Doping and phonon renormalization in carbon nanotubes.

We show that the Raman frequency associated with the vibrational mode at approximately 1,580 cm(-1) (the G mode) in both metallic and semiconducting carbon nanotubes shifts in response to changes in the charge density induced by an external gate field. These changes in the Raman spectra provide us with a powerful tool for probing local doping in carbon nanotubes in electronic device structures, or charge carrier densities induced by environmental interactions, on a length scale determined by the light diffraction limit. The G mode shifts to higher frequency and narrows in linewidth in metallic carbon nanotubes at large fields. This behaviour is analogous to that observed recently in graphene. In semiconducting carbon nanotubes, on the other hand, induced changes in the charge density only shift the phonon frequency, but do not affect its linewidth. These spectral changes are quantitatively explained by a model that involves the renormalization of the carbon nanotube phonon energy by the electron-phonon interaction as the carrier density in the carbon nanotube is changed.

Electrically induced optical emission from a carbon nanotube FET.

Polarized infrared optical emission was observed from a carbon nanotube ambipolar field-effect transistor (FET). An effective forward-biased p-n junction, without chemical dopants, was created in the nanotube by appropriately biasing the nanotube device. Electrical measurements show that the observed optical emission originates from radiative recombination of electrons and holes that are simultaneously injected into the undoped nanotube. These observations are consistent with a nanotube FET model in which thin Schottky barriers form at the source and drain contacts. This arrangement is a novel optical recombination radiation source in which the electrons and holes are injected into a nearly field-free region. Sucha source may form the basis for ultrasmall integrated photonic devices.

Hemolytic anemia after atrioventricular septal defect repair without synthetic material.

We report a rare case of severe hemolytic anemia following repair of a congenital heart defect without the use of prosthetic material. A review of the literature, diagnosis, and management are described. Although this is an unusual complication following congenital heart surgery, a high index of suspicion must be maintained and a possible mechanical cause should be sought and corrected.

The phantom of "myocardial sinusoids": a historical reappraisal.

The concept of myocardial sinusoids has been described in the literature during the past 60 years. They have been the basis of several revascularization procedures, such as the "Vineberg" procedure and more recently transmural laser revascularization. This article will review the historical evolution as well as the validity of the concept of "myocardial sinusoid."

Biological perspective on "myocardial preconditioning".

There has been an upsurge of research on myocardial preconditioning because of its potential clinical application in areas such as cardiology, cardiac surgery, and transplantation. From a broad biological standpoint, a conceptual framework may help in both promoting understanding and suggesting future research paths. The living organism's tendency toward developing evolutionarily advantageous strategies has led to a fight or flight response, for which the authors consider preconditioning a component. Added to preconditioning, the production of stress proteins and altered myocardial states (especially that of "hibernating myocardium") can be seen as a series of biological strategies developed and maintained during evolution. An increased understanding of the mechanisms involved in the body's self-defense strategies should lead to better approaches, those in which we can help the cells, including those comprising the myocardium, to preserve themselves.

Epitope analysis of an HLA-B27-derived synthetic peptide: a possible approach to analyzing HLA class I antigens.

A monoclonal antibody, F3H7, was generated by immunizing mice with a synthetic peptide corresponding to residues 63-84 of the B*2705 allele of the HLA-B27 antigens. The reactive epitope and the contact residues on the peptide were localized by ELISA using a large panel of overlapping peptides as well as peptides with substituted amino acids. Residues corresponding to R75, D77 and L78 on the HLA-B27 protein appeared to be critical. The clarity of these results indicate that this is a potentially useful approach to the study of HLA class I epitopes.

[The polymorphisms of HTC-defined HLA specificities in the Shanghai Chinese population].

