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  • 1
    Online Resource
    Online Resource
    Magnetic Domain Walls in Bubble Materials : Advances in Materials and Device Research. (1979)
    San Diego :Elsevier Science & Technology,
    Details
    Keywords: Domain structure. ; Electronic books.
    Type of Medium: Online Resource
    Pages: 1 online resource (335 pages)
    Edition: 1st ed.
    ISBN: 9781483214764
    URL: https://ebookcentral.proquest.com/lib/geomar/detail.action?docID=1834424
    Language: English
    Note: Front Cover -- Magnetic Domain Walls in Bubble Materials -- Copyright Page -- Table of Contents -- PREFACE -- Chapter 1. Introduction -- Chapter 2. Resume of Classical Magnetism and Bubble Domain Statics -- 1. Static Material Parameters -- 2. Domain Statics -- 3. Landau-Lifshitz Equation and Dynamic Material Parameters -- Chapter 3. Experimental Techniques -- 4. Techniques of Domain-Wall Observation -- 5. Dynamical Techniques with a Restoring Force -- 6. Gradient Propagation of Bubbles: The Case of Zero Restoring Force -- Chapter 4. Domain-Wall Statics -- 7. One-Dimensional Model -- 8. Bloch-Line Statics -- 9. Bloch Points, State Transitions, and Capping Layers -- Chapter 5. Wall Dynamics in One Dimension -- 10. One-Dimensional Theory -- 11. Applications of the One-Dimensional Theory and Comparison to Experiment -- Chapter 6. Wall Dynamics in Three Dimensions -- 12. General Domain Dynamics -- Chapter 7. Low-Velocity Dynamics with Vertical Bloch Lines -- 13. Hard-Wall Dynamics -- 14. Small Numbers of Vertical Bloch Lines -- Chapter 8. Nonlinear Wall Motion in Two Dimensions -- 15. Bloch-Line Model -- 16. Comparison to Experiment -- 17. Advanced Topics in Two Dimensions -- Chapter 9. Nonlinear Bubble Translation -- 18. Theory of Nonlinear Bubble Translation -- 19. Comparison to Experiment -- 20. Gradientless Propulsion or Automotion -- 21. Device Dynamics -- Chapter 10. Wall Waves and Microwave Effects -- 22. Wall-Wave Spectra -- 23. Microwave Effects -- REFERENCES -- LIST OF COMMONLY USED SYMBOLS -- AUTHOR INDEX.
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  • 2
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    Acid-Adapted Strains of Escherichia coli K-12 Obtained by Experimental Evolution [Genetics and Molecular Biology] (2015)
    The American Society for Microbiology (ASM)
    Details
    Publication Date: 2015-02-28
    Description: Enteric bacteria encounter a wide range of pHs throughout the human intestinal tract. We conducted experimental evolution of Escherichia coli K-12 to isolate clones with increased fitness during growth under acidic conditions (pH 4.5 to 4.8). Twenty-four independent populations of E. coli K-12 W3110 were evolved in LBK medium (10 g/liter tryptone, 5 g/liter yeast extract, 7.45 g/liter KCl) buffered with homopiperazine- N , N '-bis-2-(ethanosulfonic acid) and malate at pH 4.8. At generation 730, the pH was decreased to 4.6 with HCl. By 2,000 generations, all populations had achieved higher endpoint growth than the ancestor at pH 4.6 but not at pH 7.0. All evolving populations showed a progressive loss of activity of lysine decarboxylase (CadA), a major acid stress enzyme. This finding suggests a surprising association between acid adaptation and moderation of an acid stress response. At generation 2,000, eight clones were isolated from four populations, and their genomes were sequenced. Each clone showed between three and eight missense mutations, including one in a subunit of the RNA polymerase holoenzyme ( rpoB , rpoC , or rpoD ). Missense mutations were found in adiY , the activator of the acid-inducible arginine decarboxylase ( adiA ), and in gcvP (glycine decarboxylase), a possible acid stress component. For tests of fitness relative to that of the ancestor, lacZ :: kan was transduced into each strain. All acid-evolved clones showed a high fitness advantage at pH 4.6. With the cytoplasmic pH depressed by benzoate (at external pH 6.5), acid-evolved clones showed decreased fitness; thus, there was no adaptation to cytoplasmic pH depression. At pH 9.0, acid-evolved clones showed no fitness advantage. Thus, our acid-evolved clones showed a fitness increase specific to low external pH.
