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Ong S, Cai SJ, Bernal C, Rhee D, Qiu X, Pidgeon C. Phospholipid immobilization on solid surfaces. Anal Chem 1994; 66:782-92. [PMID: 8179206 DOI: 10.1021/ac00078a004] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Single chain ether phospholipids (PLs) containing omega-carboxyl groups in the alkyl chain were immobilized on silica propylamine (SPA) to form IAM chromatography packing material. The PL ligands are analogs of phosphatidylglycerol (PG), phosphatidylserine (PS), phosphatidylethanolamine (PE), and phosphatidic acid (PA). All of these PLs contain polar functional groups in the lipid head group that require protection prior to PL immobilization and then deprotection after immobilization. The IAM surface was prepared in four steps: (i) the omega-carboxyl group was activated with carbonyldiimidazole, (ii) the activated PL-imidazolide ligand was bonded to SPA, (iii) the surface was end capped with a long chain anhydride and then end-capped with a short chain anhydride, and (iv) protecting groups were removed to form the IAM surface. The extent of deblocking the protecting groups was typically > or = 90%. This immobilization strategy generated a phospholipid surface that was stable when solvated with all organic solvents and aqueous buffers between pH 2 and 8. Both FT-IR spectroscopy and elemental analysis indicated that the bonding densities were 64-83 mg of PL/g of SPA, which corresponds to an area per molecule of 66-104 A2. These bonding densities for the immobilized PLs are very close to the area per molecule of mobile phospholipids comprising liposome membrane. The similar areas per molecule of immobilized PLs and mobile phospholipid in liposomes indicate that the lipid environments are similar.
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277
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Qiu X, Pidgeon C. Membrane properties of antiviral phospholipids containing heteroatoms in the acyl chains. Biochemistry 1994; 33:960-72. [PMID: 8305444 DOI: 10.1021/bi00170a015] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Phospholipids containing heteroatoms in the lipid acyl chains, e.g., 1,2-bis(12-methoxydodecanoyl)-sn-3-phosphocholine (L-AC2), exhibit potent anti-HIV activity [Pidgeon, C., Markovich, R. J., Liu, M. D., Holzer, T., Novak, R., & Keyer, K. (1993) J. Biol. Chem. 268, 7773-7778]. AC2 is a synthetic chemical analog of the long-chain phospholipid, dimyristoylphosphatidylcholine (DMPC). Sonicated AC2 lipid dispersions would not entrap either Dextran-4000 or Mn2+ used as aqueous space markers. The lack of entrapment of aqueous space markers indicates that the AC2 structures do not contain an aqueous core that is the characteristic morphology of conventional lipid vesicles formed by sonication. Transmission electron microscopy (TEM) showed that sonicated AC2 lipid dispersions are small homogeneous particles approximately 70-100 A in diameter. 1H NMR experiments using Mn2+ as a broadening reagent indicated that Mn2+ was accessible to all of the AC2 phospholipid headgroups in the AC2 lipid particles formed by sonication. The temperature dependence of 1H spin-lattice (T1) relaxation time measurements revealed that the motional activation energies increased from the choline headgroup to the end of the acyl chains of AC2 molecules in the AC2 lipid particles formed by sonication. Collectively these results demonstrate that AC2 forms micelles. NOESY experiments showed that the AC2 molecules forming the micelle structures have hindered motion compared to conventional short-chain phosphatidylcholine micelles. 31P NMR spectroscopy and TEM showed that the AC2 micelles extensively fuse into giant bilayer liposomes (single-layered) when the temperature is reduced from above to below the main phase transition temperature of AC2. This micelle-to-liposome transition is an irreversible process; increasing the temperature above the Tm does not cause the formation of micelles. Thus, a main finding is that AC2 micelles formed by sonication are not thermodynamically stable because they fuse into large unilamellar vesicles that are stable to further changes in temperature. These unusual membrane properties of sonicated AC2 dispersions may be important for the antiviral activity and metabolism of the phospholipids.
