Detection of single bacterial pathogens with semiconductor quantum dots

Semiconductor quantum dots (QDs) have been used in a simple fluorometric assay to detect single cells of the pathogenic Escherichia coli O157:H7 serotype. Composed of CdSe/ZnS core/shell QDs conjugated to streptavidin, this system exhibits 2 orders of magnitude more sensitivity than a similar assay using a common organic dye. Selectivity for this pathogenic bacterial strain over a common lab strain (E. coli DH5alpha), which is gained from the use of specific biotinylated antibodies, is also demonstrated for QD labeling. Under continuous excitation, these QDs retain high fluorescence intensities for hours, whereas a typical organic dye bleaches within seconds, allowing for more rapid and accurate identification of E. coli O157:H7 in single-cell fluorescence-based assays. This indirect QD labeling method, based on antibody-antigen and streptavidin-biotin interactions, is flexible enough to expand to other systems and has great potential for use in simultaneous multicolor detection schemes.     

Shell distribution on colloidal CdSe/ZnS quantum dots

Scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) was used to determine the chemical distribution of semiconductor shell material around colloidal core-shell CdSe/ZnS quantum dots (QDs). EELS signals from positions around the QD indicate a well-defined shell of ZnS surrounding the CdSe core, but the distribution of the shell material is highly anisotropic. This nonuniformity may reflect the differences in chemical activity of the crystal faces of the core QD and implies a nonoptimal QD surface passivation.     

An outbreak of hepatitis A during a military field training exercise

Current practice for the selection of unrelated donors involves serological typing of HLA-A, -B and -DR antigens, DNA analysis of the class II region and the MLR. However, even after matching for the class II loci at the DNA level, a significant proportion of matched unrelated pairs remain MLR reactive. Ideal matching for BMT would be a match for the whole MHC haplotype rather than individual HLA loci. In the present study, we have evaluated the complementary role of class III typing in determining MHC identity. A group of 86 donor/recipient pairs, of which 14 were unrelated, was investigated using C4, Bf, HSP70 and TNF DNA probes. Phenotypically HLA-matched siblings were always identical at the C4 locus which is the most polymorphic of all the loci examined. Nine of the 14 HLA serologically matched MLR non-reactive (RRI < 20%) unrelated pairs had class III mismatching. Four of these pairs with class III mismatching were matched at the DRB and DQB loci by RFLP analysis. These results demonstrate that serological identity, DRB/DQB RFLP-matching and a negative MLR do not always match the whole haplotype in unrelated pairs. It can be concluded that the linkage of the class III loci to both HLA regions makes this region a reliable marker of the whole MHC haplotype.     

The evaluation of tempered martensite embrittlement in 4130 steel by instrumented charpy V-notch testing

Tempered martensite embrittlement (TME) was studied in vacuum-melted 4130 steel with either 0.002 or 0.02 wt pct P. TME was observed as a severe decrease in Charpy V-notch impact energy, from 46 ft-lb. at 200 °C to 35 ft-lb. at 300 °C in the low P alloy. The impact energy of the high P alloy was consistently lower than that of the low P alloy in all tempered conditions. Fracture was transgranular for all specimens; therefore, segregation of P to the prior austenitic grain boundaries was not a factor in the o°Currence of TME. Analysis of load-time curves obtained by instrumented Charpy testing revealed that the embrittlement is associated with a drop in the pre-maximum-load and post-unstable-fracture energies. In specimens tempered at 400 °C the deleterious effect of phosphorus on impact energy became pronounced, a result more consistent with classical temper embrittlement rather than TME. A constant decrease in pre-maximum-load energy due to phosphorus content was observed. The pre-maximum-load energy decreases with increasing tempering temperature in the range of 200 °C to 400 °C, a result explained by the change in work hardening rate. Carbon extraction replicas of polished and etched as-quenched specimens revealed the presence of Fe₂MoC and/or Fe₃C carbides retained after austenitizing. Ductile crack extension close to the notch root was related to the formation of fine micro voids at the retained carbides. This paper is based on a presentation made at the “pcter G. Winchell Symposium on Tempering of Steel” held at the Louisville Meeting of The Metallurgical Society of AIME, October 12-13, 1981, under the sponsorship of the TMS-AIME Ferrous Metallurgy and Heat Treatment Committees.     

