3,790 research outputs found
Enhancement of vortex pinning in superconductor/ferromagnet bilayers via angled demagnetization
We use local and global magnetometry measurements to study the influence of
magnetic domain width w on the domain-induced vortex pinning in
superconducting/ferromagnetic bilayers, built of a Nb film and a ferromagnetic
Co/Pt multilayer with perpendicular magnetic anisotropy, with an insulating
layer to eliminate proximity effect. The quasi-periodic domain patterns with
different and systematically adjustable width w, as acquired by a special
demagnetization procedure, exert tunable vortex pinning on a superconducting
layer. The largest enhancement of vortex pinning, by a factor of more than 10,
occurs when w ~ 310 nm is close to the magnetic penetration depth.Comment: 5 pages, 3 figures, accepted to Phys. Rev. B, Rapid Communication
Archiving scientific data
We present an archiving technique for hierarchical data with key structure. Our approach is based on the notion of timestamps whereby an element appearing in multiple versions of the database is stored only once along with a compact description of versions in which it appears. The basic idea of timestamping was discovered by Driscoll et. al. in the context of persistent data structures where one wishes to track the sequences of changes made to a data structure. We extend this idea to develop an archiving tool for XML data that is capable of providing meaningful change descriptions and can also efficiently support a variety of basic functions concerning the evolution of data such as retrieval of any specific version from the archive and querying the temporal history of any element. This is in contrast to diff-based approaches where such operations may require undoing a large number of changes or significant reasoning with the deltas. Surprisingly, our archiving technique does not incur any significant space overhead when contrasted with other approaches. Our experimental results support this and also show that the compacted archive file interacts well with other compression techniques. Finally, another useful property of our approach is that the resulting archive is also in XML and hence can directly leverage existing XML tools
Diversity and hierarchy in supramolecular assemblies of triphenylalanine: from laminated helical ribbons to toroids
Microstructures from small phenylalanine-based peptides have attracted great attention lately because these compounds are considered to be a new class of tunable materials. In spite of the extensive studies on uncapped diphenylalanine and tetraphenylalanine peptides, studies on the self-assembly of uncapped triphenylananine (FFF) are very scarce and nonsystematic. In this work, we demonstrate that FFF assemblies can organize in a wide number of well-defined supramolecular structures, which include laminated helical-ribbons, leaflike dendrimers, doughnut-, needle-, and flower-shapes. These organizations are produced by the attractive or repulsive interactions between already formed assemblies and therefore can be controlled through the choice of solvents used as the incubation medium. Thus, the formation of the desired supramolecular structures is regulated through the protonation/deprotonation of the terminal groups, the polarity of the incubation medium, which affects both peptide···solvent interactions and the cavity solvation energy (i.e., solvent···solvent interactions), and the steric interactions between own assemblies that act as building blocks. Finally, the ß-sheet disposition in the latter structural motifs has been examined using both theoretical calculations and Fourier transform infrared spectroscopy. Results indicate that FFF molecules can adopt both parallel and antiparallel ß-sheets. However, the former one is the most energetically favored because of the formation of p–p stacking interactions between the aromatic rings of hydrogen-bonded strands.Preprin
Coherent dynamics of a photon-dressed qubit
We consider the dynamics and stationary regime of a capacitively-shunted
transmon-type qubit in front of a mirror, affected by two signals: probe and
dressing signals. By varying the parameters of these signals and then analyzing
the probe signal (reflected by the atom-mirror system), it is possible to
explore the system dynamics, which can be described by the Bloch equation. The
obtained time-dependent occupation probabilities are related to the
experimentally measured reflection coefficient. The study of this type of
dynamics opens up new horizons for better understanding of the system
properties and underlying physical processes, such as
Landau-Zener-Stuckelberg-Majorana transitions
Disorder and transport in cuprates: weak localization and magnetic contributions
We report resistivity measurements in underdoped YBaCuOand overdoped TlBaCuO single crystals in which the
concentration of defects in the CuO planes is controlled by electron
irradiation. Low upturns of the resistivity are observed in both cases for
large defect content. In the Tl compound the decrease of conductivity scales as
expected from weak localization theory. On the contrary in
YBaCuO the much larger low T contribution to the
resistivity is proportional to the defect content and might then be associated
to a Kondo like spin flip scattering term. This would be consistent with the
results on the magnetic properties induced by spinless defects.Comment: latex rullier1.tex, 5 files, 4 pages [SPEC-S01/003], submitted to
Phys. Rev. Let
Methionine Adenosyltransferase I/III Deficiency in Portugal: High Frequency of a Dominantly Inherited Form in a Small Area of Douro High Lands
Methionine adenosyltransferase deficienc(MAT I/III deficiency) is an inborn error of metabolism resulting in isolated hypermethioninemia, and usually inherited as an autosomal recessive trait, although a dominant form has been reported in several families. During the last 6 years, approximately 520,000 newborns were screened in the Portuguese Newborn Screening Laboratory by MS/MS, and 21 cases of persistent hypermethioninemia were found. One case was confirmed to be a deficiency of cystathionine b-synthase and 20 cases were confirmed by MAT1A gene analysis to have an elevation of methionine due to MAT I/III deficiency, which indicates an incidence for this condition of 1/26,000. Twelve of the MAT I/III deficient newborns, belonging to 11 families, were identified in the northern region of Portugal and sent to the same treatment center, where they are under follow-up. Clinical, biochemical, and genetic characteristics of individuals from these 11 families are presented. Plasma methionine and homocysteine concentrations were found to be moderately increased in all
newborns, and molecular analysis revealed that they all were heterozygous for R264H mutation. Normal growth,development, and neurological examination were observed in all cases, and cerebral MRI performed in six cases revealed myelination abnormalities in one case. Plasma methionine concentration for all 12 cases was always below 300 mM, and they are all on a normal diet for their age
Extended Impurity Potential in a d_{x^2-y^2} Superconductor
We investigate the role of a finite potential range of a nonmagnetic impurity
for the local density of states in a d_{x^2-y^2} superconductor. Impurity
induced subgap resonances are modified by the appearance of further scattering
channels beyond the --wave scattering limit. The structure of the local
density of states (DOS) in the vicinity of the impurity is significantly
enhanced and therefore improves the possibility for observing the
characteristic anisotropic spatial modulation of the local DOS in a d_{x^2-y^2}
superconductor by scanning tunneling microscopy.Comment: 4 pages, Revtex, with 4 embedded eps figures. Submitted to Phys. Rev.
