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  • 1
    Electronic Resource
    Electronic Resource
    Photoluminescence study of Sr+ ion-implanted GaAs (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4828-4830 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-temperature photoluminescence experiments were carried out for Sr+ ion-implanted GaAs substrates as a function of Sr concentration and excitation intensity. It was found that the Sr impurity produces four emissions denoted by (Sr°, X), "G1'', "G2'', and "H'' in the near band emission region in GaAs grown by molecular beam epitaxy. "G1'' emission presents a red shift with increasing Sr concentration, while "G2'' does not shift. In a Sr+ ion-implanted impure GaAs substrate grown by the liquid-encapsulated Czochralski method, all four of the above emissions were missing. Instead there appeared two other emissions, SM1 and SM2, which are considered to be related to two deep acceptor levels of Sr in GaAs. All results indicate that the Sr impurity produces both shallow and deep energy levels in GaAs and a small amount of the residual impurity will quench the emissions related to shallow energy levels. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359408
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  • 2
    Electronic Resource
    Electronic Resource
    Cis-acting sequences that affect somatic hypermutation of Ig genes (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Immunological reviews 162 (1998), S. 0 
    Details
    ISSN: 1600-065X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Summary: We review our studies on the mechanism of somatic hypermutation of immunoglobulin genes. Most experiments were carried out using Ig transgenes. We showed in these experiments that all required cisacting elements are present within the 10–16 kb of a cransgene. Only the Ig variable region and its proximate flanks are mutated, not the constant region. Several Ig gene enhancers are permissive for somatic mutation. Association of the enhancer with its natural Ig promoter is not necessary. However, the mutation process seems specific for Ig genes. No mutations were found in housekeeping genes from cells with high levels of somatic hypermutation of their Ig genes. The Ig enhancers may provide the Ig gene specificity. An exception may he the BCL6 gene, which was mutated in but not hut not in mouse B cellsTranscription of a region is required for its mutability When the transcriptional promoter located upstream of the variable region is duplicated upstream of the constant region, this region also becomes mutable. This suggests a model in which a mutator factor associates with the RNA polymerase at the promoter, travels with the polymerase during elongation, and causes mutations during polymerase pausing. The DNA repair systems, nucleotide excision repair and DNA mismatch repair, are not required. Our recent data with an artificial substrate of somatic mutation suggest that pausing may be due to secondary structure of the DNA or nascent RNA, and the specific mutations to preferences of the mutator factor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-065X.1998.tb01438.x
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  • 3
    Electronic Resource
    Electronic Resource
    Stripping voltammetry of copper and lead using gold electrodes modified with self-assembled monolayers (1997)
    Springer
    Journal of solid state electrochemistry 1 (1997), S. 241-247 
    Details
    ISSN: 1433-0768
    Keywords: Key words Underpotential deposition ; Stripping analysis ; Self-assembled monolayers ; Multiple stripping peaks ; Heavy metals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract One problem associated with using bare solid metal electrodes, such as gold and platinum, in stripping analysis to determine heavy metal ions such as lead and copper ions in dilute solutions is that underpotential deposition (UPD) gives multiple stripping peaks in the analysis of mixtures. These peaks are often overlapped and cannot be conveniently used for analytical purposes. Bifunctional alkylthiols, such as 3-mercaptopropionic acid, with an ionizable group on the other terminal end of the thiol can form self-assembled monolayers (SAMs) on the surface of the gold electrode. It is shown that such an SAM-modified gold electrode minimizes the UPD effects for the stripping analysis of lead and copper. The anodic peak potential shifts and the peak shape changes, indicating that the SAM changes the deposition and stripping steps of these heavy metal ions. Thus, the sensitivity levels for both single species and mixtures can be significantly improved for the conventional solid electrodes. The mechanism of the deposition reaction at the SAM-modified gold electrodes is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100080050055
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  • 4
    Electronic Resource
    Electronic Resource
    Blocking behavior of self-assembled monolayers on gold electrodes (1997)
