4,514 research outputs found
Non-birational twisted derived equivalences in abelian GLSMs
In this paper we discuss some examples of abelian gauged linear sigma models
realizing twisted derived equivalences between non-birational spaces, and
realizing geometries in novel fashions. Examples of gauged linear sigma models
with non-birational Kahler phases are a relatively new phenomenon. Most of our
examples involve gauged linear sigma models for complete intersections of
quadric hypersurfaces, though we also discuss some more general cases and their
interpretation. We also propose a more general understanding of the
relationship between Kahler phases of gauged linear sigma models, namely that
they are related by (and realize) Kuznetsov's `homological projective duality.'
Along the way, we shall see how `noncommutative spaces' (in Kontsevich's sense)
are realized physically in gauged linear sigma models, providing examples of
new types of conformal field theories. Throughout, the physical realization of
stacks plays a key role in interpreting physical structures appearing in GLSMs,
and we find that stacks are implicitly much more common in GLSMs than
previously realized.Comment: 54 pages, LaTeX; v2: typo fixe
C-reactive Protein and Temperament: An Instrumental Variable Analysis
BACKGROUND:
Temperament is associated with circulating inflammatory biomarkers, such as C-reactive protein (CRP), which has been associated with various health conditions, including depression. This study aims to investigate whether genetic disposition for increased circulating CRP concentration may influence temperament over the life-course.
METHODS:
Using a longitudinal cohort that began in 1980—the Cardiovascular Risk in Young Finns Study (YFS)—we included 920 participants (59.8% female) aged 3–12 years old at baseline (childhood), and the same participants again at ages 30–39 years old (adulthood) in this study. We used both ordinary least-squares regression (OLS linear regression) and instrumental variable (IV) regression to assess associations between CRP concentration and temperament dimensions (negative emotionality, activity, and sociability). To represent genetically determined risk for increase in circulating CRP concentration, we calculated a weighted genetic risk score (GRS) which reflects risk for increased circulating CRP concentration.
RESULTS:
In OLS linear regression analyses, we found that increased circulating CRP concentration in childhood was associated with slightly higher scores for sociability in childhood (19% increase, CI = 7–32%) and adulthood (13% increase, CI = 2–27%), and lower activity scores in adulthood (15% decrease, CI = 3–25%). For all IV regressions, there were no apparent associations between GRS and temperament in either childhood or adulthood (all p>0.3). The Durbin-Wu-Hausman test for endogeneity produced p-values (all>0.05) that suggest there is no evidence for disagreement between the OLS and IV estimates.
CONCLUSIONS:
We found no clear evidence for an association of GRS for elevated CRP with childhood or adulthood emotionality, activity, or sociability, although circulating CRP was associated with some of these traits
Fortnightly Fluctuations in the O-C Diagram of CS 1246
Dominated by a single, large-amplitude pulsation mode, the rapidly-pulsating
hot subdwarf B star CS 1246 is a prime candidate for a long-term O-C diagram
study. We collected nearly 400 hours of photometry with the PROMPT telescopes
over a time span of 14 months to begin looking for secular variations in the
pulse timings. Interestingly, the O-C diagram is dominated by a strong
sinusoidal pattern with a period of 14.1 days and an amplitude of 10.7
light-seconds. Underneath this sine wave is a secular trend implying a decrease
in the 371.7-s pulsational period of Pdot = -1.9 x 10^-11, which we attribute
to the evolution of the star through the H-R diagram. The sinusoidal variation
could be produced by the presence of a low-mass companion, with m sin i ~ 0.12
Msun, orbiting the subdwarf B star at a distance of 20 Rsun. An analysis of the
combined light curve reveals the presence of a low-amplitude first harmonic to
the main pulsation mode.Comment: Accepted for publication in MNRAS. 11 pages, 8 figures, 5 table
System engineering toolbox for design-oriented engineers
This system engineering toolbox is designed to provide tools and methodologies to the design-oriented systems engineer. A tool is defined as a set of procedures to accomplish a specific function. A methodology is defined as a collection of tools, rules, and postulates to accomplish a purpose. For each concept addressed in the toolbox, the following information is provided: (1) description, (2) application, (3) procedures, (4) examples, if practical, (5) advantages, (6) limitations, and (7) bibliography and/or references. The scope of the document includes concept development tools, system safety and reliability tools, design-related analytical tools, graphical data interpretation tools, a brief description of common statistical tools and methodologies, so-called total quality management tools, and trend analysis tools. Both relationship to project phase and primary functional usage of the tools are also delineated. The toolbox also includes a case study for illustrative purposes. Fifty-five tools are delineated in the text
