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Morad SAF, Madigan JP, Levin JC, Abdelmageed N, Karimi R, Rosenberg DW, Kester M, Shanmugavelandy SS, Cabot MC. Tamoxifen magnifies therapeutic impact of ceramide in human colorectal cancer cells independent of p53. Biochem Pharmacol 2013; 85:1057-65. [PMID: 23353700 DOI: 10.1016/j.bcp.2013.01.015] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2012] [Revised: 01/16/2013] [Accepted: 01/18/2013] [Indexed: 12/28/2022]
Abstract
Poor prognosis in patients with later stage colorectal cancer (CRC) necessitates the search for new treatment strategies. Ceramide, because of its role in orchestrating death cascades in cancer cells, is a versatile alternative. Ceramide can be generated by exposure to chemotherapy or ionizing radiation, or it can be administered in the form of short-chain analogs (C6-ceramide). Because intracellular P-glycoprotein (P-gp) plays a role in catalyzing the conversion of ceramide to higher sphingolipids, we hypothesized that administration of P-gp antagonists with C6-ceramide would magnify cell death cascades. Human CRC cell lines were employed, HCT-15, HT-29, and LoVo. The addition of either tamoxifen, VX-710, verapamil, or cyclosporin A, antagonists of P-gp, enhanced C6-ceramide cytotoxicity in all cell lines. In depth studies with C6-ceramide and tamoxifen in LoVo cells showed the regimen induced PARP cleavage, caspase-dependent apoptosis, mitochondrial membrane permeabilization (MMP), and cell cycle arrest at G1 and G2. At the molecular level, the regimen, but not single agents, induced time-dependent upregulation of tumor suppressor protein p53; however, introduction of a p53 inhibitor staved neither MMP nor apoptosis. Nanoliposomal formulations of C6-ceramide and tamoxifen were also effective, yielding synergistic cell kill. We conclude that tamoxifen is a favorable adjuvant for enhancing C6-ceramide cytotoxicity in CRC, and demonstrates uniquely integrated effects. The high frequency of expression of P-gp in CRC presents an adventitious target for complementing ceramide-based therapies, a strategy that could hold promise for treatment of resistant disease.
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Morad SAF, Messner MC, Levin JC, Abdelmageed N, Park H, Merrill AH, Cabot MC. Potential role of acid ceramidase in conversion of cytostatic to cytotoxic end-point in pancreatic cancer cells. Cancer Chemother Pharmacol 2012; 71:635-45. [PMID: 23263160 DOI: 10.1007/s00280-012-2050-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Accepted: 12/04/2012] [Indexed: 12/29/2022]
Abstract
PURPOSE Acid ceramidase (AC) occupies an important place in the control of cancer cell proliferation. We tested the influence of AC inhibition on the effects of PSC 833, a P-glycoprotein antagonist with potent ceramide-generating capacity, to determine whether AC could be a therapeutic target in pancreatic cancer. METHODS Ceramide metabolism was followed using (3)H-palmitate, and molecular species were determined by mass spectroscopy. Apoptosis was measured by DNA fragmentation, autophagy by acridine orange staining, and cell cycle was assessed by flow cytometry and RB phosphorylation. AC was measured in intact cells using fluorescent substrate. RESULTS Exposure of human PANC-1 or MIA-PaCa-2 cells to PSC 833 promoted increases in de novo (dihydro)ceramides, (dihydro)glucosylceramides, and (dihydro)sphingomyelins, demarking ceramide generation and robust metabolism. Despite the multifold increases in (dihydro)ceramide levels, cells were refractory to PSC 833. However, PSC 833 produced a dose-dependent decrease in DNA synthesis and dose- and time-dependent decreases in RB phosphorylation, consistent with cell cycle arrest as demonstrated at G1. Cytostatic effects of PSC 833 were converted to cytotoxic end-point by acid ceramidase inhibition. Cytotoxicity was accompanied by formation of acridine orange-stained acidic vesicles and an increase in LC3 expression, indicative of autophagic response. Cell death was not reversed by preexposure to myriocin, which blocks PSC 833-induced ceramide generation. CONCLUSION Although the role of ceramide in end-point cytotoxicity is unclear, our results suggest that acid ceramidase is a viable target in pancreatic cancer. We propose that AC inhibition will be effective in concert with other anticancer therapies.