    Print ISSN: 0099-2240
    Electronic ISSN: 1098-5336
    Topics: Biology
    Published by The American Society for Microbiology (ASM)
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  • 3
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    Benzoate- and Salicylate-Tolerant Strains of Escherichia coli K-12 Lose Antibiotic Resistance during Laboratory Evolution [Physiology] (2016)
    The American Society for Microbiology (ASM)
    Details
    Publication Date: 2016-12-31
    Description: Escherichia coli K-12 W3110 grows in the presence of membrane-permeant organic acids that can depress cytoplasmic pH and accumulate in the cytoplasm. We conducted experimental evolution by daily diluting cultures in increasing concentrations of benzoic acid (up to 20 mM) buffered at external pH 6.5, a pH at which permeant acids concentrate in the cytoplasm. By 2,000 generations, clones isolated from evolving populations showed increasing tolerance to benzoate but were sensitive to chloramphenicol and tetracycline. Sixteen clones grew to stationary phase in 20 mM benzoate, whereas the ancestral strain W3110 peaked and declined. Similar growth occurred in 10 mM salicylate. Benzoate-evolved strains grew like W3110 in the absence of benzoate, in media buffered at pH 4.8, pH 7.0, or pH 9.0, or in 20 mM acetate or sorbate at pH 6.5. Genomes of 16 strains revealed over 100 mutations, including single-nucleotide polymorphisms (SNPs), large deletions, and insertion knockouts. Most strains acquired deletions in the benzoate-induced multiple antibiotic resistance (Mar) regulon or in associated regulators such as rob and cpxA , as well as the multidrug resistance (MDR) efflux pumps emrA , emrY , and mdtA . Strains also lost or downregulated the Gad acid fitness regulon. In 5 mM benzoate or in 2 mM salicylate (2-hydroxybenzoate), most strains showed increased sensitivity to the antibiotics chloramphenicol and tetracycline; some strains were more sensitive than a marA knockout strain. Thus, our benzoate-evolved strains may reveal additional unknown drug resistance components. Benzoate or salicylate selection pressure may cause general loss of MDR genes and regulators. IMPORTANCE Benzoate is a common food preservative, and salicylate is the primary active metabolite of aspirin. In the gut microbiome, genetic adaptation to salicylate may involve loss or downregulation of inducible multidrug resistance systems. This discovery implies that aspirin therapy may modulate the human gut microbiome to favor salicylate tolerance at the expense of drug resistance. Similar aspirin-associated loss of drug resistance might occur in bacterial pathogens found in arterial plaques.
    Print ISSN: 0099-2240
    Electronic ISSN: 1098-5336
    Topics: Biology
    Published by The American Society for Microbiology (ASM)
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  • 4
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    Acid Evolution of Escherichia coli K-12 Eliminates Amino Acid Decarboxylases and Reregulates Catabolism [Evolutionary and Genomic Microbiology] (2017)
    The American Society for Microbiology (ASM)
    Details
    Publication Date: 2017-06-01
    Description: Acid-adapted strains of Escherichia coli K-12 W3110 were obtained by serial culture in medium buffered at pH 4.6 (M. M. Harden, A. He, K. Creamer, M. W. Clark, I. Hamdallah, K. A. Martinez, R. L. Kresslein, S. P. Bush, and J. L. Slonczewski, Appl Environ Microbiol 81:1932–1941, 2015, https://doi.org/10.1128/AEM.03494-14 ). Revised genomic analysis of these strains revealed insertion sequence (IS)-driven insertions and deletions that knocked out regulators CadC (acid induction of lysine decarboxylase), GadX (acid induction of glutamate decarboxylase), and FNR (anaerobic regulator). Each acid-evolved strain showed loss of one or more amino acid decarboxylase systems, which normally help neutralize external acid (pH 5 to 6) and increase survival in extreme acid (pH 2). Strains from populations B11, H9, and F11 had an IS 5 insertion or IS-mediated deletion in cadC , while population B11 had a point