With reference sera and homozygous typing cells (HTCs) of 3rd Asia-Oceania Histocompatibility Workshop Conference, 56 healthy unrelated subjects in Shanghai were typed for HLA-A, B, C, DR, DQ, and Dw. This paper presents the results of HLA-Dw typing, its relationship to serological class II antigens, and the distribution of Dw in the population. The polymorphism patterns of Chinese Dw specificities were quite different from those in Caucasoids and Japanese. The predominant Dw phenotypes detected in Shanghai Chinese were Dw 2, Dw 3, DKT 2, Dw 7 c, (Dw7 + Dw 17) and Dw 23 (DB 5). And significant correlations were observed between Dw 1 and DR 1, Dw 2 and DR 2, Dw 3 and DR 3, Dw 7 c and DR 7, DB 7 and DRw 8, as well as Dw 23 and DR 9. SMY 129, a novel Dw specificity defined by local HTCs and co-studied by the laboratories joined for Dw typing in 3rd AOHWC showed its correlation with DR 5. Nevertheless, more than fifty percent of Dw specificities could not be assigned in the four correspondent designated serological antigens, DR 2, DR 5, DRw 8 and DR 9, respectively, which, together with other blank Dw specificities, gave a total blank Dw gene frequency as high as 43.2% in the population. It was suggested by further analysis that novel Dw specificities might be identified more effectively if efforts would be concentrated on DR 5 and DR 9, two antigen families which, in some way, might represent the characteristics of HLA system in Chinese. Besides, certain HTC-defined antigens, e.g. Dw 3 and the DR 4-related Dw specificities, have been revealed to be in linkage disequilibrium with other DR antigens in addition with the correspondent designated ones, resulting in some unique haplotype combinations in Shanghai Chinese. It seems to us that the particular patterns of polymorphisms of serum- and cell-defined HLA class II antigens would be helpful to elucidate the mechanisms by which certain diseases are in association with HLA in Chinese in a different manner as compared with that in Caucasoids.

Relationship of prodigiosin condensing enzyme activity to the biosynthesis of prodigiosin and its precursors in Serratia marcescens.

Prodigiosin condensing enzyme (PCE) activities were present in Serratia marcescens wild type 08, mutants OF, WF and 9-3-3. Their specific activities exhibited different maxima and at different times during the late log phase or the early stationary phase of cell growth. The levels of prodigiosin and its precursors also showed a significant increase at this period. The results support that prodigiosin and/or its precursors are secondary metabolites. The ubiquity of the PCE activity in mutants deficient in prodigiosin biosynthesis suggest that this particular enzyme may also be present in non-pigmented clinical isolates.

Inhibitory effect of some transition metal ions on growth and pigment formation of Serratia marcescens.

The inhibitory effect of several first transition metal ions on growth and pigment formation on three strains of Serratia marcescens was studied by the method of minimal inhibitory concentration. From this study it can be concluded that several of the first transition metal ions, namely Cr (II), Mn (II), Fe (II), Co (II) and Cu (II), with the inclusion of Zn (II), have a definite inhibitory effect on both growth (strains 08, WF, 933) and pigment formation (strain 08) of Serratia marcescens. Based on their electron configuration and their effectiveness, these first transition metal ions can be divided into two groups: Cr (II), Mn (II), Fe (II) and Co (II), Ni (II), Cu (II) and Zn (II). Several suggestions were made to explain their inhibitory actions.

Enhancement by Sodium Dodecyl Sulfate of Pigment Formation in Serratia marcescens O8.

Three methods were used to determine the enhancement by sodium dodecyl sulfate (SDS) of prodigiosin formation in Serratia marcescens O8. The results of the agar disk diffusion method indicated that pigment formation was dependent upon the concentration of SDS. Diameters of the pigment zones were proportional to the logarithm of SDS concentrations of 300 to 1,500 mug/ml. When bacteria were grown in broth containing SDS from 0 to 800 mug/ml and the pigment extracts were analyzed spectrophotometrically, a similar enhancement of pigment formation was observed. Finally, these results were confirmed by high-performance liquid chromatographic analysis of the extracts. Prodigiosin appeared to be the sole component with increased synthesis. The possible mechanism of the SDS enhancement effect could be explained by an increase in negative binding sites by the association of SDS with a cell envelope component(s). These binding sites may be required for prodigiosin synthesis.

Pigments and antibiogram of transconjugants from nonpigmented mutants of Serratia marcescens.

Serratia marcescens produces a characteristic red pigment, prodigiosin, which is formed by the enzymatic coupling of 4-methoxy-2,2'-bipyrrole-5-bipyrrole-5-carboxaldehyde (MBC) and 2-methyl-3-amylpyrrole (MAP). Many clinical isolates which are resistant to multiple antibiotics are nonpigmented. However, the relationship of pigmentation (or nonpigmentation) to drug resistance of the strains has not yet been established. In this study we demonstrated the pigment synthesizing capability in the transconjugants obtained from nonpigmented mutants WF and 9-3-3 of S. marcescens under the condition of cell-to-cell contact. Mutant WF produces MAP while mutant 9-3-3 synthesized only MBC. After genetic transfer, the color of the recombinant colonies was red indicating the successful transfer of the pigment synthesizing capability. The antibiogram of the transconjugants indicated that they inherited the resistance characteristics to polymyxin B and chloramphenicol from their parent strains. further supportive evidence was obtained by spectroscopic and high performance liquid chromatographic analysis of the resulting pigments extracted from the pigmented transconjugants. The pigments produced by the transconjugants were similar, if not identical, to those produced by the wild type strain 08 and those synthesizes syntrophically. The possibility of simultaneous transfer of pigment synthesizing capability and drug resistance remains to be explored .

