368 research outputs found
Patterning molecular scale paramagnets at Au Surface: A root to Magneto-Molecular-Electronics
Few examples of the exploitation of molecular magnetic properties in
molecular electronics are known to date. Here we propose the realization of
Self assembled monolayers (SAM) of a particular stable organic radical. This
radical is meant to be used as a standard molecule on which to prove the
validity of a single spin reading procedure known as ESR-STM. We also discuss a
range of possible applications, further than ESR-STM, of magnetic monolayers of
simple purely organic magnetic molecule.Comment: This preprint is currently partially under revisio
Multi-storey Building Retrofit by ADAS- Equipped Braces
Incorporation of dissipative bracing systems is an emerging seismic retrofit strategy for frame structures. Among the
several types of devices currently adopted as passive protection elements, Added Damping and Stiffness (ADAS) steel
dissipaters have a well-established tradition. This is a consequence of their plain working principle, based on the
elastic-plastic behaviour of the constituting plates, as well as of their relatively easy installation. In spite of this, the
design of ADAS dampers is not simple, because it requires a proper balance between the addition of energy dissipation
and horizontal translational stiffness. An energy-based design criterion is formulated to this aim in this study, which
directly relates the total number of plates of the dissipaters to the supplemental damping energy needed to jointly
reduce stress states and storey drifts, expressly taking into account the reduction of the fundamental vibration period
due to the stiffening effect of the bracing system. A seismic retrofit intervention is demonstratively designed by
applying this criterion for a 6-storey building with reinforced concrete structure, an assessment analysis of which
shows poor seismic performance capacities. A comparative analysis among three different installation hypotheses of
the ADAS devices allows to select the distribution capable of attaining the best performance of the retrofit measure
Quantum Double and Differential Calculi
We show that bicovariant bimodules as defined by Woronowicz are in one to one
correspondence with the Drinfeld quantum double representations. We then prove
that a differential calculus associated to a bicovariant bimodule of dimension
n is connected to the existence of a particular (n+1)--dimensional
representation of the double. An example of bicovariant differential calculus
on the non quasitriangular quantum group E_q(2) is developed. The construction
is studied in terms of Hochschild cohomology and a correspondence between
differential calculi and 1-cocycles is proved. Some differences of calculi on
quantum and finite groups with respect to Lie groups are stressed.Comment: Revised version with added cohomological analysis. 14 pages, plain
te
Magnetic properties and spin dynamics in single molecule paramagnets Cu6Fe and Cu6Co
The magnetic properties and the spin dynamics of two molecular magnets have
been investigated by magnetization and d.c. susceptibility measurements,
Electron Paramagnetic Resonance (EPR) and proton Nuclear Magnetic Resonance
(NMR) over a wide range of temperature (1.6-300K) at applied magnetic fields,
H=0.5 and 1.5 Tesla. The two molecular magnets consist of
CuII(saldmen)(H2O)}6{FeIII(CN)6}](ClO4)38H2O in short Cu6Fe and the analog
compound with cobalt, Cu6Co. It is found that in Cu6Fe whose magnetic core is
constituted by six Cu2+ ions and one Fe3+ ion all with s=1/2, a weak
ferromagnetic interaction between Cu2+ moments through the central Fe3+ ion
with J = 0.14 K is present, while in Cu6Co the Co3+ ion is diamagnetic and the
weak interaction is antiferromagnetic with J = -1.12 K. The NMR spectra show
the presence of non equivalent groups of protons with a measurable contact
hyperfine interaction consistent with a small admixture of s-wave function with
the d-function of the magnetic ion. The NMR relaxation results are explained in
terms of a single ion (Cu2+, Fe3+, Co3+) uncorrelated spin dynamics with an
almost temperature independent correlation time due to the weak magnetic
exchange interaction. We conclude that the two molecular magnets studied here
behave as single molecule paramagnets with a very weak intramolecular
interaction, almost of the order of the dipolar intermolecular interaction.
Thus they represent a new class of molecular magnets which differ from the
single molecule magnets investigated up to now, where the intramolecular
interaction is much larger than the intermolecular one
Energy Barrier Enhancement by Ligand Substitution in Tetrairon(III) Single Molecule Magnets
A dramatic increase of the energy barrier (Ueff) in tetrairon(III) single-mol. magnets can be achieved by simple chem. modification. Site-specific replacement of the six methoxide bridges in [Fe4(OMe)6(dpm)6] (Hdpm = dipivaloylmethane; Ueff/kB = 3.5 K) with two tripodal 1,1,1-tris(hydroxymethyl)ethane (H3thme) ligands affords [Fe4(thme)2(dpm)6] with Ueff/kB = 15.6(2) K and a magnetic relaxation time exceeding 1000 s at T <0.2 K. The prepd. complex is trigonal, space group R-3c, Z = 6, R1 = 0.0370, R2 = 0.1089
Two fermion relativistic bound states: hyperfine shifts
We discuss the hyperfine shifts of the Positronium levels in a relativistic
framework, starting from a two fermion wave equation where, in addition to the
Coulomb potential, the magnetic interaction between spins is described by a
Breit term. We write the system of four first order differential equations
describing this model. We discuss its mathematical features, mainly in relation
to possible singularities that may appear at finite values of the radial
coordinate. We solve the boundary value problems both in the singular and non
singular cases and we develop a perturbation scheme, well suited for numerical
computations, that allows to calculate the hyperfine shifts for any level,
according to well established physical arguments that the Breit term must be
treated at the first perturbative order. We discuss our results, comparing them
with the corresponding values obtained from semi-classical expansions.Comment: 16 page
Integrated photonic structures for photon-mediated entanglement of trapped ions
Trapped atomic ions are natural candidates for quantum information processing
and have the potential to realize or improve quantum computing, sensing, and
networking. These applications often require the collection of individual
photons emitted from ions into guided optical modes, in some cases for the
production of entanglement between separated ions. Proof-of-principle
demonstrations of such photon collection from trapped ions have been performed
using high-numerical-aperture lenses and single-mode fibers, but integrated
photonic elements in ion-trap structures offer advantages in scalability and
manufacturabilty over traditional optics. In this paper we analyze structures
monolithically fabricated with an ion trap for collecting single photons from
ions, coupling them into integrated waveguides, and manipulating them via
interference. We discuss practical considerations for realizing photon-mediated
entanglement between trapped ions using these waveguide-based devices.Comment: 17 pages, 6 figures, 2 table
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