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A Zettl

Publications and source records attributed to A Zettl.

At least 19 recordsLinked to original sources
PubMed2002

Electron holography of field-emitting carbon nanotubes.

Electron holography performed in situ inside a high resolution transmission electron microscope has been used to determine the magnitude and spatial distribution of the electric field surrounding individual field-emitting carbon nanotubes. The electric field (and hence the associated field emission current) is concentrated precisely at the tips of the nanotubes and not at other nanotube defects such as sidewall imperfections. The electric field magnitude and distribution are stable in time, even in cases where the nanotube field emission current exhibits extensive temporal fluctuations.

Journal Article↗
PubMed2002

[Myelosarcoma of the proximal jejunum. A rare primary condition of acute myelogenous leukemia].

Myelosarcoma (chloroma) is a rare primary condition in patients with either a myelodysplastic syndrome, or an acute or chronic leukemia. It is an extramedullary neoplasm which does not commonly present with changes in peripheral blood or bone marrow. The rarity and histomorphological similarity to malignant non-Hodgkin lymphoma renders the diagnosis notoriously difficult. Due to its coincidental or secondary manifestation followed by myelogenous leukemia, this tumor needs to be seen as a primary systemic disease. We present a 40 year old man with myelosarcoma of the jejunum and discuss this entity and its therapeutic options.

Adult↗
PubMed2001

New vortex-matter size effect observed in Bi(2)Sr(2)CaCu(2)O(8 + delta).

The vortex-matter 3D to 2D phase transition is studied in micron-sized Bi(2)Sr(2)CaCu(2)O(8 + delta) single crystals using local Hall magnetization measurements. At a given temperature, the second magnetization peak, the signature of a possible 3D--2D vortex phase transition, disappears for samples smaller than a critical length. We suggest that this critical length should be equated with the 2D vortex lattice ab-plane correlation length R(2D)(c). The magnitude and temperature dependence of R(2D)(c) agree well with Larkin-Ovchinnikov collective pinning theory.

Journal Article↗
PubMed2001

Thymic epithelial tumors can develop along two different pathogenetic pathways.

To investigate genetic abnormalities associated with the development of thymic epithelial tumors, we performed microsatellite analysis of 26 thymomas belonging to three different World Health Organization types (A, B3, and C) using 48 repeats. The most frequent aberration seen was loss of heterozygosity (LOH) in the region 6q23.3-25.3 detected in 11 tumors (45.8% of informative cases). Further consistent LOHs were detected in regions 3p22-24.2, 3p14.2 (FHIT gene locus), 5q21 (APC), 6p21, 6q21-22.1, 7p21-22, 8q11.21-23, 13q14 (RB), and 17p13.1 (p53). Microsatellite instability was extremely rare, occurring in one type B3 thymoma only, although, at 12.5% of the analyzed loci. Comparing the allelotypes of the analyzed thymomas, we were able to identify two pathogenetic pathways these tumors develop along, characterized by the 6q23.3-25.3 and 5q21 LOHs, respectively. The APC aberration on 5q21 showed significant associations with LOH in the 3p22-24.2, 13q14, and 17p13.1 regions. Interestingly, type A thymomas presented with consistent LOH in the region 6q23.3-25.5 only, they did not reveal any aberrations in the APC, RB, and p53 gene loci or regions 3p22-24.2 and 8q11.21-23. The absence of these aberrations might be the reason for the well-known benign behavior of type A thymomas as compared to types B3 and C tumors.

Adult↗
PubMed2001

Pathology of lymphoma progression.

Reflecting the stepwise process of oncogenesis, lymphomas may cumulatively develop a more aggressive phenotype during the course of disease, a process referred to as lymphoma progression. Although morphological, clinical and biological aspects of lymphoma progression do not always overlap, changes in lymphoma morphology frequently indicate alterations in the clinical and biological behaviour of the disease. Indolent and aggressive lymphomas in disease progression can either be clonally related or represent clonally unrelated neoplasms. We propose to use the term 'lymphoma progression' in a biological sense denoting only clonal development of and within a lymphoma entity. The term 'composite lymphoma' should be used as a merely descriptive morphological designation for different lymphoma entities in one individual irrespective of clonal relationship. Many types of aggressive B-cell non-Hodgkin's lymphomas and Hodgkin's lymphomas are reported to secondarily develop in lymphoma progression. Genetic changes associated with lymphoma progression frequently abrogate the differentiating effects of alterations occurring in indolent lymphomas, leading to increased cell proliferation. Within different lymphoma entities, high-risk disease variants mimicking lymphoma progression exist.

