1,305 research outputs found
Gaussian multiplicative chaos through the lens of the 2D Gaussian free field
The aim of this review-style paper is to provide a concise, self-contained
and unified presentation of the construction and main properties of Gaussian
multiplicative chaos (GMC) measures for log-correlated fields in 2D in the
subcritical regime. By considering the case of the 2D Gaussian free field, we
review convergence, uniqueness and characterisations of the measures; revisit
Kahane's convexity inequalities and existence and scaling of moments; discuss
the measurability of the underlying field with respect to the GMC measure and
present a KPZ relation for scaling exponents.Comment: 28p, less typos in the 3rd, published version, still no figures, I
remain thankful for comment
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Intergroup contact throughout the lifespan modulates implicit racial biases across perceivers’ racial group
Few researchers have investigated how contact across the lifespan influences racial bias and whether diversity of contact is beneficial regardless of the race of the perceiver. This research aims to address these gaps in the literature with a focus on how diversity in childhood and current contact shapes implicit racial bias across perceivers’ racial group. In two investigations, participants completed an Implicit Association Test and a self-report measure of the racial diversity of their current and childhood contact. In both studies, increased contact with Black compared with White individuals, both in childhood (Study 2) and currently (Studies 1 and 2), was associated with reduced implicit pro-White racial bias. For Black individuals (Study 2) more contact with Black compared with White individuals also was associated with reduced implicit pro-White racial bias. These findings suggest that diversity in contact across the lifespan may be related to reductions in implicit racial biases and that this relationship may generalize across racial groups
A generalized theory of semiflexible polymers
DNA bending on length scales shorter than a persistence length plays an
integral role in the translation of genetic information from DNA to cellular
function. Quantitative experimental studies of these biological systems have
led to a renewed interest in the polymer mechanics relevant for describing the
conformational free energy of DNA bending induced by protein-DNA complexes.
Recent experimental results from DNA cyclization studies have cast doubt on the
applicability of the canonical semiflexible polymer theory, the wormlike chain
(WLC) model, to DNA bending on biological length scales. This paper develops a
theory of the chain statistics of a class of generalized semiflexible polymer
models. Our focus is on the theoretical development of these models and the
calculation of experimental observables. To illustrate our methods, we focus on
a specific toy model of DNA bending. We show that the WLC model generically
describes the long-length-scale chain statistics of semiflexible polymers, as
predicted by the Renormalization Group. In particular, we show that either the
WLC or our new model adequate describes force-extension, solution scattering,
and long-contour-length cyclization experiments, regardless of the details of
DNA bend elasticity. In contrast, experiments sensitive to short-length-scale
chain behavior can in principle reveal dramatic departures from the linear
elastic behavior assumed in the WLC model. We demonstrate this explicitly by
showing that our toy model can reproduce the anomalously large
short-contour-length cyclization J factors observed by Cloutier and Widom.
Finally, we discuss the applicability of these models to DNA chain statistics
in the context of future experiments
Analytical Guidance Laws and Integrated Guidance/Autopilot for Homing Missiles
An approach to integrated guidance/autopilot design is considered in this study. It consists of two parts: 1) recognizing the importance of polar coordinates to describe the end game in terms of problem description and measurement acquisition, the terminal guidance problem is formulated in terms of polar coordinates; 2a) through the use of the state transition matrix of the intercept dynamics, a closed form solution for the transverse command acceleration is obtained; and 2b) through a commonly used approximation on time-to-go and a coordinate transformation, a family of proportional navigation optimal guidance laws is obtained in a closed form. A typical element of such a guidance law is combined with the autopilot dynamics to result in a feedback control law in terms of output variable
Simultaneous estimation of attenuation and structure parameters of aggregated red blood cells from backscatter measurements
The analysis of the ultrasonic frequency-dependent backscatter coefficient of
aggregating red blood cells reveals information about blood structural
properties. The difficulty to apply this technique in vivo is due to the
frequency-dependent attenuation caused by intervening tissue layers that
distorts the spectral content of backscattering properties from blood
microstructures. An optimization method is proposed to simultaneously estimate
tissue attenuation and blood structure factor. In an in vitro experiment, the
method gave satisfactory estimates with relative errors below 22% for
attenuations between 0.101 and 0.317 dB/cm/MHz, signal-to-noise ratios>28 dB
and kR<2.7 (k being the wave number and R the aggregate radius)
The critical velocity effect as a cause for the H\alpha emission from the Magellanic stream
Observations show significant H\alpha-emissions in the Galactic halo near the
edges of cold gas clouds of the Magellanic Stream. The source for the
ionization of the cold gas is still a widely open question. In our paper we
discuss the critical velocity effect as a possible explanation for the observed
H\alpha-emission. The critical velocity effect can yield a fast ionization of
cold gas if this neutral gas passes through a magnetized plasma under suitable
conditions. We show that for parameters that are typical for the Magellanic
Stream the critical velocity effect has to be considered as a possible
ionization source of high relevance.Comment: 9 pages, 2 figures. accepted, to appear in The Astrophysical Journa
Characterization of the K2-18 multi-planetary system with HARPS: A habitable zone super-Earth and discovery of a second, warm super-Earth on a non-coplanar orbit
The bright M dwarf K2-18 at 34 pc is known to host a transiting
super-Earth-sized planet orbiting within the star's habitable zone; K2-18b.
