Electron field emission characteristics and field evaporation of a single carbon nanotube

Direct transmission electron microscope (TEM) observations of the field emission and evaporation process of emitting carbon nanotubes (CNTs) shown that the tip structure of the CNT is in general composed of irregular shaped graphitic sheets which extend typically more than 10 nm from the end of the CNT. It is found that the irregular shaped graphitic sheets at the tip of the CNT may greatly enhance the field emission characteristics of the CNT when compared with that having an ideal circular edge. The field evaporation of the CNT proceeds typically via the removal of the irregular shaped graphitic sheets from the tip of the CNT, and field emission characteristics of a CNT depend far more sensitively on the tip structure than on the geometric length of the CNT.

REW– exit-wave reconstruction and alignments for focus-variation high-resolution transmission electron microscopy images

A Windows-based computer program has been developed for exit-wave reconstruction and experimental high-resolution transmission electron microscopy image alignment. While the exit-wave reconstruction is performed mainly using the maximum-likelihood method, image alignments may be carried out using several algorithms, including the time-consuming but robust genetic algorithm.

Time-resolved MR angiography: optimal parallel imaging method

BACKGROUND AND PURPOSE

Time-resolved (TR) MR angiography (MRA) using parallel imaging techniques is proving to have clinical utility for improving MRA spatial and temporal resolution and separating arterial from venous anatomy. The purpose of this study was to evaluate TR MRA of the intracranial vessels at different integrated parallel acquisition technique (IPAT) factors.

MATERIALS AND METHODS

3D TR MRA using time-resolved echo-shared angiographic technique was performed with different IPAT factors (0, 2, 3) at 1.5 T, resulting in temporal resolutions of 4.0, 1.7, and 1.3 seconds, respectively. We studied 14 subjects, comprising 12 patients with various pathologic conditions and 2 healthy subjects. The brain volume was covered by 36 partitions, and a bolus of 5 mL of gadopentate dimeglumine was administered. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), the number of frames that distinguished between arterial and venous phases, the conspicuity of the vasculature, and artifacts were analyzed.

RESULTS

There was no significant difference in SNR between IPAT factors 0 and 2. Moreover, SNR was significantly lower with IPAT 3 than with IPAT 0 or 2. Smaller vessel segments (M3 and P3) were rated significantly inferior with TR MRA IPAT 2 or 3 compared with MRA without IPAT. For larger proximal vessels (A1 and A2 segments of anterior cerebral artery, M1 and M2 segments of middle cerebral artery, P2 segment of posterior cerebral artery, and basilar artery), there was no difference between TR MRA IPAT 0 and 2.

CONCLUSION

To obtain arterial and venous information in a clinical setting, intracranial TR MRA is best performed with an IPAT factor of 2 with at least 5 mL of contrast.

A comparative study on SWCNT and DWCNT field-effect transistors

Field-effect transistors have been fabricated using single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs), and their electrical transport properties have been studied comparatively. While a semiconducting SWCNT exhibits better field-effect characteristics than a DWCNT counterpart, the DWCNT shows more complicated response to external gate modulation. Depending on the nature of the two shells of a DWCNT, i.e., whether the shell is semiconducting (S) or metallic (M), a DWCNT device can be described as either S-S, or S-M, or M-S, or M-M. It was found that the S-S and M-M or M-S devices show similar field-effect characteristics to those found in SWCNT devices. But for S-M DWCNT devices, distinct field-effect characteristic was found and attributed to the combined effects of intershell interactions and screening by free carriers of the inner metallic shell. The S-M DWCNT devices thus provide a perfect system for studying the important intershell interaction, and information on the effect of this interaction on the electrical properties of a multi-walled carbon nanotube can be obtained by a comparative study of S-M DWCNT and S-SWCNT devices.