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Morad SAF, Levin JC, Shanmugavelandy SS, Kester M, Fabrias G, Bedia C, Cabot MC. Ceramide--antiestrogen nanoliposomal combinations--novel impact of hormonal therapy in hormone-insensitive breast cancer. Mol Cancer Ther 2012; 11:2352-61. [PMID: 22962326 DOI: 10.1158/1535-7163.mct-12-0594] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Although the sphingolipid ceramide exhibits potent tumor suppressor effects, efforts to harness this have been hampered by poor solubility, uptake, bioavailability, and metabolic conversion. Therefore, identification of avenues to improve efficacy is necessary for development of ceramide-based therapies. In this study, we used mutant p53, triple-negative breast cancer (TNBC) cells, a type of breast cancer highly refractory to treatment, and cell-permeable nanoliposomal C6-ceramide in conjunction with the antiestrogen tamoxifen, which has been shown to be an effective modulator of ceramide metabolism. We show for the first time that nanoliposomal tamoxifen enhances nanoliposomal C6-ceramide cytotoxicity in cultured TNBC cells, a response that was accompanied by induction of cell-cycle arrest at G(1) and G(2), caspase-dependent induction of DNA fragmentation, and enhanced mitochondrial and lysosomal membrane permeability at 18 and 2 hours, respectively. Tamoxifen metabolites were also effective. Only tamoxifen promoted lysosomal membrane permeability. In addition, we show for the first time that tamoxifen inhibits acid ceramidase, as measured in intact cell assays; this effect was irreversible. Together, our findings show that tamoxifen magnifies the antiproliferative effects of C6-ceramide via combined targeting of cell-cycle traverse and lysosomal and mitochondrial integrity. We adduce that C6-ceramide-induced apoptosis is amplified by tamoxifen's impact on lysosomes and perhaps accompanying inhibition of acid ceramidase, which could result in decreased levels of sphingosine 1-phosphate. This drug regimen could serve as a promising therapy for chemoresistant and triple-negative types of breast cancer, and thus represents an indication for tamoxifen, irrespective of estrogen receptor status.
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Morad SA, Levin JC, Kester M, Shanmugavelandy SS, Cabot MC. Abstract 3833: Ceramide/tamoxifen nanoliposomal combination - A promising strategy for treatment of chemoresistant breast cancer. Cancer Res 2012. [DOI: 10.1158/1538-7445.am2012-3833] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Drug resistance in breast and other cancers results from multiple gene interactions. Ceramide, a key intermediate in the sphingolipid pathway, can act as a powerful tumor suppressor. The employ of ceramide-based agents as opposed to the administration of ceramide generators such as daunorubicin, could be a smart strategy for cancer therapy. Polychemotherapy remains the best option for treatment of breast cancer at the aggressive, metastatic stage. The aim of our study was to investigate the cytotoxic and antiproliferative effects of ceramide (short-chain C6-ceramide) administered in combination with tamoxifen, used here as an inhibitor of ceramide glycosylation. We previously demonstrated the cytotoxicity of this combination in MDA-MB-231 cells; however, little regarding mechanism was established. The present study employs nanoliposomal formulations of both agents, a strategy to enhance efficacy. Four triple-negative chemoresistant breast cancer cell lines, MDA-MB-231, MDA-MB-468, BT-20 and Hs578T were used. Cytotoxicity assays revealed that C6-ceramide/tamoxifen synergistically reduced viability, compared to single agents in all four cell lines. For example, in MDA-MB-468 cells, nanoliposomal C6-ceramide (2.5 µM), tamoxifen (5 µM), and the combination reduced cell viability to 70, 85, and 10% of control, respectively (96 hr). A hallmark of cancer, implicated in tumor growth as well as metastasis, is resistance to induction of apoptosis. Assessment of cellular apoptosis showed that C6-ceramide/tamoxifen treatment promoted DNA fragmentation in a dose-dependant manner, attaining a value that was 36% over control at 24 hr. Introduction of the pan-caspase inhibitor, z-VAD-fmk, completely reversed DNA fragmentation, showing that apoptosis was mediated by caspase activation. The aggressive and metastatic behavior of any tumor is dependent on the ability of the cells to proliferate. Interestingly, the lower concentrations of our drug combination (2.5 µM) induced cell cycle arrest at G1, the first growth phase. In summary, this approach has potential to circumvent limitations of ceramide-based therapies, such as rapid ceramide clearance due to metabolism, the inability to attain therapeutic levels when ceramide-generating agents are employed, and inherent insolubility that is encountered. These findings demonstrate the in vitro efficacy of combination C6-ceramide/tamoxifen nanoliposomal formulations for suppressing growth of breast cancer cells, and suggest that tamoxifen may be an effective adjuvant for enhancing ceramide-driven cell death cascades. Supported by NIGMS 77391 and ABC's, Los Angeles.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3833. doi:1538-7445.AM2012-3833
