570 research outputs found
Testing the Ginzburg-Landau approximation for three-flavor crystalline color superconductivity
It is an open challenge to analyze the crystalline color superconducting
phases that may arise in cold dense, but not asymptotically dense, three-flavor
quark matter. At present the only approximation within which it seems possible
to compare the free energies of the myriad possible crystal structures is the
Ginzburg-Landau approximation. Here, we test this approximation on a
particularly simple "crystal" structure in which there are only two condensates
and whose position-space dependence is that of two
plane waves with wave vectors and at arbitrary angles.
For this case, we are able to solve the mean-field gap equation without making
a Ginzburg-Landau approximation. We find that the Ginzburg-Landau approximation
works in the limit as expected, find that it correctly predicts
that decreases with increasing angle between and meaning that the phase with has the lowest
free energy, and find that the Ginzburg-Landau approximation is conservative in
the sense that it underestimates at all values of the angle between
and .Comment: 16 pages, 6 figures. Small changes only. Version to appear in Phys.
Rev.
Initialization Approach for Nonlinear State-Space Identification via the Subspace Encoder Approach
The SUBNET neural network architecture has been developed to identify
nonlinear state-space models from input-output data. To achieve this, it
combines the rolled-out nonlinear state-space equations and a state encoder
function, both parameterised as a neural network. The encoder function is
introduced to reconstruct the current state from past input-output data. Hence
it enables the forward simulation of the rolled-out state-space model. While
this approach has shown to provide high-accuracy and consistent model
estimation, its convergence can be significantly improved by efficient
initialization of the training process. This paper focuses on such an
initialisation of the subspace encoder approach using the Best Linear
Approximation (BLA). Using the BLA provided state-space matrices and its
associated reconstructability map both the state-transition part of the network
and the encoder are initialized. The performance of the improved initialisation
scheme is evaluated on a Wiener-Hammerstein simulation example and a benchmark
dataset. The results show that for a weakly nonlinear system, the proposed
initialisation based on the linear reconstructability map results in a faster
convergence and a better model quality.Comment: Accepted for presentation at the IFAC World Congress 202
A low energy theory for superfluid and solid matter and its application to the neutron star crust
We formulate a low energy effective theory describing phases of matter that
are both solid and superfluid. These systems simultaneously break translational
symmetry and the phase symmetry associated with particle number. The symmetries
restrict the combinations of terms that can appear in the effective action and
the lowest order terms featuring equal number of derivatives and Goldstone
fields are completely specified by the thermodynamic free energy, or
equivalently by the long-wavelength limit of static correlation functions in
the ground state. We show that the underlying interaction between particles
that constitute the lattice and the superfluid gives rise to entrainment, and
mixing between the Goldstone modes. As a concrete example we discuss the low
energy theory for the inner crust of a neutron star, where a lattice of ionized
nuclei coexists with a neutron superfluid.Comment: 21 pages, 1 figur
Ecosystem Graphs: The Social Footprint of Foundation Models
Foundation models (e.g. ChatGPT, StableDiffusion) pervasively influence
society, warranting immediate social attention. While the models themselves
garner much attention, to accurately characterize their impact, we must
consider the broader sociotechnical ecosystem. We propose Ecosystem Graphs as a
documentation framework to transparently centralize knowledge of this
ecosystem. Ecosystem Graphs is composed of assets (datasets, models,
applications) linked together by dependencies that indicate technical (e.g. how
Bing relies on GPT-4) and social (e.g. how Microsoft relies on OpenAI)
relationships. To supplement the graph structure, each asset is further
enriched with fine-grained metadata (e.g. the license or training emissions).
We document the ecosystem extensively at
https://crfm.stanford.edu/ecosystem-graphs/. As of March 16, 2023, we annotate
262 assets (64 datasets, 128 models, 70 applications) from 63 organizations
linked by 356 dependencies. We show Ecosystem Graphs functions as a powerful
abstraction and interface for achieving the minimum transparency required to
address myriad use cases. Therefore, we envision Ecosystem Graphs will be a
community-maintained resource that provides value to stakeholders spanning AI
researchers, industry professionals, social scientists, auditors and
policymakers.Comment: Authored by the Center for Research on Foundation Models (CRFM) at
the Stanford Institute for Human-Centered Artificial Intelligence (HAI).