mutation affecting the arginine activator adiY . The cadC and adiY mutants failed to neutralize acid in the presence of exogenous lysine or arginine. In strain B11-1, reversion of an rpoC (RNA polymerase) mutation partly restored arginine-dependent neutralization. All eight strains showed deletion or downregulation of the Gad acid fitness island. Strains with the Gad deletion lost the ability to produce GABA (gamma-aminobutyric acid) and failed to survive extreme acid. Transcriptome sequencing (RNA-seq) of strain B11-1 showed upregulated genes for catabolism of diverse substrates but downregulated acid stress genes (the biofilm regulator ariR , yhiM , and Gad). Other strains showed downregulation of H 2 consumption mediated by hydrogenases ( hya and hyb ) which release acid. Strains F9-2 and F9-3 had a deletion of fnr and showed downregulation of FNR-dependent genes ( dmsABC , frdABCD , hybABO , nikABCDE , and nrfAC ). Overall, strains that had evolved in buffered acid showed loss or downregulation of systems that neutralize unbuffered acid and showed altered regulation of catabolism. IMPORTANCE Experimental evolution of an enteric bacterium under a narrow buffered range of acid pH leads to loss of genes that enhance fitness above or below the buffered pH range, including loss of enzymes that may raise external pH in the absence of buffer. Prominent modes of evolutionary change involve IS-mediated insertions and deletions that knock out key regulators. Over generations of acid stress, catabolism undergoes reregulation in ways that differ for each evolving strain.
    Print ISSN: 0099-2240
    Electronic ISSN: 1098-5336
    Topics: Biology
    Published by The American Society for Microbiology (ASM)
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  • 5
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    Experimental Evolution of Escherichia coli K-12 at High pH and with RpoS Induction [Genetics and Molecular Biology] (2018)
    The American Society for Microbiology (ASM)
    Details
    Publication Date: 2018-07-18
    Description: Experimental evolution of Escherichia coli K-12 W3110 by serial dilutions for 2,200 generations at high pH extended the range of sustained growth from pH 9.0 to pH 9.3. pH 9.3-adapted isolates showed mutations in DNA-binding regulators and envelope proteins. One population showed an IS 1 knockout of phoB (encoding the positive regulator of the phosphate regulon). A phoB :: kanR knockout increased growth at high pH. phoB mutants are known to increase production of fermentation acids, which could enhance fitness at high pH. Mutations in pcnB [poly(A) polymerase] also increased growth at high pH. Three out of four populations showed deletions of torI , an inhibitor of TorR, which activates expression of torCAD (trimethylamine N -oxide respiration) at high pH. All populations showed point mutations affecting the stationary-phase sigma factor RpoS, either in the coding gene or in genes for regulators of RpoS expression. RpoS is required for survival at extremely high pH. In our microplate assay, rpoS deletion slightly decreased growth at pH 9.1. RpoS protein accumulated faster at pH 9 than at pH 7. The RpoS accumulation at high pH required the presence of one or more antiadaptors that block degradation (IraM, IraD, and IraP). Other genes with mutations after high-pH evolution encode regulators, such as those encoded by yobG ( mgrB ) (PhoPQ regulator), rpoN (nitrogen starvation sigma factor), malI , and purR , as well as envelope proteins, such as those encoded by ompT and yahO . Overall, E. coli evolution at high pH selects for mutations in key transcriptional regulators, including phoB and the stationary-phase sigma factor RpoS. IMPORTANCE Escherichia coli in its native habitat encounters high-pH stress such as that of pancreatic secretions. Experimental evolution over 2,000 generations showed selection for mutations in regulatory factors, such as deletion of the phosphate regulator PhoB and mutations that alter the function of the global stress regulator RpoS. RpoS is induced at high pH via multiple mechanisms.
