5,584 research outputs found
Microscopic Analysis of Low-Frequency Flux Noise in YBaCuO Direct Current Superconducting Quantum Interference Devices
We use low-temperature scanning electron microscopy combined with SQUID
detection of magnetic flux to image vortices and to investigate low-frequency
flux noise in YBaCuO thin film SQUIDs. The low-frequency flux noise
shows a nonlinear increase with magnetic cooling field up to 60 T. This
effect is explained by the surface potential barrier at the SQUID hole. By
correlating flux noise data with the spatial distribution of vortices, we
obtain information on spatial fluctuations of vortices on a microscopic scale,
e.g. an average vortex hopping length of approximately 10 nm.Comment: submitted to Applied Physics Letter
Probing the Mechanisms of Fibril Formation Using Lattice Models
Using exhaustive Monte Carlo simulations we study the kinetics and mechanism
of fibril formation using lattice models as a function of temperature and the
number of chains. While these models are, at best, caricatures of peptides, we
show that a number of generic features thought to govern fibril assembly are
present in the toy model. The monomer, which contains eight beads made from
three letters (hydrophobic, polar, and charged), adopts a compact conformation
in the native state. The kinetics of fibril assembly occurs in three distinct
stages. In each stage there is a cascade of events that transforms the monomers
and oligomers to ordered structures. In the first "burst" stage highly mobile
oligomers of varying sizes form. The conversion to the aggregation-prone
conformation occurs within the oligomers during the second stage. As time
progresses, a dominant cluster emerges that contains a majority of the chains.
In the final stage, the aggregation-prone conformation particles serve as a
template onto which smaller oligomers or monomers can dock and undergo
conversion to fibril structures. The overall time for growth in the latter
stages is well described by the Lifshitz-Slyazov growth kinetics for
crystallization from super-saturated solutions.Comment: 27 pages, 6 figure
Biological synthesis of fluorescent nanoparticles by cadmium and tellurite resistant Antarctic bacteria: exploring novel natural nanofactories
Indexación: Web of ScienceBackground: Fluorescent nanoparticles or quantum dots (QDs) have been intensely studied for basic and applied research due to their unique size-dependent properties. There is an increasing interest in developing ecofriendly methods to synthesize these nanoparticles since they improve biocompatibility and avoid the generation of toxic byproducts. The use of biological systems, particularly prokaryotes, has emerged as a promising alternative. Recent studies indicate that QDs biosynthesis is related to factors such as cellular redox status and antioxidant defenses. Based on this, the mixture of extreme conditions of Antarctica would allow the development of natural QDs producing bacteria.
Results: In this study we isolated and characterized cadmium and tellurite resistant Antarctic bacteria capable of synthesizing CdS and CdTe QDs when exposed to these oxidizing heavy metals. A time dependent change in fluorescence emission color, moving from green to red, was determined on bacterial cells exposed to metals. Biosynthesis was observed in cells grown at different temperatures and high metal concentrations. Electron microscopy analysis of treated cells revealed nanometric electron-dense elements and structures resembling membrane vesicles mostly associated to periplasmic space. Purified biosynthesized QDs displayed broad absorption and emission spectra characteristic of biogenic Cd nanoparticles.
Conclusions: Our work presents a novel and simple biological approach to produce QDs at room temperature by using heavy metal resistant Antarctic bacteria, highlighting the unique properties of these microorganisms as potent natural producers of nano-scale materials and promising candidates for bioremediation purposes.http://microbialcellfactories.biomedcentral.com/articles/10.1186/s12934-016-0477-
Propensity to form amyloid fibrils is encoded as excitations in the free energy landscape of monomeric proteins
Protein aggregation, linked to many of diseases, is initiated when monomers
access rogue conformations that are poised to form amyloid fibrils. We show,
using simulations of src SH3 domain, that mechanical force enhances the
population of the aggregation prone () states, which are rarely populated
under force free native conditions, but are encoded in the spectrum of native
fluctuations. The folding phase diagrams of SH3 as a function of denaturant
concentration (), mechanical force (), and temperature exhibit an
apparent two-state behavior, without revealing the presence of the elusive
states. Interestingly, the phase boundaries separating the folded and
unfolded states at all [C] and fall on a master curve, which can can be
quantitatively described using an analogy to superconductors in a magnetic
field. The free energy profiles as a function of the molecular extension (),
which are accessible in pulling experiments, (), reveal the presence of a
native-like with a disordered solvent-exposed amino terminal
-strand. The structure of the state is identical to that found in
Fyn SH3 by NMR dispersion experiments. We show that the time scale for fibril
formation can be estimated from the population of the state, determined
by the free energy gap separating the native structure and the state, a
finding that can be used to assess fibril forming tendencies of proteins. The
structures of the state are used to show that oligomer formation and
likely route to fibrils occur by a domain-swap mechanism in SH3 domain.Comment: 12 pages, 8 figures, 9 supplementary figures (on 5 more pages), 2
supplementary movies (on youtube
New physics searches in flavour physics
The origin of flavour and CP violation is among the most important open questions in particle physics. Imminent results from the LHC as well as planned dedicated flavour physics experiments might help to shed light on this puzzle. This talk concentrates on the NP sensitivity of the rare B decays Bs,d → μ+μ− and B → K∗μ−μ− and of the CP-violating phase in Bs mixing. A brief summary of a
supersymmetric model with interesting signatures in the flavour sector is presented
Protectionist Responses to the Crisis: Global Trends and Implications
In this paper we take a systematic look at recent trends in global protectionism and at the potential implications of a protectionist backlash for economic growth, using results from the recent economic literature and new model simulations. We find that there has so far been a moderate increase in actual protectionist measures to restrict trade through tariff and non-tariff barriers. At the same time, evidence from surveys shows that public pressure for more economic protection has been mounting since the mid-2000s, and has possibly intensified since the start of the financial crisis. However, no World Trade Organization (WTO) member has retreated into widespread trade restrictions or protectionism to date. Our model-based simulations suggest that the impairment of the global flow of trade would hamper the recovery from the crisis, as well as the long-term growth of the global economy. At the same time, it is unlikely that protectionism would help to correct existing current account imbalances. Moreover, the countries implementing protectionist measures should expect a deterioration of their international competitiveness, which would further affect the potential for longer-term real GDP growth.Protectionism ; trade ; financial crisis ; competitiveness ; World Trade Organization ; global imbalances.
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