Given the superlative nature of this system for studying an exoplanetary
atmosphere receiving similar levels of insolation as the Earth, we aim to
characterize the planet's mass which is required to interpret atmospheric
properties and infer the planet's bulk composition. We obtain precision radial
velocity measurements with the HARPS spectrograph and couple those measurements
with the K2 photometry to jointly model the observed radial velocity variation
with planetary signals and a radial velocity jitter model based on Gaussian
process regression. We measure the mass of K2-18b to be
M with a bulk density of g/cm which may correspond
to a predominantly rocky planet with a significant gaseous envelope or an ocean
planet with a water mass fraction %. We also find strong evidence
for a second, warm super-Earth K2-18c at days with a semi-major axis
2.4 times smaller than the transiting K2-18b. After re-analyzing the available
light curves of K2-18 we conclude that K2-18c is not detected in transit and
therefore likely has an orbit that is non-coplanar with K2-18b. A suite of
dynamical integrations with varying simulated orbital eccentricities of the two
planets are used to further constrain each planet's eccentricity posterior from
which we measure and at 99% confidence. The discovery
of the inner planet K2-18c further emphasizes the prevalence of multi-planet
systems around M dwarfs. The characterization of the density of K2-18b reveals
that the planet likely has a thick gaseous envelope which along with its
proximity to the Solar system makes the K2-18 planetary system an interesting
target for the atmospheric study of an exoplanet receiving Earth-like
insolation.Comment: 13 pages, 8 figures including 4 interactive figures best viewed in
Adobe Acrobat. Submitted to Astronomy & Astrophysics. Comments welcom
Low Energy Electron Point Projection Microscopy of Suspended Graphene, the Ultimate "Microscope Slide"
Point Projection Microscopy (PPM) is used to image suspended graphene using
low-energy electrons (100-200eV). Because of the low energies used, the
graphene is neither damaged or contaminated by the electron beam. The
transparency of graphene is measured to be 74%, equivalent to electron
transmission through a sheet as thick as twice the covalent radius of
sp^2-bonded carbon. Also observed is rippling in the structure of the suspended
graphene, with a wavelength of approximately 26 nm. The interference of the
electron beam due to the diffraction off the edge of a graphene knife edge is
observed and used to calculate a virtual source size of 4.7 +/- 0.6 Angstroms
for the electron emitter. It is demonstrated that graphene can be used as both
anode and substrate in PPM in order to avoid distortions due to strong field
gradients around nano-scale objects. Graphene can be used to image objects
suspended on the sheet using PPM, and in the future, electron holography
New antibacterial paper made of silver phosphate cellulose fibers: a preliminary study on the elimination of Staphylococcus aureus involved in diabetic foot ulceration
Aim. To evaluate in vitro the antibacterial effect of a paper made of silver phosphate cellulose fibers (SPCF) on Staphylococcus aureus, the most common diabetic foot ulceration (DFU) pathogen when compared with other common commercial products. Methods. The antibacterial activity of SPCF samples was evaluated through time with cell counting on agar plates. SPCF samples were then compared with commercial wound care products currently in use in DFU treatments (Silvercel™, Acticoat 7, and Aquacel Ag ExtraTM) through time on agar plates (growth inhibition zones). Results. After 6 hours, there was no viable bacterial cell detected on either plate (p < 0.05). There was a net growth inhibition zone for SPCF samples but no significant difference between the two silver concentrations. Compared with common commercial products, SPCF paper provides results equal to Acticoat 7 (p < 0.05) and superior to Aquacel AG ExtraTM and Silvercel™ at lower silver concentrations (p < 0.001). Conclusions. These results have shown the efficiency of SPCF paper to eliminate Staphylococcus aureus in these conditions. SPCF papers are effective when compared with other common commercial products and could have an industrial potential in wound care. Infected DFU could benefit from the antibacterial effectiveness of SPCF, but more relevant experimentations related to foot ulcers are needed
The Tyrosine Kinase Csk Dimerizes through Its SH3 Domain
The Src family kinases possess two sites of tyrosine phosphorylation that are critical to the regulation of kinase activity. Autophosphorylation on an activation loop tyrosine residue (Tyr 416 in commonly used chicken c-Src numbering) increases catalytic activity, while phosphorylation of a C-terminal tyrosine (Tyr 527 in c-Src) inhibits activity. The latter modification is achieved by the tyrosine kinase Csk (C-terminal Src Kinase), but the complete inactivation of the Src family kinases also requires the dephosphorylation of the activation loop tyrosine. The SH3 domain of Csk recruits the tyrosine phosphatase PEP, allowing for the coordinated inhibition of Src family kinase activity. We have discovered that Csk forms homodimers through interactions mediated by the SH3 domain in a manner that buries the recognition surface for SH3 ligands. The formation of this dimer would therefore block the recruitment of tyrosine phosphatases and may have important implications for the regulation of Src kinase activity
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