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Lyon WR, Madden JC, Levin JC, Stein JL, Caparon MG. Mutation of luxS affects growth and virulence factor expression in Streptococcus pyogenes. Mol Microbiol 2001; 42:145-57. [PMID: 11679074 DOI: 10.1046/j.1365-2958.2001.02616.x] [Citation(s) in RCA: 157] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Adaptive responses of bacteria that involve sensing the presence of other bacteria are often critical for proliferation and the expression of virulence characteristics. The autoinducer II (AI-2) pathway has recently been shown to be a mechanism for sensing other bacteria that is highly conserved among diverse bacterial species, including Gram-positive pathogens. However, a role for this pathway in the regulation of virulence factors in Gram-positive pathogens has yet to be established. In this study, we have inactivated luxS, an essential component of the AI-2 pathway, in the Gram-positive pathogen Streptococcus pyogenes. Analyses of the resulting mutants revealed the aberrant expression of several virulence properties that are regulated in response to growth phase, including enhanced haemolytic activity, and a dramatic reduction in the expression of secreted proteolytic activity. This latter defect was associated with a reduced ability to secrete and process the precursor of the cysteine protease (SpeB) as well as a difference in the timing of expression of the protease. Enhanced haemolytic activity of the luxS strain was also shown to be linked with an increased expression of the haemolysin S-associated gene sagA. Disruptions of luxS in these mutants also produced a media-dependent growth defect. Finally, an allelic replacement analysis of an S. pyogenes strain with a naturally occurring insertion of IS1239 in luxS suggested a mechanism for modulation of virulence during infection. Results from this study suggest that luxS makes an important contribution to the regulation of S. pyogenes virulence factors.
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Levin JC, Wessels MR. Identification of csrR/csrS, a genetic locus that regulates hyaluronic acid capsule synthesis in group A Streptococcus. Mol Microbiol 1998; 30:209-19. [PMID: 9786197 DOI: 10.1046/j.1365-2958.1998.01057.x] [Citation(s) in RCA: 232] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The hyaluronic acid capsule of group A Streptococcus (GAS) is an important virulence factor, but little is known about mechanisms that regulate capsule expression. Transposon Tn916 mutagenesis of the poorly encapsulated M-type 3 GAS strain DLS003 produced a transconjugant that exhibited a mucoid colony morphology, reflecting increased hyaluronic acid capsule production. Analysis of chromosomal DNA sequence immediately downstream of the transposon insertion identified two open reading frames, designated csrR and csrS, which exhibited sequence similarity to bacterial two-component regulatory systems. We constructed an in-frame deletion mutation within csrR, which encodes the putative response component. Replacement of the native csrR gene in the DLS003 chromosome with the mutant allele resulted in a sixfold increase in capsule production and a corresponding increase in transcription of the has operon, which contains the essential genes for hyaluronic acid synthesis. Increased capsule production by the csrR mutant strain was associated with enhanced resistance to complement-mediated opsonophagocytic killing in vitro and with a 500-fold increase in virulence in mice. These results establish CsrR as a negative regulator of hyaluronic acid capsule synthesis and suggest that it is part of a two-component regulatory system that influences capsule expression and virulence.
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Levin JC, Stein DC. Cloning, complementation, and characterization of an rfaE homolog from Neisseria gonorrhoeae. J Bacteriol 1996; 178:4571-5. [PMID: 8755886 PMCID: PMC178225 DOI: 10.1128/jb.178.15.4571-4575.1996] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Neisseria gonorrhoeae WS1 is a spontaneous pyocin (a bacteriocin produced by Pseudomonas aeruginosa)-resistant mutant of N. gonorrhoeae FA19 that produces a truncated lipooligosaccharide (LOS) and is non-transformable. The LOS-specific mutation in WS1 was moved into a transformable background by transforming FA19 with chromosomal DNA from WS1 (generating strain JWS-1). A clone (pJCL2) capable of restoring JWS-1 to wild-type LOS expression, as detected by its acquisition of reactivity with monoclonal antibodies and by its complemented sodium dodecyl sulfate-polyacrylamide gel electrophoresis profile, was isolated. Sequential unidirectional deletion and DNA sequence analysis of pJCL2 identified an open reading frame, designated lsi-7, that could complement the defect in JWS-1. Homology searches against various databases indicated that lsi-7 bad homology with several Escherichia coli genes involved in the phosphorylation of sugars. lsi-7 is adjacent to the lsi-6 gene, another gene involved in LOS biosynthesis. Complementation studies using Salmonella typhimurium lipopolysaccharide mutants showed lsi-6 and lsi-7 to be gonococcal homologs of S. typhimurium rfaD and rfaE, respectively. Reverse transcriptase PCR analysis demonstrated that lsi-6 and lsi-7 are part of the same transcriptional unit.
