1,915 research outputs found
Tradeoffs in manipulator structure and control. Part 1: Summary
The study of various aspects of manipulator design and control is summarized, focusing on the interaction of the structure's flexible dynamics and the dynamics of the joint control system, including specific information on modeling and design, modal analysis and control, and the flexible manipulator analysis computer program, FMAP
Desisting from Prescription Drug Abuse: An Application of Growth Models to Rx Opioid Users
Modern desistance research has examined many facets of desistance, in terms of theoretical predictors of desistance and recidivism, and in terms of differing types of offending. Though predicting desistance from illegal drug use is among these topics, no research to date has examined the predictors of desisting from prescription opioid abuse. This study uses longitudinal data from 318 prescription opioid users to analyze the effects of various predictors of desistance on declining nonmedical prescription opioid use, with an emphasis on gender differences among participants. Results indicate that theoretical and demographic characteristics correspond with differing rates of decline and further vary by gender
Associations between Prenatal Exposure to Black Carbon and Memory Domains in Urban Children: Modification by Sex and Prenatal Stress
Background
Whether fetal neurodevelopment is disrupted by traffic-related air pollution is uncertain. Animal studies suggest that chemical and non-chemical stressors interact to impact neurodevelopment, and that this association is further modified by sex.
Objectives
To examine associations between prenatal traffic-related black carbon exposure, prenatal stress, and sex with children’s memory and learning.
Methods
Analyses included N = 258 mother-child dyads enrolled in a Boston, Massachusetts pregnancy cohort. Black carbon exposure was estimated using a validated spatiotemporal land-use regression model. Prenatal stress was measured using the Crisis in Family Systems-Revised survey of negative life events. The Wide Range Assessment of Memory and Learning (WRAML2) was administered at age 6 years; outcomes included the General Memory Index and its component indices [Verbal, Visual, and Attention Concentration]. Relationships between black carbon and WRAML2 index scores were examined using multivariable-adjusted linear regression including effect modification by stress and sex.
Results
Mothers were primarily minorities (60% Hispanic, 26% Black); 67% had ≤12 years of education. The main effect for black carbon was not significant for any WRAML2 index; however, in stratified analyses, among boys with high exposure to prenatal stress, Attention Concentration Index scores were on average 9.5 points lower for those with high compared to low prenatal black carbon exposure (P3-way interaction = 0.04).
Conclusion
The associations between prenatal exposure to black carbon and stress with children’s memory scores were stronger in boys than in girls. Studies assessing complex interactions may more fully characterize health risks and, in particular, identify vulnerable subgroups
A Dynamic Model of Cascades on Random Networks with a Threshold Rule
Cascades on random networks are typically analyzed by assuming they map onto
percolation processes and then are solved using generating function
formulations. This approach assumes that the network is infinite and weakly
connected, yet furthermore approximates a dynamic cascading process as a static
percolation event. In this paper we propose a dynamic Markov model formulation
that assumes a finite network with arbitrary average nodal degree. We apply it
to the case where cascades follow a threshold rule, that is, that a node will
change state ("flip") only if a fraction, exceeding a given threshold, of its
neighbors has changed state previously. The corresponding state transition
matrix, recalculated after each step, records the probability that a node of
degree k has i flipped neighbors after j steps in the cascade's evolution. This
theoretical model reproduces a number of behaviors observed in simulations but
not yet reported in the literature. These include the ability to predict
cascades in a domain previously predicted to forbid cascades without assuming
that the network is locally tree-like, and, due to the dynamic nature of the
model, a "near death" behavior in which cascades initially appear about to die
but later explode. Cascades in the "no cascades" region require a sufficiently
large seed of initially flipped nodes whose size scales with the size of the
network or else the cascade will die out. Our theory also predicts the well
known properties of cascades, for instance that a single node seed can start a
global cascade in the appropriate regime regardless of the (finite) size of the
network. The theory and simulations developed here are compared with a
foundational paper by Watts which used generating function theory.Comment: Rev 1: Added citation to prior work by Gleeson and Cahalane. Revised
abstract to sui
Reconstructing pedigrees: some identifiability questions for a recombination-mutation model
Pedigrees are directed acyclic graphs that represent ancestral relationships
between individuals in a population. Based on a schematic recombination
process, we describe two simple Markov models for sequences evolving on
pedigrees - Model R (recombinations without mutations) and Model RM
(recombinations with mutations). For these models, we ask an identifiability
question: is it possible to construct a pedigree from the joint probability
distribution of extant sequences? We present partial identifiability results
for general pedigrees: we show that when the crossover probabilities are
sufficiently small, certain spanning subgraph sequences can be counted from the
joint distribution of extant sequences. We demonstrate how pedigrees that
earlier seemed difficult to distinguish are distinguished by counting their
spanning subgraph sequences.Comment: 40 pages, 9 figure
Mid-infrared interferometry of the massive young stellar object NGC3603 - IRS 9A
We present observations and models for one of these MYSO candidates, NGC3603
IRS 9A. Our goal is to investigate with infrared interferometry the structure
of IRS 9A on scales as small as 200AU, exploiting the fact that a cluster of O
and B stars has blown away much of the obscuring foreground dust and gas.