Let
Spin-charge conversion in multiterminal Aharonov-Casher ring coupled to precessing ferromagnets: A charge conserving Floquet-nonequilibrium Green function approach
We derive a non-perturbative solution to the Floquet-nonequilibrium Green
function (Floquet-NEGF) describing open quantum systems periodically driven by
an external field of arbitrary strength of frequency. By adopting the
reduced-zone scheme, we obtain expressions rendering conserved charge currents
for any given maximum number of photons, distinguishable from other existed
Floquet-NEGF-based expressions where, less feasible, infinite number of photons
needed to be taken into account to ensure the conservation. To justify our
derived formalism and to investigate spin-charge conversions by spin-orbit
coupling (SOC), we consider the spin-driven setups as reciprocal to the
electric-driven setups in S. Souma et. al., Phys. Rev. B 70, 195346 (2004) and
Phys. Rev. Lett. 94, 106602 (2005). In our setups, pure spin currents are
driven by the magnetization dynamics of a precessing ferromagnetic (FM) island
and then are pumped into the adjacent two- or four-terminal mesoscopic
Aharonov-Casher (AC) ring of Rashba SOC where spin-charge conversions take
place. Our spin-driven results show reciprocal features that excellently agree
with the findings in the electric-driven setups mentioned above. We propose two
types of symmetry operations, under which the AC ring Hamiltonian is invariant,
to argue the relations of the pumped/converted currents in the leads within the
same or between different pumping configurations. The symmetry arguments are
independent of the ring width and the number of open channels in the leads,
terminals, and precessing FM islands, In particular, net pure in-plane spin
currents and pure spin currents can be generated in the leads for certain
setups of two terminals and two precessing FM islands with the current
magnitude and polarization direction tunable by the pumping configuration, gate
voltage covering the two-terminal AC ring in between the FM islands.Comment: Submitted to Physical Review
Imbalanced Superfluid Phase of a Trapped Fermi Gas in the BCS-BEC Crossover Regime
We theoretically investigate the ground state of trapped neutral fermions
with population imbalance in the BCS-BEC crossover regime. On the basis of the
single-channel Hamiltonian, we perform full numerical calculations of the
Bogoliubov-de Gennes equation coupled with the regularized gap and number
equations. The zero-temperature phase diagram in the crossover regime is
presented, where the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing state
governs the weak-coupling BCS region of a resonance. It is found that the FFLO
oscillation vanishes in the BEC side, in which the system under population
imbalance turns into a phase separation (PS) between locally binding superfluid
and fully polarized spin domains. We also demonstrate numerical calculations
with a large particle number O(10^5), comparable to that observed in recent
experiments. The resulting density profile on a resonance yields the PS, which
is in good agreement with the recent experiments, while the FFLO modulation
exists in the pairing field. It is also proposed that the most favorable
location for the detection of the FFLO oscillation is in the vicinity of the
critical population imbalance in the weak coupling BCS regime, where the
oscillation periodicity becomes much larger than the interparticle spacing.
Finally, we analyze the radio-frequency (RF) spectroscopy in the imbalanced
system. The clear difference in the RF spectroscopy between BCS and BEC sides
reveals the structure of the pairing field and local ``magnetization''.Comment: 16 pages, 13 figures, replaced by the version to appear in J. Phys.
Soc. Jp
Asymmetric Domain Nucleation and Unusual Magnetization Reversal in Ultrathin Co Films with Perpendicular Anisotropy
We report unexpected phenomena during magnetization reversal in ultrathin Co films and Co/Pt multilayers with perpendicular anisotropy. Using magneto-optical Kerr microscopy and magnetic force microscopy we have observed asymmetrical nucleation centers where the reversal begins for one direction of the field only and is characterized by an acute asymmetry of domain-wall mobility. We have also observed magnetic domains with a continuously varying average magnetization, which can be explained in terms of the coexistence of three magnetic phases: up, down, and striped
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