Characteristics and microstructure in the evolution of shear localization in ti-6al-4v alloy

A new interrupting method was proposed and the split Hopkinson torsional bar (SHTB) was modified in order to eliminate the effect of loading reverberation on post-mortem observations. This makes the comparative study of macro- and microscopic observations on tested materials and relevant transient measurement of tau - gamma curve possible. The experimental results of the evolution of shear localization in in Ti-6Al-4V alloy studied with the modified SHTB are reported in the paper. The collapse of shear stress seems to be closely related to the appearance of a certain critical coalescence of microcracks. The voids may form within the localized shear zone at a quite early stage. Finally, void coalescence results in elongated cavities and their extension leads to fracture along the shear band.

Microstructure of shear localization in low-carbon ferrite pearlite steel

A study has been made of the microstructure of the thermally assisted band in a low carbon ferrite-pearlite steel, resulting from high speed torsional testing with an average strain rate of about 1500 s−1. Metallographic examination showed that there are several fine shear bands distributed over a deformed region (the gauge length of the specimen). The width of these bands is estimated to be of the order of magnitude of 50 μm, and the spacing between them is roughly about 100 μm. Detailed scanning electron microscopy studies indicate that damage of the microstructure within the band is very apparent, as evidenced by microcrack initiation and coalescence along the shear deformation band. However, there is no evidence that the material in the band had become microcrystalline or non-crystalline.

Two Nuclear Localization Signals in USP1 Mediate Nuclear Import of the USP1/UAF1 Complex

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Elastic and statistically brittle (ESB) model, damage localization and catastrophic rupture

In this paper, an elastic and statistically brittle (ESB) model is applied to the process of damage evolution induced catastrophic rupture and the influence of localization and softening on catastrophic rupture is discussed. According to the analysis, the uncertainty of catastrophic rupture should be attributed to the unknown scale of localized zone. Based on the elastic and statistically brittle model but local mean field approximation, the relation between the scale of localized zone and catastrophic rupture is obtained and then justified with experiments. These results can not only give a deeper understanding of the mechanism governing catastrophic rupture, but also provide a possible tool to foresee the occurrence of catastrophic rupture.

Adiabatic shear localization: occurrence, theories, and applications

Exploration of new drug delivery pathways: I. Mechanism of folate uptake in cultured human cells. II. Role of nuclear localization signal peptides in the delivery of oligonucleotide into reconstituted nuclei

The roles of the folate receptor and an anion carrier in the uptake of 5- methyltetrahydrofolate (5-MeH_4folate) were studied in cultured human (KB) cells using radioactive 5-MeH_4folate. Binding of the 5-MeH_4folate was inhibited by folic acid, but not by probenecid, an anion carrier inhibitor. The internalization of 5-MeH_4folate was inhibited by low temperature, folic acid, probenecid and methotrexate. Prolonged incubation of cells in the presence of high concentrations of probenecid appeared to inhibit endocytosis of folatereceptors as well as the anion carrier. The V_(max) and K_M values for the carrier were 8.65 ± 0.55 pmol/min/mg cell protein and 3.74 ± 0.54µM, respectively. The transport of 5-MeH4folate was competitively inhibited by folic acid, probenecid and methotrexate. The carrier dissociation constants for folic acid, probenecid and methotreate were 641 µM, 2.23 mM and 13.8 µM, respectively. Kinetic analysis suggests that 5-MeH_4folate at physiological concentration is transported through an anion carrier with the characteristics of the reduced-folate carrier after 5-MeH_4folate is endocytosed by folate receptors in KB cells. Our data with KB cells suggest that folate receptors and probenecid-sensitive carriers work in tandem to transport 5-MeH_4folate to the cytoplasm of cells, based upon the assumption that 1 mM probenecid does not interfere with the acidification of the vesicle where the folate receptors are endocytosed.

