569 research outputs found
On the feasibility of studying vortex noise in 2D superconductors with cold atoms
We investigate the feasibility of using ultracold neutral atoms trapped near
a thin superconductor to study vortex noise close to the
Kosterlitz-Thouless-Berezinskii transition temperature. Alkali atoms such as
rubidium probe the magnetic field produced by the vortices. We show that the
relaxation time of the Zeeman sublevel populations can be conveniently
adjusted to provide long observation times. We also show that the transverse
relaxation times for Zeeman coherences are ideal for studying the vortex
noise. We briefly consider the motion of atom clouds held close to the surface
as a method for monitoring the vortex motion.Comment: 4 pages, 1 figur
Programmable trap geometries with superconducting atom chips
We employ the hysteretic behavior of a superconducting thin film in the
remanent state to generate different traps and flexible magnetic potentials for
ultra-cold atoms. The trap geometry can be programmed by externally applied
fields. This new approach for atom-optics is demonstrated by three different
trap types realized on a single micro-structure: a Z-type trap, a double trap
and a bias field free trap. Our studies show that superconductors in the
remanent state provide a new versatile platform for atom-optics and
applications in ultra-cold quantum gases
The Utrecht-Management of IdentityCommitments Scale (U-MICS)Italian Validation and Cross-National Comparisons
The present study examined the psychometric properties of the Dutch and Italian versions of the Utrecht-Management of
Identity Commitments Scale (U-MICS) in large community samples of adolescents from Italy (N = 1,975) and The Netherlands (N =
1,521). Confirmatory factor analyses indicated that the three-factor model, consisting of commitment, in-depth exploration, and reconsideration
of commitment, provided a better fit to the data than alternative one- and two-factor models. The three-factor model fit
equivalently across sex and across age groups (early and middle adolescents). Furthermore, we demonstrated cross-national equivalence
of the factor structure of the U-MICS. Additionally, results indicated that the latent means for commitment were higher in the Dutch
sample, while latent means for both in-depth exploration and reconsideration of commitment were substantially higher in the Italian
sample. The three identity processes were found to be meaningfully related to measures of self-concept, psychosocial problems, and
parent-adolescent relations in both countries. These findings suggest that the U-MICS is a reliable tool for assessing identity processes
in Italian and Dutch adolescents
Sensitivity of a cavityless optomechanical system
We study the possibility of revealing a weak coherent force by using a
pendular mirror as a probe, and coupling this to a radiation field, which acts
as the meter, in a cavityless configuration. We determine the sensitivity of
such a scheme and show that the use of an entangled meter state greatly
improves the ultimate detection limit. We also compare this scheme with that
involving an optical cavity.Comment: 4 pages, RevTex file, 2 eps figures, provisionally accepted by Phys.
Rev.
Conformational Disorder Analysis of the Conditionally Disordered Protein CP12 from Arabidopsis thaliana in Its Different Redox States
CP12 is a redox-dependent conditionally disordered protein universally distributed in oxygenic photosynthetic organisms. It is primarily known as a light-dependent redox switch regulating the reductive step of the metabolic phase of photosynthesis. In the present study, a small angle X-ray scattering (SAXS) analysis of recombinant Arabidopsis CP12 (AtCP12) in a reduced and oxidized form confirmed the highly disordered nature of this regulatory protein. However, it clearly pointed out a decrease in the average size and a lower level of conformational disorder upon oxidation. We compared the experimental data with the theoretical profiles of pools of conformers generated with different assumptions and show that the reduced form is fully disordered, whereas the oxidized form is better described by conformers comprising both the circular motif around the C-terminal disulfide bond detected in previous structural analysis and the N-terminal disulfide bond. Despite the fact that disulfide bridges are usually thought to confer rigidity to protein structures, in the oxidized AtCP12, their presence coexists with a disordered nature. Our results rule out the existence of significant amounts of structured and compact conformations of free AtCP12 in a solution, even in its oxidized form, thereby highlighting the importance of recruiting partner proteins to complete its structured final folding
Cholesterol derivatives make large part of the lipids from epidermal molts of the desert-adapted Gila monster lizard (Heloderma suspectum)
In order to understand the cutaneous water loss in the desert-adapted and venomous lizard Heloderma suspectum, the microscopic structure and lipid composition of epidermal molts have been examined using microscopic, spectroscopic and chemical analysis techniques. The molt is formed by a variably thick, superficial beta-layer, an extensive mesos-region and few alpha-cells in its lowermost layers. The beta-layer contains most corneous beta proteins while the mesos-region is much richer in lipids. The proteins in the mesos-region are more unstructured than those located in the beta-layer. Most interestingly, among other lipids, high contents of cholesteryl-β-glucoside and cholesteryl sulfate were detected, molecules absent or present in traces in other species of squamates. These cholesterol derivatives may be involved in the stabilization and compaction of the mesos-region, but present a limited permeability to water movements. The modest resistance to cutaneous water-loss of this species is compensated by adopting other physiological strategies to limit thermal damage and water transpiration as previous eco-physiological studies have indicated. The increase of steroid derivatives may also be implicated in the heat shock response, influencing the relative behavior in this desert-adapted lizard
Trapping cold atoms near carbon nanotubes: thermal spin flips and Casimir-Polder potential
We investigate the possibility to trap ultracold atoms near the outside of a
metallic carbon nanotube (CN) which we imagine to use as a miniaturized
current-carrying wire. We calculate atomic spin flip lifetimes and compare the
strength of the Casimir-Polder potential with the magnetic trapping potential.
