5,179 research outputs found
Structural variability of 4f and 5f thiocyanate complexes and dissociation of uranium(III)–thiocyanate bonds with increased ionicity
A series of complexes [Et4N][Ln(NCS)4(H2O)4] (Ln = Pr, Tb, Dy, Ho, Yb) have been structurally characterized, all showing the same structure, namely a distorted square antiprismatic coordination geometry, and the Ln–O and Ln–N bond lengths following the expected lanthanide contraction. When the counterion is Cs+, a different structural motif is observed and the eight-coordinate complex Cs5[Nd(NCS)8] isolated. The thorium compounds [Me4N]4[Th(NCS)7(NO3)] and [Me4N]4[Th(NCS)6(NO3)2] have been characterized, and high coordination numbers are also observed. Finally, attempts to synthesize a U(III) thiocyanate compound has been unsuccessful; from the reaction mixture, a heterocycle formed by condensation of five MeCN solvent molecules, possibly promoted by U(III), was isolated and structurally characterized. To rationalize the inability to isolate U(III) thiocyanate compounds, thin-layer cyclic voltammetry and IR spectroelectrochemistry have been utilized to explore the cathodic behavior of [Et4N]4[U(NCS)8] and [Et4N][U(NCS)5(bipy)2] along with a related uranyl compound [Et4N]3[UO2(NCS)5]. In all examples, the reduction triggers a rapid dissociation of [NCS]− ions and decomposition. Interestingly, the oxidation chemistry of [Et4N]3[UO2(NCS)5] in the presence of bipy gives the U(IV) compound [Et4N]4[U(NCS)8], an unusual example of a ligand-based oxidation triggering a metal-based reduction. The experimental results have been augmented by a computational investigation, concluding that the U(III)–NCS bond is more ionic than the U(IV)–NCS bond
A survey of spinning test particle orbits in Kerr spacetime
We investigate the dynamics of the Papapetrou equations in Kerr spacetime.
These equations provide a model for the motion of a relativistic spinning test
particle orbiting a rotating (Kerr) black hole. We perform a thorough parameter
space search for signs of chaotic dynamics by calculating the Lyapunov
exponents for a large variety of initial conditions. We find that the
Papapetrou equations admit many chaotic solutions, with the strongest chaos
occurring in the case of eccentric orbits with pericenters close to the limit
of stability against plunge into a maximally spinning Kerr black hole. Despite
the presence of these chaotic solutions, we show that physically realistic
solutions to the Papapetrou equations are not chaotic; in all cases, the
chaotic solutions either do not correspond to realistic astrophysical systems,
or involve a breakdown of the test-particle approximation leading to the
Papapetrou equations (or both). As a result, the gravitational radiation from
bodies spiraling into much more massive black holes (as detectable, for
example, by LISA, the Laser Interferometer Space Antenna) should not exhibit
any signs of chaos.Comment: Submitted to Phys. Rev. D. Follow-up to gr-qc/0210042. Figures are
low-resolution in order to satisfy archive size constraints; a
high-resolution version is available at http://www.michaelhartl.com/papers
Dimer, trimer and FFLO liquids in mass- and spin-imbalanced trapped binary mixtures in one dimension
We present a systematic investigation of attractive binary mixtures in
presence of both spin- and mass-imbalance in one dimensional setups described
by the Hubbard model. After discussing typical cold atomic experimental
realizations and the relation between microscopic and effective parameters, we
study several many-body features of trapped Fermi-Fermi and Bose-Bose mixtures
such as density profiles, momentum distributions and correlation functions by
means of numerical density-matrix-renormalization-group and Quantum Monte Carlo
simulations. In particular, we focus on the stability of
Fulde-Ferrell-Larkin-Ovchinnikov, dimer and trimer fluids in inhomogeneous
situations, as typically realized in cold gas experiments due to the harmonic
confinement. We finally consider possible experimental signatures of these
phases both in the presence of a finite polarization and of a finite
temperature.Comment: 19 pages, 25 figure
An aperture masking mode for the MICADO instrument
MICADO is a near-IR camera for the Europea ELT, featuring an extended field
(75" diameter) for imaging, and also spectrographic and high contrast imaging
capabilities. It has been chosen by ESO as one of the two first-light
instruments. Although it is ultimately aimed at being fed by the MCAO module
called MAORY, MICADO will come with an internal SCAO system that will be
complementary to it and will deliver a high performance on axis correction,
suitable for coronagraphic and pupil masking applications. The basis of the
pupil masking approach is to ensure the stability of the optical transfer
function, even in the case of residual errors after AO correction (due to non
common path errors and quasi-static aberrations). Preliminary designs of pupil
masks are presented. Trade-offs and technical choices, especially regarding
redundancy and pupil tracking, are explained.Comment: SPIE 2014 Proceeding -- Montrea
Broadband Phase-Noise Suppression in a Yb-Fiber Frequency Comb
We report a simple technique to suppress high frequency phase noise of a
Yb-based fiber optical frequency comb using an active intensity noise servo.