Differential localization of the GluR1 and GluR2 subunits of the AMPA-type glutamate receptor among striatal neuron types in rats

Differences among the various striatal projection neuron and interneuron types in cortical input, function, and vulnerability to degenerative insults may be related to differences among them in AMPA-type glutamate receptor abundance and subunit configuration. We therefore used immunolabeling to assess the frequency and abundance of GluR1 and GluR2, the most common AMPA subunits in striatum, in the main striatal neuron types. All neurons projecting to the external pallidum (GPe), internal pallidum (GPi) or substantia nigra, as identified by retrograde labeling, possessed perikaryal GluR2, while GluR1 was more common in striato-GPe than striato-GPi perikarya. The frequency and intensity of immunostaining indicated the rank order of their perikaryal GluR1:GluR2 ratio to be striato-GPe>striatonigral>striato-GPi. Ultrastructural studies suggested a differential localization of GluR1 and GluR2 to striatal projection neuron dendritic spines as well, with GluR1 seemingly more common in striato-GPe spines and GluR2 more common in striato-GPi and/or striatonigral spines. Comparisons among projection neurons and interneurons revealed GluR1 to be most common and abundant in parvalbuminergic interneurons, and GluR2 most common and abundant in projection neurons, with the rank order for the GluR1:GluR2 ratio being parvalbuminergic interneurons>calretinergic interneurons>cholinergic interneurons>projection neurons>somatostatinergic interneurons. Striosomal projection neurons had a higher GluR1:GluR2 ratio than did matrix projection neurons. The abundance of both GluR1 and GluR2 in striatal parvalbuminergic interneurons and projection neurons is consistent with their prominent cortical input and susceptibility to excitotoxic insult, while differences in GluR1:GluR2 ratio among projection neurons are likely to yield differences in Ca(2+) permeability, desensitization, and single channel current, which may contribute to differences among them in plasticity, synaptic integration, and excitotoxic vulnerability. The apparent association of the GluR1 subunit with synaptic plasticity, in particular, suggests striato-GPe neuron spines as a particular site of corticostriatal synaptic plasticity, presumably associated with motor learning.

TTDN1 is a Plk1-interacting protein involved in maintenance of cell cycle integrity

Polo-like kinase 1 (Plk1) is a highly conserved serine/threonine kinase that plays critical roles in many cell cycle events, especially in mitosis. In the present study, we identified TTDN1 as a potential interacting partner of Plk1 in yeast two-hybrid screens. Sequence analysis indicates that TTDN1 contains a consensus Plk1-binding motif at its C terminus. TTDN1 colocalizes with Plk1 at the centrosome in mitosis and the midbody during cytokinesis. TTDN1 is phosphorylated by Cdk1 in mitosis, and this is required for its interaction with Plk1. Site-directed mutagenesis indicates that TTDN1 is phosphorylated at multiple residues, including Ser93 and Ser104. Mutation of Thr120 of TTDN1 abolishes its interaction with Plk1, suggesting phosphorylation of Thr120 in the consensus Plk1-binding motif is required for its interaction with Plk1. Overexpression of TTDN1 or its knockdown by siRNA causes multi-polar spindles and multiple nuclei, suggesting that TTDN1 plays a role in regulating mitosis and cytokinesis.

Characterization of HLA-B*5516, -B*1313, -B*9512, and -DRB1*1457 alleles identified in a southwest Chinese population

The human leukocyte antigen (HLA)-B*5516 allele differs from the B*5502 by a single 97 T --> C substitution (His to Tyr at position 33) in exon 2. The B*1313 allele results from 419 T --> A and 420 A --> C substitutions, encoding a Leu to Tyr substitution at 140 in exon 2 of the B*1301 allele. The B*9512 allele differs from B*1502 by a single 360 G --> C substitution (Gln to His at 120) in exon 3. The DRB1*1457 allele appears to be a hybrid molecule generated by recombination between the DRB1*13 and DRB1*14 alleles. The serological equivalents of these new alleles are HLA-B22, -B13, -B15, and DR13, respectively. Family studies detected two rare haplotypes: A*11, B*9512, DRB1*14 and A*24, B*52, Cw*07, DRB1*1457, DRB3*020201, DQB1*050301. The gene frequencies of these alleles in the Chinese population are less than 0.0001.

