3,958 research outputs found
Charge superconductivity from pair density wave order in certain high temperature superconductors
A number of spectacular experimental anomalies\cite{li-2007,fujita-2005} have
recently been discovered in certain cuprates, notably {\LBCO} and {\LNSCO},
which exhibit unidirectional spin and charge order (known as ``stripe order'').
We have recently proposed to interpret these observations as evidence for a
novel ``striped superconducting'' state, in which the superconducting order
parameter is modulated in space, such that its average is precisely zero. Here,
we show that thermal melting of the striped superconducting state can lead to a
number of unusual phases, of which the most novel is a charge
superconducting state, with a corresponding fractional flux quantum .
These are never-before observed states of matter, and ones, moreover, that
cannot arise from the conventional Bardeen-Cooper-Schrieffer (BCS) mechanism.
Thus, direct confirmation of their existence, even in a small subset of the
cuprates, could have much broader implications for our understanding of high
temperature superconductivity. We propose experiments to observe fractional
flux quantization, which thereby could confirm the existence of these states.Comment: 5 pages, 2 figures; new version in Nature Physics format with a
discussion of the effective Josephson coupling J2 and minor changes. Mildly
edited abstract. v3: corrected versio
New acoustic velocity measurements on CaOâMgOâAl 2 O 3 âSiO 2 liquids: Reevaluation of the volume and compressibility of CaMgSi 2 O 6 âCaAl 2 Si 2 O 8 liquids to 25 GPa
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95309/1/jgrb15318.pd
Phase space reduction of the one-dimensional Fokker-Planck (Kramers) equation
A pointlike particle of finite mass m, moving in a one-dimensional viscous
environment and biased by a spatially dependent force, is considered. We
present a rigorous mapping of the Fokker-Planck equation, which determines
evolution of the particle density in phase space, onto the spatial coordinate
x. The result is the Smoluchowski equation, valid in the overdamped limit,
m->0, with a series of corrections expanded in powers of m. They are determined
unambiguously within the recurrence mapping procedure. The method and the
results are interpreted on the simplest model with no field and on the damped
harmonic oscillator.Comment: 13 pages, 1 figur
Controlled interfacial assembly of 2D curved colloidal crystals and jammed shells
Assembly of colloidal particles on fluid interfaces is a promising technique
for synthesizing two-dimensional micro-crystalline materials useful in fields
as diverse as biomedicine1, materials science2, mineral flotation3 and food
processing4. Current approaches rely on bulk emulsification methods, require
further chemical and thermal treatments, and are restrictive with respect to
the materials employed5-9. The development of methods that exploit the great
potential of interfacial assembly for producing tailored materials have been
hampered by the lack of understanding of the assembly process. Here we report a
microfluidic method that allows direct visualization and understanding of the
dynamics of colloidal crystal growth on curved interfaces. The crystals are
periodically ejected to form stable jammed shells, which we refer to as
colloidal armour. We propose that the energetic barriers to interfacial crystal
growth and organization can be overcome by targeted delivery of colloidal
particles through hydrodynamic flows. Our method allows an unprecedented degree
of control over armour composition, size and stability.Comment: 18 pages, 5 figure
A Method to Optimize Geometric Errors of Machine Tool based on SNR Quality Loss Function and Correlation Analysis
Instead improving the accuracy of machine tool by increasing the precision of key components level blindly in the production process, the method of combination of SNR quality loss function and machine tool geometric error correlation analysis to optimize five-axis machine tool geometric errors will be adopted. Firstly, the homogeneous transformation matrix method will be used to build five-axis machine tool geometric error modeling. Secondly, the SNR quality loss function will be used for cost modeling. And then, machine tool accuracy optimal objective function will be established based on the correlation analysis. Finally, ISIGHT combined with MATLAB will be applied to optimize each error. The results show that this method is reasonable and appropriate to relax the range of tolerance values, so as to reduce the manufacturing cost of machine tools
Macromolecular crowding modulates folding mechanism of alpha/beta protein apoflavodoxin
Protein dynamics in cells may be different from that in dilute solutions in
vitro since the environment in cells is highly concentrated with other
macromolecules. This volume exclusion due to macromolecular crowding is
predicted to affect both equilibrium and kinetic processes involving protein