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Wehlitz R, Hentges R, Prümper G, Farhat A, Buslaps T, Berrah N, Levin JC, Sellin IA, Becker U. Compton double-to-single ionization ratio of helium at 57 keV. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1996; 53:R3720-R3722. [PMID: 9913451 DOI: 10.1103/physreva.53.r3720] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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34
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Levin JC, Armen GB, Sellin IA. Photoionization and Compton double ionization of helium from threshold to 20 keV. PHYSICAL REVIEW LETTERS 1996; 76:1220-1223. [PMID: 10061666 DOI: 10.1103/physrevlett.76.1220] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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35
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Armen GB, Levin JC, Sellin IA. Radiationless resonant Raman scattering interpretation of argon photoion yields measured in coincidence with K-LL Auger decay. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1996; 53:772-784. [PMID: 9912949 DOI: 10.1103/physreva.53.772] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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36
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Danaher RJ, Levin JC, Arking D, Burch CL, Sandlin R, Stein DC. Genetic basis of Neisseria gonorrhoeae lipooligosaccharide antigenic variation. J Bacteriol 1995; 177:7275-9. [PMID: 8522539 PMCID: PMC177611 DOI: 10.1128/jb.177.24.7275-7279.1995] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Neisseria gonorrhoeae lipooligosaccharide (LOS) undergoes antigenic variation at a high rate, and this variation can be monitored by changes in a strain's ability to bind LOS-specific monoclonal antibodies. We report here the cloning and identification of a gene, lsi-2, that can mediate this variation. The DNA sequence of lsi-2 has been determined for N. gonorrhoeae 1291, a strain that expresses a high-molecular-mass LOS, and a derivative of this strain, RS132L, that produces a truncated LOS. In the parental strain, lsi-2 contains a string of 12 guanines in the middle of its coding sequence. In cells that had antigenically varied to produce a truncated LOS, the number of guanines in lsi-2 was altered. Site-specific deletions were constructed to verify that expression of a 3.6-kDa LOS is due to alterations in lsi-2.
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Lucas CE, Hagman KE, Levin JC, Stein DC, Shafer WM. Importance of lipooligosaccharide structure in determining gonococcal resistance to hydrophobic antimicrobial agents resulting from the mtr efflux system. Mol Microbiol 1995; 16:1001-9. [PMID: 7476176 DOI: 10.1111/j.1365-2958.1995.tb02325.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Levels of gonococcal resistance to antimicrobial hydrophobic agents (HAs) are controlled by the mtr (multiple transferrable resistance) system, composed of the mtrRCDE genes. The mtrR gene encodes a transcriptional repressor that appears to regulate expression of the upstream and divergent mtrCDE operon. The mtrCDE genes encode membrane proteins analogous to the MexABOprK proteins of Pseudomonas aeruginosa that mediate export of structurally diverse antimicrobial agents. In this study we found that a single base pair deletion in a 13 bp inverted repeat sequence within the mtrR promoter resulted in increased resistance of gonococci to both crystal violet (CV) and erythromycin (ERY) as well as to the more lipophilic non-ionic detergent Triton X-100 (TX-100). However, this cross-resistance was contingent on the production of a full-length lipooligosaccharide (LOS) by the recipient strain used in transformation experiments. Introduction of this mutation (mtrR-171) into three chemically distinct deep-rough LOS mutants by transformation resulted in a fourfold increase in resistance to TX-100 compared with a 160-fold increase in an isogenic strain producing a full-length LOS. However, both wild-type and deep-rough LOS strains exhibited an eightfold increase in resistance to CV and ERY as a result of the mtrR-171 mutation. This suggests that gonococci have different LOS structural requirements for mtr-mediated resistance to HAs that differ in their lipophilic properties. Evidence is presented that gonococci exclude HAs by an energy-dependent efflux process mediated by the mtr system.