Ecosystem Graphs available at https://crfm.stanford.edu/ecosystem-graphs
Novel cis-trans interactions are involved in post-transcriptional regulation of cyclin-dependent kinase inhibitor p21WAF1/CIP1 mRNA
BACKGROUND: A variety of pathways target CDKI p21WAF1/CIP1 expression at transcriptional, post-transcriptional as well as translational levels. We previously found that cell growth suppressing retinoid CD437 enhanced expression of p21WAF1/CIP1 and DNA damage inducible GADD45 proteins in part by elevating their mRNA stability.
RESULTS: Here, we investigated molecular mechanisms of CD437-dependent post-transcriptional regulation of p21WAF1/CIP1 expression. By utilizing MDA-MB-468 HBC cells expressing chimeric rabbit beta-globin-p21WAF1/CIP1 transcripts we mapped multiple CD437-responsive sequences located within positions 1195 to 1795 of the 3\u27-untranslated region of p21WAF1/CIP1 mRNA. Several cytoplasmic proteins present in MDA-MB-468, MCF-7 HBC as well as HL-60R leukemia cells bound specifically, in vitro, with these CD437-responsive sequences. CD437 treatment of cells resulted in elevated binding of ~85 kD and ~55 kD cytoplasmic proteins with putative CD437-responsive sequences. A 12 nt RNA sequence (5\u27-UGUGGUGGCACA-3\u27) present within CD437-responsive region of p21WAF1/CIP1 mRNA displayed specific and elevated binding with the above noted proteins. Treatment of cells with ActD or CHX prior to CD437 exposure did not abrogate RNA-protein interactions. However, treatment of cytoplasmic protein extracts with proteinase K or alkaline phosphatase resulted in loss of RNA-protein interactions.
CONCLUSIONS: CD437 regulates cell growth in part by regulating stability of p21WAF1/CIP1 mRNA that involves specific RNA-protein interactions that are phosphorylation-dependent, while not requiring nascent transcription or protein synthesis
Novel cis-trans interactions are involved in post-transcriptional regulation of cyclin-dependent kinase inhibitor p21\u3csup\u3eWAF1/CIP1 \u3c/sup\u3emRNA
Abstract
Background
A variety of pathways target CDKI p21WAF1/CIP1 expression at transcriptional, post-transcriptional as well as translational levels. We previously found that cell growth suppressing retinoid CD437 enhanced expression of p21WAF1/CIP1 and DNA damage inducible GADD45 proteins in part by elevating their mRNA stability.
Results
Here, we investigated molecular mechanisms of CD437-dependent post-transcriptional regulation of p21WAF1/CIP1 expression. By utilizing MDA-MB-468 HBC cells expressing chimeric rabbit β-globin-p21WAF1/CIP1 transcripts we mapped multiple CD437-responsive sequences located within positions 1195 to 1795 of the 3\u27-untranslated region of p21WAF1/CIP1 mRNA. Several cytoplasmic proteins present in MDA-MB-468, MCF-7 HBC as well as HL-60R leukemia cells bound specifically, in vitro, with these CD437-responsive sequences. CD437 treatment of cells resulted in elevated binding of ~85 kD and ~55 kD cytoplasmic proteins with putative CD437-responsive sequences. A 12 nt RNA sequence (5\u27-UGUGGUGGCACA-3\u27) present within CD437-responsive region of p21WAF1/CIP1 mRNA displayed specific and elevated binding with the above noted proteins. Treatment of cells with ActD or CHX prior to CD437 exposure did not abrogate RNA-protein interactions. However, treatment of cytoplasmic protein extracts with proteinase K or alkaline phosphatase resulted in loss of RNA-protein interactions.