Apoptosis↗
PubMed2000

Is the intrinsic thermoelectric power of carbon nanotubes positive?

The thermoelectric power (TEP) of single-walled carbon nanotubes (SWNTs) is extremely sensitive to gas exposure history. Samples exposed to air or oxygen have an always positive TEP, suggestive of holelike carriers. However, at fixed temperature the TEP crosses zero and becomes progressively more negative as the SWNTs are stripped of oxygen. The time constant for oxygen adsorption/desorption is strongly temperature dependent and ranges from seconds to many days, leading to apparently "variable" TEP for a given sample at a given temperature. The saturated TEP can be accounted for within a model of strong oxygen doping of the semiconducting nanotubes.

Journal Article↗
PubMed2000

Low-friction nanoscale linear bearing realized from multiwall carbon nanotubes

We demonstrate the controlled and reversible telescopic extension of multiwall carbon nanotubes, thus realizing ultralow-friction nanoscale linear bearings and constant-force nanosprings. Measurements performed in situ on individual custom-engineered nanotubes inside a high-resolution transmission electron microscope demonstrated the anticipated van der Waals energy-based retraction force and enabled us to place quantitative limits on the static and dynamic interwall frictional forces between nested nanotubes. Repeated extension and retraction of telescoping nanotube segments revealed no wear or fatigue on the atomic scale. Hence, these nanotubes may constitute near perfect, wear-free surfaces.

Journal Article↗
PubMed2000

Scanned probe microscopy of electronic transport in carbon nanotubes.

We use electrostatic force microscopy and scanned gate microscopy to probe the conducting properties of carbon nanotubes at room temperature. Multiwalled carbon nanotubes are shown to be diffusive conductors, while metallic single-walled carbon nanotubes are ballistic conductors over micron lengths. Semiconducting single-walled carbon nanotubes are shown to have a series of large barriers to conduction along their length. These measurements are also used to probe the contact resistance and locate breaks in carbon nanotube circuits.

Journal Article↗
PubMed2000

Crossed nanotube junctions

Junctions consisting of two crossed single-walled carbon nanotubes were fabricated with electrical contacts at each end of each nanotube. The individual nanotubes were identified as metallic (M) or semiconducting (S), based on their two-terminal conductances; MM, MS, and SS four-terminal devices were studied. The MM and SS junctions had high conductances, on the order of 0.1 e(2)/h (where e is the electron charge and h is Planck's constant). For an MS junction, the semiconducting nanotube was depleted at the junction by the metallic nanotube, forming a rectifying Schottky barrier. We used two- and three-terminal experiments to fully characterize this junction.

Journal Article↗
PubMed2000

Extreme oxygen sensitivity of electronic properties of carbon nanotubes

The electronic properties of single-walled carbon nanotubes are shown here to be extremely sensitive to the chemical environment. Exposure to air or oxygen dramatically influences the nanotubes' electrical resistance, thermoelectric power, and local density of states, as determined by transport measurements and scanning tunneling spectroscopy. These electronic parameters can be reversibly "tuned" by surprisingly small concentrations of adsorbed gases, and an apparently semiconducting nanotube can be converted into an apparent metal through such exposure. These results, although demonstrating that nanotubes could find use as sensitive chemical gas sensors, likewise indicate that many supposedly intrinsic properties measured on as-prepared nanotubes may be severely compromised by extrinsic air exposure effects.

Journal Article↗
PubMed2000

Genetic aberrations common in gastric high-grade large B-cell lymphoma.

Genetic aberrations associated with the development of extranodal high-grade large B-cell lymphoma originating in the stomach have not been fully identified yet. We analyzed 31 such lymphomas using 73 microsatellite markers for allelic imbalance and microsatellite instability. The highest frequency (42%) of loss of heterozygosity (LOH) was found on the long arm of chromosome 6. We identified 2 LOH hot spots on 6q21-22.1 and 6q23.3-25, flanked by markers D6S246-D6S261 and D6S310-D6S441, respectively, containing putative tumor suppressor genes (TSGs). These 6q aberrations were found to be the sole allelic imbalance in 1 patient only; they were mostly accompanied by additional abnormalities. Several known TSGs, namely, the APC, p15/p16, p53, and DCC genes, were found to suffer frequent LOH during lymphomagenesis. LOH was also detected in regions containing putative TSGs on 7q and 13q14. Frequent amplification of genomic material was found in the 2p, 3q27 at the BCL-6 gene locus, 6p, 7q, 11q23-24 at the MLL gene locus, and 18q regions. Analysis of the pattern of occurrence of these aberrations revealed an association of the amplification of the MLL gene region with LOH at the p53 locus (P =.02). Only low frequency of microsatellite instability (MSI) was detected in these lymphomas and MSI incidence increased with age (P =.01). Karyotypic instability thus plays the main role in the development of gastric high-grade large B-cell lymphoma. Common genetic aberrations responsible for lymphomagenesis are deletions of 6q, loss of p53, and amplification of the 3q27 and the MLL gene regions. (Blood. 2000;95:1180-1187)