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MacDonald MA, Southworth SH, Levin JC, Henins A, Deslattes RD, LeBrun T, Azuma Y, Cowan PL, Karlin BA. Evolution of x-ray resonance Raman scattering into x-ray fluorescence from the excitation of xenon near the L3 edge. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1995; 51:3598-3603. [PMID: 9912026 DOI: 10.1103/physreva.51.3598] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Deslattes RD, Levin JC, Walker MD, Henins A. Noninvasive high-voltage measurement in mammography by crystal diffraction spectrometry. Med Phys 1994; 21:123-6. [PMID: 8164576 DOI: 10.1118/1.597243] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Wavelength dispersive crystal diffraction spectrometry has been applied to the measurement of the accelerating voltage on an x-ray source in a prototype experiment in the mammographic source. The results indicate that this noninvasive approach can yield determinations of such voltages within 0.1 kV, a level of imprecision that appears adequate for high-level standardization of such potentials.
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Levin JC, Short RT, Biedermann C, Cederquist H, Elston SB, O C, Sellin IA. Determination of mean energies and impact parameters characteristic of charge-changing reactions. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1994; 49:228-235. [PMID: 9910223 DOI: 10.1103/physreva.49.228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Levin JC, Sellin IA, Johnson BM, Lindle DW, Miller RD, Berrah N, Azuma Y, Berry HG, Lee D. High-energy behavior of the double photoionization of helium from 2 to 12 keV. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1993; 47:R16-R19. [PMID: 9908985 DOI: 10.1103/physreva.47.r16] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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42
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Cederquist H, Andersson H, Beebe E, Biedermann C, Broström L, Gao H, Hutton R, Levin JC, Liljeby L, Pajek M, Quinteros T, Selberg N, Sigray P. Increase of true double-electron-capture cross sections in slow Xeq+-(Xe,He) collisions at very high q. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1992; 46:2592-2595. [PMID: 9908417 DOI: 10.1103/physreva.46.2592] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Kravis SD, Church DA, Johnson BM, Meron M, Jones KW, Levin JC, Sellin IA, Azuma Y, Berrah-Mansour N, Berry HG, Druetta M. Electron transfer from H2 and Ar to stored multiply charged argon ions produced by synchrotron radiation. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1992; 45:6379-6387. [PMID: 9907758 DOI: 10.1103/physreva.45.6379] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Andersson LR, Cederquist H, Bárány A, Liljeby L, Biedermann C, Levin JC, Keller N, Elston SB, Gibbons JP, Sellin IA. One- and two-step double-electron capture in slow Ar6+-He collisions. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1992; 45:R4-R7. [PMID: 9906763 DOI: 10.1103/physreva.45.r4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Levin JC, Lindle DW, Keller N, Miller RD, Azuma Y, Mansour NB, Berry HG, Sellin IA. Measurement of the ratio of double-to-single photoionization of helium at 2.8 keV using synchrotron radiation. PHYSICAL REVIEW LETTERS 1991; 67:968-971. [PMID: 10045036 DOI: 10.1103/physrevlett.67.968] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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46
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Andersson LR, Cederquist H, Bárány A, Liljeby L, Biedermann C, Levin JC, Keller N, Elston SB, Gibbons JP, Kimura K, Sellin IA. Simultaneous single-electron capture and projectile-core excitation enhanced through configuration interaction in very slow Ar6+-He collisions. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1991; 43:4075-4078. [PMID: 9905504 DOI: 10.1103/physreva.43.4075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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47
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Kimura K, Gibbons JP, Elston SB, Biedermann C, DeSerio R, Keller N, Levin JC, Breinig M, Burgdörfer J, Sellin IA. Convoy electrons emitted from resonant coherently excited ions. PHYSICAL REVIEW LETTERS 1991; 66:25-28. [PMID: 10043133 DOI: 10.1103/physrevlett.66.25] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Biedermann C, Levin JC, Short RT, Elston SB, Gibbons JP, Sellin IA, Cederquist H, Andersson LR, Andersson H, Liljeby L. Total-capture cross sections for very slow Ar4+-Ar and Ar6+-Ar collisions. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1990; 42:6905-6908. [PMID: 9903994 DOI: 10.1103/physreva.42.6905] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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49
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Levin JC, Biedermann C, Keller N, Liljeby L, O C, Short RT, Sellin IA, Lindle DW. Argon-photoion-Auger-electron coincidence measurements following K-shell excitation by synchrotron radiation. PHYSICAL REVIEW LETTERS 1990; 65:988-991. [PMID: 10043077 DOI: 10.1103/physrevlett.65.988] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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50
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Biedermann C, Cederquist H, Andersson LR, Levin JC, Short RT, Elston SB, Gibbons JP, Andersson H, Liljeby L, Sellin IA. Experimental and model angular distributions of one- and two-electron capture processes in 0.5-20 eV/u Ar4+-Ar collisions. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1990; 41:5889-5908. [PMID: 9902989 DOI: 10.1103/physreva.41.5889] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/11/2023]
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