1,497 research outputs found
Applications of control theory
Applications of control theory are considered in the areas of decoupling and wake steering control of submersibles, a method of electrohydraulic conversion with no moving parts, and socio-economic system modelling
Butterfly hysteresis loop at non-zero bias field in antiferromagnetic molecular rings: cooling by adiabatic magnetization
At low temperatures, the magnetization of the molecular ferric wheel NaFe
exhibits a step at a critical field due to a field-induced
level-crossing. By means of high-field torque magnetometry we observed a
hysteretic behavior at the level-crossing with a characteristic butterfly shape
which is analyzed in terms of a dissipative two-level model. Several unusual
features were found. The non-zero bias field of the level-crossing suggests the
possibility of cooling by adiabatic magnetization.Comment: 4 pages, 5 figures, REVTEX4, to appear in PR
Mapping the Evolution of Optically-Generated Rotational Wavepackets in a Room Temperature Ensemble of D
A coherent superposition of rotational states in D has been excited by
nonresonant ultrafast (12 femtosecond) intense (2 10
Wcm) 800 nm laser pulses leading to impulsive dynamic alignment.
Field-free evolution of this rotational wavepacket has been mapped to high
temporal resolution by a time-delayed pulse, initiating rapid double
ionization, which is highly sensitive to the angle of orientation of the
molecular axis with respect to the polarization direction, . The
detailed fractional revivals of the neutral D wavepacket as a function of
and evolution time have been observed and modelled theoretically.Comment: 4 pages, 3 figures. Accepted for publication in Phys. Rev. A. Full
reference to follow.
Lie bialgebras of generalized Witt type
In a paper by Michaelis a class of infinite-dimensional Lie bialgebras
containing the Virasoro algebra was presented. This type of Lie bialgebras was
classified by Ng and Taft. In this paper, all Lie bialgebra structures on the
Lie algebras of generalized Witt type are classified. It is proved that, for
any Lie algebra of generalized Witt type, all Lie bialgebras on are
coboundary triangular Lie bialgebras. As a by-product, it is also proved that
the first cohomology group is trivial.Comment: 14 page
Ferromagnetic coupling and magnetic anisotropy in molecular Ni(II) squares
We investigated the magnetic properties of two isostructural Ni(II) metal
complexes [Ni4Lb8] and [Ni4Lc8]. In each molecule the four Ni(II) centers form
almost perfect regular squares. Magnetic coupling and anisotropy of single
crystals were examined by magnetization measurements and in particular by
high-field torque magnetometry at low temperatures. The data were analyzed in
terms of an effective spin Hamiltonian appropriate for Ni(II) centers. For both
compounds, we found a weak intramolecular ferromagnetic coupling of the four
Ni(II) spins and sizable single-ion anisotropies of the easy-axis type. The
coupling strengths are roughly identical for both compounds, whereas the
zero-field-splitting parameters are significantly different. Possible reasons
for this observation are discussed.Comment: 7 pages, 7 figure
Neutron-Capture Elements in the Early Galaxy: Insights from a Large Sample of Metal-Poor Giants
New abundances for neutron-capture (n-capture) elements in a large sample of
metal-poor giants from the Bond survey are presented. The spectra were acquired
with the KPNO 4-m echelle and coude feed spectrographs, and have been analyzed
using LTE fine-analysis techniques with both line analysis and spectral
synthesis. Abundances of eight n-capture elements (Sr, Y, Zr, Ba, La, Nd, Eu,
Dy) in 43 stars have been derived from blue (lambda = 4070--4710, R~20,000, S/N
ratio~100-200) echelle spectra and red (lambda = 6100--6180, R~22,000, S/N
ratio~100-200) coude spectra, and the abundance of Ba only has been derived
from the red spectra for an additional 27 stars. Overall, the abundances show
clear evidence for a large star-to-star dispersion in the heavy element-to-iron
ratios. The new data also confirm that at metallicities [Fe/H] <~ --2.4, the
abundance pattern of the heavy (Z >= 56) n-capture elements in most giants is
well-matched to a scaled Solar System r-process nucleosynthesis pattern. The
onset of the main r-process can be seen at [Fe/H] ~ --2.9. Contributions from
the s-process can first be seen in some stars with metallicities as low as
[Fe/H] ~ --2.75, and are present in most stars with metallicities [Fe/H] >
--2.3. The lighter n-capture elements (Sr-Y-Zr) are enhanced relative to the
heavier r-process element abundances. Their production cannot be attributed
solely to any combination of the Solar System r- and main s-processes, but