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278
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Singal D, Qiu X. Polymorphism in the upstream regulatory region and level of expression of HLA-DRB genes. Hum Immunol 1994. [DOI: 10.1016/0198-8859(94)91748-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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279
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Mainka SA, Qiu X, He T, Appel MJ. Serologic survey of giant pandas (Ailuropoda melanoleuca), and domestic dogs and cats in the Wolong Reserve, China. J Wildl Dis 1994; 30:86-9. [PMID: 8151830 DOI: 10.7589/0090-3558-30.1.86] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Sera from captive and recently rescued giant pandas (Ailuropoda melanoleuca) in the Wolong Reserve, China, were examined by serum neutralization or hemagglutination inhibition for antibodies to canine distemper virus (CDV), canine coronavirus (CCV), canine herpesvirus (CHV), pseudorabies virus (PRV), canine adenovirus type 2 (CAV), and canine parvovirus (CPV). Serum samples from village domestic dogs and cats, which run free throughout the reserve also were examined. Antibodies against CPV were detected in six of eight giant pandas and all dogs and cats tested. The origin of the virus was not determined. Two of eight giant pandas and two of seven dogs had CDV antibody titers. Three of eight pandas and three of seven dogs had CCV antibody titers. Four of eight pandas and two of seven dogs had CAV titers; the titers in dogs were very high. No pandas or dogs had evidence of exposure to CHV or PRV.
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280
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Singal DP, Ye M, Qiu X, D'Souza M. Polymorphisms in the TAP2 gene and their association with rheumatoid arthritis. Clin Exp Rheumatol 1994; 12:29-33. [PMID: 8162639] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The human major histocompatibility complex (MHC) contains two closely related genes (TAP) that encode a family of transporter proteins. It is known that the TAP genes, like other MHC (class I and class II) genes, are polymorphic. In this study we investigated the polymorphisms in the ATP-binding domain of the TAP2 gene and examined the relationship of these polymorphisms to susceptibility to rheumatoid arthritis (RA). On the basis of the distribution of polymorphisms in these genes, three TAP2 alleles could be identified in homozygous typing cell lines, RA patients and normal subjects: TAP2*0101-1693.G, TAP2*0101-1693.A and TAP2*0201-1693.G. The prevalence of the variant (nucleotide A at position 1693), and thus also of the TAP2*0101-1693.A allele, was significantly (p < 0.006, RR = 4.25) higher in RA patients (35.3%) than in normal controls (11.4%). In addition, the TAP2*0101-1693.A allele showed significant (r = 0.45, p < 0.0003) association with HLA-DR4 only in RA patients and the prevalence of both TAP2*0101-1693.A and DR4 genes gave the highest relative risk (RR = 19.21, p < 0.0002) for RA. These data suggest that the MHC region containing both class II and TAP genes confers the strongest susceptibility to RA, with the highest RR value reported so far. It is likely that the genetic variability in the putative peptide transporter could also be implicated in immunological disorders associated with MHC.
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281
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Qiu X, Yin M, Padmanabhan KP, Krstenansky JL, Tulinsky A. Structures of thrombin complexes with a designed and a natural exosite peptide inhibitor. J Biol Chem 1993; 268:20318-26. [PMID: 8376390] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The structures of two hirudin-based fibrinogen recognition exosite peptide inhibitors with significantly different sequences complexed with alpha-thrombin at a site distinct from the active site (exosite) have been determined crystallographically at 2.2 and 2.3 A resolution. One is a designed synthetic peptide with some nonconventional amino acid residues (MDL-28050), and the other is a natural COOH-terminal peptide isolated from the leech Hirudinaria manillensis (hirullin P18). The structures have been refined by restrained least squares methods to R values of 0.161 and 0.155, respectively. The first stretch of each peptide, corresponding to hirudin 55-59, associates with thrombin similar to hirudin and hirugen (hirudin 53-64). Although the remaining residues of the inhibitors interact with and bind to thrombin, the binding is accomplished. through a rigid body conformational adjustment of the peptide with respect to the conformation displayed by hirudin and hirugen (40 degrees rotation about the Ile59, CA-C bond). This causes the side groups of cyclohexylalanine 64' of MDL-28050 and Ile60, of hirullin to point in the opposite direction of the all important Tyr63, ring of hirudin and hirugen but permits the residues to penetrate and interact with the 3(10) turn hydrophobic binding pocket of thrombin. Thus, the hydrophobic interaction is accomplished in a different way by virtue of the substrate conformational readjustment. The results show that the first stretch of peptide makes concerted and efficient binding interactions with thrombin, and the peptide positions of the inhibitors are fairly specific and homologous so that the stretch appears to be related to specific recognition associated with the exosite. The relative flexibility of structure and sequence of the second stretch is a display of tolerance of imprecision by thrombin in its COOH-terminal hydrophobic association with hirudin-based inhibitors.