Age Factors↗
PubMed2000

Electron spin density distribution in the polymer phase of CsC60: assignment of the NMR spectrum.

We present high resolution 133Cs-13C double resonance NMR data and 13C-13C NMR correlation spectra of 13C enriched samples of the polymeric phase of CsC60. These data lead to a partial assignment of the lines in the 13C NMR spectrum of CsC60 to the carbon positions on the C60 molecule. A plausible completion of the assignment can be made on the basis of an ab initio calculation. The data support the view that the conduction electron density is concentrated at the C60 "equator," away from the interfullerene bonds.

Journal Article↗
PubMed2000

Recurrent genetic aberrations in thymoma and thymic carcinoma.

Apart from single reported aberrant karyotypes, genetic alterations in thymic epithelial neoplasms have not been investigated so far. In this study, 12 World Health Organization classification type A thymomas (medullary thymomas), 16 type B3 thymomas (well-differentiated thymic carcinomas), and nine type C thymomas, all of them primary thymic squamous cell carcinomas, were analyzed by comparative genomic hybridization and fluorescence in situ hybridization. With the exception of one single case, type A thymomas did not reveal chromosomal gains or losses in comparative genomic hybridization. In contrast, all type B3 thymomas showed chromosomal imbalances, with gain of 1q, loss of chromosome 6, and loss of 13q occurring in 11 (69%), six (38%), and five (31%) of 16 cases, respectively. In primary thymic squamous cell carcinoma, the most frequent chromosomal losses were observed for 16q (six of nine cases, 67%), 6 (4 of 9, 44%), and 3p and 17p (three of nine each, 33%), whereas recurrent gains of chromosomal material were gains of 1q (5 of 9, 56%), 17q, and 18 (three of nine each, 33%). This study shows that the distinct histological thymoma types A and B3 exhibit distinct genetic phenotypes, whereas type B3 thymoma and primary thymic squamous cell carcinoma partially share genetic aberrations. In addition to the possible tumorigenic role, the deletion in type B3 thymoma of chromosome 6, harboring the HLA locus, might play a role in the pathogenesis of paraneoplastic autoimmunity characteristic of thymoma.

Adult↗
PubMed2000

Genetic imbalances in primary gastric diffuse large B-cell lymphomas: comparison of comparative genomic hybridization, microsatellite, and cytogenetic analysis.

Extranodal malignant non-Hodgkin's lymphomas account for about 40% of lymphoid neoplasms, but few data are available concerning the genetic background of primary gastric diffuse large B-cell lymphoma (DLBCL). A study was performed of 27 primary gastric DLBCLs and 5 gastric DLBCLs with a concomitant low grade component of mucosa-associated lymphoid tissue-type lymphoma using comparative genomic hybridization (CGH), microsatellite studies, classic cytogenetics, and fluorescence in situ hybridization (FISH) to search for specific genetic aberrations. The most frequent aberrations were losses of material on chromosome 6q and gains of parts of chromosome 3. In three cases, a total of six high level DNA amplifications were detected, with five of them involving chromosomal regions not having been reported before in gastric DLBCL. A high overall concordance of 91.4% between microsatellite analysis and CGH was observed using DNA extracted from the same tissue block. The concordance achieved using DNA from different tissue blocks of the same patient was 85%. Microsatellite studies, CGH, FISH, and classic cytogenetics represent complementary techniques that facilitate a comprehensive view of genetic alterations in malignancies such as primary gastric DLBCL.

Adult↗
PubMed1998

T cell receptor repertoire in rheumatoid arthritis.

