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ZrN, a refractory ceramic material, finds many potential applications in advanced nuclear reactors. However, the grain size dependent radiation response in nanocrystalline (nc) ZrN under high dose heavy ion irradiation has not yet been studied to date. Here, we compare the radiation response of nc-ZrN films (with a respective average grain size of ~9 and 31nm) to Fe2+ ion irradiations up to a damage level of 10 displacements-per-atom (dpa). The ZrN film with the average grain size of 9nm shows prominently enhanced radiation tolerance as evidenced by suppressed grain growth, alleviated radiation softening, as well as reduced variation in electrical resistivity. In contrast, ZrN with the larger average grain size of 31 nm shows prominent radiation softening and resistivity increase, attributed to the high density of defect cluster formed inside the grains. The influence of grain boundaries on enhanced irradiation tolerance in nc-ZrN is discussed. [ABSTRACT FROM AUTHOR]

Nanotwinned metals are potential radiation-tolerant materials because they contain high-density coherent and incoherent twin boundaries that may serve as sinks to radiation-induced defects. The behavior of nanotwinned metals subject to ex situ and in situ irradiation remains however largely unexploited. This article offers an overview of the recent studies on the microstructural response of nanotwinned metals to in situ heavy ion irradiation, focusing on the interactions of defect clusters with twin boundaries and the radiation-induced twin boundary migration. Several radiation-tolerant nanotwinned metals are also highlighted. [ABSTRACT FROM AUTHOR]

We investigate size dependent strengthening mechanisms in sputtered Fe/W multilayers with individual layer thickness, h, varying from 1 to 200 nm. Microstructure analyses reveal that Fe/W has incoherent bcc/bcc interface when h is greater than 5 nm. When h decreases to 1-2.5 nm, the interface becomes semicoherent, and Fe and W show significant lattice distortions comparing to their bulk counterpart due to interface constraint. The layer thickness dependent drastic variations in x-ray diffraction profiles are simulated well by using an analytical model. Film hardness increases with decreasing h, and approaches a maximum value of 12.5 GPa when h is 1 nm. The layer thickness dependent film hardnesses are compared with analytical models. Koehler's image force plays a major role in determining the maximum strength of composites at smaller h [ABSTRACT FROM AUTHOR]

Aluminium typically deforms via full dislocations due to its high stacking fault energy. Twinning in aluminium, although difficult, may occur at low temperature and high strain rate. However, the 9R phase rarely occurs in aluminium simply because of its giant stacking fault energy. Here, by using a laser-induced projectile impact testing technique, we discover a deformation-induced 9R phase with tens of nm in width in ultrafine-grained aluminium with an average grain size of 140 nm, as confirmed by extensive post-impact microscopy analyses. The stability of the 9R phase is related to the existence of sessile Frank loops. Molecular dynamics simulations reveal the formation mechanisms of the 9R phase in aluminium. This study sheds lights on a deformation mechanism in metals with high stacking fault energies. [ABSTRACT FROM AUTHOR]

Nanocrystalline Ag, Cu, and Ni thin films and their coarse grained counterparts are patterned using focused ion beam and then irradiated by Kr ions within an electron microscope at room temperature. Irradiation induced in-plane strain of the films is measured by tracking the location of nanosized holes. The magnitude of the strain in all specimens is linearly dose-dependent and the strain rates of nanocrystalline metals are significantly greater as compared to that of the coarse grained metals. Real-time microscopic observation suggests that substantial grain boundary migration and grain rotation are responsible for the significant in-plane strain. [ABSTRACT FROM AUTHOR]

Presents a study which examined heteroepitaxial growth of zinc selenide (ZnSe) on a gallium arsenide/silicon (GaAs/Si) substrate. Examination of the crystallinity of ZnSe/GaAs/Si; Relative relationship of thermal mismatch and lattice mismatch of ZnSe to GaAs; Conclusion.

Nanotwinned metals received significant interest lately as twin boundaries may enable simultaneous enhancement of strength, ductility, thermal stability, and radiation tolerance. However, nanotwins have been the privilege of metals with low-to-intermediate stacking fault energy (SFE). Recent scattered studies show that nanotwins could be introduced into high SFE metals, such as Al. In this paper, we examine several sputter-deposited, {111} textured Ag/Al, Cu/Ni, and Cu/Fe multilayers, wherein growth twins were observed in Al, Ni, and face-centered cubic (fcc) Fe. The comparisons lead to two important design criteria that dictate the introduction of growth twins in high SFE metals. The validity of these criteria was then examined in Ag/Ni multilayers. Furthermore, another twin formation mechanism in high SFE metals was discovered in Ag/Ni system. [ABSTRACT FROM AUTHOR]