Out-of-loop measurements of the phase noise using an optical heterodyne beat
with a continuous wave (cw) laser show suppression of phase noise by \geq7 dB
out to Fourier frequencies of 100 kHz with a unity-gain crossing of -700 kHz.
These results are enabled by the strong correlation between the intensity and
phase noise of the laser. Detailed measurements of intensity and phase noise
spectra, as well as transfer functions, reveal that the dominant phase and
intensity noise contribution above -100 kHz is due to amplified spontaneous
emission (ASE) or other quantum noise sources.Comment: 4 pages, 3 figure
Fokker-Planck and Landau-Lifshitz-Bloch Equations for Classical Ferromagnets
A macroscopic equation of motion for the magnetization of a ferromagnet at
elevated temperatures should contain both transverse and longitudinal
relaxation terms and interpolate between Landau-Lifshitz equation at low
temperatures and the Bloch equation at high temperatures. It is shown that for
the classical model where spin-bath interactions are described by stochastic
Langevin fields and spin-spin interactions are treated within the mean-field
approximation (MFA), such a ``Landau-Lifshitz-Bloch'' (LLB) equation can be
derived exactly from the Fokker-Planck equation, if the external conditions
change slowly enough. For weakly anisotropic ferromagnets within the MFA the
LLB equation can be written in a macroscopic form based on the free-energy
functional interpolating between the Landau free energy near T_C and the
``micromagnetic'' free energy, which neglects changes of the magnetization
magnitude |{\bf M}|, at low temperatures.Comment: 9 pages, no figures, a small error correcte
Local and nonlocal solvable structures in ODEs reduction
Solvable structures, likewise solvable algebras of local symmetries, can be
used to integrate scalar ODEs by quadratures. Solvable structures, however, are
particularly suitable for the integration of ODEs with a lack of local
symmetries. In fact, under regularity assumptions, any given ODE always admits
solvable structures even though finding them in general could be a very
difficult task. In practice a noteworthy simplification may come by computing
solvable structures which are adapted to some admitted symmetry algebra. In
this paper we consider solvable structures adapted to local and nonlocal
symmetry algebras of any order (i.e., classical and higher). In particular we
introduce the notion of nonlocal solvable structure
Peptide substrate identification for yeast Hsp40 Ydj1 by screening the phage display library
We have identified a peptide substrate for molecular chaperone Hsp40 Ydj1 by utilizing the combination of phage display library screening and isothemol titration calirimetry (ITC). The initial peptide substrate screening for Hsp40 Ydj1 has been carried out by utilizing a 7-mer phage display library. The peptide sequences from the bio-panning were synthesized and object to the direct affinity measurement for Hsp40 Ydj1 by isothemol titration calirimetry studies. The peptide which has the measurable affinity with Ydj1 shows enriched hydrophobic residues in the middle of the substrate fragment. The peptide substrate specificity for molecular chaperone Hsp40 has been analyzed
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