    Print ISSN: 0099-2240
    Electronic ISSN: 1098-5336
    Topics: Biology
    Published by The American Society for Microbiology (ASM)
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  • 6
    Electronic Resource
    Electronic Resource
    Origin of biquadratic exchange in magnetic multilayers (invited) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5957-5962 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We postulate localized-electron states with unpaired spin located within or at the interfaces of an otherwise nonmagnetic metallic spacer layer. Loose exchange coupling of these spins to two ferromagnets mediates a non-Heisenberg exchange coupling between them which includes a biquadratic term. A particular version of the model assumes that each interfacial layer of magnetic atoms is weakly exchange coupled to the remainder of the ferromagnets. This model permits interpretation of the biquadratic-coupling data of Gutierrez et al. for Fe/Al/Fe trilayers and of Fuss et al. for Fe/Au/Fe. According to this interpretation, the observed biquadratic coupling is intrinsic to the ideal multilayer structure rather than due to impurities or structural defects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353483
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamics of magnetic domains and walls : 35TH ANNUAL CONFERENCE ON MAGNETISM AND MAGNETIC MATERIALS San Diego, California (USA) 29 Oct−1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4590-4592 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: General equations are proposed to describe the simultaneous rotations of the magnetization vectors and the displacements of curved domain walls in one pair of magnetostatically coupled magnetic films separated by a variable distance. Leakage-field energy is written in the "transmission-line'' approximation. The effects of dissipation and the constraint of flux continuity across a domain wall are handled by d'Alembert's virtual work principle. The result is a set of coupled equations of the following kinds: (1) dynamic torque balance at each point inside a domain, (2) wall-domain constraint due to flux continuity, (3) boundary condition on domain magnetization which depends on instantaneous wall positions, and (4) wall velocity. Within certain limitations these equations apply to the core of an inductive magnetic recording head.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348320
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetic theory of very small devices (invited) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5341-5346 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A principal theme of this report is that the exchange-stiffness parameter replaces magnetic anisotropy as the principal core-material parameter (besides MS) governing the sensitivity of a read head when the cross-sectional dimensions of the core are less than 1 μm. A cylindrical magnetic tube within the core of a read head would provide micromagnetic advantages. Under certain conditions the unstable exchange energy stored in a magnetic vortex interacts with the stabilizing effect of self-demagnetization to amplify the stored flux by drawing fringing flux from the underlayer and shield. Reading characteristics which are valid, from the micromagnetic standpoint, down to storage-cell areas as small as (40 nm)2 are predicted. For sensitive reading, the core length must be near 100 (D/1 μm)2 μm, where D is the outer diameter of the tube.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344606
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  • 9
    Electronic Resource
    Electronic Resource
    Observation of magnetic switching in submicron magnetic-tunnel junctions at low frequency (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5267-5269 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Understanding the magnetic switching behavior in micron and submicron scale specimens is important for a number of applications. In this study, magnetic-tunnel junctions of various sizes and shapes were fabricated and their switching behavior was studied in detail. Using exchange bias to offset the magnetic response of one electrode, the response of the other (free) electrode was determined from measurements of junction resistance. Switching threshold curves were measured by sweeping magnetic fields in both easy and hard direction. Single domain like switching was observed in some of our smallest submicron junctions. The observed behavior was compared with predictions from the Stoner–Wohlfarth rotational model and from numerical calculations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369850
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  • 10
    Electronic Resource
    Electronic Resource
    Exchange coupling through ferromagnetic bridges in magnetic multilayers (abstract) : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6474-6474 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It has been known for 27 years1 that ferromagnetic bridges joining two ferromagnetic films can result in a cos θ dependence of the exchange-coupling energy Wb only under very restricted circumstances. In more natural circumstances, considered here, one expects Wb=Cθ2≥0 to hold in the full angular range 0≤θ≤π. The principal condition for this relation to hold is that local spontaneous spin polarization actually exists at the given temperature for all sites composing complete chains of exchange-coupled local spins extending between the ferromagnetic films. One easily finds estimation formulas in special limits; e.g., for a set of thin uniform filamentary bridges, C=Aφ/w, where A is the exchange stiffness, φ is the fractional cross section of filaments, and w is the spacer thickness. Because of this peculiar angular dependence of Wb, ferromagnetic bridges are conducive to noncolinear arrangements of the sublayer moments. In particular, nearly 90°-domain arrangements are favored in epitaxial (100) multilayers which have sufficiently strong positive cubic anisotropy Wk. Observed 90° arrangements were previously attributed to biquadratic coupling.2 One condition for 90° arrangements due to bridges is that the additional coupling Wa=−J cos θ through the normal-metal spacer medium is antiferromagnetic and its strength is in the appropriate range. Let the total energy be W=Wk+Wa+Wb. Then, if W(0) is thus made nearly equal to W(π), the θ2 dependence of the bridge term insures that W is minimized near θ=π/2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356967
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