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282
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Maryanoff BE, Qiu X, Padmanabhan KP, Tulinsky A, Almond HR, Andrade-Gordon P, Greco MN, Kauffman JA, Nicolaou KC, Liu A. Molecular basis for the inhibition of human alpha-thrombin by the macrocyclic peptide cyclotheonamide A. Proc Natl Acad Sci U S A 1993; 90:8048-52. [PMID: 8367461 PMCID: PMC47285 DOI: 10.1073/pnas.90.17.8048] [Citation(s) in RCA: 89] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The macrocyclic peptide cyclotheonamide A (CtA), isolated from the marine sponge Theonella sp., represents an unusual class of serine protease inhibitor. A complex of this inhibitor with human alpha-thrombin, a protease central to the bioregulation of thrombosis and hemostasis, was studied by x-ray crystallography. This work (2.3-A resolution) confirms the structure of CtA and reveals intimate details about its molecular recognition within the enzyme active site. Interactions due to the "Pro-Arg motif" (Arg occupancy of the S1 specificity pocket; formation of a hydrogen-bonded two-strand antiparallel beta-sheet with Ser214-Gly216) and the alpha-keto amide group of CtA are primarily responsible for binding to thrombin, with the alpha-keto amide serving as a transition-state analogue. A special interaction with the "insertion loop" of thrombin (Tyr60A-Thr60I) is manifested through engagement of the hydroxyphenyl group of CtA with Trp60D as part of an "aromatic stacking chain." Biochemical inhibition data (Ki values at 37 degrees C) were obtained for CtA with thrombin and a diverse collection of serine proteases. Thus, CtA is just a moderate inhibitor of human alpha-thrombin (Ki = 0.18 microM) but a potent inhibitor of trypsin (Ki = 0.023 microM) and streptokinase (Ki = 0.035 microM). The relative lack of potency of CtA as a thrombin inhibitor is discussed with respect to certain structural features of the enzyme complex. We also report the total synthesis of CtA, by a convergent [2 + 3] fragment-condensation approach, to serve the preparation of cyclotheonamide analogues for structure-function studies.