CD4+ T cells are a major component of the inflammatory infiltrate in rheumatoid synovitis. Within synovial lesions, clonal CD4+ T cell populations are detectable, supporting the notion of an antigen specific recognition even in the joint. In general, the clonal size of individual T cell clones is small and does not lead to a marked distortion of the synovial T cell receptor (TCR) repertoire. Comparison of TCR sequences derived from different patients has not provided evidence for common sequences. Either multiple antigens are recognized or the TCR repertoire is sufficiently plastic with a multitude of different TCR structures responding to the same antigen(s). However, within one individual, the repertoire of clonal T cell populations is restricted. Identical T cell clones can be identified in different joints and at different timepoints of the disease, emphasizing that the spectrum of antigens recognized is conserved over time and that the T cell response pattern is not subject to evolution. Characterization of antigens involved in the latter stages of the disease may thus provide critical information on disease-initiating events. Recent data have led to the new concept that the role of T cells in rheumatoid arthritis (RA) is not limited to synovial inflammation. Evidence has been provided that the premorbid TCR repertoires of RA patients and normal controls can be distinguished. The T cell repertoire in RA patients is prone to recognize certain microbial products and autoantigens. The selection of this response pattern can only partially be attributed to the disease associated HLA-DRB1 alleles. Additional factors common in RA patients but not in HLA-DR matched control individuals seem to be important in shaping the TCR repertoire. Furthermore, the repertoire of mature T cells in RA patients is characterized by oligoclonality which involves T cells in the peripheral blood compartment. Possibly, these clonal T cell populations react to widespread autoantigens, raising the possibility that RA patients have a defect in controlling peripheral tolerance and an anomaly of lymphoproliferation. In contrast to joint residing CD4+ T cells, expanded clonotypes isolated from the blood of different patients have been described to share TCR beta chain structures. How these characteristic features of the global TCR repertoire in RA patients translate into mechanisms of disease remains to be elucidated.

Arthritis, Rheumatoid↗
PubMed1997

Single-Electron Transport in Ropes of Carbon Nanotubes

The electrical properties of individual bundles, or "ropes," of single-walled carbon nanotubes have been measured. Below about 10 kelvin, the low-bias conductance was suppressed for voltages less than a few millivolts. In addition, dramatic peaks were observed in the conductance as a function of a gate voltage that modulated the number of electrons in the rope. These results are interpreted in terms of single-electron charging and resonant tunneling through the quantized energy levels of the nanotubes composing the rope.

Journal Article↗
PubMed1997

Multiple mechanisms support oligoclonal T cell expansion in rheumatoid synovitis.

BACKGROUND: The synovial T cell infiltrate in rheumatoid arthritis (RA) is diverse but contains clonally expanded CD4+ populations. Recent reports have emphasized that RA patients have a tendency to develop CD4+ T cell oligoclonality which also manifests in the peripheral blood. Clonal dominance in the tissue may thus result from antigen specific stimulation in the synovial membrane or may reflect the infiltration of expanded clonotypes present throughout the lymphoid system. We have explored to what extent clonal populations amongst tissue CD4+ T cells display joint specificity as defined by their restriction to the joint, their persistence over time, and their expression of markers indicative for local activation. MATERIALS AND METHODS: Matched samples of peripheral blood and synovial fluid or synovial tissue were collected from 14 patients with active RA and CD4+ IL-2R+ and CD4+ IL-2R- T cells from both compartments were purified. Clonal populations of CD4+ T cells were detected by RT-PCR amplification of T cell receptor (TCR) transcripts with BV and BJ specific primers followed by size fractionation and direct sequencing of dominant size classes of TCR transcripts. RESULTS: Clonal CD4+ T cells were detected in the synovial fluid and synovial tissue of all patients. All patients carried synovial clonotypes that were undetectable in the blood but were present in independent joints or at several non-adjacent areas of the same joint. These joint restricted CD4+ clonotypes were generally small in size, were preferentially found in the IL-2R+ subpopulation, and persisted over time. A second type of clonogenic T cells in the synovial infiltrate had an unrestricted tissue distribution and was present at similar frequencies amongst activated and nonactivated T cells in the blood and affected joints. Ubiquitous clonotypes isolated from two different patients expressed sequence homologies of the TCR beta chain. CONCLUSIONS: Two types of expanded CD4+ clonotypes contribute to the T cell infiltrate in rheumatoid synovitis. Differences in the distribution pattern and in molecular features suggest that distinct mechanisms are supporting the clonal outgrowth of these two groups of clonotypes. Clonally expanded T cells restricted to the joint but present in several independent joints appear to respond to locally residing antigens. Clonogenic cells with an unrestricted distribution pattern and widespread activation in the blood and tissue may react to a different class of antigens which appear to be shared by multiple patients. T cell recognition in RA may be involved at several different levels and may be related to more than one pathomechanism.

Adult↗