Ni41.7Ti38.8Nb19.5 shape memory alloy films were sputter-deposited onto silicon substrates and annealed at various temperatures. A narrow thermal hysteresis was obtained in the Ni-Ti-Nb films with a grain size of less than 50 nm. The small grain size, which means an increase in the volume fraction of grain boundaries, facilitates the phase transformation and reduces the hysteresis. The corresponding less transformation friction and lower heat transfer during the shear process, as well as reduced spontaneous lattice distortion, are responsible for this reduction of the thermal hysteresis. [ABSTRACT FROM AUTHOR]

In this paper, we present the design, the implementation details, and the evaluation results of an intrusion detection and defense system for distributed denial-of-service (DDoS) attack. The evaluation is conducted using an experimental testbed. The system, known as intrusion detection router (IDR), is deployed on network routers to perform online detection on any DDoS attack event, and then react with defense mechanisms to mitigate the attack. The testbed is built up by a cluster of sufficient number of Linux machines to mimic a portion of the Internet. Using the testbed, we conduct real experiments to evaluate the IDR system and demonstrate that IDR is effective in protecting the network from various DDoS attacks. [ABSTRACT FROM AUTHOR]

A retrospective study was conducted to assess radiographically the thymus size in well and sick neonates and to search for a possible relationship to perinatal events. Thymus size was expressed as cardiothymic:thoracic ratio (CT/T) by measuring the width of the cardiothymic shadow at the level of carina and dividing it by the width of the thorax at the costophrenic angles. The CT/T was measured on chest radiographs obtained on day 1 in well term neonates consecutively born in our nursery and sick neonates with meconium staining of the amniotic fluid, meconium aspiration syndrome or respiratory distress syndrome (RDS). Neonates with congenital anomalies, congenital heart disease or intrauterine growth retardation were excluded. There were no significant relationships between CT/T and sex, birth route, birthweight or gestational age in well and sick term neonates. The CT/T were comparable among well and sick term neonates and were significantly greater in the preterm neonates with RDS than in the preterm neonates without RDS. The CT/T was correlated to the birth route only in the preterm neonates. We conclude that thymus involution in the perinatal period is a complex process and the response is different between term and preterm neonates. [ABSTRACT FROM AUTHOR]

A novel tri-band, multifingered antenna is proposed. With the integration of the electromagnetic bandgap as an impedance-matching element, a wider impedance bandwidth response is obtained. The proposed antenna is also noted to be smaller in size, as compared to the conventional microstripfed tri-band antenna. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 206–208, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20253 [ABSTRACT FROM AUTHOR]

Heteroepitaxial growth of InP on Si with an intermediate GaAs buffer layer by low-pressure organometallic vapor phase epitaxy is reported. Excellent crystallinity of InP epilayers with specular surfaces can be reproducibly obtained. The carrier concentration profile shows that the carrier distribution in the InP layer is very uniform, while an apparent reduction in concentration occurs at the InP/GaAs interface. The 77 K photoluminescence (PL) of the InP layer exhibits a strong near-band-edge emission. No evident shift in PL peak energy for the InP/GaAs/Si sample compared with that for the InP homoepitaxial sample was first observed in this study. These results are superior to those reported previously for the InP/Si heteroepitaxy. [ABSTRACT FROM AUTHOR]

Stacking-fault tetrahedra are detrimental defects in neutron- or proton-irradiated structural metals with face-centered cubic structures. Their removal is very challenging and typically requires annealing at very high temperatures, incorporation of interstitials or interaction with mobile dislocations. Here we present an alternative solution to remove stacking-fault tetrahedra discovered during room temperature, in situ Kr ion irradiation of epitaxial nanotwinned Ag with an average twin spacing of ~8?nm. A large number of stacking-fault tetrahedra were removed during their interactions with abundant coherent twin boundaries. Consequently the density of stacking-fault tetrahedra in irradiated nanotwinned Ag was much lower than that in its bulk counterpart. Two fundamental interaction mechanisms were identified, and compared with predictions by molecular dynamics simulations. In situ studies also revealed a new phenomenon: radiation-induced frequent migration of coherent and incoherent twin boundaries. Potential migration mechanisms are discussed. [ABSTRACT FROM AUTHOR]

Oxide dispersion strengthened ferritic alloys have superior radiation tolerance and thus become appealing candidates as fuel cladding materials for next generation nuclear reactors. In this study we constructed a model system, Fe/Y2O3 nanolayers with individual layer thicknesses of 10 and 50 nm, in order to understand their radiation response and corresponding damage mitigation mechanisms. These nanolayers were subjected to in situ Kr ion irradiation at room temperature up to ~8 displacements-per-atom. As-deposited Y2O3 layers had primarily amorphous structure. Radiation induced prominent nanocrystallization and grain growth in 50 nm thick Y2O3 layers. Conversely, little crystallization occurred in 10 nm thick Y2O3 layers implying size dependent enhancement of radiation tolerance. In situ video also captured grain growth in both Fe and Y2O3 and outstanding morphological stability of layer interfaces against Kr ion irradiation. [ABSTRACT FROM AUTHOR]