    Springer
    Journal of solid state electrochemistry 1 (1997), S. 148-154 
    Details
    ISSN: 1433-0768
    Keywords: Key words Self-assembled monolayers ; Thiols ; Gold ; Electrode ; Adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Self-assembled monolayers (SAMs) with metal electrodes, especially thiols on gold, are the subject of this investigation because of the unique properties of SAM-modified surfaces. Normal alkanethiols are used to modify the surface of a conventional gold electrode to block certain ions such as Pb(II) and Cu(II) from the surface of the electrode. Normal alkanethiols are also used to study the SAM-gold interfacial adsorption-desorption behavior of the self-assembled monolayer. The effects of varying chain length of SAMs, varying concentration of the alkanethiol solutions, immersion time of the pure gold electrode in the SAM solution, and the stability of a SAM-modified gold electrode in fresh chloroform are investigated using the oxidation-reduction peaks of gold. Conditions that optimize the surface coverage and the uniformity of the SAMs have been determined. Normal alkanethiols proved to be a good insulator on the electrode surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100080050039
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  • 5
    Electronic Resource
    Electronic Resource
    Changes in trkA expression in the dorsal root ganglion after peripheral nerve injury (1999)
    Springer
    Experimental brain research 127 (1999), S. 141-146 
    Details
    ISSN: 1432-1106
    Keywords: Key words Axotomy ; Nerve growth factor ; Neuropathic pain ; TrkA-immunoreactivity ; trkA mRNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Most of the biological effects of nerve growth factor (NGF) are mediated by TrkA, the high affinity receptor for NGF. Previous studies have shown that NGF levels in the dorsal root ganglia (DRG) fluctuate following a peripheral nerve injury. The present study examined changes of TrkA immunoreactivity and trkA mRNA expression in the DRG after segmental nerve ligation. In the normal L5 DRG of the rat, there were, on average, 4700 TrkA-immunoreactive (TrkA-IR) neurons, representing 42% of the total neuronal population. Following L5 spinal nerve ligation, the number of TrkA-IR neurons in the L5 DRG slowly declined, reducing by 25% at 1 week and 35% at 3 weeks postoperation (PO). In contrast, trkA mRNA in these ganglia showed a significant decrease from 3 days to 3 weeks PO and was followed by a full recovery at 2 months PO. The early decrease of trkA mRNA is likely due to deprivation of target-derived NGF, which is caused by nerve ligation, and the recovery might be because substitute sources of NGF become available. Despite the decline in trkA mRNA in the ganglion, 3000 injured DRG neurons sustain TrkA immunoreactivity, suggesting that exogenous NGF can still influence these TrkA expressing neurons, even though they are isolated from the periphery. Accordingly, the effects of endogenous NGF should be as well manifested by local administration of NGF to the ganglion as to the stump of the damaged nerve.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050783
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  • 6
    Electronic Resource
    Electronic Resource
    Finding the k most vital edges with respect to minimum spanning tree (1999)
    Springer
    Acta informatica 36 (1999), S. 405-424 
    Details
    ISSN: 1432-0525
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract. For a connected, undirected and weighted graph G = (V,E), the problem of finding the k most vital edges of G with respect to minimum spanning tree is to find k edges in G whose removal will cause greatest weight increase in the minimum spanning tree of the remaining graph. This problem is known to be NP-hard for arbitraryk. In this paper, we first describe a simple exact algorithm for this problem, based on t he approach of edge replacement in the minimum spanning tree of G. Next we present polynomial-time randomized algorithms that produce optimal and approximate solutions to this problem. For $|V|=n$ and $|E|=m$ , our algorithm producing optimal solution has a time complexity of O(mn) with probability of success at least $e^{-\frac{\sqrt{2k}}{k-2}}$ , which is 0.90 for $k\geq 200$ and asymptotically 1 when k goes to infinity. The algorithm producing approximate solution runs in $O(mn+nk^2\log k)$ time with probability of success at least $1-\frac{1}{4}(\frac{2}{n})^{k/2-2}$ , which is 0.998 for $k\geq 10$ , and produces solution within factor 2 to the optimal one. Finally we show that both of our randomized algorithms can be easily parallelized. On a CREW PRAM, the first algorithm runs in O(n) time using $n^2$ processors, and the second algorithm runs in $O(\log^2n)$ time using mn/logn processors and hence is RNC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002360050166
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