Substantial leaps in the understanding of quantum systems have been driven by exploring geometry, topology, dimensionality and interactions in ultracold atomic ensembles
. A system where atoms evolve ...while confined on an ellipsoidal surface represents a heretofore unexplored geometry and topology. Realizing an ultracold bubble-potentially Bose-Einstein condensed-relates to areas of interest including quantized-vortex flow constrained to a closed surface topology, collective modes and self-interference via bubble expansion
. Large ultracold bubbles, created by inflating smaller condensates, directly tie into Hubble-analogue expansion physics
. Here we report observations from the NASA Cold Atom Lab
facility onboard the International Space Station of bubbles of ultracold atoms created using a radiofrequency-dressing protocol. We observe bubble configurations of varying size and initial temperature, and explore bubble thermodynamics, demonstrating substantial cooling associated with inflation. We achieve partial coverings of bubble traps greater than one millimetre in size with ultracold films of inferred few-micrometre thickness, and we observe the dynamics of shell structures projected into free-evolving harmonic confinement. The observations are among the first measurements made with ultracold atoms in space, using perpetual freefall to explore quantum systems that are prohibitively difficult to create on Earth. This work heralds future studies (in orbital microgravity) of the Bose-Einstein condensed bubble, the character of its excitations and the role of topology in its evolution.
Abstract Non-Hermitian (NH) physics predicts open quantum system dynamics with unique topological features such as exceptional points and the NH skin effect. We show that this new paradigm of ...topological systems can serve as probes for bulk Hamiltonian parameters with quantum-enhanced sensitivity reaching Heisenberg scaling. Such enhancement occurs close to a spectral topological phase transition, where the entire spectrum undergoes a delocalization transition. We provide an explanation for this enhanced sensitivity based on the closing of point gap, which is a genuinely NH energy gap with no Hermitian counterpart. This establishes a direct connection between energy-gap closing and quantum enhancement in the NH realm. Our findings are demonstrated through several paradigmatic NH topological models in various dimensions and potential experimental implementations.
Extending the understanding of Bose-Einstein condensate (BEC) physics to new geometries and topologies has a long and varied history in ultracold atomic physics. One such new geometry is that of a ...bubble, where a condensate would be confined to the surface of an ellipsoidal shell. Study of this geometry would give insight into new collective modes, self-interference effects, topology-dependent vortex behavior, dimensionality crossovers from thick to thin shells, and the properties of condensates pushed into the ultradilute limit. Here we propose to implement a realistic experimental framework for generating shell-geometry BEC using radiofrequency dressing of magnetically trapped samples. Such a tantalizing state of matter is inaccessible terrestrially due to the distorting effect of gravity on experimentally feasible shell potentials. The debut of an orbital BEC machine (NASA Cold Atom Laboratory, aboard the International Space Station) has enabled the operation of quantum-gas experiments in a regime of perpetual freefall, and thus has permitted the planning of microgravity shell-geometry BEC experiments. We discuss specific experimental configurations, applicable inhomogeneities and other experimental challenges, and outline potential experiments.
The current goal on PEMFCs research points towards the optimization of devices working at temperatures above 100
°C and at low humidity levels. Acid-doped polybenzimidazoles are particularly ...appealing because of high proton conductivity without humidification and promising fuel cells performances.
In this paper we present the development of new proton conducting membranes based on different polybenzimidazole (PBI) structures. Phosphoric acid-doped membranes, synthesized from benzimidazole-based monomers with increased basicity and molecular weight, are presented and discussed. Test of methanol crossover and diffusion were performed in order to check the membrane suitability for DMFCs.
Both the acid doping level and proton conductivity remarkably increase with the membrane molecular weight and basicity, which strictly depend on the amount of NH-groups as well as on their position in the polymer backbone. In particular, a conductivity value exceeding 0.1
S
cm
−1 at RH
=
40% and 80
°C was reached in the case of the pyridine-based PBI.
Geometric phase in open systems Carollo, A; Fuentes-Guridi, I; Santos, M França ...
Physical review letters,
04/2003, Letnik:
90, Številka:
16
Journal Article
Recenzirano
Odprti dostop
We calculate the geometric phase associated with the evolution of a system subjected to decoherence through a quantum-jump approach. The method is general and can be applied to many different ...physical systems. As examples, two main sources of decoherence are considered: dephasing and spontaneous decay. We show that the geometric phase is completely insensitive to the former, i.e., it is independent of the number of jumps determined by the dephasing operator.