Observations in the N-band were carried out with the MIDI beam combiner
attached to the VLTI. Additional interferometric observations which probe the
structure of IRS 9A on larger scales were performed with an aperture mask
installed in the T-ReCS instrument of Gemini South. The spectral energy
distribution (SED) is constrained by the MIDI N-band spectrum and by data from
the Spitzer Space Telescope. Our efforts to model the structure and SED of IRS
9A range from simple geometrical models of the brightness distribution to one-
and two-dimensional radiative transfer computations. The target is resolved by
T-ReCS, with an equivalent (elliptical) Gaussian width of 330mas by 280mas
(2300 AU by 2000 AU). Despite this fact, a warm compact unresolved component
was detected by MIDI which is possibly associated with the inner regions of a
flattened dust distribution. Based on our interferometric data, no sign of
multiplicity was found on scales between about 200AU and 700AU projected
separation. A geometric model consisting of a warm (1000 K) ring (400 AU
diameter) and a cool (140 K) large envelope provides a good fit to the data. No
single model fitting all visibility and photometric data could be found, with
disk models performing better than spherical models. While the data are clearly
inconsistent with a spherical dust distribution they are insufficient to prove
the existence of a disk but rather hint at a more complex dust distribution.Comment: 8 pages, 11 figures. Accepted for publication in A&
Phosphatase Rtr1 Regulates Global Levels of Serine 5 RNA Polymerase II C-Terminal Domain Phosphorylation and Cotranscriptional Histone Methylation
In eukaryotes, the C-terminal domain (CTD) of Rpb1 contains a heptapeptide repeat sequence of (Y1S2P3T4S5P6S7)n that undergoes reversible phosphorylation through the opposing action of kinases and phosphatases. Rtr1 is a conserved protein that colocalizes with RNA polymerase II (RNAPII) and has been shown to be important for the transition from elongation to termination during transcription by removing RNAPII CTD serine 5 phosphorylation (Ser5-P) at a selection of target genes. In this study, we show that Rtr1 is a global regulator of the CTD code with deletion of RTR1 causing genome-wide changes in Ser5-P CTD phosphorylation and cotranscriptional histone H3 lysine 36 trimethylation (H3K36me3). Using chromatin immunoprecipitation and high-resolution microarrays, we show that RTR1 deletion results in global changes in RNAPII Ser5-P levels on genes with different lengths and transcription rates consistent with its role as a CTD phosphatase. Although Ser5-P levels increase, the overall occupancy of RNAPII either decreases or stays the same in the absence of RTR1 Additionally, the loss of Rtr1 in vivo leads to increases in H3K36me3 levels genome-wide, while total histone H3 levels remain relatively constant within coding regions. Overall, these findings suggest that Rtr1 regulates H3K36me3 levels through changes in the number of binding sites for the histone methyltransferase Set2, thereby influencing both the CTD and histone codes
A multispectral view of the periodic events in eta Carinae
A full description of the 5.5-yr low excitation events in Eta Carinae is
presented. We show that they are not as simple and brief as previously thought,
but a combination of two components. The first, the 'slow variation' component,
is revealed by slow changes in the ionization level of circumstellar matter
across the whole cycle and is caused by gradual changes in the wind-wind
collision shock-cone orientation, angular opening and gaseous content. The
second, the 'collapse' component, is restricted to around the minimum, and is
due to a temporary global collapse of the wind-wind collision shock. High
energy photons (E > 16 eV) from the companion star are strongly shielded,
leaving the Weigelt objects at low ionization state for >6 months. High energy
phenomena are sensitive only to the 'collapse', low energy only to the 'slow
variation' and intermediate energies to both components. Simple eclipses and
mechanisms effective only near periastron (e.g., shell ejection or accretion
onto the secondary star) cannot account for the whole 5.5-yr cycle.
We find anti-correlated changes in the intensity and the radial velocity of P
Cygni absorption profiles in FeII 6455 and HeI 7065 lines, indicating that the
former is associated to the primary and the latter to the secondary star. We
present a set of light curves representative of the whole spectrum, useful for
monitoring the next event (2009 January 11).Comment: 16 pages, 7 EPS figures, accepted for publication on MNRA
The interactome of the atypical phosphatase Rtr1 in Saccharomyces cerevisiae
The phosphatase Rtr1 has been implicated in dephosphorylation of the RNA Polymerase II (RNAPII) C-terminal domain (CTD) during transcription elongation and in regulation of nuclear import of RNAPII. Although it has been shown that Rtr1 interacts with RNAPII in yeast and humans, the specific mechanisms that underlie Rtr1 recruitment to RNAPII have not been elucidated. To address this, we have performed an in-depth proteomic analysis of Rtr1 interacting proteins in yeast. Our studies revealed that hyperphosphorylated RNAPII is the primary interacting partner for Rtr1. To extend these findings, we performed quantitative proteomic analyses of Rtr1 interactions in yeast strains deleted for CTK1, the gene encoding the catalytic subunit of the CTD kinase I (CTDK-I) complex. Interestingly, we found that the interaction between Rtr1 and RNAPII is decreased in ctk1Δ strains. We hypothesize that serine-2 CTD phosphorylation is required for Rtr1 recruitment to RNAPII during transcription elongation
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