123 research outputs found
Atomistic Monte Carlo simulation of lipid membranes
Biological membranes are complex assemblies of many different molecules of which analysis demands a variety of experimental and computational approaches. In this article, we explain challenges and advantages of atomistic Monte Carlo (MC) simulation of lipid membranes. We provide an introduction into the various move sets that are implemented in current MC methods for efficient conformational sampling of lipids and other molecules. In the second part, we demonstrate for a concrete example, how an atomistic local-move set can be implemented for MC simulations of phospholipid monomers and bilayer patches. We use our recently devised chain breakage/closure (CBC) local move set in the bond-/torsion angle space with the constant-bond-length approximation (CBLA) for the phospholipid dipalmitoylphosphatidylcholine (DPPC). We demonstrate rapid conformational equilibration for a single DPPC molecule, as assessed by calculation of molecular energies and entropies. We also show transition from a crystalline-like to a fluid DPPC bilayer by the CBC local-move MC method, as indicated by the electron density profile, head group orientation, area per lipid, and whole-lipid displacements. We discuss the potential of local-move MC methods in combination with molecular dynamics simulations, for example, for studying multi-component lipid membranes containing cholesterol
Building Partner Capacity/Security Force Assistance: A New Structural Paradigm
The Civil Response Corps (CRC) would function much like our military reserve. It would ease the burden on the Armed Forces by allowing the hiring of civilians with critical skills to serve on missions abroad when America needs them. The CRC is a product of the efforts of State Department’s Coordinator for Reconstruction and Stabilization (S/CRS). The core mission of S/CRS is to lead, coordinate, and institutionalize U.S. Government civilian capacity to prevent or prepare for post-conflict situations, and to help stabilize and reconstruct societies in transition from conflict or civil strife, so they can reach a sustainable path toward peace, good governance, and a market economy. As the General Purpose Force looks forward to expanding roles in Irregular Warfare, Foreign Internal Defense, Security Assistance and Stability Operations, does the U.S. Army or the Department of Defense have the proper force structure and minimal capability to fight and win through all phases of conflict? This paper analyzes this construct and provides a framework for identifying proponency, institutionalizing lessons learned, and providing a military, police, and governance structure as a tool for global engagement. This new structural paradigm complements S/CRS\u27s efforts to provide the United States with the ability to access, influence, and build capacity throughout this new world order.https://press.armywarcollege.edu/monographs/1356/thumbnail.jp
Atomistic Monte Carlo simulation of lipid membranes
Biological membranes are complex assemblies of many different molecules of which analysis demands a variety of experimental and computational approaches. In this article, we explain challenges and advantages of atomistic Monte Carlo (MC) simulation of lipid membranes. We provide an introduction into the various move sets that are implemented in current MC methods for efficient conformational sampling of lipids and other molecules. In the second part, we demonstrate for a concrete example, how an atomistic local-move set can be implemented for MC simulations of phospholipid monomers and bilayer patches. We use our recently devised chain breakage/closure (CBC) local move set in the bond-/torsion angle space with the constant-bond-length approximation (CBLA) for the phospholipid dipalmitoylphosphatidylcholine (DPPC). We demonstrate rapid conformational equilibration for a single DPPC molecule, as assessed by calculation of molecular energies and entropies. We also show transition from a crystalline-like to a fluid DPPC bilayer by the CBC local-move MC method, as indicated by the electron density profile, head group orientation, area per lipid, and whole-lipid displacements. We discuss the potential of local-move MC methods in combination with molecular dynamics simulations, for example, for studying multi-component lipid membranes containing cholesterol
Overcoming losses with gain in a negative refractive index metamaterial
On the basis of a full-vectorial three-dimensional Maxwell-Bloch approach we
investigate the possibility of using gain to overcome losses in a negative
refractive index fishnet metamaterial. We show that appropriate placing of
optically pumped laser dyes (gain) into the metamaterial structure results in a
frequency band where the nonbianisotropic metamaterial becomes amplifying. In
that region both the real and the imaginary part of the effective refractive
index become simultaneously negative and the figure of merit diverges at two
distinct frequency points.Comment: 4 pages, 4 figure
Control and Dynamic Competition of Bright and Dark Lasing States in Active Nanoplasmonic Metamaterials
Active nanoplasmonic metamaterials support bright and dark modes that compete
for gain. Using a Maxwell-Bloch approach incorporating Langevin noise we study
the lasing dynamics in an active nano-fishnet structure. We report that lasing
of the bright negative-index mode is possible if the higher-Q dark mode is
discriminated by gain, spatially or spectrally. The nonlinear competition
during the transient phase is followed by steady-state emission where bright
and dark modes can coexist. We analyze the influence of pump intensity and
polarization and explore methods for mode control.Comment: 5 pages, 4 figure
|\epsilon|-Near-Zero materials in the near-infrared
We consider a mixture of metal coated quantum dots dispersed in a polymer
matrix and, using a modified version of the standard Maxwell-Garnett mixing
rule, we prove that the mixture parameters (particles radius, quantum dots
gain, etc.) can be chosen so that the effective medium permittivity has an
absolute value very close to zero in the near-infrared, i.e. |Re(epsilon)|<<1
and |Im (epsilon)|<<1 at the same near-infrared wavelength. Resorting to
full-wave simulations, we investigate the accuracy of the effective medium
predictions and we relate their discrepancy with rigorous numerical results to
the fact that |epsilon|<<1 is a critical requirement. We show that a simple
method for reducing this discrepancy, and hence for achieving a prescribed
value of |\epsilon|, consists in a subsequent fine-tuning of the nanoparticles
volume filling fraction.Comment: 3 pages, 3 figure
A recoil detector for the measurement of antiproton-proton elastic scattering at angles close to 90
The design and construction of a recoil detector for the measurement of
recoil protons of antiproton-proton elastic scattering at scattering angles
close to 90 are described. The performance of the recoil detector has
been tested in the laboratory with radioactive sources and at COSY with proton
beams by measuring proton-proton elastic scattering. The results of laboratory
tests and commissioning with beam are presented. Excellent energy resolution
and proper working performance of the recoil detector validate the conceptual
design of the KOALA experiment at HESR to provide the cross section data needed
to achieve a precise luminosity determination at the PANDA experiment.Comment: 10 pages, 15 figure
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