We generate coherent ultraviolet radiation at 313 nm as the third harmonic of an external-cavity diode laser. We use this radiation for laser cooling of trapped beryllium atomic ions and sympathetic ...cooling of co-trapped beryllium-hydride molecular ions. An LBO crystal in an enhancement cavity generates the second harmonic, and a BBO crystal in a doubly resonant enhancement cavity mixes this second harmonic with the fundamental to produce the third harmonic. Each enhancement cavity is preceded by a tapered amplifier to increase the fundamental light. The 36-mW output power of this all-semiconductor-gain system will enable quantum control of the beryllium ions' motion.
Schistosomiasis is a parasitic disease that affects more than 250 million people. The treatment is limited to praziquantel and the control of the intermediate host with the highly toxic molluscicidal ...niclosamide. Marine algae are a poorly explored and promising alternative that can provide lead compounds, and the use of multivariate analysis could contribute to quicker discovery. As part of our search for new natural compounds with which to control schistosomiasis, we screened 45 crude extracts obtained from 37 Brazilian seaweed species for their molluscicidal activity against
embryos and schistosomicidal activities against
. Two sets of extracts were taxonomically grouped for metabolomic analysis. The extracts were analyzed by GC-MS, and the data were subjected to Pattern Hunter and Pearson correlation tests. Overall, 22 species (60%) showed activity in at least one of the two models. Multivariate analysis pointed towards 3 hits against
veliger embryos in the
set, 5 hits against
blastula embryos, and 31 against
in the Ochrophyta set. Preliminary annotations suggested some compounds such as triquinane alcohols, prenylated guaianes, dichotomanes, and xenianes. Despite the putative identification, this work presents potential candidates and can guide future isolation and identification.
Plants produce a wide range of secondary metabolites. Within a single species, chemotypes can be distinguished by the differences in the composition of the secondary metabolites. Herein, we evaluated ...Nectandra megapotamica (Spreng.) chemotypes and the balance of different classes of metabolites to verify how significant differences in plant metabolism are regarding chemotypes. We collected N. megapotamica leaves from eight adult plants in two Brazilian states. The essential oils and ethanol/water extracts were analyzed by GC-MS and LC-DAD-MS, respectively. Histochemical tests were performed, as well as chemical analyses of leaves from adaxial and abaxial foliar surfaces of N. megapotamica, and the stereochemistry of α-bisabolol was determined. Two different chemotypes, based on volatile compounds, were identified, distinguished by the presence of isospathulenol, α-bisabolol, β-bisabolene, and (E)-nerolidol for chemotype A, and bicyclogermacrene and elemicin for chemotype B. A stereochemical analysis of chemotype A extract revealed (+)-α-bisabolol enantiomer. Histochemical tests of chemotypes showed similar results and suggested the presence of essential oil in idioblasts stained with the dye NADI. The analyses of chemotype A leaves by GC-MS revealed similar compositions for abaxial and adaxial surfaces, such pattern was also observed for chemotype B. Medium and high polarity metabolites showed high chemical similarities between the chemotypes, highlighting the presence of proanthocyanidins and glycosylated flavonoids (O- and C-glycosides). Thus, N. megapotamica produced distinct volatile chemotypes with highly conserved medium to high polarity compounds. Such results suggest that phenolic derivatives have a basal physiological function, while genetic or environmental differences lead to differentiation in volatile profiles of N. megapotamica.
Coloration of plant organs such as fruit, leaves and flowers through anthocyanin production is governed by a combination of MYB and bHLH type transcription factors (TFs). In this study we introduced ...Rosea1 (ROS1, a MYB type) and Delila (DEL, a bHLH type), into Nicotiana benthamiana leaves by agroinfiltration. ROS1 and DEL form a pair of well-characterized TFs from Snapdragon (Antirrhinum majus), which specifically induce anthocyanin accumulation when expressed in tomato fruit. In N. benthamiana, robust induction of a single anthocyanin, delphinidin-3-rutinoside (D3R) was observed after expression of both ROS1 and DEL. Surprisingly in addition to D3R, a range of additional metabolites were also strongly and specifically up-regulated upon expression of ROS1 and DEL. Except for the D3R, these induced compounds were not derived from the flavonoid pathway. Most notable among these are nornicotine conjugates with butanoyl, hexanoyl, and octanoyl hydrophobic moieties, and phenylpropanoid-polyamine conjugates such as caffeoyl putrescine. The defensive properties of the induced molecules were addressed in bioassays using the tobacco specialist lepidopteran insect Manduca sexta. Our study showed that the effect of ROS1 and DEL expression in N. benthamiana leaves extends beyond the flavonoid pathway. Apparently the same transcription factor may regulate different secondary metabolite pathways in different plant species.
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