81 research outputs found
Observation of condensed phases of quasi-planar core-softened colloids
We experimentally study the condensed phases of repelling core-softened
spheres in two dimensions. The dipolar pair repulsion between superparamagnetic
spheres trapped in a thin cell is induced by a transverse magnetic field and
softened by suitably adjusting the cell thickness. We scan a broad density
range and we materialize a large part of the theoretically predicted phases in
systems of core-softened particles, including expanded and close-packed
hexagonal, square, chain-like, stripe/labyrinthine, and honeycomb phase.
Further insight into their structure is provided by Monte Carlo simulations
Extended Ginzburg-Landau formalism: systematic expansion in small deviation from the critical temperature
Based on the Gor'kov formalism for a clean s-wave superconductor, we develop
an extended version of the single-band Ginzburg-Landau (GL) theory by means of
a systematic expansion in the deviation from the critical temperature T_c,
i.e., tau=1-T/T_c. We calculate different contributions to the order parameter
and the magnetic field: the leading contributions (~ tau^1/2 in the order
parameter and ~ tau in the magnetic field) are controlled by the standard
Ginzburg-Landau (GL) theory, while the next-to-leading terms (~ tau^3/2 in the
gap and ~ tau^2 in the magnetic field) constitute the extended GL (EGL)
approach. We derive the free-energy functional for the extended formalism and
the corresponding expression for the current density. To illustrate the
usefulness of our formalism, we calculate, in a semi-analytical form, the
temperature-dependent correction to the GL parameter at which the surface
energy becomes zero, and analytically, the temperature dependence of the
thermodynamic critical field. We demonstrate that the EGL formalism is not just
a mathematical extension to the theory - variations of both the gap and the
thermodynamic critical field with temperature calculated within the EGL theory
are found in very good agreement with the full BCS results down to low
temperatures, which dramatically improves the applicability of the formalism
compared to its standard predecessor
Structure and Function of the First Full-Length Murein Peptide Ligase (Mpl) Cell Wall Recycling Protein
Bacterial cell walls contain peptidoglycan, an essential polymer made by enzymes in the Mur pathway. These proteins are specific to bacteria, which make them targets for drug discovery. MurC, MurD, MurE and MurF catalyze the synthesis of the peptidoglycan precursor UDP-N-acetylmuramoyl-L-alanyl-γ-D-glutamyl-meso-diaminopimelyl-D-alanyl-D-alanine by the sequential addition of amino acids onto UDP-N-acetylmuramic acid (UDP-MurNAc). MurC-F enzymes have been extensively studied by biochemistry and X-ray crystallography. In Gram-negative bacteria, ∼30–60% of the bacterial cell wall is recycled during each generation. Part of this recycling process involves the murein peptide ligase (Mpl), which attaches the breakdown product, the tripeptide L-alanyl-γ-D-glutamyl-meso-diaminopimelate, to UDP-MurNAc. We present the crystal structure at 1.65 Å resolution of a full-length Mpl from the permafrost bacterium Psychrobacter arcticus 273-4 (PaMpl). Although the Mpl structure has similarities to Mur enzymes, it has unique sequence and structure features that are likely related to its role in cell wall recycling, a function that differentiates it from the MurC-F enzymes. We have analyzed the sequence-structure relationships that are unique to Mpl proteins and compared them to MurC-F ligases. We have also characterized the biochemical properties of this enzyme (optimal temperature, pH and magnesium binding profiles and kinetic parameters). Although the structure does not contain any bound substrates, we have identified ∼30 residues that are likely to be important for recognition of the tripeptide and UDP-MurNAc substrates, as well as features that are unique to Psychrobacter Mpl proteins. These results provide the basis for future mutational studies for more extensive function characterization of the Mpl sequence-structure relationships
Beach sand and the potential for infectious disease transmission: observations and recommendations
Cell surface engineering with polyelectrolyte-stabilized magnetic nanoparticles: A facile approach for fabrication of artificial multicellular tissue-mimicking clusters
Double-beta decay with emission of single free electron
We study a new mode of the neutrinoless and two-neutrino double-beta decays in which one of the electrons is emitted from the atom, while the other is directly produced in one of the available s1/2 or p1/2 subshells of the daughter ion. We calculate the phase-space factors, estimate the half-lives and derive the single-electron spectra for 0+ → 0+ ground-state nuclear transitions of the most relevant double-beta-decay isotopes: 48Ca, 76Ge, 82Se, 100Mo, 136Xe and 150Nd. The relativistic electron wave functions are evaluated at the nuclear radius by means of the multiconfiguration Dirac–Hartree–Fock package Grasp2K. We discuss the prospects for detecting these new modes in the tracking-and-calorimetry experiments NEMO-3 and SuperNEMO
Stochastic resonance in colloidal systems
We investigate the dynamical properties of a colloidal particle
in a double-well potential which is periodically modulated in
time. In case of the modulation corresponding to a tilt of the
potential (asymmetric modulation), stochastic resonance is
observed when the modulation frequency matches one
half of the Kramers frequency of the unperturbed potential. In
contrast, when only the potential barrier height is modulated
(symmetric modulation), no synchronization between the modulation
and the particle dynamics is observed as demonstrated by the lack
of a peak in the power spectrum at
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