Normal and shear strain estimation using beam steering on linear-array transducers

In current ultrasound elastography, only the axial component of the displacement vector is estimated and used to produce strain images. A method was recently proposed by our group to estimate both the axial and lateral components of a displacement vector following a uniaxial compression. Previous work evaluated the technique using both simulations and a mechanically translated phased array transducer. In this paper, we present initial results using beam steering on a linear array transducer attached to a commercial scanner to acquire echo signals for estimating 2-D displacement vectors. Single-inclusion and anthropomorphic breast phantoms with different boundary properties between the inclusion and background material are imaged by acquiring echo data along beam lines ranging from -15 degrees to 15 degrees relative to the compression direction. 1-D cross-correlation is used to calculate "angular displacements" in each acquisition direction, yielding axial and lateral components of the displacement vector. Strain tensor components are estimated from these displacements. Features on shear strain images generated for the inclusion phantom agree with those predicted using FEA analysis. Experimental results demonstrate the utility of this technique on clinical scanners. Shear strain tensors obtained using this method may provide useful information for the differentiation of benign from malignant tumors. For the linear array transducer used in this study, the optimum angular increment is around 3 degrees. However, more work is required for the selection of an appropriate value for the maximum beam angle for optimal performance of this technique.

Clonality analysis of intraductal proliferative lesions using the human androgen receptor assay

Recently, it is accepted that invasive breast carcinoma is of monoclonal origin. Ductal intraepithelial neoplasia (DIN) may progress toward invasive carcinoma with an increased risk. However, it is not fully understood whether DIN is polyclonal or monoclonal. In this current study, we detected clonal origin of DIN using x-inactivation at the human androgen receptor (HUMARA) locus. Lesional and normal breast gland cells were microdissected from paraffin-embedded tissues using a laser capture microdissection system. Genomic DNA was extracted. After digestion by restriction enzyme Hpa II, the HUMARA exon1 was amplified by a fluorescent nested-PCR procedure and the PCR products were separated on DNA sequencer and analyzed the fluorescent intensity of the two HUMARA alleles. DNA from 88 of 101(87%) patients was able to be amplified at the HUMARA locus and 68 of them (77.3%) were heterozygous and informative. 9/12 usual ductal hyperplasia (UDH) and 5/18 DIN 1A showed a polyclonal inactivation. 3/12 UDH, 13/18 DIN 1A, 28/28 DIN 1B, 10/10 carcinoma in situ are of monoclonal origin. Taken together, DIN 1A, 1B and carcinoma in situ, are monoclonal and DIN 1, but not UDH, represents the obligate and direct precursor of DCIS.

Prostaglandin E2 regulates Foxo activity via the Akt pathway: implications for pancreatic islet beta cell dysfunction

AIMS/HYPOTHESIS

Prostaglandin E(2) (PGE(2)) is a well-recognised inhibitor of glucose-stimulated insulin secretion (GSIS). The aim of this study was to investigate the signalling pathway of PGE(2) in beta cell function regulation in HIT-T15 cells and isolated rat islets.

MATERIALS AND METHODS

mRNA levels of the prostaglandin E receptor 3 (Ptger3) were measured by real-time PCR. Western blot analysis was used to detect changes in the levels of PTGER3, phosphorylated and total Akt, phosphorylated and total forkhead box 'Other' (Foxo). Transient transfection and reporter assays were used to measure Foxo transcriptional activity. The biological significance of PGE(2) in beta cell function was analysed using MTT, flow cytometry and GSIS assays.