Conclusions
CD437 regulates cell growth in part by regulating stability of p21WAF1/CIP1 mRNA that involves specific RNA-protein interactions that are phosphorylation-dependent, while not requiring nascent transcription or protein synthesis
The rigidity of crystalline color superconducting quark matter
We calculate the shear modulus of crystalline color superconducting quark
matter, showing that this phase of dense, but not asymptotically dense,
three-flavor quark matter responds to shear stress like a very rigid solid. To
evaluate the shear modulus, we derive the low energy effective Lagrangian that
describes the phonons that originate from the spontaneous breaking of
translation invariance by the spatial modulation of the gap parameter .
These massless bosons describe space- and time-dependent fluctuations of the
crystal structure and are analogous to the phonons in ordinary crystals. The
coefficients of the spatial derivative terms of the phonon effective Lagrangian
are related to the elastic moduli of the crystal; the coefficients that encode
the linear response of the crystal to a shearing stress define the shear
modulus. We analyze the two particular crystal structures which are
energetically favored over a wide range of densities, in each case evaluating
the phonon effective action and the shear modulus up to order in a
Ginzburg-Landau expansion, finding shear moduli which are 20 to 1000 times
larger than those of neutron star crusts. The crystalline color superconducting
phase has long been known to be a superfluid -- by picking a phase its order
parameter breaks the quark-number symmetry spontaneously. Our results
demonstrate that this superfluid phase of matter is at the same time a rigid
solid. We close with a rough estimate of the pinning force on the rotational
vortices which would be formed embedded within this rigid superfluid upon
rotation. Our results raise the possibility that (some) pulsar glitches could
originate within a quark matter core deep within a neutron star.Comment: 38 pages, 5 figures. v3. Two new paragraphs in Section V
(Conclusion); some additional small changes. A paragraph discussing
supercurrents added in Section I (Introduction). Version to appear in Phys.
Rev.
Structural Changes Induced by Flash in a Single Crystal of Pr2CuO4
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Topical, Biological and Clinical Challenges in the Management of Patients with Acne Vulgaris
Acne vulgaris is one of the most common chronic inflammatory skin disorders among adolescents and young adults. It is associated with substantial morbidity and, rarely, with mortality. The exact worldwide incidence and prevalence are currently unknown. Current challenges involve improving understanding of the underlying pathophysiology of acne vulgaris and developing a practical treatment consensus. Expert panel discussions were held in 2013 and 2014 among a group of scientists and clinicians from the Omani and United Arab Emirate Dermatology Societies to ascertain the current optimal management of acne vulgaris, identify clinically relevant end-points and construct suitable methodology for future clinical trial designs. This article reviews the discussions of these sessions and recent literature on this topic
Structural changes induced by electric currents in a single crystal of PrCuO
We demonstrate a novel approach to the structural and electronic property
modification of perovskites, focusing on PrCuO, an undoped parent
compound of a class of electron-doped copper-oxide superconductors. Currents
were passed parallel or perpendicular to the copper-oxygen layers with the
voltage ramped up until a rapid drop in the resistivity was achieved, a process
referred to as "flash". The current was then further increased tenfold in
current-control mode. This state was quenched by immersion into liquid
nitrogen. Flash can drive many compounds into different atomic structures with
new properties, whereas the quench freezes them into a long-lived state.
Single-crystal neutron diffraction of as-grown and modified PrCuO
revealed a x superlattice due to oxygen-vacancy order.
The diffraction peak intensities of the superlattice of the modified sample
were significantly enhanced relative to the pristine sample. Raman-active
phonons in the modified sample were considerably sharper. Measurements of
electrical resistivity, magnetization and two-magnon Raman scattering indicate
that the modification affected only the Pr-O layers, but not the Cu-O planes.
These results point to enhanced oxygen-vacancy order in the modified samples
well beyond what can be achieved without passing electrical current. Our work
opens a new avenue toward electric field/quench control of structure and
properties of layered perovskite oxides
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