Oligodeoxynucleotides designed to hybridize to specific mRNA sequences (antisense oligonucleotides) or double stranded DNA sequences have been used to inhibit the synthesis of a number of cellular and viral proteins (Crooke, S. T. (1993) FASEB J. 7, 533-539; Carter, G. and Lemoine, N. R. (1993) Br. J. Cacer 67, 869-876; Stein, C. A. and cohen, J. S. (1988) Cancer Res. 48, 2659-2668). However, the distribution of the delivered oligonucleotides in the cell, i.e., in the cytoplasm or in the nucleus has not been clearly defined. We studied the kinetics of oligonucleotide transport into the cell nucleus using reconstituted cell nuclei as a model system. We present evidences here that oligonucleotides can freely diffuse into reconstituted nuclei. Our results are consistent with the reports by Leonetti et al. (Proc. Natl. Acad. Sci. USA, Vol. 88, pp. 2702-2706, April 1991), which were published while we were carrying this research independently. We also investigated whether a synthetic nuclear localization signal (NLS) peptide of SV40 T antigen could be used for the nuclear targeting of oligonucleotides. We synthesized a nuclear localization signal peptide-conjugated oligonucleotide to see if a nuclear localization signal peptide can enhance the uptake of oligonucleotides into reconstituted nuclei of Xenopus. Uptake of the NLS peptide-conjugated oligonucleotide was comparable to the control oligonucleotide at similar concentrations, suggesting that the NLS signal peptide does not significantly enhance the nuclear accumulation of oligonucleotides. This result is probably due to the small size of the oligonucleotide.

The interplay of localization and interactions in quantum many-body systems

Disorder and interactions both play crucial roles in quantum transport. Decades ago, Mott showed that electron-electron interactions can lead to insulating behavior in materials that conventional band theory predicts to be conducting. Soon thereafter, Anderson demonstrated that disorder can localize a quantum particle through the wave interference phenomenon of Anderson localization. Although interactions and disorder both separately induce insulating behavior, the interplay of these two ingredients is subtle and often leads to surprising behavior at the periphery of our current understanding. Modern experiments probe these phenomena in a variety of contexts (e.g. disordered superconductors, cold atoms, photonic waveguides, etc.); thus, theoretical and numerical advancements are urgently needed. In this thesis, we report progress on understanding two contexts in which the interplay of disorder and interactions is especially important.

The first is the so-called “dirty” or random boson problem. In the past decade, a strong-disorder renormalization group (SDRG) treatment by Altman, Kafri, Polkovnikov, and Refael has raised the possibility of a new unstable fixed point governing the superfluid-insulator transition in the one-dimensional dirty boson problem. This new critical behavior may take over from the weak-disorder criticality of Giamarchi and Schulz when disorder is sufficiently strong. We analytically determine the scaling of the superfluid susceptibility at the strong-disorder fixed point and connect our analysis to recent Monte Carlo simulations by Hrahsheh and Vojta. We then shift our attention to two dimensions and use a numerical implementation of the SDRG to locate the fixed point governing the superfluid-insulator transition there. We identify several universal properties of this transition, which are fully independent of the microscopic features of the disorder.

The second focus of this thesis is the interplay of localization and interactions in systems with high energy density (i.e., far from the usual low energy limit of condensed matter physics). Recent theoretical and numerical work indicates that localization can survive in this regime, provided that interactions are sufficiently weak. Stronger interactions can destroy localization, leading to a so-called many-body localization transition. This dynamical phase transition is relevant to questions of thermalization in isolated quantum systems: it separates a many-body localized phase, in which localization prevents transport and thermalization, from a conducting (“ergodic”) phase in which the usual assumptions of quantum statistical mechanics hold. Here, we present evidence that many-body localization also occurs in quasiperiodic systems that lack true disorder.

Controllable atom localization via double-dark resonances in a tripod system

We propose an atom localization scheme for a tripod-type atom making use of the sharp absorption peak resulting from interacting double-dark resonances. It is demonstrated that the probability of finding the atom at a particular position, as well as the localization precision, can be dramatically enhanced. The probability can be doubled by adjusting the Rabi frequency of the control field to the maximum Rabi frequency of the standing-wave field. Moreover, much better spatial resolution can be achieved for smaller detunings of the control and the standing-wave fields. (c) 2006 Optical Society of America.

Constitutive plasma membrane targeting and microdomain localization of Dok5 studied by single-molecule microscopy

In the present study, single-molecule fluorescence microscopy was used to examine the characteristics of plasma membrane targeting and microdomain localization of enhanced yellow fluorescent protein (eYFP)-tagged wild-type Dok5 and its variants in living Chinese hamster ovary (CHO) cells. We found that Dok5 can target constitutively to the plasma membrane, and the PH domain is essential for this process. Furthermore, single-molecule trajectories analysis revealed that Dok5 can constitutively partition into microdomain on the plasma membrane. Finally, the potential mechanism of microdomain localization of Dok5 was discussed. This study provided insights into the characteristics of plasma membrane targeting and microdomain localization of Dok5 in living CHO cells. (C) 2008 Elsevier B.V. All rights reserved.