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283
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Qiu X, Yin M, Padmanabhan K, Krstenansky J, Tulinsky A. Structures of thrombin complexes with a designed and a natural exosite peptide inhibitor. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(20)80731-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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284
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Qiu X, Mande S, Safarty S, Hol WGJ, Stewart L, Champoux JJ, Vink C, Plasterk RHA. Purification and preliminary crystallization experiments on DNA-binding proteins human topoisomerase 1 and HIV-2 integrase. Acta Crystallogr A 1993. [DOI: 10.1107/s0108767378098190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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285
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Huang X, Haimson B, Plesha M, Qiu X. An investigation of the mechanics of rock joints—Part I. Laboratory investigation. ACTA ACUST UNITED AC 1993. [DOI: 10.1016/0148-9062(93)92729-a] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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286
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Qiu X, Mirau PA, Pidgeon C. Magnetically induced orientation of phosphatidylcholine membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1147:59-72. [PMID: 8466932 DOI: 10.1016/0005-2736(93)90316-r] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Lipid bilayers prepared from natural phospholipids orient in magnetic fields with the long axis of the lipid molecules perpendicular to the magnetic field. This magnetically induced orientation was studied at high (11.7 Tesla (T)), mid (9.36 T), and low (4.68 T) magnetic field strengths using lipid aggregates prepared from natural and synthetic phosphatidylcholine analogs. Phosphatidylcholine analogs containing saturated diacylated chains (12 to 16 carbons/chain) exhibited extensive orientation of the lipid when bilayer formation occurred by gentle hydration conditions. Gentle hydration involved incubating dried phosphatidylcholine C above the main phase transition (Tm); brief shaking or swirling by hand was occasionally needed to completely disperse the lipids. The method of bilayer formation significantly influenced the amount of lipid that orients in magnetic fields. Thus the supramolecular structures (and % orientation) above Tm in an 11.7 T field of dimyristoylphosphatidylcholine (DMPC) bilayers are SUV (0%), LUV (approximately 15%), SPLV (approximately 40%), vortexed-MLV (approximately 60%) and non-vortexed MLV (approximately 90%). Single layered vesicles prepared by the REV method exhibited orientation at 11.7 T similar to LUV prepared by freeze thaw cycles. Aqueous dispersions of eggPC prepared by gentle hydration exhibit approximately 40% orientation at 11.7 T which decreased to approximately 30% orientation if 30% cholesterol is added to the membrane. Magnetic orientation of bilayers thus appears to be a general phenomenon for both saturated and unsaturated natural phospholipids either with or without cholesterol in the membrane.
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Abstract
alpha-thrombin possesses at least three independent binding sites for substrate, inhibitor and effector molecules. The S1 subsite of the active site is specific for an arginine side group while S2 is a more extended apolar site. The fibrinogen recognition exosite, which usually operates in concert with catalysis, appears to circumnavigate about a third of the surface, although evidence suggests that recognition of a tetra- or pentapeptide sequence is sufficient. Another highly electropositive region of thrombin, which binds the second kringle of prothrombin through salt bridges, is also most likely the heparin binding site. All three sites display distinct binding modes with different molecules. In the active site, these can arise from different optical enantiomorphs combined with reversal of main chain direction, while in the fibrinogen anion binding exosite, certain peptide side chains (hydrophobic) are tolerated of imprecision or are not relevant for binding or undergo a conformational change in substrate binding. Such apparently indiscriminant behaviour easily accounts for the diversity of thrombin functions at the molecular level.
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288
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Singal DP, D'Souza M, Sood SK, Qiu X. Sequence-specific interactions of the nuclear proteins with polymorphic upstream regulatory regions of HLA-DRB genes. Transplant Proc 1993; 25:180-2. [PMID: 8438265] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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289
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Singal DP, Qiu X, D'Souza M, Sood SK. Polymorphism in the upstream regulatory regions of HLA-DRB genes. Immunogenetics 1993; 37:143-7. [PMID: 8423054 DOI: 10.1007/bf00216839] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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290