Our analysis indicates that the Casimir-Polder force is the dominant loss
mechanism and we compute the minimum distance to the carbon nanotube at which
an atom can be trapped.Comment: 8 pages, 3 figure
Exploring Coral Calcification by Calcium Carbonate Overgrowth Experiments
The Scleractinia coral biomineralization process is a representative example of a heterogeneous process of nudeation and growth of biogenic CaCO3 over a mineral phase. Indeed, even if the biomineralization process starts before settlement, the bulk formation of the skeleton takes place only when the larvae attach to a solid substrate, which can be Mg-calcite from coralline algae, and the following growth proceeds on the Mg-calcite surface of the formed baseplate of the planula. Despite this peculiarity and central role of the Mg-calcite substrate, the in vitro overgrowth of CaCO3 on single crystals of Mg-calcite, or calcite, in the presence of magnesium ions and the soluble organic matrix (SOM) extracted from coral skeletons has not been performed until now. In this study, the SOMs from Stylophora pistillata and Oculina patagonica skeletons were used in a set of overgrowth experiments. The overgrown CaCO3 was characterized by microscopic, diffractometric, and spectroscopic techniques. Our results showed that CaCO3 overgrowth in the presence of S. pistillata or O. patagonica SOM produces different effects. However, there appears to be a minor distinction between samples when magnesium ions are present in solution. Moreover, the Mg-calcite substrate appears to be a favorable substrate for the overgrowth of aragonite, differently from calcite. These observations fit with the observed settling of coral larvae on Mg-calcite-based substrates and with the in vivo observation that in the planula aragonite forms on first-formed Mg-calcite crystals. The overall results of this study highlight the importance of magnesium ions, either in the solution or in the substrate, in defining the shape, morphology, and polymorphism of biodeposited CaCO3. They also suggest a magnesium-dependent biological control on the deposition of coral skeletons
Recovering and Exploiting Aragonite and Calcite Single Crystals with Biologically Controlled Shapes from Mussel Shells
Control over the shape and morphology of single
crystals is a theme of great interest in fundamental science and for
technological application. Many synthetic strategies to achieve this
goal are inspired by biomineralization processes. Indeed, organisms
are able to produce crystals with high fidelity in shape and
morphology utilizing macromolecules that act as modifiers. An
alternative strategy can be the recovery of crystals from
biomineralization products, in this case, seashells. In particular,
waste mussel shells from aquaculture are considered. They are
mainly built up of single crystals of calcite fibers and aragonite
tablets forming an outer and an inner layer, respectively. A simple
mechanochemical treatment has been developed to separate and
recover these two typologies of single crystals. The characterization
of these single crystals showed peculiar properties with respect to the calcium carbonate from quarry or synthesis. We exploited these
biomaterials in the water remediation field using them as substrate adsorbing dyes. We found that these substrates show a high
capability of adsorption for anionic dye, such as Eosin Y, but a low capability of adsorption for cationic dyes, such as Blue Methylene.
The adsorption was reversible at pH 5.6. This application represents just an example of the potential use of these biogenic single
crystals. We also envision potential applications as reinforcing fillers and optical devices
Trapping of ultra-cold atoms with the magnetic field of vortices in a thin film superconducting micro-structure
We store and control ultra-cold atoms in a new type of trap using magnetic
fields of vortices in a high temperature superconducting micro-structure. This
is the first time ultra-cold atoms have been trapped in the field of magnetic
flux quanta. We generate the attractive trapping potential for the atoms by
combining the magnetic field of a superconductor in the remanent state with
external homogeneous magnetic fields. We show the control of crucial atom trap
characteristics such as an efficient intrinsic loading mechanism, spatial
positioning of the trapped atoms and the vortex density in the superconductor.
The measured trap characteristics are in good agreement with our numerical
simulations.Comment: 4pages, comments are welcom
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