How acoustic cavitation can improve adhesion

In general, ultrasound is commonly used at low power level for non-destructive testing (NDT) and detection of delaminations in adhesive bonded structures. The present paper instead presents an approach where power ultrasound is used to improve interface formation prior to the bonding process and to ensure the quality of adhesive bonds by using acoustic cavitation in the liquid adhesive.Results from high-speed videos, rheological and thermal measurements and destructive testing of adhesive bonds with contaminated surfaces are presented and discussed. Power ultrasound can be used in general to improve adhesion and significantly to improve contamination tolerance and robustness of adhesive bonding processes.     

Nonlinear optics in glasses: How can we analyze?

Maximal optical nonlinearity obtainable in amorphous materials at telecommunication wavelengths of ∼1.5 μm is predicted. Applying a semiconductor concept, we suggest that nonlinear properties become greater in the materials with smaller optical gaps. This trend makes the chalcogenide glass such as As₂Se₃ promising for fiber devices (∼1 m), including optical switches, intensity stabilizers, and stimulated Raman amplifiers. However, for integrated devices with optical path lengths of ∼1 cm, greater nonlinearity is needed.     

Calculations of electric field gradients in solids: How theory can complement experiment

Increasing computer power and the development of user-friendly, yet highly sophisticated bandstructure programs have made it possible that theoretical EFG calculations can nowadays be performed for fairly complex materials science problems. We show that a combination of these theoretical calculations with experimentally obtained quadrupole splittings can lead to new insight into various interesting problems. This is illustrated for the determination of nuclear quadrupole moments, investigations of samples containing impurities or other imperfections and for Na₂[Fe(CN)₅NO], a promising material for holographic storage applications. This revised version was published online in August 2006 with corrections to the Cover Date.     

Spontaneous emission in cavities: How much more classical can you get?

Cavity-induced changes in atomic spontaneous emission rates are often interpreted in terms of quantum electrodynamical zero-point field fluctuations. A completely classical method of computing this effect in terms of the unquantized normal mode structure of the cavity is presented here. Upon applying the result to a classical dipole radiating between parallel mirrors, we obtain the same cavity correction as that for atomic spontaneous emission in such a cavity. The theory is then compared with a recent experiment in the radio-frequency domain.It is a pleasure and an honor to dedicate this paper to Professor Asim O. Barut, who, as my teacher, advisor, and friend, has been a great inspiration to me as well as many, many others.Work supported by the National Research Council of the United States.     

Complex classical trajectories in tunnelling: How instanton bounces can become real processes

Summary Instanton bounces in complex-time and high temporal density can be related to complex classical trajectories when the potential barrier is slightly perturbed. The bounce duration in real and imaginary times is found to be in good agreement with the one evaluated by the phase-time method. On this basis, a plaustible interpretational model of the tunnelling processes is suggested.     

Diffusion of gases into the lung: How physics can help to understand physiology

In the human lung, the gas transfer between air and blood is achieved in terminal units that are called ‘acini’. Whereas convection is still the predominant transport phenomenon at the acinus entrance, most of the acinar surface is in fact accessed by diffusion. The transition between convection and diffusion, and thus the size of the diffusion unit, depends on the air velocity at the acinus entrance. In this paper, we present a gas transport model which takes into account both the diffusion into the acinus and the diffusion across the alveolar membrane. It is shown that the physiological sizes of the diffusion unit in the lung, at rest or at exercise, can be explained by physical arguments. In that sense, diffusion is the ‘dimensioning criterion’ of the lung at the acinar level. This approach shows that, due to diffusional screening at inspiration and at rest, there exists a permanent spatial inhomogeneity of oxygen and carbon dioxide partial pressure which reduces the effective surface efficiency of the human acinus to a value of only 30 to 40%. This model casts a new light on the properties of this physiological transport system. It permits in particular to understand how several diseases among which pulmonary edema may remain asymptomatic in their early stages.      

Passivated B-O,B-S codoping to improve the photocatalytic efficiency in C2N monolayer: First-principles study

In this paper, we explored systematically the effects of non-metal elements (B, O, and S) monodoping and passivated codoping of B-S and B-O in C₂N monolayer. The band structure, band edge position and charge density distribution of doped-C₂N are investigated. Our results show that the monodoping of B, O, S introduce flat impurity bands around the Fermi level. The passivated codoping of B-O or B-S can effectively decrease the bandgap, and the band edge position is more favorable for water splitting compared with that of C₂N monolayer. A large dispersion of conduction and valance band can be observed for B-S or B-O codoping, which is beneficial for the carriers' mobility. Moreover, the separation of electron and hole density to extend after doping can decrease the combination rate in photocatalytic. Our results predict that passivated B-S or B-O doped C₂N are promising water-splitting photocatalyst.     

How the choice of data reduction can strongly influence uncertainty assessment: A re-analysis of Mn-bath experiments

The Mn-bath technique is widely used, especially by standardization laboratories, for the absolute determination of neutron emission rates. Understanding the limitations of the technique, and in particular the total measurement uncertainty, is crucial if quality results, fit for purpose, are to be reported. In this work, we show that the way in which the acquired data is analyzed can strongly influence the uncertainty assessment. We take a carefully performed set of Mn-bath measurements from the literature as our example and show that the same data when reanalyzed can be used to justify an uncertainty smaller by about an order of magnitude than was originally reported. This finding should caution all those involved in radiation measurements to critically assess their approach to data analysis and to perform a careful uncertainty analysis taking into account possible alternatives.     

How can nanobiotechnology oversight advance science and industry: examples from environmental,health, and safety studies of nanoparticles (nano-EHS)

Nanotechnology has great potential to transform science and industry in the fields of energy, material, environment, and medicine. At the same time, more concerns are being raised about the occupational health and safety of nanomaterials in the workplace and the implications of nanotechnology on the environment and living systems. Studies on environmental, health, and safety (EHS) issues of nanomaterials have a strong influence on public acceptance of nanotechnology and, eventually, affect its sustainability. Oversight and regulation by government agencies and non-governmental organizations (NGOs) play significant roles in ensuring responsible and environmentally friendly development of nanotechnology. The EHS studies of nanomaterials can provide data and information to help the development of regulations and guidelines. We present research results on three aspects of EHS studies: physico-chemical characterization and measurement of nanomaterials; emission, exposure, and toxicity of nanomaterials; and control and abatement of nanomaterial releases using filtration technology. Measurement of nanoparticle agglomerates using a newly developed instrument, the Universal NanoParticle Analyzer (UNPA), is discussed. Exposure measurement results for silicon nanoparticles in a pilot scale production plant are presented, as well as exposure measurement and toxicity study of carbon nanotubes (CNTs). Filtration studies of nanoparticle agglomerates are also presented as an example of emission control methods.