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Qiu X, Padmanabhan KP, Carperos VE, Tulinsky A, Kline T, Maraganore JM, Fenton JW. Structure of the hirulog 3-thrombin complex and nature of the S' subsites of substrates and inhibitors. Biochemistry 1992; 31:11689-97. [PMID: 1445905 DOI: 10.1021/bi00162a004] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The X-ray crystallographic structure of the human alpha-thrombin complex with hirulog 3 (a potent, noncleavable hirudin-based peptide of the "hirulog" class containing a beta-homoarginine at the scissile bond), which is isomorphous with that of the hirugen-thrombin crystal structure, was solved at 2.3-A resolution by starting with a model for thrombin derived from the hirugen-thrombin complex and was refined by restrained least squares methods (R = 0.132). Residues of hirulog 3 were well-defined in the electron density, which included most of the pentaglycine linker and the C-terminal helical turn that was disordered in a related structure of thrombin with hirulog 1. The interactions of D-Phe1'-Pro2'-beta-homoArg3' with the active site of thrombin were essentially identical to those of related structures of PPACK- (D-Phe-Pro-Arg chloromethyl ketone) and hirulog 1-thrombin, with the guanidinium function of the arginyl P1 residue forming a hydrogen-bonding ion pair with Asp189 of the S1 site. A noticeable shift in the CA atom of beta-homoArg3' due to the methylene insertion displaces the scissile bond from attack by Ser195, thus imparting proteolytic stability to the beta-homoArg hirulog derivative. Resolution of the pentaglycine spacer, linking N- and C-terminal functional domains into a single oligopeptide bivalent inhibitor, permitted delineation of corresponding S' subsites of thrombin. The position of Gly4' (P1') is stabilized by three hydrogen bonds with His57, Lys60F, and Ser195, while the conformational angles maintained in a strained, nonallowed configuration for non-glycyl amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)
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291
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Esfarjani K, Chui ST, Qiu X. Dislocation waves in a two-dimensional Coulomb lattice. PHYSICAL REVIEW. B, CONDENSED MATTER 1992; 46:4638-4643. [PMID: 10004220 DOI: 10.1103/physrevb.46.4638] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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292
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Singal DP, Qiu X, Sood SK. Molecular analysis of novel HLA-DR2.DQwl haplotypes in Asian Indians. TISSUE ANTIGENS 1992; 40:104-7. [PMID: 1412415 DOI: 10.1111/j.1399-0039.1992.tb01968.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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293
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Che H, Xia Y, Lin DL, Qiu X, Zheng H. Interface spin waves in a bilayer of two-sublattice ferrimagnets. PHYSICAL REVIEW. B, CONDENSED MATTER 1991; 44:9444-9453. [PMID: 9998926 DOI: 10.1103/physrevb.44.9444] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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294
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Qiu X, Ruiz-Garcia J, Stine KJ, Knobler CM, Selinger JV. Direct observation of domain structure in condensed monolayer phases. PHYSICAL REVIEW LETTERS 1991; 67:703-706. [PMID: 10044967 DOI: 10.1103/physrevlett.67.703] [Citation(s) in RCA: 63] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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295
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Chui ST, Qiu X. Wigner solid from finite-cluster studies. PHYSICAL REVIEW. B, CONDENSED MATTER 1991; 43:14293-14296. [PMID: 9997313 DOI: 10.1103/physrevb.43.14293] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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296
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Qiu X, Wu XL, Xue JZ, Pine DJ, Weitz DA, Chaikin PM. Hydrodynamic interactions in concentrated suspensions. PHYSICAL REVIEW LETTERS 1990; 65:516-519. [PMID: 10042940 DOI: 10.1103/physrevlett.65.516] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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297
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Qiu X, Joynt R, MacDonald AH. Phase transitions in a multiple quantum well in strong magnetic fields. PHYSICAL REVIEW. B, CONDENSED MATTER 1990; 42:1339-1352. [PMID: 9995547 DOI: 10.1103/physrevb.42.1339] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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298
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Qiu X, Conrad JR, Dodd RA, Worzala FJ. Plasma source nitrogen ion implantation of Ti-6Al-4V. ACTA ACUST UNITED AC 1990. [DOI: 10.1007/bf02672581] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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299
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Qiu X, Joynt R, MacDonald AH. Phases of the multiple quantum well in a strong magnetic field: Possibility of irrational charge. PHYSICAL REVIEW. B, CONDENSED MATTER 1989; 40:11943-11946. [PMID: 9991806 DOI: 10.1103/physrevb.40.11943] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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300
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Qiu X, Ou-Yang HD, Pine DJ, Chaikin PM. Self-diffusion of interacting colloids far from equilibrium. PHYSICAL REVIEW LETTERS 1988; 61:2554-2557. [PMID: 10039155 DOI: 10.1103/physrevlett.61.2554] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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