154 research outputs found
The Works of Stefan George
This translation of all the poems in the main body of the work of George extensively revises the first publication of "The Works of Stefan George" which appeared in 1949. The editors have also expanded the volume, adding a number of George's early poems under the collective title "Drawings in Grey", two essays (including the eulogy on Hölderin), and the lyrical drama "The Lady's Praying" along with a commentary by the translators
Fluctuating Nonlinear Spring Model of Mechanical Deformation of Biological Particles
We present a new theory for modeling forced indentation spectral lineshapes
of biological particles, which considers non-linear Hertzian deformation due to
an indenter-particle physical contact and bending deformations of curved beams
modeling the particle structure. The bending of beams beyond the critical point
triggers the particle dynamic transition to the collapsed state, an extreme
event leading to the catastrophic force drop as observed in the force
(F)-deformation (X) spectra. The theory interprets fine features of the
spectra: the slope of the FX curves and the position of force-peak signal, in
terms of mechanical characteristics --- the Young's moduli for Hertzian and
bending deformations E_H and E_b, and the probability distribution of the
maximum strength with the strength of the strongest beam F_b^* and the beams'
failure rate m. The theory is applied to successfully characterize the
curves for spherical virus particles --- CCMV, TrV, and AdV
Tubulin bond energies and microtubule biomechanics determined from nanoindentation in silico
Microtubules, the primary components of the chromosome segregation machinery,
are stabilized by longitudinal and lateral non-covalent bonds between the
tubulin subunits. However, the thermodynamics of these bonds and the
microtubule physico-chemical properties are poorly understood. Here, we explore
the biomechanics of microtubule polymers using multiscale computational
modeling and nanoindentations in silico of a contiguous microtubule fragment. A
close match between the simulated and experimental force-deformation spectra
enabled us to correlate the microtubule biomechanics with dynamic structural
transitions at the nanoscale. Our mechanical testing revealed that the
compressed MT behaves as a system of rigid elements interconnected through a
network of lateral and longitudinal elastic bonds. The initial regime of
continuous elastic deformation of the microtubule is followed by the transition
regime, during which the microtubule lattice undergoes discrete structural
changes, which include first the reversible dissociation of lateral bonds
followed by irreversible dissociation of the longitudinal bonds. We have
determined the free energies of dissociation of the lateral (6.9+/-0.4
kcal/mol) and longitudinal (14.9+/-1.5 kcal/mol) tubulin-tubulin bonds. These
values in conjunction with the large flexural rigidity of tubulin
protofilaments obtained (18,000-26,000 pN*nm^2), support the idea that the
disassembling microtubule is capable of generating a large mechanical force to
move chromosomes during cell division. Our computational modeling offers a
comprehensive quantitative platform to link molecular tubulin characteristics
with the physiological behavior of microtubules. The developed in silico
nanoindentation method provides a powerful tool for the exploration of
biomechanical properties of other cytoskeletal and multiprotein assemblie
Fluctuating nonlinear spring theory:Strength, deformability, and toughness of biological nanoparticles from theoretical reconstruction of force-deformation spectra
We developed the Fluctuating Nonlinear Spring (FNS) model to describe the dynamics of mechanical deformation of biological particles, such as virus capsids. The theory interprets the force-deformation spectra in terms of the “Hertzian stiffness” (non-linear regime of a particle's small-amplitude deformations), elastic constant (large-amplitude elastic deformations), and force range in which the particle's fracture occurs. The FNS theory enables one to quantify the particles’ elasticity (Young's moduli for Hertzian and bending deformations), and the limits of their strength (critical forces, fracture toughness) and deformability (critical deformations) as well as the probability distributions of these properties, and to calculate the free energy changes for the particle's Hertzian, elastic, and plastic deformations, and eventual fracture. We applied the FNS theory to describe the protein capsids of bacteriophage P22, Human Adenovirus, and Herpes Simplex virus characterized by deformations before fracture that did not exceed 10–19% of their size. These nanoshells are soft (~1–10-GPa elastic modulus), with low ~50–480-kPa toughness – a regime of material behavior that is not well understood, and with the strength increasing while toughness decreases with their size. The particles’ fracture is stochastic, with the average values of critical forces, critical deformations, and fracture toughness comparable with their standard deviations. The FNS theory predicts 0.7-MJ/mol free energy for P22 capsid maturation, and it could be extended to describe uniaxial deformation of cylindrical microtubules and ellipsoidal cellular organelles
Identification and Characterization of Six Spectroscopically Confirmed Massive Protostructures at
We present six spectroscopically confirmed massive protostructures, spanning
a redshift range of in the Extended Chandra Deep Field South
(ECDFS) field discovered as part of the Charting Cluster Construction in VUDS
and ORELSE (C3VO) survey. We identify and characterize these remarkable systems
by applying an overdensity measurement technique on an extensive data
compilation of public and proprietary spectroscopic and photometric
observations in this highly studied extragalactic field. Each of these six
protostructures, i.e., a large scale overdensity (volume \thinspace
cMpc) of more than above the field density levels at
these redshifts, have a total mass and one or more
highly overdense (overdensity) peaks. One of the
most complex protostructures discovered is a massive
() system at that contains six peaks and
55 spectroscopic members. We also discover protostructures at and
that appear to at least partially overlap on sky with the
protostructure at , suggesting a possible connection. We
additionally report on the discovery of three massive protostructures at
, 2.80, and 4.14 and discuss their properties. Finally, we discuss the
relationship between star formation rate and environment in the richest of
these protostructures, finding an enhancement of star formation activity in the
densest regions. The diversity of the protostructures reported here provide an
opportunity to study the complex effects of dense environments on galaxy
evolution over a large redshift range in the early universe.Comment: 10 pages, 4 figures, 1 tabl
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using
ultracold atoms in an optical lattice. We investigate the phase evolution of an
array of essentially non-interacting matter waves and observe matter-wave
collapse and revival in the form of a Talbot interference pattern. By using
long expansion times, we image momentum space with sub-recoil resolution,
allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure
Azimuthal anisotropy at RHIC: the first and fourth harmonics
We report the first observations of the first harmonic (directed flow, v_1),
and the fourth harmonic (v_4), in the azimuthal distribution of particles with
respect to the reaction plane in Au+Au collisions at the Relativistic Heavy Ion
Collider (RHIC). Both measurements were done taking advantage of the large
elliptic flow (v_2) generated at RHIC. From the correlation of v_2 with v_1 it
is determined that v_2 is positive, or {\it in-plane}. The integrated v_4 is
about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8)
harmonics upper limits on the magnitudes are reported.Comment: 6 pages with 3 figures, as accepted for Phys. Rev. Letters The data
tables are at
http://www.star.bnl.gov/central/publications/pubDetail.php?id=3
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