2,201 research outputs found
Imaging geometry through dynamics: the observable representation
For many stochastic processes there is an underlying coordinate space, ,
with the process moving from point to point in or on variables (such as
spin configurations) defined with respect to . There is a matrix of
transition probabilities (whether between points in or between variables
defined on ) and we focus on its ``slow'' eigenvectors, those with
eigenvalues closest to that of the stationary eigenvector. These eigenvectors
are the ``observables,'' and they can be used to recover geometrical features
of
Organized Current Patterns in Disordered Conductors
We present a general theory of current deviations in straight current
carrying wires with random imperfections, which quantitatively explains the
recent observations of organized patterns of magnetic field corrugations above
micron-scale evaporated wires. These patterns originate from the most efficient
electron scattering by Fourier components of the wire imperfections with
wavefronts along the direction. We show that long range
effects of surface or bulk corrugations are suppressed for narrow wires or
wires having an electrically anisotropic resistivity
Disorder Potentials near Lithographically Fabricated Atom Chips
We show that previously observed large disorder potentials in magnetic
microtraps for neutral atoms are reduced by about two orders of magnitude when
using atom chips with lithographically fabricated high quality gold layers.
Using one dimensional Bose-Einstein condensates, we probe the remaining
magnetic field variations at surface distances down to a few microns.
Measurements on a 100 um wide wire imply that residual variations of the
current flow result from local properties of the wire.Comment: submitted on September 24th, 200
Long-Range Order in Electronic Transport through Disordered Metal Films
Ultracold atom magnetic field microscopy enables the probing of current flow
patterns in planar structures with unprecedented sensitivity. In
polycrystalline metal (gold) films we observe long-range correlations forming
organized patterns oriented at +/- 45 deg relative to the mean current flow,
even at room temperature and at length scales orders of magnitude larger than
the diffusion length or the grain size. The preference to form patterns at
these angles is a direct consequence of universal scattering properties at
defects. The observed amplitude of the current direction fluctuations scales
inversely to that expected from the relative thickness variations, the grain
size and the defect concentration, all determined independently by standard
methods. This indicates that ultracold atom magnetometry enables new insight
into the interplay between disorder and transport
Plantar Erythrodysesthesia Caused by Antiretroviral Treatment: A Case Report and Review of the Literature
Palmoplantar erythrodysesthesia is an uncommon localised cutaneous reaction to certain chemotherapeutic agents and characterized by painful palmoplantar erythema and dysesthesia. To the best of our knowledge, we report the first case of plantar erythrodysesthesia in a 40-year-old male patient receiving an antiretroviral combination therapy for HIV
Designing potentials by sculpturing wires
Magnetic trapping potentials for atoms on atom chips are determined by the
current flow in the chip wires. By modifying the shape of the conductor we can
realize specialized current flow patterns and therefore micro-design the
trapping potentials. We have demonstrated this by nano-machining an atom chip
using the focused ion beam technique. We built a trap, a barrier and using a
BEC as a probe we showed that by polishing the conductor edge the potential
roughness on the selected wire can be reduced. Furthermore we give different
other designs and discuss the creation of a 1D magnetic lattice on an atom
chip.Comment: 6 pages, 8 figure
Cluster density functional theory for lattice models based on the theory of Mobius functions
Rosenfeld's fundamental measure theory for lattice models is given a rigorous
formulation in terms of the theory of Mobius functions of partially ordered
sets. The free-energy density functional is expressed as an expansion in a
finite set of lattice clusters. This set is endowed a partial order, so that
the coefficients of the cluster expansion are connected to its Mobius function.
Because of this, it is rigorously proven that a unique such expansion exists
for any lattice model. The low-density analysis of the free-energy functional
motivates a redefinition of the basic clusters (zero-dimensional cavities)
which guarantees a correct zero-density limit of the pair and triplet direct
correlation functions. This new definition extends Rosenfeld's theory to
lattice model with any kind of short-range interaction (repulsive or
attractive, hard or soft, one- or multi-component...). Finally, a proof is
given that these functionals have a consistent dimensional reduction, i.e. the
functional for dimension d' can be obtained from that for dimension d (d'<d) if
the latter is evaluated at a density profile confined to a d'-dimensional
subset.Comment: 21 pages, 2 figures, uses iopart.cls, as well as diagrams.sty
(included
The RNA Helicase DDX6 Controls Cellular Plasticity by Modulating P-Body Homeostasis
Post-transcriptional mechanisms have the potential to influence complex changes in gene expression, yet their role in cell fate transitions remains largely unexplored. Here, we show that suppression of the RNA helicase DDX6 endows human and mouse primed embryonic stem cells (ESCs) with a differentiation-resistant, âhyper-pluripotentâ state, which readily reprograms to a naive state resembling the preimplantation embryo. We further demonstrate that DDX6 plays a key role in adult progenitors where it controls the balance between self-renewal and differentiation in a context-dependent manner. Mechanistically, DDX6 mediates the translational suppression of target mRNAs in P-bodies. Upon loss of DDX6 activity, P-bodies dissolve and release mRNAs encoding fate-instructive transcription and chromatin factors that re-enter the ribosome pool. Increased translation of these targets impacts cell fate by rewiring the enhancer, heterochromatin, and DNA methylation landscapes of undifferentiated cell types. Collectively, our data establish a link between P-body homeostasis, chromatin organization, and stem cell potency
A trapped-ion local field probe
We introduce a measurement scheme that utilizes a single ion as a local field
probe. The ion is confined in a segmented Paul trap and shuttled around to
reach different probing sites. By the use of a single atom probe, it becomes
possible characterizing fields with spatial resolution of a few nm within an
extensive region of millimeters. We demonstrate the scheme by accurately
investigating the electric fields providing the confinement for the ion. For
this we present all theoretical and practical methods necessary to generate
these potentials. We find sub-percent agreement between measured and calculated
electric field values
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