Search Results - (Author, Cooperation:D. Ng)

2013-05-11

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Communicable Diseases, Emerging/*transmission/*virology ; Humans ; Influenza A virus/*physiology ; Influenza in Birds/*transmission ; Influenza, Human/*virology

2018-11-09

American Chemical Society (ACS)

0002-7863

1520-5126

Chemistry and Pharmacology

2012-11-03

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2018-09-28

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Geosciences

Computer Science

Medicine

Natural Sciences in General

Physics

Medicine, Diseases, Online Only

1089-7550

AIP Digital Archive

Physics

Specimens of α-phase solid solution of iron-rich FeCu(1.07 at. % Cu) were thermally aged at 700 °C for different time durations. Precipitation and growth of εCu took place during the heat treatments. The specimens were polished and were examined with a transmission electron microscope. The size, density, and shape of the precipitates were determined for different aging conditions. These parameters were fit into the strong and weak domain wall pinning models, allowing values of the coercive field Hc to be predicted. Comparison between the predicted and measured coercive fields shows that weak pinning theory agrees with the observed Hc in low age specimens. For specimens aged over 1700 min, strong pinning theory can provide acceptable calculated Hc values. The pinning index β' related to the ratio of the domain wall area per pin in the static and dynamic states is also calculated for each specimens. β' values in low age specimens are found to be 〈1, which indicates weak pinning. For prolonged age specimens, β' values are close to or larger than 1, and strong pinning is indicated.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Magnetoacoustic emission (MAE) is under development as a technique for the nondestructive measurement of stress in magnetic materials. However, structural defects create additional boundaries which alter the magnetic domain configuration and could perturb the MAE response of the material. MAE is therefore employed to investigate the effect of additional surfaces on the domain structure close to and some distance from artificially implanted holes in a mild steel bar. The MAE profile, a result of non-180° wall motion, obtained before the hole drilling, shows two outer peaks of equal height one at each knee of the magnetization curve. This suggests that the energies dissipated by the domain nucleation and annihilation processes are the same. However, the MAE profile obtained near an 8 mm hole shows a large initial peak and a small final peak, indicating that the enlargement of reverse domains is mainly due to the unpinning of trapped walls at the edges of the hole. This process is discrete and sudden and, therefore, the initial signal peak is large. In the largest field applied, the reverse domains are not completely annihilated, causing the final peak to be small. A further practical problem is that variations of magnetic coupling can have a significant effect on the MAE profile. This is also investigated, and it is concluded that using a spacer of optimal thickness between the magnet and the specimen could reduce the sensitivity to this effect.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The structural and magnetic properties of off-stoichiometric 2:17-type compounds Sm2Fe17−xTxM (T=Co, Ti; M=Al, Si; x=0–4) were studied by x-ray powder diffraction, thermomagnetic analysis, and magnetic measurements. All these compounds were of the Th2Zn17 type. The substitution of Co or Ti for Fe, and the addition of Si or Al into the Sm2Fe17 did not alter the rhombohedral structure. The Co replacement increased the Curie temperature Tc due to the strong coupling between Fe and Co. A small substitution of Ti also led to an increase of Tc. However, when x〉3, the exchange coupling became less effective as the separation between the Fe atoms became large, and Tc decreased. The maximum Tc=713 K was found in Sm2Fe17−xCoxSi when x=4. As for the saturation magnetization Ms, Sm2Fe17−xTixAl had its Ms decreased monotonically with increasing Ti, while Ms of other compounds increased first and then decreased with the content of Co or Ti. The maximum Ms=159 emu/g was recorded in Sm2Fe15Co2Al. To make use of these compounds as permanent magnets, Sm2Fe15Co2Si is preferred because it has Tc=641 K and Ms=142 emu/g. The dual substitutions of Fe by using Co or Ti, and by Al or Si to improve Tc and Ms of Sm2Fe17, are more effective than using single substitution. © 1999 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