Cognitive Information Processing
Contains reports on seven research projects split into three sections.Joint Services Electronics Program by the U. S. Army Research Office, Durham, under Contract DA36-039-AMC-03200(E)National Science Foundation (Grant GP-2495)National Institutes of Health (Grant MH-04737-05)National Aeronautics and Space Administration (Grant NsG-496
Stabilized immersed isogeometric analysis for the Navier-Stokes-Cahn-Hilliard equations, with applications to binary-fluid flow through porous media
Binary-fluid flows can be modeled using the Navier-Stokes-Cahn-Hilliard
equations, which represent the boundary between the fluid constituents by a
diffuse interface. The diffuse-interface model allows for complex geometries
and topological changes of the binary-fluid interface. In this work, we propose
an immersed isogeometric analysis framework to solve the
Navier-Stokes-Cahn-Hilliard equations on domains with geometrically complex
external binary-fluid boundaries. The use of optimal-regularity B-splines
results in a computationally efficient higher-order method. The key features of
the proposed framework are a generalized Navier-slip boundary condition for the
tangential velocity components, Nitsche's method for the convective
impermeability boundary condition, and skeleton- and ghost-penalties to
guarantee stability. A binary-fluid Taylor-Couette flow is considered for
benchmarking. Porous medium simulations demonstrate the ability of the immersed
isogeometric analysis framework to model complex binary-fluid flow phenomena
such as break-up and coalescence in complex geometries
Critical time-step size analysis and mass scaling by ghost-penalty for immersogeometric explicit dynamics
In this article, we study the effect of small-cut elements on the critical
time-step size in an immersogeometric context. We analyze different
formulations for second-order (membrane) and fourth-order (shell-type)
equations, and derive scaling relations between the critical time-step size and
the cut-element size for various types of cuts. In particular, we focus on
different approaches for the weak imposition of Dirichlet conditions: by
penalty enforcement and with Nitsche's method. The stability requirement for
Nitsche's method necessitates either a cut-size dependent penalty parameter, or
an additional ghost-penalty stabilization term is necessary. Our findings show
that both techniques suffer from cut-size dependent critical time-step sizes,
but the addition of a ghost-penalty term to the mass matrix serves to mitigate
this issue. We confirm that this form of `mass-scaling' does not adversely
affect error and convergence characteristics for a transient membrane example,
and has the potential to increase the critical time-step size by orders of
magnitude. Finally, for a prototypical simulation of a Kirchhoff-Love shell,
our stabilized Nitsche formulation reduces the solution error by well over an
order of magnitude compared to a penalty formulation at equal time-step size
Enhanced root-to-shoot translocation of cadmium in the hyperaccumulating ecotype of Sedum alfredii
Sedum alfredii (Crasulaceae) is the only known Cd-hyperaccumulating species that are not in the Brassica family; the mechanism of Cd hyperaccumulation in this plant is, however, little understood. Here, a combination of radioactive techniques, metabolic inhibitors, and fluorescence imaging was used to contrast Cd uptake and translocation between a hyperaccumulating ecotype (HE) and a non-hyperaccumulating ecotype (NHE) of S. alfredii. The Km of 109Cd influx into roots was similar in both ecotypes, while the Vmax was 2-fold higher in the HE. Significant inhibition of Cd uptake by low temperature or metabolic inhibitors was observed in the HE, whereas the effect was less pronounced in the NHE. 109Cd influx into roots was also significantly decreased by high Ca in both ecotypes. The rate of root-to-shoot translocation of 109Cd in the HE was >10 times higher when compared with the NHE, and shoots of the HE accumulated dramatically higher 109Cd concentrations those of the NHE. The addition of the metabolic inhibitor carbonyl cyanide m-chlorophenylhydrazone (CCCP) resulted in a significant reduction in Cd contents in the shoots of the HE, and in the roots of the NHE. Cd was distributed preferentially to the root cylinder of the HE but not the NHE, and there was a 3–5 times higher Cd concentration in xylem sap of the HE in contrast to the NHE. These results illustrate that a greatly enhanced rate of root-to-shoot translocation, possibly as a result of enhanced xylem loading, rather than differences in the rate of root uptake, was the pivotal process expressed in the Cd hyperaccumulator HE S. alfredii
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