conformational changes. To quantify macromolecular crowding effects on protein
folding mechanisms, here we have investigated the folding energy landscape of
an alpha/beta protein, apoflavodoxin, in the presence of inert macromolecular
crowding agents using in silico and in vitro approaches. By coarse-grained
molecular simulations and topology-based potential interactions, we probed the
effects of increased volume fraction of crowding agents (phi_c) as well as of
crowding agent geometry (sphere or spherocylinder) at high phi_c. Parallel
kinetic folding experiments with purified Desulfovibro desulfuricans
apoflavodoxin in vitro were performed in the presence of Ficoll (sphere) and
Dextran (spherocylinder) synthetic crowding agents. In conclusion, we have
identified in silico crowding conditions that best enhance protein stability
and discovered that upon manipulation of the crowding conditions, folding
routes experiencing topological frustrations can be either enhanced or
relieved. The test-tube experiments confirmed that apoflavodoxin's
time-resolved folding path is modulated by crowding agent geometry. We propose
that macromolecular crowding effects may be a tool for manipulation of protein
folding and function in living cells.Comment: to appear in Biophysical Journal (2009). to appear in Biophysical
Journal (2009
Sexual Size Dimorphism and Body Condition in the Australasian Gannet
Funding: The research was financially supported by the Holsworth Wildlife Research Endowment. Acknowledgments We thank the Victorian Marine Science Consortium, Sea All Dolphin Swim, Parks Victoria, and the Point Danger Management Committee for logistical support. We are grateful for the assistance of the many field volunteers involved in the study.Peer reviewedPublisher PD
Two-dimensional Vortices in Superconductors
Superconductors have two key characteristics. They expel magnetic field and
they conduct electrical current with zero resistance. However, both properties
are compromised in high magnetic fields which can penetrate the material and
create a mixed state of quantized vortices. The vortices move in response to an
electrical current dissipating energy which destroys the zero resistance
state\cite{And64}. One of the central problems for applications of high
temperature superconductivity is the stabilization of vortices to ensure zero
electrical resistance. We find that vortices in the anisotropic superconductor
BiSrCaCuO (Bi-2212) have a phase transition from
a liquid state, which is inherently unstable, to a two-dimensional vortex
solid. We show that at high field the transition temperature is independent of
magnetic field, as was predicted theoretically for the melting of an ideal
two-dimensional vortex lattice\cite{Fis80,Gla91}. Our results indicate that the
stable solid phase can be reached at any field as may be necessary for
applications involving superconducting magnets\cite{Has04,Sca04,COHMAG}. The
vortex solid is disordered, as suggested by previous studies at lower
fields\cite{Lee93,Cub93}. But its evolution with increasing magnetic field
displays unexpected threshold behavior that needs further investigation.Comment: 5 pages and 4 figures. submitted to Nature Physic
Climate projections and their impact on policy and practice
This article examines the relationship between projections of climate change and the responses to those projections. First, it discusses uncertainty and its role in shaping not only the production of climate projections but also the use of these projections by decision makers. We find that uncertainty critically affects the way climate projections move from useful to usable, where usefulness is defined by scientists' perception of users' needs, and usability is defined by users' perception of what knowledge can be readily applied to their decision. From the point of view of the natural scientist, we pose that there is an uncertainty fallacy, that is, a belief that the systematic reduction of uncertainty in climate projections is required in order for the projections to be used by decision makers. Second, we explore the implications of climate projections for policy and decision making, using examples from the seasonal climate forecast applications literature as an analog. We examine constraints and opportunities for their application in policy and practice and find that over-reliance on science and technical solutions might crowd out the moral imperative to do what is needed to improve livelihoods and to guarantee ecosystems' long-term sustainability. We conclude that, in the context of high uncertainty, decision makers should not look for âperfectâ forecasts, but seek to implement knowledge systems that integrate climate projections with other kinds of knowledge and that consider the multiple stressors that shape their decision environment. Copyright © 2010 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs websitePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78059/1/71_ftp.pd
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