RESULTS

We found that treating HIT-T15 cells with exogenous PGE(2) stimulated Ptger3 gene expression specifically, and diminished cAMP generation. These were accompanied by the downregulation of Akt and Foxo phosphorylation in HIT-T15 cells and isolated rat islets. Moreover, PGE(2) upregulated basal and partially reversed constitutively active Akt-inactivated Foxo transcriptional activity. Furthermore, GSIS was impaired in PGE(2)-treated HIT-T15 cells and isolated islets. However, the dosage used in the above experiments did not affect beta cell viability and apoptosis. In addition, insulin-like growth factor 1 (IGF-1) pretreatment reversed the effects of PGE(2), and wortmannin treatment abolished the preventive effects of IGF-1.

CONCLUSIONS/INTERPRETATION

Our observations strongly suggest that PGE(2) can induce pancreatic beta cell dysfunction through the induction of Ptger3 gene expression and inhibition of Akt/Foxo phosphorylation without impacting beta cell viability. These results shed light on the mechanisms of PGE(2) actions in pancreatic beta cell dysfunction.

Activated endothelial cells resist displacement by trophoblast in vitro

BACKGROUND

Transformation of the spiral arteries by invading trophoblasts is an essential prerequisite to the development of a healthy fully grown fetus. Reduced transformation of the spiral arteries is a characteristic feature of pregnancies complicated by several diseases of pregnancy including preeclampsia. The aim of this study was to investigate further the hypothesis that spiral artery endothelial cells can contribute to the mechanism of shallow trophoblast invasion.

METHOD

Fluorescently labeled Jar cells were added to monolayers of fluorescently-labeled endothelial cells that had been activated by treatment with TNFalpha, INF gamma or necrotic cell bodies. The ability of the Jars to displace endothelial cells from the monolayers was quantified by measuring the area of Jar cells "islands" formed in the endothelial cell monolayers by confocal microscopy and digital image.

RESULTS

The area of Jar cell islands formed in monolayers of activated endothelial cells was significantly smaller that the area of islands formed in control resting/non-activated endothelial cell monolayers regardless of the activator.

DISCUSSION

This work demonstrates that activated endothelial cells are more resistant to trophoblast displacement than resting endothelial cells and adds weight to the suggestion that endothelial cells could contribute to shallow invasion of the spiral arteries by trophoblasts in diseases such as preeclampsia.

Clinic-based evaluation of Clearview Chlamydia MF for detection of Chlamydia trachomatis in vaginal and cervical specimens from women at high risk in China

OBJECTIVES

To determine the performance of a rapid Chlamydia trachomatis (CT) test (Clearview Chlamydia MF) compared to the current "gold standard" (Roche Amplicor CT assay) test, and to assess acceptability of the tests to patients.

METHODS

A total of 1497 women at sexually transmitted diseases (STD) clinics or re-education centres in six urban cities (Shanghai, Nanjing, Shenzhen, Guangzhou, Chengdu and Fuzhou) in China participated in the study. Three vaginal and three cervical swabs were collected from each participant. Rapid CT tests were performed locally on the first vaginal and cervical swabs and the results were read independently by two staff members. The second and third swabs were randomised for performing the Roche CT assay at the National STD Reference Laboratory. Acceptability of the rapid tests to patients was determined by asking patients in clinics about their willingness to wait for the results.

RESULTS

The prevalence of CT was 13.2% (197/1497), as determined by the Roche assay with cervical specimens. CT was detected in 78 vaginal and 127 cervical specimens by the rapid test and the positive rates determined with cervical specimens were significantly higher than those with vaginal specimens (p<0.001). There was good agreement between the results read by two independent staff for either vaginal or cervical specimens (both kappa = 0.98, p<0.001). Sensitivities for vaginal and cervical specimens were 32.8% and 49.7%, respectively, and specificities were 99.2% and 97.9%, respectively. The positive predictive value was 85.7% for vaginal and 78.4% for cervical specimens. The vast majority of the patients (99.1%) were willing to wait up to two hours for the results.

CONCLUSION

Clearview Chlamydia MF, while yielding a rapid result and requiring minimal laboratory facilities, had unacceptably low sensitivity compared to a nucleic acid amplification test. Rapid tests yielding results within one hour are generally accepted by the clients.