NdFeB permanent magnets are coated by two different methods, dip coating and evaporation coating, with Al. It is found that an intermetallic reaction has occurred and formed a dominant phase of FeAl2.5Bx at the interface between the Al coating and the magnet material. Such reaction enhances strong bonding between the coating and the magnet. When Al(Fe) is used for the coating, no detectable intermetallic phase is observed, and therefore the amount of magnet material is conserved. We have studied the effect of the intermetallic phase on corrosion protection of the magnet. It is found that this phase is less resistive towards HNO3 solution than pure Al; but it is more resistive towards NaOH and NaCl. The investigation of the changes of microstructures of the coatings under different tempering conditions have also been carried out. The results show that the heat treatment at 500 °C for 10 min for a ∼ 2 μm thick Al coating by evaporation can produce an optimal layer of intermetallics. If the temperature is too low, the coating will not adhere to the magnet or if too high, it will fully react with the magnet and produce a rough coating surface. © 1996 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Magnetoacoustic emission (MAE) measurements have been made on nickel and mild steel samples subjected to a magnetizing field of various frequencies f. In both samples, the MAE signals are found to increase with increasing f. The experimental results are in good agreement with the predictions of a model relating the generation of MAE to domain wall nucleation-annihilation and domain wall motion. When f is large, the contribution of wall motion to the generation of MAE is predicted to be dominant. Conversely, when f is small, MAE is generated mainly by domain wall nucleation-annihilation processes. At high frequencies, the amount of MAE from both nickel and mild steel samples is found to vary linearly with f0.5. As f decreases, the MAE deviates from the f0.5 relationship for f〈10 Hz in mild steel, and for f〈2 Hz for nickel. The results suggest that in nickel, wall motion remains the dominant source of MAE generation over a wider frequency range than in steel. © 1996 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Barkhausen emission (BE) and magnetoacoustic emission (MAE) measurements have been made on a nickel bar before and after it is torn apart by a tensile stress. The BE and MAE profiles obtained are all single-peaked. The peaks obtained after fracture are found at the lower field regions of the profiles, and this suggests that the field required for the domain wall motion in the fractured bar has been lowered. In the BE measurement, the signals show an increase of 44% (away from fracture end) to 144% (at fracture end); on the contrary, the MAE signals show a reduction of 43% (away from fracture end) to 14% (at fracture end). As the nickel bar is fractured, we find that in the broken pieces, the grains have been elongated in the stressed direction, and there is an increase of defects such as dislocations, voids and microcracks, especially near the fracture end of the bar. BE which is sensitive to these factors, has therefore been intensified. On the other hand, the plastically elongated grains, which have a lower absolute magnetostriction, enhance the reduction of MAE activity. The results measured from the nickel bar will be compared with those obtained from a fractured mild steel bar, which has different magnetostriction and other magnetic properties. © 1996 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Magnetoacoustic emission (MAE) has been measured from a Ni bar and a mild steel bar. The magnetizing field was produced by a c-core electromagnet, which was separated from the specimen surface by a nonmagnetic spacer layer (thickness la). In Ni, the MAE profile contains a single peak when la is small. As la increases, a second peak appears and then a third peak, indicating that MAE is not only caused by domain wall creation and annihilation, but also by domain wall motion. In the case of the mild steel bar, only two peaks are detected, which are increasingly separated as la increases. The different results between the two materials can be explained by the different mobility of non-180° domain walls. The present results also indicate that the MAE profile obtained from Ni is less sensitive to la than that obtained from mild steel. This difference can be explained by considering the reluctance of the magnetic circuit.

Electronic Resource

1365-2958

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

Type III secretion systems identified in bacterial pathogens of animals and plants transpose effectors and toxins directly into the cytosol of host cells or into the extracellular milieu. Proteins of the type III secretion apparatus are conserved among diverse and distantly related bacteria. Many type III apparatus proteins have homologues in the flagellar export apparatus, supporting the notion that type III secretion systems evolved from the flagellar export apparatus. No type III secretion apparatus genes have been found in the complete genomic sequence of Campylobacter jejuni NCTC11168. In this study, we report the characterization of a protein designated FlaC of C. jejuni TGH9011. FlaC is homologous to the N- and C-terminus of the C. jejuni flagellin proteins, FlaA and FlaB, but lacks the central portion of these proteins. flaC null mutants form a morphologically normal flagellum and are highly motile. In wild-type C. jejuni cultures, FlaC is found predominantly in the extracellular milieu as a secreted protein. Null mutants of the flagellar basal rod gene (flgF) and hook gene (flgE) do not secrete FlaC, suggesting that a functional flagellar export apparatus is required for FlaC secretion. During C. jejuni infection in vitro, secreted FlaC and purified recombinant FlaC bind to HEp-2 cells. Invasion of HEp-2 cells by flaC null mutants was reduced to a level of 14% compared with wild type, suggesting that FlaC plays an important role in cell invasion.

Electronic Resource

0022-4731

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Electronic Resource

0550-3213

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0003-3472

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Electronic Resource

0370-2693

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0370-2693

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0273-1177

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Electronic Resource

0304-8853

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0304-8853

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource