser-target interaction strikes at the economy of the source. Here, we review the use of concepts and computer modeling, originally developed for hypervelocity impact analysis, to study this problem.     

Energy-aware wireless networking with directional antennas: the case of session-based broadcasting and multicasting

We consider ad hoc wireless networks that use directional antennas and have limited energy resources. To explore quantitatively the advantage offered by the use of directional antennas over the case of omnidirectional antennas, we consider the case of connection-oriented multicast traffic. Building upon our prior work on multicasting algorithms, we introduce two protocols that exploit the use of directional antennas and evaluate their performance, We observe significant improvement with respect to the omnidirectional case, in terms of both energy efficiency and network lifetime. Additionally, we show that further substantial increase in the network's lifetime can be achieved by incorporating a simple measure of a node's residual energy into the node's cost function.     

Calculated and Experimental Estimation of Absorbed Mechanical Work in Deformation of Synthetic Fibres

Methods are proposed for obtaining the elastic and absorbed components of deformation and mechanical work expended in the region of a nondestructive mechanical effect from the stress-strain diagrams or by calculated prediction. The closeness of the values of the absorbed and correspondingly the elastic components obtained with the measured or predicted stress-strain diagram totally confirm the satisfactory reliability of modeling the physicomechanical properties of a fibre in the form of an integral equation in which the nonlinear-hereditary kernel analytically reflects the activating character of the mechanical effect combined with the concept of the deformation-time analogy in normalized form [5].     

Propagation of Isothermal Flame in the Low-Pressure Thermal Decomposition of Nitrogen Trichloride

The inhibition and promotion of isothermal NCl₃ flame by NOCl and H₂, respectively, are explained. The crossover from the isothermal mode of flame propagation to the thermal one is analyzed for NCl₃–He mixtures. Calculations based on a kinetic mechanism taking into account energy chain branching are performed, and qualitative agreement between the calculated and observed data is demonstrated. The one-dimensional problem of chain–thermal flame propagation by a chain reaction involving a nonlinear-branching step has two solutions corresponding, one corresponding the isothermal mode of flame propagation and the other corresponding to the chain–thermal one. Nonlinear chain branching shortens the time needed for thermal ignition and increases the flammability of the combustible mixture.     

A quantum full adder for a scalable nuclear spin quantum computer

We demonstrate a strategy for implementation a quantum full adder in a spin chain quantum computer. As an example, we simulate a quantum full adder in a chain containing 201 spins. Our simulations also demonstrate how one can minimize errors generated by non-resonant effects.