requires a mixture of material from the r-process and from an additional
n-capture process which can operate at early Galactic time.Comment: Text + 5 Tables and 11 Figures: Submitted to the Astrophysical
Journa
Influenza virus capture using membrane chromatography: Improving selectivity by matrix design and pseudo-affinity ligand interactions
Because next generation cell-based influenza vaccines have to be produced faster and in greater quantities than traditional vaccines, future purification processes will require more efficient unit operations for their isolation and purification. Membrane chromatography has already demonstrated a number of positive characteristics for the bind&elute purification of viral particles like e.g. adenoviruses or influenza viruses. The technology not only addresses the diffusion limitations of porous particle media but also offers dramatic advantages in binding capacity in a disposable format. Therefore, the last remaining challenge for the easy adoption of this technology in the vaccine industry represents selectivity and recovery. We present here a novel cellulose based stationary phase whose active specific surface area is designed for maximum virus accessibility. The resulting gain in selectivity and recovery but also in binding capacity is further maximized by using highly selective pseudo affinity ligands for influenza viruses
Model Exact Low-Lying States and Spin Dynamics in Ferric Wheels; Fe to Fe
Using an efficient numerical scheme that exploits spatial symmetries and
spin-parity, we have obtained the exact low-lying eigenstates of exchange
Hamiltonians for ferric wheels up to Fe. The largest calculation
involves the Fe ring which spans a Hilbert space dimension of about 145
million for M=0 subspace. Our calculated gaps from the singlet ground state
to the excited triplet state agrees well with the experimentally measured
values. Study of the static structure factor shows that the ground state is
spontaneously dimerized for ferric wheels. Spin states of ferric wheels can be
viewed as quantized states of a rigid rotor with the gap between the ground and
the first excited state defining the inverse of moment of inertia. We have
studied the quantum dynamics of Fe as a representative of ferric wheels.
We use the low-lying states of Fe to solve exactly the time-dependent
Schr\"odinger equation and find the magnetization of the molecule in the
presence of an alternating magnetic field at zero temperature. We observe a
nontrivial oscillation of magnetization which is dependent on the amplitude of
the {\it ac} field. We have also studied the torque response of Fe as a
function of magnetic field, which clearly shows spin-state crossover.Comment: Revtex, 24 pages, 8 eps figure
Masked suffix priming and morpheme positional constraints
Although masked stem priming (e.g., dealer\u2013DEAL) is one of the most established effects in visual word identification (e.g., Grainger et al., 1991), it is less clear whether primes and targets sharing a suffix (e.g., kindness\u2013WILDNESS) also yield facilitation (Giraudo & Grainger, 2003; Du\uf1abeitia et al., 2008). In a new take on this issue, we show that prime nonwords facilitate lexical decisions to target words ending with the same suffix (sheeter\uac\u2013TEACHER) compared to a condition where the critical suffix was substituted by another one (sheetal\u2013TEACHER) or by an unrelated non\u2013morphological ending (sheetub\u2013 TEACHER). We also show that this effect is genuinely morphological, as no priming emerged in non\u2013complex items with the same orthographic characteristics (sportel\u2013BROTHEL vs. sportic\u2013BROTHEL vs. sportur\u2013BROTHEL). In a further experiment, we took advantage of these results to assess whether suffixes are recognized in a position\u2013specific fashion. Masked suffix priming did not emerge when the relative order of stems and suffixes was reversed in the prime nonwords\u2014ersheet did not yield any time saving in the identification of teacher as compared to either alsheet or obsheet. We take these results to show that \u2013er was not identified as a morpheme in ersheet, thus indicating that suffix identification is position specific. This conclusion is in line with data on interference effects in nonword rejection (Crepaldi, Rastle, & Davis, 2010), and strongly constrains theoretical proposals on how complex words are identified. In particular, because these findings were reported in a masked priming paradigm, they suggest that positional constraints operate early, most likely at a pre\u2013lexical level of morpho\u2013orthographic analysi
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