Stability Is Not Everything: The Case of the Cyclisation of a Thrombin-Binding Aptamer

With the aim of developing a new approach to obtain improved aptamers, a cyclic thrombin-binding aptamer (TBA) analogue (cycTBA) has been prepared by exploiting a copper(I)-assisted azide–alkyne cycloaddition. The markedly increased serum resistance and exceptional thermal stability of the G-quadruplex versus TBA were associated with halved thrombin inhibition, which suggested that some flexibility in the TBA structure was necessary for protein recognition.     

Imaging of delta- and mu-opioid receptors in temporal lobe epilepsy by positron emission tomography

The authors report the postoperative magnetic resonance (MR) imaging findings in 36 patients with advanced Parkinson's disease who underwent unilateral microelectrode-guided posteroventral pallidotomy. The lesions were placed within 1 mm of the ventral border of the globus pallidus internus (GPi) to include pallidothalamic outflow pathways. Sequential MR studies were obtained within 1 to 3 days postoperatively and at 6-month follow-up examination. Thirty-four (94%) of the 36 patients enjoyed sustained moderate or marked improvement of their parkinsonian symptoms 6 months postoperatively. Transient side effects occurred in five patients (14%), but there were no persistent complications. The pallidal radiofrequency lesions were prolate spheroid shaped and were composed of three concentric zones in the early postoperative studies. The mean volume of the middle zone, corresponding to the area of hemorrhagic coagulation necrosis, was 44.4 +/- 17.6 mm3; the mean lesion volume as defined by the outer zone, corresponding to perilesional edema, was 262.2 +/- 111.6 mm3. Additional edema spreading to the internal capsule was noted in 32 of 34 cases and to the optic tract in 11 of 34 cases. In two patients small ischemic infarctions involving the corona radiata were found, and in one a venous infarction was detected. Ischemic infarction resulted in mild transient Broca's aphasia in one patient, but there was no detectable neurological deficit in the other two. The mean volume of late-phase (6 months) lesions was 22 +/- 28.8 mm3. In three patients no lesion was identified despite sustained clinical improvement. The lesion was located in the posteroventral GPi in all cases except in one patient in whom it was confined to the GP externus (GPe). This 49-year-old woman did not experience sustained benefit. The authors found no consistent correlations between lesion size and location and clinical outcome as measured by a global outcome score, the Unified Parkinson's Disease Rating Scale motor, activities of daily living, and bradykinesia "off" scores or rating of dyskinesias. Lesioning of pallidal and subpallidal pathways may contribute to the sustained clinical benefit in this series. Magnetic resonance imaging analysis showed that intraoperative microelectrode recording facilitated accurate placement of the lesion in this critical area.     

A confessional account of community entry: doing critically reflexive ICT4D work in a deep rural community in South Africa*

ABSTRACT

In this paper I reflect on the community entry phases of doing a critical ethnography in a traditional Zulu community in a deep rural part of South Africa. I present my reflections in the form of confessional narratives on community entry and on how an Information Communication Technology for Development (ICT4D) project was introduced in the community. Drawing on a basic principle of doing social science research, I ask: In what ways should I achieve self-emancipation, in order to ensure the on-going emancipation and empowerment of the people I engage with? I also ask: How should one do critically reflexive community entry and ICT4D project introduction in communities that embrace a people-orientated worldview? The paper is practice-orientated in that it demonstrates critical self-reflexive community entry in a particular ICT4D project situation, how community entry encounters informed follow-up work, and how cultural interpreters empowered me to do community entry successfully. Methodologically, the paper contributes by demonstrating the value of using narrative examples to represent virtuoso expertise of how I developed knowledge of self-reflexivity while excavating hidden social meanings from an ICT4D project situation.     

Abrasion of Steel by Ceramic Coatings: Comparison of RF-DLC to Sputtered B4C

The abrasion rates of steel balls sliding against a very smooth diamond-like carbon (DLC) coating and a rough boron carbide (B₄C) coating are compared. The initial abrasiveness of the B₄C coating is about 2 orders of magnitude greater than that of the DLC coating. Both coatings exhibit a rapid decrease in their abrasiveness with sliding distance, but the details of the abrasion kinetics of these coatings are quite different. The abrasiveness of B₄C falls according to a simple power law, while the abrasiveness of the DLC remains constant for a duration that depends on the load and then switches rather suddenly to zero. An explanation for this different behavior is proposed. During the abrasion process the asperities on the B₄C are smoothed to a startling extent.