Removal of Paracoccus denitrificans outer membrane material by sodium chloride.

The effects of water washing and NaCl treatment on the cell surface of P. denitrificans were studied. Both treatments caused a release of material from cells. Chemical studies showed that NaCl treatment released material containing components characteristic of outer membrane. This treatment also increased the susceptibility of the organism to lysozyme. Scanning electron microscopy was used to monitor the effects of water washing and NaCl treatment on the cell surface. Both treatments were shown to alter the appearance of the cell surface. The disruptive effects of these procedures were found to be dependent upon the age of the culture.

Electron microscopic observations of polysaccharide components in polymyxin B treated outer membranes from Serratia marcescens.

Treatment of outer membranes of Serratia marcescens with polymyxin B results in the formation of blebs. This effect is thought to be due to the action of the antibiotic on the lipopolysaccharides, proteins, phospholipids or a combination thereof. It is unclear whether this effect is dissociative, degradative or due to an inhibition of the assembly of outer membrane components. Prior studies showed that lipopolysaccharides and polymyxin B form complexes, but direct visualization of the in situ action of polymyxin B had not been accomplished. Isolated outer membranes normally exhibit a periodicity of the polysaccharide molecules when stained by the thiosemicarbazide-silver technique. Polymyxin B treated outer membranes display a change in their basic morphology. This effect is very drastic in the sensitive strain as demonstrated by the large gaps in the deposition of the granules in the modified outer membrane structure. Thus it appears that the polysaccharide molecules (probably the lipopolysaccharide) either alone or in association with protein or phospholipids are the primary targets of the antibiotic.

Release of alkaline phosphatase activity by aqueous-ether treatment of whole cells of Serratia marcescens.

The effect of aqueous-ether treatment according to the method of Ribi et al. (1961) on the release of alkaline phosphatase from cells of two strains of Serratia marcescens was studied. By this method, lipopolysaccharide-protein (endotoxin) complexes associated with alkaline phosphatase activities were released from both strain 08 and strain Bizio. SDS-polyacrylamide gel electrophoresis followed by enzymatic assay showed the presence of two active components in each strain. Fractions released from strain 08 contained alkaline phosphatase A (140,000 dalton) and alkaline phosphatase B (110,000) daltons) while those from strain Bizio contained alkaline phosphatase A' (190,000 daltons) and alkaline phosphatase B (110,000 daltons). Although it is known that saline plays a role in the release of alkaline phosphatase activities from cell envelope of Gram-negative bacteria the presence of saline in the extracting medium affects only slightly the chemical composition and not at all on the enzymatic nature of the released components. By comparing the enzymatic profiles of the materials released by other techniques, such as polymyxin B treatment and osmotic shock, it appears that alkaline phosphatase activities released by aqueous-ether treatment of whole cells of S. marcescens originate from the periplasmic space.

Chemical and electrophoretic changes induced by polymyxin B on outer membrane components from Serratia marcescens.

The effects of polymyxin B (PB) on outer membrane (OM) components from resistant (strain 08) and sensitive (strain Bizio) cells of Serratia marcescens were characterized by chemical analysis and polyacrylamide gel electrophoresis (PGE) in sodium dodecylsulfate. Chemical analysis revealed no major differences in the OM fractions after PB treatment of both strains, except for the loss of protein in PB treated OM of the sensitive strain. The yield and composition between the lipopolysaccharides (LPS) of the two strains were different both before and after treatment. PGE revealed that there was a complex formation between the LPS of resistant strain and PB but both dissociation and degradation occurred in the LPS components in the sensitive strain. In addition, it was found that the protein components were destabilized by PB with subsequent loss of some of the components from OM of the sensitive strain. The difference in the amount of LPS and their ability to complex with PB may reflect different degrees of antibiotic susceptibility of these two strains of S. marcescens. A sequential multistep mechanism is proposed for the action of PB on outer membranes of this species.